Optical gratings are a common and very useful tool in many applications such as spectrometers, refractive index sensors, surface plasmon resonance (SPR) excitation and waveguide light couplers. However, commercially available gratings are expensive because of their nanometer dimensions, which limits their use in very cost-effective devices.
DVD and Blu-Ray discs have been proposed as a good alternative when no specific pitch size is required. By considering both periodicities (740 and 320 nm) and different polymers and coatings, it is possible to fabricate a variety of gratings with different responses to an incident light beam.
Figure: A grating-coupled SPR disc with various pitch sizes and periodic structures (Fabricating microstructures using a modified optical-disc process, SPIE 10.1117/2.1201106.003680)
DVD-based devices involve a periodicity close to, but greater than the wavelenght of visible light. This implies resonant responses in the visible spectrum, which is desirable to fabricate and interrogate sensors.
In Blu-Ray based devices, where visible light interacts with a nanostructured medium (Blu-ray grooves) it is interacting with structures smaller than its wavelength. In this regimen the interaction between light and matter exhibits anomalies and exotic phenomena, which allows to enhance parameters of interest and improve optical devices (artificial refractive index tuning, imaging beyond the diffraction limit, extra-ordinary transmittance, zero-order gratings...)
Figure: Examples of SPR based sensor approaches. (Surface Plasmon Resonance Sensors for Detection of Chemical and Biological Species, Chem. Rev. 2008, 108, 462-493)
Therefore, both DVD and Blu-Ray represent a suitable basis to fabricate 1D grating-based devices such as Surface Plasmon Resonance (SPR) sensors. Furthermore, by recording pit marks in the disks it is possible to define 2D structures with a custom defined pitch and fill factor in one dimension (minimum pit mark ~400nm in DVD and ~150nm in Blue-ray).
1) Fabricate DVD and Blu-Ray based gratings using different approaches (Diffraction, Surface Plasmon Resonance, Zero-order gratings...) and techniques (Coating, Photolithography, Laser Direct Image (LDI), Imprinting…) to obtain a variety of gratings with different spectral responses.
2) Modify a commercial Optical Disc Drive (ODD) to selectively modify (write) the structure of the optical discs, and analyze them (read).
3) Characterization of the fabricated devices using commercial devices (microscope, SEM, spectrometer...) and a modified ODD.
4) Demonstrate the sensing capability of fabricated gratings by integrating them in a cross-reactivity-based gas sensor. The combined spectral response of a variety of gratings will lead to distinct signal signatures when exposing the device to different gas analytes.
Figure: Left: Laser Direct Imaging device. Right: Optical Disc Drive.
grating, optical, sensor, photonics, sensor, nanostructure
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