JPH0529686A - Optical amplifier - Google Patents

Abstract

(57) [Abstract] [Purpose] To reduce the number of parts of an optical amplifying device, realize simplification of the configuration, increase gain by round-trip amplification of signal light, and reduce noise. [Structure] An optical circulator 1, a rare earth-doped optical waveguide 2, a wavelength selection optical filter 3, and an excitation light source 4. The wavelength selection optical filter 3 passes the excitation light and reflects the signal light. Therefore, the output light of the excitation light source 4 is injected into the rare earth-doped optical waveguide 2 through the wavelength selection filter 3 to excite the optical waveguide 2. The signal light input from the optical circulator side is amplified in the waveguide 2, reflected by the wavelength selective optical filter 3, amplified again in the waveguide 2, and output from the port 12 of the optical circulator. [Effect] An optical coupler for inputting pumping light is not required, the device is simplified, and a high gain optical amplifier device with less spontaneous emission noise can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplifying device, and more particularly to an optical amplifying device using a rare earth-doped optical waveguide used in an optical transmission system and an optical signal system.

2. Description of the Related Art Conventionally, as an effective optical amplifying device used in an optical transmission system and an optical signal system, an optical amplifying device using a rare-earth doped optical waveguide has been described in the literature, 16th European Conference on Optical Communication, 1990. Proceedings, Volume 1, M OG 4.3, pp. 99-102
Page (16th European Conference
e on Optical Communicatio
n 1990, Proceedings, Volume
-1, MoG4.3, pp. 99-102. )It is described in.

FIG. 10 shows the configuration of a conventional optical amplifier device described in the above document. The signal light input is applied to the rare earth-doped optical fiber 2 via the optical circulator 1 and the wavelength division multiplexing optical coupler 6. The pumping light from the pumping light source 4 is also added to the rare earth-doped optical fiber 2 via the wavelength multiplexing optical coupler 6. A reflection mirror 7 is arranged at one end of the optical fiber 2, and is configured to reflect the signal light and the excitation light and re-enter the optical fiber 2. In this configuration, the wavelength multiplexing optical coupler 6 having the pumping light input port, the signal light input port, and the wavelength multiplexing light output port is used to input the pumping light into the rare earth-doped optical fiber together with the signal light.
Further, although it is a reciprocal amplification type using the reflection mirror 7, it is a configuration that uses only the reflection characteristic for the signal light and does not use the transmission characteristic for the excitation light.

[0003]

In the structure of the optical amplifying device, reduction of the number of parts and integration are important issues for downsizing. The conventional optical amplifying device shown in FIG. 10 has an advantage of increasing the gain by the round trip amplification of the signal light, but the wavelength multiplexing optical coupler 6 having the pumping light input port, the signal light input port and the wavelength multiplexing light output port. Is used, the structure of the device is complicated, and no special consideration is given to the characteristics of the reflection mirror 7. Therefore, in addition to the amplified signal light, spontaneous emission noise is considerably included, and the signal noise ratio is high. Is deteriorating. An object of the present invention is to reduce the number of components, simplify the optical amplifier configuration, and realize high reliability by integration, maintain the gain due to round-trip amplification of signal light, and reduce spontaneous emission optical noise. It is to realize the device.

[0004]

In order to achieve the above object, the present invention provides an optical amplifier for amplifying signal light by adding signal light and pumping light to a rare earth-doped optical waveguide. A first wavelength-selective optical filter that allows the pumping light to pass therethrough and reflects the signal light is installed between the two to configure an optical amplifier. An optical fiber is desirable as the rare earth-doped optical waveguide, but other optical integrated circuit type optical waveguides may be used. As a preferred embodiment of the present invention, in the optical amplifying device having the above-mentioned configuration, the second end that reflects the pumping light and allows the signal light to pass through to the other end of the rare earth-doped optical waveguide opposite to the pumping light input section. A wavelength selective optical filter is provided.

[0005]

In the optical amplifying device according to the present invention, the first wavelength selecting optical filter that functions as a pass filter for pumping light and as a reflection mirror for signal light is provided at the pumping light input end of the rare earth-doped optical waveguide. Since it is installed, the excitation light is injected into the rare earth-doped optical waveguide through this wavelength selective optical filter. Therefore, it is possible to remove the wavelength multiplexing coupler required in the conventional optical amplifier and to make a simple device configuration.

On the other hand, the signal light is input from the other end of the rare earth-doped optical waveguide, amplified in the excited optical waveguide, reflected by the wavelength selective optical filter, amplified again, and output. Therefore, the gain of the optical amplifying device is increased as compared with the conventional one. Further, by using the second wavelength selective optical filter, the pumping light can be reflected and reused in the optical amplifier, so that the gain of the optical amplifier is further improved.

Here, by providing the first wavelength selective optical filter with a narrow band reflection characteristic that reflects only the signal light, the spontaneous emission light is suppressed and the signal-to-noise ratio is improved. Further, the signal-to-noise ratio is further improved by providing the second wavelength selective optical filter with a narrow bandpass characteristic for the signal light.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of the configuration of a first embodiment of an optical amplifier according to the present invention. This optical amplifying device comprises an optical circulator 1, a rare earth-doped optical waveguide 2, a wavelength selection optical filter 3 and an excitation light source 4.

The signal light is input to one end of the rare earth-doped optical waveguide 2 through the input port 11 of the optical circulator 1. Further, the optical circulator 1 is used to output the output light, which is obtained by amplifying the signal light and returning again from the rare earth-doped optical fiber 2, to the output port 12. Since this function can be realized by an optical coupler as well, the optical circulator 1 may be replaced by an optical coupler. Further, by replacing the rare earth-doped optical waveguide 2 with a rare earth-doped optical fiber, it is possible to configure an optical amplification device having good compatibility with the optical fiber transmission system.

Ideally, the wavelength selective optical filter 3 has the structure shown in FIG.
It has the characteristics shown in. λs is the wavelength of the signal light, and λp is the wavelength of the pumping light. Therefore, the wavelength selection optical filter 3 acts as a pass filter for the excitation light and as a reflection mirror for the signal light. Therefore, the output light of the excitation light source 4 is efficiently injected into the rare earth-doped optical waveguide 2 through the wavelength selection filter 3, and the rare earth-doped optical waveguide 2 is excited. The signal light input from the optical circulator 1 side is amplified in the excited rare earth-doped optical waveguide 2, then reflected by the wavelength selection optical filter 3 and again amplified in the rare earth-doped optical waveguide 2, and the output of the optical circulator 1 It is output from the port 12. Rare earth doped optical waveguide 2
Then, in addition to the amplified signal light, there is spontaneous emission light that is a noise component in a wide wavelength band.
Since the spontaneous emission light other than the wavelength region near the signal light is not reflected, the spontaneous emission light returning to the optical circulator 1 is suppressed and the spontaneous emission light noise is reduced.

FIG. 3 is a block diagram of the configuration of a second embodiment of the optical amplifying device according to the present invention. The basic configuration is the same as that of the first embodiment (the same functions and components are designated by the same reference numerals and their description is omitted. The same applies to the following embodiments). In the present embodiment, as the wavelength selection filter 3, an optical waveguide built-in type wavelength selection optical filter 3 ′ constituted by a diffraction grating manufactured in an optical waveguide or an optical fiber is used. This wavelength selective optical filter 3'with a built-in optical waveguide also has the characteristics shown in FIG. Since this filter 3'is integrated with the optical waveguide, it is not necessary to insert an individual bulk component, and the device is downsized and highly reliable.

FIG. 4 is a block diagram of a wavelength selective optical filter 3'having a built-in optical waveguide. As shown in the figure, the refractive indices n ₁ and n ₂ are perpendicular to the optical axis (light traveling direction) in the optical waveguide or optical fiber.
Is a periodic structure composed of a plurality of different thin layers. As a method of making a grating, a method of making a grating known in the field of semiconductor lasers such as a distributed feedback semiconductor laser is used. Generally, it can be produced by interference of an ultraviolet laser beam. Further, a technique of manufacturing a selective optical filter with an optical fiber has been conventionally known (for example, Electronic Letters “ELE”).
CTRONICS LETTERS "24th May
1990 Vol. 26 No. 26. 11 "ALL-FI
BRE NARROW BAND REFLECTION
GRATINGS AT 1500 nm ").

FIG. 5 is a block diagram showing the configuration of a third embodiment of the optical amplifying device according to the present invention. The basic configuration is the same as that of the second embodiment, but the optical components other than the excitation light source 4 are integrated on the same glass substrate 8, and the excitation light source 4 is hybrid-mounted on the substrate 8. The signal light input and the signal light output are separated by an optical coupler integrated on the glass substrate 8. As described above, by producing the integrated optical amplifying device, there is an effect that further miniaturization and high reliability of the device can be achieved.

FIG. 6 is a block diagram showing the configuration of a fourth embodiment of the optical amplifier according to the present invention. The optical amplifying device of this embodiment comprises an optical circulator 1, a second wavelength selection optical filter 5, a rare earth-doped optical waveguide 2, a first wavelength selection filter 3 and a pumping light source 4. Except for the second wavelength selective optical filter 5, it is the same as the optical amplifying device shown in FIG.

The wavelength selective optical filter 5 has the characteristics shown in FIG. In FIG. 7, λs is the wavelength of the signal light and λp is the wavelength of the pump light. Therefore, the wavelength selection optical filter 5 acts as a reflection mirror for the excitation light and as a pass filter for the signal light. In FIG. 6, the signal light of wavelength λs input from the optical circulator 1 side passes through the wavelength selective optical filter 5, is input to the rare earth-doped optical waveguide 2, is amplified in the rare earth-doped optical waveguide 2, and then the wavelength The light is reflected by the selective optical filter 3, amplified again in the rare earth-doped optical waveguide 2, and output from the port 12 of the optical circulator through the wavelength selective optical filter 5.

The output light of the pumping light source 4 is injected into the rare earth-doped optical waveguide 2 through the wavelength selection optical filter 3, reflected by the wavelength selection optical filter 5 and injected again into the rare earth-doped optical waveguide 2 to excite the rare earth-doped optical waveguide 2. To be done. Since the excitation light can be reciprocated and reused in this way,
Highly efficient optical amplification becomes possible. Since the characteristics of the wavelength selection optical filter 3 are narrow band reflection characteristics for the signal light and the characteristics of the wavelength selection optical filter 5 are the narrow band pass characteristics, spontaneous emission light other than the wavelength near the signal light can be removed. The noise of spontaneous emission light is reduced. Also in this embodiment, by replacing the rare earth-doped optical waveguide 2 with a rare earth-doped optical fiber, it is possible to construct an optical amplifier having good compatibility with the optical fiber transmission system.

FIG. 8 is a block diagram showing the configuration of a fifth embodiment of the optical amplifying device according to the present invention. The basic structure is the same as that of the fourth embodiment. In the present embodiment, the optical waveguide built-in type wavelength selective optical filters 3'and 5'in which the wavelength selective optical filter is composed of a diffraction grating formed in the optical waveguide or the optical fiber are used. This wavelength selective optical filter with a built-in optical waveguide also has the characteristics shown in FIG. Since this optical filter is integrated with the optical waveguide, it is not necessary to insert an individual bulk component, and the device can be downsized and highly reliable.

FIG. 9 is a block diagram of a sixth embodiment of the optical amplifying device according to the present invention. The basic structure is the same as that of the fifth embodiment, but the optical components other than the excitation light source 4 are integrated on the same glass substrate 8, and the excitation light source 4 is hybrid-mounted on the substrate. As described above, by manufacturing the integrated optical amplifier device, there is an effect that further miniaturization and high reliability of the device can be achieved.

[0019]

According to the present invention, in an optical amplifying device using a rare earth-doped optical waveguide or a rare earth-doped optical fiber, the structure is simplified, at the same time, gain is increased and pumping efficiency is increased, and spontaneous emission light is increased. Has the effect of reducing noise by suppressing it. Furthermore, by integrating the optical components, further miniaturization and higher reliability are realized.

[Brief description of drawings]

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

FIG. 2 is a characteristic diagram of the wavelength selective optical filter 3 of FIG.

FIG. 3 is a configuration block diagram of a second embodiment of the optical amplifying device according to the present invention.

FIG. 4 is a configuration diagram of a wavelength selective optical filter with a built-in optical waveguide.

FIG. 5 is a configuration block diagram of a third embodiment of the optical amplifier according to the present invention.

FIG. 6 is a configuration block diagram of a fourth embodiment of the optical amplifier according to the present invention.

FIG. 7 is a characteristic diagram of another wavelength selective optical filter.

FIG. 8 is a configuration block diagram of a fifth embodiment of the optical amplifier according to the present invention.

FIG. 9 is a configuration block diagram of a sixth embodiment of the optical amplifying device according to the present invention.

FIG. 10 is a block diagram showing a configuration of a conventional optical amplifier.

[Explanation of symbols]

1: optical circulator, 2: rare earth-doped optical waveguide,
3, 5: wavelength selective optical filter, 4: excitation light source,
3 ', 5': Wavelength selective optical filter with built-in optical waveguide, 6:
WDM optical coupler, 7: reflective mirror,
8: Glass substrate, 11: Input port, 12: Output port.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication location G02B 6/12 H 7036-2K G02F 1/35 501 501246-2K H01S 3/07 8934-4M

Claims (8)

[Claims] 1. An optical amplifier for amplifying signal light by adding signal light and pumping light to a rare earth-doped optical waveguide, wherein pumping light is passed between the rare earth-doped optical waveguide and the pumping light source,
An optical amplifying device, characterized in that a wavelength selective optical filter for reflecting signal light is installed. 2. The optical amplifying device according to claim 1, wherein the wavelength selective optical filter comprises a diffraction grating formed in an optical waveguide formed on a substrate of an optical integrated circuit. Amplification device. 3. The optical amplifying device according to claim 1, wherein the rare earth-doped optical waveguide comprises a rare earth-doped optical fiber. 4. The optical amplifying device according to claim 3, wherein the wavelength selective optical filter is composed of a diffraction grating formed in a fiber. 5. An optical amplifier including a pumping light source for adding pumping light to a rare earth-doped optical waveguide as a constituent element, wherein the first wavelength-selective light that passes the pumping light and reflects the signal light at one end of the rare earth-doped optical waveguide. An optical amplifying device comprising a filter and a second wavelength selective optical filter which reflects pumping light and transmits signal light at the other end. 6. The optical amplifying device according to claim 5, wherein at least one of the first and second wavelength selective optical filters is a diffraction grating formed in an optical waveguide formed on a substrate of an optical integrated circuit. An optical amplifying device characterized by being configured. 7. The optical amplifying device according to claim 5, wherein the rare earth-doped optical waveguide comprises a rare earth-doped optical fiber. 8. The optical amplifying device according to claim 5, wherein at least one of the first and second wavelength selective optical filters is composed of a diffraction grating formed in an optical fiber. apparatus.