JPH02153327A - Light amplification module - Google Patents

Abstract

PURPOSE:To decrease the number of components and adjustment positions and to reduce light loss by using a narrow-band interference filter. CONSTITUTION:High-output exciting light 111 from a light source 11 for excitation is passed through a collimator lens 12 and reflected by the narrow-band interference filter 15 to pass through the collimator lens 16, thereby entering a long-sized transmission optical fiber 17. Signal light which is propagated in the fiber 17, on the other hand, enters the filter 15 through a lens 16. Therefore, the light 111 and signal light coexist in the fiber 17 and the signal light is amplified by Raman scattering with the light 111. Then the amplified signal light in multiple light is transmitted through the filter 15, the majority of the exciting light except a component nearby the signal light frequency is reflected by the filter 15, and the amplified signal light enters the fiber 13 through a lens 14. A multiplexer demultiplexer is not necessary as compared with a case wherein a multiplexer demultiplexer and a narrow-band filter are used to decrease the number of components and adjustment points, thereby reducing the light loss.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical amplification module used in an optical direct amplification system that amplifies signal light using stimulated Raman scattering of an optical fiber.

(Prior Art) Conventionally, it has been known to utilize stimulated Raman scattering of an optical fiber as one means for directly amplifying signal light transmitted through an optical transmission line.

FIG. 2 is a configuration diagram showing an example of an optical direct amplification system using stimulated Raman scattering (for example, "Showa 60
"Collection of lectures at the Annual National Conference of the Institute of Electronics and Communication Engineers [Volume 4]" (
1986-3-5) Institute of Electronics and Communication Engineers P, 4-239
). In FIG. 2, the signal light to be amplified passes through a signal light optical fiber 21 and a multiplexer/demultiplexer 22 and enters a transmission fiber 23. After the incident signal light propagates through the transmission optical fiber 23, it passes through the multiplexer/demultiplexer 26 and the narrowband optical filter 2 that constitute the fiber Raman amplification module 28.
7 and exits. On the other hand, the pumping light for amplification emitted from the pumping light source 24 passes through the pumping light optical fiber 25,
It is wavelength-multiplexed with the signal light from the transmission optical fiber 23 by the multiplexer/demultiplexer 26, and enters the transmission fiber 23 from the receiving side to the transmitting side. At this time, the excitation light does not leak to the narrow band optical filter 27 side. After the excitation light incident on the transmission optical fiber 23 propagates therein, it is separated from the signal light by the multiplexer/demultiplexer 22, enters the terminator, and does not enter the signal light optical fiber 2.

By the way, when light with an angular frequency ω is incident on a material, the angular frequency ω corresponding to the transition between the excited state and rotational state unique to the material
A phenomenon (Raman scattering) in which light of ±Δω is generated is known. Here, light having an angular frequency of ω-Δω is called Stokes light. The optical direct amplification system shown in FIG. 2 utilizes this Raman scattering, and the pumping light is adjusted so that the wavelength of the Stokes light generated by the pumping light is almost the same as the wavelength of the signal light to be amplified. The wavelength is selected. In other words, when strong excitation light is input from the back of the transmission optical fiber 23 and signal light is input from the front, stimulated Raman scattering occurs and part of the energy of the excitation light is transferred to the signal light, and the signal light loses its energy. The signal is amplified and output from the rear side of the transmission optical fiber 23.

However, as shown in FIG. 3, natural Raman scattered light is generated from the excitation light over a range from several tens of nanometers to over a hundred nanometers near the wavelength of Stokes light. The intensity of this natural Raman scattered light is
It is strongest at the excitation light entrance of the transmission optical fiber 23, which is not attenuated by loss in the transmission optical fiber 23, and is isotropic. Therefore, in the case of an optical amplification method in which the pumping light is propagated from the receiving side to the transmitting side as shown in Fig. 2, so-called backward fiber Raman amplification, the pumping light is propagated along with the signal light on the receiving side as shown in Fig. 4. Although stronger natural Raman scattered light is emitted, this natural Raman scattered light is a noise component unrelated to the signal, and therefore causes deterioration of the receiving sensitivity of the optical direct amplification system.

In order to prevent this deterioration of reception sensitivity, conventionally, a narrowband optical filter 27 with an extremely narrow passband width as shown in FIG.
was installed after the multiplexer/demultiplexer 26, and as shown in FIG. 6, the signal light was passed through with low loss and most of the natural Raman scattered light was removed.

(Problems to be Solved by the Invention) However, in the optical direct amplification system having the above configuration, the optical amplification module 28 wavelength-multiplexes the pumping light and the signal light,
Since the multiplexer/demultiplexer 26 was provided separately to extract only the signal light, and the narrowband optical filter 27 was separately provided to remove the natural Raman scattering light mixed into the signal light, the optically amplified signal When the light passes through the optical amplification module, the LWPF (Long Wave P
a5s Filter) and B of the narrowband optical filter 27
There is a problem in that a loss is caused by a PF (Band Pa5s Filter).

An object of the present invention is to eliminate the above-mentioned problems and provide an optical amplification monoyl with low loss for signal light.

(Means for Solving the Problems) The present invention provides a narrow-band light beam having a narrow bandwidth for inputting excitation light into a transmission optical fiber and extracting only signal light from the light emitted from the transmission optical fiber. It is equipped with a filter.

(Function) The light emitted from the transmission optical fiber is amplified by stimulated Raman scattering and is accompanied by strong natural Raman scattering light based on the excitation light, but when passing through the optical amplification module, the signal light Most of the natural Raman scattered light is removed by a narrow-band optical filter with a narrow bandwidth that also performs wavelength multiplexing of the light and the excitation light, thereby preventing a decrease in reception sensitivity. Therefore, it is not necessary to separately provide a narrowband optical filter in addition to the multiplexer/demultiplexer as in the conventional case, so that the loss to the signal light can be reduced.

(Example) FIG. 1 is a configuration diagram showing a first example of the present invention,
This corresponds to the optical amplification module 28 in the optical direct amplification system shown in FIG.

In Fig. 1, No. 1 is an excitation light source that emits high-output excitation light using a solid-state laser such as YAG or Er or a semiconductor laser as an excitation light source. In order to obtain high-power pumping light, the outputs from multiple semiconductor lasers having the same wavelength are polarized and combined, and if necessary, the outputs from semiconductor lasers having similar wavelengths are wavelength-multiplexed. 12, 14, and 16 are collimating lenses with anti-reflection coating, 13 is a signal light filter, and 15 is a narrow band interference filter that functions as a narrow band optical filter. This narrow band interference filter 15 reflects light near the wavelength of the excitation light, transmits light within a bandwidth of several nanometers near the wavelength of the signal light, and even transmits light within a bandwidth of several nanometers to hundreds of nanometers near the wavelength of the signal light. Natural Raman scattered light emitted over several nanometers is reflected except for light in the vicinity of the wavelength of the signal light. Reference numeral 17 denotes a transmission optical fiber through which signal light and excitation light propagate, and corresponds to the transmission optical fiber 23 shown in FIG. Note that the wavelength of the signal light is set to the 1.3 μm band or 1.3 μm band, where the transmission loss of the optical fiber 17 is small.
If the 5 μm band is selected, the wavelength of the pumping light for performing fiber Raman amplification needs to be set in the vicinity of 1.2 μm or 1.4 μm.

Next, the operation of this embodiment will be explained.

The high-power excitation light 11 emitted from the excitation light source 11 passes through the collimating lens 12 and passes through the narrow band interference filter 15.
incident on . The incident excitation light 111 is reflected by the narrow band interference filter 15, passes through the collimating lens 16, enters the transmission optical fiber 17, and propagates therein. On the other hand, the signal light propagating from the front through the long transmission optical fiber 17 passes through the collimating lens 16 and enters the narrow band interference filter 15 . Therefore, in the transmission optical fiber 17, high-power excitation light entering from the rear direction and signal light entering from the front direction coexist, and the signal light is converted into excitation light by stimulated Raman scattering. amplified. The signal light incident on the narrowband interference filter 15 is transmitted as it is, passes through the collimating lens 14, and is connected to the signal light optical fiber 1.
3. The natural Raman scattered light emitted in the transmission optical fiber 17 passes through the collimating lens 16 together with the signal light and enters the narrow band optical filter 15. Since all but a small portion of the light is reflected, it does not enter the signal optical fiber 13. In other words, the narrowband interference filter 15 wavelength-multiplexes the pumping light and the signal light, extracts only the signal light, and removes most of the natural Raman scattered light, and furthermore, the narrowband interference filter 15 functions to wavelength-multiplex the pumping light and the signal light, and removes most of the natural Raman scattered light. It works to minimize the leakage of water.

As explained above, according to this embodiment, the optical amplification module is configured with one narrowband interference filter, so the conventional optical amplification module shown in FIG. Compared to the amplification module 28, loss for signal light can be reduced.

FIG. 7 is a configuration diagram showing a second embodiment of the present invention,
A diffraction grating 77 is used as a narrowband optical filter in place of the narrowband interference filter 15 shown in FIG. 1, and the same effects as in the first embodiment can be obtained.

In FIG. 7, excitation light from an excitation light source 71 passes through a collimator lens 72, a diffraction grating 77, and a collimator lens 76, enters a transmission optical fiber 74, and propagates. At this time, the excitation light is transmitted to the signal light optical fiber 73.
It will not leak into the system. On the other hand, the signal light from the transmission optical fiber 74 passes through the collimating lens 76 and the diffraction grating 7.
7 and a collimating lens 75 to enter the signal light optical fiber 73. At this time, the transmission optical fiber 74
Natural Raman scattered light is also emitted along with the signal light, but most of it is removed by the diffraction grating 77 and does not enter the signal light optical fiber 73.

Although the first and second embodiments described above are applied to optical amplification by backward stimulated Raman scattering, they can also be applied to optical amplification by forward stimulated Raman scattering.

(Effects of the Invention) As described above in detail, according to the present invention, an optical amplification module that conventionally consisted of a multiplexer/demultiplexer and a narrowband optical filter can be replaced with a single narrowband optical amplifier having a very narrow bandwidth. Since it is constituted by an optical filter, it is possible to reduce the loss to the optical signal, and it is possible to obtain substantially the same effect as increasing the amplification degree.

Furthermore, the number of parts and adjustment parts constituting the optical amplification module are reduced, and costs can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the first embodiment of the present invention, Fig. 2 is a block diagram showing a conventional optical direct amplification system using stimulated Raman scattering, and Fig. 3 is a diagram showing the wavelength characteristics of natural Raman scattering light. , FIG. 4 is a diagram showing the wavelength characteristics of signal light and natural Raman scattered light, and FIG. 5 is a diagram showing the wavelength characteristics of a narrowband interference filter.
FIG. 6 is a diagram showing wavelength characteristics of signal light and natural Raman scattered light after passing through a narrow band interference filter, and FIG. 7 is a configuration diagram showing a second embodiment of the present invention. 11.71...Excitation light source, 12, 14, 16°72
．． 75.76...Collimating lens, 13°73...
- Optical fiber for signal light No. 5... Narrow band interference filter, 17.74... Optical fiber for transmission 77... Diffraction grating. Patent applicant: Oki Electric Industry Co., Ltd. Honsha vp a'14. I v implementation license] Fig. 1 28 Kyuko % mo 2 le Kijo 7 Sophistry Raman kgL IM to Hikari ni Tsubaki 1 - Narushizu 7
Figure 2

Claims (1)

[Claims] It is characterized by being equipped with a narrow band optical filter that allows excitation light to enter the transmission optical fiber, removes natural Raman scattered light from the light emitted from the transmission optical fiber, and extracts only the signal light. optical amplification module.