In an effort to increase areal density of magnetic storage media, it is desirable to reduce the volume of magnetic material used to store bits of information in magnetic storage media. Superparamagnetic instabilities become an issue as the grain volume is reduced. The superparamagnetic effect is most evident when the grain volume V is sufficiently small that the inequality KuV/kBT>70 can no longer be maintained. Ku is the material's magnetic anisotropy energy density, kB is Boltzmann's constant, and T is the absolute temperature. When this inequality is not satisfied, thermal energy demagnetizes the stored bits. Therefore, as the grain size is decreased in order to increase the areal density, a threshold is reached for a given material Ku and temperature T such that stable data storage is no longer feasible.
The thermal stability can be improved by employing a recording medium made of a material with a very high Ku. However, with the available materials current recording heads are not able to provide a sufficient or high enough magnetic writing field to write on such a medium. Accordingly, it has been proposed to overcome the recording head field limitations by employing thermal energy to heat a local area on the recording medium before or at about the time of applying the magnetic write field to the medium. By heating the medium, the Ku or the coercivity is reduced such that the magnetic write field is sufficient to write to the medium. Once the medium cools to ambient temperature, the medium has a sufficiently high value of coercivity to assure thermal stability of the recorded information.
Heat assisted magnetic recording allows for the use of small grain media, which is desirable for recording at increased areal densities, with a larger magnetic anisotropy at room temperature to assure sufficient thermal stability. Heat assisted magnetic recording can be applied to any type of magnetic storage media, including tilted media, longitudinal media, perpendicular media and patterned media.
For heat assisted magnetic recording, an electromagnetic wave of, for example, visible, infrared or ultraviolet light can be directed onto a surface of a data storage medium to raise the temperature of the localized area of the medium to facilitate switching of the magnetization of the area. Well-known solid immersion lenses (SILs) have been proposed for use in reducing the size of a spot on the medium that is subjected to the electromagnetic radiation. In addition, solid immersion mirrors (SIMS) have been proposed to reduce the spot size. SILs and SIMs may be either three-dimensional or two-dimensional. In the latter case they correspond to mode index lenses or mirrors in planar waveguides. A metal pin can be inserted at the focus of a SIM to guide a confined beam of light out of the SIM to the surface of the recording medium. Commonly assigned U.S. Pat. No. 6,795,630, which is hereby incorporated by reference, discloses several waveguides having a metallic pin transducer for concentrating optical energy into a small spot.
Data storage systems often incorporate optical components to assist in the recording of information. Such systems may include, for example, optical recording systems, magneto-optical recording systems or other thermal or heat assisted type recording systems, as described herein. An important aspect of such systems utilizing optical components may include the ability to generate small and intense optical spots of energy. The optical spots can be used for various functions in the recording process, such as aiding in the reading or writing of bits of information.
Prior to generating the small and intense optical spots of energy, it is usually necessary to couple an electromagnetic wave from an energy source into a desired optical condenser, such as a waveguide. One known structure for coupling the electromagnetic wave into the optical condenser is a diffraction grating. Diffraction gratings are generally known components in an optical system that mutually enhance the effects of diffraction to concentrate the diffracted electromagnetic wave in specific directions determined by the spacing of the lines and by the wavelength of the electromagnetic wave.
There is an increased emphasis on improving the areal densities of data storage systems. Thus, all components of a data storage system are being improved to achieve higher areal densities. For example, those systems that incorporate optical components to assist in the recording of information are in need of the ability to efficiently generate even smaller and more intense optical spots of energy to support the data storage systems of the future.
Accordingly, there is identified a need for improved devices that overcome limitations, disadvantages, and/or shortcomings of known devices for coupling electromagnetic waves and generating smaller and intense optical spots of energy.