Frequency band-pass filters

Frequency band-pass filters are designed for spectral selection of incident radiation. Such filters in the band-pass mode pass waves in the surroundings of the set frequency with the transmission coefficient close to 1 and fully reflect or disperse the radiation outside the pass band. Electrodynamic optimization and the unique structure of the designed band-pass filters provide the high contrast of the frequency filtration with the low level of parasitic high-frequency harmonics leak. To maximise the radiation blocking outside the required selection band it is possible to use two filters successively; meanwhile the transmission value in the selection band area decreases insignificantly. 

In addition to band-pass filters for a fixed wavelength it is possible to design and produce filters for selection of several wavelengths spaced apart in the spectrum as well as band-stop filters. The latter provide deep suppresion of radiation at the set frequency (as the result of reflection resonance) at a high level of side frequency transmission.

All optical elements are produced on the basis of multi-layered frequency-selective surfaces - thin planar metal-coated microstructures with cells of special geometric shape, the topology of which defines the frequency properties of the element. Frequency-selective surfaces are resonant electrodynamic structures operated in the mode, in which the resonance frequency is below the point of excitation of high-order diffraction harmonics. This approach allows to create optical elements with unique properties unachievable or hard-hitting within the frames of traditional optics.

We can produce filters with properties required for solution of our client specific task. Filter properties can be optimised for use in various applications including space studies and studies in cryogenic conditions. 

A black aluminium casing with protective coating is supplied together with the filter.

Technical specification:

Selection band center frequency 0.05 to 3 THz
Filtration fractional bandwidth (FWHM)  9 to 30%
Maximum transmission (at the center frequency) 80 to 97%
Suppression outside the pass band 30 to 45 dB
Cross-polarization level below -35 dB
Radial aperture diameter 25 to 70 mm
Possibility of work in cryogenic conditions Yes
Possibility of use in vacuum conditions Yes

Examples of standard filter spectra, showing filter capacities for blocking of radiation outside the selection band.

Possible areas of application

  • Optical element as a part of quasi-optical systems for spectral analysis and monitoring of broad-band source emission dedicated to improve the radiation monochromatization
  • Suppression of undesirable flash exposure of radiation THz detectors by off-band spectral background 

Standard filter models:

Filter number Selection band center frequency Maximum transmission  Selection fractional bandwidth Transmission outside center frequency 
1 0.075 0.95 0.15 <= 10-4
2 0.094 0.95 0.15 <= 10-4
3 0.100 0.95 0.15 <= 10-4
4 0.140 0.94 0.15 <= 10-4    
5 0.140 0.94 0.20 <= 2*10-4
6 0.150 0.94 0.20 <= 2*10-4
7 0.190 0.94 0.20 <= 2*10-4
8 0.220 0.94 0.15 <= 2*10-4
9 0.220 0.94 0.20 <= 2*10-4
10 0.260 0.93 0.20 <= 3*10-4
11 0.300 0.92 0.20 <= 3*10-4
12 0.350 0.91 0.15 <= 4*10-4
13 0.350 0.92 0.20 <= 4*10-4
14 0.480 0.92 0.20 <= 5*10-4
15 0.500 0.92 0.20 <= 5*10-4
16 0.600 0.92 0.20 <= 5*10-4
17 0.650 0.90 0.15 <= 5*10-4
18  0.650 0.92 0.20 <= 5*10-4
19  0.800 0.90 0.15 <= 6*10-4
20 0.800 0.92 0.20 <= 6*10-4
21 1.000 0.90 0.15 <= 8*10-4
22 1.000 0.91 0.20 <= 1*10-3
23 1.300 0.89 0.15 <= 1*10-3
24 1.300 0.91 0.20 <= 3*10-3
25 1.600 0.89 0.15 <= 1*10-3
26 1.600 0.91 0.20 <= 3*10-3
27 1.900 0.88 0.15 <= 3*10-3
28 2.400 0.88 0.15 <= 4*10-3
29 3.000 0.88 0.15 <= 5*10-3

Options and accessories:

  • Special filter holders including a holder for simultaneous use of two filters

  • Use of several selection bands on one filter

  • Polarization discrimination option

  • Special filter treatment for use in cryogenic conditions

  • Special filter treatment for use in vacuum conditions

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