Abstract

We discuss technology options and challenges for scaling intra-datacenter interconnects beyond 1 Tb/s bandwidths, with focus on two possible approaches: pulse amplitude modulation (PAM)-based intensity modulation-direct detection (IM-DD) and baud-rate sampled coherent technology. In our studies, we compare the performance of various orders of PAM modulation (PAM4 to 8). In addition to these fixed PAM signaling options, a flexible PAM (FlexPAM) technique leveraging granularity in spectral efficiency (SE) is proposed to maximize link margin. For baud-rate sampled coherent technology, we propose a simplified digital signal processing (DSP) architecture to bring down power consumption of the coherent approach closer to that of IM-DD PAM. We also propose two new phase noise tolerant 2D coherent modulation formats to relax the laser linewidth requirement. In closing, a comparative study of fixed IM-DD PAM versus coherent polarization multiplexed-quadrature amplitude modulation (PM-QAM) is presented for a 1.6 Tb/s solution (200 Gb/s per dimension), with consideration of link loss/reach budget, power consumption, implementation complexity, as well as fan-out granularity.

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  3. X. Zhou, H. Liu, R. Urata, and S. Zebian, “Scaling large data center interconnects: Challenges and solutions,” Opt. Fiber Technol., vol. 44, pp. 61–68, 2018.
  4. W. Way and T. Chan, “MPI penalties for 400GBASE-FR8/LR8 links,” in Proc. IEEE802.3bs 400 GbE Meeting, Sep. 2015, pp. 1–8.
  5. X. Zhou and H. Liu, “Constellation shaping: Can it be useful for datacenter reach communication,” in Proc. Eur. Conf. Opt. Commun., 2017, pp. 1–9.
  6. X. Zhou, R. Urata, and H. Liu, “Beyond 1 Tb/s datacenter interconnect technology: Challenges and solutions,” in Proc. Opt. Fiber Commun. Conf. Exhib., San Diego, CA, USA, 2019, Paper Tu2F.5.
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  15. G. Lu, T. Sakamoto, and T. Kawanishi, “Experimental investigation of sampling phase sensitivity in baud-rate sampled coherent receiver for Nyquist pulseshaped high-order QAM signals,” in Proc. Conf. Lasers Electro-Opt., Laser Sci. Photon. Appl., San Jose, CA, USA, 2014, Paper SW1J.2.
  16. A. Gorshteina, D. Sadota, and G. Dormanb, “MIMO equalization optimized for baud rate clock recovery in coherent 112 Gbit/sec DP-QPSK metro systems,” Opt. Fiber Technol., vol. 22, pp. 23–27, 2015.
  17. X. Zhou and H. Liu, “Pluggable DWDM: Considerations for campus and metro DCI applications,” in Proc. Eur. Conf. Opt. Commun., 2016, Paper WS3.
  18. C. R. S. Fludger, “Coherent equalization and POLMUX-RZ-DQPSK for robust 100-GE transmission,” J. Lightw. Technol., vol. 26, no. 1, pp. 64–72, 2008.
  19. K. Matsuda, R. Matsumoto, and N. Suzuki, “Hardware-efficient adaptive equalization and carrier phase recovery for 100 Gb/s/λ-based coherent WDM-PON systems,” in Proc. Eur. Conf. Opt. Commun., 2017, Paper Th.1.B.2.
  20. J. Cheng, C. Xie, M. Tang, and S. Fu, “A low-complexity adaptive equalizer for digital coherent short-reach optical transmission systems,” in Proc. Opt. Fiber Commun. Conf. Exhib., San Diego, CA, USA, 2019, Paper M3H.2.
  21. J. G. Proakis, Digital Communication, 3rd ed.New York, NY, USA: McGraw-Hill, 1995, ch. 6.
  22. K. H. Mueller and M. S. Müller, “Timing recovery in digital synchronous data receivers,” IEEE Trans. Commun., vol. COM-24, no. 5, pp. 516–531, 1976.
  23. B. Smith, J. Riani, I. Lyubomirsky, and S. Bhoja, Interleaving and pilot insertion for CFEC oif2017.535.00.
  24. S. Bhoja, “PAM4 signaling for intra-data center and data center to data center connectivity (DCI),” in Proc. Opt. Fiber Commun. Conf. Exhib., Los Angeles, CA, USA, 2017, Paper W4D.5.
  25. X. Zhou, “High spectral efficiency 400 Gb/s transmission using PDM time-domain hybrid 32–64 QAM and training-assisted carrier recovery,” J. Lightw. Technol., vol. 31, no. 7, pp. 999–1005, 2013.
  26. F. Buchali, F. Steiner, G. Böcherer, L. Schmalen, P. Schulte, and W. Idler, “Rate adaptation and reach increase by probabilistically shaped 64-QAM: An experimental demonstration,” J. Lightw. Technol., vol. 34, no. 7, pp.  1599–1609, 2016.
  27. “400G CWDM8 MSA 2 km optical interface technical specifications,” Rev. 1, Feb. 13, 2018.

2018 (2)

X. Zhou, H. Liu, R. Urata, and S. Zebian, “Scaling large data center interconnects: Challenges and solutions,” Opt. Fiber Technol., vol. 44, pp. 61–68, 2018.

“400G CWDM8 MSA 2 km optical interface technical specifications,” Rev. 1, Feb. 13, 2018.

2016 (1)

F. Buchali, F. Steiner, G. Böcherer, L. Schmalen, P. Schulte, and W. Idler, “Rate adaptation and reach increase by probabilistically shaped 64-QAM: An experimental demonstration,” J. Lightw. Technol., vol. 34, no. 7, pp.  1599–1609, 2016.

2015 (2)

A. Singh, “Jupiter rising: A decade of clos topologies and centralized control in Google's datacenter network,” Commun. ACM, vol. 59, no. 9, pp. 88–97, 2015.

A. Gorshteina, D. Sadota, and G. Dormanb, “MIMO equalization optimized for baud rate clock recovery in coherent 112 Gbit/sec DP-QPSK metro systems,” Opt. Fiber Technol., vol. 22, pp. 23–27, 2015.

2013 (1)

X. Zhou, “High spectral efficiency 400 Gb/s transmission using PDM time-domain hybrid 32–64 QAM and training-assisted carrier recovery,” J. Lightw. Technol., vol. 31, no. 7, pp. 999–1005, 2013.

2010 (1)

A. Gorshtein, O. Levy, G. Katz, and D. Sadot, “Coherent compensation for 100G DP-QPSK with one sample per symbol based on antialiasing filtering and blind equalization MLSE,” IEEE Photon. Technol. Lett., vol. 22, no. 16, pp. 1208–1210, 2010.

2008 (1)

C. R. S. Fludger, “Coherent equalization and POLMUX-RZ-DQPSK for robust 100-GE transmission,” J. Lightw. Technol., vol. 26, no. 1, pp. 64–72, 2008.

1976 (1)

K. H. Mueller and M. S. Müller, “Timing recovery in digital synchronous data receivers,” IEEE Trans. Commun., vol. COM-24, no. 5, pp. 516–531, 1976.

Bai, Y.

F. Zhu, Y. Wen, and Y. Bai, “Component BW requirement of 56 Gbaud modulations for 400 GbE 2 & 10 km PMD” in Proc. IEEE 802.3bs 400 GbE Task Force Plenary Meeting, Jul. 2014, pp. 1–13.

Barroso, L.

L. Barroso, U. Hölzle, and P. Ranganathan, The Datacenter as a Computer: An Introduction to the Design of Warehouse-Scale Machines, 3rd ed.San Rafael, CA, USA: Morgan & Claypool, 2018.

Bayvel, P.

D. Millar, D. Lavery, R. Maher, B. C. Thomsen, P. Bayvel, and S. J. Savory, “A baud-rate sampled coherent transceiver with digital pulse shaping and interpolation,” in Proc. Opt. Fiber Commun. Conf. Expo. Nat. Fiber Opt. Engineers Conf., Anaheim, CA, USA, 2013, Paper Tu2I.2.

Bhoja, S.

S. Bhoja, “PAM4 signaling for intra-data center and data center to data center connectivity (DCI),” in Proc. Opt. Fiber Commun. Conf. Exhib., Los Angeles, CA, USA, 2017, Paper W4D.5.

B. Smith, J. Riani, I. Lyubomirsky, and S. Bhoja, Interleaving and pilot insertion for CFEC oif2017.535.00.

Böcherer, G.

F. Buchali, F. Steiner, G. Böcherer, L. Schmalen, P. Schulte, and W. Idler, “Rate adaptation and reach increase by probabilistically shaped 64-QAM: An experimental demonstration,” J. Lightw. Technol., vol. 34, no. 7, pp.  1599–1609, 2016.

Buchali, F.

F. Buchali, F. Steiner, G. Böcherer, L. Schmalen, P. Schulte, and W. Idler, “Rate adaptation and reach increase by probabilistically shaped 64-QAM: An experimental demonstration,” J. Lightw. Technol., vol. 34, no. 7, pp.  1599–1609, 2016.

Chan, T.

W. Way and T. Chan, “MPI penalties for 400GBASE-FR8/LR8 links,” in Proc. IEEE802.3bs 400 GbE Meeting, Sep. 2015, pp. 1–8.

Cheng, J.

J. Cheng, C. Xie, M. Tang, and S. Fu, “A low-complexity adaptive equalizer for digital coherent short-reach optical transmission systems,” in Proc. Opt. Fiber Commun. Conf. Exhib., San Diego, CA, USA, 2019, Paper M3H.2.

Dormanb, G.

A. Gorshteina, D. Sadota, and G. Dormanb, “MIMO equalization optimized for baud rate clock recovery in coherent 112 Gbit/sec DP-QPSK metro systems,” Opt. Fiber Technol., vol. 22, pp. 23–27, 2015.

Fludger, C. R. S.

C. R. S. Fludger, “Coherent equalization and POLMUX-RZ-DQPSK for robust 100-GE transmission,” J. Lightw. Technol., vol. 26, no. 1, pp. 64–72, 2008.

Fu, S.

J. Cheng, C. Xie, M. Tang, and S. Fu, “A low-complexity adaptive equalizer for digital coherent short-reach optical transmission systems,” in Proc. Opt. Fiber Commun. Conf. Exhib., San Diego, CA, USA, 2019, Paper M3H.2.

Gorshtein, A.

A. Gorshtein, O. Levy, G. Katz, and D. Sadot, “Coherent compensation for 100G DP-QPSK with one sample per symbol based on antialiasing filtering and blind equalization MLSE,” IEEE Photon. Technol. Lett., vol. 22, no. 16, pp. 1208–1210, 2010.

Gorshteina, A.

A. Gorshteina, D. Sadota, and G. Dormanb, “MIMO equalization optimized for baud rate clock recovery in coherent 112 Gbit/sec DP-QPSK metro systems,” Opt. Fiber Technol., vol. 22, pp. 23–27, 2015.

Hölzle, U.

L. Barroso, U. Hölzle, and P. Ranganathan, The Datacenter as a Computer: An Introduction to the Design of Warehouse-Scale Machines, 3rd ed.San Rafael, CA, USA: Morgan & Claypool, 2018.

Idler, W.

F. Buchali, F. Steiner, G. Böcherer, L. Schmalen, P. Schulte, and W. Idler, “Rate adaptation and reach increase by probabilistically shaped 64-QAM: An experimental demonstration,” J. Lightw. Technol., vol. 34, no. 7, pp.  1599–1609, 2016.

Katz, G.

A. Gorshtein, O. Levy, G. Katz, and D. Sadot, “Coherent compensation for 100G DP-QPSK with one sample per symbol based on antialiasing filtering and blind equalization MLSE,” IEEE Photon. Technol. Lett., vol. 22, no. 16, pp. 1208–1210, 2010.

Kawanishi, T.

G. Lu, T. Sakamoto, and T. Kawanishi, “Experimental investigation of sampling phase sensitivity in baud-rate sampled coherent receiver for Nyquist pulseshaped high-order QAM signals,” in Proc. Conf. Lasers Electro-Opt., Laser Sci. Photon. Appl., San Jose, CA, USA, 2014, Paper SW1J.2.

Lavery, D.

D. Millar, D. Lavery, R. Maher, B. C. Thomsen, P. Bayvel, and S. J. Savory, “A baud-rate sampled coherent transceiver with digital pulse shaping and interpolation,” in Proc. Opt. Fiber Commun. Conf. Expo. Nat. Fiber Opt. Engineers Conf., Anaheim, CA, USA, 2013, Paper Tu2I.2.

Levy, O.

A. Gorshtein, O. Levy, G. Katz, and D. Sadot, “Coherent compensation for 100G DP-QPSK with one sample per symbol based on antialiasing filtering and blind equalization MLSE,” IEEE Photon. Technol. Lett., vol. 22, no. 16, pp. 1208–1210, 2010.

Liu, H.

X. Zhou, H. Liu, R. Urata, and S. Zebian, “Scaling large data center interconnects: Challenges and solutions,” Opt. Fiber Technol., vol. 44, pp. 61–68, 2018.

R. Urata, X. Zhou, and H. Liu, “Beyond 400G: Business as usual or coherent convergence?” in Proc. OFC Workshop Talk: Beyond 400G Hyperscale DCs Workshop, 2019, pp. 1–7.

R. Urata, H. Liu, X. Zhou, and A. Vahdat, “Datacenter interconnect and networking: From evolution to holistic revolution,” in Proc. Opt. Fiber Commun. Conf. Exhib., Los Angeles, CA, USA, 2017, Paper W3G.1.

X. Zhou and H. Liu, “Pluggable DWDM: Considerations for campus and metro DCI applications,” in Proc. Eur. Conf. Opt. Commun., 2016, Paper WS3.

X. Zhou and H. Liu, “Constellation shaping: Can it be useful for datacenter reach communication,” in Proc. Eur. Conf. Opt. Commun., 2017, pp. 1–9.

X. Zhou, R. Urata, and H. Liu, “Beyond 1 Tb/s datacenter interconnect technology: Challenges and solutions,” in Proc. Opt. Fiber Commun. Conf. Exhib., San Diego, CA, USA, 2019, Paper Tu2F.5.

Lu, G.

G. Lu, T. Sakamoto, and T. Kawanishi, “Experimental investigation of sampling phase sensitivity in baud-rate sampled coherent receiver for Nyquist pulseshaped high-order QAM signals,” in Proc. Conf. Lasers Electro-Opt., Laser Sci. Photon. Appl., San Jose, CA, USA, 2014, Paper SW1J.2.

Lyubomirsky, I.

B. Smith, J. Riani, I. Lyubomirsky, and S. Bhoja, Interleaving and pilot insertion for CFEC oif2017.535.00.

Maher, R.

D. Millar, D. Lavery, R. Maher, B. C. Thomsen, P. Bayvel, and S. J. Savory, “A baud-rate sampled coherent transceiver with digital pulse shaping and interpolation,” in Proc. Opt. Fiber Commun. Conf. Expo. Nat. Fiber Opt. Engineers Conf., Anaheim, CA, USA, 2013, Paper Tu2I.2.

Matsuda, K.

K. Matsuda, R. Matsumoto, and N. Suzuki, “Hardware-efficient adaptive equalization and carrier phase recovery for 100 Gb/s/λ-based coherent WDM-PON systems,” in Proc. Eur. Conf. Opt. Commun., 2017, Paper Th.1.B.2.

Matsumoto, R.

K. Matsuda, R. Matsumoto, and N. Suzuki, “Hardware-efficient adaptive equalization and carrier phase recovery for 100 Gb/s/λ-based coherent WDM-PON systems,” in Proc. Eur. Conf. Opt. Commun., 2017, Paper Th.1.B.2.

Millar, D.

D. Millar, D. Lavery, R. Maher, B. C. Thomsen, P. Bayvel, and S. J. Savory, “A baud-rate sampled coherent transceiver with digital pulse shaping and interpolation,” in Proc. Opt. Fiber Commun. Conf. Expo. Nat. Fiber Opt. Engineers Conf., Anaheim, CA, USA, 2013, Paper Tu2I.2.

Mueller, K. H.

K. H. Mueller and M. S. Müller, “Timing recovery in digital synchronous data receivers,” IEEE Trans. Commun., vol. COM-24, no. 5, pp. 516–531, 1976.

Müller, M. S.

K. H. Mueller and M. S. Müller, “Timing recovery in digital synchronous data receivers,” IEEE Trans. Commun., vol. COM-24, no. 5, pp. 516–531, 1976.

Proakis, J. G.

J. G. Proakis, Digital Communication, 3rd ed.New York, NY, USA: McGraw-Hill, 1995, ch. 6.

Ranganathan, P.

L. Barroso, U. Hölzle, and P. Ranganathan, The Datacenter as a Computer: An Introduction to the Design of Warehouse-Scale Machines, 3rd ed.San Rafael, CA, USA: Morgan & Claypool, 2018.

Riani, J.

B. Smith, J. Riani, I. Lyubomirsky, and S. Bhoja, Interleaving and pilot insertion for CFEC oif2017.535.00.

Sadot, D.

A. Gorshtein, O. Levy, G. Katz, and D. Sadot, “Coherent compensation for 100G DP-QPSK with one sample per symbol based on antialiasing filtering and blind equalization MLSE,” IEEE Photon. Technol. Lett., vol. 22, no. 16, pp. 1208–1210, 2010.

Sadota, D.

A. Gorshteina, D. Sadota, and G. Dormanb, “MIMO equalization optimized for baud rate clock recovery in coherent 112 Gbit/sec DP-QPSK metro systems,” Opt. Fiber Technol., vol. 22, pp. 23–27, 2015.

Sakamoto, T.

G. Lu, T. Sakamoto, and T. Kawanishi, “Experimental investigation of sampling phase sensitivity in baud-rate sampled coherent receiver for Nyquist pulseshaped high-order QAM signals,” in Proc. Conf. Lasers Electro-Opt., Laser Sci. Photon. Appl., San Jose, CA, USA, 2014, Paper SW1J.2.

Savory, S. J.

D. Millar, D. Lavery, R. Maher, B. C. Thomsen, P. Bayvel, and S. J. Savory, “A baud-rate sampled coherent transceiver with digital pulse shaping and interpolation,” in Proc. Opt. Fiber Commun. Conf. Expo. Nat. Fiber Opt. Engineers Conf., Anaheim, CA, USA, 2013, Paper Tu2I.2.

Schmalen, L.

F. Buchali, F. Steiner, G. Böcherer, L. Schmalen, P. Schulte, and W. Idler, “Rate adaptation and reach increase by probabilistically shaped 64-QAM: An experimental demonstration,” J. Lightw. Technol., vol. 34, no. 7, pp.  1599–1609, 2016.

Schulte, P.

F. Buchali, F. Steiner, G. Böcherer, L. Schmalen, P. Schulte, and W. Idler, “Rate adaptation and reach increase by probabilistically shaped 64-QAM: An experimental demonstration,” J. Lightw. Technol., vol. 34, no. 7, pp.  1599–1609, 2016.

Shannon, C. E.

C. E. Shannon and W. Weaver, The Mathematical Theory of Communication. Urbana, IL, USA: Univ. Illinois Press, 1998.

Singh, A.

A. Singh, “Jupiter rising: A decade of clos topologies and centralized control in Google's datacenter network,” Commun. ACM, vol. 59, no. 9, pp. 88–97, 2015.

Smith, B.

B. Smith, J. Riani, I. Lyubomirsky, and S. Bhoja, Interleaving and pilot insertion for CFEC oif2017.535.00.

Steiner, F.

F. Buchali, F. Steiner, G. Böcherer, L. Schmalen, P. Schulte, and W. Idler, “Rate adaptation and reach increase by probabilistically shaped 64-QAM: An experimental demonstration,” J. Lightw. Technol., vol. 34, no. 7, pp.  1599–1609, 2016.

Suzuki, N.

K. Matsuda, R. Matsumoto, and N. Suzuki, “Hardware-efficient adaptive equalization and carrier phase recovery for 100 Gb/s/λ-based coherent WDM-PON systems,” in Proc. Eur. Conf. Opt. Commun., 2017, Paper Th.1.B.2.

Tang, M.

J. Cheng, C. Xie, M. Tang, and S. Fu, “A low-complexity adaptive equalizer for digital coherent short-reach optical transmission systems,” in Proc. Opt. Fiber Commun. Conf. Exhib., San Diego, CA, USA, 2019, Paper M3H.2.

Thomsen, B. C.

D. Millar, D. Lavery, R. Maher, B. C. Thomsen, P. Bayvel, and S. J. Savory, “A baud-rate sampled coherent transceiver with digital pulse shaping and interpolation,” in Proc. Opt. Fiber Commun. Conf. Expo. Nat. Fiber Opt. Engineers Conf., Anaheim, CA, USA, 2013, Paper Tu2I.2.

Urata, R.

X. Zhou, H. Liu, R. Urata, and S. Zebian, “Scaling large data center interconnects: Challenges and solutions,” Opt. Fiber Technol., vol. 44, pp. 61–68, 2018.

R. Urata, X. Zhou, and H. Liu, “Beyond 400G: Business as usual or coherent convergence?” in Proc. OFC Workshop Talk: Beyond 400G Hyperscale DCs Workshop, 2019, pp. 1–7.

R. Urata, H. Liu, X. Zhou, and A. Vahdat, “Datacenter interconnect and networking: From evolution to holistic revolution,” in Proc. Opt. Fiber Commun. Conf. Exhib., Los Angeles, CA, USA, 2017, Paper W3G.1.

X. Zhou, R. Urata, and H. Liu, “Beyond 1 Tb/s datacenter interconnect technology: Challenges and solutions,” in Proc. Opt. Fiber Commun. Conf. Exhib., San Diego, CA, USA, 2019, Paper Tu2F.5.

Vahdat, A.

R. Urata, H. Liu, X. Zhou, and A. Vahdat, “Datacenter interconnect and networking: From evolution to holistic revolution,” in Proc. Opt. Fiber Commun. Conf. Exhib., Los Angeles, CA, USA, 2017, Paper W3G.1.

Way, W.

W. Way and T. Chan, “MPI penalties for 400GBASE-FR8/LR8 links,” in Proc. IEEE802.3bs 400 GbE Meeting, Sep. 2015, pp. 1–8.

Weaver, W.

C. E. Shannon and W. Weaver, The Mathematical Theory of Communication. Urbana, IL, USA: Univ. Illinois Press, 1998.

Wen, Y.

F. Zhu, Y. Wen, and Y. Bai, “Component BW requirement of 56 Gbaud modulations for 400 GbE 2 & 10 km PMD” in Proc. IEEE 802.3bs 400 GbE Task Force Plenary Meeting, Jul. 2014, pp. 1–13.

Xie, C.

J. Cheng, C. Xie, M. Tang, and S. Fu, “A low-complexity adaptive equalizer for digital coherent short-reach optical transmission systems,” in Proc. Opt. Fiber Commun. Conf. Exhib., San Diego, CA, USA, 2019, Paper M3H.2.

Zebian, S.

X. Zhou, H. Liu, R. Urata, and S. Zebian, “Scaling large data center interconnects: Challenges and solutions,” Opt. Fiber Technol., vol. 44, pp. 61–68, 2018.

Zhou, X.

X. Zhou, H. Liu, R. Urata, and S. Zebian, “Scaling large data center interconnects: Challenges and solutions,” Opt. Fiber Technol., vol. 44, pp. 61–68, 2018.

X. Zhou, “High spectral efficiency 400 Gb/s transmission using PDM time-domain hybrid 32–64 QAM and training-assisted carrier recovery,” J. Lightw. Technol., vol. 31, no. 7, pp. 999–1005, 2013.

X. Zhou and H. Liu, “Pluggable DWDM: Considerations for campus and metro DCI applications,” in Proc. Eur. Conf. Opt. Commun., 2016, Paper WS3.

R. Urata, H. Liu, X. Zhou, and A. Vahdat, “Datacenter interconnect and networking: From evolution to holistic revolution,” in Proc. Opt. Fiber Commun. Conf. Exhib., Los Angeles, CA, USA, 2017, Paper W3G.1.

R. Urata, X. Zhou, and H. Liu, “Beyond 400G: Business as usual or coherent convergence?” in Proc. OFC Workshop Talk: Beyond 400G Hyperscale DCs Workshop, 2019, pp. 1–7.

X. Zhou, R. Urata, and H. Liu, “Beyond 1 Tb/s datacenter interconnect technology: Challenges and solutions,” in Proc. Opt. Fiber Commun. Conf. Exhib., San Diego, CA, USA, 2019, Paper Tu2F.5.

X. Zhou and H. Liu, “Constellation shaping: Can it be useful for datacenter reach communication,” in Proc. Eur. Conf. Opt. Commun., 2017, pp. 1–9.

Zhu, F.

F. Zhu, Y. Wen, and Y. Bai, “Component BW requirement of 56 Gbaud modulations for 400 GbE 2 & 10 km PMD” in Proc. IEEE 802.3bs 400 GbE Task Force Plenary Meeting, Jul. 2014, pp. 1–13.

Commun. ACM (1)

A. Singh, “Jupiter rising: A decade of clos topologies and centralized control in Google's datacenter network,” Commun. ACM, vol. 59, no. 9, pp. 88–97, 2015.

IEEE Photon. Technol. Lett. (1)

A. Gorshtein, O. Levy, G. Katz, and D. Sadot, “Coherent compensation for 100G DP-QPSK with one sample per symbol based on antialiasing filtering and blind equalization MLSE,” IEEE Photon. Technol. Lett., vol. 22, no. 16, pp. 1208–1210, 2010.

IEEE Trans. Commun. (1)

K. H. Mueller and M. S. Müller, “Timing recovery in digital synchronous data receivers,” IEEE Trans. Commun., vol. COM-24, no. 5, pp. 516–531, 1976.

J. Lightw. Technol. (3)

X. Zhou, “High spectral efficiency 400 Gb/s transmission using PDM time-domain hybrid 32–64 QAM and training-assisted carrier recovery,” J. Lightw. Technol., vol. 31, no. 7, pp. 999–1005, 2013.

F. Buchali, F. Steiner, G. Böcherer, L. Schmalen, P. Schulte, and W. Idler, “Rate adaptation and reach increase by probabilistically shaped 64-QAM: An experimental demonstration,” J. Lightw. Technol., vol. 34, no. 7, pp.  1599–1609, 2016.

C. R. S. Fludger, “Coherent equalization and POLMUX-RZ-DQPSK for robust 100-GE transmission,” J. Lightw. Technol., vol. 26, no. 1, pp. 64–72, 2008.

Opt. Fiber Technol. (2)

X. Zhou, H. Liu, R. Urata, and S. Zebian, “Scaling large data center interconnects: Challenges and solutions,” Opt. Fiber Technol., vol. 44, pp. 61–68, 2018.

A. Gorshteina, D. Sadota, and G. Dormanb, “MIMO equalization optimized for baud rate clock recovery in coherent 112 Gbit/sec DP-QPSK metro systems,” Opt. Fiber Technol., vol. 22, pp. 23–27, 2015.

Other (19)

X. Zhou and H. Liu, “Pluggable DWDM: Considerations for campus and metro DCI applications,” in Proc. Eur. Conf. Opt. Commun., 2016, Paper WS3.

B. Smith, J. Riani, I. Lyubomirsky, and S. Bhoja, Interleaving and pilot insertion for CFEC oif2017.535.00.

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