This presentation will describe the Air Force Research Laboratory Highly Integrated Photonics Program (AF HIP) and its objective to integrate on a monolithic device, all of the optical components required to serve as a bus coupler in an all optical data communication network. This research and development program utilizes advanced technologies in silicon on insulator (SOI) and silica planar lightwave circuits (PLC) to design, develop, characterize, and demonstrate highly integrated photonic devices that can be transitioned into both current and emerging tactical platforms for the U.S. Air Force. This effort strives to overcome several existing constraints with respect to the integration and packaging aspects of the current generation of COTS optical devices. Monolithic integration (chips fabricated out of a single material system) remains the ultimate vision for integrated optics.

APIC (Advanced Photonics Integrated Circuits) Corporation is engaged in the research, development, and production of highly integrated photonic (HIP) and highly integrated photonic and electronic (HIPE) chip technology for a variety of defense and homeland security applications. This technology allows for significantly reduced chip size while also eliminating numerous pigtails and interconnects, thereby improving system reliability while reducing cost. APIC's Mid-Pacific Photonics Prototyping Facility (M3PF) is a Navy-funded 6" and 8" silicon-on-insulator (SOI) photonic prototyping facility that was constructed specifically to meet this need. Among other high-tech equipment, M3PF is equipped with a high-resolution ASML QML stepper, a lithography tool that is capable of achieving 0.25- μm resolution with a field size of 22 mm by 32.5 mm. APIC is developing processing techniques for fiber-compatible core-size waveguides as well as for complementary metal-oxide semiconductor (CMOS)- compatible core-size waveguides. In this paper, APIC's SOI photonic technology and M3PF capabilities will be described in detail. In addition, processed chips and their performance and applications will be discussed to demonstrate the efficacy of M3PF. APIC's additional processing capabilities--such as wafer bonding for heterogeneous integration processing, which plays a key role in HIPE chip implementation-- will be described as well.

Laser communication terminals have been developed which can be integrated into an aircraft or used in a ground station for transmitting 2.5 Gbps data between aircraft or from an aircraft to ground. The terminals were built under the Air Force Research Laboratory's EO Sensor Technology & Evaluation Research (ESTER) program. Lessons were learned during the fabrication of the terminals which provided insight into the optical and electrical aspects of performance. Upon integration of most of the system components into the terminal assemblies, the first two units were taken to northeast Ohio for a series of initial outdoor field measurements. These measurements provided insight into environmental impacts to system performance, primarily atmospheric scintillation and turbulence as well as pointing stability. In this paper we provide a description of our terminal hardware, field test results to date, and outline the future program activities.

The advent of network centric operations and the Global Information Grid have highlighted the need for ultra-wide bandwidth networks to efficiently and securely route multi-gigabit data streams among air, space, and ground platforms. Boeing, with expertise in platform integration and network centric operations, in conjunction with OptiComp Corporation's (OCC) advanced photonic technology, is developing an all-optical network using wavelength division multiplexing (WDM) and vertical-cavity surface-emitting lasers (VCSEL). Current VCSEL-based solutions have not integrated WDM or other functionality enhancements for improved network performance. OCC is developing a novel approach that implements advanced switching architectures by distributing integrated, WDM, VCSEL-based modules at each node in the network. This network design enables high data throughput and switching speeds, low latency, and system scalability through advanced system topologies and monolithically integrated optoelectronics. The distributed WDM switch consists of pairs of monolithically integrated VCSELs and resonant cavity photodetectors, each at a different wavelength, interconnected along a common waveguide with all multiplexing and demultiplexing done on-chip. Different levels of connectivity and functionality are available by interconnecting the optoelectronic switches in various configurations. A distributed crossbar switch with N access ports, referred to as an N³ architecture (N³ interconnect paths), can be realized by interconnecting an N-element VCSEL array with an array of N photodetectors. Each VCSEL and photodetector are connected using an interconnect medium such as silica-based waveguides and/or optical fibers. Using this configuration, each port can listen to all interconnect paths simultaneously. When a port senses no traffic on an interconnect path, it can transmit its signal onto that path. This implementation can use single-wavelength switches on parallel interconnect paths, or alternatively an N³ network can be realized with WDM optical switches operating along a single interconnect path. Further complexity in network topology allows for the realization of N⁴ architectures by using parallel, WDM-based, N³ systems. N⁴ topologies allow for increased scalability, thus dramatically increasing the data handling capacity of the network, as well as the number of nodes that can be accommodated.

Optical or gigabit communication links could currently allow petabytes of data to be transferred to geographically distributed tera-scale computing facilities at beyond 10Gbps rates. While the bandwidth is available in network link technology, transport protocols like TCP/IP and common network host architectures severely limit the attainable throughput over such links. Traditional layering -that is implemented through excessive per-byte (word) memory bandwidth constrained buffer copying- transport processing complexity, combined error and congestion control and trial and error timeout-based approaches result in prohibitively increasing performance degradation as network speeds increase. In this paper we present TCP-Fiber, a TCP version that is based on direct measurements of available and bottleneck link bandwidth and is able to perform decoupled error and congestion control while supporting zero-copy from application to network interface. A key innovation in TCP-Fiber is a variable length "packet train" based method that allows sensing ultra high bandwidth related quantities in a network independent fashion with relaxed requirements to timers and system resources (as related to interrupts, system calls etc). A TCP-Fiber connection is able to fairly send at the full network rate without extensive trial-and-error convergence procedures or waiting on time-out for unacknowledged packets, while maintaining network stability.

We present results from the multiplexing and transmission of amplitude modulated, frequency modulated, and video analog signals over fiber. The optical carrier's wavelengths for these signals were centered in the 1545-1560nm telecommunication wavelength regimes. A direct modulation format was used for the AM signals whereas external modulation formats were used for the FM and video signals. Standard telecommunication WDM components were used for multiplexing and demultiplexing of the signals. The study presents a comparison of the original electrical signal and the transmitted signals. In particular we indicated intermodulation effects, and signal-to-noise ratio as a function of wavelength separation of the optical carriers and transmission distance respectively. The practical application of this research will help stimulate the growing trend to add fiber optic cable to the "Last Mile". The Last Mile, a reference to the connection between the residential customer and the Central Office is currently dominated by three independent technologies Copper Wire, Wireless and Coaxial cable. These methods of transmitting Analog signals dictate the speed and the amount of information that can be delivered to the residential customer. The preferred transmission media used to connect computers, the primary source of digital signals, either locally or over long distances is through Fiber Optic Cable. If Fiber Optic Cable could replace the existing last mile, this would elevate the present bandwidth issues. The addition of yet another cable into the home for a single application is prohibitively expensive. Therefore the need to combine all existing signals both digital and analog into any additional transmission media on the Last Mile is essential.

Electrical wiring harnesses have been used to interconnect control and communication equipment in mobile platforms for over a century. Although they have served this function successfully, they have three problems that are inherent in their design: they are mechanically heavy and stiff, and they are prone to electrical faults, including arcing and Electro-Magnetic Interference (EMI), and they are difficult to maintain when faults occur. These properties are all aspects of the metallic conductors used to build the harnesses. The Optical Harness^TM is a photonic replacement for the legacy electrical wiring harness. The Optical Harness^TM uses light-weight optical fiber to replace signal wires in an electrical harness. The original electrical connections to the equipment remain, making the Optical Harness^TM a direct replacement for the legacy wiring harness. In the backshell of each connector, the electrical signals are converted to optical, and transported on optical fiber, by a deterministic, redundant and fault-tolerant optical network. The Optical Harness^TM: * Provides weight savings of 40-50% and unsurpassed flexibility, relative to legacy signal wiring harnesses; * Carries its signals on optical fiber that is free from arcing, EMI, RFI and susceptibility to HPM weapons; * Is self-monitoring during operation, providing non-intrusive predictive and diagnostic capabilities.

High detection sensitivity and large multi-user interference rejection are key requirements to accommodate a higher number of users in an optical coherent CDMA system. In this work, we propose efficient coherent homodyne receiver system configurations, as well as, demonstrate experimentally the performance of coherent homodyne pulse detection using a synchronized modelocked semiconductor laser system. We present the significant improvement of coherent gain and signal-to-noise ratio of the NRZ ASK format modulated PRBS data detection compared with direct detection.

The impact of chromatic dispersion on the complex electric field of an optical phase-coded duobinary signal is investigated through numerical simulation. The evolution of the optical field is most clearly represented by the optical constellation diagram at varying transmission distances. Dispersion causes distortion and rotation of the optical constellation, leading to eye closure of the received signal. When direct detection is employed rapid eye closure starts after approximately 213km. In this letter, the use of coherent detection is suggested to extend this transmission distance. A decision directed phase locked loop is suggested to establish the feasibility of use of coherent detection for this modulation format. Employing coherent detection increases this dispersion limit by 70km.

Characterization of 10 Gb/s RZ-BPSK signal was demonstrated by measuring complex constellation diagram, chirp, and intensity profile using coherent homodyne detection with a cw local oscillator from the same laser source for optical data modulation. A new stabilization method was used for the homodyne detection. This measurement technique can be used for the characterization and diagnostic of a transmitter based on BPSK at transmission site.

We report the development of a coherent heterodyne balanced fiber optic receiver with a small laboratory footprint. The receiver incorporates a DFB or a solid state laser local oscillator, fiber optic combiner/splitter, adjustable fiber optic delay line, balanced PIN photodiodes, RF post amplifier, optical phase lock loop, polarization control, and precision power supplies in a small instrument case. We will show shot noise limited detection of amplitude modulated signals, cancellation of laser RIN noise, and line narrowing of the IF signal. Several examples of coherent balanced detection as enabling technology for high value applications in fiber optic communication and remote sensing will be presented.

A silica capped impurity-free vacancy induced disordering has been used in the fabrication of an all-optical integrated Mach-Zehnder switch incorporating a linear waveguide directional coupler with nonlinear multiple quantum well (MQW) sections. Using the switch we have been able to demonstrate all-optical wavelength conversions at a rate of 1GHz that was limited by our laser source, a modelocked erbium doped fiber laser. In principle the device performance is expected to be undiminished up to repetition rates of 10Gb/s and higher.

Electro-optic (EO) polymer modulators have demonstrated high speed external modulation of optical signals. Additionally, EO polymers have closely matched refractive indices at optical and microwave wavelengths, which enables high bandwidth operation. An EO polymer includes a polymer matrix and an organic "push-pull" chromophore that can be modified to give poled polymers with high EO activity. This high EO activity and optical-microwave velocity match offer the promise of accomplishing broadband, high speed optical modulation with low drive voltage. Such optical signal modulation is critical for applications in phased array radar and RF photonics. However, practical fabrication of optical modulators that realize the potential of EO polymers requires clad materials with optimized properties such as conductivity, dielectric constant, optical loss, and refractive index. In addition, other practical issues such as electrode design, optical fiber coupling, and hermetic packaging are critical in final device performance. We report on high-speed electrode parameters as well as electro-optic performance versus frequency of modulators fabricated on 6" silicon wafers. The r₃₃ values measured on single layer thin films are compared with those resulting from V_π measurements on devices. We compare the effect of EO polymer morphology on device fabrication and optical loss for different EO polymers.

A tunable multimode interference (MMI) coupler that operates by modifying the phase of the multiple images that are formed around the midpoint of the MMI section is demonstrated. The phase change is achieved by current injection, and therefore minimizing current spreading is crucial for optimal operation. A zinc in-diffusion process has been implemented to selectively define p-i-n regions and effectively regulate the current spreading by controlling the depth of the zinc doping. Using this process a tunable 3-dB MMI coupler has been fabricated. Our initial results show that the device can be easily tuned all the way from a 90:10 to a 30:70 splitting ratio of the optical power transmitted through the two output ports. We believe that further improvement on the device fabrication will lead to a more symmetric tuning response of the device. Nevertheless, the initial results are very encouraging since, to our knowledge, this degree of tuning has never been experimentally demonstrated in similar MMI devices. Furthermore, this device processing technique can easily be applied to a wide variety of semiconductor photonic switches that operate on MMI effects.

The matrix method provides a rapid method of analyzing propagation through layered media in integrated optics, fiber Bragg filters, thin film layers and geophysical oil exploration. In this paper we investigate an extension to analyze a planar layered dielectric media that is bent around a cylinder, causing leaky waves to propagate out radially from the layered waveguide. The intensity of the leaking light is determined by first converting the cylindrical configuration into a Cartesian coordinate system. In the process the dielectric media is altered to provide an equivalent plane layer model. This model is solved using the matrix method to determine how the strength of the radiation depends on the curvature of the waveguide. This problem can arise when determining losses due to the bends in integrated optic circuits mounted on cylindrical forms.

The Air Force Research Laboratory, Binoptics Corp., and Infotonics Technology Center worked collaboratively to package and characterize recently developed diode based ring lasers that operate at 1550 nm in a diamond shaped cavity. The laser modes propagate bi-directionally; however, uniaxial propagation may be induced by optical injection or by integrating a mirror. Round trip cavity length was 500 μm in 3.5 μm wide ridge waveguides, and four polarization-maintaining lensed fibers provided access to the input and output modes. A signal from a tunable diode laser, incident at one port, served to injection lock both of the counter-propagating circulating modes. When the input signal was time-encoded by an optical modulator, the encoding was transferred to both modes with an inverted time-intensity profile. Performance, in terms of fidelity and extinction ratio, is characterized for selected pulsed and monochromatic formats from low frequencies to those exceeding 12 GHz. A rate equation model is proposed to account for certain aspects of the observed behavior and analog and digital applications are discussed.

Mode locked fiber lasers are important for generation of short pulses for future high speed optical time division multiplexed (OTDM) transmission systems. The design and performance of mode locked fiber lasers are described in this talk.

Quantum-dot lasers have shown remarkable properties, such as temperature-insensitive operation, low loss, efficient carrier recombination, ultrafast gain recovery time, suppression of beam filamentation, reduced sensitivity to optical feedback, etc. These excellent performances will contribute to open new cost effective and improved lightwave communication systems. We exploit the performance of mode-locking of quantum-dot lasers for ultrashort, high power, and low noise optical pulse generation using two-section mode-locked laser diodes and a semiconductor optical amplifier (SOA)-based ring laser cavity.

We study the characteristics of wavelength tunable quantum-dot mode-locked lasers using a curved two-section device, external grating, and optical bandpass filter. Wide wavelength tunability is demonstrated due to the fact that the center wavelength of mode-locking is extended to excited state transitions as well as ground state transitions of the quantum-dot gain media.

Frequency stabilized modelocked lasers have recently garnered much attention owing to their potential in metrology, communications, and signal processing applications. The possibility of optical source technology that is economical, compact, and electrically efficient suggests that semiconductor gain media could allow frequency stabilized ultrafast sources to rapidly gain a foothold in communication and signal processing applications. This work will summarize recent work in the area of stabilized modelocked semiconductor diode lasers, and highlight unique features that will impact photonic signal processing applications.

We report on supermode noise suppression of a harmonically modelocked laser by optical injection. The modelocked laser was injection locked to a CW narrow linewidth source. Injection locking selects a single supermode group reducing the supermode noise spurs in the photodetected signal by 20 dB to a level of -130 dBc/Hz.

The intracavity gain dynamics of an external cavity semiconductor hybrid mode-locked laser are measured under three wavelength operation. The results show a partial coherence and a temporal skew among pulses corresponding to different wavelength channels. The temporal skew broadens the temporal pulse profile and the partial coherence decreases the temporal beating between wavelength channels. A measurement of the temporal evolution of the gain reveals a slow gain depletion, avoiding nonlinearities, and gain competition between wavelength channels, making multiwavelength operation feasible.

Methods of fabrication of the photonic band gap materials are reviewed, advantages of the combined use of templating and self-assembling methods are stressed. The envelope function approach was used to consider the light field in perfect photonic crystal as the zero-order approximation. Then distortion of the photonic structure has been introduced as perturbation. The simple model used in this paper allows consideration of the effects of short-range and long-range irregularities on transmission spectra. The examples of possible application of the suggested modeling approach and micro- and nanofabrication methods include the enhancement of target detectability, as possible functional elements in focal plane arrays of infrared detectors, controlled introduction of defects, prevention certain waves from propagating though or from photonic band gap materials, detection of direction to the light source, control of temperature distribution by thermal management of microstructure, negative permeability at visible frequencies.

A new architecture of single-frequency high efficiency mini-solid-state lasers is proposed. The application of a metallic nano-film selector has been investigated theoretically and experimentally. It has been shown that a cobalt thinfilm selector with a thickness between 8 and 10 nm provides a single- frequency output within a power range of up to 0.6 W with a 1-mm thick Nd:YVO₄ gain crystal. At single-mode operation, it accumulated 85% of the multimode laser output. Slope efficiencies of single-frequency oscillation from 41% to 53% have been demonstrated for different crystals. The output coupler movement by piezoceramic transducer provided single-frequency operation, with slow smooth tuning, or chirping. The laser, with a cavity length less than 1", provided smooth tuning up to 10 GHz, frequency chirping up to 4 GHz with a repetition rate of about 0.5 kHz, and hop tuning over 150 GHz at a maximum pump power of 1.8 W. Double-frequency operation with a separation of 1.5 to 2.5 GHz was realized in a laser with a cavity length up to 100 mm. Physical and technical limitations caused by the wide-gain bandwidth, thermal effects, and mechanical vibrations of the cavity elements are discussed. The new specific regime of frequency self-stabilization provided with a thin-film metallic selector has been proposed. Slow, periodical self-modulation phenomena in the diode-pumped singlefrequency Nd:YVO₄ laser with a cobalt thin-film selector have been demonstrated. Pulses with duration of about l to 3s and periods of about 3 to 10 s have been observed.

A proposed method, called "eXtreme Chirped Pulse Amplification(X-CPA)", to overcome the limitation of small storage energy of semiconductor optical amplifiers is demonstrated experimentally and theoretically. Results show an efficient energy extraction, a nonlinear suppression, and an excellent optical signal-to-noise ratio. In addition, we built an all-semiconductor X-CPA system using a highly dispersive chirped fiber Bragg grating which possesses 1600ps/nm with 6nm bandwidth at 975nm which generates sub-picosecond optical pulses with >kW record peak power output at 95MHz.

Spectrally resolved interferometry combining up-chirped and down-chirped pulses allows for millimeter range resolution in laser ranging applications. Key in our approach is the use of temporally stretched optical pulses of 5 nanoseconds in duration. These stretched pulses were obtained from a femtosecond semiconductor mode-locked laser and were up-chirped and down-chirped using a chirped fiber Bragg grating and recombined to realize spectral interferometry. This approach provides a means to achieve the high pulse energies required for a laser radar application which are easy to achieve using nanosecond pulses but maintains the high spatial resolution associated with femtosecond optical pulses.

This paper presents 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. This paper presents the preliminary study of the photonic processor, analytical justification, and simulated results. The technology has a broad range of applications including aerospace and defense and in medical imaging.

A novel method incorporating time division multiplexing technique with optical parabolic phase modulation has been introduced to overcome the limitations on optical generation of chirped RF signals. Extension of the frequency span and frequency sweep time of a RF chirp signal has been experimentally realized. A chirped RF signal with a center frequency of 100 MHz, frequency span of 20 MHz and sweep time of 200 ns has been generated via this novel method. This chirp signal agrees well with the chirp signal generated by conventional methods.

We present a novel single photon detector based on a nano-injector. This method, in principle, is capable of single photon detection at room temperature at λ~1.7 μm. Also, the process is not based on avalanche multiplication, and hence the device has no excess noise. Moreover, the device can cover a wide range of wavelengths from UV to mid-infrared, since the detection and amplification processes are completely decoupled and delocalized. Unlike avalanche-based detectors, this device operates at a very low bias that makes it possible to produce large 2D arrays with a good uniformity.

High-speed wavelength-swept lasers capable of providing wide frequency chirp and flexible temporal waveforms could enable numerous advanced functionalities for defense and security applications. Powered by high spectral intensity at rapid sweep rates across a wide wavelength range in each of the 1060nm, 1300nm, and 1550nm spectral windows, these swept-laser systems have demonstrated real-time monitoring and superior signal-to-noise ratio measurements in optical frequency domain imaging, fiber-optic sensor arrays, and near-IR spectroscopy. These same capabilities show promising potentials in laser radar and remote sensing applications. The core of the high-speed swept laser incorporates a semiconductor gain module and a high-performance fiber Fabry- Perot tunable filter (FFP-TF) to provide rapid wavelength scanning operations. This unique design embodies the collective advantages of the semiconductor amplifier's broad gain-bandwidth with direct modulation capability, and the FFP-TF's wide tuning ranges (>200nm), high finesse (1000 to 10,000), low-loss (<3dB), and fast scan rates reaching 20KHz. As a result, the laser can sweep beyond 100nm in 25μsec, output a scanning peak power near mW level, and exhibit excellent peak signal-to-spontaneous-emission ratio >80dB in static mode. When configured as a seed laser followed by post amplification, the swept spectrum and power can be optimized for Doppler ranging and remote sensing applications. Furthermore, when combined with a dispersive element, the wavelength sweep can be converted into high-speed and wide-angle spatial scanning without moving parts.

Optical time-frequency processing requires a combination of high-speed, quadratic phase modulators and dispersive delay lines. The latter is typically achieved using optical fibers, but can be compactly implemented and tunable using dispersive filters. Time scaling, either dilation or compression, can be achieved with these building blocks. While basic time scaling followed by direct detection has been demonstrated, we focus on cascading time-scale operations for potential signal processing applications and implementations using integrated-optic platforms. For cascaded operations, both the phase and amplitude of the scaled output must be correct. Time scaling is studied analytically and by simulations. Practical implementation issues are addressed such as the time aperture limits imposed by using sinusoidal phase modulation to approximate the desired quadratic response. The chirp and dispersion relationships are given for "factor of one half" and "factor of two" time scaling. The evolution of the signal's time support at intermediate points in the time-scaling operation is shown to be a critical parameter for practical implementations. Two optical time-scaling architectures are studied, and one is clearly better in this respect. Furthermore, a special case arises for a Gaussian input pulse whereby the number of elements needed to realize the time scaling can reduced by a factor of two. Applications for cascaded time scaling operations are discussed, including optical wavelet processing and photonic-assisted analog-to-digital conversion. By using the time-scale operation in the optical domain to mimic the discrete-time downsampling operation, we show that physical scaling of the optical filters between subsequent decomposition levels is not required.