System and method for generating a frequency modulated linear laser waveform

Patent metadata

Field	Value
Publication number	US-9712250-B2
Application number	US-201414550028-A
Country	US
Kind code	B2
Filing date	Nov 21, 2014
Priority date	Jun 20, 2012
Publication date	Jul 18, 2017
Grant date	Jul 18, 2017

Abstract

A system for generating a frequency modulated linear laser waveform includes a single frequency laser generator to produce a laser output signal. An electro-optical modulator modulates the frequency of the laser output signal to define a linear triangular waveform. An optical circulator passes the linear triangular waveform to a band-pass optical filter to filter out harmonic frequencies created in the waveform during modulation of the laser output signal, to define a pure filtered modulated waveform having a very narrow bandwidth. The optical circulator receives the pure filtered modulated laser waveform and transmits the modulated laser waveform to a target.

First claim

The invention claimed is:

1. A system generating a frequency modulated laser waveform, the system comprising:
a laser capable of producing a laser output signal having a single frequency and a linewidth centered at ω o ;
an electro-optical modulator coupled to the laser and configured to receive the laser output signal from the laser;
a electric ramp generator including a voltage controlled oscillator controlled by a digital micro-controller, the electric ramp generator coupled to the electro-optical modulator and capable of generating a ramp having a frequency chirp with a bandwidth B over a time period T, and a modulation offset frequency ω m for controlling the electro-optical modulator to modulate the laser output signal to define a modulated waveform including harmonic frequencies, wherein the digital micro-controller is capable of generating a linear ramp;
a band-pass optical filter coupled to the electro-optical modulator and capable of receiving the modulated waveform and filtering out the harmonic frequencies created by the electro-optical modulator during modulation of the laser output signal and reflecting a filtered modulated waveform; and
an optical circulator separate from the band-pass optical filter and interconnecting the electric ramp generator and the band-pass optical filter, the optical circulator being configured to transmit the filtered modulated waveform from the band-pass filter to a target;
wherein the band-pass optical filter includes a bandwidth BW greater than the modulation bandwidth B and less than the modulation offset frequency ω m , and is centered at the frequency of the laser output signal ω o plus the modulation offset frequency ω m , wherein the linear ramp includes a deviation less than or equal to 71 Khz, and wherein the modulation offset frequency ω m of the linear ramp is between the range of 5.0 GHz and 30 GHz, and the bandwidth B of the linear ramp is between the range of 300 MHz and 3.0 GHz over a time period T between the range of 0.01 msec and 0.20 msec.

2. A method of generating a laser frequency modulated waveform, the method comprising:
generating a laser output signal having an ultra narrow linewidth defining a sine wave;
generating a linear ramp having a frequency chirp with a bandwidth B over a time period T, and a modulation offset frequency ω m ;
modulating the laser output signal from the single frequency laser with an electro-optical modulator driven by the linear ramp to define a modulated waveform including harmonic frequencies;
filtering the modulated waveform from the electro-optical modulator with a band-pass optical filter having a bandwidth BW that is greater than the modulation bandwidth B and less than the modulation offset frequency ω m and is centered at a frequency of the laser output signal ω o plus the modulation offset frequency ω m to remove the harmonic frequencies in the modulated waveform created by the electro-optical modulator during modulation of the laser output signal to produce a pure filtered modulated waveform;
reflecting the pure modulated waveform from the band-pass optical filter to an optical circulator separate from the band-pass optical filter and interconnecting the linear ramp and the band-pass optical filter; and
transmitting the pure modulated waveform from the optical circulator to a target, wherein modulating the laser output signal includes modulating the laser output signal to define a linear triangular waveform, wherein the linear ramp includes a deviation less than or equal to 71 Khz and wherein the modulation offset frequency ω m of the linear ramp is between the range of 5.0 GHz and 30 GI-z, and the bandwidth B of the linear ramp is between the range of 300 MHz and 3.0 GHz over a time period T between the range of 0.01 msec and 0.20 msec.

3. The method as set forth in claim 2 , further comprising transmitting the modulated waveform from the electro-optical modulator to the band-pass optical filter through the optical circulator.

4. The method as set forth in claim 3 , further comprising reflecting the pure filtered modulated waveform from the band-pass optical filter back to the optical circulator.

Assignees

• Nasa

Inventors

• Pierrottet Diego F
• Petway Larry B
• Amzajerdian Farzin
• Barnes Bruce W
• Lockard George E
• Hines Glenn D

Classifications

• G01S7/4911

  Transmitters · CPC title

• G01S17/32

  using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated · CPC title

• H04B10/5563 Primary

  Digital frequency modulation · CPC title

• H04B10/2575

  Radio-over-fibre, e.g. radio frequency signal modulated onto an optical carrier · CPC title

• H04B10/548 Primary

  Phase or frequency modulation · CPC title