Power adjustment of in-phase and quadrature components at a coherent optical receiver
View Patent ↗It is disclosed an optical coherent receiver for an optical communication network. The optical coherent receiver is configured to receive a modulated optical signal and to process it for generating an in-phase component and a quadrature component. The optical coherent receiver comprises a power adjuster in turn comprising a multiplying unit and a retroactively connected digital circuit. The multiplying unit is configured to multiply the in-phase and quadrature components by in-phase and quadrature gains, respectively, thereby providing power-adjusted in-phase and quadrature components. The digital circuit is configured to compute: a common gain indicative of a sum of the powers of the power-adjusted in-phase and quadrature components; a differential gain indicative of a difference between the powers of the power-adjusted in-phase and quadrature components; and the in-phase and quadrature gains as a product and a ratio, respectively, between the common gain and the differential gain.
1. An optical coherent receiver for an optical communication network, said optical coherent receiver being configured to receive a modulated optical signal and to process said modulated optical signal for generating an in-phase component and a quadrature component, said in-phase component and said quadrature component being electrical signals, said optical coherent receiver comprising a power adjuster in turn comprising:
a multiplying unit configured to multiply said in-phase component by an in-phase gain thereby providing a power-adjusted in-phase component, and to multiply said quadrature component by a quadrature gain thereby providing a power-adjusted quadrature component; and
a digital circuit connected between output and input of said multiplying unit and configured to compute:
a common gain indicative of a sum of a power of said power-adjusted in-phase component and a power of said power-adjusted quadrature component, and a differential gain indicative of a difference between said power of said power-adjusted in-phase component and said power of said power-adjusted quadrature component; and
said in-phase gain as a product between said common gain and said differential gain, and said quadrature gain as a ratio between said common gain and said differential gain.
2. An optical coherent receiver according to claim 1 , wherein it further comprises an analog-to-digital unit connected at the input of said power adjuster, said analog-to-digital unit being configured to sample said in-phase component and said quadrature component for providing N in-phase component and N quadrature component samples to said power adjuster at each clock cycle of a clock signal generated at said optical coherent receiver, N being an integer equal to or higher than 1.
3. An optical coherent receiver according to claim 2 , wherein said multiplying unit is a digital unit configured to multiply said N in-phase component samples by said in-phase gain thereby providing N power-adjusted in-phase component samples, and to multiply said N quadrature component samples by said quadrature gain thereby providing N power-adjusted quadrature component samples.
4. An optical coherent receiver according to claim 1 , wherein said multiplying unit is an analog unit.
5. An optical coherent receiver according to claim 4 , wherein said power adjuster comprises an analog-to-digital unit connected at the output of said multiplying unit, said analog-to-digital unit being configured to sample said power-adjusted in-phase component and said power-adjusted quadrature component for providing N power-adjusted in-phase component samples and N power-adjusted quadrature component samples at each clock cycle of a clock signal generated at said optical coherent receiver, N being an integer equal to or higher than 1.
6. An optical coherent receiver according to claim 3 , wherein said digital circuit comprises a computation module configured to receive said N power-adjusted in-phase component samples and said N power-adjusted quadrature component samples and to calculate a common metric according to the following equation:
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k
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N
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I
k
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2
+
Q
k
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2
,
c being said common metric, I′ k being said N power-adjusted in-phase component samples and Q′ k being said N power-adjusted quadrature component samples.
7. An optical coherent receiver according to claim 3 , wherein said digital circuit comprises a computation module configured to receive said N power-adjusted in-phase component samples and said N power-adjusted quadrature component samples and to calculate a common metric according to the following equation:
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c being said common metric, I′ k being said N power-adjusted in-phase component samples and Q′ k being said N power-adjusted quadrature component samples.
8. An optical coherent receiver according to claim 6 , wherein said digital circuit further comprises a cascade of an adder, a common multiplier and a common accumulator connected at the output of said computation module, wherein:
said adder is configured to calculate c−2T, T being a target value that the power of said power-adjusted in-phase component and the power of said power-adjusted quadrature component should reach;
said common multiplier is configured to calculate S c ·(c−2T), S c being a common loop gain; and
said common accumulator is configured to update its content (a c [n−1]) by adding S c ·(c−2T) to it, thereby providing an updated common content (a c [n]).
9. An optical coherent receiver according to claim 8 , wherein said computation module is further configured to calculate a differential metric according to the following equation:
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,
d being said differential metric, I′ k being said N power-adjusted in-phase component samples and Q′ k being said N power-adjusted quadrature component samples.
10. An optical coherent receiver according to claim 9 , wherein said digital circuit further comprises a cascade of a differential multiplier and a differential accumulator connected at the output of said computation module, wherein:
said differential multiplier is configured to calculate S d ·d, S d being a differential loop gain; and
said differential accumulator is configured to update its content (a d [n−1]) by adding S d ·d to it, thereby providing an updated differential content (a d [n]).
11. An optical coherent receiver according to claim 10 , wherein said differential loop gain is lower than said common loop gain.
12. An optical coherent receiver according to claim 8 , wherein said digital circuit further comprises an in-phase adder and a quadrature adder connected both to said common accumulator and to said differential accumulator, wherein:
said in-phase adder is configured to provide a sum (a c [n]+a d [n]) of said updated common content (a c [n]) and said updated differential content (a d [n]); and
said quadrature adder is configured to provide a difference (a c [n]−a d [n]) between said updated common content (a c [n]) and said updated differential content (a d [n]).
13. An optical coherent receiver according to claim 12 , wherein said digital circuit further comprises an in-phase exponential module connected between said in-phase adder and said multiplying unit and a quadrature exponential module connected between said quadrature adder and said multiplying unit, wherein:
said in-phase exponential module is configured to calculate said in-phase gain as a negative exponential function of said sum; and
said quadrature exponential module is configured to calculate said quadrature gain as a negative exponential function of said difference.
14. A node for a communication network comprising an optical coherent receiver, said optical coherent receiver being configured to receive a modulated optical signal and to process said modulated optical signal for generating an in-phase component and a quadrature component, said in-phase component and said quadrature component being electrical signals, said optical coherent receiver comprising a power adjuster in turn comprising:
a multiplying unit configured to multiply said in-phase component by an in-phase gain thereby providing a power-adjusted in-phase component, and to multiply said quadrature component by a quadrature gain thereby providing a power-adjusted quadrature component; and
a digital circuit connected between output and input of said multiplying unit and configured to compute:
a common gain indicative of a sum of a power of said power-adjusted in-phase component and a power of said power-adjusted quadrature component, and a differential gain indicative of a difference between said power of said power-adjusted in-phase component and said power of said power-adjusted quadrature component; and
said in-phase gain as a product between said common gain and said differential gain, and said quadrature gain as a ratio between said common gain and said differential gain.
15. A method for adjusting power of an in-phase component and a quadrature component of a modulated optical signal received at an optical coherent receiver for an optical communication network, said in-phase component and said quadrature component being electrical signals, said method comprising:
multiplying said in-phase component by an in-phase gain thereby providing a power-adjusted in-phase component, and multiplying said quadrature component by a quadrature gain thereby providing a power-adjusted quadrature component; and
computing:
a common gain indicative of a sum of a power of said power-adjusted in-phase component and a power of said power-adjusted quadrature component, and a differential gain indicative of a difference between said power of said power-adjusted in-phase component and said power of said power-adjusted quadrature component; and
said in-phase gain as a product between said common gain and said differential gain, and said quadrature gain as a ratio between said common gain and said differential gain.