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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 8 — Apr. 11, 2011
  • pp: 7062–7067
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30GHz Ge electro-absorption modulator integrated with 3μm silicon-on-insulator waveguide

Ning-Ning Feng, Dazeng Feng, Shirong Liao, Xin Wang, Po Dong, Hong Liang, Cheng-Chih Kung, Wei Qian, Joan Fong, Roshanak Shafiiha, Ying Luo, Jack Cunningham, Ashok V. Krishnamoorthy, and Mehdi Asghari  »View Author Affiliations


Optics Express, Vol. 19, Issue 8, pp. 7062-7067 (2011)
http://dx.doi.org/10.1364/OE.19.007062


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Abstract

We demonstrate a compact waveguide-based high-speed Ge electro-absorption (EA) modulator integrated with a single mode 3µm silicon-on-isolator (SOI) waveguide. The Ge EA modulator is based on a horizontally-oriented p-i-n structure butt-coupled with a deep-etched silicon waveguide, which transitions adiabatically to a shallow-etched single mode large core SOI waveguide. The demonstrated device has a compact active region of 1.0 × 45µm2, a total insertion loss of 2.5-5dB and an extinction ratio of 4-7.5dB over a wavelength range of 1610-1640nm with −4V pp bias. The estimated Δα/α value is in the range of 2-3.3. The 3dB bandwidth measurements show that the device is capable of operating at more than 30GHz. Clear eye-diagram openings at 12.5Gbps demonstrates large signal modulation at high transmission rate.

© 2011 OSA

1. Introduction

In this paper, we demonstrate a Ge EA modulator that can operate at 30GHz modulation speed. The device is integrated with single mode 3μm thick large core SOI waveguides [21

21. N.-N. Feng, D. Feng, H. Liang, W. Qian, C.-C. Kung, J. Fong, and M. Asghari, “Low-loss polarization-insensitive silicon-on-insulator-based WDM filter for triplexer applications,” IEEE Photon. Technol. Lett. 20(23), 1968–1970 (2008). [CrossRef]

,22

22. D. Feng, W. Qian, H. Liang, C.-C. Kung, J. Fong, B. J. Luff, and M. Asghari, “Novel fabrication tolerant flat-top demultiplexers based on etched diffraction gratings in SOI,” 5rd Int. Conf. Group IV Photonics, Sorrento, Italy (September 17–19, 2008), pp. 386–388.

], and uses a horizontally-oriented p-i-n structure fabricated in a deep-etched silicon trench. The Ge EA modulator section is butt-coupled to a deep-etched silicon waveguide, which transitions adiabatically to a shallow-etched 3μm single mode SOI waveguide [21

21. N.-N. Feng, D. Feng, H. Liang, W. Qian, C.-C. Kung, J. Fong, and M. Asghari, “Low-loss polarization-insensitive silicon-on-insulator-based WDM filter for triplexer applications,” IEEE Photon. Technol. Lett. 20(23), 1968–1970 (2008). [CrossRef]

,22

22. D. Feng, W. Qian, H. Liang, C.-C. Kung, J. Fong, B. J. Luff, and M. Asghari, “Novel fabrication tolerant flat-top demultiplexers based on etched diffraction gratings in SOI,” 5rd Int. Conf. Group IV Photonics, Sorrento, Italy (September 17–19, 2008), pp. 386–388.

] (see Fig. 1(a)
Fig. 1 (a) Schematic view of the Ge EA modulator integrated with large core single mode SOI waveguide. (b) Cross-section views and optical modes of the deeply-etched Si waveguide region and (c) the Ge modulator region. The amplitude difference between two adjacent contours is 3dB.
). The demonstrated device has a very compact active region of 1.0 × 45µm2 and exhibits a strong EA effect in the wavelength range of 1570-1640nm. The total insertion loss of the device (including the transition loss) is measured as being between 2.5 and 5dB in the wavelength range of 1610-1640nm. Around 4-7.5dB extinction ratio has been achieved over this wavelength range. It is estimated that the transition loss between Si and Ge waveguides is around 1.3dB for a 1.0µm wide Ge ridge. The insertion loss induced by the Ge absorption from the modulator section is 1.2-3.8dB. Therefore, the Δα/α value of the reported device is estimated in the range of 2-3.3 with around 55kV/cm electric field. The 3dB bandwidth measurement shows that the device can operate at more than 30GHz under −4Vpp bias. A clear eye-opening at a transmission rate of 12.5Gbps demonstrates the capability of high-bit-rate large signal modulation.

2. Device structure and measurement results

Figure 1(a) shows the schematic view (half structure at input end) of the demonstrated Ge EA modulator integrated with a large core single mode SOI waveguide. The device was fabricated on a six inch SOI wafer with 0.375µm thick buried oxide (BOX) and 3µm think epitaxial-Si layer. The process began with the formation of a Si deep-etched recess area with 0.3µm thick remaining Si slab for Ge selective-area epitaxial growth. A 100nm thin buffer Ge layer was selectively grown in the recess area at low temperature (400°C) followed by a 3.0µm thick Ge layer selectively grown at high temperature (670°C). The Ge was intentionally grown thicker than the silicon epitaxial layer to compensate for thickness reduction in a later chemical-mechanical polishing (CMP) step. The target Ge thickness is 2.7µm after CMP. The Ge waveguide was formed by etching a 2.4µm Ge ridge. The resulting Ge section was protected by photoresist with the Si sections exposed and the wafer was further etched to form the single mode Si waveguides and the deeply-etched adiabatic transition trench between the shallow ridge waveguide and the deep ridge waveguide (see Fig. 1(a)). Cross-sectional views of the deep-etched Si and Ge waveguides are shown in Figs. 1(b) and 1(c). The figures also show the optical mode profiles of the waveguides. From the mode distributions, it is seen that the mode centers of the two waveguides are matched well. With an optimized design, the light input from the left side Si waveguide can be butt-coupled to the Ge waveguide with a transition loss less than 0.15dB. After waveguide etching, the Ge waveguide was implanted with boron and phosphorous on the sidewalls and the Ge slab as depicted in Fig. 1(a) to form a horizontally-oriented p-i-n structure and p- and n-type ohmic contact areas. The metal contacts for both p and n were formed by depositing and patterning a Ti/Al metal stack on top of the heavily doped areas. Figure 2
Fig. 2 Top view and cross-sectional view SEM images of the fabricated Ge EA modulator.
shows the top and cross-sectional scanning electron microscopy (SEM) images of a fabricated device with 1.0μm Ge width. From the images, the Si taper and the deeply-etched trench can be clearly observed. We also measured the remaining Si and Ge slab thicknesses to be 0.23μm and 0.6μm, respectively. The beam propagation simulation predicts that the thicker Ge slab (compared to the 0.3μm target thickness) can impose 1.3dB additional transition loss to a device with a 1.0μm wide Ge ridge due to the mode mismatch. This is a correctable process and the insertion loss of the EA modulator is expected to show 1.2dB improvement after the correction.

The transmission loss can be estimated by measuring the device loss at longer wavelengths, for example, at 1640nm, where the absorption loss is small. From experimental measurement [18

18. S. Jongthammanurak, J. Liu, K. Wada, D. D. Cannon, D. T. Danielson, D. Pan, L. C. Kimerling, and J. Michel, “Large electro-optic effect in tensile strained Ge-on-Si films,” Appl. Phys. Lett. 89(16), 161115 (2006). [CrossRef]

], the absorption coefficient of Ge at 1640nm is about 60cm−1, which corresponds to 1.16dB absorption loss for a 45μm long device. The transition loss is hence estimated to be 1.34dB given that the total insertion loss at this wavelength is 2.5dB. The numerical simulation also confirms this estimate. For the device with a 1.0µm wide Ge ridge, the transition loss is calculated as being around 1.3dB due to the unintentionally fabricated thicker Ge slab (0.6µm versus the targeted value of <0.3µm). This calculation agrees well with the experimental data. Using this value for the transition loss, the excess loss induced by the Ge absorption is 1.2-3.8dB. Δα/α can be easily calculated and is in the range of 2-3.3 with around a 55kV/cm electric field, which is within the range of the experimental results from bulk material [18

18. S. Jongthammanurak, J. Liu, K. Wada, D. D. Cannon, D. T. Danielson, D. Pan, L. C. Kimerling, and J. Michel, “Large electro-optic effect in tensile strained Ge-on-Si films,” Appl. Phys. Lett. 89(16), 161115 (2006). [CrossRef]

]. This figure of merit can be improved further (Δα/α >4) by using narrower devices with the cost of higher transition loss and lower modulation speed. Further, the working wavelength range of the device can be tailored by using GeSi material. For example, with a Si composition at 0.75%, the working wavelength can shift to around 1550nm [17

17. J. F. Liu, M. Beals, A. Pomerene, S. Bernardis, R. Sun, J. Cheng, L. C. Kimerling, and J. Michel, “Waveguide-integrated, ultralow-energy GeSi electro-absorption modulators,” Nat. Photonics 2(7), 433–437 (2008). [CrossRef]

].

The eye-diagram measurement used a similar experimental setup. A pseudorandom binary sequence (PRBS) signal with (223-1) pattern length at a 12.5Gbps transmission rate was used for the measurement although the device can achieve much higher transmission rates. The PRBS signal was amplified by a commercial modulator driver with ~4Vpp. The signal was combined with −2V DC bias using a bias tee and applied to the modulator. The modulated light signal was amplified by an L-band EDFA and coupled into a commercial photodetector attached to a digital communication analyzer. The eye-diagrams at three different wavelengths, 1590, 1600 and 1610nm were measured and are shown in Fig. 4(b). Eye openings with >5dB extinction ratio were achieved with only 4V reverse bias over greater than 20nm wavelength range. With a 30GHz 3dB bandwidth, the device is capable of achieving a 40Gbps data transmission rate [15

15. L. Liao, A. Liu, D. Rubin, J. Basak, Y. Chetrit, H. Nguyen, R. Cohen, N. Izhaky, and M. Paniccia, “40 Gbit/s silicon optical modulator for high speed applications,” Electron. Lett. 43(22), 1196–1198 (2007). [CrossRef]

].

Note that the demonstrated device with an active area of 1.0μm x 45μm is estimated to have a low capacitance of only 25fF. A simple formula to calculate the average energy consumption per bit for the dynamic modulation is given by energy/bit = 1/4CV2, where C is the junction capacitance, and V is the reverse bias voltage. It is calculated that the energy/bit for the demonstrated EA modulator at −4V bias is only 100fJ/bit. The energy consumption level of the reported device is much lower than for Mach-Zehnder type modulators [14

14. 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]

,15

15. L. Liao, A. Liu, D. Rubin, J. Basak, Y. Chetrit, H. Nguyen, R. Cohen, N. Izhaky, and M. Paniccia, “40 Gbit/s silicon optical modulator for high speed applications,” Electron. Lett. 43(22), 1196–1198 (2007). [CrossRef]

]. With a 25Gbps data transmission rate, the dynamic power consumption is only 2.5mW under −4V bias. Additionally, the photo-generated currents at “on” and “off” states also contribute to the total power consumption. However, they are not considered in the estimation due to the dependence on the input optical power.

3. Conclusions

In conclusion, we have demonstrated a compact, high-speed, low driving voltage Ge EA modulator integrated with large core silicon-on-isolator (SOI) waveguides. The Ge EA modulator employed a horizontally-oriented p-i-n structure. The demonstrated device has a very compact active area of 1.0 × 45µm2, shows a strong EA effect in the wavelength range of 1570-1640nm and has achieved 4-7.5dB ER with 2.5-5dB total IL, including the transition loss between Si and Ge waveguides, in the wavelength range of 1610-1640nm. A Δα/α value of 2-3.3 was achieved under −4V pp bias. The 3dB bandwidth measurement shows that the device is capable of operating at more than 30GHz speed. A clear eye-opening at transmission rate of 12.5Gbps is demonstrated with −4Vpp bias. The device has a low dynamic energy consumption of 100fJ/bit and low power consumption only 2.5mW at 25Gbps transmission speed under −4Vpp bias. The device can be made to operate in the C-band wavelength range by using GeSi material with suitable Si composition. This type of Ge/Si EA modulator will be particularly useful for use in inter-chip optical interconnects where compact size and low energy consumption are highly desirable.

Acknowledgment

The authors acknowledge funding of this work by Defense Advanced Research Projects Agency (DARPA) MTO office under the UNIC program supervised by Jagdeep Shah (contract agreement with SUN Microsystems HR0011-08-9-0001). The authors greatly acknowledge Dr. Jonathan Luff from Kotura Inc. for helpful discussions.

The views expressed are those of the authors and do not reflect the official policy or position of the Department of Defense or the U.S. Government. The paper is approved for public release, distribution unlimited.

References and links

1.

L. C. Kimerling, D. Ahn, A. B. Apsel, M. Beals, D. Carothers, Y.-K. Chen, T. Conway, D. M. Gill, M. Grove, C.-Y. Hong, M. Lipson, J. Liu, J. Michel, D. Pan, S. S. Patel, A. T. Pomerene, M. Rasras, D. K. Sparacin, K.-Y. Tu, A. E. White, and C. W. Wong, “Electronic-photonic integrated circuits on the CMOS platform,” Proc. SPIE 6125, 612502, 612502-10 (2006). [CrossRef]

2.

G. T. Reed and A. Knights, Silicon Photonics (Wiley, 1993–97, 2004).

3.

A. V. Krishnamoorthy, Ron Ho, H. Xuezhe Zheng, Schwetman, P. Jon Lexau, Koka, I. GuoLiang Li, Shubin, and J. E. Cunningham, “Computer systems based on silicon photonic interconnects,” Proc. IEEE 97(7), 1337–1361 (2009). [CrossRef]

4.

O. Boyraz and B. Jalali, “Demonstration of a silicon Raman laser,” Opt. Express 12(21), 5269–5273 (2004). [CrossRef] [PubMed]

5.

A. W. Fang, H. Park, O. Cohen, R. Jones, M. J. Paniccia, and J. E. Bowers, “Electrically pumped hybrid AlGaInAs-silicon evanescent laser,” Opt. Express 14(20), 9203–9210 (2006). [CrossRef] [PubMed]

6.

J. Liu, X. Sun, R. Camacho-Aguilera, L. C. Kimerling, and J. Michel, “Ge-on-Si laser operating at room temperature,” Opt. Lett. 35(5), 679–681 (2010). [CrossRef] [PubMed]

7.

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]

8.

L. Vivien, M. Rouvière, J. M. Fédéli, D. Marris-Morini, J. F. Damlencourt, J. Mangeney, P. Crozat, L. El Melhaoui, E. Cassan, X. Le Roux, D. Pascal, and S. Laval, “High speed and high responsivity germanium photodetector integrated in a Silicon-On-Insulator microwaveguide,” Opt. Express 15(15), 9843–9848 (2007). [CrossRef] [PubMed]

9.

T. Yin, R. Cohen, M. M. Morse, G. Sarid, Y. Chetrit, D. Rubin, and M. J. Paniccia, “31 GHz Ge n-i-p waveguide photodetectors on Silicon-on-Insulator substrate,” Opt. Express 15(21), 13965–13971 (2007). [CrossRef] [PubMed]

10.

D. Feng, S. Liao, P. Dong, N.-N. Feng, H. Liang, D. Zheng, C.-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]

11.

N.-N. Feng, P. Dong, D. Zheng, S. Liao, H. Liang, R. Shafiiha, D. Feng, G. Li, J. E. Cunningham, A. V. Krishnamoorthy, and M. Asghari, “Vertical p-i-n germanium photodetector with high external responsivity integrated with large core Si waveguides,” Opt. Express 18(1), 96–101 (2010). [CrossRef] [PubMed]

12.

Q. Xu, B. Schmidt, S. Pradhan, and M. Lipson, “Micrometre-scale silicon electro-optic modulator,” Nature 435(7040), 325–327 (2005). [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]

14.

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]

15.

L. Liao, A. Liu, D. Rubin, J. Basak, Y. Chetrit, H. Nguyen, R. Cohen, N. Izhaky, and M. Paniccia, “40 Gbit/s silicon optical modulator for high speed applications,” Electron. Lett. 43(22), 1196–1198 (2007). [CrossRef]

16.

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 VπL integrated on 0.25μm silicon-on-insulator waveguides,” Opt. Express 18(8), 7994–7999 (2010). [CrossRef] [PubMed]

17.

J. F. Liu, M. Beals, A. Pomerene, S. Bernardis, R. Sun, J. Cheng, L. C. Kimerling, and J. Michel, “Waveguide-integrated, ultralow-energy GeSi electro-absorption modulators,” Nat. Photonics 2(7), 433–437 (2008). [CrossRef]

18.

S. Jongthammanurak, J. Liu, K. Wada, D. D. Cannon, D. T. Danielson, D. Pan, L. C. Kimerling, and J. Michel, “Large electro-optic effect in tensile strained Ge-on-Si films,” Appl. Phys. Lett. 89(16), 161115 (2006). [CrossRef]

19.

Y.-H. Kuo, Y. K. Lee, Y. Ge, S. Ren, J. E. Roth, T. I. Kamins, D. A. B. Miller, and J. S. Harris, “Strong quantum-confined Stark effect in germanium quantum-well structures on silicon,” Nature 437(7063), 1334–1336 (2005). [CrossRef] [PubMed]

20.

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

21.

N.-N. Feng, D. Feng, H. Liang, W. Qian, C.-C. Kung, J. Fong, and M. Asghari, “Low-loss polarization-insensitive silicon-on-insulator-based WDM filter for triplexer applications,” IEEE Photon. Technol. Lett. 20(23), 1968–1970 (2008). [CrossRef]

22.

D. Feng, W. Qian, H. Liang, C.-C. Kung, J. Fong, B. J. Luff, and M. Asghari, “Novel fabrication tolerant flat-top demultiplexers based on etched diffraction gratings in SOI,” 5rd Int. Conf. Group IV Photonics, Sorrento, Italy (September 17–19, 2008), pp. 386–388.

OCIS Codes
(060.4080) Fiber optics and optical communications : Modulation
(130.3120) Integrated optics : Integrated optics devices
(200.4650) Optics in computing : Optical interconnects
(250.7360) Optoelectronics : Waveguide modulators

ToC Category:
Optoelectronics

History
Original Manuscript: January 4, 2011
Revised Manuscript: March 21, 2011
Manuscript Accepted: March 21, 2011
Published: March 29, 2011

Virtual Issues
Vol. 6, Iss. 5 Virtual Journal for Biomedical Optics

Citation
Ning-Ning Feng, Dazeng Feng, Shirong Liao, Xin Wang, Po Dong, Hong Liang, Cheng-Chih Kung, Wei Qian, Joan Fong, Roshanak Shafiiha, Ying Luo, Jack Cunningham, Ashok V. Krishnamoorthy, and Mehdi Asghari, "30GHz Ge electro-absorption modulator integrated with 3μm silicon-on-insulator waveguide," Opt. Express 19, 7062-7067 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-8-7062


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References

  1. L. C. Kimerling, D. Ahn, A. B. Apsel, M. Beals, D. Carothers, Y.-K. Chen, T. Conway, D. M. Gill, M. Grove, C.-Y. Hong, M. Lipson, J. Liu, J. Michel, D. Pan, S. S. Patel, A. T. Pomerene, M. Rasras, D. K. Sparacin, K.-Y. Tu, A. E. White, and C. W. Wong, “Electronic-photonic integrated circuits on the CMOS platform,” Proc. SPIE 6125, 612502, 612502-10 (2006). [CrossRef]
  2. G. T. Reed and A. Knights, Silicon Photonics (Wiley, 1993–97, 2004).
  3. A. V. Krishnamoorthy, Ron Ho, H. Xuezhe Zheng, Schwetman, P. Jon Lexau, Koka, I. GuoLiang Li, Shubin, and J. E. Cunningham, “Computer systems based on silicon photonic interconnects,” Proc. IEEE 97(7), 1337–1361 (2009). [CrossRef]
  4. O. Boyraz and B. Jalali, “Demonstration of a silicon Raman laser,” Opt. Express 12(21), 5269–5273 (2004). [CrossRef] [PubMed]
  5. A. W. Fang, H. Park, O. Cohen, R. Jones, M. J. Paniccia, and J. E. Bowers, “Electrically pumped hybrid AlGaInAs-silicon evanescent laser,” Opt. Express 14(20), 9203–9210 (2006). [CrossRef] [PubMed]
  6. J. Liu, X. Sun, R. Camacho-Aguilera, L. C. Kimerling, and J. Michel, “Ge-on-Si laser operating at room temperature,” Opt. Lett. 35(5), 679–681 (2010). [CrossRef] [PubMed]
  7. 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]
  8. L. Vivien, M. Rouvière, J. M. Fédéli, D. Marris-Morini, J. F. Damlencourt, J. Mangeney, P. Crozat, L. El Melhaoui, E. Cassan, X. Le Roux, D. Pascal, and S. Laval, “High speed and high responsivity germanium photodetector integrated in a Silicon-On-Insulator microwaveguide,” Opt. Express 15(15), 9843–9848 (2007). [CrossRef] [PubMed]
  9. T. Yin, R. Cohen, M. M. Morse, G. Sarid, Y. Chetrit, D. Rubin, and M. J. Paniccia, “31 GHz Ge n-i-p waveguide photodetectors on Silicon-on-Insulator substrate,” Opt. Express 15(21), 13965–13971 (2007). [CrossRef] [PubMed]
  10. D. Feng, S. Liao, P. Dong, N.-N. Feng, H. Liang, D. Zheng, C.-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]
  11. N.-N. Feng, P. Dong, D. Zheng, S. Liao, H. Liang, R. Shafiiha, D. Feng, G. Li, J. E. Cunningham, A. V. Krishnamoorthy, and M. Asghari, “Vertical p-i-n germanium photodetector with high external responsivity integrated with large core Si waveguides,” Opt. Express 18(1), 96–101 (2010). [CrossRef] [PubMed]
  12. Q. Xu, B. Schmidt, S. Pradhan, and M. Lipson, “Micrometre-scale silicon electro-optic modulator,” Nature 435(7040), 325–327 (2005). [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]
  14. 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]
  15. L. Liao, A. Liu, D. Rubin, J. Basak, Y. Chetrit, H. Nguyen, R. Cohen, N. Izhaky, and M. Paniccia, “40 Gbit/s silicon optical modulator for high speed applications,” Electron. Lett. 43(22), 1196–1198 (2007). [CrossRef]
  16. 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 VπL integrated on 0.25μm silicon-on-insulator waveguides,” Opt. Express 18(8), 7994–7999 (2010). [CrossRef] [PubMed]
  17. J. F. Liu, M. Beals, A. Pomerene, S. Bernardis, R. Sun, J. Cheng, L. C. Kimerling, and J. Michel, “Waveguide-integrated, ultralow-energy GeSi electro-absorption modulators,” Nat. Photonics 2(7), 433–437 (2008). [CrossRef]
  18. S. Jongthammanurak, J. Liu, K. Wada, D. D. Cannon, D. T. Danielson, D. Pan, L. C. Kimerling, and J. Michel, “Large electro-optic effect in tensile strained Ge-on-Si films,” Appl. Phys. Lett. 89(16), 161115 (2006). [CrossRef]
  19. Y.-H. Kuo, Y. K. Lee, Y. Ge, S. Ren, J. E. Roth, T. I. Kamins, D. A. B. Miller, and J. S. Harris, “Strong quantum-confined Stark effect in germanium quantum-well structures on silicon,” Nature 437(7063), 1334–1336 (2005). [CrossRef] [PubMed]
  20. R. A. Soref and B. R. Bennett, “Electro-optical effects in silicon,” IEEE J. Quantum Electron. 23(1), 123–129 (1987). [CrossRef]
  21. N.-N. Feng, D. Feng, H. Liang, W. Qian, C.-C. Kung, J. Fong, and M. Asghari, “Low-loss polarization-insensitive silicon-on-insulator-based WDM filter for triplexer applications,” IEEE Photon. Technol. Lett. 20(23), 1968–1970 (2008). [CrossRef]
  22. D. Feng, W. Qian, H. Liang, C.-C. Kung, J. Fong, B. J. Luff, and M. Asghari, “Novel fabrication tolerant flat-top demultiplexers based on etched diffraction gratings in SOI,” 5rd Int. Conf. Group IV Photonics, Sorrento, Italy (September 17–19, 2008), pp. 386–388.

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