Giant optical gain in a rare-earth-ion-doped microstructure

Modal gain per unit length versus launched pump power is predicted and measured in a 47.5 at.% Yb(3+) -doped potassium double tungstate channel waveguide. The highest measured gain exceeds values previously reported for rare-earth-ion-doped materials by two orders of magnitude.     

Performance of Ar/sup +/-milled Ti:sapphire rib waveguides as single transverse-mode broadband fluorescence sources

Rib waveguides have been fabricated in pulsed-laser-deposited Ti:sapphire layers using photolithographic patterning and subsequent Ar/sup +/-beam milling. Fluorescence output powers up to 300 /spl mu/W have been observed from the ribs following excitation by a 3-W multiline argon laser. Mode intensity profiles show high optical confinement and the measured beam propagation factors M/sub x//sup 2/ and M/sub y//sup 2/ of 1.12 and 1.16, respectively, indicate single transverse-mode fluorescence emission. Loss measurements using the self-pumped phase conjugation technique have yielded comparable values (1.7 dB/cm) for the ribs and the unstructured planar waveguide counterparts. The combination of optimum modal properties and strong optical confinement, together with sufficient levels of fluorescence output, make the single-moded Ti:sapphire rib waveguides a very interesting candidate as a fluorescence source for optical coherence tomography applications.     

Efficiency of integrated waveguide probes for the detection of light backscattered from weakly scattering media

A semianalytical model for light collection by integrated waveguide probes is developed by extending previous models used to describe fiber probes. The efficiency of waveguide probes is compared to that of different types of fiber probes for different thicknesses of a weakly scattering sample. The simulation results show that integrated probes have a collection efficiency that is higher than that of small-core fiber probes, and, in the particular case of thin samples, also exceeds the collection efficiency of large-core highly multimode fiber probes. An integrated waveguide probe with one excitation and eight collector waveguides is fabricated and applied to excite and collect luminescence from a ruby rod. The experimental results are in good agreement with the simulation and validate the semianalytical model.     

Integrated Al O :Er Zero-Loss Optical Amplifier and Power Splitter With 40-nm Bandwidth

A combined planar lossless optical amplifier and 1 $,times,$2 power splitter device has been realized in Al$_2$ O$_3$:Er$^{3+}$ on silicon. Net internal gain was measured over a wavelength range of 40 nm across the complete telecom $C$ -band (1525–1565 nm). Calculations predict net gain in a combined amplifier and 1$,times,$ 4 power splitter device over the same wavelength range for a total injected pump power as low as 30 mW.      

Efficient high power operation of erbium 3 μm fibre laserdiode-pumped at 975 nm

Efficient CW operation of a 2.71 μm Er,Pr:ZBLAN double-clad fibre laser pumped with a single diode laser operating at a wavelength of 975 nm is described. A maximum output power of 0.5 W and a slope efficiency of 25% (with respect to the launched pump power) were obtained. Threshold pump powers of <200 mW launched were measured and consistent relaxation oscillations in the output from the fibre laser indicate the presence of a saturable absorption mechanism     

Reliable Low-Cost Fabrication of Low-Loss $hbox{Al}_{2}hbox{O} _{3}{:}hbox{Er}^{3+}$ Waveguides With 5.4-dB Optical Gain

A reliable and reproducible deposition process for the fabrication of Al₂O₃ waveguides with losses as low as 0.1 dB/cm has been developed. The thin films are grown at ~ 5 nm/min deposition rate and exhibit excellent thickness uniformity within 1% over 50times50 mm² area and no detectable OH^- incorporation. For applications of the Al₂O₃ films in compact, integrated optical devices, a high-quality channel waveguide fabrication process is utilized. Planar and channel propagation losses as low as 0.1 and 0.2 dB/cm, respectively, are demonstrated. For the development of active integrated optical functions, the implementation of rare-earth-ion doping is investigated by cosputtering of erbium during the Al₂O₃ layer growth. Dopant levels between 0.2-5times10²⁰ cm^-3 are studied. At Er³⁺ concentrations of interest for optical amplification, a lifetime of the ⁴I_13/2 level as long as 7 ms is measured. Gain measurements over 6.4-cm propagation length in a 700-nm-thick Al₂O₃:Er³⁺ channel waveguide result in net optical gain over a 41-nm-wide wavelength range between 1526-1567 nm with a maximum of 5.4 dB at 1533 nm.     

Energy recycling versus lifetime quenching in erbium-doped 3-μmfiber lasers

Based on recently published spectroscopic measurements of the relevant energy-transfer parameters, we performed a detailed analysis of the population mechanisms and the characteristics of the output from Er ³⁺-singly-doped and Er³⁺, Pr³⁺-codoped ZBLAN fiber lasers operating at 3 μm, for various Er³⁺ concentrations and pump powers. Whereas both approaches resulted in similar laser performance at Er³⁺ concentrations <4 mol.% and pump powers <10 W absorbed, it is theoretically shown here that the Er³⁺-singly-doped system will be advantageous for higher Er³⁺ concentrations and pump powers. In this case, energy recycling by energy-transfer upconversion from the lower to the upper laser level can increase the slope efficiency to values greater than the Stokes efficiency, as is associated with a number of Er³⁺-doped crystal lasers. Output powers at 3 μm on the order of 10 W are predicted     

Analysis of heat generation and thermal lensing in erbium 3-/spl mu/m lasers

The influence of energy-transfer upconversion (ETU) between neighboring ions in the upper and lower laser levels of erbium 3-/spl mu/m continuous-wave lasers on heat generation and thermal lensing is investigated. It is shown that the multiphonon relaxations following each ETU process generate significant heat dissipation in the crystal. This undesired effect is an unavoidable consequence of the efficient energy recycling by ETU in erbium 3-/spl mu/m crystal lasers, but is further enhanced under nonlasing conditions. Similar mechanisms may affect future erbium 3-/spl mu/m fiber lasers. In a three-dimensional finite-element calculation, excitation densities, upconversion rates, heat generation, temperature profiles, and thermal lensing are calculated for a LiYF/sub 4/:Er/sup 3+/ 3-/spl mu/m laser. In the chosen example, the fraction of the absorbed pump power converted to heat is 40% under lasing and 72% under nonlasing conditions. The heat generation in a LiYF/sub 4/:Er/sup 3+/ 3-/spl mu/m laser is 1.7 and the thermal-lens power up to 2.2 times larger than in a LiYF/sub 4/:Nd/sup 3+/ 1-/spl mu/m laser under equivalent pump conditions, thus, also putting a higher risk of rod fracture on the erbium system.     

Modelling of high-power diode-pumped erbium 3 μm fibre lasers

Abstract

We present theoretical calculations that relate to the cw operation of a high-power Er³⁺, Pr³⁺:ZBLAN double-clad fibre laser. Using the measured energy-transfer, energy-transfer-upconversion and cross-relaxation parameters relevant to Er³⁺-doped and Er³⁺, Pr³⁺-codoped ZBLAN, we compare the theoretical calculations from the model with recent experimental measurements. The model is then used to analyse the important pump and interionic processes occurring in Er³⁺, Pr³⁺:ZBLAN fibre lasers. The theoretical results indicate that energy transfer from Er³⁺ to Pr³⁺ leads to a fast depletion of the lower laser level and, due to the cw threshold condition, to low population densities in both laser levels. Thus, ground-state bleaching, pump excited-state absorption and energy-transfer upconversion amongst the Er³⁺ ions are avoided.