Limits...
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)–(f) Resonance images of resist blocks as refractive index contrast is lowered. Δn ≈ 0.077, 0.062, 0.046, 0.029, 0.010, and −0.010 in (a)–(f), respectively. (The negative value indicates that the index of the surrounding liquid is now greater than that of the resist.) The width and the spacing of the bars in each frame is 7 μm for the top group, increasing to 8.5 μm for the bottom group, and the bars are aligned parallel to the grating grooves. Resolution is thus measured perpendicular to the grating grooves, as in Fig. 2(b). (g) Zoomed-in region indicating locations of pixels for the spectra in (h). Average resonance wavelength (i) and FWHM (j) of background pixels vs. surrounding refractive index. Error bars show the standard deviations.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 5: (a)–(f) Resonance images of resist blocks as refractive index contrast is lowered. Δn ≈ 0.077, 0.062, 0.046, 0.029, 0.010, and −0.010 in (a)–(f), respectively. (The negative value indicates that the index of the surrounding liquid is now greater than that of the resist.) The width and the spacing of the bars in each frame is 7 μm for the top group, increasing to 8.5 μm for the bottom group, and the bars are aligned parallel to the grating grooves. Resolution is thus measured perpendicular to the grating grooves, as in Fig. 2(b). (g) Zoomed-in region indicating locations of pixels for the spectra in (h). Average resonance wavelength (i) and FWHM (j) of background pixels vs. surrounding refractive index. Error bars show the standard deviations.

Mentions: Fig. 5(a)–(f) shows the resonance images of groups of four blocks on top of a 1-D grating as the index of the surrounding liquid is increased. The background becomes red (corresponding to a higher resonance wavelength) because the higher index shifts the resonance upwards in wavelength. The final two images [see Fig. 5(e) and (f)] are taken near Δn = 0, with Fig. 5(f) indicating that we have passed Δn = 0 as the blocks themselves are now lighter than the background (they have a lower resonance wavelength), even though they cannot be individually resolved at this low contrast. We refer to an index contrast that has passed Δn = 0 as being “negative” in this context. Fig. 5(g) indicates the locations of pixels used for the spectra shown in Fig. 5(h), as we move across the edge of a block of resist.


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)–(f) Resonance images of resist blocks as refractive index contrast is lowered. Δn ≈ 0.077, 0.062, 0.046, 0.029, 0.010, and −0.010 in (a)–(f), respectively. (The negative value indicates that the index of the surrounding liquid is now greater than that of the resist.) The width and the spacing of the bars in each frame is 7 μm for the top group, increasing to 8.5 μm for the bottom group, and the bars are aligned parallel to the grating grooves. Resolution is thus measured perpendicular to the grating grooves, as in Fig. 2(b). (g) Zoomed-in region indicating locations of pixels for the spectra in (h). Average resonance wavelength (i) and FWHM (j) of background pixels vs. surrounding refractive index. Error bars show the standard deviations.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4561521&req=5

Figure 5: (a)–(f) Resonance images of resist blocks as refractive index contrast is lowered. Δn ≈ 0.077, 0.062, 0.046, 0.029, 0.010, and −0.010 in (a)–(f), respectively. (The negative value indicates that the index of the surrounding liquid is now greater than that of the resist.) The width and the spacing of the bars in each frame is 7 μm for the top group, increasing to 8.5 μm for the bottom group, and the bars are aligned parallel to the grating grooves. Resolution is thus measured perpendicular to the grating grooves, as in Fig. 2(b). (g) Zoomed-in region indicating locations of pixels for the spectra in (h). Average resonance wavelength (i) and FWHM (j) of background pixels vs. surrounding refractive index. Error bars show the standard deviations.
Mentions: Fig. 5(a)–(f) shows the resonance images of groups of four blocks on top of a 1-D grating as the index of the surrounding liquid is increased. The background becomes red (corresponding to a higher resonance wavelength) because the higher index shifts the resonance upwards in wavelength. The final two images [see Fig. 5(e) and (f)] are taken near Δn = 0, with Fig. 5(f) indicating that we have passed Δn = 0 as the blocks themselves are now lighter than the background (they have a lower resonance wavelength), even though they cannot be individually resolved at this low contrast. We refer to an index contrast that has passed Δn = 0 as being “negative” in this context. Fig. 5(g) indicates the locations of pixels used for the spectra shown in Fig. 5(h), as we move across the edge of a block of resist.

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