David J. DiGiovanni

Spectrum-sliced fiber amplifier light source for multichannel WDM applications

A potentially inexpensive light source for multichannel WDM applications is proposed. The high-power amplified spontaneous emission (ASE) from an erbium-doped fiber amplifier (EDFA), which is already in the single-mode fiber, can be efficiently divided into many channels by using an integrated optic wavelength-division-multiplexing (WDM) demultiplexer. This spectrum-sliced ASE can be used as light sources for WDM systems in place of several wavelength-selected DFB lasers. To demonstrate the principle, the 40-nm-wide ASE spectrum of an EDFA was sliced using a narrow optical filter (3-dB bandwidth: 1.3 nm), and the resulting source was used for the transmission of up to 1.7 Gb/s of data. The problem of spontaneous-spontaneous beat noise in these sources is dealt with. It is estimated that the total capacity would be about 40 Gb/s, realistically, since the channel spacing should be at least three times the optical bandwidth of each channel to avoid crosstalk.<<ETX>>

Stable single-mode erbium fiber-grating laser for digital communication

In this paper we report the fabrication of a short, robust, single-mode Er/sup 3+/ fiber-grating laser. This laser is proven by the successful outcome of a long-term bit-error-rate test at the 10/sup -15/ level in a 5- G/s fiber transmission experiment. In the process we present a new pumping geometry, the elucidation of one origin of relaxation oscillations that have plagued previous lasers and the demonstration of a simple electronic feedback scheme for suppressing them. This prototype source shows real promise for use in a high-speed communications system. >

Ultraviolet laser fabrication of ultrastrong optical fiber gratings and of germania-doped channel waveguides

We report the fabrication of low loss (<0.2 dB) fiber Bragg gratings of 10 nm reflection bandwidth, and of 19 nm bandwidth lossy gratings. With this technology we also demonstrate the direct writing of channel waveguides in commercial germania‐doped wafers without the use of photoresist and etching.

EFFECTS OF CONCENTRATION AND CLUSTERS IN ERBIUM-DOPED FIBER LASERS

We report a low-threshold, high-conversion-efficiency erbium-doped fiber laser in a 100-parts-in-106 fiber pumped at 1.48 μm. The threshold and efficiency are found to deteriorate noticeably as the erbium concentration is increased. We propose that this is due mostly to rapid cross relaxation between ion pairs or clusters, and through modeling we show that the cluster content increases with concentration.

Highly nonlinear near-resonant photodarkening in a thulium-doped aluminosilicate glass fiber.

Permanent photoinduced optical attenuation has been observed in Tm(3+)-doped aluminosilicate glass fibers on exposure to near-resonance mode-locked 1064-nm radiation at 300 K. The rate of this darkening was observed to follow a 4.7 +/- 0.4 power dependence on the 1064-nm intensity. The result shows that absorption of infrared light of moderate intensity can lead to photoionization in rare-earth-doped glass, provided that a multiphoton stepwise excitation channel exists.

Characterization of erbium-doped fibers and application to modeling 980-nm and 1480-nm pumped amplifiers

Erbium-doped fibers are characterized using loss and gain coefficients, and one amplifier saturation parameter. With a large-signal amplifier model that resolves the amplified spontaneous emission spectrum, these easily measured parameters allow the fiber performance in 980-nm or 1480-nm pumped optical amplifiers to be assessed rapidly. In tests at 980-nm pump wavelength, good agreement between the theoretical and experimentally measured gains was obtained with amplifiers having either germano-silicate or germano-alumino-silicate core fibers.<<ETX>>

Refractive index perturbations in optical fibers resulting from frozen-in viscoelasticity

We show that frozen-in viscoelasticity has a significant impact on the refractive index profile of optical fibers. Viscoelastic strains can be frozen into an optical fiber during draw, or by cooling down a drawn fiber from its fictive temperature while under tension. The resulting refractive index perturbation is concentrated in the highest viscosity region of the fiber, exhibits minimal birefringence, and can significantly alter critical performance characteristics. Our quantitative theory for the refractive index perturbation is in excellent agreement with measured data. Frozen-in viscoelasticity can also be harnessed to serve as the basis for optical fiber devices.

Dynamic gain compensation in saturated erbium-doped fiber amplifiers

Dynamic compensation of low-frequency gain fluctuations in saturated erbium-doped fiber amplifiers is demonstrated. This compensation, based on a simple feedback-loop scheme makes it possible to reduce transient gain fluctuations efficiently across the whole amplifier bandwidth using only a low-power optical feedback signal. Such an, automatic gain control technique could be applied to suppress data packet interference due to traffic bursts in multiple-access networks, as well as in the implementation of long-haul fiber systems using erbium fiber amplifiers.<<ETX>>

Nonlinear wave mixing and induced gratings in erbium-doped fiber amplifiers

We present a study of nonlinear wave mixing in erbium-doped fiber amplifiers. Wave mixing is demonstrated in dynamic gain gratings induced by counterpropagating beams from a diode laser.

Concentration-dependent /sup 4/I/sub 13/2/ lifetimes in Er/sup 3+/-doped fibers and Er/sup 3+/-doped planar waveguides

We report on the concentration- and pump-dependent lifetimes of the spontaneous emission in Er/sup 3+/-doped fibers and Er/sup 3+/-doped waveguides. In addition, we measure the concentration dependence of the 550-nm fluorescence due to excited state absorption (ESA).<<ETX>>