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Leo T. Varghese

Publications and source records attributed to Leo T. Varghese.

4 recordsLinked to original sources

Rapidly reconfigurable radio-frequency arbitrary waveforms synthesized on a CMOS photonic chip

Photonic methods of radio-frequency waveform generation and processing provide performance and flexibility over electronic methods due to the ultrawide bandwidth offered by the optical carriers. However, they suffer from lack of integration and slow reconfiguration speed. Here we propose an architecture of integrated photonic RF waveform generation and processing, and implement it on a silicon chip fabricated in a semiconductor manufacturing foundry. Our device can generate programmable RF bursts or continuous waveforms with only the light source, electrical drives/controls and detectors being off chip. It turns on and off an individual pulse in the RF burst within 4 nanoseconds, achieving a reconfiguration speed three orders of magnitude faster than thermal tuning. The on-chip optical delay elements offers an integrated approach to accurately manipulate individual RF waveform features without constrains set by the speed and timing jitter of electronics, and should find broad applications ranging from high-speed wireless to defense electronics.

physics.optics

A Silicon Optical Transistor

A fundamental road block for all-optical information processing is the difficulty in realizing a silicon optical transistor with the ability to provide optical gain, input output isolation and buffer action. In this work, we demonstrate an all-optical transistor using optical nonlinearity in microrings. By using weak light to control strong light, we observed an On/Off ratio up to 20 dB. It can compensate losses in other optical devices and provide fan-out capability. The device is ultra compact and is compatible with current complementary metal-oxide-semiconductor (CMOS) processing.

physics.optics

New Constraints from PAMELA anti-proton data on Annihilating and Decaying Dark Matter

Recently the PAMELA experiment has released its updated anti-proton flux and anti-proton to proton flux ratio data up to energies of ~200GeV. With no clear excess of cosmic ray anti-protons at high energies, one can extend constraints on the production of anti-protons from dark matter. In this letter, we consider both the cases of dark matter annihilating and decaying into standard model particles that produce significant numbers of anti-protons. We provide two sets of constraints on the annihilation cross-sections/decay lifetimes. In the one set of constraints we ignore any source of anti-protons other than dark matter, which give the highest allowed cross-sections/inverse lifetimes. In the other set we include also anti-protons produced in collisions of cosmic rays with interstellar medium nuclei, getting tighter but more realistic constraints on the annihilation cross-sections/decay lifetimes.

astro-ph.HE