High-flexibility and high-accuracy phase delay calibration method for MEMS-based fringe projection systems

High-speed 3D measurement using the kinoform array and light source shift

A new, to the best of our knowledge, fringe projector using the kinoform is proposed in this Letter. The kinoform array makes the hologram easy to manufacture, and the phase shift is realized by light source shift. The fringes can be shifted at a high speed due to the high-speed switch of the light source. An active binocular 3D measurement system using the proposed projector is demonstrated, and a binocular matching algorithm from coarse to fine using a laser speckle and fringe phase is proposed. Three laser diodes are adopted as light sources, and the three-step phase-shifting is achieved. The dimension of the projector is 30 mm × 26 mm × 12 mm and the switching speed is up to 1.5 kHz. The 3D measurement speed reaches 70 fps in the experiment.

Projection superimposition for the generation of high-resolution digital grating

Fringe projection profilometry based on MEMS micro-vibration mirrors is very promising due to its rapid projection, large depth of field, compact size, and low cost. Although high-frequency fringes can achieve accurate reconstruction, the projector must offer sufficient pixel resolution. In this paper, we proposed a high-resolution projection technique called the delay superposition method. During a single exposure time of the camera, the projector projects a group of low-resolution fringe patterns, which are delayed according to the movement characteristics of the vibration mirror. Then, the camera exposure superimposes these low-resolution images to form a high-resolution image. These two steps effectively subdivide the angle intervals, thereby achieving a pixel interpolation. Finally, experimental results show that the proposed method can significantly improve the projector's pixel resolution and reconstruction accuracy. The proposed method allows the MEMS projector's pixel resolution (along one direction) to far exceed that of common DLP projectors. It holds great application potential for high-frequency fringe projection.

Simple modulation of Lissajous MEMS laser beam scanning with reconfigurable structured light patterns for 3D imaging

Structured light 3D imaging systems commonly employ panel-based projectors or 1-axis MEMS mirrors with beam expander lens to project multi-frame barcodes or dot clouds, addressing challenges posed by objects with multi-scale feature sizes. However, these methods often result in large system volumes due to the required projection multi-lens modules, high hardware costs, or limited light pattern generation capabilities that hindering measurement precision enhancement. This paper introduces an innovative approach to reconfigurable spatial light pattern projection using a single bi-axial MEMS mirror with Lissajous scanning. In contrast to the pixel-by-pixel pre-defined image patterns encoding of conventional 2D laser beam scanning, the proposed method simply aligns the MEMS bi-axial resonance frequencies with laser pulse modulation, enabling the projection of diverse structured light patterns such as stripes, lines, dot matrices, and random dot clouds, which can adapt to different 3D imaging algorithms demands. It eliminates the need for multi-frame encoding and streamlines data caching, simplifies digital logic hardware. A prototype 3D imaging system was developed to demonstrate the mathematical model for laser modulation and the technical feasibility based on the proposed principle. Beyond its lens-free essence, the system supports focal-free optics and a compact projection form factor, which accommodates to a broad range of projection distances and field-of-views based on object's location. 3D depth map of polynomial surface and blocks objects are extracted through single-frame pattern projection with a relative high accuracy. The presented modulation theory for diverse structured light pattern generation opens avenues for versatile and compact 3D imaging applications of LiDAR and robotic 3D vision.

Focus Issue Introduction: 3D Image Acquisition and Display: Technology, Perception and Applications

This Feature Issue of Optics Express is organized in conjunction with the 2022 Optica conference on 3D Image Acquisition and Display: Technology, Perception and Applications which was held in hybrid format from 11 to 15, July 2022 as part of the Imaging and Applied Optics Congress and Optical Sensors and Sensing Congress 2022 in Vancouver, Canada. This Feature Issue presents 31 articles which cover the topics and scope of the 2022 3D Image Acquisition and Display conference. This Introduction provides a summary of these published articles that appear in this Feature Issue.

Development of an Optoelectronic Integrated Sensor for a MEMS Mirror-Based Active Structured Light System

Micro-electro-mechanical system (MEMS) scanning micromirrors are playing an increasingly important role in active structured light systems. However, the initial phase error of the structured light generated by a scanning micromirror seriously affects the accuracy of the corresponding system. This paper reports an optoelectronic integrated sensor with high irradiance responsivity and high linearity that can be used to correct the phase error of the micromirror. The optoelectronic integrated sensor consists of a large-area photodetector (PD) and a receiving circuit, including a post amplifier, an operational amplifier, a bandgap reference, and a reference current circuit. The optoelectronic sensor chip is fabricated in a 180 nm CMOS process. Experimental results show that with a 5 V power supply, the optoelectronic sensor has an irradiance responsivity of 100 mV/(μW/cm2) and a -3 dB bandwidth of 2 kHz. The minimal detectable light power is about 19.4 nW, which satisfies the requirements of many active structured light systems. Through testing, the application of the chip effectively reduces the phase error of the micromirror to 2.5%.