Long-length fiber Bragg creating sequential UV writing by probing phase mask

A method for manufacturing a sequentially joined fiber grating longer than a phase mask, comprising steps of:

• (1) aligning a reference phase mask in parallel with an photosensititve optical fiber to be exposed, wherein the reference phase mask has a period which is an integer number of times as long as a period of a UV fringe to be written, and forming a grating section on the photosensitive optical fiber by using a UV interferometric exposure;
• (2) producing a first probe beam and a second probe beam having a defined relationship by dividing an original probe beam, and projecting the first probe beam and the second probe beam into the reference phase mask along a normal direction thereof at two ends of the reference phase mask, respectively, so as to generate respective first-order diffraction beams simultaneously, which interfere with a first reference beam and a second reference beam, respectively, to generate fringes on a first image recording device and a second image recording device, respectively;
• (3) moving the stage so that the fiber and the grating are moved together and repeating steps (1) and (2) to form a plurality of grating sections, and joining each of the plurality of the grating sections sequentially with a desired phase shift;
• (4) moving the stage until the first probe beam is located at another end of the phase mask, and using the fringe on the first image recording device for phase analysis and real-time position monitoring each time when a locating point for an overlapping UV exposure is to be determined;
• and
• (5) determining and calibrating a phase shift Δθ between the fringe on the first image recording device and the fringe on the second image recording device when the first probe beam is relatively translated to the other end of the reference phase mask and two first-order diffraction beams are generated simultaneously;
• and afterwards using the fringe on the second image recording device resulting from the second probe beam and the second reference beam for phase analysis and real-time position monitoring, thereby joining each of the plurality of grating sections sequentially, wherein the recorded phase shift Δθ is added to each said grating section as an additional phase shift.