Wide-bandwidth 25-dB amplitude noise suppression in a pump-and-signal-resonant optical parametric oscillator.

We present a pump-and-signal-resonant optical parametric oscillator that provides 25 dB of amplitude noise suppression of the transmitted pump beam from dc to 20 kHz. The upper frequency range of the optical limiter increases as the pump power is increased, up to 1 MHz with 580 mW of input power. The amount of noise suppression is limited by pump-depletion effects. The upper frequency range is limited by the temporal response of the device. We present a numerical analysis that predicts this behavior.

Single-frequency mid-infrared optical parametric oscillator source for coherent laser radar.

We report on the design and characterization of a highly coherent mid-IR source at 3.57mum based on a single-frequency optical parametric oscillator. Detailed frequency and amplitude noise spectra have been measured. The rms intensity noise from 1.2 to 1000 Hz was 0.03%, and a rms frequency drift of 8 kHz in 1 ms was observed. We have also demonstrated the utility of this source for coherent laser radar applications by measuring micro-Doppler spectra from vibrating targets.

High-energy femtosecond pulse amlification in a quasi-phase-matched parametric amplifier.

A new type of solid-state femtosecond amplifier is demonstrated that is based on quasi-phase-matched parametric amplification. Such gain media are different from conventional solid-state amplifiers in that their amplification bandwidths and pump and signal wavelengths can be engineered. Furthermore, high gain is characteristic of parametric amplification, permitting extraction of high energies without the need to resort to multiple-pass configurations. We report a parametric chirped pulse amplification system in which femtosecond pulses from a mode-locked Er-doped fiber laser system are amplified to 1-mJ energies in a single pass by use of a 5-mm-long periodically poled LiNbO(3) (PPLN) crystal. This amplifier is pumped by 5-mJ and 0.5-ns pulses at 786 nm, demonstrating that limitations associated with a low optical-damage threshold for long pump pulses can be overcome because of the high nonlinearity of PPLN and that relatively simple Q -switched lasers can be used with such parametric amplifiers.

Engineerable femtosecond pulse shaping by second-harmonic generation with Fourier synthetic quasi-phase-matching gratings.

We describe a pulse-shaping technique that uses second-harmonic generation with Fourier synthetic quasi-phase-matching gratings. We demonstrate both amplitude and phase tailoring by generating a picosecond squarelike pulse as well as trains of femtosecond pulses with a terahertz-range repetition rate from either a compressed or a chirped pump pulse.

1.5-microm-band wavelength conversion based on difference-frequency generation in LiNbO3 waveguides with integrated coupling structures.

We report wavelength conversion within the 1.5-mum telecommunications band based on difference-frequency generation in periodically poled lithium niobate waveguides with integrated coupling structures. A conversion efficiency of -7 dB and a normalized efficiency of 260%/W are demonstrated. Static tests show that the conversion bandwidth is 72 nm and the conversion efficiency is constant over the 20-dB range of input powers tested.

Chirped-pulse-amplification circuits for fiber amplifiers, based on chirped-period quasi-phase-matching gratings.

A new type of compact chirped-pulse-amplification circuit for high-power amplification of femtosecond pulses in an optical fiber is demonstrated. This circuit is based on a novel pulse compressor, chirped-period quasi-phase-matching gratings in electric-field-poled lithium niobate. The main advantages of this circuit are simplicity, the small number of components, compactness, and wavelength conversion of Er-doped fiber output to the technologically important 780-nm wavelength region.

Frequency Stabilization of a Diode Laser at 1540 nm by Locking to Sub-Doppler Lines of Potassium at 770 nm.

An external cavity 1540-nm diode laser was frequency doubled in a 3-cm-long periodically poled LiNbO(3) waveguide doubler with 150% W(-1) conversion efficiency, thereby generating more than 3 muW at 770 nm. Second-harmonic light was used to detect and lock to sub-Doppler lines of the (39)K D(1) transition.

Frequency Stability at the Kilohertz Level of a Rubidium-Locked Diode Laser at 192.114 THz.

The frequency stability of a 1560-nm diode laser, whose second harmonic was locked to (87)Rb sub-Doppler lines, was characterized by measuring the beat frequency relative to a 780-nm reference laser that was locked to sub-Doppler lines of another rubidium cell. The square root of the Allan variance reached a minimum value of 7.5 x 10(-12) in 1 s, which corresponded to frequency variations of 1.44 kHz for the 1560-nm laser. The frequency reproducibility of the system was approximately 1 x 10(-9). These values are better than those that can be achieved by locking to Doppler-broadened transitions at the 1550-nm wavelength band.

Pulse compression during second-harmonic generation in aperiodic quasi-phase-matching gratings.

We propose a simple means for compressing optical pulses with second-harmonic generation. Aperiodic quasi-phase-matching gratings impart a frequency-dependent phase shift on the second-harmonic pulse relative to the fundamental pulse and can be engineered to correct for arbitrary phase distortions. The mechanism is discussed, and a detailed analysis of the compression of quadratic phase (linear frequency) chirped pulses is presented.

Singly resonant optical parametric oscillation in periodically poled lithium niobate waveguides.

We report quasi-phase-matched singly resonant optical parametric oscillation in electric-field-poled lithium niobate waveguides. Parametric gains as high as 250%/W, an oscillation threshold of 1.6 W (peak), idler output powers of 220 mW, and a tuning range of 1180-2080 nm for pump wavelengths of 756-772 nm have been observed. Pump depletion is limited to 40% because of the multiple launched transverse modes at the pump wavelength. We predict that fully optimized waveguide singly resonant oscillators can have thresholds of ~100 mW, accessible to cw diode pumping.

Frequency doubling of femtosecond erbium-fiber soliton lasers in periodically poled lithium niobate.

We report efficient frequency doubling of passively mode-locked femtosecond erbium-fiber lasers. Quasi-phase-matched second-harmonic generation in periodically poled lithium niobate is used to generate 8.1 mW of 190-fs (FWHM), 90-pJ pulses at 777 nm with a conversion efficiency greater than can be obtained with existing birefringently phase-matched nonlinear materials. A dispersion-compensation-free soliton oscillator generating transform-limited 230-fs (FWHM) pulses at 1554 nm is used as a pump laser.

Fiber-laser-based femtosecond parametric generator in bulk periodically poled LiNbO(3).

A diode-pumped system for optical parametric generation of wavelength-tunable femtosecond pulses is demonstrated. It comprises an Er-doped fiber mode-locked laser, a fiber chirped-pulse amplifier, and a bulk periodically poled LiNbO(3) (PPLN) optical parametric generator. The parametric generator is pumped at 777 nm with frequency-doubled microjoule pulses from the fiber amplifier and produces 300-fs pulses tunable from 1 to 3microm with output energies up to ~200 nJ. Use of a PPLN nonlinear crystal substantially reduces the pump energies required for efficient parametric generation. Saturated single-pass parametric energy conversion of 38% (internal) has been achieved with only 220 nJ of pump inside the crystal. A parametric generation threshold of 54 nJ is observed, and efficient parametric conversion is obtained with repetition rates up to 200 kHz.

Engineerable compression of ultrashort pulses by use of second-harmonic generation in chirped-period-poled lithium niobate.

We demonstrate the use of an aperiodic quasi-phase-matching (QPM) grating to generate second-harmonic pulses that are stretched or compressed relative to input pulses at the fundamental frequency. We frequency doubled an externally chirped erbium-doped fiber laser generating 17-ps (FWHM) pulses at 1560nm to produce near-transform-limited 110-fs (FWHM) pulses at 780nm by use of a 5-cm-long lithium niobate crystal poled with a QPM grating chirped from an 18.2- to a 19.8-microm period.

Broadly tunable mid-infrared femtosecond optical parametric oscillator using all-solid-state-pumped periodically poled lithium niobate.

We describe a high-repetition-rate femtosecond optical parametric oscillator (OPO) that was broadly tunable in the mid infrared. The all-solid-state-pumped OPO was based on quasi-phase matching in periodically poled lithium niobate. The idler was tunable from approximately 1.7 mum to beyond 5.4 mum, with maximum average power levels greater than 200 mW and more than 20 mW of average power at 5.4 mum. We used interferometric autocorrelation to characterize the mid-infrared idler pulses, which typically had durations of 125 fs. This OPO had a pumping threshold as low as 65 mW of average pump power, a maximum conversion efficiency of >35% into the near-infrared signal, a slope efficiency for the signal of approximately 60%, and a maximum pump depletion of more than 85%.

Amplitude squeezing by means of quasi-phase-matched second-harmonic generation in a lithium niobate waveguide.

We demonstrate that traveling-wave second-harmonic generation produces amplitude-squeezed light at both the fundamental and the harmonic frequencies. Quasi-phase-matched second-harmonic conversion efficiencies approaching 60% were obtained in a 26-mm-long single-mode LiNbO(3) waveguide with pulses from a mode-locked laser at 1.53 microm. The amplitude noise of the transmitted fundamental field was measured to be 0.8 dB below the shot-noise level, and the generated 0.765-microm harmonic light was measured to be amplitude squeezed by 0.35 dB. The conversion-efficiency dependence of the observed squeezing at both wavelengths agrees with theoretical predictions. Waveguide losses appear to degrade the squeezing, but the maximum observed squeezing is currently limited only by the available input power.

Adiabatically tapered periodic segmentation of channel waveguides for mode-size transformation and fundamental mode excitation.

We report modeling, fabrication, and characterization of tapered waveguides, using periodically segmented annealed proton exchange in LiNbO(3). For a taper transforming the 1/e full width (intensity) mode size from 6.0 microm x 4.4 microm to 2.0 microm x 1.3 microm, 0.4-dB excess loss was observed. The large, slightly elliptical mode can ease coupling to single-mode fibers and circular free-space beams. The same taper structure was used to excite a highly multimoded (13 modes) waveguide with more than 95% of the power stably launched into the lowest-order mode. This function is useful for nonlinear waveguide devices, such as difference-frequency generators, in which modes at highly disparate wavelengths interact.

Quasi-phase-matched frequency doubling in a waveguide of a 1560-nm diode laser and locking to the rubidium D(2) absorption lines.

An external-cavity 1560-nm diode laser was frequency doubled in a 3-cm-long periodically poled LiNbO(3) waveguide doubler with 120% W(-1) conversion efficiency. The 780-nm light was used to detect the D(2) transitions of Rb, and the laser frequency was locked to Doppler-broadened lines of Rb. Furthermore, the ~1 microW of second-harmonic power was sufficient for detecting the sub-Doppler lines of Rb, and the laser was locked to a (87)Rb crossover line.

Quasi-phase-matched optical parametric amplification and oscillation in periodically poled LiNbO(3) waveguides.

We report quasi-phase-matched optical parametric amplification and oscillation in a periodically poled LiNbO(3) waveguide. Single-pass parametric gains of 4.1 dB, corresponding to 18%/W efficiency, were achieved at a signal wavelength of 1.55 microm with a pump wavelength of 782.2 nm. We formed a low-finesse cavity resonant at both signal and idler wavelengths by attaching mirrors to the waveguide end faces. Parametric oscillation was observed at wavelengths between 1.4 and 1.7 microm with a peak output power of 700 mW for pump wavelengths between 779 and 782 nm.