The potential exploitation of the metal-dissolution effect in chalcogenide glass for the fabrication of diffractive structures is investigated. Evaporated As-S films form the host chalcogenide glass for optical or thermally stimulated dissolution from a metal source, usually an evaporated Ag film. A potentially more flexible alternative fabrication method in which the source is a photolithographically generated metal grating is considered. Ag gratings with periods of 6-12<I>μ</I>m and thicknesses up to 0.4<I>μ</I>m are produced on fused silica substrates and coated with 1-2<I>μ</I>m thick As-S layers. The resultant metal-dissolved structures have diffraction efficiencies of 4-7% when replayed with a HeNe laser (λ = 633nm) and remain well defined in the lateral dimensions despite some sideways leakage of Ag evident for both the thermal and optical dissolution regimes. Higher efficiencies should be possible using this method with optimised structures. The gratings are stable for HeNe beam powers of 6mW once all the Ag source has dissolved. The thermal coefficients of the optical thickness (<I>nd</I>) of the metal-rich and metal-free glass phases were measured in the infrared to assess the potential of metal-dissolved gratings in the field of athermalised optical systems. The metal-rich glass phase was found to have a coefficient 2.5x that for the metal-free phase, the films being annealed in each case. Coupled-wave theory is used to predict the likely behaviour of metal-dissolved gratings for various profiles and modulations in refractive index. Low modulation bulk gratings can give high diffraction efficiencies (>90%, neglecting reflection losses) and it is shown that the square-wave structure has particular merit because of its reduced grating depth requirements. For a bulk square-wave grating with a larger modulation the diffraction efficiency is shown to be over 80% when the grating depth is twice the period (<I>d </I>= 2Λ).
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:649076 |
| Date | January 1996 |
| Creators | Dale, Gary |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/13545 |
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