Materials Today Communications
Doubly electrically tuned cylindrical Bragg fiber waveguide inline optical filter for multiwavelength LASER applications
Introduction
As per demand of the present scenario, optical instrument testing, optical signal processing, optical communications, modern telecommunications, fiber sensor systems, and sensors multiplexing industry have a greater interest in multiwavelength LASER sources. These laser sources not only provide great potential in the optical instrument test etc. while they also utilized in the measurement of wavelength division multiplexing (WDM) components [1,2]. The requirements of such optical sources are for larger number of components/channels over wide wavelength span, inline behavior, less to moderate output power with good signal to noise ratio, narrower channel width i.e., least full width at half maxima (FWHM)of signal, etc. for single-mode operation of each laser line. Achieving all these requirements simultaneously is a kind of tough job to implement. Numerous scientific methods have been used to realize narrow-line width fiber lasers. Researchers have used the liquid crystal etalon filter as the wavelength tuning element electronically to design tunable fiber laser [1]. This wavelength-tunable laser work in infrared has a wide range of applications, but the wavelength span is considerably least, and this is also limit over infrared only. Hernandez et al. [2] presented Erobium doped tunable multiwavelength LASER based on a Mach–Zehnder interferometer with photonic crystal fiber. Even at room temperature, the laser has greater stability, but this is very limited to emit a single, double, triple or quadruple line tuned from 1530nm to 1556nmonly by controlling the polarization state. Further many scientists and researchers have presented multiwavelength LASER model using various kind of filter as fiber Bragg gratings (FBGs) [3,4], acoustic optical filters (AOFs) [5], Sagnec interferometers (SIs) [6], Mach-Zender interferometers (MZIs) [7,8] and Fabry-Perot interferometers (FPIs) [9,10]. Multiwavelength lasers based on such optical filters have various advantages in a different domain, but all these useful techniques are limited by size, single-mode operation, working wavelength span, low power consumption, inline behavior, switchability and repeatability operation, etc. Therefore, the cylindrical Bragg fiber waveguide structure [11,12] has a bright scope and will be very useful in multiwavelngth LASER applications. The periodic arrangement of high and low refractive index based concentric cylinders are the basic foundation of Bragg fiber waveguide (BFW) structure, where electromagnetic wave is propagate through the hollow core by the process of multiple Bragg reflection through the periodic claddings [13]. Further, BFW structure must show a photonic band gap (PBG). PBG is a range of wavelengths which is forbidden to propagate through the BFW structure. BFW has many promising applications in biosensors [14], high-temperature sensor [15], intensity and wavelength modulation [16] etc. therefore, in this present communication, the high refractive index contrast chalcogenide glass Arsenic tri-selenide and polymer film Poly-ether-imide (PEI) based cylindrical multi-clad BFW structure with hollow core has been considered. Since, to enhance the overall performance of the proposed application, narrow transmission bandwidth (i.e. resonant transmission peak) and constant intensity for inline application are much desirable as an output signal. This property can be achieved in the present periodic structure by introducing a PMMA defect cavity in the cladding periodicity which is used to obtain a resonant transmission peak in PBG region. This defect cavity is just introduced by breaking the periodic symmetry with a PMMA defect layer in the periodic arrangement. The transfer matrix method and mathematical Henkel formalism have been used to study the transmission characteristic of the electromagnetic wave through the BFW structure. The present structure is self-capable to tune the PBG and the output signal by the modulation in incidence angle. Further, tuning will be obtained by using piezoelectric properties and electromechanical behavior of the ferro-electric single crystal (PMN-PT) [17]. Various researchers have reported well the piezoelectric and electromechanical behavior and properties of such materials [18,19].
Due to its reversible domain switching mechanism with fast response time, accurate control and small device size [17,18], the ferroelectric PMN-PT single crystal can produce a giant recoverable strain for both positive and negative applied DC voltage, which is most important for the present study as a reproducibility and switching issue. Researchers also stated that the electromechanical coupling coefficient () of single crystal PMN-PT is of 94 % and the piezoelectric constant () is 2800pC/N (for both positive and negative DC bias voltages) which is quite adequate and capable of modulating the material thickness of approximately 2.8nm/V [17,18]. Therefore, in the present communication, doubly electrically tuned cylindrical BFW inline optical filter for multiwavelength LASER application has been discussed. For an inline and reliable transmission signal in the optical networks, the cylindrical BFW structure is chosen.
The proposed framework for current correspondence is as follows: section 2 is the detailed overview of the proposed framework. The theoretical modeling of the structure by using the Transfer matrix method and Henkel formalism is found in section 3. The results achieved are addressed in Section 4. Section 5 provides a conclusion.
Section snippets
Comprehensive description of BFW structure
The thickness and refractive index profile of the hollow core BFW structure with a defect cavity has been shown in Fig. 1. The proposed waveguide is symmetrical about the longitudinal axis i.e. propagation axis. The present structure is composed by the periodic repetition of bilayer high refractive index chalcogenide glassy material Arsenic tri-Selenide () (nH, dH) and low refractive index polymeric layer poly-ether-imide (PEI) (nL, dL). Additionally, a low refractive index polymer PMMA
Theoretical modeling of the structure using transfer matrix and Henkel formalism in cylindrical coordinates
The detailed description of the proposed structure has already been discussed in section 2. Further, in the present section, the theoretical modeling of the structure using the transfer matrix and Henkel formalism in cylindrical coordinates has been presented. The refractive index profile preferred for this framework is as follows:
This waveguide’s solution to reflection and
Results and discussion
The BFW structure having 15 cm length (free from bending effect) is theoretically modeled for the design wavelength . The refractive index of the center air core is and diameter . The thickness of periodic layer , PEI and cavity layer PMMA follow the quarter wave stack condition for the maximum transmission. For , PEI and PMMA, the corresponding refractive index is 2.82, 1.66 [11,14] and 1.498 [17]. The single crystal PMN-PT also has
Conclusion
In the vicinity of PMMA cavity with single crystal ferroelectric PMN-PT, Doubly electrically tuned high refractive index contrast BFW inline optical filter is investigated for the low power multiwavelength LASER applications. The resonant transmission peak through such structure has been obtained with nearly 90 % transmission efficiency in considered PBG by regulating the incidence angle and deploying electrical DC voltages. Since an external voltage on PMN-PT single crystal is required to
Author agreement
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Declaration of Competing Interest
The authors report no declarations of interest.
Acknowledgment
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. The authors acknowledge Dr. Vivek Singh, Institute of Science, Department of Physics, B.H.U. Varanasi for his continuous valuable support.
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