Compact, spatial-mode-interaction-free, ultralow-loss, nonlinear photonic integrated circuits

Abstract

Multi-mode waveguides are ubiquitously used in integrated photonics. Although interaction among different spatial waveguide eigenmodes can induce novel nonlinear phenomena, spatial mode interaction is typically undesired. Adiabatic bends, such as Euler bends, have been favoured to suppress spatial mode interaction. Here, we adapt and optimize Euler bends to build compact racetrack microresonators based on ultralow-loss, multi-mode, silicon nitride photonic integrated circuits. The racetrack microresonators feature a footprint of only 0.21 mm2 for 19.8 GHz free spectral range, suitable for tight photonic integration. We quantitatively investigate the suppression of spatial mode interaction in the racetrack microresonators with Euler bends. We show that the low optical loss rate (15.5 MHz) is preserved, on par with the mode interaction strength (25 MHz). This results in an unperturbed microresonator dispersion profile. We further generate a single dissipative Kerr soliton of 19.8 GHz repetition rate without complex laser tuning schemes or auxiliary lasers. The optimized Euler bends and racetrack microresonators can be building blocks for integrated nonlinear photonic systems, as well as linear circuits for programmable processors or photonic quantum computing.

A photonic integrated circuit based erbium-doped amplifier

“…The amplified soliton is able to deliver a strong microwave signal, resulting in a reduced phase noise (in blue) for offset frequencies of > 10 kHz, reaching -120 dBc/Hz at 100 kHz and -126 dBc/Hz at 1 MHz, respectively. The spectral bumps around 4 kHz offset frequencies is attributed the characteristic laser phase noise (Toptica CTL), while the spectral spikes between 10 kHz and 100 kHz stem from the laser amplitude-to-phase noise conversion observed in prior works [40,42,43]. The 'step-like' phase noise at offset frequencies above 100 kHz is dominated by the phase noise analyzer noise floor (the dashed dotted line).…”

“…where µ is the comb mode number counting away from the pump line, β 2 is the group velocity dispersion coefficient, D 1 /2π = 19.8GHz is the cavity FSR and ∆ω s is the comb spectral bandwidth, yielding a maximum line power of about -29 dBm and a total microcomb power of about 0.3 mW. Parameters used for the soliton microcomb power fitting are extracted from the reported Si 3 N 4 Euler-bend racetrack microrsonator [40]. The group velocity dispersion β 2 is -14.1 fs 2 /mm, corresponding to D 2 /2π =34.9 kHz.…”

Review on all-optical logic gates: design techniques and classifications – heading toward high-speed optical integrated circuits

“…A truly optical system will consist of PICs similar to electronic integrated circuits wherein a large number of optical devices are integrated on a single chip. 188 A lot of research is being done on PICs in recent years to realize all-optical systems/devices. 189 With the evolution of PIC technology, many platforms have been developed such as SOI, SiN, InP, silica, and so on for specific requirements.…”

Broadband high-Q multimode silicon concentric racetrack resonators for widely tunable Raman lasers

“…In such multimode racetrack resonators, the fundamental mode can couple to the higher-order mode in the multimode bends, leading to the reduction in Q factors of the fundamental mode-based resonances 44 – 46 . This is a well-known problem and has been previously tackled by using single-mode bends 47 , 48 , Euler bends 42 , 43 , 49 , and Bezier bends 50 to suppress the higher-order modes at the bends and maintain a high Q factor for the fundamental mode.…”