JP2022153113A - Light blocking film formation method and double layer type diffraction optical element - Google Patents

Abstract

To provide a light blocking film formation method capable of easily forming a light blocking film and a double layer type diffraction optical element.SOLUTION: The light blocking film formation method includes forming a light blocking film on a double layer type diffraction optical element that comprises a pair of plastic-made diffraction grating layers each having a diffraction optical surface with a plurality of concentrically and circularly arranged protrusions thereon and having a sawtooth-shaped cross section in a radial direction, and in which the convexoconcaves of the diffraction optical surfaces are fitted with each other. The light blocking film formation method further includes defining one inclined plane of two inclined planes extending from a ridge line of the protrusions as lattice plane and defining the other inclined plane as side wall surface, using a laser beam to carbonize part of the diffraction grating layer in a borderline region between facing side wall surfaces of the pair of diffraction optical surfaces being fitted, thereby forming a light blocking film that blocks a transmitted beam transmitting through the borderline region from among incident beams incident into the diffraction optical surface.SELECTED DRAWING: Figure 9

Description

The technology of the present disclosure relates to a light shielding film forming method and a multilayer diffractive optical element.

Multilayer diffractive optical elements are known. A multi-layer diffractive optical element includes, for example, a diffraction grating section having a pair of diffraction grating layers, and a pair of lenses bonded to both surfaces of the diffraction grating section. A multilayer diffractive optical element that combines a diffraction grating section and a lens is also called a diffractive lens. Diffractive lenses have chromatic aberration properties that are opposite to lenses that exhibit only normal refractive action. Therefore, the diffractive lens is used, for example, as a lens for correcting chromatic aberration.

Patent Document 1 describes a diffraction lens having a light shielding film. The light-shielding film can cut unnecessary light such as obliquely incident light incident on the diffraction lens from an oblique direction, so that ghost, flare, and the like can be reduced. In Patent Document 1, the light shielding film is formed by a vapor deposition method and a coating method such as an inkjet process.

JP 2012-18380 A

However, the vapor deposition method and the coating method require a material for forming the light-shielding film in addition to the diffraction grating layer, and also require steps of forming and removing a mask to cover areas other than the region where the light-shielding film is to be formed. , there is a problem that the method of forming the light shielding film becomes complicated.

The technique of the present disclosure provides a light-shielding film forming method and a multilayer diffractive optical element that enable the light-shielding film to be formed more easily than conventional methods.

A light-shielding film forming method according to the technology of the present disclosure includes a pair of diffraction grating layers each having a plurality of ridges arranged concentrically and each having a diffractive optical surface with a sawtooth-shaped cross-section in the radial direction, comprising: A light-shielding film forming method for forming a light-shielding film on a multi-layered diffractive optical element having a pair of diffraction grating layers formed from When one of the two slopes extending from the ridgeline is the grating surface and the other slope is the side wall surface, a laser beam is applied to the boundary region between the side wall surfaces facing each other in the pair of diffractive optical surfaces in a fitted state. By carbonizing a part of the diffraction grating layer using light, a light-shielding film is formed that shields the transmitted light that is transmitted through the boundary region among the incident light incident on the diffractive optical surface.

Further, by irradiating a part of the boundary region with a laser beam, a carbonized region in which the plastic diffraction grating layer is carbonized is formed, and a laser beam is formed along the circumferential direction of the boundary region in the plane of the diffractive optical surface. It may include forming a light shielding film over the entire periphery of the boundary region by expanding the carbonized region in the circumferential direction while changing the focus position of light.

A laser beam may be irradiated from a direction facing the diffractive optical surface.

The laser beam may be irradiated from a direction along the side wall surface of the protrusion.

The laser light may be irradiated along the optical axis direction of the diffractive optical surface.

At one irradiation position of the laser light in the plane of the diffractive optical surface, the focus position of the laser light when the laser light is condensed by the condensing optical system is the height direction of the side wall surface extending in the irradiation direction of the laser light. , the carbonized region may be developed along the height direction of the side wall surface.

The laser light may be pulsed laser light.

The pulsed laser light may be ultrashort pulsed laser light with a pulse time width in the range of picoseconds to femtoseconds.

Dot-shaped carbonized regions may be formed in the diffraction grating layer by pulsed laser light, and pulse irradiation may be repeated in such a manner that the dots of adjacent carbonized regions partially overlap each other.

The focal position of the laser light may be moved by displacing the multi-layer diffraction optical element while fixing the laser irradiation section that irradiates the laser light.

The focal position of the laser light may be moved by displacing the laser irradiation section that irradiates the laser light while the multilayer diffractive optical element is fixed.

A multi-layered diffractive optical element according to the technology of the present disclosure includes a pair of diffraction grating layers each having a diffractive optical surface having a sawtooth-shaped radial cross-sectional shape and having a plurality of concentrically arranged ridges. , a multi-layered diffractive optical element comprising a pair of diffraction grating layers made of plastic, in which the concave and convex portions of the diffractive optical surfaces are fitted to each other; When the inclined surface is the grating surface and the other inclined surface is the side wall surface, the boundary region between the side wall surfaces facing each other in the pair of diffractive optical surfaces in the fitted state is carbonized by partially carbonizing the diffraction grating layer. A light shielding film formed by regions is provided for shielding the transmitted light that is transmitted through the boundary region among the incident light incident on the diffractive optical surface.

The carbonized region is formed of a plurality of dots, and adjacent dots may be arranged in a state where they partially overlap each other.

The plurality of dots may have an elliptical cross section and may be arranged in a posture in which the longitudinal direction extends in the height direction of the side wall surface.

In the ridge, the thickness of the light shielding film in the radial direction of the diffractive optical surface may be 10% or less of the width of the ridge.

In the ridge, the thickness of the light shielding film in the radial direction of the diffractive optical surface may be 1% or less of the width of the ridge.

A diffraction grating section having a pair of diffraction grating layers and a pair of lenses cemented to both surfaces of the diffraction grating section may be provided.

According to the technique of the present disclosure, it is possible to form the light shielding film more easily than in the conventional art.

FIG. 4 is an explanatory diagram of a zoom lens incorporating a diffractive lens; It is a figure explaining the chromatic aberration characteristic of a diffraction lens. 3A is a cross-sectional view of a diffractive lens (shown in FIG. 3A) and a plan view of a grating layer (shown in FIG. 3B); FIG. 3 is an enlarged view of a diffraction grating section; FIG. FIG. 4 is an enlarged view of a pair of diffraction grating layers; FIG. 4 is an explanatory diagram of the action of a light shielding film in a diffraction grating layer; It is a figure which shows the comparative example without a light shielding film. It is a figure which shows the formation method of a diffraction grating part. 1 is a schematic diagram of a laser processing apparatus for forming a light shielding film; FIG. FIG. 4 is an explanatory diagram of focal positions of laser light; FIG. 3 is an explanatory diagram of pulsed laser light; FIG. 4 is an explanatory diagram of parameters that determine the spot diameter of a beam spot; FIG. 4 is an explanatory diagram of a light shielding film formed by a plurality of carbonized dots; FIG. 5 is a diagram showing a scanning method of laser light when forming a plurality of carbonized dots in the height direction of the ridge. FIG. 5 is a diagram showing a scanning method of laser light when forming a plurality of carbonized dots in the circumferential direction of a ridge. FIG. 4 is an explanatory diagram of the shape of carbonized dots; FIG. 4 is an explanatory diagram of a posture in which carbonized dots are formed; FIG. 4 is an explanatory diagram of the film thickness of a light shielding film; 5 is a flow chart showing a procedure for forming a light shielding film; It is a figure which shows the modification of the formation position of a light shielding film. FIG. 10 is a diagram for explaining the orientation of carbonized dots when side wall surfaces are inclined; It is a modified example of the posture of the carbonized dots with respect to the side wall surface. FIG. 4 is an explanatory diagram of a scanning mechanism having a galvanomirror; FIG. 3 is an explanatory diagram of CW laser light;

(Function of diffractive lens)
A diffractive lens 10, which is an example of a multilayer diffractive optical element according to the technology of the present disclosure, will be described with reference to the drawings. As shown in FIG. 1, the diffraction lens 10 is used, for example, in an imaging optical system 110. As shown in FIG. The photographic optical system 110 shown in FIG. 1 has, for example, a three-group configuration of a first lens group G1, a second lens group G2, and a third lens group G3, and forms an image of a subject on an image sensor 111. FIG. The photographing optical system 110 is, for example, a zoom lens, and the second lens group G2 is a zooming lens movable in the optical axis OA direction. For example, when the second lens group G2 moves along the optical axis OA from the position shown in FIG. 1A to the position shown in FIG. image formation magnification changes.

In the imaging optical system 110, as an example, the diffraction lens 10 is incorporated in the third lens group G3. The diffractive lens 10 is also called a DOE (Diffractive Optical Element) lens. One example of the function of the diffraction lens 10 incorporated in the imaging optical system 110 is a chromatic aberration correction function.

FIG. 2 is an explanatory diagram of the chromatic aberration correction function of the diffraction lens 10. As shown in FIG. FIG. 2A shows chromatic aberration of a convex lens 120 having only refractive action as a comparative example. Chromatic aberration is a color shift of an image, and is caused in the convex lens 120 by different refractive indices depending on wavelengths. In the case of the convex lens 120, among the incident light rays SR, the shorter the wavelength of the light, the higher the refractive index. As shown in FIG. 2A, the shorter the wavelength of light, that is, the shorter the focal length is in the order of blue (B: Blue), green (G: Green), and red (R: Red). On the other hand, the diffractive lens 10 has a chromatic aberration characteristic opposite to that of the convex lens 120. As shown in FIG. ), green (G), and blue (B). The chromatic aberration characteristic of the diffraction lens 10 is due to the fact that the diffraction lens 10 has a light diffraction effect, unlike the convex lens 120 that only has a light refraction effect.

The diffraction lens 10 of this example includes a diffraction grating section 12 made of plastic and two lenses 13 and 14 made of glass. 12 are sandwiched. The diffractive lens 10 of this example achieves chromatic aberration characteristics as shown in FIG. 2B by a combination of the diffraction action of the diffraction grating section 12 and the action caused by the difference in refractive index between plastic and glass.

(Configuration of diffraction lens)
As shown in FIGS. 3 to 5, in the diffraction lens 10, one surface of the diffraction grating section 12 and the lens 13 are cemented together, and the other surface of the diffraction grating section 12 and the lens 14 are cemented together. As an example, the lens 13 is a meniscus lens having one surface convex and the other surface concave, and the lens 14 is a convex lens having both surfaces convex. The diffraction grating portion 12 has one surface that is convex and the other surface that is concave, and has a meniscus lens-like shape as a whole. The convex surface of the diffraction grating portion 12 and one concave surface of the lens 13 are joined together, and the concave surface of the diffraction grating portion 12 and one convex surface of the lens 14 are joined together.

The diffraction grating section 12 has a pair of diffraction grating layers 12A and 12B made of plastic. 3B is a plan view of the diffraction grating layer 12B, and FIG. 3A is a cross-sectional view of the diffractive lens 10 taken along the line AA in FIG. 3B. In FIG. 3B, each of the diffraction grating layers 12A and 12B, like the lens 13 and the lens 14, has a circular shape in plan view, with the diffraction grating layer 12B shown as an example. have As shown in FIG. 3B, the diffractive optical surface 18 has a plurality of ridges 20 arranged concentrically around the optical axis OA. As shown in FIG. 5, the diffractive optical surface 18 has a serrated cross-sectional shape in the radial direction of the diffractive lens 10 . One ridge portion 20 has two slopes extending from the ridge line 20C of the ridge portion 20 (see FIGS. 3B and 5). One slope is the grating surface 20A and the other slope is the side wall surface 20B. The grating surface 20A is a surface that produces a diffraction effect. The grating surface 20A is a slope that intersects with the optical axis OA, and the inclination with respect to the optical axis OA is steeper than that of the side wall surface 20B. Therefore, as shown in FIG. 3B, when the diffractive optical surface 18 is viewed from above, the grating surface 20A is wider than the side wall surface 20B. The side wall surface 20B of this example is a surface parallel to the optical axis OA.

As shown in FIGS. 4 and 5, in the diffractive lens 10, the pair of diffraction grating layers 12A and 12B are fitted with the unevenness of the respective diffractive optical surfaces 18. As shown in FIGS. As will be described later, the pair of diffraction grating layers 12A and 12B are formed by resin molding, for example. In this case, the diffraction optical surfaces 18 of the pair of diffraction grating layers 12A and 12B are fitted to each other after resin molding.

More specifically, the ridges 20 have the same size and pitch on each diffraction optical surface 18 of the pair of diffraction grating layers 12A and 12B. The pair of diffraction grating layers 12A and 12B are fitted with the sawtooth-shaped unevenness formed by the plurality of ridges 20, respectively. In the fitted state, the lattice surfaces 20A of the ridges 20 face each other, and the side wall surfaces 20B face each other. The lattice surfaces 20A are in close contact with each other without an air layer between them, and the side wall surfaces 20B are also in close contact with each other. Furthermore, the ridge line 20C, which is the vertex of one of the ridges 20 of the pair of diffraction grating layers 12A and 12B, contacts the valley of the other ridge 20. As shown in FIG.

In the drawing, the ridges 20 are shown enlarged in size for convenience of explanation, but the actual width of the ridges 20 in the radial direction when the diffractive optical surface 18 is viewed from above (see FIG. 3B) (that is, the width of the grating surface 20A) is about several mm (millimeters). Moreover, the height of the ridge portion 20 (the height from the valley to the ridge line 20C) is about several tens of μm (micrometers).

Further, as shown in FIG. 4, a light shielding film 22 is provided in the boundary region BR between the side wall surfaces 20B facing each other in the pair of diffractive optical surfaces 18 (see FIG. 5) in the fitted state. The light shielding film 22 has a film surface formed along the side wall surface 20B in the boundary region BR. The light shielding film 22 covers substantially the entire side wall surface 20B. The light shielding film 22 shields the transmitted light that is transmitted through the boundary region BR among the incident light that enters the diffractive optical surface 18 .

The function of the light shielding film 22 will be described with reference to FIGS. 6 and 7. FIG. FIG. 6 shows the diffractive lens 10, and FIG. 7 shows the diffractive lens 200 of the comparative example. The diffraction lens 10 has the light shielding film 22 in the boundary region BR, and the diffraction lens 200 does not have the light shielding film 22 . Since the only difference between the two is the presence or absence of the light shielding film 22, the same parts are denoted by the same reference numerals.

In FIGS. 6 and 7, the incident light beam R1 is incident on the grating surface 20A of the ridge portion 20 and exits as an output light beam R1A. When incident on the grating surface 20A like the incident light beam R1, the emitted light beam R1A corresponding to the incident light beam R1 does not become unnecessary light. On the other hand, for example, the incident light beam R2 enters the side wall surface 20B of the protrusion 20, is refracted by the side wall surface 20B, and exits as the outgoing light beam R2A. The incident light beam R3 is scattered by the side wall surface 20B and emitted as an output light beam R3B. The incident light beam R4 is reflected by the side wall surface 20B and emitted as an output light beam R4B. Light rays refracted, scattered, or reflected by the side wall surface 20B, such as the emitted light rays R2A to R4A, become unnecessary light and cause flare, ring-shaped ghost, and the like. If the side wall surface 20B is not provided with the light shielding film 22 as in the diffractive lens 200 shown in FIG. As shown in FIG. 6, in the diffraction lens 10, the light shielding film 22 is provided in the boundary region BR between the side wall surfaces 20B, so that the refraction, scattering or reflection of light rays on the side wall surfaces 20B is suppressed.

However, even if the light shielding film 22 is not provided like the diffraction lens 200 shown in FIG. The path of the incoming ray does not change. Therefore, by appropriately designing the width, pitch, inclination angle, etc. of the grating surface 20A, generation of unnecessary light can be suppressed by suppressing light rays that enter the side wall surface 20B and cause refraction, scattering, or reflection on the side wall surface 20B. can be suppressed.

However, when the diffraction lens 200 is incorporated into a zoom lens having a variable focal length, as in the imaging optical system 110 shown in FIG. Since the path of light rays inside the system changes, the path of the incident light rays entering the diffractive lens 200 also changes. Therefore, it is difficult to suppress light rays that are refracted, scattered, or reflected at the side wall surfaces 20B by the method of adjusting the width, pitch, inclination angle, and the like of the grating surface 20A.

Therefore, by providing the light-shielding film 22 in the boundary region BR as in the diffraction lens 10 of this example shown in FIG. This makes it possible to apply the diffractive lens 10 to a zoom lens as well. That is, even if there are incident light beams R2 to R4 incident on the side wall surface 20B of the diffraction lens 10, the incident light beams R2 to R4 are not reflected by the light shielding film because the path of light rays inside the optical system changes as the focal length changes. 22, generation of unnecessary light is suppressed. As a result, the occurrence of flares and ring-shaped ghosts is suppressed.

(Method for Forming Diffraction Grating Portion of Diffraction Lens)
FIG. 8 shows an example of a method of forming the diffraction grating portion 12 of the diffraction lens 10. As shown in FIG. First, in step 1, a mold 31 is coated with a plastic material 32 that will be the material of the diffraction grating layer 12B. The plastic material 32 is, for example, a photo-curing resin, and is cured by ultraviolet UV, for example. The plastic material 32 is in a liquid state before being irradiated with light such as ultraviolet rays UV, and is cured by being irradiated with light. A liquid plastic material 32 is applied to the entire surface of the mold 31 . The mold 31 is formed with sawtooth unevenness of the diffractive optical surface 18 . A lens 14 is pressed against a mold 31 coated with a liquid plastic material 32 . As a result, the plastic material 32 is sandwiched between the mold 31 and the lens 14, and the uneven shape of the mold 31 is transferred to one surface of the plastic material 32, while the other surface of the plastic material 32 is one surface of the lens 14. adhere to.

In step 2, the plastic material 32 sandwiched between the mold 31 and the lens 14 is irradiated with ultraviolet rays UV. When the ultraviolet rays UV are irradiated, the plastic material 32 is cured while the uneven shape of the mold 31 is transferred, and the cured plastic material 32 becomes the diffraction grating layer 12B. A diffraction optical surface 18 is formed on one surface of the diffraction grating layer 12B, and the lens 14 is bonded to the other surface.

In step 3, the diffraction grating layer 12A is formed using the diffraction optical surface 18 of the diffraction grating layer 12B bonded to the lens 14 as a mold. The entire surface of the lens 13 is coated with a plastic material 33 which is the material of the diffraction grating layer 12A. The plastic material 33 is also, for example, a photocurable resin that is cured by UV rays. The diffractive optical surface 18 of the diffraction grating layer 12B bonded to the lens 14 is pressed against the plastic material 33 applied on the lens 13. As shown in FIG. As a result, the uneven shape of the diffractive optical surface 18 of the diffraction grating layer 12B is transferred to one surface of the plastic material 33, and the other surface is brought into close contact with one surface of the lens 13. FIG.

In step 4, the plastic material 33 sandwiched between the diffraction grating layer 12B bonded to the lens 14 and the lens 13 is irradiated with ultraviolet rays UV. When the ultraviolet rays UV are irradiated, the plastic material 33 is cured while the uneven shape of the diffraction optical surface 18 of the diffraction grating layer 12B is transferred, and the cured plastic material 33 becomes the diffraction grating layer 12A. A diffractive optical surface 18 is formed on one surface of the diffraction grating layer 12A, and the lens 13 is bonded to the other surface. Thereby, the diffraction grating portion 12 having the pair of diffraction grating layers 12A and 12B is formed. When step 4 is finished, as shown in FIG. 4, the concave and convex portions of the diffraction optical surfaces 18 of the pair of diffraction grating layers 12A and 12B are fitted. At the stage when step 4 is completed, the basic structure of the diffraction lens 10 is completed although the light shielding film 22 is not provided.

The plastic materials 32 and 33 are, for example, acrylic resin. Materials for the plastic materials 32 and 33 are appropriately selected according to the optical characteristics that the diffractive lens 10 aims for.

(Light-shielding film forming method)
Next, a method of forming the light shielding film 22 on the diffraction lens 10 will be described with reference to FIGS. 9 to 19. FIG. As shown in FIG. 9, the light shielding film 22 is formed by partially carbonizing the plastic diffraction grating layers 12A and 12B using the laser beam LB emitted by the laser processing device 41. As shown in FIG. When a material such as a plastic material whose main component is a carbon compound is heated in a state in which oxygen is blocked, the carbon compound is decomposed, and a solid carbon component with low volatility remains. Such a phenomenon is commonly called carbonization. When the focal position F of the laser beam LB is set inside the diffraction grating portion 12 when the laser beam LB is condensed, and the laser beam LB is irradiated in that state, the diffraction grating layers 12A and 12B are formed around the focal position F. A portion is heated, and a carbonized region is produced centering on the focal position F. By forming such a carbonized region along the side wall surface 20B and the ridge line 20C of the protrusion 20, a carbonized region is formed in the boundary region BR between the side wall surfaces 20B. Since the carbonized region becomes black, the carbonized region formed along the side wall surface 20B functions as a light shielding film 22 that absorbs light. In this way, the light shielding film 22 is formed by performing laser processing for forming a carbonized region in a part of the diffraction grating section 12 using the laser beam LB.

As shown in FIG. 9 , the laser processing device 41 includes a laser irradiation section 42 , a condensing optical system 43 , a moving stage 44 and a holder 45 . The laser irradiation unit 42 is a light source that emits laser light LB. The condensing optical system 43 converges the laser beam LB on the focal position F of the condensing optical system 43 . As shown in FIG. 10, due to the focusing action of the focusing optical system 43, the cross-sectional area S of the beam in the direction perpendicular to the irradiation direction of the laser beam LB is reduced toward the focal position F, and is minimized at the focal position F. becomes. As the cross-sectional area S is smaller, the energy of the laser beam LB is concentrated, so that the power density, which is the light intensity per unit area of the beam spot of the laser beam LB, is increased. Here, the beam spot refers to a converging point at the focal position F of the laser beam LB when the laser beam is condensed by the condensing optical system 43 .

The moving stage 44 is a scanning mechanism for scanning a focal position F, which is a processing position for laser processing. The diffraction lens 10 to be laser-processed is set on the moving stage 44, and the moving stage 44 moves the diffraction lens 10 relative to the focal position F of the laser beam LB.

The moving stage 44 has a rotating stage 44A and a three-axis stage 44B. The rotary stage 44A rotates around an axis parallel to the Z direction. A holder 45 for fixing the diffraction lens 10 is provided on the rotary stage 44A. On the rotating stage 44A, the diffraction lens 10 is set on the holder 45 with the optical axis OA aligned with the Z direction. Accordingly, when the rotary stage 44A rotates, the diffraction lens 10 rotates around the optical axis OA. The laser beam LB is irradiated from a direction facing the diffractive optical surface 18 of the diffractive lens 10 .

More specifically, in this example, the laser beam LB is irradiated from a direction parallel to the optical axis of the diffractive optical surface 18 , that is, the optical axis OA of the diffractive lens 10 . Further, in this example, the height direction of the side wall surface 20B of the ridge portion 20 is also parallel to the optical axis OA of the diffraction lens 10 . Therefore, the laser beam LB is irradiated from the direction along the side wall surface 20B of the protrusion 20 .

The 3-axis stage 44B is a stage that can move in the 3-axis directions of the X direction, the Y direction, and the Z direction. The Z direction is a direction parallel to the optical axis OA, and the X and Y directions are planes perpendicular to the Z direction. The 3-axis stage 44B moves the diffraction lens 10 fixed to the rotary stage 44A in 3-axis directions of X, Y and Z directions. The rotary stage 44A is rotatably attached to the three-axis stage 44B. The rotary stage 44A and the three-axis stage 44B are driven by actuators (not shown).

As shown in FIG. 10, the irradiation position of the laser beam LB corresponding to the focal position F in the XY plane is positioned at a position corresponding to the ridge line 20C of one ridge 20 by the three-axis stage 44B. When the rotary stage 44A is rotated in this state, the focal position F of the laser beam LB moves along the circumferential direction of the circular ridge line 20C of the protrusion 20 in the XY plane. In this way, the laser processing device 41 changes the focal position F of the laser beam LB along the circumferential direction of the boundary region BR (see FIG. 4 and the like) including the ridgeline 20C and the side wall surface 20B, while carbonizing in the circumferential direction. Expand your territory. Then, by expanding the carbonized region in the circumferential direction, the light shielding film 22 is formed over the entire circumference of the boundary region BR.

Further, by moving the three-axis stage 44B in the Z direction at one irradiation position of the laser beam LB, the focal position F moves along the height direction of the ridge portion 20, that is, along the side wall surface 20B. In this manner, the laser processing apparatus 41 sets the focal position F of the laser beam LB at one irradiation position of the laser beam LB in the plane of the diffractive optical surface 18 to the height of the side wall surface 20B extending in the irradiation direction of the laser beam LB. The carbonized region is developed along the height direction of the side wall surface 20B while changing in the height direction. By developing the carbonized region in the height direction of the side wall surface 20B, the light shielding film 22 having a width in the height direction of the side wall surface 20B is formed.

In this manner, the moving stage 44 three-dimensionally moves the relative positions of the diffraction lens 10 and the focal position F of the laser beam LB, thereby moving the boundary region including the ridge lines 20C and the side wall surfaces 20B of the plurality of ridges 20. Scan the focus position F along the BR. That is, the focal position F of the laser beam is moved by displacing the diffraction lens 10 while the laser irradiation unit 42 that irradiates the laser beam LB is fixed.

As shown in FIG. 11, the laser light LB is, for example, a pulsed laser light in which a plurality of pulses are repeatedly irradiated by pulse oscillation. Compared to continuous wave CW (Continuous Wave) laser light, pulsed laser light can have a higher power density and can form a carbonized region in a short time. Furthermore, the pulsed laser beam of this example is an ultrashort pulsed laser beam having a pulse width PW, which is the time width of the pulse, within the range of picoseconds to femtoseconds. When the pulse width PW is short, the effect of thermal diffusion on the periphery of the beam spot at the focal position F is small, so the spread of the carbonized region around the beam spot can be suppressed compared to when the pulse width PW is long. .

FIG. 12 is an explanatory diagram of parameters for changing the spot diameter SD of the beam spot. 12A to 12C are profiles of the light intensity of the beam spot when the horizontal axis is the position in the cross-sectional direction of the luminous flux of the laser beam LB and the vertical axis is the light intensity. Taking the size of the spot diameter SD shown in FIG. 12B as a reference, the spot diameter SD becomes smaller as shown in FIG. 12A as the light collecting performance of the light collecting optical system 43 increases. In this case, since the light collecting performance of the light collecting optical system 43 is high, the energy of the laser beam LB is concentrated, and the light intensity also increases. This results in high power density. On the other hand, as shown in FIG. 12C, increasing the output of the laser irradiation unit 42 increases the light intensity of the beam spot, but also increases the spot diameter SD. In this manner, the spot diameter SD is set using the condensing performance of the condensing optical system 43 and the output of the laser irradiation unit 42 as parameters.

As shown in FIG. 13, the laser processing apparatus 41 forms dot-shaped carbonized regions with laser light LB, which is a pulsed laser beam, and repeats pulse irradiation in such a manner that the dots of adjacent carbonized regions partially overlap each other. 13A is a perspective view showing part of the diffraction grating section 12. FIG. FIG. 13A shows how the light shielding film 22 is formed along the circumferential direction of the side wall surface 20B of the protrusion 20 and the boundary region BR. FIG. 13B is a cross-sectional view when the diffraction grating section 12 is cut in the radial direction. FIG. 13C is a developed view of the light shielding film 22 formed along the circumferential direction of the side wall surface 20B and the boundary region BR. Here, the dot-shaped carbonized regions are referred to as carbonized dots 22A. As shown in FIGS. 13B and 13C, the laser processing device 41 repeats the scanning of the focal position F of the laser beam LB and the pulse irradiation, thereby forming a plurality of carbonized dots 22A on the side wall surface 20B of the protrusion 20. The light shielding films 22 arranged in the Z direction, which is the height direction, and in the circumferential direction of the side wall surface 20B are formed. As shown in FIGS. 13A and 13B, the light shielding film 22 is formed along the side wall surfaces 20B of the plurality of ridges 20 in the boundary region BR. In the light shielding film 22, the carbonized dots 22A that are adjacent to each other in both the height direction and the circumferential direction are arranged in a state where they are partially overlapped. This prevents a gap through which light is transmitted between the adjacent carbonized dots 22A.

One carbonized dot 22A is formed by one pulse irradiation as an example. Of course, one carbonized dot 22A may be formed by a plurality of pulse irradiations, but since the processing time increases as the number of pulse irradiations increases, one carbonized dot 22A should be formed by one pulse irradiation. is preferred. As shown in FIG. 13, the carbonized dot 22A is shaped like a rugby ball and has an elliptical cross section whose longitudinal direction is the irradiation direction of the laser beam LB, although the reason will be described later.

FIG. 14 shows how the focal position F is scanned in the height direction along the side wall surface 20B of the ridge 20 at one irradiation position in the XY plane. In FIG. 14, the focal position F is scanned from the bottom to the top in the height direction. That is, the focal position F is scanned from the downstream side to the upstream side in the irradiation direction of the laser beam LB. As for the scanning method in the height direction, it is preferable to scan from the downstream side to the upstream side of the laser beam LB as in this example. This is because if carbonization is started from the upstream side in the irradiation direction of the laser beam LB, the laser beam LB is blocked by the carbonized dots 22A that have already been formed on the upstream side in the case of carbonizing the more downstream side in the irradiation direction. because it is easy. Further, as shown in FIG. 15, when the focal position F is scanned by one row in the height direction, the irradiation position in the XY plane moves by one row in the circumferential direction, and the focal position F is moved in the row after the movement. Scanned in the height direction. As for the method of scanning the side wall surface 20B in the height direction, it is preferable to scan from the downstream side to the upstream side of the laser beam LB as in this example, but scanning may be performed in the opposite direction.

The scanning speed of the focal position F is set so that the focal position F of the laser beam LB changes each time the pulse irradiation is performed. When it is desired to increase the speed of forming the light shielding film 22, the pulse irradiation repetition frequency is set high and the scanning speed is set high. Also, the amount of overlapping of adjacent carbonized dots 22A in the height direction and the circumferential direction is adjusted by the scanning speed of the focus position F in the height direction and the circumferential direction.

Since the laser processing for forming the carbonized region in the plastic diffraction grating portion 12 is internal processing of the plastic material, the wavelength of the laser light LB is preferably within the wavelength range through which the plastic material is transmitted. In plastic materials, internal carbonization is generally difficult below 365 nm or above 1030 nm because the plastic material begins to absorb light. In addition, since the internal carbonization utilizes the phenomenon of multiphoton absorption, relatively short wavelengths are more likely to cause multiphoton absorption. Considering this, the wavelength range of the laser beam LB capable of internal carbonization of the plastic material is preferably in the range of about 300 nm to about 800 nm.

FIG. 16 is a diagram explaining why the carbonized dots 22A are shaped like a rugby ball. The luminous flux of the laser beam LB converges from the condensing optical system 43 toward the focal position F, and diverges when the focal position F is exceeded. It shrinks with it and expands with its divergence. More specifically, the light intensity profile at the position CS1 in the irradiation direction of the laser beam LB has a large cross-sectional area and a small light intensity. At position CS2 closer to focal position F than at position CS1, the cross-sectional area is smaller and the light intensity is higher. At CS3, which is the focal position F, the cross-sectional area of the luminous flux is minimized and the light intensity is maximized. Beyond the focal position F, the cross-sectional area increases and the light intensity decreases as shown at position CS4. All the light intensity profiles at the positions CS1 to CS4 are Gaussian distributions.

Thus, the light intensity profile at each position in the irradiation direction of the laser beam LB is symmetrical with respect to the focal position F, and the cross-sectional area of the luminous flux increases from the focal position F toward the upstream side and the downstream side, respectively. becomes larger and the light intensity becomes smaller. Therefore, the distribution of carbonization energy for plastic materials also follows such a light intensity profile. As a result, the carbonized dot 22A is also shaped like a rugby ball centered on the CD, which is the position corresponding to the focal position F. In the carbonized dots 22A, the length in the lateral direction perpendicular to the irradiation direction is the maximum at the center CD, and the length is the minor axis D1. The short diameter D1 is approximately the same size as the spot diameter SD of the beam spot. In addition, in the carbonized dots 22A, the length in the longitudinal direction along the irradiation direction also becomes maximum at the position of the center CD, and this length becomes the major axis D2 of the carbonized dots 22A. Thus, the carbonized dot 22A has a longitudinal direction along the irradiation direction of the laser beam LB, and the shape of the vertical cross section cut along the longitudinal direction is elliptical. The cross-sectional shape of the carbonized dot 22A cut along the lateral direction, which is the direction perpendicular to the irradiation direction, is circular, similar to the cross-sectional shape of the beam spot.

In FIG. 17, the carbonized dots 22A are formed by irradiating the laser beam LB from the direction along the side wall surface 20B of the protrusion 20. In FIG. As shown in FIG. 16, the carbonized dots 22A have a shape like a rugby ball whose irradiation direction is the longitudinal direction, so the vertical cross section in the longitudinal direction is elliptical. Therefore, as shown in FIG. 17A, the carbonized dots 22A are formed in a posture in which the direction along the side wall surface 20B, that is, the height direction of the side wall surface 20B of the protrusion 20 is the longitudinal direction. Although only one carbonized dot 22A is shown in FIG. 17A, a plurality of carbonized dots 22A are arranged in the orientation shown in FIG. 17A. Further, in this example, since the direction in which the side wall surface 20B extends coincides with the direction of the optical axis OA of the diffractive optical surface 18, as shown in FIG. becomes.

As is clear from these figures, in this example, the short diameter D1 of the carbonized dots 22A, which has approximately the same size as the spot diameter SD, is the film thickness FT of the light shielding film 22. FIG. In this example, the minor axis D1 of one carbonized dot 22A becomes the film thickness FT because in the radial direction of the diffractive optical surface 18 (see FIGS. 13 and 17A), one line of the carbonized dots 22A is This is because only the When two rows of carbonized dots 22A are arranged in the radial direction, the film thickness FT is twice the minor axis D1.

The film thickness FT of the light shielding film 22 must be a thickness that can ensure the light shielding performance, but it is not preferable that the film is too thick. This is because if the film thickness FT is increased, not only the incident light beams incident on the side wall surface 20B but also the incident light beams incident on the grating surface 20A are blocked. Therefore, as shown in FIG. 18, the ratio of the film thickness FT of the light shielding film 22 to the width RW of the projection 20 in the radial direction of the diffractive optical surface 18 is about 10% or less (FT/RW≤10%). It is preferably 1% or less (FT/RW≤1%), more preferably. By setting the ratio of the film thickness FT to the width RW to such a value, it is possible to suppress the adverse effect of the light shielding film 22 on the incident light incident on the grating surface 20A. As a numerical example of FT/RW being 1% or less, for example, the width RW of the protrusion 20 is about 1000 μm (micrometers), and the film thickness FT of the light shielding film 22 is about 10 μm (micrometers).

Here, the range of the boundary region BR in the radial direction of the diffractive optical surface 18 is as follows. First, the width in the radial direction based on the boundary line between the side wall surfaces 20B is defined as WH (see FIG. 18). The reference range of ±WH is defined as the range of the boundary region BR. The width WH is defined as a ratio to the width RW of the ridge portion 20 in the same manner as the film thickness FT of the light shielding film 22 . The ratio of the width WH to the width RW of the protrusion 20 is about 10% (WH/RW=10%). Moreover, it is preferable that the light shielding film 22 is arranged as close to the side wall surface 20B as possible within the range of the boundary region BR. This is because if there is a gap between the side wall surface 20B and the light shielding film 22, it becomes difficult to block the light incident on the side wall surface 20B. Therefore, it is preferable that the light shielding film 22 is formed within a range of about 1% of the width RW of the protrusion 20 with respect to the boundary line between the side wall surfaces 20B.

FIG. 19 is a flow chart showing the procedure for forming the light shielding film 22. As shown in FIG. The diffraction lens 10 having the diffraction grating portion 12 formed by the procedure shown in FIG. Thereafter, in step S100, the laser processing device 41 moves the diffraction lens 10 with respect to the laser irradiation unit 42 via the moving stage 44, thereby setting the focal position F of the laser beam LB to the initial position. The focal position F is set in the boundary region BR of the side wall surface 20B inside the diffraction lens 10 .

Then, in step S200, the laser processing device 41 starts pulse irradiation of the laser beam LB and scanning of the focal position F. As shown in FIG. The laser irradiation unit 42 irradiates a pulsed laser beam at a preset repetition frequency. When the boundary region BR is irradiated with the pulsed laser light, carbonization occurs at the focal position F in the diffraction grating section 12 made of plastic, thereby forming carbonized dots 22A. In this example, one carbonized dot 22A is formed by one pulse irradiation. The moving stage 44 rotates the rotary stage 44A at a preset number of rotations, and moves the three-axis stage 44B at preset timings. As a result, scanning of the focal position F as shown in FIGS. 10, 14 and 15 is performed.

In step S300, the laser processing device 41 determines whether the focal position F has reached the final position. If not (NO in step S300), pulse irradiation and scanning are continued, If so (YES in step S300), pulse irradiation and scanning are terminated. In this way, the laser processing device 41 forms the light shielding film 22 over the entire circumference of the boundary region BR by scanning the focal position F in the height direction and the circumferential direction of the boundary region BR between the side wall surfaces 20B. .

As described above, the laser processing apparatus 41 of this example includes a pair of diffraction grating layers 12A each having a plurality of ridges 20 arranged concentrically and having diffraction optical surfaces 18 each having a sawtooth cross-sectional shape in the radial direction. and 12B, which is an example of a multilayered diffractive optical element including a pair of diffractive grating layers 12A and 12B made of plastic, in which the unevenness of the diffractive optical surfaces is fitted to each other, A light shielding film 22 is formed. In this light-shielding film forming method, the laser processing apparatus 41 performs fitting when one of the two slopes extending from the ridge line 20C of the protrusion 20 is the grating surface 20A and the other slope is the side wall surface 20B. Part of the diffraction grating layers 12A and 12B is carbonized in the boundary region BR between the side wall surfaces 20B facing each other in the pair of diffractive optical surfaces 18 in the folded state, so that the diffraction grating layers 12A and 12B are incident on the diffractive optical surface 18. A light shielding film 22 is formed to shield the transmitted light that passes through the boundary region BR among the incident light.

As described above, in the light shielding film forming method of this example, the light shielding film 22 is formed by partially carbonizing the diffraction grating layers 12A and 12B made of plastic. can be easily formed as compared to That is, in the vapor deposition method and the coating method, a special material for forming the light shielding film 22 is required separately from the diffraction grating layers 12A and 12B. The method of forming the light shielding film 22 is relatively complicated, such as the need for the process of . According to the manufacturing method according to the technology of the present disclosure, since the light shielding film 22 is formed by partially carbonizing the diffraction grating layers 12A and 12B, no special material is required. In addition, since the carbonization is performed by irradiating the laser beam LB, the processing procedure is also simple. Therefore, it can be formed easily compared with the conventional manufacturing method. These merits also contribute to cost reduction.

Further, in the light shielding film forming method of this example, by irradiating a part of the boundary region BR with the laser beam LB, the carbonized regions (carbonized dots 22A as an example) in which parts of the plastic diffraction grating layers 12A and 12B are carbonized. ), and in the plane of the diffractive optical surface 18, along the circumferential direction of the boundary region BR, while changing the focal position F of the laser beam LB, by developing the carbonized region in the circumferential direction, the boundary It includes forming the light shielding film 22 over the entire circumference of the region BR. Since the carbonized region is partially formed and expanded in this way, it is effective when the region where the light shielding film 22 is formed is relatively large.

Further, in the method of forming the light shielding film of this example, the laser processing device 41 is used to irradiate the laser beam LB from the direction facing the diffractive optical surface 18 . Therefore, the control of the incident position and the incident angle of the laser beam LB within the plane of the diffractive optical surface 18 becomes easier than in the case of irradiating the laser beam from a direction not facing the diffractive optical surface 18 . Therefore, it is effective when there are a plurality of ridges 20 concentrically within the diffractive optical surface 18 .

Further, in the method of forming the light shielding film of this example, the laser processing device 41 is used to irradiate the laser beam LB from the direction along the side wall surface 20B of the protrusion 20 . As shown in FIGS. 16 and 17, the carbonized region (carbonized dot 22A as an example) has a major axis D2 in the irradiation direction of the laser beam LB and a minor axis D1 in the direction of the spot diameter of the laser beam LB perpendicular to the irradiation direction. Shaped like a rugby ball. Therefore, by irradiating the laser light LB from the direction along the side wall surface 20B, the film thickness FT of the light shielding film corresponding to the minor axis D1 can be made thinner compared to the case of irradiating from other directions.

As described above, if the film thickness FT of the light-shielding film 22 in the ridges 20 is too thick, the incident light entering the grating surface 20A may be blocked, and the optical performance of the multi-layered diffractive optical element may deteriorate. It may lead to deterioration. Therefore, it is preferable to form the film thickness FT of the light shielding film 22 as thin as possible within the range where the light shielding performance can be ensured. Therefore, from the viewpoint of thinning the film thickness FT, it is preferable to irradiate the laser beam LB from the direction along the side wall surface 20B of the protrusion 20 as in this example.

Further, in the above embodiment, the laser beam LB is irradiated along the direction of the optical axis OA of the diffractive optical surface 18 . Side wall surfaces 20B of the ridges 20 are often formed substantially parallel to the optical axis OA. In this case, by irradiating the laser beam LB from the direction of the optical axis OA of the diffractive optical surface 18, the light shielding film 22 having a thin film thickness FT can be formed. Further, when forming the light shielding film 22 while rotating the diffractive optical surface 18 around the optical axis, considering adjustment of the irradiation direction of the laser irradiation unit 42, etc., the irradiation direction of the laser beam LB and the direction of the optical axis OA are the same, it is preferable from the viewpoint of simplification of the device configuration.

In the above-described embodiment, the laser processing apparatus 41 has the laser beam LB when the laser beam LB is condensed by the condensing optical system 43 at one irradiation position of the laser beam LB in the plane of the diffraction optical surface 18. While changing the focal position F in the height direction of the sidewall surface 20B extending in the irradiation direction, the carbonized region is developed along the height direction of the sidewall surface 20B. Therefore, a carbonized region (carbonized dots 22A as an example) can be developed along the height direction of the side wall surface 20B by a simple method of changing the focal position F of the laser beam LB.

Moreover, in the above embodiment, the laser beam LB is a pulsed laser beam. As described above, the pulsed laser light of pulse oscillation can have a higher power density than the CW laser light of continuous oscillation, and can form carbonized regions (carbonized dots 22A as an example) in a short time.

In the above embodiment, the laser beam LB is, as described above, an ultrashort pulse laser beam having a pulse width PW within the range of picoseconds to femtoseconds. The shorter the pulse width PW, the less the effect of thermal diffusion on the periphery of the beam spot at the focal position F. Therefore, compared to the case where the pulse width PW is long, the spread of the carbonized region around the beam spot can be suppressed. . Further, as shown in FIG. 17, the size of the carbonized dots 22A affects the film thickness FT of the light shielding film 22. As shown in FIG. Therefore, by using the ultrashort pulse laser beam, it is easy to accurately control the film thickness FT of the light shielding film 22 by controlling the spot diameter SD of the beam spot.

In the above embodiment, the laser processing device 41 forms the carbonized dots 22A, which are dot-shaped carbonized regions, with the pulsed laser beam, and repeats the pulse irradiation such that the adjacent carbonized dots 22A partially overlap each other. As a result, the occurrence of gaps between the carbonized dots 22A is suppressed, and light leaking from the light shielding film 22 is suppressed, so that the light shielding performance of the light shielding film 22 can be improved. Furthermore, it is more effective if the adjacent carbonized dots 22A are overlapped so as not to create a gap between the adjacent carbonized dots 22A.

In the above embodiment, the laser processing apparatus 41 displaces the diffractive lens 10, which is an example of a multi-layer diffractive optical element, while fixing the laser irradiation unit 42 that irradiates the laser beam LB. Move the focus position F of LB. According to this, it is not necessary to move the laser irradiation unit 42 . This is effective in the case of a configuration in which the laser irradiation section 42 is difficult to move.

Further, as shown in the above embodiment, the diffractive lens 10, which is an example of a multi-layered diffractive optical element, has a plurality of ridges 20 arranged concentrically and has a serrated cross-sectional shape in the radial direction. A pair of grating layers 12A and 12B each having a surface 18, the pair of grating layers 12A and 12B being made of plastic, with the recesses and projections of the diffractive optical surfaces 18 interlocking. When one of the two slopes extending from the ridgeline of the ridge portion 20 is the grating surface 20A and the other slope is the side wall surface 20B, the pair of diffractive optical surfaces 18 in the fitted state face each other. In the boundary region BR between the wall surfaces 20B, a light shielding film 22 formed of a carbonized region (carbonized dots 22A as an example) obtained by carbonizing a part of the diffraction grating layers 12A and 12B is provided. A light-shielding film 22 is provided to block light that is transmitted through the boundary region BR.

In such a multi-layered diffractive optical element, the light shielding film 22 is formed of carbonized regions obtained by partially carbonizing the diffraction grating layers 12A and 12B made of plastic. Similarly to , it is easier to manufacture than a multi-layer diffractive optical element in which a light-shielding film is formed by a vapor deposition method, a coating method, or the like. The fact that no special materials are required and the processing procedure is simple also contributes to cost reduction.

In the above embodiment, like the carbonized dot 22A shown as an example, the carbonized region is formed of a plurality of dots, and adjacent dots are arranged in a partially overlapping state. By partially overlapping adjacent dots, leakage of light from gaps between dots can be suppressed.

In the above-described embodiment, like the carbonized dots 22A shown as an example, the plurality of dots have an elliptical cross section and are arranged in a posture that extends in the longitudinal direction in the height direction of the side wall surface 20B. In the boundary region BR, the film thickness FT of the light shielding film 22 is the length of the diffractive optical surface 18 in the radial direction perpendicular to the height direction of the side wall surface 20B. Therefore, by arranging a plurality of dots in the above posture, the minor axis D1 in the short side direction of the elliptical shape can be used as the film thickness FT of the light shielding film 22, so that the film thickness FT can be reduced. As described above, if the film thickness FT is too large, the optical performance is degraded, so the above configuration that enables the film thickness FT to be thin is preferable.

In the above-described embodiment, the film thickness FT of the light shielding film 22 in the radial direction of the diffractive optical surface 18 in the ridge portion 20 is 10% or less, more preferably 1% or less, of the width RW of the ridge portion 20 % or less. As a result, it is possible to block the light beam incident on the side wall surface 20B while preventing the light beam incident on the grating surface 20A from being blocked. This suppresses unnecessary light that causes flare, ring-shaped ghost, and the like.

In the above embodiment, the diffraction lens 10, which is an example of a multilayer diffraction optical element, includes a diffraction grating section 12 having a pair of diffraction grating layers 12A and 12B, and a pair of of lenses 13 and 14. By combining the diffraction grating section 12 and the lenses 13 and 14, it becomes possible to combine the diffraction action and the refraction action, and the optical performance of the diffraction optical element can be improved.

(Modification 1: Formation position of the light shielding film)
The technique of the present disclosure is not limited to the above embodiment, and various modifications shown in FIGS. 20 to 24 are possible. FIG. 20 shows a modification of the position where the light shielding film 22 is formed. In the above embodiment, as shown in FIG. 13B, the light shielding film 22 is formed on the diffraction grating layer 12B of the pair of diffraction grating layers 12A and 12B in the boundary region BR of the side wall surface 20B in the diffraction grating section 12. ing. In the example shown in FIG. 20A, a light shielding film 22 is formed on the diffraction grating layer 12A. Further, as shown in FIG. 20B, a light shielding film 22 may be formed across the pair of diffraction grating layers 12A and 12B. Thus, the light shielding film 22 may be formed in the boundary region BR between the side wall surfaces 20B of the pair of diffraction grating layers 12A and 12B.

(Modification 2: Inclination of side wall surface and irradiation direction of laser light)
In the modification shown in FIG. 21, in the ridge portion 60 having the grating surface 60A and the side wall surface 60B, the side wall surface 60B is inclined in the height direction corresponding to the Z direction of the diffraction lens 10, that is, with respect to the optical axis OA. is doing. When the side wall surface 60B is inclined with respect to the optical axis OA in this way, it is preferable that the laser beam LB is irradiated from the direction along the side wall surface 60B of the protrusion 60 . As a result, the longitudinal direction of the carbonized dots 22A can be aligned with the direction along the side wall surface 60B. can be brought closer to the side wall surface 60B. If the light shielding film 22 and the side wall surface 60B are too far apart, unnecessary light is likely to be generated from the side wall surface 60B. Unnecessary light can be suppressed by bringing the light shielding film 22 closer to the side wall surface 60B.

(Modification 3: Posture of Carbonized Dots)
In the above-described embodiment, as shown in FIG. 17, the carbonized dots 22A are formed so that the longitudinal direction extends along the side wall surface 20B. However, as shown in FIG. It may be formed in a direction orthogonal to 20B, that is, in a posture along the radial direction of the diffraction lens 10 . Similar to FIG. 17A, FIG. 22A shows the attitude of the carbonized dots 22A when the ridge 20 is viewed from a direction perpendicular to the height direction and the radial direction. Similarly to FIG. 17B, FIG. 22B shows the attitude of the carbonized dots 22A when the ridges 20 are viewed from the direction of the optical axis OA. As shown in FIG. 22, when the longitudinal direction of the carbonized dots 22A is perpendicular to the side wall surface 20B, the length D2 of the carbonized dots 22A is the film thickness FT of the light shielding film 22. As shown in FIG. The carbonized dots 22A may be formed as shown in FIG. 22, but as described above, if the film thickness FT of the light shielding film 22 is too thick, there is also an adverse effect. preferably formed.

(Modification 4: Modification of scanning method)
FIG. 23 shows a scanning mechanism 81 using galvanomirrors 83 and 84 as a scanning mechanism for scanning the laser beam LB. The scanning mechanism 81 includes, for example, a collimator 82 that collimates the laser beam LB, galvanometer mirrors 83 and 84, and a condensing optical system 85. As shown in FIG. The galvanomirrors 83 and 84 each include a mirror portion that reflects the laser beam LB and a mechanism that rotates the attitude of the mirror portion around the axis. By rotating the attitude of each mirror portion of the galvanomirrors 83 and 84, the focal position F of the laser beam LB can be scanned. The scanning mechanism 81 is incorporated in the laser irradiation section 42 . That is, in this example, the focal position F of the laser beam LB is moved by displacing the laser irradiation unit 42 including the scanning mechanism 81 while the diffractive lens 10, which is an example of the multilayer diffractive optical element, is fixed. . This enables scanning of the focal position F without moving the diffraction lens 10 . This example is effective when the diffraction lens 10 is difficult to move, such as when the diffraction lens 10 is large.

(Modification 5: CW laser light)
In the above embodiment, as shown in FIG. 11, an example in which a pulsed laser beam is used as the laser beam LB has been described, but as shown in FIG. 24, a CW laser beam may be used as the laser beam LB. Of course, as described above, pulsed laser light has various advantages, so it is preferable to use pulsed laser light rather than CW laser light.

(Modification 6: Method for Forming Diffraction Grating Section)
In the above embodiment, as shown in FIG. 8, after forming one diffraction grating layer 12B, the other diffraction grating layer 12A is formed using the diffraction grating layer 12B as a mold. , the diffraction grating portion 12 may be formed as follows. That is, in addition to the diffraction grating layer 12B, the mold 31 is also used to form the diffraction grating layer 12A. Then, after forming the pair of diffraction grating layers 12A and 12B, the respective diffraction optical surfaces 18 may be bonded together with an adhesive. The pair of diffraction grating layers 12A and 12B are in a state in which the diffraction optical surface 18 is fitted after being bonded together with an adhesive.

(Modification 7: Application)
In the above example, the diffraction lens 10 is applied to a camera zoom lens such as the imaging optical system 110 shown in FIG. 1, but it may be applied to a projection optical system of a projector.

(Modification 8: Formation area of light shielding film)
Further, the light shielding film 22 may be formed on a part of the plurality of ridges 20 formed concentrically, or the light shielding film 22 may be formed on all of them. For example, the light shielding film 22 may be formed only on the ridges within the range of the effective diameter of the diffractive optical surface 18 . The effective diameter refers to the diameter of the lens corresponding to the range on which light rays contributing to image formation are incident, for example, when the multi-layered diffractive optical element is incorporated in an optical system such as a camera or a projector.

(Modification 9: number of lenses)
Although the diffractive lens 10 having the two lenses 13 and 14 has been described as an example of the multi-layered diffractive optical element, it may have, for example, three or more lenses. Also, only one lens may be used. In this case, for example, one surface of the diffraction grating section 12 is bonded to a transparent glass substrate that does not have a lens surface. In other words, the number of lenses may be any number, and the multi-layered diffractive optical element only needs to have a pair of diffraction grating layers 12A and 12B.

It should be noted that the technique of the present disclosure can also be appropriately combined with the above-described embodiment and various modifications. Moreover, it is needless to say that various configurations can be employed without departing from the scope of the present invention without being limited to the above-described embodiment.

The description and illustration shown above are detailed descriptions of the parts related to the technology of the present disclosure, and are merely examples of the technology of the present disclosure. For example, the above descriptions of configurations, functions, actions, and effects are descriptions of examples of configurations, functions, actions, and effects of portions related to the technology of the present disclosure. Therefore, unnecessary parts may be deleted, new elements added, or replaced with respect to the above-described description and illustration without departing from the gist of the technology of the present disclosure. Needless to say. In addition, in order to avoid complication and facilitate understanding of the portion related to the technology of the present disclosure, the descriptions and illustrations shown above require particular explanation in order to enable implementation of the technology of the present disclosure. Descriptions of common technical knowledge, etc., that are not used are omitted.

As used herein, "A and/or B" is synonymous with "at least one of A and B." That is, "A and/or B" means that only A, only B, or a combination of A and B may be used. Also, in this specification, when three or more matters are expressed by connecting with "and/or", the same idea as "A and/or B" is applied.

All publications, patent applications and technical standards mentioned herein are expressly incorporated herein by reference to the same extent as if each individual publication, patent application and technical standard were specifically and individually noted to be incorporated by reference. incorporated by reference into the book.

10 Diffraction lens 12 Diffraction grating parts 12A, 12B Diffraction grating layers 13, 14 Lens 18 Diffraction optical surface 20 Ridge part 20A Grating surface 20B Side wall surface 20C Ridge line 22 Light shielding film 22A Carbonized dot 31 Mold 32, 33 Plastic material 41 Laser processing Apparatus 42 Laser irradiation section 43 Condensing optical system 44 Moving stage 44A Rotating stage 44B 3-axis stage 45 Holder 60 Ridge section 60A Lattice surface 60B Side wall surface 81 Scanning mechanism 82 Collimators 83, 84 Galvanomirror 85 Condensing optical system 110 Photographing optics System 111 Image sensor 120 Convex lens 200 Diffraction lens BR Boundary area CD Center CS1, C2, CS3, CS4 Position D1 Minor diameter D2 Major diameter F Focus position FT Film thickness G1 First lens group G2 Second lens group G3 Third lens group LB Laser Light OA Optical axis PW Pulse width R1 Incident ray R1A Emitted ray R2 Incident ray R2A Emitted ray R3 Incident ray R3B Emitted ray R4 Incident ray R4B Emitted ray RW Width of ridge S Cross-sectional area SD Spot diameter SR Light ray UV Ultraviolet

Claims (17)

A pair of diffraction grating layers having a plurality of ridges arranged concentrically and each having a diffractive optical surface with a sawtooth-shaped cross section in the radial direction, comprising a pair of diffraction grating layers made of plastic. and a light shielding film forming method for forming a light shielding film on a multilayer diffractive optical element in which the unevennesses of the diffractive optical surfaces are fitted to each other, the method comprising:
When one of the two slopes extending from the ridge line of the ridge portion is a lattice surface and the other slope is a side wall surface, the side wall surface facing the pair of diffractive optical surfaces in a fitted state. By carbonizing part of the diffraction grating layer using a laser beam, a light-shielding film is formed that shields light transmitted through the boundary region among incident light incident on the diffractive optical surface. A method for forming a light shielding film. forming a carbonized region in which the diffraction grating layer made of plastic is carbonized by irradiating a portion of the boundary region with the laser beam;
In the plane of the diffractive optical surface, along the circumferential direction of the boundary region, while changing the focal position of the laser beam, the carbonized region is expanded in the circumferential direction, thereby covering the entire circumference of the boundary region. 2. The method of forming a light-shielding film according to claim 1, further comprising forming the light-shielding film across. 3. The method of forming a light-shielding film according to claim 2, wherein the laser beam is applied from a direction facing the diffractive optical surface. 4. The method of forming a light-shielding film according to claim 3, wherein the laser beam is applied from a direction along the side wall surface of the ridge. 5. The method of forming a light-shielding film according to claim 4, wherein the laser beam is irradiated along the optical axis direction of the diffractive optical surface. At one irradiation position of the laser light in the plane of the diffractive optical surface, the focal position of the laser light when the laser light is condensed by a condensing optical system extends in the irradiation direction of the laser light. 6. The method of forming a light-shielding film according to claim 3, wherein the carbonized region is developed along the height direction of the side wall surface while being varied in the height direction of the side wall surface. 7. The method of forming a light-shielding film according to claim 1, wherein said laser light is pulsed laser light. 8. The method of forming a light-shielding film according to claim 7, wherein said pulsed laser light is ultrashort pulsed laser light having a pulse time width in the range of picoseconds to femtoseconds. 9. The pulse laser beam according to claim 7, wherein dot-shaped carbonized regions are formed in the diffraction grating layer by the pulsed laser light, and pulse irradiation is repeated in such a manner that the dots of adjacent carbonized regions partially overlap each other. A method for forming a light shielding film. 10. The focal position of the laser light is moved by displacing the multi-layered diffractive optical element while fixing the laser irradiation unit that irradiates the laser light. The method for forming a light shielding film according to 1. 10. Any one of claims 1 to 9, wherein a focal position of the laser light is moved by displacing a laser irradiation unit that irradiates the laser light while the multilayer diffractive optical element is fixed. The method for forming a light-shielding film according to the item. A pair of diffraction grating layers having a plurality of ridges arranged concentrically and each having a diffractive optical surface with a sawtooth-shaped cross section in the radial direction, comprising a pair of diffraction grating layers made of plastic. , a multilayer diffractive optical element in which the unevenness of the diffractive optical surfaces is fitted to each other,
When one of the two slopes extending from the ridge line of the ridge portion is a lattice surface and the other slope is a side wall surface, the side wall surface facing the pair of diffractive optical surfaces in a fitted state. A boundary region between the two is a light-shielding film formed by a carbonized region obtained by carbonizing a part of the diffraction grating layer, and the transmitted light that is transmitted through the boundary region among the incident light incident on the diffractive optical surface is blocked. A multi-layer diffractive optical element provided with a light shielding film for shielding light. 13. The multi-layered diffractive optical element according to claim 12, wherein said carbonized region is formed of a plurality of dots, and said adjacent dots are arranged in a partially overlapping state. 14. The multi-layered diffractive optical element according to claim 13, wherein the plurality of dots have an elliptical cross section and are arranged in a posture in which the longitudinal direction extends in the height direction of the side wall surface. 15. Any one of claims 12 to 14, wherein the thickness of the light-shielding film in the radial direction of the diffractive optical surface in the ridge is 10% or less of the width of the ridge. 10. The multi-layered diffractive optical element according to the above item. 16. The multi-layered diffractive optical element according to claim 15, wherein the thickness of the light shielding film in the radial direction of the diffractive optical surface in the ridges is 1% or less of the width of the ridges. a diffraction grating section having the pair of diffraction grating layers;
16. The multi-layered diffractive optical element according to any one of claims 12 to 15, comprising a pair of lenses cemented to both surfaces of said diffraction grating section.

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