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Final Report Summary - GRATING (Gratings in air-core photonic bandgap fibres for applications within communications, lasers and sensors)


Project Number PIIF-GA-2009-235487

Project Acronym: GRATING
Researcher: Dr Yiping Wang
Host: Prof. Libo Yuan

This GRATING project with a number of PIIF-GA-2009-235487 aims to inscribe novel gratings, including fibre Bragg gratings (FBGs) and long period fibre gratings (LPFGs), in air-core photonic bandgap fibres (PBFs), opening the door to a new class of grating-based devices in hollow-core PBGFs. Because almost 100% of the light propagates in the air holes of the PBF and not in the glass, hollow-core PBGFs represent an important platform for the development of novel grating-based devices, offering potentially enhanced properties for applications in telecommunications, lasers and sensing.

During the returning phase of the project, with the support of Marie Curie International Fellowships, we continued the previous research of the project to carry out the project aims and to solve the problems occurred in the coming phase. As reported in the final report for the incoming phase, it is very difficult to write LPFGs and/or FBGs in the hollow-core PBFs by employing a point-to-point technique. Hence, in the returning phase we designed and built a two-beam interference system and for writing novel gratings in the hollow-core PBFs with photosensitivity. Furthermore, we investigated the potential applications of photonic crytal fibers (PCFs).

The following results were achieved:
(1) A two-beam interference system for writing gratings was designed and built by employing a femtosecond UV laser. Such a system solved the problem of the laser beam alignment during writing grating by using a point-to-point technique employing in the incoming phase. A few grating with high-qualities were written successfully in the normal glass fibers and the solid-core photonic crystal fibers.

(2) A Ge-doped air-core PBFs with a photosensitive inner core ring was employed to use a femtosecond UV laser to write a grating in this ring. Unfortunately, no gratings were successfully written in the type of PBF. The reason for our unsuccessful experiments that the Ge-doped air-core PBF employed in our current experiments is not a desired single mode fiber.

(3) We developed a versatile technique for filling selectively a fluid, i.e. thermo- or electro-optic polymers or other advanced materials, into desired air holes in a photonic crystal fiber (PCF). By the thermo-optic effect of the fluid filled in the air holes, we demonstrated an invertible fiber-type transformation from a photonic crystal fiber into an index-guiding photonic bandgap fiber. Such a transformation could be used to develop an in-fiber optical switch/attenuator with a high-extinction ratio of more than 35 dB.

(4) We also demonstrated the orientation-dependent bending-properties of a half-filed PCF. In other words, the bending properties of the half-filled PCF strongly depend on the bending orientations of the fiber. Such unique bend properties could be used to simultaneously monitor the bending orientation and the curvature of the engineering structures.

The reason for our unsuccessful experiments on writing gratings in the Ge-doped air-core PBF is that making such a PBF is hugely challenging so that a suitable air-core PBGFs with a photosensitive ring have been not commercially available so far. The Ge-doped air-core PBF employed in our current experiments is only prototype fiber sample made in the Institute of Photonic Technology (IPHT), Jena, Germany and is not a desired single mode fiber.

As a result, until single-mode hollow-core PBFs with high photosensitivity is commercially and gratings are produced the application development aspects of the project will need to remain on hold. We hope to achieve a single-mode air-core PBF with high photosensitivity soon. And then we will continue our current effects on writing gratings in hollow-core PBFs and investigating their potential sensing and communication applications.

Reported by

Harbin Engineering University
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