JPH04291973A - Optical fiber amplifier - Google Patents

Abstract

PURPOSE:To reduce a coupling loss and to simplify a constitution by emitting an exciting light and a signal light in parallel beams, mixing the parallel beams by a wavelength multiplex branching mixer, and coupling the mixed light to a rare earth element-added optical fiber. CONSTITUTION:An exciting light of a semiconductor laser 1 having a wavelength lambdaa is formed to a parallel beam 11, a signal light having a wavelength lambdab to be propagated through an optical fiber 2 is formed to a parallel beam 12, the beams 11, 12 are mixed to a composite light 13 on the same optical axis by a wavelength multiplex branching mixer 3, and the light 13 is coupled to a rare earth element-added optical fiber 4.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention is an optical system that converts excitation light and signal light into parallel lights, converts the parallel lights into multiplexed light using a wavelength multiplexing/demultiplexing multiplexer, and couples this combined light into a rare earth-doped optical fiber. It is about fiber amplifiers.

0002

2. Description of the Related Art An optical fiber amplifier amplifies a rare earth doped optical fiber by inputting pumping light of a specific wavelength into the fiber to excite it, and passing a signal light in an amplification wavelength band through the fiber. Since the amplification gain of an optical fiber amplifier is determined by the pumping light intensity, in order to increase the amplification gain, it is necessary to couple a large amount of pumping light to the rare earth-doped optical fiber.

Next, the configuration of a conventional optical fiber amplifier will be explained with reference to FIG. In FIG. 2, 6 is a light emitting module that emits excitation light with wavelength λa, 7 is an optical fiber through which signal light with wavelength λb propagates, 8 is a fiber type wavelength multiplexing/demultiplexing multiplexer, and 9 is a rare earth doped optical fiber. In FIG. 2, the output of the light emitting module 6 and the output of the optical fiber 7 are connected to a fiber-type wavelength multiplexing/demultiplexing/multiplexing multiplexer 8 to combine them, and the output end of the fiber type wavelength multiplexing/demultiplexing/multiplexing multiplexer 8 is doped with rare earth. optical fiber 9
connect to configure an optical fiber amplifier.

0004

[Problems to be Solved by the Invention] Before the excitation light from the semiconductor laser inside the light emitting module 6 enters the rare earth-doped optical fiber 9, it is connected to the optical system inside the light emitting module 6 and undergoes fiber-type wavelength multiplexing and demultiplexing. It passes through the wave device 8. There is a coupling loss of approximately 3 dB in the optical system inside the light emitting module 6, and a passage loss of approximately 1 dB in the fiber type wavelength multiplexing/demultiplexing multiplexer 8, so the coupling loss of the excitation light to the rare earth-doped optical fiber 9 is approximately It becomes 4dB.

[0005] The fiber-type wavelength multiplexing/demultiplexing/combining device 8 has wavelength dependence in its branching ratio, and when excitation light outside a limited wavelength range passes through, the passage loss increases. The limited wavelength range is, for example, a narrow range of about 20 nm. When the optical fiber amplifier oscillates and an excessive amount of return light near the wavelength λb is generated, the fiber type wavelength multiplexing/demultiplexing multiplexer 8 returns 10% of the returned light.
The semiconductor laser inside the light emitting module 6 may be damaged because the amount of light is transmitted to the light emitting module 6 side.

[0006] This invention makes the excitation light and the signal light into parallel lights, converts the parallel lights into multiplexed light using a wavelength multiplexing/demultiplexing multiplexer, and couples the combined light to a rare earth-doped optical fiber, thereby reducing coupling loss. The purpose of the present invention is to provide an optical fiber amplifier with a simple configuration.

[0007]

[Means for Solving the Problems] In order to achieve this object, in the present invention, the excitation light of the semiconductor laser 1 with the wavelength λa is made into parallel light 11, and the signal light with the wavelength λb propagating through the optical fiber 2 is made into the parallel light 12. Then, the parallel light 11 and the parallel light 12 are converted into a multiplexed light 13 on the same optical axis by a wavelength multiplexing/demultiplexing multiplexer 3, and the multiplexed light 13 is coupled to a rare earth-doped optical fiber 4.

[0008]

[Operation] Next, the configuration of the optical fiber amplifier according to the present invention will be explained with reference to FIG. In FIG. 1, 1 is a semiconductor laser, 2 is an optical fiber, 3 is a wavelength multiplexing/demultiplexing multiplexer, 4 is a rare earth doped optical fiber, and 5A, 5B, and 5C are lenses. The light emitted from the semiconductor laser 1 is converted into parallel light 11 by a lens 5A, and becomes excitation light with a wavelength λa. Wavelength λ from optical fiber 2
The signal light b is converted into parallel light 12 by the lens 5B. The parallel light 11 and the parallel light 12 are combined into a multiplexed light 13 on the same optical axis by a wavelength multiplexing/demultiplexing/combining device 3 composed of a dielectric multilayer film. The dielectric multilayer film used is one that transmits parallel light 11 with wavelength λa and reflects parallel light 12 with wavelength λb. Combined light 13
is coupled to the rare earth doped optical fiber 4 through the lens 5C. In order to prevent oscillation, the end face of each optical fiber is processed to reduce reflectance, such as diagonal polishing and anti-reflection coating.

The coupling loss when the output light of the semiconductor laser 1 shown in FIG. 1 is coupled to the rare earth doped optical fiber 4 is approximately 3 dB.
This can be reduced by about 1 dB compared to FIG. Further, the coupling loss when the signal light emitted from the optical fiber 2 is coupled to the rare earth doped optical fiber 4 is about 1 dB, which is the same as in FIG.

The wavelength multiplexing/demultiplexing/combining device 3 has a transmission range of 95% in a wavelength range of approximately 40 nm for transmitting the parallel light 11, for example.
There are the above, and the stop band for reflecting the parallel light 12 has a loss of 30 dB or more in a wavelength range of about 40 nm. As a result, the wavelength range that can be used as pumping light is improved to about twice that in FIG. It also has the function of protecting the

Even if the positional relationship between the semiconductor laser 1 and the optical fiber 2 in FIG. 1 is replaced and the wavelength characteristics of the transmission region and reflection region of the wavelength multiplexing/demultiplexing/combining device 3 are reversed, an optical fiber amplifier can be constructed in the same way. be able to. The wavelength λa of the semiconductor laser 1 in FIG. 1 is 1.48 μm band, and the wavelength λb of the signal light is 1.5
By using an erbium-doped optical fiber as the rare earth-doped optical fiber 4 for the 5-μm band, a high-performance optical fiber amplifier for the 1.55-μm band can be obtained.

0012

[Effects of the Invention] According to the present invention, the pumping light and the signal light are each made into parallel lights, the parallel lights are made into a multiplexed light by a wavelength multiplexing/demultiplexing multiplexer, and this multiplexed light is coupled to a rare earth-doped optical fiber. , has the following effects.

First, the pumping light of the semiconductor laser 1 is directly coupled from the wavelength multiplexing/demultiplexing/multiplexing device to the rare earth-doped optical fiber. As a result, the fiber type wavelength division multiplexing/demultiplexing multiplexer shown in Fig. 2 can be removed from the system, and the pumping light can be coupled to the rare earth-doped optical fiber with high efficiency, thereby obtaining an optical fiber amplifier with a large amplification gain. be able to.

The second method is to use a wavelength multiplexing/demultiplexing multiplexer having characteristics equivalent to those of a dielectric multilayer film. The features of the wavelength multiplexing/demultiplexing multiplexer are the ability to multiplex pump light and signal light,
It also has the function of protecting the semiconductor laser from returning light. Even if the optical fiber amplifier oscillates and an excessive amount of return light near the wavelength λb is generated, the semiconductor laser is
．． Since it reaches only 1% or less, the semiconductor laser will not be damaged.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an optical fiber amplifier according to the present invention.

FIG. 2 is a configuration diagram of an optical fiber amplifier according to the prior art.

[Explanation of symbols]

1 Semiconductor laser 2 Optical fiber 3 Wavelength multiplexing/demultiplexing multiplexer 4 Rare earth doped optical fiber 5A lens 5B Lens 5C lens 11 Parallel light 12 Parallel light 13 Combined light

Claims (1)

[Claims] Claim 1: The excitation light of a semiconductor laser (1) with a wavelength λa is made into a first parallel light (11), and the excitation light is connected to an optical fiber (2).
The signal light with wavelength λb propagating through is made into a second parallel light (12), and the first parallel light (11) and second parallel light (12) are combined into the same light by a wavelength multiplexing/demultiplexing/combining device (3). Combined light on the axis (13
), and the combined light (13) is transferred to a rare earth-doped optical fiber (4).
An optical fiber amplifier characterized in that it is coupled to.