JPH0429104A - Fine optical fiber collimator - Google Patents

Abstract

PURPOSE:To obtain high coupling efficiency and enable inexpensive manufacture by coupling a specific fiber lens at the tip part of an optical fiber. CONSTITUTION:One end of the fiber lens which consists of SiO2 or principally of SiO2 and has a single refractive index and is long enough for beam expansion by Gaussian diffusion is made into a curved surface lens, and an optical fiber 8 which has the same external diameter is united by fusion splicing. Consequently, the fiber lens can be spliced directly to the optical fiber by fusion, so an optical component which has high reliability unlike an adhesion system is obtained and there is no border surface formed, so low reflection loss and high coupling efficiency are realized; and the optical axes need not be adjusted at the time of assembly, so the collimator system which includes even a pigtail part is formed at low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to the structure of a micro optical fiber collimator for various optical components such as optical switches, optical multiplexers/demultiplexers, and optical isolators.

[Background Art] With the development of optical communications, there is a desire for miniaturization of optical devices and optical components used. In particular, optical isolators, optical circulators, optical multiplexers/demultiplexers, and the like are required to be miniaturized and simplified in VA construction when coupled with optical fibers. In general, in a pigtailed optical isolator with an optical fiber, as shown in FIG. , the emitted light is similarly condensed onto the optical fiber 1 and coupled.

[Problems to be Solved by the Invention] Conventional collimating systems have had problems with adjusting the optical axis positions of the optical fiber and lens, and the cost of assembly equipment and the like has been high, making the optical fiber collimating product expensive. Further, in the case of the conventional method, as shown in FIG. 3, a refractive index matching agent 5 made of an organic substance is used to prevent reflection. Therefore, there are issues regarding weather resistance and heat resistance. Furthermore, since the light emitting surface 6 in FIG. 3 is coated with an optical fiber cord attached to form an anti-reflection film, it is coated with a hard coat heated to about 300°C like normal vapor deposition. However, due to the heat resistance of the optical fiber coating and gas generation, a coating using ion assist or the like was adopted, which hindered uniformity and cost reduction. Furthermore, from the standpoint of miniaturization of optical devices, the luminous flux is sufficiently narrow (for example, 1
Although fiber collimated light (below 00Q) is required, conventional optical fiber collimators can only provide at least 300 beams.

Recently, attempts have been made to form microcollimated light.

Journal of Lightwave Tech
nologyVol LT-5No9. In 1987, William L. Emkey et al. proposed coupling a micro-collimated light of up to about 40μ by fusing a multimode graded index fiber (HMGIF) to a single mode fiber (SHF). Here, coupling is performed over a distance of about three wires with a coupling loss of 0.1 to 1.6 dB. However, in the structure using HHGrF, the beam expansion is about 40μ, and there is no flexibility in the collimation distance, and the distribution state and wavelength pitch of the gradient index fiber portion must be adjusted individually during the manufacturing process. However, it has the disadvantage of being unsuitable for mass production and being expensive.

[Means for Solving the Problems] The present invention solves the above-mentioned drawbacks by adding S02 or SiO2 to the tip of an optical fiber having a waveguide structure in the center.
It is a structure in which optical fibers with the same outer diameter are integrated by fusion, with one end of a fiber lens having a single refractive index of 2 as the main component and having the length necessary for beam expansion by Gaussian diffusion, with a curved lens at one end. . Furthermore, the curved lens forms an antireflection coating that is compatible with the wavelength band used.

[Example] An optical collimator tip of the present invention was manufactured as shown in the example of FIG. 1(a). Tip SiQ 2 fiber lens 7
, relay fiber 8. Pigtail fiber main line9. It consists of a ferrule 10 for protecting the tip end, and a relay fiber 8.
The tip protection ferrule 10 can also be omitted. Figure 1(b) shows the transmission state of light, where the diameter of the SHF output beam is 2 w o , the length of the SiO2 fiber lens 7, and the point of convergence (beam waste) of the light emitted from the lens. When the distance is 2, and the refractive index of SiQ 2 at wavelength λ is n, the degree of spread of the Gaussian beam by propagating through the fiber lens 7 is
It is shown by the formula.

That is, by controlling L, it is possible to expand the diameter to near the optical fiber diameter.

Core diameter: 10 mm, outer diameter: 1251 m, core refractive index: approximately 1.47
Use a counterfeit SiO2 or SiO2 fiber with an outer diameter of 125mm, which is the same as the SHF fiber main line. At a wavelength of 1.31M, the maximum length of L is approximately 1.1. It is good if it is less than ll1a×. In FIG. 1(b), the ray matrix of light passing from the SMF to the beam waste has the relationship of the following equation, where R is the curvature of the tip lens of the 5iOz fiber.

Roughly speaking, the ray equation of the Gaussian beam becomes the 0 equation, and the distance to the beam waste @2 can be obtained.

However, a=λ/πnWo2.

It consists of the ■, ■ formula and the Gaussian beam ray formula,
L was calculated from the formula (2) so that the expanded beam diameter would be 90 μm, and L = 0.7 m was selected. In this case, the beam diameter will be twice the beam diameter of 40μ according to the conventional proposal. SiQ, the curvature R of the fiber tip lens is at the beam waste position 2
It also has a large effect on the beam diameter 2W. Table 1 shows the relationship.

[Outgoing beam diameter 2 W = 90μ Therefore, when the curvature R = 200μ, the beam waste position is 1.8m +
The beam diameter was 88μ, and when the beam waist was set as the center of symmetry and the same optical system was installed at the opposite position to measure the coupling state, the coupling loss was 0.5 dB. However, the distance between the lenses is 3.6 am.

"Effects of the Invention" According to the present invention, a fiber lens can be directly fused to an optical fiber, so unlike the adhesive method, it becomes a highly reliable optical component, and since there is no interface, low reflection loss and high coupling efficiency can be achieved. Furthermore, when using an HHGI fiber as a lens, the wavelength pitch affects the light focusing ability, so the lens length must be adjusted with strict intersection.Also, since there is no need to adjust the optical axis during assembly, the collimator, including the pigtail part, It has the advantage that it can be supplied as a system at a low price.In particular, by adjusting the curvature, it can be applied to a wide range of applications such as optical isolators, optical switches, optical multiplexers and demultiplexers, etc. as optical fiber array coupling parts.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the tip of the optical collimator of the present invention. FIG. 2 is a schematic diagram of an optical fiber optical system. FIG. 3 is a cross-sectional view of a conventional optical fiber collimator. 1 Optical fiber 2゛ Ball lens 3, refractive index gradient lens 4: Optical device 7, 3102 fiber lens 8゛ Relay fiber pigtail fiber Main line tip protection ferrule P゛ Fusion part

Claims (4)

[Claims] (1) At the tip of the optical fiber, a fiber lens is coupled, which is mainly composed of SiO_2 or SiO_2 and has a single refractive index, and has a length necessary for beam expansion and a convex curved surface necessary for collimation. A miniature optical fiber collimator featuring: (2) The micro optical fiber collimator according to claim (1), wherein the fiber lens is integrated with the optical fiber by fusion. (3) The micro optical fiber collimator according to claim (1), wherein the optical fiber and the fiber lens forming the waveguide structure have the same outer diameter. (4) The micro optical fiber collimator according to claim (1), wherein an anti-reflection film suitable for the wavelength band used is formed on the curved surface of the fiber lens.