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Spatial Resolution and Refractive Index Contrast of Resonant Photonic Crystal Surfaces for Biosensing.

Triggs GJ, Fischer M, Stellinga D, Scullion MG, Evans GJ, Krauss TF - IEEE Photonics J (2015)

Bottom Line: Our experimental results and finite-difference time-domain (FDTD) simulations at different refractive index contrasts show that the spatial resolution of our device reduces with reduced contrast, which is an important consideration in biosensing, where the contrast may be of order 10(-2).At very low index contrast, the resolution worsens dramatically, particularly for Δn < 0.01, where we observe a resolution exceeding 10 μm for our device.In addition, we measure a reduction in the resonance linewidth as the index contrast becomes lower, corresponding to a longer resonant mode propagation length in the structure and contributing to the change in spatial resolution.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physics, University of York, York YO24 1UB, U.K.

ABSTRACT

By depositing a resolution test pattern on top of a Si3N4 photonic crystal resonant surface, we have measured the dependence of spatial resolution on refractive index contrast Δn. Our experimental results and finite-difference time-domain (FDTD) simulations at different refractive index contrasts show that the spatial resolution of our device reduces with reduced contrast, which is an important consideration in biosensing, where the contrast may be of order 10(-2). We also compare 1-D and 2-D gratings, taking into account different incidence polarizations, leading to a better understanding of the excitation and propagation of the resonant modes in these structures, as well as how this contributes to the spatial resolution. At Δn = 0.077, we observe resolutions of 2 and 6 μm parallel to and perpendicular to the grooves of a 1-D grating, respectively, and show that for polarized illumination of a 2-D grating, resolution remains asymmetrical. Illumination of a 2-D grating at 45° results in symmetric resolution. At very low index contrast, the resolution worsens dramatically, particularly for Δn < 0.01, where we observe a resolution exceeding 10 μm for our device. In addition, we measure a reduction in the resonance linewidth as the index contrast becomes lower, corresponding to a longer resonant mode propagation length in the structure and contributing to the change in spatial resolution.

No MeSH data available.


Related in: MedlinePlus

(a) Grating structure. (b) Transmission spectra of gratings with slightly different periods. (c) SEM image of a group of four blocks of FOx resist on top of a silicon nitride grating. (d) Resonance image of two groups of four blocks. The color scale indicates the resonance wavelength in nanometers. (Bottom) Illustration of decreasing the width and the spacing of the groups of resist blocks used to determine the spatial resolution for Fig. 2. (e) Measured spectra from regions indicated by the white circles in (d), showing measured data points (black markers), and fitted Gaussian curves (blue and red dashed lines).
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Figure 1: (a) Grating structure. (b) Transmission spectra of gratings with slightly different periods. (c) SEM image of a group of four blocks of FOx resist on top of a silicon nitride grating. (d) Resonance image of two groups of four blocks. The color scale indicates the resonance wavelength in nanometers. (Bottom) Illustration of decreasing the width and the spacing of the groups of resist blocks used to determine the spatial resolution for Fig. 2. (e) Measured spectra from regions indicated by the white circles in (d), showing measured data points (black markers), and fitted Gaussian curves (blue and red dashed lines).

Mentions: To fabricate a resonant surface, a slab of high refractive index dielectric is structured to form a grating waveguide layer that supports a guided mode resonance (GMR) [15], [16], as shown in Fig. 1(a). For a specific incidence angle, wavelength, grating fill factor, period, thickness, polarization and refractive index, the grating supports a resonant mode excited by diffraction. This resonance manifests itself as a dip or peak in the transmission or reflection spectra, with the thickness of the grating layer being the main parameter which controls whether the device acts as a bandpass or a bandstop filter (the spectra in Fig. 1(b) show the device working as a bandstop filter in transmission). A change of refractive index in the vicinity of the grating shifts the resonance wavelength, which provides the information used to create the final image.


Spatial Resolution and Refractive Index Contrast of Resonant Photonic Crystal Surfaces for Biosensing.

Triggs GJ, Fischer M, Stellinga D, Scullion MG, Evans GJ, Krauss TF - IEEE Photonics J (2015)

(a) Grating structure. (b) Transmission spectra of gratings with slightly different periods. (c) SEM image of a group of four blocks of FOx resist on top of a silicon nitride grating. (d) Resonance image of two groups of four blocks. The color scale indicates the resonance wavelength in nanometers. (Bottom) Illustration of decreasing the width and the spacing of the groups of resist blocks used to determine the spatial resolution for Fig. 2. (e) Measured spectra from regions indicated by the white circles in (d), showing measured data points (black markers), and fitted Gaussian curves (blue and red dashed lines).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
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getmorefigures.php?uid=PMC4561521&req=5

Figure 1: (a) Grating structure. (b) Transmission spectra of gratings with slightly different periods. (c) SEM image of a group of four blocks of FOx resist on top of a silicon nitride grating. (d) Resonance image of two groups of four blocks. The color scale indicates the resonance wavelength in nanometers. (Bottom) Illustration of decreasing the width and the spacing of the groups of resist blocks used to determine the spatial resolution for Fig. 2. (e) Measured spectra from regions indicated by the white circles in (d), showing measured data points (black markers), and fitted Gaussian curves (blue and red dashed lines).
Mentions: To fabricate a resonant surface, a slab of high refractive index dielectric is structured to form a grating waveguide layer that supports a guided mode resonance (GMR) [15], [16], as shown in Fig. 1(a). For a specific incidence angle, wavelength, grating fill factor, period, thickness, polarization and refractive index, the grating supports a resonant mode excited by diffraction. This resonance manifests itself as a dip or peak in the transmission or reflection spectra, with the thickness of the grating layer being the main parameter which controls whether the device acts as a bandpass or a bandstop filter (the spectra in Fig. 1(b) show the device working as a bandstop filter in transmission). A change of refractive index in the vicinity of the grating shifts the resonance wavelength, which provides the information used to create the final image.

Bottom Line: Our experimental results and finite-difference time-domain (FDTD) simulations at different refractive index contrasts show that the spatial resolution of our device reduces with reduced contrast, which is an important consideration in biosensing, where the contrast may be of order 10(-2).At very low index contrast, the resolution worsens dramatically, particularly for Δn < 0.01, where we observe a resolution exceeding 10 μm for our device.In addition, we measure a reduction in the resonance linewidth as the index contrast becomes lower, corresponding to a longer resonant mode propagation length in the structure and contributing to the change in spatial resolution.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physics, University of York, York YO24 1UB, U.K.

ABSTRACT

By depositing a resolution test pattern on top of a Si3N4 photonic crystal resonant surface, we have measured the dependence of spatial resolution on refractive index contrast Δn. Our experimental results and finite-difference time-domain (FDTD) simulations at different refractive index contrasts show that the spatial resolution of our device reduces with reduced contrast, which is an important consideration in biosensing, where the contrast may be of order 10(-2). We also compare 1-D and 2-D gratings, taking into account different incidence polarizations, leading to a better understanding of the excitation and propagation of the resonant modes in these structures, as well as how this contributes to the spatial resolution. At Δn = 0.077, we observe resolutions of 2 and 6 μm parallel to and perpendicular to the grooves of a 1-D grating, respectively, and show that for polarized illumination of a 2-D grating, resolution remains asymmetrical. Illumination of a 2-D grating at 45° results in symmetric resolution. At very low index contrast, the resolution worsens dramatically, particularly for Δn < 0.01, where we observe a resolution exceeding 10 μm for our device. In addition, we measure a reduction in the resonance linewidth as the index contrast becomes lower, corresponding to a longer resonant mode propagation length in the structure and contributing to the change in spatial resolution.

No MeSH data available.


Related in: MedlinePlus