The Finnish research team based a wide-tuned hybrid laser with LIGENTEC low-loss Si3N4 photonic integrated optical path reflection cavity

A wide-tuned (2.47-2.64 micron) hybrid Laser based on a GaSb/GaInAsSb quantum well and a LIGENTEC low-loss Si3N4 photonic integrated optical path reflection cavity has been reported in Laser and Photonics Reviews by a team from Finland.

"Photonic integrated optical paths manufactured using silicon nitride waveguide platforms exhibit low losses in wide wavelength regions extending from visible light to more than 2 microns. Using this feature, we demonstrate a high-performance integrated laser that exhibits extensive wavelength tunability near the 2.6 micron wavelength region. The laser is based on a silicon nitride photonic integrated optical path containing a tunable reflector and an AlGaInAsSb/GaSb quantum well gain element. We show that the laser has a wavelength tuning range of 170 nm (2,474-2,644 nm) and a maximum power of 6.4 milliwatts at room temperature for single-mode continuous operation, the highest continuous output power of over 2.1 microns and the widest tuning range of over 1.7 microns ever reported for an optically integrated chip-based tunable laser. This performance is achieved by utilizing several basic building blocks realized in silicon nitride, namely low-loss Y-shaped branch tubes, inverted cones, and a double-ring resonator with a free spectral range of ≈160 nm. In addition, the limits of wavelength coverage were explored using LIGENTEC silicon nitride waveguides and it was shown that the platform supports low propagation losses up to 3.5 microns.

Finally, we analyze the possibility of achieving improved mode matching between silicon nitride and GaSb waveguides that can further improve the performance of this hybrid laser platform and support wavelength extensions beyond 3 microns."

In this paper, a hybrid Si3N4-GaSb laser in the 2.6 micron wavelength region is presented for the first time, which utilizes the vernier effect between two thermally tunable microring resonators MRRS as a wavelength filtering and tuning mechanism. The hybrid laser has an operating voltage of 1.7V and an injection current of 300mA, indicating that the GasB-based integrated platform is suitable for low-power applications such as wearable sensors.

FIG. 1. Schematic diagram of a GaSb/Si3N4 hybrid laser with wide wavelength tunability shown in this work. The hybrid laser includes a GaSb based reflective semiconductor optical amplifier (RSOA) that provides gain in the 2.47-2.64 micron wavelength region. The P-side of the RSOA is bonded to an AlN subseat facing down and coupled to a silicon nitride chip edge, which consists of a two-ring resonator with adjustable resistance. The optical path has a phase shifter that allows the PIC to phase match the RSOA. RSOA and PIC surfaces have anti-reflection (AR) coatings to reduce parasitic reflections and maximize transmission.

Figure 2. a) Two-dimensional basic TE mode field diagram of Si3N4 1.65 micron ×0.8 micron waveguide and b) Relationship diagram between loss and spiral length of helical waveguide.

Figure 3. Optical path diagram of silicon nitride chip. The red line represents the silicon nitride waveguide and the yellow area represents the resistive heating phase shifter.

Figure 4. a) Optimized Y-branch structure, b) the relationship between insertion loss and the number of Y-branches.

Figure 5. The relationship between the output power of the hybrid laser and the wavelength when 325 mA current is injected at room temperature.

Source: stone light communication network