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For reliable three dimensional (3D) imaging system, it is necessary for the optical shutter to have a wide spectral bandwidth operation and enhanced modulation depth. We propose an electro-absorption modulator (EAM) based on coupled Fabry-Perot cavities with micro-cavity (CCMC) which uses asymmetric tandem quantum wells (ATQWs) to obtain improved spectral bandwidth and enhanced modulation depth. Several modulator designs are investigated to obtain improved modulation performance such as wider spectral bandwidth and enhanced modulation depth. It was found that among all the studied modulator geometries, CCMC structure with ATQWs provides the widest spectral bandwidth of 9.6nm and high modulation depth in excess of 50% at -24V, which is good agreement with theoretical calculations. These results suggest that EAM has excellent potential as optical shutter for 3D imaging application.

Large aperture image modulators used as demodulator in receiver path are an important component for the use in three dimensional (3D) image sensing. For practical applications, low voltage operation and high modulation performance are the key requirements for modulators. Here, we propose an asymmetric Fabry-Perot modulator (AFPM) with asymmetric tandem quantum wells (ATQWs) for 3D image sensing. By using ATQWs for the AFPM design, the device operated at -4.25V, and the operating voltage was significantly lower by about 23% compared to -5.5V of a conventional AFPM with 8nm thick multiple QW with a single QW thickness (SQWs), while achieving high reflectivity modulation in excess of 50%. The performance of the fabricated devices is in good agreement with theoretical calculations. The pixelated device shows a high modulation speed of 21.8 MHz over a large aperture and good uniformity. These results show that AFPM with ATQWs is a good candidate as an optical image modulator for 3D image sensing applications.

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.

We present an electro-absorption modulator based on the enhanced electro-optic effect of an asymmetric coupled triple quantum well (ACTQW) to achieve a large transmittance difference at a low driving voltage for high-definition (HD) three-dimensional (3D) imaging applications. Our numerical calculations show that an ACTQW structure can provide a significantly lower-voltage operation without degrading the absorption coefficient change at the operating wavelength of 850 nm. The fabricated electro-absorption modulator (EAM) based on an ACTQW shows that the operating voltage can be reduced by nearly 50% compared with an EAM based on a conventional rectangular quantum well while also achieving a large transmittance difference in excess of 50%, which is in good agreement with the numerical calculation results. These results suggest that using an EAM with an ACTQW is a promising approach for the realization of a high-resolution 3D imaging system.