Systems and methods for low noise frequency multiplication, division, and synchronization

• US 10,454,238 B2
• Filed: 10/05/2017
• Issued: 10/22/2019
• Est. Priority Date: 04/08/2015
• Status: Active Grant

• Current Assignee: IMRA America Incorporated (Aisin Corp.)
• Original Assignee: IMRA America Incorporated (Aisin Corp.)
• Inventors: Fermann, Martin E., Kuse, Naoya
• Primary Examiner(s): Pascal, Leslie C
• Application Number:
  US15/725,849
• Publication Number:
  US 20180048113A1
• Time in Patent Office: 747 Days
• CPC Class Codes: H01S 3/0014 Monitoring arrangements not otherwise provided for photometry G01J1/00, e.g. G01J1/4257; radiation pyrometry G01J5/00; measuring coherence of light G01J9/00; measuring wavelength of light G01J9/00, e.g. G01J9/0246; measuring optical pulses G01J11/00; calorimetrically measuring power of laser beams G01K17/003
• CPC Class Codes: H01S 3/0057 Temporal shaping, e.g. pulse compression, frequency chirping soliton generation and propagation G02F1/3513, H01S3/063 and H01S3/108
• CPC Class Codes: H01S 3/0078 Frequency filtering
• CPC Class Codes: H01S 3/0085 Modulating the output, i.e. the laser beam is modulated outside the laser cavity
• CPC Class Codes: H01S 3/0092 Nonlinear frequency conversion, e.g. second harmonic generation [SHG] or sum- or difference-frequency generation outside the laser cavity nonlinear frequency conversion per se G02F1/35
• CPC Class Codes: H01S 3/06712 Polarising fibre; Polariser
• CPC Class Codes: H01S 3/06791 Fibre ring lasers fibre laser gyrometers G01C19/72
• CPC Class Codes: H01S 3/107 using electro-optic devices, e.g. exhibiting Pockels or Kerr effect H01S3/1061, H01S3/1063, H01S3/1065 take precedence
• CPC Class Codes: H01S 3/1118 Semiconductor saturable absorbers, e.g. semiconductor saturable absorber mirrors [SESAMs]; Solid-state saturable absorbers, e.g. carbon nanotube [CNT] based
• CPC Class Codes: H01S 3/1304 by using an active reference, e.g. second laser, klystron or other standard frequency source H01S3/139 takes precedence; automatic control of electronic generators H03L7/00
• CPC Class Codes: H01S 3/1305 Feedback control systems
• CPC Class Codes: H01S 3/1306 Stabilisation of the amplitude
• CPC Class Codes: H01S 3/1307 Stabilisation of the phase
• CPC Class Codes: H01S 3/136 by controlling devices placed within the cavity
• CPC Class Codes: H01S 3/2391 emitting at different wavelengths
• CPC Class Codes: H03B 17/00 Generation of oscillations using radiation source and detector, e.g. with interposed variable obturator
• CPC Class Codes: H03B 2200/009 Reduction of phase noise
• CPC Class Codes: H03D 7/14 Balanced arrangements
• CPC Class Codes: H03F 3/08 controlled by light
• CPC Class Codes: H03L 7/24 using a reference signal directly applied to the generator

Abstract

Low phase noise radio frequency (RF) sources generated by voltage controlled oscillators (VCOs) are described. Optical modulators driven by a VCO may be used to generate optical side-bands to cw lasers. The spectral extent of said side-bands can be increased via frequency broadening in highly nonlinear waveguides. Free running mode locked low phase noise comb oscillators can be used as reference oscillators to generate beat signals between those side-bands and individual comb modes at distal spectral regions, thereby creating an error signal used to reduce the phase noise of VCOs and the generation of low phase noise RF signals. VCO phase noise may be reduced by using free-running modelocked comb lasers phase locked to external frequency references, by omitting a reference comb and using a nonlinear interferometer for generating an error signal, or by locking a slave comb to the modulation frequency of an intra-cavity modulator driven by the VCO.

Claims

1. A source of low phase noise microwave frequencies, said source comprising:

a continuous wave (cw) laser;

said cw laser configured to be modulated with an optical modulator;

said optical modulator configured to be driven by a microwave frequency,

said optical modulator configured to generate side-bands to the cw laser in a frequency domain with a frequency spacing given by a modulation frequency of the optical modulator;

a nonlinear medium to nonlinearly broaden the spectral extent of said side-bands and to generate a supercontinuum spectrum;

a nonlinear interferometer configured to generate a beat signal; and

a detector to detect said beat signal;

wherein said beat signal comprises amplified phase noise from said microwave frequency, and

wherein said source is configured to use feedback from said beat signal to reduce the amplified phase noise from said microwave frequency.

2. The source of low phase noise microwave frequencies according to claim 1, wherein said nonlinear interferometer comprises an f-2f interferometer.

3. The source of low phase noise microwave frequencies according to claim 2, wherein said nonlinear interferometer comprises a nonlinear waveguide.

4. The source of low phase noise microwave frequencies according to claim 1, wherein said low phase noise is obtainable with microwave frequencies greater than about 25 GHz and up to about 1000 GHz, and wherein said phase noise is lower than −

120 dBc/Hz at a frequency offset of about 100 kHz.

5. The source of low phase noise microwave frequencies according to claim 1, further comprising:

a radio frequency (RF) reference configured to provide an RF reference signal which, together with an output of said detector, provides for generation of an error signal and reduction of phase noise via said feedback.

6. The source of low phase noise microwave frequencies according to claim 5, wherein said feedback comprises a feedback loop.

7. The source of low phase noise microwave frequencies according to claim 5, said source comprising:

a controllable microwave generator configured to receive said error signal and to generate a phase-noise reduced output thereof.

8. The source of low phase noise microwave frequencies according to claim 7, wherein said phase-noised reduced output of said controllable microwave generator is coupled to said optical modulator via a feedback arrangement.

9. The source of low phase noise microwave frequencies according to claim 7, wherein said controllable microwave generator comprises a voltage controlled oscillator (VCO).

10. The source of low phase noise microwave frequencies according to claim 1, wherein said nonlinear interferometer comprises a 2f-3f interferometer or a 3f-4f interferometer.

11. The source of low phase noise microwave frequencies according to claim 1, wherein said nonlinear interferometer comprises a waveguide interferometer.

12. The source of low phase noise microwave frequencies according to claim 11, wherein said waveguide interferometer comprises a periodically poled Lithium Niobate (PPLN) waveguide arranged in a 2f-3f interferometer configuration in which a 2f-3f beat signal at a red wavelength is generated.

13. The source of low phase noise microwave frequencies according to claim 1, wherein said optical modulator comprises:

one or more cascaded phase modulators disposed downstream from said cw laser and arranged such that an output of said cw laser, including the spectral content of said side-bands, is frequency broadened via phase modulation.

14. The source of low phase noise microwave frequencies according to claim 1, wherein said source comprises at least one fiber amplifier disposed between said optical modulator and said nonlinear medium.

15. The source of low phase noise microwave frequencies according to claim 14, wherein said at least one fiber amplifier comprises an Erbium-doped amplifier.

16. The source of low phase noise microwave frequencies according to claim 1, wherein said optical modulator is configured to generate a pulse train at a repetition rate corresponding to said modulation frequency, said source further comprising an optical amplitude modulator configured to reduce the repetition rate of said pulse train to a reduced repetition rate.

17. The source of low phase noise microwave frequencies according to claim 16, further configured to inject the pulse train at said reduced repetition rate into said nonlinear medium.

18. The source of low phase noise microwave frequencies according to claim 16, wherein said optical modulator is configured to drive a frequency near 25 GHz.

19. The source of low phase noise microwave frequencies according to claim 16, wherein said reduced repetition rate is near 1 GHz.