| 摘要 |
PURPOSE:To correct light output variation and linearity deterioration due to temperature fluctuations automatically by converting part of a light output photoelectrically and then feeding the resulting signal back to the bias circuit of a laser diode. CONSTITUTION:A video signal from a terminal VIDEO IN has the DC level fixed by a clamping circuit CLP to control the operational amplifier A4 of a constant current driving circuit, and a bias current I0 and a video signal current IV flow to a transistor TR2. On the other hand, a bias current IB flows to a TR1 and a current IO+IV+IB flows to a laser diode LD, generating an optical modulation output corresponding to the video signal. Part of this output is converted by a photoelectric converting element PD into an electric signal and through a sample holding circuit S.H, smoothing LPF, comparator A2 with a reference DC potential, amplifier A3 for a constant current driving circuit, etc., the current IB is fed back. Thus, output variation of the laser diode and linearity deterioration due to temperature fluctuations are corrected automatically. |
