Sang-Kyung Choi

Traveling-wave optical parametric amplifier: investigation of its phase-sensitive and phase-insensitive gain response

We experimentally investigate the gain response of a frequency-degenerate but polarization-nondegenerate traveling-wave optical parametric amplifier that consists of a type II phase-matched potassium titanyl phosphate crystal pumped by a frequency-doubled Q-switched mode-locked Nd:YAG laser. Both the optical phase-sensitive and phase-insensitive configurations of the parametric amplifier are studied. Experimental results are in excellent agreement with the theory of an optical parametric amplifier when the Gaussian-beam nature of the various fields is taken into account. In the phase-sensitive configuration a gain of >100 (20 dB) could be easily obtained in the amplified quadrature, which is limited only by the available pump power. Because of gain-induced diffraction and phase fluctuations, however, maximum deamplification in the orthogonal quadrature is limited to <0.5(-3xa0dB).

Measurement of quantum-noise correlations in parametric image amplification

We demonstrate quantum-noise correlations between the spatial frequencies of a parametrically amplified signal image and the generated conjugate (idler) image. Test images were amplified by an optical parametric amplifier that can be operated either as a low-pass or a band-pass amplifier for spatial frequencies. Direct difference detection of the signal and idler spatial frequencies at +- 16 mm{;{-1}} resulted in noise that fell below the shot-noise level by approx. 5 dB. Parametric-gain and phase-mismatch dependence of the observed quantum-noise reduction is in good agreement with the theory of a spatially-broadband optical parametric amplifier.

Gaussian-wave theory of sub-Poissonian light generation by means of travelling-wave parametric deamplification

A Gaussian wave theory is developed to analyse the sub-Poissonian light generated by means of a travelling-wave optical parametric deamplification. The Gaussian spatial profile of the pump beam limits the observable Fano factor to -3 dB (0.5). Gain-induced diffraction of the signal beam and classical fluctuations of the pump-signal relative phase cause further degradation. The theory is compared with our recent experimental results, and excellent agreement is found after the effect of non-ideal photoelectron efficiency is taken into account.

Room temperature high speed InGaAs/InP avalanche photodiode single photon counters

We have developed high speed gated-mode single photon counters based on In-GaAs/InP avalanche photodiodes. Room temperature operation allows for afterpulsing below 0.2% up to 14 MHz gate rate. We measure quantum efficiency of 14% with dark count probability of 0.2%.

Measurement of Joint Photon-Number Distribution of a Twin-Beam State by Means of Optical Homodyne Tomography

We report the first measurement of the joint photon-number probability distribution for a two-mode quantum state created by a nondegenerate optical parametric amplifier. The measured distribution exhibits inherently quantum correlations between the signal and idler photon numbers, whereas the marginal distributions are thermal as expected for parametric fluorescence.

Observation of Noiseless Image Amplification by an Optical Parametric Amplifier

A spatially-broadband optical parametric amplifier is used for image amplification. In the phase-sensitive configuration, we observe a noise figure of −0.1± 0.3dB for a gain of 2.4, which is 2dB lower than the quantum limit for an ideal phase-insensitive amplifier. Image pre-amplification before loss is shown to improve the detected signal-to-noise ratio.

Quantum Properties of The Traveling-Wave x(2) Process: Theory, Experiments, and Applications

Novel quantum states of light can be obtained through the interaction of intense light pulses in a x (2) nonlinear medium. Over the past several years we have investigated the processes of parametric amplification, sum-frequency, and second-harmonic generation (SHG) to produce highly squeezed pulses of light. In this paper we give an overview of the various generation schemes including results from our recent SHG experiments. Progress in the application of squeezed light in imaging is also described.