Holographic gratings with asymmetric structure are widely used to couple light into and out of waveguides due to
their high diffraction efficiencies and planar packaging. In this paper, a holographic grating coupler based on the
photopolymer has been designed and experimentally demonstrated at wavelength of 405nm. To achieve the high
diffraction efficiencies in the structure, we investigated the optical properties of the coupler according to the
exposure energy at the 405nm wavelength. In the holographic recording for the asymmetrical geometry, we
researched the optical characteristics of the Dupont photopolymer HRF150-38 as the correction of the Bragg angles
shift because of shrinkage factor and the diffraction efficiency. The performance and the optical characteristics of
the coupler using volume holographic grating will discussed in detail.
In this paper, we design a subwavelength binary grating working as a diffractive polarizing beamsplitter. The polarizing beamsplitter is then optimized by using a genetic algorithm to increase its extinction ratios up to as high as 238 and 82. We use the rigorous coupled-wave analysis method to calculate the parameters of the beamsplitter during the optimizing process.
Holographic transmission gratings with 0o;-Bragg angle are widely used to couple light into and out of waveguides due to their high diffraction efficiencies and planar packaging. In this paper, a holographic grating coupler based on the photopolymer has been designed and experimentally demonstrated. To achieve the high diffraction efficiencies, we investigate the optical properties of the coupler according to the exposure energy at the 405 nm wavelength. For the asymmetrical geometry with 72othe correction of the Bragg angles shift of about 0.95o; and 3.45o;, which are induced by the 7.86% shrinkage factor, is successfully demonstrated. The performance and the optical characteristics of the coupler using volume holographic grating are discussed in detail.
The small form factor optical data storage devices are developing rapidly nowadays. Since it is designed for portable and compatibility with flesh memory, its components such as disk, head, focusing actuator, and spindle motor should be assembled within 5 mm. The thickness of focusing actuator is within 2 mm and the total working range is +/-100um, with the resolution of less than 1μm. Since the thickness is limited tightly, it is hard to place the yoke that closes the magnetic circuit and hard to make strong flux density without yoke. Therefore, Halbach array is adopted to increase the magnetic flux of one side without yoke. The proposed Halbach array type focusing actuator has the advantage of thin actuation structure with sacrificing less flex density than conventional magnetic array.
The optical head unit is moved on the swing arm type tracking actuator. Focusing coil is attached to swing arm, and Halbach magnet array is positioned at the bottom of deck along the tracking line, and focusing actuator exerts force by the Fleming's left hand rule. The dynamics, working range, control resolution of focusing actuator are analyzed and performed.
A new structure of polarization-selective elements consisting of two holographic gratings and a dove prism coupler is proposed. The absence of a multi-stage wave-guide, compact size, and lightweight volume are the outstanding features of the new structure. Based on the coupled-wave theory, the analysis and design of the structure are discussed in detail to calculate the required index modulation. Several parameters such as the recording intensity, the exposure time, and the recording angles for the fabrication of the proposed element are determined. Under the conditions the element is fabricated in Dupont photopolymer HRF-150-38 material and with the operating wavelength of 532nm. A simplified pick-up head is constructed to evaluate the performance of the fabricated element.
A polymer focusing waveguide grating coupler(FGC) was implemented by UV nanoimprinting method. The size of this focusing grating is 1 mm X 1 mm and the total device size is 8 mm X 2 mm. We use the UV sensible polymer which is coated by spin coating method. After nanoimprinting the device, the residual thickness on the slab waveguide is about 10 nm ~ 30 nm. The spot size of this polymer FGC is 347 nm for blue laser and the coupling efficiency is 28.2%.
A focusing grating coupler (FGC) using a blue laser of a wavelength of 400 nm as a light source was fabricated for the first time. The FGC was designed to have a numerical aperture of 0.48 and a focusing angle of zero. The focal length and the grating area were 900 μm and 1×1mm2, respectively. Grating pattern of a minimum period of 0.2μm was fabricated on a single mode waveguide based on the boron phosphor silicate glass (BPSG) material by electron-beam lithography process using the vector scan method. The spot size at the full width (1/e2) was measured at 0.85 and 0.92μM in x and y direction, respectively, and these values are nearly same as the diffraction limited size.
A micro-optical pickup has been implemented by using a focusing waveguide grating coupler. The grating coupler was designed and fabricated on a single mode BPSG (boron phosphor silica glass) waveguide layer. The coupling area was 1×1mm2 containing more than 1,500 grating lines, where the maximum and minimum grating pitch were 296nm and 811nm, respectively. The focal length and the numerical aperture of the present grating coupler were 530 μm and 0.68 with 632.8nm He-Ne red laser. The full width half maximum diameter of the focal spot was measured to be 450 nm and 510 nm in x and y direction.