We report a light-dispersing device comprised of two transmission gratings and a wave plate. The gratings split the light incident at the Bragg angle into two orthogonally polarized components. The wave plate, which is placed between the gratings, functions as a polarization converter for oblique illumination. Appropriate assembly of these optical parts results in efficient diffraction of the unpolarized light with high spectral resolution. Using coupled-wave theories and Mueller matrix analysis, we constructed a device with a grating period of 400 nm for the spectral range of 680 ± 50 nm. We verified the proposed polarization-independent light-dispersing concept from the evaluation of this device.
We report a non-digitized diffractive beam splitter with a split count of 45, a 95% splitting efficiency, and a 0.90
splitting uniformity. The splitter was iteratively designed and was created on fused silica by laser writing lithography.
Antireflection coatings were added to the splitter to ensure high efficiency. This splitter was applied to the manufacture
of inkjet printer heads, in which silicon wafers were drilled with a 532-nm, nanosecond pulse laser with an average
output of 10 W and were wet-etched to produce microfluidic channels. We also discuss large beam arrays for process
throughput and subwavelength structures formed on the splitter for efficient laser power use.
We demonstrate the use of ultraviolet (UV) laser lithography in the production of subwavelength metal gratings. A laser writing system with a 413-nm Kr laser is used to write patterns on a resist-coated fused silica substrate mounted on a rotating table with a linear slider. One- and two-dimensional patterns are written in the resist at a selected sampling pitch or grating period, and the substrate is dry etched and coated with Au to obtain metallized gratings. Surface plasmon resonance dips, which appear in the reflectance spectra of the gratings, shift depending on the orientation of the incident polarization, because the gratings lack perfect symmetry owing to a system-induced skew in the writing beam. This dip shift can be considered tolerable when the gratings are used as a signal enhancer in Raman sensing applications. We conclude that UV laser writing based on polar coordinates is a candidate method for surface structuring on submicron scales. Devising a method to attain an unskewed beam will be the subject of future work.
We demonstrated the use of ultraviolet (UV) laser lithography in the production of subwavelength structures. A laser
writing system with a 413-nm Kr laser was used to write patterns on a resist-coated fused silica substrate mounted on a rotating table with a linear slider. One- and two-dimensional patterns were written on the resist at a fixed sampling
frequency, and then, the substrate was dry etched and coated with Au to obtain metallized gratings. Surface plasmon
resonance dips, which appeared in the reflectance spectra of the gratings, shifted for different orientations of the incident linear polarization. However, this dip shift can be considered tolerable for practical purposes, provided that the gratings that couple light with surface plasmons are used as a near-field enhancer. Hence, we concluded that UV laser writing based on polar coordinates is a candidate method for submicron-scale structuring.
Highly efficient diffractive beam splitters surface-structured on submicron scale are presented. Submicron relief
structures formed on the surfaces of a splitter work as an anti-reflective layer to improve the beam-splitting efficiency.
Surface structuring is conducted using deep-UV, liquid-immersion interference lithography and dry etching. Rigorously
designed structures with a period of 140 nm and a depth of 55 nm are lithographed onto fused-silica splitters. Splitting
efficiencies at 266 nm are increased by 8% to agree favorably with a theoretical value, while Fresnel reflections are
substantially reduced. Surface-structured beam splitters reported here are of great use in industrial machining
applications using high-power pulsed lasers.
We demonstrate a laser-based micro-bonding method for Vertical Cavity Surface Emitting Lasers (VCSELs) that enables
practically sufficient joint strength, while securing the output power before bonding. VCSELs have great potential for
optical interconnects because of their low threshold current and high-speed modulation capability. As for packaging of
VCSELs, flip-chip bonding (FCB), among others, has been investigated because it facilitates the coupling of laser
emission into fibers and waveguides. Conventional schemes for FCB, however, entail thermo-compressing stages and
therefore the thermal and mechanical stresses involved are prone to cause defects in the lasing media, leading to quality
defects. To overcome this problem, we have come up with a modified FCB method that can reduce such stress by
employing laser irradiation to efficiently heat joints minimizing heat-affected regions. A micro-bonding system used in
the experiments has an infrared fiber laser for heating, a diffractive beam splitter for parallel processing, a mounting head,
and a slider for precise alignment and translation. VCSEL pads are kept in contact with counter pads on a substrate with
AuSn solder placed between them. The split and focused beams by the element are guided to strike the joining points
through the substrate, heating and melting the solder to attain a tight joint.
In this study, a commercial BD (Blu-ray disc) and BD optics (blue laser and NA0.85) were used for multilevel recording. The goal is to double both the present capacity and data transfer rate. To achieve this, it is necessary to overcome severe inter-symbol interference (ISI) from outer cells at a small cell length. In order to suppress ISI, we have developed an advanced data detection method that uses CBDD (Cell Boundary Data Detection) and TCM (Trellis-Coded-Modulation), and have achieved an areal density of 34.6-Gbit/in2 multilevel recording.
As a means to accomplish high-throughput and damage-free processes, non-digitized diffractive beam splitters are effectual: they can afford to fully suppress undesired diffraction beams by containing as much light energy as possible
in a fan-out of beams meant for the process. The surface-relief structures of the splitters are designed using a Fourier-
iterative algorithm and are formed on high-quality fused silica substrates using direct laser writing and reactive ion
etching. For a 13-beam splitter, for example, a non-digitized element gives an efficiency of 97% with SN=38, whereas a
binary counterpart is as efficient as 78% with SN=5, where SN is defined as the ratio between the minimum of the fanout
beam intensities and the maximum of higher-order diffraction intensities. We have tested these two types of
elements in laser-cutting experiments and verified that the non-digitized element is far superior to the binary element.
We present a grating array illuminator that serves at two different wavelengths. The grating was designed by simulated annealing method and drawn in photoresist by direct laser lithography that we have developed on optical disk mastering technology. Upon grating reconstruction with two chosen wavelengths, 1064 and 532 nm, from Nd:YAG lasers, two arrays of 9 split beams with the same pitch were reconstructed. The illuminator performance was found rather sensitive to profile errors, which was supported by computer analysis.
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