Led by Dr. Massimiliano Guasoni, the Multimode Photonics Group focuses on the design and fabrication of optical waveguides where strong interactions between different spatial modes take place. The exploitation of these interactions paves the way towards exceptional opportunities and novel functionalities well beyond those available in traditional optical devices.
Optical waveguides are physical structures that guide light. Optical fibers, which are the backbone of the modern Internet network, represent a popular and relevant example of waveguide.
Light can propagate into a waveguide in the form of different beams, each one characterized by a specific spatial shape (see figure below). These beams are called spatial modes.
Despite the existence of an infinity of different modes, however current technology is mainly based on the exploitation of just one spatial mode, which is the mode with circular shape. This is the case, for example, of the light travelling in optical fibers or emitted from a laser pointer (see below). Nevertheless, in recent years a new paradigm has emerged in optics, which is the exploration of several modes beyond the circular-shaped one (so called higher-order modes).
When several different modes are confined into a waveguide, they can strongly interact via the nonlinear response of the waveguide material. In this way, photons from a given mode at some frequency can be converted into a new mode at a different frequency. It becomes therefore possible to generate light in a very broad spectral region inaccessible so far and, at the same time, to control the spatial profile of light, which allows the generation of beams with many different shapes.
A precise design of the waveguide material and geometry is of utmost importance to maximize the frequency conversion. The design and fabrication of optimal waveguides is the main objective of our work. Different kind of waveguides are explored. From long optical fibers, where the frequency conversion can be exploited to develop broadband optical amplifiers to speed up the Internet network, up to tiny on-chip waveguides, where different modal interactions can be exploited to generate light in a very broad infrared spectrum, which finds application in medicine, sensing and security.
Our research focuses on the design and fabrication of innovative optical waveguides. Both tasks are accomplished through the exploitation of world-class facilities available at the ORC.
The IRIDIS supercomputer, one of the most powerful in UK, allows running the heavy and complex numerical simulations required at the design stage.
For the fabrication and characterization of optical fibers and on-chip waveguides we have access to fiber-drawing towers, a dedicated centre for nanofabrication (including e-beam and optical lithography, chemical vapour deposition, sputterers, evaporators) and a wide range of optical sources (high-power fiber lasers and laser diodes, optical parametric oscillators, supercontinuum sources).
Our group works in close collaboration with several research groups, both within the ORC and worldwide.
Internal collaborations (ORC groups):
Huawei Technologies Co.
We aim at developing novel silicon-based waveguides where the nonlinear interaction between different pairs of spatial modes gives rise to light generation in a broad infrared spectrum. The ultimate goal is the development of a single device, based on silicon-germanium waveguides, capable of emitting light in the full spectral range from 2 to 15 um, well beyond what is possible in state-of-the art technology. We envisage that such a tiny, wideband device would find application in several fields, from medicine (non-invasive breath analysis), to environment (air-pollution monitoring) up to security (explosive detection and aircraft anti-missile defence systems).
Mode Division Multiplexing (MDM) has recently emerged as a promising breakthrough technology to boost the data transmission speed of the Internet network to unprecedented levels. In MDM each spatial mode of an optical fiber carries an independent data channel, so that exploiting for example 10 modes can increase the data transmission speed up to 10 times. However, in order to move from a pure academic research to a fully exploitable commercial technology, MDM requires the development of novel devices that must be urgently addressed. The most important are multimode optical amplifiers, capable of amplifying simultaneously several different spatial modes. We aim at developing a novel idea of fiber optical multimode parametric amplification where four-wave-mixing between different fiber modes is exploited to amplify several modes in a wide bandwidth covering the main telecom windows (C+L bands). This is done through the design of novel optical fibers having special refractive-index profile.
We are currently recruiting PhD students to work in the project “Design and fabrication of multimode on-chip waveguides for infrared generation”.
Please contact Dr. Massimiliano Guasoni (email@example.com) for more details