Incoherent Optical Processing Research Articles

Hybrid algorithm for twin image removal in optical scanning holography

Optical scanning holography is an incoherent optical image processing system. It is a technique, where the complete information of an object or image will be recorded as a hologram and later reconstructed to get back the original image. In the hologram reconstruction process, a virtual image is formed along with the real image, which appears as a twin image noise. To eliminate such noises, a technique of hybrid algorithm is used while recording the hologram itself. The MATLAB R2012b image processing tool is used for simulation and the simulated values are tabulated and compared with the existing method in terms of peak signal to noise ratio, mean square error. In the reconstruction, the proposed method results are having 26% increment in the MSE and PSNR values. To further improve the MSE and PSNR values a case study using different denoising techniques combined with the proposed hybrid algorithm is used and found considerable improvement of 32%. Hence the image quality is increased.

Hybrid Algorithm for Twin Image Removal in Optical Scanning Holography

Optical scanning holography is an incoherent optical image processing system. It is a technique, where the complete information of an object or image will be recorded as a hologram and later recons...

Single-shot incoherent optical processing of microwave signals: opening the path to low cost high performance analog photonics

Single-shot incoherent optical processing of microwave signals: opening the path to low cost high performance analog photonics

Reconfigurable single-shot incoherent optical signal processing system for chirped microwave signal compression

We propose and demonstrate a reconfigurable and single-shot incoherent optical signal processing system for chirped microwave signal compression, using a programmable optical filter and a multi-wavelength laser (MWL). The system is implemented by temporally modulating a specially shaped MWL followed by a suitable linear dispersive medium. A microwave dispersion value up to 1.33ns/GHz over several GHz bandwidth is achieved based on this approach. Here we demonstrate a single-shot compression for different linearly chirped microwave signals over several GHz bandwidth. In addition, the robustness of the proposed system when input RF signals are largely distorted is also discussed.

Design of strict optical orthogonal codes with nonconstant weights for use in optical code-division multiplexing multimedia systems

We report the design of a new family of strict optical orthogonal codes (SOOCs) that permit the use of nonconstant code weights in optical code-division multiplexing (OCDM) systems. Because this new code can possess any number of pulses (i.e., 1s) in each codeword while still maintaining the minimum autocorrelation and cross-correlation constraints (i.e., “1”) for incoherent optical processing, its use can flexibly support multimedia applications in an OCDM system to meet varieties of transmission performance and traffic requirements which are demanded by different types of communication services. The method of designing the proposed codes is presented, and the bound on code length is also given.

Design of nonconstant-weight strict optical orthogonal codes

New strict optical orthogonal codes (SOOCs) are presented, which can possess any number of pulses in each codeword while maintaining the minimum auto- and cross-correlation constraint for incoherent optical processing. The proposed nonconstant-weight SOOCs (NCW-SOOCs) can be used to support data transmissions cost effectively with different quality of services in optical code-division-multiplexing systems. The design of NCW-SOOCs is discussed.

Optical scanning cryptography for secure wireless transmission.

We propose a method for secure wireless transmission of encrypted information. By use of an encryption key, an image or document is optically encrypted by optical heterodyne scanning and hence encryption is performed on the fly. We call this technique optical scanning cryptography. The output of the heterodyne encrypted signal is at radio frequency and can be directly sent through an antenna to a secure site for digital storage to be prepared for decryption. In the secure site, an identical optical scanning system to that used for encryption is used, together with a decryption key, to generate an electrical signal. The electrical signal is then processed and sent to a computer to be used for decryption. Utilizing the stored information received from the encryption stage and the electrical information from the secure site, a digital decryption unit performs a decryption algorithm. If the encryption key and the decryption key are matched, the decryption unit will decrypt the image or document faithfully. The overall cryptosystem can perform the incoherent optical processing counterpart of the well-known coherent double-random phase-encoding technique. We present computer simulations of the idea.

Bacteriorhodopsin modules for data processing with incoherent light

Incoherent optical processing with films made from the biological photochrome bacteriorhodopsin (BR) is accomplished by use of the photoinducible anisotropy of polymeric BR films. BR has two spectrally well separated states, B and M, both of which show a high degree of optical anisotropy. Whereas with green and blue light the BR molecule can be switched between the two states, the accompanying changes in the refractive index may be nondestructively read out by wavelengths in the red, e.g., at 676nm. As the sensitivity of CCD arrays is quite high for such wavelengths, even low-power light sources are sufficient for detection. We describe a BR-based XOR computing module for incoherent optical data processing.

Optical CDMA codes for use in a lightwave communication network with multiple data rates

AbstractThis paper presents a new kind of optical code‐division multiple‐access (CDMA) codes, called unequal‐length optical orthogonal codes (UL‐OOC's), for multirate data communications. The autocorrelation and cross‐correlation functions of UL‐OOC's are dependent only on each individual codeword, in spite of either an aperiodic or a periodic pulse‐sequence pattern at the input of optical CDMA decoders. This property can be thus used to support multirate data communications in a lightwave network, without any violation of the minimum correlation constraint (i.e., “1”) for incoherent optical processing. Theory and simple design of UL‐OOC's are presented. Applications of the proposed codes to multirate optical CDMA is also explained in detail.

All-optical code-division-multiplexing technique supporting multirate data communications and local-area-network interconnections.

An efficient all-optical code-division-multiplexing (AOCDM) technique is proposed to support multirate data communications and local-area-network (LAN) interconnections with multiple protocols. To achieve this goal, we use a strict optical orthogonal code (OOC) in multirate AOCDM systems to guarantee that both cross- and autocorrelation constraints are minimum (i.e., 1) for incoherent optical processing. In contrast, the use of a conventional OOC may result in correlation constraints of 2, which in turn can degrade system performance. Moreover, implementation issues on AOCDM systems are discussed. These include the design of low-cost optical transmitters and the trade-off among coherence time, spectral width, and pulse width for AOCDM systems. It is shown that multirate AOCDM systems have a high operation flexibility to support data communications and LAN interconnections of both equal and multiple bit rates. For multirate data transmissions, the proposed system can have a better bandwidth efficiency and a lower bit error rate than a system that uses a conventional OOC.

Fiber-optic code division add-drop multiplexers

We propose a new fiber-optic code division add-drop multiplexer (ADM) which not only possesses the inherent advantages of the fiber-optic code division multiple access (CDMA), but also is fully reconfigurable. Because incoherent optical signal processing is unipolar, the dropping process is accomplished by adding the inversion of the received code. The proposed ADM is applicable to both the bus and the ring topologies. The corresponding-system performance is calculated with the consideration of thermal noise, shot noise, and the amplified spontaneous emission (ASE) noise of the optical amplifier. Many interesting and useful conclusions such as the suboptimum value of various system parameters are presented.

Proposed airborne optical fiber asynchronous CDMA systems using fully optical orthogonal codes for real-time avionic data distributions and computer interconnects

We report the design of optical fiber asynchronous code-division multiple-access (CDMA) systems using fully optical orthogonal codes (FOOCs), which can be employed to support future airborne real-time communication services. The use of incoherent optical CDMA (IO-CDMA) can result in lower complexity and more reliable implementation than that of the coherent version, so this makes IO-CDMA more adequate for operation in the severe aircraft environment. When FOOCs are used in the IO-CDMA systems, the peaks of all the cross-correlation functions and all the sidelobes of any auto-correlation function are then limited to "1" (i.e., the minimum correlation constraint for incoherent optical processing) in fully asynchronous transmissions. Moreover, proposed systems can effectively support multi-rate and variable-rate data communications with no violation of the minimum correlation constraint and no change of IO-CDMA encoders/decoders. This characteristic can be used to improve the system flexibility and availability. A basic experiment is also demonstrated to verify the characteristics of FOOCs.

New photonic asynchronous-transfer-mode switch with optical signal processing and code-division multiple access

We present the design of new photonic asynchronoustransfer- mode (ATM) switches that use optical code-division multiple access (CDMA) and strict optical orthogonal codes (OOCs). All the peaks of cross-correlation functions and all the sidelobes of any autocorrelation functions for a strict OOC are always limited to be a unit pulse-amplitude (i.e., 1 in the normalized case) for incoherent optical processing, regardless of whether an aperiodic or a periodic pulse sequence is input to optical CDMA decoders. Since the coding and correlation of strict OOCs are performed in the optical domain by using optical delay lines, the processing speed of the proposed photonic ATM switch can be very high. This, in turn, can support real-time broadband communications. Owing to the correlation characteristics of strict OOCs, the proposed ATM switch can flexibly handle both equal-rate and variable-rate/ multirate communication services without violating the cross-correlation and autocorrelation constraints of 1 and with no change of optical CDMA encoders and decoders. This, in turn, can substantially improve the switch flexibility without increasing system complexity.

Coding for coherent optical CDMA networks

The adoption of incoherent optical signal processing in CDMA LANs faces limitation of the absence of complementary elements which hinder the design of optical code sequences that are fully orthogonal to each other. Coherent optical processing has been shown to be able to overcome the limitation. The paper looks at the coding aspect of CDMA LANs with coherent optical processing. The architectures of encoder/decoder and their basic phase properties are described. Based on the phase properties, methods of generating families of optical phase codes with good correlation properties are presented. The phase code families generated are then compared with optical codes used in incoherent systems, in terms of codelength, family size and correlation properties. From the comparison, it is shown that, generally, phase codes exhibit more desired features in these aspects than the conventional optical codes, and, therefore, render higher data rate and more secured transmission.

Microwave filtering realized through incoherent optical processing

Analogue microwave filters can be produced using optical components when the microwave signal is modulated onto an optical carrier wave, processed optically, and then recovered electrically. The fiber-optic network presented here displays a bandpass filter response to the modulating signal. The processing operation is based on the transversal tapped delay line technique forming an infinite impulse response structure. By employing an incoherent optical carrier wave for signal transmission, the structure's responses are modelled using linear discrete signal processing techniques.

Novel optical fiber code-division multiple access networks supporting real-time multichannel variable-bit-rate (VBR) video distributions

we design novel code-division multiple access (CDMA) networks which use strict optical orthogonal codes (OOCs) and incoherent optical processing for multichannel variable-bit-rate (VBR) video broadcasting. The proposed techniques possess the characteristics of fast access tunability and bit-rate flexibility. This in turn can facilitate real-time VBR video distributions for entertainment HDTV applications. Compared with conventional OOCs, the use of strict OOCs can ensure both auto- and cross-correlation constraints to be minimum (i.e., "1") for multichannel VBR video broadcasting and high-speed photonic switching applications. A parallel-serial hybrid architecture for all-optical tunable decoders (or encoders) is also presented to strict OOCs, which has a fast reconfiguration time to support real-time video applications in high-speed optical fiber CDMA networks.

Introduction to Fourier Optics

This is the second edition of the extremely sucessful and much acclaimed original. It deals with the extensive and fast growing field of Fourier Optics from the viewpoint of the electronics engineer or applied physicist who wishes not only to understand the underlying theoretical background (which is the basis of scalar diffraction theory), but also how optical processing can be applied. It is ideal for the student wishing to learn about Fourier Optics, as well as for the reseacher looking for an extensive summary of the relevant background, basic principles and device technology. The book can be read largely as a self contained text, but also includes an extensive and up-to-date list of references. The major changes to the original edition are a wide ranging up-date of the background chapters and the inclusion of recent advances in processing architectures and device technology. The background sections cover all the main aspects of the field including two-dimensional, space-invariant linear systems, diffraction theory, analysis of coherent and incoherent optical processing and imaging systems. The application related text addresses wavefront modulation using a variety of spatial light modulators, descriptions of passive components, information processing techniques and architectures, holography and other related recent device technology. The author, following the pattern of the first edition, presents a fresh and easy to read explanation of basic principles that describe how familiar optical components such as lenses can be treated as processing and transforming elements. He then describes how these elements can be used for signal processing including a frank and clear explanation of their scope and limitations. In a logical and flowing manner designed to enable the reader to understand the significance of the text, he regularly punctuates the explanations with real world examples to identify both the strengths and weaknesses of the techniques and technologies discussed. Each chapter includes an extensive set of questions at the end to aid learning and stimulate thought.

Shift-and-Add Method with Optically Pre-Processed Stellar Specklegrams

We propose a simple optical approach for the convolutional pre-processing of stellar specklegrams in the shift-and-add (SAA) method. It uses an incoherent optical processing, where a speckle pattern on a displaying device is re-imaged and a point-spread-function of the re-imaging system is used as the convolution kernel. This approach is suitable for use in the real-time SAA-system recently proposed. Experimental results using observational stellar specklegrams displayed on a cathode-ray-tube-monitor are reported to demonstrate that the optical pre-processing improves the signal-to-noise ratio of the final image.

Variable-bit-rate video transmission systems using optical fiber code-division multiplexing scheme

Code-division multiplexing (CDM) systems using a novel optical orthogonal code (OOC) are proposed for multichannel variable-bit-rate (VBR) video transmission over an optical fiber channel. Compared with a conventional OOC, the proposed code fully guarantees the peaks of its cross-correlation functions and the sidelobes of its autocorrelation function to equal 1 which is the minimum correlation constraint for incoherent optical signal processing, and therefore, high-performance VBR video transmission can be realized. We also give an approach for designing novel OOCs and present the principle of VBR video transmission systems using optical fiber CDM. To verify the correlation characteristics of the proposed OOC, we also demonstrate an experiment on the two-channel optical fiber CDM system. It is shown that using this novel type of OOCs one can implement a more cost-effective CDM system for VBR video transmission than the use of conventional OOCs.

Ultrafast all-optical code-division multiple-access (CDMA) fiber-optic networks

Abstract With the advanced development of fiber-optics, the large bandwidth-expansion required by spread spectrum code-division multiple-access (CDMA) can now be accomodated by using a fiber-optic channel for transmission and incoherent optical signal processing for code generation and correlation. Optical synchronous CDMA (S/CDMA), a synchronous transmission format, is introduced and compared with optical (asynchronous) CDMA. Using modified prime sequence codes, S/CDMA is shown to accomodate a larger number of subscribers and more simultaneous users than CDMA. A two-user experiment demonstrating the feasibility of optical S/CDMA is performed at 10 Mbit/s (500 Mchip/s), using optical signal processing. (A chip is a bit-representation component; please see Section 2.) An environment in which S/CDMA would be particularly suited is also discussed. In addition, recent research shows that the feasibility of optical CDMA is also determined by the architecture of the optical encoders/decoders. The coding architecture affects, for example, the amount of power loss and length of optical delays associated with code sequence generation and correlation, which, in turn, affect the power budget, size, and cost of an optical CDMA system. Therefore, a new, modified 2 n coding architecture is proposed and compared with prime and 2 n coding architectures. Study shows that the modified 2 n architecture performs the best and is particularly suitable for ultrafast all-optical processing and waveguides implementation for the future all-optical CDMA networks. A 100 Mbit/s optical CDMA experiment in free space demonstrating the feasibility of the modified 2 n coding architecture, using a serial combination of 50/50 beam splitters and retroreflectors, at 10 Tchip/s (i.e., 100,000 chip/bit) with 100 fs laser pulses is also reported.