October 04, 2020

Optical Filters

Optical filters are optical elements that allow selective transmission, reflection, and absorption of optical wavelengths (colors). Optical filters are essential optical elements in most systems and apparatuses and can be found in cameras, color correction and imaging systems, microscopes, characterization tools, and many more. Optical filters are distinguished by their spectral transmission and reflection windows. 

In the 3DOptix software, we support the following types of filters and coated mirrors:

Short-pass filter, Long-pass filters, Bandpass filters, Notch filters, Color glasses, Dichroic mirrors/filters, laser line filters, Spectral shape and calibration filters, Neutral density filters, hot/cold mirrors, and more. 

The major differences can be found below:

 

Short-pass vs long-pass optical filter

Short-pass optical filter transmits (passes) the short wavelengths below a cut-off wavelength and reflects (or absorbs) the longer wavelength. On the contrary, long-pass filter transmits the longer optical wavelength above a cut-on wavelength and reflects (or absorbs) the shorter wavelengths.   

Bandpass vs bandstop optical filter 

Bandpass optical filter transmits (passes) a group of wavelengths between two wavelengths and reflects (or absorbs) the rest of the wavelength. On the contrary, the bandstop filter transmits all the wavelengths that are outside a specific regime reflects (or absorbs) all the colors that are in between.

Narrowband vs broadband bandpass optical filter

The bandwidth of a bandpass filter can be narrow band, meaning that only a specific color band will be transmitted, or broadband, meaning that and the spectral range that will be transmitted is relatively wide.

Bandstop optical filter vs notch filters

Both optical filters are in fact bandstop filters, i.e. transmit all the wavelengths that are outside a specific regime reflects (or absorbs) all the colors that are in between. Yet, the bandwidth of notch filters is commonly very narrow, i.e. stopping only specific color/s.

Dichroic Filter vs. Dichroic mirror

Dichroic Mirror is a filter that transmits light in a specific wavelength range and reflects light outside this range. Dichroic filter is a filter that transmits light in a specific wavelength range and absorbs light outside this range. Dichroic filters and mirrors can be long-pass, short-pass, or bandpass types.

Cut-On vs Cut-Off Wavelength

Cut-On Wavelength is the wavelength at which the transmission is 50% in a long-pass filter, whereas Cut-Off Wavelength is the wavelength at which the transmission is 50% a short-pass filter.

Cold mirrors vs hot mirrors

Cold mirrors are specific types of long-pass dichroic filters designed to have high reflectivity in the visible spectrum while maintaining high transmission in the infrared. Hot mirrors are specific types of short pass dichroic filters designed to have high reflectivity in the infrared spectrum and high transmission in the visible. 

Reflecting filters vs. absorptive filters

Reflecting filters are ND filters that reflect most of the incident light, and have minimal absorption. On contrary, absorption filters are ND filters that absorb most of the incident light and have a minimal reflection. Both types of filters transmit a predetermined percentage of the incident light according to the required optical density.

Example for a long-pass Dichroic Mirror (Thorlabs DLMP 567), where the longer wavelengths (above 567nm) of a broadband laser are transmitted and the shorter wavelengths (below 567nm) are being reflected.

Example for a Short-pass Dichroic Mirror (Thorlabs DSMP 505), where the shorter wavelengths (below 505nm) of a broadband laser are transmitted and the longer wavelengths (above 505nm) are being reflected.

 

Table for filter comparison

 

Filter type	Short-pass filters	Long-pass filters	Bandpass filters	Bandpass and Notch filters
Reflection/ Absorption	Above cut-off wavelength	Below cut-on wavelength	Outside a band of wavelengths	In between a band of wavelengths
Transmission	below cut-off wavelength	Above cut-on wavelength	In between a band of wavelengths	Outside a band of wavelengths

3DOptix has recently launched a one-of-a-kind filter search tool, where optical filters can be found in a snap. 3Doptix has the largest filter database with more than 7000 different filters from the leading vendors. 

Q&A

Can I simulate Off-the-shelf filters with the 3DOptix software?

Yes, 3DOptix Database includes a huge variety of filter catalogs from some of the leading vendors.

Can I run a cross vendor filter search?

Yes. 3DOptix Filter search tool is capable to scan our database and provide with the best matches for the query

What are the filter types that the 3DOptix software supports?

Short-pass filter, Long-pass filters, Bandpass filters, Notch filters, Color glasses, Dichroic mirrors/filters, laser line filters, Spectral shape and calibration filters, Neutral density filters, hot/cold mirrors, and more

 

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