Abstract: A two-way transmission system, which utilizes solid state circuitry and a pair of opto-couplers, achieves high linearity and provides high electrical isolation between input and output signals without the use of the traditional hybrid transformer. Each opto-coupler includes a single light emitting diode (LED), two light detecting diodes (LDDs), and an amplifier. The LED is connected to the output of the amplifier and is physically located with respect to the two LDDs such that light emitted by the LED impinges on the photosensitive areas of the LDDs. The first LDD is coupled to the input of the amplifier, and the second LDD is coupled to output circuitry. This opto-coupler is relatively temperature insensitive and compensates for the inherent nonlinearity of the LED. These characteristics facilitate the use of the opto-coupler in systems which require relatively high linearity and temperature stability.