Frequency encoded optical four-bit adder/subtractor with control input using semiconductor optical amplifiers

Optical adder/subtractor for two four-bit frequency encoded binary numbers are proposed and designed based on four wave mixing, add drop multiplexing and frequency conversion in semiconductor optical amplifier. The input bits and the control input are intensity-modulated signal of two specific frequencies suitable for optical communication in the C band of wavelength. The device can distinguish negative and positive results and controlled operation are most promising in this proposal. The use of semiconductor optical amplifiers along with frequency encoding makes the system very fast and useful for future optical communication and computation systems.     

All-optical carry lookahead adder with the help of terahertz optical asymmetric demultiplexer

An all-optical model of carry lookahead adder (CLA) implemented with a semiconductor optical amplifier (SOA)-assisted Sagnac interferometer (TOAD) is presented. The model accounts for the SOA small signal gain, linewidth enhancement factor, the switching pulses energy and width and the Sagnac loop asymmetry. Adder is a very basic component in a central processing unit. The CLA is the highest speed adder nowadays. Theoritical model is presented and verified through numerical simulation. The method promises both higher processing speed and accuracy. The model can be enhanced the functionality in which carry lookahead adder is the basic building block.     

Demonstration of an optical pipeline adder and design concepts for its microintegration

A fully functional optical pipeline adder based on systolic arrays and optical symbolic substitution (OSS) is demonstrated. By pupil division four OSS-rules are applied to a dataplane in one single optical path. The design concept includes the possibility of microintegration by adapting the modular system design to features of typical micro-optical devices.     

One-step optical negabinary and modified signed-digit adder

A one-step algorithm for parallel negabinary addition of two negabinary numbers is achieved by minimizing the truth-table for the two-step algorithm. Without increasing the encoding cell size or adding complexity of the corresponding optical system, the proposed one-step scheme doubles the computation speed. The optical system can also be used to realize a one-step modified signed digit adder. Additionally, optical implementation of negabinary multiplication using this proposed one-step optical adder is discussed.     

Analytical approach of developing wavelength encoded AND, NAND and X-OR logic operations and implementation of the theory using semiconductor optical amplifiers

Frequency encoding technique is a very promising and faithful technology for very fast long-haul optical communication and super fast computation. Implementation of different logic gates based on the principle of frequency conversion is the key mechanism of frequency encoded data processing and networking. It is established that semiconductor optical amplifiers (SOA) have been used successfully for the purpose of frequency conversion. One of the important techniques of frequency conversion is the conjugate beam generation by four wave mixing (FWM) in SOA and ultimately conversion of it into desired frequency by means of reflecting semiconductor optical amplifier (RSOA). However the efficiency of conjugate beam generation is restricted by polarization dependent gain saturation of SOA. This dependency can be successfully removed using polarization diversity scheme. Another technique of the frequency conversion is based on nonlinear rotation of the state of polarization of the linearly polarized probe beam. An important advantage of using polarization rotation in SOA is that a small change in rotation of the state of polarization will lead to a large difference in output power. Here in our present communication we propose a method of developing wavelength encoded AND, NAND and X-OR logic operations exploiting the above mentioned functions of SOA. For this purpose we have developed an analytical treatment based on which above mentioned three logic gates are conducted. The satisfactory simulation result proves also the validity of the developed theory.     

All-optical prefix tree adder with the help of terahertz optical asymmetric demultiplexer

We propose and describe an all-optical prefix tree adder with the help of a terahertz optical asymmetric demultiplexer (TOAD) using a set of optical switches. The prefix tree adder is useful in compound adder implementation. It is preferred over the ripple carry adder and the carry lookahead adder. We also describe the principle and possibilities of the all-optical prefix tree adder. The theoretical model is presented and verified through numerical simulation. The new method promises higher processing speed and accuracy. The model can be extended for studying more complex all-optical circuits of enhanced functionality in which the prefix tree adder is the basic building block.     

All-optical adder/subtractor based on terahertz optical asymmetric demultiplexer

An all-optical adder/subtractor （A/S） unit with the （TOAD） is proposed. The all-optical A/S unit with help of terahertz optical asymmetric demultiplexer a set of all-optical full-adders and optical exclusive- ORs （XORs）, can be used to perform a fast central processor unit using optical hardware components. We try to exploit the advantages of TOAD-based optical switch to design an integrated all-optical circuit which can perform binary addition and subtraction. With computer simulation results confirming the described methods, conclusions are given.     

Optical computation based on nonlinear total reflectional optical switch at the interface

A new scheme of binary half adder and full adder is proposed. It realizes a kind of all-optical computation which is based on the polarization coding technique and the nonlinear total reflectional optical switches.      

A new scheme of all-optical adder logic operation based on nonlinear property of the material and polarization encoding technique

Optical nonlinear materials have been used for several digital logic and arithmetic operations. These operations are conducted in real time domain as per their operational speed is concerned. In this paper authors propose a new method of all optical half adder scheme. This type of switching is based on polarization properties of light along with nonlinear properties of material. As the state of polarization of light ensures that the field intensity level of the light signal is the same in whole operation, the scheme may be extended to some wide applications in all optical parallel computation and information processing.     

Quantum Dot Versus Quantum Well Semiconductor Optical Amplifiers for Subpicosecond Pulse Amplification

The performance of quantum well and quantum dot semiconductor optical amplifiers was theoretically investigated. The effects on subpicosecond pulse propagation due to gain and refractive index dispersion, calculated using a microscopic polarization equation and a reduced wave equation in the linear regime including the background refractive index dispersion, were used in the comparison. In particular, the spectral shift and phase modulation imposed on the pulse were compared. It is shown that quantum dot amplifiers suffer comparable spectral shifts to the quantum well amplifier, strong linear frequency chirp and large pulse broadening. In quantum dot amplifiers with small inhomogeneous broadening, similar pulse break-up is shown as that calculated for the quantum well amplifier. In quantum dot amplifiers with large inhomogeneous broadening, the background refractive index dispersion makes the linear frequency chirp the dominant feature. In the light of our calculations, the advantages and disadvantages of quantum dot and quantum well amplifiers are discussed.     

Enhancement of ring network in presence of optimized semiconductor optical amplifiers

By utilization of optimized semiconductor optical amplifiers, the design of ring network is achieved for a large number of nodes with reasonable quality and zero power penalty. The gain fluctuation occurs due to variation in parameters of the semiconductor optical amplifier for ring network. It is evaluated that nodes go on decreasing with increase in gain saturation of the semiconductor optical amplifier.     

Strained layer quantum well semiconductor optical amplifiers: Polarization insensitive amplification

Polarization insensitive optical amplification was demonstrated in newly developed semiconductor optical amplifiers that have strained GalnAsP quantum well structures. We tailored the active region of the quaternary strained layer quantum well structure with a small biaxially tensile strain of 0.2% in the well layers for polarization insensitive operation.     

Dynamics of optical pulse amplification and saturation in multiple state quantum dot semiconductor optical amplifiers

We have developed a novel analytical model, which describes the dynamic characteristics of optical pulse amplification and saturation in three state quantum dot (QD) semiconductor optical amplifiers (SOAs). The model takes into account the effect of the ground state, the excited state and the 2-dimensional wetting layer. The model is simple, accurate and fast, which makes it suitable for device design and characterization. The derived model has been utilized to study large-signal cross-gain modulation and crosstalk in multi-channel QD-SOA. Analytical expressions for large signal cross-gain modulation and crosstalk in multichannel SOA are derived. The effect of the dot relaxation/escape lifetimes and energy separation between QD states on cross-gain modulation and crosstalk are also studied. Our calculations show that by reducing QD energy state separation, via engineering the dot size and composition, one can reduce the cross-gain modulation efficiency and reduce crosstalk in multi-channel QD-SOAs.     

A method of implementation of frequency encoded all optical encryption decryption using four wave mixing

All optical encryption decryption method using frequency encoding is proposed based on semiconductor optical amplifiers. The plain text and key are encoded in frequency encoding format i.e. the states of information ‘0’ and ‘1’ are represented by two different frequencies in the c-band. The ultra fast speed of operation of the devices used for the implementation of this system makes it very attractive for future all optical secure communication network. A simple method of conversion of frequency encoded data stream and intensity encoded data stream is also described, which enables us to use same technology of production and detection of intensity encoded data signals until new techniques based on frequency encoding comes out.     

A novel frequency encoded all optical logic gates exploiting polarization insesensitive four wave mixing in semiconductor optical amplifier, filtering property of ADD/DROP multiplexer and non-linearity of reflective semiconductor amplifier

All optical logic gates exploiting polarization independent four wave mixing in semiconductor optical amplifier (SOA), filtering property of ADD/DROP multiplexer (ADM) and non-linearity in reflective semiconductor optical amplifier (RSOA) have been proposed. The logic gates proposed are polarization independent which ensures hardware simplicity and greater speed. The all optical frequency encoded logic gates NOT, OR, NOR, AND, NAND, X-OR, X-NOR are implemented which are very useful in optical computing ad signal processing, cryptography, etc. The logic gates proposed have the advantages that there is no intensity loss dependent problem, and are polarization and temperature insensitive.     

Method of implementing frequency-encoded NOT,OR and NOR logic operations using lithium niobate waveguide and reflecting semiconductor optical amplifiers

Optics has already proved its strong potentiality for the conduction of parallel logic, arithmetic and algebraic operations. In the last few decades several all-optical data processors were proposed. To implement these processors different data encoding/decoding techniques have been reported. In this context, polarization encoding technique, intensitybased encoding technique, tristate and quaternary logic operation, multivalued logic operations, symbolic substitution techniques etc. may be mentioned. Very recently, frequency encoding/decoding technique has drawn interest from the scientific community. Frequency is the fundamental character of any signal; and it remains unaltered in reflection, refraction, absorption etc. during the propagation and transmission of the signal. This is the most important advantage of frequency encoding technique over the conventional encoding techniques. In this communication the authors propose a new scheme for implementing NOT, OR and NOR logic operations. For this purpose co-propagating beams having different frequencies in C-band (1535–1560 nm) have been used for generating cascaded sum and difference frequency, exploiting the nonlinear response character of periodically poled LiNbO₃ waveguide. The cross-gain modulation property of the semiconductor optical amplifier (SOA) and the wavelength conversion property of the reflecting semiconductor optical amplifiers (RSOA) are exploited here to implement the desired optical logic and arithmetic operations.     

All optical read only memory with frequency encoded addressing technique

A semiconductor amplifier (SOA) based all optical read only memory (ROM) is proposed and discussed using non linear polarization rotation. The ROM based on 2-4 line decoder is based on frequency encoded addressing technique, which has several advantages over other encoding techniques. The SOA has sufficiently high switching speed with property of efficient ON/OFF contrast ratio, which makes it attractive for all optical processors in computation and communication. The author has discussed the addressing and storing of the characters of American standard code for exchange of information.     

Strained layer quantum well semiconductor optical amplifiers: Polarization insensitive amplification

Abstract

Polarization insensitive optical amplification was demonstrated in newly developed semiconductor optical amplifiers that have strained GalnAsP quantum well structures. We tailored the active region of the quaternary strained layer quantum well structure with a small biaxially tensile strain of 0.2% in the well layers for polarization insensitive operation.     

Novel effects in extremely broadband semiconductor optical amplifiers with non-identical quantum wells

An extremely broad emission spectrum is obtained for semiconductor optical amplifiers with multiple quantum wells fabricated on the substrate. The spectral width is nearly 400 nm (1200–1600 nm), which covers the entire usable bandwidth of an optical fiber. Broadband characteristics allow observing three novel effects: (i) the bi-directional guided effect of lasing mode in a bent waveguide of semiconductor optical amplifiers, (ii) the optical switching effect in one semiconductor optical amplifier for optical communication band, and (iii) the effect of separate confinement heterostructure layer thickness.     

Design and analysis of optically pumped semiconductor VECSEL with ANECz optical control layer

Through the reversible isomerization of trans-cis-trans under the linear polarization light, the molecules of azo materials have the same tropism which is vertical to the polarization of light. This means that azo materials have photo-induced birefringence which is related to optical power and polarization angle of the light. Based on the photo-induced birefringence of azo materials, we design a new type of optically pumped semiconductor vertical external cavity surface emitting laser （OPS-VECSEL） which can control the polarization and frequency of the ejection laser. The functional molecules of azo materials are [3-azo- （4＇nitro）]- （9-ethyl）-carbazole （ANECz）.