As autonomous vehicles rapidly transition to fully automated operations, the ability of these systems to make critical safety decisions in real-time remains of paramount concern. Successful implementation will rely on maintaining the highest possible fidelity of the underlying image data while operating in the challenging automotive light detection and ranging (LIDAR) environment. In addition to three dimensional (3D) depth data, some proposed systems seek to overlay data from multiple sources in order to further improve decision quality and safety margin. The requirement to establish and maintain system calibration over life, including overlay of various fields of view suggests the need for an optical reference that could be used to routinely recalibrate the system in the field. The ability to validate and re-calibrate LIDAR systems in the field without the need for operator intervention would also serve to ensure consistent data quality as well as removing the need to take vehicles offline for periodic re-calibration. Diffractive-Optical-Elements (DOEs) are well suited for use as optical calibration references. In addition to their small size and lithographic precision, fused silica DOEs exhibit extreme stability and mechanical strength, potentially allowing for direct integration into the LIDAR system itself. In this paper, we examine the use of DOEs as LIDAR calibration standards, including the impact of material properties on the stability of the generated reference patterns and consequently on the reliability of the imaging system data.
The promise of fully autonomous vehicles to replace the judgment of human drivers with real-time algorithmic decision-making based on optoelectronic systems relies fundamentally on the quality of the available data. Limitations imposed by sensor-resolution, available optical power, and achievable signal-to-noise ratios have been well studied in the light detection and ranging (LIDAR) application space. Additionally, the problem of integrating multiple sources of image data as well as the need to establish and maintain the system calibration over life are critically important to system reliability and safety. These latter concerns will receive even greater attention as self-driving vehicles begin to transition toward fully autonomous operation. Because of the importance of calibration to system performance and safety, the process of validating and recalibrating the system will ideally be integrated into the LIDAR system itself with calibration occurring automatically “anywhere and at any time,” without dedicated external infrastructure. Mass-market adoption is also being driven by the systems’ size and weight, as well as reliable manufacturability and resilience to environmental stresses. Due to their extreme stability, manufacturability, and small size, diffractive optical elements (DOEs) are well suited for use as optical calibration references. Current three-dimensional (3D) mapping systems based on structured light illumination already rely on DOEs as precision pattern generators to provide 3D depth sensing in a wide array mobile devices. We examine the potential use of DOEs as calibration elements in multicamera or LIDAR systems, including appropriate choices of materials, designs, and fabrication methods to ensure reliable long-term performance under automotive use conditions. We present simulations of the impact of DOE material properties on the accuracy of the generated dot patterns and consequently on the depth accuracy and lateral distortion of the 3D image. Additionally, we present requirements for DOE manufacture using conventional semiconductor fabrication technologies optimized for creating engineered surface nanostructures capable of transforming the output of a laser or other narrow-band source into a precise reference pattern.
The introduction of source mask optimization (SMO) to the design process addresses an urgent need for the 32nm node
and beyond as alternative lithography approaches continue to push out. To take full advantage of SMO routines, an
understanding of the characteristic properties of diffractive optical elements (DOEs) is required. Greater flexibility in the
DOE output is needed to optimize lithographic process windows. In addition, new and tighter constraints on the DOEs
used for off-axis illumination (OAI) are being introduced to precisely predict, control and reduce the effects of pole
imbalance and stray light on the CD budget. We present recent advancements in the modeling and optical performance
of these DOEs.
We present a method for optimizing a free-form illuminator implemented using a diffractive optical element (DOE). The
method, which co-optimizes the source and mask taking entire images of circuit clips into account, improves the
common process-window and 2-D image fidelity. We compare process-windows for optimized standard and free-form
DOE illuminations for arrays and random placements of contact holes at the 45 nm and 32 nm nodes. Source-mask cooptimization
leads to a better-performing source compared to source-only optimization. We quantify the effect of typical
DOE manufacturing defects on lithography performance in terms of NILS and common process-window.
We present advancements in the manufacture of high-performance diffractive optical elements (DOEs) used in
stepper/scanner off-axis illumination systems. These advancements have been made by employing high resolution
lithographic techniques, in combination with precision glass-etching capabilities. Enhanced performance of DOE designs
is demonstrated, including higher efficiency with improved uniformity for multi-pole illumination at the pupil plane,
while maintaining low on-axis intensity.
Theoretical predictions of the performance for several classes of DOE designs will be presented and compared with
experimental results.
This new process capability results in improved performance of current DOE designs, and enables greater customization
including control of the output spatial intensity distribution for future designs. These advancements will facilitate
continuous improvements in off-axis illumination optimization required by the end user to obtain larger effective
lithographic process windows.
As CDs continue to shrink, lithographers are moving towards using off-axis illumination while continuing to decrease the operating wavelength to improve their CD budget. Currently DUV lithography at 248nm and 193nm are driving the ability of the foundries and IDM’s to meet or exceed the SIA roadmap for semiconductor chip performance. In time, however, the industry will migrate to the even shorter wavelengths of 157nm and 13nm. To meet today’s needs with 248nm and 193nm requires the use of Resolution Enhancement Techniques such as Optical Proximity Correction, Phase Shift Mask, and Off Axis Illumination. The need for these techniques will be only slightly reduced as the industry migrates to 157nm in several years. Off-axis illumination (the topic of this paper) has been shown to significantly increase the lithographic process window and there have been several papers over the last few years describing various illumination profiles designed for application specific optimization. These include various annular and quadrupole illumination schemes including weak quadrupole, CQUEST, and Quasar Diffractive optics, if incorporated into the design of the illumination system, can be used to create arbitrary illumination profiles without the associated light loss, thus maintaining throughput while optimizing system performance. We report on the design and fabrication of such devices for use with KrF, ArF, and F2 scanners.
As CDs continue to shrink, lithographers are moving more towards using off-axis illumination schemes to increase their CD budget. There have been several papers over the last few years describing various custom illumination profiles designed for application specific optimization. These include various annular and quadrupole illumination schemes including weak quadrupole, CQUEST, and QuasarTM. Diffractive optics, if incorporated into the design of the illumination system, can be used to create arbitrary illumination profiles without the associated light loss, thus maintaining throughput while optimizing system performance. Diffractive optical elements used to generate efficient illumination profiles for 248 nm and 193 nm excimer laser-source scanners, have been reported and realized in fused silica. The fabrication of such elements in calcium fluoride (CaF2), for use in 157 nm wavelength lithographic projection tools has been developed and is presented in this paper. Three different categories of elements are shown: large-diagonal-cluster diffusers, medium- and small-rectangular-cluster diffusers. The diffusers were fabricated as binary phase devices, in order to determine calcium fluoride processing capabilities.
Graded index fiber has a limited bandwidth due to defects introduced in the fiber manufacturing process. In this paper, an alternative launch technique is presented using a diffractive element to excite specific modes in a fiber to maximize the bandwidth of graded index fiber.
Previously, a method of incorporating a microlens within a standard fiber optic ferrule was described. In this paper, the micro-rod and wafer fabrication concepts are explained, the wafer mapping/layout processes used to create the microlens substrate are detailed, and packaging in standard ferrules and v-grooves are described along with coupling results.
Standard laser welding practices are limited by the intensity profile of the beam and spot size. The introduction of Diffractive Optical Elements (DOE) to the welding process allows for new beam shapes that are better suited to the welding process. A particular problem in laser welding is the joining of dissimilar materials. Because these materials have different material properties including different melting temperatures, it is difficult to synchronize the welding process using a single spot. Additionally, significant thermal stresses are introduced by the welding process because of the keyhole weld shape formed by a gaussian beam. By using a power splitting DOE, two spots of unequal intensity distributions may be projected onto each side of the weld joint. This paper discusses the use of DOEs in laser welding and joining of dissimilar materials. Results are presented from the testing of several candidate aerospace materials.
Silicon v-groove structures have been utilized for passive positioning of optical fiber for fiber optic and opto- electronic applications. In this paper, we will present our results of using micro-machined silicon v-groove arrays to passively align optical fiber arrays to micro rod optics. We will also demonstrate the integration of N fiber arrays bonded into the silicon v-groove with a 1xN micro lens array, which is composed of a 2 inch-phase level diffractive optics. For the assembly of 1x6 fiber array and lens array with 16 phase level diffractive optics, the experimental results indicated that total insertion loss per link is typically 1.5-2.0 dB/channel.
The technical approach and progress achieved under the Polymer Optical Interconnect Technology (POINT) program are described in this paper. The POINT program is a collaborative effort among GE, Honeywell, AMP, AlliedSignal, Columbia University, and University of California at San Diego (UCSD), sponsored by DARPA/ETO, to develop affordable optoelectronic packaging and interconnect technologies for board and backplane applications. Specifically, progress is reported on (a) development of a plastic VCSEL array packaging technology using batch and planar fabrication, (b) demonstration of high-density optical interconnects for board and backplane applications using polymer waveguides to a length of 50 cm at an I/O density of 250 channels per inch, (c) development of low-loss optical polymer waveguides with loss less than 0.1 dB/cm at 850 nm, and (d) development of passively alignment processes for efficient coupling between a VCSEL array and polymer waveguides. Significant progress has also been made under the POINT program at Columbia University, in applying CAD tools to simulate multi-mode-guided wave systems and, at UCSD, to assist mechanical and thermal design in optoelectronic packaging. Because of space limitations, these results will be described elsewhere in future publications.
Optical connectors utilize microlens elements for coupling light into and out of fibers. Typically, these lenses are based on sapphire ball lenses or Gradient Index lens elements.However, lenses that are on the same scale as the single-mode fiber itself have not been previously realized. This paper introduces an optical lens element that fits into the single-mode optical ferrule, without any modifications to the connector package. This approach offers substantial performance and cost benefits over other methods.Both theoretical and experimental results are presented.
This paper describes the technical approach and progresses of the POINT program. This project is a collaborative effort among GE, Honeywell, AMP, AlliedSignal, Columbia University and University of California at San Diego, sponsored by DARPA/ETO to develop affordable optoelectronic packaging and interconnect technologies for board and backplane applications. In this paper, we report the development of a backplane interconnect structure using polymer waveguides to an interconnect length of 280 mm to demonstrate high density and high speed interconnect, and the related technical development efforts on: (a) a high density and high speed VCSEL array packaging technology that employs planar fabrication and batch processing for low-cost manufacturing, (b) passive alignment techniques for reducing recurrent cost in optoelectronic assembly, (c) low-cost optical polymers for board and backplane level interconnects, and (d) CAD tools for modeling multimode guided wave systems and assisting optoelectronic packaging mechanical design.
The development of multimode passive polymer optical waveguide components for board and backplane interconnect applications, such as in the DARPA-sponsored, polymer optical interconnect technology (POINT) program, require several optics design issues to be addressed including efficiency and modal noise. For example, the mating of arrays of sources, detectors, and fibers requires appropriate fanout structures to match the component pitch. Here we consider designs for such structures employing multimode polymer waveguides, including both abrupt and smooth bending elements. We investigate these structures using a new multimode BPM simulation CAD tool, and consider the bend losses as a function of geometry, angle, and source condition. The results are compared with experimental observations on devices fabricated for use in the POINT demonstration module. The simulation closely matches the experiment, demonstrating the utility of such efforts in practical component development.
The coupling of a vertical cavity surface emitting laser (VCSEL) array into an array of multimode polymer waveguides through a 45 degree endface mirror is investigated. A coupling model for the VCSEL and waveguide interface is developed and compared with our experimental results.
The Polymer Optical Interconnect Technology (POINT) represents a major collaborative effort among GE, Honeywell, AMP, AlliedSignal, Columbia University and the University of California at San Diego (UCSD), sponsored by ARPA, in developing affordable optoelectronic module packaging and interconnect technologies for board- and backplane- level optical interconnect applications for a wide range of military and commercial applications. The POINT program takes a novel development approach by fully leveraging the existing electronic design, processing, fabrication and module packaging technologies to optoelectronic module packaging. The POINT program further incorporates several state-of-the-art optoelectronic technologies that include high-speed VCSEL for multichannel array data TM transmission; flexible optical polymers such as Polyguide or coupling of device-to-fiber using a passively alignment process; a low-loss polymer for backplane interconnect to provide a high I/O density; low-cost diffractive optical elements (DOE) for board-to-backplane interconnect; and use of molded MT array ferrule to reduce overall system size, weight, and cost. In addition to further reducing design and fabrication cycle times, computer simulation tools for optical waveguide and mechanical modeling will be advanced under the POINT program.
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