Laser-induced graphene electrically tunable passively mode-locked fiber laser

Abstract

The present invention discloses an electrically tunable passively mode-locked fiber laser based on laser-induced graphene, belonging to the technical field of mode-locked fiber lasers. The laser comprises: a semiconductor pump source, a wavelength division multiplexer, an erbium-doped gain fiber, a Co2+:ZnS saturable absorber, a polarization controller, an optical isolator, an optical coupler, a laser-induced graphene electrically tunable device, and a direct current power supply. The laser-induced graphene electrically tunable device consists of a laser-induced graphene electrode and a long-period fiber grating (LPFG). The laser is stably mode-locked by utilizing the saturable absorber properties of the Co2+:ZnS material. Simultaneously, the graphene electrode converts the electrical energy of the DC power supply into thermal energy. Temperature changes in the graphene electrode cause changes in the transmission spectrum of the long-period fiber grating, thereby achieving output wavelength tuning of the mode-locked laser. The wavelength-tunable mode-locked laser has the advantages of simple preparation, low cost, fast tuning speed, high tuning accuracy, ease of use, and an all-optical structure, making it easy to industrialize and apply.

Description

Technical Field

[0001] The present invention relates to the field of ultrafast fiber lasers, and in particular to a laser-induced graphene electrically tuned passively mode-locked fiber laser. Background Art

[0002] Wavelength-tunable mode-locked fiber lasers have been widely used in fields such as sensing, spectral analysis, biomedical research, materials processing, and optical communication networks. As communication capacity increases, coherent optical communications require greater bandwidth and transmission speeds, placing increasing demands on the laser's linewidth and tuning speed. The application of tunable mode-locked fiber lasers in modern optical communication systems not only reduces costs but also achieves higher transmission rates, providing strong technical support for the future development of high-rate dense wavelength division multiplexing systems and coherent optical communications.

[0003] Traditional wavelength tuning methods often control the net gain of the laser cavity by controlling the loss within the cavity. However, this loss affects the overall effective cavity gain, potentially disrupting stable mode-locking. Furthermore, several existing all-fiber optical filters suffer from shortcomings such as a small tuning range, low damage threshold, complex fabrication processes, and high cost. Utility Model Content

[0004] The present invention aims to provide a tunable passively mode-locked fiber laser with a simple structure, a large tuning range, a fast tuning speed, a low cost, and a stable output. The spectral shift is approximately 14.63 nm.

[0005] The present invention adopts the following technical solutions:

[0006] A laser-induced graphene electrically tunable passively mode-locked fiber laser comprises: a semiconductor pump source; the semiconductor pump source is sequentially connected to an input end of a wavelength division multiplexer, an erbium-doped gain fiber, a tapered Co2+:ZnS thin film saturable absorber, a polarization controller, a polarization-independent optical isolator, an optical coupler, and a laser-induced graphene electrically tunable device; the laser-induced graphene electrically tunable device is then connected to an output end of the wavelength division multiplexer, thereby forming a ring resonant cavity to achieve mode-locked laser output; the semiconductor pump source serves as a light source, which is coupled into the erbium-doped gain fiber through the wavelength division multiplexer, and the erbium-doped gain fiber serves as a gain medium of the fiber laser; when the pump light is incident on the erbium-doped gain fiber, spontaneous radiation and stimulated radiation occur to emit photons; the tapered Co2+:ZnS thin film saturable absorber is a mode-locked device based on evanescent waves, and serves as an optical modulator in the resonant cavity to emit light during the mode-locking process. It plays an important role in periodically modulating the loss in the resonant cavity to achieve mode-locked laser output; by adjusting the polarization controller, the polarization state of the optical fiber can be changed, and the transmission state of light in the cavity can be changed; the polarization-independent isolator ensures the unidirectional transmission of the laser in the cavity, suppressing the adverse effects of reflected light waves on the light source; the optical coupler divides the light wave in the cavity into two paths, one is connected to the subsequent laser-induced graphene electric tuning device, so that the light wave continues to be transmitted and amplified in the fiber laser cavity, and the other light wave serves as the output end of the mode-locked laser; the laser-induced graphene electric tuning device consists of a laser-induced graphene electrode and a long-period fiber grating, which is used to adjust the loss of light waves of different wavelengths in the cavity to achieve tuning of the output wavelength of the mode-locked laser; the graphene electrode can convert the electrical energy of the DC power supply into thermal energy to achieve precise temperature control; the long-period fiber grating is used as a narrowband filter device, and its transmission spectrum is controlled by temperature. The graphene electrode acts as a temperature control source, converting the electrical energy of the DC power supply into thermal energy to achieve precise temperature control. The temperature control is further transmitted to the long-period fiber grating. The wavelength shift of the long-period fiber grating caused by temperature control can be expressed as follows: Indicates, where λ0 is the center wavelength, Λ is the grating period, and n co and are the effective refractive indices of the core fundamental mode and the mth mode of the cladding, respectively, and T is the temperature. The wavelength shift caused by the temperature effect on long-period fiber gratings is due to the thermo-optical effect (the first term on the right) and the thermal expansion of the grating period (the second term on the right). In standard optical fibers, the thermo-optic coefficient of the core layer composed of SiO2+GeO2 is greater than that of the cladding composed solely of SiO2, resulting in a wavelength shift toward longer wavelengths. Furthermore, the tapered Co2+:ZnS thin film saturable absorber is a passive mode-locking device based on evanescent waves. It is fabricated by vacuum coating Co2+:ZnS material onto a micro-nano fiber cone with a beam waist diameter of 10μm to 30μm.

[0007] Furthermore, the output wavelength of the semiconductor pump source is 976 nm.

[0008] Furthermore, the cavity loss-related gain spectrum and spectral filtering effect are changed by rotating the knob of the intracavity polarization controller.

[0009] Furthermore, the laser-induced graphene electrically tunable device is composed of a laser-induced graphene electrode and a long-period fiber grating.

[0010] Furthermore, the graphene electrode is formed by writing a pattern on a commercially available polyimide (PI) film using a carbon dioxide (CO2) laser.

[0011] Furthermore, the operating wavelength of the long-period fiber grating is 1520 nm to 1580 nm.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] 1. A tapered Co2+:ZnS saturable absorber and nonlinear polarization rotation effect are introduced into the fiber laser cavity. By rationally adjusting the polarization controller, the cavity loss-related gain spectrum and spectral filtering effect are changed to obtain stable ultrashort pulse output.

[0014] 2. The laser-induced graphene electric tunable device proposed in the present invention has the characteristics of simple preparation, low cost, fast tuning speed and high tuning accuracy. Its application in mode-locked fiber lasers can achieve wide-range wavelength tuning.

[0015] 3. The laser-induced graphene electrically tunable passively mode-locked fiber laser proposed in the present invention adopts an all-fiber structure, has high stability and strong repeatability, and provides a new technical solution for spectrally tunable mode-locked fiber lasers. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic diagram of the preparation process of the laser-induced graphene electric tunable device adopted in the present invention;

[0017] Figure 2 This is a schematic structural diagram of the laser-induced graphene electric tunable device used in the present invention;

[0018] Figure 3 This is a structural diagram of the laser-induced graphene electrically tunable passively mode-locked fiber laser used in the present invention;

[0019] Figure 4 is a graph showing the relationship between the transmission spectrum of the long-period fiber grating of the present invention and the change in voltage;

[0020] Figure 5Characteristic diagram of the fundamental frequency mode-locked pulse generated by the laser-induced graphene electrically tunable passively mode-locked fiber laser used in the present invention, (a) is the spectrum diagram of the fundamental frequency mode-locked pulse, (b) is the radio frequency spectrum diagram, and (c) is the pulse sequence diagram.

[0021] Figure 6 This is a spectrum shift diagram of the laser-induced graphene electrically tuned passively mode-locked fiber laser used in the present invention.

[0022] Glossary: ​​Pump Laser: semiconductor pump source, WDM: wavelength division multiplexer, EDF: erbium-doped fiber, Co2+:ZnS: zinc sulfide-doped cobalt ion saturable absorber, PC: polarization controller, ISO: polarization-independent isolator, OC: coupler, LPFG: long-period fiber grating, SMF: single-mode fiber, PI: polyimide, DC: direct current power supply. DETAILED DESCRIPTION

[0023] The following detailed description of specific embodiments of the present invention is provided in conjunction with the technical solutions and accompanying drawings. Those skilled in the art will readily appreciate the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention.

[0024] like Figure 1 As shown in the figure, the fabrication process for the laser-induced graphene electrically tunable device provided by the present invention involves a computer-controlled CO2 laser cutting system that transforms the surface of a PI sheet into porous graphene under laser induction. The dark contrast represents the LIG after exposure to the laser, while the lighter background corresponds to the PI. The laser power used to create the pattern, which consists of two 10x5mm rectangles separated by 10mm, was 3.5W. Conductive silver paste was used to connect copper wires to the ends of the graphene to create graphene electrodes.

[0025] like Figure 2 As shown in FIG, a schematic structural diagram of the laser-induced graphene electric tunable device provided by the present invention, a long-period fiber grating is placed in the middle of an electrode, and a MS1201D DC power supply is used to provide different voltages at both ends of the electrode.

[0026] like Figure 3 As shown, the laser-induced graphene electrically tuned passively mode-locked fiber laser provided by the present invention comprises: a semiconductor pump source (1), the semiconductor pump light source (1) is sequentially connected to a 980 / 1550 nm wavelength division multiplexer (2), a gain medium (3), a tapered Co2+:ZnS thin film saturable absorber mode-locked device (4), a polarization control device (5), a polarization-independent optical isolator (6), an output coupling device (7), a laser-induced graphene electrically tuned device (8) and a single-mode optical fiber;

[0027] A semiconductor pump source is used as the light source, which is coupled into the erbium-doped fiber through a wavelength division multiplexer. The erbium-doped fiber serves as the gain medium of the fiber laser. When the pump light is incident on the erbium-doped gain fiber, spontaneous radiation and stimulated radiation will occur to emit photons. The tapered Co2+:ZnS thin film saturable absorber is a mode-locked device based on the evanescent wave. As an optical modulator in the resonant cavity, it plays an important role in the mode-locking process. It can periodically modulate the loss in the resonant cavity to achieve mode-locked laser output. By adjusting the polarization controller, the polarization state of the optical fiber can be changed, and the transmission state of the light in the cavity can be changed. The polarization-independent isolator is used to ensure that the laser is locked in the cavity. One-way transmission suppresses the adverse effects of reflected light waves on the light source; the optical coupler divides the light wave in the cavity into two paths, one path is connected to the subsequent laser-induced graphene electric tuning device, so that the light wave continues to be transmitted and amplified in the fiber laser cavity, and the other light wave serves as the output end of the mode-locked laser; the laser-induced graphene electric tuning device is composed of a laser-induced graphene electrode and a long-period fiber grating, which is used to adjust the loss of light waves of different wavelengths in the cavity to achieve tuning of the output wavelength of the mode-locked laser; the graphene electrode can convert the electrical energy of the DC power supply into thermal energy to achieve precise temperature control; the long-period fiber grating is used as a narrowband filter device, and its transmission spectrum is controlled by temperature. As a temperature control source, the graphene electrode converts the electrical energy of the DC power supply into thermal energy to achieve precise temperature control. The temperature control is further transmitted to the long-period fiber grating. The wavelength shift of the long-period fiber grating caused by the temperature control can be expressed as follows: Indicates, where λ0 is the center wavelength, Λ is the grating period, and n co and are the effective refractive indices of the core fundamental mode and the mth mode of the cladding, respectively, and T is the temperature. The wavelength shift caused by temperature on a long-period fiber grating is due to the thermo-optical effect (the first term on the right) and the thermal expansion of the grating period (the second term on the right). In standard optical fibers, the thermo-optic coefficient of the core (composed of SiO2 + GeO2) is greater than that of the cladding (composed solely of SiO2), resulting in a wavelength shift toward longer wavelengths.

[0028] like Figure 4 FIG. 1 is a diagram showing the relationship between the transmission spectrum of the long-period fiber grating of the present invention and the change in voltage. It can be seen that when the voltage gradually increases and the temperature gradually rises, the transmission spectrum undergoes a red shift.

[0029] like Figure 5 As shown in FIG, the characteristic diagram of the fundamental frequency mode-locked pulse generated by the laser-induced graphene electrically tunable passively mode-locked fiber laser of the present invention. When the pump power reaches 400mW, a stable mode-locked pulse can be generated, and the pulse spectrum is as follows: Figure 3 As shown in (a), the central wavelength is 1549.13nm, the 3dB bandwidth is 3.26nm, and the Kelly sidebands in the spectrum are typical traditional soliton outputs. Figure 3 (b) is a radio frequency spectrum diagram, showing a frequency signal-to-noise ratio (SNR) of approximately 51dB, indicating that the present invention produces highly stable mode-locked pulses. The corresponding fundamental frequency repetition frequency is approximately 13.08MHz. According to the relationship between the fundamental frequency mode-locked pulse repetition frequency and the laser cavity length: f = c / n L, where f and L are the fundamental frequency repetition frequency and the cavity length of the fiber laser, respectively, c is the speed of light, and n is the refractive index of the fiber. It can be seen that the pulse fundamental frequency repetition frequency of 13.08MHz is consistent with the laser cavity length of 15.7m. As shown in Figure 3 (c), the mode-locked soliton timing diagram and the soliton intensity are basically consistent, reflecting that the fiber laser output fundamental frequency mode-locked solitons are relatively stable.

[0030] like Figure 6 The figure shows the spectrum produced by the laser-induced graphene electrically tunable passively mode-locked fiber laser of the present invention as a function of voltage. Increasing the voltage modulates the losses within the cavity, thereby tuning the output wavelength of the mode-locked laser. Increasing DC1 from 0V to 6V shifts the spectrum from a central wavelength of 1549nm to 1550.98nm. Keeping DC1 constant at 6V and increasing DC2 from 0V to 6V shifts the spectrum again to 1563.63nm. The total spectral shift is approximately 14.63nm.

Claims

1. A laser-induced graphene electrically tunable passively mode-locked fiber laser, characterized in that: include: Semiconductor pump source; The semiconductor pump source is connected in sequence to the input of the wavelength division multiplexer, the erbium-doped gain fiber, the tapered Co 2+ : ZnS thin film saturable absorber, polarization controller, polarization-independent optical isolator, optical coupler, laser-induced graphene electric tunable device, the laser-induced graphene electric tunable device is then connected to the output end of the wavelength division multiplexer to form a ring resonator to achieve mode-locked laser output; a semiconductor pump source is used as the light source, and the light source is coupled into the erbium-doped gain fiber through the wavelength division multiplexer. The erbium-doped gain fiber serves as the gain medium of the fiber laser. When the pump light is incident on the erbium-doped gain fiber, spontaneous radiation and stimulated radiation will occur to emit photons; a tapered Co 2+ : ZnS thin film saturable absorber is a mode-locked device based on evanescent wave. As an optical modulator in the resonant cavity, it plays an important role in the mode-locking process. It can periodically modulate the loss in the resonant cavity to achieve mode-locked laser output. By adjusting the polarization controller, the polarization state of the optical fiber can be changed, and the transmission state of the light in the cavity can be changed. The polarization-independent isolator is used to ensure the unidirectional transmission of the laser in the cavity, suppressing the adverse effects of the reflected light wave on the light source. The optical coupler divides the light wave in the cavity into two paths, one of which is connected to the subsequent laser-induced graphene electrical tunable device, so that the light wave continues to be transmitted and amplified in the fiber laser cavity, and the other light wave is used as the mode-locked laser. The output end of the optical device; the laser-induced graphene electric tunable device consists of a laser-induced graphene electrode and a long-period fiber Bragg grating, which is used to adjust the loss of light waves of different wavelengths in the cavity to achieve tuning of the output wavelength of the mode-locked laser; the graphene electrode can convert the electrical energy of the DC power supply into thermal energy to achieve precise temperature control; the long-period fiber Bragg grating is used as a narrowband filter device, and its transmission spectrum is controlled by temperature; the graphene electrode is used as a temperature control source to convert the electrical energy of the DC power supply into thermal energy to achieve precise temperature control, and the temperature control is further transmitted to the long-period fiber Bragg grating. The wavelength shift of the long-period fiber Bragg grating caused by temperature control can be expressed by the formula Indicates, where λ0 is the center wavelength, Λ is the grating period, and n co and are the effective refractive indices of the core fundamental mode and the m-th mode of the cladding, respectively; T is the temperature. The wavelength shift caused by the temperature effect on the long-period fiber grating is caused by the thermo-optical effect (the first term on the right) and the thermal expansion of the grating period (the second term on the right); in standard optical fibers, the thermo-optic coefficient of the core layer composed of SiO2+GeO2 is greater than that of the cladding composed only of SiO2, so the wavelength will shift to a longer wavelength.

2. The laser-induced graphene electrically tunable passively mode-locked fiber laser according to claim 1, characterized in that ,The semiconductor pump source is a 976nm semiconductor laser with a pigtail.

3. The laser-induced graphene electrically tunable passively mode-locked fiber laser according to claim 1, characterized in that , the wavelength division multiplexer is a 980 / 1550nm wavelength division multiplexer.

4. The laser-induced graphene electrically tunable passively mode-locked fiber laser according to claim 1, characterized in that: Conical Co 2+ ZnS thin film saturable absorber is a mode-locked device based on evanescent wave, which is made by vacuum coating technology to 2 + : A passive mode-locked device is prepared by depositing ZnS material onto a micro-nano fiber cone with a beam waist diameter of 10μm to 30μm.

5. The laser-induced graphene electrically tunable passively mode-locked fiber laser according to claim 1, characterized in that The graphene electrodes were formed by writing patterns on a commercially available polyimide (PI) film using a carbon dioxide (CO2) laser.

6. The laser-induced graphene electrically tunable passively mode-locked fiber laser according to claim 1, characterized in that The operating wavelength of long-period fiber grating is 1520nm~1580nm.

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