Erbium was introduce into GaAs/AlGaAs quantum well structures in the process of growth by MBE in an attempt to enhance semiconductor-Er transfer by means of a resonance between quantum well and Er ion transitions. Instead the quantum well was washed out by efficient interdiffusion of Ga and Al and diffusion of Er. We have demonstrated also that erbium interacts with aluminum in arsenides; this interaction leads to the formation of Er-containing Al- enriched clusters.

Recent developments in rare-earth (RE)-doped glasses are presented. The paper includes an overview of UV, blue, green and IR fluoride glass fiber lasers, together with the performances of RE optical amplifiers of the first, second, and third telecommunication windows. Spectroscopic results concerning low-photon-energy sulfide and chloro-fluoride glasses for 1.3 micrometers amplification are discussed. A special section is devoted to phosphate glass lasers with high thermal loading capability for high laser power applications at 1.03 micrometers , 1.05 micrometers and in the eye-safe optical domain at 1.54 micrometers .

Recent studies of photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy in rare earth-doped chalcogenide glasses have discovered a novel broad excitation band for the rare earth emissions. This band is attributed to the absorption of light in the Urbach tail of the band edge absorption of the host glass, with a subsequent non-radiative transfer of the absorbed energy to the rare earth atoms. The present work provides new insight concerning the energy transfer mechanism through an investigation of the efficiency, peak energy, and lineshape of the board band excitation as a function of the bandgap energy of the host glass. The bandgap energy has been altered by changing the host glass composition, and by obtaining the PL and PLE spectra at temperatures ranging from 5K to 300K. In agreement with prediction, it is found that the spectral position of the broad PLE band tracks with the bandgap, shifting to higher energies as the bandgap is increased. It is also found, again agreeing with prediction, that in glasses with larger bandgaps the broad band PLE mechanism can excite higher lying transitions of the rare earth dopants.

Glasses containing Er³⁺ ions of 0.3 to 7 cation mol percent were prepared in the system of Ga₂S₃-GeS₂-LaS₃. Frequency upconversion spectra of Er³⁺ in the glasses were measured under the excitation at 800 nm and 980 nm. Green emissions at 533 nm (²H_11/2yields⁴I_15/2) and 552 nm (⁴S_3/2yields⁴I_15/2), and red emission at 665 nm (⁴F_9/2yields⁴I_15/2) were observed.In addition to these emission bands, 497 nm emission assigned to the ⁴F_7/2yields⁴I_15/2 transition was observed. The spectral properties are analyzed from the view points of low phonon energy property and high refractive index.

This paper investigates the resonantly enhanced nonlinearity in active-medium densely doped composite materials the interparticle collective effects due to the high concentration of dopants significantly enhances the nonlinear index of refraction and results in a density- dependent distortion of the dispersive spectra. Two types of active composite materials, organically modified silicate (ORMOSIL) incorporated with perylimide dye molecules and silica incorporated with erbium ions, which represent, respectively, molecular and atomic nonlinear system, are examined. Perylimide dye doped ORMOSILs exhibit more obvious collective effects at a relative lower doping level than erbium ions in silica. The enhancement of nonlinear index of refraction in active-medium densely doped composites provides a new possibility for the low-intensity operation of switching devices and self-guiding nonlinear devices. The gain properties are also studied.

There has been significant progress since 1990 on development of rare-earth-doped glass integrated optics amplifiers and lasers. Several fabrication processes were utilized to make rare-earth-doped waveguides. Neodymium and erbium doped waveguides were successfully produced, and amplifiers and lasers were demonstrated. Recently, high performance erbium-doped amplifiers in phosphate glasses were achieved. In this paper, we review the progress in development of neodymium and erbium doped lasers and amplifiers.

During the last few years, integrated optical waveguide lasers have been demonstrated in a variety of rare earth doped materials. Different techniques were used to fabricate such devices: ion exchange in neodymium doped glass ion implantation in crystals such as Nd:YAG² and Nd:LiNbO₃³, titanium diffusion in Nd:LiNbO₃⁴, Er:LiNbO₃⁵, and Nd:LiTaO₃⁶, and proton exchange in Nd:MgO:LiNbO₃⁷ and Nd:LiTaO₃⁸. Due to their electro-optic and nonlinear properties, rare earth doped lithium niobate and tantalate are very attractive for realizing mode-locked and Q-switched devices as well as intracavity frequency doubled sources. Following the success we had in realizing such functions in annealed proton exchanged Nd:MgO:LiNbO₃ waveguides, we tried to transpose this technique to Nd:LiTaO₃⁸ which has the reputation of having a higher optical damage threshold than LiNbO₃, and has ben used to produce efficient guided- wave frequency doublers using the periodic domain inversion technique, and Er:LiNbO₃ which allows applications in the telecommunication domain. This transposition turns out to be more difficult than expected. In this paper, I will explain these difficulties starting with some information in concerning the proton exchange technique itself. I will then present the results we obtained on the different crystals, to focus the discussion on the reduction of the excited state lifetime induced by the different kinds of proton exchange processes.

We report on the growth of erbium doped ZrF₄-LaF₃- BaF₂ glass films by metalorganic chemical vapor deposition (MOCVD) for the construction of planar waveguide devices. Our process provides the growth of high quality, uniform in thickness, and continuous films on a wide variety of common substrates. A protective layer of MgF₂ was deposited in-situ onto the Er-doped glass films under the same CVD deposition conditions. The luminescence of Er around 1.55 micrometers was observed in films on all the substrates used. The emission line shapes are the same as those observed from Er-doped fluorozirconate glass. MOCVD proved to be a feasible technology to grow rare-earth doped fluoride films for planar waveguide devices.

Guiding structures have been produced on the surface of fluoride glass by ionic exchange between fluoride ions of the substrate and chloride ions of HCl gas. The waveguides have been qualified by using analytical tools and optical characterizations. The active properties of Nd-doped channel waveguides are presented.

A planar sputter-deposited erbium-doped glass ridge was re- shaped into a hollow microcylinder using only photolithography, wet-etching and annealing. It is believed that selective build-up of gas is primarily responsible for this phenomenon, which is similar to glass-blowing. Other factors, such as the width and depth of the original ridge, the adhesion of the ridge to the underlying surface and the duration of the anneal, influence the eventual shape of the hollow microcylinder. By varying the processing parameters, a wide range of microcylinder shapes and sizes were obtained: circular and semi-circular profiles with 9.0 micrometers diameter or flatter 'tunnel-shaped' profiles ranging u pt o 25 micrometers in height and 100 micrometers in width. Microcylinders up to 1 cm long were fabricated. Water was sen to enter these hollow devices through capillary action. He-Ne light propagation through the hollow portion of the device was observed. These observations confirm that the microcylinders are hollow over their entire length. Hollow microcylinders or microchannels may find application in microfluidics and micro-optics.

In this paper, I will survey the field of ion-exchanged glass waveguide lasers and amplifiers. Ion-exchanged waveguide devices have significant virtues, such as low propagation losses and suitability for mass production. The progress in realizing lasers and amplifiers has been impressive, but more work is needed to produce commercially viable devices.

Modeling results for Er³⁺-doped waveguide amplifiers fabricated by various ion-exchange processes are presented. The gain performance of these devices for 977 nm and 1.48 micrometers pump wavelengths are compared. Measured spectroscopic properties of a phosphate glass with Er³⁺ concentration of 3.7 X 10²⁰ cm^-3 are used throughout the modeling, and waveguide propagation loss of 0.1 dB/cm is used. It is shown that gain coefficients exceeding 5 dB/cm are feasible utilizing optimized ion- exchanged waveguides in this glass. The modeling is performed for glasses doped with erbium only, excluding possible ytterbium codoping.

A rigorous scalar model for predicting the characteristics of rare-earth-doped waveguide lasers has been developed. The model consists of two nonhomogeneous wave equations: one for the forward-propagating laser signal power, the other for the backward-propagating laser signal. These equations are coupled with one forward-propagating, nonhomogeneous wave equation representing the pump signal. The three wave equations are coupled with the space dependent laser rate equations to form a system of time dependent differential equations. This large system of equations is solved, using appropriate initial and boundary conditions, by the method of lines using collocation for the spatial approximation. The solutions to this system yield data which predict the time and position-dependent laser signal power, pump power, and population densities in a waveguide laser cavity supporting an arbitrary guided mode. The assumptions made in this new model are that the transverse field maintains the same shape as a function of longitudinal position in the laser cavity and that the effects of spatial hole burning and standing waves are neglected. We have used this model to predict continuous wave and Q-switched laser performance for Er an Er/Yb-doped lasers. We have achieved favorable comparisons with actual laboratory operation of cw Yb/Er-co- doped waveguide lasers. Results from simulations of Er-doped and Yb/Er-doped Q-switched lasers are presented which show that high peak powers on the order of 500 W and 1 ns pulse widths can be achieved.

Erbium-ytterbium co-doped is an attractive system for short, efficient lasers and amplifiers operating in the 1.5 micron band. Co-doping permits a cooperative cross-relaxation process to transfer energy from excited ytterbium ions to the erbium system. This process can be used as a transfer energy from excited ytterbium ions to the erbium system. This process can be used as a pumping mechanism at 980 nanometers to significantly increase the absorbed pump power.Efficient energy transfer between the ytterbium and erbium ions enables the operation of compact laser devices with low erbium concentration, thus avoiding parasitic effects. The material parameters of a co-doped glass, including the cross-relaxation coefficient, are measured. A rate equation analysis of the co-doped system is developed, and approximate analytic expressions are derived for the lasing threshold, slope efficiency, and maximum output power. Short, ion-exchanged, waveguide lasers are fabricated in co-doped erbium-ytterbium glass. Lasing is achieved around 1537 nanometers with a launch power threshold and slope efficiency of approximately 15 milliwatts and 5.5 percent, respectively.

Erbium and erbium/ytterbium co-doped silicate glass waveguide lasers have been fabricated by silver ion-exchange and their characteristics analyzed. We report on measurements and comparisons made in the lasing properties of these devices, including threshold, slope-efficiencies and pump tuning ranges. The results presented show that through proper choice of host glass, it is possible to make low-threshold lasers both in singly and co-doped devices.

Recent developments in Er-doped glass waveguide amplifiers on silicon will be reviewed. In a number of devices usable gain at practical pump powers was demonstrated in packaged devices. Challenges of integration of waveguide amplifier devices into silicon optical bench technology will be discussed.

The state-of-the-art of Er-doped integrated optical lasers in LiNbO₃ is reviewed. They are fabricated in Er- diffusion doped substrates with Ti-diffused channel guides of high quality. The laser resonators are formed by dielectric mirrors vacuum-deposited on the polished waveguide end faces. Five different types of Ti:Er:LiNbO₃ waveguide lasers are presented.Among them are free running Fabry-Perot lasers of six different wavelengths in the range 153nm < (lambda) < 1610nm with a cw-output power up to 63mW. They have a shot noise limited relative intensity noise at frequencies above 50MHz. Tunable lasers have been developed by the intracavity integration of an acoustooptical amplifying wavelength filter yielding a tuning range up to 31nm. With an intracavity electrooptic phase modulator modelocked laser operation has been obtained with pulse repetition frequencies up to 10GHz; pulses of only a few ps width could be generated. With an intracavity amplitude modulator Q-switched laser operation has been achieved with up to 2.4W pulse peak power at 2kHz repetition frequency. Moreover, distributed Bragg reflector lasers of emission linewidth < 8kHz have been developed using a dry- etched surface grating as one of the mirrors of the laser cavity.

A means of reproducibly fabricating stable cw channel waveguide lasers in rare-earth-doped Ti:LiNbO₃ is demonstrated, through careful choice of the light propagation direction. Z-propagating waveguides have been fabricated in Nd:Ti:LiNbO₃ and room-temperature cw laser operation has been obtained by pumping in the 800 nm-band, with greatly reduced photorefractive instability. The reduced photorefractive damage susceptibility in this waveguide configuration has been used to our advantage in the realization, for the first time, of a 980 nm-pumped laser in Er:Ti:LiNbO₃. The device showed a lasing threshold of 10.5 mW of absorbed pump power and a slope efficiency of 8.5 percent.

This paper describes the optical amplification characteristics and reliability of praseodymium-doped and erbium-doped fluoride optical fiber amplifiers, with a view to their application in practical optical systems.

In this paper, we report second harmonic generation in a tunable/Q-switch Nd3+-doped fiber laser using a LiNbO₃-integrated optics device. The component is a low-voltage asymmetric Mach-Zehnder Interferometer. Laser emission occurs simultaneously at two wavelengths (lambda) ₀ equals 1088 nm et (lambda) ₂ equals 544 nm. As a driving voltage is applied to the LiNbO₃ component, the lasing wavelengths are tuned by mode hopping. We demonstrate a Q-switch mode operating of that laser.

This communication deals with optical noise measurements of an erbium-doped fiber amplifier with input signal. We are able to determine the net gain and the noise factor from only these low frequency electrical noise measurements and new simple relations. It is presented as alternative to optical analyzer measurements and it has no limitation for high input signals.

Dependence of the noise characteristics of high concentration erbium doped fiber amplifiers (EDFA's) on different pumping configurations have been numerically simulated for pump wavelengths of 514.5nm, 532nm, 800nm, 980nm and 1480nm and experimentally studied for the 514.5nm pump wavelength. Our studies show that for highly doped EDFA's with significant upconversion losses, contradirectional pumping scheme offers lower noise figures at high pump powers. When excited state absorption at the pump wavelength dominates over upconversion losses, codirectional pumping gives lower noise figures.

In this paper, a fiber amplifier 1.3 micrometers is presented. It was made of Nd-doped fluoride glass fiber with a core diameter of 9 micrometers , which is developed in our institute. A DBF pulsed laser at (lambda) equals 1.327 micrometers is injected into one end of the fiber as the source of amplified signal and the pumping light source at (lambda) equals 0.8 micrometers is injected into the other end of the fiber through a coated plate that is fully transparent at 0.8 micrometers , totally reflective at 1.3 micrometers wavelength. The amplified signal at 1.3 micrometers wavelength is detected having a gain of 8.5 dB.

Cooperative upconversion processes and Yb-Er energy transfer efficiencies in high Er concentration phosphate glasses were studied. The cooperative upconversion coefficients were deduced from the pump intensity dependence of luminescence decay curves. Cooperative upconversion coefficients of ⁴I_13/2 level, for Er³⁺ concentrations higher than 1 X 10²⁰ cm^-3, are one order of magnitude smaller than the ones reported for silica glass. The increase in the cooperative upconversion coefficient with the increase in Er³⁺ concentration was found to be small and Er³⁺ concentrations as high as 3.7 X 10²⁰ cm³⁺ in this glass are feasible. Yb-Er energy transfer efficiency in Yb/Er co-doped phosphate glasses, with Er concentrations as high as 1.9 X 10²⁰ cm^-3 and 2.4 X 10²⁰ cm^-3, were measured with a pump and probe technique and also estimated from lifetime measurements. The energy transfer efficiencies exceed 95 percent, although the ratio of the concentrations, Yb/Er, is only about 1.2 and 2 in the samples studied.This confirms that efficient pumping of high Er³⁺ concentration phosphate glass, required in waveguide amplifiers, can be achieved utilizing Yb/Er co-doping.