JP4703026B2 - Broadband ASE light source - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a broadband spontaneous emission light source that uses spontaneous emission light generated from an erbium-doped optical fiber as a light source, and is suitable for use as a light source for wavelength multiplexing optical communication systems, optical measurement, and the like.
[0002]
[Prior art]
An erbium-doped optical fiber has a characteristic that a large gain can be obtained with respect to a certain wavelength by entering excitation light in a certain wavelength range. For this reason, it is possible to greatly increase the light intensity of the signal light by transmitting the signal light in the wavelength band having gain into the erbium-doped optical fiber (hereinafter referred to as EDF). Widely used in the field. When excitation light is incident on the EDF, the EDF generates a gain of the signal light and also spontaneously emits light. The generated spontaneous emission light is affected by the gain and the light output increases. The light generated in this way is called Amplified Spontaneous Emission Light (hereinafter referred to as ASE light).
[0003]
The EDF can emit an ASE output with a large gain of itself, and can be used as a broadband light source. In recent years, with the expansion of communication capacity, wavelength division multiplexing optical communication systems for multiplexing and transmitting / receiving optical signals having different wavelengths using a wide wavelength band have been actively studied. A broadband light source using ASE light is used as an incoherent WDM light source and as a test light source for optical components for WDM systems.
[0004]
In order to increase the communication capacity, the wavelength band used for optical communication is being expanded. In addition to the 1530 to 1560 nm band (1550 nm band) that has been used so far, the 1570 to 1610 nm band (1580 nm band) has come to be used. As the wavelength band expands, optical components for optical communication must operate at 1530 to 1610 nm or more. In order to measure the loss wavelength characteristics, this output is high in order to cover this wavelength band and widen the measurement dynamic range. There is a need for a broadband light source.
[0005]
FIG. 6 is a diagram showing a configuration of a conventional broadband ASE light source (Japanese Patent Laid-Open No. 11-330593). The optical fiber 10 includes an erbium-doped optical fiber 10, first and second excitation light sources 20 a and 20 b, first and second wavelength multi-polymerization wave units 30 a and 30 b, an optical output port 40, and a non-reflection end 50.
[0006]
Excitation light from the excitation light sources 20a and 20b is added to the non-reflecting end 50 side and the optical output port 40 side of the erbium-doped optical fiber 10, and the EDF 10 causes the ASE light generated on the non-reflecting end 50 side to enter the optical output port 40 side. The ASE light that is generated by the excitation light from the non-reflecting end 50 and propagates through the EDF 10 and the light output is of a length or absorption characteristic in which the short wavelength component is mainly absorbed and the long wavelength component remains. In this configuration, both the ASE light generated by the excitation light from the port 40 side is output from the light output port 40 side. The length of the EDF 10 is 360 m, the light intensity of the excitation light source 2 a is 170 mW, and the excitation light source 2 b is 34 mW.
[0007]
Although not shown in Japanese Patent Application Laid-Open No. 11-330593, a polarization-independent optical isolator is generally arranged in front of the output port 40. The role of this optical isolator is to remove the reflected return light to the EDF 10 and suppress parasitic oscillation due to the reflected return light and a decrease in gain due to multiple reflection of the ASE light.
[0008]
FIG. 7 is a diagram showing a spectrum waveform of a conventional broadband ASE light source. The spectrum density is −20 dBm (1530 to 1610 nm) and −12 dBm (1550 to 1600 nm).
[0009]
[Problems to be solved by the invention]
However, since the conventional broadband ASE light source shown in FIGS. 6 and 7 covers 1530 to 1610 nm as the ASE output band, one end is the non-reflective end 50. Therefore, the ASE light propagating to the non-reflective end 50 side is The non-reflecting end 50 does not reflect on the EDF 10 side, and does not contribute to the ASE light output on the output port 40 side. There was no idea of amplifying the ASE light propagating toward the non-reflecting end 50 back into the EDF. In other words, sufficient studies have not been made for higher output.
[0010]
The ASE output intensity in the 1565 to 1610 nm band (1580 nm band) is about one-tenth that of the 1530 to 1565 nm band (1550 nm band), and large excitation is required to increase the ASE output light intensity in the 1565 to 1610 nm band (1580 nm band). Since the light intensity is required, the prior art requires an excitation light intensity of 170 mW on the non-reflective end side and 34 mW on the output port side, which requires a very high power of 204 mW in total.
[0011]
Also, the EDF length is as long as 360 m, which is not suitable for downsizing of the apparatus. Thus, the high power of the excitation light source and the long EDF length have the disadvantage that the apparatus is also expensive.
[0012]
Furthermore, the conventional technique has a drawback that a compensation filter is required to flatten the spectrum.
[0013]
The present invention has been made to solve the above-described conventional problems, and covers the 1530 to 1610 nm band, which has a high output, a small size, and a low price with a small excitation light intensity, and improves spectral flatness without using a compensation filter. It is an object of the present invention to provide a broadband ASE light source.
[0014]
[Means for Solving the Problems]
The present invention is to solve these problems,
A pump light source with a wavelength of 980 nm band is connected to one end of the erbium-doped optical fiber and an output terminal via an optical isolator, and a pump light source with a wavelength of 980 nm band and a reflector are connected to the other end, from the output terminal An ASE light source that outputs light in the 1550 nm band and the 1580 nm band, wherein the erbium-doped optical fiber has an erbium-doped concentration of 1000 ppm or more, and the pump light source at one end has a higher light intensity than the pump light source at the other end , the excitation light of the excitation light source of the other end amplifies the ASE light of 1580nm band are reflected by the reflector, the total light intensity of the excitation light source of the other end as an excitation light source of said one end a 120mW The length of the erbium-doped optical fiber is set to 12 m to 18 m.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
The broadband ASE light source according to the present invention will be described below.
[0018]
FIG. 1 is a block diagram showing a first embodiment of the present invention. The erbium-doped optical fiber (EDF) No. 5 is a silica-based optical fiber capable of amplifying signal light to which 1000 ppm or more of the rare earth element erbium is added. The ASE light in the 1550 nm band (first wavelength band) generated at one end when light is incident has a length that is converted to the 1580 nm band (second wavelength band) when propagating to the other end. .
[0019]
Reference numeral 4 denotes an optical multiplexer, which is made by fusing and drawing an optical fiber. Reference numeral 3 denotes an excitation light source. Reference numeral 6 shows a structure in which a total reflection mirror composed of a dielectric multilayer film is bonded and connected to an end face of an optical fiber so that an optical signal is reflected by a reflector. Reference numeral 2 denotes an optical isolator that functions to allow an optical signal to pass only in one direction. The principle is that using a Faraday rotator.
[0020]
A semiconductor laser pumping light source 3 is connected to one end of the EDF 5 via a multiplexer 4, a reflector 6 is connected to the other end of the EDF 5, and an optical isolator 2 is connected to one end of the multiplexer 4. ASE light is output from the output terminal 1 through the optical isolator 2. When the reflected light from the output terminal 1 returns to the EDF 5, the ASE light becomes unstable. However, by preventing the reflected light from the output terminal 1 side from returning to the EDF 5 by the optical isolator 2, the ASE light is not generated. It can be prevented from becoming stable.
[0021]
The excitation light output from the excitation light source 3 has a wavelength of 1480 nm band or 980 nm band, and is guided to the EDF 5 via the multiplexer 4. When the excitation light from the excitation light source 3 is incident, ASE light in the 1550 nm band (first wavelength band) is first emitted from the first half of one end side of the EDF 5 to which the multiplexer 4 is connected, and propagates to both sides of the EDF 5. To do. The ASE light propagated to the optical isolator 2 side is in the 1550 nm band and passes through the optical isolator 2 and is output from the output terminal 1. Further, the ASE light in the 1550 nm band (first wavelength band) propagating to the reflector 6 side is absorbed by the latter half portion of the EDF 5 in the middle thereof, and when propagated to the other end, the 1580 nm band (second wavelength band). 1580 nm band ASE light is reflected by the reflector 6 and returns to the EDF 5 to be amplified in the EDF 5 and output from the output terminal 1. In this state, the ASE light in the 1550 nm band and the 1580 nm band is output from the output terminal 1 in a relatively flat and combined state.
[0022]
When EDF is used as an optical amplification fiber, the EDF length used in the optical amplifier can be shortened by increasing the erbium addition concentration, which can improve productivity in EDF manufacturing and downsize the optical amplifier. It becomes. However, if the concentration of erbium is increased too much, the output of ASE decreases due to the interaction between erbium ions in the excited state. In the case of silica-based optical fibers, this phenomenon (called concentration quenching) occurs when the erbium concentration of EDF exceeds 100 ppm, but concentration quenching does not occur even at an erbium addition concentration of about 1000 ppm by co-adding aluminum (Al). Absent. In addition, the fiber has a high NA structure to increase the excitation light intensity of the erbium-doped core, and the high-efficiency can be realized because the region where the excitation light intensity is weak does not overlap the core (reference: erbium addition) Optical fiber amplifier, Shoichi Sudo, Optronics, 149-152PP).
[0023]
Conventionally, since the erbium addition concentration of EDF is about 200 ppm to 400 ppm, the EDF length when configuring a 1550 nm band ASE light source needs to be 10 m to 20 m, and when configuring a 1580 nm band ASE, it needs to be close to 50 m to 100 m. It was. In the present invention, by setting the erbium addition concentration of EDF5 to 1000 ppm or more, the EDF length can be reduced to 10 to 20 m, which is the same as the 1550 nm band, or less in an ASE light source covering the 1580 nm band.
[0024]
If the erbium addition concentration can be further increased in the future, the apparatus can be further miniaturized. For example, if an EDF with an erbium addition concentration of 5000 ppm can be produced without causing concentration quenching, the EDF used in the present invention becomes 2 m to 4 m in length, and the apparatus can be further miniaturized.
[0025]
Here, the EDF 5 of the present invention has a length that is converted to the 1580 nm band (second wavelength band) when the ASE light in the 1550 nm band (first wavelength band) generated at one end propagates to the other end. Whether the length is such can be confirmed by actually inputting the light in the first wavelength band.
[0026]
FIGS. 5A and 5B illustrate the length of an erbium-doped optical fiber (EDF) in which the ASE light in the first wavelength band is converted into the second wavelength band. FIG. 5A shows a simulation of the ASE spectrum waveform output from the other end of the EDF when 1480 nm band excitation light is input from the one end of the EDF. EDF is a silica-based optical fiber that has a function of amplifying signal light to which erbium, a rare earth element, is added, and is the most frequently used optical fiber for optical amplification today. When the excitation light intensity is 100 mW and the EDF length is changed from 20 m to 150 m, the ASE has a first wavelength band of 1530 nm to 1560 nm when the EDF length is 20 m to 30 m, but when the EDF length is 100 m, the ASE at 1540 nm. The output decreases by 30 dB or more, and shifts to the 1565 nm to 1610 nm band (1580 nm band) which is the second wavelength band.
[0027]
This phenomenon is explained as follows. A 1550 nm band ASE is generated in the first half of the fiber by 1480 nm band excitation or 980 nm band excitation. As the 1550 nm band ASE is absorbed in the latter half of the fiber, 1580 nm band amplification occurs. As the fiber is lengthened, the output of the ASE changes from the 1550 nm band to the 1580 nm band. This length is called the converted length (reference: Ono et al., Amplification characteristics of 1.58 μm band Er3 + doped optical fiber amplifier, IEICE Technical Report, OSC97-5, pp25-30, 1997).
[0028]
FIG. 5B shows a simulation of an ASE spectrum waveform output from one end of the EDF when 1480 nm band excitation light is input from one end of the EDF. The excitation light intensity is 100 mW and the EDF length is 20 m to 150 m. The 1530 to 1565 nm band ASE remains as it is, and no transition to the 1580 nm band is observed.
[0029]
By selecting an erbium high-concentration EDF co-doped with aluminum and optimizing the EDF length, the configuration of the present invention can realize a broadband ASE light source with high output, small size, and low cost.
[0030]
FIG. 2 shows a second embodiment of the present invention.
[0031]
1, the second pumping light source 8 is connected to the end of the EDF 5 on the reflector 6 side via the optical multiplexer 7. The excitation light source 8 has a wavelength of 1480 nm band or 980 nm band. In order to obtain a high output ASE, the light intensity of the excitation light source 3 and the excitation light source 8 is preferably large. However, when flattening the spectrum density, the light intensity of the one end side excitation light source 3 of the EDF 5 is the other end side. It is preferable to make it larger than the excitation light source 8. This is because the excitation light source 8 mainly contributes to the amplification of the 1580 nm band ASE reflected by the reflector 6, and the 1580 nm band ASE is efficiently amplified due to the presence of the reflector.
[0032]
Therefore, the ASE spectrum density can be flattened by appropriately selecting the light intensity ratio between the excitation light source 3 and the excitation light source 8.
[0033]
【Example】
As a first embodiment of the broadband ASE light source of the present invention, the ASE light source shown in FIG. 1 was prototyped. Each component and configuration will be described below.
[0034]
FIG. 3A and FIG. 3B show the prototype results for the ASE light source of the embodiment shown in FIG. The excitation light source 3 has a wavelength of 1480 nm and an excitation output of 110 mW in FIG. 3A and 130 mW in FIG. As the EDF 5, a commercially available silica-based erbium-doped optical fiber was used. The EDF was confirmed to have an erbium concentration of 1200 ppm and an EDF length of 13.5 to 18 m. The reflectance of the reflector is 90%.
[0035]
The operating wavelength band is almost the same as that of the conventional technology, but when the excitation intensity is increased (to 110 mW to 130 mW), the output on the long wavelength side (1570 to 1610 nm) increases and at the same time the ASE light intensity increases. When the EDF length is short, the ASE output on the short wavelength side decreases, and when the EDF length is increased, the long wavelength side ASE output decreases. The optimum EDF length is about 13.5 m when the excitation light intensity is 110 mW and about 15 m when the excitation light intensity is 130 mW.
[0036]
The ASE output light spectral density is −20 dBm (1530 to 1610 nm) and −12 dBm (1550 to 1600 nm) in the prior art, but in FIG. 3B of the present invention, −12 dBm (1530 to 1610 nm) and −7 dBm (1550 to 1550 nm). 1600 nm) and high output. Moreover, the excitation light intensity can be suppressed to 130 mW / 204 mW (≈54%) compared to the conventional case. The EDF length can be improved to 15 m / 360 m (≈4%) compared to the conventional one, and the spectrum flatness (difference between the maximum output value and the minimum output value in the spectrum) in the 1530 to 1600 nm wavelength band is 15 dB or less.
[0037]
As a result, by using a reflector and using an erbium high-concentration EDF, a wide-band ASE light source having a high output, a short EDF, a small size, and a short EDF length can be developed.
[0038]
Further, as a second embodiment of the broadband ASE light source of the present invention, the ASE light source shown in FIG. 2 was prototyped. Each component and configuration will be described below. FIG. 4 is a trial result of the ASE light source of the embodiment shown in FIG. The pumping light source 3 and the pumping light source 8 have a wavelength of 980 nm, the total power of the pumping light sources 3 and the pumping light source 8 combined is 120 mW, and the rest is the same as in the first embodiment.
[0039]
In the above state, the EDF length and the excitation light intensity ratio were optimally adjusted so that the ASE spectrum density was flat. When the fiber length was changed from 12 m to 18 m, the light intensity of the excitation light source 8 and the excitation light source 3 was 48 mW and 720 mW, respectively, when the fiber was 18 m. It was found that when the fiber length is shortened, the light intensity of the excitation light source 3 should be further increased, and the ASE output will be increased.
[0040]
For example, when the EDF length is 16 m, the excitation light source 8 is 41 mW, the excitation light source 3 is 79 mW, and the ASE output intensity is 14.4 dBm. At this time, the spectral density is −10 dBm / nm (1528 to 1610 nm), and the flatness of the spectrum is 7 dB, which is considerably better than the conventional case.
[0041]
From the above, it was confirmed that the flatness of the spectrum can be improved in this method, and the light intensity of the excitation light source 3 is larger than that of the excitation light source 8 at this time.
[0042]
【The invention's effect】
As described above, according to the present invention, an ASE light source in which an excitation light source and an output terminal are connected to one end of an erbium-doped optical fiber via an optical isolator and a reflector is connected to the other end, the erbium-doped light The fiber has an erbium addition concentration of 1000 ppm or more and a length that is converted into the second optical wavelength band when ASE light having the first optical wavelength band generated on one end side propagates to the other end. It is possible to obtain a broadband ASE with high output and excellent spectral flatness in the 1530 to 1600 nm wavelength band with a low pumping power and a short rare earth doped fiber, thereby realizing a reduction in size and price.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing a first embodiment of a broadband ASE light source according to the present invention.
FIG. 2 is a configuration diagram showing a second embodiment of a broadband ASE light source according to the present invention.
FIGS. 3A and 3B are experimental results showing an ASE spectrum of the first embodiment of the present invention.
FIG. 4 is an experimental result showing an ASE spectrum according to the second embodiment of the present invention.
FIGS. 5A and 5B are diagrams for explaining the length of an erbium-doped optical fiber in which ASE light in a first wavelength band is converted into a second wavelength band.
FIG. 6 is a diagram showing a conventional ASE light source.
FIG. 7 is a diagram showing an ASE spectrum of a conventional ASE light source.
[Explanation of symbols]
1: output terminal 2: optical isolator 3: excitation light source 4: multiplexer 5: erbium-doped optical fiber 6: reflector 7: multiplexer 8: excitation light source

Claims (1)

A pump light source with a wavelength of 980 nm band is connected to one end of the erbium-doped optical fiber and an output terminal via an optical isolator, and a pump light source with a wavelength of 980 nm band and a reflector are connected to the other end, from the output terminal An ASE light source that outputs light in the 1550 nm band and the 1580 nm band, wherein the erbium-doped optical fiber has an erbium-doped concentration of 1000 ppm or more, and the pump light source at one end has a higher light intensity than the pump light source at the other end , the excitation light of the excitation light source of the other end amplifies the ASE light of 1580nm band are reflected by the reflector, the total light intensity of the excitation light source of the other end as an excitation light source of said one end a 120mW A broadband ASE light source characterized in that the length of the erbium-doped optical fiber is set to 12 m to 18 m.

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