Waveguide attenuation measurement

Fig. 6—Attenuation measured for nematic waveguides consisting of MBBA layers with hemeotropic aiignment.

A classical setup for microwave conductivity measurements is based on the utilization of the waveguides. A simple installation consists of a microwave generator (typically a gun diode) which, when the Ka-band is used, can be operated in the frequency region of 28-40 Gc/s this is protected by an isolator against back-reflections from the rest of the microwave circuit. The microwave power is conducted by an attenuator across a circulator into the microwave conductor branch at the end of which the electrochemical cell is mounted. The microwave power reflected from the electrochemical sample is conducted via the circulator into the microwave detector. It typically consists of a diode that acts as an antenna, receiving the electrical alternating field, rectifying it, and con-... 

Distributed circuit methods use coaxial lines, waveguides and resonant cavities at microwave frequencies. The circuits are designed for measuring an attenuation factor and a phase factor, from which sample dielectric properties can be calculated. The sample may form the dielectric medium between the two conductors of a coaxial line (Scaife et al, 1971), or an open coaxial line is brought into contact with the sample surface (Roussy and Pearce, 1995). Fagan et al, (2004) used an open coaxial line method to demonstrate that the moisture and salt contents of processed cheese could be predicted by measuring dielectric properties over a range of frequencies. 

An antibody is immobilized on the surface of a waveguide (a quartz, glass, or plastic slide, or a gold- or silver-coated prism), and binding of an antigen is measured directly by total internal reflection fluorescence, surface plasmon resonance, or attenuated total reflection. 

In the case of planar waveguides in integrated optics, the quality requirements are much more stringent because of the long path inside the film [217]. Low loss values reported here are listed in Table 12. Determinations of the light attenuation in waveguides enable loss measurements of 0.1 dB cm 1, corresponding to an extinction coefficient of lxlO 7 or an a value of 0.02 cm 1 (a = 633 nm) [218]. 

Teng, C.C. 1993. Precision measurements of the optical attenuation profile along the propagation path in thin-film waveguides. Appl Opt 32 1051—1054. 

There are two mechanisms that causes losses in waveguides dielectric losses and metal losses. In both cases, these losses cause the amplitudes of the propagating modes to decay as exp(—az), where a is the attenuation constant, measured in neper/meter. Typically, the attenuation constant is considered as the sum of two components a = cKdie + met) where aaie and aniet arc the dielectric and metal attenuation... 

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