It is now well understood that any inhomogeneity in an otherwise homogeneous medium can cause at least a partial reflection of any energy passing therethrough. For example, when light encounters an interface between two different dielectrics, a partial (or, in some cases, total) reflection occurs, the magnitude of which depends on the physical parameters of the dielectrics. A common measure of the expected reflection intensity at an interface is the reflection coefficient, which is the ratio of the intensity of the reflected light to that of the incident light. For nonmagnetic media, reflectivity depends on the polarization of the incident light, the angle of incidence, the dielectric constants of the media, and also the wavelength of the incident light, since the optical properties may depend on the wavelength (referred to as dispersion).
Although occasionally it is desirable to enhance the reflectivity at an interface, it is more common to seek to reduce it. The air-glass interface provides one common example of a scenario where a reduction in reflectivity is often sought. As an example, it is often a must for optical instrumentation to suppress reflection at the many interfaces of the optical components in order to increase the light throughput.
The λ/4 technique for reducing reflectivity at an interface is a well-known one. In brief, in order to reduce reflectivity at an interface for light at wavelength λ, a thin film of thickness λ/4 is introduced between the two media. The refractive index of the thin film is typically chosen to be intermediate between that of the medium of incidence and that of the substrate. The physical principle that enables the operation of a λ/4 plate is the fact that waves reflected back in the medium of incidence from the two interfaces cancel each other in a destructive interference. Clearly, for a given polarization and angle of incidence, this approach will only be optimal for a single wavelength. Thus, perturbing any of the foregoing parameters will tend to reduce the amount of destructive interference, thereby resulting in greater reflection at the interface.
Generally speaking, antireflection coatings today suffer from limited bandwidths as well as very restricted range of angles of incidence for satisfactory operation. The limited wavelength range and angle range of existing films render them unsuitable for disparate applications eliminating the off-the-shelf, immediate delivery of such components.
Therefore what is needed is a system and method for addressing the above and related issues.
Before proceeding to the description of the present invention, however, it should be noted and remembered that the description of the invention which follows, together with the accompanying drawings, should not be considered as limiting the invention to the examples (or preferred embodiments) shown and described. This is so because those skilled in the art to which the invention pertains will be able to devise other forms of the invention within the ambit of the appended claims.
USPTO Backgrounds
USPTO Backgrounds