Terahertz fiber laser

Abstract

The invention discloses a terahertz fiber laser, which relates to the technical field of terahertz, and comprises a pumping source and an annular light path, and further comprises a doped fiber, a polarization control element and a saturable absorber which are arranged on the annular light path, pumping light emitted by the pumping source excites the doped optical fiber to radiate photons to form spontaneous radiation light, the saturable absorber has a polarization characteristic and is used for converting the received continuous laser into pulse laser, and the polarization control element is used for controlling the polarization state of light of the annular light path. And adjusting the state of the pulse laser output by the annular light path, according to the terahertz fiber laser, the width of the laser pulse emitted by the terahertz fiber laser is adjustable through the saturable absorber with the polarization characteristic, the polarization control element and the like which are arranged in the annular light path, and therefore the requirements for pulse lasers with different pulse widths in various fields such as biological medicine, communication, micromachining, remote sensing and military are met.

Description

Technical Field

[0001] The present invention relates to the field of terahertz technology, and in particular to a terahertz fiber laser. Background Art

[0002] Terahertz waves refer to electromagnetic waves with a frequency of 0.1 to 10 THz. They have many unique advantages, such as being able to penetrate non-metallic materials and non-polarized substances, and having extremely low photon energy. Therefore, they are widely used in medical imaging, security inspections, environmental monitoring, atmospheric remote sensing, and basic physics research. The existing technologies have the following problems:

[0003] Because after the existing terahertz fiber lasers are manufactured, the pulse lasers they output are also determined. When building different terahertz system applications such as the time domain and frequency domain, laser pulses with different pulse widths are required for adjustable dynamic operations, which makes the current terahertz fiber lasers unable to meet the corresponding wide range of terahertz system needs. Summary of the invention

[0004] The present invention provides a terahertz fiber laser to solve the problems raised in the above background technology.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] A terahertz fiber laser comprises a pump source and a ring light path. The terahertz fiber laser further comprises a doped fiber, a polarization control element and a saturable absorber arranged on the ring light path. The pump light emitted by the pump source excites the doped fiber to radiate photons to form spontaneous radiation light. The saturable absorber has polarization characteristics and is used to convert the received continuous laser into pulsed laser. The polarization control element is used to control the polarization state of the light in the ring light path to adjust the state of the pulsed laser output by the ring light path, wherein the pulse widths of the pulsed lasers in different states are different.

[0007] A further improvement of the technical solution of the present invention is that it further includes a first coupling element arranged on the annular optical path, the first coupling element is used to split the received pulsed laser into a feedback laser beam and an output laser beam, the feedback laser beam is used to feed back to the doped optical fiber, and the output laser beam is used as the output of the terahertz fiber laser.

[0008] A further improvement of the technical solution of the present invention is that it further includes a second coupling element arranged on the annular optical path, and the second coupling element is used to combine the received pump light with the feedback laser beam to form a combined light signal, and emit the combined light signal to the doped optical fiber.

[0009] A further improvement of the technical solution of the present invention is that it further includes an isolation element arranged on the annular optical path, and the isolation element is arranged on the optical path between the doped optical fiber and the saturable absorber to make the spontaneous radiation light emitted by the doped optical fiber unidirectionally transmitted to the saturable absorber.

[0010] A further improvement of the technical solution of the present invention is that: the first coupling element is a coupler, the second coupling element is a wavelength division multiplexer, and the isolation element is an isolator.

[0011] A further improvement of the technical solution of the present invention is that it further includes a single-mode optical fiber arranged on the annular optical path, and the single-mode optical fiber is used to enhance the nonlinear polarization rotation effect of the annular optical path.

[0012] A further improvement of the technical solution of the present invention is that: the pump source is a semiconductor pump source, and the doped optical fiber is an erbium-doped gain optical fiber.

[0013] A further improvement of the technical solution of the present invention is that: the polarization control element comprises a first polarization controller and a second polarization controller, and a three-dimensional graphene-micro-nano optical fiber integrated device is arranged on the optical path between the first polarization controller and the second polarization controller;

[0014] The further improvement of the technical solution of the present invention is that: the three-dimensional graphene-micro-nano optical fiber integrated device comprises a support rod, the outer surface of the support rod is covered with a graphene film and a micro-nano optical fiber, the micro-nano optical fiber is non-overlappingly wrapped around the surface of the graphene film, and Teflon polymer films are arranged on both sides of the graphene film;

[0015] A further improvement of the technical solution of the present invention is that the pulse laser output by the annular optical path includes a Q-switched pulse laser and a rectangular wave mode-locked pulse laser.

[0016] Due to the adoption of the above technical solution, the present invention has the following technical advances compared with the prior art:

[0017] 1. The present invention provides a terahertz fiber laser. By arranging a saturable absorber and a polarization control element with polarization characteristics in a ring optical path, the pulse width of the laser emitted by the terahertz fiber laser can be adjusted, thereby meeting the needs for pulse lasers with different pulse widths in various fields such as biomedicine, communications, micromachining, remote sensing and military. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the module structure of the terahertz fiber laser;

[0019] Figure 2 Schematic diagram of the structure of terahertz fiber laser;

[0020] Figure 3 Schematic diagram of the structure of the saturable absorber of the present invention.

[0021] In the figure: 21, semiconductor pump source; 22, wavelength division multiplexer; 23, erbium-doped gain fiber; 24, isolator; 25, first polarization controller; 26, three-dimensional graphene-micro-nano optical fiber integrated device; 261, support rod; 262, Teflon polymer film; 263, graphene film; 264, micro-nano optical fiber; 27, second polarization controller; 28, single-mode optical fiber; 29, coupler. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below in conjunction with embodiments:

[0023] Example 1

[0024] like Figure 1As shown, the present invention provides a terahertz fiber laser, a terahertz fiber laser, which may include a ring optical path and a pump source, as well as components such as a doped fiber, a saturable absorber with polarization characteristics, and a polarization control element arranged on the ring optical path. The pump source can be used to emit pump light into the ring optical path, and the doped fiber is stimulated by the pump light emitted by the pump source to radiate photons and then form spontaneous radiation light, that is, under the action of the above pump light, the energy level of the rare earth ions in the doped fiber is increased, and when the high-energy-level rare earth ions transition to a low-energy-level state, photons are radiated outward, and then spontaneous radiation light can be formed, and continuous laser can be formed through the action of the resonant cavity;The saturable absorber performs mode-locking operation on the continuous laser emitted by the above-mentioned doped optical fiber to form a pulsed laser. The polarization control element can control the feedback state of the annular optical path, and the state of the pulsed laser output by the annular optical path in the positive feedback state or the negative feedback state is different. That is, by adjusting the polarization control element, the annular optical path as a resonant cavity is in different feedback states, and then the state of the pulsed laser emitted by the annular optical path can be adjusted. For example, the annular optical path can be in different feedback states by adjusting the polarization control element, and then the pulsed laser output by the terahertz fiber laser can be adjusted. The terahertz fiber laser can switch between Q pulse laser and rectangular wave mode-locked pulse laser. The terahertz fiber laser can further include a first coupling element for splitting the received pulse laser. The first coupling element can be a device with optical signal splitting function such as an optical fiber coupler. The first coupling element can split the pulse laser adjusted by the polarization control element into an outgoing laser beam and a feedback laser beam. The outgoing laser beam is output through the first output port of the first coupling element as the output laser of the terahertz fiber laser. The feedback laser beam is emitted to the doped optical fiber through the second output port of the first coupling element as the doped optical fiber. The terahertz fiber laser can further include a second coupling element for combining the received optical signal, and the second coupling element can be a device with an optical signal combining function such as a wavelength division multiplexer. The second coupling element can combine the pump light emitted by the pump source with the feedback laser beam emitted by the first coupling element to form a combined optical signal, and send the combined optical signal to the doped optical fiber, thereby more efficiently stimulating the doped optical fiber to radiate photons to form a more stable laser beam. The terahertz fiber laser can also be further The first step includes an isolation element for enabling unidirectional transmission of optical signals in a ring optical path. The isolation element may be a device such as a polarization-independent isolator that enables unidirectional transmission of optical signals. The isolation element may be arranged on the optical path between the doped optical fiber and the saturable absorber. Since the doped optical fiber is excited to generate laser light that propagates in all directions, the return light is isolated by the isolation element, thereby ensuring unidirectional propagation of the pulsed laser light. That is, the isolation element may enable the pulsed laser light emitted from the doped optical fiber to propagate along the ring optical path toward the saturable absorber, thereby improving the optical performance of the terahertz fiber laser. ;

[0025] In this embodiment, since the saturable absorber with polarization characteristics on the annular optical path can realize two laser pulse state operations at the same time, the annular optical path is placed in different feedback states by adjusting the polarization control element, so that the terahertz fiber laser can output pulse lasers in different states. Since the pulse lasers in different states have different pulse widths, the terahertz fiber laser outputs pulse lasers with different pulse widths to meet the terahertz system's demand for pulse lasers with different pulse widths. The above-mentioned pump source can be a semiconductor pump source, such as a 980nm semiconductor pump source or a 1480nm semiconductor pump source; the doped optical fiber can be an erbium-doped gain optical fiber such as OFS EDF80, and the corresponding erbium atoms in the doped optical fiber undergo transitions to radiate photons to form lasers with a wavelength of 1550nm.

[0026] Example 2

[0027] like Figure 1 As shown, on the basis of Example 1, the present invention provides a technical solution: preferably, the terahertz fiber laser may further include a single-mode optical fiber for enhancing the nonlinear polarization rotation effect of the annular optical path, the polarization control element may include a first polarization controller and a second polarization controller, and a saturable absorber is arranged on the annular optical path between the first polarization controller and the second polarization controller to improve the adjustment accuracy of the polarization controller for the pulse width of the pulsed laser output by the terahertz fiber laser, and the saturable absorber may include a support rod with a graphene film covered on the outer surface and non-overlapping micro-nano optical fibers wound on the surface of the graphene film. Since graphene has a wide-spectrum absorption characteristic and the micro-nano optical fiber has a large evanescent field, the three-dimensional device formed by winding the micro-nano optical fiber can be used as a saturable absorber with polarization characteristics.

[0028] In this embodiment, based on the annular optical path that can be used as a resonant cavity, the pump light emitted by the pump source is transmitted to the doped optical fiber through the second coupling element. The doped optical fiber is stimulated by the pump light to radiate photons to form spontaneous radiation light. The spontaneous radiation light can form a continuous laser that propagates in all directions after being acted on by the resonant cavity. After the isolation element isolates the laser propagating in the opposite direction on the annular optical path, a unidirectional continuous laser that propagates along the doped optical fiber toward the saturable absorber is formed in the annular optical path. The saturable absorber converts the incident unidirectional continuous laser into a pulsed laser, and because the saturable absorber has a polarization characteristic, a pulsed laser can be formed in two mode-locked modes at the same time. The polarization control element can be adjusted so that the annular optical path is in a positive feedback state or a negative feedback state, so as to correspondingly convert the doped The pulsed laser emitted from the optical fiber is converted into a Q-switched pulse or a rectangular wave mode-locked pulse; the first coupling element converts the above-mentioned pulsed laser into a Q-switched pulse and a rectangular wave mode-locked pulse for beam splitting to form an output laser and a feedback laser, the output laser is emitted to the outside through the first output port as the output of the terahertz fiber laser, and the feedback laser is sent to the second coupling element through the second output port; the second coupling element combines the pump light emitted by the pump source with the above-mentioned feedback laser and emits them into the doped optical fiber, which can effectively improve the quality and efficiency of the spontaneous radiation light generated by the doped optical fiber under stimulation, wherein the nonlinear polarization rotation effect of the annular optical path can also be improved by arranging a single-mode optical fiber on the annular optical path, so as to further improve the stability of the pulsed laser output by the terahertz fiber laser.

[0029] Example 3

[0030] like Figure 2 , Figure 3As shown, the present invention provides a terahertz fiber laser: comprising a semiconductor pump source 21, a wavelength division multiplexer 22, an erbium-doped gain fiber 23, an isolator 24, a first polarization controller 25, a three-dimensional graphene-micro-nano fiber integrated device 26, a second polarization controller 27, a single-mode fiber 28 and a coupler 29 connected in sequence; the output end d of the coupler 29 is connected to the wavelength division multiplexer 22, so that the wavelength division multiplexer 22, the erbium-doped gain fiber 23, the isolator 24, the first polarization controller 25, as a saturable absorber The three-dimensional graphene-micro-nano optical fiber integrated device 26, the second polarization controller 27, the single-mode optical fiber 28 and the coupler 29 together constitute a ring-shaped resonant cavity, wherein the output end c of the coupler 29 serves as the pulse laser output port of the terahertz fiber laser, and the three-dimensional graphene-micro-nano optical fiber integrated device 26 may include a support rod 261, a Teflon polymer film 262, a graphene film 263 and a micro-nano optical fiber 264; the Teflon polymer film 262 covers the outer surface of the support rod 261, and is transferred to the Teflon polymer film 262 on the surface of the support rod 261. A graphene film 263 is formed on the exposed surface of the fluoropolymer film 262, and a micro-nano optical fiber 264 is wound on the surface of the graphene film 263; wherein the support rod 261 is made of polymethyl methacrylate. Since the micro-nano optical fiber 264 is wound on the support rod 261 to which the graphene film 263 is transferred, the interaction distance between the graphene and the light field can be effectively increased, thereby improving the optical performance of the terahertz fiber laser. Since the micro-nano optical fiber 264 has a strong evanescent field and the micro-nano optical fiber The direction of one of the two electric fields in 264 is parallel to the extension direction of the graphene film 263, and the direction of the other electric field is perpendicular to the transmission and action direction of the graphene, which will make the transmission loss of the laser of the micro-nano optical fiber 264 in the two electric field directions different, thereby producing a distinct extinction ratio. At the same time, since the graphene film 263 has better wide-spectrum absorption characteristics and excellent saturable absorption characteristics, the three-dimensional graphene-micro-nano optical fiber integrated device 26 can be regarded as a saturable absorption device with polarization characteristics.

[0031] In this embodiment, the connection between the various components in the terahertz fiber laser can be directly connected through ports or through single-mode optical fibers to achieve the transmission of optical signals in an all-optical fiber structure. At the same time, the various components in the terahertz fiber laser can be connected by fusion splicing optical fibers to effectively avoid the generation of reflected light in the ring light path, so as to further improve the optical performance of the terahertz fiber laser.

[0032] Example 4

[0033] like Figure 2 , Figure 3As shown, on the basis of Example 3, the present invention provides a technical solution: preferably, the length of the erbium-doped gain fiber 23 can be about 7m. In order to ensure that the terahertz fiber laser has better stability, the difference between the two extreme values ​​of the length range of the erbium-doped gain fiber 23 does not exceed 2m; for example, the length range of the erbium-doped gain fiber 23 can be 6.5-7.5m, that is, the length of the erbium-doped gain fiber 23 can be specifically 6.5m, 6.8m, 7m, 7.3m or 7.5m, etc., and the length of the single-mode fiber 28 can be about 220m. Similarly, in order to ensure that the terahertz fiber laser has better stability, the difference between the two extreme values ​​of the length range of the single-mode fiber 28 should not exceed 2m; for example, the length range of the single-mode fiber 28 can be 219.5m-220.5m, that is, the length of the single-mode fiber 28 The specific length can be 219.5m, 219.8m, 220m, 220.3m or 220.5m, etc. The coupler 29 can be an optical fiber coupler with an output ratio of 10%, that is, the ratio of the pulsed laser power output by the output end c of the coupler 29 to the pulsed laser power output by the output end d of the coupler 29 is 1:9, which can also be understood as the ratio of the power of the outgoing laser beam formed by the beam splitting of the coupler 29 to the power of the feedback laser beam is 1:9. In another optional embodiment, the coupler 29 can be an optical fiber coupler with an output ratio of 30%, that is, the ratio of the pulsed laser power output by the output end c of the coupler 29 to the pulsed laser power output by the output end d of the coupler 29 is 3:7, which can also be understood as the ratio of the power of the outgoing laser beam formed by the beam splitting of the coupler 29 to the power of the feedback laser beam is 3:7.

[0034] In this embodiment, in the terahertz fiber laser, the transmission coefficient formula of nonlinear polarization rotation can be expressed as: Where △φ=△φ PC +△φ LB +△φ NL is the total phase delay between the fast axis and the slow axis of the optical fiber, △φPC is the delay introduced by the polarization controller, and △φ NL =-2γLPcos(2θ) / 3 is the nonlinear phase change introduced by the fiber nonlinearity, △φ LB =2πLB m / λ is the linear phase shift introduced by the birefringence of the optical fiber, θ and φ are the angles between the polarizer and the analyzer and the fast axis of the optical fiber respectively. When the optical path of the terahertz fiber laser is completed, θ and φ can be regarded as a constant. Therefore, the transmission coefficient formula of the above nonlinear polarization rotation can be simplified to: |T|2~cos(△φPC+△φLB+△φNL), that is, when the optical signal is transmitted in the laser cavity based on the nonlinear polarization rotation structure, the loss of the cavity has a very large relationship with the phase delay. At the same time, due to the three-dimensional structure of the graphene-micro-nano optical fiber integrated device 26, it has both saturable absorption characteristics and polarization characteristics, that is, Figure 2 The terahertz fiber laser shown can generate two kinds of mode locking modes at the same time, so by adjusting Figure 2 The first polarization controller 25 and / or the second polarization controller 27 shown in the figure can realize the laser resonant cavity (i.e., the ring optical path) working in the positive feedback or negative feedback region, that is, the feedback state in the terahertz fiber laser can be changed by modulating the polarization controller, and then on the basis of the graphene-micro-nano fiber integrated device 26 based on the three-dimensional structure, the pulse laser output by the terahertz fiber laser can be switched between the Q-switched pulse laser and the rectangular wave mode-locked pulse laser. In addition, since there is a certain actual polarization contrast between the graphene-micro-nano fiber in the terahertz fiber laser, the effect of nonlinear polarization rotation in the laser can be enhanced by increasing the length of the single-mode fiber. For example, when Figure 2 When the three-dimensional graphene-micro-nano optical fiber integrated device 26 shown in the figure has an actual polarization contrast of about 2 dB, a single-mode optical fiber 28 with a length of about 220 m can be used to further enhance the effect of nonlinear polarization rotation in the terahertz fiber laser, thereby improving the stability of the terahertz fiber laser.

[0035] The working principle of the terahertz fiber laser is described in detail below.

[0036] like Figure 1-3 As shown, by arranging a saturable absorber and a polarization control element with polarization characteristics in the annular optical path, the laser pulse width emitted by the terahertz fiber laser can be adjusted, thereby meeting the needs for pulse lasers with different pulse widths in various fields such as biomedicine, communications, micromachining, remote sensing and military.

[0037] The above generally describes the present invention in detail, but it is obvious to a person skilled in the art that some modifications or improvements can be made to the present invention. Therefore, modifications or improvements that do not depart from the spirit of the present invention are within the scope of protection of the present invention.

Claims

1. A terahertz fiber laser, comprising a pump source and a ring optical path, characterized in that: The terahertz fiber laser further includes a doped optical fiber, a polarization control element and a saturable absorber arranged on the annular optical path. The pump light emitted by the pump source excites the doped optical fiber to radiate photons to form spontaneous radiation light. The saturable absorber has polarization characteristics and is used to convert the received continuous laser into a pulsed laser. The polarization control element is used to control the polarization state of the light in the annular optical path to adjust the state of the pulsed laser output by the annular optical path, wherein the pulse widths of the pulsed lasers in different states are different.

2. A terahertz fiber laser according to claim 1, characterized in that: It further includes a first coupling element arranged on the annular optical path, the first coupling element is used to split the received pulsed laser into a feedback laser beam and an output laser beam, the feedback laser beam is used to feed back to the doped optical fiber, and the output laser beam is used as the output of the terahertz fiber laser.

3. A terahertz fiber laser according to claim 2, characterized in that: It further comprises a second coupling element arranged on the annular optical path, the second coupling element is used for combining the received pump light with the feedback laser beam to form a combined light signal, and emitting the combined light signal to the doped optical fiber.

4. A terahertz fiber laser according to claim 3, characterized in that: The method further comprises an isolation element arranged on the annular optical path, wherein the isolation element is arranged on the optical path between the doped optical fiber and the saturable absorber so as to make the spontaneous radiation light emitted from the doped optical fiber be transmitted unidirectionally to the saturable absorber.

5. A terahertz fiber laser according to claim 4, characterized in that: The first coupling element is a coupler, the second coupling element is a wavelength division multiplexer, and the isolation element is an isolator.

6. The terahertz fiber laser according to claim 1, characterized in that: It further includes a single-mode optical fiber arranged on the annular optical path, and the single-mode optical fiber is used to enhance the nonlinear polarization rotation effect of the annular optical path.

7. The terahertz fiber laser according to claim 1, characterized in that: The pump source is a semiconductor pump source, and the doped optical fiber is an erbium-doped gain optical fiber.

8. The terahertz fiber laser according to claim 1, characterized in that: The polarization control element comprises a first polarization controller and a second polarization controller, and a three-dimensional graphene-micro-nano optical fiber integrated device is arranged on the optical path between the first polarization controller and the second polarization controller.

9. A terahertz fiber laser according to any one of claims 1 to 8, characterized in that: The three-dimensional graphene-micro-nano optical fiber integrated device comprises a support rod, the outer surface of which is covered with a graphene film and a micro-nano optical fiber, the micro-nano optical fiber is non-overlappingly wrapped around the surface of the graphene film, and Teflon polymer films are arranged on both sides of the graphene film.

10. A terahertz fiber laser according to any one of claims 1 to 8, characterized in that: The pulse laser output by the annular optical path includes Q-switched pulse laser and rectangular wave mode-locked pulse laser.

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