Long-wavelength Cutoff Filter Research Articles

A Multipurpose and Highly-Compact Plasmonic Filter Based on Metal-Insulator-Metal Waveguides

A multipurpose and ultra-compact nanoplasmonic wavelength filter based on stub structure in a metal-insulator-metal (MIM) waveguide is suggested and numerically investigated. A novel approach of connecting two stepped-like apertures to both input and output ports is applied to form Fabry-Perot (FP) cavities, which enabled the structure to act as a dual band-pass filter at wavelengths 1310 nm and 1550 nm. It is shown that the variation in cavities’ length allows to realize a long-wavelength cutoff filter, and cutoff wavelength can be easily tuned by adjusting the length of the cavities. Furthermore, it is revealed that increasing the gap between the stepped-like apertures and the cavities provides a triple band-pass at telecom wavelengths, e.g., 1267.5 nm, 1414.19 nm, and 1644.7 nm. The tunable broadband high-pass wavelength filter is then achieved while the lengths of stepped-like apertures and stub resonators are set to be identical. Finally, a tunable nearly perfect absorber can be obtained by varying the width of stub resonators. Therefore, because of functionality, size, as well as efficiency the proposed plasmonic filter may greatly contribute to miniaturization of next generation of photonic integrated circuits (PICs), and find applications in on-chip integration and wavelength-division multiplexing (WDM) in optical communication systems.

High-Efficiency Nanoplasmonic Wavelength Filters Based on MIM Waveguides

Two ultra-compact nanoplasmonic wavelength filters based on stepped impedance low-pass prototype filter in metal-insulator-metal waveguides are suggested. The transmission and reflection efficiency of both high-pass wavelength and long-wavelength cutoff filter is more than 93%, respectively. Simulation results reveal that similar to the tunability of the structure's transmission spectrum by changing the thickness of the insulator medium, the variations of the width of steps' discontinuities in the high-pass device not only provide an effective method to adjust the transmission peak/cutoff wavelength position, but also give rise to the structure to realize a long-wavelength cutoff filter. On the contrary, modifying the value of aperture length in the proposed long-wavelength cutoff filter gives the capability to control the cutoff wavelength. Moreover, changing the insulator medium to silica converts the device as a dual band bandpass filter at the wavelengths of 1300 and 1550 nm with efficiency of more than 85.2% and 78.1%, respectively. Hence, because of their excellent performance, features, and optimized size, they may have applications in high density photonic integrated circuits.

Implementation of long-wavelength cut-off filters based on critical angle

Our first attempts at the fabrication of long-wavelength infrared cut-off filters with extended transmission and rejection regions that are based on the use of the critical angle, the dispersion of refractive indices, and on thin-film interference were not very successful. The design of the filter consisted of layers placed at the interface between two high-index prisms. Using the available deposition equipment, the layers produced were porous and very rough. The pores adsorbed water vapor, which resulted in absorption. The roughness made the process of optical contacting very difficult. In this paper we describe the adjustments in the design and deposition processes that allowed us to obtain filters with a better and more stable performance.

Design and manufacture of metal/dielectric long-wavelength cutoff filters

Thin films of high reflecting metal, such as Ag, have a high reflectance in the long-wavelength region. When they are combined with dielectric layers, it is possible, through thin film interference effects, to induce transmission in certain shorter wavelength regions. Thus, they are useful components for the design of long-wavelength cutoff filters with a broad rejection region. In this paper, metal/dielectric multilayer designs based on this principle are numerically investigated. Three designs with different cutoff wavelengths and with very broad transmission regions in the visible or near-IR spectral ranges are presented. An excellent rejection on the long-wavelength side extends beyond 20 μm. Experimental results for one of the designs produced in our magnetron sputtering system are given.

Modified multicomponent band pass optical reflection filters at oblique incidence

Reflection and transmission characteristics of a modified long-wavelength cutoff filter using a three-component system with an angular dependence are studied. In this case, a layer of high refractive index is sandwiched between edge layers of equivalent refractive index with the base structure [G(0.5AB0.5A)]N; then, an optimized structure of the form [(0.5AB0.5A)N−X (0.5AB0.5A)X (0.5AB0.5A)N−X] is taken and its spectral properties are studied. In the case of a short-wavelength three-component cutoff filter, a layer of low refractive index is sandwiched between two edge layers of high equivalent refractive index with a base structure [G(0.5BA0.5D)]N and its spectral characteristics are studied. Then, the structure is optimized [(0.5BA0.5B)N− X(0.5BA0.5B)X(0.5BA0.5B)N−tX] and spectral characteristics of this structure are also studied. Spectral properties of band pass optical reflection filters of the type [G(XY)A] whose components are the proposed long-wavelength cutoff [(0.5AB0.5B)N− X(0.5AB0.5A)X(0.5BA0.5B)N−X] and short-wavelength cutoff [(0.5BA0.5B)N−X(0.5BA0.5B)X(0.5BA0.5B)N−X] filter structures are studied with angular dependences. No increase in the bandwidth with the least oscillatory components at the edges can be precisely formed by known classes of a two-component system at normal incidence. It is shown that the use of reflection and transmission filters with oblique bands yields an ideal polarizer. Angular dependences of the filter and the transmission and reflection band shapes on the parameters of a high-reflectance multilayer coating, such as the thickness, refractive indices, and the number of layers, are analyzed in detail.

Long-wavelength cutoff filters of a new type

A method for the design of cutoff filters is proposed that is based on the use of light at nonnormal angles of incidence and on the use of coating materials with a large dispersion of the optical constants. The optical constants are presented of several films made from indium tin oxide--a material that satisfies this requirement. The filtering is due to absorption, critical angle effects, or both. The theory of this type of filter is described, and the calculated performance of two long-wavelength cutoff filters based on the use of indium tin oxide films is given. The angular performance and the producibility of one of these filters are examined. Some applications for these filters are considered, and the feasibility of producing similar filters for other spectral regions is discussed.