A III-V-on-Si ultra-dense comb laser

Abstract

Optical frequency combs emerge as a promising technology that enables highly sensitive, near-real-time spectroscopy with a high resolution. The currently available comb generators are mostly based on bulky and high-cost femtosecond lasers for dense comb generation (line spacing in the range of 100 MHz to 1 GHz). However, their integrated and low-cost counterparts, which are integrated semiconductor mode-locked lasers, are limited by their large comb spacing, small number of lines and broad optical linewidth. In this study, we report a demonstration of a III-V-on-Si comb laser that can function as a compact, low-cost frequency comb generator after frequency stabilization. The use of low-loss passive silicon waveguides enables the integration of a long laser cavity, which enables the laser to be locked in the passive mode at a record-low 1 GHz repetition rate. The 12-nm 10-dB output optical spectrum and the notably small optical mode spacing results in a dense optical comb that consists of over 1400 equally spaced optical lines. The sub-kHz 10-dB radio frequency linewidth and the narrow longitudinal mode linewidth (<400 kHz) indicate notably stable mode-locking. Such integrated dense comb lasers are very promising, for example, for high-resolution and real-time spectroscopy applications.

Novel Light Source Integration Approaches for Silicon Photonics

“…Figure shows the schematic of the III‐V/Si ultra‐dense comb laser . The III‐V is integrated on the silicon‐on‐insulator wafer (400 nm Si device layer thickness) using a 30‐nm thick DVS‐BCB bonding layer (not shown in the figure).…”

“…The black dots are the measured data, and the red curve is the corresponding Lorentzian fitting. (Reproduced from).…”

“…Measured RF spectra of the MLL output when it is (a) passively and (b) hybrid mode‐locked. (Reproduced from).…”

“…[25,57] Figure 6 shows the schematic of the III-V/Si ultra-dense comb laser. [58,59] The III-V is integrated on the silicon-on-insulator wafer (400 nm Si device layer thickness) using a 30-nm thick DVS-BCB bonding layer (not shown in the figure). A long and low loss (0.7 dB/cm) silicon spiral waveguide of 37.4 mm length forms the major part of the long laser cavity.…”

“…Schematic of the ultra-dense III-V/Si comb laser. (Reproduced from [58] ) p-contact layer to electrically isolate it from the gain sections. Because both the amplifiers and the SA share the same InGaAsPbased multi-quantum well layer, [60] the fabrication process is easy to implement.…”