Behzad Moslehi

Fiber-optic lattice signal processing

We discuss the implementation of fiber-optic lattice structures incorporating single-mode fibers and directional couplers. These fiber structures can be used to perform various high-speed time-domain and frequency-domain functions such as matrix operations and frequency filtering. In this paper we mainly consider systems in which the signals (optical intensities) and coupling coefficients are nonnegative quantities; these systems fit well in the theory of positive systems. We use this theory to conclude, for example, that for such systems the pole of the system transfer function with the largest magnitude is simple and positive-valued (in the Z-plane), and that the magnitude of the frequency response can nowhere exceed its value at the origin. We also discuss the effects of various noise phenomena on the performance of fiber-optic signal processors, particularly considering the effects of laser source phase fluctuations. Experimental results are presented showing that the dynamic range of the fiber systems, discussed in this paper, is limited, not by the laser source intensity noise or shot noise, but by the laser phase-induced intensity noise. Mathematical analyses of lattice structures as well as additional applications are also presented.

Fiber-optic signal processor with applications to matrix–vector multiplication and lattice filtering

A new fiber-optic signal processor is proposed to implement systolic matrix-vector multipliers and lattice filters. 10(9) multiplications/sec can be achieved with currently available components for matrix-vector multiplications that involve Toeplitz matrices. A 2 x 2 (Toeplitz) matrix-vector multiplier has been experimentally demonstrated using single-mode fibers and directional couplers. The filtering characteristics of the device are also discussed.

Laser phase noise effects in fiber-optic signal processors with recirculating loops.

The power spectrum of the optical intensity at the output of a single-mode-fiber recirculating delay line driven by a multimode semiconductor laser is shown to exhibit a spectral structure with notches at zero frequency as well as at other multiples of 1/(loop delay). A theoretical model based on laser phase noise is suggested to explain the experimental data.

Spectral Structure Of Phase-Induced Intensity Noise In Recirculating Delay Lines

The dynamic range of fiber optic signal processors driven by relatively incoherent multimode semiconductor lasers is shown to be severely limited by laser phase-induced noise. It is experimentally demonstrated that while the noise power spectrum of differential length fiber filters is approximately flat, processors with recirculating loops exhibit noise with a periodically structured power spectrum with notches at zero frequency as well as at all other multiples of 1/(loop delay). The experimental results are aug-mented by a theoretical analysis.

Optical fiber gratings for structural health monitoring in high-temperature environments

Fiber gratings are proving to provide versatile discrete sensor elements for structural health monitoring systems. For example, they outperform traditional resistive foil strain gages in terms of temperature resistance as well as multiplexing capability, relative ease of installation, electromagnetic interference immunity and electrical passivity. However, the fabrication method and post-fabrication processing influences both performance and survivability in extreme temperature environments. In this paper, we compare the performance and survivability when making strain measurements at elevated temperatures for a range of fabrication and processing conditions such as UV-laser and electric-arc writing and post-fabrication annealing. The optimum method or process will depend on the application temperatures (e.g., up to 300°C, 600°C or 1000°C), and times at these temperatures. As well, other sensing requirements, including the number of sensors, measurand and sensitivity may influence the grating choice (short or long period).

Fiber-Optic Defect and Damage Locator System for Wind Turbine Blades

IFOS in collaboration with Auburn University demonstrated the feasibility of a Fiber Bragg Grating (FBG) integrated sensor system capable of providing real time in-situ defect detection, localization and quantification of damage. In addition, the system is capable of validating wind turbine blade structural models, using recent advances in non-contact, non-destructive dynamic testing of composite structures. This new generation method makes it possible to analyze wind turbine blades not only non-destructively, but also without physically contacting or implanting intrusive electrical elements and transducers into the structure. Phase I successfully demonstrated the feasibility of the technology with the construction of a 1.5 kHz sensor interrogator and preliminary instrumentation and testing of both composite material coupons and a wind turbine blade.

A Review of Fiber Optic Technology for Turbine Engine Instrumentation Channel: Control, PHM, and Test Cell Applications

The next generation of gas turbine engines will potentially have Full Authority Digital Eengine Control (FADEC) Systems that consists of wired, wireless, and fiber optics technologies. This paper focuses on the fiber optics technologies for engine applications. Optical fiber sensors have the potential to deliver new and effective measurement in many applications aided by the following properties: (a) immunity to and non-generation of electromagnetic interference (EMI), (b) electrical passivity and thus safety in explosive environments, (c) transmission of sensed information over long distances and through difficult to access regions, (d) very small diameter size allowing integration into smart materials, (d) high durability in many environments, (e) minimal mass, particularly important in aerospace applications, (f) geometric flexibility coupled with capability for multiple functionality, enabling non-line-of-sight measurements and contributing to ease of installation compared with alternative approaches. For practical application a fiber optic sensing system needs to include: sensors, fiber optic link, interrogator (comprising photonics, electronics and firmware/software), data interpretation and decision-aid algorithms/software. Fiber optics for diagnostics and troubleshooting are used in varying capacities to test, measure, analyze, transmit, distribute, and/or simulate an optical signal with which procedures and processes associated with maintenance, problem solving, and calibration of equipment and/or networks can be performed. With all the scientific and engineering advancements in the field of fiber optic sensing, the maturity of this technology is high enough and well beyond the experimental lab environment. With its rather low cost, fiber optics sensing technology is a proper option for turbine engine industry.

Generalized Lightweight Fiber Optic Aero-Engine Control Network

Avionics systems today accommodate increasing communication needs by overlaying new dedicated point-to-point copper interconnects. This approach increases weight, wiring, and design complexity as the system expands. To address the need for an integrated, lightweight, reliable and scalable communication platform, we recently proposed AViAtion real-Time Adaptive Ring (AVATAR), leveraging the mature Wavelength-Division Multiplexing (WDM) ubiquitous Ethernet technology, to support real-time aero-engine control operation. AVATAR features unidirectional WDM ring, constructed by interconnected Recon gurable Optical Add/Drop Multiplexors (ROADMs) via multi-wavelength bers, where the various hardware components are signi cantly lighter in weight compared to copper parts. In this paper, we generalize AVATAR using a more exible ROADM architecture that is Colorless, Directionless, Contentionless (CDC). To e ciently exploit spatial reuse and high capacity, we study the multi-channel scheduling of unsplittable, real-time, deterministic tra c over AVATAR. The problem can be formulated as a Mixed Integer Linear Program (MILP). Optimal frame layouts are obtained for di erent network con gurations to guide the design.

A tracking and stabilization oriented fiber optic gyroscope

We demonstrate for an unpolarized Fiber Optic Gyroscope (FOG) with open-loop electronics, that, by applying more source power and conserving optical power in the optical path, we can achieve improved Angle Random Walk (ARW) performance without enlarging loop or put in multiple turns of fiber. The predicted trends are demonstrated by the experiment in terms of bandwidth. Power-law dependency is shown within the accuracy of the instrumentation.