Gain switch picosecond laser generator

Abstract

The utility model discloses a gain switch picosecond laser generator, which comprises a frequency adjustable sinusoidal signal generator, a radio frequency amplifier, a step recovery diode, a direct current bias circuit, a semiconductor laser, a polarization controller, a 1 * 2 optical fiber coupler and an adjustable Bragg fiber grating, the step recovery diode and the direct current bias circuit provide fast pulse driving current for the laser diode. The gain switch picosecond laser generator has the advantages that the stability, the reliability and the output optical quality of the gain switch picosecond laser generator are greatly improved.

Description

Technical Field

[0001] The utility model relates to the field of laser generators, in particular to a gain-switched picosecond laser generator. Background Art

[0002] With the rapid development of laser technology and applications, the application of ultrafast lasers including picosecond lasers is becoming more and more widespread. There are two main methods for generating picosecond lasers: mode locking and gain switching. The gain-switched picosecond laser generator has the advantages of simple and reliable structure and easy control. By directly driving the laser with a large amplitude and fast electrical pulse, short pulses with a pulse duration of less than 50ps can be easily generated in a semiconductor laser. The electrical pulse width should be quite short and should be in the range of 100-200ps. At sub-GHz or GHz frequencies, direct modulation of the bias below the threshold by a sinusoidal signal can also result in the generation of gain-switched picosecond light pulses. However, the peak power and energy of a single pulse in this frequency band are very low, and the effect of direct use is not much different from that of using a continuous laser, so complex pulse extraction must be performed to reduce the frequency before amplification.

[0003] The current gain-switched picosecond laser generation has problems such as high frequency, narrow range, large time jitter of the output laser pulse, and spectrum side mode diffusion, so there is room for improvement. Utility Model Content

[0004] The purpose of the utility model is to provide a gain-switched picosecond laser generator to solve the problems raised in the above-mentioned background technology, which has the advantages of greatly improving the stability, reliability and output optical quality of the gain-switched picosecond laser generator.

[0005] To achieve the above-mentioned purpose, the utility model provides the following technical solutions: a gain-switched picosecond laser generator, including a frequency-adjustable sinusoidal signal generator, a radio frequency amplifier, a step recovery diode, a DC bias circuit, a semiconductor laser, a polarization controller, a 1X2 fiber coupler and an adjustable Bragg fiber grating. The sinusoidal signal transmitter, power driver, step recovery diode and DC bias circuit provide a fast pulse drive current for the laser diode.

[0006] By adopting the above technical solution, the DC bias circuit provides a fast pulse driving current for the laser diode, so that the laser diode works in a gain switching working state to generate an ultrashort laser pulse output. The frequency of the laser output pulse can be adjusted by changing the frequency of the sinusoidal signal.

[0007] Preferably, the semiconductor laser has a pigtail, and the semiconductor laser is a distributed feedback laser diode.

[0008] Preferably, the polarization-controlled optical fiber, 1X2 optical fiber coupler and adjustable Bragg fiber grating form a two-level frequency-selective cavity.

[0009] By adopting the above technical solution, it is not only possible to suppress the increase of side modes caused by the generation of gain-switched lasers and stabilize the output wavelength of the laser generator, but also to greatly reduce the time jitter of the output pulses of the gain-switched lasers.

[0010] Preferably, the central wavelength of the tunable fiber Bragg grating can be changed by stretching the optical fiber.

[0011] Preferably, the output pigtail of the laser diode is coupled to a polarization controller and then connected to a fiber coupler.

[0012] Preferably, the DC bias circuit is a constant current source circuit or a resistor current limiting circuit.

[0013] As a further solution of the utility model: one side of the RF amplifier is connected to a resistor R1 and an inductor L1, the other end of L1 is connected to the cathodes of two step recovery diodes D1 and D2, the anode of D1 is grounded, and the anode of D2 is connected to the anode of a 14-pin butterfly packaged distributed feedback laser diode with a pigtail after coupling through a capacitor C1. There is also a DC bias current source connected to the anode of the laser diode to provide a bias current slightly below the threshold to the distributed feedback laser diode.

[0014] By adopting the above technical solution, the signal generated by the sinusoidal signal generator is amplified by the RF amplifier and connected to the resistor R1 and the inductor L1. The other end of L1 is connected to the cathodes of the two step recovery diodes D1 and D2. The anode of D1 is grounded, and the anode of D2 is connected to the anode of the 14-pin butterfly packaged distributed feedback laser diode with pigtail after coupling through the capacitor C1. At the same time, a DC bias current source is connected to the anode of the laser diode to provide a bias current slightly lower than the threshold to the distributed feedback laser diode. 50% of the energy is used as the output of the picosecond laser generator from one coupling end, and 50% of the energy is connected to an adjustable Bragg grating from the other coupling end, which emits the laser of the central wavelength back to the secondary cavity formed with the internal reflection surface of the laser diode as the seed light, thereby completing the function of frequency selection and mode stabilization.

[0015] Compared with the prior art, the beneficial effects of the utility model are:

[0016] The utility model proposes a gain-switched picosecond laser generator based on a step recovery diode and a self-stabilizing mode two-stage frequency-selective cavity, which can overcome the problems of too high pulse frequency, narrow range, large output laser pulse time jitter, and spectrum side mode diffusion in the existing gain-switched picosecond laser generation, and greatly improve the stability, reliability and output optical quality of the gain-switched picosecond laser generator. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a structural schematic diagram of an embodiment;

[0018] Figure 2 It is the current pulse waveform diagram;

[0019] Figure 3 Laser output pulse waveform for a system without self-stabilizing mode structure

[0020] Figure 4 It is the laser output pulse waveform of the system with self-stabilizing mode structure. DETAILED DESCRIPTION

[0021] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0022] In the embodiment of the utility model,

[0023] A gain-switched picosecond laser generator comprises a frequency-adjustable sinusoidal signal generator, a radio frequency amplifier, a step recovery diode, a DC bias circuit, a semiconductor laser, a polarization controller, a 1X2 fiber coupler and an adjustable Bragg fiber grating. The sinusoidal signal transmitter, power driver, step recovery diode and DC bias circuit provide a fast pulse drive current for the laser diode.

[0024] The semiconductor laser has a pigtail and is a distributed feedback laser diode.

[0025] The polarization control optical fiber, 1X2 optical fiber coupler and adjustable Bragg optical fiber grating constitute a secondary frequency selection cavity.

[0026] The central wavelength of the tunable fiber Bragg grating can be changed by stretching the optical fiber.

[0027] The output pigtail of the laser diode is coupled to a polarization controller and then connected to a fiber coupler.

[0028] The DC bias circuit is a constant current source circuit or a resistor current limiting circuit.

[0029] One side of the RF amplifier is connected to a resistor R1 and an inductor L1, the other end of L1 is connected to the cathodes of two step recovery diodes D1 and D2, the anode of D1 is grounded, and the anode of D2 is connected to the anode of a 14-pin butterfly packaged distributed feedback laser diode with a pigtail after coupling through a capacitor C1. A DC bias current source is also connected to the anode of the laser diode to provide a bias current slightly below the threshold to the distributed feedback laser diode.

[0030] The sine signal generator can be an external signal generator or a frequency synthesizer included in the circuit. Its typical frequency range is 20MHz to 200MHz, but this range is not a limitation of the frequency range of the utility model.

[0031] The power supply Vd of the radio frequency amplifier is adjustable. Amplification is performed through one or more radio frequency triodes to provide a gain switch operating current of about 200mA for the laser diode. Adjusting the voltage of the power supply Vd can change the amplitude of the sinusoidal signal output by the amplifier, thereby changing the pulse width of the picosecond laser output. In the utility model, the Vd voltage is determined to be 10 to 15V.

[0032] The resistor R1 is a low-value resistor, and its resistance value can be between 0 ohm and 40 ohm. Its function is mainly to provide a certain current limiting and impedance matching function. In practical applications, the resistance value of R1 can be set to 0 ohm.

[0033] The inductor L1 is a low value inductor, and the inductance value is between 5 nanohenries and 20 nanohenries. The picosecond laser pulse width and shape can be fine-tuned by changing the inductance value. In the case where fine-tuning is not required, L1 can be represented by the inductance of the circuit board trace.

[0034] The step recovery diodes D1 and D2 are turned on when forward biased, and when the step recovery diodes are turned from forward biased to reverse biased, they will remain in the on state for a short time before the charge stored in the PN junction is exhausted. Generally, the time for a step recovery diode to transition from the conduction state when reverse biased to the non-conducting state is usually less than 100 picoseconds. When a forward-biased step recovery diode is suddenly reverse-biased, it will initially show near-zero impedance, and then its impedance will quickly rise to its normal high reverse-bias impedance. This extremely fast impedance conversion enables the step recovery diode to be used to generate fast pulses. As an implementation example, D1 and D2 in the utility model use MACOM's MMDB35, which has a typical conversion time of 35 picoseconds.

[0035] The DC bias circuit can be a constant current source circuit or a simple resistor current limiting circuit, and its purpose is to provide a DC bias current lower than the threshold current for the distributed feedback laser diode when the sinusoidal signal is not triggered, so as to facilitate the realization of a shorter pulse output in the gain switching state. As a use example, the threshold current of the distributed feedback laser diode used in the utility model is about 25 mA, so the DC bias can be set at 20 mA.

[0036] The capacitor C1 provides AC coupling for ultrashort pulse and DC biased distributed laser diodes, and its capacitance value can be selected between 22 pF and 47 pF.

[0037] The distributed feedback laser diode can be extended to all semiconductor lasers with pigtails. As a use case, the utility model specifies that the distributed feedback laser diode is for obtaining single-mode, narrow-linewidth picosecond laser pulse output, the specific model is PL-DFB-1064-A-A81-SA, the output wavelength is 1064 nanometers, using 5.5 micron inner core / 125 micron outer diameter single-mode optical fiber, and the continuous output laser power is 40 milliwatts. In other use cases, the wavelength of the distributed feedback laser diode can be 1064nm, 1550nm, 1950nm, or other wavelengths.

[0038] The above description constitutes a use case, such as Figure 2 As shown, after amplification, the sinusoidal signal is converted into a pulse current with a pulse width of 100 to 150 picoseconds by the driving circuit including the step recovery diode, and is coupled with the adjustable DC bias current to achieve gain switching of the distributed feedback laser diode and generate picosecond pulse laser output. When a 100MHz sinusoidal signal and a 40mW 1064nm distributed feedback laser diode PL-DFB-1064-A-A81-SA are used, the peak pulse current is 200mA, the peak power of the laser pulse is 100mW to 150mW, and the typical width of the optical pulse output is 25 to 50 picoseconds.

[0039] The adjustable Bragg fiber grating, together with the fiber coupler and the polarization controller, constitutes a frequency-selective and mode-stabilized secondary cavity. When the distributed feedback laser diode operates in the gain switching mode, its side mode suppression ratio will decrease. By tuning the central wavelength of the fiber grating to the main mode wavelength, the laser of the main mode wavelength can be reflected into the secondary cavity to form a seed light, so that the secondary cavity operates in a self-stabilized mode state similar to mode locking. Such feedback causes the main mode excitation to be higher than the spontaneous radiation noise level, resulting in the laser emission being a strong single mode, which has a good side mode suppression effect.

[0040] The polarization controller forms an independent adjustment wave plate by winding the optical fiber on two or three spools, and uses the stress-induced birefringence effect to change the polarization direction of the transmitted light in the single-mode optical fiber. The power and side mode suppression ratio of the output laser can be maximized by adjusting the polarization state of the laser in the optical fiber. As a use case, the model of the polarization controller used in the utility model is FPC564.

[0041] The 1X2 fiber coupler is used for applications where the input port is divided into two output ports at a specified coupling rate. An example model used in the utility model is TW1064R5A1A, which is designed to use a wavelength of 1064 nanometers and can provide a 50:50 coupling rate. The upper port shown in the figure is used for the output of picosecond pulse lasers, and the lower port is connected to an adjustable Bragg fiber grating to emit the main longitudinal mode laser back to the fiber coupler.

[0042] The center wavelength of the adjustable Bragg fiber grating can be changed by stretching the optical fiber. It forms a frequency-selective and mode-stabilized secondary cavity together with the optical fiber coupler and the polarization controller. When the distributed feedback laser diode operates in the gain switching mode, its side mode suppression ratio will decrease. By tuning the center wavelength of the fiber grating to the main longitudinal mode wavelength, the laser of the main longitudinal mode wavelength can be reflected into the secondary cavity to form seed light. By adjusting the length of the optical fiber forming the secondary cavity according to the frequency of the laser pulse, it can be ensured that the laser pulse injected and the laser pulse generated by the gain switch are synchronized, so that the secondary cavity operates in a self-stabilizing mode state similar to mode locking. An example of the use of the adjustable Bragg fiber grating is RLS / GTL-FBG-TB-890-W1064, with a center wavelength of 1064 nanometers and a bandwidth of 0.5 nanometers. Such feedback causes the main mode excitation to be higher than the spontaneous radiation noise level, resulting in the laser emission being a strong single mode with a good side mode suppression effect.

[0043] As a result of a practical example, the self-stabilizing mode structure described above can improve the side mode suppression of the picosecond pulse laser output generated above by 10 dB to more than 30 dB, and the inter-pulse time jitter is reduced from Figure 3 5 picoseconds shown, reduced to Figure 4 1.5 picoseconds shown.

[0044] Working principle:

[0045] 1. The DC bias circuit provides a fast pulse drive current for the laser diode, so that the laser diode works in a gain switching state to generate ultra-short laser pulse output.

[0046] 2. The frequency of the laser output pulse can be adjusted by changing the frequency of the sinusoidal signal.

[0047] 3. The polarization-controlled fiber, 1X2 fiber coupler and adjustable Bragg fiber grating form a secondary frequency-selective cavity, which can not only suppress the increase of side modes caused by the generation of gain-switched lasers, stabilize the output wavelength of the laser generator, but also greatly reduce the time jitter of the gain-switched laser output pulses.

[0048] 4. The signal generated by the sinusoidal signal generator is amplified by an RF amplifier and connected to resistor R1 and inductor L1. The other end of L1 is connected to the cathodes of two step recovery diodes D1 and D2. The anode of D1 is grounded, and the anode of D2 is coupled through capacitor C1 to the anode of a 14-pin butterfly packaged distributed feedback laser diode with a pigtail. At the same time, a DC bias current source is connected to the anode of the laser diode to provide a bias current slightly below the threshold to the distributed feedback laser diode. The output pigtail of the laser diode is coupled to a polarization controller and then connected to a fiber coupler. 50% of the energy is used as the output of the picosecond laser generator from one coupling end, and 50% of the energy is connected to an adjustable Bragg grating from the other coupling end, which emits the laser of the central wavelength back to the secondary cavity formed with the internal reflection surface of the laser diode as the seed light, thereby completing the function of frequency selection and mode stabilization.

[0049] 5. The adjustable Bragg fiber grating, together with the fiber coupler and polarization controller, forms a frequency-selective and mode-stabilized secondary cavity. When the distributed feedback laser diode operates in the gain switching mode, its side mode suppression ratio will decrease. By tuning the central wavelength of the fiber grating to the main mode wavelength, the laser of the main mode wavelength can be reflected into the secondary cavity to form the seed light, so that the secondary cavity operates in a self-stabilized mode state similar to mode locking. Such feedback causes the main mode excitation to be higher than the spontaneous radiation noise level, resulting in the laser emission being a strong single mode with a good side mode suppression effect.

[0050] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes within the technical scope disclosed by the present invention according to the technical scheme and the utility model concept of the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A gain-switched picosecond laser generator, characterized in that: It includes a frequency-adjustable sinusoidal signal generator, a radio frequency amplifier, a step recovery diode, a DC bias circuit, a semiconductor laser, a polarization controller, a 1X2 fiber coupler and an adjustable Bragg fiber grating. The sinusoidal signal generator, the power driver, the step recovery diode and the DC bias circuit provide a fast pulse drive current for the laser diode.

2. A gain-switched picosecond laser generator according to claim 1, characterized in that: The semiconductor laser has a pigtail and is a distributed feedback laser diode.

3. A gain-switched picosecond laser generator according to claim 1, characterized in that: Polarization control fiber, 1X2 fiber coupler and tunable Bragg fiber grating constitute a two-level frequency-selective cavity.

4. A gain-switched picosecond laser generator according to claim 1, characterized in that: The central wavelength of the tunable fiber Bragg grating can be changed by stretching the optical fiber.

5. A gain-switched picosecond laser generator according to claim 2, characterized in that: The output pigtail of the laser diode is coupled to a polarization controller and then connected to a fiber coupler.

6. A gain-switched picosecond laser generator according to claim 1, characterized in that: The DC bias circuit is a constant current source circuit or a resistor current limiting circuit.

7. The gain-switched picosecond laser generator according to claim 3, characterized in that: One side of the RF amplifier is connected to a resistor R1 and an inductor L1, the other end of L1 is connected to the cathodes of two step recovery diodes D1 and D2, the anode of D1 is grounded, and the anode of D2 is connected to the anode of a 14-pin butterfly packaged distributed feedback laser diode with a pigtail after coupling through a capacitor C1. A DC bias current source is also connected to the anode of the laser diode to provide a bias current slightly below the threshold to the distributed feedback laser diode.

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