US Patent 11153009 High-lane count optical transceiver with built-in self test

An optical device such as an optical transceiver can include a cascaded built-in self-test structure that can be configured in testing mode using an active power mode and can sufficiently attenuate light away from a loopback path in an inactive power mode. The optical device can include a wafer top emitter that can be used to tune a light source for testing and calibration of optical components while the built-in self-test structure is in active mode.