Properties of photon-coupled devices

This paper describes the properties of electronic circuit isolators which utilize fiber optic bundles to couple the emission from a GaAs luminescent diode to a silicon PIN photodiode. There results a unilateral signal coupling element whose characteristics are essentially independent of the voltage that exists between the input and output ports of the device. The input-output isolation exceeds that of most other devices and is applicable from dc to the microwave region. The input port of this structure is a GaAs diode which converts electrons to photons in a quasi-linear fashion. A portion of the generated photons are emitted into the optic fiber bundle and propagate toward a reverse biased photodiode with a wide intrinsic region. The PIN photodiode acts as a linear quantum detector. Design considerations and resultant performance of the isolators will be discussed with respect to factors as: 1. Length of the optic bundle. 2. Numerical aperture of the optic bundle. 3. Angular and spectral distribution of the photons. 4. The effects of optic bundle-semiconductor interface materials. 5. Electrical and optical dimensions and geometry. 6. Input-to-output parasitic impedances. 7. Quantum efficiencies, gains, and bandwidths. 8. Transfer linearity, dynamic range, and noise. The importance of these factors in specific applications, such as "dc pulse transformers", circuit isolators, and modulators, will be considered.