An erbium-doped fiber amplifier and its reflective optical composite device

Abstract

The present invention provides an erbium-doped fiber amplifier and a reflective optical composite device thereof. The reflective optical composite device comprises a four-wire pigtail containing two pump fibers and two signal fibers. A collimating lens is disposed at one end of the four-wire pigtail, and a filter is disposed at the end of the collimating lens remote from the four-wire pigtail. The filter reflects pump light emitted from the pump fiber to the signal fiber, and the signal light emitted from the signal fiber passes through the filter. A polarization rotator is disposed at the end of the filter remote from the collimating lens, and a reflector is disposed at the end of the polarization rotator remote from the filter. The reflector reflects the signal light back to the signal fiber along its original path. The present invention also provides an erbium-doped fiber amplifier having the reflective optical composite device. The present invention can reduce the size of the optical composite device and lower the production cost of the optical composite device.

Description

Technical Field

[0001] The present invention relates to a reflective optical composite device, in particular to a reflective optical composite device for an erbium-doped optical fiber amplifier and an erbium-doped optical fiber amplifier having the reflective optical composite device. Background Art

[0002] An erbium-doped fiber amplifier (EDFA) is an important optical device in fiber optic systems. It can be connected to the back stage of a combiner to amplify the power of the combined optical signal, thereby increasing the optical power of the signal light.

[0003] Existing Erbium-doped fiber amplifiers (EDFAs) can receive both signal light and pump light, boosting the signal light's optical power by simultaneously channeling the pump and signal light into a single optical fiber. However, in existing EDF amplifiers, signal light typically passes through the EDF only once. Since the signal light is amplified within the EDF, the amplified optical power is related to the length of the EDF. To achieve higher optical power, a longer EDF is often required. This results in a longer EDF, hindering EDF amplifier miniaturization and increasing production costs.

[0004] The Chinese invention patent application with publication number CN115579725A discloses a MOPA laser system, which is equipped with a seed light source, a pump source, an isolator, a circulator, a combiner, a gain fiber, a wavelength division multiplexer, and a first reflector and a second reflector. The signal light of this system can pass through the gain fiber twice to increase the optical power of the signal light. However, because the signal light and the pump light are first combined by the combiner and then pass through the gain fiber, the subsequent stage needs to use a wavelength division multiplexer to split the combined optical signal to obtain the signal light and the pump light respectively, and two reflectors need to be provided to reflect the signal light and the pump light respectively. The system uses many optical components, especially the wavelength division multiplexer and the first reflector and the second reflector, which makes the entire laser system more complicated. The optical circulator is also required, which is not conducive to the miniaturization of the laser system and has a high production cost.

[0005] In addition, since the system only has one optical fiber for pump light injection, which is connected to a pump light source that emits pump light of a specific wavelength, only pump light of a specific wavelength can be injected. For scenarios where pump light of two different wavelengths needs to be injected, the laser system cannot meet the requirements.

[0006] In addition, after the signal light passes through the isolator and enters the combiner, it is combined with the pump light and reflected. It will pass through the combiner again and be received by the filter and output. In other words, the signal light passes through the combiner twice. If the signal light is polarized light, the signal light will easily interfere due to the birefringence effect, which will affect the output optical signal. Summary of the Invention

[0007] A first object of the present invention is to provide an optical composite device that is small in size and low in production cost.

[0008] A second object of the present invention is to provide an erbium-doped fiber amplifier having an optical composite device.

[0009] In order to achieve the above-mentioned first objective, the present invention provides an optical composite device including a four-wire pigtail, wherein two pump optical fibers and two signal optical fibers are arranged in the four-wire pigtail; wherein a collimating lens is provided at one end of the four-wire pigtail, and a filter is provided at the end of the collimating lens away from the four-wire pigtail, the filter reflects the pump light emitted from the pump optical fiber to the signal optical fiber, and the signal light emitted from the signal optical fiber passes through the filter; a polarization state rotator is provided at the end of the filter away from the collimating lens, and a reflector is provided at the end of the polarization state rotator away from the filter, and the reflector reflects the signal light along the original path to the signal optical fiber.

[0010] As can be seen from the above scheme, the present invention, by reflecting the signal light, allows the signal light to pass twice through the erbium-doped fiber connected to the signal fiber, thereby reducing the length of the erbium-doped fiber and facilitating the miniaturization of the erbium-doped fiber amplifier. Furthermore, because the pump light is not combined with the signal light before being reflected, the pump light and signal light are reflected separately. Therefore, there is no need for an optical splitter to separate the combined optical signal into pump light and signal light, nor is there a need for two independent reflective devices to reflect the pump light and signal light separately. Furthermore, there is no need for an optical circulator within the optical composite device. Consequently, the optical composite device uses fewer optical components, resulting in lower production costs and further facilitating its miniaturization.

[0011] In addition, since a polarization state rotation device is provided in the optical composite device, the polarization state of the signal light can be changed each time the signal light passes through the polarization state rotation device, so that the polarization state of the signal light is different when it passes through the erbium-doped optical fiber twice, which can avoid birefringence and reduce interference with the signal light.

[0012] In a preferred solution, the polarization state rotation device includes a Faraday rotator, and the polarization direction of the signal light is rotated by 45° along the same rotation direction each time the signal light passes through the Faraday rotator.

[0013] It can be seen that after the signal light passes through the Faraday rotator twice, the polarization direction will be rotated 90°, that is, the polarization states of the incident signal light and the outgoing signal light are perpendicular to each other, which can effectively avoid the interference caused by the birefringence effect.

[0014] A further solution is that the reflector is a lens-type reflector, a roof prism-type reflector, or a concave mirror. Thus, the lens-type reflector, the roof prism-type reflector, or the concave mirror can allow the two signal light beams to be perpendicularly incident on the reflective film on the reflector, respectively, so that the two signal light beams can return along the original path.

[0015] A further solution is that a reflective film is provided on the end face of the reflector away from the polarization state rotator, or a reflective film is provided on the end face of the reflector close to the polarization state rotator.

[0016] It can be seen that for the transmission reflector and the roof prism reflector, since the reflective film is provided on the end face of the reflector away from the polarization state rotation device, the signal light can change the optical path inside the lens reflector or the roof prism reflector so that the two beams of signal light are respectively incident on the reflector perpendicularly, which is conducive to the two signal lights being able to return along the original path.

[0017] A further solution is that the filter is a flat plate or a thin plate with a wedge angle. Using a thin plate with a wedge angle can prevent interference of the signal light.

[0018] A further solution is that the collimating lens is a beam expander lens, a gradient refractive index lens, a spherical lens or an aspherical lens.

[0019] A further solution is that the pump fiber is a standard core fiber, an expanded beam fiber, an erbium-doped fiber or a small bend radius fiber; and / or the signal fiber is a standard core fiber, an expanded beam fiber, an erbium-doped fiber or a small bend radius fiber.

[0020] A further solution is that the two pump fibers and the two signal fibers are arranged in a straight line, a square, or a diamond shape within the quad-fiber pigtail.

[0021] In order to achieve the second objective mentioned above, the erbium-doped fiber amplifier provided by the present invention includes a pump light source and the above-mentioned reflective optical composite device, wherein the pump light source is fused with two pump optical fibers.

[0022] A preferred solution is that the erbium-doped fiber amplifier further includes an optical circulator, and the two signal optical fibers are respectively connected to two adjacent ports of the optical circulator.

[0023] As can be seen, the signal light emitted from a signal fiber after the first stage of amplification enters the first port of the optical circulator, then enters the second signal fiber through the second port of the optical circulator for the second stage of amplification. After the second stage of amplification, the signal light is then emitted from the optical circulator. In this way, the two-stage amplification of the signal light uses the same optical components such as the filter, polarization rotator, and reflector, achieving two-stage amplification of the signal light while reducing the size of the optical composite device.

[0024] In addition, two pump fibers can be connected to emit pump lights of different wavelengths, which is beneficial to improving the optical power of the signal light. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 FIG. 1 is a structural diagram of a first embodiment of a reflective optical composite device of an erbium-doped fiber amplifier according to the present invention.

[0026] Figure 2 FIG. 1 is a structural diagram of a second embodiment of a reflective optical composite device of an erbium-doped fiber amplifier according to the present invention.

[0027] Figure 3 It is a structural diagram of an embodiment of an erbium-doped fiber amplifier of the present invention.

[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments. DETAILED DESCRIPTION

[0029] An optical composite device of the present invention can be used in an erbium-doped fiber amplifier. For example, a portion of the optical fiber of the optical composite device is fused to the erbium-doped fiber. The optical composite device can amplify the optical power of the optical signal and also realize wavelength division multiplexing and polarization state rotation functions.

[0030] First embodiment of optical composite device:

[0031] See also Figure 1The optical composite device of this embodiment includes a quad-fiber pigtail 110, a collimating lens 120, a filter 130, a polarization rotator 140, and a reflector 150. The quad-fiber pigtail 110 includes a capillary tube, within which are disposed four optical fibers: a pump fiber 111, a pump fiber 112, and a signal fiber 113, 114. The pump fibers 111 and 112 are respectively connected to a pump light source. Preferably, the pump light sources connected to the two pump fibers 111 and 112 generate the same pump light. Of course, the wavelength of the pump light generated by the pump light source connected to the pump fiber 111 may also be different from the wavelength of the pump light generated by the pump light source connected to the pump fiber 112. For example, the pump light generated by the pump light source connected to the pump fiber 111 may have a wavelength of 980 nm, while the pump light generated by the pump light source connected to the pump fiber 112 may have a wavelength of 1480 nm.

[0032] Signal fibers 113 and 114 can receive signal light, and the polarization state of the light can be adjusted by a polarization rotator 140. Pump fibers 111 and 112 can be standard-core fibers, beam-expanding fibers, erbium-doped fibers, or fibers with a small bend radius. Similarly, signal fibers 113 and 114 can also be standard-core fibers, beam-expanding fibers, erbium-doped fibers, or fibers with a small bend radius. Furthermore, the two pump fibers 111 and 112 and the two signal fibers 113 and 114 are arranged in a straight line, a square, or a diamond pattern within the quad fiber pigtail 110.

[0033] The collimating lens 120 is disposed at one end of the quad-fiber pigtail 110. The pump light emitted from the pump fibers 111 and 112 or the signal light emitted from the signal fibers 113 and 114 passes through the collimating lens 120. The collimating lens 120 can be a beam expander lens, a gradient index lens, a spherical lens, or an aspherical lens. Preferably, the collimating lens 120 can be a beam expander lens to increase the diameter of the light beam and, of course, adjust the divergence angle of the light beam.

[0034] A filter 130 is provided at one end of the collimating lens 120 away from the four-wire pigtail 110. The filter 130 reflects optical signals of a specific wavelength, while optical signals of other wavelengths can pass through the filter 130. In this embodiment, the filter 130 reflects the pump light emitted from the pump fibers 111 and 112, while optical signals emitted from the signal fibers 113 and 114 can pass through the filter 130. Since the wavelength of the pump light generated by the pump light source is fixed, the corresponding filter 130 can be set according to the wavelength of the pump light, so that the filter 130 can reflect the pump light of a specific wavelength. The reflected pump light will be incident on the signal fiber. For example, the pump light emitted from the pump fiber 111 is reflected to the signal fiber 114 after passing through the filter 130, and the pump light emitted from the pump fiber 112 is reflected to the signal fiber 113 after passing through the filter 130. Figure 1 Therefore, it is necessary to set the angles of the pump fibers 111 and 112 and the signal fibers 113 and 114 so that the pump light emitted from the pump fibers 111 and 112 can be reflected into the signal fibers 114 and 113 respectively.

[0035] Of course, the filter 130 can be a flat plate or a thin plate with a wedge angle, preferably a thin plate with a wedge angle. The thin plate with a wedge angle can reflect the pump light to the corresponding signal fiber and avoid interference with the signal light. The signal light can pass through the filter 130 and be incident on the polarization rotator 140.

[0036] In this embodiment, the polarization rotator 140 is positioned at the end of the filter 130 away from the collimating lens 120. It comprises a Faraday rotator with a magnetic ring 141 positioned outside the Faraday rotator. When the magnetic ring 141 is energized and generates a magnetic field, the polarization of the signal light passing through the Faraday rotator rotates in a direction that follows the right-hand rule. By controlling the magnetic field strength of the magnetic ring 141, the polarization direction of the signal light can be rotated 45°. The polarization-rotated signal light is then incident on the reflector 150.

[0037] The lens reflector 150 of this embodiment has a convex surface 151, which faces the polarization rotator 140. The lens reflector 150 can be a spherical lens, an aspherical lens, or a combination of a lens and a reflector. The convex surface 151 of the lens reflector 150 is located near the end face of the polarization rotator 140, and a reflective coating 152 is coated on the flat end of the lens reflector 150. The signal light emitted from the signal fibers 113 and 114, after passing through the collimating lens 120, intersects at the front focal point of the lens reflector 150. The signal light then strikes the convex surface 151, refracts, and strikes the reflective coating 152 perpendicularly and parallel to each other. The reflective coating 152 reflects the signal light, returning it to its original path. Specifically, the signal light emitted from the signal fiber 113 is reflected back to the signal fiber 113, and the signal light emitted from the signal fiber 114 is reflected back to the signal fiber 114.

[0038] The returning signal light passes through the polarization rotation device 140 again, where its polarization direction is rotated 45° in the same direction. Specifically, when the signal light first passes through the Faraday rotator, its polarization direction is rotated 45° in a direction that follows the right-hand rule. After being reflected, the signal light passes through the Faraday rotator again, and again in a direction that follows the right-hand rule. Therefore, after passing through the Faraday rotator twice, the polarization state of the signal light has rotated 90° compared to when it was not incident on the Faraday rotator. Therefore, the polarization directions of the reflected signal light and the incident signal light are perpendicular to each other. This prevents interference between the incident and reflected signal light due to birefringence, ensuring that the optical signals emitted from the signal fibers 113 and 114 are not distorted.

[0039] After passing through polarization rotator 140, the reflected signal light passes through filter 130 again and is incident on collimating lens 120. After passing through collimating lens 120, it is incident on the corresponding signal fibers 113 and 114. Because the pump light also enters signal fibers 113 and 114, the signal light reflected from signal fibers 113 and 114 is combined with the pump light, coupling the pump light into the signal light. This coupled light beam increases its optical power when passing through the erbium-doped fiber, thereby amplifying the optical power of the signal light.

[0040] Because the signal light passes through the erbium-doped fiber twice, the optical power of the signal light is boosted during these passages. Compared to traditional optical composite devices, this can achieve the same optical power boost by half the length of the erbium-doped fiber. This reduces both the production cost and the size of the optical composite device. Furthermore, since the optical composite device does not require an optical circulator or beam splitter, and only requires a single reflector, fewer components are used, further reducing the production cost and size of the optical composite device.

[0041] Second embodiment of the optical composite device:

[0042] See also Figure 2 The optical composite device of this embodiment includes a quad-fiber pigtail 210, a collimating lens 220, a filter 230, a polarization rotator 240, and a reflector 250. The quad-fiber pigtail 210 includes a capillary tube, within which are disposed four optical fibers: a pump fiber 211, a pump fiber 212, and a signal fiber 213, 214.

[0043] Collimating lens 220 is disposed at one end of quad-fiber pigtail 210. Pump light emitted from pump fibers 211 and 212, or signal light emitted from signal fibers 213 and 214, both pass through collimating lens 220. A filter 230 is disposed at the end of collimating lens 220 away from quad-fiber pigtail 210. This filter 230 reflects the pump light emitted from pump fibers 211 and 212, while allowing the optical signals emitted from signal fibers 213 and 214 to pass through filter 230. Specifically, the pump light emitted from pump fiber 211 passes through filter 230 and is then reflected to signal fiber 214. The pump light emitted from pump fiber 212 passes through filter 230 and is then reflected to signal fiber 213. Filter 230 can be a flat plate or a thin plate with a wedge angle, preferably a thin plate with a wedge angle.

[0044] The polarization state rotator 240 is disposed at one end of the filter 230 away from the collimating lens 220. The polarization state rotator 240 includes a Faraday rotator with a magnetic ring 241 disposed outside the Faraday rotator. When the magnetic ring 241 generates a magnetic field, the polarization state of the signal light will rotate when it passes through the Faraday rotator. The signal light with the rotated polarization direction will be incident on the reflector 250.

[0045] Unlike the first embodiment, the reflector 250 of this embodiment is a roof prism reflector. Its end face, which is close to the polarization rotator 240, is a protruding roof surface 251, while its end face, which is far from the polarization rotator 240, is coated with a reflective coating 252. After the signal light emitted from the signal optical fibers 213 and 214 is incident on the roof surface 251, the propagating optical path within the reflector 250 is deflected and perpendicularly incident on the reflective coating 252 in a mutually parallel manner. The reflective coating 252 reflects the signal light, returning it along its original path.

[0046] When the returning signal light passes through the polarization rotator 240 again, the polarization direction is rotated by 45° in the same direction again, so that the polarization state of the signal light is rotated by 90° compared to when it does not enter the Faraday rotator. This can avoid the problem of signal light interference caused by birefringence between the incident signal light and the reflected signal light.

[0047] After passing through polarization rotator 240, the reflected signal light passes through filter 230 again and is incident on collimating lens 220. After passing through collimating lens 220, it is incident on the corresponding signal fibers 213 and 214. Because the pump light also enters signal fibers 213 and 214, the signal light reflected from signal fibers 213 and 214 will couple with the pump light. The coupled light beam will achieve an increase in optical power when it passes through the erbium-doped fiber.

[0048] Example of Erbium-Doped Fiber Amplifier:

[0049] See also Figure 3 This embodiment has a four-port optical circulator 310 and an optical composite device 330 , wherein the optical composite device 330 can adopt the optical composite device of the above embodiment.

[0050] The optical circulator 310 has four ports, namely a first port 311, a second port 312, a third port 313, and a fourth port 314. Optical signals can only be transmitted in one direction within the optical circulator 310. That is, an optical signal incident from the first port 311 can only be emitted from the second port 312, an optical signal incident from the second port 312 can only be emitted from the third port 313, and an optical signal incident from the third port 313 can only be emitted from the fourth port 314.

[0051] The optical composite device 330 also has four ports: a first port 331, a second port 332, a third port 333, and a fourth port 334. The first port 331 is connected to a pump light source via an optical fiber 324. Pump light generated by the pump light source is input to the first port 331 via the optical fiber 324. Within the optical composite device 330, the first port 331 is connected to a single pump fiber. Similarly, the fourth port 334 is connected to another pump light source via an optical fiber 322. Pump light generated by the pump light source is input to the fourth port 334 via the optical fiber 322. Within the optical composite device 330, the fourth port 334 is connected to another pump fiber.

[0052] A segment of erbium-doped fiber 323 is connected between the second port 332 of the optical composite device 330 and the second port 312 of the optical circulator 310. Another segment of erbium-doped fiber 321 is connected between the third port 333 of the optical composite device 330 and the third port 313 of the optical circulator 310. The second port 332 and the third port 333 of the optical composite device 330 are respectively connected to two signal optical fibers. Preferably, the second port 332 and the third port 333 are fusion-spliced to the erbium-doped fibers 323 and 321, respectively.

[0053] The first port 311 of the optical circulator 310 receives signal light, which then exits from the second port 312 and passes through the erbium-doped fiber 323 before entering the optical composite device 330. The signal light entering the optical composite device 330 couples with the pump light emitted from the optical fiber 324. The coupled optical signal then passes through the second port 332 and the erbium-doped fiber 323 again. The optical power of the signal light is amplified while propagating within the erbium-doped fiber 323. Consequently, the optical power of the signal light returning to the second port 312 of the optical circulator 310 has been amplified by the first stage.

[0054] The signal light incident on the second port 312 of the optical circulator 310 is emitted from the third port 313 and, after passing through the erbium-doped fiber 321, is incident on the third port 333 of the optical composite device 330. At this point, the signal light undergoes further optical power amplification within the erbium-doped fiber 321. The amplified signal light is then incident on another signal fiber from the third port 333 of the optical composite device 330 and coupled with the pump light emitted from the fiber 322. The coupled optical signal is then emitted from the third port 333 of the optical composite device 330 again, passing through the erbium-doped fiber 321 again, and returning to the third port 313 of the optical circulator 310. Passing through the erbium-doped fiber 321 again, the optical power is further amplified, achieving a second stage of amplification of the initially incident signal light. Finally, the signal light incident on the third port 313 of the optical circulator 310 is emitted from the fourth port 314 of the optical circulator 310.

[0055] In this way, during the two-stage amplification process of the signal light, it passes through the erbium-doped optical fibers 323 and 321 twice respectively, so that the signal light is amplified twice in the erbium-doped optical fibers 323 and 321. When the same amplification factor is performed, the length of the erbium-doped optical fiber used can be reduced, thereby reducing the production cost of the erbium-doped optical fiber amplifier and reducing the volume of the erbium-doped optical fiber amplifier.

[0056] Of course, the above scheme is only a preferred embodiment of the present invention. There are more changes in actual application, such as changes in the arrangement of the pump fiber and the signal fiber in the four-wire pigtail, or changes in the specific structure of the reflector, etc. These changes should also be included in the scope of protection of the claims of the present invention.

Claims

1. A reflective optical composite device for an erbium-doped fiber amplifier, comprising: A four-wire pigtail, wherein two pump fibers and two signal fibers are provided in the four-wire pigtail; Its characteristics are: A collimating lens is provided at one end of the four-wire pigtail, and a filter is provided at the end of the collimating lens away from the four-wire pigtail, wherein the filter reflects the pump light emitted from the two pump fibers to the two signal fibers respectively, and the signal light emitted from the signal fibers passes through the filter; A polarization state rotation device is provided at one end of the filter away from the collimating lens, and a reflector is provided at one end of the polarization state rotation device away from the filter. The reflector reflects the signal light back to the signal optical fiber.

2. The reflective optical composite device of the erbium-doped fiber amplifier according to claim 1, characterized in that: The polarization state rotation device includes a Faraday rotator. Each time the signal light passes through the Faraday rotator, the polarization direction rotates by 45° along the same rotation direction.

3. The reflective optical composite device of the erbium-doped fiber amplifier according to claim 1 or 2, characterized in that: The reflector is a lens reflector, a roof prism reflector or a concave mirror.

4. The reflective optical composite device of the erbium-doped fiber amplifier according to claim 3, characterized in that: The end face of the reflector away from the polarization state rotation device is provided with a reflective film; or the end face of the reflector close to the polarization state rotation device is provided with a reflective film.

5. The reflective optical composite device of the erbium-doped fiber amplifier according to claim 1 or 2, characterized in that: The filter is a flat plate or a thin plate with a wedge angle.

6. The reflective optical composite device of the erbium-doped fiber amplifier according to claim 1 or 2, characterized in that: The collimating lens is a beam expander lens, a gradient refractive index lens, a spherical lens or an aspherical lens.

7. The reflective optical composite device of the erbium-doped fiber amplifier according to claim 1 or 2, characterized in that: The pump fiber is a standard core fiber, an expanded beam fiber, an erbium-doped fiber, or a small bending radius fiber; and / or The signal optical fiber is a standard core diameter optical fiber, a beam expanding optical fiber, an erbium-doped optical fiber or an optical fiber with a small bending radius.

8. The reflective optical composite device of the erbium-doped fiber amplifier according to claim 1 or 2, characterized in that: The two pump optical fibers and the two signal optical fibers are arranged in a straight line, a square or a diamond shape in the four-wire pigtail.

9. An erbium-doped fiber amplifier, characterized in that: include: A pump light source and the reflective optical composite device according to any one of claims 1 to 8, wherein the pump light source is fused with the two pump optical fibers.

10. The erbium-doped fiber amplifier according to claim 9, characterized in that: An optical circulator is also included, and the two signal optical fibers are respectively connected to two adjacent ports of the optical circulator.

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