Nonlinear fiber loop and all-normal dispersion pump-protected figure-eight cavity and laser

Abstract

The application belongs to the technical field of ultra-short pulse laser, and particularly relates to a nonlinear fiber loop and full positive dispersion pump protection type 8-shaped cavity and a laser. The nonlinear fiber loop comprises a first circulator provided with three ports, a second circulator provided with three ports and a beam combiner. The first port of the first circulator is used to connect the third port of a coupler, the second port of the first circulator is connected with the third port of the second circulator, and the third port of the first circulator is connected with the output end of the beam combiner. The first port of the second circulator is used to connect the fourth port of the coupler through a first gain fiber, the second port of the second circulator is connected with the signal end of the beam combiner, and the first input end of the beam combiner is connected with a first pump light source.

Description

Technical Field

[0001] This invention belongs to the field of ultrashort pulse laser technology, and particularly relates to a nonlinear fiber loop and a figure-eight cavity and laser with full positive dispersion pump protection. Background Technology

[0002] Currently, the technology for generating ultrashort laser pulses is often referred to as mode-locking technology. There are many methods for achieving mode-locking, but they can generally be divided into two main categories: active mode-locking and passive mode-locking. Active mode-locking refers to periodically changing the gain or loss of the laser by providing a modulation signal externally; while passive mode-locking utilizes the nonlinear absorption or nonlinear phase transition characteristics of materials to generate ultrashort laser pulses. Passive mode-locked lasers are linear cavity ultrashort pulse lasers composed of semiconductor saturable absorber mirrors as mode-locking devices. Ring cavity ultrashort pulse fiber lasers have made significant progress in ultrashort pulses, single-pulse energy, and repetition frequency. Mode-locked lasers obtained through passive mode-locking using SESAM are currently the mainstay of the global femtosecond fiber laser market. As an alternative to the SESAM solution, the figure-eight cavity mode-locking solution has significant advantages in terms of lifespan and material manufacturing processes. SESAM, as a grown semiconductor, is easily damaged by prolonged exposure to laser radiation, and its advanced manufacturing process has been difficult to popularize. While the figure-eight cavity solution does not have these problems, the difficulty in starting mode lock and the easy damage of the secondary ring LD (Laser diode) in the NALM solution have been troubling. The LD is expensive to manufacture and cannot be repaired after damage. How to protect the LD from the ASE light in the figure-eight cavity and make the figure-eight cavity more convenient to start up are the urgent problems facing the figure-eight cavity solution. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a nonlinear fiber loop and a fully positive dispersion pumped protected figure-eight cavity laser. Specifically:

[0004] On the one hand, this application provides a nonlinear optical fiber loop, which includes: a first circulator with three ports, a second circulator with three ports, and a combiner;

[0005] The first port of the first circulator is used to connect to the third port of a coupler, the second port of the first circulator is connected to the third port of the second circulator, and the third port of the first circulator is connected to the output of the beam combiner through the first gain light.

[0006] The first port of the second circulator is used to connect to the fourth port of the coupler, and the second port of the second circulator is connected to the signal terminal of the combiner;

[0007] The first input terminal of the beam combiner is connected to a first pump light source.

[0008] Preferably, in the above-mentioned nonlinear optical fiber loop, the first gain fiber is a 0.5m 06 / 125 gain fiber.

[0009] On the other hand, this application provides a fully positive dispersion pumped protected figure-eight cavity, which includes a nonlinear fiber loop as described in any of the above claims, a main oscillation cavity, and a coupler connected between the main oscillation cavity and the nonlinear fiber loop, wherein the first port and the second port of the coupler are respectively connected to the main oscillation cavity; and the third port and the fourth port of the coupler are connected to the nonlinear fiber loop.

[0010] Preferably, in the above-mentioned all-positive dispersion pump-protected figure-eight cavity, the coupler is formed by a 5:5 beam splitter.

[0011] Preferably, in the above-mentioned fully positive dispersion pumped protected figure-eight cavity, the main oscillation cavity includes:

[0012] First optical pump,

[0013] An optical amplifier repeater is connected to the first optical pump;

[0014] Ytterbium-doped optical fiber is connected to the optical amplifier repeater;

[0015] A transmission optical fiber is used to connect the ytterbium-doped optical fiber;

[0016] An isolator, one end of which is connected to the transmission optical fiber, and the other end of which is connected to the first port of the coupler;

[0017] The 2:8 beam splitter has one end connected to the second port of the coupler, and the first output end connected to the optical amplifier repeater, so that the optical amplifier repeater, ytterbium-doped fiber, transmission fiber, isolator, and 2:8 beam splitter form a loop, and the second output end is used to output laser signals.

[0018] Preferably, the above-mentioned all-positive dispersion pump-protected figure-eight cavity further includes a filter connected between the first output terminal of the 2:8 beam splitter and the optical amplifier repeater.

[0019] Preferably, in the above-mentioned fully positive dispersion pumped protected figure-eight cavity, the ytterbium-doped fiber is a 1.2m 06 / 125 gain fiber.

[0020] Preferably, in the above-mentioned fully positive dispersion pumped protected figure-eight cavity, the transmission optical fiber is a PM980 polarization-maintaining fiber.

[0021] Preferably, in the above-mentioned positive dispersion pumped protected figure-eight cavity, the cavity length of the transmission optical fiber is adjustable.

[0022] Finally, this application provides a laser comprising a figure-eight cavity with full positive dispersion pump protection as described in any of the preceding claims.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] 1. In a nonlinear optical fiber loop, the clockwise optical signal does not pass through the first pump source 14 and the combiner 13, meaning the excitation signal of the first pump source 14 is only the counterclockwise optical signal. This significantly reduces the operating current of the first pump source 14, thereby increasing its threshold current. Furthermore, while the clockwise and counterclockwise optical signals are the same signal at input, at output, the counterclockwise optical signal undergoes combining and gain processing, resulting in different return signals received by the third and fourth ports of the coupler 10. The phase shift between the counterclockwise and clockwise optical signals increases, causing optical interference at the coupler, thus creating a "stronger light becomes stronger, weaker light becomes weaker" filtering effect.

[0025] 2. In a fully positive dispersion pump-protected figure-eight cavity technology, only the fourth optical signal is illuminated into the second optical pump through the combiner 33. This reduces the optical flux returning to the second optical pump, increasing the damage threshold current of the second optical pump in the nonlinear fiber loop, allowing the second optical pump to withstand a relatively high operating current. Furthermore, only the fourth optical signal is amplified to form the fifth optical signal, while the third optical signal remains unprocessed. This increases the phase shift between the output fifth and third optical signals, increasing the phase difference between them entering the coupler 30. This lowers the mode-locking threshold of the main oscillator cavity, which can also be understood as reducing the difficulty of mode-locking. Attached Figure Description

[0026] The accompanying drawings are provided to further illustrate embodiments of the present invention and form part of the specification. They are used together with the following detailed description to explain the embodiments of the present invention, but do not constitute a limitation thereof. In the drawings:

[0027] Figure 1 This is a schematic diagram of a nonlinear optical fiber loop provided in an embodiment of the present invention.

[0028] Figure 2 This is a schematic diagram of a fully positive dispersion pump protection figure-eight cavity provided in an embodiment of the present invention. Detailed Implementation

[0029] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the scope of the present invention.

[0030] In embodiments of the present invention, unless otherwise stated, directional terms such as "upper," "lower," "top," and "bottom" are generally used to describe the relative positional relationships of components in relation to the directions shown in the accompanying drawings or in relation to the vertical, perpendicular, or gravitational directions.

[0031] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0032] Example 1

[0033] like Figure 1 As shown, on one hand, this application provides a nonlinear optical fiber loop, which includes: a first circulator 11 with three ports, a second circulator 12 with three ports, and a combiner 13;

[0034] The first port of the first circulator 11 is used to connect to the third port of a coupler 10, the second port of the first circulator 11 is connected to the third port of the second circulator 12, and the third port of the first circulator 11 is connected to the output of the combiner 13 through the first gain fiber 15.

[0035] The first port of the second circulator 12 is connected to the fourth port of the coupler 10, and the second port of the second circulator 12 is connected to the signal end of the combiner 13; furthermore, the first gain fiber 15 is a 0.5m 06 / 125 gain fiber. The optical path of the optical signal passing through the first gain fiber 15 is adjusted, and the power of the optical signal is also changed.

[0036] The first input terminal of the beam combiner 13 is connected to a first pump light source 14, which is used to generate a first pump light signal in an excited state.

[0037] The working process of a nonlinear fiber optic loop is as follows:

[0038] The third and fourth ports of the coupler 10 are used to receive the same optical signal. This optical signal enters the nonlinear fiber loop through the third and fourth ports. The optical path formed by the optical signal through the third port is opposite in direction to the optical path formed by the optical signal through the fourth port. Schematic, the optical signal input at the third port is the clockwise optical signal, and the optical signal input at the fourth port is the counterclockwise optical signal. The clockwise optical signal is transmitted to the fourth port of the coupler 10 through the first circulator 11 and the second circulator 12. The counterclockwise optical signal is transmitted to the first port of the coupler 10 through the second circulator 12, the combiner 13 (which combines the counterclockwise optical signal with the first pump light emitted from the first pump source 14), the first gain fiber 15, and the first circulator 11. The first gain fiber 15 performs gain processing on the counterclockwise optical signal and simultaneously changes the optical path of the counterclockwise optical signal (i.e., the clockwise and counterclockwise optical signals arrive at the combiner 13 at different times), increasing the phase shift between the clockwise and counterclockwise optical signals.

[0039] The clockwise optical signal mentioned above does not pass through the first gain fiber 14 and the combiner 13. That is, the excitation signal of the first pump light source 14 is only the counterclockwise optical signal, which greatly reduces the operating current of the first pump light source 14, thereby increasing the threshold current of the first pump light source 14. In addition, the clockwise and counterclockwise optical signals are the same signal in the input state, but in the output state, the counterclockwise optical signal undergoes beam combining and gain processing, which makes the return signals received by the third and fourth ports of the coupler 10 different signals. Moreover, the phase shift between the counterclockwise and clockwise optical signals increases, and the clockwise and counterclockwise optical signals interfere with each other at the coupler, thus forming a "strong light becomes stronger, weak light becomes weaker" filtering effect.

[0040] Example 2

[0041] like Figure 2 As shown, a figure-eight cavity with all-positive dispersion pump protection includes a main oscillation cavity, a nonlinear fiber loop, and a coupler 30 connected between the main oscillation cavity and the nonlinear fiber loop. The first port and the second port of the coupler 30 are respectively connected to the main oscillation cavity. The coupler 30 can be formed by a 5:5 beam splitter.

[0042] The main oscillation cavity includes a first optical pump 21, an optical amplifier repeater 22, a ytterbium-doped fiber 23, a transmission fiber 24, a coupler 30, a 2:8 beam splitter 26, and a filter 27 connected in sequence to form a ring. The first port of the coupler is connected to the transmission fiber, and the third port of the coupler is connected to the input of the 2:8 beam splitter.

[0043] The nonlinear fiber optic loop includes a first circulator 31, a second circulator 32, and a combiner 33 connected in sequence. The first circulator 31 has three ports. The first port of the first circulator 31 is connected to the third port of the coupler 30, the second port of the first circulator 31 is connected to the third port of the second circulator 32, and the third port of the first circulator 31 is connected to the output of the combiner 33 through a first gain fiber 15.

[0044] The first port of the second circulator 32 is connected to the fourth port of the coupler 30, and the second port of the second circulator 32 is connected to the signal terminal of the combiner 33;

[0045] The first input terminal of the beam combiner 33 is connected to the second optical pump 34.

[0046] The working principle of the above-mentioned positive dispersion pump-protected figure-eight cavity is as follows: The first optical pump outputs a first optical signal. The first optical signal passes through the optical amplifier repeater 22 and the ytterbium-doped fiber 23 to form a second optical signal. The second optical signal is transmitted through the transmission fiber 24 and the isolator 25 to the coupler 30. The coupler 30 performs beam splitting on the second optical signal to form a third optical signal and a fourth optical signal. The third optical signal and the fourth optical signal have opposite directions. The third optical signal is output from the third port of the coupler 30, transmitted to the first port of the first circulator 31, and output from the second port of the first circulator 31. The fourth optical signal is input from the third port of the second circulator 32 and output from the first port of the second circulator 32 to the fourth port of the coupler 30. The fourth optical signal is output from the fourth port of the coupler 30, transmitted to the first port of the second circulator 32, and output from the second port of the second circulator 32 to the combiner 33. The combiner 33 performs beam combining on the fourth optical signal according to the second pump optical signal output by the second optical pump 34 to form a fifth optical signal, which is output to the third port of the first circulator 31. The fifth optical signal is output from the first port of the first circulator 31 to the third port of the coupler 30. The interference between the third and fifth optical signals in the coupler 30 achieves the purpose of "strong light enhancement and weak light reduction". The interfered optical signal is output through the coupler 30. A portion of the interfered optical signal is lost by the isolator 25, and a portion of the interfered optical signal is processed by the 2:8 beam splitter. 80% of the interfered optical signal continues to oscillate in the main oscillation cavity, and 20% of the interfered optical signal is output until mode-locked.

[0047] In this invention, only the fourth optical signal is illuminated into the second optical pump through the combiner 33. This reduces the optical flux returning to the second optical pump, increasing the damage threshold current of the second optical pump in the nonlinear fiber loop, allowing the second optical pump to withstand a relatively high operating current. Furthermore, only the fourth optical signal is amplified to form the fifth optical signal, while the third optical signal remains unprocessed. This increases the phase shift between the output fifth and third optical signals, thus increasing the phase difference between the fifth and third optical signals entering the coupler 30. This lowers the mode-locking threshold of the main oscillator, which can also be understood as reducing the difficulty of mode-locking.

[0048] Here is a specific example:

[0049] Continue with Figure 2 For example, except for the optical pump and pump protector which use non-polarity-maintaining fusion splicing, all other fusion splices in the entire optical path connection are polarity-maintaining fusion splices. Centered on the 5:5 beam splitter, the wiring of the protected figure-eight cavity begins. The third and fourth ports of the 5:5 beam splitter are connected to the nonlinear fiber loop, and the third and fourth ports of the 5:5 beam splitter are connected to the main oscillator cavity. Both the third and fourth ports of the 5:5 beam splitter are connected to a circulator, namely the first circulator and the second circulator. The second port of the first circulator is directly connected to the third port of the second circulator. The third port of the first circulator is then connected to a 0.5m 06 / 125 gain fiber, which is then connected to a combiner. The combiner is connected to the pump protector of the second optical pump, and the signal port of the combiner is connected to the second port of the second circulator. Thus, the nonlinear fiber loop is completed.

[0050] The main oscillation cavity also starts with a 5:5 beam splitter, with one section directly connected to a 20:80 beam splitter. Port 20 of the 20:80 beam splitter serves as the output, and port 80 (typically marked in black) is connected to a filter. The filter then connects to the signal port of the WDM, and the pump port is also connected to the pump protector of the first optical pump. The common port connects to approximately 1.2m of 06 / 125 gain fiber. The gain fiber is then connected to a PM980 transmission fiber used to adjust the cavity length, and then to an isolator. From there, it connects to the remaining port of the 5:5 beam splitter.

[0051] After the first optical pump in the main oscillator cavity is activated, a first optical signal with a wavelength of 976 nm is generated. This first optical signal is reflected by an optical amplifier repeater and enters the ytterbium-doped gain fiber. After being absorbed and emitted by the ytterbium-doped gain fiber, the 976 nm first optical signal is converted into a second optical signal with a wavelength of 1030 nm. The second optical signal then passes through a transmission fiber and an isolator to reach a 5:5 beam splitter, forming a third and fourth optical signal respectively. These signals enter the nonlinear fiber loop. The third optical signal returns to the 5:5 beam splitter in a clockwise direction through the first and second circulators. The fourth optical signal... After passing through the second circulator in a counter-clockwise direction, the optical signal is combined with the second optical pump signal in the beam combiner to form the fifth optical signal. The fifth optical signal returns to the 5:5 beam splitter via the first circulator. The third and fifth optical signals interfere at the 5:5 beam splitter to form the sixth optical signal. Part of the sixth optical signal is output through the first port of the 5:5 beam splitter to the isolator for loss, while another part is transmitted through the second port of the 5:5 beam splitter to the 8:2 beam splitter. 20% of the sixth optical signal is output, and 80% is transmitted to the optical amplifier repeater for further oscillation processing. The entire nonlinear loop is equivalent to a large SESAM. During the interference process, as long as the nonlinear loop maintains a normal modulation for strong and weak light (strong light transmission, weak light reflection), that is, the transmission curve is in the region with a positive slope, it can filter strong light to achieve mode-locking. After mode-locking, the mode-locked laser is output from port 2 of the 2:8 beam splitter.

[0052] Example 3

[0053] The present invention further provides a laser comprising any of the positive dispersion pumped protected figure-eight cavities provided in Embodiment 2 above. The working principle and beneficial effects of the positive dispersion pumped protected figure-eight cavity in the laser are the same as those in Embodiment 2, and will not be repeated here.

[0054] The optional embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the embodiments of the present invention are not limited to the specific details in the above embodiments. Within the scope of the technical concept of the embodiments of the present invention, various simple modifications can be made to the technical solutions of the embodiments of the present invention, and these simple modifications all fall within the protection scope of the embodiments of the present invention.

[0055] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the embodiments of the present invention will not describe the various possible combinations separately.

Claims

1. A nonlinear optical fiber loop, characterized in that: include, A first circulator with three ports, a second circulator with three ports, and a bundle combiner; The first port of the first circulator is used to connect to the third port of a coupler, the second port of the first circulator is connected to the third port of the second circulator, and the third port of the first circulator is connected to the output of the combiner through the first gain fiber. The first port of the second circulator is used to connect to the fourth port of the coupler, and the second port of the second circulator is connected to the signal terminal of the combiner; The first input terminal of the beam combiner is connected to a first pump light source.

2. The nonlinear fiber optic loop according to claim 1, characterized in that, The first gain fiber is a 0.5m 06 / 125 gain fiber.

3. A fully positive dispersion pump-protected figure-eight cavity, characterized in that: The nonlinear optical fiber loop according to any one of claims 1 to 2 further includes a main oscillating cavity and a coupler connected between the main oscillating cavity and the nonlinear optical fiber loop, wherein the first port and the second port of the coupler are respectively connected to the main oscillating cavity; The third and fourth ports of the coupler are connected to the nonlinear optical fiber loop.

4. The figure-eight cavity with fully positive dispersive pump protection according to claim 3, characterized in that: The coupler is formed by a 5:5 beam splitter.

5. The figure-eight cavity with fully positive dispersion pumping protection according to claim 3, characterized in that: The main oscillation cavity includes, First optical pump, An optical amplifier repeater is connected to the first optical pump; Ytterbium-doped optical fiber is connected to the optical amplifier repeater; A transmission optical fiber is used to connect the ytterbium-doped optical fiber; An isolator, one end of which is connected to the transmission optical fiber, and the other end of which is connected to the first port of the coupler; The 2:8 beam splitter has one end connected to the second port of the coupler, and the first output end connected to the optical amplifier repeater, so that the optical amplifier repeater, ytterbium-doped fiber, transmission fiber, isolator, and 2:8 beam splitter form a loop, and the second output end is used to output laser signals.

6. The figure-eight cavity with fully positive dispersive pump protection according to claim 5, characterized in that: It also includes a filter connected between the first output of the 2:8 beam splitter and the optical amplifier repeater.

7. The figure-eight cavity with fully positive dispersive pump protection according to claim 5, characterized in that: The ytterbium-doped fiber is a 1.2m 06 / 125 gain fiber.

8. The figure-eight cavity with fully positive dispersive pump protection according to claim 5, characterized in that: The transmission optical fiber is a PM980 polarization-maintaining fiber.

9. The figure-eight cavity with fully positive dispersive pump protection according to claim 5, characterized in that: The cavity length of the transmission optical fiber is adjustable.

10. A laser, characterized in that: It includes the figure-eight cavity with full positive dispersion pump protection as described in any one of claims 3-8.

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