CA2256216C - Optical control device and method for making the same - Google Patents
Optical control device and method for making the same Download PDFInfo
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Abstract
An optical control device has a LiNbO3 or LiTaO3 crystalline substrate having an electro-optic effect, a channel-type optical waveguide which is formed in the crystalline substrate by doping metal into first regions of a surface layer of the substrate, a first film layer which is optically-transparent and formed on the crystalline substrate, a second film layer, and electrodes formed on the optically-transparent first film layer. The portion of the surface layer of the crystalline substrate into which metal is not doped is defined as a remainder region. The second film layer is formed between the crystalline substrate and the the first film layer so as to be positioned adjacent at least a portion of the remainder region. The second film layer is made of a material that is different from that of the crystalline substrate and the first film layer.
Description
CA 022~6216 1998-12-29 OPTICAL CONTROL DEVICE AND METHOD FOR MAKING THE SAME
This application is a divisional application of Canadian Patent Appln. 2,159,129, filed on September 26, 1995.
This invention relates to an optical control device for switching light paths, modulating a light wave and filtering a light wavelength, and more particularly to, an optical control device of a waveguide-type in which the control is carried out by using optical waveguides which are formed on an electro-optic-effect crystalline substrate made of lithium-containing material such as LiNbO3, LiTaO3 or similar material, and to a method for making the same.
Along with the utilization of an optical communi-cation system, a large capacity and multi-function system is desired. Also, enhanced functions such as high-speed generation of optical signals, high-speed switching of an optical transmission line, and high-speed exchanging are required.
As a means for switching optical transmission lines and exchanges in a network, an optical switch is used.
The optical switch now available is operated by switching light paths according to the mechanical movement of a prism, mirror, fiber or the like. However, it has problems that the operating speed is low and that it is too large to construct a matrix switch. To overcome the problems, a waveguide-type optical switch which employs optical wave-CA 022~6216 1998-12-29 guides has been developed. It has advantages in that high-speed operation, integration of numerous elements, and high reliability can be realized. In particular, the optical switch which employs a ferroelectric material such as lithi-um niobate(LiNbO3) or the like has low light absorption andhigh efficiency caused by the large electro-optic effect.
Various types of optical control devices are reported, for example, a directional-coupler-type, mach-zender-type, balance-bridge-type, total-reflection-type optical switch.
Recently, the high-density integration of the waveguide-type optical switch using a directional coupler which is formed in an electro-optic-effect LiNbO3 crystalline substrate has been developed. H. Nishimoto (the inventor of this application) et al., "Polarization Independent 8x8 LiNbO3 Optical Matrix Switch", Electronic Information Communication Society, OQE88-147, pp. 67-74 reports the 8x8 matrix optical switch in which 64 directional-coupler-type optical switches is integrated in the LiNbO3 crystalline substrate. Also, a device such as an external optical modulator which comprises a single optical switch has been developed.
The characteristics concerning such waveguide-type devices are stability in operation, switching voltage (power), crosstalk, extinction ratio, loss, switching speed and so on. The most important characteristic of these is stability in operation.
CA 022~6216 1998-12-29 However, the conventional optical control device has a problem of DC drift which significantly affects stability in operation and reliability of the device. The DC drift is a phenomenon in which an optical-output to applied-voltage characteristic shifts while a DC voltage is continuously applied.
Accordingly, it is an object of the invention to provide an optical control device in which the DC drift can be effectively suppressed to afford high reliability.
It is a further object of the invention to provide a method for making an optical control device in which the DC drift can be effectively suppressed to afford high reliability.
In one form, the invention is an optical control device that includes: a LiNbO3 or LiTaO3 crystalline sub-strate having an electro-optic effect; a channel-type opti-cal waveguide which is formed in said crystalline substrate by doping metal into first regions of a surface layer of the substrate, a remainder of the surface layer being defined as a remainder region; an optically-transparent film layer formed on said crystalline substrate; a second film layer which is formed between the crystalline substrate and the first film layer so as to be positioned adjacent at least a portion of the remainder region, the second film layer being made of a material that is different from that of the cry-stalline substrate and the first film layer; and electrodes formed on said optically-transparent first film layer.
CA 022~6216 1998-12-29 The second film layer may be formed so as to be positioned adjacent the whole of the remainder region. The material of the second film layer may be a material in which it is difficult to generate ionic polarization when an elec-tric field is applied thereto. The material of the secondfilm layer may be a single-element material selected from the group consisting of Si, Ti, Cu, V, Fe, Mo and Cr, or the material may be a semiconductor, organic material or metal alloy. Specifically, the material of the second film layer may be titanium.
In another form, the invention is a method for making an optical control device, comprising the initial step of preparing a LiNbO3 crystalline substrate having an electro-optic effect. A metal is then thermally diffused into first regions of a surface layer of the crystalline substrate for forming in the crystalline substrate a channel-type optical waveguide, a remainder of the surface layer being defined as a remainder region. One film layer is then formed on the surface layer of the crysalline sub-strate so as to be positioned adjacent at least a portion ofthe remainder region. Then, an optically-transparent other film layer is formed over the one film layer and over a re-maining part of the surface layer that remains uncovered by the one film layer. The method of the invention may also comprise an additional step of removing at least a part of both the one film layer and the other film layer over an intermediate region of the surface layer, the intermediate CA 022~6216 1998-12-29 region being positioned between the first regions of the surface layer.
The invention will next be explained in more detail in conjunction with the appended drawings, wherein:
Figure 1 is a cross-sectional view of a conven-tional optical control device;
Figure 2 is a cross-sectional view of an optical control device in a first preferred embodiment according to the invention;
Figure 3 is a graph illustrating variation of the amount of lithium mixed into a buffer layer depending on the existence of a lithium blocking layer;
Figure 4 is a cross-sectional view of an optical control device in a second preferred embodiment according to the invention;
Figure 5 is a cross-sectional view of an optical control device in a third preferred embodiment according to the invention;
Figures 6A and 6B are cross-sectional views of an optical control device in a process for making an optical control device according to the invention;
Figures 7A and 7B are cross-sectional views of an optical control device in another process for making an optical control device according to the invention;
Figure 8 is a cross-sectional view of an optical control device in a fourth preferred embodiment according to the invention;
CA 022~6216 1998-12-29 Figure 9 is a cross-sectional view of an optical control device in a fifth preferred embodiment according to the invention;
Figure 10 is a cross-sectional view of an optical control device in a sixth preferred embodiment according to the invention;
Figures llA to llC are cross-sectional views of an optical control device in a process for making the optical control device in the fifth embodiment according to the invention; and, Figure 12 is a graph illustrating variation of the amount of lithium mixed into a buffer layer depending on the existence of a lithium blocking layer.
Before explaining an optical control device in the preferred embodiment, the aforementioned conventional opti-cal control device in Figure 1 will be explained.
As shown in Figure 1, the conventional optical control device comprises an electro-optic crystalline sub-strate 1 which is made of LiNbO3, LiTaO3 or like material, and in which channel-type optical waveguides 2a and 2b form a directional coupler 5. A buffer layer 3 is formed on the electro-optic crystalline substrate 1, and metal electrodes 4a and 4b to which external control signals are applied extend on buffer layer 3.
The buffer layer 3 of optically-transparent film is used as an optical buffer layer to prevent the absorption of the waveguided-light caused by the metal electrodes 4a CA 022~6216 1998-12-29 and 4b. It is generally made of sio2 since sio2 does not absorb light and has a refractive index significantly less than that of a LiNbO3 or LiTaO3 substrate. The electrodes 4a and 4b generally employ a metal with low volume resistivity so as to provide a high-speed operation, and are disposed near the channel-type optical waveguides 2a and 2b.
The optical control devices of an optical wave-guide-type having the above structure, such as an optical switch or optical modulator, have been suggested. However, they can not yet be put into practice since there is an open question of DC drift which affects reliability of the device. The DC drift is a phenomenon wherein an optical-output to applied-voltage characteristic shifts while a DC
voltage is continuously applied. The DC drift is caused by the impurity ions which are included in the buffer layer 3 which is deposited on the electro-optic crystalline sub-strate 1 by the CVD or sputtering method. Namely, the impurity ions may move according to the polarity thereof under the electric field in the buffer layer 3 which is generated by the voltage applied to the electrodes 4a and 4b. Due to the movement of ions, the anti-electric-field which negates the electric field in the buffer layer 3 is formed. This phenomenon is a cause of the DC drift. The impurity ions contributory to the DC drift include sodium or potassium which is naturally mixed, as well as lithium mixed in the buffer layer 3 from the LiNbO3 or LiTaO3 substrate.
The mixing of lithium from the LiNbO3 or LiTaO3 substrate is CA 022~6216 1998-12-29 . ~
promoted by plasma or heat generated in the deposition by the CVD or sputtering method.
Next, an optical control device in the first preferred embodiment will be explained in Figure 2, wherein like parts are indicated by like reference numerals as used in Figure l.
The optical control device in the first embodiment is provided with an optical circuit 5 which has two channel-type optical waveguides 2a and 2b, and electrodes 4a and 4b which are formed on a buffer layer 3 of optically-trans-parent film and are disposed over the channel-type optical waveguides 2a and 2b. Herein, the optical circuit 5 may employ a directional-coupler-type, mach-zender-type, balance-bridge-type or a similar type. The buffer layer 3 is preferably made of sio2, but it also may be made of Al2O3, MgF2, SioN, Si3N4 or similar material. The depositing of the buffer layer 3 may be performed by the CVD method, sput-tering method, vapor deposition method or similar method.
The electrodes 4a and 4b may be made of various conductive materials, such as Au, Al, Mo, Cu, WSi, ITO, ZnO or conduc-tive polymer.
Further, in Figure 2, a metal-doped layer 6 (hereinafter referred to as "lithium blocking layer") is on the entire surface of the LiNbO3 crystalline substrate l, as well as on the surface of the channel-type optical wave-guides 2a and 2b; the waveguides are made by doping metal into parts of the surface of the LiNbO3 crystalline substrate CA 022~6216 1998-12-29 . ~
1. The doping metal for forming the channel-type optical waveguides 2a and 2b and lithium blocking layer 6 may in-clude Ti, Cu, V, Fe, Mo, Cr or similar material. The doping of metal may be performed by the thermal diffusion method, ion implantation method or the like. Herein, the doping of metal should be performed such that the refractive index of the channel-type optical waveguides 2a and 2b is greater than that of the lithium blocking layer 6.
Both the channel-type optical waveguides 2a and 2b and lithium blocking layer 6 in the first embodiment are formed by doping titanium by the thermal diffusion method.
Herein, the doping of titanium is performed such that the refractive index of the channel-type optical waveguides 2a and 2b is greater than that of the lithium blocking layer 6.
In this embodiment, based on the refractive index increasing with thickening of the titanium-deposited layer, the tita-nium-deposited layer for the channel-type optical waveguides 2a and 2b is formed to be thicker than that for the lithium blocking layer 6 to obtain a desired difference in refrac-tive index. Namely, the titanium-deposited layer for the channel-type optical waveguides 2a and 2b has a thickness of 0.05 to 0.15 nm, while the titanium-deposited layer for the lithium blocking layer 6 has a thickness of between 1/100 and 4/5 the thickness of the titanium-deposited layer for the channel-type optical waveguides 2a and 2b. Then, both the titanium-deposited layers are processed by the thermal diffusion at 850 to 1100~C for 0.5 to 20 hours to form the CA 022~6216 1998-12-29 . ~
channel-type optical waveguides 2a and 2b and lithium blocking layer 6.
The inventor has found that lithium, which is a component of the crystalline substrate 1, is mixed from the LiNbO3 or LiTaO3 crystalline substrate 1 into the buffer layer 3 of sio2 or the like due to plasma or heat when the buffer layer 3 is deposited by CVD method, sputtering method, vapor deposition method or the like. Furthermore, he has found that the mixing of lithium is significantly reduced at the region where the lithium blocking layer 6 is formed as compared with at the region where the lithium blocking layer 6 is not formed.
Figure 3 shows variation of the amount of lithium mixing into the sio2 buffer layer 3, depending on the exist-ence of the lithium blocking layer 6; i.e., on the right end point of the horizontal axis, the lithium blocking layer is formed on the surface of the LiNbO3 crystalline substrate 1;
on the left end point of the horizontal axis, the lithium blocking layer is not formed on the surface of the LiNbO3 crystalline substrate 1. The sio2 buffer layer 3 is formed by the sputtering method. Due to the lithium blocking layer 6, the amount of lithium mixing into the SiO2 buffer layer is reduced to about 1/50 the amount otherwise mixing.
Thus, according to the optical control device in the first embodiment, the lithium mixing from the LiNbO3 crystalline substrate 1 into the sio2 buffer layer 3 due to plasma or heat when the SiO2 buffer layer 3 is deposited by CA 022~6216 1998-12-29 CVD method, sputtering method, vapor deposition method or similar method can be effectively reduced. Thereby, the DC
drift of the device can be suppressed to provide an optical control device with high reliability.
Meanwhile, it will be easily appreciated that the above optical control device can be obtained if only the amount and depth of metal doped is set such that the chan-nel-type optical waveguides 2a and 2b serve as a waveguide, i.e., the amount, depth and type of metal doped are not limited by the other condition.
With reference to Figure 4, an optical control device in the second preferred embodiment will be explained.
In this embodiment, an optical circuit 5 is a directional coupler, and a lithium blocking layer 6 is formed on the surface of a crystalline substrate 1 except in the region where the waveguided-light propagates between channel-type optical waveguides 2a and 2b. The lithium blocking layer 6 is not formed in the region between the channel-type optical waveguides 2a and 2b of the directional coupler, since the waveguided-light propagates therebetween. The second embodiment can provide a similar advantage to that of the first embodiment. In addition, the optical control device in the second embodiment does not affect the propagation characteristic of the waveguided-light through the channel-type optical waveguides 2a and 2b. Therefore, reduction ofsteps in processing and designing of the device, and a higher yield, can be realized.
CA 022~6216 1998-12-29 ~ .
With reference to Figure 5, an optical control device in the third preferred embodiment will be explained.
In this embodiment, channel-type optical waveguides 2a and 2b are formed on the surface of a LiTaO3 crystalline sub-strate 1 by proton exchanging, and a lithium blocking layer 6 is formed by doping metal on the entire surface of the LiTaO3 crystalline substrate 1. The proton exchanging that forms the channel-type optical waveguides 2a and 2b may employ benzoic acid, pyrophosphoric acid or the like. When the crystalline substrate 1 is made of LiTaO3, the lithium blocking layer 6 is doped by ion implantation. When the crystalline substrate 1 is made of LiNbO3, the lithium blocking layer 6 is doped by thermal diffusion or ion implantation. The doping metal for forming the lithium blocking layer 6 may include Ti, Cu, V, Fe, Mo, Cr or a similar metal. The third embodiment can also provide a similar advantage to that of the first embodiment.
Meanwhile, it will be easily appreciated that the above optical control device can be obtained if only the proton exchanging and the metal doping into the lithium blocking layer 6 are performed such that the channel-type optical waveguides 2a and 2b serve as a waveguide, i.e., the amount and depth of the proton exchanging, and the amount, depth and type of metal doped are not limited by the other condition.
CA 022~6216 1998-12-29 Figures 6A and 6B show the process for making an optical control device in the first preferred embodiment according to the invention.
First, on a LiNbO3 crystalline substrate 1, a patterned metal layer 7a for forming channel-type optical waveguides 2a and 2b and a metal layer 7b for forming a lithium blocking layer 6 are formed (Figure 6A). The depositing of the metal layers 7a and 7b may be performed by CVD, sputtering, vapor deposition method or the like. The patterning of the metal layer 7a is by the standard litho-graphy technique. Herein, the metal layer 7b for the lithium blocking layer 6 may be patterned such that a region is left for propagating waveguided-light without the lithium blocking layer.
Next, by doping the metal in the metal layers 7a and 7b into the LiNbO3 crystalline substrate 1 by the thermal diffusion, the channel-type optical waveguides 2a and 2b and lithium blocking layer 6 are simultaneously formed (Figure 6B).
Though the patterned metal layer 7a for forming the channel-type optical waveguides 2a and 2b is mounted on the metal layer 7b for forming the lithium blocking layer 6 in Figure 6A, it will be easily appreciated that the rela-tionship in the mounting can be changed upside down, i.e., the metal layer 7b may be mounted on the metal layer 7a.
The doping metal may include Ti, Cu, V, Fe, Mo, Cr, or similar metal. In this embodiment, both the channel-CA 022~6216 1998-12-29 type optical waveguides 2a and 2b and lithium blocking layer 6 are formed by using titanium as the doping metal.
Figures 7A and 7B show the process for making an optical control device in the second preferred embodiment according to the invention. First, after depositing a metal layer 7a for forming channel-type optical waveguides 2a and 2b as shown in Figure 6A on a LiNbO3 crystalline substrate 1, the metal layer 7a is processed by thermal diffusion to form the channel-type optical waveguides 2a and 2b (Figure 7A).
Next, after depositing a metal layer 7b for forming a lithium blocking layer 6 as shown in Figure 6A on the LiNbO3 crystalline substrate 1, the metal layer 7b is processed by thermal diffusion to form the lithium blocking layer 6 (Figure 7B). Herein, the metal layer 7b for the lithium blocking layer 6 may be patterned such that a region is left for propagating waveguided-light without the lithium blocking layer.
Similarly to the process in the first embodiment, the depositing of the metal layers 7a and 7b may be per-formed by CVD, sputtering, vapor deposition method orsimilar method. The patterning of the metal layer 7a is by the standard lithography technique.
Though, in this embodiment, the lithium blocking layer 6 is formed after the formation of the channel-type optical waveguides 2a and 2b, the lithium blocking layer 6 can be formed before the formation of the channel-type optical waveguides 2a and 2b.
CA 022~6216 1998-12-29 . .
Meanwhile, it will be easily appreciated that the above optical control device can be obtained if only the channel-type optical waveguides 2a and 2b serve as a wave-guide, i.e., the relationship in depth between the channel-type optical waveguides 2a and 2b and the lithium blockinglayer 6 is not limited by the other condition.
The doping metal may include Ti, Cu, V, Fe, Mo, Cr or other similar metal. In this embodiment, both the channel-type optical waveguides 2a and 2b and lithium blocking layer 6 are formed by using titanium as the doping metal.
With reference to Figure 8, an optical control device in the fourth preferred embodiment will be explained.
The optical control device in the fourth embodi-ment is provided with an optical circuit 5 which has twochannel-type optical waveguides 2a and 2b which are formed on a LiNbO3 crystalline substrate 1 by the thermal diffusion method, and electrodes 4a and 4b which are formed on a buf-fer layer 3 of optically-transparent film and are disposed over the channel-type optical waveguides 2a and 2b. Herein, the optical circuit 5 may employ a directional-coupler-type, mach-zender-type, balance-bridge-type or similar type. The buffer layer 3 is preferably made of sio2, and it also may be made of Al2O3, MgF2, SioN, Si3N4 or like material. The depositing of the buffer layer 3 may be performed by the CVD
method, sputtering method, vapor deposition method or simi-lar method. The electrodes 4a and 4b may be made of various CA 022~6216 1998-12-29 conductive materials, such as Au, Al, Mo, Cu, WSi, ITO, ZnO
or conductive polymer.
Between the LiNbO3 crystalline substrate 1 and the buffer layer 3, a film layer 6 (hereinafter referred to as "lithium blocking layer") which is separated from the buffer layer 3 is provided. Herein, the lithium blocking layer 6 is not formed in the region for propagating waveguided-light. Thus, when the optical circuit 5 employs a direc-tional coupler or X-type, the lithium blocking layer 6, as shown in Figure 8, is not formed on the channel-type optical waveguides 2a and 2b nor between the channel-type optical waveguides 2a and 2b.
The lithium blocking layer 6 may be made of a metal or semiconductor material of a single element in-cluding Si, Ti, Cu, V, Fe, Mo, Cr or similar material, or a dielectric, metal, semiconductor, organic material or similar material in which is difficult to generate ionic polarization by applying an electric field, such as crystal doped by phosphorus, MgF2, Si3N4, WSi, GaAs, Inp, polyimide.
The substrate 1 is limited to the LiNbO3 crystal-line substrate, and any lithium-containing crystalline sub-strate such as a LiTaO3 crystalline substrate may be used.
The depositing of the lithium blocking layer 6 may be performed by CVD, sputtering, vapor deposition method or similar method. The standard lithography technique is employed to preclude the formation of the lithium blocking layer at the region for propagating waveguided-light.
CA 022~6216 1998-12-29 . .
A titanium-deposited layer with a thickness of 0.02 to 0.15 nm is processed by the thermal diffusion at 850 to 1100~C for 0.5 to 20 hours to form the channel-type optical waveguides 2a and 2b.
With reference to Figure 9, an optical control device in the fifth preferred embodiment will be explained.
In this embodiment, on the intermediate step in the process for making the optical control device, a lithium blocking layer 6 and buffer layer 3 between two channel-type optical waveguides 2a and 2b is partially removed. This structure is suitable for the case that the lithium blocking layer 6 between the channel-type optical waveguides 2a and 2b is not proper, i.e., when the optical circuit 5 is a directional coupler, X-type or the like. Because the covering area of the lithium blocking layer 6 is greater than that of the lithium blocking layer 6 in the fourth embodiment, the lithium mixing into the buffer layer 3 when the buffer layer 3 is deposited can be further reduced to further suppress the DC drift and provide an optical control device with higher reliability.
With reference to Figure 10, an optical control device in the sixth preferred embodiment will be explained.
This embodiment is suitable for the case in which waveguided-light in optical circuit 5 does not propagate between two channel-type optical waveguides 2a and 2b, such as when a mach-zender-type, balance-bridge-type is employed.
Namely, a lithium blocking layer 6 is also formed between CA 022~6216 1998-12-29 the channel-type optical waveguides 2a and 2b. Because the covering area of the lithium blocking layer 6 is greater than that of the lithium blocking layer 6 in the fourth embodiment, the lithium mixing into the buffer layer 3 when the buffer layer 3 is deposited can be further reduced to further suppress the DC drift and provide an optical control device with higher reliability.
Figures llA to llC show the process for making the optical device in the fifth embodiment.
First, as shown in Figure llA, after forming the directional coupler 5 of the channel-type optical waveguides 2a and 2b on the LiNbO3 crystalline substrate 1 by the ther-mal diffusion of titanium, the lithium blocking layer 6 is deposited on the LiNbO3 crystalline substrate 1, except on the channel-type optical waveguides 2a and 2b. In this embodiment, the lithium blocking layer 6 is deposited with chromium by electron-beam vapor deposition, thermal deposi-tion, sputtering method or similar method. Thereafter, the lithium blocking layer 6 corresponding to the region where the electrodes 4a and 4b will be provided is removed by using the standard photolithography technique and etching.
Next, as shown in Figure llB, SiO2 is deposited thereon to form a buffer layer 3, by CVD, a sputtering method or a similar method. Optionally, the buffer layer 3 may be annealed. Thereafter, the lithium blocking layer 6 and buffer layer 3 between the channel-type optical wave-CA 022~6216 1998-12-29 ~ .
guides 2a and 2b are removed by using the standard photo-lithography technique and etching.
Finally, as shown in Figure llC, the layer for forming the electrodes 4a and 4b is deposited by electron-beam vapor deposition, thermal vapor deposition, sputtering method or similar method, thereafter forming the electrodes 4a and 4b by using the standard photolithography technique and etching. The electrodes are mainly made of gold.
Alternatively, the removing of the lithium blocking layer 6 and buffer layer 3 between the channel-type optical waveguides 2a and 2b as in Figure llB may be simul-taneously carried out after the forming of the electrodes 4a and 4b.
From the above-mentioned process, the process for making the optical control devices in the fourth and sixth embodiments will be easily understood. Namely, after forming the directional coupler 5 of two waveguides 2a and 2b on the LiNbO3 crystalline substrate 1 by the thermal diffusion, the layer for forming the lithium blocking layer 6 is deposited. Thereafter, the lithium blocking layer 6 corresponding to the region where the electrodes 4a and 4b will be formed, or the lithium blocking layer 6 corres-ponding to the above-mentioned region and the region between the electrodes 4a and 4b, is removed. Thereafter, the buf-fer layer 3 is deposited thereon. Finally, similarly to the fifth embodiment, the electrodes 4a and 4b are formed on the buffer layer 3.
CA 022~6216 1998-12-29 Figure 12 shows an amount of lithium mixing into the SiO2 buffer layer 3, depending on the existence of the lithium blocking layer 6, i.e., on the right end point of the horizontal axis, the lithium blocking layer is formed on the surface of the LiNbO3 crystalline substrate 1 (in the fourth to sixth embodiments); on the left end point of the horizontal axis, the lithium blocking layer is not formed on the surface of the LiNbO3 crystalline substrate 1. The sio2 buffer layer 3 is formed by the sputtering method. Due to the lithium blocking layer 6, the amount of lithium mixture into the sio2 buffer layer 3 is reduced to about 1/50 the amount otherwise.
Thus, according to the optical control device, the lithium mixing from the LiNbO3 crystalline substrate 1 into the sio2 buffer layer 3 due to plasma or heat when the sio2 buffer layer 3 is deposited by CVD method, sputtering method, vapor deposition method or similar method can be effectively reduced.
Although the invention has been described with respect to specific embodiment for complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art and which fairly fall within the basic teaching herein set forth.
This application is a divisional application of Canadian Patent Appln. 2,159,129, filed on September 26, 1995.
This invention relates to an optical control device for switching light paths, modulating a light wave and filtering a light wavelength, and more particularly to, an optical control device of a waveguide-type in which the control is carried out by using optical waveguides which are formed on an electro-optic-effect crystalline substrate made of lithium-containing material such as LiNbO3, LiTaO3 or similar material, and to a method for making the same.
Along with the utilization of an optical communi-cation system, a large capacity and multi-function system is desired. Also, enhanced functions such as high-speed generation of optical signals, high-speed switching of an optical transmission line, and high-speed exchanging are required.
As a means for switching optical transmission lines and exchanges in a network, an optical switch is used.
The optical switch now available is operated by switching light paths according to the mechanical movement of a prism, mirror, fiber or the like. However, it has problems that the operating speed is low and that it is too large to construct a matrix switch. To overcome the problems, a waveguide-type optical switch which employs optical wave-CA 022~6216 1998-12-29 guides has been developed. It has advantages in that high-speed operation, integration of numerous elements, and high reliability can be realized. In particular, the optical switch which employs a ferroelectric material such as lithi-um niobate(LiNbO3) or the like has low light absorption andhigh efficiency caused by the large electro-optic effect.
Various types of optical control devices are reported, for example, a directional-coupler-type, mach-zender-type, balance-bridge-type, total-reflection-type optical switch.
Recently, the high-density integration of the waveguide-type optical switch using a directional coupler which is formed in an electro-optic-effect LiNbO3 crystalline substrate has been developed. H. Nishimoto (the inventor of this application) et al., "Polarization Independent 8x8 LiNbO3 Optical Matrix Switch", Electronic Information Communication Society, OQE88-147, pp. 67-74 reports the 8x8 matrix optical switch in which 64 directional-coupler-type optical switches is integrated in the LiNbO3 crystalline substrate. Also, a device such as an external optical modulator which comprises a single optical switch has been developed.
The characteristics concerning such waveguide-type devices are stability in operation, switching voltage (power), crosstalk, extinction ratio, loss, switching speed and so on. The most important characteristic of these is stability in operation.
CA 022~6216 1998-12-29 However, the conventional optical control device has a problem of DC drift which significantly affects stability in operation and reliability of the device. The DC drift is a phenomenon in which an optical-output to applied-voltage characteristic shifts while a DC voltage is continuously applied.
Accordingly, it is an object of the invention to provide an optical control device in which the DC drift can be effectively suppressed to afford high reliability.
It is a further object of the invention to provide a method for making an optical control device in which the DC drift can be effectively suppressed to afford high reliability.
In one form, the invention is an optical control device that includes: a LiNbO3 or LiTaO3 crystalline sub-strate having an electro-optic effect; a channel-type opti-cal waveguide which is formed in said crystalline substrate by doping metal into first regions of a surface layer of the substrate, a remainder of the surface layer being defined as a remainder region; an optically-transparent film layer formed on said crystalline substrate; a second film layer which is formed between the crystalline substrate and the first film layer so as to be positioned adjacent at least a portion of the remainder region, the second film layer being made of a material that is different from that of the cry-stalline substrate and the first film layer; and electrodes formed on said optically-transparent first film layer.
CA 022~6216 1998-12-29 The second film layer may be formed so as to be positioned adjacent the whole of the remainder region. The material of the second film layer may be a material in which it is difficult to generate ionic polarization when an elec-tric field is applied thereto. The material of the secondfilm layer may be a single-element material selected from the group consisting of Si, Ti, Cu, V, Fe, Mo and Cr, or the material may be a semiconductor, organic material or metal alloy. Specifically, the material of the second film layer may be titanium.
In another form, the invention is a method for making an optical control device, comprising the initial step of preparing a LiNbO3 crystalline substrate having an electro-optic effect. A metal is then thermally diffused into first regions of a surface layer of the crystalline substrate for forming in the crystalline substrate a channel-type optical waveguide, a remainder of the surface layer being defined as a remainder region. One film layer is then formed on the surface layer of the crysalline sub-strate so as to be positioned adjacent at least a portion ofthe remainder region. Then, an optically-transparent other film layer is formed over the one film layer and over a re-maining part of the surface layer that remains uncovered by the one film layer. The method of the invention may also comprise an additional step of removing at least a part of both the one film layer and the other film layer over an intermediate region of the surface layer, the intermediate CA 022~6216 1998-12-29 region being positioned between the first regions of the surface layer.
The invention will next be explained in more detail in conjunction with the appended drawings, wherein:
Figure 1 is a cross-sectional view of a conven-tional optical control device;
Figure 2 is a cross-sectional view of an optical control device in a first preferred embodiment according to the invention;
Figure 3 is a graph illustrating variation of the amount of lithium mixed into a buffer layer depending on the existence of a lithium blocking layer;
Figure 4 is a cross-sectional view of an optical control device in a second preferred embodiment according to the invention;
Figure 5 is a cross-sectional view of an optical control device in a third preferred embodiment according to the invention;
Figures 6A and 6B are cross-sectional views of an optical control device in a process for making an optical control device according to the invention;
Figures 7A and 7B are cross-sectional views of an optical control device in another process for making an optical control device according to the invention;
Figure 8 is a cross-sectional view of an optical control device in a fourth preferred embodiment according to the invention;
CA 022~6216 1998-12-29 Figure 9 is a cross-sectional view of an optical control device in a fifth preferred embodiment according to the invention;
Figure 10 is a cross-sectional view of an optical control device in a sixth preferred embodiment according to the invention;
Figures llA to llC are cross-sectional views of an optical control device in a process for making the optical control device in the fifth embodiment according to the invention; and, Figure 12 is a graph illustrating variation of the amount of lithium mixed into a buffer layer depending on the existence of a lithium blocking layer.
Before explaining an optical control device in the preferred embodiment, the aforementioned conventional opti-cal control device in Figure 1 will be explained.
As shown in Figure 1, the conventional optical control device comprises an electro-optic crystalline sub-strate 1 which is made of LiNbO3, LiTaO3 or like material, and in which channel-type optical waveguides 2a and 2b form a directional coupler 5. A buffer layer 3 is formed on the electro-optic crystalline substrate 1, and metal electrodes 4a and 4b to which external control signals are applied extend on buffer layer 3.
The buffer layer 3 of optically-transparent film is used as an optical buffer layer to prevent the absorption of the waveguided-light caused by the metal electrodes 4a CA 022~6216 1998-12-29 and 4b. It is generally made of sio2 since sio2 does not absorb light and has a refractive index significantly less than that of a LiNbO3 or LiTaO3 substrate. The electrodes 4a and 4b generally employ a metal with low volume resistivity so as to provide a high-speed operation, and are disposed near the channel-type optical waveguides 2a and 2b.
The optical control devices of an optical wave-guide-type having the above structure, such as an optical switch or optical modulator, have been suggested. However, they can not yet be put into practice since there is an open question of DC drift which affects reliability of the device. The DC drift is a phenomenon wherein an optical-output to applied-voltage characteristic shifts while a DC
voltage is continuously applied. The DC drift is caused by the impurity ions which are included in the buffer layer 3 which is deposited on the electro-optic crystalline sub-strate 1 by the CVD or sputtering method. Namely, the impurity ions may move according to the polarity thereof under the electric field in the buffer layer 3 which is generated by the voltage applied to the electrodes 4a and 4b. Due to the movement of ions, the anti-electric-field which negates the electric field in the buffer layer 3 is formed. This phenomenon is a cause of the DC drift. The impurity ions contributory to the DC drift include sodium or potassium which is naturally mixed, as well as lithium mixed in the buffer layer 3 from the LiNbO3 or LiTaO3 substrate.
The mixing of lithium from the LiNbO3 or LiTaO3 substrate is CA 022~6216 1998-12-29 . ~
promoted by plasma or heat generated in the deposition by the CVD or sputtering method.
Next, an optical control device in the first preferred embodiment will be explained in Figure 2, wherein like parts are indicated by like reference numerals as used in Figure l.
The optical control device in the first embodiment is provided with an optical circuit 5 which has two channel-type optical waveguides 2a and 2b, and electrodes 4a and 4b which are formed on a buffer layer 3 of optically-trans-parent film and are disposed over the channel-type optical waveguides 2a and 2b. Herein, the optical circuit 5 may employ a directional-coupler-type, mach-zender-type, balance-bridge-type or a similar type. The buffer layer 3 is preferably made of sio2, but it also may be made of Al2O3, MgF2, SioN, Si3N4 or similar material. The depositing of the buffer layer 3 may be performed by the CVD method, sput-tering method, vapor deposition method or similar method.
The electrodes 4a and 4b may be made of various conductive materials, such as Au, Al, Mo, Cu, WSi, ITO, ZnO or conduc-tive polymer.
Further, in Figure 2, a metal-doped layer 6 (hereinafter referred to as "lithium blocking layer") is on the entire surface of the LiNbO3 crystalline substrate l, as well as on the surface of the channel-type optical wave-guides 2a and 2b; the waveguides are made by doping metal into parts of the surface of the LiNbO3 crystalline substrate CA 022~6216 1998-12-29 . ~
1. The doping metal for forming the channel-type optical waveguides 2a and 2b and lithium blocking layer 6 may in-clude Ti, Cu, V, Fe, Mo, Cr or similar material. The doping of metal may be performed by the thermal diffusion method, ion implantation method or the like. Herein, the doping of metal should be performed such that the refractive index of the channel-type optical waveguides 2a and 2b is greater than that of the lithium blocking layer 6.
Both the channel-type optical waveguides 2a and 2b and lithium blocking layer 6 in the first embodiment are formed by doping titanium by the thermal diffusion method.
Herein, the doping of titanium is performed such that the refractive index of the channel-type optical waveguides 2a and 2b is greater than that of the lithium blocking layer 6.
In this embodiment, based on the refractive index increasing with thickening of the titanium-deposited layer, the tita-nium-deposited layer for the channel-type optical waveguides 2a and 2b is formed to be thicker than that for the lithium blocking layer 6 to obtain a desired difference in refrac-tive index. Namely, the titanium-deposited layer for the channel-type optical waveguides 2a and 2b has a thickness of 0.05 to 0.15 nm, while the titanium-deposited layer for the lithium blocking layer 6 has a thickness of between 1/100 and 4/5 the thickness of the titanium-deposited layer for the channel-type optical waveguides 2a and 2b. Then, both the titanium-deposited layers are processed by the thermal diffusion at 850 to 1100~C for 0.5 to 20 hours to form the CA 022~6216 1998-12-29 . ~
channel-type optical waveguides 2a and 2b and lithium blocking layer 6.
The inventor has found that lithium, which is a component of the crystalline substrate 1, is mixed from the LiNbO3 or LiTaO3 crystalline substrate 1 into the buffer layer 3 of sio2 or the like due to plasma or heat when the buffer layer 3 is deposited by CVD method, sputtering method, vapor deposition method or the like. Furthermore, he has found that the mixing of lithium is significantly reduced at the region where the lithium blocking layer 6 is formed as compared with at the region where the lithium blocking layer 6 is not formed.
Figure 3 shows variation of the amount of lithium mixing into the sio2 buffer layer 3, depending on the exist-ence of the lithium blocking layer 6; i.e., on the right end point of the horizontal axis, the lithium blocking layer is formed on the surface of the LiNbO3 crystalline substrate 1;
on the left end point of the horizontal axis, the lithium blocking layer is not formed on the surface of the LiNbO3 crystalline substrate 1. The sio2 buffer layer 3 is formed by the sputtering method. Due to the lithium blocking layer 6, the amount of lithium mixing into the SiO2 buffer layer is reduced to about 1/50 the amount otherwise mixing.
Thus, according to the optical control device in the first embodiment, the lithium mixing from the LiNbO3 crystalline substrate 1 into the sio2 buffer layer 3 due to plasma or heat when the SiO2 buffer layer 3 is deposited by CA 022~6216 1998-12-29 CVD method, sputtering method, vapor deposition method or similar method can be effectively reduced. Thereby, the DC
drift of the device can be suppressed to provide an optical control device with high reliability.
Meanwhile, it will be easily appreciated that the above optical control device can be obtained if only the amount and depth of metal doped is set such that the chan-nel-type optical waveguides 2a and 2b serve as a waveguide, i.e., the amount, depth and type of metal doped are not limited by the other condition.
With reference to Figure 4, an optical control device in the second preferred embodiment will be explained.
In this embodiment, an optical circuit 5 is a directional coupler, and a lithium blocking layer 6 is formed on the surface of a crystalline substrate 1 except in the region where the waveguided-light propagates between channel-type optical waveguides 2a and 2b. The lithium blocking layer 6 is not formed in the region between the channel-type optical waveguides 2a and 2b of the directional coupler, since the waveguided-light propagates therebetween. The second embodiment can provide a similar advantage to that of the first embodiment. In addition, the optical control device in the second embodiment does not affect the propagation characteristic of the waveguided-light through the channel-type optical waveguides 2a and 2b. Therefore, reduction ofsteps in processing and designing of the device, and a higher yield, can be realized.
CA 022~6216 1998-12-29 ~ .
With reference to Figure 5, an optical control device in the third preferred embodiment will be explained.
In this embodiment, channel-type optical waveguides 2a and 2b are formed on the surface of a LiTaO3 crystalline sub-strate 1 by proton exchanging, and a lithium blocking layer 6 is formed by doping metal on the entire surface of the LiTaO3 crystalline substrate 1. The proton exchanging that forms the channel-type optical waveguides 2a and 2b may employ benzoic acid, pyrophosphoric acid or the like. When the crystalline substrate 1 is made of LiTaO3, the lithium blocking layer 6 is doped by ion implantation. When the crystalline substrate 1 is made of LiNbO3, the lithium blocking layer 6 is doped by thermal diffusion or ion implantation. The doping metal for forming the lithium blocking layer 6 may include Ti, Cu, V, Fe, Mo, Cr or a similar metal. The third embodiment can also provide a similar advantage to that of the first embodiment.
Meanwhile, it will be easily appreciated that the above optical control device can be obtained if only the proton exchanging and the metal doping into the lithium blocking layer 6 are performed such that the channel-type optical waveguides 2a and 2b serve as a waveguide, i.e., the amount and depth of the proton exchanging, and the amount, depth and type of metal doped are not limited by the other condition.
CA 022~6216 1998-12-29 Figures 6A and 6B show the process for making an optical control device in the first preferred embodiment according to the invention.
First, on a LiNbO3 crystalline substrate 1, a patterned metal layer 7a for forming channel-type optical waveguides 2a and 2b and a metal layer 7b for forming a lithium blocking layer 6 are formed (Figure 6A). The depositing of the metal layers 7a and 7b may be performed by CVD, sputtering, vapor deposition method or the like. The patterning of the metal layer 7a is by the standard litho-graphy technique. Herein, the metal layer 7b for the lithium blocking layer 6 may be patterned such that a region is left for propagating waveguided-light without the lithium blocking layer.
Next, by doping the metal in the metal layers 7a and 7b into the LiNbO3 crystalline substrate 1 by the thermal diffusion, the channel-type optical waveguides 2a and 2b and lithium blocking layer 6 are simultaneously formed (Figure 6B).
Though the patterned metal layer 7a for forming the channel-type optical waveguides 2a and 2b is mounted on the metal layer 7b for forming the lithium blocking layer 6 in Figure 6A, it will be easily appreciated that the rela-tionship in the mounting can be changed upside down, i.e., the metal layer 7b may be mounted on the metal layer 7a.
The doping metal may include Ti, Cu, V, Fe, Mo, Cr, or similar metal. In this embodiment, both the channel-CA 022~6216 1998-12-29 type optical waveguides 2a and 2b and lithium blocking layer 6 are formed by using titanium as the doping metal.
Figures 7A and 7B show the process for making an optical control device in the second preferred embodiment according to the invention. First, after depositing a metal layer 7a for forming channel-type optical waveguides 2a and 2b as shown in Figure 6A on a LiNbO3 crystalline substrate 1, the metal layer 7a is processed by thermal diffusion to form the channel-type optical waveguides 2a and 2b (Figure 7A).
Next, after depositing a metal layer 7b for forming a lithium blocking layer 6 as shown in Figure 6A on the LiNbO3 crystalline substrate 1, the metal layer 7b is processed by thermal diffusion to form the lithium blocking layer 6 (Figure 7B). Herein, the metal layer 7b for the lithium blocking layer 6 may be patterned such that a region is left for propagating waveguided-light without the lithium blocking layer.
Similarly to the process in the first embodiment, the depositing of the metal layers 7a and 7b may be per-formed by CVD, sputtering, vapor deposition method orsimilar method. The patterning of the metal layer 7a is by the standard lithography technique.
Though, in this embodiment, the lithium blocking layer 6 is formed after the formation of the channel-type optical waveguides 2a and 2b, the lithium blocking layer 6 can be formed before the formation of the channel-type optical waveguides 2a and 2b.
CA 022~6216 1998-12-29 . .
Meanwhile, it will be easily appreciated that the above optical control device can be obtained if only the channel-type optical waveguides 2a and 2b serve as a wave-guide, i.e., the relationship in depth between the channel-type optical waveguides 2a and 2b and the lithium blockinglayer 6 is not limited by the other condition.
The doping metal may include Ti, Cu, V, Fe, Mo, Cr or other similar metal. In this embodiment, both the channel-type optical waveguides 2a and 2b and lithium blocking layer 6 are formed by using titanium as the doping metal.
With reference to Figure 8, an optical control device in the fourth preferred embodiment will be explained.
The optical control device in the fourth embodi-ment is provided with an optical circuit 5 which has twochannel-type optical waveguides 2a and 2b which are formed on a LiNbO3 crystalline substrate 1 by the thermal diffusion method, and electrodes 4a and 4b which are formed on a buf-fer layer 3 of optically-transparent film and are disposed over the channel-type optical waveguides 2a and 2b. Herein, the optical circuit 5 may employ a directional-coupler-type, mach-zender-type, balance-bridge-type or similar type. The buffer layer 3 is preferably made of sio2, and it also may be made of Al2O3, MgF2, SioN, Si3N4 or like material. The depositing of the buffer layer 3 may be performed by the CVD
method, sputtering method, vapor deposition method or simi-lar method. The electrodes 4a and 4b may be made of various CA 022~6216 1998-12-29 conductive materials, such as Au, Al, Mo, Cu, WSi, ITO, ZnO
or conductive polymer.
Between the LiNbO3 crystalline substrate 1 and the buffer layer 3, a film layer 6 (hereinafter referred to as "lithium blocking layer") which is separated from the buffer layer 3 is provided. Herein, the lithium blocking layer 6 is not formed in the region for propagating waveguided-light. Thus, when the optical circuit 5 employs a direc-tional coupler or X-type, the lithium blocking layer 6, as shown in Figure 8, is not formed on the channel-type optical waveguides 2a and 2b nor between the channel-type optical waveguides 2a and 2b.
The lithium blocking layer 6 may be made of a metal or semiconductor material of a single element in-cluding Si, Ti, Cu, V, Fe, Mo, Cr or similar material, or a dielectric, metal, semiconductor, organic material or similar material in which is difficult to generate ionic polarization by applying an electric field, such as crystal doped by phosphorus, MgF2, Si3N4, WSi, GaAs, Inp, polyimide.
The substrate 1 is limited to the LiNbO3 crystal-line substrate, and any lithium-containing crystalline sub-strate such as a LiTaO3 crystalline substrate may be used.
The depositing of the lithium blocking layer 6 may be performed by CVD, sputtering, vapor deposition method or similar method. The standard lithography technique is employed to preclude the formation of the lithium blocking layer at the region for propagating waveguided-light.
CA 022~6216 1998-12-29 . .
A titanium-deposited layer with a thickness of 0.02 to 0.15 nm is processed by the thermal diffusion at 850 to 1100~C for 0.5 to 20 hours to form the channel-type optical waveguides 2a and 2b.
With reference to Figure 9, an optical control device in the fifth preferred embodiment will be explained.
In this embodiment, on the intermediate step in the process for making the optical control device, a lithium blocking layer 6 and buffer layer 3 between two channel-type optical waveguides 2a and 2b is partially removed. This structure is suitable for the case that the lithium blocking layer 6 between the channel-type optical waveguides 2a and 2b is not proper, i.e., when the optical circuit 5 is a directional coupler, X-type or the like. Because the covering area of the lithium blocking layer 6 is greater than that of the lithium blocking layer 6 in the fourth embodiment, the lithium mixing into the buffer layer 3 when the buffer layer 3 is deposited can be further reduced to further suppress the DC drift and provide an optical control device with higher reliability.
With reference to Figure 10, an optical control device in the sixth preferred embodiment will be explained.
This embodiment is suitable for the case in which waveguided-light in optical circuit 5 does not propagate between two channel-type optical waveguides 2a and 2b, such as when a mach-zender-type, balance-bridge-type is employed.
Namely, a lithium blocking layer 6 is also formed between CA 022~6216 1998-12-29 the channel-type optical waveguides 2a and 2b. Because the covering area of the lithium blocking layer 6 is greater than that of the lithium blocking layer 6 in the fourth embodiment, the lithium mixing into the buffer layer 3 when the buffer layer 3 is deposited can be further reduced to further suppress the DC drift and provide an optical control device with higher reliability.
Figures llA to llC show the process for making the optical device in the fifth embodiment.
First, as shown in Figure llA, after forming the directional coupler 5 of the channel-type optical waveguides 2a and 2b on the LiNbO3 crystalline substrate 1 by the ther-mal diffusion of titanium, the lithium blocking layer 6 is deposited on the LiNbO3 crystalline substrate 1, except on the channel-type optical waveguides 2a and 2b. In this embodiment, the lithium blocking layer 6 is deposited with chromium by electron-beam vapor deposition, thermal deposi-tion, sputtering method or similar method. Thereafter, the lithium blocking layer 6 corresponding to the region where the electrodes 4a and 4b will be provided is removed by using the standard photolithography technique and etching.
Next, as shown in Figure llB, SiO2 is deposited thereon to form a buffer layer 3, by CVD, a sputtering method or a similar method. Optionally, the buffer layer 3 may be annealed. Thereafter, the lithium blocking layer 6 and buffer layer 3 between the channel-type optical wave-CA 022~6216 1998-12-29 ~ .
guides 2a and 2b are removed by using the standard photo-lithography technique and etching.
Finally, as shown in Figure llC, the layer for forming the electrodes 4a and 4b is deposited by electron-beam vapor deposition, thermal vapor deposition, sputtering method or similar method, thereafter forming the electrodes 4a and 4b by using the standard photolithography technique and etching. The electrodes are mainly made of gold.
Alternatively, the removing of the lithium blocking layer 6 and buffer layer 3 between the channel-type optical waveguides 2a and 2b as in Figure llB may be simul-taneously carried out after the forming of the electrodes 4a and 4b.
From the above-mentioned process, the process for making the optical control devices in the fourth and sixth embodiments will be easily understood. Namely, after forming the directional coupler 5 of two waveguides 2a and 2b on the LiNbO3 crystalline substrate 1 by the thermal diffusion, the layer for forming the lithium blocking layer 6 is deposited. Thereafter, the lithium blocking layer 6 corresponding to the region where the electrodes 4a and 4b will be formed, or the lithium blocking layer 6 corres-ponding to the above-mentioned region and the region between the electrodes 4a and 4b, is removed. Thereafter, the buf-fer layer 3 is deposited thereon. Finally, similarly to the fifth embodiment, the electrodes 4a and 4b are formed on the buffer layer 3.
CA 022~6216 1998-12-29 Figure 12 shows an amount of lithium mixing into the SiO2 buffer layer 3, depending on the existence of the lithium blocking layer 6, i.e., on the right end point of the horizontal axis, the lithium blocking layer is formed on the surface of the LiNbO3 crystalline substrate 1 (in the fourth to sixth embodiments); on the left end point of the horizontal axis, the lithium blocking layer is not formed on the surface of the LiNbO3 crystalline substrate 1. The sio2 buffer layer 3 is formed by the sputtering method. Due to the lithium blocking layer 6, the amount of lithium mixture into the sio2 buffer layer 3 is reduced to about 1/50 the amount otherwise.
Thus, according to the optical control device, the lithium mixing from the LiNbO3 crystalline substrate 1 into the sio2 buffer layer 3 due to plasma or heat when the sio2 buffer layer 3 is deposited by CVD method, sputtering method, vapor deposition method or similar method can be effectively reduced.
Although the invention has been described with respect to specific embodiment for complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art and which fairly fall within the basic teaching herein set forth.
Claims (10)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An optical control device, comprising:
a LiNbO3 or LiTaO3 crystalline substrate having an electro-optic effect;
a channel-type optical waveguide which is formed in said crystalline substrate by doping metal into first regions of a surface layer of the substrate, a remainder of the surface layer being defined as a remainder region;
a first film layer which is optically-transparent and formed on said crystalline substrate;
a second film layer which is formed between said crystalline substrate and said first film layer so as to be positioned adjacent at least a portion of the remainder region, said second film layer being made of a material that is different from that of said crystalline substrate and said first film layer; and, electrodes formed on said optically-transparent first film layer.
a LiNbO3 or LiTaO3 crystalline substrate having an electro-optic effect;
a channel-type optical waveguide which is formed in said crystalline substrate by doping metal into first regions of a surface layer of the substrate, a remainder of the surface layer being defined as a remainder region;
a first film layer which is optically-transparent and formed on said crystalline substrate;
a second film layer which is formed between said crystalline substrate and said first film layer so as to be positioned adjacent at least a portion of the remainder region, said second film layer being made of a material that is different from that of said crystalline substrate and said first film layer; and, electrodes formed on said optically-transparent first film layer.
2. An optical control device, according to claim 1, wherein the second film layer is formed so as to be positioned adjacent the whole of the remainder region.
3. An optical control device, according to claim 1 or 2, wherein said material of said second film layer is a material in which it is difficult to generate ionic polarization when an electric field is applied thereto.
4. An optical control device, according to claim 3, wherein said material of said second film layer is a single-element material selected from the group consisting of Si, Ti, Cu, V, Fe, Mo and Cr.
5. An optical control device, according to claim 3, wherein said material of said second film layer is a semiconductor material.
6. An optical control device, according to claim 3, wherein said material of said second film layer is an organic material.
7. An optical control device, according to claim 3, wherein said material of said second film layer is a metal alloy.
8. An optical control device, according to claim 1 or 2, wherein said material of said second film layer is titanium.
9. A method for making an optical control device, comprising the steps of:
preparing a LiNbO3 crystalline substrate having an electro-optic effect;
thermally diffusing a metal into first regions of a surface layer of said crystalline substrate for forming in said crystalline substrate a channel-type optical waveguide, a remainder of the surface layer being defined as a remainder region;
forming one film layer on the surface layer of the crystalline substrate so as to be positioned adjacent at least a portion of the remainder region; and, forming an optically-transparent other film layer over the one film layer and over a remaining part of the surface layer that remains uncovered by the one film layer.
preparing a LiNbO3 crystalline substrate having an electro-optic effect;
thermally diffusing a metal into first regions of a surface layer of said crystalline substrate for forming in said crystalline substrate a channel-type optical waveguide, a remainder of the surface layer being defined as a remainder region;
forming one film layer on the surface layer of the crystalline substrate so as to be positioned adjacent at least a portion of the remainder region; and, forming an optically-transparent other film layer over the one film layer and over a remaining part of the surface layer that remains uncovered by the one film layer.
10. A method for making an optical control device, as in claim 9, and also comprising the step of:
removing at least a part of both the one film layer and the other film layer over an intermediate region of the surface layer, the intermediate region being positioned between the first regions of the surface layer.
removing at least a part of both the one film layer and the other film layer over an intermediate region of the surface layer, the intermediate region being positioned between the first regions of the surface layer.
Applications Claiming Priority (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP6231754A JP2809112B2 (en) | 1994-09-27 | 1994-09-27 | Light control device and manufacturing method thereof |
| JP6-231754 | 1994-09-27 | ||
| JP6292625A JP2624199B2 (en) | 1994-11-28 | 1994-11-28 | Light control device and manufacturing method thereof |
| JP6-292625 | 1994-11-28 | ||
| CA002159129A CA2159129C (en) | 1994-09-27 | 1995-09-26 | Optical control device and method for making the same |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002159129A Division CA2159129C (en) | 1994-09-27 | 1995-09-26 | Optical control device and method for making the same |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2256216A1 CA2256216A1 (en) | 1996-03-28 |
| CA2256216C true CA2256216C (en) | 1999-11-30 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002256216A Expired - Fee Related CA2256216C (en) | 1994-09-27 | 1995-09-26 | Optical control device and method for making the same |
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| Country | Link |
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| CA (1) | CA2256216C (en) |
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