Dr. Vijit Sabnis

Department of Electrical Engineering

Ph. D. Electrical Engineering, Stanford University, M.S. Electrical Engineering, Stanford University, B. S. Electrical Engineering and Computer Sciences, University of California at Berkeley

Email: vsabnis(at)snow(dot)stanford(dot)edu

 

 

Optically-controlled electroabsorption modulators

Research Summary

Over the last ten years wavelength-division-multiplexing (WDM) has emerged as a powerful technique to increase the information transmission capabilities of optical networks.  The introduction of erbium doped fiber amplifiers enabled WDM systems to economically transmit multiple wavelength channels down a single optical fiber.  To accommodate increasing bandwidth demands, network service providers will continue to increase the wavelength channel count per optical fiber.  Wavelength contention occurs in a WDM system when two or more channels operating at the same wavelength are routed to the same optical fiber.  In current systems one channel is sent, while the other channels are buffered and resent at a later time, degrading the overall network performance.  Wavelength conversion, the ability to dynamically change the wavelength of an optical channel, can alleviate wavelength contention and is the first step towards achieving a transparent optical network.  My research explored two generations of optically-controlled electroabsorption modulators that can be used for optical switching and wavelength conversion applications and offer significant advantages over competing techniques.

Wavelength conversion is currently performed using an optical-electronic-optical converter, comprising an optical receiver, electronic amplifiers and signal conditioning circuits, and an optical transmitter.  This technique suffers from high packaging costs, high complexity, large space and power consumption, and a lack of scalability.  A variety of all-optical approaches have been investigated to alleviate these problems.  Semiconductor optical amplifiers relying on cross gain or cross phase modulation have achieved high performance results at bit rates exceeding the capabilities of current electronics.  Similarly, wavelength conversion using four wave mixing and difference frequency generation in nonlinear optical materials has been demonstrated successfully.  These techniques, however, require large electrical or optical power consumption and cannot be conveniently scaled into two dimensions.  The optically-controlled electroabsorption modulators we investigated consume low electrical and optical powers, require simple electrical packaging, are input polarization independent, can monitor network performance, are electronically-reconfigurable, and possess realistic two-dimensional scalability.

The first generation device, shown below, was a GaAs-based, single diode, surface-normal optically-controlled electroabsorption modulator.  The optical switching relies on electric field screening of multiple quantum wells and diffusive electrical conduction.  We theoretically investigated this device and concluded that wavelength conversion at switching frequencies exceeding 50 GHz is possible.  In a proof-of-concept experiment, we demonstrated wavelength-converting optical switching at frequencies up to 2.5 GHz using only 2.4 mW of optical power. 

Figure:  Single-diode optically-controlled electroabsorption modulator

The second generation device was an InP-based, multicomponent  optoelectronic integrated circuit that alleviates the design tradeoffs present in the first generation device.  We developed a fabrication process, incorporating a selective area regrowth technique, that monolithically integrates a waveguide electroabsorption modulator, a surface-illuminated photodetector, and a thin film resistor into a compact circuit for performing optical switching and wavelength conversion.  Using mW-level optical powers, we demonstrated optically-controlled switching up to 2.5 Gb/s with > 10 dB extinction ratio.  Wavelength conversion over the entire center telecommunication band (1530-1565 nm) was demonstrated at 1.25 Gb/s with > 10 dB extinction ratio using a fixed input optical power of 5.6 mW.  We theoretically investigated high-speed operation at 10-40 Gb/s and identified the device requirements and optimization criteria for achieving these goals.   

 

Figure: (top) illustration and (bottom) top view microscope picture of a fabricated second generation switch.

By employing an optimized multiple-quantum-well active region and enhancing the integration process, future versions of this device will be able to perform partial optical regeneration.  This work is the first step towards creating a multichannel, optical crossbar switch that simultaneously performs wavelength conversion and optical regeneration. 

 

Publications

Dissertation

  1. V. A. Sabnis, Optically-controlled electroabsorption modulators for future generation optical networks, Ph.D. thesis, Stanford University, 2003.

Journal Articles

  1. V. A. Sabnis, H. V. Demir, M. B. Yairi, J. S. Harris, Jr., and D. A. B. Miller, "High-speed, optical switching based on diffusive conduction in an optical waveguide with surface-normal optical control," to be published in Journal of Applied Physics on March 1, 2004.

  1. V. A. Sabnis, H. V. Demir, O. Fidaner, J. S. Harris, Jr., D. A. B. Miller, J.-F. Zheng, N. Li, T.-C. Wu, H.-T. Chen, and Y.-M. Houng, "Optically-controlled electroabsorption modulators for unconstrained wavelength conversion," to be published in Applied Physics Letters on January 26, 2004.

  1. H. V. Demir, V. A. Sabnis, J.-F. Zheng, O. Fidaner, J. S. Harris, Jr., and D. A. B. Miller, "Scalable wavelength-converting crossbars," submitted to IEEE Photonics Technology Letters (manuscript PTL-12711-2003).

  2. H. V. Demir, V. A. Sabnis, O. Fidaner, J. S. Harris, Jr., D. A. B. Miller, and J.-F. Zheng, "Dual-diode quantum-well modulator for C-band wavelength conversion and broadcasting," submitted to OSA Optics Express.

  3. H. V. Demir, J.-F. Zheng, V. A. Sabnis, O. Fidaner, J. P. Hanberg, J. S. Harris, Jr., and D. A. B. Miller, "Self-aligning planarization and passivation in the integration of III-V semiconductor devices," submitted to IEEE Transactions on Semiconductor Manufacturing.

  4. V. A. Sabnis, H. V. Demir, J.-F. Zheng, O. Fidaner, J. S. Harris, Jr., D. A. B. Miller, N. Li, T.-C. Wu, H.-T. Chen, and Y.-M. Houng, "Monolithic integration of chip-scale photodiode-modulator switches," in preparation for submission to Thin Solid Films.

  5. H. V. Demir, V. A. Sabnis, O. Fidaner, J.-F. Zheng, J. S. Harris, Jr., and D. A. B. Miller, "Multi-functional optically-switched quantum-well modulators," in preparation for submission to IEEE Journal of Quantum Electronics.

  6. H. V. Demir, V. A. Sabnis, M. B. Yairi, J. S. Harris, Jr., and D. A. B. Miller, "Functional uses and limits of diffusive conduction in optically-controlled distributed-RC optoelectronic switches," in preparation for submission to Journal of Applied Physics.

  7. J.-F. Zheng, H. V. Demir, V. A. Sabnis, O. Fidaner, J. P. Hanberg, J. S. Harris, Jr., and D. A. B. Miller, "Novel self-aligned via formation in the integration of III-V semiconductor devices," in preparation for submission to Microelectronic Engineering, Elsevier V. B.

Conference Presentations

  1. H. V. Demir, O. Fidaner, V. A. Sabnis, J. S. Harris, Jr., D. A. B. Miller, and J.-F. Zheng, "Photodiode-driven quantum-well modulators for C-band wavelength conversion and broadcasting," submitted to IEEE/LEOS-OSA Conference on Lasers and Electro-Optics 2004 (CLEO) (manuscript 04-C-705-CLEO).

  2. H. V. Demir, V. A. Sabnis, O. Fidaner, J. S. Harris, Jr., D. A. B. Miller, J.-F. Zheng, N. Li, T.-C. Wu, and Y.-M. Houng, "Novel scalable wavelength-converting crossbar," accepted for publication in the Proceedings of IEEE-OSA Optical Fiber Communications Conference (OFC), Los Angeles, CA (February 22-27, 2004). Paper FD5.

  3. J.-F. Zheng, J. P. Hanberg, H. V. Demir, V. A. Sabnis, O. Fidaner, J. S. Harris, Jr., and D. A. B. Miller, "Novel passivation and planarization in the integration of III-V semiconductor devices," accepted for publication in the Proceedings of SPIE Photonics West Conference, San Jose, CA (January 24-29, 2004). Paper 5356-9.

  4. H. V. Demir, V. A. Sabnis, O. Fidaner, S. Latif, J. S. Harris, Jr., D. A. B. Miller, J.-F. Zheng, N. Li, T.-C. Wu, and Y.-M. Houng, "Novel optically-controlled optical switch based on intimate integration of surface-normal photodiode and waveguide electroabsorption modulator for wavelength conversion," Proceedings of IEEE Lasers and Electro-Optics Society 2003 Annual Meeting (LEOS), pp. 644-645, Tucson, AZ (October 26-30, 2003). Paper WU1. (Presentation)

  5. V. A. Sabnis, H. V. Demir, O. Fidaner, J. S. Harris, Jr., D. A. B. Miller, J.-F. Zheng, N. Li, T.-C. Wu, and Y.-M. Houng, "Optically-switched dual-diode electroabsorption modulators," OSA Conference on Integrated Photonics Research (IPR), pp. 12-14, (OSA Technical Digest, Optical Society of America, Washington, DC, 2003). Paper IMB3.

  6. V. A. Sabnis, H. V. Demir, M. B. Yairi, D. A. B. Miller, and J. S. Harris, Jr., "Observation of wavelength-converting optical switching at 2.5 GHz in a surface-normal illuminated waveguide," Proceedings of IEEE Lasers and Electro-Optics Society 2001 Annual Meeting (LEOS), pp. 362-363, San Diego, CA (November 12-15, 2001). Paper TuCC2.

Patents

Issued

  1. R. I. Aldaz, G. A. Keeler, V. A. Sabnis, J. S. Harris, Jr., and D. A. B. Miller, "Monolithically-integrated mode-locked vertical cavity surface emitting laser (VCSEL)," US patent number 6,628,695 B1, issued September 30, 2003. 

Pending

  1. H. V. Demir, D. A. B. Miller, and V. A. Sabnis, "Semiconductor device for rapid optical switching by modulated absorption," US patent application number 10/075,921, filed in February 2002; accepted for issuing.  "Optically controlled optical switches with hybrid integrated photodetectors and modulators," continuation-in-part, Stanford docket number S03-119, disclosed in April 2003.

  2. H. V. Demir, D. A. B. Miller, and V. A. Sabnis, "Highly-integrated, multi-functional optoelectronic microchips for next generation optical networks," Stanford docket number S03-118, disclosed in April 2003.  Application to be filed by March 2004.

  3. H. V. Demir, O. Fidaner, D. A. B. Miller, V. A. Sabnis, and J.-F. Zheng, "Wafer-level quasi-planarization and passivation for multi-height structures," Intel Corporation reference number P16479 and Stanford docket number S03-175, US patent application filed in June 2003.