JP4993309B2 - Optical waveguide device, wavelength conversion device, and harmonic laser light source device - Google Patents

Description

  The present invention relates to an optical waveguide element, a wavelength conversion element, and a harmonic laser light source device.

  Laser light is used in various technologies, but the field of use is often regulated by wavelength. For example, green laser light having a wavelength of 500 to 600 nm is “observation of fluorescent protein”, red laser light, blue Combined with laser light, it is used for “high brightness color laser display”. Further, a mid-infrared laser beam having a wavelength of 2 μm or more is used for “gas detection such as methane gas and carbon dioxide”.

  By the way, at present, the green laser light and the mid-infrared laser light cannot be generated by a single semiconductor laser (LD). As a method for generating laser light in these wavelength ranges, a “wavelength conversion method using a nonlinear optical effect” is known.

The “nonlinear optical effect” is a phenomenon that appears due to the interaction between the polarization structure of the crystal and the light when the laser beam passes through the nonlinear optical crystal. For example, “second-order nonlinear effect (sum frequency generation)” is used. As a result, the second harmonic and the third harmonic can be generated. For example, infrared laser light from an Nd: YAG laser or the like is subjected to KTP (KTiOPO ₄ ), KDP (KH ₂ PO ₄ ), LBO (LiB ₃ O ₅ ), CLBO (C ₅ LiB) while satisfying the phase matching conditions. ₆ O ₁₀ ) or the like can pass through a nonlinear optical crystal to obtain “laser light in the green or ultraviolet region”, and conversely, by utilizing “difference frequency generation” in the second-order nonlinear optical effect, a visible laser “Long wavelength laser light such as infrared light to terahertz wave” can also be generated from light.

When wavelength conversion is performed using a nonlinear optical crystal, it is preferable to guide “fundamental mode light” through an optical waveguide formed by the nonlinear optical crystal.
As an example, a case where the second harmonic is generated will be described. A fundamental wave (laser light having an original frequency (fundamental frequency) with respect to the harmonic) is incident on an optical waveguide formed by a nonlinear optical crystal, Propagation distance: Second harmonic generation efficiency when propagating by L: η is expressed by the following formula:
η = | κ | ² P ₀ L ² [{sin (Δ · L)} / (Δ · L)] ² (1)
Given in.

Here, P ₀ is “incident power”, Δ is the wavelength of the fundamental wave: λ, and the equivalent refractive index of the nonlinear optical crystal for the fundamental wave and the second harmonic wave propagating through the optical waveguide: n ₁ and n _2. The following formula,
Δ = 2π (n ₂ −n ₁ ) / λ (2)
It is an amount defined by Further, κ is “a coupling coefficient between a fundamental wave and a harmonic”, and is proportional to an “overlap integral” between the waveguide modes.

When the second harmonic is generated from the fundamental wave, the intensity of the second harmonic: I ^(2ω) is given by
I ^(2ω) ｄ d ² [{sin (Δ · L)} / (Δ · L)] ² (3)
Given in. d is “second-order nonlinear optical constant”, and L is “light propagation distance”.

As is apparent from the equation (1), in order to increase the second harmonic generation efficiency: η, the coupling coefficient: κ, the incident power: P ₀ , the propagation distance: L are increased, and the equation is defined by the equation (2). It is preferable to reduce “Δ”. When an optical waveguide is formed of a nonlinear optical crystal, the power density of light can be increased, and the incident power: P ₀ can be increased to obtain “highly efficient output light (second harmonic)”. In order to increase the intensity of the second harmonic: I ^(2ω) , it is preferable to select a crystal having a large “second-order nonlinear optical constant: d” as the nonlinear optical crystal.

The harmonic intensity: I ^(2ω) “increases in proportion to d ² ” only when Δ = 0, that is, n ₁ = n ₂ is satisfied, but is periodic with respect to the change of L when n ₁ ≠ n ₂ The value also becomes very small as L increases. Up to half the period length (propagation distance at which Δ · L = 2π): harmonics intensify in phase until L _c = λ / (4 | n ₂ −n ₁ |), but the latter half distance Until it is weakened in the opposite phase, the intensity of the harmonic does not increase but decreases while periodically changing. The above L _c is called “coherent length”. Therefore, in order to generate harmonics with high efficiency, it is necessary to set n ₁ = n ₂ , which is called “phase matching”.

The well known as a specific method of the phase matching is "angular alignment method utilizing the birefringence of crystal", for example "extraordinary refractive index: n e _<ordinary index of refraction: uniaxial crystal n _o" Then, Δ = 0 can be realized by selecting a propagation angle θ satisfying n _1o = n _2e . However, in this phase matching, an optical waveguide must be formed using “uniaxial crystal having such conditions”.
As another phase matching method, a “pseudo phase matching method using a periodically poled crystal” is known (Patent Document 1).
A “ridge-type optical waveguide” is known as an optical waveguide structure capable of increasing the coupling coefficient: κ (Patent Document 2).
“Ridge type optical waveguide” is a method of confining light in the film thickness direction by bonding a nonlinear optical crystal such as LiNbO ₃ to a support substrate and then “thinning the film to a thickness of several μm” by precision polishing or the like. It is an optical waveguide that has been subjected to dicing and etching processes to provide a “thickness difference (ridge)” to the thin film to enable optical confinement in the thin film width direction (direction perpendicular to the thickness direction and the waveguide direction). Light can be strongly confined in the nonlinear optical crystal thin film since the thickness of the crystal film is as small as several μm.

  However, the “ridge-type optical waveguide” has a larger optical crystal thin film thickness than the single-mode condition of the optical waveguide, and the optical waveguide itself is a “multimode optical waveguide”, so that the fundamental wave propagates through the optical waveguide. In this case, there is a “possibility that a higher mode is excited”. When the higher-order mode is excited, the field shape of the excited higher-order mode is very different from the field shape of the fundamental mode (0th-order mode), so “overlapping integration with harmonic fundamental wave components” is very high. The coupling coefficient: κ becomes smaller and the wavelength conversion with high efficiency becomes difficult.

  In order to avoid such a problem, the ridge type optical waveguide may be made to “operate in a single mode”. For this purpose, it is necessary to reduce the thickness of the crystal thin film to “about 1 μm or less”. Therefore, it is not always easy to “maintain the entire thickness of the optical waveguide” with such an extremely thin film thickness, and it is difficult to realize a single-mode optical waveguide having a desired optical waveguide length.

JP 2007-121515 A JP 2005-221894A

  The present invention has been made in view of the above-described circumstances, and is an optical waveguide element that enables an increase in power density of light and a substantially single mode operation, and enables wavelength conversion with good conversion efficiency. And a wavelength conversion element using the optical waveguide element and a harmonic laser light source device having the wavelength conversion element.

An optical waveguide device according to the present invention is an “optical waveguide device that receives a fundamental wave and generates and propagates harmonic light”, and includes a core layer, a light absorption layer, and one or more cladding structure layers.
The “core layer” is made of a nonlinear optical material. As the nonlinear optical material, for example, “nonlinear optical crystal” represented by lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), or the like can be used.
One or more “cladding constituent layers” are provided, and each cladding constituent layer is configured by “stacking the first cladding and the second cladding from the core layer side”.

The “first cladding” has a refractive index smaller than that of the core layer and is formed thinner than the core layer.
The “second cladding” has a refractive index larger than that of the first cladding, is thinner than the core layer, and is thicker than the first cladding.
That is, assuming that the refractive index of the core layer is Nc, the thickness is Ec, the refractive index of the first cladding is N1, the thickness is E1, the refractive index of the second cladding is N2, and the thickness is E2, these magnitude relationships are It is as follows.

N1 <Nc, N1 <N2, E1 <E2 <Ec
The “light absorption layer” is formed so as to sandwich the clad structure layer together with the core layer.
The core layer and the clad structure layer have light “interference reflected” between them, and the reflectance of the interference reflection is large with respect to the fundamental wave of the fundamental mode. By being set low relative to the light, the fundamental wave of the fundamental mode is “substantially confined in the core layer and guided”, and the light of the higher mode generated in the core layer is “clad structure layer”. The harmonic light generated in the core layer is “substantially confined in the core layer and guided in the core layer together with the fundamental mode fundamental wave”. It is configured.

  That is, as described above, the core layer, the light absorption layer, and the one or more clad structure layers are substantially confined in the core layer to propagate the fundamental mode harmonic wave and the harmonic wave, and transmit the higher order mode light. The characteristic of interference reflection is set to “leak from the core layer to the clad structure layer side”.

  The “interference reflection” is a reflection in which the reflected light at the interface between the first cladding and the core layer interferes with the reflected light from the cladding structure layer side to determine the reflected light intensity. As described above, the reflectance is designed so as to be “substantially close to 1 for fundamental mode fundamental wave and harmonic light, and small for higher order mode light”.

  That is, the optical waveguide device of the present invention is a “leak structure optical waveguide having a nonlinear optical material as a core layer”. The conventionally known “optical waveguide type wavelength converting element” is a device that confins and propagates light by total reflection. In the optical waveguide element of the present invention, “guided light is transmitted between the core layer and the cladding layer. The wave is guided by repeated interference reflection. Since interference reflection is not total reflection, “reflectance is smaller than 1.0”, but since it can be designed to realize a reflectance very close to 1.0, light propagation with sufficiently low loss is possible.

  For high-order mode light, “the reflectance of interference reflection is set low”, and only the fundamental mode light (fundamental wave) of the waveguide mode propagates with low loss. Even an optical waveguide that is radiated out of the core layer and has a “thickness of the core that allows multimode propagation in a normal total reflection optical waveguide” can be operated substantially in a single mode.

  Such “leak structure optical waveguides” are conventionally known as “ARROW (Anti-Resonant Reflecting Optical Waveguide)”, and are designed to increase the production tolerance and apply them to wavelength demultiplexing devices. Although what is referred to as a “core layer” has been reported, an example of application to a “core layer using a nonlinear optical material” such as the optical waveguide element of the present invention is not known.

  Since the optical waveguide device according to claim 1 is configured as described above, even if higher-order mode light is generated in the core layer, the generated higher-order mode light leaks to the cladding structure layer side. Since it is absorbed in the light absorption layer and rapidly attenuates in the core layer, it is possible to effectively reduce the “coupling coefficient: κ becomes small” due to the light of the higher order mode. That is, the optical waveguide device according to claim 1 can perform “substantially single mode operation”. Further, since it has an optical waveguide structure, the “light power density” is large. Therefore, high wavelength conversion efficiency can be realized.

The optical waveguide device according to claim 1 has one or more cladding structure layers as described above. Therefore, the clad structure layer can be single or plural.
When there is a single clad structure layer, the clad structure layer is formed on one side of the core layer and becomes “a structure sandwiched between the core layer and the light absorption layer”.
When there are a plurality of clad structure layers, these may be formed by being laminated on one side of the core layer, or may be formed on both sides of the core layer. For example, when there are two clad structure layers, these may be laminated on one side of the core layer, and the “two laminated clad structure layers” may be sandwiched between the core layer and the light absorption layer. Alternatively, a structure in which one clad structure layer is formed on each side of the core layer and the both sides of the core layer are sandwiched between the core layer and the light absorption layer can be adopted.

  As described above, a structure in which a plurality of clad structure layers are provided and sandwiched between the core layer and the light absorption layer “on one side or both sides of the core layer” may be employed. The same applies to the case where three or more clad structure layers are formed.

  The optical waveguide device according to any one of claims 1 to 3 can have “an optical buffer layer that totally reflects light in contact with any one of the core layer, the clad structure layer, and the light absorption layer” (claim) Item 4).

  The optical waveguide device according to any one of claims 1 to 4, wherein at least "a portion constituted by a core layer, a light absorption layer, and one or more cladding structure layers" is integrally formed on a support substrate. (Claim 5). It goes without saying that the optical buffer layer can be integrated on the support substrate together with the “part constituted by the core layer, the light absorption layer, and one or more cladding structure layers”.

  The optical waveguide device according to claim 5 may be configured such that the “light absorption layer is in close contact with the support substrate” (claim 6), and when the optical buffer layer is provided, “the optical buffer layer is the support substrate” It is possible to adopt a configuration in which it is in close contact with (claim 7). In this case, the optical buffer layer can be used to realize adhesion between other portions and the support substrate.

The optical waveguide element according to any one of claims 1 to 7, wherein the core layer can have “a periodically poled region in the light guiding direction” (claim 8).
The optical waveguide device according to any one of claims 1 to 8 may have a configuration in which “the core layer has a step in thickness , and light is guided through the core layer portion having a large thickness” (claim) Item 9).
That is, as will be described later, when the light guiding direction is the z direction, the thickness direction of the core layer is the y direction, and the direction perpendicular to the z direction and the y direction is the x direction, the core layer has a thickness in the x direction. There is a step, and the light is guided through the “thick core layer portion” in the x direction.

The optical waveguide device according to any one of claims 1 to 8 may be configured such that the core layer has a “light propagation region having a refractive index higher than that of the nonlinear optical material” (claim 10). .
The optical waveguide device according to any one of claims 1 to 8, wherein the optical waveguide element is formed of a non-linear optical material along at least one end in a width direction of the core layer (a direction perpendicular to the thickness direction of the core layer and the optical waveguide direction). It can be configured to have a light non-propagating region with a small refractive index.

The optical waveguide device according to any one of claims 1 to 11, wherein, among the first clad and the second clad constituting the clad structure layer, the second clad has the same refractive index as the core layer (that is, N2 = Nc) and the thickness thereof is preferably approximately ½ of the core layer (E2 = Ec / 2) ”(claim 12).
The optical waveguide device according to any one of claims 1 to 12 may be configured to have “a refractive index adjusting electrode in the vicinity of a region where light propagates” (claim 13).

  The “wavelength conversion element” of the present invention generates harmonic light while guiding the fundamental wave in the fundamental mode in the optical waveguide element, and guides the generated harmonic light together with the fundamental wave of the fundamental mode. A wavelength conversion element that separates and emits harmonic light from the fundamental wave from the output end, and is provided at the optical waveguide element and the output end of the optical waveguide element to separate the harmonic light from the fundamental wave. It has a separating means, and the optical waveguide element is any one of claims 1 to 13 (claim 14).

  “Wavelength separation means provided at the output end of the optical waveguide device to separate the harmonic light from the fundamental wave” uses a filter that absorbs the fundamental wave and selectively transmits the harmonic light, or a diffraction grating. be able to.

  A “harmonic laser light source device” of the present invention includes the wavelength conversion element according to claim 14 and a laser light source that emits a fundamental wave guided by the wavelength conversion element (claim 15). .

  As described above, according to the present invention, a novel optical waveguide element, wavelength conversion element, and harmonic laser light source device can be realized. Since the optical waveguide device of the present invention has the above-described configuration, wavelength conversion with high conversion efficiency is possible. Therefore, the wavelength conversion element using this optical waveguide element can efficiently obtain harmonic light, and the harmonic laser light source using this wavelength conversion element can realize high-output harmonic light.

  FIG. 1 shows an example of an “embodiment according to the most basic structure” of an optical waveguide element.

  FIG. 1 schematically shows a cross-sectional view of an optical waveguide element. As shown in the figure, when the y direction is set in the vertical direction, the z direction is set in the horizontal direction, and the x direction is set in the direction orthogonal to the drawing, the y direction is set. Is the thickness direction of the core layer, and the z direction is the waveguide direction.

  In FIG. 1, reference numeral 0101 denotes a core layer, reference numeral 0102 denotes a cladding structure layer, and reference numeral 01055 denotes a light absorption layer. That is, the optical waveguide element shown in FIG. 1 includes a core layer 0101, a cladding structure layer 0102, and a light absorption layer 0105.

The core layer 0101 is “a portion that mainly guides light” and is made of a nonlinear optical material. The clad structure layer 0102 is formed by laminating a first clad 0103 and a second clad 0104 from the core layer 0101 side. The light absorption layer 0105 is formed so as to sandwich the clad structure layer 0102 together with the core layer 0101.
The left part of FIG. 1 shows “the refractive index / thickness relationship of the core layer 0101, the first cladding 0103, the second cladding 0104, and the light absorption layer 0105”. As shown, the first cladding 0103 has a refractive index smaller than that of the core layer 0101 and is thinner than the core layer 0101, and the second cladding 0104 has a refractive index larger than that of the first cladding 0103. It is formed to be thinner than the core layer 0101 and thicker than the first cladding 0103. The light absorption layer 0105 has a higher refractive index than the core layer 0101, the first cladding 0103, and the second cladding 0104.

The nonlinear optical material forming the core layer 0101 is, for example, a nonlinear optical crystal typified by lithium niobate (LiNbO ₃ ) or lithium tantalate (LiTaO ₃ ).

  When the fundamental wave propagates in the z direction in the core layer 0101, vibration polarization occurs at each position of the core layer, and harmonics using the vibration polarization as a secondary wave source are generated. For example, when vibration polarization with a frequency of 2ω occurs with respect to the frequency of the fundamental wave: ω, second harmonic (SHG) is generated.

When the film thickness of the core layer 0101 is reduced, the power density of the light propagating inside the core layer is increased, and the incident power: P ₀ in the formula (1) is increased, which enables highly efficient wavelength conversion. If the film thickness of the layer 0101 is made too thin, “incident of fundamental wave into the core layer (coupling)” becomes difficult, and therefore the thickness of the core layer 0101 is preferably in the range of “about 1 to 10 μm”. It is.

  The refractive index of the second cladding 0103 is ideally equal to that of the core layer 0101, and the film thickness of the second cladding 0103 is ideally about half of the thickness of the core layer 0101. This is the case in the embodiment of FIG.

Suitable materials for the first clad 0103 and the second clad 0104 include “glass materials such as SiO ₂ , Ta ₂ O ₅ , TiO ₂ ”, or materials obtained by mixing these glass materials. It is possible to obtain “a desired refractive index from a low refractive index to a high refractive index” by changing the mixing ratio of the glass materials.

  The material constituting the second cladding 0104 is ideally the same optical crystal material as that of the core layer 0101. The same nonlinear optical crystal as that of the core layer 0101 may be thinned and stacked as the second cladding 0104. It is more realistic to form the second clad 0104 by forming “mixed glass having substantially the same refractive index” as the material of the core layer 0101 from the viewpoint of simplicity of the manufacturing process.

  Light is confined by “interference reflection, not total reflection” at the boundary between the core layer 0101 and the clad structure layer 0102. Accordingly, part of the propagating light is not reflected inside the core layer 0101 by the clad structure layer 0102 but is emitted outside the core layer 0101.

  The clad structure layer 0102 reflects “only the fundamental wave of the fundamental mode” in the light propagating through the optical waveguide to the inside of the core layer 0101 with “reflectance very close to 1.0”, and “higher order modes other than the fundamental mode” It is designed so that the reflectivity is small for the light of ”. Accordingly, part of the higher-order mode light is emitted outside the core layer 0101 and the rest is reflected inside the core layer. “High-order mode light” emitted to the outside of the core layer 0101 is absorbed by the light absorption layer 0105 and does not return to the core layer 0101.

  The material of the light absorption layer 0105 may be “a material with a very large real part” or “a material with a relatively large imaginary part” having a complex refractive index. For example, “Cr, Au, Ag, Ti, Ni, etc.” The “metal material” and “semiconductor material such as a-Si” are preferable.

  That is, light is interference-reflected between the core layer 0101 and the clad structure layer 0102, and the reflectance of this interference reflection is large with respect to the light in the fundamental mode (usually 99.9% or more) and is generated in the core layer 0101. The fundamental mode fundamental wave is substantially confined in the core layer 0101 and guided, and the higher order mode light generated in the core layer 0101 is set. Leaks to the cladding structure layer 0102 side and is absorbed by the light absorption layer 0105.

  The fundamental wave input into the optical waveguide element is totally reflected at the boundary between the core layer 0101 and the air region (the region above the core layer 0101 in FIG. 1), and the boundary between the core layer 0101 and the clad structure layer 0102. In the case of interference reflection, the total reflection and interference reflection are repeated and propagated.

  Since the “reflectance of interference reflection” is set sufficiently high for the fundamental wave propagating in the fundamental mode as described above, the fundamental wave propagates with “very low loss in the fundamental mode”. Since higher-order mode light has “low reflectance of interference reflection”, it propagates while repeating radiation for each interference reflection, resulting in a large propagation loss. Therefore, even if the thickness of the core layer 0101 is “a thickness that allows a multimode operation in a normal total reflection type optical waveguide”, a single mode optical waveguide in which only fundamental mode light propagates substantially. Become.

  When the higher order mode is excited by the fundamental wave propagation, the coupling coefficient with the harmonic light propagation mode decreases and phase matching becomes difficult. Is effective. In the optical waveguide device according to the present invention, as described above, the higher-order mode excited from the light propagating through the optical waveguide is attenuated very quickly. As a result, “high-order mode excitation is suppressed” and “high-efficiency wavelength is suppressed”. Conversion "is possible.

In FIG. 1, reference numeral 0106 denotes “distribution in the y direction of the propagation light field (the electric field strength in the x direction) of the light (fundamental wave) in the fundamental mode”.

Hereinafter, a specific configuration example of the optical waveguide device of FIG. 1 will be described.
The operating wavelength (wavelength of the fundamental wave) was 1064 nm.
The nonlinear optical material constituting the core layer 0101 is a crystal of lithium niobate (refractive index: 2.156), and the thickness of the core layer 0101 is 6.0 μm.
The refractive index of the second cladding 0104 was 2.156, the same as that of the core layer 0101, and the thickness was 3.0 μm (1/2 of the thickness of the core layer). The material of the light absorption layer 0105 was Cr, and its complex refractive index was 4.53 + 4.3i.

Under such conditions, the “refractive index and film thickness” of the first cladding 0103 was changed as a parameter, and the propagation loss of the fundamental mode (0th order mode) and the higher order mode was calculated.
The simulation results of the relationship between the film thickness of the first cladding 0103 and the “propagation loss in the optical waveguide mode” when the refractive index of the first cladding 0103 is 2.0 and 2.1 are shown in FIG. Shown in a) and (b). Higher order modes were considered up to the second order mode.

As shown in FIG. 13A, when the refractive index of the first cladding 0103 is 2.0, the higher-order mode (primary mode) is obtained by setting the film thickness to about 0.2 to 0.3 μm. (Mode, secondary mode) light propagation loss can be 10 dB / cm or more.
The “propagation loss of the fundamental mode fundamental wave” at this time is about 0.2 dB / cm, which is a sufficiently low loss.

  As shown in FIG. 13 (b), when the refractive index of the first cladding 0103 is 2.1, the propagation loss of the higher order mode (10 dB or more) is obtained by setting the film thickness to about 0.4 μm. Compared to the above, only the light in the fundamental mode can be propagated with extremely low loss (about 0.2 dB / cm). Thus, by optimizing the cladding structure layer 0102, an “optical waveguide device capable of substantially transmitting only fundamental mode light” can be realized.

  FIG. 14 shows “distribution of electric field (Ex) in x direction (direction perpendicular to the thickness direction of the core layer and the waveguide direction) (propagation field distribution)” of the optical waveguide mode propagating in the optical waveguide. . The solid line indicates the propagation field of the fundamental wave (wavelength: 1064 nm) and the broken line indicates the second harmonic light (wavelength: 532 nm). In this case, the optical waveguide has a refractive index of 2.0 and a thickness of 0.2 μm of the first cladding 0103 in the above-described optical waveguide configuration. As shown in FIG. 14, “propagation field distribution of fundamental wave and harmonic light” agrees very well, and these “overlap integrals” are sufficiently large, and “coupling coefficient between fundamental wave and harmonic light in equation (1)”. : Κ ”can be increased, and“ highly efficient wavelength conversion ”can be performed.

  That is, the harmonic light generated in the core layer 0101 is substantially confined in the core layer 0101 and guided in the core layer 0101 together with the fundamental mode fundamental wave.

FIG. 2 is a view for explaining another embodiment of the optical waveguide device.
FIG. 2 schematically shows a cross-sectional view of the optical waveguide device in accordance with FIG.
A core layer 0202 is laminated on the support substrate 0201 via the optical buffer layer 0207, and a first clad 0204 and a second clad 0205 are sequentially laminated thereon to form a clad structure layer 0203. Absorption layer 0206 is formed.
The core layer 0202 is made of “nonlinear optical material”.

  The optical waveguide element shown in FIG. 1 is “the thickness of the nonlinear optical material is very thin, about several μm, compared with the wavelength conversion element based on the bulk crystal”. However, as in the embodiment shown in FIG. “Element robustness” can be improved by making the element “integrated with the support substrate (Claim 5)”.

  Specifically, a “thinned crystal material” is bonded onto the support substrate 0201. The support substrate material is preferably the same material as the core layer 0202 in order to make the “core layer thinning process” described later easier, but may be cheaper silicon, quartz glass, or the like.

Although the optical buffer layer 0207 is sandwiched between the core layer 0202 and the support substrate 0201, the refractive index of the optical buffer layer 0207 is lower than the refractive index of the material of the core layer 0202 (relationship of the refractive index in the left part of FIG. 2). See figure showing). The nonlinear optical material used as the core layer 0202 has a refractive index as large as about 2.0 or more in a lithium niobate crystal or the like. Therefore, various materials can be used for the optical buffer layer 0207. Specifically, “Glass materials such as SiO ₂ and polymer materials” are suitable.

  At the boundary between the core layer 0202 and the optical buffer layer 0207, light is confined inside the core layer 0202 by “total reflection”. Therefore, the thickness of the optical buffer layer 0207 needs to be “thick enough to prevent the light propagating through the core layer 0202 from being emitted to the support substrate 0201 (greater than the thickness of the region where the evanescent light is present)”.

Specifically, when the core layer 0202 is formed of lithium niobate and the optical buffer layer 0207 is formed of SiO ₂ , the thickness of the optical buffer layer may be about 1.0 μm or more.

In FIG. 2, reference numeral 0208 denotes “distribution in the y direction of the propagation light field (the electric field strength in the x direction) of the fundamental mode light (fundamental wave)”.

A manufacturing process of the optical waveguide device shown in FIG. 2 will be described with reference to FIG.
In process 2001, an optical buffer layer 0207 is formed on the surface of “core material (nonlinear optical crystal)” 02 to be a core layer. When the optical buffer layer 0207 is formed of a glass material, it can be formed by a general glass thin film forming method such as high-frequency sputtering, vacuum deposition, or chemical vapor deposition (CVD). The film thickness of the optical buffer layer 0207 may be about 1 μm or more. In process 2002, the deposition surface of the optical buffer layer 0207 and a supporting substrate (indicated as “substrate” in the drawing) 0201 are bonded.

  This “bonding” is preferably direct bonding by heating and pressurization, or direct bonding at normal temperature or low temperature using plasma activation of the surface of the support substrate 0201 or surface activation by irradiation with an ion beam or the like. In addition, “bonding using an adhesive or the like” may be performed more simply. In process 2003, the core material is thinned to form a core layer (indicated as “core” in the figure) 0202. The thickness of the core layer 0202 is about 1 to 10 microns.

  The method of “thinning” is simple in precision polishing. The core layer 0202 can also be formed by thinning the film by an ion slicing method (Crystal Ion Slicing) that combines ion implantation into the core material 02 and heat separation. In processes 2004 and 2005, a first clad 0204 and a second clad 0205 are sequentially formed on the core layer 0202.

  When these first and second cladding materials are glass materials, they can be formed by film forming techniques such as sputtering, vapor deposition, and CVD, as with the optical buffer layer 0207. Usually, the film thickness of the first clad 0204 is about 1 μm or less, and the film thickness of the second clad 0205 is half of the film thickness of the core layer 0202. Finally, a light absorption layer 0206 is formed in process 2006. The light absorption layer 0206 can be formed by “in the case of a metal material, vacuum deposition or high frequency sputtering”. Although the thickness of the light absorption layer 0206 is not particularly limited, light leaking from the core layer 0202 can be sufficiently absorbed if the thickness is about 50 nm or more.

  FIG. 3 is a view for explaining another embodiment of the optical waveguide device.

The optical waveguide device of FIG. 2 described above is “an example in which an optical material is stacked in order from the buffer layer 0207 on the support substrate 0201”, but the light absorption layer is formed on the support substrate 0301 as shown in FIG. The effect of the configuration in which 0306, the second cladding 0305, the first cladding 0304, the core layer 0302, and the optical buffer layer 0307 are sequentially stacked is not changed. In the form of FIG. 3, the optical buffer layer 0307 is not necessarily required, and the upper surface of the core layer 0302 may be “in contact with air”.
In FIG. 3, reference numeral 0308 denotes “ distribution in the y direction of the propagation light field (the electric field strength in the x direction) of the fundamental mode light (fundamental wave)”.

  A manufacturing process of the optical waveguide device shown in FIG. 3 is shown in FIG.

  In process 2101, process 2102, and process 2103, a first cladding layer 0304, a second cladding layer 0305, and a light absorption layer 0306 are sequentially formed on the core material (nonlinear optical crystal) 03. Next, in process 2104, the light absorption layer 0306 having the above-described deposition structure is bonded to a supporting substrate (indicated as “substrate” in the drawing) 0301. In process 2105, the core material 03 is thinned to form a core layer (indicated as “core” in the drawing) 0302 of the optical waveguide. Finally, an optical buffer layer (indicated as “buffer layer” in the drawing) 0307 is formed in process 2106. All the manufacturing processes can be realized by the same manufacturing technique as shown in FIG.

FIG. 4 shows another embodiment of the optical waveguide device.
FIG. 4 is a cross-sectional view of the optical waveguide device, which is shown in FIG. 1. An optical buffer layer 0406, a core layer 0402, a first cladding 0403, a second cladding 0404, and a light absorption layer 0405 are formed on a substrate 0401. They are sequentially stacked. Light propagates in the z-axis direction inside the optical waveguide. The core layer 0402 has a polarization inversion region 0407 in which “the polarization is alternately inverted in the z direction”.
In FIG. 4, reference numeral 0408 denotes “distribution in the y direction of the propagation light field (the electric field strength in the x direction) of the fundamental mode light (fundamental wave)”.

  The configuration shown in FIG. 4 corresponds to the configuration “provided with a domain-inverted region in the core layer” in the configuration shown in FIG. Similarly, a domain-inverted region can be formed in the core layer of the optical waveguide structure shown in FIGS.

  If the “propagation constants” of the fundamental wave and the harmonic wave propagating in the optical waveguide are different, the intensity of the generated harmonic wave changes periodically, and it is difficult to generate the harmonic wave with high efficiency as it is. The fundamental wave and the harmonics can be phase-matched by periodically inverting the polarization of the nonlinear optical material forming the core layer 0402 in the waveguide direction (Z direction).

The pitch of polarization inversion: Λ may be “coherent length: twice the length of L _c (= λ / 4 | n ₂ −n ₁ |)”. n ₁ and n ₂ are the equivalent refractive indices for the fundamental wave and the harmonic wave, respectively, and λ is the wavelength of the fundamental wave. As a specific example, a case where the core layer 0402 is composed of a lithium niobate crystal and “a second harmonic wave having a wavelength of 1064 nm to a wavelength of 532 nm is generated” will be described.

Since the propagating light propagating through the optical waveguide is strongly confined in the core layer 0402, the equivalent refractive index of the optical waveguide is assumed to be equal to the refractive index of the nonlinear optical material. When the refractive index of the crystal of lithium niobate is 2.156 at a wavelength of 1064 nm and 2.2342 at a wavelength of 532 nm,
Λ = 2L _c = λ / (2 | n ₂ −n ₁ |)
= 1.064 μm / 2 (2.2342-2.156) = 1.064 / 0.1564
= 6.803 μm
Therefore, phase matching can be achieved by setting the pitch of polarization inversion to 6.8 μm.

  As a method of forming a domain-inverted region in a “bulk substrate made of a nonlinear optical material (crystal)”, a predetermined in both surfaces (+ Z plane and −Z plane, or + C plane and −C plane) of a substrate having a uniform polarization direction are used. A method of forming an electrode pattern and applying a voltage to “reverse the polarization direction of the portion sandwiched between the electrodes” is well known.

  The optical waveguide device according to the embodiment shown in FIG. 4 is replaced with “a nonlinear optical crystal substrate 02 serving as a core layer” shown in FIG. It can be manufactured by the manufacturing process shown in FIG.

FIG. 5 is a diagram showing another embodiment of the optical waveguide device.
FIG. 5 shows a cross-sectional view of the optical waveguide device, following FIG. In this embodiment, the optical waveguide element has a structure in which an optical buffer layer 0508, a core layer 0502, clad structure layers 0503 and 0504, and a light absorption layer 0507 are laminated in the above order on a support substrate 0501. . In other words, this embodiment has a structure in which two clad structure layers 0503 and 0504 are laminated on one surface (the upper surface in the drawing) of the core layer 0502.

  The two clad structure layers 0503 and 0504 have the same structure, in which the first clad 0505 is laminated on the core layer 0502 side and the second clad 0506 is laminated on the light absorption layer 0507 side. The refractive indexes and film thicknesses of the first cladding and the second cladding in the structural layers 0503 and 0504 are the same. With such a structure, low-loss propagation of the fundamental wave propagating in the fundamental mode and further improvement of the radiation of the higher-order mode light out of the core layer are possible.

In FIG. 5, reference numeral 0509 denotes “ distribution in the y direction of the propagation light field (the electric field strength in the x direction) of the fundamental mode light (fundamental wave)”.

  FIG. 15 shows the calculation result of the propagation loss of the “optical waveguide device having two clad structure layers” as shown in FIG. The operating wavelength (wavelength of the fundamental wave) was 1064 nm. The material of the core layer 0502 was a crystal of lithium niobate, the refractive index was 2.156, and the thickness was 4.0 μm. The second cladding 0506 had a refractive index of 2.156, which was the same as that of the core layer, and a thickness of 2.0 μm. The material of the light absorption layer 0507 was Cr, and its complex refractive index was 4.53 + 4.3i.

  Further, with the refractive index of the first cladding 0505 as 2.1 and the film thickness of the first cladding 0505 as a parameter, the film thickness of the first cladding was calculated such that only the fundamental mode light propagates with low loss.

  As shown in FIG. 15, if the film thickness of the first cladding 0505 is 0.2 to 0.3 μm, the propagation loss of high-order mode light can be increased to 10 dB / cm or more, and the propagation loss of fundamental mode light. Can be made as small as 0.1 dB / cm or less. That is, the optical waveguide element in which the first clad 0505 has a film thickness of 0.2 to 0.3 μm functions as a “single mode optical waveguide element capable of guiding only the fundamental mode light”. Since the higher-order mode is not constantly excited when propagating, high-efficiency wavelength conversion becomes possible.

  In the embodiment shown in FIG. 5, the number of clad structure layers is two, but the clad structure layers may be further laminated in multiple layers. Further, in the “configuration having no support substrate” shown in FIG. 1 and the “configuration having a clad structure layer between the core layer and the support substrate” shown in FIG. It is effective for wavelength conversion of efficiency.

FIG. 6 is a view showing two examples of another embodiment of the optical waveguide device.
FIG. 6 shows a cross-sectional view of the optical waveguide element. 6A and 6B show cross sections of the optical waveguide device, and the z direction in which light is guided is a direction orthogonal to the drawing.
In the embodiment shown in FIGS. 6A and 6B, a “ridge shape” is formed in the optical waveguide device shown in FIGS. The film thickness of the core layer indicated by reference numeral 0602 common to FIGS. 6A and 6B is “a ridge shape different for each region in the x direction”. The guided light is confined in the lateral direction (x direction) in the “thick region 0607 of the core layer 0602” in the x direction and propagates.

  This is because the thick region 0607 of the core layer 0602 has a “relatively large equivalent refractive index of the optical waveguide” as compared to “a thin region of the core layer (regions on both sides in the x direction of the region 0607)”. The principle of optical confinement is the same as the well-known “ridge type optical waveguide”. Light is confined using interference reflection in the film thickness direction (y direction), and light is confined in the lateral direction by total reflection due to the difference in equivalent refractive index. Thereby, it is possible to form a three-dimensional optical waveguide for confining and propagating light vertically and horizontally in the figure.

FIG. 19 shows a manufacturing process of the optical waveguide device shown in FIG.
The process is different from the process shown in FIG. 17 only in that “the ridge-shaped processing process 2204 is added to the core layer”. For other manufacturing processes, the same processing method as that shown in FIG. 17 can be applied. In the process 2204 for processing the ridge shape into the core layer, the ridge width is about 1 to 10 μm, and the “ridge depth” can be smaller than the thickness of the second cladding 0604, so that it is 5 μm or less. For such ridge-shaped processing, for example, cutting both sides of the core layer (indicated as “core” in the drawing) by dicing processing, dry etching processing, or the like is suitable.

  When dry etching is performed, since the ridge width is about several μm, a mask pattern for an optical waveguide may be formed using a normal photolithography technique. After the mask pattern is formed, the core material 02 is etched using a dry etching technique such as reactive ion etching (RIE), ICP etching, NLD plasma etching, focused ion (FIB) etching, and the step of the ridge is provided. After the ridge processing is performed on the core layer 0602, a three-dimensional optical waveguide can be formed by laminating the first cladding, the second cladding, and the light absorption layer in this order on the entire optical waveguide element. Although not shown, an optical waveguide structure as shown in FIG. 6B can be manufactured by performing ridge processing after forming the core layer in the manufacturing process shown in FIG.

  FIG. 20 shows a manufacturing process in the case where the above-described ridge processing is applied to the optical waveguide element whose embodiment is shown in FIG. Processes 2301 to 2304 are the same as processes 2201 to 2304 shown in FIG. In the process 2304, the depth of the ridge to be formed is set to “approximately half the core thickness”. Thereafter, from the processes 2305 to 2309, two clad structure layers and a light absorption layer are sequentially laminated.

  Ideally, since the film thickness of the second cladding is “half the thickness of the core layer”, in the process 2306 of forming the second cladding of the first cladding structure layer, the core layer in the light propagation region is formed. The height and the height of the second cladding in the region where light does not propagate are substantially equal. In a region where light does not propagate, a “structure in which the first cladding 0505 is sandwiched between the second cladding and the core material” is formed.

  Since the refractive index of the first cladding is lower than the refractive index of the core layer, the first cladding plays a “role for confining light in the lateral direction (x direction)”. Therefore, in the above manufacturing process, “a ridge-shaped step does not occur around the light propagation region”, but in the region where light does not propagate, the structure includes a low refractive index layer in the middle of the core layer. A three-dimensional optical waveguide that confines light in the direction can be realized.

FIG. 7 is a view showing two examples of another embodiment of the optical waveguide device.
FIG. 7 is a cross-sectional view of the optical waveguide element, taken along FIG. 7A and 7B show cross sections of the optical waveguide element, and the Z direction in which light is guided is a direction orthogonal to the drawing.
In these optical waveguide devices shown in FIGS. 7A and 7B, light is confined in the light propagation region 0707 and propagates in the z direction (direction orthogonal to the drawing).

  In the embodiment shown in FIG. 6 described above, “a step is provided in the core layer to achieve confinement in the lateral direction (x direction)”, but in the embodiment shown in FIGS. 7A and 7B, “Parts other than the light propagation region 0707” in the core layer 0702 are completely removed. In this case, light confinement in the core layer 0702 in the lateral direction (x direction) is due to “total reflection at the boundary between the nonlinear optical material forming the core layer 0702 and air”. Further, the “location where the core layer material is removed” may be filled with another optical material. The optical material used in this case may be any material as long as its refractive index is “lower than the refractive index of the nonlinear optical material”.

  In order to manufacture the structure shown in FIG. 7, after forming the optical waveguide in FIG. 17 or FIG. 18, the “band-shaped mask” that becomes the light propagation region 0707 is patterned by the photolithography technique, and then dry etching or dicing is performed. What is necessary is just to remove even a core layer part by etc. In the structure shown in FIG. 7, “the entire thickness of the core layer 0702 is etched” except for the portion to be the light propagation region 0707, but further “deeper” is etched until the support substrate 0701 is reached. Also good.

FIG. 8 shows another embodiment of the optical waveguide device.
FIG. 8 shows a cross-sectional view of the optical waveguide element, and the z direction, which is the light propagation direction, is a direction orthogonal to the drawing. In this embodiment, light is confined in the light propagation region 0807 and propagates in the z-axis direction. In the embodiment of FIG. 6 described above, “light confinement in the lateral direction (x direction) is realized by changing the thickness of the core layer 0603.

  In the optical waveguide device shown in FIG. 8, the thickness of the core layer 0802 is constant even in “a region other than the light propagation region 0807 in the x direction”, but the refractive index is a portion of the light propagation region 0807 in the x direction. In the x direction which is the lateral direction by making the refractive index of the light propagation region 0807 “larger than the portions on both sides”, the “light is a region having a relatively large refractive index”. It can be confined and propagated in the light propagation region 0807 ”.

  The confinement of light in the y direction is performed using “interference reflection”. In this way, three-dimensional light confinement is possible in which light is confined in the x and y directions and light is propagated in the z direction (direction orthogonal to the drawing).

  The refractive index of the refractive index changing region 0808 of the core layer 0802 corresponding to the light propagation region 0807 is higher than that of the regions on both sides thereof. As a method for increasing the refractive index in this way, the well-known “Ti diffusion method or proton exchange method” can be used.

  In the manufacturing process, the nonlinear optical crystal that is the core layer material is provided with a “region with a relatively high refractive index” by the Ti diffusion or proton exchange described above, and thereafter the manufacturing process described above is applied as it is. The optical waveguide element shown in FIG. 8 can be manufactured.

FIG. 9 shows another embodiment of the optical waveguide device.
FIG. 9 shows a cross-sectional view of the optical waveguide element, and the z direction, which is the light propagation direction, is a direction orthogonal to the drawing. In this embodiment, light is confined in the light propagation region 0907 and propagates in the z-axis direction.

  In the optical waveguide device shown in FIG. 8, the refractive index of the core layer 0802 is “higher than both sides in the light propagation region 0807”, but in the optical waveguide device shown in FIG. The refractive index of “the portion 0608 on both sides in the x direction of the light propagation region 0907 is lower than the portion of the light propagation region 0907” makes the refractive index of the portion of the light propagation region 0907 “relative to the portions 0608 on both sides thereof”. "High".

As a method of reducing the refractive index of the nonlinear optical crystal, “ion implantation into a crystal material” can be used. That is, in general, when, for example, “H ⁺ ions or He ⁺ ions” are implanted into a crystal, the atomic density in the crystal decreases due to “partial lattice disturbance (damage)” caused by atomic collisions, and refraction occurs. The rate goes down. For example, when He ⁺ ions are implanted into a lithium niobate crystal at a high energy of about 1 MeV, ions are implanted to a depth of about 2 μm, but with an ion implantation amount of “about 1.0 × 10 ¹⁶ / cm ² ” A refractive index drop of about 2% "occurs. This is a sufficient value as “diffractive index difference for confining propagating light in the left-right direction (x direction) of the light propagation region 0907”.

  The above ion implantation process can be easily incorporated into the optical waveguide device fabrication process shown in FIG. For example, an ion implantation process may be performed on the substrate of the nonlinear optical crystal at the beginning of the process. Alternatively, the ion implantation process may be performed after thinning the substrate of the nonlinear optical crystal. Although it is necessary to prevent ion implantation in the portion of the light propagation region 0907 of the optical waveguide device of FIG. 9, a waveguide pattern that functions as a protective mask is formed on the surface of the light propagation region 0907 (the surface on which ion implantation is performed). do it.

As a material for the protective mask, a glass material such as SiO ₂ or a metal material is suitable. For example, when ions collide with the pattern of SiO ₂ glass, since SiO ₂ is an amorphous material, collision with ions occurs everywhere, and ions cannot reach inside the crystal. By utilizing this phenomenon, a region where no ions are implanted (light propagation region 0907) can be formed.

FIG. 10 shows another embodiment of the optical waveguide device.
FIG. 10 is a cross-sectional view of the optical waveguide element, following FIG. In this optical waveguide element, the upper and lower sides of the core layer 1102 are sandwiched between “a clad structure layer 1103 and a clad structure layer 1104 made of a first clad and a second clad”. That is, in this example, two clad structure layers 1103 and 1194 are formed on both surfaces of the core layer 1102.

  The clad structure layers 1103 and 1104 have the same structure, and a first clad 1105 is formed on the core layer 1102 side. A second clad 1106 is formed so that the first clad 1105 is sandwiched with the core layer 1102. . The clad structure layers 1103 and 1104 are sandwiched between the core layer 1102 and the light absorption layer 1107 on both sides of the core layer 1102.

  That is, the optical waveguide device of FIG. 10 is configured to propagate only the light in the fundamental mode with low loss by “interference reflection” on both sides in the y direction of the core layer 1102. The optical buffer layer 1108 interposed between the support substrate 1101 and the light absorption layer 1107 has a function of reflecting the fundamental mode and higher-order mode light to the core layer 1102 side with total reflection (reflectance: 100%). However, since the light absorption layer 1107 is provided outside the two clad structure layers 1103 and 1104, the higher-order mode light emitted from the core layer 1102 in the y-direction reflection is light. Since light is absorbed by the absorption layer 1107, only light in the fundamental mode is propagated with low loss.

In FIG. 10, reference numeral 1109 indicates “ distribution in the y direction of the propagation light field (the electric field strength in the x direction) of the light (fundamental wave) in the fundamental mode”.
In the case of this optical waveguide element, the optical buffer layer 1108 is not necessarily required. However, when the adhesion between the support substrate 1101 and the light absorption layer 1106 is poor, it is effective to provide the optical buffer layer 1108 in order to improve the adhesion.

FIG. 16 shows the result of calculating the light propagation loss in the “optical waveguide structure in which both surfaces of the core layer are sandwiched between clad structure layers” as shown in FIG.
The fundamental wavelength (operating wavelength) was 1064 nm, the core layer material was lithium niobate crystal, the refractive index was 2.156, and the thickness was 4.0 microns.

  The refractive index of the second cladding 1106 was 2.156, the same as that of the core layer 1102, the thickness was 2.0 μm, Cr was assumed as the material of the light absorption layer 1107, and the complex refractive index was 4.53 + 4.3i. The refractive index of the first cladding 1105 was 2.1.

  Under such conditions, the film thickness of the first cladding 1105 was used as a parameter, and the film thickness was calculated such that only the fundamental mode light propagated with low loss.

  As shown in FIG. 16, when the film thickness of the first cladding is 0.8 μm or more, the propagation loss of the higher-order mode light can be extremely large as 20 dB / cm or more, and the propagation loss of the fundamental mode light is 0. 1B / cm or less and very small. That is, the optical waveguide element configured in this manner functions as a “single mode optical waveguide capable of effectively guiding only fundamental mode light”. When the fundamental wave propagates, the higher-order mode is not constantly excited, so that highly efficient wavelength conversion is possible.

  As shown in the embodiment of FIG. 4, by providing a “periodic polarization inversion region in the nonlinear optical crystal serving as the core layer”, the phase matching between the fundamental wave input to the core layer and the “harmonic generated by wavelength conversion” As a result, the output of the harmonic can be “increased with an increase in the light propagation length”. However, due to “manufacturing error in the formation process of the domain-inverted region”, the inversion pitch may not always be as designed.

  In addition, the equivalent refractive index of light propagating through the optical waveguide is slightly different from the “refractive index of the nonlinear optical crystal material itself”, and the value is “the thickness of the core layer” or three-dimensional confinement, for example, In the case of a ridge optical waveguide (FIG. 6 and the like), depending on “ridge width and ridge depth”, complete phase matching may be difficult due to these manufacturing errors.

  To solve this problem, it is effective to “change the refractive index of the material constituting the optical waveguide element slightly”. Specifically, as shown in FIG. 11A, an electrode 1308 serving as a heater is provided so as to sandwich a substantial part of the optical waveguide element in the y direction, and a voltage is applied between these electrodes to thereby generate “optical The operating temperature of the waveguide element can be changed. " Reference numeral 1310 denotes a “light propagation region”.

  Since the equivalent refractive index difference between the fundamental wave and the harmonic light is “depending on the temperature”, it is possible to always maintain the “phase-matched state” by adjusting the temperature while monitoring the output of the harmonic light.

Further, the refractive index of the nonlinear optical material crystal slightly changes due to the electro-optical effect when an electric field is formed inside the crystal. For example, the refractive index of a crystal of lithium niobate or a crystal of lithium tantalate changes in proportion to the amount of electric field due to the Pockels effect. The “refractive index change amount due to the electro-optic effect” is as small as about 1.0 × 10 ⁻³ at the maximum, but is sufficiently large for the purpose of correcting phase matching.

  As shown in FIG. 11B or FIG. 11C, the electric field is formed inside the optical crystal by allocating substantial portions (core layer, clad structure layer, light absorption layer, optical buffer layer) of the optical waveguide element on both sides in the stacking direction. Can be realized by applying a voltage between the electrodes. For example, in FIG. 11B, the electrode can be formed only by adding a step of forming an electrode layer after forming the optical buffer layer 1307 on the nonlinear optical crystal substrate.

  Further, in FIG. 11B, a light absorption layer 1306 for absorbing light in a higher-order propagation mode is used as the electrode 1308. Similarly, in FIG. 11C, the light absorption layer 1306 also plays the role of “lower electrode 1308”, and in order to form an electric field, the metal electrode 1308 is formed after the substantial part of the optical waveguide element is manufactured. Only need. As described above, the above phase matching can be achieved only by adding a process for forming one metal layer to the conventional device manufacturing process.

FIG. 12 shows two embodiments of the harmonic laser light source device.
In FIG. 12, reference numeral 10 denotes a “laser light source”. Reference numerals 12 and 121 denote wavelength conversion elements.
The wavelength conversion elements 12 and 121 indicate that “the optical waveguide element generates harmonic light while guiding the fundamental wave in the fundamental mode, and guides the generated harmonic light together with the fundamental wave of the fundamental mode. A wavelength conversion element that separates and emits harmonic light from the fundamental wave, and is provided at the output end of the optical waveguide element 12A and the optical waveguide element 12A to separate the harmonic light from the fundamental wave. Or have 12C.

As the optical waveguide element 12A, the various elements described above can be used.
In FIG. 12, a laser light source 10 includes a semiconductor laser 10A that emits “laser light that becomes a fundamental wave”, and a condensing lens 10B that couples the emitted laser light to the core layer of the optical waveguide element 12A for incidence. have.

  In the embodiment shown in FIG. 12A, the wavelength separation means 12B is a “filter”, which absorbs the fundamental wave guided through the optical waveguide element 12A and transmits the harmonic light, thereby fundamentally using the harmonic light. Separate and output from the wave.

  In the embodiment shown in FIG. 12B, the wavelength separation means 12C is a “diffraction grating”, and the fundamental wave and the harmonic light guided by the optical waveguide element 12A are diffracted at different diffraction angles and emitted. Separates the harmonic light from the fundamental wave and outputs it.

  In the above description, the case where the second harmonic is used as the harmonic light has been mainly described. However, the present invention is not limited to this, and laser light having a wavelength of the third harmonic or twice, three times the fundamental wave is generated. Needless to say, it can also be done.

It is a figure for demonstrating embodiment of an optical waveguide element. It is a figure for demonstrating embodiment of an optical waveguide element. It is a figure for demonstrating embodiment of an optical waveguide element. It is a figure for demonstrating embodiment of an optical waveguide element. It is a figure for demonstrating embodiment of an optical waveguide element. It is a figure for demonstrating embodiment of an optical waveguide element. It is a figure for demonstrating embodiment of an optical waveguide element. It is a figure for demonstrating embodiment of an optical waveguide element. It is a figure for demonstrating embodiment of an optical waveguide element. It is a figure for demonstrating embodiment of an optical waveguide element. It is a figure for demonstrating embodiment of an optical waveguide element. It is a figure for demonstrating embodiment of a harmonic laser light source apparatus. It is a figure for demonstrating the waveguide characteristic of an optical waveguide element. It is a figure for demonstrating the waveguide characteristic of an optical waveguide element. It is a figure for demonstrating the waveguide characteristic of an optical waveguide element. It is a figure for demonstrating the waveguide characteristic of an optical waveguide element. It is a figure for demonstrating the manufacturing process of an optical waveguide element. It is a figure for demonstrating the manufacturing process of an optical waveguide element. It is a figure for demonstrating the manufacturing process of an optical waveguide element. It is a figure for demonstrating the manufacturing process of an optical waveguide element.

Explanation of symbols

0101 Core layer 0202 First cladding 0203 Second cladding 0204 Clad structure layer 0205 Light absorption layer

Claims (15)

An optical waveguide element that receives a fundamental wave and generates and propagates harmonic light,
A core layer, a light absorption layer, and one or more cladding structure layers;
The core layer is made of a nonlinear optical material,
The clad structure layer is formed by laminating a first clad and a second clad from the core layer side,
The first cladding has a refractive index smaller than that of the core layer and is formed thinner than the core layer,
The second cladding has a refractive index greater than that of the first cladding, is thinner than the core layer, and is thicker than the first cladding;
The light absorption layer is formed so as to sandwich the cladding structure layer together with the core layer,
Light is interference-reflected between the core layer and the clad structure layer, and the reflectance of this interference reflection is larger than that of the fundamental mode light of the fundamental wave, and the higher-order mode light generated in the core layer. By setting it to be low, the fundamental wave is substantially confined in the core layer and guided in the fundamental mode, and light of higher-order modes generated in the core layer is reflected in the cladding structure layer. Leaked to the side and absorbed by the light absorbing layer,
Harmonic light generated in the core layer is substantially confined in the core layer and guided in the core layer together with the fundamental wave of the fundamental mode. Optical waveguide element. The optical waveguide device according to claim 1, wherein
An optical waveguide device having a structure in which a single clad structure layer is formed on one side of a core layer and is sandwiched between the core layer and a light absorption layer. The optical waveguide device according to claim 1, wherein
A plurality of clad structure layers are formed on one side or both sides of the core layer, and are sandwiched between the core layer and the light absorption layer on one side or both sides of the core layer. An optical waveguide element. In the optical waveguide device according to any one of claims 1 to 3,
An optical waveguide device comprising an optical buffer layer that totally reflects light in contact with any one of a core layer, a clad structure layer, and a light absorption layer. In the optical waveguide device according to any one of claims 1 to 4,
An optical waveguide device characterized in that at least a portion constituted by a core layer, a light absorption layer, and one or more cladding structure layers is integrally formed on a support substrate. The optical waveguide device according to claim 5, wherein
An optical waveguide device characterized in that a light absorption layer is in close contact with a support substrate. The optical waveguide device according to claim 5, wherein
An optical waveguide device comprising an optical buffer layer, wherein the optical buffer layer is in close contact with a support substrate. In the optical waveguide device according to any one of claims 1 to 7,
An optical waveguide element, wherein the core layer has a periodically domain-inverted region in the light guiding direction. In the optical waveguide device according to any one of claims 1 to 8,
When the light guiding direction is the z direction, the thickness direction of the core layer is the y direction, and the direction orthogonal to the z direction and the y direction is the x direction,
An optical waveguide element, wherein the core layer has a step in thickness in the x direction, and light is guided through a core layer portion having a large thickness in the x direction . In the optical waveguide device according to any one of claims 1 to 8,
An optical waveguide device characterized in that the core layer has a light propagation region whose refractive index is higher than that of the nonlinear optical material. In the optical waveguide device according to any one of claims 1 to 8,
An optical waveguide element having an optical non-propagating region having a refractive index smaller than that of the nonlinear optical material along at least one end in the width direction of the core layer. The optical waveguide device according to any one of claims 1 to 11,
Of the first clad and the second clad constituting the clad structure layer, the second clad has the same refractive index as that of the core layer, and the thickness thereof is approximately ½ of the core layer. An optical waveguide device. In the optical waveguide device according to any one of claims 1 to 12,
An optical waveguide device comprising an electrode for adjusting a refractive index in the vicinity of a region where light propagates. The optical waveguide device is configured to generate a harmonic light while guiding the fundamental wave in the fundamental mode, to guide the generated harmonic light together with the fundamental wave of the fundamental mode, and to transmit the harmonic light from the output end of the optical waveguide device. In the wavelength conversion element that emits separately from the fundamental wave,
An optical waveguide element, provided at an output end of the optical waveguide element, having wavelength separation means for separating the harmonic light from the fundamental wave;
14. The wavelength conversion element according to claim 1, wherein the optical waveguide element is any one of claims 1 to 13.   A harmonic laser light source device comprising: the wavelength conversion element according to claim 14; and a laser light source that emits a fundamental wave guided by the wavelength conversion element.

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