Bandpass Filter is an optical device composed of multilayer dielectric coatings deposited on glass or fused silica substrates. It is engineered to allow only a defined spectral band to pass while rejecting wavelengths outside the target range. The filter performance is controlled by coating thickness, refractive index contrast, and interference design. It is widely used in fluorescence imaging, spectroscopy, machine vision, and optical communication systems. These filters ensure accurate wavelength selection and high optical contrast.