A method for generating a Kerr-brewster high-signal-to-noise ratio narrow-line-width optical comb

Abstract

The application discloses a Kerr-Briou high signal-to-noise ratio narrow line width optical comb generation method. First, a Kerr single soliton optical comb tooth is obtained by pumping laser and auxiliary laser on the output of an optical microcavity. Then, any number of continuous distribution comb teeth with power reaching an erbium-doped fiber amplifier amplification threshold are selected and shaped to make the comb tooth power consistent. Finally, the selected and shaped Kerr single soliton optical comb tooth is power amplified and then input into a fiber ring cavity to excite a Briou effect, so that a comb tooth with higher signal-to-noise ratio, narrower line width and lower frequency noise, i.e. a Kerr-Briou high signal-to-noise ratio narrow line width optical comb, is obtained.

Description

Technical Field

[0001] This invention belongs to the field of optical communication technology, and more specifically, relates to a method for generating a Kerber-Brillouin high signal-to-noise ratio narrow linewidth optical comb that combines the Kerr nonlinear effect and the Brillouin effect. Background Technology

[0002] To meet the growing global demand for data transmission, optical interconnect networks based on silicon photonic integrated circuits will replace traditional electrical interconnect networks as the main development trend of communication networks. As an important component of optical communication systems, light sources lay the foundation for achieving low cost, high stability, and high bandwidth.

[0003] Kerr soliton optical combs are a series of frequency comb teeth generated by a laser-pumped optical resonator through various nonlinear effects. They are not only suitable for on-chip integration, but their waveforms also remain undistorted during transmission, exhibiting high stability and a smooth spectral envelope. This makes them an ideal multi-wavelength broadband light source with potential applications in short- and long-distance wavelength division multiplexing (WDM) optical communication systems, miniaturized optical clocks, and low-noise microwave signal generation. Currently, the main methods for generating Kerr soliton optical combs include rapid thermal tuning, assisted laser heating, and self-injection locking.

[0004] While Kerr soliton optical combs offer the advantages mentioned above, their noise and linewidth still have significant room for optimization to further improve communication quality. Even when using highly stable, ultra-narrow linewidth lasers as pump sources, their frequency noise and linewidth are not optimal. Researchers worldwide are still exploring methods to minimize frequency noise and narrow linewidth, such as self-injection locking and PDH-Locking; however, many of these methods involve considerable system complexity or impose certain equipment requirements.

[0005] The stimulated Brillouin effect is a common nonlinear optical effect in fiber optic communication systems. When the pump light enters the Brillouin gain medium and reaches the threshold, it generates Stokes light through electrostriction. Stokes light has the same frequency as the sound wave but propagates in the opposite direction to the pump light. Stokes light has a significantly narrower linewidth than the gain medium and a much lower noise level than the incident light. However, its extremely narrow gain bandwidth also makes its application extremely difficult. Currently, the method for stimulating the Brillouin effect involves using a single laser beam as the pump light and feeding it into the Brillouin gain medium. Brillouin gain has been applied to spectral line extraction and pulse shaping in optical frequency combs, as well as to improving the carrier-to-noise ratio to reduce signal distortion after carrier modulation. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for generating a Kerbrillouin high signal-to-noise ratio narrow linewidth optical comb. This method generates a Kerbrillouin high signal-to-noise ratio narrow linewidth optical comb by generating a Kerbrillouin soliton optical comb in an optical microcavity and then using an optical fiber ring cavity to excite the Brillouin effect.

[0007] To achieve the above-mentioned objective, the present invention provides a method for generating a Kerbrillon high signal-to-noise ratio narrow linewidth optical comb, characterized by utilizing the Kerbrillon soliton optical comb teeth to excite the Brillon effect, thereby optimizing the frequency noise and linewidth. Specifically, the method includes the following steps:

[0008] (1) Obtain the comb teeth of the Kerr monosole optical comb.

[0009] Two optical bandstop filters are used to filter out the pump laser and auxiliary laser in the Kerr soliton optical comb output from the optical microcavity, respectively, to obtain the Kerr soliton optical comb teeth.

[0010] (2) Select and shape the comb teeth

[0011] A wavelength-selective switch is used to select any number of continuously distributed comb teeth in the Kerr single soliton optical comb with power reaching the amplification threshold of the erbium-doped fiber amplifier. Then, the comb teeth are shaped to make all comb teeth have the same power and are sent to the erbium-doped fiber amplifier.

[0012] (3) Generate a Kerbrillouin high signal-to-noise ratio narrow linewidth optical comb

[0013] Erbium-doped fiber amplifiers amplify the power of the selected and shaped Kerr soliton optical comb teeth, and then input them into the fiber ring cavity to excite the Brillouin effect, resulting in comb teeth with higher signal-to-noise ratio, narrower linewidth, and lower frequency noise, i.e., Kerr-Brillouin high signal-to-noise ratio narrow linewidth optical comb.

[0014] The objective of this invention is achieved as follows:

[0015] The present invention discloses a method for generating a Kerbrillouin high signal-to-noise ratio narrow linewidth optical comb. First, a pump laser and an auxiliary laser are applied to a Kerbrillouin soliton optical comb output from an optical microcavity to obtain Kerbrillouin soliton comb teeth. Then, any number of continuously distributed comb teeth with power reaching the amplification threshold of an erbium-doped fiber amplifier are selected and shaped to ensure consistent power. Finally, the selected and shaped Kerbrillouin soliton comb teeth are amplified and then input into an optical fiber ring cavity to excite the Brillouin effect, resulting in a comb with a higher signal-to-noise ratio, narrower linewidth, and lower frequency noise, i.e., a Kerbrillouin high signal-to-noise ratio narrow linewidth optical comb.

[0016] The Kerbrillouin high signal-to-noise ratio narrow linewidth optical comb generation method of the present invention has the following beneficial effects:

[0017] (1) It has a significant effect on reducing the frequency noise of Kerr soliton optical combs. The frequency noise of a single optical comb is reduced by three orders of magnitude in the frequency range of 10Hz-100Hz and by four to five orders of magnitude at 100kHz.

[0018] (2) It has a significant effect on narrowing the linewidth of the Kerr soliton optical comb. The linewidth of the Brillouin optical comb before and after the excitation of a single optical comb tooth is compressed by about 50 times, and the resulting Kerr-Brillouin optical comb tooth linewidth is about 44Hz.

[0019] (4) The generated optical comb teeth have a high signal-to-noise ratio, which is greater than 60dB and can support communication requirements.

[0020] (5) The Brillouin gain medium used is only an optical fiber ring cavity, which is small in size, low in cost, and simple to manufacture.

[0021] (6) Currently, the method of exciting Brillouin is to use a single wavelength laser, while the present invention utilizes the dissimilarity of the comb teeth to excite Brillouin simultaneously on each comb tooth.

[0022] (7) By combining the Brillouin effect with the Kerr optical comb, the frequency noise and linewidth of the Kerr soliton optical comb are reduced by utilizing the Brillouin gain. Since the Kerr soliton optical comb itself has good stability, there is no need for an additional complex locking feedback link, which ensures excellent performance while keeping the system complexity low. Attached Figure Description

[0023] Figure 1 This is a flowchart of a specific embodiment of the Kerbrillouin high signal-to-noise ratio narrow linewidth optical comb generation method of the present invention;

[0024] Figure 2 This is a schematic diagram illustrating the principle of a specific embodiment of the Kerbrillouin high signal-to-noise ratio narrow linewidth optical comb generation method of the present invention;

[0025] Figure 3 These are the Q-value test results for silicon nitride optical microcavities;

[0026] Figure 4 This is the spectrum of the Kerr soliton optical comb teeth generated by a silicon nitride optical microcavity;

[0027] Figure 5 The image shows a comparison of the signal-to-noise ratio of the optical comb before and after Brillouin excitation, where (a) is before Brillouin excitation and (b) is after Brillouin excitation.

[0028] Figure 6 This is a noise diagram of the comb teeth frequency without Brillouin excitation;

[0029] Figure 7 This is a frequency noise diagram of the comb teeth after Brillouin excitation. Detailed Implementation

[0030] The specific embodiments of the present invention will now be described with reference to the accompanying drawings to enable those skilled in the art to better understand the invention. It should be particularly noted that in the following description, detailed descriptions of known functions and designs that might obscure the main content of the invention will be omitted here.

[0031] This invention utilizes the Kerr soliton optical comb teeth to excite the Brillouin effect, thereby increasing the Brillouin gain of the Kerr soliton optical comb teeth and thus optimizing frequency noise and linewidth. For example... Figure 1 , 2 As shown, in this embodiment, the procedure specifically includes the following steps:

[0032] Step S1: Generate auxiliary laser

[0033] A tunable laser is used as an auxiliary laser source to output a continuous auxiliary laser with tunable wavelength. A polarization controller is used to align the polarization state of the auxiliary laser with the TE or TM mode of the silicon nitride optical microcavity. Then, the power is amplified by an erbium-doped fiber amplifier and the spontaneous emission noise introduced by the amplifier is filtered out by an optical filter. The filtered auxiliary laser is input from port 1 of the circulator and input into the optical microcavity from port 2. At the same time, two paths are split from port 3 of the circulator by an optical coupler. One path is used to connect to a pump laser power meter to observe the output power of the pump laser after entering the optical microcavity. This path is also used to connect to a spectrometer to observe the generated optical comb spectrum. The other path is used as the output of the optical microcavity, i.e., the Kerr soliton optical comb.

[0034] Step S2: Generate pump laser

[0035] In addition, a tunable laser is selected as the pump laser source, which outputs a continuous pump laser with tunable wavelength. A polarization controller is used to align the polarization state of the pump laser with the TE or TM mode of the optical microcavity. Similarly, after power amplification using an erbium-doped fiber amplifier, an optical filter is used to filter out the amplifier's spontaneous emission noise. The filtered pump laser is input through port 1 of another circulator, and then input into the optical microcavity through port 2. Port 3 is connected to an auxiliary laser power meter to observe the output power of the auxiliary laser after it enters the optical microcavity.

[0036] Step S3: Generate Kerr soliton optical comb

[0037] Step S3.1: Tune the auxiliary laser to bring it into the optical microcavity resonance peak.

[0038] The auxiliary laser is input into the optical microcavity. While observing the power value of the auxiliary laser power meter, the wavelength of the auxiliary laser is tuned. When the power value shows a significant drop, it proves that the auxiliary laser has entered the resonant peak of the optical microcavity. The spectrometer is then observed, and the wavelength of the auxiliary laser is tuned until an optical comb with a symmetrical distribution about the wavelength of the auxiliary light can be observed.

[0039] Step S3.2: Utilize the auxiliary laser heating effect to stably introduce the pump laser into the optical microcavity resonance peak.

[0040] The pump laser is input into the optical microcavity from a direction different from that of the auxiliary laser. The power value of the pump laser power meter is observed. When the power value shows a significant drop, it proves that the pump laser has entered the optical microcavity resonance peak. The spectrometer is then used to continue tuning the pump laser wavelength. The optical comb states excited by the pump laser are observed in sequence as the primary optical comb state, the secondary optical comb state, and the chaotic optical comb state. The pump laser wavelength is then tuned again. Due to the thermal nonlinear effect of the optical microcavity, when the pump laser sweeps into the red detuning region of the microcavity resonance peak, the self-thermal locking state in the microcavity is broken, and the resonance peak is redshifted. However, because the auxiliary laser cancels the thermal effect generated by the pump laser entering the red detuning region in the blue detuning region of the microcavity resonance peak, the pump laser is able to stably enter the optical microcavity resonance peak, generating a Kerr soliton optical comb.

[0041] Step S4: Excite the Brillouin effect using Kerr soliton optical comb teeth

[0042] Step S4.1: Obtain the comb teeth of the Kerr soliton optical comb.

[0043] For the Kerr soliton optical comb output from the optical microcavity, two optical bandstop filters are used to filter out the pump laser and auxiliary laser in the Kerr soliton optical comb, respectively, to obtain the Kerr soliton optical comb teeth.

[0044] Step S4.2: Select and shape the comb teeth

[0045] A wavelength-selective switch is used to select any number of continuously distributed comb teeth in the Kerr single soliton optical comb with power reaching the amplification threshold of the erbium-doped fiber amplifier. Then, the comb teeth are shaped to make all comb teeth have the same power and are sent to the erbium-doped fiber amplifier.

[0046] Step S4.3: Generate a Kerbrillouin high signal-to-noise ratio narrow linewidth optical comb

[0047] Erbium-doped fiber amplifiers amplify the power of the selected and shaped Kerr soliton optical comb teeth, and then input them into the fiber ring cavity to excite the Brillouin effect, resulting in comb teeth with higher signal-to-noise ratio, narrower linewidth, and lower frequency noise, i.e., Kerr-Brillouin high signal-to-noise ratio narrow linewidth optical comb.

[0048] To demonstrate the feasibility of generating Kerr soliton optical combs in optical microcavities, a specific embodiment was used for experimental verification.

[0049] First, the Q-value characteristics of the silicon nitride microring cavity were tested, and the test results are as follows: Figure 3 As shown: Free Spectrum Ratio (FSR) = 150 GHz; Figure 3 As shown, within the C-band range, the highest quality factor Q value in TE mode is 5.3*10. 6 The minimum is 2.5*10 6 In TM mode, the highest quality factor Q value is 3.1*10. 6 The lowest is 9.9*10 5 In this embodiment, the polarization states of both the pump laser and the auxiliary laser are aligned with the TM mode of the optical microcavity. The pump laser wavelength is 1550.06 nm, and the quality factor Q of the corresponding resonance peak is 1.29 * 10⁻⁶. 6 The auxiliary laser wavelength is 1531.70 nm, corresponding to a quality factor Q of 1.97 * 10⁻⁶ for the resonance peak. 6 .

[0050] In this embodiment, the optical microcavity utilizes two microlenses to focus the light spot in the input and output lens fibers and calibrate the optical path, allowing light to pass smoothly through the optical microcavity and thus encapsulating it into a low-loss optical microcavity device. The pump laser comes from a tunable laser with a center wavelength set at 1550.06 nm. A polarization controller is used to adjust the polarization state of the pump laser to align it with the TM mode of the optical microcavity. After mode alignment, the pump laser's optical power is amplified to 100 mW using an erbium-doped fiber amplifier. The amplified pump laser is then input to an optical filter to remove spontaneous emission noise introduced by the amplifier, and then enters one end of the optical microcavity through a circulator. Similar to the pump laser, the auxiliary laser comes from another tunable laser with a center wavelength set at 1531.70 nm and a polarization state aligned with the TM mode of the optical microcavity. Likewise, the optical power is amplified to 100 mW using an erbium-doped fiber amplifier, and then the amplified auxiliary laser is input to an optical filter and then enters the other end of the optical microcavity through a circulator. The auxiliary laser wavelength is tuned so that it enters cavity mode from the blue detuning region of the resonance peak. This heats the microcavity, causing a redshift of all resonance peaks. Following this, the pump laser wavelength is tuned so that it enters cavity mode from the blue detuning region of the resonance peak. By appropriately tuning the pump and auxiliary laser wavelengths, the frequency detuning between them is optimized, balancing the heat flow generated within the microcavity due to thermal nonlinearity. This allows the pump laser to smoothly scan the entire resonance peak region without significant thermal effects. The final Kerr soliton optical comb spectrum, filtered out of the pump and auxiliary lasers, is shown below. Figure 4 As shown.

[0051] To better illustrate how the Kerr soliton optical comb teeth excite the Brillouin effect to generate a high signal-to-noise ratio narrow linewidth optical comb in this invention, the experimental setup in this embodiment is as follows: Figure 1 As shown, ten comb teeth with wavelengths located on the longer wavelength side of the pump laser were selected using a wavelength selection switch for filtering and shaping. The shaped comb teeth were then amplified by an erbium-doped fiber amplifier to achieve the threshold power for stimulated Brillouin scattering. The comb teeth were then input into the fiber optic ring cavity to excite the Brillouin effect, thereby generating a high signal-to-noise ratio, narrow-linewidth optical comb. The outputs of the erbium-doped fiber amplifier and the fiber optic ring cavity were connected to a spectrometer, and the two spectra were compared, as shown below. Figure 5 As shown, the signal-to-noise ratio (SNR) of the Kerber soliton optical comb teeth before and after Brillouin excitation can be clearly seen. The SNR of the optical comb teeth after Brillouin excitation is at least 20 dB higher than that of the optical comb teeth without Brillouin excitation. The SNR of the generated Kerber-Brillouin optical comb is greater than 60 dB, which proves that the Kerber-Brillouin optical comb teeth generated by this invention have a high SNR.

[0052] To better illustrate the technical effects of the present invention, some improvements were made based on the above embodiments. In this embodiment, the Kerr soliton optical comb teeth without excited Brillouin effect were directly input into an unbalanced Mach-Zehnder interferometer and then connected to a phase noise meter. The frequency noise corresponding to the Kerr soliton optical comb teeth without excited Brillouin effect was calculated as follows: Figure 6 As shown. Furthermore, the excited Brillouin comb teeth were input into an unbalanced Mach-Zehnder interferometer and then connected to a phase noise meter. The frequency noise results were measured and calculated as follows: Figure 7 As shown. Comparison Figure 6 and Figure 7 This demonstrates that frequency noise is effectively suppressed after Brillouin effect excitation. Taking the first comb tooth on the right side of the pump laser (wavelength 1551.26nm) as an example, the integral linewidth before Brillouin effect excitation is calculated to be 2.35kHz based on the measured frequency noise, and the integral linewidth after Brillouin effect excitation is 44Hz. It can be seen that the integral linewidth is greatly compressed, thus proving that the Krillouin comb tooth generated by this invention has the characteristic of narrow linewidth.

[0053] Although the illustrative specific embodiments of the present invention have been described above to enable those skilled in the art to understand the invention, it should be understood that the invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of the present invention are protected.

Claims

1. A method for generating a Kerbrillouin high signal-to-noise ratio narrow linewidth optical comb, characterized in that, The Brillouin effect is excited by the teeth of a Kerr soliton optical comb, thereby generating a Kerr-Brillouin optical comb with high signal-to-noise ratio and narrow linewidth. The specific steps include: (1) Obtain the comb teeth of the Kerr monosole; Two optical bandstop filters are used to filter out the pump laser and auxiliary laser in the Kerr soliton optical comb output from the optical microcavity, respectively, to obtain the Kerr soliton optical comb teeth. (2) Select and shape the comb teeth; A wavelength-selective switch is used to select any number of continuously distributed comb teeth in the Kerr single soliton optical comb with power reaching the amplification threshold of the erbium-doped fiber amplifier. Then, the comb teeth are shaped to make all comb teeth have the same power and are sent to the erbium-doped fiber amplifier. (3) Generate a Kerbrillouin high signal-to-noise ratio narrow linewidth optical comb; Erbium-doped fiber amplifiers amplify the power of the selected and shaped Kerr soliton optical comb teeth, and then input them into the fiber ring cavity to excite the Brillouin effect, resulting in comb teeth with higher signal-to-noise ratio, narrower linewidth, and lower frequency noise, i.e., Kerr-Brillouin high signal-to-noise ratio narrow linewidth optical comb.

2. The method for generating a Kerbrillon high signal-to-noise ratio narrow linewidth optical comb according to claim 1, characterized in that, The steps for generating the Kerr soliton optical comb output from the optical microcavity are as follows: Step S1: Generate auxiliary laser; A tunable laser is used as an auxiliary laser source to output a continuous auxiliary laser with tunable wavelength. A polarization controller is used to align the polarization state of the auxiliary laser with the TE or TM mode of the silicon nitride optical microcavity. Then, the power is amplified by an erbium-doped fiber amplifier and the spontaneous emission noise introduced by the amplifier is filtered out by an optical filter. The filtered auxiliary laser is input from the first port (1) of the circulator and input into the optical microcavity from the second port (2). At the same time, two paths are split off from the third port (3) of the circulator by an optical coupler. One path is used to connect to a pump laser power meter to observe the output power of the pump laser after entering the optical microcavity. This path is also used to connect to a spectrometer to observe the generated optical comb spectrum. The other path is used as the output of the optical microcavity, i.e., the Kerr soliton optical comb. Step S2: Generate pump laser; In addition, a tunable laser is selected as the pump laser source to output a continuous pump laser with tunable wavelength. A polarization controller is used to align the polarization state of the pump laser with the TE or TM mode of the optical microcavity. Similarly, after power amplification by an erbium-doped fiber amplifier, an optical filter is used to filter out the amplifier's spontaneous emission noise. The filtered pump laser is input through the first port (1) of another circulator and input into the optical microcavity through the second port (2). The third port (3) is connected to an auxiliary laser power meter to observe the output power of the auxiliary laser after it enters the optical microcavity. Step S3: Generate Kerr soliton optical comb; Step S3.1: Tune the auxiliary laser to bring it into the optical microcavity resonance peak; The auxiliary laser is input into the optical microcavity. While observing the power value of the auxiliary laser power meter, the wavelength of the auxiliary laser is tuned. When the power value shows a significant drop, it proves that the auxiliary laser has entered the resonant peak of the optical microcavity. The spectrometer is then observed, and the wavelength of the auxiliary laser is tuned until an optical comb with a symmetrical distribution about the wavelength of the auxiliary light can be observed. Step S3.2: Utilize the auxiliary laser heating effect to stably bring the pump laser into the optical microcavity resonance peak; The pump laser is input into the optical microcavity from a direction different from that of the auxiliary laser. The power value of the pump laser power meter is observed. When the power value shows a significant drop, it proves that the pump laser has entered the optical microcavity resonance peak. The spectrometer is then used to continue tuning the pump laser wavelength. The optical comb states excited by the pump laser are observed in sequence as the primary optical comb state, the secondary optical comb state, and the chaotic optical comb state. The pump laser wavelength is then tuned again. Due to the thermal nonlinear effect of the optical microcavity, when the pump laser sweeps into the red detuning region of the microcavity resonance peak, the self-thermal locking state in the microcavity is broken, and the resonance peak redshifts. However, because the auxiliary laser cancels the thermal effect generated by the pump laser entering the red detuning region in the blue detuning region of the microcavity resonance peak, the pump laser is able to stably enter the optical microcavity resonance peak, generating a Kerr soliton optical comb.

3. The method for generating a Kerbrillon high signal-to-noise ratio narrow linewidth optical comb according to claim 2, characterized in that, The polarization states of both the pump laser and the auxiliary laser are aligned with the TM mode of the optical microcavity. The pump laser wavelength is 1550.06 nm, and the quality factor Q of the corresponding resonance peak is 1.29 * 10⁻⁶. 6 The auxiliary laser wavelength is 1531.70 nm, corresponding to a quality factor Q of 1.97 * 10⁻⁶ for the resonance peak. 6 .

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