A Raman fiber laser with continuously adjustable pulse width over a wide range

Abstract

The present invention relates to a Raman fiber laser with continuously adjustable pulse width in a wide range, characterized in that: the Raman laser seed source outputs nanosecond pulses, a three-way selector relay starts a trigger signal to provide a duty cycle frequency signal to a logic gate circuit and a time delay device, and then inputs it into an analog switch high-frequency high-current laser driver. The high-frequency high-current laser driver has 6 channels, and the six channels are connected in parallel to drive the Raman laser seed source laser, and then amplified by a Raman laser amplifier; the Raman laser seed source is a semiconductor LD with a high beam quality of 1178 nm, or an LD with a wavelength in the range of 1-2 μm; the corresponding pulse width parameters can be set according to different processing materials, so that one laser can meet the processing requirements of most materials with different materials.

Description

Technical Field

[0001] The present invention relates to a Raman fiber laser with continuously adjustable pulse width in a wide range, belonging to the technical field of lasers. Background Art

[0002] A laser is a device that can emit laser light. The first microwave quantum amplifier was made in 1954, obtaining a highly coherent microwave beam. In 1958, A.L. Schawlow and C.H. Townes extended the principle of the microwave quantum amplifier to the optical frequency range. In 1960, T.H. Maiman et al. made the first ruby laser. In 1961, A. Javan et al. made a helium-neon laser. In 1962, R.N. Hall et al. developed a gallium arsenide semiconductor laser. Since then, the types of lasers have become more and more. Classified by the working medium, lasers can be divided into four categories: gas lasers, solid lasers, semiconductor lasers, and dye lasers. Recently, free electron lasers have also been developed. High-power lasers usually output in a pulsed mode.

[0003] Currently, the structure of pulsed Raman fiber lasers can be divided into Q-switched Raman fiber lasers and MOPA Raman fiber lasers. MOPA (Master Oscillator Power-Amplifier) is a master oscillator power amplifier. A seed signal light with high beam quality and a pump light are coupled into a gain fiber, so that the seed source outputs high power, and the output light is consistent with the seed signal light in terms of frequency and pulse width.

[0004] Currently, the single nanosecond adjustable MOPA-structured Raman fiber lasers on the market have certain limitations in processing materials. Some materials require a nanosecond Raman laser for high energy and heat, while some thermosensitive materials and materials that require high peak power require a picosecond Raman laser. Conventional MOPA Raman fiber lasers cannot well meet the market demand. Summary of the Invention

[0005] The purpose of the present invention is to provide a Raman fiber laser with continuously adjustable pulse width in a wide range, which is a MOPA-structured Raman fiber laser that realizes adjustable pulse width from picosecond to microsecond by triggering signal derivation, and can set corresponding pulse width parameters according to different processing materials, so that one laser can meet the processing requirements of most materials with different materials.

[0006] The technical solution of the present invention is implemented as follows: A Raman fiber laser with continuously adjustable pulse width in a wide range, characterized in that: the wide pulse range includes 1) driving by an ultra-short fast pulse picosecond laser from 100 ps to 5 ns; 2) driving by a TTL signal high-frequency high-current laser from 5 ns to 1 μs; 3) driving by a constant current with an arbitrary waveform laser from 100 ns to 1 μs; when the Raman laser seed source outputs a nanosecond pulse, a three-way selection relay starts a trigger signal to provide a frequency signal with a certain duty cycle, which is given to a logic gate circuit and a time delay device to identify the rising edge of the frequency signal and generate a nanosecond pulse with the same frequency as the trigger signal, and then input it into an analog switch high-frequency high-current laser driver. The high-frequency high-current laser driver has 6 channels, and each channel can work at a DC current of up to 500 mA. The six channels are connected in parallel to achieve a driving capacity of 3 A for the Raman laser seed source laser, and then amplified by a Raman laser amplifier; the Raman laser seed source generates a nanosecond pulse light with the same frequency as the trigger signal. The Raman laser seed source is a semiconductor LD with a high beam quality of 1178 nm, or an LD with a wavelength in the range of 1 - 2 μm; when the Raman laser seed source outputs a picosecond pulse, a three-way selection relay starts a trigger signal to provide a frequency signal with a certain period. After being identified by an ultra-short fast pulse laser driver for the signal rising edge, a picosecond pulse with the same frequency as the trigger signal is output. The ultra-short fast pulse laser driver also has the function of driving the Raman laser seed source laser. It is connected to an external device through an SPI bus, and the current and pulse width parameters are written into the driver. The Raman laser seed source generates a picosecond pulse light with the same frequency as the trigger signal;

[0007] When the Raman laser seed source outputs an arbitrary waveform pulse, the three-way selection relay starts a trigger signal, which is added to a differential amplifier circuit after passing through a high-speed digital-to-analog converter. It is necessary to use a high-speed operational amplifier to match it, adjust the amplification factor of the circuit, and output arbitrary waveforms with different amplitudes as the set point of the constant current circuit, so that the constant current circuit can quickly modulate the peak power output by the laser, realizing the arbitrary waveform output of the Raman laser seed source laser.

[0008] The high-speed digital-to-analog converter is an 8-bit resolution product of a CMOS digital-to-analog converter (DAC). Its pins are also compatible with 10, 12, and 14-bit resolution products, and support an update rate of 125 MSPS. It provides a differential current output, with an internal 1.2 V on-chip reference voltage source and a reference voltage control amplifier. Data is written into it in parallel through an FPGA or an MCU to make it output any desired voltage value. The output waveforms include sine waves and triangular waves.

[0009] The pulse output power of the described Raman laser seed source is relatively low and requires multi-stage amplification by a Raman laser amplifier. An isolator needs to be added between each stage of amplification to prevent the damage to the laser caused by the backward light, and TEC temperature control is coordinated to enable the laser to output more stably at different temperatures. The Raman laser amplifier includes an isolator, which causes damage to the Raman laser seed source due to the backward light generated during the amplification of the Raman laser seed source. The beam combiner adopts a (2 + 1)*1 structure to couple the light of the Raman laser seed source and the pump light into the gain fiber for power amplification of the Raman laser seed source. The Raman gain fiber absorbs the pump light and amplifies the signal light generated by the Raman laser seed source. The amplified laser state is consistent with that of the Raman laser seed source. After being amplified by the gain fiber, the laser contains pump light, and a filter can be added at the output end to strip the pump light to ensure the purity of the output laser. The Raman laser pump source provides energy for the gain fiber and plays a role in amplifying the seed source. The laser output selects different output modes according to different applications, including collimated output, collimated plus isolation output, and fiber jumper output.

[0010] The positive effect of the present invention is that the pulse modulation range of a common fiber laser is adjustable in the ns range, while this laser realizes adjustable pulse width in the range of 100 ps - 1 μs, improving the overall performance parameters of the Raman fiber laser. The wider and more precise pulse width adjustment mechanism can set corresponding pulse width parameters according to different processing materials, enabling one laser to meet the processing requirements of most materials with different materials. Three working modes of the laser are provided, namely (a) driven by a 100 ps to 5 ns ultra-short fast pulse picosecond laser, (b) driven by a TTL signal high-frequency high-current laser with a pulse width of 5 ns to 1 μs, and (c) driven by a constant current drive method to realize an arbitrary waveform laser with a pulse width of 100 ns to 1 μs; by changing the working state of the seed source, finally realizing an arbitrarily adjustable pulse width in the range of ps to us and an arbitrarily shaped seed source drive method. Brief Description of the Drawings

[0011] Figure 1 It is a structural schematic diagram of the device.

[0012] Trigger signal 1, logic gate circuit 2, time delay device 3, high-frequency high-current laser driver 4, ultra-short fast pulse laser driver 5, high-speed digital-to-analog converter 6, differential amplifier circuit 7, constant current drive circuit 8, three-way selection relay 9, Raman laser seed source 10, Raman laser amplifier 11;

[0013] Figure 2 It is the optical structure of the amplification part of the Raman laser.

[0014] Isolator 11-1, beam combiner 11-2, Raman gain fiber 11-3, filter 11-4, Raman pump source 11-5, laser output 11-6. Detailed implementation manners

[0015] The present invention will be further described below in conjunction with the accompanying drawings and embodiments: As Figure 1 shown: A Raman fiber laser with continuously adjustable pulse width in a wide range, characterized in that: the wide pulse width range includes 1) driving by an ultrashort fast pulse picosecond laser with a pulse width ranging from 100 ps to 5 ns; 2) driving by a TTL signal high-frequency high-current laser with a pulse width ranging from 5 ns to 1 μs; 3) driving by an arbitrary waveform laser with a pulse width ranging from 100 ns to 1 μs using constant current driving; when the system needs to output nanosecond pulses, the three-way selector relay 9 will select the structure of the nanosecond pulse for output, and the trigger signal 1 provides a periodic signal with a fixed duty cycle (i.e., a fixed frequency signal), and the signal acts on the logic gate circuit 2. The logic gate circuit 2 integrates the incoming signal, so that the trigger signals 1 in different modes can be converted into the trigger signals required by the time delay device 3 through the logic gate circuit 2. The trigger signal 1 output by the logic gate circuit 2 passes through the time delay device 3. The time delay device 3 delays the trigger signal 1 to a certain extent and outputs the inverted delay signal. The generated delay time is the pulse width of the Raman laser seed source. Since the delay time can be adjusted in the range of 5 ns - 1 μs, the nanosecond pulse width of the Raman laser seed source can be adjusted in the range of 5 ns - 1 μs. The output ability of this signal driving the Raman laser seed source is slightly low, and it is necessary to drive the Raman laser seed source through a high-frequency high-current laser driver 4. This high-frequency high-current laser driver 4 is a six-channel laser driver, which can achieve spike-free switching of laser diodes within the range of a switching frequency less than 200 MHz. The six fast switches are independently controlled by TTL-type trigger signal inputs, and a three-channel mode with LVDS-type trigger signal inputs can also be selected. Each channel can operate at a DC current of up to 500 mA, and the six channels in parallel can achieve a driving ability of 3 A for the seed source laser, realizing tunable pulsed laser output in the range of 5 ns - 1 μs under high-current control, which is convenient for Raman amplification.

[0016] When the system needs to output picosecond pulse width, the three-way selector relay 9 will select the structure of the nano-picosecond pulse for output. Similarly, the trigger signal 1 provides a periodic signal with a fixed duty cycle (i.e., a fixed frequency signal). This signal acts on the ultrashort fast pulse laser driver 5 to generate a picosecond pulse width with a fixed frequency. The driver can control the pulse width to be adjustable in the range of 100 ps to 5 ns, and the precision adjustment can be selected as a wide-range coarse adjustment mode or a narrow-range fine adjustment mode. The coarse adjustment mode allows the pulse width to be configured in steps of usually 250 ps, and each wide-range adjustment step allows for more fine-grained small-step adjustment to ensure the output of picosecond pulses.

[0017] When the system wants to output an arbitrary waveform, the three - way relay 9 will select the structure of the arbitrary pulse for output. Similarly, the trigger signal 1 provides a periodic signal with a fixed duty cycle (i.e., a fixed - frequency signal). The signal directly acts on the 6 - channel high - speed digital - to - analog converter. The high - speed digital - to - analog converter is an 8 - bit resolution product of a high - performance, low - power CMOS digital - to - analog converter (DAC). Its pins are also compatible with 10 - bit, 12 - bit, and 14 - bit resolution products and support an update rate of 125 MSPS. It provides a differential current output and has an on - chip reference voltage source of 1.2 V and a reference voltage control amplifier. Data is written into it in parallel through an FPGA or MCU to make it output the desired arbitrary voltage value. To ensure a high - refresh - rate change of the output voltage value, this can be regarded as a quantization process of a continuous signal, and thus an arbitrary waveform output can be obtained. Higher - resolution DACs with pin compatibility can also be selected to increase the smoothness of the output waveform. The high - speed digital - to - analog converter, under the control of an external trigger signal, can achieve continuous adjustment of the pulse width in the range of 100 ns - 1 μs with arbitrary shapes. The output of the waveform is a sine wave, a triangular wave, or other waveforms. Since the DAC of the differential amplifier circuit 7 is a differential output, a differential amplifier circuit is added at the subsequent stage. A high - speed operational amplifier must be used to match it, and the amplification factor of the circuit is adjusted to output arbitrary waveforms with different amplitudes. (8) The set point of the constant - current drive circuit enables the constant - current circuit to quickly modulate the peak power output by the laser, realizing the arbitrary - waveform output of the seed - source laser. Cooperating with the differential circuit, the high - speed digital - to - analog converter can drive the laser seed source to generate arbitrary - wave pulses with high peaks, facilitating the amplification of the laser power.

[0018] The Raman laser seed source 10 selects an LD with a high beam quality of 1178 nm or an LD with a wavelength in the range of 1 - 2 μm.

[0019] (1) Since the power of the seed signal light is relatively low and to meet the requirements for the laser to be used in material processing, the Raman laser seed source needs to be Raman - laser - amplified. To meet the performance requirements for high power, it needs to be amplified step by step, that is, a MOPA Raman fiber pulsed laser. The structure of the Raman laser amplifier 11 is as Figure 2 shown. The Raman laser seed source 10 passes through the isolator 11 - 1 to ensure that the backward light generated during the amplification of the seed source does not damage the seed source. Then, through the beam combiner 11 - 2. Generally, the beam combiner adopts a (2 + 1)*1 structure to couple the signal light of the seed source and the Raman pump light 11 - 3 into the gain fiber for power amplification of the seed source. The Raman gain fiber 11 - 4 absorbs the Raman pump light to amplify the signal light generated by the seed source. The amplified laser state is consistent with that of the seed source. After being amplified by the gain fiber, the laser contains pump light. Therefore, a filter 11 - 5 is added at the output end to remove the excess Raman pump light and ensure the purity of the output laser. The laser output 11 - 6 can select different output methods according to different application conditions.

[0020] Collimated output, collimated isolation output, and fiber optic jumper output can be adopted.

[0021] This invention can select different pulse width modes according to different materials. When micro-machining materials such as plastics, glass, and circuit boards, there are requirements for high peak value and low heat of the laser. The picosecond pulse mode can provide a deeper etching effect and a lower heat-affected area. First, the picosecond laser mode; when marking or rust-removing materials such as stainless steel and aluminum alloy, there are often requirements for high heat and high average power of the laser. The nanosecond pulse width mode can provide a high average power while ensuring a high peak power output. First, the nanosecond laser mode; when the laser seed source pulse is a square wave, when amplifying the laser seed source, the pulse front will be preferentially amplified, resulting in a spiked pulse. This spiked pulse is not conducive to the generation of high average power and is prone to non-linear effects. Therefore, the shape of the pulse can be changed to make the front edge slower. After being driven by a constant current drive circuit, the seed source generates a laser pulse output with an arbitrary waveform. In this way, through fiber amplification, the generation of non-linearity is suppressed to a certain extent, and the output power of the laser is increased to meet the processing requirements of wide pulse width and high power.

Claims

1. A Raman fiber laser with continuously adjustable pulse width in a wide range, characterized in that: The pulse width range includes: 1) driving by an ultra-short fast pulse picosecond laser from 100 ps to 5 ns; 2) driving by a TTL signal high-frequency high-current laser from 5 ns to 1 μs; 3) driving by an arbitrary waveform laser from 100 ns to 1 μs with constant current drive. When the Raman laser seed source outputs nanosecond pulses, a three-way selectable relay starting trigger signal provides a frequency signal with a certain duty cycle to the logic gate circuit and the time delay device to identify the rising edge of the frequency signal and generate a nanosecond pulse with the same frequency as the trigger signal, which is then input into the analog switch high-frequency high-current laser driver. The high-frequency high-current laser driver has 6 channels, and each channel can operate at a DC current of up to 500 mA. The six channels are connected in parallel to achieve a driving capacity of 3 A for the Raman laser seed source laser. Then, it is amplified by the Raman laser amplifier. The Raman laser seed source generates a nanosecond pulse light with the same frequency as the trigger signal. The Raman laser seed source is a high beam quality semiconductor LD of 1178 nm, or an LD with a wavelength in the range of 1 - 2 μm. When the Raman laser seed source outputs picosecond pulses, a three-way selectable relay starting trigger signal provides a frequency signal with a certain period. The ultra-short fast pulse laser driver identifies the rising edge of the signal and outputs a picosecond pulse with the same frequency as the trigger signal. The ultra-short fast pulse laser driver also has the function of driving the Raman laser seed source laser and is connected to external devices through the SPI bus. The current and pulse width parameters are written into this driver. The Raman laser seed source generates a picosecond pulse light with the same frequency as the trigger signal. When the Raman laser seed source outputs arbitrary waveform pulses, a three-way selectable relay starting trigger signal is added to the differential amplifier circuit after passing through the high-speed digital-to-analog converter. A high-speed operational amplifier must be used to match it, and the amplification factor of the circuit is adjusted to output arbitrary waveforms with different amplitudes, which serve as the set point of the constant current circuit, enabling the constant current circuit to quickly modulate the peak power output by the laser, realizing the arbitrary waveform output of the Raman laser seed source laser. The high-speed digital-to-analog converter has an on-chip reference voltage source of 1.2 V and a reference voltage control amplifier. Data is written into it in parallel through the FPGA or MCU to make it output the desired arbitrary voltage value. The output waveforms include sine waves and triangular waves. The pulse output power of the Raman laser seed source is relatively low and requires multi-stage amplification by the Raman laser amplifier. An isolator needs to be added between each stage of amplification to prevent the damage to the laser caused by the backward light, and it is combined with TEC temperature control to make the laser output more stably at different temperatures. The Raman laser amplifier includes an isolator, which can prevent the backward light generated during the amplification process of the Raman laser seed source from damaging the Raman laser seed source. The beam combiner adopts a (2 + 1)*1 structure to couple the light of the Raman laser seed source and the pump light into the gain fiber for power amplification of the Raman laser seed source. The Raman gain fiber absorbs the pump light and amplifies the signal light generated by the Raman laser seed source. The amplified laser state is consistent with that of the Raman laser seed source. After being amplified by the gain fiber, the laser contains pump light, and a filter is added at the output end.

2. The Raman fiber laser with continuously adjustable pulse width in a wide range according to claim 1, wherein The described time delay processor can output pulsed lasers with a positive bandwidth ranging from 5 ns to 1 μs; the high-frequency high-current laser driver is an analog switch used for driving the laser seed source; the ultrashort fast-pulse laser driver can control the pulse width to be adjustable within the range of 100 ps to 5 ns, and the precision adjustment can be selected in a wide-range coarse-tuning mode or a narrow-range fine-tuning mode. The coarse-tuning mode allows the pulse width to be configured in steps of usually 250 ps, and each wide-range adjustment step allows for finer small-step adjustments to ensure the output of picosecond pulses; for the differential amplifier circuit, the DAC has a differential output and is matched with a high-speed operational amplifier to adjust the circuit amplification factor and output arbitrary waveforms with different amplitudes; the constant-current drive circuit quickly modulates the peak power output by the laser, enabling the arbitrary waveform output of the seed-source laser. In cooperation with the differential circuit, the high-speed digital-to-analog converter can drive the laser seed source to generate arbitrary-wave pulses with high peak values; for the Raman laser seed source, an LD with a high beam quality at 1178 nm is selected, or an LD with a wavelength within the range of 1 - 2 μm is selected.

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