Optical Transceiver with Built-in Dispersion Compensation for High Bit-Rate Applications

Abstract

The optical configuration for providing chromatic dispersion compensation in high data rate communication systems is based on using optical dispersion compensation in the receive signal path before O / E conversion. The function of chromatic dispersion compensation in the optical domain thus provides a "corrected" optical signal as input to the photodetector device. By incorporating optically based chromatic dispersion compensation, higher data rates can be used without introducing unacceptable bit error rates. Also, the reach of data communication networks can be increased by using optically based dispersion compensation.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Application No. 63 / 317,606, filed March 8, 2022, which is incorporated herein by reference.

[0002] This specification discloses an arrangement for providing chromatic dispersion compensation at an optical receiver in a high speed data network, and more particularly, an optically based compensation that mitigates the effects of dispersion before performing optical / electrical conversion of the received signal. [Background technology]

[0003] Chromatic dispersion in optical communication systems can be thought of as the broadening of pulses that occurs as a transmitted signal propagates along an optical fiber signal path. Until now, chromatic dispersion has not been a problem in data communication systems because the link lengths between optical transmitters and receivers are relatively short (typically less than 2 km) and the supported data rates are relatively low (e.g., less than 100 Gb / s). However, as optical transceiver capacity requirements move into the terabit / second range, data path line rates are increasing to, for example, 400 G / s, and chromatic dispersion is now within reach for such short reach applications, with pulses traveling only a few kilometers apart.

[0004] One approach to compensating for chromatic dispersion in data communication systems is to utilize coherent transmission techniques, which compensate for the effects of dispersion on the transmitted pulses, but require complex and expensive electronics, optics, and local oscillators at the receiver to properly recover the transmitted data. Summary of the Invention

[0005] This specification discloses an arrangement for providing chromatic dispersion compensation to optical receivers operating in high data rate networks, and more particularly, an optically-based compensation arrangement that corrects distortions in the optical domain before the input optical signal is coupled to the receiver's photodetector device.

[0006] In particular, it has been proposed to utilize chromatic dispersion components in the form of GT etalons, ring resonators, VIPs, or other types of optical components that can introduce a phase shift that compensates for the pulse broadening that occurs in a transmitted high data rate optical signal.

[0007] In accordance with the principles of the present disclosure, increased transmission capacity (or increased optical path length "reach") can be obtained by utilizing optically-based chromatic dispersion compensation without requiring any other changes to the transceiver architecture itself. For example, a transceiver configured to support eight separate channels (lanes) of optical signal path each operating at 100 Gb / s (hence 800G capacity) can double its data rate to operate at 200 Gb / s simply by incorporating chromatic dispersion compensation within the receiver.

[0008] Advantageously, the types of optical elements that can be used to perform chromatic dispersion compensation can be integrated with the photodetector itself in a photonic integrated circuit, thus providing a relatively compact receiver structure.

[0009] An exemplary embodiment of the present invention may take the form of an optical receiver for use in a high data rate optical communications network comprising an optically-based chromatic dispersion compensation element configured to be responsive to an input optical data signal and to introduce an optical phase delay sufficient to compensate for chromatic dispersion associated with the fiber link, a photodetector for converting the compensated optical data signal into an electrical equivalent signal, and electronic receiver circuitry coupled to an output of the photodetector for recovering electrical clock and data signals from the compensated optical data signal input.

[0010] Other and further examples and embodiments representative of the present disclosure will become apparent during the course of the following description and by reference to the accompanying drawings. [Brief description of the drawings]

[0011] With reference to the drawings: [Figure 1] FIG. 1 is a simplified block diagram of a typical prior art optical transceiver used to support data communications in short-haul optical data networks. [Diagram 2] FIG. 2 illustrates an example optical transceiver configured in accordance with the present disclosure to provide optical-based dispersion compensation at an optical receiver input. [Diagram 3] FIG. 3 shows an embodiment of a receiver based on the integration of a photodiode array and a chromatic dispersion compensation element. [Figure 4] FIG. 4 illustrates another disclosed embodiment, in this example, where multiple tunable chromatic dispersion elements are integrated with a photodiode array. [Diagram 5] FIG. 5 illustrates another type of optical transceiver that utilizes optical-based chromatic dispersion compensation on a received data signal in accordance with the disclosed teachings. [Figure 6] FIG. 6 illustrates yet another embodiment of an optical transceiver formed in accordance with the present disclosure, this time utilizing the multi-wavelength capabilities of FIG. 5 in combination with the M-dimensional architecture. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The continued evolution of services that rely on the ability to transmit large amounts of data (currently reaching terabit levels) presents challenges that are different from networks designed to transmit voice and data communications over long distances. In particular, new services such as data centers, Internet of Things (IoT), industrial IoT, and cloud computing utilize only short links of optical fiber from one transceiver to the next (typically no more than a few kilometers). To provide the desired amount of data transmission from one transceiver to the next, data networks interconnect the transceivers using parallel communication paths, typically 4, 8 or 16 paths (also called "lanes").

[0013] Currently, the data rates used in these data networks need to be higher than the current 100 Gb / s (per lane), which introduces chromatic dispersion into the signal path. Although these links are relatively short (compared to telecommunication span lengths), the ever-increasing data rates are sufficient to cause pulse broadening and dispersion between the transmitter and receiver. Prior art solutions use coherent transmission systems (which effectively cancel the dispersion), but at the expense of reduced bandwidth and more complex electronics in the receiver.

[0014] Instead, an alternative approach to compensating for chromatic dispersion in optical data communication systems is proposed, as described in more detail below. In particular, it is proposed to incorporate an all-optical chromatic dispersion compensation device at the input of an optical receiver to perform dispersion compensation in the optical domain and provide a "corrected" optical signal as input to an optical detection device. By incorporating optical-based chromatic dispersion compensation, higher data rates can be used without incurring unacceptable bit error rates. Also, the use of optical-based dispersion compensation can increase the reach of data communication networks.

[0015] FIG. 1 is a simplified block diagram of a typical prior art optical transceiver 1 used to support data communications in short reach optical data networks (e.g., data center environments). In an exemplary data center application, the distance (reach) between one transceiver and another may be on the order of about 500 meters. Describing FIG. 1 from left to right, the electrical connections to the optical transceiver 1 include a first group of electrical signal paths 2E (designated as the "egress" signal paths) and a second group of electrical signal paths 2I (designated as the "ingress" electrical output signal paths). These electrical signal paths interface with the transceiver's telecommunications module 3, which functions in a manner known in the art to perform the necessary encoding / decoding of signals passing through it. In most architectures, the number of individual signal paths (also called "lanes") is typically four or eight, but can be as high as sixteen.

[0016] A transmit encoder 3.1 receives the parallel data signal paths 2E and imparts a predetermined modulation format to these signals (e.g., NRZ, PAM4, PAM8, etc.). A set of parallel output signals from the transmitter module 3.1 are shown, each used to operate a separate driver circuit 4. The driver circuits 4 are used to excite associated laser devices 5 to generate a number of data modulated optical output signals. The optical signals are coupled to optical fibers 6 that are used as parallel data paths to other transceivers in a data center (or other short reach) environment.

[0017] In the reverse direction, a second set of fibers 7 is coupled to the transceiver 1, the fibers in this case being used to introduce an optical data signal from another transceiver into the transceiver 1. A photodiode array 8 is used to convert the modulated optical signal into an electrical current. An associated transimpedance amplifier 9 is used to convert the current signal into an amplified voltage. As shown in prior art FIG. 1, the amplified voltage outputs are provided as parallel inputs to the receive decoder 3.2 of the telecommunications module 3. As previously mentioned, in this direction the module 3 is used to recover the clock and data signals from the provided inputs and pass them along the appropriate input signal paths 2I.

[0018] To provide higher bandwidth (i.e., higher capacity) over this fixed number of signal paths (lanes), solutions typically use higher data rates and more complex modulation formats. As data rates continue to increase, the received optical signal may accumulate enough chromatic dispersion to widen the pulse width and ultimately introduce errors into the clock and data recovery process performed by the module 3. In fact, even in relatively short-reach environments such as data centers, as transmission capacity increases into the terabit range, the received optical signal will have a sufficient amount of dispersion that some correction will be required to accurately recover the transmitted data. Therefore, to ensure accurate recovery of the transmitted data, it has been proposed to incorporate optically-based chromatic dispersion compensation into the received optical signal before O / E conversion.

[0019] FIG. 2 illustrates an exemplary optical transceiver 10 configured in accordance with the present disclosure to provide optical-based dispersion compensation at an optical receiver input. As illustrated, most of the components that make up the transceiver 10 are similar to those described above with respect to the prior art transceiver 1. However, here, the optical-based dispersion compensation is performed at the input to the receiver, illustrated as a number of optical dispersion compensation elements 20 disposed at the input to the array of photodiode devices 8. In this particular embodiment, the optical dispersion compensation elements 20 are associated with the photodiode devices 8 in a one-to-one relationship, and are illustrated here (for purposes of clarity) with only optical dispersion compensation element 20-1 disposed at the input to photodiode 8-1 and optical dispersion compensation element 20-N (where N is typically 4, 8, or 16) disposed at the input to photodiode 8-N. The optical-based chromatic dispersion compensation elements 20 can be configured in a number of different configurations, including, but not limited to, a Gire-Tournois (GT) etalon (either air gap or solid form), a ring resonator, or similar types of optically based delay elements. The GT etalons and ring resonators may consist of single elements or may be formed by cascading similar units. For example, each GT etalon in the dispersion compensation element 20 has an individual group delay response (as do the individual rings in the resonator configuration). Using multiple individual delay devices in cascade, these individual group delays are summed into an "aggregate" group delay, designed to provide an inverse filtering effect on the received signal, essentially canceling the accumulated chromatic dispersion. Advantageously, these all-optical type chromatic dispersion compensation elements can be integrated with the photodetector array in a photonic integrated circuit to maintain a relatively compact configuration of the receiver.

[0020] By incorporating chromatic dispersion compensation at the input to the photodiode, receive errors due to the link's chromatic dispersion are mitigated before recovering the transmitted data, thereby increasing the "reach" of the link and / or increasing the supported data rates. Optical chromatic dispersion compensation elements are relatively low cost (as opposed to the receive electronics required for coherence-based systems) and can be dependent on the transceiver's modulation technique.

[0021] FIG. 3 illustrates an embodiment of a receiver based on the integration of a photodiode array 8 with a chromatic dispersion compensation element. In this particular embodiment, a number of individual chromatic dispersion compensation elements 32 are integrated in a common photonic integrated circuit 30 with the photodiode array 8. Also shown in this integrated configuration are a number of input fibers 7 coupled to a number of similar optical waveguides 34 formed in the photonic integrated circuit 30. The "distorted" input optical signals propagating along the waveguides 34 are first passed through the associated chromatic dispersion elements 32. The chromatic dispersion elements 32 serve to mitigate the effects of chromatic dispersion (which can, for example, cause intersymbol interference) and provide these "corrected" optical signals as input to the photodiodes 8. By applying optical compensation to the received optical signal, the converted electrical signal is then provided as input to a transimpedance amplifier 9, which is largely distortion-free, and proceeds to a clock and data recovery (CDR) circuit 3.3 of the receiver 3.2, which decodes the electrical signal to recover the transmitted data. As the input optical signal has been corrected to compensate for chromatic dispersion, the decoding is performed with a bit error rate (BER) within industry standards.

[0022] As mentioned above, the level of distortion introduced to a propagating optical signal varies not only with the fiber path length (i.e., "reach") over which the signal propagates, but also with the line rate used to initially encode the data signal. Thus, the amount of dispersion compensation that needs to be performed by the all-optical chromatic dispersion element of the present disclosure may vary as the line rate (and / or modulation format) changes. FIG. 4 illustrates another disclosed embodiment in which multiple tunable chromatic dispersion elements 42 are integrated with photodiodes 8 in a photonic integrated circuit 40. An external control signal (which may be sent, for example, from a network management component) may be used to adjust / tune the operation of the dispersion compensation element 42 based on the known type of signal format being used in a particular application. This tuning may be performed, for example, by changing the ambient temperature of the dispersion compensator (thermal tuning) or by controlling the number of cascaded stages used to provide the desired phase adjustment to the received optical signal.

[0023] Incorporating multiple (N) chromatic dispersion elements 20-1 through 20-N, as in the architecture of transceiver 10 of FIG. 2, can extend the "reach" of a conventional transceiver or increase the line rate, the latter being important for increasing transmission capacity in short reach applications. For example, a conventional transceiver may include 16 egress electrical lanes 2E that form a plurality of eight separate lanes of modulated signals applied to eight separate lasers. In the prior art, a modulation (data) rate of 100 Gb / s is typically used to generate 800 Gb / s capacity. By incorporating optically based dispersion compensation in accordance with the teachings of this disclosure, the data rate doubles to 200 Gb / s, thereby increasing the transmission capacity to 1600 Gb / s. In fact, incorporating optically based dispersion compensation can provide distortion correction for received data signals operating at 400 Gb / s. Using this data range in the "8-lane" configuration of FIG. 2, a transmission capacity of 3200 Gb / s is possible.

[0024] FIG. 5 illustrates another type of optical transceiver that utilizes optically based chromatic dispersion compensation on received data signals in accordance with the disclosed teachings. In this model, a high data rate optical transceiver 50 is configured to support data transmission at multiple (N) distinct wavelengths, λ1 through λN. The transceiver 50 includes multiple (N) laser sources 52, each configured to operate at one of the selected wavelengths, λ1 through λN. Multiple (N) separate signal paths, each supporting the propagation of a data signal at a different wavelength, are shown applied as separate inputs to an optical wavelength division multiplexer (MUX) 54. In a conventional process well known in the art, the MUX 54 combines these individual signals into a single output fiber 56 exiting the transceiver 50.

[0025] Turning to the receiver configuration of this multi-wavelength embodiment, as shown in FIG. 5, all N received data signals propagate along a single input fiber 58. In accordance with the principles of the present disclosure, an optical chromatic dispersion compensator 60 is shown coupled to the input fiber 58 and used to provide compensation for dispersion experienced by the data transmitted at each of the different wavelengths. The single multi-wavelength output from the chromatic dispersion compensator 60 is then provided as an input to a wavelength division demultiplexer (DEMUX) and used to direct each of the optical data signals at different wavelengths λ1 through λN to associated photodiodes 8-1 through 8-N. The ability to provide increased reach and signal capacity in this multi-wavelength transceiver 50 is similar to that described above with respect to the transceiver 10 of FIG. 2.

[0026] FIG. 6 illustrates yet another embodiment of an optical transceiver constructed in accordance with the present disclosure, utilizing the multi-wavelength functionality described above with respect to transceiver 50 of FIG. 5 in combination with an M-dimensional architecture. That is, the components illustrated in transceiver 60-1 are replicated in additional transceiver modules to provide increased transmission capacity. In the example of FIG. 6, multiple (M) transceiver units 60-i through 60-M are included. In one embodiment, each transceiver 60-i may utilize a set of four lasers 62 operating at different defined wavelengths selected from the group of λ1, λ2, λ3, and λ4. As with multi-wavelength transceiver 50, each transceiver 60-i includes a MUX 64 that couples each of the four signals to a common output fiber link 66.

[0027] The M-dimensional multi-wavelength transceiver 60 also receives a plurality (M) of multi-wavelength optical input signals that are received on a plurality (M) of different input fibers 68 (e.g., fiber 68-1 of transceiver element 60-1 shown in FIG. 6 ). Similar to the configuration of FIG. 5 , the input multi-wavelength signals are first passed through an associated optically-based chromatic dispersion compensator 70-i. The “corrected” (compensated) multi-wavelength output from compensator 70-i is then provided as an input to DEMUX 72-i, which separates the signals into four individual wavelengths and directs them to the appropriate photodiodes.

[0028] In summary, disclosed are embodiments of optical transceivers (or optical receivers) suitable for use in data communications, with integrated optical chromatic dispersion compensation along the received signal input. Given the need for continued increases in data rates in optical data communications networks (even as link lengths remain short), it is believed that an optically based chromatic dispersion device used to correct the incoming distorted optical signal before it reaches the conversion photodetector can enable higher data rates and, if necessary, extend the reach of a given data link. In such data communications applications, line rates in excess of, for example, 100 Gb / s ("100G") are envisioned, and indeed various standards are currently being developed aiming for line rates of 400G. The integrated all-optical chromatic dispersion compensation of the present disclosure is believed to be a key element of optical receivers used in these applications.

[0029] While the present disclosure has been shown and described herein with reference to preferred embodiments and specific examples thereof, it will be readily apparent to those skilled in the art that other embodiments and examples may perform similar functions and / or achieve similar results, and all such equivalent embodiments and examples are deemed to be fully encompassed by the scope of the appended claims.

Claims

1. 1. An optical receiver for use in a high data rate optical communications network, comprising: an optically-based chromatic dispersion compensating element responsive to an input optical data signal and configured to introduce an optical phase delay sufficient to compensate for chromatic dispersion associated with the fiber link; a photodetector for converting the corrected optical data signal into an equivalent electrical signal; an electronic receiver circuit coupled to the output of said photodetector for recovering electrical clock and data signals from a corrected optical data signal input; An optical receiver comprising:

2. The optical receiver of claim 1 , wherein the optically-based chromatic dispersion compensation element comprises at least one GT etalon.

3. 3. The optical receiver of claim 2, wherein the at least one GT etalon comprises a plurality of separate GT etalon elements cascaded together, each element introducing a group delay value into the phase delay, the cascaded elements providing an aggregate group delay.

4. The optical receiver of claim 1 , wherein the optically-based chromatic dispersion compensation element comprises one or more optical ring resonators that include a delay component within the ring.

5. 5. The optical receiver of claim 4, wherein the one or more ring resonators comprise a plurality of separate ring resonators cascaded together, each ring resonator introducing a group delay value into the phase delay, the plurality of cascaded ring resonators providing an aggregate group delay.

6. 1. An optical receiver for use in a high data rate optical transceiver, comprising: a plurality of (N) parallel optical fibers, each of which supports the transmission of a high data rate signal; a plurality (N) of optically-based chromatic dispersion compensating elements coupled in a one-to-one relationship to the plurality (N) of parallel optical fibers, each configured to impart a phase delay to an associated received optical signal sufficient to compensate for chromatic dispersion accumulated along the optical fiber; a plurality (N) of photodetectors coupled in a one-to-one relationship to the plurality (N) of optically-based chromatic dispersion compensation elements, each photodetector converting a chromatic dispersion compensated optical data signal into an electrical equivalent signal; an electronic receiver circuit for receiving a plurality (N) of electrically equivalent signals as parallel inputs and recovering therefrom a recovered clock signal and a recovered data signal; An optical receiver comprising:

7. The optical receiver of claim 6 , wherein the optically-based chromatic dispersion compensation element comprises at least one GT etalon.

8. 8. The optical receiver of claim 7, wherein the at least one GT etalon comprises a plurality of separate GT etalon elements cascaded together, each element introducing a group delay value into the phase delay, the cascaded elements providing an aggregate group delay.

9. The optical receiver of claim 6 , wherein the optically-based chromatic dispersion compensation element comprises one or more optical ring resonators that include a delay component within the ring.

10. 10. The optical receiver of claim 9, wherein the one or more ring resonators comprise a plurality of separate ring resonators cascaded together, each ring resonator introducing a group delay value into the phase delay, the plurality of cascaded ring resonators providing an aggregate group delay.

11. 1. An optical receiver for use in a multi-wavelength high data rate optical transceiver, comprising: an input optical fiber supporting the transmission of multiple (N) high data rate signals, each operating at a different optical wavelength; an optically-based chromatic dispersion compensating element coupled to the input optical fiber and configured to impart a phase delay to the multi-wavelength input optical signal sufficient to compensate for chromatic dispersion accumulated along the optical fiber; a wavelength division demultiplexer coupled to an output of the optically-based chromatic dispersion compensation element for separating the plurality (N) high data rate signals and directing each high data rate signal to a separate signal path; a plurality (N) of photodetectors, each of which receives as an input a respective one of the plurality (N) of outputs from the wavelength division demultiplexer and converts the received, compensated optical data signal into an electrical equivalent signal; an electronic receiver circuit for receiving the plurality (N) of electrically equivalent signals as parallel inputs and recovering therefrom a recovered clock signal and a recovered data signal; An optical receiver comprising:

12. The optical receiver of claim 11 , wherein the optically-based chromatic dispersion compensation element comprises at least one GT etalon.

13. 13. The optical receiver of claim 12, wherein the at least one GT etalon comprises a plurality of separate GT etalon elements cascaded together, each element introducing a group delay value into the phase delay, the cascaded elements providing an aggregate group delay.

14. The optical receiver of claim 11 , wherein the optically-based chromatic dispersion compensation element comprises one or more optical ring resonators that include a delay component within the ring.

15. 15. The optical receiver of claim 14, wherein the one or more ring resonators comprise a plurality of separate ring resonators cascaded together, each ring resonator introducing a group delay value into the phase delay, the plurality of cascaded ring resonators providing an aggregate group delay.

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