Optical Angular Sensor for Space Applications

This paper describes a silicon/glass sensing structure for axial angle measurements. The presented optical angular sensor can statically measure the angle φ of any apparatus depending on the torsion of the optical component against the sensor housing. Core element of the sensor is an optical medium with an etched structure, which diffracts light from an LED according to the Fresnel equation. Two photodiodes, one for angle determination and one as reference, conduct the measurement. Hence, the signal splits up into two parts: one part transmits trough the optical system and the second part (the reflected wave) is used as reference signal. For self-referencing purposes, the wavelength spectrum of the LED has its maximum in the infrared regime near to the wavelength where silicon gets transparent (l~1000 nm). More precisely, torsion angle and light intensity show a dependency given by Tstot if a straight etching structure (refraction profile) is used. To avoid multiple reflections of light, a coating layer restricts the illuminated area in the optical medium. With this setting a resolution of 0.05-degree rotation angle has been achieved and by stacking the construction, the sensor can measure an angular range from 30° up to 270°.

Determination of the Optical Properties of Thylakoid Membranes from Whole Leaf Reflectance Measurements Using a Capacitor and Unbound Electron Model

This paper demonstrates that a capacitor equivalent along with unbound electrons can be used to model thylakoid membranes in grana stacks. From whole leaf reflectance measurements at normal incidences at 660nm wavelength and taken from the literature, refractive indices are obtained from the Fresnel equation for transverse electric (TE) and transverse magnetic (TM) polarization. The TE and TM polarizations for external reflectance depict the Brewster angle at which the magnitude of the reflected electric vector is zero; the internal reflections show that there is a narrow angle window of about 10 degrees before the internally refracted light goes into critical angle. The clustering and separation of reflection measurements with angle of incidence is explained using Fresnel equation; the cross-over angle is located beyond the Brewster angle for internal reflection. The predicted relaxation times from a capacitor and unbound electron model gave favorable comparisons against commonly reported fluorescence times in the 0.1 to 1 ns range (our results gave 0.5-0.8 ns). The di-electric constant for the membrane is estimated to be 5. The stacking number (number of grana layers) is consistent with the light penetration depth (skin depth). The magnetic permeability was shown to be close to that of vacuum and therefore the thylakoid lacks any magnetic properties as would be expected for such a transparent media. An in-vivo estimate based on thermal equilibrium of molecules for the permanent dipole moment of the chlorophyll molecule gave 2,025D (Debye).

Sensitivity Enhancement of Surface Plasmon Resonance Sensor with Two Dimensional Materials Covered on Silver-Nickel Bimetallic Thin Solid Films

In this paper a new sensing configuration with enhanced sensitivity utilizing 2D materials on the bimetallic layers of Magnetic Material Ni over Ag for Kretschmann configuration is proposed and analyzed numerically using Fresnel equation and transfer matrix method. Results show that such a hybrid configuration with well optimized thickness of metallic layer and utilization of specific no. of 2D materials can increases the sensitivity as high as 298°/RIU is absorbed for the configuration consist 10 nm of Ni over 40 nm thickness of Ag added with a 2 layers of WSe2.

A Side-Coupled Optical-Fiber Liquid Level Sensor

A side-coupled optical-fiber liquid level sensor is proposed to realize intrinsically safe measurement to liquid level in flammable environments. The sensor consists of two parallel side-polished fibers is based on the different coupling coefficient between the fibers in different media according to the Fresnel equation. One of the fibers is for emitting and the other is for receiving, and a reflector is attached to the end of the fibers to enhance the power of light. The power of the light from the top of receiving fiber is measured by the signal processing circuit which is mainly organized by an instrumentation amplifier and a correlator. This sensor is fabricated in the laboratory and the results of the experiments show good performance. It is demonstrated that the sensor is safe and sensitive, but there is still a lot of work to do before its commercial usage.