Abstract: A driving system region which is a region where a light projector, a light receiver, and a signal processing circuit are installed together is disposed on one side of an optical system region comprising a light-projecting region and a light-receiving region, so that wires such as their mutual signal lines are kept from passing through the optical system region, whereby an omnidirectional distance detecting apparatus capable of complete 360-degree omnidirectional distance detection can be obtained. The influence of electric noise caused by the driving system of rotary mechanism and the like upon light-receiving signals and the like is suppressed, whereby the accuracy in distance detection can be improved.

Abstract: A driving system region which is a region where a light projector, a light receiver, and a signal processing circuit are installed together is disposed on one side of an optical system region comprising a light-projecting region and a light-receiving region, so that wires such as their mutual signal lines are kept from passing through the optical system region, whereby an omnidirectional distance detecting apparatus capable of complete 360-degree omnidirectional distance detection can be obtained. The influence of electric noise caused by the driving system of rotary mechanism and the like upon light-receiving signals and the like is suppressed, whereby the accuracy in distance detection can be improved.

Abstract: In a device 100 for measuring distance, a signal generating circuit 20 generates a driving signal. The driving signal is serially modulated in phase into at least three states. The signal generating circuit 20 further generates reference signals having frequencies the same as the driving signal. A light source 30 is driven by the driving signal to emit detection light which is time-divisionally modulated in phase in accordance with the driving signal. An optical detector 40 receives the detection light which has been emitted from the light source 30 and scattered and reflected by the target. The optical detector 40 generates a detection signal which is time-divisionally modulated in phase in accordance with the received detection light. Homodyne processing circuits 50 and 60 superimpose the detection signal and the reference signals to generate homodyne signals (interference signals). Temporal mean values of intensities of the homodyne signals are obtained.

Abstract: A bias circuit for applying a bias voltage to an avalanche photodiode APD2 for detecting light comprises a first diode APD1, a power supply V.sub.H connected to the first diode APD1, for applying a voltage to make the diode in breakdown between an anode and a cathode of the first diode APD1, and a constant voltage circuit V2 connected to the avalanche photodiode APD2 for detecting light, for applying a voltage difference of a breakdown voltage generated between the anode and the cathode of the first diode APD1 minus a constant voltage to the avalanche photodiode. The constant voltage is substantially independent from current flowing in the avalanche photodiode APD2 for detecting light to the avalanche photodiode.

Abstract: A photodetecting circuit using an avalanche photodiode of the present invention has an avalanche photodiode, and a bias control means for applying a bias voltage to the avalanche photodiode to drive the avalanche photodiode at a high multiplication factor. The bias control means has a diode having the same temperature dependence of a breakdown voltage as that of the avalanche photodiode, and a control circuit for applying positive and negative potentials with respect to the ground potential between the anode and the cathode of the diode such that the diode is set in a breakdown state at a predetermined current. A positive or negative potential is applied from one of the anode and the cathode of the avalanche photodiode as a bias voltage, and a photocurrent is output from the other terminal of the avalanche photodiode.