Abstract: A bandpass optical filter is provided that is formed within an optical fiber in the form of a Bragg grating. The grating includes multiple Fabry Perot cavities disposed along the waveguide. Each of the cavities includes a pair of reflectors. Each reflector comprises alternating high-low index regions within the waveguide, each region having a thickness of one quarter-wave at a bandpass wavelength, each alternate region being of a different index of refraction than an adjacent region. A multiple odd quarter-wave or quarter-wave high or low index region is sandwiched between each pair of reflectors. The number of high/low regions within a reflector is selected in accordance with the refractive index difference between two alternate adjacent regions.

Abstract: A broad band low reflectance neutral density optical filter. A neutral density filter having substantially flat transmittance and low reflectivity over a wide range of wavelengths from the ultraviolet through the visible region of the spectrum includes a transparent substrate, two successive layers of different dielectric materials on the substrate, at least two layers of metallic material, each metallic layer being separated from the preceding metallic layer by a layer of dielectric material, and finally, two succeeding layers of different dielectric mateials. The resultant neutral density filter thus has two layers of different dielectric materials between the substrate and the first layer of metallic material, and two layers of different dielectric materials between the atmosphere and the final layer of metallic material.