Shifted Bragg Grating Research Articles

Fabrication and Sensing Application of Phase Shifted Bragg Grating Sensors.

As a special kind of Bragg grating, phase-shifted fiber Bragg grating (PS-FBG) has attracted extensive attention because of its extremely narrow transmission window and excellent sensing performance. The main purpose of this manuscript is to discuss the PS-FBG with special sensing characteristics and explore the influence of different inscription technologies on the sensing characteristics of PS-FBG by comparing the existing inscription methods. The sensing characteristics, advantages and disadvantages of PS-FBG with different structures are analyzed.

Nanostructuring improves the coupling of dielectric waveguides with plasmonic nanoresonators

Certain metallic nanostructures exhibiting localized surface plasmon resonances (LSPR) are capable of sensing extremely low-volume analytes down to attoliters, especially when used in a single particle configuration. Incorporating them into integrated photonics sensing platforms could result in a reduced limit of detection (LOD), and increased dynamic range and multiplexing capabilities. Despite the potential of this platform, several challenges remain, like low coupling efficiencies between integrated waveguides and plasmonic nanoantennae, and the need for off-chip readout. We numerically investigate the optical response of phase shifted Bragg grating (PSBG) and sub-wavelength grating (SWG) waveguides loaded with plasmonic nanoresonators in silicon nitride (Si3N4) integrated photonics platform operating in an aqueous environment. In comparison with a strip waveguide, a 3-4 times improvement in coupling, up to 5 times improvement in local intensity enhancement and 6-7 times improvement in intensity-shift sensitivity are predicted for the structured waveguide configurations. In particular, the PSBG configuration exhibited slightly improved coupling and intensity-shift sensitivity compared to the SWG configuration. On the other hand, the device footprint of the SWG configuration was only a fifth of that of PSBG and also exhibited nearly two times larger local intensity enhancement. A systematic study of the design space and sensitivity analysis is performed to assess the optimal configuration for single-ID single-wavelength refractometric sensing, on-chip excitation and off-chip readout, and SERS sensing.

Multi-wavelength add-drop filter with phase-modulated shifted Bragg grating.

We present, for the first time to the best of our knowledge, a multichannel add-drop operation with a phase-modulated shifted Bragg grating based filter. The device is realized in a silicon-on-insulator waveguide platform with TiO2 as a coating material to reduce the refractive index contrast. The operation is shown for three and five wavelength channels within the telecom C-band. A line width of 0.6nm with an extinction ratio of 20dB is achieved. The shifted Bragg grating is modulated maintaining a modal phase-matching condition for multiple wavelengths. The phase function is calculated with an iterative Fourier transform algorithm. The experimental results are in very good agreement with the design.

Add-drop filter based on TiO2 coated shifted Bragg grating.

We present a titanium dioxide coated shifted Bragg grating in a silicon-on-insulator platform enabling optical add-drop functionality. The device works on the basis of mode conversion due to shifted sidewall structure followed by mode splitting based on an asymmetric Y-coupler. We experimentally demonstrate the working principle of the device. A reflection bandwidth of 2.2 nm with 14 dB extinction ratio is obtained with a 300 μm long shifted Bragg grating. The performance of the device is also compared without the titanium dioxide coating. A scope of spectral tunability with titanium dioxide re-coating (0.8 nm per 1 nm re-coating) by atomic layer deposition is experimentally verified.

Phase shifted Bragg gratings formed in optical fibres by post-fabrication thermal processing

Fibre Bragg gratings have been post-fabrication processed using localised heat treatment, with significant changes to their transmission and reflection characteristics being observed. Experimental results of the spectral changes, together with an explanation of their origin, are provided in this article.