Le Nguyen Binh

Novel realization of monotonic Butterworth-type lowpass, highpass, and bandpass optical filters using phase-modulated fiber-optic interferometers and ring resonators

A novel realization of monotonic Butterworth-type lowpass, highpass, and bandpass optical filters (from their electrical digital filter characteristics) by cascading the all-pole and all-zero resonators is presented. A graphical method for fast derivation of the transfer functions, quick inspection of the resonance effects, and important characteristics of any photonic circuits is described. It is shown that incorporation of the optical amplifiers and optical phase modulators into the delay lines of two basic optical resonators, whose pole and zero can be adjusted independently of each other, provides great design flexibility which would otherwise not possible using conventional passive optical resonators. Possible applications of these optical filters as optical pulse equalizers and receiver shaping filters in long-haul coherent lightwave transmission systems are discussed. Possible application of basic resonators comprising of optical phase modulators as tunable optical filters for spectrum analyzers is also considered. >

Graphical representation and analysis of the Z-shaped double-coupler optical resonator

A graphical technique for obtaining the transfer function between any input and output optical ports of photonic circuits is presented. The Z-shaped double-coupler optical resonator is chosen as an example for illustration of the graphical approach. A theoretical study of this photonic circuit is described using z-transformation of the optical transfer function. An expression for the pole-dependent resonator finesse analogous to the Fabry-Perot resonator finesse is derived. Possible applications of this resonating system as optical bandpass digital and/or notch filters and as an all-optical timing recovery circuit are discussed. >

Optical realization of Newton-cotes-based integrators for dark soliton generation

An optical integrator is an analog optical signal processor that performs the time integral of an input optical signal. This paper presents a theory of Newton-Cotes optical integrators for high-speed optical signal processing. The Newton-Cotes optical integrators are designed using the cascade of a finite impulse response (FIR) optical waveguide filter with an infinite impulse response (IIR) optical waveguide filter. To demonstrate the effectiveness of the proposed optical integrators, the authors show, by means of computer simulations, that a trapezoidal optical integrator can generate a fundamental dark-soliton pulse that can propagate stably over a large distance of single-mode optical fiber. Although the analysis is directed at optical integrators implemented using waveguide technology, the theory, design method, and results are applicable to other physical systems such as optical systems based on free-space optics, fiber optics, and fiber gratings.

Programmable incoherent Newton-Cotes optical integrator

A discrete-time integrator is a processor whose output pulse sequence is obtained by approximating the integral of a continuous-time signal from the samples of that signal. A programmable incoherent Newton-Cotes optical integrator (INCOI) is theoretically proposed. The classical numerical integration technique is employed to develop, to our knowledge, for the first time, a generalised theory of the Newton-Cotes digital integrator. Based on this developed theory, we propose algorithms and techniques for the synthesis and realisation of the programmable INCOI processor using incoherent amplified fibre-optic signal processing architectures. Several types of input pulse sequences, such as polynomials of various orders and the exponential pulse, are chosen as examples for illustration of the incoherent processing accuracy of the proposed programmable INCOI processor in the time domain. Although the analysis is directed at fibre-optic signal processors, the methodology and the results are applicable to other physical systems.

Synthesis of tunable optical waveguide filters using digital signal processing technique

A highly versatile synthesis method for the design of a variety of tunable optical waveguide filters with independently variable bandwidths and tunable center frequencies and arbitrary infinite impulse response (IIR) characteristics is presented. The synthesized Mth-order tunable optical filter consists of the concatenation of M all-pole filters (APFs) with M all-zero filters (AZFs). The bandwidth and the center frequency of the designed tunable optical filter can be independently tuned by applying electric power to thin-film heaters loaded on the waveguides of both APFs and AZFs. One unique advantage of the proposed synthesis technique is that the poles and zeros of the filter can be adjusted independent of each other to enable the design of tunable optical filters with arbitrary IIR characteristics. By means of computer simulation, the effectiveness of the synthesis method is demonstrated with the design of second-order Butterworth bandpass and bandstop tunable optical filters with variable bandwidths and tunable center frequencies. To study the effects of fabrication tolerances on filter performances, the maximum allowable deviations of filter parameters from their designed values are also determined. The proposed synthesis method is general and flexible enough to enable the design of a variety of tunable optical filters with arbitrary IIR characteristics, which include Chebyshev and elliptic filter types

Fiber-optic array algebraic processing architectures

A high-accuracy fiber-optic array processor (FOAP) based on the algorithm of digital multiplication by analog convolution is proposed. The FOAP architecture is a local regularly interconnected processor that utilizes an array of identical all-optical elemental-processing lattice units, namely, an optical splitter, an optical combiner, and a binary programmable fiber-optic transversal filter. Various FOAP matrix multipliers are proposed for nonnegative and twos-complement binary arithmetic matrix-vector, matrix-matrix, triple-matrix, and high-order matrix operations. The overall performances of the FOAP matrix multipliers are compared with the time-integrating and space-integrating architectures and with the digital multipliers. Extension of the digital-multiplication-by-analog-convolution algorithm is also considered.

Single and Dual-Level Minimum Shift Keying Optical Transmission Systems

We present optical transmission systems employing minimum shift keying modulation formats of single and dual-amplitude level under linear, weakly nonlinear, strongly nonlinear variation of the lightwave carrier within a bit-period depending on whether the phase variation within a symbol period is linear or nonlinear. These formats are externally modulated, incoherently and differentially detected based on the Mach-Zehnder delay interferometric optical balanced receiver. Transmission performance of these optical transmission systems is evaluated in terms of receiver sensitivity, amplification stimulated emission noise loading, dispersion tolerances. These performance characteristics are compared with return-to-zero (RZ) differential phase shift keying (DPSK) and carrier-suppressed RZ on-off keying modulation formats. Accurate bit-error ratios are obtained and confirmed by different statistical techniques: Monte Carlo, single-Gaussian or multiple Gaussian distributions and generalized Pareto distribution statistical methods, especially when the eye diagrams are distorted. Among the three minimum shift keying (MSK) types, the weakly nonlinear optical MSK is found to be the most promising because of its robust transmission performance and more importantly, its reduced-complexity of the electrical driving signals for transmitter in modulating the lightwave carrier as compared to the linear MSK counterpart. Transmission performance of dual-level MSK optical transmission systems depends on the intensity-splitting ratio of the two levels. The performance of three ratios: 0.7/0.3,0.8/0.2, and 0.9/0.1 are demonstrated. The spectral attributes of 80 Gb/s dual-level MSK optical signals for these three ratios are similar to each other and compatible with that of 40 Gb/s optical MSK, but narrower than that of 40 Gb/s optical nonreturn-to-zero DPSK, hence high spectral efficiency of the dual-level MSK.

Simulink model and FPGA-based OFDM communication system: a simulation and hardware integrated platform

Ultra-broadband networks are currently attracting significant interests in employing wireless access and optical fiber access to the home and to the building at symbol rate reaching Gb/s. OFDM is a multicarrier modulation technique and considered to offer significant reduction of the data symbol to be carried per carrier channel, especially in ultra-high speed optical communications with bit rate reaching 100 Gb/s or even higher. This paper thus presents a novel and generic OFDM system employing both MATLAB Simulink and FPGA-based development software platform for simulation as well as hardware implementation for the generation and detection of OFDM signals for wireless and optical communications transmission media. Although the transmission medium is modeled with delay distortion filter in the baseband, this model would be valid for passband signals as the amplitude is represented by complex amplitude whose phase would be the phase of the carrier. The Simulink and hardware models presented hereunder are scalable to much higher speed allowing possible implementation in multi-Giga samples per second electronic processors. The sub-systems of the OFDM transmitter and receiver are presented to demonstrate the feasibility of such models for ultra-wideband communication systems such as wireless access and long haul optical fiber communication backbone networks.

Optical dispersion eigencompensators for high-speed long-haul IM/DD lightwave systems: computer simulation

Abskuct- This paper proposes what is believed to he the first linear optical dispersion-compensating technique capable of more effectively compensating for dispersively chirped signal than dispersively chirp-free signal. An effective digital eigenfilter approach is introduced for designing optical dispersion eigencompensators (ODEC’s) for compensation of the combined effects of laser chirp and fiber chromatic dispersion at 1550 nm in high-speed long-haul intensity-modulation direct-detection (IM/DD) lightwave systems. An integrated-optic synthesis of the ODEC using planar lightwave circuit (PLC) technology is proposed to enable high-speed signal regeneration. The proposed eigencompensating scheme is shown to result in the phenomenon of optical power enhancement: the combined effects of laser chirp, fiber chromatic dispersion and ODEC group delay can re-open the receiver eye further than the ideal eye-opening. The eigencompensating approach is shown to compare favorably with the Chehyshev filter technique in both the frequency and time domains. HE ADVENT of the erbium-doped fiber amplifier T (EDFA) has created a need for dispersion-compensating techniques to be developed to solve the important problem of fiber chromatic dispersion in optical communication systems operating in the vicinity of the minimum-loss 1550 nm wavelength. The combined effects of laser chirp, fiber nonlinearity, and fiber dispersion, which result in significant broadening and distortion of the optical signal spectrum, are the critical factors limiting the maximum bit rate-distance in high-speed long-haul IMDD systems. In order to exploit the potential benefits of the EDFA for long-distance transmission at 1550 nm, the detrimental effects of the laser chirp, fiber nonlinearity and fiber dispersion must be minimized either by using dispersion-shifted fiber (DSF) with zero-dispersion wavelength near 1550 nm or by using 1300-nm optimized standard single-mode fiber (SMF) with some means of dispersion compensation. The use of DSF’s to upgrade the already-embedded fiber network is clearly not an economical way to enhance network performance. The employment of DSF’s in conjunction with EDFA’s as repeaters is seen to be a flexible and cost-effective choice of technology for the new

Amplified double-coupler double-ring optical resonators with negative optical gain.

Optical resonators with a double-coupler and double-ring configuration incorporated into optical amplifiers that have negative gain are analyzed. The resonators are presented with a unique signal-flow graph together with z-transform variables for sampled optical signals. Their optical transfer functions are obtained by a graphical technique. The poles and zeroes in the z plane of the transfer functions are examined, which leads to some unique design features of the resonators for optical-filtering applications.