Optical Signal Processors and Applications

Synthetic Aperture Radar (SAR) systems typically generate copious amounts of data in the form of complex values difficult to compress. Processing this data provides real-valued images that are easier to compress, however comprehensive processing capabilities are required. Optical processor architectures provide inherent parallel computing capabilities that could be used advantageously for SAR data processing. Onboard SAR image generation would provide local access to processed information paving the way for real-time decisions. This could also provide benefits to navigation strategy or automatic instruments orientation. Moreover, for interplanetary missions or unmanned aerial vehicles (UAVs), onboard analysis of images could provide important feature identification clues and could help select the appropriate images to be transmitted to the ground (Earth). This would reduce the data throughput requirements and the related transmission bandwidth. This paper reviews the preliminary work performed for the analysis of SAR image generation using an optical processor and describes the set-up of an optical SAR processor prototype. Results of optical reconstruction of SAR signals acquired with a state-of-the-art SAR satellite are presented. Real-time processing capabilities and dynamic range calculations for a tracking optical processor architecture are also discussed.

: High efficient nonlinear optical materials (NOMS) are highly required for optical computing and optical signal processing. However, currently no such practical NOMs are available. In this project, new organic NOMs have been researched and developed. New organic NOM design principle and approach have been reviewed and investigated. Four new organic NOMs, namely, CMVI, DVDA, MOHNS and HMONS have been synthesized and purified. Nonlinear optical responses of these four samples have been demonstrated and preliminary been characterized. Device fabrication and application for optical computing and optical signal processing have been investigated.

Graphene silicon devices have attracted significant attention due to their outstanding electronic and optical properties. By electrically tuning the Fermi level of the monolayer graphene sheet, electro-optic (EO) modulators have been widely analyzed. Despite significant progress has been achieved on high-speed modulation with integrated graphene silicon waveguides, it remains challenging to realize a high modulation efficiency since the light absorption in graphene is limited. Here, we propose and experimentally demonstrate a high efficiency EO modulator using a graphene-assisted tapered silicon ring resonator, where the tapered zone is covered by a graphene/graphene capacitor. This graphene-assisted tapered zone strongly enhances the graphene-light interaction that the achieved static and dynamic modulation (1KHz) depths are up to 26 dB and 12 dB, respectively. Physical mechanism of the modulation based on this nanostructure is also discussed in detail. The proposed nanostructure provides a promising alternative method for high-performance EO modulator, which is essential for th<underline>e</underline> on-chip optical communication, optical computing and optical signal processing.

Summary form only given. The author discusses developments in optical signal processing and highlights the many ways in which the technology of optical and electronic signal processing is converging.

A CMOS Infrared Optical Signal Processor for Remote Control

Optical signal processing for lightwave communications and computation: Part one

We have investigated an optical signal processor using electro-optic polymer waveguides operating at a wavelength of 1.55 mum. Due to recent developments, many useful optical devices have become available such as optical filters, modulators, switches, and multiplexers. It will be useful to have a single optical device, which is reconfigurable to implement all of these functions. We call such a device an ldquooptical signal processor,rdquo which will play a similar role to digital signal processors in electrical circuits. We realize such an optical device in a planar lightwave circuit. Since the planar lightwave circuits are based on the multiple interference of coherent light and can be integrated with significant complexity, they have been implemented for various purposes of optical processing such as optical filters. However, their guiding waveguides are mostly passive, and the only viable mechanism to reconfigure their functions is thermal effects, which is slow and cannot be used for high-speed applications such as optical modulators or optical packet switches. On the other hand, electro-optic polymer has a very high electro-optic coefficient and a good velocity match between electrical and optical signals, thus, permitting the creation of high-speed optical devices with high efficiency. Therefore, we have implemented a planar lightwave circuit using the electro-optic polymer waveguides. As a result, the structure is complex enough to generate arbitrary functions and fast enough to obtain high data rates. Using the optical signal processor, we investigate interesting applications including arbitrary waveform generators.

Design and analysis of all-optical 4 × 1 multiplexer based on 2D photonic crystal

Lenses are among the key components in optical signal processing and computing systems(1). Realization of such optical systems in a waveguide substrate has long been considered one of the major applications of integrated optics. Recently, the prospects for this realization are significantly advanced through progress in guided-wave microoptic components of both active and passive types. Aside from the study on integrated acoustooptic RF spectrum analyzers(2) that has become an international effort, serious attempts to utilize the integrated optic devices for optical computation of both analog and digital data are also being made at various research institutions. Accordingly, it is of great importance to develop viable techniques for fabrication of waveguide lenses with application to optical computing. A variety of planar waveguide lenses including the geodesic, chirp-grating, Fresnel, and Luneburg types have been reported in the literature. A common characteristic of these lenses is a relatively long focal length and a relatively small numerical aperture. It is to be noted that a channel waveguide lens involving multiple coupled-waveguides has also been proposed most recently(3). In this paper we report on the single-mode planar waveguide microlenses and microlens arrays in LiNbO3 that are formed using titanium indiffused-proton exchange technique(4). These waveguide lenses have demonstrated desirable properties including very short focal length, large numerical aperture, very small focal spot size for a wide range of focal length, and low optical insertion loss at the 6328 Å He-Ne laser wavelength.

There has been much recent interest in certain organic materials for applications in the field of nonlinear optics, where they have been shown to have significant advantages over the inorganic compounds that are used at present. A brief review of nonlinear optical effects is given, along with a description of the role of the new organic materials, including their design, fabrication and characterisation. Applications of these materials in optical signal processing and optical computing are outlined.

Optical devices using magnetostatic surface waves (MSSWs) have important applications in optical signal processing and optical computing. In this paper we propose the analysis and design of an optical mode conversion device that features improved switching efficiency achieved by the use of a new material with increased magneto-optic effect. The device consists of cerium- and bismuth-doped thin and thick garnet films. The design features 100% mode conversion over an interaction length of about 5 mm for an applied microwave power density in the range 1–10 mW/mm. Cerium- and bismuth-doped Yttrium Iron Garnet (YIG) films are fabricated by rf sputtering and their crystal properties are studied using X-ray microanalyzer and X-ray diffractometer.

We propose a surface plasmon polarization-controlled beam splitter based on plasmonic slot waveguides (PSWs). It couples light of different polarizations from a silicon nanowire into multilevel plasmonic networks. Two orthogonal PSWs are utilized as the guiding waveguides for each polarization. The proposed structure overcomes inherent polarization limitation in plasmonic structures by providing multilevel optical signal processing. This ability of controlling polarization can be exploited to achieve 3-D multilevel plasmonic circuits and polarization controlled chip to chip channel. Our device is of a compact size and a wide band operation. The device utilizes both quasi-TE and quasi-TM polarizations to allow for increased optical processing capability. The crosstalk is minimal between the two polarizations propagating in two different levels. We achieve good transmission efficiency at a wavelength of 1.55 µm for different polarizations. We analyze and simulate the structure using the FDTD method. The proposed device can be utilized in integrated chips for optical signal processing and optical computations.

We propose a surface plasmon multilevel coupler based on the orthogonal junction coupling technique between silicon nanowires and plasmonic slot waveguides (PSWs). It couples light of different polarizations from a silicon nanowire into multilevel plasmonic networks. Two orthogonal PSWs are employed to guide each polarization to its respective port. The proposed structure splits the polarizations and allows for simultaneous processing at different horizontal layers. Our device overcomes inherent polarization limitation in plasmonic structures by providing multilevel optical signal processing. This ability of controlling polarization can be exploited to achieve 3-D multilevel plasmonic circuits and polarization controlled chip to chip channel. Our device is of a compact size and a wideband operation. The device utilizes both quasi-TE and quasi-TM polarizations to allow for increased optical processing capability. The crosstalk is minimal between the two polarizations propagating in two different levels. We achieve -4.5 dB transmission efficiency at a wavelength of 1.55 &mu;m for the different polarizations in the respective ports. A transmission efficiency of -21 dB is achieved in the subsidiary port. We analyze and simulate the structure using the FDTD method. The proposed device can be utilized in integrated chips for optical signal processing and optical computations.

Interferometers are one of the basic devices in many photonics applications. Interferometers can be used in the design of optical filters, wavelength de-multiplexing (WDM), electro-optical modulators and optical sensors. They can also form the building block of optical digital signal processor (DSP). In this work, we propose novel integrated Michelson interferometer based on the Silicon on Insulator (SOI) technology with 220nm silicon device layer and working in the near infrared region. The Interferometer consists of input splitter directional coupler, two waveguide arms and directional coupler combiner with loop reflector. The interferometer transfer function and its parameters including the free spectral range (FSR), the full width half maximum (FWHM) and sensitivity were derived analytically. Using our proposed interferometer instead of the conventional Mach Zehnder Interferometer (MZI) as optical filter, electro-optical modulator or sensor will reduce the size of the device needed by a factor of two while achieving the same performance. Here, we use our Michelson Interferometer with four different path length differences resulting in FSR from 0.8nm to 6.4nm. A strip waveguide with 500nm width platform is used. These devices are suitable for optical filtering as well as wavelength de-multiplexing WDM applications. The simulation results of the proposed designs are extracted using Lumerical MODE and INTERCONNECT software tools that use scattering matrices of optical components to determine the transfer function of photonic integrated circuits (PICs). The designs were verified with three-dimensional finite-difference-time-domain (3D-FDTD) solver and show good agreement. Finally, the designs were fabricated using Electron Beam Lithography (EBL) and characterized showing also good matching with the numerical simulations results.

Slow-light transmission with high group index and large normalized delay bandwidth product through successive defect rods on intrinsic photonic crystal waveguide