JPS6378007A - Measuring instrument for distance between lens and object - Google Patents

Abstract

PURPOSE:To measure with high accuracy an optical axis distance between a green rod lens and an object, by joining closely an auxiliary green rod lens to the green rod lens, so that their total lens length becomes length for giving the maximum magnification of the lens. CONSTITUTION:To an incident light end face of a green rod lens 11, if possible, an auxiliary green rod lens 30 of the same kind is joined closely so that each end face is aligned. In this case, length l2 is selected so that the total length L of the lens (length l1) and the lens 30 (length l2) becomes length for giving the maximum magnification of the lens. As a result, a variation of a distance S between the lens 11 and an optical fiber 13 appears as a large variation of a diameter (a) of an image P'. In this way, when the diameter (a) of the image P' is measured by using a microscope 21 whose magnification is, for instance, about 50 times, a shift against its design value can be measured, even if the distance S is, for instance, scores of mum. Accordingly, an optical axis direction distance between the green rod lens and the optical fiber can be measured exactly and easily.

Description

[Detailed Description of the Invention] [Summary] When indirectly optically measuring the distance in the optical axis direction between the end face of an existing Grinrod lens and an object adjacent to the Grinrod lens, Measurement accuracy is improved by connecting an auxiliary Greenrod lens with an optical axis length of let

[Industrial application field]

The present invention is a Grinrod lens (Grated Inde
This invention relates to a device for optically measuring the distance between the end face of a Greenrod lens and another object in an optical system using an xRod Lens, simply and accurately using a non-destructive method.

For example, in an optical coupling system in which laser light from a light source is converged onto an optical fiber using a Greenrod lens (a rod-shaped lens with a distributed refractive index), the optical axis distance between the lens and the end face of the optical fiber becomes important. This is because when the Greenrod lens and the optical fiber are in contact, they stress each other, causing problems such as deterioration of optical coupling characteristics due to distortion of the lens, and chipping of the lens due to environmental temperature changes. This is because the system is not realized.

As described above, since the Greenrod lens and the optical fiber need to be fixed apart from each other by a very small distance, a method for accurately measuring that distance is required.

[Conventional technology]

A conventional Gwan lens-optical fiber pole measurement method is shown in FIG.

The Greenrod lens 11 and the optical fiber 13 are connected to the holder 1
5 and are arranged on the optical axis at a predetermined distance S. The optical fiber 13 is also held by a holder (ferrule) 17. Here, when light enters the lens 11 from the left side of the figure, an image (virtual image) P of the tip (left end) of the fiber 13 is formed within the lens 11 by the action of the lens 11. This image P is enlarged and copied on a monitor television 23 etc. through an electron microscope 21, and the size of the image P' is determined by the size of the image (for example, the diameter).
By measuring , the above-mentioned distance S can be measured.

-C In a rod lens, the magnification m is a function of the optical axis length, and the lens length that provides the maximum magnification m, □ is uniquely determined.

However, in the above-mentioned optical system, the size of the Greenloff lens is determined by various design requirements of the optical system (optical coupling characteristics, etc.). Therefore, it is not possible to select the lens length.

If the Greenrod lens is not used at maximum magnification, the image P' will remain unchanged even if the distance S between the lens and the optical fiber is changed.
The size of the image P' hardly changes, so if S is minute, it is impossible to distinguish even S=0 and S〉0.Also, the size of the image P' is measured while slightly changing S, and then conversely, S It has been difficult to know this and keep the value of S within a predetermined tolerance range.

[Problem that the invention seeks to solve]

The problem to be solved by the present invention is that in order to accurately measure the optical axis distance between an existing Greenrod lens and an object (such as an optical fiber) facing it, the magnification of the Greenrod lens must be set to the maximum magnification during measurement. It is essential to use
Therefore, the question is how to achieve this.

As mentioned above, since the magnification of the Greenrod lens is a function of its lens length, it can be seen that the lens length can be adjusted to obtain the maximum magnification.

The purpose of the present invention is to tightly bond an auxiliary Grinrod lens of a lens product that is insufficient to the existing Grinrod lens so that the total lens length of both Grinrod lenses becomes a length that provides the maximum magnification of the lens. It is an object of the present invention to solve the above problems and enable the optical axis distance between a Greenrod lens and an object to be measured with high precision.

[Means for solving problems]

In order to achieve the above object, the present invention provides a device for indirectly measuring the distance in the optical axis direction between an end face of a Greenrod lens and an object adjacent to the Greenrod lens, the apparatus comprising: An auxiliary Greenrod lens having a predetermined optical axis length is joined one end face to the other, and the total length of both Greenrod lenses in the optical axis direction is selected to be a length that provides the maximum magnification of the lens. A lens-object distance measuring device is provided.

[For production]

By adding an auxiliary Greenrod lens, the overall lens length of the Greenrod lens can be selected in any way.
Therefore, a lens length that provides maximum lens magnification can be easily achieved. The auxiliary Greenrod lens is removed after the measurement, as it is no longer needed. When the Greenrod lens is used at maximum magnification, the image size changes greatly even with a small change in the distance MS, and therefore S can be easily and accurately determined from the image size.

〔Example〕

FIG. 1 shows the principle of the present invention, and parts corresponding to those in FIG. 4 are indicated by corresponding numbers. In FIG. 1, 14 indicates the core of the optical fiber.

According to the present invention, the auxiliary Greenrod lens 30, preferably of the same type (although not necessarily), is closely bonded to the incident light measurement end surface of the Greenrod lens 11, with the end surfaces aligned.

By the way, it is known that in the Greenrod lens, the magnification m and the lens length are expressed by the following equation.

However, m: Magnification 9 L: Lens length (L=1!, +zz)
.

no: refractive index of optical axis, A: oil curvature distribution constant.

xl　: Distance between the entrance end face of the lens and the end face of the optical fiber.

x2 ; Distance between the exit end face of the lens and the image Among the above parameters, n6. A is the Greenrod lens 11 used.
It is a constant determined by xl + xZ, and the design value when designing the necessary optical system (for example, optical coupling system) can be substituted, so the lens length that gives m, llx, which maximizes m, can be easily found. Seek.

FIG. 2 shows an embodiment of the present invention applying the principle of FIG. 1, except that an auxiliary Greenrod lens 30 is held by a holder 33 and one end face is joined to the existing Greenrod lens 11. It is similar to FIG. Holder 3
3 is removably fixed to the outer periphery of the holder 15 with bolts 35, for example. Note that 24 indicates a pattern mask attached to make the screen of the monitor 23 easier to see.

Figure 3 shows the relationship between the diameter a and the distance S of the image P' when the auxiliary Greenrod lens is attached and the lens has maximum magnification (the present invention) and when the auxiliary Greenrod lens is not attached (prior art). FIG. 2 is a graph showing experimental results. In addition, the optical fiber core 108m1, the pinch of the Greenrod lens 12 = 0.16, the pitch of the auxiliary Greenrod lens 30 -
It was set as 0.08.

As is clear from FIG. 3, the Greenrod lens 11 (length -2+) and the auxiliary Greenrod lens 30 (length = 12
) and select 12 so that the total length L (L=j!++Zz) maximizes m in the above equation, the distance S between the lens and the optical fiber can be changed. appears as a large change in the diameter a of the image P'. Therefore, by measuring the diameter a of the image P', it is possible to accurately measure the deviation of S from the designed value, even if it is in the order of several tens of micrometers, if the magnification of the microscope 21 is, for example, about 50 times.

In addition, it will be understood that in the conventional technology (broken line) in FIG. 3, S hardly changes.

〔Effect of the invention〕

As described above, according to the present invention, the distance in the optical axis direction between the Grinrod lens and the object can be changed by simply adding an auxiliary Grinrod lens whose length is insufficient to the lens length that provides the maximum magnification of the Grinrod lens determined by calculation. can be measured accurately and easily.

[Brief explanation of the drawing]

FIG. 1 is a diagram explaining the present invention in detail, FIG. 2 is a sectional view showing an embodiment of the present invention, and FIG. 3 is a comparison between the present invention and the prior art, showing the distance between the lens and the object and the size of the image formed. FIG. 4 is a diagram illustrating a conventional measurement method. 11... Greenrod lens, 13... Optical fiber, 30... Auxiliary Greenrod lens.

Claims (1)

[Claims] A device for indirectly measuring the distance in the optical axis direction between an end face of a Grinrod lens and an object adjacent to the Grinrod lens, wherein an auxiliary Grinrod lens having a predetermined optical axis length is attached to the Grinrod lens between the end face and the object adjacent to the Grinrod lens. A lens-object distance measuring device characterized in that the total length in the optical axis direction of both Greenrod lenses is selected to give the maximum magnification of the lens when the end faces are connected.