An ultra-wide spectrum continuous picosecond pulse laser light source and a method for generating laser light

Abstract

The present application relates to a wide-spectrum continuous picosecond pulse laser source and a laser generation method, comprising a controller and a seed laser diode, a plurality of amplification stages and a photonic crystal fiber connected in sequence, the controller being connected with the seed laser diode and the plurality of amplification stages; wherein the controller stores a plurality of editable repetition frequency parameters of the seed laser diode, amplification parameters of the amplification stages corresponding to each repetition frequency, and a switching strategy of different repetition frequencies, for selecting the repetition frequency of the seed laser diode as needed and outputting a repeatable continuous spectrum. The present application can generate picosecond light pulses in an ultra-wide continuous spectrum range of 400 nm to 2100 nm, the output spectrum has the spatial characteristics and high brightness of laser, and at the same time provides the bandwidth characteristics of incandescent lamps or fluorescent lamps. Through the setting of the present application, a repeatable output spectrum can be generated at all repetition frequencies, there is zero loss in output power, and no light pulse is lost during output.

Description

Technical Field

[0001] This invention relates to the field of spectrometer light sources, and more particularly to an ultrawideband continuous picosecond pulse laser source and a method for generating laser light. Background Technology

[0002] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art.

[0003] Supercontinuum white light is the process of converting short, high-power laser pulses into a very broad, continuous spectrum. Spectral broadening is typically achieved by propagating the light pulse through strongly nonlinear materials such as bulk glass, waveguide structures, or photonic crystal fibers. The nonlinear effect depends on the dispersion within the material. Supercontinuum white light sources provide high spatial coherence and high brightness, with a wide wavelength range of spectral output. Current supercontinuum white light sources use megahertz-frequency mode-locked fiber lasers to generate light pulses, which are then amplified and extracted using a pulse selector. This approach provides a repeatable output spectrum at all repetition frequencies when the light pulse passes through a photonic crystal fiber (PCF), but this system design suffers from very high optical losses. Because the fundamental frequency of the mode-locked laser is in the megahertz range, when the pulse selector is operated at a lower frequency, such as in the kilohertz range, the system only extracts the desired pulse, but still generates and amplifies the pulse at the fundamental frequency. These discarded pulses result in significant losses within the system. Furthermore, the combination of mode-locked fiber lasers and optical pulse selectors is costly to manufacture, and if the system only operates at a repetition frequency lower than the fiber laser's fundamental frequency, there is no need to use such a system.

[0004] Supercontinuum white light sources are ideal for lifetime testing of fluorescent and phosphorescent materials because of their wide spectral range. When testing different molecules, the optimal excitation wavelength can be selected based on the molecule's maximum absorption wavelength, whereas single-wavelength lasers often require compromises due to wavelength limitations. Supercontinuum white light is used for measuring luminescence lifetime; high frequencies (e.g., kHz) are needed for short lifetime testing, while low frequencies (e.g., Hz) are needed for long lifetime testing. Therefore, fluorescence lifetime testing applications require a supercontinuum white light source that can operate at both high and low frequencies. Summary of the Invention

[0005] Technical issues

[0006] In view of this, the technical problem to be solved by the present invention is to provide an ultrawideband continuous picosecond pulse laser source and a method for generating laser.

[0007] This invention uses a seed laser diode to generate light pulses. Multiple system amplification stages are designed to amplify these pulses. A controller controls the seed laser diode and the amplification system. A continuous spectrum from 400nm to 2100nm is then generated via photonic crystal fiber. The continuous spectrum generated by this laser source not only produces a consistent output spectrum at all repetition frequencies, but also exhibits zero power loss and no loss of light pulses during output.

[0008] Solution

[0009] To address the above technical problems, this invention provides an ultrawideband continuous picosecond pulsed laser source, comprising a controller and a seed laser diode, several amplification stages, and a photonic crystal fiber connected in sequence. The controller is connected to the seed laser diode and the several amplification stages. The seed laser diode is used to generate seed laser pulses. The controller stores several editable repetition frequency parameters of the seed laser diode, amplification parameters of the amplification stages corresponding to each repetition frequency, and switching strategies for different repetition frequencies. This allows for the selection of the repetition frequency of the seed laser diode as needed and the output of a repeatable continuous spectrum. The seed laser diode is a laser source capable of generating laser pulses of a specific wavelength, such as a 1064nm seed laser pulse.

[0010] In this invention, the amplification parameters of the amplification stage corresponding to each repetition frequency refer to the preset amplification parameters of the amplification stage when a certain repetition frequency is selected, so that the output continuous spectrum has good repeatability.

[0011] In this invention, the amplification stage is used to amplify the seed laser pulse; the photonic crystal fiber is used to generate a continuous spectrum.

[0012] Furthermore, the controller controls or adjusts the repetition frequency by changing the timing of the trigger pulses sent to the seed laser diode.

[0013] Furthermore, the amplification parameters include the drive current parameters of the amplification stage, which are used to adjust the output power of the spectrum by adjusting the drive current.

[0014] Furthermore, the switching strategy includes adjusting the drive current of each amplification stage sequentially in chronological order. Optionally, adjusting the drive current of each amplification stage sequentially in chronological order includes: decreasing or increasing the drive current of the amplification stage sequentially in a preset time order. Optionally, the switching strategy includes: when switching from a low repetition rate to a high repetition rate, the drive current of the initial amplification stage is increased first, and the drive current of subsequent amplification stages is increased sequentially in chronological order; when switching from a high repetition rate to a low repetition rate, the drive current of the final amplification stage is decreased first, and the drive current of the preceding amplification stages is decreased sequentially in chronological order.

[0015] In this invention, the amplification stages are named sequentially along the laser transmission direction as the first amplification stage, the second amplification stage, ..., the Nth amplification stage. The first amplification stage is the initial amplification stage, and subsequent amplification stages are named the second amplification stage, ..., the Nth amplification stage; the Nth amplification stage is the final amplification stage, and preceding amplification stages are named the (N-1)th amplification stage, ..., the first amplification stage. N can be 3, 4, 5, ..., etc. (Sometimes N can be 2, meaning only two amplification stages, and the timing order is adjusted by only two amplification stages). Therefore, the designation of the initial and final stages in this invention is primarily for distinguishing the direction.

[0016] Furthermore, the controller stores parameters of the seed laser diode, including drive current, pulse width, and / or drive voltage, which are used to adjust the corresponding parameters as needed.

[0017] Furthermore, the controller also stores a switching program to prevent large peak values ​​from occurring during amplification.

[0018] Furthermore, the seed laser diode is an optical fiber coupled DFB laser diode.

[0019] Furthermore, the seed laser diode is a distributed feedback type.

[0020] Furthermore, the output frequency of the seed laser diode is adjustable, for example, it can be adjusted from 10kHz to 250MHz.

[0021] Furthermore, the seed laser diode is packaged in a 14-pin butterfly package.

[0022] Furthermore, the seed laser diode is equipped with a TEC for temperature control and stabilization.

[0023] Furthermore, the optical pulse bandwidth generated by the seed laser diode is ~100ps, and the average power is in the microwatt range when operating at 1MHz.

[0024] Furthermore, each amplification stage includes a pump laser diode and a ytterbium-doped fiber; the pump laser diode is used to generate pump light, and the ytterbium-doped fiber is used as a gain medium to amplify the seed laser pulse; each amplification stage removes the pump light from the amplified pulse after amplification.

[0025] Optionally, the pump laser diode can generate 980nm pump light.

[0026] Furthermore, the pump laser diode is a fiber-coupled laser diode.

[0027] And / or, the amplification stage is an all-fiber arrangement.

[0028] And / or, the controller stores the drive current parameters of the pump laser diode, which are used to adjust the drive current through preset or selected control to control the output power.

[0029] Furthermore, the amplification stages include a first amplification stage, a second amplification stage, and a third amplification stage connected together.

[0030] Furthermore, the ytterbium-doped fiber in the first amplification stage is a first ytterbium-doped fiber, and the first amplification stage further includes a wavelength division multiplexer that transmits the pump light and the seed laser pulse to the first ytterbium-doped fiber; optionally, the first ytterbium-doped fiber is a single-clad core-pumped ytterbium-doped fiber.

[0031] Furthermore, the ytterbium-doped fiber in the second amplification stage is a second ytterbium-doped fiber, and the second amplification stage also includes a second tapered coupler that transmits the pump light and the seed laser pulse amplified in the first stage to the second ytterbium-doped fiber; optionally, the cross-sectional shape of the second ytterbium-doped fiber is hexagonal.

[0032] Furthermore, the ytterbium-doped fiber in the third amplification stage is a third ytterbium-doped fiber, and the third amplification stage further includes a third tapered coupler that transmits the pump light and the seed laser pulse amplified in the second stage to the third ytterbium-doped fiber. Optionally, the third ytterbium-doped fiber is a double-clad clad-pumped ytterbium-doped fiber; optionally, the cross-sectional shape of the third ytterbium-doped fiber is hexagonal.

[0033] Furthermore, the first amplification stage also includes a three-port circulator and a fiber Bragg grating; the first port, second port, and third port of the three-port circulator are respectively connected to the seed laser diode, the wavelength division multiplexer, and the second amplification stage; the fiber Bragg grating is used to reflect the seed laser pulse in the laser pulse amplified by the first ytterbium-doped fiber back to the first ytterbium-doped fiber and discard the pump light; the seed laser pulse is amplified twice by the first ytterbium-doped fiber and then input into the second amplification stage from the third port.

[0034] Furthermore, the second amplification stage also includes a pump light remover, a single-stage isolator, and a bandpass filter connected sequentially between the second and third amplification stages.

[0035] Furthermore, the third amplification stage also includes a pump light remover and a mode field adapter connected sequentially between the third amplification stage and the photonic crystal fiber.

[0036] Furthermore, the controller also stores the following control strategy: when the repetition frequency changes, the drive current of the laser diode is adjusted sequentially in time to maintain the expected output: when changing from a high repetition rate to a low repetition rate, the drive current of the pump laser diode of the third amplification stage decreases first, then the drive current of the pump laser diode of the second amplification stage decreases, and finally the drive current of the pump laser diode of the first amplification stage decreases; when changing from a low repetition rate to a high repetition rate, the drive current of the pump laser diode of the first amplification stage increases first, then the drive current of the pump laser diode of the second amplification stage increases, and finally the drive current of the pump laser diode of the third amplification stage increases.

[0037] Furthermore, the first amplification stage also includes a two-stage isolator and a bandpass filter connected sequentially between the first and second amplification stages.

[0038] Furthermore, the cross-sectional shape of the photonic crystal fiber is hexagonal;

[0039] The photonic crystal fiber is an optical fiber capable of generating a continuous spectrum from 400 nm to 2100 nm.

[0040] Furthermore, the photonic crystal fiber is connected to the amplification stage via a cold-joint method.

[0041] Furthermore, the output end of the photonic crystal fiber is provided with a UV Bi convex optical lens to generate a collimated beam by outputting a continuous spectrum.

[0042] Furthermore, it also includes a UV plano-convex optical lens for producing a focused beam from the collimated beam.

[0043] On the other hand, a method for generating ultrawideband continuous picosecond pulsed laser is provided, comprising: selecting the repetition frequency of a seed laser diode on demand, amplifying it through multiple stages, and generating a repeatable continuous spectrum using a photonic crystal fiber; wherein the repetition frequency is controlled or adjusted by changing the timing of the trigger pulse sent to the seed laser diode, and each repetition frequency corresponds to an amplification control strategy. The photonic crystal fiber can generate a continuous spectrum from 400 nm to 2100 nm.

[0044] Furthermore, the desired spectrum can be obtained by selecting and adjusting the driving current, pulse width, driving voltage, and repetition frequency of the seed laser diode.

[0045] Furthermore, the amplification control strategy includes adjusting the output power of the spectrum by selecting and adjusting the drive current of the pump laser diode in the amplification stage.

[0046] Furthermore, when switching repetition frequencies, the following strategy is employed: When switching from a low repetition rate to a high repetition rate, the drive current of the initial amplification stage increases first, and then the drive current of subsequent amplification stages increases sequentially in chronological order; when switching from a high repetition rate to a low repetition rate, the drive current of the final amplification stage decreases first, and then the drive current of the preceding amplification stages decreases sequentially in chronological order. For example, in a three-stage amplification, when switching from a high repetition rate to a low repetition rate, the drive current of the pump laser diode in the third amplification stage decreases first, then the drive current of the pump laser diode in the second amplification stage decreases, and finally the drive current of the pump laser diode in the first amplification stage decreases; when switching from a low repetition rate to a high repetition rate, the reverse procedure is followed.

[0047] Beneficial effects

[0048] (1) This invention uses a DFB fiber-coupled laser diode to generate light pulses. Multiple system amplification stages are designed to amplify the light pulses from the seed laser diode. A controller controls the seed laser diode and the amplification system. A continuous spectrum from 400nm to 2100nm can then be generated via photonic crystal fiber. The output spectrum exhibits the spatial characteristics and high brightness of a laser, while also providing the bandwidth characteristics of an incandescent or fluorescent lamp. Through the structural design of this invention, a repeatable output spectrum can be generated at all repetition frequencies, with zero power loss and no loss of light pulses during output.

[0049] (2) This invention also allows users to directly change the repetition frequency of the laser without stopping the laser output, and without losing any optical pulses during output. This is because the parameters of the seed laser diodes are preset using a controller (e.g., software from Edinburgh Instruments) during broadband generation. Since each seed laser diode is slightly different, the fiber length varies in each system, and the parameters set in each system are also slightly different, the more repetition frequencies that need to be output, the more pre-programmed schemes are required. This solves the energy loss caused by setting the amplifier to the fundamental frequency of the fiber laser and the pulse pickup selecting the repetition frequency in traditional methods. With this invention, the repetition frequency of the operating unit can be flexibly changed simply by setting the selection and control program for different repetition frequencies in the controller; the selection and control program can flexibly adjust the repetition frequency according to parameters such as the drive current, pulse width, and drive voltage of each diode, and the amplification stage settings can better match the fiber laser arrangement.

[0050] (3) By selecting and controlling the connection, the loss between the amplification stage and the PCF can be made negligible because a "cold splicing" technique is used. This splicing not only provides a safe and reliable connection but also maintains the internal structure of the PCF, which is impossible with standard fiber optic splicing techniques.

[0051] (4) The present invention can apply the continuous wavelength picosecond light source to transient fluorescence testing, and can select the precise wavelength at the maximum molecular absorption wavelength for excitation, which is difficult to cover by single wavelength lasers.

[0052] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it according to the contents of the specification, and to make the above and other objects, technical features and advantages of the present invention easier to understand, one or more preferred embodiments are listed below and described in detail with reference to the accompanying drawings. Attached Figure Description

[0053] One or more embodiments are illustrated by way of example with reference numerals in the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Elements with the same reference numerals in the drawings are denoted as similar elements. Unless otherwise stated, the figures in the drawings are not to be limited by scale.

[0054] Figure 1 This is a schematic diagram of component connections for one embodiment of the ultrawideband continuous picosecond pulse laser source of the present invention;

[0055] Figure 2 This is a schematic diagram of the internal structure of the single-clad core-pumped ytterbium-doped optical fiber of the present invention;

[0056] Figure 3 This is a schematic diagram of the internal structure of the second or third cladding pumped ytterbium-doped fiber of the present invention.

[0057] Figure 4 This is a schematic diagram of the internal structure of the photonic crystal fiber (PCF) of the present invention;

[0058] Figure 5 It is the spectrum output using the ultrawideband continuous picosecond pulse laser source of this invention;

[0059] Figure 6 The output curves are obtained by using the ultrawideband continuous picosecond pulsed laser source of the present invention and selecting a 485nm wavelength and a single-wavelength laser (EPL) to conduct experiments on diluted fluorescein solution luminescent samples;

[0060] Figure 7 The output curve is obtained by using the ultrawideband continuous picosecond pulsed laser source of the present invention and selecting a wavelength of 540nm to conduct experiments on the Rhodamine 101 photoluminescent sample. Detailed Implementation

[0061] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0062] Unless otherwise expressly stated, throughout the specification and claims, the term "comprising" or its variations such as "including" or "comprises" shall be understood to include the stated elements or components without excluding other elements or other components.

[0063] In this document, for ease of description, spatial relative terms such as “below,” “under,” “down,” “above,” “above,” “upper,” etc., are used to describe the relationship of one element or feature to another element or feature in the accompanying drawings. It should be understood that spatial relative terms are intended to encompass different orientations of an object in use or operation, in addition to those depicted in the figures. For example, if an object in the figure is flipped, an element described as “below” or “under” another element or feature would be oriented “above” that element or feature. Thus, the exemplary term “below” can encompass both the downward and upward orientations. An object may also have other orientations (rotated 90 degrees or other orientations), and the spatial relative terms used herein should be interpreted accordingly.

[0064] In this document, the terms "first," "second," etc., are used to distinguish two different elements or parts, and are not used to define specific positions or relative relationships. In other words, in some embodiments, the terms "first," "second," etc., can also be used interchangeably.

[0065] This invention provides an embodiment of an ultrawideband continuous picosecond pulsed laser source, such as... Figures 1 to 6 As shown, the system includes a controller and a seed laser diode, several amplification stages, and a photonic crystal fiber connected in sequence. The controller is connected to the seed laser diode and the amplification stages. The seed laser diode is used to generate seed laser pulses. The controller stores several editable repetition frequency parameters for the seed laser diode, amplification parameters for each repetition frequency corresponding to the amplification stage, and switching strategies for different repetition frequencies. This allows for the selection of the repetition frequency of the seed laser diode as needed and the output of a repeatable continuous spectrum. The seed laser diode is a laser source capable of generating laser pulses of a specific wavelength, such as a 1064nm seed laser pulse.

[0066] This invention provides a device for generating picosecond-level optical pulses in an ultrawide continuous spectral range of 400 nm to 2100 nm. In use, this invention allows control of the repetition frequency of the seed laser pulse as needed. For example, the repetition frequency can be controlled or adjusted by changing the timing of the trigger pulse sent to the seed laser diode. Each repetition frequency corresponds to an amplification parameter (amplification strategy), ensuring that the amplification gain is repeatedly output. By setting several amplification stages, the peak power of the picosecond optical pulse from the seed laser diode can be increased from microwatts to watts. Preferably, three amplification stages are designed to reduce the amount of spontaneous emission amplification (ASE).

[0067] Furthermore, the repetition frequency of the seed laser diode within the controller is preset, allowing selection of the appropriate repetition frequency as needed. Users can select the repetition frequency via the controller; for example, the repetition frequency can be any value between 0-250MHz. At different repetition frequencies, the pump laser diodes of each amplification stage need to be set with different drive currents and output voltages to produce a consistent and desired continuous spectrum. The controller also stores the drive current (amplification parameters) of the pump laser diodes in each amplification stage. The drive current and output power of the pump laser diodes in each amplification stage can differ; generally, lower power is required in the first amplification stage, while higher power is required in the third amplification stage.

[0068] Furthermore, the controller controls or adjusts the repetition frequency by changing the timing of the trigger pulses sent to the seed laser diode.

[0069] Furthermore, the amplification parameters include the drive current parameters of the amplification stage, which are used to adjust the output power of the spectrum by adjusting the drive current.

[0070] Depending on the required repetition frequency of the seed laser diode, the controller can control different drive currents for each amplification stage (pump laser diode). For example, for a lower repetition frequency, the required output power will be lower than that required for a higher repetition frequency. The values ​​of all drive currents at all repetition frequencies can be preset in the controller, thus enabling the generation of a repeatable output spectrum at each repetition frequency.

[0071] Furthermore, the switching strategy includes adjusting the drive current of each amplification stage sequentially in time. Optionally, adjusting the drive current of each amplification stage sequentially in time includes: decreasing or increasing the drive current of the amplification stage sequentially in a preset time order. Optionally, the switching strategy includes: when switching from a low repetition rate to a high repetition rate, the drive current of the initial amplification stage is increased first, and the drive current of subsequent amplification stages is increased sequentially in time; when switching from a high repetition rate to a low repetition rate, the drive current of the final amplification stage is decreased first, and the drive current of the preceding amplification stages is decreased sequentially in time.

[0072] In this invention, the amplification stages are named sequentially along the laser transmission direction as the first amplification stage, the second amplification stage, ..., the Nth amplification stage. The first amplification stage is the initial amplification stage, and subsequent amplification stages are named the second amplification stage, ..., the Nth amplification stage; the Nth amplification stage is the final amplification stage, and preceding amplification stages are named the (N-1)th amplification stage, ..., the first amplification stage. N can be 3, 4, 5, ..., etc. (Sometimes N can be 2, meaning only two amplification stages, and the timing order is adjusted by only two amplification stages). Therefore, the designation of the initial and final stages in this invention is primarily for distinguishing the direction.

[0073] In this switching strategy, the timing sequence of the controller switching from one repetition frequency to another is specifically preset. This method does not require shutting down the device before switching frequencies. When switching repetition frequencies, the controller changes the repetition frequency of the seed laser diode (which can be changed by altering the timing of the seed laser diode's trigger pulse). The output power of the pump laser diodes in each amplification stage also changes accordingly, and the changes in the drive current of each amplification stage are sequential. The controller can precisely adjust the drive current of the pump laser diodes in a precise timing sequence to maintain the desired output. For example, in a three-stage amplification, when switching from a high repetition rate to a low repetition rate, the drive current of the third-stage pump laser diode decreases first, then the drive current of the second-stage pump laser diode decreases, and finally the drive current of the first-stage pump laser diode decreases. These changes occur within milliseconds. When switching from a low repetition rate to a high repetition rate, the reverse procedure is followed.

[0074] Furthermore, the controller stores parameters of the seed laser diode, including drive current, pulse width, and / or drive voltage, which are used to adjust the corresponding parameters as needed. Adjustments can generate light pulses with a width of 100 ps.

[0075] Furthermore, the controller also stores a switching program to prevent large peak values ​​from occurring during amplification.

[0076] Furthermore, the seed laser diode is a fiber-coupled DFB laser diode. This laser diode can be of distributed feedback type, with an output frequency adjustable from 10kHz to 250MHz. The laser diode can be packaged in a 14-pin butterfly package. The laser diode can have a TEC for temperature stability control, and the repetition frequency of the diode can be controlled via a controller (e.g., Edinburgh Instruments software). The generated optical pulse bandwidth is ~100ps, and the average power is in the microwatt range when operating at 1MHz.

[0077] Furthermore, each amplification stage includes a pump laser diode and a ytterbium-doped fiber; the pump laser diode is used to generate pump light, and the ytterbium-doped fiber is used as a gain medium to amplify the seed laser pulse; each amplification stage removes the pump light from the amplified pulse after amplification; optionally, the pump laser diode generates 980nm pump light.

[0078] The key component of each amplification stage in this invention is ytterbium-doped fiber. When pumped by a 980nm pump laser diode, this ytterbium-doped fiber acts as the gain medium, amplifying the seed laser pulse as it passes through. The level of amplification depends on the length and structure of the ytterbium-doped fiber, as well as the power of the 980nm light source used for pumping. In the three amplification stages, each stage uses a different length of ytterbium-doped fiber; the details of the three fiber stages are as follows:

[0079] i: 2.1 meters long, 6 μm core diameter, single cladding, core-pumped ytterbium-doped fiber;

[0080] ii: 1.5 meters long, 6 μm core diameter, double cladding, cladding-pumped ytterbium-doped fiber;

[0081] iii: 2.5 meters long, 10 μm core diameter, double cladding, cladding-pumped ytterbium-doped fiber;

[0082] The structural differences between single-clad core-pumped ytterbium-doped fiber and double-clad clad-pumped ytterbium-doped fiber can be seen in... Figure 2 and Figure 3 As seen in the image, double-clad cladding-pumped ytterbium-doped fiber has an internal hexagonal structure, rather than the circular structure commonly seen in standard fibers. The modification to the double-clad fiber and the increase in core size are to ensure greater amplification or to protect already partially amplified optical pulses.

[0083] Furthermore, the pump laser diodes are fiber-coupled laser diodes, preferably continuous-wave fiber-coupled laser diodes. The power of each pump laser diode (pump diode) depends on the repetition frequency of the seed laser pulse and the gain required to amplify the signal. Due to the need for additional gain in later stages and the increase in the core size and length of the ytterbium-doped fiber, the power of the three pump laser diodes increases with the increase of the amplification stage.

[0084] At each repetition frequency of the seed laser diode, the drive current required for the pump diode of each amplification stage needs to be preset during the production stage. This setting ensures good stability of the generated supercontinuous white light. In the amplification stage setup corresponding to each repetition frequency, the output power of the pump diode in each amplification stage varies, ranging from tens of microwatts in the first amplification stage to watts in the last. Traditional fiber lasers and optical pulse selectors do not require this step.

[0085] When using a pump light with a wavelength of 980 nm and a seed light pulse with a wavelength of 1064 nm (~100 ps), after multiple stages of amplification, a light pulse with a wavelength of 1064 nm and a bandwidth of ~150 ps will be generated. The average power amplification at 1 MHz is in the watt range. The increased pulse bandwidth compared to the initial seed laser pulse comes from the increased fiber size.

[0086] The amplified seed light pulse does not need to undergo selection or other operations before generating a supercontinuum through the PCF.

[0087] Furthermore, the amplification stage is an all-fiber arrangement; the amplification stage of this invention arranges all the optical fibers in an all-fiber arrangement. Figure 1 The components are arranged and fused together in a manner that minimizes power loss between components and maximizes gain. In the entire connection, all components are connected by optical fibers, which prevent light from propagating in free space.

[0088] And / or, the controller stores the drive current parameters of the pump laser diode, which are used to adjust the drive current to control the output power through preset or selected control.

[0089] Furthermore, the amplification stages include a first amplification stage, a second amplification stage, and a third amplification stage connected in series. The seed laser pulse of this invention undergoes three stages of amplification, with the power gradually increasing. This arrangement avoids ASE (Advanced Amplification Stage), a potential problem in single-stage amplification processes. ASE causes the optical pulse to emit an unwanted wavelength, affecting the amplification process at the desired wavelength.

[0090] All optical elements in the amplification stage of this invention are suitable for the wavelength and rated processing system power level used.

[0091] Furthermore, the ytterbium-doped fiber in the first amplification stage is a first ytterbium-doped fiber, and the first amplification stage further includes a wavelength division multiplexer that transmits the pump light and the seed laser pulse to the first ytterbium-doped fiber; optionally, the first ytterbium-doped fiber is a single-clad core-pumped ytterbium-doped fiber.

[0092] Furthermore, the ytterbium-doped fiber in the second amplification stage is a second ytterbium-doped fiber, and the second amplification stage also includes a second tapered coupler that transmits the pump light and the seed laser pulse amplified in the first stage to the second ytterbium-doped fiber; optionally, the cross-sectional shape of the second ytterbium-doped fiber is hexagonal.

[0093] Furthermore, the ytterbium-doped fiber in the third amplification stage is a third ytterbium-doped fiber, and the third amplification stage further includes a third tapered coupler that transmits the pump light and the seed laser pulse amplified in the second stage to the third ytterbium-doped fiber. Optionally, the third ytterbium-doped fiber is a double-clad clad-pumped ytterbium-doped fiber; optionally, the cross-sectional shape of the third ytterbium-doped fiber is hexagonal.

[0094] Furthermore, the first amplification stage also includes a three-port circulator and a fiber Bragg grating; the first port, second port, and third port of the three-port circulator are respectively connected to the seed laser diode, the wavelength division multiplexer, and the second amplification stage; the fiber Bragg grating is used to reflect the seed laser pulse in the laser pulse amplified by the first ytterbium-doped fiber back to the first ytterbium-doped fiber and discard the pump light; the seed laser pulse is amplified twice by the first ytterbium-doped fiber and then input into the second amplification stage from the third port.

[0095] Furthermore, the second amplification stage also includes a pump light remover, a single-stage isolator, and a bandpass filter connected sequentially between the second and third amplification stages.

[0096] Furthermore, the third amplification stage also includes a pump light remover and a mode field adapter connected sequentially between the third amplification stage and the photonic crystal fiber.

[0097] Furthermore, the controller also stores the following control strategy: when the repetition frequency changes, the drive current of the pump laser diode is adjusted sequentially in time to maintain the expected output: when changing from a high repetition rate to a low repetition rate, the drive current of the pump laser diode of the third amplification stage decreases first, then the drive current of the pump laser diode of the second amplification stage decreases, and finally the drive current of the pump laser diode of the first amplification stage decreases; when changing from a low repetition rate to a high repetition rate, the reverse procedure is followed.

[0098] Furthermore, the first amplification stage also includes a two-stage isolator and a bandpass filter connected sequentially between the first and second amplification stages.

[0099] Furthermore, the cross-sectional shape of the photonic crystal fiber is hexagonal;

[0100] Photonic crystal fiber is an optical fiber capable of generating a continuous spectrum from 400 nm to 2100 nm.

[0101] Furthermore, the photonic crystal fiber is connected to the amplification stage via a cold-joint method.

[0102] Furthermore, the output end of the photonic crystal fiber is equipped with a UV Bi convex optical lens to generate a collimated beam from the continuous spectrum output.

[0103] Furthermore, it also includes a UV plano-convex optical lens for producing a focused beam from the collimated beam.

[0104] One embodiment of the present invention in use can be as follows ( Figure 1 ):

[0105] 1) First-level magnification:

[0106] a) The first 980nm pump laser beam passes through a wavelength division multiplexer (WDM) to the first ytterbium-doped fiber of the first amplification stage, forming the gain medium. The first 980nm pump light is generated by the pump laser diode of the first amplification stage.

[0107] b) A 1064nm seed laser pulse (~100ps) is transmitted from port 1 to port 2 of the three-port circulator, and the ytterbium-doped fiber amplifies the pulse.

[0108] c) The amplified 1064nm optical pulse is reflected by a fiber Bragg grating (FBG). The FBG only reflects light with a wavelength of 1064nm, and then propagates again through a ytterbium-doped fiber to amplify the pulse again.

[0109] In the first amplification stage, the 980nm pump light will be discarded from the FBG because the FBG component only reflects one wavelength, and proper discarding can prevent damage to the system.

[0110] d) The 1064nm pulse, which is doubly amplified by the first amplification stage, is transmitted back to port 2 of the three-port circulator through the wavelength division multiplexer and output through port 3. It then passes through a two-stage isolator and a bandpass filter in sequence.

[0111] The two-stage isolator prevents any back-propagating pulses from damaging previous components, while the bandpass filter prevents any light other than the 1064nm optical pulse from propagating further through the system.

[0112] 2) Second-stage magnification:

[0113] a) The second 980nm pump light enters the ytterbium-doped fiber of the second amplification stage through a tapered coupler to form a gain medium; wherein, the second 980nm pump light is generated by the pump laser diode of the second amplification stage.

[0114] b) The 1064nm optical pulse, amplified by the first stage, propagates through a tapered coupler and combines with the 980nm pump light in the ytterbium-doped fiber to produce amplification.

[0115] When the 1064nm optical pulse, amplified by the first stage, and the remaining 980nm pump light pass through the pump light remover, the 980nm light is removed, allowing only the 1064nm optical pulse to pass through the single-stage isolator and bandpass filter.

[0116] Similar to the previous components, the single-stage isolator prevents any back-propagating pulses from damaging the previous components, while the bandpass filter prevents any light other than the 1064nm optical pulse from propagating further through the system.

[0117] 3) Third-level magnification:

[0118] a) The third 980nm pump light (generated by the pump laser diode of the third amplification stage) enters the ytterbium-doped fiber of the third amplification stage through a tapered coupler to form the gain medium; wherein, the third 980nm pump light is generated by the pump laser diode of the third amplification stage.

[0119] b) The 1064nm optical pulse, after being amplified in two stages, is combined with the 980nm pump light in the ytterbium-doped fiber through a tapered coupler to generate amplification.

[0120] When the 1064nm optical pulse, amplified by the second stage, and the remaining 980nm pump light pass through the pump light remover, the 980nm light is removed, allowing only the 1064nm optical pulse to pass through the mode field adapter (MFA).

[0121] The MFA's input fiber has a larger core diameter to match the ytterbium-doped, 10μm core double-clad fiber used in the final amplification stage. The MFA's output fiber has a smaller core diameter than the input fiber, thus its mode field diameter is closer to that of the PCF.

[0122] The similarity in mode field diameter between the amplification stage output and the PCF allows for better transmission of 1064nm optical pulses.

[0123] 4) Regarding PCF optical fiber

[0124] A 20-meter-long PCF fiber is used to generate an ultrawide continuous spectrum;

[0125] The length of the PCF is a key factor for the desired wavelength range and wavelengths below the UV (<400nm) region.

[0126] The structure of the PCF (Polydioxanone Fiber) is another key factor in achieving the desired spectral range. Unlike standard optical fibers, PCF has a hexagonal structure in which a solid fiber core is surrounded by a hollow tube, such as... Figure 3 As shown, the arrangement of holes around the fiber core determines wavelength mixing and subsequent spectral broadening to achieve an ultrawide continuous spectrum.

[0127] The PCF (Polymer Fiber) is connected to the output fiber end of the amplifier stage via a fusion splicing method to maximize transmission efficiency. This special splicing differs from standard fusion splicing, where the fiber tips are melted and pushed together, causing the PCF's aperture to collapse and resulting in poor transmission quality. The PCF and amplifier output use a "cold splicing" method. This method brings the fiber ends together and heats them for a very short time, melting only the outer surface of the fibers and fusing them. This process ensures a rigid connection between the two fibers while preserving the internal structure of the PCF.

[0128] 4) The ultrawide continuous spectrum output of photonic crystal fiber (PCF) is collimated by a free-space UVBi convex optical lens with a focal length of 12.7 mm.

[0129] 5) The collimated beam is focused by a free-space UV plano-convex optical lens with a focal length of 25.0 mm, and can be used with the Edinburgh Instruments FLS1000 fluorescence spectrometer. Figure 5 The typical output spectrum of this unit is shown.

[0130] The device was coupled to an Edinburgh Instruments FLS1000 spectrometer for various luminescence measurements in TCSPC and MCS modes. Results are as follows: Figure 6 , Figure 7 As shown.

[0131] After selecting an output wavelength of 485 nm from this device, the TCSPC attenuation of the diluted fluorescein solution sample was measured. An additional single-wavelength laser (EPL) was used as a control. Figure 6 The attenuation curves of this device and a single wavelength are shown, demonstrating that the present invention can achieve attenuation signal measurements that are consistent with or even stronger than those of a single wavelength.

[0132] Further experiments were conducted on a rhodamine 101 photoluminescent sample using this invention. The sample's maximum absorption wavelength was 540 nm, which could not be excited by a single-wavelength laser used as a reference. This device can be used to adjust the output wavelength to 540 nm. Figure 7 The attenuation curves after using this invention are shown. The results demonstrate that this device was successfully connected to the Edinburgh Instruments and is suitable for testing various types of samples by changing different output wavelengths.

[0133] On the other hand, a method for generating ultrawideband continuous picosecond pulsed laser is provided, comprising: selecting the repetition frequency of a seed laser diode on demand, amplifying it through multiple stages, and generating a repeatable continuous spectrum using a photonic crystal fiber; wherein the repetition frequency is controlled or adjusted by changing the timing of the trigger pulse sent to the seed laser diode, and each repetition frequency corresponds to an amplification control strategy. This photonic crystal fiber can generate a continuous spectrum from 400 nm to 2100 nm.

[0134] Furthermore, the desired spectrum can be obtained by selecting and adjusting the driving current, pulse width, driving voltage, and repetition frequency of the seed laser diode.

[0135] Furthermore, the amplification control strategy includes adjusting the output power of the spectrum by selecting and adjusting the drive current of the pump laser diode in the amplification stage.

[0136] Furthermore, when switching repetition frequencies, the following strategy is employed: When switching from a low repetition rate to a high repetition rate, the drive current of the initial amplification stage increases first, and then the drive current of subsequent amplification stages increases sequentially in chronological order; when switching from a high repetition rate to a low repetition rate, the drive current of the final amplification stage decreases first, and then the drive current of the preceding amplification stages decreases sequentially in chronological order. For example, in a three-stage amplification: when switching from a high repetition rate to a low repetition rate, the drive current of the pump laser diode in the third amplification stage decreases first, then the drive current of the pump laser diode in the second amplification stage decreases, and finally the drive current of the pump laser diode in the first amplification stage decreases; when switching from a low repetition rate to a high repetition rate, the reverse procedure is followed.

[0137] The foregoing description of specific exemplary embodiments of the present invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. Any simple modifications, equivalent changes, and alterations made to the foregoing exemplary embodiments should fall within the scope of protection of the present invention.

Claims

1. An ultrawideband continuous picosecond pulse laser source, characterized in that, The system includes a controller and a seed laser diode, several amplification stages, and a photonic crystal fiber connected in sequence. The controller is connected to the seed laser diode and the several amplification stages. The seed laser diode is used to generate seed laser pulses. The controller stores several editable repetition frequency parameters of the seed laser diode, amplification parameters of the amplification stage corresponding to each repetition frequency, and switching strategies for different repetition frequencies, which are used to select the repetition frequency of the seed laser diode as needed and output a repeatable continuous spectrum. Each amplification stage includes a pump laser diode and a ytterbium-doped fiber; the pump laser diode is used to generate pump light, and the ytterbium-doped fiber is used as a gain medium to amplify the seed laser pulse; each amplification stage removes the pump light from the amplified pulse after amplification. In the three-stage amplification, each stage used ytterbium-doped fiber of different lengths. The three-stage fibers are as follows: i: 2.1 meters long, 6 μm core diameter, single cladding, core-pumped ytterbium-doped fiber; ii: 1.5 meters long, 6 μm core diameter, double cladding, cladding-pumped ytterbium-doped fiber; iii: 2.5 meters long, 10 μm core diameter, double cladding, cladding-pumped ytterbium-doped fiber; The double-clad cladding-pumped ytterbium-doped fiber has an internal hexagonal structure.

2. The ultrawideband continuous picosecond pulse laser source according to claim 1, characterized in that, The controller controls or adjusts the repetition frequency by changing the timing of the trigger pulses sent to the seed laser diode. And / or, the amplification parameters include the drive current parameters of the amplification stage; And / or, the switching strategy includes adjusting the drive current of each amplification stage sequentially in chronological order. Optionally, adjusting the drive current of each amplification stage sequentially in chronological order includes: decreasing or increasing the drive current of the amplification stages sequentially in a preset chronological order. Optionally, the switching strategy includes: when switching from a low repetition rate to a high repetition rate, the drive current of the initial amplification stage is increased first, and the drive current of subsequent amplification stages is increased sequentially in chronological order; when switching from a high repetition rate to a low repetition rate, the drive current of the final amplification stage is decreased first, and the drive current of the preceding amplification stages is decreased sequentially in chronological order. And / or, the controller stores parameters of the seed laser diode, including drive current, pulse width and / or drive voltage, for adjusting the corresponding parameters as needed; And / or, the controller also stores a switching program to prevent large peaks from occurring during amplification.

3. The ultrawideband continuous picosecond pulse laser source according to claim 1 or 2, characterized in that, The seed laser diode is a fiber-coupled DFB laser diode; And / or, the seed laser diode is a laser diode with a TEC, the TEC being used to control temperature stability.

4. The ultrawideband continuous picosecond pulse laser source according to claim 3, characterized in that, The controller stores the driving current parameters of the pump laser diode, which are used to adjust the driving current through preset or selected control to control the output power. And / or, the amplification stage is an all-fiber arrangement.

5. The ultrawideband continuous picosecond pulse laser source according to claim 4, characterized in that, Several amplification stages include a first amplification stage, a second amplification stage, and a third amplification stage connected together; The ytterbium-doped fiber in the first amplification stage is the first ytterbium-doped fiber, and the first amplification stage also includes a wavelength division multiplexer that transmits the pump light and the seed laser pulse to the first ytterbium-doped fiber. The ytterbium-doped fiber in the second amplification stage is a second ytterbium-doped fiber, and the second amplification stage also includes a second tapered coupler that transmits the pump light and the seed laser pulse amplified in the first stage to the second ytterbium-doped fiber. The ytterbium-doped fiber in the third amplification stage is a third ytterbium-doped fiber, and the third amplification stage also includes a third tapered coupler that transmits the pump light and the seed laser pulse amplified in the second stage to the third ytterbium-doped fiber.

6. The ultrawideband continuous picosecond pulse laser source according to claim 5, characterized in that, The first amplification stage further includes a three-port circulator and a fiber Bragg grating; the first port, second port, and third port of the three-port circulator are respectively connected to the seed laser diode, the wavelength division multiplexer, and the second amplification stage; the fiber Bragg grating is used to reflect the seed laser pulse in the laser pulse amplified by the first ytterbium-doped fiber back to the first ytterbium-doped fiber and discard the pump light; the seed laser pulse is amplified twice by the first ytterbium-doped fiber and then input into the second amplification stage from the third port; And / or, the first amplification stage further includes a two-stage isolator and a bandpass filter connected in sequence between the first and second amplification stages; the second amplification stage further includes a pump light remover, a single-stage isolator and a bandpass filter connected in sequence between the second and third amplification stages; the third amplification stage further includes a pump light remover and a mode field adapter connected in sequence between the third amplification stage and the photonic crystal fiber.

7. The ultrawideband continuous picosecond pulse laser source according to claim 5, characterized in that, The controller also stores the following control strategy: when the repetition frequency changes, the drive current of the pump laser diode is adjusted sequentially in time to maintain the expected output: when changing from a high repetition rate to a low repetition rate, the drive current of the pump laser diode in the third amplification stage decreases first, then the drive current of the pump laser diode in the second amplification stage decreases, and finally the drive current of the pump laser diode in the first amplification stage decreases; when changing from a low repetition rate to a high repetition rate, the drive current of the pump laser diode in the first amplification stage increases first, then the drive current of the pump laser diode in the second amplification stage increases, and finally the drive current of the pump laser diode in the third amplification stage increases.

8. The ultrawideband continuous picosecond pulse laser source according to claim 3, characterized in that, The cross-sectional shape of the photonic crystal fiber is hexagonal; And / or, the photonic crystal fiber is connected to the amplification stage by a cold-joint method; And / or, the output end of the photonic crystal fiber is provided with a UV Bi convex optical lens and / or a UV plano-convex optical lens, the UV Bi convex optical lens is used to generate a collimated beam from the continuous spectrum output, and the UV plano-convex optical lens is used to generate a focused beam from the collimated beam.

9. A method for generating ultrawideband continuous picosecond pulse laser, based on the ultrawideband continuous picosecond pulse laser source as described in any one of claims 1-8, characterized in that, include: By selecting the repetition frequency of the seed laser diode on demand, and through multi-stage amplification, a repeatable continuous spectrum is generated using photonic crystal fiber. The repetition frequency is controlled or adjusted by changing the timing of the trigger pulse sent to the seed laser diode, and each repetition frequency corresponds to an amplification control strategy.

10. The method of production according to claim 9, characterized in that, The desired spectrum can be obtained by selecting and adjusting the driving current, pulse width, driving voltage, and repetition frequency of the seed laser diode; And / or, the amplification control strategy includes: adjusting the output power of the spectrum by selecting and adjusting the drive current of the pump laser diode in the amplification stage; And / or, when it is necessary to switch the repetition frequency, the following strategy is adopted: when switching from a low repetition rate to a high repetition rate, the drive current of the initial amplifier stage is increased first, and the drive current of the subsequent amplifier stages is increased in chronological order; when switching from a high repetition rate to a low repetition rate, the drive current of the final amplifier stage is decreased first, and the drive current of the preceding amplifier stages is decreased in chronological order.

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