JP2003270494A - Fiber type optical device - Google Patents

Abstract

(57) [Summary] [Problem] In an optical system for coupling a tip ball and a laser diode, there is a problem that the tip ball hits the laser diode during mounting because the distance between the tip ball and the laser diode is short. SOLUTION: A first optical fiber body is composed of a GI fiber 31 whose light incident end is a multimode fiber having a core having at least a square-shaped refractive index distribution, and the GI fiber 31 is fused with a coreless fiber 41 in a subsequent stage. Are joined. Further, the second optical fiber body includes an optical isolator 5.
1, a coreless fiber 42, a GI fiber 32, which is a multimode fiber fusion-bonded to the coreless fiber having a square refractive index distribution core, and a single-mode fiber 61 fusion-bonded to the coreless fiber 42. Are connected in tandem in this order, and the tip of a GI fiber 31 constituting the first optical fiber body is formed in a spherical lens (front sphere) 21. Further, a GI fiber constituting the first optical fiber body is formed. The melting point of 31 is higher than the melting point of GI fiber 32 constituting the second optical fiber body.

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]

BACKGROUND OF THE INVENTION A fiber type optical device mounted on a laser module provided with a light emitting element is considered. For example, as shown in FIG. 2, this fiber type optical device comprises a single mode fiber 232 and a multimode fiber having a core of a squared refractive index distribution (hereinafter,
GI fiber) 242, coreless fiber 25
2, optical isolator chip 261, coreless fiber 2
51, 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 laser diode 211, which is a light emitting element, is optically coupled to the single mode fiber 231 having the tip sphere 221. The Gaussian beam emitted from the single mode fiber 231 undergoes image conversion by the GI fiber 241 functioning as a lens, and a beam waist is formed at the center of the isolator chip. After that, image conversion is further performed by the GI fiber 242 functioning as a lens, and the light is optically coupled to the single mode fiber 232 again.

In the optical system shown in FIG. 2, since the laser beam is directly optically coupled to the single mode fiber, in order to obtain a high coupling efficiency of about 60%, the curvature of the tip of the single mode fiber 231 can be obtained. Radius about 7 μm
The front ball 221 must be processed and the front ball 221 portion must be placed at a position about 10 μm away from the emitting end of the laser diode 211. However, at a distance of about 10 μm, the front ball 221 of the single mode fiber 231 may come into contact with the laser diode 211 during mounting, and the laser diode 211 may be destroyed.

Although the fibers are fusion-spliced to each other, in the above configuration, there are at least four fusion points (between the single mode fiber 232 and the GI fiber 242,
Between the GI fiber 242 and the coreless fiber 252,
Between the coreless fiber 251 and the GI fiber 241,
And GI fiber 241 and single mode fiber 23
(Between 1 and 1) is required, so that there is a drawback that fusion time is required during manufacturing.

Further, generally, in a silica-based optical fiber, for example, a coreless fiber not doped with germanium (Ge) and a GI fiber doped with germanium (Ge), for example, have a large difference in melting point. Between the fiber 252,
It was difficult to perform fusion splicing at two points between the coreless fiber 251 and the GI fiber 241.

[0007] Therefore, an object of the present invention is to provide a fiber type optical device which can increase the distance from a light emitting element, is easy to manufacture, and has excellent reliability and characteristics.

[0008]

SUMMARY OF THE INVENTION A fiber type optical device of the present invention which achieves the above object is provided with a first optical fiber body on which light emitted from a light emitting element is incident and a light emitted from the first optical fiber body. A second optical fiber body to be incident is configured to be optically connected through an optical element, and a light incidence end of the first optical fiber body is composed of a multimode fiber having a core of at least square-shaped refractive index distribution. At the same time, the second optical fiber body includes a portion in which a multi-mode fiber having a core having a squared refractive index distribution and a single-mode fiber are connected in series in this order from the arrangement side of the optical element. Is characterized by.

Further, the multimode fiber of the first optical fiber body is characterized in that the tip is formed into a spherical lens.

Further, the coreless fibers are connected in cascade in the latter stage of the multimode fiber of the first optical fiber body, and the coreless fibers are connected in cascade in the front stage of the multimode fiber of the second optical fiber body. And 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.

[0011]

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 has a first optical fiber body made of, for example, a silica-based fiber, into which light emitted from a laser diode 11 which is a light emitting element is incident, and the first optical fiber. The light emitted from the fiber body is made incident, and for example, the second optical fiber body of a silica-based fiber is optically connected through an optical element such as an optical isolator or a wavelength filter (optical isolator 51 in this embodiment). It's done like this.

Here, the first optical fiber body comprises a GI fiber 31 which is a multimode fiber having a light incidence end having a core of at least square-shaped refractive index distribution.
The I fiber 31 is the coreless fiber 4 of the same diameter in the latter stage.
1 and fusion bonded. In addition, the second optical fiber body,
From the installation side of the optical isolator 51, the coreless fiber 4
2, a GI fiber 32 that is a fusion-bonded to this and is a multi-mode fiber having a core of a square-shaped refractive index distribution of substantially the same diameter, and a single-mode fiber 61 that is fusion-bonded to this and has a substantially the same diameter. The columns are connected in this order.

The tip of the GI fiber 31 forming the first optical fiber body is formed into a spherical lens (front sphere) 21 having a predetermined radius of curvature. Further, the melting point of the GI fiber 31 forming the first optical fiber body is higher than the melting point of the GI fiber 32 forming the second optical fiber body. That is, the core diameter of the GI fiber 31 is equal to the GI fiber 32.
Since the core diameter is smaller than the core diameter, the concentration of germanium (Ge) doped to form the core in the matrix phase (for example, silicon oxide) of the GI fiber 31 is low, and the melting point is higher. As a result, the GI fiber 3 having a high melting point
1 and a coreless fiber 41 having a melting point close to this melting point
It is possible to easily perform fusion bonding with. Further, the fusion-bonded portions are located between the GI fiber 31 and the coreless fiber 41, between the coreless fiber 42 and the GI fiber 32,
And only three places between the GI fiber 32 and the single mode fiber 61.

In FIG. 1, the light beam emitted from the laser diode 11 can be considered as a Gaussian beam. Further, a light beam having a spot size ω3 is emitted, and image conversion is performed by the compound lens 71 composed of the front sphere 21 and the GI fiber 31. Various parameters and lengths of the front sphere 21 and the GI fiber 31 can be set so that the beam waist 81 is formed in the optical isolator 51 of the isolator chip. At this time, the beam spot size of the beam waist 81 in the optical isolator 51 is ω6.

The Gaussian beam having the beam spot size ω6 is subjected to image conversion again by the GI fiber 32 functioning as a lens, and the single mode fiber 6
The parameters (core diameter, relative refractive index difference) and length of the GI fiber 32 are set so that the beam waist is located at the end face of No. 1 and the beam spot size ω5 matches the mode field diameter of the single mode fiber. be able to.

The ray matrix in the optical system from the laser diode 11 to the central portion of the optical isolator 51 is M1, the distance from the laser diode 11 to the front sphere 21 is d1, the refractive index of the medium between them is n1, and the core of the GI fiber 31 is Is n2, the radius of curvature of the front sphere 21 is R, the focusing parameter A0 of the GI fiber 31, the length of the GI fiber 31 is d2, the refractive indices of the coreless fibers 41 and 42 are n3, and the length of the coreless fiber 41 is d10, optical isolator 5
The refractive index of 1 is n6, the distance from the coreless fiber 41 to the center of the optical isolator 51 (the position where the beam waist is formed) is d9, the wavelength of the light passing through the optical isolator 51 is λ6, and the Gaussian in the optical isolator 51 is The beam spot diameter of the beam is ω6, the laser diode 11
The wavelength of the light emitted from the optical isolator 51 is λ1, the ray matrix in the optical system from the central portion of the optical isolator 51 (the position where the beam waist is formed) to the incident end of the single mode fiber 61 is M2, and the central portion of the optical isolator 51 ( The distance from the position where the beam waist is formed) to the light incident end of the coreless fiber 42 is d8, the length of the coreless fiber 42 is d7, the length of the GI fiber 32 is d5, and the mode field diameter of the single mode fiber 61 is ω5. , The wavelength of the light propagating through the single mode fiber 61 is λ5,
When the elements of the determinant are A, B, C, and D, equations (1) to
It is configured to satisfy (6). Where equation (2),
(3), (5), and (6) are conditional expressions for the propagating light beam being a Gaussian beam.

[0018]

[Equation 1]

By satisfying the above relational expression, the Gaussian beam emitted from the laser diode 11 on the input side can obtain the maximum coupling efficiency when being transmitted to the single mode fiber 61 on the output side.

In the optical system configuration of the comparative example shown in FIG. 2, when the Gaussian beam emitted from the laser diode 211 is to be obtained with a coupling efficiency of about 60% at the final output, the radius of curvature of the front sphere 221 is about 7 μm. You have to make something that becomes. At this time, the distance between the front ball 221 and the laser diode 211 is about 10 μm.

In the optical system configuration according to the present invention, when the Gaussian beam emitted from the laser diode 11 is to be obtained at the final output with a coupling efficiency of about 60%, the length of the GI fiber 31 is adjusted to adjust the length of the sphere. The radius of curvature of 21 can be about 20 μm, and the distance between the front ball 21 and the laser diode 11 is about 35 μm. By doing so, mounting can be facilitated without destroying the laser diode 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. The GI fiber 32 of a fixed length that functions as a lens is fusion-spliced to the single mode fiber 61, and then the coreless fiber 40 of 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, by forming the front ball 21 at the tip of the GI fiber 31, an optical system for coupling with the laser diode 11 is completed.

As a method for mounting an optical element such as an optical isolator in this optical system, the optical element may be mounted after fixing the fiber body in the V groove formed on the substrate, but the optical system is a ferrule. The optical device may be mounted after being inserted and fixed.

For example, when the optical system is mounted on the ferrule, as shown in FIG. 4, 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.
A groove 131 shorter than 1600 μm, for example, is cut in the coreless fiber portion (40), an isolator chip 51 is inserted, and an optical adhesive 141 such as an epoxy resin, an acrylic resin, or a silicone resin is used for adhesive fixing.

In the optical system of the present invention shown in FIG. 3, the radius of curvature of the front sphere 21 and the length of the GI fiber 31 are adjusted to adjust the laser diode 11 and the front sphere 2 at the maximum coupling efficiency.
1 is the distance between the laser diode 11 and the front ball 21 (about 10 μm) in the optical system of the comparative example shown in FIG.
It is possible to make it longer (30 μm or more).

Thus, according to the fiber type optical device of the present invention, the light incident end of the first optical fiber body is at least 2.
The second optical fiber body comprises a multimode fiber having a core having a square-shaped refractive index distribution (GI fiber), and the second optical fiber body has a multimode fiber having a core having a squared-shaped refractive index distribution and a single mode. Since the fiber and the part are connected in series in this order, it is possible to perform optical coupling before and after the optical element with high efficiency, and by adjusting the multimode fiber that functions as a lens, the light emitting element can be adjusted. The distance between the optical fiber and the multimode fiber can be adjusted appropriately, and it becomes possible to easily mount a highly efficient fiber type optical device. In particular, by forming the tip of the multimode fiber of the first optical fiber body into a spherical lens, the distance between the light emitting element and the multimode fiber can be adjusted by adjusting the curvature of this lens.

Further, coreless fibers are connected in cascade at the subsequent stage of the multimode fiber of the first optical fiber body,
The coreless fibers are connected in cascade in the preceding stage of the multimode fiber of the second optical fiber body, and 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. It can be performed with high accuracy and yield, and the fusion splicing of the multimode fiber and the coreless fiber 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

Although an example in which an optical isolator 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 or an optical attenuator is applied instead of the optical isolator. However, other configurations can be appropriately modified and implemented without departing from the scope of the present invention.

[0029]

EXAMPLES Next, examples in which the present invention is further embodied will be described.

The single-mode fiber is a single-mode fiber SM which is a silica optical fiber manufactured by Corning.
F-28 was used, and the GI fiber was a large diameter GI fiber. These parameters are shown in Table 1. In addition,
In the table, MFD is the mode field diameter, and Δ is the relative refractive index difference. In this example, the two GI fibers have the same melting point. A laser diode manufactured by Mitsubishi Electric, model number 725C8F, having a wavelength of 1.31 μm was used.

[0031]

[Table 1]

The GI fiber 32, which is fusion-spliced to the single mode fiber 61, has a length of 781 μm, the coreless fiber 40 has a length of 1600 μm, the GI fiber 31 has a length of 7624 μm, and the radius of curvature R of the front ball 21 is 20 μm. did.

As described above, in the optical system shown in FIG.
The binding efficiency up to 64.2% was obtained. A Faraday rotator as shown in FIG. 1 sandwiched between an analyzer and a polarizer has a size of 0.3 mm × 0.3 mm × 0.8 m.
When the m isolator chip was inserted as an optical element, the coupling efficiency was 57%. At this time, the distance between the laser diode and the front sphere of the GI fiber could be set to 35 μm, and the mounting and manufacturing of the fiber type optical device could be facilitated.

[0034]

As described above in detail, according to the fiber type optical device of the present invention, the light incident end of the first optical fiber body is formed of a multimode fiber having at least a square-shaped refractive index distribution core. 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 Optical coupling before and after can be performed with high efficiency. Further, by adjusting the multimode fiber (GI fiber) that functions as a lens, the distance between the light emitting element and the multimode fiber can be adjusted to be long, and the highly efficient fiber type optical device can be mounted easily and quickly. It will be possible. Furthermore, by making the tip of the multi-mode fiber of the first optical fiber body a spherical lens, the distance between the light emitting element and the multi-mode fiber can be adjusted by adjusting the curvature of this lens. Can provide an excellent fiber type optical device.

Further, coreless fibers are connected in cascade at the subsequent stage of the multimode fiber of the first optical fiber body,
The coreless fibers are connected in series in the preceding stage of the multimode fiber of the second optical fiber body, and the melting point of the multimode fiber of the first optical fiber body is made higher than that of the multimode fiber of the second optical fiber body. The fusion splicing of the multimode fiber and the coreless fiber can be performed easily and quickly. 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.

[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: laser diode 21: front sphere 31, 32: multimode fiber (GI fiber) having a core of a squared refractive index distribution 40, 41, 42: coreless fiber 51: optical isolator 61: single mode fiber 91: ferrule

Claims (3)

[Claims] 1. A first device for allowing light emitted from a light emitting element to enter
A fiber-type optical device configured to optically connect an optical fiber body and a second optical fiber body on which the light emitted from the first optical fiber body is incident, via an optical element, the first optical fiber device The light incident end of the fiber body is composed of a multi-mode fiber having a core having at least a square-shaped refractive index distribution, and the second optical fiber body has a core having a square-shaped refractive index distribution from the side where the optical element is arranged. A fiber-type optical device comprising: a multi-mode fiber having a and a single-mode fiber, and a part connected in cascade 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 tandem in a subsequent stage of the multimode fiber of the first optical fiber body, and a coreless fiber is connected in a tandem in front of the multimode fiber of the second optical fiber body. The fiber type optical device according to claim 1, wherein 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.