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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 27 — Dec. 19, 2011
  • pp: 26936–26947
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Low-voltage high-performance silicon photonic devices and photonic integrated circuits operating up to 30 Gb/s

Gyungock Kim, Jeong Woo Park, In Gyoo Kim, Sanghoon Kim, Sanggi Kim, Jong Moo Lee, Gun Sik Park, Jiho Joo, Ki-Seok Jang, Jin Hyuk Oh, Sun Ae Kim, Jong Hoon Kim, Jun Young Lee, Jong Moon Park, Do-Won Kim, Deog-Kyoon Jeong, Moon-Sang Hwang, Jeong-Kyoum Kim, Kyu-Sang Park, Han-Kyu Chi, Hyun-Chang Kim, Dong-Wook Kim, and Mu Hee Cho  »View Author Affiliations


Optics Express, Vol. 19, Issue 27, pp. 26936-26947 (2011)
http://dx.doi.org/10.1364/OE.19.026936


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Abstract

We present high performance silicon photonic circuits (PICs) defined for off-chip or on-chip photonic interconnects, where PN depletion Mach-Zehnder modulators and evanescent-coupled waveguide Ge-on-Si photodetectors were monolithically integrated on an SOI wafer with CMOS-compatible process. The fabricated silicon PICoff-chip for off-chip optical interconnects showed operation up to 30 Gb/s. Under differential drive of low-voltage 1.2 Vpp, the integrated 1 mm-phase-shifter modulator in the PICoff-chip demonstrated an extinction ratio (ER) of 10.5dB for 12.5 Gb/s, an ER of 9.1dB for 20 Gb/s, and an ER of 7.2 dB for 30 Gb/s operation, without adoption of travelling-wave electrodes. The device showed the modulation efficiency of VπLπ ~1.59 Vcm, and the phase-shifter loss of 3.2 dB/mm for maximum optical transmission. The Ge photodetector, which allows simpler integration process based on reduced pressure chemical vapor deposition exhibited operation over 30 Gb/s with a low dark current of 700 nA at −1V. The fabricated silicon PICintra-chip for on-chip (intra-chip) photonic interconnects, where the monolithically integrated modulator and Ge photodetector were connected by a silicon waveguide on the same chip, showed on-chip data transmissions up to 20 Gb/s, indicating potential application in future silicon on-chip optical network. We also report the performance of the hybrid silicon electronic-photonic IC (EPIC), where a PICintra-chip chip and 0.13μm CMOS interface IC chips were hybrid-integrated.

© 2011 OSA

Advancement of silicon photonics technology can offer a new dimension in chip-level data communications by providing high-performance optical interconnects with un-precedent bandwidth based on the cost-effective silicon photonic/CMOS platform [1

1. M. Haurylau, G. Chen, H. Chen, J. Zhang, N. A. Nelson, D. H. Albonesi, E. G. Friedman, and P. M. Fauchet, “On-chip optical interconnect roadmap: challenges and critical directions,” IEEE J. Sel. Top. Quantum Electron. 12(6), 1699–1705 (2006). [CrossRef]

5

5. K. Preston, L. Chen, S. Manipatruni, and M. Lipson, “Silicon photonic interconnect with micrometer-scale devices,” 6th International Conference on Group IV Photonics, WA2, 1–3 (2009).

]. In recent years, silicon photonics has shown remarkable progress [6

6. A. Narasimha, S. Abdaila, C. Bradbury, A. Clark, J. Clymore, J. Coyne, A. Dahl, S. Gloeckner, A. Gruenberg, D. Guckenberger, S. Gutierrez, M. Harrison, D. Kucharski, K. Leap, R. LeBlanc, V. Liang, M. Mack, D. Martinez, G. Masini, A. Mekis, R. Menigoz, C. Ogden, M. Peterson, T. Pinguet, J. Redman, J. Rodriguez, S. Sahni, M. Sharp, T. Sleboda, D. Song, V. Wang, B. Welch, J. Witzens, W. Xu, K. Vokoyama, and P. DobbeIaere, “An ultra low power CMOS photonics technology platform for H/S optoelectronic transceivers at less than $1 per Gbps,” in Proc. OFC 2010, San Diego, USA (2010).

35

35. X. Zheng, D. Patil, J. Lexau, F. Liu, G. Li, H. Thacker, Y. Luo, I. Shubin, J. Li, J. Yao, P. Dong, D. Feng, M. Asghari, T. Pinguet, A. Mekis, P. Amberg, M. Dayringer, J. Gainsley, H. F. Moghadam, E. Alon, K. Raj, R. Ho, J. E. Cunningham, and A. V. Krishnamoorthy, “Ultra-efficient 10 Gb/s hybrid integrated silicon photonic transmitter and receiver,” Opt. Express 19(6), 5172–5186 (2011). [CrossRef] [PubMed]

], and is starting to find its position in practical applications in telecommunications and data communications.

Increasing the integration level in silicon photonics is required to develop compact high-performance optical interconnects for future systems. There have been reports on silicon photonic integration at various levels [31

31. T. Pinguet, B. Analui, E. Balmater, D. Guckenberger, M. Harrison, R. Koumans, D. Kucharski, Y. Liang, G. Masini, A. Mekis, S. Mirsaidi, A. Narasimha, M. Peterson, D. Rines, V. Sadagopan, S. Sahni, T. J. Sleboda, D. Song, Y. Wang, B. Welch, J. Witzens, J. Yao, S. Abdalla, S. Gloeckner, P. De Dobbelaere, and G. Capellini, “Monolithically Integrated High-Speed CMOS Photonic Transceivers,” in Proc. IEEE Int. Conf. Group IV Photonics, 362–364 (2008).

35

35. X. Zheng, D. Patil, J. Lexau, F. Liu, G. Li, H. Thacker, Y. Luo, I. Shubin, J. Li, J. Yao, P. Dong, D. Feng, M. Asghari, T. Pinguet, A. Mekis, P. Amberg, M. Dayringer, J. Gainsley, H. F. Moghadam, E. Alon, K. Raj, R. Ho, J. E. Cunningham, and A. V. Krishnamoorthy, “Ultra-efficient 10 Gb/s hybrid integrated silicon photonic transmitter and receiver,” Opt. Express 19(6), 5172–5186 (2011). [CrossRef] [PubMed]

]. Monolithic integration of multiple optical components on the same wafer to realize silicon photonic integrated circuits (PICs) can cost-effectively increase both functionality and performance. Continued performance improvement of silicon photonic devices and their integration levels based on CMOS fabrication technology is necessary for full utilization of silicon photonics in chip-level data communications and telecommunications.

Silicon optical modulators and Ge-on-Si photodetectors, which are the main active components in silicon optical transceiver circuits, have made remarkable progress [6

6. A. Narasimha, S. Abdaila, C. Bradbury, A. Clark, J. Clymore, J. Coyne, A. Dahl, S. Gloeckner, A. Gruenberg, D. Guckenberger, S. Gutierrez, M. Harrison, D. Kucharski, K. Leap, R. LeBlanc, V. Liang, M. Mack, D. Martinez, G. Masini, A. Mekis, R. Menigoz, C. Ogden, M. Peterson, T. Pinguet, J. Redman, J. Rodriguez, S. Sahni, M. Sharp, T. Sleboda, D. Song, V. Wang, B. Welch, J. Witzens, W. Xu, K. Vokoyama, and P. DobbeIaere, “An ultra low power CMOS photonics technology platform for H/S optoelectronic transceivers at less than $1 per Gbps,” in Proc. OFC 2010, San Diego, USA (2010).

35

35. X. Zheng, D. Patil, J. Lexau, F. Liu, G. Li, H. Thacker, Y. Luo, I. Shubin, J. Li, J. Yao, P. Dong, D. Feng, M. Asghari, T. Pinguet, A. Mekis, P. Amberg, M. Dayringer, J. Gainsley, H. F. Moghadam, E. Alon, K. Raj, R. Ho, J. E. Cunningham, and A. V. Krishnamoorthy, “Ultra-efficient 10 Gb/s hybrid integrated silicon photonic transmitter and receiver,” Opt. Express 19(6), 5172–5186 (2011). [CrossRef] [PubMed]

]. The silicon optical modulator, a key device for transmitting optical data, is based on the free-carrier plasma dispersion effect, where the refractive index of a silicon waveguide can be modulated by either carrier injection in a PIN diode or carrier-depletion effect in a PN diode [6

6. A. Narasimha, S. Abdaila, C. Bradbury, A. Clark, J. Clymore, J. Coyne, A. Dahl, S. Gloeckner, A. Gruenberg, D. Guckenberger, S. Gutierrez, M. Harrison, D. Kucharski, K. Leap, R. LeBlanc, V. Liang, M. Mack, D. Martinez, G. Masini, A. Mekis, R. Menigoz, C. Ogden, M. Peterson, T. Pinguet, J. Redman, J. Rodriguez, S. Sahni, M. Sharp, T. Sleboda, D. Song, V. Wang, B. Welch, J. Witzens, W. Xu, K. Vokoyama, and P. DobbeIaere, “An ultra low power CMOS photonics technology platform for H/S optoelectronic transceivers at less than $1 per Gbps,” in Proc. OFC 2010, San Diego, USA (2010).

18

18. M. Watts, W. Zortman, D. Trotter, R. Young, and A. Lentine, “Low-voltage, compact, depletion-mode, silicon Mach–Zehnder modulator,” IEEE J. Sel. Top. Quantum Electron. 16(1), 159–164 (2010). [CrossRef]

]. In the modulator for chip-level optical interconnects, it is important to achieve high modulation efficiency up to high data rates with low optical loss while minimizing size for high energy efficiency. Intensive work has been done in this area in recent years. Silicon Mach–Zehnder (MZ) modulators and resonator-type modulators based on a PN junction in reverse bias modes have shown potential for wideband high-speed performance due to their faster modulations utilizing fast carrier depletion effects. Using vertical and lateral PN junctions, depletion-mode modulators with various efficiencies in high speed operation from 10 Gb/s up to 40 Gb/s have been reported [7

7. R. Soref and B. Bennett, “Electrooptical effects in silicon,” IEEE J. Quantum Electron. 23(1), 123–129 (1987). [CrossRef]

11

11. J. W. Park, J.-B. You, I. G. Kim, and G. Kim, “High-modulation efficiency silicon Mach-Zehnder optical modulator based on carrier depletion in a PN Diode,” Opt. Express 17(18), 15520–15524 (2009). [CrossRef] [PubMed]

, 14

14. N. N. Feng, S. Liao, D. Feng, P. Dong, D. Zheng, H. Liang, R. Shafiiha, G. Li, J. E. Cunningham, A. V. Krishnamoorthy, and M. Asghari, “High speed carrier-depletion modulators with 1.4V-cm V(π)L integrated on 0.25microm silicon-on-insulator waveguides,” Opt. Express 18(8), 7994–7999 (2010). [CrossRef] [PubMed]

18

18. M. Watts, W. Zortman, D. Trotter, R. Young, and A. Lentine, “Low-voltage, compact, depletion-mode, silicon Mach–Zehnder modulator,” IEEE J. Sel. Top. Quantum Electron. 16(1), 159–164 (2010). [CrossRef]

]. Most of the reported silicon MZ modulators require relatively high driving voltages greater than 6 to 7 Vpp to achieve efficient modulation depths. Low driving voltages below 1.2 Vpp potentially allow a modulator to be driven by monolithically integrated high-speed CMOS driving circuits, and also indicate low energy consumption. The Ge-on-Si photodetector, the key device for receiving optical data in a silicon chip, has also shown impressive progress in performance. Several Ge photodetectors have been reported for their large bandwidths and high responsivities. The reported waveguide-type Ge photodetectors [19

19. D. Ahn, C. Y. Hong, J. Liu, W. Giziewicz, M. Beals, L. C. Kimerling, J. Michel, J. Chen, and F. X. Kärtner, “High performance, waveguide integrated Ge photodetectors,” Opt. Express 15(7), 3916–3921 (2007). [CrossRef] [PubMed]

24

24. S. Liao, N. N. Feng, D. Feng, P. Dong, R. Shafiiha, C. C. Kung, H. Liang, W. Qian, Y. Liu, J. Fong, J. E. Cunningham, Y. Luo, and M. Asghari, “36 GHz submicron silicon waveguide germanium photodetector,” Opt. Express 19(11), 10967–10972 (2011). [CrossRef] [PubMed]

] and vertical-illumination type Ge photodetectors [25

25. M. Morse, O. Dosunmu, T. Yin, Y. Kang, H. D. Liu, G. Sarid, E. Ginsburg, R. Cohen, S. Litski, and M. Zadka, “Performance of Ge/Si receivers at 1310 nm,” Physica E 41(6), 1076–1081 (2009). [CrossRef]

30

30. J. Joo, S. Kim, I. Kim, K. Jang, and G. Kim, “Progress in high-responsivity vertical-illumination type Ge-on-Si photodetecor operating at λ ~1.55 μm,” in Proc. OFC 2011, Los Angeles, USA (2011).

] have achieved high performance comparable to conventional semiconductor photodetectors.

Simultaneous increases in the photonic integration level and the performance levels of the constituent devices are important. We previously reported a high-efficiency carrier-depletion PN-diode-based 12.5 Gb/s silicon MZ modulator [11

11. J. W. Park, J.-B. You, I. G. Kim, and G. Kim, “High-modulation efficiency silicon Mach-Zehnder optical modulator based on carrier depletion in a PN Diode,” Opt. Express 17(18), 15520–15524 (2009). [CrossRef] [PubMed]

] and a 12.5 Gb/s racetrack resonator-type silicon optical modulator [12

12. J.-B. You, M. Park, J.-W. Park, and G. Kim, “12.5 Gbps optical modulation of silicon racetrack resonator based on carrier-depletion in asymmetric p-n diode,” Opt. Express 16(22), 18340–18344 (2008). [CrossRef] [PubMed]

]. We also presented high-performance vertical-illumination-type Ge-on-Si photodetectors grown by reduced pressure chemical vapor deposition (RPCVD), and a 10 Gb/s Ge photoreceiver with −19.5 dBm sensitivity for a BER of 1 × 10−12 at λ~1550nm [28

28. D. Suh, S. Kim, J. Joo, and G. Kim, “36-GHz high-responsivity Ge photodetectors grown by RPCVD,” IEEE Photon. Technol. Lett. 21(10), 672–674 (2009). [CrossRef]

30

30. J. Joo, S. Kim, I. Kim, K. Jang, and G. Kim, “Progress in high-responsivity vertical-illumination type Ge-on-Si photodetecor operating at λ ~1.55 μm,” in Proc. OFC 2011, Los Angeles, USA (2011).

], which can readily replace conventional III-V compound semiconductor photodetectors. In this paper, we have investigated simultaneous increases in the silicon photonic integration level and the performance levels of constituent silicon photonic devices.

Silicon PICs for chip-level optical data I/Os (inputs/outputs), that is, off-chip (inter-chip) and on-chip (intra-chip) optical interconnections have been fabricated, into which both silicon MZ modulators (MZM) and Ge waveguide photodetectors (PDs) were monolithically integrated on a Si-on-insulator (SOI) wafer, using a fabrication process compatible with CMOS integration. The integrated modulators of the PICs were optimized in terms of speed, efficiency, driving voltage, and optical loss simultaneously. For the monolithic integration of the Ge PDs, a simplified fabrication process was performed based on selective expitaxy growth (SEG) using RPCVD with omitting chemical mechanical polishing (CMP) and doping for Ge. Also to further increase of the integration level to electronic-photonic IC (EPIC), we hybrid-integrated a silicon PIC chip with 0.13μm CMOS interface circuit chips, which include modulator-drivers, trans-impedance amplifiers (TIAs) and limiting amplifiers (LAs). In the followings, the design, fabrication, performance characterizations up to 30 Gb/s operation are described. The silicon photonic devices and CMOS circuits were designed and fabricated in array form in this work.

The two types of silicon PICs for the off-chip optical interconnect (PICoff-chip) and the on-chip optical interconnect (PICintra-chip) consist of carrier-depletion-type asymmetric MZ modulators for 8-channel photonic transmitter parts, evanescent-coupled waveguide-type Ge PD for 8-channel photonic receiver parts, and grating couplers (GCs) for optical I/O coupling of fiber with silicon waveguides, which were monolithically integrated on a 6-inch SOI wafer with a top Si thickness of 220nm and a buried oxide thickness of 1μm as shown in Fig. 1
Fig. 1 Top views of microscopy images of the fabricated monolithically-integrated silicon photonic IC (PIC) chips for (a) off-chip optical interconnect (PICoff-chip) and (b) on-chip optical interconnect (PICintra-chip). The TEM, SEM cross sectional images and schematic diagrams of (c) monolithically integrated silicon MZ modulator phase shifter, and (d) integrated Ge photodetector.
. Figure 1(a) shows top-view microphotographs of a fabricated 8.7mm×3.5mm PICoff-chip chip, and Fig. 1(b) shows a fabricated 6.3mm×3.5mm PICintra-chip chip. The integrated MZ modulators are shown in the top regions of the PICoff-chip and the PICintra-chip chip, and the integrated Ge PDs are shown in the bottom region of each chip. The modulator is defined on an asymmetric Mach-Zehnder interferometer (MZI) with 2x1 multi mode interferometers (MMIs) and lateral PN junction phase shifters embedded in both arms. The Ge PD is integrated onto an 8 μm-wide silicon waveguide. The PICoff-chip chip shown in Fig. 1(a) has three kinds of GCs for surface normal coupling to fibers. GC1 is for input coupling of the external CW laser light into the chip to feed the MZMs, and GC2 is for the modulated optical outputs transmitted off the chip. GC3 couples the externally modulated input signals into the chip to be delivered to the integrated Ge PDs. The performance of the integrated active components in the PICoff-chip, therefore, can be characterized individually. On the other hand, in the PICintra-chip for intra-chip optical interconnection, the integrated modulator and the Ge PD are directly connected by the waveguide on the same chip, and GC1 for input coupling of the external CW laser light into the chip is integrated in Fig. 1(b). The optical signal modulated across a MZ modulator is transmitted through the connecting waveguide, the width of which is tapered from 0.5μm to 8μm, to be directly detected by the monolithically integrated Ge PD in the PICintra-chip. High-resolution focused ion beam (FIB) transmission electron microscope (TEM) and scanning electron microscope (SEM) cross-sectional images and schematic views of the modulator phase shifter and the integrated Ge PD are shown in Fig. 1(c) and Fig. 1(d), respectively.

For the device characterization, continuous wave (CW) light from a tunable laser source was coupled to the GC on a chip through a polarization controller to feed a modulator, and the electrical signal from an external driver was connected to drive the modulator in a PIC. In the PICoff-chip chip, the optical signal modulated across an integrated MZM was transmitted off the chip through the output GC to fiber, and boosted using an erbium doped fiber amplifier (EDFA). This optical signal was measured by an Agilent 86100A Digital Communication Analyzer (DCA). Also the external optical input data signal was fed to the GC to be detected by the integrated Ge PD, and this detected electrical signal was measured by the Agilent DCA.

Figure 2
Fig. 2 Optical transmission spectra of the integrated asymmetric MZ modulator (MZM) with 1-mm-long phase shifter at biases from 0V to −9V, and (b) the voltage-induced phase shifts.
plots the measured transmission spectrum of the integrated modulator of the PICoff-chip as a function of the wavelength, which demonstrates high modulation efficiency. Figure 2(a) shows typical optical transmission spectra of the 1mm-phase-shifter MZM measured at various DC biases. Here, only one phase shifter arm is biased. An avalanche breakdown of the device occurs around −10 V. The black solid curve in Fig. 2(a) represents the transmission spectrum of the unbiased modulator. As is shown in the figure, total optical loss at the maximum of the transmission for a 1mm-phase-shifter MZM is measured to be ~22 dB at λ~1538.1 nm, which includes 1.7 dB/MMI loss, phase-shifter loss of 3.2 dB/mm, passive waveguide propagation loss of ~0.2 dB/mm, and ~7.5 dB loss for each grating coupler. Large coupling loss through grating couplers, which requires resolution of 315 nm, resulted from the I-line lithography limit greater than 350 nm. The free spectral range (FSR) of the integrated modulator is ~5.4 nm. The yellow solid curve represents transmission spectrum of the modulator biased at −6 V, which shows the wavelength shift, Δλ of ~1.0 nm. The voltage-induced wavelength shift, Δλ/ΔV, is measured to be ~0.17 nm/V. The voltage-induced phase shifts, Δϕ=2πΔλ/FSR for a 1 mm-phase-shifter MZM are shown in Fig. 2(b). The modulation efficiency, VπLπ, the applied voltage and length required to obtain Δϕ = π, was ~1.59 V·cm.

The high-speed performance of the integrated modulator was characterized by measuring the 3dB bandwidth and eye-diagrams at high transmission rates. The electrical speed of the modulator using a reverse biased PN junction is limited by capacitance. The measured capacitance of the modulator is < 840 fF near −3 VDC. The predicted RC-limit −3dB bandwidth, f-3dB = 1/(2πRC), of the modulator was ~22 GHz.

The frequency response measurement of the integrated modulator of a PICoff-chip was carried out using a 20GHz HP 8730A lightwave component analyzer (LCA). The high-speed electrical signal and DC bias voltage were applied to the modulator through a bias-tee and a 40 GHz RF probe. The modulated output signal was amplified using an EDFA, before it was fed into the LCA. The measured frequency responses of the 1mm-phase-shifter MZM with varying reverse bias on one phase-shifter arm are shown in Fig. 3(a)
Fig. 3 Frequency response of the MZ modulator shows the −3 dB bandwidth (f-3dB) of 15.0 GHz at −5 VDC bias and 14.3 GHz at −2 VDC bias for the wavelength of 1539.5nm.
. As shown in the graph, the measured bandwidth of a modulator is ~14.3 GHz at −2 VDC bias, and 15.0 GHz at −5 VDC bias. Here, a travelling-wave electrode was not adopted for the device. The discrepancy between the measured bandwidth and the RC-limit bandwidth of the device resulted from the un-optimized metal electrode.

On-wafer measurements of eye diagrams were performed at various bit rates from 12.5 Gb/s to 30 Gb/s for the integrated modulator in PICoff-chip. The non-return-to-zero (NRZ) pseudo-random bit sequence (PRBS) 231-1 signal of the Anritsu MP1758A pulse pattern generator (PPG) was combined with a DC bias using a bias-tee, and applied to the modulator. The modulator was driven differentially with RF signals from 1.2 Vpp to 2.5 Vpp. The input CW beam from a tunable laser was passed through a polarization controller and coupled to GC1 of Fig. 1(a) to feed the modulator. Due to the large GC coupling loss, relatively high optical input power was required in the measurement. The modulated output signal from the PICoff-chip chip was coupled to fiber probe aligned with GC3. EDFA was used to boost the modulated output signal, and a tunable wavelength filter was used before light signal was detected with a Discovery DSC1OH 43GHz photodiode and the Agilent DCA with an 8611A 70 GHz remote sampling module.

Figure 5
Fig. 5 High-speed operations of an integrated 1 mm-phase-shifter MZM driven in differential mode of 1.2 Vpp for 20Gb/s and 30Gb/s modulations for λ~1541.2 nm in the PICoff-chip. Measured ERs are 9.1 dB at −3VDC for 20Gb/s modulation, and 7.2 dB at −4 VDC for 30Gb/s modulation.
shows measured eye-diagrams of the integrated 1 mm-phase-shifter MZM of the PICoff-chip driven differentially with 1.2 Vpp swing using 20 Gb/s and 30 Gb/s PRBS signal for λ~1541.2 nm. As seen in the figure, the measured eye diagrams exhibit good eye openings up to 30 Gb/s operations. The measured ER is 9.1 dB at 20 Gb/s data transmission with −3 VDC bias, and 7.2 dB at 30 Gb/s data transmission with −4 VDC bias.

The higher driving voltage of 2.5 Vpp resulted in larger extinction ratios. Figure 6
Fig. 6 On-wafer measurements of a monolithic-integrated 1 mm-phase-shifter MZM driven in differential mode of 2.5 Vpp for 20 Gb/s and 30 Gb/s operation, show ~12.6dB ER at 20Gb/s, ~9.4dB ER at 30Gb/s, with −5VDC bias in the PICoff-chip.
exhibits the performance of the integrated 1 mm-phase-shifter MZM of the PICoff-chip for 2.5Vpp drive with −5 VDC bias. The measured ERs are 12.68 dB and 9.41 dB for 20 Gb/s and 30 Gb/s operation, respectively. Here, the measured additional optical losses at the ‘1’ level of the signal compared to the maximum optical transmission are 1.4dB and 1.9dB for 20 Gb/s and 30 Gb/s operation, respectively. Also, the same modulator at 12.5 Gb/s operation exhibits a high ER of 13.45 dB for 2.5Vpp drive.

For characterization of the 6×23μm2 Ge PIN waveguide photodetector integrated on the silicon waveguide in a PICoff-chip, the external light data signal was delivered to the PD through GC3 of Fig. 1(a) coupled to an optical fiber probe. The device exhibited low dark current under 700 nA at 1 V reverse bias. The frequency response was measured by impulse response measurement with a Pritel femtosecond pulse laser and the Agilent DCA with an 8611A 70 GHz remote sampling module. Figure 7(a)
Fig. 7 (a) On-wafer measurement for the frequency response of integrated 6 × 23μm2 Ge-PIN waveguide photodetector, which shows −3dB bandwidth (f-3dB) greater than 27 GHz at −3V. (b) The eye-diagram measured at (b) 20 Gb/s and (c) 30 Gb/s operations at −3V bias.
shows the normalized frequency response of a Ge PD. As shown in the figure, the measured −3dB bandwidths are 23.5 GHz at −1V bias and 27 GHz at −3 V bias. Figures 7(b) and 7(c) exhibit good eye-diagrams of the Ge PD at 20 Gb/s and 30 Gb/s operation at −3V bias for λ~1550 nm. The measured responsivity was ~0.3 A/W. This value is lower than expected. The Ge PD on 220nm SOI showed lower responsivity than the measured ~1 A/W responsivity of the same PD integrated on 450nm SOI. This reflects that Ge SEG process on the over-etched thin top silicon in SOI can affect the quality of the Ge epilayer in the bottom region, and this is under investigation. This suggests room for further optimization of the SEG process on the thin top Si layer of a SOI in RPCVD.

As are shown in the above, both integrated modulators and Ge photodetectors of the PICoff-chip have demonstrates 30 Gb/s operations in data transmitting and receiving separately. The modulators showed improved characteristics of high modulation depth at high-speed operations with low-voltage driving voltages, and the integrated photodetectors exhibited high-speed performance with low dark current.

In the measurements of the PICintra-chip, where intra-chip photonic interconnect could be investigated, higher optical input power was required than in PICoff-chip case. The CW light from a tunable laser was amplified by an EDFA and was coupled into the grating coupler through an optical filter and a polarization controller to feed the integrated MZM. Also, the PRBS electrical input signal was applied to drive the modulator. The optical signal modulated by the MZM transmits through the connecting silicon waveguide to be detected and converted into the electrical output signal by the monolithically integrated Ge PD in the same chip. The electrical output signal reflecting on-chip optical data interconnection was measured by the DCA with an 86105C 20 GHz electrical module.

Figure 8(a)
Fig. 8 The detected photocurrent curves for the optical transmission spectra of a integrated modulator by the monolithically integrated PD in the PICintra-chip. The modulator is biased from 0V to −9V, and the PD is biased −3V.
shows the measured photocurrent curves corresponding to the typical optical transmission spectra through an integrated 1 mm-phase-shifter MZM, detected by the monolithically integrated Ge PD in a PICintra-chip chip. Here, the modulator was biased from 0V to −10V, and the detecting PD was biased at −1V. The measured FSR of the integrated modulator is ~5.6 nm in the figure. The black solid curve is the transmission spectrum through the unbiased modulator, and the violet solid curve is the measured photocurrent curve for the transmission spectrum through the modulator biased at −9 V, which shows the wavelength shift, Δλ ~1.4 nm. The voltage-induced wavelength shift, Δλ/ΔV was measured to be ~0.157 nm/V. Figure 8(b) shows the voltage-induced phase shifts as a function of the modulator bias voltage. Although the same modulators as those used in the PICoff-chip were integrated, the modulation efficiency in the PICintra-chip were measured to the larger value of VπLπ ~1.78 V·cm.

Figure 9
Fig. 9 On-wafer measurements of optical eye-diagrams for 12.5Gb/s, 15 Gb/s and 20 Gb/s on-chip optical interconnect signals in the monolithic integrated PICintra-chip, with 2.5Vpp at the wavelength λ = 1542.7 nm.
shows on-wafer measurements of optical eye diagrams in the PICintra-chip, where on-chip data transmissions of 12.5 Gb/s up to 20 Gb/s occur from the integrated 1 mm-phase-shifter MZM to the monolithically integrated Ge PD at λ~1542.7 nm. The NRZ PRBS signal from the Anritsu PPG was applied to the MZM. Here, the modulator was driven with a 2.5 Vpp signal at −5VDC bias and the PD was biased at −3V. This measured eye patterns were raw signals detected by the integrated Ge PD without any preamplifier ICs involved.

Although the same devices were integrated, the performance showed degradation compared with that of the 30 Gb/s PICoff-chip case, resulting from the high input optical power. The background heat in the chip and the ASE noise of EDFA limit the performance of both integrated devices. Further improvement in the coupling efficiency of the grating coupler andthe responsivity of the integrated PD with the use of a smaller MZ modulator with high modulation efficiency can reduce the burden of high input power and result in improved on-chip transmission characteristics in the PICintra-chip chip.

To further increase the integration level to the electronic-photonic IC, we hybrid-integrated a silicon PICintra-chip chip with 0.13μm CMOS interface circuit chips. Figure 10(a)
Fig. 10 (a) Silicon EPIC on a test PCB, where a silicon PICintra-chip chip is hybrid-integrated with 0.13μm CMOS VLSI chips. Top chip is a CMOS modulator-driver IC, the middle chip is a silicon PICintra-chip chip, and the bottom chip is a TIA-LA CMOS IC chip. Test setup for hybrid silicon EPIC characterization is shown in the inset. (b) The measured electrical eye of CMOS ICs at 7 Gb/s and 10 Gb/s operations. (c) Eye diagrams of the hybrid silicon EPIC at 5 Gbps, 8 Gbps, and 10 Gbps measured with 1.3 Vpp PRBS signal. Here, on-chip EPIC characteristics are limited by the 0.13μm CMOS interface circuits.
shows photographic images of the hybrid silicon EPIC. The test setup for EPIC characterization is shown in the inset. The EPIC assembly is die-attached and wire-bonded on a test PCB, and a fiber is aligned with the grating coupler for optical input. In the figure, the top chip is a CMOS modulator-driver IC, the middle chip is a silicon PICintra-chip chip and the bottom chip is a CMOS TIA-LA IC chip. The CMOS modulator-driver IC is the cascode voltage-mode driver designed for high voltage swings up to 3Vpp with a measured bandwidth of 5 GHz. The TIA is designed based on an RGC feedback loop with two coupled shunt series peaking inductors [36

36. K. Park, B. Yoo, M. Hwang, H. Chi, H. Kim, J. Park, G. Kim, and D. Jeong, “A 10-Gb/s optical receiver front-end with 5-mW transimpedance amplifier,” IEEE Asian Solid-State Circuits Conference, Beijing, 3–5 (2010).

]. The measured bandwidth of the TIA in the chip is 7.9 GHz. The limiting amplifier is designed to have 6 gain stages with an offset compensator. The buffer and output driver IC are also included in the TIA-LA IC chip. Figure 10(b) shows the electrical performance of the modulator-driver IC and the TIA-LA IC measured at 7 Gb/s and 10 Gb/s operation. The size of the 8-channel CMOS modulator-driver chip is 4.3mm × 1.5mm, and the chip size of 8-channel CMOS TIA and LA is 4.2mm × 1.8mm. Figure 10(c) shows the measured “eye” diagram of the hybrid silicon EPIC for on-chip optical interconnection for 5, 8, 10 Gbps operation with VRF = 1.3 Vpp. As seen in the figure, the performance of the EPIC is limited by the performance of the 0.13μm CMOS interface circuits. Upgrading in CMOS interface ICs with a lower driving voltage design can improve the performance of silicon EPICs. With continued improvements in CMOS interface ICs and silicon photonic devices, we expect to develop even more efficient silicon PICs and EPICs leading to high performance interconnections for future inter/intra-chip applications.

In conclusion, we presented the performance of silicon photonic integrated circuits for off-chip optical interconnects (PICoff-chip), where monolithically integrated PN depletion-mode MZ modulators and evanescent-coupled Ge waveguide PD on a SOI wafer demonstrated data transmissions up to 30 Gb/s. For the low-voltage drive of 1.2 Vpp, the integrated 1mm-phase-shifter modulator of the PICoff-chip demonstrated a phase shift efficiency of VπLπ ~1.59 V/cm with 10.5dB ER for 12.5 Gb/s modulation, 9.1dB ER for 20 Gb/s modulation and 7.2dB ER for 30 Gb/s modulation. The integrated Ge waveguide PD grown by RPCVD showed good eye diagram for 30 Gb/s operations with low dark current levels. Also, the silicon PIC for intra-chip optical interconnect (PICintra-chip), where the light signal modulated by the integrated modulator is detected by the monolithically integrated Ge PD in the same chip, exhibited on-chip optical interconnection up to 20 Gb/s. We also presented the silicon EPIC, where a silicon PICintra-chip chip and 0.13μm CMOS interface circuit chips for modulator- driver and preamplifier IC were hybrid-integrated. Based on our results, further optimizations in the smaller MZ modulator with high efficiency and the integrated PD, and improvement in CMOS interface ICs can lead to more efficient silicon PICs and EPICs for future inter/intra-chip interconnect applications.

References and links

1.

M. Haurylau, G. Chen, H. Chen, J. Zhang, N. A. Nelson, D. H. Albonesi, E. G. Friedman, and P. M. Fauchet, “On-chip optical interconnect roadmap: challenges and critical directions,” IEEE J. Sel. Top. Quantum Electron. 12(6), 1699–1705 (2006). [CrossRef]

2.

C. Gunn, “CMOS photonics for high-speed interconnects,” IEEE. Micro. 26(2), 58–66 (2006). [CrossRef]

3.

A. Shacham, K. Bergman, and L. P. Carloni, “Photonic networks-on-chip for future generations of chip multiprocessors,” IEEE Trans. Comput. 57(9), 1246–1260 (2008). [CrossRef]

4.

D. Miller, “Device requirements for optical interconnects to silicon chips,” Proc. IEEE 97(7), 1166–1185 (2009). [CrossRef]

5.

K. Preston, L. Chen, S. Manipatruni, and M. Lipson, “Silicon photonic interconnect with micrometer-scale devices,” 6th International Conference on Group IV Photonics, WA2, 1–3 (2009).

6.

A. Narasimha, S. Abdaila, C. Bradbury, A. Clark, J. Clymore, J. Coyne, A. Dahl, S. Gloeckner, A. Gruenberg, D. Guckenberger, S. Gutierrez, M. Harrison, D. Kucharski, K. Leap, R. LeBlanc, V. Liang, M. Mack, D. Martinez, G. Masini, A. Mekis, R. Menigoz, C. Ogden, M. Peterson, T. Pinguet, J. Redman, J. Rodriguez, S. Sahni, M. Sharp, T. Sleboda, D. Song, V. Wang, B. Welch, J. Witzens, W. Xu, K. Vokoyama, and P. DobbeIaere, “An ultra low power CMOS photonics technology platform for H/S optoelectronic transceivers at less than $1 per Gbps,” in Proc. OFC 2010, San Diego, USA (2010).

7.

R. Soref and B. Bennett, “Electrooptical effects in silicon,” IEEE J. Quantum Electron. 23(1), 123–129 (1987). [CrossRef]

8.

L. Liao, A. Liu, D. Rubin, J. Basak, Y. Chetrit, H. Nguyen, R. Cohen, N. Izhaky, M. Paniccia, N. Izhaky, and M. Paniccia, “40Gbit/s silicon optical modulator high-speed applications,” Electron. Lett. 43(22), 1196–1197 (2007). [CrossRef]

9.

A. Liu, L. Liao, D. Rubin, H. Nguyen, B. Ciftcioglu, Y. Chetrit, N. Izhaky, and M. Paniccia, “High-speed optical modulation based on carrier depletion in a silicon waveguide,” Opt. Express 15(2), 660–668 (2007). [CrossRef] [PubMed]

10.

W. M. Green, M. J. Rooks, L. Sekaric, and Y. A. Vlasov, “Ultra-compact, low RF power, 10 Gb/s silicon Mach-Zehnder modulator,” Opt. Express 15(25), 17106–17113 (2007). [CrossRef] [PubMed]

11.

J. W. Park, J.-B. You, I. G. Kim, and G. Kim, “High-modulation efficiency silicon Mach-Zehnder optical modulator based on carrier depletion in a PN Diode,” Opt. Express 17(18), 15520–15524 (2009). [CrossRef] [PubMed]

12.

J.-B. You, M. Park, J.-W. Park, and G. Kim, “12.5 Gbps optical modulation of silicon racetrack resonator based on carrier-depletion in asymmetric p-n diode,” Opt. Express 16(22), 18340–18344 (2008). [CrossRef] [PubMed]

13.

P. Dong, S. Liao, D. Feng, H. Liang, D. Zheng, R. Shafiiha, C.-C. Kung, W. Qian, G. Li, X. Zheng, A. V. Krishnamoorthy, and M. Asghari, “Low Vpp, ultralow-energy, compact, high-speed silicon electro-optic modulator,” Opt. Express 17(25), 22484–22490 (2009). [CrossRef] [PubMed]

14.

N. N. Feng, S. Liao, D. Feng, P. Dong, D. Zheng, H. Liang, R. Shafiiha, G. Li, J. E. Cunningham, A. V. Krishnamoorthy, and M. Asghari, “High speed carrier-depletion modulators with 1.4V-cm V(π)L integrated on 0.25microm silicon-on-insulator waveguides,” Opt. Express 18(8), 7994–7999 (2010). [CrossRef] [PubMed]

15.

F. Y. Gardes, D. J. Thomson, N. G. Emerson, and G. T. Reed, “40 Gb/s silicon photonics modulator for TE and TM polarizations,” Opt. Express 19(12), 11804–11814 (2011). [CrossRef]

16.

D. J. Thomson, F. Y. Gardes, Y. Hu, G. Mashanovich, M. Fournier, P. Grosse, J.-M. Fedeli, and G. T. Reed, “High contrast 40Gbit/s optical modulation in silicon,” Opt. Express 19(12), 11507–11516 (2011). [CrossRef] [PubMed]

17.

G. Rasigade, M. Ziebell, D. Marris-Morini, J.-M. Fédéli, F. Milesi, P. Grosse, D. Bouville, E. Cassan, and L. Vivien, “High extinction ratio 10 Gbit/s silicon optical modulator,” Opt. Express 19(7), 5827–5832 (2011). [CrossRef] [PubMed]

18.

M. Watts, W. Zortman, D. Trotter, R. Young, and A. Lentine, “Low-voltage, compact, depletion-mode, silicon Mach–Zehnder modulator,” IEEE J. Sel. Top. Quantum Electron. 16(1), 159–164 (2010). [CrossRef]

19.

D. Ahn, C. Y. Hong, J. Liu, W. Giziewicz, M. Beals, L. C. Kimerling, J. Michel, J. Chen, and F. X. Kärtner, “High performance, waveguide integrated Ge photodetectors,” Opt. Express 15(7), 3916–3921 (2007). [CrossRef] [PubMed]

20.

L. Vivien, J. Osmond, J. M. Fédéli, D. Marris-Morini, P. Crozat, J. F. Damlencourt, E. Cassan, Y. Lecunff, and S. Laval, “42 GHz p.i.n Germanium photodetector integrated in a silicon-on-insulator waveguide,” Opt. Express 17(8), 6252–6257 (2009). [CrossRef] [PubMed]

21.

D. Feng, S. Liao, P. Dong, N. Feng, H. Liang, D. Zheng, C. Kung, J. Fong, R. Shafiiha, J. Cunningham, A. V. Krishnamoorthy, and M. Asghari, “High-speed Ge photodetector monolithically integrated with large cross-section silicon-on-insulator waveguide,” Appl. Phys. Lett. 95(26), 261105 (2009). [CrossRef]

22.

H. Yu, S. Ren, W. Jung, A. Okyay, D. Miller, and K. Saraswat, “High-efficiency p-i-n photodetectors on selective-area-grown Ge for monolithic integration,” IEEE Electron Device Lett. 30(11), 1161–1163 (2009). [CrossRef]

23.

S. Assefa, F. Xia, and Y. A. Vlasov, “Reinventing germanium avalanche photodetector for nanophotonic on-chip optical interconnects,” Nature 464(7285), 80–84 (2010). [CrossRef] [PubMed]

24.

S. Liao, N. N. Feng, D. Feng, P. Dong, R. Shafiiha, C. C. Kung, H. Liang, W. Qian, Y. Liu, J. Fong, J. E. Cunningham, Y. Luo, and M. Asghari, “36 GHz submicron silicon waveguide germanium photodetector,” Opt. Express 19(11), 10967–10972 (2011). [CrossRef] [PubMed]

25.

M. Morse, O. Dosunmu, T. Yin, Y. Kang, H. D. Liu, G. Sarid, E. Ginsburg, R. Cohen, S. Litski, and M. Zadka, “Performance of Ge/Si receivers at 1310 nm,” Physica E 41(6), 1076–1081 (2009). [CrossRef]

26.

Y. Kang, H.-D. Liu, M. Morse, M. J. Paniccia, M. Zadka, S. Litski, G. Sarid, A. Pauchard, Y.-H. Kuo, H.-W. Chen, W. S. Zaoui, J. E. Bowers, A. Beling, D. C. McIntosh, X. Zheng, and J. C. Campbell, “Monolithic germanium/silicon avalanche photodiodes with 340 GHz gain–bandwidth product,” Nature Photon. 3, 59–63 (2009).

27.

M. Jutzi, M. Berroth, G. Wöhl, M. Oehme, and E. Kasper, “Ge-on-Si vertical incidence photodiodes with 39-GHz bandwidth,” IEEE Photon. Technol. Lett. 17(7), 1510–1512 (2005). [CrossRef]

28.

D. Suh, S. Kim, J. Joo, and G. Kim, “36-GHz high-responsivity Ge photodetectors grown by RPCVD,” IEEE Photon. Technol. Lett. 21(10), 672–674 (2009). [CrossRef]

29.

J. Joo, S. Kim, I. Kim, K. Jang, and G. Kim, “High- sensitivity 10 Gbps Ge-on- Si photoreceiver operating at λ ~ 1.55 µm ,” Opt. Express 18, 16474–16479 (2010). [CrossRef] [PubMed]

30.

J. Joo, S. Kim, I. Kim, K. Jang, and G. Kim, “Progress in high-responsivity vertical-illumination type Ge-on-Si photodetecor operating at λ ~1.55 μm,” in Proc. OFC 2011, Los Angeles, USA (2011).

31.

T. Pinguet, B. Analui, E. Balmater, D. Guckenberger, M. Harrison, R. Koumans, D. Kucharski, Y. Liang, G. Masini, A. Mekis, S. Mirsaidi, A. Narasimha, M. Peterson, D. Rines, V. Sadagopan, S. Sahni, T. J. Sleboda, D. Song, Y. Wang, B. Welch, J. Witzens, J. Yao, S. Abdalla, S. Gloeckner, P. De Dobbelaere, and G. Capellini, “Monolithically Integrated High-Speed CMOS Photonic Transceivers,” in Proc. IEEE Int. Conf. Group IV Photonics, 362–364 (2008).

32.

X. Zheng, F. Liu, D. Patil, H. Thacker, Y. Luo, T. Pinguet, A. Mekis, J. Yao, G. Li, J. Shi, K. Raj, J. Lexau, E. Alon, R. Ho, J. E. Cunningham, and A. V. Krishnamoorthy, “A sub-picojoule-per-bit CMOS photonic receiver for densely integrated systems,” Opt. Express 18(1), 204–211 (2010). [CrossRef] [PubMed]

33.

T. Y. Liow, K. W. Ang, Q. Fang, J. F. Song, Y. Z. Xiong, M. B. Yu, G. Q. Lo, and D. L. Kwong, “Silicon modulators and germanium photodetectors on SOI: Monolithic integration, compatibility, and performance optimization,” IEEE Sel. Top. Quantum Electron. 16(1), 307–315 (2010). [CrossRef]

34.

M. Rasras, D. Gill, M. Earnshaw, C. Doerr, J. Weiner, C. Bolle, and Y. Chen, “CMOS silicon receiver integrated with Ge detector and reconfigurable optical filter,” IEEE Photon. Technol. Lett. 22(2), 112–114 (2010). [CrossRef]

35.

X. Zheng, D. Patil, J. Lexau, F. Liu, G. Li, H. Thacker, Y. Luo, I. Shubin, J. Li, J. Yao, P. Dong, D. Feng, M. Asghari, T. Pinguet, A. Mekis, P. Amberg, M. Dayringer, J. Gainsley, H. F. Moghadam, E. Alon, K. Raj, R. Ho, J. E. Cunningham, and A. V. Krishnamoorthy, “Ultra-efficient 10 Gb/s hybrid integrated silicon photonic transmitter and receiver,” Opt. Express 19(6), 5172–5186 (2011). [CrossRef] [PubMed]

36.

K. Park, B. Yoo, M. Hwang, H. Chi, H. Kim, J. Park, G. Kim, and D. Jeong, “A 10-Gb/s optical receiver front-end with 5-mW transimpedance amplifier,” IEEE Asian Solid-State Circuits Conference, Beijing, 3–5 (2010).

OCIS Codes
(040.5160) Detectors : Photodetectors
(040.6040) Detectors : Silicon
(060.4510) Fiber optics and optical communications : Optical communications
(130.0250) Integrated optics : Optoelectronics
(130.3120) Integrated optics : Integrated optics devices
(200.4650) Optics in computing : Optical interconnects
(250.5300) Optoelectronics : Photonic integrated circuits
(250.7360) Optoelectronics : Waveguide modulators
(130.4110) Integrated optics : Modulators

ToC Category:
Integrated Optics

History
Original Manuscript: October 19, 2011
Revised Manuscript: November 30, 2011
Manuscript Accepted: December 8, 2011
Published: December 16, 2011

Citation
Gyungock Kim, Jeong Woo Park, In Gyoo Kim, Sanghoon Kim, Sanggi Kim, Jong Moo Lee, Gun Sik Park, Jiho Joo, Ki-Seok Jang, Jin Hyuk Oh, Sun Ae Kim, Jong Hoon Kim, Jun Young Lee, Jong Moon Park, Do-Won Kim, Deog-Kyoon Jeong, Moon-Sang Hwang, Jeong-Kyoum Kim, Kyu-Sang Park, Han-Kyu Chi, Hyun-Chang Kim, Dong-Wook Kim, and Mu Hee Cho, "Low-voltage high-performance silicon photonic devices and photonic integrated circuits operating up to 30 Gb/s," Opt. Express 19, 26936-26947 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-27-26936


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References

  1. M. Haurylau, G. Chen, H. Chen, J. Zhang, N. A. Nelson, D. H. Albonesi, E. G. Friedman, and P. M. Fauchet, “On-chip optical interconnect roadmap: challenges and critical directions,” IEEE J. Sel. Top. Quantum Electron.12(6), 1699–1705 (2006). [CrossRef]
  2. C. Gunn, “CMOS photonics for high-speed interconnects,” IEEE. Micro.26(2), 58–66 (2006). [CrossRef]
  3. A. Shacham, K. Bergman, and L. P. Carloni, “Photonic networks-on-chip for future generations of chip multiprocessors,” IEEE Trans. Comput.57(9), 1246–1260 (2008). [CrossRef]
  4. D. Miller, “Device requirements for optical interconnects to silicon chips,” Proc. IEEE97(7), 1166–1185 (2009). [CrossRef]
  5. K. Preston, L. Chen, S. Manipatruni, and M. Lipson, “Silicon photonic interconnect with micrometer-scale devices,” 6th International Conference on Group IV Photonics, WA2, 1–3 (2009).
  6. A. Narasimha, S. Abdaila, C. Bradbury, A. Clark, J. Clymore, J. Coyne, A. Dahl, S. Gloeckner, A. Gruenberg, D. Guckenberger, S. Gutierrez, M. Harrison, D. Kucharski, K. Leap, R. LeBlanc, V. Liang, M. Mack, D. Martinez, G. Masini, A. Mekis, R. Menigoz, C. Ogden, M. Peterson, T. Pinguet, J. Redman, J. Rodriguez, S. Sahni, M. Sharp, T. Sleboda, D. Song, V. Wang, B. Welch, J. Witzens, W. Xu, K. Vokoyama, and P. DobbeIaere, “An ultra low power CMOS photonics technology platform for H/S optoelectronic transceivers at less than $1 per Gbps,” in Proc. OFC 2010, San Diego, USA (2010).
  7. R. Soref and B. Bennett, “Electrooptical effects in silicon,” IEEE J. Quantum Electron.23(1), 123–129 (1987). [CrossRef]
  8. L. Liao, A. Liu, D. Rubin, J. Basak, Y. Chetrit, H. Nguyen, R. Cohen, N. Izhaky, M. Paniccia, N. Izhaky, and M. Paniccia, “40Gbit/s silicon optical modulator high-speed applications,” Electron. Lett.43(22), 1196–1197 (2007). [CrossRef]
  9. A. Liu, L. Liao, D. Rubin, H. Nguyen, B. Ciftcioglu, Y. Chetrit, N. Izhaky, and M. Paniccia, “High-speed optical modulation based on carrier depletion in a silicon waveguide,” Opt. Express15(2), 660–668 (2007). [CrossRef] [PubMed]
  10. W. M. Green, M. J. Rooks, L. Sekaric, and Y. A. Vlasov, “Ultra-compact, low RF power, 10 Gb/s silicon Mach-Zehnder modulator,” Opt. Express15(25), 17106–17113 (2007). [CrossRef] [PubMed]
  11. J. W. Park, J.-B. You, I. G. Kim, and G. Kim, “High-modulation efficiency silicon Mach-Zehnder optical modulator based on carrier depletion in a PN Diode,” Opt. Express17(18), 15520–15524 (2009). [CrossRef] [PubMed]
  12. J.-B. You, M. Park, J.-W. Park, and G. Kim, “12.5 Gbps optical modulation of silicon racetrack resonator based on carrier-depletion in asymmetric p-n diode,” Opt. Express16(22), 18340–18344 (2008). [CrossRef] [PubMed]
  13. P. Dong, S. Liao, D. Feng, H. Liang, D. Zheng, R. Shafiiha, C.-C. Kung, W. Qian, G. Li, X. Zheng, A. V. Krishnamoorthy, and M. Asghari, “Low Vpp, ultralow-energy, compact, high-speed silicon electro-optic modulator,” Opt. Express17(25), 22484–22490 (2009). [CrossRef] [PubMed]
  14. N. N. Feng, S. Liao, D. Feng, P. Dong, D. Zheng, H. Liang, R. Shafiiha, G. Li, J. E. Cunningham, A. V. Krishnamoorthy, and M. Asghari, “High speed carrier-depletion modulators with 1.4V-cm V(π)L integrated on 0.25microm silicon-on-insulator waveguides,” Opt. Express18(8), 7994–7999 (2010). [CrossRef] [PubMed]
  15. F. Y. Gardes, D. J. Thomson, N. G. Emerson, and G. T. Reed, “40 Gb/s silicon photonics modulator for TE and TM polarizations,” Opt. Express19(12), 11804–11814 (2011). [CrossRef]
  16. D. J. Thomson, F. Y. Gardes, Y. Hu, G. Mashanovich, M. Fournier, P. Grosse, J.-M. Fedeli, and G. T. Reed, “High contrast 40Gbit/s optical modulation in silicon,” Opt. Express19(12), 11507–11516 (2011). [CrossRef] [PubMed]
  17. G. Rasigade, M. Ziebell, D. Marris-Morini, J.-M. Fédéli, F. Milesi, P. Grosse, D. Bouville, E. Cassan, and L. Vivien, “High extinction ratio 10 Gbit/s silicon optical modulator,” Opt. Express19(7), 5827–5832 (2011). [CrossRef] [PubMed]
  18. M. Watts, W. Zortman, D. Trotter, R. Young, and A. Lentine, “Low-voltage, compact, depletion-mode, silicon Mach–Zehnder modulator,” IEEE J. Sel. Top. Quantum Electron.16(1), 159–164 (2010). [CrossRef]
  19. D. Ahn, C. Y. Hong, J. Liu, W. Giziewicz, M. Beals, L. C. Kimerling, J. Michel, J. Chen, and F. X. Kärtner, “High performance, waveguide integrated Ge photodetectors,” Opt. Express15(7), 3916–3921 (2007). [CrossRef] [PubMed]
  20. L. Vivien, J. Osmond, J. M. Fédéli, D. Marris-Morini, P. Crozat, J. F. Damlencourt, E. Cassan, Y. Lecunff, and S. Laval, “42 GHz p.i.n Germanium photodetector integrated in a silicon-on-insulator waveguide,” Opt. Express17(8), 6252–6257 (2009). [CrossRef] [PubMed]
  21. D. Feng, S. Liao, P. Dong, N. Feng, H. Liang, D. Zheng, C. Kung, J. Fong, R. Shafiiha, J. Cunningham, A. V. Krishnamoorthy, and M. Asghari, “High-speed Ge photodetector monolithically integrated with large cross-section silicon-on-insulator waveguide,” Appl. Phys. Lett.95(26), 261105 (2009). [CrossRef]
  22. H. Yu, S. Ren, W. Jung, A. Okyay, D. Miller, and K. Saraswat, “High-efficiency p-i-n photodetectors on selective-area-grown Ge for monolithic integration,” IEEE Electron Device Lett.30(11), 1161–1163 (2009). [CrossRef]
  23. S. Assefa, F. Xia, and Y. A. Vlasov, “Reinventing germanium avalanche photodetector for nanophotonic on-chip optical interconnects,” Nature464(7285), 80–84 (2010). [CrossRef] [PubMed]
  24. S. Liao, N. N. Feng, D. Feng, P. Dong, R. Shafiiha, C. C. Kung, H. Liang, W. Qian, Y. Liu, J. Fong, J. E. Cunningham, Y. Luo, and M. Asghari, “36 GHz submicron silicon waveguide germanium photodetector,” Opt. Express19(11), 10967–10972 (2011). [CrossRef] [PubMed]
  25. M. Morse, O. Dosunmu, T. Yin, Y. Kang, H. D. Liu, G. Sarid, E. Ginsburg, R. Cohen, S. Litski, and M. Zadka, “Performance of Ge/Si receivers at 1310 nm,” Physica E41(6), 1076–1081 (2009). [CrossRef]
  26. Y. Kang, H.-D. Liu, M. Morse, M. J. Paniccia, M. Zadka, S. Litski, G. Sarid, A. Pauchard, Y.-H. Kuo, H.-W. Chen, W. S. Zaoui, J. E. Bowers, A. Beling, D. C. McIntosh, X. Zheng, and J. C. Campbell, “Monolithic germanium/silicon avalanche photodiodes with 340 GHz gain–bandwidth product,” Nature Photon.3, 59–63 (2009).
  27. M. Jutzi, M. Berroth, G. Wöhl, M. Oehme, and E. Kasper, “Ge-on-Si vertical incidence photodiodes with 39-GHz bandwidth,” IEEE Photon. Technol. Lett.17(7), 1510–1512 (2005). [CrossRef]
  28. D. Suh, S. Kim, J. Joo, and G. Kim, “36-GHz high-responsivity Ge photodetectors grown by RPCVD,” IEEE Photon. Technol. Lett.21(10), 672–674 (2009). [CrossRef]
  29. J. Joo, S. Kim, I. Kim, K. Jang, and G. Kim, “High- sensitivity 10 Gbps Ge-on- Si photoreceiver operating at λ ~ 1.55 µm ,” Opt. Express18, 16474–16479 (2010). [CrossRef] [PubMed]
  30. J. Joo, S. Kim, I. Kim, K. Jang, and G. Kim, “Progress in high-responsivity vertical-illumination type Ge-on-Si photodetecor operating at λ ~1.55 μm,” in Proc. OFC 2011, Los Angeles, USA (2011).
  31. T. Pinguet, B. Analui, E. Balmater, D. Guckenberger, M. Harrison, R. Koumans, D. Kucharski, Y. Liang, G. Masini, A. Mekis, S. Mirsaidi, A. Narasimha, M. Peterson, D. Rines, V. Sadagopan, S. Sahni, T. J. Sleboda, D. Song, Y. Wang, B. Welch, J. Witzens, J. Yao, S. Abdalla, S. Gloeckner, P. De Dobbelaere, and G. Capellini, “Monolithically Integrated High-Speed CMOS Photonic Transceivers,” in Proc. IEEE Int. Conf. Group IV Photonics, 362–364 (2008).
  32. X. Zheng, F. Liu, D. Patil, H. Thacker, Y. Luo, T. Pinguet, A. Mekis, J. Yao, G. Li, J. Shi, K. Raj, J. Lexau, E. Alon, R. Ho, J. E. Cunningham, and A. V. Krishnamoorthy, “A sub-picojoule-per-bit CMOS photonic receiver for densely integrated systems,” Opt. Express18(1), 204–211 (2010). [CrossRef] [PubMed]
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