Within this background, the present work proposes the study of other kinds of narrow-bandpass filters that present some advantages over the classical Fabry–Perot multiple-cavity filters. Unfortunately, no further studies were published about these systems. Then Rusell and others in a patent proposed the application of quarter-wave systems, calling them conjugated filters for reasons that we explain below. It is worth mentioning that the knowledge of the existence of these modes is not new, since they were first mentioned by Turner and Baumeister, but they considered them more a nuisance than a potentially useful bandpass filter. Although Fabry–Perot filters are useful for solving many important design problems, these photonic-crystal–photonic-crystal bandpass filters deserve a detailed study to explore their properties and potential applications. When observed under reflectance or transmittance, surface modes appear as sharp troughs or peaks, respectively, that are similar to Fabry–Perot guided modes. These surface modes are waves that propagate along the surface of the photonic crystal with evanescent fields in the perpendicular direction away from the surface plane, constituting a mechanism for energy loss-via tunneling-of localized bulk excitations. When a photonic crystal is truncated, electromagnetic excitations can appear at the surface of the photonic crystal in contact with any other bulk medium, such as a dielectric, a metal, or even another photonic crystal.
![crystal filter design crystal filter design](https://www.w0qe.com/Projects/images/14-7MHzXtalData.png)
These systems, which constitute periodic arrays in one, two, and three dimensions of dielectric materials, present characteristic regions in the dispersion plane (frequency versus parallel component of the wave vector) that are called band structures, with bands where the light can propagate (the so-called bulk bands) and bands where light cannot propagate (bandgaps).Īlthough a photonic crystal represents an infinitely periodic system, in engineering applications they are finite or semi-infinite.
![crystal filter design crystal filter design](https://ieee-uffc.org/files/ieeeuffcorg/styles/large/public/2021-09/fig4.gif)
Photonic crystals have been an interesting field of intense research during the past years because of their potential to be applied in the development of all-optical circuits and their interesting properties.
#Crystal filter design series
To design bandpass filters that are similar in many respects to multiple-cavity Fabry–Perot filters, we also consider the coupling conditions for these surface modes for multiple photonic crystals placed in series to form a multiple-junction system. The properties of surface modes present in the junction of two different one-dimensional photonic crystals placed in series are studied to assess the possibility of applying them in the design of narrow-bandpass filters.
![crystal filter design crystal filter design](https://www.filtro.net/wp-content/uploads/2016/10/Service-Images_0000_Custom-Filter-Design-e1542732845523.jpg)
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