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Optical Bistability Sampling Oscilloscope

IP.com Disclosure Number: IPCOM000042918D
Original Publication Date: 1984-Jun-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 3 page(s) / 63K

Publishing Venue

IBM

Related People

Faris, SM: AUTHOR

Abstract

This article relates generally to the measurement of waveform characteristics and more particularly to the replication of unknown waveforms using optically bistable devices as a nonlinear switching element. Investigation of optical phenomena in the picosecond time scale is a subject of great importance. The tools available today are limited to a restricted class. For example, it is possible to measure the duration of an optical pulse at frequency 1o by nonlinear cross-correlation techniques involving nonlinear optics. A crystal is needed to generate the second harmonic, 21o, the intensity of which is given by: (Image Omitted) where f1 and f2 are two optical pulses at 1o . To carry out this measurement, not only should these pulses have the same frequency, but also their phases must be matched with those of the crystal.

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Optical Bistability Sampling Oscilloscope

This article relates generally to the measurement of waveform characteristics and more particularly to the replication of unknown waveforms using optically bistable devices as a nonlinear switching element. Investigation of optical phenomena in the picosecond time scale is a subject of great importance. The tools available today are limited to a restricted class. For example, it is possible to measure the duration of an optical pulse at frequency 1o by nonlinear cross- correlation techniques involving nonlinear optics. A crystal is needed to generate the second harmonic, 21o, the intensity of which is given by:

(Image Omitted)

where f1 and f2 are two optical pulses at 1o . To carry out this measurement, not only should these pulses have the same frequency, but also their phases must be matched with those of the crystal. These constraints make this a technique of limited utility which is restricted to situations requiring the unknown signal under investigation to be coherent with the strobing pulse in addition to being synchronized with it. This article describes a general sampling oscilloscope system using an optically bistable device, such as a nonlinear switching element. The system permits the replication of general unknown signals which may have frequencies different from that of the strobing pulse and phase matching is not necessary. An optically bistable element has an input- output characteristic like that shown in Fig. 1. It is possible to increase the input intensity, Iin, while the output intensity remains negligibly small, until a threshold intensity Ith is reached, causing the output to suddenly increase (switch) to a high intensity state. This optical switch is hysteretic in that it remains in the high intensity state even after reducing the input to levels well below Ith . There are many bistable device configurations 1. There are those which utilize optical cavity resonators (Fabry-Perot) which contain nonlinear media. The transmission of a given optical signal through the cavity is controlled by a second signal. There is a hybrid variety (2) which utilizes an electro-optic medium within the resonator. The transmission through the cavity is controlled electronically by a signal produced by a photodetector which is driven by the output optical signal. Bistable devices which utilize cavities have speeds of response which are determined by the Q thereof and tend to be slower than those which depend on jumps in total internal reflection (TIR) at the interface of a nonlinear medium [3]. The latter, because of its speed, is preferred for the present sampling oscilloscope. Sampling Principles Fig. 2 illustrates the sampling principle using a bistable element controlled by four input signals which may have different frequencies. The bistable device is biased at a fixed intensity IB(lo) and, when switched by adding the strobing pulse Ip (t+t) the unknown signal, Ix (t) and a CW signa...