Orbital angular momentum generating apparatus for polarization modulation of orbital angular momentum and method thereof

An orbital angular momentum generating apparatus for polarization modulation of orbital angular momentum, wherein:

• a gaussian light source module, a first orbital angular momentum modulation module, a second orbital angular momentum modulation module and a multiplexing module;
• the Gaussian light source module comprises a pumping light source and a polarizer;
• the pumping light source is used for generating Gaussian pulse light;
• the polarizer modulates the Gaussian pulse beam into a required polarization state;
• the first orbital angular momentum modulation module comprising:
• a first delayer, a first quarter-wave plate, a first holographic grating switch, a first spiral phase plate and a first total reflector;
• the first holographic grating switch, the first spiral phase plate and the first total reflector are sequentially connected to form a first round-trip light path;
• the second orbital angular momentum modulation module comprising:
• a second delayer, a second quarter-wave plate, a second holographic grating switch, a second spiral phase plate and a second total reflector;
• the second holographic grating switch, the second spiral phase plate and the second total reflector are sequentially connected to form a second round-trip light path;
• the multiplexing module comprising:
• a first polarization beam splitter, a second polarization beam splitter, a third polarization beam splitter, a half-wave plate and a beam combiner;
• the Gaussian light pulse enters the first orbital angular momentum modulation module or the second orbital angular momentum modulation module, the Gaussian light pulse firstly passes through the first delayer or the second delayer, then the first quarter-wave plate or the second quarter-wave plate rotates the polarization state of the light pulse for the first time, the light pulse enters the first round-trip light path or the second round-trip light path, thus realizing the modulation of the specific orbital angular momentum state by controlling the switching time of the first holographic grating switch or the second holographic grating switch;
• the modulated light pulses are emitted along the original light path and enter a beam combiner of the multiplexing module to be superposed to generate an orbital angular momentum state or a superposed state.