JPH0398025A - Optical amplifying device - Google Patents

Abstract

PURPOSE:To remove variation in gain pertaining to variation of a plane of polarization and to obtain a stable gain by using an isolator for light with polarization nondependency and providing a loss means. CONSTITUTION:Assuming that the gain of a semiconductor laser amplifier 12 is larger in TE mode than in TM mode and varies periodically, the loss means which has loss corresponding to the gain difference between the TE mode and TM mode, e.g. a Fabri-Perot resonator 31 having loss in a medium in etalon is interposed in the optical path of TE-mode light 24 for an amplifier having the characteristics. Light beams in the TE mode 24 and TM mode 25 are made incident on a 2nd optical circuit 19 and multiplexed. The multiplexed light is converged by a lens 22 and coupled optically with an optical fiber 23. Consequently, light inputted to the optical amplifying device becomes amplified light having no variation in gain between the TE mode and TM mode and stable gain is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an optical amplification device that can be used in an optical communication device.

(Prior Art) FIG. 6 shows a tII diagram of an optical amplification device used in a conventional optical communication device. In FIG. 6, 41 is an optical fiber, 42 is a semiconductor laser amplifier that amplifies an incident optical signal, 43.
45 is an optical system, for example a lens. 46 is an optical fiber.The light 40 output from the optical fiber 41 enters the semiconductor laser amplifier 42, where it is The amplified light is converted into parallel light by a lens 43, transmitted through an optical isolator 44, focused by a lens 45, and optically coupled to an optical fiber 46.

The above-mentioned optical isolator prevents the reflected light from the fiber connector that connects the optical fiber and other optical components from being optically coupled to the semiconductor laser amplifier again, and prevents the semiconductor laser amplifier from causing unstable operation. It is something.

For example, in the case of FIG. 6, light reflected by a fiber connector (not shown) that connects the optical fiber 46 and other members enters the polarizing prism 49 from the optical fiber 46 via the lens 45. The light is split into transmitted light and reflected light. Since the polarization plane of the transmitted light is converted by 45" by the 45" Faraday rotator 48, this light is reflected by the polarizing prism 47 and is prevented from being supplied to the semiconductor laser amplifier 42.

Such optical isolators generally have strong polarization dependence. Therefore, as shown in Figure 6, when coupled with a semiconductor laser amplifier, for example, only one of the TE mode and TM mode of laser light is transmitted, and the loss of the other mode is infinite. Because of the transmission, only optical amplification devices with extremely high polarization dependence could be constructed.

In ordinary single mode fiber, the plane of polarization is not conserved;
The plane of polarization changes over time. Therefore, when a conventional optical amplifier is inserted into a normal single mode fiber system, since the optical isolator has polarization dependence, a mode of light that does not pass through the isolator is generated, and as the polarization plane changes in the fiber, optical amplification occurs. The gain of the device changes significantly. Therefore, there was a problem that stable optical communication could not be realized.

(Problem to be solved by the invention) Conventional optical amplification devices have strong polarization dependence, and when inserted into a normal single mode fiber system, the gain changes greatly as the polarization plane changes, so it is difficult to stabilize the optical amplifier. There was a problem that no gain could be obtained.

The present invention was made to eliminate the above-mentioned drawbacks, and an object of the present invention is to provide an optical amplification device that can obtain stable gain.

[Structure of the Invention] (Means for Solving the Problem) In order to achieve the above object, the present invention provides a semiconductor laser amplifier that amplifies light output from an optical fiber, and an input side and an output side of the semiconductor laser amplifier. The first feature is that the optical isolator is provided on at least one side of the optical isolator so that the loss of manually generated light does not depend on the polarization plane of the light.

Furthermore, a semiconductor laser amplifier that amplifies the light output from the optical fiber, and an optical isolator provided on at least one of the input side and output side of the semiconductor laser amplifier, so that the loss of the manually generated light does not depend on the polarization plane of the light. and a loss means for causing a predetermined amount of loss of at least one of the lights separated into TE mode and TM mode by the semiconductor laser amplifier within the optical isolator. In particular, the loss means is a Fabry-Bello resonator.

(Operation) In the optical amplification device having the configuration of the first feature, polarization independent 1j
When an optical isolator is installed on the output side of a semiconductor laser amplifier, the output light from the optical fiber is amplified by the semiconductor laser amplifier, and the light amplified by the semiconductor laser amplifier passes through this isolator regardless of its polarization plane. Since it passes through without loss, stable gain can be obtained.

In the optical intensifier having the second feature, light output from an optical fiber is amplified by a semiconductor laser amplifier, and this light is transmitted through a polarization-independent optical isolator. The light manually applied to this optical isolator is the T of the semiconductor laser amplifier.
The loss means inserted into the isolator removes the loss of the light that has a higher amplification factor in the semiconductor laser amplifier among the separated lights, which are separated into E mode and TM mode, and the gain of the other light is increased. By making sure that they are equal, a stable gain can be obtained.

(Example) Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing HR regulations according to an embodiment of the present invention.

In FIG. 1, 11 is an optical fiber, for example, a tipped fiber is used. 12 is a semiconductor laser amplifier, and 13.22 is an optical system, which is a lens. 14 is a first optical circuit consisting of a polarizing beam splitter 15 and a mirror 16, 17 is a 45'' Faraday rotator, and 18 is a 1/2 wavelength plate.

One is a second optical path consisting of a polarizing beam splitter 20 and a mirror 21, which includes a first optical circuit door, a 45° Faraday rotator, a 15.1/2 wavelength plate 16, and a second optical circuit. ” constitutes “optical isolator 1”.

23 is an optical fiber.

The light emitted from the optical fiber 11 passes through the semiconductor laser amplifier 12, where it is amplified, and then becomes parallel light at the lens 13. This parallel light is incident on the first optical circuit 14, and is split by the polarizing beam splitter 15 into two, for example, TE mode light 24 and TM mode light 25 of the semiconductor laser amplifier 12. The polarizing beam splitter 15 has a property of, for example, reflecting light having an electric field component in a direction perpendicular to the plane of the paper in FIG. 1, and transmitting light having a component parallel to the plane of the paper. Each divided light 24.25
is incident on a 45" Faraday rotator 17, where the plane of polarization is rotated by 45 degrees. Next, both modes of light pass through a 172 wavelength plate 18, where each plane of polarization is rotated by a 45 degree Faraday rotator. 17 is returned to the polarization direction of the polarization plane before incidence.Then, both modes are combined in the second optical circuit 19,
The light is focused by a lens 22 and optically coupled to an optical fiber 23 .

When the optical amplification device is configured as described above, one side of the optical isolator is polarization-independent in that the loss of transmitted light does not depend on the polarization plane of the light, so both modes of light Transparent regardless of

Therefore, compared to a conventional optical amplification device that uses a polarization-dependent optical isolator to transmit only one mode of light, a more stable gain can be obtained.

Furthermore, in this embodiment, even if the reflected light from a fiber connector or the like is emitted from the optical fiber 23, this reflected light does not return to the semiconductor laser amplifier 12, so that unstable operation of the semiconductor laser amplifier 12 can be prevented. can.

This is because the reflected light from the optical fiber 23 is demultiplexed by the second optical circuit 19, transmitted through the 1/2 wavelength plate 18 and the 45'' Faraday rotator 17, and the plane of polarization is converted to the first light. When these two waves are input to the circuit LA, the light a=t from the mirror 16 to the polarizing beam splitter 15 is transmitted through the polarizing beam splitter 15, and the other light is reflected by this beam splitter 15. Therefore, , semiconductor laser amplifier 1
2, the reflected light is not optically coupled.

The optical isolator 30 is provided on the output side of the semiconductor laser amplifier 1-2 in the case of FIG.
1 and the semiconductor laser amplifier 12. Further, the optical isolator 1' may be provided on both the input side and the output side of the semiconductor laser amplifier 12.

Next, an embodiment of an optical amplification device in which a loss means is provided in an optical isolator will be described. FIG. 2 is a diagram showing the configuration of this embodiment. Components in FIG. 2 that are the same as those in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted.

The light emitted from the optical fiber 11 passes through the semiconductor laser amplifier 12 and is optically amplified, and then becomes parallel to the lens 13 . The parallel light is divided into two lights, TE mode 24 and TM mode 25, by the first optical circuit 14. TE mode 2
4 and TM mode 25 pass through 45@Faraday rotator 17, their respective planes of polarization are rotated by 45 degrees, and further,
172 wavelength plate 18, 45° Faraday rotator 1
7 Return to the polarization plane before incidence.

By the way, assume that the gain of the semiconductor laser amplifier 12 is larger in the TE mode than in the TM mode and changes periodically, as shown in FIG. 3(a), for example. In the case of an amplifier with such characteristics, a loss means having a loss (shown in FIG. 3(b)) corresponding to the gain difference between the TE mode and TM mode in FIG. 3(a), for example, in the medium inside the etalon, is A Fabry Bellow resonator 31 having a loss is inserted into the optical path of the TE mode light 24.

Both the TE mode 24 and TM mode 25 lights are input into one second optical circuit and are combined there. The multiplexed light is focused by a lens 22 and optically coupled to an optical fiber 23.

With the above purchase, the light manually input to this optical amplification device becomes amplified light whose output has no difference in gain between TE mode and TM mode.

Furthermore, if the characteristics of the semiconductor laser amplifier are such that the gain of one mode changes significantly periodically with respect to the wavelength as shown in FIG. A Fabry-Bello resonator with the characteristic of canceling periodic components is installed in the optical path within the optical isolator.

As a result, the TE mode and TM mode are output with the same amplification factor.

Fabry bellow resonators with various characteristics are selected depending on the characteristics of the semiconductor laser amplifier. Further, by making the optical length (product of refractive index and length) of the Fabry-Bello resonator match the optical length of the laser and tilting the Fabry-Bello resonator, the harmonic characteristics of each mode can be finely tuned.

Furthermore, in order to provide a constant loss regardless of the wavelength, for example, a light absorption plate coated with Cr or the like should be inserted into the optical path, or a TE
A loss may be caused in the optical fiber coupling by slightly shifting the second optical circuit of the light beam combining section of the mode and TM mode.

Furthermore, the optical isolator 30 and Fab-Perot resonator 31 shown in FIG. It is sufficient if a predetermined amount of light can be optically coupled to the amplifier 12.

Throughout the embodiment shown in FIG. 1 and the embodiment shown in FIG. It is also possible to use birefringent tentatives 32, 33.

Furthermore, in FIGS. 1 and 2, the 1/'2 wavelength plate 18 is
This is provided to match the plane of polarization of each mode with the plane of polarization before entering the optical isolator, and by doing so, the first optical circuit 14 and the second optical circuit 19 can have the same groove configuration. I can do it. However, as long as both modes can be combined, there is no need for the two optical circuits to have the same structure, and there is no need to provide a 172-wave plate.

[Effects of the Invention] As detailed above, according to the optical amplifying device of the present invention, by using a polarization-independent optical isolator and further providing a loss means, f′V It is possible to eliminate the undesirable gain changes and obtain a stable gain.

[Brief explanation of drawings]

FIG. 1 shows {11} one embodiment of the optical amplification device according to the present invention.
Figure 2 shows the structure of an embodiment of the preamplifier equipped with a loss means. Figures 3 and 4 show the TE mode and TM mode (7) 1' conductor with respect to wavelength. Figure 5 is a diagram showing the change in gain of a laser amplifier, Figure 5 is a diagram showing the structure of an embodiment using a birefringent plate as an optical isolator, and Figure 6 is a diagram showing the {14-circle} of a conventional optical amplification device. It is. 11.23... Optical fiber] 2... Semiconductor laser amplifier 13.22... Lens 14... First optical circuit 17... 45° Faraday rotator l8... 1/2 wavelength One board...Second optical circuit 30...Optical isolator

Claims (3)

[Claims] (1) A semiconductor laser amplifier that amplifies the light output from the optical fiber, and is provided on at least one of the input side and output side of the semiconductor laser amplifier, so that the loss of the input light does not depend on the polarization plane of the light. An optical amplification device comprising an optical isolator. (2) A semiconductor laser amplifier that amplifies the light output from the optical fiber, and is provided on at least one of the input side and output side of the semiconductor laser amplifier, so that the loss of the input light does not depend on the polarization plane of the light. An optical amplification comprising an optical isolator and a loss means for causing a predetermined amount of loss of at least one of the lights separated into the TE mode and TM mode of the semiconductor laser amplifier within the optical isolator. Device. (3) The optical amplification device according to claim 2, wherein the loss means is a Fabry-Bello resonator.