Fabry-Perot Optical Filter

A Fabry-Perot (FP) interferometer can be used in an optical sensing system to pass a specific part of the spectrum, functioning like a monochromator. An FP structure is the most suitable for passband optical filters. A Fabry-Perot optical filter consists of two parallel mirrors with a resonance cavity in the middle (Fig. 2). The equation 7u = 2nd shows its operation principle, where n is the refractive index of the cavity medium, d the cavity length, X the incident wavelength, and q the interference order q = 1,2,3,...). 

Figure 4.24 T unable Fabry-Perot optical filter. (Figure courtesy of Ms. Mary Ann Maher, SoftMEMS.)...

Lay out a tunable Fabry-Perot optical filter in a multiproject wafer process as shown in Figure 4.24. The top Bragg mirror should be composed of a stack of dielectric films and should be flat to within a fraction of a wavelength of light that will be filtered. 

Computed evaluation of the spectral profile during the deposition of a Fabry-Perot interference filter (according to E. Pelletier, 1981), e = optical thickness of the individual layers. 

D. Bonaccini, L. Casini, P. Stefanini. Fabry-Perot tunable filter for the visible and near IR using nematic liquid crystals. In Current Developments in Optical Engineering IV, Robert E. Fischer and Warren J. Smith, eds. SPIE—The International Society for Optical Engineering, San Diego, CA, 1990, 1334 221-230. 

Kersey A D, Berkoff T A and Morey W W, Multiplexed fiber Bragg grating sensor system with a fiber Fabry-Perot wavelength filter . Optics Lett., 1993,18(16), 1370-2. 

Y. Mitsuhashi, Saturable Fabry-Perot filter for nonlinear optical image processing, Opt. Lett., 6, 111-113 (1981). 

For processes faster than about 10-10 sec, diffraction gratings are used as the filter. For the slower processes with relaxation times in the range of about 10-6-10-10 sec Fabry-Perot interfermeters are used (See Appendix 4.A). Filter experiments do not have sufficient resolution to study processes slower than about 10 6 sec. For fluctuations in the time range 1—10—6 sec optical mixing techniques must be used. 

A line filter is essentially a Fabry-Perot etalon with a very small optical path nd between the two reflecting surfaces. The technical realization uses two highly reflecting coatings (either silver coatings or dielectric multilayer coatings) that are separated by a nonabsorbing layer with a low refractive index (Fig. 4.60). For instance, for nd = 0.5 p,m the transmission maxima for vertical incidence are obtained from (4.62a) at Ai = 1 xm, A2 = 0.5 p,m, A3 = 0.33 p,m, etc. In the... 

Receiving equipment for aircraft astrophysical investigations in the far infrared has been developed and flown in 1974-1975 on board the AN-30 aircraft. Four types of infrared and submillimeter detectors mainly of photoresistor type are used in the wavelength region from 10 mkm to 1 mm. Thermal background at the detectors is limited by cooled bandpass filters and by optimal matching of the detectors with the telescope optics. The spectral filters used are combinations of quasiresonance metal mesh filters of different structure and Q-factor from 2 to 7 with the Yamada cut-off powder filters. A tunable Fabry-Perot interferometer, a polarimeter for linear polarization measurements and an aircraft 25 cm-telescope are briefly described. 

Fabry-Perot etalon devices based on materials sensitive to electric fields have been studied as tuneable optical filters. Gan et al. [165] presented in their work a hybrid organic/inorganic sol-gel material based on 3-methacryloxypropyl trimethoxysilane as precursor and TCBD (15% mol) as NLO chromophore that was covalently incorporated into the silica network. They demonstrated an optical filter having large tunability and high finesse. The EO sol-gel film was corona poled with 5 kV/cm at 170°C for 30 min. 

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