Rekha Mehra

Optical computing with semiconductor optical amplifiers

Increasing communication traffic and plans to increase various services may cause a serious problem towards the power consumption of network equipment. One of the causes of large power consumption in the present network is the multiplexing scheme, such as wavelength division multiplexing (WDM) and electrical routing of the packet signals. WDM requires O/E (optical to electrical) and E/O (electrical to optical) signal con- version circuits with the same number as that of wavelength, resulting in an increase in power consumption. In addition to this electrical signal pro- cessing for the IP packet, routing, and switching at the router consumes a large amount of power. If we could process ultrafast signals using electro- magnetic light waves without converting to electrical signals, this would reduce the power consumption of routers. One of the ways to overcome these problems is the development of all-optical computing devices. All-optical computing devices are based on the nonlinear interaction of light waves, which is an electromagnetic wave. The use of electromagnetic light waves makes computing, such as switching, possible at very high frequencies of more than 100 GHz. We discuss all-optical computing devices based on semiconductor optical amplifiers with the main emphasis on all-optical logic gates.

Design and Simulation of All-Optical OR Logic Gate based on 2-D Photonic Crystal

this paper, we present the design of All-optical OR logic gate based on 2-D (two dimension) photonic crystals. To realize this, we consider the photonic crystals (PCs) with a square lattice of dielectric rods (refractive index=3.40). These rods are surrounded by air (refractive index=1).First we design the structure using the Finite Difference Time Domain (FDTD) method and in second step, we compute the band gap by plane wave expansion (PWE) method. These methods are kept to analyze the behavior of the structure. Band gap width is 0.2516 and normalized central frequency of band gap is 0.6451. Overall size of the logic gate designed is 13µm * 8µm i.e. 104 µm 2 with the lattice constant 540 nm.

Design and Simulation of 2-D Photonic Crystal Based All-Optical AND Logic Gate

In this paper, All-optical AND logic gate with square cavity in 2-D (two dimensions) photonic crystal with GaAs have been demonstrated. The square cavity is created by removing rods from a rectangular lattice of dielectric cylinders in air substrate. Photonic crystal (PC) has periodic dielectric structure that has an important characteristic of PC and that is known as photonic band gap (PBG). The property of PBG is that, wavelength within the band gap cannot propagate through the crystal. In this research work, this property is used to design an All-optical AND logic gate. The operation of this logic gate is verified at third optical window i.e. 1550 nm, which is the most widely used window in present optical communication system.

Ultrafast all-optical 4-bit digital encoders using differential phase modulation in semiconductor optical amplifier-Mach-Zehnder interferometer configuration

Abstract. A novel approach for all-optical digital encoder for both binary-to-gray code and gray-to-binary code have been proposed. Design is based on the basic concept of digital encoder using the exclusive OR (XOR) addition. The XOR gate used in these encoders has been implemented using differential phase modulation between two arms of the Mach-Zehnder interferometer (MZI), in which a semiconductor optical amplifier is placed symmetrically in both arms of MZI. For the most severely degraded output bit, i.e., least significant bit for gray-to-binary encoder, the extinction ratio obtained is 2.35 while the minimum bit error rate is zero at 10  GB/s. For the second most significant bit of gray-to-binary encoder and for all the three bits except the most significant bit of binary-to-gray encoder, the extinction ratio obtained is around 27 dB. For the most significant bit, as input and output bits are same, the extinction ratio is very high, approaching infinity.

An Improvement in Performance of Optical Communication System Using Linearly Chirped Apodized Fiber Bragg Grating

In this paper, a proposal for analyzing the performance of an optical system by using linear chirped apodized fiber Bragg grating has been put forth. Here, we have compared two 10 Gbps systems, one with fiber Bragg grating and the other without fiber Bragg grating. Various parameters used for this analysis are input power, distance, and attenuation coefficient. The performance is analyzed in terms of gain, Q-factor, bit error rate (BER), and eye diagram. It is found that the use of FBG in an optical communication system gives better system performance as compared to a system without FBG.

Comparison of two in-line MZI concentration sensors using FDTD method

In this work, we design, simulate and compare the performance of two in-line MZI concentration sensors; in one sensor, Thinned Fibre (TF) is sandwiched between two conventional Single Mode Fibres (SMFs) and in other Photonic Crystal Fibre (PCF) is sandwiched between two Single Mode Fibres (SMFs). Change in concentration which results in change in refractive index change is measured using both the sensors. Sensitivity of the sensor using PCF is found better as compared to that using TF.

All optical half adder design based on semiconductor optical amplifier

In this paper, All Optical Half Adder design based on nonlinear characteristics of Semiconductor Optical Amplifier (SOA) is proposed. Sum output of this adder is implemented using SOA-MZI configuration and carry output is implemented using SOA assisted by filtering. To make output of both the gates compatible for logic levels, an EDFA with suitable parameters is included at the output end of AND gate i.e. for carry. Truth table of Half Adder is verified on the basis of O/P power as well as by time domain analysis. Bit error rate and quality factor have been calculated at different bit rates. Satisfactory performance is obtained up to 80Gb/s.

Comparison of temperature sensors using polymer materials in long period fiber grating

Long period fiber grating (LPFG) is the most widely used in measurement of temperature, strain, pressure, bending radius, external index of refraction etc. This proposed work exhibits LPFG as temperature sensor. Basically, the shift in resonant wavelength of LPFG temperature sensor depends on thermo-optic effect. To enhance this effect thermo-optic coefficients for core and cladding are optimized. The polymers with negative thermo-optic coefficients can be used as core materials to enhance thermo-optic effect. This enhancement in thermo-optic effect shifts LPFG resonant wavelength towards negative direction. Using this concept, different sensitivities are achieved for different polymers in this research work. This design of LPFG temperature sensor uses Polycarbonate, Polymethyl methacrylate (PMMA) and Ormocomp polymers. The shift of LPFG resonant wavelength towards negative direction is the largest in Ormocomp polymer. Ormocomp as core material provides 24.6nm/°C temperature sensitivity over range from 25°C to 80°C temperature.

Performance Analysis of an Optical System Using Dispersion Compensation Fiber & Linearly Chirped Apodized Fiber Bragg Grating

In this paper, a proposal for analyzing the performance of an optical system by using dispersion compensation fiber (DCF) and linear chirped apodized fiber Bragg grating (FBG) has been put forth. Both systems have three different schemes pre, post and symmetrical. Various parameters used for this analysis are input power, distance & input bit rate. Performance is analyzed in terms of Q factor, Bit Error Rate (BER) and Eye Diagram. It is found that use of FBG as a dispersion compensating element gives better system performance as compared to DCF.

Double Layer Anti-Reflective Coating of SiO2/ZnO for Photovoltaic Cell

In this paper silicon based photo voltaic (PV) cells has been designed using double layer (SiO2/ZnO) anti-reflective coating (ARC). Here reflection spectrum of single layer anti-reflective coating (SLAR) of SiO2&ZnO individually and double layer anti-reflective coatings (DLAR) of SiO2/ZnO are compared. ZnO is a wide band semiconductor which provides good transparency and high electron mobility. The results indicated that the DLAR of SiO2/ZnO proved to be a valuable achievement to obtain highly absorbent surfaces. The results are obtained with planar surface of crystalline silicon substrate using Air Mass 1.5 Global (AM 1.5 G) spectrums. The average reflectance of 6.5% has been achieved within the range of 300-1400nm as maximum solar spectral irradiance of AM 1.5 G is in this region.