Method for detecting intrusion

An intrusion detecting method using an intrusion detecting system which includes an optical fiber line installed in an area in which intrusion is to be detected, a laser diode inputting an optical signal to the optical fiber line, a photodiode detecting a reflected optical signal when the optical signal is reflected from the optical fiber line, an intrusion determining unit comparing a waveform of the reflected optical signal detected by the photodiode with a set reference waveform to determine whether an intrusion has occurred, and a laser diode temperature measuring unit measuring a temperature of the laser diode, the intrusion detecting method comprising:

• designating, by the intrusion determining unit, a temperature of the laser diode at a first point in time as a first temperature and setting, to a reference waveform, a waveform of a first reflected optical signal caused by an input optical signal input by the laser diode at the first point in time;
• comparing, by the intrusion determining unit, a waveform of a second reflected optical signal caused by the input optical signal input by the laser diode at a second point in time after the first point in time with the set reference waveform and determining that an intrusion has occurred;
• designating, by the intrusion determining unit, a temperature of the laser diode at the second point in time as a second temperature and determining whether the second temperature is within an allowable range with respect to the first temperature;
• when it is determined that the second temperature exceeds the allowable range, suspending, by the intrusion determining unit, the determination that an intrusion has occurred;
• selecting, by the intrusion determining unit, a third point in time which comes after the first point in time and comes before the second point in time and at which the temperature of the laser diode is within the allowable range with respect to the second temperature;
• resetting, by the intrusion determining unit, to a reference waveform, a waveform of a third reflected optical signal caused by the input optical signal input by the laser diode at the third point in time;
• comparing, by the intrusion determining unit, a waveform of the second reflected optical signal with the reset reference waveform to re-determine whether an intrusion has occurred;
• and
• when it is determined that an intrusion has occurred as a result of the re-determination, canceling, by the intrusion determining unit, the suspended determination, and when it is determined that an intrusion has not occurred as a result of the re-determination, canceling, by the intrusion determining unit, the determination that an intrusion has occurred.

An intrusion detecting method using an intrusion detecting system which includes an optical fiber line installed in an area in which intrusion is to be detected, a laser diode inputting an optical signal to the optical fiber line, a photodiode detecting a reflected optical signal when the optical signal is reflected from the optical fiber line, an intrusion determining unit comparing a waveform of the reflected optical signal detected by the photodiode with a set reference waveform to determine whether an intrusion has occurred, and a photodiode temperature measuring unit measuring a temperature of the photodiode, wherein the photodiode is an avalanche photodiode, the intrusion detecting method comprising:

• designating, by the intrusion determining unit, a temperature of the photodiode at a first point in time as a first temperature and setting, to a reference waveform, a waveform of a first reflected optical signal detected by the photodiode at the first point in time;
• designating, by the intrusion determining unit, a temperature of the photodiode at a second point in time after the first point in time as a second temperature and determining whether the second temperature is within an allowable range with respect to the first temperature;
• and
• when it is determined that the second temperature exceeds the allowable range, resetting, by the intrusion determining unit, to the reference waveform, a waveform of a second reflected optical signal detected by the photodiode at the second point in time.