EP4690392A1

EP4690392A1 - Multi-laser comb source with optical referencing scheme for mutually stabilizing laser combs to internal optical reference

Info

Publication number: EP4690392A1
Application number: EP24804187.3A
Authority: EP
Inventors: Sergey Vasilyev; Mikhail Mirov
Original assignee: IPG Photonics Corp
Current assignee: IPG Photonics Corp
Priority date: 2023-05-08
Filing date: 2024-05-08
Publication date: 2026-02-11
Also published as: CN121128049A; KR20260007274A; WO2024233631A1

Abstract

A mufti laser-based comb (MLC) source is configured with a plurality of laser combs. The-MLC is further configured with a narrow briswidth optical pump including a single frequency laser which is common to the laser combs. The pump light from, the narrow linewidth optical pump is coupled into and energizes the laser combs to output respective frequency combs each spanning over a single or multiple octaves. The laser combs each are phase-locked to the SF laser of the optical pump which thus provides the laser combs with a high degree of mutual coherence.

Description

MULTI-LASER COMB SOURCE WITH OPTICAL REFERENCING SCHEME FOR

MUTUALLY STABILIZING LASER COMBS TO INTERNAL OPTICAL REFERENCE

BACKGROUND OF THE DISCLOSURE

Field of the Disclosure

[0001] The disclosure generally relates to optical frequency comb generation. In particular, the disclosure relates to a multi laser-based comb (MLC) source configured with a referencing scheme for providing high mutual phase coherence and stabilization transfer among frequency combs of the source by phase locking each to a narrow linewidth optical pump common to all laser combs.

Kown Art

[0002] Broadband frequency combs attract particular attention because they enable a plethora of important applications related to the study and non-intrusive diagnostics of complex molecular systems. One of well-established approaches for generating frequency combs is based on Kerr mode-locked (KLM) ultrafast sources high power pulsed lasers energized by respective pumps. These sources allow direct generation and amplification of ultrashort fs pulses at a fixed pulse repetition frequency (FRF) f_rep the desired spectral range, for example, in the mid-IR (MIR) spectral range (2-20 μm). The KLM sources are based on polycrystalline bulk materials selected, for example, from the-TM:II-VI family which includes among others chromium-doped zinc sulfide and zinc selenide (Cr:ZnS-and Cr:ZnSe, respectively) crystals. The latter are disclosed in US Patents 10,483,709, 10,216,063 and 10,886,690 which are incorporated herein in their entirety.

[0003] In its basic form, an exemplary KLM source includes a bulk material, such as Cr:ZnS crystal, generating optical frequency combs by generating cross-phase modulation (XPM) between a femtosecond (fs) pulse train and a CW pump laser beam which co-propagate through the crystal, The latter generates an output including an infinite train of periodic fs pulses at a fundamental frequency f and its harmonics via random quasi phase matching (RQPM) process within the bulk. The furrier-transformation of each of these pulses results in a continuous super-broad spectrum or supercontinuum represented by equidistantly spaced lines which correspond to respective mutually coherent fundamental and harmonic frequency combs. There are two degrees of freedom associated with the frequency comb. The interval between adjacent frequencies is directly defined by the laser comb pulse repetition frequency (PRF). The other degree of freedom is the rate of slipping of the carrier-envelope offset (CEO) from pulse to pulse.

[0004] Referring to FIGs. 1A , the spacing between adjacent frequencies is equal to the PRF f_rep.

In time domain, adjacent pulses are uniformly separated, from one another at To stabilize- the PRF. the frequency laser comb has to be mode/phase-locked which means that the longitudinal modes of the laser's resonant cavity are in a fixed, phase relation resulting in constructive interference between these modes which causes a train of ultrashort pulses. One of the PRF control techniques utilizes phase-locked loops (PEL) to adjust the laser cavity length.

[0005] The nonuniformity of pulses seen in FIG. 1A is a result of the laser intracavity chromatic and nonlinearities which cause a slip of the CEO f_ceo from pulse to pulse. The slip occurs because the group and phase velocities inside the laser cavity are slightly different on a pulse-to-pulse basis. To control the slip, the PEL adjusts the pump power to keep the CEO to a defined setpoint.

[0006] When the PRF and CEO are both stabilized, a FOurier transformation of the output pulses results in a sharp radio-frequency (RF) spectrum or optical frequency comb as seen in FIG. 1B. In. summary, if the PRF and CEO are known, then all frequencies of the output are known, and: the output frequency comb is used as an "optical ruler."

[0007] The operation of MLC source requires high mutual coherence time (of the order of seconds) among its laser combs because it enables fast measurements with broad spectral coverage and high resolution (~0.1 GHz). The mutual coherence occurs when two laser combs are locked in phase, i.e., the phase of one tracks the other. Without this, adjacent teeth of output frequency eomb blend together,. sacrificing orders of magnitude in. spectral resolution and obscuring both the frequency and. amplitude accuracy possible with this technique.

[9008] Referring to FIG. 2, the MLC source found a broad, application in a. variety of industries including, for example, MIR dual comb spectroscopy (DCS) diagrammatic shown in F1G.2. The known high-end. MLC sources with high, mutual coherence time rely on the laser combs' referencing to an external narrowband continuous wave (CW) etalon laser. The latter provides the reference for obtaining coherence between optical signals because it operates at the required high optical frequencies unobtainable by the electronics. This approach exhibits excellent results, but it adds structural complexity and very high cost anti requires close operating wavelengths of respective frequency laser combs.

[0009] A need therefore exists in a MLC source provided with a referencing scheme for obtaining a high degree of mutual phase coherence between two or more laser combs without the use of external etalon lasers.

SUMMARY OF THE DISCLOSURE

[0010] The disclosed MLC source, including two or more frequency laser combs, is based on a referencing scheme including a narrow linewidth pump which energizes laser combs and, at the same time, provides an internal reference for phase locking each of these lasers. Since the laser combs each are phase-locked to the same internal reference, they are highly mutually coherent eliminating the need tor external lasers/references of the known devices.

[0011] Structurally, the disclosed two or more laser combs output respective trains of ultrashort pulses each of which has a super-broad single octave - multi-octave long (and greater) output frequency comb - supercontinuum. The laser combs are energized by the narrow linewidth laser pump, and each laser is phase-locked to the pump rendering the laser combs highly mutually coherent.

[0012] According to one feature of the MC source, the mode-locked laser combs have respective master Oscillator (MO) power amplifier/supercontinuum generator (PA SCG) architectures each including a master oscillator and power amplifier. Alternatively, a suitable high power SF pulsed laser can replace the MOPA configuration of the laser combs.

[0013] In accordance with another feature of the disclosed MC source, both the MO and PA SCG of each laser comb are selected from the TM:II-VI family. For example, both MO and PA of each SC laser are either Cr:ZnS or Cr:ZnSe or one of the MO and PA is Cr:ZnS and the other is CrZnSe.

[0014] The PA SCGs of respective laser combs are energized by the narrow linewidth pump light with the intensity sufficient to cause the onset of nonlinear effects in the PA SCO which govern the propagation of fs pulses through this amplifier. The nonlinear effects include intra-pulse three- wave mixings due to the RQPM, self-phase modulation (SPM) that results in a spectral broadening of pulses' spectrum to an octave or greater, and cross-phase modulation (XPM) between PA SCG (ωi.comb) and the narrow-linewidth pump (ωp), creating a new comb such that: As a result, the spectrum of each laser comb's output includes the amplified fundamental frequency comb (f) which is superimposed with the pump frequency comb, 2nd harmonic (SH) frequency comb (2_f), and sum-frequency generation (SFG) responsible for third 3_f, fourth 4_f, and higher frequency fombs respectively.

[0015] In accordance with another feature of the inventive source, the narrow linewidth pump includes a SF CW laser. The single SF CW laser simultaneously may be coupled into a plurality of pump amplifiers which energize respective SC lasers. The SF CW laser can be selected from SF solid-state lasers including SF semiconductor, SF fiber laser or SF diode-pumped bulk laser Operating in the desired frequency range, such as MIR spectral region, and have a Fabry-Perrot or ring resonator configuration. The pump amplifiers can be selected from solid-state or fiber amplifiers.

[0016] One structural possibility is to have a single pump amplifier energizing both the MO and PA of each comb laser. Still another possibility is to have two pump amplifiers energizing respective MO and PA of each laser comb, Regardless of the number of pump amplifiers, they all are .seeded by the same SF CW pump laser.

[0017] Alternatively, tire pump may include only the SF laser outputting pump light which is coupled directly to the plurality of SC lasers. Obviously the SF CW laser has to be configured to output powers sufficient to assist the generation of octave-long frequency combs. Currently, fiber and bulk SF CW lasers have been reported to output of up to 1 KW.

[0018] The outputs of respective laser combs are incident on frequency discriminators, such as dichroic mirrors, separating a few combs from the rest of the harmonic combs which exit through one or designated source outputs. The filtered frequency combs are further guided through two distinct PLLs of each laser comb the operation of which is well-known to one of ordinary skill in the mode-locked laser arts.

[0019] The narrow linewidth pump does not have to be necessarily based on a SF CW laser with or without the pump amplifier. It may be configured as a pulsed device which should operate as a laser comb generating a fs frequency comb.

[0020] In particular, one of the PLL operates based on the phase difference between the detected two SC lasers. It includes a phase-frequency detector (PFD) and provides a beatnote signal applied to an actuator which adjusts the length of the resonant cavity of the MO corresponding to the phase adjustment between the laser comb and pump, Having the phase adjusted indirectly corrects the PRE since the frequency mode spacing of the fs frequency comb is equal to the inverse of the cavity round trip time, The other PLL controls the CEO. While configured similarly to die above- discussed PLL, the control signal modulates the pump power. ???

[0021] Stil olther features are discussed in detail below. Moreover, it is to be understood that both the foregoing information and the following detailed description are merely illustrative examples of various aspects and features which indicate that a particular feature, structure, or characteristic described may be included in at least with one other or all of the disclosed features.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Various aspects of the disclosure are discussed below wi th reference to the accompanying figures, which are not intended to be drawn to scale. The figures are included to provide an illustration and a further understanding of the various features, and are incorporated in and constitute a part of this specification, but are not intended as a definition of the limits of any particular embodiment. In the figures:

[0023] FIGs. 1A and 1B illustrate known principles of operation of mode-locked lasers;

[0024] FIG. 2 is a highly diagrammatic schematic of MLC of the known art;

[0025] FIG. 3 is an optical schematic of one of fee laser combs of fee inventive MLC;

[0026] FIG. 4A shows an electric field of a pulse signal at the focal point inside die PA of the laser comb of FIG. 3;

[0027] FIG. 4B illustrates and electric field of the SF CW pomp signal;

[0028] FIGs. 5 A and 5B are normalized spectral distributions of respective pulsed and CW pump signals at focal point inside the PA of the laser comb of F1G. 3;

[0029] FIG. 5C illustrates a pump comb generated within a super continuum generator (PA SCG) of each of laser combs of the disclosed source;

[0030] FIG. 6 is RF spectra of pump and SH frequency comb interference detected by a PD); and

[0031] FIGs. 7A and 7B are respective zoomed-in spectral regions of the pump and SH combs of fee spectrum of FIG. 6. SPECIFIC DESCRIPTION

[0032] The following description is focused on a MLC source configured with a phase referencing scheme operative to provide its multiple laser combs with a high degree of mutual coherence and stability transfer, The optical referencing scheme is based on a phase locking technique for sphase- locking multiple laser combs each against the source's internal narrow CW pump common to all laser Combs. As a result, the disclosed MLC source is characterized by high mutual coherence (of the order of tens of seconds) between two or more laser combs, stability transfer, simplified structural complexity and cost associated with the known MC setups.

[0033] Referring to FIG. 3, the inventive MC source 10 is configured with two or more laser combs 12 - ultrashort pulsed lasers outputting respective multi-octave frequency combs each of which spans from the bandgap edge of comb-generating nonlinear material to its phonon cut-off. While only one of laser Combs 12 is shown, the rest of laser combs are all configured identically to the shown, one and pumped by a narrow linewidth pump 14 of the shown laser comb. As illustrated, laser comb 12 has a MOPA architecture with, a MO 16 and PA supercofttinuum generator (PA SCG) 18 which are both based, for example, oft polycrystalline Cr:ZnS. The MO 16 may have a single- or multi-pass resonant cavity. The illustrated MO 16 is a 3-cycle (24 fs) oscillator.

[0034] The laser combs 12 each are phase-locked to the same reference- narrow linewidth pump 14 which amounts to stability transfer between each laser comb 12 and pump 14 while rendering laser combs 12 highly mutually phase coherent Since laser combs 12 output respective frequency combs spanning over multiple octaves, pump 14 can operate at any wavelength ranging between 0,35 nm and about 12 pm. In the shown exemplary schematic, SF CW pump laser 20 operates in a C-band which is somewhat between 1530 and 1565 nm corresponding to the amplification range of erbium (Er) doped pump amplifier 18 which boosts a 5 mW output of laser 16 to a few watts (W). As shown in FIG. 3, 5 mW SF pump light is amplified to 7 W light coupled into MO 16 and to 10 W light energizing PA SCG 18.

[0035] The narrow linewidth pump 14 necessarily includes a SF device, such as SF CW laser 20, and may also have at least one amplifier 22. The rest of not shown laser combs 12 each are directly coupled to the shown SF pump laser 20 which thus operates as the etalon laser/reference. The SF CW pump laser 20 may be selected from diode lasers, bulk or fiber lasers, while pump amplifier 22 is preferably either a fiber or bulk amplifier doped with any of the known light generating ions. [0036] If the pump amplifiers are used, as shown, then SF CW laser 20 seeds two Er-doped fiber pump amplifiers (EDFL) 22 energizing respective MO 12 16 and PA. SCG 18 of laser comb 12. Importantly, each laser comb 12 is provided a pair of pump amplifiers 22 so that SF CW pump laser 20 also seeds the pump amplifiers 22 of respective additional laser combs 12. One obvious modification of pump 14 includes using a single pump amplifier 22 for each laser comb 12. Still, another modification of the pump scheme may include illustrated narrow linewidth pump 14 utilized in its entirety to energize all laser combs 12. In the latter modification, if a SF CW laser 20 meets power and other requirements, pump amplifiers 22 may not be necessary. In summary, the only nun-negotiable condition narrow linewidth pump 14 should meet is the use of SF CW laser which in the shown example is SF CW pump laser 20,

[0037] Returning to the power condition of narrow linewidth pump 14, pump light should have a sufficiently high power to trigger die on-set of nonlinear effects (NLE) at least in PA SCG 18, but possibly in both MO 16 and PA SCG 18 of laser comb 12. In the shown schematic, the intensity threshold for NLEs may be approximately within a 20 - 40 GW/cm² exemplary range. Several nonlinear effects govern the propagation of fs pulses through the FA-SCG stage: optical rectification (0f) increasing the fundamental wavelength, intrapulse three-wave mixings due to RQPM, self-phase modulation (SPM) that results in a spectral broadening of pulses' spectrum to an octave, and cross-phase modulation (XPM) between the Cr:ZnS comb (ωi.comb) and the narrow-linewidth pump (ωp). The latter creates a new comb referred to as a pump frequency comb (p-comb) in which each tooth can be numbered as wherein i and j are integers. Thus, the output of PA-SGG 18, which is illustrated in FIG. 5A, includes the amplified fundamental frequency comb (f) which is superimposed with secondary frequency combs. The latter are generated by respective different nonlinear processes, such as optical rectification (0f), 2nd HG (2f), SFG (3f, 4f, etc.) and, importantly, the p-comb generated via XPM. The mode spacing of all frequency combs, which is in tire shown exemplary schematic fR = 80 MHz, is defined by the PRF of MO. The CEO offset frequency of the p-comb is where ωP is the pump laser frequency which in the shown example is 191 THz.

[0038] Considering FIG. 3 in combination with FIGs, 4A and 5 A, in the above disclosed process of multi-octave frequency comb generation of the exemplary schematics of FIG. 3, MO 16 generates input fs pulses 32 each centered at fundamental f-frequency of 125 THz. FIG. 4 A shows the temporal distribution of the pulsed signal resulting from the superposition of 0f-, f-and 2f- hfrequency combs, and higher harmonic combs in the focal point inside PA SCG 18 and corresponding to the highest instantaneous intensity upon coupling input pulses 32 each into the PA SCG 18. Co-propagating with pump light along PA SCG 18, the spectra of input pulse 32 within PA SCG 18 begin to broaden due to the above-disclosed NLEs turning eventually into output pulse 34 better seen in FIG. 4A. It is easy to see from FIGs. 3 and 5A that the fundamental f-frequency comb of output pulse 34 is not only broader than that of input pulse 32, but also it includes generated in PA SCG 18 pump p-comb 38 and SH 2f comb 36. Also, the output pulse 34 contains rectified frequency comb Of and third and fourth harmonic combs 3f and 4f all generated within PA SCG 18 of FIG. 3 along with possible other higher harmonic combs.

[0039] Returning to narrow-linewidth pump 14, it is readily apparent for one of ordinary skill in the laser arts that the CW operating regime of pump 14 is not the only regime at which the pump may operate within the context of disclosed source 10. The pump 14 may operate in a pulsed regime as well outputting a train of fs pulses, i.e>, another laser comb in addition to laser combs 12 in addition to laser combs 12. (One of the conditions to be met in case of the pump laser comb, is to prove that this comb has the required temporal stability sufficient to obtain the beat note signal. The latter represents the phase difference developed during the operation of source 10 between the pump and other laser combs due to the interference between pump and selected frequency combs as disclosed hereinbelow. Still another condition relates to crystal amplifiers PA SCG 18 - they have to be awfully good to withstand high light intensities.

[0040) FIGs. 4B and 5B illustrate p-comb 38 taken in a spectral, zone 40 of FIG. 5A where the fundamental frequency and SH combs 34, 36, respectively, merge. The zone 40 is selected for subsequent measurements of the CEO frequency, but, in addition, this zone is of interest because it contains p-comb 38. As shown in FIG. 5C, PA SCCG 18 receives the near IR narrowband spectrum of SF CW input 42 (FIG. 5B) and generates a p-comb 38 including the IR narrow band component.

[0041] The light-guiding optics of MC source 10 may have a variety of configurations. As shown, MO 16 and PA SCG 18 are in optical communication through an output coupler 24 of the MO resonant cavity, reflector 26 and a first dichroic minor (DM) 28 which is transparent to pump light but deflects the seed light from MO 16 so that the pump and MO outputs co-propagate before being coupled into PA SCG 18.

[0042] The output frequency comb of laser comb 12 is incident on another DM 28 separating a near-lR part of the output from the fundamental frequency corn. This near-infrared part contains a narrowband pump component , i.e., the SF of pump laser 20, the p-comb generated in PA SCG 18 of laser comb 12, SHG 2f comb (03 W), arid a short-wave part of the fundamental frequency f-comb. The narrowband pump component is then attenuated with a notch filter 46 to ensure the fidelity of the measured signals at PD 30 - an InGaAs photodiode. A bandpass filter 48 filters out the optical signal to the 1.55 μm band, and the f-p-2f light signal including overlapping combs at the output of the bandpass filter is detected by PD 30. The later generates an RF signal having an RF spectrum which is shown in FIG. 6. The RF spectrum reveals the beatings between fundamental f-comb and SHG 2f-comb at the offset frequency f0 as well as the beatings between both f and 2f combs against the p-comb at a beating frequency fb. Accordingly the output RF signal from PD 30 includes two RF frequency components fl) and fb further used for adjusting the CEO frequency of laser comb 12 and its phase respectively.

[0043] The output signal from PD 30 is then split into two paths defined by respective PLLs. The underlying mechanism of a PLL operates based on the phase difference between two signals. In the exemplary schematic, both PLLs are identically configured. Each PLL includes a phase frequency detector (PFD) 48 having two inputs: one for fb or f0 component and the other for a reference signal which, in the shown schematic, is a stable signal from rubidium (Rb) clock 56. Upon the comparison, if needed, two control signals are generated by respective PFDs 48. The other structural component of each PLL is a servo-amplifier 50. One of the control amplified signals is coupled into an acousto-optical modulator (AOM) 52 which modulates the pump's power thereby adjusting the CEO frequency. The other LLP measuring the mutual phase relationship between narrow linewidth pump 14 and laser comb 12 delivers the other control signal to a piezo-actuator 54. The latter adjusts the length of the resonator of laser comb 12 thereby phase locking laser comb 12 to pump 14 and adjusting the PRF of MO 16.

[0044] FIGs. 7 A and 7B show respective rf spectra of phase-locked f0 and fb signals, measured in-loop. While the XPM effect can be observed in a great variety of materials, these figures demonstrate that this effect is sufficient to generate a detectable signal corresponding to the pump p-comb which substantially matches the strength of the signal corresponding to SH comp36. In the exemplary schematics of FIG. 3, both the SH and pump output frequency are in a 1 pm range which facilitates the detection and measurement of the p-comb. In other words, the results of experiments shown in these figures conclusively demonstrate that the optical power of the p-comb is sufficiently high for controlling, the phase locking process of each of laser combs 12 io narrow linewidth pump 14.

[0045] Having thus described multiple features of the disclosed source, it is to be appreciated that various alterations, modifications, and improvements will readily occur to those skilled in the art. For instance, the materials arid wavelengths used herein for laser combs can be substituted for other known materials used in generating frequency combs. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the scope of the examples discussed herein. Accordingly, the foregoing description and drawings are by way of example only.

[0046] What is claimed is:

Claims

1. A multi laser-based comb (MLC) source, comprising: a narrow linewidth laser-based optical pump outputting pump light; a plurality of frequency laser combs coupled to the optical pump and each energized by the received pump light to generate an output frequency comb spanning over a range between a single octave and multiple octaves, wherein the laser combs each are phase-locked to the optical pump and mutually coherent.

2. The MLC source of claim 1, wherein the narrow linewidth pump includes a single frequency (SF) pump laser common to the plurality of laser combs and operating in a continuous wave (CW) or pulsed regimes so that the pump light emitted from the SF pump laser is coupled into the combs.

3. The MLC source of claim 2, wherein the pump light propagating within each of the laser combs assists in generating nonlinear effects (NLE) upon being coupled into each of the laser combs, the NLE including three-wave mixings, self-phase modulation (SPM) and cross-phase modulation (XPM) in the PA of each laser comb, the output frequency combs output by respective laser combs each including superimposed combs of at least respective fundamental (f)-frequency, second harmonic (2f-SH) and broadband pump combs with the pump comb (p-camb) having, a near IR narrowband frequency component of the narrowband linewidth optical pump.

4. The MLC source of claim 3, wherein the output frequency comb further includes at least one additional harmonic comb higher than the 2f-SH comb.

5. The MLC source of claim 3, wherein the optical combs each are configured with a master oscillator (MO) power amplifier (PA) architecture including a MO which seeds a PA, the MO generating a train of ultrashort pulses at the f frequency which co-propagates with the pump light upon coupling into the PA generating the output frequency comb.

6. The MLC source of claim 3, wherein the optical combs each are configured with a laser receiving the pump light and generating the output frequency comb.

7. The MLC source of claim 5, wherein the MO and PA of each laser comb are selected from polycrystalline materials of the TM:II-VI family, the polycrystalline materials used for respective MO and PA of each laser comb being identical or different from one another.

8. The MLC source of claim 2 further comprising a plurality of pump amplifiers coupled between the SF laser and respective laser combs and each receiving and amplifying the pump light which energiz.es the laser combs.

9. The MLC source of claim 8, wherein the laser combs each include a MOPA configuration with a MO and PA, the MO and PA of each laser comb being energized by a single pump amplifier or the MO and PA of each laser comb each being energized respective pump amplifiers.

10. The MLC source of claim 8, wherein the common SF pump laser is selected from SF semiconductor, SF fiber laser or SF diode-pumped bulk laser and having a Fabry-Perrot or ring resonator configuration, the pump amplifier being solid-state or fiber amplifier.

11. The MLC of claim 3 further comprising beam guiding optic systems each directing the output frequency comb of the laser comb along a path through a frequency discriminator which reflects overlapping p-comb, f-frequency and SH combs off the path and transmits a portion of one of the fundamental frequency or SH combs.

12. The MLC of claim 11 further comprising a polarity of notch filters each separating the narrowband component of the narrow linewidth pump from the rest of the pump comb so that an output of the notch filter includes the filtered pump, f-frequency and SH combs.

13. The MLC of claim 1.2 further comprising a plurality of photodetectors (PD) each detecting the output from the notch filter and outputting a RF signal which has spectra including f0 and fb signals, wherein the f0 signal corresponds to a carrier-enveiop offset (CEO) frequency of the laser comb and is a result of beating between the f-frequency and SH combs, and the fb signal corresponds to a mutual phase relationship between the narrow linewidth pump and laser comb is a beat note of heterodyning the f-frequency, SH and filtered p-combs.

14. The MLC of claim 13 further comprising a plurality of phase locked loops (LLP) each pair of which receives respective f() and fb signals from the PD, the LLPs of each pair including respective phase frequency detectors (PFD) which receive and compare respective f0 and fb signals to a reference signal, the PFDs outputting respective control signals which are coupled into respective servo-amplifiers upon determining a mismatch between each of the f0 and fb signals and reference.

15. The MLC of claim 14 further comprising a plurality of acousto-optical modulators (AOM) and comb laser resonant cavity actuators, wherein each pair of the AOMs and cavity actuator are operatively connected to the laser comb and coupled to respective servo-amplifier outputs so that the AOM modulates a power of the narrow linewidth pump to adjust the CEO of the laser comb, and the resonant cavity actuator adjusts the length of a resonator cavity of the laser comb to phase lock the laser comb to tbe narrow linewidth pump.