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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 26 — Dec. 10, 2012
  • pp: B393–B398

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Compact and high-sensitivity 100-Gb/s (4 × 25 Gb/s) APD-ROSA with a LAN-WDM PLC demultiplexer

Toshihide Yoshimatsu, Masahiro Nada, Manabu Oguma, Haruki Yokoyama, Tetsuichiro Ohno, Yoshiyuki Doi, Ikuo Ogawa, Hiroshi Takahashi, and Eiji Yoshida  »View Author Affiliations


Optics Express, Vol. 20, Issue 26, pp. B393-B398 (2012)
http://dx.doi.org/10.1364/OE.20.00B393


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Abstract

We demonstrate an integrated 100GbE receiver optical sub-assembly (ROSA) that incorporates a monolithic four-channel avalanche photodiode (APD) array and a planer lightwave circuit (PLC) based LAN-WDM demultiplexer. A record minimum receiver sensitivity of −20 dBm and 50-km error-free SMF transmission without an optical amplifier have been achieved.

© 2012 OSA

1. Introduction

To deal with the explosive growth in data traffic, high-capacity and high-sensitivity optical transceivers are needed in optical transport networks. Crucial issues in spreading the 100-Gb/s transceiver further are its size and power consumption. A small, high-sensitivity optical module with low power consumption is indispensable for improving port density on line cards and reducing installation space of equipment in buildings such as data centers. CFP2 (41.5 × 107.5 × 12.4 mm3) and CFP4 (21.5 × 89 × 9.5 mm3) form factors are currently being discussed for the next Ethernet optical transceivers in CFP MSA [1

http://www.cfp-msa.org.

]. An ultra-small transmitter optical sub-assembly (TOSA) with 8-mm width [2

S. Kanazawa, T. Fujisawa, N. Nunoya, A. Ohki, K. Takahata, H. Sanjoh, R. Iga, and H. Ishii, “Extremely small-form 100GbE transmitter optical sub-assembly for future inter data center cloud networks,” in Proceedings of OFC/NFOEC 2012, PDP5B.8 (2012).

] has been reported, but a comparably small receiver optical sub-assembly (ROSA) has not. Moreover, a compact, low-power consumption 100-Gb/s ROSA for ≥40 km transmission has not been reported yet, because an additional optical amplifier, such as a semiconductor optical amplifier (SOA), has been required to improve receiver sensitivity.

We have reported a novel p-down inverted InAlAs/InGaAs avalanche photodiode (APD) structure with a low–high–low electric field profile [3

M. Nada, Y. Muramoto, H. Yokoyama, N. Shigekawa, T. Ishibashi, and S. Kodama, “Inverted InAlAs/InGaAs avalanche photodiode with low–high–low electric field profile,” Jpn. J. Appl. Phys. 51(2), 02BG03.1–02BG03, 4 (2012). [CrossRef]

] and demonstrated a high multiplied responsivity-bandwidth product of 18.5 × 9.1 = 168 A/W·GHz [4

M. Nada, Y. Muramoto, H. Yokoyama, T. Ishibashi, and S. Kodama, “InAlAs APD with high multiplied responsivity-bandwidth product (MR-bandwidth product) of 168 A/W.GHz for 25 Gbit/s high-speed operations,” Electron. Lett. 48(7), 397–399 (2012). [CrossRef]

] and 25-Gb/s 40-km transmission at 1.3-um wavelength using a single-channel TO-CAN type APD-ROSA [5

M. Nada, Y. Muramoto, H. Yokoyama, T. Ishibashi, and S. Kodama, “High-sensitivity 25 Gbit/s avalanche photodiode receiver optical sub-assembly for 40 km transmission,” Electron. Lett. 48(13), 777–778 (2012). [CrossRef]

]. The APD is a key device for realizing a high-sensitivity, low-power-consumption receiver with a small footprint.

In this paper, we present an integrated 4 × 25 Gb/s APD-ROSA with high sensitivity. To reduce the width of the module, we used a planer lightwave circuit (PLC) filter as a LAN-WDM demultiplexer (demux). To the best of our knowledge, ours is the smallest integrated 4 × 25 Gb/s ROSA in width, footprint, and volume ever reported. We also succeeded in error-free transmission of 100-Gb/s (4 × 25 Gb/s) signal on 50-km SMF without an optical amplifier.

2. Design and structure of 4-ch APD-ROSA

Figure 1 shows a schematic view of the 4-ch APD-ROSA, which includes a PLC demux, micro-lens array, a monolithic 4-ch APD array, and a 4-ch transimpedance amplifier (TIA). A p-down mesa-type InAlAs/InGaAs 4-ch APD array chip with a high gain-bandwidth product of 235 GHz [4

M. Nada, Y. Muramoto, H. Yokoyama, T. Ishibashi, and S. Kodama, “InAlAs APD with high multiplied responsivity-bandwidth product (MR-bandwidth product) of 168 A/W.GHz for 25 Gbit/s high-speed operations,” Electron. Lett. 48(7), 397–399 (2012). [CrossRef]

] was flip-chip mounted on a subcarrier. From on-wafer measurements, the fabricated APD has 3-dB bandwidths of 20 and 16 GHz for multiplication factors (M) of 3 and 10, respectively.

Fig. 1 Schematic view of the 4-ch APD-ROSA.

As an 800-GHz-spacing LAN-WDM demux, we fabricated a silica-based PLC arrayed waveguide grating (AWG) with a very small chip size of 5.0 × 9.3 mm2 using high-index-contrast waveguides of Δ = 2%. We adopted the multimode waveguides for the AWG output ports to achieve a low loss and flat-top pass-band characteristics simultaneously. The fabricated PLC demux chip has a low on-chip insertion loss of less than 1.2 dB and a high adjacent channel isolation of more than 25 dB. A glass micro-lens array and the APD array on the subcarrier were attached to the output end of the PLC demux chip. In order to minimize coupling loss between the multimode waveguides and the APD, the light-sensitive area of the APD has a racetrack shape. Compared to the other approaches with thin-film-filter-based optics, the PLC is attractive because it can be fabricated in a single wafer process without the need for any precise and complicated assembly process for filter chips.

Figure 2 shows a photograph of the 100-Gb/s APD-ROSA with the PLC demux. Two separate polyimide-based flexible-printed circuits (FPCs) were attached at the rear end of the package as electrical interfaces, through which supply voltages are input to the APD and TIA, and 4-ch differential RF signals are output. The package body size, excluding the LC receptacle and FPCs, is 7.7 × 20 × 5.8 mm3 (1.54 cm2 in footprint and 0.89 cm3 in volume) [6

T. Yoshimatsu, M. Nada, M. Oguma, H. Yokoyama, T. Ohno, Y. Doi, I. Ogawa, and E. Yoshida, “Compact and High-Sensitivity 100-Gb/s (4 × 25 Gb/s) APD-ROSA with a LAN-WDM PLC Demultiplexer,” in Proceedings of ECOC 2012, Th.3.B.5 (2012).

], which is smaller in width, footprint, and volume than previously reported 4 × 25 Gb/s LAN-WDM ROSAs [7

K. Mochizuki, H. Itamoto, H. Aruga, K. Akiyama, Y. Horiguchi, S. Nishikawa, M. Nakaji, R. Takemura, and A. Sugitatsu, “Built-in Optics for 4ch-WDM ROSA in 100Gbps Ethernet,” in Proceedings of OECC 2010, 7E3–2 (2010).

,8

Y. Baek, Y. T. Han, C. W. Lee, D. H. Lee, O. K. Kwon, J. W. Shin, S. H. Park, and Y. A. Leemet, “Optical Components for 100G Ethernet Transceivers,” in Proceedings of OECC 2012, 4D1–2 (2012).

]. Total power consumption of the APD-ROSA is as low as 630 mW for one channel optical input power of −20 dBm with an APD bias voltage of 34 V at room temperature.

Fig. 2 Photograph of APD-ROSA prototype.

3. Experimental results

Figure 3 shows responsivity spectra of the 4-ch APD-ROSA. The responsivity was obtained from the ratio of the APD photocurrent to the optical input power. Applied bias voltages to the APD (Vapd) were set to 20 V, where we estimate M = 2.7 from I-V measurements. Optical input power was measured at the end of the LC connector of the input fiber and set to −10 dBm. The responsivities at centre wavelengths for lanes 0, 1, 2, and 3 are 1.17, 1.18, 1.18, and 1.21 A/W, respectively. Assuming the APD on-chip responsivity of 0.7-0.8 A/W at M = 1, total insertion loss (including the PLC on-chip loss and optical coupling losses) is estimated to be 2.0-2.6 dB. The pass-band ripples obtained from responsivity measurements of the APD-ROSA for lane 0, 1, 2, and 3 are 0.11, 0.06, 0.09, and 0.16 dB in peak-to-peak, respectively. These results show the optical coupling between the multimode output waveguide from the AWG and APD can provide flat-top filtering characteristics.

Fig. 3 Responsivity spectra of the 4-ch APD-ROSA.

To investigate the receiver performance, we measured minimum receiver sensitivity, which is defined as the average optical input power necessary to obtain a bit error rate (BER) of 10−12. Figure 4 shows the experimental setup. A 25.78-Gb/s non-return-to-zero (NRZ) on-off keying optical signal consisting of a 231-1 pseudo-random bit sequence (PRBS) was generated using a tunable laser source and a LiNbO3 Mach-Zehnder (LN) modulator. Wavelength was set at 1309.14 nm (lane3) and the extinction ratio (ER) was 10.3 dB. Figure 5 shows sensitivity dependence versus the APD bias voltage Vapd. The receiver sensitivity improved as Vapd was increased from 20 V (M = 2.7). We obtained the best receiver sensitivity of −20 dBm for Vapd = 34 V (M = 11).

Fig. 4 BER measurement setup.
Fig. 5 Minimum receiver sensitivity versus APD bias voltage.

Then we measured the transmission characteristics of the 4 × 25-Gb/s signals using the 4-ch APD-ROSA and 50-km conventional SMF. Note that we did not use optical amplifiers in the experiment. Figures 6(a) and 6(b) show the measured electrical output waveforms and the BER curves for back-to-back (BtoB) and after 50-km transmission. The wavelengths for lanes 0, 1, 2, and 3 were set at 1295.56, 1300.05, 1304.58, and 1309.14 nm, respectively. An LN modulator was used to modulate the four CW signals. The fiber input power was −1 dBm for each channel and the ER was approximately 10 dB. The chirp parameter of the LN modulator was + 0.7 ± 0.1. The insertion loss of the 50-km SMF was about 17 dB, with a zero dispersion wavelength and a dispersion slope of 1319.5 nm and 0.091 ps/(nm2·km). The APD bias voltage Vapd was set at 34 V for all four channels of APD array. In electrical waveform measurements, average received power was set to −20 dBm.

Fig. 6 Electrical output waveforms (a) and BER curves (b) for back-to-back and after 50 km transmission.

As shown in Fig. 6(a), we observed clear eye openings of electrical waveforms both for BtoB and after 50-km transmission. From BER measurements in Fig. 6(b), receiver sensitivities for BtoB were −20.0, −20.3, −20.1, and −20.0 dBm for lanes 0, 1, 2, and 3, respectively. After 50-km transmission, no significant transmission penalties were observed. Negative values of power penalties are explained by the relationship between the positive chirp parameter of the modulator and the normal chromatic dispersion of the 50-km SMF.

4. Conclusion

We successfully demonstrated a 100-Gb/s (4 × 25-Gb/s) integrated ROSA using a monolithic 4-ch APD array and an ultra-small PLC-based LAN-WDM demultiplexer. The module is the smallest as a 100GbE integrated ROSA ever reported. The module exhibits minimum receiver sensitivities of −20 dBm and below for BtoB. We have succeeded in 50-km error-free transmission without an optical amplifier. These results indicate that this module can contribute to the reduction in size and power consumption of 100GbE optical transceivers. Moreover, the proposed approach for integrating the ROSA provides significant scalability with an AWG toward the future 400 GbE and 1 TbE multi-wavelength networks.

Acknowledgments

The authors thank Y. Muramoto, T. Ishibashi, S. Kodama, M. Itoh, and M. Itoh for valuable discussions, and T. Akeyoshi and Y. Inoue for their continuous encouragement.

References and links

1.

http://www.cfp-msa.org.

2.

S. Kanazawa, T. Fujisawa, N. Nunoya, A. Ohki, K. Takahata, H. Sanjoh, R. Iga, and H. Ishii, “Extremely small-form 100GbE transmitter optical sub-assembly for future inter data center cloud networks,” in Proceedings of OFC/NFOEC 2012, PDP5B.8 (2012).

3.

M. Nada, Y. Muramoto, H. Yokoyama, N. Shigekawa, T. Ishibashi, and S. Kodama, “Inverted InAlAs/InGaAs avalanche photodiode with low–high–low electric field profile,” Jpn. J. Appl. Phys. 51(2), 02BG03.1–02BG03, 4 (2012). [CrossRef]

4.

M. Nada, Y. Muramoto, H. Yokoyama, T. Ishibashi, and S. Kodama, “InAlAs APD with high multiplied responsivity-bandwidth product (MR-bandwidth product) of 168 A/W.GHz for 25 Gbit/s high-speed operations,” Electron. Lett. 48(7), 397–399 (2012). [CrossRef]

5.

M. Nada, Y. Muramoto, H. Yokoyama, T. Ishibashi, and S. Kodama, “High-sensitivity 25 Gbit/s avalanche photodiode receiver optical sub-assembly for 40 km transmission,” Electron. Lett. 48(13), 777–778 (2012). [CrossRef]

6.

T. Yoshimatsu, M. Nada, M. Oguma, H. Yokoyama, T. Ohno, Y. Doi, I. Ogawa, and E. Yoshida, “Compact and High-Sensitivity 100-Gb/s (4 × 25 Gb/s) APD-ROSA with a LAN-WDM PLC Demultiplexer,” in Proceedings of ECOC 2012, Th.3.B.5 (2012).

7.

K. Mochizuki, H. Itamoto, H. Aruga, K. Akiyama, Y. Horiguchi, S. Nishikawa, M. Nakaji, R. Takemura, and A. Sugitatsu, “Built-in Optics for 4ch-WDM ROSA in 100Gbps Ethernet,” in Proceedings of OECC 2010, 7E3–2 (2010).

8.

Y. Baek, Y. T. Han, C. W. Lee, D. H. Lee, O. K. Kwon, J. W. Shin, S. H. Park, and Y. A. Leemet, “Optical Components for 100G Ethernet Transceivers,” in Proceedings of OECC 2012, 4D1–2 (2012).

OCIS Codes
(130.0250) Integrated optics : Optoelectronics
(230.7390) Optical devices : Waveguides, planar
(040.1345) Detectors : Avalanche photodiodes (APDs)

ToC Category:
Waveguide and Optoelectronic Devices

History
Original Manuscript: October 16, 2012
Manuscript Accepted: November 2, 2012
Published: November 29, 2012

Virtual Issues
European Conference on Optical Communication 2012 (2012) Optics Express

Citation
Toshihide Yoshimatsu, Masahiro Nada, Manabu Oguma, Haruki Yokoyama, Tetsuichiro Ohno, Yoshiyuki Doi, Ikuo Ogawa, Hiroshi Takahashi, and Eiji Yoshida, "Compact and high-sensitivity 100-Gb/s (4 × 25 Gb/s) APD-ROSA with a LAN-WDM PLC demultiplexer," Opt. Express 20, B393-B398 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-26-B393


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References

  1. http://www.cfp-msa.org .
  2. S. Kanazawa, T. Fujisawa, N. Nunoya, A. Ohki, K. Takahata, H. Sanjoh, R. Iga, and H. Ishii, “Extremely small-form 100GbE transmitter optical sub-assembly for future inter data center cloud networks,” in Proceedings of OFC/NFOEC 2012, PDP5B.8 (2012).
  3. M. Nada, Y. Muramoto, H. Yokoyama, N. Shigekawa, T. Ishibashi, and S. Kodama, “Inverted InAlAs/InGaAs avalanche photodiode with low–high–low electric field profile,” Jpn. J. Appl. Phys.51(2), 02BG03.1–02BG03, 4 (2012). [CrossRef]
  4. M. Nada, Y. Muramoto, H. Yokoyama, T. Ishibashi, and S. Kodama, “InAlAs APD with high multiplied responsivity-bandwidth product (MR-bandwidth product) of 168 A/W.GHz for 25 Gbit/s high-speed operations,” Electron. Lett.48(7), 397–399 (2012). [CrossRef]
  5. M. Nada, Y. Muramoto, H. Yokoyama, T. Ishibashi, and S. Kodama, “High-sensitivity 25 Gbit/s avalanche photodiode receiver optical sub-assembly for 40 km transmission,” Electron. Lett.48(13), 777–778 (2012). [CrossRef]
  6. T. Yoshimatsu, M. Nada, M. Oguma, H. Yokoyama, T. Ohno, Y. Doi, I. Ogawa, and E. Yoshida, “Compact and High-Sensitivity 100-Gb/s (4 × 25 Gb/s) APD-ROSA with a LAN-WDM PLC Demultiplexer,” in Proceedings of ECOC 2012, Th.3.B.5 (2012).
  7. K. Mochizuki, H. Itamoto, H. Aruga, K. Akiyama, Y. Horiguchi, S. Nishikawa, M. Nakaji, R. Takemura, and A. Sugitatsu, “Built-in Optics for 4ch-WDM ROSA in 100Gbps Ethernet,” in Proceedings of OECC 2010, 7E3–2 (2010).
  8. Y. Baek, Y. T. Han, C. W. Lee, D. H. Lee, O. K. Kwon, J. W. Shin, S. H. Park, and Y. A. Leemet, “Optical Components for 100G Ethernet Transceivers,” in Proceedings of OECC 2012, 4D1–2 (2012).

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