Widely tunable oscillator stabilization using analog fiber optic delay line

A circuit for stabilizing the frequency of an oscillator output signal of an oscillator device, comprising:

• delay line means comprising a long optical fiber receiving at one end thereof an optical output signal modulated by said oscillator output signal and transmitting at an opposite end thereof a delayed version of said optical output signal representing a delayed version of said oscillator output signal;
• phase detector means for detecting a change in a phase relationship between said oscillator output signal and said delayed version of said oscillator output signal;
• and
• means responsive to said phase detector means for changing the frequency of said oscillator output signal so as to counteract said change in phase relation whereby to stabilize said frequency;
• wherein said phase detector means and said delay line means comprise a delay line discriminator characterized by a sensitivity which is a function of the length of said optical fiber, said delayed optical output signal is attenuated in said optical fiber as a function of said length, and said length is such as to optimize said sensitivity against said attenuation.

A circuit for stabilizing the frequency of an oscillator output signal of an oscillator device, comprising:

• delay line means comprising a long optical fiber receiving at one end thereof an optical output signal modulated by said oscillator output signal and transmitting at an opposite end thereof a delayed version of said optical output signal representing a delayed version of said oscillator output signal;
• phase detector means for detecting a change in a phase relationship between said oscillator output signal and said delayed version of said oscillator output signal;
• and
• means responsive to said phase detector means for changing the frequency of said oscillator output signal so as to counteract said change in phase relationship, whereby to stabilize said frequency;
• wherein said phase detector means comprises an optical phase detector having two inputs, said system further comprising beam splitter means for dividing said optical output signal into a pair of optical output signals, one of said pair of optical output signals being transmitted through said optical fiber and the other being transmitted to one input of said optical phase detector, said opposite end of said optical fiber being coupled to the other input of said optical phase detector.

A circuit for stabilizing the frequency of an oscillator output signal of an oscillator device, comprising:

• delay line means comprising a long optical fiber receiving at one end thereof an optical output signal modulated by said oscillator output signal and transmitting at an opposite end thereof a delayed version of said optical output signal representing a delayed version of said oscillator output signal;
• phase detector means for detecting a change in a phase relationship between said oscillator output signal and said delayed version of said oscillator output signal;
• and
• means responsive to said phase detector means for changing the frequency of said oscillator output signal so as to counteract said change in phase relationship, whereby to stabilize said frequency;
• wherein said oscillator device comprises a mode locked laser having an optical carrier amplitude-modulated at a mode locking frequency of said laser, said amplitude-modulated optical carrier comprising said optical output signal and said mode locked laser comprising a laser diode and a mirror displaced from said laser diode by an optical path length corresponding to said mode locking frequency.

A circuit for stabilizing an oscillator device having an oscillator output signal and a frequency control for controlling the frequency of said oscillator device, comprising:

• a long optical fiber delay line which receives at one end thereof an optical carrier with modulation corresponding to said oscillator output signal and transmits at another end thereof a delayed version of said optical carrier including said modulation;
• a phase detector for sensing a phase difference between the modulation of said optical carrier and the modulation of said delayed version of said optical carrier, whereby to generate an error signal;
• and
• means for feeding back said error signal to said oscillator frequency control input;
• wherein said frequency control input is capable of varying said frequency across a band lying in a range from microwave to optical frequencies.

A circuit for stabilizing an oscillator device having an oscillator output signal and a frequency control input, comprising:

• a long optical fiber delay line which receives at one end thereof an optical carrier with modulation corresponding to said oscillator output signal and transmits at another end thereof a delayed version of said optical carrier including said modulation;
• phase detector for sensing a phase difference between the modulation of said optical carrier and the modulation of said delayed version of said optical carrier, whereby to generate an error signal;
• and
• means for feeding back said error signal to said oscillator frequency control input;
• wherein said oscillator device comprises a mode locked laser which generates said optical carrier, wherein the frequency of said oscillator output signal is a mode locking frequency of said laser, said circuit further comprising means for changing said mode locking frequency in response to an externally commanded change.

A method for stabilizing an oscillator device having an oscillator output signal and a frequency control input, said method comprising:

• transmitting through a long optical fiber delay line an optical carrier with modulation corresponding to said oscillator output signal whereby to produce a delayed version of said optical carrier including said modulation;
• sensing a phase difference between the modulation of said optical carrier and the modulation of said delayed version of said optical carrier, whereby to generate an error signal;
• feeding back said error signal to said oscillator frequency control input so as to change said frequency in such a way as to decrease said error signal;
• and
• controlling said frequency input in a frequency band laying in a range from microwave to optical frequencies.