JP3093092B2 - Optical fiber connection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for connecting optical fibers having different mode field diameters in an erbium-doped optical fiber (hereinafter, EDF) amplifier or the like.

[0002]

2. Description of the Related Art In recent years, the operation of erbium-doped optical fiber amplifiers (hereinafter referred to as EDFAs) in systems has been actively studied, and the systems have been put into practical use. When designing a system using various optical amplifiers including this EDFA, several types of optical fibers are used as the optical fibers used in the optical amplifier. Then, by connecting these optical fibers to each other, an optical amplifier is formed. When these optical fibers are connected to each other, it is necessary to reduce light loss in this connection.

At this time, as shown in FIG. 10, an optical fiber 101 having a mode field diameter (hereinafter, referred to as MFD) 101a, which will be described later, and an MFD 101a larger than the MFD 101a.
When the optical fiber having the FD 102a is connected by butt, the spot sizes of the two optical fibers 101 and 102 become discontinuous at the connection point. Therefore, when the optical fiber 101 and the optical fiber 102 are butt-connected, a large connection loss occurs. In this way, connecting optical fibers having different MFDs causes a large loss in principle. The connection loss between the optical fibers having different MFDs as shown in FIG. 10 is 20log ₁₀ ｛(2w ₁ w ₂ ) / (w ₁ ² +, where the MFDs of the respective optical fibers are w ₁ and w _2. w ₂ ² )｝ [dB]. (D. Marcuse "Loss Analysis of Single-Mode F
iber Splices "BSTJ pp703-717, 1977) Therefore, for example, the connection loss due to the matching of a single mode optical fiber (hereinafter, referred to as SMF) having an MFD of 10 μm and an EDF having an MFD of 5 μm is given by the above equation.
It becomes 1.94 dB.

[0004] Usually, among optical components constituting an EDFA,
Optical isolators and wavelength multiplexers other than EDFs (hereinafter WD)
For example, an SMF optical fiber having a larger MFD than the EDF is used as the optical fiber connected to the M. Also, S
Since the connection loss between the MF and the EDF causes deterioration of the noise characteristic of the EDFA and reduction of the gain efficiency, the connection loss is generally 0.2 dB.
It is desirable to make the following. In order to connect the optical fibers with low loss, for example, a method as shown in FIG. 11 has been adopted.

FIG. 11 is a configuration diagram in which one core is enlarged and optical fibers having different MFDs are connected to each other. As shown in FIG. 11, the core 112a of the optical fiber 112 is larger than the core 111a of the optical fiber 111. Therefore, by heating the end face portion of the optical fiber 111, the core 111a of the optical fiber 111 is enlarged, and the optical fiber 111
MFD is expanded. As described above, the core 111a of the optical fiber 111 heats the end face of the optical fiber 111, so that the MFD of the optical fiber 111 expands in the axial direction of the optical fiber 111 and the MF of the optical fiber 112 increases.
It is almost the same size as D. In this case, the MFD
Even if optical fibers of different types are connected, they can be connected with low loss.

FIG. 12 shows a conventional forward-pumped EDFA constructed by the above connection method. The 1.55 μm band signal light, which is the first wavelength, is applied to a wavelength multiplexer (hereinafter, WDM).
) 123. Also, the pump light in the 1.48 μm band, which is the second wavelength, is input to the WDM 123. The WDM 123 combines the light of the first wavelength and the light of the second wavelength. These lights combined by the WDM 123 are transmitted through the optical fiber 121.

Here, the MFD is a length between points where the electric field intensity is 1 / e on a plane perpendicular to the light propagation direction as shown in FIG. Between the points where the electric field intensity is 1 / e, the light intensity distribution has a maximum value. The optical fiber 121 is connected to the optical fiber 122 by using the above-described method for connecting optical fibers having different MFDs. In this manner, optical fibers having different MFDs can be fusion-spliced with low loss.

[0008]

The ED shown in FIG.
The wavelengths used in the FA are the excitation light wavelength in the 1.48 μm band and the signal light wavelength in the 1.55 μm band. EDF
In A120, since the signal light wavelength and the pump light wavelength are configured to be close to each other, both the pump light wavelength and the signal light wavelength can be fusion-spliced with low loss.

However, the value at which the fusion splice loss between the pump light wavelength band of 0.98 μm and the signal light wavelength band of 1.55 μm is minimized is different. As a result, the excitation light wavelength is 0.98 μm
In the case of a band, it is conceivable that the connection method described above causes a large loss of light in connection between optical fibers. In addition, the excitation light wavelength is 0.8 μm band, 0.65 μm band, 0.1 μm band.
In the case of the 5 μm band, in the connection method described above, the value at which the fusion splice loss between these pump light wavelength band and the signal light wavelength band of 1.55 μm band becomes the smallest is much different.

[0010] The present invention has been made in view of the above points, and uses a first wavelength and a second wavelength having different wavelength bands to connect optical fibers having different MFDs.
An object of the present invention is to provide an optical fiber connection method that can be connected with low loss.

[0011]

In order to solve the above-mentioned problems, the present invention is directed to a light having a first MFD for transmitting a first wavelength light and a second wavelength light having different wavelength bands. In the optical fiber connection method for connecting the optical fiber 1 and the optical fiber 2 having the second MFD, before connecting the optical fiber 1 and the optical fiber 2, the first wavelength light is input to the input end of the optical fiber 1. A multiplexer for multiplexing with the second wavelength light is connected, the output power of the first wavelength light and the output power of the second wavelength light at the output end of the optical fiber 1 are measured, and the output of the optical fiber 2 is measured. A distributor for separating the first wavelength light and the second wavelength light is connected to the end, and the loss of the first wavelength light and the loss of the second wavelength light in the optical fiber 2 and the demultiplexer are measured. After connecting the optical fiber 1 and the optical fiber 2, the optical power meter 16 for measuring the output power of the first wavelength light separated by the distributor, and the optical power meter 16 of the second wavelength light separated by the distributor. By connecting the optical power meter 17 for measuring the output power and heating the end face portion of the optical fiber having the smaller MFD, the MFD is locally expanded, and the MFD output from the distributor is changed by heating. The output power of the first wavelength light is measured by the optical power meter 16, the output power of the second wavelength light output from the distributor is measured by the optical power meter 17, and the first wavelength at the output end of the optical fiber 1 is measured. The output power of the light and the output power of the second wavelength light, the loss of the first wavelength light and the loss of the second wavelength light in the optical fiber 2 and the demultiplexer, and the optical power meter 16 and the optical power meter The loss of the first wavelength light and the second wavelength light at the connection between the optical fiber 1 and the optical fiber 2 is calculated based on the output power of the first wavelength light and the second wavelength light measured by the data 17. Then, when the calculated loss of the first wavelength light and the second wavelength light reaches an arbitrarily set value, the heating is stopped.

According to a second aspect of the present invention, in the first aspect, a rare earth element-doped optical fiber having an optical amplification effect is used as the optical fiber 1.

According to a third aspect of the present invention, in the optical fiber connection method according to the second aspect, both the first wavelength light, the second wavelength light, or any one of the wavelength lights is transmitted to the rare earth element-doped optical fiber. The wavelength light deviates from the optical amplification wavelength band.

[0014]

[0015]

[0016]

[0017]

[0018]

[0019]

[0020]

[0021]

[0022]

[0023]

[0024]

[0025]

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the optical fiber connecting method according to the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing a first embodiment of the present invention. The first wavelength light is input to a multiplexer 11 such as a wavelength multiplexer or an optical coupler. Further, the second wavelength light is also input to the multiplexer 11. The power of each wavelength light input to the multiplexer 11 is constant. The multiplexer 11 combines the first wavelength light and the second wavelength light. The combining port 11 is connected to the multiplexer 11 for transmitting and connecting the first wavelength light and the second wavelength light combined by the multiplexer 11 to an optical fiber. The combining port 12 is connected to the optical fiber 1 in order to transmit the first wavelength light and the second wavelength light combined by the multiplexer 11. Here, as a method for connecting the combining port 12 and the optical fiber 1, there is no need to attach and detach the combining port 12 and the optical fiber 1, and therefore, fusion connection by arc discharge or the like can be mentioned. The optical fiber 1 is connected to the optical fiber 2 at the connection point A.
Connected to As a result, the first wavelength light and the second wavelength light synthesized by the multiplexer 11 are separated by the optical fiber 1
To the optical fiber 2. The connection between the optical fiber 1 and the optical fiber 2 at the connection point A is performed by fusion for a long time or fusion for a short time by arc discharge or the like, and fusion-splicing the optical fiber 1 and the optical fiber 2 is performed. After the fusion splicing, as shown in FIG. 11, the optical fiber with the smaller MFD is heated for a long time to enlarge the MFD.

As a method of connecting the optical fiber 1 and the optical fiber 2 at the connection point A and a method of heating, whether only the fusion of the optical fiber and the expansion of the MFD are performed using only the optical fiber fusion machine, Alternatively, there is a method in which the MFD is expanded by using another heating device such as a micro torch after fusion with an optical fiber fusion machine. Any of these methods may be used.

The optical fiber 2 is connected to the combining port 14. Here, as a connection method between the optical fiber 2 and the combining port 14, a connector connection such as a ferrule type connector for attaching and detaching the optical fiber 2 and the combining port 14 will be described later. Then, the combining port 14 connected to the optical fiber 2 by a connector is connected to the duplexer 15. From the above, the first wavelength light and the second wavelength light are combined by the multiplexer 11, and the wavelength multiplexed light combined by the multiplexer 11 is combined by the combining port 12 of the combiner 11,
The light propagates through the optical fiber 1, the optical fiber 2, and the combining port 14 and is input to the duplexer 15.

The first wavelength light and the second wavelength light combined by the multiplexer 11 may be transmitted to the duplexer 15 without using the combining port 12 described above. That is, the multiplexer 11 is configured by using the optical fiber 1 instead of the combining port 12. Therefore, the first wavelength light and the second wavelength light are combined by the multiplexer 11, and the wavelength multiplexed light combined by the multiplexer 11 is combined with the optical fiber 1, the optical fiber 2, and the combining port 14. And is input to the duplexer 15.

The splitter 15 splits the wavelength multiplexed light of the first wavelength light and the second wavelength light transmitted from the optical fiber 2. The demultiplexer 15 converts the first wavelength light from the demultiplexed first wavelength light and second wavelength light into an optical power meter (hereinafter, referred to as an optical power meter).
OPM) 16. In addition, the duplexer 15
The second wavelength light is output to the OPM 17 from the demultiplexed first wavelength light and second wavelength light. OPM16 uses this OP
This is an apparatus for measuring the output power of the first wavelength light input to M16. The OPM 17 is a device that measures the power of the second wavelength light input to the OPM 17. The change in loss at the connection point A between the optical fiber 1 and the optical fiber 2 is monitored by measuring the output power of the first wavelength light and the power of the second wavelength light using the OPMs 16 and 17.

An optical fiber connection method in an EDFA excited at 0.98 μm based on the configuration of FIG. 1 will be described with reference to FIG. The 1.55 μm band signal light, which is the first wavelength light, is transmitted through the optical fiber 1 and input to the WDM 31. Also, the pump light in the 0.98 μm band, which is the second wavelength light, is transmitted to the WDM 31 through the optical fiber 1. At this time, the WDM3
An optical isolator 30 is provided between the optical fibers 1 to prevent light generated in the optical fiber 1 or 2 and returning to the input side.

The WDM 31 is a 0.98 μm / 1.55 μm WDM since signal light in the 1.55 μm band and pump light in the 0.98 μm band are input to the WDM 31. The wavelength-division multiplexed light composed of the 1.55 μm band signal light and the 0.98 μm band pump light combined by the WDM 31 propagates from the WDM 31 through the optical fiber 1, the optical fiber 2 and the combining port 34, Is input to Since the wavelength division multiplexed light composed of the signal light in the 1.55 μm band and the pump light in the 0.98 μm band is input to the demultiplexer 35, the demultiplexer 35 is a 0.98 μm / 1.55 μm WDM.

The demultiplexer 35 demultiplexes the propagated wavelength-division multiplexed light into signal light in the 1.55 μm band as the first wavelength and pump light in the 0.98 μm band as the second wavelength. I do. The splitter 35 has a first wavelength of 1.55, which is the split wavelength.
0.98 μm which is the signal light and light of the μm band and the second wavelength light
From the pump light of the band, the signal light of the 1.55 μm band is
Output to Further, the demultiplexer 35 converts the demultiplexed signal light and light in the 1.55 μm band, which is the first wavelength, and the pump light in the 0.98 band, which is the second wavelength light, into 0.98 μm pump light. The light is output to the OPM 17.

Here, as the optical fiber 1, SMF, which is an optical fiber for WDM, is used. EDF is used for the optical fiber 2. This means that, as described above, in the optical components constituting the EDFA, the optical fiber connected to an optical isolator other than the EDF, a WDM, or the like is usually used.
An SMF optical fiber having a larger MFD than the EDF is used. Therefore, at the connection point A, the optical fiber 1 S
The MF and the EDF as the optical fiber 2 are connected. Therefore, the SMF that is the optical fiber 1 and the EDF that is the optical fiber 2 have a signal light of 1.55 μm band and 0.98 μm.
The m-band excitation light propagates. In EDF,
The signal light in the 1.55 μm band is amplified by the pump light in the 0.98 μm band.

As described above, at the connection point A, the optical fiber 1 and the optical fiber 2 are connected. This connection point A
The connection loss between the optical fiber 1 and the optical fiber 2 changes according to the heating time by the heating device. Also, the loss for the heating time depends on the wavelength.

FIG. 2 is a diagram showing the ratio between the wavelength and the loss with respect to the heating time. The wavelength in the 1.55 μm band has the smallest loss when the heating time is 20 seconds to 30 seconds. 0.
The wavelength in the 98 μm band has the smallest loss when the heating time is 8 sec to 10 sec. As described above, the point where the loss is minimized depends on the wavelength. Therefore, for example, when it is desired to minimize the loss at the first wavelength, the heating is stopped when the power of the OPM1 becomes maximum.
On the other hand, when it is desired to minimize the loss at the second wavelength, the heating is stopped when the power of the OPM2 becomes the largest. As described above, by measuring the power of the first wavelength light and the power of the second wavelength light using the OPM 16 and the OPM 17, a change in loss at the connection point A between the optical fiber 1 and the optical fiber 2 is monitored.

Here, in general, if the connection loss between the optical fibers in the optical amplifier is large, the noise characteristics of the light are deteriorated, and the output signal light power after amplification is also reduced.

Here, the relationship between the optical noise characteristic of the optical noise characteristic or the output signal light power and the loss at the connection point A will be described below. EDFA noise figure: NF is EDF noise figure NFE
By DF [dB] and loss Lin [dB] from the input point of the EDFA to the EDF, NF = NFEDF [dB] + Lin [dB]. Lin is an optical isolator or WDM for preventing oscillation
Along with the loss, the loss at the signal light wavelength at the connection point A also has an effect. Therefore, in order to reduce the noise figure of the EDFA of FIG. 3, it is necessary to reduce the loss of signal light in the 1.55 μm band at the connection point A.

On the other hand, the relationship between the output signal light power after amplification and the loss at the connection point A among the optical noise characteristics or the output signal light power will be described below with reference to FIG.
The power of the first wavelength light input to the connection point A is Psin, and the power of the second wavelength light input to the connection point A is Ppin
And the loss at the first wavelength light at the connection point A is L1,
The loss at the second wavelength light at the connection point A is assumed to be L2, where the larger the numerical values of L1 and L2, the greater the loss.
Let the transmittance of the loss L1 be T1, and let the transmittance of the loss L2 be T2. Here, if the loss L = 0, the transmittance T = 1 and the loss
As L increases, the transmittance T decreases. In addition, loss L = ∞
Is the transmittance T = 0. The power of the first wavelength light input to the optical fiber 2 is Ps, the power of the second wavelength light input to the optical fiber 2 is Pp, and the power of the first wavelength light output from the optical fiber 2 is Ps. Is Psout, Ps = Psin × T1 (1) Pp = Ppin × T2 (2) Further, assuming that the conversion efficiency from the pump light as the second wavelength light to the signal light as the first wavelength light in the optical fiber 2 is η, Psout = Ps + ηPp (3). Substituting equations (1) and (2) into equation (3), Psout = Psin × T1 + ηPpin × T2 (4) Here, the following two states are considered. First, when the transmittance T2 of the loss L2 is better than the transmittance T1 of the loss L1,
That is, T1 <T2 In this case, T1 and T2 are T11 and T21, respectively, and the power of the first wavelength light output from the optical fiber 2 is Psout
Let it be 1. Next, when the transmittance T1 of the loss L1 is better than the transmittance T2 of the loss L2, that is, T1> T2 In this case, T1 and T2 are T12 and T22, respectively, and the first output from the optical fiber 2 is Psout power of wavelength light
Let it be 2. That is, T11 <T12, T21> T22. From equation (4), Psout1−Psout2 = Psin × T11 + ηPpin × T21− (Ps
in × T12 + ηPpin × T22) = Psin (T11−T12) + ηPpin (T21−T22) Here, Psin≪ηPpin because usually Psin <1 mw and ηPpin> 50 mw. In addition, the aforementioned T11 <T1
2. From T21> T22, T11-T12 <0, T21-T2
2> 0, but | T11−T12 | ≒ | T21−T22 |
If Psout1−Psout2> 0, then Psout1> Pso
ut2.

From this, in order to obtain a larger amplified output signal light power, it is necessary to reduce the loss of the pump light in the 0.98 μm band at the connection point A. The relationship between the noise characteristic of the light and the loss at the connection point A, and the relationship between the amplified output signal light power and the loss at the connection point A are 0.98 as described above.
In addition to the excitation light at μm, 0.8, 0.65, 0.5
Similar results are obtained with excitation light at μm.

The noise figure of the forward-pumped EDFA is as follows:
In order to satisfy both the amplified output signal light power and the amplified output signal light power, with reference to FIG. 2, heating in the heating device is performed for a predetermined time period in which both loss values satisfy arbitrarily set values. You just need to stop.

After the optical fiber 1 and the optical fiber 2 are connected with low loss by using the above-described method, at the connection point B, the optical fiber 2 and the composite port 34 connected to the connector are removed. Light can be transmitted by connecting the optical fiber 2 to another optical fiber or the like with a connector. Here, at the connection point B, the optical fiber 2 and another optical fiber or the like may be fusion-spliced. When the optical fiber 2 is to be fusion-spliced with another optical fiber or the like, the end face of the optical fiber 2 is cut, and the cut end face of the optical fiber 2 is abutted with another optical fiber for optical transmission.

As described above, according to the first embodiment, when the optical fiber 2 and another optical fiber 1 having a different MFD from the optical fiber 2 are fusion-spliced, the loss at each wavelength is monitored. It is possible to perform fusion splicing after confirming that a desired loss has occurred, such as making the loss the lowest at any wavelength.

FIGS. 4 and 5 are block diagrams showing a second embodiment of the present invention. In FIGS. 4 and 5, those having the same structures as those shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. In the configuration of the second embodiment, as shown in FIG. 4, first, an OPM 16 for measuring the output power of the first wavelength light is provided at the output end of the optical fiber 1. Then, only the first wavelength light is input to the multiplexer 41. The first wavelength light is transmitted through the optical fiber 1 from the multiplexer 41 and is input to the OPM 16. The OPM 16 measures the output power of the first wavelength light input from the optical fiber 1.

Next, as shown in FIG. 5, an OPM 1 for measuring the output power of the second wavelength light is provided at the output end of the optical fiber 1.
7 is provided. Then, only the second wavelength light is input to the multiplexer 41. The first wavelength light is transmitted from the multiplexer 41 through the optical fiber 1 and is input to the OPM 17. OPM17
Measures the output power of the second wavelength light input from the optical fiber 1. After the output power of the first wavelength light and the output power of the second wavelength light are measured by the OPM 16 and the OPM 17, the OPM is removed, and the optical fiber 1 and the optical fiber 2 are connected as shown in FIG. .

From this, after measuring the output power of the first wavelength light and the output power of the second wavelength light by the OPM 16 and the OPM 17, the OPM 16 and the OPM 17 are removed, and the optical fiber 1 and the optical fiber 2 are connected. By connecting, the configuration becomes the same as that of FIG. That is, in the second embodiment, before connecting the optical fibers 1 and 2,
The optical fiber 1 is connected to OPM16 and OPM17. The output power of the first wavelength light and the output power of the second wavelength light at the connection point A are measured by the OPM 16 and the OPM 17, respectively.

Thereafter, as in the first embodiment, the first wavelength light and the second wavelength light are input to the multiplexer 41. Multiplexer 41
Combines the first wavelength light and the second wavelength light. The wavelength-division multiplexed light composed of the first wavelength light and the second wavelength light is transmitted from the multiplexer 41 to the optical fiber 1, the optical fiber 2, and the combining port 14, and is input to the demultiplexer 15. . The wavelength division multiplexed light is separated by the demultiplexer 15 into the first wavelength light and the second wavelength light. The separated first wavelength light is input to the OPM 16, and the output power is measured.
Further, the separated second wavelength light is input to the OPM 17, and the output power is measured.

Although not shown, the loss of the first wavelength light at the connection point B between the splitter 15 and the optical fiber 2 and the loss between the splitter 15 and the optical fiber 2 are measured using a measuring instrument. The loss of the second wavelength light at the connection point B is also measured.

As described above, the loss of the first wavelength light at the connection point A between the optical fiber 1 and the optical fiber 2 is determined before the optical fiber 1 and the optical fiber 2 are connected.
And the OPM 16, the output power of the first wavelength light measured by the OPM 16 for the first wavelength light, and the first power separated by the demultiplexer 15 after connecting the optical fiber 1 and the optical fiber 2. The output power of the first wavelength light measured by the OPM 16 for the wavelength light of the first wavelength and the connection point between the splitter 15 and the optical fiber 2 measured by using a measuring device (not shown).
The loss of the first wavelength light in B is obtained by conversion.

Regarding the loss of the second wavelength light at the connection point A between the optical fiber 1 and the optical fiber 2, the loss at the second wavelength light is converted in the same manner as the above-described method of converting the loss of the first wavelength light. Ask.

Hereinafter, a method for obtaining a loss value at the connection point A based on the above-described elements will be described. In FIG. 4, before connecting the optical fiber 1 and the optical fiber 2, the OPM is connected to the optical fiber 1, and the OPM 16 and the OPM 17 are connected.
Let the output power of the first wavelength light and the output power of the second wavelength light measured by (1) be Pref1 and Pref2, respectively. In FIG. 1, after the optical fiber 1 and the optical fiber 2 are connected, the loss of the first wavelength light at the connection point B between the splitter 15 and the optical fiber 2 measured by a measuring device is represented by LWD.
After connecting the optical fiber 1 and the optical fiber 2 with M1, the measurement was performed by a measuring device.
The loss of the second wavelength light at the connection point B with LWDM2 is defined as LWDM2. In FIG. 1, after the optical fiber 1 and the optical fiber 2 are connected, the output power of the first wavelength light obtained by measuring the first wavelength light separated by the demultiplexer 15 by the OPM 16 is Pout1, and the optical fiber 1 After connecting the optical fiber 2 with the optical fiber 2, the output power of the second wavelength light obtained by measuring the second wavelength light separated by the demultiplexer 15 by the OPM 17 is defined as Pout2. Assuming that the loss at the connection point A at the first wavelength is Loss1 and the loss at the connection point A at the second wavelength is Loss2, Loss1 = | Pout1-Pref1 + LWDM1 | Loss2 = | Pout2-Pref2 + LWDM2 | However, the units of the output power level and the loss at this time are [dBm] and [dB], respectively. In addition, the loss is a code whose loss is 0 dB or more.

As described above, according to the second embodiment, the first
In addition to the embodiment, the connection point between the optical fiber 1 and the optical fiber 2
The loss at A can be monitored. Further, according to the second embodiment, it is found that the loss at the connection point increases due to poor fusion splicing such as dirt and scratches on the connection end face of the optical fiber and misalignment of the optical fiber 1 and the optical fiber 2. Therefore, the second embodiment is different from the first embodiment.
A connection loss with higher accuracy is obtained than the loss at the connection point A between the optical fiber 1 and the optical fiber 2 obtained from the embodiment.

A rare earth element-doped optical fiber such as EDF is
Since the absorption loss is large, it is conceivable to use a rare earth element-doped optical fiber such as EDF as the optical fiber 1.

FIGS. 6 and 7 are block diagrams showing a third embodiment of the present invention. In FIGS. 6 and 7, those having the same structures as those shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. The configuration of the third embodiment is shown in FIG.
As shown in (1), first, an OPM 16 for measuring the output power of the first wavelength light is provided at the output end of the optical fiber 1. Then, in the third embodiment, both wavelengths of the first wavelength light and the second wavelength light are input to the multiplexer 41. The wavelength multiplexed light combined by the multiplexer 41 is transmitted from the multiplexer 61 to the optical fiber 1.
Transmitted to From this, the optical fiber 1 has the first
Wavelength multiplexed light consisting of the light of the second wavelength and the light of the second wavelength is transmitted. Here, an optical filter 62 for removing the second wavelength light is provided on the optical fiber 1. This allows O
Only the first wavelength light is input to PM16. OPM
16 measures the output power of the first wavelength light input from the optical filter 62.

Next, as shown in FIG. 7, the OPM 1 for measuring the output power of the second wavelength light is provided at the output end of the optical fiber 1.
7 is provided. Then, both wavelengths of the first wavelength light and the second wavelength light are input to the multiplexer 41. The wavelength multiplexed light combined by the multiplexer 71 is transmitted from the multiplexer 41 to the optical fiber 1.
Transmitted to Here, an optical filter 72 for removing the first wavelength light is provided on the optical fiber 1. As a result, only the second wavelength light is input to the OPM 17.
The OPM 17 measures the output power of the first wavelength light input from the optical filter 72. OPM16, OPM17
Respectively, the output power of the first wavelength light and the second power
After measuring the output power of the wavelength light of
6. By removing the OPM 17 and connecting the optical fiber 1 and the optical fiber 2, the configuration becomes the same as that of FIG.

The loss of the first wavelength light at the connection point A between the optical fiber 1 and the optical fiber 2 is determined before the optical fiber 1 and the optical fiber 2 are connected.
16 and the optical filter 61 connects the output power of the first wavelength light measured by the OPM 16 with the output power of the first wavelength light and the optical fiber 1 and the optical fiber 2.
The first wavelength light separated by the demultiplexer 15 is converted to OPM1
6, the output power of the first wavelength light, the optical fiber 1 and the optical fiber 2, and the splitter 15 and the optical fiber 2, which were measured using a measuring device (not shown) after being connected.
And the loss of the first wavelength light at the connection point B is calculated by conversion. Connection point A between optical fiber 1 and optical fiber 2
The loss of the second wavelength light at
In the same manner as the conversion method of the loss of the second wavelength light, the loss can be obtained by converting the loss of the second wavelength light.

In the configuration of the second embodiment, as shown in FIGS. 4 and 5, an OPM for measuring the output power of wavelength light is provided at the output end of the optical fiber 1 in advance. Then, only the other wavelength light is input to the multiplexer 41, and the other output power input to the multiplexer 41 is measured by OPM. However, when the optical fiber 1 described in the second embodiment is actually a rare earth element-doped optical fiber such as EDF, the signal light as the first wavelength light at the connection point A is, as shown in FIG. After the optical fiber 1 and the optical fiber 2 are connected, the first wavelength light and the second wavelength light are input to the combiner 11, and are amplified by the excitation light that is the second wavelength light.
Therefore, the conversion of the loss of the signal light amplified by the pump light at the connection point A uses the output power of the unamplified signal light measured by the OPM before connecting the optical fiber 1 and the optical fiber 2. Will be. Therefore,
The loss of the signal light amplified by the pump light at the connection point A cannot be accurately converted. Therefore, in the configuration of the third embodiment, both wavelength lights are input to the multiplexer 41 in advance,
By measuring the output power of the other by the OPM, the loss of the signal light amplified by the pump light at the connection point A can be converted.

The configuration of the fourth embodiment will be described below. In the fourth embodiment, one of the signal light of the first wavelength and the pump light of the second wavelength is set to a wavelength outside the optical amplification wavelength band.

Here, in the case of the 0.98 μm pumped EDFA, the optical amplification characteristics of the signal light as the first wavelength light and the pump light as the second wavelength light are as shown in FIGS. 8 and 9, respectively. It is. According to FIG. 8, in the case of the 0.98 μm pumped EDFA, the loss in the optical amplification characteristics is reduced by using the signal light in the 1.55 μm band at a wavelength smaller than the 1.50 μm band or a wavelength larger than the 1.60 μm band. I do. Signal light having a wavelength smaller than the 1.50 μm band or signal light having a wavelength larger than the 1.60 μm band is a wavelength deviating from the optical amplification wavelength band.

On the other hand, as shown in FIG.
In the case of A, the signal light in the 0.98 μm band is
By using a wavelength smaller than the band or a wavelength larger than the 1.02 μm band, the loss in the optical amplification characteristics is reduced. That is, signal light having a wavelength smaller than the 0.94 μm band or signal light having a wavelength larger than the 1.02 μm band is a wavelength deviating from the optical amplification wavelength band.

From the above, the signal light having the first wavelength is converted into the signal light in the 1.50 μm band, the signal light in the 1.60 μm band, or the second light as the first wavelength light used in the 0.98 μm pumped EDFA. By using the pump light of the 0.94 μm band or the 1.02 μm band as the wavelength light, this signal light is not amplified by the pump light.

In the fourth embodiment, the second embodiment is constituted by using the above-mentioned wavelength light. As a result, in the case where the optical fiber 1 is a rare earth element-doped optical fiber such as EDF, after the optical fiber 1 and the optical fiber 2 are connected, the signal light having the first wavelength shown in FIG. Even if the pumping light having the second wavelength is input to the multiplexer 11 at the same time, the signal light having the first wavelength is not amplified by the pumping light having the second wavelength. From the above, by configuring the second embodiment using the wavelength light described in the fourth embodiment, the connection point
The loss of the signal light at A can be converted.

[0063]

As described above, according to the present invention, the MF is achieved by using the first wavelength and the second wavelength having different wavelength bands.
Optical fibers having different D can be fusion-spliced with low loss. Therefore, it is possible to realize an optical amplifier having good noise characteristics or large output signal light power.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an overall configuration of a first embodiment.

FIG. 2 is an explanatory diagram of a loss with respect to a heating time for each wavelength band.

FIG. 3 is a configuration diagram of an EDFA excited at 0.98 μm in the first embodiment.

FIG. 4 is a configuration diagram of an EDFA in which only a first wavelength light of a second embodiment is input to a multiplexer.

FIG. 5 is a configuration diagram of an EDFA in which only a second wavelength light of a second embodiment is input to a multiplexer.

FIG. 6 is a configuration diagram of the EDFA of the third embodiment in which only the first wavelength light is input to the multiplexer.

FIG. 7 is a configuration diagram of an EDFA of the third embodiment in which only the second wavelength light is input to the multiplexer.

FIG. 8 is an explanatory diagram showing optical amplification characteristics in a 1.55 μm band.

FIG. 9 is an explanatory diagram showing optical amplification characteristics in a 0.98 μm band.

FIG. 10 is a configuration diagram of an optical fiber connection with a different MFD according to a conventional method.

FIG. 11 is a configuration diagram of an optical fiber connection with different MFD using the core enlargement of the conventional method.

FIG. 12 is a configuration diagram of an EDFA excited at 1.48 μm according to a conventional method.

FIG. 13 is an explanatory diagram showing a configuration of an MFD.

[Explanation of symbols]

 1,2 optical fiber 11,31,41,51,61,71 multiplexer 15,35 demultiplexer 16,17 optical power meter 62,72 optical filter

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G02B 6/255 H01S 3/10

Claims (3)

(57) [Claims] 1. An optical fiber 1 having a first MFD for transmitting a first wavelength light and a second wavelength light having different wavelength bands.
And an optical fiber connection method for connecting the optical fiber 2 having the second MFD, before connecting the optical fiber 1 and the optical fiber 2: the first wavelength is input to the input end of the optical fiber 1. A multiplexer for multiplexing light and the second wavelength light is connected, and the output power of the first wavelength light and the output power of the second wavelength light at the output end of the optical fiber 1 are measured. A distributor for separating the first wavelength light and the second wavelength light is connected to an output end of the optical fiber 2, and a loss of the first wavelength light in the optical fiber 2 and the demultiplexer is connected. And measuring the loss of the second wavelength light, and after connecting the optical fiber 1 and the optical fiber 2: an optical power meter for measuring the output power of the first wavelength light separated by the distributor. 16 and separated by the distributor The MFD is locally expanded by connecting an optical power meter 17 for measuring the output power of the second wavelength light and heating the end face portion of the optical fiber having the smaller MFD, and the MFD is changed by the heating. , The output power of the first wavelength light output from the distributor to the optical power meter 16.
And the output power of the second wavelength light output from the distributor is measured by the optical power meter 17. The output power of the first wavelength light at the output end of the optical fiber 1 and the second power Output power of the second wavelength light, the loss of the first wavelength light and the loss of the second wavelength light in the optical fiber 2 and the branching filter, and the optical power meter 16 and the optical power meter 17. Based on the measured output powers of the first wavelength light and the second wavelength light, the first wavelength light and the second wavelength light at the connection between the optical fiber 1 and the optical fiber 2 are An optical fiber connection method, comprising: calculating a loss; and stopping the heating when the calculated loss of the first wavelength light and the second wavelength light reaches an arbitrarily set value. 2. The optical fiber connection method according to claim 1, wherein a rare earth element-doped optical fiber having an optical amplification effect is used as said optical fiber. 3. The optical fiber connection method according to claim 2, wherein the first wavelength light, the second wavelength light, or both of the wavelength light is converted to an optical amplification wavelength of the rare earth element-doped optical fiber. An optical fiber connection method, wherein wavelength light is out of band.