Real-time sensing of 3D geometric information is essential for autonomous vehicles and robots for detection of obstacles and environment. In most case of autonomously maneuvering robots, the relative motion of 3D sensor and the target object is involved so that accurate 3D geometry, as well as the relative velocity, need to be acquired for safe operation. In this paper, a small form-factor scanner-based 3D sensing system and operating architecture, so-called homodyne mixing method and its experimental verification are presented. Special attention is put on the accuracy improvement with small size realization under relative motion between sensor and objects in the application to autonomous working robots operating under various working environment. In the homodyne mixing method, as the working principle, phase delay induced by the time-of-flight of the amplitude-modulated light wave flying between camera and object is indirectly measured.1 The homodyne mixing method has less computational and hardware complexity than other 3D sensing methods and it is robust to external light and has advantages in miniaturization. However, the homodyne mixing method is sensitive to the relative movement between the sensor and targeting object because it uses continuously modulated light wave. In this paper, an improved light processing methodology is established to tackle this weakness in a moving situation. The presented light processing methodology is robust to the relative movement and has the advantage to control the measurement precision of 3D depth information through variable scanning FOV (Field of View). As the application of suggesting a 3D sensing device and system to recognition in the robot system, we propose a geometry recognition method that extracts typical geometric features of objects from point-cloud data obtained from the 3D sensor. The result shows that the recognition of the geometry of an object is quick and accurate more than previous recognition technology using only an RGB color image.2 By combining the sensor system and object geometry recognition method, we can provide the solution of the 3D object recognition system for autonomous robot operating in an undetermined environment. The experimental verification is presented for the evaluation of the 3D sensing system.
A time-of-flight (TOF) based three dimensional (3D) image capturing system and its enhanced optical modulating device are presented. The 3D image capturing system includes 850nm IR emitter (typically compact Laser diodes) and high speed image modulator, so called optical shutter. The optical shutter consists of multi-layered optical resonance cavity and electro-absorptive layers. The optical shutter is a solid-state controllable filter which modulates the IR image to extract the phase delay due to TOF of the emitting IR light. This presentation especially addresses robustness issues and solutions when operated under practical environments such as ambient temperature variation and existence of strong ambient light (e.g. outdoors). The wavelength of laser diode varies substantially depending on the ambient temperature, which degrades the modulation efficiency. To get a robust operation, the bandwidth of transmittance of the optical shutter is drastically improved with a novel coupled Fabry-Perot resonance cavity design to come up with the wavelength variation of the laser diode. Also, to suppress the interference of solar irradiance to IR source signal, a novel driving scheme is applied, in which IR light and optical shutter modulation duties are timely localized, i. e. ‘bursted’. Suggested novel optical shutter design and burst driving scheme enable capturing of a full HD resolution of depth image under the realistic usage environments, which so far tackle the commercialization of TOF cameras. Design, fabrication, and evaluation of the optical shutter; and, 3D capturing system prototype, image test results are presented.
A 20-MHz switching high-speed light-modulating device for three-dimensional (3-D) image capturing and its system prototype are presented. For 3-D image capturing, the system utilizes a time-of-flight (TOF) principle by means of a 20-MHz high-speed micromachined electro-absorptive modulator, the so-called optical shutter. The high-speed modulation is obtained by utilizing the electro-absorption mechanism of the multilayer structure, which has an optical resonance cavity and light-absorption epilayers grown by metal organic chemical vapor deposition process. The optical shutter device is specially designed to have small resistor–capacitor–time constant to get the high-speed modulation. The optical shutter is positioned in front of a standard high-resolution complementary metal oxide semiconductor image sensor. The optical shutter modulates the incoming infrared image to acquire the depth image. The suggested novel optical shutter device enables capturing of a full high resolution-depth image, which has been limited to video graphics array (VGA) by previous depth-capturing technologies. The suggested 3-D image sensing device can have a crucial impact on 3-D–related business such as 3-D cameras, gesture recognition, user interfaces, and 3-D displays. This paper presents micro-opto-electro-mechanical systems-based optical shutter design, fabrication, characterization, 3-D camera system prototype, and image evaluation.
We suggest a Time-of-Flight (TOF) video camera capturing real-time depth images (a.k.a depth map), which are generated from the fast-modulated IR images utilizing a novel MOEMS modulator having switching speed of 20 MHz. In general, 3 or 4 independent IR (e.g. 850nm) images are required to generate a single frame of depth image. Captured video image of a moving object frequently shows motion drag between sequentially captured IR images, which results in so called ‘motion blur’ problem even when the frame rate of depth image is fast (e.g. 30 to 60 Hz). We propose a novel ‘single shot’ TOF 3D camera architecture generating a single depth image out of synchronized captured IR images. The imaging system constitutes of 2x2 imaging lens array, MOEMS optical shutters (modulator) placed on each lens aperture and a standard CMOS image sensor. The IR light reflected from object is modulated by optical shutters on the apertures of 2x2 lens array and then transmitted images are captured on the image sensor resulting in 2x2 sub-IR images. As a result, the depth image is generated with those simultaneously captured 4 independent sub-IR images, hence the motion blur problem is canceled. The resulting performance is very useful in the applications of 3D camera to a human-machine interaction device such as user interface of TV, monitor, or hand held devices and motion capturing of human body. In addition, we show that the presented 3D camera can be modified to capture color together with depth image simultaneously on ‘single shot’ frame rate.
20 Mega-Hertz-switching high speed image shutter device for 3D image capturing and its application to system
prototype are presented. For 3D image capturing, the system utilizes Time-of-Flight (TOF) principle by means of
20MHz high-speed micro-optical image modulator, so called 'optical shutter'. The high speed image modulation is
obtained using the electro-optic operation of the multi-layer stacked structure having diffractive mirrors and optical
resonance cavity which maximizes the magnitude of optical modulation. The optical shutter device is specially designed
and fabricated realizing low resistance-capacitance cell structures having small RC-time constant. The optical shutter is
positioned in front of a standard high resolution CMOS image sensor and modulates the IR image reflected from the
object to capture a depth image. Suggested novel optical shutter device enables capturing of a full HD depth image with
depth accuracy of mm-scale, which is the largest depth image resolution among the-state-of-the-arts, which have been
limited up to VGA. The 3D camera prototype realizes color/depth concurrent sensing optical architecture to capture
14Mp color and full HD depth images, simultaneously. The resulting high definition color/depth image and its capturing
device have crucial impact on 3D business eco-system in IT industry especially as 3D image sensing means in the fields
of 3D camera, gesture recognition, user interface, and 3D display. This paper presents MEMS-based optical shutter
design, fabrication, characterization, 3D camera system prototype and image test results.
A small sized, low power consuming, shock proven optical scanner with a capacitive comb-type rotational sensor for the application of mobile projection display is designed, fabricated, and characterized. To get a 2-D video image, the present device horizontally scans a vertical line image made through a line-type diffractive spatial optical modulator. To minimize, device size as well as power consumption, the mirror surface is placed on the opposite side of the coil actuator. To prevent thermal deformation of the mirror, the mirror is partially connected to the center point of the coil actuator. To be shock proof, mechanical stoppers are constructed in the device. The scanner is fabricated from two silicon wafers and one glass wafer using bulk micromachining technology. The packaged scanner consists of the scanner chip, a pair of magnets, yoke rim, and base plate. The fabricated package size is 9.2×10×3 mm (0.28 cc) and the mirror size is 3×1.5 mm. The scanner chip receives no damage under the shock test with an impact of 2000 G in 1 ms. In the case of a full optical scan angle of 30 deg at 120-Hz driving frequency, linearity, repeatability, and power consumption are measured at 98%, 0.013 deg, and 60 mW, respectively, which are suitable for mobile display applications.
A small size, low power consuming, shock proven optical scanner with capacitive comb type rotational sensor for the
application of mobile projection display was designed, fabricated, and characterized. To get a 2-dimensional video image,
the present device horizontally scans a vertical line image made through a line-type diffractive spatial optical modulator.
In order to minimize device size as well as power consumption, the mirror surface was placed on the opposite side of the
coil actuator. To prevent thermal deformation of the mirror, the mirror was partially connected to the center point of the
coil actuator. For shock proof, mechanical stoppers were constructed in the device. The scanner was fabricated from two
silicon wafers and one glass wafer using a bulk micromachining technology. The packaged scanner consists of the
scanner chip, a pair of magnets, yoke rim, and base plate. The fabricated package size is 9.2mmx10mmx3mm (0.28cc)
and the mirror size is 3mmx1.5mm. The scanner chip has no damage under the shock test with impact of 2,000G in 1ms.
In case of full optical scan angle of 30° at 120Hz driving frequency, linearity and power consumption are measured 98%
and 60mW, respectively, which are suitable for mobile display applications.
AlInGaN based blue and blue-green LDs were investigated with regard to the
characteristics of GaN semiconductor laser diodes. High power, single mode blue LDs with
high COD level (~334mW under CW operation at 25°C, kink-free at 150mW) and long lifetime
(~10000 hours under CW operation, 50mW 25°C) were achieved. No significant characteristic
differences between blue LDs on LEO-GaN/sapphire and GaN substrate were observed. The
blue-green LD which has the wavelength of 485 nm was successfully fabricated and
demonstrated under CW operation 25°C, while it showed poor performances of LD
characteristics compared to those of blue LDs. We believe that the poor performance of blue-green
LDs were caused by the piezo-electric effect by lattice mismatch along C-axis of GaN, In
fluctuation by lattice mismatch and In solubility limit in InGaN QWs and thermal annealing
which was performed during the p-layer growth.
An electrostatic 1 dimensionally (1D) scanning mirror for HD resolution display is introduced. Vertical comb drive was
used to tilt the micro mirror. To minimize the moment of inertia and maximize the tilting angle of the mirror having the
diameter of 1.6 mm, the rib was patterned on the backside of the mirror surface and optimized. Via the finite element
simulation, the dynamic deformation of 45nm was achieved within the reflecting area in operating resonant mode thanks
to the optimized rib structure. The actuating part of scanner was also optimized manipulating with several design
variables to get maximum tilting angle. As the fabrication result, mechanical tilting angle of ±12.0 degree was achieved
with the resonant frequency of 24.75kHz and the sinusoidal driving voltage of 280Vpp. For stable resonant motion of the
scanner, the feedback control algorithm was realized in the driving circuit. Rigorous reliability characterization was
carried out using statistical analysis on the fabricated samples. As a result, HD-resolution image with 720 progressive
horizontal lines was demonstrated.
The customers' demand for real life-like display with natural colors and high definition is increasing and hence laser display with the best expression of natural color is being proposed as a way to realize this. In particular, the raster scanning display using the high-speed reflective MEMS scanner plus compact laser sources enables realization of ultrasmall optical engine with great optical efficiency. By the way, in recent years the emerging display systems including FPD (Flat Panel Display) and projection systems based on the microdisplay devices show rapid improvements in terms of picture quality, form factor as well as cost. The object of this paper is introducing a technology analysis of success factors of the MEMS based rater scanning display in order to get high-level development roadmap, through a comparison study with the conventional displays. Proper specifications of brightness, color, contrast, resolution, form factor, power consumption and cost-effectiveness are suggested for mobile projector application. The technical challenges toward achievement of the specifications are summarized.