Generation of optical signals with RF components

A method of generating an encrypted optical signal having a first RF component including a first RF carrier frequency and an information component, the method comprising the following steps:

• i) generating a first optical signal having a second RF component including a second RF carrier frequency different from said first RF carrier frequency;
• ii) generating a control signal having a third RF component including a third RF carrier frequency different from said first RF carrier frequency;
• said second of said third RF component including the information component,
• iii) applying the first optical signal to an optical modulator and
• iv) applying the control signal to the optical modulator to modulate the first optical signal so as to produce an output optical signal modulated by said first RF carrier frequency and said information component, said first carrier frequency being said second carrier frequency up-converted by said third carrier frequency or by an integer multiple of said third carrier frequency,
• wherein both the input optical signal and the control signal include an information component, one of which is a predetermined encryption code.

An apparatus for generating an optical signal having a first RF component, which includes a first RF carrier frequency and an information component, said apparatus comprising:

• i) an optical modulator having an optical input, and optical output, and a control input;
• ii) means for supplying to the optical input a modulated optical signal having a second RF component including a second RF carrier frequency different from said first RF carrier frequency;
• iii) means for supplying to the control input a control signal having a third non-zero RF component including a third RF carrier frequency different from said first RF carrier frequency;
• and
• iv) means for applying a modulation comprising said information component to said optical signal or said control input;
• the arrangement being such that there is produced at the optical output an optical signal modulated by said first RF carrier frequency and said information component, said first carrier frequency being said second carrier frequency up-converted by said third carrier frequency or by an integer multiple of said third carrier frequency, wherein an amplitude of said control signal is controlled to control a desired harmonic output.

An encryption device for generating an encrypted optical signal having a first RF component, which includes a first RF carrier frequency and an information component, said device comprising

• i) an optical modulator having an optical input, an optical output, and a control input;
• ii) means for supplying to the optical input a modulated optical signal having a second RF component including a second RF carrier frequency different from said first RF carrier frequency;
• iii) means for supplying to the control input a control signal having a third RF component including a third RF carrier frequency different from said first RF carrier frequency,
• iv) means for applying a modulation comprising said information component to said optical signal or said control input;
• the arrangement being such that there is produced at the optical output an optical signal modulated by said first RF carrier frequency and said information component, said first carrier frequency being said second carrier frequency up-converted by said third carrier frequency or by an integer multiple of said third carrier frequency;
• and
• means for applying modulation comprising information components to both the optical signal and the control signal, one of the information components being a predetermined encryption code.

A method of generating an output optical signal having an RF modulation, said method comprising:

• applying an input optical signal to an optical input of a modulator having a non-linear transfer function;
• and
• applying a control signal having a control RF frequency to control input of the modulator;
• the amplitude of the control signal being controlled to control a desired harmonic output such that the output optical signal is modulated by an RF frequency which is an integer multiple of the control RF frequency.

A method of generating an electrical or radio signal having a first RF component including a first RF carrier frequency and an information component, the method comprising the following steps:

• i) generating a first optical signal having a second RF component including a second, non-zero, RF carrier frequency different from said first RF carrier frequency;
• ii) generating a control signal having a third RF component including a third, non-zero, RF carrier frequency different from said first RF carrier frequency;
• said second or third RF component including the information component;
• iii) applying the first optical signal to an optical modulator;
• iv) applying the control signal to the optical modulator to modulate the first optical signal so as to produce an output optical signal modulated by said first RF carrier frequency and said information component, said first carrier frequency being said second carrier frequency up-converted by said third carrier frequency or by an integer multiple of said third carrier frequency, wherein an amplitude of said control signal is controlled to control a desired harmonic output;
• and
• v) extracting from said optical signal the first RF component having said first carrier frequency and information component.

An apparatus for generating an electrical or radio signal having a first RF component, which includes a first RF carrier frequency and in information component, said apparatus comprising:

• i) an optical modulator having an optical input, an optical output, and a control input;
• ii) means for supplying to the optical input a modulated optical signal having a second RF component including a second, non-zero, RF carrier frequency different from said first RF carrier frequency;
• iii) means for supplying to the control input a control signal having a third, non-zero, RF component including a third RF carrier frequency different from said first RF frequency;
• iv) means for applying a modulation comprising said information component to said optical signal or said control input;
• v) means for transmitting the optical signal to a detection means;
• and
• vi) the detection means being arranged to extract from the optical signal an RF component including said first carrier frequency and information component;
• the arrangement being such that the detection means extracts a signal modulated by said first RF carrier frequency and said information component, said first carrier frequency being said second carrier frequency up-converted by said third carrier frequency or by an integer multiple of said third carrier frequency, wherein an amplitude of said control signal is controlled to control a desired harmonic output.

A method for generating an up-converted modulated RF carrier on an optical carrier signal, said method comprising the steps of:

• applying a first RF sub-carrier-modulated optical input at a first non-zero sub-carrier radio frequency to an optical modulator;
• applying a second RF sub-carrier electrical input at a second non-zero sub-carrier radio frequency to said optical modulator;
• at least one of said first and second RF sub-carriers having been modulated to carry data therewith;
• and
• providing an optical carrier output signal from said optical modulator including an upconverted data-modulated third RF carrier frequency higher than either said first and second sub-carrier RF frequencies.

Apparatus for generating an upconverted data-modulated RF carrier on an optical carrier signal, said apparatus comprising:

• an optical signal source providing a first RF sub-carrier-modulated optical signal at a first non-zero sub-carrier radio frequency;
• an electrical signal source providing a second RF sub-carrier electrical signal at a second non-zero sub-carrier radio frequency;
• an information signal modulator connected to modulate at least one of said first and second RF sub-carriers with data;
• an electro-optical signal modulator having an optical input connected to receive said first RF sub-carrier-modulated optical signal, having an electrical control input connected to receive said second RF sub-carrier electrical signal, and having an optical output providing an upconverted data-modulated RF carrier at a third RF carrier frequency higher than either of said first and second RF sub-carrier frequencies.