Low Noise & Low-SWaP High-Repetition Rate Mode-Locked Lasers for High-Speed Photonics

Mode-locked semiconductor lasers can support high repetition rates up to 100 GHz due to the high gain and fast gain recovery unlike in fiber lasers or doped dielectric gain medium lasers. While harmonic mode-locking or pulse interleaving can be used to increase the repetition rate into the 4 to 10 GHz range each of these techniques lack a pure microwave signal. High repetition rate semiconductor lasers can provide the low-noise microwave signal due to the fundamental mode-locking that can be achieved in the gigahertz range with a semiconductor saturable absorber mirror (SESAM). This offers a compact, efficient, low-noise, high-speed option for connecting the optical and microwave domain enabling integration with photonic integrated circuits (PICs) or COTs components. Currently a commercially available stabilized low-noise laser in the 6 to 12 GHz range is lacking. A promising approach is a technique enabling a two-element cavity design for high-repetition rate lasers has been demonstrated [1,2]. By including the semiconductor saturable absorber with a dielectric output coupler the overall cavity length can be made shorter for high-repetition rates without complex gain structures and without high curvature cavity optics. In the near-infrared (NIR) this was demonstrated on a curved output coupler with a bonded quantum well saturable absorber resulting in a hybrid SESAM [1] achieving pulse-widths of about 400 fs at repetition rates from 2.8 to 8 GHz. In the visible spectrum a similar technique was applied with a flat dielectric mirror, constructing what was coined as a membrane saturable absorber mirror (MESAM) [2]. Due to the output coupler and saturable absorber being independent the repetition rate remained low but still achieved picosecond pulses. Integrating these elements via direct membrane bonding of the saturable absorber allows higher repetition rates and has been demonstrated for high-power applications [3]. It is envisioned that this approach, or other proposed solutions, can be extended throughout the NIR and into the SWIR, particularly in the O-band and C-band for compatibility with PICs and COTs components. The developed lasers should be able to operate at a repetition rate between 6 and 12 GHz, achieve 50 mW or greater average power, with a pulse width of a picosecond or less. The laser can be optically- or electrically-pumped but must have the repetition rate stabilized with custom or COTs electronics while achieving low relative intensity noise (RIN) and long-term power stability. It is expected that the overall SWaP of the laser itself and necessary electronics will be minimized with differentiating goals highlighted in Phase I, II, and III. No government materials, equipment, data, or facilities will be provided.