Fujitsu Corporation

Takayoshi Morita

Akira Nagayama

Akihiko Ichikawa

A laser diode drive circuit comprising a laser diode; a drive pulse current source for emitting light or not emitting light of the laser diode according to an input signal; and a biasing unit for optimally operating the laser diode, the biasing unit having a bias voltage source for applying a bias voltage to the laser diode, which bias voltage can feed an optimum bias current to the laser diode. The laser diode drive circuit can maintain a bias current at a predetermined value with high precision and with high stability.

Circuit and method for driving laser diode

An input pulse signal is applied to an input terminal of a pulse width controlling logic circuit and integrated by an integrating circuit. A desired output signal is obtained at an output terminal via a C-MOS logic element having an input threshold level that depends on a power supply voltage applied thereto, and an ACC circuit. An average level detecting unit detects an average level of the input pulse signal so that an average level converting unit supplied with an output from the average level detecting unit controls the power supply voltage applied to the C-MOS logic element. The pulse width controlling logic circuit operates on a principle that, as a pulse width is decreased, an average level of the pulse is lowered, and, as a pulse width is increased, an average level of the pulse is raised. Since an input threshold level of a C-MOS logic element depends on the power supply voltage applied thereto such that the threshold level is 1/2 the level of the power supply voltage. By controlling the power supply voltage, the threshold level is lowered or raised so that the pulse width is increased or decreased. Accordingly, the circuit outputs a signal having a desired pulse width.

Pulse width controlling logic circuit

A remote light signal control apparatus is disclosed wherein the level of the light output thereof is fixed with a high degree of accuracy and, even when an ALC loop is opened, a laser diode can emit light at a stable level to assure a high degree of reliability of the laser diode. A first control section is provided in one of a light reception section and a light transmission section. The light transmission section includes a second light detection section for detecting a light emitting condition of a light source, a second control section for outputting, in response to light detection information detected by the second light detection section, a light control signal for controlling the state of a light signal from the light source, and a switch section for selectively outputting to the light source one of the light control signal from the first control section and the light control signal from the second control section with which the level of the light signal from the light source is controlled lower than that with the other.

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Sapporo, Japan

Takayoshi Morita