An adiabatic dynamic tuning inflection point based time domain optical fiber sensing system and method

Abstract

The present application relates to the field of optical fiber sensing and spectrum detection, and discloses a kind of time-domain optical fiber sensing system and method based on adiabatic dynamic tuning inflection point, including the dynamic current driving of light source is applied to make it complete wavelength tuning under adiabatic condition, at least one adiabatic dynamic tuning inflection point is formed in the tuning process;With the inflection point as time domain reference feature, determine the relevant time domain feature position in sensing signal;The time variation law of time domain feature is analyzed, and the sensing parameter information is obtained, the adiabatic dynamic tuning inflection point is formed by the specific pulse current waveform formed by driving circuit structure, and multipoint optical fiber sensing measurement can be realized in combination with time division multiplexing.The present application actively constructs stable time domain reference feature point, does not need passive feature device, simplifies demodulation process, improves the stability and applicability of sensing system in complex environment, reduces system cost, and is beneficial to the engineering and large-scale application of optical fiber sensing technology.

Description

Technical Field

[0001] This invention relates to a time-domain fiber optic sensing system and method based on adiabatic dynamic tuning inflection point, belonging to the field of fiber optic sensing and spectral detection technology. Background Technology

[0002] Fiber optic sensing technology, with its advantages of resistance to electromagnetic interference, long transmission distance, high sensitivity, and small size, has been widely used in industrial monitoring, environmental monitoring, aerospace, and biomedicine. Wavelength scanning and spectral demodulation are the core components of fiber optic sensing systems. In existing technologies, these components typically rely on continuously scanning light sources or tunable filters, with the core being the measurement and analysis of the sensing signal within the wavelength domain.

[0003] However, existing wavelength domain scanning demodulation methods have many technical defects, which have become key factors restricting the engineering and large-scale application of fiber optic sensing technology.

[0004] 1. Lack of stable and directly calibrated feature points: Existing methods do not have actively constructed reference feature points. In interferometric sensor detection or dense spectrum detection scenarios, the sensor signal has periodicity and multi-value problems, which makes it impossible to uniquely determine the spectral features and the demodulation results are prone to ambiguity.

[0005] 2. Complex demodulation algorithms and poor environmental adaptability: For single-peak spectral characteristic devices such as fiber Bragg gratings, simple demodulation can be achieved by constructing characteristic wavelengths. However, for interferometric sensors such as Fabry-Perot interferometers, Michelson interferometers, and Mach-Zehnder interferometers, as well as sensing objects with periodic or multi-peak characteristics such as gas absorption spectra, traditional frequency sweeping methods rely on complex real-time tracking algorithms. Under conditions of large-scale wavelength scanning or multi-period spectra, the algorithm is prone to lock-out and the demodulation stability drops significantly.

[0006] 3. High system cost and high implementation complexity: To compensate for the lack of feature points, existing technologies usually require the introduction of dedicated passive feature devices such as fiber Bragg gratings or the use of high-precision tunable modules. This not only increases the hardware cost of the system, but also increases the difficulty of optical path construction and circuit debugging, and reduces the system's integration and reliability.

[0007] Therefore, developing a fiber optic sensing method and system that can actively construct stable and calibrable feature points, realize the mapping of spectral information to the time domain, and does not require complex algorithms and dedicated passive devices has become an urgent technical problem to be solved in this field. Summary of the Invention

[0008] To overcome the shortcomings of existing fiber optic sensing technologies, such as the lack of stable calibrable feature points in wavelength scanning demodulation, the need for complex algorithms for demodulating periodic / multi-peak spectral signals, and high system costs and complex implementation, this invention provides a time-domain fiber optic sensing system and method based on adiabatic dynamic tuning inflection points. By dynamically controlling the light source tuning process, a repeatable and calibrable adiabatic dynamic tuning inflection point is actively constructed, solving the problem of the lack of stable feature points in wavelength domain demodulation. This enables the mapping of spectral information to time-domain features, completing the demodulation of sensing signals in the time domain. It reduces the dependence on precise wavelength calibration and complex real-time tracking algorithms, eliminates the use of dedicated passive feature devices and high-precision tunable modules, simplifies the system structure, reduces system costs and implementation complexity, and improves the stability and applicability of interferometric fiber optic sensors and dense spectral detection under complex environments and large-scale scanning conditions, thus promoting the engineering and large-scale application of fiber optic sensing technology.

[0009] A time-domain fiber optic sensing system based on adiabatic dynamic tuning inflection point includes:

[0010] The driving circuit is electrically connected to the semiconductor laser and integrates a voltage regulator circuit, logic control circuit, signal generation circuit, pulse generation circuit, waveform shaping circuit and high-frequency switching driving circuit. It is used to generate and output a dynamic current driving signal to the semiconductor laser that meets the requirements for the formation of the adiabatic dynamic tuning inflection point, and at the same time realize the start and stop control of the tuning process and the switching of the modulation mode.

[0011] The temperature control system, which is a temperature controller or constant temperature chamber, is connected to the semiconductor laser. The temperature control accuracy is ≤0.1℃. It is used to stably control the operating temperature of the semiconductor laser and avoid temperature drift that would reduce the wavelength tuning accuracy.

[0012] A semiconductor laser, whose optical output end is connected to the first input end of a coupler; it is a DFB / VCSEL / FP laser with a center wavelength in the low-loss band of 0.8 µm-1.8 µm communication optical fiber. Under dynamic current drive and temperature stability control, it emits pulsed light and completes adiabatic wavelength tuning, forming an adiabatic dynamic tuning inflection point.

[0013] The coupler has a first output end connected to a reflector and a second output end connected to one end of a delay fiber. The coupler is a fiber optic coupler that realizes the splitting and combining of optical signals. Its first input end receives the pulse light from the semiconductor laser, its first output end transmits the trigger light signal to the reflector, its second output end transmits the sensing light signal to the delay fiber and the fiber optic sensor, and its second input end receives the trigger return light from the reflector and the sensing return light from the fiber optic sensor, combines them, and transmits them to the photodetector.

[0014] The reflector is used to provide the trigger signal for signal acquisition; it is a Faraday mirror or an optical fiber end face reflection structure used to reflect the trigger optical signal and provide the trigger reference for signal acquisition. If the reflector is removed, an optical signal can be led out by beam splitting and connected to a second photodetector to achieve equivalent triggering.

[0015] The delay fiber is connected to the fiber optic sensor at the other end; it is used to adjust the transmission timing of the sensing optical signal and provide a basis for timing differentiation for multi-point sensing.

[0016] Fiber optic sensor: This is a reflective sensor. Depending on the detection requirements, a fiber optic grating or fiber optic interferometer is selected to convert the change of the measured physical quantity into the time-domain characteristic change of the optical signal.

[0017] A photodetector, whose optical input terminal is connected to the second input terminal of a coupler, and whose electrical output terminal is electrically connected to the signal acquisition system, is used to convert the optical signal from fiber optic sensing into an electrical signal. A PIN photodiode is used to convert the optical signal output from the coupler into an electrical signal, thus achieving optical / electrical signal conversion.

[0018] The signal acquisition system, which is an oscilloscope or acquisition card, is used to acquire and store the electrical signals output by the photodetector, and to perform time-domain analysis and processing of the signals to calculate the sensing parameters.

[0019] The driving circuit includes a voltage regulator circuit, a logic control circuit, a signal generation circuit, a pulse generation circuit, a waveform shaping circuit, and a high-frequency switching driving circuit. The emitted pulse width is at least 10 ns, the pulse repetition frequency is at least 1 kHz, and the pulse current needs to be greater than the threshold current for normal continuous operation of the semiconductor laser. The pulse waveform generated by the driving circuit needs to meet the driving mode requirements for forming an adiabatic dynamic tuning inflection point. The voltage regulator circuit is used to provide a stable power supply. The signal generation circuit works with the pulse generation circuit to generate a basic pulse signal. The waveform shaping circuit is used to shape the basic pulse signal so that the output current waveform meets the requirement that the current amplitude has an extreme point. The logic control circuit is used to realize the start and stop control and modulation mode switching of the tuning process. The high-frequency switching driving circuit is used to convert the voltage signal into a high-current signal that meets the driving requirements of the semiconductor laser.

[0020] The temperature control system is a temperature controller or a constant temperature chamber. The temperature controller, combined with a PID algorithm, is controlled by a host computer to achieve stable temperature control around the laser. It integrates a voltage drive circuit and a resistance detection circuit. When the semiconductor laser integrates a laser chip, a thermoelectric cooler, and a thermistor, the temperature controller monitors the temperature through the thermistor and adjusts the thermoelectric cooler by adjusting the output voltage to achieve temperature control. When the semiconductor laser only has a laser chip, the constant temperature chamber provides stable temperature control around the laser with a temperature control accuracy of ≤0.1℃.

[0021] The semiconductor laser is one of a DFB laser, a VCSEL laser, or an FP laser, with its center wavelength in the low-loss transmission band of communication optical fiber of 0.8µm-1.8µm; the coupler is an optical fiber coupler; the reflector is a Faraday mirror or an optical fiber end face reflection structure. If the reflector is removed, a single optical signal is output through beam splitting and connected to a second photodetector, which provides a trigger signal and enables power fluctuation monitoring.

[0022] Specifically, in order to satisfy the trigger channel, the reflector itself can be removed. However, in this case, an additional optical signal needs to be led out to the second photodetector as the trigger channel. For example, the output optical signal can be connected to another coupler for beam splitting and then connected to the second photodetector for triggering and power fluctuation monitoring. In this way, the function of the reflector is equivalently replaced, and it should not be limited to this method.

[0023] The signal acquisition system is an oscilloscope or a data acquisition card; the photodetector is a PIN photodiode.

[0024] The time-domain fiber optic sensing system is a multi-point fiber optic sensing and measurement system, comprising multiple segments of delayed fiber and multiple fiber optic sensors. The multiple segments of delayed fiber are connected in parallel to the second output of the coupler via fiber optic splitters. Each segment of delayed fiber is connected to a corresponding fiber optic sensor. Alternatively, the multiple segments of delayed fiber are cascaded with multiple couplers in sequence, and the second output of each coupler is connected to a fiber optic sensor. The length difference of the multiple segments of delayed fiber satisfies the condition that it is greater than the fiber optic transmission length converted from pulse width time.

[0025] The semiconductor laser operates in a pulsed manner under dynamic current drive, emitting pulsed light and completing a wavelength scanning process. The center operating wavelength of the laser is adjusted by a temperature control system, and the pulse parameters are adjusted by a drive circuit to change the wavelength scanning range. In one specific embodiment, by setting the pulse width, the injected current exhibits a process of first increasing and then decreasing within a single pulse time window, thereby forming a transition interval from the rising segment to the falling segment during the current change. This transition interval corresponds to the moment when the instantaneous scanning rate approaches zero during the light source tuning process. When measuring the output signal of the fiber optic sensor in the time domain, a stable and repeatable adiabatic dynamic tuning inflection point characteristic can be obtained near this moment.

[0026] It should be noted that the pulse width, current change rate, and transition position can be adjusted according to actual system requirements and do not constitute a limitation of this invention.

[0027] For multi-point fiber optic sensing and measurement systems, the optical path can be constructed using parallel or cascade methods:

[0028] Parallel type: The second output of the coupler is connected to multiple segments of delayed optical fiber through an optical fiber splitter, and each segment of delayed optical fiber corresponds to one optical fiber sensor;

[0029] Cascaded: Multiple segments of delayed optical fiber are cascaded with multiple couplers in sequence, and the second output of each coupler is connected to an optical fiber sensor; wherein, the length difference of the multiple segments of delayed optical fiber must be greater than the optical fiber transmission length converted from pulse width time to ensure that the signal timing of different sensing units does not overlap.

[0030] A sensing method for a time-domain fiber optic sensing system based on adiabatic dynamic tuning inflection points includes the following steps:

[0031] Step 1: Apply dynamic current drive to the semiconductor laser to enable the semiconductor laser to complete the wavelength tuning process under adiabatic conditions; the dynamic current drive is a pulse drive with a pulse width of at least 10ns, a pulse repetition frequency of at least 1kHz, a pulse current greater than the threshold current for normal continuous operation of the semiconductor laser, and the current waveform satisfies the requirement that the amplitude has an extreme point, that is, the current monotonically increases and then turns into monotonically decreasing.

[0032] Step 2: Control the waveform characteristics of the dynamic current drive. Utilize the waveform characteristics of the dynamic current to form at least one adiabatic dynamic tuning inflection point during the wavelength tuning process. The adiabatic dynamic tuning inflection point corresponds to the moment when the instantaneous scanning rate approaches zero during the wavelength scanning process of the semiconductor laser. It is the transition interval between the rising and falling segments of the light source tuning.

[0033] Step 3: Using the adiabatic dynamic tuning inflection point as a unified time-domain reference feature, the output optical signal of the fiber optic sensing system is collected by a photodetector and converted into an electrical signal. The electrical signal is then captured by a signal acquisition system to determine the location of the time-domain feature in the signal related to the adiabatic dynamic tuning inflection point.

[0034] Step 4: Analyze the variation law of the time domain feature position with time, establish a mapping relationship between the variation law and the variation of the measured physical quantity (temperature, pressure, strain, gas concentration, etc.), and calculate the corresponding sensing parameter information.

[0035] The waveform of the dynamic current drive in step one satisfies the existence of an extreme point in the current amplitude, specifically, the current increases monotonically for a period of time and then turns to decrease monotonically. The implementation forms of the dynamic current drive include: continuous waveform drive generated by analog circuit, modulation drive of pulse current within a single pulse, sinusoidal modulation drive of monostable circuit combined with filter network, DC and AC signal superposition drive implemented by RF bias, triangular wave / sawtooth wave / nonlinear waveform drive output by signal generator, and arbitrary waveform drive implemented by digital circuit or programmable logic.

[0036] Specifically, the dynamic current driving method includes, but is not limited to, the following implementation forms: driving with a continuous waveform generated by an analog circuit; modulating with a pulse current within a single pulse; forming a sinusoidal modulation by combining a monostable circuit with a filter network; superimposing DC and AC signals by an RF bias; driving with a triangular wave, sawtooth wave, or other nonlinear waveform output by a signal generator; and driving with an arbitrary waveform implemented by a digital circuit or programmable logic. In all the above forms, the current amplitude must have an extreme point, for example, after monotonically increasing for a period of time, it suddenly turns and begins to monotonically decrease.

[0037] Any driving method that can form an adiabatic dynamic tuning inflection point during the tuning process falls within the protection scope of this invention.

[0038] Furthermore, the method of this invention is applicable to various fiber optic sensing structures and spectral detection scenarios based on spectral detection, including: fiber Bragg grating sensors (long-period fiber gratings, few-mode / multi-mode fiber gratings, uniform fiber gratings, chirped gratings, etc.), interferometric fiber optic sensors (Fabry-Perot interferometers, Michelson interferometers, Mach-Zehnder interferometers, etc.). This invention is also applicable to gas absorption spectral detection and other sensing applications based on spectral changes.

[0039] Furthermore, the method of this invention can be combined with time-division multiplexing to achieve multi-point fiber optic sensing measurement: a multi-point sensing optical path is built through fiber optic splitters or cascaded couplers, different sensing units are distinguished by pulse timing, and the adiabatic dynamic tuning inflection point is used as a unified time-domain feature marker to complete the synchronous analysis of multi-channel sensing signals. Regarding the measurement system and multi-point multiplexing, the method described in this invention can be combined with time-division multiplexing to achieve multi-point fiber optic sensing measurement, and multiple sensing units can be distinguished by pulse timing. In the above multi-point structure, the adiabatic dynamic tuning inflection point can be used as a unified time-domain feature marker for the synchronous analysis of multi-channel signals.

[0040] The dynamic current drive in step one is a pulsed current drive with a pulse width of at least 10 ns, a pulse repetition frequency of at least 1 kHz, and a pulse current greater than the threshold current for normal continuous operation of the semiconductor laser. By setting the pulse width, the injected current exhibits a process of first increasing and then decreasing within a single pulse time window, forming a transition interval from the rising segment to the falling segment. The transition interval is the formation interval of the adiabatic dynamic tuning inflection point.

[0041] The driving implementation method of the adiabatic dynamic tuning inflection point includes the following steps:

[0042] S11: Generation of dynamic tuning time window: A square wave generating circuit is constructed using a timer chip. By adjusting the external timing resistor and capacitor, a square wave signal is generated as the dynamic tuning time window to realize the control of pulse repetition frequency and pulse width.

[0043] S12: Timing shaping of the tuning signal: The square wave signal is input into the pulse generation unit composed of a high-speed bistable trigger circuit to generate a monostable pulse with controllable width, which limits the effective time interval of dynamic tuning of the light source and ensures the repeatability of the tuning pulse in each cycle.

[0044] S13: Enable and select the tuning process: A logic selection unit is constructed using a logic chip to perform gating and enable control on the monostable pulse, thereby realizing the start and stop of the tuning process and the switching of the modulation mode.

[0045] S14: Construction of the injected current waveform: The pulse signal output by the logic selection unit is input into the voltage-to-current drive unit composed of power devices to convert the voltage control signal into a large current signal. By designing the amplitude and phase of the AC modulation signal, the injected current exhibits a waveform characteristic of monotonically rising in the first half and monotonically falling in the second half within the pulse window.

[0046] S15: Formation of the adiabatic dynamic inflection point: The pulsed current with the waveform characteristics is injected into the semiconductor laser. The laser completes wavelength tuning under adiabatic conditions. The inflection interval of the current change corresponds to the moment when the instantaneous wavelength scanning rate approaches zero, thus forming a stable and repeatable adiabatic dynamic tuning inflection point.

[0047] Compared with the prior art, the technical solution of the present invention achieves temporal demodulation of spectral information by actively constructing an adiabatic dynamic tuning inflection point, which has the following outstanding technical effects:

[0048] 1. Actively construct stable and calibrable time-domain feature points to solve the problem of missing feature points: By driving the adiabatic tuning process of the light source through dynamic current, the adiabatic dynamic tuning inflection point formed has the characteristics of being repeatable and calibrable, and the physical characteristic of the corresponding wavelength scanning instantaneous rate tending to zero can be used as a time-domain reference point to completely solve the problem of non-unique feature points and inability to be directly calibrated in traditional wavelength domain demodulation.

[0049] 2. Achieve spectral-time domain mapping and simplify demodulation algorithm: Convert the spectral changes of the sensing signal into changes in the time domain feature position. The demodulation process does not require precise wavelength calibration in the wavelength domain, nor does it require a complex real-time tracking algorithm. Even for spectral signals with periodic and multi-peak characteristics, stable demodulation can be achieved in the time domain, which greatly reduces the complexity of signal processing.

[0050] 3. Eliminating dedicated passive feature devices, reducing system cost and implementation difficulty: This invention actively constructs feature points through circuit driving, eliminating the need for dedicated passive feature devices such as etalons, as well as high-precision tunable modules. This simplifies the optical path and circuit structure, reduces hardware costs, and improves system integration and reliability, while facilitating on-site installation and debugging.

[0051] 4. Strong environmental adaptability and improved sensing stability: The time-domain demodulation method is less affected by the external environment (such as vibration and temperature drift). The adiabatic dynamic tuning inflection point can still maintain stable time-domain characteristics in complex environments, which effectively improves the availability and stability of interferometric fiber optic sensors and dense spectral detection under large-scale scanning and harsh working conditions.

[0052] 5. Compatible with multi-point multiplexing measurement, expanding the application range: Combined with time-division multiplexing, multi-point fiber optic sensing measurement can be easily realized. The thermal dynamic tuning inflection point is used as a unified time-domain feature marker to complete the synchronous analysis of multi-channel signals. Moreover, the optical path is flexible (parallel / cascade is possible), which is suitable for the distributed monitoring needs of multiple measurement points in industrial sites.

[0053] 6. Wide range of applications and strong versatility: The method of this invention is not only applicable to traditional fiber Bragg grating sensors, but also has good compatibility with various interferometric fiber sensors, gas absorption spectroscopy detection and other sensing applications based on spectral changes. It does not require major modifications for different sensing objects and has strong versatility. Attached Figure Description

[0054] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0055] Figure 1 This is a schematic diagram of the structure of a time-domain fiber optic sensing system and method based on adiabatic dynamic tuning inflection point according to the present invention.

[0056] Figure 2 This is a flowchart illustrating the simulation circuit driving implementation of the adiabatic dynamic tuning inflection point of this invention.

[0057] Figure 3 This is a typical pulse current waveform diagram from Embodiment 2 of the present invention;

[0058] Figure 4 This is a typical time-domain characteristic signal diagram of the adiabatic dynamic tuning inflection point after the interferometric fiber optic sensor is connected to the present invention;

[0059] Figure 5 This is a schematic diagram of the parallel multi-point time-domain fiber optic sensing system of the present invention;

[0060] Figure 6 This is a schematic diagram of the cascaded multi-point time-domain fiber optic sensing system of the present invention.

[0061] In the diagram: 1-Drive circuit, 2-Temperature control system, 3-Semiconductor laser, 4-Coupled, 401-First input terminal, 402-Second input terminal, 403-First output terminal, 404-Second output terminal, 5-Reflector, 6-Delay fiber, 7-Photodetector, 8-Signal acquisition system, 9-Fiber optic sensor; 6001-Parallel delay fiber, 901-Parallel fiber optic sensor; 601-Cascaded delay fiber, 4001-Cascaded coupler, 9001-Cascaded fiber optic sensor. Detailed Implementation

[0062] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0063] Example 1:

[0064] This embodiment provides a time-domain fiber optic sensing system based on adiabatic dynamic tuning inflection points, such as... Figure 1 As shown, it includes a driving circuit 1, a temperature control system 2, a semiconductor laser 3, a coupler 4, a reflector 5, a delay fiber 6, a photodetector 7, a signal acquisition system 8, and a fiber optic sensor 9.

[0065] Specifically, the driving circuit 1 drives the semiconductor laser 3 by emitting pulses. The driving circuit 1 emits pulses with a pulse width of 10 ns (here, 500 ns), a pulse repetition frequency of at least 1 kHz, and a pulse current greater than the threshold current for normal continuous operation of the semiconductor laser. The pulse waveform generated by the driving circuit needs to have the characteristic of generating an adiabatic dynamic tuning inflection point, as detailed in Embodiment 2.

[0066] The temperature control system 2 is a temperature controller, including a voltage drive circuit and a resistance detection circuit. By combining a PID algorithm, the thermoelectric cooler can be controlled by a host computer to achieve stable temperature control. The temperature control system 2 is electrically connected to the thermoelectric cooler and thermistor of the semiconductor laser 3.

[0067] The semiconductor laser 3 integrates a laser chip, a thermoelectric cooler, and a thermistor. The temperature control system 2 is connected to the semiconductor laser 3, monitors the temperature through the thermistor, and controls the laser temperature by adjusting the cooler through the output voltage.

[0068] It should be noted that temperature controllers and PID algorithms are both conventional techniques, so they will not be described in detail in this embodiment.

[0069] In a further embodiment, the coupler 4 is an optical fiber coupler with a first input terminal 401 and a second input terminal 402, a first output terminal 403 and a second output terminal 404. In this embodiment, the splitting ratio is 90:10.

[0070] The semiconductor laser 3 is connected to the first input terminal 401 of the coupler 4, the first output terminal 403 of the coupler 4 is connected to the reflector 5, the second input terminal 402 of the coupler 4 is connected to the photodetector 7, the second output terminal 404 of the coupler 4 is connected to the delay fiber 6, and the photodetector 7 is connected to the oscilloscope 8.

[0071] Specifically, reflector 5 can be a Faraday mirror or an optical fiber end face reflector. In this embodiment, an optical fiber end face reflector is sufficient, with a reflectivity ≥4%.

[0072] The photodetector 8 is a PIN photodiode.

[0073] The signal acquisition system 8 is a conventional oscilloscope with typical parameters including bandwidth ≥100MHz and sampling rate ≥1GS / s.

[0074] The fiber optic sensor 9 is a reflective sensor, including various fiber optic gratings and various fiber optic interferometers. In this example, a Fabry-Perot interferometer (FPI) sensor is used.

[0075] Furthermore, the semiconductor laser includes, but is not limited to, DFB, VCSEL, FP, and other lasers, with a center wavelength sufficient for low-loss transmission within the 0.8µm-1.8µm range of the communication optical fiber. In this embodiment, the semiconductor laser 2 is a DFB laser with a center wavelength of 1550nm. The pulse control unit 1 drives the semiconductor laser 2 to emit pulsed light, adjusting the pulse width to 500ns and the peak pulse current to approximately 1A. The pulsed light passes through the first input terminal 401 of the coupler 4 and is output from the second output terminal 404. After passing through the first output terminal 403 of the coupler 4 and entering the reflector 5, the pulsed light returns to the coupler 4 and is received by the photodetector 8 at the second input terminal 402 of the coupler 4 as a trigger. The pulsed light then passes through the second output terminal 404 of the coupler and enters the delay fiber 6, is reflected back to the second input terminal 402 of the coupler 4 by the fiber optic sensor 9, and is received by the photodetector 7 and transmitted to the signal acquisition system 8 for sensing signal processing in the time domain.

[0076] System debugging: The target temperature of the temperature controller is set to 25℃ via the host computer. The drive circuit is started to output a preset pulse current. The semiconductor laser completes wavelength tuning under adiabatic conditions. The tuning scanning range is about 2.5nm (covering the FSR of the FPI sensor = 0.9 nm). An adiabatic dynamic tuning inflection point is formed at 200 ns when the current rises to falls (the instantaneous wavelength scanning rate approaches zero). The oscilloscope uses the backlight of the fiber optic end face reflector 5 as the trigger signal to collect the electrical signal output by the photodetector 7. A stable time-domain characteristic inflection point can be captured at 200ns, completing the system debugging.

[0077] Example 2:

[0078] This embodiment provides a method for driving the inflection point of adiabatic dynamic tuning based on analog circuits. By constructing a current modulation waveform with rising and falling segments within a pulse time window, it is used to drive a semiconductor light source to complete the adiabatic dynamic tuning process.

[0079] This embodiment uses analog circuitry to drive the adiabatic dynamic tuning inflection point. The core is to construct a rising-falling current modulation waveform within a single pulse time window to drive the semiconductor laser to complete adiabatic dynamic tuning. Figure 2 As shown, the process includes five steps: S11 generation of dynamic tuning time window, S12 timing shaping of tuning signal, S13 enabling and selecting the tuning process, S14 construction of injected current waveform, and S15 formation of adiabatic dynamic inflection point.

[0080] The generation of the dynamic tuning time window S11 can be achieved by using a timer chip NE555 to construct a square wave generating circuit, generating a periodic square wave signal. By adjusting the timing resistor and capacitor parameters of the NE555, the period and high-level duration of the square wave can be independently set, thereby controlling the pulse repetition frequency and the pulse time window. It should be noted that the specific frequency and duty cycle of the square wave are not limiting conditions of this invention, as long as the adiabatic dynamic tuning process can be completed within a single pulse cycle.

[0081] After the generation of the dynamic tuning time window (S11), the timing shaping of the tuning signal (S12) begins. In this embodiment, the square wave signal is further input to the pulse generation unit composed of the high-speed bistable trigger circuit HC123M-1. Under trigger conditions, HC123M-1 generates a monostable pulse with controllable width. The pulse width is determined by an external timing element and used to define the effective time interval for dynamic tuning of the light source. This method can generate a highly repeatable tuning pulse in each cycle, providing a uniform time window for the rise and fall of the current within the pulse.

[0082] After timing shaping of the tuning signal in step S12, the tuning process enters the enable and selection step S13. In this embodiment, an SN74LVC1G08DCKR logic chip is used to construct a logic selection unit for gating and enabling the pulse signal. This logic selection unit can selectively output the pulse signal according to the system operating state, thereby realizing the start and stop control of the tuning process and the switching between multiple modulation modes. The specific logical relationship of the logic selection unit can be configured according to the actual system requirements and is not intended to limit the invention.

[0083] After enabling and selecting S13 in the tuning process, the process proceeds to step S14, which involves constructing the injected current waveform. In this embodiment, the pulse signal is input to the voltage-to-current drive unit after passing through the logic selection unit. The voltage-to-current drive unit uses a high-current drive circuit composed of power devices such as the IRF7403 to convert the voltage control signal into a drive current for injecting into the semiconductor light source. This drive circuit supports the superposition of DC bias and AC modulation signals. By designing the amplitude and phase of the AC modulation signal, a current waveform with rising and falling segments can be formed within a single pulse time window. The formed current waveform exhibits a monotonically rising trend in the initial stage of the pulse and a monotonically falling trend in the latter half of the pulse, thereby achieving a continuous dynamic tuning process within the pulse and forming an adiabatic dynamic tuning inflection point during the tuning process (by designing the amplitude and phase of the AC modulation signal, the injected current exhibits a waveform characteristic of monotonically rising for the first 200 ns and monotonically falling for the last 300 ns within a 500 ns pulse window (e.g.)). Figure 3 As shown).

[0084] After constructing the injected current waveform in S14, a pulsed current of a specific waveform is generated by the aforementioned circuit and injected into the semiconductor laser. Within a single pulse time window, the current undergoes a continuous change, corresponding to a continuous change in its output wavelength or optical frequency over time. When the rate of current change meets adiabatic conditions, the light source tuning process does not introduce abrupt transitions, forming a stable inflection point characteristic in the tuning curve, i.e., achieving the formation of the adiabatic dynamic inflection point in step S15. This inflection point can serve as a characteristic marker in the time domain for subsequent spectral demodulation and sensor signal analysis.

[0085] This embodiment also includes a voltage regulator circuit, an overcurrent protection circuit, and necessary electrical protection structures to ensure the stability and safety of the drive circuit. All circuits are modularly designed for easy debugging and replacement.

[0086] The circuits described above are all conventional techniques in this field, and will not be described in detail here, nor do they constitute a limitation of this invention.

[0087] Example 3:

[0088] This embodiment provides a typical current waveform obtained in Embodiment 2. In order to achieve the inflection point of adiabatic dynamic tuning, it is necessary to present a waveform feature of rising first and then falling within the pulse. Specifically, in this embodiment, the pulse width reaches 500ns. The current shows a monotonically rising characteristic in the first 200ns and the current begins to decay in the last 300ns. It is worth noting that the specific waveform of the rising and falling process is not limited. The key point is that there is a turning point between rising and falling.

[0089] Example 4:

[0090] This embodiment provides a method for using an adiabatic dynamic tuning inflection point in time-domain sensing measurements after being connected to an interferometric fiber optic sensor. In such cases... Figure 1 In the system shown, an interferometric fiber optic sensor is connected to the output of the light source. By applying adiabatic dynamic tuning drive to the light source, the wavelength scanning process is completed within a single pulse time window, and an adiabatic dynamic tuning inflection point is formed during the tuning process. Figure 4 The image shows a typical signal in the time domain after the interferometric fiber optic sensor is connected, with the solid line representing the simulation result and the dashed line representing the measured result. In this embodiment, a Michelson interferometer is used, and its free spectral range (FSR) can be set to 0.9 nm. Without introducing an adiabatic dynamic tuning inflection point, the interferometric fiber optic sensor should exhibit a strictly periodic time-domain interference signal during wavelength scanning. However, in this embodiment, the time-domain signal exhibits a significant aperiodic characteristic around approximately 200 ns, corresponding to the position where the driving current transitions from the rising phase to the falling phase.

[0091] From a physical perspective, this characteristic corresponds to the moment when the instantaneous scanning rate during the wavelength scanning process of the light source approaches zero, i.e., the position where the equivalent time-domain dispersion approaches zero, thereby disrupting the original strictly periodic interference structure in the time domain. This moment is the adiabatic dynamic tuning inflection point proposed in this invention.

[0092] To ensure that at least one interference feature usable for sensing and demodulation is formed during the tuning process, the free spectral range (FSR) of the interferometric fiber optic sensor needs to satisfy that at least one interference period falls within the scanning range of the light source.

[0093] In this embodiment, the scanning range of the light source under pulsed driving conditions is approximately 2.5 nm, therefore the FSR of the interferometric fiber optic sensor needs to be less than or equal to this scanning range.

[0094] This embodiment also provides a time-domain physical definition of the adiabatic dynamic tuning inflection point:

[0095] In this embodiment, when the wavelength of the light source changes with time (For example, in the case of frequency chirping caused by adiabatic tuning of current), the derivative of phase with respect to time is:

[0096]

[0097] Therefore, the rate of change of phase over time is determined by two factors: the phase sensitivity in the wavelength domain. (and (Related) Time-domain scan rate with wavelength Therefore, two types of "" can be obtained The first type is the passive case, where the phase sensitivity to wavelength approaches zero. The second type is the active case, where the instantaneous scanning rate of the wavelength approaches zero. The adiabatic dynamic tuning inflection point proposed in this invention belongs to the second type of case, corresponding to the retrace or transition moment in the wavelength scanning process. Further, at the time point... Simultaneously satisfy:

[0098] and

[0099] At this time, when hour, ( (Not infinite) Under this condition, the first-order phase change no longer dominates the time-domain interference structure, and its second-order time derivative will determine the dynamic evolution characteristics of the interference signal near the inflection point, thus forming a stable and repeatable time-domain feature.

[0100] This embodiment also provides an explanation of the sensing mechanism based on inflection points:

[0101] When external physical quantities such as temperature, pressure, or strain change, the optical path difference of the interferometric fiber optic sensor changes, thereby causing a change in the interference phase characteristics.

[0102] Since the inflection point of adiabatic dynamic tuning has a stable and identifiable characteristic location in the time domain, it can be used as a time domain reference point to focus on the changes in the characteristics of interference signals in its vicinity over time.

[0103] By analyzing the positional changes of peaks, troughs, or other time-domain features near the inflection point, the changes in time-domain features can be mapped to the corresponding changes in the measured physical quantity, thereby realizing time-domain fiber optic sensing measurement based on adiabatic dynamic tuning inflection points.

[0104] This embodiment uses an interferometric fiber optic sensor as an example only. It should be noted that any fiber optic sensor with spectral measurement characteristics, such as a fiber optic grating, is applicable to this method.

[0105] Example 5:

[0106] This embodiment presents a multi-point time-domain fiber optic sensing system structure based on adiabatic dynamic tuning inflection points. The functionality of this invention is not limited to a single measurement point; it is applicable to all fiber-optic multi-point measurement structures. The optical path based on time-division multiplexing is as follows: Figure 5 As shown, the sensing unit can be connected to multiple parallel delay fiber segments 6001 via an optical fiber splitter, and then to multiple parallel optical fiber sensors 901, thus enabling multi-point time-domain measurement. The difference between the multiple parallel delay fiber segments 6001 needs to be greater than the length converted from pulse width time. For example, if the pulse width is 500ns, then the difference between the delay fibers needs to be ≥500ns * the speed of light, i.e., 150m.

[0107] Example 6:

[0108] This embodiment presents another multi-measurement point connection method. Unlike the parallel connection of multiple sensors in Embodiment 5, this method uses a cascaded connection. The pulse light from the sensing portion passes through a cascaded delay fiber 601 and sequentially enters a cascaded coupler 4001, another cascaded delay fiber 601, another cascaded coupler 4001, and another cascaded delay fiber 601. The splitting ratio of the coupler 4001 is at least 90:10. The second output of the cascaded coupler 4001 enters a cascaded fiber optic sensor 9001, serving as a cascaded multi-measurement point scheme.

[0109] This invention overcomes the lack of stable feature points in traditional frequency sweeping methods by actively constructing an adiabatic dynamic tuning inflection point through dynamic control during the tuning process. It achieves stable demodulation of periodic or multi-valued spectral signals without the need for passive feature devices such as fiber Bragg gratings, significantly expanding the application range of interferometric fiber optic sensors. By mapping spectral variation information to time-domain features for demodulation, this invention reduces reliance on precise wavelength calibration and complex real-time tracking algorithms, significantly simplifying the demodulation process. This invention improves the usability and stability of interferometric fiber optic sensors and dense spectral detection under complex environments and large-scale scanning conditions. Furthermore, this invention helps reduce overall system costs and implementation difficulty, providing favorable conditions for the engineering application and large-scale promotion of fiber optic sensing technology.

[0110] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A time-domain fiber optic sensing system based on adiabatic dynamic tuning inflection point, characterized in that: include: The driving circuit, electrically connected to the semiconductor laser, is used to output a dynamic current driving signal to the semiconductor laser that meets the requirements for forming the adiabatic dynamic tuning inflection point. The formation of the adiabatic dynamic tuning inflection point includes: applying a dynamic current drive to the semiconductor laser to enable the semiconductor laser to complete the wavelength tuning process under adiabatic conditions, and controlling the waveform characteristics of the dynamic current drive to form at least one adiabatic dynamic tuning inflection point during the wavelength tuning process. The adiabatic dynamic tuning inflection point corresponds to the moment when the instantaneous scanning rate approaches zero during the wavelength scanning process of the semiconductor laser. A temperature control system, connected to the semiconductor laser, is used to stably control the operating temperature of the semiconductor laser. A semiconductor laser, the optical output terminal of which is connected to the first input terminal of a coupler; A coupler, the first output of which is connected to a reflector, and the second output of which is connected to one end of a delay fiber; A reflector is used to provide a trigger signal for signal acquisition. The delay fiber is connected at one end to a fiber optic sensor at the other. A photodetector, whose optical input end is connected to the second input end of a coupler, and whose electrical output end is electrically connected to a signal acquisition system; used to convert optical signals from fiber optic sensing into electrical signals. A signal acquisition system is used to acquire, store, and process electrical signals.

2. The time-domain fiber optic sensing system based on adiabatic dynamic tuning inflection point according to claim 1, characterized in that: The driving circuit includes a voltage regulator circuit, a logic control circuit, a signal generation circuit, a pulse generation circuit, a waveform shaping circuit, and a high-frequency switching driving circuit. The voltage regulator circuit provides a stable power supply. The signal generation circuit works with the pulse generation circuit to generate a basic pulse signal. The waveform shaping circuit shapes the basic pulse signal so that the output current waveform meets the requirement that the current amplitude has an extreme point. The logic control circuit controls the start and stop of the tuning process and switches the modulation mode. The high-frequency switching driving circuit converts the voltage signal into a high-current signal that meets the driving requirements of the semiconductor laser.

3. The time-domain fiber optic sensing system based on adiabatic dynamic tuning inflection point according to claim 1, characterized in that: The temperature control system is a temperature controller or a constant temperature chamber. The temperature controller is controlled by a host computer using a PID algorithm and integrates a voltage drive circuit and a resistance detection circuit. When the semiconductor laser integrates a laser chip, a thermoelectric cooler, and a thermistor, the temperature controller monitors the temperature through the thermistor and adjusts the output voltage to regulate the thermoelectric cooler to achieve temperature control.

4. A time-domain fiber optic sensing system based on an adiabatic dynamic tuning inflection point according to claim 1, characterized in that: The semiconductor laser is one of a DFB laser, a VCSEL laser, or an FP laser, with its center wavelength in the low-loss transmission band of communication optical fiber of 0.8µm-1.8µm; the coupler is an optical fiber coupler; the reflector is a Faraday mirror or an optical fiber end face reflection structure; the signal acquisition system is an oscilloscope or a data acquisition card; and the photodetector is a PIN photodiode.

5. A time-domain fiber optic sensing system based on an adiabatic dynamic tuning inflection point according to claim 1, characterized in that: The time-domain fiber optic sensing system is a multi-point fiber optic sensing and measurement system, comprising multiple segments of delayed fiber and multiple fiber optic sensors. The multiple segments of delayed fiber are connected in parallel to the second output of the coupler via fiber optic splitters. Each segment of delayed fiber is connected to a corresponding fiber optic sensor. Alternatively, the multiple segments of delayed fiber are cascaded with multiple couplers in sequence, and the second output of each coupler is connected to a fiber optic sensor. The length difference of the multiple segments of delayed fiber satisfies the condition that it is greater than the fiber optic transmission length converted from pulse width time.

6. A sensing method for a time-domain fiber optic sensing system based on an adiabatic dynamic tuning inflection point according to any one of claims 1-5, characterized in that: Includes the following steps: Step 1: Apply dynamic current to drive the semiconductor laser to enable it to complete the wavelength tuning process under adiabatic conditions; Step 2: Control the waveform characteristics of the dynamic current drive to form at least one adiabatic dynamic tuning inflection point during the wavelength tuning process. The adiabatic dynamic tuning inflection point corresponds to the moment when the instantaneous scanning rate approaches zero during the wavelength scanning process of the semiconductor laser. Step 3: Using the adiabatic dynamic tuning inflection point as a time-domain reference feature, acquire the output signal of the fiber optic sensing system and determine the location of the time-domain feature in the output signal related to the adiabatic dynamic tuning inflection point. Step 4: Analyze the variation of the time-domain feature position over time, map the variation to the change of the measured physical quantity, and obtain the corresponding sensing parameter information.

7. The sensing method for a time-domain fiber optic sensing system based on an adiabatic dynamic tuning inflection point according to claim 6, characterized in that: The waveform of the dynamic current drive in step one satisfies that the current amplitude has an extreme point, and the current increases monotonically for a period of time and then turns to decrease monotonically. The implementation forms of the dynamic current drive include: continuous waveform drive generated by analog circuit, modulation drive of pulse current within a single pulse, sinusoidal modulation drive of monostable circuit combined with filter network, DC and AC signal superposition drive implemented by RF bias, triangular wave / sawtooth wave / nonlinear waveform drive output by signal generator, and arbitrary waveform drive implemented by digital circuit or programmable logic.

8. The sensing method for a time-domain fiber optic sensing system based on an adiabatic dynamic tuning inflection point according to claim 6, characterized in that: The dynamic current drive in step one is a pulsed current drive with a pulse width of at least 10 ns, a pulse repetition frequency of at least 1 kHz, and a pulse current greater than the threshold current for normal continuous operation of the semiconductor laser. By setting the pulse width, the injected current exhibits a process of first increasing and then decreasing within a single pulse time window, forming a transition interval from the rising segment to the falling segment. The transition interval is the formation interval of the adiabatic dynamic tuning inflection point.

9. The sensing method for a time-domain fiber optic sensing system based on an adiabatic dynamic tuning inflection point according to claim 6, characterized in that: The driving implementation method of the adiabatic dynamic tuning inflection point in step two includes the following steps: S11: Generation of dynamic tuning time window: A square wave generating circuit is constructed using a timer chip. By adjusting the external timing resistor and capacitor, a square wave signal is generated as the dynamic tuning time window to realize the control of pulse repetition frequency and pulse width. S12: Timing shaping of the tuning signal: The square wave signal is input into the pulse generation unit composed of a high-speed bistable trigger circuit to generate a monostable pulse with controllable width, which limits the effective time interval of dynamic tuning of the light source and ensures the repeatability of the tuning pulse in each cycle. S13: Enable and select the tuning process: A logic selection unit is constructed using a logic chip to perform gating and enable control on the monostable pulse, thereby realizing the start and stop of the tuning process and the switching of the modulation mode. S14: Construction of the injected current waveform: The pulse signal output by the logic selection unit is input into the voltage-to-current drive unit composed of power devices to convert the voltage control signal into a large current signal. By designing the amplitude and phase of the AC modulation signal, the injected current exhibits a waveform characteristic of monotonically rising in the first half and monotonically falling in the second half within the pulse window. S15: Formation of the adiabatic dynamic inflection point: The pulsed current with the waveform characteristics is injected into the semiconductor laser. The laser completes wavelength tuning under adiabatic conditions. The inflection interval of the current change corresponds to the moment when the instantaneous wavelength scanning rate approaches zero, thus forming a stable and repeatable adiabatic dynamic tuning inflection point.

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