Laser pulse width stretching device and system

Abstract

The application discloses a kind of laser pulse width broadening device and system, its device includes pulse broadening structure, main control circuit structure and pulse polarization conversion structure, pulse broadening structure is used to be connected with seed oscillator, receives the laser pulse output by seed oscillator, and laser pulse is transmitted multiple annular, to make laser pulse broadening;Main control circuit is used for monitoring the transmission time of laser pulse in annular pulse broadening structure, when monitoring the transmission time of laser pulse reaches preset transmission time, polarization control instruction is sent;Pulse polarization conversion structure is connected with annular pulse broadening structure and main control circuit structure, for receiving polarization control instruction and laser pulse, the polarization state of laser pulse after broadening is adjusted, and from the port not connected with pulse broadening structure is output.The application can reuse the broadening characteristics of CFBG in annular structure pulse broadening structure, and laser pulse can be transmitted multiple annular, to make laser pulse broadening.

Description

Technical Field

[0001] This invention relates to the field of laser technology, specifically to a laser pulse width broadening device and system. Background Technology

[0002] In the field of ultrafast lasers, chirped pulse amplification (CPA) is currently the most successful technology, and its inventors were awarded the Nobel Prize in Physics. CPA can be broadly divided into four stages: seed oscillator, pulse broadening, power / energy amplification, and compression. The broadening stage involves large-scale dispersion of the pulses generated by the seed oscillator (typically on the order of several picoseconds) in the time domain, thereby widening the pulse width from a few picoseconds to hundreds of picoseconds or even wider.

[0003] Currently, two main types of devices are used in the broadening stage of all-fiber structures. One is single-mode fiber, which relies on the dispersion of laser light during transmission in single-mode fiber to broaden wavelengths in the time domain. However, due to the low dispersion coefficient of fiber (approximately 40 ps / nm / km), it is generally necessary to use fiber lengths on the order of kilometers to achieve a broadening of hundreds of picoseconds. This leads to two problems: first, the price per meter of fiber is not high, but the total cost of fiber on the order of kilometers is still high; second, when laser light is transmitted in fiber on the order of kilometers, in addition to the dispersion effect, various nonlinear effects occur. These nonlinear effects will cause the pulse to carry incompressible nonlinear components, which will lead to the widening of the compressible narrowest pulse width and the presence of pulse bases, resulting in degraded pulse quality.

[0004] The second type of device is the chirped fiber grating (CFBG). Compared to single-mode fiber, this device has significant advantages. First, its length is very short; pulse broadening can be achieved within a transmission length of less than one meter, thus introducing very weak nonlinear effects. Second, CFBGs can be designed to compensate for nonlinear effects such as third-order dispersion in subsequent power / energy amplification processes. Third, in mass production, the cost of CFBGs can be lower than that of single-mode fiber. Therefore, CFBGs have become the preferred component for all-fiber structure broadening in CPA (Continuous Power Amplification). However, using CFBGs for pulse broadening also has its limitations. Due to the limitations of fiber grating manufacturing principles and processes, the product of the dispersion coefficient and the reflection bandwidth of a CFBG has an upper limit. Since the time-domain pulse width and spectral width of femtosecond ultrafast lasers satisfy the Fourier transform relationship, a wide spectral width must be maintained to obtain a narrow pulse width. Therefore, the reflection bandwidth of the CFBG needs to be kept relatively large, which limits the value of its dispersion coefficient.

[0005] To address this issue, a multi-stage cascaded broadening approach can be adopted, which involves connecting two or more CFBGs in series to continuously increase the laser pulse broadening. However, the cost of this approach increases rapidly as the number of CFBGs doubles, and the inconsistencies between different CFBGs can also negatively impact subsequent compression. Therefore, this approach currently generally results in a broadening of less than 2 nanoseconds, which does not meet the requirements for large broadening and cannot allow for large-scale adjustments to the broadening. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the above-mentioned background technology and provide a laser pulse width broadening device that can reuse the broadening characteristics of the CFBG pulse broadening structure in the ring structure, and can perform multiple ring transmissions of the laser pulse to broaden the laser pulse.

[0007] In a first aspect, a laser pulse width broadening device is provided, comprising:

[0008] A pulse broadening structure is used to connect to a seed oscillator, receive laser pulses output by the seed oscillator, and perform multiple circular transmissions of the laser pulses to broaden the laser pulses.

[0009] The main control circuit structure is connected to the ring pulse stretching structure and is used to monitor the transmission time of the laser pulse in the ring pulse stretching structure. When the monitored transmission time of the laser pulse reaches a preset transmission time, a polarization control command is issued; and,

[0010] The pulse polarization conversion structure is connected to the ring pulse stretching structure and the main control circuit structure. It is used to receive polarization control commands and laser pulses, adjust the polarization state of the laser pulses after stretching, and output the pulses from the port that is not connected to the pulse stretching structure.

[0011] The pulse broadening structure and the pulse polarization conversion structure are connected to form a ring structure.

[0012] In some embodiments, the pulse broadening structure includes a first input terminal of a coupler for connection to a seed oscillator, an input terminal of a circulator connected to the output terminal of the coupler, a chirped fiber grating connected to the middle terminal of the circulator, and a delay fiber connected to the output terminal of the circulator, wherein the delay fiber is connected to the input terminal of the coupler through the pulse polarization conversion structure.

[0013] In some embodiments, the pulse polarization conversion structure includes a polarization controller connected to both the delay fiber and the main control circuit structure, and an input terminal of a polarization combiner connected to the polarization controller. The first output terminal of the polarization combiner is connected to the second input terminal of the coupler, and the second output terminal of the polarization combiner is a laser pulse broadening completion output port.

[0014] In some embodiments, a signal enhancement structure connected to both the polarization controller and the delay fiber is further included. The signal enhancement structure is used to amplify the power of the laser pulse and to suppress the gain narrowing of the amplified laser pulse.

[0015] In some embodiments, the signal enhancement structure includes a filter connected to the delay fiber, a first input terminal of a wavelength division multiplexer connected to the filter, a pump laser connected to a second input terminal of the wavelength division multiplexer, and a gain fiber connected to the output terminal of the wavelength division multiplexer, the gain fiber being connected to the polarization controller.

[0016] The pulse broadening structure, the pulse polarization conversion structure, the filter, the wavelength division multiplexing unit, and the gain fiber are connected to form a ring structure.

[0017] In some embodiments, the delay fiber is configured as a length-adjustable fiber; the gain fiber is configured as a length-adjustable fiber.

[0018] Secondly, a laser pulse width stretching system is provided, comprising:

[0019] Seed oscillator; and,

[0020] The laser pulse width stretching device described above.

[0021] Compared to existing technologies, this invention, by connecting a pulse broadening structure and a pulse polarization conversion structure to form a ring structure, can reuse the broadening characteristics of the CFBG in the pulse broadening structure within the ring structure. This allows for multiple ring transmissions of the laser pulse to broaden it, thus widening the pulse width to tens or even hundreds of nanoseconds, far exceeding currently used pulse broadening schemes. Simultaneously, the pulse polarization conversion structure can adjust the polarization state of the laser pulse and output it from a port never connected to the pulse broadening structure. This allows the broadened laser pulse to be output after polarization state adjustment without further broadening within the ring structure, making the design flexible and gradual. Furthermore, this device can also be used in pulse-width tunable lasers, where all components in the ring structure are reusable, and there is no mechanical adjustment device, resulting in significant advantages in beam quality and pointing stability. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a laser pulse width stretching system according to an embodiment of the present invention.

[0023] Icon labels:

[0024] 1. Seed oscillator; 2. Coupler; 3. Circulator; 4. Chirped fiber grating; 5. Delay fiber; 6. Filter; 7. Wavelength division multiplexer; 8. Pump source; 9. Gain fiber; 10. Polarization controller; 11. Polarization combiner. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] See Figure 1 As shown, an embodiment of the present invention provides a laser pulse width stretching device, characterized in that it includes:

[0027] A pulse broadening structure is used to connect to a seed oscillator, receive laser pulses output by the seed oscillator, and perform multiple circular transmissions of the laser pulses to broaden the laser pulses.

[0028] The main control circuit structure is connected to the ring pulse stretching structure and is used to monitor the transmission time of the laser pulse in the ring pulse stretching structure. When the monitored transmission time of the laser pulse reaches a preset transmission time, a polarization control command is issued; and,

[0029] The pulse polarization conversion structure is connected to the ring pulse stretching structure and the main control circuit structure. It is used to receive polarization control commands and laser pulses, adjust the polarization state of the laser pulses after stretching, and output the pulses from the port that is not connected to the pulse stretching structure.

[0030] The pulse broadening structure and the pulse polarization conversion structure are connected to form a ring structure.

[0031] Specifically, in this embodiment, given that in current CFBG cascade stretching schemes, the cost increases rapidly with the number of cascaded CFBGs, and the inconsistencies between different CFBGs also negatively impact subsequent compression, this invention avoids these adverse effects by connecting a pulse stretching structure and a pulse polarization conversion structure to form a ring structure. This allows for the reuse of the stretching characteristics of the CFBGs in the ring structure, enabling multiple ring transmissions of the laser pulse to stretch it. This stretches the pulse width to tens or even hundreds of nanoseconds, far exceeding currently used pulse stretching schemes. Simultaneously, the pulse polarization conversion structure can adjust the polarization state of the laser pulse and output from a port never connected to the pulse stretching structure. This allows the stretched laser pulse to be output after polarization state adjustment without further stretching within the ring structure. Therefore, this invention offers flexible and gradual design, with significant application prospects in CPA. Furthermore, this device can also be used in pulse-width tunable lasers, where all components in the ring structure are reusable, and there is no mechanical adjustment device, resulting in significant advantages in beam quality and pointing stability.

[0032] Optionally, the pulse broadening structure includes a first input terminal of a coupler 2 for connection to a seed oscillator 1, an input terminal of a circulator 3 connected to the output terminal of the coupler 2, a chirped fiber grating 4 connected to the middle terminal of the circulator 3, and a delay fiber 5 connected to the output terminal of the circulator 3. The delay fiber 5 is connected to the input terminal of the coupler 2 through the pulse polarization conversion structure.

[0033] Specifically, in this embodiment,

[0034] A seed oscillator 1 with a frequency of 1MHz after frequency reduction is selected, with a center wavelength of 1030nm, a bandwidth of 10nm, and a pulse width of 3ps;

[0035] A 1×2 polarization-maintaining coupler 2 with a working center wavelength of 1030nm is selected. The pulsed laser with a center wavelength of 1030nm output from the seed oscillator 1 enters from the first input port 2-1# of the coupler 2 and is output from the output port 2-3#.

[0036] A three-port polarization-maintaining circulator 3 with a working center wavelength of 1030nm is selected. The pulsed laser with a center wavelength of 1030nm is output from the 2-3# ports of the coupler 2 and enters the input port 3-1# of the circulator 3. It is then output from the middle port 3-2#, and then enters the chirped fiber grating CFBG. After being reflected by the CFBG, it enters the middle port 3-2# ​​again, and then is output from the output port 3-3#.

[0037] A chirped fiber grating (CFBG) with a dispersion coefficient of 20 ps / nm and a reflection bandwidth greater than 20 nm is selected. After reflection by the CFBG, the seed light signal will be broadened to approximately 203 ps.

[0038] Select a section of PM980 optical fiber and adjust its length to ensure that the total length of the optical fiber in the ring structure is approximately 5 meters. At this time, the corresponding time for the laser pulse to travel one revolution within the ring structure is 25 nanoseconds.

[0039] Optionally, the pulse polarization conversion structure includes a polarization controller 10 connected to both the delay fiber 5 and the main control circuit, and an input terminal of a polarization combiner 11 connected to the polarization controller 10. The first output terminal of the polarization combiner 11 is connected to the second input terminal of the coupler 2, and the second output terminal of the polarization combiner 11 is the output port for laser pulse broadening.

[0040] Specifically, in this embodiment, the polarization controller 10 does not change the polarization state of the laser pulse for most of the time during the operation of the laser pulse within the ring structure. At this time, the laser pulse will maintain a certain polarization state and be transmitted unidirectionally in a ring. When the polarization controller 10 receives a polarization state conversion command, it will rotate the polarization state of the laser pulse passing through the polarization controller 10 by a certain angle, and then output it from the second output port of the polarization combiner 11 that is not connected to the ring structure.

[0041] The polarization combiner 11 is a three-port device, in which one polarized light propagates between ports 11-1# and 11-3#, and the other polarized laser propagates between ports 11-2# and 11-3#. Therefore, when the laser pulse propagates in the ring structure, it propagates between ports 11-1# and 11-3# and to the second input port 2-2# of the coupler 2. However, after receiving a command, the polarization controller 10 changes the polarization state of the laser pulse in the ring structure, and the laser pulse will be output from the second output port 11-2#. Ports 11-1# and 11-3# are slow-axis output inputs, and port 11-2# is a fast-axis output.

[0042] Optionally, it also includes a signal enhancement structure connected to both the polarization controller 10 and the delay fiber 5. The signal enhancement structure is used to amplify the power of the laser pulse and to narrow the gain of the amplified laser pulse.

[0043] Optionally, the signal enhancement structure includes a filter 6 connected to the delay fiber 5, a first input terminal of a wavelength division multiplexer 7 connected to the filter 6, a pump laser connected to a second input terminal of the wavelength division multiplexer 7, and a gain fiber 9 connected to the output terminal of the wavelength division multiplexer 7, the gain fiber 9 being connected to the polarization controller 10.

[0044] The pulse broadening structure, the pulse polarization conversion structure, the filter 6, the wavelength division multiplexing unit, and the gain fiber 9 are connected to form a ring structure.

[0045] Specifically, in this embodiment,

[0046] A filter 6 with a concave center and a transmission center of 1030nm is selected. Filter 6 is used to adjust the spectrum of the pulsed light signal to avoid the narrowing of the spectrum caused by the gain narrowing effect during the amplification process.

[0047] A wavelength-locked single-mode pump laser with a center wavelength of 974nm was selected; in order to ensure that the seed light power is not too large as the cumulative insertion loss in the transmission path, the 974nm pump source 8 was turned on simultaneously.

[0048] A 976nm / 1030nm wavelength division multiplexer (WDM) is selected. The WDM combines the laser pulse and the pump light into a single beam and then sends it into the gain fiber 9 for amplification. That is, the laser pulse is input from the first input port 7-1#, and the laser output from the pump laser is input from the second input port 7-2# and then output from the output port 7-3#.

[0049] A 1-meter-long single-mode polarization-maintaining gain fiber 9 is selected. The laser pulse and 974nm pump light will pass through this gain fiber 9, and then the signal light will be amplified. The gain fiber 9 can be a rare earth-doped special fiber such as ytterbium-doped, erbium-doped, erbium-ytterbium co-doped, thulium-doped, holmium-doped, or neodymium-doped fiber, which can amplify the optical signal.

[0050] Optionally, the delay fiber 5 is configured as a length-adjustable (multi-layered circular) fiber; the gain fiber 9 is configured as a length-adjustable (multi-layered circular) fiber.

[0051] Optionally, the transmission spectrum of the filter 6 can be in a specific shape, such as a central depression, a central convexity with two concave sides, or a convex left side with a concave right side. In this embodiment, the transmission spectrum of the filter 6 is set to a central depression. In order to suppress the gain narrowing effect during amplification, the selected transmission spectrum of the filter 6 is centrally depressed, which effectively suppresses the gain narrowing effect.

[0052] This invention provides a laser pulse width broadening device. After a laser pulse is injected into a ring structure, it takes approximately 25 nanoseconds to propagate through the ring structure once, and the broadening amount through one CFBG is 200 ps. The time interval between the next pulse and the next pulse is 1000 nanoseconds. Before the arrival of the next pulse, the pulse is allowed to run 15 times in the ring cavity, with a cumulative transmission time of approximately 375 nanoseconds, and the seed light is broadened to 3 nanoseconds. After the transmission time is monitored and confirmed by the main control circuit structure-timing circuit, the polarization controller 10 is activated. After the seed light signal has been broadened 15 times, its polarization direction is rotated by 90 degrees after passing through the polarization controller 10, and it is output from port 11-2# after passing through the polarization combiner 11.

[0053] In another embodiment, a seed oscillator with a down-frequency of 5MHz is selected, with a center wavelength of 1064nm, a bandwidth of 0.1nm, and a pulse width of 3ps. A 1×2 polarization-maintaining coupler with a working center wavelength of 1064nm and a three-port polarization-maintaining circulator with a working center wavelength of 1064nm are selected. The 1064nm pulsed laser is output from port 2-2# of the coupler and enters port 3-1# of the circulator, and is output from port 3-2#. Then it enters CFBG1, is reflected by the CFBG, enters port 3-2# ​​again, and is output from port 3-3#. A chirped fiber grating (CFBG) with a dispersion coefficient of 100ps / nm and a reflection bandwidth greater than 10nm is selected. After reflection by the CFBG, the seed light signal will be broadened by approximately 10ps. Select a section of PM980 delay fiber and adjust its length to ensure that the fiber length of the entire ring structure is approximately 5 meters. At this time, the time for the light to travel one revolution in the ring structure is 25 nanoseconds. Select an electro-optic polarization controller with a rise and fall time of approximately 1 nanosecond. Select a polarization-maintaining beam combiner with a working center wavelength of 1064nm.

[0054] After the laser pulse is injected into the ring structure through port 2-1#, it takes approximately 25 nanoseconds to propagate through the ring structure once, with a CFBG broadening of 10 ps. The next pulse arrives 200 nanoseconds later. Before the next pulse arrives, the pulse is allowed to travel three times within the ring cavity, with a cumulative propagation time of approximately 75 nanoseconds, and the seed light is broadened to 30 picoseconds. Monitoring by the synchronization circuit, 40 nanoseconds after the seed pulse enters the coupler, the polarization controller is activated. After three broadenings, the seed light signal passes through the polarization controller, its polarization direction is rotated 90 degrees, and it is output through the polarization combiner.

[0055] This invention also provides a laser pulse width stretching system, including a seed oscillator and a laser pulse width stretching device as described above.

[0056] In the description of this invention, it should be noted that the terms "upper," "lower," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two elements. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0057] It should be noted that in this invention, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0058] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features of the invention herein.

Claims

1. A laser pulse width stretching device, characterized by, The laser pulse width expansion device comprises: a pulse expansion structure connected with a seed oscillator, receiving laser pulses output by the seed oscillator, and performing multiple ring transmissions on the laser pulses to expand the laser pulses; a main control circuit structure connected with the pulse expansion structure, used for monitoring the transmission time of the laser pulses in the pulse expansion structure, and issuing a polarization control instruction when the transmission time of the laser pulses reaches a preset transmission time; a pulse polarization conversion structure connected with the pulse expansion structure and the main control circuit structure, used for receiving the polarization control instruction and the laser pulses, adjusting the polarization state of the expanded laser pulses, and outputting from a port not connected with the pulse expansion structure; wherein the pulse expansion structure and the pulse polarization conversion structure form a ring structure; the pulse expansion structure comprises a first input end of a coupler connected with the seed oscillator, an input end of a circulator connected with the output end of the coupler, a chirped fiber grating connected with the intermediate end of the circulator, and a delay fiber connected with the output end of the circulator and the input end of the coupler through the pulse polarization conversion structure. the pulse polarization conversion structure comprises a polarization controller connected with the delay fiber and the main control circuit structure, and an input end of a polarization beam combiner connected with the polarization controller, a first output end of the polarization beam combiner connected with a second input end of the coupler, and a second output end of the polarization beam combiner as a laser pulse expansion completion output port.

2. The laser pulse width stretching device of claim 1, wherein, The laser pulse width expansion device further comprises a signal enhancement structure connected with the polarization controller and the delay fiber, used for power amplifying the laser pulses and gain narrowing the power amplified laser pulses.

3. The laser pulse width stretching device of claim 2, wherein, the signal enhancement structure comprises a filter connected with the delay fiber, a first input end of a wavelength division multiplexer connected with the filter, a pump laser connected with a second input end of the wavelength division multiplexer, and a gain fiber connected with an output end of the wavelength division multiplexer, the gain fiber being connected with the polarization controller; 4. The laser pulse width stretching device of claim 3, wherein, wherein the pulse expansion structure, the pulse polarization conversion structure, the filter, the wavelength division multiplexer, and the gain fiber form a ring structure. The delay fiber is a length-adjustable fiber, and the gain fiber is a length-adjustable fiber.

5. The laser pulse width stretching device of claim 4, wherein, The laser pulse width expansion device comprises:

6. A laser pulse width stretching system, characterized by, a seed oscillator; and any one of claims 1 to 5. ​

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