WO2023195280A1

WO2023195280A1 - Optical cable, electronic device, and optical communication system

Info

Publication number: WO2023195280A1
Application number: PCT/JP2023/007948
Authority: WO
Inventors: 寛森田; 雄介尾山; 一彰鳥羽; 真也山本
Original assignee: ソニーグループ株式会社
Priority date: 2022-04-07
Filing date: 2023-03-03
Publication date: 2023-10-12

Abstract

The present invention makes it possible to increase transmittable distance while suppressing a decrease in optical power coupling efficiency.　Connectors (32, 33) for spatial coupling are connected to end parts of an optical fiber (31). A portion other than end sides of the optical fiber (31) is configured as a first structure, the end side portions of the optical fiber (31) are configured as second structures, the first structure has a smaller inter-mode propagation delay difference than the second structures, and the second structures have higher coupling efficiency than the first structure. For example, the first structure is configured such that the refractive index of the core has a dipped graded-index shape, and the second structures are configured such that the refractive index of the core has a dipless graded-index shape or a stepped index shape.

Description

Optical cables, electronic equipment and optical communication systems

The present technology relates to optical cables, electronic equipment, and optical communication systems, and specifically relates to optical cables and the like that can extend the transmission distance while suppressing a decrease in optical power coupling efficiency.

Conventionally, optical communication using spatial coupling (see, for example, Patent Document 1) is known. In the case of such optical communication, particularly in single mode fibers, a large loss of optical power occurs due to positional deviation. Therefore, in the past, precision requirements for parts were high in order to suppress misalignment, leading to increased costs.

International Publication No. 2017/056889

The purpose of this technology is to make it possible to extend the possible transmission distance while suppressing a decrease in the coupling efficiency of optical power.

The concept of this technology is
optical fiber and
a connector for spatial coupling connected to the end of the optical fiber;
A part of the optical fiber other than a part on the end side has a first structure, and a part of the optical fiber on the end side has a second structure,
The first structure has a smaller inter-mode propagation delay difference than the second structure, and the second structure has a higher optical power coupling efficiency than the first structure. .

The optical cable in the present technology includes an optical fiber and a connector for spatial coupling connected to the end of the optical fiber. Then, the part other than the part on the end side of the optical fiber has the first structure, and the part on the end side of the optical fiber has the second structure, and the first structure has a higher propagation rate between modes than the second structure. The second structure has a structure in which the delay difference is small, and the second structure has a higher optical power coupling efficiency than the first structure.

For example, the first structure may be a structure in which the refractive index shape of the core is a graded index type with a dip. In this case, for example, the second structure may be a structure in which the refractive index shape of the core is a dip non-graded index type or a step index type.

Further, for example, an optical fiber propagates only the fundamental mode at a first wavelength, and communication is performed using light having a second wavelength and having at least a first-order mode component in addition to the fundamental mode. The second wavelength may be such that the optical fiber can propagate at least the first order mode along with the fundamental mode. Here, for example, the first wavelength may be a wavelength in the 1310 nm band, and the second wavelength may be a wavelength in the 850 nm band. In this case, depending on the direction of optical axis deviation, it is possible to increase the coupling efficiency of optical power.

In this case, an optical element that adjusts the optical path, such as a GRIN (gradient index) lens, may be placed at the end of the optical fiber. By arranging the GRIN lens in this manner, it is possible to reduce optical power coupling loss that occurs when communication is performed using light that has at least a primary mode component as well as a fundamental mode.

In this way, in the present technology, the part other than the part on the end side of the optical fiber has the first structure, the part on the end side of the optical fiber has the second structure, and the first structure has the second structure. The second structure has a smaller propagation delay difference between modes than the first structure, and the second structure has a higher optical power coupling efficiency than the first structure, making it possible to transmit optical power while suppressing a decrease in optical power coupling efficiency. It is possible to extend the distance.

Other concepts of this technology are:
Equipped with an optical interface structure in which a connector for spatial coupling is connected to the end of the optical fiber,
A part of the optical fiber other than a part on the end side has a first structure, and a part of the optical fiber on the end side has a second structure,
The first structure has a smaller inter-mode propagation delay difference than the second structure, and the second structure has a higher optical power coupling efficiency than the first structure. be.

The electronic device according to the present technology includes an optical interface structure in which a connector for spatial coupling is connected to the end of an optical fiber. Then, the part other than the part on the end side of the optical fiber has the first structure, and the part on the end side of the optical fiber has the second structure, and the first structure has a higher propagation rate between modes than the second structure. The second structure has a structure in which the delay difference is small, and the second structure has a higher optical power coupling efficiency than the first structure.

For example, the first structure is a structure in which the refractive index shape of the core is a graded index type with a dip, and the second structure is a structure in which the refractive index shape of the core is a non-dip graded index type or a step index type. This is the structure that is used.

In this case, an optical element for adjusting the optical path, such as a GRIN lens, may be placed at the end of the optical fiber. By arranging the GRIN lens in this manner, it is possible to reduce optical power coupling loss that occurs when communication is performed using light that has at least a primary mode component as well as a fundamental mode.

Furthermore, for example, the connector may be a connector for connecting external equipment via an optical cable. Furthermore, for example, the connector may constitute an input section or an output section for optical signals.

In addition, other concepts of this technology are:
optical cable and
an optical communication device having a connector for connecting one end of the optical cable; the optical cable has a configuration in which a connector for spatial coupling is connected to an end of an optical fiber;
A part of the optical fiber other than a part on the end side has a first structure, and a part of the optical fiber on the end side has a second structure,
The first structure has a smaller inter-mode propagation delay difference than the second structure, and the second structure has a higher optical power coupling efficiency than the first structure. Optical communication system. It is in.

The optical communication system according to the present technology includes an optical cable and an optical communication device having a connector for connecting one end of the optical cable. Then, the part other than the part on the end side of the optical fiber has the first structure, and the part on the end side of the optical fiber has the second structure, and the first structure has a higher propagation rate between modes than the second structure. The second structure has a structure in which the delay difference is small, and the second structure has a higher optical power coupling efficiency than the first structure.

Furthermore, for example, the optical communication device may be an optical communication device on the transmitting side. In this case, for example, it may further include a receiving-side optical communication device having a connector for connecting the other end of the optical cable.

FIG. 1 is a diagram showing an overview of optical communication using spatial coupling. 1 is a diagram showing the basic structure of an optical fiber and the LPml mode of a step type optical fiber. It is a diagram when considering the normalized frequency V in the case of 1310 nm, which is common in single mode. FIG. 2 is a diagram showing an example of optical communication using spatial coupling. FIG. 2 is a diagram showing an example of optical communication using spatial coupling. FIG. 2 is a diagram for explaining that when light with a wavelength of 850 nm is input to a single mode fiber of 1310 nm, a fundamental mode of LP01 and a primary mode of LP11 may exist. FIG. 4 is a diagram for considering a case where an optical axis shift occurs under the condition that only the fundamental mode of LP01 exists in the input light. It is a graph showing the simulation results of the amount of loss when the wavelength of input light is 1310 nm and 850 nm. FIG. 6 is a diagram showing that in a state where there is no optical axis shift, only the fundamental mode exists in the input light, but when there is an optical axis shift, a part of the fundamental mode is converted into a first-order mode. It is a graph for explaining that the fundamental mode is converted to the primary mode according to the shift. FIG. 3 is a diagram simulating the intensity distribution of light transmitted within an optical fiber. FIG. 3 is a diagram for explaining the angle at which light travels when it is emitted from a fiber end face. FIG. 2 is a diagram for explaining optical communication using spatial coupling. FIG. 3 is a diagram for explaining an optical axis shift in which the position of an optical fiber is shifted in a direction perpendicular to a lens. 3 is a graph showing simulation results of optical power coupling efficiency. FIG. 3 is a diagram for explaining an optical axis shift in which the position of an optical fiber shifts in a direction perpendicular to a lens. 3 is a graph showing simulation results of optical power coupling efficiency. FIG. 3 is a diagram showing an example in which a GRIN lens as an optical path adjustment section is provided on the incident side of an optical fiber. FIG. 6 is a diagram for explaining the reason why light can be returned toward the center even when the optical axis is shifted. 3 is a graph showing simulation results of optical power coupling efficiency. It is a graph in which a fundamental mode (0-order mode) component and a first-order mode component are described separately. FIG. 3 is a diagram for explaining the occurrence of a propagation delay difference between modes. FIG. 3 is a diagram showing an example of intensity distribution when a fundamental mode (0th mode) and a first mode propagate in an optical fiber. FIG. 3 is a diagram showing an example of the difference in propagation delay between modes when the refractive index shape of the core of an optical fiber is changed. FIG. 3 is a diagram showing an example of a simulation of the intensity distribution of light transmitted within an optical fiber when the refractive index shape of the core of the optical fiber is changed. When the refractive index shape of the core of an optical fiber is GI (with dip) type or GI (without dip) type, the intensity distribution of light transmitted within the optical fiber expands or narrows periodically in the optical axis direction. FIG. 4 is a diagram for explaining pitches defined when repeating. 3 is a graph illustrating an example of a simulation result of the coupling efficiency of optical power with respect to pitch in each of a GI (with dip) fiber and a GI (without dip) fiber. FIG. 2 is a diagram for explaining an optical axis shift in which the positions of a GRIN lens and an optical fiber on the receiving side are shifted in a direction perpendicular to the optical axis in optical communication using spatial coupling. 2 is a graph showing simulation results of optical power coupling efficiency with respect to optical axis deviation amount in each of a GI (with dip) fiber and a GI (without dip) fiber. It is a figure showing an example of composition of an optical cable. 1 is a diagram showing a configuration example of an optical communication system. FIG. 2 is a cross-sectional view showing a specific example of the configuration of an optical cable. FIG. 2 is a cross-sectional view showing an example of the configuration of a connector of a transmitter and a connector of an optical cable connected thereto. FIG. 2 is a cross-sectional view showing a configuration example of a light emitting section in a transmitter and a connector connected to the light emitting section via an optical fiber.

Hereinafter, modes for carrying out the invention (hereinafter referred to as "embodiments") will be described. Note that the explanation will be given in the following order.
1. Embodiment 2. Variant

<1. Embodiment>
[Description of technology related to embodiment]
First, technology related to the embodiment will be explained. FIG. 1 shows an overview of optical communication using spatial coupling. In this case, the light emitted from the transmission-side optical fiber 10T is shaped into collimated light by the lens 11T, which is an optical element, and then emitted. This collimated light is then condensed by a lens 11R on the receiving side and enters the optical fiber 10R. In the case of this optical communication, particularly in a single mode fiber, a large loss of optical power occurs due to positional deviation. The

optical fibers

10T and 10R have a double structure including a core 10a at the center serving as an optical path and a cladding 10b surrounding the core 10a.

Next, the basic idea of modes will be explained. When propagating in a single mode in an optical fiber, it is necessary to determine parameters such as the refractive index and core diameter of the optical fiber so that only one mode exists.

Figure 2(a) shows the basic structure of an optical fiber. An optical fiber has a structure in which a central portion called a core is covered with a layer called a cladding. In this case, the core has a high refractive index n1 and the cladding has a low refractive index n2, and light is confined within the core and propagates.

FIG. 2(b) shows the LPml (Linearly Polarized) mode of the stepped optical fiber, and shows the normalized propagation constant b as a function of the normalized frequency V. The vertical axis is the normalized propagation constant b, and in a state where a certain mode does not pass (blocked), b=0, and the more optical power is confined within the core (the more it can propagate), the closer b approaches 1. The horizontal axis is the normalized frequency V, which can be expressed by the following equation (1). Here, d is the core diameter, NA is the numerical aperture, and λ is the wavelength of light.
V=πdNA/λ...(1)

For example, when V=2.405, LP11 is cut off, so only LP01 exists as the mode. Therefore, a state where V=2.405 or less becomes a single mode. Here, LP01 is the basic mode (zero-order mode), and thereafter LP11, LP21, . . . become the first-order mode, second-order mode, . . . , respectively.

For example, consider the normalized frequency V in the case of 1310 nm, which is common in single mode, as shown in FIG. 3(a). Here, if the core diameter d and numerical aperture NA are respectively general parameters of a 1310 nm optical fiber, d = 8 μm and NA = 0.1, and the wavelength of the light propagating through the optical fiber is 1310 nm, the formula (1) Therefore, V=1.92.

Therefore, as shown in FIG. 3(b), since the normalized frequency V is 2.405 or less, only the fundamental mode of LP01 is propagated, resulting in a single mode. Here, increasing the core diameter increases the number of modes that can be propagated. Incidentally, for example, a general multimode fiber propagates several hundred modes by setting the core diameter to a value such as 50 μm.

When considering optical communication using spatial coupling as shown in Figure 1, in single mode, since the core diameter is small, the alignment of the optical coupling part on the transmitting side and receiving side becomes severe, and it is difficult to align the optical axis accurately. There is a problem that the accuracy requirement becomes high.

To solve this problem, generally, high-precision parts are used or the light input part to the optical fiber is processed to make it easier to insert light into the fiber core. However, connectors and systems for single-mode communications are generally expensive because high-precision parts are expensive, and items that require machining are expensive to process.

FIGS. 4 and 5 show examples of factors that degrade the accuracy of optical axis alignment. For example, as shown in FIG. 4A, optical axis misalignment occurs due to uneven amounts of fixing

materials

16T and 16R for fixing

ferrules

15T and 15R and

optical fibers

10T and 10R. Further, for example, as shown in FIG. 4B, optical axis deviation occurs due to insufficient shaping precision of the

lenses

11T and 11R.

Furthermore, as shown in FIGS. 5A and 5B, optical axis misalignment occurs due to insufficient precision of the positioning mechanisms (recesses 17T and protrusions 17R) provided on the

ferrules

15T and 15R. Note that the protrusion 17R shown in FIGS. 5(a) and 5(b) may be a pin.

"Description of embodiment"
This embodiment makes it possible to reduce the cost by relaxing the accuracy of optical axis alignment. In this embodiment, the optical fiber is capable of propagating only the fundamental mode at a first wavelength, and the optical fiber communicates using light of a second wavelength capable of propagating at least the first mode along with the fundamental mode. configured to do so.

For example, when light with a wavelength of 850 nm instead of 1310 nm is input into an optical fiber under the same conditions as in FIG. 3(a), the normalized frequency V=2.96, as shown in FIG. 6(b). Therefore, as shown in FIG. 6(a), there may be a basic mode of LP01 and a primary mode of LP11.

When assembling an optical system as shown in Figure 7(a), if the position of the receiving optical fiber is shifted perpendicularly to the optical axis under the condition that only the fundamental mode of LP01 exists in the input light. (See the arrows in FIGS. 7(a) and 7(b)), that is, consider the case where optical axis deviation occurs.

FIG. 8 is a graph showing the simulation results of the optical power coupling efficiency in that case. The horizontal axis represents the amount of optical axis deviation, and the vertical axis represents the coupling efficiency. When there is no shift, 100% of the power propagates into the optical fiber, and the coupling efficiency is 1. For example, if only 50% of the power of the input light is propagated into the optical fiber, the coupling efficiency will be 0.5.

Comparing the input light wavelengths of 1310 nm and 850 nm, it can be seen that the characteristics are better in the case of 850 nm. The reason for this is that in the case of 1310 nm, only the fundamental mode can propagate, whereas in the case of 850 nm, the primary mode as well as the fundamental mode can propagate (see FIG. 6(a)).

In other words, in a state where there is no optical axis deviation, only the fundamental mode exists in the input light, as shown in FIG. 9(a). On the other hand, in a state where there is an optical axis misalignment, as shown in FIG. 9(b), a part of the fundamental mode is converted into a first-order mode using a phase difference caused by the difference in refractive index between the cladding and the core. In the case of 1310 nm, this first-order mode cannot be propagated, but in the case of 850 nm, this first-order mode can also be propagated, so that the characteristics in the case of 850 nm are improved.

In the graph of FIG. 10, the fundamental mode (0-order mode) component and the 1st-order mode component are shown separately, and the sum becomes the total curve. Since the input light has only the fundamental mode, it can be seen that the fundamental mode is converted to the primary mode according to the shift. On the other hand, in the case of 1310 nm, only the fundamental mode can propagate as shown in FIG. 3(a), so the fundamental mode is purely reduced as shown in FIG.

In Figure 8, when comparing 1310nm and 850nm with a coupling efficiency of 0.8 (approximately -1 dB), the position is approximately 1.8 times larger, and when comparing with a coupling efficiency of 0.9 (approximately -0.5 dB), the position is approximately 2.35 times larger. The accuracy with respect to deviation can be relaxed.

In this way, the optical fiber is capable of propagating only the fundamental mode at a first wavelength (for example, 1310 nm), and the optical fiber is capable of propagating light at a second wavelength (for example, 850 nm) in which at least the first mode as well as the fundamental mode can be propagated. By configuring to perform communication using , it becomes possible to increase the coupling efficiency of optical power.

Furthermore, this embodiment is configured to perform communication using light having at least a primary mode component as well as a fundamental mode.

FIG. 11 is a diagram simulating the intensity distribution of light transmitted within an optical fiber. FIG. 11A shows an example of transmitting light having only fundamental mode components. In this case, the strength is highest at the center of the optical fiber core, and the strength decreases as it approaches the cladding. FIG. 11(b) shows an example of transmitting light having fundamental mode and first-order mode components. In this case, high-strength locations appear alternately in one direction and the other direction with respect to the center of the core, and in the example shown, in the upward and downward directions.

In the state shown in Fig. 11(b), when light is emitted from the fiber end face as shown in Fig. 12, the light travels at a certain angle in the direction of higher intensity with respect to the center of the core. Become something.

Consider optical communication using spatial coupling as shown in Figure 1. As shown in FIG. 13(a), light emitted from the center of the transmitting-side core 10a is coupled to the center of the receiving-side core 10a. However, as shown in FIG. 13(b), when transmitting light having fundamental mode and first-order mode components, light whose intensity distribution is biased upward from the center of the transmitting core 10a, It is coupled downward with respect to the center of the core 10a on the receiving side.

Let us consider a case where an optical axis shift occurs in which the position of the optical fiber 10R on the receiving side is shifted in a direction perpendicular to the lens 11R, as shown in FIG. 14, under the conditions shown in FIG. 13(b). In this case, the illustrated state is a state in which the amount of optical axis deviation is zero. When the optical axis shift is in the positive (+) direction, the portion where the light intensity is high is the direction in which the light enters the core 10a of the optical fiber 10R, making it easier to couple. On the other hand, when the optical axis shift is in the negative (-) direction, the core 10a of the optical fiber 10R moves in the opposite direction to the direction in which the light travels, resulting in a decrease in coupling efficiency.

Figure 15 shows the simulation results of the optical power coupling efficiency when the input light (light emitted from the transmitting side) has fundamental mode and first-order mode components, and the ratio is 1:1. It is a graph. The horizontal axis represents the amount of optical axis deviation, and the vertical axis represents the coupling efficiency. In the illustrated example, the fundamental mode (zero-order mode) and the first-order mode are shown separately, and the sum becomes the total curve. If only the fundamental mode was used, the coupling efficiency would drop significantly when shifted in the negative (-) direction, but thanks to the conversion of the fundamental mode to the first mode component, the coupling efficiency would be 0.0 with a shift of -1.5 μm. It is about 7.

Here, in optical communication using spatial coupling as shown in Fig. 13, the case where the component included in the input light (light emitted from the transmitting side) is only the fundamental mode, and the case where the fundamental mode and the primary mode are mixed. As shown in FIG. 16, consider the case where an optical axis shift occurs in which the position of the optical fiber 10R on the receiving side is shifted in a direction perpendicular to the lens 11R.

FIG. 17 is a graph showing the simulation results of the optical power coupling efficiency when the input light has only the fundamental mode component and when the input light has the fundamental mode and first-order mode components. The horizontal axis represents the amount of optical axis deviation, and the vertical axis represents the coupling efficiency. Here, in order to align the standards, the coupling efficiency at the point where the strength is maximum is standardized as 1.

When the input light has fundamental mode and first-order mode components, when the optical axis shift is in the positive (+) direction, the coupling efficiency is better than when the input light has only the fundamental mode components. This is because, as described above, when the optical axis misalignment is in the positive (+) direction, the location where the light intensity is high is the direction in which the light enters the core 10a of the optical fiber 10R, making it easier to couple.

However, if the input light has fundamental mode and first-order mode components, and the optical axis misalignment is in the negative (-) direction, the coupling efficiency will be worse than when the input light has only fundamental mode components. . This is because the core 10a of the optical fiber 10R moves in the opposite direction to the direction in which the light travels, as described above.

By configuring communication to use light that has at least a first-order mode component in addition to the fundamental mode, it is possible to respond to optical axis deviations by using light consisting of fundamental mode components depending on the direction of the deviation. It is possible to increase the coupling efficiency of optical power compared to the case where communication is performed using In this case, by designing the optical fiber so that the axis misalignment of the optical fiber can only be tolerated in the same direction as the traveling direction of the input light, the input light having the fundamental mode and first-order mode components is better than the input light having only the fundamental mode component. Light is more resistant to axis misalignment.

In addition, in this embodiment, when communication is performed using light having at least a first-order mode component as well as a fundamental mode, the coupling efficiency of optical power is increased with respect to optical axis deviation in the negative (-) direction. Therefore, the optical waveguide is configured to include an optical path adjusting section that adjusts the optical path so as to guide the input light to the core of the optical waveguide.

FIG. 18 shows an example in which an optical element as an optical path adjustment section, in this case a GRIN lens (gradient index lens) 22R, is provided on the input side of the optical fiber 10R. This GRIN lens 22R is a member having a refractive index distribution. The refractive index of this GRIN lens 22R has a refractive index equivalent to, for example, the core 10a of the optical fiber 10R on the optical axis, and has a gradation structure in which the refractive index decreases as it moves away from the optical axis in the vertical direction.

By providing the GRIN lens 22R on the incident side of the optical fiber 10R in this manner, the light that has entered the GRIN lens 22R travels while being curved in the optical axis direction due to the gradation effect. Furthermore, even if the optical axis is shifted, the light can be returned toward the center. The reason for this is that when the optical path is shifted downward with respect to the optical axis, as shown by the broken line in Figure 19, the light near the optical axis has a small refractive index difference, so the amount of bending is small, and the light that is further away from the optical axis This is because the difference in refractive index is large, so the amount of bending is large, and therefore the light is concentrated near the center of the core 10a. This makes it possible to increase the coupling efficiency of optical power against optical axis deviation in the negative (-) direction.

FIG. 20 is a graph showing the simulation results of the optical power coupling efficiency in the case of a double lens (Double Lens) provided with the GRIN lens 22R and in the case of a single lens (Single Lens) not provided with the GRIN lens 22R. The horizontal axis represents the amount of optical axis deviation, and the vertical axis represents the coupling efficiency. For example, when the GRIN lens 22R is provided for optical axis deviation in the negative (-) direction, the coupling efficiency is higher than in the case of a single lens. In addition, in the graph of FIG. 21, when the GRIN lens 22R is provided, the fundamental mode (0th mode) component and the 1st mode component are shown separately, and the sum is the total. It becomes a curve.

As described above, when the GRIN lens 22R as an optical path adjustment section is provided at the end of the optical fiber 10 on the reception side, it is better to arrange the lens as an optical path adjustment section on both the transmission side and the reception side in terms of optical design. In order to minimize the influence of aberrations, it is necessary to provide a similar lens at the end of the optical fiber 10T on the transmitting side.

Hereinafter, an example in which a GRIN lens is provided at the end of an optical fiber will be described. Although detailed explanation will be omitted, the same applies to the case where other lenses having similar functions are provided at the end of the optical fiber.

In addition, in this embodiment, the optical cable that connects the transmitter, which is an optical communication device on the transmitting side, and the receiver, which is an optical communication device on the receiving side, increases the possible transmission distance while suppressing a decrease in the coupling efficiency of optical power. Constructed to allow stretching.

Figure 22 shows a conventional 1310 nm fiber (single-mode optical fiber that propagates only the 0-order mode (fundamental mode) at a wavelength of 1310 nm), and shows the 0-order mode component and the 1-order mode component at a wavelength of 850 nm from an 850 nm light source. An example of transmitting light (optical signal) consisting of

In this case, a propagation delay difference occurs between the zero-order mode and the first-order mode at the output end of the optical fiber. Such a difference in propagation delay between modes is caused by a difference in reflection angles of light components of each mode within the optical fiber. In this case, the reflection angle becomes steeper as the order increases. That is, since the optical path length changes depending on the mode, a propagation delay difference between modes occurs.

As shown in FIG. 22, when "1" is expressed by the power of the sum of the zero-order mode and the first-order mode at the input end of the optical fiber, when a propagation delay difference between modes occurs at the output end of the optical fiber, " A step will occur in the waveform rising from "0" to "1" or falling from "1" to "0". This phenomenon results in waveform distortion in data transmission, resulting in signal quality deterioration. This signal quality deterioration becomes more pronounced as the optical fiber becomes longer and the data rate becomes higher.

When waveform distortion that causes signal quality deterioration occurs in this way, it is possible to correct the waveform distortion and suppress the signal quality deterioration, but a waveform distortion correction circuit is required on the transmitting and receiving sides. , leading to increased costs and increased power consumption.

There are methods to reduce the propagation delay difference between modes. When each mode of light propagates within an optical fiber, its intensity distribution does not fit within the core and propagates through the cladding. FIG. 23 shows an example of the intensity distribution when the fundamental mode (0-order mode) and the first-order mode propagate in the optical fiber. As shown in the figure, it can be seen that the intensity distribution of both the fundamental mode and the primary mode penetrates into the cladding.

The refractive index of the core and cladding is higher in the core, which means that the propagation speed of light is slower in the core. In general, the higher the order of the mode, the steeper the angle of total reflection when propagating within the optical fiber, so the propagation path extends in the direction of propagation, but the intensity distribution of light passing through the cladding side increases, resulting in refraction of the core and cladding By appropriately controlling the rate distribution, it becomes possible to uniformly control the propagation speed for each mode.

FIGS. 24(a) to 24(c) show an example of the difference in propagation delay between modes when the refractive index shape of the core of the optical fiber is changed. This example shows an example in which light with a wavelength of 850 nm having fundamental mode and first-order mode components is input into a 1310 nm single mode fiber. Here, the inter-mode propagation delay difference is "fundamental mode propagation velocity - primary mode propagation velocity."

In FIG. 24(a), the refractive index shape of the core of the optical fiber is a step index type (SI type), and the propagation delay difference between modes is 1630 ps/km. Figure 24(b) shows that the refractive index shape of the core of the optical fiber is a non-dip graded index type (GI (no dip) type), and the inter-mode propagation delay difference is 165 ps/km, compared to the SI type. It becomes possible to reduce it to about 1/10.

This is because in the case of the GI (no dip) type, light passing near the center has a high refractive index, which means the speed is slow, and the closer it gets to the cladding, the lower the refractive index, which means the speed becomes faster, and the first-order mode This is because the propagation speed of is close to the propagation speed of the fundamental mode. In this case, the primary mode that easily passes through the cladding has a long optical path length but has a low refractive index and a high speed, while the fundamental mode that easily passes through the center has a short optical path length but has a high refractive index and a slow speed. The delay difference between

In FIG. 24(c), the refractive index shape of the core of the optical fiber is a graded index type with a dip (GI (with dip) type), and the propagation delay difference between modes is 39 ps/km, which can be further reduced. becomes possible. In the case of the GI (with dip) type, by providing a dip with a lower refractive index in the center of the core, the propagation speed of the fundamental mode passing through the center is finely adjusted to match the propagation speed of the primary mode. This is because adjustments are being made.

FIGS. 25(d) to (f) show an example of a simulation of the intensity distribution of light transmitted within an optical fiber when the refractive index shape of the core of the optical fiber is changed. This example shows a case where light with a wavelength of 850 nm having only a fundamental mode component is input into a 1310 nm single mode fiber.

FIG. 25(e) shows an example in which the refractive index shape of the core of the optical fiber is a GI (no dip) type (see FIG. 25(b)). In this case, the light intensity distribution periodically expands and narrows in the optical axis direction.

FIG. 25(f) shows an example in which the refractive index shape of the core of the optical fiber is a GI (with dip) type (see FIG. 25(c)). In this case, the light intensity distribution also periodically expands and narrows in the optical axis direction, but the degree of expansion and narrowing is slightly larger than in the case of the GI (no dip) type.

FIG. 25(d) shows an example in which the refractive index shape of the core of the optical fiber is an SI type (see FIG. 25(a)). The light intensity distribution in this case does not periodically expand or narrow in the optical axis direction, unlike in the GI (without dip) type and the GI (with dip) type.

Note that, in order to make it easier to understand the phenomena that appear, FIGS. 25(d) to (f) are examples in which light with a wavelength of 850 nm having only the fundamental mode component is input into a 1310 nm single mode fiber. Although not shown, a similar example is obtained when light with a wavelength of 850 nm having fundamental mode and primary mode components is input into a 1310 nm single mode fiber, and the refractive index shape of the core of the optical fiber is GI (without dip). ) type or GI (with dip) type, the light intensity distribution periodically repeats expansion and narrowing in the optical axis direction.

Although not shown, the intensity distribution of light when light with a wavelength of 1310 nm is input into a single mode fiber of 1310 nm is that the refractive index shape of the core of the optical fiber is GI (without dip) type or GI (with dip) type. ) type, there is almost no periodic expansion or narrowing in the optical axis direction. This is a problem with the way light travels, and is because light spreads more easily at 1310 nm than at 850 nm.

When transmitting over long distances, it is necessary to reduce the propagation delay difference between modes. As described above, it can be seen that the difference in propagation delay between modes can be minimized when the refractive index shape of the core of the optical fiber is GI (with dip) type. However, it has been found that when the refractive index shape of the core of the optical fiber is a GI (with dip) type, the coupling efficiency of optical power deteriorates.

Here, consider optical communication using spatial coupling as shown in FIG. 26(a). On the transmitting side, a GRIN lens 22T for adjusting the optical path is arranged between the optical fiber 10T and the lens 11T. Further, on the receiving side, a GRIN lens 22R for adjusting the optical path is arranged between the lens 11R and the optical fiber 10R.

In this case, the light emitted from the transmitting side optical fiber 10T is incident on the lens 11T via the GRIN lens 22T, and is shaped into collimated light by this lens 11T and emitted. This collimated light is then condensed by a lens 11R on the receiving side, and is input to an optical fiber 10R via a GRIN lens 22R.

Similar to FIG. 25(f), FIG. 26(b) shows transmission in the optical fiber when the refractive index shape of the core of the optical fiber is GI (with dip) type (see FIG. 25(c)). An example of a simulation of light intensity distribution is shown. Here, the pitch is 0 (P0) when the light is emitted from the optical fiber under the conditions where the intensity distribution is the widest, and the pitch is 0.25 (P0.25) when the light is emitted from the optical fiber under the conditions where the intensity distribution is the narrowest. It is defined as Although not shown, the same applies to the intensity distribution of light transmitted within an optical fiber when the refractive index shape of the core of the optical fiber is GI (no dip) type (see FIG. 25(b)). is defined as

FIG. 27 is a graph showing an example of the simulation results of the coupling efficiency of optical power with respect to pitch in each of the GI (with dip) fiber and the GI (without dip) fiber. The horizontal axis represents pitch, and the vertical axis represents coupling efficiency.

Here, the GI (with dip) fiber means an optical fiber whose core has a GI (with dip) type refractive index shape, and the simulation in that case is based on the

optical fibers

10T and 10R in FIG. 26(a). The experiment was carried out using a GI (dip-equipped) fiber, under the condition that light with a wavelength of 850 nm having only a fundamental mode component was propagated from the transmitting side to the receiving side in a 1310 nm single mode fiber.

In addition, GI (no dip) fiber means an optical fiber whose core has a GI (no dip) type refractive index shape, and the simulation in that case shows that the

optical fibers

10T and 10R in FIG. 26(a) are The experiment was carried out under the conditions that light with a wavelength of 850 nm having only a fundamental mode component was propagated from the transmitting side to the receiving side in a 1310 nm single mode fiber using a GI (no dip) fiber.

From the graph in Figure 27, it can be seen that the GI (with dip) fiber has lower optical power coupling efficiency than the GI (without dip) fiber, and also depends on the pitch, that is, the light is emitted from the optical fiber on the transmitting side. It can be seen that the coupling efficiency varies greatly depending on the shape of the actual intensity distribution.

As mentioned above, when light with a wavelength of 1310 nm is input into a 1310 nm single mode fiber, the intensity distribution of the light is determined depending on whether the refractive index shape of the core of the optical fiber is GI (without dip) or GI (with dip). Even in the case of a mold, there is almost no periodic expansion or narrowing in the optical axis direction, and therefore there is no deterioration in the coupling efficiency of optical power due to such a pitch. In other words, the problem of deterioration of optical power coupling efficiency due to this pitch is considered to be unique to the so-called double mode in which, for example, 850 nm light is propagated in a 1310 nm single mode fiber.

Furthermore, as shown in FIG. 28, in optical communication using spatial coupling similar to that shown in FIG. Let us consider the case where the optical axis shifts (see the arrow in FIG. 28), that is, the optical axis shifts.

FIG. 29 is a graph showing the simulation results of the optical power coupling efficiency with respect to the amount of optical axis deviation in each of the GI (with dip) fiber and the GI (without dip) fiber. The horizontal axis represents the amount of optical axis deviation, and the vertical axis represents the coupling efficiency.

Here, the GI (with dip) fiber means an optical fiber whose core has a refractive index shape of the GI (with dip) type, and the simulation in that case shows that the

optical fibers

10T and 10R in FIG. The experiment was carried out under the condition that light with a wavelength of 850 nm having only the fundamental mode component was propagated from the transmitting side to the receiving side in a 1310 nm single mode fiber.

Further, GI (no dip) fiber means an optical fiber whose core has a refractive index shape of GI (no dip) type, and the simulation in that case shows that the

optical fibers

From the graph in Figure 29, it can be seen that the GI (with dip) fiber has a lower optical power coupling efficiency than the GI (without dip) fiber, and the optical power coupling efficiency increases as the axis misalignment increases. It can be seen that the rate of decline is also steep.

In this way, since the GI (with dip) fiber can make the difference in propagation delay between modes smaller than the GI (without dip) fiber (see FIG. 24), it is possible to extend the possible transmission distance. However, since GI (with dip) fiber has lower optical power coupling efficiency than GI (without dip) fiber (see Figures 27 and 29), highly accurate components are required to ensure quality. This leads to increased costs.

FIG. 30 shows an example of the configuration of the optical cable 30 in this embodiment. This optical cable 30 has an optical fiber 31, connectors (plugs) 32 and 33 for spatial coupling, and GRIN lenses 34 and 35. A connector (plug) 32 is connected to one end of the optical fiber 31 via a GRIN lens 34, and a connector (plug) 33 is connected to the other end of the optical fiber 31 via a GRIN lens 35. In the illustrated example, only lens portions are shown as the connectors 32 and 33.

The optical fiber 31 is a GI (with dip) fiber (indicated by "GI-d" in the figure) except for a part on the end side, and a part on the end side is a GI (without dip) fiber (indicated by "GI-d" in the figure). (Indicated by "GI" in the figure). The connection between the GI (with dip) fiber and the GI (without dip) fiber is performed, for example, by fusion splicing.

By configuring the optical fiber 31 in this way, the optical cable 30 can extend the transmission distance while suppressing a decrease in the coupling efficiency of optical power.

[Optical communication system]
FIG. 31 shows a configuration example of the optical communication system 100. This optical communication system 100 includes a transmitter 200, a receiver 300, and an optical cable 400. The transmitter 200 constitutes an optical communication device on the transmitting side. The receiver 300 constitutes an optical communication device on the receiving side.

The transmitter 200 is, for example, an AV source such as a personal computer (PC), a game console, a disc player, a set-top box, a digital camera, or a mobile phone. The receiver 300 is, for example, a television receiver, a projector, a PC monitor, or the like. Transmitter 200 and receiver 300 are connected via optical cable 400.

The transmitter 200 has a light emitting section 201, a connector 202 as a receptacle, and an optical fiber 203 that propagates the light emitted from the light emitting section 201 to the connector 202. The light emitting unit 201 includes a laser element such as a VCSEL or a light emitting element (light source) such as an LED (light emitting diode). The light emitting unit 201 converts an electrical signal (transmission signal) generated by a transmission circuit (not shown) into an optical signal. Light (optical signal) emitted by the light emitting section 201 is propagated to the connector 202 through the optical fiber 203.

Further, the receiver 300 includes a connector 301 as a receptacle, a light receiving section 302, and an optical fiber 303 that propagates the light obtained from the connector 301 to the light receiving section 302. The light receiving section 302 includes a light receiving element such as a photodiode. The light receiving unit 302 converts the optical signal sent from the connector 301 into an electrical signal (received signal) and supplies it to a receiving circuit (not shown).

The optical cable 400 has

connectors

402 and 403 as plugs at one end and the other end of an optical fiber 401. A connector 402 at one end of the optical fiber 401 is connected to the connector 202 of the transmitter 200, and a connector 403 at the other end of the optical fiber 401 is connected to the connector 301 of the receiver 300.

In this optical communication system 100, the optical fiber of the present technology is applied to the optical fiber 203 of the transmitter 200, the optical fiber 303 of the receiver 300, and the optical fiber 401 of the optical cable 400, and under double mode conditions, for example, with an 850 nm light source. A combination of 1310 nm fibers is applied for communication.

Here, the optical fiber 401 is a GI (with dip) fiber except for a part on the end side, and a part on the end side is a GI (without dip) fiber (see FIG. 30). This makes it possible to extend the possible transmission distance while suppressing a decrease in optical power coupling efficiency.

FIG. 32 shows a specific configuration example of the optical cable 400. This optical cable 400 has a configuration in which

connectors

402 and 403 serving as plugs are connected to one end and the other end of an optical fiber 401. As mentioned above, the optical fiber 401 is a GI (dip) fiber (indicated by "GI-d" in the figure) except for a part on the end side, and a part on the end side is a GI (dip) fiber (indicated by "GI-d" in the figure). dipless) fiber (indicated by "GI" in the figure).

The connector 402 includes a connector body 421. The connector body 421 is made of a light-transmitting material such as synthetic resin or glass, or a material such as silicon that transmits a specific wavelength, and has a ferrule configuration with a lens.

By configuring the connector body 421 as a ferrule with a lens in this way, it is possible to easily align the optical axes of the optical fiber and the lens. Further, since the connector main body 421 is configured as a ferrule with a lens in this way, even in the case of multi-channel communication, multi-channel communication can be easily realized by simply inserting an optical fiber into the ferrule.

A concave light entrance portion (light transmission space) 423 is formed on the front side of the connector body 421. A lens (convex lens) 424 is integrally formed on the connector main body 421 so as to be located at the bottom of the light incidence section 423.

In addition, the connector body 421 is provided with an optical fiber insertion hole 426 extending from the back side to the front in alignment with the lens 424. The optical fiber 401 has a double structure including a core 401a at the center serving as an optical path and a cladding 401b surrounding the core.

The optical fiber insertion hole 426 is shaped so that the core 401a of the optical fiber 401 inserted therein and the optical axis of the lens 424 coincide. Further, the optical fiber insertion hole 426 is shaped so that when the optical fiber 401 is inserted, its tip (incidence end) matches the focal position of the lens 424.

Furthermore, an adhesive injection hole 422 extending downward from the top surface side is formed in the connector body 421 so as to communicate with the vicinity of the bottom position of the optical fiber insertion hole 426. After the optical fiber 401 is inserted into the optical fiber insertion hole 426, the adhesive 427 is injected around the optical fiber 401 from the adhesive injection hole 422, thereby fixing the optical fiber 401 to the connector body 421. In this case, a GRIN lens 428 is placed on the tip side of the optical fiber 401.

In the connector 402, the lens 424 has a function of condensing the incident collimated light. In this case, the collimated light is incident on the lens 424 and condensed, and this condensed light is incident on the input end of the optical fiber 401 through the GRIN lens 428 at a predetermined NA.

The connector 403 includes a connector body 431. The connector body 431 is made of a light-transmitting material such as synthetic resin or glass, or a material such as silicon that transmits a specific wavelength, and has a ferrule configuration with a lens.

By configuring the connector body 431 as a ferrule with a lens in this way, it is possible to easily align the optical axes of the optical fiber and the lens. Further, since the connector main body 431 is configured as a ferrule with a lens in this way, even in the case of multi-channel communication, multi-channel communication can be easily realized by simply inserting an optical fiber into the ferrule.

A concave light emitting portion (light transmission space) 433 is formed on the front side of the connector body 431. A lens (convex lens) 434 is integrally formed on the connector main body 431 so as to be located at the bottom of the light emitting section 433.

Further, the connector body 431 is provided with an optical fiber insertion hole 436 extending from the back side to the front, in alignment with the lens 434.

The optical fiber insertion hole 436 is shaped so that the core 401a of the optical fiber 401 inserted therein and the optical axis of the lens 434 coincide. Further, the optical fiber insertion hole 436 is shaped so that when the optical fiber 401 is inserted, its tip (incidence end) matches the focal position of the lens 434.

Furthermore, an adhesive injection hole 432 extending downward from the top surface side is formed in the connector body 431 so as to communicate with the vicinity of the bottom position of the optical fiber insertion hole 436. After the optical fiber 401 is inserted into the optical fiber insertion hole 436, the adhesive 437 is injected around the optical fiber 401 from the adhesive injection hole 432, thereby fixing the optical fiber 401 to the connector body 431. In this case, a GRIN lens 438 is placed on the tip side of the optical fiber 401.

In the connector 403, the lens 434 has a function of shaping the light emitted from the optical fiber 401 into collimated light and emitting the collimated light. Thereby, the light emitted from the emitting end of the optical fiber 401 with a predetermined NA enters the lens 434 through the GRIN lens 438, is shaped into collimated light, and is emitted.

FIG. 33 shows a configuration example of the connector 202 of the transmitter 200 and the connector 402 of the optical cable 400 connected thereto. This configuration example is one example, and is not limited to this.

The connector 202 includes a connector body 221. The connector body 221 is made of a light-transmitting material such as synthetic resin or glass, or a material such as silicon that transmits a specific wavelength, and has a ferrule configuration with a lens.

By configuring the connector body 221 as a ferrule with a lens in this way, it is possible to easily align the optical axes of the optical fiber and the lens. Further, since the connector main body 221 is configured as a ferrule with a lens in this way, even in the case of multi-channel communication, multi-channel communication can be easily realized by simply inserting an optical fiber into the ferrule.

A concave light emitting portion (light transmission space) 223 is formed on the front side of the connector body 221. A lens (convex lens) 224 is integrally formed on the connector main body 221 so as to be located at the bottom of the light emitting section 223.

Furthermore, the connector body 221 is provided with an optical fiber insertion hole 226 extending from the back side to the front in alignment with the lens 224. The optical fiber insertion hole 226 is shaped so that the optical axis of the lens 224 and the core 203a of the optical fiber 203 inserted therein coincide with each other. Further, the optical fiber insertion hole 226 is shaped so that when the optical fiber 203 is inserted, its tip (incidence end) matches the focal position of the lens 224. Note that the optical fiber 203 is a GI (dipless) fiber (indicated by "GI" in the figure).

Furthermore, an adhesive injection hole 222 extending downward from the top surface side is formed in the connector body 211 so as to communicate with the vicinity of the bottom position of the optical fiber insertion hole 226. After the optical fiber 203 is inserted into the optical fiber insertion hole 226, the adhesive 227 is injected around the optical fiber 203 from the adhesive injection hole 222, thereby fixing the optical fiber 203 to the connector body 221. In this case, a GRIN lens 228 is placed on the tip side of the optical fiber 203.

The connector 402 is the same as that described using FIG. 32 above, so its description will be omitted here.

In the connector 202, the lens 224 has a function of shaping the light emitted from the optical fiber 203 into collimated light and emitting the collimated light. As a result, the light emitted from the output end of the optical fiber 203 with a predetermined NA enters the lens 224 through the GRIN lens 228, is formed into collimated light, and is emitted toward the connector 402.

Furthermore, in the connector 402, the light emitted from the connector 202 enters a lens 424 and is focused. Then, this focused light enters the input end of the optical fiber 401 through the GRIN lens 428 and is sent through the optical fiber 401.

Although detailed explanation is omitted, the connector 403 of the optical cable 400 and the connector 301 of the receiver 300 connected thereto are configured in the same manner as the configuration example of the connector 202 of the transmitter 200 and the connector 402 of the optical cable 400 described above. .

As described above, in the optical communication system 100 shown in FIG. 31, the

optical fibers

203, 303, and 401 propagate only the fundamental mode at the first wavelength (for example, 1310 nm), and propagate the fundamental mode at the second wavelength (for example, 850 nm). It is capable of propagating at least the first-order mode along with the second wavelength, and communication is performed using light of a second wavelength. Therefore, at least the first-order mode component generated by the optical axis misalignment propagates together with the fundamental mode component, making it possible to reduce optical power coupling loss due to the optical axis misalignment.

Furthermore, in the optical communication system 100 shown in FIG. 31, the connectors 402 and 301 are provided with optical path adjusting members (GRIN lenses) for guiding input light to the input ends of the optical fibers 401 and 303. Therefore, if there is a positional shift, the input light that does not go to the input ends of the optical fibers 401, 303 is guided to the input ends of the optical fibers 401, 303 by the optical path adjustment of the optical path adjustment member, resulting in a coupling loss of optical power. can be reduced.

In addition, in the optical communication system 100 shown in FIG. 31, the optical fiber 401 of the optical cable 400 is a GI (with dip) fiber except for a part on the end side, and a GI (without dip) fiber in a part on the end side. This makes it possible to extend the possible transmission distance while suppressing a decrease in optical power coupling efficiency.

<2. Modified example>
In addition, in the above-mentioned embodiment, an example was shown in which the GRIN lens was arranged at the end of the optical fiber, but a configuration in which the GRIN lens is not arranged is also conceivable. Furthermore, instead of the GRIN lens being arranged, another optical element having a similar function may be arranged.

In addition, in the above-described embodiment, an example in which the optical fibers constituting the optical cable are GI (with dip) fiber except for a part on the end side, and GI (without dip) fiber is used in a part on the end side. Although shown, it is not limited to this.

The parts other than the part on the end side of the optical fiber have the first structure, and the part on the end side of the optical fiber has the second structure, and the first structure has a smaller propagation delay difference between modes than the second structure. It is sufficient that the second structure has a higher optical power coupling efficiency than the first structure. For example, the optical fibers constituting an optical cable are GI (dip) fibers except for a part on the end side, and the part on the end side is an optical fiber whose core refractive index shape is a step index type (SI type). It is also possible to use a fiber (SI fiber).

In addition, in the above-described embodiment, an example is described in which the optical fibers constituting the optical cable are GI (with dip) fibers except for a part on the end side, and GI (without dip) fibers are used in the part on the end side. However, for example, in a transmitter 200 or a receiver 300 as an electronic device, the optical fiber connected to the connector is a GI (dip equipped) fiber except for the part on the end side connected to the connector. It is also conceivable that a part of the end side is made into a GI (non-dip) fiber to extend the possible transmission distance while suppressing a decrease in optical power coupling efficiency. In this case, the transmitter 200 and the receiver 300 have an optical interface structure in which an optical connector for spatial coupling is connected to the end of an optical fiber.

FIG. 34 shows a configuration example of the light emitting section 201 in the transmitter 200 and the connector 202 connected to it via the optical fiber 203. This configuration example is one example, and is not limited to this.

The light emitting unit 201 and the connector 202 are connected by an optical fiber 203. The optical fiber 203 is a GI (with dip) fiber except for a part on the end side connected to the connector 202, and a part on the end side is a GI (without dip) fiber.

The light emitting section 201 includes a ferrule 211. The ferrule 211 is made of a light-transmitting material such as synthetic resin or glass, or a material such as silicon that transmits a specific wavelength.

The ferrule 211 is provided with an optical fiber insertion hole 216 extending rearward from the front side. After the optical fiber 203 is inserted into the optical fiber insertion hole 216, it is fixed to the ferrule 211 with an adhesive 217.

Further, a substrate 212 on which a light emitting element 213 and a light emitting element driving driver 218 are mounted is fixed to the lower surface side of the ferrule 211. In this case, a light emitting element 213 is placed on the substrate 212 in alignment with the optical fiber 203. Here, the position of the substrate 212 is adjusted and fixed so that the emission part of the light emitting element 213 coincides with the optical axis of the optical fiber 203.

Further, the ferrule 211 is formed with an arrangement hole 214 extending upward from the lower surface side. In order to change the optical path of the light from the light emitting element 213 toward the optical fiber 203, the bottom part of the arrangement hole 214 is formed into an inclined surface, and a mirror (optical path changing section) 215 is arranged on this inclined surface. There is. Regarding the mirror 215, it is conceivable to not only fix a separately generated mirror to the inclined surface, but also to form it on the inclined surface by vapor deposition or the like.

The connector 202 is the same as that described using FIG. 33 above, so its description will be omitted here.

Further, in the above embodiment, the optical fiber 401 in the optical cable 400 connecting the transmitter 200 and the receiver 300 is a GI (dip equipped) fiber except for a part on the end side, and the part on the end side is a GI (dip equipped) fiber. Although we have shown an example of using a GI (no dip) fiber, when an electronic device has a configuration in which a transmitting section and a receiving section are connected using an optical fiber to perform optical communication, it is necessary to use a GI (no dip) fiber. It is also conceivable to use GI (with dip) fiber for the rest of the fiber, and use GI (without dip) fiber for the part on the end side to extend the possible transmission distance while suppressing a decrease in the coupling efficiency of optical power. In this case, the electronic device is equipped with an optical interface structure in which an optical connector for spatial coupling is connected to the end of an optical fiber.

Further, in the above-described embodiment, the first wavelength has been described as 1310 nm, but since a laser light source or an LED light source may be used as the light source, the first wavelength may be, for example, between 300 nm and 5 μm. I can think of something.

Further, in the above-described embodiment, the first wavelength is described as 1310 nm, but it is also possible that this first wavelength is a wavelength in the 1310 nm band that includes 1310 nm. Further, in the above-described embodiment, the first wavelength is described as 1310 nm, but it is also possible that the first wavelength is 1550 nm or a wavelength in the 1550 nm band that includes 1550 nm. Moreover, although the second wavelength has been described as 850 nm, it is also possible that the second wavelength is a wavelength in the 850 nm band that includes 850 nm.

Furthermore, in the above-described embodiments, an example in which the optical waveguide is an optical fiber has been described, but the present technology can of course be applied to an optical waveguide other than an optical fiber, such as a silicon optical waveguide.

Although preferred embodiments of the present disclosure have been described above in detail with reference to the accompanying drawings, the technical scope of the present disclosure is not limited to such examples. It is clear that a person with ordinary knowledge in the technical field of the present disclosure can come up with various changes or modifications within the scope of the technical idea described in the claims. It is understood that these also naturally fall within the technical scope of the present disclosure.

Furthermore, the effects described in this specification are merely explanatory or illustrative, and are not limiting. In other words, the technology according to the present disclosure may have other effects that are obvious to those skilled in the art from the description of this specification, in addition to or in place of the above effects.

Note that the present technology can also have the following configuration.
(1) Optical fiber,
a connector for spatial coupling connected to the end of the optical fiber;
A part of the optical fiber other than a part on the end side has a first structure, and a part of the optical fiber on the end side has a second structure,
The first structure has a smaller inter-mode propagation delay difference than the second structure, and the second structure has a higher optical power coupling efficiency than the first structure.
(2) The optical cable according to (1), wherein the first structure is a structure in which the refractive index shape of the core is a graded index type with a dip.
(3) The optical cable according to (2), wherein the second structure is a structure in which the refractive index shape of the core is a dip non-graded index type or a step index type.
(4) the optical fiber propagates only the fundamental mode at the first wavelength;
Communication is performed through the optical fiber using light having a second wavelength and having at least a first-order mode component together with the fundamental mode,
The optical cable according to any one of (1) to (3), wherein the second wavelength is a wavelength at which the optical fiber can propagate at least a primary mode together with the fundamental mode.
(5) The optical cable according to (4), wherein the first wavelength is a wavelength in a 1310 nm band, and the second wavelength is a wavelength in an 850 nm band.
(6) The optical cable according to (4) or (5), wherein an optical element for adjusting an optical path is arranged at an end of the optical fiber.
(7) The optical cable according to (6) above, wherein the optical element is a GRIN lens.
(8) Equipped with an optical interface structure in which a connector for spatial coupling is connected to the end of the optical fiber,
A part of the optical fiber other than a part on the end side has a first structure, and a part of the optical fiber on the end side has a second structure,
The first structure has a smaller inter-mode propagation delay difference than the second structure, and the second structure has a higher optical power coupling efficiency than the first structure.
(9) The first structure is a structure in which the refractive index shape of the core is a graded index type with a dip,
The electronic device according to (8), wherein the second structure is a structure in which the refractive index shape of the core is a dip non-graded index type or a step index type.
(10) the optical fiber propagates only the fundamental mode at the first wavelength;
Communication is performed through the optical fiber using light having a second wavelength and having at least a first-order mode component together with the fundamental mode,
The electronic device according to (8) or (9), wherein the second wavelength is a wavelength at which the optical fiber can propagate at least a first-order mode together with the fundamental mode.
(11) The electronic device according to (10), wherein the first wavelength is a wavelength in a 1310 nm band, and the second wavelength is a wavelength in an 850 nm band.
(12) The electronic device according to (10) or (11), wherein an optical element for adjusting an optical path is arranged at an end of the optical fiber.
(13) The connector is a connector for connecting external equipment via an optical cable,

The electronic device according to any one of (8) to (12), wherein the connector constitutes an input section or an output section of an optical signal.
(14) Optical cable,
an optical communication device having a connector for connecting one end of the optical cable; the optical cable has a configuration in which a connector for spatial coupling is connected to an end of an optical fiber;
A part of the optical fiber other than a part on the end side has a first structure, and a part of the optical fiber on the end side has a second structure,
The first structure has a smaller inter-mode propagation delay difference than the second structure, and the second structure has a higher optical power coupling efficiency than the first structure. Optical communication system. .
(15) The first structure is a structure in which the refractive index shape of the core is a graded index type with a dip,
The optical communication system according to (14), wherein the second structure is a structure in which the refractive index shape of the core is a dip non-graded index type or a step index type.
(16) the optical fiber propagates only the fundamental mode at the first wavelength;
Communication is performed through the optical fiber using light having a second wavelength and having at least a first-order mode component together with the fundamental mode,
The optical communication system according to (14) or (15), wherein the second wavelength is a wavelength at which the optical fiber can propagate at least the primary mode together with the fundamental mode.
(17) The optical communication system according to (16), wherein the first wavelength is a wavelength in a 1310 nm band, and the second wavelength is a wavelength in an 850 nm band.
(18) The optical communication system according to (16) or (17), wherein an optical element for adjusting an optical path is arranged at an end of the optical fiber.
(19) The optical communication system according to any one of (14) to (18), wherein the optical communication device is a transmitting side optical communication device.
(20) The optical communication system according to claim 19, further comprising a receiving side optical communication device having a connector for connecting the other end of the optical cable.

10T, 10R... Optical fiber 10a... Core 10b...

Clad

11T, 11R... Lens 22R, 22T... GRIN lens 30... Optical cable 31... Optical fiber 32, 33... connector (plug)
34, 35... GRIN lens 100... Optical communication system 200... Transmitter 201... Light emitting section 202... Connector (receptacle)
203... Optical fiber 203a... Core 203b... Clad 211... Ferrule 212... Substrate 213... Light emitting element 214... Hole for arrangement 215... Mirror (optical path changing part)
216... Optical fiber insertion hole 217... Adhesive 218... Light emitting element drive driver 221... Connector body (ferrule)
222...Adhesive injection hole 223...Light emission part (light transmission space)
224...Lens (convex lens)
226... Optical fiber insertion hole 227... Adhesive 228... GRIN lens 300... Receiver 301... Connector (receptacle)
302... Light receiving section 303... Optical fiber 400... Optical cable 401... Optical fiber 402,403... Connector (plug)
421...Connector body (ferrule)
422... Adhesive injection hole 423... Light incidence part (light transmission space)
424...Lens (convex lens)
426...Optical fiber insertion hole 427...Adhesive 428...GRIN lens 431...Connector body (ferrule)
432...Adhesive injection hole 433...Light emission part (light transmission space)
434...Lens (convex lens)
436...Optical fiber insertion hole 437...Adhesive 438...GRIN lens

Claims

optical fiber and
a connector for spatial coupling connected to the end of the optical fiber;
A part of the optical fiber other than a part on the end side has a first structure, and a part of the optical fiber on the end side has a second structure,
The first structure has a smaller inter-mode propagation delay difference than the second structure, and the second structure has a higher optical power coupling efficiency than the first structure.
The optical cable according to claim 1, wherein the first structure has a core whose refractive index shape is a dipped graded index type.
The optical cable according to claim 2, wherein the second structure has a core having a refractive index shape of a dip non-graded index type or a step index type.
the optical fiber propagates only a fundamental mode at a first wavelength;
Communication is performed through the optical fiber using light having a second wavelength and having at least a first-order mode component together with the fundamental mode,
The optical cable according to claim 1, wherein the second wavelength is a wavelength at which the optical fiber can propagate at least a primary mode together with the fundamental mode.
The optical cable according to claim 4, wherein the first wavelength is a wavelength in a 1310 nm band, and the second wavelength is a wavelength in an 850 nm band.
The optical cable according to claim 4, wherein an optical element for adjusting an optical path is arranged at an end of the optical fiber.
The optical cable according to claim 6, wherein the optical element is a GRIN lens.
Equipped with an optical interface structure in which a connector for spatial coupling is connected to the end of the optical fiber,
A part of the optical fiber other than a part on the end side has a first structure, and a part of the optical fiber on the end side has a second structure,
The first structure has a smaller inter-mode propagation delay difference than the second structure, and the second structure has a higher optical power coupling efficiency than the first structure.
The first structure is a structure in which the refractive index shape of the core is a graded index type with a dip,
The electronic device according to claim 8, wherein the second structure has a core having a refractive index shape of a dip non-graded index type or a step index type.
the optical fiber propagates only a fundamental mode at a first wavelength;
Communication is performed through the optical fiber using light having a second wavelength and having at least a first-order mode component together with the fundamental mode,
The electronic device according to claim 8, wherein the second wavelength is a wavelength at which the optical fiber can propagate at least a first-order mode together with the fundamental mode.
The electronic device according to claim 10, wherein the first wavelength is a wavelength in a 1310 nm band, and the second wavelength is a wavelength in an 850 nm band.
The electronic device according to claim 10, wherein an optical element for adjusting an optical path is arranged at an end of the optical fiber.
The connector is a connector for connecting external equipment via an optical cable,
The electronic device according to claim 8, wherein the connector constitutes an input section or an output section of an optical signal.
optical cable and
an optical communication device having a connector for connecting one end of the optical cable; the optical cable has a configuration in which a connector for spatial coupling is connected to an end of an optical fiber;
A part of the optical fiber other than a part on the end side has a first structure, and a part of the optical fiber on the end side has a second structure,
The first structure has a smaller inter-mode propagation delay difference than the second structure, and the second structure has a higher optical power coupling efficiency than the first structure. Optical communication system. .
The first structure is a structure in which the refractive index shape of the core is a graded index type with a dip,
15. The optical communication system according to claim 14, wherein the second structure has a core having a refractive index shape of a dip non-graded index type or a step index type.
the optical fiber propagates only a fundamental mode at a first wavelength;
Communication is performed through the optical fiber using light having a second wavelength and having at least a first-order mode component together with the fundamental mode,
The optical communication system according to claim 14, wherein the second wavelength is a wavelength at which the optical fiber can propagate at least a primary mode together with the fundamental mode.
The optical communication system according to claim 16, wherein the first wavelength is a wavelength in a 1310 nm band, and the second wavelength is a wavelength in an 850 nm band.
The optical communication system according to claim 16, wherein an optical element for adjusting an optical path is arranged at an end of the optical fiber.
The optical communication system according to claim 14, wherein the optical communication device is a transmitting side optical communication device.
The optical communication system according to claim 19, further comprising a receiving side optical communication device having a connector for connecting the other end of the optical cable.