Prism coupling

The most common approach to excitation of surface plasmons is by means of a prism coupler and the attenuated total reflection method (ATR). There are two configurations of the ATR method - Kretschmann geometry [5] and 

Otto geometry [4], In the Kretschmann geometry of the ATR method, a high refractive index prism with refractive index p is interfaced with a metal-dielectric waveguide consisting of a thin metal film with permittivity Sm and thickness q, and a semi-infinite dielectric with a refractive index n n rip). Fig. 21. 

3 = Re 0 = Re-In terms of effective index, this coupling condition can be written as follows  

The attenuated total reflection method can be also used to excite coupled surface plasmons on thin metal films. The couphng of a hght into a symmetric or antisymmetric surface plasmon supported by a thin film (Sect. 2.2) can be in principle achieved in a geometry similar to the Otto geometry (Fig. 23) in which the semi-infinite metal is replaced by a thin metal film [20]. 

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Fig. 5.2 Hemispherical prism coupling scheme. The microsphere is in a V groove channel for the solvent and analyte. Left, polar view showing input and output coupling. Right, equatorial view illustrating how precessed light is collected at the drop port. Reprinted from Ref. 3 with permission 2008 Optical Society of America...

Advantages of Prism-Coupled Microtube-Based Sensors... 

The sensitivity of a prism-coupled microtube resonator can be evaluated by employing the Mie theory70. For this calculation, the optical field in air is modified as ... 

Ling, T. Guo, L. J., A unique resonance mode observed in a prism coupled micro tube resonator sensor with superior index sensitivity, Opt. Exp. 2007, 15, 17427 17432... 

Fig. 9.10 The calculated angular reflection spectra for an SPR sensor with and without a 2 nm thick film on the gold surface. The assumed film index is n 1.5. The diagram at right shows the schematic prism coupling geometry for measuring the SPR reflectivity angle dependence...

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 mode coupling condition for prism coupling (Fig. 15.4a) is similar to the grating condition. For prism coupling the prism often constitute the substrate of the waveguide structure, or the RI of the prism and that of the substrate is matched, and thus the mode s effective index can be calculated from... 

The prism and shde may be optically coupled with glycerol, cyclohexanol, or microscope immersion oil, among other liquids. Immersion oil has a higher refractive index (thereby avoiding possible TIR at the prism/coupling liquid interface at low incidence angles), but it tends to be more autofluorescent (even the extremely low fluorescence types). 

Pan, Y.-L. and Chang, R.K., 2003, Highly efficient prism coupling to whispering gallery modes of a square p cavity, Appl. Phys. Lett. 82(4) 487-489. 

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.

The experiment of phase matched SHG had been carried out by taking off one substrate and putting a coupling prism on the wave guide with lateral translation of the system for thickness adjustment of the waveguide. The MNA film is unbearably weak for repetitive prism coupling and physically weak in ambient atmosphere. 

The experimental value reported for PDN6S in Table V is very preliminary and is based on only three experimental points derived from prism-coupled waveguide reflectivity measurements. At this point, spurious effects due to heating, photoinduced birefringence etc. can not be conclusively ruled out. This preliminary data is presented only to provide a comparison with the calculated value. 

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. 

Fig. 3 Schematic illustrating methods of coupling incident light into the waveguide, (a) Simple end firing, (b) Prism coupling, typically requires the presence of index matching fluid, (c) Grating coupling...

Fig. 8 Light coupling methods into waveguides, (a) Grating coupling, (b) prism coupling, (c) front-face coupling via optical lens (d) front-face coupling via optical fiber...

Fig. 7 Optical waveguide-coupling methods, (a) end-firing focused beam and end-firing optical fiber (b) prism coupling (c) grating coupling...

The studies described in Sects. 4.1 and 4.2 were performed with monochromatic laser sources. To provide the information content of broadband spectroscopy, Bradshaw et al. [3] extended the prism coupling approach of broad angular width... 

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