Thermally Tuned High-Performance III-V/Si₃N₄ External Cavity Laser

Abstract

Silicon nitride (Si 3 N 4) has a higher nonlinear threshold compared to silicon, which reduces the effect of two-photon absorption. However, the low thermo-optic coefficient and the reduced refractive index contrast of thin Si 3 N 4 waveguides lead to a low thermal tuning speed and low thermal efficiency. This paper demonstrates a widely tunable III-V/Si 3 N 4 hybrid-integrated external cavity laser with a relatively faster switching time. The Si 3 N 4 external feedback circuit is based on 800-nm-thick Si 3 N 4 waveguides with an optical confinement factor of 87%. It allows the reduction of the oxide under-cladding layer thickness to 4 μm and the oxide upper-cladding layer to 1.7 μm without additional loss. The switching time between two non-adjacent lasing wavelengths is 60.7 μs. The maximum output power is 34 mW under 500 mA injection current. The side mode suppression ratio is more than 70 dB over the tuning range of 58.5 nm. The laser intrinsic linewidth is 2.5 kHz.

A Review of Capabilities and Scope for Hybrid Integration Offered by Silicon-Nitride-Based Photonic Integrated Circuits

“…Recent advances in telecom-wavelength lasing based on high-gain GaAs QDs heteroepitaxially grown on Si and SOI substrates with low thresholds and high temperature stability [282], indicate that it is a promising gain material for III-V/SiN monolithic integration and there is a strong possibility that 100 mW level heterogeneous/monolithic III-V/SiN lasers are achievable in the near future. [239,, (c) schematic layout of a heterogeneous III-V/SiN laser and its optical taper between SiN and III-V gain sections [245] and (d) development of linewidth of III-V/SiN lasers [244,246,248,249,252,254,[256][257][258][261][262][263][264]266,267,270,[272][273][274][275][276]279,280,[283][284][285].…”

“…Benefiting from the fast-developing SiN devices, especially resonators with Q up to >200 M [294], a highly precise phase (factor A) and spectral (factor B) feedback [295,296] is achievable in addition to an extended cavity length (thereby reducing ∆ω 0 ), likely to generate ultranarrow linewidth. Figure 11d displays the state-of-the-art linewidth of III-V/SiN-coupled lasers in terms of integration method [244,246,248,249,252,254,[256][257][258][261][262][263][264]266,267,270,[272][273][274][275][276]279,280,[283][284][285]]. It appears that significant progress has been made with hybrid integration when compared to heterogenous/monolithic integration, though the latter started its development at a later stage.…”

“…Figure 11. Development of (a) threshold current and (b) maximum output power of III-V/SiNcoupled lasers[239,, (c) schematic layout of a heterogeneous III-V/SiN laser and its optical taper between SiN and III-V gain sections[245] and (d) development of linewidth of III-V/SiN lasers[244,246,248,249,252,254,[256][257][258][261][262][263][264]266,267,270,[272][273][274][275][276]279,280,[283][284][285].…”

Research on Narrow Linewidth External Cavity Semiconductor Lasers

“…In 2021, Guo Y Y et al [35] reported a widely tunable III-V/Si 3 N 4 hybrid integrated external cavity laser. Under 500 mA injection current, the maximum output power was 34 mW.…”

Sub-milliwatt, widely-tunable coherent microcomb generation with feedback-free operation

“…It is noted that the relative frequency of the left branch is shifted towards the red side as the temperature decreases. Moreover, Since the n T of AlGaAs (2.3 × 10 −4 K −1 ) is an order of magnitude larger than those of silica and Si 3 N 4 , the on-chip thermotuning efficiency in AlGaAsOI can be much higher (∼5 GHz/ • C) than those platform , showing great efficiency for AMX operation 33 .…”