# US 7,466,926 B2 · Method and apparatus for RZ-DPSK optical signal generation > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,466,926 B2 - Document ID: US7466926B2 - Status: Granted - Kind: B2 - Application number: 10/856,729 - Filed: 2004-05-28 - Published: 2005-12-01 - Granted: 2008-12-16 - Earliest claimed: 2004-05-28 - Assignees: Alcatel-Lucent USA Inc. - Inventors: Yuan-Hua Kao; Xiang Liu - Web page: https://patentgrep.com/patent/US7466926B2 ## CPC - H04B 10/5561: {Digital phase modulation} - H04B 10/505: {using external modulation} - H04B 10/508: Pulse generation, e.g. generation of solitons - H04B: TRANSMISSION ## Abstract An apparatus and method for generating chirp-free return-to-zero differential phase-shift keyed optical signals using a modulator driven by at least one 3-level return-to-zero drive signals. ## Claims ### Claim 1 A method of generating a return-to-zero (RZ) differential phase-shift-keyed (DPSK) optical signal comprising the steps of: generating a 3-level RZ drive signal; and driving a modulator with the 3-level RZ drive signal to generate the RZ-DPSK optical signal, wherein the step of generating the 3-level RZ drive signal includes the steps of: performing a logic AND operation on a differentially encoded data signal and a clock signal to generate a first 2-level drive signal, wherein the differentially encoded data signal is a binary signal having first and second binary states; performing a logic AND operation on an inverse of the differentially encoded data signal and the clock signal to generate a second 2-level drive signal; and differentially amplifying the first and second 2-level drive signals to generate the 3-level RZ drive signal, wherein each occurrence of a binary state in the differentially encoded data signal is represented in the 3-level RZ drive signal by a positive pulse or a negative pulse relative to a reference level. ### Claim 2 (depends on 1) The method of claim 1 wherein the modulator is a single Mach-Zehnder modulator. ### Claim 3 (depends on 1) The method of claim 1 wherein driving the modulator with the RZ drive signal provides simultaneous RZ pulse formatting and DPSK modulation. ### Claim 4 (depends on 1) The method of claim 1 wherein the generated RZ-DPSK signal is chirp-free. ### Claim 5 (depends on 1) The method of claim 1 further comprising amplifying the 3-level RZ drive signal. ### Claim 6 (depends on 1) The method of claim 1, wherein the modulator is a Z-cut LiNbO3 Mach-Zehnder modulator. ### Claim 7 (depends on 1) The method of claim 1, wherein said reference level is a level of the RZ drive signal at which the modulator outputs substantially no light. ### Claim 8 A method for generating return-to-zero (RZ) differential phase-shift-keyed (DPSK) optical signals comprising the steps of: performing a logic AND operation on a differentially encoded data signal and a clock signal to generate a first 2-level drive signal, wherein the differentially encoded data signal is a binary signal having first and second binary states, performing a logic AND operation on an inverse of the differentially encoded data signal and the clock signal to generate a second 2-level drive signal, differentially amplifying the first 2-level drive signal with the second 2-level drive signal to generate a first 3-level RZ drive signal; differentially amplifying the inverse of the first 2-level RZ drive signals to generate the RZ-DPSK optical signals, wherein, for at least one of the first and second 3-level RZ drive signals each occurrence of a binary state in the differentially encoded data signal is represented in the 3level RZ drive signal by a positive pulse or a negative pulse relative to a reference level. ### Claim 9 (depends on 8) The method of claim 8, wherein said reference level is a level of the RZ drive signal at which the modulator outputs substantially no light. ### Claim 10 A method of generating a return-to-zero (RZ) M-ary differential-phase amplitude-shift-keyed (DP-ASK) optical signal, comprising the steps of: generating an M-level RZ drive signal, wherein M is an integer greater than three; and driving a modulator with the M-level RZ drive signal, wherein the modulator modulates both intensity and phase of an optical beam to generate the RZ M-ary DP-ASK optical signal, wherein the step of generating the M-level RZ drive signal includes the steps of: performing a logic AND operation on a plurality of differentially encoded data signals and a clock signal to generate a plurality of first 2-level drive signals, performing a logic AND operation on an inverse of the plurality of differentially encoded data signals and the clock signal to generate a plurality of second 2-level drive signals, power combining each first 2-level drive signal with an inverse of the corresponding second 2-level drive signal to generate each of a plurality of 3-level RZ drive signals; and power combining the plurality of 3-level RZ drive signals to generate the M-level RZ drive signal. ### Claim 11 (depends on 10) The method of claim 10 wherein the modulator is a single Mach-Zehnder modulator. ### Claim 12 An apparatus for generating an RZ-DPSK optical signal, comprising: drive circuitry adapted to generate at least one 3-level RZ drive signal; and a modulator coupled to the drive circuitry such that the at least one 3-level RZ drive signal drives the modulator to generate the RZ-DPSK optical signal, wherein the drive circuitry comprises: a first logic AND gate adapted to perform a logic AND operation on a differentially encoded data signal and a clock signal to generate a first 2-level drive signal, wherein the differentially encoded data signal is a binary signal having first and second binary states; a second logic AND gate adapted to perform a logic AND operation on an inverse of the differentially encoded data signal and the clock signal to generate a second 2-level drive signal, and a differential amplifier adapted to differentially amplify the first and second 2-level drive signals to generate the 3-level RZ drive signal, wherein each occurrence of a binary state in the differentially encoded data signal is represented in the 3-level RZ drive signal by a positive pulse or a negative pulse relative to a reference level. ### Claim 13 (depends on 12) The apparatus of claim 12 wherein the modulator is a single single-drive Mach-Zehnder modulator. ### Claim 14 (depends on 13) The apparatus of claim 13 wherein the single-drive Mach-Zehnder modulator is an X-cut LiNbO3 modulator. ### Claim 15 (depends on 13) The apparatus of claim 13 wherein the single-drive Mach-Zehnder modulator is a semiconductor-based modulator. ### Claim 16 (depends on 12) The apparatus of claim 12 wherein the modulator is a single dual-drive Mach-Zehnder modulator. ### Claim 17 (depends on 16) The apparatus of claim 16 wherein the modulator is coupled to the drive circuitry such that two complementary 3-level RZ drive signals drive the modulator to generate the RZ-DPSK optical signals. ### Claim 18 (depends on 16) The apparatus of claim 16 wherein the dual-drive Mach-Zehnder modulator is a Z-cut LiNbO3 modulator. ### Claim 19 (depends on 16) The apparatus of claim 16 wherein the dual-drive Mach-Zehnder modulator is a semiconductor-based modulator. ### Claim 20 (depends on 12) The apparatus of claim 12, wherein said reference level is a level of the RZ drive signal at which the modulator outputs substantially no light. ### Claim 21 An apparatus for generating RZ-DPSK optical signals comprising: a first differential amplifier adapted to receive a differentially encoded data signal and a clock signal and generate a first 2-level drive signal, wherein the differentially encoded data signal is a binary signal having first and second binary states; a second differential amplifier adapted to receive an inverse of the differentially encoded data signal and the clock signal and generate a second 2-level drive signal; an inverter for inverting the second 2-level drive signal; a third differential amplifier adapted to receive the first 2-level drive signal and the inverted second 2-level drive signal to generate a 3-level RZ drive signal, wherein each occurrence of a binary state in the differentially encoded data signal is represented in the 3-level RZ drive signal by a positive pulse or a negative pulse relative to a reference level; and a modulator coupled to the third differential amplifier such that the 3-level RZ drive signal drives the modulator to generate RZ-DPSK optical signals. ### Claim 22 (depends on 21) The apparatus of claim 21, wherein said reference level is a level of the RZ drive signal at which the modulator outputs substantially no light. ### Claim 23 An apparatus for generating a return-to-zero (RZ) M-ary differential-phase-amplitude-shift-keyed (M-ary DP-ASK) optical signal, comprising: means for generating an M-level RZ drive signal and for driving a single modulator with the drive signal, wherein M is an integer greater than three and the modulator is adapted to modulate both intensity and phase of an optical beam to generate the RZ M-ary DP-ASK optical signal, wherein the means for generating comprises: a first plurality of logic AND gates, each adapted to perform a logic AND operation on a respective signal of a plurality of differentially encoded data signals and a clock signal to generate a plurality of first 2-level drive signals, a second plurality of logic AND gates, each adapted to perform a logic AND operation on an inverse of the plurality of differentially encoded data signals and the clock signal to generate a plurality of second 2-level drive signals, a plurality of power combiners, each adapted to power combine a corresponding one of the first 2-level drive signals with an inverse of the corresponding second 2-level drive signal to generate a corresponding one of a plurality of 3-level RZ drive signals; and an additional power combiner adapted to power combine the plurality of 3-level RZ drive signals to generate the M-level RZ drive signal. ### Claim 24 (depends on 23) The apparatus of claim 23, further comprising the modulator, wherein the modulator is a Mach-Zehnder modulator. ### Claim 25 A method of generating a return-to-zero (RZ) M-ary differential-phase amplitude-shift-keyed (DP-ASK) optical signal, comprising the steps of: generating a multi-level RZ drive signal; and driving a modulator with the drive signal to generate the RZ M-ary DP-ASK optical signal, wherein the step of generating the multi-level RZ drive signal further includes the steps of: performing a logic AND operation on a plurality of differentially encoded data signals and a clock signal to generate a plurality of first 2-level drive signals, performing a logic AND operation on each of an inverse of the plurality of differentially encoded data signals, and the clock signal to generate a plurality of respective second 2-level drive signal, power combining each of the plurality of first 2-level drive signals with a respective inverse of the plurality of respective second 2-level drive signals to generate a plurality of 3-level RZ drive signals; and power combining the plurality of 3-level RZ drive signals to generate the multi-level RZ drive signal.