Broadband quantum-dot frequency-modulated comb laser

Noise characteristics of semiconductor lasers with narrow linewidth

Narrow-linewidth semiconductor lasers are highly valued in scientific research and industrial applications owing to their high coherence and low phase noise characteristics, particularly in high-performance optical communications, sensing, and microwave photonic systems. Accuracy, a key objective of many application systems, is determined by the noise of the light source. As system accuracy improves, the requirements for the light source become more stringent, with linewidth reduction and noise reduction being the top priorities. Currently, extensive attention and research are focused on suppressing noise generated by narrow-linewidth lasers. This paper presents noise measurement methods, analyses of the mechanisms for noise suppression, and recent research progress in low-noise semiconductor lasers, focusing on material optimization, structural design, and feedback control. The limitations of current technological solutions are discussed, and future scientific trends are outlined.

Intensity noise reduction in quantum dot comb laser by lower external carrier fluctuations

This work investigates the impact of carrier noise induced by an external current source on the linewidth enhancement factor (LEF) and relative intensity noise (RIN) of a 100 GHz quantum dot fourth-order colliding-pulse mode-locked laser (MLL), driven by a normal pump with Gaussian-distributed carrier sequences and a quiet pump with sub-Poissonian-distributed carrier sequences. The results indicate that under a normal pump, the LEFs are approximately zero for reverse saturable absorber (SA) bias voltages ranging from 0 to 2.5 V, and the laser achieves a RIN as low as -156 dB/Hz. When using a quiet pump, both the LEF and RIN are reduced across all SA bias conditions, particularly at low reverse SA bias voltages. Specifically, the LEF decreases by up to 0.58 at 0 V, and the average RIN spectrum is reduced by more than 3 dB at the same voltage. This work provides a straightforward approach for the development and optimization of multi-channel light sources for dense wavelength division multiplexing (DWDM) technologies with low optical noise.

Efficient, high-power, narrow-linewidth, continuous-wave quantum-dot semiconductor comb laser

We report a continuous-wave, O-band quantum-dot semiconductor comb laser for WDM optical interconnects exhibiting a 2.2 THz optical bandwidth with up to 89 comb wavelengths spaced at 25 GHz, over 30% peak ex-facet electrical-to-optical power conversion efficiency, up to 270 mW of usable laser power, relative intensity noise below - 135 dB/Hz per individual mode, individual laser mode linewidth of 140 kHz, mode beating linewidths of 50 kHz across all modes, and stable far-field output with 75% coupling efficiency to PM fiber in a butterfly package.

Optical frequency comb assisted reconfigurable broadband spread spectrum signal generation

A photonic-assisted scheme for spread spectrum communication signals generation is proposed and demonstrated in this article. The spreading sequence and the baseband data codes are modulated on the photonic link by electro-optic modulators, and the spread spectrum process is completed through stream processing on the analog microwave photonic link. By combining optical frequency comb and injection locking technologies, the carrier frequency of the communication signals can be tuned over an ultra-broadband range of 3-39 GHz. In the proof-of-concept experiments, spread spectrum signals at 3 GHz and 6 GHz are obtained with a spread factor of 31. The analysis results indicate that the generated signals possess excellent reconfiguration, anti-interference, and anti-interception properties. Overall, our proposed scheme offers a flexible photonic architecture with significant potential in the application of ultra-broadband covert communication systems.