Light emitting device, light receiving system and image pickup system

A light-detecting system comprising:

• a light-emitting device for irradiating a subject with light;
• a light-detecting device for detecting reflected light from the subject;
• and
• a control device for controlling the light-emitting device and the light-detecting device,
• wherein the light-emitting device comprises:
• a diffused light source having a light emission surface, the longest side of which has a length of 1.5 mm or greater;
• and
• a drive circuit for supplying drive pulses to the diffused light source in response to a light emission command input thereto in a constant cyclic period, to enable the diffused light source to emit at least two pulsed lights intermittently;
• wherein the diffused light source comprises a plurality of semiconductor laser bars each having a linear array of light-emission regions, the semiconductor laser bars being stacked together;
• heat radiating plates interposed between the semiconductor laser bars, an anode terminal plate mounted on one of the semiconductor laser bars, which is positioned at an end of the diffused light source, and a cathode terminal plate mounted on one of the semiconductor laser bars, which is positioned at an opposite end of the diffused light source;
• and
• wherein a drive circuit is provided to drive such that:
• the pulsed lights emitted from the diffused light source have a pulse duration longer than 1 nanosecond and shorter than 0.25 second;
• a single pulse of the pulsed lights has a light energy less than 66.8 μ[J];
• the constant cyclic period exceeds 18 μsec;
• the at least two pulsed lights make up a light pulse train having an average energy less than 3.75 μ[J];
• the pulsed lights have an average power less than 74.0 m [W];
• and
• the duty ratio of the pulsed lights to the constant cyclic period is 1% or less;
• wherein the light-detecting device comprises:
• a photodetector for detecting the reflected light and generating photoelectrons by the detected reflected light;
• a first capacitor and a second capacitor for storing the photoelectrons from the photodetector;
• a photoelectron discharger for discharging the photoelectrons from the photodetector;
• and
• a first switching element, a second switching element, and a third switching element for selectively allocating the photoelectrons from the photodetector to the first capacitor, the second capacitor, and the photoelectron discharger in synchronization with driving of the light-emitting device;
• and
• wherein the control device turns on the first switching element to transfer the photoelectrons from the photodetector to the first capacitor during a first period that resides within a period in which the pulsed lights are not emitted from the light-emitting device;
• turns on the second switching element to transfer the photoelectrons from the photodetector to the second capacitor during a second period that resides within a period in which the pulsed lights are emitted from the light-emitting device;
• turns on the third switching element to discharge the photoelectrons from the photodetector to the photoelectron discharger during a period other than the first period and the second period;
• and
• acquires luminance information of the reflected light independent of ambient light, based on a difference between a photoelectron quantity transferred to the first capacitor and a photoelectron quantity transferred to the second capacitor,
• wherein a combination of the first period and the second period is intermittently repeated a plurality of times;
• the photoelectrons from the photodetector are transferred to and stored in the first capacitor during the first period, which is repeated a plurality of times;
• the photoelectrons from the photodetector are transferred to and stored in the second capacitor during the second period, which is repeated a plurality of times;
• and
• luminance information of the reflected light independent of the ambient light is acquired based on the difference between a photoelectron quantity transferred to and stored in the first capacitor and a photoelectron quantity transferred to and stored in the second capacitor.