Dynamic structured light projector based on resonance domain diffractive optical elements
The field is the 3D scanning for sensing, imaging, 3D printing and computer-integrated manufacturing. We develop a critical device for dynamic creation of the structured light (SL) patterns that was a bottleneck in triangulation-based 3D sensing with active illumination. Resorting to matured technology of lasers arrays as well as to emerging academically proven technology of nano-engineered diffractive optical elements (DOEs), lifts an existing tradeoff in power, spatial sharpness and fast dynamics of the structured light patterns. The projector will be capable of projecting any time sequence of SL patterns onto a 3D scanned object. The laser and laser arrays will be dynamically controlled in their turning on and off. The DOE converts the laser light into a pattern. Entire of the SL patterns will be formed by a different combination of turned on and off lasers. The performance of the projector will be optimized by resorting to simultaneous generation of highly specialized SL patterns for 3D scanning. Therefore we resort to time scanning with frequencies of hundreds Hz, simulataneously form each spatial pattern and, accordingly, avoid problematic spatial scanning that is present in existing devices. Our hight efficiency DOEs are fabricated with direct e-beam writing and plasma etching technology and provide performance similar to quality volume holograms. In particular, our DOEs break a long lasting trade-off in efficiency and numerical aperture (NA) that was inherent in the field of diffractive optics. The project is focused on the design, fabrication and integration of DOEs with dynamically controlled lasers. The combination of high NA and efficient DOE with lasers is expected to deliver a projecting device exceeding competitors in the field of SL triangulation by higher sharpness, scalable light power, fast dynamics and cost margins.
We gain from following features:
• Scalability for high optical power based on array of lasers.
• Narrow spectrum of the structured patterns in laser light.
• High optical power lasers and laser arrays enabls outdoor scanning.
• Reduced temporal coherence and minimized speckle noise.
• Wide angular range for extension of the structured light pattern.
• Independent on and off switching of hundreds of separate line stripes for the projection of binary or gray level structured patterns onto a scanned scene.
• Extremely fast dynamics.
• Unprecedented light projection efficiency of about 80%, no projection lens.
Therefore, proposed technology compared to existing industrial technologies, enables up to x20 distance (20m vs. 1m), is capable of operating in bright sun light or other bright light (because of narrow spectral width of the patterns), substantially saves in cost of the projector and final 3D scanner product.
Commercially available state of the art dynamic projectors are based on spatial light modulators (SLM) such as DLP, LCD, and LCoS with incoherent light sources, or a micro-scanning mirror with a single laser. In specific application for projection of structured light (SL) patterns, these generic projectors have severe limitations for power and limited number of pixels, which yields insufficient contrast of in a background light. Accordingly, resolution, range and object size in the 3D scanning with structured light is limited today. Overcoming these limitations often comes at a cost of bulkiness, complexity, extremely high price, and limited time frame rate. High power lasers are not suitable for DLP, LCD, and LCoS, as they essentially require incoherent light source, and a micro-scanning mirror may have laser safety problems. Therefore develpede in this project new technology of dedicated SL patterns projector is necessary.
A dedicated compact dynamic projector for the field of SL triangulation, exceeding competitors by higher sharpness, simultaneous formation of pattewrns, increased speed, scalable light power and cost margins. Such projector should be offered as a key block of a high resolution 3D scanner for indoor, outdoor and mid-range ( 5-10 ms) distances. The fields of applications for 3D scanning with our dedicated projector might be but not restricted to following:
• Outdoor scanning of building, or parts of buillding or vehicles.
• Unmanned vehicles that require high resolution 3D scanning of driving or landing surface.
• Compact portable 3D scanners for 3D printing.
• 3D sensing and imaging, augmented reality, Internet of things, robotics.
• Inspection for security and production quality control, machine vision
STAGE OF DEVELOPMENT
Applied research and prototype fabrication. We have already developed high efficiency diffractive optical elements and started to test them in environment of a dynamic structured light projector, as shown in Fig. 1.
Fig.1. Structured light patterns obtained in experiments by combination of high efficiency diffractive optical elements and lasers.
1. M.A. Golub and A.A. Friesem, Effective grating theory for the resonance domain surface relief diffraction gratings, J. Opt. Soc. Am. A 22 , 1115-1126, 2005.
2. O. Barlev, M. A. Golub, and A. A. Friesem, and M. Nathan “Design and experimental investigation of highly efficient resonance domain diffraction gratings in the visible spectral region,” Appl. Optics 51, 8074-8080, 2012.
3. O. Barlev, and M. A. Golub," Resonance domain surface relief diffractive lens for the visible spectral region," Appl. Optics 52, 1531–1540 ,2013.
4. M. A. Golub, "Design of dense transmission diffraction gratings for high efficiency”, J. Opt. Soc. Am. A . 32, 108-123 2015.
5. O. Barlev and M. Golub, "Chromatic dispersion of high-efficiency resonance domain diffractive lens," Appl. Opt. 54, 6098-6102, 2015.
6. O. Barlev and M. Golub, "High resolution compact spectrometer based on a resonance domain diffractive lens," Ph. Tech. Lett. 28, 577-580, 2016.
7. O. Barlev, M.A. Golub, “Coherent imaging with a resonance domain diffractive lens in laser light,” Applied Optics 55, 4820-4826, 2016.