Volume 41, Issue 3 -

The interminable need of number of channels in communication systems escorts more number of wavelengths to be used. This broad spectrum of wavelengths when expands in both C and L band, the need of hybrid optical amplifiers (HOA) comes into play. In this work, we proposed an automatic gain-controlled HOA using Residual pumping for C/L band. The desired gain is fixed at 27 dB at pump power swinging between 300 and 400 mW. The input powers are automatically adjusted so as to provide invariable and flat gain eliminating the wavelength dependency of optical amplifier to great extents. Analysis is carried out in a 32 channel WDM system and power transients are also measured in terms of powers of surviving channels and excursion amplitudes by adding and dropping up to 28 channels. The output is adjudicated in terms of maximum gain achieved, OSNR, BER, gain flatness, noise figure and power transient excursion amplitudes.

This article investigates the performance of differential phase shift key system with different hybrid optical amplifiers with equal and unequal channel spacing. The differential phase shift key signals are transmitted with equal channel spacing of 0.1 THz and unequal channel spacing of 0.05, 0.075, 0.1 and 0.15 THz at 96×20 Gbps bit rate. The maximum transmission distance of 230 km is achieved with unequal channel spacing. It is observed that the interference between adjacent channels decreases due to unequal channel spacing and gives better results than equal channel spacing in terms of bit error rate and quality factor. It is found that the maximum distance of 220 km is achieved with equal channel spacing using Raman-erbium-doped fiber amplifier hybrid amplifier.

The impact of physical parameters of uniform fiber Bragg grating (U-FBG) like grating period, length of grating, and width of grating on the performance of U-FBG fiber by using finite differences time domain (FDTD) based on surface plasmon polaritons (SPP) is evaluated. An FBG is similar to a distributed Bragg reflector created in a small segment of optical fiber that reflects some particular wavelengths of light and transmits the other wavelengths. It is observed that the maximum received optical power at the reflected port achieved is −1.67×10 -6 w/m 2 with silver (Ag) profile material of U-FBG at 0.1 w/m 2 input transmission power and wavelength of 1.55 μm with 0.9 μm grating length and 0.2 μm grating width. The result shows that the received optical power is changing by optimizing the physical parameters of U-FBG.

In this article, first the model of 2×2 reversible logic gate is proposed after then the performance of the proposed designed is evaluated. With the increasing flow of information, data rate is increasing very rapidly. This has resulted in increased amount of heat dissipation from the processing nodes. Generally, electronic processors dissipate heat if the data rate is very high. Hence, this model will be very helpful for solving this problem. Evaluated performance of this model is based on the value of quality factor and extinction ratio. The quality factor and extinction ratio are evaluated under different conditions. The average extinction ratio of the design is 19.58 dB and the average quality factor is 53.03 dB. The optical cost of the proposed circuit is 1.

In the present study, the propagation of electromagnetic waves in a square-lattice photonic crystal waveguide (PCW) is investigated using the finite-difference time-domain (FDTD) method. Then, the plane wave expansion (PWE) method is utilized to calculate the 2D photonic crystal band structure. To realize the desired waveguide, nano-line defects are introduced. The results of the numerical simulations and optimization scanning indicate that for the proposed photonic crystal structure consisting of silicon circular dielectric rods with a radius of 84 nm, a band gap can be achieved in the wavelength range of 1.34 μm<λ<1.93 μm. This wavelength range covers E, S, C, L, and U communication bands. Subsequently, by eliminating the rods in four parts of the structure, an all-optical 4-channel splitter can be designed. The numerical simulation results indicate that by coupling a light source to the main path of the structure and propagating it through each channel, the powers of the 4 output facets become approximately the same. The output power of channels 1 and 2 equals to 24.5 % of the input power, and the output power of channels 3 and 4 is 21 % of the input power and the remaining 9 % is lost in the structure as the leakage power. Since the 1.55 μm wavelength is within the band gap, that is the telecommunication band C, this device can be used as a power splitter.

Here, we proposed a high performance 16-channel optical demultiplexer using two-dimensional photonic crystal ring resonator for telecommunication systems. By plane wave expansion (PWE) method the photonic band gap (PBG) of proposed structure calculated. Then, with finite difference time domain (FDTD) method the performance parameters of designed two-dimensional photonic crystal demultiplexer are analyzed. It is found that the channel wavelength of wavelength-division multiplexing (WDM) is truly tuned by changing the structure parameters of the demultiplexer and position of rod. Output peaks located in the optical communication C-band and L-band with the transmission efficiency of 99 %. The demultiplexer exhibits high-quality factor of 5176, and spectral width of 0.3. Very low crosstalk values are between −19 dB and −90 dB where, device only occupies an area of 1708.65 µm 2 . The proposed compact 16-channel demultiplexer can find more applications for the ultra-compact WDM systems in highly integrated telecommunication circuits.

To improve the performance of optical fiber transmission and to compensate the fiber chromatic dispersion (CD), we propose to use fiber Bragg grating (FBG) in intensity modulator/direct detection IM/DD optical orthogonal frequency division multiplexing (OOFDM) system, and experimentally demonstrate 2.5-Gbit/s QPSK-OFDM transmission over 200 km SMF-28. FBG used before the detection as a chromatic dispersion compensation module, reducing the beating noise between ASE noise and OFDM signal. By using the FBG in IM/DD OOFDM system, our experimental results show that the receiver sensitivity was improved about 2 dB at a bit error rate (BER) of 1×10−3$1 \times {10^{ - 3}}$ for 2.5 Gbit/s QPSK-OFDM signals after 200 km SMF-transmission compared to regular system without FBG.

In this paper, we aim to design an all-optical structure that can be employed as optical OR/AND logic gates. To do so, a nonlinear photonic crystal-based ring resonator will be designed whose resonant wavelength depends on the variation of optical intensity. Then, by adding some optical waveguides, the optical logic circuit structure will be obtained that can function as optical OR/AND logic gates. The maximum time delay for the proposed structure is about 1.5 ps. Total footprint of the proposed structure is about 372 mm 2 . The proposed structure has lower time delay, lower footprint and lower optical input power compared with previously proposed structures.

MZI switches are well-known devices for high speed communication applications. A lot of researchers have designed MZI switches by using lithium niobate and potassium niobate material. But the major problem of using these type of material includes high insertion losses and required high switching voltage. So, in this research paper we have designed a 2×2 electro-optic switch using optical waveguide designed with Titanium (Ti) diffused in Strontium barium niobate (SBNO3) material which can operate at wavelength of 1.3 um. Results show that the proposed structure gives better output in terms of extinction ratio (=29.9 db) as well as for insertion losses (≤0.018). Further, we have designed various optical gates i. e. XNOR, XOR and AND optical gates and their performance is also evaluated by varying electrode voltages. It is inferred from the results that the proposed model gives better results even in terms of output power which can be used for commercial purpose.

In time division, multiple access (TDMA)-based passive optical network (PONs), a dynamic bandwidth assignment (DBA) is necessary for efficient utilization of the available bandwidth of the upstream link. An efficient DBA scheme can improve the upstream performance of a traffic class of an ONU in two ways. First, it can increase the bandwidth assignment to it by efficiently utilizing the available bandwidth. Secondly, it can reduce the channel and frame idle time by increasing the polling frequency and by assigning extra surplus bandwidth not used by the other ONUs. Many DBA schemes have been reported for both ITU PONs (GPON and XGPON) and IEEE PONs (EPON and 10 G EPON). In this study, we explain the impact of DBA scheme on the upstream performance of PON and then do a thorough survey of both PON standards, categorize the DBA schemes and review them critically. Based on the literature review we also give our opinion on the most suitable DBA scheme for both type PONs on the basis of upstream delays, frame loss and bandwidth utilization efficiency.

Increasing the number of users presents a limitation in one-dimensional (1D) spectral amplitude coding (SAC) for Optical Code Division Multiple Access (OCDMA) system. In order to overcome this disadvantage, a new architecture of the two-dimensional wavelength/spatial SAC-OCDMA system using the multi-diagonal (MD) code has been proposed. The 2D-MD code possesses the same properties of 1D-MD code, which leads to total suppression of the multiple access interference. Unlike conventional receivers used in precedent studies, where the phase-induced intensity noise (PIIN) is a drawback, the suggested structure not only eliminates PIIN but reduces the system architecture. The results show that the user’s number reached by the proposed system is the user number’s multiplication of the 1D system and the couplers’ number. Moreover, the new 2D-MD system presents good performances at the high data rate.

This paper explores the design of multiservice code (MS) in spectral, time spreading and wavelength domains (3-Dimensional). The proposed 3D code is designed in such a manner that follows the ideal in phase unit cross correlation in spectral, time spreading and wavelength domains. The proposed encoder generates the MS code effectively in 3D domain and decoder suppresses the multi-user interferences successfully. Performance analyses are carried out by considering the all noises such as phase induce intensity noise(PIIN), shot noise and thermal noise. The analysis of 3D-MS code for variable code length is also performed for measurement of variation in bit error rate against the received power and number of active users in the design. The observed performances are also compared with existing codes such as 2D-MDW, 3D-PDC and 1D-MS code and the proposed code shows the better performance. The analysis of bit error rate of proposed code is carried out against the number of users at 0.622Gbits/s data rate and 0 dBm received power and comparison is also formed with the existing code such as 3D PD( M =21, N =3, P =3), 2DMDW( M =63, P =3), PDC( M =57, P =3) and 1D MS Code. It is noted that 3D MS code shows the better performance than the existing methods. Analysis is also evaluated for variable weight and variable length codes in order to observe the variation in bit error rate with variation in received power and number of simultaneous users.

This article presents a novel encoder technique of spectral amplitude coded multiple access (SAC-OCDMA) systems. The proposed technique is based on two orthogonal polarization states of the same one dimensional optical code. This method is usually applied to increase the number of simultaneous users in a network, and it can double the number of potential users against the one-dimensional code. The results obtained in this work show that optical zero cross-correlation code can accommodate more users simultaneously for the typical bit error rate of optical communication system of  10−9${\ }{10^{ - 9}}$.

MIMO-OFDM is a key technology being widely used these days for 4 G communication systems but its main drawback is high PAPR. Selected mapping is commonly used approach for PAPR reduction but in SLM there is requirement of side information (SI) to be sent along with the input data signal and leading to the loss in data rate and increased complexity. In this article, we have come up with a technique for PAPR reduction in which there is no requirement of transmission of side information and therefore preserves the data rate and also provides sufficient reduction in the PAPR. In this technique, SI embedding is performed in the form of subcarrier location (index) by increasing its power. The simulation results demonstrate that the scheme which has been proposed provides the favorable response in terms of bit error rate (BER), PAPR reduction and SI detection capability.

High PAPR poses a large hindrance to high data rate Orthogonal Frequency Division Multiplexing (OFDM) signals. A companding transform converts the Probability distribution function (PDF) of the transmitted OFDM signal in a way which reduces the Peak-to-average power-ratio (PAPR). In this paper, we have performed the study of companding techniques and analyzes the PAPR and BER performances of these schemes. Here, we have considered μ-law companding, exponential companding, trapezoidal companding (TC) and trigonal companding for comparison. In this paper, we have demonstrated that μ-law companding, exponential companding and trigonal companding schemes have no adaptability in designing the companding function, and along these lines an exchange off between BER performance and PAPR reduction ability is unrealistic to accomplish. However, TC scheme has two parameters ( a and b ) to design the companding function and hence a trade-off between PAPR reduction capability and BER performance is possible to achieve. BER performance and PAPR reduction capabilities of the scheme under consideration are evaluated and compared through computer simulations. We have also presented an approach to obtain the minimum BER and PAPR of TC and found out the values of design parameters ( a and b ) for which TC scheme has minimum BER and PAPR.