Figure 1. Optical Add-Drop Multiplexer, using a Fiber Bragg Grating and Two Circulators [13]
The need for higher communication medium is endless as the newer technologies have been came so far, and there is always a search for a more efficient and promising scheme as compared to the present system. The current communication system is the most modern mode of communication. Today, most of the transmission takes place in 1550 nm window. So, the purpose of this paper is to present the simulation of Wavelength Division De-Multiplexing using a Photonic Crystal four-Channel Drop filter, and design it for multi channel Add-Drop filter with Wavelength Division Multiplexing and De-multiplexing, as it can provide the result in 1530 nm to 1570 nm window, which is quite ideal for present optical communication system. A crystal is a periodic arrangement of atoms and molecules and the pattern which the atoms and molecules are repeated in space is the crystal lattice. In the PhC, the atoms or molecules are replaced by macroscopic media with differing dielectric constants and the periodic potential is replaced by a periodic dielectric function. The Wavelength Division Multiplexing (WDM) is considered to be a propitious scheme for high capacity optical interconnects and communications.
Currently, Optical communication is one of the best solutions used in data transmission across very large distances while keeping high bit rates. In order to have full advantage of optical communication networks, an optical network is needed, which is composed of full optical devices such as optical filters, optical de-multiplexers, optical switches, etc.
Optical filters are essential and crucial passive components for modern optical communication systems. Micro waveguide and fiber based ring resonator are also good due to their versatile functionalities and compactness. They can be designed for different applications.
Extremely compact Photonic Crystal (PhC) based bandpass filter are attractive for their strong potential for large scale integration in Wavelength Division Multiplexing (WDM) communication networks. Many theoretical and experimental works have reported very promising results in particular with the realization of 4 channels-WDM Optical Add-Drop Multiplexer (OADM), demonstrating its technology readiness level [4]. Photonic Crystals (PCs), which can confine light in small regions, are very suitable candidates for photonic integration. Such structures offer the versatile platform for realizing a variety of different devices. Band-stop filters, band pass filters, channel drop filters and add drop filters are some reported examples of PC based devices in research laboratories [10].
In wavelength-division multiplexing systems for multiplexing and routing, such as different channels of light into or out of a Single Mode Fiber (SMF), an Optical Add-Drop Multiplexer (OADM) is used. Channel add-drop filter are critical components for WDM, and have been previously demonstrated in micro-ring resonators whose travelling wave mode structure enables complete separation of input, drop and through ports without the need of optical circulators.
Photonic Crystal is a periodic crystal structure of dielectric characteristic or showing periodicity in a certain direction. When an electromagnetic (EM) wave propagates in a periodic structure whose period is equal to the wavelength of impulse, then it generates a Complete Photonic Band Gap (CPBG). Creation of new defects into the PC structure engenders that particular range of wavelength can be used as a propagation region inside the structure.
These defects are mainly of two types: 1. point defect or micro-cavity and 2. line defect or waveguide. 2DPCs consist of dielectric rods in air host (high dielectric pillars implanted in a low dielectric medium) or air holes in a dielectric region (low dielectric rods in a higher dielectric lattice). There are lots of applications related to the photonic crystal ring resonator which may act as demultiplexers, band stop and band pass filters. Due to the miniaturization, PCRRs (Photonic Crystal Ring Resonator) are the most commonly needed filter used for the design of integrated optics.
Many types of PCRRs are commercially available in the market. They have been delineated in previous work. The circular PCRR-based optical filters provide better performance than others. This makes the PCRRs an alternative to current micro-ring resonators for ultracompact WDM components and applications in highdensity photonic integration [1]. The single ring resonator has been proposed to filter the unwanted band of wavelengths whose coupling efficiency was 93%. Lshaped ring resonators have been found for the purpose of normalized transmission [3]. But those designs had some drawback like less quality factor and they were achieved only in the square lattice.
An Optical Add-Drop Multiplexer (OADM) is a device used in wavelength-division multiplexing systems for multiplexing and routing different channels of light into or out of a Single Mode Fiber (SMF). This is a type of optical node, which is generally used for the formation and the construction of optical telecommunications networks. ”Add” and ”drop” here refer to the capability of the device to add one or more new wavelength channels to an existing multiwavelength WDM signal, and/or to drop (remove) one or more channels, passing those signals to another network path. An OADM may be considered to be a specific type of optical cross connect. The optical add-drop multiplexer can be of many types. Figure 1 shows a basic diagram of an Optical add-drop multiplexer using a fiber Bragg grating and two circulators [13].
Figure 1. Optical Add-Drop Multiplexer, using a Fiber Bragg Grating and Two Circulators [13]
A traditional OADM consists of three stages: an optical demultiplexer, an optical multiplexer, and between them a method of reconfiguring the paths between the demultiplexer, the multiplexer and a set of ports for adding and dropping signals. The de-multiplexer separates wavelengths in an input fiber onto ports. The reconfiguration can be achieved by a fiber patch panel or by optical switches which direct the wavelengths to the multiplexer or to drop ports. The multiplexer multiplexes the wavelength channels that are to continue on from demultiplexer ports with those from the add ports, onto a single output fiber [13].
An optical ring resonator is a set of wave-guides in which at least one is a closed loop coupled to some sort of light input and output (These can be, but are not limited to being, wave-guides). The concepts behind optical ring resonators are the same as those behind whispering galleries except that they use light and obey the properties behind constructive interference and total internal reflection. When light of the resonant wavelength is passed through the loop from input waveguide, it builds up in intensity over multiple round-trips due to constructive interference and is output to the output bus waveguide, which serves as a detector waveguide. The basic structure of an optical ring resonator is shown in Figure 2 [12] .
Figure 2. Basic Structure of Optical Ring Resonator [12]
Artificial structures with periodic dielectric modulation, such as Photonic Crystals (PhC), can exhibit frequency ranges in which the propogation of electromagnetic waves is prohibited. This prohibition of wave propogation is tagged Photonic Band Gaps (PBG's). These structures have many potential applications because of their ability to control light-wave propogation and to be integrated into optical circuits. In this paper, a photonic crystal multi-channel drop filter based on ring resonators is proposed and its properties are investigated numerically by using the Finite- Difference Time Domain (FDTD) method. This structure is constructed in a two-dimensional square lattice. Their multi-channel drop filter is composed of three waveguides and three ring resonators. These ring resonators are located in two different regions (heterostructure) in which each region has specific dielectric constant. At resonance of each ring resonator, the power with certain wavelength transferred to one of the three drop waveguides is found to be more than 81%.
In this paper, an optical Add-Drop Filter (ADF) design based on ultra-compact Photonic Crystal Ring Resonators (PCRRs) is presented. The normalized transmission spectra for single-ring configurations have been investigated by using the two-dimensional Finite-Difference Time Domain (FDTD) technique in a square lattice dielectric-rod photoniccrystal structure. The different types of PCRRs with various lattice structure is shown in Figure 3. The introduction of four scatterers at the corners of quasi-square-ring PCRR, high wavelength selectivity and close to 100% drop efficiency can be obtained.
Figure 3. Photonic Crystal Ring Resonators (PCRRs), (a) Quasisquare Ring PCRR in Square Lattice, (b) Hexagonal Ring PCRR in Triangular Lattice, (c) Circular Ring PCRR in Quasi-photonic Crystal Structure (12-fold symmetry as shown [2])
In this paper, the authors have proposed a new class of ultra-compact optical add-drop filter based on photoniccrystal ring resonators. More than 96% drop efficiency can be obtained with the modal quality Q varying from 160 to over 1000. Both backward and forward-dropping can be achieved in dual-ring PCRRs as selected by different coupling schemes for the optical coupling of different resonator modes based on the modal symmetry.
Two-dimensional circular Photonic Crystal Ring Resonator (2D PCRR) based Add Drop Filter (ADF) using circular rods is designed for ITU-T G.694.2 eight channel Coarse Wavelength Division Multiplexing (CWDM) systems to add/drop a channel centered at a resonant wavelength of 1491 nm. The Plane Wave Expansion (PWE) method and 2D Finite Difference Time Domain (FDTD) method are employed to obtain the Photonic Band Gap (PBG) range and output spectra of the ADF. Close to 100% of coupling and dropping efficiencies, 13 nm of pass band width and 114.69 of quality factor are observed for the designed filter at 1491 nm which is highly sufficient and fulfill the requirement of ITU-TG.694.2 CWDM system.
The resonant wavelength tuning possibilities of ADF are theoretically studied to cover the lower channels of CWDM systems. The structural parameters such as refractive index, lattice constant, and radius of the rod in the structure are considered for resonant wavelength tuning.
The characteristics of biochemical sensors based on Photonic Crystal (PC) resonators are investigated in this work. The PC structure consists of holes arranged in a hexagonal lattice on a silicon slab. The nanoring resonator is formed by removing certain holes along a hexagonal trace. The hexagonal nanoring resonator is sandwiched by two PC waveguides that are formed by removing two lines of holes.
The authors have demonstrated the feasibility of PC single and dual-nanoring resonators for bio sensing applications. The PC nanoring resonator is considered to be formed by removing certain holes from a 2-D silicon PC slab. In applications of bio sensing, the whole nanoring resonator is embedded inside a micro fluidic channel.
In this paper, combining a square lattice photonic crystal with a 12-fold quasicrystal, the authors have proposed a new design for an optical channel-drop filter. The proposed structure has a transmission efficiency very close to 1 and the band width and quality factor values for this structure are 4.5 nm and 344, respectively. The band structure of basic PhC is shown in Figure 4. After designing the channeldrop filter, the effect of different parameters on the output wavelength of the filter are investigated. It has been shown that by changing the dielectric rods refractive index, radius of initial structure rods, and the radius of the 12-fold quasicrystal rod’s different output wavelengths of the filter can be obtained.
Figure 4. The Band Structure of the basic PhC Structure [5]
For combining a square lattice PhC structure with a 12-fold quasicrystal, a tunable optical CDF is proposed. Using numerical methods such as PWE and FDTD methods, the optical properties of the proposed structure are obtained and the effect of different parameters on the drop are investigated. Wavelength of the CDF increases the aperture diameter, Q-Factor also increases.
A new optical Channel Drop Filters (CDFs) configuration based on Photonic Crystals Ring Resonators (PCRRs) is provided. The transmission characteristics for single-ring and multiple-ring configurations have been investigated by using the two-dimensional (2D) Finite-Difference Time- Domain (FDTD) technique in triangular lattice Photonic Crystal (PC) silicon rods. Both forward and backward dropping were achieved in dual-ring PCRR structures. In this filter, 100% drop efficiency and acceptable quality factor can be obtained at 1550 nm. The present device can be used in the future photonic integrated circuits.
In this paper, a new design of Channel Drop Filters (CDFs) based on Photonic Crystals Ring Resonators (PCRRs) is presented. The filter characteristics for single-ring and dualring configurations based on two-dimensional (2D) triangular lattice Photonic Crystal (PC) silicon rods have been investigated by using the two-dimensional (2D) Finite- Difference Time-domain (FDTD) method. The dependence of resonant frequency is based on dielectric constant of whole rods of the structure as well as radius of the coupling rods. The transmission spectra at port D for different dielectric constant of the rods is depicted by Figure 5. This device can be used as an Optical Channel Drop Filter (OCDF) in future communication applications.
Figure 5. Normalized Transmission Spectra of Single- Ring PCRR based CDF at Port D for different Dielectric Constant of whole Rods [6]
A new design of Channel Drop Filters (CDFs) based on Photonic Crystals Ring Resonators (PCRRs) is proposed and numerically demonstrated in two-dimensional triangular lattice silicon rods. Backward dropping efficiency of 96% and forward dropping efficiency up to 98% can be achieved in third communication window. The proposed structure provides a possibility of channel drop filter and has the ability to be suitable for integration.
This paper discusses an optical filter designed using the two-dimensional (2D) Photonics Crystal. The filter has been designed to work in Dense Wavelength Division Multiplexing (DWDM) communication using ultra cell resonant cavity. The filter analysis was initially carried out by changing the attributes of photonic crystal such as radius of inner ring rods and refractive index.
The Radius of the outer, inner, and coupling rods of the proposed demultiplexer is given in Table 1 and the Refractive index for the proposed tunable port demultiplexer is shown in Table 2. Hence, it is possible to tune the wavelengths with characteristics according to DWDM standard. The filter is designed to work in 1552 nm, 1553 nm, 1554 nm, 1555 nm, 1556 nm, 1557 nm and 1558 m with 1nm channel spacing and 0.2 m spectral line width, 96% to 100% transmission efficiency, and quality factor to be 8000, respectively. The proposed filter was designed and stimulated with Finite-Difference Time-Domain (FDTD) algorithms and the results are discussed at the end for the use in Photonic Integrated Circuits.
Table 1. Radius of the Outer, Inner, and Coupling Rods of the Proposed Demultiplexer [7]
Table 2. Refractive Index for Proposed Tunable Port Demultiplexer [7]
This review paper is concerned to a variety of researches done into Wavelength Division De-Multiplexing using a Photonic Crystal four-Channel Drop filter, and designing of multi channel Add-Drop Filter with Wavelength Division Multiplexing and De-multiplexing. The various parameters of photonic crystals can be used for the increasing efficiency and the Q-factor of any signal. The multichannel in the system can also be convenient instead of using particular number of channels. This kind of devices would be more useful for the realization of Integrated optic circuits for CWDM systems and, future access and metro networking applications.
After going through various reference papers, the authors have found out that,
The expected result is to be able to simulate channels by wavelength division multiplexing and de-multiplexing using a Photonic Crystal Add-Drop Filter, instead of a photonic crystal drop filter which can simulate the particular number of channels in a system.
As the Add-Drop Filter is very critical and essential part of an WDM system, the performance of an optical filter can enhance the overall output signal quality and efficiency.
The authors would like of acknowledge the Department of Electronics and Telecommunications Engineering of Shri Shankaracharya Technical Campus for providing the facilities to carry out this work, and to the supervisors Mr. Vikas Sahu and Mr. Sharad Mohan Shrivastava for their guidance and cooperation throughout the whole paperwork.