R. Wyatt

Spectroscopy Of Rare Earth Doped Fibres

In this paper we describe work aimed at identifying and measuring properties of rare earth doped fibres which may affect their use and application in oscillators and amplifiers. The main dopants of interest are erbium(1.55μm), and neodymium (0.9, 1.06, 1.3μm). We shall discuss the measurement, and effects, of parasitic absorption from the upper laser level (known as excited state absorption, or ESA), at both pump and signal wavelengths. We shall also consider how detailed measurements of fluorescence decay from the excited level can yield information about quenching, upconversion, and energy transfer processes.

Pump excited state absorption in Er3+ doped optical fibres

Abstract Ground and excited state absorption coefficients in the wavelength range 420–850 nm of Er 3+ doped optical fibres have been measured for various composition silica and fluorozirconate based fibres. Detailed results are presented for features near 650 nm and 800 nm. Excited state absorption near 800 nm is significant for all the fibres studied. Other possible pump wavelengths are discussed.

Alternative Gaussian spot size polynomial for use with doped fiber amplifiers

The validity of the usual Marcuse-Gaussian approximation for fiber modes is discussed in the context of doped fiber amplifiers and an proposed: omega /a=(0.616+1.66/V/sup 1.5/+0.987/V/sup 6/). The polynomials use is illustrated by extending the range of a simple Gaussian-based, numerical model of an erbium-doped fiber amplifier. Excellent agreement with a real-field-based model is demonstrated for practical fiber V values.<<ETX>>

Ultra narrow-band optical fibre sidetap filters

We present a new fibre structure for use in sidetap filters for telecommunications applications with low insertion loss due to splices and bends and a filter FWHM bandwidth of only 3.4 nm. The aim of our research in this area has been to find fibre and grating designs yielding very narrow filter responses while maintaining low backreflection by the appropriate choice of blaze angle, and low insertion loss due to splices and bends by the appropriate choice of index profile.

10 Gbit/s directly-modulated, high temperature-stability, external fibre grating laser for dense WDM networks

We report on the modulation performance and temperature stability of a fast (up to 10 Gbit/s) InGaAsP-InP MQW semiconductor external fibre grating laser. The combination of high speed direct modulation with low static and dynamic chirp makes this laser very attractive for application in dense WDM optical networks.

Efficient, high-power, high-gain Er3+-doped silica fiber amplifier

We present results demonstrating that Er doped silica fibres may be operated as efficient high power oscillators and high gain power amplifiers in the 1i5um telecommunications window. Investigation of the saturation behaviour of a number of different fibre types is undertaken. The best of these provides 140mW of amplified output for a 1mW input signal at 1. SSpm pumped with 180mW at 1. 48pm. Pumping with higher powers at 980nm provides in excess of 500mW output for the same input signal power. Quantum efficiencies greater than 80 are achieved for both pump wavelengths. A 980nm contra-directionally pumped grating tuned oscillator is demonstrated giving a tunable output of over 250mW for lasing wavelengths between 1. 52jm and 1. S7jm and a launched power of 540mW. This represents an internal quantum efficiency in excess of 95. The results of two systems experiments utilising the power amplifiers are also presented. The first demonstrates a ten channel WDM network broadcasting to over 7 users111 and the second an unrepeatered 250km 2. 4Gbit/s transmission system12

Modulation bandwidth of high-speed, directly-modulated semiconductor laser with detuned external fibre grating reflector

We have studied theoretically and experimentally the impact of operating wavelength detuning on the modulation performance of high-speed directly modulated semiconductor laser with an external fibre grating resonator. It was shown that FGL modulation bandwidth increases with wavelength detuning and can be doubled, up to /spl sim/18 GHz.

High-speed operation of an optically amplified system in the first telecommunications (800-850 nm) window

A diode pumped, commercially packaged, thulium doped fluoride fiber amplifier, (TDFFA) operating in the region of 0.8 /spl mu/m has been used in a series of high speed (1.2 Gb/s) systems experiments in the 1st telecommunications window. The results of this work indicate that the application of this amplifier unit could have significant benefits for future LAN/MAN type systems architectures involving large signal splits to customer premises.

Rare-earth-doped fluoride fibers for optical amplification (Invited Paper)

Rare earth-doped fluorozirconate fibres show potential as optical amplifiers from the visible to the mid IR. This paper reviews the current status of their application in telecommunications, concentrating on Tm and Er-dopants for the 1st window and Nd and Pr-dopants for the 2nd window. A 1300 nm system operating at 2.5 Gbits/s using a Pr-doped fibre amplifier is described.

Use of fibre gratings for bit skew compensation in all optical bit parallel WDM systems

We demonstrate transmission of two wavelength division multiplexed (WDM) bit parallel channels over 100 km of standard single mode fibre link using direct-modulated laser diodes at 10 Gbit/s channel. Step-chirped fibre gratings are used to simultaneously compensate to bit skew and dispersion. Bit skew of approximately 2.5 ns due to the fibre dispersion is completely compensated. Our work show shows that the step-chirped fibre grating technique can eliminate the bit skew for bit parallel WDM systems operating at Gbit rate over hundreds of kilometres of fibre link.