JPH03261925A - Light wavelength converter - Google Patents

Abstract

PURPOSE:To obtain high efficiency by forming a ring resonance type waveguide of a 1st and a 2nd optical waveguide on a substrate and converting all of wavelength-converted light, which is emitted from the entire periphery of the 2nd optical waveguide, into parallel light or a beam having the same focus by a grating. CONSTITUTION:On the reverse surface or top surface of the substrate 30, the grating 40 is formed which shapes the waveform of the higher harmonic light or sum frequency light emitted from the entire periphery of the 2nd optical waveguide 34 into the light which passes the same focus or parallel light. Therefore, higher harmonics from the entire periphery of the 2nd waveguide 34 including a curved part can be utilized and the optical waveguides are formed in circular shapes which are as small as possible so as to minimize the sum of the curvature loss and propagation loss of the optical waveguides, thereby increasing resonance magnitude. Consequently, the efficiency can be improved more than the mere utilization of the wavelength-converted light from the entire periphery.

Description

Detailed Description of the Invention (a) Industrial Application Field The present invention relates to an optical wavelength conversion device that shortens the wavelength of a laser beam by generating a second or third harmonic or a sum frequency, and further relates to More specifically, the present invention relates to an optical wavelength conversion device that is used to improve performance by shortening the wavelength of laser light in products that use laser light, such as optical disk devices, laser beam printers, and optical measuring instruments.

(b) Conventional technology In recent years, with the practical use of semiconductor lasers, which have the advantages of small size, high efficiency, and low cost, laser applications have progressed in general industrial equipment and consumer equipment, where it was difficult to use conventional laser light sources. There is. In particular, there has been remarkable progress in devices that process information using semiconductor lasers, such as optical disk devices and laser beam printers. The oscillation wavelength of the semiconductor laser light used in these devices is usually 780 nm or 8 nm.
30n-, but the wavelength of the laser beam and the focused spot diameter (
- the minimum condensed diameter of light), and the smaller the condensed spot diameter, the more the storage density of the optical disc can be increased in an optical disc device, and the higher the resolution can be obtained in a laser beam printer.

Furthermore, even in some optical application measurement fields such as interferometric measurements, measurement accuracy can be improved by using short wavelength laser light. In order to improve the performance of devices that utilize laser light, there is a need for a laser light generating device with a shorter wavelength.

In order to shorten the oscillation wavelength of the semiconductor laser itself, InG
Laser light with a wavelength of 6B0 nm has been obtained using aAIP-based semiconductor materials, but there are still many problems such as reliability.Furthermore, short wavelength semiconductor lasers are in the early stages of research and have not yet been put into practical use. There are no prospects for future change.

Therefore, at present, when short-wavelength laser light such as green or blue is required, there is no choice but to rely on gas lasers, which are large and inconvenient to handle.

Another method of obtaining short wavelength laser light using a small device is optical wavelength conversion. Here, the methods of optical wavelength conversion include sum frequency generation in which the frequencies of multiple lights are added together, second harmonic generation in which two or three frequencies of the same frequency are added together, and third harmonic generation in which the frequencies of two or three lights of the same frequency are added together. There is a method called harmonic generation. Due to the harmonic generation of Wt2,
Currently, for example, green laser light with a wavelength of 0.53 μm and wavelengths of 0.83 to 0.84 are used using a YAC (yttonium aluminum garnet) laser with a wavelength of 1.06 μm.
0.415-0.42μl using μl semiconductor laser
The generation of blue laser light has been realized.

(c) Problems to be Solved by the Invention The current major problem in such optical wavelength conversion is to achieve high efficiency conversion using a low-output fundamental wave light source such as a semiconductor laser. The wavelength conversion efficiency is proportional to the fundamental wave density, and the harmonic output increases in proportion to the square of the fundamental wave density. Therefore, in order to amplify the fundamental wave density, the first method is optical confinement using a waveguide, and the second method is optical amplification using an optical resonator.Furthermore, by combining the two methods, significantly high efficiency can be achieved. It has also been proposed to improve the

Currently, as this type of device, a configuration has been proposed in which a ring resonator is formed into a waveguide and harmonic output is extracted as radiation light to a substrate. This configuration is shown in FIG.

In the figure, the fluorescent light (fundamental wave) emitted from a semiconductor laser 100 that oscillates in a single mode with a wavelength of 0.83 μm and an output of 100 mW is focused by a lens 101, and is deposited on a two-cut substrate 10B of MgO-doped L i N b O3. The light enters the optical waveguide 102λ. Each optical waveguide is fabricated by a proton exchange method. When the light from the optical waveguide 102a passes through the forward coupler 103, part of the light is coupled to the ring waveguide 104, and the rest passes through the optical waveguide 102b and enters the light receiving element 105. Resonance control is performed by the control circuit 107 so that the amount of received light is minimized. Harmonics are emitted from each section of ring waveguide 104 into the substrate.

In particular, the light generated from the straight portion 104a on the lower side of the figure was taken out from one end of the substrate and shaped by the lens 106 to become parallel light.

According to experiments, when the fundamental wave light amount is 100 mW, of which the coupling amount of the optical waveguide 102a is about 35 mW, the intensity of the harmonic wave passing through the lens 106 is about 3 mW. As a result, the total amount of light emitted from the entire ring optical waveguide 104 is approximately 1
It is estimated that it reaches 0mW.

In the above example, only the second harmonic generated from one straight part of the ring optical waveguide is effectively used, and the second harmonic light emitted from the curved part of the ring optical waveguide and the other straight part is wasted. I'm throwing it away. In this regard,
Furthermore, an optical wavelength conversion device has been proposed that has a configuration that suppresses the generation of harmonics in the optical waveguide in a portion where the harmonics are not effectively used, and suppresses the loss of the fundamental wave accompanying wavelength conversion.

However, waveguide loss still exists in areas where harmonics are not generated, which limits the resonance magnification of the fundamental wave.

The present invention has been made in consideration of the above circumstances, and in order to effectively utilize the wavelength-converted light generated from all parts of the ring waveguide, it is possible to effectively utilize the wavelength-converted light emitted from any part of the ring waveguide. The present invention aims to provide an optical wavelength conversion device capable of converting light into cofocal light or parallel light.

(d) 9 means and actions for solving the problem This invention (i)
, a first optical waveguide that grows an optical input portion to the outside of the substrate, a second optical waveguide formed in a circumferential shape and whose core or cladding layer is made of a nonlinear optical material, and a first optical waveguide and a second optical waveguide. An optical directional coupler for optically coupling between the optical waveguides is formed on the same substrate, and the light emitted from the laser light source enters the optical input part of the first optical waveguide as a fundamental wave, and In an optical wavelength conversion device that generates harmonic branch end or sum frequency light in a substrate from an optical waveguide with an angular change that satisfies a phase matching condition, the light is emitted from the entire circumference of the second optical waveguide on the back or front surface of the substrate. This is an optical wavelength conversion device characterized by forming a grating that shapes the waveform of harmonic branch end or sum frequency light so that it becomes light that passes through the same focal point or becomes parallel light.

In the above configuration, because the grating is formed on the back or front surface of the substrate, conventionally only the wavelength-converted light emitted from the straight portion of the optical waveguide could be used, whereas the second waveguide including the curved portion can be used. Harmonics from all around can now be used. Furthermore, by making the optical waveguide as small as possible in a circular shape so that the sum of the bending loss and propagation loss of the optical waveguide is minimized, the resonance magnification can be increased. Efficiency can be improved more than possible.

(e) Examples Hereinafter, examples of the present invention will be described in detail with reference to the drawings, but the present invention is not limited to the following examples.

Embodiment 1 FIG. 1 is a block diagram showing the configuration of an optical wavelength conversion device that is a first embodiment of the present invention.

In the figure, light (fundamental wave) emitted from a semiconductor laser IO that oscillates in a single mode with a wavelength of 0.83μ11 and an output of 100mW is focused by a lens 20, and the MgO-doped L
iNbOs two-cut substrate (hereinafter referred to as substrate) 3
The light enters the optical waveguide 32g on the optical waveguide 32g through the optical input section 32c. When this light passes through the optical directional coupler 36, a part of the light is coupled to a circular optical waveguide (hereinafter referred to as a ring optical waveguide) 34 with a radius of 0.7JII, and the rest passes through the optical waveguide 32b to the light receiving element 50. incident on the Resonance control is performed by a method described later so that the amount of received light is minimized. In a resonant state, harmonics are transmitted from each part of the ring optical waveguide 34 to the substrate 3.
It is radiated into 0.

A grating 40 is formed on the back surface of the substrate 30 in a closed curve region having a certain width, that is, in a region between an outer radius of 1.36 iz and an inner radius of 1.18 zz. The direction of the second harmonic radiated from the ring optical waveguide 34 to the substrate 30 is changed by the grating 40, and the second harmonic wave is incident perpendicularly to the surface of the substrate 30, and becomes parallel light Lp outside the substrate 30.
becomes.

Each optical waveguide 32, 34 is manufactured as follows. The substrate 30 is immersed in phosphoric acid at 220° C. for 25 minutes to form a proton exchange layer with a depth of about 0.4 μm in a predetermined shape. The optical waveguide width is Ium. The radius of the bend is 0.7x
Let it be the arc of x. The propagation loss of an optical waveguide having such dimensions was 0.8 dB/am.

In the case of a proton exchange optical waveguide, since the increase in the refractive index of the optical waveguide portion is as large as approximately 0.13, the bending loss in the optical waveguide with a radius of 0.7u+ can be ignored, and the ring optical waveguide 3
The loss at 4 is given only by the hag propagation loss.

The shape of the grating 40 will be explained based on FIG. 2. FIG. 2(a) shows the optical waveguide 3 from the top surface of the substrate 30.
2, 34, a view of the grating 40, Figure 2 (b
) is a cross-sectional view of the substrate 30 in a plane including points A and B.

The harmonics emitted from point A of the ring optical waveguide 34 in the direction of the substrate 30 along the tangential plane of the optical waveguide reach point B on the back surface. Grating 40 is designed to reflect this light in a direction perpendicular to substrate 30. In FIG. 2(a), the direction of the grating lines is the direction that is direct to the straight line AB, and the pitch is the Cerenkov angle θ-16°,
Since the refractive index of the substrate 30 with respect to harmonics is n-2, 3, and the wavelength of high frequency λ≠0.415 μs, λ/n-cos θ=0.
The area shall be 18 ha.

Note that this value is rather small for actual fabrication, so it may be set to an integer multiple of 0, 375 μ-, etc.

The cross-sectional shape of the grating 40 is blazed so that the normal BP of the reflecting surface divides #ABC into three equal parts, as shown in FIG. 2(b).

The grating 40 was produced by the following procedure.

First, an electron beam resist is applied to the back surface of the substrate 30, and the valleys (the portions to be scraped) of the grating 40 are exposed to the electron beam and developed, thereby removing the resist 310 (FIG. 3) in the portions that were not exposed to the electron beam. leave. Next, in order to create blazed grooves of the grating 40,
Perform ion beam etching. Since the direction of the grating grooves is unidirectional, it is not possible to blaze them in the same direction every time. Therefore, as shown in FIG. 3, only a part of the grating area is etched by the obliquely incident Ar ion beam 330. A mask 320 with a window portion was arranged as shown, and the substrate 30 was attached to a rotating holder 340, and etching was performed while rotating, thereby etching the entire circumference.

Thereafter, an aluminum reflective film 39 was deposited on the back surface.

On the surface of the group 30, a layer 38 of 690 SiO was formed. This 5iOz layer 38 not only protects the optical waveguide, but also acts as an anti-reflection film for the second harmonic that is changed in direction by the grating 40 and transmitted through the surface of the substrate 30.

The fundamental wave incident/output surfaces of the substrate 30 were optically polished and coated with an antireflection coating for the fundamental wave wavelength.

In this way, by making the incident surface and the exit surface of the fundamental wave the same surface, both anti-reflection coatings can be applied at the same time.

The optical directional coupler 36 was fabricated by arranging optical waveguides 32 and 34 in parallel over a quarter circumference (approximately 1.1 zm) with a distance of 1 to 4 μl. Note that in order to couple almost all of the light from the waveguide path 32a to the ring optical waveguide 34, it is necessary to set the optimal coupling length and the distance between the optical waveguides according to the ring optical waveguide loss. In this example, optimization is achieved by keeping the coupling length constant and adjusting the distance between the optical waveguides. Generally, the smaller the loss of the ring optical waveguide, the larger the distance between the optical waveguides of the optical directional coupler. Note that there are multiple optimal bond lengths, but in this example, the shortest one among them was chosen.

The resonance state of the ring optical waveguide 34 can be detected when the amount of light received by the light receiving element 50 becomes minimum. In this embodiment, in order to maintain the resonance condition, the dependence of the semiconductor laser oscillation wavelength on the injection current is used, and the injection current is controlled by the control circuit 60 so that the amount of received light is always minimal. In this control method, control becomes unstable due to mode hopping of the semiconductor laser, so the experiment was conducted with the temperature of the semiconductor laser 10 kept approximately constant. Note that resonance control is also possible by driving the semiconductor laser 10 with a completely constant current and precisely controlling its temperature so that the amount of light received is minimal.

According to experiments, when the amount of light of the fundamental wave was 100 mW, of which the amount of light coupled to the optical waveguide 32 was about 45 mW, the intensity of the harmonics emitted from the surface of the substrate 30 was about 17 mW.

Note that although a single mode semiconductor laser is used in this embodiment, a multimode semiconductor laser may be used.

In particular, when the longitudinal mode interval of the semiconductor laser is an integral multiple of the resonant wavelength interval of the ring resonator, most of the output of the multimode semiconductor laser enters the ring resonator, effectively generating the second high frequency. Strictly speaking, a type of sum frequency generation occurs in which the frequencies of two different longitudinal modes of the semiconductor laser are added together to generate a high frequency.

Embodiment 2 A configuration diagram of a second embodiment is shown in FIG. In this example, in order to solve the difficulty in aligning the waveguide on the front surface and the grating on the back surface in the first example, the back surface is made a good flat surface, and the second high-frequency light is emitted on the flat surface. Total reflection is performed, and a grating is formed on the surface to shape the $2 harmonic light. Since this grating is of a reflective type, the second harmonic is emitted from the back surface. The grating was formed in a region sandwiched between circles with an outer diameter of 2.406 zm and an inner diameter of 2.006 z and w.

The optical waveguide substrate and manufacturing method are the same as in Example 1.

The same components will be described with the same reference numerals as in the first embodiment.

The ring optical waveguide 34 has a radius of 0.7u and a width of lμ.

Grating couplers 31a and 31b are used in the fundamental wave input section and the output section. The manufacturing procedure is to first perform proton exchange on the waveguide, then to replace the grating 40,
Grating Kabra 31λ.

31b pattern was created using the same electron beam lithography system,
It was processed into a predetermined shape by Ar ion beam etching. After that, put Sin on the entire back side.

A film of 38° was deposited.

In the first embodiment, the light passing through the grating was a parallel beam, but in this embodiment, it was a convergent beam Lc.

High wavelength exchange efficiency was also obtained in this example.

Example 3 In the third example, MNA (2-methyl-4-nitroaniline), which is one of the organic materials among nonlinear optical materials having a large nonlinear optical effect, was used as the optical waveguide material. FIG. 5 shows a perspective view of a main part for explaining an optical waveguide portion using MNA. Note that the arrangement of the optical waveguides in the substrate is the same as in the first embodiment.

Width 2μ-1 depth 0 on glass substrate 90λ (lower surface in the figure)
．． A Zn0I film layer 92 with a thickness of 2 μm is formed, and 1 to 1
Another glass substrate 90b is placed on top of the substrate with a minute gap of about 0 μm in between, and MNA 94, which is in a liquid state at a temperature higher than the melting point, is sucked into the gap and solidified by cooling.

In this structure, the fundamental wave propagates along the ZnO thin film layer 92, and the MNA 94 acts as a cladding layer. The relationship between the refractive index of the ZnO thin film layer 92 and the MNA 94 satisfies the second harmonic radiation condition into the substrate.

A small YAG laser excited by a semiconductor laser was used as a light source. For resonance control, since control using electro-optic effects cannot be performed due to the nature of the material, the temperature of the entire substrate was adjusted using changes in the optical path length due to temperature changes in the refractive index.

With this configuration, generation of the second high frequency was observed.

Since MNA has a very high nonlinear optical constant, it is thought that good efficiency can be obtained by improving waveguide loss, MNA orientation, etc.

Various nonlinear optical materials can be used as long as they satisfy the conditions for harmonics to be radiated into the substrate (Cherenkov radiation conditions). In addition to L i N b Os used in Examples 1 and 2, typical examples include L 1 TaOs, KNbOs, and KTP (KT i
0PO4), KTA (KT i 0ASO,), β
-B i B @ Oa, Lil0a, LiB.

05, B N N (B l t N L N b s
O, s ), K D P (KHx P 04 )
, ZnS, Zn5e and other inorganic materials, as well as MNA used in Example 3 and NPP (N-(4-n1troph
enyl)-(L)-prolinol), POM(3
-sethyl -4-nitropyridine-
1-owide), DAN (4-(N, N
-diaethylamino)-3-acetami
donitrobenzene), MAP (3-s+
ethyl-2,4-dinitrophenyl a
minopropanate), mNA (metanitroaniline), L A P (L-Arginine P
phosphate monohydrate), DLA
It is conceivable to use organic materials such as P (monohydrogenated LAP), D I VA (methoxydicyanovinylanisole), chalcone derivatives, and cyanine derivatives.

As the substrate material, it is possible to use a nonlinear optical material itself as in Examples 1 and 2, or to use another substrate such as glass as in Example 3. As the substrate, sapphire, M, O, silicon, GλAs, etc. may be used.

(F) Effects of the Invention According to the present invention, a ring resonant waveguide is formed on the substrate by the first optical waveguide and the second optical waveguide, and the second optical waveguide is formed on the substrate.
Since all the wavelength-converted light emitted from the entire circumference of the optical waveguide is converted by the grating into parallel light or beams with the same focus, the utilization rate of the wavelength-converted light can be reduced to approximately 10.
It can be reduced to 0%.

Further, the length of the second optical waveguide can be minimized, and the resonance magnification can be improved by reducing waveguide loss, so that optical wavelength conversion can be performed with high efficiency.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention, and FIG. 2 (
a) and (b) are explanatory diagrams explaining the arrangement and shape of the grating in the first example, FIG. 3 is an explanatory diagram of the method for producing the grating in the first example,
FIG. 4 is a block diagram showing the second embodiment of the present invention, FIG. 5 is an enlarged perspective view of the main part showing the structure of the waveguide used in the third embodiment of the present invention, and FIG. 6 is a conventional example. FIG. 0... Laser light source, 20... Lens,
0... Substrate, 32... Optical waveguide, 4...
... Ring optical waveguide, 6 ... Optical directional coupler, 0 ... Grating, 0 ... Control circuit. 50... Light receiving element,

Claims (1)

[Claims] 1. A first optical waveguide having an optical input portion to the outside of the substrate, a second optical waveguide formed in a circumferential shape and whose core or cladding layer is made of a nonlinear optical material; An optical directional coupler for optically coupling between the optical waveguide and the second optical waveguide is formed on the same substrate, and the light emitted from the laser light source is used as a fundamental wave to enter the optical input part of the first optical waveguide. incident,
In an optical wavelength conversion device that generates harmonic light or sum frequency light in a substrate from the second optical waveguide at an angle that satisfies a phase matching condition, An optical wavelength conversion device comprising a grating that shapes the waveform of emitted harmonic light or sum frequency light so that it becomes light passing through the same focal point or parallel light.