OPTICAL TRANSMITTER-RECEIVER

摘要

PROBLEM TO BE SOLVED: To facilitate the assembling by adopting a structure that a variable reflectance optical element with a large cross sectional area of optical path is fixed to a wide light receiving face of a light receiving device to eliminate the need for high precision optical axis alignment. SOLUTION: The optical transmitter-receiver 19 is configured by fixing a liquid crystal display element 29 onto a light receiving face 21 of a light receiving element 20. In the case of reception, a light transmitted through the liquid crystal display element 29 is received by the light receiving element without application of a voltage to the liquid crystal display element 29 so as to minimize the reflectance. In the case of transmission, a voltage is applied to the liquid crystal display element 29 receiving a light with a prescribed intensity to modulate the light by changing the reflectance and the modulated light is reflected and returned to a sender. The optical path is switched by transmitting or reflecting the light, the liquid crystal display element 29 being able to conduct modulation by changing its reflectance is employed for the optical transmitter-receiver and the element 29 and the light receiving element are connected in series with respect to the optical axis to obtain the optical transmitter-receiver not using an LD element. Then the transmitter-receiver adopts a structure of direct coupling of a variable reflectance optical element 22 consisting of the element 29 with the light receiving element 20 and then the optical loss is reduced.