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US 7,460,793 B2Granted
Coherent optical detection and signal processing method and system
OwnerMichael George Taylorinventor
Life of this patent
Estimating the term…
Abstract
A method and system of coherent detection of optical signals. The system utilizes a digital signal processor to recover an incoming optical signal. The system employs a local oscillator, which does not need to be phase locked to the signal. The signal may be consistently recovered, even when the polarization state varies over time. Additionally, the signal may be recovered when it comprises two channels of the same wavelength that are polarization multiplexed together. In addition, any impairment to the signal may be reversed or eliminated.
Claims34
A coherent optical detection system receiving an incoming optical signal in an optical communications network, said system comprising:
- a local oscillator emitting light;
- a phase diverse hybrid for generating two replicas of the incoming signal and two replicas of the local oscillator light, said phase diverse hybrid combining the first replica of the incoming optical signal and the first replica of the local oscillator light into a first output and combining the second replica of the incoming optical signal and the second replica of the local oscillator light into a second output and wherein said local oscillator does not have to be phase locked to the incoming optical signal;
- wherein the phase relationship between the optical signal and the local oscillator light in the first output is different from 0 degrees and different from 180 degrees compared to the phase relationship between the local oscillator light and the optical signal in the second output and the state of polarization of the optical signal relative to the local oscillator light in the first output is not orthogonal to the state of polarization of the optical signal relative to the local oscillator light in the second output;
- and
- two photodetectors communicating with the phase diverse hybrid, wherein said two photodetectors receive optical signals from the two outputs and convert them to electrical signals;
- the electrical signals received by the two photodetectors are digitized by two A/D converters to create digital values;
- and
- a digital signal processor multiplies the digital values from the two A/D converters by two coefficients and sums them to form a complex number, then multiplies the complex number by a rotating phase factor to provide a complex representation of the envelope of the electric field of the incoming optical signal or a component of the complex representation of the envelope of the electric field of the incoming optical signal, the rotating phase factor having a frequency and a phase equal to estimates of the frequency and the phase of the incoming optical signal with respect to the local oscillator light.
5 more elements
A method of receiving an incoming optical signal in a coherent optical detection system, said method comprising the steps of:
- emitting light from a local oscillator, said local oscillator not requiring a phase lock with the incoming optical signal;
- generating two replicas of the incoming signal and two replicas of the local oscillator light by a phase diverse hybrid;
- combining, by the phase diverse hybrid, the first replica of the incoming optical signal and the first replica of the local oscillator light into a first output;
- combining the second replica of the incoming optical signal and the second replica of the local oscillator light into a second output, wherein the phase relationship between the optical signal and the local oscillator light in the first output is different from 0 degrees and different from 180 degrees compared to the phase relationship between the local oscillator light and the optical signal in the second output and the state of polarization of the optical signal relative to the local oscillator light in the first output is not orthogonal to the state of polarization of the optical signal relative to the local oscillator light in the second output;
- receiving optical signals from the two outputs by two photodetectors in communication with the phase diverse hybrid;
- converting the optical signals from the two outputs into electrical signals;
- digitizing the electrical signals by two A/D converters to create digital values;
- multiplying digital values from the two A/D converters by coefficients and summing them to form a sequence of complex numbers;
- and
- multiplying the complex numbers by a rotating phase factor whose frequency is equal to an estimate of the frequency of the signal with respect to the local oscillator light and whose phase is equal to an estimate of the phase of the incoming optical signal with respect to the local oscillator light, to provide a complex representation or component thereof of the electric field envelope of the incoming optical signal.
7 more elements
A coherent optical detection system receiving an incoming optical signal in an optical communications network, said system comprising:
- a local oscillator emitting light;
- a phase diverse hybrid for generating two replicas of the incoming signal and two replicas of the local oscillator light, said phase diverse hybrid combining the first replica of the incoming optical signal and the first replica of the local oscillator light into a first output and combining the second replica of the incoming optical signal and the second replica of the local oscillator light into a second output and wherein said local oscillator does not have to be phase locked to the incoming optical signal;
- wherein the phase relationship between the optical signal and the local oscillator light in the first output is different from 0 degrees and different from 180 degrees compared to the phase relationship between the local oscillator light and the optical signal in the second output and the state of polarization of the optical signal relative to the local oscillator light in the first output is not orthogonal to the state of polarization of the optical signal relative to the local oscillator light in the second output;
- and
- two photodetectors communicating with the phase diverse hybrid, wherein said two photodetectors receive optical signals from the two outputs and convert them to electrical signals;
- wherein the electrical signals received by the two photodetectors are digitized by two A/D converters;
- and
- a digital signal processor performing a computation on digital values from the A/D converters to provide a complex representation of the envelope of the electric field of the incoming optical signal or a component of the complex representation of the envelope of the electric field of the incoming optical signal.
5 more elements
A method of receiving an incoming optical signal in a coherent optical detection system, said method comprising the steps of:
- emitting light from a local oscillator, said local oscillator not requiring a phase lock with the incoming optical signal;
- generating two replicas of the incoming signal and two replicas of the local oscillator light by a phase diverse hybrid;
- combining, by the phase diverse hybrid, the first replica of the incoming optical signal and the first replica of the local oscillator light into a first output;
- combining the second replica of the incoming optical signal and the second replica of the local oscillator light into a second output, wherein the phase relationship between the optical signal and the local oscillator light in the first output is different from 0 degrees and different from 180 degrees compared to the phase relationship between the local oscillator light and the optical signal in the second output and the state of polarization of the optical signal relative to the local oscillator light in the first output is not orthogonal to the state of polarization of the optical signal relative to the local oscillator light in the second output;
- receiving optical signals from the two outputs by two photodetectors in communication with the phase diverse hybrid;
- and
- converting the optical signals from the two outputs into electrical signals;
- digitizing the electrical signals by two A/D converters;
- and
- performing a computation on digital values from the A/D converters by a digital signal processor to provide a complex representation of the envelope of the electric field of the incoming optical signal or a component of the complex representation of the envelope of the electric field of the incoming optical signal.
7 more elements
Dependencies are inferred from the claim text.