Optical transceivers comprising optical loopback circuits are described. The optical transceiver may comprise a housing, which may host a transmitter, a receiver and the optical loopback circuit. The optical loopback circuit may be configured to route at least a portion of a modulated optical signal from the transmitter to the receiver. The optical loopback circuit may comprise tap couplers and/or optical switches. The optical transceiver may be switched between a normal mode and a calibration mode. The optical transceiver may maintain the same fiber connections even when the optical transceiver is switched from one mode to another. The transmitter, the receiver and the optical loopback circuit may be disposed on a common substrate, or on separate substrates.