An erbium-doped multimode optical fiber amplifier

The authors describe the first experimental study of an erbium-doped multimode fiber amplifier. The focus has been to characterize an intermediate core erbium-doped optical fiber, a fiber that is capable of propagating many guided modes at both the signal and pump wavelengths, and to determine the feasibility of using such an active fiber as a multimode fiber amplifier, by measuring its gain, noise, and pump power requirements. For a 2-m length of a 13-μm-core erbium-doped fiber, the authors measured gain as high as 16 dB at a signal wavelength of 1543 nm, with approximately 100 mW pump power (980 nm). For these same test conditions, the smallest excess noise factor β was 42     

4 Gb/s soliton data transmission over 136 km using erbium dopedfiber amplifiers

The use of semiconductor-laser-pumped erbium-doped fiber amplifiers and an externally modulated mode-locked external-cavity semiconductor laser to obtain soliton data transmission at 4 Gb/s over 136 km of nondispersion shifted fiber is described. After 136 km of transmission and at low pulse powers, the ~80 ps fiber input pulse width was broadened to ~150 ps. At high pulse powers the output pulse width was maintained at 80 ps, as expected for N=1 solitons. N =3 solitons were also observed at lower data rates     

High performance optical wavelength shifter

A broadband (>50 nm) wavelength shifter capable of switching multigigabit data between optical frequencies in the 1.5 mu m region is presented. The device, based on gain saturation in a semiconductor optical amplifier, is tunable, has gain, and is nearly polarisation insensitive. Data degradation after wavelength shifting is negligible.<>     

Optical fiber up-tapers with high beam expansion ratios forcomponent fabrication

Optical fibre up-tapers with beam expansion ratios of 10, about twice the previously achieved value for the same taper outer diameter, have been fabricated and characterized. The increased beam expansion is achieved with a near step-index profile for the core of the taper. The excess coupling loss between two tapers is less than 0.1 dB. A lateral offset of more than 20 μm or an axial displacement of 4 mm between tapers caused an excess loss of 1 dB. The angular tolerance for this loss is a manageable 0.3°. These tapers permit, for a given beam expansion ratio, the manufacture of smaller outer diameter, more compact structures of self-aligned beam expansion. They also permit the insertion of optical elements into the expanded beam for the fabrication of inline single-mode passive fiber components     

Integrated MQW optical amplifier/noise-filter/photodetectorphotonic circuit

A monolithically integrated photonic circuit with an InGaAs/InGaAsP multiple-quantum-well (MQW) traveling-wave optical amplifier, a Bragg reflection grating-folded noise filter, and an MQW photodetector has been demonstrated. This photonic circuit offers potential as a preamplified lightwave receiver in high-data-rate applications because of its compactness and potentially low cost     

Characterization and modeling of amplified spontaneous emission in unsaturated erbium-doped fiber amplifiers

The generation of amplified spontaneous emission (ASE) in erbium-doped fiber amplifiers (EDFAs) is characterized. A theoretical model, leading to closed-form analytical expressions for the backward and forward ASE power spectra, is developed for the unsaturated gain regime. This study shows that for the unsaturated gain regime, both power and spectral distributions of the ASE can be well described through the closed-form expressions, which require only measurable experimental parameters.<>     

Star couplers with gain using multiple erbium-doped fibers pumped with a single laser

An economical method for combining erbium-doped fiber (EDF) amplifiers and star couplers, is presented. It involves simultaneously pumping EDFs placed at the input or output ports of the coupler with a single laser pump source distributed through the coupler itself. In this way, many amplifiers can share the cost of a single pump laser, and the need for individual pump/signal combiners is eliminated.<>     

A 1.5- mu m laser package frequency-locked with a novel miniature discharge lamp

The authors report a packaged distributed feedback (DFB) laser frequency-locked to the Kr 1s/sub 2/-2p/sub 8/ transition at 1.54782 mu m using a novel miniature discharge lamp. This transition is not only close to the wavelength where typical single-mode optical fibers show minimum attenuation but also gives a large optogalvanic signal. This lamp generates more than an order of magnitude larger optogalvanic signal for the same input power than conventional indicator lamps of comparable size. The frequency stability of the laser package is better than 2 MHz, and the fiber-to-laser coupling loss (<2 dB) is very stable against temperature fluctuations and mechanical vibrations.<>     

Asymmetric fiber microlenses for efficient coupling to ellipticallaser beams

It is demonstrated that it is possible to fabricate asymmetric hyperbolic microlenses directly on the ends of single-mode optical fiber to enhance the fiber's coupling to elliptical laser beams. The lenses, with controlled eccentricity ratios, are made by micromachining the end of the fiber with a pulsed CO₂ laser, as the fiber is directed by computer control about the focussed laser beam. Coupling efficiencies of 84% (-0.74 dB) have been realized with single transverse mode lasers at a wavelength of 0.98 μm having an approximately 3 to 1 beam ellipticity. With multitransverse-mode lasers at 1.48 μm having similar ellipticities, the asymmetric lenses demonstrate a 2-dB increase in coupling efficiency over symmetric hyperbolic microlenses. The authors have coupled about 120 mW from such a 360 mW laser, used to pump erbium-doped fiber amplifiers, into single-mode fiber     

Single-mode optical fibre tapers for self-aligned beam expansion

We demonstrate that optical fibre tapers can be utilised as a new means for achieving self-aligned beam expansion in single-mode fibres. These devices, which have a standard single-mode geometry at one end and gradually increase to a core size in the order of 100 ?m at the other end, have greatly reduced sensitivities to lateral and axial displacements and an excess coupling loss between two tapers of less than 0.1 dB.