Laterally-distributed fiber Bragg gratings for fiber laser and fiber sensing applications

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Fiber Bragg grating (FBG) has been widely used in telecommunication, fiber laser and fiber sensors since its invention in Canada about 40 years ago. In order to achieve more functions, many designs have been introduced into the FBG structure, such as sampled FBG, phase-shifted FBG and chirped Moire FBG etc. However those designs all vary the FBG structure along the optic fiber axis. With the advancement of high power fiber lasers and sensors, more sophisticated functions are required to control not only the wavelength, but also polarization and mode content etc. In this grant application, I propose two dimensional FBGs, in which additional FBG structures are designed in lateral direction that can be called laterally-distributed FBG. With the available photolithography technology that can etching a groove as small as 300 nm on a phase mask, it becomes feasible to have many corrugated phase masks within the dimension of the fiber core; for example 8 micrometer for telecommunication fiber and 20 micrometer for large-mode-area fiber. With this added degree of freedom, the laterally-distributed FBG can achieve much more functionality. For example: 1) If several pi-phase shifted FBGs of different wavelengths are made in the core but laterally-separated, it can realize stable multi-wavelength lasing since the pi-phase for each wavelength is preserved. 2) If the central FBG is made at the LP01 mode wavelength and two side FBGs at LP11 mode wavelength, the device can be used to reduce the high order mode if the output coupler FBG reflects mainly LP01 wavelength. 3) If the centre FBG and two side FBGs are made at three different wavelengths, it can be used to measure multiple parameters such as strain, temperature and bending simultaneously. Those are just a few examples. In this proposal the concept and designs of the laterally-separated FBGs will be presented and their applications in fiber lasers and sensors will be described.