# US 7,411,726 B2 · Multi-channel differentially encoded phase shift keyed receivers > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,411,726 B2 - Document ID: US7411726B2 - Status: Granted - Kind: B2 - Application number: 11/715,670 - Filed: 2007-03-08 - Published: 2007-09-20 - Granted: 2008-08-12 - Earliest claimed: 2004-12-23 - Assignees: Massachusetts Institute of Technology - Inventors: David O. Caplan - Web page: https://patentgrep.com/patent/US7411726B2 ## CPC - H04J 14/02: Wavelength-division multiplex systems - H04B 10/677: {for differentially modulated signal, e.g. DPSK signals} - H04J: MULTIPLEX COMMUNICATION (transmission in general H04B; peculiar to transmission of digital information H04L5/00; systems for the simultaneous or sequential transmission of more than one television signal H04N7/08; in exchanges H04Q11/00; stereophonic systems H04S) - H04B: TRANSMISSION ## Abstract An optical, multi-channel, Differential Phase Shift Keying (DPSK) receiver demodulates multiple Wavelength Division Multiplexed (WDM) channels using at least one interferometer. This distributes expense of the interferometer(s) over all channels of an optical signal, allowing for deployment of cost-effective, scalable, wideband, WDM DPSK systems. For example, for an 80 channel WDM link, the receiver uses a single interferometer instead of eighty interferometers and associated stabilization hardware, dramatically reducing size, weight, power, and cost. The receiver is architecturally compatible with existing interferometer technologies so previous development and qualification efforts can be leveraged. This allows for expedited technology insertion into existing optical communications networks, including terrestrial and space-based optical networks. ## Claims ### Claim 1 An apparatus for demodulating an optical signal having Differentially Encoded Phase Shift Keying (DPSK) channels, the apparatus comprising: multiple delay line interferometers to (i) delay at least one channel in an optical signal by multiple bits, (ii) demodulate the optical signal from having DPSK channels to an optical signal having channels modulated in intensity and (iii) output the demodulated optical signal onto at least one main output optical path, optical signal including DQPSK or 8-DPSK WDM optical signal pulses; and channel selectors in the at least one main output optical path to direct channels onto tributary optical paths. ### Claim 2 (depends on 1) The apparatus according to claim 1 further including optoelectronic converters in the tributary optical paths to convert the demodulated optical signal into respective, corresponding, electrical signals. ### Claim 3 (depends on 1) The apparatus according to claim 1 wherein multiple delay line interferometers delay at least one channel by at least one bit. ### Claim 4 (depends on 1) The apparatus according to claim 1 wherein the delay line interferometers are selectably adjustable to interfere optical signal pulses offset by a selectable number. ### Claim 5 (depends on 1) The apparatus according to claim 1 wherein the interferometers include an electronically tunable phase shifter to receive incoming wavelengths. ### Claim 6 (depends on 1) The apparatus according to claim 1 wherein wavelength spacing between carrier wavelengths defining the channels is an integer multiple of a channel rate of the optical signal. ### Claim 7 (depends on 1) The apparatus according to claim 1 wherein wavelength spacing between carrier wavelengths defining the channels is evenly divisible by an odd number of half channel rates of the optical signal. ### Claim 8 (depends on 7) The apparatus according to claim 7 further including a polarity corrector to correct polarity of the channels. ### Claim 9 (depends on 8) The apparatus according to claim 8 wherein the polarity corrector is configured to correct polarity of electrical signals corresponding to the channels. ### Claim 10 (depends on 8) The apparatus according to claim 8 wherein the polarity corrector is configured to optically correct polarity of the channels. ### Claim 11 (depends on 1) The apparatus according to claim 1 wherein channel rates are integer multiples of interferometer delay. ### Claim 12 (depends on 1) The apparatus according to claim 1 further including a feedback processor to generate signal(s) transmitted to a transmitter(s) of the optical signal(s) to cause the transmitter to tune carrier wavelengths defining the channels for adjusting wavelength position or channel separation. ### Claim 13 (depends on 1) The apparatus according to claim 1 further including a low noise optical amplifier to receive the optical signal and outputting the received amplified optical signal to the interferometers. ### Claim 14 (depends on 1) The apparatus according to claim 1 wherein the channel selectors include optical filters. ### Claim 15 (depends on 1) The apparatus according to claim 1 wherein the interferometers are configured to receive at least one pilot signal to allow for stabilization and control of the interferometer and wavelength alignment of the incoming optical signal(s). ### Claim 16 (depends on 1) The apparatus according to claim 1 used in an optical regenerator. ### Claim 17 (depends on 1) The apparatus according to claim 1 used in a free space optic communications network. ### Claim 18 (depends on 1) The apparatus according to claim 1 used in a fiber optic communications network. ### Claim 19 (depends on 1) The apparatus according to claim 1 wherein the optical signal includes multiple-rate WDM signals. ### Claim 20 (depends on 1) The apparatus according to claim 1 wherein two delay line interferometers are orthogonally phased. ### Claim 21 (depends on 20) The apparatus according to claim 20 wherein the optical signals are WDM optical signals that are spaced by odd multiples of the interferometer FSR/4. ### Claim 22 (depends on 1) The apparatus according to claim 1 wherein two interferometers have different delays. ### Claim 23 A method of demodulating an optical signal having Differentially Encoded Phase Shift Keying (DPSK) channels, the method comprising: delaying at least one first series of differentially encoded optical signal pulses in respective DPSK channels of the at least one first series of optical signal pulses by a multiple bit duration to align the at least one first series optical signal pulses with at least one respective second series of differentially encoded optical signal pulses also in the respective DPSK channels, the optical pulses including DQPSK or 8-DPSK WDM optical pulses; respectively interfering the at least one first and second series of optical signal pulses in an aligned state to demodulate the optical signals from having DPSK channels to at least one optical signal having channels modulated in intensity; outputting the demodulated optical signal onto respective main output optical paths; and directing channels in the respective main output optical paths onto tributary optical paths. ### Claim 24 (depends on 23) The method according to claim 23 further including converting the demodulated optical signal on the tributary optical paths into respective, corresponding, electrical signals. ### Claim 25 (depends on 23) The method according to claim 23 wherein demodulating the optical signal includes interfering adjacent optical signal pulses. ### Claim 26 (depends on 23) The method according to claim 23 wherein demodulating the optical signal includes interfering non-adjacent optical signal pulses. ### Claim 27 (depends on 23) The method according to claim 23 wherein demodulating the optical signal includes interfering optical signal pulses offset by a selectable number. ### Claim 28 (depends on 23) The method according to claim 23 wherein demodulating the optical signal includes tuning at least one interferometer for receiving incoming wavelengths. ### Claim 29 (depends on 28) The method according to claim 28 wherein the at least one interferometer is controlled using a pilot signal. ### Claim 30 (depends on 23) The method according to claim 23 wherein wavelength spacing between carrier wavelengths defining the channels is an integer multiple of a channel rate of the optical signal. ### Claim 31 (depends on 23) The method according to claim 23 wherein delaying the at least one first series of optical signal pulses further comprises delaying the at least one first series of optical signal pulses relative to its respective series by a different amount from at least one other first series of optical signal pulses relative to its respective second series. ### Claim 32 (depends on 23) The method according to claim 23 wherein wavelength spacing between carrier wavelengths defining the channels is evenly divisible by an odd number of half channel rates of the optical signal. ### Claim 33 (depends on 32) The method according to claim 32 further including correcting polarity of the channels. ### Claim 34 (depends on 33) The method according to claim 33 wherein correcting the polarity of the channels includes optically correcting polarity of the channels. ### Claim 35 (depends on 32) The method according to claim 32 wherein correcting the polarity of the channels includes correcting polarity of electrical signals corresponding to the channels. ### Claim 36 (depends on 23) The method according to claim 23 wherein the delay is achieved with two orthogonally phased delay line interferometers. ### Claim 37 (depends on 36) The method according to claim 36 wherein wavelength spacing between carrier wavelengths defining the channels is an odd multiple of the delay line interferometer FSR/4. ### Claim 38 (depends on 23) The method according to claim 23 wherein channel rate bit durations are integer multiples of demodulating delay. ### Claim 39 (depends on 23) The method according to claim 23 further including feeding back signal(s) to transmitter(s) of the optical signal(s) to cause the transmitter to tune carrier wavelengths defining the channels for adjusting wavelength position or channel separation. ### Claim 40 (depends on 23) The method according to claim 23 further including optically amplifying the optical signals prior to demodulating the optical signal. ### Claim 41 (depends on 23) The method according to claim 23 wherein directing the channels onto the tributary optical paths includes filtering the phase demodulated optical signals. ### Claim 42 (depends on 23) The method according to claim 23 further including controlling at least one demodulating interferometer based on at least one pilot signal. ### Claim 43 (depends on 23) The method according to claim 23 used in an optical regenerator. ### Claim 44 (depends on 23) The method according to claim 23 used in a free space optic communications network. ### Claim 45 (depends on 23) The method according to claim 23 used in a fiber optic communications network. ### Claim 46 An apparatus for demodulating an optical signal having Differentially Encoded Phase Shift Keying (DPSK) channels, the apparatus comprising: means for delaying at least one first series of differentially encoded optical signal pulses in at least one respective DPSK channel of the optical signal by a multiple bit duration to align the at least one series of first optical signal pulses with at least one second series of differentially encoded optical signal pulses also in the at least one respective DPSK channel, the optical signal pulses including DQPSK or 8-DPSK WDM optical signal pulses; means for interfering the at least one first and second series differentially encoded optical signal pulses in an aligned state to demodulate the optical signal from having DPSK channels to a respective optical signal having channels modulated in intensity; means for outputting the respective demodulated optical signal onto at least one respective main output optical path; and means for directing channels in the at least one respective main output optical path onto tributary optical paths. ### Claim 47 A method for demodulating an optical signal having Differentially Encoded Phase Shift Keying (DPSK) channels, the method comprising: feeding back a signal to constrain wavelength spacing of DPSK channels in an optical signal, the optical signal including DQPSK or 8-DPSK WDM optical signal pulses; and interfering offset optical signal pulses in the optical signal to demodulate the optical signal from being DPSK modulated to being intensity modulated. ### Claim 48 (depends on 47) The method according to claim 47 further including directing channels in the demodulated optical signal from at least one main optical path onto tributary optical paths. ### Claim 49 A system for demodulating an optical signal having Differentially Encoded Phase Shift Keying (DPSK) channels, the system comprising: means for feeding back a signal to constrain wavelength spacing of DPSK channels in an optical signal, where the optical signal includes DQPSK, and/or 8-DPSK WDM optical signal; and means for interfering offset optical signal pulses in the optical signal to demodulate the optical signal from being DPSK modulated to being intensity modulated. ### Claim 50 (depends on 49) The method according to claim 49 further including means for directing channels in the demodulated optical signal from at least one main optical path onto tributary optical paths. ### Claim 51 An apparatus for demodulating an optical signal having Differentially Encoded Phase Shift Keying (DPSK) channels, the apparatus comprising: a processor to feed back a signal to constrain wavelength spacing of DPSK channels in an optical signal, the optical signal including DQPSK or 8-DPSK WDM optical signal pulses; and at least one interferometer that interferes offset optical signal pulses in the optical signal to demodulate the optical signal from being DPSK modulated to being intensity modulated. ### Claim 52 (depends on 51) The apparatus according to claim 51 wherein the at least one interferometer directs channels in the demodulated optical signal from at least one main optical path onto tributary optical paths. ### Claim 53 An apparatus for demodulating an optical signal having Differentially Encoded Phase Shift Keying (DPSK) channels, the apparatus comprising: multiple delay line interferometers to (i) demodulate an optical signal from having DPSK channels to an optical signal having channels modulated in intensity (ii) output the demodulated optical signal onto at least one main output optical path, and (iii) receive at least one pilot signal to allow for stabilization and control of the multiple interferometers and wavelength alignment of the incoming optical signal(s), the optical signal(s) including DQPSK or 8-DPSK WDM optical signal pulses; and channel selectors in the at least one main output optical path to direct channels onto tributary optical paths. ### Claim 54 An apparatus for demodulating an optical signal having Differentially Encoded Phase Shift Keying (DPSK) channels, the apparatus comprising: at least one delay line interferometer to (i) delay at least one channel in an optical signal by multiple bits, (ii) demodulate the optical signal from having DPSK channels to an optical signal having channels modulated in intensity and (iii) output the demodulated optical signal onto at least one main output optical path, the optical signal including multiple-rate WDM signals; and channel selectors in the at least one main output optical path to direct channels onto tributary optical paths. ### Claim 55 An apparatus for demodulating an optical signal having Differentially Encoded Phase Shift Keying (DPSK) channels, the apparatus comprising: at least two delay line interferometers to (i) delay at least one channel in an optical signal by multiple bits, (ii) demodulate the optical signal from having DPSK channels to an optical signal having channels modulated in intensity and (iii) output the demodulated optical signal onto at least one main output optical path, at least two of the delay line interferometers being orthogonally phased; and channel selectors in the at least one main output optical path to direct channels onto tributary optical paths. ### Claim 56 An apparatus for demodulating an optical signal having Differentially Encoded Phase Shift Keying (DPSK) channels, the apparatus comprising: at least two delay line interferometers to (i) delay at least one channel in an optical signal by multiple bits, (ii) demodulate the optical signal from having DPSK channels to an optical signal having channels modulated in intensity and (iii) output the demodulated optical signal onto at least one main output optical path, at least two of the interferometers having different delays; and channel selectors in the at least one main output optical path to direct channels onto tributary optical paths. ### Claim 57 A method of demodulating an optical signal having Differentially Encoded Phase Shift Keying (DPSK) channels, the method comprising: delaying at least one first series of differentially encoded optical signal pulses in respective DPSK channels by a multiple bit duration to align the at least one first series of optical signal pulses with at least one respective second series of differentially encoded optical signal pulses also in the respective DPSK channels, the delaying including delaying the at least one first series of differentially encoded optical signal pulses relative to its respective second series by a different amount from at least one other first series of differentially encoded optical signal pulses relative to its respective second series; respectively interfering the at least one first and second series of optical signal pulses in an aligned state to demodulate the optical signals from having DPSK channels to at least one optical signal having channels modulated in intensity; outputting the demodulated optical signals onto respective main output optical paths; and directing channels in the respective main output optical paths onto tributary optical paths. ### Claim 58 A method of demodulating an optical signal having Differentially Encoded Phase Shift Keying (DPSK) channels, the method comprising: delaying at least one first series of differentially encoded optical signal pulses in respective DPSK channels by a multiple bit duration to align the at least one first series optical signal pulses with at least one respective second series of differentially encoded optical signal pulses also in the respective DPSK channels, the delay being achieved with two orthogonally phased delay line interferometers; respectively interfering the at least one first and second series of optical signal pulses in an aligned state to demodulate the optical signals from having DPSK channels to at least one optical signal having channels modulated in intensity; outputting the demodulated optical signal onto respective main output optical paths; and directing channels in the respective main output optical paths onto tributary optical paths. ### Claim 59 An apparatus for demodulating an optical signal having Differentially Encoded Phase Shift Keying (DPSK) channels, the apparatus comprising: delay line interferometers to (i) delay at least one channel in an optical signal by multiple bits, (ii) demodulate the optical signal from having DPSK channels to an optical signal having channels modulated in intensity and (iii) output the demodulated optical signal onto at least one main output optical path, the optical signal including 2k-DPSK WDM optical signals with k-bits/symbol, k being greater than or equal to 1; and channel selectors in the at least one main output optical path to direct channels onto tributary optical paths.