Abstract: The object of the present invention is to control the amplification rate of a photoperiodic circuit by stable negative feedback control, thereby suppressing fluctuations in the circulating light in the photoperiodic circuit. The circulating light in the photoperiodic circuit is converted into an electrical signal, indicating the intensity of the circulating light, which is held in a first sample-and-hold circuit. Additionally, an electrical signal indicating the intensity of circulating light of the circuit previous to that of the first sample-and-hold circuit is held in a second sample-and-hold circuit. The difference in the value between the electrical signals which indicate intensities of the circulating light are determined by a subtraction circuit. The result is supplied to an addition circuit through a third sample-and-hold circuit.

Abstract: A high fidelity optical amplifier having a stable amplification gain is presented. The problem of signal distortion in an output optical signal caused by an imbalance of light energy generation and consumption within the optical fiber is resolved by generating a delayed correction signal to be used in a feedback control circuitry. An incoming optical signal is split into two signals: one split signal is forwarded to a photo-detector element for generation of the correction signal while the other split signal is forwarded to a signal delay circuit. The optical delay circuit delays the timing of inputting the correction signal into output optical fiber for a specific duration of time to attain a full amplification gain within the optical fiber. The correction signal generation circuit performs differentiation of an electrical input signal followed by detection and selection of a maximum amplitude over a standard reference voltage.