Spectrum Filtering Research Articles

Rectangular optical filter based on high-order silicon microring resonators

The rectangular optical filter is one of the most important optical switching components in the dense wavelength division multiplexing (DWDM) fiber-optic communication system and the intelligent optical network. The integrated highorder silicon microring resonator (MRR) is one of the best candidates to achieve rectangular filtering spectrum response. In general, the spectrum response rectangular degree of the single MRR is very low, so it cannot be used in the DWDM system. Using the high-order MRRs, the bandwidth of flat-top pass band, the out-of-band rejection degree and the roll-off coefficient of the edge will be improved obviously. In this paper, a rectangular optical filter based on highorder MRRs with uniform couplers is presented and demonstrated. Using 15 coupled race-track MRRs with 10 μm in radius, the 3 dB flat-top pass band of 2 nm, the out-of-band rejection ratio of 30 dB and the rising and falling edges of 48 dB/nm can be realized successfully.

A Modeling Investigation on High-Speed Broad Spectrum Filtering System Based on Electric Fluid Technology

By combining advanced fluid control technology with surface plasmonic resonance phenomenon, we could take advantage of various unique characteristics of plasmonics without changing the original structure to realize a tunable color filtering system. By modifying the wetting properties of solid surface with an electric field, electro-fluid control technology could tune the curvature of two-phase fluid interface continuously and, therefore, change the distributions of silver nanoparticles on the interface accordingly. Based on this fluidic optical design, we investigated the influencing factors of color filtering performance by modeling, finally got an optimized design to achieve broad spectrum filtering system. As the color filtering function is realized simply and rapidly by charging, and therefore, this design could improve the efficiency of the electro-optical systems and is a promising idea for many applications, such as the dynamic display devices.

Experimental investigation of solar photovoltaic thermal system using water, coconut oil and silicone oil as spectrum filters

In the current study, the performance of a photovoltaic thermal system with easily available and less expensive liquids as spectrum filters is analyzed. The absorption and transmission spectrum of different liquids is investigated using a UV–VIS–NIR spectrophotometer for the wavelength range of 200–2500 nm (terrestrial solar spectrum). Among all the selected liquids; tap water, silicone oil and coconut oil were found transparent to the response range of C-Si solar cell and shows absorption in UV and IR region. In the current work, the electrical performance of the solar cell with these liquids as spectrum filters is analyzed using a solar simulator at 1 Sun, AM 1.5 G. The simulator experiment shows the improvement in the electrical performance of the solar cell. To investigate the performance of the system under natural sunlight, the experiments were performed on a 10 W C-Si PV module, with 1 cm thick liquid spectrum filter in the month of April. In these experiments, an average electrical efficiency of 12.53% and average thermal efficiency of 47% was recorded. The detailed experimentation, findings and scope for further research are discussed in this article.

Diamonds X-ray luminescent separation efficiency increase through spectrum filtering

Diamonds X-ray luminescent separation efficiency increase through spectrum filtering

Design of an Active Tunable Bandpass Filter for Spectrum Sensing Application in the TVWS Band

In this paper, we propose an active tunable bandpass filter (BPF) for efficient spectrum sensing in the TV White Space (TVWS) band. By designing a narrow bandwidth, it is possible to improve the sensing probability. The basic circuit configuration involves switching the PIN diode compromising capacitor bank to change the capacitance of the LC resonant circuit. To cover the whole TVWS band effectively, we add a varactor diode, and the bandwidth is set to 25-MHz. We improve the insertion loss by using the active capacitance circuit. The tunable BPF in the TVWS band with a 20-MHz interval is designed to have 11 channels with a bandwidth of 25 MHz and a low insertion loss of 1.7-2.0 dB.

Self-starting passively mode-locked all fiber laser based on carbon nanotubes with radially polarized emission

We demonstrate an all fiber passively mode-locked laser emitting a radially polarized beam by using a few-mode fiber Bragg grating to achieve mode selection and spectrum filtering. An offset splicing of single-mode fiber with four-mode fiber is utilized as a mode coupler in the laser cavity. Carbon nanotubes are introduced into the laser cavity as the saturable absorber to achieve self-start mode locking. The laser operates at 1547.5 nm with a narrow spectrum width of 0.3 nm at 30 dB. The emitted mode-locked pulses have a duration of 22.73 ps and repetition of 10.61 MHz. A radially polarized beam has been obtained with high mode purity by adjusting the polarization in the laser cavity.

Investigations of Different Liquid Based Spectrum Beam Splitters for Combined Solar Photovoltaic Thermal Systems

In the spectrum beam split approach of combined solar photovoltaic thermal system (PVT), the complete solar spectrum is splitted. The unwanted part of the solar spectrum for photovoltaic (PV) applications is filtered out and is used separately as heat. In this work, some inexpensive, clear, and easily available selective fluids are identified which can be used as both volumetric heat absorbers and selective spectrum filters for C-Si-based PVT. The electrical performance of a C-Si solar PV cell using these fluid-based filters is analyzed using a solar simulator at 1 Sun, AM 1.5 G. To check the volumetric heat absorbing potential, the required thermophysical properties of these selected fluids are estimated using a solar radiation pyranometer and standard experiments. The study concludes that water, coconut oil, and hydrotreated silicone transformer oil are some of the potential beam splitters and heat absorbers suitable for C-Si based spectrum beam split PVT applications.

Narrow-band imaging: Breakthrough at the forefront of medicine

The most common head and neck malignancy is squamous cell carcinoma. The result of surgical and oncological treatment of large tumors leads to a significant mutilation of the affected individual. Early detection of tumors is, therefore, one of the most important factors of treatment success. Efforts to achieve the earliest detection of malignant disease have led to the development of new endoscopic examination methods such as autofluorescence, contact endoscopy, and optical coherence tomography. In the last few years, narrow-band imaging (NBI) method has been introduced. Superficial mucosal lesions that would be missed by regular white light endoscopy can be identified, in view of their neoangiogenetic pattern of vasculature, using the NBI in head and neck mucosa. NBI is an optical technique that applies narrow-band spectrum filters to enhance the visualization of mucosal and submucosal microvascular patterns, based on the principle of the different penetration depth of light according to its wavelength. It requires no special dyes and allows for easy inspection of the superficial vascular bed. This studywill be discussing NBI, highlighting its application in early detection of head and neck cancer, thus helping in giving a better prognosis.

Electro-optically spectrum tailorable intracavity optical parametric oscillator.

We report a unique, pulsed intracavity optical parametric oscillator (IOPO) whose output spectrum is electro-optically (EO) tailorable based on an aperiodically poled lithium niobate (APPLN) working simultaneously as an optical parametric gain medium and an active gain spectrum filter in the system. We have successfully obtained from the IOPO the emission of single to multiple narrow-line signal spectral peaks in a near-infrared (1531 nm) band simply by electro-optic control. The power spectral density of the EO tailored signal can be enhanced by up to 10 times over the original (nontailored) signal.

A Soft Spectrum Filter to Improve the Dosimetric and Biologic Aspects of Flattening Filter Free TrueBeam

Design a Soft-Spectrum-Filter (SPECTER) and improve the dosimetric and biologic aspects of Flattening-Filter-Free TrueBeam by reducing the dose to organ-at-risk (OAR) while keeping the high dose rate. In the first part, clinical comparison was made to investigate the dosimetric and biological differences between the flattened beam and the FFF beam. In the second part, a new filter was designed based on the Monte-Carlo (MC) simulation. Varian TrueBeam system was commissioned on the Eclipse. Photon beams of 6 MV and 10 MV were studied to plan fourteen clinical cases. Static intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) were compared. A Matlab code was used to calculate the dose-volume-histogram (DVH), biological effective dose (BED), and equivalent uniform dose (EUD) based on the DICOM files exported from Eclipse. Based on Gay and Niemierko's model, tumor control probability (TCP) and normal tissue complication probability (NTCP) were calculated. For the MC simulation, IAEA phase space data generated by the VirtuaLinac system was used to simulate the beam spectrum of the TrueBeam system. BEAMnrc and DOSXYZnrc were used to model the SPECTER and calculate the dose. Simulation results were benchmarked with the clinical measurement data. SPECTER was designed using the EGSnrc coding system. Comparative target coverage was obtained from the FFF beam as the flattened beam. For OARs with high radiation sensitivity and low dose (e.g. lens of the eye), the FFF beam had up to 38% reduction in mean dose and 34% reduction in maximum dose compared with the flattened beam, leading to 85% reduction in the NTCP value. For OARs which were closer to the radiation field and received higher dose (e.g. brainstem), the FFF beam had up to 14% mean dose reduction, 10% maximum dose reduction and 55% reduction in the NTCP value. For the MC simulation, lead SPECTER with circular cross section provided the best dose attenuation in the out-of-field region. Compared with FFF beam, the SPECTER beam provided 3% reduction for the total dose and 2.5% reduction for the internal scatter dose for 25x25 cm2 field size in the water tank at d = 10 cm depth. FFF beam could provide similar target coverage as the flattened beam in all 14 clinical cases. Significant dose sparing effect of the FFF beam was observed for the head and neck cases with relative large treatment field (e.g. 16x20 cm2). Due to the speed limitation of the MLC, the maximum dose rate of the FFF beam may not always be achievable for large treatment field size (e.g. 20x20 cm2).A new filter is proposed to further reduce the dose in the tail region of the FFF beam in order to improve the dose sparing effect of the FFF beam. The geometry of the SPECTER enables us to keep the high dose rate of the FFF beam.

Power scaling of narrowband high-power all-fiber superfluorescent fiber source to 1.87 kW.

We demonstrate a high-power narrowband all-fiber superfluorescent fiber source employing three-stages master oscillator power-amplifier chain. Narrowband seed light is selected from a broadband-amplified spontaneous-emission source by a spectrum filter combing with fiber circulator and fiber Bragg grating. In the main amplifier, the maximal output power is 1.87 kW with an optical-to-optical conversion efficiency of 77.4% and a full width at half-maximum (FWHM) linewidth of 1.7 nm. The corresponding power fluctuation is ±1.4% in 100 s operation, and no parasitic oscillation or self pulsation is observed. A beam quality of M(2)=1.71 is measured at 1.4 kW output power. This manuscript investigates the spectral evolution in high-power amplification. The central wavelength shifted from 1079.5 nm to 1080.7 nm, and the FWHM linewidth narrowed from 2 nm to 1.7 nm at full power, respectively. These effects could be inferred as hybrid effects of many factors, such as wavelength shifting of pump LD, nonoptimized length of gain fiber, and enhancement of temperature level of gain fiber. The narrowband-maintained characteristic in spectral domain under high-power amplification is significant for applications such as spectral beam combination, and further power scaling is available as the output power is only limited by the pump power.

SU-F-207-01: Comparison of Beam Characteristics and Organ Dose From Four Commercial Multidetector Computed Tomography Scanners

Purpose: To compare dosimetric properties and patient organ doses from four commercial multidetector CT (MDCT) using Monte Carlo (MC) simulation based on the absorbed dose measured using a Farmer chamber and cylindrical water phantoms according to AAPM TG-111. Methods: Four commercial MDCT were modeled using the GMctdospp (IMPS, Germany) based on the EGSnrc user code. The incident photon spectrum and bowtie filter for MC simulations were determined so that calculated values of aluminum half-value layer (Al-HVL) and off-center ratio (OCR) profile in air agreed with measured values. The MC dose was calibrated from absorbed dose measurements using a Farmer chamber and cylindrical water phantoms. The dose distributions of head, chest, and abdominal scan were calculated using patient CT images and mean organ doses were evaluated from dose volume histograms. Results: The HVLs at 120 kVp of Brilliance, LightSpeed, Aquilion, and SOMATOM were 9.1, 7.5, 7.2, and 8.7 mm, respectively. The calculated Al-HVLs agreed with measurements within 0.3%. The calculated and measured OCR profiles agreed within 5%. For adult head scans, mean doses for eye lens from Brilliance, LightSpeed, Aquilion, and SOMATOM were 21.7, 38.5, 47.2 and 28.4 mGy, respectively. For chest scans, mean doses for lung from Brilliance, LightSpeed, Aquilion, and SOMATOM were 21.1, 26.1, 35.3 and 24.0 mGy, respectively. For adult abdominal scans, the mean doses for liver from Brilliance, LightSpeed, Aquilion, and SOMATOM were 16.5, 21.3, 22.7, and 18.0 mGy, respectively. The absorbed doses increased with decreasing Al-HVL. The organ doses from Aquilion were two greater than those from Brilliance in head scan. Conclusion: MC dose distributions based on absorbed dose measurement in cylindrical water phantom are useful to evaluate individual patient organ doses.

LED Based Spectrophotometer can compete with conventional one

Spectrophotometers are the common devise used for blood analysis. These analyses are simply optioned from the transmittance of monochromatic light through a blood sample. It disperses their light sources by different techniques; the simplest one is the use of interference filters in front of broad-band light source. As Interference bandpass filters are relatively inexpensive wavelength selectors. Interference filters that allow transmission of a predetermined wavelength while rejecting or blocking other wavelengths are widely used in instrumentation for clinical chemistry. On the other hand, the lights emitting diodes (LEDs) emits a specified band and have a wide selection options. An economic device based on LEDs (LED based spectrometer) is explained in this work. Instead of the wide spectrum light source and filters (commercial spectrophotometer), The LED based spectrophotometer is calibrated with standard solutions, and its measurement results is compared with the Mindray BS-200 Chemistry Analyzer (commercial spectrophotometer). The comparison shows acceptable results between both spectrophotometers with maximum error 2.33%. The errors can be reduced by applying more fining alignment. Another benefit of the new designee is to minimize testing costs.

One watt gallium arsenide class‐E power amplifier with a thin‐film bulk acoustic resonator filter embedded in the output network

Integration of a class-E power amplifier (PA) and a thin-film bulk acoustic wave resonator (FBAR) filter is shown to provide high power added efficiency in addition to superior out-of-band spectrum suppression. A discrete gallium arsenide pseudomorphic high-electron-mobility transistor is implemented to operate as a class-E amplifier from 2496 to 2690 MHz. The ACPF7041 compact bandpass FBAR filter is incorporated to replace the resonant LC tank in a traditional class-E PA. To reduce drain voltage stress, the supply choke is replaced by a finite inductance. The fabricated PA provides up to 1 W of output power with a peak power added efficiency (PAE) of 58%. The improved out-of-band spectrum filtering is compared to a traditional class-E with discrete LC resonant filtering. Such PAs can be combined with linearisation techniques to reduce out-of-band emissions.

Evaluation of organ doses in adult and paediatric CT examinations based on Monte Carlo simulations and in-phantom dosimetry.

The aim of this study was to validate the computed tomography dose index (CTDI) and organ doses evaluated by Monte Carlo simulations through comparisons with doses evaluated by in-phantom dosimetry. Organ doses were measured with radio-photoluminescence glass dosemeter (RGD) set at various organ positions within adult and 1-y-old anthropomorphic phantoms. For the dose simulations, the X-ray spectrum and bow-tie filter shape of a CT scanner were estimated and 3D voxelised data of the CTDI and anthropomorphic phantoms from the acquired CT images were derived. Organ dose simulations and measurements were performed with chest and abdomen-pelvis CT examination scan parameters. Relative differences between the simulated and measured doses were within 5 % for the volume CTDI and 13 % for organ doses for organs within the scan range in adult and paediatric CT examinations. The simulation results were considered to be in good agreement with the measured doses.

Noise Robust Speech Parameterization using Relative Spectra and Auditory Filterbank

In the present study, a new feature extraction method based on relative spectra and gammachirp auditory filterbank is proposed for robust noisy speech recognition. The relative spectra filtering are applied to the log of the output of the gammachirp filterbank which incorporates the properties of the cochlear filter in order to remove uncorrelated additive noise components. The performances of this method have been evaluated on the isolated speech word corrupted by real-world noisy environments using the continuous Gausian-Mixture density Hidden Markov Model. The evaluation of the experimental results shows that the proposed method achieves best recognition rates compared to the conventional techniques like Perceptual Linear Prediction (PLP), Linear Predictive Cepstral Coefficients (LPCC) and Mel-Frequency Cepstral Coefficients (MFCC).

Achieving angle-insensitive spectrum filter with the slit nanoresonator array structure

The spectrum filtering behavior of the slit nanoresonator array structure is based on the coupling between the slit resonance and the Wood’s anomaly of grating array, and therefore has angle dependence, which is not desirable for some applications. To achieve an angle-insensitive spectrum filter, such a coupling should be disrupted. We show that reducing the period of the slit array helps decouple these two resonances. Additionally, by enhancing the light confinement inside the slits through either shrinking the slit width or filling the slits with a high-index medium, a narrow transmission peak is maintained at a small period so that an angle-insensitive spectrum filter is achieved.

Generation of broadband laser by high-frequency bulk phase modulator with multipass configuration.

A new technique is presented for obtaining a large broadband nanosecond-laser pulse. This technique is based on multipass phase modulation of a single-frequency nanosecond-laser pulse from the integrated front-end source, and it is able to shape the temporal profile of the pulse arbitrarily, making this approach attractive for high-energy-density physical experiments in current laser fusion facilities. Two kinds of cavity configuration for multipass modulation are proposed, and the performances of both of them are discussed theoretically in detail for the first time to our knowledge. Simulation results show that the bandwidth of the generated laser pulse by this approach can achieve more than 100nm in principle if adjustment accuracy of the time interval between contiguous passes is controlled within 0.1% of a microwave period. In our preliminary experiment, a 2ns laser pulse with 1.35-nm bandwidth in 1053nm is produced via this technique, which agrees well with the theoretical result. Owing to an all-solid-state structure, the energy of the pulse achieves 25μJ. In the future, with energy compensation and spectrum filtering, this technique is expected to generate a nanosecond-laser pulse of 3nm or above bandwidth with energy of about 100μJ.

Out-of-Band Ambiguity Analysis of Nonuniformly Sampled SAR Signals

High-resolution and wide-swath synthetic aperture radar (SAR) images can be obtained by multichannel sampling. However, a nonoptimum pulse-repetition frequency is associated with a nonuniform spatial sampling in azimuth. A spectrum reconstruction algorithm and a filter group algorithm can be used to reconstruct the spectrum in azimuth with a nonuniform sampling. In this letter, a comparison of spectrum reconstruction algorithm and filter group algorithm is given. Through a transformation matrix, the relationship between out-of-band signals and the out-of-band signals after reconstruction is built. Furthermore, an equivalent spectrum after reconstruction is obtained, and simulation results proved that it is precise. From the equivalent spectrum, it shows that multichannel SAR can be seen as uniform sampling system but with a different original signal. Finally, channel imbalance is discussed. Simulation results have proved that the imbalance targets have the same location with corresponding ambiguous targets.

인지 무선 시스템에서 스펙트럼 센싱을 위한 이항 필터

본 논문에서는 인지 무선통신에서 스펙트럼 센싱을 위해 사용할 수 있는 세 가지 형태의 이항 필터를 제안하였다. 세 가지 필터는 이항 필터 및 부적 이항필터, 복합 이항 필터이며 이들 전달함수의 주파수 응답을 각각 분석하였으며 필터에 요구되는 감쇠를 위해 필요한 단계 수를 도출하였다. 또한 각 필터에 대해 요구되는 감쇠에 필요한 단계수를 성능으로 하여 분석한 결과 부적 이항 필터 및 복합 이항 필터가 기본 이항 필터에 비해 성능이 더 우수한 것으로 나타났다. 제안된 세 가지 필터는 통합된 직렬 구조를 가지고 있고 곱셈기가 필요 없어 구현에 용이하므로 광범위한 응용이 가능하다. In this paper, we proposed three types of binomial filter for spectrum sensing in cognitive radio system. Three filters are binomial, negative binomial and composite binomial filters and the frequency responses of their transfer functions are analyzed and the numbers of stages to meet the required attenuation are driven. As a result of performance analysis in terms of the number of stages, negative and composite binomial filters are superior to the binomial filter. Since the proposed three filters have a unified cascaded structure and are easy to be implemented without any multiplier, it is expected that they will have wide applications.