+1/-1 order phase masks (FBG)

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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.

Features

Any deviation from the desired grating structure in the Phase mask is transferred directly to 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 period and through the 1310 and 1550 nm wavelength ranges

  • Period accuracy and uniformity better than 0.01 nm

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

  • Optimized for illumination from 193 nm to 800 nm

  • Inherently free of stitching errors

  • Continuous linear chirp available

  • Multiple period phase masks are possible

  • Tilted gratings are possible

  • Phase shifts are possible

  • Optimized for any illumination wavelength

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

+1/-1 order Phase mask

Definition of polarization conventions

The polarization of light incident upon a grating is defined by the orientation of its electric and magnetic fields relative to the plane of incidence, where the plane of incidence is defined by the two vectors being the propagation vector of the illumination and the grating normal.

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Principle

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 illumination.

Documentation

0/-1 order Phase mask principle sketch

Product range and specifications

ParameterSpecification
Grating periods260 nm - 2600 nm
Illumination wavelengths193 nm - 800 nm
MaterialUV grade fused silica
Period accuracy+/- 0.01 nm
Period uniformity+/- 0.01 nm
Chirp rates0 - 30 nm/cm
Standard grating sizes10 mm x 10 mm
25 mm x 10 mm
50 mm x 10 mm
100 mm x 10 mm
Guaranteed 0. order suppression<3% (lower spec optional)
Typical 0. order suppression0-2 %
0. order uniformity
Grating length 10 mm+/- 0.5 %
Grating length 25 mm+/- 0.75 %
Grating length 50 mm+/- 1.0 %
Grating length 100 mm+/- 1.5 %

Which phase mask to use?

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