Paul Urquhart

Compound optical-fiber-based resonators

The relative merits of three designs of compound optical-fiber-based resonators for application to line narrowing in fiber lasers and demultiplexing in optical-communications systems are discussed. The three resonator designs are a set of concatenated rings, a three-reflector resonator with loop mirrors, and a fiber Fox–Smith interferometer.

A Nd 3+ -doped cw fiber laser using all-fiber reflectors

We demonstrate a novel all-fiber resonant optical cavity which uses two-fiber reflectors, each formed by a single loop of fiber between the output ports of a fiber directional coupler. The reflectivities of the fiber mirrors are each determined by the coupling ratio and the insertion loss of the fused couplers. When the cavity is formed in this way using a continuous length of Nd(3+)-doped fiber and pumped using a GaAs laser diode, lasing occurs at a wavelength of 1064 nm. Both theoretical and practical descriptions of the device are given.

Transversely coupled fiber Fabry-Perot resonator: theory.

The theory of output intensities and field strengths of two variants of a four-port fiber-based device called a transversely coupled fiber Fabry-Perot interferometer is presented. The analysis is sufficiently general to consider both input and output from all four arms in both variants. Finesse is calculated for all modes of operation.

Wavelength-division-multiplexed distributed optical fiber amplifier bus network for data and sensors.

A wavelength-division-multiplexed data-gathering network that uses a distributed fiber amplifier bus is demonstrated. A prototype, which is suitable for simultaneous data transmission and wavelength multiplexing of sensors, has been constructed based on lightly doped erbium fiber and fiber Bragg reflection gratings. The potential size to which such a network can be extended is discussed.

Long span fiber amplifiers

We examine the theory of optical amplification in long span single-mode fibers which have low levels of erbium dopant. When pumped from the transmitter end at a suitable wavelength, lightly doped fibers can form a distributed amplifier, capable of overcoming transmission losses due to the intrinsic attenuation of the host glass at the signal wavelength. The entire communications link in effect becomes a fiber amplifier. We critically examine the potential of a long span erbium doped fiber amplifier and compare it to a system consisting of a short span power amplifier, followed by an undoped transmission fiber.

Fiber lasers with loop reflectors

The theory of homogeneously broadened four level fiber lasers, which use fiber loops as distributed reflective elements, is examined. Such cavities can be made entirely from rare earth doped fiber. The amplifying characteristics of doped fiber loops are examined. The threshold pump power and the loop reflectivity necessary to optimize the lasing output power from an oscillator formed from two loops in series are predicted.

Transversely coupled fiber Fabry-Perot resonators: performance characteristics

The experimentally determined performance characteristics of the transversely coupled fiber Fabry-Perot (TCFFP) resonator are discussed. The frequency variation for two important input-output configurations agrees well with theory. Both channel passing and channel dropping outputs are demonstrated. We examine the variation of finesse and visibility with the coupling ratio. The visibility, as defined, is a measure of the filtering efficiency on-resonance. We show that with high quality optical components it is possible to obtain good finesse and visibility simultaneously. The TCFFP resonator, therefore, has potential application to demultiplexing and spectral analysis and as a resonant cavity for fiber lasers.

Optical Fiber Bus Protection Network to Multiplex Sensors: Self-Diagnostic Operation

We present a mathematical model for a wavelength- division multiplexed self-healing optical fiber bus network to interconnect an array of sensors. The network uses protection switching to reestablish service after the failure of one or more of its constituent elements. Our model is a matrix-vector formalism that divides the network into blocks. It predicts which wavelengths arrive at the receiver node when damage has occurred in one or more places. We study single and multiple failures within one block, categorizing and tabulating all combinations of surviving wavelengths. In this way, we correlate the received wavelengths with the failure location(s). The network thus provides “self-diagnosis,” which we define to be the determination of its own sites of failure from network management information, without requiring external resources.

Optical Amplifiers for Telecommunications

This paper reviews optical amplifier technologies for telecommunications networks. The operation and applications of erbium doped fibre amplifiers (EDFAs), fibre Raman amplifiers (FRAs), erbium doped waveguide amplifiers (EDWAs) and semiconductor optical amplifiers (SOAs) are described. The factors that influence their gain, operating bandwidths, spectral profiles and noise are also discussed.

Single and double distributed optical amplifier fiber bus networks with wavelength division multiplexing for photonic sensors

Two different optical fiber bus networks are compared and demonstrated experimentally as means of gathering information from four wavelength-division-multiplexed photonic sensors. Both topologies include distributed amplification, which allows one to overcome the limitation in the maximum number of sensors that can be multiplexed in a single structure. Results obtained with a dual-bus topology are compared with those achieved with a single-bus network.