Near infrared optical interference filters with improved transmission

A method of manufacturing an interference filter, the method comprising:

• forming a layers stack comprising a plurality of layers of at least:
• (i) layers of amorphous hydrogenated silicon with added nitrogen (a-Si:H,N), the a-Si:H,N layers having a refractive index in the range 3.3 to 3.5 inclusive, and
• (ii) layers of one or more dielectric materials having a refractive index lower than the refractive index of the a-Si:H,N;
• wherein the a-Si:H,N has an atomic concentration of hydrogen between 1% and 8% and an atomic concentration of nitrogen between 2% and 7%;
• wherein the layers of one or more dielectric materials include at least one layer of a dielectric material having a refractive index in the range 1.9 to 2.7 inclusive;
• and
• wherein the layers stack includes repeating units of two or more layers.

A method of fabricating an interference filter, the method comprising:

• forming a layers stack comprising alternating layers of:
• (i) amorphous hydrogenated silicon with added nitrogen (a-Si:H,N), the a-Si:H,N layers having a refractive index in the range 3.3 to 3.5 inclusive, and
• (ii) silicon-based dielectric layers having a refractive index lower than the refractive index of the a-Si:H,N;
• wherein the a-Si:H,N layers have an atomic concentration of hydrogen between 4% and 8% and an atomic concentration of nitrogen between 2% and 12%;
• and
• wherein the interference filter has a passband wavelength range of 750-1100 nm inclusive.