Bandpass filter is a filter which is adjacent to cut-off band on both sides of transmission band of spectral characteristic curve. Bandpass filter can be roughly divided into broadband filter and narrowband filter according to the spectral characteristics, two kinds of filter are usually combined, the application of light wave interference principle to prepare bandpass filter, and bandpass filter has been widely used in various fields.
The filter with cut-off zone on both sides of transmission band of spectral characteristic curve is called band-pass filter. Bandpass filter is an important optical thin film element, which is widely used in chemistry, spectroscopy, laser, astrophysics, optical fiber communication, biology and other fields. In the spectral curve of band-pass filter prepared by the principle of light wave interference, the transmission region of the spectrum near the wavelength is called the passband of the filter, usually with cutoff region on both sides, and there may be bypass band around the cutoff region, usually need to use colored glass, absorption film or cut-off filter to eliminate the bypass band.