Patent ID: 8238202

Claim:
A thermally assisted magnetic recording (TAMR) head comprising: (a) a light source that employs a power to generate light and transmit into a main waveguide and towards an air bearing surface (ABS) that is proximate to a magnetic medium thereby forming an ABS/media interface; (b) the main waveguide for transmitting light to a nearfield device, said main waveguide has a lengthwise dimension in a direction perpendicular to the ABS with one end at the ABS and a second end proximate to said light source; (c) the nearfield device that converts light from the waveguide into plasmon waves and delivers energy from the plasmon waves onto a localized region of said magnetic medium thereby heating said localized region and reducing its magnetic coercivity and anisotropy, said energy produces back reflected light as a result of an impedance change at the ABS/media interface, the back reflected light is captured by an end of the main waveguide at the ABS; (d) a first detection waveguide that captures a portion of back reflected light in the main waveguide, said first detection waveguide has an end facing away from the ABS and that is proximate to a photo detector and comprises: (1) a first section formed substantially parallel to the main waveguide and located a gap distance therefrom, said first section is recessed a certain distance from the ABS and has a first end facing the ABS, and a second end connected to a second section of the first detection waveguide; and (2) the second section that has a first end adjoining the second end of the first section and a second end that is formed a greater (separation) distance from the main waveguide than said gap distance; (e) the photo detector that receives back reflected light from the detection waveguide and performs a light intensity measurement to generate light intensity data; and (f) a controller that receives light intensity data from the photo detector, calculates a power adjustment, and sends a command regarding power adjustment to the light source to maintain a constant energy at the ABS/media interface during a TAMR write process.