Optical transceiver with integrated optical loopback

Abstract

A photonic integrated circuit for an optical transceiver includes an optical Rx circuit, an optical Tx circuit, and an integrated optical loopback circuit configured to switchably direct a loopback optical signal from an output of the optical Tx circuit to an input of the optical Rx circuit. The integrated optical loopback circuit enables in-field testing of the optical transceiver. The integrated optical loopback circuit may include an optical mixer for mixing polarization channels in dual-polarization embodiments of the optical transceiver. A phase tuner may be provided for tuning the optical phase of local oscillator light for mixing I and Q channels of the loopback optical signals in embodiments operating with quadrature modulated signals.

We claim: 
     
         1 . An optical transceiver comprising:
 an input port for receiving an input optical signal;   an output port for transmitting an output optical signal;   an optical receiver optically coupled to the input port and configured to process the input optical signal for conversion into one or more electrical Rx signals;   an optical transmitter optically coupled to the output port, the optical Tx circuit configured to provide the output optical signal comprising a first optical channel and a second optical channel; and   a loopback optical circuit configured to couple at least a portion of the output optical signal as a loopback optical signal comprising the first optical channel and the second optical channel into the optical Rx circuit for testing the optical transceiver.   
     
     
         2 . The optical transceiver according to  claim 1 , wherein the loopback optical circuit comprises a loopback channel mixer configured to mix the first optical channel and the second optical channel. 
     
     
         3 . The optical transceiver according to  claim 1 , wherein the first optical channel and the second optical channel comprise a same wavelength; and
 wherein the output port includes a polarization rotator and combiner configured to rotate the polarization of one of the first optical channel or the second optical channel, and to combine the first optical channel and the second optical channel for polarization multiplexing.   
     
     
         4 . The optical transceiver according to  claim 1 , wherein the first optical channel and the second optical channel comprise a same wavelength; and wherein the optical receiver is configured for coherent optical detection; whereby the loopback optical signal is coherently mixed with local oscillator light. 
     
     
         5 . The optical transceiver according to  claim 4 , further comprising an optical phase shifter configured to dynamically tune an optical phase of the local oscillator light to evaluate phase recovery processing in the optical receiver in dependence on a phase difference between the loopback optical signal and the local oscillator light. 
     
     
         6 . The optical transceiver according to  claim 4 , further comprising a light source for providing light to the optical transmitter and the local oscillator light. 
     
     
         7 . The optical transceiver according to claim  21 , wherein the optical transmitter includes: a first optical modulator configured to output the first optical channel, and a second optical modulator configured to output the second optical channel;
 wherein the loopback optical circuit includes a loopback channel mixer configured to mix the first optical channel and the second optical channel, and to output a first mixed optical signal and a second mixed optical signal;   wherein the optical receiver includes: a first Rx optical mixer optically coupled to the loopback channel mixer for receiving the first mixed optical signal, and to a source of local oscillator light; and a second Rx optical mixer, the second Rx optical mixer optically coupled to the loopback optical mixer for receiving the second mixed optical signal, and to the source of local oscillator light.   
     
     
         8 . The optical transceiver according to  claim 7 , further comprising:
 a light source for generating input light;   a first splitter for splitting the input light into transmitter light and the local oscillator light;   a second splitter for splitting the transmitter light into first modulator light for the first optical modulator, and second modulator light for the second optical modulator;   a third splitter for splitting the local oscillator light for the first Rx optical mixer and the second Rx optical mixer.   
     
     
         9 . The optical transceiver according to  claim 7 , wherein the optical transmitter comprises a quadrature optical modulator;
 wherein the first optical modulator is configured to generate the first optical channel as an in-phase optical signal; and   wherein the second optical modulator is configured to generate the second optical channel as a quadrature phase optical signal.   
     
     
         10 . The optical transceiver according to  claim 9 , wherein the in-phase (I) optical signal is response to an I-channel electrical Tx signal, and the quadrature-phase optical signal is responsive to a Q-channel electrical Tx signal;
 wherein the optical receiver is configured to generate an I-channel electrical Rx signal and a Q-channel electrical Rx signal responsive to the loopback optical signal; and   further comprising a processor configured to compare the I-channel electrical Tx signal and the Q-channel electrical Tx signal with the I-channel electrical Rx signal and the Q-channel electrical Rx signal.   
     
     
         11 . The optical transceiver according to  claim 10 , wherein the processor is also configured to estimate at least one of: an IQ skew of an Rx signal path of the optical transceiver, an IQ skew of a Tx signal path of the optical transceiver. 
     
     
         12 . The optical transceiver according to  claim 10 , wherein the processor is also configured to estimate an electro-optic parameter of a Tx signal path of the optical transceiver, or an electro-optic parameter of an Rx signal path of the optical transceiver. 
     
     
         13 . The optical transceiver according to  claim 10 , further comprising an optical phase tuner configured to dynamically tune an optical phase of the local oscillator light to explore various degrees of mixing the in-phase optical signal and the quadrature optical signal. 
     
     
         14 . The optical transceiver according to  claim 9 , wherein the optical transmitter is configured to generate the output optical signal carrying an in-phase and a quadrature optical channels in each of two orthogonal polarizations; and wherein the loopback optical signal comprises the first optical channel (XI), the second optical channel (XQ), a third optical channel (YI), and a fourth optical channel (YQ). 
     
     
         15 . The optical transceiver according to  claim 1 , wherein the loopback optical circuit comprises a switching circuit configured to switch between a pass-through state coupling the loopback optical signal into the optical receiver and a blocking state blocking the optical receiver from receiving the loopback optical signal. 
     
     
         16 . The optical transceiver according to  claim 15 , wherein the switching circuit is further configured to block an optical connection between the optical receiver and the input port when the loopback optical signal is coupled into the optical receiver. 
     
     
         17 . The optical transceiver according to of  claim 16 , wherein the switching circuit is further configured to block an optical connection between the optical transmitter and the output port when the loopback optical signal is coupled into the optical receiver. 
     
     
         18 . The optical transceiver according to  claim 15 , wherein the switching circuit is configured to couple the output optical signal from the optical transmitter to the optical output port or to the optical receiver as the loopback optical signal. 
     
     
         19 . The optical transceiver according to  claim 15 , wherein the switching circuit comprises one or more optical shutters. 
     
     
         20 . The optical transceiver according to  claim 1 , wherein the loopback optical circuit comprises a first output optical coupler having a first output coupler port optically coupled to the output port, and a second output coupler port optically coupled to the input port.