Prism coupling techniques

There are two main configurations with regards to the prism coupling technique Kretschmann configuration and Otto configuration. Optical excitation of SPs by the method of attenuated total reflection was demonstrated by Kretschmann and Otto... 

Figure 8. The trace of guided light in the polyoctylthiophene film (a) introduced by means of prism coupling technique (schematic representation in (b)).

Several techniques can be employed to couple an optical beam propagating in free space into a thin-film optical waveguide. Grating coupling and prism coupling (Fig. 15.4) are briefly outlined here, since these methods are applied in actual reverse waveguide and MCLW configurations, respectively. 

The waveguides were optically characterized at X = 632.8 nm. The effective mode indices were determined by the m-line technique, based on a standard two prism coupling set-up. The refractive index depth profiles of the fabricated waveguides were reconstructed by the means of the inverse WKB procedure . 

Figure 4. Techniques for coupling an external radiation field into optical waveguides (a) prism coupling, (b) grating coupling, and (c) end-fire coupling.

An example of quasi CW THz detection [86] uses a THz wave parametric oscillator (TPO) consisting of a Q-switched Nd YAG laser and parametric oscillator [87,88], In this technique, MgO LiNb3 is employed as a non-linear material to generate CW THz. Silicon prisms couple the THz radiation from the non-linear crystal where it is detected using a pyroelectric detector. THz images are collected at discrete THz frequencies and then spectroscopically analyzed using a component spatial pattern analysis method to determine sample composition. 

As we can observe in Fig. 1.7 the magnitude of the SPP momentum k, is always larger than that of a photon in the dielectric medium bounding the metal,, y a>/c this means that the SPP mode has a non-radiative or bound nature and cannot be excited by incident plane-wave light. In the context of photonics, light and SPP modes have to be coupled with different techniques (prism coupling, near-field excitation, diffraction grating...) [4,7,12,14]. 

---