Photodetecting apparatus having intensity tuneable light irradiating unit

A photodetecting apparatus comprising:

• intensity tuneable light irradiating means for generating a first number of lights each having a different predetermined wavelength to irradiate a scattering and absorption medium, an intensity of each said light being modulated by a modulating signal having an ac component with a predetermined frequency, an amount of modulation of generating light or a quantity of generating light being adjustable in accordance with an external instruction;
• light branching means for receiving optical signals each having said predetermined frequency component emerging from said scattering and absorption medium after said optical signals are generated from said intensity tuneable light irradiating means, irradiate said scattering and absorption medium and propagate in said scattering and absorption medium, and branching said optical signals into said first number of lights each having said predetermined wavelength;
• photodetecting means comprising said first number of photodetecting units arranged for each said light having said predetermined wavelength, for detecting light emitted from said light branching means;
• feedback means for receiving an optically detected signal for each said predetermined wavelength corresponding to the intensity of said optical signal for each said predetermined wavelength emitted from said photodetecting means, sending an instruction to said intensity tuneable light irradiating means to increase the quantity of generating light having the respective wavelength or to increase the amount of modulation of generating light having the respective wavelength when the intensity of an ac component of said optically detected signal detected by said photodetecting means is smaller than a predetermined value, and sending an instruction to said intensity tuneable light irradiating means to decrease the quantity of generating light having the respective wavelength or to decrease the amount of modulation of generating light having the respective wavelength when the intensity of the ac component of said optically detected signal detected by said photodetecting means is larger than the predetermined value;
• and
• processing means for receiving said modulating signal and said optically detected signals and obtaining one of a timing difference between said modulating signal and said optically detected signal, and a phase difference between said modulating signal and said optically detected signal, for each said predetermined wavelength.