Abstract: 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.

Abstract: 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.

Abstract: 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.