JP2004029348A - Method for forming low resistive part on substrate for optical component, substrate for optical component and optical component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form a low resistive part on a substrate for an optical component with no necessity for directly applying a metallic material thereon. <P>SOLUTION: The substrate 1 for the optical component consisting of a compound oxide composed of lithium and a metal element other than lithium is subjected to ion irradiation as shown by arrows A so as to form the low resistive part 4 with resistance lower than that of the compound oxide. The low resistive part 4 has an oxygen deficit composition consisting of the compound oxide from which some portion of oxygen is lost and thereby has sheet resistance lower than that of the surrounding compound oxide. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a low resistance portion on a substrate for optical components, a substrate for optical components, and an optical component.
[0002]
2. Description of the Related Art In general optical information processing technology, in order to realize high-density optical recording, a blue light laser that oscillates blue light having a wavelength of about 400 to 430 nm stably at an output of 30 mW or more has been demanded. And there is a development competition. As a blue light source, an SHG blue laser combining an infrared laser used as a fundamental wave and a wavelength conversion element formed with QPM grading is expected.
[0003] In a wavelength conversion device, QPM grading is realized by a periodically poled structure having a predetermined period, and a so-called voltage application method is known as a method of forming the periodically poled structure. In the voltage application method, a periodically poled structure is formed along an electrode pattern formed of metal.
[0004] For example, in Japanese Patent No. 3005225, a first electrode (comb-shaped electrode) is arranged on one main surface of a ferroelectric optical material subjected to single domain processing, and a second electrode (comb-shaped electrode) is arranged on the other electrode. A uniform electrode) is arranged, and a voltage is applied between the first electrode and the second electrode to form a periodically poled structure.
[0005]
However, in this method, it is necessary to provide an electrode by forming a metal film made of tantalum or the like on the surface of the ferroelectric optical material. This electrode film becomes unnecessary after forming the periodically poled structure by the voltage application method. For this reason, the metal material is wasted. Further, if the periodic polarization inversion structure is processed to form, for example, a second harmonic generation element, the metal film may remain in the final second harmonic generation element, which may adversely affect the characteristics of the element. Further, depending on the design, a step of removing the metal electrode film used for applying the voltage after forming the periodically poled structure is necessary, but this step is complicated, and the surface after the removal of the metal electrode film has Electrode traces remain.
An object of the present invention is to form a low-resistance portion on an optical component substrate without directly applying a metal material.
[0007]
According to the present invention, there is provided an optical component base comprising a composite oxide of lithium and a metal element other than lithium. Wherein the low-resistance portion is generated by irradiating the optical component base material with ions.
Further, the present invention provides a method for forming a low-resistance portion having a lower resistance value than the resistance value of a composite oxide on a substrate for an optical component comprising a composite oxide of lithium and a metal element other than lithium. Wherein a low-resistance portion is generated by causing oxygen deficiency in the composite oxide.
The present invention also relates to a base material for an optical component comprising a composite oxide of lithium and a metal element other than lithium, wherein the base material is formed by irradiating ions to the base material for an optical component. It is characterized by including a low resistance portion having a resistance value lower than the resistance value.
[0010] The present invention also relates to a base material for an optical component comprising a composite oxide of lithium and a metal element other than lithium, wherein the composite oxide is formed by causing oxygen deficiency in the composite oxide. It is characterized by including a low resistance portion having a resistance value lower than the resistance value.
[0011] The present invention also relates to an optical component, comprising the optical component base material.
The present inventor has succeeded in generating a low-resistance portion by irradiating ions to a base for an optical component comprising a composite oxide of lithium and a metal element other than lithium. This low-resistance portion can be formed without the need to directly apply a metal material to the optical component base material. The low-resistance portion has a sheet resistance value that is at least four orders of magnitude lower than that of a normal optical component base material of, for example, about 20 kΩ / □, and thus functions sufficiently effectively as a conductive functional portion such as an electrode. And arrived at the present invention.
[0013]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below.
For example, as shown in FIG. 1A, a mask 2 is formed on a main surface 1a of a flat optical component substrate 1. In the present example, a stripe-shaped opening 3 is formed in the mask 2. In this state, ions are irradiated toward the main surface 1a of the substrate 1 as shown by an arrow A. Then, as shown in FIG. 1B, a low-resistance portion 4 having a predetermined pattern is formed in the opening 3 of the mask 2. Next, the mask 2 is removed as shown in FIG. Thereby, the optical component substrate 1 on which the low resistance portion 4 is formed is obtained.
In the present invention, the substrate for an optical component means a substrate that can be used for an optical component, and its form is not limited. The optical component is not particularly limited, and may be various devices having an optical waveguide, for example, an optical modulator, an optical switching element, a wavelength conversion element, and a harmonic generation element.
In the composite oxide of lithium and a metal element other than lithium, the metal element other than lithium is not particularly limited. However, it is preferable that the metal element other than lithium contains one or more metal elements selected from the group consisting of niobium, tantalum and potassium. Examples of such oxide single crystals include lithium niobate, lithium tantalate, lithium niobate-lithium tantalate solid solution, potassium lithium niobate, potassium lithium tantalate, and potassium lithium niobate-potassium lithium tantalate solid solution. In each of these materials, metal elements other than lithium, potassium, niobium, and tantalum may be doped as long as the crystal structure of the oxide single crystal is not destroyed.
For example, in order to further improve the light damage resistance of the three-dimensional optical waveguide, at least one metal selected from the group consisting of magnesium (Mg), zinc (Zn), scandium (Sc) and indium (In). Elements can be included, with magnesium being particularly preferred.
The composite oxide single crystal may contain a rare earth element as a doping component. This rare earth element acts as an additional element for laser oscillation. As the rare earth element, Nd, Er, Tm, Ho, Dy, and Pr are particularly preferable.
By irradiating the composite oxide single crystal with ions, a low-resistance portion can be generated in the surface region of the composite oxide. When the composite oxide is irradiated with ions, an oxygen vacancy composition in which oxygen atoms constituting the crystal lattice of the composite oxide are partially missing occurs. In the oxygen deficiency composition, the sheet resistance value is lower than that of a composite oxide having a composition in which the surrounding oxygen is not deficient.
Here, preferable conditions for ion irradiation are as follows.
Kind of ion to be irradiated Argon ion irradiation energy 100 to 1000 Watt irradiation method Plasma etching Also, by heating the composite oxide in a nitrogen atmosphere, a low resistance having an oxygen deficiency composition in the surface region of the composite oxide is obtained. A part can be formed. The heating temperature at this time varies depending on the type of the composite oxide, but is generally preferably 400 to 600 ° C. The heating time is preferably 12 to 24 hours.
The sheet resistance of the low resistance portion is lower than the sheet resistance of the composite oxide before the oxygen deficiency treatment. Preferably, the sheet resistance of the low resistance portion is 1000 kΩ / □ or less, and more preferably 100 kΩ / □ or less. Further, the ratio (the sheet resistance of the low-resistance portion / the sheet resistance of the composite oxide before the oxygen deficiency treatment) is preferably 1/1000 or less, more preferably 1/10000 or less.
The oxygen deficiency composition of the composite oxide is, for example, as follows.
LiNbO3-x (0 <x ≦ 0.5)
LiTaO3-x (0 <x ≦ 0.5)
In a preferred embodiment, the low resistance part is an electrode. This electrode may be an electrode for applying a modulation signal to light, in which case the electrode remains on the light modulation element.
In a preferred embodiment, the electrode is an electrode for forming a periodically poled structure on an optical component substrate by a voltage application method. In this case, a step of removing the electrode after forming the periodically poled structure is not required. Further, according to the test results of the present inventor, it was possible to form a periodically poled structure having the same form as the case where an electrode made of a tantalum film was used. Hereinafter, this embodiment will be mainly described.
FIG. 2 is a view for explaining an example of a wavelength conversion device manufacturing process. In the wavelength conversion device manufacturing process, first, a periodically poled structure is formed on the flat optical component substrate 1 by a voltage application method. In this example, an MgO-doped lithium niobate off-cut substrate is used as the substrate 1. Since the polarization direction B of the composite oxide single crystal is inclined at a predetermined angle, for example, 5 ° with respect to the front surface 1a and the back surface 1b, the substrate 1 is called an off-cut substrate.
A comb-shaped electrode 9 and a counter electrode 5 are formed on the front surface 1a of the substrate 1, and a uniform electrode 4A is formed on the back surface 1b. The comb-shaped electrode 9 includes a plurality of elongated electrode pieces 9c that are periodically arranged and an elongated power supply electrode 9a that connects the plurality of electrode pieces 9c. The counter electrode 5 is provided so as to face the tip 9b of the electrode piece 9c.
In this embodiment, as shown in FIGS. 2 and 3A, the comb-shaped electrode 9 and the counter electrode 5 are made of a metal film. On the other hand, the uniform electrode 4A is obtained by generating a portion having an oxygen-deficient structure on the back surface 1b of the substrate 1 according to the present invention. In this example, the uniform electrode 4A is provided over substantially the entire back surface 1b. Therefore, when irradiating the back surface 1b with ions, it is not necessary to form a mask on the back surface 1b.
First, the entire substrate 1 is polarized in the direction B, that is, in the non-polarization inversion direction D. Then, for example, when a voltage V1 is applied between the comb-shaped electrode 9 and the counter electrode 5 and a voltage V2 is applied between the comb-shaped electrode 9 and the uniform electrode 4A, the polarization inversion unit 6 From the tip 9b of the piece 9c, it gradually develops parallel to the direction B. The polarization inversion direction C, which is the direction of polarization of the polarization inversion section 6, is exactly opposite to the non-polarization inversion direction D. A non-polarization inversion portion 7 is formed at a position not corresponding to the electrode piece 9c, that is, between adjacent polarization inversion portions 6. In this manner, a periodically poled structure 13 in which the domain-inverted portions 6 and the non-domain-inverted portions 7 are alternately arranged is formed.
Further, as shown in FIG. 3B, a low resistance portion 4B according to the present invention can be formed in the surface region on the surface 1a side of the substrate 1. The low resistance portion 4B needs to be patterned so as to constitute the comb electrode 9 as a whole. In this case, a uniform electrode 26 made of a metal film can be formed on the back surface 1b. Then, a voltage is applied between the comb-shaped electrode 4B and the uniform electrode 26 to form a periodically poled structure. In this example, after forming the periodically poled structure, a step of removing the comb-shaped electrode 9 made of a metal film becomes unnecessary.
Hereinafter, with reference to FIGS. 4 and 5, a description will be given of a wavelength conversion device manufacturing process after the periodic domain inversion structure 13 is formed.
FIG. 4 shows a state where the fixing substrate 16 is joined to the base material 1 in the wavelength conversion device manufacturing process. The fixing substrate 16 is bonded to the surface 1 a of the base material 1 via the bonding layer 15. In FIG. 4, unlike FIG. 2, the surface 1a faces downward. Reference numeral 14 denotes a planar pattern of the three-dimensional optical waveguide to be formed. After joining to the fixing substrate, the substrate 1 is processed from the back surface 1b side to make it thin. However, at this stage, it is difficult to make the substrate 1 thin enough to confine light in the thickness direction. Therefore, part or all of the removal parts 25A and 25B at both ends thereof are removed except for the edges 14b to 14c of the optical waveguide pattern 14.
At the time of this processing, the thickness of the optical waveguide 14a is adjusted. Such processing can be performed by, for example, a dicing processing apparatus or a laser processing apparatus.
FIG. 5 is a view showing the wavelength conversion device 17 in which the ridge type optical waveguide 20 is formed. As a result of the removal portions 25A and 25B being removed from the base material 1, the three-dimensional optical waveguide 20 is formed. In this example, relatively thin flat plate portions 22 remain on both sides of the optical waveguide 20, respectively.
Of course, the optical waveguide can be formed by processing from the surface 1a side of the substrate 1. Further, the optical waveguide may be an optical waveguide formed by an ion exchange method such as a proton exchange optical waveguide. Further, an optical waveguide formed by an internal diffusion method, such as a titanium diffusion optical waveguide, may be used.
In the above embodiment, the base material 1 is bonded to the fixing substrate 16 by the bonding layer 15. In this case, the refractive index of the bonding layer 15 is preferably lower than the refractive index of the substrate 1, and the bonding layer 15 is preferably amorphous. The difference between the refractive index of the bonding layer 15 and the refractive index of the substrate 1 is preferably 5% or more, and more preferably 10% or more.
The material of the bonding layer 15 is preferably an organic resin or glass (particularly preferably low melting glass). Examples of the organic resin include an acrylic resin, an epoxy resin, and a silicone resin. As the glass, a low-melting glass mainly containing silicon oxide is preferable.
As a material for forming a mask pattern for forming the low resistance portion and the periodically poled structure 13, a resist, SiO ₂ , Ta or the like can be exemplified. As a method for forming a mask pattern, a photolithography method can be exemplified.
The material of the fixing substrate 16 is not particularly limited as long as it has a predetermined structural strength. However, it is preferable that physical properties such as the thermal expansion coefficient and the optical waveguide are close to each other, and lithium niobate, lithium tantalate, lithium niobate-lithium tantalate solid solution, potassium lithium niobate, potassium lithium tantalate, lithium lithium niobate- Each single crystal of potassium lithium tantalate solid solution is particularly preferred.
When the device of the present invention is used as a second harmonic generator, the wavelength of the harmonic is preferably from 330 to 1600 nm, particularly preferably from 400 to 430 nm.
In each of the above examples, the substrate 1 is, for example, a 5 ° off-cut substrate, but the off-cut angle is not particularly limited. Particularly preferably, the off-cut angle is 1 ° or more, or 20 ° or less.
As the substrate 1, a so-called X-cut substrate, Y-cut substrate or Z-cut substrate can be used. When using an X-cut substrate or a Y-cut substrate, the electrodes 4A and 26 are not provided on the back surface 1b, but are provided on the front surface 1a, and a voltage is applied between the comb-shaped electrodes 9 and 4B and the electrodes 4A and 26. Can be. In this case, the counter electrode 5 may not be provided, but may be left as a floating electrode. When a Z-cut substrate is used, the uniform electrodes 4A and 26 are provided on the back surface 1b, and a voltage can be applied between the comb electrodes 9 and 4B and the uniform electrodes 4A and 26. In this case, the counter electrode 5 is not necessarily required, but may be left as a floating electrode.
[0042]
EXAMPLES Specific experimental results will be described below.
According to the method described with reference to FIGS. 1, 2 and 3A, a periodically poled structure was formed. Specifically, a base material 1 having a diameter of 3 inches and a thickness of 1.0 mm and made of lithium niobate single crystal doped with 5% of magnesium was prepared. The substrate 1 was placed in a vacuum chamber, and argon gas was introduced into the chamber at a flow rate of 50 sccm to generate high-frequency plasma. At this time, by applying a bias voltage of 50 W to the substrate, argon ions were irradiated to the back surface 1 b side of the substrate 1. By performing this process for 10 minutes, the low resistance portion 4A was formed on the back surface of the base material.
The sheet resistance of the lithium niobate single crystal doped with 5% of magnesium was several hundred MΩ / □ or more, and the sheet resistance of the low resistance portion 4A was 20 kΩ / □. The sheet resistance of tantalum is 20Ω / □.
A comb electrode 9 and a counter electrode 5 made of metal tantalum were formed by photolithography. The pitch of the electrode pieces 9c was 3 μm in order to obtain SHG light having a wavelength around 400 nm. A pulsed voltage of 4.0 kV (pulse width: 20 msec, 25 Hz, number of pulses: 6, pulse current: upper limit: 2 mA) was generated from the power supply, and the periodically poled structure 13 was formed.
As a result, a periodically poled structure having the same contour as the case where the uniform electrode 4A was formed of a tantalum film was obtained.
[0046]
As described above, according to the present invention, a low-resistance portion can be formed on an optical component substrate without the need to directly apply a metal material. Further, by applying a voltage to the low resistance portion thus obtained, it is possible to form a periodically poled structure.
[Brief description of the drawings]
FIG. 1A shows a state in which ions are applied to an optical component substrate 1 on which a mask 2 is formed, and FIG. 1B shows a substrate 1 on which a low resistance portion 4 is formed. (C) shows the substrate 1 after the mask 2 is removed.
FIG. 2 is a perspective view of an optical component substrate 1 for explaining a process of forming a periodically poled structure by a voltage application method.
FIGS. 3A and 3B are cross-sectional views illustrating examples of a substrate 1, comb electrodes 9 and 4B, and uniform electrodes 4A and 26, respectively.
FIG. 4 is a perspective view showing the base member 1 after a periodically poled structure is formed, and a fixing substrate 16 bonded to the base member 1.
FIG. 5 is a perspective view showing an optical waveguide element 17 on which a ridge type three-dimensional optical waveguide 20 is formed.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Substrate for optical components 1a Surface of substrate 1 for optical components 1b Back surface of substrate 1 for optical components 2 Mask 3 Opening of mask 2 4 Low resistance part 4A Low resistance part functioning as uniform electrode 4B Functioning as comb-shaped electrode 5 Low resistance part 5 Counter electrode 6 Polarization inversion part 7 Non-polarization inversion part 9 Comb electrode 13 Periodically polarization inversion structure 14 Design pattern of three-dimensional optical waveguide 15 Bonding layer 16 Fixing substrate 17 Optical waveguide element 20 Three-dimensional optical waveguide A ion Irradiation

Claims (11)

A method for forming a low-resistance portion having a lower resistance value than the resistance value of the composite oxide on a base for an optical component comprising a composite oxide of lithium and a metal element other than lithium,
A method for forming a low-resistance portion on an optical component substrate, wherein the low-resistance portion is generated by irradiating the optical component substrate with ions. A method for forming a low-resistance portion having a lower resistance value than the resistance value of the composite oxide on a base for an optical component comprising a composite oxide of lithium and a metal element other than lithium,
A method of forming a low-resistance portion on an optical component substrate, wherein the low-resistance portion is generated by causing oxygen deficiency in the composite oxide. 3. The method according to claim 1, wherein the low resistance portion is an electrode. The method according to claim 3, wherein the electrode is an electrode for forming a periodically poled structure by a voltage application method. The composite oxide is selected from the group consisting of lithium niobate, lithium tantalate and lithium niobate-lithium tantalate solid solution, wherein the composite oxide is selected from the group consisting of: the method of. An optical component substrate comprising a composite oxide of lithium and a metal element other than lithium,
An optical component base, comprising: a low resistance portion having a lower resistance than the composite oxide and generated by irradiating the optical component base with ions. An optical component substrate comprising a composite oxide of lithium and a metal element other than lithium,
An optical component substrate, comprising: a low resistance portion having a lower resistance value than a resistance value of the composite oxide, which is generated by causing oxygen deficiency in the composite oxide. The optical component substrate according to claim 6, wherein the low-resistance portion is an electrode. The optical component substrate according to claim 8, wherein the electrode is an electrode for forming a periodically poled structure by a voltage application method. The composite oxide according to any one of claims 6 to 9, wherein the composite oxide is selected from the group consisting of lithium niobate, lithium tantalate, and a lithium niobate-lithium tantalate solid solution. Substrate for optical components. An optical component, comprising the optical component substrate according to any one of claims 6 to 10.

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