Silicon - the ideal photonic material at longer wavelength
Silicon is the material of choice for the microelectronics industry, but its use in Photonics is limited by effects such as two-photon absorption and the resulting free-carrier absorption. At wavelengths above 2.2 µm, however, these limitations no longer apply, and silicon exhibits some of the most favourable properties of any photonic material. The aim of this project is to explore the potential of silicon in this wavelength regime, especially with respect to resonantly enhanced functionality as occurs in slow light waveguides and cavities. Examples include the following,
1. - Enhanced nonlinear effects in cavities and slow light waveguides. We have already observed many exciting nonlinear effects in silicon in the near-IR wavelength regime (Overview: T. F. Krauss, "Why do we need slow light?," Nature Photonics, 2 (8), 448-450 (2008); Third harmonic: B. Corcoran, C. Monat, C. Grillet, D. J. Moss, B. J. Eggleton, T. P. White, L. O'Faolain, T. F. Krauss, "Green light emission in silicon through slow-light enhanced third-harmonic generation in photonic-crystal waveguides," Nature Photonics, 3 (4), 206-210 (2009); and M. Galli, D. Gerace, K. Welna, T. F. Krauss, L. O'Faolain, G. Guizzetti, L. C. Andreani, "Low-power continuous-wave generation of visible harmonics in silicon photonic crystal nanocavities," Optics Express, 18 (25), 26613-26624 (2010); Four wave mixing: J. Li, L. O'Faolain, I. H. Rey, T. F. Krauss, "Four-wave mixing in photonic crystal waveguides: slow light enhancement and limitations," Optics Express, 19 (5), 4458-4463 (2011)). These effects will be orders of magnitude stronger in the MID-IR, thus opening a truly novel realm of all-optical signal processing.
2. - Emission control. It may be possible to create novel light emitters with photonic-crystal controlled emission, thus providing novel and versatile sources.
3. - Sensing and filtering. Gas sensing and related environmental sensing is one of the most important applications for MID-IR photonics. Using the exquisite filtering properties of photonic crystal lattices and cavities, advanced sensing functionalities can be realised.
The project will be based in the Microphotonics Group at St Andrews University (www.st-andrews.ac.uk/microphotonics) and will involve the design, fabrication and characterisation of waveguides, cavities and devices with the above fundamental and applied functionalities in mind. Some of the work will be carried out in the departmental cleanroom and the student will become proficient in all of the relevant technologies, including electron-beam lithography, dry etching and thin film deposition. The structures will be characterised with a tunable Optical Parametric Oscillator operating in the 2.5-3.4 µm range. |
Silicon light emission in photonic crystal nanocavities
Due to its indirect bandgap, silicon is an intrinsically poor light emitter. Surprisingly, a combination of material treatment and enhanced light-matter interaction in photonic crystal cavities does offer interesting opportunities for providing laser-like light sources. Having already demonstrated some of the highest Q-factor cavities and lowest loss waveguides in silicon, we have recently observed suprisingly efficient photoluminescence and elelctroluminescence from silicon nanocavities (R. Lo Savio, S. L. Portalupi, D. Gerace, A. Shakoor, T. F. Krauss, L. O'Faolain, L. C. Andreani, M. Galli, "Room-temperature emission at telecom wavelengths from silicon photonic crystal nanocavities," Appl. Phys. Lett., 98 (20), 201106 (2011)). The resulting spectral and spatial density of emission in terms of power per unit area and wavelength is amongst the most efficient silicon light emitters ever realised, and is beginning to approach that of III-V materials.
The project involves working with materials scientists in order to understand the luminescence process better, which is based on Hydrogen incorporation into the silicon lattice. In addition, you will design novel tpyes of cavities and coupled cavity structures that further enhance the radiation effiiciency, with the goal of achieving laser emission in due course. If successful, this project will introduce silicon as a viable light emitting material and transform the field of Photonics.
The project will be based in the Microphotonics Group at St Andrews University (www.st-andrews.ac.uk/microphotonics) and will involve the design, fabrication and characterisation of cavities and devices designed to maximise lighrt-mastter interaction and light emission. Some of the work will be carried out in the departmental cleanroom and the student will become proficient in all of the relevant technologies, including electron-beam lithography, dry etching and thin film deposition. |
