Linewidth narrowing in self-injection-locked on-chip lasers

Abstract

Stable laser emission with narrow linewidth is of critical importance in many applications, including coherent communications, LIDAR, and remote sensing. In this work, the physics underlying spectral narrowing of self-injection-locked on-chip lasers to Hz-level lasing linewidth is investigated using a composite-cavity structure. Heterogeneously integrated III–V/SiN lasers operating with quantum-dot and quantum-well active regions are analyzed with a focus on the effects of carrier quantum confinement. The intrinsic differences are associated with gain saturation and carrier-induced refractive index, which are directly connected with 0- and 2-dimensional carrier densities of states. Results from parametric studies are presented for tradeoffs involved with tailoring the linewidth, output power, and injection current for different device configurations. Though both quantum-well and quantum-dot devices show similar linewidth-narrowing capabilities, the former emits at a higher optical power in the self-injection-locked state, while the latter is more energy-efficient. Lastly, a multi-objective optimization analysis is provided to optimize the operation and design parameters. For the quantum-well laser, minimizing the number of quantum-well layers is found to decrease the threshold current without significantly reducing the output power. For the quantum-dot laser, increasing the quantum-dot layers or density in each layer increases the output power without significantly increasing the threshold current. These findings serve to guide more detailed parametric studies to produce timely results for engineering design.

On-Chip Lasers for Silicon Photonics

“…Quantum-dot (QD) lasers are preferred over quantum-well lasers because they have a greater laser thermal stability and lower lasing threshold due to 3D confinement of the carriers. A theoretical framework for heterogeneous integration of QD lasers on Si can be found in [57,58]. Quantum-dot lasers bonded on Si have been reported recently.…”

Optimization of the coupling efficiency under self-injection locking in a narrow linewidth hybrid wavelength tunable laser diode

“…12) Therefore, self-injection locking using an external cavity has been employed in various applications, enabling significant linewidth narrowing in semiconductor lasers. [13][14][15][16][17][18][19][20] The self-injection locking effect is generated by injecting a feedback light from an external cavity with a high Q-factor into the laser cavity. Microring resonators, whispering gallery mode resonators, and fiber ring resonators have been used as external cavities.…”

“…Microring resonators, whispering gallery mode resonators, and fiber ring resonators have been used as external cavities. [13][14][15][16][17][18][19][20] The coupling efficiency is important for self-injection locking. If the coupling efficiency is too high, coherence collapse occurs and the linewidth increases, whereas, if the coupling efficiency is too small, the self-injection locking effect weakens, and linewidth narrowing does not occur.…”

Efficient Integrated Amplifier-Assisted Laser on Erbium-Doped Lithium Niobate

“…The requirements of ideal chip-scale lasers include sufficient large power with high power efficiency, continuous-wave emission in fiber-based communication bands, compatibility with CMOS (complementary metal oxide semiconductor) processes, and so on . Taking silicon-based PIC as an example, Group III–V lasers have been commercialized for a long time and have been explored extensively to combine with silicon photonics using hybrid and heterogeneous integration. − Meanwhile, silicon-based Raman lasers, silicon quantum dots lasers, and other Group IV lasers that could be monolithically integrated with silicon photonics are attracting researchers’ attention.…”