JPH01200224A - Position adjusting method for grating lens - Google Patents

Abstract

PURPOSE:To accurately align plural grating lenses on the same optical axis at intervals of prescribed length by forming a dummy grating, which focuses light from one prescribed point on another prescribed point without aberration, on the surface opposite to the surface where the grating is formed of each grating lens. CONSTITUTION:A positioning grating 11' is formed on the rear face of a substrate of a grating lens G1. The grating 11' has the same axis as a grating 11 and has such optical characteristic that the light from a light source LD14 is focused on the just middle point Q between both grating lenses G1 and G2 without aberration. Similarly, the positioning grating 11' is formed on the rear face of the substrate of the second grating lens G2. The second grating lens G2 is placed on the first grating lens G1, and they are observed with a microscope 17 to adjust the position of the grating lens G2 so that a point image R on an image surface is free from aberration, thereby accurately aligning both grating lenses G1 and G2.

Description

[Detailed Description of the Invention] [Summary] A plurality of grating lenses, especially with their substrate surfaces opposite to the gratings facing each other,
Regarding the position adjustment method of grating lenses that are precisely arranged on the same optical axis at predetermined intervals, we have developed a precise position adjustment method for the spacing and optical axis alignment of multiple grating lenses, which was previously impossible to do only by using a microscope. For the purpose of realizing this, when aligning the axes of a plurality of grating lenses (Gl, G2) having a grating lens (11) on one surface of the substrate at a predetermined interval while observing with an optical microscope (17), A dummy grating (11') is formed on the surface opposite to the grating to focus light from a predetermined point on a predetermined point without aberration.
It consists of:

[Industrial application field]

The present invention relates to a method for aligning a grating lens, and in particular, to positioning a diffraction grating in which a plurality of concentric diffraction gratings are arranged on the same optical axis at predetermined intervals with their substrate surfaces facing each other. Regarding the adjustment method.

Flat grating lenses have the advantages of being simple, compact, and lightweight, and active attempts are being made to apply them to optical systems (eg, optical heads) that use coherent light sources.

On the other hand, however, in the case of an optical device using a plurality of grating lenses, the optical axis adjustment has a disadvantage in that the tolerance margin is smaller than that of a conventional optical lens. This is the point where a diffractive lens (grating lens) is inferior to a general refractive lens. Generally, in an optical system that requires high precision, it is necessary to adjust the optical axis with precision on the order of microns. Furthermore, precision on the order of microns (I!rn) is often required for the lens spacing in the optical axis direction as well.

[Conventional technology]

In this case, two grating lenses G, G2 having concentric diffraction gratings on a substrate 13 as shown in FIG. 4 are arranged at a predetermined interval d with their central axes aligned with the optical axis O as shown in FIG. Suppose.

First, as shown in FIG. 6A, the grating lens G,
. It can be adjusted by using

That is, as shown in FIG. 6B, first observe the center of the first grating lens G with the microscope 17, set the center at the center of the field of view, and place the cross mark 21 (on the eyepiece) perpendicular to the position within the field of view. (It is common to incorporate it in advance). Note that 19 is a microscope objective lens.

FIG. 6D shows a microscope field image in a state where the cross EI]21 is aligned with the center.

The center positioning of the field image is performed by slightly displacing the microscope tube or grating lens G in the optical axis direction using a stage system S, and the position scale of the micro-displacement stage system is read in advance.

Next, the lens G or the microscope tube is moved in the optical axis direction by a predetermined distance d based on the scale using the stage system S1 or S3 (FIG. 6C). After that, the second grating lens G2 is inserted between the objective lens 19 and G, and the relative position of G2 is adjusted in the same way as the stage system S2.
and align the center of G2 with the cross mark 21 (Fig. 6D).

Note that the central axes of G, , and G2 are orthogonal to three axes (x.

It is adjusted in advance so as to coincide with one movement direction of the stage system that can be finely moved with respect to (y, z) (for example, the Z direction).

If Gt is accurately focused using the known method described above, theoretically G and Gt will be aligned on the same optical axis O with an interval d.

[Problem to be solved by the invention]

However, in the above method, the distance between the two grating lenses GI and Gz, the deviation of the optical axes, and the parallelism depend entirely on the mechanical accuracy of the stage system, and therefore there is a limit to the accuracy. Furthermore, when the grating lenses G, , G are fixed so that their gratings 11 are located on opposite sides of the substrate 13 as shown in FIG. 5, the following disadvantages occur in the above method.

That is, as shown in FIG. 7, when the grating 11 is observed from the substrate 13 side, spherical aberration occurs and Gr, G
It becomes difficult to accurately set the distance between t. As is well known, this aberration becomes more pronounced as the thickness of the G (or G2) substrate increases.

An object of the present invention is to realize a method that can accurately and easily align a plurality of grating lenses regardless of their orientation.

In particular, it is an object of the present invention to provide a method for accurately aligning a plurality of concentric grating lenses on the same optical axis at predetermined intervals.

As mentioned above, the conventional method cannot accurately align the axis when the gratings of the grating lens are oriented in opposite directions with respect to the substrate, so the present invention is particularly advantageous to apply in such a case. Yes, but
It is not limited to this in any way.

[Means to solve the problem]

In order to achieve the above object, according to the present invention, when a plurality of grating lenses (G+1, G2) having gratings on one surface of a substrate are aligned at predetermined intervals while being observed with an optical microscope, the grating lenses are aligned at predetermined intervals. The structure is characterized in that a dummy grating is formed on the surface opposite to the grating to focus light from a predetermined point on a predetermined point without aberration.

[For production]

The dummy grating is formed in advance on the opposite surface of the substrate so that the light from one predetermined point is focused on one predetermined point without aberration, so no matter which side of the grating lens the light is irradiated from, there will be aberrations within each grating lens. are completely canceled out, and therefore, by observing with a microscope the image point of the first grating lens and the image point of the second grating lens, it is possible to accurately align the two grating lenses.

Since the dummy grating is unnecessary after the alignment is completed, it is removed using a solvent or the like.

〔Example〕

FIG. 1 shows an embodiment of the optical system used in the present invention.

Basically, two grating lenses G.

G2 is a light source 14 (semiconductor laser LD, etc.) and an optical microscope 1
7 is placed in an optical system consisting of 7. According to the invention, G
,,The most distinctive feature is that a dummy grating 11' for alignment is formed on the back surface of each substrate of G11G2 (the surface opposite to the grating 11) when aligning G2.

That is, first, as shown in FIG. 2A, a positioning grating 11' is placed on the back surface of the substrate of the grating lens G1.
Create. Grating 11' is grating 1
1, and has optical characteristics (lens characteristics) such that when the light source LD 14 and the grating 11 are in a predetermined positional relationship, the light from the point P (LD 14) is imaged on any one point Q without aberration. I can give it.

Note that point Q is located between both grating lenses G+ shown in FIG.
, Gz is a position equal to half (-1) of the distance between them.

Note that it is preferable to stabilize the oscillation wavelength of the LD 14 by adjusting the temperature or the like. In this way, the positions of the light source LD 14 and the grating lens G1 can be determined by observing the point image Q using the microscope 17 and adjusting the positions so as to obtain an aberration-free image.

This adjustment is performed using a known stage system 50A as shown in FIG.
(for light source) or 50B (for Gl). Similarly, a dummy grating 11' for positioning is created on the back surface of the second grating lens G (the surface opposite to the grating 11). As shown in FIG. 2B, this dummy grating 11' is coaxial with the grating 11, and has lens characteristics such that light from a light source (corresponding to the above-mentioned point Q) is focused on a predetermined point R without aberration. .

Therefore, as shown in FIG. 1, after the second grating lens G2 is juxtaposed to the first grating lens G1 at an interval of approximately d (or may be placed overlapping each other initially), the image is formed while observing with the microscope 17. If the position of the grating lens G2 is adjusted by the stage system 50C so that the point image R of the surface I (Fig. 1) has no aberration, the grating lenses G+, Gz, and LD14 are correctly placed at the predetermined positions. .

In other words, the position of G2 may be adjusted using the stage system 50C so that the point image R overlaps the cross mark 21 within the field of view of the microscope. 'An image observed by the microscope 17 is displayed on a monitor 55 by a TV camera 53, if necessary.

As a stage system, one using a piezo element or one using a feed mechanism or the like is generally used.

The dummy grating 11' can be created holographically (coherent light interference exposure) or by electron beam drawing.

Incidentally, in order to easily align the gratings 11 and 11' on both sides of the substrate, it is preferable to provide alignment marks (not shown) on the substrate. After the alignment is completed, the dummy grating can be easily erased by wiping it with a cleaning agent such as acetone.

The gratings 11 of G, , Gt are not necessarily the same, and therefore the dummy gratings 11' are not necessarily the same.

According to the method of the invention, each grating lens G, , G
2 has a structure in which aberrations are absorbed.In other words, the dummy grating is designed so that, for example, when light is irradiated from the back side (11' side) of the substrate at G, it will be focused on point Q without aberration. 11', no aberration problem occurs at all. Therefore, it is possible to align the two grating lens systems without aberration, which was a problem with the conventional method, especially with the grating surfaces facing inward.

〔Effect of the invention〕

As described above, according to the present invention, precise position adjustment of concentric circular diffraction gratings can be easily and reliably performed. In particular, when the substrate surfaces of concentric diffraction gratings face each other, precise position adjustment (lens spacing and lens center axis alignment) cannot be performed using only conventional microscopes due to aberrations.
According to the present invention, it can be performed without aberration.

[Brief explanation of the drawing]

FIG. 1 is a diagram explaining the position adjustment method according to the present invention, and FIG.
Figure A is an illustrative diagram of the first grating lens in the present invention, Figure 2B is an illustrative diagram of the second grating lens in the present invention, and Figure 3 is an illustrative diagram showing an example of the adjustment system used in the present invention. Figure 4 shows a concentric diffraction grating, Figure 5 shows how to align the center axes of two concentric diffraction gratings, and Figures 6A, 6B, 6C, and 6D show conventional concentric diffraction gratings. FIG. 7 is a diagram showing a method for aligning the center axis of a shaped diffraction grating, and FIG. 7 is a diagram showing a conventional drawback (occurrence of aberration). 11... Grating, 11'... Dummy grating, 13... Substrate, 17... Microscope, Gl, G2...
・Grating lens.

Claims (1)

[Claims] When a plurality of grating lenses (G_1, G_2) having a grating (11) on one surface of the substrate are aligned at predetermined intervals while being observed with an optical microscope (17), the gratings of the grating lenses are aligned at predetermined intervals. A method for adjusting the position of a grating lens, characterized in that a dummy grating (11') is formed on a surface opposite to the dummy grating (11') for focusing light from a predetermined point on a predetermined point without aberration.