JP2004029450A - Optical connector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical connector usable for the connection of optical fibers for high power transmission. <P>SOLUTION: In the optical connector for connecting the end faces of the optical fibers with each other by applying a load and tightly adhering them, by enlarging the respective cores 41 of the optical fibers 4 to be connected in a tapered shape toward connection end faces 43, optical power per unit area at a connection part is reduced, peak power is reduced, and thus the optical signals (or exciting light) of high power are propagated. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical connector that can be used at a connection portion even when a high-power (for example, 1 W or more) optical signal propagates in an optical fiber in a transmission system using WDM, Raman amplification, or the like. .
[0002]
[Prior art]
In recent years, communication systems using optical fibers have been increasingly demanded. Various optical fibers, such as a multi-mode optical fiber and a single-mode optical fiber, are used, and various optical connectors are used at the connection portions.
[0003]
Optical connectors have been designed so as to reduce the axial loss, inclination, and gap between optical fibers when connected, in order to reduce the optical loss. By controlling these parameters, various low-loss optical connectors have been realized. In particular, in the case of a physical contact type (hereinafter, PC type) optical connector, connection loss and reflection have been reduced by bringing optical fibers into close contact with each other.
[0004]
FIG. 1 shows an example of a PC-type optical connector, here a well-known SC connector, in which an optical connector plug 2 including an end of an optical fiber 1 to be connected as a component and a pair of optical connector plugs 2 (however, (Only one is shown in FIG. 1). The adapter 3 (which may be integrated with one of the optical connector plugs) 3 detachably connects the pair of optical connector plugs 2 to the adapter 3. In the state where the optical fibers 1 are mounted, the end faces of the respective optical fibers 1 are brought into close contact with each other by applying a load, and are connected.
[0005]
2A and 2B show an outline of the connection between optical fibers in a conventional PC-type optical connector. FIG. 2A is an enlarged view of the optical fiber in a connected state immediately before connection, and FIG. Here, the state of the optical fiber is the optical fiber 1, but in FIG. 1, the state where the optical fiber is coated is referred to as the optical fiber 1.)
[0006]
The optical fiber 1 includes a core 11 and a clad 12, and an optical signal (or pump light) propagates while being confined in the core 11. The radius of the core 11 is as small as about 5 μm in a single mode optical fiber. In the PC-type optical connector, in order to bring the cores 11 into close contact with each other, the end surface 13 at the tip of the optical fiber 1 is polished to a spherical surface, and a load is applied from both sides of the optical fiber 1 to achieve the close contact.
[0007]
That is, as shown in FIG. 2B, when a load P0 indicated by an arrow is applied to the optical fiber 1, the end face 13 of the optical fiber 1 is deformed, and the cores 11 of the optical fibers come into close contact with each other. As a result, the core 11 through which the optical signal (or the pumping light) propagates is brought into close contact, and good connection characteristics can be obtained.
[0008]
By the way, even if the optical connector is designed perfectly, a small flaw on the end face of the optical fiber causes an increase in connection loss. If the connection loss is less than the specified value, there is no problem. If the connection loss is not less than the specified value, the end face is polished again to eliminate scratches.
[0009]
Further, since the optical connector is often used in a place where attachment and detachment are frequently performed, dust may adhere to the end face and increase the optical connection loss. Also in this case, there is no problem if the loss is equal to or less than the specified value, and if the loss is equal to or more than the specified value, the connection can be canceled once, the end face cleaned, and then the connection can be avoided again.
[0010]
[Problems to be solved by the invention]
However, recently, with the development of WDM transmission technology and transmission technology based on Raman amplification, a case where a high-power optical signal (or pumping light) is incident on a single-mode optical fiber has occurred. In that case, various problems have begun to be pointed out in the single-mode optical fiber because light of high power propagates inside the core (radius of about 5 μm).
[0011]
In particular, the problem is remarkable in the optical connection portion, and a fiber fuse phenomenon in which dust caught between optical fiber end faces is ignited and burned by a high-power optical signal to destroy the end faces (however, the exact cause is unknown). For example, phenomena such as breakage of an optical fiber based on the end face of a connection portion of an optical connector have been reported so far.
[0012]
An object of the present invention is to realize an optical connector that can be used for connecting an optical fiber for high power transmission.
[0013]
[Means for Solving the Problems]
When connecting a single-mode optical fiber to various optical devices, the difference in spot size becomes a problem. Technology has been reported. In this technique, since the core can be enlarged, it is considered that the energy intensity distribution at the connection portion changes.
[0014]
In order to solve the above-mentioned problem, the present invention reduces the optical power per unit area at the connection part by employing the above-described core-expanded fiber technology, and can transmit a high-power optical signal (or pumping light) without any problem. Realizing a simple optical connector.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 3 shows an example of an embodiment of an optical connector according to the present invention, in which an outline of connection between optical fibers in an embodiment corresponding to claims 1, 2, and 3 is shown. Immediately before, FIG. 1B is an enlarged view of the optical fiber in a connected state.
[0016]
The optical fiber 4 includes a core 41 and a clad 42, and an optical signal (or pump light) propagates while being confined in the core 41. The core 41 has a structure that expands in a tapered shape from a predetermined position toward the connection end face 43. That is, the radius a of the core 41 before the predetermined position is about 5 μm, which is the same as that of the single mode optical fiber, but it gradually increases as approaching the connection end face 43, and has a maximum radius a _max at the connection end face 43. ing.
[0017]
As in the conventional case, the end face 43 of the optical fiber 4 is polished to a spherical surface in order to bring the cores 41 into close contact with each other, and a load P indicated by an arrow is applied to the optical fiber 4 as shown in FIG. With this addition, the end face 43 of the optical fiber 4 is deformed, and the cores 41 come into close contact with each other. As a result, the core 41 that propagates the optical signal (or the excitation light) comes into close contact with each other, so that good connection characteristics can be obtained.
[0018]
FIG. 4 shows how the optical power changes in the optical connector of the present invention. In the single mode optical fiber, the optical signal (and the pumping light) is confined in the core 41 and propagates with a Gaussian distribution. It can be seen that the light propagating in the core 41 has its power spatially expanded due to the core 41 expanding near the connection end face 43, and as a result, the peak power has decreased. It can be seen that the peak power at the connection decreases in inverse proportion to the magnitude of the radius a of the core 41 at the connection end face.
[0019]
Thus, according to the first aspect of the present invention, the optical power density at the connection portion can be reduced by enlarging the core of the optical fiber at the connection portion.
[0020]
In the optical connector of the present invention, since the core 41 is larger than the core of the ordinary optical fiber, the connection end face 43 of the optical fiber is required to realize the PC connection as shown in FIG. It is necessary to appropriately design the curvature radius R and the load P between the end faces 43.
[0021]
Here, when the connection end surface 43 which is spherically polished and has a radius of curvature R is deformed by the load P, the radius r of the deformed connection surface is
r = ^{[{3 · (1-ν 2} ) · P · R} / (4 · E) ] ^1/3 ... (1)
Is calculated by Here, R is the radius of curvature of the connection end face, E is Young's modulus, ν is Poisson's ratio, and P is the load applied between the end faces. FIG. 5 is a graph showing the relationship between the load P between the end faces and the radius r using Expression (1).
[0022]
For example, when the maximum core radius a _max at the connection end face 43 is set to be three times the core radius a of the normal portion (a = 15 μm), the peak power can be reduced to 1/9 by a simple area calculation. Because it is possible, this value is considered to be an effective value for reducing the peak power. From FIG. 5, when the radius of curvature R of the connection end face 43 is 10 mm, and when the radius of curvature R is 100 mm, the load P is 0.1 kg and r> a _max , so that PC connection can be realized with this connection end face 43. become. It can be said that the value of 0.1 kg has no problem in the design of the optical connector.
[0023]
In addition, when the core of the optical fiber is expanded in a tapered shape, unless the expansion ratio γ of the core and the length L of the tapered portion are designed to appropriate values, a loss will occur in that portion. Here, according to the theory of the core-enlarged fiber, if the connection loss at the connection part is ignored, the loss of the core-enlarged part is
Loss (dB) =-10 log (T1, T1, T2) (2)
Here, T1 = [1 + {(1/2) · (γ−1) · ((π · n0 · ω ² ) / (λ · L))} ² ] ⁻¹
T2 = [1+ {γ · (γ−1) · ((π · n0 · ω ² ) / (λ · L))} ² ] ⁻¹
γ = a _max / a
Indicated by Here, n0 is the refractive index of the core, ω is the mode field diameter, and λ is the wavelength of the propagating optical signal (excitation light).
[0024]
The minimum value Lc of the possible values of L is
Lc = {γ · (γ−1)} ^1/2 · {(π · n0 · ω ² ) / (λ · L)} (3)
Indicated by
[0025]
It is also known that L is required to be 1 to 3 mm when the enlargement ratio γ of the core is 2 to 3 times. When these factors are taken into consideration in addition to the expressions (2) and (3), when the magnification γ of the core is tripled, L is about 3 mm, and an insertion loss of about 0.05 dB is obtained.
[0026]
Since the length L is sufficiently long to fit inside a connector ferrule of a generally used SC connector or MT connector, it is considered that the above design can be applied to an optical connector. Therefore, according to the present invention, when applied to the well-known SC connector as shown in FIG. 1, it can be used without any problem in appearance or design.
[0027]
FIG. 6 shows another example of the embodiment of the optical connector according to the present invention, in which the outline of the connection between the optical fibers in the embodiment according to the first, second, third and fourth aspects is shown. The optical power distribution control component or member 5 that reduces the difference in the intensity distribution depending on the position of the optical signal incident from one end and emits from the other end is inserted between the connection end faces 43 of FIG. Thereby, as shown in FIG. 7, the spatial distribution Gaussian distribution 61 of the energy density of the optical signal (or the pumping light) from one optical fiber passes through the optical power distribution control component or member 5 and becomes rectangular. Since the distribution has a close distribution 62, the peak power can be reduced.
[0028]
This technology can also be used without changing the shape of the conventional optical connector by incorporating the optical power distribution control component or member 5 into the adapter 3 of the SC connector as shown in FIG. 8, for example.
[0029]
FIG. 9 shows an example of a light power distribution control component or member, here a beam homogenizer, in which 51 is a beam magnifying lens, 52 and 53 are condenser lenses, 54 is a lens array, and 55 is a condenser surface. is there.
[0030]
The beam homogenizer is used when a laser beam is incident on an optical fiber, and the spot size D on the light-converging surface 55 and the angle θ formed by the marginal rays with the optical axis are as follows:
D = ω2 · (f2 / f1)
tan θ = (1/2) · {(ω1 / f2) + (ω2 / f1)} (4)
Indicated by Here, f1 and f2 are the focal lengths of the lens array 54 and the condenser lens 53, and ω1 and ω2 are the width of the laser beam incident on the lens array 54 and the width of the small lenses forming the lens array.
[0031]
By using the beam homogenizer, it is possible to reduce the peak power of light from one optical fiber and receive the light with the other optical fiber.
[0032]
【The invention's effect】
As described above, according to the present invention, in a connection portion of an optical transmission line using high peak power, light that can endure an optical signal (or pump light) having a high peak power incorporating the technology of the present invention. By using the connector, the optical connector technology will be used even in places where connection was originally considered dangerous.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an example of a PC-type optical connector. FIG. 2 is a schematic view showing a connection between optical fibers in a conventional PC-type optical connector. FIG. 3 shows an example of an embodiment of an optical connector of the present invention. Schematic diagram of connection between optical fibers. FIG. 4 is an explanatory diagram showing a state of change in optical power in the optical connector of the present invention. FIG. 5 is a graph showing a relationship between a load between end faces and a radius of a deformed connection surface. FIG. 6 is a schematic view of the connection between optical fibers showing another example of the embodiment of the optical connector of the present invention. FIG. 7 is an explanatory view showing the state of change of the optical power distribution by an optical power distribution control component or member. FIG. 8 is an explanatory diagram showing an example of an optical connector incorporating an optical power distribution control component or member. FIG. 9 is a configuration diagram showing an example of an optical power distribution control component or member.
2: optical connector plug, 3: adapter, 4: core expanded optical fiber, 41: core, 42: clad, 43: connection end face, 5: optical power distribution control component or member, 51: beam expansion lens, 52, 53: Condensing lens, 54: Lens array, 55: Condensing surface, 61: Spatial distribution of energy density of signal light (or excitation light) (Gaussian type), 62: Spatial distribution of energy density of signal light (or excitation light) (Rectangular type).

Claims (4)

In an optical connector for connecting by applying a load to the end faces of the optical fibers and bringing them into close contact with each other,
An optical connector, wherein each core of an optical fiber to be connected is enlarged in a tapered shape toward a connection end face. 2. The optical connector for high-power transmission according to claim 1, wherein the enlargement ratio of the core and the length of the tapered portion are appropriately adjusted so that loss in the tapered portion is minimized. 3. The optical connector for high-power transmission according to claim 1, wherein the radius of curvature of the connection end surface polished to a spherical surface and the load between the end surfaces are appropriately adjusted so that loss at the connection portion is minimized. . 4. A power distribution control component or member for reducing a difference in intensity distribution depending on the position of an optical signal incident from one end and emitting from the other end between the optical fibers to be connected. An optical connector as described in Crab.

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