Mode locked laser array monolithically integrated with SOA and EA modulatorL. Hou, M. Haji, A. E. Kelly, J. M. Arnold, A. C. Bryce
Outline
• Motivation• Device fabrication• Wafer and device structure• DBR optimization• Material characterization and QWI results• Device characterization• Conclusions
Motivations
• OCDMA• RZ source • Optical sampling• Terahertz Generation
Device features
• AlGaInAs/InP material
• Planarisation using Hydrogen Silsesquioxane (HSQ)
• Surface-etched DBR:• Require only a single epitaxial growth step• Simultaneously fabricated with the ridge waveguide• Al-containing active layers can be used without the risk
of oxidization
• Using QWI to fabricate the passive sections• Phase section , DBR section, S-bend, and MMI• Postgrowth tuning of the QW band edge• Simple, flexible and low-cost alternative compared with
the selective etching and re-grow process
Device Structure
L CH1-4 = 734-740 nm
Lslot = 180 nm
LDBR-eff =55 μm
LMLLD-eff = 4280 μm
WMMI =30 μm
Ls-bend=1200 μm
EAM output tilt angle=10˚
Optimisation of DBR gratings
• Simultaneous etching of waveguide mesa and grating
• RIE lag effects
• 3rd order gratings investigated with CAMFR software
• Low-loss and efficient DBRs are obtainable for narrow slots
• Slot width of 180 nm is selected as a trade-off between reduced losses and fabrication
AlGaInAs/InP material characterisation
Fast recovery times < 3psInternal loss is ~15/cm
Input Pulse recovery time
λ converted
Quantum Well Intermixing results
L-I characteristics of the four channels and SOA
Four channels simultaneous measurement
• Channels tuned in wavelength and frequency to allow visibility of all 4 channels
Mode locking range for the mode-locked DBR laser
Peak wavelength, pulse repetition frequency, pulse width and TBP tuning by DBR section
(b)
(a) (c)
(d)
(a) pulse repetition frequency Fr, (b) Emission peak wavelength WP, (c) TBPs vs. IDBR,(d) Pulse width Pw
Igain = 120 (black), 180 (red), and 240 mA (green), while VSA= -3.0 V, ISOA = 200 mA and all other sections are left floating.
Peak wavelength, pulse repetition frequency, pulse width and TBP tuning by phase section
The shortest pulse and its corresponding optical spectrum , RF signal, and SSB noise
Frequency=10 GHz;
WP = 1561.3 nm, Δλ=1.27 nm;
=3.84, Δt = 2.49 ps;
TBP = 0.389;
Timing jitter=6ps (100 kHz-100 MHz)
Pulse Stabilisation using Synchronous Mode Locking
Optical attenuator compressor
Pritel(10 GHz active fibre MLL)
EDFA
Pulse compressor
Polarization controller
OSAESA+ SHG Autocorrelator
Circulator
Injected Signal Characteristics
Injected Pulse
Injected Spectrum
2 Channel Synchronisation
Timing jitter=0.3ps(100 Hz-100 MHz)
~100 MHz Locking Range
Conclusions
Mode-Locked Laser Array Monolithically Integrated with SOA and EA Modulator :
• Surface etched DBR mode locked laser• QWI for the postgrowth tuning of the QW band edge• Each channel can tune the peak wavelength, pulse repetition rate, and
pulse width by using DBR, phase section or SA section • Minimum pulse width of 2.49 ps with 3 dB optical spectral bandwidth of
1.27 nm and TBP of 0.389 (sech2)• Synchronization of the mode-locked laser array by using injection mode-
locked technique
Acknowledgements
• P. Stolarz for his automated LabView measurements system• R. Dylewicz for input to grating designs• The technical staff of JWNC at the University of Glasgow• This work was funded via EPSRC EP/E065112/1 ‘High Power,
High Frequency Mode-locked Semiconductor Lasers’