JP2006309124A - Optical modulator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical modulator capable of modulating up to high frequencies by keeping a symmetric structure of modulation electrodes and capable of controlling a chirp amount, and to provide an optical modulator with extremely high productivity in which a chirp amount can be easily controlled even in a post-process of manufacture. <P>SOLUTION: The optical modulator includes a substrate 1 made of a material having an electro-optic effect, a Mach-Zehnder optical waveguide fabricated on the top or back face of the substrate, and modulation electrodes 4, 5 fabricated on the top face of the substrate to modulate light passing in the optical waveguide, wherein the modulator is characterized in that: the minimum thickness of the substrate is 50 μm or less; and thickness of the substrate in at least a part of the region where two branched waveguides 3 of the Mach-Zehnder optical waveguide are fabricated differs by the respective branched waveguides. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical modulator, and more particularly to an optical modulator in which chirp control related to optical modulation is performed on an optical modulator having a Mach-Zehnder type optical waveguide.

Conventionally, in the optical communication field and the optical measurement field, a waveguide type optical modulator in which an optical waveguide and a modulation electrode are formed on a substrate having an electro-optic effect has been widely used. In particular, in long-distance fiber communication systems, chirp control related to optical modulation is performed.
The chirp represents how much the phase difference modulation component is superimposed when intensity modulation is performed in the optical modulator, and the chirp parameter α representing the chirp amount is expressed by the following equation (1).
α = (dφ / dt) / (1 / 2S · dS / dt)...
Here, S represents the light intensity, φ represents the amount of phase change, and t represents time.

As shown in FIG. 1A, in the case of a Mach-Zehnder interferometer type intensity modulator in which a Mach-Zehnder type optical waveguide 2 is formed on a substrate 1, the chirp amount is the amount of phase change φ1, φ2 for each branch waveguide 3 And can be expressed as a chirp parameter as shown in Equation 2. In FIG. 1A, modulation electrodes such as signal electrodes and ground electrodes are not shown.
α = (φ1 + φ2) / (φ1-φ2)... Formula 2

When LiNbO ₃ (hereinafter referred to as “LN”) is used as the substrate 1 having an electro-optic effect, for example, when an optical waveguide as shown in FIG. 1A is formed using an X-cut LN substrate, As shown in FIG. 1B, which is a cross-sectional view taken along the dotted line A in FIG. 1A, the two branch waveguides 3 are often arranged symmetrically with respect to the signal electrode 4 and the ground electrode 5. For this reason, since the electric field 6 applied to each branch waveguide has the same strength and the opposite direction, the relationship of φ1 = −φ2 is established in the phase change amount of each branch waveguide. The value of the chirp parameter α of 2 is zero, and no chirp is generated.

  On the other hand, when an optical waveguide is configured using a Z-cut LN substrate, one branching waveguide 3 is connected to the signal electrode 4 as shown in FIG. 1C, which is a sectional view taken along the dotted line A in FIG. The other branch waveguide 3 is often disposed below the ground electrode 5. For this reason, since the electric field 6 applied to each branching waveguide has different strengths, the relationship of φ1 ≠ −φ2 is established in the phase change amount of each branching waveguide, and only the unequal portion of the applied electric field is satisfied. Chirp will occur. Reference numeral 7 denotes a buffer layer for suppressing light waves propagating through the optical waveguide by the modulation electrode or the like from being scattered and absorbed.

Usually, since the required chirp parameter of the optical modulator differs depending on the transmission system (transmission method) to be used, it is necessary to arbitrarily adjust the chirp parameter of the optical modulator.
In Patent Document 1, in order to make it possible to apply chirps having different polarities without applying a large DC bias voltage, as shown in FIG. 2A, the first ground electrode 11, the signal electrode 10, In addition, the alignment direction of the second ground electrode having the first portion 12 and the second portion 13 divided in the length direction of the optical waveguide is parallel to the main surface 15 of the substrate 1 and the crystal axis of the substrate 1 Further, the first ground electrode, the signal electrode, and the second ground electrode constitute a modulation electrode that is symmetrical with respect to the centers of the two branch waveguides 3. The first portion 12 and the second portion 13 are electrically connected by a conductive thin film 14.
JP 2002-107682 A

Further, in Non-Patent Document 1, in order to obtain a chirp amount (α = 0.65) equivalent to that of a Z-cut LN optical modulator with an X-cut LN optical modulator, as shown in FIG. 4 and the ground electrode 5 are configured to be different on the left and right with the signal electrode 4 interposed therebetween. The substrate 1 is a thin thin plate of 8.5 μm, and a reinforcing plate 16 is bonded via a low dielectric layer 15.
Kenji Aoki, et al., “Pre-chirped X-cut LiNbO3 thin plate optical modulator using asymmetrical CPW electrodes”, Proceedings of Electronics Society Conference of the Institute of Electronics, Information and Communication Engineers (C-3-103), p. 235, September 2004

  However, when the modulation electrode has an asymmetric structure as shown in FIG. 2B, an X-cut optical modulation having a conventional symmetrical electrode structure (a structure in which the distance between the signal electrode and the two ground electrodes is equal). There is a drawback that it is difficult to increase the bandwidth up to a high frequency compared to the instrument. In addition, as shown in FIGS. 2A and 2B, the arrangement of the modulation electrode and the optical waveguide is determined at the manufacturing stage, so that it is difficult to adjust the chirp amount in the post-manufacturing process, and the productivity is lowered. Cause problems.

  The problem to be solved by the present invention is to provide an optical modulator that solves the above-mentioned problems, maintains the structure of the modulation electrode symmetrically, enables modulation up to a high frequency, and adjusts the chirp amount. It is to be. In addition, the chirp amount can be easily adjusted even in a post-manufacturing process, and an optical modulator with extremely high productivity is provided.

  In the invention according to claim 1, a substrate formed of a material having an electro-optic effect, a Mach-Zehnder type optical waveguide formed on the front surface or the back surface of the substrate, and formed on the surface of the substrate, And a modulation electrode for modulating light passing through the substrate, the minimum thickness of the substrate is 50 μm or less, and at least one of the two branch waveguides of the Mach-Zehnder optical waveguide is formed. The thickness of the substrate in the region of the portion has a different portion for each branching waveguide.

  In the invention according to claim 2, a substrate formed of a material having an electro-optic effect, a Mach-Zehnder type optical waveguide formed on the front surface or the back surface of the substrate, and formed on the surface of the substrate, And a modulation electrode for modulating light passing through the substrate, the minimum thickness of the substrate is 50 μm or less, and at least one of the two branch waveguides of the Mach-Zehnder type optical waveguide is formed. A member having a different dielectric constant or dielectric thickness is arranged for each branch waveguide on the back surface of the substrate in the region of the portion.

In the invention according to claim 3, a substrate formed of a material having an electro-optic effect, a Mach-Zehnder type optical waveguide formed on the front surface or the back surface of the substrate, and formed on the surface of the substrate, And a modulation electrode for modulating light passing through the substrate, the minimum thickness of the substrate is 50 μm or less, and one of the two branch waveguides of the Mach-Zehnder type optical waveguide A high refractive index member or a conductive member is disposed adjacent to at least a part of the back surface of the substrate in the region where the waveguide is formed.
The refractive index of the “high refractive index member” is different from the member disposed on the back surface of the substrate in the region where the branched waveguide is formed, such as an adhesive layer, a reinforcing plate, a dielectric, or a hole. This means that the refractive index is higher than the refractive index.

  In the invention according to claim 4, a substrate formed of a material having an electro-optic effect, a Mach-Zehnder type optical waveguide formed on the front surface or the back surface of the substrate, and formed on the surface of the substrate, In a light modulator including a modulation electrode for modulating light passing through the substrate, a minimum value of the thickness of the substrate is 50 μm or less, and in a region where two branch waveguides of the Mach-Zehnder type optical waveguide are formed A reinforcing plate is bonded to the back surface of the substrate via an adhesive layer having a different thickness for each branching waveguide.

  According to a fifth aspect of the present invention, in the optical modulator according to any one of the first to third aspects, a reinforcing plate is bonded to the back side of the substrate.

According to the first aspect of the invention, since the minimum value of the substrate thickness is 50 μm or less, the electric field formed by the modulation electrode leaks under the substrate in the portion where the thickness of the substrate is 50 μm or less. And, since the thickness of the substrate in at least a part of the region where the two branch waveguides of the Mach-Zehnder type optical waveguide are formed has a different part for each branch waveguide, the amount of electric field leakage for each branch waveguide As a result, since the electric field distribution applied to each branch waveguide is different, the amount of phase change generated in each branch waveguide is different and chirp is generated.
In addition, the substrate thickness can be adjusted easily by the polishing / cutting process even after the modulation electrode and the optical waveguide are formed, and the production yield of the optical modulator can be improved. Is possible.
In addition, the minimum value of the thickness of a board | substrate is 50 micrometers or less, Preferably it is 20 micrometers or less. However, even if the substrate has a thickness outside these numerical ranges, as long as the chirp can be changed by changing the thickness of the substrate as in the present invention, the technical scope of the present invention. Is included.

  According to the invention of claim 2, since the minimum value of the thickness of the substrate is 50 μm or less, the electric field formed by the modulation electrode reaches the bottom of the substrate in the portion where the thickness of the substrate is 50 μm or less as in the case of claim 1. Leaks out. Since a member having a different dielectric constant or dielectric thickness is arranged for each branch waveguide on the back surface of the substrate in at least a part of the region where the two branch waveguides of the Mach-Zehnder optical waveguide are formed. Depending on the dielectric constant and thickness of the dielectric, the amount of electric field leakage differs for each branch waveguide, and as a result, the electric field distribution applied to each branch waveguide differs, resulting in a difference in the amount of phase change that occurs in each branch waveguide. A chirp will occur. Further, the adjustment of the member disposed on the back surface of the substrate can be performed even after the process of forming the modulation electrode and the optical waveguide, and the yield relating to the production of the optical modulator can be improved.

  According to the invention of claim 3, the minimum value of the thickness of the substrate is 50 μm or less, and at least one of the back surfaces of the substrate in the region where one of the two branch waveguides of the Mach-Zehnder type optical waveguide is formed. Since the high refractive index member or the conductive member is arranged close to the part, the leakage amount of the electric field differs for each branch waveguide depending on the refractive index and conductivity of the arranged member. Since the applied electric field distribution is different, the amount of phase change generated in each branching waveguide is different and chirp is generated. Further, the adjustment of each member arranged on the back surface of the substrate can be performed even after the process of forming the modulation electrode and the optical waveguide, and the yield related to the production of the optical modulator can be improved.

According to the invention according to claim 4, the minimum value of the thickness of the substrate is 50 μm or less, and the thickness of each branch waveguide is increased on the back surface of the substrate in the region where the two branch waveguides of the Mach-Zehnder type optical waveguide are formed. Since the reinforcing plate is bonded via different adhesive layers, the amount of electric field leakage differs for each branching waveguide, particularly depending on the thickness of the adhesive layer and the distance between the substrate and the reinforcing plate. Since the electric field distribution applied to the waveguide is different, the amount of phase change generated in each branching waveguide is different and chirp is generated. Further, the adjustment of the thickness of the adhesive layer on the back surface of the substrate can be performed in the process after the modulation electrode or the optical waveguide is formed, and the yield related to the production of the optical modulator can be improved. .
The thickness of the adhesive layer is not particularly limited. For example, the thickness of the adhesive layer is 50 μm or less, and can be adjusted within a range where the chirp amount varies depending on the thickness of the adhesive layer.

  The invention according to claim 5 provides an optical modulator having high mechanical strength even when a thin plate having a minimum thickness of 50 μm or less is used because a reinforcing plate is bonded to the back side of the substrate. It becomes possible to do.

Hereinafter, the present invention will be described in detail using preferred examples.
In the present invention, the minimum value of the thickness of the substrate formed of a material having an electro-optic effect is 50 μm or less, in particular, the thickness of the substrate in the region where the two branch waveguides of the Mach-Zehnder type optical waveguide are formed, A thin plate having a portion having a thickness of 50 μm or less is used. In the thickness portion of 50 μm or less, the electric field formed by the modulation electrode leaks on the back surface of the substrate, and the leakage amount of the electric field Is adjusted to adjust the electric field distribution applied to the branching waveguide. Then, the difference in electric field distribution results in different amounts of phase change (φ1, φ2) generated in the branch waveguide, and as a result, it is possible to generate and control chirp.

FIG. 3 is a top view of an optical modulator applied to the present invention, a substrate 1 formed of a material having an electro-optic effect, a Mach-Zehnder type optical waveguide 2 formed on the surface of the substrate, Modulating electrodes 4 and 5 are formed on the surface of the substrate and modulate light passing through the optical waveguide. Since the structure of the modulation electrode in the vicinity of the branching waveguide 3 is maintained symmetrically, modulation up to a high frequency is possible.
As a material having an electro-optic effect, for example, lithium niobate, lithium tantalate, PLZT (lead lanthanum zirconate titanate), quartz-based materials, and combinations thereof can be used. In particular, a lithium niobate (LN) crystal having a high electro-optic effect is preferably used.

As a method for forming the optical waveguide, it can be formed by diffusing Ti or the like on the substrate surface by a thermal diffusion method or a proton exchange method. The modulation electrodes such as the signal electrode 4 and the ground electrode 5 can be formed by forming a Ti / Au electrode pattern, a gold plating method, or the like. Furthermore, if necessary, a buffer layer (not shown) such as dielectric SiO ₂ may be provided on the surface of the substrate after the optical waveguide is formed, and a modulation electrode may be formed on the buffer layer.

FIG. 4 shows a first embodiment of an optical modulator according to the present invention.
4 shows a cross-sectional view taken along the dotted line B in the optical modulator of FIG. The same applies to FIGS.
The feature of the first embodiment is that the thickness of the substrate in the region where the two branch waveguides 3 of the Mach-Zehnder type optical waveguide 2 are formed is different for each branch waveguide. Then, in at least a part of the substrate in the region where the branching waveguide 3 is formed, the distribution of the electric field applied to the two branching waveguides is different and the chirp is generated when the thickness of the substrate is 50 μm or less. .

As a specific configuration, in FIG. 4A, the thickness of the substrate is adjusted to be different for each branching waveguide by making the back surface of the substrate 1 an inclined surface. In FIG. 4 (b), the right half of the back surface of the substrate is removed as 21, and in FIG. 4 (c), a notch is formed as 22 in the back surface of the substrate of one branching waveguide. The thickness of the substrate in the two branch waveguides is adjusted.
Further, in FIG. 4D, a ridge 23 is formed on the substrate surface, and different substrate thicknesses are realized in the two branched waveguides.
As an application of the present invention, when an inclined surface or a concave portion is formed on the back surface of the substrate 1 as shown in FIG. 4, another LN substrate or a dielectric with the substrate 1 through a glue or the like as necessary. Members formed of materials having different rates may be joined to adjust the dielectric constant in the vicinity of the back surface of the substrate 1 or to reinforce the mechanical strength of the substrate 1.

Further, in FIGS. 4B and 4C, the case where a part of the back surface of the substrate is removed or the groove is formed has been described. However, the present invention is not limited to this. For example, when both the waveguide and the electrode are on the substrate surface In the method of forming a groove or a cut portion in a place excluding the electrode on the surface, or when the waveguide and the electrode are on different surfaces, the electrode is not formed on the surface on which the electrode is formed. It is also possible to control the chirp by forming a groove or a cut portion at the place.
It is also possible to adjust the chirp by arranging both the groove and the cut portion.
Furthermore, when an X-cut substrate is used, it is possible to adjust the electric field distribution formed by the electrodes by arranging a low dielectric constant material such as an adhesive on or near the waveguide by coating or the like. .

FIG. 5 shows a second embodiment of the optical modulator according to the present invention.
The feature of the second embodiment is that the thickness of the substrate 1 in the region where the two branch waveguides 3 of the Mach-Zehnder type optical waveguide 2 are formed is the same, but the thickness of the substrate is 50 μm or less. By adjusting the dielectric constant and thickness of the dielectric disposed on the back surface of the substrate, the distribution of the electric field applied to the two branch waveguides is made different to generate chirp.

  Specifically, as shown in FIG. 5A, members 30 and 31 having different dielectric constants are arranged on the back surface of the substrate on which each branched waveguide is formed. In FIG. 5B, a part of the dielectric 30 disposed on the back surface of the substrate is removed as 32 (or not formed in advance), and the dielectric constant in the vicinity of the back surface of the substrate is different for each branch waveguide. It is configured to be in a state. Further, as shown in FIG. 5C, the back surface of the dielectric layer 33 can be inclined so that the thickness of the dielectric is different on the back surface of the substrate on which each branched waveguide is formed.

The dielectric materials that can be used for an optical modulator of the present _invention, include _{ZnO 2, TiO 2, Ta 2} O 3, SiO 2, adhesion to the LN substrate also _good, SiO 2, TiO _2, etc. Can be used particularly preferably.

FIG. 9 shows an application example of the second embodiment of FIG.
FIGS. 9A to 9C correspond to FIGS. 5A to 5C, respectively, and a Mach-Zehnder type optical waveguide including two branching waveguides 3 ′ is formed on the back surface of the substrate 1. FIG. There is a feature in the point.
In the method of manufacturing an optical modulator having a waveguide on the back surface of the substrate 1 shown in FIG. 9, after forming an optical waveguide on one surface of the substrate 1, the other surface is polished to form a substrate 1 having a predetermined thickness. Process. Next, a buffer layer and a modulation electrode are formed on the polished surface. Then, a dielectric such as 30, 31, or 33 is disposed on one surface where the optical waveguide is formed.

FIG. 6 shows a third embodiment of the optical modulator according to the present invention.
The feature of the third embodiment is that the thickness of the substrate 1 in the region where the two branch waveguides 3 of the Mach-Zehnder type optical waveguide 2 are formed is the same, but the thickness of the substrate is 50 μm or less. By disposing a member having a higher refractive index (dielectric constant) than that of the adhesive layer 41 or a conductive member on the back surface side, the distribution of the electric field applied to the two branch waveguides is made different to generate chirp. It is.

As a specific configuration, as shown in FIG. 6A, a member 40 having a dielectric constant higher than that of the adhesive layer 41 is disposed in the vicinity of the back surface of the substrate 1, and the electric field distribution applied to the two branch waveguides is different. It is possible to make adjustments. As the 40 materials, _Al 2 _{O 3} or _the like can be used. In addition, as shown in FIG. 6B, the electric field distribution applied to the branching waveguide can be adjusted by arranging the conductive material 42 in the same manner. The arrangement positions of the members 40 and 42 may be in close contact with the substrate 1 as shown in FIG. 6A or separated as shown in FIG. Reference numerals 41 and 43 denote adhesive layers for arranging and fixing the members 40 and 42 on the back surface of the substrate, and an ultraviolet curable adhesive or the like can be used. Reference numeral 44 denotes a reinforcing plate.

FIG. 10 shows an application example of the third embodiment of FIG.
FIGS. 10A and 10B correspond to FIGS. 6A and 6B, respectively, and a Mach-Zehnder type optical waveguide including two branching waveguides 3 ′ is formed on the back surface of the substrate 1. FIG. There is a feature in the point.
In the method of manufacturing an optical modulator having a waveguide on the back surface of the substrate 1 shown in FIG. 10, after forming an optical waveguide on one surface of the substrate 1, the other surface is polished, and the substrate 1 is formed to a predetermined thickness. Process. Next, a buffer layer and a modulation electrode are formed on the polished surface. Then, the adhesive layer 41 or 43, the high dielectric constant member 40, the conductive material 42, the reinforcing plate 44, or the like is disposed on one surface where the optical waveguide is formed.
In addition, when using the reinforcement board 44 like FIG.10 (b), it replaces with the manufacturing method mentioned above, and the following manufacturing methods are also possible. After forming the optical waveguide on one surface of the substrate 1, the adhesive layer 43, the conductive material 42, and the reinforcing plate 44 are disposed on the one surface on which the optical waveguide is formed, and then the reinforcing plate is mounted on the substrate. Used as a holding member during polishing. Alternatively, the adhesive layer 43 and the conductive material 42 are formed on the reinforcing plate 44 and then placed on the substrate 1. In this state, the other surface of the substrate 1 is polished and processed into a substrate 1 having a predetermined thickness. Next, a buffer layer and a modulation electrode are formed on the polished surface.

FIG. 7 shows a fourth embodiment of the optical modulator according to the present invention.
The feature of the fourth embodiment is that the thickness of the substrate 1 in the region where the two branch waveguides 3 of the Mach-Zehnder type optical waveguide 2 are formed is the same, but the thickness of the substrate is 50 μm or less. The reinforcing plate 51 is adhered to the back surface of each of the branching waveguides via an adhesive layer 50 having a thickness different for each branching waveguide, whereby the distribution of the electric field applied to the two branching waveguides is made different to generate chirp. It is.

  In the fourth embodiment, the factors affecting the electric field distribution include not only the change in thickness of the adhesive layer but also the dielectric constant and conductivity of the reinforcing plate when the thickness of the adhesive layer is thin. Influence. Moreover, in order to adjust the thickness of the adhesive to a predetermined thickness, a spacer (not shown) can be disposed between the substrate 1 and the reinforcing plate 51 as necessary.

  As the material of the adhesive layer 50, various adhesives such as an epoxy adhesive, a thermosetting adhesive, an ultraviolet curable adhesive, solder glass, a thermosetting, photocurable or photothickening resin adhesive sheet, etc. It is possible to use materials. In particular, an ultraviolet curable adhesive or the like can be suitably used.

FIG. 11 shows an application example of the fourth embodiment of FIG.
FIG. 11 is characterized in that a Mach-Zehnder type optical waveguide including two branching waveguides 3 ′ is formed on the back surface of the substrate 1 as compared with FIG. 7.
In the method of manufacturing an optical modulator having a waveguide on the back surface of the substrate 1 shown in FIG. 11, an optical waveguide is formed on one surface of the substrate 1, and then the other surface is polished to form a substrate 1 having a predetermined thickness. Process. Next, a buffer layer and a modulation electrode are formed on the polished surface in a state of being placed on the polishing jig. Then, the adhesive layer 50 and the reinforcing plate 51 are disposed on the one surface where the optical waveguide is formed. Alternatively, after the adhesive layer 50 and the reinforcing plate 51 are disposed on one surface where the optical waveguide is formed, a buffer layer and a modulation electrode are formed on the polished surface.
Moreover, it can replace with the manufacturing method mentioned above and the following manufacturing methods are also possible. After the optical waveguide is formed on one surface of the substrate 1, the adhesive layer 50 and the reinforcing plate 51 are disposed on the one surface, and then the reinforcing plate is used as a holding member during substrate polishing. The other surface is polished and processed into a substrate 1 having a predetermined thickness. Next, a buffer layer or a modulation electrode may be formed on the polished surface.

The above description has focused on an example using an X-cut substrate, but the present invention also applies the first to fourth embodiments or application examples thereof to an optical modulator using a Z-cut substrate. Is possible. FIG. 8 shows a fifth embodiment of the optical modulator according to the present invention.
The feature of the fifth embodiment is that the technique according to the first embodiment is applied to an optical modulator using a Z-cut substrate. In other words, the conventional Z-cut optical modulator itself has a chirp amount, but each branching waveguide is formed in order to further increase the chirp amount or approach the chirp amount to zero. The thickness of the substrate is adjusted.

  For example, in FIG. 8A, the branch waveguide on the left side of the figure has a weaker electric field strength than that on the right side, but in order to further reduce the strength of the electric field, the removal portion 60 is provided on the back surface of the substrate. By forming and reducing the thickness of the substrate, the amount of electric field leakage from the back surface of the substrate is increased. In FIG. 8B, conversely, a removal unit 61 is provided to weaken the electric field applied to the right branching waveguide.

Any of the first to fifth embodiments described above or application examples thereof can be implemented in the process after forming the modulation electrode and the optical waveguide, and improve the yield related to the production of the optical modulator. Is possible.
Moreover, although each said Example can also be implemented independently, it is also possible to combine and utilize as needed.
Furthermore, in the present invention, since a substrate (thin plate) having a portion with a thickness of 50 μm or less is used, it is necessary to increase the mechanical strength of the optical modulator. It is preferable to adhere a reinforcing plate to the back surface.

Next, the change in the chirp amount was evaluated by simulation for the example according to the optical modulator of the present invention.
The thin plate light modulation element uses an X-cut LN substrate as the substrate, forms a Mach-Zehnder optical waveguide by Ti diffusion, and assumes a 28 μm high modulation electrode formed by plating using Au is doing.

(Simulation 1)
As shown in FIG. 4B, when the thickness of the substrate is assumed to be 10 μm for the right half and 30 μm for the left half, the chirp amount is calculated as shown in FIG. Obtained.

(Simulation 2)
With respect to the thin light modulation element, the thickness of the substrate is 10 μm, and as shown in FIG. 6A, a metal member 40 with a thickness of 5 μm of Au is disposed on the back surface of the substrate 1 and the periphery thereof is dielectric. It was assumed that an adhesive layer 41 having a thickness of 4 and a thickness of 30 μm was disposed. The chirp amount in this case was α = 0.41.

  It is understood from this simulation that an arbitrary amount of chirp can be set by adopting the configuration of the optical modulator according to the present invention.

  As described above, according to the present invention, it is possible to provide an optical modulator that maintains the modulation electrode structure symmetrically, enables modulation up to a high frequency, and adjusts the chirp amount. In addition, the amount of chirp can be easily adjusted even in a post-manufacturing process, and an optical modulator with extremely high productivity can be provided.

It is the schematic of the conventional optical modulator. It is a figure which shows the example of the optical modulator which performs the conventional chirp control. It is a top view of the optical modulator of the present invention. It is a figure which shows the 1st Example of this invention. It is a figure which shows the 2nd Example of this invention. It is a figure which shows the 3rd Example of this invention. It is a figure which shows the 4th Example of this invention. It is a figure which shows the 5th Example of this invention. It is a figure which shows the application example of the 2nd Example of this invention. It is a figure which shows the application example of the 3rd Example of this invention. It is a figure which shows the application example of the 4th Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Mach-Zehnder type optical waveguide 3, 3 ′ Branched waveguide 4 Signal electrode 5 Ground electrode 6 Electric field 7 Buffer layer 20 Inclined portion 21, 22 Removed portion 23 Ridge portion 30, 31, 33 Dielectric 40 High refractive index member 41 , 43, 50 Adhesive layer 42 Conductive members 44, 51 Reinforcing plate

Claims (5)

A substrate formed of a material having an electro-optic effect, a Mach-Zehnder type optical waveguide formed on the front surface or the back surface of the substrate, and a light formed on the surface of the substrate and modulating light passing through the optical waveguide An optical modulator including a modulation electrode of
The minimum value of the thickness of the substrate is 50 μm or less, and the thickness of the substrate in at least a part of the region where the two branch waveguides of the Mach-Zehnder type optical waveguide are formed has a portion different for each branch waveguide. An optical modulator characterized by that. A substrate formed of a material having an electro-optic effect, a Mach-Zehnder type optical waveguide formed on the front surface or the back surface of the substrate, and a light formed on the surface of the substrate and modulating light passing through the optical waveguide An optical modulator including a modulation electrode of
The minimum value of the thickness of the substrate is 50 μm or less, and a dielectric constant or dielectric constant is provided for each branch waveguide on the back surface of the substrate in at least a part of the region where the two branch waveguides of the Mach-Zehnder optical waveguide are formed. An optical modulator characterized in that members having different body thicknesses are arranged. A substrate formed of a material having an electro-optic effect, a Mach-Zehnder type optical waveguide formed on the front surface or the back surface of the substrate, and a light formed on the surface of the substrate and modulating light passing through the optical waveguide An optical modulator including a modulation electrode of
The minimum value of the thickness of the substrate is 50 μm or less, and at least part of the back surface of the substrate in the region where one of the two branch waveguides of the Mach-Zehnder optical waveguide is formed has a high refractive index. An optical modulator characterized in that a member or a conductive member is arranged close to each other. A substrate formed of a material having an electro-optic effect, a Mach-Zehnder type optical waveguide formed on the front surface or the back surface of the substrate, and a light formed on the surface of the substrate and modulating light passing through the optical waveguide An optical modulator including a modulation electrode of
The minimum value of the thickness of the substrate is 50 μm or less, and an adhesive layer having a different thickness is provided on the back surface of the substrate in the region where the two branch waveguides of the Mach-Zehnder type optical waveguide are formed. An optical modulator characterized by adhering a reinforcing plate. 4. The optical modulator according to claim 1, wherein a reinforcing plate is bonded to the back side of the substrate.

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