US20220109503A1 - Auto-tuneable optical transceiver modules - Google Patents
Auto-tuneable optical transceiver modules Download PDFInfo
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- US20220109503A1 US20220109503A1 US17/062,289 US202017062289A US2022109503A1 US 20220109503 A1 US20220109503 A1 US 20220109503A1 US 202017062289 A US202017062289 A US 202017062289A US 2022109503 A1 US2022109503 A1 US 2022109503A1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/40—Transceivers
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/50—Transmitters
- H04B10/516—Details of coding or modulation
- H04B10/54—Intensity modulation
- H04B10/541—Digital intensity or amplitude modulation
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
- G02B6/29302—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means based on birefringence or polarisation, e.g. wavelength dependent birefringence, polarisation interferometers
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/07—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems
- H04B10/073—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an out-of-service signal
- H04B10/0731—Testing or characterisation of optical devices, e.g. amplifiers
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/60—Receivers
- H04B10/66—Non-coherent receivers, e.g. using direct detection
- H04B10/67—Optical arrangements in the receiver
Definitions
- Embodiments presented in this disclosure generally relate to electronic communications. More specifically, embodiments disclosed herein relate to fiber optic communications.
- Fiber optic communication systems use silicon photonic (SIP) technology and pulse amplitude modulation (PAM).
- PAM pulse amplitude modulation
- SIP silicon photonic
- PAM4 modulation can be used to transmit data across an optical system.
- Fiber optic communication systems can modulate optical signals using Mach-Zehnder Delay-Interferometer (MZDI) based modulators.
- MZDI Mach-Zehnder Delay-Interferometer
- VOAs variable optical attenuators
- VOAs are typically calibrated and tuned to improve performance and accuracy of the system. This can be done manually using a test bench, for example.
- FIG. 1 illustrates an optical signal path for an example optical communication system, according to an embodiment.
- FIG. 2 illustrates a testing system for an example optical communication system, according to an embodiment.
- FIG. 3 illustrates auto-tuning for an example optical communication system, according to an embodiment.
- FIG. 4 is a flowchart illustrating auto-tuning for an example optical communication system, according to an embodiment.
- FIG. 5 is a flowchart illustrating tuning transmission side components for an example optical communication system, according to an embodiment.
- FIG. 6 is a flowchart illustrating tuning receiver side components for an example optical communication system, according to an embodiment.
- FIG. 7 illustrates compression schemes for modulation in an optical communication system, according to an embodiment.
- FIG. 8 illustrates power level ratios for a level separation mismatch ratio used for modulation in an optical communication system, according to an embodiment.
- Embodiments include a method.
- the method includes enabling a first tuning mode for an optical communication system.
- the optical communication system includes a first signal path for transmitting data.
- the first signal path includes an optical source, a first one or more variable optical attenuators (VOAs), a modulator, and a transmission fiber.
- the optical communication system further includes a second signal path for receiving data.
- the second signal path includes a receiver fiber and a second one more VOAs.
- the method further includes tuning the first one or more VOAs, using the optical source in the first signal path for transmitting data, based on comparing a plurality of optical signal power values in the first path while the first tuning mode is enabled.
- the method further includes enabling a second tuning mode for the optical communication system.
- the method further includes tuning the second one or more VOAs, using the optical source in the first signal path for transmitting data, based on comparing a plurality of optical signal power values in the second path while the second tuning mode is enabled.
- the method further includes enabling a communication mode, in which the optical communication system is configured to use the first signal path for transmitting data and the second signal path for receiving data.
- Embodiments further include an optical communication system, including a first signal path for transmitting data.
- the first signal path includes an optical source, a first one or more VOAs, a modulator, and a transmission fiber.
- the optical communication system further includes a second signal path for receiving data.
- the second signal path includes a receiver fiber, and a second one more VOAs.
- the optical communication system is configured to enable a first tuning mode for tuning the first one or more VOAs, using the optical source in the first signal path for transmitting data, based on comparing a plurality of optical signal power values in the first path while the first tuning mode is enabled.
- the optical communication system is further configured to enable a second tuning mode for tuning the second one or more VOAs, using the optical source in the first signal path for transmitting data, based on comparing a plurality of optical signal power values in the second path while the second tuning mode is enabled.
- the optical communication system is further configured to enable a communication mode, in which the optical communication system is configured to use the first signal path for transmitting data and the second signal path for receiving data.
- Embodiments further include a method.
- the method includes transmitting data using a first signal path in an optical communication system.
- the first signal path includes an optical source, a first one or more VOAs, a modulator, and a transmission fiber.
- the method further includes receiving data using a second signal path in the optical communication system, the second signal path including a receiver fiber, and a second one more VOAs.
- the first one or more VOAs are configured to be tuned, using the optical source in the first signal path, based on comparing a plurality of optical signal power values in the first path while a first tuning mode is enabled.
- the second one or more VOAs are configured to be tuned, using the optical source in the first signal path, based on comparing a plurality of optical signal power values in the second path while a second tuning mode is enabled.
- MZDI modulators with variable optical attenuators (VOAs) to transmit data (e.g., using 4-level pulse amplitude modulation (PAM4) modulation).
- VOAs variable optical attenuators
- PAM4 modulation 4-level pulse amplitude modulation
- MZDI modulator can be tuned so that its bias point is set to the quadrature point, where the modulator characteristics are linear.
- the swing of the modulated signal can be optimized (e.g., based on the depth of the radio frequency (RF) modulation).
- RF radio frequency
- the VOAs can also be tuned, both on the transmitter side and the receiver side.
- the transmitter-side VOA can be used to control the modulator output power (e.g., allowing attenuation of the output power without setting the laser too low, which can cause mode-hop issues).
- the receiver-side VOA can be used to control the receiver input power, in order to avoid saturating later stages when too much input power is present.
- These VOAs can be separately tuned to provide appropriate relative attenuation on each side.
- these VOAs can be tuned manually (e.g., during manufacturing) using a test bench. This is discussed further below with regard to FIG. 2 . According to one or more embodiments disclosed herein, these VOAs can also be tuned without requiring external equipment. For example, as discussed below with regard to FIG. 3 , an optical system can be setup to provide automatic tuning for transmission side and receiver side components by, for example, toggling one or more optical switches between optical signal paths, and using components already in the system. This tuning can be done without external equipment (e.g., without requiring a test bench). Further, as will be discussed further below with regard to FIGS.
- setting a PAM4 modulation scheme to use bottom-compression can further improve system performance by improving the return loss robustness of the system.
- the tuning techniques described in connection with FIGS. 3-6 can be used to tune an optical communication system to use bottom-compression in modulation.
- FIG. 1 illustrates an optical signal path for an example optical communication system 100 , according to an embodiment.
- a laser 102 emits an optical signal.
- any suitable laser for an optical communication system can be used (e.g., a distributed feedback laser (DFB)).
- a laser is merely one example of an optical source. Any suitable optical source could be used.
- a coupler 104 receives the optical signal and divides the signal between a VOA 106 and a monitor 105 (e.g., an electro-optical monitoring device, or any other suitable monitoring device) that generates a signal IFF_IN (e.g., an electrical signal).
- IFF_IN indicates the power of the optical signal transmitted by the laser 102 .
- the VOA 106 attenuates the optical signal and transmits it to a coupler 108 .
- the VOA 106 is used to attenuate the signal to avoid setting the output of the laser 102 below a desired level. For example, setting the laser 102 such that it generates an optical signal whose power is below an output threshold can result in undesirable noise or mode hopping.
- Using the VOA 106 allows the laser 102 to operate above a preferred range, while still controlling the transmission power of the optical signal as it propagates through the system.
- the coupler 108 divides the signal between a modulator 110 and a monitor 109 that generates a signal IFF_ 1 (e.g., an electrical signal).
- IFF_ 1 indicates the power of the optical signal after it has been attenuated by the VOA 106 .
- the modulator 110 modulates the optical signal to add data for transmission along a fiber.
- the modulator 110 is an MZDI based modulator that implements PAM4 modulation. These are merely examples, however, and any suitable modulator and modulation scheme can be used.
- the modulator 110 transmits the signal to a coupler 112 , which divides the signal between a transmission fiber 114 and a monitor 113 that generates a signal IFF_ 2 (e.g., an electrical signal).
- IFF_ 2 indicates the power of the optical signal after it has been modulated by the modulator 110 .
- the modulator 110 can introduce a small signal loss.
- the coupler 112 transmits the signal to the transmission fiber 114 using any suitable coupling technique.
- the optical signal then travels toward its destination using the transmission fiber 114 .
- a silicon chip containing the optical components 104 - 112 can end after the coupler 112 and can transmit the optical signal to a customer transmission fiber 114 .
- a receiver fiber 120 carries an optical signal (e.g., the optical signal transmitted through the transmission fiber 114 ).
- the receiver fiber 120 could be the other side of an optical system in which a signal is transmitted from a source, using transmission fiber 114 , to a destination where it is received using receiver fiber 120 .
- the receiver fiber 120 provides the signal to a coupler 122 (e.g., using a prong coupler or any other suitable coupling technique).
- the coupler 122 divides the signal between a polarization splitter 124 and a monitor 123 that generates a signal IPMon (e.g., an electrical signal).
- the signal IPMon indicates the power of the optical signal received from the receiver fiber 120 .
- the polarization splitter 124 transmits the signal to a VOA 126 .
- the VOA 126 attenuates the different polarization components of the signal differently, after the signal has been split by the polarization splitter.
- the VOA 126 transmits the signal to a receiver 128 (e.g., a photodiode) where the optical power of the signal is detected and converted in an electrical signal.
- the VOA on the transmitter side e.g., the VOA 106 illustrated in FIG. 1
- the VOA on the receiver side e.g., the VOA 126 illustrated in FIG. 1
- the VOA 106 can be calibrated based on the relative power difference between the signals IFF_IN, IFF_ 1 , and IFF_ 2 , Comparing IFF_IN with IFF_ 1 captures the attenuation provided by the VOA 106 . Comparing IFF_ 1 with IFF_ 2 captures any signal loss provided by the modulator 110 .
- the VOA 106 can be tuned based on both comparisons, to provide desired attenuation of the input optical signal from the laser 102 while also taking into account signal loss from the modulator 110 .
- the VOA 126 can be tuned based on the relative power difference between the signal IPMon and the signal generated by the receiver 128 .
- the VOAs 106 and 126 can be tuned manually using an external test bench, as described in relation to FIG. 2 below.
- the VOAs 106 and 126 can be tuned automatically without using an external test bench, as described in relation to FIGS. 3-6 , below.
- FIG. 1 illustrates one example of an optical communication system. Any suitable optical communication system can be used.
- FIG. 2 illustrates a testing system 200 for an example optical communication system, according to an embodiment.
- transmission modules e.g., the modulator 110 and the VOA 106 illustrated in FIG. 1
- a laser in the optical communication system 100 is turned on (e.g., the laser 102 illustrated in FIG. 1 ).
- the laser bias is set to a constant value (e.g., IFF_IN illustrated in FIG. 1 ).
- a modulator e.g., the modulator 110 illustrated in FIG. 1
- the computer 202 and database 204 are used to set the bias values for the modulator.
- a transmission side VOA (e.g., the VOA 106 illustrated in FIG. 1 ) is swept across a suitable range of attenuation values (e.g., in increments of 0.5 dB granularity).
- the computer 202 and database 204 are used to set the values for the transmission side VOA.
- the various IFF signal values in the optical system, the laser bias used to match quadrature, and the power received at the power meter 214 are measured to generate a table of suitable values to tune the modulator and the transmission side VOA.
- the table of tuned values (e.g., for operating the modulator and the transmission side VOA) is stored in the database 204 for use in production systems and is stored in the optical system which will use them during operations.
- the transmission side VOA (and other components) can be tuned using any other suitable algorithm.
- receiver side modules can be tuned using an external laser 216 and a polarization scrambler 212 .
- the external laser 216 and the polarization scrambler 212 can be turned on.
- the receiver side components operate with an indeterminate polarization.
- the receiver side is compatible with on a variety of polarization values.
- the polarization scrambler 212 can scramble the polarization of the signal output by the external laser 216 , to allow tuning of the polarization paths in the VOA (e.g., across possible polarization values).
- the VOA 126 can be swept across a range of attenuation values (e.g., in 0.5 dB increments) along the polarization paths (e.g., using the computer 202 and the database 204 ).
- the insertion loss can be calibrated based on measuring IPMon and received signal strength (RSSI) (e.g., at receiver 128 illustrated in FIG. 1 ).
- RSSI received signal strength
- tuning values are stored in the database 204 for eventual use in production systems and is stored in the optical system which will use them during operations.
- the testing system 200 can be used to tune multiple modules in a serial fashion by switching between inputs and outputs for the different modules (e.g., using the router 206 ).
- the testing system 200 can be used to tune the various components of the optical system. It uses, however, numerous external components for tuning, including the power meter 214 , the external laser 216 , and the polarization scrambler 212 . Further, the external components are operated manually to tune the transmitter side modulator and VOA and receiver side VOA (e.g., an engineer operates the external components for fiber management). This can be inefficient, expensive, and time-consuming.
- FIGS. 3-6 illustrate an example automated solution for tuning the VOAs.
- FIG. 3 illustrates auto-tuning for an example optical communication system 300 , according to an embodiment.
- FIG. 3 enables normal transmission of an optical signal (e.g., from a laser 302 to a transmission fiber 316 ) and normal receipt of an optical signal (e.g., from a receiver fiber 340 ) in a manner similar to the optical communication system 100 illustrated in FIG. 1 .
- FIG. 3 also, however, enables auto-tuning of a modulator (e.g., a modulator 310 ), a transmission VOA (e.g., a VOA 306 ) and receiver VOAs (e.g., VOAs 352 A and 352 B).
- a modulator e.g., a modulator 310
- a transmission VOA e.g., a VOA 306
- receiver VOAs e.g., VOAs 352 A and 352 B.
- a pair of optical switches 312 and 330 are used to select the optical signal path of the optical signal and to switch between normal transmission, tuning of the transmission side components (e.g., Mode A), and tuning of the receiver side components (e.g., Mode B).
- a laser 302 emits an optical signal.
- any suitable laser for an optical communication system can be used (e.g., a distributed feedback laser (DFB)).
- a laser is merely one example of an optical source. Any suitable optical source could be used.
- a coupler 304 receives the optical signal and divides the signal between a VOA 306 and a monitor 305 (e.g., an electro-optical monitoring device, or any other suitable monitoring device) that generates a signal IFF_IN (e.g., an electrical signal).
- IFF_IN indicates the power of the optical signal transmitted by the laser 302 .
- the VOA attenuates the signal and transmits it to a coupler 308 .
- the coupler 308 divides the signal between a modulator 310 and a monitor 309 that generates a signal IFF_ 1 (e.g., an electrical signal).
- IFF_ 1 indicates the power of the optical signal after it has been attenuated by the VOA 306 .
- the modulator 310 modulates the optical signal to add data for transmission along a fiber.
- the modulator 310 is an MZDI based modulator that implements PAM4 modulation. These are merely examples, however, and any suitable modulator and modulation scheme can be used.
- the modulator 310 transmits the signal to an optical switch 312 .
- the optical switch 312 can be used to swap between an auto-tuning mode for the VOA 306 and normal transmission. Assuming the optical switch 312 is set for normal transmission, the modulator 310 transmits the optical signal to a coupler 314 .
- the coupler 314 divides the signal between a transmission fiber 316 and a monitor 315 that generates a signal IFF_ 2 (e.g., an electrical signal).
- IFF_ 2 indicates the power of the optical signal after it has been modulated by the modulator 310 .
- the coupler 314 can transmit the signal to the transmission fiber 316 using any suitable coupling technique. In an embodiment, the optical signal then travels to its destination using the transmission fiber 316 .
- the optical switch is instead set to enable auto-tuning mode (i.e., Mode A) for the transmission side components (e.g., the modulator 310 and the VOA 306 ).
- the modulator 310 transmits the optical signal to the optical switch 330 , via the optical switch 312 , instead of to the coupler 314 .
- the optical switch 330 is used to allow the receiver device 332 (e.g., a photo-diode) to be used both for tuning the transmission VOA (e.g., in Mode A) and the receiver VOAs (e.g., in Mode B).
- the modulator 310 transmits the optical signal to the receiver device 332 , bypassing the components to the left of the optical switch 330 .
- the receiver device 332 is used to tune the transmission VOA 306 and any signal loss introduced by the modulator 310 . Further, the modulator 310 can be tuned so that its bias point is set to the quadrature point, where the modulator characteristics are linear. In an embodiment, the receiver device 332 acts in place of the power meter 214 illustrated in FIG. 2 .
- the optical communication system 300 can further be used to tune the receiver side VOAs 352 A and 352 B. In an embodiment, this is done by switching from Mode A to Mode B.
- the optical switch 312 can be changed to transmit the signal from the modulator 310 to the coupler 314 and the transmission fiber 316 .
- a loopback cable 320 can be used to connect the transmission fiber 316 with a receiver fiber 340 , for tuning of the VOAs 352 A and 352 B. This allows the laser 302 to be used as a source for this tuning (e.g.; instead of requiring an external laser, like the external laser 216 illustrated in FIG. 2 ).
- the receiver fiber 340 provides the signal to a coupler 342 (e.g., using a prong coupler or any other suitable coupling technique).
- the coupler 342 divides the signal between a polarization splitter 344 and a monitor 343 that generates a signal IPMon (e.g., an electrical signal).
- the signal IPMon indicates the power of the optical signal received from the receiver fiber 340 .
- the optical signal received from the receiver fiber 340 has an unknown polarization.
- the optical signal can include a combination of transverse electric (TE) polarization and transverse magnetic (TM) polarization, but the orientation of these components (and of the signal as a whole) is unknown.
- the VOA 352 A can be used to attenuate signal components with one polarization (e.g., TE) while the VOA 352 B can be used to attenuate signal components with another polarization (e.g., TM), Because the combined received signal polarization is unknown, in one embodiment the VOAs 352 A-B are tuned across the possible polarizations.
- the coupler 342 transmits the optical signal to a polarization splitter 344 .
- the polarization splitter 344 divides the signal into polarization components (e.g., TE and TM).
- polarization components e.g., TE and TM.
- One polarization component is sent along the upper path (e.g., 346 A to 348 A to 350 A to 352 A) while the other polarization component is sent along the lower path (e.g., 346 B to 348 B to 350 B to 352 B).
- the optical switches 346 A and 346 B and 350 A and 350 B can be used to select which polarization component to tune, or to bypass the tuning completely.
- the polarization splitter 344 sends the TE polarization component to the optical switch 346 A.
- the optical switches 346 A and 350 A can either transmit the TE polarization component to a polarization rotator 348 A, for tuning the VOA 352 A, or can transmit the TE polarization component to the VOA 352 A and bypass the polarization rotator 348 A.
- the optical switches 346 B and 350 B can be used to either transmit the TM polarization component to a polarization rotator 348 B, for tuning the VOA 352 B, or can transmit the TM polarization component to the VOA 352 B and bypass the polarization rotator 348 B.
- the polarization rotators 348 A and 348 B are used to rotate the polarization components to mimic any possible polarization of the optical signal, to allow for tuning of the VOAs 352 A and 352 B.
- the optical switches 346 A and 350 A are engaged to transmit the TE polarization from the polarization splitter 344 to the polarization rotator 348 A.
- the polarization rotator 348 A can be swept across possible polarization orientations, to allow for accurate tuning across a large number of possible input polarizations.
- optical switches 346 B and 350 B are engaged to transmit the TM polarization from the polarization splitter 344 to the polarization rotator 348 B.
- the polarization rotator 348 B can be swept across possible polarization orientations.
- the polarization rotators 348 A and 348 B can be used in place of an external polarization scrambler (e.g., the polarization scrambler 212 illustrated in FIG. 2 ).
- the relative signal power value at the receiver device 332 can be compared with IPMon to tune the VOAs 352 A and 352 B.
- optical switches 346 A and 346 B, and 350 A and 350 B can be set to bypass the respective polarization rotators 348 A and 348 B, allowing for signal transmission without tuning.
- the optical communication system 300 illustrated in FIG. 3 is merely one example of a system for auto-tuning of transmission side components and a receiver side VOA.
- Other suitable configurations and components can be used for auto-tuning of the modulator VOAs.
- one or more of the techniques described herein for auto-tuning could be applied to a coherent optical system, or any other suitable optical communication system.
- FIG. 4 is a flowchart 400 illustrating auto-tuning for an example optical communication system, according to an embodiment.
- the blocks illustrated in FIG. 4 correspond with a process for auto-tuning an optical communication system (e.g., the optical communication system 300 illustrated in FIG. 3 ).
- the process enables a laser (e.g., the laser 302 illustrated in FIG. 3 ) to initiate transmission of an optical signal.
- the process enables a first tuning mode (e.g., Mode A illustrated in FIG. 3 ).
- a first tuning mode e.g., Mode A illustrated in FIG. 3
- an optical switch 312 can be set to transmit from a modulator 310 to a second optical switch 330 , instead of to a coupler 314 and transmission fiber 316 .
- an optical switch 330 can be set to transmit to a receiver device 332 (e.g., a photodiode).
- the process tunes the transmission side components (e.g., the VOA 306 and modulator 310 illustrated in FIG. 3 ).
- the process can tune an MZDI modulator so that its bias point is set to the quadrature point. This is discussed further with regard to FIG. 5 , below.
- the process enables a second tuning mode (e.g., Mode B illustrated in FIG. 3 ).
- the optical switch 312 can be set to transmit the optical signal from the modulator 310 to the coupler 314 and the transmission fiber 316 (e.g., for normal operation of the transmission side of the optical system).
- the optical switch 330 can be set to transmit the optical signal from the VOAs 352 A and 352 B to the receiver device 332 .
- a loopback cable 320 can be used to transmit an optical signal from the transmission fiber 316 to the receiver fiber 340 .
- the process tunes the receiver side VOAs (e.g., the VOAs 352 A and 352 B illustrated in FIG. 3 ). For example, the system compares the relative signal power value at IPMon and 332 to tune the VOAs 352 A and 352 B (e.g., to set a table of attenuation values for use by the VOAs 352 A and 352 B). This is discussed further with regard to FIG. 6 , below.
- the process stores the tuning configuration (e.g., for the modulator 310 and the VOAs 306 , 352 A, and 352 B).
- the process stores attenuation values corresponding to each of the VOAs in a table, for use during operation of the system.
- the table can be stored in non-volatile memory, or any other suitable non-volatile media, and can be stored locally in a controller, remotely, or any other suitable location for use in the optical communication system.
- FIG. 5 is a flowchart illustrating tuning transmission side components for an example optical communication system, according to an embodiment.
- FIG. 5 corresponds with block 406 illustrated in FIG. 4 .
- a first tuning mode e.g., Mode A illustrated in FIG. 3
- a process e.g., the one driving the optical communication system 300 illustrated in FIG. 3
- sets the laser bias e.g., for the laser 302 illustrated in FIG. 3
- constant value e.g., to set a constant IFF_ 1
- the process sweeps the modulator (e.g., the modulator 310 illustrated in FIG. 3 ) and sets the value to quadrature.
- the system reads the received signal strength indication (RSSI) (e.g., at the receiver device 332 illustrated in FIG. 3 ).
- RSSI received signal strength indication
- the process determines the laser bias settings to use in operation.
- the process sets the calibration for the transmission VOA (e.g., the VOA 306 illustrated in FIG. 3 ). For example, the process can compare the RSSI at the receiver device 332 with IFF_ 1 to set an attenuation table for the VOA 306 .
- the system stores the tuning values (e.g., the laser bias settings for the modulator 310 and the attenuation settings for the VOA 306 illustrated in FIG. 3 ).
- FIG. 6 is a flowchart illustrating tuning receiver side components for an example optical communication system, according to an embodiment.
- FIG. 6 corresponds with block 410 illustrated in FIG. 4 .
- a second tuning mode e.g., Mode B illustrated in FIG. 3
- the process enables the polarization rotators (e.g., the polarization rotators 348 A and 348 B illustrated in FIG. 3 .
- the process can enable two optical switches (e.g., the optical switches 346 A and 350 A illustrated in FIG. 3 ) to open a path from a polarization splitter (e.g., the polarization splitter 344 illustrated in FIG. 3 ) to a polarization rotator (e.g., the polarization rotator 348 A illustrated in FIG. 3 ).
- the process enables four optical switches (e.g., the optical switches 346 A, 350 A and 346 B, 350 B) to open paths to two polarization rotators (e.g., the polarization rotators 348 A and 348 B) simultaneously.
- the process enables two optical switches (e.g., the optical switch 346 A and 350 A) and one polarization rotator (e.g., the polarization rotator 348 A) at a time, then disables that two optical switches and enables two other optical switches (e.g., the optical switches 346 B and 350 B) and another polarization rotator (e.g., the polarization rotator 348 B).
- the process sweeps the VOAs (e.g., the VOAs 352 A and 352 B) across a suitable range of attenuation values.
- the process creates a table of attenuation values for the VOAs.
- the process sets the VOAs to a default setpoint.
- the process calibrates the receiver VOAs (e.g., the VOAs 352 A and 352 B). For example, the process can compare RSSI values indicated at an optical receiver device (e.g., the receiver device 332 illustrated in FIG. 3 ) with a received power level (e.g., IPMON illustrated in FIG. 3 ). This can be used to populate the table of attenuation values for the VOAs. The table of attenuation values can then be used during operation of the optical system.
- a received power level e.g., IPMON illustrated in FIG. 3
- FIG. 7 illustrates compression schemes for modulation in an optical communication system, according to an embodiment.
- the auto-tuning techniques described in relation to FIGS. 3-6 can also be used to set compression for modulation.
- auto-tuning can be used to set a modulator (e.g., the modulator 310 illustrated in FIG. 3 ) using PAM4 modulation to use a bottom compression scheme. This can significantly improve the return loss robustness of the optical communication system (e.g., lessening the multi-path interference (MPI)).
- MPI multi-path interference
- the diagram 700 depicts two compression schemes for PAM4 modulation.
- Illustration 710 shows a top-compression scheme, in which a top “eye” 712 of the modulation scheme is compressed as compared to the “uniform case” 720 eyes in the scheme.
- Illustration 720 shows a uniform scheme, in which the middle eye 722 is uniform as compared to the other eyes in the scheme.
- Illustration 730 shows a bottom compression scheme, in which a bottom eye 732 is compressed as compared to the other eyes in the scheme.
- a modulator e.g., the modulator 310 illustrated in FIG. 3
- optical loopback e.g., using the loopback cable 320 illustrated in FIG. 3
- a digital signal processor DSP
- the DSP can be provisioned to send a balanced pattern (e.g.; a pseudorandom binary sequence (PRBS)) from the transmitter to the receiver.
- the DSP can retrieve histograms of the four levels constituting the PAM4 eye.
- the modulator can be changed in fine steps to enable a bottom compression scheme. Further, the level separation mismatch ratio (R LM ) can be managed.
- R LM level separation mismatch ratio
- FIG. 8 illustrates power level ratios used for modulation in an optical communication system, according to an embodiment.
- an optical communication system can use PAM4 modulation.
- RUM can be used to indicate vertical linearity of PAM4 modulation signal.
- the table 800 illustrates example power level ratio values for an example 1.1, 1.34, 1.46, and 1.85 scheme. In an embodiment, these power level ratio values can provide improved performance.
- the auto-tuning techniques discussed in relation to FIGS. 3-6 , above, can be used to configure a production optical communication system to use the power level ratio values illustrated in the table 800 .
- embodiments disclosed herein may be embodied as a system, method or computer program product. Accordingly, embodiments may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.” Furthermore, embodiments may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon.
- Program code embodied on a computer readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, etc., or any suitable combination of the foregoing.
- These computer program instructions may also be stored in a computer readable medium that can direct a computer, other programmable data processing apparatus, or other device to function in a particular manner, such that the instructions stored in the computer readable medium produce an article of manufacture including instructions which implement the function/act specified in the block(s) of the flowchart illustrations and/or block diagrams.
- the computer program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable apparatus or other device to produce a computer implemented process such that the instructions which execute on the computer, other programmable data processing apparatus, or other device provide processes for implementing the functions/acts specified in the block(s) of the flowchart illustrations and/or block diagrams.
- each block in the flowchart illustrations or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s).
- the functions noted in the block may occur out of the order noted in the Figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved.
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Abstract
Techniques for tuning an optical communication system are disclosed. The system includes a first signal path for transmitting data, including an optical source, a first one or more variable optical attenuators (VOAs), a modulator, and a transmission fiber. The system further includes a second signal path for receiving data, including a receiver fiber and a second one more VOAs. The first one or more VOAs are tuned using the optical source in the first signal path for transmitting data, based on comparing a plurality of optical signal power values in the first path while a first tuning mode is enabled. The second one or more VOAs are tuned, using the optical source in the first signal path for transmitting data, based on comparing a plurality of optical signal power values in the second path while a second tuning mode is enabled.
Description
- Embodiments presented in this disclosure generally relate to electronic communications. More specifically, embodiments disclosed herein relate to fiber optic communications.
- Many modern fiber optic communication systems use silicon photonic (SIP) technology and pulse amplitude modulation (PAM). For example, 4-level PAM (PAM4) modulation can be used to transmit data across an optical system. Fiber optic communication systems can modulate optical signals using Mach-Zehnder Delay-Interferometer (MZDI) based modulators. Further, variable optical attenuators (VOAs) can be used on both the transmitter and receiver sides of the system to control output and input power, respectively, and improve performance. These VOAs are typically calibrated and tuned to improve performance and accuracy of the system. This can be done manually using a test bench, for example.
- So that the manner in which the above-recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate typical embodiments and are therefore not to be considered limiting; other equally effective embodiments are contemplated.
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FIG. 1 illustrates an optical signal path for an example optical communication system, according to an embodiment. -
FIG. 2 illustrates a testing system for an example optical communication system, according to an embodiment. -
FIG. 3 illustrates auto-tuning for an example optical communication system, according to an embodiment. -
FIG. 4 is a flowchart illustrating auto-tuning for an example optical communication system, according to an embodiment. -
FIG. 5 is a flowchart illustrating tuning transmission side components for an example optical communication system, according to an embodiment. -
FIG. 6 is a flowchart illustrating tuning receiver side components for an example optical communication system, according to an embodiment. -
FIG. 7 illustrates compression schemes for modulation in an optical communication system, according to an embodiment. -
FIG. 8 illustrates power level ratios for a level separation mismatch ratio used for modulation in an optical communication system, according to an embodiment. - To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially used in other embodiments without specific recitation.
- Embodiments include a method. The method includes enabling a first tuning mode for an optical communication system. The optical communication system includes a first signal path for transmitting data. The first signal path includes an optical source, a first one or more variable optical attenuators (VOAs), a modulator, and a transmission fiber. The optical communication system further includes a second signal path for receiving data. The second signal path includes a receiver fiber and a second one more VOAs. The method further includes tuning the first one or more VOAs, using the optical source in the first signal path for transmitting data, based on comparing a plurality of optical signal power values in the first path while the first tuning mode is enabled. The method further includes enabling a second tuning mode for the optical communication system. The method further includes tuning the second one or more VOAs, using the optical source in the first signal path for transmitting data, based on comparing a plurality of optical signal power values in the second path while the second tuning mode is enabled. The method further includes enabling a communication mode, in which the optical communication system is configured to use the first signal path for transmitting data and the second signal path for receiving data.
- Embodiments further include an optical communication system, including a first signal path for transmitting data. The first signal path includes an optical source, a first one or more VOAs, a modulator, and a transmission fiber. The optical communication system further includes a second signal path for receiving data. The second signal path includes a receiver fiber, and a second one more VOAs. The optical communication system is configured to enable a first tuning mode for tuning the first one or more VOAs, using the optical source in the first signal path for transmitting data, based on comparing a plurality of optical signal power values in the first path while the first tuning mode is enabled. The optical communication system is further configured to enable a second tuning mode for tuning the second one or more VOAs, using the optical source in the first signal path for transmitting data, based on comparing a plurality of optical signal power values in the second path while the second tuning mode is enabled. The optical communication system is further configured to enable a communication mode, in which the optical communication system is configured to use the first signal path for transmitting data and the second signal path for receiving data.
- Embodiments further include a method. The method includes transmitting data using a first signal path in an optical communication system. The first signal path includes an optical source, a first one or more VOAs, a modulator, and a transmission fiber. The method further includes receiving data using a second signal path in the optical communication system, the second signal path including a receiver fiber, and a second one more VOAs. The first one or more VOAs are configured to be tuned, using the optical source in the first signal path, based on comparing a plurality of optical signal power values in the first path while a first tuning mode is enabled. The second one or more VOAs are configured to be tuned, using the optical source in the first signal path, based on comparing a plurality of optical signal power values in the second path while a second tuning mode is enabled.
- As discussed above, many SiP based fiber optic communication systems use MZDI modulators with variable optical attenuators (VOAs) to transmit data (e.g., using 4-level pulse amplitude modulation (PAM4) modulation). To improve performance, several different characteristics can be tuned. For example, the MZDI modulator can be tuned so that its bias point is set to the quadrature point, where the modulator characteristics are linear. Further, the swing of the modulated signal can be optimized (e.g., based on the depth of the radio frequency (RF) modulation).
- The VOAs can also be tuned, both on the transmitter side and the receiver side. As discussed further below with regard to
FIG. 1 , the transmitter-side VOA can be used to control the modulator output power (e.g., allowing attenuation of the output power without setting the laser too low, which can cause mode-hop issues). The receiver-side VOA can be used to control the receiver input power, in order to avoid saturating later stages when too much input power is present. These VOAs can be separately tuned to provide appropriate relative attenuation on each side. - As discussed above, these VOAs can be tuned manually (e.g., during manufacturing) using a test bench. This is discussed further below with regard to
FIG. 2 . According to one or more embodiments disclosed herein, these VOAs can also be tuned without requiring external equipment. For example, as discussed below with regard toFIG. 3 , an optical system can be setup to provide automatic tuning for transmission side and receiver side components by, for example, toggling one or more optical switches between optical signal paths, and using components already in the system. This tuning can be done without external equipment (e.g., without requiring a test bench). Further, as will be discussed further below with regard toFIGS. 7 and 8 , setting a PAM4 modulation scheme to use bottom-compression can further improve system performance by improving the return loss robustness of the system. The tuning techniques described in connection withFIGS. 3-6 can be used to tune an optical communication system to use bottom-compression in modulation. -
FIG. 1 illustrates an optical signal path for an exampleoptical communication system 100, according to an embodiment. Alaser 102 emits an optical signal. In an embodiment, any suitable laser for an optical communication system can be used (e.g., a distributed feedback laser (DFB)). Further, in an embodiment, a laser is merely one example of an optical source. Any suitable optical source could be used. Acoupler 104 receives the optical signal and divides the signal between aVOA 106 and a monitor 105 (e.g., an electro-optical monitoring device, or any other suitable monitoring device) that generates a signal IFF_IN (e.g., an electrical signal). In an embodiment, IFF_IN indicates the power of the optical signal transmitted by thelaser 102. - The
VOA 106 attenuates the optical signal and transmits it to acoupler 108. In an embodiment, theVOA 106 is used to attenuate the signal to avoid setting the output of thelaser 102 below a desired level. For example, setting thelaser 102 such that it generates an optical signal whose power is below an output threshold can result in undesirable noise or mode hopping. Using theVOA 106 allows thelaser 102 to operate above a preferred range, while still controlling the transmission power of the optical signal as it propagates through the system. - The
coupler 108 divides the signal between a modulator 110 and amonitor 109 that generates a signal IFF_1 (e.g., an electrical signal). In an embodiment, IFF_1 indicates the power of the optical signal after it has been attenuated by theVOA 106. By comparing the signals IFF_IN and IFF_1, one can determine the level of attenuation from theVOA 106. - In an embodiment, the
modulator 110 modulates the optical signal to add data for transmission along a fiber. In an embodiment, themodulator 110 is an MZDI based modulator that implements PAM4 modulation. These are merely examples, however, and any suitable modulator and modulation scheme can be used. - The
modulator 110 transmits the signal to acoupler 112, which divides the signal between atransmission fiber 114 and amonitor 113 that generates a signal IFF_2 (e.g., an electrical signal). In an embodiment, IFF_2 indicates the power of the optical signal after it has been modulated by themodulator 110. In an embodiment, themodulator 110 can introduce a small signal loss. Thecoupler 112 transmits the signal to thetransmission fiber 114 using any suitable coupling technique. In an embodiment, the optical signal then travels toward its destination using thetransmission fiber 114. Further, in an embodiment, a silicon chip containing the optical components 104-112 can end after thecoupler 112 and can transmit the optical signal to acustomer transmission fiber 114. - A
receiver fiber 120 carries an optical signal (e.g., the optical signal transmitted through the transmission fiber 114). For example, thereceiver fiber 120 could be the other side of an optical system in which a signal is transmitted from a source, usingtransmission fiber 114, to a destination where it is received usingreceiver fiber 120. Thereceiver fiber 120 provides the signal to a coupler 122 (e.g., using a prong coupler or any other suitable coupling technique). Thecoupler 122 divides the signal between apolarization splitter 124 and amonitor 123 that generates a signal IPMon (e.g., an electrical signal). In an embodiment, the signal IPMon indicates the power of the optical signal received from thereceiver fiber 120. - The
polarization splitter 124 transmits the signal to aVOA 126. In an embodiment, theVOA 126 attenuates the different polarization components of the signal differently, after the signal has been split by the polarization splitter. TheVOA 126 transmits the signal to a receiver 128 (e.g., a photodiode) where the optical power of the signal is detected and converted in an electrical signal. - In an embodiment, the VOA on the transmitter side (e.g., the
VOA 106 illustrated inFIG. 1 ) and the VOA on the receiver side (e.g., theVOA 126 illustrated inFIG. 1 ) are each tuned. For example, theVOA 106 can be calibrated based on the relative power difference between the signals IFF_IN, IFF_1, and IFF_2, Comparing IFF_IN with IFF_1 captures the attenuation provided by theVOA 106. Comparing IFF_1 with IFF_2 captures any signal loss provided by themodulator 110. In an embodiment, theVOA 106 can be tuned based on both comparisons, to provide desired attenuation of the input optical signal from thelaser 102 while also taking into account signal loss from themodulator 110. - The
VOA 126 can be tuned based on the relative power difference between the signal IPMon and the signal generated by thereceiver 128. In an embodiment, theVOAs FIG. 2 below. Alternatively, or in addition, theVOAs FIGS. 3-6 , below.FIG. 1 illustrates one example of an optical communication system. Any suitable optical communication system can be used. -
FIG. 2 illustrates atesting system 200 for an example optical communication system, according to an embodiment. Starting with the transmission side, transmission modules (e.g., themodulator 110 and theVOA 106 illustrated inFIG. 1 ) can be tuned using thepower meter 214. A laser in theoptical communication system 100 is turned on (e.g., thelaser 102 illustrated inFIG. 1 ). The laser bias is set to a constant value (e.g., IFF_IN illustrated inFIG. 1 ). A modulator (e.g., themodulator 110 illustrated inFIG. 1 ) is swept for quadrature. In an embodiment, thecomputer 202 anddatabase 204 are used to set the bias values for the modulator. - A transmission side VOA (e.g., the
VOA 106 illustrated inFIG. 1 ) is swept across a suitable range of attenuation values (e.g., in increments of 0.5 dB granularity). In an embodiment, thecomputer 202 anddatabase 204 are used to set the values for the transmission side VOA. The various IFF signal values in the optical system, the laser bias used to match quadrature, and the power received at thepower meter 214 are measured to generate a table of suitable values to tune the modulator and the transmission side VOA. In an embodiment, the table of tuned values (e.g., for operating the modulator and the transmission side VOA) is stored in thedatabase 204 for use in production systems and is stored in the optical system which will use them during operations. Alternatively, or in addition, the transmission side VOA (and other components) can be tuned using any other suitable algorithm. - Similarly, receiver side modules (e.g., the
receiver VOA 126 illustrated inFIG. 1 ) can be tuned using anexternal laser 216 and apolarization scrambler 212. For example, theexternal laser 216 and thepolarization scrambler 212 can be turned on. In an embodiment, as discussed further below, the receiver side components operate with an indeterminate polarization. For example, the receiver side is compatible with on a variety of polarization values. Thepolarization scrambler 212 can scramble the polarization of the signal output by theexternal laser 216, to allow tuning of the polarization paths in the VOA (e.g., across possible polarization values). TheVOA 126 can be swept across a range of attenuation values (e.g., in 0.5 dB increments) along the polarization paths (e.g., using thecomputer 202 and the database 204). - The insertion loss can be calibrated based on measuring IPMon and received signal strength (RSSI) (e.g., at
receiver 128 illustrated inFIG. 1 ). In an embodiment, tuning values are stored in thedatabase 204 for eventual use in production systems and is stored in the optical system which will use them during operations. Further, in an embodiment, thetesting system 200 can be used to tune multiple modules in a serial fashion by switching between inputs and outputs for the different modules (e.g., using the router 206). - As illustrated, the
testing system 200 can be used to tune the various components of the optical system. It uses, however, numerous external components for tuning, including thepower meter 214, theexternal laser 216, and thepolarization scrambler 212. Further, the external components are operated manually to tune the transmitter side modulator and VOA and receiver side VOA (e.g., an engineer operates the external components for fiber management). This can be inefficient, expensive, and time-consuming. In an embodiment,FIGS. 3-6 illustrate an example automated solution for tuning the VOAs. -
FIG. 3 illustrates auto-tuning for an exampleoptical communication system 300, according to an embodiment. In an embodiment,FIG. 3 enables normal transmission of an optical signal (e.g., from alaser 302 to a transmission fiber 316) and normal receipt of an optical signal (e.g., from a receiver fiber 340) in a manner similar to theoptical communication system 100 illustrated inFIG. 1 .FIG. 3 also, however, enables auto-tuning of a modulator (e.g., a modulator 310), a transmission VOA (e.g., a VOA 306) and receiver VOAs (e.g.,VOAs optical switches - A
laser 302 emits an optical signal. In an embodiment, any suitable laser for an optical communication system can be used (e.g., a distributed feedback laser (DFB)). Further, in an embodiment, a laser is merely one example of an optical source. Any suitable optical source could be used. Acoupler 304 receives the optical signal and divides the signal between aVOA 306 and a monitor 305 (e.g., an electro-optical monitoring device, or any other suitable monitoring device) that generates a signal IFF_IN (e.g., an electrical signal). In an embodiment, IFF_IN indicates the power of the optical signal transmitted by thelaser 302. - The VOA attenuates the signal and transmits it to a
coupler 308. Thecoupler 308 divides the signal between a modulator 310 and amonitor 309 that generates a signal IFF_1 (e.g., an electrical signal). In an embodiment, IFF_1 indicates the power of the optical signal after it has been attenuated by theVOA 306. By comparing the signals IFF_IN and IFF_1, one can determine the level of attenuation from theVOA 306. - In an embodiment, the
modulator 310 modulates the optical signal to add data for transmission along a fiber. In an embodiment, themodulator 310 is an MZDI based modulator that implements PAM4 modulation. These are merely examples, however, and any suitable modulator and modulation scheme can be used. - The
modulator 310 transmits the signal to anoptical switch 312. In an embodiment, theoptical switch 312 can be used to swap between an auto-tuning mode for theVOA 306 and normal transmission. Assuming theoptical switch 312 is set for normal transmission, themodulator 310 transmits the optical signal to acoupler 314. Thecoupler 314 divides the signal between atransmission fiber 316 and amonitor 315 that generates a signal IFF_2 (e.g., an electrical signal). In an embodiment, IFF_2 indicates the power of the optical signal after it has been modulated by themodulator 310. Thecoupler 314 can transmit the signal to thetransmission fiber 316 using any suitable coupling technique. In an embodiment, the optical signal then travels to its destination using thetransmission fiber 316. - Returning to the
optical switch 312, assume the optical switch is instead set to enable auto-tuning mode (i.e., Mode A) for the transmission side components (e.g., themodulator 310 and the VOA 306). Themodulator 310 transmits the optical signal to theoptical switch 330, via theoptical switch 312, instead of to thecoupler 314. In an embodiment, theoptical switch 330 is used to allow the receiver device 332 (e.g., a photo-diode) to be used both for tuning the transmission VOA (e.g., in Mode A) and the receiver VOAs (e.g., in Mode B). Assuming theoptical switches modulator 310 transmits the optical signal to thereceiver device 332, bypassing the components to the left of theoptical switch 330. - The
receiver device 332 is used to tune thetransmission VOA 306 and any signal loss introduced by themodulator 310. Further, themodulator 310 can be tuned so that its bias point is set to the quadrature point, where the modulator characteristics are linear. In an embodiment, thereceiver device 332 acts in place of thepower meter 214 illustrated inFIG. 2 . - The
optical communication system 300 can further be used to tune thereceiver side VOAs optical switch 312 can be changed to transmit the signal from themodulator 310 to thecoupler 314 and thetransmission fiber 316. Aloopback cable 320 can be used to connect thetransmission fiber 316 with areceiver fiber 340, for tuning of theVOAs laser 302 to be used as a source for this tuning (e.g.; instead of requiring an external laser, like theexternal laser 216 illustrated inFIG. 2 ). - The
receiver fiber 340 provides the signal to a coupler 342 (e.g., using a prong coupler or any other suitable coupling technique). Thecoupler 342 divides the signal between apolarization splitter 344 and amonitor 343 that generates a signal IPMon (e.g., an electrical signal). In an embodiment, the signal IPMon indicates the power of the optical signal received from thereceiver fiber 340. - In an embodiment, the optical signal received from the
receiver fiber 340 has an unknown polarization. For example, the optical signal can include a combination of transverse electric (TE) polarization and transverse magnetic (TM) polarization, but the orientation of these components (and of the signal as a whole) is unknown. TheVOA 352A can be used to attenuate signal components with one polarization (e.g., TE) while theVOA 352B can be used to attenuate signal components with another polarization (e.g., TM), Because the combined received signal polarization is unknown, in one embodiment theVOAs 352A-B are tuned across the possible polarizations. - The
coupler 342 transmits the optical signal to apolarization splitter 344. Thepolarization splitter 344 divides the signal into polarization components (e.g., TE and TM). One polarization component is sent along the upper path (e.g., 346A to 348A to 350A to 352A) while the other polarization component is sent along the lower path (e.g., 346B to 348B to 350B to 352B). - In an embodiment, the
optical switches polarization splitter 344 sends the TE polarization component to theoptical switch 346A. Theoptical switches 346A and 350A can either transmit the TE polarization component to a polarization rotator 348A, for tuning theVOA 352A, or can transmit the TE polarization component to theVOA 352A and bypass the polarization rotator 348A. Similarly, assuming thepolarization splitter 344 transmits the TM polarization to theoptical switch 346B, theoptical switches polarization rotator 348B, for tuning theVOA 352B, or can transmit the TM polarization component to theVOA 352B and bypass thepolarization rotator 348B. - In an embodiment, the
polarization rotators 348A and 348B are used to rotate the polarization components to mimic any possible polarization of the optical signal, to allow for tuning of theVOAs optical switches 346A and 350A are engaged to transmit the TE polarization from thepolarization splitter 344 to the polarization rotator 348A. During tuning, the polarization rotator 348A can be swept across possible polarization orientations, to allow for accurate tuning across a large number of possible input polarizations. - Similarly, assume the
optical switches polarization splitter 344 to thepolarization rotator 348B. During tuning, thepolarization rotator 348B can be swept across possible polarization orientations. Thepolarization rotators 348A and 348B can be used in place of an external polarization scrambler (e.g., thepolarization scrambler 212 illustrated inFIG. 2 ). The relative signal power value at thereceiver device 332 can be compared with IPMon to tune theVOAs optical switches respective polarization rotators 348A and 348B, allowing for signal transmission without tuning. - The
optical communication system 300 illustrated inFIG. 3 is merely one example of a system for auto-tuning of transmission side components and a receiver side VOA. Other suitable configurations and components can be used for auto-tuning of the modulator VOAs. For example, one or more of the techniques described herein for auto-tuning could be applied to a coherent optical system, or any other suitable optical communication system. -
FIG. 4 is aflowchart 400 illustrating auto-tuning for an example optical communication system, according to an embodiment. In an embodiment, the blocks illustrated inFIG. 4 correspond with a process for auto-tuning an optical communication system (e.g., theoptical communication system 300 illustrated inFIG. 3 ). Atblock 402, the process enables a laser (e.g., thelaser 302 illustrated inFIG. 3 ) to initiate transmission of an optical signal. - At
block 404, the process enables a first tuning mode (e.g., Mode A illustrated inFIG. 3 ). For example, in the exampleoptical communication system 300 illustrated inFIG. 3 , anoptical switch 312 can be set to transmit from amodulator 310 to a secondoptical switch 330, instead of to acoupler 314 andtransmission fiber 316. Similarly, anoptical switch 330 can be set to transmit to a receiver device 332 (e.g., a photodiode). - At
block 406, the process tunes the transmission side components (e.g., theVOA 306 andmodulator 310 illustrated inFIG. 3 ). As an example, the process can tune an MZDI modulator so that its bias point is set to the quadrature point. This is discussed further with regard toFIG. 5 , below. - At
block 408, the process enables a second tuning mode (e.g., Mode B illustrated inFIG. 3 ). For example, theoptical switch 312 can be set to transmit the optical signal from themodulator 310 to thecoupler 314 and the transmission fiber 316 (e.g., for normal operation of the transmission side of the optical system). Similarly, theoptical switch 330 can be set to transmit the optical signal from theVOAs receiver device 332. Further, aloopback cable 320 can be used to transmit an optical signal from thetransmission fiber 316 to thereceiver fiber 340. - At
block 410, the process tunes the receiver side VOAs (e.g., theVOAs FIG. 3 ). For example, the system compares the relative signal power value at IPMon and 332 to tune theVOAs VOAs FIG. 6 , below. - At
block 412, the process stores the tuning configuration (e.g., for themodulator 310 and theVOAs -
FIG. 5 is a flowchart illustrating tuning transmission side components for an example optical communication system, according to an embodiment. In an embodiment,FIG. 5 corresponds withblock 406 illustrated inFIG. 4 . Further, as discussed above in relation to block 404, a first tuning mode (e.g., Mode A illustrated inFIG. 3 ) has been enabled. Atblock 502, a process (e.g., the one driving theoptical communication system 300 illustrated inFIG. 3 ) sets the laser bias (e.g., for thelaser 302 illustrated inFIG. 3 ) to constant value (e.g., to set a constant IFF_1). Atblock 504, the process sweeps the modulator (e.g., themodulator 310 illustrated inFIG. 3 ) and sets the value to quadrature. - At
block 506, the system reads the received signal strength indication (RSSI) (e.g., at thereceiver device 332 illustrated inFIG. 3 ). Atblock 508, the process determines the laser bias settings to use in operation. Atblock 510, the process sets the calibration for the transmission VOA (e.g., theVOA 306 illustrated inFIG. 3 ). For example, the process can compare the RSSI at thereceiver device 332 with IFF_1 to set an attenuation table for theVOA 306. In an embodiment, the system stores the tuning values (e.g., the laser bias settings for themodulator 310 and the attenuation settings for theVOA 306 illustrated inFIG. 3 ). -
FIG. 6 is a flowchart illustrating tuning receiver side components for an example optical communication system, according to an embodiment. In an embodiment,FIG. 6 corresponds withblock 410 illustrated inFIG. 4 . Further, as discussed above in relation to block 408, a second tuning mode (e.g., Mode B illustrated inFIG. 3 ) has been enabled. Atblock 602 the process enables the polarization rotators (e.g., thepolarization rotators 348A and 348B illustrated inFIG. 3 . For example, the process can enable two optical switches (e.g., theoptical switches 346A and 350A illustrated inFIG. 3 ) to open a path from a polarization splitter (e.g., thepolarization splitter 344 illustrated inFIG. 3 ) to a polarization rotator (e.g., the polarization rotator 348A illustrated inFIG. 3 ). - In an embodiment, the process enables four optical switches (e.g., the
optical switches polarization rotators 348A and 348B) simultaneously. Alternatively, or in addition, the process enables two optical switches (e.g., theoptical switch 346A and 350A) and one polarization rotator (e.g., the polarization rotator 348A) at a time, then disables that two optical switches and enables two other optical switches (e.g., theoptical switches polarization rotator 348B). - At
block 604 the process sweeps the VOAs (e.g., theVOAs block 606, the process creates a table of attenuation values for the VOAs. Atblock 608, the process sets the VOAs to a default setpoint. Atblock 610, the process calibrates the receiver VOAs (e.g., theVOAs receiver device 332 illustrated inFIG. 3 ) with a received power level (e.g., IPMON illustrated inFIG. 3 ). This can be used to populate the table of attenuation values for the VOAs. The table of attenuation values can then be used during operation of the optical system. -
FIG. 7 illustrates compression schemes for modulation in an optical communication system, according to an embodiment. In an embodiment, the auto-tuning techniques described in relation toFIGS. 3-6 can also be used to set compression for modulation. For example, auto-tuning can be used to set a modulator (e.g., themodulator 310 illustrated inFIG. 3 ) using PAM4 modulation to use a bottom compression scheme. This can significantly improve the return loss robustness of the optical communication system (e.g., lessening the multi-path interference (MPI)). - The diagram 700 depicts two compression schemes for PAM4 modulation.
Illustration 710 shows a top-compression scheme, in which a top “eye” 712 of the modulation scheme is compressed as compared to the “uniform case” 720 eyes in the scheme.Illustration 720 shows a uniform scheme, in which themiddle eye 722 is uniform as compared to the other eyes in the scheme.Illustration 730 shows a bottom compression scheme, in which abottom eye 732 is compressed as compared to the other eyes in the scheme. - Typically, many optical systems use a uniform or middle compression scheme (e.g., as shown in illustration 720). Using a bottom compression scheme, however, as shown in
illustration 730, can be beneficial. One or more of the auto-tuning techniques described in relation toFIGS. 3-6 can be used to enable and tune such a bottom compression scheme for PAM4 modulation. - For example, a modulator (e.g., the
modulator 310 illustrated inFIG. 3 ) can be set to quadrature, and optical loopback (e.g., using theloopback cable 320 illustrated inFIG. 3 ) can be used to connect a transmission fiber (e.g., thetransmission fiber 316 illustrated inFIG. 3 ) with a receiver fiber (e.g., thereceiver fiber 340 illustrated inFIG. 3 ). A digital signal processor (DSP) can be provisioned to send a balanced pattern (e.g.; a pseudorandom binary sequence (PRBS)) from the transmitter to the receiver. The DSP can retrieve histograms of the four levels constituting the PAM4 eye. The modulator can be changed in fine steps to enable a bottom compression scheme. Further, the level separation mismatch ratio (RLM) can be managed. -
FIG. 8 illustrates power level ratios used for modulation in an optical communication system, according to an embodiment. In an embodiment, an optical communication system can use PAM4 modulation. RUM can be used to indicate vertical linearity of PAM4 modulation signal. The table 800 illustrates example power level ratio values for an example 1.1, 1.34, 1.46, and 1.85 scheme. In an embodiment, these power level ratio values can provide improved performance. The auto-tuning techniques discussed in relation toFIGS. 3-6 , above, can be used to configure a production optical communication system to use the power level ratio values illustrated in the table 800. - In the current disclosure, reference is made to various embodiments. However, the scope of the present disclosure is not limited to specific described embodiments. Instead, any combination of the described features and elements, whether related to different embodiments or not, is contemplated to implement and practice contemplated embodiments. Additionally, when elements of the embodiments are described in the form of “at least one of A and B,” it will be understood that embodiments including element A exclusively, including element B exclusively, and including element A and B are each contemplated. Furthermore, although some embodiments disclosed herein may achieve advantages over other possible solutions or over the prior art, whether or not a particular advantage is achieved by a given embodiment is not limiting of the scope of the present disclosure. Thus, the aspects, features, embodiments and advantages disclosed herein are merely illustrative and are not considered elements or limitations of the appended claims except where explicitly recited in a claim(s). Likewise, reference to “the invention” shall not be construed as a generalization of any inventive subject matter disclosed herein and shall not be considered to be an element or limitation of the appended claims except where explicitly recited in a claim(s).
- As will be appreciated by one skilled in the art, the embodiments disclosed herein may be embodied as a system, method or computer program product. Accordingly, embodiments may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.” Furthermore, embodiments may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon.
- Program code embodied on a computer readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, etc., or any suitable combination of the foregoing.
- Aspects of the present disclosure are described herein with reference to flowchart illustrations and/or block diagrams of methods, apparatuses (systems), and computer program products according to embodiments presented in this disclosure. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the block(s) of the flowchart illustrations and/or block diagrams.
- These computer program instructions may also be stored in a computer readable medium that can direct a computer, other programmable data processing apparatus, or other device to function in a particular manner, such that the instructions stored in the computer readable medium produce an article of manufacture including instructions which implement the function/act specified in the block(s) of the flowchart illustrations and/or block diagrams.
- The computer program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable apparatus or other device to produce a computer implemented process such that the instructions which execute on the computer, other programmable data processing apparatus, or other device provide processes for implementing the functions/acts specified in the block(s) of the flowchart illustrations and/or block diagrams.
- The flowchart illustrations and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments. In this regard, each block in the flowchart illustrations or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the Figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustrations, and combinations of blocks in the block diagrams and/or flowchart illustrations, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.
- In view of the foregoing, the scope of the present disclosure is determined by the claims that follow.
Claims (20)
1. A method, comprising:
enabling a first tuning mode for an optical communication system, the optical communication system comprising:
a first signal path for transmitting data, comprising:
an optical source;
a first one or more variable optical attenuators (VOAs):
a modulator; and
a transmission fiber; and
a second signal path for receiving data comprising:
a receiver fiber; and
a second one more VOAs;
tuning the first one or more VOAs, using the optical source in the first signal path for transmitting data, based on comparing a plurality of optical signal power values in the first path while the first tuning mode is enabled;
enabling a second tuning mode for the optical communication system;
tuning the second one or more VOAs, using the optical source in the first signal path for transmitting data, based on comparing a plurality of optical signal power values in the second path while the second tuning mode is enabled; and
enabling a communication mode wherein the optical communication system is configured to use the first signal path for transmitting data and the second signal path for receiving data.
2. The method of claim 1 , wherein enabling the first tuning mode comprises changing a first one or more optical switches in the optical communication system.
3. The method of claim 2 , wherein enabling the second tuning mode comprises changing a second one or more optical switches in the optical communication system.
4. The method of claim 1 , wherein the second signal path comprises a polarization splitter, and wherein enabling the second tuning mode comprises enabling a third signal path comprising a plurality of polarization rotators.
5. The method of claim 4 , wherein tuning the second one or more VOAs comprises using at least one polarization rotator, of the plurality of polarization rotators, to rotate a polarization component of an optical signal received from the receiver fiber.
6. The method of claim 4 , wherein the polarization splitter is configured to divide an optical signal received from the receiver fiber into a transverse electric (TE) polarization and a transverse magnetic (TM) polarization, and wherein a first polarization rotator of the plurality of polarization rotators is configured to rotate the TE polarization and a second polarization rotator of the plurality of polarization rotators is configured to rotate the TM polarization.
7. The method of claim 1 , further comprising tuning the modulator while the first tuning mode is enabled.
8. The method of claim 1 , wherein tuning the first one or more VOAs comprises comparing a first optical signal power value indicated in the first signal path before the one or more VOAs with a second optical signal power value indicated in the first signal path after the one or more VOAs.
9. The method of claim 1 , wherein the modulator comprises a pulse amplitude modulation (PAM) modulator, the method further comprising setting the modulator to use bottom compression.
10. The method of claim 9 , further comprising tuning the modulator to use bottom compression while the first tuning mode is enabled.
11. The method of claim 1 , wherein tuning the first one or more VOAs and tuning the second one or more VOAs each comprises storing a respective plurality of tuning values in a table in a non-volatile media.
12. An optical communication system, comprising:
a first signal path for transmitting data, comprising:
an optical source;
a first one or more variable optical attenuators (VOAs);
a modulator; and
a transmission fiber; and
a second signal path for receiving data comprising:
a receiver fiber; and
a second one more VOAs;
wherein the optical communication system is configured to:
enable a first tuning mode for tuning the first one or more VOAs, using the optical source in the first signal path for transmitting data, based on comparing a plurality of optical signal power values in the first path while the first tuning mode is enabled;
enable a second tuning mode for tuning the second one or more VOAs, using the optical source in the first signal path for transmitting data, based on comparing a plurality of optical signal power values in the second path while the second tuning mode is enabled; and
enable a communication mode wherein the optical communication system is configured to use the first signal path for transmitting data and the second signal path for receiving data.
13. The optical communication system of claim 12 , wherein the first tuning mode is configured to be enabled by changing a first one or more optical switches in the optical communication system, and wherein the second tuning mode is configured to be enabled by changing a second one or more optical switches in the optical communication system.
14. The optical communication system of claim 12 , wherein the second signal path comprises a polarization splitter, wherein enabling the second tuning mode comprises enabling a third signal path comprising a plurality of polarization rotators, and wherein the second one or more VOAs are configured to be tuned using at least one polarization rotator, of the plurality of polarization rotators, to rotate a polarization component of an optical signal received from the receiver fiber.
15. The optical communication system of claim 14 , wherein the polarization splitter is configured to divide an optical signal received from the receiver fiber into a transverse electric (TE) polarization and a transverse magnetic (TM) polarization, and wherein a first polarization rotator of the plurality of polarization rotators is configured to rotate the TE polarization and a second polarization rotator of the plurality of polarization rotators is configured to rotate the TM polarization.
16. The optical communication system of claim 12 , wherein the optical communication system is further configured to tune the modulator while the first tuning mode is enabled.
17. The optical communication system of claim 12 , wherein the modulator comprises a pulse amplitude modulation (PAM) modulator, and wherein the modulator is configured to use bottom compression.
18. A method, comprising:
transmitting data using a first signal path in an optical communication system, the first signal path comprising:
an optical source;
a first one or more variable optical attenuators (VOAs);
a modulator; and
a transmission fiber;
receiving data using a second signal path in the optical communication system, the second signal path comprising:
a receiver fiber; and
a second one more VOAs;
wherein the first one or more VOAs are configured to be tuned, using the optical source in the first signal path, based on comparing a plurality of optical signal power values in the first path while a first tuning mode is enabled, and
wherein the second one or more VOAs are configured to be tuned, using the optical source in the first signal path, based on comparing a plurality of optical signal power values in the second path while a second tuning mode is enabled.
19. The method of claim 18 , wherein the optical communication is configured to enable the first tuning mode by changing a first one or more optical switches, and wherein the optical communication is configured to enable the second tuning mode by changing a second one or more optical switches.
20. The method of claim 18 , wherein the second signal path comprises a polarization splitter, wherein enabling the second tuning mode comprises enabling a third signal path comprising a plurality of polarization rotators, and wherein the second one or more VOAs are configured to be tuned using at least one polarization rotator, of the plurality of polarization rotators, to rotate a polarization component of an optical signal received from the receiver fiber.
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US5923450A (en) * | 1998-09-30 | 1999-07-13 | Alcatel Network Systems, Inc. | Optical channel regulator and method |
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US7162113B2 (en) * | 2002-10-08 | 2007-01-09 | Infinera Corporation | Deployment of electro-optic amplitude varying elements (AVEs) and electro-optic multi-functional elements (MFEs) in photonic integrated circuits (PICs) |
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WO2007003208A1 (en) | 2005-06-30 | 2007-01-11 | Pirelli & C. S.P.A. | Method and system for hitless tunable optical processing |
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