| 摘要 |
PURPOSE:To contrive to simplify the readjustment of the titled circuit attended with replacements of element and to economize the circuit through the relaxation of requirements to element characteristics by using an avalanche photodiode for a light receiving element and making its bias voltage variable so as to vary the multiplication factor. CONSTITUTION:The avalanche photodiode 8 coupled optically with a semiconductor laser 4 receives an optical power Pr from the semiconductor laser 4, sends a demodulation output current iAPD in response to the multiplication factor decided by the bias voltage VAPD to an amplifier 6, which amplifies a demodulation output current iAPD and gives it to a subtracter 2. Even if the coupling factor between the semiconductor laser 4 and the avalanche photodiode 8 differs from components, the transfer ratio alpha from a semiconductor laser drive current iLD into the demodulation output current iAPD is always kept constant by varying the bias voltage VAPD from the variable bias circuit 9 so as to vary the multiplication factor M of the avalanche photodiode 8 thereby eliminating the need for occasional adjustment. |
