1. Pressure tuning of red and infrared laser diodes W. Trzeciakowski 1, A. Bercha 1,3, P. Adamiec 1,2, F. Dybała 1,2, R. Bohdan 1 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

2. 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

3. 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)

4. Schematic view of the pressure cell microlens Laser diode Sapphire window Piston with wires

5. Two types of optical coupling Microlens plus sapphire window Butt coupling to optical fiber

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

7. Results for 980 nm laser: spectra 140 nm tuning range

8. Results for 980 nm laser: L-I characteristics Constant I th and efficiency!

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

10. Results for 780 nm laser: cw spectra cw spectra at 20°C (black) and at -30 °C (blue)

11. Results for 780 nm laser: threshold currents At higher pressures some cooling necessary!

12. 660 nm high-power laser: spectra Emission spectra at 20°C (black) and one at 0°C (blue)

13. 660 nm high-power laser: threshold currents In order to avoid increase in I th we have to cool the laser

14. 640 nm laser: spectra at different temperatures Even the yellow can be achieved if we cool under pressure...

15. 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