1.  Field
Apparatuses and methods consistent with the present invention relate to an optoelectronic shutter in which gain modulation is performed by using a current gain of a phototransistor, a method of operating the same, and an optical apparatus including the optoelectronic shutter. 
2.  Description of the Related Art
Optoelectronic shutters open and close according to an electrical waveform or pulse applied thereto.  Such optoelectronic shutters may be used to modulate light that is incident on an image capture device such as a charge-coupled device (CCD) camera.  For example, optoelectronic shutters may be used as a unit for obtaining information about distances between a camera and an object. 
The information about the distances between the camera and the object may be obtained by using a binocular stereo vision method using two cameras or a triangulation method using structured light and a camera.  However, in the binocular stereo vision method or the triangulation method, as the distances between the camera and the object increases, the accuracy of the information about the distances rapidly decreases, and the distances are dependent on the surface state of the object.  Thus it is difficult to obtain accurate information about the distances. 
In order to solve the problem, a time-of-flight (TOF) method has been developed.  In a TOF method, a light flight time, in which modulated light is irradiated onto an object and then the light is reflected from the object and received by a light receiving unit, is measured.  TOF methods include a TOF method using direct time measuring, a TOF method using correlation, and a TOF method using phase delay measuring. 
In a TOF method using direct time measuring, the time in which pulse light is projected onto an object and is reflected from the object is measured. 
In a TOF method using correlation, pulsed light is projected onto an object and distances between the camera and the object are measured by using information about brightness that is obtained by multiplying a gating signal that is synchronized to the projected pulsed light by a light receiving unit by a reflection light signal.  In the TOF method using correlation, the amount of light of a near object that is received by the camera is large and thus the image of the object looks relatively bright, whereas the amount of light of a far object that is received by the camera is small and thus the image of the object looks relatively dark. 
In a TOF method using phase delay measuring, light having a continuous wave sine wave is projected onto an object, reflected by the object, and a phase difference, that is a phase delay, of the light is detected to calculate distance.  One method of phase delay measuring is that light having a frequency-modulated sine waveform that is projected onto an object and is reflected by the object is mixed at an optical modulator that is placed at a front end of a light receiving portion of the camera, and then the phase delay is measured from the mixed signal in a CCD camera.  Another method of phase delay measuring is that the phase delay is measured from mixing or demodulation in a cell of the CCD camera without the optical modulator. 
In addition, general optoelectronic shutters may be used as a high-speed shutter for a high-speed camera or may be used to convert or modulate incident light into data optically encoded by an optical operation system.