Differential phase-shift-keying demodulation by coherent perfect absorption in silicon photonics.

We demonstrate a novel differential phase-shift-keying (DPSK) demodulator based on coherent perfect absorption (CPA). Our DPSK demodulator chip device, which incorporates a silicon ring resonator, two bus waveguide inputs, and monolithically integrated detectors, operates passively at a bit rate of 10 Gbps at telecommunication wavelengths, and fits within a mm-scale footprint. Critical coupling is used to achieve efficient CPA by tuning the gap between the ring and bus waveguides. The device has a vertical eye opening of 12.47 mV and a quality factor exceeding 3×104. The fundamental principle behind this photonic circuit can be extended to other formats of integrated demodulators.

Temporal Simultons in Optical Parametric Oscillators.

We report the first demonstration of a regime of operation in optical parametric oscillators (OPOs), in which the formation of temporal simultons produces stable femtosecond half-harmonic pulses. Simultons are simultaneous bright-dark solitons of a signal field at frequency ω and the pump field at 2ω, which form in a quadratic nonlinear medium. The formation of simultons in an OPO is due to the interplay of nonlinear pulse acceleration with the timing mismatch between the pump repetition period and the cold-cavity round-trip time and is evidenced by sech^{2} spectra with broad instantaneous bandwidths when the resonator is detuned to a slightly longer round-trip time than the pump repetition period. We provide a theoretical description of an OPO operating in a regime dominated by these dynamics, observe the distinct features of simulton formation in an experiment, and verify our results with numerical simulations. These results represent a new regime of operation in nonlinear resonators, which can lead to efficient and scalable sources of few-cycle frequency combs at arbitrary wavelengths.

Fiber-feedback optical parametric oscillator for half-harmonic generation of sub-100-fs frequency combs around 2 µm.

We demonstrate a femtosecond fiber-feedback optical parametric oscillator (OPO) at degeneracy. The OPO cavity comprises an 80-cm-long fiber composed of a combination of normal and anomalous dispersion sections that provide a net intracavity group delay dispersion close to zero. By using a mode-locked, Yb-doped fiber laser as the pump, we achieved half-harmonic generation of 250-MHz, 1.2-nJ nearly transform-limited 97-fs pulses centered at 2090 nm with a total conversion efficiency of 36%.

Fractional-length sync-pumped degenerate optical parametric oscillator for 500-MHz 3-µm mid-infrared frequency comb generation.

We demonstrate a mid-IR frequency comb centered at 3120 nm with 650-nm (20-THz) bandwidth at a comb-teeth spacing of 500 MHz. The generated comb is based on a compact ring-type synchronously pumped optical parametric oscillator (SPOPO) operating at degeneracy and pumped by a mode-locked Er-doped 1560 nm fiber laser at a repetition rate of 100 MHz. We achieve high-repetition rate by using a fractional-length cavity with a roundtrip length of 60 cm, which is one-fifth of the length dictated by conventional synchronous pumping.

Sub-50 fs pulses around 2070 nm from a synchronously-pumped, degenerate OPO.

We report generation of 48 fs pulses at a center wavelength of 2070 nm using a degenerate optical parametric oscillator (OPO) synchronously-pumped with a commercially available 36-MHz, femtosecond, mode-locked, Yb-doped fiber laser. The spectral bandwidth of the output is ~137 nm, corresponding to a theoretical, transform-limited pulse width of 33 fs. The threshold of the OPO is less than 10 mW of average pump power. By tuning the cavity length, the output spectrum covers a spectral width of more than 400 nm, limited only by the bandwidth of the cavity mirrors.