In the world today, the expansion of communicative devices and the growing need of the human community to establish a diverse, fast and low-cost communication on the one hand, and the speed and broadband of optical devices on the other, have led to the development of optical communication systems. Therefore, the design, simulation and fabrication of optical devices have been more and more respected by researchers in this field . At present, photonic crystals are one of the important goals of light and photonic electronics researchers. In recent years, these crystals have attracted great attention in many cases due to their use in electronics, telecommunications, and optical information processing . In these years, photonic crystals based on photonic crystals have been very much considered due to photonic crystal features such as low losses, very low bandwidth, flexibility in shape and dimensions, as well as suitability for integrated circuits in Nano scale dimensions [3, 4]. In general, crystals photons structures of dielectric materials, and given that the refractive index of one, two and three dimensions periodically with a period of about a wavelength of light varies, divided into three main groups, the next one, two-dimensional and three -dimensional. This variation in the refractive index results in the formation of a prohibition band in the band's structure of these structures, which is the most important feature of photonic crystals [5, 6]. The banned band in these structures has a large number of frequencies in which no electromagnetic wave can be embedded inside structure, so using this intrinsic property can be used to design optical filters. Indeed, optical photon crystals have been of great interest to researchers, in view of their unique properties (such as high transmittance, low losses, proper output, high quality, selectivity, and adjustability) compared to conventional filters [7, 8].
Photonic crystals are Nano scale materials, in which the periodic periodicity of dielectric constant creates a photonic band gap. This type of structure provides a method for controlling the photon or, in general, electromagnetic waves in a dielectric environment. A photon, with a particular wavelength, or specific energy, cannot be transmitted through crystal. This means that control of the passage of the photons, which is mainly provided by creating a defect in photonic crystals, is available to the designer. The defect in the photonic crystal is caused by the change in dielectric radius or sex, or the removal of the rod [9, 10]. Defects in photonic crystals may be used to create a waveform that can pass light through a given path as an optical channel. Also, it may be used to build micro cavities in order to concentrate photons . Basically there are three different types of wavelength filter: resonance type, numerical coupling type, and diffraction type. What has recently become more prominent is the study of high-speed high - speed transmissions and the preservation of light emission in photonic crystal structures. The cavities are designed in photonic crystals so that the frequency of resonance in the network is prohibited, which produces high-quality optical modules . The most flexible type of wavelength filter in photonic crystals is the resonance type filters. In a photonic crystal, a point defect can act as a small hole to exacerbate a particular wavelength. In order to target a resonant frequency, the defect size should be controlled accurate in the nanometer range . The optical data transmission space is optical fiber. In optical WDM systems, multiple optical waves combined with different wavelengths are sent as a set into an optical fiber, which will increase the capacity (number of channels) of the optical network. These channels have different central wavelengths, therefore, optical filters play a vital role in channel selection and the removal of remaining channels [14, 15]. Also, filters with a high-quality factor are used to prevent diffraction phenomena when transmitting information from optical fibers [16, 17].