S. A. Newton

Limitation of rotation sensing by scattering.

There appear to be limitations in the operation of optical-fiber Sagnac gyro rotation sensors that have imposed a minimum measurable rotation rate that is much higher than that caused by quantum noise. We show that one source of limitation, namely, the superposition of a nonreciprocal pair of waves generated by backward scattering from the incident waves, can result in significant error but can be mitigated by appropriate system design and signal modulation.

Single Mode Fiber Recirculating Delay Line

Recirculating delay lines have been made using loops of single mode fiber that are closed, without splices, using one or more single mode fiber directional couplers. The use of an all single mode fiber system allows the accurate storage of high frequency analog or digital signals for long delay periods. Such devices can be used as wideband transient or buffer memories. Recirculating fiber loops are also useful as transversal filters that can exhibit uniform notch and bandpass filter characteristics over a wide range of frequencies from 1 MHz to 1.3 GHz.

1‐Gbit/s code generator and matched filter using an optical fiber tapped delay line

The macrobend optical fiber tapped delay line is a new device which is ideally suited for the processing of signals that have very large bandwidths. Two new applications of this device are presented: code generation and matched filtering. An 8‐bit code at 1 Gbit/s was generated with a programmable eight tap delay line having 1‐ns tap intervals. Matched filtering at a rate of 1 Gbit/s was also demonstrated with a similar deivce. This letter presents the first fiber optic code generator/matched filter of its kind.

Optical fiber V‐groove transversal filter

A novel single mode optical fiber tapped delay line that uses silicon V‐groove substrates to align an array of directional coupler taps has been demonstrated as a transversal filter. The device was used to generate and correlate 4‐bit, 400‐Mb/s coded sequences. The generated codes exhibited an amplitude uniformity of ±0.04 dB. The electrical correlation output was linear over a range of 25 dB and was limited by electronic components external to the fiber filter itself. Extension of the fabrication technique to include hundreds of taps at intervals as short as several picoseconds may be possible.

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.

Single-mode-fiber 1 × N directional coupler

We report the development of an adjustable single-mode-fiber multiterminal directional coupler that exhibits efficient coupling and uniform terminal output over a wide range of coupling coefficients. The device is made using a new technique that employs silicon V-groove substrates in the fabrication of arrays of evanescently coupled taps on single-mode fibers. The coupler is highly directional and polarization independent and exhibits excess loss as low as 0.09 dB per terminal in a 1 x 7 device. The fabrication technique may be extended to produce devices having large numbers of terminals. Applications include use in fiber data-bus systems and as a tapped delay line for broadband signal processing.

Single-mode fiber-optic components

In the process of studying single-mode fiber optic systems it became rapidly apparent a few years ago that it would be desirable to perform a number of functions with in-line components, which would allow for signal processing without the removal of the optical signal from the fiber. Some advantages of single-mode fiber optic components over conventional bulk optic components would be reduction of insertion loss, high stability, and compactness. They would also be free of difficulties involved in interfacing their integrated optic counterparts to single mode fiber optic systems.

Fiber-optic delay line devices for GigaHertz signal processing

Single mode optical fiber is an excellent delay medium for broadband signal processing because it exhibits extremely low loss and dispersion. Two new forms of a fiber delay line are presented, each capable of performing a variety of signal processing functions. In the macrobend tapped delay line, the optical signal is tapped by forming sharp bends in a fiber coil. A 16-tap device with 1 ns tap intervals has been demonstrated as a 1 Gb/s sequence generator and matched filter. A 19-tap device was demonstrated as a frequency filter with a fundamental passband at 1 GHz. The v-groove tapped delay line makes use of arrays of silicon v-grooves to precisely align and position an array of adjustable evanescently coupled fiber taps. A 4-tap v-groove device was used as a 500 Mb/s sequence generator and matched filter. A similar 7-tap device was demonstrated as a discretely variable delay line, and as a programmable filter whose fundamental passband could be varied in discrete steps from 69 MHz to 1.67 GHz. Both of the delay line designs presented appear to be extendable to include large numbers of closely spaced taps.

Single Mode Fiber Optic Components

Optical systems composed of single-mode fiber are finding increasing utility as high-band-width transmission systems, interferometers, and sensors. In addition to the unique properties of single mode fibers that permit such applications, these systems have an important advantage over their conventional bulk optics equivalents - namely, a compact, lightweight, flexible, and completely guided optical path. If fiber systems are to exploit this advan-tage to the fullest, however, compatible components are needed to perform some of the basic functions (power division, polarization control and filtering, etc.) that may be required in any optical system.

High-speed fiber-optic tapped delay line correlator/code generator

Tapped delay lines are basic components for performing a wide variety of signal processing op- orations, such as convolution, correlation, Fourier transformation, and the various processing and filtering functions which derive from them. These operations can be performed using a variety of approaches, such as surface acoustic wave tapped delay lines1 or charge-coupled devices.2 The problem is the extension of these conventional technologies to the processing of signals having bandwidths well in excess of 1 GHz. The macrobend optical fiber tapped delay line is a new device which uses single-mode optical fiber as the delay medium.3 It is ideally suited for high-speed signal processing because of the inherently large time- bandwidth product and low loss of single-mode fiber. In this presentation we describe two new applications of this device, namely, the use of the macrobend optical fiber tapped delay line as a code generator and as a correlator.