Random fiber laser based on fiber Bragg grating

Abstract

This disclosure provides a random fiber laser based on a fiber Bragg grating, including an optical input end, a gain fiber, and a random feedback mechanism. The optical input end receives pump light from a pump source. The gain fiber is configured to receive the pump light and output a first optical signal within a first wavelength range. The random feedback mechanism includes a feedback fiber and a string of fiber Bragg gratings formed on the feedback fiber. The fiber Bragg grating string receives the first optical signal and provides random feedback to the first optical signal to output a second optical signal within a second wavelength range smaller than the first wavelength range. The fiber Bragg grating string includes multiple grating arrays, and along the direction in which the first optical signal is incident on the fiber Bragg grating string, the grating periods of the multiple grating arrays increase sequentially. The distance between adjacent fiber Bragg gratings in the multiple fiber Bragg gratings is random. Therefore, wide tunability can be achieved while shortening the fiber length.

Description

Technical Field

[0001] This disclosure relates to fiber lasers, and more particularly to a random fiber laser based on a fiber Bragg grating. Background Technology

[0002] Random fiber lasers utilize the random distributed feedback mechanism of optical fibers, combined with the nonlinear gain or doped active gain of the fiber, to cause photons to undergo multiple scattering and amplification in the fiber, thereby generating random laser light.

[0003] Early random fiber lasers relied primarily on the randomness of Rayleigh scattering feedback within the fiber. Because Rayleigh scattering feedback is wavelength-independent, this non-selective scattering mechanism can provide feedback at any wavelength, enabling random fiber lasers to achieve a wide tunable range.

[0004] However, due to the weak Rayleigh scattering coefficient in optical fibers, very long optical fibers are required to achieve laser output with the required light intensity. These fibers typically need to be several kilometers to tens of kilometers long. The use of long optical fibers significantly increases the size and complexity of random fiber lasers, which poses a challenge to practical applications and integration. Summary of the Invention

[0005] This disclosure is made in view of the above-mentioned situation, and its purpose is to provide a widely tunable random fiber laser based on a fiber Bragg grating that can achieve a shorter fiber length.

[0006] To this end, a first aspect of this disclosure provides a random fiber laser based on a fiber Bragg grating, comprising an optical input end, a gain fiber, and a random feedback mechanism; the optical input end is configured to receive pump light from a pump source; the gain fiber is configured to receive the pump light and output a first optical signal in a first wavelength range, wherein the gain fiber has a gain medium excited by the pump light; the random feedback mechanism includes a feedback fiber and a string of fiber Bragg gratings formed on the feedback fiber, the string of fiber Bragg gratings being configured to receive the first optical signal and provide random feedback for the first optical signal to output a second optical signal in a second wavelength range, wherein the second wavelength range is smaller than the first wavelength range, the string of fiber Bragg gratings includes a plurality of grating arrays corresponding to different grating periods, the grating periods of the plurality of grating arrays increasing sequentially along the direction in which the first optical signal is incident on the string of fiber Bragg gratings, each of the plurality of grating arrays including a plurality of fiber Bragg gratings, the distance between adjacent fiber Bragg gratings being random.

[0007] In this disclosure, the grating periods of multiple grating arrays are sequentially increased, facilitating the acquisition of continuous wavelengths to achieve continuous wide tunability. Furthermore, the distances between adjacent fiber Bragg gratings in the multiple fiber Bragg gratings are random, providing random feedback. Additionally, the multiple fiber Bragg gratings allow the first optical signal to be continuously reflected; the more reflections and the longer the reflection time, the higher the intensity of the resulting second optical signal, thus improving the Q value of the second optical signal in short optical fibers. Therefore, wide tunability can be achieved while shortening the fiber length, and the Q value can be improved.

[0008] Additionally, in the random fiber laser disclosed herein, optionally, the optical input end is a wavelength division multiplexer, comprising two input ports and one output port. The two input ports respectively receive the pump light and the second optical signal and transmit them to the gain fiber through the output port. This allows for amplification of the second optical signal while reducing the size of the laser.

[0009] Additionally, in the random fiber laser disclosed herein, optionally, the gain fiber is erbium-doped fiber, and the first wavelength range is 1530 nm to 1570 nm. In this case, the first wavelength range can be placed in the C-band, thereby facilitating the generation of C-band target laser.

[0010] Additionally, in the random fiber lasers disclosed herein, the second wavelength range may optionally be from 1540 nm to 1560 nm. In this case, a wavelength range with the largest possible wavelength span can be obtained with a relatively short feedback fiber length, facilitating wide tunability while maximizing C-band coverage, and enabling a flatter reflection spectrum.

[0011] Furthermore, in the random fiber lasers disclosed herein, optionally, the second wavelength range is no greater than 20 nm. Therefore, limiting the wavelength span to the aforementioned range facilitates tuning within a range of tens of nanometers and enables the acquisition of a relatively flat reflection spectrum.

[0012] Additionally, in the random fiber lasers disclosed herein, optionally, the gain fiber is an erbium-doped fiber, the length of the gain fiber is on the order of meters, and the length of the fiber Bragg grating string is on the order of meters.

[0013] Additionally, in the random fiber laser disclosed herein, optionally, when the gain of the first optical signal is greater than the loss, the random feedback mechanism is further configured to receive the first optical signal and transmit it to output a third optical signal.

[0014] Additionally, the random fiber laser disclosed herein may optionally include a circulator, which includes a first port, a second port, and a third port. The first port receives the first optical signal and outputs it to the random feedback mechanism through the second port. The second optical signal enters the optical input end through the third port to be amplified by the gain fiber. In this configuration, a ring-shaped laser cavity can be constructed, facilitating repeated amplification of the second optical signal and improving the laser's efficiency.

[0015] Additionally, the random fiber laser disclosed herein may optionally include a first isolator disposed between the optical input end and the circulator. This allows the circulator to transmit only unidirectional optical signals.

[0016] Additionally, the random fiber laser disclosed herein may optionally include a filter configured to limit the available output wavelength range, wherein the second optical signal is input to the optical input terminal, and the filter is disposed between the optical input terminal and the random feedback mechanism. Thus, a second optical signal with a specific wavelength range can be selected to be input to the optical input terminal.

[0017] According to this disclosure, a random fiber laser based on a fiber Bragg grating is provided that can achieve wide tunability while shortening the fiber length. Attached Figure Description

[0018] This disclosure will now be explained in further detail by way of example only with reference to the accompanying drawings.

[0019] Figure 1A This is a schematic diagram illustrating a first embodiment of the laser according to the examples of this disclosure.

[0020] Figure 1B This is a schematic diagram illustrating a second embodiment of the laser involved in the examples of this disclosure.

[0021] Figure 2 This is a schematic diagram illustrating the random feedback mechanism involved in the example of this disclosure.

[0022] Figure 3 This is a schematic diagram illustrating the reflection spectrum of the random feedback mechanism involved in the example of this disclosure.

[0023] Figure 4 This is a schematic diagram illustrating the grating array involved in the example of this disclosure.

[0024] Figure 5A This is a schematic diagram illustrating a third embodiment of the laser involved in the examples of this disclosure.

[0025] Figure 5BThis is a schematic diagram illustrating a fourth embodiment of the laser involved in the examples of this disclosure.

[0026] Figure 6 This is a schematic diagram illustrating the spectrum of the target laser involved in the example of this disclosure. Detailed Implementation

[0027] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the following description, the same reference numerals are used for the same components, and repeated descriptions are omitted. Furthermore, the drawings are merely schematic diagrams, and the proportions of the components or the shapes of the components may differ from actual figures. It should be noted that the terms "comprising" and "having," and any variations thereof, in this disclosure, do not necessarily limit the process, method, system, product, or apparatus to the explicitly listed steps or units, but may include or have other steps or units not explicitly listed or inherent to these processes, methods, products, or apparatuses.

[0028] First, let me introduce the relevant terminology used in this disclosure.

[0029] "Meter level" can refer to objects whose length is between 1 meter and 10 meters.

[0030] "Random feedback" can refer to an optical feedback mechanism that arises within a laser due to the random distribution of scattering centers.

[0031] "Flatness" can refer to the uniformity of light intensity across different wavelengths in a spectrum (such as a gain spectrum or a reflection spectrum). The higher the flatness of a spectrum, the more uniform the light intensity across different wavelengths in the spectrum.

[0032] "Gain spectrum" can refer to the spectrum of the fiber optic output.

[0033] "Reflection spectrum" can refer to the spectrum formed by reflection from a random feedback mechanism.

[0034] As mentioned above, existing solutions increase the size and complexity of random fiber lasers. Furthermore, the extended fiber length not only increases the cost and physical size of the random fiber laser but also significantly increases the number of modes and introduces nonlinear effects within the fiber, increasing laser noise and instability. The inventors discovered that refractive index modulation with random periods or random distances can be introduced into the fiber to form random fiber gratings or random fiber Bragg gratings, thereby enabling higher intensity random feedback over shorter fiber lengths.

[0035] Further research by the inventors revealed that the fabrication length and refractive index modulation depth of random fiber gratings are limited, and the reflection spectrum of random fiber gratings exhibits a low Q-value (quality factor). Furthermore, the light intensity varies significantly between wavelengths of the reflection spectrum of random fiber gratings (i.e., low uniformity of light intensity), resulting in random laser generation only at certain specific wavelengths, making continuous tunability of the laser impossible.

[0036] Therefore, the inventors have provided solutions that provide random feedback through the fiber Bragg grating string described in this disclosure, thereby addressing at least a portion of the aforementioned problems.

[0037] The random fiber laser (hereinafter referred to as the laser) based on a fiber Bragg grating disclosed herein can achieve wide tunability while shortening the fiber length. Additionally, the laser disclosed herein may also be referred to as a random laser or a random feedback laser. Furthermore, for ease of distinction, the laser output from the laser will be referred to as the target laser.

[0038] Examples of this disclosure will now be described in detail with reference to the accompanying drawings. Figure 1A This is a schematic diagram illustrating a first embodiment of the laser 1 according to the example of this disclosure. Figure 1B This is a schematic diagram illustrating a second embodiment of the laser 1 according to the present disclosure. It should be noted that, for ease of understanding, the schematic diagram of the laser 1 according to the present disclosure schematically shows the components involved in a simplified manner.

[0039] In some examples, reference Figure 1A The laser 1 may include an optical input terminal 11. The optical input terminal 11 may be configured to receive optical signals. In addition, the optical signals received by the optical input terminal 11 may be transmitted to components in the laser 1 (such as the gain fiber 12 or the random feedback mechanism 13 described later).

[0040] In some examples, reference Figure 1A The optical input terminal 11 can be configured to receive an optical signal from the pump source 2, and the received optical signal can be pump light. This facilitates the excitation of the gain medium in the laser 1. In some examples, the wavelength of the pump source 2 can be 980 nm. In some examples, the laser 1 may also include the pump source 2.

[0041] In some examples, reference Figure 1B The optical input terminal 11 can be configured to receive an optical signal (i.e., the second optical signal, described later) from the random feedback mechanism 13 (described later). This facilitates the entry of the optical signal from the random feedback mechanism 13 into the gain fiber 12.

[0042] In some examples, the optical input 11 can be a wavelength division multiplexer (WDM). A WDM allows multiple optical signals of different wavelengths to be transmitted through the same optical fiber. This reduces the size of the laser 1. In some examples, for the optical input 11 as a WDM, refer to... Figure 1B The optical input terminal 11 may include two input ports (i.e., the first input port P11 and the second input port P12) and one output port P13.

[0043] Furthermore, the two input ports of optical input terminal 11 can receive pump light and a second optical signal, respectively, and output them through output port P13. This allows for amplification of the second optical signal while reducing the size of laser 1. For example, the two input ports of optical input terminal 11 can receive pump light with a wavelength of 980 nm and a second optical signal with a wavelength of 1540 nm, respectively. In some examples, the optical signals received by the two input ports can be transmitted to gain fiber 12 through output port P13.

[0044] In some examples, reference Figure 1A and Figure 1B Laser 1 may include gain fiber 12. In some examples, gain fiber 12 may be configured to receive pump light and output a first optical signal within a first wavelength range. Furthermore, the first wavelength range may be associated with gain fiber 12. That is, different gain fibers 12 may correspond to different first wavelength ranges, and the first wavelength range can also be determined when gain fiber 12 is determined.

[0045] In some examples, the gain fiber 12 can also be configured to amplify the gain of the incident optical signal in a first wavelength range, whereby the first optical signal may include the amplified incident optical signal. That is, the gain fiber 12 can provide gain. In other words, within the first wavelength range, the gain fiber 12 can act as an amplifier. In some examples, the incident optical signal may be a second optical signal received by the optical input terminal 11.

[0046] In some examples, the gain fiber 12 may have a gain medium. The gain medium can be excited by pump light. Under the excitation of pump light, the gain medium can achieve stimulated emission and amplify the gain of the incident light signal. Specifically, after the gain medium in the gain fiber 12 absorbs the energy of the pump light, the ions in the gain medium transition from the ground state to a higher energy level. Since the higher energy level is unstable, the ions quickly transition to the metastable energy level, i.e., the upper laser energy level, in a non-radiative manner. The ions have a longer lifetime in the upper energy level, so they can gradually accumulate with the continuous pump light to achieve population inversion, thereby realizing stimulated emission and amplifying the gain of the incident light signal.

[0047] In some examples, the gain fiber 12 can be erbium-doped fiber. In this case, the first wavelength range can be in the C-band, thus facilitating the generation of C-band target laser. In some examples, for the gain fiber 12 to be erbium-doped fiber, the first wavelength range can be from 1530 nm to 1570 nm. In other examples, the gain fiber 12 can also be replaced with other fibers besides erbium-doped fiber, depending on the wavelength of the target laser.

[0048] Furthermore, the flatness of the gain spectrum generated by gain fibers 12 of different lengths can vary. That is, the flatness of the first optical signal generated by gain fibers 12 of different lengths can also vary. In some examples, the length of the gain fiber 12 can be determined by the flatness of the target laser. This facilitates improving the flatness of the target laser. In some examples, the length of the gain fiber 12 can be determined based on the flatness of the target laser and the flatness of the reflection spectrum of the random feedback mechanism 13. Specifically, the gain fiber 12 and the random feedback mechanism 13 are the two major factors affecting the flatness of the target laser. The random feedback mechanism 13, due to the influence of parameters such as the power it is inscribed, cannot maintain the same flatness as theoretical simulations. Therefore, improving the flatness of the target laser by controlling the length of the gain fiber 12 is more effective.

[0049] In some examples, for erbium-doped fiber, the length of the gain fiber 12 can be on the order of meters. In this case, it is convenient to improve the flatness of the first optical signal, thereby improving the flatness of the target laser and reducing the hopping of the target laser. In some examples, for erbium-doped fiber, the length of the gain fiber 12 can be 1 meter. In this case, it is possible to improve the flatness of the first optical signal.

[0050] In some examples, reference Figure 1A and Figure 1B The gain fiber 12 can be connected to the optical input terminal 11. Thus, it can receive the optical signal output from the optical input terminal 11.

[0051] In some examples, reference Figure 1A and Figure 1B The laser 1 may include a random feedback mechanism 13. The random feedback mechanism 13 may be configured to receive an optical signal and provide random feedback to the optical signal to output a feedback optical signal. That is, in the laser 1, the random feedback mechanism 13 can provide random feedback.

[0052] In some examples, the optical signal received by the random feedback mechanism 13 can be a first optical signal, and the corresponding feedback optical signal can be referred to as a second optical signal. The following description of the random feedback mechanism 13 using the first optical signal as an example does not imply any limitation on this disclosure. In some examples, when the gain of the first optical signal is greater than its loss, the random feedback mechanism 13 can also be configured to receive the first optical signal and transmit it to output a third optical signal (i.e., the target laser).

[0053] In some examples, reference Figure 1A and Figure 1B The random feedback mechanism 13 can be connected to the gain fiber 12. This allows it to receive the first optical signal.

[0054] Figure 2 This is a schematic diagram illustrating the random feedback mechanism 13 involved in the example of this disclosure. Figure 3 This is a schematic diagram showing the reflection spectrum of the random feedback mechanism 13 involved in the example of this disclosure.

[0055] In some examples, reference Figure 2 The random feedback mechanism 13 may include a feedback fiber 131 and a fiber Bragg grating string 132 formed on the feedback fiber 131.

[0056] Alternatively, the feedback fiber 131 can be an optical fiber. In some examples, the feedback fiber 131 can be a standard single-mode fiber. This facilitates the acquisition of target lasers corresponding to the communication band (e.g., 1550 nm) of the standard single-mode fiber.

[0057] Additionally, the fiber Bragg grating string 132 may include fiber Bragg gratings and be configured to provide random feedback. In some examples, the fiber Bragg grating may be a second-order Bragg grating. In some examples, the fiber Bragg grating may be a strongly scattering grating.

[0058] In some examples, when the optical signal input to the random feedback mechanism 13 is a first optical signal within a first wavelength range, the fiber Bragg grating string 132 can be configured to receive the first optical signal and provide random feedback to the first optical signal to output a second optical signal within a second wavelength range. Specifically, the fiber Bragg grating string 132 can reflect the first optical signal to output the second optical signal.

[0059] In some examples, the second wavelength range can be smaller than the first wavelength range. That is, the second wavelength range can be within the first wavelength range but not equal to it. This facilitates obtaining a flatter second optical signal and makes it easier to cooperate with the gain fiber 12 to improve the flatness of the target laser. Furthermore, the second optical signal, being within the second wavelength range, is easily amplified by the gain fiber 12 when passing through it. As an example of the reflection spectrum of the fiber Bragg grating string 132 (i.e., the reflection spectrum of the random feedback mechanism 13), see [reference]. Figure 3 When the reflection spectrum is in the range of 1540 nm to 1560 nm, although the light intensity decreases slightly with increasing wavelength, it is relatively flat.

[0060] In some examples, the gain fiber 12 can be combined to suppress the decrease in light intensity as the wavelength increases. In some examples, for cases where the light intensity decreases as the wavelength in the reflection spectrum increases, the gain fiber 12 can be made to increase the light intensity as the wavelength increases within the corresponding range. Thus, the combination of the gain fiber 12 and the random feedback mechanism 13 can improve the flatness of the target laser. For example, by adjusting the length of the erbium-doped fiber, the high intensity of the gain spectrum of the erbium-doped fiber can correspond to the low intensity of the reflection spectrum of the fiber Bragg grating string 132.

[0061] In some examples, the wavelength span of the second optical signal may not exceed 20 nm. Since a larger wavelength span requires a longer fiber Bragg grating, the flatness of the reflection spectrum decreases after a certain length. Therefore, limiting the wavelength span to the aforementioned range facilitates tuning within tens of nanometers when the length of the feedback fiber 131 is on the order of meters, and also enables the acquisition of a relatively flat reflection spectrum. Preferably, the wavelength span of the second optical signal can be 20 nm. That is, it can be tuned within a 20 nm range. This allows for a tuning range suitable for most scenarios and the acquisition of a flatter reflection spectrum.

[0062] In some examples, when the wavelength range of the first optical signal is 1530 nm to 1570 nm, the second wavelength range can be 1540 nm to 1560 nm (reference). Figure 3 In this case, a wavelength range with the largest possible wavelength span can be obtained with a relatively short length of feedback fiber 131, which facilitates wide tunability while covering the C-band as much as possible, and also enables a flatter reflection spectrum.

[0063] In some examples, the fiber Bragg grating string 132 can have high reflectivity. In some examples, the reflectivity of the fiber Bragg grating string 132 can be 20 dB.

[0064] In some examples, when the gain of the first optical signal is greater than the loss, the fiber Bragg grating string 132 can also receive the first optical signal and transmit it to output a third optical signal.

[0065] In some examples, the fiber Bragg grating string 132 can be fabricated using a femtosecond laser.

[0066] In some examples, reference Figure 2 The fiber Bragg grating string 132 may include multiple grating arrays 1321, which may correspond to different grating periods. Different grating periods may correspond to different wavelengths in the second optical signal.

[0067] Additionally, the grating array 1321 may include fiber Bragg gratings, with the grating period of the grating array 1321 being the grating period of the fiber Bragg gratings within it. Since the grating period of the fiber Bragg grating is fixed, the reflection spectrum is narrow, preventing the realization of wide tunability of the laser wavelength. In this case, by changing the grating periods of multiple grating arrays 1321, the second optical signal can have multiple wavelengths, thus facilitating wide tunability. Furthermore, adjacent grating arrays 1321 within the multiple grating arrays 1321 may have spacing. As an example, Figure 2 A schematic diagram of two grating arrays 1321 is shown, which may include a first array A1 and a second array A2.

[0068] In some examples, the multiple grating periods of the multiple grating arrays 1321 can be sequentially increased or decreased. In this case, it is convenient to obtain continuous wavelengths to achieve continuous wide tunability.

[0069] In some examples, the grating periods of multiple grating arrays 1321 can be sequentially increased along the direction in which the first optical signal is incident on the fiber Bragg grating string 132 (hereinafter referred to as the incident direction). That is, the grating period of the grating array 1321 can gradually increase in the incident direction.

[0070] In some examples, the wavelength increment corresponding to the increment of the grating period can be negatively correlated with the continuity of the wavelength in the second optical signal. That is, the larger the wavelength increment, the more discontinuous the wavelength. In some examples, the wavelength increment corresponding to the increment of the grating period can be determined through simulation and debugging on the writing platform.

[0071] In some examples, the increment of the grating period can be the same. In some examples, the increment of the grating period corresponds to a wavelength increment of 0.2 nm. In this case, the continuity of wavelength can be improved, thereby achieving continuous wide tunability, and the length of the feedback fiber 131 is more suitable. For example, for a second-order Bragg grating with a refractive index of 1.4401, an increment of 0.1388 nm in the grating period can correspond to a wavelength increment of 0.2 nm. If the number of grating arrays 1321 is 100, the length of the fiber Bragg grating string 132 can be approximately 4 meters.

[0072] In some examples, the number of grating arrays 1321 can be from 50 to 150. This facilitates obtaining a tuning range of tens of nanometers while the length of the feedback fiber 131 is on the order of meters. For example, the number of grating arrays 1321 can be 50, 70, 90, 100, 120, or 150. In some examples, the number of grating arrays 1321 can be 100. In this case, a tuning range of 20 nm can be obtained with a wavelength increment of 0.2 nm, and the length of the fiber Bragg grating string 132 does not exceed 5 meters.

[0073] Figure 4 This is a schematic diagram illustrating the grating array 1321 involved in the example of this disclosure.

[0074] In some examples, reference Figure 4 Each grating array 1321 may include multiple fiber Bragg gratings. In some examples, the length of the grating array 1321 may be determined based on the number and length of the fiber Bragg gratings in the grating array 1321.

[0075] In some examples, the number of fiber Bragg gratings in the grating array 1321 can be adjusted according to the laser intensity requirements. In some examples, the number of fiber Bragg gratings in the grating array 1321 can be positively correlated with the intensity of the randomly fed-out light (i.e., the intensity of the reflected spectrum).

[0076] In some examples, the number of fiber Bragg gratings in the grating array 1321 can be six. This allows for a reflection spectrum with good randomness, and the randomly fed-back light intensity facilitates the formation of laser intensity suitable for most scenarios. As an example, Figure 4 Six fiber Bragg gratings are shown, which may include a first grating M1, a second grating M2, a third grating M3, a fourth grating M4, a fifth grating M5, and a sixth grating M6.

[0077] In some examples, the length of the fiber Bragg grating in the grating array 1321 can be negatively correlated with the saturation of the reflection spectrum. That is, the longer the fiber Bragg grating in the grating array 1321, the easier it is for the light intensity of the reflection spectrum to saturate.

[0078] In some examples, the fiber Bragg gratings in the grating array 1321 can have the same length. In other examples, the length of the fiber Bragg gratings in the grating array 1321 can be 0.1 mm. This reduces the possibility of light intensity saturation in the reflected spectrum.

[0079] In some examples, reference Figure 4 In the grating array 1321, the grating period of each fiber Bragg grating can be fixed, and multiple fiber Bragg gratings can be identical. Furthermore, a fixed grating period can mean that the distances between modulation points (also called refractive index change points) in the fiber Bragg grating are equal. As an example of the grating period of a fiber Bragg grating, Figure 4 The diagram shows a schematic of the grating period T of the first grating M1.

[0080] In some examples, the distance between adjacent fiber Bragg gratings in a plurality of fiber Bragg gratings can be random. This allows for random feedback. Furthermore, using multiple fiber Bragg gratings enables the first optical signal to be continuously reflected; the more reflections and the longer the reflection time, the higher the intensity of the resulting second optical signal. This allows for improving the Q value of the second optical signal in short optical fibers (e.g., fibers with lengths on the order of meters) and reducing the linewidth of the second optical signal. Thus, wide tunability can be achieved while shortening the fiber length.

[0081] Furthermore, since a narrower linewidth results in fewer modes (i.e., preventing more mode competition), laser 1 becomes more stable and its noise is weaker. Additionally, a narrower linewidth also improves the filtering effect of ASE (Amplified Spontaneous Emission) noise. Therefore, the stability of laser 1 can be improved and its noise reduced.

[0082] In some examples, the distance between adjacent fiber Bragg gratings can be randomly distributed within the range of 1 mm to 10 mm. In this case, more fiber Bragg gratings can be arranged on the shorter feedback fiber 131, which can improve the light intensity of the second optical signal. For example, taking six fiber Bragg gratings as an example, the distances between adjacent fiber Bragg gratings can be 5 mm, 8 mm, 2 mm, 7 mm, and 3 mm, respectively. As an example of the fiber Bragg grating distance, Figure 4 The distance D between the third grating M3 and the fourth grating M4 is shown.

[0083] In some examples, the length of the fiber Bragg grating string 132 can be on the order of meters. In this case, it is convenient to obtain a suitable light intensity and wavelength span of the second optical signal with a shorter fiber Bragg grating string 132.

[0084] In some examples, the length of the fiber Bragg grating string 132 can be determined by the light intensity and wavelength span of the second optical signal. In some examples, the length of the fiber Bragg grating string 132 can be positively correlated with the light intensity and wavelength span of the second optical signal.

[0085] In some examples, when laser 1 generates C-band target laser light, the length of the fiber Bragg grating string 132 can be from 3 m to 5 m. For example, the length of the fiber Bragg grating string 132 can be 3 m, 4 m, or 5 m. Preferably, the length of the fiber Bragg grating string 132 can be 4 m. In this case, a more suitable light intensity (e.g., -10 dB) and a larger wavelength span (e.g., 20 nm) of the second optical signal can be obtained with a shorter fiber Bragg grating string 132, and the impact of noise can be reduced compared to kilometer-scale optical fibers (e.g., Rayleigh scattering fibers).

[0086] Furthermore, to facilitate understanding of the fiber Bragg grating string 132, this disclosure also provides a method for fabricating the fiber Bragg grating string 132. It should be noted that this does not constitute a limitation of this disclosure. The basic idea of ​​the random feedback mechanism 13 has been disclosed in this disclosure, and those skilled in the art can make corresponding adjustments as needed to fabricate a random feedback mechanism 13 capable of outputting a target laser with a corresponding wavelength range and light intensity. In this embodiment, the fiber Bragg grating string 132 can be obtained by changing the grating period and random distance. Thus, a fiber Bragg grating string 132 with a wide bandwidth and high Q value can be obtained.

[0087] Specifically, in the femtosecond laser etching system, a femtosecond laser with a pulse energy of 62 nJ (nanojoules), a wavelength of 515 nm, and a pulse repetition rate of 200 kHz (kilohertz) is focused onto a standard single-mode fiber (i.e., a type of feedback fiber 131) through a 63x oil-immersion objective lens. Randomly spaced fiber Bragg gratings (i.e., grating array 1321) are then written into the fiber using a point-by-point technique, forming a strongly scattering fiber Bragg grating capable of providing random feedback. Furthermore, by changing the grating period, multiple grating arrays 1321 corresponding to various wavelengths can be etched.

[0088] In this way, a fiber Bragg grating string 132 with a wide bandwidth and high Q value can be formed, overcoming the technical bottleneck of using short-length fiber feedback to construct a wide-tunable and narrow-linewidth laser 1. It should be noted that this disclosure is not limited to the parameters for fabricating the fiber Bragg grating string 132 described above, and those skilled in the art can adjust them or choose other fabrication methods as needed.

[0089] The structure of the fiber Bragg grating string 132 is described below using a 4-meter fiber Bragg grating string 132 as an example. The second wavelength range is 1540 nm to 1560 nm, and the fiber Bragg grating is a second-order Bragg grating. It should be noted that this does not imply any limitation on this disclosure.

[0090] The fiber Bragg grating string 132 can be composed of a grating array 1321 with 100 grating periods incremented by 0.1388 nm. The range of the grating periods is from 1.0693 μm to 1.0832 μm, which can correspond to a second wavelength range of 1540 nm to 1560 nm. The wavelength increment corresponding to the 0.1388 nm increment can be 0.2 nm.

[0091] Each grating array 1321 can consist of six identical fiber Bragg gratings. Each fiber Bragg grating can be 0.1 mm long and consists of multiple modulation points with the same grating period. The distances between adjacent fiber Bragg gratings are randomly distributed in the range of 1 mm to 10 mm, for example, 5 mm, 8 mm, 2 mm, 7 mm, and 3 mm respectively. In this case, the total number of modulation points can be approximately 55,800.

[0092] In some examples, when the laser 1 includes both the gain fiber 12 and the random feedback mechanism 13, the light intensity of the target laser (hereinafter referred to as laser intensity) can be determined jointly by the gain fiber 12 and the random feedback mechanism 13. That is, the laser intensity can be determined by the light intensity of the gain spectrum of the gain fiber 12 and the light intensity of the reflection spectrum of the random feedback mechanism 13. For example, the laser intensity can be determined by combining the gain spectrum with an intensity of -10 dB and the reflection spectrum with an intensity of -20 dB.

[0093] In some examples, the second optical signal output by the random feedback mechanism 13 can be input to the optical input terminal 11. In this case, when the gain fiber 12 is connected to the optical input terminal 11, the second optical signal can be repeatedly amplified until the gain is greater than the loss, and then the target laser is output.

[0094] Figure 5A This is a schematic diagram illustrating a third embodiment of the laser 1 according to the examples of this disclosure. Figure 5B This is a schematic diagram illustrating a fourth embodiment of the laser 1 according to the examples of this disclosure. Figure 6 This is a schematic diagram illustrating the spectrum of the target laser involved in the example of this disclosure.

[0095] In some examples, reference Figure 5A The second optical signal can be introduced into the optical input terminal 11 through the circulator 14. That is, a ring cavity can be formed. In this case, a ring-shaped laser cavity can be constructed, facilitating repeated amplification of the second optical signal and improving the efficiency of the laser 1. Specifically, refer to... Figure 5A The laser 1 may include a circulator 14. The circulator 14 may be configured to receive a first optical signal and transmit it to a random feedback mechanism 13, and to receive a second optical signal and transmit it to an optical input terminal 11.

[0096] In some examples, reference Figure 5A The circulator 14 may include a first port P21, a second port P22, and a third port P23. The first port P21 receives a first optical signal and outputs it to the random feedback mechanism 13 via the second port P22. The second optical signal from the random feedback mechanism 13 enters the optical input terminal 11 via the third port P23. In some examples, the second optical signal from the random feedback mechanism 13 may be incident on the second port P22 and enter the optical input terminal 11 via the third port P23.

[0097] In some examples, the second optical signal entering the optical input terminal 11 can be amplified by the gain fiber 12. That is, the gain fiber 12 can also be configured to amplify the second optical signal. This facilitates ensuring that the gain of the optical signal in the laser 1 is greater than the loss so as to output the target laser.

[0098] In some examples, the circulator 14 can be unidirectionally isolated. This allows the optical signal to be restricted from propagating in the opposite direction to the direction in which the second optical signal enters the optical input terminal 11.

[0099] In some examples, reference Figure 5A Laser 1 may include filter 15. Filter 15 may be configured to limit the available output wavelength range (i.e., the wavelength range of the target laser). In some examples, filter 15 may be tunable. Thus, it is possible to select optical signals of different wavelengths to output the target laser of the corresponding wavelength.

[0100] Additionally, filter 15 can be positioned at any location that defines the output wavelength range. In some examples, refer to... Figure 5A When the second optical signal is input to the optical input terminal 11, the filter 15 can be positioned between the optical input terminal 11 and the random feedback mechanism 13. This allows selection of a specific wavelength range of the second optical signal input to the optical input terminal 11. In other words, the filter 15 can be used to adjust the wavelength of the second optical signal input to the optical input terminal 11.

[0101] In some examples, the parameters of filter 15 can be adjusted according to the wavelength range of the target laser. For example, for a target laser with a wavelength range of 1540 nm to 1560 nm, the bandwidth of filter 15 can be tuned from 32 pm (picometers) to 650 pm, and the wavelength range can be from 1480 nm to 1620 nm.

[0102] In some examples, reference Figure 5B The laser 1 may include a first isolator 16. The first isolator 16 may be configured to restrict the optical signal from entering the random feedback mechanism 13 in the opposite direction to the direction in which the second optical signal enters the optical input terminal 11. In some examples, the first isolator 16 may be disposed between the optical input terminal 11 and the circulator 14. This allows the circulator 14 to pass only unidirectional optical signals. In some examples, the first isolator 16 may be disposed between the optical input terminal 11 and the circulator 14, and directly connected to the optical input terminal 11.

[0103] In some examples, reference Figure 5B Laser 1 may include a second isolator 17. The second isolator 17 may be configured to restrict external optical signals from entering the random feedback mechanism 13. In this case, the risk of multimode light formation due to the influence of external optical signals can be reduced, and single-mode light formation can be facilitated. In some examples, a third optical signal can be output after the second isolator 17.

[0104] In addition, to facilitate understanding of the laser 1 involved in this disclosure, this disclosure also provides a specific example of the laser 1.

[0105] Specifically, refer to Figure 5B Laser 1 may include an optical input terminal 11 (wavelength division multiplexer), a gain fiber 12 (erbium-doped fiber), a circulator 14, a random feedback mechanism 13, a second isolator 17, a filter 15, and a first isolator 16. The wavelength division multiplexer may include a first input port P11, a second input port P12, and an output port P13. The first input port P11 may be connected to a pump source 2, and the output port P13 may be connected to one end of the erbium-doped fiber. The circulator 14 may include a first port P21, a second port P22, and a third port P23. The other end of the erbium-doped fiber may be connected to the first port P21. The second port P22 may be connected to the random feedback mechanism 13 and then to the second isolator 17. The third port P23 may be connected sequentially to the filter 15, the first isolator 16, and the second input port P12 of the wavelength division multiplexer. The target laser is output from one end of the second isolator 17.

[0106] Based on the laser 1 described above, the pump light emitted from the pump source 2 passes through the optical input terminal 11 (which is a wavelength division multiplexer) and enters the gain fiber 12 (which is an erbium-doped fiber). After the erbium-doped ions absorb the energy of the pump light, population inversion occurs, thereby generating ASE light (i.e., a type of first optical signal). For example, pump light with a center wavelength of 980 nm can generate a first optical signal with a first wavelength range of 1530 nm to 1570 nm via the erbium-doped fiber. In addition, when stimulated emission occurs, the gain fiber 12 can also amplify the incident light signal within the first wavelength range.

[0107] The ASE light can enter the random feedback mechanism 13 through the circulator 14. The portion of the optical signal entering the random feedback mechanism 13 within the second wavelength range, when the gain is less than the loss, can be reflected and enter the wavelength division multiplexer through the third port P23 of the circulator 14 to be further amplified by the erbium-doped fiber and enter the random feedback mechanism 13. For example, an optical signal with a wavelength of 1550 nm entering the erbium-doped fiber can output an optical signal with a wavelength of 1550 nm and enhanced light intensity; within the second wavelength range, when the gain is greater than the loss, it can be transmitted through the random feedback mechanism 13 to output the target laser.

[0108] Furthermore, the unidirectional isolation of the circulator 14 via the first isolator 16 can prevent bidirectional laser oscillation. Additionally, to block strong Fresnel reflections from the fiber end face, a second isolator 17 can be placed after the random feedback mechanism 13, from which the target laser outputs.

[0109] As described above, the optical signal entering the random feedback mechanism 13 can enter the wavelength division multiplexer after being reflected by the random feedback mechanism 13. A filter 15 can be set in the optical path of the reflected optical signal entering the wavelength division multiplexer, thereby obtaining a wide-tunable, narrow-linewidth, and low-noise target laser by changing the wavelength of the filter 15. As an example, Figure 6 A schematic diagram of the spectrum of the target laser is shown.

[0110] In some examples of this disclosure, a wide bandwidth and high Q value random feedback is achieved by using a fiber Bragg grating with a random distance in the random feedback mechanism 13, and the optical gain is amplified by combining it with the gain fiber 12. In addition, a circulator 14 is used to construct a ring cavity in a short laser cavity length to make the structure of the laser 1 compact, thereby providing a compact, wide tunable, narrow linewidth and low noise laser 1.

[0111] In some examples, the output of laser 1 can be connected in sequence to a spectrometer and an interferometer (e.g., a Mach-Zern interferometer). By changing the wavelength of filter 15, the spectral and linewidth characteristics of the target laser at different wavelengths can be observed.

[0112] The laser 1 disclosed herein is capable of increasing the intensity of random feedback light over a wide wavelength range of tens of nanometers and has a high Q value. Combined with the wide bandwidth gain of erbium-doped fiber, it enables the realization of a wide tunable and narrow linewidth laser 1 in a short-distance feedback system.

[0113] The laser 1 disclosed herein, compared with the prior art, greatly shortens the laser cavity length and achieves at least one of the following objectives: wide tunability, continuous tunability, narrow linewidth, and single-mode laser output. It has the advantages of simple structure, easy manufacturing, low cost, and excellent performance.

[0114] While the present disclosure has been specifically described above in conjunction with the accompanying drawings and examples, it is to be understood that the foregoing description does not limit the present disclosure in any way. Those skilled in the art can make modifications and variations to the present disclosure as needed without departing from its essential spirit and scope, and all such modifications and variations shall fall within the scope of the present disclosure.

Claims

1. A random fiber laser based on a fiber Bragg grating, characterized in that, It includes an optical input terminal, a gain fiber, and a random feedback mechanism; the optical input terminal is configured to receive pump light from a pump source; The gain fiber is configured to receive the pump light and output a first optical signal within a first wavelength range, wherein the gain fiber has a gain medium excited by the pump light; the random feedback mechanism includes a feedback fiber and a string of fiber Bragg gratings formed on the feedback fiber, the fiber Bragg grating string being configured to receive the first optical signal and provide random feedback for the first optical signal to output a second optical signal within a second wavelength range, wherein the second wavelength range is smaller than the first wavelength range, the fiber Bragg grating string including multiple grating arrays corresponding to different grating periods, the multiple grating periods of the multiple grating arrays increasing sequentially along the direction of the first optical signal incident on the fiber Bragg grating string, the increment of the multiple grating periods being the same, the number of the multiple grating arrays being 50-150 to obtain a tuning range of tens of nanometers and to make the length of the feedback fiber on the order of meters, each grating array in the multiple grating arrays including multiple fiber Bragg gratings, the distance between adjacent fiber Bragg gratings in the multiple fiber Bragg gratings being random.

2. The random fiber laser according to claim 1, characterized in that, The optical input terminal is a wavelength division multiplexer, which includes two input ports and one output port. The two input ports receive the pump light and the second optical signal respectively and transmit them to the gain fiber through the output port.

3. The random fiber laser according to claim 1, characterized in that, The gain fiber is an erbium-doped fiber, and the first wavelength range is 1530nm to 1570nm.

4. The random fiber laser according to claim 3, characterized in that, The second wavelength range is 1540nm to 1560nm.

5. The random fiber laser according to any one of claims 1 to 4, characterized in that, The second wavelength range is no greater than 20 nm.

6. The random fiber laser according to claim 1, characterized in that, The gain fiber is an erbium-doped fiber, and the length of the gain fiber is on the order of meters. The length of the fiber Bragg grating string is on the order of meters.

7. The random fiber laser according to claim 1, characterized in that, When the gain of the first optical signal is greater than the loss, the random feedback mechanism is further configured to receive the first optical signal and transmit it to output a third optical signal.

8. The random fiber laser according to claim 1, characterized in that, It also includes a circulator, which includes a first port, a second port and a third port. The first port receives the first optical signal and outputs it to the random feedback mechanism through the second port. The second optical signal enters the optical input terminal through the third port to amplify the second optical signal through the gain fiber.

9. The random fiber laser according to claim 8, characterized in that, It also includes a first isolator, which is disposed between the optical input terminal and the circulator.

10. The random fiber laser according to claim 1, characterized in that, It also includes a filter configured to limit the range of available output wavelengths, wherein the second optical signal is input to the optical input terminal, and the filter is disposed between the optical input terminal and the random feedback mechanism.

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