3D bragg grating waveguide devices

Abstract

Over the past decade, ultrashort pulse laser processing has opened a large suite of photonic devices that can be formed inside bulk optical glasses by direct writing. Such processes promise rapid and seamless integration into novel three-dimensional optical circuits. One obstacle towards commercial application of this technology has been finding an effective means for inscribing high-quality grating devices. Such gratings, when embedded within the laser written waveguides, enable multi-functional spectral filters to be tailored to specific applications required in optical sensing, fiber lasers, and telecommunications. In this chapter, a new Bragg grating waveguide device is introduced that can be fabricated directly inside transparent glass materials by ultrashort laser direct writing. These Bragg grating waveguide devices are composed of arrays of partially overlapped refractive index voxels (volume pixels), defining a finely pitched segmented waveguide which simultaneously offers low-loss light guiding and strong Bragg filter resonances. Two approaches, a single-pulse writing method and a burst writing method, are introduced for inscribing the grating waveguide devices with respective low-and high-repetition rate ultrashort laser systems. Optimal laser exposure parameters are presented for fabricating high rejection notch filters (>35 dB) with narrow spectral bandwidth (0.2 nm) in the 1550-nm telecom band. Examples of Bragg grating waveguide circuits are presented for filter and sensor applications.