JP7459519B2 - Optical communication device, optical communication method, and optical communication system - Google Patents

Description

This technology relates to an optical communication device, an optical communication method, and an optical communication system, and more specifically to an optical communication device that can reduce the precision of optical axis misalignment.

Conventionally, optical communication using spatial coupling (see, for example, Patent Document 1) has been known. In this type of optical communication, particularly in single-mode fibers, a large loss of optical power occurs due to misalignment of the optical axis. For this reason, conventionally, high precision was required for parts in order to suppress misalignment of the optical axis, leading to increased costs.

International Publication No. 2017/056889

The purpose of this technology is to reduce costs by relaxing the precision requirements for optical axis misalignment.

The concept of this technology is
comprising an optical waveguide that propagates only the fundamental mode at the first wavelength;
Communicate using light of a second wavelength having at least a first-order mode component together with the fundamental mode,
In the optical communication device, the second wavelength has a predetermined wavelength width and is a wavelength at which the optical waveguide can propagate at least the primary mode as well as the fundamental mode.

The present technology includes an optical waveguide that propagates only the fundamental mode at the first wavelength. For example, the optical waveguide may be an optical fiber or a silicon optical waveguide. Furthermore, for example, the first wavelength may be a wavelength at which chromatic dispersion is zero. Also, for example, the first wavelength may be between 300 nm and 5 μm. In this case, for example, the first wavelength may be in the 1310 nm band or the 1550 nm band.

In the present technology, communication is performed using light of a second wavelength having at least a primary mode component as well as a fundamental mode. Here, the second wavelength has a predetermined wavelength width and is a wavelength at which the optical waveguide can propagate at least the primary mode as well as the fundamental mode. In this case, the second wavelength is shorter than the first wavelength. For example, the second wavelength may be in the 850 nm band.

In this way, the present technology includes an optical waveguide that propagates only the fundamental mode at the first wavelength, has a predetermined wavelength width, and is capable of propagating at least the first-order mode along with the fundamental mode. Communication is performed using light having a second wavelength and having at least a primary mode component as well as a fundamental mode.

Since the optical waveguide performs communication using light of a second wavelength that can propagate at least the first-order mode together with the fundamental mode, at least the first-order mode generated by the optical axis misalignment on the input end side of the optical waveguide on the receiving side is Since the component propagates through the optical waveguide together with the fundamental mode component, it is possible to reduce optical power coupling loss due to optical axis deviation.

In addition, since the second wavelength has a predetermined wavelength width, the light intensity distribution on the output end side of the transmitting optical waveguide can be configured not to be biased with respect to the center of the core, and it is possible to obtain good coupling efficiency similar to that when light having only fundamental mode components is propagated, regardless of the direction of the optical axis misalignment. Therefore, it is no longer necessary to use additional parts or a light source with a complex structure to propagate light having only fundamental mode components, and parts costs can be reduced.

Another concept of the present technology is
a receiving section having an optical waveguide that propagates only a fundamental mode at a first wavelength;
a transmitting section which has an optical waveguide which propagates only a fundamental mode at the first wavelength, and which inputs light of a second wavelength having a fundamental mode component and at least a first-order mode component to an input end side of the optical waveguide of the receiving section through the optical waveguide;
In the optical communication system, the second wavelength has a predetermined wavelength width and is a wavelength at which the optical waveguide of the receiving section and the optical waveguide of the transmitting section can propagate at least a first-order mode together with a fundamental mode.

The present technology includes a receiving section and a transmitting section. The receiving section and the transmitting section have optical waveguides that propagate only the fundamental mode at the first wavelength. Light of a second wavelength having a fundamental mode and at least a first-order mode component is input from the optical waveguide of the transmitter to the input end side of the optical waveguide of the receiver. Here, the second wavelength has a predetermined wavelength width and is a wavelength at which the optical waveguide of the receiving section and the optical waveguide of the transmitting section can propagate at least the first-order mode together with the fundamental mode.

For example, the transmitting unit may further include a light emitting unit that inputs light of a second wavelength having at least a first-order mode component in addition to the fundamental mode at the incident end of the optical waveguide of the transmitting unit. Also, for example, the transmitting unit may be a receptacle of a transmitter or a plug of a cable. Also, for example, the receiving unit may be a plug of a cable or a receptacle of a receiver.

In this way, in this technology, the receiving section and the transmitting section have optical waveguides that propagate only the fundamental mode at a first wavelength, and the optical waveguide of the transmitting section has a second wavelength that has a predetermined wavelength width from the optical waveguide of the transmitting section to the input end side of the optical waveguide of the receiving section, and the optical waveguide of the transmitting section and the optical waveguide of the receiving section have a second wavelength that can propagate at least the first mode as well as the fundamental mode, and light that has at least a first mode component as well as the fundamental mode is input.

As a result, communication is performed using light of a second wavelength that can propagate at least the first-order mode along with the fundamental mode through the optical waveguides of the receiving unit and the transmitting unit, and at least the first-order mode components generated by the optical axis shift on the input end side of the optical waveguide of the receiving unit propagate through the optical waveguide along with the fundamental mode components, making it possible to reduce coupling loss of optical power due to the optical axis shift.

In addition, since the second wavelength has a predetermined wavelength width, the light intensity distribution on the output end side of the optical waveguide of the transmitter can be configured so as not to be biased with respect to the center of the core, and can be configured so that it is not biased depending on the direction of optical axis deviation. It is possible to obtain good coupling efficiency similar to that in the case of propagating light having only the fundamental mode component without causing any damage. Therefore, it is not necessary to use additional parts or a light source with a complicated structure to propagate light having only the fundamental mode component, and the cost of parts can be reduced.

FIG. 1 is a diagram illustrating 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. This is a diagram when considering the normalized frequency V in the case of a typical single mode wavelength of 1310 nm. FIG. 2 is a diagram showing an example of optical communication using spatial coupling. FIG. 1 is a diagram illustrating 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. 1 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. 13 is a diagram showing that when there is no optical axis misalignment, only the fundamental mode exists in the input light, but when there is an optical axis misalignment, part of the fundamental mode is converted to the first-order mode. It is a graph for explaining that the fundamental mode is converted to the primary mode according to the deviation. 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. 1 is a diagram for explaining optical communication using spatial coupling. 7 is a graph showing simulation results of optical power coupling efficiency when an optical axis shift occurs in which the position of the optical fiber is shifted in a direction perpendicular to the lens. 13 is a graph showing the results of a simulation of the coupling efficiency of optical power when an optical axis shift occurs in which the position of the optical fiber is shifted in a direction perpendicular to the lens. FIG. 7 is a diagram for explaining a case where the second wavelength is configured to have a predetermined wavelength width. 2 is a diagram simulating the light intensity distribution when light having fundamental mode and first-order mode components is transmitted in an optical fiber, and a graph showing the relationship between wavelength [nm] and period [μm]. FIG. 2 is a diagram showing an image of the period of the intensity distribution of light propagating in an optical fiber at (850-f) [nm] and (850+f) [nm], and a diagram showing the light intensity distribution at the output side end face of the optical fiber. FIG. 3 is a diagram showing a spread light intensity distribution shape (σ=0.65) in the 850 nm band and the wavelength positions of (850−f) [nm] and (850+f) [nm] therein. Simulation of optical power coupling efficiency in the case of a wavelength of (850-f) [nm] and a wavelength of (850+f) [nm] when the optical fiber position is shifted perpendicularly to the lens and the optical axis is shifted. This is a graph showing the results. 1 is a block diagram showing a configuration example of a transmitting/receiving system as an embodiment. FIG. FIG. 2 is a perspective view showing a configuration example of a transmitter connector and a cable connector. FIG. 2 is a perspective view showing a configuration example of a transmitter connector and a cable connector. FIG. 2 is a cross-sectional view showing an example of a transmitter connector and a cable connector. FIG. 3 is a cross-sectional view showing a state in which the connector of the transmitter and the connector of the cable are connected. 4A to 4C are cross-sectional views showing configuration examples of a light-emitting unit and a connector in a transmitter.

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

<1. Embodiment>
[Basic explanation regarding this technology]
First, the technology related to this technology will be explained. FIG. 1 shows an overview of optical communication using spatial coupling. In this case, the light emitted from the optical fiber 10T on the transmission side is shaped into collimated light by the lens 11T and 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, especially in single mode fibers, a large loss of optical power occurs due to optical axis misalignment. 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 concept 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 fiber so that only one mode exists.

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

Figure 2(b) shows the LPml (Linearly Polarized) mode of a step-index optical fiber, with the normalized propagation constant b shown as a function of normalized frequency V. The vertical axis is the normalized propagation constant b, where b = 0 when a certain mode does not pass (is blocked), 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, and only LP01 mode exists. Therefore, the state below V = 2.405 is a single mode. Here, LP01 is the fundamental mode (zeroth mode), and LP11, LP21, ... are the first mode, second 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 light propagating through the fiber is 1310 nm, then from equation (1), 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, there is a problem with single mode, in that the small core diameter means that alignment of the optical coupling parts on the transmitting and receiving sides becomes very difficult, and the precision required to accurately align the optical axis is high.

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

FIGS. 4 and 5 show an example 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 accuracy 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.

In order to solve this problem, generally, high-precision components are used or the light input portion of 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.

This technology makes it possible to reduce the cost by reducing the precision of optical axis misalignment. In this technology, firstly, the optical fiber is capable of propagating only the fundamental mode at the first wavelength, and the optical fiber is capable of propagating the primary mode along with the fundamental mode using light of the second wavelength. configured to communicate.

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. In a state where there is no optical axis 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, when there is no optical axis misalignment, only the fundamental mode exists in the input light, as shown in Figure 9(a). On the other hand, when there is an optical axis misalignment, as shown in Figure 9(b), part of the fundamental mode is converted to the first-order mode by utilizing the phase difference caused by the refractive index difference between the cladding and the core. In the case of 1310 nm, this first-order mode cannot propagate, but in the case of 850 nm, this first-order mode can also propagate, resulting in better characteristics in the case of 850 nm.

In the graph in Figure 10, the fundamental mode (0th mode) component and the 1st mode component are plotted separately, and the sum of these forms the total curve. Since the input light only contains the fundamental mode, it can be seen that the fundamental mode is converted to the 1st mode depending on the deviation. On the other hand, in the case of 1310 nm, only the fundamental mode can propagate, as shown in Figure 3 (a), so the fundamental mode is purely reduced, as shown in Figure 8.

In Figure 8, when comparing 1310nm and 850nm with a coupling efficiency of 0.8 (approximately -1 dB), the amount of light is approximately 1.8 times, and when comparing with a coupling efficiency of 0.9 (approximately -0.5 dB), the amount of light is approximately 2.35 times greater. Accuracy with respect to axis misalignment can be relaxed.

In this way, the optical fiber is made to be able to propagate only the fundamental mode at the first wavelength (for example, 1310 nm), and the optical fiber is made to be able to propagate light at the second wavelength (for example, 850 nm) in which the first mode and the fundamental mode can be propagated. By configuring the device to perform communication using the optical fiber, it is possible to increase the coupling efficiency of optical power.

Secondly, this technology is configured to perform communication using light that has a fundamental mode component as well as a first-order mode component.

FIG. 11 is a diagram simulating the intensity distribution of light transmitted within an optical fiber. FIG. 11A shows an example in which light having only fundamental mode components propagates. 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 in which light having fundamental mode and first-order mode components propagates. In this case, high-strength locations alternately appear in one direction and in another direction opposite to this one direction, in the illustrated example, upward and downward, with respect to the center of the core. FIG. 11(c) shows the light intensity distribution at the output end face, that is, the output end face of the optical fiber shown in FIG. 11(b).

In the state shown in Figure 11(b), when light is emitted from the fiber end face, it travels at an angle in the direction of higher intensity relative to the center of the core. Figure 12 shows an example of light being emitted from the fiber end face. In this example, the area of higher intensity is located above the center of the core, and light is emitted from the fiber end face at an angle in the upward direction.

Consider optical communication using spatial coupling as shown in FIG. 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 light with fundamental mode and first-order mode components propagates, the light whose intensity distribution is biased upward from the center of the transmitting core 10a is received. It is coupled downward with respect to the center of the side core 10a.

Let us consider the case where, under the conditions shown in Figure 13(b), an optical axis misalignment occurs in which the position of the receiving optical fiber 10R is shifted vertically relative to the lens 11R, as shown in Figure 14(a). In this case, the state shown is one in which the amount of optical axis misalignment is zero. When the optical axis misalignment is in the positive (+) direction, the areas of high light intensity are in the direction that enters the core 10a of the optical fiber 10R, making coupling easier. On the other hand, when the optical axis misalignment is in the negative (-) direction, the core 10a of the optical fiber 10R moves in the opposite direction to the light's traveling direction, reducing the coupling efficiency.

Figure 14(b) 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. This is a graph showing the following. 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.

Here, in optical communication using spatial coupling as shown in Figure 13, we consider the cases where the components contained in the input light (light emitted from the transmitting side) are only in the fundamental mode, and in the fundamental mode and first-order mode, and where an optical axis shift occurs in which the position of the optical fiber 10R on the receiving side is shifted vertically relative to the lens 11R, as shown in Figure 15(a).

Figure 15(b) is a graph showing the simulation results of the optical power coupling efficiency when the input light has only fundamental mode components and when the input light has fundamental mode and first-order mode components. The horizontal axis represents the optical axis deviation, and the vertical axis represents the coupling efficiency. Here, to align the standards, the coupling efficiency at the point where the intensity is maximum is standardized as 1.

When the input light has fundamental mode and first-order mode components, the coupling efficiency is better when the optical axis shift is in the positive (+) direction 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, when the input light has fundamental mode and first-order mode components, if the optical axis misalignment is in the negative (-) direction, the coupling efficiency is worse than when the input light has only fundamental mode components. This is because, as described above, the core 10a of the optical fiber 10R moves in the opposite direction to the light's traveling direction.

When communication is configured to use light that has components of the primary mode as well as the fundamental mode, depending on the direction of the optical axis shift, the light that has only the components of the fundamental mode may There is a problem in that the coupling efficiency is lower than when communicating using . It is desirable to be able to obtain good coupling efficiency, as in the case of communication using light having only the fundamental mode component, regardless of the direction of the optical axis shift.

It is known that in general inexpensive systems, when light from a light emitting element is input into an optical fiber, it becomes light that has a primary mode component as well as a fundamental mode. Therefore, when performing communication using light consisting only of fundamental mode components, it is necessary to use additional parts and a light source with a complicated structure, and if the position of the light source and the fiber core is misaligned, the fundamental mode will shift to the primary mode. mode, it is generally difficult to communicate purely using the basic mode.

Further, in the present technology, thirdly, the second wavelength is configured to have a predetermined wavelength width. In FIG. 16(a), a wavelength (first wavelength) in the 850 nm band is transmitted from a light source 20 to the input end face, that is, the incident side end face, of an optical fiber (1310 nm optical fiber) 21 that propagates only the fundamental mode at a wavelength of 1310 nm (first wavelength). This shows a state in which light having a fundamental mode and first-order mode components is incident. In this case, the second wavelength is not a single wavelength but has a predetermined wavelength width.

In this case, as shown in FIG. 16(b), the second wavelength has a wavelength spread with 850 nm as the center wavelength. Here, the shape of the light intensity distribution for each wavelength included in the second wavelength is assumed to be a normal distribution shape. FIG. 16(b) shows examples where the standard deviation σ is 0.16, 0.32, and 0.65.

In this case, the intensity distribution of the light output from the optical fiber 21, that is, the light intensity distribution at the output end face, that is, the output end face of the optical fiber 21, changes in tendency depending on the wavelength spread of the input light. For example, when the wavelength spread of the input light is narrowed, for example, when σ = 0.16, the light intensity distribution at the output side end face of the optical fiber 21 becomes biased, as shown in FIG. 16 (c3). (same as the state in FIG. 11(c)). In this case, when the wavelength spread of the input light is widened to σ = 0.32 and further to 0.65, the light intensity distribution gradually widens as shown in Fig. 16 (c2) and (c1). The bias will disappear.

This occurs because, when the period of the intensity distribution of light (fundamental mode + first mode) propagating through an optical fiber is T [μm] as shown in Figure 17(a), the period varies depending on the wavelength. The graph in Figure 17(b) shows the relationship between wavelength [nm] and period T [μm], and it can be seen that the shorter the wavelength, the longer the period T, and the closer the wavelength is to about 900 nm, the shorter the period T becomes. Also, for wavelengths of 900 nm or more, the optical fiber no longer functions as a double-mode fiber capable of propagating the first mode in addition to the fundamental mode, so the period T tends to increase.

Since the period of movement of the light intensity differs depending on the wavelength, the light intensity distribution of the second wavelength light having a predetermined wavelength width is dispersed for each wavelength by passing through the optical fiber. Therefore, the total light intensity is evenly distributed with respect to the core of the optical fiber (see FIG. 16(c1)).

FIG. 18(a1) shows an image of the period Ta of the intensity distribution of light propagating in the optical fiber when the wavelength is (850-f) [nm] shown in FIG. , shows the light intensity distribution at the output side end face of the optical fiber in that case. Moreover, FIG. 18(b1) shows an image diagram of the period Tb of the intensity distribution of light propagating in the optical fiber when the wavelength is (850+f) [nm] shown in FIG. 19, and FIG. 18(b2) , shows the light intensity distribution at the output side end face of the optical fiber in that case.

In this case, the period of the intensity distribution of the light propagating through the optical fiber is different for wavelengths of (850-f) [nm] and (850+f) [nm], so the light intensity distribution at the output end face of the optical fiber is biased upward for a wavelength of (850-f) [nm] (see FIG. 18(a2)), and downward for a wavelength of (850+f) [nm] (see FIG. 18(b2)).

These two wavelengths of light propagate through the same optical fiber in a superimposed state. Figure 18 (c1) shows an image of the intensity distribution of light propagating through the optical fiber in this case, and Figure 18 (c2) shows the light intensity distribution at the output end face of the optical fiber in this case. In this case, the light intensity distribution at the output end face of the optical fiber is not biased upward or downward.

Now, consider the case where, in optical communication using spatial coupling as shown in FIG. 13, an optical axis misalignment occurs in which the position of the receiving optical fiber 10R is shifted vertically relative to the lens 11R, as shown in FIG. 20(a), for wavelengths of (850-f) [nm] and (850+f) [nm].

Figure 20(b) is a graph showing the simulation results of the optical power coupling efficiency for wavelengths of (850-f) [nm] and (850+f) [nm]. The horizontal axis represents the optical axis deviation, and the vertical axis represents the coupling efficiency. Here, to align the standards, the coupling efficiency at the point where the intensity is maximum is standardized as 1.

In the case of a wavelength of (850-f) [nm], when the optical axis misalignment is in the positive (+) direction, the loss increases, but when the optical axis misalignment is in the negative (-) direction, the loss characteristics are good. I understand. On the other hand, in the case of a wavelength of (850+f) [nm], when the optical axis misalignment is in the negative (-) direction, the loss increases, but when the optical axis misalignment is in the positive (+) direction, the loss characteristics are good. I understand. Therefore, loss can be reduced regardless of whether the deviation is in the positive or negative direction.

When using a light source with a wide wavelength range such as σ = 0.65 in Figure 16 (b) (Figure 19), as shown in Figure 20 (b), there are wavelengths that reduce loss for both positive and negative axial misalignment, and this shows that the characteristics have been improved compared to the solid line in Figure 15 (b), which shows large loss for misalignment in the negative direction.

The solid line in Figure 15(b) shows that the coupling efficiency is flat (near 1) up to about 3 μm when shifted in the positive direction, whereas in Figure 20(b) the coupling efficiency drops once at about 2 μm and then rises again. This is due to the simulation conditions, and even in Figure 20(b) the power intensity distribution becomes flat if the conditions are such that the fiber output end face is completely biased toward the lower or upper side.

In this way, by configuring the second wavelength to have a predetermined wavelength width, it is possible to obtain good coupling efficiency, similar to when communication is performed using light that has only fundamental mode components, regardless of the direction of the optical axis shift.

Note that the shape of the light intensity distribution for each wavelength included in the wavelength (second wavelength) of light from the light source 20 is not limited to that described above. For example, instead of having one power peak as shown in FIG. 16(b), it may have a plurality of peaks of light intensity, or it may have a flat light intensity. Further, the wavelength band and wavelength width of the light from the light source 20 are not limited to those described above.

As a method for changing the wavelength width of the light from the light source 20, for example in the case of a VCSEL (Vertical Cavity Surface Emitting LASER), the band gap of the active layer can be controlled by changing the material and growth parameters of the active layer in the device structure, and the center frequency and wavelength width of the resonance spectrum can be changed by shifting or widening the amplification region.

[Transmitting and receiving system]
21 shows a transmission/reception system 100 according to an embodiment. The transmission/reception system 100 includes a transmitter 200, a receiver 300, and a cable 400. The transmitter 200 is an AV source such as a personal computer (PC), a game machine, a disc player, a set-top box, a digital camera, or a mobile phone. The receiver 300 is a television receiver, a projector, or a PC monitor. The transmitter 200 and the receiver 300 are connected via the cable 400.

The transmitter 200 has a light emitting unit 201, a connector 202 as a receptacle, and an optical fiber 203 that propagates the light emitted by the light emitting unit 201 to the connector 202. The light emitting unit 201 has a light emitting element such as a laser element such as a VCSEL or 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. The light (optical signal) emitted by the light emitting unit 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 cable 400 has connectors 402, 403 as plugs at one end and the other end of the optical fiber 401. The connector 402 at one end of the optical fiber 401 is connected to the connector 202 of the transmitter 200, and the connector 403 at the other end of the optical fiber 401 is connected to the connector 301 of the receiver 300.

In this embodiment, optical fiber 203 of transmitter 200, optical fiber 303 of receiver 300, and optical fiber 401 of cable 400 are assumed to propagate only the fundamental mode at the first wavelength. Further, these optical fibers are configured so that chromatic dispersion becomes zero at the first wavelength. Here, the first wavelength is 1310 nm, the core diameter d and the numerical aperture NA are general parameters of a 1310 nm optical fiber, d=8 μm and NA=0.1, and the normalized frequency V=1. 92. Thereby, these optical fibers function as single mode fibers at a wavelength of 1310 nm (see Figure 3).

In addition, in this embodiment, communication is performed using light of a second wavelength having at least a first-order mode component as well as the fundamental mode. Here, the second wavelength has a predetermined wavelength width and is a wavelength at which each of the above-mentioned optical fibers can propagate at least the first-order mode as well as the fundamental mode. The wavelength of the light emitted by the light-emitting unit 201 is this second wavelength.

Here, the second wavelength is, for example, a wavelength in the 850 nm band as shown in FIG. 19, and has a predetermined wavelength width with 850 nm as the center frequency. When light of this second wavelength is used, in each of the above-mentioned optical fibers, the normalized frequency V = 2.96 at the center frequency of 850 nm, so in addition to the fundamental mode, the first mode can also propagate. Therefore, it functions as a double mode fiber (see Figure 6).

The light in the 850 nm band emitted by the light emitting unit 201 is input into the optical fiber 203 which is a 1310 nm single mode fiber, and is propagated to the connector 202. In this case, when there is an optical axis shift of the light incident on the optical fiber 203, the primary mode generated by the optical axis shift is propagated together with the fundamental mode, so the coupling loss of optical power is reduced (Fig. 8). Therefore, it is possible to reduce the cost by reducing the precision of optical axis misalignment.

Furthermore, at the connection point between the connector 202 of the transmitter 200 and the connector 402 of the cable 400, the 850 nm band light emitted from the connector 202 enters the optical fiber 401, which is a 1310 nm single mode fiber, and is directed to the receiver 300 side. Propagated. In this case, when there is an optical axis shift of the light incident on the optical fiber 401, the primary mode generated by the optical axis shift is propagated together with the fundamental mode, so that the coupling loss of optical power is reduced (Fig. 8). Therefore, it is possible to reduce the cost by reducing the precision of optical axis misalignment.

In this case, the 850 nm band light propagated to the connector 202 by the optical fiber 203 has a predetermined wavelength width (see FIG. 19), so the light intensity distribution at the output end face of the optical fiber 203 is not biased in one direction with respect to the center of the core (see FIG. 16(c1)). Therefore, it is possible to obtain good coupling efficiency, similar to the case of communication using light having only fundamental mode components, regardless of the direction of the optical axis shift.

In addition, at the connection point between connector 403 of cable 400 and connector 301 of receiver 300, the 850 nm band light emitted from connector 403 is input to optical fiber 303, which is a 1310 nm single mode fiber, and propagates to light receiving unit 302. In this case, when there is an optical axis shift of the light input to optical fiber 303, the first mode generated by the optical axis shift propagates together with the fundamental mode, reducing the coupling loss of optical power (see Figure 8). This makes it possible to relax the precision of the optical axis shift and reduce costs.

In addition, in this case, since the 850 nm band light propagated to the connector 403 by the optical fiber 401 has a predetermined wavelength width (see FIG. 19), the intensity distribution of the light at the output end face of the optical fiber 401 is is not biased in one direction with respect to the center of the core (see FIG. 16(c1)). Therefore, it is possible to obtain good coupling efficiency, as in the case where communication is performed using light having only the fundamental mode component, regardless of the direction of the optical axis shift.

Figure 22 is a perspective view showing an example of the configuration of the connector 202 of the transmitter 200 and the connector 402 of the cable 400. Figure 23 is also a perspective view showing an example of the configuration of the connector 202 of the transmitter 200 and the connector 402 of the cable 400, but viewed from the opposite direction to that of Figure 22. The illustrated example corresponds to the parallel transmission of optical signals of multiple channels. Note that, although an example corresponding to the parallel transmission of optical signals of multiple channels is shown here, an example corresponding to the transmission of an optical signal of one channel can also be configured in the same way, although a detailed explanation will be omitted. In the case of multiple channels, multiple combinations of transmitters and receivers will be provided.

The connector 202 has a connector body (ferrule) 211 that has a roughly rectangular parallelepiped appearance. A plurality of optical fibers 203 corresponding to each channel are connected to the rear side of the connector body 211 in a horizontally aligned state. The tip side of each optical fiber 203 is inserted and fixed in the optical fiber insertion hole 216.

Further, an adhesive injection hole 212 having a rectangular opening is formed on the upper surface side of the connector main body 211. An adhesive for fixing the optical fiber 203 to the connector body 211 is injected through the adhesive injection hole 212 .

Furthermore, a concave light emitting section (light transmission space) 213 having a rectangular opening is formed on the front side of the connector main body 211, and a concave light emitting section (light transmission space) 213 is formed at the bottom of the light emitting section 213 to correspond to each channel. A plurality of lenses (convex lenses) 214 are formed side by side in the horizontal direction. This prevents the surface of the lens 214 from accidentally hitting a mating connector or the like and causing damage.

In addition, a convex or concave position restriction portion 215 is integrally formed on the front side of the connector body 211 for aligning with the connector 402, and in the illustrated example, is concave. This makes it easy to align the optical axis when connecting with the connector 402.

The connector 402 includes a connector body (ferrule) 411 having a substantially rectangular parallelepiped appearance. A plurality of optical fibers 401 corresponding to each channel are connected to the back side of the connector main body 411 in a horizontally lined state. The distal end side of each optical fiber 401 is inserted into an optical fiber insertion hole 416 and fixed.

Further, an adhesive injection hole 412 having a rectangular opening is formed on the upper surface side of the connector main body 411. An adhesive for fixing the optical fiber 401 to the connector body 411 is injected through the adhesive injection hole 412.

Furthermore, a concave light entrance part (light transmission space) 413 having a rectangular opening is formed on the front side of the connector body 411, and the bottom part of the light entrance part 413 is provided with a concave light entrance part 413 corresponding to each channel. A plurality of lenses (convex lenses) 414 are formed side by side in the horizontal direction. This prevents the surface of the lens 414 from accidentally hitting a mating connector or the like and causing damage.

In addition, a position restriction portion 415 that is concave or convex, and in the illustrated example, convex, for aligning with the connector 202 is integrally formed on the front side of the connector body 411. This makes it easy to align the optical axis when connecting with the connector 202. Note that the position restriction portion 415 and the restriction portion 215 are not limited to being integrally formed with the connector body 411 and the connector body 211, respectively, and may use a pin or may be performed by another method.

Figure 24(a) is a cross-sectional view showing an example of the connector 202 of the transmitter 200. In the illustrated example, the position restriction unit 215 (see Figure 22) is omitted. The connector 202 will be further described with reference to this Figure 24(a).

The connector 202 includes a connector body 211. The connector body 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, and has a ferrule configuration with a lens.

By configuring the connector body 211 as a ferrule with a lens in this way, it is easy to align the optical axis of the optical fiber with the lens. Also, by configuring the connector body 211 as a ferrule with a lens in this way, even in the case of multiple channels, multi-channel communication can be easily achieved by simply inserting the optical fiber into the ferrule.

The connector body 211 has a concave light emitting section (light transmission space) 213 formed on its front side. In addition, this connector body 211 has a plurality of lenses (convex lenses) 214 corresponding to each channel, which are aligned horizontally and integrally formed at the bottom of the light emitting section 213.

Further, the connector body 211 is provided with a plurality of optical fiber insertion holes 216 extending from the back side to the front and arranged horizontally in line with the lenses 214 of each channel. The optical fiber 203 has a double structure including a core 203a at the center serving as an optical path and a cladding 203b surrounding the core 203a.

The optical fiber insertion hole 216 of each channel is shaped so that the core 203a of the optical fiber 203 inserted therein coincides with the optical axis of the corresponding lens 214. In addition, the optical fiber insertion hole 216 of each channel is shaped so that its bottom position, that is, the contact position of the tip (incident end) of the optical fiber 203 when inserted, coincides with the focal position of the lens 214.

Furthermore, an adhesive injection hole 212 extending downward from the top side is formed in the connector body 211 so as to communicate with the vicinity of the bottom position of a plurality of optical fiber insertion holes 216 arranged in a horizontal direction. . After the optical fiber 203 is inserted into the optical fiber insertion hole 216, the adhesive 217 is injected around the optical fiber 203 from the adhesive injection hole 212, thereby fixing the optical fiber 203 to the connector body 211.

In the connector 202, the lens 214 has the function of shaping the light emitted from the optical fiber 203 into collimated light and emitting it. As a result, the light emitted from the output end of the optical fiber 203 with a specified NA is incident on the lens 214, shaped into collimated light, and emitted.

Figure 24(b) is a cross-sectional view showing an example of the connector 402 of the cable 400. In the illustrated example, the position restriction portion 415 (see Figures 22 and 23) is omitted. The connector 402 will be further described with reference to this Figure 24(b).

The connector 402 has a connector body 411. The connector body 411 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 is configured as a ferrule with a lens.

A concave light entrance portion (light transmission space) 413 is formed on the front side of the connector body 411. A plurality of lenses (convex lenses) 414 corresponding to each channel are integrally formed in the connector main body 411 so as to be located at the bottom of the light incidence section 413 and arranged horizontally. .

Further, the connector main body 411 is provided with a plurality of optical fiber insertion holes 416 extending from the back side to the front and arranged horizontally in line with the lenses 414 of each channel. 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 416 of each channel is shaped so that the core 401a of the optical fiber 401 inserted therein coincides with the optical axis of the corresponding lens 414. Furthermore, the optical fiber insertion hole 416 of each channel is shaped so that its bottom position, that is, the contact position of its tip (incidence end) when the optical fiber 401 is inserted, matches the focal position of the lens 414. ing.

In addition, an adhesive injection hole 412 extending downward from the top side is formed in the connector body 411 so as to communicate with the vicinity of the bottom position of a plurality of optical fiber insertion holes 416 arranged in a horizontal direction. . After the optical fiber 401 is inserted into the optical fiber insertion hole 416, the adhesive 417 is injected around the optical fiber 401 from the adhesive injection hole 412, thereby fixing the optical fiber 401 to the connector body 411.

In the connector 402 of the cable 400, the lens 414 has a function of condensing the incident collimated light. In this case, the collimated light is incident on the lens 414 and focused, and this focused light is incident on the input end of the optical fiber 401 with a predetermined NA.

FIG. 25 shows a cross-sectional view of a state in which the connector 202 of the transmitter 200 and the connector 402 of the cable 400 are connected. In the connector 202, the light sent through the optical fiber 203 is emitted from the output end of the optical fiber 203 at a predetermined NA. This emitted light enters the lens 214, is shaped 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 414 and is focused. Then, this focused light enters the input end of the optical fiber 401 and is sent through the optical fiber 401.

Although a detailed explanation will be omitted, the connector 403 of the cable 400 and the connector 301 of the receiver 300 are configured similarly to the configuration example of the connector 202 of the transmitter 200 and the connector 402 of the cable 400 described above.

Figure 26 shows an example configuration of the light-emitting unit 201 and connector 202 in the transmitter 200. This example configuration is just one example, and the configuration of the transmitter 200 is not limited to this.

The light emitting section 201 includes a ferrule 221. The ferrule 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.

The ferrule 221 is provided with an optical fiber insertion hole 226 extending rearward from the front side. After the optical fiber 203 is inserted into the optical fiber insertion hole 226, it is fixed to the ferrule 221 with an adhesive 227.

A substrate 222 on which the light emitting element 223 and the light emitting element driver 228 are mounted is fixed to the underside of the ferrule 221. In this case, the light emitting element 223 is mounted on the substrate 222 in accordance with each optical fiber 203. Here, the position of the substrate 222 is adjusted and fixed so that the emission part of the light emitting element 223 coincides with the optical axis of the optical fiber 203.

Further, the ferrule 221 is formed with an arrangement hole 224 extending upward from the lower surface side. In order to change the optical path of the light from the light emitting element 223 to the direction of the optical fiber 203, the bottom part of the arrangement hole 224 is made into an inclined surface, and a mirror (optical path changing section) 225 is arranged on this inclined surface. There is. Regarding the mirror 225, 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. Here, the light emitting element 223 and the optical fiber 203 constitute an optical module.

As for the connector 202, it is the same as that described above using FIG. 24, so its description will be omitted here.

In the transmission/reception system 100 shown in FIG. 21, the optical fibers 203, 401, and 303 are 1310 nm single mode fibers, but since communication is performed using light in the 850 nm band, in addition to the fundamental mode, the primary mode is also used. It becomes capable of propagation and functions as a double mode fiber (see FIG. 6). Therefore, when there is an optical axis shift of the light incident on the optical fibers 203, 401, 303, the primary mode generated thereby is propagated together with the fundamental mode, reducing the coupling loss of optical power (Fig. 8), it is therefore possible to reduce the precision of optical axis deviation and reduce costs.

Furthermore, in the transmission/reception system 100 shown in FIG. 21, since the 850 nm band light propagated to the connectors 202, 403 through the optical fibers 203, 401 has a predetermined wavelength width (see FIG. 19), the light The intensity distribution of light at the output end face of the fibers 203, 401 is not biased in one direction with respect to the center of the core (see FIG. 16(c1)). Therefore, when there is a deviation in the optical axis of the light incident on the optical fibers 401, 303, the same problem occurs when communication is performed using light having only the fundamental mode component, regardless of the direction of the optical axis deviation. , it becomes possible to obtain good coupling efficiency. Therefore, it is not necessary to use additional parts or a light source with a complicated structure to propagate light having only the fundamental mode component, and the cost of parts can be reduced.

<2. Modified example>
In the above embodiment, the first wavelength is 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. It is possible that

In the above 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. In the above embodiment, the first wavelength is described as 1310 nm, but it is also possible that this first wavelength is 1550 nm or a wavelength in the 1550 nm band that includes 1550 nm.

Further, 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.

Moreover, 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.

The present technology can also be configured as follows.
(1) An optical waveguide that propagates only a fundamental mode at a first wavelength;
communicating using light of a second wavelength having a component in at least a first mode in addition to the fundamental mode;
The second wavelength has a predetermined wavelength width and is a wavelength at which the optical waveguide can propagate at least a first-order mode along with a fundamental mode.
(2) The optical communication device according to (1), wherein the first wavelength is a wavelength at which chromatic dispersion is zero.
(3) The optical communication device according to (1) or (2), wherein the first wavelength is between 300 nm and 5 μm.
(4) The optical communication device according to (3), wherein the first wavelength is a wavelength in the 1310 nm band or the 1550 nm band.
(5) The optical communication device according to any one of (1) to (4), wherein the second wavelength is a wavelength in the 850 nm band.
(6) The optical communication device according to any one of (1) to (5), wherein the optical waveguide is an optical fiber.
(7) The optical communication device according to any one of (1) to (5), wherein the optical waveguide is a silicon optical waveguide.
(8) An optical communication device including an optical waveguide that propagates only a fundamental mode at a first wavelength,
communicating using light of a second wavelength having a component in at least a first mode in addition to the fundamental mode;
The second wavelength has a predetermined wavelength width and is a wavelength at which the optical waveguide can propagate at least a first-order mode along with a fundamental mode.
(9) a receiving section having an optical waveguide that propagates only a fundamental mode at a first wavelength;
a transmitting section which has an optical waveguide which propagates only a fundamental mode at the first wavelength, and which inputs light of a second wavelength having a fundamental mode component and at least a first-order mode component to an input end side of the optical waveguide of the receiving section through the optical waveguide;
An optical communication system, wherein the second wavelength has a predetermined wavelength width and is a wavelength at which at least a first-order mode can be propagated along with a fundamental mode through the optical waveguide of the receiving unit and the optical waveguide of the transmitting unit.
(10) The optical communication system according to (9), further comprising a light emitting section for emitting light of the second wavelength having a fundamental mode component and at least a first-order mode component to an incident end of the optical waveguide of the transmitting section.
(11) The optical communication system according to (9) or (10), further comprising a plurality of combinations of the receiving unit and the transmitting unit.
(12) The optical communication system according to any one of (9) to (11), wherein the transmitting unit is a receptacle of a transmitter or a plug of a cable.
(13) The optical communication system according to any one of (9) to (12), wherein the receiving unit is a plug of a cable or a receptacle of a receiver.

100: Transmission/reception system 200: Transmitter 201: Light-emitting unit 202: Connector (receptacle)
203: Optical fiber 203a: Core 203b: Clad 211: Connector body 212: Adhesive injection hole 213: Light emission part (light transmission space)
214...Lens (convex lens)
Reference Signs List 215: Position regulating portion 216: Optical fiber insertion hole 217: Adhesive 221: Ferrule 222: Substrate 223: Light emitting element 224: Arrangement hole 225: Mirror 226: Optical fiber insertion hole 227: Adhesive 228: Light emitting element driver 300: Receiver 301: Connector (receptacle)
302: Light receiving unit 303: Optical fiber 400: Cable 401: Optical fiber 401a: Core 401b: Clad 402, 403: Connector (plug)
411: Connector body 412: Adhesive injection hole 413: Light entrance portion (light transmission space)
414...Lens (convex lens)
415: Position control portion 416: Optical fiber insertion hole 417: Adhesive

Claims (13)

an optical waveguide that propagates a fundamental mode at a first wavelength ;
A circuit for inputting light of a second wavelength having at least a first-order mode component together with the fundamental mode on the input side end face of the optical waveguide ,
The optical waveguide propagates at least the primary mode along with the fundamental mode in communication using light of the second wavelength,
The second wavelength has a predetermined wavelength width set so that the light intensity distribution on the output side end face of the optical waveguide is not biased with respect to the center of the core . The optical communication device according to claim 1, wherein the first wavelength is a wavelength at which chromatic dispersion is zero. The optical communication device according to claim 1 , wherein the first wavelength is between 300 nm and 5 μm. The optical communication device according to claim 3 , wherein the first wavelength is a wavelength in the 1310 nm band or the 1550 nm band. The optical communication device according to claim 1 , wherein the second wavelength is in the 850 nm band. The optical communication device according to claim 1, wherein the optical waveguide is an optical fiber. The optical communication device according to claim 1, wherein the optical waveguide is a silicon optical waveguide. In an optical communication device including an optical waveguide that propagates a fundamental mode at a first wavelength,
Injecting light of a second wavelength having at least a first-order mode component together with the fundamental mode into the input side end face of the optical waveguide;
The optical waveguide propagates at least the primary mode along with the fundamental mode in communication using light of the second wavelength,
The second wavelength has a predetermined wavelength width set so that the light intensity distribution on the output side end face of the optical waveguide is not biased with respect to the center of the core . a receiver having a first optical waveguide that propagates a fundamental mode at a first wavelength;
a transmitter having a second optical waveguide that propagates light in a fundamental mode at the first wavelength, and that transmits light of a second wavelength having a fundamental mode component and at least a first-order mode component to the first optical waveguide through the second optical waveguide ;
the second wavelength enables the first optical waveguide and the second optical waveguide to propagate at least the first order mode along with the fundamental mode;
the second wavelength has a predetermined wavelength width that is set so that the light intensity distribution at the emission end face of the second optical waveguide is not biased with respect to the center of the core . The optical communication system according to claim 9 , further comprising a light emitting section for emitting light of the second wavelength having a component of at least the first mode as well as the fundamental mode to an incident end face of the second optical waveguide. The optical communication system according to claim 9 , comprising a plurality of combinations of the receiving unit and the transmitting unit. The optical communication system according to claim 9, wherein the transmitter is a receptacle of a transmitter or a plug of a cable. The optical communication system according to claim 9, wherein the receiving section is a cable plug or a receiver receptacle.

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