SYSTEMS AND METHODS FOR LOW NOISE FREQUENCY MULTIPLICATION, DIVISION, AND SYNCHRONIZATION

• US 20180048113A1
• Filed: 10/05/2017
• Published: 02/15/2018
• 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
• Granted Patent: US 10,454,238 B2
• Time in Patent Office: 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, the source comprising:

a mode locked comb laser;

a continuous wave (cw) laser,

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

wherein said optical modulator is configured to be driven by a micro-wave frequency generated with a controllable microwave generator,

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

a nonlinear medium to nonlinearly broaden the spectral extent of said side-bands,

a detector arrangement configured to detect primary beat signals between two individual comb modes from said comb laser with the frequency side-bands from the cw laser,

a radio frequency (RF) mixer configured to mix said two primary beat signals thereby generating a secondary beat signal,

said secondary beat signal comprising amplified phase noise from said micro-wave frequency generated by said controllable microwave generator; and

a servo loop configured to use feedback from said secondary beat signal to reduce the phase noise of said micro-wave frequency.

2. A source of low phase noise microwave frequencies according to claim 1, wherein a comb mode of said mode locked comb laser is locked to a cw laser to increase stability of said mode locked comb laser.

3. A source of low phase noise microwave frequencies according to claim 1, said optical modulator comprising an electro-optic phase modulator.

4. A source of low phase noise microwave frequencies according to claim 1, said optical modulator comprising more than one cascaded electro-optic phase modulators and at least one electro-optic amplitude modulator.

5. A source of low phase noise microwave frequencies according to claim 1, further comprising at least one optical amplifier.

6. A source of low phase noise microwave frequencies according to claim 1, wherein said mode locked comb laser is free running, and comprises one or more of a solid-state, fiber or diode mode locked laser.

7. A source of low phase noise microwave frequencies according to claim 6, said comb laser being constructed from all polarization maintaining fiber.

8. A source of low phase noise microwave frequencies according to claim 6, said comb laser further comprising a nonlinear amplifying loop mirror.

9. A source of low phase noise microwave frequencies according to claim 1, configured to produce a single-side band phase noise density for a 10 GHz carrier of less than −

140 dBc/Hz at a frequency offset of 100 kHz.

10. A source of low phase noise microwave frequencies according to claim 1, further configured to produce a single-side band phase noise density for a 10 GHz carrier of less than −

160 dBc/Hz at a frequency offset of 100 kHz.

11. A source of low phase noise microwave frequencies according to claim 1, further configured to produce for an RF carrier frequency of x GHz a single-side band phase noise density less than −

140 dBc/Hz+10*log (x/10 GHz)² dBc/Hz at a frequency offset of 100 kHz.

12. A source of low phase noise microwave frequencies according to claim 1, further comprising at least one stable cw reference laser, said comb laser further configured to allow for phase locking of at least one isolated comb mode from said comb laser to said at least one stable cw reference laser.

13. A source of low phase noise microwave frequencies according to claim 12, further configured to produce a tertiary beat signal.

14. A source of low phase noise microwave frequencies according to claim 13, wherein said controllable microwave generator comprises a voltage controlled oscillator (VCO),

said source further comprising an RF divider to divide said tertiary beat signal by a constant factor, and an RF mixer to mix said divided tertiary beat signal with said secondary signal, thereby creating a quaternary beat signal, said quaternary signal comprising amplified phase noise from said micro-wave frequency generated by said VCO;

said source using feedback from said quaternary beat signal to reduce the phase noise of said micro-wave frequency.

15. A source of low phase noise microwave frequencies according to claim 1, said primary beat signals further being obtained via the use of cw transfer oscillators.

16. A source of low phase noise microwave frequencies according to claim 1, wherein said controllable microwave generator comprises a voltage controller oscillator (VCO),

said source further comprising a frequency divider to divide the frequency generated by the VCO by a constant factor before applying it to the optical modulator.

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

a low phase noise free running mode locked comb laser;

an optical filter to isolate two of the comb modes from the comb laser,

said isolated comb modes being modulated with an optical modulator;

said optical modulator configured to be driven by a micro-wave frequency generated from a voltage controlled oscillator (VCO),

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

a nonlinear medium to nonlinearly broaden the spectral extent of said side-bands,

two detectors to detect a beat signal between two higher order side-bands originating from the two different individual comb modes;

said beat signal comprising amplified phase noise from said micro-wave frequency generated by said VCO; and

a servo loop configured to use feedback from said beat signal to reduce the phase noise of said micro-wave frequency.

18. A source of low phase noise microwave frequencies according to claim 17, configured to produce for an RF carrier frequency of x GHz a single-side band phase noise density less than −

140 dBc/Hz+10*log (x/10 GHz)² dBc/Hz at a frequency offset of 100 kHz.

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

a continuous wave (cw) laser;

a cw laser output divided optically into a slave and master system by an optical splitter;

said master system comprising a micro-comb configured for broadband supercontinuum generation seeded by said cw laser;

said slave system including a modulator arrangement downstream from said splitter;

said modulator driven by a voltage controlled oscillator (VCO);

a supercontinuum generation stage downstream from said modulator arrangement;

at least one optical beam splitter to combine the spectral output from said master and slave system and at least one narrow bandpass optical filter configured to isolate a spectral region common to both the master and slave system from said combined spectral output; and

at least one detector configured to detect a beat signal in said isolated spectral region corresponding to interference of comb modes originating from said master and slave system,

said beat signal comprising amplified phase noise from said micro-wave frequency generated by said VCO; and

a servo loop configured to use feedback from said beat signal to reduce the phase noise of said micro-wave frequency.

20. A source of low phase noise microwave frequencies according to claim 19, further comprising

at least one transfer oscillator configured to facilitate detection of a beat signal in said isolated spectral region corresponding to interference of comb modes originating from said master and slave system.

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

a mode locked comb laser;

a continuous wave (cw) laser configured to generate a cw output;

an optical modulator operatively arranged to modulate said cw output, wherein said optical modulator is driven by a micro-wave frequency generated with a controllable microwave generator, said optical modulator configured to generate side-bands in the frequency domain with a frequency spacing given by the modulation frequency of the optical modulator;

a nonlinear medium disposed downstream from said optical modulator to nonlinearly broaden the spectral extent of said side-bands;

a detector arrangement configured to detect primary beat signals between two individual comb modes from said comb laser with the frequency side-bands;

a radio frequency (RF) mixer to mix said two primary beat signals thereby generating a secondary beat signal,

said secondary beat signal comprising amplified phase noise from said micro-wave frequency generated by said controllable microwave generator; and

a servo loop configured to use feedback from said secondary beat signal to reduce the phase noise of said micro-wave frequency.

22. The source of low phase noise microwave frequencies according to claim 21, wherein said controllable microwave generator comprises a voltage controlled oscillator (VCO).