Transmitter optical signal to noise ratio improvement through receiver amplification in single laser coherent systems
A transceiver having an improved transmitter optical signal to noise ratio, and methods of making and using the same.
1. An optical transceiver for receiving an electrical input signal and outputting an optical output signal responsive to the electrical input signal, and for receiving an optical input signal and outputting an electrical output signal responsive to the optical input signal, comprising:
a first shared optical source configured to generate input light;
a first splitter configured to divide the first input light into transmitter light and local oscillator (LO) light;
an optical transmitter configured to receive the transmitter light and the electrical input signal and to transmit the optical output signal;
a second shared optical source configured to emit pump light;
a second splitter configured to divide the pump light into a first transmitter pump light portion and a second receiver pump light portion;
a first gain-controlled optical amplifier configured to amplify the optical output signal;
a second free-running optical amplifier configured to amplify the optical input signal;
a coherent optical receiver configured to receive the input optical signal and the local oscillator (LO) light and to output the electrical output signal;
a first control loop configured to sample the optical output signal and increasing power to the pump light, thereby increasing power to the first transmitter pump light portion for the first optical amplifier to increase amplification of the optical output signal, resulting in an increase in power to the second receiver pump light portion for the second optical amplifier to increase amplification of the optical input signal; and
a variable optical attenuator (VOA) configured to attenuate the optical input signal in response to the amplification of the optical input signal by the second optical amplifier resulting from an increase in power to the pump light for amplification of the optical output signal by the first optical amplifier.
2. The transceiver according to claim 1 , further comprising a second control loop configured to sample a portion of an output from the coherent optical receiver, and provide a control signal to the VOA for controlling optical power of the optical input signal received by the coherent optical receiver based on the amplification of the second optical amplifier, and an optical power of the LO light.
3. The transceiver according to claim 1 , wherein the second splitter is configured to split the pump light, whereby the first transmitter pump light portion is greater than the second receiver pump light portion.
4. The transceiver according to claim 3 , wherein the second splitter comprises a 1:4 splitter, whereby the first transmitter pump light portion comprises four times the pump power as the second receiver pump light portion.
5. The transceiver according to claim 1 , further comprising a first optical coupler disposed to couple the first transmitter pump light portion into the first optical amplifier; and a second optical coupler disposed to couple the second receiver pump light portion into the second optical amplifier.
6. The transceiver according to claim 1 , wherein the first control loop is configured to vary current to the second shared optical source in dependence upon the power of the output optical signal.
7. The transceiver according to claim 1 , wherein the second splitter comprises a variable optical power splitter.
8. The transceiver according to claim 7 , wherein the variable optical power splitter is configured to lower power of the LO light when gain in the second optical amplifier increases.
9. The transceiver according to claim 1 , wherein the first shared optical source comprises a wavelength-tunable laser, and the second shared optical source comprises a pump laser.
10. The transceiver according to claim 1 , wherein at least one of the first optical amplifier and the second optical amplifier comprises a fiber amplifier.
11. The transceiver according to claim 1 , wherein the first control loop includes a photodetector for sampling the optical output signal, and a feedback loop controller.