# US 2014/0153075 A1 · Optical signal modulation > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2014/0153075 A1 - Document ID: US20140153075A1 - Status: Published application - Kind: A1 - Application number: 13/693,457 - Filed: 2012-12-04 - Published: 2014-06-05 - Earliest claimed: 2012-12-04 - Assignees: Telefonaktiebolaget L M Ericsson (publ) - Applicants: Telefonaktiebolaget L M Ericsson (Publ) - Inventors: Antonio MALACARNE; Francesco FRESI; Jonathan KLAMKIN; Luca POTI - Web page: https://patentgrep.com/patent/US20140153075A1 ## CPC - H04B 10/541: {Digital intensity or amplitude modulation} - H04B 10/5053: {using a parallel, i.e. shunt, combination of modulators} - H04B: TRANSMISSION ## Abstract A 2n quadrature amplitude modulation optical modulator has an optical input for receiving an optical signal. A first splitter is coupled to the optical input and has first and second outputs. A first optical modulation apparatus, coupled to the first output, applies a modulation scheme having 2n-2 constellation points to produce a first modulated optical signal representing an in-phase component. A second optical modulation apparatus, coupled to the second output, applies a modulation scheme having 2n-2 constellation point to produce a second modulated optical signal representing a quadrature component. An optical combiner combines the first and second modulated optical signals to produce an output modulated optical signal which is modulated with a modulation scheme having 2n constellation points. ## Claims ### Claim 1 A 2n quadrature amplitude modulation optical modulator comprising: an optical input for receiving an optical signal; a first optical splitter coupled to the optical input, the first optical splitter having a first output and a second output; a first optical modulation apparatus coupled to the first output of the first optical splitter which is arranged to apply a modulation scheme having 2n-2 constellation points to produce a first modulated optical signal representing an in-phase component; a second optical modulation apparatus coupled to the second output of the first optical splitter which is arranged to apply a modulation scheme having 2n-2 constellation point to produce a second modulated optical signal, representing a quadrature component; an optical combiner for combining the first modulated optical signal and the second modulated optical signal to produce an output modulated optical signal which is modulated with a modulation scheme having 2n constellation points, wherein each of the first optical modulation apparatus and the second optical modulation apparatus comprises a dual-drive Mach Zehnder modulator having an input optical splitter with an unequal split ratio. ### Claim 2 (depends on 1) The 2n quadrature amplitude modulation optical modulator according to claim 1 wherein a vectorial sum of the 2n-2 constellation points of the modulation scheme of the first optical modulation apparatus has a zero DC offset and wherein a vectorial sum of the 2n-2 constellation points of the modulation scheme of the second optical modulation apparatus has a zero DC offset. ### Claim 3 (depends on 1) The 2n quadrature amplitude modulation optical modulator according to claim 1 wherein each of the first optical modulation apparatus and the second optical modulation apparatus comprise a first arm having an input for receiving a first electrical modulating signal and a second arm having an input for receiving a second electrical modulating signal, and wherein the optical modulator further comprises a driver circuit which is arranged to receive a data signal input and to output the first and second modulating signals with substantially equal peak-to-peak voltages. ### Claim 4 (depends on 3) The 2n quadrature amplitude modulation optical modulator according to claim 3 wherein the driver circuit is arranged to output the first and second modulating signals with a peak-to-peak voltage for causing a π phase shift between the first arm and the second arm of the modulator. ### Claim 5 (depends on 1) The 2n quadrature amplitude modulation optical modulator according to claim 1 further comprising a phase rotator which is arranged to apply a phase rotation which causes the second modulated optical signal to be offset by π/2 with respect to the first modulated optical signal. ### Claim 6 (depends on 1) The 2n quadrature amplitude modulation optical modulator according to claim 1 wherein at least one of the input optical splitters has a tunable split ratio. ### Claim 7 (depends on 6) The 2n quadrature amplitude modulation optical modulator according to claim 6 wherein the first input optical splitter has a tunable split ratio. ### Claim 8 (depends on 6) The 2n quadrature amplitude modulation optical modulator according to claim 6 wherein at least one of the input optical splitters comprises one of: a Mach Zehnder interferometer; a directional coupler with a tuning element; a multimode interference coupler with a tuning element. ### Claim 9 (depends on 1) The 2n quadrature amplitude modulation optical modulator according to claim 1 wherein the split ratio of the input optical splitter in the first optical modulation apparatus is 80/20 and the split ratio of the input optical splitter in the second optical modulation apparatus is 80/20. ### Claim 10 (depends on 1) The 2n quadrature amplitude modulation optical modulator according to claim 1 wherein the split ratio of the first optical splitter is 55/45, the split ratio of the input optical splitter in one of the first optical modulation apparatus and the second optical modulation apparatus is 75/25 and the split ratio of the input optical splitter in the other of the first optical modulation apparatus and the second optical modulation apparatus is 80/20. ### Claim 11 (depends on 1) The 2n quadrature amplitude modulation optical modulator according to claim 1 wherein n is an even number and is at least 4. ### Claim 12 (depends on 1) The 2n quadrature amplitude modulation optical modulator according to claim 1 wherein n is 4. ### Claim 13 (depends on 1) An optical signal transmission apparatus comprising: an optical source having an optical output for emitting an optical signal; a 2n quadrature amplitude modulation optical modulator according to claim 1, wherein the optical output of the optical source is coupled to the optical input of the modulator. ### Claim 14 A method of 2n quadrature amplitude modulation comprising: receiving an optical signal to be modulated; modulating a first portion of the received optical signal with a modulation scheme having 2n-2 constellation points to produce a first modulated optical signal representing an in-phase component; modulating a second portion of the received optical signal with a modulation scheme having 2n-2 constellation points to produce a second modulated optical signal representing a quadrature component; combining the first modulated optical signal and the second modulated optical signal to produce an output modulated optical signal which is modulated with a modulation scheme having 2n constellation points, wherein each of the modulating steps uses a dual-drive Mach Zehnder modulator which splits the received optical signal with an unequal split ratio. ### Claim 15 (depends on 14) The method according to claim 14 wherein a vectorial sum of the 2n-2 constellation points of the modulation scheme of the first optical modulation apparatus has a zero DC offset and a vectorial sum of the 2n-2 constellation points of the modulation scheme of the second optical modulation apparatus has a zero DC offset. ### Claim 16 (depends on 14) The method according to claim 14 wherein the step of modulating a second portion of the received optical signal comprises applying a phase rotation which causes the second modulated optical signal to be offset by π/2 with respect to the first modulated optical signal. ### Claim 17 (depends on 14) The method according to claim 14 wherein the steps of modulating a first portion of the received optical signal and modulating a second portion of the received optical signal each use a first electrical modulating signal and a second electrical modulating signal and the method further comprises receiving a data signal input and outputting the first and second modulating signals with substantially equal peak-to-peak voltages. ### Claim 18 (depends on 17) The method according to claim 17 wherein the first and second modulating signals are output with a peak-to-peak voltage for causing a π phase shift between the first arm and the second arm of the modulator.