JPH11135868A - Unequal coupler for multimode pumping optical amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a twin-coupled system, which enhances the pumping efficiency of a double-clad optical-fiber amplifier, and the manufacturing method thereof. SOLUTION: A twin-coupled system includes first and second optical couplers 3600 and 3700, which connect a multimode pump fiber to a double-clad active main fiber. A pump fiber 3800 carries the multimode pump power from a multimode source. In the meantime, main fibers 3100 and 3200 carry optical information signal on a single-mode core, which is amplified by the pump power. In the manufacturing system and method of the twin-coupled system, the first coupler is formed by performing the adhesion to the main fiber and the pump fiber and taper forming process at the first part, and the second coupler is formed by performing adhesion to the main fiber and the pump fiber and tape formation at the second part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates generally to high power multimode pumped fiber optic amplifiers.
More specifically, regarding a multimode pomped optical fiber amplifier, a twin-coupled system that increases pumping efficiency of a double-clad optical fiber amplifier.
m).

[0002]

2. Description of the Related Art A conventional optical fiber amplifier comprises an active fiber having a core doped with a rare earth element.
e fiber). The pump power at the characteristic wavelength for the rare earth element, when injected into the active fiber, excites the rare earth element ions and gains in the core for the information signal propagating along the fiber.

[0003] Rare earth elements used for doping typically include erbium (Er), neodymium (Nd), ytterbium (Yb), samarium (Sm), and praseodymium (Pr). The specific rare earth element to be used is determined according to the wavelength of the input signal light and the wavelength of the pump light. For example, Er ions are input signal light having a wavelength of 1.55 μm and a wavelength of 1.48 μm or 0.98 μm.
m pump power, Er ions and Yb
Doped with ions, further enabling the use of different broader pump wavelength bands.

Conventional pump sources include single mode laser diodes and multimode broadband lasers (mull).
timode broad area laser) coupled to active fiber on a single mode and multimode pumping fiber, respectively, to provide pump power. Single mode lasers typically provide low pump power, on the order of 100 mW. On the other hand, wide area lasers
Provide a high pump power of about 00 mW. However, these high power lasers cannot effectively inject light into the small core of a single mode fiber. As a result, the use of high power broadband lasers requires the use of large cores and multimode fibers to pump optical amplifiers.

[0005] Broadband lasers generate multimode pump power and input the pump power into inactive pumping fiber. On the other hand, this inactive
The pumping fiber typically inputs the pump power via a coupler to the inner cladding of a double-clad active fiber that acts as a multimode core for the pump power.

In the amplifier fiber, the pump power is
The fiber is guided into the inner multi-mode cladding of the fiber, from where it is transmitted to a single-mode core doped with active dopants.

A fused fiber multimode coupler has a theoretical coupling coefficient that is directly proportional to the area ratio of the two fibers that make up the coupler itself. In the ideal case for two identical fibers, the coupling coefficient is about 50%.
Typically, coupling coefficients range from 45 to 48%. This means that approximately 45-48 of the total pump power output by the pump source to the pumping fiber will actually pass from the pumping fiber to the inner cladding of the double clad active fiber. % Only, the remaining 52-55%
Means that they remain in the pumping fiber.

Some systems use two optical fibers with multimode cores of different diameters to improve the coupling coefficient of the multimode coupler. However, such a configuration often wastes power because it is difficult to match the taper shapes of two cores of different sizes.

FIG. 1 is a block diagram of a conventional amplification system that includes a multimode pump source coupled to a main fiber via a single conventional coupler. The main fiber 1100 is a double clad fiber. The information signal passes through its single mode core. Amplifier 12
00 is an Er / Yb-doped double clad active
It can take the form of a fiber, which amplifies the information signal as it propagates through the single mode core of main fiber 1100.

The multi-mode pump 1300 comprises a multi-mode pump fiber 1400 and a coupler 150
0 to the main fiber 1100.

[0011] The multi-mode pump power generated by multi-mode pump 1300 is transmitted through multi-mode pump fiber 1400 and coupler 1500.
Coupled to main fiber 1100. The coupler 1500 is
Conventional fused fiber wavelength division multiplexer (WD
It is a M (wavelength division multiplexer) type coupler. The WDM coupler behaves as a multi-mode coupler to the pump power, transmitting a single-mode signal along the main fiber without substantially coupling to the pump fiber. WDM couplers have a maximum coupling coefficient of 50% for pump power, and typically have a coupling coefficient in the range of about 45%.

The multi-mode pump 1300 can take the form of a broadband laser and is approximately 450 to 500 meters.
Output W pump power. However, due to the coupling coefficient of the coupler 1500, about 45% of this pump power enters the main fiber 1100, or about 2%.
Only between 00 and 225 mW. The remaining 55% of the pump power is lost when it is emitted from pump fiber 1400.

[0013] Some modern systems attempt to recover lost pump power. FIG. 2 is a block diagram of one of these systems. The main fiber through which the information signal passes is a matched double-clad fiber (m
signal fiber 210 which is an atched double-clad fiber
0 and the signal fiber 2200 and the amplifiers 2300, 2
400. The amplifiers 2300 and 2400 have Er /
A Yb-doped double-clad active filter can be provided to amplify the information signal as it propagates through the single mode core of the main fiber.

In this system, multimode pump 2500 includes pump fiber 2800 and pump
Through fiber 2900, each is coupled to the main fiber via two identical couplers 2600, 2700. Pump fibers 2800, 2900 are matched multimode fibers and combiners 2600, 2
At some point between 700 are splices with each other.

The multimode pump 2500 provides multiport pump power to the pump fiber 2800
Output through Due to the coupling coefficient of the coupler 2600, only about 45% of the pump power enters the signal fiber 2100. However, with this configuration, the remaining 55% of the pump power is not lost,
Instead, it enters pump fiber 2900 and
Via 700, it is coupled to a signal fiber 2200.

Applicants have observed that the addition of the pump fiber 2900 and the coupler 2700, however, does not significantly improve the overall pump power transfer on the one coupling system described above. There are several reasons for this. First, the pump fiber 2800 and the pump fiber
Due to the splice to fiber 2900, pump power is lost. Second, pump fiber 2
As a result of the initial coupling of the 800 with the signal fiber 2100,
Most of the external modes of the pump power are
00 and only the internal mode is left in the second coupling. This results in inefficient transmission of the remaining pump power in combiner 2700. Such a structure seeks to recombine the internal mode of the multimode pump power, ie, most of the poorest coupling efficiencies. As a result, the combined pump power and output power of the multi-mode amplifier do not change significantly on the single combined system described above.

In the patent and non-patent literature, several articles are directed to multi-mode coupling techniques, but none of them overcome the deficiencies of other conventional approaches described above. WO 95/10868 discloses a fiber optic amplifier comprising a fiber having two concentric cores.
lifier). Pump power provided by the multimode source couples transversely to the outer core of the fiber via the multimode fiber and the multimode optical coupler. The pump power propagates through the outer core, interacts with the inner core, and pumps the active material contained within the inner core.

US Pat. No. 5,185,814 discloses an optical communication network in which an amplifier amplifies an optical signal as it propagates along a waveguide. A single optical pump source coupled to the optical fiber pumps the amplifier.

US Pat. No. 5,533,163 discloses a double-clad optical fiber configuration that includes a core doped with an active gain material and an inner cladding surrounding the core. If the external pump source is a multimode
Pump energy into the inner cladding. The multi-mode pump energy in the inner cladding transfers the energy to the core by a repeated interaction between the energy and the active dopant inside the core.

[0020] WO 93/15536 discloses a composite glass fiber that includes an outer cladding, an inner cladding, and a single mode central core. The inner cladding is a cross-sectional profile optimized for receiving multimode pumping radiation.
e). The single mode core is located within the inner cladding and is doped with a lasant material to maximize the transfer of multimode pumping radiation to the single mode doped core.

US Pat. No. 5,170,458 discloses an optical fiber optical amplifier including an optical fiber having a central core through which signal light propagates, and a pumping light generating device for applying pumping light to the optical fiber in an oblique direction. Is disclosed.
The pump light propagates through the fiber, but is absorbed by the central core and excites it to amplify the signal light propagating through the optical fiber.

[0022]

From the Applicant's point of view, none of these known documents show that the conventional system fails to recombine sufficient pump power, and therefore the overall pump power. No one has adequately addressed the applicant's finding that the transmission efficiency is inadequate.

[0023]

SUMMARY OF THE INVENTION The present invention recombines more multimode pump power into a double clad optical amplifier than conventional systems by having couplers with different tapers. Addressing the aforementioned problems in twin coupled systems.

According to the present invention, as set forth in its embodiments and broad description, the present invention, in one aspect thereof, comprises:
Fusing a signal fiber configured to receive and carry an optical signal, a pump fiber configured to receive and carry a pump power, and the signal fiber and the pump fiber by a first amount; A first coupler for transmitting a portion of the pump power from the pump fiber to the signal fiber and fusing the signal fiber and the pump fiber and including the second fiber as a taper; A second coupler for transmitting at least some of the remaining pump power from the pump fiber to the signal fiber. The second taper depends entirely on the first taper and provides the twin coupling system with maximum overall coupling efficiency.

In another aspect, the present invention includes a method of manufacturing a twin-coupling system. In this manufacturing method, a first coupler is formed by preparing a first portion of a main fiber and a pump fiber for fusion and tapering of coupling and performing of a main fiber and a pump fiber in a first portion. A second coupler is formed by preparing a second portion of the main fiber and the pump fiber for the fusion of the coupling of the main fiber and the pump fiber, the fusion of the forming, and the taper operation in the second portion. The fusing and tapering action in the second part is
The pump power from the pump fiber is used to obtain the maximum coupling coefficient to the main fiber for the entire twin coupling system,
It depends on the fusing and tapering performed in the first part.

In another aspect, the present invention includes an apparatus for manufacturing the twin coupling system described above. The apparatus includes means for preparing the first and second portions of both the signal fiber and the pump fiber for coupling, and fusing and stretching the signal and pump fibers in the first and second portions. Means to perform. The fusing and elongating treatment in the first part forms the first coupling means, and the fusing and elongating treatment in the second part forms the second coupling means and occurs in forming the first coupler. Depends on the fusion and elongation treatment.

The present invention further provides a multi-mode pump.
An apparatus for manufacturing at least a first and a second optical coupler of a multiple coupling system for coupling a fiber to a double clad active signal fiber. The apparatus includes means for providing a multimode optical signal to the pump fiber; means for fusing the signal fiber and the pump fiber at first and second spaced apart locations;
Means for tapering the signal and pump fibers in the first and second positions;
And controlling the fusing and tapering means based on the amount of the multi-mode optical signal transmitted from the pump fiber to the signal fiber to monitor the first coupler. Heating and stretching the signal and pump fibers at a first location to create a first coupler and controlling the fusing and tapering means based on the determined coupling efficiency; Means for heating and stretching the signal fiber and the pump fiber at the second location based on the coupling coefficient for the second coupler and the coupling coefficient monitored for the second coupler to create a second coupler.

In another aspect, the invention relates to a dual clad active signal fiber and a multimode pump.
A method for manufacturing at least a first and a second optical coupler of a multi-coupling system for coupling with a fiber is included.
The method includes providing a multimode optical signal to a pump fiber, heating and stretching a first portion of the signal fiber and the pump fiber to create a first coupler; Monitoring a coupling coefficient for the first coupler based on an amount of the multi-mode optical signal transmitted from the pump fiber to the signal fiber; and controlling a first section heating and elongation step, the first section comprising: Maximizing the coupling efficiency of the signal and pump fibers,
Heating the portion and stretching to create a second coupler, wherein at the second coupler, a second coupling is performed based on an amount of the multi-mode optical signal transmitted from the pump fiber to the signal fiber. Monitoring the coupling efficiency to the coupler and controlling the heating and elongation steps of the second portion to determine a multiplicity based on the maximum coupling efficiency obtained for the first coupler and the coupling efficiency for the second coupler. Obtaining the maximum overall coupling efficiency for the coupling system.

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, explain the objects, advantages, and principles of the invention.

It will be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.

[0031]

BRIEF DESCRIPTION OF THE DRAWINGS The following detailed description of the invention refers to the drawings. Identical reference numbers shall identify identical or similar elements.

While this description includes representative embodiments, other embodiments are possible, and modifications may be made to the embodiments described without departing from the spirit and scope of the invention.

A system and method in accordance with the principles of the present invention employs a twin coupled system having two different couplers to provide efficient transmission of multimode pumping power to an active information-carrying double-clad fiber. To achieve.

FIG. 3 is an illustration of an amplification system having a twin coupling system according to the principles of the present invention. This amplification system can be combined as a high power optical amplifier in an optical fiber communication system. In this case, the input of fiber 3100 and the output of amplifying fiber 3400 are typically spliced into a single mode fiber of the communication system. The amplification system has the advantage that a power booster amplifier or a line amplifier can be configured.

The system includes two different types of multi-mode / single-mode optical fibers, a main fiber and a pump fiber, both coupled to two different couplers. The main fiber is an embedded single mode
It includes a core and carries information signals.

The main fibers are the signal fibers 3100, 3
200 and optical amplifiers 3300 and 3400. The signal fibers 3100, 3200 are matched double clad optical fibers, while the optical amplifiers 3300, 3400
Is a double clad E doped to amplify the information signal as it propagates through the main fiber.
r / Yb fiber. FIG. 4A is a diagram showing a cross-sectional view of the main fiber, and FIG. 4B is a graph of different refractive indexes of the main fiber.

As shown in FIGS. 4A and 4B, the main fiber (3100, 3200) includes three types of glass forming concentric regions 4100, 4200, 4300. They have different indices of refraction n1, n2, n3 and different diameters d1, d2, d3, respectively. In one embodiment according to the principles of the present invention, the main fiber has an index of refraction n1.
<N2 <n3, and three concentric regions 410
The diameters d1, d2, and d3 of 0, 4200, and 4300 are configured to perform single mode light propagation for the information signal in the region 4300 and to perform multimode light propagation for the pump power in the region 4200. You. In other words, the area 4300 surrounded by the area 4200 forms a single mode core for information signals. On the other hand, region 4200 surrounded by region 4100 forms a multi-mode core for pump power.

In one embodiment according to the principles of the present invention,
The refractive indices and diameters of the concentric regions 4100, 4200, 4300 have the following relationship.

[0039]

The multi-mode pump 3500 is connected to the main fiber (3100, 3100) via the couplers 3600, 3700.
3200) to provide pump power. In one embodiment according to the principles of the present invention, multi-mode pump 3500 is a broadband laser and outputs multi-mode pump power to pump fiber 3800. Pump fiber 3800 is a multi-mode optical fiber and carries multi-mode pump power. FIG. 5A shows a cross-sectional view of the pump fiber 3800, and FIG. 5B is a graph of different refractive indices of the pump fiber 3800.

As shown in FIGS. 5A and 5B, the pump fiber 3800 includes two different types of glass forming concentric regions 5100, 5200. Region 510
0,5200 are different refractive indices n1 ′, n, respectively.
2 ′ and each have a different diameter d1 ′, d2 ′. In one embodiment according to the principles of the present invention, the pump
The fiber 3800 is configured such that the above-mentioned refractive index has a relationship of n1 ′ <n2 ′. Two concentric regions 51
The diameters d1 ', d2' of 00, 5200 provide multi-mode light propagation for pump power in region 5200. In other words, the area 5200 surrounded by the area 5100 is a multi-mode pump with respect to pump power.
Form the core.

In one embodiment according to the principles of the present invention,
The refractive index and the diameter of the concentric regions 5100 and 5200 have the following relationship.

[0043]

The concentric area of the pump fiber 3800 is
It is not necessary, even though it is described as having the same refractive index and diameter as the concentric regions of the main fibers (3100, 3200).

Both the main fiber (3100, 3200) and the pump fiber 3800 have outer concentric regions (41).
00,5100) around, including a protective plastic coating. In one embodiment according to the principles of the present invention, the protective plastic coating comprises a primary fiber (3100, 3200) and a pump fiber 380.
0 have a thickness such that both outer diameters are about 250 μm. Of course, the outer diameter may be a different value, and the main fiber (31
00,3200) and the pump fiber 3800 need not be the same outer diameter.

The couplers 3600 and 3700 are different optical fiber couplers and transfer the pump power from the pump fiber 3800 to the main fibers (3100 and 3200). In one embodiment according to the principles of the present invention, the couplers 3600, 3700 include a fusion biconical tapering technique described below.
e).

FIGS. 6-9 are flow charts describing a method of fabricating a twin-coupling system in accordance with the principles of the present invention. FIG. 10 is a simplified block diagram of the twin coupling system of FIG. FIGS. 11 and 13 are block diagrams of equipment used to manufacture the first and second couplers 3600 and 3700 of FIG. 3, respectively.

Turning first to FIG. 11, equipment used in a manufacturing method in accordance with the principles of the present invention will be described first to facilitate the description of the manufacturing method with respect to FIGS. The manufacturing equipment consists of conventional equipment, a controller 8100, a multi-mode source 8200, a mode
Scrambler 8300, quartz capillary 840
0, cylindrical heater 8500, electric stage 8620,
8640, detectors 8720, 8740 with adapters 8760, 8780, pyrometer 8800, and pyrometer controller 8900.

The controller 8100 is an IBM (trademark)
It can take the form of a personal computer, such as a compatible computer. The controller 8100 includes:
Controls the operation of manufacturing equipment. Multimode source 82
00 may be any light source that generates a multi-mode optical signal, such as a wide area laser. According to one embodiment, in accordance with the principles of the present invention, a multi-mode source 8
200 generates a multimode optical signal having a wavelength equal to 0.98 μm. Mode scrambler
The rambler 8300 is connected (splice) to the output fiber of the multimode source 8200, and scrambles the mode of the multimode optical signal generated by the multimode source 8200.

[0050] Quartz capillary
8400 secures the signal fiber 3100 and the pump fiber 3800 for fusion and tapering. The cylindrical heater 8500 is a quartz capillary 8
400, a signal fiber 3100 and a pump
Heat is applied to fuse the fibers 3800 together to form the coupler 3600. Motorized stage 8620,864
0 is the signal fiber 3100 and the pump fiber 3
800 are gripped on both sides of the cylindrical heater 8500. The motorized stages 8620 and 8640 include a controller 81
Under control of 00, the signal fiber 3100 and the pump fiber 3800 are extended to form a coupler 3600.

The detectors 8700, 8740 are attached to the ends of the signal fiber 3100 and the pump fiber 3800, opposite the multimode source 8200, via appropriate adapters 8760, 8780. Detectors 8720, 8740 detect the amount of power signal transmission (ie, coupling efficiency) from pump fiber 3800 to signal fiber 3100 that occurs at coupler 3600 and report this amount to controller 8100. The pyrometer 8800, together with the pyrometer controller 8900, may be used to form the cylindrical heater
Monitor the temperature of the 0 outer wall.

Next, the description will proceed to FIGS. When a manufacturing method according to the principle of the present invention is started, first, a double-clad optical fiber (that is, a main fiber) is connected to the signal fiber section 3.
100A and the signal fiber section 3100B (FIG. 10) are cut to a length substantially equal to the sum of the predicted lengths [step 61
10]. Next, a portion 380 of the pump fiber 3800
Cut the multimode optical fiber (ie, pump fiber 3800) to have a length approximately equal to the sum of the predicted lengths of OA, 3800B, 3800C [step 6110].

The mode scrambler 8300 is connected to the output fiber of the multimode source 8200 (splic
e) while splicing the pump fiber 3800 to the mode scrambler 8300 [step 612].
0]. Next, strip signal fiber 3100 and pump fiber 3800 over a length of about 4 cm (ie, remove the coating) [step 6130].
The signal fiber 3100 is stripped at a position equal to the length of the signal fiber section 3100A, and the pump fiber 3800 is stripped at a position equal to the length of the pump fiber section 3800A. Stripping may be performed by any conventional method.

The signal fiber 3100 and the pump fiber 3800 are inserted into the quartz capillary 8400. The quartz capillary 8400 is located at the center inside the cylindrical heater 8500 [Step 6140].
Fiber stripping area is quartz capillary 840
0 so that the signal fiber section 3100A and the pump fiber section 3800A are located on the same side of the quartz capillary 8400.
00 and the pump fiber 3800 are inserted into the quartz capillary 8400. Next, the signal fiber 310
Twist 0 and pump fiber 3800 to ensure contact with each other in the stripped area [step 615].
0]. The twisting operation may be performed by any of the conventional methods.

Next, the signal fiber 3100 and the pump fiber 3800 are connected to the quartz capillary 8400.
Are attached to the motorized stages 8620 and 8640 on both sides of the [Step 6210]. The ends of the signal fiber 3100 and the pump fiber 3800 on the side opposite the multi-mode source 8200 are cut off, and the detector 872 is connected via appropriate adapters 8760 and 8780, respectively.
0, 8740 [Step 6220].

The multi-mode source 8200 outputs a multi-mode optical power signal to the mode scrambler 8300 [Step 6230]. The mode scrambler 8300 scrambles the mode of the power signal and converts the scrambled power signal into the pump fiber section 3800.
A is output to A [Step 6230]. Detector 8720,
8740 monitors the amount of power signal transmitted from pump fiber 3800 to signal fiber 3100 and reports this information to controller 8100.

The controller 8100 includes the cylindrical heater 8
The fusion and taper forming processes performed by the motor 500 and the electric stages 8620 and 8640, respectively, are started [Step 6240]. The pyrometer 8800, together with the pyrometer controller 8900, constantly monitors the temperature of the outer wall of the cylindrical heater 8500, and monitors this temperature with the controller 810.
Report to 0.

The controller 8100 includes the cylindrical heater 8
When the 500 heats the signal fiber 3100 and the pump fiber 3800, the fusion stage and the taper forming process are adjusted based on the temperature of the cylindrical heater 8500, and the motorized stages 8620 and 8640 connect the signal fiber 3100 and the pump fiber 3800 to each other. When extending, the speed is adjusted, and the fusion time is adjusted before the electric stages 8620 and 8640 start extending. 12A and 12B are graphs illustrating the temperature and speed characteristics of the fusion and taper forming processes, respectively, in forming the coupler 3600. In one embodiment according to the principles of the present invention, variables t1-t7 (in seconds), T1-T4
(° C.), V1 and V2 (μm / sec) are as follows.

T1 = 10 T1 = 850 t2 = 20 T2 = 1150 t3 = 30 T3 = 1380 t4 = 60 T4 = 900 t5 = 80 V1 = 30 t6 = 380 V2 = 20 t7 = 390

Once the controller 8100 has the coupler 360
If 0 determines that maximum multi-mode power transfer from the pump fiber 3800 to the signal fiber 3100 has been achieved with the least amount of power loss, the controller 8100
Stops the fusion and taper forming processes. When the controller 8100 makes this determination, the detectors 8720, 874
The information received from 0 is used as a reference. Based on information from the previously presented embodiment, combiner 3600 has a maximum multi-mode power transfer efficiency of 44%, ie, coupling efficiency,
And a power loss of 0.29 dB.

The controller 8100 is connected to the combiner 3600
Once the maximum coupling efficiency and minimum power loss have been obtained, the structure formed by the fused and tapered fibers can be combined with a quartz capillary 8400 by epoxy.
To complete the coupler 3600 [Step 6250]. Controller 8100 records this result and assists in calculating the overall coupling efficiency of the final twin coupling system [step 6250].

Once the controller 8100 has the coupler 360
After completing 0, combiner 3700 is formed while keeping the monitoring system online (see FIG. 13). The double clad optical fiber (that is, the main fiber) is cut into a length substantially equal to the sum of the predicted lengths of the signal fiber portion 3200A and the signal fiber portion 3200B (FIG. 10) [step 6310]. Next, both the signal fiber 3200 and the pump fiber 3800 are stripped over a length of about 4 cm [step 6320]. Signal fiber 32
00 is stripped at a location equal to the length of the signal fiber section 3200A, and the pump fiber 3800 is equal to the sum of the lengths of the pump fiber sections 3800A and 3800B from the end connected to the multimode source 8200. Remove in position. Stripping may be performed by any of the conventional methods.

In FIG. 13, the signal fiber 3200 and the pump fiber 3800 are connected to a cylindrical heater 850.
0 is inserted into a quartz capillary 8400 arranged at the center inside [Step 6330]. The stripped area of the fiber is centrally located within the quartz capillary 8400, and the signal fiber section 3200A and the pump
Fiber section 3800B is quartz capillary 8400
The signal fiber 3200 and the pump fiber 3800 are placed on the same side as the quartz capillary 8.
Insert into 400. Next, the signal fiber 3200 and the pump fiber 3800 are twisted to ensure contact with each other in the stripped area [Step 6340]. The twisting operation may be performed by any of the conventional methods.

Next, the signal fiber 3200 and the pump fiber 3800 are attached to the motorized stages 8620 and 8640 on both sides of the quartz capillary 8400 [Step 6350]. Multi mode source 8
The end of the signal fiber 3200 opposite the 200 is cut off, and both the signal fiber 3200 and the pump fiber 3800 are inserted into the detectors 8720, 8740 via appropriate adapters 8760, 8780, respectively [step] 6410].

The multi-mode source 8200 converts the multi-mode optical power signal into a mode scrambler 8300
[Step 6420]. The mode scrambler 8300 scrambles the mode of the power signal,
The scrambled power signal is supplied to the pump fiber section 380.
Output to 0A [step 6420]. Detector 872
0.8740 monitors the amount of power signal transmitted from the pump fiber 3800 to the signal fiber 3200;
This information is reported to the controller 8100.

The controller 8100 includes the cylindrical heater 8
The fusion and taper forming processes performed by the motor 500 and the motorized stages 8620 and 8640, respectively, are started [step 6430]. The pyrometer 8800, together with the pyrometer controller 8900, constantly monitors the temperature of the outer wall of the cylindrical heater 8500, and monitors this temperature with the controller 810.
Report to 0.

The controller 8100 includes the cylindrical heater 8
When the 500 heats the signal fiber 3200 and the pump fiber 3800, the fusion and taper forming processes are adjusted based on the temperature of the cylindrical heater 8500, and the motorized stages 8620 and 8640 allow the signal fiber 3200 and the pump fiber 3800 to be heated. When elongating, the speed is adjusted, and the fusion time is adjusted before the electric stages 8620 and 8640 start elongating. FIGS. 14A and 14B are graphs respectively illustrating the temperature and speed characteristics of the fusion and taper forming processes in forming the coupler 3700. In one embodiment according to the principles of the present invention, variables t1-t8 (in seconds), T1-T5
(° C.), V1 and V2 (μm / sec) are as follows.

T1 = 10 T1 = 850 t2 = 20 T2 = 1150 t3 = 30 T3 = 1400 t4 = 60 T4 = 1370 t5 = 80 T5 = 900 t6 = 90 V1 = 30 t7 = 420 V2 = 20 t8 = 430

The temperature and speed characteristics for forming coupler 3700 are different from the characteristics for forming coupler 3600. The controller 8100 causes the coupler 3700 to have a steeper slope than the coupler 3600 and a taper of a different shape. This is because the mode distribution of the power signal remaining in the pump fiber section 3800B after the coupler 3600 is different from the mode distribution of the power signal in the pump fiber section 3800A.

The controller 8100 includes a coupler 3600
As a result of the mode distribution of the power signal remaining at the rear,
Adjust the fusing and tapering process to maximize the bonding characteristics. By forming coupler 3700 in a tapered shape, a consistent mode scramble of the power signal remaining in pump fiber section 3800B behind coupler 3600 is obtained.

Once the controller 8100 determines that the process has obtained the maximum value of all multimode power transfer from the pump fiber 3800 to the main fiber, it stops the fusion and tapering process. Controller 810
0 makes such a determination based on information received from detectors 8720 and 8740 in forming combiner 3700 and information previously recorded from combiner 3600.

Based on information from the embodiments presented above, a twin-coupling system according to the principles of the present invention has a total coupling efficiency of 66%, much higher than the 50-55% obtained with conventional systems. With proper choice of length and doping of the amplifying fiber, the total coupled pump power is 300 mW and the saturated output power of the amplifier is equal to 18.5 dBm. Controller 8
Once 100 has obtained the maximum of the total coupling efficiency, the coupler 3700 is completed by fixing the structure formed by the fused and tapered fibers in a quartz capillary with epoxy [step 664].
0].

A system and method in accordance with the principles of the present invention provide multi-mode pump power to an active double-clad fiber by using a pair of different couplers to increase coupling efficiency over conventional systems. introduce.

The above description of the preferred embodiment of the present invention
Although illustrated and described, it is not intended that the form exactly disclosed is all of the invention, ie, limit the invention to the form exactly disclosed. Modifications and variations are possible in light of the above teachings or may be acquired by practicing the invention.

For example, while the foregoing has disclosed an amplification system for single mode optical signals, those skilled in the art will employ fibers having multimode signal cores instead of single mode cores where appropriate. This allows the invention to be used with multi-mode signal amplification systems.

The foregoing description has included specific data values obtained from experiments. These values are provided by way of example only, and the scope of the present invention is defined solely by the appended claims and equivalents thereof.

[Brief description of the drawings]

FIG. 1 is a block diagram of a conventional system that includes a multimode pump source coupled to a main fiber via a single conventional coupler.

FIG. 2 is a block diagram of a system for recovering a portion of lost pump power.

FIG. 3 is a diagram of a twin coupling system according to the principles of the present invention.

4 is composed of A and B, FIG. 4A is a cross-sectional view of the main fiber of FIG. 3, and FIG. 4B is a graph of different refractive indexes of the main fiber of FIG.

5 is composed of A and B, FIG. 5A is a sectional view of the pump fiber of FIG. 3, and FIG. 5B is a pump fiber of FIG.
4 shows a graph of different refractive indices of a fiber.

FIG. 6 shows a portion of a flow chart illustrating a method of manufacturing a twin coupled system in accordance with the principles of the present invention.

FIG. 7 shows a portion of a flow chart illustrating a method of manufacturing a twin coupled system in accordance with the principles of the present invention.

FIG. 8 shows a portion of a flow chart illustrating a method of manufacturing a twin-coupling system in accordance with the principles of the present invention.

FIG. 9 shows a portion of a flow chart illustrating a method of manufacturing a twin coupled system in accordance with the principles of the present invention.

FIG. 10 is a block diagram of a simplified version of the twin coupling system of FIG.

FIG. 11 is a block diagram of an apparatus used to manufacture the first coupler of FIG. 3;

12 is a diagram showing A and B, FIG. 12A is a graph showing temperature characteristics for fusing and tapering processing to form a first coupler, and FIG. 12B is a first coupler. 7 is a graph showing speed characteristics for fusing and tapering processing for producing a tape.

FIG. 13 is a block diagram of an apparatus used to manufacture the second coupler of FIG. 3;

FIG. 14 is composed of A and B, and FIG.
FIG. 14B is a graph showing temperature characteristics for fusing and tapering to form a second coupler, and FIG. 14B is a graph showing speed characteristics for fusing and tapering to form a second coupler.

[Explanation of symbols]

1100 Main fiber 1300 Multimode pump 1400 Multimode pump fiber 1500 Coupler 2100,2200 Signal fiber 2300,2400 Amplifier 2500 Multimode pump 2600,2700 Coupler 2800,2900 Pump fiber 3100,3200 Signal fiber 3300, 3400 Optical amplifier 3500 Multimode pump 3600,3700 Coupler 3800 Pump fiber 4100,4200,4300,5100,5200
Glass forming concentric region 8100 Controller 8200 Multi mode source 8300 Mode scrambler 8400 Quartz capillary 8500 Cylindrical heater 8620, 8640 Motorized stage 8760, 8780 Adapter 8720, 8740 Detector 8800 Pyrometer 8900 Pyrometer controller

 ──────────────────────────────────────────────────の Continuation of front page (71) Applicant 591011856 Pirelli Cavies System e. p. A (72) Inventor Aurelio Pianchola Italy 27045 Castelgio Pavia, Via Giuseppe Verdi 6

Claims (20)

[Claims] 1. An optical amplification system, comprising: a signal fiber configured to receive and carry an optical signal; a pump fiber configured to receive and carry pump power; A first coupler for fusing and pumping the pump fiber and including a first amount in a tapered manner, and transmitting a portion of the pump power from the pump fiber to the signal fiber; A second coupler for fusing the pump fiber and tapering by a second amount to transfer at least some of the remaining pump power from the pump fiber to the signal fiber; , Wherein said second quantity is dependent on said first quantity and provides said optical amplification system with a maximum overall coupling efficiency. Optical amplification system that. 2. The optical amplification system according to claim 1, wherein said signal fiber is coupled to said pump fiber via said first coupler and said first double-clad active fiber. A second double-clad active fiber coupled to the pump fiber via the second coupler. 3. The optical coupling system according to claim 2, wherein said signal fiber further comprises an optical amplifier coupled between said first and second double-clad active fibers. An optical amplification system comprising an active double clad fiber doped with a rare earth element. 4. The optical amplification system according to claim 1, wherein said pump fiber is a multi-mode pump.
An optical amplification system comprising a multi-mode pump fiber configured to receive and carry power. 5. The optical amplification system according to claim 4, wherein said multi-mode pump fiber is connected to said first mode.
And a single multimode fiber coupled to said signal fiber via a second coupler. 6. The optical amplification system according to claim 1, wherein the total coupling efficiency of the optical amplification system is about 66%. 7. A first and a second fiber for coupling a pump fiber configured to carry pump power to a main fiber configured to carry an optical information signal.
A method for manufacturing an optical amplifier configured in a twin-coupling system having an optical coupler, wherein preparing for coupling to a first portion of the main fiber and the pump fiber; and Fusing and tapering the main fiber and the pump fiber to form the first coupler; and preparing for coupling to the main fiber and the second portion of the pump fiber. Performing, in the second portion, performing a fusion and tapering process on the main fiber and the pump fiber to form the second coupler, and performing a fusion and tapering process in the second portion. Performing the welding and tapering performed in the first portion. 8. The method of claim 7, further comprising providing a multi-mode optical signal to the pump fiber, wherein the step of fusing and tapering the first coupler comprises: A sub-step of determining when a maximum transmission of said multi-mode optical signal from said pump fiber to said main fiber is obtained during said fusion and tapering process in said first portion; A sub-step of interrupting the fusing and tapering process on the first portion when it is determined that transmission has been obtained. 9. The method of claim 8, wherein the step of fusing and tapering to the second coupler comprises: transmitting the largest multi-mode optical signal obtained at the first portion; Based on the maximum multi-mode optical signal transmission obtained in the two sections, during the fusion and tapering process in the second section, of the multi-mode optical signal from the pump fiber to the main fiber. Sub-step of determining when a maximum full transmission is obtained; and interrupting the fusing and tapering process in the second portion when it is determined that the maximum full multi-mode optical signal transmission is obtained. A manufacturing step. 10. The method of claim 7, wherein preparing the first portion comprises: stripping the first portion of the main fiber; and removing the first portion of the pump fiber. A method of manufacturing, comprising: a sub-step of stripping; and a sub-step of twisting the main fiber and the pump fiber together at the first stripped portion. 11. The manufacturing method according to claim 10, wherein
The method of manufacturing, wherein the step of fusing and tapering for the first coupler further comprises the step of completing the first coupler formed by the fused and tapered fiber. . 12. The method of claim 7, wherein the step of preparing the second portion comprises the steps of: stripping the second portion of the main fiber; and removing the second portion of the pump fiber. A method of manufacturing, comprising: a sub-step of stripping; and a sub-step of twisting the main fiber and the pump fiber together at the second stripped portion. 13. The method according to claim 12, wherein
The method of manufacturing, wherein the step of fusing and tapering for the second coupler further comprises the step of completing the second coupler formed by the fused and tapered fiber. . 14. An apparatus for manufacturing a twin coupler having first and second optical coupling means for coupling a pump fiber to a signal fiber, comprising: a first and a second optical fiber coupling means for both the signal fiber and the pump fiber. Means for preparing the part for coupling; means for performing fusion and extension processing on the signal fiber and the pump fiber in the first and second parts, wherein the fusion in the first part is performed. And the elongation process forms the first coupling means, and the fusing and elongating processes in the second portion form the second coupling means, and the fusing and elongating processes performed in the first portion are performed. Dependent means. 15. The apparatus of claim 14, further comprising: multi-mode source means for providing a multi-mode signal to said pump fiber; and wherein said fusing and stretching process in said first portion comprises said pump fiber. Determine when the maximum transmission of the multi-mode signal from the main fiber to the main fiber is obtained,
Means for interrupting the fusion and elongation process in the first portion when it is determined that the maximum multi-mode signaling has been obtained. 16. The apparatus of claim 15, further comprising: the maximum multi-mode signaling obtained in the first part and the maximum multi-mode signaling obtained in the second part. Determining when a maximum full transmission of the multimode signal from the pump fiber to the main fiber is obtained during the fusion and elongation process in the second portion. Means for interrupting the fusion and elongation process in the second portion when it is determined that mode signaling has been obtained. 17. The apparatus of claim 14, wherein the means for preparing comprises: means for stripping the first portion of the signal fiber; means for stripping the first portion of the pump fiber; Means for twisting said signal fiber and said pump fiber together in a first stripped portion. 18. The apparatus of claim 14, wherein the means for preparing comprises: means for stripping the second portion of the signal fiber; means for stripping the second portion of the pump fiber; Means for twisting said signal fiber and said pump fiber together at a second stripping portion. 19. An apparatus for manufacturing at least a first and a second optical coupler of a multi-coupling system for coupling a multi-mode pump fiber to a multi-mode signal fiber, said multi-mode optical signal being coupled to said multi-mode optical fiber. Means for feeding a pump fiber; means for fusing the signal fiber and the pump fiber at first and second spaced positions; and means for fusing the signal fiber at the first and second positions. Means for tapering the pump fiber; and wherein the first and second couplers monitor coupling efficiency based on an amount of the multi-mode optical signal transmitted from the pump fiber to the signal fiber. Means for controlling the fusing and tapering means, based on the coupling efficiency monitored for the first coupler. Wherein heating the signal fiber and the pump fiber and extended to create the first coupler in the first position,
And controlling the fusing and taper forming means,
Heating and stretching the signal fiber and the pump fiber at the second location based on the coupling coefficient for the coupler of and the coupling coefficient monitored for the second coupler. Means to create,
An apparatus, comprising: 20. A method of manufacturing at least first and second optical couplers of a multi-coupling system for coupling a multi-mode signal fiber and a multi-mode pump fiber, comprising: Feeding the pump fiber; heating and stretching the signal fiber and a first portion of the pump fiber to create the first coupler; and wherein the first coupler comprises: Monitoring a coupling coefficient for the first coupler based on an amount of the multi-mode optical signal transmitted from the pump fiber to the signal fiber; controlling a heating and stretching step of the first portion; Obtaining a maximum in said coupling efficiency for a first coupler; and a second portion of said signal fiber and said pump fiber. Heating and stretching to create the second coupler; wherein at the second coupler, based on an amount of the multi-mode optical signal transmitted from the pump fiber to the signal fiber; Monitoring the coupling efficiency for the second coupler; controlling the heating and elongation steps of the second portion to obtain the maximum coupling efficiency obtained for the first coupler and the coupling for the second coupler. Obtaining a maximum total coupling efficiency for said multiple coupling system based on the efficiency.