JP6805923B2 - Light modulator - Google Patents

Description

The present invention relates to an optical modulator, and more particularly to an optical modulator having a flexible substrate as an electrical interface unit.

In the field of optical communication, transmitters and receivers using optical modulators are used. In recent years, due to the demand for miniaturization of optical transmission systems, the RF interface connection, which is the electrical interface portion of the optical modulator built in the optical transmitter / receiver module (transponder), has also tended to be shortened.

As a specific example of the electrical interface unit, a lead pin, a flexible printed circuit board (FPC), or the like is used as an interface unit for surface mounting. These interface units are cheaper than coaxial cables such as push-on type coaxial connectors, and have the advantage of being able to be directly connected to the electric circuit of the board inside the transponder.

FIG. 1 shows a state in which the optical modulator 1 is arranged on the circuit board 2 constituting the optical transmitter / receiver module. In FIG. 1, a flexible substrate 3 is used as a means for realizing shortening.
FIG. 2 is a diagram showing a cross section at the alternate long and short dash line AA'in FIG. The light modulator 1 houses the light modulation element 4 in a metal housing 10, is closed by a lid 11, and is airtightly sealed. The electrodes (signal electrode and ground electrode) 41 formed on the optical modulation element 4 are the lead pin 5 arranged in the through hole of the housing 10 and the electric transmission line (signal electrode and ground electrode) formed on the flexible substrate 3. It is electrically connected to the electric circuit of the circuit board 2 via 31. In FIG. 2, the electric transmission line 31 on the flexible substrate 3 and the lead pin 5 are directly connected by solder or the like. Further, the lead pin 5 and the electrode 41 on the light modulation element 4 are wire-bonded (6) with a gold wire or the like.

Since the flexible substrate has a surface-mounted structure, when measuring RF characteristics, a high-frequency probe for supplying a high-frequency signal to the flexible substrate is stably attached to the signal electrode and the ground electrode constituting the electric transmission line on the flexible substrate. Need to be contacted. In addition, when contacting a high-frequency probe, it is necessary to strictly adjust the position of the electrical transmission line of the flexible substrate and the drive amount (the amount of pressurization of the probe after the probe is contacted with the electrode) so as not to damage the probe. ..

On the other hand, as the electric transmission line on the flexible substrate, a transmission line structure in which a microstrip line and a coplanar waveguide are mixed is often used. 3A to 3C show a part of the electric transmission line 31 formed on the flexible substrate 3 in the optical modulator according to the conventional example. FIG. 3A is a plan view showing an electric transmission line configured by connecting a microstrip line (MSL) and a coplanar line (CPW). FIG. 3B is a plan view showing a state in which the high frequency probe 7 is brought into contact with the CPW portion in the electric transmission line of FIG. 3A. FIG. 3C is a diagram showing a cross section at the alternate long and short dash line BB'in FIG. 3B.

The CPW unit is used as a terminal for electrically connecting to an external circuit (for example, an electric circuit on a circuit board 2 such as a board inside a transponder). The CPW portion to be solder-connected to the external circuit is intentionally separated from the signal electrode S2 and the ground electrode G2 in consideration of solder mountability, and its characteristic impedance is, for example, 70Ω or more. In the line condition when the characteristic impedance of the CPW line of the flexible substrate is, for example, 50Ω, the distance between the signal electrode and the ground electrode becomes narrow, and there is a possibility that a short circuit may occur between the electrodes when soldering to an external circuit.

When a high-frequency probe is brought into contact with the CPW portion on the flexible substrate, the reflection component at the contact position and the reflection component at the electrode end face on the flexible substrate affect the measured value. Further, when the characteristic impedances of the high-frequency probe and the CPW portion are different from 50Ω and 70Ω, respectively, there is a problem that the mismatch of the characteristic impedance is superimposed and the measurement accuracy is lacking.
FIG. 4 is a diagram showing electrical reflection characteristics depending on the contact position of the high frequency probe. FIG. 4 shows the electrical reflection characteristics measured by setting the contact position of the high-frequency probe in the CPW section as a position 100 μm, a position 200 μm, and a position 300 μm from the boundary between the MSL section and the CPW section. From the figure, it can be understood that the measurement result of the electric reflection characteristic differs depending on the contact position of the high frequency probe.

The contact position with respect to the CPW portion on the flexible substrate changes depending on the drive amount, which is the pressurization amount of the probe after the high frequency probe is brought into contact with the CPW portion. Moreover, since the flexible substrate is generally flexible, there is a concern that the contact position may shift due to the deformation of the flexible substrate due to the pushing of the high frequency probe. For this reason, it is difficult to perform the measurement at an accurate position, and the measurement of the electric reflection characteristic lacks reproducibility.

Japanese Unexamined Patent Publication No. 2016-200652

The problem to be solved by the present invention is the light capable of solving the above-mentioned problems and stably contacting the high-frequency probe in the measurement and inspection process of the optical modulator having a flexible substrate in the electric interface section. It is to provide a modulator.

In order to solve the above problems, the optical modulator of the present invention has the following technical features.
(1) In an optical modulator including a housing, an optical modulation element arranged inside the housing, and a substrate arranged outside the housing, the substrate is connected to an electrode of the optical modulation element. At least a part of the electric transmission line is formed, and a recess that does not penetrate the electric transmission line is formed on a part of the surface of the electric transmission line formed on the substrate, and the electricity formed on the substrate. The transmission line is configured by connecting a microstrip line and a coplanar line, the coplanar line is used as a terminal for electrically connecting to an external circuit, and the recess is formed in the coplanar line. , It is characterized in that it is arranged at a position of 100 μm or less from the boundary between the microstrip line and the coplanar line .

(2) In the optical modulator according to (1 ) above, the substrate is a flexible substrate.

(3) In the light modulator according to (1) or (2 ) above, the recess is contacted with a probe for electrical measurement.

According to the present invention, it is possible to provide an optical modulator capable of stably contacting a high frequency probe in the measurement and inspection of an optical modulator having a flexible substrate in an electric interface section.

It is a figure which shows the appearance which the optical modulator is arranged on the external circuit board. It is a figure which shows the cross section at the one-dot chain line AA'in FIG. It is a top view which shows a part of the electric transmission line formed on the flexible substrate which concerns on the prior art. FIG. 3 is a plan view showing a state in which a high-frequency probe is brought into contact with a CPW portion in the electric transmission line of FIG. 3A. It is a figure which shows the cross section at the one-dot chain line BB'of FIG. 3B. It is a figure which shows the electric reflection characteristic by the contact position of a high frequency probe. It is a top view which shows a part of the electric transmission line formed on the flexible substrate which concerns on one Embodiment of this invention. FIG. 5 is a plan view showing a state in which a high frequency probe is brought into contact with a CPW portion in the electric transmission line of FIG. 5A. It is a figure which shows the cross section at the one-dot chain line CC'of FIG. 5B. It is a figure which shows the shape of the concave part assuming the case of using the high frequency probe which has a plurality of contact terminals parallel to each other. It is a figure which shows the shape of the concave part assuming the case of using the high frequency probe which has a plurality of contact terminals radially. It is a figure which shows the example of the recess which forms a triangular shape. It is a figure which shows the example of the concave part having a trapezoidal shape.

Hereinafter, the optical modulator according to the present invention will be described in detail.
5A to 5C show a part of the electric transmission line 31 formed on the flexible substrate 3 in the optical modulator according to the embodiment of the present invention. FIG. 5A is a plan view showing an electric transmission line configured by connecting a microstrip line (MSL) and a coplanar line (CPW). FIG. 5B is a plan view showing a state in which the high frequency probe 7 is brought into contact with the CPW portion in the electric transmission line of FIG. 5A. FIG. 5C is a diagram showing a cross section at the alternate long and short dash line CC'in FIG. 5B.

The light modulator 1 according to the present invention includes a housing 10, a light modulation element 4 arranged inside the housing 10, and a flexible substrate 3 arranged outside the housing 10. At least a part of the electric transmission line 31 connected to the electrode 41 of the light modulation element 4 is formed. A recess R2 that does not penetrate the electric transmission line 31 is formed on a part of the surface of the electric transmission line 31 formed on the flexible substrate 3.

The electric transmission line 31 formed on the flexible substrate 3 has an MSL portion and a CPW portion. In the MSL portion, a signal electrode S1 is formed on the lower surface of the substrate, and a ground electrode G1 is formed on the upper surface of the substrate. In the CPW portion, a signal electrode S2 is formed on the lower surface of the substrate, two ground electrodes G2 are formed so as to sandwich the signal electrode S2, and a similar signal electrode S2 and a ground electrode G2 are also formed on the upper surface of the substrate. The signal electrode S2 and the ground electrode G2 on the upper surface of the substrate and the signal electrode S2 and the ground electrode G2 on the lower surface of the substrate are electrically connected by a via hole H2 penetrating the substrate and a casting C2 formed on the end surface of the substrate. A conductor is plated on the surfaces of the via hole H2 and the casting C2 to form a conductor layer.

The MSL unit is electrically connected to the electrodes (signal electrode and ground electrode) 41 of the light modulation element 4 inside the light modulator 1 via a lead pin 5 or the like. The CPW unit is used as a terminal for electrically connecting to an external circuit (for example, a circuit on a circuit board 2 such as a board inside a transponder).
A recess R2 that serves as a contact destination for the high-frequency probe 7 is formed in the CPW portion. The recess R2 can be formed by various methods. For example, it can be formed by pressing a punch tool, laser trimming, mechanical cutting, etching, or the like.

When the electrical measurement of the light modulator 1 is performed using the high frequency probe 7, the contact position is uniquely determined by immersing the tip portion of the contact terminal 71 of the high frequency probe 7 into the recess R2. Therefore, the contact position of the high-frequency probe 7 is stable, and the impedance mismatch of the flexible substrate 3 can be minimized. Further, since the contact position of the high frequency probe 7 with respect to the flexible substrate 3 is accurately determined, the reproducibility of measurement is improved.

Here, the recess R2 provided in the CPW portion of the flexible substrate 3 also functions as a solder pool when excessive solder is applied at the time of soldering to the external circuit. Therefore, it is possible to reduce a short circuit between the signal electrodes S2 and the ground electrode G2 in the CPW section.
Further, by forming the recess R2, the heat capacity of the CPW portion is reduced. Therefore, the solder can be heated efficiently, and the soldering time can be shortened.
Further, the recess R2 provided in the CPW portion of the flexible substrate 3 can also be used as a mark when mounting the flexible substrate 3. Therefore, the work of mounting the flexible substrate 3 at an accurate position becomes easy.

In order to improve the accuracy of electrical measurement, it is preferable to provide the recess R2 at a position as close as possible to the MSL portion side of the CPW portion. This is because the impedance mismatch is smaller and the effect on the measurement result is smaller when the high-frequency probe 7 with the characteristic impedance of 50Ω is brought closer to the MSL part with the characteristic impedance of 50Ω instead of the CPW part with the characteristic impedance of 70Ω. is there. More specifically, it is preferable that the recess R2 is provided at a position where the distance d from the boundary between the MSL portion and the CPW portion is 100 μm or less. However, it is necessary to provide an interval such that the high frequency probe 7 does not get caught in the coverlay (protective film) formed on the surface of the MSL portion.
In this example, the signal electrode S2 and the ground electrode G2 on the lower surface of the substrate in the CPW portion are provided with the recess R2, but the recess R2 may be provided on the upper surface side, or the recess R2 may be provided on both sides. Further, the CPW unit may be a coplanar line with a ground, or another type of electric transmission line may be used.

It is preferable that at least one of the directions in which the tip portion of the contact terminal 71 moves or the direction orthogonal to the tip portion of the contact terminal 71 is larger than the outer diameter of the tip portion of the contact terminal 71 when the high frequency probe 7 is contacted and pressurized. Further, the outer diameter of the concave portion R2 in any part of the direction may be larger than the outer diameter of the tip portion of the contact terminal 71 regardless of the direction in which the tip portion of the contact terminal 71 moves. Further, the concave portion R2 may have an outer diameter in which the entire tip portion of the contact terminal 71 is accommodated.

FIG. 6A is a diagram showing the shape of the recess R2 assuming the case of using a high frequency probe 7 having a plurality of contact terminals 71 parallel to each other. FIG. 6B is a diagram showing the shape of the recess R2 assuming the case where the high frequency probe 7 is used for the plurality of contact terminals 71 arranged radially. Since the tip diameter φ of the contact terminal 71 is about 150 μm, it is conceivable to provide the recess R2 with a width of about 300 μm as an example.

In both FIGS. 6A and 6B, the recess R2 has a shape having a certain width along the direction in which the tip portion of the contact terminal 71 moves. As a result, the tip portion of the contact terminal 71 moves by contacting the concave portion R2 and then applying pressure, but the movement is restricted by contacting the end surface of the concave portion R2 with only a small movement. Therefore, even if the position where the high frequency probe 7 is brought into contact is slightly deviated, it will be corrected to an appropriate position.

In this example, the concave portion R2 has a rectangular shape, but the shape of the concave portion R2 is not limited to this, and various shapes such as a circle, an ellipse, a square, a rectangle, and a trapezoid may be used. Can be done. In particular, as shown in FIGS. 7A and 7B, the shape of the recess R2 is a triangle having a shape in which the width narrows along the direction in which the tip portion of the contact terminal 71 moves when the high frequency probe 7 is contacted and pressurized. When trapezoidal, the high frequency probe can be contacted more stably.

Although the present invention has been described above based on the examples, it goes without saying that the present invention is not limited to the above-mentioned contents, and the design can be appropriately changed without departing from the spirit of the present invention.

According to the present invention, it is possible to provide an optical modulator capable of stably contacting a high frequency probe in an inspection of an optical modulator having a flexible substrate in an electric interface portion.

1 Optical modulator 2 Circuit board 3 Flexible substrate 4 Optical modulation element 5 Lead pin 6 Wire bonding 7 High frequency probe 10 Housing 11 Lid 31 Electrical transmission line 41 Electrode 71 Contact terminal S1, S2 Signal electrode G1, G2 Ground electrode H2 Via hole C2 Caster R2 recessed MSL microstrip line CPW coplanar line

Claims (3)

In an optical modulator having a housing, an optical modulation element arranged inside the housing, and a substrate arranged outside the housing.
At least a part of the electric transmission line connected to the electrode of the light modulation element is formed on the substrate.
A recess that does not penetrate the electric transmission line is formed on a part of the surface of the electric transmission line formed on the substrate .
The electric transmission line formed on the substrate is configured by connecting a microstrip line and a coplanar line.
The coplanar line is used as a terminal for electrically connecting to an external circuit.
The light modulator is characterized in that the recess is formed in the coplanar line and is arranged at a position of 100 μm or less from the boundary between the microstrip line and the coplanar line . In the light modulator according to claim 1 ,
The substrate is an optical modulator characterized by being a flexible substrate. In the light modulator according to claim 1 or 2 .
An optical modulator characterized in that a probe for electrical measurement is contacted with the recess.

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