JPS60129704A - Aspherical optical member for convergence - Google Patents

Abstract

PURPOSE:To mass-produce a lens for an extremely small spot by using plastic by forming an aspherical surface so that its generating line is a smooth curved line at the center part and beltlike parts which are polygonally sectioned and conneced one after another are formed as the peripheral part. CONSTITUTION:A surface 2a of the condenser lens 2 is plane and the other surface 2b is a smooth hyperboloid of rotation at the center part and has a composite curved line with polygonally sectioned conic rings 3 fromed by connecting polygonal lines to said hyperboloid one after another. This composite curved line is rotated around a center axis to form the shape of the lens. Consequently, aberrations of convergence due to slight errors in curved lines and refractive index are eliminated by the interference of light beams from numbers of belt parts to obtain a light spot extremely close to an ideal focus image. Consequently, even when a plastic material is used, aberrations are hard to generate and the lens for an extremely small spot is mass-produced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an aspherical optical member for condensing light that almost eliminates aberrations, is easy to manufacture, and can be suitably used with monochromatic light.

Since the advent of semiconductor lasers, lasers have been able to
2) There are many applications in which light is focused on a very small spot of Lm. 1 to 2 on the disk using a very small spot light.
A method for reading out bit information as small as 1 Lm is used in digital audio discs, optical video discs, and the like. Recently, the number of lenses used has increased rapidly, and along with this, there has been an increasing demand for high-performance, inexpensive lenses that have a simple structure using plastic materials.

As a lens for obtaining such a tiny spot light, an aspheric lens such as a hyperboloid of revolution or an ellipsoid of revolution is used.
It is known to be completely aberration-free in terms of geometric optics.
considered to be the most powerful. However, as will be described later, the deviation of the lens shape from the ideal shape must be extremely small for these aspheric lenses. Furthermore, unlike spherical lenses, aspherical lenses do not have the same shape over the entire area, making it nearly impossible to polish them with high precision.
At present, very few aspherical lenses have been put to practical use to obtain such extremely small spot light.

Even if it were possible to create a mold for such an aspherical lens using expensive T machine tools and skilled polishing techniques, it would be difficult to use this mold due to the high coefficient of thermal expansion and high compression ratio of the plastic material. It is difficult to keep the dimensional accuracy of manufactured plastic lenses within required tolerances. Furthermore, changes in shape and refractive index due to changes in temperature and moisture absorption cause significant fluctuations in the light-gathering properties of the lens, making it impossible to put aspheric lenses made of plastic materials into practical use.

In order to clarify the present invention, it will be theoretically shown below that the relationship between the shape error of an aspherical lens made of plastic material and the aberration caused by it is extremely sensitive.

Here, a hyperboloid of rotation lens, which is most necessary, will be described as an example.

For a rotational hyperboloid lens l as shown in Figure 1, if the eccentricity e of the hyperbola that is the generating line of the hyperboloid completely matches the value of the optical refractive index n of the lens material, the proof will be omitted. However, no aberration occurs. That is, plane 1 perpendicular to optical axis 0
A ray parallel to optical axis 0 that is incident on a is a lens surface 1b that is a hyperboloid of revolution that rotates the generating line of the hyperbola around optical axis 0.
The light is refracted at the second focal point F of the hyperbola with no aberration in terms of geometrical optics.

However, in reality, it is inevitable that a shape error will occur when producing the one-turn hyperboloid lens 1. In order to investigate the influence of this error on the aberrations, we calculated the magnitude of the axial-hypospherical aberration Δδ that occurs when the eccentricity lae has an error of ε and e=n+ε...(1) When illustrated, it becomes a graph diagram shown in FIG.

To explain this calculation to the members, as shown in Figure 3, the first focus of the hyperbola is Fl, the second focus is F, the distance between the origin and the vertex C of the hyperbola is a, and the distance between the origin and the second focus F is The equation of the generating line of the hyperbola when the distance is ae is x2/a2- y2/(a2(e2-1))=1 ・
...It is expressed as (2). Assume that there is an error in the eccentricity e as shown in equation (1) by a minute amount ε, and that the point 4 where the ray intersects the optical axis is shifted by δ from the focal point F,
The relationship between ε and δ is expressed by the following equation (3). however,
Since ε and δ are minute amounts, ε2δ2 (V with higher order terms of 6 or more being zero).

δ=(1+n(y/a))2. ae/(-n2-1)・
...(3) Also, if δ when y/a = 1 is the deviation from the focus of paraxial light and δ0, then δ. = (1+n)2aεban2-1) ...(4)
So, Δδ=δ−δ. When we define axial aberration, Δ δ = [(1+n(y/a))2/(n2-1
)-(n+1)/(n-1)] aε-(5).

This equation (5) can be expressed as Δδ=g·a·ε (6). However, here, g is a constant determined by (y/a) and the refractive index n. In other words, in Figure 2, it is assumed that the incident light is incident at a height of y along the X axis parallel to the optical axis O, and (y/a) is taken as the horizontal axis, and the error of the eccentricity e from n [by It represents the resulting spherical aberration Δδ. Also, Δδ
Specifically, as shown in Fig. 3, the optical axes of incident rays other than the paraxial rays are incident parallel to the optical axis at various heights y/a) from the focal point F for this paraxial ray. It represents the aberration on O.

As is clear from Figure 2, the height y of the incident light from the X axis
It can be seen that as the medium 'd has a small refractive index, the spherical aberration Δδ increases with increasing acceleration. In particular, acrylic, a transparent plastic material, has a refractive index of 1.
．． 491, and the spherical aberration is large. When the focal length #f of a hyperboloid lens is defined as the distance from the vertex C of the lens l to the second focal point F of the hyperbola, f=a (1+e) (7).

Generally, in an ideal lens with a circular aperture that minimizes the focal spot radius R0, the spot radius R0 is Ro It is known that it is given by =1.22·f input/(2Y) (8). As is clear from equation (8), in order to reduce the spot radius R0, it is necessary to make f smaller and Y larger, thereby increasing the aperture of the lens. As an example, f=5mm, 'Y=3mm
(lens diameter 6 mm), n = 1.491 (acrylic), from equation (7), a is approximately 2 mm, and (y/a)
is 1.5, so the value of g is 5 from FIG. Therefore, the value of the axial spherical aberration Δδ is obtained from equation (6) by lo*@m
m. If ε is set to 1/2000, for example, the spherical aberration Δδ becomes 571 m as shown in Fig. 4, and in a hyperboloid lens, the large spherical aberration Δδ is It is clear that this occurs.

As is clear from the above example, not only is it necessary to have extremely high dimensional accuracy when forming a hyperboloid, but if a plastic material is used, the value of its refractive index n must be precisely constant. and the refractive index n
and dimensions are significantly affected by temperature and humidity.
The diameter of the light spot changes depending on the environmental conditions. This serious defect has hindered the industrialization of aspheric lenses made of plastic materials.

An object of the present invention is to provide an aspherical optical member for condensing light for a very small spot, which solves the above-mentioned problems very cleverly, does not easily cause aberrations even when using plastic materials, and is suitable for mass production. The gist of the method is to approximate the generatrix of the aspheric surface with a large number of minutely long broken lines on the sides of an aspherical optical member that has light-converging properties, and move the broken line portion in a direction perpendicular to the generatrix. This feature is characterized in that a large number of belt portions having substantially flat surfaces are formed by this.

Next, the present invention will be explained in detail with reference to the embodiments shown in FIG. 5 and below.

In order to clarify the main points of the present invention, FIG. 5(a),
(b) shows an example of the condenser lens 2 with its features exaggerated. One surface 2a of this condensing lens 2 is a flat surface, and the other surface 2b is approximately a hyperboloid of rotation. The difference from a conventional hyperboloid of revolution is that the range of the diameter D0 extending over the apex C of the central portion of the curved surface of the lens 2 is a smooth hyperboloid of revolution having an eccentricity e equal to the refractive index n of the lens material. Although,
In the area near the periphery, n conical ring zones 3 are provided so as to be in contact with this rotational hyperboloid. The width of this conical ring zone 3, that is, the value of ΔS shown in FIG. As shown in (b), the cross section of each conical ring zone 3 is a broken line segment tangent to a hyperbola.

As shown in FIG. 2, the spherical aberration Δδ increases rapidly as the distance My from the center of the condenser lens 2 increases.
When (y'/a) is about 0.75 to 1.0, it is not very large, so in a hyperbolic lens with the dimensions shown above, if the annular zone 3 is provided around half the lens diameter, For example, since the spherical aberration Δδ occurring in the central part of the condensing lens 2 with an annular zone 3 shown in FIG. 5 without an annular zone is small, it can be ignored. However, since the aperture of the condensing lens 2 becomes small if only the light from this part is used, the spot diameter becomes larger than that when the entire surface of the lens 2 satisfies the ideal condition (e=n), and As is well known as a Fraunhofer diffraction image of a circular aperture, the light amplitude distribution shows an amplitude distribution as shown by the solid line in FIG. 6.

The solid line in Figure 6 is from Kazumi Murata's "Optics" (
Published by Science Publishing, October 1978), page 98, Figure 6.
It is the same as 6.

That is, as shown in FIG. 5, when the annular zone 3 is provided at the periphery from approximately half the lens diameter (this is Do), the annular zone 3 is provided from the part where the annular zone 3 is not attached. The position where the amplitude of the light on the focal plane due to the light is zero, that is, the focal point F
The distance from #X is nl = 1, 220 f/D.

x2=2,23・f input/D.

! 13 = 3, 240f included/D.

becomes.

Specifically, the shape parameters of the lens are F=5mm, Do
= 3 mm, these values xl, x2, x3,
...is approximately, ! 1=2 inputs, x2yo 3.7 inputs, x345.4λ,...-
becomes.

On the other hand, the light from the conical zone 3 at the periphery of the condenser lens 2 is
The light from the annular zone 3 causes interference on the focal plane, resulting in an amplitude distribution as shown by the dotted line in FIG. Qualitative considerations regarding this will be described later, but the light distribution from the annular zone 3 indicated by the dotted line in FIG. 6 is a superposition of light waves from each annular zone 3. Therefore, by theoretically performing Fresnel integration on the light from the entire surface of the lens, the amplitude and intensity of the light spot on the focal plane can be calculated.

The procedure for this theoretical calculation will be explained next. As shown in Fig. 7, ζ-
A point P' near the focal point F on one plane (in cylindrical coordinates, R
The amplitude and phase of the light from the lens at point 2O, Z) are calculated from any point P (r, ψ, second point) on the lens surface to Po
It is determined by determining the amplitude and phase of the light waves that reach the lens and superimposing them over the entire surface of the lens. The phase of the light wave that passes through the apex C of the lens and reaches the focal point F is taken as a reference, and the phase difference with respect to this of the light wave that passes through the point P on the lens surface and reaches the point Po is defined as φ. Furthermore, if the amplitude distribution of the light incident on the lens is rotationally symmetric and represented by a function A(r) of only r, then the composite amplitude including the phase of the light at point Po! teeth.

I can be fooled. However, rQ is the outer diameter of the lens, and K
is a constant.

Considering that the peripheral part of the lens surface is a conical zone 3, 1jK
If we perform the integration for each ring zone 3, add this for all the ring zones 3, and add it to the integral value at the center of the lens, we get
The city of equation (10) can be calculated. This integral is actually quite complex and can only be performed by numerical calculations using a single calculator for electrons, so it is not possible to explain the whole process in detail in this specification, but only the results of the calculations are presented below. Let me illustrate it. That is, the refractive index of the lens material is n=1.4.
When using No. 91 acrylic, the value of error ε according to equation (1) from the aberration-free condition of the hyperboloid plano-convex lens is 1.491.
・(1/1000), 1.491・(2/IC)00)
The intensity of light near the focal point when increasing is 1!12
The distributions are shown in FIGS. 8(a) and 8(b), respectively, with the light intensity at the center of the spot being 1.

As shown in Fig. 4, when there is no conical ring on the lens surface, even when the value of ε is 172,000, the geometrical optical aberration is axial spherical aberration of about 5 pLm, which causes a large focal image. Compared to blurring, when ε is about 3/1000, that is, l/2 when conical zone 3 exists.
Even in the case of 6, which is about 6 times as large as 000, there is almost no change in the diameter of the light spot near the center. When a hyperbolic lens of acrylic acid was cut using the next-order surface generation method and this was confirmed through experiments, results were obtained that were almost consistent with the results shown in FIG. 8. Furthermore, the shape of the light spot was examined by changing the degree of stability of this prototype lens from room temperature to 80° C., but there was almost no change within the range of measurement error. Furthermore, the prototype lens was soaked in a thermos flask containing warm water at 80°C for 24 hours, and the impregnated water content was reduced to approximately 0 by weight.
．． When the sample was taken out and the spot shape was measured, almost no change was observed.

If changes in lens shape are not measured with an accuracy of about 0.1 pm, minute changes in spot shape and corresponding shape changes cannot be measured. Although numerical measurements were not possible, including all of these parameters and changes in the lens shape, the spot shape of the acrylic hyperbolic plano-convex lens with the conical ring zone 3 is approximately equal to the ideal focal image. With a hyperbolic plano-convex lens that does not have a 0-ring zone, we were able to obtain an amazing result in which the ideal focus was maintained, even for approximately 176 fluctuations in these parameter fluctuations performed in this experiment. The significance of the invention becomes clear when compared with the fact that the deviations from the image are observed to be of considerable magnitude.

Although the detailed explanation of the present invention and the explanation of the experimental data are as described above, the theory is too complex to be explained in detail in this specification. presents the following qualitative considerations.

Since light waves have amplitude and phase, in order to intuitively understand this superposition, it is convenient to represent the complex representation of light waves as a two-dimensional vector. That is, the complex number A.
As shown in Figure 9, exp(iψ) is expressed as a vector of length A having an inclination of ψ from the real axis on the Gaussian plane, and these additions are performed by vector composition. .

Below, we will proceed with the discussion by displaying the amplitude and phase of light using this complex vector. FIG. 10(a) shows how light emitted from one conical zone 3 is projected onto the focal plane S. However, this Fig. 10 is a planar cross section that includes the optical axis 0, and in an actual rotating lens, the 10th
The distribution of light waves is obtained by rotating the diagram around the optical axis O.

The light rays emitted from one side 3a of this annular zone 3 and the symmetrical opposite side 3b across the optical axis have a width A2A3 (=Δ
Since S) has the value shown in equation (8), it does not spread much and travels almost parallel, and on the focal plane S, the zero-order light of that diffraction is projected between Q+ and Q2 in Figure 10 (a). The distance from the annular zone 3 to the focal plane S is the ratio p/ΔS of the width ΔS of the annular zone 3, which is the same as ΔS/in. Because of the size of
This diffraction becomes Fresnel diffraction, which is l compared to the intensity of the zero-order light.
The intensity of the first-order and higher-order light is extremely small.

Therefore, we will consider only the zero-order light, and assume that the light flux approximately travels in parallel.The area where the light from one side 3a of the 0-cone ring zone 3 and the light from the other side 3b interfere with each other on the focal plane S. Figure 10(b) shows an enlarged view of the intersection of the two light beams at points A and B on the conical ring zone 3 in Figure 1o(a).
, respectively, are points touching an ideal hyperboloid shown by a dotted line, that is, a hyperboloid whose eccentricity e is equal to the refractive index n, then the rays Lal and Lbl from points A, , and B both have a focal point F. I will pass. Therefore, most of the light rays emitted from between A2 and A3 on one side 3a of one conical ring zone 3 and between B and B3 on the other side 3b are transmitted to Ql"Q7 on the focal plane S.
The two rays will interfere with each other. At one point Q+ on the focal plane S, the ray La2 from the point A2 on one side 3a of the conical zone 3 in Fig. 1O(a) and the ray La2 on the other side 3
0 points A2 to A where the rays Lb3 from point B3 of b interfere with each other
Among the rays La from contact point A, the ray Lal from contact point A intersects with the ray Lb from contact point B'1 at the focal point F, and their phases are equal, so they strengthen each other, and the wavefront of the light is in the traveling direction. Therefore, the wavefront of the ray La1 from the point A on the upper side 3a of the conical ring zone 3 in FIG. 10(a) is at the focal point F.
When the wavefront of the ray La2 reaches the point C2, the ray L
a3 has reached point c3, and the wavefront of the light ray La emitted from the width A2A3 is a straight line 02FC3. Similarly, at the same time, the wavefront of the light ray Lb from the lower side 3b of the conical ring zone 3 becomes a straight line D2FD3 connecting the points D2D3. Therefore, if the wavefront at the focal point F is set to zero phase, Fig. 10 (b
), the phase φa(x) of the ray La at a point X at a distance #X upward from the focal point F on the focal plane S of λ·(11), and the phase φb(x) of the light ray Lb at the same point is φb01)=−2π·Zb/in (12), where zb is the length of the straight line XH.

Note that the negative sign means a delayed phase. The angle θa that the light cabinet La makes with the optical axis is equal to the angle θb that the light ray Lb makes with the optical axis, so if both are expressed as θ, then Za= 'Zb= * Si
lθ ・' (13). Therefore, φa(x) = φb(x) = 2 πX sinθ/in
(14).

For ease of discussion, it is assumed that the amplitudes of the light waves reaching the focal plane S from all conical zones 3 are equal. If the annular zone 3 is arranged between approximately half the diameter Dn of the condensing lens 2, that is, from the point with a diameter Do to the lens periphery, then the angle that the ray from the annular zone 3 makes with the optical axis is Since θ changes from θwin, that is, the angle that the ray from the annular zone 3 at the diameter Do makes with the optical axis, to the maximum value θwax, that is, the angle that the ray from the annular zone 3 at the diameter Dn makes with the optical axis, the point The phase difference φ of the light wave in Therefore, the first ring zone 3 is numbered 1.2, .- from the one closest to the center of the lens, and the outer ring zone 3 is numbered n, and the focal point of the light wave that reaches point X from each ring zone 3 simultaneously. For the light from the upper side of the annular zone 3, the phase difference based on the phase of the light wave of F is φa1, φa2,
...for light from the lower part of ring zone 3, φan,
bl.

It is assumed that φb2, . . . , φbn. Then, the phases φa1 to φan of the light waves from the upper side 3a of the annular zone 3 advance, and the phases of the light waves from the upper side 3b of the annular zone 3 advance.
The phases φh1 to φbn of the light waves from are delayed.

FIG. 11 is an example showing the phase relationship of the light waves from each annular zone 3. The minimum phase angles φal and φb1 are calculated as follows, where θ in equation (14) is θwin, φal=2πx*5in(0m1n)/input φbl=
-2πx*5in(θ1n)/in, and the maximum phase angles φan and φbn are φan=2πx@5in
(θwax) /λφbn= −2πx a 5in(
It is given by θwax)/λ.

As an example, in the case of f = 5 mm, lens diameter D = 6 mm, and ewn = 1.491 (acrylic) as shown above, there is an annular zone 3 from half of the lens diameter to the periphery. Let's consider the case where In this case, the angle that the light that reaches the focal point F from the outermost ring zone 3 of the lens makes with the optical axis is 0max (f), the value of the sine of 5 inches (θw
ax) is 0.427, and the value of the sine of the angle θmin between the optical axis and the light that reaches the focal point F from the innermost part of the annular zone 3 is 5.
injθ5in) is 0.268. Therefore, φa+=-φbls2πX'/λ5in(θl1lin
)=O, 535πx/in (15) φan=-φbn=o, 854wx/in (1B), and the value of this average value φan=-φbn is φa;-φb
Output 0.7wx/input (17).

Since the composite vector obtained by combining the vectors from φal to φan is generated at a phase approximately between φal and φan, φa and φb are considered to be the phases of the composite vector. When X gradually increases from O, 1 phase angle φa1~φ
an gradually increases from 0, and the total vector that combines this vector and the vectors φb1 to φbn is:
When XXO, φa1 to φan are all O, so they are maximum and have the maximum amplitude at the focal point F. When X becomes slightly larger than 0, φal=π/3, φan=2
When π/3, the average phase φd is π/2 and φb is -
Since π/2, the combined vector of both becomes zero and the amplitude becomes zero, which is the case when χ=0.7. When X becomes even larger, the total amplitude becomes negative, that is, the phase becomes π,
Next, when the average phase φa is 13/2π, φb is 13/2π
Since they cancel each other out, the total amplitude becomes zero, and this is the case where x = 2.1 people.The zero-order total amplitude becomes zero because φa = 5 / 2 tc, φa = -572
In the case of
There are 6.4 people, and 1wi convergence becomes smaller as the value of X becomes larger. Based on these considerations, the relationship between the amplitude and X is illustrated in FIG. 12.

As in the above-mentioned example, the diameter of the hyperbolic condenser lens 2 is 6 mm, the focal length f is 5 mm, and the diameter of the portion without the conical zone 3 is 3 mm, which is half the lens diameter. Therefore(
Using equation 8), we calculate the ideal focal radius R0 of only the part of the lens without the annular zone 3, and when input = O, 8p, m, we get the solid curve in Figure 6. , RO=1.22・5-0.8/3 2 people with 1.6 m out...(18). ξ means the radius at which the amplitude of the zero-order light at the focal point is zero. Therefore, in order to obtain a composite of the amplitudes of light from the entire surface of the condensing lens 2, it is necessary to combine the light from the 3 mm diameter portion at the center of the condensing lens 2, that is, the solid line in FIG. It is sufficient to combine the light from 3, that is, with the dotted line in FIG. As a result of this synthesis, as shown in FIG. 13, the zero-order diffracted light becomes sharp, and the first-order and higher-order diffracted lights become weaker, making it possible to obtain an extremely good spot.

It will be described next that the effect of the conical ring zone 3 proposed in the present invention is particularly remarkable when the eccentricity e of the hyperboloid is slightly deviated from the refractive index n, e=n+ε. FIG. 14 shows an example in which the error ε of the eccentricity e is negative. As the eccentricity e becomes smaller, the slope of the tangent to the hyperbolic generatrix at the periphery of the lens 2 becomes smaller, so that the rays from the conical zone 3 at the periphery are closer to the focal plane S than in the case shown in FIG. The central rays intersect in front of. If ring zone 3 does not exist, the 14th
As shown by the solid line in the figure, the light is not focused at the focal point F in terms of geometrical optics, but is distributed between points F' and F'' due to lateral spherical aberration. When the band 3 is present at the periphery of the lens 2, the ray La is shifted to the focal plane S as shown in FIG.
is irradiated between Qal and Qaz, and the light beam Lb is Qb, ~Q
Irradiated during b2. In this way, the rays La and Lb do not overlap completely, but near the focal point F of the paraxial ray, that is, Q
The rays La and 1.b overlap between aI''Qaz and interfere with each other. This interference pattern is exactly the same as that shown in FIG. As shown in the middle, the light from both the upper and lower parts of the annular zone 3 overlaps 5 and does not match, and is diffused at a far distance from the focal point F.
This means that some of the light intensity at the center has been lost. If the deviation of the eccentricity e from the refractive index n in the absence of the annular zone 3 is small, the amount of lateral aberration will remain within 2 to 3 gm, and the amount of movement of the light ray is almost the same as this amount of lateral aberration, so the annular zone The width of the ray from 3 at the focal plane is 20-30g for the lens in the previous example.
m, but this is only shifted by 2 to 3 pm, and the light amplitude distribution near the focal point hardly changes. When the annular zone 3 exists in this way, the spot shape will hardly change even if there is a deviation in the eccentricity "Je."

The deviation from the ideal hyperboloid is not only due to the error in the eccentricity e,
It also occurs due to other causes that occur during manufacturing, such as expansion and contraction of the material, changes in the refractive index n, deformation due to moisture absorption, and changes in the refractive index. It will be easily understood from the above description that the hyperboloid lens with the conical ring zone 3 around the lens according to the present invention can eliminate aberrations caused by these other causes at once.Furthermore, the present invention The embodiment having the annular zone 3 is not limited to hyperboloid lenses, but is extremely useful for optical members using aspheric surfaces such as ellipsoidal lenses and paraboloidal mirrors of revolution. The reason is that if these aspherical surfaces are made accurately, the phases of the light converging at the focal point F will be completely the same, so even if there is a slight error, this same phase condition will be approximate. This is because the above interference effect causes the spot image to become sharper.

A linear cutting blade or a flat grinding face plate is moved so as to be in contact with a quadratic curve, and a rotating quadratic curved surface is created while rotating the lens material. When creating a curved surface, the cutting blade etc. gradually moves while touching the surface of the quadratic curved surface that is rotating around the optical axis and finishes the quadratic curved surface with high precision. By adjusting the combination of the rotation axis around the optical axis and the feed rate of the cutting blade, etc., it is possible to create a spiral conical ring zone 3 on the condenser lens 2 as shown in FIGS. 15(a) and 15(b). I can do it. This spiral conical ring zone 3
In this case, most of the light rays are condensed at the focal point F at the center, just like the above-mentioned conical ring zone 3, and an extremely small light spot can be formed as in the embodiments already described. This method of manufacturing the spiral conical ring zone 3 has high mechanical precision and is extremely convenient for machine operation.
This means that an extremely high-performance condensing lens 2 can be manufactured using a relatively inexpensive machine.

Further, the significance of the present invention is particularly apparent when mass-producing high-performance condensing lenses made of plastic materials. That is, a concave mold is created using a convex rotational quadratic curved surface finished with a cutting blade or the like corresponding to the tangent to the quadratic curved surface as a matrix,
If this is used to manufacture quadratic curved lenses by injection molding of thermosetting resin or casting of thermosetting resin, a large quantity of 2
It is possible to produce a high-performance condensing lens using a curved surface. Originally, when lenses are molded by injection molding or casting, minute changes in surface shape and changes in refractive index occur due to sink marks and changes in the degree of polymerization based on the coefficient of thermal expansion of the resin. Therefore, if the conical zone 3 does not have the effect of maintaining the spot shape, it would be impossible to realize an extremely small light spot with a diameter of 1 to 27 tm using such a mass-produced lens. However, since the conical ring zone 3 according to the present invention has a width As of several tens of gm, it is difficult to undergo gradual deformation due to sink marks or changes in the degree of polymerization, and for the reasons mentioned above, it is difficult to always accurately focus light. It can be achieved. Furthermore, with plastic lenses, their light-gathering properties are subject to significant deterioration due to changes in temperature and moisture absorption; however, by providing the annular zone 3 according to the present invention, the deterioration of light-gathering properties due to these causes can be avoided. It can be prevented.

FIG. 16(a), (N further indicates a lens 4 of another embodiment of the present invention, in which a hyperbolic generatrix having a tangential broken line 1 at the periphery is parallel to the central axis and set at a constant distance. One side 4b has a curved surface created by rotation around the axis,
The other surface 4a is a plane perpendicular to this rotation axis.

Then, an annular zone 5 is formed around the ring-shaped apex as in the previous embodiment. As shown in FIG. 17, this lens 4 condenses light rays parallel to the optical axis 0 that are perpendicularly incident on the plane side 4a into an extremely thin ring shape with a thickness of 1 to 2 gm that continuously forms a focal point F. be able to.

Note that the present invention is not limited to lenses or mirrors having a rotational quadratic curved surface. FIG. 18 shows another embodiment of the present invention, in which a lens or mirror is formed by moving parallel in a direction perpendicular to the generatrix of a hyperbola. It is a hyperboloid columnar lens 6 called a so-called kamaboko lens, and the central part of the hyperbolic generatrix on the surface 6b side is a smooth hyperbola, and the part deviated from the central axis of the hyperbola toward the side is a broken line tangent to the hyperbola. A striped band portion 7 is formed by moving the approximate hyperbola in a direction perpendicular to the generatrix. This band 7 has the same role as the ring 3.5 described above. The opposite surface 6a of the lens 6 is a plane perpendicular to the central axis of the hyperbola, and parallel rays are directed from the flat side 6a parallel to the central axis of the hyperbola, that is, the optical axis 0 of the lens 6, as shown in FIG. If it is incident,
An extremely sharp focus @FF can be obtained. The thickness of this focal line FF can be about 1 to 2 ILm, and such an extremely thin linear image of light is effective for many uses. Note that it is also possible to realize an aspherical toric lens having striped band portions 7 in the same manner.

Each line segment of the broken line used in the compound curve used in the present invention is
Needless to say, it does not have to be a perfect straight line, but may be an approximate straight line such as a convex shape or a convex arc having a radius of curvature that is about one order of magnitude larger than the focal length f of these lenses, or other curved lines. ,Also, even if the corners of the joints of the folded lines are slightly enlarged for some reason during the manufacturing process,
There is no problem as long as the width of this rounded part is sufficiently small compared to the length of each folded line.The fact that such an error is allowed gives an extremely flexible degree of freedom in the manufacturing technology of this optical member. It is something to give.

As described above, in the aspherical optical member for focusing light according to the present invention, the generatrix of the aspherical surface used may be any higher-order curve, such as a quadratic curve such as a hyperbola, a parabola, or an ellipse, and the center portion thereof may be The present invention is characterized in that it is a compound curve that is a smooth curve and has a band of cross-sectional broken lines made by connecting, for example, tangents of this curve to the peripheral part. It proposes an optical member having an approximate curved surface created by rotating it around the central axis or an axis parallel to the central axis, or by, for example, making the radius of rotation infinite, that is, by moving it in parallel. Focusing aberrations due to slight errors in the curved surface or refractive index are canceled out by using the interference of light rays from multiple bands, and the image is extremely close to the ideal focused image despite parameter variations from the ideal lens. It was devised so that a light spot could be obtained.

Therefore, the present invention has made it possible for the first time to mass produce quadratic curved condensing lenses, which were not suitable for mass production because they required extremely high machining precision, for the first time using plastic materials. The ripple effect is extremely large.

[Brief explanation of the drawing]

Figure 1 is an illustration of a hyperbolic lens, Figure 2 is a graph based on the refractive index of axial spherical aberration, Figure 3 is an illustration of a hyperbola, Figure 4 is an illustration of aberration Δδ, and Figure 5 is an illustration of aberration Δδ. The following figures show examples of the aspherical optical member for condensing light according to the present invention, and FIG. 5(a)
is a front view of a hyperboloid lens, (b) is a side view thereof, Fig. 6 is an amplitude characteristic diagram of a diffraction image, Fig. 7 is an explanatory diagram of the principle of calculating the convergence of light waves of a lens with annular zones, Fig. 8 is an explanatory diagram of the calculation result of the focal image of a lens with an annular zone, Figure 9 is a two-dimensional vector diagram, Figure 10 (a) is a diagram of the projected wavefront on the focal plane, (b, )
is an enlarged view, and Figure 11 is a vector diagram of the phase relationship of light.
Figures 12 and 13 are amplitude characteristic diagrams of the diffraction image, Figure 14 is a diagram of the projected wavefront on the focal plane when there is an eccentricity error, and Figure 1
Figure 5 (a) is a front view of a lens with a spiral ring zone, (b)
) is a side view of the lens, FIG. 16(a) is a front view of a lens with two optical axes, FIG. 16(b) is a side view thereof, FIG. 17 is an optical path diagram thereof, and FIG. 18 is a perspective view of a hyperboloid prismatic lens. It is a diagram. 2 is a condenser lens, 3.5 is an annular zone, 4.6 is a lens,
7 is the obi part. Patent applicant Machida Opto Gikenyo Co., Ltd. Patent attorney Yukihiko Hibiya, a)! Arrow B. Figure 1 Figure 10 Figure 11 CII ~ Φan Φb1 ~ Φb1 Turn now bear h Figure 12 Figure 8B15 (a) (b) Figure 16

Claims (1)

[Claims] 1. In the side portion of the aspherical optical member having light condensing properties,
The generating line of the aspherical surface is approximated by a large number of broken lines of minute length, and the broken line portions are moved in a direction perpendicular to the generating line to form a large number of band portions having a substantially flat surface. Aspherical optical member for focusing light. 2. When f is the focal length of the aspherical optical member and input is the wavelength of light, the length ΔS of the broken line is (f/λ)'/I of 00
The aspherical optical member for condensing light according to claim 1, wherein the aspherical optical member has a value of 1 to 2 times. 3. The aspherical optical member for condensing light according to claim 1, wherein the band portion is formed in an annular shape around the rotating aspherical lens. 4. The aspherical optical member for condensing light according to claim 3, wherein the annular band portion is formed in a spiral shape. 5. The aspherical optical member for condensing light according to claim 1, wherein the band portion is formed in a stripe shape on the side of the aspherical columnar lens. 6. The aspherical optical member for condensing light according to claim 1, wherein the material of the aspherical optical member is plastic.