An Integrated-Photonics Optical-Frequency Synthesizer

Integrated-photonics microchips now enable a range of advanced functionalities for high-coherence applications such as data transmission, highly optimized physical sensors, and harnessing quantum states, but with cost, efficiency, and portability much beyond tabletop experiments. Through high-volume semiconductor processing built around advanced materials there exists an opportunity for integrated devices to impact applications cutting across disciplines of basic science and technology. Here we show how to synthesize the absolute frequency of a lightwave signal, using integrated photonics to implement lasers, system interconnects, and nonlinear frequency comb generation. The laser frequency output of our synthesizer is programmed by a microwave clock across 4 THz near 1550 nm with 1 Hz resolution and traceability to the SI second. This is accomplished with a heterogeneously integrated III/V-Si tunable laser, which is guided by dual dissipative-Kerr-soliton frequency combs fabricated on silicon chips. Through out-of-loop measurements of the phase-coherent, microwave-to-optical link, we verify that the fractional-frequency instability of the integrated photonics synthesizer matches the $7.0*10^{-13}$ reference-clock instability for a 1 second acquisition, and constrain any synthesis error to $7.7*10^{-15}$ while stepping the synthesizer across the telecommunication C band. Any application of an optical frequency source would be enabled by the precision optical synthesis presented here. Building on the ubiquitous capability in the microwave domain, our results demonstrate a first path to synthesis with integrated photonics, leveraging low-cost, low-power, and compact features that will be critical for its widespread use.Comment: 10 pages, 6 figure

Recent Advances on Nonlinear Optics in Silicon Nitride Waveguides

Nonlinear phenomena based on the material 2nd or 3rd order nonlinear susceptibility tensor χ(2) and χ(3), respectively, offer potential in a wide variety of applications by exploiting wave-mixing capabilities. The integration of these nonlinear effects at the chip scale represents the best path towards portable, compact and low power optical signal processing devices. A significant body of work has been done recently in this direction, in particular focusing on CMOS-compatible platforms. While many nonlinear effects have been demonstrated in Silicon, Silicon Nitride has recently sparked significant interest. Owing to a larger band gap, wide transparency window and low loss, the potential of SiN waveguides for linear and nonlinear optics is now well established. In this paper, we report recent results on nonlinear processes in SiN waveguides. In particular we will cover generation of an extremely broad supercontinuum extending 400 THz from the visible to 3.6 µm pumped by a turnkey telecom wavelength pulsed source. We will also report on a tunable pulse source based on dispersive wave generation in an engineered thick waveguide. Finally, we will show that SiN offers some interesting potential for χ(2) based nonlinear effects, an important step towards integrating second order nonlinearity on chip

Mid-infrared frequency comb via coherent dispersive wave generation in silicon nitride nanophotonic waveguides

Mid-infrared optical frequency combs are of significant interest for molecular spectroscopy due to the large absorption of molecular vibrational modes on the one hand, and the ability to implement superior comb-based spectroscopic modalities with increased speed, sensitivity and precision on the other hand. Here, we demonstrate a simple, yet effective, method for the direct generation of mid-infrared optical frequency combs in the region from 2.5 to 4.0 mu m (that is, 2,500-4,000 cm(-1)), covering a large fraction of the functional group region, from a conventional and compact erbium-fibre-based femtosecond laser in the telecommunication band (that is, 1.55 mu m). The wavelength conversion is based on dispersive wave generation within the supercontinuum process in an unprecedented large-cross-section silicon nitride (Si3N4) waveguide with the dispersion lithographically engineered. The long-wavelength dispersive wave can perform as a mid-infrared frequency comb, whose coherence is demonstrated via optical heterodyne measurements. Such an approach can be considered as an alternative option to mid-infrared frequency comb generation. Moreover, it has the potential to realize compact dual-comb spectrometers. The generated combs also have a fine teeth-spacing, making them suitable for gas-phase analysis

Demonstration of Multiple Kerr-Frequency-Comb Generation Using Different Lines from Another Kerr Comb Located up to a 50 km Distance

We experimentally demonstrate multiple Kerr-frequency-comb generation using different lines from another Kerr comb located up to a 50 km distance. The master and generated slave combs are mutually coherent and have a small variance of frequency error