JP5117082B2 - Light modulator - Google Patents

Description

The present invention utilizes an electro-optical effect or thermal optical effect relates to an optical modulator for emitting an optical signal pulse by modulating light incident on the optical waveguide.

  There is an optical modulator using a dielectric material as a typical optical modulation device. In recent years, high-speed and large-capacity optical communication systems have been put into practical use, and development of high-speed, small, and low-cost optical modulators for incorporation into such high-speed and large-capacity optical communication systems is required. Yes.

As an optical modulator that meets such demands, a light modulator such as lithium niobate (LiNbO ₃ ) is used for a substrate having a so-called electro-optical effect (hereinafter abbreviated as an LN substrate) whose refractive index changes by applying an electric field. There is a traveling wave electrode type lithium niobate optical modulator (hereinafter abbreviated as an LN optical modulator) in which a waveguide and a traveling wave electrode are formed. This LN optical modulator is applied to a large capacity optical communication system of 2.5 Gbit / s and 10 Gbit / s because of its excellent chirping characteristics. Recently, application to a 40 Gbit / s ultra-high capacity optical communication system is also being studied.

  Hereinafter, the characteristics of each LN optical modulator using the electro-optic effect of lithium niobate, which has been practically used or proposed, will be described in order.

(First prior art)
FIG. 9 is a perspective view of the first prior art LN optical modulator disclosed in Patent Document 1 configured using a z-cut LN substrate, and FIG. 10 is taken along line AA ′ of FIG. It is sectional drawing.

  An optical waveguide 3 is formed on the z-cut LN substrate 1. The optical waveguide 3 is an optical waveguide formed by thermally diffusing metal Ti at 1050 ° C. for about 10 hours, and constitutes a Mach-Zehnder interference system (or Mach-Zehnder optical waveguide). Therefore, in the region where the high-frequency electrical signal (or RF electrical signal) of the optical waveguide 3 shown as I in FIG. The working optical waveguides 3a and 3b, that is, two arms of the Mach-Zehnder optical waveguide are formed.

An SiO ₂ buffer layer 2 is formed on the upper surface of the optical waveguide 3, and a traveling wave electrode 4 is formed on the upper surface of the SiO ₂ buffer layer 2. As the traveling wave electrode 4, a coplanar waveguide (CPW) having one central conductor 4a and two ground conductors 4b and 4c is used. Normally, the traveling wave electrode 4 is made of Au. Reference numeral 5 denotes a conductive layer for suppressing temperature drift caused by the pyroelectric effect peculiar to the LN modulator manufactured using the z-cut LN substrate 1, and a Si conductive layer is usually used. For simplification of description, the Si conductive layer 5 shown in FIG. 9 is omitted in FIG.

  When a high frequency (RF) electric signal for modulation is supplied to the center conductor 4a and the ground conductor 4b via the high frequency electric signal feeder 6 of this optical modulator, an electric field is applied between the center conductor 4a and the ground conductor 4b. . Since the z-cut LN substrate 1 has an electro-optic effect, a refractive index change is caused by this electric field, and a shift occurs in the phase of light propagating through the two interactive optical waveguides 3a and 3b. When this deviation becomes π, a high-order mode is excited in the multiplexing portion of the optical waveguide 3 as the Mach-Zehnder optical waveguide, and the light is turned off. Reference numeral 7 denotes a high-frequency electric signal output line, which may be replaced with a termination resistor.

As can be seen from FIG. 10, the characteristics of the optical modulator of Patent Document 1 shown in FIG. 9 are as follows: 1) The width S of the central conductor 4a is about 6 μm to 12 μm, which is substantially the same as the width of the interaction optical waveguides 3a and 3b. 2) The gap W between the center conductor 4a and the ground conductors 4b and 4c is widened to 15 to 30 μm. 3) The center conductor 4a and the ground conductor 4b of light propagating through the interaction optical waveguides 3a and 3b, By utilizing the fact that the relative dielectric constant of the SiO ₂ buffer layer 2 that has been used only to suppress absorption by the metal constituting the traveling wave electrode 4 made of 4c is relatively low, 4 to 6, the SiO ₂ buffer layer 2 of by increasing the order of 400nm~1.5μm the thickness D, by reducing the microwave effective index _{n m} of the high-frequency electrical signals, the interaction optical waveguides 3a, 3b and guided light equivalent refractive index _{n o} Close to Together, it is possible close to the 50Ω characteristic impedance. In the first prior art shown in FIG. 10, the microwave equivalent refractive index _nm is further reduced by increasing the thickness T of the traveling wave electrode 4 disclosed in Patent Document 2, so that the equivalent of light can be obtained. and close to the refractive index _{n o.}

By adopting such a structure, the width S of the center conductor 4a is about 30 μm, the gap W between the center conductor 4a and the ground conductors 4b, 4c is about 6 μm, and the thickness D of the SiO ₂ buffer layer 2 is about 300 nm. Compared with this structure, the characteristics as an optical modulator, such as the optical modulation band and characteristic impedance, can be greatly improved. However, further improved characteristics are required with respect to the light modulation band, drive voltage, characteristic impedance, etc., and a so-called ridge structure has been proposed as a second conventional technique described below.

(Second prior art)
FIG. 11 and FIG. 12 show the ridge structure proposed in Patent Document 3 and Patent Document 4 as the second prior art in order to further improve the performance of the first prior art. Here, 8a is a ridge below the central conductor 4a, 8b is a ridge below the ground conductor 4b, 8c is a ridge below the ground conductor 4c, and 9 is a SiO ₂ buffer layer. 10a is a gap between the ridges 8a and 8b, and 10b is a gap between the ridges 8a and 8c.

  In FIG. 12, reference numerals 11a and 11b denote electric lines of force that exit from the central conductor 4a and enter the ground conductors 4b and 4c, respectively, and change their refractive indices by acting on the interaction optical waveguides 3a and 3b (or mutual mutuals). It can also be said that it interacts with the light propagating through the working optical waveguides 3a and 3b).

In the second prior art, ridges such as 8a and 8b are formed on the z-cut LN substrate 1, so that the electric lines of force 11a are the gaps 10a between the ridges 8a and 8b, and the electric lines of force 11b are the ridges 8a and 8c. I feel the gap 10b. As a result, the more reduced the microwave equivalent refractive index n _m of the high-frequency electrical signals, high interaction optical waveguides 3a, 3b approaches the equivalent refractive index n _o of the light guided to, or characteristic impedance towards the 50Ω There is an advantage of becoming. Furthermore, since the electric lines of force 11a and 11b have a property of being confined in a region where the relative dielectric constant is high, the efficiency of interaction with the light propagating through the interaction optical waveguides 3a and 3b is increased, resulting in a drive voltage being reduced. Can be reduced. Usually, the height H of the ridges 8a, 8b, 8c is about 2 to 5 μm, the thickness T of the traveling wave electrode is about 6 to 18 μm, and the thickness of the SiO ₂ buffer layer 2 is about 400 nm to 1.5 μm. The

  With this second conventional technique, characteristics such as an optical modulation band, drive voltage, characteristic impedance, etc., which are significantly improved as compared with the first conventional technique shown in FIG.

However, there is still room for improvement in the second prior art. Next, this point will be discussed with reference to FIGS. The important characteristics of the LN optical modulator, such as the driving voltage at high frequency, strongly depend on the length L _int of the interaction part I where the high-frequency electrical signal interacts with the light propagating through the interaction optical waveguides 3a and 3b. The length L _int of the interaction part I is determined by the length L _LN of the z-cut LN substrate 1.

FIG. 14 shows Vπ (half-wave voltage at a static voltage) with respect to the length L _int of the interaction part I as a very simple guideline for evaluating the performance. As can be seen from the figure, it can be said that the longer the length L _int of the interaction part I, the lower Vπ, which is advantageous in terms of performance. This Vπ and the length of the interaction part I (the length of the interaction optical waveguide or the interaction length) L _int is important as a figure of merit as often discussed as Vπ · L _int , and the interaction length L _A longer _int is advantageous for reducing the drive voltage and increasing the degree of freedom in design.

In conventional LN optical modulators, the length L _int of the interaction part I is limited by the size of the package and the size of the wafer, so that the short interaction length is as short as about 40 mm and at most 40 mm. It is no exaggeration to say that it was limiting the performance of.
Japanese Patent No. 2126214 Japanese Patent No. 2126887 Japanese Patent No. 2612948 Japanese Patent No. 2728150

  As described above, the optical modulator according to the second prior art which can greatly improve the characteristics as the optical modulator such as the optical modulation band, the driving voltage, and the characteristic impedance is also limited in the interaction length by the length of the LN substrate. As a result, basic characteristics as an optical modulator such as a high-frequency driving voltage and characteristic impedance have been determined. In other words, it can be said that the length of the LN substrate determines the characteristics of the optical modulator.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an optical modulator that is small in size, has a low driving voltage, has a wide optical modulation band, and is greatly improved in characteristic impedance.

In order to solve the above problems, an optical modulator according to claim 1 of the present invention includes a substrate, an optical waveguide formed on the substrate, and an electrode for applying a high-frequency electric signal, and the optical waveguide includes: In an optical modulator constituting a Mach-Zehnder optical waveguide including two interactive optical waveguides whose refractive index is changed by applying a high-frequency electric signal to the electrode, and an output optical waveguide from which modulated light is output the two interaction optical waveguides, the number of turns is constructed spiral of one or more times Rutotomoni are arranged across at least two radii of curvature different curve, the curve having the greatest radius of curvature When a circle centering on the center of curvature is drawn, the circle includes the center of curvature of a curve having the smallest radius of curvature .
An optical modulator according to claim 2 of the present invention includes a substrate, an optical waveguide formed on the substrate, and an electrode for applying a high-frequency electric signal, and the optical waveguide applies a high-frequency electric signal to the electrode. In the optical modulator constituting the Mach-Zehnder optical waveguide including the two interactive optical waveguides whose refractive index is changed and the output optical waveguide from which the modulated light is output, the two interactive optical waveguides The waveguide is arranged with at least two curves having different radii of curvature, and when a circle centered on the center of curvature of the curve having the largest radius of curvature is drawn, the smallest radius of curvature is drawn in the circle. A center of curvature of the curve is included, and the pattern of the two interactive optical waveguides is point-symmetric with respect to the center of the overall arrangement of the patterns for the two interactive optical waveguides. Toss .

The optical modulator according to claim 3 of the present invention is characterized in that the lengths of the portions of the two interactive optical waveguides where the refractive index changes are equal to each other.

The optical modulator according to claim 4 of the present invention is characterized in that the two interactive optical waveguides cross each other.

The optical modulator according to claim 5 of the present invention is characterized in that the two interactive optical waveguides are arranged so as not to cross each other.

The optical modulator according to claim 6 of the present invention is characterized in that the output optical waveguide intersects the two interactive optical waveguides.

The optical modulator according to claim 7 of the present invention is characterized in that the output optical waveguide is disposed so as not to intersect the two interactive optical waveguides.

An optical modulator according to an eighth aspect of the present invention is characterized in that at least a part of the two interactive optical waveguides has a ridge structure.

The optical modulator according to claim 9 of the present invention is characterized in that at least one substrate in the vicinity of the two interactive optical waveguides is thin.

  In the present invention, the interaction optical waveguide whose refractive index is changed by applying a voltage is configured by a curved shape, so that the interaction length can be arbitrarily set even with an extremely small chip size which has not been conventionally achieved, and is also made extremely long. It is also possible to achieve a significant reduction in size as a module of an optical modulation device. And if the interaction length is longer, not only can the drive voltage be reduced, but also the buffer layer can be set thick, so that the speed of the high-frequency electrical signal and light can be easily matched (speed matching), and the characteristic impedance is 50Ω. There are advantages such as being close to each other or reducing the propagation loss of the high-frequency electrical signal. Furthermore, since the gap between the center conductor 14a and the ground conductors 14b and 14c can be set wide, the characteristic impedance can be made closer to 50Ω, and the propagation loss of the high-frequency electric signal can be further reduced. As described above, as a result of applying the present invention to increase the interaction length, the performance of the optical modulator is remarkably improved, and high-speed optical modulation is possible with a low driving voltage. Alternatively, when the thermo-optic effect is used, high-efficiency light modulation can be performed with a very small calorific value.

  Hereinafter, embodiments of the present invention will be described. However, since the same reference numerals as those in the related art shown in FIGS. 9 to 13 correspond to the same functional units, description of the functional units having the same reference numerals is omitted here. To do.

(First embodiment)
FIG. 1 shows an optical waveguide 13 according to a first embodiment of the present invention. Reference numerals 13a and 13b denote ridge-structure interaction optical waveguides in which high-frequency electrical signals interact with light propagating through the optical waveguide. In FIG. 1, the four corners of the z-cut LN substrate 1 are curved and face each side. Although it may be a straight line, for the sake of simplicity of explanation, it is assumed that most are formed by a curved line. Further, VII is a branching portion of the optical waveguide 3, VIII is a multiplexing portion of the optical waveguide, and 13c is an output optical waveguide. The shape of the interaction optical waveguides 13a and 13b may be a curve other than an arc, such as a spiral or an ellipse, but is an arc here for the sake of simplicity.

Here, the interaction region II, the interaction optical waveguides 13a, 13b are located inside and outside of each of the radius R ₁ circle. As a result, in the interaction region II, the interaction optical waveguide 13b is longer than the interaction optical waveguide 13a. And since there is provided a crossing portion III of the optical waveguide, the interaction region IV in the interaction optical waveguide 13b, 13a are located inside and outside of each of the curvature radius R ₂ circles. That is, in the region IV, the interaction optical waveguide 13a is longer than the interaction optical waveguide 13b.

  Since the outer arc is longer than the inner arc in this way, in the present embodiment, by providing the intersection portion III of the optical waveguide, it is possible to reach each other from the branching portion VII to the multiplexing portion VIII of the optical waveguide 3. The working optical waveguides 13a and 13b are devised to have the same overall length.

  If the lengths of the interaction optical waveguides 13a and 13b are different from each other as a whole, the insertion loss fluctuates when the wavelength is changed or is equivalent to this, but the interaction optical waveguide 13a also changes when the environmental temperature changes. , 13b changes in optical length, and the insertion loss also fluctuates. In order to avoid this, in this embodiment, the optical lengths of the interaction optical waveguides 13a and 13b are made the same by introducing the intersection portion III of the optical waveguide. In the first embodiment of the present invention shown in FIG. 1, the output optical waveguide 13c intersects the interaction optical waveguides 13a and 13b.

Further, if the centers of the arcs of the interaction region II and the interaction region IV are V and VI, respectively, the center V and the center VI may or may not coincide with each other. However, the present invention defines as a center VI curve of the interaction region IV falls within the circle drawn the entire circumference with a radius of curvature R ₁ of the larger center as the center V curve of the interaction region II ing. In this way, the overall dimensions can be reduced.

  When the curvature changes with the position of the interaction optical waveguides 13a and 13b as in a curve other than a spiral or arc, the curvature radius of some curves or the center of the curve may be used. Here, the center of the curve means the center of rotation of the arc (or circle) drawn by the curvature radius.

  In FIG. 2, the traveling wave electrode 14 is noted. Here, 14a is a central conductor, and 14b and 14c are ground conductors. As can be seen from this figure, the central conductor 14a is formed on the interaction optical waveguide 13b over the interaction region II, the intersection III of the optical waveguide, and the interaction region IV.

Next, advantages that can be realized by this embodiment will be considered. The width of the ground conductor 14b between the interaction region II and the interaction region IV (denoted as GW in FIG. 2) is at most several times the gap (15 to 30 μm) between the center conductor 14a and the ground conductor 14b. Since it is small, the radius of curvature R ₁ of the arc in the interaction region II is almost equal to the radius of curvature R ₂ of the arc in the interaction region IV (that is, it can be approximated as R ₁ ≈R ₂ ). That is, when the interaction region formed by the curvature radius R ₁ and the curvature radius R ₂ is composed of, for example, a 360-degree circle, the length (interaction length) may be considered to be approximately 2πR ₁ .

FIG. 3 shows the relationship between the _total length L _total of the interaction length and the number of turns of the circle when the curvature radius R ₁ is 4 mm. In addition, the range (20-40 mm) of the interaction length in the prior art shown in FIG. 9 and FIG. 13 is also shown in the figure. As can be seen, even if the radius of curvature R ₁ of a circle as in the present embodiment is as small as 4 mm, since the interaction length of 25.1mm in one turn, the interaction length of the prior art in this embodiment Can be realized with only 0.8 to 1.6 turns.

  Therefore, it is desirable that the central angle of the arc (or curve) formed by the interactive optical waveguides 13a and 13b is 250 degrees or more, further 360 degrees or more as shown in FIG. By doing so, the interaction length can be freely set without increasing the size of the chip of the LN optical modulator, and the length of the interaction length can be remarkably increased. As a result, the effect of the present invention can be remarkably exhibited.

In other words, as described above, even if a circle is made into multiple turns, the radius of each circle hardly changes, so that an extremely long interaction length can be easily realized. For example, an interaction length as long as 120 mm can be obtained by setting 5 turns. In this case the radius of curvature _{R 1} of the circle also are 4mm and small size of the chip of the optical modulator may be 8.5mmx8.5mm or as small as about 9Mmx9mm,.

  When an optical modulator module is manufactured using a chip of an optical modulator according to the prior art, the width is slightly over 12 to 14 mm and the length is about 75 to 100 mm. Accordingly, when an optical modulator module is manufactured using the optical modulator chip of the present invention, the width is almost the same as the conventional optical modulator module and the length is as short as about 12 to 15 mm. As compared with the length of the module of the vessel, it becomes possible to achieve a significant downsizing of about 1/5 to 1/7.

  Further, as described with reference to FIG. 3, if the interaction length is longer, it is advantageous for the driving voltage, so that the buffer layer can be set thick. Therefore, there are advantages that the speed of the high-frequency electric signal and the light can be easily matched (speed matching), the characteristic impedance can be close to 50Ω, or the propagation loss of the high-frequency electric signal can be reduced. In addition, since the gap between the center conductor 14a and the ground conductors 14b and 14c can be set wide, the characteristic impedance can be made closer to 50Ω, and the propagation loss of high-frequency electrical signals can be further reduced.

  As a result, the performance of the optical modulator is remarkably improved, and high-speed optical modulation is possible with a low driving voltage. It should be noted that the increase in insertion loss that occurs at the location where the optical waveguides intersect like the intersection III is 0.2 dB or less, which is not a big problem.

  In the above description, the radius of curvature of the arc has been described as 4 mm. However, this is only an example and may be more than that, or conversely, may be about 2 mm or 3 mm. And although the chip size is as small as 4 mm × 4 mm or 6 mm × 6 mm, an unprecedented high-performance LN optical modulator can be realized.

(Second Embodiment)
FIG. 4 shows a second embodiment of the present invention. In the present embodiment, there is no crossing portion of the optical waveguide provided in order to make the lengths of the intersections III of the optical waveguides, that is, the interaction optical waveguides 13a and 13b in the first embodiment shown in FIG. As described above, the interaction optical waveguide 13b outside the circle is longer than the interaction optical waveguide 13a inside the circle. Therefore, as can be seen from FIG. 5 showing the traveling wave electrode 14 as a main component, the center conductor 14a is made to interact with the interaction light so that the electric lines of force emerging from the center conductor 14a do not act on the interaction optical waveguide 13b in the region IX. They are shifted from the top of the waveguide 13b. As a result, the length of interaction between the high-frequency electrical signal and the light is made equal in the interaction optical waveguides 13a and 13b. By doing so, an appropriate chirp characteristic as an LN optical modulator can be secured.

(Third embodiment)
FIG. 6 shows a third embodiment of the present invention. In this embodiment, the center VI of the curve of the interaction region IV and the center V of the curve of the interaction region II coincide with each other, and the entire pattern of the interaction optical waveguides 13a and 13b is at the centers VI and V of this curve. It has a point-symmetric structure.

By doing so, the radius of curvature R ₁ of the arc in the interaction region II and the interaction region IV is equal to the radius of curvature R ₂ of the arc in the interaction region IV (R ₁ = R ₂ ). The lengths of the waveguides 13a and 13b are equal.

  Since the interaction optical waveguides 13a and 13b do not cross each other, the light insertion loss is the lowest.

The center VI curve of the interaction region IV in this embodiment of the curve being shaped by the radius of curvature R ₁ at is contained within a circle depicting the entire circumference or the interaction optical waveguides 13a,, 13b Further, the present invention is characterized in that, for example, interactive optical waveguides 13a and 13b made of curves exist outside the centers X and XI on the circumference of the curve made up of the minimum curvature radius.

  As can be said for all embodiments of the present invention, the output optical waveguide 13c may or may not intersect with the interaction optical waveguides 13a and 13b as shown in FIG. Needless to say.

(Fourth embodiment)
FIG. 7 shows a mounting method of an electrical termination using the first embodiment of the present invention shown in FIGS. 1 and 2 as a fourth embodiment of the present invention. Here, 15 is a housing of the optical modulator module. Reference numeral 16 denotes an electrical terminal connected to the traveling wave electrode 14, and reference numeral 17 denotes a mounting plate made of a metal plate or a metallized insulator plate. The electrical termination 16 generates heat because it converts the high frequency electrical signal into Joule heat. Accordingly, by providing a separate mounting plate 17 as shown in FIG. 7 without mounting on the z-cut LN substrate 1, the heat is not transmitted to the z-cut LN substrate 1. That is, the mounting plate 17 also serves as a heat sink. In order to prevent the mounting plate 17 from affecting the high-frequency electrical signal propagating through the traveling wave electrode 14, a sufficient distance, for example, on the order of millimeters is provided on the back surface of the mounting plate 17 and the upper surface of the traveling wave electrode 14.

(Fifth embodiment)
FIG. 8 shows another mounting method of the electrical termination 16 using the first embodiment of the present invention shown in FIGS. 1 and 2 as the fifth embodiment of the present invention. Here, the electrical termination 16 is connected to the traveling wave electrode 14 through electrical lines 19 a, 19 b, 19 c formed on the mounting plate 18 made of an insulator. Even in this method, the heat generated at the electrical terminal 16 is not transmitted to the z-cut LN substrate 1 but is radiated to the housing 15. In the fifth embodiment, the back surface of the mounting plate 18 and the upper surface of the traveling wave electrode 14 are sufficiently in the order of millimeters so that the mounting plate 18 does not affect the high-frequency electrical signal propagating through the traveling wave electrode 14. A distance is provided.

(Each embodiment)
Although the optical modulator has been described above as an example, the present invention can be applied to other optical modulation devices such as an optical switch in which light input or light output is composed of two or more optical waveguides. In addition to the Ti thermal diffusion method, various optical waveguide formation methods such as a proton exchange method can be applied as the optical waveguide formation method, and various materials other than SiO ₂ such as Al ₂ O ₃ can be applied as the buffer layer. .

  Further, the radiation light to the monitor PD used for DC bias control is designed so that, for example, in FIG. 1, two radiation lights radiated from the multiplexing part VIII of the optical waveguide are emitted from different sides of the LN substrate. If this is done, stable monitoring is possible because the two emitted lights do not interfere with each other.

  Also, the z-cut LN substrate has been described, but other cut LN substrates such as x-cut, y-cut, or a mixture of them may be used, a lithium tantalate substrate, a quartz substrate, a semiconductor substrate, or the like. Other substrates may be used.

  The above embodiment has been described using the ridge structure. The reason is that the ridge structure not only has excellent performance as an optical modulator, but also increases the insertion loss very little even when bent at a radius of curvature of the order of millimeters. Needless to say, if the curvature may be increased, or if there is some strong confinement as an optical waveguide, the ridge structure is not necessary. Further, since light is likely to be radiated in the outward direction of the curvature forming the spiral or arc, it is possible to form a ridge structure only on one side by etching at least a part of the substrate of the interaction optical waveguide corresponding to the outside of the curvature. Needless to say. Although most of the interactive optical waveguide has been described as a curve, it goes without saying that a combination of a curve and a straight line may be used.

  As the electrode configuration, a configuration using a CPW electrode having a symmetrical structure has been described. However, a CPW electrode having an asymmetrical structure may be used. good.

  Furthermore, the scope of application of the present invention is not limited to an optical modulator that operates at high speed using an electro-optic effect in a so-called dielectric or semiconductor that changes a refractive index by applying a voltage. The present invention can also be applied to an optical device using a so-called thermo-optic effect in which a current is applied by applying a voltage and heat is generated by a heater formed on a substrate and the refractive index of the optical waveguide is changed by the heat. As an optical device using such a thermo-optic effect, for example, there is a quartz optical waveguide (PLC). By using the present invention, since the interaction length between heat and light becomes long, it is possible to operate with a low calorific value, and low power can be achieved.

  As described above, according to the present invention, it is possible to achieve ultra-miniaturization and to increase the interaction length, so that the driving voltage is low, and as a result, the light modulation band, characteristic impedance, etc. are greatly improved. An optical modulator can be provided.

1 is a top view of an optical waveguide constituting an optical modulator according to a first embodiment of the present invention. FIG. 3 is a top view of electrodes constituting the optical modulator according to the first embodiment of the present invention. The figure explaining the principle of this invention The top view of the optical waveguide which comprises the optical modulator concerning the 2nd Embodiment of this invention Top view of electrodes constituting an optical modulator according to the second embodiment of the present invention The top view of the optical waveguide which comprises the optical modulator concerning the 3rd Embodiment of this invention The figure explaining the optical modulator concerning the 4th Embodiment of this invention The figure explaining the optical modulator concerning the 5th Embodiment of this invention The perspective view which shows schematic structure about the optical modulator of 1st prior art Sectional view taken along line AA 'in FIG. Sectional drawing which shows schematic structure about the optical modulator of 2nd prior art The figure explaining the principle of operation of the 2nd prior art The figure explaining the problem in the optical modulator of the 1st and 2nd prior art The figure explaining Vπ of the optical modulators of the first and second prior art

Explanation of symbols

1: z-cut LN substrate (substrate)
2, 9: SiO ₂ buffer layer 3, 13: Mach-Zehnder optical waveguide (optical waveguide)
3a, 3b, 13a, 13b: interaction optical waveguide 13c: output optical waveguide 4, 14: traveling wave electrode (electrode)
4a, 14a: Center conductor 4b, 4c, 14b, 14c: Ground conductor 5: Si conductive layer 6: High frequency (RF) electric signal feeder 7: High frequency (RF) electric signal output line 8a: Ridge under the central conductor 4a 8b: Ridge under ground conductor 4b 8c: Ridge under ground conductor 4c 10a, 10b: Air gap between ridges 12a, 12b: Line of electric force 15: Housing 16: Electrical termination 17, 18: Mounting plate R ₁ , R ₂ : radius of curvature VI: center

Claims (9)

A substrate, an optical waveguide formed on the substrate, and an electrode for applying a high-frequency electrical signal, the optical waveguide having two mutual refractive indexes that change when a high-frequency electrical signal is applied to the electrode. In the optical modulator constituting the Mach-Zehnder optical waveguide including the working optical waveguide and the output optical waveguide from which the modulated light is output,
The two interaction optical waveguides, Rutotomoni number of turns is constructed spiral of one or more times, it is disposed across the at least two radii of curvature different curves, the curvature of the curve having the greatest radius of curvature An optical modulator characterized in that when a circle centered at the center is drawn, the center of curvature of a curve having the smallest radius of curvature is included in the circle . A substrate, an optical waveguide formed on the substrate, and an electrode for applying a high-frequency electrical signal, the optical waveguide having two mutual refractive indexes that change when a high-frequency electrical signal is applied to the electrode. In the optical modulator constituting the Mach-Zehnder optical waveguide including the working optical waveguide and the output optical waveguide from which the modulated light is output,
The two interactive optical waveguides are arranged with at least two curves having different radii of curvature, and when a circle centered on the center of curvature of the curve having the largest radius of curvature is drawn, Contains the center of curvature of the curve with the smallest radius of curvature,
The optical modulator characterized in that the pattern of the two interactive optical waveguides is point-symmetric with respect to the center of the overall arrangement of the patterns for the two interactive optical waveguides . 3. The optical modulator according to claim 1, wherein the lengths of the portions where the refractive indexes of the two interactive optical waveguides are equal are equal to each other . 4. The optical modulator according to claim 1, wherein the two interactive optical waveguides cross each other . The optical modulator according to claim 1, wherein the two interactive optical waveguides are arranged so as not to cross each other . 6. The optical modulator according to claim 1, wherein the output optical waveguide intersects with the two interactive optical waveguides . 6. The optical modulator according to claim 1, wherein the output optical waveguide is disposed so as not to intersect the two interactive optical waveguides . 8. The optical modulator according to claim 1, wherein at least a part of the two interactive optical waveguides has a ridge structure . 8. The optical modulator according to claim 1, wherein at least one substrate in the vicinity of the two interactive optical waveguides is thin .

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