Walter Margulis

Dye laser pumped by Nd:YAG laser pulses frequency doubled in a glass optical fiber

Efficient frequency doubling of a cw Q-switched and mode-locked Nd:YAG laser has been observed in commercial single-mode optical glass fibers. Pulses of duration ~55 psec and intensities as high as ~0.55 kW were produced at 0.53 microm. The maximum peak power-conversion efficiency measured was ~3%. The frequency-doubled light generated in the glass fibers was sufficient to pump a commercial Rh6G dye laser with ~19% efficiency at 570 nm.

Experimental studies on efficient frequency doubling in glass optical fibers

Experiments were carried out in order to investigate efficient second-harmonic generation in phosphor-doped glass fibers. Peak conversion efficiencies > 5% corresponding to peak powers> 1 kW at 0.53 microm have been obtained. By measuring the side light emitted and also by cutting the fibers, both the second-harmonic output power and the generation rate were studied along the fiber. Other measurements, including the polarization and mode structure of the frequency-doubled output, are also described.

Integrated fiber Mach-Zehnder interferometer for electro-optic switching.

Molten alloys under high pressure were used to obtain fibers with long internal electrodes that are solid at room temperature. An integrated Mach-Zehnder interferometer was constructed from a twin-core twin-hole fiber that permitted application of an electric field preferentially to one of the cores. Good stability and a switching voltage of 1.4kV were measured with a 1-m-long fiber device with a quadratic voltage dependence.

Grating formation in pure silica-core fibers

Strong grating formation in pure silica-core fibers by use of 193-nm ArF-laser radiation is reported. Unsaturated refractive-index changes of Dn~0.3x10(-3) were observed in nontreated fiber, and changes of Dn~0.5x10(-3) were observed in fibers with a high hydroxyl concentration. Possible mechanisms of photosensitivity in pure silica-core fibers are discussed.

A spectrally tunable microstructured optical fibre Bragg grating utilizing an infiltrated ferrofluid

The spectral response of a Bragg grating reflector inscribed in a microstructured optical fibre is tuned by employing an infiltrated ferrofluid, while modifying the overlap of the ferrofluidic medium with the grating length. Significant spectral changes in terms of Bragg grating wavelength shift and extinction ratio were obtained under static magnetic field actuation. Spectral measurements revealed non-bidirectional propagation effects dependent upon the relative position between the ferrofluid and the grating. The actuation speed of the device was measured to be of the order of few seconds.

Inducing a large second-order optical nonlinearity in soft glasses by poling

Electrothermal poling of soft glasses (soda lime and borosilicate glass) at relatively high currents led to the creation of a second-order optical nonlinearity. The second-harmonic generation efficiency decays in time, and the decay rate can be accelerated by exposure to intense infrared radiation.

Large increase in photosensitivity through massive hydroxyl formation

We report a large increase in photosensitivity of germanium-doped silicate fibers by rapid heat treatment of hydrogen-loaded fibers at 1000 degrees C before exposure of the fibers to 242-nm radiation. The increase in photosensitivity is compared with thermally induced absorption caused by introduction of massive amounts of hydroxyl species. The absorption loss was measured to be 0.02 dB/cm mol.% OH at 1.55 mum. Strong gratings (Dn > 1 x 10(-4)) in germanium-free phosphorous-doped fibers in the presence of 242-nm radiation have also been manufactured by this technique.

Phase-shifted Bragg microstructured optical fiber gratings utilizing infiltrated ferrofluids

Results are presented on the efficient spectral manipulation of uniform and chirped Bragg reflectors inscribed in microstructured optical fibers utilizing short lengths of ferrofluids infiltrated in their capillaries. The infiltrated ferrofluidic defects can generate either parasitic reflection notch features in uniform Bragg reflectors of up to 80% visibility and ~0.1 nm spectral shift or tunability of the bandwidth and strength reflection up to 100% when introduced into chirped gratings. Spectra are presented for different spatial positions and optical characteristics of the ferrofluidic section.

Optofluidic magnetometer developed in a microstructured optical fiber

A directional, in-fiber optofluidic magnetometer based on a microstructured optical fiber (MOF) Bragg-grating infiltrated with a ferrofluidic defect is presented. Upon application of a magnetic field, the ferrofluidic defect moves along the length of the MOF Bragg grating, modifying its reflection spectrum. The magnetometer is capable of measuring magnetic fields from 317 to 2500 G. The operational principle of such in-fiber magnetic field probe allows the elaboration of directional measurements of the magnetic field flux.

Who needs a cathode? Creating a second-order nonlinearity by charging glass fiber with two anodes

We report that it is possible to create a fiber electret by having both internal electrodes of a twin-hole fiber at the same anodic potential, i.e., without the use of a contacted cathode electrode. We find that a stronger and more temperature-stable charge distribution results when the fiber core is subjected to an external field near zero. Negative charges from the air surrounding the fiber are sufficient for the recording of an electric field across the core of the fiber that is twice stronger than when one anode and one cathode electrode are used. The enhancement in stability and in the strength of the effective chi((2)) induced are a significant step towards the wider use of fibers with a second order optical nonlinearity.