| 摘要 |
PURPOSE:To eliminate need for an optical system including a light source at the reception side and to attain miniaturization and low cost by modulating an optical signal coming from the sender side during no modulation period and reflecting it to the sender side so as to be returned thereto. CONSTITUTION:When a transmission data from the sender side 20 is lost, a CPU 20 outputs a command of non modulation period and a modulation transmission signal 22a being at a high level '1' by a prescribed period T2 from the modulator 22 is outputted. When a CPU 26 keeps the fetched data at a high level '1' for a time DELTAT or over, the CPU 36 recognizes the sender side at a non modulation period T2 and outputs simple information such as ID number or the like as a reply data 36a. In this case, a voltage corresponding to the reply data 36a is applied to a liquid crystal cell 38 via a liquid crystal cell drive circuit 39, the liquid crystal cell 38 shuts of a reflection light signal 44 when a reply data 36a is at a high level '1' and passes the reflection light signal 44 as it is when the reply data 36a is at a low level '0'. |
