THE LASER PHYSICS CENTRE

• Production and Characterisation of Single Mode Polymer Optical Waveguides Using Simple Moulding Techniques
  
  Supervisors: Anna Samoc, Marek Samoc and Robbie Charters
  
  Development of the methods for inexpensive fabrication of planar waveguides and patterned structures on a silicon chip is one of the important requirements for advancing photonic technologies in data communication and optical computing. Photolithography and direct writing are the key technologies in which radiation-sensitive polymers (photoresists) are patterned with photons to form a stencil (a rigid mask) to transfer the circuit pattern to underlying layers. Among possible technologies for fabrication of patterned structures, a modification of photolithographic method using an elastomeric mask obtained in direct moulding with a possibility to use it in fabrication of rib-like polymer-based waveguides appear to be very attractive because of potential for mass production. Recent work by the group of G. Whitesides [J.A. Rogers, K.E. Paul. R.J. Jackman and G.M. Whitesides, "Using an elastomeric mask for sub-100 nm photolithography in the optical near field", Appl. Phys. Lett. 70, 2658 (1997); G.M. Whitesides and Y. Xia, "Replica molding: complex optics at lower costs", Photonics Spectra, January 1997, p. 90] has brought an interesting proposal for the technology which essentially consists of the following steps:
  • preparation of a master relief pattern by photolithography
    
  • transfer of the negative of the pattern to a mould made by in-situ polycondensation of an elastomer polymer (Dow Corning Sylgard 184) to form an elastomeric mask
    
  • contact printing of the waveguide pattern into an optical polymer
  
  
  We would like to use this technology to produce single mode waveguide structures which can be patterned to be a part of optical circuits, e.g. adiabatic couplers, splitters etc and we would like to characterise their optical properties, especially the loss factors. Morphology of the structures will be studied with electron microscopy. The project will require a candidate with broad scientific interests in physics, material science and engineering and a feel for practical technological issues.

• Laser Patterning Linear and Nonlinear Optical Films for Applications in Photonics.
  
  Supervisors: Anna Samoc, Marek Samoc and Robbie Charters
  
  In photonic technologies light beams carrying signals (information) are transmitted through fibres, the processing of the signals, however, needs the development of passive and active photonic devices which can be made in the form of planar waveguide structures. While the transmission of information requires the weak interaction of light beams (many streams of information can be carried together in parallel), an active device requires nonlinear optical material that causes light beams to interact strongly affecting the signals. This corresponds to operations such as switching or amplification. Photonic devices such as couplers, splitters, interferometers can be made by suitable patterning of waveguiding thin films obtained by a number of techniques. Plasma deposited silica films, spin-coated polymer films, films obtained by a sol-gel technique are examples of materials which can be suitable for optical low-loss waveguiding that is confining the light beams to propagate within the thickness of a thin film. Additional confinement can be achieved within waveguide channels and structures made of these channels. This requires additional processing of the films like direct writing or photolithography. We are currently using a UV laser system coupled with a high precision computer-driven X-Y stage to write waveguide patterns into some materials in which exposure to laser light results in an increase of the refractive index: allowing one to define channel waveguides. Alternatively, one can use laser light to reduce the refractive index in some materials by a bleaching process.
  
  The proposed project will involve the use of laser patterning in optical materials which will also involve novel materials based on p-conjugated polymers with structures derived from poly(p-phenylenevinylene) (PPV). PPV is a polymer exhibiting very high third-order nonlinearity characterised by the nonlinear refractive index n2 (A. Samoc, M. Samoc, M. Woodruff and B. Luther-Davies, "Tuning the properties of poly(p-phenylenevinylene) for use in all-optical switching", Optics Letters, 20,1241 (1995).
  The project will involve fabrication of thin films, patterning, material and waveguide characterisation by a number of techniques involving Laser Physics Centre facilities. The project will require a candidate with broad scientific interests in physics, chemistry, material science and engineering and interested in developing research skills.