109 research outputs found
Modelling and analysis of vector and vector vortex beams reflection for optical sensing
No full textLight Detection and Ranging (LiDAR) sensors can precisely determine object distances using the pulsed time of flight (TOF) or amplitude-modulated continuous wave (AMCW) TOF methods and velocity using the frequency-modulated continuous wave (FMCW) approach. In this paper, we focus on modelling and analysing the reflection of vector beams (VBs) and vector vortex beams (VVBs) for optical sensing in LiDAR applications. Unlike traditional TOF and FMCW methods, this novel approach uses VBs and VVBs as detection signals to measure the orientation of reflecting surfaces. A key component of this sensing scheme is understanding the relationship between the characteristics of the reflected optical fields and the orientation of the reflecting surface. To this end, we develop a computational model for the reflection of VBs and VVBs. This model allows us to investigate critical aspects of the reflected field, such as intensity distribution, intensity centroid offset, reflectance, and the variation of the intensity range measured along the azimuthal direction. By thoroughly analysing these characteristics, we aim to enhance the functionality of LiDAR sensors in detecting the orientation of reflecting surfaces
Method for optimising the performance of PML in anchor-loss limited model via COMSOL
No full textPerfectly matched layer has been used for solving anchor-loss limited quality factor in the Micro electromechanical systems. However, setting up a well-behaved perfectly matched layer requires users to change the parameters of a perfectly matched layer to give correct results, while the current existing methods for choosing the right parameters are vague and lack theoretical support. Based on the mathematical theory of perfectly matched layer and simulation results of a beam structure's quality factor, this paper proposes a method for choosing the parameter to optimise the performance of perfectly matched layer in COMSOL. The accuracy of the proposed method is proved by matching the effect of substrate height on beam's quality factor with theory prediction. The author also studies the effect of beam height and beam width on the quality factor of the beam. The results demonstrate that simulated quality factors are in agreement with analytical values when the ratio of height over length is small but will show great divergence when height equals the length. This trend can be observed for the beam width as well. Especially for larger ratio of beam width over beam length, instead of decreasing monotonously as analytical equitation would expect, the simulated quality factor will converge into a stable value of 1700, which matches the result of two-dimensional model for the same beam structure. This means that a three-dimensional model has to be used for estimating the quality factor of a beam structure
Optical mode localization sensing based on fiber-coupled ring resonators
No full textMode localization is widely used in coupled micro-electro-mechanical system (MEMS) resonators for ultra-sensitive sensing. Here, for the first time to the best of our knowledge, we experimentally demonstrate the phenomenon of optical mode localization in fiber-coupled ring resonators. For an optical system, resonant mode splitting happens when multiple resonators are coupled. Localized external perturbation applied to the system will cause uneven energy distributions of the split modes to the coupled rings, this phenomenon is called the optical mode localization. In this paper, two fiber-ring resonators are coupled. The perturbation is generated by two thermoelectric heaters. We define the normalized amplitude difference between the two split modes as: (T
M1 − T
M
2)/T
M
1 × 100%. It is found that this value can be varied from 2.5% to 22.5% when the temperature are changed by the value from 0K to 8.5K. This brings a ∼ 2.4%/K variation rate, which is three orders of magnitude greater than the variation rate of the frequency over temperature changes of the resonator due to thermal perturbation. The measured data reach good agreement with theoretical results, which demonstrates the feasibility of optical mode localization as a new sensing mechanism for ultra-sensitive fiber temperature sensing.
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Geometric representation of vector vortex beams: the total angular momentum-conserving Poincaré sphere and its braid clusters
No full textThis paper presents the total angular momentum-conserving Poincaré sphere (TAM-C PS), which offers a novel framework for efficiently characterizing a wide range of vector vortex beams. Unlike other types of Poincaré spheres, the TAM-C PS achieves a better balance between generality and validity, while also providing clearer physical interpretation. By linking the poles of different spheres, the study also introduces two distinct categories of TAM-C PS braid clusters, enabling the representation of various Poincaré spheres within a unified framework. The Poincaré spheres include classical, higher-order, hybrid-order, Poincaré sphere with orbital angular momentum, and TAM-C PS. This is the first clear and unified approach to express multiple Poincaré spheres within a single framework. The TAM-C PS and its braid cluster can be employed to guide the creation of targeted vector vortex light beams, offer a geometric description of optical field evolution, and calculate the geometric phase of optical cyclic evolution
Tailorable stimulated Brillouin scattering in a partially suspended aluminium nitride waveguide in the visible range
No full textStimulated Brillouin scattering (SBS) has been widely applied in narrow line-width laser, microwave filters, optical gyroscopes, and other fields. However, most research is limited within near-infrared to mid-infrared range. This is due to the limited transparent window in most materials, such as silicon and germanium. Aluminium nitride (AlN) is a novel III-V material with a wide transparent window from 200 nm and an appropriate refractive index to confine the light. In this paper, we first validate the full-vectorial formalism to calculate SBS gain based on the measured results from a silicon platform. Compared to previous research, our model achieves higher accuracy in terms of frequency, Q factor, as well as Brillouin gain coefficient without modifying the waveguide width. It also reveals the importance of matching rotation matrix and crystalline coordinate system. Then, we investigate the SBS in a partially suspended AlN waveguide at 450 nm based on the validated method. It shows a wide tunability in frequency from 16 GHz to 32 GHz for forward SBS and a range from 42 GHz to 49 GHz for backward SBS. We numerically obtain the value of Brillouin gain of 1311 W-1m-1 when Q factor is dominated by anchor loss for forward SBS of transverse electric mode. We also find out that in the case for forward SBS of transverse-magnetic mode, anchor loss could be greatly suppressed when the node point of the selected acoustic mode matches with the position of pillar anchor. Our findings, to the best of our knowledge, pave a new way to obtain Brillouin-related applications in integrated photonic circuit within the visible range.</p
Dataset in support of the paper 'Optical mode localized sensing in on-chip coupled microring resonators'
No full textThis dataset provides the data for plotting Fig. 2b, Fig.3, Fig. 4, Fig. 5 and Fig. 6 in the paper (Title: Optical mode localized sensing in on-chip coupled microring resonators) published in journal Optics Express.</span
Frequency resolution quantification of Brillouin distributed optical fibre sensors
No full textNoise analysis using Monte Carlo method is conducted in this paper to correct the relationship between the frequency resolution, the Q-factor, Signal-to-Noise Ratio (SNR), and frequency step in the Brillouin distributed optical fibre sensors. The quantification of the Brillouin gain spectrum is important in distributed Brillouin sensors in order to improve the Brillouin frequency resolution and the corresponding strain and temperature resolutions. Two analytical expressions are derived in order to estimate the error in the determination of the Brillouin central frequency with or without second order polynomialfitting
Thermodynamic control of MEMS meteorology pressure sensing element in low-temperature application down to −45°C
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