Tiejun Chang

Multigigahertz range-Doppler correlative signal processing in optical memory crystals

Analog optical signal processing of complex radio-frequency signals for range-Doppler radar information is theoretically described and experimentally demonstrated using crystalline optical memory materials and off-the-shelf photonic components. A model of the range-Doppler processing capability of the memory material for the case of single-target detection is presented. Radarlike signals were emulated and processed by the memory material; they consisted of broadband (> 1 GHz), spread-spectrum, pseudorandom noise sequences of 512 bits in length, which were binary phase-shift keyed on a 1.9 GHz carrier and repeated at 100 kHz over 7.5 ms. Delay (range) resolution of 8 ns and Doppler resolution of 130 Hz over 100 kHz were demonstrated.

Recovery of spectral features readout with frequency-chirped laser fields

A data-processing technique is proposed for use with conventional frequency-chirped absorption spectroscopy to ensure accurate mapping of spectral features into time-domain signatures with arbitrarily fast readout chirp rates. This technique recovers the spectrum from a signal that is distorted owing to the fast chirp rate and therefore facilitates fast measurement of the spectral features over a broad spectral range with high resolution. Both numerical simulations and experimental results are presented.

Design and modeling of waveguide-coupled microring resonator

Abstract The design and the simulation of high-Q microcavity ring resonators coupled to submicron-width waveguides are investigated. Nanofabrication results and optical properties of SiO2–TiO2 planar waveguides are presented. Key optical design parameters are characterized using Finite-Difference Time-Domain (FDTD) solutions of the full-wave Maxwells equations.

Broadband photonic arbitrary waveform generation based on spatial-spectral holographic materials

We discuss an approach for the practical implementation of photonic arbitrary waveform generation of microwave signals. We describe and demonstrate an approach using spatial-spectral (S2) holography in rare earth ion doped crystals that has the potential to achieve extremely wide bandwidths (>40 GHz) using conventional electro-optic phase modulators and low bandwidth (<100 MHz) control electronics. We provide analysis of this approach, show simulations, and perform experimental demonstrations of the technique. We show a pulse compression factor of ~15,000 and demonstrate the largest effective bandwidth of 3.8 GHz to date for pulse compression using S2 holography. We also show control and manipulation of up to 30 independent compressed pulses for the creation of arbitrary waveforms.

Optical linear sideband chirp compression for microwave arbitrary waveform generation

A novel approach for the practical implementation of photonic arbitrary waveform generation of microwave signals is explored. Here we describe and demonstrate linear sideband chirp compression over 1 GHz bandwidth with a compression factor of >4000.

Analog optical signal processing of baseband codes in Tm:YAG up to 10 Gb/s

Aspects of analog signal processing are explored using baseband codes from 1 to 10 Gb/s modulated onto a 378 THz optical carrier and processed by spectral holographic techniques in Tm:YAG. Results include processing of signals buried in additive noise, variation of time delays over 5 /spl mu/s, and material signal losses as low as /spl sim/1 dB//spl mu/s.

Reconfiguration of spectral absorption features using a frequency-chirped laser pulse

A technique is proposed to manipulate atomic population in an inhomogeneously broadened medium, which can set an arbitrary absorption spectrum to a uniform transparency (erasure) or to a nearly complete inversion. These reconfigurations of atomic spectral distribution are achieved through excitation of electronic transitions using a laser pulse with chirped frequency, which precisely affects selected spectral regions while leaving the rest of the spectrum unperturbed. An erasure operation sets the final atomic population inversion to zero and the inversion operation flips the population between the ground and the excited states, regardless of the previously existing population distribution. This technique finds important applications both in optical signal processing, where fast, recursive processing and high dynamic range are desirable and in quantum memory and quantum computing, which both require high efficiency and high fidelity in quantum state preparation of atomic ensembles. Proof-of-concept demonstrations were performed in a rare-earth doped crystal.

Efficiency and uniformity considerations in optical coherent transient devices

The efficiency and uniformity of photon echoes are investigated in optical coherent transient sequences using temporally overlapped linear frequency-chirped programming pulses. Distortions in the power spectrum of the programming pulses due to edge effects are found to cause fluctuations in echo efficiency as a function of echo time delay. Smoothing the edges of the programming pulse envelopes is found to significantly reduce distortion in the power spectrum of the pulses, which leads to echoes that are both more efficient and more uniform than those generated by pulses without smoothed edges. The effect of programming pulse strength on echo efficiency and uniformity is shown and discussed through simulations for an optically thin medium and through experiment in Tm3+:YAG at 4 K.

Temporal and spatial behavior of photon echoes stimulated from long pulses

Abstract To evaluate the coherent saturation effects of continuous optical processing using optical coherent transients we studied the time dependence of the photon echoes stimulated by probe fields with constant amplitudes and durations comparable to the coherent dephasing time. The propagation directions of the long echoes were also found to be different from brief pulse echoes. Echoes in the non-causal direction were predicted with a theory based on Maxwell–Bloch equations, observed experimentally, and explained analytically.

Demonstration of Basic Geometric Rotations on Rare-Earth Atomic Ensemble

Two basic Bloch vector rotations on a rare-earth ensemble were demonstrated through geometric paths driven by composite laser pulses, which can be used to compose any single qubit gate. The operation fidelity was evaluated.