JPH063714A - Nonlinear optical thin film element and its production - Google Patents

Abstract

PURPOSE:To obtain a nonlinear optical thin film element consisting of thin film crystal of 3-methyl-4-nitropyridine-N-oxide (POM) which has high nonlinear susceptibility and excellent characteristics as a nonlinear optical material. CONSTITUTION:This nonlinear optical thin film element has a such structure that the thin film crystal layer of 3-methyl-4-nitropyridine-N-oxide (POM) and a transparent protective layer for preventing the sublimation of POM are successively formed on a substrate. In such a case, the thin film crystal layer of POM is formed by the vacuum vapor deposition of POM while cooling the substrate at <=0 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-linear optical thin film element made of an organic compound, which is useful as a wavelength conversion element for a laser, and a method for producing the same.

[0002]

2. Description of the Related Art Non-linear optical materials are used as optical elements such as wavelength conversion elements and optical modulators because light transmitted through the material is converted into higher harmonics. Conventionally, an inorganic material such as KDP (potassium dihydrogen phosphate) has been used as a nonlinear optical material, but in recent years, an organic nonlinear optical material has attracted attention because of its high nonlinear susceptibility. For example, 3-methyl-4-nitropyridine-N-oxide (hereinafter referred to as POM) having the following structural formula is
The cut-off wavelength is 414 nm, which is a short wavelength, exhibits nonlinear optical characteristics even in the blue wavelength region, and has a second-order nonlinear figure of merit that is 1600 times higher than KDP. Laser & Optics, p59,19
87.11.), Second harmonic generation, parametric oscillation, etc. have been observed for the bulk crystal (J.Zyss,
DSChemia and JFNicoud, Journalof Chemical Physi
cs , 74, p4800,1981; J.Zyss, I.Ledoux, RBHierle, RK
Rajand JLOudar, IEEE Journal of Quantum Electron
ics, QE-21, p1286, 1985).

[0003]

[Chemical 1]

[0004]

By the way, in order to use POM as a non-linear device which operates with a small light intensity, it is essential to fabricate an optical waveguide with POM in order to effectively use light. However, the technology for that purpose is still under study and has not been established. That is, MN
A (2-methyl-4-nitroaniline), DAN (1-
Other organic non-linear optical materials such as dimethylamino-2-acetamido-4-nitrobenzene) are processed into a slab-shaped or fiber-shaped waveguide by melting the material and then gradually cooling it. However, if this method is applied to POM, it cannot be applied because POM is thermally decomposed. Therefore, as a method of producing an optical waveguide of POM, only the production of a thin film waveguide by a single crystal production method from a solution has been attempted.

The present invention is intended to solve such a problem of the prior art, and makes it possible to easily obtain a non-linear optical thin film element composed of a POM thin film crystal, thereby manufacturing a POM thin film optical waveguide. The aim is to make the POM possible to be used as a non-linear device operating at low light intensity.

[0006]

The inventor of the present invention can form a crystal thin film of POM by vacuum vapor deposition, and further provide a transparent protective layer on the crystal thin film to keep POM in the form of a thin film crystal.
They have found that they can be used as thin film optical waveguides, and completed the present invention.

That is, the present invention provides a POM on a substrate.
Provided is a non-linear optical thin film element in which a thin film crystal layer and a transparent protective layer are sequentially laminated.

As a method for manufacturing such a non-linear optical thin film element, the substrate is cooled to 0 ° C. or lower and POM is vacuum-deposited to form a POM thin film crystal layer on the substrate, and then a transparent protective film is formed thereon. Provided is a method for manufacturing a non-linear optical thin film element characterized by forming a layer.

As described above, the nonlinear optical thin film element of the present invention has a structure in which the POM thin film crystal layer and the transparent protective layer are laminated on the glass substrate. As this POM thin film crystal layer, it is not always necessary to provide a POM single crystal layer, but a POM thin film layer in which the size of the POM crystal has grown to a certain size is provided according to the application of the nonlinear optical thin film element. For example, when used as a wavelength conversion element,
The size of the POM crystal is preferably larger than the fundamental wavelength.

As a method of forming the POM thin film crystal layer on the substrate, it is preferable to cool the substrate to a temperature of 0 ° C. or less and vacuum deposit the POM by the method of the present invention. By forming the POM thin film crystal layer by the vacuum deposition method, the film thickness of the POM thin film crystal layer can be precisely controlled, and by cooling the substrate temperature to 0 ° C. or less, the POM thin film crystal layer in which the POM crystal has grown Can be formed. When forming the POM thin film crystal layer by vacuum vapor deposition, masking may be performed as necessary to form a pattern. As a result, it becomes possible to apply to a minute nonlinear optical circuit.

In the present invention, as the transparent protective layer laminated on the POM thin film crystal layer, a transparent layer capable of preventing sublimation of POM is provided. Since POM has a high vapor pressure, if the thin film crystal layer is simply formed on the substrate, it quickly sublimes and disappears at room temperature. However, by providing a transparent protective layer, the POM thin film crystal layer is formed on the substrate. It becomes possible to hold it stably.

As such a transparent protective layer, a transparent layer made of various organic compounds or inorganic compounds can be provided. For example, polystyrene, polymethylmethacrylate, polybutadiene, polyethylene, polyethylene glycol, polyisobutylene, polymethylstyrene. It is possible to provide a transparent film made of an organic polymer compound such as, or a transparent film made of magnesium fluoride, cryolite, or the like.

The transparent protective layer is preferably formed by vacuum vapor deposition. This makes it possible to form the POM thin film crystal layer by vacuum vapor deposition and subsequently form the transparent protective layer with the same apparatus.

[0014]

According to the nonlinear optical thin film element of the present invention, since the transparent protective layer is further laminated on the POM thin film crystal layer on the substrate, a POM having a high nonlinear susceptibility and excellent characteristics as a nonlinear optical material. The thin film crystal layer is stably retained on the substrate without disappearing due to sublimation.

Further, according to the method for manufacturing a nonlinear optical thin film element of the present invention, since the POM thin film crystal layer is formed by vacuum vapor deposition, it is possible to precisely control the film thickness, and masking is performed during vapor deposition. Thus, it is possible to form a pattern. Further, according to the method for manufacturing a non-linear optical thin film element of the present invention, the substrate temperature is cooled to 0 ° C. or less, so that the size of the POM crystal in the POM thin film crystal layer is the fundamental wave when used as a wavelength conversion element. It becomes possible to make it sufficiently large.

[0016]

EXAMPLES The present invention will be described in detail below based on examples.

Example 1 FIG. 1 is a block diagram of a vacuum vapor deposition apparatus used for producing the nonlinear optical thin film element of the present invention. In the vacuum vapor deposition apparatus of the same figure, N ₂ gas is supplied to the liquid N ₂ dewar 2 through the solenoid valve 1 as shown by the arrow, and the low temperature N ₂ gas vaporized from the liquid N ₂ in the duar 2 is deposited in the vapor deposition chamber 3 The substrate mounting portion 4 can be cooled by supplying it to the back surface of the substrate mounting portion 4. Further, a thermocouple 5 is provided in the substrate mounting portion 4, and the temperature of the substrate mounting portion 4 can be controlled by controlling the supply amount of N ₂ gas by the temperature controller 6.

Using such an apparatus, a glass substrate was used as a vapor deposition substrate, a POM vaporization source was placed in a tungsten vaporization boat (BP-16, manufactured by Furuuchi Chemical Co., Ltd.), and the substrate temperature was set to -4 ° C. POM was deposited to a thickness of 500 nm. In this case, the degree of vacuum at the start of vapor deposition was set to 10 ⁻³ Pa or higher. The vapor deposition was performed by a resistance heating method, and the power source used was a variable current of 2.5 V and 100 A. The evaporation rate of the POM evaporation source and the film thickness of the vapor deposition film on the glass substrate were measured using a crystal vibration type film thickness meter.

After the POM was vapor-deposited on the glass substrate, a styrene oligomer (molecular weight: 1250) was vaporized from another vaporization boat by the same apparatus to vapor-deposit it to a thickness of 200 nm, to fabricate the nonlinear optical thin film element of the present invention. Then, after the temperature of this nonlinear optical thin film element rose to room temperature, it was taken out of the apparatus.

When the obtained nonlinear optical thin film element was observed with an optical microscope, crystals of about 10 to 40 μm were observed.

Further, in the second harmonic observation apparatus having the configuration shown in FIG. 2, the obtained nonlinear optical thin film element is placed in the sample chamber, and a dye laser (laser dye, laser dye, which emits XeCl excimer laser (wavelength 308 nm)) is excited. Wavelength 86 with styryl 9)
The second harmonic was observed by irradiating with 0 nm light. In this case, the energy per pulse was 1.6 mJ and the pulse width was about 20 ns. As a result, the waveform of the second harmonic generated corresponding to the oscillation waveform of the dye laser was observed by the transient digitizer as shown in FIG. For comparison, the second harmonic was similarly observed by using powdered POM instead of the nonlinear optical thin film element of the present invention.
The results are also shown in FIG. Accordingly, the intensity of the second harmonic when the nonlinear optical thin film element of the present invention is used is
The effectiveness of the present invention was confirmed, being about 10 times larger than the case of using powdered POM. As described above, the larger intensity can be obtained in the nonlinear optical element of the present invention.
It seems that the distance for nonlinear interaction was increased by the crystal formation.

Example 2 The temperature of the glass substrate was set to -25 ° C., POM was vapor-deposited to a thickness of 500 nm in the same manner as in Example 1, and then a styrene oligomer (molecular weight 1250) was vapor-deposited to a thickness of 200 nm. Then, after the temperature of this substrate rose to room temperature, it was taken out of the apparatus. When this was observed with an optical microscope, crystals with a size of 20 to 50 μm were observed.

Comparative Example 1 The temperature of the glass substrate was set to 20 ° C. (room temperature), and Example 1 was used.
In the same manner as above, POM was vapor-deposited to a thickness of 200 nm. Thereafter, it was observed that the vapor deposition film thickness of POM decreased while the evaporation boat cooled. After 5 minutes, the vapor deposition chamber was returned from the vacuum state to normal pressure, and the glass substrate was taken out. As a result, only a slight amount of POM adhered to the substrate.

Comparative Example 2 The temperature of the glass substrate was set to 2 ° C., POM was vapor-deposited to a thickness of 500 nm in the same manner as in Example 1, and then a styrene oligomer (molecular weight 1250) was vapor-deposited to a thickness of 200 nm.
Then, after the temperature of this substrate rose to room temperature, it was taken out of the apparatus. When this was observed with an optical microscope, crystals with a size of 1 to 2 μm were observed. It has been confirmed that a crystal of this size is not suitable for producing an optical waveguide because it has the same wavelength as the fundamental wave, and that the glass substrate should be cooled to a lower temperature during POM deposition.

Comparative Example 3 The temperature of the glass substrate was set to −2 ° C., and POM was deposited to a thickness of 500 nm in the same manner as in Example 1. Then, the substrate temperature was returned to room temperature without depositing the styrene oligomer thereon, and it was taken out of the apparatus. As a result, P
The OM deposited film sublimated and did not remain on the substrate. Then, the temperature of the glass substrate at the time of vapor deposition of POM was further lowered and the same experiment was repeated, but the result was the same.

As a result, even if the POM vapor deposition film is formed on the glass substrate by cooling the glass substrate during the POM vapor deposition, if the protective layer for preventing sublimation of POM does not exist on the POM vapor deposition film, It was confirmed that POM sublimes and disappears because of its high vapor pressure.

[0027]

According to the present invention, it becomes possible to easily obtain a non-linear optical thin film element made of a thin film crystal of POM having a high non-linear susceptibility and excellent characteristics as a non-linear optical material. It can be used as an operating non-linear device.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a vacuum vapor deposition apparatus used for manufacturing a nonlinear optical thin film element.

FIG. 2 is a configuration diagram of a second harmonic observation device.

FIG. 3 is a waveform diagram of a second harmonic.

[Explanation of symbols]

1 Solenoid valve 2 Liquid N ₂ Dewar 3 Deposition chamber 4 Substrate mounting part 5 Thermocouple 6 Temperature controller

Claims (4)

[Claims] 1. A non-linear optical thin film element comprising a substrate, on which a thin film crystal layer of 3-methyl-4-nitropyridine-N-oxide and a transparent protective layer are sequentially laminated. 2. The nonlinear optical thin film element according to claim 1, wherein the transparent protective layer is made of an organic polymer compound. 3. The substrate is cooled to 0.degree.
A method for producing a non-linear optical thin film element, which comprises vacuum-depositing 4-nitropyridine-N-oxide to form a thin film crystal layer thereof on a substrate, and then forming a transparent protective layer thereon. 4. The method for producing a nonlinear optical thin film element according to claim 3, wherein the transparent protective layer is formed by vacuum deposition of an organic polymer compound.