JP4118727B2 - Optical passive components - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical passive component such as an optical circulator and an optical combiner.
[0002]
[Prior art]
In optical communications, optical passive components such as optical circulators and optical combiners are widely used. Here, the optical circulator is used for rearranging optical signal paths, and is used in optical amplifiers, optical communication systems that handle wavelength division multiplexing, dispersion compensation circuits, and the like. Conventional optical circulators are described in Patent Documents 1 to 3, for example.
FIG. 6 shows a schematic configuration of an example of a conventional optical circulator. The optical circulator 30 is made of an optical fiber and is an element type provided with first to third ports 31a, 31b, 31c for inputting / outputting light, polarizers 32a, 32b, and a Faraday rotator 33. It is. Here, the polarizers 32a and 32b transmit only light in a certain polarization direction, and the Faraday rotator 33 rotates the polarization direction.
The optical circulator 30 has a function of outputting light input from the first port 31a to the second port 31b and outputting light input from the second port 31b to the third port 31c. Some of such optical circulators have a function of outputting light input from the third port to the first port.
[0003]
[Patent Document 1]
Japanese Patent Publication No. 60-49887 [Patent Document 2]
Japanese Patent Publication No. 58-10726 [Patent Document 3]
Japanese Patent No. 2539563 [0004]
[Problems to be solved by the invention]
When manufacturing such a conventional optical circulator, it is necessary to connect an optical fiber and an element such as a polarizer or a Faraday rotator. However, the connection between the optical fiber and the element requires precise alignment of the optical axis, which requires careful work and increases the time for manufacturing the optical circulator. Moreover, since a polarizer, a Faraday rotator, and the like are special elements, it has been difficult to reduce the price. Moreover, since it is difficult to align the optical axis with high accuracy, the loss is large and the reliability of the product is low. In addition, an adhesive is often used for the connection, and in the conventional optical circulator, since light passes through the adhesive, there are problems in environmental resistance and high optical power resistance.
Conventionally, as an optical combiner, a polarization beam combiner using a polarization-maintaining optical fiber has been mainstream, but this optical combiner also has the same problems as an optical circulator.
In addition, since the polarization beam combiner synthesizes light having polarization axes orthogonal to each other, it is necessary to adjust the polarization axis of incident light, and the number of lights that can be synthesized is up to two.
The present invention has been made in view of the above circumstances, and an object thereof is to provide an optical passive component that has low cost, high reliability, and low loss, and is excellent in environmental resistance and high optical power resistance.
[0005]
[Means for Solving the Problems]
The optical passive component according to claim 1 of the present invention includes first to third ports made of optical fibers, and the fundamental mode (LP ₀₁ ) light input from the second port remains in the fundamental mode. A first mode converter having a function of outputting to the first port, converting the fundamental mode light input from the third port into a higher-order mode and outputting to the second port;
A first port and a second port made of optical fiber are provided, and light in the fundamental mode input from the first port is output to the second port in the fundamental mode and input from the first port. A second mode having a function of converting light of a higher-order mode into a fundamental mode and outputting the fundamental mode light to the second port, and outputting the fundamental mode light inputted from the second port to the first port in the fundamental mode. A mode converter and
The second port of the first mode converter and the first port of the second mode converter are connected by an optical fiber.
[0006]
The optical passive component according to claim 2 of the present invention is the optical passive component according to claim 1, wherein the first mode converter outputs the fundamental mode light input from the first port to the second port while maintaining the fundamental mode. It has the function to perform.
The optical passive component according to claim 3 of the present invention is characterized in that, in claim 1 or 2, the first mode converter is obtained by melting and stretching a plurality of optical fibers.
An optical passive component according to a fourth aspect of the present invention is the optical passive component according to any one of the first to third aspects, wherein the second mode converter has a single-mode waveguide portion of an optical fiber capable of propagating a plurality of modes. It is characterized by being processed into a taper shape so as to propagate only.
An optical passive component according to a fifth aspect of the present invention is the optical passive component according to any one of the first to fourth aspects, wherein the second mode converter is formed by processing an optical fiber forming the second port of the first mode converter. It is characterized by that.
The optical passive component according to a sixth aspect of the present invention is the optical passive component according to any one of the first to fifth aspects, wherein the light of the higher mode propagating between the first mode converter and the second mode converter is It is characterized by being LP ₀₂ mode light.
An optical passive component according to a seventh aspect of the present invention is the optical passive component according to the sixth aspect, wherein at least part of the optical fiber connecting the first mode converter and the second mode converter propagates the LP ₀₂ mode. The LP ₀₃ mode is not propagated.
An optical passive component according to an eighth aspect of the present invention is the optical passive component according to any one of the first to fifth aspects, wherein light of a higher-order mode propagating between the first mode converter and the second mode converter is It is characterized by being LP ₁₁ mode light.
The optical passive component according to claim 9 of the present invention is the optical passive component according to claim 8, wherein at least a part of the optical fiber connecting the first mode converter and the second mode converter propagates the LP ₁₁ mode. The LP ₂₁ mode is not propagated.
An optical passive component according to a tenth aspect of the present invention is the optical passive component according to any one of the first and third to ninth aspects, wherein the fundamental mode input from the third port (port I) of the first mode converter is the same. Output as a basic mode from the second port (port II) of the second mode converter and convert the basic mode input from the second port (port II) of the second mode converter to the first mode An optical circulator that outputs as a fundamental mode from the first port (port III) of the device.
An optical passive component according to an eleventh aspect of the present invention is the optical passive component according to any one of the second to ninth aspects, wherein the fundamental mode input from the third port (port I) of the first mode converter is the second mode. The basic mode input from the first port (port III) of the first mode converter is output as the basic mode from the second port (port II) of the converter, and the second mode converter 2 This is an optical combiner that outputs as a basic mode from the port (port II).
[0007]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of an optical passive component according to the present invention will be described with reference to the drawings. In the present embodiment, the optical passive component is an optical circulator.
FIG. 1 shows the configuration of the optical circulator of this embodiment. The optical circulator 10 includes a first mode converter 12 having first to third ports 11a, 11b, and 11c for inputting and outputting light, and a first mode 13 having a first port 13a and a second port 13b. 2 mode converter 14, the second port 11 b of the first mode converter 12 and the first port 13 a of the second mode converter 14 are connected by an optical fiber 15. It is. Moreover, in this optical circulator 10, all the ports are made of optical fibers.
The first port 11a of the first mode converter 12 is the port (III) of the optical circulator 10, the third port 11c of the first mode converter 12 is the port (I) of the optical circulator 10, and The second port 13b of the second mode converter 14 is used as the port (II) of the optical circulator 10.
[0008]
As shown in FIG. 2A, the first mode converter 12 outputs the light of the fundamental mode (LP ₀₁ ) input from the second port 11b to the first port 11a while remaining in the fundamental mode. As shown in FIG. 2B, the function of converting the light of the basic mode (LP ₀₁ ) input from the third port 11c into a higher-order mode (for example, LP ₀₂ ) and outputting it to the second port 11b. Have
The first mode converter 12 in this embodiment is obtained by melting and stretching a plurality of optical fibers. Since the mode converter in which a plurality of optical fibers are melt-drawn has a simple configuration, the reliability can be further improved and the cost can be reduced.
Further, since the input / output port is necessarily an optical fiber, there is an advantage that it is not necessary to connect the input / output port optical fiber.
[0009]
Techniques for producing a mode converter by melting and stretching a plurality of optical fibers are described in the following references 1 and 2.
Reference 1: Hayashi et al., “Fused Tapered Optical Fiber Mode Converter”, IEICE Transactions, C-1, Vol. J81-C-I, No11, pp650-651, November 1998 Reference 2: Kwang Yong Song et al. , VOL. 14, no. 4, April 2002 In addition, these references only describe the function of converting the light in the fundamental mode input from the third port into a higher-order mode and outputting it to the second port. The mode converter has a function of outputting the fundamental mode light input from the second port to the first port in the basic mode, as shown in FIG. 2C, and is input from the first port 11a. It also has a function of outputting the light in the basic mode to the second port 11b while remaining in the basic mode.
[0010]
As shown in FIG. 3A, the second mode converter 14 outputs the light of the basic mode (LP ₀₁ ) input from the first port 13a to the second port 13b while remaining in the basic mode. As shown in FIG. 3B, the light of the higher-order mode (for example, LP ₀₂ ) input from the first port 13a is converted into the fundamental mode (LP ₀₁ ) and output to the second port 13b. As shown in FIG. 3C, it has a function of outputting the light of the basic mode (LP ₀₁ ) input from the second port 13b to the first port 13a while remaining in the basic mode.
In the second mode converter 14 in this embodiment, the waveguide portion of the optical fiber capable of propagating a plurality of modes is processed into a tapered shape so as to propagate only a single mode. A structure in which a waveguide portion of an optical fiber capable of propagating a plurality of modes is formed into a tapered shape has a simple configuration, can further improve reliability, and is lower in price.
[0011]
Examples of the method of processing the waveguide portion of the optical fiber into a taper shape include a method of melt-drawing the optical fiber and a method of thermally diffusing the core of the optical fiber. Further, assuming that the waveguide portion of the optical fiber capable of propagating a plurality of modes is processed into a tapered shape, the collimator is used as parallel light whose diameter is increased, and this parallel light is again transmitted to the optical fiber by the collimator. Something that leads to
[0012]
In addition, since the second mode converter 14 can simplify the optical circulator, it is preferable that the optical fiber forming the second port 11b of the first mode converter 12 is processed.
[0013]
Since the high-order mode light propagating between the first mode converter 12 and the second mode converter 14 is easily subjected to mode conversion, it is preferably a lower-order mode light. Further, it is preferably LP _0X mode light having a peak of electric field distribution at the center of the optical fiber. Therefore, as the higher order mode light, the LP ₀₂ mode light which is the lowest order LP _0X mode is most preferable.
When the higher-order mode light is the LP ₀₂ mode light, the first mode converter 12 converts a part of the LP ₀₁ mode light into a higher-order mode light other than the LP ₀₂ mode. Depending on the performance of the second mode converter 14, this may be a loss. If no loss occurs, an interference system is formed between the first mode converter 12 and the second mode converter 14, and the optical characteristics become unstable. From the above, at least a part of the optical fiber 15 connecting the first mode converter 12 and the second mode converter 14 propagates the LP ₀₂ mode and does not propagate the LP ₀₃ mode. Is preferred. The V value (normalized frequency) of such an optical fiber is about 4 to 7 in the step index type optical fiber.
In higher-order modes other than the LP _0X mode, since the electric field at the center of the optical fiber is 0, conversion from the LP ₀₁ mode can be suppressed by devising the optical fiber profile.
[0014]
Further, there is no problem even if the higher-order mode light is a higher-order mode other than the LP ₀₂ mode. For example, if importance is attached to the ease of manufacturing the first mode converter, the light of the LP ₁₁ mode is used. It is preferable that
When the higher-order mode light is LP _11- mode light, the first mode converter 12 converts part of the LP _01- mode light into light of a higher-order mode other than the LP ₁₁ mode. Depending on the performance of the second mode converter 14, this may be a loss. If no loss occurs, an interference system is formed between the first mode converter 12 and the second mode converter 14, and the optical characteristics become unstable. From the above, at least a part of the optical fiber 15 connecting the first mode converter 12 and the second mode converter 14 propagates the LP ₁₁ mode and does not propagate the LP ₂₁ mode. Is preferred. The V value (normalized frequency) of such an optical fiber is a bimode fiber of about 2.4 to 4 in a step index type optical fiber.
[0015]
The optical circulator having such a configuration emits light of the fundamental mode (LP ₀₁ ) incident from the port (I) as it is in the fundamental mode from the port (II), and enters the fundamental mode (LP ₀₁ ) incident from the port (II). Is emitted from the port (III) in the basic mode.
[0016]
Since the optical circulator 10 as described above is manufactured by processing an optical fiber, the connection between the optical fiber and the element can be omitted. Therefore, since the work of precisely aligning the optical axis can be omitted, the manufacturing time can be shortened, the loss can be reduced, and the reliability of the product is improved. Further, since no special element such as a polarizer or a Faraday rotator is used, the cost can be reduced. Furthermore, since no adhesive is used, light does not pass through the adhesive, and the environment resistance and the high light power resistance are excellent. Such an optical circulator is suitably used for an optical amplifier, an optical communication system that handles wavelength division multiplexing, a dispersion compensation circuit, and the like.
[0017]
The optical circulator described above also has a function of outputting the fundamental mode light input from the first port to the second port in the fundamental mode, so that the ports (I) and (III) Any incident light exits from port (II). What has such a function is nothing but an optical combiner. That is, the optical passive component having the configuration shown in FIG. 1 can also be used as an optical combiner.
If the configuration shown in FIG. 1 is used as an optical combiner, it is not necessary to use a polarization maintaining optical fiber for the optical combiner, so that it is not necessary to adjust the polarization axis of incident light. Therefore, the work time can be shortened and the reliability can be improved. Further, since the polarization axes do not need to be orthogonal, it is possible to synthesize three or more incident lights in a tree structure, which is impossible with a polarization beam combiner.
[0018]
Note that the present invention is not limited to the above-described embodiments. For example, in the above-described embodiment, the first mode converter and the second mode converter are processed optical fibers, but other mode converters may be used. Even in that case, the configuration is simplified compared to the optical circulator using the element, so that the reliability is high and the price is low.
[0019]
【Example】
With reference to FIG. 4 and FIG. 5, the Example of the optical passive component of this invention is described. In light having a wavelength of 1550 nm, an optical fiber A in a region (V value: about 4 to 7) that propagates the LP ₀₂ mode and does not propagate the LP ₀₃ mode, and a normal single mode fiber B are prepared. The two optical fibers were arranged so as to contact each other. Next, the first mode converter 21 was manufactured by melt-drawing and reducing the diameter so that the LP ₀₂ mode propagation constant of the optical fiber A and the LP ₀₁ mode propagation constant of the optical fiber B were substantially equal. At that time, the light having a wavelength of 1550 nm incident from the optical fiber B (the optical fiber B is a single mode fiber, so this light is the fundamental mode LP ₀₁ ) is stretched so as to be 100% coupled to the LP ₀₂ mode of the optical fiber A. The conditions were adjusted. In the thus obtained mode converter 21, and the propagation constant of the LP ₀₁ mode optical fiber A, since the propagation constant of the LP ₀₁ mode of the optical fiber B are different, melt drawing portion from the optical fiber A 22 The LP ₀₁ mode light incident on the light propagates through the optical fiber A as it is without being coupled to the optical fiber B.
Further, the optical fiber B is fusion spliced to one end face of the optical fiber A, and the vicinity of the fusion splicing portion is heated, so that the cores 23a and 23b of the optical fibers A and B are formed as shown in FIG. The second mode converter 24 having a structure in which a single mode is propagated from an optical fiber capable of propagating a plurality of modes is manufactured by enlarging the taper so that a plurality of modes can be propagated. Got.
[0020]
In this optical passive component 20, one end 25 a of the optical fiber A is used as a port (I), and one end 25 c of the optical fiber B is used as a port (III). An end portion 25b of the optical fiber B that is connected to the connection is defined as a port (II). The optical passive component 20 having such a configuration emits the fundamental mode (LP ₀₁ ) incident from the port (I) as it is from the port (II), and enters the fundamental mode from the port (II). The light of (LP ₀₁ ) is emitted from the port (III) in the fundamental mode. Therefore, this optical passive component 20 has a function as an optical circulator.
The light of the fundamental mode (LP ₀₁ ) incident from the port (I) is emitted from the port (II) as the fundamental mode, and the light of the fundamental mode (LP ₀₁ ) incident from the port (III) is emitted from the port (II). Output from II) in the basic mode. Therefore, this optical passive component also has a function as an optical combiner.
[0021]
Since this optical passive component is manufactured only from an optical fiber and the configuration is simplified, it can be easily manufactured, and the loss is small and the reliability is high. Furthermore, since no adhesive is used for connection, the environment resistance and the high optical power resistance were excellent.
[0022]
【The invention's effect】
According to the present invention, since the connection between the optical fiber and the element can be omitted, the manufacturing time can be shortened, the cost can be reduced, and the loss can be reduced, thereby improving the reliability of the product. Furthermore, since no adhesive is used for connection, it is excellent in environmental resistance and high optical power resistance.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing an embodiment of an optical passive component according to the present invention.
FIG. 2 is a diagram illustrating the function of a first mode converter.
FIG. 3 is a diagram illustrating a function of a second mode converter.
FIG. 4 is a diagram schematically showing an embodiment of an optical passive component according to the present invention.
5 is a diagram showing a second mode converter of the optical passive component shown in FIG. 4. FIG.
FIG. 6 is a diagram schematically showing an example of a conventional optical circulator.
[Explanation of symbols]
10... Optical circulator (optical passive component), 11 a... (First mode converter) first port, 11 b... (First mode converter) second port, 11 c. 3rd port (of 1st mode converter), 12, 21 ... 1st mode converter, 13a ... 1st port (of 2nd mode converter), 13b ... · Second port (of second mode converter), 14, 24 ... second mode converter, 15 ... optical fiber

Claims (11)

Comprises first to third ports composed of an optical fiber, the light of the fundamental mode input from the second port (LP ₀₁₎ and output to the first port remains in the fundamental mode, input from the third port A first mode converter having a function of converting the fundamental mode light converted into a higher-order mode and outputting the light to the second port;
A first port and a second port made of optical fiber are provided, and light in the fundamental mode input from the first port is output to the second port in the fundamental mode and input from the first port. A second mode having a function of converting light of a higher-order mode into a fundamental mode and outputting the fundamental mode light to the second port, and outputting the fundamental mode light inputted from the second port to the first port in the fundamental mode. A mode converter and
An optical passive component, wherein the second port of the first mode converter and the first port of the second mode converter are connected by an optical fiber. 2. The optical passive component according to claim 1, wherein the first mode converter has a function of outputting the fundamental mode light input from the first port to the second port while maintaining the fundamental mode. 3. 3. The optical passive component according to claim 1, wherein the first mode converter is obtained by melting and stretching a plurality of optical fibers. The second mode converter is characterized in that a waveguide portion of an optical fiber capable of propagating a plurality of modes is formed into a tapered shape so as to propagate only a single mode. 4. The optical passive component according to any one of 3 above. The optical passive component according to claim 1, wherein the second mode converter is obtained by processing an optical fiber forming the second port of the first mode converter. Higher order mode light propagating between the first mode converter and the second mode converter is LP ₀₂ The optical passive component according to claim 1, which is mode light. At least a portion of the optical fiber connecting the first mode converter and the second mode converter is LP ₀₂ LP while propagating mode ₀₃ The optical passive component according to claim 6, which does not propagate a mode. Higher order mode light propagating between the first mode converter and the second mode converter is LP ₁₁ The optical passive component according to claim 1, which is mode light. At least a portion of the optical fiber connecting the first mode converter and the second mode converter is LP ₁₁ LP while propagating mode ₂₁ The optical passive component according to claim 8, wherein the optical passive component does not propagate a mode. The basic mode input from the third port (port I) of the first mode converter is output as the basic mode from the second port (port II) of the second mode converter, and the second mode conversion is performed. 2. An optical circulator that outputs a fundamental mode input from a second port (port II) of the optical device as a fundamental mode from the first port (port III) of the first mode converter. And the optical passive component in any one of Claims 3-9. The basic mode input from the third port (port I) of the first mode converter is output as the basic mode from the second port (port II) of the second mode converter, and the first mode conversion is performed. 3. An optical combiner that outputs the fundamental mode input from the first port (port III) of the optical device as the fundamental mode from the second port (port II) of the second mode converter. The optical passive component in any one of -9.

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