Thin Film Fabry-Perot Filter Research Articles

Vignetted-aperture correction for spectral cameras with integrated thin-film Fabry–Perot filters

Spectral cameras with integrated thin-film Fabry-Perot filters have become increasingly important in many applications. These applications often require the detection of spectral features at specific wavelengths or to quantify small variations in the spectrum. This can be challenging since thin-film filters are sensitive to the angle of incidence of the light. In prior work, we modeled and corrected for the distribution of incident angles for an ideal finite aperture. Many real lenses, however, experience vignetting. Therefore, in this paper, we generalize our model to the more common case of a vignetted aperture, which changes the distribution of incident angles. We propose a practical method to estimate the model parameters and correct undesired shifts in measured spectra. This is experimentally validated for a lens mounted on a visible-to-near-infrared spectral camera.

Finite aperture correction for spectral cameras with integrated thin-film Fabry-Perot filters.

Spectral cameras with integrated thin-film Fabry-Perot filters enable many different applications. Some applications require the detection of spectral features that are only visible at specific wavelengths, and some need to quantify small spectral differences that are undetectable with RGB color cameras. One factor that influences the central wavelength of thin-film filters is the angle of incidence. Therefore, when light is focused from an imaging lens onto the filter array, undesirable shifts in the measured spectra are observed. These shifts limit the use of the sensor in applications that require fast lenses or lenses with large chief ray angles. To increase flexibility and enable new applications, we derive an analytical model that explains and can correct the observed shifts in measured spectra. The model includes the size of the aperture and physical position of each filter on the sensor. We experimentally validate the model with two spectral cameras: one in the visible and near-infrared region and one in the short wave infrared region.

The influence of beam-cone-angle on the high energy laser induced damage of optical thin film

A continuous wave (cw) laser beam with extremely high power density is needed in the experimental study of the optical film’s thermal damage. In order to achieve such high power density, the incident beam generally needs to converge. In this situation, the cone-angle of the converged beam is inevitable, which may affect the damage process of the optical film. A thin-film Fabry–Perot filter is taken as an example. The influence of the beam cone angle on the thermal damage of the optical film is theoretically studied. Under the irradiation of high power cw laser, the film absorbs the laser energy and the heat accumulates continuously in the film. The cone-angle changes the laser intensity distribution, i.e. the heat source, in the multilayer film. The temperature distribution and the temperature rising process are also related to the cone-angle. Only when the cone’s half angle is smaller than 2°, the influence of the cone-angle may be ignored.

Ultracompact Multilayer Fabry–Perot Filter Deposited in a Micropit

We fabricate a multilayer Fabry–Perot filter (FPF) on a GaN-on-silicon platform. Being significantly different from conventional thin film FPFs formed on smooth flat surfaces, this FPF is deposited in a micropit, and takes a suspended GaN membrane as its carrier, which makes the whole structure ultracompact. The reflection spectra of the FPF are characterized by using an angle-resolved microreflection measurement system. The experimental results show that its spectra generally have a considerable blue shift in comparison with that of its conventional counterpart formed on the smooth flat surface; moreover, its thickness is not uniform but varies along its lateral dimension, suggesting that its spectral properties are highly localized. Resonable explanations are provided to illuminate its particular spectral phenomena. Finally, the localized thicknesses of the thin films composing the FPF are obtained by fitting the measured reflection curves with the simulated ones. This kind of FPF may be integrated monolithically into a batch of suspended membrane devices to endow them with the desired wavelength selectivity.

Theoretical investigation of a tunable external cavity diode laser based on a single cavity all-dielectric thin-film Fabry–Perot filter

The single cavity all-dielectric thin film Fabry–Perot filter (s-AFPF) has been theoretically investigated in this paper as a means of tuning the wavelength in an external cavity diode laser (ECDL), and the means of limiting longitudinal mode hopping has been also theoretically investigated. When a TE or TM plane wave irradiates an s-AFPF, a quasi-linear relationship is found in a certain wavelength range between the optical intensity peak transmittance wavelength of s-AFPF and the cosine value of plane wave incident angle at s-AFPF. Based on this feature, we proposed and theoretically investigated an ECDL configuration based on an s-AFPF. By theoretical calculation, the actuator flat edge against the steel ball may be replaced by a bent edge to convert the mode-hop wavelength region into mode-hop-free wavelength region. The ECDL can be used in the application of environmental monitoring, atomic and molecular laser spectroscopy research, precise measurements, and so on.

Multispectral interference filter arrays with compensation of angular dependence or extended spectral range.

Thin film Fabry-Perot filter arrays with high selectivity can be realized with a single patterning step, generating a spatial modulation of the effective refractive index in the optical cavity. In this paper, we investigate the ability of this technology to address two applications in the field of image sensors. First, the spectral tuning may be used to compensate the blue-shift of the filters in oblique incidence, provided the filter array is located in an image plane of an optical system with higher field of view than aperture angle. The technique is analyzed for various types of filters and experimental evidence is shown with copper-dielectric infrared filters. Then, we propose a design of a multispectral filter array with an extended spectral range spanning the visible and near-infrared range, using a single set of materials and realizable on a single substrate.

Design of Optical Thin Film Filter for Sensor Network

Human body detection is very important especially in the countries prone to earthquakes. Fabry-Perot filter as an ideal option in this field needs to be explored. This filter is useful for detection of objects that have temperature around that of the human body. In the presented research, an optical thin film Fabry-Perot filter (FPF) at the wavelength about 8 um to 14 um is investigated. The important factors on transmission spectrum and the band width of filter are discussed. Additionally structural factors such as layers material and their thickness are explored. Various materials with high and low refractive index are examined by TFCalc3.5 for thin film layers. Germanium (Ge) with the refractive index 4.20 is selected for layer with high refractive index and Silicon Dioxide (SiO2) with the refractive index 1.46 is selected for low refractive index layer. Our simulation results lead to optimum parameters as: Germanium layer with 196nm thickness and Silicon Dioxide layer with 451nm thickness. Simulation of proposed filter indicated that the transfer coefficient is more than 90% in desired spectrum. Filter structure can be used on Infrared detectors to improve their resolutions and detection.

Reduction of the diffraction in strongly resonant thin-film Fabry–Perot filters between single-mode fibers

Simulations show that the cumbersome diffraction losses occurring in narrow bandpass thin-film Fabry-Perot filters (TF-FP filters) inserted between two narrow-core optical fibers are strongly reduced by introducing into the filter a pair of film materials with high refraction index contrast. They are even further reduced by transforming the optically resonant layers of the filter into gradient index photo-refractive resonant lenses. This permits the design of compact TF-FP filters between fibers with passbands as narrow as those of TF-FP filters deposited on bulk substrates.

Theoretical analysis of the wavelength tuning characteristics in a tunable ECDL based on a s-AFPF

The single cavity all-dielectric thin film Fabry-Perot filter (s-AFPF) is investigated in this letter as a means of tuning the wavelength in an external cavity diode laser (ECDL), and the means of limiting longitudinal mode hopping is also investigated. When a TE or TM plane wave irradiates a s-AFPF, a quasilinear relationship is found in a certain wavelength range between the optical intensity peak-transmittance wavelength of s-AFPF and the cosine value of plane wave incident angle at s-AFPF. Based on this feature, we propose and investigate a configuration with a s-AFPF in a tunable ECDL. By theoretical calculation, a mode-hop-free wavelength tuning range of ∼5 nm around 1 550 nm is achieved. The ECDL can be used in the application of environmental monitoring, atomic and molecular laser spectroscopy research, precise measurements, and so on. OCIS codes: 140.2020, 140.3600, 310.6860. doi: 10.3788/COL201210.S11411. Tunable external cavity diode lasers (ECDLs) are playing an increasingly important role in coherent optical telecommunications, atomic and molecular laser spectroscopy, precise measurements, and environmental monitors [1] . Currently, two principal configurations in tunable ECDLs are the Littrow configuration [2−7] and the Littman–Metcalf configuration [8−11] and in both the

Enhanced superprism effect based on positive/negative lateral shift of reflective beam in a Fabry-Perot filter

It is found that when a light beam is incident obliquely on a thin film Fabry-Perot filter (FPF) from different incident media (air or substrate), the reflective beam will be shifted in both the forward and the backward directions. Based on this inverted spatial dispersion effect, two thin film FPFs with different directional lateral shifts are assembled to get a thin film superprism with a wider dispersion band. The thin film samples are fabricated as well as tested, and the results are in approximate agreement with numerical simulation.

Negative Goos–Hänchen Effect in Thin-Film Fabry–Perot Filter

We investigate the Goos–Hänchen effect of a Gaussian light beamreflected by the thin-film Fabry–Perot filter. It is shown that theGoos–Hänchen shift can be either negative or positive. TheGaussian-beam analysis and stationary phase method are introduced tocalculate the lateral shift between the incident beam and the reflectedbeam at different wavelengths and to analyse the Goos-Hänchen effect inthe thin-film Fabry-Perot filter. The effect of the incident beamdiameter is also discussed.

Reflected Gaussian beam splitting phenomenon in the thin-film Fabry-Perot filter

A numerical method to simulate the splitting of the reflected Gaussian beam in the thin-film Febry-Perot filter is described. The splitting can be simply explained by studying the reflection curve. The thin-film Febry-Perot filter has been fabricated by coating TiO2 and SiO2 on glass. The reflected beam splitting phenomenon is observed and measured in practice. The theoretical result is in accord with the experimental result.

Tunable spatial demultiplexer based on the Fabry-Perot filter

Superprism effect is exhibited in one-dimensional thin film stacks due to their abnormal dispersion and anisotropy properties near the bandgap. Thin film Fabry-Perot filter (FPF) was designed and fabricated to realize this effect. Furthermore, the polychromatic light was operated at different incident angles onto the device to get more demultiplexing channels at different wavelength range. This means FPF, which fabricated low-costly and simply can be used as a tunable demultiplexing device. Meanwhile, distinguished with other researchers' arithmetic, transfer matrix method (TMM) with the Gaussian angular spectrum method was introduced to calculate more accurate spatial shift at different wavelength as well as to analysis beam splitting phenomena in FPF.

Superprism Effect in Thin Film Fabry-Perot Filter

For the sake of achieving remarkable superprism effect, we investigate in thin film Fabry-Perot filter which possess drastic change in phase and large group delay around wavelength of peak transmittance. The group delay and spatial dispersion shift are simulated numerically; while the device is fabricated and tested with the maximum spatial separation shift reach to 65�m . We also analyze Gaussian beam propagating in the device to give the interpretation of the spot splitting phenomenon in this experiment. Compared with the traditional prism, the total thickness of our structure is only 3.3�m , and shows a very large deflection angle about 30 ◦ /nm.