Abstract:We describe wavelength tuning in a one dimensional (1D) silicon nitride nano-grating guided mode resonance (GMR) structure under conical mounting configuration of the device. When the GMR structure is rotated about the axis perpendicular to the surface of the device (azimuthal rotation) for light incident at oblique angles, the conditions for resonance are different than for conventional GMR structures under classical mounting. These resonance conditions enable tuning of the GMR peak position over a wide range… Show more
“…A linearly polarized light is incident on the grating at an angle θ inc as shown in the figure. After diffraction from the grating, the first order diffracted light travels inside the waveguide whose phase information 15, 16 can be obtained from equation (1) as given below.whereandThe above expression of ‘n eff ’ gives the effective index of the guided mode obtained from the phase matching condition 17, 18 for the case of a GMR structure under conical diffraction 19, 20 regime. The derivation of equation (3) is provided in the supplementary materials section.…”
Section: Resultsmentioning
confidence: 99%
“…It is also to be noted that, to tune the GMR peak wavelength exactly to our laser source wavelength (632.8 nm), we rotated the GMR structure azimuthally with the help of a φ-rotation stage as shown in the figure. This gives us additional degrees of freedom (in addition to θ rotation) to tune the GMR peak position precisely 19, 23 .Figure 3MZI setup. Schematic of the experimental setup of Mach Zehnder Interferometer to measure the phase shift of the GMR signal (drawn using Google SketchUp).
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We report an ultra-sensitive refractive index (RI) sensor employing phase detection in a guided mode resonance (GMR) structure. By incorporating the GMR structure in to a Mach-Zehnder Interferometer, we measured the phase of GMR signal by calculating the amount of fringe shift. Since the phase of GMR signal varies rapidly around the resonance wavelength, the interference fringe pattern it forms with the reference signal becomes very sensitive to the surrounding RI change. The sensitivity comes out to be 0.608π phase shift per 10−4 RI change in water medium which is more than 100 times higher than the other reported GMR based phase detection method. In our setup, we can achieve a minimum phase shift of (1.94 × 10−3) π that corresponds to a RI change of 3.43 × 10−7, outperforming any of reported optical sensors and making it useful to detect RI changes in gaseous medium as well. We have developed a theoretical model to numerically estimate the phase shift of the GMR signal that predicts the experimental results very well. Our phase detection method comes out to be much more sensitive than the conventional GMR sensors based on wavelength or angle resolved scanning methods.
“…A linearly polarized light is incident on the grating at an angle θ inc as shown in the figure. After diffraction from the grating, the first order diffracted light travels inside the waveguide whose phase information 15, 16 can be obtained from equation (1) as given below.whereandThe above expression of ‘n eff ’ gives the effective index of the guided mode obtained from the phase matching condition 17, 18 for the case of a GMR structure under conical diffraction 19, 20 regime. The derivation of equation (3) is provided in the supplementary materials section.…”
Section: Resultsmentioning
confidence: 99%
“…It is also to be noted that, to tune the GMR peak wavelength exactly to our laser source wavelength (632.8 nm), we rotated the GMR structure azimuthally with the help of a φ-rotation stage as shown in the figure. This gives us additional degrees of freedom (in addition to θ rotation) to tune the GMR peak position precisely 19, 23 .Figure 3MZI setup. Schematic of the experimental setup of Mach Zehnder Interferometer to measure the phase shift of the GMR signal (drawn using Google SketchUp).
…”
We report an ultra-sensitive refractive index (RI) sensor employing phase detection in a guided mode resonance (GMR) structure. By incorporating the GMR structure in to a Mach-Zehnder Interferometer, we measured the phase of GMR signal by calculating the amount of fringe shift. Since the phase of GMR signal varies rapidly around the resonance wavelength, the interference fringe pattern it forms with the reference signal becomes very sensitive to the surrounding RI change. The sensitivity comes out to be 0.608π phase shift per 10−4 RI change in water medium which is more than 100 times higher than the other reported GMR based phase detection method. In our setup, we can achieve a minimum phase shift of (1.94 × 10−3) π that corresponds to a RI change of 3.43 × 10−7, outperforming any of reported optical sensors and making it useful to detect RI changes in gaseous medium as well. We have developed a theoretical model to numerically estimate the phase shift of the GMR signal that predicts the experimental results very well. Our phase detection method comes out to be much more sensitive than the conventional GMR sensors based on wavelength or angle resolved scanning methods.
“…While the properties of guided resonance can be engineered by structure design, tuning guided resonance after the structure is fabricated remains a challenge. Some previous work relies on perturbing the refractive index of the film (10,(30)(31)(32)(33), changing the incident angle (34), or by using a two-layer structure and changing the interlayer gap size (35,36). The tuning range of all these techniques in practice is quite limited.…”
We experimentally demonstrate tunable guided resonance in twisted bilayer photonic crystals. Both the numerically and the experimentally obtained transmission spectra feature resonances with frequencies strongly dependent on the twist angle, as well as resonances with frequencies that are largely independent of the twist angle. These resonant features can be well understood with a simple analytic theory based on band folding. Our work illustrates the rich tunable resonance physics in twisted bilayer systems.
“…Due to the common-path interferometer, this system was not sensitive to environmental noise and achieved a low detection limit. Because the resonance condition of a GMR device can also be achieved by changing the azimuth angle, GMR filters under conical mounting have been studied [9,10]. Based on this concept, a GMR sensor with reflection-type phase detection using a Mach-Zehnder interferometer was proposed to maintain the direction of the reflected light and achieve improved resonance by altering the azimuth angle of the GMR device [11].…”
A high-sensitivity phase-detection system is proposed for a reflection-type guided-mode resonance (GMR) sensor, which achieves the resonance condition by rotating the azimuth angle and utilizes an electro-optic (EO) heterodyne interferometer. By rotating the GMR sensor azimuthally, the direction of the reflected light can be maintained in reflection-type detection, and the optical system can be compactly constructed because the light-tracking rotation stage is not required. The phase-detection sensitivity can be enhanced in this common-path EO heterodyne interferometer by rotating the analyzer in front of the photodetector; therefore, this system can achieve both a high sensitivity and low limit of detection. Numerical and experimental results of the reflectivity and phase response curves versus the azimuth angle were compared. The proposed system was used to perform gas sensing, and its detection sensitivity and limit were 3.73 × 104 deg/RIU and 2.68 × 10−7 RIU, respectively.
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