Condenser-Transducer Configuration for Improving Radiation Efficiency of Near-Field Optical Transducers
- PDF / 220,220 Bytes
- 9 Pages / 612 x 792 pts (letter) Page_size
- 35 Downloads / 144 Views
J3.8.1
Condenser-Transducer Configuration for Improving Radiation Efficiency of Near-Field Optical Transducers Kursat Sendur, Chubing Peng, and William Challener Seagate Technology Research Center 1251 Waterfront Place Pittsburgh, PA 15222, U.S.A. ABSTRACT Near-field radiation efficiency of the ridge waveguide transducer is investigated in the vicinity of a recording magnetic medium. Near-field radiation from a ridge waveguide transducer is expressed in terms of power density quantities. This allows us to quantify the near-field radiation efficiency from the near-field transducer with respect to the input optical power. Finite element method (FEM), which is capable of modeling focused beams, is used to simulate various geometries involving ridge waveguides. The incident electric field near the focal region is determined using a Gaussian beam expression and Richards-Wolf vector field equations for low NA and high NA beams, respectively. First, the ridge waveguide transducer is placed at the focal point of an optical lens system. The maximum value of the absorbed optical power in the recording medium is 1.6*10-4 mW/nm3 for a 100 mW input optical power. Finally, the ridge waveguide is placed adjacent to a solid immersion lens but separated by a low-index dielectric layer. For this case, the maximum value of the absorbed optical power in the recording medium is 7.5*10-4 mW/nm3 for a 100 mW input optical power. The improvement in the transmission efficiency is a result of two factors: 1. Increased incident electric field over the transducer surface due to increased NA of the optical system, 2. Surface plasmon enhancement obtained by placing a low-index dielectric material between the solid immersion lens and ridge waveguide.
INTRODUCTION There has been an increasing interest for generating intense optical spots smaller than the diffraction limit of an objective lens [1-5]. In addition to near-field imaging [1], intense subwavelength optical spots have potential applications in lithography and bio-chemical sensing. Near-field techniques that enhance localized surface plasmons are potential candidates to obtain intense optical spots beyond the diffraction limit for optical data storage. The magnetic storage industry is also interested in sub-wavelength optical spots for heat assisted magnetic recording [6] to overcome the superparamagnetic limit [7], which bounds the areal density of the conventional magnetic recording techniques. Areal density growth has been achieved by continuous downscaling of the bit dimensions. However, the magnetic data storage industry is observing a slowdown in the rate of the areal density growth. Perpendicular recording technology provides several advantages [8-9] over the currently employed longitudinal recording technology, and it could extend the areal density limit of longitudinal recording to 1 Tb/in2 [10-11]. A recording density of 1 Tb/in2 requires a recorded mark size of 25 nm. For this density the grain size in the recording medium must be less than 5 nm to obtain a sufficient signal-
Data Loading...
