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Optics Express

Optics Express

  • Editor: Michael Duncan
  • Vol. 13, Iss. 2 — Jan. 24, 2005
  • pp: 654–659
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Symmetrical 1×2 digital photonic splitting switch with low electrical power consumption in SiGe waveguides

Baojun Li, Yao Zhang, Lihua Teng, Yuzhou Zhao, Soo-Jin Chua, and Xiangrong Wang  »View Author Affiliations


Optics Express, Vol. 13, Issue 2, pp. 654-659 (2005)
http://dx.doi.org/10.1364/OPEX.13.000654


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Abstract

A symmetrical digital photonic splitting switch with a low insertion loss and a low driving voltage is developed using carrier injection in a silicon-germanium material for optical communication systems and networks at a wavelength of 1.55 µm. The switch structure has been improved based on a traditional 1×2 Y-shaped configuration by using two widened carrier injection regions. The switch has a threshold voltage of 1.0 V and a corresponding threshold current of 85 mA on one of the two output waveguide arms. The calculated driving current density is 5.7 kA/cm2 and the calculated power consumption is 85 mW at the 85 mA of threshold current. The measured insertion loss and the crosstalk are 5.2 dB and -9.6 dB, respectively, at driving voltage over 2 V.

© 2005 Optical Society of America

1. Introduction

Photonic switch is a fundamental device in integrated optoelectronics and a key component for wide bandwidth high-speed fiber-optic networks. Photonic switches can be implemented using X or Y-shaped optical waveguides. The Y-shaped optical waveguide switch consists of one input waveguide and two output waveguides. The input waveguide is connected to the output waveguides at a branching point with a small branching angle. The 1×2 Y-branching digital photonic splitting switch (DPS) has an advantage in that the output optical power of the switch is insensitive to voltage variations or drift in the applied controlling voltage. When an appropriate controlling voltage is applied to one of the two output waveguides, propagation of the light is allowed in one of the output optical waveguides and blocked in the other output optical waveguide. The optical output power in either of the output waveguides can also be controlled and modulated by an appropriate voltage.

To achieve good reliability and highly monolithic integration with Si-based chips, SiGe material was used to fabricate multifunctional and highly integrated photonic devices [9

9. B. J. Li and S. J. Chua, “High carrier injection optical switch based on two-mode interference in SiGe alloy,” Appl. Phys. Lett. 80, 180–182 (2002). [CrossRef]

,10

10. B. J. Li, J. Li, Y. Z. Zhao, X. B. Lin, S. J. Chua, L. Y. Miao, E. A. Fitzgerald, M. L. Lee, and B. S. Chaudhari, “Ultracompact, multifunctional, and highly integrated 3×2 photonic switches,” Appl. Phys. Lett. 84, 2241–2243 (2004). [CrossRef]

,15

15. R. Normandin, D. C. Houghton, and M. S. Normandin, “All-optical, silicon-based, fiber optic modulator using a near cutoff region,” Can. J. Phys. 67, 412–418, (1989). [CrossRef]

,16

16. R. R. Whiteman, A. P. Knights, D. George, I. E. Day, A. Vonsovici, A. A. House, G. F. Hopper, and M. Asghari, “Recent progress in the design, simulation and fabrication of small cross-section silicon-on-insulator VOAs,” in Photonics Packaging and Integration III , R. A. Heyler, D. J. Robbins, and G. E. Jabbour, eds., Proc. SPIE 4997, 146–156 (2003).

] because of low propagation loss (<0.5 dB/cm) in the wavelength region of λ=1.3 ~1.55 µm. SiGe epitaxy has the advantage that its fabrication techniques are compatible with large scale Si integration. Due to greater electron mobility and smaller bandgap in germanium, remarkable improvements in the performance of devices can be achieved, with virtually no changes in existing all-silicon designs. SiGe is also relatively easy to fabricate using existing silicon facilities.

DPS devices with a large number of inputs-outputs such as 1×N, N×1, N×M, and N×N block DPS arrays can be constructed. In this work, we report the first DPS fabricated in Si-based SiGe material. We have used an epitaxial SiGe layer as a core optical waveguide. The symmetrical 1×2 DPS was designed for free carrier injection for operation at 1.55 µm. It can be useful for dense wavelength division multiplexed (DWDM) networks and associated applications. To reduce the switching length, and at the same time to reduce the switching voltage and power consumption, two widened carrier injection regions are employed in the two output arms of the switch. The measured device performances are satisfactory.

2. Device description

Fig.1. Schematic diagram of a symmetrical waveguide Y-branch digital photonic splitting switch (a) top view and (b) A-A cross-section view. (not in scales)

3. Simulation

The device parameters were determined by the following considerations. The thickness of the rib waveguide was chosen for the single-mode rib waveguide operation to be 2.5 µm, the widths of input rib waveguide, branch 1 and branch 2 were chosen to be 8 µm. To enhance the switch performance and therefore to reduce the switching power consumption, the widths of the two carrier injection regions were chosen to be 10 µm, but still it will support single mode operation. The separation of the two outputs waveguide at the ends is only 16 µm, permitting the use of only a single output fiber at one time. The etching depth of all ridge waveguides was 1.2 µm for Ge content of 4%. The effective index method was employed to analyze the behavior of the mode propagation and determine the branch angle of the switch. In our optimum design, the Y-branching angle of the switch is optimized to be 1.273 degree. The total length of the switch is 900 µm and the length of the active region is L active=150 µm. The distance of the electrode to the facet of the output waveguide is 50 µm. The device performance is simulated by the Beam Propagation Method (BPM) and the results are shown in Fig. 2. From Fig. 2(a), we can see that for a Y-branch, the output optical powers at the two arms are 47.6% when a switch is ON for both the branches. This means the insertion loss, which is defined as -10log10(Ptotal-output/Ptotal-input), is 0.2 dB. For a DPS response as shown in Fig. 2(b), the output optical powers in the two arms are 58.7% and 3%, whenever a switch is ON for branch 2 and OFF for branch 1. Exactly similar results are obtained whenever the branch 2 is OFF and branch 1 is ON, as shown in Fig. 2(c). The calculated insertion loss is 2.1 dB and the crosstalk is -12.9 dB in both the cases.

Fig. 2. Simulation results of the switch using beam propagation method, (a) switch-ON state on both branches, (b) switch-ON state on branch 2 and OFF state on branch 1, (c) switch-ON state on branch 1 and OFF state on branch 2.

4. Experiment

The samples were grown in an UHV-CVD system at 900°C. The substrate used is a p+-type Si (100) wafer. A~5 nm p-type Si buffer layer with a concentration of about 2×1016 cm-3 had been grown followed by a 2.5 µm p-type strained Si0.96Ge0.04 core waveguide layer (2×1016 cm-3). On the top of the sample, an abrupt n+p junction was formed by growing a 5 nm n+-type Si with a concentration of 1×1018 cm-3. The device was fabricated by a standard Si device technology. The ridge waveguides were shaped by lithography and reactive ion etching. Then, the n+ and p+ ohmic contact electrodes were deposited by evaporating 1.0 µm thick Al layer followed by alloying at 450°C. The whole device surface was passivated by a SiO2 layer. The chips were diced and the input and output facets of the switch were polished. The incident light from a single-mode fiber was coupled to the waveguide.

5. Results and discussion

This device is also a splitter combined with a blocking attenuator on each arm. As a result there is a minimum 3 dB loss per switch. The injection current density of 5–7 kA/cm2 in this work of the SiGe DPS is smaller than the reported of 9 kA/cm2 by Liu et al. [11

11. Y. L. Liu, E. K. Liu, S. L. Zhang, G. Z. Li, and J. S. Luo, “Silicon 1×2 digital optical switch using plasma dispersion,” Electron. Lett. 30, 130–131 (1994). [CrossRef]

] and 22 kA/cm2 in InAgAsP/InP carrier injection-based PDS by Abdalla et al. [5

5. S. Abdalla, S. Ng, P. Barrios, D. Celo, A. Delâge, S. El-Mougy, I. Golub, J.-J. He, S. Janz, R. McKinnon, P. Poole, S. Raymond, T. J. Smy, and B. Syrett, “Carrier injection-based digital optical switch with reconfigurable output waveguide arms,” IEEE Photon. Technol. Lett. 16, 1038–100 (2004). [CrossRef]

]. In comparison to other optoelectronic material DPSs reported in the literature, the digital response power of 85 mW and cut-off power of 190 mW in this work for SiGe material is higher than those previously reported by Vinchant et al. (60 mW in GaInAsP/InP by carrier injection) [3

3. J. F. Vinchant, M. Renaud, A. Goutelle, M. Erman, P. Svensson, and L. Thylen, “Low driving voltage or current digital optical switch on InP for multiwavelength system applications,” Electron. Lett. 28, 1135–1137 (1992). [CrossRef]

] and Keil et al. (45 mW in polymer by thermo-optic effect) [12

12. N. Keil, H. H. Yao, and C. Zawadzki, “2×2 digital optical switch realized by low cost polymer waveguide technology,” Electron. Lett. 32, 1470–1471 (1996). [CrossRef]

]. Our results are similar to that reported by Yang et al. (165–180 mW in polymer using the thermo-optic effect) [7

7. M. S. Yang, Y. O. Noh, Y. H. Won, and W. Y. Hwang, “Very low crosstalk 1×2 digital optical switch integrated with variable optical attenuators,” Electron. Lett. 37, 587–588 (2001). [CrossRef]

] and superior than those reported by Siebel et al. (200 mW in polymer by thermo-optic effect) [2

2. U. Siebel, R. Hauffe, and K. Petermann, “Crosstalk-enhanced polymer digital optical switch based on a W-shape” IEEE Photon. Technol. Lett. 12, 40–41 (2000) [CrossRef]

], Abdalla et al. (800 mW in InGaAsP/InP by carrier injection) [5

5. S. Abdalla, S. Ng, P. Barrios, D. Celo, A. Delâge, S. El-Mougy, I. Golub, J.-J. He, S. Janz, R. McKinnon, P. Poole, S. Raymond, T. J. Smy, and B. Syrett, “Carrier injection-based digital optical switch with reconfigurable output waveguide arms,” IEEE Photon. Technol. Lett. 16, 1038–100 (2004). [CrossRef]

], Toyoda et al. (380 mW in silicone resin by thermo-optic effect) [13

13. S. Toyoda, N. Ooba, Y. Katoh, T. Kurihara, and T. Maruno, “Low crosstalk and low loss 2×2 thermo-optic digital switch using silicon resin waveguides,” Electron. Lett. 36, 1803–1804 (2000). [CrossRef]

], and Lee et al. (250 mW in polymer by thermo-optic effect) [14

14. M. H. Lee, Y. H. Min, S Park, J. J. Ju, J. Y. Do, and S. K. Park, “Fully packaged polymeric four arrayed 2×2 digital optical switch,” IEEE Photon. Technol. Lett. 14, 615–617 (2002). [CrossRef]

]. The results show that the proposed DPS is a promising device to fulfill monolithic integration with other Si-based optoelectronic devices and for 1.31 to 1.55 µm fiber-optic communication and networking applications.

Fig. 3. Output optical power versus the applied forward bias.

6. Conclusions

A symmetrical 1×2 digital photonic splitting switch has been fabricated in SiGe materials by UHV-CVD growth. The operation of the switch is found to be optimized at 2 V forward bias. The measured insertion loss is around 5.2 dB, and the crosstalk is -9.6 dB.

Acknowledgments

This work is supported in part by the National Natural Science Foundation of China (No. 90401008), the Program for New Century Excellent Talents in University, the Key Project of Chinese Ministry of Education (No. 104144), the Research Fund for the Doctoral Program of Higher Education (No. 20040558009), the Guangdong Provincial Science and Technology Program Foundation (No. 2003A1060201), and the Guangzhou Science and Technology Program Foundation (No. 2004Z3-D2051).

References and links

1.

H. Okayama, T. Ushikubo, and M. Kawahara, “Low drive voltage y-branch digital optical switch,” Electron. Lett. 27, 24–26 (1991). [CrossRef]

2.

U. Siebel, R. Hauffe, and K. Petermann, “Crosstalk-enhanced polymer digital optical switch based on a W-shape” IEEE Photon. Technol. Lett. 12, 40–41 (2000) [CrossRef]

3.

J. F. Vinchant, M. Renaud, A. Goutelle, M. Erman, P. Svensson, and L. Thylen, “Low driving voltage or current digital optical switch on InP for multiwavelength system applications,” Electron. Lett. 28, 1135–1137 (1992). [CrossRef]

4.

M. N. Khan, B. I. Miller, E. C. Burrows, and C. A. Burrus, “Crosstalk-, loss-, and length-reduced digital optical Y-branch switches using a double-etch waveguide structure,” IEEE Photon. Technol. Lett. 11, 1250–1252 (1999). [CrossRef]

5.

S. Abdalla, S. Ng, P. Barrios, D. Celo, A. Delâge, S. El-Mougy, I. Golub, J.-J. He, S. Janz, R. McKinnon, P. Poole, S. Raymond, T. J. Smy, and B. Syrett, “Carrier injection-based digital optical switch with reconfigurable output waveguide arms,” IEEE Photon. Technol. Lett. 16, 1038–100 (2004). [CrossRef]

6.

Sneh, J. E. Zucker, and B. I. Miller, “Compact, low-crosstalk, and low-propagation-loss quantum-well y-branch switches,” IEEE Photon. Technol. Lett. 8, 1644–1646 (1996). [CrossRef]

7.

M. S. Yang, Y. O. Noh, Y. H. Won, and W. Y. Hwang, “Very low crosstalk 1×2 digital optical switch integrated with variable optical attenuators,” Electron. Lett. 37, 587–588 (2001). [CrossRef]

8.

H. Okayama and M. Kawahara, “Reduction of voltage-length product for y-branch digital optical switch,” J. Lightwave Technol. 11, 379–387 (1993). [CrossRef]

9.

B. J. Li and S. J. Chua, “High carrier injection optical switch based on two-mode interference in SiGe alloy,” Appl. Phys. Lett. 80, 180–182 (2002). [CrossRef]

10.

B. J. Li, J. Li, Y. Z. Zhao, X. B. Lin, S. J. Chua, L. Y. Miao, E. A. Fitzgerald, M. L. Lee, and B. S. Chaudhari, “Ultracompact, multifunctional, and highly integrated 3×2 photonic switches,” Appl. Phys. Lett. 84, 2241–2243 (2004). [CrossRef]

11.

Y. L. Liu, E. K. Liu, S. L. Zhang, G. Z. Li, and J. S. Luo, “Silicon 1×2 digital optical switch using plasma dispersion,” Electron. Lett. 30, 130–131 (1994). [CrossRef]

12.

N. Keil, H. H. Yao, and C. Zawadzki, “2×2 digital optical switch realized by low cost polymer waveguide technology,” Electron. Lett. 32, 1470–1471 (1996). [CrossRef]

13.

S. Toyoda, N. Ooba, Y. Katoh, T. Kurihara, and T. Maruno, “Low crosstalk and low loss 2×2 thermo-optic digital switch using silicon resin waveguides,” Electron. Lett. 36, 1803–1804 (2000). [CrossRef]

14.

M. H. Lee, Y. H. Min, S Park, J. J. Ju, J. Y. Do, and S. K. Park, “Fully packaged polymeric four arrayed 2×2 digital optical switch,” IEEE Photon. Technol. Lett. 14, 615–617 (2002). [CrossRef]

15.

R. Normandin, D. C. Houghton, and M. S. Normandin, “All-optical, silicon-based, fiber optic modulator using a near cutoff region,” Can. J. Phys. 67, 412–418, (1989). [CrossRef]

16.

R. R. Whiteman, A. P. Knights, D. George, I. E. Day, A. Vonsovici, A. A. House, G. F. Hopper, and M. Asghari, “Recent progress in the design, simulation and fabrication of small cross-section silicon-on-insulator VOAs,” in Photonics Packaging and Integration III , R. A. Heyler, D. J. Robbins, and G. E. Jabbour, eds., Proc. SPIE 4997, 146–156 (2003).

OCIS Codes
(060.1810) Fiber optics and optical communications : Buffers, couplers, routers, switches, and multiplexers
(230.3120) Optical devices : Integrated optics devices

ToC Category:
Research Papers

History
Original Manuscript: October 29, 2004
Revised Manuscript: January 19, 2005
Published: January 24, 2005

Citation
Baojun Li, Yao Zhang, Lihua Teng, Yuzhou Zhao, Soo-Jin Chua, and Xiangrong Wang, "Symmetrical 1x2 digital photonic splitting switch with low electrical power consumption in SiGe waveguides," Opt. Express 13, 654-659 (2005)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-13-2-654


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References

  1. H. Okayama, T. Ushikubo, and M. Kawahara, �??Low drive voltage y-branch digital optical switch,�?? Electron. Lett. 27, 24-26 (1991). [CrossRef]
  2. U. Siebel, R. Hauffe, and K. Petermann, �??Crosstalk-enhanced polymer digital optical switch based on a W-shape,�?? IEEE Photon. Technol. Lett. 12, 40-41 (2000) [CrossRef]
  3. J. F. Vinchant, M. Renaud, A. Goutelle, M. Erman, P. Svensson, and L. Thylen, �??Low driving voltage or current digital optical switch on InP for multiwavelength system applications,�?? Electron. Lett. 28, 1135-1137 (1992). [CrossRef]
  4. M. N. Khan, B. I. Miller, E. C. Burrows, and C. A. Burrus, �??Crosstalk-, loss-, and length-reduced digital optical Y-branch switches using a double-etch waveguide structure,�?? IEEE Photon. Technol. Lett. 11, 1250-1252 (1999). [CrossRef]
  5. S. Abdalla, S. Ng, P. Barrios, D. Celo, A. Delâge, S. El-Mougy, I. Golub, J.-J. He, S. Janz, R. McKinnon, P. Poole, S. Raymond, T. J. Smy, and B. Syrett, �??Carrier injection-based digital optical switch with reconfigurable output waveguide arms,�?? IEEE Photon. Technol. Lett. 16, 1038-100 (2004). [CrossRef]
  6. Sneh, J. E. Zucker, and B. I. Miller, �??Compact, low-crosstalk, and low-propagation-loss quantum-well y-branch switches,�?? IEEE Photon. Technol. Lett. 8, 1644-1646 (1996). [CrossRef]
  7. M. S. Yang, Y. O. Noh, Y. H. Won, and W. Y. Hwang, �??Very low crosstalk 1�?2 digital optical switch integrated with variable optical attenuators,�?? Electron. Lett. 37, 587-588 (2001). [CrossRef]
  8. H. Okayama and M. Kawahara, �??Reduction of voltage-length product for y-branch digital optical switch,�?? J. Lightwave Technol. 11, 379-387 (1993). [CrossRef]
  9. B. J. Li and S. J. Chua, �??High carrier injection optical switch based on two-mode interference in SiGe alloy,�?? Appl. Phys. Lett. 80, 180-182 (2002). [CrossRef]
  10. B. J. Li J. Li, Y. Z. Zhao, X. B. Lin, S. J. Chua, L. Y. Miao, E. A. Fitzgerald, M. L. Lee, and B. S. Chaudhari, �??Ultracompact, multifunctional, and highly integrated 3�?2 photonic switches,�?? Appl. Phys. Lett. 84, 2241-2243 (2004). [CrossRef]
  11. Y. L. Liu, E. K. Liu, S. L. Zhang, G. Z. Li, and J. S. Luo, �??Silicon 1�?2digital optical switch using plasma dispersion,�?? Electron. Lett. 30, 130-131 (1994). [CrossRef]
  12. N. Keil, H. H. Yao, and C. Zawadzki, �??2�?2 digital optical switch realized by low cost polymer waveguide technology,�?? Electron. Lett. 32, 1470-1471 (1996). [CrossRef]
  13. S. Toyoda, N. Ooba, Y. Katoh, T. Kurihara, and T. Maruno, �??Low crosstalk and low loss 2�?2 thermo-optic digital switch using silicon resin waveguides,�?? Electron. Lett. 36, 1803-1804 (2000). [CrossRef]
  14. M. H. Lee, Y. H. Min, S Park, J. J. Ju, J. Y. Do, and S. K. Park, �??Fully packaged polymeric four arrayed 2�?2 digital optical switch,�?? IEEE Photon. Technol. Lett. 14, 615-617 (2002). [CrossRef]
  15. R. Normandin, D. C. Houghton, and M. S. Normandin, �??All-optical, silicon-based, fiber optic modulator using a near cutoff region,�?? Can. J. Phys. 67, 412-418, (1989). [CrossRef]
  16. R. R. Whiteman, A. P. Knights, D. George, I. E. Day, A. Vonsovici, A. A. House, G. F. Hopper, and M. Asghari, �??Recent progress in the design, simulation and fabrication of small cross-section silicon-on-insulator VOAs,�?? in Photonics Packaging and Integration III, R. A. Heyler, D. J. Robbins, and G. E. Jabbour, eds., Proc. SPIE 4997, 146-156 (2003).

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