Hitachi, Ltd.

Opnext Japan, Inc.

Hideyuki Serizawa

Yasuhiro Yamada

Norio Chujo

Naohiko Baba

Tadashi Hatano

Akihiro Hayami

Kazuyoshi Yamaki

A control apparatus for stabilizing optical wavelength output by a laser module in which a laser element, temperature sensor and cooling/heating element are installed, comprises a temperature deviation detecting circuit comprising a temperature monitor for detecting a laser temperature, and a first comparator for outputting a first control signal indicating a difference between the laser temperature and a control target value, a wavelength deviation detecting circuit comprising a wavelength monitor for detecting light output from the laser element, and a second comparator for outputting a second control signal indicating a difference between the wavelength of the detected output light and a control target value, a selector circuit for selecting either of the detecting circuits according to the external conditions of the laser element, and a current controller for controlling the current supplied to the cooling/heating element based on the output signal from the selected detecting circuit.

Control method and apparatus for stabilizing optical wavelength

In the application of the optical transmitter to any system for the compensation of passing degradation, the invention provides the optical transmitter which maintains constant modulator output and the highly reliable optical transmission by tuning, the alpha parameter for given systems. As the optical element back-face output power detected by PDdepends on the optical element driving current amount, the electronic absorption amount of the EA optical modulator monitored by the electronic absorption monitor depends on the optical output of the optical elementand the EA optical modulator driving point of the driving part. It is possible to detect a change in the driving point in the EA optical modulator by taking a difference between the amount monitored by the PDand the amount monitored by the electronic absorption monitor. Consequently by applying to the driving current sourcethe current corresponding to the change of the EA optical modulator driving point, it is possible to automatically compensate the modulator outputwhen the driving point of the EA optical modulator changes due to the change of the alpha parameter and the passing degradation.

Optical transmitter and optical transmission system using electro absorption modulator

An optical transmitter includes a plurality of optical wavelength stability control apparatuses, each of which is capable of compensating for a wavelength drift by varying a laser diode drive current. Each of the optical wavelength stability control apparatuses detects a laser diode drive current, which is controlled by an auto power control circuit, by using a laser diode drive current detector. The laser diode drive current is normalized by a laser diode drive current increase/decrease normalization unit. A laser diode temperature control target value is generated at a compensated reference voltage generator, in response to the normalized laser diode drive current, to control a current value applied to a thermoelectric cooler so that an output value of a temperature monitor circuit approaches a predetermined laser diode temperature control target value.

Optical wavelength stability control apparatus, optical transmitter and multiple wavelength transmitter

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Ueda, Japan

Hideyuki Serizawa