JP2009244324A - Optical waveguide element module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical waveguide element module which has a filter circuit including a capacitor disposed on a line for inputting a modulation signal into a modulation electrode of an optical waveguide element, the optical waveguide element module having a smoothed optical response frequency characteristic over a wide band of several dozen GHz even when using a multilayer ceramic capacitor as the capacitor. <P>SOLUTION: The optical waveguide element module includes: an optical waveguide element having a substrate 1 formed of a material having an electro-optic effect, an optical waveguide 2 formed on the substrate, and a modulation electrode (3) for modulating optical waves propagated over the optical waveguide; and a filter circuit (7) which is disposed on a line, inputs a modulation signal into the modulation electrode and includes a capacitor. As for the capacitor, only a multilayer ceramic capacitor having ≤3 pF per capacitance is used. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical waveguide device module, and more particularly to an optical waveguide device module in which a filter circuit including a capacitor is arranged on a line for inputting a modulation signal to a modulation electrode of the optical waveguide device.

2. Description of the Related Art Conventionally, in an optical communication field or an optical measurement field, an optical waveguide element in which an optical waveguide is formed on a substrate having an electrooptic effect, such as an optical modulator, is frequently used as a means for controlling an optical wave.
In recent years, when evaluating an optical waveguide element, attention has been paid to a characteristic called jitter that indicates temporal fluctuation of an optical signal obtained when the optical waveguide element is driven. Jitter is an index indicating temporal fluctuation of an optical signal, and is defined as the width of a place where signals cross each other by integrating optical eye pattern waveforms.

In order to improve the jitter of the optical signal obtained when the optical waveguide element is driven, the following characteristics improvements are required for the optical waveguide element and the driver for driving and controlling the optical waveguide element.
(1) Driver for driving The gain has a flat frequency characteristic from a low frequency region to a high frequency region so that the input electric signal is amplified without deterioration.
(2) Optical waveguide element The frequency of the electrical / optical conversion response is flat from low frequency to high frequency so that the input electrical signal is converted into an optical signal without deterioration.

  As described above, when the frequency characteristics of the driving driver and the optical waveguide element are infinitely flat (there is no frequency dependence), the above-mentioned jitter does not occur. In both optical modulators, the frequency characteristics in the low frequency range are not flat, or the frequency characteristics in the high frequency range tend to deteriorate to the right, and therefore jitter occurs. In particular, in an optical waveguide device having a transmission speed of the order of gigahertz, the occurrence of this jitter is an important problem.

As a method of flattening the response characteristics of the electric signal applied to the optical waveguide element and the light wave output from the optical waveguide element, as shown in FIG. 1, the modulation of the driver 6 for driving is applied to the modulation electrode 3 of the optical waveguide element. A method of applying a signal through a relay substrate 7 such as a filter circuit when applying a signal, or connecting a termination circuit 8 such as a termination resistor to the termination portion of the modulation electrode 3 is performed. 1 includes an optical waveguide 2 formed on a substrate 1 having an electro-optic effect, and a modulation electrode 3 for modulating a light wave propagating through the optical waveguide 2 (a signal electrode and a ground electrode are included in the modulation electrode). However, only the arrangement of the signal electrodes is shown in FIG. 1 for the sake of simplicity. In addition, an optical fiber for input 4 and an optical fiber for output 5 are connected to the optical waveguide element, and are responsible for the incidence of the light wave to the optical waveguide element and the emission of the light wave from the optical waveguide element.
The optical waveguide element is accommodated in one housing 9 together with the relay substrate 7 and the termination circuit 8.

As the one using the termination circuit, there is one that improves the frequency characteristics of the optical modulator by adjusting the impedance of the termination portion of the modulation electrode of the optical modulator, as in Patent Document 1.
However, it is difficult to flatten the frequency characteristics up to a high frequency region that enables transmission of several tens of Gbps with only the termination circuit, and traveling wave type light can be achieved only by adjusting the impedance of the termination portion disclosed in Patent Document 1. Of the frequency characteristics of the electrical / optical conversion response of the modulator, it is also difficult to change the frequency to be adjusted.
Japanese Patent No. 3088888

Patent Document 2 or 3 discloses a relay board having a filter circuit. In order to flatten the frequency characteristics of the electrical / optical response, a high-pass filter in which a capacitor 10 and a resistor 11 are connected in parallel as shown in FIG. 2 is used as a basic configuration of the filter circuit. Reference numerals 12 and 13 in FIG. 2 denote electric lines, and reference numeral 7 denotes a relay board including a filter circuit.
JP 2007-10942 A Japanese Patent Application No. 2006-26396 (Filing date: September 28, 2006)

In particular, Patent Document 2 discloses that a capacitor and a resistor constituting a filter circuit on a relay substrate are constituted by a plurality of thin films on an electric line.
The circuit configuration using such a thin film contributes to the downsizing of the filter circuit, but the manufacturing process is complicated, and in particular, the process of forming and removing the thin film many times is required to configure the capacitor with a thin film. Necessary. In addition, it is necessary to adjust the value of the capacitor and resistance according to the frequency characteristics of the optical waveguide element, but in the case of resistance, it can be easily adjusted by trimming only a part of the thin film, In the case of a capacitor, if trimming is performed, the electrodes may be short-circuited, which makes adjustment difficult.

The inventors of the present invention tried to solve this problem by using a multilayer ceramic capacitor.
Specifically, as shown in FIG. 3, the electric lines 12 and 13 are formed on the relay substrate body 14, and the chip-type multilayer ceramic capacitor 10 is disposed so as to connect the two electric lines. Multilayer ceramic capacitors have the advantage of being extremely small and available at low cost, such as 0.3 mm in length, 0.6 mm in width, and 0.3 mm in height (0603 size).

  In the multilayer ceramic capacitor, as shown in FIG. 4 (showing a cross-sectional view of the capacitor), electrodes 22 and 23 are formed in a comb-teeth shape so as to sandwich the ceramic material 24, and each electrode is connected to the terminal 20 at both ends. 21 is connected.

However, when a multilayer ceramic capacitor is used, it has been found that the frequency characteristic of the optical response generates a resonance phenomenon (resonance frequency f ₀ ) as shown in FIG. For this reason, a multilayer ceramic capacitor was considered unsuitable as a component of the filter circuit connected to the optical waveguide element.

  The problem to be solved by the present invention is to solve the above-mentioned problems, in an optical waveguide device module in which a filter circuit including a capacitor is arranged on a line for inputting a modulation signal to a modulation electrode of the optical waveguide device. An object of the present invention is to provide an optical waveguide device module capable of flattening optical response frequency characteristics over a wide band of several tens of GHz even when a multilayer ceramic capacitor is used as the capacitor.

In order to solve the above-mentioned problems, the present inventors have conducted extensive research, and as a result, found out that the cause of the resonance phenomenon is due to the comb-shaped electrode as shown in FIG. The present invention has been completed by discovering that the resonance frequency f _{0 of} FIG. 5 changes corresponding to the capacitance, and in particular, f ₀ tends to decrease as the capacitance increases. is there.

In the invention according to claim 1, an optical waveguide element having a substrate made of a material having an electro-optic effect, an optical waveguide formed on the substrate, and a modulation electrode that modulates a light wave propagating through the optical waveguide; In the optical waveguide device module including a filter circuit including a capacitor, which is disposed on a line for inputting a modulation signal to the modulation electrode, the capacitor is a multilayer ceramic capacitor, and one capacitance is 3 pF or less It is characterized by using only those.
The “optical waveguide device module” in the present invention means a device in which a filter circuit is connected to the optical waveguide device, and is limited to one housed in one housing 9 as shown in FIG. Absent. Further, the filter circuit is not limited to the one provided on the relay substrate 7 as shown in FIG. 1, and the case where the filter circuit is incorporated on the substrate on which the optical waveguide element is formed is also included in the technical scope of the present invention. It is.

  According to a second aspect of the present invention, in the optical waveguide element module according to the first aspect, when a plurality of multilayer ceramic capacitors are used, the capacitors are arranged by stacking the multilayer ceramic capacitors on the filter circuit board. Features.

  According to a third aspect of the present invention, in the optical waveguide element module according to the first or second aspect, the filter circuit includes an electric resistance due to a film body formed on the filter circuit substrate.

  According to a fourth aspect of the present invention, in the optical waveguide element module according to the third aspect, a multilayer ceramic capacitor is disposed so as to overlap the electric resistance.

  The invention according to claim 5 is the optical waveguide element module according to any one of claims 1 to 4, characterized in that a termination circuit is connected to a termination portion of the modulation electrode.

  According to the invention of claim 1, an optical waveguide device comprising a substrate made of a material having an electro-optic effect, an optical waveguide formed on the substrate, and a modulation electrode that modulates a light wave propagating through the optical waveguide; In the optical waveguide device module including a filter circuit including a capacitor, which is disposed on a line for inputting a modulation signal to the modulation electrode, the capacitor is a multilayer ceramic capacitor, and one capacitance is 3 pF or less Therefore, even when a multilayer ceramic capacitor is used for the filter circuit, it is possible to flatten the frequency characteristics of the electrical / optical response over a wide band exceeding 20 GHz.

  According to the second aspect of the present invention, when a plurality of multilayer ceramic capacitors are used, since the multilayer ceramic capacitors are stacked on the filter circuit board, the capacitor does not increase in size, and the capacitor parallel circuit Can be easily realized, and can cope with a case where a capacitance larger than 3 pF is required.

  According to the invention of claim 3, since the filter circuit includes an electric resistance due to the film body formed on the filter circuit substrate, the electric resistance of the filter circuit can be reduced, and the resistance value can be easily adjusted by trimming or the like. It is also possible. For this reason, the capacitor capacity can be adjusted by replacing the multilayer ceramic capacitor or using multiple capacitors, and the resistance value of the electrical resistance can be adjusted by trimming, etc., to easily adjust the filter circuit suitable for each optical waveguide element. Is possible.

  According to the fourth aspect of the present invention, the multilayer ceramic capacitor is disposed so as to overlap the electric resistance, so that the filter circuit can be further downsized.

  According to the invention of claim 5, since the termination circuit is connected to the termination portion of the modulation electrode, the electrical / optical response frequency can be flattened by combining both the filter circuit and the termination circuit. It is possible to adjust the planarization of the optical waveguide element. In addition, the reflection characteristic (S11 characteristic) of the optical waveguide element by the termination circuit can be improved.

Hereinafter, the present invention will be described in detail using preferred examples.
The present invention relates to an optical waveguide device having a substrate made of a material having an electro-optic effect, an optical waveguide formed on the substrate, a modulation electrode for modulating a light wave propagating through the optical waveguide, and the modulation electrode And an optical waveguide device module including a filter circuit including a capacitor, the capacitor being a multilayer ceramic capacitor, and having only one capacitance of 3 pF or less. It is characterized by using.
The optical waveguide element module of the present invention is basically the same as the conventional one shown in FIG. 1 except that a specific multilayer ceramic capacitor is used. Therefore, it is possible to easily obtain an optical waveguide element module with flattened electrical / optical response frequency characteristics without greatly changing the conventional manufacturing process.

An optical waveguide device to which the present invention is applied will be described.
The substrate 1 is a substrate having an electro-optic effect, and is composed of, for example, lithium niobate, lithium tantalate, PLZT (lead lanthanum zirconate titanate), and a quartz-based material. It is preferable to use lithium niobate (LN) because it is composed of an X-cut plate, a Y-cut plate, and a Z-cut plate, and is particularly easy to configure as an optical waveguide device and has high anisotropy. .

The optical waveguide 2 is a so-called Mach-Zehnder type optical waveguide, and can be formed on the substrate 1 by diffusing titanium (Ti) or the like on the substrate surface by a thermal diffusion method or a proton exchange method. As another method, it is also possible to form an optical waveguide by forming a ridge structure in a portion corresponding to the optical waveguide as shown in Patent Document 4. Furthermore, the above-described method using Ti or the like and a ridge structure can be used in combination.
JP-A-6-289341

In order to modulate the light wave propagating through the optical waveguide 2, a modulation electrode is disposed on the upper side or the vicinity of the optical waveguide 2 as necessary.
The modulation electrode can be formed on the front surface or the back surface of the substrate 1 by forming a Ti / Au electrode pattern, a gold plating method, or the like. The modulation electrode includes a signal electrode 3 that propagates a modulation signal (AC signal or DC signal) and a ground electrode that is disposed around the signal electrode.

Although not particularly shown, a buffer layer such as SiO ₂ can be formed between the substrate 1 and the modulation electrode described above. Accordingly, it is possible to effectively prevent the light wave propagating through the optical waveguide from being absorbed or scattered by the modulation electrode. It also contributes to speed matching between the modulation signal applied from the modulation electrode and the light wave guided in the optical waveguide.

  In the optical waveguide device module of the present invention, the multilayer ceramic capacitor 10 is arranged as shown in FIG. Electric lines 12 and 13 are formed on a relay substrate body (a substrate constituting an optical waveguide element may be used as a relay substrate body) 14, and a multilayer ceramic capacitor chip is disposed so as to electrically connect both.

The multilayer ceramic capacitor disposed in the filter circuit needs to be 3 pF or less. By using a multilayer ceramic capacitor having such a capacitance, it has been confirmed that the generation of the resonance frequency in the electrical / optical response frequency characteristics as shown in FIG. 5 is shifted to f ₀ = 25 GHz.

Moreover, when securing a capacitance larger than 3 pF, it is preferable to use a plurality of multilayer ceramic capacitors. In this case, as shown in FIG. 6, by arranging the laminated ceramic capacitors 10 on the filter circuit board 14, a parallel circuit of capacitors can be easily realized without increasing the size of the filter circuit board.
Moreover, by stacking the multilayer ceramic capacitors, the resonance frequency can be shifted to a higher frequency side, and the high frequency characteristics can be improved. For example, when one capacitor of 2 pF is mounted, the resonance frequency is 30 GHz. However, when two capacitors of 1 pF are stacked, the resonance frequency is shifted to 45 GHz which is a resonance frequency of 1 pF.

In order to configure the electric resistance in the filter circuit, it is possible to use a chip-type resistor as in the case of the capacitor. However, as shown in Patent Document 2, a film body such as Ti ₂ N formed on the substrate 14 is used. It is also possible to use electrical resistance due to. The electrical resistance of such a film body can reduce the electrical resistance of the filter circuit, and can easily adjust the resistance value by trimming or the like.

  Furthermore, as shown in FIG. 7, it is possible to further reduce the size of the filter circuit by arranging the multilayer ceramic capacitor 10 so as to overlap the electric resistance 11 of the film body.

  Further, in the optical waveguide element module of the present invention, as shown in FIG. 1, a termination circuit 8 can be connected to the termination portion of the modulation electrode. As a result, as described in Patent Documents 1 to 3, the effect of flattening the electrical / optical response frequency of the termination circuit and the effect of improving the reflection characteristic (S11 characteristic) of the optical waveguide element can also be expected. In particular, a synergistic effect by the combination with the filter circuit of the present invention can be expected.

Next, an experimental example will be described regarding the change in the frequency characteristics of the electrical / optical conversion response regarding the optical waveguide element module of the present invention.
An LN modulator (manufactured by Sumitomo Osaka Cement Co., Ltd., T.MXH1.5-10) was used as the optical waveguide element, and a high-pass filter shown in FIG. 2 was installed between the input interface and the modulation electrode.

Capacitors 1, 2, and 3 pF of multilayer ceramic capacitors (manufactured by Matsushita Electric Industrial Co., Ltd., ECD series 0603 size) are used for the capacitors of the high pass filter, and the resistors are resistors formed between Ti electric wires with Ti ₂ N thin films The value was about 10Ω.

The frequency characteristic of the electrical / optical conversion response was measured by an optical component analyzer (manufactured by Agilent, 86030A), and the resonance frequency f ₀ was measured. As a result, f ₀ was 25 GHz for 3 pF and f ₀ was 30 GHz for 2 pF. Furthermore, in the case of ₁ pF, f ₀ was 45 GHz.
From this, when using the multilayer ceramic capacitor, it is easily understood that the flattening of the electrical / optical response frequency characteristic can be expanded to 20 GHz or more by using the one having 3 pF or less.

  As described above, according to the present invention, in the optical waveguide device module in which the filter circuit including the capacitor is arranged on the line for inputting the modulation signal to the modulation electrode of the optical waveguide device, the multilayer ceramic capacitor is used for the capacitor. Even in this case, it is possible to provide an optical waveguide device module capable of flattening the optical response frequency characteristics over a wide band of several tens of GHz.

It is the schematic for demonstrating an optical waveguide element module. It is a figure which shows an example of a filter circuit. It is the figure which has arrange | positioned the multilayer ceramic capacitor to the filter circuit. It is sectional drawing of a multilayer ceramic capacitor. It is a figure which shows the electrical / optical response frequency characteristic at the time of using a multilayer ceramic capacitor for a filter circuit. It is a figure which shows a mode that the multilayer ceramic capacitor was laminated | stacked and arrange | positioned. It is a figure which shows a mode that the multilayer ceramic capacitor has been arrange | positioned above the electrical resistance of a film body.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Board | substrate 2 Optical waveguide 3 Signal electrode 4 Optical fiber for input 5 Optical fiber for output 6 Driver for drive 7 Relay substrate 8 Termination circuit 9 Case 10 Capacitor (multilayer ceramic capacitor)
11 Electrical resistance (film resistance)
12, 13 Electrical line 14 Relay board body (filter circuit board)
20, 21 Terminal 22, 23 Electrode 30 Electrical / optical response frequency characteristics

Claims (5)

An optical waveguide device having a substrate made of a material having an electro-optic effect, an optical waveguide formed on the substrate, and a modulation electrode that modulates a light wave propagating through the optical waveguide;
In an optical waveguide device module that is disposed on a line for inputting a modulation signal to the modulation electrode and includes a filter circuit including a capacitor,
The capacitor is a multilayer ceramic capacitor, and only one having a capacitance of 3 pF or less is used.   2. The optical waveguide device module according to claim 1, wherein when a plurality of multilayer ceramic capacitors are used, the multilayer ceramic capacitors are stacked on the filter circuit board.   3. The optical waveguide device module according to claim 1, wherein the filter circuit includes an electric resistance due to a film body formed on the filter circuit substrate.   4. The optical waveguide element module according to claim 3, wherein a multilayer ceramic capacitor is disposed so as to overlap the electric resistance.   5. The optical waveguide device module according to claim 1, wherein a termination circuit is connected to a termination portion of the modulation electrode.

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