Phase-matched four-photon mixing processes in birefringent fibers

Femtosecond optical parametric chirped-pulse amplification in birefringent step-index fiber

We demonstrate an optical parametric chirped-pulse amplifier (OPCPA) that uses birefringence phase matching in a step-index single-mode optical fiber. The OPCPA is pumped with chirped pulses that can be compressed to sub-30-fs duration. The signal (idler) pulses are generated at 905 nm (1270 nm), have 26 nJ (20 nJ) pulse energy, and are compressible to 70 fs duration. The short compressed signal and idler pulse durations are enabled by the broad bandwidth of the pump pulses. Numerical simulations guiding the design are consistent with the experimental results and predict that scaling to higher pulse energies will be possible. Forgoing a photonic crystal fiber for phase-matching offers practical advantages, including allowing energy scaling with mode area.

Cross-polarized photon-pair generation and bi-chromatically pumped optical parametric oscillation on a chip

Nonlinear optical processes are one of the most important tools in modern optics with a broad spectrum of applications in, for example, frequency conversion, spectroscopy, signal processing and quantum optics. For practical and ultimately widespread implementation, on-chip devices compatible with electronic integrated circuit technology offer great advantages in terms of low cost, small footprint, high performance and low energy consumption. While many on-chip key components have been realized, to date polarization has not been fully exploited as a degree of freedom for integrated nonlinear devices. In particular, frequency conversion based on orthogonally polarized beams has not yet been demonstrated on chip. Here we show frequency mixing between orthogonal polarization modes in a compact integrated microring resonator and demonstrate a bi-chromatically pumped optical parametric oscillator. Operating the device above and below threshold, we directly generate orthogonally polarized beams, as well as photon pairs, respectively, that can find applications, for example, in optical communication and quantum optics.

Interplay of four-wave mixing processes with a mixed coherent-incoherent pump

We experimentally demonstrate the existence of multiple, simultaneous, independent four-wave mixing processes in optical fibers. In particular we observe competition between phase-matched and non-phasematched processes involving the same mixed coherent-incoherent pump. Further investigation reveals that narrow-band degenerate four-wave mixing with an incoherent pump can lead to efficient wavelength conversion.

Nondegenerate four-wave mixing in a birefringent optical fiber pumped by a dye laser

An efficient nondegenerate four-wave-mixing process in a highly birefringent optical fiber pumped by a dye laser is reported. The output beam from a dye laser (at ~610 nm) was found to mix with the accompanying superfluorescent light (from 575 to 600 nm) in a birefringent fiber to generate a distinct frequency-shifted beam, which could be Stokes or anti-Stokes radiation, depending on which mode of the fiber was excited. The frequency shift was comparable with that observed in the well-known pump-divided degenerate process, as confirmed by the theory.

Distributed optical-fiber sensing by four-photon mixing pulse walk-off

We propose a distributed optical-fiber sensing scheme using four-photon mixing pulse walk-off. We use a copropagating system in which only a pump wave is launched into the fiber. We analyze the performance by including the effects of fiber birefringence, group-velocity dispersion, and self-phase modulation. A short system with high sensitivity and good resolution can be built. The useful operating length is limited by self-phase-modulation-induced pulse broadening.

Characteristics and applications of birefringent-fiber Kerr-couplers

We consider the effects of the pump power and the interaction length on the efficiency of polarization coupling induced by the optical Kerr effect in high-birefringence fibers. An efficiency of up to 100% is predicted for suitable combinations of the length and the strength of the birefringence grating in the fiber. The device is rapidly tunable, highly selective in wavelength, and independent of any thermal drift in the fiber. Potential applications include real-time tuning in wavelength-division demultiplexers, wavelength selection in optical spectrum analyzers, and band rejection in tunable notch filters.

Energy conversion in degenerate four-photon mixing in birefringent fibers

We predict that the third-order parametric mixing of a pump with a pair of orthogonally polarized sidebands in a birefringent single-mode optical fiber may be spatially unstable. The interaction may exhibit both periodic and nonperiodic energy conversion and period doubling. This analysis allows us to propose a new scheme for all-optical switching as well as to predict the most efficient conditions for energy conversion when pump depletion is accounted for.

Multiple four-wave mixing process in an optical fiber

We report the results of a theoretical and experimental investigation of multiple four-wave mixing processes in the simultaneous propagation of two pump waves through an optical fiber. The pump waves at frequencies omega(1) and omega(2) are observed to generate sidebands at 2omega(2) - omega(1) and 2omega(1) - omega(2) owing to four-wave mixing in the fiber. The power in the sidebands is studied as a function of pump power and detuning. The experimental observations provide a direct verification of the theoretical formalism.

Initial demonstration of a novel broadband optical amplifier using the Kerr effect in an optical fiber

A potentially ultrafast optical amplifier is outlined and demonstrated. The amplification involves an optical signal's modulating the polarization of a high-power optical pump by use of the high-speed optical Kerr effect in an optical fiber. The pump and signal wavelengths are different, and information transfers to the pump wavelength. The maximum available gain is limited by the onset of other nonlinear effects.

Pump-intensity-dependent frequency shift in Stokes and anti-Stokes spectra generated by stimulated four-photon mixing in birefringent fiber

The output spectra of the Stokes and anti-Stokes fields generated by stimulated four-photon mixing in birefringent fiber are investigated both experimentally and theoretically and are found to be dependent on the pump intensity. The pump-intensity-dependent changes in their frequency shifts are measured in 15-m long birefringent fiber by time-resolved spectroscopy using a 500-H(z)Q-switched Nd:YAG laser (lambda = 1.0642microm) as the pump source. Also, the Stokes gain coefficient is calculated as a function of the frequency shift and the pump power for the present phase-matching process where the mutually perpendicular polarization components are involved. The theoretical results agree well with the experimental data obtained.