D. B. Ostrowsky

Erbium-doped silica fibers for intrinsic fiber-optic temperature sensors

The variation in the green intensity ratio ((2)H(11/2) and (4)S(3/2) energy levels to the ground state) of Er ions in silica fibers has been studied as a function of temperature. The different processes that are used to determine the population of these levels are investigated, in particular 800-nm excited-state absorption in Er-doped fibers and 980-nm energy transfer, in Yb-Er-codoped fibers. The invariance of the intensity ratio at a fixed temperature with respect to power, wavelength, and doped fiber length has been investigated and shown to permit the realization of a high-dynamic-range (greater than 600 °C), autocalibrated fiber-optic temperature sensor.

Thermalization effects between upper levels of green fluorescence in Er-doped silica fibers

We present a spectroscopic study of the green fluorescence resulting from pump excited-state absorption in Er-doped silica fibers excited in the 800-nm range. The absorption and emission bands are selectively attributed to the (4)S(3/2) and (2)H(11/2) levels. The fluorescence response at two excitation wavelengths, the temperature behavior, and lifetime measurements demonstrate a fast thermalization between the (4)S(3/2) and (2)H(11/2) levels. This explains an important part of the (2)H(11/2) emission and the increase of the fluorescence intensity at high temperature.

Nd:MgO:LiNbO/sub 3/ channel waveguide laser devices

A report is presented on the fabrication and efficient CW operation at 1.085 mu m of Nd:MgO:LiNbO/sub 3/ proton-exchanged channel waveguide lasers and amplifiers optically pumped at 0.814 mu m. Thresholds as low as 1.5 mW and slope efficiencies up to 34% were achieved in monolithic miniature laser devices. Up to 14 mW of output power could be achieved without observation of photorefractive damage. Diode laser pumping was also demonstrated. For the amplifier a small-signal gain of 7.5 dB was achieved for 22 mW of coupled pump power. Experimental results were analyzed with the use of a mode overlap formalism and a value of 0.93 was found for the pump quantum efficiency. Absorption spectra, fluorescence spectra, and lifetime measurements are also reported for the bulk and waveguide material. >

Cerenkov configuration second harmonic generation in proton-exchanged lithium niobate guides

A theoretical and experimental study of second-harmonic generation using the Cerenkov configuration with proton-exchanged lithium niobate guides is presented. The analytic solution of the problem for the case of planar step-index guides makes it possible to identify the essential role played by the discontinuity of the nonlinear polarization at the guide-substrate interface. This leads to the prediction of an increasing conversion efficiency for decreasing values of guide nonlinearity. It is shown that the experimental results are consistent with a reduction of 50 to 70% of the value of the nonlinear coefficient in unannealed waveguides fabricated in slightly diluted or pure benzoic acid. The results presented permit the optimization of guide design for efficient second-harmonic generation in the Cerenkov configuration. >

High dynamic range temperature point sensor using green fluorescence intensity ratio in erbium-doped silica fiber

We propose a sensor based on the temperature dependant behavior of the two lines of green emission of the erbium ion. The ratio of the intensities of these two lines presents a very low dependance on pump wavelength and pump power fluctuations. The sensitivity of the ratio is 0.013//spl deg/C between room temperature and 600/spl deg/C. In addition, the measurement is self-calibrated. >

High-performance guided-wave asynchronous heralded single-photon source

We report on a guided-wave asynchronous heralded single-photon source based on the creation of nondegenerate photon pairs by spontaneous parametric downconversion in a periodically poled lithium niobate wave-guide. We show that, by use of the signal photon at 1310 nm as a trigger, a gated detection process permits announcement of the arrival of single photons at 1550 nm at the output of a single-mode optical fiber with a high probability of 0.37. At the same time the multiphoton emission probability is reduced by a factor of 10 compared with Poissonian light sources. Furthermore, the model we have developed to calculate those figures of merit is shown to be accurate. This study can therefore serve as a paradigm for the conception of new quantum communication and computation networks.

Clustering effects on double energy transfer in heavily ytterbium–erbium-codoped silica fibers

We study clustering effects in heavily ytterbium–erbium-codoped silica fibers. We demonstrate that the fraction of both ions found in clusters can exceed 50% in such fibers. A clustering effect is at the origin of an efficient double energy transfer process that generates a green fluorescence. An original method, based on a dynamic analysis of the ytterbium–erbium system, permits determination of the intracluster transfer rates involved, which are found to be high enough to compensate for the weak metastability of the erbium intermediate level.

Modeling and experimental observation of parametric fluorescence in periodically poled lithium niobate waveguides

We present a theoretical and experimental study of parametric generation in a guided wave quasi-phase-matched configuration. A numerical model taking into account inverted domain shape, electrooptic and photorefractive effects, as well as waveguide profiles allows calculation of the observed phase matching curves. The observed parametric fluorescence efficiencies can be explained by assuming a slight reduction of nonlinear coefficient and/or a partial degradation of the nonlinear grating. Optimization of the grating depth profile would permit room temperature parametric oscillation using pump wavelengths and powers attainable with diode lasers. >

Clustering-induced nonsaturable absorption phenomenon in heavily erbium-doped silica fibers.

Nonsaturable absorption experiments in heavily erbium-doped fibers demonstrate that the behavior of the absorption with pump power cannot be interpreted with an ion-pair model but requires that the presence of larger clusters be taken into account. Numerical modeling permits the determination of the percentage of ions organized in clusters, as much as 52% of the dopants in the tested fiber, and the intracluster transfer rate, up to 2 × 106 s−1.

Crystalline and optical quality of proton exchanged waveguides

In this paper we demonstrate the possibility of obtaining high-quality proton-exchanged (PE) lithium niobate guides by performing the exchange at high temperatures (300°C) in benzoic acid diluted with lithium benzoate. Rutherford backscattering studies suggest that the higher exchange temperatures avoid the production of niobium dislocations, and, IR absorption measurements suggest that the use of lithium benzoate diluted melts prevents the creation of interstitial hydrogen.