A dual optical comb interlocking system based on self-injection locking

Abstract

The application discloses a kind of based on self-injection locking double optical comb interlocking system, including first and second DFB laser, first and second micro ring, first-third waveguide, first and second electro-optic modulator, adjustable optical filter, photodetector, microwave source, phase-locked loop, signal source, frequency mixer and lock frequency circuit;Backscattering light in the second micro ring is fed back to the second DFB laser, so that the wavelength of the second DFB laser is locked to the pump wavelength of the first DFB laser, so as to lock the first degree of freedom of double optical comb;The microcavity optical comb generated by the first DFB laser pumping the first micro ring is used as the main comb, and the microcavity optical comb generated by the second DFB laser pumping the second micro ring is used as the slave comb;Another set of aligned comb teeth outside the pump wavelength is filtered out through the adjustable optical filter, and the comb tooth beat signal is frequency-doubled to lock the repetition frequency difference of the main comb and the slave comb, so as to lock the second degree of freedom of double optical comb.The application can realize the interlocking of self-injection locking double optical comb.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of microcavity double optical comb interlocking, and particularly relates to a double optical comb interlocking system based on self-injection locking. BACKGROUND

[0002] Optical frequency comb is periodic pulse in time domain and equal-interval comb teeth in frequency domain. Soliton pulse excited by microcavity is called microcavity optical comb. The self-injection locking microcavity optical comb directly pumps the microcavity by a laser diode, has the characteristics of simple structure and strong anti-interference ability, and has great potential in on-chip integration and multi-scene adaptation. The self-injection locking double optical comb technology has the advantages of on-chip integration, and is more suitable for laboratory applications compared with traditional double optical comb technology. After the interlocking of double optical comb is completed, as a new high-resolution and wide-band optical measurement technology, it has important applications in gas absorption monitoring, absolute distance measurement, pump detection and electromagnetic spectrum measurement. However, in the existing self-injection locking microcavity optical comb system, there is a one-to-one strong coupling relationship between the pump light source and the microcavity. Neither single pump excitation double optical comb nor single cavity double comb technology is suitable for the generation of self-injection locking double optical comb, which poses a challenge to the interlocking of self-injection locking double optical comb. SUMMARY

[0003] The purpose of the present application is to provide a double optical comb interlocking system based on self-injection locking, which can realize the interlocking of self-injection locking double optical comb.

[0004] In order to achieve the above purpose, one aspect of the present application provides a double optical comb interlocking system based on self-injection locking, comprising first and second DFB lasers, first and second micro-rings, first to third waveguides, first and second electro-optic modulators, an adjustable optical filter, a photodetector, a microwave source, a phase-locked loop, a signal source, a frequency mixer and a frequency locking circuit,

[0005] The first DFB laser pumps the first micro-ring through the first waveguide, and the second DFB laser pumps the second micro-ring through the second waveguide. The pump wavelength of the first DFB laser is equal to that of the second DFB laser. The first micro-ring and the second micro-ring are coupled to form an asymmetric structure through the third waveguide. The resonance peaks of the first micro-ring and the second micro-ring at the pump wavelength are aligned.

[0006] The pump light of the first DFB laser resonates through the first micro-ring and is coupled into the third waveguide. The pump light of the first DFB laser has the same phase as the resonant light of the second DFB laser entering the second micro-ring. The backscattered light in the second micro-ring is fed back to the second DFB laser, which induces the output wavelength of the second DFB laser to be synchronized with the pump light of the first DFB laser, so that the output wavelength of the second DFB laser is locked to the pump wavelength of the first DFB laser.

[0007] The first DFB laser pumps the first micro-ring to generate a first self-injection-locked microcavity optical comb as a master comb, the second DFB laser pumps the second micro-ring to generate a second self-injection-locked microcavity optical comb as a slave comb, the master comb and the slave comb pass through an adjustable optical filter, another set of aligned comb teeth other than the pump light wavelength is filtered out, the beat frequency output radio frequency signal is obtained through a photoelectric detector, the radio frequency signal is output through a phase-locked loop, and the frequency of the signal source is referenced to the frequency multiplication signal output by the phase-locked loop through a frequency locking circuit;

[0008] The microwave signal output by the microwave source is divided into first and second microwave signals, wherein the first microwave signal is connected to the first electro-optical modulator after being mixed with the output signal of the signal source through a mixer, the repetition frequency of the master comb is locked on the modulation microwave output by the first electro-optical modulator, and the second microwave signal is connected to the second electro-optical modulator, and the repetition frequency of the slave comb is locked on the modulation microwave output by the second electro-optical modulator, so that the double optical comb interlocking is realized.

[0009] According to the double optical comb interlocking system based on self-injection locking according to the above aspect of the present application, the injection locking effect after the backscattered light is injected into the DFB laser is used, the wavelength of the slave DFB laser is locked to the wavelength of the master DFB laser, so that the first degree of freedom of the double optical comb is locked, the comb tooth other than the pump light of the double optical comb is selected and the beat frequency is locked, the second degree of freedom of the double optical comb is locked, and the double optical comb interlocking is realized. BRIEF DESCRIPTION OF DRAWINGS

[0010] In order to more clearly illustrate the technical solutions of the present application, the following will briefly introduce the drawings used in the description of the embodiments of the present application. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0011] Figure 1 The block diagram of the double optical comb interlocking system based on self-injection locking of an embodiment of the present application. DETAILED DESCRIPTION

[0012] In order to make the purpose, technical scheme and advantages of the present application more clear, the technical scheme of the present application will be described clearly and completely in the following with reference to the drawings. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0013] One embodiment of the present invention provides a dual optical comb interlocking system based on self-injection locking. The interlocking is achieved by locking two sets of aligned comb teeth, one main comb and one slave comb, respectively. One pair of comb teeth corresponds to the pump light of the dual optical comb, and the other pair consists of another set of comb teeth with similar wavelengths. Figure 1 As shown, the dual optical comb interlocking system of this invention includes a laser chip 1, a microcavity chip 4, a waveguide chip 19, and an electrical component.

[0014] The laser chip 1 includes a first DFB laser 2 and a second DFB laser 3. In this embodiment, the first DFB laser 2 and the second DFB laser 3 are C-band InP pump lasers with a wavelength of 1550 nm.

[0015] The first DFB laser 2 and the second DFB laser 3 directly pump the microcavity chip 4 based on the silicon nitride integrated photonic platform. The microcavity chip 4 includes a first microring 5, a second microring 6, a first waveguide 7, a second waveguide 8, a third waveguide 9, a fourth waveguide 10, a fifth waveguide 11, a first heater 12, a second heater 13, a third heater 14, a fourth heater 15, a fifth heater 16, a sixth heater 17, and a seventh heater 18.

[0016] The microcavity chip 4 is directly coupled to the waveguide chip 19 based on the lithium niobate integrated photonic platform. The waveguide chip 19 includes a first optical filter 20, a second optical filter 21, a first electro-optic modulator 22, a second electro-optic modulator 23, a first waveguide beam splitter 24, and a second waveguide beam splitter 25.

[0017] The electrical components include a tunable light filter 26, a photodetector 27, a microwave source 28, a phase-locked loop 29, a signal source 30, a single-sideband mixer 31, and a frequency-locking circuit 32. Light from the waveguide chip 19 is coupled out through an optical fiber, passes through a first optical fiber splitter 33, a second optical fiber splitter 34, and a combiner 35, and then passes through the tunable light filter 26 before entering the photodetector 27.

[0018] The dual-comb excitation and interlocking process revolves around the microcavity chip 4. In this embodiment, the resonance peaks of the first microring 5 and the second microring 6 are designed to be around 1550 nm, with free spectral ranges (FSR) of 21 GHz and 20 GHz, respectively.

[0019] The first DFB laser 2 is used to directly pump the first microring 5 through the first waveguide 7, and the second DFB laser 3 is used to directly pump the second microring 6 through the second waveguide 8. The first microring 5 and the second microring 6 are coupled through the third waveguide 9 to form an asymmetric structure. The resonance peaks of the first microring 5 and the second microring 6 at 1550 nm are aligned by tuning the third heater 14 and the fourth heater 15. The injection currents of the first DFB laser 2 and the second DFB laser 3 are adjusted so that their wavelengths are equal to the aligned microcavity resonance peaks.

[0020] The pump light from the first DFB laser 2 resonates through the first microring 5 and couples into the third waveguide 9. Its phase is altered by tuning the fifth heater 16, making the pump light from the first DFB laser 2 phase-to-phase with the resonant light from the second DFB laser 3 entering the second microring 6 through the second waveguide 8. The backscattered light within the second microring 6 is then fed back to the second DFB laser 3, inducing the output wavelength of the second DFB laser 3 to synchronize with the pump light from the first DFB laser 2. At this point, the output wavelength of the second DFB laser 3 is locked to the pump wavelength of the first DFB laser 2, making the first DFB laser 2 the master laser and the second DFB laser 3 the slave laser.

[0021] By tuning the first heater 12 to change the phase of the pump light of the first DFB laser 2, a first self-injection locked microcavity optical comb is generated as the master comb. By tuning the second heater 13 to change the phase of the pump light of the second DFB laser 3, a second self-injection locked microcavity optical comb is generated as the slave comb.

[0022] After the main comb is coupled to the waveguide chip 19 via the first waveguide 7, it is split into a first main comb and a second main comb by the first waveguide beam splitter 24. The first main comb is output through optical fiber coupling, and the second main comb passes through the first optical filter 20 to filter out the pump light. It then returns to the microcavity chip 4 through the first electro-optic modulator 22 and is coupled through the fourth waveguide 10 to be injected into the first microring 5. The sixth heater 17 is used to adjust the phase of the injected light to synchronize with the phase of the resonant light in the first microring 5. The modulation signal of the first electro-optic modulator 22 is close to the free spectral range of the first microring 5. The injection of the microwave modulation signal can lock the repetition frequency of the main comb to the modulation microwave of the first electro-optic modulator 22, avoiding the influence of noise in the first microring 5.

[0023] After the pump light is coupled to the waveguide chip 19 via the second waveguide 8, it is split into a first slave comb and a second slave comb by the second waveguide beam splitter 25. The first slave comb is output through optical fiber coupling, and the second slave comb passes through the second optical filter 21 to filter out the pump light. It then returns to the microcavity chip 4 through the second electro-optic modulator 23, and is coupled through the fifth waveguide 11 to be injected into the second microring 6. The seventh heater 18 is used to adjust the phase of the injected light to synchronize with the phase of the resonant light in the second microring 6. The function of the second electro-optic modulator 23 is similar to that of the first electro-optic modulator 22.

[0024] The first master comb and the first slave comb pass through the tunable light filter 26, which filters out another set of aligned comb teeth with a wavelength different from the pump light. The signal is then output as a radio frequency signal by the photodetector 27. The radio frequency signal is then output as a frequency-doubled signal by the phase-locked loop 29. The frequency-doubled signal output by the phase-locked loop 29 is equal to the difference between the repetition frequencies of the master comb and the slave comb, which is 1 GHz.

[0025] The microwave source 28 outputs a microwave signal that is divided into two paths: a first microwave signal and a second microwave signal. The first microwave signal is mixed with the output signal of the signal source 30 by a single-sideband mixer 31 and then connected to the first electro-optic modulator 22. The second microwave signal is directly connected to the second electro-optic modulator 23. The frequency of the signal source 30 is referenced to the frequency multiplier signal output by the phase-locked loop 29 through the frequency-locked circuit 32. This achieves dual optical comb interlocking.

[0026] In this embodiment of the invention, both the master comb and the slave comb are microcavity optical combs based on the self-injection locking principle, with a pump light wavelength of 1550nm, which is locked to the microcavity resonant peak through the self-injection locking effect.

[0027] The waveguide chip 19 is implemented based on a thin-film lithium niobate integrated photonic platform. It includes a first electro-optic modulator 22 with a modulation bandwidth designed to be 30 GHz, greater than the free spectral range of 21 GHz for the first microring 5. A second electro-optic modulator 23 also has a modulation bandwidth designed to be 30 GHz, greater than the free spectral range of 20 GHz for the second microring 6. A first optical filter 20 has a filtering bandwidth of 18 GHz, less than the free spectral range of 21 GHz for the first microring 5. A second optical filter 21 has a filtering bandwidth of 18 GHz, less than the free spectral range of 20 GHz for the second microring 6. The center wavelengths of the first and second optical filters 20 and 21 are adjustable, with the center wavelength near the pump wavelength of the first and second DFB lasers (1550 nm), aligned with the resonant peaks of the first and second microrings 5 ​​and 6. An adjustable optical filter 26 has a center wavelength near another set of resonant peaks aligned with the first and second microrings 5, but its corresponding wavelength is not equal to the resonant peak wavelength near 1550 nm.

[0028] The microwave source 28 outputs a microwave frequency near the free spectral range of the second microring 6, approximately 20 GHz. Due to the RF injection lock-in effect of the microcavity optical comb, the repetition frequency of the excited slave comb is equal to the microwave source frequency. The single-sideband mixer 31 outputs a frequency near the free spectral range of the first microring 5, approximately 21 GHz. Due to the RF injection lock-in effect of the microcavity optical comb, the repetition frequency of the excited master comb is equal to the output frequency after mixing. The frequency output by the signal source 30 is near the difference between the repetition frequencies of the master and slave combs, approximately 1 GHz, and has a fixed multiple relationship with the frequency multiplier signal output by the phase-locked loop 29. By locking the two through the frequency-locking circuit 32 and fine-tuning the signal source frequency through feedback, an interlocked dual optical comb can be obtained.

[0029] The self-injection locking dual-comb interlocking system of this invention uses dual DFB lasers to pump dual microcavities to excite dual optical combs. Through the asymmetric coupling design of the micro-ring cavity, the output wavelength of the slave DFB laser is synchronized to the output wavelength of the master DFB laser, achieving coherent synchronization of the pump source of the self-injection locking dual-comb system. Another set of aligned comb teeth is filtered out by an optical filter, and the beat frequency signal of the comb teeth is frequency-multiplied and locked with the difference in repetition frequency between the master and slave combs, ultimately achieving self-injection locking dual-comb interlocking. The working principle is as follows:

[0030] Let the output wavelength of the main DFB laser be... f 1. The output wavelength of the DFB laser is f 2. Since the pump light from the main DFB laser can propagate within the two microring resonators, the backscattered light from the corresponding microring resonator of the DFB laser includes the wavelength component of the main DFB laser. Through the synchronization effect induced by the backscattered light, it enables… f 1 and f 2 equal, denoted as f λ For an optical frequency comb, starting from the comb tooth corresponding to the pump light, the first... m The frequency corresponding to the root comb tooth is denoted as f m ,have:

[0031] (1)

[0032] in f rep This represents the repetition frequency of the optical frequency comb. The repetition frequency of the main comb is denoted as... f r1 The repetition frequency of the comb is denoted as f r2 Since the repetition frequencies of the master comb and the slave comb are different, their repetition frequency difference is denoted as . δf Besides the pump comb teeth, another set of closely spaced comb teeth is designated as the main comb's first... m root comb teeth and the first comb teethn The root comb teeth then have:

[0033] (2)

[0034] (3)

[0035] The beat frequency signal of the comb teeth can be written as:

[0036] (4)

[0037] For the other set of aligned comb teeth closest to the pump comb teeth, the corresponding values ​​of m and n differ by 1, therefore equation (4) can be written as:

[0038] (5)

[0039] Furthermore, due to the beat frequency signal of the comb teeth and δf Locked, available

[0040] (6)

[0041] Where k represents the multiple relationship between the repetition frequency difference of the two optical combs and the selected aligned comb beat frequency signal. When implemented through a frequency multiplier circuit, the value of k is a definite natural number or fraction.

[0042] Combining equations (5) and (6), we can obtain:

[0043] (7)

[0044] because f r2 It is a constant. Based on equation (7), it is established that... f m and f n The relationship is such that the pumps and teeth of both the main comb and the secondary comb are mutually locked, thus achieving interlocking of the dual combs.

[0045] In summary, the self-injection locking-based dual-comb interlocking system of this invention addresses the difficulty of achieving dual-comb interlocking in existing self-injection locking microcavity optical comb systems, where there is a one-to-one strong coupling relationship between the pump source and the microcavity. Through an asymmetric double-ring coupling design between the microcavities, coherent synchronization of the pump source of the self-injection locking dual-comb is achieved. Simultaneously, the asymmetric structure automatically divides the self-injection locking dual-comb into a master comb and a slave comb. This invention utilizes the injection-locking effect after backscattered light is injected into the DFB laser, locking the wavelength of the slave DFB laser to the wavelength of the master DFB laser, thereby locking the first degree of freedom of the dual-comb. By selecting comb teeth other than the pump light and locking their beat frequency, the second degree of freedom of the dual-comb is locked, ultimately achieving dual-comb interlocking.

[0046] The self-injection locking dual-comb interlocking system of this invention has the following advantages: This invention supports complete on-chip integration of the optical system, enabling a compact microcavity dual-comb interlocking system; This invention achieves coherent synchronization of the self-injection locking dual-comb pump source through an asymmetric dual-ring coupling design, and, combined with the vernier effect of the dual-comb, locks another set of comb teeth with similar wavelengths, thereby eliminating the degrees of freedom of the dual-comb and realizing dual-comb interlocking, eliminating the need for high-stability frequency sources such as atomic clocks as external references; This invention provides a technical implementation method for a fully on-chip integrated self-injection locking microcavity dual-comb, which has great application prospects in the fields of dual-comb ranging, dual-comb spectroscopy, and laser frequency stabilization.

[0047] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A dual optical comb interlocking system based on self-injection locking, characterized in that, It includes first and second DFB lasers, first and second microrings, first to third waveguides, first and second electro-optic modulators, tunable optical filters, photodetectors, microwave sources, phase-locked loops, signal sources, mixers, and frequency-locking circuits. The first DFB laser pumps the first microring through the first waveguide, and the second DFB laser pumps the second microring through the second waveguide. The pump wavelengths of the first DFB laser and the second DFB laser are equal. The first microring and the second microring are coupled through the third waveguide to form an asymmetric structure. The resonant peaks of the first microring and the second microring at the pump wavelength are aligned. The pump light of the first DFB laser is coupled into the third waveguide after passing through the first microring resonance. The pump light of the first DFB laser and the resonant light of the second DFB laser entering the second microring are in phase. The backscattered light in the second microring is fed back to the second DFB laser, inducing the output wavelength of the second DFB laser to be synchronized with the pump light of the first DFB laser. Thus, the output wavelength of the second DFB laser is locked to the pump wavelength of the first DFB laser. The first DFB laser pumps the first microring to generate a first self-injected locked microcavity optical comb as the master comb, and the second DFB laser pumps the second microring to generate a second self-injected locked microcavity optical comb as the slave comb. The master comb and the slave comb pass through a tunable optical filter to filter out another set of aligned comb teeth outside the pump light wavelength. The signal is then beat-frequency output by a photodetector. The radio frequency signal passes through a phase-locked loop to output a frequency-doubled signal. The frequency of the signal source is referenced to the frequency-doubled signal output by the phase-locked loop through a frequency-locking circuit. The microwave signal output from the microwave source is divided into two paths: a first microwave signal and a second microwave signal. The first microwave signal is mixed with the output signal of the signal source by a mixer and then connected to the first electro-optic modulator. The repetition frequency of the main comb is locked to the modulated microwave output by the first electro-optic modulator. The second microwave signal is connected to the second electro-optic modulator, and the repetition frequency of the secondary comb is locked to the modulated microwave output by the second electro-optic modulator, thereby achieving dual optical comb interlocking.

2. The system as described in claim 1, characterized in that, It also includes a fourth waveguide, a fifth waveguide, a first optical filter, a second optical filter, a first waveguide beamsplitter, and a second waveguide beamsplitter; The main comb is coupled out through the first waveguide and split into the first main comb and the second main comb through the first waveguide beam splitter. The first main comb is coupled out through the optical fiber, and the second main comb is filtered out through the first optical filter. The pump light is then returned through the first electro-optic modulator and coupled through the fourth waveguide to be injected into the first micro-ring. The pump light is output through the second waveguide coupling and split into a first and a second pump light by the second waveguide beam splitter. The first pump light is output through optical fiber coupling and the second pump light is filtered out by the second optical filter, then returned through the second electro-optic modulator and injected into the second micro-ring through the fifth waveguide coupling.

3. The system as described in claim 2, characterized in that, It also includes a first heater, a second heater, a third heater, a fourth heater, a fifth heater, a sixth heater, and a seventh heater; The first heater is used to change the pump light phase of the first DFB laser, and the second heater is used to change the pump light phase of the second DFB laser. The third and fourth heaters are used to align the resonant peaks of the first and second microrings, and the pump wavelengths of the first and second DFB lasers are equal to the aligned resonant peaks. The fifth heater is used to change the phase of the third waveguide so that the pump light of the first DFB laser is in phase with the resonant light of the second DFB laser entering the second microring. The sixth heater is used to synchronize the phase of the injected light injected into the first microring through the fourth waveguide with the phase of the resonant light inside the first microring. The seventh heater is used to synchronize the phase of the injected light injected into the second microring through the fifth waveguide with the phase of the resonant light in the second microring.

4. The system as described in claim 3, characterized in that, The first and second microrings have different ring radii and unequal free spectral ranges.

5. The system as described in claim 4, characterized in that, The modulation bandwidth of the first electro-optic modulator is greater than the free spectral range of the first microring, and the modulation bandwidth of the second electro-optic modulator is greater than the free spectral range of the second microring.

6. The system as described in claim 5, characterized in that, The filtering bandwidth of the first optical filter is smaller than the free spectral range of the first microring, and the filtering bandwidth of the second optical filter is smaller than the free spectral range of the second microring. The center wavelengths of the first and second optical filters are adjustable and are near the pump wavelengths of the first and second DFB lasers, aligned with a set of resonant peaks of the first and second microrings.

7. The system as described in claim 6, characterized in that, The center wavelength of the tunable filter is near another set of resonant peaks aligned with the first and second microrings.

8. The system as described in any one of claims 1-7, characterized in that, The microwave frequency output by the microwave source is near the free spectral range of the second microring. Due to the radio frequency injection lock-in effect of the microcavity optical comb, the repetition frequency of the comb is equal to the microwave frequency.

9. The system as described in claim 8, characterized in that, The output frequency of the mixer after mixing is near the free spectral range of the first microring. Due to the RF injection lock-in effect of the microcavity optical comb, the repetition frequency of the main comb is equal to the output frequency after mixing.

10. The system as described in claim 9, characterized in that, The signal source output frequency is near the difference between the repetition frequencies of the main comb and the slave comb, and has a fixed multiple relationship with the frequency multiplier signal output by the phase-locked loop.

Images