A optical bandpass filter, short as BPF, is to transmit light within a specific wavelength range while blocking light outside the passband. The basic parameters of a bandpass filter include the central wavelength(CWL), bandwidth(FMHW), transmission rate and cut-off depth, etc. Unlike the electronic bandpass filters, which operate on electrical frequencies, optical bandpass filters work with light wavelengths, typically measured in nanometers (nm).
What Does a optical bandpass filter do?
In generally, there are four core functions for a optical bandpass filter:
- Spectral selection: selectively transmits a specific wavelength band, allowing the devices to observe or analyze only the target spectral range.
- Noise reduction: filtering out interfering spectral components, reducing noise and improving the signal‑to‑noise ratio.
- Spectral separation: block specific spectral range in spectroscopic analysis.
- Detector protection: limits the intensity of light reaching the detector, preventing damage from excessively strong signals
What are the types of bandpass filters?
The commonly used bandpass filters type are:
- Narrow Bandpass Filters: short as NBPF, it refers to a bandpass filter with very narrow bandwidth such as 5nm or 10nm. There is no standard definition how narrow it should be, normally those with FWHM less than 20nm is classified as NBP Filters.
- Dual Bandpass Filters: It can pass through two independent bands simultaneously. Each passband can be either narrowband or broad. Compared to a single-bandpass filter, its transmission rate will decrease, usually to around 80-85%, and the manufacturing cost will also be higher.
- Triple or Multi-Bandpass Filters: Supports three or more passband to achieve high-throughput multispectral detection. However, the design and manufacturing are extremely challenging, with the transmittance possibly dropping to 75-80% and the cost is also very high.
Additionally, based on the spectral band range, they can be also classified as ultraviolet(UV) bandpass filters, visible light(VIS) bandpass filters, and infrared(IR) bandpass filters.
What are typical application for the optical bandpass filters?
The optical bandpass filters are widely used in fluorescence microscopy, machine vision, laser systems, spectroscopy, biomedical imaging, astronomy, and optical sensing.