We propose a "slot-to-slot" coupler to convert power between optical and metal-insulator-metal (MIM) plasmonic
modes. Coupling efficiency of larger than 60% is obtained from 2D FDTD simulation. Based on this prototype, a quasi-MIM plasmonic junction is demonstrated using e-beam lithography onto an SOI substrate. The junction is formed by
depositing a thin layer of gold (~20 nm) on part of a dielectric slot. When probed by 1520-nm laser, coupling efficiency
of 36% is achieved for a 500-nm long quasi-MIM junction. Optical modulation is under investigation by pumping the
device using visible light to change the optical property of gold.
In this paper, ultra low cross talk is achieved by using a resonant cavity at the intersection between two strip waveguides
formed in a square lattice photonic crystal structure (PhC). Two PhC structures are studied: one consists of cylindrical
rods and another consists of cubic rods. The Q-Factor of the cavity is changed by increasing the number of rods that form
the cavity and by decreasing the spacing between the waveguide and the cavity. Our two dimensional simulation results
show that the latter method resulted in cross talk reduction of more than 21 dB for both structures. The overall cross talk
was -90.50 dB for the cylindrical rods structure and -105.0 dB for the cubic rods structure. The optimized PhC structures
were fabricated on a silicon-on-insulator platform. The rods were buried in silicon oxide in order to maximize the
photonic band gap and provide index guiding in the vertical direction.
We propose a new pumping method for optical fiber amplifiers at 1480nm and 980nm that is able to provide high gain and low noise-figure. The gain and noise figure obtained was 38 dB and 6 dB with an improvement of 4 dB and 1.4 dB, respectively, at 1550nm, for -30dBm input power when compared to its counter-pumped design. This design also delivers higher gain and lower noise figure when compared to the common bi-directional dual-pumped designs. A power conversion efficiency of 45% was achieved in this design.
We are proposing a novel application for fiber optic sensors in measuring acceleration. This novel design accelerometer is based on a fiber Bragg grating (FBG). The device we are proposing is capable of measuring acceleration in three axes simultaneously.
Diffractive optical elements (DOE) utilize diffraction to manipulate light in optical systems. These elements have a wide range of applications including optical interconnects, coherent beam addition, laser beam shaping and refractive optics aberration correction. Due to the wide range of applications optimal design of DOE has become an important research problem. In the design of the DOEs, existing techniques utilize the Fresnel diffraction theory to compute the phase at the desired location at the output plane. Since this process involves solving nonlinear integral equations, various numerical methods along with robust optimization algorithms have been proposed. However all the algorithms proposed so far assume that the size and the spacing of the elements as independent variables in the design of optimal diffractive gratings. Therefore search algorithms need to be called every time the required geometry of the elements changes, resulting in a computationally expensive design procedure for systems utilizing a large number of DOEs.
In this work, we have developed a novel algorithm that uses neural networks with multiple hidden layers to overcome this limitation and arrives at a general solution for the design of the DOEs for a given application. Inputs to this network are the spacing between the elements and the input/output planes. The network outputs the phase gratings that are required to obtain the desired intensity at the specified location in the output plane. The network was trained using the back-propagation technique. The training set was generated by using genetic algorithm approach as described in literature. The mean square error obtained is comparable to conventional techniques but with much lower computational costs.
We propose a novel reconfigurable erbium doped fiber amplifier (EDFA) design for high performance optical pre-amplifier applications. A fiber Bragg grating (FBG) with high reflection at a specific single channel wavelength and two circulator are used in the EDFA design to realize higher gain and optical signal-to-noise ratio (OSNR). This proposed system was compared with conventional co- and counter propagating EDFA normally used as pre-amplifiers. The selected channel amplification was in the C-band. A maximum gain of 38dB with a gain improvement of 10.8dB was achieved at input signal level of - 40dBm at 1550 nm. An OSNR improvement of 12.6dB was achieved as compared to the other two designs. An average noise figure of 5.6dB was obtained and with the appropriate selection of FBG, the design can be configured as a pre-amplifier for any channel within the C-band. The experimental results were compared and agreed with modeling results of the system.
We report a 94% coupling efficiency between silica waveguide (SWG) and planar photonic crystal (PPC). This is achieved using a tapered PPC with a hybrid photonic crystal structure. The hybrid structure combines triangular and rectangular crystals.
In this paper, we designed different structures for PPC tapered waveguide to enhance the coupling between silica waveguide (SWG) and planar photonic crystal (PPC). The designed structures are based on changing the radii of the inner PPC tapered waveguide's crystals before and after adding extra defects. We found that above 88% transmission efficiency is possible by using extra defects followed by radii changes. We also found that changing the operating wavelength from 1.55μm to 1.558μm increases the transmission efficiency to 90% since the field is more confined at the later wavelength.
We propose a novel Stokes vector imagery system that is capable of determining the full Stokes vector of each pixel in an image simultaneously without any movable parts or modulation. The proposed system creates four channels by utilizing a fixed and rugged lenslet array to produce an exact replica of the incident image through each channel. Analysis of the instrument matrix singularities is discussed. Since all Stokes vector images are determined simultaneously, the processing speed of such a system is high, makes it very attractive for several important applications. Furthermore, the proposed system is expected to reduce several errors associated with conventional imaging polarimeters that employ movable parts.
A novel micro-optical crossconnect switch based on the use of diffractive optical elements is introduced. A set of micro-actuated diffractive optical elements are used to reshape the optical beam as well as establish the interconnection required between two arrays of input and output optical fibers. The coupling efficiency of the switch is shown to be far higher than those using reflecting mirrors. Possible techniques for the fabrication of the switch are discussed.
In this paper we describe novel designs of IR versions of the parallel-slab division-of-amplitude photopolarimeter (IR-PS-DOAP) to measure the state of polarization of light as determined by the four Stokes parameters. The IR-PS-DOAP uses no movable parts or modulation and thus fast and simultaneous measurement is obtained. We present two different designs. The first employs a uniform, thin, transparent, film coating on the front surface of the parallel-slab. The second employs strips of thin, transparent, film coating on the front surface of the parallel-slab. A performance analysis comparison between the two will be presented. For wavelengths up to approximately 3.5 micrometers , SiO<SUB>2</SUB>, is totally transparent and is selected to be the slab material for the IR-PS-DOAP. For wavelengths beyond 3.5 micrometers , SiO<SUB>2</SUB> becomes absorbent and will be replaced by another transparent material like Irtran2, for example. The instrument matrix of the system is non- singular; hence the state of polarization is completely determined. The IR-PS-DOAP is compact, light-weight, rugged and based on reflective optics, so that predictive theory of instrument performance is applicable.
We present a novel photopolarimeter capable of compete measurement of the state of polarization of light, as determined by the four Stokes parameters. This photopolarimeter uses a diffractive-optical-element as a beam splitter to divide the incident beam into four or more components. It uses no movable parts or modulation and thus fast and simultaneous measurements of the four Stokes parameters are obtained. The instrument matrix of this element photopolarimeter is compact, lightweight, and rugged, hence, it can be easily integrated for number of applications.
In this paper the projection-slice SDF (PSDF) filter for rotation invariant response is discussed for pattern recognition applications. This method uses one half of a slice of the Fourier transform of the object to generate the transfer function of the filter. This is accomplished by repeating the half slice in the Fourier domain through 2(pi) radians about the zero-frequency point of the Fourier plane. This filter has the advantage of always matching at least one half of a slice of the Fourier transform of any rotation of the image. An analytical discussion of the filter transfer function and impulse response are presented along with simulated correlation results for a particular target scene including decoys. These results are evaluated using the peak correlation value, peak correlation energy, and the Fisher metric for performance.
Low latency, high bandwidth interconnecting networks that directly link arbitrary pairs of processing elements without contention are very desirable for parallel computers. The simultaneous optical multiprocessor exchange bus (SOME-Bus) based on a fiber optic interconnect is such a network. The SOME-Bus provides a dedicated channel for each processor for data output and thus eliminates global arbitration. Each processor can receive data simultaneously from all other processors in the system using an array of receivers. The architecture allow for simultaneous multicast and broadcast messages using several processors with zero setup time and no global scheduling. In this paper, we discuss the design of a possible opto-electronic implementation of the SOME-Bus along with an optical power budget analysis. Slant Bragg fiber grains arranged to couple light out of a fiber ribbon cable into an array of amorphous silicon detectors vertically integrated on a silicon are presented as a low cost novel means of interconnecting 10 to 120 processors.
The projection-slice theorem, often used in tomographic applications for medical imaging, is utilized in conjunction with the SDF concept to implement a distortion-invariant filter. The marriage of these two well-known fields results in an effective tool for invariant pattern recognition. 1D filtering and phase-only techniques are used to implement the projection-slice synthetic discriminant function filter, which is then compared with bench-mark filters, such as the SDF filter and the matched filter in both complex and phase- only forms for a particular set of images.
Waveguide output couplers fabricated in Norlund Optical Adhesive (NOA) #81 are investigated. The output coupler is implemented using periodic relief gratings on a planar waveguide. Design theory of the coupler is based ont he perturbation approach. Coupling of light from waveguide propagation modes to output radiation modes is described by coupled mode theory and the transmission line approximation of the perturbed area (grating structure). Using these concepts, gratings can be accurately designed to output a minimum number of modes at desired output angles. Waveguide couplers were designed using these concepts. The couplers were fabricated and analyzed for structural accuracy, output beam accuracy, and output efficiency. Applications for these couplers include databus and clock distribution system interfaces requiring coupling to out-of- plane detectors.
Mine and minelike target detection using optical correlators is presented. Minelike targets in experimentally collected data are used. The targets are situated in different environments. Optical correlators employing a variety of spatial filters are examined and their target recognition performance evaluated. Very good results were obtained in detecting the targets in most of the backgrounds used.
In this paper, cascaded diffractive optical elements are investigated using a design strategy combining genetic algorithms with beam propagation methods. Results are presented for a two element cascaded system for multiple wavelength performance.
A massively parallel signal and image processing architecture is considered. The architecture is comprised of 2D arrays of cells that simulate the response of retina neurons. The results of simulations are compared to previously published experimental results and the system is applied to detection of spatio-temporal features in sequences of images representative of pulse- doppler radar images. By arranging the output layer so that the cells respond to various key input features an array of feature extraction cells can be obtained. The system is characterized by developing an image space to feature space mapping.
Two optical fiber pressure sensor techniques are applied to the measurement of the distributed pressure of an O-ring. These sensors are polarimetrically and interferometrically based. Experimental results are presented for measuring the pressure exerted on an O-ring placed in a vacuum chamber and are compared with analytical results. Resolution and dynamic range of the fiber sensors are discussed.
A new class of composite filters is proposed. This class of filters can be used in optical correlator based recognition systems. It introduces a novel approach for rotation and scale invariant systems. Also it can be used to improve power throughput without sacrificing the signal-to-ratio in optical correlators based on complex matched filters.
A simple target which contains a wide variety of spatial frequencies has been developed for use in testing optical correlators. This target is designed to be complicated enough to provide an adequate test of many correlator and filter architectures, but yet simple enough to be used by researchers without the need for special equipment. Computer simulations and experimental results are presented for using the target in testing some correlator filter designs.
Measurement of the turbulent flow field distribution arises in aero-optics problems is considered. Moiré deflectometry technique are proposed for the quantitative measurement of the flow field density distribution. Experimental results for the density of simple axis-symmetric phase objects are presented. Optical tomography system based on Moiré deflectometry for quantitative measurement of the flow field for asymmetric phase objects is proposed.
In this paper, an optical implementation of an associative memory based on parallel rank-one interconnections and time integration is proposed and experimental results are demonstrated. Optical parallel rank-one interconnections based on singular value decomposition and time-integration are useful in implementing real-time, programmable, and adaptable neural networks with arbitrary order. Input patterns can have the same size as the outer-product memory matrix at the expense of time usage proportional to the dimensionality of the input pattern. Computer simulation results are given to show that this time usage can be reduced by using singular value decomposition and principal components analysis, without substantial degradation of the performance of the system. This consequently allows efficient utilization of the spatial parallelism that optical systems can offer.
A novel optical architecture is presented that is based on the Hartley transform implementation of the classical adaptive least mean square (LMS) algorithm. The Hartley transform is employed to transform the time-domain signal of interest into the frequency domain, where filtering is performed via multiplication by the adaptively controlled filter transfer function. The inverse Hartley transform is then applied to this product resulting in the desired signal estimate, which is then subtracted from the desired signal to obtain the error to be used to update the filter transfer function. In addition to the presentation of this algorithm and the optical implementation, performance assessments based on the number of calculations required for the digital and optical approaches are provided.
A novel acoustooptic architecture that implements linear least-mean square adaptive filtering and prediction and has the potential for very wide bandwidth signal processing is described and analyzed in this paper. This architecture maintains coherent operation (providing complex weights) and employs a single acoustooptic device, a photodiode, and a laser diode. The application of a multichannel acoustooptic processor to multiple antenna adaptive interference cancellation is then presented.
Using the bimodal optical computer for training a hetroassociative memory of a neural network is introduced. The storage capacity of the trained hetroassociative memory is shown to be much higher than that for the Hopefield model. A comparison with the pseudoinverse model shows that in the proposed method the vector recall accuracy is higher when the number of vectors is greater than their size. This method has the potential of being faster than the other methods because of its parallel processing nature. I.