JPH1062648A - Optical fiber collimator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber collimator that has a large amount of reflecting damping effect without a side-blow to the external frame, and is excellent in workability with a simple structure and also is excellent in the function for converging the light rays diverged from an optical fiber to the optical fiber. SOLUTION: In an optical fiber collimator that has a function for converging the light rays diverged from an optical fiber 1 to the optical fiber and that is made up by combining the optical fiber 1 and a collimator lens 2, the optical fiber whose end has been obliquely polished is tilted and fixed to the center line of the collimator lens at an inclined anle as shown by the expression θ= sin<-1> (n*sinθ)-θ', where θ= the inclination angle of the optical fiber, θ' = the polishing angle of the optical fiber, and n = the reflective index of the optical fiber core.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber collimator having a large return loss and having no tilt with respect to an external frame.

[0002]

2. Description of the Related Art An optical transmission system using an optical fiber includes an optical component having various functions, such as an optical isolator for blocking reflected light returning in the reverse direction, a specific wavelength, and the like. It is necessary to insert an optical filter or the like that blocks or transmits light. When these optical components are used, the optical fiber is cut and an element having the above function is inserted between the optical fibers.However, since the light emitted from the optical fiber still diverges, the light is transmitted through the element. However, there is a drawback that the coupling efficiency with the optical fiber on the light receiving side is significantly reduced.

[0003] In order to solve the above-mentioned drawbacks, an optical fiber collimator is usually used in an optical transmission system using an optical fiber as a method of converting divergent light into parallel light using a lens. This optical fiber collimator integrates an optical fiber and a lens, and is assembled so as to emit a parallel beam. By keeping a pair of optical fiber collimators facing each other and inserting a functional element between them, the coupling loss is kept small. Optical components can be incorporated as they are.

However, when an optical component is inserted between optical fibers, there is a problem not only in coupling loss but also in reflected light from the cut end of the optical fiber. In general, the power reflectance (R) at the interface between two materials having the refractive indices n ₁ and n ₂ is represented by the following equation (2).

[0005]

(Equation 1)

In this case, among the reflected light, in particular, the reflected light at the interface between the optical fiber core and the air adversely affects the transmission system. Therefore, in order to reduce the reflectance at the interface, a non-reflective coating made of a dielectric thin film is required. It is generally applied to optical fibers. However, it was difficult to completely suppress reflection by this method.

Therefore, in recent years, in order to solve this problem, a method has been adopted in which the end face of the optical fiber is polished with an inclination of usually about 6 to 8 °. According to this method, the recombination of the reflected light into the optical fiber is suppressed, and the return loss of 50 to 60 dB or more required in the optical transmission system can be obtained.

[0008] However, problems remain in this method. That is, as shown in FIG. 1, the light emitted from the optical fiber 1 polished obliquely (θ ′) is emitted (θ) inclined (θ) with respect to the center axis of the optical fiber 1 due to refraction of the light (FIG. A)). When the optical axis is tilted with respect to the optical fiber in this manner, a step of maximizing the light coupling efficiency by facing a pair of collimators (collimator alignment step).
In addition, there is a disadvantage in that the step of adjusting the lens to a position where parallel light is obtained (the step of positioning the lens) becomes complicated.

As a solution to this drawback, it is common to convert the divergent light inclined within the effective diameter of the lens into a beam parallel to the central axis of the fiber. However, if the optical axis is inclined with respect to the optical fiber as shown in FIG. 1 (B), the outgoing light is off the center of the collimator lens 2 so that the lens aberration is easily picked up, and the lens positioning step described later is difficult. There was a problem of becoming.

There is also a method using a wedge-shaped compensator 3 as shown in FIG. However, when such a wedge-shaped compensating plate for optical axis correction is used, the reflected light from the compensating plate is used despite the fact that an obliquely polished optical fiber is used to secure a large return loss. In some cases, the optical fiber is re-coupled to the optical fiber, and a sufficient amount of return loss cannot be obtained. In addition, there is a problem that the number of parts increases and the assembly process becomes complicated.

Here, usually, the light emitted from the optical fiber polished obliquely is inclined from the central axis of the optical fiber as described above. In this case, as described above, the inclination can be corrected within the effective diameter of the lens, but it is difficult to position the lens by a commonly used method of assembling an optical fiber collimator. That is, generally, the assembly of the optical fiber collimator is performed by the steps shown in FIG. First, as shown in FIG. 2A, the optical fiber 1 is set on the frame 5 so that the beam emitted from the optical fiber collimator 4 serving as a reference has maximum coupling, and then, as shown in FIG. 2B. The collimator lens 2 is positioned so that the coupling efficiency to the optical fiber 1 is maximized, and the optical fiber 1 and the lens 2 are fixed.

When such an assembling method is adopted,
In order to produce an optical fiber collimator having no tilt with respect to the optical fiber 1 and the frame 5 using the obliquely polished optical fiber, a reference beam and obliquely polished light are used in a process as shown in FIG. Fiber 1
It is necessary to set the optical fiber 1 so that the (frame 5) is parallel. At this time, since the coupling efficiency to the optical fiber 1 is not maximized, there is a disadvantage that setting is difficult.

In the process shown in FIG. 2D, when the collimator lens 2 is moved closer to the optical fiber 1, the coupling efficiency is adjusted to be maximum.
It was necessary to move the beam in a plane perpendicular to the beam and approach it diagonally, which was very troublesome to adjust.

As described above, the above steps are complicated and the alignment and positioning of the collimator are very troublesome, and the development of a higher-performance optical fiber collimator free of these problems has been desired.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides an optical fiber collimator which has a large return loss, has no tilt with respect to an external frame, has a small number of parts, and can easily perform a step of positioning a collimator lens. The purpose is to provide.

[0016]

According to the present invention, there is provided an optical fiber collimator comprising a combination of an optical fiber and a collimator lens. On the other hand, the following equation (1) θ = sin ⁻¹ (n · sin θ) −θ ′ (1) (where, θ is the inclination angle of the optical fiber, θ ′ is the polishing angle of the optical fiber, and n is the light The optical fiber collimator is characterized in that the optical fiber collimator is tilted and fixed at an inclination angle represented by a refractive index of the fiber core.

According to the present invention, when an optical fiber whose end face has been conventionally polished obliquely is used, the optical fiber is fixed and used by being inclined at a specific angle.
It is possible to manufacture an optical fiber collimator without tilt that makes it easy to align the collimator without complicating the process.It is simple, has good workability, has a large return loss, and minimizes the number of parts. It is possible to simplify the assembling process, and to obtain an optical fiber collimator having an excellent function of condensing light diverging from an optical fiber to another optical fiber.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to FIGS.
This will be specifically described with reference to FIG. An optical fiber collimator according to one embodiment of the present invention is, for example, an optical fiber collimator comprising a combination of an optical fiber 1 and a collimator lens 2 as shown in FIG. The lens 2 is arranged so as to be inclined with respect to the central axis of the lens 2 by an inclination angle θ represented by the following equation (1), and the optical fiber is fixed to the outer frame 5 by being inclined at the same angle. θ = sin ⁻¹ (n · sin θ) −θ ′ (1) (where, θ is the inclination angle of the optical fiber, θ ′ is the polishing angle of the optical fiber, and n is the refractive index of the optical fiber core. .)

In the above-described optical fiber collimator, as the collimator lens, for example, an aspherical lens can be used in addition to a spherical lens and a gradient index lens.

Next, in order to confirm the above effect, the tip was
An optical fiber collimator was manufactured by the following procedure using a single mode fiber polished at an angle and an aspherical collimator lens (see FIG. 4). The optical surface was provided with a non-reflective coating for use wavelength of λ = 1.55 μm. Θ = sin ⁻¹ (n · sin θ) · θ ′ = 3.6 ° in advance
The optical fiber 1 (which is fixed to a ferrule made of zirconia and then polished at an angle of 8 °) was fixed to a metal frame 5 having a hole which was machined at an angle of (θ ′ = 8 °, n = 1.444). (FIG. 4 (A)). The position and angle between the optical fiber and the frame 5 were adjusted so that the parallel light from the reference collimator 4 was maximally coupled to the optical fiber 1 (FIG. 4B). The collimator lens 2 was slightly moved in a direction perpendicular to the beam at a position separated from the focal length of the lens, and adjusted so as to obtain the maximum coupling efficiency (FIG. 4C). Thereafter, the collimator lens 2 was moved closer to the optical fiber 1 to determine a position where the maximum coupling efficiency was obtained, and the frame 5 and the collimator lens 2 were fixed (FIG. 4D).

The return loss of the optical fiber collimator (example) prototyped by the above method was measured. For comparison, the return loss of a collimator (comparative example) using a conventional compensator was also measured. FIG. 5 shows the results. Return Loss Measurement Method Measurement was performed using a precision reflectometer as a relative evaluation method.

From the results shown in FIG. 5, it has been confirmed that the optical fiber collimator of the present invention has an improved return loss compared to the return loss (50 dB or less) of the optical fiber collimator of the comparative example.

[0023]

The optical fiber collimator of the present invention has a large return loss, does not tilt the external frame, is simple and has good workability, and has a function of condensing light diverging from the optical fiber to the optical fiber. Is excellent.

[Brief description of the drawings]

FIGS. 1A to 1C are state diagrams of beam images of light emitted from optical fibers polished at an angle.

FIGS. 2A to 2D are schematic views showing the order of an assembling method of an optical fiber collimator.

FIG. 3 is a schematic view showing the assembly of the optical fiber collimator of the present invention.

FIGS. 4A to 4D are schematic views showing the order of manufacturing steps of the optical fiber collimator of the embodiment.

FIG. 5 is a graph showing the frequency with respect to the return loss of the optical fiber collimator of the example and the comparative example.

[Description of Signs] 1 Optical fiber 2 Collimator lens 3 Compensator 4 Reference optical fiber collimator 5 External frame

Claims (1)

[Claims] 1. An optical fiber collimator comprising a combination of an optical fiber and a collimator lens, wherein the optical fiber whose tip is polished obliquely is defined by the following equation (1) with respect to the center line of the collimator lens: θ = sin ⁻¹ (n · sin θ) ) −θ ′ (1) (where, θ is the inclination angle of the optical fiber, θ ′ is the polishing angle of the optical fiber, and n is the refractive index of the optical fiber core). An optical fiber collimator, which is fixed.