JP4615201B2 - Wavelength flat type optical coupler and manufacturing method thereof - Google Patents

Description

  The present invention relates to a wavelength flat type optical coupler that is manufactured by melting and stretching a coupling region of a plurality of optical fibers and a method for manufacturing the same.

Optical couplers used in optical transmission systems start with products that use optical components using lenses, and currently products that use optical fibers are the mainstream. Among optical couplers using an optical fiber, there is one called a fused taper type optical fiber coupler because of its manufacturing method. A fused taper type optical fiber coupler has two or more optical fibers placed close to each other in parallel, fixed at both ends thereof, placed on a jig, and heated with a microtorch or the like part of the two or more optical fibers. At the same time as being melt-integrated, it is produced by stretching in the longitudinal direction. By melting and stretching, the two optical fibers are reduced in diameter, the cores come close to each other, and branching and coupling of light propagating in the core is performed.

  The melt taper type optical fiber coupler can be manufactured by bringing two or more optical fibers into close contact in parallel and melting and stretching, so that it is a relatively easy manufacturing method. By the way, not only the fused taper type optical fiber coupler but generally the optical coupler has a very important branching ratio. In order to obtain a predetermined branching ratio in producing a melt-tapered optical fiber, strict control of heating temperature, tensile tension, stretching amount, etc. is required.

  An optical fiber coupler formed by melting uses two or more optical fibers, twists them together several times, heats the twisted part, while stretching the twisted part and gradually reduces the diameter. To taper shape and melt each other. In this type of coupler, an optical signal propagating in one of a number of optical fibers can be coupled to a number of other fibers.

Such an optical fiber coupler is suitable for use in an optical fiber communication network because of its low loss, excellent temperature stability, mechanical rigidity, and easy manufacture.
However, it is known that the coupling ratio of these optical fiber couplers depends on the wavelength. In a 2 × 2 port optical coupler fused to each other, it is necessary to divide the power coupled to the two receiver fibers to about 50 to 50, so that the power is divided into 50 to 50 at 1.55 μm. If the coupler is stretched during manufacture, the split ratio at 1.31 μm will be very different. Therefore, it is not sufficient for use in communication networks that need to operate at both wavelengths of 1.55 μm and 1.31 μm. In practice, an optical fiber coupler whose coupling ratio does not depend on the wavelength is required.

  Japanese Patent Application Laid-Open No. 8-304662 discloses an optical fiber coupler that reduces the wavelength dependence of the coupling ratio of the optical fiber coupler. That is, in order to provide an optical fiber coupler having a small coupling ratio wavelength dependency, that is, a substantially flat coupling ratio characteristic with respect to the wavelength, the optical fiber coupler disclosed in Japanese Patent Application Laid-Open No. 8-304662 is a propagation of one optical fiber. A coupling region of a predetermined length in which light is coupled to one or more other optical fibers, the propagation constant being slightly different from the propagation constants of the other optical fibers within the coupling region of the one optical fiber; In the set optical fiber coupler, the predetermined length is set equal to the minimum length at which the coupling ratios at the two preselected wavelengths are initially equal when the optical fiber coupler is formed.

According to JP-A-8-304662, it is disclosed that, for example, a 2 × 2 port optical fiber coupler capable of dividing optical power into about 50% vs. 50% with radiation of 1.3 μm and 1.52 μm can be manufactured. Yes.
JP-A-8-304662

  According to the above-described prior art, it is expected to obtain an optical fiber coupler having the same coupling coefficient at two preset wavelengths and a flat coupling ratio characteristic with respect to the wavelength. However, reducing the wavelength dependence of the coupling ratio, i.e., setting the length of the coupling region equal to the minimum length such that the coupling ratios at the two preselected wavelengths are initially equal is good. There is a problem that a flat type optical coupler cannot be obtained. That is, when the above-described optical coupler is applied to a transmission system, there is a problem that the quality of the transmission system deteriorates.

  Accordingly, it is an object of the present invention to provide a wavelength flat type optical coupler having excellent performance by solving the conventional problems.

  The present inventor has intensively studied to solve the conventional problems described above. As a result, in order to obtain a wavelength flat type optical coupler with excellent performance, the wavelength dependence of the coupling ratio is reduced, that is, the coupling ratio at the two preselected wavelengths is first selected. It was found that it was necessary to consider the polarization dependence rather than setting it to be equal to the minimum length that would be equal to. In particular, in order to improve the quality of the transmission system, it is necessary to minimize the polarization dependency, and even in an optical coupler as one element constituting the transmission system, the polarization dependency can be minimized. is important.

  That is, the insertion loss at two predetermined wavelengths (for example, 1310 nm and 1550 nm) was measured, and it was found that the polarization dependence was not reduced under the condition that the insertion loss at the two wavelengths was equal. That is, it is necessary to satisfy two requirements of insertion loss (wavelength dependence) and polarization loss (polarization dependence). To that end, it was found that a wavelength flat optical coupler with excellent performance can be obtained by setting the length of the coupling region so that the polarization dependence is minimized within the allowable insertion loss range. did.

The present invention has been made based on the above research results, and the first aspect of the method of manufacturing the wavelength flat optical coupler of the present invention is that two or more optical fibers are twisted together,
Applying melt stretching to the bonding region of the two or more optical fibers twisted together,
This is a method for manufacturing a wavelength flat type optical coupler, in which when the polarization dependency of the input wavelength light becomes minimum with an insertion loss within a predetermined range, the melt stretching is stopped and an optical coupler is manufactured.

The second aspect of the manufacturing method of the wavelength flat type optical coupler of the present invention is that when a predetermined optical fiber is reduced in diameter and melted and stretched, an insertion loss difference between two input wavelengths of light is inputted. There set preliminary stretching conditions to be within a predetermined range, and, the melt drawing conditions polarization dependency in the insertion loss within the predetermined range becomes minimum set respectively,
The two or more optical fibers obtained by subjecting at least one of the two or more optical fibers to pre-stretching so as to satisfy the pre-stretching condition, twisting the two or more optical fibers together and twisting each other. The coupling region is melt-stretched, and when the length of the coupling region satisfies the melt-stretching condition, the melt-stretching is stopped and the optical coupler is fabricated.

A third aspect of the method for manufacturing a wavelength flat optical coupler according to the present invention is a method for manufacturing a wavelength flat optical coupler, wherein the melt stretching is performed while monitoring insertion loss at a shorter one of the two predetermined wavelengths. Is the method.

  According to a fourth aspect of the method for producing a wavelength flat optical coupler of the present invention, the melt-stretching condition measures the insertion loss at two predetermined wavelengths, respectively, and determines the difference in insertion loss between the two wavelengths. A polarization-dependent optical coupler, wherein the polarization dependence corresponding to the insertion loss difference is obtained, and the melt-stretching is stopped at the point where the polarization dependence is minimized with the insertion loss within a predetermined range. It is a manufacturing method.

  According to a fifth aspect of the method of manufacturing a wavelength flat optical coupler of the present invention, the pre-stretching condition includes changing the pre-stretch length to optimize the pre-stretching. It is a manufacturing method.

  According to a sixth aspect of the method of manufacturing the wavelength flat optical coupler of the present invention, the two wavelengths are 1310 nm and 1550 nm, and the difference in insertion loss is obtained by subtracting the insertion loss at 1550 nm from the insertion loss at 1310 nm. This is a manufacturing method of the type optical coupler.

A seventh aspect of the method for producing a wavelength flat type optical coupler according to the present invention is a method for producing a wavelength flat type optical coupler, wherein the coupling ratio is in the range of 99: 1 to 50:50 at 1310 nm and 1550 nm.
Furthermore, an eighth aspect of the method for manufacturing a wavelength flat optical coupler according to the present invention is the method for manufacturing the wavelength flat optical coupler according to the first aspect, wherein the coupling ratios of two predetermined wavelengths are not equal and within a predetermined range. This is a method of manufacturing a flat wavelength optical coupler in which the melt-stretching is stopped and the optical coupler is manufactured when the polarization dependence becomes minimum due to the insertion loss.

  According to the present invention, not only the insertion loss (wavelength dependence) but also the polarization dependence loss (polarization dependence) is set, so that the coupling region length of the melt-stretching is set. A coupler can be provided.

The embodiment of the wavelength flat type optical coupler and the manufacturing method thereof according to the present invention will be described in detail with reference to the drawings.
One aspect of the method of manufacturing the flat wavelength optical coupler according to the present invention is to set a pre-stretching condition and a melt-stretching condition that minimizes polarization dependence with an insertion loss within a predetermined range for a predetermined optical fiber. And
The two or more optical fibers obtained by subjecting at least one of the two or more optical fibers to pre-stretching so as to satisfy the pre-stretching condition, twisting the two or more optical fibers together, and joining each other. The bonding region is melt-stretched while monitoring at a shorter one of the two predetermined wavelengths, and when the length of the bonding region satisfies the melt-stretching condition, the melt-stretching is stopped to A manufacturing method of a flat wavelength optical coupler to be manufactured.

  That is, the melt stretching conditions (that is, the length of the bonding region) are set as follows. First, the insertion loss at two predetermined wavelengths (for example, 1310 nm and 1550 nm) is measured, and the difference in insertion loss between the two wavelengths is obtained. Next, the insertion loss (wavelength dependence) and polarization dependence loss (polarization dependence) corresponding to the insertion loss difference are plotted, and the coupling region is such that the polarization dependence is minimized within the allowable insertion loss range. Set the length of.

In another aspect of the method of manufacturing a wavelength flat type optical coupler according to the present invention, the pre-stretching condition includes changing the pre-stretch length to optimize the pre-stretching. Further, the two wavelengths are 1310 nm and 1550 nm, and the difference in insertion loss is obtained by subtracting the insertion loss at 1550 nm from the insertion loss at 1310 nm. Further, at 1310 nm and 1550 nm, the bond ratio is in the range of 99: 1 to 50:50.

That is, in the method of manufacturing a flat wavelength optical coupler according to the present invention, first, for a predetermined type of optical fiber, pre-stretching conditions and melt-stretching conditions that minimize polarization dependence with an insertion loss within a predetermined range. Set each.
Pre-stretching conditions optimize pre-stretching by changing the pre-stretching length. As described above, the melt drawing conditions are such that the insertion loss at two predetermined wavelengths (for example, 1310 nm and 1550 nm) is measured to determine the difference in insertion loss between the two wavelengths. Next, the insertion loss (wavelength dependence) and polarization dependence loss (polarization dependence) corresponding to the insertion loss difference are plotted, and the coupling region is such that the polarization dependence is minimized within the allowable insertion loss range. Is set as a melt-stretching condition.

That is, the insertion loss and the polarization dependence are obtained with respect to the insertion loss difference defined by the following equation:
Insertion loss difference = (insertion loss at 1310 nm) − (insertion loss at 1550 nm)
Next, the extension length is obtained so that the polarization dependence is minimized within the allowable range of insertion loss.

FIG. 1 is a diagram for explaining the melt stretching conditions of the present invention. As shown in FIG. 1, the coupling ratio of the long wavelength (1550 nm) and the short wavelength (1310 nm) is equal at the point A. On the other hand, the polarization dependent loss (PDL) is minimum at point B. The melt-stretching condition, that is, the melt-stretching length is set not at the point A where the coupling ratio is equal, but at the point B where the polarization dependent loss (PDL) is minimized.
Based on the pre-stretching conditions and the melt-stretching conditions set as described above, pre-stretching is performed, and melt-stretching is performed while monitoring the shorter wavelength of the two wavelengths.

  Hereinafter, as an example, a method for manufacturing an optical coupler having a coupling ratio of 90:10 at 1310 nm and 1550 nm will be described. The same method is basically used for other varieties.

Two optical fibers are brought together to melt stretch the bonded region. At this time, one optical fiber of the two optical fibers is stretched (preliminarily stretched) so as to have a smaller diameter than the other optical fiber.
Melt stretching is performed while monitoring light is incident (the wavelength of incident light is 1310 nm), and the melt stretching is stopped when the set bond region length is reached.

FIG. 2 is a graph showing the insertion loss corresponding to the insertion loss difference when the coupling ratio is 90:10. FIG. 2 shows measurement data after the preliminary stretch length is substantially optimized. The vertical axis represents the insertion loss (dB), and the horizontal axis represents the insertion loss difference (dB).
As shown in FIG. 2, the insertion loss at a wavelength of 1310 nm changes from 9.9 to 10.6 (dB). On the other hand, the insertion loss at the wavelength of 1550 nm changes from 9.3 to 10.7 (dB). The insertion loss difference is -0.5 (that is, the insertion loss at the wavelength of 1550 nm exceeds the insertion loss at the wavelength of 1310 nm) to 1.0 (the insertion loss at the wavelength of 1310 nm exceeds the insertion loss at the wavelength of 1550 nm). It is moving between. As is clear from FIG. 2, when the insertion loss difference is 0.0, the insertion loss at the wavelength 1310 nm and the wavelength 1550 nm is 10.3 dB, and the condition that the insertion loss at the two wavelengths is equal can be found.

  FIG. 3 is a graph showing the polarization dependence corresponding to the insertion loss difference when the coupling ratio is 90:10. FIG. 3 also shows measurement data after the preliminary stretch length is substantially optimized. The vertical axis represents the polarization dependent loss (dB), and the horizontal axis represents the insertion loss difference (dB). The polarization-dependent loss at a wavelength of 1310 nm changes from 0.01 to 0.07 (dB). On the other hand, the polarization dependent loss at the wavelength of 1550 nm changes from 0.04 to 0.21 (dB). The insertion loss difference is -0.5 (that is, the insertion loss at the wavelength of 1550 nm exceeds the insertion loss at the wavelength of 1310 nm) to 1.0 (the insertion loss at the wavelength of 1310 nm exceeds the insertion loss at the wavelength of 1550 nm). It is moving between.

As is clear from FIG. 3, when the insertion loss difference is 0.0, the polarization dependent loss at a wavelength of 1310 nm is 0.04 dB, whereas the polarization dependent loss at a wavelength of 1550 nm is 0.16 dB. It can be seen that the polarization dependent loss is not minimized when the insertion loss difference is 0.0.
In the case shown in FIGS. 2 and 3, the insertion loss difference is +0.7 dB.
FIG. 8 is a graph showing the insertion loss corresponding to the insertion loss difference when the coupling ratio is 80:20. FIG. 9 is a graph showing the polarization dependence corresponding to the insertion loss difference when the coupling ratio is 80:20. As shown in FIGS. 8 and 9, even when the coupling ratio is 80:20, the polarization dependent loss is not minimized when the insertion loss difference is 0.0, as in the case of the coupling ratio 90:10. I understand that.
FIG. 10 is a graph showing the insertion loss corresponding to the insertion loss difference when the coupling ratio is 50:50. FIG. 11 is a graph showing the polarization dependence corresponding to the insertion loss difference when the coupling ratio is 50:50. As shown in FIGS. 10 and 11, even when the coupling ratio is 50:50, the polarization dependent loss is not minimized when the insertion loss difference is 0.0, as in the case of the coupling ratio 90:10. I understand that.

  As described above, a wavelength flat optical coupler with excellent performance can be obtained simply by stopping the melt stretching under the conditions where the insertion loss at the two wavelengths 1310 nm and 1550 nm is equal and determining the length of the coupling region. Absent. That is, it is important to determine the length of the coupling region that satisfies the two requirements of insertion loss and polarization dependence, and stop the melt drawing. In other words, an optical coupler is manufactured by determining the length of the coupling region under the condition that the insertion loss is within the allowable range of the product and the polarization dependence is as small as possible. Obtainable.

Next, the wavelength flat type optical coupler of the present invention will be described.
One aspect of the wavelength flat type optical coupler of the present invention sets, for a predetermined optical fiber, a melt stretching condition that minimizes polarization dependence with an insertion loss within a predetermined range,
Preliminary stretching is performed on at least one optical fiber of the two or more optical fibers, the two or more optical fibers are twisted together, and the two or more optical fibers obtained by joining are melt-stretched. This is a wavelength flat type optical coupler having a coupling region formed by melt drawing so as to satisfy the conditions.
That is, the wavelength flat type optical coupler of the present invention is an optical coupler coupler manufactured by the manufacturing method having the above-described features.

  Next, the wavelength flat type optical coupler of the present invention will be further described with reference to examples.

As described above, first, melt drawing conditions were set. That is, the insertion loss and polarization dependence are obtained with respect to the insertion loss difference defined by the following formula: insertion loss difference = (insertion loss at 1310 nm) − (insertion loss at 1550 nm), and then allowance for insertion loss. The melt drawing conditions are set so that the polarization dependence is minimized within the range.
Two optical fibers were brought together to melt stretch the bonded region. At this time, one optical fiber of the two optical fibers was stretched (preliminarily stretched) so as to have a smaller diameter than the other optical fiber. Light was incident while performing melt stretching (the wavelength of incident light was 1310 nm), and melt stretching was performed with the bond length set to satisfy the above-described melt stretching conditions.

First, the wavelength and insertion loss of the optical coupler and the wavelength and polarization dependency were examined.
FIG. 4 is a diagram showing the wavelength dependence (relationship between wavelength and insertion loss) of the optical coupler in the case of the port 1-2.

As shown in FIG. 4, the relationship between the wavelength of the optical coupler and the insertion loss in Samples 1 to 11 was examined. As a result, in sample 1, from 1270 nm to 1350 nm, in sample 1, the insertion loss changes from 0.49 dB, 0.51 dB, 0.5 dB, 0.48 dB, and 0.5 dB. In 1590 nm, it has changed with 0.4 dB, 0.42 dB, 0.4 dB, 0.42 dB, 0.38 dB, and 0.39 dB.
In the sample 2, the insertion loss changes from 0.55 dB, 0.55 dB, 0.55 dB, 0.58 dB, and 0.58 dB from the wavelength 1270 nm to the wavelength 1350 nm, and 0.5 dB from the wavelength 1510 nm to the wavelength 1590 nm. 0.5dB, 0.5dB, 0.42dB, 0.5dB.

Similarly, in Samples 3 to 11, the insertion loss is flat between about 0.4 dB and 0.6 dB at wavelengths of 1270 nm to 1350 nm and wavelengths of 1510 nm to 1590 nm.

FIG. 6 is a diagram illustrating the polarization dependency (relationship between wavelength and polarization loss) of the optical coupler in the case of the port 1-2.
As shown in FIG. 6, the polarization dependency (relationship between wavelength and polarization loss) of the optical couplers in Samples 1 to 11 was examined. As a result, in sample 1, the polarization loss changes from 0.001 dB to 0.001 dB from the wavelength 1270 nm to the wavelength 1350 nm, and from 0.005 dB to 0.005 dB, and from the wavelength 1510 nm to the wavelength 1590 nm. 0.18 dB, 0.02 dB, 0.03 dB, 0.01 dB, and 0.018 dB.

In sample 2, the polarization loss changes from 0.01 dB, 0.01 dB, 0.017 dB, 0.02 dB, and 0.01 dB from the wavelength 1270 nm to the wavelength 1350 nm, and is 0. 0 from the wavelength 1510 nm to the wavelength 1590 nm. 014 dB, 0.018 dB, 0.027 dB, 0.022 dB, and 0.02 dB are maintained.
In the samples 3 to 11 as well, the polarization loss similarly changes between approximately 0.00 and 0.02 dB from the wavelength 1270 nm to the wavelength 1350 nm, and approximately 0.00 to 0.00 from the wavelength 1510 nm to the wavelength 1590 nm. It is changing between 04dB.

Next, the wavelength dependency and polarization dependency of the optical coupler in the case of the port 1-3 are shown.
FIG. 5 is a diagram showing the wavelength dependence (relationship between wavelength and insertion loss) of the optical coupler in the case of the port 1-3. From the wavelength 1270 nm to the wavelength 1350 nm, in the sample 1, the insertion loss changes from 10.3 dB, 10.28 dB, 10.18 dB, 10.19 dB, 10.2 dB, and from the wavelength 1510 nm to the wavelength 1590 nm, 10.55 dB. 10.7 dB, 10.7 dB, 10.8 dB, 10.98 dB, and 11.0 dB.

In samples 2 to 11, the insertion loss has a tendency similar to that of sample 1 in the wavelength range from 1270 nm to 1350 nm. A difference appears in the insertion loss from the wavelength 1510 nm to the wavelength 1590 nm.

FIG. 7 is a diagram illustrating the polarization dependency (relationship between wavelength and polarization loss) of the optical coupler in the case of the port 1-3.
In Sample 1, the polarization loss changes from 0.055 dB, 0.058 dB, 0.06 dB, 0.07 dB, and 0.08 dB from the wavelength 1270 nm to the wavelength 1350 nm, and from the wavelength 1510 nm to the wavelength 1590 nm, the polarization loss is 0. It has changed with 18dB, 0.19dB, 0.21dB, 0.22dB, 0.23dB, and 0.25dB.

The relationship between the insertion loss difference and the insertion loss was obtained from FIG. 5 described above. This is shown in FIG. Furthermore, the relationship between the insertion loss difference and the polarization dependent loss was obtained from FIG. 7 described above. This is shown in FIG.
As described with reference to FIGS. 2 and 3, the coupling ratio is approximately 90:10 in the 1310 nm band and the 1550 nm band, but the polarization dependence of the optical coupler with good wavelength flatness is not necessarily small. I understand that there is no.

  Accordingly, the length of the coupling region is extended while monitoring at a wavelength of 1310 nm during manufacturing, and the extension is stopped when the predetermined insertion loss, that is, the insertion loss within the manufacturing allowable range and the polarization dependent loss are minimized. . In this manner, a wavelength flat type optical coupler with excellent performance can be manufactured.

  As described above, according to the present invention, not only the insertion loss (wavelength dependence) but also the polarization dependence loss (polarization dependence) is set, so that the coupling region length of the melt stretching is set, so that excellent performance is achieved. Can be provided, and has high industrial utility value.

FIG. 1 is a diagram for explaining the melt stretching conditions of the present invention. FIG. 2 is a graph showing the insertion loss corresponding to the insertion loss difference when the coupling ratio is 90:10. FIG. 3 is a graph showing the polarization dependence corresponding to the insertion loss difference when the coupling ratio is 90:10. FIG. 4 is a diagram showing the wavelength dependence (relationship between wavelength and insertion loss) of the optical coupler in the case of the port 1-2. FIG. 5 is a diagram showing the wavelength dependence (relationship between wavelength and insertion loss) of the optical coupler in the case of the port 1-3. FIG. 6 is a diagram illustrating the polarization dependency (relationship between wavelength and polarization loss) of the optical coupler in the case of the port 1-2. FIG. 7 is a diagram illustrating the polarization dependency (relationship between wavelength and polarization loss) of the optical coupler in the case of the port 1-3. FIG. 8 is a graph showing the insertion loss corresponding to the insertion loss difference when the coupling ratio is 80:20. FIG. 9 is a graph showing the polarization dependence corresponding to the insertion loss difference when the coupling ratio is 80:20. FIG. 10 is a graph showing the insertion loss corresponding to the insertion loss difference when the coupling ratio is 50:50. FIG. 11 is a graph showing the polarization dependence corresponding to the insertion loss difference when the coupling ratio is 50:50.

Claims (8)

Twist two or more optical fibers together,
Applying melt stretching to the bonding region of the two or more optical fibers twisted together,
A method of manufacturing a wavelength flat type optical coupler, wherein when a polarization dependent loss becomes minimum with an insertion loss within a predetermined range for light of an input wavelength, the melt stretching is stopped and an optical coupler is manufactured. It is a manufacturing method of the wavelength flat type optical coupler according to claim 1,
For a given optical fiber, and smaller diameter, when melted stretched, entered two predetermined preliminary stretching conditions insertion loss difference between the light is set to be within a predetermined range of wavelength, and wherein polarization dependent loss in the insertion loss within a predetermined range set respectively melt drawing conditions which minimizes,
After pre-stretching so that at least one optical fiber of the two or more optical fibers satisfies the pre-stretch condition, the two or more optical fibers are twisted together and twisted together. A method of manufacturing a wavelength flat type optical coupler, wherein melt coupling is performed on a coupling region of an optical fiber, and when the length of the coupling region satisfies the melt stretching condition, the melt stretching is stopped and an optical coupler is fabricated. 3. The method of manufacturing a wavelength flat type optical coupler according to claim 2, wherein the melt stretching is performed while monitoring insertion loss at a shorter one of two predetermined wavelengths. The melt stretching condition is to measure the insertion loss at two predetermined wavelengths, determine the insertion loss difference between the two wavelengths, determine the polarization dependence corresponding to the insertion loss difference, and within a predetermined range. 4. The method of manufacturing a wavelength flat type optical coupler according to claim 2, wherein the melt-stretching is stopped at a point where the polarization dependence is minimized by the insertion loss of the optical fiber. 5. The method of manufacturing a wavelength flat optical coupler according to claim 2, wherein the pre-stretching condition includes changing the pre-stretch length to optimize the pre-stretching. 5. The method of manufacturing a wavelength flat optical coupler according to claim 3, wherein the two wavelengths are 1310 nm and 1550 nm, and the difference in insertion loss is obtained by subtracting the insertion loss at 1550 nm from the insertion loss at 1310 nm. The method for producing a wavelength flat optical coupler according to any one of claims 2 to 6, wherein the coupling ratio is within a range of 99: 1 to 50:50 at 1310 nm and 1550 nm. It is a manufacturing method of the wavelength flat type optical coupler according to claim 1,
A wavelength flat type optical coupler for producing an optical coupler by stopping the melting and stretching when the coupling ratio of two predetermined wavelengths is not equal, the insertion loss is within a predetermined range, and the polarization dependence is minimized. Production method.

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