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, Volume: 16( 6) DOI: DOI: 10.37532/0974-7494.2022.16(6).174

High Sensitivity and Ultra-High-Quality Factor for an All-Optical Temperature Sensor Based on Photonic Crystal Technology

Kouddad Elhachemi Telecommunication and Digital Signal Processing Laboratory, Faculty of Electrical Engineering, Department of Telecommunications, University Djillali Liabes, Sidi-Bel-Abbes 22000, Algeria E-mail:

Received date: 16-November-2022, Manuscript No. tsnsnt-22-80037; Editor assigned: 18-November-2022, PreQC No. tsnsnt-22-80037 (PQ); Reviewed: 30-November-2022, QC No. tsnsnt-22-80037 (Q); Revised: 12-December-2022, Manuscript No. tsnsnt-22-80037 (R); Published: 20- December-2022 DOI: 10.37532/0974-7494.2022.16(6).174

Citation: Elhachemi K., Leila D., Rafah N. High Sensitivity and Ultra-High-Quality Factor for an all-Optical Temperature Sensor Based on Photonic Crystal Technology. Nano Tech Nano Sci IndJ.2022;16(6):174


In our work, we propose a novel temperature sensor design based on a Two-Dimensional (2D) photonic crystal resonant cavity structure designed to detect and monitor temperature under very harsh environmental conditions from 0°C to 500ºC. The sensitivity of the proposed structure is 109.8 pm/ºC, an ultra-high quality factor, high transmission efficiency and ultra-compact size. The characteristics of the proposed sensor under different temperatures are simulated using the Plane Wave Expansion (PWE) method and Finite Difference Time Domain (FDTD) method to calculate, respectively, the Photonic Band Gap (PBG) and transmission efficiency. The results obtained show that the wavelength of the resonant cavity increases linearly with increasing temperature. Our sensor is suitable for applications based on nanotechnology


Resonant cavities; Sensitivity; Photonic crystal; PWE method; FDTD method; Quality factor


In recent years, Photonic Crystal (PhC) has attracted a lot of attention because of its more important properties for controlling and manipulating light through the crystal. Based on this characteristic, many scientists are finding designs and applications for various optical devices, such as optical decoders, logic gas, sensors etc[1-7].

Due to their several advantages such as bandwidth properties and the flexibility of miniaturization, PhC-based devices are now playing a very important role in new fields such as optical sensing [8].

Recently, optical sensors have attracted the attention of researchers because of their advantage over electronic sensors, which are limited in transferring large data at a very higher speed, which can be solved by all-optical sensors, optical switches, and tunable filters [9-13]. Optical sensors have been used effectively in many applications to detect various parameters such as pressure, biochemical sensors, gas, electric field, and temperature [14-18]. Temperature measurements are very important and are widely used in the risk control application of the petrochemical industry, automotive industry, avionics, industrial safety, biomedicine, and in many other applications[19-22].

Different optical temperature sensors based on 2D-PhC can be realized by ring resonators and waveguides structure [23,24]. Although nanosensors based on ring resonators offer high normalized transmission efficiency, high sensitivity, and highquality factor [25]. PhC waveguide-based nano-sensors have a good standardized transmission efficiency but a very lowquality factor [26].

In the present work, we have proposed a new hexagonal nanosensor based on a resonant cavity to detect the temperature in the range of 0°C to 500°C. The proposed temperature sensor has a wide range of applications in the defence, chemical, civil, metal production, semiconductor industry, and other fields. Temperature monitoring is also important for estimating the structural health of the device. The proposed design is more compact and simpler. Also, it offers a very high-quality factor and high sensitivity.

Materials and Methods

Bandgap analysis

In this section, we proposed the initial temperature sensor structure based on 2D PhC, with a hexagonal array of circular silicon pillars whose refractive index is equal to 3.42 suspended in the air. The numbers of the pillars in the x and z directions are respectively 23 and 17 and the ratio between the radius « R » and the lattice constant « a » is 0.3 FIG. 1(a).

In general, we use the PWE method to obtain the photonic bandgap which depends on three major parameters such as the lattice constant, the permittivity of dielectric materials, and the radius of the pillars. As shown in FIG. 1(b), there are three PBG regions for the Transverse Electric (TE) mode. The normalized frequency ( a /λ ) ranges for the three regions are (0.23-0.32), (0.42-0.54), and (.64-0.75). The second wavelength range of the PBG is between 1481.48 nm and 1904.76 nm, which is suitable for the proposed sensor design because it belongs to the third window of optical telecommunications.


Figure 1: Initial Structure (a) Pillars in the air (hexagonal lattice) (b) Band gap structure for the TE mode.

Analysis of temperature effects

In our study, using the FDTD method that allows us to calculate the spectral efficiency due to the propagation of the optical field from solving the differential equations of Maxwell in the time domain. Based on these Maxwell's equations, we can calculate the optical field in each position of the space inside the 2D structures based on photonic crystals for the TE mode, written as follows:

To optimize the two-dimensional calculations to the simulation of an optical wave, using the Perfectly Matched Layer (PML) as the boundary conditions of absorption which is defined by the following equation:

c is the speed of light in a vacuum.

The detection operation of an all-optical temperature sensor is based on the refractive index variation as a function of the thermooptical effect. The refractive index will be modified according to the temperature, which allows the photonic band gap and the centre wavelength of the structure to be changed, and this variation is given as [27]:

n° is the refractive index of the medium at zero temperature ( 0° C), α is the thermo-optical coefficient given by 2.4×10−4/° C is the refractive index of the medium at zero temperature ( 0° C) for silicon and ∆T is the temperature difference [28].

Results and Discussion

The designed temperature sensor structure of the 2D hexagonal shape based on the resonant cavity is shown in FIG. 2. Our sensor is composed of two quasi-waveguides in the horizontal in-line direction, and a resonant cavity is located between them. The inline quasi-waveguides are created by removing nine silicon pillars for both sides as input and output. The resonant cavity is created by optimizing rays of some internal pillars such as black rods (R*1.3), blue rods (R*0.5), and green rods (R*0.45) placed in the hexagonal array to couple the light signal into quasi-in-line waveguides from the input to the output. The resonance wavelength is observed using the monitor which is placed at the sensor output. The total size of our sensor is18µm ×12 µm.


Figure 2: Proposed design for the temperature sensor.

This section describes the optical detection results obtained for the proposed sensor structure. FIG. 3 shows the electric field distribution of the resonant cavity for the wavelength 1682.1 nm at the output of our proposed device in the temperature range of 0°C to 500°C with a 50°C step size. FIG. 4 graphically represents the normalized transmission at the output of the proposed sensor at a zero temperature (0°C) which corresponds to an intensity of 81.5% at the wavelength 1682.1 nm. On the other hand, the relationship of resonance wavelengths as a function of temperature has been illustrated in FIG. 5 and recapitulated in the TABLE 1. The necessary functional parameters of our designed temperature sensor are compared with the already mentioned sensors, which are summarized in TABLE 2. It indicates that the dynamic range, quality factor(Q) = λ0 / ∆λ , and sensitivity of the proposed temperature sensor are better than those of the previously existing sensor [28-34]. These results are obtained by using the Q-Finder model in RSoft software which is combined by the 2D-FDTD method with fast harmonic analysis to calculate the quality factor Q [35,36].


Figure 3: Electric field distribution of resonant cavity at 1682.1 nm.


Figure 4: Resonant wavelength of a resonant cavity at 0°C.


Figure 5: The linear relation between resonant wavelengths and temperature.

TABLE 1. Functional parameters for the temperature sensor at different temperature

Temperature (°C) Refractive index (RIU) Resonance wavelength (nm) Transmission efficiency (%) Quality factor Wavelength shift
0 3.42 1682.1 81.5 17 156 /
50 3.432 1687.5 62 14 688 5.4 nm
100 3.444 1693.2 64.6 12 525 5.7 nm
150 3.456 1698.6 89.6 10 943 5.4 nm
200 3.468 1704.1 92.2 10 182 5.5 nm
250 3.48 1709.7 66.7 10 412 5.6 nm
300 3.492 1714.9 96.8 11 707 5.2 nm
350 3.504 1720.6 98 14 027 5.7 nm
400 3.516 1725.9 50.8 17 234 5.3 nm
450 3.528 1731.6 53 21 105 5.7 nm
  3.54 1737 50.1 25 349 5.4 nm

TABLE 2. The proposed functional parameters of the temperature sensor compared with the previous works.

Reference Dynamic Range (°C) Quality factor Temperature sensitivity         (pm/°C)
Present work 0 to 500 17 156 109.8
[27] 0 to 100 / 6.6
[29] 25 to 200 214 /
[30] 0 to 450 738.7 59.25
[31] 0 to 80 2506.5 93.61
[32] 20 to 90 / 84
[33] 20 to 70 415.7 88.7
[34] 0 to 360 / 92.3


In this paper, we presented a two-dimensional hexagonal structure based on the resonant cavity designed for temperature sensing applications. The presence of the thermo-optical effect of the ‘Si’ material plays a very important role in the all-optical temperature sensor. The results of the PWE simulation show that the resonance frequency is shifted to a lower frequency by increasing the temperature. The study of all the functional characteristics of our proposed sensor is realized by using the PWE and FDTD methods. For temperature detection, the resonant cavity structure has a maximum quality factor of 17,156, a very high sensitivity of about 109.8 pm/°C, a dynamic range is 0°C to 500°C, and a size of 2 26µm- .It is therefore a design that is simple, stable, and suitable for various applications in integrated optics.


This work was supported by the Directorate General for Scientific Research and Technological Development (DGRSDT).


Awards Nomination

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