Laser detection system

A two-way communication system comprising:

• a Mach Zehnder interferometer, the Mach Zehnder interferometer comprising:
• an entry beam splitter for splitting incident light into a first arm, having an arm length L1 and a second arm having an arm length L2;
• a modulation stage for receiving a modulation signal and applying a phase difference to the second arm, a magnitude of the phase difference depending upon a magnitude of the modulation signal;
• an exit beam splitter for recombining light from the first arm with light from the second arm to create a first output and a second output;
• a detection stage comprising a first detector at the first output for detecting intensity modulation caused by interference of the recombined light;
• a retroreflection stage at the second output;
• and
• a signal processor communicably connected to both the modulation stage and the detection stage.

A method of two way communication between a first entity and a second entity, the method comprising:

• providing a laser detection system, the laser detection system comprising:
• a Mach Zehnder interferometer, the Mach Zehnder interferometer comprising:
• an entry beam splitter for splitting incident light into a first arm, having an arm length L1 and a second arm having an arm length L2;
• a modulation stage for receiving a modulation signal and applying a phase difference to the second arm, a magnitude of the phase difference depending upon a magnitude of the modulation signal;
• an exit beam splitter for recombining light from the first arm with light from the second arm to create a first output and a second output;
• a detection stage comprising a first detector at the first output for detecting intensity modulation caused by interference of the recombined light;
• a retroreflection stage at the second output;
• and
• a signal processor communicably connected to both the modulation stage and the detection stage;
• receiving light at the laser detection system from the first entity;
• and
• encoding the modulation signal with information to be sent to the first entity via the retroreflection stage.

A laser detection system comprising:

• a Mach Zehnder interferometer, the Mach Zehnder interferometer comprising:
• an entry beam splitter for splitting incident light into a first arm, having an arm length L1 and a second arm having an arm length L2;
• a modulation stage for receiving a modulation signal and applying a phase difference to the second arm, a magnitude of the phase difference depending upon a magnitude of the modulation signal;
• an exit beam splitter for recombining light from the first arm with light from the second arm to create a first output and a second output;
• a detection stage comprising a first detector at the first output for detecting intensity modulation caused by interference of the recombined light;
• a signal processor communicably connected to both the modulation stage and the detection stage;
• and
• a second detector located at the second output, wherein a range of wavelengths over which the second detector can detect is different from a range of wavelengths over which the first detector can detect.