JPH0511137A - Optical collimator - Google Patents

Abstract

PURPOSE:To obtain stable optical coupling characteristics by reducing temperature characteristic variation of a light output. CONSTITUTION:The outer peripheral part in a cylindrical lens 1 is soldered and fixed uniformly in a lens holder 2, the bare wire 3a of an optical fiber 3 is inserted and fixed by adhesion in a sleeve 5 which is nearly equal in coefficient of thermal expansion and arranged on the internal end surface 1b of the cylindrical lens 1 through spacer 6, and the end surface of the sleeve 5 is pressed and held inside with an elastic body, thereby reducing variation in the relative position between the cylindrical lens 1 and the tip end surface 3b of the optical fiber 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical collimator applied to a detecting section of an optical fiber sensor.

[0002]

2. Description of the Related Art A conventional optical collimator attaches importance to the optical coupling efficiency and the reduction rate of reflected return light. Therefore, the optical coupling efficiency can be improved by fixing the lens and the optical fiber at optimum positions. Consideration has been given to reducing the amount of reflected return light by polishing the end faces obliquely.

For example, JP-A-60-159712,
In Japanese Utility Model Laid-Open No. 61-160406, the bare wire 3 of the optical fiber 3 fixed to the sleeve 5 is shown in FIG.
In order to collect a parallel light flux on the front end surface 3b of a and to perform efficient optical coupling, the lens 1 is fixed by the adhesive fixing portion 13 at approximately the center of the lens holder 2, and the inner end surface 1b of the lens 1 and the light A structure has been proposed in which a spacer 6 is interposed between the fiber tip surface 3b to match the optical axes and to appropriately set the focal position.

[0004]

However, in the conventional optical collimator configured as described above, the lens 1 and the tip portion 3a of the optical fiber 3 are minutely changed with the change of the ambient temperature (-20 ° C to + 70 ° C). No particular consideration was given to such misalignment. For example, since an adhesive is used for the adhesive fixing portion 13 of the lens 1, when the outer peripheral portion of the lens 1 is fixed by the adhesive, a non-uniform fixing state tends to occur. 1
Changes in angle may occur. Also, the optical fiber 3
The sleeve 5 to which is adhered and fixed is fixed to the lens holder 2 by the adhesive fixing portion 14 using an adhesive, but is easily affected by the difference in thermal expansion coefficient between the lens holder 2 and the sleeve 5. Further, in the case of the heat-curable adhesive, the error in the initial position setting between the lens 1 and the optical fiber 3 becomes large. For this reason, the coupling characteristics of light often change beyond the permissible variation due to changes in ambient temperature, making it difficult to use as a component such as an optical sensor of the type that detects optical output intensity. In addition, 15 is an optical fiber adhesive fixing part.

A change in the relative position between the lens and the optical fiber has a great influence on the optical coupling characteristic even if the change amount is minute. This slight change in position is the difference in the coefficient of thermal expansion of the components. Differences in clearance between mounted parts and uniformity of fixing position and fixing state of lens, optical fiber and sleeve. Depends on Matching all coefficients of thermal expansion of components is difficult in practice. Further, in order to reduce the influence of the difference in thermal expansion coefficient, it is conceivable to bond and fix the lens 1 near the inner end surface 1b and near the tip of the sleeve 5, but in this case, the outer peripheral portions of the lens 1 and the sleeve 5 are It is difficult to bond them uniformly.

Therefore, the present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to provide an optical collimator capable of obtaining stable optical coupling characteristics with respect to changes in ambient temperature. There is.

[0007]

In order to achieve such an object, in an optical collimator according to the present invention, a cylindrical lens is fixed by soldering an outer peripheral portion of the cylindrical lens on the optical fiber side to a lens holder inner wall surface. A bare wire is inserted and fixed in a sleeve whose thermal expansion coefficient is almost the same, and is arranged on the inner end surface of the cylindrical lens via a spacer.The sleeve end surface is pressed and held by the elastic body on the cylindrical lens side, and It is configured to reduce the fluctuation of the relative position with respect to the fiber tip surface.

[0008]

In the optical collimator according to the present invention, since the relative position between the lens and the front end surface of the optical fiber is held constant, the optical coupling characteristic can be stabilized even when the ambient temperature changes.

[0009]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a sectional view showing the configuration of an embodiment of an optical collimator according to the present invention. In the figure, a gradient index cylindrical lens (hereinafter referred to as a lens) 1 is, for example, S
It is housed in a lens holder 2 made of US430 material, and an outer peripheral portion in the vicinity of an inner end surface 1b opposed to the outer end surface 1a thereof is fixedly arranged by a solder fixing portion 7 which is melted and fixed uniformly by melting ring solder. In this case, the lens holder 2 in which the outer periphery of the lens 1 on the optical fiber side is housed
A hollow space 2a is formed on the inner wall surface of the lens as shown in the enlarged cross-section of FIG. 2 (a), and after the lens 1 is set at a predetermined position, the ring-shaped solder is placed in the space 2a. 8 is set and heated to melt in the void portion 2a, and as shown in FIG. 2B, the lens 8 is closely attached to the outer peripheral portion of the lens 1 on the optical fiber side and uniformly fixed by soldering. Also, FIG.
In the optical fiber 3, the bare optical fiber 3a is inserted into the sleeve 5a for bare optical fiber made of, for example, zirconia material having a similar thermal expansion coefficient, and is bonded and fixed by the adhesive fixing portion 9. Wire sleeve 5a
Is inserted into the lens holder 2 and the optical fiber coating portion 3c is adhesively fixed to the optical fiber core wire sleeve 5b. The optical fiber core wire sleeve 5b is provided with a gap G for the bare optical fiber sleeve 5a. Is fixed to the other end of the. In this case, the surfaces of the optical fiber tip surface 3b and the end surface of the optical fiber bare wire sleeve 5a are ground so that they are flush with each other, and are formed on the same plane. Further, a spacer 6 for setting an initial position between the lens 1 and the optical fiber 3 is interposed between the inner end surface 1b of the lens 1 and the sleeve 5a for the bare optical fiber of the sleeve 5, and the optical fiber core is further provided. The compression spring 10 is arranged on the flange portion of the wire sleeve 5b and is screwed to the opening of the lens holder 2 by a coupling nut 11. By tightening the coupling nut 11, the optical fiber naked The optical fiber bare wire sleeve 5a to which the wire 3a is fixed is crimped, and the pressure generated here causes the distance between the lens end surface 1b and the end surface of the bare optical fiber sleeve 5a (optical fiber tip surface 3b) to be constant. Held in.

According to such a configuration, as shown in FIG. 3, the influence of the distance change Δx between the end surface 1b of the lens 1 and the end surface 3b of the optical fiber 3 on the optical axis, the central axis of the lens 1 and the light Since the influence of the change Δy in the distance from the center axis of the fiber 3 and the influence of the change Δθ in the angle between the center axis of the lens 1 and the center axis of the optical fiber 3 can be surely removed, the lens 1 is not affected by the change in the ambient temperature. End face 1b of optical fiber 3 and end face 3b of optical fiber 3
The change in relative position between and can be minimized,
Therefore, the distance between both end surfaces can be kept substantially constant regardless of the presence or absence of thermal expansion of the component due to the change in ambient temperature. Further, since the lens holder 2 and the sleeve 5 are detachable, it is easy to set the distance between the end surface 1b of the lens 1 and the end surface 3b of the optical fiber 3 at an optimum position.

FIG. 4 is a cross-sectional view of an essential part showing the structure of another embodiment of the optical collimator according to the present invention. 1 is different from FIG. 1 in that the tip of the optical fiber 3 is fixed to the tip of the optical fiber bare wire sleeve 5a by a solder fixing portion 12.

With this structure, it is possible to further reduce the influence of the difference in thermal expansion coefficient between the optical fiber 3 and the bare optical fiber sleeve 5a.

Next, a temperature characteristic test was conducted using two pairs of samples for the optical collimator having the conventional configuration and the optical collimator having the configuration according to the present invention. The ambient temperature of the conventional optical collimator is -20 ° C to + 70 ° C.
As a result of actually measuring the change in the optical output by changing
Data as shown in (a) and FIG. 5 (b) were obtained. That is, it was found that in the optical collimator having the conventional configuration, the optical output greatly changed with the change of the ambient temperature, and the optical coupling characteristic changed more than the allowable variation value. On the other hand, as a result of performing the same temperature characteristic test on the optical collimator according to the present invention, the data as shown in FIGS. 6 (a) and 6 (b) were obtained. That is, in the optical collimator having the configuration according to the present invention, it was confirmed that the change in the optical output was extremely small with respect to the change in the ambient temperature, and the optical coupling characteristic was suppressed within the fluctuation allowable value.

[0014]

As described above, according to the present invention,
Even if the ambient temperature changes, it is possible to minimize the variation in the relative position between the lens and the end of the optical fiber.
The optical coupling characteristics can be made more stable. Also, 2
Even when light of different wavelengths is introduced into the same optical collimator, the fluctuation of the coupling characteristics of each light is small, and the distance between the lens and the optical fiber is set optimally to reduce the light quantity ratio. Since the fluctuation can be extremely reduced, it is possible to obtain an extremely excellent effect such that an optical fiber sensor of a light intensity type having an excellent temperature characteristic can be configured.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration according to an embodiment of an optical collimator according to the present invention.

FIG. 2 is an enlarged sectional view of an essential part for explaining a joint structure between a lens and a lens holder according to the present invention.

FIG. 3 is a diagram for explaining the effect of the embodiment of the present invention.

FIG. 4 is a sectional view of an essential part showing the configuration of another embodiment of the optical collimator according to the present invention.

FIG. 5 is a diagram showing temperature characteristics of a conventional optical collimator.

FIG. 6 is a diagram showing temperature characteristics of the optical collimator according to the present invention.

FIG. 7 is a diagram showing a configuration of a conventional optical collimator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Refractive index distribution type cylindrical lens (lens) 1a Outer end surface 1b Inner end surface 2 Lens holder 2a Hollow part 3 Optical fiber 3a Optical fiber bare wire 3b Optical fiber tip surface 3c Optical fiber coating part 5 Sleeve 5a Optical fiber bare wire sleeve 5b Optical fiber core sleeve 6 Spacer 7 Lens solder fixing part 8 Ring-shaped solder 9 Adhesive fixing part 10 Compression spring 11 Coupling nut 12 Lens adhesive fixing part 13 Lens solder fixing part 14 Sleeve adhesive fixing part 15 Optical fiber adhesive fixing part

Claims (1)

Claim: What is claimed is: 1. An optical collimator in which a tip end surface of an optical fiber is arranged at a focal position of a cylindrical lens, wherein the cylindrical lens has an outer peripheral portion on the optical fiber side on a lens holder inner wall surface. Soldered and fixed, the bare wire of the optical fiber is inserted and fixed in a sleeve having a thermal expansion coefficient substantially matching, and is arranged on the inner end surface of the cylindrical lens through a spacer, and the end surface of the sleeve is on the cylindrical lens side. An optical collimator which is held under pressure by an elastic body to reduce fluctuations in the relative position between the cylindrical lens and the end surface of the optical fiber.