Advances in Waveguide Bragg Grating Structures, Platforms, and Applications: An Up-to-Date Appraisal

Abstract

A Bragg grating (BG) is a one-dimensional optical device that may reflect a specific wavelength of light while transmitting all others. It is created by the periodic fluctuation of the refractive index in the waveguide (WG). The reflectivity of a BG is specified by the index modulation profile. A Bragg grating is a flexible optical filter that has found broad use in several scientific and industrial domains due to its straightforward construction and distinctive filtering capacity. WG BGs are also widely utilized in sensing applications due to their easy integration and high sensitivity. Sensors that utilize optical signals for sensing have several benefits over conventional sensors that use electric signals to achieve detection, including being lighter, having a strong ability to resist electromagnetic interference, consuming less power, operating over a wider frequency range, performing consistently, operating at a high speed, and experiencing less loss and crosstalk. WG BGs are simple to include in chips and are compatible with complementary metal-oxide-semiconductor (CMOS) manufacturing processes. In this review, WG BG structures based on three major optical platforms including semiconductors, polymers, and plasmonics are discussed for filtering and sensing applications. Based on the desired application and available fabrication facilities, the optical platform is selected, which mainly regulates the device performance and footprint.

Keywords: Bragg grating; filter; metal-insulator-metal waveguide; plasmonics; polymer; sensor; silicon-on-insulator platform.

Figure 1

Outline of the review paper. BG structures are based on different platforms such as semiconductors [15], polymers, and plasmonics utilized in filtering [16] and sensing applications [17].

Figure 2

FBG structure and its spectral response.

Figure 3

Phase shifted BG. (a) A quarter-wave phase-shifted BG with N = 50% duty cycle square wave variations of the period along both sides of a length phase shift facet. Adapted with permission from [43]. (b) Transmission of a SiN BG using the TMM model with (solid) and without (dashed) quarter-wave phase shift. Adapted with permission from [43]. (c) The response of a phase-shifted BG with the distinctive transmission peak at the center wavelength. Adapted with permission from [43].

Figure 4

SOI WG-based BG. (a) SEM image of the BG WG [62], (b) cross-sectional view of the BG WG. Adapted with permission from [62], (c) experimental setup. Adapted with permission from [62], (d) BG WG output spectrum at different temperatures. Adapted with permission from [62], (e) wavelength-to-temperature plot. Adapted with permission from [62].

Figure 5

Manufacturing of the multimode optical WGs by utilizing R2P NIL. (a) Manufacturing of the PDMS stamp layer. Adapted with permission from [91], (b) separating stamp and Ni-mold. Adapted with permission from [91], (c) manufacturing of the Varnish 311 UV layer. Adapted with permission from [91], (d,e) manufacturing of the U-groove into the Varnish 311 UV substrate layer by the R2P process. Adapted with permission from [91], (f) manufacturing of the core layer into the U-groove Varnish 311 substrate. Adapted with permission from [91], (g) manufacturing of the Varnish 311 UV cover cladding layer. Adapted with permission from [91], (h) untying the WG structure from the glass substrate. Adapted with permission from [91], (i) optical microscope picture of the WG. Adapted with permission from [91], (j) light at 650 nm propagating in the WG. Adapted with permission from [91].

Figure 6

TWFs based on polymer WG. (a) Two-stage cascaded TWF. Adapted with permission from [107], (b) reflection spectrum measurement setup. Adapted with permission from [107], (c) reflection spectra taken by utilizing the heating power on the integrated microheaters in every step. Adapted with permission from [107], (d) ultimate wavelength of the reflection bands for the utilized thermal power. Adapted with permission from [107].

Figure 7

Epoxy-based sensor pad employed for examining the aorta and radial artery pulse signs of a patient. Adapted with permission from [114].

Figure 8

FSU-8 polymer BG biosensor. (a) 3D representation. Adapted with permission from [115], (b) top view. Fabrication process. Adapted with permission from [115]. (c) Spin-coated FSU film. Adapted with permission from [115], (d) UV written sensing gratings. Adapted with permission from [115], (e) spin-coat PMMA cladding. Adapted with permission from [115], (f) formation of the sensing window. Adapted with permission from [115], (g) biosensor chip. Adapted with permission from [115].

Figure 9

Utilizations of SPR sensors in bioimaging [133], temperature sensors [134], food safety [135], telemedicine [136], early disease detection [137], medical diagnostics [138], and colorimetric sensors [139].

Figure 10

Plasmonic BG filter. (a) Graphical illustration of V-grooves along the device cross-bar. Adapted with permission from [193], (b) a 6 mm × 6 mm Au device adjacent to a matchstick. Adapted with permission from [193], (c) SEM photo of a V-groove comprising a BG filter. Adapted with permission from [193], (d) experimental system for NSOM and transmission measurements. Adapted with permission from [193], (e) transmission spectrum. Adapted with permission from [193].

Figure 11

Plasmonic BG structure based on MIM WG. (a) BG without a cavity. Adapted with permission from [197], (b) BG with a cavity in the middle. Adapted with permission from [197], (c) transmission spectrum of a BG with and without a cavity. Adapted with permission from [197], (d) transmission spectrum of a BG with a cavity concerning the change in the ambient RI. Adapted with permission from [197].

Figure 12

Modified BG structure established on an MIM WG. (a) Schematic representation. Adapted with permission from [198] and (b) transmission continuum of the modified BG formation. Adapted with permission from [198].