Hye Jeong Chang

Reducing pulse distortion in fast-light pulse propagation through an erbium-doped fiber amplifier

When a pulse superposed on a cw background propagates through an erbium-doped fiber amplifier with a negative group velocity, either pulse broadening or pulse compression can be observed. These effects can be explained in terms of two competing mechanisms: gain recovery and pulse spectrum broadening. The distortion of the pulse shape caused by these effects depends on input pulse width, pump power, and background-to-pulse power ratio. With the proper choice of these three parameters, we can obtain significant pulse advancement with minimal pulse distortion.

Holographically generated twisted nematic liquid crystal gratings

A reflection holographic method is introduced to fabricate an electro-optically tunable twisted nematic (TN) liquid crystal (LC) grating, forgoing the geometrical drawing. The photoisomerization process occurring on the LC alignment layers of an LC cell in the reflection holographic configuration gives a control over the twist angle, and the grating spacing is determined by the slant angle of reflection holographic configuration. The resulting diffraction grating is in a structure of a reverse TN LC, permitting a polarization-independent diffraction efficiency. The electro-optic tunability of the diffraction efficiency is also demonstrated.

Quantum spatial superresolution by optical centroid measurements.

Quantum lithography (QL) has been suggested as a means of achieving enhanced spatial resolution for optical imaging, but its realization has been held back by the low multiphoton detection rates of recording materials. Recently, an optical centroid measurement (OCM) procedure was proposed as a way to obtain spatial resolution enhancement identical to that of QL but with higher detection efficiency (M. Tsang, Phys. Rev. Lett. 102, 253601 (2009)). Here we describe a variation of the OCM method with still higher detection efficiency based on the use of photon-number-resolving detection. We also report laboratory results for two-photon interference. We compare these results with those of the standard QL method based on multiphoton detection and show that the new method leads to superresolution but with higher detection efficiency.

Large nonlinear optical response of polycrystalline Bi 3.25 La 0.75 Ti 3 O 12 ferroelectric thin films on quartz substrates

We measure the nonlinear susceptibility of Bi(3.25)La(0.75)Ti(3)O(12) (BLT) thin films grown on quartz substrates using the Z-scan technique with picosecond laser pulses at a wavelength of 532 nm. The third-order nonlinear refractive index coefficient gamma and absorption coefficient beta of the BLT thin film are 3.1 x 10(-10) cm(2)/W and 3 x 10(-5) cm/W, respectively, which are much larger than those of most ferroelectric films. The results show that the BLT thin films on quartz substrates are good candidate materials for applications in nonlinear optical devices.

Implementation of sub-Rayleigh-resolution lithography using an N-photon absorber

A nonlinear optical, phase-shifted-grating method for improving the resolution of feature sizes is implemented experimentally using an N-photon lithographic material. For the recording medium, we used poly(methyl-methacrylate) (PMMA), which is a UV lithographic material that can be excited by multi-photon absorption in the visible region. We achieved a two-fold enhancement of the resolution over the standard Rayleigh limit of half of the wavelength.

Quantum spatial super-resolution by the optical centroid measurement method

We demonstrate experimentally a new procedure for obtaining spatial super-resolution in quantum imaging by measuring optical centroid. Our results show spatial resolution enhancement identical to that of quantum lithography but with higher detection efficiency.

Experimental Demonstration of Quantum Spatial Superresolution by Optical Centroid Measurements

We demonstrate experimentally quantum spatial superresolution with two-photon N00N state by measuring the centroid positions of the entangled photons. The optical centroid measurement shows higher detection efficiency than the conventional scheme based on multiphoton absorption.

Pulse broadening or compression in fast-light pulse propagation through an erbium-doped fiber amplifier

Pulse broadening or compression in an Er3+-doped fiber amplifier is observed, and explained by gain recovery and pulse spectrum broadening effects. Maximal pulse advancement and minimal pulse distortion are obtained by optimizing these competing effects.

Giant nonlinear optical properties of Bi3.25La0.75Ti3O12 ferroelectric thin films on quartz substrate

The nonlinear properties of Bi_3.25La_0.75Ti₃O₁₂ thin film grown on quartz substrate is measured using the Z-scan technique with ps-laser pulses at 532-nm wavelength. The nonlinear refractive index and absorption coefficients are 0.31times10 cm²/W and 3times10^-5 cm/W, respectively, indicating Bi_3.25La_0.75Ti₃O₁₂ film on quartz is a good candidate for applications in nonlinear optical devices.

Sub-Rayleigh Lithography Using a Multiphoton Absorber

We demonstrate sub-Rayleigh lithography for enhancing the resolution of optical interferometric patterns using poly(methyl-methacrylate)(PMMA). We exceed standard Rayleigh resolution limit by a factor of three and calculate the multiphoton absorption cross section of PMMA.