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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 26 — Dec. 12, 2011
  • pp: B777–B783
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100-Gbps CMOS transceiver for multilane optical backplane system with a 1.3 cm2 footprint

Takashi Takemoto, Fumio Yuki, Hiroki Yamashita, Shinji Tsuji, Yong Lee, Koichiro Adachi, Kazunori Shinoda, Yasunobu Matsuoka, Kenji Kogo, Shinji Nishimura, Masaaki Nido, Masahiko Namiwaka, Taro Kaneko, Takara Sugimoto, and Kazuhiko Kurata  »View Author Affiliations


Optics Express, Vol. 19, Issue 26, pp. B777-B783 (2011)
http://dx.doi.org/10.1364/OE.19.00B777


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Abstract

A compact 4 × 25 Gbps optical transceiver has been fabricated for an optical backplane system, which consists of a 4 × 25 Gbps DFB-LD array, a 4 × 25 Gbps PIN-PD array, and a CMOS transceiver chip. These are directly mounted on 9 × 14 mm2 multi-layer ceramic package with an electromagnetic shield structure to suppress inner-channel crosstalk effectively. The transceiver includes an analog front-end as well as an electrical interface function to interface with the switch LSI or CPU. Power consumption was as low as 20 mW/Gbps, and a transmission experiment was successfully conducted at 25 Gbps.

© 2011 OSA

1. Introduction

We are currently focused on an optical backplane for a high-speed router as a test bed for demonstration, in which network interface (NIF) cards and a switch (SW) card are connected optically [5

5. S. Nishimura, K. Shinoda, Y. Lee, G. Ono, K. Fukuda, F. Yuki, T. Takemoto, H. Toyoda, M. Yamada, S. Tsuji, and N. Ikeda, “Components and interconnection technologies for photonic-assisted routers toward green networks,” IEEE J. Sel. Top. Quantum Electron. 17(2), 347–356 (2011). [CrossRef]

]. To construct an optical backplane, we have developed a compact 100 Gbps transceiver with a 9 × 14 mm2 footprint, which consists of a surface-emitting distributed feedback (DFB) laser array, a PD array, and a CMOS chip hybrid integrated onto a multi-layer ceramic package [6

6. T. Takemoto, F. Yuki, H. Yamashita, S. Tsuji, Y. Lee, K. Adachi, K. Shinoda, Y. Matsuoka, K. Kogo, S. Nishimura, M. Nido, M. Namiwaka, T. Kaneko, T. Sugimoto, and K. Kurata, “100 Gbps CMOS Transceiver for Multilane Optical Backplane System with a 1.3 cm Square Footprint,” in ECOC 2011, OSA Technical Digest (CD), paper Th.12.B.5, 2011.

]. Here, we describe key technologies of the transceiver, namely, packaging and CMOS chip technology. The CMOS chip contains electrical interface (IF) circuits to convert 4 × 25 Gbps into 10 × 10 Gbps at the data rate of CPU or switch LSI inside ICT systems, as well as a laser diode driver (LDD) and TIA functions. The total power consumption is as low as 20 mW/Gbps, which is 1/5 that of the electrical backplane transmission. We conducted a transmission experiment using the module as a transmitter, and clear receiving signals at 20 Gbps and 25 Gbps were demonstrated under air-cooling conditions.

2. Optical transceiver for optical backplane system

Figure 1
Fig. 1 Overall architecture of 100 Gbps transceiver.
shows a block diagram of our optical module, which consists of a 4 × 25 Gbp surface emitting DFB LD array, a 4 × 25 Gbps photodiode (PD) array, and a CMOS transceiver chip all directly mounted on a 9 × 14mm2 multi-layer ceramic package. The transceiver includes an analog frontend (FE) as well as an electrical IF to interface with the SW LSI or CPU.

To construct an optical backplane system with large throughput, the optical transceiver needs to operate under air-cooling conditions inside the ICT system. However, it is difficult to design a 25-Gbps VCSEL that is operable at high-temperature. Therefore, we have developed a highly efficient 1.3-μm DFB-LD with slope efficiency of 0.29 W/A [7

7. K. Adachi, K. Shinoda, T. Kitatani, T. Fukamachi, Y. Matsuoka, T. Sugawara, and S. Tsuji, “25-Gb/s multichannel 1.3-μm surface-emitting lens-integrated DFB laser arrays,” J. Lightwave Technol. 29(19), 2899–2905 (2011). [CrossRef]

] and PIN-PD with a responsivity of a 0.8 A/W array [8

8. Y. Lee, K. Nagatsuma, K. Hosomi, T. Ban, K. Shinoda, K. Adachi, S. Tsuji, Y. Matsuoka, S. Tanaka, R. Mita, T. Sugawara, and M. Aoki, “A 35-GHz, 0.8-A/W and 26-m, Misalignment Tolerance Microlens-Integrated p-i-n Photodiodes,” IEICE Trans. Electron. E 94-C, 116–119 (2010).

], which are both surface emitting or receiving types integrated with a monolithic lens. These devices decrease the output optical power necessary to backplane transmission effectively. The surface emitting DFB-LD provides compact optical coupling to multi-mode fibers (MMFs) using a common PETIT© optical connector. Moreover, note that generated heat at DFB-LD is dissipated through the transceiver chip to keep LD temperature less than 65 °C.

Inner-channel crosstalk is one of the main problems in multi-channel optical transceivers, especially at a high data rate with close channel separation, such as 250 μm. To reduce the crosstalk, output signals from the optical devices are connected to inputs of the CMOS chip through coplanar lines, which are sandwiched by upper and lower ground layers in addition to right-and-left ground lines inside the multi-layer ceramic package. No bonding wire is used. This structure is very effective in avoiding mutual inductive couplings between channels. Figure 2
Fig. 2 Low crosstalk multi-layer packaging technique.
shows the simulated 25-Gbps eye diagrams for the receiver side. The eye diagram without a shield structure is significantly degraded by large mutual inductive coupling between channels. In contrast, the eye diagram of our multi-layer structure is greatly improved by reducing the mutual inductive coupling. To evaluate the effectiveness of our packaging technology, we fabricated an optical receiver consisting of a 4 × 25 Gbps PIN-PD array and CMOS TIA array, which were flip-chip mounted on a 16-mm square ceramic multi-layer package. Clear eye openings were found for all channels. The crosstalk penalty was only 0.8 dB at the data rate of 25 Gbps [4

4. T. Takemoto, F. Yuki, H. Yamashita, Y. Lee, T. Saito, S. Tsuji, and S. Nishimura, “A compact 4 x 25-Gb/s 3.0 mW/Gb/s CMOS-based optical receiver for board-to-board interconnects,” J. Lightwave Technol. 28(23), 3343–3350 (2010).

].

3. Fabricated CMOS optical transceiver

Figure 4
Fig. 4 4 × 25 Gbps optical transceiver assembly.
depicts a photograph of a 4 × 25 Gbps optical transceiver assembly. The DFB-LD array, PIN-PD array, and transceiver chip were directly mounted on the multi-layer ceramic package. The transceiver chip was fabricated in the 65-nm CMOS process and was 3.6 × 5.2 mm2. Optical signals were accessed via standard 12-MMF arrays. The fiber alignment was conducted to fit on the DFB-LD array because PIN-PD array has larger optical coupling tolerance owing to the back-side-etched aspheric microlens on an InP substrate [8

8. Y. Lee, K. Nagatsuma, K. Hosomi, T. Ban, K. Shinoda, K. Adachi, S. Tsuji, Y. Matsuoka, S. Tanaka, R. Mita, T. Sugawara, and M. Aoki, “A 35-GHz, 0.8-A/W and 26-m, Misalignment Tolerance Microlens-Integrated p-i-n Photodiodes,” IEICE Trans. Electron. E 94-C, 116–119 (2010).

]. The positional accuracy at PIN-PD array was less than ±15 μm, which was an adequate value for maintaining high optical-coupling efficiency at a 25-Gbps data rate.

Figure 5
Fig. 5 Fabricated optical transceiver.
shows a photograph of a fabricated optical CMOS transceiver. The package is as small as 9 × 14mm2. Throughput of the transceiver was 100 Gbps including 10 × 10 Gbps electrical I/O and 4 × 25 Gbps optical interfaces. The optical transceivers are set to SW and NIF boards via land grid array (LGA) sockets. This structure is suitable for a board-soldering process that does not degrade fiber array.

To evaluate its TX transmission with a PRBS of 231-1 from the internal PRBS generator, the output signal from the transceiver was measured while it was linked to our previously fabricated optical receiver [4

4. T. Takemoto, F. Yuki, H. Yamashita, Y. Lee, T. Saito, S. Tsuji, and S. Nishimura, “A compact 4 x 25-Gb/s 3.0 mW/Gb/s CMOS-based optical receiver for board-to-board interconnects,” J. Lightwave Technol. 28(23), 3343–3350 (2010).

] via MMF. The 20- and 25-Gbps clear eye diagrams were observed using a digital oscilloscope as shown in Fig. 6
Fig. 6 Measured 20- and 25-Gbps eye diagrams.
.

Table 2

Table 2. Performance summary

table-icon
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and Fig. 7
Fig. 7 Estimated power consumption.
summarize the performance and estimated power consumption. Throughput of the transceiver was 100 Gbps including the 10 × 10-Gbps electrical IOs and 4 × 25-Gbps. The analog FEs in optical devices, 25-Gbps SerDes, 10-Gbps SerDes, and IF Logic were 782 mW, 1714 mW, 200 mW, and 100 mW, respectively. The total power consumption was about 2.0 watts, which is less than 1/15 that of a CFP Multi-Source Agreement (MSA) compliant 100-Gbps Ethernet (100GbE) transceiver [11

11. CFP MSA Hardware Specification, Revision 1.4, 7 June 2010, http://www.cfp-msa.org/Documents/CFP-MSA-HW-Spec-rev1-40.pdf.

].

4. Conclusion

We developed a 4 × 25 Gbps compact optical transceiver for an optical backplane system required in coming high-speed servers, routers, and storages. Our transceiver consists of a DFB LD array, a PIN-PD array, and a high-speed IF chip mounted on a 9 × 14 mm2 ceramic package. Optical devices, a transceiver chip that includes analog FE and electrical IF, and package structure are key features in realizing low power, high speed, and a small footprint for an optical transceiver. The power dissipation was only 20 mW/Gbps at a data rate of 25 Gbps, which is less than 1/15 that of a CFP 100GbE module. To the best of our knowledge, we have developed the first 25-Gbps multi-channel transceiver with electrical IF, which is needed to introduce optical interconnects into ICT systems.

Acknowledgments

The authors thank Prof. T. Asami of the University of Tokyo, and N. Ikeda and his colleagues at Alaxala Network Corp. for their valuable discussions. This work was supported in part by “Next-generation High-efficiency Network Device Project,” which Photonics Electronics Technology Research Association (PETRA) contracted with New Energy and Industrial Technology Development Organization (NEDO).

References and links

1.

B. G. Lee, C. L. Schow, A. V. Rylyakov, F. E. Doany, R. A. John, and J. A. Kash, “Lower-power CMOS-Driven Transmitters and Receivers,” in OSA/CLEO/QELS 2010, CMB5, 2010.

2.

C. P. Lai, C. C. L. Schow, A. V. Rylyakov, B. G. Lee, F. E. Doany, R. A. John, and J. A. Kash, “20-Gb/s Power-Efficient CMOS-Driven Multimode Links,” in OSA/OFC/NFOEC 2010, OTuQ2, 2010.

3.

F. E. Doany, C. L. Schow, C. W. Baks, D. M. Kuchta, P. Pepeljugoski, L. Schares, R. Budd, F. Libsch, R. Dangel, F. Horst, B. J. Offrein, and J. A. Kash, “160 Gb/s bidirectional polymer-waveguide board-level optical interconnects using CMOS-based transceivers,” IEEE Trans. Adv. Packag. 32(2), 345–359 (2009). [CrossRef]

4.

T. Takemoto, F. Yuki, H. Yamashita, Y. Lee, T. Saito, S. Tsuji, and S. Nishimura, “A compact 4 x 25-Gb/s 3.0 mW/Gb/s CMOS-based optical receiver for board-to-board interconnects,” J. Lightwave Technol. 28(23), 3343–3350 (2010).

5.

S. Nishimura, K. Shinoda, Y. Lee, G. Ono, K. Fukuda, F. Yuki, T. Takemoto, H. Toyoda, M. Yamada, S. Tsuji, and N. Ikeda, “Components and interconnection technologies for photonic-assisted routers toward green networks,” IEEE J. Sel. Top. Quantum Electron. 17(2), 347–356 (2011). [CrossRef]

6.

T. Takemoto, F. Yuki, H. Yamashita, S. Tsuji, Y. Lee, K. Adachi, K. Shinoda, Y. Matsuoka, K. Kogo, S. Nishimura, M. Nido, M. Namiwaka, T. Kaneko, T. Sugimoto, and K. Kurata, “100 Gbps CMOS Transceiver for Multilane Optical Backplane System with a 1.3 cm Square Footprint,” in ECOC 2011, OSA Technical Digest (CD), paper Th.12.B.5, 2011.

7.

K. Adachi, K. Shinoda, T. Kitatani, T. Fukamachi, Y. Matsuoka, T. Sugawara, and S. Tsuji, “25-Gb/s multichannel 1.3-μm surface-emitting lens-integrated DFB laser arrays,” J. Lightwave Technol. 29(19), 2899–2905 (2011). [CrossRef]

8.

Y. Lee, K. Nagatsuma, K. Hosomi, T. Ban, K. Shinoda, K. Adachi, S. Tsuji, Y. Matsuoka, S. Tanaka, R. Mita, T. Sugawara, and M. Aoki, “A 35-GHz, 0.8-A/W and 26-m, Misalignment Tolerance Microlens-Integrated p-i-n Photodiodes,” IEICE Trans. Electron. E 94-C, 116–119 (2010).

9.

K. Fukuda, H. Yamashita, G. Ono, R. Nemoto, E. Suzuki, N. Masuda, T. Takemoto, F. Yuki, and T. Saito, “A 12.3-mW 12.5-Gb/s complete transceiver in 65-nm CMOS Process,” IEEE J. Solid-State Circuits 45(12), 2838–2849 (2010). [CrossRef]

10.

G. Ono, K. Watanabe, T. Muto, H .Yamashita, K. Fukuda, N. Masuda, R. Nemoto, E. Suzuki, T. Takemoto, F. Yuki, M. Yagyu, H. Toyoda, A. Kambe, T. Saito, and S. Nishimura, “10:4 MUX and 4:10 DEMUX Gearbox LSI for 100-Gigabit Ethernet Link,” ISSCC Dig. Tech. Papers, 148–149 Feb. 2011.

11.

CFP MSA Hardware Specification, Revision 1.4, 7 June 2010, http://www.cfp-msa.org/Documents/CFP-MSA-HW-Spec-rev1-40.pdf.

OCIS Codes
(200.0200) Optics in computing : Optics in computing
(200.4650) Optics in computing : Optical interconnects
(250.3140) Optoelectronics : Integrated optoelectronic circuits

ToC Category:
Subsystems for Optical Networks

History
Original Manuscript: November 2, 2011
Manuscript Accepted: November 23, 2011
Published: December 6, 2011

Virtual Issues
European Conference on Optical Communication 2011 (2011) Optics Express

Citation
Takashi Takemoto, Fumio Yuki, Hiroki Yamashita, Shinji Tsuji, Yong Lee, Koichiro Adachi, Kazunori Shinoda, Yasunobu Matsuoka, Kenji Kogo, Shinji Nishimura, Masaaki Nido, Masahiko Namiwaka, Taro Kaneko, Takara Sugimoto, and Kazuhiko Kurata, "100-Gbps CMOS transceiver for multilane optical backplane system with a 1.3 cm2 footprint," Opt. Express 19, B777-B783 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-26-B777


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References

  1. B. G. Lee, C. L. Schow, A. V. Rylyakov, F. E. Doany, R. A. John, and J. A. Kash, “Lower-power CMOS-Driven Transmitters and Receivers,” in OSA/CLEO/QELS 2010, CMB5, 2010.
  2. C. P. Lai, C. C. L. Schow, A. V. Rylyakov, B. G. Lee, F. E. Doany, R. A. John, and J. A. Kash, “20-Gb/s Power-Efficient CMOS-Driven Multimode Links,” in OSA/OFC/NFOEC 2010, OTuQ2, 2010.
  3. F. E. Doany, C. L. Schow, C. W. Baks, D. M. Kuchta, P. Pepeljugoski, L. Schares, R. Budd, F. Libsch, R. Dangel, F. Horst, B. J. Offrein, and J. A. Kash, “160 Gb/s bidirectional polymer-waveguide board-level optical interconnects using CMOS-based transceivers,” IEEE Trans. Adv. Packag.32(2), 345–359 (2009). [CrossRef]
  4. T. Takemoto, F. Yuki, H. Yamashita, Y. Lee, T. Saito, S. Tsuji, and S. Nishimura, “A compact 4 x 25-Gb/s 3.0 mW/Gb/s CMOS-based optical receiver for board-to-board interconnects,” J. Lightwave Technol.28(23), 3343–3350 (2010).
  5. S. Nishimura, K. Shinoda, Y. Lee, G. Ono, K. Fukuda, F. Yuki, T. Takemoto, H. Toyoda, M. Yamada, S. Tsuji, and N. Ikeda, “Components and interconnection technologies for photonic-assisted routers toward green networks,” IEEE J. Sel. Top. Quantum Electron.17(2), 347–356 (2011). [CrossRef]
  6. T. Takemoto, F. Yuki, H. Yamashita, S. Tsuji, Y. Lee, K. Adachi, K. Shinoda, Y. Matsuoka, K. Kogo, S. Nishimura, M. Nido, M. Namiwaka, T. Kaneko, T. Sugimoto, and K. Kurata, “100 Gbps CMOS Transceiver for Multilane Optical Backplane System with a 1.3 cm Square Footprint,” in ECOC 2011, OSA Technical Digest (CD), paper Th.12.B.5, 2011.
  7. K. Adachi, K. Shinoda, T. Kitatani, T. Fukamachi, Y. Matsuoka, T. Sugawara, and S. Tsuji, “25-Gb/s multichannel 1.3-μm surface-emitting lens-integrated DFB laser arrays,” J. Lightwave Technol.29(19), 2899–2905 (2011). [CrossRef]
  8. Y. Lee, K. Nagatsuma, K. Hosomi, T. Ban, K. Shinoda, K. Adachi, S. Tsuji, Y. Matsuoka, S. Tanaka, R. Mita, T. Sugawara, and M. Aoki, “A 35-GHz, 0.8-A/W and 26-m, Misalignment Tolerance Microlens-Integrated p-i-n Photodiodes,” IEICE Trans. Electron. E94-C, 116–119 (2010).
  9. K. Fukuda, H. Yamashita, G. Ono, R. Nemoto, E. Suzuki, N. Masuda, T. Takemoto, F. Yuki, and T. Saito, “A 12.3-mW 12.5-Gb/s complete transceiver in 65-nm CMOS Process,” IEEE J. Solid-State Circuits45(12), 2838–2849 (2010). [CrossRef]
  10. G. Ono, K. Watanabe, T. Muto, H .Yamashita, K. Fukuda, N. Masuda, R. Nemoto, E. Suzuki, T. Takemoto, F. Yuki, M. Yagyu, H. Toyoda, A. Kambe, T. Saito, and S. Nishimura, “10:4 MUX and 4:10 DEMUX Gearbox LSI for 100-Gigabit Ethernet Link,” ISSCC Dig. Tech. Papers, 148–149 Feb. 2011.
  11. CFP MSA Hardware Specification, Revision 1.4, 7 June 2010, http://www.cfp-msa.org/Documents/CFP-MSA-HW-Spec-rev1-40.pdf .

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