JPH0645679A - Optical fiber amplifier - Google Patents

Abstract

PURPOSE:To reduce in size and cost an optical fiber amplifier by forming two isolators having no polarization dependence and installed at front and rear sides of an Er-doped fiber of one isolator unit. CONSTITUTION:An isolator unit has an isolator 21 having no polarization dependence, an array 22 held at a predetermined interval at fibers 27, 29, and an array 25 held at one ends of filters 28, 30 at a predetermined interval, a lens 23 for introducing signal lights irradiated from one ends of the fibers 27, 29, and a lens 24 for condensing the light irradiated from the isolator 21 to one ends of the fibers 28, 30. It is used instead of two isolators to be mounted at front and rear sides of the fiber 28.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber amplifier in an optical communication device.

[0002]

2. Description of the Related Art In recent years, an Er-doped optical fiber amplifier that directly amplifies light has appeared, and large-capacity, long-distance optical communication has been developed more and more, and it has been applied to subscriber systems to start providing various services. There is. In order to achieve further development, it is necessary to reduce the size and cost of the optical amplifier.

An Er-doped fiber optical amplifier is constructed as shown in FIG. 2. 1 is an Er-doped fiber, 2 is a first polarization-independent isolator, 3 is a pumping light source, 4 is an optical multiplexer, 5 Is a second polarization-independent isolator (an optical signal passes in the direction of the arrow in the figure, but does not pass in the opposite direction). These are connected by a single mode fiber. Here, when the input signal light 11 having a wavelength of 1.55 μm is inputted from the optical connector 6, it is inputted to the Er-doped fiber 1 through the polarization independent isolator 2. On the other hand, a semiconductor laser with a wavelength of 1.48 μm or 0.98 μm
When a high-power light of several tens mW to hundreds of tens mW from a pumping light source 3 using a semiconductor laser of m or the like is wavelength-combined through an optical multiplexer 4 and input to the Er-doped fiber 1, The pumped signal light having a wavelength of 1.55 μm is amplified, passes through the second polarization-independent isolator 5, and becomes the output signal light 12, and the amplified light is the optical connector 7.
Is output from.

The polarization-independent isolator does not depend on the polarization so as to transmit without loss in any polarization state of the optical fiber, which is the transmission path, and it can be isolated from optical parts such as optical connectors. This is an isolator that does not reliably prevent the return light of. This is provided before and after the Er-doped fiber 1 in order to prevent multiple reflection at the front and rear optical connectors or the like and oscillation at a wavelength other than the required wavelength. In addition, the polarization-independent isolator enlarges the signal light from the fiber with the lens 8 and separates the signal light into two with the birefringent member, and again synthesizes with the birefringent member via the Faraday rotator.
It is focused on the fiber with.

[0005]

However, in the optical amplifier constructed in this way, the individual components are expensive, and E
The r-doped fiber, optical multiplexer, and pumping light source may be cheap due to mass production technology of optical fiber and semiconductor, but the polarization-independent isolator polishes crystal materials such as lenses, birefringent materials, and Faraday rotators. It is difficult to reduce the cost because micro optics technology such as adjustment and fixing is required.

The present invention has been made in view of the above problems. One isolator is used, two input / output fibers are arranged in an array, and they are coupled by two lenses before and after the isolator. An object of the present invention is to provide an optical fiber amplifier which is cheaper and smaller in size than the conventional one, in which the coupling system is also composed of one pair.

[0007]

To achieve the above object, the present invention provides an optical fiber amplifier using an Er-doped fiber, a polarization-independent isolator, and a first and a second polarization-independent isolator.
From one end of the first optical fiber, and a second array in which one end of the optical fiber is held at a fixed interval, a second array in which one end of the third and fourth optical fibers is held at a fixed interval, The first optical signal emitted from one end of the second optical fiber and the first optical signal emitted from one end of the second optical fiber, and the first optical signal emitted from the isolator. An isolator section comprising a second lens for collecting the second optical signal on one end of the third optical fiber and collecting the second optical signal on the one end of the fourth optical fiber,
The other end of the third optical fiber is connected to the front side of the Er-doped fiber, and the other end of the second optical fiber is connected to the Er.
The signal light is connected to the rear side of the doped fiber, the signal light is input from the other end of the first optical fiber, and the amplified signal light is output from the other end of the fourth optical fiber.

[0008]

According to the present invention, two polarization-independent isolators installed before and after the Er-doped fiber are constituted by one isolator section, and two signal lights inputted into the isolator section are separated by one. Since the first lens enters the polarization-independent isolator and the two signal lights emitted from the isolator are condensed and output by the single second lens, the optical fiber amplifier has a large capacity. It is possible to reduce the size and cost.

[0009]

1 is a block diagram showing an optical fiber amplifier according to an embodiment of the present invention, and FIG. 3 is a block diagram showing an isolator portion of the optical fiber amplifier shown in FIG.

First, the isolator section will be described. In FIG. 3, reference numeral 21 denotes a polarization-independent isolator, which has the same principle configuration as the conventional example shown in FIG. 22 is a single mode fiber 27 for inputting signal light to the isolator 21.
And a single-mode fiber 29 for transmitting the output of the Er-doped fiber 1 arranged in an array at a constant interval, and 23 is two single-mode fibers 27, 2
A lens that magnifies the signal light from 9 parallel to each other (it is not necessarily parallel depending on the structure of the isolator,
It is also possible to collect light at a certain distance and diffuse it again.)
Reference numeral 24 is a lens that collects the two light beams emitted from the isolator 21, and 25 is a fiber on the input side that is a single mode fiber 28 that inputs the signal light into the Er-doped fiber and a single mode fiber 30 that transmits the output signal light. It is a fiber array arranged in an array at intervals equal to the intervals in the array 22. The signal light condensed by the lens 24 is supplied to each of the single mode fibers 28, 30.
Is incident on.

Next, an optical amplifier using the above isolator section will be described with reference to FIG. Reference numeral 20 is an isolator portion shown in FIG.
Reference numerals 7, 12, and 13 are the same as those denoted by the same reference numerals in FIG.

Input signal light 1 input from the optical connector 6
1 is input to the isolator unit 20 through the single mode fiber 27, is expanded into parallel light by the lens 23, is condensed into the single mode fiber 28 by the lens 24 through the polarization independent isolator 21, and is Er-doped fiber 1 Entered in. In addition, single mode fiber 2
8 and the Er-doped fiber 1 are usually fusion spliced.
On the other hand, the pumping light output from the pumping light source 3 is combined by the optical multiplexer 4 and input into the Er-doped fiber 1 from behind.
As a result, the signal light input to the Er-doped fiber 1 is amplified. The amplified signal light passes through the optical multiplexer 4, passes through the single mode fiber 29, and isolators 2
The signal is again input to 0, is expanded into parallel light by the lens 23, passes through the isolator 21, and is condensed by the lens 24 on the output single-mode fiber 30 to be output signal light 12 which is output from the optical connector 7.

As described above, according to this embodiment, only one polarization-independent isolator can bring about the isolator effect before and after the Er-doped fiber and prevent oscillation due to reflection from the outside. Although the pumping light is multiplexed from the rear side of the Er-doped fiber here, the optical fiber amplifier can be constructed and the present invention can be applied by the method of pumping from the front side and the both sides.

[0014]

As described above in detail, according to the present invention, one polarization-independent isolator brings about the isolator effect before and after the Er-doped fiber, and the input and output optical fibers to and from the isolator are respectively provided. Since the lenses arranged before and after the polarization-independent isolator are arranged in an array, one lens each is provided, so that it is possible to provide an optical fiber amplifier that is inexpensive and can be significantly downsized.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a configuration diagram of a conventional optical fiber amplifier.

FIG. 3 is a configuration diagram of an isolator section 20.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Er-doped fiber 3 Excitation light source 4 Optical multiplexer 6,7 Optical connector 20 Isolator part 27-30 Single mode fiber

Claims (1)

[Claims] 1. An optical fiber amplifier using an Er-doped fiber, a polarization-independent isolator, a first array in which one ends of first and second optical fibers are held at regular intervals, and third and third A second array in which one end of the fourth optical fiber is held at a constant interval, a first signal light emitted from one end of the first optical fiber, and a second signal light emitted from one end of the second optical fiber. And a first lens that makes the optical signal of the second optical signal incident on the isolator, and a first optical signal that is emitted from the isolator be condensed at one end of the third optical fiber, and a second optical signal that is the fourth optical signal. A second lens for condensing the light on one end of the optical fiber, the other end of the third optical fiber is connected to the front side of the Er-doped fiber, and the other end of the second optical fiber is connected. Er is the end
An optical fiber which is connected to the rear side of a doped fiber, inputs signal light from the other end of the first optical fiber, and outputs amplified signal light from the other end of the fourth optical fiber. amplifier.