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Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 16 — Aug. 12, 2013
  • pp: 19202–19208
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Performance comparison between electrical copper-based and optical fiber-based backplanes

Anna Boletti, Daniela Giacomuzzi, Giorgio Parladori, Pierpaolo Boffi, Maddalena Ferrario, and Mario Martinelli  »View Author Affiliations


Optics Express, Vol. 21, Issue 16, pp. 19202-19208 (2013)
http://dx.doi.org/10.1364/OE.21.019202


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Abstract

A performance comparison between the electrical Cu-based backplane and a full-optical fiber-based backplane is presented in terms of capacity and power consumption. By means of systematic simulations we find the electrical configuration, which allows to optimize the Cu-based backplane by exploiting the best technologies available today. On the other hand, a fiber-based optical backplane is proposed by exploiting the most performing VCSEL sources. Limitations of the electrical and optical approaches are discussed, considering their capabilities to support up to about 25-Gb/s transmission and the possibility to evolve towards higher bit-rates.

© 2013 OSA

1. Introduction

The aim of this paper is to compare the performance achievable with the best technologies available today for the electrical backplane with the ones provided by an optical backplane designed by means of fiber-based interconnections. We present a simulative analysis on different Cu-based electrical backplane architectures implemented using the technologies and materials available on the market, finding the best Cu-based backplane achievable nowadays. Moreover, we propose a fiber-based optical backplane realized exploiting VCSELs as optical sources. The most performing VCSELs proposed in literature are taken into account for our comparison. A comparative analysis in terms of capacity, power budget and consumption between the found best achievable electrical (Cu-based) backplane configuration and the designed optical solution is finally proposed.

2. Simulative analysis of performances/limits of Cu-based electrical backplane

3. Analysis of a fiber-based backplane

In order to achieve a comparison with the optical solution in terms of power we have ideally designed an optical backplane by replacing (see Fig. 6
Fig. 6 Optical solution scheme: optical fibers based interconnections
) the Cu-based interconnection line with silica optical fiber (for example standard multi-mode fiber); the output buffer of electrical line driver with a VCSEL source; at last, the first input stage of receiver buffer with a photodiode.

We have taken into account optical single mode and multimode VCSEL sources. VCSELs are already considered a very attractive solution for data communications. They are capable to deliver highest modulation speeds beyond 40Gb/s [10

10. P. Westbergh, R. Safaisini, E. Haglund, B. Kögel, J. S. Gustavsson, A. Larsson, M. Geen, R. Lawrence, and A. Larsson, “High-speed 850nm VCSELs with 28GHz modulation bandwidth operating error-free up to 44Gbit/s,” Electron. Lett. 48(18), 1145–1147 (2012). [CrossRef]

]. At the same time they consume small amounts of power and can be mass fabricated at very low cost. In order to realize energy-efficient high-speed performance, large resonance frequencies must be achieved at a low drive current [11

11. W. Hofmann and D. Bimberg, “VCSEL-Based Light Sources—Scalability Challenges for VCSEL-Based Multi-100-Gb/s Systems,” J. Photon. 4(5), 1831–1843 (2012). [CrossRef]

]. Recently, large progress on energy-efficient VCSEL was made at different bit rate [12

12. N. N. Ledentsov, J. A. Lott, P. Wolf, P. Moser, J. R. Kropp, and D. Bimberg, “High Speed VCSELs for Energy-Efficient Data Transmission,” Proc. ISLC 2012, paper WB1 (2012). [CrossRef]

]. For our analysis we have referred to data and performances from the present literature. For example, we have considered a very efficient single-mode 850-nm VCSEL with 56-fJ dissipated energy for 25-Gb/s operation. The threshold current is 0.15 mA and the bias current is about 1 mA to achieve error-free transmission [13

13. P. Moser, J. A. Lott, P. Wolf, G. Larisch, H. Li, N. N. Ledentsov, and D. Bimberg, “56 fJ dissipated energy per bit of oxide-confined 850 nm VCSELs operating at 25 Gbit/s,” Electron. Lett. 48(20), 1292 (2012). [CrossRef]

]. The achievable transmittable power is about −3 dBm. If we consider a commercial device to directly modulate the VCSEL, with a 3.3V supply the power consumption for the VCSEL is 5.56 dBm.

Instead, if we use a multimode 850-nm VCSEL the power consumption of the VCSEL is 6.68 dBm. The transmittable power is about 0 dBm. A V-I-Systems D30-850M photodetector can be employed with sensitivity about −9.5 dBm (BER = 10−12 at 25 Gb/s) and the received power remains always higher than sensitivity value. Hence, for very short distance typical of optical interconnects, the transmitted frequency is not limited by the backplane implementation realized by means of optical fiber, but only by the bandwidth of the exploited optical Tx/Rx devices. In our analysis we have considered the performance of only commercially available devices.

4. Comparison between the electrical and optical backplane solutions

In Table 2

Table 2. Comparison between electrical and optical solution.

table-icon
View This Table
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we summarize the results in both solutions taken into account. In the electrical solution with no equalization we observe an upper limit of 6-7 Gb/s. With equalization it is possible to reach about 22 Gb/s, paying in terms of complexity and costs of the interfaces. It is a matter of fact that for the Cu-based electrical solution the main limitation remains the backplane line losses. In the optical solution we report the absorption power achievable in case of different VCSEL sources taken into account at different bit rate. For our comparison we use a V-I-Systems photodetector described above, with a −3-dB bandwidth of 30 GHz and we consider the consumed power to achieve error free transmission.

Regarding the transmission up to 25 Gb/s, from the calculated results for our optical design taken into account, using the data reported in Table 2 and by the comparison with the results for the electrical solution, we deduce that considering the same power budget the optical solution can easily reach 25 Gb/s only depending on the transmitter /receiver bandwidth characteristics, consuming almost a quarter of power with respect to use electrical interconnections.

As example in Table 2 we report also the performance of a multimode 850-nm VCSEL working at 40 Gb/s [14

14. S. A. Blokhin, J. A. Lott, A. Muting, G. Fiol, N. N. Ledentsov, M. V. Maximov, A. M. Nadtochiv, V. A. Shchukin, and D. Bimberg, “Oxide-confined 850 nm VCSELs operating at bit rates up to 40 Gbit/s,” Electron. Lett. 45(10), 501 (2009). [CrossRef]

]. We obtained half power consumption per Gb/s doubling the bit rate with respect to electrical condition. Furthermore, to minimize the total power consumption in case of optical interconnection it is necessary to work on driving electronics besides the single transmitter and receiver bandwidths. Significant works continue to be done in this direction, promoting an increased chip-level of integration [15

15. B. Offrein, “Silicon Photonics packaging requirements,” in Proc, IBM Silicon Photon. Workshop, Munich, Germany, 1–14 (2011). http://www.siliconphotonics.eu/munich_slides/2_IBM.pdf

]. Anyway, in fiber-based optical solution there is no limitation due to the backplane line.

5. Conclusions

In this paper we have achieved by simulations the best performance of the optimized configuration of a Cu-based backplane exploiting the technology available today and we have realized a power analysis to compare the electrical solution with respect to a possible future optical solution based on a full optical fiber-based backplane.

In the electrical solution with equalization at a bit rate lower than about 20-22 Gb/s we achieve that the power consumption per Gb/s is higher than 0.8 mW. It is a matter of fact that for the Cu-based electrical solution the main limitation remains the backplane line losses.

References and links

1.

S. Kipp, “The Limit of Switch Bandwidth,” Proc. OFC 2011, Los Angeles, CA, paper OMV1 (2011). [CrossRef]

2.

A. Taubenblatt, “Optical Interconnects for High-Performance Computing,” J. Lightwave Technol. 30(4), 448–457 (2012). [CrossRef]

3.

N. Fehratovic and S. Aleksic, “Power Consumption and Scalability of Optically Switched Interconnects for High-Capacity Network Elements,” Proc. OFC 2011, Los Angeles, CA, paper JWA84 (2001).

4.

D. M. Kuchta, A. V. Rylyakov, C. L. Schow, J. E. Proesel, C. Baks, C. Kocot, L. Graham, R. Johnson, G. Landry, E. Shaw, A. MacInnes, and J. Tatum, “A 55Gb/s Directly Modulated 850nm VCSEL-Based Optical Link,” Proc. IEEE Photonics Conference (IPC 2012), paper PD1.5 (2012). [CrossRef]

5.

P. Boffi, A. Gatto, A. Boletti, P. Martelli, and M. Martinelli, “12.5 Gbit/s VCSEL-based transmission over legacy MMFs by centre-launching technique,” Electron. Lett. 48(20), 1289 (2012). [CrossRef]

6.

http://researcher.watson.ibm.com/researcher/files/ussasha/OFC_2012_OTh1E1_40G_SiGe_Link_Rylyakov_v5.pdf

7.

N. N. Ledentsov, J. A. Lott, J.-R. Kropp, V. A. Shchukin, D. Bimberg, P. Moser, G. Fiol, A. S. Payusov, D. Molin, G. Kuyt, A. Amezcua, L. Y. Karachinskiy, S. A. Blokhin, I. I. Novikov, N. A. Maleev, C. Caspar, and R. Freund, “Progress on single mode VCSELs for data- and tele-communications,” Proc. SPIE 8276, 82760K, 82760K-11 (2012). [CrossRef]

8.

C. Berger, B. J. Offrein, and M. Schmatz, “Challenges for the introduction of board-level optical interconnect technology into product development roadmaps,” Proc. SPIE 6124, 61240J, 61240J-12 (2006). [CrossRef]

9.

http://www.altera.com/devices/fpga/stratix-fpgas/stratix-v/stxv-index.jsp

10.

P. Westbergh, R. Safaisini, E. Haglund, B. Kögel, J. S. Gustavsson, A. Larsson, M. Geen, R. Lawrence, and A. Larsson, “High-speed 850nm VCSELs with 28GHz modulation bandwidth operating error-free up to 44Gbit/s,” Electron. Lett. 48(18), 1145–1147 (2012). [CrossRef]

11.

W. Hofmann and D. Bimberg, “VCSEL-Based Light Sources—Scalability Challenges for VCSEL-Based Multi-100-Gb/s Systems,” J. Photon. 4(5), 1831–1843 (2012). [CrossRef]

12.

N. N. Ledentsov, J. A. Lott, P. Wolf, P. Moser, J. R. Kropp, and D. Bimberg, “High Speed VCSELs for Energy-Efficient Data Transmission,” Proc. ISLC 2012, paper WB1 (2012). [CrossRef]

13.

P. Moser, J. A. Lott, P. Wolf, G. Larisch, H. Li, N. N. Ledentsov, and D. Bimberg, “56 fJ dissipated energy per bit of oxide-confined 850 nm VCSELs operating at 25 Gbit/s,” Electron. Lett. 48(20), 1292 (2012). [CrossRef]

14.

S. A. Blokhin, J. A. Lott, A. Muting, G. Fiol, N. N. Ledentsov, M. V. Maximov, A. M. Nadtochiv, V. A. Shchukin, and D. Bimberg, “Oxide-confined 850 nm VCSELs operating at bit rates up to 40 Gbit/s,” Electron. Lett. 45(10), 501 (2009). [CrossRef]

15.

B. Offrein, “Silicon Photonics packaging requirements,” in Proc, IBM Silicon Photon. Workshop, Munich, Germany, 1–14 (2011). http://www.siliconphotonics.eu/munich_slides/2_IBM.pdf

OCIS Codes
(060.2330) Fiber optics and optical communications : Fiber optics communications
(200.4650) Optics in computing : Optical interconnects
(140.7260) Lasers and laser optics : Vertical cavity surface emitting lasers

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: May 16, 2013
Revised Manuscript: June 22, 2013
Manuscript Accepted: June 22, 2013
Published: August 6, 2013

Citation
Anna Boletti, Daniela Giacomuzzi, Giorgio Parladori, Pierpaolo Boffi, Maddalena Ferrario, and Mario Martinelli, "Performance comparison between electrical copper-based and optical fiber-based backplanes," Opt. Express 21, 19202-19208 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-16-19202


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References

  1. S. Kipp, “The Limit of Switch Bandwidth,” Proc. OFC 2011, Los Angeles, CA, paper OMV1 (2011). [CrossRef]
  2. A. Taubenblatt, “Optical Interconnects for High-Performance Computing,” J. Lightwave Technol.30(4), 448–457 (2012). [CrossRef]
  3. N. Fehratovic and S. Aleksic, “Power Consumption and Scalability of Optically Switched Interconnects for High-Capacity Network Elements,” Proc. OFC 2011, Los Angeles, CA, paper JWA84 (2001).
  4. D. M. Kuchta, A. V. Rylyakov, C. L. Schow, J. E. Proesel, C. Baks, C. Kocot, L. Graham, R. Johnson, G. Landry, E. Shaw, A. MacInnes, and J. Tatum, “A 55Gb/s Directly Modulated 850nm VCSEL-Based Optical Link,” Proc. IEEE Photonics Conference (IPC 2012), paper PD1.5 (2012). [CrossRef]
  5. P. Boffi, A. Gatto, A. Boletti, P. Martelli, and M. Martinelli, “12.5 Gbit/s VCSEL-based transmission over legacy MMFs by centre-launching technique,” Electron. Lett.48(20), 1289 (2012). [CrossRef]
  6. http://researcher.watson.ibm.com/researcher/files/ussasha/OFC_2012_OTh1E1_40G_SiGe_Link_Rylyakov_v5.pdf
  7. N. N. Ledentsov, J. A. Lott, J.-R. Kropp, V. A. Shchukin, D. Bimberg, P. Moser, G. Fiol, A. S. Payusov, D. Molin, G. Kuyt, A. Amezcua, L. Y. Karachinskiy, S. A. Blokhin, I. I. Novikov, N. A. Maleev, C. Caspar, and R. Freund, “Progress on single mode VCSELs for data- and tele-communications,” Proc. SPIE8276, 82760K, 82760K-11 (2012). [CrossRef]
  8. C. Berger, B. J. Offrein, and M. Schmatz, “Challenges for the introduction of board-level optical interconnect technology into product development roadmaps,” Proc. SPIE6124, 61240J, 61240J-12 (2006). [CrossRef]
  9. http://www.altera.com/devices/fpga/stratix-fpgas/stratix-v/stxv-index.jsp
  10. P. Westbergh, R. Safaisini, E. Haglund, B. Kögel, J. S. Gustavsson, A. Larsson, M. Geen, R. Lawrence, and A. Larsson, “High-speed 850nm VCSELs with 28GHz modulation bandwidth operating error-free up to 44Gbit/s,” Electron. Lett.48(18), 1145–1147 (2012). [CrossRef]
  11. W. Hofmann and D. Bimberg, “VCSEL-Based Light Sources—Scalability Challenges for VCSEL-Based Multi-100-Gb/s Systems,” J. Photon.4(5), 1831–1843 (2012). [CrossRef]
  12. N. N. Ledentsov, J. A. Lott, P. Wolf, P. Moser, J. R. Kropp, and D. Bimberg, “High Speed VCSELs for Energy-Efficient Data Transmission,” Proc. ISLC 2012, paper WB1 (2012). [CrossRef]
  13. P. Moser, J. A. Lott, P. Wolf, G. Larisch, H. Li, N. N. Ledentsov, and D. Bimberg, “56 fJ dissipated energy per bit of oxide-confined 850 nm VCSELs operating at 25 Gbit/s,” Electron. Lett.48(20), 1292 (2012). [CrossRef]
  14. S. A. Blokhin, J. A. Lott, A. Muting, G. Fiol, N. N. Ledentsov, M. V. Maximov, A. M. Nadtochiv, V. A. Shchukin, and D. Bimberg, “Oxide-confined 850 nm VCSELs operating at bit rates up to 40 Gbit/s,” Electron. Lett.45(10), 501 (2009). [CrossRef]
  15. B. Offrein, “Silicon Photonics packaging requirements,” in Proc, IBM Silicon Photon. Workshop, Munich, Germany, 1–14 (2011). http://www.siliconphotonics.eu/munich_slides/2_IBM.pdf

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