Optical Signal Beam Research Articles

An invertible wavefront switching system with a high extinction ratio

We report the development of an invertible wavefront switching system, consisting of a spatial light modulator (SLM), a diffuser, a signal beam, and a control beam. The shaped optical signal beam can be switched between on and off states by disturbing the diffuser with a control beam via thermo-optic effect. During the wavefront shaping process, the extinction ratio of the signal beam is iteratively optimized. We demonstrate a high extinction ratio of nearly 20. In addition, when the control beam is on, a switch with either on or off state can be configured to via encoding different wavefront patterns to the signal beam. This work potentially advances many physical or bio-medical applications employing all-optical switches.

Theory of lossless polarization attraction in telecommunication fibers

In this work, polarization attraction is meant to be the conservative nonlinear effect that transforms any arbitrary input state of polarization (SOP) of an intense optical signal beam fed to a nonlinear medium into approximately one and the same SOP at the output, provided that the medium is driven by a relatively stronger counterpropagating pump beam. Essentially, the combination of the nonlinear medium and the pump beam serves as a lossless polarizer for the signal beam. The degree of polarization of the outcoming signal beam can be close to 100% (90% in our present simulations). With an eye toward the development of such lossless polarizers for fiber optics applications, we theoretically study the polarization attraction effect in the optical fibers that are used in telecommunication links; i.e., randomly birefringent fibers. A generic model for the fiber-based lossless polarizers is derived, and a statistical scheme for the quantification of their performance is proposed.

Solid-state ultrafast all-optical streak camera enabling high-dynamic-range picosecond recording

We demonstrate an ultrafast optical recording system based on a novel optical beam deflection technique. An optical pump temporarily creates an array of prisms that deflect an optical signal beam within a GaAs/AlGaAs planar waveguide. The fabricated device yielded, to our knowledge, the fastest sustained optical deflection reported to date and was used to create spatial representations of ultrafast temporal waveforms. A conventional camera was then used to record single-shot waveforms with a 2.5 ps resolution over a 50 ps record with a dynamic range in excess of 3000:1. Through further development, this all-optical streak camera could provide insight into previously unmeasurable phenomena in many fields.

Nonlinear diffraction and total internal reflection in optical-beam interaction in defocusing media

We elaborate the theory of reflection of an optical signal beam from an inhomogeneous channel created by a high-power laser beam of different frequency in a nonlinear defocusing medium. We study the effects of total internal reflection and nonlinear diffraction in the interaction of these beams. We derive and analyze the equation for the trajectory of the reflected signal beam and obtain the expression for the critical value of beam-intersection angle below which the total internal reflection occurs. We discuss the results of numerical modeling of nonlinear Schr¨odinger equations for envelopes of the beams in media with quadratic, photorefractive, and thermal nonlinearities. We present experimental data on the interaction of beams of argon and helium–neon lasers in a cuvette with tinted alcohol.

Selfrouting optical interconnects

A new type of selfrouting optical interconnect (SROI) is described where an optical signal beam or optical data packet is routed to a destination using an all optical switch where the destination is defined within the optical signal by the autocorrelation function of the optical signal.

Evaluation of power penalty due to beat noise induced by connector reflection

Power penalties caused by beat noise in a received optical signal beam were evaluated experimentally and theoretically. It was found that power penalties could be suppressed when the beam relative intensity noise was reduced to less than −135 dB/Hz below 2.4 Gbit/s. This goal can be satisfied using a commercially available physical contact optical connector, which has less than −20 dB reflection.

Optical bistability using a Fabry–Perot semiconductor-laser amplifier with two holding beams

Bistable switching of an optical signal beam by a control beam with a different wavelength, using the nonlinearity of a Fabry-Perot semiconductor-laser amplifier, is reported for the first time to the authors' knowledge. Depending on the initial detuning of the optical signal beam, both normal (counterclockwise) and reverse (clockwise) hysteresis are theoretically and experimentally obtained in the signal output power as a function of the control input power.

Laser Doppler measurements of localized pulsatile fluid velocity.

An optical Doppler velocimeter utilizing optical heterodyning techniques was used to measure radial velocity profiles of pulsatile flow in a cardiovascular circulation model. The light source was a single-mode frequency-stabilized He-Ne CW laser (6328 A, 0.1 mW). The laser beam was focused to a 30-?m in diameter spot in the flow stream. Polystyrene spheres 0.73 ?m in diameter, suspended in distilled water, were used as light scatterers. The optical signal beam contained Doppler-shifted scattered light. The reference beam was split from the source beam in one configuration; in a second configuration an acoustical frequency modulator was installed in the reference beam pathway as part of a directional flow measurement system. The circulation model consisted of an artificial heart, a Windkessel model, a peripheral resistance, a capillary model, a reservoir, and an optical glass window section. The flow test section was positioned by a three-dimensional finely adjustable holder. From 10 to 34 point measurements were obtained to plot one velocity profile, which covered 95 percent of the tube diameter.