Compact Optical Head Research Articles

Design and Testing of a Compact Optical Angle Sensor for Pitch Deviation Measurement of a Scale Grating with a Small Angle of Diffraction

The design and testing of different optical heads were performed to evaluate the pitch deviation of a diffraction scale grating with a small diffraction angle. Based on the proposed pitch deviation evaluation method employing optical angle sensors based on laser autocollimation, a modified optical head with position-sensitive detectors (PSDs) is first designed and constructed by following the conventional optical configuration. Owing to the small angle of diffraction of the first-order diffracted beams, the modified optical head has a large working distance, resulting in poor sensor stability. Therefore, a novel and compact optical head employing a pair of small prisms is designed and developed to shorten the working distance of the optical head. An additional modification was also made to the developed compact optical head in such a way that collimator objectives (COs) in the laser autocollimation units are removed to improve the sensor sensitivity. Experimental comparisons were conducted using the three types of optical heads to verify the feasibility of the developed optical angle sensor with PSDs.

Ghost Beam Suppression in Deep Frequency Modulation Interferometry for Compact On-Axis Optical Heads.

We present a compact optical head design for wide-range and low noise displacement sensing using deep frequency modulation interferometry (DFMI). The on-axis beam topology is realised in a quasi-monolithic component and relies on cube beamsplitters and beam transmission through perpendicular surfaces to keep angular alignment constant when operating in air or in a vacuum, which leads to the generation of ghost beams that can limit the phase readout linearity. We investigated the coupling of these beams into the non-linear phase readout scheme of DFMI and implemented adjustments of the phase estimation algorithm to reduce this effect. This was done through a combination of balanced detection and the inherent orthogonality of beat signals with different relative time-delays in deep frequency modulation interferometry, which is a unique feature not available for heterodyne, quadrature or homodyne interferometry.

Three-dimensional target monitoring technique based on a morphology correlation for high-power laser applications.

Existing monitoring and target positioning systems used in high-power laser fusion experiments have a complex structure and size, making their operation slow and calibration difficult. A simple and accurate positioning technique is proposed here that is based on cross-correlation between the morphology of the target measured at various positions. The morphology of the target is obtained using a spectral interferometer at a video frequency, and its three-dimensional (3D) position is determined by the position of the maximum spatial correlation coefficient. This technique can determine the 3D position and orientation of the target at the sub-micrometer range using only a single compact optical head. The proposed technique is quite simple in its structure and very convenient in operation. The feasibility and performance of the proposed technique is demonstrated in experiments.

A compact optical pickup head in blue wavelength with high horizontal stability for laser thermal lithography

A compact optical pickup head in blue wavelength with a single-axial actuator i.e. focusing, for laser thermal lithography was designed, fabricated, and tested. The numerical aperture of the objective lens was 0.85. The linear range of the focus error signal was 3 μm. A planar spring structure for improving the horizontal stability was designed and incorporated into the actuator. We applied a modified push-pull method together with a static Blu-ray re-writable disc to test the horizontal stability of the pickup head. We found that the in-plane jitter of the pickup head in two orthogonal directions were 0.34 nm and 1.59 nm, respectively. We demonstrated an example of applying the pickup head to write an inorganic photo-resist GeSbSnO film, and well-defined pattern was obtained with ~220 nm spot size.

A compact optical homing head adaptive to the approach conditions

This paper shows that, when an optical homing head (OHH) approaches a target, so that the radiation power that it receives and the angular size of the target's image greatly increase, it is necessary in the output signal of a rotating photodetector device (PDD) to encode appropriately the angular error of the OHH and a parameter that characterizes the radiation power received by the OHH, in order to ensure stable operation of the OHH with the adaptive automatic-gain-adjustment system traditionally used in such cases. Encoding in this case means that the variation of the radiation transmission in the PDD channel and accordingly of its output-signal parameters are organized as a function of the angular error either by choosing the PDD's topology or by varying the transmission of a mask at its input. It is shown that these codes can be varied during the approach, and that the signal-processing algorithms must vary in accordance with them.

The Design of an Integrated Pick-Up Head for High-Density Digital Versatile Disk, Digital Versatile Disk and Compact Disk

A novel design of triple-wavelength design for a compact optical pickup head is presented here. We propose the use of two rhomboid beam-splitter prisms for HD-DVD, DVD and CD devices to align signals with three different wavelengths on the same optical axis. The light is collimated by a collimating lens. The parallel beams are incident on the wavelength selector. The wavelength selector separates the wavelengths with different numerical apertures. The different wavelength signals are focused on the disc by an objective lens.

Coherent range-gated laser displacement metrology with compact optical head

We describe a new architecture for laser displacement metrology with a drastic reduction in the size and complexity of the optical head. Connected by a single optical fiber, the compact heads are easy to integrate and readily multiplexed to support applications requiring large numbers of sensors. The approach is made possible by modulating the outgoing laser light with a binary random noise code, allowing the detected signals to be discriminated based on their propagation delay. We demonstrate a displacement resolution of 1.1 nm rms.

Design of multiple-function long trace profiler

The long trace profiler (LTP) is a useful optical metrology instrument for measuring the figure and slope error of cylindrical aspheres commonly used as synchrotron radiation (SR) optics. A multiple-function LTP (LTP-MF) is developed at the optical metrology laboratories of Brookhaven National Laboratory (BNL) with a goal of increasing the accuracy of the measurement and extending the range of applications to other areas. Characteristics of the LTP-MF are a very compact and lightweight optical head, a large angular test range (±16 mrad), and high accuracy. The LTP-MF can be used in various configurations: as a laboratory-based LTP, as an in situ LTP or penta-prism LTP, as an angle monitor, as a portable LTP, and as a small-radius-of-curvature test instrument. The system configuration, designs of the compact optical head and slide, and analysis of different measurements modes and systematic error correction methods are introduced. Preliminary comparison measurements between the LTP-MF and the LTP-II are presented.

Toward terabyte two-photon 3D disk

253GB have been recorded in 300 layers inside the volume of one of our two-photon 3D disks. Each layer contains the equivalent of CD layer bit-densities recorded with a 0.5NA objective lens. A new 1.0NA lens with the desirable first order optical properties of long working distance and small diameter, 1.2mm and 4.5mm, and a self-compensating spherical aberration correction mechanism is designed, manufactured and integrated into our single beam two-photon 3D automated recording system. Experimental data obtained with the 1.0NA lens are presented. The resulting bit densities obtained with our new high-performance liquid immersion singlet (LIS) objective lens indicate that our system is capable of full disk recordings from 0.5 to 1 TB within a standard optical disk form factor of 120mm x 1.2mm thick utilizing our very stable and efficient materials. A compact optical head based on our new objective lens capable of TB storage is described.

Fiber‐optic acoustic transducer utilizing a dual‐core collimator combined with a reflective micromirror

AbstractA photonic acoustic transducer utilizing a dual‐core fiber collimator and a membrane type micromirror was proposed and demonstrated. The collimator and the mirror serve as a compact optical head and a reflective diaphragm, respectively. The micromirror diaphragm is suspended by a silicon bar connected to a frame, allowing for displacement induced by acoustic waves. The optical head incorporating dual collimators integrated in a single housing provides light to and receives it from the diaphragm. It facilitates the initial adjustment of the distance between it and the diaphragm, thanks to its slowly varying beam profiles. For the proposed acoustic transducer, the static characteristics were measured to find the operation point defined as the optimum distance between the head and the diaphragm, and a frequency response with a variation of ∼±5 dB was achieved for the range of up to 3 kHz. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1833–1836, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21789

Optical microphone based on a reflective micromirror diaphragm

AbstractAn optical microphone incorporating a reflective diaphragm and a fiber‐optic head is demonstrated. The diaphragm is made of a micromirror membrane which is suspended by a silicon bar connected to a frame, allowing for displacement induced by acoustic waves. A compact and simple optical head is implemented by exploiting a single multimode fiber. For the assembled microphone, the static characteristics are investigated in order to find the operation point, defined as the optimum distance between the head and the diaphragm, and a flat frequency response with a variation of ∼2 dB for the range of 0.1 to 2 kHz is accomplished. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 707–709, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21450.

Triple-wavelength optical pickup head designs for compact disk, digital versatile disk and high-density digital versatile disk devices

We present a triple-wavelength design for a compact optical pickup head which uses two rhomboid prisms in parallel with three laser diodes. The design can be used for compact disk, digital versatile disk and high-density digital versatile disk devices. The specific prism lens used decreases the geometrical size and reduces the total number of optical components. The trade-off between tolerance and fabrication is also presented.

Blu-ray Disc Pickup Head for Dual Layer

For dual-layer Blu-ray disc (BD) recording systems, the compensation of thickness differences is required. In addition the influence from the other layer should be considered. As a spherical compensation method, we have adopted a liquid crystal panel to fabricate a compact pickup head. Furthermore we have inserted a polarization diffractive optical element to reduce the influence from the other layer. In this paper, we report the readout test results of a dual-layer disc using a compact optical head.

High speed sub-micron bit detection using tapered aperture mounted optical slider flying above a patterned metal medium

Rapid advances in the development of the digital network society have necessitated both large capacity and higher data transfer rate for every type of digital storage equipment. Proximity optical recording based on the near-field interaction principle promises to provide breakthroughs in overcoming rigid optical diffraction limits and wave length shortening limits. We have previously presented a compact optical head assembly consisting of a combination of a pyramidal hole processed silicon slider and light-wave guide combined suspension. Attaining higher recording density requires both a much smaller sized aperture and a highly efficient laser power delivery mechanism. To satisfy these requirements, we have introduced a planar lens and tapered aperture processed optical slider, delivering laser power through a single mode optical fiber, and we have demonstrated sub-micron size (150–200 nm-long) bit signals at more than a 10 MHz frequency band.

Readout signal evaluation of optical flying head slider with visible light-wave guide flexure

The need for both higher recording density and faster transfer rates continues to propel the research and development of high-performance storage equipment. The optical first-surface recording method promises to overcome tough optical diffraction limits and/or wavelength-shortening limits. We have already proposed a novel compact optical head suspension assembly combining a flying optical slider with a resin-based flexible light-wave guide flexure, and we have confirmed this assembly's stable flying performance during head-arm out-of-plane disturbances. Following this technical progress, we here describe the successful detection of optical signals of sub-micron-size bits by flying this slider above a metal patterned medium through spacing of several tens of nanometers. Signal amplitude dependencies upon both bit pattern lengths and spacings are evaluated in detail, and it is predicted that sub-micron-long and -wide bit will be able to detect increasing the incident laser power up to its maximum value of several mW in our system.

Portable long trace profiler: Concept and solution

Since the early development of the penta-prism long trace profiler (LTP) and the in situ LTP, and following the completion of the first in situ distortion profile measurements at Sincrotrone Trieste (ELETTRA) in Italy in 1995, a concept was developed for a compact, portable LTP with the following characteristics: easily installed on synchrotron radiation beam lines, easily carried to different laboratories around the world for measurements and calibration, convenient for use in evaluating the LTP as an in-process tool in the optical workshop, and convenient for use in temporarily installation as required by other special applications. The initial design of a compact LTP optical head was made at ELETTRA in 1995. Since 1997 further efforts to reduce the optical head size and weight, and to improve measurement stability have been made at Brookhaven National Laboratory. This article introduces the following solutions and accomplishments for the portable LTP: (1) a new design for a compact and very stable optical head, (2) the use of a small detector connected to a laptop computer directly via an enhanced parallel port, and there is no extra frame grabber interface and control box, (3) a customized small mechanical slide that uses a compact motor with a connector-sized motor controller, and (4) the use of a laptop computer system. These solutions make the portable LTP able to be packed into two laptop-size cases: one for the computer and one for the rest of the system.

Printing System and Printing Characteristics of Laser Dye Thermal Transfer using a High-Power Laser

In laser dye transfer printing, the small laser spot provides high resolution, but the printing speed is relatively low compared to that of thermal head printing, in which a large number of dots can be recorded simultaneously. To shorten the printing time, a compact high-power Nd:YAG laser is used for the light source in our printing system. We have developed a practical laser dye transfer printing system with a newly developed Nd:YAG laser and compact optical head. Printing characteristics with a short pulse, of the order of 1 ms, are evaluated in this printing system. As a result, continuous-tone printing with a pulse of 2 μs is feasible when laser power is 1.0 W, indicating a significant advance in printing speeds. The transfer efficiency as a function of pulse width has a peak that can be observed. A thick ink layer produces aximum optical density, although a reduction in efficiency results from increasing the layer thickness. Good halftone printing is also performed using this system.

Mosaic laser velocimeter for large facilities

Detailed flow characterization and turbulence investigation in large facilities using laser velocimetry present several difficulties essentially due to the size of the optics to be installed, the limited optical access and the required window quality. The mosaic laser velocimeter is a new instrument: its compact and robust optical head is a probe introduced into the flow, but with a 467 mm working distance, so that negligible disturbances are induced at the probe volume level. The basic principle is the following: the image of the trajectory of a particle, crossing a 400 mu m probe volume illuminated by a focused argon laser beam, is made by a receiving optics on a mosaic of optical fibres, each fibre being linked to a photomultiplier; these fibres are arranged along two concentric circles: the external one is used for measurements, the internal one for validation purposes. Two velocity components, in the plane perpendicular to the receiving optics axis, are deduced from the recognition of the addresses of the lighted fibres and from the measured time interval between the pulses delivered by the corresponding detectors. The possibilities of this new instrument have been compared with those of a classical 3D laser velocimeter by making detailed measurements in the wake and in the boundary layer of an aerofoil in a 1.4 m by 1.8 m subsonic wind tunnel: the good agreement obtained with respect to the results of mean velocities and turbulence have brought a high degree of confidence for the future employment of the mosaic laser velocimeter in larger subsonic or transonic facilities.

Compact optical head using a holographic optical element for CD players

A small-size lightweight optical head using a holographic optical element (HOE) for optical disk systems has been developed. This optical head consists of only four optical elements. The HOE has the three optical functions required for an optical head: splitting the reflected beam; focusing error detection; and tracking error detection. A new optical configuration has been designed for this optical head to remove the influence of wavelength variation in the light source. The offset signal in the tracking error signal, which causes unstable operation, has been reduced by introduction of the holograms which are used only for detecting tracking error.

High density magneto-optical recording using 0.67 mu m band high power laser diode

High-density optical recording on a magnetooptical disk has been achieved by a compact optical head that uses a 0.67- mu m-band high-power visible-light laser diode. The recording density has been improved to 1.5 times that for conventional optical recording, using a 0.83- mu m laser diode, as a result of the increase in linear density and track density. The C/N ratio for the readout signal is greater than 50 dB. >