Dual-wavelength Filter Research Articles

Numerical analysis of a dual-wave band guided-mode resonance filter with embedded bilayer asymmetric metallic gratings

In this paper, a novel guided-mode resonances (GMRs) based embedded dual-wavelength filter, which had the bilayer gratings located at the two sides of dielectric substrate and arranged at asymmetric position, was investigated and studied theoretically. As compared to symmetric structures that usually provided single wavelength of transmission resonance, as one normal incidence was used for transverse magnetic polarized light, the designed asymmetric structure could generate two remarkable narrow band wavelengths of transmission resonance. The parameters to affect the resonance wavelengths and the transmission resonance Q value (Q = λ/Δλ) of two bands were the distance between the two metallic gratings, the relatively lateral positions of the upper and lower gratings, the number of structure period, the thicknesses of metallic gratings, and the thickness of dielectric film. By optimizing the designed parameters, a GMR device with two resonance wavelengths located at 1239 and 1302 nm showed relative optimal performance because they had high transmission depth (99.9% and 90%) and ultra-narrow transmission bandwidth (2.8 and 1.8 nm) at the two resonance wavelengths. The presented structure can offer a potential route towards dual-band narrow-band filters and refractive index sensors in the near infrared.

Dual-wavelengths filter operating at visible wavelength region using subwavelength grating on waveguide structure

A dual-wavelength filter was experimentally demonstrated using subwavelength grating (SWG)/waveguide structure. We designed the structural parameters of the SWG and the waveguide to find the reflection peaks in the visible wavelength region. To investigate the optical response of the designed SWG/waveguide structure, finite-difference time-domain (FDTD) numerical calculations were performed for electromagnetic field distribution. The dual reflection peaks from our proposed structure were predicted in visible wavelength regions by the FDTD calculation. The calculated electromagnetic field distribution also revealed that the reflection peaks were associated with resonances in the SWG and waveguides. We fabricated the SWG/waveguide with typical electron-beam lithography techniques, and two reflection peaks were observed at wavelengths of 486 nm and 590 nm with bandwidths of 45 nm and 58 nm, respectively. These experimental results indicate that dual-wavelength filters can be successfully realized without complex fabrication processes.

Prussian Blue-Viologen Inorganic–Organic Hybrid Blend for Improved Electrochromic Performance

Electrochromic performance of an inorganic–organic layered blend consisting of prussian blue and ethyl viologen has been studied in the form of a device designed to test its performance as well as identify the working mechanism. Initially the sky-blue colored device, consisting of prussian blue and ethyl viologen electrodes, switches reversibly between transparent and dark blue states on application of electrical bias of up to 1.5 V with appropriate polarity. Raman spectroscopic and electrochemical investigations along with control experiments very clearly suggest that reversible redox switching of the two species are responsible for the electrochromism in the device. The fabricated device shows a good optical modulation of more than 50% in dual wavelength region of 400 and 600 nm (blue and red), serving as dual wavelength filter, while maintaining its optical durability for more than 8400 s (1400 pulses) with high coloration efficiency. The inorganic–organic hybrid device comprised of prussian blue and e...

Light-controlled tunable terahertz filters based on photoresponsive liquid crystals

We theoretically propose and investigate a light-controllable narrow-band terahertz (THz) filter and a dual-wavelength filter employing a square lattice photonic crystal with point and line defects. The point defects filled the photoresponsive liquid crystal. The change of the refractive index of the liquid crystal mixture material caused by the linearly polarized ultraviolet (UV) light and visible light results in a shift of the resonant wavelength of the cavity in the filter. We calculate transmittance spectra for the proposed THz wave filters, which have a full width at half maximum of 10 GHz and a transmittance of 95% at the resonant frequencies. By changing the polarized directions of UV and visible light, the performance characteristics of the filters can be adjusted.

Tunable dual-wavelength filter and its group delay dispersion in domain-engineered lithium niobate

A tunable dual-wavelength filter is experimentally demonstrated in domain-engineered lithium niobate. Application of an electric field on the y-surfaces of the sample results in the optical axes rotating clockwise and anticlockwise, which makes selective polarization rotation. The quasi phase-matching wavelengths could be adjusted through suitable domain design. A unique dual valley spectrum is obtained in a periodically poled lithium niobate structure with a central defect if the sample is placed between two parallel polarizers. The expected bandwidth could be varied from ∼1 nm to ∼40 nm. Moreover, both the spectral response and group delay dispersion could be engineered.

MMI filters configuration for dual-wavelength generation in a ring cavity erbium-doped fibre laser

Dual wavelength laser generation has been of constant interest due to their applications in optical communications and teraheartz generation. A novel configuration for Dual-wavelength laser generation based on the use of a couple of multimode interference (MMI) filters is demonstrated in a ring cavity Erbium-doped fibre laser. The MMI filters consist of a segment of no-core fibre spliced between two SMF-28 single mode fibre segments. The MMI filters configured as a Mach-Zehnder interferometer, are used as transmission spectral filters for simultaneous generation of two laser wavelengths. An optical attenuator is used to adjust the intra-cavity losses for dual-wavelength laser generation. Laser emission at 1540.4 and 1554 nm for a wavelength separation of ~13.6 nm is obtained. The laser wavelengths output power stability variations with the applied pump power is also experimentally discussed. The use of MMI filters in the proposed dual-wavelength laser filter is experimentally demonstrated as a reliable device for dual-wavelength generation in fibre lasers.

Dual-wavelength filters based on two-dimensional photonic crystal degenerate modes with a ring dielectric rod inside the defect cavity.

A tunable dual-wavelength filter based on degenerate modes with a ring dielectric rod inside the single point defect cavity is proposed. The band structures and mode profiles are computed by the plane-wave expansion method. The normalized transmission spectra for this structure are investigated by using the two-dimensional finite-difference time-domain method. The two orthogonal output modes of the filter can be regarded as the combination of the original degenerate cavity modes and both excited due to the introduced perturbation rod. The influences of the perturbation rod on the localized modes, band separations, and the tuning ranges are all investigated and analyzed based on the perturbation theory. With the ring dielectric rod being introduced into the defect, a narrower wavelength bandwidth and a wider wavelength tuning range can be obtained, which are superior to that of the filter based on a cavity with a larger radius rod. Besides, the perturbation rod can also be used for splitting degenerate modes for multiwavelength filters. The proposed filter has a simple structure and may be potentially applied in various integrated circuits, such as multiwavelength filters.

Dual wavelength filtering properties and applications of the π-phase-shifted sampled fiber Bragg gratings

Multi-ð-phase-shifted fiber Bragg gratings and ð-phase-shifted sampled fiber Bragg gratings (SFBGs) with dual wavelength filtering properties are compared. Results show that both of these gratings have the dual wavelength reflective spectra. However, the side lobe of the reflective spectrum of ð-phase-shifted SFBGs is lower than that of multi-ð-phaseshifted gratings. By adjusting the duty cycle in the range of 0.66 0.80, the filtering properties of ð-phase-shifted SFBGs are optimized, and the side lobe suppression ratio (SLSR) is the lowest when the duty cycle is 0.75. The application of the ð-phase-shifted SFBGs in the dual-wavelength laser is also demonstrated.

Switchable dual-wavelength single-longitudinal-mode erbium-doped fiber laser using an inverse-Gaussian apodized fiber Bragg grating filter and a low-gain semiconductor optical amplifier

We present a stable and switchable dual-wavelength erbium-doped fiber laser. In the ring cavity, an inverse-Gaussian apodized fiber Bragg grating serves as an ultranarrow dual-wavelength passband filter, a semiconductor optical amplifier biased in the low-gain regime reduces the gain competition of the two wavelengths, and a feedback fiber loop acts as a mode filter to guarantee a stable single-longitudinal-mode operation. Two lasing lines with a wavelength separation of approximately 0.1 nm are obtained experimentally. A microwave signal at 12.51 GHz is demonstrated by beating the dual wavelengths at a photodetector.

Analysis of inverse-Gaussian apodized fiber Bragg grating

Inverse-Gaussian apodized fiber Bragg gratings (IGAFBGs) are numerically studied using the transfer matrix method and fabricated by the commonly used phase-mask scanning technique in a single-step scanning process. The IGAFBG can serve as a dual-wavelength passband filter, whose wavelength spacing can be continuously tuned by introducing a tunable chirp through applying a strain gradient in principle. Also, an IGAFBG with identical dual passbands having 0.144nm wavelength spacing is experimentally achieved. We also show that an IGAFBG can act as a multipassband filter with varied free spectral ranges (FSRs), and the largest FSR variation of this IGAFBG is nearly seven times more than that in a comparable FBG pair filter. An IGAFBG with varied FSRs of approximately 16.125, approximately 12.25, approximately 8.5, and approximately 6.375GHz is fabricated. This multipassband varying-FSR IGAFBG filter can find applications in step-tunable microwave generations.

相移光栅及取样光栅的双峰滤波特性

相移光栅及取样光栅的双峰滤波特性

Wavelength filtering characteristics of Šolc filter based on Ti:PPLN channel waveguide

We have analyzed the Solc filtering characteristics in a periodically poled Ti:LiNbO3 (Ti:PPLN) multimode waveguide. The single- and dual-wavelength filtering were achieved under the optimized guiding condition for the TEM(00)-like mode and two mode (TEM(00)- and TEM(01)-like mode), respectively. The full width at half-maximum of the filter was about 0.21 nm at both guiding conditions. We found that the origin of two peaks of the dual-wavelength Solc filter in the two-mode guiding condition is the different effective refractive index between the TEM(00)- and TEM(01)-like modes. The wavelength difference of two peaks is about 0.8 nm at room temperature.

A double immunofluorescent method for simultaneous analysis of progesterone-dependent changes in proliferation and the oestrogen receptor in endometrium of rhesus monkeys

A double immunofluorescent technique that permitted the nuclear localization of both the oestrogen receptor and the Ki-67 antigen (marker of cell proliferation) within the same tissue section was developed and used to determine the relationship between the oestrogen receptor and proliferation within the major zones of the primate endometrium. Endometrial tissue was obtained from ovariectomized rhesus monkeys in which the hormonal pattern of oestradiol and progesterone was simulated with Silastic implants containing each hormone. The oestrogen receptor was detected using the H222 rat monoclonal antibody and Texas Red conjugated streptavidin. Immunofluorescent staining of a mouse monoclonal antibody to the Ki-67 antigen was detected by an antibody to mouse IgG conjugated with fluorescein isothiocyanate. Primary antibodies were co-incubated with tissue sections followed by sequential detection of the oestrogen receptor and Ki-67. A dual wavelength filter was used to monitor simultaneously both immunofluorescent patterns. Application of this technique to study regulation of endometrial proliferation and oestrogen receptor content by progesterone showed that the endometrium exhibited two different responses to progesterone: luminal and glandular epithelia and stromal cells in the functionalis and zone III of the basalis showed coincident decreases of oestrogen receptor and proliferation, whereas the oestrogen receptor in glandular epithelia of zone IV (basalis) was not downregulated and there was an increase in proliferation.

Multiple channel operation of integrated acousto-optic tunable filter

Demonstrates an integrated bulk-wave acousto-optic tunable filter (1.0 nm FWHM) in a multiwavelength crosstalk measurement experiment. With 16 channels present, individual channel crosstalk was lower than -15 dB for both single-wavelength and dual-wavelength filtering. The RF drive power for 70% efficiency was 180 mW/wavelength. >

A high-performance dual-wavelength spectrophotoometer and fluorometer

In recent years it has become increasingly desirable to investigate the kinetic behavior of molecules in order to obtain information about their function. A relatively inexpensive high-performance dual-wavelength filter spectrophotometer and fluorometer is described employing both home-made and purchased parts. This system can be easily set up by any modestly equipped workshop.