Design guidelines for normal-dispersion fiber optical parametric chirped-pulse amplifiers

Abstract

We theoretically investigate methods of controlling pulse generation in normal-dispersion fiber optical parametric chirped-pulse amplifiers. We focus on high-energy, ultrashort pulses at wavelengths widely separated from that of the pump, and find that within this regime, a number of simple properties describe the essential phase and gain dynamics. Of primary importance are the relationships between the chirps of the pump, seed, and parametric gain, which we theoretically predict and then experimentally validate. By properly arranging these parameters, the signal and idler waves can be widely customized to fulfill a remarkable range of application requirements, spanning from narrowband to few-cycle.

FIG. 1:

Wavevector mismatch for negative group-velocity dispersion and zero fourth-order dispersion (solid red), and for positive group-velocity dispersion and negative fourth-order dispersion (dashed blue). Phase-matching is obtained at the marked points.

FIG. 2:

Simulated pump power (solid) and frequency (dashed; spurious oscillations at low powers are masked) at the output of an FOPCPA that is either unseeded (blue) or CW-seeded (red).

FIG. 3:

Measured FROG reconstructions of residual pump pulses at the output of a FOPCPA system with and without a seed present. (a) Temporal intensity and instantaneous frequency. (b) Spectral intensity. (c) Measured and retrieved FROG traces for the unseeded and seeded cases.

FIG. 4:

(a) Powers and (b) instantaneous frequencies of the pump, seed, and idler at the output of the CW-seeded FOPCPA system described in the text. The frequencies have been transformed as labeled to visually show their adherence to equation 2.

FIG. 5:

Illustration comparing a launched, nonlinearly-chirped pulse (solid red) to one with an equivalent, linear chirp (dashed blue) for a Gaussian intensity (solid black). B = 30π is used for the nonlinear case.

FIG. 6:

Simulated idler (a) energy and (b) duration (dechirped and transform-limited) as a function of nonlinear phase pre-applied to the pump.

FIG. 7:

Temporal Strehl ratios of the dechirped (green) initial pump and (violet) generated idler pulses as a function of nonlinear phase pre-applied to the pump.

FIG. 8:

Scaling CW-seeded FOPCPA simulations in the time domain at constant pump energy. The resulting pump (solid green) and idler (dashed red) pulses are shown, while the labels give the initial pump peak powers and the output idler energies. Note the changing axis scales.

FIG. 9:

Pump and idler pulses at the output of simulated FOPCPAs with different gain chirp factors obtained by varying β₃.

FIG. 10:

Idler energies and chirped (FWHM) durations obtained from simulated FOPCPAs with different gain chirp factors.

FIG. 11:

Simulations of FOPCPAs with the dispersion coefficients at the pump wavelength given. Left: output pump (green) and idler (red) in the time domain. Right: corresponding spectra. The CW parametric gain spectra (dashed violet) calculated at the central pump frequencies vary widely in bandwidth, while the resulting pump and idler pulses remain largely unchanged.

FIG. 12:

Signal and idler parameters for different gain chirp factors. In each case, the seed chirp is perfectly matched to the gain chirp. In all cases, durations are measured using the full-width-at-half-maximum. TL: transform limit. Inset: initial pump and output pump, signal, and idler powers for ρ = 3.

FIG. 13:

Signal and idler parameters for different relative seed chirps, α_s/α_p, and a constant gain chirp factor of ρ = 1. The point where the seed is matched to the gain chirp is shown as a dashed line. Durations are measured using the full-width-at-half-maximum.

FIG. 14:

Signal and idler parameters for different relative seed chirps, α_s/α_p, and a constant gain chirp factor of ρ = 10. The point where the seed is matched to the gain chirp is shown as a dashed line. Durations are measured using the full-width-at-half-maximum.

FIG. 15:

(a) Schematic of an experimental FOPCPA system. EDFA: Er-doped fiber amplifier. YDFA: Yb-doped fiber amplifier. HNLF: highly-nonlinear fiber. DSF: dispersion-shifted fiber. TBPF: tunable bandpass filter. ODL: optical delay line. PCF: photonic crystal fiber. (b) Input spectra of the pump (solid black) and seed (dashed red), and (c) autocorrelation of the pump pulses before the grating compressor.

FIG. 16:

Experimental (a) idler and (b) signal spectra measured as a function of the pump duration. Pump autocorrelation FWHM durations are given in the legend.

FIG. 17:

(a) Bandwidths of the spectra shown in Figure 16. (b) Idler power conversion efficiency as a function of the pump duration.