Jayantilal S. Patel

Programmable shaping of femtosecond optical pulses by use of 128-element liquid crystal phase modulator

Programmable shaping of femtosecond pulses by using a 128-element liquid crystal modulator to manipulate the phases of optical frequency components which are spatially dispersed within a grating-and-lens pulse shaping apparatus is described. This apparatus makes possible gray-level control of the spectral phases and allows modification of the pulse shape on a millisecond time scale under electronic control. Refinements in the design of the multielement modulator result in pulse shaping fidelity comparable to that which can be achieved with microlithographically fabricated masks. Several examples of pulse shaping operation, including pulse position modulation, programmable pulse compression, and adjustable cubic phase distortion, are described. >

Programmable femtosecond pulse shaping by use of a multielement liquid-crystal phase modulator.

We report programmable shaping of femtosecond optical pulses by use of a multielement liquid-crystal modulator to manipulate the phases of spatially dispersed optical frequency components. Our approach provides for continuously variable control of the optical phase and permits the pulse shape to be reconfigured on a millisecond time scale. We use the apparatus to demonstrate femtosecond pulse-position modulation as well as programmable compression of chirped femtosecond pulses.

Electrically tunable optical filter for infrared wavelength using liquid crystals in a Fabry–Perot étalon

Using the refractive index modulation in liquid crystals by an externally applied electric field, we show that common nematic liquid crystals can be used in a Fabry–Perot etalon to produce an electrically tunable optical filter for use in the infrared region. Using commercial liquid crystals we demonstrate that the wavelength can be tuned over 175 nm using less than 10 V. In our first device the free‐spectral range of the etalon is about 75 nm with a passband of about 1–2 nm which is determined by the quality of the mirrors that we have used.

Acoustically tuned erbium-doped fiber ring laser

We report what is to our knowledge the first narrow-linewidth, continuously tunable laser that uses an acousto-optic filter to achieve a broad tuning range. The unidirectional ring-laser configuration incorporates an erbium-doped fiber amplifier as the gain medium and an integrated, frequency-shift-compensated acousto-optic filter as the tuning element. Using a 980-nm optical pump with 60 mW of launched power, we obtained nearly 2 mW of laser output with 10% output coupling. A tuning range of 40 nm was achieved, centered about 1545 nm. Single-longitudinal-mode operation with a 10-kHz linewidth was demonstrated, although the laser wavelength hopped between nearby longitudinal modes because of path-length fluctuations. Wavelength switching at rates up to 100 kHz was examined.

Dynamic holographic interconnects with analog weights in photorefractive crystals

A photorefractive interconnect system with coherently erasable synapses (PISCES) is described. Comparing holographic erasure by intensity and phase modulation of the writing beams, we find that the timeaverage technique is most amenable to system implementation. Calculations derived from a simple model of diffraction show that it is possible to find configurations that maximize the interconnection capacity. The PISCES includes Fresnel zone plates for spot array generation, amplitude and phase spatial light modulators based on liquid crystal technology, and detector arrays, in addition to the photorefractive crystal. Alternatives for each of these elements are described.

Holographic implementation of a learning machine based on a multicategory perceptron algorithm

An optical learning machine that has multicategory classification capability is demonstrated. The system exactly implements the single-layer perceptron algorithm and is fully parallel and analog. Experimental results on the learning by examples obtained from the system are described.

Use of a multiwavelength surface-emitting laser array in a four-channel wavelength-division-multiplexed system experiment

The first wavelength-division-multiplexed system experiment using a monolithically integrated two-dimensional surface-emitting laser array is reported. Four lasers at a wavelength separation of 1.5 nm in the 980-nm region were operated simultaneously and a bit-error rate of 10/sup -9/ (155 Mb/s) was attained with negligible optical and electrical crosstalk between the lasers.<<ETX>>

Electro-optic switch using a liquid crystal Fabry-Perot filter (Invited Paper)

We describe the use of liquid crystals in a Fabry-Perot cavity to produce optical modulation. It is shown that these devices can be used not only as electrically tunable wavelength filters but also as narrow wavelength optical switches with high contrast. The performance of the device is illustrated by experiments using nematic and smectic liquid crystals. Using nematic liquid crystals, for example, it is shown that the device can be used to produce an optical pulse of 10 microsecond(s) at low voltages.

Holographic On-Line Learning Machine for Multicategory Classification

A holographic on-line learning machine that is capable of multicategory classification is described. The system exactly implements the single-layer perceptron algorithm in a fully parallel and analog fashion. The performance of the adaptive network is successfully tested for up to 24 characters with different scale and rotation. Also, a compact and robust version of the holographic learning machine is proposed.

Multichannel free-space optical switch using liquid-crystal polarization-control devices

This paper describes a four-channel optical switch module prototype for a reconfigurable optical interconnection network using a polarization-switched architecture and liquid crystal polarization control devices. Compact size and low insertion loss have been achieved by using integrated optical elements. The successful switching of 1 Gbps optical signals with little skew has been demonstrated.