All optical XOR, AND, and, OR functionality has been demonstrated experimentally using semiconductor optical amplifier (SOA) based devices at 40 Gb/s, 80 Gb/s. The performance of the optical logic operations has been analyzed by solving the rate equation of the SOA numerically. The high-speed operation is limited by the gain and phase recovery times in the SOA. In order to solve these limitations, a differential scheme for XOR operation has been experimentally investigated. This scheme is potentially capable of XOR operation to > 100 Gb/s.

Many military and defense related applications require the use of large-scale photonic switch matrixes in order to increase the capacity for processing a large amount of information within a minimum period of time. Existing photonic switches relying on electro-optic effect or MEMS technology are limited in terms of switch scale size or switch reconfiguration rate. Moreover, these conventional photonic switches utilize analog electric signals for switch operation, making them extremely sensitive to electromagnetic interference that limits their military applications. To address these issues, we have developed a new photonic switch matrix using commercial erbium doped optical fiber and other commodity fiber optic components. Using this technology, all-optical controlled photonic switching operation can be realized. The optical amplification provided by erbium doped optical fibers further ensures the implementation of large-scale switch formation with low or no overall insertion loss. In addition, this new photonic switch is highly reliable and durable since it contains no moving parts without any related bearing or wearing issues, making it extremely suitable for military and defense related applications. In this presentation, the design and fabrication of a 4 × 4 erbium doped fiber based photonic switch matrix are described. Full performance characteristics of the fabricated switch matrix including switching speed and cross talk are given, and the potential military and defense related applications of this technology are highlighted.

All-optical logic allows high bit rate computation and fast switching, free from electromagnetic interference. Combinational and sequential logic are considered, the latter having memory which allows feedback structures such as flip-flops from which shift registers for storing binary words are constructed. Optical microring resonators are shown to be capable of implementing logic gates such as NOR and AND and they also exhibit bistabiltiy suitable for construction of 1-bit memories or flip-flops. Further, they can be fabricated in silicon on silicon dioxide using standard CMOS VLSI lithography for future integration with electronic VLSI. Microring resonators are a few microns in diameter, enabling high bit rate computation, in the tens or hundreds of Gbps, and fast picosecond switches and latches. A novel combination of microring resonator gates and microring resonator bistable devices is discussed for an all-optical shift register.

Fiber-Optic Variable Optical Attenuators (VOAs) are demonstrated using Liquid Crystals (LC) for broadband as well as wavelength tunable applications. Attenuation is achieved by using a beam spoiling approach implemented via electrically reconfigurable non-pixelated no moving parts Nematic LC deflectors. The VOAs feature in-line architecture and polarization insensitive design without the use of bulky polarization splitting and combining optics. The proof-of-concept VOAs in the 1550 nm band demonstrate >30 dB attenuation ranges, low polarization dependent losses and low power consumption. Applications for these VOAs include agile wavelength tunable secure data communications networks and RF sensor systems.

We have developed 10, 20, 30, and 40 Gb bandwidth balanced photoreceivers which have applications for both analog and digital fiber optic communications. The devices can operate at C and L optical bands as well as 1064 nm and 1310 nm wavelengths. The analog applications include low noise RF photonic links. The digital applications include 10 Gb and 40 Gb DPSK and DQPSK modulation formats for enhanced sensitivities. The advantages of balanced photoreceivers are: RIN noise cancellation, suppression of even order harmonics, doubling the optical power handling capacity of a photonic link, and better reliability.

An approach that modifies an analog fiber optic link with a recirculating optical loop as a means to realize a high-speed, high-resolution Analog-to-Digital Converted (ADC) is presented. The loops stores 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 data is presented which shows that a periodic extension of the input signal can be sustained for well over one hundred periods that in turn suggests an electronic ADC speed-up factor of over 100. The data also shows that polarization effects must be carefully managed to inhibit the loops tendency to lase even though the loop itself contains no frequency-selective elements.

The Advanced Radars and Electro-Optical Sensors group at the University of Missouri is constructing a new all-optical analog-to-digital converter (ADC) platform. This integrated optics application especially suits the data acquisition and processing requirements of mobile sensor systems that have dramatically increased alongside the requirements for reductions in system mass, volume, and power consumption. The platform of the ADC is composed of a direct-modulated laser (DML) at λ = 1.55 μm with a 40 G bits/sec sampling optical pulse source; a prism LiTaO₃ (lithium tantalate) electro-optical deflector; an integrated focusing unit; a three-dimensional binary-coded spatial filter array; and collection optics. Using discrete Fourier transform, we also investigate both the center frequency-shifting phenomenon of the optical pulse propagation, and the frequency response. The simulations are calculated by using the two-dimensional Finite Difference Time Domain (FDTD) method, the results of which are much more reliable than Beam Propagation Methods (BPM). The spatial filter array and collection optics will be fabricated by the separated implanted oxygen process (SIMOX), silicon on insulator (SOI). Also, a new design and simulation of LiTaO3 (lithium tantalate) electro-optical deflector to be integrated in the same substrate is proposed. This platform is to be tested for 50 Giga-samples/sec analog-to-digital conversion, and be the prototype of a 100 Giga-samples/sec ADC.

We describe the design and implementation of an eight channel optical sampling technique for analog-to-digital (A/D) converters. A single mode-locked laser source with a pulse reprtition rate of 250 MHz is used to generate eight highly synchronized smapling clocks each running at 500 MHz. The basic sampling circuit consistes of a reversed-biased photodiode which operates as a very fast optoelectronic switch. Actuating the photodiode ON and OFF with mode-locked laser pulses produce sampled RF signals. In the implementation of this A/D architecture, the optical clocks are delayed relative to each other using fixed passive delay lines. The time-shifted clock signals allow for sampling different phases of the input RF signal resulting in an aggregate sampling rate of 4 Gigasamples/sec (GSPS). We shall show the optical clock setup necessary in order to achieve a 4 BSPS rate. We shall also present sampling results for input RF signals with frequencies ranging from 10 to 500. Interleaving of the sampled RF output from different sampling channels will also be demonstrated.

A novel time division multiplexing technique has been incorporated with optical serrodyne phase modulation to generate a single microwave tone with up to 1 MHz tunability. Sideband spurs due to finite phase reset time in ordinary serrodyne phase modulation have been suppressed to more than 40 dB below the carrier. These results show that endless phase modulation can easily be achieved using this novel technique.

A hybridly modelocked grating-coupled surface-emitting laser (GCSEL) with pulse duration 2.8psec at 980nm is demonstrated. The unpumped grating section of the GCSEL is used as a saturable absorber to generate pulses with a 535MHz repetition rate. The peak power of 0.31W and a spectral bandwidth of 1.1nm are obtained.

In this paper, we present an overview of 3-D image sensing, formation, and visualization using integral imaging (II). As 2-D sensors and 2D display panel technologies advance rapidly, real-time 3D sensing and imaging have shown great promise for 3-D sensing, 3D TV and 3D visualization.

This paper discusses use of optical frequency combs generated by modelocked semiconductor lasers for coherent photonic signal processing applications. Key in our approach is a high Q cavity, supermode suppression and low spontaneous emission. Targeted applications of the stabilized optical frequency combs lie in areas of metrology, optical sampling, arbitrary waveform generation and communications using coherent detection.

We present two novel modulation formats, namely, optical differential 8-level phase-shift keying (OD8PSK) and differential polarization-phase-shift keying (DPolPSK) for high-spectral efficiency optical transmission. Both formats are constant-amplitude, tolerant to fiber nonlinearities, especially cross-phase modulation (XPM). Both formats use direct detection without the use of either active polarization control or phase locking at the receiver. DPolPSK also addresses practical use of polarization.

In this paper we present a Coherent Optical Multiple-Input Multiple-Output (COMIMO) communication system and its ability to exploit the inherent information capacity of Multi-Mode Fiber (MMF). COMIMO technique is a promising approach to unlock the information capacity of MMF as it ensures the necessary diversity for practically any fiber length. When exceeding the bandwidth-length product of the link, MIMO adaptive equalization can be used to mitigate inter-symbol interference (ISI). Furthermore, COMIMO link provides additional security in the physical layer that complements encryption.

We have demonstrated coherent heterodyne detection for an arrayed coherent receiver system based on synchronized modelocked semiconductor lasers. Dual-mode injection locking technique is employed to achieve excellent oscillator synchronization between two independent modelocked semiconductor laser systems.

Wavelength Division Multiplexing (WDM) is a photonic technology capable to transport over a single fiber more than a Tbit/s aggregate traffic. Currently, WDM is the only deployed method in transcontinental and transoceanic applications. In the optical network, each fiber link consists of segments, each several kilometers long, the connecting points of which are amenable to tapping. When a small amount of optical signal is extracted from a tap, when the signal is properly amplified it can be monitored by unauthorized personnel thus threatening communications and land-security. Since each WDM channel carries traffic from one customer, it is not difficult for the connoisseur to demultiplex a specific channel, isolate a specific payload and break the encrypted datagram. Therefore, in addition to data encryption, high-speed communications security should also rely on securing the optical links. In this paper, we present a WDM link security method that, even if fiber is tapped, constitutes channel monitoring and information decrypting by an eavesdropper or unauthorized personnel virtually impossible. In addition, we describe the circuit building blocks behind the method that makes eavesdropping impossible.

Measurement of refractive index, surface quality and temperature of the process materials in defense, petrochemical, power systems, glass, and metal industries is a fundamental need for precision systems performance. However, making these measurements in a super noisy defense or industrial environment is a big challenge faced by sensor technologies. Reported in this paper is the first ever demonstration of a wavelength multiplexed heterodyne interferometer using a single acousto-optic device (AOD). Heterodyne interferometry is pivotal in realizing a highly stable low noise interferometer. Inspite of the physical separation of the two arms of the interferometer, the sensor demonstrates Angstrom level optical path length sensitivity. The proposed sensor can be used in optical path length measurement-based sensing of parameters such as surface profile, refractive index, temperature, and pressure. Proof-of-concept experiment features a high resolution, low-loss, ultra compact, free space scanning interferometer implementation. Results include measurement of surface quality of a test mirror.

The ability to coherently generate and process arbitrary waveforms over wide frequency range is recognized as the core technology required for spectral dominance. Low observable (LO) radar technologies are expected to radically change the nature of tracking, acquisition and targeting in future combat environments. While passive LO designs drastically reduce backscatter radar cross section (RCS), they inherently compromise the performance of the airframe: a minimal RCS solution is not necessarily the optimal aerodynamic geometry. Recent demonstrations unify both LO and wide flight envelope. However, the approach dictates very high per-unit cost and is unlikely to lead to mass production seen in the past. In contrast, active LO techniques do not compromise aerodynamic properties, while still drastically reducing RCS. Unfortunately, active LO is expected to proliferate in the near term: it is cost-effective and can be used to qualitatively improve capability of the existing air forces by retrofitting not only the manned fleet, but also the existing missile ordnance. Airframes in service are simply upgraded by portable (100kg or less) units reducing the RCS section by more than two orders of magnitude. Unlike passive LO that can be countered by receiver spatial diversity, active LO reduces both backscattered and refracted radiation, requiring spectral, rather than spatially diverse countermeasures.

We demonstrate a novel method of polarization control that combines rotatable waveplates (angle control) and variable retarders (retardance control). Such a “hybrid” polarization controller performs far better than conventional controllers, allowing nearly perfect arbitrary-to-arbitrary polarization transformations. We show theoretically that the two control parameters augment one another because they tend to result in orthogonal movements on the Poincaré sphere.

Fiber-optic variable optical attenuators (VOAs) are required for light power control in numerous applications such as test and instrumentation, optical fiber telecommunications, industrial fiber-optic sensing, biomedical imaging and sensing, and photonic signal processing for antennas and radar systems. The requirements for the VOA, such as dynamic range and resolution, vary depending on the application. A VOA can demonstrate high end performance when it possesses critical attributes like super resolution precision and high dynamic range. Reported in this paper is the demonstration of a hybrid analog-digital fiber-optic VOA design that employs microelectromechanical systems (MEMS) technology. The VOA demonstrates simultaneously a super high controlled dynamic range of 81 dB as well as super 0.1 dB resolution attenuation controls. Proof-of-concept experiments exhibit an optical loss of 2.5 dB and C-band operations.

All-optical regeneration of differential phase-shift keyed signals based on phase-sensitive amplification in a nonlinear fiber Sagnac interferometer is described. Nearly ideal phase regeneration can be achieved in the undepleted pump regime, with output differential phase noise limited only by fast fluctuations of the pump phase relative to the DPSK signal. Operating in the depleted pump regime offers the possibility of simultaneously regenerating both phase and amplitude information of DPSK signals while providing low noise, phase-sensitive gain.

Recent progress toward implementing high-density, optical-digital building blocks necessary to accomplish efficient, end-to-end optical interconnect architecture on low cost FR-4 boards has been demonstrated. The optical interconnect system consists of fabricating an optical buffer layer separating board metallurgy from the optical lightwave circuit layer, and implementing optical links between embedded lasers and detectors. We will show an example of 1310 nm light from an edge emitting distributed-feedback or Fabry-Perot laser operating at 10 Gb/s being guided to the photo-detector by a polymer waveguide. Both lasers and detector are embedded in the waveguide and all construction is built on a low-cost FR-4 board with 3 levels of metallurgy.

We present high-performance surface-normal modulators based on unique properties of stepped quantum wells (SQWs) around the eye-safe wavelength of 1550 nm. Fabricated devices show nearly two times better efficiency and 7 dB higher extinction ratio compared with the conventional devices with rectangular and coupled-quantum well active layers. Moreover, the optical bandwidth is about 70 nm at a 3dB modulation depth, which is more than five times wider than the optical bandwidth of the conventional devices. Such a wide optical bandwidth eliminates the need for a temperature controller. This is a critical advantage for many applications such as unmanned aerial vehicles (UAVs) and dynamic optical tags (DOTs), where limited volume, power, and weight can be allocated to the modulator system.

Vertical external cavity surface emitting lasers (VECSELs) have been considered the “ultimate disk-laser” due to their extremely thin active regions and because they take advantage of the high gain found in semiconductor material. This paper discusses power scaling limitations, including heating effects, surface roughness losses, and laterally guided amplified spontaneous emission (ASE).

The gain dynamics of a semiconductor optical amplifier (SOA) are studied for the amplification of long, short and multiwavelength pulses from an external cavity semiconductor mode-locked laser. Nonlinear effects such as carrier heating and cooling, four wave mixing, and self phase modulation are observed, and it is shown how the inherent chirp of semiconductor mode-locked laser pulses helps to avoid these nonlinear effects.

Using an intracavity Pound-Drever-Hall technique, simultaneous optical frequency comb stabilization within ±3 MHz range and supermode phase noise suppression were demonstrated for a 10 GHz harmonically modelocked semiconductor ring laser resulting in timing jitter of 63.5 fs integrated from 10 Hz to 10 MHz.

We report on low noise performance of a 10 GHz actively mode-locked laser. The laser is a fiberized ring laser using a commercially available semiconductor optical amplifier (SOA) as the gain medium. The noise properties as a function of cavity length and optical spectrum are investigated. It is found that supermode noise is reduced when the cavity length is increased past a certain threshold. Best performance is achieved with a 20 meter cavity whose pulses are down chirped. No active feedback control is utilized to reduce the noise, yet the integrated jitter is only 29 fs (10Hz-100MHz).

The generation of stable mode-locked pulses in the 1550 nm regime is required for high resolution signal processing used in transient probes, optical clocks, and optical A-D converters. More recently the frequency combs comprising these pulses have been applied to innovative methods of arbitrary waveform generation (AWG) in the optical domain. Temporal stability, however, limits the performance in some of those applications. We show here that a Pound-Drever-Hall (PDH) technique applied to a mode-locked Erbium Doped Waveguide Laser (EDWL) effectively stabilizes the frequency comb for extended time intervals. The ultra-compact waveguide configuration offers greater packaging flexibility. The system performance in terms of temporal stability is also found to compare favorably with those of a high grade commercial erbium-doped fiber laser (EDFL).

Thin nanocrystalline arrays constructed using shear-flow crystallization of polystyrene colloidal nanoparticles consist of two types of domains D1 and D2 which are clearly visible on scanning electron microscopy patterns. Both kinds of domains have cubic close packing (ccp) and are distinguished by their orientation with regards to substrate surface. Positions of main minima in the visible-near-IR transmittance spectrum and their angular dependence on the angle between light direction and normal to the film are interpreted in terms of coexistence of different domain types and band gap structure.

In an increasingly digital world, the need for high speed and high fidelity analog-to-digital (A/D) converters is paramount. Performance improvements in electronic A/Ds have not kept pace with demand, hence the need to consider alternative technologies. One such technology is photonics, as it takes advantage of optical sampling, high speed optical switches and low cross-talk interconnects. Optical sampling derives its advantage from the application of ultra low timing jitter (<100fs) mode locked lasers utilised to provide high speed clock pulses. In this paper we report on our investigation into the feasibility and simulated performance of a photonic sigma-delta quantiser. The first-order sigma-delta architecture requires the functional elements of a subtractor, comparator and delay. We constructed optoelectronic versions of a subtractor and a comparator using self-electro-optic devices (SEED) based upon multiple quantum well (MQW) p-i-n devices. Comparator and subtractor operation were experimentally demonstrated and the inclusion of gain was shown to improve the subtractor performance to that demanded by the sigma-delta architecture. A numerical simulation based upon experimentally derived data was performed to include the non-idealities of the comparator and subtractor. A photonic implementation of the sigma-delta was proposed and simulated to demonstrate the feasibility of the architecture design and to determine the signal-to-quantisation-noise ratio (SQNR) as a function input amplitude. A peak SQNR of 54dB was obtained for an oversampling ratio of 100.

Atmospheric turbulence corrupts astronomical images formed by ground-based telescopes. Adaptive optics (AO) systems allow the effects of turbulence-induced aberrations to be reduced for a narrow field of view (FOV) corresponding approximately to the isoplanatic angle θ₀. For field angles larger than θ₀, the point spread function (PSF) gradually degrades as the field angle increases. Knowledge of the space-varying PSF is essential for image reconstruction. In this paper, we present a technique to predict the PSF as function of the field angle. The results are validated by mean of simulations. The predicted PSF is compared to the simulated PSF and we obtain a mean square (MS) error of 4.3% between the predicted and the simulated PSF in the worse case.