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Optical Filters

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Optical filters selectively allow certain wavelengths of light to pass freely while blocking other wavelengths. Shanghai Optics manufactures a wide range of optical filters for engineering, scientific, and photographic applications.

Our hard coated optical filters are dichroic filters composed of a single substrate with a dense hard coating. These hard sputtered filters are more expensive to produce, but they have excellent performance and are ideal for applications where precision is of paramount importance.  Since they have only one substrate covered with a relatively thin film, these filters are much thinner than traditional coated filters and offer much higher transmission.

Custom Glass Filter

Traditional coated optical filters consist of a complex assembly of absorbing material, metallic layers, and interference coatings. These are primarily used for analytical instrumentation and laboratory equipment, as the environmental stability is intrinsically limited.

Our colored glass filters consist of a simple glass substrate with dye injected in the manufacturing process. The absorption and transmission can be controlled by the concentration of the dye used and by the thickness of the filter. These absorptive filters are highly stable and less expensive than other options, but the optical properties are also more limited.

Shanghai Optics produces shortpass, longpass, and bandpassfilters. Shortpass filters block wavelengths longer than a certain cut off while allowing short wavelengths of light to pass through unimpeded. These include hot mirrors, heat absorbing glass, and IR cutoff filters. Longpass filters block shorter wavelengths of light, and transmit longer wavelengths. Bandpass filters transmit a certain wavelength range (known as the pass band) and block or restrict all others.  The pass band may be narrow (2-10 nm) or broad (50-80 nm). Bandpass filters are more angle sensitive than other types, so you will want to pay extra attention to mounting and setup if you use a filter of this type.

Both shortpass and longpass filters are sometimes referred to as edge filters.

Types Of Optical Filters

Types of Specification in Optical Filters

There are a number of specifications you will want to keep in mind as you select the optimal optical filter for your application.

Cut-on Wavelength is the wavelength at which the transmission has reached half, or 50 percent, in a longpass filter. Similarly, cut-off wavelength is the wavelength at which the transmission has reached 50 percent in a shortpass filter.

The slope of an edge filter, is given as a percentage of the cut wavelength with a designated starting and end points. For instance, if the start and end points are considered to be 10 percent and 80 percent transmission, a 600 nm filter with 1 percent slope would transition from 10 to 80 percent transmission over a 6 nm bandwidth.

Optical density relates to the amount of light attenuated by a filter, and is calculated by the transmission percentage in the blocked region. Since the optical density is calculated with a negative log, a higher optical density value will indicate lower transmission.  For fluorescence microscopy, you may need a filter with optical density of 6 or greater. Laser separation and chemical detection require optical densities in the 3-4 range, while filters with OD of less than 2 are best for such applications as color sorting or spectral separations.

The Blocking Range tells you the wavelength range blocked by the filter; typically, the range where transmission is less than 50 percent.

Bandwidth describes the portion of the spectrum is transmitted through the filter. It is also called Full Width Half Maximum (FWHM), and describes the area where the filter achieves more than 50 percent transmission.

The Central Wavelength is the wavelength of the central point, or midpoint, of the FWHM. It may be the point of maximum transmission, especially for traditional coated optic filters.

Shanghai Optics filters are designed for a wide variety of applications, and we are able to customize as needed to fit your requirements.

 

 

 

 

 

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