Binary Optics Research Articles

The even device fabricated by the deep etched binary optics technology for the exposure system of the quasi-molecule laser

By applying the specific properties and the fabricating technology of the deep etched elements presented by us, the even device of deep etched binary optics has been designed and fabricated which can be used in quasi-molecule laser exposure system. This even device is light in weight, easy to adjust and has a high utilization rate of energy and is able to project well-distributed light beams. So it is better than the conventional one which was an array made up of quartz sticks. The properties and designed parameters were studied and simulated. The fabricated even was precisely tested by high precision Alpha-Steper. The testing result of the surface relief structures of the even has been profoundly analyzed by introducing “boundary errors”. The theory agrees well with the results of the experiment. This is the first successful application of the deep etched theory and technology of binary optics to the exposure system of microfabrication.

Monolithic Integration of Diffractive Microlens Arrays and Infrared Focal Plane Arrays

Monolithic integration method has been demonstrated to increase the fill factor of the infrared focal plane arrays (IRFPA). Which is consists of 256×256 Pt-Si schottky barrier charge coupled devices(CCD) operation in 3-5μm IR region. The relative silicon 256×256 element diffractive microlens arrays have been fabricated on the back side of the substrate of the IRFPA using binary optics technology. The aligning process between IRFPA and microlens arrays on each side of the substrate has been completed by IR mask aligner. The testing results show that the imaging quality is very good and the average optical response of the IR FPA is increased by a factor of 3.0, which is improved by about 25% compared with the hybrid integration method in the previous work.

Analysis of Near-Field Intensity Distributions of High-Compression Talbot Array Illuminators Using Rigorous Diffraction Theory

The technology nowadays employed in the field of binary optics allows a relatively easy fabrication of grating structures down to the wavelength region. The analysis of light propagation through such grating structures requires the use of rigorous diffraction theories such as the rigorous coupled-wave analysis (RCWA), in order to take proper account of polarization effects in the electric and magnetic field and the thickness of the grating. In this paper, we examine the near-field intensity distributions and associated illumination efficiencies of Talbot array illuminators (TAIL#x0027;s) with compression ratios of 8 and 16 using RCWA. The high illumination efficiency observed close to the grating surface is expected to bring about new applications of TAIL#x0027;s in the field of super-resolution and near-field optics.

Exposure characteristics and three-dimensional profiling of SU8C resist using electron beam lithography

The properties of a new type of chemically amplified resist, SU8C, are evaluated for electron beam lithography. This resist is a modification of the ultraviolet sensitive negative epoxy SU8. Experimental results show that the sensitivity of SU8C is one of the highest among the different kinds of commercially available resists. At 50 keV energy exposure, the saturation dosage of SU8C is ∼3.8 μC/cm2 while that of PMMA is ∼500 μC/cm2. This implies that SU8C resist is suitable for large area exposure. The contrast γ can also be adjusted to near unity by adjusting the postannealing time, and this is essential for multilevel profiling. 16 level steps have been exposed in one electron beam exposure by changing the clock frequency in sequence, and a vertical profile resolution of 20 nm has been achieved. Lines as narrow as 100 nm have been produced, showing that the resist has high resolution down to the nanoscale. Hardness measurements have also been carried out, and SU8C is an order of magnitude harder than epoxy and PMMA. SU8C resist has high refractive index, high resolution, high sensitivity, and large hardness, making it suitable for microscale binary optics fabrication. To demonstrate the suitability of SU8C resist in microscale optical device fabrication, an array of Fresnel lenses has been designed and demonstrated.

Hybrid Integration Between Long Focus Microlens Array and IR Detector Array

A special method, named step simulation method, is proposed for fabricating Si microlens array to improve the performance of infrared focal plane array (IR FPA). The focus length of rectangle-based multistep microlens array with element dimension of 40 µm×30 µm is 885.4 µm by the method, which is much longer than the focus length of microlens array fabricated by conventional Fresnel binary optics technique., The large-scale 256×256 element microlens array is hybridintegrated with the PtSi Schottky-barrier IR FPA by optical adhesive. The test results show that diffractive spot size of the microlens is 17 µm×15 µm and the average optical response of the IR FPA is increased by a factor of 2.4.

High transverse mode discrimination in apertured resonators using diffractive binary optics

We demonstrate theoretically that the discrimination between TEM 00 and TEM 01 modes achieved by a hard apertured resonator is greatly enhanced by the insertion of a simple binary diffractive optic inside the resonator. The latter, known as π/2 plate, introduces a constant phase shift in the central region of the beam.

Electromagnetic effects for the resonance-domain IR diffractive optics

Binary optics technology enables the manufacture of arrays of diffractive micro-optical elements which are used in many optoelectronic devices, e.g. the focal plane collection optics. The first-order diffraction grating efficiency decreases in the best part of the resonance-domain region of diffraction, i.e. when the grating period is close to the optical wavelength in the substrate material. A large fraction of the fast binary lens surface relief is built of staircase annular structures whose width is of wavelength scale. Therefore, the rigorous electromagnetic theory of gratings has been applied in this paper to calculate and analyze the diffraction effects for the resonance-domain longwave (8–12 μm) infrared (LWIR) binary optics. It is shown that electromagnetic effects limit the speed of the LWIR first-order diffractive lenses and the optical gain achievable with the diffractive lenses used as the focal plane collection optics in the IR detection systems.

Analytic approach for optimal quantization of diffractive optical elements

One of the most important factors that limit the performance of diffractive optical elements (DOE's) is the depth accuracy of the relief structure. A common procedure for fabricating DOE's is the binary optics procedure, in which binary masks are used for the fabrication of a multilevel relief structure. Here an analytic procedure for calculating the optimal depth levels of DOE's, the phase bias, and the decision levels is presented. This approach is based on the minimization of the mean-squared error caused by the quantization of the continuous profile. As a result of the minimization an optimal value for the etching depth of each photolithographic mask is determined. The obtained depth values are, in general, different from the depth values used by the conventional multilevel approach. Comprehensive mathematical analysis is given, followed by several computer simulations that demonstrate the advantages of the proposed procedure.

Binary optics and confocal imaging

The use of two-level phase masks or spatial light modulators in confocal imaging systems is considered. It is shown how, although such masks can modify or correct the effective point-spread function of a system, their behavior for planar objects may not be as desired as a result of phase-wrapping effects. Overcoming this problem with a multilevel mask or a pair of two-level masks is discussed.

Complex acoustic waveforms excited with multiple picosecond transient gratings formed using specially designed phase-only beam-shaping optics

This paper describes a method for using a pulsed laser and specialized low cost beam-shaping optics to launch complex acoustic waveforms with user-definable geometries; diffraction of a continuous wave probe laser from these waveforms reveals their temporal evolution in real time. Methods are introduced for designing and fabricating simple binary phase optics for beam-shaping that is useful for high-frequency measurements on thin films. Experiments on films of platinum on silicon demonstrate the approach.

Design of widely tunable semiconductor lasers and the concept of binary superimposed gratings (BSG's)

We propose a new concept of binary superimposed gratings (BSG's) as multiwavelength grating reflectors and show it as an effective structural improvement over the existing designs, to both the fabrication process and device performance. We also present a study of key design issues for widely tunable lasers based on grating mirrors with a comb-like reflection spectrum and summarize simple design rules for the grating part of the laser, based on analytical and numerical analysis. The binary supergrating consists of elements of equal size whose refractive index is allowed to be one of two possible values, which are sequenced according to a binary optics formalism to effect a spatial superposition of multiple sets of single-frequency gratings, and its implementation is well within the standard e-beam lithography limits. The calculations of lasing frequency, mode, and side-mode suppression ratio of the tunable laser are formulated and presented along with numerical examples.

Binary-optic smoothing with isotropic etching

Binary optics are an important part of modern optics, but they have some inherent problems because of their binary nature. The optics cannot achieve maximum efficiency unless the rms surface error can be reduced. A technique for smoothing jagged surfaces by use of isotropic etching is presented. We show that etching smoothes the binary nature and improves the optical efficiency.

Micro-optic integration with focal plane arrays

The large detector size of conventional focal plane arrays (FPAs) often acts as a limiting source of noise currents and requires these devices to run at undesirably low temperatures. To reduce the detector size without reducing the detector’s quantum efficiency (QE), we have developed efficient on-focal-plane collection optics consisting of arrays of thin-film binary-optics microlenses and photoresist-based refractive microlenses on the back surface of hybrid detector array structures. Photodiodes of p/n polarity, of an unusual planar-mesa geometry, were fabricated in epitaxial HgCdTe deposited by molecular beam epitaxy (MBE) on the front side of a CdZnTe substrate. Diffractive (8- to 16-phase-level) Ge microlenses were deposited on 48-µm centers in a registered fashion (using an IR mask aligner and appropriate marks on the front surface of the CdZnTe) on the back side of the substrate using a lifting process. The lifting circumvents some of the process limitations of the more conventional chemical etching methods on diffractivemicrolens processing, allowing the microlenses to approach more closely their theoretical efficiency limit of .95%. Photoresist microlenses were fabricated by reflow of photolithographically defined photoresist islands. Prior to microlens deposition, but after diode fabrication, the test structures were flip-chip bonded or ‘‘hybridized’’ using indium interconnections to metallic striplines that had been photolithographically deposited on sapphire dice (a process equally compatible with a siliconintegrated- circuit readout). After hybridization, the CdZnTe was thinned to equal the focal length of the lenses in the CdZnTe material. Optical characterization has demonstrated that the microlenses combined with the detector mesas concentrate light sufficiently to increase the effective collection area. The optical size of the mesa detectors being larger than the theoretical diffraction limit of the microlenses precludes determining whether the lenses themselves produce the theoretical diffraction-limited gain, but they clearly decrease the required detector area by at least 3 to 6 times. To our knowledge, this is the first successful demonstration of IR detectors and binary optics and of photoresist refractive-microlens integration.

Development of Optical Engineering. Diffraction Efficiency and Fabrication Technology of Surface-Relief Diffractive Optical Elements.

In the field of microoptics, surface-relief diffractive optical elements (DOEs) are of great interest. Their thin film structure makes it possible to produce and integrate them with other optical components. Recent development in microfabrication technology including electron-beam lithography and binary optics lithography has demonstrated DOEs with blazed/multilevel relief structure. Such relief structure can improve diffraction efficiency of DOEs. Electron-beam lithography has several advantages such as a potential for submicron patterning and flexibility in design and fabrication. In addition, blazed structure can be formed by one process. Binary optics lithography is also attractive because high efficiency DOEs with multilevel structure can be fabricated by semiconductor techniques used in electronic integrated circuits. Typical DOEs with blazed/multilevel structure and their application to micro infrared sensor are demonstrated. Such surface-relief DOEs are expected to be used in various optical systems.

Binary optics: A VLSI-based microoptics technology

Binary optics technology applies VLSI and ULSI processing techniques to the field of microoptics to enable the fabrication of unique wavefront engineering devices from x-ray to IR wavelengths. The nested character of these stepped diffractive surface relief structures, coupled with submicron linewidths and precise etch depths, puts stringent demands on process tolerances. We summarize our efforts to produce high-optical-quality diffractive and refractive microoptics with this technology. We also describe novel techniques developed to fabricate the deep structures needed to form high-aspect-ratio gratings and analog refractive lenslet arrays, including thick resist processing and deep anisotropic etching.

Preparation of microfocusing optics using synchrotron radiation sources (invited, abstract)

X-rays are used for microfabrication of high-aspect-ratio structures because of their high penetrating power for microfabrication of integrated circuits because of their very high spatial resolution. An uncommon application is the development of phase-shifting optics for hard x-rays, where both requirements (high aspect ratio and high resolution) must be met at the same time. In the hard x-ray region (8 keV and up), conventional absorbing binary diffractive optics are very inefficient because of the low contrast of most elements. It is instead possible to achieve very high efficiency using phase-shifting optics. To achieve a phase shift of Pi, several microns of material are needed. At the same time, the spatial resolution is determined by the finest line in the pattern, of the order of 0.2–0.1 μm. This yields aspect ratios of 10-50, posing great challenges to microfabrication because the submicron dimensions require a much more delicate process than that found, for instance, in LIGA. We have overcome these hurdles, and succeeded in manufacturing Fresnel phase plates with 0.1 μm smallest features for operation at 8 keV. We use a combination of x-ray and electron-beam lithography to process the masks. In particular, the use of an x-ray aligner, capable of multiple exposures, has allowed us to fabricate multilevel FPPs, with ‘‘blazed’’ zone profile of efficiency approaching 80% in the first order focus. We will review the techniques that are at the basis of our fabrication process, describe our approach, and present some of the most recent results.

Binary adaptive optics: atmospheric wave-front correction with a half-wave phase shifter: addenda

We describe a binary approach to adaptive wave-front correction, especially suitable for narrow band applications, which would be simpler than conventional adaptive technology. Appropriate parts of the aberrant wave front are phase retarded by half a wavelength to ensure that none of the image-forming rays add together destructively. Simulations for monochromatic light show that the residual wave-front errors, in the absence of other errors, would result in Strehl ratios of ~40% with diffraction-limited widths at visible wavelengths. We simulate the imaging performance of such a system and describe a possible implementation that uses a ferroelectric liquid-crystal spatial light modulator.

APLLICATION OF GENETIC ALGORITHM TO LASER BEAM RESHAPING

Genetic algorithm is used to design a binary optical system with 8 grey levels to implement the wavefront transformation from gaussian beam to circularly flat - top beam. The comparison with the staionary phase method and the input - output method shows that genetic algorithm is more appropriate to design binary optics for profile reshaping than the other two methods.

Prisms in the Medical and Surgical Management of Strabismus

This concise approach to prism use provides ophthalmologists with practical information on the most up-to-date tests, prescriptions, and uses for prisms in managing strabismus. It covers such topics as laser-induced corneal prisms and binary optics to provoke future exploration and application.

Profile control in dry development of high-aspect-ratio resist structures

Anisotropic etching for dry development of thick resist layers in oxygen-based plasmas has been developed for two particular applications: trilayer resist for planarization of steep binary optics structures, and top surface imaged (silylated) resists for deep submicron lithography. To reduce linewidth degradation during etching of high-aspect-ratio resist structures, lateral etching and bow are minimized in two different reactors, a conventional parallel-plate reactive ion etching (RIE) system and a low-pressure, high-ion-density helicon etcher. In the conventional RIE system, C5H8, a polymer-forming gas is added to the O2 feed gas to form a sidewall inhibition layer. In the helicon reactor, very low temperatures (−100 °C) are used to suppress sidewall etching. Different optimization conditions are found for trilayer resist etching and pattern transfer of silylated resist in the helicon reactor.