Search

This work develops a tunable chirped guided-mode resonant (GMR) filter that has a hybrid splay–twist (HST) liquid crystal as a cladding layer. The GMR filter is a color reflector that strongly reflects light at the resonance wavelength, and its chirped grating structure supports tuning of the resonance peak over a wavelength range of over 50 nm. The HST-LC configuration serves as an achromatic polarization rotator that can rotate the axis of polarization of linearly polarized light by providing effective twist angles in the LC layer under an applied voltage. The HST-LC is used to change the direction of the polarization axis of the light that is reflected by the GMR filter; continuous angles of rotation of ∼ 90 ∘ are achieved and the linear polarization is retained under applied voltages. The proposed filter enables an ultrabroadband polarization rotation and still maintains a high degree of linear polarization, which allows more degrees of freedom in spectral and polarization controls.

A deep-ultraviolet (DUV) narrowband tunable filter with a central wavelength of 225.0 nm is designed, fabricated, and demonstrated experimentally. The simulation results showed a transmittance of about 42.1% at 225.0 nm and a full width at half-maximum (FWHM) of ∼ 1.2 n m . The experimental results for normal incidence light revealed a corresponding central wavelength of 225.0 nm, a transmittance of 27.7%, and a FWHM of 1.9 nm. By changing the incident angle, the central wavelength can be tuned from 225.0 to 224.5 nm. This DUV narrowband tunable filter has been shown to demonstrate good performance and has broad applicability.

Fully reconfigurable optical filters are indispensable building blocks to realize reconfigurable photonic networks/systems. This paper proposes a reconfigurable and dual-polarization optical filter based on a subwavelength grating waveguide operating in the Bragg reflection mechanism and combined with a low-loss phase change material G e 2 S b 2 S e 4 T e 1 . Numerical simulations indicate that, for TE(TM) polarization, the presented Bragg grating filter offers up to 20 nm (17 nm) redshift with amplitude modulation of 6 dB (0.15 dB) at 1550 nm. Using the effective medium theory, we obtained the six-level crystallization performance of the optical filter. The proposed optical filter has potential applications in wavelength-division-multiplexing systems, optical signal processing, and optical communications.

We report a widely tunable optically pumped vertical-external-cavity surface-emitting laser. The multiple quantum wells in the active region of the gain chip are generally designed to form the resonant periodic gain structure, and three different methods are used to tune the oscillating wavelength. The maximum wavelength coverage of 45 nm is obtained when a 2 mm thickness birefringent filter is introduced in a straight-line cavity, while the tuning range of 8 nm is performed by employing a 0.15 mm thickness uncoated Fabry–Perot etalon. For the first time, to the best of our knowledge, we present an 11 nm tuning range by the use of an inserted blade as the tuning element, and the related wavelength tuning mechanism is analyzed.

In autonomous driving, cars rely on light detection and ranging (lidar) to navigate the surroundings, but interference from the environment makes it difficult to retrieve useful information. To address this problem, this paper develops a noise reduction method to filter lidar point clouds (i.e., an adaptive radius outlier removal filter based on principal component analysis). We believe this method can outperform existing clustering algorithms when applied to point cloud images captured at a large distance from the lidar. Compared to traditional methods, the proposed method has higher precision and recall with an F-score up to 0.876 and complexity reduced by at least 50%.

A single-frequency (SF) fiber laser is widely applied in many fields. A superior ultra-narrow-bandwidth fiber filter, which consists of an in-series commercial common fiber Bragg grating (FBG) filters with a partial overlap in their reflection spectrum, is presented in this paper. The bandwidth of the filter with a center reflection wavelength of 1549.83 nm reaches 0.024 nm at 3 dB reflection, a remarkable reduction of approximately 300% by combination usage narrower than a single FBG used bandwidth. We also demonstrate a method to further narrowing of the filter bandwidth by increasing the usage times of filters, and the bandwidth can reach 0.0025 nm at 3 dB reflection. A long linear cavity single-frequency fiber laser with an entire cavity of 30 cm is implemented with the linewidth of 941 Hz at 3 dB, which is about 210% narrower than the previous record of SF fiber laser based on FBG filters in a linear cavity. This research may open a new door toward ultra-narrow-bandwidth filters and SF fiber lasers.

Subwavelength engineering and utilizing phase-change materials with large contrast in their optical properties have become powerful design tools for integrated silicon photonics. Reversible phase-transition of phase-change materials such as G e 2 S b 2 T e 5 (GST) provide a new degree of freedom and open up the possibility of adding new functionalities to the designed devices. We present an optical filter based on a silicon subwavelength grating (SWG) waveguide evanescently coupled to phase-change material loading segments arranged periodically around the SWG core. The effect of the GST loading segments’ geometry and their distance from the SWG core on the filter’s central wavelength and bandwidth are studied with three-dimensional finite-difference time-domain simulations. The employment of GST in the structure adds a switching functionality with an extinction ratio of 28.8 dB. We also examine the possibility of using the proposed structure as a reconfigurable filter by controlling the partial crystallization of the GST offering a blueshift of more than 4 nm.

Remote detection of spectral line emission is an important capability in a number of areas, including defense and environmental science. In this paper, we report on a mechanism for spectral line emission detection that is not based on narrow bandpass filters or hyperspectral imagers, but is instead based on the use of switchable spectral filters. The use of a switchable filter enables a single sensor to perform remote sensing tasking in a broad passband, while also detecting emission in a particular spectral line. In this case, the switchable spectral filter studied is a holographic polymer dispersed liquid crystal (HPDLC) reflection grating. The concept is demonstrated through modeling a sensor with an integrated HPDLC filter and building a detection algorithm capable of detecting spectral line emission. The modeling framework is built upon four components: the background scene, the spectral line source, the HPDLC filter, and the sensor. Results from the model show probability of detection and probability of false alarm for spectral line sources of varying strength for a particular background scene.

Spectrally narrowband imaging in remote sensing applications can be advantageous for detecting atomic emission features. This is especially useful in detecting specific constituents within rocket plumes, which are challenging to discern from naturally occurring sunglints. In this paper, we demonstrate a dual-beam technique, implemented with a Wollaston prism, for calibrating a Voigt magneto-optical filter for a linear polarizer’s finite extinction ratio, as well as optical misalignment between the linear polarizers’ transmission axes. Such a strategy would be key towards expanding the filter’s field of view while maintaining its classification capabilities. Validation of the potassium Voigt filter is demonstrated using the simulation tool ElecSus in combination with a potassium hollow cathode lamp. RMS error between the filter’s temperature response and that of the simulation was approximately 2%. We then demonstrate the detection of a potassium model rocket motor outdoors alongside a sunglint. Results indicate a 20-fold increase in contrast when using our dual-beam calibration strategy.

We developed a wideband quasi-optical band-pass filter covering 170-520 GHz by exploiting the recent advancements in commercially available flexible printed circuit (FPC) fabrication technologies. We designed and fabricated a three-layered stack of loaded hexagonal grid metal meshes using a copper pattern with a narrowest linewidth of $50~\mu\mathrm{m}$ on a polyimide substrate. The measured frequency pass-band shape was successfully reproduced through a numerical simulation using a set of parameters consistent with the dimensions of the fabricated metal meshes. FPC-based metal mesh filters will provide a new pathway toward the on-demand development of millimeter/submillimeter-wave quasi-optical filters at low cost and with a short turnaround time., Comment: 14 pages, 11 figures, 2 tables, accepted for publication in Applied Optics

The wavefront error (WE) of a surface with an optical coating (“filter”) is ideally measured at the in-band wavelength of the filter. However, quite often this is not possible, requiring that the filter be measured at an out-of-band wavelength (typically 633 nm), assuming that the filter transmits (for transmitted WE, or TWE) or reflects (for reflected WE, or RWE) at this wavelength. This out-of-band TWE/RWE is generally assumed to provide a good estimation of the desired in-band TWE/RWE. It will be shown in this paper that this is not the case for a large class of filters (i.e., bandpass) where the group delay is significantly different at the in-band and out-of-band wavelengths and where the optical filter exhibits a thickness non-uniformity across the surface. A theoretical explanation will be given along with an approach to predict the in-band TWE/RWE based on the coating non-uniformity, the measured out-of-band TWE/RWE, and the theoretical properties of the optical filter at the in-band and out-of-band wavelengths. A reasonable agreement between theory and measurement was demonstrated by measuring the TWE of an 11 nm wide bandpass filter (centered at 1048 nm) at both in-band ( λ = 1048 n m ) and out-of-band ( λ = 625 n m ) wavelengths. A similar treatment is provided for RWE.

In order to meet the needs of on-site, accurate, fast, and remote detection, we design a smartphone-based handheld dual-channel optical fiber fluorescence sensor (DOFFS), which is composed of a semiconductor laser for exciting fluorescence signals, a smartphone with a dual-bandpass filter for collecting fluorescence signals, a fiber coupler for transmitting light, and batteries for laser power supply. All the components are integrated into a 3D printed shell, on the side of which there are two fiber flanges used for fiber probe connection. The fluorescence signals of green and red quantum dots modified on the fiber probes can be captured by the smartphone camera and calculated by a self-developed Android application. The comparisons of single-channel and dual-channel fluorescence signals with pH show that the performance of the sensor is good. The proposed sensor not only can simultaneously detect dual-channel signals for fast detection needs, but it also is handheld with a small size of 79 × 57 × 154 m m 3 and inner power supply, and the fiber probes can be easily replaced, supporting remote and on-site applications. It is a potential tool for many occasions in many fields.

This paper presents research work about the design and fabrication of a 44-layer optical reflective notch filter. The performance of the fabricated notch filter was studied at normal (0°) and oblique (45°) incidence angle. In addition, the paper also discusses a three-layer broadband antireflective coating on both sides of the multilayer stack to suppress the ripples in the passband region. The thickness-modulated reflective stack of the filter was designed by using the materials A l 2 O 3 (1.63) and S i O 2 (1.46). Optimization of the multilayer stack was carried out by using the damped least-squares algorithm. The theoretical and experimental results from the ion-assisted e-beam deposited samples for single notch reflective filters are presented. Good agreement in the design and experimental results was observed when the deposition process was controlled by time of evaporation. Further, the filter was characterized for the optical properties by using a UV-VIS-NIR spectrophotometer, surface morphology and protective properties using field emission scanning electron microscopy, a coherence correlation interferometer, and water contact angle.

Here we report our study on methods proposed for the design and fabrication of a metallic irregular Fabry–Perot (F–P) filter array for a miniature spectrometer to improve its performance and convenience in implementation. The method in designing suggests including both types of unit-cell filters that have broader single passband peaks of lower-order resonance modes and narrower multiple passband peaks of higher-order resonance modes in the F–P filter array for improved performance in reconstructive measurement of a spectrum with both finer and broader features in a wide spectral range. The fabrication method suggests using fewer film-deposition steps to form a larger number of different film thicknesses for the interspacing dielectric layers in the arrayed F–P filters. The processes involve inexpensive facilities and low-resolution patterning techniques in defining the unit cells of the filter array and can be conveniently fabricated using standard planar processing technologies. Resonant transmission spectrum profiles and passband peak positions of unit-cell filters are irregularly distributed in as-designed and -fabricated filter arrays. Based on the route of acquiring spectrum via computational reconstruction, such irregularities can facilitate designing and fabrication of F–P-type filter arrays for miniature spectrometers to achieve both high performance and low cost.

To flatten the Gaussian spectrum of superluminescent diodes (SLDs), a fiber-optic spectrum equalization filter based on an extrinsic Fabry–Perot interferometric (EFPI) cavity is proposed. By the proper usage of a low-finesse EFPI cavity and the delicate design of a splitting and recombining fiber-optic path, the Gaussian spectrum of an SLD can be effectively flattened, which is verified by a numerical simulation and an experiment. An SLD with a center wavelength of 1568 nm and a 3-dB spectral width of 98 nm is spectrum-equalized to obtain a spectrum flatness of 0.27 dB in the wavelength range 1544.8–1605.6 nm. When the SLD is with a max power of 3.38 mW, the output power after the fiber-optic spectrum equalization filter can reach 178.06 μW.

A femtosecond x-ray streak camera based on photoelectron filter technology is reported in this paper. Photoelectrons are collimated through the slit and channel of the photoelectron filter, so that transit time spread and space charge effect of electrons are reduced. A planar-focusing high-voltage electron-optical system is designed to match the filter. The channel length of the filter is 300 μm, and the slit width is 20 μm. The streak tube using the photoelectron filter is 273 mm in length, and the extraction field value between the Au photocathode and the filter is 10 kV/mm. An experimental platform is set up to calibrate the streak camera, which is excited by a 266 nm, 130 fs UV laser. The experimental results show that temporal resolution is 357 fs and dynamic range is 182:1 of this developed camera.

CMOS photodiodes are used in many light sensing applications; however, the performance can be limited by oscillations in the spectral response caused by light interference from the back-end oxide. Gray-scale lithography has been used to fabricate wedge-like structures in the back-end oxide, which reduces the light interference and oscillations over the entire silicon sensitivity range. Dielectric filter stacks have been deposited on top of the structures, demonstrating an improved spectral response over photodiodes, with filters deposited directly on silicon. The present approach is suitable for mass production and fully compatible with CMOS.

A plasmonic bandpass filter based on parallel bulk Dirac semimetals (BDSs) is proposed and numerically investigated using the finite-difference time-domain method. The proposed filter is realized by the evanescent coupling between the resonator and waveguide, and Fabry–Parot resonant theory is used to analyze its realization mechanism. The performance of the filter can be tuned by changing the coupling distance, length of the resonator, and Fermi levels of the BDSs. We further simulate a plasmonic broadband filter using coupling mode splitting by locating two identical resonators along the waveguide direction. The pass band of the proposed broadband filter can be tuned by adjusting the coupling distances between the resonators and waveguide.

How to reduce the bandwidth and insertion loss (IL) of a planar filter at high frequency is challenging work. We investigate the design, simulation, fabrication, and measurement of a terahertz (THz) planar filter with easy integration, low IL, and narrow passband. The direct feeding microstrip filter (DFMF) has a center frequency ( f 0 ) of 140 GHz, IL of 2 dB, and 3 dB fractional bandwidth ( F B W 3 d B ) of 6%, while traditional coupled feeding microstrip filter with the same configurations has F B W 3 d B of 20%. The proposed DFMF filter employs direct feeding mode to narrow bandwidth and miniaturized size. The DFMF does not need small coupling gaps in the feeding structures, showing good dimensional insensitivity. Benzocyclobutene is introduced as an interlayer dielectric to reduce IL owing to its controllable ultrathin thickness and low-loss tangent. The introduced planar microelectromechanical system technology is suitable for large-scale fabrication at a low cost. The test results based on through-reflect-line de-embedding technology agree well with the simulation results. The DFMF lays a foundation for realizing the planarization and integration of THz systems.

A dispersion-compensating filter for next-generation low-cost analog and digital optical links is developed. In these high-frequency optical channels, even weak dispersion can be detrimental to data encoding (e.g., radar detection). Dispersion-compensating filters must be affordable for these low-cost channels, and they must be reliable for weak dispersion channels. In this paper, we design a dispersion-compensating filter based on three properties of the analog channel: weak modulation depth, a spectrally bounded signal, and a low-dispersion channel. We calculate the fundamental performance limits of the channel with and without the filter and quantify the improvement. Furthermore, numerical simulations are taken to estimate the filter’s performances for both pulse amplitude modulation digital channels and for analog ones. The simulations agree with the analytical derivation, and, in both cases, the filter’s integration improves the channels’ performances considerably.

Hyperspectral imaging for agricultural applications provides a solution for non-destructive, large-area crop monitoring. However, current products are bulky and expensive due to complicated optics and electronics. A linear variable filter was developed for implementation into a prototype hyperspectral imaging camera that demonstrates good spectral performance between 450 and 900 nm. Equipped with a feature extraction and classification algorithm, the proposed system can be used to determine potato plant health with ∼ 88 % accuracy. This algorithm was also capable of species identification and is demonstrated as being capable of differentiating between rocket, lettuce, and spinach. Results are promising for an entry-level, low-cost hyperspectral imaging solution for agriculture applications.

A wavelength-spacing-controllable multi-wavelength polarization-maintaining erbium-doped fiber laser (MW-PM-EDFL) in a linear cavity configuration is presented based on a Lyot–Sagnac filter and a nonlinear optical loop mirror (NOLM). Using a Lyot–Sagnac filter as the wavelength selective filter makes the wavelength spacing controllable by adjusting the effective length of polarization-maintained fiber (PMF) segments. An NOLM inducing wavelength-dependent cavity loss can be used as an amplitude equalizer, which is employed to suppress the mode competition resulting from the homogeneous line broadening effect of the erbium-doped fiber in the cavity. Thus, a stable wavelength-spacing-controllable MW-PM-EDFL is realized. In this experiment, 20 stable lasing wavelengths are obtained with a pump power of 170 mW at 980 nm when the length of the PMF is 13 m. When the length of the PMF is 8 m, 10 stable lasing wavelengths are obtained at 185 mW pump power. The power fluctuations and wavelength shifts are less than 2 dB and 0.02 nm in 1 h at room temperature. The demonstrated multi-wavelength fiber laser has great potential for applications in optical communications and optical sensing systems.

In this study, an ultra-compact optoelectronic bandpass filter is proposed. A single piece of graphene nanoribbon (GNR) is placed between two input-output GNRs to form a Fabry-Perot-like cavity. The GNR, as a mid-infrared surface waveguide, enhances the compatibility with complementary metal oxide-semiconductor processing technologies. The transmission characteristics of the bandpass filter are tuned by the modulation of surface charge carrier density simply through changing the bias voltage applied on the GNR cavity, and thus a tunable filter at room temperature is achieved. It is found that increasing the gate voltage and the silica substrate thickness or middle GNR width alters the max peak of transmission spectra of the filter toward smaller wavelengths. In contrast, increasing the middle GNR length redshifts max peak of the filter toward longer wavelengths. The finite different time domain (FDTD) inhouse code has been employed to verify the designs.

A single as well as a multichanneled filter in the terahertz region has been proposed by designing a one-dimensional photonic crystal (PhC) structure using a high-temperature superconductor air-dielectric ternary periodic structure. The filter is designed without incorporating any defect, which has rarely been proposed in a ternary PhC structure. The theoretical study of transmittance was performed by applying the transfer matrix method. The transition from single channel to desired multichannel is achieved by adjusting the number of periods. Furthermore, the impact of the thicknesses and dielectric constants of the constituting layers was investigated. In addition to this, the tunability is achieved by the influence of temperature-dependent dielectric constant of the superconductor.

Narrowband pass filters are generally poor as narrowband angle filters. A tilted narrowband pass filter, however, is an improved narrowband angle filter, but only for rays in one plane of incidence. It is shown that a combination of two tilted narrowband pass filters will select light from all narrow angle patches in an incident cone. Furthermore, a design is presented for a narrow-angle filter for three wavelengths, enabling transmission of tristimulus color gamut images, while rejecting out-of-band sources and off-angle sources.

The classical single-layer waveguide grating structure is often designed as a reflection filter under 0° azimuthal angle conditions. A new method for achieving a transmission filter by modulating incident conditions is proposed rather than adjusting structural parameters. A 90° azimuthal angle ensures single resonance peaks, and large incident angles provide a low-transmittance background. When the proposed single-layer waveguide grating structure is irradiated with an incident light azimuthal angle of 90° and incident angle of 86°, numerical results show that a high transmission peak emerges at 1550 nm with linewidth $\Delta \lambda = 7.2\,\,{\rm nm}$Δλ=7.2nm. Moreover, the transmission peak has nearly 100% transmittance. These findings show that modulating the incident conditions is also an effective means apart from optimizing the structural parameters. The classical reflection filter can be reversed into a transmission filter using this method.

Quantifying the coloration and luminous transmittance of eyewear filters is essential to understand their impact on human visual performance. Accurate measurements require the use of a spectrophotometer, with such equipment often being prohibitively expensive for wide-scale use. This paper details a new technique to characterize eyewear filters using only a digital camera and a sheet of white paper. Images of the paper are captured with and without the filter in front of the camera lens, and then subsequent analysis of pixel intensities allows the filter coloration and luminous transmittance to be determined. The technique has been applied to six different eyewear filters using three different camera and illumination configurations, demonstrating a reasonable match to the spectrophotometer data. This technique is suited to implementation in a smartphone app, in order to provide a low-cost and widely deployable solution to monitor the ageing of eyewear inventory.

A near-infrared (NIR) spectral sensor consisting of a 25-channel dielectric multi-patterned filter array (MFA) and CCD is proposed and fabricated. The MFA consists of a wavy dielectric multilayer with a gradient layer profile on a silica substrate with surface grating. The incoming NIR spectrum is predicted by Wiener estimation utilizing the MFA's spectral responses and a set of training spectral data. Estimation performance is evaluated under various optical shot-noise conditions.

This paper shows the opto-mechanical design of a new filter radiometer built at the Physikalisch-Technische Bundesanstalt, Germany, for the accurate determination of the thermodynamic temperature of high-temperature blackbodies. The filter radiometer is based on a three-element reflection-type trap detector that uses three large active area silicon photodiodes. Its spectral coverage and field of view are defined by a detachable narrow-band filter and a diamond-turned precision aperture, respectively. The temperature of the filter radiometer is stabilized using a water-streamed housing and is measured using a thin-film platinum thermometer placed onto the first photodiode element. The trap "mount" has been made as compact as possible, which, together with the large active area of the chosen photodiodes, allows a wide field of view. This work presents the design of the filter radiometer and discusses the criteria that have been considered in order for the filter radiometer to suit the application.

For a linearly variable Fabry-Perot filter, the peak transmission wavelengths change linearly with the transverse position shift of the substrate. Such a Fabry-Perot filter is designed and fabricated and used as an output coupler of a c-cut Nd:YVOsub4/sublaser experimentally in this paper to obtain a 1062 and 1083 nm dual-wavelength laser. The peak transmission wavelengths are gradually shifted from 1040.8 to 1070.8 nm. The peak transmission wavelength of the Fabry-Perot filter used as the output coupler for the dual-wavelength laser is 1068 nm and resides between 1062 and 1083 nm, which makes the transmissions of the desired dual wavelengths change in opposite slopes with the transverse shift of the filter. Consequently, powers of the two wavelengths change in opposite directions. A branch power, oppositely tunable 1062 and 1083 nm dual-wavelength laser is successfully demonstrated. Design principles of the linear variable Fabry-Perot filter used as an output coupler are discussed. Advantages of the method are summarized.

In this paper, design and analysis of planar graphene-based low-pass filters in the terahertz band are proposed. Using the proposed approach, it is possible to design plasmonic low-pass filters with the desired properties in the form of open stubs. The transfer matrix method is used based on the transmission line model for analyzing filters. The propagation constant and characteristic impedance required for this method are obtained according to the electrostatic scaling law and power-current approach, respectively. A typical fifth-degree low-pass filter is designed and analyzed according to the mentioned process. The frequency response of the low-pass filter indicates insertion loss of less than 2 dB, roll-off rate of 17 dB/THz, return loss higher than 10 dB, and constant group delay of 0.3 ps. The results of the full-wave simulation confirm the analytical ones. Also, the theory of graphene equivalent circuit variation to the different chemical potentials is expressed so the filter frequency response can be explicitly predicted for any bias value. These filters, due to their compact structure and integrated electrical and physical shape, are the suitable choice for use in full-integrated planar circuits of terahertz systems.

This paper demonstrates the design and fabrication of a 128×128 micro-electro-mechanical systems Fabry-Perot (F-P) cavity filter array, which can be applied for the hyperspectral imager. To obtain better mechanical performance of the filters, F-P cavity supporting structures are analyzed by multi-physics finite element modeling. The simulation results indicate that Z-arm is the key component of the structure. The F-P cavity array with Z-arm structures was also fabricated. The experimental results show excellent parallelism of the bridge deck, which agree with the simulation results. A conclusion is drawn that Z-arm supporting structures are important to hyperspectral imaging system, which can achieve a large tuning range and high fill factor compared to straight arm structures. The filter arrays have the potential to replace the traditional dispersive element.

For superconducting nanowire single-photon detectors, we designed and fabricated an on-chip narrow-bandpass filter at the central wavelength of 1.5 μm to reduce the influence of blackbody radiation from the fiber. The bandpass filter was prepared on a thermally oxidized Si substrate, and it provided a peak transmittance of 88% at the central passband wavelength and 30 dB suppression at the stop bands. We investigate the temperature dependence of the filter from room temperature to 2.9 K. The central wavelength of the passband blue-shifted from 1545±2 nm (295 K) to 1526±2 nm (2.9 K). This effect is explained by the different indices of refraction of Si at different temperatures.

Over the past 75 years, birefringent filter technology has evolved significantly. For nearly that same period of time, these filters have been designed and used by solar scientists to study the Sun. Prior to assembling these types of filters, each component, e.g., polarizers and wave plates, is characterized to determine its polarimetric parameters to ensure the desired filter design performance. With time and cost becoming an ever increasing issue, it is imperative to test components designated for a birefringent filter efficiently. This article addresses a shift to increased efficiency when testing components of very low volume (

A plasmonic bandpass filter based on graphene is proposed and numerically investigated using the finite-difference time-domain method. The proposed filter has a very simple structure, including two graphene nanoribbon waveguides laterally coupled to a graphene ribbon resonator. The transmission efficiency can be tuned by altering the coupling distance between the ribbons. At the same time, the variation of the transmission spectra is investigated by tuning the size of the graphene resonant ribbon. Notably, due to the unique electronic tunability of graphene, the transmission spectra can be freely tuned in a broad frequency range by choosing the chemical potential, which exhibits more flexible tunability than that used in conventional metallic devices. Attributed to the standing wave distribution of different modes excited in the graphene resonant ribbon, the proposed filter can be used for the plasmonic device with the capability of band selection or power splitting by locating the output waveguide ports in the suitable positions.

This paper proposes a novel framework for multi-objective optimization of photonic crystal (PhC) filters and compares it with a single-objective optimization approach. In this framework, an optimizer called the Multi-Objective Gray Wolf Optimizer has been utilized to automatically find the optimal designs. The proposed method is able to design any kind of PhC filter. As a case study, a new structure of super defect PhC filter for application in the wavelength-division multiplexer (WDM) is designed using the framework. The results show that the proposed framework is comprehensive and able to find a significantly wide range of optimal designs for general and specific application, such as WDM with respect to each defined WDM standard.

To solve the problem of poor real-time measurement caused by a hyperspectral imaging system and to simplify the design in passive ranging technology based on oxygen absorption spectrum, a filter-based non-imaging ranging method is proposed. In this method, three bandpass filters are used to obtain the source radiation intensities that are located in the oxygen absorption band near 762 nm and the band’s left and right non-absorption shoulders, and a photomultiplier tube is used as the non-imaging sensor of the passive ranging system. Range is estimated by comparing the calculated values of band-average transmission due to oxygen absorption, τO2 , against the predicted curve of τO2 versus range. The method is tested under short-range conditions. Accuracy of 6.5% is achieved with the designed experimental ranging system at the range of 400 m.

In this paper, we investigate a phase correction method for compensation of the nonlinearity of conventional wavelength swept laser sources based on a fiber Fabry-Perot tunable filter as a wavelength selective element. A triangular waveform signal is commonly used to drive the filter. We however extract the zero crossings from the interferograms and modify the shape of the triangular signal accordingly. This algorithm was tested for different values of the optical path length difference (OPD) in the interferometer set-up. Significant compensation for the nonlinearity of the filter was obtained.

In this work, a single-layer, multiple-channel guided mode resonance (GMR) Brewster filter with controllable spectral separation is proposed using the plane waveguide method and rigorous coupled-wave analysis. Based on the normalized eigenvalue equation, the controllability of the spectral separation is analyzed when the fill ratio of the grating layer is changed while its effective index is identical to that of the substrate. The location and the separation between resonances can be specifically controlled by modifying the fill ratio of the grating layer. In contrast to the ordinary GMR filter, where the location of the resonances is material dependent, it is demonstrated that the spectral separation for the first and second resonances can be linearly controlled by altering the fill ratio of the grating layer. In addition, the maximal shift of the second resonance is up to 5% of the first resonant wavelength using the single-layer Brewster filter.

A multispectral camera concept is presented. The concept is based on using a patterned filter in the focal plane, combined with scanning of the field of view. The filter layout has stripes of different bandpass filters extending orthogonally to the scan direction. The pattern of filter stripes is such that all bands are sampled multiple times, while minimizing the total duration of the sampling of a given scene point. As a consequence, the filter needs only a small part of the area of an image sensor. The remaining area can be used for conventional 2D imaging. A demonstrator camera has been built with six bands in the visible and near infrared, as well as a panchromatic 2D imaging capability. Image recording and reconstruction is demonstrated, but the quality of image reconstruction is expected to be a main challenge for systems based on this concept. An important advantage is that the camera can potentially be made very compact, and also low cost. It is shown that under assumptions that are not unreasonable, the proposed camera concept can be much smaller than a conventional imaging spectrometer. In principle, it can be smaller in volume by a factor on the order of several hundred while collecting the same amount of light per multispectral band. This makes the proposed camera concept very interesting for small airborne platforms and other applications requiring compact spectral imagers.

A broadband transmission filter from 400 to 1100 nm was selected for the manufacturing problem contest. The purpose of the contest is to test the state of the art of current optical thin film manufacturing capabilities. A total of 37 people from 15 teams participated in the contest and submitted 17 samples. Diverse approaches were taken by participants to tackle the problem. A range of different solutions was obtained where the number of layers varied from 22 to 608, and the total layer thickness ranged from 1.859 to 23.099 μm. Two independent laboratories performed sample evaluation measurements. Three teams shared the best result with the lowest average measured merit function.

A Rugate notch filter is fabricated by atomic layer deposition. By regulating the thickness ratio of TiO2 and Al2O3 in a nanoscale layer, the refractive index is tailored between the refractive indices of the two materials. With the method of equivalent refractive index, the continuously variable refractive index of the designed Rugate filter is dispersed into several discrete ones, so that it can be realized by the refractive index tailoring. To coincide with the thickness, the nanoscale layer is iteratively deposited in the equivalent layer. The experimental reflectance matches the designed one well, and the average reflectance is 86.7% (510–590 nm).

Guided optimization of a good starting design can lead to a final design that can be reverse engineered. We apply this to a wide bandpass filter and indicate its deposition with optical monitoring.

We present a model of an atomic filter based on laser-induced optical anisotropy that is achieved by the combination of a double selective pump. Most of these kinds of atomic optical filters reported previously adopt only one pump to make the atoms populate on particular sublevels. In this paper, another pump is added to the filter system to make sure all the atoms are in the pump–probe cycle. The feasibility of the re-pump is analyzed by employing the rate equation, and the contribution of the re-pump to the filter is discussed under various conditions. Simulation results show that the re-pump can not only enhance the transmission of the filter, but also vary the transmission spectrum peak wavelength.

This work presents what we believe is a novel design of a hybrid plasmonic-transmission blue filter for visible light communication systems that employ yellow phosphor-coated blue light-emitting diodes. The proposed filter balances the trade-off between transmission performance and tolerance to variation in angles of incidence (AOIs) while maintaining a low cost with limited complexity design. The designed filter operation is based upon quasi-plasmon mode excitation in a hybrid structure of alternating layers of silver and titanium dioxide over a silica substrate. A primary design approach for a hybrid plasmonic filter of five alternating layers is illustrated in detail. Needle optimization technique is further applied to achieve the required filter performance. The designed filter has an insertion loss of ∼1 dB over a spectral range of 400-485 nm and a minimal close to zero polarization-dependent loss for a wide range of AOI (slightly above 50°). The tolerance of the proposed design against fabrication errors is also tested. The performances of the proposed filters are tested for individual and simultaneous variations from the designed thicknesses, with a ±10% standard deviation from each layer's thickness.

We describe a high etendue (0.12 cm(2) sr) camera that, without moving parts, simultaneously images four ultraviolet bands centered at 140, 175, 215, and 255 nm on a single detector into a minimum of ~7500 resolution elements. In addition to being an efficient way to make color photometric measurements of a static scene, the camera described here enables detection of spatial and temporal information that can be used to reveal energy dependent physical phenomena to complement the capability of other instruments ranging in complexity from filter wheels to integral field spectrographs.

Pattern-integrated interference (PII) is described as a logical progression starting from the primary precursors of interference and holography. PII produces, in a single-exposure step, a periodic interference pattern with preselected periods absent. These blocked periods, for example, can form the nonperiodic functional elements of a photonic-crystal device or the circuit elements in a periodic-layout-design semiconductor chip. Various possible system configurations for PII are presented and compared. Example PII-produced intensity patterns for a photonic-crystal microresonator filter and an optical switch are simulated and discussed.

This paper presents a dual-band microwave photonic filter for a wireless local area networks with independently tunable passband center frequencies and bandwidths. The two bands of the filter were 2.4 GHz and 5.725 GHz, respectively. The filter was based on a stimulated Brillouin scattering and an optical frequency comb (OFC) scheme. We created this filter using OFC pumps instead of a single pump. The OFC scheme consists of a cascaded Mach-Zehnder modulator (MZM) and a dual-parallel MZM (DPMZM) hybrid modulation that generated seven and 11 lines. The experimental results show that the two passbands of the filter were 80 and 130 MHz.

In this work we suggest a new technique to form a box-like filter response using a single microring resonator. The new design is based on exploiting the multimode propagation in the ring. The technique is implemented in the case of a two-mode ring resonator for different designs. The obtained results show that the new designs allow getting 1 to 10 dB spectral width shape factor better than 0.4, as verified by the FDTD simulation at different wavelengths and for different spectral widths. This new design methodology opens the door for more compact optical filters with controlled box-like response.

We propose a subwavelength B-shaped metallic hole array filter with an embedded thermally tunable InSb semiconductor bar in the terahertz regime. The resonance frequency of this filter can be actively tuned by controlling the temperature of InSb. The transmissions of the filter are calculated with the finite-difference time domain method at various temperatures. Narrowband THz wave with the full width at half maximum of 235 GHz can be selected in the frequency range from 0.74 to 2.02 THz at temperatures from 160 to 350 K.