JP2000056112A - Three-dimensional diffractive optical element and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a three-dimensional diffractive optical element capable of producing a high-performance diffractive optical element in optical glass by distributing a permanent refractive index change three-dimensionally, and a method of manufacturing the same. provide. SOLUTION: A wavelength of 200 nm to 2000 n having a pulse width of 1 nanosecond to 1 femtosecond to the optical glass 1.
The three-dimensional diffraction grating 2 as a three-dimensional refractive index distribution 13 written in the optical glass 1 by utilizing a permanent refractive index change or optical damage due to multiphoton absorption of the ultrashort pulse laser beam 11 of m Is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a three-dimensional diffractive optical element and a method for manufacturing the same, and more particularly to a three-dimensional diffractive optical element in glass by ultra-short pulse laser beam processing and a method for manufacturing the same.

[0002]

2. Description of the Related Art At present, diffractive optical elements that can obtain an arbitrary amplitude or intensity distribution in a diffraction field by drawing an amplitude or phase object pattern on a two-dimensional plane with a computer have been used. This diffractive optical element has versatility not found in conventional optical elements, and has been applied to various fields such as a CD pickup optical system.

[0003]

However, such conventional diffractive optical elements have a low degree of freedom because they are all developed on a two-dimensional plane or a curved surface. Also,
Chromatic aberration cannot be corrected. Further, the diffraction efficiency is low. There is also a problem that a signal path connecting specific points cannot be formed.

[0004] Since the processing of these diffractive optical elements is limited to a plane or a curved line, the performance thereof is naturally limited. At least, it is impossible to remove the wavelength dependence of the diffractive optical element written on one plane. In this regard, in the case of a diffractive optical element having a three-dimensional structure, it is easy to achieve a diffraction efficiency of 100%. Furthermore, various optical elements having little aberration including chromatic aberration can be manufactured by utilizing three-dimensional degrees of freedom.

The spatial concentration of electromagnetic energy is the basis of optical processing, but the use of an ultrashort pulse laser beam as a light source and the temporal and spatial concentration of power density makes it possible to use the nonlinear effect. . In addition, examples of writing bits of an optical memory and writing of a linear waveguide using a permanent refractive index change by irradiating an ultrashort laser pulse light into an optical glass have already been reported (Laser Research, 2nd Report).
Vol. 6, No. 2, p. 150-154, "Induced Refractive Index Change Inside Glass by Ultrashort Pulse Laser", 1998.
Month).

The present invention is based on the development of such prior art, and provides a three-dimensional diffractive optical element capable of dispersing a permanent refractive index change three-dimensionally and producing a high-performance diffractive optical element in optical glass. An object of the present invention is to provide an optical element and a method for manufacturing the same.

[0007]

According to the present invention, there is provided a three-dimensional diffractive optical element having a pulse width of 1 nanosecond to 1 femtosecond to optical glass. 20
It has a three-dimensional refractive index distribution written in the optical glass by utilizing a permanent refractive index change or optical damage due to multiphoton absorption of an ultrashort pulse laser beam from 0 nm to 2000 nm. .

[2] In the three-dimensional diffractive optical element according to the above [1], the optical glass is silica glass. [3] The three-dimensional diffractive optical element according to [1], wherein the silica glass contains hydrogen gas. [4] In the three-dimensional diffractive optical element according to the above [1], the optical glass is a soda glass having breakage resistance.

[5] In the three-dimensional diffractive optical element according to [1], the optical glass is an optical plastic. [6] In the three-dimensional diffractive optical element according to the above [5], the optical plastics is acrylic. [7] In the method for manufacturing a three-dimensional diffractive optical element, the optical glass is irradiated with an ultrashort pulse laser beam having a pulse width of 1 nanosecond to 1 femtosecond and having a wavelength of 200 nm to 2000 nm, A permanent refractive index change or optical damage due to multiphoton absorption of the ultrashort pulse laser light is caused, and written into the optical glass.
This is to generate a dimensional refractive index distribution.

[8] In the method for manufacturing a three-dimensional diffractive optical element according to the above [7], a three-dimensional refractive index distribution to be written in the optical glass is generated by scanning the ultrashort pulse laser beam. It is intended to be.

[9] In the method for manufacturing a three-dimensional diffractive optical element according to the above [7], the three-dimensional refractive index distribution is a Bragg diffraction grating.

[0011]

Embodiments of the present invention will be described below. The present invention collects ultrashort pulse laser light having a pulse width of 1 nanometer to 1 femtosecond and a wavelength of 200 nm to 2000 nm in a transparent optical glass such as an optical plastic such as silica glass, soda glass, or acrylic. Produces a diffractive optical element having a three-dimensionally distributed refractive index, such as a Bragg diffraction grating, in optical glass by emitting light and causing a permanent refractive index change or optical damage by multiphoton absorption. Things.

FIG. 1 is a schematic view showing a method for manufacturing a three-dimensional diffractive optical element according to the present invention. In this figure, 1
Is a bulk optical glass, and 2 is a three-dimensional diffraction grating written in the optical glass as a three-dimensional refractive index distribution. Here, an ultrashort pulse laser beam 11 having a pulse width of 1 nanometer to 1 femtosecond and having a wavelength of 200 nm to 2000 nm is applied to the optical glass 1 via a condenser lens 12, and the ultrashort pulse laser beam 11 The permanent refractive index change or optical damage due to multiphoton absorption is used to generate a three-dimensional refractive index distribution 13 written in the optical glass 1. In FIG. 1, reference numeral 14 denotes raster scanning of a beam (lens).

[Example 1] In a silica glass, a wavelength of 800
By focusing the amplified titanium sapphire laser pulse of nm, 0.1 picosecond and 1 millijoule, and scanning the focal point, regular Bragg diffraction of 1 mm length and width, 3 micron period, and about 30 micron depth A lattice was made.

In this embodiment, the scanning in the depth direction is not performed, but the scanning in the depth direction makes it possible to produce a thicker three-dimensional diffraction grating. If a curved scan is performed, a lens function can be added. The tertiary diffraction grating 2 of the three-dimensional diffractive optical element manufactured in this manner is, as shown in FIG.
When irradiated with the laser beam 21, an asymmetrical diffraction phenomenon, which is a feature of the volume diffraction grating, could be confirmed. In addition,
In FIG. 2, reference numeral 22 denotes diffracted light, and 23 denotes undiffracted light.

Although the diffraction efficiency is still low and is currently several percent, it is possible in principle to achieve a diffraction efficiency of 100% by optimizing the laser beam intensity, writing conditions and scanning method. is there. As described above, according to this embodiment, it is possible to obtain asymmetrical diffraction development and high diffraction efficiency, which are characteristics of the volume diffraction grating.

At present, the diffraction efficiency is a few percent, but as described above, with a little contrivance, 10%
It is possible to achieve a diffraction efficiency of 0%. In addition,
By including hydrogen gas in silica glass, the writing sensitivity of ultrashort laser light can be improved. [Embodiment 2] In the case of a breaker-resistant sorter glass as an optical glass, an example of writing many spots having a diameter of several michrome is shown in an academic journal report or the like, and application to that is also conceivable.

[Embodiment 3] In the case of optical plastics such as acrylic as the optical glass, an example of writing a waveguide and a volume diffraction grating is shown in a report of a conference in the 1970's. Application is also conceivable. As described above, according to the method for manufacturing a three-dimensional diffractive optical element, a three-dimensional refractive index distribution can be created. With this degree of freedom, for example, a three-dimensional Bragg of an arbitrary shape designed by a computer Fabrication of a diffraction grating is possible. In other words, in the diffraction element of the present invention that uses a three-dimensional space, this degree of freedom has the degree of freedom of the three-dimensional space itself. In this respect, the degree of freedom of the lens is limited to a curved surface, that is, a spherical surface.

The three-dimensional diffractive optical element of the present invention is a general chemical instrument or imaging device (camera) in the field of optical instruments, an optical transmission switching device, a wavelength multiplexing optical communication device in the field of optical communications, In the field of optical measurement, optical interferometers,
A wide range of applications such as a biological light measurement device can be applied. Further, a combination of the three-dimensional diffractive optical element of the present invention and a lens is also conceivable, and many applications are conceivable. For example, a three-dimensional diffraction grating can be written in a conventional lens, and can be used for, for example, focus detection of a photographic lens and photometry. Furthermore, it can be a double focus.

Further, as a usage method, application to security and encryption can be considered. For example, it is possible to write an ID (personal identification number) or the like on a small glass part using a three-dimensional hologram. Since the information capacity is large, various applications are possible. In addition,
The present invention is not limited to the above embodiments, and various modifications are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0020]

As described above, according to the present invention, the following effects can be obtained. (A) It is possible to produce a high-performance diffractive optical element in optical glass by distributing a permanent refractive index change three-dimensionally.

(B) A three-dimensional refractive index distribution can be created. With this degree of freedom, for example, a three-dimensional Bragg diffraction grating of an arbitrary shape designed by a computer can be manufactured. (C) It is possible to obtain an asymmetrical diffraction development and a high diffraction efficiency, which are characteristics of the stacked diffraction grating.

[Brief description of the drawings]

FIG. 1 is a schematic view illustrating a method for manufacturing a three-dimensional diffractive optical element according to the present invention.

FIG. 2 is a schematic diagram illustrating the operation of a three-dimensional diffractive optical element according to an embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 optical glass as bulk 2 three-dimensional diffraction grating as three-dimensional refractive index distribution 11 ultrashort pulse laser beam 12 condenser lens 13 three-dimensional diffraction grating (three-dimensional refractive index distribution) 21 He-Ne laser beam 22 Diffracted light 23 Non-diffracted light

Claims (9)

[Claims] 1. A wavelength of 200 nm to 2000 nm having a pulse width of 1 nanosecond to 1 femtosecond on optical glass.
Three-dimensional diffraction, which has a three-dimensional refractive index distribution written in the optical glass using a permanent refractive index change or optical damage due to multiphoton absorption of ultrashort pulse laser light Optical element. 2. A three-dimensional diffractive optical element according to claim 1, wherein said optical glass is silica glass. 3. The three-dimensional diffractive optical element according to claim 1, wherein said silica glass contains hydrogen gas. 4. The three-dimensional diffractive optical element according to claim 1, wherein the optical glass is a soda glass having a breakage resistance. 5. The three-dimensional diffractive optical element according to claim 1, wherein the optical glass is an optical plastic. 6. The three-dimensional diffractive optical element according to claim 5, wherein said optical plastic is acrylic. 7. A method according to claim 1, wherein the optical glass has a pulse width of 1 nanosecond to 1 femtosecond and a wavelength of 200 nm to 2000 nm.
(b) causing a permanent refractive index change or optical damage to the optical glass by multiphoton absorption of the ultrashort pulse laser light, and (c) writing into the optical glass. A method for producing a three-dimensional diffractive optical element, wherein a three-dimensional refractive index distribution is generated. 8. The method for manufacturing a three-dimensional diffractive optical element according to claim 7, wherein the ultra-short pulse laser beam is scanned to generate a three-dimensional refractive index distribution written in the optical glass. A method for manufacturing a three-dimensional diffractive optical element. 9. The method for manufacturing a three-dimensional diffractive optical element according to claim 7, wherein said three-dimensional refractive index distribution is a Bragg diffraction grating. .