This PDF file contains the front matter associated with SPIE Proceedings Volume 6975, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

We will discuss a passive thermal emission management surface that can manipulate the direction and wavelength bands of emission. We are designing and fabricating diffractive optics in materials that support surface-polariton plasmons. We use a grating in this material to couple the thermally-generated plasmons to photons. Grating parameters, such as grating depth and duty cycle, are varied to optimize the plasmon/photon coupling efficiency. The grating configuration ensures a phased, radiative response if the plasmon decay length along the surface traverses many grating periods. All of these parameters, material indices and dimensions, determine the specular and angular "shape" of emission.

A new electro-optic waveguide platform, which provides unprecedented electro-optical phase delays (> 1mm), with very low loss (< 0.5 dB/cm) and rapid response time (sub millisecond), is presented. This technology, developed by Vescent Photonics, is based upon a unique liquid-crystal waveguide geometry, which exploits the tremendous electro-optic response of liquid crystals while circumventing historic limitations of liquid crystals. The exceedingly large optical phase delays accessible with this technology enable the design and construction of a new class of previously unrealizable photonic devices. Examples include: a 1-D non-mechanical, analog beamsteerer with an 80° field of regard, a chip-scale widely tunable laser, a chip-scale Fourier transform spectrometer (< 5 nm resolution demonstrated), widely tunable micro-ring resonators, tunable lenses, ultra-low power (< 5 microWatts) optical switches, true optical time delay (up to 10 ns), and many more. All of these devices may benefit from established manufacturing technologies and ultimately may be as inexpensive as a calculator display. Furthermore, this new integrated photonic architecture has applications in a wide array of commercial and defense markets including: remote sensing, micro-LADAR, OCT, laser illumination, phased array radar, optical communications, etc. Performance attributes of several example devices are presented.

This paper describes a new concept for a photonic implementation of a time reversed RF antenna array beamforming system. The process does not require analog to digital conversion to implement and is therefore particularly suited for high bandwidth applications. Significantly, propagation distortion due to atmospheric effects, clutter, etc. is automatically accounted for with the time reversal process. The approach utilizes the reflection of an initial interrogation signal from off an extended target to precisely time match the radiating elements of the array so as to re-radiate signals precisely back to the target's location. The backscattered signal(s) from the desired location is captured by each antenna and used to modulate a pulsed laser. An electrooptic switch acts as a time gate to eliminate any unwanted signals such as those reflected from other targets whose range is different from that of the desired location resulting in a spatial null at that location. A chromatic dispersion processor is used to extract the exact array parameters of the received signal location. Hence, other than an approximate knowledge of the steering direction needed only to approximately establish the time gating, no knowledge of the target position is required, and hence no knowledge of the array element time delay is required. Target motion and/or array element jitter is automatically accounted for. Presented here are experimental results that demonstrate the ability of a photonic processor to perform the time-reversal operation on ultra-short electronic pulses.

All-optical flip-flops provide many advantages over electrical circuitry, mainly the ability to operate at a faster speed and a cheaper cost. However, current models use a more than desirable amount of power and only operate with a single method for turning the flip-flop on and off, such as a single wavelength of light or a single current. The purpose of this work is to create an all-optical flip-flop that has multiple on and off wavelengths as well as a range of on and off currents at which it can successfully operate, in addition to using relatively less power. By creating a circuit consisting of a semiconductor optical amplifier, a lyot filter, and an isolator and testing the effects of various wavelengths and currents, we are able to create an optical flip-flop that operates at a power of only 1.002mW. Our signal turns off at 1554.955nm, 1558.955nm, and 1559.955nm or between 290-340mA, turns on at 1563.955nm, 1564.955nm, and 1568.955nm or between 80-120mA, and changes state between 170-210mA, while maintaining its state at all other wavelengths and currents. This all-optical flip-flop is a great improvement over other current models and, if put to practical use, could vastly increase the viability of these components.

A RF spectrum analyzer with high performance and unique capabilities that traditional all-electronic spectrum analyzers do not exhibit is demonstrated. The system is based on photonic signal processing techniques that have enabled us to demonstrate the spectral analysis of a 1.5 GHz bandwidth with a 1.4 ms update time and a resolution bandwidth of 31 kHz. We observed a 100% probability of intercept for all signals, including short pulses, during the measurement window. The spectrum analyzer operated over the 0.5 to 2.0 GHz range and exhibited a spur-free dynamic range of 42 dB. The potential applications of such a system are extensive and include: detection and location of transient electromagnetic signals, spectrum monitoring for adaptive communications such as spectrum-sensing cognitive radio, and battlefield spectrum management.

It is critical to know the free spectral range (FSR) of an etalon for telecommunication applications. In this paper, we have improved the Pound-Drever-Hall (PDH) based technique for measuring the FSR of an etalon by 2 orders of magnitude. This improved technique results 1 part in 10⁶ precision. To our knowledge this is the most precise measurement of FSR.

High-resolution digital images with high refresh rates cause an enormous amount of data that must be forwarded from the source to the recipient. This is where wireless transmission as an RF technology quickly reaches its limits. With its high bandwidth, laser-based data transmission avoids this problem. An added benefit is a higher level of security against eavesdropping that can be further increased through the use of quantum optical encryption techniques. For military applications, several scenarios will be considered. Especially for the navy, communication between a ship and land for remote forces using free space air at the eye-safe laser wavelength of 1550 nm is necessary. Data transfer at this wavelength between ships is also important for an exchange of tactical images of the local situation. In the future, the direct communication between a ship and a submarine through water will be required. Bug-proof and broad bandwidth transmission of reconnaissance data will be necessary over distances of approx. several 100 m at the laser wavelength of 532 nm. This paper will show how experiences gained through the development of optical data links from satellites to ground stations can be used as an enabling technology for additional applications for the development of stable data connections under atmospheric conditions.

Optical transmission is recognized to be a cost-efficient method. Optical technology, lasers, detectors, fiber or free space and other photonic components support ultra-high data rates that exceed many Gbps per channel. Free space optical communication has an additional advantages over fiber; although it does not currently support many channels, it is fast deployable as it does not require long-term planning and installation as fiber does, and, the optical link has additional security features. In this paper we present a mesh free space optical network, which is reconfigurable, it supports "fused" payloads (voice, data, video, image) it supports wireless communication services, and it supports sensor grids. We also discuss FSO engineering, traffic and fault management, security features and deployability to disaster areas.

A free space optics based identification and interrogation system has been designed. The applications of the proposed system lie primarily in areas which require a secure means of mutual identification and information exchange between optical readers and tags. Conventional RFIDs raise issues regarding security threats, electromagnetic interference and health safety. The security of RF-ID chips is low due to the wide spatial spread of radio waves. Malicious nodes can read data being transmitted on the network, if they are in the receiving range. The proposed system provides an alternative which utilizes the narrow paraxial beams of lasers and an RSA-based authentication scheme. These provide enhanced security to communication between a tag and the base station or reader. The optical reader can also perform remote identification and the tag can be read from a far off distance, given line of sight. The free space optical identification and interrogation system can be used for inventory management, security systems at airports, port security, communication with high security systems, etc. to name a few. The proposed system was implemented with low-cost, off-the-shelf components and its performance in terms of throughput and bit error rate has been measured and analyzed. The range of operation with a bit-error-rate lower than 10-9 was measured to be about 4.5 m. The security of the system is based on the strengths of the RSA encryption scheme implemented using more than 1024 bits.

The common approach in digital imaging today is to capture as many pixels as possible and later to compress the captured image by digital means. The recently introduced theory of compressed sensing provides the mathematical foundation necessary to change the order of these operations, that is, to compress the information before it is captured. In this paper we present an optical implementation of compressed sensing. With this method a compressed version of an object's image is captured directly. The compression is accomplished by optical means with a single exposure. One implication of this imaging approach is that the effective space-bandwidth-product of the imaging system is larger than that of conventional imaging systems. This implies, for example, that more object pixels may be reconstructed and visualized than the number of pixels of the image sensor.

Photonics Analog-to-Digital Converters (ADCs) utilize a train of optical pulses to sample an electrical input waveform applied to an electrooptic modulator or a reverse biased photodiode. In the former, the resulting train of amplitude-modulated optical pulses is detected (converter to electrical) and quantized using a conversional electronics ADC- as at present there are no practical, cost-effective optical quantizers available with performance that rival electronic quantizers. In the latter, the electrical samples are directly quantized by the electronics ADC. In both cases however, the sampling rate is limited by the speed with which the electronics ADC can quantize the electrical samples. One way to increase the sampling rate by a factor N is by using the time-interleaved technique which consists of a parallel array of N electrical ADC converters, which have the same sampling rate but different sampling phase. Each operating at a quantization rate of fs/N where fs is the aggregated sampling rate. In a system with no real-time operation, the N channels digital outputs are stored in memory, and then aggregated (multiplexed) to obtain the digital representation of the analog input waveform. Alternatively, for real-time operation systems the reduction of storing time in the multiplexing process is desired to improve the time response of the ADC. The complete elimination of memories come expenses of concurrent timing and synchronization in the aggregation of the digital signal that became critical for a good digital representation of the analog signal waveform. In this paper we propose and demonstrate a novel optically synchronized encoder and multiplexer scheme for interleaved photonics ADCs that utilize the N optical signals used to sample different phases of an analog input signal to synchronize the multiplexing of the resulting N digital output channels in a single digital output port. As a proof of concept, four 320 Megasamples/sec 12-bit of resolution digital signals were multiplexed to form an aggregated 1.28 Gigasamples/sec single digital output signal.

Experimental results for a photonic recirculating delay line for high-speed, high-resolution Analog-to-Digital Converted (ADC) and other applications is presented. The approach modifies an analog fiber optic link with a recirculating optical loop as a means to store a time-limited microwave signal so that it may be digitized by using a slower, conventional electronic ADC. Detailed analytical analysis of the dynamic range and noise figure shows that under appropriate conditions the microwave signal degradation is sufficiently small so as to allow the digitization of a multi-gigahertz signal with a resolution greater than 10 effective bits. Experimental results provided support the theory.

A novel optoelectronic scheme for optical sampling and parallel demultiplexing of different phases (polyphase) of an input analog signal is presented. With this scheme higher sampling rate can be attained by scaling. A unique feature of this approach is that the electrical-in to electrical-out signal transfer is maintained for the optoelectronic sampling and demultiplexing process. We demonstrate the basic tenets of this approach by implementing an optoelectronics two-stages divide-by-four decimator circuit where the first stage demultiplexs a sampled signal having a repetition rate f into its even and odd subsamples with each subsample having a repetition rate of f/2 , and the second stage demultiplexs the even and odd subsamples into four subsamples, odd/odd, odd/even, even/odd and even/even, each subsample having a repetition rate of . f/4 As a practical testing, a 100MHz RF electrical signal was sampled at the rate of 1.28GSPS (Giga/Samples/Sec) and demultiplexed into four 320GSPS sampled signals.

We experimentally demonstrate optical clock recovery from quantum dot mode-locked semiconductor lasers by interband optical pulse injection locking. The passively mode-locked slave laser oscillating on the ground state is locked through the injection of optical pulses generated via the first excited state transition from the hybridly mode-locked master laser. When an optical pulse train generated via the first excited state from the master laser is injected to the slave laser oscillating via ground state, the slave laser shows an asymmetric locking bandwidth around the nominal repetition rate of the slave laser.

We are investigating optical frequency comb generation by direct modulation of CW light. Our scheme is based on three cascaded modulators; one amplitude modulator and two phase modulators. The modulation scheme is optimized for flatness and power efficiency. A stable optical spectrum has been generated with ~100 comb lines with 0.625 GHz spacing and 3 dB flatness. We also investigate comb generation via phase only modulation.

We are developing a low noise high power ultra-stable diode pumped Er-Yb co-doped phosphate glass laser. Erbium doped phosphate glass permits high co-doping with ytterbium ions that strongly absorb at 976 nm and efficiently transfer their energy to the active erbium material. This drastically decreases the absorption length at the 976 nm pump wavelength and thus the overall size of the laser. Aside from the advantage for packaging a short cavity length results in a large longitudinal mode-spacing (>40 GHz), which allows for single longitudinal mode operation in the 1530-1565 nm C-band for telecommunication by inserting a tunable low-finesse etalon in the laser cavity. In addition, due to the energy transfer between the co-dopant and the active material, the laser shows a strongly reduced sensitivity to fluctuations in pump power. The strong peak in the RIN spectrum at the relaxation oscillation frequency (0.1-1 MHz) due to cavity-loss perturbations can be drastically reduced with a non-linear absorbing material inside the laser cavity. Using this approach for an optimized laser cavity design we have achieved -160 dB/Hz RIN at 1 MHz for 35 mW output. Above 100 MHz the RIN becomes shot noise limited (-168 dB/Hz @ 20mA photocurrent). The laser has excellent long-term frequency stability when locked to our wavelength locker (<250 kHz). Furthermore, the laser has been shown to have a narrow intrinsic linewidth (~10 Hz) that we are working towards by means of intra-cavity phase modulation.

An eXtreme Chirped Pulse Oscillator (XCPO) implemented with a Theta cavity and based on a semiconductor optical amplifier (SOA) is presented for generating 10ns frequency-swept pulses and 3.6ps compressed pulses directly from the oscillator. In this experiment, we show the two distinct characteristics of the XCPO which are the scalability of the output energy and the mode-locked spectrum. The laser cavity design allows for low repetition rate operation <100MHz, as well. The cavity, significantly, reduces nonlinear carrier dynamics, integrated self phase modulation (SPM), and fast gain recovery in an SOA. Due to the laser's ability to generate directly frequency-swept pulses from the oscillator, this oscillator can be used for high speed frequency-swept optical coherence tomography (OCT) and time-stretched photonic analog to digital converters (P-ADC).

An electroabsorption modulator (EAM) is designed to optimize dynamic range performance over 20 GHz bandwidth. The single stripe waveguide enables an extremely compact and integrated package to be fabricated with single mode fiber pigtails. The transfer function's shape permits suppression of higher order intermodulation products, yielding a spur-free dynamic range exceeding that of Mach- Zehnder designs. A dilute optical core diverts energy flow from absorbing layers into low loss waveguide; the 20 dBm optical power tolerance is significantly higher than that of commercially available electroabsorption devices. The tunable performance over 20 GHz is characterized and applications are discussed. New approaches to the broadband impedance matching requirements are calculated and the impact on system performance is assessed.

Externally coupled electroabsorption modulators (EAM) are commonly used in order to transmit RF signals on optical fibers. Recently an alternative device design with diluted waveguide structures has been developed. [1] Bench tests show benefits of lower propagation loss, higher power handling (100 mW), and higher normalized slope efficiency. This paper addresses the specific issues involved in packaging the diluted waveguide EAM devices. An evaluation of the device requirements was done relative to the standard processes. Bench tests were performed in order to characterize the optical coupling of the EAM. The photo current maximum was offset from the optical power output maximum. The transmissions vs. bias voltage curves were measured, and an XY scanner was used to record the mode field of the light exiting from the EAM waveguide in each position. The Beam Propagation Method was used to simulate the mode field and the coupling efficiency. Based on the bench tests and simulation results, a design including mechanical, optical and RF elements was developed. A Newport Laser Welding system was utilized for fiber placement and fixation. The laser welding techniques were customized in order to meet the needs of the EAM package design.

Optical down-conversion techniques have become an increasingly popular architecture to realize Multi-band Enterprise Terminals (MET), Synthetic Aperture Radar (SAR), Optical Arbitrary Waveform Generation (OAWG), RF Channelizers and other technologies that need rapid frequency agile tunability in the microwave and millimeter RF bands. We describe recent SFDR, NF, Gain, and Noise modeling and measurements of Erbium-doped-fiber amplified analog RF optical links implementing all-optical down-conversion and balanced photodiode receivers. We describe measurements made on our newly designed extensive test-bed utilizing a wide array of high powered single and balanced photodiodes, polarization preserving output LN modulators, EAMs, LIMs, tunable lasers, EDFAs, RF Amplifiers, and other components to fully characterize direct and coherent detection techniques. Additionally, we compare these experimental results to our comprehensive MATLAB system modeling and optimization software tools.

The performance of microwave photonic systems can be improved by utilizing high power handling photodetectors. Operation at higher photocurrents enables larger output RF signals to be produced directly by the photodetector. This reduces the requirement of signal amplification by RF amplifiers, thereby simultaneously improving the dynamic range and the noise figure. In optical coherent systems, high power handling photodetectors enable operation at high local oscillator power levels to boost the coherent gain and the detection sensitivity. Thus, techniques to enhance the power handling capability of photodetectors are of interest for both free space and fiber based applications. Photodetector current saturates at high optical power levels due to space-charge screening effect. The saturation effect is maximized where the illumination intensity, and the resulting photocurrent density, is largest. In this work, we focus on optimizing the optical field profile incident on top-illuminated InGaAs photodiodes to minimize the peak photocurrent density. This was achieved by employing graded-index (GRIN) lens coupling to uniformly distribute the optical power across the diode cross-section. We demonstrate 5dB improvement in photodiode's power handling capability and linearity by employing GRIN lens coupling as compared to single mode fiber (SMF) coupling. Our GRIN lens-coupled photodetectors have achieved small-signal 1dB compression current of >50mA and 12.5dBm amplifier-free RF output. These devices also exhibit linear behavior for a peak-to-peak RF pulse output of >2.5V, at ~30ps pulse width. This constitutes a 100% improvement over SMF coupled devices. Further, the GRIN photodiodes demonstrate pulse broadening =0.65ps/mW, as compared to 2ps/mW for SMF devices.

In the implementation of laser-induced fluorescence (LIF) for the detection of vapor-phase organic compounds that accompany hazardous materials, multiphoton excitation offers a significant advantage over single photon methods. In particular, if the absorption spectra of unwanted background molecules overlap that of the target molecule, single photon LIF is plagued by false positives. Multiphoton methods alleviate this difficulty by requiring that the target molecule be in resonance with multiple molecular transitions. A promising multiphoton method is stimulated Raman adiabatic passage (STIRAP). This method involves a counterintuitive sequence of laser pulses which is capable of transferring 100% of the target molecules to the desired excited state from which fluorescence is to be observed. As a precursor to more complex molecules, we demonstrate the STIRAP technique on sodium vapor using the 3p (²P_1/2) ← 3s (²S_1/2) and 5s (²S_1/2) ← 3p (²P_1/2) transitions. This is the first time STIRAP has been achieved on a vapor using picosecond lasers. We produced light to couple the states using two synchronously pumped OPG/OPAs (pumped by the 355 nm light from a picosecond YAG). We measured the fluorescence from the 5s state to both 3p states (²P_1/2, ²P_3/2) and from both 3p states to the 3s state with monochromator using a gated CCD to eliminate Rayleigh scattered light. Our results indicate a four to five-fold increase in the transfer efficiency to the 5s state when the laser pulse that couples the 3p and 5s states precedes the laser pulse tuned to the 3p ← 3s transition.