JPH05107577A - Waveguide-type nonlinear optical element and its production - Google Patents

Abstract

PURPOSE:To provide a waveguide-type nonlinear optical element having high performance and low loss by combining a low-loss glass waveguide and an org. material-based nonlinear optical material having advantages for nonlinear optical coefft. or switching rate. CONSTITUTION:This nonlinear optical element has such a structure that a part of core 2a in a glass waveguide 2 is replaced with a nonlinear optical material 4. The nonlinear optical material 4 is used the org. material having the refractive index within <=0.04 difference from that of the glass waveguide 2, >=10<-8>esu second-order nonlinear optical coefft. chi<(2)> and >=10<-12>esu cubic nonlinear optical coefft chi<(3)>.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide type non-linear optical element which can be used in an optical functional device such as an electro-optical effect element, a wavelength conversion element, an optical harmonic generation element, an optical car shutter, an optical bistable element, an optical switch and the like. The present invention relates to an element and a manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, an inorganic material has been generally used as a non-linear optical material forming a waveguide type non-linear optical element utilizing a second-order non-linear optical effect, and various optical elements have been realized. The nonlinear optical element using an inorganic material has an advantage that the input power is very small because the second-order nonlinear optical effect of the material is large, but the optical damage is large, and the waveguide manufacturing process is complicated. It has drawbacks.

On the other hand, semiconductors, semiconductor-doped glass, and the like have hitherto been typical as non-linear optical materials constituting a non-linear optical element utilizing the third-order non-linear optical effect, and various optical switches have been proposed. There is. This type of optical switch has an advantage that the input power can be very small because the third-order nonlinear optical effect of the material is large, but the switching speed is at most several ps, and higher switching speed cannot be desired. It has the drawback of Further, when semiconductor-doped glass is used, there is a drawback that the third-order nonlinear optical coefficient χ ⁽³⁾ is large only in a limited wavelength region such as the visible region.

On the other hand, the non-linear optical material made of an organic material is resistant to optical damage, has excellent workability such as thinning, has a switching speed of several tens of fs, and has a χ ⁽³⁾ in a wide wavelength range. It is expected as a material for high performance nonlinear optical elements such as large size.

[0005]

As described above, the organic material has various advantages as the nonlinear optical material, but in reality, the nonlinear material made of the organic material is used for forming a waveguide effective for increasing the efficiency of the nonlinear optical effect. There are few examples using optical materials, and low-loss waveguide-type nonlinear optical devices using such organic materials have not been reported.

An object of the present invention is to provide a low-loss glass waveguide for which a technique for producing a low-loss waveguide has been almost established up to the present (for reference, see, for example, Masao Kawauchi, "Quartz-based optical waveguides and optical integrated components. Application, "Optics, Vol. 118, No. 12, 681 (1989)
Etc.) and an organic material-based nonlinear optical material advantageous in terms of nonlinear optical coefficient and switching speed, to provide a low-loss and high-performance waveguide-type nonlinear optical element and its manufacturing method. ..

[0007]

A waveguide type nonlinear optical element according to the present invention comprises a silicon substrate, a glass waveguide or a glass waveguide film provided on the silicon substrate, and the glass waveguide or the glass waveguide. In a waveguide type non-linear optical element composed of a non-linear optical material that replaces a part of a core portion of a film, the non-linear optical material is made of an organic material, and the glass waveguide or the glass waveguide film and the non-linear optical material. And the difference in the refractive index is 0.04 or less,
The second-order nonlinear optical coefficient χ ^{(2) of the} nonlinear optical material is 1
It is 0 ^-8 esu or more, and the third-order nonlinear optical coefficient χ ^{(3) of the} nonlinear optical material is 10 ^-12 esu or more.

A method of manufacturing a waveguide type nonlinear optical element according to the present invention comprises a silicon substrate, a glass waveguide or a glass waveguide film provided on the silicon substrate, and a core of the glass waveguide or the glass waveguide film. A method of manufacturing a waveguide type non-linear optical element constituted by a non-linear optical material that replaces a part of a part, wherein the non-linear optical material comprises:
The difference in refractive index from the glass waveguide or glass waveguide film is 0.04 or less, and the second-order nonlinear optical coefficient χ ⁽²⁾ is 1
An organic material having a third-order nonlinear optical coefficient χ ^{(3) of} 0 ^-8 esu or more and a third-order nonlinear optical coefficient χ ⁽³⁾ of 10 ^-12 esu or more is used, and the glass waveguide or the waveguide film is formed on the silicon substrate, A part of the core portion of the glass waveguide or the glass waveguide film is removed by etching to form a groove portion, and then the groove portion is filled with the nonlinear optical material.

[0009]

[Function] By setting the difference in refractive index between the glass waveguide or the glass waveguide film and the nonlinear optical material to be 0.04 or less, the loss of light when light enters or exits the nonlinear optical material is reduced. It is possible to realize a waveguide type non-linear optical element with low loss as a whole. When the difference in refractive index exceeds 0.04, the loss at the interface becomes large, so that it is not possible to achieve low loss, and it becomes difficult to satisfy the single mode waveguide condition. Also, for the second-order and third-order nonlinear optical constants χ ⁽²⁾ and χ ⁽³⁾ , 10
By setting ^-8 esu and 10 ^-12 esu or more,
The optical path length of the non-linear optical material portion can be shortened, and the loss of the glass waveguide or the glass waveguide film portion is extremely low, and the overall loss can be reduced. 10 ^-8 es for each of χ ⁽²⁾ and χ ⁽³⁾
If u and 10 ^-12 esu or more, the optical path length of the nonlinear optical material for exerting an effective nonlinear optical effect becomes extremely long, and it becomes impossible to obtain a highly functional nonlinear optical element with low loss. Therefore, the difference in refractive index is set to 0.04 or less, and χ ⁽²⁾ and χ ⁽³⁾ are respectively 10 ^−8.
Esu and 10 ^-12 esu or more are required.

As the organic material constituting the non-linear optical material used in the present invention, it is desirable to use a polymeric material because it is easy to reduce loss and has a high degree of freedom in processing. As such a polymer material, one having a functional group having a nonlinear optical effect bonded to its side chain is preferable, and one containing a fluorine atom for controlling the refractive index to a desired value is preferable. desirable. Therefore, the first functional group having a nonlinear optical effect is bound to the side chain.
It is preferable to use a copolymer of the above polymer and a second polymer containing fluorine. The skeleton of the first polymer is
A vinyl polymer such as a methacrylate polymer, an acrylate polymer or a styrene polymer is preferable.

On the other hand, when the second polymer is a fluoroalkyl methacrylate polymer, a fluoroalkyl alkylate polymer, or a fluorinated polystyrene, good results are often obtained. Also,
A polymer obtained by substituting a trifluoromethyl group for a methyl group directly bonded to the main chain of an alkyl methacrylate polymer also gives good results. Even when the second polymer is a copolymer composed of two or more kinds of fluorinated monomers or polymers, good results can be obtained. That is, the second polymer is a copolymer of two or more fluoroalkyl methacrylate monomers, a copolymer of a fluoroalkyl methacrylate monomer and a fluoroalkyl acrylate monomer, or a copolymer of a fluoroalkyl methacrylate and another vinyl monomer. Polymer, copolymer of fluorinated styrene and fluoroalkyl methacrylate monomer, copolymer of fluorinated styrene and fluoroalkyl acrylate monomer, or copolymer of fluorinated styrene and different vinyl monomer May be

As the fluorine-based polymer forming the copolymer, that is, the second polymer, it is desirable to use a compound in which three or more atoms of fluorine are bonded to the aliphatic group or aromatic group constituting the second polymer. That is, when the number of fluorine atoms in the repeating unit of the fluorine-based polymer is 1 or 2, even if the fluorine-containing polymer fraction in the copolymer is 90% or more, the silica optical fiber or the silica glass waveguide is used. It is difficult to obtain a low-refractive index copolymer sufficient to achieve a refractive index matching with, and the effect of the present invention may not be sufficiently exhibited. When a polymer composed of repeating units having three or more atoms of fluorine bonded thereto is used as the fluorine-based polymer, a polymer having a functional group having a nonlinear optical effect bonded to the main chain or side chain (the above-mentioned first It is possible to achieve a low refractive index even when the ratio of the polymer) is 10% or more, and it is extremely possible to combine a functional group having a second-order or third-order optical nonlinearity required as a nonlinear optical element. It will be easier.

Such a fluorine-based polymer, that is, the second polymer, is bonded to the main chain of a fluoroalkyl methacrylate polymer or fluoroalkyl acrylate polymer containing 3 or more atoms of fluorine, fluorinated polystyrene or alkyl methacrylate polymer. It is effective to use a polymer in which a methyl group is replaced with a trifluoromethyl group. For example, by subjecting these to a copolymerization reaction with a vinyl monomer or vinyl polymer having a functional group having a nonlinear optical effect in the side chain, the objective nonlinear optical A copolymer having an effect, that is, a polymer material that can be used in the present invention is obtained. Also, when the fluoropolymer is a copolymer of vinyl polymers containing 3 or more atoms of fluorine, the terpolymer may be ternary together with, for example, a vinyl monomer or vinyl polymer having a functional group having a nonlinear optical effect in its side chain. A copolymer having a desired non-linear optical effect can be obtained by performing a copolymerization reaction of at least the system. Examples of such fluoropolymers containing fluorine of 3 atoms or more include fluoroalkyl methacrylate polymers such as 2,2,3,3-tetrafluoropropyl methacrylate, 1H, 1H, 5H-octafluoropentyl methacrylate, and 2, 2,2-trifluoroethyl methacrylate, 1H, 1H, 2H, 2H-heptadecafluorodecyl methacrylate, 1H, 1H, 3H-hexafluorobutyl methacrylate, 2,2,3,3-tetrafluorotertiary pentyl methacrylate, 2 , 2,3,3,4,4-Hexafluorotertiary hexyl methacrylate, 2,2,3,4,4,4-hexafluoroisopentyl methacrylate, 2,2,3,3,4,4-hexafluoro A copolymer such as isopentyl methacrylate, and further in the following formula

[0014]

[Chemical 1] R is CF ₃ CFHCF ₂ CH (CH ₂ CH ₃ )-, CF ₃ CFH
CF ₂ CH (CH ₂ CH ₂ CH ₃ )-, CF ₃ CFHCF ₂ C (C
_{H 3) 2 -, CF 3} CFHCF 2 C (CH 3) (CH 2 CH 3) -, C
_{F 3 CFHCF 2 C (CH 3} ) 2 CH 2 - and the like polymers and other fluoroalkyl methacrylate as a.
Also, as a fluoroalkyl acrylate polymer,
2,2,3,3-tetrafluoropropyl acrylate, 1H, 1H,
5H-octafluoropentyl acrylate, 2,2,2-trifluoroethyl acrylate, 1H, 1H, 2H, 2H-heptadecafluorodecyl acrylate, 1H, 1H, 3H-hexafluorobutyl acrylate, 2,2,3,3 -Tetrafluorotertiary pentyl acrylate, 2,2,3,3,4,4-hexafluorotertiary hexyl acrylate, 2,2,3,4,4,4-
Hexafluoroisopentyl acrylate, 2,2,3,3,4,
A copolymer such as 4-hexafluoroisopentyl acrylate, and further in the following formula

[0015]

[Chemical 2] R is CF ₃ CFHCF ₂ CH (CH ₂ CH ₃ )-, CF ₃ CFH
CF ₂ CH (CH ₂ CH ₂ CH ₃ )-, CF ₃ CFHCF ₂ C (C
_{H 3) 2 -, CF 3} CFHCF 2 C (CH 3) (CH 2 CH 3) -, C
_{F 3 CFHCF 2 C (CH 3} ) 2 CH 2 - and the like polymers and other fluoroalkyl acrylates such as is. Examples of fluorinated polystyrene include polymers such as pentafluorostyrene, trifluorostyrene, pentafluoro-α-methylstyrene, and trifluoro-α-methylstyrene. Copolymers obtained by combining these polymers can also be effectively used in the present invention.

[0016]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a perspective view showing a typical configuration example of the waveguide type nonlinear optical element of the present invention.

This waveguide type nonlinear optical element includes a silicon flat substrate 1, a glass waveguide 2 provided on the silicon flat substrate 1, and a core portion (waveguide layer) 2a of the glass waveguide 2. It comprises a non-linear optical material 4 partially replaced with an organic polymer material, and a cladding material layer 5 laminated so as to cover the glass waveguide 2 and the non-linear optical material 4 together. The clad material layer 5
May be provided as necessary, and the clad material layer 5 may not be provided. As the nonlinear optical material 4 made of an organic polymer material, the difference in refractive index from the glass constituting the glass waveguide 2 is 0.04 or less, and the second-order nonlinear optical coefficient χ ⁽²⁾ is 10 ^-8 esu. Thus, the third-order nonlinear optical coefficient χ ⁽³⁾ of 10 ⁻¹² esu or more is used.

Next, a method of manufacturing this waveguide type non-linear optical element will be described with reference to FIGS.

First, the surface of a silicon substrate is ground into a flat surface to form a silicon flat substrate 1, and a glass waveguide 2 is formed thereon by a known method. This glass waveguide 2 is
It has a core portion 2a, and the core portion 2a has, for example, a rectangular cross section [FIG. 2 (a)]. Subsequently, as shown in FIG. 2B, a part of the core portion 2a is removed by etching, and the removed portion is used as a groove portion 3. Then, the groove portion 3 is filled with the nonlinear optical material 4 made of the organic polymer material described above [FIG.
(c)]. Finally, the nonlinear optical material overflowing from the groove portion 3 is removed, and the cladding material layer 5 is provided so as to cover the glass waveguide 2 and the nonlinear optical material 4, whereby the waveguide type nonlinear optical element as shown in FIG. Is completed. Since the non-linear optical material 4 is made of an organic polymer material, it has excellent workability, and even when the non-linear optical material 4 is filled in the fine groove portions 3, the non-linear optical material 4 is filled well by a method of fluidizing by applying heat. be able to.

Next, the waveguide type non-linear optical element of the present invention will be described in more detail by showing examples in which it is applied to various optical functional devices.

Example 1 A directional coupler type optical switch 10 shown in FIG. 3 was produced using the waveguide type nonlinear optical element of the present invention. First, the glass waveguide 12 was formed on the silicon substrate 11. The glass waveguide 12 has two core portions (waveguide layers) 13a and 13b. The two core portions 13a and 13b form a single mode waveguide, and are arranged in parallel close to each other over a certain length to form a directional coupler. The coupling length as the directional coupler was 10 mm, the interval between the core portions 13a and 13b in the coupling portion was 6 μm, and the width and thickness of each of the core portions 13a and 13b were 8 μm. The difference in refractive index between the core portions 13a and 13b and the surrounding portion (so-called clad portion) was about 0.3%. Then, a part of one core part 13a was removed by etching, and the removed part was filled with a nonlinear optical material 14 made of an organic polymer material represented by the following formula. For the method of synthesizing the organic polymer material represented by this formula, see, for example, Applied Phys.
ys. Letters (Applied Physics Letters),
Volume 51, page 1 (1987). The size of the portion removed by etching had a width of 8 μm and a depth of 8 μm.

[0022]

[Chemical 3] The refractive index of the glass waveguide 12 is 1.456 for light having a wavelength of 1.3 μm, the refractive index of the nonlinear optical material 14 is 1.4565, and the difference is 0.0005. In addition, the second-order nonlinear optical coefficient χ ^{(2) of} this nonlinear optical material
Is 10 ⁻⁸ esu or more, and the third-order nonlinear optical constant χ
⁽³⁾ was 10 ^-12 esu or more. Next, the excess non-linear optical material in the filling portion was removed by a photo process to form a waveguide in which the glass waveguide 12 and the non-linear optical material 14 were integrated, and the optical switch 10 was completed.

The insertion loss of the optical switch 10 as the element itself is about 5 dB, and no significant increase in loss was observed as compared with the insertion loss of 4 dB before filling the nonlinear optical material 14. Next, the switching characteristics of this optical switch 10 were measured. When a YAG laser beam with a wavelength of 1.3 μm is made incident from the end surface of one core portion 13a and the intensity of the emitted light is examined, the refractive index of the nonlinear optical material 14 changes depending on the intensity of the incident light. The characteristics were obtained.

Example 2 Using the waveguide type nonlinear optical element of the present invention, the optical modulation element 20 shown in FIG. 5 was produced.
First, the glass waveguide 22 was formed on the silicon substrate 21. The glass waveguide 22 has a core portion (waveguide layer) 23 and constitutes a single mode waveguide. The glass waveguide 22 has a length of 40 mm, and the core portion 23 has a width and a thickness of 8 μm, respectively.
m. After that, part of the core portion 23 is 20 m long
m, a width of 8 μm, and a depth of 8 μm by etching, and on both sides of the part removed by this etching,
A pair of stripe-shaped electrodes 25 formed by a photo process
Formed. Next, the portion removed by etching was filled with a nonlinear optical material 24 made of an organic polymer material represented by the following formula. For the method of synthesizing the organic polymer material represented by this chemical formula, see, for example, Applied Phys.
ys. Letters (Applied Physics Letters),
Volume 51, page 1 (1987).

[0025]

[Chemical 4] The refractive index of the glass waveguide 22 is 1.456 for light having a wavelength of 1.3 μm, the refractive index of the nonlinear optical material 24 is 1.46, and the difference between them is 0.024. The second-order nonlinear optical coefficient χ ⁽²⁾ of this nonlinear optical material is 10
^-8 esu or more, and the third-order nonlinear optical constant χ ⁽³⁾ is 1
It was 0 ^-12 esu or more. Next, the silicon substrate 21 itself is heated up to 100 ° C. so that the space between the pair of electrodes 25 is 2
An electric field of MV / cm is applied, and the nonlinear optical material 24 is poled by cooling to room temperature while applying the electric field.
The light modulation element 20 was completed. The insertion loss of the light modulation element 20 itself is about 3 dB, and no significant increase in loss was observed as compared with the insertion loss of 2 dB before filling the nonlinear optical material 24.

Next, an optical modulation experiment was conducted using this optical modulation element 20. First, on the end face of the light modulation element 20,
Light having a wavelength of 1.3 μm from the laser diode was entered. Next, when a voltage was applied between the pair of electrodes 25 to apply an electric field to the nonlinear optical material 24 to change the refractive index of the nonlinear optical material 24, a modulation characteristic as shown in FIG. 6 was obtained. The half-wave voltage was about 5V.

Example 3 The wavelength conversion element 30 shown in FIG. 7 was produced using the waveguide type nonlinear optical element of the present invention. First, the glass waveguide 32 was formed on the silicon substrate 31. The glass waveguide 32 has a core portion (waveguide layer) 33.
To form a single mode waveguide. Glass waveguide 3
2 has a length of 40 mm, and the core portion 23 has a width and a thickness of 8 μm, respectively. After that, part of the core part 33 is 5 m long
m, a width of 8 μm, and a depth of 8 μm were removed by etching, and the removed portion was filled with a nonlinear optical material 34 made of an organic polymer material represented by the following formula. The method for synthesizing the organic polymer material represented by this chemical formula is described in, for example, Applied Phys. Letters, Vol. 51, p. 1 (1987).

[0028]

[Chemical 5] The refractive index of the glass waveguide 2 is 1. 3 for light with a wavelength of 1.3 μm.
456, and the refractive index of this nonlinear optical material 34 is 1.
46, and the difference is 0.024. The second-order nonlinear optical coefficient χ ⁽²⁾ of this nonlinear optical material is 10 ^-8
esu or more, and the third-order nonlinear optical constant χ ⁽³⁾ is 10
^-12 esu or more. Next, the silicon substrate 31 itself was heated to 130 ° C., and the nonlinear optical material 24 was subjected to a poling treatment by a corona poling method to complete the wavelength conversion element 30. The insertion loss of the wavelength conversion element 30 itself is about 3 dB, and no significant increase in loss was observed as compared with the insertion loss of 2 dB before filling the nonlinear optical material 34.

Next, a wavelength conversion experiment was conducted using this wavelength conversion element 30. First, on the end face of the wavelength conversion element 30, the wavelength from the laser diode is 1.3 μm and the intensity is 5 μm.
When 0 mW of light was made incident, a second harmonic (SHG) having a wavelength of 0.65 μm was observed from the lower part of the opposite end face. The conversion efficiency was about 0.02%. Cherenkov radiation was used for phase matching.

The embodiments of the present invention have been described above.
As the glass waveguide or glass waveguide film that can be used in the present invention, there are waveguides such as Mach-Zehnder interference type and loop mirrors in addition to the above-mentioned linear waveguide and directional coupler, and these waveguides are also effective. Available.

[0031]

As described above, according to the present invention, as the nonlinear optical material, the difference in refractive index from the glass waveguide or the glass waveguide film is 0.04 or less, and the second-order nonlinear optical coefficient χ ^{(2 )} Is greater than or equal to 10 ⁻⁸ esu and the third-order nonlinear optical coefficient χ ⁽³⁾ is greater than or equal to 10 ⁻¹² esu. This waveguide-type nonlinear optical element can be an important element in constructing a device or system incorporating, for example, a wavelength conversion element, an optical modulator, an optical switch, an optical bistable element, or the like. Have advantages.

[Brief description of drawings]

FIG. 1 is a perspective view showing a typical configuration example of a waveguide type nonlinear optical element of the present invention.

2 (a) to (c) are views for explaining a manufacturing process of the waveguide type nonlinear optical element of FIG. 1, respectively.

FIG. 3 is a perspective view showing a configuration of an optical switch of Example 1.

FIG. 4 is a characteristic diagram showing switching characteristics of the optical switch of FIG.

FIG. 5 is a perspective view showing a configuration of an optical modulator of Example 2.

6 is a characteristic diagram showing light modulation characteristics of the light modulation element of FIG.

FIG. 7 is a perspective view showing a configuration of a wavelength conversion element of Example 3.

[Explanation of symbols]

 1 Silicon Flat Substrate 2,12,22,32 Glass Waveguide 2a, 13a, 13b, 23,33 Core Part 3 Groove Part 4,14,24,34 Nonlinear Optical Material 5 Clad Material Layer 10 Optical Switch 11,21,31 Silicon Substrate 20 Light modulation element 30 Wavelength conversion element

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Makoto Hikita 1-6, Uchisaiwai-cho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation (72) Inventor Atsushi Abe 1-6, Uchiyuki-cho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corp. (72) Inventor Yoshinori Hibino 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corp.

Claims (3)

[Claims] 1. A silicon substrate, a glass waveguide or a glass waveguide film provided on the silicon substrate, and a non-linear optical material replacing a part of a core portion of the glass waveguide or the glass waveguide film. In the constructed waveguide type nonlinear optical element, the nonlinear optical material is made of an organic material, and a difference in refractive index between the glass waveguide or glass waveguide film and the nonlinear optical material is 0.04 or less, The second-order nonlinear optical coefficient χ ⁽²⁾ of the nonlinear optical material is 10 ^-8 esu or more, and the third-order nonlinear optical coefficient χ ^{(3) of the} nonlinear optical material is
Is 10 ^-12 esu or more, a waveguide type nonlinear optical element. 2. The waveguide type nonlinear optical element according to claim 1, wherein the organic material forming the nonlinear optical material is a polymer material. 3. A silicon substrate, a glass waveguide or a glass waveguide film provided on the silicon substrate, and a non-linear optical material which replaces a part of a core portion of the glass waveguide or the glass waveguide film. A method of manufacturing a constructed waveguide type nonlinear optical element, wherein the difference in refractive index from the glass waveguide or the glass waveguide film as the nonlinear optical material is 0.04 or less.
The following nonlinear optical coefficient χ ⁽²⁾ is more than 10 ^-8 esu,
An organic material having a third-order nonlinear optical coefficient χ ⁽³⁾ of 10 ^-12 esu or more is used, and the glass waveguide or the waveguide film is formed on the silicon substrate. A method of manufacturing a waveguide type non-linear optical element, which comprises removing a part of the core part by etching to form a groove, and then filling the groove with the non-linear optical material.