Research ArticleDesign and Analysis of a Novel 25 GHz Interleaver forDWDM Applications with Two Ring Configurations
Tsair-Chun Liang and Chun-Ting Chen
Graduate Institute of Electrical Engineering National Kaohsiung FirstUniversity of Science andTechnology KaohsiungCity 811 Taiwan
Correspondence should be addressed to Tsair-Chun Liang tcliangnkfustedutw
Received 19 June 2014 Accepted 2 August 2014
Academic Editor Teen-Hang Meen
Copyright copy 2015 T-C Liang and C-T Chen This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited
We present a novel scheme of an excellent flat-top 25GHz optical interleaver based on two ring configurations And the AdvancedSystemsAnalysis Program (ASAP) opticalmodeling software has been utilized for the interleaver designThe optical path differencefor interference and the phase shift are provided by the interferometer with two birefringent crystals and dual-ring arrangementThe proposed structure exhibits the passband utilization of more than 90 and the channel isolation greater than 95 dB withinthe C-band Furthermore we improve the dispersion performance by employing 1205826 wave plates as birefringent compensators forinterleavers The research results illustrate that our proposed scheme with compensator can improve the dispersion of more than858 Comparing the performance with the previous studies of optical interleavers with birefringent crystal and ring structurethe proposed system can achieve an excellent 25GHz multichannel filter for dense wavelength division multiplexing (DWDM)transmission systems
1 Introduction
Due to the growing demand for network communicationscapacity dense wavelength division multiplexing (DWDM)[1 2] has emerged as vital component for optical fiber net-works Several techniques for flexibility in all-optics dynamicnetworks have been engaged in DWDM systems [3 4] Andhow to increase the number of channels is an importantissue [5] A spectral interleaver is capable of separating aset of channels into two sets twice the channel spacing Anoptical interleaver has been verified as an effective techniquein increasing channel counts by doubling or quadrupling thenumber of optical channels when the channel spacing is inthe range of 02 nm [6ndash8]
Conventional interleavers are based on interferometersthat employ Gires-Tournois etalons (GTEs) as a phase-dispersion element [9 10] These interferometers employ apolarization beam splitter (PBS) to split the input signal intotwo beams and then recombine them at the beam splitterby using two GTEs to provide the redirection path theseinterferometers can be Michelson interferometers or Mach-Zehnder interferometers When a path length difference
exists between the two interfering beams these conventionalinterleavers provide a square-like spectrum transmissionfunction However in conventional etalons involving thinfilm coatings the performance is often optimized in a smallspectral region within the C-band They cannot carry on theentire C-band
To provide a uniform performance over the entire C-band the partial reflecting mirrors of the optical resonatormust maintain constant reflectivity over the entire C-bandSuch requirements are difficult to achieve by using con-ventional thin-film coating technology In this research theAdvanced Systems Analysis Program (ASAP) [11] opticalmodeling software has been utilized for the interleaverdesign The ASAP model is configured based on the actualcomponent parameters that compared with the actual size is1 1 The greatest shortcoming of conventional interleavers isan inferior dispersion In this study we propose a new schemeof birefringent optical interleaver employing dual-ring struc-tures including the quarter-wave (1205824) plates trapezoidprisms and the 1205826 wave plates to improve the dispersion
The next section presents the design procedures of a highperformance interleaver using quarter-wave (1205824) plates and
Hindawi Publishing CorporationMathematical Problems in EngineeringVolume 2015 Article ID 936493 7 pageshttpdxdoiorg1011552015936493
2 Mathematical Problems in Engineering
polarization opticsThen the design of an improved structureof interleaver is illustratedWe can get a very good dispersionimprovement to employ this proposed configuration Thesimulation result is performed to evaluate the performanceof this design method in Section 3 Finally we conclude thispaper in Section 4
2 The Proposed Interleaver Based onTwo Ring Configurations
Figure 1 shows the schematic configuration (noncompensa-tion) of the dual-ring structure based birefringent opticalinterleaver consisting of two birefringent crystals (the lengthof YVO
4is 30mm) two trapezoid prisms (transmission
rate is 914 and refraction index is 16) a polarizationbeam splitter (PBS) two 1205824 wave plates and four highlyreflective mirrors (reflectivity is 998) A beam of unpo-larized light is transmitting through the PBS and then thebeams are directed toward the YVO
4birefringent crystal and
the quarter-wave plate (1205824 45∘) The YVO4birefringent
crystal is used for appropriate retardance of interferenceThe quarter-wave plate is employed to rotate the polarizationstates of these two beams by 45 degrees As a result thebeams inside the birefringent crystals consist of both ordinaryand extraordinary waves but with equal amplitudes Whilethe beams propagate inside the birefringent crystals a phaseretardation exists between these two waves at the end of thecrystals These beams consisting of both ordinary and extra-ordinary waves are then directed toward the ring structureas shown in Figure 1
In both birefringent crystals (see Figure 1) the ordinarywave corresponds to the s-wave while the extraordinary onecorresponds to the p-wave The trapezoid prism interface ofthe ring structure exhibits different Fresnel reflectivities forthese two polarization components (s- and p-) of the beamAs a result of these different reflectivities the two polarizationcomponents experience further phase retardation by thequarter-wave plate (1205824 45∘) after the birefringent crystaland different phase shifts upon transmitting (or reflecting)through the ring arrangement Before both components ofthe beam are mixed and recombined by the PBS a phaseretardation by the birefringent crystal reoccurs again Thebirefringent crystal (YVO
4) acts as an interferometer and the
ring structure is configured by a prism and twomirrors (withair in the resonator)The ring configuration acting as aGires-Tounois Etalon is formed by the mirrors M
1 M2andM
3 M4
and the prism-air interface which are aligned perpendicular-wise to the light beams
The prism is cut in a trapezoid-shape to provide theappropriate angle of incidence so that the desired Fresnelreflectivities 119877
119900and 119877
119890 are obtained and 119877
119890and 119877
119900are the
reflectivity of the air-prism interface for the 119890-component(extraordinary beam) and 119900-component (ordinary beam)The normalized intensity of one of the output ports can beexpressed as follows [13ndash15]
1198681=1198680
2[1 + cos(4120587
120582Δ119899119871 + (120601
119890minus 1206010))] (1)
where 1198680is the intensity of the unpolarized incident beam
and 119871 is the length of the two birefringent crystals 120601119890and
120601119900are the phase shifts of the beam upon reflection from
the ring structure and (Δ119899 = 119899119890minus 119899119900) is the refractive
index difference of 119899119890and 119899
119900 The channel isolation of the
interleaver with the dual-ring structure is near 95 dB and thecalculated results of the stopband and channel isolation of a25GHz channel spacing application odd channels and evenchannels of partial C-band are shown in Figures 2(a) and2(b) respectively In Figure 2 the 25 dB stopband was foundto be 0173 nm (21625GHz) and a 05 dB wide passbandof 0156 nm (195GHz) hence we can reach the passbandutilization of 9017 (=0156 nm0173 nm times 100) And thechannel isolation of the interleaver is greater than 95 dB Thehigher passband utilization means that the output was closerto square wave results The more close to a square wave out-put the better the performance of interleaver These resultsclearly indicate that an interleaver with a ring structure canprovide a wide 05 dB passband and a good 25 dB stopband
3 Optimal Design of Improved DispersionInterleaver by Compensators
Chromatic dispersion compensation is the most deservingprogress in this study This interleaver with improved dis-persion compensation is shown in Figure 3 The polarizationazimuth angle of the birefringent crystal [16ndash19] is obtainedby employing 1205824wave plates (1205824 45∘) and 1205826 wave plates(1205826 30∘) The phase shifts of 1205824wave plates and 1205826waveplates can be expressed as (2) and (3) respectively
structure of 1205824wave plates and 1205826wave plates respectively119877(120595) is the coordinate rotation matrix and 119908
0is the Jones
matrix depending on the retarder platesThe output group delay after compensation can be viewed
as the average group delay from two modes 120591(120596) = [120591119890(120596) +
1205910(120596)]2 where 120596 = 2120587119888120582 is the optical angular frequency
and can be demonstrated as
120591 (120596) =119879
2
(1 minus 1198770)
1 + 1198770minus 2radic119877
0cos [(4120587120582) 119871
119877]
+ (1 minus [119877119890
(11990821+ 11990832)])
Mathematical Problems in Engineering 3
Prism
Birefringentcrystal
Birefringentcrystal
Prism
PBS
Source
Output 1
Output 2
M1
M2
M3M4
1205824
1205824
Y
X
Z
Figure 1 A schematic drawing of a 25GHz channel spacing interleaver based on two ring configurations
15530 1555015546155421553815534Wavelength (nm)
100
minus10
minus20
minus30
minus40
minus50
minus60
minus70
minus80
minus90
minus100
Tran
smiss
ion
(dB)
(a)
15530 1555015546155421553815534Wavelength (nm)
100
minus10
minus20
minus30
minus40
minus50
minus60
minus70
minus80
minus90
minus100
Tran
smiss
ion
(dB)
(b)
Figure 2 The transmission of a 25GHz interleaver passband utilization of 9549 (a) output port 1 (partial odd channels) and (b) outputport 2 (partial even channels) of C-band
4 Mathematical Problems in Engineering
Prism
Birefringentcrystal
Birefringentcrystal
Prism
PBS
Source
Output 1
Output 2
M1
M2
M3M4
1205824
12058241205826
1205826Y
X
Z
Figure 3 The ASAP layout of improved dispersion configuration
times (1 + [119877119890
(11990821+ 11990832)]
minus2[119877119890
(11990821+ 11990832)]
12
cos [(4120587120582) 119871119877])
minus1
(4)
In (4) 119871119877is the round-trip optical path of the ring structure
119879 = 119871119877119888 is the round-trip time and 120582 = 119888] Both 119908
1and
1199082are the transmission matrixes of 1205824 wave plates and 1205826
wave plates respectively After the dispersion is compensatedthe configuration as shown in Figure 3 the group velocitydispersion (GVD) is given by119863(120582) = 119889120591119889120582 [psnm] and canbe expressed as follows
119863 (120582) =4120587119871119877119879 sin ((4120587120582) 119871
119877)
1205822
times
(1198770)12
(1 minus 1198770)
[1 + 1198770minus 2(119877
0)12 cos ((4120587120582) 119871
119877)]2
+ ([(119877119890)
(11990821+ 11990832)]
12
[1 minus (119877119890
(11990821+ 11990832))])
times ([1 + (119877119890
(11990821+ 11990832)) minus 2(
119877119890
(11990821+ 11990832))
12
times cos((4120587120582) 119871119877)]
2
)
minus1
(5)
Figure 4 shows the path of the ring cavity which is con-figured by a trapezoid prism and two mirrors The incidentlight hits trapezoid prism at a perpendicular angle and totalreflects by the second surface and finally transmits throughthe first surface of prism perpendicular again In Figure 41205791and 120579
2are the incident and transmitted angles at third
surface and 1198991and 119899
2are the reflective indices of prism and
air respectively At the prism-air surface the different Fresnelreflectivities for ordinary wave and extraordinary wave (s-and p-polarization components) can be presented by [6]
According to (1) and (5) calculated by the simulationsoftware ASAP we can get normalized intensity of the output
Mathematical Problems in Engineering 5
Prism M1
M2
n1
n2
1205791
1205791
1205792
1205792
Figure 4 Optical path between the prism and air schematic chart
05
00
155278 155281155280155279Wavelength (nm)
Tran
smiss
ion
(dB)
minus05
minus10
minus15
minus20
minus25
minus30
minus35
minus40
minus45
minus50
times10minus9
Figure 5 The simulation result of the flat-top ripple in a 25GHzchannel spacing
channels and their chromatic dispersion In this study theoptimum incident angle 120579
1is about 345∘ At this angle
of incidence the reflectivities of the flat-top bandwidthinterleaver are about 119877
119900= 1701 and 119877
119890= 839
And the ripple of output power intensity of the 25GHzchannel spacing is 0227397times10minus9 dB (see Figure 5) Figure 6shows that the dispersion comparison of a 25GHz channelspacing of partial C-band with- and without-compensationThe research results illustrate that our modified schemecan improve the dispersion of more than 858 (=(15243ndash21593)15243)The effect of improved dispersion of a 25GHzinterleaver can be observed as shown in Figure 7The opticalintensities of without-compensating and with-compensatingschemes are 0546 au and 0936 au respectively The eyediagrams for 10Gbs application of with-compensation andwithout-compensation by pseudorandom binary sequence(PRBS) (231-1) have beenmeasured as shown in Figure 8Theresearch results are compared with other related issues suchas a ring-cavity architecture system [6 12] and using Gires-Tournois etalons as phase dispersive mirrors in a Michelsoninterferometer system [9] (see Table 1)
4 Conclusions
We have analyzed a flat-top 25GHz optical interleaver basedon a dual-ring architecture with fewer components Com-pared to previous studies our interleaver exhibited a 05 dB
15530 155361553415532Wavelength (nm)
20
15
10
05
00
With-compensationWithout-compensation
15243 psnm
21593 psnm
Chro
mat
ic d
isper
sion
(ps
nm)
times103
minus05
minus10
minus15
minus20
Figure 6 The chromatic dispersion comparison between with-compensation and without-compensation of a 25GHz channelspacing of partial C-band
1009080706050403020100
0 5 10 15 20 25
With-compensationWithout-compensation
0936
0546
Inte
nsity
(au
)
minus25 minus20 minus15 minus10 minus5
Z (nm) times10minus3
Figure 7 The optical intensity comparisons of a 25GHz chan-nel spacing the calculated intensities are 0936 au of with-compensation and 0546 au of without-compensation
passband larger than 0156 nm (195 GHz) a 25 dB stop-band greater than 0173 nm (21625GHz) a channel isolationgreater than 95 dB and an excellent flat-top ripple which issmaller than 0227 times 10minus9 dB The benefit of this interleaveris that it utilizes the Fresnel principle to achieve precisereflectivity Unlike dielectric mirrors with thin-film coatingsthe reflectivities of the Fresnel reflection are insensitive towavelength variations in the transmission band Uniformreflectivities are essential to ensure the same performanceover the entire C-band In particular the novel interleavercan simultaneously produce an excellent performance ofchromatic dispersion which can achieve an improvement of
6 Mathematical Problems in Engineering
0 105Time (bit period)
Eye diagram analyzer
800
600
400
200
0
Am
plitu
de (a
u)
(a)
0 105Time (bit period)
Eye diagram analyzer
800
600
400
200
0
Am
plitu
de (a
u)
(b)
Figure 8 The eye diagrams by PRBS 231-1 for 10Gbs application (a) with-compensation and (b) without-compensation
Table 1 The characteristics comparison of interleaver systems
Characteristics System typeLee et al [6] Lee et al [12] Hsieh et al [9] This work
Filter channel spacing 25GHz 25GHz 50GHz 25GHzStructure technique Sagnac interferometer and ring cavity Ring cavity Gires-Tournois etalons Two-ring cavityChannel isolation (dB) 45 gt36 30 9505 dB passband (nm) 0182 gt0145 035 015625 dB stopband (nm) 0155 gt0145 032 0173Flat-top ripple (dB) lt10minus3 sim10minus3 NA 0227 times 10minus9
858when wemodify the interleavers structure by 1205826waveplatesThis unique interleaver is suitable for capacity upgradein DWDM and FTTx applications
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
The authors would like to gratefully acknowledge the Min-istry of Science and Technology of Taiwan for their fundingsupport under MOST 103-2622-E-327-007-CC3
References
[1] T Liang and S Hsu ldquoThe L-band EDFA of high clamped gainand low noise figure implemented using fiber Bragg grating anddouble-pass methodrdquo Optics Communications vol 281 no 5pp 1134ndash1139 2008
[2] S V Kartalopoulos Introduction to DWDMTechnology Data ina Rainbow chapter 1 IEEE Press New York NY USA 2000
[3] T C Liang C M Tsai and B C Wu ldquoA wavelength routingdevice by using cyclic AWGs and tunable FBGsrdquo Optical FiberTechnology vol 19 no 3 pp 189ndash193 2013
[4] R Saunders ldquoCoherent DWDM technology for high speedoptical communicationsrdquo Optical Fiber Technology vol 17 no5 pp 445ndash451 2011
[5] RCasellas RMunoz JM Fabrega et al ldquoGMPLSPCE controlof flexi-grid DWDM optical networks using CO-OFDM trans-missionrdquo Journal of Optical Communications and Networkingvol 4 no 11 Article ID 6360163 pp B1ndashB10 2012
[6] C W Lee R Wang P Yeh and W H Cheng ldquoA flat-top birefringent interleaver based on ring-cavity architecturerdquoOptics Communications vol 260 no 1 pp 311ndash317 2006
[7] A Zeng X-G Ye J Chon and F Liang ldquo25 GHz interleaverswith ultra-low chromatic dispersionrdquo in Proceedings of the Opti-cal Fiber Communication Conference and Exhibit (OFC rsquo02) pp396ndash398 March 2002
[8] T C Liang and C T Chen ldquoInvestigation of dispersion andperformance based on ring cavity by birefringent interleaverfor DWDM transmission systemsrdquo Mathematical Problems inEngineering vol 2013 Article ID 740412 5 pages 2013
[9] C Hsieh R Wang Z J Wen et al ldquoFlat-top interleavers usingtwo Gires-Tournois etalons as phase-dispersive mirrors in aMichelson interferometerrdquo IEEE Photonics Technology Lettersvol 15 no 2 pp 242ndash244 2003
Mathematical Problems in Engineering 7
[10] J Zhang and X Yang ldquoUniversal Michelson Gires-Tournoisinterferometer optical interleaver based on digital signal pro-cessingrdquo Optics Express vol 18 no 5 pp 5075ndash5088 2010
[11] ASAP (Advanced Systems Analysis Program) Breault ResearchOrganization Inc Tucson Ariz USA
[12] C Lee R Wang P Yeh and W Cheng ldquoSagnac interferometerbased flat-top birefringent interleaverrdquo Optics Express vol 14no 11 pp 4636ndash4643 2006
[13] P YehOpticalWaves in LayeredMedia JohnWileyamp SonsNewYork NY USA 1998
[14] S Cao J Chen J N Damask et al ldquoInterleaver technologycomparisons and applications requirementsrdquo Journal of Light-wave Technology vol 22 no 1 pp 281ndash289 2004
[15] B B Dingel and M Izutsu ldquoMultifunction optical filter with aMichelson-Gires-Tournois interferometer for wavelength-divi-sion-multiplexed network system applicationsrdquo Optics Lettersvol 23 no 14 pp 1099ndash1101 1998
[16] L Wei and J W Y Lit ldquoDesign optimization of flattop inter-leaver and its dispersion compensationrdquo Optics Express vol 15no 10 pp 6439ndash6457 2007
[17] J Zhang L Lin and Y Zhou ldquoNovel and simple approach fordesigning lattice-form interleaver filterrdquo Optics Express vol 11no 18 pp 2217ndash2224 2003
[18] M Oguma T Kitoh Y Inoue et al ldquoCompact and low-lossinterleave filter employing lattice-form structure and silica-based waveguiderdquo Journal of Lightwave Technology vol 22 no3 pp 895ndash902 2004
[19] K Jinguji and M Oguma ldquoOptical half-band filtersrdquo Journal ofLightwave Technology vol 18 no 2 pp 252ndash259 2000
polarization opticsThen the design of an improved structureof interleaver is illustratedWe can get a very good dispersionimprovement to employ this proposed configuration Thesimulation result is performed to evaluate the performanceof this design method in Section 3 Finally we conclude thispaper in Section 4
2 The Proposed Interleaver Based onTwo Ring Configurations
Figure 1 shows the schematic configuration (noncompensa-tion) of the dual-ring structure based birefringent opticalinterleaver consisting of two birefringent crystals (the lengthof YVO
4is 30mm) two trapezoid prisms (transmission
rate is 914 and refraction index is 16) a polarizationbeam splitter (PBS) two 1205824 wave plates and four highlyreflective mirrors (reflectivity is 998) A beam of unpo-larized light is transmitting through the PBS and then thebeams are directed toward the YVO
4birefringent crystal and
the quarter-wave plate (1205824 45∘) The YVO4birefringent
crystal is used for appropriate retardance of interferenceThe quarter-wave plate is employed to rotate the polarizationstates of these two beams by 45 degrees As a result thebeams inside the birefringent crystals consist of both ordinaryand extraordinary waves but with equal amplitudes Whilethe beams propagate inside the birefringent crystals a phaseretardation exists between these two waves at the end of thecrystals These beams consisting of both ordinary and extra-ordinary waves are then directed toward the ring structureas shown in Figure 1
In both birefringent crystals (see Figure 1) the ordinarywave corresponds to the s-wave while the extraordinary onecorresponds to the p-wave The trapezoid prism interface ofthe ring structure exhibits different Fresnel reflectivities forthese two polarization components (s- and p-) of the beamAs a result of these different reflectivities the two polarizationcomponents experience further phase retardation by thequarter-wave plate (1205824 45∘) after the birefringent crystaland different phase shifts upon transmitting (or reflecting)through the ring arrangement Before both components ofthe beam are mixed and recombined by the PBS a phaseretardation by the birefringent crystal reoccurs again Thebirefringent crystal (YVO
4) acts as an interferometer and the
ring structure is configured by a prism and twomirrors (withair in the resonator)The ring configuration acting as aGires-Tounois Etalon is formed by the mirrors M
1 M2andM
3 M4
and the prism-air interface which are aligned perpendicular-wise to the light beams
The prism is cut in a trapezoid-shape to provide theappropriate angle of incidence so that the desired Fresnelreflectivities 119877
119900and 119877
119890 are obtained and 119877
119890and 119877
119900are the
reflectivity of the air-prism interface for the 119890-component(extraordinary beam) and 119900-component (ordinary beam)The normalized intensity of one of the output ports can beexpressed as follows [13ndash15]
1198681=1198680
2[1 + cos(4120587
120582Δ119899119871 + (120601
119890minus 1206010))] (1)
where 1198680is the intensity of the unpolarized incident beam
and 119871 is the length of the two birefringent crystals 120601119890and
120601119900are the phase shifts of the beam upon reflection from
the ring structure and (Δ119899 = 119899119890minus 119899119900) is the refractive
index difference of 119899119890and 119899
119900 The channel isolation of the
interleaver with the dual-ring structure is near 95 dB and thecalculated results of the stopband and channel isolation of a25GHz channel spacing application odd channels and evenchannels of partial C-band are shown in Figures 2(a) and2(b) respectively In Figure 2 the 25 dB stopband was foundto be 0173 nm (21625GHz) and a 05 dB wide passbandof 0156 nm (195GHz) hence we can reach the passbandutilization of 9017 (=0156 nm0173 nm times 100) And thechannel isolation of the interleaver is greater than 95 dB Thehigher passband utilization means that the output was closerto square wave results The more close to a square wave out-put the better the performance of interleaver These resultsclearly indicate that an interleaver with a ring structure canprovide a wide 05 dB passband and a good 25 dB stopband
3 Optimal Design of Improved DispersionInterleaver by Compensators
Chromatic dispersion compensation is the most deservingprogress in this study This interleaver with improved dis-persion compensation is shown in Figure 3 The polarizationazimuth angle of the birefringent crystal [16ndash19] is obtainedby employing 1205824wave plates (1205824 45∘) and 1205826 wave plates(1205826 30∘) The phase shifts of 1205824wave plates and 1205826waveplates can be expressed as (2) and (3) respectively
structure of 1205824wave plates and 1205826wave plates respectively119877(120595) is the coordinate rotation matrix and 119908
0is the Jones
matrix depending on the retarder platesThe output group delay after compensation can be viewed
as the average group delay from two modes 120591(120596) = [120591119890(120596) +
1205910(120596)]2 where 120596 = 2120587119888120582 is the optical angular frequency
and can be demonstrated as
120591 (120596) =119879
2
(1 minus 1198770)
1 + 1198770minus 2radic119877
0cos [(4120587120582) 119871
119877]
+ (1 minus [119877119890
(11990821+ 11990832)])
Mathematical Problems in Engineering 3
Prism
Birefringentcrystal
Birefringentcrystal
Prism
PBS
Source
Output 1
Output 2
M1
M2
M3M4
1205824
1205824
Y
X
Z
Figure 1 A schematic drawing of a 25GHz channel spacing interleaver based on two ring configurations
15530 1555015546155421553815534Wavelength (nm)
100
minus10
minus20
minus30
minus40
minus50
minus60
minus70
minus80
minus90
minus100
Tran
smiss
ion
(dB)
(a)
15530 1555015546155421553815534Wavelength (nm)
100
minus10
minus20
minus30
minus40
minus50
minus60
minus70
minus80
minus90
minus100
Tran
smiss
ion
(dB)
(b)
Figure 2 The transmission of a 25GHz interleaver passband utilization of 9549 (a) output port 1 (partial odd channels) and (b) outputport 2 (partial even channels) of C-band
4 Mathematical Problems in Engineering
Prism
Birefringentcrystal
Birefringentcrystal
Prism
PBS
Source
Output 1
Output 2
M1
M2
M3M4
1205824
12058241205826
1205826Y
X
Z
Figure 3 The ASAP layout of improved dispersion configuration
times (1 + [119877119890
(11990821+ 11990832)]
minus2[119877119890
(11990821+ 11990832)]
12
cos [(4120587120582) 119871119877])
minus1
(4)
In (4) 119871119877is the round-trip optical path of the ring structure
119879 = 119871119877119888 is the round-trip time and 120582 = 119888] Both 119908
1and
1199082are the transmission matrixes of 1205824 wave plates and 1205826
wave plates respectively After the dispersion is compensatedthe configuration as shown in Figure 3 the group velocitydispersion (GVD) is given by119863(120582) = 119889120591119889120582 [psnm] and canbe expressed as follows
119863 (120582) =4120587119871119877119879 sin ((4120587120582) 119871
119877)
1205822
times
(1198770)12
(1 minus 1198770)
[1 + 1198770minus 2(119877
0)12 cos ((4120587120582) 119871
119877)]2
+ ([(119877119890)
(11990821+ 11990832)]
12
[1 minus (119877119890
(11990821+ 11990832))])
times ([1 + (119877119890
(11990821+ 11990832)) minus 2(
119877119890
(11990821+ 11990832))
12
times cos((4120587120582) 119871119877)]
2
)
minus1
(5)
Figure 4 shows the path of the ring cavity which is con-figured by a trapezoid prism and two mirrors The incidentlight hits trapezoid prism at a perpendicular angle and totalreflects by the second surface and finally transmits throughthe first surface of prism perpendicular again In Figure 41205791and 120579
2are the incident and transmitted angles at third
surface and 1198991and 119899
2are the reflective indices of prism and
air respectively At the prism-air surface the different Fresnelreflectivities for ordinary wave and extraordinary wave (s-and p-polarization components) can be presented by [6]
According to (1) and (5) calculated by the simulationsoftware ASAP we can get normalized intensity of the output
Mathematical Problems in Engineering 5
Prism M1
M2
n1
n2
1205791
1205791
1205792
1205792
Figure 4 Optical path between the prism and air schematic chart
05
00
155278 155281155280155279Wavelength (nm)
Tran
smiss
ion
(dB)
minus05
minus10
minus15
minus20
minus25
minus30
minus35
minus40
minus45
minus50
times10minus9
Figure 5 The simulation result of the flat-top ripple in a 25GHzchannel spacing
channels and their chromatic dispersion In this study theoptimum incident angle 120579
1is about 345∘ At this angle
of incidence the reflectivities of the flat-top bandwidthinterleaver are about 119877
119900= 1701 and 119877
119890= 839
And the ripple of output power intensity of the 25GHzchannel spacing is 0227397times10minus9 dB (see Figure 5) Figure 6shows that the dispersion comparison of a 25GHz channelspacing of partial C-band with- and without-compensationThe research results illustrate that our modified schemecan improve the dispersion of more than 858 (=(15243ndash21593)15243)The effect of improved dispersion of a 25GHzinterleaver can be observed as shown in Figure 7The opticalintensities of without-compensating and with-compensatingschemes are 0546 au and 0936 au respectively The eyediagrams for 10Gbs application of with-compensation andwithout-compensation by pseudorandom binary sequence(PRBS) (231-1) have beenmeasured as shown in Figure 8Theresearch results are compared with other related issues suchas a ring-cavity architecture system [6 12] and using Gires-Tournois etalons as phase dispersive mirrors in a Michelsoninterferometer system [9] (see Table 1)
4 Conclusions
We have analyzed a flat-top 25GHz optical interleaver basedon a dual-ring architecture with fewer components Com-pared to previous studies our interleaver exhibited a 05 dB
15530 155361553415532Wavelength (nm)
20
15
10
05
00
With-compensationWithout-compensation
15243 psnm
21593 psnm
Chro
mat
ic d
isper
sion
(ps
nm)
times103
minus05
minus10
minus15
minus20
Figure 6 The chromatic dispersion comparison between with-compensation and without-compensation of a 25GHz channelspacing of partial C-band
1009080706050403020100
0 5 10 15 20 25
With-compensationWithout-compensation
0936
0546
Inte
nsity
(au
)
minus25 minus20 minus15 minus10 minus5
Z (nm) times10minus3
Figure 7 The optical intensity comparisons of a 25GHz chan-nel spacing the calculated intensities are 0936 au of with-compensation and 0546 au of without-compensation
passband larger than 0156 nm (195 GHz) a 25 dB stop-band greater than 0173 nm (21625GHz) a channel isolationgreater than 95 dB and an excellent flat-top ripple which issmaller than 0227 times 10minus9 dB The benefit of this interleaveris that it utilizes the Fresnel principle to achieve precisereflectivity Unlike dielectric mirrors with thin-film coatingsthe reflectivities of the Fresnel reflection are insensitive towavelength variations in the transmission band Uniformreflectivities are essential to ensure the same performanceover the entire C-band In particular the novel interleavercan simultaneously produce an excellent performance ofchromatic dispersion which can achieve an improvement of
6 Mathematical Problems in Engineering
0 105Time (bit period)
Eye diagram analyzer
800
600
400
200
0
Am
plitu
de (a
u)
(a)
0 105Time (bit period)
Eye diagram analyzer
800
600
400
200
0
Am
plitu
de (a
u)
(b)
Figure 8 The eye diagrams by PRBS 231-1 for 10Gbs application (a) with-compensation and (b) without-compensation
Table 1 The characteristics comparison of interleaver systems
Characteristics System typeLee et al [6] Lee et al [12] Hsieh et al [9] This work
Filter channel spacing 25GHz 25GHz 50GHz 25GHzStructure technique Sagnac interferometer and ring cavity Ring cavity Gires-Tournois etalons Two-ring cavityChannel isolation (dB) 45 gt36 30 9505 dB passband (nm) 0182 gt0145 035 015625 dB stopband (nm) 0155 gt0145 032 0173Flat-top ripple (dB) lt10minus3 sim10minus3 NA 0227 times 10minus9
858when wemodify the interleavers structure by 1205826waveplatesThis unique interleaver is suitable for capacity upgradein DWDM and FTTx applications
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
The authors would like to gratefully acknowledge the Min-istry of Science and Technology of Taiwan for their fundingsupport under MOST 103-2622-E-327-007-CC3
References
[1] T Liang and S Hsu ldquoThe L-band EDFA of high clamped gainand low noise figure implemented using fiber Bragg grating anddouble-pass methodrdquo Optics Communications vol 281 no 5pp 1134ndash1139 2008
[2] S V Kartalopoulos Introduction to DWDMTechnology Data ina Rainbow chapter 1 IEEE Press New York NY USA 2000
[3] T C Liang C M Tsai and B C Wu ldquoA wavelength routingdevice by using cyclic AWGs and tunable FBGsrdquo Optical FiberTechnology vol 19 no 3 pp 189ndash193 2013
[4] R Saunders ldquoCoherent DWDM technology for high speedoptical communicationsrdquo Optical Fiber Technology vol 17 no5 pp 445ndash451 2011
[5] RCasellas RMunoz JM Fabrega et al ldquoGMPLSPCE controlof flexi-grid DWDM optical networks using CO-OFDM trans-missionrdquo Journal of Optical Communications and Networkingvol 4 no 11 Article ID 6360163 pp B1ndashB10 2012
[6] C W Lee R Wang P Yeh and W H Cheng ldquoA flat-top birefringent interleaver based on ring-cavity architecturerdquoOptics Communications vol 260 no 1 pp 311ndash317 2006
[7] A Zeng X-G Ye J Chon and F Liang ldquo25 GHz interleaverswith ultra-low chromatic dispersionrdquo in Proceedings of the Opti-cal Fiber Communication Conference and Exhibit (OFC rsquo02) pp396ndash398 March 2002
[8] T C Liang and C T Chen ldquoInvestigation of dispersion andperformance based on ring cavity by birefringent interleaverfor DWDM transmission systemsrdquo Mathematical Problems inEngineering vol 2013 Article ID 740412 5 pages 2013
[9] C Hsieh R Wang Z J Wen et al ldquoFlat-top interleavers usingtwo Gires-Tournois etalons as phase-dispersive mirrors in aMichelson interferometerrdquo IEEE Photonics Technology Lettersvol 15 no 2 pp 242ndash244 2003
Mathematical Problems in Engineering 7
[10] J Zhang and X Yang ldquoUniversal Michelson Gires-Tournoisinterferometer optical interleaver based on digital signal pro-cessingrdquo Optics Express vol 18 no 5 pp 5075ndash5088 2010
[11] ASAP (Advanced Systems Analysis Program) Breault ResearchOrganization Inc Tucson Ariz USA
[12] C Lee R Wang P Yeh and W Cheng ldquoSagnac interferometerbased flat-top birefringent interleaverrdquo Optics Express vol 14no 11 pp 4636ndash4643 2006
[13] P YehOpticalWaves in LayeredMedia JohnWileyamp SonsNewYork NY USA 1998
[14] S Cao J Chen J N Damask et al ldquoInterleaver technologycomparisons and applications requirementsrdquo Journal of Light-wave Technology vol 22 no 1 pp 281ndash289 2004
[15] B B Dingel and M Izutsu ldquoMultifunction optical filter with aMichelson-Gires-Tournois interferometer for wavelength-divi-sion-multiplexed network system applicationsrdquo Optics Lettersvol 23 no 14 pp 1099ndash1101 1998
[16] L Wei and J W Y Lit ldquoDesign optimization of flattop inter-leaver and its dispersion compensationrdquo Optics Express vol 15no 10 pp 6439ndash6457 2007
[17] J Zhang L Lin and Y Zhou ldquoNovel and simple approach fordesigning lattice-form interleaver filterrdquo Optics Express vol 11no 18 pp 2217ndash2224 2003
[18] M Oguma T Kitoh Y Inoue et al ldquoCompact and low-lossinterleave filter employing lattice-form structure and silica-based waveguiderdquo Journal of Lightwave Technology vol 22 no3 pp 895ndash902 2004
[19] K Jinguji and M Oguma ldquoOptical half-band filtersrdquo Journal ofLightwave Technology vol 18 no 2 pp 252ndash259 2000
Figure 1 A schematic drawing of a 25GHz channel spacing interleaver based on two ring configurations
15530 1555015546155421553815534Wavelength (nm)
100
minus10
minus20
minus30
minus40
minus50
minus60
minus70
minus80
minus90
minus100
Tran
smiss
ion
(dB)
(a)
15530 1555015546155421553815534Wavelength (nm)
100
minus10
minus20
minus30
minus40
minus50
minus60
minus70
minus80
minus90
minus100
Tran
smiss
ion
(dB)
(b)
Figure 2 The transmission of a 25GHz interleaver passband utilization of 9549 (a) output port 1 (partial odd channels) and (b) outputport 2 (partial even channels) of C-band
4 Mathematical Problems in Engineering
Prism
Birefringentcrystal
Birefringentcrystal
Prism
PBS
Source
Output 1
Output 2
M1
M2
M3M4
1205824
12058241205826
1205826Y
X
Z
Figure 3 The ASAP layout of improved dispersion configuration
times (1 + [119877119890
(11990821+ 11990832)]
minus2[119877119890
(11990821+ 11990832)]
12
cos [(4120587120582) 119871119877])
minus1
(4)
In (4) 119871119877is the round-trip optical path of the ring structure
119879 = 119871119877119888 is the round-trip time and 120582 = 119888] Both 119908
1and
1199082are the transmission matrixes of 1205824 wave plates and 1205826
wave plates respectively After the dispersion is compensatedthe configuration as shown in Figure 3 the group velocitydispersion (GVD) is given by119863(120582) = 119889120591119889120582 [psnm] and canbe expressed as follows
119863 (120582) =4120587119871119877119879 sin ((4120587120582) 119871
119877)
1205822
times
(1198770)12
(1 minus 1198770)
[1 + 1198770minus 2(119877
0)12 cos ((4120587120582) 119871
119877)]2
+ ([(119877119890)
(11990821+ 11990832)]
12
[1 minus (119877119890
(11990821+ 11990832))])
times ([1 + (119877119890
(11990821+ 11990832)) minus 2(
119877119890
(11990821+ 11990832))
12
times cos((4120587120582) 119871119877)]
2
)
minus1
(5)
Figure 4 shows the path of the ring cavity which is con-figured by a trapezoid prism and two mirrors The incidentlight hits trapezoid prism at a perpendicular angle and totalreflects by the second surface and finally transmits throughthe first surface of prism perpendicular again In Figure 41205791and 120579
2are the incident and transmitted angles at third
surface and 1198991and 119899
2are the reflective indices of prism and
air respectively At the prism-air surface the different Fresnelreflectivities for ordinary wave and extraordinary wave (s-and p-polarization components) can be presented by [6]
According to (1) and (5) calculated by the simulationsoftware ASAP we can get normalized intensity of the output
Mathematical Problems in Engineering 5
Prism M1
M2
n1
n2
1205791
1205791
1205792
1205792
Figure 4 Optical path between the prism and air schematic chart
05
00
155278 155281155280155279Wavelength (nm)
Tran
smiss
ion
(dB)
minus05
minus10
minus15
minus20
minus25
minus30
minus35
minus40
minus45
minus50
times10minus9
Figure 5 The simulation result of the flat-top ripple in a 25GHzchannel spacing
channels and their chromatic dispersion In this study theoptimum incident angle 120579
1is about 345∘ At this angle
of incidence the reflectivities of the flat-top bandwidthinterleaver are about 119877
119900= 1701 and 119877
119890= 839
And the ripple of output power intensity of the 25GHzchannel spacing is 0227397times10minus9 dB (see Figure 5) Figure 6shows that the dispersion comparison of a 25GHz channelspacing of partial C-band with- and without-compensationThe research results illustrate that our modified schemecan improve the dispersion of more than 858 (=(15243ndash21593)15243)The effect of improved dispersion of a 25GHzinterleaver can be observed as shown in Figure 7The opticalintensities of without-compensating and with-compensatingschemes are 0546 au and 0936 au respectively The eyediagrams for 10Gbs application of with-compensation andwithout-compensation by pseudorandom binary sequence(PRBS) (231-1) have beenmeasured as shown in Figure 8Theresearch results are compared with other related issues suchas a ring-cavity architecture system [6 12] and using Gires-Tournois etalons as phase dispersive mirrors in a Michelsoninterferometer system [9] (see Table 1)
4 Conclusions
We have analyzed a flat-top 25GHz optical interleaver basedon a dual-ring architecture with fewer components Com-pared to previous studies our interleaver exhibited a 05 dB
15530 155361553415532Wavelength (nm)
20
15
10
05
00
With-compensationWithout-compensation
15243 psnm
21593 psnm
Chro
mat
ic d
isper
sion
(ps
nm)
times103
minus05
minus10
minus15
minus20
Figure 6 The chromatic dispersion comparison between with-compensation and without-compensation of a 25GHz channelspacing of partial C-band
1009080706050403020100
0 5 10 15 20 25
With-compensationWithout-compensation
0936
0546
Inte
nsity
(au
)
minus25 minus20 minus15 minus10 minus5
Z (nm) times10minus3
Figure 7 The optical intensity comparisons of a 25GHz chan-nel spacing the calculated intensities are 0936 au of with-compensation and 0546 au of without-compensation
passband larger than 0156 nm (195 GHz) a 25 dB stop-band greater than 0173 nm (21625GHz) a channel isolationgreater than 95 dB and an excellent flat-top ripple which issmaller than 0227 times 10minus9 dB The benefit of this interleaveris that it utilizes the Fresnel principle to achieve precisereflectivity Unlike dielectric mirrors with thin-film coatingsthe reflectivities of the Fresnel reflection are insensitive towavelength variations in the transmission band Uniformreflectivities are essential to ensure the same performanceover the entire C-band In particular the novel interleavercan simultaneously produce an excellent performance ofchromatic dispersion which can achieve an improvement of
6 Mathematical Problems in Engineering
0 105Time (bit period)
Eye diagram analyzer
800
600
400
200
0
Am
plitu
de (a
u)
(a)
0 105Time (bit period)
Eye diagram analyzer
800
600
400
200
0
Am
plitu
de (a
u)
(b)
Figure 8 The eye diagrams by PRBS 231-1 for 10Gbs application (a) with-compensation and (b) without-compensation
Table 1 The characteristics comparison of interleaver systems
Characteristics System typeLee et al [6] Lee et al [12] Hsieh et al [9] This work
Filter channel spacing 25GHz 25GHz 50GHz 25GHzStructure technique Sagnac interferometer and ring cavity Ring cavity Gires-Tournois etalons Two-ring cavityChannel isolation (dB) 45 gt36 30 9505 dB passband (nm) 0182 gt0145 035 015625 dB stopband (nm) 0155 gt0145 032 0173Flat-top ripple (dB) lt10minus3 sim10minus3 NA 0227 times 10minus9
858when wemodify the interleavers structure by 1205826waveplatesThis unique interleaver is suitable for capacity upgradein DWDM and FTTx applications
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
The authors would like to gratefully acknowledge the Min-istry of Science and Technology of Taiwan for their fundingsupport under MOST 103-2622-E-327-007-CC3
References
[1] T Liang and S Hsu ldquoThe L-band EDFA of high clamped gainand low noise figure implemented using fiber Bragg grating anddouble-pass methodrdquo Optics Communications vol 281 no 5pp 1134ndash1139 2008
[2] S V Kartalopoulos Introduction to DWDMTechnology Data ina Rainbow chapter 1 IEEE Press New York NY USA 2000
[3] T C Liang C M Tsai and B C Wu ldquoA wavelength routingdevice by using cyclic AWGs and tunable FBGsrdquo Optical FiberTechnology vol 19 no 3 pp 189ndash193 2013
[4] R Saunders ldquoCoherent DWDM technology for high speedoptical communicationsrdquo Optical Fiber Technology vol 17 no5 pp 445ndash451 2011
[5] RCasellas RMunoz JM Fabrega et al ldquoGMPLSPCE controlof flexi-grid DWDM optical networks using CO-OFDM trans-missionrdquo Journal of Optical Communications and Networkingvol 4 no 11 Article ID 6360163 pp B1ndashB10 2012
[6] C W Lee R Wang P Yeh and W H Cheng ldquoA flat-top birefringent interleaver based on ring-cavity architecturerdquoOptics Communications vol 260 no 1 pp 311ndash317 2006
[7] A Zeng X-G Ye J Chon and F Liang ldquo25 GHz interleaverswith ultra-low chromatic dispersionrdquo in Proceedings of the Opti-cal Fiber Communication Conference and Exhibit (OFC rsquo02) pp396ndash398 March 2002
[8] T C Liang and C T Chen ldquoInvestigation of dispersion andperformance based on ring cavity by birefringent interleaverfor DWDM transmission systemsrdquo Mathematical Problems inEngineering vol 2013 Article ID 740412 5 pages 2013
[9] C Hsieh R Wang Z J Wen et al ldquoFlat-top interleavers usingtwo Gires-Tournois etalons as phase-dispersive mirrors in aMichelson interferometerrdquo IEEE Photonics Technology Lettersvol 15 no 2 pp 242ndash244 2003
Mathematical Problems in Engineering 7
[10] J Zhang and X Yang ldquoUniversal Michelson Gires-Tournoisinterferometer optical interleaver based on digital signal pro-cessingrdquo Optics Express vol 18 no 5 pp 5075ndash5088 2010
[11] ASAP (Advanced Systems Analysis Program) Breault ResearchOrganization Inc Tucson Ariz USA
[12] C Lee R Wang P Yeh and W Cheng ldquoSagnac interferometerbased flat-top birefringent interleaverrdquo Optics Express vol 14no 11 pp 4636ndash4643 2006
[13] P YehOpticalWaves in LayeredMedia JohnWileyamp SonsNewYork NY USA 1998
[14] S Cao J Chen J N Damask et al ldquoInterleaver technologycomparisons and applications requirementsrdquo Journal of Light-wave Technology vol 22 no 1 pp 281ndash289 2004
[15] B B Dingel and M Izutsu ldquoMultifunction optical filter with aMichelson-Gires-Tournois interferometer for wavelength-divi-sion-multiplexed network system applicationsrdquo Optics Lettersvol 23 no 14 pp 1099ndash1101 1998
[16] L Wei and J W Y Lit ldquoDesign optimization of flattop inter-leaver and its dispersion compensationrdquo Optics Express vol 15no 10 pp 6439ndash6457 2007
[17] J Zhang L Lin and Y Zhou ldquoNovel and simple approach fordesigning lattice-form interleaver filterrdquo Optics Express vol 11no 18 pp 2217ndash2224 2003
[18] M Oguma T Kitoh Y Inoue et al ldquoCompact and low-lossinterleave filter employing lattice-form structure and silica-based waveguiderdquo Journal of Lightwave Technology vol 22 no3 pp 895ndash902 2004
[19] K Jinguji and M Oguma ldquoOptical half-band filtersrdquo Journal ofLightwave Technology vol 18 no 2 pp 252ndash259 2000
Figure 3 The ASAP layout of improved dispersion configuration
times (1 + [119877119890
(11990821+ 11990832)]
minus2[119877119890
(11990821+ 11990832)]
12
cos [(4120587120582) 119871119877])
minus1
(4)
In (4) 119871119877is the round-trip optical path of the ring structure
119879 = 119871119877119888 is the round-trip time and 120582 = 119888] Both 119908
1and
1199082are the transmission matrixes of 1205824 wave plates and 1205826
wave plates respectively After the dispersion is compensatedthe configuration as shown in Figure 3 the group velocitydispersion (GVD) is given by119863(120582) = 119889120591119889120582 [psnm] and canbe expressed as follows
119863 (120582) =4120587119871119877119879 sin ((4120587120582) 119871
119877)
1205822
times
(1198770)12
(1 minus 1198770)
[1 + 1198770minus 2(119877
0)12 cos ((4120587120582) 119871
119877)]2
+ ([(119877119890)
(11990821+ 11990832)]
12
[1 minus (119877119890
(11990821+ 11990832))])
times ([1 + (119877119890
(11990821+ 11990832)) minus 2(
119877119890
(11990821+ 11990832))
12
times cos((4120587120582) 119871119877)]
2
)
minus1
(5)
Figure 4 shows the path of the ring cavity which is con-figured by a trapezoid prism and two mirrors The incidentlight hits trapezoid prism at a perpendicular angle and totalreflects by the second surface and finally transmits throughthe first surface of prism perpendicular again In Figure 41205791and 120579
2are the incident and transmitted angles at third
surface and 1198991and 119899
2are the reflective indices of prism and
air respectively At the prism-air surface the different Fresnelreflectivities for ordinary wave and extraordinary wave (s-and p-polarization components) can be presented by [6]
According to (1) and (5) calculated by the simulationsoftware ASAP we can get normalized intensity of the output
Mathematical Problems in Engineering 5
Prism M1
M2
n1
n2
1205791
1205791
1205792
1205792
Figure 4 Optical path between the prism and air schematic chart
05
00
155278 155281155280155279Wavelength (nm)
Tran
smiss
ion
(dB)
minus05
minus10
minus15
minus20
minus25
minus30
minus35
minus40
minus45
minus50
times10minus9
Figure 5 The simulation result of the flat-top ripple in a 25GHzchannel spacing
channels and their chromatic dispersion In this study theoptimum incident angle 120579
1is about 345∘ At this angle
of incidence the reflectivities of the flat-top bandwidthinterleaver are about 119877
119900= 1701 and 119877
119890= 839
And the ripple of output power intensity of the 25GHzchannel spacing is 0227397times10minus9 dB (see Figure 5) Figure 6shows that the dispersion comparison of a 25GHz channelspacing of partial C-band with- and without-compensationThe research results illustrate that our modified schemecan improve the dispersion of more than 858 (=(15243ndash21593)15243)The effect of improved dispersion of a 25GHzinterleaver can be observed as shown in Figure 7The opticalintensities of without-compensating and with-compensatingschemes are 0546 au and 0936 au respectively The eyediagrams for 10Gbs application of with-compensation andwithout-compensation by pseudorandom binary sequence(PRBS) (231-1) have beenmeasured as shown in Figure 8Theresearch results are compared with other related issues suchas a ring-cavity architecture system [6 12] and using Gires-Tournois etalons as phase dispersive mirrors in a Michelsoninterferometer system [9] (see Table 1)
4 Conclusions
We have analyzed a flat-top 25GHz optical interleaver basedon a dual-ring architecture with fewer components Com-pared to previous studies our interleaver exhibited a 05 dB
15530 155361553415532Wavelength (nm)
20
15
10
05
00
With-compensationWithout-compensation
15243 psnm
21593 psnm
Chro
mat
ic d
isper
sion
(ps
nm)
times103
minus05
minus10
minus15
minus20
Figure 6 The chromatic dispersion comparison between with-compensation and without-compensation of a 25GHz channelspacing of partial C-band
1009080706050403020100
0 5 10 15 20 25
With-compensationWithout-compensation
0936
0546
Inte
nsity
(au
)
minus25 minus20 minus15 minus10 minus5
Z (nm) times10minus3
Figure 7 The optical intensity comparisons of a 25GHz chan-nel spacing the calculated intensities are 0936 au of with-compensation and 0546 au of without-compensation
passband larger than 0156 nm (195 GHz) a 25 dB stop-band greater than 0173 nm (21625GHz) a channel isolationgreater than 95 dB and an excellent flat-top ripple which issmaller than 0227 times 10minus9 dB The benefit of this interleaveris that it utilizes the Fresnel principle to achieve precisereflectivity Unlike dielectric mirrors with thin-film coatingsthe reflectivities of the Fresnel reflection are insensitive towavelength variations in the transmission band Uniformreflectivities are essential to ensure the same performanceover the entire C-band In particular the novel interleavercan simultaneously produce an excellent performance ofchromatic dispersion which can achieve an improvement of
6 Mathematical Problems in Engineering
0 105Time (bit period)
Eye diagram analyzer
800
600
400
200
0
Am
plitu
de (a
u)
(a)
0 105Time (bit period)
Eye diagram analyzer
800
600
400
200
0
Am
plitu
de (a
u)
(b)
Figure 8 The eye diagrams by PRBS 231-1 for 10Gbs application (a) with-compensation and (b) without-compensation
Table 1 The characteristics comparison of interleaver systems
Characteristics System typeLee et al [6] Lee et al [12] Hsieh et al [9] This work
Filter channel spacing 25GHz 25GHz 50GHz 25GHzStructure technique Sagnac interferometer and ring cavity Ring cavity Gires-Tournois etalons Two-ring cavityChannel isolation (dB) 45 gt36 30 9505 dB passband (nm) 0182 gt0145 035 015625 dB stopband (nm) 0155 gt0145 032 0173Flat-top ripple (dB) lt10minus3 sim10minus3 NA 0227 times 10minus9
858when wemodify the interleavers structure by 1205826waveplatesThis unique interleaver is suitable for capacity upgradein DWDM and FTTx applications
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
The authors would like to gratefully acknowledge the Min-istry of Science and Technology of Taiwan for their fundingsupport under MOST 103-2622-E-327-007-CC3
References
[1] T Liang and S Hsu ldquoThe L-band EDFA of high clamped gainand low noise figure implemented using fiber Bragg grating anddouble-pass methodrdquo Optics Communications vol 281 no 5pp 1134ndash1139 2008
[2] S V Kartalopoulos Introduction to DWDMTechnology Data ina Rainbow chapter 1 IEEE Press New York NY USA 2000
[3] T C Liang C M Tsai and B C Wu ldquoA wavelength routingdevice by using cyclic AWGs and tunable FBGsrdquo Optical FiberTechnology vol 19 no 3 pp 189ndash193 2013
[4] R Saunders ldquoCoherent DWDM technology for high speedoptical communicationsrdquo Optical Fiber Technology vol 17 no5 pp 445ndash451 2011
[5] RCasellas RMunoz JM Fabrega et al ldquoGMPLSPCE controlof flexi-grid DWDM optical networks using CO-OFDM trans-missionrdquo Journal of Optical Communications and Networkingvol 4 no 11 Article ID 6360163 pp B1ndashB10 2012
[6] C W Lee R Wang P Yeh and W H Cheng ldquoA flat-top birefringent interleaver based on ring-cavity architecturerdquoOptics Communications vol 260 no 1 pp 311ndash317 2006
[7] A Zeng X-G Ye J Chon and F Liang ldquo25 GHz interleaverswith ultra-low chromatic dispersionrdquo in Proceedings of the Opti-cal Fiber Communication Conference and Exhibit (OFC rsquo02) pp396ndash398 March 2002
[8] T C Liang and C T Chen ldquoInvestigation of dispersion andperformance based on ring cavity by birefringent interleaverfor DWDM transmission systemsrdquo Mathematical Problems inEngineering vol 2013 Article ID 740412 5 pages 2013
[9] C Hsieh R Wang Z J Wen et al ldquoFlat-top interleavers usingtwo Gires-Tournois etalons as phase-dispersive mirrors in aMichelson interferometerrdquo IEEE Photonics Technology Lettersvol 15 no 2 pp 242ndash244 2003
Mathematical Problems in Engineering 7
[10] J Zhang and X Yang ldquoUniversal Michelson Gires-Tournoisinterferometer optical interleaver based on digital signal pro-cessingrdquo Optics Express vol 18 no 5 pp 5075ndash5088 2010
[11] ASAP (Advanced Systems Analysis Program) Breault ResearchOrganization Inc Tucson Ariz USA
[12] C Lee R Wang P Yeh and W Cheng ldquoSagnac interferometerbased flat-top birefringent interleaverrdquo Optics Express vol 14no 11 pp 4636ndash4643 2006
[13] P YehOpticalWaves in LayeredMedia JohnWileyamp SonsNewYork NY USA 1998
[14] S Cao J Chen J N Damask et al ldquoInterleaver technologycomparisons and applications requirementsrdquo Journal of Light-wave Technology vol 22 no 1 pp 281ndash289 2004
[15] B B Dingel and M Izutsu ldquoMultifunction optical filter with aMichelson-Gires-Tournois interferometer for wavelength-divi-sion-multiplexed network system applicationsrdquo Optics Lettersvol 23 no 14 pp 1099ndash1101 1998
[16] L Wei and J W Y Lit ldquoDesign optimization of flattop inter-leaver and its dispersion compensationrdquo Optics Express vol 15no 10 pp 6439ndash6457 2007
[17] J Zhang L Lin and Y Zhou ldquoNovel and simple approach fordesigning lattice-form interleaver filterrdquo Optics Express vol 11no 18 pp 2217ndash2224 2003
[18] M Oguma T Kitoh Y Inoue et al ldquoCompact and low-lossinterleave filter employing lattice-form structure and silica-based waveguiderdquo Journal of Lightwave Technology vol 22 no3 pp 895ndash902 2004
[19] K Jinguji and M Oguma ldquoOptical half-band filtersrdquo Journal ofLightwave Technology vol 18 no 2 pp 252ndash259 2000
Figure 4 Optical path between the prism and air schematic chart
05
00
155278 155281155280155279Wavelength (nm)
Tran
smiss
ion
(dB)
minus05
minus10
minus15
minus20
minus25
minus30
minus35
minus40
minus45
minus50
times10minus9
Figure 5 The simulation result of the flat-top ripple in a 25GHzchannel spacing
channels and their chromatic dispersion In this study theoptimum incident angle 120579
1is about 345∘ At this angle
of incidence the reflectivities of the flat-top bandwidthinterleaver are about 119877
119900= 1701 and 119877
119890= 839
And the ripple of output power intensity of the 25GHzchannel spacing is 0227397times10minus9 dB (see Figure 5) Figure 6shows that the dispersion comparison of a 25GHz channelspacing of partial C-band with- and without-compensationThe research results illustrate that our modified schemecan improve the dispersion of more than 858 (=(15243ndash21593)15243)The effect of improved dispersion of a 25GHzinterleaver can be observed as shown in Figure 7The opticalintensities of without-compensating and with-compensatingschemes are 0546 au and 0936 au respectively The eyediagrams for 10Gbs application of with-compensation andwithout-compensation by pseudorandom binary sequence(PRBS) (231-1) have beenmeasured as shown in Figure 8Theresearch results are compared with other related issues suchas a ring-cavity architecture system [6 12] and using Gires-Tournois etalons as phase dispersive mirrors in a Michelsoninterferometer system [9] (see Table 1)
4 Conclusions
We have analyzed a flat-top 25GHz optical interleaver basedon a dual-ring architecture with fewer components Com-pared to previous studies our interleaver exhibited a 05 dB
15530 155361553415532Wavelength (nm)
20
15
10
05
00
With-compensationWithout-compensation
15243 psnm
21593 psnm
Chro
mat
ic d
isper
sion
(ps
nm)
times103
minus05
minus10
minus15
minus20
Figure 6 The chromatic dispersion comparison between with-compensation and without-compensation of a 25GHz channelspacing of partial C-band
1009080706050403020100
0 5 10 15 20 25
With-compensationWithout-compensation
0936
0546
Inte
nsity
(au
)
minus25 minus20 minus15 minus10 minus5
Z (nm) times10minus3
Figure 7 The optical intensity comparisons of a 25GHz chan-nel spacing the calculated intensities are 0936 au of with-compensation and 0546 au of without-compensation
passband larger than 0156 nm (195 GHz) a 25 dB stop-band greater than 0173 nm (21625GHz) a channel isolationgreater than 95 dB and an excellent flat-top ripple which issmaller than 0227 times 10minus9 dB The benefit of this interleaveris that it utilizes the Fresnel principle to achieve precisereflectivity Unlike dielectric mirrors with thin-film coatingsthe reflectivities of the Fresnel reflection are insensitive towavelength variations in the transmission band Uniformreflectivities are essential to ensure the same performanceover the entire C-band In particular the novel interleavercan simultaneously produce an excellent performance ofchromatic dispersion which can achieve an improvement of
6 Mathematical Problems in Engineering
0 105Time (bit period)
Eye diagram analyzer
800
600
400
200
0
Am
plitu
de (a
u)
(a)
0 105Time (bit period)
Eye diagram analyzer
800
600
400
200
0
Am
plitu
de (a
u)
(b)
Figure 8 The eye diagrams by PRBS 231-1 for 10Gbs application (a) with-compensation and (b) without-compensation
Table 1 The characteristics comparison of interleaver systems
Characteristics System typeLee et al [6] Lee et al [12] Hsieh et al [9] This work
Filter channel spacing 25GHz 25GHz 50GHz 25GHzStructure technique Sagnac interferometer and ring cavity Ring cavity Gires-Tournois etalons Two-ring cavityChannel isolation (dB) 45 gt36 30 9505 dB passband (nm) 0182 gt0145 035 015625 dB stopband (nm) 0155 gt0145 032 0173Flat-top ripple (dB) lt10minus3 sim10minus3 NA 0227 times 10minus9
858when wemodify the interleavers structure by 1205826waveplatesThis unique interleaver is suitable for capacity upgradein DWDM and FTTx applications
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
The authors would like to gratefully acknowledge the Min-istry of Science and Technology of Taiwan for their fundingsupport under MOST 103-2622-E-327-007-CC3
References
[1] T Liang and S Hsu ldquoThe L-band EDFA of high clamped gainand low noise figure implemented using fiber Bragg grating anddouble-pass methodrdquo Optics Communications vol 281 no 5pp 1134ndash1139 2008
[2] S V Kartalopoulos Introduction to DWDMTechnology Data ina Rainbow chapter 1 IEEE Press New York NY USA 2000
[3] T C Liang C M Tsai and B C Wu ldquoA wavelength routingdevice by using cyclic AWGs and tunable FBGsrdquo Optical FiberTechnology vol 19 no 3 pp 189ndash193 2013
[4] R Saunders ldquoCoherent DWDM technology for high speedoptical communicationsrdquo Optical Fiber Technology vol 17 no5 pp 445ndash451 2011
[5] RCasellas RMunoz JM Fabrega et al ldquoGMPLSPCE controlof flexi-grid DWDM optical networks using CO-OFDM trans-missionrdquo Journal of Optical Communications and Networkingvol 4 no 11 Article ID 6360163 pp B1ndashB10 2012
[6] C W Lee R Wang P Yeh and W H Cheng ldquoA flat-top birefringent interleaver based on ring-cavity architecturerdquoOptics Communications vol 260 no 1 pp 311ndash317 2006
[7] A Zeng X-G Ye J Chon and F Liang ldquo25 GHz interleaverswith ultra-low chromatic dispersionrdquo in Proceedings of the Opti-cal Fiber Communication Conference and Exhibit (OFC rsquo02) pp396ndash398 March 2002
[8] T C Liang and C T Chen ldquoInvestigation of dispersion andperformance based on ring cavity by birefringent interleaverfor DWDM transmission systemsrdquo Mathematical Problems inEngineering vol 2013 Article ID 740412 5 pages 2013
[9] C Hsieh R Wang Z J Wen et al ldquoFlat-top interleavers usingtwo Gires-Tournois etalons as phase-dispersive mirrors in aMichelson interferometerrdquo IEEE Photonics Technology Lettersvol 15 no 2 pp 242ndash244 2003
Mathematical Problems in Engineering 7
[10] J Zhang and X Yang ldquoUniversal Michelson Gires-Tournoisinterferometer optical interleaver based on digital signal pro-cessingrdquo Optics Express vol 18 no 5 pp 5075ndash5088 2010
[11] ASAP (Advanced Systems Analysis Program) Breault ResearchOrganization Inc Tucson Ariz USA
[12] C Lee R Wang P Yeh and W Cheng ldquoSagnac interferometerbased flat-top birefringent interleaverrdquo Optics Express vol 14no 11 pp 4636ndash4643 2006
[13] P YehOpticalWaves in LayeredMedia JohnWileyamp SonsNewYork NY USA 1998
[14] S Cao J Chen J N Damask et al ldquoInterleaver technologycomparisons and applications requirementsrdquo Journal of Light-wave Technology vol 22 no 1 pp 281ndash289 2004
[15] B B Dingel and M Izutsu ldquoMultifunction optical filter with aMichelson-Gires-Tournois interferometer for wavelength-divi-sion-multiplexed network system applicationsrdquo Optics Lettersvol 23 no 14 pp 1099ndash1101 1998
[16] L Wei and J W Y Lit ldquoDesign optimization of flattop inter-leaver and its dispersion compensationrdquo Optics Express vol 15no 10 pp 6439ndash6457 2007
[17] J Zhang L Lin and Y Zhou ldquoNovel and simple approach fordesigning lattice-form interleaver filterrdquo Optics Express vol 11no 18 pp 2217ndash2224 2003
[18] M Oguma T Kitoh Y Inoue et al ldquoCompact and low-lossinterleave filter employing lattice-form structure and silica-based waveguiderdquo Journal of Lightwave Technology vol 22 no3 pp 895ndash902 2004
[19] K Jinguji and M Oguma ldquoOptical half-band filtersrdquo Journal ofLightwave Technology vol 18 no 2 pp 252ndash259 2000
Figure 8 The eye diagrams by PRBS 231-1 for 10Gbs application (a) with-compensation and (b) without-compensation
Table 1 The characteristics comparison of interleaver systems
Characteristics System typeLee et al [6] Lee et al [12] Hsieh et al [9] This work
Filter channel spacing 25GHz 25GHz 50GHz 25GHzStructure technique Sagnac interferometer and ring cavity Ring cavity Gires-Tournois etalons Two-ring cavityChannel isolation (dB) 45 gt36 30 9505 dB passband (nm) 0182 gt0145 035 015625 dB stopband (nm) 0155 gt0145 032 0173Flat-top ripple (dB) lt10minus3 sim10minus3 NA 0227 times 10minus9
858when wemodify the interleavers structure by 1205826waveplatesThis unique interleaver is suitable for capacity upgradein DWDM and FTTx applications
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
The authors would like to gratefully acknowledge the Min-istry of Science and Technology of Taiwan for their fundingsupport under MOST 103-2622-E-327-007-CC3
References
[1] T Liang and S Hsu ldquoThe L-band EDFA of high clamped gainand low noise figure implemented using fiber Bragg grating anddouble-pass methodrdquo Optics Communications vol 281 no 5pp 1134ndash1139 2008
[2] S V Kartalopoulos Introduction to DWDMTechnology Data ina Rainbow chapter 1 IEEE Press New York NY USA 2000
[3] T C Liang C M Tsai and B C Wu ldquoA wavelength routingdevice by using cyclic AWGs and tunable FBGsrdquo Optical FiberTechnology vol 19 no 3 pp 189ndash193 2013
[4] R Saunders ldquoCoherent DWDM technology for high speedoptical communicationsrdquo Optical Fiber Technology vol 17 no5 pp 445ndash451 2011
[5] RCasellas RMunoz JM Fabrega et al ldquoGMPLSPCE controlof flexi-grid DWDM optical networks using CO-OFDM trans-missionrdquo Journal of Optical Communications and Networkingvol 4 no 11 Article ID 6360163 pp B1ndashB10 2012
[6] C W Lee R Wang P Yeh and W H Cheng ldquoA flat-top birefringent interleaver based on ring-cavity architecturerdquoOptics Communications vol 260 no 1 pp 311ndash317 2006
[7] A Zeng X-G Ye J Chon and F Liang ldquo25 GHz interleaverswith ultra-low chromatic dispersionrdquo in Proceedings of the Opti-cal Fiber Communication Conference and Exhibit (OFC rsquo02) pp396ndash398 March 2002
[8] T C Liang and C T Chen ldquoInvestigation of dispersion andperformance based on ring cavity by birefringent interleaverfor DWDM transmission systemsrdquo Mathematical Problems inEngineering vol 2013 Article ID 740412 5 pages 2013
[9] C Hsieh R Wang Z J Wen et al ldquoFlat-top interleavers usingtwo Gires-Tournois etalons as phase-dispersive mirrors in aMichelson interferometerrdquo IEEE Photonics Technology Lettersvol 15 no 2 pp 242ndash244 2003
Mathematical Problems in Engineering 7
[10] J Zhang and X Yang ldquoUniversal Michelson Gires-Tournoisinterferometer optical interleaver based on digital signal pro-cessingrdquo Optics Express vol 18 no 5 pp 5075ndash5088 2010
[11] ASAP (Advanced Systems Analysis Program) Breault ResearchOrganization Inc Tucson Ariz USA
[12] C Lee R Wang P Yeh and W Cheng ldquoSagnac interferometerbased flat-top birefringent interleaverrdquo Optics Express vol 14no 11 pp 4636ndash4643 2006
[13] P YehOpticalWaves in LayeredMedia JohnWileyamp SonsNewYork NY USA 1998
[14] S Cao J Chen J N Damask et al ldquoInterleaver technologycomparisons and applications requirementsrdquo Journal of Light-wave Technology vol 22 no 1 pp 281ndash289 2004
[15] B B Dingel and M Izutsu ldquoMultifunction optical filter with aMichelson-Gires-Tournois interferometer for wavelength-divi-sion-multiplexed network system applicationsrdquo Optics Lettersvol 23 no 14 pp 1099ndash1101 1998
[16] L Wei and J W Y Lit ldquoDesign optimization of flattop inter-leaver and its dispersion compensationrdquo Optics Express vol 15no 10 pp 6439ndash6457 2007
[17] J Zhang L Lin and Y Zhou ldquoNovel and simple approach fordesigning lattice-form interleaver filterrdquo Optics Express vol 11no 18 pp 2217ndash2224 2003
[18] M Oguma T Kitoh Y Inoue et al ldquoCompact and low-lossinterleave filter employing lattice-form structure and silica-based waveguiderdquo Journal of Lightwave Technology vol 22 no3 pp 895ndash902 2004
[19] K Jinguji and M Oguma ldquoOptical half-band filtersrdquo Journal ofLightwave Technology vol 18 no 2 pp 252ndash259 2000
[10] J Zhang and X Yang ldquoUniversal Michelson Gires-Tournoisinterferometer optical interleaver based on digital signal pro-cessingrdquo Optics Express vol 18 no 5 pp 5075ndash5088 2010
[11] ASAP (Advanced Systems Analysis Program) Breault ResearchOrganization Inc Tucson Ariz USA
[12] C Lee R Wang P Yeh and W Cheng ldquoSagnac interferometerbased flat-top birefringent interleaverrdquo Optics Express vol 14no 11 pp 4636ndash4643 2006
[13] P YehOpticalWaves in LayeredMedia JohnWileyamp SonsNewYork NY USA 1998
[14] S Cao J Chen J N Damask et al ldquoInterleaver technologycomparisons and applications requirementsrdquo Journal of Light-wave Technology vol 22 no 1 pp 281ndash289 2004
[15] B B Dingel and M Izutsu ldquoMultifunction optical filter with aMichelson-Gires-Tournois interferometer for wavelength-divi-sion-multiplexed network system applicationsrdquo Optics Lettersvol 23 no 14 pp 1099ndash1101 1998
[16] L Wei and J W Y Lit ldquoDesign optimization of flattop inter-leaver and its dispersion compensationrdquo Optics Express vol 15no 10 pp 6439ndash6457 2007
[17] J Zhang L Lin and Y Zhou ldquoNovel and simple approach fordesigning lattice-form interleaver filterrdquo Optics Express vol 11no 18 pp 2217ndash2224 2003
[18] M Oguma T Kitoh Y Inoue et al ldquoCompact and low-lossinterleave filter employing lattice-form structure and silica-based waveguiderdquo Journal of Lightwave Technology vol 22 no3 pp 895ndash902 2004
[19] K Jinguji and M Oguma ldquoOptical half-band filtersrdquo Journal ofLightwave Technology vol 18 no 2 pp 252ndash259 2000
