Marcus B. Mooney

Novel droplet near-field transducer for heat-assisted magnetic recording

Abstract Two main ingredients of plasmonics are surface plasmon polaritons (SPP) and localized surface plasmon resonances (LSPR) as they provide a high degree of concentration of electromagnetic fields in the vicinity of metal surfaces, which is well beyond that allowed by the diffraction limit of optics. Those properties have been used in the new technique of heat assisted magnetic recording (HAMR) to overcome an existing limit of conventional magnetic recording by utilizing a near-field transducer (NFT). The NFT designs are based on excitation of surface plasmons on a metal structure, which re-radiate with a subdiffraction limited light spot confined in the near field. In this paper, we propose a novel “droplet”-shaped NFT, which takes full advantage of a recenltly proposed Mach–Zehnder Interferometer (MZI), a coupling arrangement that allows optimal coupling of light to the transducer. The droplet design ensures better impedance match with the recording media and, consequently, better coupling of power. The droplet design results in very high enhancement of the electric field and allows the confinement of light in a spot size much smaller than the present stateof- the-art lollipop transducer.

Performance of U-Pole Writers With Straighter Field Contours

Curvature of transitions recorded onto a magnetic disc has become more pronounced as tracks narrow. Curvature creates interference between adjacent transitions recorded at high bit density, and broadens the read back signal pulse. Curved transitions have a shape similar to that of the field contours that write them. A concave write pole trailing surface, or “U-pole”, pushes the field contours near the pole edges farther down track. This straightens the contours by partially compensating for transition curvature. We used a track trimming technique to compare transition curvature of flat poles and U-poles, and verified that the U-pole reduced curvature by more than 30%. We also demonstrated that the more curved transitions written by flat poles generate ~ 1 nm more pulse broadening at the track edge relative to those written by U-poles. However, modeling predicts a ~ 10% loss in down track field gradient near the center of a U-pole. Measurements of bit error rate across the track confirm the corresponding loss in U-pole performance relative to a flat pole over all but the outer portions of a track.

AlGaAs ridge laser with 33% wall-plug efficiency at 100 °C based on a design of experiments approach

Upcoming applications for semiconductor lasers present limited thermal dissipation routes demanding the highest efficiency devices at high operating temperatures. This paper reports on a comprehensive design of experiment optimisation for the epitaxial layer structure of AlGaAs based 840 nm lasers for operation at high temperature (100 °C) using Technology Computer-Aided Design software. The waveguide thickness, Al content, doping level, and quantum well thickness were optimised. The resultant design was grown and the fabricated ridge waveguides were optimised for carrier injection and, at 100 °C, the lasers achieve a total power output of 28 mW at a current of 50 mA, a total slope efficiency 0.82 W A−1 with a corresponding wall-plug efficiency of 33%.

Wheatstone bridge configuration for evaluation of plasmonic energy transfer

We propose an internal (on-chip) Wheatstone bridge configuration to evaluate the efficiency of near-field transducers (NFT) as used in heat-assisted magnetic recording (HAMR). The electric field enhancement between the transducer and the image plane is monitored by measuring the resistance of metal electrodes composing the image plane. The absorption of the enhanced electric field causes an increase in the metal temperature, and thereby, in its resistance whose variation is monitored with an internal Wheatstone bridge which is accurately balanced in the absence of the electric field.

Novel Mach–Zehnder Interferometer Waveguide Design as a Light Delivery System for Heat-Assisted Magnetic Recording

We propose a light delivery system to the near-field transducer (NFT) of a heat-assisted magnetic recording (HAMR) head using a Mach-Zehnder interferometer (MZI) waveguide arrangement with a transverse electric (TE) mode coupled to the planar waveguide from a single mode fiber. The proposed design offers great flexibility in the coupling of light to the NFT in order to match the desired radiation pattern of the antenna and thus to optimize the energy transfer. Furthermore, it allows excitation of particular surface plasmon (SP) resonances of the transducer (quadrupole or higher) by controlling the coupling angle and the phase of the two beams of light. The optimum phase shift between the TE waveguide modes incident on the NFT can be achieved either statically by making one of the MZI arms longer/shorter compared with the other one, or dynamically by changing the mode effective index of the MZI waveguide arm through electro-optic or thermo-optic modulation. In addition, the proposed MZI waveguide arrangement enables easier coupling from a laser with coupling losses from laser to MZI waveguide being below 3 dB and the design enables an arrangement of the NFT placed either on the top of the waveguide at the termination side of the MZI or between the rib and the ridge at the maximum of the electric field of the waveguide, which maximizes the SP resonance enhancement of the NFT. Another advantage is that the magnetic-write pole, in our design, can be easily integrated on the same chip, preferably above the center of the MZI, between the two arms of the interferometer and away from the propagating mode, thus avoiding blocking of the light path.

Super-oscillatory optical needle for heat assisted magnetic recording

We demonstrate an alternative to plasmonic focusing, a super-oscillatory focusing lens capable of producing a 51nm spot for optical heating in heat assisted magnetic recording using a diode laser operating at 473 nm wavelength.