Heat assisted magnetic recording (HAMR) generally refers to the concept of locally heating a recording media to reduce the coercivity of the media so that an applied magnetic writing field can more easily direct the magnetization of the media during the temporary magnetic softening of the media caused by the heat source.  The heated area in the storage layer determines the data bit dimension.  A tightly confined, high power laser light spot is used to heat a portion of the recording media to substantially reduce the coercivity of the heated portion.  Then the heated portion is subjected to a magnetic field that sets the direction of magnetization of the heated portion.  In this manner the coercivity of the media at ambient temperature can be much higher than the coercivity during recording, thereby enabling stability of the recorded bits at much higher storage densities and with much smaller bit cells. 
One way to achieve a small confined hot spot is to use an optical near-field transducer (NFT), such as a plasmonic optical antenna or a metallic aperture, integrated in an optical waveguide of high refractive index contrast.  Light propagating in the waveguide is focused by an optical focusing element, such as a planar solid immersion mirror onto the near-field transducer.  One example uses a planar solid immersion mirror (PSIM), or lens, fabricated in a planar waveguide; and a near-field transducer in the form of an isolated metallic nanostructure, placed near the PSIM focus.  The near-field transducer is designed to reach a local surface plasmon (LSP) condition at a designated light wavelength.  At LSP, a high field surrounding the near-field transducer appears, due to collective oscillation of electrons in the metal.  Part of the field will tunnel into an adjacent media and get absorbed, raising the temperature of the media locally for recording. 
It is desirable to launch light into the waveguide with a low cost apparatus, having good alignment tolerances and high light delivery efficiency.