J.E. Román

Tunable coupled-cavity waveguide laser at room temperature in Nd-diffused Ti:LiNbO3

We report on a Y-junction channel waveguide laser, operating at room temperature, in Nd-diffused Ti:LiNbO(3). Pumping was performed with a cw Ti:A1(2)O(3) laser operating at 816 nm. With feedback provided only by the polished end faces of the device, a cw lasing threshold of ~39-mW launched pump power was obtained, with a slope efficiency of ~35%. Using 95% reflectivity mirrors at the waveguide ends, we reduced the lasing threshold to ~4 mW, with a slope efficiency of ~2.6%. Tuning of the lasing signal over a range of 2.3 nm around a center wavelength of 1092.7 nm was demonstrated, with a monolithically integrated phase modulator.

1.7 μm excited state absorption measurement in erbium‐doped glasses

We have measured, for the first time, the complete 1.7µm excited state absorption spectrum in erbium doped glasses. The spectrum is obtained by measuring the gain of an erbium doped waveguide in the 1400-1800 nm region. Using the measured spectra, we estimate the 1.5µm uniform upconversion rate by calculating the spectral overlap between the 1.5µm emission and 1.7µm ESA cross sections. The technique is applied to erbium-doped, ion-exchangeable silicate glasses, yielding upconversion constants in the range of 1-10 x 10 -18 cm 3 /s.

Fluorescence of Ti 3+ ions thermally diffused into sapphire

The thermal diffusion of Ti(3+) ions into sapphire is demonstrated, and the spectroscopic characteristics of the locally doped region are presented. The spectral line shape, polarization dependence, and excited-state lifetime of indiffused Ti:sapphire are in excellent agreement with previously published data for high-quality, bulk-doped Ti:sapphire laser crystals. The observed diffusion rate at 1950 degrees C is of the order of D = 10(-14) m(2) s(-1). These results represent a significant step in the development of a versatile broadly tunable waveguide laser based on the Ti(3+):sapphire material system established for conventional bulk lasers.

Beat-length measurement in directional couplers by thermo-optic modulation

In integrated-optical directional couplers formed by two parallel waveguides we measure the difference Deltabeta = beta(even) - ss(odd) between the propagation constants of the supermodes. We couple them locally by heating a fine spot on one of the guides. When the spot is scanned along the coupler, the output power from one of the guides is found to vary periodically. The period of variation is the modal beat length Lambda = 2pi/Deltabeta. We demonstrate this technique with directional couplers fabricated by K-ion exchange in glass. Beat lengths in the range 0.6 -2.2 mm are measured with an accuracy of +/-0.3%.

1.7 µm Excited State Absorption Measurement in Erbium-doped Silicate Glasses

Planar erbium doped waveguide amplifiers are important components in the development of integrated optical communication circuits at 1.5 μm. Such devices must achieve high gains in short lengths and thus require high erbium concentrations (>1019 cm−3). At these doping levels, however, the amplifier gain and efficiency are degraded by ion-ion interactions in the form of uniform and clustered upconversion [1], Upconversion is a problem in erbium-doped glasses because the 4I13/2→4/15/2 emission and 4I13/2→4I9/2 ESA transitions overlap. Therefore, it is of fundamental interest to measure the ESA spectrum. Wyatt [2] measured the tail of this spectrum to demonstrate that absorption of 1.55 μm photons from the 4I13/2 level could not occur. We have measured, for the first time, the full 1.7 μm ESA spectrum in erbium-doped glasses and used it to estimate the uniform upconversion rate. The silicate glasses studied are suitable for the development of ion-exchanged waveguide amplifiers at 1.5 μm.

Measurement of complex coupling coefficients of directional coupling by thermo-optic modulation

Directional coupling between two parallel singlemode optical waveguides is the functional principle underlying numerous integrated optical devices, such as modulators, filters and sensors. As the coupling efficiency depends critically on the synchronism of wave propagation and on the field overlap of the two guides, tight tolerances apply in waveguide fabrication, and a precise determination of the coupling parameters is essential.

Ion-Exchanged Waveguide Amplifier in Erbium-Doped Glass for Broad-band Communications

We discuss the fabrication, characterisation and modelling of planar erbium-doped amplifiers realised as ion-exchanged waveguides in glass.