CN114665364A - Ultra-wide spectrum continuous picosecond pulse laser source and laser generation method - Google Patents
Ultra-wide spectrum continuous picosecond pulse laser source and laser generation method Download PDFInfo
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- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
- H01S3/06—Construction or shape of active medium
- H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
- H01S3/067—Fibre lasers
- H01S3/06708—Constructional details of the fibre, e.g. compositions, cross-section, shape or tapering
- H01S3/06729—Peculiar transverse fibre profile
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- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/09—Processes or apparatus for excitation, e.g. pumping
- H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
- H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
- H01S3/0941—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a laser diode
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- H—ELECTRICITY
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- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
- H01S3/10007—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating in optical amplifiers
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- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
- H01S3/10007—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating in optical amplifiers
- H01S3/10023—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating in optical amplifiers by functional association of additional optical elements, e.g. filters, gratings, reflectors
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- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
- H01S3/10084—Frequency control by seeding
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- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
- H01S3/13—Stabilisation of laser output parameters, e.g. frequency or amplitude
- H01S3/136—Stabilisation of laser output parameters, e.g. frequency or amplitude by controlling devices placed within the cavity
- H01S3/137—Stabilisation of laser output parameters, e.g. frequency or amplitude by controlling devices placed within the cavity for stabilising of frequency
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Abstract
The invention relates to a wide-spectrum continuous picosecond pulse laser light source and a laser generation method, comprising a controller, a seed laser diode, a plurality of amplification stages and a photonic crystal fiber, wherein the seed laser diode, the plurality of amplification stages and the photonic crystal fiber are sequentially connected; the controller is internally stored with a plurality of editable repetition frequency parameters of the seed laser diode, amplification parameters of an amplification stage corresponding to each repetition frequency and switching strategies of different repetition frequencies, and is used for selecting the repetition frequency of the seed laser diode according to requirements and outputting repeatable continuous spectrums. The invention can generate picosecond-level light pulse in an ultra-wide continuous spectrum range of 400nm to 2100nm, the output spectrum has the spatial characteristic and high brightness of laser, and the bandwidth characteristic of an incandescent lamp or a fluorescent lamp is provided. By the arrangement of the invention, a repeatable output spectrum can be produced at all repetition frequencies, with zero loss in output power and no loss of any optical pulse at the output.
Description
Technical Field
The invention relates to the field of spectrometer light sources, in particular to an ultra-wide spectrum continuous picosecond pulse laser light source and a laser generation method.
Background
The information disclosed in this background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.
Supercontinuum white light is a process of converting short, high power laser pulses into a very broad continuous spectrum. Spectral broadening is typically achieved by propagating an optical pulse through a strongly nonlinear material such as bulk glass, a waveguiding structure, or a photonic crystal fiber. The nonlinear effect depends on the dispersion in the material. The supercontinuum white light source provides spectral output with high spatial coherence and high brightness, and a wide wavelength range. The existing supercontinuum white light source adopts a mode-locked fiber laser with megahertz frequency to generate light pulse, and then uses a light pulse selector to amplify and extract. In this way, a repeatable output spectrum can be provided at all repetition frequencies when light pulses are passed through a Photonic Crystal Fiber (PCF), but the optical losses of such a system design are very large. Since the fundamental frequency of the mode-locked laser is in the megahertz range, when the pulse selector is operated at a lower frequency, for example in the kilohertz range, the system extracts only the desired pulses, but still generates and amplifies the pulses at the fundamental frequency. These discarded pulses cause significant losses in the system. In addition, the use of a mode locked fiber laser in combination with an optical pulse selector can be expensive to manufacture, and a system of this configuration is not necessary if the system is to be operated only at a repetition rate below the fundamental frequency of the fiber laser.
The supercontinuum light source is an ideal light source for testing the service life of fluorescent and phosphorescent materials, because the spectral range is wide, when different molecules are tested, the optimal excitation wavelength can be selected according to the maximum absorption wavelength of the molecules, and a single-wavelength laser is often compromised due to the limitation of the wavelength. Supercontinuum white light is used for testing luminescence lifetime, high frequencies (e.g., kHz) are required for testing short lifetime, and low frequencies (e.g., Hz) are required for testing long lifetime. Based on this, the application of fluorescence lifetime testing requires a super-continuous white light source that can operate at high and low frequencies.
Disclosure of Invention
Technical problem
In view of this, the technical problem to be solved by the present invention is to provide an ultra-wide spectrum continuous picosecond pulse laser source and a laser generation method.
The invention adopts a seed laser diode to generate light pulse, designs a plurality of system amplification stages to amplify the light pulse of the seed laser diode, controls the seed laser diode and the amplification system by a controller, and can generate continuous spectrum of 400nm to 2100nm by the photonic crystal fiber. The continuous spectrum generated by the laser light source of the invention can generate a consistent output spectrum under all repetition frequencies, has zero loss on output power and does not lose any light pulse when being output.
Solution scheme
In order to solve the above technical problems, an embodiment of the present invention provides an ultra-wide spectrum continuous picosecond pulse laser light source, including a controller, and a seed laser diode, a plurality of amplification stages, and a photonic crystal fiber connected in sequence, where the controller is connected to the seed laser diode and the plurality of amplification stages, and the seed laser diode is used to generate seed laser pulses; the controller stores a plurality of editable repetition frequency parameters of the seed laser diode, amplification parameters of an amplification stage corresponding to each repetition frequency and switching strategies of different repetition frequencies, and is used for selecting the repetition frequency of the seed laser diode according to needs and outputting repeatable continuous spectrums. The seed laser diode is a laser source capable of generating laser pulses of a certain wavelength, for example, 1064nm seed laser pulses.
In the invention, the amplification parameter of the amplification stage corresponding to each repetition frequency means that when a certain repetition frequency is selected, the amplification parameter of the amplification stage is also preset and corresponding, so that the output continuous spectrum has good repeatability.
In the invention, the amplification stage is used for amplifying the seed laser pulse; the photonic crystal fiber is used for generating a continuous spectrum.
Further, the controller controls or adjusts the repetition rate by varying the time of the trigger pulse sent to the seed laser diode.
Further, the amplification parameters comprise drive current parameters of the amplification stage for adjusting the output power of the spectrum by adjusting the drive current.
Further, the switching strategy includes sequentially adjusting the magnitude of the driving current of each stage of the amplifying stage in time sequence, and optionally, sequentially adjusting the magnitude of the driving current of each stage of the amplifying stage in time sequence includes: sequentially reducing or increasing the drive current of the amplification stage according to a preset time sequence; optionally, the handover policy includes: when switching from a low repetition rate to a high repetition rate, the drive current of the amplification stage at the initial end is increased first, and the drive currents of the subsequent amplification stages are sequentially increased in time order; when switching from a high repetition rate to a low repetition rate, the drive current of the amplifier stage at the end is first reduced, and the drive currents of the amplifier stages at the end are sequentially reduced in time order.
The multiple amplification stages in the invention are named according to the laser transmission direction and can be a first amplification stage and a second amplification stage in sequence, wherein the first amplification stage is the amplification stage at the initial end, and the subsequent amplification stages are the second amplification stages in sequence; the nth amplification stage is the end amplification stage, and the successive amplification stages are sequentially the (N-1) th amplification stage. Therefore, the initial end and the final end of the present invention are mainly indicated for direction distinction.
Further, parameters of the seed laser diode are stored in the controller, and the parameters include a driving current, a pulse width and/or a driving voltage, and are used for adjusting corresponding parameters according to requirements.
Further, the controller also stores a switching program for preventing a large peak from occurring during amplification.
Further, the seed laser diode is a fiber coupled DFB laser diode.
Further, the seed laser diode is of a distributed feedback type.
Further, the output frequency of the seed laser diode is adjustable, for example, adjustable between 10kHz and 250 MHz.
Further, the seed laser diode is encapsulated by a 14-pin butterfly.
Further, the seed laser diode is provided with a TEC for controlling temperature stability.
Furthermore, the bandwidth of the optical pulse generated by the seed laser diode is 100ps, and the average power is in the microwatt range when the seed laser diode works at 1 MHz.
Further, each amplification stage comprises a pump laser diode and an ytterbium-doped fiber; the pump laser diode is used for generating pump light, and the ytterbium-doped optical fiber is used as a gain medium for amplifying the seed laser pulse; each amplification stage removes the pump light in the amplified pulses after amplifying the pulses;
alternatively, the pump laser diode may generate 980nm pump light.
Further, the pump laser diode is a fiber coupled laser diode.
And/or the amplification stage is an all-fiber arrangement.
And/or the controller stores the drive current parameter of the pump laser diode, and is used for adjusting the drive current through presetting or selecting control so as to control the output power.
Further, the plurality of amplification stages includes a first amplification stage, a second amplification stage, and a third amplification stage connected.
Furthermore, the ytterbium-doped fiber in the first amplification stage is a first ytterbium-doped fiber, and the first amplification stage further comprises a wavelength division multiplexer for inputting 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.
Furthermore, the ytterbium-doped fiber in the second amplification stage is a second ytterbium-doped fiber, and the second amplification stage further comprises a second tapered coupler which is used for inputting the pump light and the seed laser pulse amplified by the first amplification stage to the second ytterbium-doped fiber; optionally, the second ytterbium-doped fiber has a hexagonal cross-sectional shape.
Further, the ytterbium-doped fiber in the third amplification stage is a third ytterbium-doped fiber, and the third amplification stage further comprises a third tapered coupler for transmitting the pump light and the second-stage amplified seed laser pulse to the third ytterbium-doped fiber. Optionally, the third ytterbium-doped fiber is a double-clad cladding-pumped ytterbium-doped fiber; optionally, a cross-sectional shape within the third ytterbium-doped fiber is hexagonal.
Further, the first amplification stage further comprises a three-port circulator and a fiber bragg grating; the first port, the second port and the third port of the three-port circulator are respectively connected with the seed laser diode, the wavelength division multiplexer and the second amplification stage; the fiber Bragg grating is used for reflecting the seed laser pulse in the laser pulse amplified by the first ytterbium-doped fiber back to the first ytterbium-doped fiber and discarding the pump light; and the seed laser light pulse is amplified twice by the first ytterbium-doped optical fiber and then input into the second amplification stage from the third port.
Furthermore, the second amplification stage further comprises a pump light remover, a single-stage isolator and a band-pass filter which are sequentially connected between the second amplification stage and the third amplification stage.
Further, the third amplification stage further comprises a pump light remover and a mode field adapter which are sequentially connected between the third amplification stage and the photonic crystal fiber.
Further, the following control strategies are stored in the controller: when changing the repetition frequency, the drive current of the laser diode is adjusted in time sequence to maintain the desired output: when the repetition rate is changed from high repetition rate to low repetition rate, the driving current of the pumping laser diode of the third amplification stage is reduced firstly, then the driving current of the pumping laser diode of the second amplification stage is reduced, and finally the driving current of the pumping laser diode of the first amplification stage is reduced; 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.
Furthermore, the first amplification stage also comprises a double-stage isolator and a band-pass filter which are sequentially connected between the first amplification stage and the second amplification stage.
Further, the cross section of the photonic crystal fiber is hexagonal;
the photonic crystal fiber is an optical fiber capable of generating a continuous spectrum of 400nm to 2100 nm.
Furthermore, the photonic crystal fiber is connected with the amplification stage in a cold connection mode.
Furthermore, the output end of the photonic crystal fiber is provided with a UV Bi convex optical lens for outputting the continuous spectrum to generate a collimated beam;
further, the device also comprises a UV plano-convex optical lens for generating a focused light beam from the collimated light beam.
In another aspect, a method for generating an ultra-wide spectrum continuous picosecond pulse laser is provided, comprising: the repetition frequency of a seed laser diode is selected as required, and a repeatable continuous spectrum is generated by utilizing the photonic crystal fiber through multi-stage amplification; wherein the repetition rate is controlled or adjusted by varying the time of the trigger pulse sent to the seed laser diode, and each repetition rate corresponds to an amplification control strategy. The photonic crystal fiber can produce a continuous spectrum of 400nm to 2100 nm.
Further, the desired spectrum is obtained by selectively adjusting the drive current, pulse width, drive voltage, and repetition rate of the seed laser diode.
Further, the amplification control strategy comprises: the output power of the spectrum is adjusted by selectively adjusting the drive current of the pump laser diode in the amplification stage.
Further, the following strategy is adopted when the repetition frequency needs to be switched: when switching from a low repetition rate to a high repetition rate, the drive current of the amplification stage at the initial end is increased first, and the drive currents of the subsequent amplification stages are sequentially increased in time order; when switching from a high repetition rate to a low repetition rate, the drive current of the amplifier stage at the end is first reduced, and the drive currents of the amplifier stages at the end are sequentially reduced in time order. For example, in the three-stage amplification, when the repetition rate is changed from a high repetition rate to a low repetition rate, the driving current of the pump laser diode of the third amplification stage is first reduced, then the driving current of the pump laser diode of the second amplification stage is reduced, and finally the driving current of the pump laser diode of the first amplification stage is reduced; when changing from a low repetition rate to a high repetition rate, the opposite procedure is followed.
Advantageous effects
(1) The invention adopts DFB fiber coupled laser diode to generate light pulse, designs a plurality of system amplification stages to amplify the light pulse of the seed laser diode, controls the seed laser diode and the amplification system by the controller, and can generate continuous spectrum from 400nm to 2100nm by the photonic crystal fiber. The output spectrum has the spatial characteristics and high brightness of laser light while providing the bandwidth characteristics of an incandescent or fluorescent lamp. By the structural arrangement of the present invention, a repeatable output spectrum can be produced at all repetition frequencies, with zero loss in output power and without loss of any optical pulses at output.
(2) The present invention also allows the user to directly change the repetition rate of the laser without stopping the laser output and without losing any light pulses when outputting. This is because the parameters of the seed laser diode are preset using a controller (e.g., Edinburgh instruments software) during broad spectrum generation. Since each seed laser diode is slightly different, the length of the optical fiber is different on each system, the set parameters of each system are slightly different, and the more the number of repetition frequencies to be output is, the more the programming scheme is performed in advance. The energy loss caused by setting the amplifier as the fundamental frequency of the fiber laser and selecting the repetition frequency of the pulse pickup in the traditional method is solved. The invention can flexibly change the repetition frequency of the operation unit as long as the selection and control program aiming at different repetition frequencies is set in the controller; the selection and control program can flexibly adjust the repetition frequency according to the parameters of the driving current, the pulse width, the driving voltage and the like of each diode, and meanwhile, the arrangement of the fiber laser can be better matched due to the arrangement of the amplification stage.
(3) The invention can make the loss between the amplifier and PCF negligible by selection and control, because the connection is made by using 'cold connection' technique. This splice not only provides a secure and reliable connection, but also maintains the internal structure of the PCF, which is not possible with standard fiber splicing techniques.
(4) The continuous wavelength picosecond light source can be applied to transient fluorescence test, and the precise wavelength at the position with the maximum molecular absorption wavelength can be selected for excitation, which is difficult to cover by a single-wavelength laser.
The foregoing description is only an overview of the technical solutions of the present invention, and in order to make the technical means of the present invention more clearly understood and to make the technical means implementable in accordance with the contents of the description, and to make the above and other objects, technical features, and advantages of the present invention more comprehensible, one or more preferred embodiments are described below in detail with reference to the accompanying drawings.
Drawings
One or more embodiments are illustrated by way of example in the accompanying drawings, which correspond to the figures in which like reference numerals refer to similar elements and which are not to scale unless otherwise specified.
FIG. 1 is a schematic diagram of the connection of elements of one embodiment of an ultra-wide spectrum continuous picosecond pulsed laser source of the present invention;
FIG. 2 is a schematic diagram of the internal structure of a single clad core pumped ytterbium-doped fiber of the present invention;
FIG. 3 is a schematic diagram of the internal structure of a second or third cladding pumped ytterbium-doped fiber in accordance with the present invention;
FIG. 4 is a schematic view of the internal structure of a Photonic Crystal Fiber (PCF) of the present invention;
FIG. 5 is a spectrum of an output of a continuous picosecond pulsed laser source using an ultra-wide spectrum of the present invention;
FIG. 6 is an output curve of an experiment conducted on a dilute fluorescein solution luminescent sample using an ultra-broad spectrum continuous picosecond pulsed laser light source of the present invention and selecting a 485nm wavelength and a single wavelength laser (EPL);
FIG. 7 is an output curve of an experiment conducted on a rhodamine 101 photoluminescent sample using an ultra-broad spectrum continuous picosecond pulsed laser light source of the present invention and with a wavelength of 540nm selected.
Detailed Description
The following detailed description of the present invention is provided in conjunction with the accompanying drawings, but it should be understood that the scope of the present invention is not limited to the specific embodiments.
Throughout the specification and claims, unless explicitly stated otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element or component but not the exclusion of any other element or component.
Spatially relative terms, such as "below," "lower," "upper," "above," "upper," and the like, may be used herein for ease of description to describe one element or feature's relationship to another element or feature in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the object in use or operation in addition to the orientation depicted in the figures. For example, if the items in the figures are turned over, elements described as "below" or "beneath" other elements or features would then be oriented "above" the elements or features. Thus, the exemplary term "below" can encompass both an orientation of below and above. The article may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative terms used herein should be interpreted accordingly.
In this document, the terms "first", "second", etc. are used to distinguish two different elements or portions, and are not used to define a particular position or relative relationship. In other words, the terms "first," "second," and the like may also be interchanged with one another in some embodiments.
The invention provides an embodiment of an ultra-wide spectrum continuous picosecond pulse laser light source, which comprises a controller, and a seed laser diode, a plurality of amplification stages and a photonic crystal fiber which are sequentially connected, wherein the controller is connected with the seed laser diode and the amplification stages, and the seed laser diode is used for generating seed laser pulses; the controller is internally stored with a plurality of editable repetition frequency parameters of the seed laser diode, amplification parameters of the amplification stage corresponding to each repetition frequency and switching strategies of different repetition frequencies, and is used for selecting the repetition frequency of the seed laser diode according to requirements and outputting repeatable continuous spectrums. A seed laser diode is a laser source capable of generating laser pulses of a certain wavelength, for example, 1064 nm.
The present invention provides an apparatus for generating picosecond light pulses in an ultra-wide continuous spectral range of 400nm to 2100 nm. When the invention is used, the invention can control the repetition frequency of the seed laser pulse according to the requirement, for example, the repetition frequency is controlled or adjusted by changing the time of the trigger pulse sent to the seed laser diode, each repetition frequency corresponds to an amplification parameter (amplification strategy), so that the amplification gain of each time can be repeatedly output; the peak power of picosecond light pulses exiting the seed laser diode is increased from microwatts to watts by the arrangement of several amplification stages, three of which are preferably designed to reduce the amount of spontaneous emission Amplification (ASE) generated.
Further, the repetition frequency of the seed laser diode in the controller is preset, and the seed laser diode is used for selecting the corresponding repetition frequency according to requirements. The repetition rate, which may be any value from between 0-250MHz, for example, may be selected by a user via the controller, and at different repetition rates the pump laser diodes of each amplifier stage need to be set to different drive currents and output voltages to produce a consistent and desired output continuous spectrum. The controller also stores the drive current (amplification parameters) of the pump laser diodes in each amplification stage, which may be different for each stage, typically with a lower power requirement in the first amplification stage and a higher power requirement in the third amplification stage.
Further, the controller controls or adjusts the repetition rate by varying the time of the trigger pulse sent to the seed laser diode.
Further, the amplification parameters comprise drive current parameters of the amplification stage for adjusting the output power of the optical spectrum by adjusting the drive current.
Depending on the required repetition frequency of the seed laser diode, the controller may control a different drive current for each amplification stage (pump laser diode), e.g. for lower repetition frequencies the required output power will be lower than for higher repetition frequencies. The values of all drive currents at all repetition frequencies can be preset in the controller so that a repeatable output spectrum can be produced at each repetition frequency.
Further, the switching strategy includes sequentially adjusting the driving current of each amplification stage in time sequence, and optionally, sequentially adjusting the driving current of each amplification stage in time sequence includes: sequentially reducing or increasing the drive current of the amplification stage according to a preset time sequence; optionally, the handover policy includes: when switching from a low repetition rate to a high repetition rate, the drive current of the amplification stage at the initial end is increased first, and the drive currents of the subsequent amplification stages are sequentially increased in time order; when switching from a high repetition rate to a low repetition rate, the drive current of the amplifier stage at the end is first reduced, and the drive currents of the amplifier stages at the end are sequentially reduced in time order.
The multiple amplification stages in the invention can be a first amplification stage and a second amplification stage in sequence according to the naming along the laser transmission direction, wherein the first amplification stage is the amplification stage at the initial end, and the subsequent amplification stages are the second amplification stage in sequence; the nth amplification stage is the end amplification stage, and the successive amplification stages are sequentially the (N-1) th amplification stage. Therefore, the initial end and the final end of the present invention are mainly indicated for direction distinction.
In the switching strategy, the time sequence in which the controller switches from one repetition frequency to another is specifically preset. This approach does not require the device to be shut down before switching frequencies. When the repetition rate is switched, the controller changes the repetition rate of the seed laser diode (which can be changed by changing the time of the trigger pulse of the seed laser diode), the output power of the pump laser diode of each stage of amplification stage is also changed accordingly, and the change of the drive current of each stage of amplification stage is time-sequenced. The controller can adjust the drive current of the pump laser diode diodes in a precise time sequence to maintain the desired output. For example, in the three-stage amplification, when the repetition rate is changed from a high repetition rate to a low repetition rate, the drive current of the third-stage pump laser diode is first reduced, then the drive current of the second-stage pump laser diode is reduced, and finally the drive current of the first-stage pump laser diode is reduced. These changes occur within milliseconds. When changing from a low repetition rate to a high repetition rate, the opposite procedure is followed.
Further, the controller stores parameters of the seed laser diode, wherein the parameters comprise driving current, pulse width and/or driving voltage, and are used for adjusting corresponding parameters according to requirements. Optical pulses with a width of 100ps can be generated by the adjustment.
Further, the controller also stores a switching program for preventing a large peak from occurring during amplification.
Further, the seed laser diode is a fiber coupled DFB laser diode. The laser diode can be in a distributed feedback type, and the output frequency is adjustable between 10kHz and 250 MHz. The laser diode may be butterfly packaged with 14 pins. The laser diode may be provided with a TEC for temperature stabilization control, and the repetition rate of the diode may be controlled by a controller (e.g., the software from the eburg instruments). The bandwidth of the generated optical pulse is 100ps, and the average power is in the range of microwatts when the optical pulse works at 1 MHz.
Further, each amplification stage comprises a pump laser diode and an ytterbium-doped fiber; the pump laser diode is used for generating pump light, and the ytterbium-doped optical fiber is used as a gain medium for amplifying the seed laser pulse; each amplification stage removes the pump light in the amplified pulses after amplifying the pulses; optionally, the pump laser diode generates 980nm pump light.
The key component of each amplification stage in the present invention is an ytterbium-doped fiber. When a 980nm pump laser diode is used for pumping, the ytterbium-doped optical fiber is used as a gain medium, so that the seed laser pulse is amplified in the passing process. The level of amplification depends on the length and structure of the ytterbium-doped fiber, and the power of the 980nm source used for pumping. In three levels of amplification, each using a different length of ytterbium-doped fiber, the details of the three levels can be as follows:
i.e. 2.1 meters long, 6 μm core diameter, single clad, core pumped ytterbium doped fiber;
ii, a double-clad, cladding-pumped ytterbium-doped fiber with the length of 1.5 meters and the core diameter of 6 mu m;
iii, 2.5 meters long, 10 μm core diameter, double-clad, clad pumping ytterbium doped fiber;
the structural differences between single-clad core-pumped ytterbium-doped fibers and double-clad cladding-pumped ytterbium-doped fibers can be seen in fig. 2 and 3. The double-clad cladding pumped ytterbium-doped fiber has an internal hexagonal structure rather than the circular structure commonly seen in standard fibers. The changes to the double-clad fiber and the increase in core size are to ensure greater amplification or to protect the partially amplified optical pulses.
Further, the pump laser diode is a fiber coupled laser diode, preferably a continuous wave fiber coupled laser diode. The power of each pump laser diode (pump diode) depends on the repetition frequency of the seed laser pulses and the gain required to amplify the signal. The power of the three pump laser diodes increases with increasing amplifier stages due to the additional gain required later and the increase in core size and length of the ytterbium-doped fiber.
At each repetition frequency of the seed laser diode, the driving current required by the pump diode of each amplification stage needs to be preset in the production stage, and the setting can ensure that the generated super-continuous white light has good stability. In the amplifier stage setting corresponding to each repetition frequency, the output power of the pump diode of each amplifier stage is different from dozens of microwatts of the first amplifier stage to the last amplifier stage to the watt stage. Which is not required by conventional fiber lasers and optical pulse selectors.
When pump light with the wavelength of 980nm and seed light pulse with the wavelength of 1064nm (-100 ps) are adopted, the light pulse with the wavelength of 1064nm is generated through amplification of multiple levels, the bandwidth is 150ps, and the average power is amplified to be in the watt level when the laser works at 1 MHz. The increase in pulse bandwidth compared to the initial seed laser pulse results from the increased fiber size.
The amplified seed light pulse does not need to be subjected to operations such as selection before the supercontinuum is generated by the PCF.
Further, the amplification stage is an all-fiber arrangement; the amplifier stage of the present invention is constructed by arranging and splicing all the optical fibers in the manner shown in fig. 1, and all the components are connected by the optical fibers in the entire connection, so that the light does not propagate through free space, thereby reducing the power loss between the components and maximizing the gain.
And/or the controller stores the drive current parameter of the pump laser diode, and is used for adjusting the drive current through presetting or selecting control so as to control the output power.
Further, the plurality of amplification stages includes a first amplification stage, a second amplification stage, and a third amplification stage connected. The seed laser light pulse of the invention is amplified by three stages, and the power is gradually increased. This arrangement avoids ASE, which is a potential problem with single stage amplification processes. ASE will cause unwanted wavelengths to be generated by the optical pulses, affecting the amplification process at the desired wavelengths.
All optical components in the amplification stage of the present invention are suitable for the wavelength used and the rated processing system power level.
Furthermore, the ytterbium-doped fiber in the first amplification stage is a first ytterbium-doped fiber, and the first amplification stage further comprises a wavelength division multiplexer for inputting 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.
Furthermore, the ytterbium-doped fiber in the second amplification stage is a second ytterbium-doped fiber, and the second amplification stage further comprises a second tapered coupler which is used for inputting the pump light and the seed laser pulse amplified by the first amplification stage to the second ytterbium-doped fiber; optionally, a cross-sectional shape within the second ytterbium-doped fiber is hexagonal.
Further, the ytterbium-doped fiber in the third amplification stage is a third ytterbium-doped fiber, and the third amplification stage further comprises a third tapered coupler for transmitting the pump light and the second-stage amplified seed laser pulse to the third ytterbium-doped fiber. Optionally, the third ytterbium-doped fiber is a double-clad cladding-pumped ytterbium-doped fiber; optionally, a cross-sectional shape within the third ytterbium-doped fiber is hexagonal.
Further, the first amplification stage further comprises a three-port circulator and a fiber bragg grating; a first port, a second port and a third port of the three-port circulator are respectively connected with the seed laser diode, the wavelength division multiplexer and the second amplification stage; the fiber Bragg grating is used for reflecting the seed laser pulse in the laser pulse amplified by the first ytterbium-doped fiber back to the first ytterbium-doped fiber and discarding the pump light; and the seed laser light pulse is amplified twice by the first ytterbium-doped optical fiber and then input into the second amplification stage from the third port.
Furthermore, the second amplification stage also comprises a pump light remover, a single-stage isolator and a band-pass filter which are sequentially connected between the second amplification stage and the third amplification stage.
Further, the third amplification stage further comprises a pump light remover and a mode field adapter which are sequentially connected between the third amplification stage and the photonic crystal fiber.
Further, the following control strategies are stored in the controller: when changing the repetition frequency, the drive current of the pump laser diode is adjusted in time sequence to maintain the desired output: when the repetition rate is changed from high repetition rate to low repetition rate, the driving current of the pumping laser diode of the third amplification stage is reduced firstly, then the driving current of the pumping laser diode of the second amplification stage is reduced, and finally the driving current of the pumping laser diode of the first amplification stage is reduced; when changing from a low repetition rate to a high repetition rate, the opposite procedure is followed.
Furthermore, the first amplification stage also comprises a double-stage isolator and a band-pass filter which are sequentially connected between the first amplification stage and the second amplification stage.
Further, the cross section of the photonic crystal fiber is hexagonal;
photonic crystal fibers are fibers that produce a continuous spectrum of 400nm to 2100 nm.
Furthermore, the photonic crystal fiber is connected with the amplification stage in a cold connection mode.
Furthermore, the output end of the photonic crystal fiber is provided with a UV Bi convex optical lens for outputting the continuous spectrum to generate a collimated beam;
further, the device also comprises a UV plano-convex optical lens for generating a focused light beam from the collimated light beam.
One embodiment of the invention in use may be as follows (fig. 1):
1) first-stage amplification:
a) the first 980nm pump laser beam reaches the first ytterbium-doped fiber of the first amplifier stage through a Wavelength Division Multiplexer (WDM) to form a gain medium. Wherein the first beam of 980nm pump light is generated by a pump laser diode of the first amplification stage.
b)1064nm seed laser light pulse (-100 ps) is transmitted from port 1 to port 2 of the three-port circulator, and the ytterbium-doped fiber amplifies the light pulse;
c) the amplified 1064nm optical pulse is reflected by a Fiber Bragg Grating (FBG), which reflects only the 1064nm wavelength light, and then propagates again through the ytterbium-doped fiber, amplifying the pulse again.
In the first amplification stage, the 980nm pump light will be dropped from the FBG, since the FBG assembly reflects only one wavelength, and proper dropping can prevent damage to the system.
d) The 1064nm pulse doubly amplified by the first amplification stage is transmitted back to the port 2 of the three-port circulator through a wavelength division multiplexer, is output through the port 3, and sequentially passes through the two-stage isolator and the band-pass filter.
The dual stage isolator prevents any counter-propagating pulses from damaging the previous components, while the band pass filter prevents any light other than 1064nm light pulses from propagating further through the system.
2) And (3) second-stage amplification:
a) the second beam of 980nm pump light enters the second amplification level ytterbium-doped fiber through the tapered coupler to form a gain medium; wherein the second beam of 980nm pump light is generated by a pump laser diode of the second amplification stage.
b) The 1064nm optical pulse after the first-order amplification propagates through the tapered coupler and combines with the 980nm pump light in the ytterbium-doped fiber to generate amplification.
When the 1064nm optical pulse amplified by one stage and the remaining 980nm pump light pass through the pump light remover, the 980nm light is removed, and only the 1064nm optical pulse is allowed to pass through the single stage isolator and the band pass filter.
Similar to the previous components, the single stage isolator can prevent any back-propagating pulses from damaging the previous components, while the band pass filter can prevent any light other than 1064nm light pulses from propagating further through the system.
3) Third-stage amplification:
a) a third beam of 980nm pump light (generated by a pump laser diode of a third amplification stage) enters the ytterbium-doped optical fiber of the third amplification stage through the tapered coupler to form a gain medium; wherein the third 980nm pump light is generated by a pump laser diode of the third amplification stage.
b) And the 1064nm optical pulse after secondary amplification is combined with 980nm pump light in the ytterbium-doped fiber through a tapered coupler to generate amplification.
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, and only the 1064nm optical pulse is allowed to pass through a Mode Field Adapter (MFA)
The input fiber of the MFA has a larger core diameter to match the ytterbium-doped, 10 μm core double clad fiber used in the final amplification stage. The output fiber of the MFA has a smaller core diameter than the input fiber, and therefore a mode field diameter closer to that of the PCF.
The mode field diameter between the amplifier stage output and the PCF is similar, so that 1064nm optical pulses are better transmitted.
4) With respect to PCF fibers
A 20 meter long PCF fiber was used for generating an ultra-wide continuous spectrum;
the length of the PCF is a critical factor for the desired wavelength range and wavelengths below the UV (<400nm) region.
The structure of the PCF is another key factor in achieving the desired spectral range. Unlike standard optical fibers, PFCs have a hexagonal structure in which a solid fiber core is surrounded by a hollow tube, as shown in fig. 3. The arrangement of holes around the core of the fiber determines wavelength mixing and subsequent spectral broadening to achieve an ultra-broad continuum.
The PCF is connected with the output optical fiber end of the amplification stage in a fusion splicing mode so as to ensure the transmission efficiency to the maximum extent. This particular splice is different from a standard fusion splice in which the tips of the fibers are melted and pushed together, an operation that will cause the PCF's hole to collapse, resulting in poor transmission quality. The PCF and the output of the amplification stage adopt a cold connection mode. This brings the fiber ends together and heats them in a short time such that only the outer surface of the fibers is melted, fusing the fibers. The process ensures a rigid connection between the two fibers while preserving the internal structure of the PCF
4) The ultra-wide continuous spectrum output of the Photonic Crystal Fiber (PCF) is used for generating a collimated light beam through a free space UV Bi convex optical lens with the focal length of 12.7 mm;
5) the collimated beam was passed through a free space UV plano-convex optical lens with a focal length of 25.0mm to produce a focused beam that could be used with the edinburgh instrument FLS1000 fluorescence spectrometer. Fig. 5 shows a typical output spectrum of the cell.
The device was coupled to the Edinburgh Instrument FLS1000 spectrometer for various luminescence measurements in TCSPC and MCS modes. The results are shown in FIGS. 6 and 7.
The TCSPC attenuation of a diluted fluorescein solution sample was measured after the 485nm output wavelength was selected from the present apparatus. Using another single wavelength laser (EPL) as a control, fig. 6 shows the attenuation curve for the present device and single wavelength, which can show that the present invention can achieve attenuation signal measurements consistent with, or even stronger than, a single wavelength.
The rhodamine 101 photoluminescence sample is further tested by using the method, the maximum absorption wavelength of the sample is 540nm, and a single-wavelength laser used as a reference cannot be excited. The output wavelength can be adjusted to 540nm using the present apparatus and fig. 7 shows the attenuation curve after using the present invention. The result shows that the device is successfully connected with the Edinburgh instrument and is suitable for testing various samples by changing different output wavelengths.
In another aspect, a method for generating an ultra-wide spectrum continuous picosecond pulse laser is provided, comprising: the repetition frequency of a seed laser diode is selected as required, and a repeatable continuous spectrum is generated by utilizing the photonic crystal fiber through multi-stage amplification; wherein the repetition rate is controlled or adjusted by varying the time of the trigger pulse sent to the seed laser diode, and each repetition rate corresponds to an amplification control strategy. The photonic crystal fiber can produce a continuous spectrum of 400nm to 2100 nm.
Further, the desired spectrum is obtained by selectively adjusting the drive current, pulse width, drive voltage, and repetition rate of the seed laser diode.
Further, the amplification control strategy comprises: the output power of the spectrum is adjusted by selectively adjusting the drive current of the pump laser diode in the amplification stage.
Further, the following strategy is adopted when the repetition frequency needs to be switched: when switching from a low repetition rate to a high repetition rate, the drive current of the amplification stage at the initial end is increased first, and the drive currents of the subsequent amplification stages are sequentially increased in time order; when switching from a high repetition rate to a low repetition rate, the drive current of the amplifier stage at the end is first reduced, and the drive currents of the amplifier stages at the end are sequentially reduced in time order. For example, in three-stage amplification: when the repetition rate is changed from high repetition rate to low repetition rate, the driving current of the pumping laser diode of the third amplification stage is reduced firstly, then the driving current of the pumping laser diode of the second amplification stage is reduced, and finally the driving current of the pumping laser diode of the first amplification stage is reduced; when changing from a low repetition rate to a high repetition rate, the opposite procedure is followed.
The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. It is not intended to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and its practical application to enable one skilled in the art to make and use various exemplary embodiments of the invention and various alternatives and modifications as are suited to the particular use contemplated. Any simple modifications, equivalent changes and modifications made to the above exemplary embodiments shall fall within the scope of the present invention.
Claims (10)
1. The ultra-wide spectrum continuous picosecond pulse laser light source is characterized by comprising a controller, and a seed laser diode, a plurality of amplification stages and a photonic crystal fiber which are sequentially connected, wherein the controller is connected with the seed laser diode and the plurality of amplification stages, and the seed laser diode is used for generating seed laser pulses; wherein,
the controller is internally stored with a plurality of editable repetition frequency parameters of the seed laser diode, amplification parameters of an amplification stage corresponding to each repetition frequency and switching strategies of different repetition frequencies, and is used for selecting the repetition frequency of the seed laser diode according to requirements and outputting repeatable continuous spectrums.
2. The ultra-wide spectrum continuous picosecond pulse laser light source of claim 1, wherein said controller controls or adjusts the repetition rate by varying the time of the trigger pulse sent to the seed laser diode;
and/or the amplification parameter comprises a drive current parameter of the amplification stage;
and/or the switching strategy comprises sequentially adjusting the magnitude of the driving current of each stage of the amplification stage in time sequence, optionally, sequentially adjusting the magnitude of the driving current of each stage of the amplification stage in time sequence comprises: sequentially reducing or increasing the drive current of the amplification stage according to a preset time sequence; optionally, the handover policy includes: when switching from a low repetition rate to a high repetition rate, the drive current of the amplification stage at the initial end is increased first, and the drive currents of the subsequent amplification stages are sequentially increased in time order; when switching from a high repetition rate to a low repetition rate, the drive current of the amplifier stage at the end is first reduced, and the drive currents of the previous amplifier stages are sequentially reduced in time order;
and/or parameters of the seed laser diode are stored in the controller, wherein the parameters comprise driving current, pulse width and/or driving voltage and are used for adjusting corresponding parameters according to requirements;
and/or the controller further stores a switching program for preventing large peaks from occurring during amplification.
3. The ultra-wide spectrum continuous picosecond pulse laser source of claim 1 or 2, wherein said seed laser diode is a fiber coupled DFB laser diode;
and/or the seed laser diode is a laser diode with a TEC, and the TEC is used for controlling the temperature stability.
4. An ultra-wide spectrum continuous picosecond pulse laser source according to any of claims 1 to 3, wherein each amplification stage comprises a pump laser diode and a ytterbium doped fiber; the pump laser diode is used for generating pump light, and the ytterbium-doped optical fiber is used as a gain medium for amplifying the seed laser pulse; each amplification stage removes the pump light in the amplified pulses after amplifying the pulses;
and/or the controller stores the drive current parameter of the pump laser diode, and is used for adjusting the drive current through presetting or selective control so as to control the output power;
and/or the amplification stage is an all-fiber arrangement.
5. The ultra-wide spectrum continuous picosecond pulse laser light source of claim 4, wherein the plurality of amplification stages comprises a first amplification stage, a second amplification stage, and a third amplification stage connected;
the ytterbium-doped optical fiber in the first amplification stage is a first ytterbium-doped optical fiber, and the first amplification stage further comprises a wavelength division multiplexer for transmitting the pump light and the seed laser pulse to the first ytterbium-doped optical fiber;
the ytterbium-doped optical fiber in the second amplification stage is a second ytterbium-doped optical fiber, and the second amplification stage further comprises a second conical coupler which is used for transmitting the pump light and the first-stage amplified seed laser pulse to the second ytterbium-doped optical fiber;
the ytterbium-doped fiber in the third amplification stage is a third ytterbium-doped fiber, and the third amplification stage further comprises a third conical coupler which transmits the pump light and the second-stage amplified seed laser pulse to the third ytterbium-doped fiber.
6. The ultra-wide spectrum continuous picosecond pulse laser light source of claim 5, wherein said first amplification stage further comprises a three port circulator and a fiber bragg grating; the first port, the second port and the third port of the three-port circulator are respectively connected with the seed laser diode, the wavelength division multiplexer and the second amplification stage; the fiber Bragg grating is used for reflecting the seed laser pulse in the laser pulse amplified by the first ytterbium-doped fiber back to the first ytterbium-doped fiber and discarding the pump light; the seed laser light pulse is amplified twice by the first ytterbium-doped optical fiber and then is input into a second amplification stage from a third port;
and/or the first amplification stage further comprises a double-stage isolator and a band-pass filter which are sequentially connected between the first amplification stage and the second amplification stage; the second amplification stage also comprises a pump light remover, a single-stage isolator and a band-pass filter which are sequentially connected between the second amplification stage and the third amplification stage; the third amplification stage further comprises a pump light remover and a mode field adapter which are sequentially connected between the third amplification stage and the photonic crystal fiber.
7. The ultra-wide spectrum continuous picosecond pulse laser source of claim 5, wherein the controller further stores the following control strategy: when changing the repetition frequency, the drive current of the pump laser diode is adjusted in time sequence to maintain the desired output: when the repetition rate is changed from high repetition rate to low repetition rate, the driving current of the pumping laser diode of the third amplification stage is reduced, then the driving current of the pumping laser diode of the second amplification stage is reduced, and finally the driving current of the pumping laser diode of the first amplification stage is reduced; 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.
8. The ultra-wide spectrum continuous picosecond pulse laser source of any of claims 1 to 3, wherein the cross-sectional shape of said photonic crystal fiber is hexagonal;
and/or the photonic crystal fiber is connected with the amplification stage in a cold connection mode;
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 for outputting the continuous spectrum to generate collimated light beams, and the UV plano-convex optical lens is used for generating focused light beams from the collimated light beams.
9. A method for generating ultra-wide spectrum continuous picosecond pulse laser is characterized by comprising the following steps: the repetition frequency of a seed laser diode is selected as required, and a repeatable continuous spectrum is generated by utilizing the photonic crystal fiber through multi-stage amplification; wherein the repetition rate is controlled or adjusted by varying the time of the trigger pulse sent to the seed laser diode, and each repetition rate corresponds to an amplification control strategy.
10. The generation method as claimed in claim 9, wherein the desired spectrum is obtained by selectively adjusting the drive current, pulse width, drive voltage and repetition rate of the seed laser diode;
and/or, the amplification control strategy comprises: adjusting the output power of the spectrum by selectively adjusting the drive current of the pump laser diode in the amplification stage;
and/or the following strategy is adopted when the repetition frequency needs to be switched: when switching from a low repetition rate to a high repetition rate, the drive current of the amplification stage at the initial end is increased first, and the drive currents of the subsequent amplification stages are sequentially increased in time order; when switching from a high repetition rate to a low repetition rate, the drive current of the amplifier stage at the end is first reduced, and the drive currents of the amplifier stages at the end are sequentially reduced in time order.
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