Method and system for optical free space communications using non-mechanical beam steering

A method of communicating in free space comprising the steps of:

• generating a phase modulated optical communications carrier signal;
• generating a pointing and tracking beacon;
• transmitting the phase modulated optical communications signal and pointing and tracking beacon from a first communications terminal to a receiver unit of a second communications terminal;
• receiving the phase modulated optical communications signal within second communications terminal and passing the signal through a receive Bragg cell and liquid crystal of the second communications terminal;
• detecting the pointing and tracking beacon;
• generating a receive beam control signal to the receive Bragg cell and liquid crystal based on the detected pointing and tracking beacon to change the index of refraction through the receive Bragg cell and liquid crystal to compensate for receive errors;
• demodulating the phase modulated optical communications signal back into the broad band frequency division multiplexed signal;
• and
• demultiplexing the frequency division multiplexed signal into a plurality of analog communication signals.

A system for communicating in free space comprising:

• a first communications terminal including:
• means for generating a phase modulated optical communications signal;
• means for generating a pointing and tracking beacon;
• a receiver positioned at a second communications terminal that receives the optical communications signal and pointing and tracking beacon and including:
• a cascaded Bragg cell and liquid crystal that receives the optical communications signal and pointing and tracking beacon;
• a pointing and tracking detector for detecting the pointing and tracking beacon;
• and
• a controller responsive to the pointing and tracking detector for issuing control signals to the cascaded Bragg cell and liquid crystal to change the index of refraction therethrough.

A system for communicating in free space comprising:

• a first communications terminal including:
• a multiplexer circuit for multiplexing a plurality of analog communication signals into a single broad band frequency division multiplexed signal;
• a laser for generating an optical carrier signal;
• an electro-optic modulator that receives the broad band frequency division multiplexed signal and the laser generated optical carrier signal with the multiplexed signal to produce a phase modulated optical communications signal;
• means for generating a pointing and tracking beacon;
• a receiver positioned at a second communications terminal that receives the transmitted phase modulated optical communications signal and including:
• a cascaded Bragg cell and liquid crystal through which the optical communications signal and pointing and tracking beacon passes;
• a pointing and tracking detector for detecting the pointing and tracking beacon;
• and
• a controller responsive to the pointing and tracking detector for issuing control signals to the cascaded Bragg cell and liquid crystal to change the index of refraction therethrough.

A communications terminal comprising:

• a transmitter unit for transmitting a phase modulated optical communications signal and pointing and tracking beacon;
• and
• a receiver unit that receives a phase modulated optical communications signal and pointing and tracking beacon from another communications terminal, and comprising:
• a receive beam steering assembly that receives a phase modulated optical communications signal, and including:
• a cascaded Bragg cell and liquid crystal, wherein the index of refraction through the Bragg cell and receive liquid crystal is changed based on received pointing and tracking beacon.

A communications terminal comprising:

• a transmitter unit for transmitting a phase modulated optical communications signal, and comprising a multiplexer circuit for multiplexing a plurality of analog communication signals into a single broad band frequency division multiplexed signal;
• a laser for generating an optical carrier signal;
• an electro-optic modulator that receives the broad band frequency division multiplexed signal and the laser generated optical carrier signal with the multiplexed signal to produce a phase modulated optical communications signal;
• means for generating a pointing and tracking beacon;
• a transmit beam steering assembly for non-mechanically steering the optical communications signal;
• and
• a receiver unit that receives a phase modulated optical communications signal and pointing and tracking beacon from another communications terminal, and comprising:
• a cascaded Bragg cell and liquid crystal, wherein the index of refraction through the Bragg cell and liquid crystal is changed based on the received pointing and tracking beacon;
• a demodulator for demodulating the phase modulated optical communications signal back into the broad band frequency division multiplexed signal;
• and
• a demultiplexer for demultiplexing the broad band frequency division multiplexed signal into the plurality of analog communication signals.

A beam steering device for free space optical communications comprising:

• a Bragg cell having first and second Bragg cell elements for providing vertical and horizontal indexing of a phase modulated optical communication signal;
• and
• a liquid crystal cascaded with the Bragg cell and having first and second liquid crystal elements to provide vertical and horizontal indexing of a phase modulated optical communication signal;
• a pointing and tracking beacon detector for detecting a pointing and tracking beacon received with an optical communications signal;
• and
• a controller responsive to the pointing and tracking beacon detector for generating control signals to the Bragg cell and liquid crystal for changing the index of refraction therethrough.