Fujitsu Corporation

Kazuhito Ogawa

Hiroyuki Furukawa

Katsuhiko Hakomori

A broadband pulse width modulation circuit is provided which can achieve high speed responsibility while assuring an advantage of a pulse width modulation (PWM) circuit having a good power efficiency in order to satisfy a demand for reduction of power consumption and a demand for high speed responsibility in the field of optical communication. The broadband PWM circuit includes a PWM circuit for modulating and smoothing a pulse width in response to an input voltage signal to supply electric current to a load, a frequency band selection and amplification circuit for selectively amplifying only a specific frequency band of the input voltage signal, and a composition circuit for combining electric current from the pulse width modulation circuit and the electric current amplified by the frequency band selection and amplification circuit.

Broadband pulse width modulation circuit and optical amplifier using the same

An optical amplifier amplifies a light signal inputted to an optical amplifier fiber and outputs an amplified light signal, by exciting the fiber with an excitation light. The optical amplifier can keep its output light level constant and stable and reduce the excitation light when the light inputted to the fiber is cut off, just by detecting the optical output level at a post-stage of the fiber. The optical amplifier comprises a first control circuit, a second control circuit and a selector circuit. The first control circuit amplifies the difference between a first predetermined voltage and an o/e-converted voltage of the optical amplifier fiber output light to output an amplified voltage. The second control circuit amplifies the difference between the o/e-converted voltage of the excitation light and a selected one of the first control circuit output voltage and a second predetermined voltage to output an amplified voltage and controls the excitation light based on the second control circuit output voltage. The selector circuit detects a change in the first control circuit output voltage and depending on the change, selects the first control circuit output voltage or a second predetermined voltage.

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Yokohama, Japan

Kazuhito Ogawa