A Volume Holographic Grating Triplexer (VHGT) is an optical element that diffracts the 1550nm and 1490 nm signals into separate directions while transmitting the 1310 nm upstream signal. Compared to thin film interference filter, the VHGT enables the 1310 nm transmitter laser (TX) and the receivers (RX) to be on the same side, either on the same plane or at different heights, thus enabling low cost packaging.
