JP2016194544A - Broad band waveguide type optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a microwave loss and to reduce a drive voltage while achieving velocity matching and impedance matching in a waveguide type optical element.SOLUTION: A waveguide type optical element is provided, which includes a substrate 100 where an optical waveguide 104 and a control electrode are formed and a dielectric layer 102 formed on the substrate. An RF electrode 106 and ground electrodes 108a, b in parallel to the RF electrode 106 are formed on the dielectric layer. A control electrode is composed of a center conductor and side conductors formed to interpose the center conductor, in which each of the center conductor and the side conductors is divided into a plurality of segments; segments of the center conductor are electrically connected to the respective portions, different from one another along the longitudinal direction of the RF electrode 106, with respect to the RF electrode 106 formed on the dielectric layer; and segments of each of the side conductors are electrically connected to the respective portions, different from one another along the longitudinal direction of each of the ground electrodes 108a, b, with respect to the ground electrodes 108a, b formed on the dielectric layer.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a waveguide type optical element including an optical waveguide and a control electrode for controlling a light wave propagating through the optical waveguide, and more particularly to a waveguide type optical element capable of operating over a wide frequency band. .

  In recent years, in the fields of optical communication and optical measurement, waveguide-type optical elements such as an optical modulator in which an optical waveguide is formed on a substrate having an electro-optic effect are often used. A waveguide-type optical element generally includes the optical waveguide and a control electrode for controlling a light wave propagating through the optical waveguide.

  As such a waveguide type optical element, a Mach-Zehnder type optical modulator using, for example, a ferroelectric crystal lithium niobate (LiNbO3) (also referred to as “LN”) as a substrate is widely used. The Mach-Zehnder type optical modulator includes an incident waveguide for introducing light from the outside, a branching unit for propagating the light introduced by the incident waveguide in two paths, and a branching unit after the branching unit. Mach-Zehnder type optical waveguide composed of two parallel waveguides for propagating each of the generated light and an output waveguide for combining the light propagated through the two parallel waveguides and outputting them to the outside Is provided.

  In addition, the Mach-Zehnder optical modulator includes a control electrode for applying a voltage to change the phase of the light wave propagating in the parallel waveguide using the electro-optic effect. The control electrode is generally separated from an RF (high frequency) signal electrode (hereinafter referred to as “RF electrode”) formed on or near the parallel waveguide along the length direction of the parallel waveguide, and the RF electrode. And a ground electrode disposed as a CPW (Coplanar Waveguide) type electrode.

  In particular, in the design of a broadband (microwave band) Mach-Zehnder type optical modulator that controls a light wave propagating in a parallel waveguide at a higher frequency, the propagation speed of light propagating through the parallel waveguide and the propagation propagating through the RF electrode It is applied to the RF electrode for speed matching with the speed (hereinafter simply referred to as “speed matching”), matching the input impedance of the RF electrode with respect to the output impedance of the driving circuit (hereinafter referred to as impedance matching), and controlling the light wave It is necessary to balance the power voltage (drive voltage).

  That is, in the wideband Mach-Zehnder type optical modulator, it is necessary to perform speed matching and impedance matching as essential requirements and to reduce the drive voltage as much as possible.

  In order to reduce the driving voltage, generally, a distance (hereinafter referred to as an action length) in which a high-frequency signal propagating through the RF electrode acts on a light wave propagating through the parallel waveguide (that is, the RF electrode and the parallel waveguide are parallel to each other). Distance of the formed part (action part), loss of high-frequency electrical signal when propagating through the RF electrode (hereinafter referred to as microwave loss), and electric field formed in the substrate by the RF electrode propagates in the parallel waveguide The degree to which the light wave effectively acts on the light modulation (hereinafter referred to as modulation efficiency) is considered.

  For speed matching and impedance matching, the separation distance between the RF electrode configured as a CPW electrode and the ground electrode (hereinafter referred to as interelectrode distance), the distance that the RF electrode and the ground electrode are opposed to each other (hereinafter referred to as “parallel distance”) , Parallel running distance), the height of the side surfaces of the RF electrode and the ground electrode facing each other (that is, the area per unit distance of the side surface) (hereinafter referred to as electrode height), the width of the RF electrode (hereinafter referred to as electrode width), Adjustment of the effective refractive index of the LN substrate (substrate thickness, formation of a low dielectric constant buffer layer, etc.) is considered.

  Conventionally, in the design of a broadband Mach-Zehnder optical modulator, the driving voltage is mainly reduced by increasing the length of action (lengthening), and the microwave loss is reduced by increasing the distance between the electrodes. Velocity matching and impedance matching can be achieved within a range of parallel running distances equal to or longer than the action length. For this reason, the high-frequency signal propagating through the RF electrode oozes greatly in the LN substrate and in the air. For example, a plurality of Mach-Zehnders such as a QPSK (Quadrature Phase Shift Keying) optical modulator. In the configuration in which the optical modulators having the configurations are integrated and used, crosstalk is likely to occur between the RF electrodes of the adjacent optical modulators. Therefore, it is necessary to increase the distance between adjacent optical modulators, which is a limiting factor for reducing the size of the optical element as a QPSK modulator.

  As a technology for downsizing the optical element, a ground electrode is also provided on the back surface of the LN substrate (the surface opposite to the surface on which the optical waveguide is formed), so that speed matching and impedance matching are achieved, and the distance between the electrodes is reduced. A light control element that reduces the drive voltage is known (Patent Document 1). In this light control element, by reducing the distance between the electrodes, the overlap range between the electric field distribution formed by the RF electrode in the LN substrate and the intensity distribution of the light wave propagating through the optical waveguide is increased (that is, the modulation efficiency is reduced). The drive voltage can be further reduced.

  However, in the light control element of Patent Document 1, since the cross-sectional area and the skin area of the electrode are relatively small, the microwave loss is relatively large. For this reason, the effect of the drive voltage reduction by lengthening is low, and there exists room for improvement.

  As a technique to reduce microwave loss, the aspect ratio of the electrode cross section is further increased by making the RF electrode taller than the ground electrode within the range where speed matching and impedance matching are possible without lowering the modulation efficiency. There is known a waveguide type optical device having a (mushroom-like) multilayer structure composed of a narrow lower layer and a wide upper layer (Patent Document 2).

  Further, by making the RF electrode higher and making the upper layer portion of the RF electrode wider, the microwave conductor loss (skin loss) can be reduced. In the characteristic simulation, for example, when the height of the RF electrode is set to 90 μm as shown in Patent Document 3, the conductor loss of the microwave can be increased, so that the electrode length can be increased and the drive voltage can be increased. It is known that it can be reduced.

  However, in such a waveguide type optical device, the electrode formation process becomes complicated, and the mechanical stability of the electrode itself decreases. In practical device design, it is necessary to make the width of the base of the RF electrode (the part attached to the substrate forming the optical waveguide) as thin as the width of the optical waveguide. is there. The width and height of the upper layer portion of the RF electrode shown in FIG. 1 of Patent Document 4 are extremely realistic design configurations, and the vibration test (GR-) of the Telcordia test, which is a general reliability confirmation test for communication devices. 1221 6-axis 20G can be reliable enough to withstand 20 to 2000 Hz), but the width or height of the upper layer of the RF electrode is further increased by about 20-30% It is difficult.

  Even if the structural reinforcement as shown in FIG. 13 of Patent Document 3 (FIG. 13a base is reinforced with an insulator such as a polymer, FIG. 13b two bases are provided), the width and height of the upper layer part are It is difficult to make a structure exceeding 50 μm.

  In addition, when the action part electrode has a CPW structure, the structure and angle of the trench part (grooves formed on both sides of the optical waveguide) affect the electric field distribution. Therefore, as shown in FIG. It may have a slope or a structure having a sub-trench as shown in FIG. This is a matter designed by those skilled in the art depending on the design of the CPW electrode.

Japanese Patent No. 52988849 JP-A-8-122722 US Patent Application Publication No. 20050201686 US Patent Application Publication No. 2003003164 US Patent Application Publication No. 200302227666

  Based on the above background, in a waveguide type optical device that operates in a wide band, it is possible to realize a configuration capable of effectively reducing driving loss and reducing microwave loss while appropriately ensuring speed matching and impedance matching. It is desired.

One embodiment of the present invention is a waveguide-type optical element including an optical waveguide formed on a substrate having an electro-optic effect, and a control electrode that controls a light wave propagating through the optical waveguide. The waveguide type optical element has a dielectric layer on an upper surface of the substrate on which the control electrode is formed, and a high-frequency signal is formed on a surface of the dielectric layer far from the control electrode. And a ground electrode provided so as to sandwich the RF electrode by a predetermined distance in the plane direction of the substrate, and the control electrode includes a central conductor and the center Side conductors formed so as to sandwich the conductor in the plane direction of the substrate with a predetermined distance therebetween, and the center conductor and the side conductor are each the length of the optical waveguide. It is divided into a plurality of segments so as to be electrically insulated from each other along the direction, and each segment of the central conductor has a length of the RF electrode with respect to the RF electrode formed in the dielectric layer. Electricity to different parts along the direction And each segment of each of the side conductors is electrically connected to a different portion along the length direction of the ground electrode with respect to each of the ground electrodes formed on the dielectric layer. Has been.
According to another aspect of the present invention, the length of each segment of the central conductor and each segment of the side conductor along the length direction of the optical waveguide is a high-frequency signal input to the RF electrode. 1/10 or less of the wavelength at the RF electrode.
According to another aspect of the present invention, the dielectric layer has a thickness of 50 μm or more.
According to another aspect of the invention, the substrate is a lithium niobate substrate.
According to another aspect of the invention, the optical waveguide is a Mach-Zehnder type optical waveguide.
According to another aspect of the present invention, the optical waveguide has a working portion in which an electric field applied by the central conductor acts on a light wave, and the optical waveguide has a portion of the substrate on which the working portion is formed. It is an optical waveguide having a rib-type structure formed higher than the surface of the surrounding portion of the substrate.

It is a figure which shows the structure of the waveguide type optical element which concerns on the 1st Embodiment of this invention. It is a figure which shows the structure of the board | substrate of the waveguide type optical element shown in FIG. It is a figure which shows the state which formed the dielectric material layer on the board | substrate of the waveguide type optical element shown in FIG. It is sectional drawing which looked at the cross section along the plane S of the waveguide type optical element shown in FIG. 1 from the AA direction. It is a figure which shows the structure of the waveguide type optical element which concerns on the 2nd Embodiment of this invention. It is a figure which shows the structure of the dielectric material layer of the waveguide type optical element shown in FIG. It is sectional drawing for demonstrating the connection of the board | substrate shown in FIG. 2, and the dielectric material layer shown in FIG.

  Embodiments of the present invention will be described below with reference to the drawings.

[First Embodiment]
FIG. 1 is a diagram showing a configuration of a waveguide type optical element according to the first embodiment of the present invention.
The waveguide type optical element 10 is a Mach-Zehnder type optical modulator, and includes a substrate 100 on which a Mach-Zehnder (MZ) optical waveguide 104 is formed, a dielectric layer 102 provided on the substrate 100, have. On the upper surface of the dielectric layer 102, a radio-frequency (RF) electrode 106 to which a high-frequency electrical signal is input is sandwiched between the RF electrode 106 by a predetermined distance in the plane of the dielectric layer 102. Provided ground electrodes 108a and 108b are formed. Thereby, the RF electrode 106 and the ground electrodes 108a and 108b constitute a CPW type electrode.

  A high-frequency signal is input from the upper left end of the RF electrode 106 in the figure, propagates toward the lower right end of the figure, and is terminated by, for example, a termination resistor (not shown) connected to the end.

FIG. 2 is a diagram illustrating a configuration of the substrate 100.
The substrate 100 is a substrate made of lithium niobate (LN), which is an electro-optic material, and is, for example, an X-cut LN substrate. The MZ type optical waveguide 104 has parallel waveguides 200 and 202, and a central conductor 204 is formed in a region on the surface of the substrate 100 sandwiched between the parallel waveguides 200 and 202. Further, side conductors 206 and 208 are formed on the side facing the central conductor 204 with the parallel waveguides 200 and 202 interposed therebetween, at positions separated from the central conductor 204 by a predetermined distance, respectively. The central conductor 204 and the side conductors 206 and 208 constitute a control electrode that controls the light wave propagating through the parallel waveguides 200 and 202. More specifically, the center conductor 204 and the side conductor 206 constitute a control electrode that controls the light wave propagating through the parallel waveguide 200, and the center conductor 204 and the side conductor 208 propagate through the parallel waveguide 202. The control electrode which controls the light wave to perform is comprised.

  In particular, the center conductor 204 and the side conductors 206 and 208 are divided into a plurality of segments that are divided so as to be electrically insulated from each other along the length direction of the parallel waveguides 200 and 202, respectively. . That is, along the length direction of the parallel waveguides 200 and 202, the center conductor 204 is divided into center conductor segments 204a to 204h, and the side conductors 206 are divided into side conductor segments 206a to 206h. Side conductor 208 is divided into side conductor segments 208a-208h.

  The side conductor segments 206a to 206h are respectively arranged to face the central conductor segments 204a to 204h with the parallel waveguide 200 interposed therebetween, and the side conductor segments 208a to 208h respectively sandwich the parallel waveguide 202. Are disposed opposite the central conductor segments 204a to 204h.

  The MZ type optical waveguide 104 can be manufactured by using various known methods such as a method of thermally diffusing metal titanium (Ti) on the substrate 100 and a method of processing into a ridge shape.

  FIG. 3 is a diagram showing an intermediate stage state in which the dielectric layer 102 is formed on the substrate 100. A dielectric layer 102 made of a dielectric material having a predetermined dielectric constant is formed on the substrate 100. Examples of the dielectric include tan δ (dielectric loss tangent), which is a dielectric constant and dielectric loss, such as a resin such as Benzocyclobutylene (BCB), polydimethylsiloxane (PDMS), and polyimide, and a sol-gel material of silica (silicon dioxide). Both can be made of a material that is small and suitable for the thick film forming step. A so-called thick film photosensitive permanent resist such as KI-1000 series manufactured by Hitachi Chemical Co., Ltd. or SU8 series manufactured by Microchem may be used. When a material such as LN having a high relative dielectric constant in the millimeter wave band is used as a substrate (the relative dielectric constant of LN is approximately 27 to 46 and has anisotropy), the relative dielectric constant in the millimeter wave band is ε. As

の材料を選択することが望ましい。

It is desirable to select these materials.

  The dielectric layer 102 has a surface of the substrate 100 that is electrically connected to the center conductor segments 204a to 204h at positions corresponding to the positions of the center conductor segments 204a to 204h on the substrate 100, respectively. Conductors 300 a to 300 h are formed from the surface toward the surface of the dielectric layer 102. Similarly, the dielectric layer 102 is electrically connected to the side conductor segments 206a to 206h at positions corresponding to the positions of the side conductor segments 206a to 206h on the substrate 100, respectively. The conductors 302a to 302h are formed from the surface of the substrate 100 toward the surface of the dielectric layer 102, and the side conductor segments 208a are arranged at positions corresponding to the positions of the side conductor segments 208a to 208h, respectively. Conductors 304 a to 304 h are formed from the surface of the substrate 100 toward the surface of the dielectric layer 102 so as to be electrically connected to ˜208 h.

  As described above, the RF electrode 106 constituting the CPW electrode and the ground electrodes 108a and 108b are formed on the upper surface of the dielectric layer 102 in the figure (FIG. 1). In particular, the RF electrode 106 is formed so as to be electrically connected to the conductors 300a to 300h. The ground electrode 108a is formed to be electrically connected to the conductors 302a to 302h, and the ground electrode 108b is formed to be electrically connected to the conductors 304a to 304h.

  That is, the central conductor segments 204a to 204h formed on the substrate 100 are along the length direction of the RF electrode 106 with respect to the RF electrode 106 formed on the dielectric layer 102 via the conductors 300a to 300h. Are electrically connected to different parts. Similarly, the side conductor segments 206a to 206h formed on the substrate 100 are connected to the ground electrode 108a formed on the dielectric layer 102 in the length direction of the ground electrode 108a via the conductors 302a to 302h. The side conductor segments 208a to 208h formed on the substrate 100 are electrically connected to different portions along the conductors 304a to 304h with respect to the ground electrode 108b formed on the dielectric layer 102. Are electrically connected to different portions along the length direction of the ground electrode 108b.

  FIG. 4 is a cross-sectional view of the cross section along the plane S of the waveguide type optical element 10 shown in FIG. 1 as viewed from the AA direction. The central conductor segment 204d shown in this cross-sectional view is a part of a segment formed by dividing the central conductor 204 provided in a region on the substrate 100 sandwiched between the parallel waveguides 200 and 202. The side conductor segment 206d is a part of a segment formed by dividing the side conductor 206 provided on the side facing the central conductor 204 across the parallel waveguide 200, and the side conductor segment 208d. Is a part of a segment formed by dividing the side conductor 208 provided on the side facing the central conductor 204 across the parallel waveguide 202.

  The central conductor segment 204d is electrically connected to the RF electrode 106 formed on the dielectric layer 102 by a conductor 300d formed on the dielectric layer 102. Similarly, the side conductor segment 206d is electrically connected to the ground electrode 108a formed on the dielectric layer 102 by the conductor 302d formed on the dielectric layer 102, and the side conductor segment 208d is electrically connected to the dielectric layer 102. The conductor 304 d formed on the body layer 102 is electrically connected to the ground electrode 108 b formed on the dielectric layer 102.

  The conductors 300a to 300h, 302a to 302h, and 304a to 304h are formed by stacking thin layers made of the same dielectric material, for example, and the dielectric layer 102 is formed when each of the thin layers is formed. It can be manufactured by repeatedly forming a conductor such as a metal on the portion to be formed (by a so-called build-up wiring manufacturing method). Alternatively, a separate substrate on which wiring electrodes are formed may be prepared and manufactured by so-called flip chip connection. Further, the control electrode layer and the RF electrode layer may be connected via an interposer made of glass or resin.

  The waveguide type optical element 10 having the above configuration includes a central conductor 204 that is a control electrode for controlling light waves propagating through the parallel waveguides 200 and 202 of the MZ type optical waveguide 104 formed on the substrate 100, and a lateral side. Each of the conductors 206 and 208 is composed of a plurality of segments that are electrically insulated from each other, and the central conductor segments 204a to 204h, the side conductor segments 206a to 206h, and the side conductor segments 208a to 208h are each a conductor 300a. Electrically connected to different portions along the length direction of the RF electrode 106 and the ground electrodes 108a and 108b formed on the dielectric layer 102 through ~ 300h, 302a to 302h, and 304a to 304h. It is connected to the.

  For this reason, the center conductor segments 204a to 204h, the side conductor segments 206a to 206h, and the side conductor segments 208a to 208h have high-frequency waves propagating through the RF electrode 106 and the ground electrodes 108a and 108b constituting the CPW electrode, respectively. Thus, potentials at corresponding portions of the RF electrode 106 and the ground electrodes 108a and 108b are applied, and light waves propagating through the parallel waveguides 200 and 202 are caused by high-frequency signals propagating through the RF electrode 106 and the ground electrodes 108a and 108b. Will be controlled.

  The top surface of the dielectric layer 102 on which the RF electrode 106 and the ground electrodes 108a and 108b are formed, the parallel waveguides 200 and 202, the central conductor segments 204a to 204h, the side conductor segments 206a to 206h, and the side conductor segments. Since the surface on the substrate 100 on which 208a to 208h is formed is separated by the thickness of the dielectric layer 102, the design of the RF electrode 106, the ground electrodes 108a and 108b, the parallel waveguides 200 and 202, and The design of the center conductor segments 204a to 204h, the side conductor segments 206a to 206h, and the side conductor segments 208a to 208h can be performed independently of each other to some extent.

  That is, regarding the electrical high frequency characteristics of the waveguide type optical element 10 such as speed matching, impedance matching, and microwave loss, the design of the RF electrode 106 and the ground electrodes 108a and 108b (more specifically, dielectric The dielectric constant of the material used for the layer 102 and the size and arrangement of the RF electrode 106 and the ground electrodes 108a and 108b) can achieve desired characteristics. On the other hand, regarding the reduction of the driving voltage necessary for the light modulation operation, The size and arrangement of the parallel waveguides 200 and 202, the central conductor segments 204a to 204h, the side conductor segments 206a to 206h, and the side conductor segments 208a to 208h on the substrate 100 are determined to increase the modulation efficiency. Characteristics can be realized.

  As a result, it is possible to drive while achieving both microwave loss, speed matching and impedance matching without reducing the mechanical stability due to the adoption of RF electrodes with a high aspect ratio and mushroom-like cross section as in the past. The voltage can be reduced.

  The thickness of the dielectric layer 102 is desirably 50 μm or more so that the electric field from the RF electrode 106 and the ground electrodes 108 a and 108 b does not reach the substrate 100. Accordingly, the propagation speed of the RF signal transmitted through the RF electrode 106 and the ground electrodes 108a and 108b is reduced from the influence of the substrate 100 having a high relative dielectric constant, and is controlled from the segment electrode in accordance with the propagation speed of the light transmitted through the optical waveguide. This can be done by feeding a signal.

  The conductors 300a to 300h, the conductors 302a to 302h, and the conductors 304a to 304h formed in the dielectric layer are not formed, but the central conductor segments 204a to 204h, the side conductor segments 206a to 206h, and the side conductor segments 208a to 208h. , The speed of the RF signal transmitted through the RF electrode portion is faster than the propagation speed of the light transmitted through the optical waveguide, and the thickness and relative dielectric constant of the dielectric layer 102, the RF electrode 106, and the ground electrodes 108a and 108b. Depends on the shape and spacing. The central conductor segments 204a to 204h, the side conductor segments 206a to 206h, the side conductor segments 208a to 208h, and the conductors 300a to 300h, the conductors 302a to 302h, and the conductors 304a to 304h formed on the dielectric layer are RF electrodes. It can be considered that the inductor is loaded. Therefore, the effective speed of the RF signal transmitted to each segment electrode in the propagation direction of the light does not include the center conductor segments 204a to 204h, the side conductor segments 206a to 206h, and the side conductor segments 208a to 208h. It is slower than the speed of transmission through the RF electrode.

  Central conductor segments 204a to 204h, side conductor segments 206a to 206h, side conductor segments 208a to 208h, and conductors 300a to 300h, conductors 302a to 302h, and conductors 304a to 304h formed in the dielectric layer The larger the capacitance and inductor, and the higher the frequency of their formation, the greater the reduction in effective speed.

In addition, when the thickness of the dielectric layer 102 is increased (for example, 1 mm or more), or when the number of conductor segment electrodes installed in the working portion is too small, the propagation direction of the light of the signal fed to the segment electrodes is increased. The effective speed of transmission cannot be adjusted to the propagation speed of light traveling through the optical waveguide (
Etc.).

  In this case, by installing a material having a high relative dielectric constant and a low dielectric loss in the vicinity of the RF electrode layer, it is possible to reduce the speed of the RF signal so that the signal transmitted to the segment electrode is transmitted in the propagation direction. The target speed may be adjusted to the propagation speed of light traveling through the optical waveguide. However, in terms of ensuring the manufacturing cost and reliability, the thickness and relative dielectric constant of the dielectric layer 102, the shape and interval design of the RF electrode 106 and the ground electrodes 108a and 108b, and the control signal are controlled by the central conductor segments 204a to 204a. 204h, side conductor segments 206a to 206h, side conductor segments 208a to 208h, and the circuit circuit capacity of the conductor connecting the RF electrode layer and the working electrode layer, the inductor, and the installation frequency are preferably matched.

  The lengths of the central conductor segments 204a to 204h, the side conductor segments 206a to 206h, and the side conductor segments 208a to 208h along the length direction of the parallel waveguides 200 and 202 are determined by the RF electrode 106, the ground The high frequency propagating through the electrodes 108a and 108b needs to be set to be short enough to be considered to propagate through the central conductor segments 204a to 204h, the side conductor segments 206a to 206h, and the side conductor segments 208a to 208h. is there.

  Specifically, the length of each of the central conductor segments 204a to 204h, the side conductor segments 206a to 206h, and the side conductor segments 208a to 208h along the length direction of the parallel waveguides 200 and 202 is the RF electrode. It is desirable that the frequency of the high-frequency signal input to 106 is 1/10 or less of the wavelength at the RF electrode 106.

  The RF electrode is made of a material having good conductivity such as gold (Au), silver (Ag), copper (Cu), or an alloy containing them. The linear expansion coefficient of these metals is generally Whereas it is 10-15 ppm / ° C., the linear expansion coefficient of LN depends on the composition and orientation, but is about 2 ppm / ° C., which is almost an order of magnitude smaller. Therefore, the difference in strain due to temperature change is large, and the stress on the electrode mounting portion is large. However, if the thickness of the substrate 100 is about 10 μm or less, the thickness is much smaller than that of the RF electrode and its side ground electrode, and the substrate 100 is responsive to the distortion of the RF electrode and its side ground electrode. However, even if the substrate 100 is warped or undulated, since the substrate 100 is thin, the difference in expansion and contraction between the front surface and the back surface of the substrate 100 is small, so that the substrate 100 is hardly cracked.

[Second Embodiment]
Next, a waveguide type optical element according to the second embodiment of the present invention will be described.
In the waveguide type optical element 10 according to the first embodiment, the dielectric layer 102 is formed on the substrate 100. However, in the waveguide type optical element according to the second embodiment, the portion of the dielectric layer is the same. The substrate portions are manufactured individually and then mechanically and electrically connected to each other.

  FIG. 5 is a diagram showing a configuration of a waveguide type optical element according to the second embodiment of the present invention. 5 and FIG. 6 and FIG. 7 to be described later, the same reference numerals are used for the same components as those in FIG. 1, FIG. 2, and FIG. 4, and the description in the first embodiment is used. And

  The waveguide type optical element 50 has the same configuration as the waveguide type optical element 10 according to the first embodiment, but includes a dielectric layer 502 instead of the dielectric layer 102.

  FIG. 6 is a diagram showing the configuration of the dielectric layer 502. The dielectric layer 502 is produced separately from the substrate 100. The dielectric layer 502 has the same configuration as that of the dielectric layer 102, but instead of the conductors 300a to 300h, 302a to 302h, and 304a to 304h, the back surface of the dielectric layer 502 (the surface facing the substrate 100). Have conductors 600a to 600h, 602a to 602h, and 604a to 604h each having a rectangular pad portion.

  For example, solder bumps are formed on the rectangular pad portions of the conductors 600a to 600h, 602a to 602h, and 604a to 604h. The substrate 100 and the dielectric layer 502 are mechanically and electrically connected to each other by flip chip bonding. Connected.

  FIG. 7 shows a cross section of the dielectric layer 502 including the conductors 600d, 602d, and 604d and a corresponding cross section of the substrate 100 in order to explain the connection between the substrate 100 and the dielectric layer 502. Rectangular pads are provided on the exposed portions of the conductors 600d, 602d, and 604d electrically connected to the RF electrode 106 and the ground electrodes 108a and 108b, respectively, on the back surface (lower surface in the drawing) of the dielectric layer 502. Solder bumps 700 to 704 are provided on the rectangular pad.

  As a result, the illustrated back surface of the dielectric layer 502 and the illustrated top surface of the substrate 100 are brought into close contact with each other, the temperature is raised to melt the solder bumps 700 to 704, and then cooled and solidified, whereby the conductors 600d, 602d, 604d, The conductor segment 204d and the side conductor segments 206d and 208d are electrically connected to each other, and the dielectric layer 502 and the substrate 100 are mechanically fixed. Note that such electrical connection and mechanical fixing by solder bumps are also performed on the conductors 600a to 600h, 602a to 602h, and 604a to 604h, and the waveguide type optical element 50 is the waveguide according to the first embodiment. The same configuration as that of the type optical element 10 is performed.

  In the waveguide type optical device 50 according to the present embodiment, the substrate 100 and the dielectric layer 502 are individually manufactured. Therefore, as in the waveguide type optical device 10 according to the first embodiment, a dielectric is formed on the substrate 100. Compared with the structure in which the body layer 102 is formed, the stress applied to the substrate 100 during manufacturing can be reduced. For this reason, the waveguide type optical element 50 according to the present embodiment can effectively prevent the substrate 100 from being cracked.

  In the first and second embodiments described above, an X-cut LN substrate is used as the substrate 100. However, the present invention is not limited to this, and a Z-cut LN substrate may be used. When a Z-cut LN substrate is used, the central conductor and the side conductor are arranged so that the electric field applied to the optical waveguide is directed in the thickness direction of the substrate. The effect similar to the effect in a form can be show | played.

  In the above-described embodiment, the parallel waveguides 200 and 202 (that is, the action part in which the electric field applied by the central conductor 204 acts on the light wave) is formed on the uniform surface of the substrate 100. The shapes and arrangements of the optical waveguide, the central conductor, and the side conductors on the substrate 100 are not limited to the illustrated shapes and arrangement. For example, the parallel waveguides 200 and 202 serving as the above-described working parts may be optical waveguides having a rib structure. That is, by processing the surface of the substrate 100, the portion of the substrate 100 on which the parallel waveguides 200 and 202, which are the working portions, are formed is higher than the surface of the surrounding portion of the substrate 100. It can be. By using the optical layer waveguide having such a rib structure, it is possible to enlarge the overlap between the electric field distribution generated by the central conductor and the intensity distribution of the light propagating through the optical waveguide, thereby reducing the driving voltage.

  Further, as in Patent Document 1, the electrode of the action part may be narrowed. In the configuration of the working electrode described in Patent Document 1, the working efficiency of the signal electric field and the optical electric field is high, and the impedance of the working electrode can be increased. For this reason, if the configuration of the working part electrode is used as an electrode formed on the substrate 100 of the above-described embodiment, the power that is branched and fed from the RF electrode 106 to the working part electrode is reduced and propagates through the RF electrode 106. Since the attenuation of the RF signal power to be reduced is small, a highly efficient modulation efficiency can be obtained.

  DESCRIPTION OF SYMBOLS 10, 50 ... Waveguide type optical element, 100 ... Substrate, 102, 502 ... Dielectric layer, 104 ... MZ type optical waveguide, 106 ... RF electrode, 108a, 108b ... Ground electrode, 200, 202 ... Parallel waveguide, 204 ... Center conductor, 204a-204h ... Center conductor segment, 206, 208 ... Side conductor, 206a-206h, 208a-208h ... Side conductor segments, 300a to 300h, 302a to 302h, 304a to 304h, 600a to 600h, 602a to 602h, 604a to 604h... Conductor, 700, 702, 704.

Claims (6)

A waveguide-type optical element comprising an optical waveguide formed on a substrate having an electro-optic effect, and a control electrode that controls a light wave propagating through the optical waveguide,
A dielectric layer on an upper surface of the substrate on which the control electrode is formed;
On the surface of the dielectric layer far from the control electrode, an RF electrode through which a high-frequency signal propagates and a ground electrode provided so as to sandwich the RF electrode by a predetermined distance in the surface direction of the substrate And are formed,
The control electrode includes a center conductor and a side conductor formed so as to sandwich the center conductor by a predetermined distance in the plane direction of the substrate, and the center conductor and the side conductor And is divided into a plurality of segments so as to be electrically insulated from each other along the length direction of the optical waveguide,
Each segment of the central conductor is electrically connected to a different part along the length direction of the RF electrode with respect to the RF electrode formed in the dielectric layer,
Each segment of each of the side conductors is electrically connected to a different portion along the length direction of the ground electrode with respect to each of the ground electrodes formed in the dielectric layer.
Waveguide type optical element. The lengths of the segments of the central conductor and the segments of the side conductors along the length direction of the optical waveguide are 1 / wavelength of the high-frequency signal input to the RF electrode at the RF electrode. 10 or less,
The waveguide type optical device according to claim 1. The dielectric layer has a thickness of 50 μm or more.
The waveguide type optical element according to claim 1 or 2. The substrate is a lithium niobate substrate;
The waveguide type optical device according to any one of claims 1 to 3. The optical waveguide is a Mach-Zehnder type optical waveguide.
The waveguide type optical device according to any one of claims 1 to 4. The optical waveguide has an action part in which an electric field applied by the central conductor acts on a light wave,
The optical waveguide is an optical waveguide having a rib-type structure in which the portion of the substrate on which the action portion is formed is formed higher than the surface of the portion of the substrate around it.
The waveguide type optical device according to any one of claims 1 to 5.

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