Signal Isolation Capability of Rotating Wave Plate Type Electro-Optic Modulators.

摘要

The signal isolation capabilities of rotating wave plate type single sideband electro-optic modulators operating in different configurations are analyzed. Discussion includes a broadband configuration in which the microwave pump wave travels in the backward direction. Experimental results confirming the feasibility of a simple configuration are presented. In laser systems incorporating active elements such as amplifiers and oscillators, optical isolators are often required to ensure frequency stability. The most common type of isolator in use today is the Faraday rotator isolator; the principle of operation is based on the anisotropy of the Faraday rotation for optical signals traveling in opposite directions. There are other types of isolators, the principles of operation of which depend on other parameters such as signal intensity, polarization state, and frequency conversion efficiency; examples are isolators using nonlinear absorption cells, Pockels cells with quarter-wave plate, and traveling-wave single sideband electro-optic modulator. The possible use of the traveling-wave single sideband (SSB) electro-optic (EO) modulator in isolator applications was first suggested by Dorschner. No detailed analysis has been made, however. In this paper, the isolation capability of the rotating wave plate (RWP) SSB CdTe EO modulator operated alone, in tandem, or in a different configuration will be examined. It will be shown that the SSB EO modulator and a number of passive optical elements constitute an optical signal isolator with a high isolation capability. An experimental verification of an isolator of the simple configuration will be shown. Reprints. (rh)