Prism coupler
Invention of the coupler contributed to the initiation of a field of study known as integrated optics.
Starting in 1969, Shubert, Harris, and Polky at the University of Washington,[2][3][4] and, independently, Tien, Ulrich, and Martin, at Bell Laboratories[5][6][7] described the first experiments with prism coupling and its underlying theory.
[8][9] A prism coupler is used to couple the power from an incident laser beam into a thin film.
The refractive index of the film is made greater than that of the glass slide, the film can serve as a dielectric planar waveguide for light via total internal reflection off the film–glass interface (and film–air interface).
The prism coupler consists of a near cube of high–refractive-index glass and a second thin film at the bottom that contacts the waveguide film and serves the function of partially containing the guided wave over the coupling distance.
The thickness of the tunneling layer will be on the order of a fraction of a wavelength (tens to hundreds of nanometers for visible light).
In the reciprocal problem, a waveguide mode in the film (travelling to the left in the first figure) is incident on the prism coupler.
Efficient coupling of light into the film occurs when the incident beam (arriving from the left shown in the first figure), evaluated at the bottom face of the prism, has the same shape as the radiated beam in the reciprocal problem.
When the power in both the incident beam and the reciprocal waveguide mode is normalized, the fractional coupling amplitude is expressed as an integral over the product of the incident wave and the radiated reciprocal field.
From such an integral we deduce three key features: Suppressing the transverse part of the representation for the fields, and taking x as direction to the left in Fig.
1, the waveguide mode in the reciprocal problem takes the monotonically decreasing form where α(x) is the attenuation rate and
The associated transverse field at the bottom of the prism takes the form with A a normalization constant.
Adjusting α(x) permits the coupling to approach unity, barring significant geometry-dependent diffractive effects.
The Goos-Hänchen shift describes the displacement of the center point of an optical beam when it undergoes total reflection from the interface between two semi-infinite regions of different refractive index.
If the reflection of a beam from a sandwich structure that consists of a semi-infinite prism, a tunneling layer, a waveguide film layer, and a semi-infinite glass slide is investigated, the shift will be found to be much larger as a consequence of the excitation of the guided wave.
Prism couplers are instruments used to measure the refractive index/birefringence and thickness of dielectric and polymer films.
However, at certain values of the incident angle theta, the beam does not reflect back out, but instead is transmitted through the base into the film sample.
A phase matching condition is required between the propagation constant of the mth mode in the waveguide
