Linear frequency modulation control for FM laser radar

A method for maintaining linearity in the transmitted beam of a linear frequency modulated (LFM) laser radar system comprising the steps of:

• (a) emitting a beam of laser light at a preselected center frequency;
• (b) linearly modulating the frequency of said laser light beam to create said transmitted beam;
• (c) retaining a portion of said transmitted beam;
• (d) monitoring said retained portion of said modulated beam to detect non-linearities therein;
• (e) generating an error voltage which is proportional to the degree of non-linearity detected;
• (f) deriving an error correction signal from said error voltage;
• (g) applying said error correction signal to said linear modulation of said laser light beam to compensate for said detected non-linearity;
• and
• (h) modulating said retained portion of said transmitted beam onto a carrier signal.

A method for compensating for non-linearities in a transmitted beam of a linear frequency modulated (LFM) laser radar system comprising the steps of:

• (a) emitting a laser light beam at a preselected center frequency;
• (b) linearly modulating the frequency of said light beam with respect to time to create a linear frequency modulated transmitted beam;
• (c) retaining a portion of said transmitted beam;
• (d) mixing said retained portion of said transmitted beam with a local oscillator beam in a photomixer to produce an electronic signal representative of the transmitted beam and offset in frequency by an amount equal to the frequency difference between said local oscillator laser and said preselected center frequency of said laser light beam;
• (e) splitting said electronic signal into two portions and introducing a time delay into one of said portions;
• (f) mixing said delayed and undelayed portions of said electronic signal to produce a resulting signal;
• (g) mixing said resulting signal with a reference signal at a frequency substantially equal to said offset frequency to derive an error correction signal;
• (h) applying said error correction signal to said linear modulation of said light beam to compensate for non-linearities in the transmitted beam.

A frequency control system for maintaining linearity in the transmitted beam of a linear frequency modulated (LFM) chirped laser radar system comprising:

• (a) transmitter means for emitting laser light at a preselected center frequency;
• (b) means for linearly modulating the frequency of said laser light with respect to time to create a linear frequency modulation beam;
• (c) means for sensing non-linearities in the modulation of said modulation beam;
• (d) means for generating a real-time error correction signal in response to said non-linearities sensed by said sensing means;
• and
• (e) feedback means for applying said real-time error correction signal to said modulating means to compensate for said sensed non-linearities in said modulation.

A method for maintaining continuous linearity in the transmitted beam of a linear frequency modulated (LFM) chirped laser radar system comprising the steps of:

• (a) emitting a beam of laser light at a preselected center frequency;
• (b) linearly modulating the frequency of said laser light beam to create said transmitted beam;
• (c) retaining a portion of said transmitted beam;
• (d) monitoring said retained portion of said modulated beam to detect non-linearities therein;
• (e) generating an error voltage which is proportional to the degree of non-linearity detected;
• (f) deriving a real-time error correction signal from said error voltage;
• (g) applying said real-time error correction signal to said linear modulation of said laser light beam to compensate for said detected non-linearity in said modulation.