This PDF file contains the front matter associated with SPIE Proceedings Volume 6572, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Digital signal processing techniques used in conjunction with phase-diversity coherent optical receivers are presented in this paper. These techniques enable coherent detection and mitigation of optical impairments introduced in transmission. The main advantage of this approach is that the optical impairments can be handled in the digital domain instead of analog or optical domains, thus reducing various hardware requirements (e.g. dispersion compensating fibers). Dispersion compensation and carrier phase estimation techniques are discussed in detail.

Polarization insensitive all-optical carrier recovery scheme from BPSK data is proposed and demonstrated in experiment for the first time. The proposed scheme uses a degenerate optical parametric oscillator built with phase sensitive amplifier.

Recently, there has been a renewed interest in coherent optical detection. The reasons for this are: a) coherent optical receivers achieve high receiver sensitivities; b) multilevel modulation formats can be detected very efficiently; c) optical WDM systems with high spectral efficiency can be implemented; and d) preservation of the optical phase allows electrical equalizers to efficiently compensate optical channel impairments. These advantages of coherent optical detection over direct detection can be used to overcome some of the obstacles that limit the data capacity and the reach of current direct detection systems, both fiber and free-space based. The essential part of the coherent optical receiver is the optical local oscillator (LO) laser. It has to provide a high optical output power with low linewidth and low relative intensity noise (RIN). With a widely tunable LO laser a frequency-agile receiver can be constructed. To determine the best candidates for tunable LO lasers, different laser technologies are discussed in terms of output power, power variation, electrical power dissipation, switching time, control leads, package dimensions, tuning range, linewidth and RIN. A heterodyne receiver to detect 2.5 Gb/s and 10 Gb/s signals has been implemented with a standard distributed feed back (DFB) laser. Upgrades of the coherent receiver with a widely tunable LO will be presented. Experimental comparison of the LO lasers and their impact on the receiver sensitivity will be shown.

All-optical regeneration of differential phase-shift keyed signals is demonstrated experimentally. Phase-preserving amplitude regeneration can be achieved by exploiting gain saturation in a fiber optical parametric amplifier, either with or without wavelength conversion. Phase regeneration requires use of phase-sensitive amplifiers, based on either four-wave mixing or nonlinear interferometers, both of which offer the possibility of combining phase and amplitude regeneration in a single device. Both implementations are investigated experimentally.

A novel opto-electronic polyphase analog-to-digital converter scheme that entails parallel optical sampling of different phases of an input analog signal is presented. With this scheme higher sampling rate can be attained by scaling. We demonstrate the basic tenets of this approach by upscaling a 160MSPS optoelectronic analog-to-digital ADC system to design and implement a 40.96GSPS four-channel polyphase optoelectronic analog-to-digital system. An optoelectronic divide-by-two decimation technique is implemented for demultiplexing digital samples having a repetition rate f into its even and odd subsamples with each subsample having a repetition rate of f/2. A two stage concatenation of the basic divide-by-two decimation scheme is employed to demultiplex the 40.96GSPS sampled RF signals into 8 channels of demultiplexed data, each channel having a data-rate of 5.12GSPS. Detailed design parameters and experimental results are presented for both the 160MSPS and the 40GSPS, including the design and implementation of optical clock networks, polyphase RF sampling networks, and decimation or demultiplexing networks. In addition, the electronic quantization network for the 160MSPS ADC system is presented. The 160MSPS system was found to have effective bit-resolution of 6.97, third-harmonic distortion of 43.73dB, signal-to-noise-distortion of 43.73dB, and spurious free dynamic range of 41dB.

Electronically programmable, broadband analog Radio Frequency (RF) transversal filter architecture is proposed and implemented using an Acousto-Optic Tunable Filter and a Chirped Fiber Bragg Grating. Proof-of-concept filter two-tap notch filters are demonstrated with a tunable range of 2-8 GHz and notch depth of 35 dB.

Herein is described a novel approach of performing adaptive photonic beam forming of an array of optical fibers with the expressed purpose of performing laser ranging. The beam forming technique leverages the concepts of time reversal, previously implemented in the sonar community, and wherein photonic implementation has recently been described for use by beamforming of ultra-wideband radar arrays. Photonic beam forming is also capable of combining the optical output of several fiber lasers into a coherent source, exactly phase matched on a pre-determined target. By implementing electro-optically modulated pulses from frequency chirped femtosecond-scale laser pulses, ladar waveforms can be generated with arbitrary spectral and temporal characteristics within the limitations of the wide-band system. Also described is a means of generating angle/angle/range measurements of illuminated targets.

A monolithic two-section quantum dot semiconductor laser is differentially pumped to form non-uniform current injection in the gain region. We show that the nature of the spectral content in the output signal is affected by this differential pumping; despite the fact that the separately pumped gain regions are not electrically isolated in this device. Both negative (red-shift) and positive (blue-shift) spectral chirps were observed during mode-locked operation. It is also demonstrated that mode locked operation is achieved with a much larger set of injection current / absorber bias voltage pairs than was previously possible with single-pad current injection.

Mode-locked laser designs for both time and frequency domain based applications are presented. It is shown that for strictly time domain applications, simple laser cavity designs can produce pulse trains at 10 GHz with sub-5 fs relative timing jitter (1 Hz-100 MHz) using only commercially available components. Frequency stabilized sources maintain low timing jitter while achieving 1MHz maximum frequency deviations for optical spectra consisting of ~200 10 GHz spaced frequencies. Methods of characterizing pulse-to-pulse timing jitter by examining the photodetected spectrum are reviewed. The effects of the phase noise of an rf source used to drive an actively mode-locked laser on the laser's amplitude and timing fluctuations is also discussed.

Generation of stable pulses and a frequency stabilized optical comb are two key requirements for Fourier Based Arbitrary Waveform Generation (AWG) techniques. The longitudinal mode spacing of the laser must remain as stable as possible to permit effective isolation and processing of the modes for waveform synthesis. The short and long term temporal stability ultimately limits the system's precision as well as its operability in fielded systems. A packaged erbium-doped waveguide provided a highly compact gain medium for the harmonically mode-locked laser design. Stability was achieved by use of an intracavity etalon for frequency stabilization of the optical comb, a Pound-Drever- Hall (PDH) method, and an active bias feedback loop for low frequency noise suppression. The temperature was controlled to limit cavity length variation, and the contribution to stability of each method is quantitatively assessed. The system's stable operating time was increased from hours to greater than a day, and the timing jitter is demonstrated to be lower than that of commercially available erbium-doped fiber laser (EDFL) systems. Applications to optical signal synthesis and Laser Radar are briefly discussed.

We report the development of top illuminated InGaAs photodetectors pigtailed to 50 &mgr;m core multimode (MM) fibers. These PIN diodes, in conjunction with low dispersion graded index MM fibers, allow for low cost and rugged solutions for high speed digital and analog applications. Our PIN diodes have previously demonstrated high optical power handling capability at large signal bandwidths. Coupled with large collection efficiency of MM fibers, these devices are suitable for a diverse range of systems, including avionics, ultra-fast Ethernet, radio over fiber, optical backplanes and free space laser links. The effect of the MM fiber's transfer function and fiber misalignment on the photodetector response is addressed. The spatial and temporal filtering effects of the MM fiber and the photodiode are explored experimentally through a 40 Gb/s link. Enhancement in photodiode linearity due to MM fiber is also reported.

For the detection of single photons at 1.06 μm, silicon-based single photon avalanche diodes (SPADs) used at shorter wavelengths have very low single photon detection efficiency (~1 - 2%), while InP/InGaAs SPADs designed for telecommunications wavelengths near 1.5 μm exhibit dark count rates that generally inhibit non-gated (free-running) operation. To bridge this "single photon detection gap" for wavelengths just beyond 1 μm, we have developed high performance, large area (80 - 200 μm diameter) InP-based InGaAsP quaternary absorber SPADs optimized for operation at 1.06 μm. We demonstrate dark count rates that are sufficiently low to allow for non-gated operation while achieving detection efficiencies far surpassing those found for Si SPADs. At a detection efficiency of 10%, 80 μm diameter devices exhibit dark count rates below 1000 Hz and photon counting rates exceeding 1 MHz when operated at -40 °C.

Epitaxial Technologies has developed a single photon counting photoreceiver that can operate in the linear mode to avoid the drawbacks of Geiger mode detectors. The Company's linear single photon counting photoreceiver array technology is based on cascading optical amplifiers on-chip with APDs to enable single photon capability below the APD breakdown voltage through ultra-low noise gain and preamplification. We have already demonstrated components for this photoreceiver that when implemented will have single photon sensitivities for subnanosecond pulses with high photon counting efficiency and without afterpulsing at 1064 and 1550-nm.

Military imaging is the largest application sector for shortwave infrared (SWIR) detectors, followed by spectroscopy (for the sorting of products and materials), and thermal sensing. Each application places different demands on the detectors, and fulfilling these requirements has driven the production of higher-quality, lower-cost imagers. The Visible SWIR Camera images digital pictures under day and starlight-only conditions, enabling the transmission of those images between soldiers on the battlefield. Additional functions are a windowing capability for comm link reception, and range-gating ability (viewing a specific depth of field at a specified range.) The combination of gated and video imaging is achieved through a high bandwidth pixel with a capacitive transimpedance amplifier (CTIA) design. Two different sensitivities in the CTIA pixel are achieved by switching between two feedback capacitor sizes, allowing for different illumination conditions. Anti-blooming is provided in the all solidstate gated camera, to prevent charge spreading from oversaturated pixels. All pixels are gated simultaneously for "snapshot" exposure. The low dark current and high bandwidth of the InGaAs photodetectors enables both high sensitivity imaging at long exposure times and high bandwidth at short exposure times. The spectral response of InGaAs extends from 0.9 μm to 1.7 μm, The Visible SWIR Camera is very reliable, in addition to being small and lightweight.

The development of a high-resolution laser radar (ladar) exhibiting sub-mm resolution would have a great impact on standoff identification applications. It would provide biometric identification capabilities such as three-dimensional facial recognition, interrogation of skin pore patterns and skin texture, and iris recognition. The most significant technical challenge to developing such a ladar is to produce the appropriate optical waveform with high fideltiy. One implementation of such a system requires a 1.5-THz linear frequency sweep in 75 &mgr;s. Previous demonstrations of imaging with such waveforms achieved a 1 THz sweep in > 100 ms, and required additional corrections to compensate for sweep nonlinearity. The generation of high fidelity, temporally short frequency-swept waveforms is of considerable interest to the DoD community. We are developing a technique that utilizes a novel method to generate a 1 THz sweep in 50 &mgr;s from a mode-locked laser. As a proof-of-principle demonstration of this technique we have successfully generated a 20 GHz sweep in 1 µs with a fidelity sufficient to produce better than -20 dB sidelobes for a range measurement without using any additional corrections. This method is scalable to produce the entire 1 THz sweep in 50 &mgr;s.

Frequency skewed optical pulses are generated via both a composite cavity structure in a fiberized semiconductor optical amplifier ring laser and a frequency skew loop outside the laser cavity. The composite cavity technique is similar to rational harmonic mode-locking, however it is based on cavity detuning rather than frequency detuning. These frequency skewed pulses are ideal for range detection applications since their interference results in a range dependent RF signal. The intracavity frequency skewed pulse train showed superior performance in both stability and signal quality.

The demand for bandwidth and interconnectivity in aerospace and other defense networks and systems continues to expand. To meet this demand while still satisfying the unique requirements of these systems, innovative approaches are needed. For future networks to meet these goals, they will need to have high bandwidths that are scalable to the requirements of particular applications. In addition, the networks need to be very fault tolerant, protocol independent, non-blocking, low latency, and have low power consumption and small size. OptiComp Corporation has developed a unique network architecture where the hardware is distributed across the network, allowing the network to be self routing and highly fault tolerant. This network architecture is enabled by OptiComp's integrated optoelectronic technologies including waveguide coupled VCSELs and detectors, compact WDM, SOAs, and hybrid integration. Waveguide grating couplers that enable a VCSEL to be coupled bidirectionally into an internal waveguide and allow a portion of the light in a waveguide to be tapped off to a detector comprise the core of OptiComp's integrated optoelectronics. This on-chip coupling into and out of a waveguide enables coarse WDM multiplexing and demultiplexing to be accomplished in a very small area with no additional packaging, making the structure more compact and rugged. Waveguide coupled device results will be presented, including high-speed data transmission between waveguide coupled VCSELs and detectors. Preliminary results on waveguide coupled WDM components will also be discussed. In addition to the enabling components, the implementation of the network architecture will also be presented.

We demonstrate an integrated 1x3 optical switch that operates using the principle of carrier-induced refractive index change in InGaAsP multiple quantum wells. The core of the switch relies on a beam-steering concept which allows us to steer the optical beam to any of three output waveguides. The device is relatively simple, since current is only applied to two electrodes for complete operational control. The device integration is achieved using an area-selective zinc in-diffusion process that is used to channel the currents into the multiple quantum wells, thereby enhancing the efficiency of the carrier-induced effects. This results in a low electrical power consumption, allowing the switch to be operated uncooled and under d.c. current conditions. The crosstalk between channels is better than -17 dB over a range of 50 nm centered at 1565 nm.

This paper proposes novel intelligent Value Added Modules (VAMs) which employ an intelligent spatial processing technique to realize variable optical power split ratios. To demonstrate the concept of the smart VAM, the Texas Instrument (TI) Digital Micro-mirror Device (DMD^TM) has been used. Different optical power split ratios have been experimentally verified.

An analog liquid crystal lens-based axial scanning confocal microscope is demonstrated as a 48 &mgr;m continuous range optical height measurement sensor used to characterize a 2.3 &mgr;m height Indium Phosphide twin square optical waveguide chip.

Recent experiments on optical damage by ultrashort laser pulses have demonstrated that the temporal pulseshape can dramatically influence plasma generation in fused silica and sapphire. In this work a modified 3+1D nonlinear Schroedinger equation for the pulse propagation coupled to a rate equation for the plasma density in the dielectric material is used to simulate pulse propagation and plasma formation in a range of dielectric materials. We use these simulations to analyze the influence of pulse-width, pulse-shape and beam geometry on the formation of the electron plasma and hence damage in the bulk material. In particular, when possible, we simulate the effect of pulses reconstructed from experimental data. It is expected that a better understanding of the dynamics of laser-induced plasma generation will enable the accurate simulation of optical damage in a variety of dielectrics, ultimately leading to an enhanced control of optical damage to real materials and optical devices.

Distributed fiber sensing based on Brillouin gain scattering (BGS) principle is a useful way to develop devices capable to measure temperature or/and strain in optical fibers. New effects or technologies that could achieve a larger distance and/or a better spatial resolution are a topic of special interest in this fiber sensing area. The influence of the probe-pulse shape in the interaction between the pulsed light and the continuous wave laser in a pump-probe system is presented. The purpose of this study is to improve the spatial resolution of the measurement without losing stability in the BGS. Also it is showed how the backscattering Brillouin gain is affected by inducing variations on the final value of the BGS intensity; this effect is illustrated by using an experimental set up based on the Brillouin optical time-domain analysis (BOTDA). Theoretical analysis of the probe pulse in the Brillouin shift and intensity value using triangular, sinc and saw tooth shapes around the medium phonon life time (~10ns) are presented; as well as the experimental results and possible applications are explained.

We report the use of new hydrogels based on poly-N-isopropylacrilamide and MeOXA in order to measure temperature using optical transmittance. We have obtained thermo-responsive hydrogels based on the radical copolymerization of N-isopropylacrylamide (NIPAAm) and bis-macromonomers of 2-methyl-2-oxazoline (MeOXA). The hydrogels show conformational transitions at defined temperatures, which are a function of the molar ratio NIPAAm / MeOXA inside of the hydrogel. The temperatures of transition have been determined by means of ¹H NMR spectroscopy and by turbidity measurements using an optical setup with optical fibers and a diode laser. We show the first experimental results and we discuss some future applications such as an optical switch or a device for optical sensing.

Photonic crystal optical fiber from silver halide crystals is described. Both experimental and theoretical evidences are presented to establish that the fiber is effectively singlemode at wavelength 10.6 &mgr;m with numerical aperture NA = 0.16 and optical losses of 2 dB/m . Crystalline microstructured optical fibers offer key advantages over step-index optical fibers from silver halide crystals. The wide transmission range of wavelengths 2-20 &mgr;m provides great potential for applications in spectroscopy and for the development of a range of new crystalline-based non-linear optical fibers.