Optical fiber resonant cavity test system device and method

Abstract

The invention discloses an optical fiber resonant cavity testing system device and method. The optical fiber resonant cavity testing system device comprises an external cavity type semiconductor laser, an isolator, a wavelength division multiplexer, a photoelectric detector, an optical fiber resonant cavity, a high-precision tunable coupler and a signal processing and feedback module. According to the scheme of the invention, effective regulation and control of singular points are realized by accurately regulating and controlling gain, loss and coupling strength, and high-precision sensing is realized based on a singular point enhancement effect. The scheme provided by the invention has the characteristics of high sensitivity, strong anti-interference capability and low noise, and is suitable for optical sensing application in a complex environment.

Description

Technical Field

[0001] The present invention relates to the field of optical sensing technology, and in particular, to a test device and method for a second-order optical PT-symmetric system based on a fiber optic ring resonator. Background Art

[0002] In recent years, optical sensing technology has gradually transitioned from theoretical research to laboratory research. However, the system functional modules are scattered, system integration and engineering prototype design have not been achieved, and the theoretical potential for improving the sensing accuracy has not been fully exploited. Especially in the regulation of the exceptional point of the non-Hermitian system and sensing applications at room temperature, there are technical bottlenecks. As an important non-Hermitian system, the PT-symmetric system has real eigenvalues of its Hamiltonian, and can realize a classical counterpart of the quantum system through an optical system that balances the gain and loss distributions, providing a unique research platform for exceptional point sensing of non-Hermitian systems.

[0003] The optical PT-symmetric system has an ultra-high sensitivity response near the exceptional point, providing new opportunities for sensing applications. However, how to effectively regulate the exceptional point and how to achieve high-precision sensing based on the enhanced effect of the exceptional point are still the key issues in current research. Summary of the Invention

[0004] The purpose of the present invention is to provide a test device and method for a second-order optical PT-symmetric system based on a fiber optic ring resonator, which is used to solve the problems of scattered functional modules, low integration degree, and insufficient sensing accuracy in the existing optical sensing system.

[0005] To solve the above technical problems, the present invention proposes a fiber optic resonator test system device, including a first external cavity semiconductor laser, a second external cavity semiconductor laser, a signal generator, a digital oscilloscope, a photodetector, an isolator, a waveguide, and an active ring resonator; the first external cavity semiconductor laser is used to generate a signal light with a central frequency of 1550 nm and output the signal light to the active ring resonator; the second external cavity semiconductor laser is used to generate a pump light of 980 nm, and the pump light enters the active ring resonator through the isolator and a wavelength division multiplexer to excite Er 3+ Er in the optical fiber 3+Provide gain for the resonant cavity; the signal generator is used to apply triangular wave modulation to the first external cavity semiconductor laser, causing it to fluctuate repeatedly within a frequency range of ±200 MHz, and output the modulated signal light to the active ring resonator; the active ring resonator is used to receive the signal light and pump light, manufacture and change the coupling parameters through the fused biconical taper method and electrical coupling method, achieve gain tuning, and transmit the output optical field to the photodetector through the coupling waveguide; the photodetector is used to convert the detected optical field into an electrical signal and input the electrical signal into a digital oscilloscope for display; the digital oscilloscope is used to display the electrical signal output by the photodetector to observe and analyze the transmission spectrum of the active ring resonator; the isolator is used to prevent the optical signal from reflecting back to the laser and ensure the unidirectional transmission of the optical signal; the waveguide is used to transmit the optical signal from the active ring resonator to the photodetector.

[0006] Optionally, the gain of the active ring resonator is achieved by regulating the output optical power of the second external cavity semiconductor laser.

[0007] Optionally, the signal optical power is about 500 μW, and the gain of the active cavity is regulated by regulating the output optical power of the second external cavity semiconductor laser.

[0008] Optionally, both the signal optical power and the pump optical power affect the gain of the transmission spectrum, with the former being negatively correlated and the latter being positively correlated.

[0009] Optionally, the transmission spectrum of the active ring resonator exhibits different resonant spectral characteristics under different signal optical powers and scanning speeds.

[0010] Optionally, when the signal optical power decreases, the intensity of the resonant spectrum continuously decreases, while the upward peak part gradually increases, and the completely downward resonant valley is finally completely inverted into an upward resonant peak.

[0011] Optionally, when the scanning speed gradually increases, the spectral intensity basically remains unchanged, but the upward peak part also gradually increases, and the downward part in the resonant curve gradually disappears, and the transmission spectrum evolves into an ideal Lorentz resonant peak.

[0012] Optionally, the active ring resonator has an ultra-narrow full width at half maximum and a very high detection accuracy, and can perfectly achieve the gain tuning required by the system.

[0013] Optionally, the fiber optic resonator has lower transmission loss and a larger resonator length, and thus has a stronger optical energy storage ability than the optical microcavity.

[0014] Optionally, the frequency tuning method of the fiber optic resonator is more diverse, the physical parameters are easy to control, and it has better anti-interference ability in the natural environment.

[0015] Different from the prior art, the present invention proposes a test device and method for a second-order optical PT-symmetric system based on an optical fiber ring resonator, which can effectively control the singular point, achieve high-precision sensing, has lower transmission loss and a larger resonator length, and thus has a stronger optical energy storage capacity and signal response than an optical microcavity. Brief Description of the Drawings

[0016] Appendix Figure 1 is a schematic diagram of the present invention. Detailed Embodiments

[0017] The following will describe the detailed embodiments of the present invention in more detail with reference to the schematic diagrams. According to the following description, the advantages and features of the present invention will be clearer.

[0018] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0019] Please refer to Figure 1 , the embodiment of the present invention proposes an optical fiber resonator test system device, including a first external cavity semiconductor laser 6, a second external cavity semiconductor laser 2, a signal generator 7, a digital oscilloscope 8, a photodetector 9, isolators 3, 5, a waveguide 12, and an active ring resonator 4; the first external cavity semiconductor laser 6 is used to generate a signal light with a central frequency of 1550 nm and output the signal light to the active ring resonator 4; the second external cavity semiconductor laser 2 is used to generate a pump light with a wavelength of 980 nm, and after passing the pump light through the isolator 3, enter the active ring resonator 4 through a wavelength division multiplexer 13 to excite Er in the Er 3+ in the optical fiber 3+Provide gain for the resonant cavity; the signal generator is used to apply triangular wave modulation to the first external cavity semiconductor laser 6, causing it to fluctuate repeatedly within a frequency range of ±200 MHz, and output the modulated signal light to the active ring resonator 4; the active ring resonator is used to receive signal light and pump light, manufacture and change the coupling parameters through the fused biconical taper method and electrical coupling method, achieve gain tuning, and transmit the output optical field to the photodetector 9 through the coupling waveguide 12; the photodetector is used to convert the detected optical field into an electrical signal and input the electrical signal into the digital oscilloscope for display 8; the digital oscilloscope 8 is used to display the electrical signal output by the photodetector 9 to observe and analyze the transmission spectrum of the active ring resonator 4; the isolator 5 is used to prevent the optical signal from reflecting back to the laser and ensure the unidirectional transmission of the optical signal; the waveguide 12 is used to transmit the optical signal from the active ring resonator to the photodetector 9.

[0020] Specifically, in this embodiment, the gain of the active ring resonator 4 is achieved by regulating the output optical power of the second external cavity semiconductor laser 2.

[0021] Specifically, in this embodiment, the signal optical power is about 500 μW, and the gain of the active cavity 4 is regulated by regulating the output optical power of the second external cavity semiconductor laser 2.

[0022] Specifically, in this embodiment, both the signal optical power and the pump optical power affect the gain of the transmission spectrum, with the former being negatively correlated and the latter being positively correlated.

[0023] Specifically, in this embodiment, the transmission spectrum of the active ring resonator 4 exhibits different resonant spectral characteristics under different signal optical powers and scanning speeds.

[0024] Specifically, in this embodiment, when the signal optical power decreases, the intensity of the resonant spectrum continuously decreases, while the upward peak part gradually increases, and the completely downward resonant valley is finally completely inverted into an upward resonant peak.

[0025] Specifically, in this embodiment, when the scanning speed gradually increases, the spectral intensity basically does not change, but the upward peak part also gradually increases, the downward part in the resonant curve gradually disappears, and the transmission spectrum evolves into an ideal Lorentz resonant peak.

[0026] Specifically, in this embodiment, the active ring resonator has an ultra-narrow full width at half maximum and a very high detection accuracy, and can perfectly achieve the gain tuning required by the system.

[0027] Specifically, in this embodiment, the fiber optic resonator has lower transmission loss and a larger resonator length, thus having a stronger optical energy storage ability than the optical microcavity.

[0028] Specifically, in this embodiment, the frequency tuning method of the fiber optic resonator is more diverse, the physical parameters are easy to control, and it has better anti-interference ability in the natural environment.

[0029] Furthermore, when the pump light power is 0, the active cavity is in an under-coupled state. At this time, the resonance curve is a standard Lorentzian line shape. As the pump light power increases, the total loss in the cavity decreases, the line width of the Lorentzian line shape becomes narrower, and the Q value of the active cavity increases. However, when the pump light power increases until the gain g in the cavity is approximately -γ0, although it is in an over-coupled state at this time, the transmission spectrum is different from the completely symmetric Lorentzian line shape in the theoretical process, and it is an asymmetric Fano line shape spectrum. This type of Fano line shape spectrum continues to exist until g > -γ0, and it will not completely transform into an upward resonance peak until the gain g is large enough. The change of this theoretically non-existent asymmetric spectrum is related to the gain in the cavity. In fact, this spectrum change process is not a real transmission spectrum, but a special evolution under frequency scanning. The principle is as follows: Since the energy structure of Er 3+ ions is approximately a three-level system, the mode equations for the signal optical field and the pump optical field during scanning are as follows:

[0030]

[0031] Among them, s and p correspond to the subscripts of the signal optical field and the pump optical field respectively, a is the intensity of the two optical fields in the active cavity, γ0 is the corresponding transmission loss in the cavity, and γ c is the coupling loss, a i is the intensity of the input optical field, and g is the gain of the two optical fields. And there is a relationship:

[0032]

[0033] c is the speed of light in vacuum, n is the effective refractive index, N1, N2, and N3 are the numbers of Er 3+ ions in the ground state, the intermediate state, and the metastable state per unit volume respectively, σ a and σ e correspond to the absorption cross-sectional area and the emission cross-sectional area of Er 3+ ions respectively. The population number of Er 3+ ions in the cavity is described by the following equation:

[0034]

[0035] Among them, τ 31 and τ 23are the spontaneous relaxation times from the metastable state to the ground state and from the intermediate state to the metastable state respectively, A is the effective cross-sectional area of the intracavity mode field, R is the radius of the fiber ring active cavity, and h is the Planck constant. Analyzing the above formula, it can be seen that both the signal light power and the pump light power affect the gain of the transmission spectrum, with the former being negatively correlated and the latter being positively correlated. The pump light power is related to the input pump light intensity on the one hand, and the resonance of the 980 nm pump light also effectively increases the pump light power in the cavity. However, even if the pump light does not resonate, increasing the input light power can also control the pump light field. As the pump light power increases relative to the signal light power, the system loss becomes smaller and smaller. After reaching a certain threshold, the peak of the resonance spectrum will completely turn upward; but when the relative intensity of the pump light power is insufficient, different scanning speeds will result in a Fano-like waveform. That is, when the scanning speed is slow, the signal light frequency changes slowly, and the time for the input light frequency to approach and move away from the resonance frequency is long. As the signal light in the cavity continuously increases under the population inversion. The conversion speed of Er 3+ ions becomes faster, and the intracavity gain gradually weakens. The resonance spectrum gradually changes from an upward resonance peak to a downward resonance valley. On the contrary, when the scanning speed is fast, since the input light frequency quickly reaches and moves away from the vicinity of the resonance frequency, the signal light field near the resonance frequency exists in the cavity for a short time, and Er 3+ ion conversion speed is slow, and the intracavity gain is always large, so it shows a completely upward resonance peak. Similarly, it can be known that when the scanning speed is fixed, the larger the ratio of the pump light power to the signal light power, the more upward the waveform is, and the smaller the ratio, the more the waveform tends to the downward resonance valley.

Claims

1. An optical fiber resonator testing system device and method, characterized in that It includes a first external cavity semiconductor laser (6), a second external cavity semiconductor laser (2), a signal generator (7, 1), a digital oscilloscope (8), a photodetector (9), isolators (3, 5), a waveguide (12) and an active ring resonator (4); wherein, the first external cavity semiconductor laser (6) is used to generate signal light with a central frequency of 1550 nm and output the signal light to the active ring resonator (4); the second external cavity semiconductor laser (2) is used to generate pump light with a wavelength of 980 nm, and after passing through the isolator (3), the pump light enters the active ring resonator (4) through a wavelength division multiplexer (13) to excite Er 3+ in the Er 3+ doped fiber to provide gain for the resonator; the signal generator is used to apply triangular wave modulation to the first external cavity semiconductor laser (6) so that it fluctuates repeatedly within a frequency range of ±200 MHz and output the modulated signal light to the active ring resonator (4); the active ring resonator is used to receive the signal light and the pump light, manufacture and change the coupling parameters through the fused biconical taper method and the electrical coupling method to achieve gain tuning, and transmit the output optical field to the photodetector (9) through the coupling waveguide (12); the photodetector is used to convert the detected optical field into an electrical signal and input the electrical signal into the digital oscilloscope for display (8); the digital oscilloscope (8) is used to display the electrical signal output by the photodetector (9) to observe and analyze the transmission spectrum of the active ring resonator (4); the isolator (5) is used to prevent the optical signal from reflecting back to the laser to ensure the unidirectional transmission of the optical signal; the waveguide (12) is used to transmit the optical signal from the active ring resonator (4) to the photodetector (9).

2. The optical fiber resonator testing system device and method according to claim 1, characterized in that The gain of the active ring resonator (4) is achieved by regulating the output optical power of the second external cavity semiconductor laser (2).

3. The optical fiber resonator test system device and method according to claim 1, characterized in that, The signal optical power is about 500 μW, and the gain of the active cavity (4) is regulated by regulating the output optical power of the second external cavity semiconductor laser (2).

4. The optical fiber resonator testing system device and method according to claim 1, characterized in that Both the signal optical power and the pump optical power affect the gain of the transmission spectrum, with the former being negatively correlated and the latter being positively correlated.

5. The optical fiber resonant cavity testing system device and method according to claim 1, characterized in that The transmission spectral line of the active ring resonator (4) exhibits different resonant spectral characteristics under different signal optical powers and scanning speeds.

6. The optical fiber resonant cavity testing system device and method according to claim 5, characterized in that, When the signal optical power decreases, the intensity of the resonant spectrum continuously decreases, while the upward peak part gradually increases, and the completely downward resonant valley is finally completely inverted into an upward resonant peak.

7. The optical fiber resonator testing system device and method according to claim 5, characterized in that, When the scanning speed gradually increases, the spectral intensity remains unchanged, but the upward peak part also gradually increases, the downward part in the resonant curve gradually disappears, and the transmission spectrum evolves into an ideal Lorentz resonant peak.

8. The fiber optic resonator test system device and method according to claim 1, characterized in that, The active ring resonator has an ultra-narrow full width at half maximum and high detection accuracy.

9. The optical fiber resonator test system device and method according to claim 1, characterized in that, The fiber optic resonator has low transmission loss and a large resonator length.

10. The optical fiber resonant cavity testing system device and method according to claim 1, characterized in that, The frequency tuning method of the fiber optic resonator is more diverse, the physical parameters are easy to control, and it has better anti-interference ability in the natural environment.

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