Nanophotonic soliton-based microwave synthesizers

Ultralow-noise photonic microwave synthesis using a soliton microcomb-based transfer oscillator

“…Nonetheless, the residual phase noise of these combs has been shown to be suitable for frequency division 38 . Recent improvements of integrated resonators have enabled soliton microcombs with K-and X-band (20 and 10 GHz) repetition rates in integrated resonators 39 . However, the achieved spectral spans, although wider than in the crystalline case, are far from covering one octave.…”

Dynamics of soliton self-injection locking in a photonic chip-based microresonator

“…In our experiment, a commercial DFB laser diode of 120 kHz linewidth and 120 mW output power is directly butt-coupled to the Si 3 N 4 chip without using an optical isolator (see Methods). The single-frequency operation of the DBF laser diode allows to control the laser dynamics via Rayleigh backscattering from the Si 3 N 4 microresonator ("laser selfinjection locking"), which is fabricated using the photonic Damascene reflow process 38,39 and features intrinsic quality factor Q 0 exceeds 10 × 10 6 . Such backscattering is commonly undesired 40 , but is critical here for laser selfinjection locking whose dynamics is affected by the amplitude and phase of the backscattered light.…”

Packaged photonic chip-based soliton microcomb using an ultralow-noise laser

“…A particularly important phenomena in the field of Kerr combs are dissipative Kerr solitons (DKS), which constitute continuously circulated ultrashort pulses in a microresonator and offer broadband and coherent optical frequency combs [4]. A number of applications range from coherent communications [5], dualcomb spectroscopy [6], astrophysical spectrometer calibration [7,8], ultrafast distance measurement [9,10] to ultra-low noise microwave generation [11,12] have been demonstrated utilizing DKS. Platforms that generated DKS include MgF 2 , SiO 2 , Si 3 N 4 , Si, AlN, and LiNbO 3 [3].…”

“…By packaging the Si 3 N 4 microresonator, a very compact soliton microcomb system can be demonstrated which may enable the use of such devices in practical applications. Recently, a soliton microcomb operating in the microwave K-and X-band was demonstrated using photonic integrated Si 3 N 4 microresonators at a very low input power (∼ 35 mW on-chip) [12]. As pointed out in that work, given that the laser noise is transferred to the soliton comb, it is critical to use a laser with low frequency noise that can be operated at sufficiently high power (> 60 mW) to initiate soliton generation.…”

“…A packaging technique has been developed for a compact, portable microcomb system. Such a compact system is crucial for applications requiring a high power per comb line and low phase noise, such as coherent communications [5] and on-chip low-noise microwave generation [12].…”