JPH0629162U - Optical amplifier circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a novel optical amplifier circuit capable of bidirectionally amplifying signal light with a sufficient amplification degree. [Structure] The optical amplifying section 11 is made of a rare earth element such as Er or Nd.
Optical fiber 12 having a core added thereto, a semiconductor laser (LD) 13 for generating pumping light for pumping the amplifying optical fiber 12, and multiplexing / demultiplexing for multiplexing or branching the signal light and the pumping light It consists of a container 14. Next, the optical branch circuit 15
Reference numerals a and 15b are optical waveguide circuits that allow signal lights of two kinds of wavelength bands to pass in opposite directions and to pass in only one direction. It consists of two narrow band multiplexers / demultiplexers 16a, 16b or 16c, 16d and optical isolators 17a, 17b or 17c, 17d all having the same wavelength characteristic,
Isolation is usually about 45 dB to 60 dB. In the optical amplifier circuit of the present invention, the optical amplifier unit 11 has the above-mentioned 2
It is incorporated between the pair of optical branch circuits 15a and 15b.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an optical amplifier circuit that is small in size, has high gain, and directly amplifies signal light in the 1.5 μm band bidirectionally.

[0002]

[Prior art]

 Conventionally, the structure of a rare earth element erbium (hereinafter referred to as Er) -doped fiber type amplifier has been as shown in FIG. Pumping high-power semiconductor laser 1, optical combiner 2 for combining pumping light from laser 1 and input signal light in the 1.5 μm band, Er-doped fiber 3 serving as a broadening medium, light for preventing return light It consists of an isolator 4 and a narrow band filter 5 that blocks the pumping light and passes only the signal light.

Here, as the semiconductor laser 1, an InGa AsP laser (wavelength 1.48 μm), an InGaAs strained quantum well laser (wavelength 0.98 μm), or the like that matches the absorption wavelength band of Er ions is used, and the optical multiplexer 2 As such, bulk type optical circuits to which dielectric multilayer filters are applied, fusion splicing type optical fiber couplers, etc. are used. Further, the Er-doped fiber 3 serving as an amplification medium has a core portion to which a trace amount of Er, which is a rare earth element, is added, and is used in a length of about several tens of meters to several hundreds of meters. There is a vapor growth method. The optical isolator 4 is used to suppress the laser oscillation due to the reflected return light generated in the optical circuit or the connector connection, and the narrow band filter 5 removes the spontaneous emission light (ASE) and the like and reduces the signal light. It is used to reduce the noise component ratio. All of the above five components are indispensable for constructing an optical fiber type amplifier, and therefore, it can be said that the characteristics of the entire amplifier are governed by the characteristics of each individual component.

[0004]

[Problems to be solved by the device]

 By the way, in the above-mentioned conventional example, the optical isolator 4 is indispensable for preventing reflected return light, and normally, the forward pass loss is 1.0 to 1.5 dB, while the reverse pass loss is 45 to 60 dB or more. Is used. Therefore, when the optical fiber type amplifier shown in FIG. 4 is used as a repeater of a fiber transmission line, the signal light passes through the optical isolator 4 in the forward direction but not in the reverse direction. Therefore, there is a drawback that two-way communication is not possible with this circuit alone, and two independent optical fiber type amplifiers and two transmission lines are required to perform two-way communication.

Further, as shown in FIG. 3, an optical amplifier circuit capable of bidirectional communication over one transmission line is also conceivable, but in this case also, two optical fiber type amplifiers 7a and 7b are required. In addition, since the optical equalizers 6a and 6b are used, there is a drawback that a gain of 6 dB · NF (noise figure) deteriorates by 3 bB.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide a novel optical amplifier circuit capable of amplifying signal light bidirectionally with a sufficient amplification degree.

[0007]

[Means and Actions for Solving the Problems]

 In order to achieve the above object, the present invention connects two narrow-band optical multiplexers / demultiplexers having the same characteristics and two optical isolators arranged in parallel so that the signal light passage directions are opposite. An optical amplifier circuit characterized in that two sets of optical branch circuits are prepared, and an optical amplifying section including a rare earth element-doped fiber, a pumping semiconductor laser, and an optical multiplexer / demultiplexer is incorporated between the two sets of optical branch circuits. Achieved by This enables bidirectional amplification even with one optical amplifier.

The optical amplifying section in the present invention comprises a rare earth element-doped fiber, a pumping semiconductor laser, and an optical multiplexer / demultiplexer. As the rare earth element-doped fiber, for example, Er or Nd is added to the core section for amplification. It is an optical fiber for use. This amplification optical fiber has, for example, a structure in which a silica-based glass clad having a smaller refractive index is provided around a silica-based glass core. In addition to the rare earth element described above, Al or the like is provided in the core portion. These elements may be simultaneously doped.

The pumping semiconductor laser is a pumping light source that generates pumping light for pumping the amplification optical fiber, and has a wavelength of 1.48 μm or 0.98 μm when an Er-doped fiber is used as the amplification optical fiber, for example. Is used.

The multiplexer / demultiplexer is a device for multiplexing or demultiplexing the signal light and the pumping light, and as a multiplexing / demultiplexing characteristic, for example, wavelengths of 1.54 μm and 1.56 μm have isolation of 20 dB. With the above, the waves are combined and demultiplexed.

The optical branching circuit in the present invention is an optical waveguide circuit that allows signal lights of two kinds of wavelength bands to pass in opposite directions and to pass in only one direction, and all have narrow wavelength characteristics. It is configured by connecting two band multiplexers / demultiplexers and two optical isolators that pass the signal light only in one direction, and the isolation is usually 45 dB to 60 dB.

In the optical amplifier circuit of the present invention, since signals having wavelengths of 1.54 μm and 1.56 μm can be respectively amplified in opposite directions in one transmission line, these two types of signal light can be amplified. By using, it is possible to construct a bidirectional transmission system including an optical amplifier capable of bidirectional amplification in one transmission line.

[0013]

【Example】

 FIG. 1 is a block diagram of an optical amplifier circuit of the present invention. In the figure, 11 indicates a circuit portion related to the optical amplifying portion, and the optical amplifying portion includes an amplifying optical fiber 12 in which a rare earth element such as Er or Nd is added to the core, and an amplifying optical fiber 12 It comprises a semiconductor laser (LD) 13 for generating pumping light for pumping light and a multiplexer / demultiplexer 14 for multiplexing or demultiplexing the signal light and the pumping light.

Next, the optical branch circuits 15a and 15b are optical waveguide circuits that allow the signal lights of the two types of wavelength bands to pass in opposite directions and to pass in only one direction. The narrow band multiplexers / demultiplexers 16a, 16b or 16c, 16d are respectively composed of optical isolators 17a, 17b or 17c, 17d having the same wavelength characteristics, and the isolation is usually about 45 dB to 60 dB. Further, 18a and 18b are connectors for connecting optical fibers provided at both ends of the present optical amplifier circuit.

Next, the operation of the entire optical amplifier circuit will be described.

The pumping light having a wavelength of 1.48 μm generated by the semiconductor laser 13 in the optical amplification unit 11 is incident on the amplification optical fiber 12 via the multiplexer 14. Since the amplification optical fiber 12 is doped with Er, the Er element ion is excited by the excitation light. In this case, the pumping action exerted on the amplification optical fiber 12 does not change regardless of whether the pumping light is input to the amplification optical fiber 12 from either forward or reverse directions. Therefore, in this state, when the signal light in the 1.55 μm band is incident on the amplification optical fiber 12, this signal light is amplified by stimulated emission when traveling through the amplification optical fiber 12. By the way, in the optical branch circuits 15a and 15b connected before and after the optical amplifier 11, narrow band multiplexers / demultiplexers 16a 1, 16b and 16c, 16d having the same characteristics are built-in, respectively. FIG. 2 shows the multiplexing / demultiplexing characteristics of the narrow band multiplexers / demultiplexers 16a, 16b, 16c, 16d. Light with wavelengths of 1.54 μm and 1.56 μm is multiplexed / demultiplexed with isolation of 20 dB or more. Therefore, the signal light with a wavelength of 1.54 μm incident from the connection connector 18a passes through the narrow band multiplexer / demultiplexer 16a, and most of the light is sent to the optical isolator 17a side due to the multiplexing / demultiplexing characteristic. After passing through the narrow band multiplexer / demultiplexer 16b, it is sent to the optical amplifier 11. While passing through the optical amplifier 11, the signal light is amplified and sent to the narrowband multiplexer / demultiplexer 16c. Most of the increased signal light of wavelength 1.54 μm is sent to the optical isolator 17c due to the multiplexing / demultiplexing characteristics of 16c, and is connected via the narrowband multiplexer / demultiplexer 16d. It is emitted from the connector 18b. At this time, the reflected return light, which is a problem and is generated at the connecting portion or the like, is blocked by the optical isolator 17c, so that a phenomenon such as oscillation in the optical amplifier circuit 11 does not occur. When a signal light having a wavelength of 1.56 μm is input from the connector 18b for connection, the narrow band multiplexer / demultiplexer 16d, the optical isolator 17d, the narrow band multiplexer / demultiplexer 16c, the optical amplifier circuit 11, the narrow band multiplexer / demultiplexer are used. The light is emitted from the connector 18a for connection via the device 16b, the optical isolator 17b, and the narrow band multiplexer / demultiplexer 16a. At this time, it goes without saying that the signal light is amplified when passing through the optical amplifier circuit 11.

As described above, in the optical amplifier circuit according to the present embodiment, since the signal lights having the wavelengths of 1.54 μm and 1.56 μm can be amplified with the passing directions being opposite to each other, these two kinds of signal lights are amplified. If used, a bidirectional transmission system including an optical amplifier capable of bidirectional amplification can be constructed in one transmission line.

[0018]

[Effect of device]

 According to the present invention, a bidirectional transmission system with a single transmission path can be constructed by selecting signal lights of different wavelengths using a single optical amplifier circuit, which is significantly more economical than conventional ones. The system can be made and the reliability is improved because the number of components is reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a bidirectional transmission type optical fiber amplifier circuit of the present invention.

FIG. 2 is a loss wavelength characteristic of a narrow band multiplexer / demultiplexer.

FIG. 3 is a circuit diagram of a conventional bidirectional transmission type optical fiber amplifier.

FIG. 4 is a circuit diagram of a conventional optical fiber and amplifier.

[Description of Reference Signs] 1,1a, 1b Pumping semiconductor laser module 2, 2a, 2b Pumping light Signal optical multiplexer / demultiplexer 3, 3a, 3b Rare earth element-doped amplification optical fiber 4, 4a, 4b Optical isolator 5, 5a , 5b Narrow band filter 6a, 6b Optical equalizer 7a, 7b Optical fiber amplification section 11 Optical amplification section 12 Rare earth element doped amplification optical fiber 13 Pumping semiconductor laser module 14 Pumping light Signal optical multiplexer / demultiplexer 15a, 15b Optical Branch circuit 16a, 16b, 16c, 16d Narrow band multiplexer / demultiplexer 17a, 17b, 17c, 17d Optical isolator 18a, 18b Connector for connection

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H01S 3/07 8934-4M 3/094 // G02B 27/28 A 9120-2K

Claims (1)

[Scope of utility model registration request] 1. Two narrow-band optical multiplexers / demultiplexers having the same characteristics and two narrow-band optical multiplexers / demultiplexers arranged in parallel so that the signal light passing directions are opposite.
Two sets of optical branch circuits connected to the optical isolator of the stage were prepared, and an optical amplification section including a rare earth element-doped fiber, a pumping semiconductor laser, and an optical multiplexer / demultiplexer was incorporated between the two sets of optical branch circuits. An optical amplifier circuit characterized in that.