In-phase and quadrature pattern alignment for quadrature phase shift keying optical transmitters
AssigneeOpnext Subsystems, Inc.
InventorsSunil Kumar Singh Khatana, Edem Ibragimov
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Abstract
I/Q data skew in a QPSK modulator may be detected by sending identical or complementary data streams to I and Q channel PSK modulators, setting the relative carrier phase between I and Q to zero or π, and monitoring the average QPSK output power, where the data streams sent to the I and Q channels include pseudorandom streams of ones and zeroes.
Claims19
A method for monitoring and aligning in-phase (I) and quadrature (Q) data in a quadrature phase shift keying (QPSK) modulator comprising:
- sending a series of data bits to an I data channel of the QPSK modulator and a copy of the series of data bits to a Q data channel of the QPSK modulator, the series of data bits and the copy of the series of data bits having a relative skew;
- and
- measuring average modulator output power as a function of the relative skew and carrier phase Φ between I and Q data channels at least in part by
- adjusting, with a phase control, the relative carrier phase Φ,
- adjusting, with at least one adjustable data delay, the relative skew by integer numbers of unit-intervals for the adjusted relative carrier phase Φ, and
- detecting, with a detector, the average modulator output power for combinations of the adjusted relative phase Φ and of the adjusted relative skew.
A method for monitoring and aligning in-phase (I) and quadrature (Q) data in a quadrature phase shift keying (QPSK) modulator comprising:
- sending a series of data bits to an I data channel of the QPSK modulator and a complementary series of data bits to a Q data channel of the QPSK modulator, the series of data bits and the complementary series of data bits having a relative skew;
- and
- measuring average modulator output power as a function of the relative skew and carrier phase Φ between I and Q data channels at least in part by
- adjusting, with a phase control, the relative carrier phase Φ,
- adjusting, with at least one adjustable data delay, the relative skew by integer numbers of unit-intervals for the adjusted relative carrier phase Φ, and
- detecting, with a detector, the average modulator output power for combinations of the adjusted relative phase Φ and of the adjusted relative skew.
Electronic circuitry for automatically aligning in-phase (I) and quadrature (Q) data in a quadrature phase shift keying (QPSK) modulator, the electronic circuitry comprising:
- a controller communicatively coupled with I and Q data channels of the QPSK modulator;
- an adjustable data delay;
- a phase control for adjusting relative carrier phase Φ between I and Q channels of the QPSK modulator;
- and
- a detector coupled to an output of the QPSK modulator to detect average modulator output power, wherein the controller is configured to
- in response to meeting an alignment criterion, instruct the phase control to change the relative carrier phase from Φ=π/2 to Φ=0 or π, then
- provide a series of data bits to the I data channel and another series of data bits to the Q data channel, the series of data bits and the other series of data bits having a relative skew,
- measure average modulator output power as a function of skew, wherein to perform the measurements the controller is further configured to
- instruct the adjustable data delay to adjust the relative skew by integer numbers of unit-intervals, and
- read from the detector the average modulator output power for the adjusted relative skew,
- determine an adjustment of the adjustable data delay corresponding to an extremum of the measured average modulator output power to remove the relative skew,
- instruct the adjustable data delay to maintain the determined adjustment, and then
- instruct the phase control to return the relative carrier phase to Φ=π/2.
Dependencies are inferred from the claim text.