Optical Wavelength Conversion

About

Background: The network that underpins the Internet, and most modern communications, uses a range of advanced technologies, amongst which optical fibre is perhaps one of the most critical components, requiring a range of optical transmission, modulation, modification and detection technologies. Transmission of digital information from one computer to another, via the Internet, involves a range of protocols and technologies and underneath all of these, the optical fibre transmits the data in a range of formats at increasing speeds. As demand increases for more services to be delivered via the Internet, so network providers work to deliver increased speed to users, whether they are at home, at work, or on the move. Inside any given optical fibre, there are many different optical wavelengths being transmitted, each wavelength carries unique information. The capacity of any fibre to transmit information is increased by either increasing the speed of transmission or by putting more optical wavelengths down the fibre – or both. Over long distances (long-haul), this is a straightforward activity. However, when the fibre reaches, for example, the edge of a city, then there is a need to separate and route the information to many different locations. Within the city (the metro network), there are also internal communications, so there are a range of switching nodes that enable this redirection and control. Although a message may be transmitted on a long-haul fibre at one wavelength the metro network needs to use wavelengths to route data to the right address. This means that the data may arrive at a node on one wavelength but has to be sent out on a different wavelength. At present, this wavelength conversion is done electronically: the signal is converted from optical into electronic form with a detector, processed (to improve signal quality due to degradation in transmission), before it is transmitted onwards down the fibre using a new wavelength using a tuneable laser. This speed of wavelength conversion is determined by the electronics between the detector and second laser and is one of the major drivers for developing the next generation all-optical network. In addition, increasing demands on global delivery of high-performance network-based applications, such as cloud computing and (ultra) high definition video-on-demand streaming, calls for next generation all-optical networks of higher capacity and more powerful signal processing capability. Transparency (i.e. being unconcerned about the data format) and speed of operation (achieved by avoiding conversion from optical to electronic and back to optical) are the keys to a fast and successful network of the future. Wavelength conversion is therefore acknowledged as one of the most significant optical processing functions in all-optical network systems. Some of the critical functions it can fulfil include reconfigurable routing, contention resolution, wavelength reuse, multicasting, and traffic balancing.  There are a number of existing wavelength conversion techniques including optical-electrical-optical (O/E/O) conversion, cross gain modulation (XGM), cross phase modulation (XPM), frequency generation (DFG), and four wave mixing (FWM). However, none of these techniques provide the required functionality.   Current issues: The existing all-optical wavelength conversion (AOWC) techniques can be mainly classified into two categories: optical gating and coherent mixing. Optical gating wavelength conversion techniques (e.g. cross gain modulation (XGM) and cross phase modulation (XPM)) exploit carrier depletion and/or carrier density-induced refractive index changes, so only intensity-modulated input signals can be converted. Coherent mixing wavelength conversion techniques (i.e. difference frequency generation (DFG) and four wave mixing (FWM)) utilize the photon conversion function in the second- or the third-order nonlinear materials which requires phase matching for efficient conversion. FWM-based AOWC has been investigated widely in recent years in different structures such as fibers, silicon waveguides, and semiconductor optical amplifiers, and is commonly thought one of the most promising AOWC techniques because of its unique advantages of supporting format-transparent operation. However, due to the need for phase-matching, FWM suffers from poor conversion wavelength tunability, and hence channel switching capability, which could severely limit the development of the next generation of All Optical Networks.   Our new technology: The Wireless & Optoelectronic Research and Innovation Centre at the University of South Wales Optical has developed a new All-Optical Wavelength Conversion (AOWC) technology that allows all-optical wavelength conversion with the advantages of high bandwidth, high speed and low power consumption. This technology will enable the key functionality required for delivery of high-performance network-based applications and support next generation all-optical networks representing a ‘step change’ for the telecommunications industry and its users.    Benefits: The potential benefits of the University of South Wales’ AOWC technology over existing competitive products are that it can provide high-speed wavelength conversion without the need for conversion into an electronic signal. This will allow better efficiencies and services from Internet providers: The ability to select wavelengths for data transmission To do this without reference to the data form To enable data transmission and wavelength conversion without affecting transmission speed To enable new temporal buffering schemes that use dispersive optical transmission To effect dynamic dispersion compensation that allows significant improvements in quality of service (QOS). Current technology is not able to do all of this at the speeds necessary for future network speed demands.   Applications: This technology will enable the key functionality required for delivery of high-performance network-based applications and support next generation all-optical networks. It is also likely that other applications will emerge for some of the science behind the AOWC technology in spectroscopy, metrology and sensing and in any sectors where dynamic wavelength tunability is essential.   Intellectual property: US patent granted UK patent pending Validation test results Demonstrator Specialist technical/proprietary know-how