A method for guiding the optimization of a ring-down cavity cavity loss scan by an optical intensity signal

Abstract

The application discloses a method for guiding cavity loss scanning optimization of a ring-down cavity by an optical intensity signal, utilizes coupling characteristics of a narrow-line-width continuous wave semiconductor laser and the ring-down cavity, and judges boundary states of cavity loss scanning optimization of the ring-down cavity by monitoring variation of a transmission signal of the ring-down cavity. Based on the method, the cavity loss scanning optimization of the ring-down cavity can be completed only by the optical intensity signal, and other auxiliary monitoring means are not needed, so that the system is simplified. The method has high monitoring sensitivity, simple structure, and good application prospect.

Description

Technical Field

[0001] This invention relates to the field of optical cavity ringback technology, and specifically to a method for optimizing the cavity loss of a ringback cavity by guiding an optical intensity signal. Background Technology

[0002] Cavity loss is a crucial observation indicator in cavity ring-down technology, and the accuracy and precision of cavity loss observation are of paramount importance. A typical ring-down cavity consists of high-reflectivity cavity mirrors. Since the true value of the mirror reflectivity is theoretically unpredictable, the true value of the cavity loss is also unpredictable. Research shows that the observed cavity loss is closely related to the misalignment of the cavity parameters. These parameters include cavity length, mirror position misalignment, and mirror angle misalignment. In recent years, a series of techniques have been developed to address the problem of obtaining the true cavity loss value, including multiple measurements with varying cavity lengths, cavity loss scanning optimization, and multi-parameter fusion feedback cavity tuning. These research results indicate that modeling the relationship between observed cavity loss and cavity misalignment parameters to obtain the true cavity loss value is an effective technique. However, current techniques rely heavily on data sample acquisition to model the relationship between observed cavity loss and cavity misalignment parameters. A key issue in data sample acquisition is determining the scanning range of the effective samples. Currently, the determination of the scanning range relies on the monitoring of the cavity transmitted light spot morphology. The scanning range is determined by maintaining the fundamental transverse mode state of the transmitted light spot, while the acquisition of cavity loss depends on the monitoring and recording of the cavity transmitted light intensity signal. This means that the current optical cavity ring-down system relies on two types of detection devices to achieve cavity loss scanning optimization: a single-point photodetector for high-speed light intensity signal detection and an area array photodetector for transmitted light spot image detection. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention proposes a method for optimizing cavity loss scanning in a cavity decaying system guided by an optical intensity signal. This method requires only a single-point photodetector to determine the cavity loss scanning range, thereby reducing the structural and algorithmic complexity of the optical cavity decaying system and accurately determining the scanning range in cavity loss scanning optimization.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A method for optimizing the cavity loss of a ring-down cavity guided by an optical intensity signal includes the following steps:

[0006] Step (1): Construct an optical cavity ring-down system, which includes a narrow linewidth continuous wave semiconductor laser, a ring-down cavity, a photodetector, an industrial control computer, and a square wave generator. The square wave modulation signal generated by the square wave generator is used to control the narrow linewidth continuous wave semiconductor laser. The laser beam emitted by the narrow linewidth continuous wave semiconductor laser is injected into the ring-down cavity. The transmission signal of the ring-down cavity is collected by the photodetector and transmitted to the industrial control computer for recording and analysis. The ring-down cavity is pre-adjusted according to the cavity tuning evaluation criteria to ensure that the operating mode in the ring-down cavity remains in the fundamental transverse mode state.

[0007] Step (2): Adjust the angles of each cavity mirror in the horizontal and vertical directions to scan the cavity parameters. After each adjustment, collect and record the transmission signal of the decaying cavity for 10 square wave cycles, and calculate the root mean square value of the light intensity of the transmission signal of the decaying cavity at the falling edge of 10 square wave cycles.

[0008] Step (3): If the root mean square value of the statistical light intensity is less than the preset threshold, it indicates that the current cavity is still in the fundamental transverse mode state. Record the cavity loss observation value of the current cavity parameter state and continue to scan the current cavity parameters. If the root mean square value of the statistical light intensity is greater than or equal to the preset threshold, it indicates that the current cavity begins to generate mode jumps and other situations. Record this as the boundary state of the current cavity parameter scan and change the scan parameters.

[0009] Furthermore, the linewidth of a narrow-linewidth continuous-wave semiconductor laser is ≤0.5nm.

[0010] Furthermore, the cavity tuning evaluation criteria can be one of the following: cavity transmitted signal intensity, cavity transmitted light spot shape, cavity transmitted signal envelope, and cavity transmitted beam phase, or a combination of several of them.

[0011] The principle of this invention is:

[0012] The energy coupling stability between a narrow-linewidth continuous-wave semiconductor laser and its ring-down cavity is closely related to the transverse mode state within the cavity. When a stable single transverse mode operates within the ring-down cavity, the energy coupling efficiency is relatively stable; however, when multiple transverse modes are in a transitional state, the energy coupling efficiency will fluctuate. During the ring-down cavity loss scanning optimization process, a single fundamental transverse mode should operate within the scanning range. At the boundaries of the scanning interval, state transitions between the fundamental and higher-order transverse modes will occur, leading to unstable energy coupling efficiency.

[0013] The beneficial effects of this invention are as follows:

[0014] This invention can complete the scanning and optimization of the cavity loss of the ring-down cavity using only the light intensity signal, without the need for other auxiliary monitoring methods, thereby simplifying the system, achieving high monitoring sensitivity, and having a simple structure, intuitive and convenient operation, and has good application prospects. Attached Figure Description

[0015] Figure 1 This is a structural diagram of an optical cavity ring-down system according to a method for optimizing ring-down cavity loss by guiding light intensity signal scanning according to the present invention.

[0016] Figure 2 This is a schematic diagram of the signal within the scanning interval of a method for optimizing the cavity loss of a ring-down cavity guided by an optical intensity signal according to the present invention.

[0017] Figure 3 This is a schematic diagram of the signal at the critical state of the scanning interval in a method for optimizing the cavity loss of a ringing cavity guided by an optical intensity signal according to the present invention. Detailed Implementation

[0018] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0019] The present invention provides a method for optimizing the cavity loss scanning of a ring-down cavity guided by an optical intensity signal, comprising the following steps:

[0020] Step (1), according to the appendix Figure 1 The illustrated optical cavity ring-down system comprises a narrow-linewidth continuous-wave semiconductor laser 1, a ring-down cavity 2, a photodetector 3, an industrial control computer 4, and a square wave generator 5. The square wave generator produces a square wave modulation signal to control the switching on and off of the narrow-linewidth continuous-wave semiconductor laser. The laser beam emitted by the laser is injected into the ring-down cavity. The transmission signal from the ring-down cavity is acquired by the photodetector and synchronously triggered by the square wave generator before being transmitted to the industrial control computer for recording and analysis. The ring-down cavity needs to undergo preliminary pre-adjustment to ensure that the transmitted light spot remains in the fundamental transverse mode.

[0021] Among them, the linewidth of the narrow-linewidth continuous-wave semiconductor laser is within 0.5 nm. The pre-tuning evaluation criterion is the intensity of the transmitted signal light from the cavity. Pre-tuning ends when the intensity of the transmitted signal light from the cavity reaches its maximum value. At this time, the recording results of the optical cavity output signal, i.e., the ring-down cavity transmission signal, are shown in the attached figure. Figure 2 As shown. Additionally, the cavity tuning evaluation criteria can also be one or more of the following: cavity transmission spot morphology, cavity transmission signal envelope, and cavity transmission beam phase.

[0022] Step (2): Adjust the angles of each cavity mirror in the horizontal and vertical directions to scan the cavity parameters. After each adjustment, collect and record the transmission signal of 10 square wave cycles, and calculate the root mean square value of the light intensity at the falling edge of 10 square wave cycles.

[0023] Step (3): If the root mean square value of the light intensity is less than the preset threshold, it indicates that the current cavity is still a fundamental transverse mode spot. The cavity loss observation value of the current cavity parameter state can be recorded and the current cavity parameter scanning can continue. If the root mean square value of the light intensity increases significantly and exceeds the preset threshold, it indicates that the current cavity has started to produce mode jumps and other situations, and has reached the boundary state of the current cavity parameter scanning. The scanning parameters need to be changed.

[0024] In this embodiment, based on long-term experimental observation records, the threshold for the root mean square value of light intensity statistics is set to 30mV. The transmitted light intensity signal of the ring-down cavity when the scanning boundary is reached is shown in the attached figure. Figure 3 As shown, there are obvious fluctuations in light intensity.

[0025] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

Claims

1. A method for optimizing cavity loss scanning guided by light intensity signals, characterized in that, Includes the following steps: Step (1): Construct an optical cavity ring-down system, which includes a narrow linewidth continuous wave semiconductor laser, a ring-down cavity, a photodetector, an industrial control computer, and a square wave generator. The square wave modulation signal generated by the square wave generator is used to control the narrow linewidth continuous wave semiconductor laser. The narrow linewidth continuous wave semiconductor laser emits a laser beam that is injected into the ring-down cavity. The transmission signal of the ring-down cavity is collected by the photodetector and transmitted to the industrial control computer for recording and analysis. The ring-down cavity is pre-adjusted according to the cavity tuning evaluation criteria to ensure that the operating mode in the ring-down cavity remains in the fundamental transverse mode state. Step (2): Adjust the angles of each cavity mirror in the horizontal and vertical directions to scan the cavity parameters. After each adjustment, collect and record the transmission signal of the decaying cavity for 10 square wave cycles, and calculate the root mean square value of the light intensity of the transmission signal of the decaying cavity at the falling edge of 10 square wave cycles. Step (3): If the root mean square value of the statistical light intensity is less than the preset threshold, it indicates that the current cavity is still in the fundamental transverse mode state. Record the cavity loss observation value of the current cavity parameter and continue to scan the current cavity parameter. If the root mean square value of the statistical light intensity is greater than or equal to the preset threshold, it indicates that the current cavity has started to generate mode jumps. This is recorded as reaching the boundary state of the current cavity parameter scan. Change the scan parameters.

2. The method for optimizing cavity loss scanning guided by light intensity signal according to claim 1, characterized in that: The output linewidth of the narrow linewidth continuous wave semiconductor laser is ≤0.5nm.

3. The method for optimizing cavity loss scanning guided by light intensity signal according to claim 1, characterized in that: The cavity tuning evaluation criteria are one or more of the following: cavity transmission signal intensity, cavity transmission spot shape, cavity transmission signal envelope, and cavity transmission beam phase.

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