Linewidth narrowing via low-loss dielectric waveguide feedback circuits in hybrid integrated frequency comb lasers

Self-pulsing and dual-mode lasing in a square microcavity semiconductor laser

Self-pulsing and dual-mode lasing in a square microcavity semiconductor laser are studied experimentally. Self-sustained pulses originating from undamped relaxation oscillation induced by a two-mode interaction are obtained, as the injection current is slightly above the laser threshold. A repetition frequency of 4.4 GHz and a pulse width of 30-40 ps are obtained at a current of 8 mA. The laser switches to continuous-wave operation when the injection current is higher than a certain value, and dual-mode lasing with 30.7 GHz at 16 mA and 10.7 GHz at 27 mA are observed in the lasing spectra. Furthermore, the relative intensity noise spectra are presented to reveal the relationship between the lasing states and the dynamics induced by relaxation oscillation and mode beating.

Damping of relaxation oscillations, photon-photon resonance, and tolerance to external optical feedback of III-V/SiN hybrid lasers with a dispersive narrow band mirror

We address the stability of a tunable hybrid laser based on a III-V Reflective Semiconductor Optical Amplifier (RSOA) edge-coupled with a Silicon Photonic (SiPh) dispersive mirror through a model of time-delayed algebraic differential equations that accounts for the narrow band mirror. Our results allow to (i) analyze the stability of single mode lasing, (ii) quantify the impact of the mirror bandwidth on the damping of the laser relaxation oscillations and the emergence of photon-photon resonance, and (iii) study the tolerance of the laser to the external optical feedback. Thanks to this analysis, we find a mirror design that gives ultra-high stability up to an external feedback level of -10 dB. The aim of the work is providing a tool for understanding and interpreting the dynamics of these lasers and design configurations for isolator-free operation.

Self-mode-locking in a high-power hybrid silicon nitride integrated laser

Integrated mode-locked lasers are useful tools in microwave photonic applications as a local oscillator. In particular, hybrid integrated lasers could easily be integrated with passive processing circuits. In this Letter, we report on the self-mode-locking of a hybrid integrated laser comprising two indium phosphide gain sections and a silicon nitride feedback circuit that filters light using two ring resonators. The hybrid laser is shown to mode-lock and to have a mostly frequency-modulated field in the cavity using a stepped-heterodyne optical complex spectrum analysis. A mostly frequency modulated field output is good for high powers per line due to a more continuous emission, compared with mode-locked lasers using a saturable absorber; additionally, the filter limits the bandwidth of the comb, condensing the power to the fewer comb lines.

Demonstration of an external cavity semiconductor mode-locked laser

Electrically pumped semiconductor mode-locked lasers (SMLs) are promising in a wide range of applications due to compact size, high energy efficiency, and low cost. However, the long gain interaction length increases the spontaneous emission noise. In this Letter, an external cavity structure is adopted to improve the SML noise performance, as well as the flexibility to adjust the repetition rate. Two external cavity SMLs with repetition rates of 255 MHz and 10 GHz are demonstrated. For the 10 GHz SML, the signal-noise-ratio and radio frequency linewidth of the fundamental frequency reach 81.1 dB and 40 Hz, respectively. The high performance makes the laser a promising light source for microwave and communication applications.

Ring resonator enhanced mode-hop-free wavelength tuning of an integrated extended-cavity laser

Extending the cavity length of diode lasers with feedback from Bragg structures and ring resonators is highly effective for obtaining ultra-narrow laser linewidths. However, cavity length extension also decreases the free-spectral range of the cavity. This reduces the wavelength range of continuous laser tuning that can be achieved with a given phase shift of an intracavity phase tuning element. We present a method that increases the range of continuous tuning to that of a short equivalent laser cavity, while maintaining the ultra-narrow linewidth of a long cavity. Using a single-frequency hybrid integrated InP-Si₃N₄ diode laser with 120 nm coverage around 1540 nm, with a maximum output of 24 mW and lowest intrinsic linewidth of 2.2 kHz, we demonstrate a six-fold increased continuous and mode-hop-free tuning range of 0.22 nm (28 GHz) as compared to the free-spectral range of the laser cavity.

Hybrid Integrated Semiconductor Lasers with Silicon Nitride Feedback Circuits

Hybrid integrated semiconductor laser sources offering extremely narrow spectral linewidth, as well as compatibility for embedding into integrated photonic circuits, are of high importance for a wide range of applications. We present an overview on our recently developed hybrid-integrated diode lasers with feedback from low-loss silicon nitride (Si 3 N 4 in SiO 2 ) circuits, to provide sub-100-Hz-level intrinsic linewidths, up to 120 nm spectral coverage around a 1.55 μ m wavelength, and an output power above 100 mW. We show dual-wavelength operation, dual-gain operation, laser frequency comb generation, and present work towards realizing a visible-light hybrid integrated diode laser.