JPH02201322A - Nonlinear optical element and production thereof - Google Patents

Abstract

PURPOSE:To effectively confine the light and thereby enhance efficiency by providing a photosensitive polyimide layer as a clad having a groove for an optical wave guide and forming an org. nonlinear optical crystal as a core having a high refractive index in this groove. CONSTITUTION:The core part consists of the stock having the high nonlinear optical characteristic and the circumference thereof consists of the material having the refractive index lower in the wavelength region of the object than in the core part. Namely, two sheets of substrates 1, 2 are provided above and below and the photosensitive polyimide layer 4 is patterned and formed between these two substrates so as to have the groove 3 for the optical wave guide. This polyimide layer 4 is used as the clad in common use as a spacer and the org. nonlinear stock is packed into the groove 3 for the optical wave guide and is subjected to crystal growth, by which the org. nonlinear optical crystal as the core is obtd. The light is effectively confined in the narrow region in this way and the efficiency is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a nonlinear optical element that converts the wavelength of laser light and a method for manufacturing the same.

(b) Conventional technology Among various nonlinear optical phenomena, second harmonic generation (S
Since HG) can easily shorten the wavelength of laser light by half, research is being conducted in the field of optoelectronics with the aim of applying it to recording and light sources such as light sources for optical disks and light sources for laser printers. .

Recently, 2-s+ethyl-4-nitroanil
Organic crystals with a π-electron conjugated system, represented by ine (MNA), have extremely high second-order nonlinear optical properties, and they Compared to crystals! It is expected that the efficiency will be as high as 0.03, and many studies have been conducted.

Furthermore, since nonlinear optical phenomena require high optical power density, methods of confining the light in as narrow a region as possible are being studied. The methods include: (1) A method of growing the organic nonlinear optical crystal in a cylindrical glass capillary to form a circular waveguide.

(2) A method of creating a slab waveguide by growing a thin 1h single crystal of an organic nonlinear optical material in a planar shape on a glass substrate.

(3) A method of creating a three-dimensional optical waveguide by providing spacers on a glass substrate by dry etching to form an optical waveguide iJ, filling the optical waveguide groove with an organic nonlinear optical material and growing crystals.

etc. are being considered.

(c) Problems to be solved by the invention In general, in organic crystals such as MNA that have high nonlinear optical properties, the polarization axis within the crystal is limited to a certain specific orientation, and high nonlinear optical effects can be achieved in any orientation. Therefore, when used as an optical waveguide, it is necessary to match the propagation direction of light with the direction exhibiting nonlinear optical characteristics with high crystallinity.

However, in the cylindrical optical waveguide described in (1) above, it is difficult to arbitrarily control the direction of crystal growth, and it is generally difficult to grow crystals in an appropriate orientation.

In addition, in the slab waveguide described in (2) above, it is possible to select a specific direction after growing crystals on one surface, but it is not always possible to grow crystals only in the desired direction, so unnecessary parts may be This not only results in poor yield, but also makes it impossible to confine light in a narrow area in the horizontal direction.

In addition, in the three-dimensional optical waveguide described in (3) above, it is possible to secure a narrow area in both the vertical and horizontal directions and confine the light therein, but in the capillary fabrication process of organic materials, it is possible to prevent dust from entering the substrate. Due to contamination, etc., gaps are created in parts other than the optical waveguide groove, which makes it difficult to fill only the optical waveguide groove with the organic nonlinear optical material.

The purpose of the present invention is to create a three-dimensional optical waveguide groove that has a narrower area in which organic nonlinear optical materials can be confined both vertically and horizontally than conventional optical waveguides, and to efficiently obtain organic nonlinear optical materials. An object of the present invention is to provide a nonlinear optical element that fills an optical waveguide groove and makes it possible to realize higher nonlinear optical effects than ever before, and a method for manufacturing the same.

(D) Means for Solving the Problems In this invention, a photosensitive polyimide layer as a cladding having 114 for an optical waveguide is provided on a substrate, and the groove has a refractive index higher than that of the photosensitive polyimide layer. This is a nonlinear optical element in which an organic nonlinear optical crystal is formed as a core.

The optical waveguide of this nonlinear optical element is made by coating a resist solution as a material source for forming photosensitive polyimide on one substrate to form a resist film, and after baking, the optical waveguide is formed on the resist film. A mask layer having a pattern of grooves is formed, then exposed to light to form grooves for optical waveguides in the resist film, and further baked to complete imidization of the resist film to form a photosensitive polyimide film as a cladding. , the upper surface of the polyimide film is covered with another substrate, and the photosensitive polyimide film is sandwiched between both substrates, and then an organic nonlinear optical material is crystal-grown in the groove for the optical waveguide to form the IT4 for the optical waveguide. It is obtained by forming an organic nonlinear optical crystal as a core.

That is, this invention forms an optical waveguide groove using photosensitive polyimide as a spacer and cladding layer, and grows an organic nonlinear optical crystal as a core in the optical waveguide groove to form an optical waveguide with high nonlinear optical characteristics. It was designed to do so.

The substrate in this invention may be any substrate as long as it has a refractive index lower than the refractive index of the organic nonlinear optical crystal of the core, and is preferably a glass substrate, a quartz substrate, or the like.

It was concluded that photosensitive polyimide is the most desirable material for the cladding in this invention. This is because photosensitive polyimide has high adhesion to glass, and when this material is used as a spacer, organic crystals will not be sucked up to parts other than WII3 for the optical waveguide shown in Figure 2 during capillary lization. This is because, as a result, it becomes possible to efficiently confine the organic nonlinear optical material in the groove portion. Another reason for this is that photosensitive polyimide is relatively stable up to high temperatures and does not react with organic nonlinear optical materials during crystal growth by capillary lization or zone melting to create organic crystals.

The organic nonlinear optical material in this invention is 2-m
It is preferable to use only organic crystals with high second-order nonlinear optical properties having a π-electron conjugated system represented by etl+yl-4-nitroani 1ine, so-called MNA, as the material.

In addition to crystal growth by zone melting, it is also preferable to use a saturated solution of MNA as a recrystallization method using a solvent, which is obtained by dissolving MNA powder in a polar solvent such as acetone, methanol, or ethanol.

When using only the former organic crystal, zone melt (
An organic nonlinear optical crystal as a core can be placed in a groove for an optical waveguide using the Bridgman method.

That is, with the imidized photosensitive polyimide film sandwiched between both substrates, for example, MNs are placed in the groove for the optical waveguide.
A sample is prepared by filling the A crystal by the capillary lization method, and then crystal growth is performed by the horizontal Bridgman method. At this time, as shown in FIG. 5, the sample 9 was placed at 131'c (MNA
The sample 9 is held at the melting point of 2+z/sin by the motor 11 via the string lO in the direction of the arrow shown at A at a rate of 2+z/sin. In addition, in FIG. 5, 8a is a thermocouple, 12 is a voltage supply source, and 13 is a temperature controller.

In this way, the MNA single crystal serving as the core is grown.

In addition, when forming the core by this zone melt,
As mentioned above, the material is MNA crystal, but it is not limited to this, but materials with high second-order nonlinear optics, such as 3-5et
hyl-4-n1Lropyridine-1-ox
ide (POM) and 2- (n-prolino+)
-5niLropyridine (PNP) is also applicable.

On the other hand, when using the latter saturated solution, the core can be created using the above-mentioned recrystallization method using a solvent.

That is, the procedure is, for example, in the case of MNA powder: 1. Prepare an acetone saturated solution of MNA by dissolving MNA powder in acetone.

2. The solution is sucked up by capillary rise into the gap as an optical waveguide groove formed by two glass substrates.

3. Leave this in a low-temperature constant temperature oven for about 10 days.

The temperature inside the furnace at this time is preferably about 25 to 30°C.

In addition, regarding the formation of the core using this recrystallization method, not only MNA but also POM, PNP, etc. can be applied as the solute.

In this invention, the refractive index of the photosensitive polyimide layer is S~1.7, as shown in FIG. 4, and it is sufficient that the refractive index of the organic nonlinear optical crystal serving as the core is higher than that of the polyimide.

(e) In a planar nonlinear optical element in which the working core is made of a material with high nonlinear optical properties and the periphery is made of a material with a lower refractive index than the core in the target wavelength range, two substrates are provided above and below. , a photosensitive polyimide layer is patterned to have a groove for an optical waveguide between both substrates, this polyimide layer is used as a spacer and a cladding, and an organic nonlinear optical material is filled in the groove for the optical waveguide, By growing the organic nonlinear optical crystal as the core, it is possible to easily control the dimensions of the groove for the optical waveguide. You can place crystals.

In addition, since the photosensitive polyimide layer as a cladding is used as a spacer, there is a possibility that the nonlinear optical material oozes into areas other than the areas where the optical waveguide grooves are formed on both substrates during crystal growth of the organic nonlinear optical material. That's it.

Furthermore, for optical waveguide) 11! Since a photosensitive polyimide layer is used to form the photoresist, a normal photoresist coating process can be used.

(f) Examples The present invention will be described in detail below based on examples. Note that this invention is not limited by this.

In FIG. 2, the optical waveguide of the nonlinear optical element includes a photosensitive polyimide layer 4 as a cladding having a layer (for the optical waveguide) 7113 on two glass substrates l and 2, and a photosensitive polyimide layer 4 with a refractive index lower than that of this polyimide layer 4. It mainly consists of an MNA crystal 5 as a core.

Next, the manufacturing method will be explained.

In Figure 1.2.5, as shown in Figure 1(a),
A resist film 4a is formed by coating a resist solution on one glass substrate 1 [see FIG. 1(b)], and after baking, a mask having a DLT pattern for an optical waveguide is formed on the resist film 4a. Layer 6 is formed and then exposed to light [FIG.
c)] It 3 for the optical waveguide is provided on the resist film 4a, and further baked to complete the imidization of the resist film 4a to form a photosensitive polyimide@4 as a cladding.
1(d)], the upper surface of the polyimide film is covered with another glass substrate 2, and the photosensitive polyimide film 4 is sandwiched between both plates 1 and 2 [see FIG. 1(e)], Thereafter, an MNA crystal is grown at f+13 for the optical waveguide, and an MNA crystal 5 as a core is formed at '71It3 for the optical waveguide, thereby obtaining the optical waveguide 15 shown in FIG.

In the above manufacturing process, Fig. 1 (aXb) (c) (
d) shows the process of applying photosensitive polyimide as a substrate and cladding and forming a pattern, which is the same as the process of applying a resist solution as a normal photoresist and forming a pattern. is coated using a spin code method, then exposed to ultraviolet light and developed to form grooves. At this time, by adjusting the shape of the mask, the number of rotations of the spin coater, and the viscosity of the photoresist, the width is 0.8 μm or more and the depth is 0.1 μm to 10 μm.
The shape of 174 can be changed arbitrarily within the range of m.

Note that the final step of post-baking shown in FIG. 1 (+1) must be carried out at 400°C for 30ml; if carried out at a lower temperature, the imidization reaction will not be completed completely;
During the crystal growth by capillary lization or zone melting described above, it reacts with the organic nonlinear optical material, making it impossible to form an optical waveguide. On the other hand, if the temperature is higher than this, the refractive index of the polyimide thin film may increase, and if it becomes too large, it is not preferable as an optical waveguide.

FIG. 4 shows the wavelength dependence of the refractive index of the polyimide thin film produced by this process. Measurements of refractive index were performed using an automatic ellipsometer.

Thereafter, an optical waveguide was formed by covering the upper surface thus formed with another substrate, filling the gap with MNA by the capillary rise method, and performing crystal growth by the horizontal Bridgman method.

Further, FIG. 3 shows another embodiment of the present invention.

That is, in the optical waveguide obtained in the above embodiment, by peeling off the upper substrate 2, it is also possible to form an optical waveguide 16 whose upper cladding layer is made of air.

In both of the above embodiments, it is possible to form an optical waveguide having an arbitrary crystal orientation by changing the dimensions and shape of ii+T. For example, it is known that the (010) plane tends to grow on the widest surface of the MNA single crystal, and therefore the f
It is possible to grow a (010) plane on the upper surface of the 4-layer structure, or to grow a (010) plane in a direction perpendicular to this. However, this does not apply to any organic crystal.

(G) Effects of the Invention According to the present invention, the core portion is made of an organic material with high nonlinear optical properties, and the refractive index of the surrounding area is higher than the refractive index of the core portion in the target wavelength range. In a planar nonlinear optical water wave made of a small material, the optical waveguide H4
Part dimension control as well as optical waveguide d1! Since the organic nonlinear optical material can be easily contained in a portion and a three-dimensional optical waveguide is formed in the portion, the following effects can be achieved.

(1) In the nonlinear optical element of the present invention, the core portion of the optical waveguide is formed in a narrow and limited portion in both the vertical and horizontal directions, so light is effectively confined and the element is highly efficient. ing.

(2) According to the manufacturing method of the present invention, organic crystals can be grown not only in the vertical direction but also in a narrowly limited portion in the horizontal direction. Therefore, the obtained nonlinear optical element has high optical power density and high efficiency.

(3) The production method according to the present invention can be applied to many crystals that can be produced by the Bridgman method or the recrystallization method using a solvent, so it can be applied to a wide range of materials.

(4) Since the nonlinear optical element of the present invention uses photosensitive polyimide as a spacer and cladding, it can be manufactured using a normal photoresist coating process, and an optical waveguide cage pattern can be formed at low cost and with high yield.

[Brief explanation of the drawing]

FIG. 1 is a manufacturing process explanatory diagram showing one embodiment of the present invention, and FIGS. 2(a) and 2(b) are a sectional view and a plan view, respectively, of an optical waveguide in a nonlinear optical element obtained in the above embodiment. Figures 3 (a) and (b) are diagrams corresponding to Figure 2 showing other examples, respectively, and Figure 4 shows the wavelength dependence of the refractive index of the photosensitive polyimide used as a spacer and cladding in the present invention. FIG. 5 is an explanatory diagram of the main part configuration showing the above embodiment. 1.2... Glass substrate, 3... Groove for optical waveguide, 4... Photosensitive polyimide layer, 5... MNA crystal, 6... ...mask layer,
7...Bridgeman furnace, 8...Heater 8a...Thermocouple, IO...String, 1
1... Motor, 15.16... Optical waveguide. Figure 5

Claims (1)

[Claims] 1. A photosensitive polyimide layer as a cladding having a groove for an optical waveguide is provided on the substrate, and an organic nonlinear optical layer as a core having a refractive index higher than that of the photosensitive polyimide layer is provided in the groove. A nonlinear optical element made of crystals. 2. A resist solution as a material source for forming photosensitive polyimide is applied onto one substrate to form a resist film, and after baking, a mask layer having a pattern of grooves for optical waveguides is formed on the resist film. The resist film is then exposed to light to form a groove for an optical waveguide, and then baked to complete the imidization of the resist film to form a photosensitive polyimide film as a cladding. Cover the photosensitive polyimide film with a substrate and sandwich the photosensitive polyimide film between both substrates, and then crystal-grow an organic nonlinear optical material in the groove for the optical waveguide to form an organic nonlinear optical crystal as a core in the groove for the optical waveguide. A method for manufacturing a nonlinear optical element, characterized by: