JP2560148B2 - Optical fiber terminal with microlens and manufacturing method thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of an optical fiber terminal with a minute lens for various optical parts such as an optical switch, an optical multiplexer / demultiplexer, and an optical isolator, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Miniaturization of optical devices and optical components used with the development of optical communication is desired. Especially in optical isolators, optical circulators, optical multiplexers / demultiplexers, etc.
There is a demand for downsizing and simplification of the structure in a state of being coupled with an optical fiber. In addition, recently, distributed feedback lasers with a narrow spectrum width have been used in high-speed systems for optical communication.
Due to their sensitivity to back reflection, it has also been required that the ends of optical fibers have high return loss.

In general, in a pigtailed optical isolator with an optical fiber, the light emitted from the optical fiber 1 is collimated by a spherical lens 2 or a gradient index lens 3 to an optical device 4 as shown in FIG. Make it incident,
The emitted light is similarly focused again on the optical fiber 1 to be coupled.

[0004]

The conventional collimating system has a problem of adjusting the optical axis positions of the optical fiber and the lens, which requires a high cost for an assembling apparatus and the like, and is expensive as an optical fiber collimating product. Further, in the case of the conventional method, as shown in FIG. 3, a refractive index matching agent 5 made of an organic material is used to prevent reflection. Therefore, there are problems of weather resistance and heat resistance. In order to form an antireflection film on the light entrance / exit surface 6 in FIG. 3, it is carried out with an optical fiber cord attached, so a hard coat that is heated to about 300 ° C. like ordinary vapor deposition. However, since it is not used due to the heat resistance of the optical fiber coating and gas generation, a coating using ion assist or the like is adopted, which is a factor that hinders uniformity and low price.

Further, a fiber collimator light having a sufficiently small luminous flux (for example, 200 μm or less) is required from the viewpoint of miniaturization of an optical device, but the conventional optical fiber collimator can obtain only 300 μm at the smallest. In addition, although the conventional fiber collimator structure can obtain a return loss of only about -27 dB, the tip of the fiber must be angled for coupling with the lens system, or the coupling structure itself must be complicated.

[0006] In recent years, attempts have been made to form minute collimator light. Journal of Lightwave Technology Vol. LT
-5 In No. 9 (1987), a single mode fiber (hereinafter referred to as SMF) is fused with a multimode refractive index distribution fiber (hereinafter referred to as MMGIF) by William L. Emkey, etc. Proposes a join. Here, coupling is performed for a distance of up to about 3 mm with a coupling loss of 0.1 to 1.6 dB. However, with the structure that uses MMGIF, the expansion of the luminous flux is about 40 μm, which is 3 mm.
Since the coupling loss is significantly deteriorated at the above distances, there is no degree of freedom in the collimating distance, and in the manufacturing process, the distribution state of the refractive index distribution fiber part and the wavelength pitch must be adjusted individually while performing mass production. It had the drawback of being unsuitable and expensive in price.

[0007]

Means for Solving the Problems As a means for solving the above-mentioned problems, the present invention comprises a single refractive index containing SiO ₂ or SiO ₂ as a main component at the tip of an optical fiber having a waveguide structure at the center, This is a structure in which fiber lenses with the same outer diameter are formed by fusion bonding, and a spherical lens having a length and radius necessary for beam expansion by Gaussian diffusion is formed.

Specifically, the first optical fiber and a coreless second optical fiber having the same outer diameter and having an equivalent refractive index as the core portion of the optical fiber are spliced to form a second optical fiber. Is formed in a spherical shape, and the diameter of the spherical portion is set to be larger than the fiber outer diameter, which is an optical fiber terminal with a minute lens provided with a function of controlling the emission angle of the light beam, In the second optical fiber, the length is set within the range where the light beam does not contact the outer periphery, and the spherical lens at the tip is formed with an antireflection film that fits the wavelength band used. The outer peripheral portion of is covered with a light absorber and a refractive index matching agent having a refractive index equal to or higher than these. As a manufacturing method,
The spherical portion at the tip of the second optical fiber is formed by the heat melting method. By feeding the tip into the heat melting portion, a spherical lens having a target radius is formed at the tip.

[0009]

EXAMPLE An optical fiber terminal end portion of the present invention was prepared as shown in the example of FIG. 1 (a). It consists of a tip SiO ₂ fiber lens 7, a pigtail fiber main line 8, a ferrule 9 for tip protection, and a tip lens 10. 9 can be omitted. Fig. 1 (b) shows the transmission state of light, SM
Letting z be the distance between the convergence points (beam waists) of the light emitted by F, let the refractive index of SiO _{2 at} the wavelength λ be n, and the degree of spread of the Gaussian beam will be several 1 as it propagates through the fiber lens 7. Indicated by.

[Equation 1] That is, by controlling L, the diameter can be expanded to the vicinity of the optical fiber diameter or more.

Core diameter 10 μm, outer diameter 125 μm, core refractive index approx.
Using the SiO ₂ fiber of the same outer diameter 125μm and 1.47 SMF mains. At a wavelength of 1.31 μm, the maximum length of L is from the number 1 to Lmax
= It should be about 1.1 mm or less. SM in Fig. 1 (b)
The ray matrix of the light passing from F to the beam waist has the relationship of Expression 2 where R is the curvature of the tip lens of the SiO ₂ fiber.

[Equation 2] Further, from the ray formula of the Gaussian beam, Equation 3 is obtained, and the distance z to the beam waist is obtained.

(Equation 3) However, a = λ / πnw ₀ ² .

From the equations (2), (3) and the ray equation of the Gaussian beam,

[Equation 4] Therefore, L = 0.7 mm was selected by calculating from Expression 1 so that the expanded beam diameter would be 80 μm. In this case, the beam diameter is twice as large as the beam diameter of 40 μm according to the conventional proposal. The curvature R of the spherical lens of the SiO ₂ fiber greatly affects the beam waist position z and the beam diameter 2W _z . Table 1 shows the relationship.

[0012]

[Table 1]

Therefore, when the curvature R = 200 μm, the beam waist position is about 1.8 mm and the beam diameter is 88 μm. When the same optical system is measured at the opposite position with the beam waist as the center of symmetry, the coupling loss is 3.6 mm between the lens and the lens. Is 0.5
dB. The return loss was -45 dB when the antireflection film 11 and the refractive index matching agent 5 as shown in FIG. 1C were applied.

In the production of the tip ball, as shown in FIG. 5, the quartz fiber 7 was fed into the arc discharge heat melting portion 13 from above the melting portion to form a curvature R = 200 μm. Feed length h of quartz fiber
So that the volume (cylinder) of is the volume of the front sphere,
I asked.

(Equation 5) As a result, a feed length h = 2.73 mm and a curvature R = 200 μm were obtained.

[0015]

According to the present invention, since the fiber lens can be directly fused to the optical fiber, it becomes a highly reliable optical component unlike the adhesive method, and since there is no interface, reflection loss is small and high coupling efficiency can be realized. And, unlike the conventional fiber collimator, there is an advantage that it can be supplied at a low price as an optical fiber terminal system including a pigtail portion without adjusting with a high tolerance with a lens system.

During the production of the spherical fiber, it is easy to control the volume of the feed length of the quartz fiber and the volume of the sphere by the heat melting method, and the surface tension is used to form the sphere. The degree of sphericity can be improved without deterioration, and there is no problem such as polishing scratches or work-affected layer in the polishing method, and waste of time can be eliminated. Further, since the structure has a high return loss, there is no need to change the internal configuration or adjust the optical axis, unlike the conventional fiber collimator. Due to these factors, the optical isolator, the optical switch, the optical multiplexer / demultiplexer, and the like can be applied to a wide range of applications as an optical fiber array coupling section by further adjusting the curvature.

[Brief description of drawings]

FIG. 1 is a sectional view showing an optical fiber terminal of the present invention.

FIG. 2 is a schematic diagram of an optical fiber optical system.

FIG. 3 is a sectional view of a conventional optical fiber collimator.

FIG. 4 is a schematic diagram showing arc discharge thermal melting according to the present invention.

[Explanation of symbols]

1 optical fiber 2 spherical lens 3 gradient index lens 4 optical device 5 index matching agent 7 SiO ₂ fiber lens 8 pigtail fiber main line 9 ferrule for tip protection 10 tip lens 11 antireflection coating 12 arc discharge part

Claims (6)

(57) [Claims] 1. A first optical fiber and a coreless second fiber having the same outer diameter, which is equivalent to the core of the optical fiber and has a single refractive index, are joined to each other, and a tip of the second fiber is joined. Is a diameter larger than the outer diameter of the optical fiber
By forming the well One spherical shape, the light beam characteristics and the optical fiber terminal with micro lenses to control the emission angle of. 2. The optical fiber terminal with microlenses according to claim 1, wherein in the second optical fiber, the length of the optical fiber is set within a range in which the light beam does not contact the outer circumference of the optical fiber. 3. The optical fiber terminal with a microlens according to claim 1, wherein an antireflection film is formed on the spherical portion at the tip of the second optical fiber. 4. The optical fiber terminal with a microlens according to claim 1, wherein the outer peripheral portions of the first and second optical fibers are coated with a light absorbing agent or a refractive index matching agent having a refractive index equivalent to or higher than these. . 5. The method of manufacturing a microlens according to claim 1, wherein the spherical portion at the tip of the second optical fiber is formed by a heat melting method. 6. The method of manufacturing a microlens according to claim 5, wherein a spherical lens having a target radius is formed at the tip of the second optical fiber by feeding the tip of the second optical fiber into the heat melting portion.