KEYWORDS: Vertical cavity surface emitting lasers, Lithography, LIDAR, Oxides, Sensors, Defense technologies, Free space optics, Solid state lasers, Solid state electronics, High power lasers
The growing demand for cost effective LIDAR sensors in automobile and military applications in LIDAR and free space optics could be met by compact and solid state, high power 2D VCSEL arrays. In this type of an array hundreds or more high power VCSELs can be monolithically integrated. This greatly reduces the cost over separately packaged lasers. In addition, beam quality and spectral quality make high power VCSELs important laser sources for free space data links. In this talk we introduce a different type of high power VCSEL that uses an oxide-free, lithographic aperture. The aperture enables a very low effective index change to help prevent trapping of internal modes that can occur with oxide VCSELs. The zero index aperture was designed to remove the internal ring modes that oxide VCSELs have, resulting in a lasing pattern with low optical loss. The novel zero index aperture is placed near the cavity spacer to improve its effect on confinement and electrical injection, and yet minimizing internal guiding of the optical mode. The VCSELs using the new aperture have been tested for their pulsed power, pulse response, device efficiency and beam quality. Dense arrays show high beam quality and record narrow spectral emission. Measured results of multi and single transverse mode VCSELs arrays with dense packing are also reported.
This paper deals with a complex problem in scientific sensing and imaging. To overcome some inherent problems in the conventional ECG (Electrocardiogram), we investigate in depth an ‘unassisted’ approach which enables ECG measurement without the placement of sensing leads on the body. Specifically, it uses a bathtub at home with tap water in it and passive sensing leads placed on its inner surface – while the subject lies in it. In this investigation we use a widely accepted assumption that the electrical activity of the heart may be, largely, represented by a 3-D time-varying Current Dipole (3D-CD). To determine the sensing matrix responsible for transforming the 3D-CD into the potential distribution on the bathtub’s internal surface, the 3D-CD signals are applied to a bathtub-containing-ellipsoid model in COMSOL tool. The sensing matrix thereby estimated is then utilized to back reconstruct the 3D-CD signals from the bathtub leads signals. NRMSEs (Normalized Root-Mean-Squared Errors) on the order of 0.02 to 0.05 are observed. The approach is also successfully extended to the case of two ellipsoids, one inside the other, representing a pregnant female subject. Critically important from a practical standpoint, the paper examines sensitivity with respect to the locations of the two 3D-CDs in the bathtub, and reports the encouraging results. Images of the potential distribution in the composite volume in the bathtub are presented as well.
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