High hydrostatic pressure can be used for wavelength tuning of semiconductor laser diodes in a wide spectral range. Coupling the laser with external grating leads to wavelength tuning within the gain spectrum (i.e. in a narrower range than with pressure) but allows for a narrow emission line and nearly continuous tuning (mode-hop free if anti-reflecting coating is applied). Here we demonstrate a combination of pressure and external-resonator tuning for the GaInNAs laser emitting at 1343 nm at ambient conditions. Using the specially designed liquid pressure cell working up to 20 kbar we shift the emission down to 1170 nm while the external grating (used in Littrow configuration) allows for fine tuning in the ~10 nm range (at each pressure).
We demonstrate wide-range wavelength tunability of high-power laser diodes emitting at 660 nm, 808 nm, and 980 nm. Pressure shifts of the emission wavelength are due to the increase of bandgaps of III-V semiconductors under pressure with the rate of about 10 meV per kbar. For the 980 nm InGaAs/GaAs laser the threshold currents and the quantum efficiencies remain constant with pressure which allows for the constant operating current and the emitted power in the full tuning range. For 808 nm GaAs/AlGaAs and 660 nm InGaP/AlGaInP lasers there is an increase of threshold currents with pressure related to the direct-indirect crossover in the conduction band of AlGaAs and AlGaInP. This limits the tuning range unless we operate the laser at lower temperature. We designed the pressure cell with Peltier cooling allowing for independent control of temperature down to 0 Celsius and pressure up to 20 kbar. This device allows for the tuning of 980 nm laser down to 840 nm, 808 nm laser down to 720 nm, 660 nm laser down to 620 nm.
Two InGaP/AlGaInP lasers (emitting at 660 nm and at 690 nm) and one GaAs/AlGaAs laser (emitting at 780 nm) have been studied under hydrostatic pressure up to 20 kbar and at temperatures from 240 K to 300 K. The power-current characteristics and the spectra have been measured in the specially designed pressure cell. The emission spectra shifted in agreement with the pressure/temperature variation of the bandgaps in active layers of the lasers. Since at high pressure the Γ-X separation in the conduction band is strongly reduced (both in AlGaInP and in AlGaAs) the dominant loss mechanism of the lasers is the carrier leakage to X minima in the claddings. This, in turn, leads to high sensitivity of threshold currents to temperature. The dependence of threshold currents on pressure and on temperature is in good agreement with the simple phenomenological analysis taking into account the carrier leakage and the radiative and nonradiative recombination. Good description of the pressure and temperature variation of the threshold currents is obtained using three adjustable parameters. Our fits indicate that the dominant contribution to electronic leakage is drift rather than diffusion. These results are important for the application of pressure/temperature tuning of laser diodes in the 600-800 nm range. In particular, we were able to turn red laser diodes into yellow (emitting below 600 nm) and infrared 780 nm lasers into bright red. By simultanous control of pressure and temperature it is possible to obtain constant emission power of the lasers in the full tuning range (at a fixed operating current).
Wide-range wavelength tunability is demonstrated for commercial high-power laser diodes emitting at 980 nm, 830 nm, and at 808 nm. High pressure shifts the emission wavelength of the lasers due to the increase of bandgaps in the active layers with the rate of about 10 meV per kbar. For the 980 nm InGaAs/GaAs laser the threshold currents and the differential efficiencies remain constant with pressure which allows for the constant operating current and the emitted power in the full tuning range. For 830 nm and 808 nm GaAs/AlGaAs lasers there is an increase of threshold currents with pressure related to the leakage through X minima in the conduction band of AlGaAs. This limits the tuning range unless we operate the laser at lower temperature. We designed the pressure cell with Peltier cooling allowing for independent control of temperature down to 0 Celsius and pressure up to 20 kbar. The laser beam passes through the sapphire window or through the multi-mode fiber. Our device allows for the tuning of 980 nm laser down to 840 nm, 830 nm laser down to 745 nm, and 808 nm laser down to 720 nm. We were able to keep the output power fixed in the full tuning range: 300 mW for the 980 nm laser and 400 mW for the 830 nm and 808 nm lasers.
Direct bandgap of most III-V semiconductors (AlGaAs, InGaAs, InGaP, InAs) increases with hydrostatic pressure at the rate of about 10 meV per kbar. Thus the emission wavelength of semiconductor lasers shifts to the blue under the application of high pressure. We demonstrate that this effect can be used for wavelength tuning of laser diodes in a very wide spectral range. Using the specially designed liquid pressure cell working up to 20 kbar the 1550 nm laser was tuned down to 1270 nm, the 1300 nm laser was tuned down to 1100 nm, and the 980 nm laser was tuned down to 840 nm. The emitted light passes through the sapphire window or through the fiber directly coupled to the laser. The threshold current and the quantum efficiency for the 980 nm laser remained constant with pressure, for the two other lasers the thresholds decreased with pressure. Thus we obtained the constant emission power in the full tuning range. We hope that this compact device will find applications as a tool for characterization of some optical network devices or parts of optical transmission lines.