Multichannel Optical Filters Research Articles

Dynamically tunable multiple plasmon-induced transparency effect based on monolayer graphene structure system with rectangular defect cavities

In this article, a dynamically tunable multiple plasmon-induced transparency (PIT) effect in monolayer graphene structure system with rectangular defect cavities is investigated both theoretically and numerically. Because the graphene of our structure exists in a continuous form, the Fermi level of the graphene can be dynamically tuned by simply applying a bias voltage. The expressions of the theoretical transmittance are correctly deduced, and the fitting theoretical results are very consistent with the numerical simulation data. When the Fermi level of the graphene is increased from 0.8 eV to 1.2 eV, the group index of the dual-PIT system is controlled between 383 and 766. Alternatively, the group index of the triple-PIT system is maintained between 445 and 812. Moreover, the maximum group index can reach 812 at 1.2 eV, which shows that it can be designed as an excellent slow light device. Therefore, the proposed structures and results may provide strong guidance towards multichannel optical filters, dynamically tunable and excellent slow light and light storage devices.

Simultaneous FLIM, harmonic generation and hyperspectral imaging using a 4-channel detector.

We describe a method that utilizes a PMT detector with an array of 4 independent channels allowing simultaneous acquisition of high-resolution Fluorescence Lifetime Imaging Microscopy (FLIM), Phasor-based Hyperspectral Imaging (HI), and Harmonic Generation images (HG). For FLIM acquisition our system is coupled with multichannel high digital frequency domain card which allows high photon counts per unit time and channel. HI is done based on sin/cos transmission optical filters placed in the emission path of a microscope to resolve the emission wavelength of every point in an image. The sin/cos filters used cover a broad spectral range and do not require collimated light, which makes this method very suitable for imaging in scattering media. The transmission geometry of our microscope provides a high efficiency in photon harvesting from scattering media than conventional detection methods used in commercial microscopes, making it ideal for HG imaging. The combined data acquired is analyzed using the Phasor Approach, a fit-free method that does not require previous knowledge of your sample. The linear combination property of the phasor approach allows us to study metabolic autofluorescence of live 3D cultures and skin tissues. The fast parallel data acquisition eliminates problems associated with changes in the sample during measurements, i.e., cell movement, spectral emission changes due to modifications in the environment, etc. Our proposed method combining a multichannel detector and optical filters is adaptable to any microscope with FLIM capabilities.

Electro-optic properties of one-dimensional (1D) nonlinear perfect photonic crystals based on Lithium tantalate layer

Electro-optic properties of one-dimensional (1D) nonlinear perfect photonic crystals (PCs) based on Lithium tantalate (LiTaO3) layer and air were studied. Using transfer matrix method, we found that the resonance transmission peak induced by weak defocusing Kerr nonlinearity can be tuned to any wavelength when the 1D structure is subject to external electric field. We demonstrated numerically that the intensity of this localized mode either increases or decreases depending on both the magnitude and the direction of the applied electric field. In addition, the wavelength varies linearly with the applied external electrical field and depends on the incidence angle. For a critical nonlinearity strength |αc|, the single resonance peak splits into two resonances as the magnitude of the external electric field is increased. Moreover, the number of transmission resonance peaks with narrow FWHM, high Q factor and total transmission can be enhanced by increasing the intensity of the applied electric field. Results presented in the current study promote the application of our one-dimensional (1D) nonlinear perfect photonic crystal for electrically tunable narrow-band transmission multi-channel optical filters and some other optoelectronic applications.

Tunable multi-channel optical filters based on Octonacci one-dimensional photonic quasicrystals

We propose a structure for a tunable multi-channel optical filter based on a one-dimensional quasicrystal made up of ZnSe (layer H) and ZnS (layer L) layers organized following the Octonacci sequence. The fourth stage of the sequence, S4, is considered here with initial conditions S1 = L and S2 = H giving the multi-layered system a structure of HLHHHLH. The transmittance spectrum of the s-polarized (transverse electric mode) light is obtained analytically by employing a theoretical calculation based on the transfer matrix method. For normally incident waves, four output signals are transmitted out from the structure. The transmitted signals move to shorter wavelengths as the angle of incidence increases up to 89 deg. At this angle of incidence, the output signals exhibit narrow, sharp, and well-defined resonant peaks. On the other hand, the resonant peaks shift to longer wavelengths as the ambient temperature increases from room temperature to 500°C. The obtained results reveal that the proposed structure could be used as an efficient multi-channel optical filter. The overall dimension of the proposed structure is about 569 nm, which practically makes the filter easily integrated into photonic circuits.

Design of narrow band multi-channel optical filters using zero index medium

We propose a design of narrow-band multi-channel optical filter using multiple stacks of unit cell consisting of trilayer of Doubly positive medium (DPS)–Doubly negative medium (DNG)–Epsilon negative medium (ENG). Finite Difference Time Domain (FDTD) technique is used to numerically simulate the effect of optical thickness of DPS, DNG and ENG media on tunability of the transmission spectrum of such a medium. We also demonstrate the control on the number of channels at different frequencies that can be transmitted through such medium.

Multiple omnidirectional defect modes and nonlinear magnetic-field effects in metamaterial photonic superlattices with a polaritonic defect

We report the existence of multiple omnidirectional defect modes in the zero-n¯ gap of photonic stacks, made of alternate layers of conventional dielectric and double-negative metamaterial, with a polaritonic defect layer. In the case of nonlinear magnetic metamaterials, the optical bistability phenomenon leads to switching from negligible to perfect transmission around these defect modes. We hope these findings have potential applications in the design and development of multichannel optical filters, power limiters, optical-diodes and optical-transistors.

Synchronous Tuning of Twined Resonance Modes with Controllable Spectral Separation in Plasmonic Gratings

We investigated angle-resolved tuning performance of the double resonance modes of waveguide metallic grating structures, where the incident angle was changed in the plane formed by the extending direction of the grating lines and the wave vector with the grating plane tilted with respect to the vertical axis. Double resonance modes were observed due to tilting of the grating, which were tuned simultaneously to the blue with increasing the angle of incidence. The spectral separation between the resonance modes can be adjusted simply by changing the tilting angle of the grating. Such a double resonance device is important for exploring multichannel optical filters, optical switching device, or sensors.

Multichannel optical filters with an ultranarrow bandwidth based on sampled Brillouin dynamic gratings

We first propose a multichannel optical filter with an ultra-narrow 3-dB bandwidth based on sampled Brillouin dynamic gratings (SBDGs). The multichannel optical filter is generated when an optical pulse interfaces with an optical pulse train based on an ordinary stimulated Brillouin scattering (SBS) process in a birefringent optical fiber. Multichannel optical filter based on SBDG is generated with a 3-dB bandwidth from 12.5 MHz to 1 GHz. In addition, a linearly chirped SBDG is proposed to generate multichannel dispersion compensator with a 3-dB bandwidth of 300 MHz and an extremely high dispersion value of 432 ns/nm. The proposed multichannel optical filters have important potential applications in the optical filtering, multichannel dispersion compensation and optical signal processing.

Coupled atomic coherences induced by a standing wave

Atomic coherence effects with a strong standing-wave coupling field on a four-level system of hot Rb atoms are investigated. Amplitude modulation and phase modulation of the strong standing-wave field are coherently coupled in linear and nonlinear atomic polarizations in various multi-wave mixing processes. Such coupled atomic coherence effect leads to one-photon triple-bandpass filters in an electromagnetically induced transparency structure and two-photon bandgaps at two different wavelengths under two-photon resonance in the hot four-level Rb atoms. Such system can be useful for dispersion compensation in multi-channel WDM systems, all-optical switching and optical filters at multiple wavelengths.

Multichannel bandpass filters utilizing multilayer photonic crystal

We demonstrate multichannel optical bandpass filters utilizing alternating dielectric multilayers stacked on a patterned substrate. A microstructured Si/SiO(2) multilayer was formed by rf biased magnetron sputtering process on a fused silica substrate with surface gratings. The bandwidths of each filter channel were measured to be 50~175 nm in the near infrared region. Control of center wavelength and bandwidth by the grating pitch was verified.

Multichannel optical filters using birefringent planar optical platforms

Multichannel optical filters are proposed for wavelength-division multiplexing communication systems. The proposed filters utilize the multireflection property of optical beams, have stable wavelengths, and can select arbitrary channels with arbitrary transmittance. We show seven-channel filter module with 1-nm channel spacing as a feasibility study.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>