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+1/-1 order Phase Masks (FBG)

Phase masks are the production tool used to write gratings in fibers and waveguides. Ibsen Phase masks incorporate unbeatable, interferometric (holographic) patterning technology into a production friendly Phase mask.

– for easy and cost-effective fabrication of Bragg gratings

Ibsen’s +1/-1 order principle Phase masks ensure quality and facilitate production in the telecommunications, sensor and laser industries. In the production of fiber and waveguide Bragg gratings, the Phase mask is illuminated by a high-power UV laser, typically an excimer laser or frequency-doubled gas laser. Self-interference between the diffracted orders produces the required pitch in the fiber or waveguide.


Any deviation from the desired grating structure in the Phase mask is transferred directly to the the fiber or waveguide. It is therefore imperative that the Phase mask pitch is accurate, uniform and defect-free. Through scientific principles and constants of nature, our fabrication process ensures absolute pitch accuracy. In addition, geometric principles in our production equipment ensure strict uniformity, eliminating e-beam drawbacks such as stitching errors and field distortion.

Other important features of our line of +1/-1 order Phase masks are:

• Phase mask pitches for all fiber/waveguide applications, down to 260 nm and through the 1310 and 1550 nm ranges

• Period accuracy and uniformity better than 0.01 nm

• Highly suppressed residual zero order (typical: 0-2%)

• Inherently free of stitching errors

• Continuous linear chirp available

• Tilted gratings are possible

• Optimized for any illumination wavelength

• Phase mask parameters are individually specified – including unique part number – on each Phase mask


Using the +1/-1 order principle, the Phase mask is optimized to diffract light equally and maximally into the plus first and minus first orders. Self-interference between these two orders creates an interference pattern with half the pitch of the Phase mask pitch. As the diagram illustrates, a +1/-1 order Phase mask can generate additional unwanted orders. Ibsen Phase masks have highly suppressed zero order noise. The main advantage of this +1/-1 order principle (relative to the 0/-1 order principle) is its ease of use with normally incident



+1/-1 order Phase mask principle sketch

+1/-1 order Phase mask principle sketch