Volume 37, Issue 2 -

A vibration sensing system used for the Internet of Things is presented in this paper. Using the distributed feedback fiber lasers (DFB-FL) collects external sound signals and digital phase generated carrier (PGC) method realizes wavelength demodulation. The platform is designed based on an open architecture and B/S (Browser/Server) technology which makes it an ideal platform to be operated under a network environment. The sensing system is no power supply and could be monitored anytime and anywhere which is the requirement of Internet of things.

In this paper we proposed a new design for all-optical NAND gate. By combining nonlinear Kerr effect with photonic crystal ring resonators first we designed a structure, whose optical behavior can be controlled via input power intensity. The switching power threshold obtained for this structure equal to 1 kW/μm 2 . For designing the proposed optical logic gate we employed two resonant rings with the same structures, both rings at the logic gates were designed such that their resonant wavelength be at λ =1,550 nm. Every proposed logic gate has one bias and two logic input ports.

We report the theoretical study of excitation efficiency in the presence of possible transverse and angular misalignments in the case of excitation of single-mode circular core dispersion-shifted and dispersion-flattened fiber by laser diode via hemispherical microlens on the tip of the fiber. The present study takes into consideration limited aperture allowed by the hemispherical microlens. Employing ABCD matrix technique involving refraction of paraxial rays by a hemispherical microlens on the fiber tip, we formulate analytical expressions for the coupling efficiencies in the presence of the said misalignments. The estimations of the concerned efficiencies as well as associated losses by using our formulations will require little computations. But the results found are sufficiently accurate and the execution of our formalism is simple. Thus the prescribed analytical expressions are useful and new in the sense that prediction of coupling optics can be made accurately but in a simple manner without requiring lengthy numerical integrations concerned with conventional phase model technique. Moreover, the present study, as per our knowledge till date, being the first theoretical investigation of excitation efficiency for the said type of coupling device, will benefit the experimentalists, designers and packagers who are working in the field of optimum launch optics involving such coupler.

The optical switching activity is one of the most essential phenomena in the optical domain. The electro-optic effect-based switching phenomena are applicable to generate some effective combinational and sequential logic circuits. The processing of digital computational technique in the optical domain includes some considerable advantages of optical communication technology, e.g. immunity to electro-magnetic interferences, compact size, signal security, parallel computing and larger bandwidth. The paper describes some efficient technique to implement single bit magnitude comparator and 1’s complement calculator using the concepts of electro-optic effect. The proposed techniques are simulated on the MATLAB software. However, the suitability of the techniques is verified using the highly reliable Opti-BPM software. It is interesting to analyze the circuits in order to specify some optimized device parameter in order to optimize some performance affecting parameters, e.g. crosstalk, extinction ratio, signal losses through the curved and straight waveguide sections.

In this paper, for the first time transmission of 2.5 Gb/s duobinary signal is investigated for the downlink direction in 40 GHz optical millimeter-wave generation or up-conversion, utilizing a dual-arm LiNbO3${\rm{LiNb}}{{\rm{O}}_3}$ Mach–Zehnder modulator based on different modulation schemes, namely double- and single-sideband (DSB and SSB) and optical carrier suppression (OCS). The up-converted optical millimeter-wave employing OCS modulation scheme indicates the highest back-to-back received optical power and the smallest power penalty after long propagation in the single-mode fiber, in comparison to DSB and SSB. Directly modulated laser in association with OCS modulation scheme has been used to generate duobinary optical millimeter-wave signal in order to minimize the cost and complexity of the system.

This paper focuses on performances of limited range wavelength converters (LRWCs) in resolving optical packet contentions. An optical packet switch is proposed, which uses recirculation LRWC groups and recirculation fiber delay lines (FDLs) to resolve optical packet contentions. In order to make full use of the LRWCs and the FDLs, a control algorithm is also proposed. Packet loss probability of the proposed switch versus the number of FDLs, the wavelength conversion range, and the number of LRWC groups are evaluated in detail.

For a range of fiber parameters and wavelengths, the splice losses between photonic crystal fiber and a single mode fiber are calculated using our simplified and effective model of photonic crystal fiber following a recently developed elaborate method. Again, since the transverse offset and angular mismatch are the serious factors which contribute crucially to splice losses between two optical fibers, these losses between the same couple of fibers are also studied, using our formulation. The concerned results are seen to match fairly excellently with rigorous ones and consistently in comparison with earlier empirical results. Moreover, our formulation can be developed from theoretical framework over entire optogeometrical parameters of photonic crystal fiber within single mode region instead of using deeply involved full vectorial methods. This user-friendly simple approach of computing splice loss should find wide use by experimentalists and system users.

We present a round-coupling laser system with two inverse injection semiconductor lasers and discuss nonlinear dynamics in the two lasers. We make an analysis in locking, synchronization and reverse synchronization of the two lasers. We find that the injection-coupling level determines dynamics and stability of the two lasers. Locking critical condition is successfully predicted. Quasi-period and dynamics in the two lasers are investigated by controlling the current, detuning and injection levels. Many bifurcate diagrams are illustrated via varying the controlling parameters. A route to chaos after bifurcation and quasi-period is described for the two lasers.

Fiber artifacts of very well-measured length are required for the calibration of optical time domain reflectometers (OTDR). In this paper accurate length measurement of different fiber lengths using the time-of-flight technique is performed. A setup is proposed to measure accurately lengths from 1 to 40 km at 1,550 and 1,310 nm using high-speed electro-optic modulator and photodetector. This setup offers traceability to the SI unit of time, the second (and hence to meter by definition), by locking the time interval counter to the Global Positioning System (GPS)-disciplined quartz oscillator. Additionally, the length of a recirculating loop artifact is measured and compared with the measurement made for the same fiber by the National Physical Laboratory of United Kingdom (NPL). Finally, a method is proposed to relatively correct the fiber refractive index to allow accurate fiber length measurement.

In this paper, comprehensive analyses of triple-clad fibers are presented. The geometry of multiple-clad fibers has been considered as a four-layer cylindrical structure. The geometry consists of a core and three claddings. We have analyzed and compared different types of triple-clad refractive index profiles on the basis of dispersion, mode distribution and propagation constant. To enhance the optical characteristics of these three fibers, we have developed a combined formulation which is applicable for single-clad, double clad and triple-clad optical fibers. In optical fibers, two or more claddings are required for dispersion shifting, dispersion flattening and other specialized applications. Thus, an analysis of design dispersion-shifted, dispersion-flattened and dispersion-compensated fibers is presented. We have used a boundary match method for evaluating propagation wave vectors and guided modes.

Optical access networks are becoming more widespread and the use of multiple services might require a transparent optical network (TON). Multiplexing and privacy could benefit from the combination of wavelength division multiplexing (WDM) and optical coding (OC) and wavelength conversion in optical switches. The routing process needs to be cognizant of different resource types and characteristics such as fiber types, fiber linear impairments such as attenuation, dispersion, etc. as well as fiber nonlinear impairments such as four-wave mixing, cross-phase modulation, etc. Other types of impairments, generated by optical nodes or photonic switches, also affect the signal quality (Q) or the optical signal to noise ratio (OSNR), which is related to the bit error rate (BER). Therefore, both link and switch impairments must be addressed and somehow incorporated into the routing algorithm. However, it is not practical to fully integrate all photonic-specific attributes in the routing process. In this study, new routing parameters and constraints are defined that reflect the distinct characteristics of photonic networking. These constraints are applied to the design phase of TON and expressed as a cost or metric form that will be used in the network routing algorithm.

In this paper, an all-optical network composed of the ROADMs (reconfigurable optical add-drop multiplexer), L2/L3 optical packet switches, and the fiber optical cross-connection for fiber scheduling and measurement based on LCoS (liquid crystal on silicon) technologies is proposed. The L2/L3 optical packet switches are designed with optical output buffers. Only the header of optical packets is converted to electronic signals to control the wavelength of input ports and the packet payloads can be transparently destined to their output ports. An optical output buffer is designed to queue the packets when more than one incoming packet should reach to the same destination output port. For preserving service-packet sequencing and fairness of routing sequence, a priority scheme and a round-robin algorithm are adopted at the optical output buffer. The wavelength of input ports is designed for routing incoming packets using LCoS technologies. Finally, the proposed OFS (optical flow switch) with input buffers can quickly transfer the big data to the output ports and the main purpose of the OFS is to reduce the number of wavelength reflections. The all-optical content delivery network is comprised of the OFSs for a large amount of audio and video data transmissions in the future.

A new two-dimensional optical orthogonal code (OOC) named EQC/MOCS is constructed, using Extended Quadratic Congruence (EQC) code for time spreading and modified one-coincidence sequence (MOCS) for wavelength hopping. Compared with EQC/Prime code (PC), the number of wavelengths for EQC/MOCS is not limited to a prime number. Compared with EQC/OCS, the length of MOCS need not be expanded to the same length of EQC. EQC/MOCS can be constructed flexibly, and also has larger code cardinality.

In this paper we introduce a successive interference cancellation (SIC) scheme for direct sequence optical code division multiple access (DS-OCDMA) systems using pulse position modulation (PPM). Considering double-padded modified prime code (DPMPC) as a signature sequence code, results show that the system has better performance in terms of both capacity and bit error rate (BER) as compared to the one without cancellation scheme, where the system with SIC scheme can support up to 88 users while the system without SIC scheme can support only 38 users at similar BER=10 −9 . Although the receiver sensitivity is affected by the overlapping between users, which limits the system performance, the theoretical analysis of this issue indicates the influence of the size of M-ary PPM on OCDMA system. Hence, the BER value is still sufficient for good system performance.

In this paper, we demonstrated the variation of different parameters with quadrature amplitude modulation (QAM) and differential phase shift key (DPSK) sequence generator, which generates modulated signals, in data transmission for communication and analysed that how the difference of these sequence generators effect its resonant frequency (RF) value, eye diagram and electrical constellation representation of the system.

In this article, we present a numerical simulation study of encoding, decoding and propagation performance of short optical pulses and words with modulations OOK, PAM and PPM in OCDMA systems (Optical Code Division Multiple Access). The encoding and decoding of short pulses are obtained through fiber Bragg grating(FBG – FBG optical) devices, where the codes are inserted through discrete jumps in the optical phase (± π ) where Gold codes were used. A figure of merit (SNR – Signal to Noise Ratio) was obtained to quantify the interference in propagation of short optical pulses. An increase in the temporal width was observed. For decoded pulses due to the nonlinearity effect, we observed an increase of 1.3 ps considering the propagation with γ=3 W –1  km –1 and γ =24 W –1  km –1 . Analysis of coding and decoding words “a” and “w” was done. Considering the propagation (with γ =9 W –1  km –1 ) of a word “w”, an error occurred in all modulations except for simultaneous PPM/PAM modulation, which is associated to the better autocorrelation characteristics obtained with the OOK, PAM and PPM modulations alone, and could double the transmission rate. The nonlinear effects directly affect the process of the autocorrelation codes due to interference from adjacent chip components of the code.

In this hybrid WDM-TDM PON has been evaluated and compared the downstream wavelengths with equal and unequal channel spacing at 5 Gbit/s per wavelength in the scenario of triple play services with 128 optical network units (ONUs). The triple play services: data, voice and video signals are transmitted up to 50 km distance having Q factor of 6.68 and BER of 3.64e-012 with unequal channel spacing and 45 km distance having Q factor of 6.33 and BER of 2.40e-011 with equal channel spacing in downstream direction. It has been observed that downstream wavelengths with unequal channel spacing provide better results than equal channel spacing.