JPH05505474A - diffractive optical element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] diffractive optical element field of invention The present invention generally relates to diffractive optical elements.

Background of the invention It is known in the art to make diffractive optical elements that manipulate beams, and one example is A flat or spherical wavefront is converted into a generalized wavefront by optical beam manipulation. general Diffractive optics are thinner, lighter, and more versatile than standard optics. , hence laser scanners, compact discs, and laser computerized processing. Laser beam processing systems such as laser radar and bar code scanners Preferably used for stems.

The paper “Micro Fresnel Lens” by T. Represents background information about the lens.

H, Damman, published in Optik 31 in 1970. The paper "Shining Synthetic Phases - Only Holograms" by We are studying the efficiency of diffractive lenses.

A method of manufacturing a diffractive optical element and its effects are described by Gurley (GI+7) J, Suwaso Svason and Wilfrit B., Veldkamp (Veil dLamp) in the following paper: June 1989, “Diffractive optical elements used in infrared systems” Optical Engineering Vol. 28 No. 6, pp. 605-608; “Development of assembly of binary optical elements j, 5PIE Volume 437/Computer-generated formula International Conference on Holography, 1983, pp. 54-59.

Optical elements made by the Swason and Berdcan method have multiple phase zones. However, the shape of the zone is determined by the phase profile of the optical element. The zone has a series of steps, and the width of each step of the zone depends on the phase profile of the zone. Change. The number of steps per phase zone determines the efficiency of the optical element, and in this case, for example For example, eight stages create an optical element with approximately 95% efficiency, and 16 stages create an optical element with approximately 99% efficiency. Create something that is efficient. Unfortunately, the smallest zone dictates the number of stages, but this This limits the efficiency of the optical element.

The method includes the step of generating N masks, which are made of materials of the optical element. when used to erode 2N stages in each phase zone.

All stages have the same height, but the width varies depending on the zone shape.

The efficiency of the optical element made increases discontinuously with the number of masks used. , since each mask doubles the number of steps. The method achieves discrete levels of efficiency. does not provide a method for making optical elements with efficiency in between.

The efficiency measurements described above relate to a wide beam impinging on the optical element. laser s For narrow beam scanning along the optic, as is common in scanners, The efficiency of optical elements made with the methods described above varies across the optical element. this is, This is due to the fact that the stages of fortune change. If the step is wide or wider than the beam width. , the narrow beam effectively impinges on a flat surface.

U.S. Pat. No. 4,846,552 describes a two-plane optical element that utilizes holography. It describes how to make it and the coarse-scale integration (VLSI) technology.

Summary of the invention One object of the present invention is to provide an optical system in which the number of steps per zone varies across the optical element. The purpose of this invention is to produce a refractive optical element.

Accordingly, a diffractive optical element comprising a base and at least first and second phase zones is provided, where the first phase zone includes a first number of stages and a second number of stages is provided. The phase zone includes a second number of stages and in that case a first number of stages and a second number of stages. are different.

Further, in accordance with a preferred embodiment of the present invention, the height of jlrl and the 22nd multiple step is not constant.

Still further, according to a preferred embodiment of the present invention, The number of stages is generally equivalent across the optical element.

In accordance with a preferred embodiment of the invention, a method of assembling a diffractive optical element includes a stepwise phase A stage is also provided for defining a collection of masks to create a zone; At least one of the collections of blocks is partially masked in at least one phase zone. out, resulting in at least one phase zone being partially etched.

Finally, in accordance with a preferred embodiment of the present invention, a collection of masks for creating graduated phase zones is provided. A method of assembling a diffractive optical element is provided that includes the step of defining a At least one collection of masks has a partial mask alignment in at least one phase zone. and as a result at least one phase zone is partially etched and the mask collection The diffractive optical element is coated with a layer of photoresist, and the photoresist is Place one mask of the mask series on top of the photoresist layer and pass the photoresist through one mask. exposing the photoresist, thereby creating a mask pattern on the photoresist, and exposing the photoresist to light. etching the optical element and coating the diffractive optical element with a layer of photoresist; Align another mask in the collection of masks above the repeating the exposing, etching, matching and coating steps until the part is ready for use. .

Brief description of the drawing The present invention will be more fully understood and understood from the following detailed description taken in conjunction with the drawings. I think it will be recognized.

FIG. 1A is a diagram showing a cross section of an ideal diffractive optical element.

FIG. 1B illustrates the efficiency and operation of local controls made in accordance with a preferred embodiment of the present invention. FIG. 3 is a diagram showing a cross section of a refractive optical element.

FIG. 2 is a flowchart outlining a method for assembling the diffractive optical element of FIG. 1B.

Figure 3A is a horizontal view showing an ideal diffractive element labeled to show the occurrence of the East 1 mask. FIG.

FIG. 3B is a cross-sectional view of the optical element after the first mask has been etched.

FIG. 3C is a schematic diagram showing the first mask placed over the optical element to be etched.

Figure 4A is a horizontal view showing an ideal diffractive element labeled to show the generation of a second mask. FIG.

FIG. 4B is a cross-section showing the optical element after the first and second masks have been etched. It is a diagram.

FIG. 4C is a schematic diagram showing a second mask placed over the optical element to be etched.

Figure 5A is a horizontal view showing an ideal diffractive element labeled to show the generation of the third mask. FIG.

Figure 5B shows the optical element after the first, second and east 3 masks have been etched. FIG.

FIG. 5C is a schematic diagram showing a third mask placed over the optical element to be etched.

Detailed description of the invention Figure IA and Figure 2A show an ideal diffractive optical element 10 and a preferred embodiment of the present invention, respectively. 1 shows an optical element with locally controlled efficiency 11 made and operated according to an embodiment;

The ideal diffractive optical element 10 is a phase delay splitter for a given wavefront of an incoming beam of light. The base is integrally formed with a large number of phase zones 20 forming a continuous phase profile of the function. including base 12. As is known in the art, the shape of the phase zone 20 is A straight edge 16 and a smooth curve 18 on the other side.

According to a preferred embodiment of the invention, the optical element 11 is mounted as a monolithic structure on the base 13. The ideal shape of the curve 18 includes a number of phase zones 14 formed, in which case the ideal shape of the curve 18 is a series of is approximated by step 22, but its height and width vary.

The width of the steps generally corresponds to the minimum disassembly of the assembly process, as explained in more detail below. Therefore, instructions are given, and stages are thereby created. By "phase zone" 14, That step 22 approximates the complete curve 18, which means a phase zone.

The number of steps per zone 14 is generally such that the shape of each curve 18 is approximated. varies across the optical element 11. The phase zone 14 consists of multiple It is possible to have a number of closely spaced sub-steps 22 while other areas are further apart. Can have deeper stages of expansion. Alternatively, all stages of phase zone 14 Floors can be made through equal heights. The arrangement of step 22 and overall efficiency.

As will be appreciated by those skilled in the art, the generally small width of step 22 makes it possible to The optical element 11 improves the wavefront of the incoming light beam than the optical elements of the prior art. It is a good approximation and therefore efficient. Furthermore, the efficiency of the optical element 11 is ．． Not limited to the discontinuous levels of No. 895.790 are the phases of phase zone 14. This is because the number of is not constant.

Furthermore, the optical element 11 of the present invention allows for control of local efficiency. So For elements 11 such as receive. A narrow beam scanning across such an optical element is typically If the The beam is therefore generally equally diffracted throughout the scan. width Prior art optics with the same number of steps per phase zone regardless of the narrow The scanning beam is less diffracted due to the wide phase zone and is reduced to a thin phase zone. Therefore, it is diffracted even more effectively.

Now, we will explain the methods used to assemble the optical element 11 and generate the three masks. Exemplary Sections 2.3A-3C.

See Figures 4A-4C and 5A-5C. In step 50, the optical element: determined by characterizing both the incident light beam and the desired output light beam. It will be done.

This defines the optical properties of the optical element to be manufactured.

For example, a spherical phase profile for a collimating lens is: phi (1, r) = (2pi/lambda)” + qrt (z2 + y2 + F) (1 ) where lambda is the wavelength of the incident light beam.

The second example is an example of a quadrant phase profile: p h i (r, y) ・2p i/lambda ((x2+72)/2D (2) The third example is a more general non-spherical The phase profile is: phi (+12pi/lambda (sum (x, rl)) (3) where r is optical The radius from the center of the element is equal to 5prt(x2+y2), and ai is the optical element is a coefficient determined by the designed use of i is 1 and the coefficient a.

The required number of

In step 52, the phase zone is determined by the phase profile phi (x, y) modulo It is determined by evaluating 2pi. This is the location of the optical element on straight edge 16 , thereby creating a varying width Dt of the phase zone 14 (FIG. 1B). M is the number of phase zones 14 on the optical element, and i varies between 1 and M. Sara Then, the height T of the phase zone 14 is determined as follows.

T=nilamda/delta n(4) However, in Delta-1, the glass and the glass in which the element is embedded and the optical element 11 is made are Optical element materials such as gallium oxide, zinc selenide, germanium or quartz be.

The phase zones are created by VLSI etching, as explained below. for example , the essential equipment required to create the phase zone includes a device placed continuously above the optical element 11. an electronic or laser beam pattern generator that generates a series of masks to be , photoresist on top of the optical element 11 to protect the parts that are not to be etched. A spin coater (spin caster) that spreads the pattern and a continuous mask with high precision Ultraviolet (U, V, ) exposure system that aligns and exposes the photoresist and a predetermined depth whenever a given mask does not cover optical element 11. A reactive ion etching agent is included for etching the optical element 11 up to a point.

At step 54, a series of binary masks 56 are defined. As shown below, Mask 56 partially covers at least one portion of at least one phase zone 14. To etch or to etch only some of the phase zone 14 completely, It is determined that the entire phase zone 14 is etched.

Figures 3A-3C, 4A-4C and 5A-5C show that the binary mask 56 is An example circle of three phase zones 14 to be etched with blocks 56a, 56b and 56c. 2 shows how the shaped optical element 11 is defined. Figures 3A, 4A and 5A are ideal A side view of the phase zone 20 is shown.

Figures 3C, 4C and 50 are respectively 3B, 4B and 50 in plan view. Masks 56a, 56b forming the etched optical element 11 shown in side view in Figure B. and 56c.

The first example mask 56a of FIG. 3C is one in which each phase zone 14 is etched in its entirety. It is. Mask 56a includes a number of circular rings 60 shown in FIG. 3C. To create an equiphase boundary, equation 1 modulo pi by all of the circular optical elements 11 (π). First mask out of mask 56a The portion 62a spans between the first equi-phase boundary and the second equi-phase boundary. Next The area between successive equiphase boundaries of , in which case the masked out portions are marked as 62b and 62c. shown.

This operation requires two lamps, one at the height of T/2 and one on the base 13. can be assumed by subtracting in57 (in which case T is defined by Equation 2) and is shown in FIG. 3A. The intersection of curve 18 and upper line 57 is end of one of multiple masked-out portions 62a-62c of screen 56a. be marked. The beginning of each masked out portion 62a-62c is defined at point 59. However, in this case the lower line 57 intersects the curve 18.

The second mask, labeled 56b in FIG. 4C, represents the phase of the exemplary optical element 11. Two of the zones 14 are fully etched and a third phase zone 14 is partially etched. It is something. Mask 56b is created in a manner similar to that described above, with the following two exceptions: It is formed. 8) Equation 1 defines four lines 64 separated by a distance of T/4. Evaluate the equivalent modulo pi (π)/2 to subtract, and b) all the i positions For the phase zone 14, is the width of each possible step 22 to be made greater than the manufacturing resolution? A test is made for being greater than or equal to a predetermined minimum width. Possible If the width of the available step 22 is greater than the resolution, then the step 22 is etched. in other respects , the area is masked out so as not to create a possible step 22 . For example, the fourth In Figure B, the farthest step 66 has a width d that is less than the resolution of the manufacturing process. . That is, step 66 is masked out. Composite mask is part 68a-68f is masked out, but in this case portion 68f is further masked out by step 66. I go out.

A third example mask 56c is defined in which Equation 1 is spaced a distance T/8. The estimated modulo pi (π)/ It is 4. Once again, the width of each possible step 22 is checked against the minimum width. and masked out if the width is too small. Figure 5B Thus, the widths of the eight possible steps 22 in the farthest phase zone 14 are all The entire phase zone 14 smaller than the resolution, i.e. the farthest, is masked out. Ru. Further, the portions of the nearest phase zone 14 and the intermediate phase zone 14 are masked. is logged out. That is, in FIG. 5B, it is located in the closest phase zone 14. Only 7 of the 8 possible stages 22 and 8 possible stages of the intermediate zone 14 Only six of the floors will be built. In this way, some of the phase zones 14 are partially is etched, and all others are not etched.

Some of the phase zones 14 are partially etched so that the phase zones 14 are etched. The depth is not constant throughout the optical element 11. The total etching depth of the phase zone is It is defined as the distance from the top 70 of the optical element to the position of the bottom step. In other words , in FIG. 5B, the total etching depth hl of the two inner phase zones 14, respectively. and h2 are equivalent. The total etching depth h3 of the outer phase zone 14 is the total etching depth h l is smaller than l because the outer phase zone 14 is only partially etched by the mask 56b. This is because it is not etched by any of the masks 56c.

As will be appreciated, for each optical element 11 over which a narrow beam of light is scanned, The number of steps 22 in phase zone 14 is such that the narrow beam generally faces a constant number of steps. It is something like that. In this way, the diffraction of a narrow beam generally indicates that it constant as scanned over 1. This effect is due to the fact that sufficient stage 22 This is achieved by ensuring that the phase zone 14 is etched, and that As a result, their width changes are small.

As will be appreciated, the use of multiple masks 56 to etch optical element 11 is , creates a large number of stages per zone and thus the efficiency of the optical element 11 is high. . The lower bound on the number of stages is the required efficiency. The upper limit on the number of stages is determined by the resolution of the manufacturing process and and economic considerations.

Each additional mask adds to the production cost of optical element 11.

The number of masks 56 to be produced depends on the desired number of stages and the desired height of each stage 22. be done. For each mask 56, Equation 1 is evaluated modulo pi(π)/2 ('-1), where 1 is the number of masks. The etching depth or step height is T/2' for the 1 mask.

At step 80, masks 56 are printed by printing their photoplots. and then photoresolution them to the desired size of the optical element 11. alternative method As such, the mask 56 can be generated directly by an electron beam generator.

At step 82, the optical element 11 is connected to the masks 56a-56c for the above example. Both are continuously etched by the mask chain. As is known in VLSI manufacturing, First, the surface of the optical element 11 is coated with a layer of photoresist, and the first mask 56a is a photoresist layer. placed on top of the tresist. Next, the optical element 11 is irradiated with ultraviolet light. , then a photoresist is made. In other words, the pattern of the mask 56a is placed on the surface of child 11.

Optical element 11 is etched using any suitable lithographic process. appropriate process includes chemical or plasma or reactive plasma etching, thereby Each process has its own minimum manufacturing resolution.

Once etching is complete, the remaining photoresist is typically removed by a chemical process. be removed. Next, the second mask 56c is aligned onto the optical element 11 by a mask aligner. will be combined. In the above operation, the optical element 11 is eclipsed together with the entire pattern of the mask 56. It is repeated until it is engraved.

As will be appreciated by those skilled in the art, the present invention is not limited to what has been particularly shown and described above. Not limited to what you have. Rather, the scope of the invention is defined solely by the following claims. determined.

summary A diffractive optical element (11) and method of making the same are disclosed. Optical element (11 ) includes a base (13) and at least first and second phase zones (14). but in this case the first phase zone (I4) includes a first number of stages (22) and a second phase zone (I4). The phase zone comprises a second number of stages (22), in which case said first phase zone ( 14) from the i-th stage to the base (13) is at least one of i Regarding the value, from the i-th stage of the second phase (14) zone to the base (13) or The distance is different. The method for making the diffractive optical element (11) of the present invention includes the steps of defining a collection of masks to create a phase zone (14); In this case, at least one of the collections of masks has at least one phase zone (14 ) completely mask out at least one stage (22) of At least one phase (22) of both one phase zone (14) is not etched. I think that the.

Copy and translation of amendment) Submission (Article 184-7, Paragraph 1 of the Patent Act) August 1992 7 days 0r″eat　＊　娑 Botha Drive 3210 Name: Coherent-ink 1 Diffractive optical element: base; and A diffraction pattern formed on the base through a binary masking process, Each turn has multiple stages of descent toward the base, and For a given binary mask shape in one phase zone from the upper surface of the pattern, The distance of the created step from the upper surface of the pattern to the same phase in other phase zones The diffraction pattern is different from the distance to the stage where the binary mask is formed. Contains a tone.

2 The diffractive optical element that focuses the beam of light is: a base; and A diffraction pattern formed on the base through a binary masking process, The pattern includes multiple radial phase zones of different widths, each phase zone being It has multiple binary mask formation stages descending towards the base, and in this case each zone The number of stages in the phase is chosen so that the volume is also shaped into a wide radial inner phase zone. The number of steps formed is smaller than the number of steps formed in the narrowest radial outer phase zone. is also larger, so that the efficiency of the pattern is more uniform for light beams of different diameters. It is.

It is a binary mask used to create a diffractive optical element through a 32-bin masking process, The diffractive optical element includes at least two phases each having a plurality of descending steps. the mask has a pattern of The regions of the mask and unmasked regions are configured so that the shape that utilizes the mask During the formation phase, at least a portion of one existing phase in one phase zone is affected. a complete list of at least one existing phase in another phase zone while It includes said region whose surface is unchanged.

generating 41 sets of binary masks and using the masks continuously in the lithography process; Create a pattern that includes at least two phase zones, each with multiple descending steps. in which the improvement includes at least one forming step, in which case one While at least a portion of one existing phase in the phase zone of is affected, The entire surface of at least one existing stage in another phase zone remains unchanged.

5. How to assemble the diffractive optical element on the substrate: a) Cover the substrate with a layer of photoresist. b) placing a mask over said layer of photoresist; C) exposing the photoresist through the mask, thereby said exposing step of creating a mask pattern on the photoresist; d) mask; etching the substrate with a pattern; and e) A putter containing at least two phase zones, each with multiple steps of descent. Steps of repeating steps a to d each time using a different mask to create a mask , in which case at least one mask is constructed so that the combined corrosion During the eclipse phase, corrosion occurs in at least one existing phase in one phase zone. one existing phase zone, while the other phase zone A method comprising said assembly in which all surfaces of the step are unaltered.

Copy and translation of amendment) Submission (Article 184-8 of the Patent Law) August 7, 1992 Name: Coherent Ink A binary mask used to make a diffractive optical element by a 32-way masking process, , the completed diffractive optical element has at least A forming stage comprising a pattern including two phase zones and further utilizing a mask thereof. During a storey, the height of at least a portion of one existing step in one phase zone changes. , while the heights of all corresponding steps in other phase zones remain unchanged. , a binary mask consisting of a masked region and an unmasked region.

including the step of generating 41 sets of binary masks, and each step including a plurality of corresponding descending steps. Lithography that creates a complete pattern containing at least two phase zones with each In a method of assembling a diffractive optical element that uses a mask continuously in the process , comprising at least one formation step, in which in one phase zone The height of at least one part of one existing phase changes, but in other phase zones A method in which the height of all corresponding steps does not change.

5 A method for assembling a diffractive optical element on a substrate, the completed diffractive optical element being , including at least two phase zones, each having a plurality of corresponding descending stages. has a pattern, The stages are: a) coating a substrate with a layer of photoresist; b) said layer of photoresist; placing a first mask on the; C) exposing the photoresist through the mask, thereby The exposure step of creating a mask pattern on the photoresist: d) etching the substrate with a mask pattern; e) Repeat steps a to d each time using a different mask to create said pattern. during the combined etching step, the etching is performed to create two steps. performed on at least one part of one existing stage in one phase zone, while the other at least 1 such that the height of the corresponding step in the phase zone of and configuring two masks.

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Claims (1)

[Claims] 1 Diffractive optical element: base and; The first phase zone includes a first number of stages and the second phase zone includes a second number of stages. , in which case the distance from the i-th stage of the first phase zone to the base is i from the i-th stage of said second phase zone to said base for at least one value; and at least the first and second phase zones different from a distance of A diffractive optical element. 2. A diffractive optical element according to claim 1, in which the first and second plurality A diffractive optical element characterized in that the height of the steps is not constant. 3. A diffractive optical element according to claim 1, in which case a predetermined size of the optical element is Note that the number of steps per area of the optical element is generally equivalent across the optical element. Characteristic diffractive optical element. 4 In a method of assembling a diffractive optical element, a collection of masks for graduated phase zones is used. in which at least one of said collection of masks comprises at least one Completely masking out at least one phase of the phase zone so that the said at least one stage of at least one phase zone is not etched; How to characterize it. 5. A method of assembling a diffractive optical element: masking to create graduated phase zones. ・Define a collection of masks with a pattern, in which case the least number of said collection of masks and one completely masks at least one phase of at least one phase zone. out of the at least one of the at least one phase zone, such that the at least one of the at least one phase zone the step of determining that the step is not etched; the step of generating the collection of masks; ; coating the diffractive optical element with a layer of photoresist; placing one mask of the series of masks over the layer of photoresist; exposing the photoresist through the one mask, thereby exposing the photoresist to the exposing step of creating a mask pattern on the pattern; etching the optical element; coating the diffractive optical element with a layer of photoresist; aligning another mask of the collection of masks over the layer of photoresist; and; Expose, etch, align and cover until all of the mask collection is used. repeating the steps. 6 Diffractive optical element; base and; at least first and second phase zones, where the first phase zone is the second phase zone includes a first plurality of stages and has a first total etching depth; 2, comprising a plurality of stages and having a second different total etching depth. Diffractive optical element.