R. Harel

Terahertz near-field microscopy based on a collection mode detector

We report on the development of a collection mode near-field probe for the terahertz spectral range. The near-field detector is based on an aperture type probe with dimensions of 30×30 μm2. The collection mode technique provides higher sensitivity and higher resolution than the similar illumination mode approach. Spatial resolution better than 40 μm is demonstrated for a broad spectrum of 300–600 μm, which equals to λ/15 for the longest wavelength. The observed resolution is determined by the size of the probe aperture.

Design and nonlinear servo control of MEMS mirrors and their performance in a large port-count optical switch

In this paper, we demonstrate full closed-loop control of electrostatically actuated double-gimbaled MEMS mirrors and use them in an optical cross-connect. We show switching times of less than 10 ms and optical power stability of better than 0.2 dB. The mirrors, made from 10-/spl mu/m-thick single-crystal silicon and with a radius of 400-450 /spl mu/m, are able to tilt to 8/spl deg/ corresponding to 80% of touchdown angle. This is achieved using a nonlinear closed-loop control algorithm, which also results in a maximum actuation voltage of 85 V, and a pointing accuracy of less than 150 /spl mu/rad. This paper will describe the MEMS mirror and actuator design, modeling, servo design, and measurement results.

Cancellation of all Kerr nonlinearities in long fiber spans using a LiNbO/sub 3/ phase conjugator and Raman amplification

A LiNbO/sub 3/ phase-conjugator and Raman pumping in fiber are used in order to cancel all Kerr nonlinearities in long fiber spans. We demonstrate this effect in single and multichannel transmission at 10, 40, and 100 Gb/s.

Modular MEMS-based optical cross-connect with large port-count

We describe and demonstrate a modular microelectromechanical systems (MEMS)-based optical cross-connect (OXC) architecture. The OXC port count increases modularly by adding new optical modules, and a maximum cross-connectivity of /spl sim/ 350 /spl times/ 350 can be achieved in the current design. Each optical module has 16 ports with closed-loop servo-controlled MEMS mirrors. Using a prototype OXC system, mounted in a standard telecommunications equipment bay comprising optical modules, folding mirrors, and other optical elements, we demonstrate switching times of less than 10 ms, excellent optical power stability of less than /spl plusmn/ 0.15-dB variation, and immunity to stochastic vibrations. An automatic power peak-up process is performed when the power falls below 0.5-dB off the maximum coupled power for any connection.

Study of single-cycle pulse propagation inside a terahertz near-field probe

Propagation of 0.5 THz single cycle pulses inside an aperture-type near-field probe is studied. The E-field amplitude attenuation is experimentally measured at various distances from the aperture. Numerical simulations based on a two-dimensional model illustrate the pulse waveform transformation and the spectral blueshift, which is experimentally observed. The study shows that the sensitivity of such a near-field probe can be improved by more than a factor of 10 by decreasing the aperture-to-detector separation without reduction of the spatial resolution.

Terahertz near-field imaging

A near-field probe is described that enables high spatial resolution imaging with terahertz (THz) pulses. The spatial resolution capabilities of the system lie in the range of few microns and we demonstrate a resolution of 7 microm using broad-banded THz pulses with an intensity maximum near 0.5 THz. We present a study of the performance of the near-field probes in the collection mode configuration and discuss some image properties.

Nonlinear servo control of MEMS mirrors and their performance in a large port-count optical switch

In this paper, we demonstrate full closed-loop control of electrostatically actuated double-gimbaled MEMS mirrors and use them in an optical cross-connect. We show switching times of less than 10 ms and optical power stability of better than 0.2 dB. The mirrors, made from 10-/spl mu/m-thick single-crystal silicon and with a radius of 400-450 /spl mu/m, are able to tilt to 8/spl deg/ corresponding to 80% of touchdown angle. This is achieved using a nonlinear closed-loop control algorithm, which also results in a maximum actuation voltage of 85 V, and a pointing accuracy of less than 150 /spl mu/rad. This paper will describe the MEMS mirror and actuator design, modeling, servo design, and measurement results.We demonstrate full closed-loop control of electrostatically actuated double-gimbaled MEMS mirrors and use them in a free space optical cross-connect with switching times of less than 10 ms, and optical power stability of better than 0.2 dB.

Interchannel cross talk caused by pump depletion in periodically poled LiNbO 3 waveguide wavelength converters

We study experimentally and theoretically the limits of multichannel parametric wavelength conversion imposed by pump depletion in periodically poled LiNbO3 waveguides. As many as 55 channels with 6 dBm of power each can be converted simultaneously with less than a 10-9 error rate by use of 20 dBm of pump power.

Coherent Terahertz Radiation from Cavity Polaritons in GaAs/AlGaAs Microcavities

We report on the first observation of coherent terahertz (THz) electromagnetic radiation emitted from an unbiased semiconductor microcavity (MC) at low temperature. The THz radiation is emitted after resonant optical excitation of the two cavity polariton modes and its frequency is in excellent agreement with the vacuum Rabi splitting (VRS) frequency. We attribute the THz radiation to oscillations between the MC and the exciton modes with a frequency equal to the VRS, resulting in a radiating oscillating dipole.

THz transmission near-field imaging with very high spatial resolution

Summary form only given. Scanning near-field microscopy at THz frequency regime is a developing technology and different approaches have been proposed to improve spatial resolution. Recently a sensitive near-field probe that integrates a subwavelength aperture and a photoconducting switch was demonstrated. Spatial resolution of this method is defined by the probe aperture size and limited by signal attenuation. In this study we discuss attenuation of single-cycle THz pulses for various aperture sizes (10-50 /spl mu/m). The near-field probe with the 10 gm aperture provides spatial resolution of /spl sim/10 /spl mu/m at the wavelength range from 120 to 1500 /spl mu/m. To our knowledge, it is the highest resolution achieved with THz pulses in this spectral range. Near-field images can be constructed with signal to noise ratio of /spl sim/50.