JP2003337234A - Fiber type optical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fiber type optical device which can be easily manufactured and which is excellent in reliability and characteristics and high in versatility. <P>SOLUTION: The fiber type optical device is composed of a first optical fiber to introduce light into a photodiode and a second optical fiber to introduce light into the first optical fiber. Both the fibers are optically connected through a variable optical attenuator 51, and is characterized in that the exit end of the first optical fiber consists of a GI fiber 71 having a core with a quadratic index profile, the second optical fiber contains a portion where a GI fiber 32 having a core with a quadratic index profile and a single mode fiber 61 connected in series in this order from the side of the variable optical attenuator 51. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a fiber type optical device mainly used in the fields of optical communication and sensors.

[0002]

2. Description of the Related Art A fiber type optical device mounted on a light receiving module provided with a light receiving element will be considered. Figure 2
As shown in FIG. 1, this fiber type optical device is a multimode fiber (hereinafter referred to as GI) having a single mode fiber 232 and a core having a squared refractive index profile in order from the light input side.
(Also referred to as fiber) 242, coreless fiber 252,
Optical element 261 such as optical attenuator, coreless fiber 25
1, a GI fiber 241, and a single mode fiber 231 having a tip sphere 221 formed at its tip.

In the fiber type optical device having the above structure, the Gaussian beam emitted from the single mode fiber 232 functions as a GI fiber 2 which functions as a lens.
Image conversion is performed at 42, and a beam waist is formed at the center of the optical element 261. After that, image conversion is further performed by the GI fiber 241 functioning as a lens, the light is optically coupled again to the single mode fiber 231, and finally, the photodiode 2 of the light receiving element is passed through the front spherical fiber 221.
Connect to 11.

In the optical system shown in FIG. 2, the fibers are fusion-spliced. In this configuration, there are at least four fusion points (between the single mode fiber 232 and the GI fiber 242, and between the GI fiber 242 and the GI fiber 242). The coreless fiber 252, the coreless fiber 251 and the GI fiber 241, and the GI fiber 241 and the single-mode fiber 231 are required), so that there is a disadvantage that fusion time is required during manufacturing.

Further, in general, in a silica optical fiber,
For example, there is a large difference in melting point between a coreless fiber that is not doped with germanium (Ge) (no core is formed) and a GI fiber that is doped with germanium for core formation, and the GI fiber 242 has the above configuration.
Between the coreless fiber 2 and the coreless fiber 252.
It was difficult to perform fusion splicing at two points between the 51 and the GI fiber 241.

Further, a so-called fixed optical attenuator using an optical attenuating film or the like is preferably used for the reason that the optical element 261 has a simple structure and is easy to manufacture.
Since a fixed optical attenuator having a different optical attenuation depending on the installation location of the photodiode 211 must be provided, the versatility is poor.

Therefore, an object of the present invention is to provide a fiber type optical device which is easy to manufacture, has excellent reliability and characteristics, and is highly versatile.

[0008]

A fiber type optical device of the present invention which achieves the above object is a first optical fiber body for making light incident on a light receiving element and a second optical fiber for making light incident on the first optical fiber body. A fiber body is optically connected to the fiber body via an optical element, and a light emitting end of the first optical fiber body is a multimode fiber having a core having at least a square-shaped refractive index distribution. Fiber optic body
The multimode fiber and the single mode fiber having a core having a squared refractive index distribution from the side of the optical element include parts connected in series in this order.

In particular, the tip of the multimode fiber of the first optical fiber body is formed into a spherical lens. Further, coreless fibers are connected in tandem to the light incident side of the multimode fiber of the first optical fiber body, and coreless fibers are connected in tandem to the light emitting side of the multimode fiber of the second optical fiber body. The melting point of the multimode fiber of the first optical fiber body is higher than that of the multimode fiber of the second optical fiber body. Further, the optical element is a variable optical attenuator.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a fiber type device according to the present invention will be described below in detail with reference to the drawings.

As shown in FIG. 1, the fiber type optical device of the present invention includes a first optical fiber body made of, for example, quartz, which allows light to enter a photodiode 11 which is a light receiving element, and the first optical fiber body. Light is incident on the optical fiber body, and the second optical fiber body made of, for example, quartz is used as an optical element such as a variable optical attenuator or an optical filter (in this embodiment, the variable optical attenuator 51 is used). The optical connection is made through.

Here, the photodiode 11 is suitable for receiving light in a wavelength band of 1000 to 1600 nm, and is provided with a semiconductor layer of InGaAs or the like having a light receiving diameter of about several tens of μm, a pin type photodiode, an avalanche photodiode, or the like. Can be used. The variable optical attenuator 51 is, for example, PLZT, BaTiO3, or SBN.
To a substrate made of a material having an electro-optical effect, such as
A plurality of electrodes for generating an electric field are formed, and transmitted light can be deflected by the generation of the electric field.
The degree of deflection can be adjusted and the amount of light attenuation can be changed by changing the strength of the electric field.

Further, the first optical fiber body is provided with a GI fiber 31 which is a multimode fiber having a light emitting end having a core of at least square-shaped refractive index distribution, and further,
The GI fiber 31 is formed by fusion-splicing a coreless fiber 41 having substantially the same diameter as the GI fiber 31 on the light incident side. Further, the second optical fiber body is a multimode having a coreless fiber 42 from the light incident side of the variable optical attenuator 51, and a core which is fusion-bonded to the coreless fiber 42 and has substantially the same diameter as that of the square-shaped refractive index distribution. GI fiber 32 which is a fiber,
A single mode fiber 61 fused and spliced to this and having a diameter substantially the same as that of the single mode fiber 61 is configured to include a portion connected in series in this order.

Further, the tip of the GI fiber 31 constituting the first optical fiber body is provided so that the maximum coupling efficiency of the optical signal is obtained between the first fiber body and the photodiode.
It is formed on a spherical lens (front sphere) 21 having a predetermined radius of curvature. Furthermore, the GI that constitutes the first optical fiber body
The melting point of the fiber 31 is G which constitutes the second optical fiber body.
It is higher than the melting point of the I fiber 32. That is, since the core diameter of the GI fiber 31 is smaller than the core diameter of the GI fiber 32, the germanium (Ge) concentration to be doped to form the core in the matrix phase (eg, silicon oxide) of the GI fiber 31 is low. Higher melting point.
This facilitates fusion splicing of the GI fiber 31 having a high melting point and the coreless fiber 41 having a melting point close to this melting point. Further, the fusion splicing may be performed only at three positions between the GI fiber 31 and the coreless fiber 41, between the coreless fiber 42 and the GI fiber 32, and between the GI fiber 32 and the single mode fiber 61.

In FIG. 1, when an optical signal having a spot size of ω5 is emitted from the single mode fiber 61, image conversion is performed by the GI fiber 32 functioning as a lens, and the beam waist 8 in the variable optical attenuator 51.
The parameters (core diameter, relative refractive index difference) and length of the GI fiber 32 are set so that 1 is formed. The spot size at this time is ω6.

The Gaussian beam having the beam spot size ω6 is subjected to image conversion again by the compound lens 71 composed of the front sphere 21 functioning as a lens and the GI fiber 31, and the spot size ω3 is applied to the photodiode 11.
Is emitted at. The radius R of the spherical tip and the parameters of the GI fiber 31 (core diameter, relative refractive index difference) so that the beam waist is located at the end face of the photodiode and the beam spot size ω3 is smaller than the light receiving diameter of the photodiode. And the length can be set.

The light ray matrix in the optical system from the central portion of the variable optical attenuator 51 to the photodiode 11 is M1, the distance from the photodiode 11 to the front sphere 21 is d1, the refractive index of the medium between them is n1, and the GI fiber 31. The core has a refractive index of n2, the radius of curvature of the front sphere 21 is R, and the GI fiber 3
The focusing parameter A0 of 1 and the length of the GI fiber 31 are d
2, the coreless fibers 41 and 42 have a refractive index of n3, the coreless fiber 41 has a length of d10, the variable optical attenuator 51 has a refractive index of n6, and the coreless fiber 41 has a central portion (a beam waist is formed). The distance to the specified position) is d9, the wavelength of the light passing through the variable optical attenuator 51 is λ6, the beam spot diameter of the Gaussian beam in the variable optical attenuator 51 is ω6, and the wavelength of the light incident on the photodiode 11 is Is λ1, the ray matrix in the optical system from the central portion of the variable optical attenuator 51 (the position where the beam waist is formed) to the exit end of the single mode fiber 61 is M2, and the central portion of the variable optical attenuator 51 (where the beam waist is From the position where the coreless fiber 42 is formed) to d8, the length of the coreless fiber 42 is d7, and the length of the GI fiber 32 is d. , The spot size of the single mode fiber 61 .omega.5, the wavelength of the light propagating single mode fiber 61 and [lambda] 5, the elements of the determinant A, B,
When C and D are set, the formulas (1) to (6) are satisfied. Here, equations (2), (3), (5), and (6)
Is a conditional expression for the propagating light beam to be a Gaussian beam.

[0018]

[Equation 1]

By satisfying the above relational expression, the Gaussian beam emitted from the single mode fiber 61 on the input side can obtain the maximum coupling efficiency when being transmitted to the photodiode 11 on the output side. Since the photodiode 11 is used in the present invention, it is not necessary to strictly determine the distance d1 from the photodiode 11 to the front ball 21, and the beam may be incident on the light receiving portion of the photodiode 11.

As a method of manufacturing an optical system, first, an optical system composed of one fiber body as shown in FIG. 3 is manufactured. That is, the single-mode fiber 61 is fusion-spliced with the GI fiber 32 of a certain length that functions as a lens,
Next, the coreless fiber 40 having the required length is fusion-spliced to the GI fiber 32. Further, the GI fiber 31 having a constant length that functions as a lens is fusion-spliced to the coreless fiber 40. Finally, the tip sphere 21 is attached to the tip of the GI fiber 31.
By forming the above, an optical system for coupling with the photodiode 11 is completed.

As a method of mounting an optical element such as a variable optical attenuator in this optical system, the fiber body is fixed in the V groove formed in the substrate, and then the groove for providing the optical element is formed in the fiber body. , The optical element may be mounted in this groove, but after inserting the fiber body into the through hole of the ferrule and fixing the fiber body inside the ferrule by adhesion, the optical element is attached to the coreless fiber part of the fiber body and the ferrule. It is also possible to form a groove in which the optical element is provided and then mount an optical element in this groove.

For example, when the optical system is mounted on the ferrule, as shown in FIG. 4, first, the fiber body 101 is inserted into the through hole of the ferrule 91 and fixed by adhesion with an optical adhesive 111 such as epoxy resin. . Next, as shown in FIG. 5, the coreless fiber portion (40) is, for example, 1600 μm thick.
The shorter groove 131 is cut into the ferrule 91 and the fiber body, the variable optical attenuator 51 is inserted, and adhesively fixed with an optical adhesive 141 such as epoxy resin, acrylic resin, or silicone resin.

Thus, according to the fiber type optical device configured as described above, the light emitting end of the first optical fiber body is composed of a multimode fiber (GI fiber) having a core having at least a squared refractive index distribution. Since the second optical fiber body includes a portion in which a multimode fiber having a core having a squared refractive index distribution and a single mode fiber are connected in series in this order from the side where the optical element is arranged, the optical element It becomes possible to perform optical coupling before and after the process with high efficiency, and it becomes possible to easily mount a highly efficient fiber type optical device.

Further, the coreless fibers are connected in cascade to the light incident side of the multimode fiber of the first optical fiber body, and the coreless fibers are connected in cascade to the light emission side of the multimode fiber of the second optical fiber body. Since the melting point of the multi-mode fiber of the first optical fiber body is higher than that of the multi-mode fiber of the second optical fiber body, the manufacturing can be performed accurately and with good yield, and the fusion of the multi-mode fiber and the coreless fiber can be achieved. The joining can be performed easily and quickly. Further, since the fused portion can be reduced by the above configuration, manufacturing can be facilitated and the overall size can be reduced, and a high performance fiber type optical device is provided. You can

Furthermore, when a wavelength filter is used as the optical element, it is possible to receive an optical signal of a specific wavelength. Further, when a variable optical attenuator is used as the optical element, the receiving point of the light receiving element can be obtained. Whatever the location (any distance from the optical transmission means), it is possible to control the optical attenuation according to the location, and it is possible to provide a highly versatile device.

Although an example in which a variable optical attenuator is applied as an optical element has been described in the present embodiment, the same action and effect are expected even if an optical element such as a wavelength filter is applied instead of the variable optical attenuator. However, other configurations can be appropriately modified and implemented without departing from the scope of the present invention.

[0027]

As described above in detail, according to the fiber type optical device of the first aspect, the light emitting end of the first optical fiber body is a multimode fiber having a core with at least a squared refractive index profile. Since the second optical fiber body includes a portion in which a multimode fiber having a core having a squared refractive index profile and a single mode fiber are connected in series in this order from the optical element side, the second optical fiber body is provided before and after the optical element. The optical coupling can be performed with high efficiency.

Further, coreless fibers are connected in cascade to the light incident side of the multimode fiber of the first optical fiber body, and coreless fibers are connected in cascade to the light emission side of the multimode fiber of the second optical fiber body. By making the melting point of the multimode fiber of the first optical fiber body higher than that of the multimode fiber of the second optical fiber body, fusion splicing of the multimode fiber and the coreless fiber can be performed easily and quickly. it can. Moreover, since the fused portion can be reduced as much as possible by the above configuration, the manufacturing of the device can be performed easily and quickly, and the entire device can be downsized, and a high performance fiber type optical device is provided. can do.

Furthermore, when a wavelength filter is used as the optical element, it is possible to receive an optical signal of a specific wavelength. Further, when a variable optical attenuator is used as the optical element, the receiving point of the light receiving element can be obtained. Whatever the location (any distance from the optical transmission means), it is possible to control the optical attenuation according to the location, and it is possible to provide a highly versatile device.

[Brief description of drawings]

FIG. 1 is a sectional view schematically explaining an embodiment of a fiber type optical device according to the present invention.

FIG. 2 is a sectional view schematically illustrating a comparative example of a fiber type optical device.

FIG. 3 is a cross-sectional view schematically illustrating a fiber type optical device excluding an optical element in the optical system according to the present invention.

FIG. 4 is a cross-sectional view schematically showing a state in which a fiber is bonded and fixed to a ferrule.

FIG. 5 is a cross-sectional view schematically showing a state in which an isolator chip is bonded and fixed inside a ferrule.

[Explanation of symbols]

11: Photodiode (light receiving element) 21: Front sphere 31, 32: Multimode fiber (GI fiber) having a core having a squared refractive index distribution 40, 41, 42: Coreless fiber 51: Variable optical attenuator (optical element) ) 61: single mode fiber 91: ferrule

Claims (4)

[Claims] 1. A fiber configured to optically connect a first optical fiber body for making light incident on a light receiving element and a second optical fiber body for making light incident on the first optical fiber body via an optical element. Optical device, wherein the light emitting end of the first optical fiber body comprises a multimode fiber having a core of at least square-shaped refractive index distribution, and
The optical fiber body comprises a multimode fiber having a core having a squared refractive index distribution and a single mode fiber from the side of the optical element, and a part in which the multimode fiber and the single mode fiber are connected in series in this order. . 2. The fiber type optical device according to claim 1, wherein the multimode fiber of the first optical fiber body has a spherical lens at its tip. 3. A coreless fiber is connected in cascade to a light incident side of the multimode fiber of the first optical fiber body, and a coreless fiber is cascaded to a light emitting side of the multimode fiber of the second optical fiber body. 3. The fiber type optical device according to claim 1, wherein the multimode fiber of the first optical fiber body has a melting point higher than that of the multimode fiber of the second optical fiber body. 4. The fiber type optical device according to claim 1, wherein the optical element is a variable optical attenuator.