Since their introduction two years ago, quasi-phase-matched (QPM) optical parametric oscillators (OPOs) have moved into the mainstream of OPO research. This has been made possible by continuing improvements and availability of the microstructured nonlinear material periodically poled lithium niobate (PPLN). Demonstrations of PPLN OPOs now span the range of pulse formats and power levels. The most significant area of development is low-peak-power devices where operation with conventional materials is difficult. In this paper, we describe the current state of this research, including OPOs pumped by high-repetition-rate (>30 kHz) Q-switched diode-pumped solid state lasers, and CW singly resonant OPOs with >3-W output power in the 3-4-/spl mu/m range.

Periodically poled lithium niobate and quasi-phase-matched optical parametric oscillators

We report a continuous-wave singly resonant optical parametric oscillator (OPO) based on periodically poled lithium niobate. The simple, two-mirror OPO, pumped by a 1.064-μm Nd:YAG laser, had a 2.6–4.5-W threshold and an output of >1.2 W at 3.3 μm and was tuned over 1.45–1.62 μm (signal) and 3.98–3.11 μm (idler). The noise characteristics and the spectral properties of the device are described.

/pdf/continuous-wave-singly-resonant-optical-parametric-500aedcr1x.pdf

Continuous-wave singly resonant optical parametric oscillator based on periodically poled LiNbO(3).

We have achieved efficient electro-optic phase modulation at high frequencies in a resonant modulator cavity We enhance modulation by matching the phase velocities of the optical and microwave fields in the modulator substrate and by placing the modulator inside an optical cavity that is resonant for the input optical beam and the generated sidebands An optical frequency comb with a span of 3 THz and at a spacing of 17 GHz is generated with 1 W of microwave power The terahertz comb is utilized to phase lock an optical parametric oscillator at a signal-idler difference frequency of 665 GHz

Terahertz optical frequency comb generation and phase locking of an optical parametric oscillator at 665 GHz.

Lasers and Coherent Light Sources

We have demonstrated a continuous‐wave optical parametric oscillator that uses separate optical cavities to resonate independently the nondegenerate signal and idler frequencies. The three‐mirror cavity utilizes the type II phase‐matching geometry in lithium triborate, with the orthogonally polarized signal and idler fields separated by an intracavity, dichroic‐coated, Brewster‐angled beam splitter. This dual‐cavity oscillator can overcome mode and cluster hopping effects, which are characteristic of doubly resonant, continuous‐wave optical parametric oscillators. We measure a pump power threshold of ≊200 mW and smooth tuning over ≊0.4 GHz. The tuning range is limited by pump resonance effects within the idler cavity.

Continuous‐wave, dual‐cavity, doubly resonant, optical parametric oscillator

We present experimental results of frequency tuning and stabilization of a type-II phase-matched potassium titanyl phosphate (KTP) doubly resonant optical parametric oscillator. Four tuning elements were employed to control the stability and tuning of the parametric oscillator. Discrete frequency tuning of a nearly degenerate optical parametric oscillator over a range of ~3 THz was obtained by crystal angle tuning and cavity-length scanning. We achieved continuous frequency tuning over a 0.5-GHz range through the use of temperature and electro-optic tuning of the KTP crystal. Using these frequency-control techniques, we phase locked the signal–idler beat frequency to an external microwave frequency source, thus demonstrating tunable optical frequency division. The power spectral density of the residual phase noise of the phase-locked signal–idler beat note was measured to be 0.3mrad/Hz. Characteristics of two different cavity designs, their operations, tuning behavior, and stability issues are examined.

D. Lee

Papers

Stabilization and tuning of a doubly resonant optical parametric oscillator