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We present a simple model for self-pulsation instability in passively phased high power optical fiber amplifier arrays with external feedback. Its key features are, first, the feedback level's sensitivity, and thus that of the cavity Q-value, to small phase changes of the array fields, and, second, the effect of refractive index nonlinearity in the amplifiers. The model's prediction of an instability threshold for arrays of at least two amplifiers is confirmed by a linearized stability analysis of a system in ring-cavity geometry, and the magnitudes of predicted power levels are well within the domain of recent experiments. [ABSTRACT FROM PUBLISHER]

A tip-tilt-piston micromirror array based on electrothermal bimorph actuation is presented. The micromirror uses a compactly folded actuator design that can realize high fill-factor with a simple fabrication process. A 4 \times 4 micromirror array with sub-apertures of 0.9 mm and a fill-factor of 54% is demonstrated. A piston actuation of about 200 \mu\m and tip-tilt scanning of \pm 18^\circ optical angles are obtained at a driving voltage as small as 4.5 Vdc. The mirror's tip-tilt steering capability and piston control make it promising for optical phased array applications. The phased array concept is demonstrated by phasing two adjacent mirrors on the mirror array. Other device characterizations including frequency, transient response, and mirror surface quality are also reported.\hfill [2009-0296] [ABSTRACT FROM PUBLISHER]

Sensor systems provide a critical capability for maintaining situational awareness for defense and security applications. Advances in sensor system technology over the last fifty years have created sophisticated systems to collect, detect, process, and respond to radiation over much of the electromagnetic spectrum. In this article, we discuss the physical processes important to the design of photonic sensing, review programs advancing sensor technologies at the Defense Advanced Research Projects Agency, and provide some insight to future capabilities. [ABSTRACT FROM AUTHOR]

A subwavelength aperture array in a gold film is fabricated for the purpose of second harmonic generation (SHG). The sunglass aperture shape is chosen to have an apex to increase the local field; however, unlike past research on double-hole structures, the inversion symmetry of the structure is intentionally broken to enhance the SHG. A systematic study of the influence of array periodicity and aperture shape is provided. The conditions for maximum SHG are discussed in terms of local field enhancement, excitation of the localized surface plasmon resonances, and the influence of array periodicity. Fully vectorial finite-difference electromagnetic calculations provide the effective index of the aperture modes, as well as the surface electric field to quantify the discussion. Both the sunglass and double-hole structures are promising for future implementation with less-expensive optical lithography since it is mainly composed of two holes; yet they produce sharp apexes for enhanced local field and thereby enhanced nonlinear light-matter interaction. [ABSTRACT FROM PUBLISHER]

We report on the fabrication and characterization of large-area 2-D square arrays of subwavelength holes in Ag and Al films. Fabrication is based on thermal nanoimprint lithography and metal evaporation, without the need for etching, and is compatible with low-cost, large-scale production. Reflectance spectra for these arrays display an intensity minimum whose amplitude, center wavelength, and line width depend on the geometry of the array and the reflectivity of the metal film. By placing various fluids in contact with the subwavelength aperture arrays, we observe that the center wavelength of the reflectance minimum varies linearly with the refractive index of the fluid with a sensitivity of over 500 nm per refractive index unit. The surface plasmon theory is used to predict sensitivities to refractive index change with accuracies better than 0.5%. [ABSTRACT FROM PUBLISHER]

A multiple beam former using multichannel chirped fiber grating (MCFG) and tunable optical delay lines is investigated in this paper. The simulation results shown in this paper exhibited that it could form two beams, which could be operated squint-free and independently from each other at 6 GHz. The use of a MCFG along with tunable optical delay lines has greatly reduced the system complexity and components requirements. Moreover, our proposed beam-former is able to operate using fewer tunable laser sources than other similar approaches. Successfully addressing this problem in the components cost would make the implementation of the scheme far more feasible. [ABSTRACT FROM PUBLISHER]

In this paper, high-speed optical ribbon couplers for card-to-backplane interconnect applications are presented. The ribbon couplers are based on evanescent coupling between flexible multimode waveguide arrays. A soft lithographic technique is utilized to fabricate the ribbons. A flexible nonterminating optical data bus has been developed. Using BeamPROP software, we simulated the evanescent light coupling between two closely spaced ribbon waveguides to study the effects of waveguides separation, interaction length, and misalignment on coupling efficiency. Further experimental analysis and tests have been performed to quantify these effects. To investigate data transmission performance, a 12-channel optical interconnect link has been assembled. Experimental results demonstrated successful evanescent coupling; facilitating auto alignment coupling between card and backplane ribbon waveguides at data speeds as high as 10 Gb/s per channel. The evident high-speed interconnect performance and rapid ribbon prototyping approach can result in overall lower cost coupler fabrication for prospective optical interconnect applications. [ABSTRACT FROM PUBLISHER]

An optically partitioned backlight system consisting of tandem wedge-shaped light-guides (LGs) with micro-line-prism arrays was developed for scanning field-sequential-color (FSC) liquid crystal display (LCD) in large size. The unit of wedge-shaped LG combined with a light-emitting diode (LED) light-bar was designed and fabricated to collimate the extraction light within a narrow angular extent. Based on the edge lighting approach, the volume of backlight system can be reduced down to 25 mm without sacrifice of the optical behavior. As a result, 2750 nits average luminance subject to 50% duty cycle and 83% uniformity can be achieved. The leakages into the consecutive adjacent blocks were well suppressed to 11.86%. [ABSTRACT FROM PUBLISHER]

We demonstrate a universal reconfigurable add-drop optical filter based on arrays of digital micromirrors. Our approach allows for reconfiguration of the device parameters for operation in different sets of channel wavelengths, even or uneven channel-to-channel separation, adjustable channel passband, and dynamic add-drop of optical signals. The proposed device shows insertion loss at the center wavelength in the all-pass configuration of 7.6 dB, extinction ratio of 35 dB, channel isolation better than 24dB, negligible loss ripple, and possibility of reconfiguration time in the order of microseconds. Although designed for demonstration on optical telecommunication frequencies, the high-flexibility features of the proposed add-drop filter allow it to be used for other optical wavelength-based filtering/switching applications. [ABSTRACT FROM PUBLISHER]

A diamond mill (a tiny end mill) can cut aspheric lenses and mirrors with diameters smaller than 0.5 mm. The cutting tool has a two-dimensional shape and is spun about the axis of the surface to be cut. As the spinning tool is plunged into the substrate, it cuts a radially symmetric surface to sub-micron accuracies. Commercially available circular diamond tools can be modified to aspheric shapes using a focused ion beam. Fabrication examples will be presented and the optical performance of an array of micro-lenses will be described. [ABSTRACT FROM PUBLISHER]

A novel multiplexing scheme based on a low-coherence reflectometry (LCR) is proposed for a sensing array (in parallel) of self-interfering long-period fiber gratings (SI-LPGs). Each SI-LPG sensor consists of an LPG and a section of fiber with a highly reflective end (mirror). The spectral information of each LPG is sensitive to some parameters of the surrounding measurand and can be reconstructed from the corresponding subreflectograms (obtained by the LCR) through a fast Fourier transformation. The sensing signals of multiple SI-LPG sensors can be multiplexed if the length of the fiber section in each sensor is set to a different value. Experiments of measuring the surrounding temperature at different sensors are demonstrated to show the good performance of our multiplexing system. [ABSTRACT FROM PUBLISHER]

In this paper, we introduce a new aperture-type near-Held scanning optical microscopy (NSOM) imaging concept that relies on specially designed large-area (e.g. >200 nm times 200 nm) aperture geometries having sharp corners. Unlike in conventional NSOM, the spatial resolution of this near-field imaging modality is not determined by the size of the aperture, but rather by the sharpness of the corners of the large aperture. This approach significantly improves the light throughput of the near-field probe and, hence, increases the SNR. Here, we discuss the basic concepts of this near-field microscopy approach and illustrate both theoretically and experimentally how an array of detectors can be utilized to further improve the SNR of the near-field image. The results of this work are particularly relevant for imaging of biological samples at a spatial resolution of < 50 nm with significantly improved image quality. [ABSTRACT FROM PUBLISHER]

A composite optical bend loss sensor for measuring 3-D forces has been developed. The sensor is composed of two optic fiber meshes which are embedded into a polydimethylsiloxane (PDMS) slab. The sensor consists of an array of optical fibers lying in perpendicular rows and columns sandwiched inside an elastomeric pad. A map of normal and shear stress is constructed based on observed macrobending through the intensity attenuation from physical deformation of two adjacent perpendicular fibers. Due to the new addition of the composite design and acrylic holder, the stability of the present sensor is found to be significantly better than our previously reported microfabricated optical bend loss sensor. In this paper, we will report the results of an optical bend loss simulation using the beam propagation method based on a series of images captured by a CCD camera on the fiber's bending curvatures. The result from the simulation will be compared with the results obtained from the experiment. Other results include vertical force and shear measurements at a single pressure point of the sensor. A force image algorithm is used to map the force distribution detected by the sensor. Here, we will present the results of six different shape patterns and two force magnitudes on each shape using a neural network system. We will also present a radio frequency sensor module, which we developed for the composite optical bend loss sensor for remote sensing. [ABSTRACT FROM PUBLISHER]

Novel compact optical backplane connectors with 2-D arranged inputs/outputs (I/Os) are demonstrated. To meet the requirement of higher integration in an optical backplane system, we applied 3-D waveguide arrays with multichannel optical I/Os. Using laser writing and a wafer-lamination process, a single-mode waveguide array with 24 I/Os and a multimode waveguide array with 16 I/Os were, respectively, fabricated. In the assembly of the backplane connector, waveguide arrays were actively aligned and combined with polymer submounts, and then, the submounts were fixed to the backplane-connector housing. To ensure efficient coupling to the optical fibers, commercially available multimedia (MD) connectors were applied to the interface of the backplane connector. Using MD connectors with multichannel I/Os, we successfully obtained 10-Gb/s/ch transmission performance. [ABSTRACT FROM PUBLISHER]

We present a pole-zero analysis, based on the transfer matrix method, for ring resonator (RR)-based filters of Type I and Type II, consisting of mutually coupled and side-coupled RRs. The pole-zero plot determines the filter spectral characteristics and is determined primarily by the coupling coefficient between the resonators. The pole-zero dynamics (or root locus) shows how the poles and zeros move in the complex frequency plane as we vary the coupling coefficient. We show that the pole-zero dynamics for the two types of filter are complementary and, furthermore, that the pole-zero plots are related to the conditions of critical coupling and oscillation in the presence of loss or gain. We also show a pole-zero analysis for the apodization of these filters based on an actively tunable Mach-Zehnder-type coupler, where it is shown that apodization corresponds to designing pole-zero pairs with wide separations, whereas the required bandwidth determines the specific values of the coupling coefficient. [ABSTRACT FROM PUBLISHER]

Micromirror arrays are promising components for generating reflective slit masks in future multiobject spectrographs. The micromirrors, 100 mum times200 mum in size, are etched in bulk single crystal silicon, whereas a hidden suspension is realized by surface micromachining. The micromirrors are actuated electrostatically by electrodes located on a second chip. The use of silicon on insulator (SOI) wafers for both mirror and electrode chip ensures thermal compatibility for cryogenic operation. A system of multiple landing beams has been developed, which latches the mirror at a well-defined tilt angle when actuated. Arrays of 5times5 micromirrors have been realized. The tilt angle obtained is 20deg at a pull-in voltage of 90 V. Measurements with an optical profiler showed that the tilt angle of the actuated and locked mirror is stable with a precision of 1 arcmin over a range of 15 V. This locking system makes the tilt angle independent from process variations across the wafer and, thus, provides uniform tilt angle over the whole array. The surface quality of the mirrors in actuated state is better than 10-nm peak to valley and the local roughness is about 1-nm root mean square [ABSTRACT FROM PUBLISHER]

In this paper, we report an array of f- thetas microlens optical scanners developed for 3-D optical cross connect (OXC) system using the bulk-silicon micromachining technique. An electrostatic XY-stage mechanism for the 2-D lens scanner was designed to have a small footprint (2 mmtimes2 mm), compared with an integrated silicon lens (diameter 1 mm) due to the newly developed double-deck actuator design; all the mechanical parts (suspensions and frames) were made in the substrate layer of a silicon-on-insulator (SOI) wafer, and the electrostatic actuation mechanism (electrodes and electrical interconnection) was made in the SOI layer. A silicon lens was integrated on top of the XY-stage by transferring the spherical profile of a thermal-reflow photoresist pattern into the SOI layer by reactive-ion etching. The XY lens scanner was found to operate at lateral displacement of 19 mum in the X-directions and 23 mum in the Y-directions at drive voltages of 110 and 60 V, respectively. For an optical assembly of the OXC, we used additional lenses in a telescope formation to double the beam angle that was steered by the f- thetas microlens scanner by which the lens displacement could be designed to be smaller by a factor of 1/2 [ABSTRACT FROM PUBLISHER]

In this paper, we present a single-crystal-silicon (SCS) continuous membrane deformable mirror (DM) as a corrective adaptive-optics (AO) element for space-based telescopes. In order to correct the polishing errors in large aperture (~8 m) primary mirrors, a separate high-quality surface DM array must be used. Up to 400000 elements and a mirror stroke of ~100 nm are required for the correction of these polishing errors. A continuous membrane mirror formed by the the SCS device layer of a silicon-on-insulator (SOI) wafer is used to achieve a high-quality optical surface and to minimize the additional diffractive effects in the optical system. To achieve substantial local deformation needed to correct high-order errors, we use a highly deformable silicon membrane of 300-nm thickness. This thin membrane is able to deform locally by 125 nm at an operating voltage of 100 V with a pixel pitch of 200 mum. The resonance frequency of a pixel is 25 kHz with a low Q-factor of 1.7 due to squeeze-film damping. The device is fabricated by processing the microelectromechanical system (MEMS) and electronic chips separately and then combining them by flip-chip bonding. This allows optimization of the MEMS and electronics separately and also allows the use of an SOI layer for the mirror by building the MEMS bottom up. A small prototype array of 5times5 pixels with 200-mum pitch is fabricated, and we demonstrate single pixel and multiple pixel actuation [ABSTRACT FROM PUBLISHER]

In this paper, we present a piston-type spatial light modulator (SLM) as a programmable optical pattern generator for maskless lithography. The SLM is a dual-lever-type actuator with pixel-overlapping springs to achieve low voltage actuation with a small capacitor area. Large arrays of up to ~40000 mirrors with 20-mum pixels and ~17000 mirrors with 30-mum pixels have been fabricated. The arrays have various prewired configurations to alleviate the need to control all the pixels individually. The mirrors have high resonance frequencies for fast response and achieve deflections of lambda/2 (lambda=193 nm for 20-mum pixels and lambda=633 nm for 30-mum pixels) at voltages less than 100 V. The mirrors are fabricated using thin-film processing and chemical mechanical polishing of the reflector layer. Using the SLM in an aerial imaging system, we demonstrate the generation of dark lines, dark areas, linewidth modulation, and subgrid positioning. We also demonstrate compensation of image shifts due to through-focus wafer drift using a double exposure (or phase-compensated exposure) technique [ABSTRACT FROM PUBLISHER]

Multichannel wavelength filters consisting of 2-D photonic crystal (PhC) for the near-infrared wavelength region (~800 nm) are demonstrated. The filter is a thin-film wavy multilayer structure and is fabricated by the autocloning method, which is based on a radio frequency bias sputtering process. Twelve long-pass-type filter regions are integrated on a common silica substrate. Sharp cutoff characteristics and almost equal channel spacing are experimentally verified. To precisely control the effective lattice constant of PhC, a modulated lattice structure on the substrate is utilized [ABSTRACT FROM PUBLISHER]

Integrated optical filters having elliptic transfer functions are proposed using two-dimensional arrays of synchronously tuned mutually coupled microring resonators. Analysis of microring filter topologies of the most general form is facilitated by the formulation of an energy-coupling matrix for the microring array. A method for synthesizing elliptic microring filter transfer functions having the prescribed transmission poles and zeros is also presented. The approach involves representing the microring filter by an equivalent electrical network of coupled LC oscillators and applying the coupling matrix technique developed for micro-wave filters to determine the coupling parameters. An example of a sixth-order elliptic function filter is presented to demonstrate the feasibility of using mutually coupled microring resonators to realize optical filters having finite transmission zeros in the transfer function [ABSTRACT FROM PUBLISHER]

Multifiber interconnection technology is one of the important keys to increase package density in optical networks. We present a novel releasable multifiber optical connectivity solution from the initial concept to the functional prototypes. This connectivity solution relies on a V-groove alignment platform and a microlens array. It can, e.g., provide reliable connections between a fiber array and an active optoelectronic component array or between a fiber array and an optical waveguide device. Moreover, within a free-space propagation region, it provides access to collimated optical beams, thus enabling various light manipulation options. The microlens V-groove fabrication process makes use of a dedicated assembly station that has been designed for automation. The microlens array is positioned on the platform, aligned relative to the V-grooves, and fixed with a low-cost adhesive bonding technology. Uniform and stable low losses for fiber-to-fiber coupling via two lenses have been achieved for single-mode and multimode fibers at wavelengths of 850, 1300, and 1550 nm. This connectivity solution represents, therefore, a versatile cost-effective technology for releasable connections of fiber arrays to any other optical multiport device [ABSTRACT FROM PUBLISHER]

A polarization-insensitive monolithic 40-Gbps semiconductor optical amplifier (SOA)-Mach-Zehnder interferometer wavelength converter has been developed. Based on the photon-electron rate equation, we optimized the dimensions of the waveguide structure to maximize the field confinement in the active layer. An InGaAsP active layer with narrow SOA waveguide effectively enables polarization-insensitive high-speed wavelength conversion. High-precision wafer processing technique enabled the fabrication of submicrometer-wide active waveguides with low current leakage. Input waveguide arrays were fabricated at intervals of 25 mum and mounted in a module with two-lens aspherical lens optics. The 40-Gbps nonreturn-to-zero wavelength conversion experiment demonstrates a clear eye opening over full C-band operation [ABSTRACT FROM PUBLISHER]

Light propagation in multimode photonic crystal (PC) waveguides and in arrays of single-mode PC waveguides is analyzed. The dispersion relations of the modes traveling along these devices explain the numerically observed formation of single and multiple copies of the input beam. As the analogous devices constructed in a standard planar geometry, the proposed PC devices can be employed as filters and demultiplexers. The use of PC structures, where the light is truly confined by the stopband, adds the valuable benefit of a dramatic reduction of the overall geometrical dimensions [ABSTRACT FROM PUBLISHER]

A variable focusing microlens chip, which has the capability of adjusting its focal length over a wide range without any mechanical driving parts, is reported in this paper. The packaged microlens chip consists of a flexible polymer lens, a fluidic chamber, an integrated sensor, and an actuator. A thermal actuator is introduced into this variable focusing microlens to obtain relatively large actuation force and displacement. The hemispheric convex polymer lens provides an initial focal point without being actuated. The focal length change is controlled by varying the voltage applied to the thermal actuator. A 1.9-mm-diameter polymer lens is made to test the performance of the device. The focal length of this chip varies from 14.658 to 2.782 mm, which corresponds to the change of numerical aperture from 0.078 to 0.412. Based on the working mechanism and constructing method of the single lens chip, a variable focusing microlenses array has been fabricated for future testing and application. Potential sensing applications for single lens and array include cell detection and immobilization, optical sensors, lab-on-a-chip, ophthalmic lens systems, microphotonics, high throughput scanning, and confocal imaging system [ABSTRACT FROM PUBLISHER]

This paper studies how to reduce packet delay in single-hop wavelength-division-multiplexed (WDM) networks with reservation-based scheduling algorithms. A number of approaches have been proposed in previous researches to reduce different components of the packet delay. This paper proposes two approaches to reduce the packet delay. The first approach is to replace the tunable transceivers in all of the nodes with fixed transceiver arrays such that no tuning latency is required, and each node is capable of transmitting and receiving multiple signals on multiple channels at the same time. The latter property enables the network to have better tolerance to traffics with nonuniform arrivals and nonuniform distribution of destinations that are commonly seen in network traffics. With a fixed transceiver array in each of the nodes, each channel becomes an independent broadcast channel such that broadcast and multicast communications can be efficiently supported. With fixed total number of channels in a transceiver-array-based single-hop WDM network, there is a tradeoff between the number of channels used for transmitting reservation (or control) information and the number of channels used for transmitting data packets. A network with fixed numbers of control and data channels is not able to cope with different traffic patterns. The optimal combination of the numbers of control and data channels depends on the traffic patterns. Therefore, our second approach is to develop an adaptive channel allocation algorithm to dynamically adjust the numbers of control and data channels according to the traffic patterns. The proposed adaptive channel allocation algorithm enables a transceiver-array-based single-hop WDM network to dynamically choose the best combination of the numbers of control and data channels for wide ranges of traffic patterns including nonuniform arrivals, nonuniform destination distributions, broadcast/multicast communications, and different system loads. The advan- tages of the proposed approaches are demonstrated in the simulation results [ABSTRACT FROM PUBLISHER]

The authors report on a design and demonstration of a quartic-style optical true-time-delay device based on a White cell. This device is designed for 81 sequential time delays with an incremental delay of 243 ps and a maximum delay of 19.683 ns. The time delays are implemented by free-space translations, with lens trains as needed for beam containment. A digital microelectromechanical tilting micromirror array is used to send the light into different delay paths [ABSTRACT FROM PUBLISHER]

The design and optimization of a novel InP-based monolithically integrated optical channel monitor are presented. The device, which comprises a flat-field echelle grating and a slab photodetector array, can monitor signals in 40 wavelength channels separated by 100 GHz. The authors' simulations show that the novel design can result in a device of a smaller size and with a flatter and wider passband than those reported previously. It also features simpler fabrication without the need for output waveguides, thus eliminating issues related to fabrication-sensitive waveguide couplings. The shape of the slab waveguide detectors and the vertical layered structure are optimized to obtain a low crosstalk and a low polarization dependence [ABSTRACT FROM PUBLISHER]

High birefringence and low viscosity isothiocyanates liquid crystal single compounds and eutectic mixtures, based solely on laterally fluorinated aromatic rigid core structures, are reported. Extraordinarily high values of figure-of-merit were observed at room temperature and also elevated temperatures for the nematic mixtures we formulated. Potential applications of such mixtures for laser beam steering at lambda=1.55 mum using optical phased arrays are emphasized [ABSTRACT FROM PUBLISHER]

We have developed an ultra-small 16-channel variable optical attenuator (VOA) multiplexer (V-AWG) with excellent optical performance by using multichip planar lightwave circuit (PLC) integration technology. The insertion loss is 3.2 dB, and the polarization-dependent loss (PDL) at 25 dB attenuation is less than 0.3 dB. The module size is 90 mmtimes55 mmtimes14 mm. We describe our concept and developed techniques as regards to the design, fabrication, and packaging of the module, focusing particularly on a chip-scale-packaged monitor photodiode array (CSP-PD) that we developed as a key component of our technique [ABSTRACT FROM PUBLISHER]

An innovative design is presented enabling fine positioning of each individual fiber in a fiber array used in multiinput- and multioutput-port photonic integrated circuits. Hence, the coupling efficiency of lensed fiber arrays can be improved by eliminating the eccentricities of the lenses deposited on the individual fibers and the inaccuracies of the supporting V-groove substrates. In preparation, four different types of commercially available lensed fibers are characterized and coupling efficiencies to InP-based waveguides are determined in order to select the best applicable fibers for the array. The final fiber-tip position accuracy is within plusmn0.25 mum and this design is based on metal deformation by laser-welding-induced local heat. With this technique, laser-supported adjustment is possible, allowing the opportunity of fine-tuning the fiber-tip position of already secured parts in the subassembly. Owing to the accurate fiber-tip position and the assembly of the array with selected lensed fibers, coupling efficiencies of -2.9 to -3.5 dB are simultaneously measured for four fibers to InP-based waveguides with physical dimensions of 3 mum times0.6 mum. To compare these results, the performance of different types of regular, commercially available fiber arrays, whereby the fibers are mounted on silicon V-groove substrates, are determined. In contrast, the measured coupling efficiencies are of the order of -5.2 to -7.8 dB using similar InP-based waveguides [ABSTRACT FROM PUBLISHER]

In lightwave communications, the high-power-efficiency coupling between a laser diode (LD) and a single-mode fiber (SMF) is indispensable. This paper proposes an imaginative two-microlens-array (MLA) coupling scheme whereby two revolved hyperboloid MLAs were used back-to-back between the LD and the SMF, and a coupling efficiency of 83.4% (-0.79 dB) has been achieved. The study also employs a cost-effective fabrication method, with a combination of the sample-inverted reflow technique and the soft lithography replication method, to fabricate revolved hyperboloid MLAs in inorganic-organic hybrid silica-zirconia sol-gel material. As a result, the fabricated MLAs have excellent smooth profiles and negligible discrepancies from the profiles of the ideal hyperboloid MLAs. [ABSTRACT FROM PUBLISHER]

In this study, a theoretical model of the lead (delay coil and array buses) sensitivity in Sagnac sensor arrays (SSA) for underwater acoustic detection, which induces a spurious pickup and thus a sensor error, is described. In the worst-case scenario, the pickup in a 20-km coil is predicted to be reasonable in deep waters (quietest) (about 17 dB higher than the hydrophone signal) but fairly high (∼ 52 dB) in shallow waters (noisiest). We show that this pickup can be eliminated for the first few hydrophones in the array by optically folding or double winding the coil, although these approaches are not as effective for the most distant hydrophones in long arrays (≥ 1 km). These figures are confirmed experimentally in an SSA: Folding a 5-km coil decreased the relative pickup from ∼-42 dB for the first hydrophone and by ∼-8 dB for a hydrophone 1 km down the array. These results concur that for most practical arrays, it is imperative to isolate the coil in an acoustically shielded enclosure, which will reduce the coil pickup to an arbitrarily low level for all hydrophones. Theory and experiment also agree that the pickup in the array buses increases in proportion to the distance along the array. In the worst-case scenario (spherical acoustic wave incident normal to the array), the pickup in a 1-km bus is predicted to be ∼-7 dB in quiet waters and ∼-40 dB in noisy waters. However, in the field, the probability of this event is expected to be extremely low, and these values will be typically at least 15 dB weaker. Nevertheless, in long arrays, the bus pickup must be reduced, which can be achieved by desensitizing the bus fiber and/or pickup subtraction. Combined, these two techniques are expected to make the bus pickup under normal conditions negligible in deep-water applications (∼-48 dB) and acceptable in noisier shallow-water applications (∼-15 dB). [ABSTRACT FROM PUBLISHER]

A novel optical correlator employing an opto-very-large-scale-integration (VLSI) processor to construct the routing lookup table, in conjunction with an array of fiber Bragg gratings (FBGs) for multiwavelength optical header recognition is demonstrated. The FBG array provides wavelength-dependent time delays, whereas the opto-VLSI processor generates wavelength intensity profiles that match arbitrary bit patterns. The recognition of 4-b optical patterns is experimentally demonstrated at 2.2 Gb/s by showing that the correlator produces an autocorrelation waveform of high peak whenever the input bit pattern matches the wavelength intensity profile. [ABSTRACT FROM PUBLISHER]

In this paper, an optical-signal-processing device mainly designed for time-slot switching is demonstrated. The device is composed of variable delay-line arrays fabricated by planar lightwave circuit technology and high-speed optical gates. The variable delay-line arrays consist of transversal-form or lattice-form optical circuits. The operating principle is based on serial-to-parallel conversion, adjustment of the delay time between the parallel signals, and the gating of the optical bits or packets in the optical region. The device does not require any interaction between lightwaves through optical nonlinear effects or filter banks for code matching. As an example of its operation, label-processing functions are demonstrated, specifically the label swapping of optical return-to-zero pulses. The merits of the proposed device are described and problems that must be solved are also discussed. [ABSTRACT FROM PUBLISHER]

In this paper, the scattering matrix method (SMM) is used to analyze the modal properties of evanescently coupled waveguide arrays with cores spaced equidistant from a common central core. Propagation constants and field distributions of the fundamental in-phase supermodes are obtained for waveguide arrays comprising three, four, five, six, and seven cores. The authors show how the coupling strength among individual cores can be controlled by adjusting the properties of the central core, thereby providing a means of tailoring the near-field mode profile. By properly selecting the parameters of the central core, the authors also show how an equal power distribution among all cores can be achieved. A seven-core waveguide array is discussed in detail including the effects of varying core spacing and central core parameters on the supermodes and dispersion properties of the array. [ABSTRACT FROM PUBLISHER]

This study presents a novel generic multipurpose probe based on an array of 20 waveguide channels with microcantilevers acting as optical waveguides operated in the visible range. The principle of operation is based on the sensitivity of energy transfer between two butt-coupled waveguides to their misalignment with respect to each other. The technique can be considered an alternative to the known methods used for the readout of the nanomechanical response of microcantilevers to the external force exerted on them. The cantilever displacement can be detected with a resolution of 18 fm/√Hz. The limit is generally defined by the shot noise of a conventional photodetector used for the readout of the output signal. Real-time parallel monitoring of several channels can be realized. In contrast to devices based on the atomic force microscope detection principle, no preliminary alignment or adjustment, except for light coupling, is required. The detection of the cantilever deflection at subnanometer range was demonstrated experimentally. [ABSTRACT FROM PUBLISHER]

An optical true-time delay device that uses a binary counting system in a modified White cell is demonstrated. The switching engine uses four spherical mirrors and a three-state digital micromirror array. The delay part, as designed, provides 6 bits of delay ranging from 78 ps to 5 ns, using a combination of dielectric blocks for short delays and lens trains for longer ones. Long lens trains are folded for compactness. The authors describe the design and demonstrate two of the 6 bits of delays experimentally. Delays were accurate to within the measurement resolution of 1.25 ps. The insertion loss varied from 3.1-5.2 dB, depending on delay. It was found that the micromirrors do not contribute significantly to the loss. [ABSTRACT FROM PUBLISHER]

The common approach to attaching a large number of fibers to a guided-wave device is to fabricate a linear array using V-grooves. UV-curable adhesives are used to attach the fiber in V-groove for the fabrication of fiber array. Interfacial delaminations at the adhesive fiber interfaces are common after the reliability test due to uneven curing of the UV adhesive. This paper investigated the causes of uneven curing that gave rise to delamination. An analytical ray tracing technique was used to estimate the variation in light intensity or shadowing during the UV curing of adhesive. These effects were found to be very severe when the refractive index difference between the adhesive and the cladding materials is very large. Based on this study, it can be concluded that the delamination problem can be minimized by selecting a UV-curable adhesive having the same refractive index of the cladding material. It is also recommended to light illuminate from the topside for fiber packaging [ABSTRACT FROM PUBLISHER]

The authors propose a novel frequency-overlapping multigroup scheme for a passive all-optical fast-frequency hopped code-division multiple-access (OFFH-CDMA) system based on fiber Bragg grating array (FBGA). In the conventional scheme, the users are assigned those codes constructed on the nonoverlapping frequency slots, and therefore the bandgaps between the adjacent gratings are wasted. To make a more efficient use of the optical spectrum, the proposed scheme divided the users into several groups, and assigned the codes, which interleaved to each other to the different groups. In addition to the higher utilization of the spectrum, the interleaved nature of the frequency allocations of different groups will make the groups less correlated and, hence, lower the multiple-access interference (MAI). The corresponding codeset and its constraints for this new scheme are also developed and analyzed. The performance of the system in terms of the correlation functions and bit error rate (BER) are given in both the conventional and the proposed schemes. The numerical results show that, with the multigroup scheme, performance is much improved compared to the conventional scheme [ABSTRACT FROM PUBLISHER]

A methodology for designing an octic-style optical true-time-delay (TTD) device based on the White cell (WC) is investigated. The octic cell is a "polynomial" cell, one of the two classes of TTD White cells. This octic cell is designed to produce a maximum of 6399 delays in 17 bounces, with a unit delay of 3 ps. Glass blocks are used for short delays, white lens trains are used for the longer delays. The octic cell is designed to use a microelectromechanical tip/tilt micromirror array to direct light beams into various delay paths. [ABSTRACT FROM PUBLISHER]

A new high-port-count wavelength-selective switch (WSS) has been realized using two cross-scanning one-axis analog micromirror arrays in a 4-f optical system. The number of output ports is increased from N to N2, where N is the maximum linear port count limited by optical diffraction. Using surface-micromachined micromirrors with hidden vertical comb drives, large scan angles (>±5° mechanical), low drive voltages (7 V), and high fill factors (> 96.25%) are achieved for both scanning mirrors. Experimental results for WSS are demonstrated using both two-dimensional (2-D) array of discrete collimators and monolithic 2-D collimator array. A fiber-to-fiber insertion loss ranging from 6 to 18 dB and a switching time of <700 μs have been achieved. [ABSTRACT FROM PUBLISHER]

This paper describes an optical configuration that allows effective arrangement of multiple 1×N optical switches as an integrated array. An experimental compact module of 16 arrayed 1 × 8 optical switches, built by utilizing a cylindrical lens, achieves uniform performance and a mean fiber-to-fiber insertion loss of 2.75 dB. This paper also discusses various layouts that use the proposed optical switching module for both wavelength-independent and wavelength division multiplexing (WDM) applications. [ABSTRACT FROM PUBLISHER]

A modulating corner-cube reflector with one microelectromechanical-system (MEMS) mirror that deforms from a flat into a hexagonal array of concave reflective microlenses to disperse the retroreflected wavefront is demonstrated. It is shown that such retromodulators can operate under a wide range of wavelength and angle illumination using Huygens-Fresnel propagation analysis, and this analysis is verified using devices fabricated by surface micromachining. A gold-coated silicon-nitride membrane suspended over 1-mm-diameter circular cavities had a resonant frequency of 160 kHz and 0.55-μm maximum deformation with 79 V applied. While this deflection was only 2/3 of the design value of 0.8 μm, we measured an up to 7:1 modulation contrast ratio from a prototype retromodulator, which achieved 100-kHz modulation over a 100-nm optical bandwidth, a 35° range of incident angles, and temperatures ranging from 20 to 100°C. [ABSTRACT FROM PUBLISHER]

Polarization mode dispersion (PMD) is a potential limiting factor in long-haul high-speed optical communications, especially in systems beyond 10 Gb/s. Although considerable effort has been devoted to compensation methods for PMD, most of the research is restricted to a small bandwidth, within the limits of the first- and second-order PMD approximations. For the first-order approximation to be valid, the distortions induced by PMD must remain less than a few tenths of the pulse duration or the bit period for return-to-zero (RZ) or non-return-to-zero (NRZ) systems, respectively. In this work, as far as the authors know, the application of ultrafast optical pulse-shaping techniques for experimental broadband all-order PMD compensation is demonstrated for the first time. PMD is treated as arbitrary variations of state of polarization (SOP) and phase versus wavelength, in an all-order sense. Two fiber-pigtailed pulse shapers are implemented in a serial manner to compensate the polarization and phase spectra independently. The first step corrects the wavelength-dependent polarization states to a fixed wavelength-independent state. This reduces the PMD compensation problem to a generalized chromatic dispersion compensation problem. Consequently, equalization of the spectral phase in the second step restores the clean broadband pulse signal. In the experiments, compensation of subpicosecond pulses (14 nm bandwidth around 1550 nm) that are anomalously spread to more than 2 ps due to PMD is demonstrated. These results are potentially relevant for future ultra-high-speed time-division-multiplexed (TDM) systems. Research challenges that must be addressed to bring this approach to practical application are also briefly enumerated, and the potential for scaling to a range compatible with wavelength-division-multiplexed (WDM) systems is discussed. [ABSTRACT FROM PUBLISHER]

This paper describes a packaged and fiber array coupled 4×4 optical crosspoint switch designed for optical packet switching. Alignment and fixation techniques of two perpendicular fiber arrays to the integrated InP-based switch chip have been developed. Thermal management is also included in the packaging. The packaged devices demonstrate long-term stability and have been used in switch modules, including the packaged device and electronic interfaces. [ABSTRACT FROM PUBLISHER]