Design of pressure sensor using 2D photonic crystal.
The phc is a platform of exploring the research direction in optical field. Photonic crystal is a periodic natural metallo-dielectric nanostructures with low and high dielectric constant materials (refractive index) in order to affect the propagation of electromagnetic waves inside the structure. Which means periodicity of material is maintained by arranging different dielectric substrate in periodic manner. One of very important characteristics of photonic crystal is its light confinement and controlling property. These characteristics allowed the crystal to use in various sensing applications .Sensor is a analytic device which senses physical as well as biological parameters and responds according to them. In past various electronics sensors are already designed but these sensors have certain limitations. Those limitations are overcome by optical sensors. Optical sensors are designed by using of optical fiber, photonic crystal fiber and photonic crystal. There are one dimensional photonic crystals (1D), two dimensional (2D) and three dimensional photonic crystals (3DPCS) are available. Recently C.S.Mallika et al (2015) has reported a ring resonator based temperature sensor. The sensing principle of the temperature sensor is based on the wavelength shift. The refractive index of the sensor is changed by increasing the external pressure thus the wavelength get shifted . SAEED OLYAEE & DEHGAHNI(2012) has reported that,a pressure sensor based on the nano-cavity. Which means that, the by modifying the radius of rods the resonant wavelength shift have been achieved. . VIJAYASHANTHI & ROBINSON(2014) has submitted a paper on nano-cavity based pressure sensing by creating a line defect by modifying the radius of rods,the pressure has been analyzed according to the wavelength shift. In 2011, Bo li et. al developed a photonic crystal based sensor based on NEMS cantilever by using dual ring resonator. This sensor is based on the air holes type structure which is more preferable in nano-electromechanical application systems. T. Stomeo et. al(2007) designed and fabricate a 2D photonic crystal. it is strain sensitive. This sensor is also based on the resonance wavelength shift. It detects the pressure from 0.25Gpa to 5Gpa and its sensitivity is 5.18nm/Gpa. In this paper ring structure based sensor is designed based on the resonance wavelength shift.
II Structure Design:
The designed phc is based pressure sensor comprises of a triangular lattice of silicon rods surrounded by air. The circular rods with triangular provides better confinement as similar to the square array of rods and effectively operates in (TE) mode of propagation. In the triangular lattice the number of rods in X and Z direction is 20*20. The distance between two adjacent rod is 530nm which is termed as lattice constant denoted by a. the radius of the rod is 0.1[micro]m and the refractive index Of silicon rod is 3.4i.e the dielectric constant is 11.976.
The PBG of the designed sensor is calculated using plane wave expansion method (PWE band solver). The PBG is an important property of photonic crystal. Generally, the band gap inhibits the propagation of light into the photonic crystal structure. By creating point defects the periodicity of the crystal is broken and it allows the propagation of light into the band gap. Thus the defects convert the photonic band gap into propagating gap. The wave whose wavelength lies in the range of band gap is easily propagated into the structure. The proposed sensor has broad transverse band gap. The band gap of the sensor is 1.2[micro]m to 1.7[micro]m.
Fig: 2 represents the structure of the pressure sensor 2DPC. The optical source is given as the input will propagate into the pc based sensor. This sensor is used to manipulate the light with respect to the refractive index variation of the pressure. Then the manipulated light passes to the photo detector which is used to convert the optical to electrical signal. Then the signal processing unit displays sensing quantity in the readable form with the help of the lookup table. The following fig 3: represents the schematic diagram of the Photonic crystal based pressure sensor. The structure is made of a linear waveguide by creating point defect and a hexagonal ring at the center acts as a resonator, then the resonant wavelength is dropped to the output port.
III Sensing Principle:
Depending upon three important parameters such as lattice constant (a), ratio of radius to lattice constant (r/a) and refractive index of material. The change in any geometry by the application of external pressure may cause some changes in photonic band gap which will shifts the resonance wavelength of sensor[8-10]. The relation between pressure and refractive index is given by,
n = [n.sub.0] -(c1 + 2c2)[sigma] (1)
Where c1 and c2 are defined as:
c1 = [n.sub.0] (P11-2V x P12) / (2E) (2)
c2 = [n0.sup.3](P12-V(P11+P12)) / (2E) (3)
Where E is Young's modulus of silicon, for silicon its value is 130 GPa, V represent Poisson's ratio, V is 0.255 and Pij denotes the strain-optic constant. In Pressure sensor, the applying pressure has a linear relationship with the refractive index of the proposed structure. For 1GPa pressure, the refractive index of a sensor is incremented by 0.03985. In this process, the optical source act as a transducer which convert the electrical signal into optical signal and emits the optical signal which will passes to the photonic crystal based sensor. This sensor is used to maneuver the light with respect to the refractive index variation of the pressure. Then, the light passes to the photo detector which is also act as an inverse transducer convert optical signal into electrical signal. Signal processing units detects the sensed quantity of light signal in the readable form. These type of refractive index sensors can be used as humidity, stress sensors etc.
After designing the pressure sensor, the simulation is carried out using finite time domain method (FDTD) and the band gap calculation is done by plane wave expansion method. An input light signal is launched at the input port of the waveguide. The output signal is recorded by the power monitor at the output port hence the normalized output power is attained.
The 3D electric field distribution of line defect with ring resonator based pressure sensor at the wavelength 1500nm is shown in the Fig 4. The following fig 6(a),6(b) depicts the 2D electric field distribution.
The above graph represents the transmission power level for different pressure conditions. While applying the successive pressure levels, the transmitting power is getting reduced so that the quality factor gets improving.
From the above discussions, it is concluded that the 2D photonic crystal sensor is designed for pressure sensing. It is noticed that the resonant wavelength is shifted to the longer wavelength while increasing the pressure. In the absence of pressure the resonant wavelength is 1500nm and the quality factor is 150 and the power efficiency is about 60% respectively, which will be able to used for many sensing applications
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(1) T. Dharchana, (2) A. Sivanantharaja, (3) S. Selvendran
(1,2) A.C. College of Engineering and Technology, Karaikudi, Tamil Nadu, India -630 003.
(3) KL University, Green Fields, Vaddeswaram, Guntur, A.P, India-522 502
Received 28 February 2017; Accepted 29 April 2017; Available online 2 May 2017
Address For Correspondence:
T. Dharchana, A.C. College of Engineering and Technology, Karaikudi, Tamil Nadu, India -630 003.
Caption: Fig. 1: structure of TE mode band gap
Caption: Fig. 2: schematic diagram of pc based sensor
Caption: Fig. 3 : Normalized transmission spectrum at 1500nm
Caption: Fig. 4: 3D Electric field distribution
Caption: Fig. 5: Normalized transmission spectrum
Caption: Fig. 6(a): Field distribution of phc sensor
Caption: Fig. 6(b): simulation of phc pressure sensor
Table 1: Simulation Analysis Pressure level Effective Resonance Quality factor Refractive index Wavelength 0 Gpa 2.4 1500 150 1 Gpa 2.43 1510 116 2 Gpa 2.46 1525 138 3 Gpa 2.49 1530 75 4 Gpa 2.52 1545 55
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|Author:||Dharchana, T.; Sivanantharaja, A.; Selvendran, S.|
|Publication:||Advances in Natural and Applied Sciences|
|Date:||May 1, 2017|
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