Fresnel reflection loss

The loss of the NLO polymer and UV-cured resin of this QPM waveguide were 0.67 dB/ cm and 0.53 dB/cm, respectively. The Fresnel reflection loss of the grafted interface was... 

The main causes of the insertion loss in a polarization-dependent isolator are absorption loss of materials and the Fresnel reflection loss at each interface. To achieve lower insertion loss, it is important not only to use low absorption material, but also to reduce reflection at each interface. 

Fresnel Refection losses—Reflection losses that are incurred at the input and output of optical fibers due to the differences in refraction index between the core glass and immersion medium. 

As in any other laser, the lasing threshold in a semiconductor laser diode is reached when the gain of the active material overcomes the losses of the laser cavity. These losses have two basic origins, namely the finite reflectivity of the mirrors mid distributed losses due to scattering and parasitic absorption in the active medium. In contrast to other lasers, the mirrors in typical semiconductor lasers are simply formed by cleaved or etched crystal facets. Therefore, the reflectivity (Fresnel reflectivity) is rather low, about 20% in the case of the nitrides. 

A small correction is necessary for the reflection losses at the interface between two substances of widely different refractive indices such as glass-air or quartz-air. The reflection from a quartz-liquid or glass-liquid interface is negligible. The quantitative relation involved is known as Fresnel s law. 

The internal transmittance of quartz and Suprasil quartz is related to the thickness of the sample according to the Beer-Lamhert law, decreasing with increasing thickness of the quartz layer. Flow-through photoreactors (cf. Fig. 8-3) require quartz sleeves for lamp protection and hence suffer from radiation losses due to reflectance at the air (gas)/quartz and quartz/water interfaces (cf. Fig. 3-11). Reflection losses depend on the magnitude of the refraction index n and are usually in the range of about 7 to 8% for n=1.45 (Bolton, 1999, Braun et ah, 1991, Scaiano, 1989). Thus, a maximum transmittance T of quartz materials of 93% can be reached. The application of the Fresnel Law was demonstrated by Bolton (2000). 

When considering external attenuation affecting the transmission of light through optical fibres, one finds that, for short lengths of fibres, external attenuation normally is substantially larger than internal attenuation. At the entrance and exit face, both Fresnel reflection Lr and Fraunhofer diffraction Ld losses occur. 

A good description of all the factors contributing to the efficiency of an FT-IR spectrometer has been reported by Mattson [10]. He measured the effect of several different parameters that include beamsplitter efficiency, Fresnel losses at the substrate and compensator plate, reflection losses at the mirrors, radiation obscured by the mounting hardware for the HeNe laser, the emissivity of the source, and losses caused by imperfect optical alignment. He calculated the overall efficiency ( in Eq. 7.8) as being 0.096. This value is in accord with the value of 0.10 used in Section 7.1 to estimate the SNR of a commercial FT-IR spectrometer. 

Where h is the +1 diffracted order intensity and T the incident beam intensity. This equation is not considering the Fresnel losses because of the reflection in the photosensitive cell. 

In order to solve Eq. (21), we need the initial values of P at the input face X3 = 0 inside the medium. This requires the solution of transmission and reflection at the boundary surface. Let us assume that the sample is immersed in a homogeneous isotropic fluid having a refractive index rii. Without loss of generality we can choose the Xi axis along the extraordinary direction on the input face, so that (0) = 0. The extraordinary and ordinary wave components obey the Fresnel equations for normal incidence ... 

In order to estimate the magnitude of diffraction losses let us make use of a simple example. A plane wave incident onto a mirror with diameter la exhibits, after being reflected, a spatial intensity distribution that is determined by diffraction and that is completely equivalent to the intensity distribution of a plane wave passing through an aperture with diameter la (Fig. 5.5). The central diffraction maximum at 0 = 0 lies between the two first minima at d = Xlla (for circular apertures a factor 1.2 has to be included, see, e.g., [306]). About 16 % of the total intensity transmitted through the aperture is diffracted into higher orders with 0 > X/la. Because of diffraction the outer part of the reflected wave misses the second mirror M2 and is therefore lost. This example demonstrates that the diffraction losses depend on the values of a, d, X, and on the amplitude distribution A x,y) of the incident wave across the mirror surface. The influence of diffraction losses can be characterized by the dimensionless Fresnel number... 

The consideration of an RCE photodetector reduces to an analysis of a ID microcavity with losses (absorption used for the detection). The interfaces between the DBR mirrors and the wide-bandgap layers are described by the Fresnel complex reflectances rj = ri exp(i /i) and = r2 exp(i /2)-... 

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