Optoelectronic mode-locked method and mode-locked laser

Abstract

This invention relates to the field of fiber laser mode-locking technology, specifically to a photoelectric oscillation mode-locking method and a mode-locked laser. The method includes: S1, injecting pump light into a resonant cavity via a pump diode, which is absorbed by the gain fiber in the resonant cavity and converted into signal light, causing the signal light to form spike noise in the resonant cavity; S2, extracting the spike noise through a photodetector and converting it into an electrical signal, which is then amplified and used to drive a modulator connected to the resonant cavity for self-photoelectric oscillation, or using an external signal from an external signal source, which is then amplified and used to drive a modulator connected to the resonant cavity for external photoelectric oscillation, or extracting spike noise through a photodetector and converting it into an electrical signal, which is then mixed and amplified with the external signal from the external signal source to drive a modulator connected to the resonant cavity for mutual photoelectric oscillation; S3, enhancing the spike noise through self-photoelectric oscillation, external photoelectric oscillation, or mutual photoelectric oscillation, converting it into spike noise with increased intensity, relaxation oscillation, and / or Q-switched pulses, thus broadening the spectral split and completing resonant cavity mode-locking. This invention can reduce the mode-locking start-up threshold, reduce the mode-locking start-up time, and achieve rapid mode-locking start-up.

Description

Technical Field

[0001] This invention relates to the field of fiber laser mode-locking technology, specifically to a photoelectric oscillation mode-locking method and a mode-locked laser. Background Technology

[0002] Ultrafast pulsed lasers with pulse widths in the picosecond and femtosecond range possess characteristics such as high peak power, high repetition rate, and wide spectrum, making them valuable for applications in precision measurement, precision imaging, and precision machining. In recent years, the types of resonant cavities and various compact optical devices have been significantly developed, leading to continuously increasing repetition rates in mode-locked lasers and raising the required pump threshold for mode-locking. Resonant cavities include linear resonant cavities, saturable absorber resonant cavities, nonlinear polarization-rotating resonant cavities, and nonlinear ring mirror resonant cavities. By leveraging the correlation between intensity and transmittance—higher intensity resulting in higher transmittance—pulse narrowing is achieved, enabling phase locking between laser longitudinal modes and realizing ultrashort, ultrafast pulsed laser output.

[0003] Achieving stable and reliable mode-locking self-starting is a crucial issue in the formation of ultrafast lasers in mode-locked lasers, determining whether a mode-locked laser can operate stably for a long period. The laser oscillates within the cavity, completing the process of increasing light intensity. Saturable absorption causes significant losses at low light intensities, affecting the mode-locking self-starting threshold. Fiber cavities based on nonlinear effects, such as nonlinear amplifying ring mirror fiber cavities, exhibit weak nonlinear effects at low pump thresholds, making self-starting difficult and requiring higher pump thresholds. However, the mode-locking setup time is unstable, and a high pump threshold puts pressure on the resonant cavity and other components, increasing the potential damage threshold. Furthermore, as the repetition frequency increases and the resonant cavity length decreases, the phase shift accumulated within the cavity becomes insufficient, further increasing the required pump start-up threshold. Summary of the Invention

[0004] One of the objectives of this invention is to provide a photoelectric oscillation mode-locking method to solve the technical problems of long start-up time and high start-up pump threshold in the traditional pump direct start mode-locking method, and to achieve stable and reliable photoelectric oscillation mode-locking.

[0005] The photoelectric oscillation mode-locking method in this solution includes the following steps:

[0006] S1, pump light is injected into the resonant cavity through the pump diode, and the pump light is absorbed by the gain fiber in the resonant cavity and converted into signal light, so that the signal light forms spike noise in the resonant cavity;

[0007] S2 extracts peak noise through a photodetector, converts it into an electrical signal, amplifies it through signal processing, and drives the modulator connected to the resonant cavity to perform self-photoelectric oscillation; or it extracts peak noise through a photodetector, converts it into an electrical signal, and mixes it with the external signal output from the external signal source, amplifies it, and drives the modulator connected to the resonant cavity to perform mutual photoelectric oscillation.

[0008] S3 enhances the spike noise through self-photoelectric oscillation, external photoelectric oscillation, or mutual photoelectric oscillation, converting it into spike noise with increased intensity, relaxation oscillation, and / or Q-switched pulses, thereby broadening the spectrum and completing the mode-locking of the resonant cavity.

[0009] The beneficial effects of this plan are:

[0010] By setting up photoelectric oscillations, the spike noise of the mode-locked resonant cavity injected with pump light is amplified and converted into stronger spike noise, relaxation oscillations, and / or Q-switched pulses, which broadens the spectral split and allows the resonant cavity to reach the mode-locked state more quickly, thus enabling the resonant cavity to lock up.

[0011] Mode-locking initiation via self-electro-optical mode-locking allows for stable and rapid mode-locking with simple settings. Mode-locking initiation via external-electro-optical mode-locking achieves stable and rapid mode-locking with simplified laser components. Mode-locking initiation via mutual-electro-optical oscillation enables rapid and accurate mode-locking, and allows setting the frequency of the external signal output from the external signal source as the repetition frequency of the resonant cavity, keeping the resonant cavity in a frequency-locked operating state. It enables rapid single-peak pulse initiation, reduces the mode-locking initiation threshold, shortens the mode-locking initiation time, and achieves photoelectric oscillation mode-locking with high initiation stability and consistency.

[0012] The second objective of this invention is to provide a photoelectric oscillation mode-locking laser to reduce mode-locking start-up time and achieve rapid mode-locking start-up.

[0013] The optoelectronic oscillation mode-locked laser in this scheme includes a pump diode, a resonant cavity, a photodetector, a modulator, an external signal source, and a signal processor;

[0014] To implement the photoelectric oscillation mode-locking method described above, the pump diode signal is connected to the resonant cavity, one output signal of the resonant cavity is connected to one input signal of the photodetector, the photodetector detects spike noise, relaxation oscillation, Q-switching pulse, and mode-locking pulse after mode-locking is initiated when mode-locked, the other output signal of the photodetector is connected to one input signal of the signal processor, one output signal of the external signal source is connected to another input signal of the signal processor, one output signal of the signal processor is connected to one input signal of the modulator, the signal processor is used to perform signal mixing and amplification of self-photoelectric oscillation, external photoelectric oscillation, or mutual photoelectric oscillation, and the modulator is connected to the resonant cavity signal.

[0015] The beneficial effects of this plan are:

[0016] By adjusting the laser settings, the optical signal can be enhanced, the mode-locking start-up time can be reduced, photoelectric oscillation mode-locking can be achieved, mode-locking can be promoted, and the mode-locking threshold can be effectively reduced.

[0017] Furthermore, the resonant cavity includes a linear resonant cavity, a saturable absorber resonant cavity, a nonlinear polarization rotating resonant cavity, an offset filter mode-locked resonant cavity, or a nonlinear ring mirror resonant cavity.

[0018] The beneficial effect is that it allows for different resonant cavity settings, making it more flexible in its application range.

[0019] Furthermore, the modulator includes an electro-optic modulator, an acousto-optic modulator, a polarization control modulator, or a piezoelectric ceramic.

[0020] The beneficial effect is that the modulator, connected to the resonant cavity, can drive the enhanced signal to the resonant cavity for mode-locking.

[0021] Furthermore, the signal processor includes a signal selector, a PID filter amplifier, a drive amplifier, a mixer, and a phase detector. The photodetector and the reference signal source are both connected to the signal selector. The signal selector is connected to the mixer and / or the phase detector. The mixer and / or the phase detector is connected to the PID filter amplifier. The PID filter amplifier is connected to the drive amplifier. The drive amplifier is connected to the modulator.

[0022] The beneficial effect is that, by setting the signal processor, different photoelectric oscillation methods can be flexibly selected to achieve mode-locking of the resonant cavity.

[0023] Furthermore, the frequency range of the signal processor's output signal is 0-1MHz.

[0024] The beneficial effects are: unlike active mode-locking where the output frequency is strictly equal to the repetition frequency of the resonant cavity, the signal processor output signal is used to drive the modulator, which enhances the spike noise, and the output frequency can be flexibly set. Attached Figure Description

[0025] Figure 1 This is a flowchart of an embodiment of the photoelectric oscillation mode-locking method of the present invention;

[0026] Figure 2 This is a schematic diagram of the first embodiment of the photoelectric oscillation mode-locked laser of the present invention;

[0027] Figure 3 This is a schematic diagram illustrating the connection principle of the resonant cavity in Embodiment 1 of the photoelectric oscillation mode-locked laser of the present invention;

[0028] Figure 4 This is a schematic diagram of the unmode-locked waveform in Embodiment 1 of the photoelectric oscillation mode-locked laser of the present invention;

[0029] Figure 5 This is a waveform diagram of a pump power of 300mW under conventional mode locking.

[0030] Figure 6 This is a waveform diagram of a pump power of 135mW under conventional mode locking.

[0031] Figure 7 This is a schematic diagram of the waveform of the mode-locking result when the pump power is 135mW and the low threshold is activated in Embodiment 1 of the photoelectric oscillation mode-locking laser of the present invention. Detailed Implementation

[0032] The following detailed description provides further details on specific implementation methods.

[0033] Example 1

[0034] The photoelectric oscillation mode-locking method includes the following steps:

[0035] S1, pump light with gradually increasing power is input into the resonant cavity through the pump diode during the mode-locking start-up process. The pump light is absorbed by the gain fiber in the resonant cavity and converted into signal light, which causes the signal light to form spike noise in the resonant cavity.

[0036] S2 extracts peak noise through a photodetector, converts it into an electrical signal, amplifies it after signal processing, and drives the modulator connected to the resonant cavity to perform self-photoelectric oscillation. Alternatively, it extracts external signal from an external signal source, amplifies it after signal processing, and drives the modulator connected to the resonant cavity to perform external photoelectric oscillation. Or, it extracts peak noise through a photodetector, converts it into an electrical signal, mixes it with the external signal from an external signal source, amplifies it after signal mixing processing, and drives the modulator connected to the resonant cavity to perform mutual photoelectric oscillation.

[0037] S3 enhances the spike noise through self-photoelectric oscillation, external photoelectric oscillation, or mutual photoelectric oscillation, converting it into spike noise with increased intensity, relaxation oscillation, and / or Q-switched pulses. This broadens the spectrum and completes the resonant cavity mode-locking, enabling rapid single-spike pulse start-up, reducing the mode-locking start-up threshold, and shortening the mode-locking start-up time. It achieves photoelectric oscillation mode-locking with high start-up stability and consistency.

[0038] Photoelectric oscillator mode-locked laser, such as Figure 2 As shown: It includes a pump diode, a resonant cavity, a photodetector, a modulator, an external signal source, and a signal processor. In this embodiment, the modulator is a piezoelectric ceramic. The pump diode signal is connected to the resonant cavity to implement the aforementioned photoelectric oscillation mode-locking method. During the startup process of the mode-locked laser, the pump diode outputs pump light with gradually increasing power to the resonant cavity for oscillation. Spike noise, relaxation oscillation, or Q-switched pulses are formed in the resonant cavity. The signal at one output terminal of the resonant cavity is connected to one input terminal of the photodetector. The photodetector detects the spike noise, relaxation oscillation, Q-switched pulse when mode-locked, and the mode-locked pulse after startup.

[0039] The other output signal of the photodetector is connected to one input of the signal processor. The output signal of the external signal source is connected to the other input of the signal processor. The output signal of the signal processor is connected to one input of the modulator. The signal processor is used to perform mixed processing and amplification of signals from self-photoelectric oscillation, external photoelectric oscillation, or mutual photoelectric oscillation. The modulator is connected to the resonant cavity signal and is used to receive signals and modulate the resonant cavity, putting it into a frequency-locked operating state. The external signal source provides a reference frequency signal, which can be zero or any frequency. The signal processor uses comparison filtering to obtain a low-frequency relaxation oscillation signal near the center of any frequency point.

[0040] Resonant cavities include linear resonant cavities, saturable absorber resonant cavities, nonlinear polarization rotation resonant cavities, offset filtering mode-locked resonant cavities, or nonlinear ring mirror resonant cavities. In this embodiment, a nonlinear amplifying ring mirror resonant cavity is used, such as... Figure 3 As shown, the nonlinear amplifying ring mirror resonant cavity includes a wavelength division multiplexer 100, a phase shifter 110, a beam splitter 120, a fiber Bragg grating 130, a mirror 140, a gain fiber 150, and a piezoelectric ceramic 160. The wavelength division multiplexer 100, the phase shifter 110, the piezoelectric ceramic 160, and the beam splitter 120 are sequentially connected in a ring. The beam splitter 120 is connected to the mirror 140 via the gain fiber 150. The pump diode is connected to the fiber cavity via the wavelength division multiplexer 100. During startup, the pump diode current is increased, gradually increasing the pump power inside the cavity.

[0041] The modulator includes an electro-optic modulator, an acousto-optic modulator, a polarization-controlled modulator, or a piezoelectric ceramic. In this embodiment, the resonant cavity uses a piezoelectric ceramic as the modulator. The piezoelectric ceramic 160 is electrically connected to some components of the resonant cavity, that is, the piezoelectric ceramic 160 is electrically connected between the phase shifter 110 and the beam splitter 120, or the piezoelectric ceramic 160 is electrically connected to the reflector 140. The piezoelectric ceramic can stop working after mode-locking is initiated.

[0042] Pump light is injected into the resonant cavity through a pump diode. The gain fiber in the resonant cavity absorbs the pump light and converts it into signal light. The signal light forms spike noise in the resonant cavity, which contains resonant cavity information in the frequency domain. Figure 4 As shown, the spike pulse generated during mode-locked operation will remain in the mode-locked state using conventional methods at low pump power. The photodetector extracts the spike pulse signal during mode-locked operation, which is then used as the signal input for the signal processing circuit.

[0043] The signal processor includes a signal selector, a PID filter amplifier, a driver amplifier, a mixer, and a phase detector. The photodetector and reference signal source are both connected to the signal selector. The signal selector is connected to the mixer and / or phase detector, which in turn is connected to the PID filter amplifier. The specific connection between the mixer and phase detector is configured according to the actual photoelectric oscillation mode. The PID filter amplifier is connected to the driver amplifier, which in turn is connected to the modulator. The resonant cavity is mode-locked using a mutual photoelectric oscillation mode-locking method. At this time, the spike pulse signal detected by the photodetector is input to one input terminal of the signal processor, and the output signal from the external signal source is input to the other input terminal. The signal processor mixes, extracts, and amplifies the two signals to drive the piezoelectric ceramic, causing a change in the length of the piezoelectric ceramic, which modulates the resonant cavity and is used to initiate mode-locking for oscillation.

[0044] The resonant cavity is mode-locked using mutual photoelectric oscillation mode-locking. The gain fiber in the resonant cavity absorbs the pump light and converts it into signal light. The signal light states include spike noise, relaxation oscillation, and / or Q-switched pulse states. The photodetector converts the optical signal into an electrical signal and outputs it to the signal processor. An external signal source outputs an external signal to the signal processor. The signal processor mixes, processes, and amplifies the signal, driving and controlling the change in the length of the piezoelectric ceramic in the resonant cavity, which in turn acts as feedback to the resonant cavity to initiate mode-locking.

[0045] like Figure 5 As shown, conventional mode-locking methods require a high pump threshold of 300mW to achieve mode-locking. A high pump threshold corresponds to high strength. Figure 5 From the above, the first part is in a peak oscillation state, and the second part is in a mode-locked state. For example... Figure 6As shown, under conventional mode-locking, using a low pump threshold of 135mW pump power will maintain a peak oscillation state and will not achieve mode-locking. The original conventional mode-locking method of mode-locked fiber lasers requires a pump power of 300mW and can achieve mode-locking in about a second.

[0046] Compared to conventional mode-locking methods, the low-threshold start-up mode-locking laser scheme in this embodiment inputs pump light into the resonant cavity. A photodetector detects a spike pulse signal, which is then connected to one input of a signal processor. The output signal from an external signal source is connected to the other input of the signal processor. The signal processor mixes, extracts, and amplifies the two signals to drive the piezoelectric ceramic, causing a change in its length. This modulates the resonant cavity, enabling oscillation-based mode-locking. Figure 7 As shown, with Figure 6 Under the same power threshold, by using mutual photoelectric oscillation, a relatively high level of efficiency can be achieved. Figure 6 A stronger oscillation can transition the resonant cavity from a mode-locked state to a mode-locked state. Compared to conventional mode-locking methods, it can reduce the initiation mode-locking threshold by more than half, reduce the mode-locking setup time to the order of microseconds to milliseconds, and stably repeat low-threshold initiation, avoiding damage to other optical devices caused by high initiation mode-locking thresholds.

[0047] Compared to conventional mode-locking methods that use percussion to create disturbances in the laser's optical components to achieve mode-locking more quickly from a relaxed oscillation state, this embodiment utilizes the arrangement and connection of the piezoelectric ceramic in the mode-locked laser, along with improved signal processor parameters, to achieve rapid and stable mode-locking at a low pump threshold. Furthermore, since all mode-locked lasers have a repetition frequency, this embodiment uses a photodetector to convert the repetition frequency signal into an error signal. This error signal is compared with a reference frequency signal from an external signal source, generating an error signal. The signal processor amplifies this error signal to drive the piezoelectric ceramic. When the laser's repetition frequency increases, the piezoelectric ceramic elongates, reducing the laser's repetition frequency; conversely, when the laser's repetition frequency decreases, the piezoelectric ceramic shortens, increasing the laser's repetition frequency, thus making the laser's repetition frequency more stable.

[0048] Example 2

[0049] The difference between the photoelectric oscillation mode-locking method and Example 1 is that, in S2, only the peak pulse signal is directly extracted by the photodetector and output to the signal processor.

[0050] It amplifies its own signal to drive itself to complete mode-locking, regardless of the effect of external signals, enhances the unlocked state, and promotes the rapid attainment of the mode-locked state.

[0051] The difference between this photoelectric oscillation mode-locked laser and the one in Embodiment 1 is that the resonant cavity achieves mode-locking through self-photoelectric oscillation, disregarding the output of an external signal source to the signal processor. Pump light is input into the resonant cavity, and a photodetector detects a spike pulse signal, which is then connected to an input terminal of the signal processor. The signal processor amplifies the spike pulse signal, driving the piezoelectric ceramic, causing a change in the length of the piezoelectric ceramic, which modulates the resonant cavity, initiating mode-locking through oscillation. By amplifying its own signal to drive mode-locking, and disregarding the influence of external signals, the laser enhances the unlocked state and facilitates rapid attainment of mode-locking.

[0052] Example 3

[0053] The difference between the photoelectric oscillation mode-locking method and Example 1 is that, in S2, only the signal is output to the signal processor through an external signal source, without considering the output signal of the photodetector.

[0054] The difference between this photoelectric oscillation mode-locked laser and the one in Embodiment 1 is that mode-locking is achieved through photoelectric oscillation outside the resonant cavity. It only considers the output of an external signal source to the signal processor. The signal processor amplifies the external signal, drives the piezoelectric ceramic, causing a change in the length of the piezoelectric ceramic, which modulates the resonant cavity, initiating mode-locking through oscillation. This direct external signal-driven mode-locking has a wider range of applications and enhances the unlocked state, promoting faster attainment of mode-locked mode.

[0055] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific structures and characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A photoelectric oscillation mode-locking method, characterized in that, Includes the following steps: S1, pump light is injected into the resonant cavity through the pump diode, and the pump light is absorbed by the gain fiber in the resonant cavity and converted into signal light, so that the signal light forms spike noise in the resonant cavity; S2 extracts peak noise through a photodetector, converts it into an electrical signal, amplifies it through signal processing, and drives the modulator connected to the resonant cavity to perform self-photoelectric oscillation; or it extracts peak noise through a photodetector, converts it into an electrical signal, and mixes it with the external signal output from the external signal source, amplifies it, and drives the modulator connected to the resonant cavity to perform mutual photoelectric oscillation. S3 enhances the spike noise through self-photoelectric oscillation, external photoelectric oscillation, or mutual photoelectric oscillation, converting it into spike noise with increased intensity, relaxation oscillation, and / or Q-switched pulses, thereby broadening the spectrum and completing the mode-locking of the resonant cavity.

2. A photoelectric oscillation mode-locked laser, comprising a pump diode, a resonant cavity, a photodetector, a modulator, an external signal source, and a signal processor; characterized in that: To implement the photoelectric oscillation mode-locking method as described in claim 1, the pump diode signal is connected to the resonant cavity, one output signal of the resonant cavity is connected to one input signal of the photodetector, the photodetector detects spike noise, relaxation oscillation, Q-switching pulse and mode-locking pulse after mode-locking, another output signal of the photodetector is connected to one input signal of the signal processor, one output signal of the external signal source is connected to another input signal of the signal processor, one output signal of the signal processor is connected to one input signal of the modulator, the signal processor is used to perform signal mixing and amplification of self-photoelectric oscillation, external photoelectric oscillation, or mutual photoelectric oscillation, and the modulator is connected to the resonant cavity.

3. The photoelectric oscillation mode-locked laser according to claim 2, characterized in that: The resonant cavity includes a linear resonant cavity, a saturable absorber resonant cavity, a nonlinear polarization rotating resonant cavity, an offset filter mode-locked resonant cavity, or a nonlinear ring mirror resonant cavity.

4. The photoelectric oscillation mode-locked laser according to claim 2, characterized in that: The modulator includes an electro-optic modulator, an acousto-optic modulator, a polarization control modulator, or a piezoelectric ceramic.

5. A photoelectric oscillation mode-locked laser according to claim 2, characterized in that: The signal processor includes a signal selector, a PID filter amplifier, a drive amplifier, a mixer, and a phase detector. The photodetector and the reference signal source are both connected to the signal selector. The signal selector is connected to the mixer and / or the phase detector. The mixer and / or the phase detector is connected to the PID filter amplifier. The PID filter amplifier is connected to the drive amplifier. The drive amplifier is connected to the modulator.

6. The photoelectric oscillation mode-locked laser according to claim 2, characterized in that: The frequency range of the signal processor output signal is 0-1MHz.

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