A novel frequency encoded all optical CNOT gate exploiting difference frequency generation and implementation of fast binary adders using frequency encoding and nonlinear dielectric films

Optics has an important role in logic implementation and computation is established in two and half decades by many researchers. Recently frequency encoding technique is established. This technique does not suffer from intensity dependent loss problems like other schemes. Amorphous dielectric thin films with reflecting edges can also be used for logic realization and has very fast response speed. It also does not use any semiconductor device and simple to construct. In this communication the authors have proposed all optical CNOT gate using frequency encoded difference frequency generation exploiting nonlinear response of some material and implementation of binary adders by CNOT gate and dielectric thin film AND gate.     

Implementation of a novel hybrid encoding technique and realization of all optical logic gates exploiting difference frequency generation alone

A novel hybrid encoding technique scheme is proposed. Using this technique and difference frequency generation different all optical logic gates NOT, OR, AND, NAND, NOR, and X-OR are realized.     

An all optical frequency encoded demultiplexer with tri-state logic

Optics has already been established its significant application over electronics using the nonlinearity of optical medium. The use of semiconductor optical amplifier (SOA) as a nonlinear medium has remarkably extended in the field of optoelectronic technology due to his high switching speed and high extinction ratio. The SOA based devices are used in multifunctional way mainly in switching, multiplexing, de-multiplexing and wavelength conversion. Here in this paper the authors propose a new demultiplexer scheme with the broad area semiconductor optical amplifier (BSOA) using the frequency encoding techniques and tri state logic. Frequency encoding techniques and tri-state logic in optics are already been established as a potential mechanism.     

A method of optical implementation of frequency encoded different logic operations using second harmonic and difference frequency generation techniques in non-linear material

Optics has already been proved its successful roles for conduction of parallel logic, arithmetic and algebraic operations. Since last few decades many types of optical data processors were proposed. To implement these processors different data encoding/decoding techniques have been reported. In this context polarization encoding technique, tristate, quartenary logic, multivalued logic, symbolic substitution techniques etc. may be mentioned. Very recently, frequency encoding/decoding technique have also been well established. The potential advantage of frequency dependent encoding/decoding is that, as the frequency being the fundamental character of a signal; it will remain unaltered in reflection, refraction, absorption etc. during transmission of the signal. In this communication the authors propose a scheme for implementing different logic operations adopting frequency based encoding technique. For this purpose the second harmonic generation and difference frequency generation techniques are used by exploiting the non-linear response character of some materials.     

Terahertz optical frequency comb generation with optimized cascaded difference frequency generation

Optical Review - A novel scheme that generates terahertz optical frequency comb (THz OFC) based on optimized cascaded difference frequency generation (OCDFG) with an aperiodically poled lithium...     

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.     

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.     

Method of developing an all optical wavelength encoded single bit comparator exploiting four wave mixing and wavelength filtering character of nonlinear semiconductor optical amplifiers

Data Comparator is the integral part of arithmetic and logical unit of any electronic or optical data processor. Due to some inherent limitations of electronics it is not possible to obtain super fast data processing (over Terahertz limit) from electronic comparator. Again frequency encoding technique has been established as an excellent one over the other optical data encoding techniques. Semiconductor optical amplifiers (SOA) technologies have shown its potentiality of realising many all-optical systems. In this communication the authors have proposed a new all-optical wavelength encoded single bit binary comparator exploiting the four wave mixing and wavelength filtering property of nonlinear semiconductor optical amplifier.     

A novel method of developing all-optical frequency encoded memory unit exploiting nonlinear switching character of semiconductor optical amplifier

The very fast running optical memory and optical logic gates are the basic building blocks for any optical computing data processing system. Realization of a very fast memory-cell in the optical domain is very challenging. In the last two decades many methods of implementing all-optical flip-flops have been proposed. Most of these suffer from speed limitation because of low switching response of the active devices. In our present communication the authors propose a method of developing a frequency encoded memory unit based on the switching action of semiconductor optical amplifier (SOA). Nonlinear polarization rotation characters of SOA and ‘SOA based Mach-Zehnder Interferometer’ switch, i.e. ‘SOA-MZI’ switch, are exploited for the purpose of some switching action with least switching power (<−3 dB_m) and high switching contrast ratio (20 dB). Here two logic states (‘0’ state and ‘1’ state) of the memory is encoded by two different frequencies, which will remain unchanged throughout the data communication irrespective of loss of light energy due to reflection, refraction, attenuation, etc. Though the SOA based switch runs with the operational speed 100 Gb/s, still due to the presence of the other optical components in the memory unit, the overall speed of the proposed system will come down to 10 Gb/s.     

Infrared laser generation by cascaded difference frequency generation combined with optical parametric oscillator

Optical Review - We introduce an infrared laser generation scheme by cascaded difference frequency generation (CDFG) combined with optical parametric oscillator (OPO). An inventive infrared laser...     

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.     

A method of developing frequency encoded multi-bit optical data comparator using semiconductor optical amplifier

Optical data comparator is the part and parcel of arithmetic and logical unit of any optical data processor and it is working as a building block in a larger optical circuit, as an optical switch in all optical header processing and optical packet switching based all optical telecommunications system. In this article the author proposes a method of developing an all optical single bit comparator unit and subsequently extending the proposal to develop a n-bit comparator exploiting the nonlinear rotation of the state of polarization of the probe beam in semiconductor optical amplifier (SOA). Here the dataset to be compared are taken in frequency encoded/decoded form throughout the communication. The major advantages of frequency encoding over all other conventional techniques are that as the frequency of any signal is fundamental one so it can preserve its identity throughout the communication of optical signal and minimizes the probability of bit error problem. For frequency routing purpose optical add/drop multiplexer (ADM) is used which not only route the pump beams properly but also to amplify the pump beams efficiently. Switching speed of ‘MZI-SOA switch’ as well as SOA based switches are very fast with good on–off contrast ratio and as a result it is possible to obtain very fast action of optical data comparator.     

Effects of gain saturation on terahertz radiation via optical difference frequency generation

Numerical studies on stability of terahertz (THz) radiation generation based on difference frequency generation in nonlinear crystals are reported. When the gain saturation is achieved at a wavelength that corresponds to an optimal crystal length, the maximal output of THz radiation could be obtained. As a result of crystal absorption, the gain saturation region of THz radiation is unstable region for output. The stability of THz radiation is determined by the stability of pump in the stable region where behind of the gain saturation.     

Continuous-wave 4.3-mum intracavity difference frequency generation in an optical parametric oscillator

We have achieved 150 mW of cw output at 4.3mum, using difference frequency mixing in a singly resonant optical parametric oscillator (OPO). We pumped the OPO cavity, which contains periodically poled LiNbO(3) (PPLN), with a 14-W 1.06-mum Nd:YAG laser to generate a signal at 1.7 mum and an idler at 2.8 mum. Mixing of the two waves at the same crystal temperature and grating spacing yielded emission in the mid IR. This technique avoids the mid-IR absorption-high-threshold problem, which has limited the cw performance of PPLN OPO's at wavelengths beyond 4 mum. Provided that tunability is not required, this method is a simple alternative to multiple-crystal configurations.     

Alternative method of implementation of frequency encoded N bit comparator exploiting four wave mixing in semiconductor optical amplifiers

A frequency encoded all optical N bit comparator is proposed. The implementation is ultrafast one and the frequency encoding makes it intensity loss dependent problem free. The use of polarization insensitive four wave mixing makes the design polarization independent and the hardware simple. The frequency conversion by the RSOA makes the design faster compared to other SOA based design. The required gates, i.e. X-OR and AND gates for the implementation of the comparator in frequency encoded format are also discussed.     

Improved optical single-sideband generation using the self-modulation birefringence difference in semiconductor optical amplifiers

By employing the self-modulation birefringence difference in a semiconductor optical amplifier (SOA), an improved method is proposed to generate a complete optical single-sideband (OSSB) signal. Over 30 dB sideband suppression ratios (SSRs) of lower OSSB signals are obtained over a 12 dB input power range and a 36 nm wavelength span, with a maximum of over 35 dB. Upper OSSB signals with an SSR of over 15 dB are observed using a SOA for what is believed to be the first time. This method is effective even for the carrier-suppressed signal. The theory for OSSB generation in an SOA is extended and verified by experiment.     

Analysis of difference frequency generation and cascaded second-harmonic generation and difference frequency generation in lossy quasi-phase-matched semiconductor waveguides

The analytical expressions of converted wave power for difference frequency generation (DFG), cascaded second-harmonic generation and difference frequency generation (cSHG/DFG) processes have been obtained under the non-depletion approximation in lossy waveguides. It is shown that the analytical results and the numerical simulation with depletion agree very well for lossy waveguides. Employing the analytical solutions, the formulas of optimized waveguide lengths in lossy waveguides are obtained for DFG and cSHG/DFG processes. After designing an AlGaAs quasi-phase-matched ridge waveguide, we investigate and compare the characteristics of the second-order nonlinear effects with and without waveguide loss, such as conversion efficiency, conversion bandwidth, pump wavelength tolerance and temperature stability in detail.     

用于光生毫米波的双频微片激光器热致频差特性研究

研究了激光二极管端面抽运的双纵模双频微片激光器的热效应对其输出频谱的影响. 通过对端面抽运Nd:YVO₄微片的热传导方程求解得出晶体内部的温度场分布; 并进一步对微片晶体热致折射率变化进行分析, 由此计算出双频微片激光器的热致频谱变化. 实验结果表明: 当抽运功率较小时得到稳定的双纵模双频激光输出; 当抽运功率增大时, 晶体热效应使双频激光频谱双峰之间的频差减小, 各纵模波长频谱宽度加宽, 实验结果与理论分析相符合. 关键词： 光载无线通信 双频微片激光器 热效应 频率差     

High idler conversion with an intracavity optical parametric oscillator and difference frequency generation

Tunable mid IR generation is analyzed with an optical parametric oscillator (OSO) and difference frequency generation (DFG) based on two periodically poled gratings. To obtain chirped-pulse amplification techniques, in the difference frequency generation the group-velocity must be matched. If grating periods are selected, appropriately, the wider tunable range of output pulse can be obtained. Because the group velocity is matched, the parametric bandwidth and the maximum effective length will be enhanced. We theoretically demonstrate high idler conversion in a femtosecond optical parametric oscillators with two different and cascaded periodically poled gratings. In the first grating the signal and the idler 1 are generated, while in the second one, the midwave infrared idler 2 is generated. The dependence of the lengths of the two cavities on the conversion efficiency is discussed.     

Double quasi phase matching for both optical parametric oscillator and difference frequency generation

We present simultaneous phase matching of optical parametric oscillator (OPO) and difference frequency generation (DFG), using a noncollinear interaction in periodically poled crystal with single grating. Selecting proper grating period Λ and titled angle ξ between the grating vector G and the optical axis of crystal, the noncollinear scheme provides double phase matching solutions over continuous regions of the midwave infrared spectrum. At certain wavelength regions, for DFG process the group velocities between interaction pulses are matching and the phase matching bandwidth reaches maximum. Selecting the different grating period, the broadband midwave tuning and better gain spectrum can be obtained at different wavelength range. For the certain period grating the conversion efficiency is higher. Hence, using the double phase matching configuration, the broadband tunable midwave infrared wave can be produced in single grating. But the configurations have a relatively narrow angular bandwidth.