Optical Processing with Slow Wave Structures: Properties and Applications

Preface. Unconventional Imaging and Processing. Coherence Methods for Unconventional Imaging Processes E.N. Leith. Some Diffractive - Optical Systems Based on Novel Gratings A.W. Lohmann. Technologies and Potential Applications of Adaptive Optics J.C. Dainty. Pattern Recognition with Joint Transform Correlators - Recent Developments E. Marom, et al. Storage of 3D Information on 2D Elements J. Shamir. Generalized Super Resolution Approach based on the Degrees of Freedom Hyper-Space Adaptation D. Mendlovic, et al. Diffractive Elements and Microoptics. Real-Time Holographic Interferometry in Photorefractive BTO Crystals Using Optical Phase Conjugation with a Low Power Laser Diode V.I. Vlad, et al. Planar Diffractive Elements for Compact Optics Y. Amitai, et al. Design and Fabrication Issues in Subwavelength Diffractive Optical Elements P. Chavel, P. Lalanne. Subwavelength and quasi-Subwavelength Diffractive Optical Elements L.M. Bernardo. Microsystems for Optical Imaging and Interconnects R. Dandliker, et al. Micro-Optical Components for Information Technology Fabricated via LIGA Technique H.-D. Bauer, et al. Nonlinear and Ultrafast Optics. Nonlinear Photonic Engineering: Physics and Applications J. Zyss, et al. Novel Optical Phenomena in Near-Critical Photorefractive Crystals: Diffusion Driven Diffraction and Spontaneous Self-Trapping B. Crosignani, et al. Frequency Upconversion of Lasers with Optical Parametric Oscillators O. Aytur. Characterization of Nonlinear Optical Materials for Photonic Applications S. Couris, et al. Adaptive Techniques in Ultrafast Optics Y. Silberberg, et al. Nonlinear Spatio-Temporal Information Processing with Femtosecond Laser Pulses Y. Fainman, etal. Optical Communication. All-Optical Semiconductor Switching Devices for Applications in Optical Communication Systems S. Diez, et al. Computer Modeling of Optical Fibers and Waveguides M.S. Al Salameh, S.A. Alkhawaldeh. Tbit/sec Optical ATM Switch Utilizing Dynamic WDM Technology D. Sadot. Towards Uniform Channel Performance in Dynamic WDM Systems and Networks A.E. Willner. Devices, Interconnects and Switching. Resonant Structures for Optical Processing and Communication A.A. Friesem, et al. Liquid Crystal Spatial Light Modulators as Intracavity Laser Elements and Dynamic Holographic Correctors for Distortions in Optical Systems V. Berenberg, et al. Fundamental Issues in Optical Interconnections H.M. Ozaktas. The Electroholographic Optical Switches and Interconnects A.J. Agranat, et al. VIVALDI -- Variations on a Theme of Optical Crossbars T.J. Hall. Laser-Material Interactions and Optical Storage. Laser Materials Processing for Optoeelectronics and Information Systems N.A. Vainos. Recording in Quantum Dot Glasses by Pulsed Laser Irradiation Y. Kaganovskii, et al. Photorefractive Volume Holographic Memories for Associative Storage and Processing in a Multimedia Environment P.A. Mitkas, G. Betzos. Characteristics and Applications of Volume Phase Holographic Gratings Recorded in Photo-Thermo-Refractive Glasses M.G. Moharam, S. Dunn. Optical Research in Israel. Electrooptics in Israel M. Oron. Subject Index. Author Index.

Teleoperation system performance suffers from the delays in communication lines. These delays are usually variable time delays. The customary wave variable technique used for constant time delays cannot provide satisfactory results to stabilize the system under variable delays. Another problem is observed in the position tracking performance of the limited-workspace teleoperation systems. Although wave variable technique is proven to track position demands successfully under constant time delays given that there is no communication failure, position tracking performance also degrades under variable delays. In this paper, a new controller is proposed to stabilize the system and enhance position tracking performance under variable time delays. This proposed controller is then applied to an identical master-slave teleoperation configuration which qualifies as a limited-workspace teleoperation system.

Surface-Emitting-Laser-based optical functional devices have promising features for photonic switching and optical data processing. All photonic switching networks need control signals to be sent into the nodes to allow for appropriate routing of traffic.') Control injection, thus, must be taken into consideration more in photonic switches. An optical self-routing switch has been proposed where a node consists of pnpn-Vertical to Surface Transmission ElectroPhotonic Devices with Vertical Cavities (VC-VSTEPS).~) The routing for optical data signals are controlled by an optical pilot signal placed at the head of the optical data signals. However, this switch still needs electric timing signals to be applied to the VC-VSTEPs, which might cause electromagnetic interferences among a large number of internal electric lines, and a delay in the timing signals due to parasitic capacitances. Therefore, it is desirable that the timing signals are further injected optically. This paper reports on VSTEP-based pixels aiming for optically controllable nodes. The pixel consists of a VSTEP using a four-terminal pnpn structure with two distributed Bragg reflectors (DBRs) (Fig. 1). The fabrication process includes two-step mesa etching: 1) to the n-doped gate layer, and 2) to the n-doped DBR layer. The n- and p-gate electrodes are formed on the second mesa with Zn diffusion for the p-gate. In comparison to twoterminal VC-VSTEPs3), the structure provides variable switching voltage characteristics and gate turn-off operation by means of carrier injectiodextraction through the gate terminals. Also, this structure allows the formation of a hetero-junction bipolar transistor (HBT), or a hetero-junction photo-transistor (HPT) together with the pnpn-structure. These two features, in combination, expand flexibility in device configuration to meet the demands of photonic switching and processing systems. As an example, a pixel has been demonstrated for an optical self-routing switch with optical gating and optical reset operations. Figure shows an equivalent circuit of the pixel. When the optical gate pulse is incident on the HFT1, current is injected to the pnpn device, resulting in a reduction of switching voltage, and allowing turn-on by the input optical pulse. Applying the gate pulses to the pixels with proper time delays, the pilot signal can select one pixel in which the pilot signal coincides with the gate signal. 2 is used for the optical reset. The optical reset pulse incident on the HPT2 removes the stored charge in the pnpn-device through the ngate. Figure 3 shows voltage-current and light-current characteristics of the fabricated device with various current injections from the n-gate. The switching voltage without n-gate injection is 3.8 V and the threshold current is 35 mA. A common-emitter current gain of 180 is obtained for the npn-HPT using an n-gate as a collector and a cathode as an emitter. Figure 4(a) shows the optical gating operation. A bias voltage of 3V was applied to the anode. The reset is also achieved as shown in Fig. 4(b). Optical energies obtained for the input, gate and reset are 8.0 pJ, 0.5 pJ and 10 pJ, respectively. Reduction in these values will be achieved by a decrease in device size.

Bi-activated MgGa2O4 phosphors with rich defect energy levels: Spectral property and optical storage applications

Nowadays, the coherent optical communication system plays an important role in communication field because of large capability and bandwidth. A coherent optical communication, based on high-order modulation and digital signal processing technologies, consists of optical transmitters, optical fiber lines, optical amplifiers and optical receivers. In the high-speed coherent optical communication system, the phase noise from the transmitter laser and the local oscillator laser can significantly degrade the performance of the signal transmission and detection, especially for the systems using high-order modulation format, such as m-ary phase shift keying (mPSK) and m-ary quadrature amplitude modulation (m-QAM). Therefore, investigations on laser phase noise compensation algorithm based on digital signal processing technologies has become more and more significant. In this work, a multi-ring carrier phase recovery algorithm is developed for compensating the laser phase noise in optical fiber communication systems using high-order modulation formats. Degradations on the performance of communication systems due to the laser phase noise have been investigated. The system performance using the proposed algorithm and the conventional Viterbi-Viterbi algorithm were also evaluated in 9-channel and 15- channel, 32-Gbaud, Nyquist-spaced QPSK, 16-QAM, 64-QAM and 256-QAM coherent transmission systems with considering the impact of the laser phase noise. It is found that the phase noise leads to stricter constraints on the linewidths of transmitter-side and receiver-side lasers, and it can greatly degrade the achievable information rates in communication systems. Besides, compared to the conventional Viterbi-Viterbi algorithm, which is usually applied in the QPSK system, our proposed algorithm can also well mitigate the laser phase noise in 16-QAM, 64-QAM and 256-QAM optical communication systems.
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Modern optical communication systems require tunable optical delay lines for synchronization of data packages. Chirped fiber grating are typically used as a dispersive element for this application. Fiber-based schemes, however, suffer from bulkiness, slow response and/or low time resolution. Integrated photonics on silicon is one alternative approach. Several more advanced device architectures have been subsequently demonstrated on silicon, including ringresonator and photonic crystal (PhC) line-defect waveguide types. The coauthors of this paper have recently proposed a novel class of tunable optical delay lines based on apodized grating waveguides. It was shown that high bit-rate operation is achievable by cascading two complementary (inward and outward) apodized gratings. In this paper, we have experimentally demonstrated our proposed approach and studied performance of the fabricated delay lines for optical telecommunication applications. The bit-rate was extracted from broadening of transform-limited input pulses of the measured dispersion of the delay lines. Characterization of the compact delay lines shows that the single grating devices offer true-time delays as long as 164 ps, tuning range of ~ 81 ps, and a minimum bit rate of ~ 15 Gb/s. The cascaded scheme offer true-time delays of 82 ps and tuning range of 32 ps and can potentially operate at bit rates as high as 107 Gb/s.

Designs and simulated performance for W-band traveling wave tubes are presented for three slow wave structure types (dielectric, serpentine waveguide, and cavity-loaded helix). Output powers are 120 and 245 W at 94 GHz for dielectric and serpentine, respectively, with 5–6 GHz bandwidth (9 GHz in serpentine with equalization).

High speed optical communications systems are evolving rapidly. Commercial systems achieve high aggregate data rates utilizing wavelength division multiplexing, where multiple wavelength channels carry information at electronic rates, typically 2.5 Gb/s. Data encryption in these systems will most likely be implemented electronically. However, future system may also utilize time division multiple access (TDMA) schemes and technologies for 100 Gb/s, single stream TDMA networks are currently being developed. These high speed TDMA networks will rely on all-optical switches and processors to interface the high-speed electronics in the users nodes to the ultra-high-speed optical data bus. Data encryption in these networks may need to be implemented using optical logic gates. Straightforward duplication of electronic encryption circuits using optical logic gates is not feasible because optical logic gates have low fan-out, require high optical powers, are difficult to synchronize and have high latency. In this paper, we propose a high- speed electro-optic scheme for reconfigurable feedback shift registers (RFSRs) that relies upon electronic encryption circuits to reconfigure a sequence of optical logic gates and which makes use of the latency in the optical gates as memory. We show that, for linear RFSRs, the low number of optical gates is not a drawback and that the period of the sequences is generally very large. Non-linear feedforward functions, such as all-optical bit swapping, many also be introduced to improve the pseudo-random properties of the sequences.

Recent years have seen a surge in the usage of optical signals for real-time wireless data transfer in a wide range of underwater applications because of their large bandwidth, higher data rates, low latency, security, power, and cost efficiency. However, underwater optical wireless communication (UOWC) is substantially impaired by absorption, scattering, and turbulence effects that induce scintillations during optical signal propagation. A potential modulation scheme can be a promising solution to overcome such scintillations. The pulse position modulation (PPM) may address the fading and optical irradiance across the underwater channels while providing the power efficiency to the wireless sensor networks (WSNs). To access the link performance under the proposed modulation scheme, the closed-form expressions for outage probability and BER metrics are typically required. Unlike horizontal and single-layered models, this work evaluates the performance of vertical cascaded links in the North and Baltic oceans affected by the combined effects of absorption, scattering, and turbulence by utilizing an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i>-ary PPM scheme. The unified expressions for the probability density function (PDF) and cumulative distribution function (CDF) are obtained by integrating depth-dependent layered Gamma-Gamma (GG) turbulence with absorption- and scattering-based path-loss (PL) attenuations. The closed-form expressions for the outage probability (OP) and the average bit error rate (ABER) are derived by following the derived PDF and CDF to evaluate the end-to-end (E2E) performance under<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i>-ary PPM. The analytical results are validated using experimentally extracted channel parameters and rigorous Monte-Carlo (MC) simulations.

Tunable optical delay devices have numerous applications in optical communications [1] and have been successfully implemented using slow light elements and fiber or waveguide gratings. There has been considerable interest in siliconon- insulator (SOI) as a technology platform for compact integration of optical signal processing systems. SOI-based delay lines have been realized using coupled ring resonators [2], photonic crystals [3], and various Bragg grating-based configurations including single or coupled chirped sidewall gratings [4,5] as well as tapered rib waveguide gratings [6]. By linearly chirping the period in sidewall gratings, relatively small delays (a few ps) over a bandwidth of tens of nm were demonstrated [4]; with tapered waveguides, significantly larger delays (300-500 ps) were obtained, albeit over a narrower bandwidth (&lt; 2 nm) [6]. On the other hand, some signal processing applications may require large delays (e.g., tens to hundreds of ps) over large bandwidths (several to tens of nm). Several designs have been proposed to meet these requirements, e.g., a step-chirped rib waveguide grating providing 50 ps delay over 15 nm [7] or complementary apodized sidewall gratings providing up to 275 ps over 3 nm [8], however, they have not been realized experimentally. In this paper, we demonstrate discretely tunable optical delay lines that provide tens of ps delay (up to 65 ps) in steps of 15-32 ps over bandwidths of several tens of nm (35-70 nm). The devices are fabricated on SOI using electron beam lithography and implemented through two different approaches: serial sidewall Bragg grating arrays and the step-chirped sidewall Bragg gratings.

W-band TWTs are key devices for high-frequency and high-power amplifiers used in high-resolution imaging applications. This paper presents the design, simulation, and fabrication of W-band pulsed TWTs. For higher power and broader bandwidth, TWTs have been developed using all-metal folded waveguide (FWG) slow-wave structures, diamond-disc windows, and horseshoe-shaped carbonized alumina attenuators. The test results show that W-band FWG pulsed TWTs can reach over 100 W output power with 6.7 GHz bandwidth and over 33 dB saturated gain at 20% duty cycle, while the maximum output power exceeds 200 W.

One of the key elements for modern microwave circuits is a delay line, which is widely utilized for the signal generation as well as processing. Spin-wave delay lines based on ferrite films provide a high delay time and small dimensions. Typically, the performance characteristics of such lines are tuned by the variation of an externally applied magnetic field characterized by some drawbacks. The phenomenon of a metal–insulator transition (MIT) in the phase change materials permits to improve the performance characteristics of the spin-wave delay lines. In particular, this concept allows to reduce the power consumption and improve the control speed of a delay time. Aim. Development of a tunable spin-wave delay line based on ferrite and vanadium dioxide films, as well as the study of its performance characteristics. Methods. Experimental investigations were carried out for the delay line composed of the yttrium iron garnet (YIG) and vanadium dioxide (VO2) films. The ferrite waveguide was fabricated from a single-crystal YIG film grown on a gallium gadolinium garnet substrate. A vanadium dioxide film was formed on a silicon dioxide substrate by DC reactive magnetron sputtering. The microwave measurements were carried out using the vector network analyzer R&amp;S®R ZVA40. Results. It was shown that heating of the VO2 film induces a sufficient drop of its resistance that causes the transformation of the spin-wave dispersion characteristic. This leads to the decrease in the group velocity of the propagating waves providing a growth of a delay time. Namely, experimental structure of 5-mm length offers a tunable time delay range from 130 up to 150 ns at the operating frequency of 4.33 GHz. Conclusion. A proof-of-principle for the MIT control of the delay time composed on the YIG-VO2 structure has been presented. It was shown that a switch of VO2 film from the isolating into conducting state produces a 15% change in the delay time. The considered microwave delay lines look favorable for applications as a complimentary part to the traditional approach for general computing and microwave signal processing.

Deep neural networks (DNNs) have been applied to recover signals in optical communication systems and have shown competence of mitigating linear and nonlinear distortions. However, as the data throughput increases, the heavy computational cost of DNNs impedes them from rapid and power-efficient processing. In this paper, we propose an optical communication signal recovery technology based on a photonic convolutional processor, which is realized by dispersion delay unit and wavelength division multiplexing. Based on the photonic convolutional processor, we implement an optoelectronic convolutional neural network (OECNN) for signal post-equalization and experimentally demonstrate on 16QAM and 32QAM of an optical wireless communication system. With system parameters optimization, we verify that the OECNN can achieve accurate signal recovery where the bit error ratio (BER) is below the 7% forward error correction threshold of 3.8×10-3 at 2Gbps. With adding the OECNN-based nonlinear compensation, compared with only linear compensation, we improve the quality (Q) factor by 3.35 dB at 16QAM and 3.30 dB at 32QAM, which is comparable to that of an electronic neural network. This work proves that the photonic implementation of DNN is promising to provide a fast and power-efficient solution for optical communication signal processing.

Fourier methods are widely used in optical information processing for time domain waveform synthesis and detection. In such approaches an input pulse is spectrally decomposed and modulated by an appropriately designed spectral filter. In general, various ultrafast applications may need either generation or characterization of waveforms depending whether their frequency response is or is not known a priori. Ultrafast pulses prove useful in driving or probing such systems because their broad, deterministic complex spectral amplitude “sees” a large continuous portion of the system transfer function. Traditionally, space domain spectral decomposition is used to perform optical Fourier processing, where pairs of gratings and lenses are used to decompose the spectral content of the pulsed, optical waveforms. Liquid crystal and acousto-optic (AO) modulators provide a means for introduction of somewhat arbitrary system transfer functions. More recently, compact waveguide-based approaches have used arrayed waveguide gratings (AWGs) to perform an analogous spectral decomposition to those achieved with traditional, free-space coupled gratings. Information processing arrangements using the space domain for transverse spectral decomposition benefit from the maturity of such techniques, with respect to basic understanding, component quality, and the excellent phase control that free-space manipulations provide. Component insensitivity to optical power permits the shaping and detecting of high peak power pulses used to drive nonlinear optical systems. Furthermore, nonlinear optical elements can be introduced directly into these processors to provide unique ultrafast waveform synthesis capabilities with response times in the range of femtoseconds. Drawbacks to free-space approaches include scaling in volume to achieve large time bandwidth products (TBWPs) and limiting the temporal extent of waveforms coupled back into a single-mode fiber (SMF). The origin of this last restraint is the time∕space interrelation inherent in traditional pulse shaping devices. AWG approaches rely on complex waveguide elements to circumvent large processor volumes and time∕space coupling issues, but they too are practically limited by fabrication requirements. The number of resolvable spots in the output waveform for both Fourier synthesis and direct space-to-time AWG approaches is equal to the number of waveguide channels. An alternative approach to Fourier processing relying on a single transverse spatial mode can better integrate with fiber systems and photonic lightwave circuits and will scale in length only for the achievement of large TBWPs. Fiber-based and fiber-integrated processors can manipulate optical waveforms in the time domain exploiting chromatic dispersion for longitudinal spectral decomposition and applying to it Fourier synthesis techniques. Drawing on the identical mathematical treatments of diffraction in space and dispersion in time, an approximate Fourier transform (FT) of an incident optical signal is achieved via chromatic dispersion after reaching the so-called “far-field approximation.” With such an amount of dispersion, the temporal waveform closely resembles the spectrum. Such a waveform is called a longitudinal spectral decomposition wave (SDW). A time-variant element (e.g., modulator) filters this SDW. And it is possible to recompose the pulse waveform through propagation in a conjugate dispersion source matched (i.e., of opposite sign but equal magnitude) to the first dispersive element. The number of resolvable spots that such a processor offers relies on a suitable modulation scheme and the experimental ability to disperse a sub-picosecond pulse using second-order dispersion.

A phenomenological model for photochromic films incorporating bacteriorhodopsin (BR) molecules is developed. Equations for the propagation of electromagnetic waves inside a BR film and the temporal evolution of the volume population densities of the molecular states of BR are derived and subsequently coupled in a self-consistent fashion by means of an expression for the overall susceptibility of the film. Solutions for the scattered fields in a slab geometry are given in terms of the appropriate dyadic Green’s functions, and perturbative approximations through the Born and the Rytov methods are discussed. The theory provides an analytical framework within which various optical data storage and processing applications for BR films may be studied.