Summary

Current wireless or optical technologies alone can not provide economically competitive solutions for the growing demand for communication networks capable of simultaneously ensuring higher capacity, coverage, bandwidth, and mobility in environments such as conference venues, university buildings, airports, hotels, shopping centers, and in the end to small offices and homes. Optical-wireless access solutions based on the integration of radio signals into optical carrier at a central office (CO) that are then transmitted by optical fiber to the wireless access point (AP), known as radio-over-fiber (RoF) networks, are being considered the most promising solution because they can bring the optical network bandwidths closer to the fixed and to the mobile users and at same time allowing the deliver of multiple services.

The next generation wireless-communication systems will use air frequencies in the range of 2-8 GHz. With these frequencies Gb/s data rates are possible only if cell size is reduced considerably. The so-called pico-cellular optical-wireless access with few meters range cells are being considered as a highly promising route for delivering high bandwidth and mobility access for in-building applications.

Due to the moderate frequencies and the fiber transmission lengths involved (few km at maximum), the most cost-effective access point (AP) interface transponder solution is to use direct laser diode modulation for uplink and direct photo-detection for downlink. These solutions require the use of high power amplifiers and other RF processing electronics. Solutions employing electro-absorption modulators and semiconductor optical amplifiers can simplify electrical/optical conversion because these devices can perform detector/modulator functions simultaneously. However, they need complex optoelectronics and electronics for signals processing, which increase cost, complexity and power consumption.

Recognizing that a major challenge towards economically viable pico-cellular RoF networks is to implement low cost cell transponders with high efficient electrical and optical functionalities, we propose to investigate electrical optical (E/O) uplink and optical-electrical (O/E) downlink transponder functions using non-linear circuits based on the integration of resonant tunneling diode (RTD) oscillators with laser diodes (LD) and photo-detectors (PDs), respectively. The main advantages of these circuits are their intrinsic RF signals amplification and circuit simplicity, which makes them low-cost and more reliable.

The RTD is a nano-electronic device with a N shaped current-voltage characteristic exhibiting a negative differential resistance (NDR) region that can be used to implement high frequency electrical oscillators. When integrated with optoelectronic devices, such as LDs, can lead to novel optoelectronic functionalities such as optoelectronic voltage controlled oscillators (OVCO). This RTD-LD free-running oscillator when perturbed by radio-frequency broadcasted signals can synchronize and amplify very low power (<-40 dBm) incoming wireless signals, with the laser modulation depth being mainly determined by the NDR extension and not by wireless signal level. The oscillator locking range allows also a dynamic use of the frequency spectra available. This novel OVCO concept works as a wireless-to-optical interface converting a received low power wireless signal into an optical signal sub-carrier.

A complementary circuit is obtained integrating a RTD oscillator with a photoconductive region, the RTD-PD oscillator, that when directly illuminated by a modulated optical signal locks to the optical signal subcarrier. The optical injection locking capacity is used to O/E conversion to implement optical-to-wireless interfaces where the electrical output power is determined by the NDR region extension.

The objective of our proposal is to demonstrate simple and low-cost downlink and uplink transponder functions using RTD-LD and RTD-PD oscillators, based on locking to wireless and to optical injected signals, respectively. This proposal foresees a low-cost AP solution with no need of format and frequency conversion or complex optoelectronic and electronic circuitry, such as high power amplifiers. A UK patent application of this concept was filled last November.

The PI know-how on RTD based optoelectronic circuits, and other team members wide range of skills that includes knowledge of RoF systems, optical communication systems, and WDM networks, makes the team well qualified to accomplish the main goals of the proposal: implement access point E/O and O/E transponders uplink and downlink using RTD-LD and RTD-PD oscillators. Two member of the team are also involved with the project PTDC/EEA-TEL/71678/2006 aiming the demonstration of a reconfigurable RoF network operating at millimeter-wave frequencies.

Participating Institutions
Centro de Electronica Optoelectronica e Telecomunicacoes (CEOT/UAlg)
Instituto de Engenharia de Sistemas e Computadores do Porto (INESC Porto/FE/UP)

Host Institution
Universidade do Algarve (UAlg)

Research team
Jose Figueiredo (CEOT/UALG) - Principal Investigator
Bruno Romeira (CEOT/UALG)
Horacio Cantu (CEOT/UALG)
Ricardo Luz (MSc student)
Ligia Luis (MSc student)
Henrique Salgado (INESC Porto/FE/UP)
Joao Oliveira (INESC Porto/FE/UP)
Luis Pessoa (INESC Porto/FE/UP)
Ricardo Avo (CEOT/UALG)

Evaluation: Overall, the proposal is well written and detailed. The challenges that need to be addressed are clear and there is a definite research plan and roadmap in terms of what needs to be achieved and how the challenges will be addressed. If successful, the technologies developed can have a positive impact on the scientific and engineering communities.

Overall rating: 90

- Conversion of Phase Modulated Signals from Optical Network to Wireless Domain using Resonant Tunneling Diode Optoelectronic Integrated Circuits, Horacio Cantu; Bruno Romeira; Krishna Seunarine; Anthony Kelly; Charles Ironside; Jose Figueiredo; to be presented at The Optical Fiber Communication Conference 2012 (OFC/NFOEC 2012). (PDF)

- Nonlinear dynamics of a Lienard delayed-feedback optoelectronic oscillator, B. Romeira, J. M. L. Figueiredo, C. N. Ironside, K. Seunarine, and J. Javaloyes, Joint conference Third International Workshop on Nonlinear Dynamics and Synchronization (INDS'11) and Sixteenth International Symposium on Theoretical Electrical Engineering (ISTET'11), Session: Nonlinear Dynamics, chaos and Synchronization - 2, Klagenfurt, Austria, July 25-27, 2011. (PDF)

- Clock Recovery of an Injection-Locked Resonant Tunneling Diode Microwave-Photonics Oscillator, B. Romeira, L. M. Pessoa, H. M. Salgado, S. Silva, J. M. L. Figueiredo, 13th International Conference on Transparent Optical Networks (ICTON 11), paper We.C5.6, Stockholm, Sweden, June 26-30, 2011. (PDF)

- A Lienard optoelectronic oscillator with time-delayed feedback, B. Romeira, K. Seunarine, C. N. Ironside, J. Javaloyes, A. E. Kelly, J. M. L. Figueiredo, The European Conference on Lasers and Electro-Optics (CLEO) and the European Quantum Electronics Conference (EQEC) Conference Digest, OSA Technical Digest (CD) (Optical Society of America, 2011), paper CI3.2, Munich, Germany, May 22-26, 2011. (PDF)

- Review of optoelectronic oscillators based on modelocked lasers and resonant tunneling diode optoelectronics, C. N. Ironside, M. Haji, L. Hou, J. Akbar, A. E. Kelly, K. Seunarine, B. Romeira, J. M. L. Figueiredo, International Conference on Applications of Optics and Photonics (AOP11), Proc. SPIE 8001, 80011T, Braga, Portugal, May 3-7, 2011. (PDF)

- Optoelectronic Oscillator Topologies based on Resonant Tunneling Diode Fiber Optic Links, B. Romeira, J. M. L Figueiredo, K. Seunarine, C. N. Ironside, International Conference on Applications of Optics and Photonics (AOP11), Proc. SPIE 8001, 80011T, Braga, Portugal, May 3-7, 2011. (PDF)

- A Self-Synchronized Optoelectronic Oscillator based on an RTD Photo-Detector and a Laser Diode, B. Romeira, K. Seunarine, C. N. Ironside, A. E. Kelly, J. M. L. Figueiredo, Photon. Technol. Lett., 23 (16), pp. 1148-1150, 2011. (PDF)

- DC Characterization of Tunnel Diodes Under Stable Non-Oscillatory Circuit Conditions, L. Wang, J. M. L. Figueiredo, C. N. Ironside, E. Wasige, IEEE Transactions on Electron Devices, 58 (2), pp. 343-347, 2011. (PDF)

- Applications of laser diode sources with integrated resonant tunnelling diode technology, C. N. Ironside, B. Romeira, K. Seunarine, , A. E. Kelly, T. J Slight, and J. M. L. Figueiredo, Photonex2010 - Industry Programme, C6: Novel Sources and detectors, Telford, UK, 3-4 November 2010. (PDF)

- Optical Control of a Resonant Tunneling Diode Microwave-Photonic Oscillator, B. Romeira, J. M. L. Figueiredo, C. N. Ironside, A. E. Kelly, T. J. Slight, IEEE Photonics Technology Letters, vol. 22, no. 21, pp. 1610-1612, 2010. (PDF)

- An Optoelectronic Oscillator based on a Resonant Tunneling Diode Photo-Detector Integrated Chip, B. Romeira, K. Seunarine, C. N. Ironside, A. E. Kelly, T. J Slight, J. M. L. Figueiredo, The 23rd Annual Meeting of the IEEE Photonics Society, paper MD4, Denver, Colorado, USA, 7-11 November, 2010. (PDF)

- Microwave-Photonic Oscillators for Radio-over-Fibre Access Networks, J. M. L. Figueiredo, B. Romeira, T. J. Slight, C. N. Ironside, VIII Symposium On Enabling Optical Networks and Sensors (SEON 10), FEUP, Porto, Portugal, 2010. (PDF)

- Microwave Photonic Oscillators for Femtocellular Access Networks, B. Romeira, T. J. Slight, A. E. Kelly, C. N. Ironside, J. M L Figueiredo, 15th European Conference on Networks and Optical Communications (NOC 2010), Components and modulation strategies, Faro-Algarve, Portugal, 8-10 Junho 2010. (PDF)

- Interfaces and Method For Wireless-Optical and Optical-Wireless Conversion, J. M. L. Figueiredo, B. Romeira, C. N. Ironside, T. J. Slight, 2010, Patent Application GB2465184-A; Patent Application WO2010052481-A1 (publication date 14-05-2010). (PDF)

- Telecommunications interfacing systems and methods, Patent Application No GB0820432.3 (publication date 12-05-2010). (PDF)