Pressure tuning of red and infrared laser diodes

W. Trzeciakowski1, A. Bercha1,3, P. Adamiec1,2, F. Dybała1,2, R. Bohdan1

1 High Pressure Research Center UNIPRESS, Sokołowska 29/37, 01-142 Warsaw, Poland

2 Institute of Physics, Warsaw University of Technology, 00-662 Warsaw, Poland

3 Uzhgorod National University, Pidhirna 48, 88000 Uzgorod, Ukraine

Background

• Semiconductor laser diodes find many applications due to their small size, high efficiency and low cost (emission from 0.63 to 1.7 m)Optical comms, CD & DVD players, bar code readers….

• In several applications wavelength tunability is required • Possible methods of wavelength tuning:

– Temperature, current– External resonators– Tunable Bragg gratings

• The bandgap of most III-V semiconductors increases substantially with pressure the emission wavelength of the semiconductor laser can be tuned by pressure. With 20 kbar pressure we achieve:– 200 nm between 1-1.6 m, ~40÷140 nm between 0.6-1 m

• Pressure tuning yields the widest tuning range but is difficult to implement

Our unique capabilities

• Most optical experiments under high pressure are performed in the Diamond Anvil Cell which is useless for pressurizing laser diodes

• High Pressure Research Center has unique expertise in liquid pressure cells up to 20 kbar (we obtained two grants of the EU as a Center of Excellence in High Pressure Research). Currently our research in this area is sponsored by NATO within the Science for Peace program.

• Due to our recent achievements in blue laser diodes we have the access to special mounting/pigtailing techniques for laser diodes (TopGaN laboratories)

Schematic view of the pressure cell

microlensLaser diode

Sapphire windowPiston with wires

Two types of optical coupling

Microlens plus sapphire window

Butt coupling to optical fiber

Spectra for 1300 nm InGaAsP/InP laser at different pressures: 200 nm tuning range

Results for 980 nm laser: spectra140 nm tuning range

Results for 980 nm laser: L-I characteristics

Constant Ith and efficiency!

Results for 780 nm laser: pulsed spectra at room temperature: 70 nm tuning range

Results for 780 nm laser: cw spectra

710 720 730 740 750 760 770 780 790

0,0

0,2

0,4

0,6

0,8

1,011.8 8.2 6 4.1 2 0 kbar

no

rma

lize

d in

ten

sity

wavelength (nm)

cw spectra at 20°C (black) and at -30 °C (blue)

Results for 780 nm laser: threshold currents

-30 -20 -10 0 10 20 3020

30

40

50

60

70

80

90

100

110

Thr

esho

ld c

urre

nt (

mA

)

Temperature (Co)

0 kbar 2 kbar 4 kbar 6 kbar 8.2 kbar 10.2 kbar 11.8 kbar

At higher pressures some cooling necessary!

660 nm high-power laser: spectra

Emission spectra at 20°C (black) and one at 0°C (blue)

660 nm high-power laser: threshold currents

In order to avoid increase in Ith we have to cool the laser

640 nm laser: spectra at different temperatures

Even the yellow can be achieved if we cool under pressure...

Conclusions• 1300 nm lasers can be tuned down to 1100 nm• 980 nm lasers can be pressure tuned down to 840 nm with

constant operating current• 780 nm and red lasers require cooling to keep the operating

current constant with pressure• With pressure tuning and a set of commercial lasers (630,

690, 780, 840, 980, 1100, 1300, 1550 nm) we should be able to achieve any wavelength between 600 and 1550 nm

• Our method might be useful for applications requiring non-typical wavelengths or tunable sources (optical pumping, spectroscopic, medical e.g. Photo-Dynamic Therapy)

• Fiber networks may be characterized between 1100 and 1550 nm using two pressure-tuned diodes