阅读说明：本技术 光调制器 (Optical modulator ) 是由 宫崎德一 冈桥宏佑 本谷将之 于 2019-08-15 设计创作，主要内容包括：本发明提供一种光调制器,在将多个马赫-曾德尔型光波导集成化而得到的光调制器中,能够进行低电压驱动,抑制串扰现象的发生。其特征在于,在具有电光效应的基板(1)形成有光波导(10)和控制电极,该光波导具有并列地配置多个马赫-曾德尔型光波导的结构,该控制电极具备GSSG型的差动电极结构,该GSSG型的差动电极结构是对于一个所述马赫-曾德尔型光波导在2个接地电极(G)(G1与G2或G2与G3)之间配置有2个信号电极(S)(S1与S2或S3与S4)的结构,在被相邻的马赫-曾德尔型光波导夹着的该接地电极(G2),设置有用于抑制信号串扰的串扰抑制单元。(The invention provides an optical modulator, which is obtained by integrating a plurality of Mach-Zehnder optical waveguides and can be driven at low voltage to inhibit the generation of crosstalk. An optical waveguide (10) having a structure in which a plurality of Mach-Zehnder type optical waveguides are arranged in parallel, and a control electrode having a GSSG type differential electrode structure in which 2 signal electrodes (S) (S1 and S2 or S3 and S4) are arranged between 2 ground electrodes (G) (G1 and G2 or G2 and G3) for one of the Mach-Zehnder type optical waveguides are formed on a substrate (1) having an electro-optical effect, and crosstalk suppression means for suppressing signal crosstalk is provided on the ground electrode (G2) sandwiched between adjacent Mach-Zehnder type optical waveguides.)

1. A light modulator is characterized in that a light source is provided,

an optical waveguide and a control electrode are formed on a substrate having an electro-optical effect,

the optical waveguide has a structure in which a plurality of Mach-Zehnder type optical waveguides are arranged in parallel,

the control electrode has a GSSG-type differential electrode structure in which 2 signal electrodes S are arranged between 2 ground electrodes G for one Mach-Zehnder type optical waveguide,

a crosstalk suppression means for suppressing signal crosstalk is provided on the ground electrode sandwiched between adjacent Mach-Zehnder type optical waveguides.

2. The light modulator of claim 1,

the crosstalk suppression unit is set such that at least a portion of an upper surface of the ground electrode is higher than an upper surface of the signal electrode and at least a portion of a lower surface of the ground electrode is lower than a lower surface of the signal electrode.

3. The light modulator of claim 2,

the side surface portion of the ground electrode facing the signal electrode is divided from the other body portion of the ground electrode, and electrical connection is locally performed between the side surface portion and the body portion along the direction in which the optical waveguide extends.

Technical Field

The present invention relates to a modulator, and more particularly, to an optical modulator including a GSSG-type differential electrode structure in which a plurality of mach-zehnder type optical waveguides are arranged in parallel, and 2 signal electrodes S are arranged between 2 ground electrodes G for one mach-zehnder type optical waveguide.

Background

In recent years, there has been an increasing demand for higher speed and smaller optical modulators. Therefore, studies have been made on directly driving a modulator with an output Signal of a DSP (Digital Signal Processor) serving as a Signal processing element or incorporating a driving element for Signal amplification in a housing of an optical modulator.

In the output of the DSP or the driver element, a differential output structure is used in order to suppress the influence of external noise or the like during line transmission and to enable operation at a low voltage. Heretofore, in an optical modulator of a crystal (EO crystal) having an electro-optical effect such as Lithium Niobate (LN), optical modulation using a differential signal is performed using a GSGSG type electrode structure in which ground electrodes G are arranged on both sides of 2 signal electrodes S with respect to one mach-zehnder type optical waveguide as shown in patent document 1.

As an electrode arrangement for applying a differential signal, as shown in patent document 2, a so-called GSSG type electrode structure is proposed in which 1 mach-zehnder type optical waveguide is formed on an LN substrate, a signal electrode is arranged on each branched waveguide of the mach-zehnder type optical waveguide, and a ground electrode is arranged outside the optical waveguide in proximity to each signal electrode. Patent document 3 proposes a GSSG-type electrode structure using a differential electric signal in a semiconductor-type phase modulator.

On the other hand, for a modulator for coherent communication, an optical modulator having a plurality of mach-zehnder type optical waveguides integrated, such as a nested optical waveguide in which a plurality of mach-zehnder type optical waveguides are arranged in a nested shape, is used. In the conventional GSGSG type electrode structure, the number of electrodes is increased, and layout of wiring is difficult.

In addition, in the integrated optical modulator, the interval between electrodes of the mach-zehnder optical waveguides is narrowed, and a crosstalk phenomenon of modulation signals in adjacent optical modulation sections is likely to occur. Further, as the modulation speed increases, the occurrence of the crosstalk phenomenon becomes more significant, and the quality of the modulation output deteriorates to a large extent.

As a method of suppressing the crosstalk phenomenon, it is effective to enlarge the signal interval between adjacent optical modulation sections and enlarge the ground electrode width between signal electrodes, but for these purposes, it is also necessary to enlarge the interval of the optical waveguide, and the length required for bending the optical waveguide such as a branch section becomes long, and not only the size of the optical modulator itself becomes large, but also the increase in optical loss due to bending cannot be ignored.

If the GSSG-type electrode structure is adopted to reduce the number of electrodes, the gap between the ground electrodes is wider than the gsgsgsg-type electrode structure, and therefore, an electric field is likely to leak to the adjacent modulation section (action section), and a crosstalk phenomenon is more likely to occur.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2000-56282

Patent document 2: japanese laid-open patent publication No. 2-291518

Patent document 3: japanese patent laid-open publication No. 2017-142487

Disclosure of Invention

Problems to be solved by the invention

An object of the present invention is to solve the above-described problems and provide an optical modulator in which crosstalk can be suppressed while performing low-voltage driving in an optical modulator in which a plurality of mach-zehnder type optical waveguides are integrated.

Means for solving the problems

In order to solve the above problem, the optical modulator of the present invention has the following technical features.

(1) An optical modulator is characterized in that an optical waveguide having a structure in which a plurality of Mach-Zehnder type optical waveguides are arranged in parallel and a control electrode having a GSSG type differential electrode structure in which 2 signal electrodes S are arranged between 2 ground electrodes G for one Mach-Zehnder type optical waveguide are formed on a substrate having an electro-optical effect, and crosstalk suppression means for suppressing signal crosstalk is provided on the ground electrode sandwiched between adjacent Mach-Zehnder type optical waveguides.

(2) The optical modulator according to the above (1), wherein the crosstalk suppression unit is set such that at least a part of an upper surface of the ground electrode is higher than an upper surface of the signal electrode and at least a part of a lower surface of the ground electrode is lower than a lower surface of the signal electrode.

(3) The optical modulator according to the above (2), wherein a side surface portion of the ground electrode facing the signal electrode is separated from another body portion of the ground electrode, and the side surface portion and the body portion are electrically connected locally along a direction in which the optical waveguide extends.

Effects of the invention

The present invention is configured to provide an optical modulator capable of low-voltage driving and suppressing the occurrence of crosstalk, because an optical waveguide having a structure in which a plurality of mach-zehnder type optical waveguides are arranged in parallel and a control electrode having a GSSG-type differential electrode structure in which 2 signal electrodes S are arranged between 2 ground electrodes G for one mach-zehnder type optical waveguide are formed on a substrate having an electro-optical effect, and crosstalk suppressing means for suppressing signal crosstalk is provided on the ground electrode sandwiched between adjacent mach-zehnder type optical waveguides.

Drawings

Fig. 1 is a diagram showing a first embodiment of an optical modulator according to the present invention.

Fig. 2 is a diagram showing a distribution of power lines in the optical modulator of fig. 1.

Fig. 3 is a diagram showing a second embodiment of the optical modulator according to the present invention.

Fig. 4 is a diagram showing a third embodiment of the optical modulator according to the present invention.

Fig. 5 is a diagram showing a fourth embodiment of the optical modulator according to the present invention.

Fig. 6 is a view illustrating a connection structure between a side portion and a main body portion of the ground electrode of fig. 5.

Fig. 7 is a diagram showing a fifth embodiment of the optical modulator according to the present invention.

Fig. 8 is a diagram showing a sixth embodiment of the optical modulator according to the present invention.

Fig. 9 is a diagram showing a seventh embodiment of the optical modulator according to the present invention.

Fig. 10 is a diagram showing an eighth embodiment of the optical modulator according to the present invention.

Fig. 11 is a diagram illustrating a relationship between a distance between signal electrodes and a distance between a signal electrode and a ground electrode in the optical modulator of the present invention.

Fig. 12 is a diagram showing a ninth embodiment of the optical modulator according to the present invention.

Fig. 13 is a diagram showing a tenth embodiment of the optical modulator according to the present invention.

Detailed Description

The optical modulator of the present invention will be described in detail below using preferred embodiments.

As shown in fig. 1, the optical modulator of the present invention is characterized in that an optical waveguide 10 having a structure in which a plurality of mach-zehnder type optical waveguides are arranged in parallel and a control electrode having a GSSG-type differential electrode structure in which 2 signal electrodes S (S1 and S2, or S3 and S4) are arranged between 2 ground electrodes G (G1 and G2, or G2 and G3) for one mach-zehnder type optical waveguide are formed on a substrate 1 having an electro-optical effect, and crosstalk suppression means for suppressing signal crosstalk is provided on the ground electrode (G2) sandwiched between adjacent mach-zehnder type optical waveguides.

The substrate having an electro-optical effect used in the present invention may be a dielectric substrate such as lithium niobate, a resin substrate such as an EO polymer, a semiconductor substrate, or the like. When a dielectric substrate is used as the structure in which the waveguide is disposed below the signal electrode, a Z-cut substrate in which the electro-optical effect is largest in the thickness direction of the substrate is preferable.

When the substrate 1 having the electro-optical effect is used as a thin plate of, for example, 20 μm or less, the holding substrate 2 is used to improve the mechanical strength. The holding substrate 2 is made of a material having a lower refractive index than the substrate 1 having the electro-optical effect, and is made of, for example, quartz, glass, resin, or the like.

An optical modulator of the present invention includes an optical waveguide in which a plurality of mach-zehnder type optical waveguides are arranged in parallel, as in a nested optical waveguide, and fig. 1 shows a cross-sectional view in which 2 adjacent mach-zehnder type optical waveguides are cut perpendicularly to the traveling direction of an optical wave. The ridge portions (ridge portions) 10 of the substrate 1 located below the signal electrodes S1 and S2 are 2 branched waveguides constituting a mach-zehnder type optical waveguide. In addition, the ridge portion 10 located below the signal electrodes S3 and S4 is a branched waveguide of the adjacent mach-zehnder type optical waveguide. The optical waveguide may be formed only on the ridge portion of the substrate, but as described later, the optical waveguide may be formed by thermally diffusing Ti on the LN substrate.

The control electrodes are electrodes formed of conductors such as Au on the substrate by plating, and include signal electrodes (S1 to S4) and ground electrodes (G1 to G3) for applying a modulation signal, and DC bias electrodes for performing phase adjustment and drift control.

The present invention is characterized in that a differential electrode structure of GSSG type is provided to a control electrode, particularly a signal electrode or a ground electrode to which a high-speed modulation signal is applied. In the conventional GSSG type shown in patent document 2, since the distance between the differential signal electrodes is widely separated, when an electric field is applied to the optical waveguide, the electric field generated between the adjacent signal electrode and the ground electrode is exclusively used. However, in the optical modulator of the present invention, as shown in fig. 2, not only the electric field generated between the signal electrode and the ground electrode as in the conventional art (between S1 and G1 or between S2 and G2) but also the electric field between the signal electrodes (between S1 and S2) is used by making the distance between the differential signal electrodes close. Instead, the electric field between the signal electrodes is positively utilized. As shown in fig. 2, the strength of the electric field between the signal electrodes (the electric field generated by the potential difference between the in-phase signal and the inverted signal of the differential signal between S1 and S2) is higher than the strength of the electric field between the signal electrode and the ground electrode, and therefore the effect of reducing the driving voltage by the differential signal can be further improved.

In order to suppress the occurrence of crosstalk, which is a drawback of the GSSG type, the present invention is characterized in that a crosstalk suppression means for suppressing signal crosstalk is provided on the ground electrode sandwiched between adjacent mach-zehnder type optical waveguides. As a specific configuration of the crosstalk suppression unit, as shown in fig. 1, at least a part of the upper surface (height HL2) of the ground electrodes (G1 to G3) is set to be higher than the upper surface (height HL1) of the signal electrodes (S1 to S4), and at least a part of the lower surface (height LL2) of the ground electrode is set to be lower than the lower surface (height LL1) of the signal electrode. In fig. 1, the signal electrode S4 and the ground electrode G3 are used for height comparison for convenience, but this structure is also applicable to the relationship between the signal electrode (S1 and S2, or S3 and S4) and the ground electrode G2.

Fig. 3 and 4 show another embodiment of the present invention, in which a high portion is partially formed on the upper surface of the ground electrode. In fig. 3, when the ground electrode (G1 to G3) is laminated on the upper surface of the resin layer 3 made of a photoresist or other resin layer 3 made of either a thermoplastic resin or a thermosetting resin, the projection 30 is formed on the upper surface of the ground electrode in accordance with the resin layer 3. The electric field due to crosstalk is suppressed from reaching the adjacent mach-zehnder type optical waveguide or the adjacent signal electrode across the ground electrode by the protruding portion 30. Instead of the resin layer, a dielectric (SiO) may be used₂Etc.), but in the case of using a photoresist, a relatively thick layer thicker than 1 μm (about 3 to 5 μm) can be easily formed, and therefore, is more preferable in the present invention. Also, the photoresist enables to control the pattern shape with high precision and ease by the photolithography processThickness, etc., and thus can be more preferably used in the present invention.

In fig. 4, between the signal electrodes (S1 to S4) and the ground electrodes (G1 to G3), the side surface portion 41 of the ground electrode, on which the electric field concentrates, is set at the same position as the signal electrode. In addition, a portion higher than the upper surface of the signal electrode and a portion lower than the lower surface of the signal electrode are formed in the other portions of the ground electrode. The resin layer 4 may be used for forming the portions having different heights. Of course, a method of forming electrodes having different thicknesses in multiple stages is used for a step that cannot be formed only by the resin layer 4.

Fig. 5 to 7 show another embodiment, in which the side surface portions (5, 6) of the ground electrodes (G1 to G3) facing the signal electrodes (S1 to S4) are separated from the other body portions (51, 61) of the ground electrodes (G1 to G3), and electric connection portions (50, 60) are partially formed between the side surface portions and the body portions along the direction in which the optical waveguide extends.

In fig. 5, the side surface portion 5 and the main body portion 51 of the ground electrode are the same height, but in fig. 7, the side surface portion 6 where the electric field concentrates between the signal electrode and the ground electrode is set to the same height as the signal electrode, and the height of the main body portion 61 (the ground electrode portion located on the outer side than the side surface portion 6 concerned) is set higher. In the configuration of fig. 6, the electric field is further suppressed from leaking to the adjacent signal electrode beyond the ground electrode, and crosstalk is further suppressed.

In fig. 5 and 7, the connection portions (50, 60) electrically connecting the side surface portions (5, 6) of the ground electrode and the body portions (51, 61) are partially arranged along the direction in which the side surface portion 5 extends (also the direction in which the optical waveguide extends). The connecting portion 50 may be integrally formed of the same material as the side portion and the main body portion. The arrangement interval of the connecting portions 50 may be set to be not more than 4 minutes and preferably about 1 minute or 10 minutes of the wavelength of the microwave of a frequency equal to the modulation frequency or the modulation symbol rate used in the modulation signal.

As shown in fig. 8, the connection portion 70 may be formed to have an upper surface lower than the side surface portion 7 and a lower surface higher than the connection portion 70 by patterning the electrodes a plurality of times to form electrodes having different thicknesses, thereby partially connecting the main body portion 71 and the side surface portion 7.

Fig. 9 and 10 show another example, in which a stronger electric field is generated between the signal electrodes (between S1 and S2, or between S3 and S4) in the GSSG type differential electrode structure used in the optical modulator of the present invention. By disposing the optical waveguide at this position, light modulation can be performed efficiently.

Fig. 9 is a view of the optical waveguide 11 obtained by forming the thermal diffusion Ti or the like in the ridge portion of the substrate 1, and the optical waveguide 11 is formed not directly below the signal electrodes (S1 to S4) but at a position closer to another signal electrode than directly below.

In fig. 10, since the ridge portion 10 is an optical waveguide, the signal electrode S1 is disposed closer to the ground electrode G1 side and the signal electrode S2 is disposed closer to the ground electrode G2 side so that the ridge portion 10 is more exposed between the signal electrodes S1 and S2.

The thickness of the substrate at the ridge portion is about 2 to 4 μm, and the thickness of the substrate 1 excluding the ridge portion is set to 1 to 2 μm.

Fig. 11 is a diagram illustrating a relationship between a distance W1 between signal electrodes and a distance W2 between a signal electrode and a ground electrode in the optical modulator of the present invention. Assume that a signal voltage of + V is applied to the signal electrode S1 and a signal voltage of-V is applied to the signal electrode S2. In this case, since the ground electrode is ± 0, a potential difference V is generated between the signal electrode and the ground electrode (S1 and G1, S2 and G2). On the other hand, a potential difference of 2V is generated between the signal electrodes (S1 and S2).

In the optical modulator of the present invention, in order to effectively utilize the potential difference 2V between the signal electrodes, it is necessary to set the distance W1 to be less than 2 times the distance W2.

In the above description, the description has been mainly given of the example using the holding substrate 8 as shown in fig. 12, but may be configured to be held by the holding substrate 80 through the low refractive index layer 9 as shown in fig. 13. In this case, the holding substrate 80 does not need to have a low refractive index as compared with the substrate 1. In addition, an adhesive such as a resin may be used for the low refractive index layer.

Industrial applicability

As described above, according to the present invention, it is possible to provide an optical modulator in which a plurality of mach-zehnder type optical waveguides are integrated, and which can be driven at a low voltage and can suppress the occurrence of a crosstalk phenomenon.

Description of the reference symbols

1 substrate with electro-optical effect

10 Ridge section (optical waveguide)

11 optical waveguide

2. 8 holding substrate (Low refractive index material)

9 low refractive index layer

80 holding substrate

S1-S4 signal electrode

G1-G3 grounding electrode