Bragg Gratings In Planar Waveguides Research Articles

Out-of-plane beam shaping with UV-written tilted Bragg gratings for beam delivery on quantum chips.

We theoretically and numerically investigate the performance of tilted Bragg gratings in planar waveguides, fabricated by direct UV writing in photosensitive silica, to couple light out of a chip. An analytic expression is derived for the coupling efficiency and validated numerically by finite element simulations. Using the analytic result, we can design gratings to generate output beams in free space of any specific shape and calculate their overall power coupling efficiency. Our simulations indicate that for currently achievable grating index contrasts devices of millimeter length are most suitable for this technology.

High-temperature stable and sterilizable waveguide Bragg grating in planar cyclo-olefin copolymer

In this Letter, we demonstrate a high-temperature stable polymer planar waveguide Bragg grating based on cyclo-olefin copolymers. The high glass transition temperature of the polymer material amounting to 178°C, in conjunction with a high-temperature stable UV-curable adhesive used to connect the polymer sensor to a standard single-mode fiber, enables temperature readings of up to 160°C while exhibiting a temperature sensitivity of -7.3 pm/°C. The reflected power of the Bragg wavelength remains constant up to a temperature of 130°C before declining at higher temperatures with an overall reduction of 2.5dB at 160°C. However, decreasing temperature results in a complete recovery of the peak power, facilitating steam pressure sterilization (129°C, 0.17MPa) of the polymer planar waveguide Bragg grating.

TiO2 surface functionalization of COC based planar waveguide Bragg gratings for refractive index sensing

We demonstrate the applicability of a planar waveguide Bragg grating in cyclo-olefin copolymer (COC) for refractive index sensing. The polymer planar waveguide Bragg grating fabricated using a single writing step technique is coated with a high-index layer of titanium dioxide (TiO2) leading to a distinct birefringence. This in turn results in the splitting of the Bragg reflection into two distinct Bragg wavelengths, which strongly differ regarding their refractive index sensitivities. Where one wavelength is only slightly affected by the ambient refractive index, the second Bragg peak shows a strong sensitivity. Furthermore, we investigate the temperature behaviour of the functionalized sensor and discuss it with respect to applications in refractive index sensing.

Polymer Planar Bragg Gratings

AbstractCombining the advantageous properties of cyclo olefin copolymers (COC) with a rapid UV laser based fabrication process, we highlight the generation of planar waveguide Bragg gratings suitable for multi‐axial strain sensing (Fig. 1). Bragg gratings are optical filters reflecting a small wavelength band, which is determined by the spatial grating period and the effective refractive index. As both determining factors depend, e. g., on mechanical load conditions and temperature, measuring the reflected Bragg wavelength facilitates optical sensing of these conditions.

Excitation of Surface Plasmons Using Tilted Planar-Waveguide Bragg Gratings

We present a planar-integrated optical surface plasmon refractometer. The fabricated device operates by grating-matched coupling between a core waveguide mode and a set of hybrid plasmon-dielectric modes of a much wider integrated structure. The constructed device incorporates a 50-nm-thin gold layer that separates a tilted planar-waveguide Bragg grating and a liquid analyte. It is demonstrated that polarization-dependent plasmon anomalies occur in the transmission spectra of the device, which are understood using a numerical Cauchy integral mode solving approach. Sensitivities in this planar-integrated device are comparable with existing fiber-based plasmonic sensors but with the advantages of planar integration and microfluidic adaptation.

Integrated shadow mask for sampled Bragg gratings in chalcogenide (As_2S_3) planar waveguides

We have developed a new approach for producing high performance sampled Bragg gratings in planar waveguides as a platform for WDM on-chip signal processing in a compact integrated device. Using this method we have successfully integrated a shadow mask directly onto a chalcogenide (As(2)S(3)) waveguide using standard semiconductor processing, eliminating misalignment errors between the mask and waveguide that otherwise occur. Through this integrated mask we demonstrate a very low duty cycle sampled Bragg grating with very narrow rejection peaks and spanning a very broad bandwidth.

Design of discrete, nearly-uniform Bragg gratings in planar waveguides

In this paper we present an efficient method for designing discrete, nearly-uniform Bragg gratings in generic planar waveguides. Various schemes have already been proposed to design continuous Bragg gratings in optical fibers, but a general scheme for creating their discrete counterpart is still lacking. Taking a continuous Bragg grating as our starting point, we show that the same grating functionalities can also be realized in any planar waveguide by discretizing it into a series of air holes. The relationship between the two gratings is established in terms of grating strength and local grating period.

High birefringence control and polarization insensitive Bragg grating fabricated in PECVD planar waveguide with UV polarized irradiation

A method for rapid compensation of high intrinsic birefringence in plasma-enhanced chemical vapor deposition (PECVD) based planar waveguides is presented. The intrinsic waveguide birefringence is compensated by a large UV induced opposite birefringence generated with polarized UV ArF excimer laser irradiation (oriented normal to the waveguide axis) and enhanced further through hydrogen loading. The fabrication of polarization insensitive Bragg gratings in PECVD planar waveguides with a large intrinsic birefringence of 6.3×10−4 is demonstrated by trimming it to zero birefringence with a low fluence blanket UV polarized exposure. After annealing for removal of the hydrogen, the polarization insensitive nature of the Bragg grating is unchanged.

Spatial harmonics analysis of deep waveguide Bragg gratings

The spectral properties of a single-mode planar deep waveguide Bragg grating (DWBG) operating on the first diffraction order are investigated by a spatial harmonics theoretical approach. This analytical method allows us to evaluate the most important features of the propagating fields. In particular, the slowdown of the group electromagnetic propagation near the photonic band-edges is accurately modelled with a minimal computational effort, which makes this tool useful for preliminary analysis of periodic waveguides.

Thermo-optic Effects of Bragg Grating Optical Temperature Sensor

This paper demonstrates a comparison of linear and nonlinear analyses for thermo-optic effects of optical temperature sensor based on the etched silica-based planar waveguide Bragg grating. Topics include theoretical analyses and experiment of the etched planar waveguide Bragg grating optical temperature sensor. Theoretical models with nonlinear than linear temperature effect for the grating response based on waveguide and plate deformation theories agree with experiments to within acceptable tolerance.

Bragg gratings in planar polydiactylene waveguides and their application in integrated optics

We present the fabrication of high quality non-uniform Bragg gratings in planar poly(4-BCMU) channel waveguides using an optimized photobleaching set-up and report the optical characterization of the resulting photonic band gap. The suitability of our system to all-optical switching phenomena in different geometries as a result of non-linear wave propagation effects will be shown and discussed. Our results contribute to open up the wide field of device applications in integrated optics based on periodically structured planar polymer waveguides.

Apodised Bragg gratings in planar waveguides for add-drop filters

We report on the fabrication by electron-beam lithography of Bragg gratings, which serve as wavelength-selective elements of a Mach–Zehnder-type add-drop filter. To meet telecommunication network requirements, the gratings must have about 20 000 lines, corresponding to a length on the order of 10 mm. Furthermore, the coupling strength of the gratings has to be varied according to a bell-shaped taper function to suppress unwanted side lobes in the gratings’ reflection spectra. We have realised coupling coefficient variation at constant etch depth by changing the duty cycle along the grating. The employed pattern reversal process provides good line-width control of the grating ridges down to 50 nm, and good coverage by the subsequent PECVD overgrowth. Optical measurements are presented that demonstrate the excellent performance of the grating couplers.

Planar optical waveguide temperature sensor based on etched bragg gratings considering nonlinear thermo-optic effect

This paper demonstrates the development of optical temperature sensor based on the etched silica-based planar waveguide Bragg grating. Topics include design and fabrication of the etched planar waveguide Bragg grating optical temperature sensor. The typical bandwidth and reflectivity of the surface etched grating has been ∼0.2 nm and ∼9 %, respectively, at a wavelength of ∼1552 nm. The temperature-induced wavelength change is found to be slightly non-linear over ∼200 °C temperature range. Typically, the temperature-induced fractional Bragg wavelength shift measured in this experiment is 0.0132 nm/°C with linear curve fit. Theoretical models with nonlinear temperature effect for the grating response based on waveguide and plate deformation theories agree with experiments to within acceptable tolerance.

First- and second-order Bragg gratings in single-mode planar waveguides of chalcogenide glasses

First- and second order Bragg reflectors at telecommunication wavelength (1.5 /spl mu/m) were fabricated in single-mode monolayer (As/sub 2/S/sub 3/) and multilayer (AsSSe-AsS) chalcogenide glass (ChG) planar waveguides with near bandgap illumination using an interferometric technique. Reflectivities as high as 90% near 1555 nm, and index modulations up to 3/spl times/10/sup -4/ were achieved. The volume photodarkening effect is the principal mechanism involved in the formation of the Bragg gratings.