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IEEE Journal of Quantum Electronics

The gain-bandwidth of an InSb transphasor

Hameed A. Al‐Attar, Hugh Alexander MacKenzie, Frank A. P. Tooley, Andrew Walker

Published May 1, 1986• 6 citations
Publisher

Abstract

Detailed results are presented of two-beam optical transistor (transphasor) studies in a single InSb etalon using a CW CO laser to provide the bias beam and a Pb S1-xSExdiode laser to generate a modulated signal. The gain-bandwidth product has been measured to be ∼ 1.2 MHz for gain values ≥ 3 and is reduced at lower gain. A full expression for the absolute value of the optical gain is derived and shows good agreement with these results. An experimental method to estimate the device and material response time through the gain/ frequency dependence is presented. A medium response time of 230 ns ± 10 percent has been deduced for the conditions of these experiments.

DOI
10.1109/jqe.1986.1073003

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Detailed results are presented of two-beam optical transistor (transphasor) studies in a single InSb etalon using a CW CO laser to provide the bias beam and a Pb S1-xSExdiode laser to generate a modulated signal. The gain-bandwidth product has been measured to be ∼ 1.2 MHz for gain values ≥ 3 and is reduced at lower gain. A full expression for the absolute value of the optical gain is derived and shows good agreement with these results. An experimental method to estimate the device and material response time through the gain/ frequency dependence is presented. A medium response time of 230 ns ± 10 percent has been deduced for the conditions of these experiments.
Abstract InSb etalons operated at 77 K and illuminated by CO lasers (5.5 pm) exhibit continuous wave (c.w.) optical bistability. A wide range of experiments have been performed to further the basic characterization of these devices and to demonstrate their various potential applications. The latter include signal amplification, modulation and, with external switching, the construction of logic gates. Two devices on a single etalon have now been coupled to form a simple all-optical circuit. New results have also been obtained with InSb at room temperature with pulsed CO2 lasers (10.6 pm).
Detailed results are presented on optical bistability (OB) and two-beam optical transistor (transphasor) action in simple, one-element Fabry-Perot devices, with the semiconductor InSb using a CW CO laser near the bandgap region, and OB for semiconductors in general is discussed. OB and multistability are seen in transmission and reflection at 5 K. At 77 K,n_{2} \simeq 3 \times 10^{-3}cm2/W [corresponding to an effective\chi^{(3)} \sim 1ESU] is measured and OB is observed at ∼8 mW. Transphasor action at 5 K is presented and the influence of degenerate four-wave mixing is discussed. The basic physics of the microscopic mechanism for n2(bandgap-resonant saturation) is summarized and a simplified, generalized model is derived. This model and arguments on cavity optimization are used to predict order of magnitude limits to switching power, energy, and speed, both in InSb and other semiconductors, even in the absence of excitonic enhancement.
We report the realisation of optically bistable switching and memory elements, and the transphasor Can all-optical transistor) in simple one element nonlinear Fabry-Perot interferometers made from the semiconductor InSb. These devices, which operate at 5 K and 77 K with mW powers from a cw CO laser between 5 and 6 μm rely on a strongly intensity-dependent refractive index discovered near the bandgap region of InSb and explained by bandgap resonant saturation. Switching speeds are shown to be < 500 ns in these first devices and operation to much shorter timescales is predicted. Operation at room temperature and in other semiconductors at other wavelengths remains a possibility and such devices offer considerable potential for all-optical switching in integrated optics and laser pulse control.
We report the first known direct observation of the critical slowing-down effect and transient bimodality in an intrinsic semiconductor all-optically bistable device with a cw CO laser holding beam and a PbSSe diode laser switching beam. The measurements of critical slow-down effects show good agreement with the numerical model using a modified Debye dynamic equation. The switching profile has been shown to depend on both the size of the hysteresis loop and the diode pulse parameter. A scaling law for the delay time of the switching when external parameter P changes close to the critical value Pc has been indicated to fit (P − Pc)−1/2.