Optical Bandpass Filter Research Articles

Multi-band optical bandpass filter with picometer bandwidth in visible spectrum formed by prism pair coupled planar optical waveguide.

An optical bandpass filter structure of multiple bands in the visible spectrum with bandwidths in picometer scale (full width at half maximum, FWHM) is theoretically analyzed. The filter is in a form of prism pair coupled planar optical waveguide. For each individual guided mode, multiple pass-bands are obtainable in violet, green, and red regions of the visible spectrum, respectively. High efficiencies and symmetric band shape with flat null sideband can be obtained with practical material dispersion and loss taken into account. The central wavelength of each band can also be angularly tuned within a certain range with little influence on the efficiency or bandwidth. This kind of ultra-narrow bandpass optical filter can be used in high resolution spectroscopies, laser technologies, optical communications, and optical sensing.

Use of proper cavity loss for a stable single-longitudinal-mode erbium fiber laser

A stable and selectable erbium-doped fiber (EDF) ring laser configuration with single-longitudinal-mode (SLM) output is proposed and demonstrated in this paper. In the proposed laser scheme, a proper cavity loss is utilized for significant suppression of the side mode. In the experiment, the different coupling ratios required to produce various cavity losses in the proposed fiber laser are analyzed. Here, to reach the wavelength selection, several fiber Bragg gratings (FBGs) and an optical tunable bandpass filter (OTBF) in the C-band range are employed for demonstration. In addition, the output performance with respect to stability and SLM in the proposed EDF ring laser are also investigated simultaneously.

Optical Vector Network Analyzer with an Improved Dynamic Range Based on a Polarization Multiplexing Electro-Optic Modulator**Supported by the National Natural Science Foundation of China under Grant Nos 61377070, 61090391 and 61675196, and the National High-Technology Research and Development Program of China under Grant No 2013AA014203.

We present a new method to achieve an optical vector network analyzer (OVNA) based on a polarization multiplexing electro-optic modulator (PM-EOM) without an optical bandpass filter. Optical single sideband (OSSB) modulated signals with a tunable optical carrier-sideband ratio (OCSR) are obtained at the output of the PM-EOM. The OCSR can be flexibly tuned by controlling bias voltages of the PM-EOM. The dynamic range of the OVNA is expanded by taking the improvement of the OCSR into account. The transmission response of an optical device under test (ODUT) is measured based on one-to-one mapping from optical domain to electrical domain. By optimizing the OCSR of the OSSB modulated signals, the dynamic range of the OVNA can be effectively improved with 3.7 dB. An analytical model is derived to describe the transfer function of the ODUT. The magnitude and phase responses of a fiber Bragg grating are characterized with a large dynamic range.

Complex optical interference filters with stress compensation for space applications

We present hereafter a study of complex bandpass optical interference filters with central wavelengths ranging in blue region or in the near infrared. For these applications, the required functions are particularly complex as they must present a very narrow bandwidth as well as a high level of rejection over a broad spectral range. Moreover, these components must have a good flatness meaning that the stress induced by the different layers has to be taken in account in the filter design. We present a thorough study of these filters including their design, fabrication using Plasma Assisted Reactive Magnetron Sputtering (PARMS) and characterization. Excellent agreement between experimental and theoretical spectral performances associated with a final sag of 326 and 13 nm, and uniformity from −0.05 to 0.10 and −0.10 to 0.20% are demonstrated for the two manufactured filters.

Non-Dispersive Infrared Sensor for Online Condition Monitoring of Gearbox Oil.

The condition of lubricating oil used in automotive and industrial gearboxes must be controlled in order to guarantee optimum performance and prevent damage to machinery parts. In normal practice, this is done by regular oil change intervals and routine laboratory analysis, both of which involve considerable operating costs. In this paper, we present a compact and robust optical sensor that can be installed in the lubrication circuit to provide quasi-continuous information about the condition of the oil. The measuring principle is based on non-dispersive infrared spectroscopy. The implemented sensor setup consists of an optical measurement cell, two thin-film infrared emitters, and two four-channel pyroelectric detectors equipped with optical bandpass filters. We present a method based on multivariate partial least squares regression to select appropriate optical bandpass filters for monitoring the oxidation, water content, and acid number of the oil. We perform a ray tracing analysis to analyze and correct the influence of the light path in the optical setup on the optical parameters of the bandpass filters. The measurement values acquired with the sensor for three different gearbox oil types show high correlation with laboratory reference data for the oxidation, water content, and acid number. The presented sensor can thus be a useful supplementary tool for the online condition monitoring of lubricants when integrated into a gearbox oil circuit.

Investigation of utilizing a VCSEL diode to work as a tunable optical bandpass filter

Tunable optical band-pass filter (TOBPF) composed of a vertical-cavity surface-emitting laser (VCSEL) is proposed for multi-wavelength optical fiber transport systems. Experimental results prove that through properly adjusting VCSEL driving current, one of multiple injected lightwaves can properly flow through the proposed optical filter and others will be attenuated roughly 12 dB. Furthermore, by changing the VCSEL driving current, the pass-band window of the VCSEL-based TOBPF can be shifted to align with different designated injected lightwave and to block the others. By employing the TOBPF in multi-wavelength optical fiber transport systems, proper eye diagrams are experimentally observed for each dedicated optical signal. The proposed scheme is shown to be a practical and flexible component for multi-wavelength optical fiber transport systems.

Color Stereo-Digital Image Correlation Method Using a Single 3CCD Color Camera

This paper presents a novel color stereo-digital image correlation (stereo-DIC) method using a single 3CCD color camera for full-field shape, motion, and deformation measurements without any sacrifice of the camera sensor spatial resolution. With the aid of a specially designed color separation device using a beam splitter and two optical bandpass filters, images of blue and red colors are simultaneously recorded by the 3CCD camera from two different optical paths. The blue and red channel sub-images extracted from the recorded color images can be analyzed using the regular stereo-DIC algorithm to obtain the full-field three dimensional (3D) information of a test object surface. The effectiveness and accuracy of the proposed technique are demonstrated by a series of real shape, in-plane and out-of-plane translation, and 3D deformation tests.

A paper-based multiplexed resonance energy transfer nucleic acid hybridization assay using a single form of upconversion nanoparticle as donor and three quantum dots as acceptors

Monodisperse aqueous upconverting nanoparticles (UCNPs) were covalently immobilized on aldehyde modified cellulose paper via reductive amination to evaluate the multiplexing capacity of luminescence resonance energy transfer (LRET) between UCNPs and quantum dots (QDs). This is the first account of a multiplexed bioassay strategy that demonstrates the principle of use of a single form of UCNP as donor and three different color emitting QDs as acceptors to concurrently determine three analytes. Broad absorbance profiles of green, orange and red QDs that spanned from the first exciton absorption peak to the UV region were in overlap with a blue emission band from UCNPs composed of NaYF4 that was doped with 30% Yb3+, 0.5% Tm3+, allowing for LRET that was stimulated using 980 nm near-infrared radiation. The characteristic narrow and well-defined emission peaks of UCNPs and QDs allowed for the collection of luminescence from each nanoparticle using a band-pass optical filter and an epi-fluorescence microscope. The LRET system was used for the concurrent detection of uidA, Stx1A and tetA gene fragments with selectivity even in serum samples, and reached limits of detection of 26 fmol, 56 fmol and 76 fmol, respectively.

Evaluation of a newly developed mid-infrared sensor for real-time monitoring of yeast fermentations

A mid-infrared (MIR) sensor using the attenuated total reflection (ATR) technique has been developed for real-time monitoring in biotechnology. The MIR-ATR sensor consists of an IR emitter as light source, a zinc selenide ATR prism as boundary to the process, and four thermopile detectors, each equipped with an optical bandpass filter. The suitability of the sensor for practical application was tested during aerobic batch-fermentations of Saccharomyces cerevisiae by simultaneous monitoring of glucose and ethanol. The performance of the sensor was compared to a commercial Fourier transform mid-infrared (FT-MIR) spectrometer by on-line measurements in a bypass loop. Sensor and spectrometer were calibrated by multiple linear regression (MLR) in order to link the measured absorbance in the transmission ranges of the four optical sensor channels to the analyte concentrations. For reference analysis, high-performance liquid chromatography (HPLC) was applied. Process monitoring using the sensor yielded in standard errors of prediction (SEP) of 6.15g/L and 1.36g/L for glucose and ethanol. In the case of the FT-MIR spectrometer the corresponding SEP values were 4.34g/L and 0.61g/L, respectively. The advantages of optical multi-channel mid-infrared sensors in comparison to FT-MIR spectrometer setups are the compactness, easy process implementation and lower price.

Study on 100-Gb/s reconfigurable all-optical logic gates using a single semiconductor optical amplifier.

We experimentally demonstrated all-optical NOR, OR and AND logic gates at 100 Gb/s with a single semiconductor optical amplifier (SOA) assisted by optical filtering. The logics can be conveniently reconfigured by deploying or not continuous wave (CW) light at the input of the SOA and adjusting the tunable optical band pass filter (OBPF) at SOA output. Correct logic functions and high quality of the output signals can be achieved as proved by clear eye opening and bit error rate (BER) measurement. Influences of optical filter parameters and the SOA device length on the logical performance are experimentally investigated.

Widely Tunable Photonic-Assisted Microwave Phase Shifter Based on Single Polarization Multiplexing Electro–Optic Modulator

We demonstrate an approach to achieve a widely tunable photonic-assisted microwave phase shifter (MPS) based on single polarization multiplexing electro-optic modulator (PM-EOM). The PM-EOM can generate orthogonally polarized and phase coherent optical signals. A phase shifted microwave signal is generated by combining the orthogonally polarized signals and generating the signal in a photodetector. A polarization controller (PC) continuously tunes phase of the recovered microwave signals and ensure its magnitude is constant. Through joint adjusting of the wavelength plates inside the PC before a polarizer, phase of the recovered microwave signal in a frequency range of 1–18 GHz can be fully tuned over 360°. Phase deviation is less than 1.5°. The corresponding magnitude almost remains unchanged. Magnitude deviation is less than 2 dB. Phase drift is less than 4° within 120 s. The motivation of this work lies in the fact that the previously reported MPSs using EOMs are hard to be realized with single modulator without special devices or an optical bandpass filter. The photonic-assisted MPS can be expanded into a phase shifter array with a help of a 1 × N optical coupler, which can be applied in optically controlled beamforming.

Preparation of Er2O3 and TiO2 Multilayer Films as Optical Filter Using Magnetron Sputtering Deposition

Dispersion relations of refractive indexes and extinction coefficients of constituent materials were obtained by comparing the experimental and simulated transmission spectra of single-layer Er2O3 and TiO2 films. We designed multilayer thin films of [Er2O3/TiO2]6/[Er2 O3]2/[TiO2/Er2O3]6 such that they can act as photonic crystals exhibiting a resonance wavelength of 514 nm. We prepared single-layer TiO2 and Er2O3 thin films on quartz glass substrates by employing a magnetron sputtering deposition method. Uniform films exhibiting very high transmittance values were obtained. Deposition rates of the TiO2 and Er2O3 films were 0.44 and 0.82 nm/s, respectively. [Er2O3/TiO2]6/[Er2 O3]2/[TiO2/Er2O3]6 multilayer films, to be used for optical bandpass filter applications, were also prepared using a multitarget sputtering deposition method. Uniform and transparent films were obtained; however, the wavelength corresponding to the highest transmittance was observed around 490 nm through ultraviolet-visible near-infrared spectroscopic measurements. The shift in the wavelength can be attributed to the low crystallinity and variations in the thicknesses of Er2O3 and TiO2 films.

Fiber ring laser for axial micro-strain measurement by employing few-mode concentric ring core fiber

Abstract We proposed and demonstrated a novel few-mode concentric-ring core fiber (FM-CRCF) for axial micro-strain measurement with fiber ring laser based on few-mode-singlemode-few-mode fiber structure. The core area of CRCF consists of four concentric rings which refractive indices are 1.448, 1.441, 1.450, 1.441, respectively. LP 01 and LP 11 are two dominated propagating mode groups contributing in the CRCF. In this few-mode-singlemode-few-mode structure, two sections of CRCF act as the mode generator and coupler, respectively. The basis of sensing is the center single mode fiber. Moreover, this structure can be used as an optical band-pass filter. By using fiber ring cavity laser, the axial micro-strain sensing system has high intensity (∼20 dB), high optical signal to noise ratio (∼45 dB) and narrow 3 dB bandwidth (∼0.1 nm). In the axial micro-strain range from 0 to 1467 μ e , the lasing peak wavelength shifts from 1561.05 nm to 1559.9 nm with the experimentally sensitivity of ∼ 0.81 pm / μ e .

Single-step fabrication of thin-film linear variable bandpass filters based on metal-insulator-metal geometry.

A single-step fabrication method is presented for ultra-thin, linearly variable optical bandpass filters (LVBFs) based on a metal-insulator-metal arrangement using modified evaporation deposition techniques. This alternate process methodology offers reduced complexity and cost in comparison to conventional techniques for fabricating LVBFs. We are able to achieve linear variation of insulator thickness across a sample, by adjusting the geometrical parameters of a typical physical vapor deposition process. We demonstrate LVBFs with spectral selectivity from 400 to 850nm based on Ag (25nm) and MgF2 (75-250nm). Maximum spectral transmittance is measured at ∼70% with a Q-factor of ∼20.

Phase-Shift Method-Based Optical VSB Modulation Using High-Pass Hilbert Transform

This report presents a novel method of generating an optical vestigial sideband (VSB) modulated signal without using optical bandpass filters. Using a modified Hilbert transformer based on digital signal processing, an optical VSB-modulated signal is generated using the phase-shift method. The proposed method is demonstrated experimentally for an optical binary phase-shift keying (BPSK) signal. The proposed method is wavelength-transparent compared to an optical bandpass filtering method, where the wavelength dependence of the optical bandpass filter limits applications. Furthermore, the optical bandwidth of the modulated signal is readily adjustable by changing the cutoff frequency of the high-pass Hilbert transformer. Fiber transmission characteristics of a single-channel optical BPSK-VSB signal are analyzed using a 100-km transmission link. Results of fiber transmission analysis show tolerance of the proposed modulation scheme to fiber nonlinearity-based signal distortions. For a 10 Gbit/s non-return-to zero(NRZ) sequence, a self-phase modulation threshold of 13 dBm is reported for the studied system.

Switchable Microwave Photonic Filter Between Low-Pass and High-Pass Responses

A novel and simple microwave photonic filter (MPF) is proposed and experimentally demonstrated. The MPF can be switched between low-pass and high-pass frequency responses. The MPF is realized by using an electro-optic phase modulator (EOPM) and two cascaded tunable optical bandpass filters (TOBFs). One TOBF (TOBF1) is used to change the modulation format of the phase modulated signal and, consequently, switch the MPF between low-pass and high-pass frequency responses. The other TOBF (TOBF2) is used to adjust the cutoff frequencies of the low-pass and the high-pass frequency responses. In the experiment, a switchable MPF from 0 to 40 GHz is demonstrated. By changing the center wavelength of TOBF2, the cutoff frequencies of the low-pass and the high-pass frequencies are continuously changed from 2.9 to 20.1 GHz and from 15.4 to 31.2 GHz, respectively.

A single-frame full spatiotemporal field distribution measurement method

In this paper, based on the spatially and temporally resolved intensity and phase evaluation device: full information from a single hologram (STRIPED FISH), an improved single-frame full spatiotemporal field distribution measurement method is proposed. In our scheme, between diffractive optical element (DOE) and band-pass filter (BPF), and between BPF and the CCD camera, digital micromirror devices (DMD) are introduced to perfect the setup. Compared with the STRIPED FISH, our improved scheme can simultaneously improve the frame rate and maximize the utilization efficiency of the SBP of CCD. And simulation is carried out to demonstrate the process of the implementation, which confirmed the feasibility of the proposal.

On the potential of Wireless Sensor Networks for the in-situ assessment of crop leaf area index

A precise and continuous in-situ monitoring of bio-physical crop parameters is crucial for the efficiency and sustainability in modern agriculture. The leaf area index (LAI) is an important key parameter allowing to derive vital crop information. As it serves as a valuable indicator for yield-limiting processes, it contributes to situational awareness ranging from agricultural optimization to global economy. This paper presents a feasible, robust, and low-cost modification of commercial off-the-shelf photosynthetically active radiation (PAR) sensors, which significantly enhances the potential of Wireless Sensor Network (WSN) technology for non-destructive in-situ LAI assessment. In order to minimize environmental influences such as direct solar radiation and scattering effects, we upgrade such a sensor with a specific diffuser combined with an appropriate optical band-pass filter. We propose an implementation of a distributed WSN application based on a simplified model of light transmittance through the canopy and validate our approach in various field campaigns exemplarily conducted in maize cultivars. Since a ground truth LAI is very difficult to obtain, we use the LAI-2200, one of the most widely established standard instruments, as a reference. We evaluate the accuracy of LAI estimates derived from the analysis of PAR sensor data and the robustness of our sensor modification. As a result, an extensive comparative analysis emphasizes a strong linear correlation (r2=0.88, RMSE=0.28) between both approaches. Hence, the proposed WSN-based approach enables a promising alternative for a flexible and continuous LAI monitoring.

Colorless beat interference cancellation receiver for the orthogonally polarized SSB-OOFDM signal with reduced guard band.

In the paper, we have proposed a novel optical orthogonal frequency division multiplexing (OOFDM) link scheme with the colorless beat interference cancellation receiver (BICR) structure for the single-sideband OOFDM (SSB-OOFDM) signal with an orthogonally polarized optical carrier and sideband, which is generated by using a polarization modulator and an optical band-pass filter. The BICR, employing only a polarization beam splitter and a balanced photodiode pair, can colorlessly mitigate the signal-signal beat interference (SSBI) induced by the square-law detection in a photodiode and thus the spectral efficiency (SE) is improved by reducing the guard band (GB) between the optical carrier and OOFDM signal. A simulation link for the 40 Gbit/s 16-QAM SSB-OOFDM signal with a reduced GB is built to demonstrate the feasibility of our proposed scheme. The simulation results indicate that the link has a higher SE compared to the conventional intensity modulation and direction detection scheme and the BICR exhibits a better performance in suppressing SSBI according to the error vector magnitude and the constellation diagrams.

Principle and applications of semiconductor optical amplifiers-based turbo-switches

All-optical high-speed turbo-switches can effectively increase the switching speed using cascaded semiconductor optical amplifiers (SOAs). The overall recovery time or the bandwidth of turbo-switch was numerically analyzed with time-domain and frequency-domain SOA models. The turbo-switch was explored from the fundamental carrier dynamics in SOAs for the purpose of further increasing its operation speed. An integrated turbo-switch was also been proposed and demonstrated, where a phase adjustable Mach-Zehnder interferometer (MZI) was applied as an optical band-pass filter between SOAs. Wavelength conversion was first demonstrated at 84.8 Gbit/s using the integrated turbo-switch.