Ashish Madhukar Vengsarkar

Optical fiber long-period grating sensors

We present a novel class of highly sensitive sensors based on long-period fiber gratings that can be implemented with simple and inexpensive demodulation schemes. Temperature, strain, and refractive-index resolutions of 0.65 degrees C, 65.75 micro, and 7.69 x 10(-5), respectively, are demonstrated for gratings fabricated in standard telecommunication fibers.

Simultaneous strain and temperature measurement with long-period gratings

The differential modulation of the attenuation bands in a long-period grating is used for simultaneous sensing of axial strain and temperature. A grating fabricated in a conventional optical fiber is demonstrated for concurrent measurements of strain over a range of 2100 micro? and temperature over a range of 125 degrees C, with maximum errors of 58 micro? and 1 degrees C, respectively.

All-optical switching in long-period fiber gratings

Nonlinear pulse propagation in long-period fiber gratings is studied with a mode-locked Q -switched laser pulse approximately 80ps in duration at a wavelength of 1.05 microm . Optical switching, pulse reshaping, and optical limiting are found at intensities in the range of 1-20 GW/cm(2).

USING MICROCONTACT PRINTING TO GENERATE AMPLITUDE PHOTOMASKS ON THE SURFACES OF OPTICAL FIBERS : A METHOD FOR PRODUCING IN-FIBER GRATINGS

This letter describes a method for producing in-fiber gratings that reduces the effects of mechanical and optical instabilities limiting other methods. In this technique, opaque lines formed on the outside of the fiber using a procedure known as microcontact printing, serve as an amplitude photomask for exposure to ultraviolet light. Long-period fiber optic attenuators formed by ths technique demonstrate its advantages.

Broadband fiber dispersion compensation for sub-100-fs pulses with a compression ratio of 300

We report what is, to our knowledge, the first experimental demonstration of nearly dispersion-free transmission of sub-100-fs pulses over several tens of meters of fiber. 62-fs pulses are broadened initially and recompressed by a ratio of 300 over a 42-m concatenated fiber link consisting of standard single-mode and dispersioncompensating fibers. This dispersion-compensated fiber link is estimated to have a third-order dispersion ~6 times lower than that of dispersion-shifted fiber.

Long-period fiber grating sensors

Summary form only given. We propose novel long-period grating-based optical fiber sensors that possess high sensitivities and simple demodulation schemes, and can be easily configured for multiparameter measurements.

Fiber Bragg grating sensor demodulation system using in-fiber long period grating filters

We demonstrate a passive fiber Bragg grating sensor demodulator based on the wavelength-dependent transmission of long period grating filters. Strain resolution of the system was 1 (mu) (epsilon) for dc strain in a 3.3 Hz bandwidth. Quasi-static and dynamic operation of the system were investigated.

Optical Fiber Devices

Fiber-grating based devices for add/drop multiplexing, gain-equalization, and high-power generation are discussed. Advantages of using all-fiber devices are presented and current state-of-the-art performance is summarized.

High Temperature Fabry-Perot Based Strain Sensor for Ceramic Cross Flow Filters

The objectives of this research program were to develop instrumentation methods to allow in-situ analysis of ceramic cross flow (CXF) filters. Information from such instrumentation is needed to determine how the filters perform during operation, how subsequent filter and combustor designs may be improved based on the knowledge of such performance, and how and where damage and degradation occur. CXF filters are used for hot gas clean-up of coal-fired power generation systems, such as pressurized fluidized-bed combustors and integrated gasifier-combined cycles. The ceramic cross flow filter is analogous to cross-flow heat exchangers, except gas is passed between channels instead of thermal energy (heat). The CXF filters are made from multiple layers of thin, flat, porous ceramic (alumina or silicon nitride) with grooves which form channels in each layer. The layers are stacked to form a filter element that is approximately 30 cm high by 30 cm long by 10 cm wide. Consecutive layers of ceramic are oriented such that the channels formed are perpendicular to each other. One of the sides of the filter element is sealed. Gas enters the filter through the openings of the channel on the two sides that are perpendicular to the sealed end, permeates the porous ceramic, and exits through the openings on the side that is parallel to the sealed end.