# US 2018/0323871 A1 · Apparatus and methods for timing tone based transmitter skew alignment in an optical communication system > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2018/0323871 A1 - Document ID: US20180323871A1 - Status: Published application - Kind: A1 - Application number: 16/024,105 - Filed: 2018-06-29 - Published: 2018-11-08 - Earliest claimed: 2015-09-04 - Assignees: Inphi Corporation - Applicants: Inphi Corporation - Inventors: Shu Hao FAN; Damian Alfonso MORERO; Mario Rafael HUEDA - Web page: https://patentgrep.com/patent/US20180323871A1 ## CPC - H04B 10/07955: {Monitoring or measuring power} - H04B 7/005: Control of transmission; Equalising - H04B 7/0413: MIMO systems - H04B 10/40: Transceivers - H04B 10/50: Transmitters - H04B 10/5053: {using a parallel, i.e. shunt, combination of modulators} - H04B 10/5161: {Combination of different modulation schemes} - H04B 10/532: Polarisation modulation - H04B 10/61: Coherent receivers - H04B 10/616: {Details of the electronic signal processing in coherent optical receivers} - H04L 25/03: Shaping networks in transmitter or receiver, e.g. adaptive shaping networks - H04L 25/14: Channel dividing arrangements {, i.e. in which a single bit stream is divided between several baseband channels and reassembled at the receiver} - H04B: TRANSMISSION - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract Apparatus and method for transmitter alignment in an optical communication system are provided. In certain configurations, a method of correcting for transmitter skew is provided. The method includes generating an optical signal using a transmitter based on an in-phase (I) component and a quadrature-phase (Q) component of a transmit signal, the optical signal having a baud rate that is based on a timing tone. The method further includes receiving the optical signal as an input to a receiver, and generating a signal vector representing the optical signal using the receiver. The signal vector includes an I component and a Q component. The method further includes calculating a power of the timing tone based on processing the signal vector using a tone power calculator of the receiver, and correcting for a skew of the transmitter based on the calculated power. ## Claims ### Claim 1 A transmitter error compensation device for a digital signal processing circuit in a receiver for an optical communications system, the device comprising: a MIMO equalizer configured to receive a digital signal vector from an analog front-end and to generate a compensated digital vector, wherein the digital signal vector comprises a digital representation of an in-phase (I) component and a quadrature-phase (Q) component of an optical signal received from a transmitter; wherein the MIMO equalizer is configured to compensate for a modulating biasing error of the transmitter; a first SISO equalizer configured to generate an I component of the compensated digital vector; a second SISO equalizer configured to generate a Q component of the compensated digital vector; wherein the first and second SISO equalizers are configured to compensate for a transmit skew error of the transmitter; an I signal path including the MIMO equalizer and the first SISO equalizer; and a Q signal path including the MIMO equalizer and the second SISO equalizer. ### Claim 2 (depends on 1) The device of claim 1 further comprising a slicer configured to generate an output digital signal vector based on slicing the compensated digital signal vector. ### Claim 3 (depends on 2) The device of claim 2 further comprising a first digital adaption engine configured to control a plurality of coefficients of the first and second SISO equalizers based on a first error signal comprising a difference between the compensated digital signal vector and the output digital signal vector. ### Claim 4 (depends on 3) The device of claim 3 further comprising an error back propagation system configured to generate a second error signal based on the first error signal and the plurality of coefficients of the first and second equalizers. ### Claim 5 (depends on 4) The device of claim 4 further comprising a second digital adaption engine configured to control a plurality of coefficients of the MIMO equalizer based on the second error signal. ### Claim 6 (depends on 1) The device of claim 1 configured to adapt a plurality of coefficients of the first and second SISO equalizers based on a least mean squares (LMS) stochastic gradient algorithm. ### Claim 7 (depends on 1) The device of claim 1 wherein the digital signal vector is derived from an optical signal comprising a multi-level quadrature modulation (QAM) signal, a discrete multitoned (DMT) modulation signal, an orthogonal frequency division multiplexing (OFDM) signal, or a phase-shift keying (PSK) signal. ### Claim 8 (depends on 1) The device of claim 1 wherein the digital signal vector comprises data representing a single polarization modulation or a dual-polarization modulation. ### Claim 9 A method of operating an transmitter error compensation device for a digital signal processing circuit in a receiver for an optical communications systems, the method comprising: receiving, from an analog front-end, a digital signal vector, wherein the digital signal vector comprises a digital representation of an in-phase (I) component and a quadrature-phase (Q) component of an optical signal received from a transmitter; generating, by a MIMO equalizer, a compensated digital vector by compensating for a modulating biasing error of the transmitter; generating, by a first SISO equalizer, an I component of the compensated digital vector, wherein the first SISO equalizer is configured in an I signal path with the MIMO equalizer; generating, by a second SISO equalizer, a Q component of the compensated digital vector, wherein the second SISO equalizer is configured in a Q signal path with the MIMO equalizer; and compensating, by the first and second SISO equalizers, for a transmit skew error of the transmitter. ### Claim 10 (depends on 9) The method of claim 9 further comprising generating, by a slicer, an output digital signal vector based on slicing the compensated digital signal vector. ### Claim 11 (depends on 10) The method of claim 10 further comprising controlling, by a first digital adaptation engine, a plurality of coefficients of the first and second SISO equalizers based on a first error signal comprising a difference between the compensated digital signal vector and the output digital signal vector. ### Claim 12 (depends on 11) The method of claim 11 further comprising generating, by an error back propagation system, a second error signal based on the first error signal and the plurality of coefficients of the first and second equalizers. ### Claim 13 (depends on 12) The method of claim 12 further comprising controlling, by a second digital adaptation engine, a plurality of coefficients of the MIMO equalizer based on the second error signal. ### Claim 14 (depends on 9) The method of claim 9 further comprising adapting a plurality of coefficients of the first and second SISO equalizers based on a least means square (LMS) stochastic gradient algorithm. ### Claim 15 (depends on 9) The method of claim 9 wherein the digital signal vector is derived from an optical signal comprising a multi-level quadrature modulation (QAM) signal, a discrete multitoned (DMT) modulation signal, an orthogonal frequency division multiplexing (OFDM) signal, or a phase-shift keying (PSK) signal. ### Claim 16 (depends on 9) The method of claim 9 wherein the digital signal vector comprises data representing a single polarization modulation or a dual-polarization modulation ### Claim 17 A receiver for an optical communications system, the device comprising: an analog front-end configured to convert an analog signal vector representing an optical signal into a digital signal vector, the optical signal having a baud rate that is based on a timing tone, wherein the digital signal vector comprises a digital representation of an in-phase (I) component and a quadrature-phase (Q) component of an optical signal received from a transmitter; a digital signal processing circuit configured to process the digital signal vector to recover data from symbols of the optical signal, wherein the symbols change at the baud rate; wherein the digital signal processing circuit further comprises a transmitter error compensation system configured to compensate the digital signal vector for at least one of a transmit skew error or a modulator biasing error of the transmitter; wherein the transmitter error compensation system comprises: a MIMO equalizer configured to receive the digital signal vector from the analog front-end and to generate a compensated digital vector; wherein the MIMO equalizer is configured to compensate for a modulating biasing error of the transmitter; a first SISO equalizer configured to generate an I component of the compensated digital vector; a second SISO equalizer configured to generate a Q component of the compensated digital vector; wherein the first and second SISO equalizers are configured to compensate for a transmit skew error of the transmitter; an I signal path including the MIMO equalizer and the first SISO equalizer; and a Q signal path including the MIMO equalizer and the second SISO equalizer. ### Claim 18 (depends on 17) The device of claim 17 further comprising a slicer configured to generate an output digital signal vector based on slicing the compensated digital signal vector. ### Claim 19 (depends on 18) The device of claim 18 further comprising a first digital adaption engine configured to control a plurality of coefficients of the first and second SISO equalizers based on a first error signal comprising a difference between the compensated digital signal vector and the output digital signal vector. ### Claim 20 (depends on 19) The device of claim 19 further comprising an error back propagation system configured to generate a second error signal based on the first error signal and the plurality of coefficients of the first and second equalizers. ### Claim 21 (depends on 20) The device of claim 20 further comprising a second digital adaption engine configured to control a plurality of coefficients of the MIMO equalizer based on the second error signal. ### Claim 22 (depends on 17) The device of claim 17 configured to adapt a plurality of coefficients of the first and second SISO equalizers based on a least mean squares (LMS) stochastic gradient algorithm. ### Claim 23 (depends on 17) The device of claim 17 wherein the digital signal vector is derived from an optical signal comprising a multi-level quadrature modulation (QAM) signal, a discrete multitoned (DMT) modulation signal, an orthogonal frequency division multiplexing (OFDM) signal, or a phase-shift keying (PSK) signal. ### Claim 24 (depends on 17) The device of claim 17 wherein the digital signal vector comprises data representing a single polarization modulation or a dual-polarization modulation.