Electro-optic Filter Research Articles

Analysis and Design of a High Transmittivity and Narrowband Tunable Lithium Niobate Filter With Double FP Cavities

Tunable Fabry-Perot (FP) filters are being increasingly employed in tunable fiber lasers for wavelength selection and tuning. To address single cavity restrictions on transmittivity and achieve narrowband simultaneously, we propose a narrowband tunable electro-optic (EO) filter based on double FP cavities. Lithium niobate (LiNbO3, LN) platform and MgF2 are utilized as film pairs to effectively eliminate the effect of flat-top respond triggered by two cascaded cavities. Thus we can design the FP cavities with a high transmittivity and narrow passband of approximately 99.9% and 0.3 nm, respectively, making it more tolerant to the loss in the cavities. The resonance wavelength around 1550 nm can be blue shifted by 102 nm when the electric voltage is raised from −150 V to 150 V. The error analysis indicates that the incident angle exhibits a certain tuning effect on the wavelength, and the difference between the optical thicknesses of the cavities should be kept to a minimum. The proposed tunable LN filter with double FP cavities may be used in promising applications such as optical communication and photoelectric integration.

Fast Switching Dual-Frequency Nematic Liquid Crystal Tunable Filters.

We develop tunable optical filters with dual-frequency nematic liquid crystal optical retarders to enable fast switching between the passed wavelengths. The filters are composed of a series of two liquid crystal optical retarders. We select the specific thicknesses of the liquid crystal retarders and use individual biasing schemes to continuously tune the wavelength and bandwidth of the filter. This enables fine-tuned filter switching speeds of filter operation in the ms regime. We present theoretical predictions and experimental results for the electro-optical filter characterization as well as an example application for our filter in total internal reflection fluorescence microscopy. We find that our filter switching speeds can be as short as a few ms, an order of magnitude improvement over typical mechanical filter wheel switching speeds. The quality of our fluorescence images is similar to those obtained by conventional filters.

Electrically switchable electro-optic filters for spectral line emission detection.

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.

Terahertz electro-optical multi-functional modulator and its coupling mechanisms based on upper-layer double graphene ribbons and lower-layer a graphene strip

A terahertz multifunction modulator composed of upper-layer double graphene ribbons and lower-layer a graphene strip, which can generate a Fano resonance produced by hybrid between a broad mode and a narrow mode, is proposed to realize electro-optical switch and filtering function. The electric field distribution, hybrid theory, and quantum level theory are all employed to explain the Fano resonance, whose transmission spectra are fitted by coupled mode theory. In comparison to other graphene-based terahertz modulators, the amplitude modulation degree can reach 99.57%, meaning an excellent electro-optical switch can be realized. Moreover, the extinction ratio of Fano resonance can reach 99.70%, demonstrating an unparalleled electro-optical filter is implemented. Finally, variations in the lateral and longitudinal lengths of the lower-layer a graphene strip enable excellent dual-band, triple-band filters. Thus, this work provides a new way to implement terahertz multi-function modulators.

Signal Processing Criteria Based on Electro-Optic Filters for Fiber Optic Access Transceiver Systems

Abstract The study outlines the different types of electro-optic filters that are used in fiber optic access transceiver systems. These filters are classified into the electrical filter in the receiver side and optical filters are located between fiber optic and transmitter. The optical filters are, namely, Fabry Perot, Gaussian, and Bessel filters. While electrical filters that are namely low pass Bessel, low pass Gaussian, and low pass squared raised cosine roll-off filters. The study emphasizes the important criteria in the employment of electro-optic filters in this system for signal fast processing. The Fabry Perot optical filters in addition to low pass squared raised cosine roll-off filters are clarified the best-obtained results in the comparison with other proposed filters.

Tunable broadband filter based on lithium-niobate asymmetric Mach–Zehnder interferometer for coarse wavelength-division multiplexing applications

Channel-select filtering technology is a very promising solution for realizing reconfigurable demultiplexing components required in a flexible coarse wavelength-division multiplexing system. Here, we propose and demonstrate an electro-optic tunable broadband filter based on an asymmetric Mach–Zehnder interferometer formed on lithium niobate for this application. The counter-tapered directional coupler is introduced to replace the conventional one formed with uniform waveguides so that a splitting ratio of 50%:50% is much easier to be realized over a wide wavelength range and, hence, increase bandwidth of the filter. In addition, to reduce the bending loss in the long-wavelength region, the waveguide width and the height of the involved S-bend waveguides are optimized experimentally. Our fabricated filter, which has a total length of ∼30 mm, exhibits an extinction ratio of ∼15 dB and a wide tuning range of >40 nm with an electrical wavelength tuning sensitivity of ∼4.5 nm / V.

Electro‐optic filter based on guided‐mode resonance for optical communication

An electro-optic filter based on guided-mode resonance for optical communication has been designed and fabricated. The rigorous coupled-wave analysis is used to calculate the reflection spectra of the designed filter. The grating structure of the filter is patterned by interference lithography with two ultraviolet laser beams. The polymer-dispersed liquid crystal is injected into the gap between the glass substrate and the bottom of the grating to fabricate the electro-optic filter. The measured spectra of the fabricated filter exhibit a 38.7 nm shift of the resonant reflected wavelength by controlling the applied voltage.

Ultrasensitive and compact tunable electro-optic filter in a 2D silicon photonic-crystal cavity

In this work, we designed and simulated a high Q-factor photonic crystal cavity with a PN junction to demonstrate a high-sensitivity and high tunable electro-optic filter (EOF). For this purpose, we used a cavity based on 2D photonic crystal structures and created a PN junction with 1 μm width in the center of the cavity to change the refractive index of it. The electro-optic sensitivity of the cavity was improved by reducing modal volume and scattering power. Reverse bias in the range of (−3.88 V–0.288 V) is applied to the PN junction and the output spectrum is investigated for various bias voltages. The output wavelengths of designed EOF can be tuned by manipulating cavity cells. In final response of EOF the maximum transmission efficiency is more than 93%, the overall Q-factor is more than 14 500. The whole device fits in a compact 102.6 μm2 (17.4 μm × 5.9 μm) footprint.

Low power Electro-optical filter: Constructed using silicon nanobeam resonator and PIN junction

In this paper, a high tunable Electro-optical filter is designed and simulated with low electric power consumption. A silicon nanobeam resonator based on one-dimensional photonic crystal in the form of Fabry–Perot structure, silicon-on-insulator waveguide, is proposed with a PIN junction. In designing nanobeam resonator, “deterministic design method” is used to achieve the high quality factor and high-transmission rate. Tuning of the resonant wavelength in the output channel of the filter is achieved by manipulating the refractive index of the active area by using the free-carrier dispersion effect. The output wavelengths of designed device can be tuned for the telecom-friendly 1.55µm range. The device shows a wavelength shift higher than 3nm for a power consumption of only 0.9mW. Finally, the simulation results show that the provided device can be considered as a narrowband and tunable Electro-optical filter that is suitable for DWDM communication system.

Tunable electro-optic filter based on metal-ferroelectric nanocomposite for VLC.

The emerging technology of visible light communications (VLC) will provide a new modality of communication. This technology uses illumination lighting to carry information. We propose to add a smart capability to mitigate interferences from unwanted light sources. This is achieved by adaptively filtering interference light using a tunable filter to block interferences dynamically. In this Letter, we present an innovative concept for a tunable notch filter based on ferroelectric thin films embedded with noble metal nanoparticles. The adaptivity of the filter is achieved by controlling the external applied voltage. This voltage creates an electric field that changes the refractive index of the host film through the linear electro-optic effect. Moreover, the fundamental characteristics of the filter are determined by the layer's parameters, such as film thickness, nanoparticles concentration and geometry, and the material of both the host thin film and nanoparticles. We study the tunability of lead zirconate titanate (PZT) embedded with Ag nanoparticles that reaches approximately 50 nm, between 530 and 590 nm. Moreover, we showed that a PZT notch filter embedded with Ag nanoshells has its stop band shifted to shorter wavelengths. These tunable filters can be used as mode selectors inside a laser resonator, spatial light filters for imaging and communication both for VLC and infrared communication.

Application of finite impulse response network concept in wavelength-tunable electro-optic filter

We present a model of wavelength-tunable electro-optic filter on x-cut, y-propagation Ti-diffused lithium niobate. The filter is composed of two polarization beam splitters and a polarization converter which is controlled by an N-stage cascade of alternating coupled-mode and phase-shifted electrodes. The concept of finite impulse response digital filtering is used to calculate the voltage matrices and in the z field, which control the mode coupling and phase shift respectively. By changing the input voltages, a wavelength-tunable bandpass filter or a non-periodic multi-wavelength selector can be obtained. For the bandpass filter, the rectangular degree of passband can be improved by increasing the number of cascading stages . If is equal to 24, the side mode suppression ratio (SMSR) could reach 25 dB. And the passband can be tuned by simply changing the voltage matrix . For the multi-wavelength selector, the design process can be fulfilled by the discrete Fourier transform method. The bandwidth of each selected wavelength increases but the number of selected wavelengths decreases when the number of cascading stages decreases. If is equal to 24, a bandwidth of 0.29 nm with a SMSR of 12 dB is achieved within a 8 nm range centered at 1550 nm.

POLICRYPS composite structures: realization, characterization and exploitation for electro-optical and all-optical applications

The acronym POLICRYPS indicates a nano/micro composite structure made of films of well aligned nematic liquid crystal (NLC) alternated to slices of almost pure polymer. Structures are fabricated by curing a homogeneous mixture of mesogenic material, monomer and a curing agent with UV radiation, under suitable physical and geometrical conditions. In particular, geometrical conditions determine (in the range 0.2 ÷ 15 μ m) the spatial periodicity of the realized sample, which can be utilized for transmitting, diffracting or reflecting an impinging light beam, with negligible scattering losses. The spatial modulation of the refractive index (from polymer to NLC) can be switched ON and OFF both by applying an electric field of few V/μ m or, in some cases, by irradiating the sample with a light beam of suitable wavelength. This electrical/optical tuneability is responsible for a series of distinctive characteristics of the optical effects produced by the structure, and determines the range of possible applications. In fact, in different geometries, the POLICRYPS can be exploited as a switchable holographic grating, a switchable optical phase modulator, a switchable beam splitter, a tuneable Bragg filter or it can be exploited as an electro-optical edge filter in an optical interrogation system.

Controlled focus shaping with generalized cylindrical vector beam

An optical system is proposed for the controlled focus shaping of generalized cylindrical vector beams by a high-numerical-aperture lens. A segmented electro-optical filter with four concentric belts is introduced and works with a double-λ/2-plate. By controlling the rotational angle of the plate and the voltage applied to the filter with proper azimuth angle, a three-dimensional engineered focusing field, such as an electrically controlled axial-shifted focus, extended depth of focus, and a diffraction-limited optical tube, can be achieved. The main advantage of this focusing system is that the focused field can be adjusted and formed by the applied voltage and the rotational angle of the half-wave plates. It can provide a new focus shaping technique with free adjustability and flexibility.

电光双折射扫描滤波法提高啁啾脉冲对比度

电光双折射扫描滤波法提高啁啾脉冲对比度

Fast response liquid crystal glasses

The consequences of misadaptation when suddenly exposed to bright light can by minimised by gradually darkening (photochromic) glasses and this permits better vision. However, the reaction time of such glasses is of the order of a few seconds which is slow enough to cause visual discomfort when the lighting changes rapidly. The current invention presents an eye device with a fast response time, designed to proportionately filter electromagnetic radiation. This system, consisting of a photo-sensitive sensor, an electronic circuit and two liquid crystal lenses, inserted into an eyeglass frame, gives reaction times in the range 50–100 ms. Such liquid crystal electro-optic filters enhance global visual comfort and can also improve the security of users, e.g. by avoiding the glare to a driver at the exit of a tunnel, as well as being useful during outdoor activities and maybe in some medical conditions.

Thermally tunable 100 GHz spaced four-wavelength electro-optic filter based onaperiodically poled lithium niobate

We propose theoretically a method for designing a narrowband multi-wavelengthŠolc-type filter based on the linear electro-optic effect in aperiodically poledlithium niobate. As one of its applications we demonstrate a thermally tuned100 GHz spaced four-wavelength filter, whose working electric field is only 0.219 kV mm − 1 in an 8 cm long crystal. The filter allows four wavelengths to pass simultaneously with a3 dB bandwidth of 0.26 nm, a passband of 32.5 GHz and a channel isolation ofmore than 8 dB, which can be tuned by temperature in a wide range at a rate of − 0.69 nm °C − 1. It is found that the domain errors of the aperiodically poled lithium niobatecrystal within 25% are beneficial to the performance of the filter. The filter will beuseful for dense wavelength division multiplexing optical communication systems.

A wide tuning range electro-optic filter based on long-period waveguide grating

We present the design of an electro-optic filter with polarization insensitivity based on a long period waveguide grating. The filter exhibits an ultra-large wavelength tuning range of exceeding 35 nm and covering the whole C band (1530 to 1565 nm) in a bias voltage range from −84 to 84 V. In the whole tuning range, the transmission coefficients for quasi TE modes are over 97% and the 3 dB bandwidths are below 0.8 nm. The wavelength sensitivity to the tunable voltage is about 0.208 nm/V. This electro-optic filter can be used in dynamic WDM networks for fast wavelength scanning/selection, communication channel reconfiguration, and optical switching.

Design and Simulation of a Narrow Passband Electro-Optical Tunable Filter with Band-pass and Band-rejection Output

An electro-optical tunable filter comprised of two paralleled identical long-period waveguide gratings is proposed in this paper. The filter has one input port and two separate output ports, outputting band-pass and band-rejection light respectively. Using poled electro-optical polymer material to fabricate its waveguide cores enable the filter’s tuning speed to approach nanosecond order. With the aid of long-period waveguide gratings, the tuning range of the filter is Λ times larger than the conventional electro-optical filters. We built up a model to design and simulate the proposed tunable optical filter. We investigate the relationship between the parameters of the long-period waveguide grating and the characteristics of the tunable filter, such as tuning range and FWHM. The simulation results show that the tunable optical filter can realize high-speed tuning in the wavelength range of 1530 nm to 1560 nm, and the FWHM width can reach 0.8 nm. Compared with the conventional optical filters, the results show that a high-speed widely tunable optical filter with narrow pass band can be achieved.

Opening of Hybrid Bandgaps in Two-Dimensional Photonic Crystals of Pb(Mg$_{1/3}$Nb$_{1/3}$)O$_{3}$–PbTiO$_{3}$ Having Very Low Refractive Index Contrast

The effect of anisotropy on two-dimensional photonic crystals of hexagonally arranged Pb(Mg <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/3</sub> Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/3</sub> )O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -PbTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (PMNT) rods in air background was analyzed using a finite-difference time-domain method. The refractive index contrast between PMNT (n = 2.47) and air is low compared to conventional semiconductor-air photonic crystals. Yet, hybrid (polarization-independent) photonic bandgaps were achieved for anisotropic PMNT rods by adjusting the structural parameters and the anisotropy. The maximum bandwidth found was 20 nm. It was possible to engineer the center wavelength of this bandgap to 980, 1300, and 1550 nm, for potential applications as switches, electrooptic filters, and modulators in this region.

Reconfigurable microwave photonic transversal filter using a variable gain tilt filter

A novel and simple technique to realize reconfigurable microwave photonic transversal filter is presented. In the proposed method, a multi-wavelength source and a dispersive medium are applied to achieve multiple taps; and an electro-optic ceramic material-based variable gain tilt filter (VGTF) is utilized to control the tap weights of the filter. The VGTF is computer-controlled via a universal serial bus interface, which enables real-time reconfiguration of the filter. Filter responses with different passband bandwidth and different sidelobe suppression can be achieved. Compared with previous approaches, the given method features in less optical components involved and faster response speed. A three-tap reconfigurable filter with sub-millisecond response speed is experimentally demonstrated.