JP2013160913A - Signal transmission path and optical modulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress unnecessary spurious in a signal transmission path.SOLUTION: A signal transmission path includes: a first mounting member; a second mounting member disposed so as to be separated from the first mounting member across a space; a dielectric substrate 28 disposed by being bridged in the space between the first mounting member and the second mounting member; a signal line 22 formed on a top surface of the dielectric substrate 28; a first conductive layer 24 which is formed on an undersurface of the dielectric substrate 28 and has reference potential; and a second conductor layer 26 which is electrically connected to the first conductive layer 24 and is formed on a side surface of the dielectric substrate 28.

Description

  The present invention relates to a signal transmission path and an optical modulation device, for example, a signal transmission path and an optical modulation device that suppress unwanted spurious in the signal transmission path.

  An optical modulator that modulates signal light is used in an optical module for high-speed optical communication. The optical modulator modulates the intensity of the optical signal output in accordance with the electrical input signal. For example, Patent Document 1 describes an optical component using an EA (Electro-Absorption) light modulator. The optical modulator intensity-modulates the continuous light based on the input modulation signal. This modulation signal reaches 10 to 40 GHz or more. For this reason, the modulation signal transmission is designed in consideration of high-frequency transmission.

JP-A-2005-252251

  For example, in the above optical component, the modulation signal is input to the optical modulator via the transmission line. However, when unnecessary spurious occurs in the transmission line, the unnecessary spurious is input to the optical modulator via the transmission line. For this reason, the optical signal waveform modulated by the optical modulator deteriorates. Thus, it is required to suppress unnecessary spurious in the signal transmission path.

  The present invention has been made in view of the above problems, and an object thereof is to suppress unnecessary spurious in a signal transmission path.

  The present invention provides a first mounting member, a second mounting member that is spaced apart from the first mounting member across a space, and the space between the first mounting member and the second mounting member on the space. A dielectric substrate arranged in a bridge, a signal line formed on the upper surface of the dielectric substrate, a first conductive layer formed on the lower surface of the dielectric substrate and having a reference potential, and the first conductive layer And a second conductor layer formed on a side surface of the dielectric substrate, and a signal transmission path. According to the present invention, unnecessary spurious in the signal transmission path can be suppressed.

  In the above configuration, the signal line and the second conductor layer are arranged in parallel on the top surface of the dielectric substrate, and the signal line and the second conductor layer on the top surface of the dielectric substrate are The distance between them may be larger than the width of the signal line.

  The said structure WHEREIN: The width | variety of the said dielectric substrate can be set as the structure which is 1/6 or less of the transmission signal wavelength in the said dielectric substrate.

  In the above structure, a pad electrically connected to the first conductor layer can be provided.

  The said structure WHEREIN: It can be set as the structure which comprises the via wiring which penetrates the said dielectric base | substrate vertically and electrically connects the said pad and the said 1st conductor layer.

  In the above configuration, one side of the pad may be in contact with the second conductor layer.

  The present invention provides a dielectric substrate, a signal line formed on the upper surface of the dielectric substrate, a first conductive layer formed on the lower surface of the dielectric substrate and having a reference potential, and the first conductive layer And a second transmission layer formed on a side surface of the dielectric substrate, a first transmission member that mounts the optical modulator, and a modulation driver that modulates the optical modulator And a second mounting member spaced apart from the first mounting member by a space, and the signal transmission path is located on the space between the first mounting member and the second mounting member. The optical modulation device is arranged by bridging and electrically connecting the output terminal of the modulation driver and the electrode of the optical modulator.

  According to the present invention, unnecessary spurious in the signal transmission path can be suppressed.

FIG. 1 is a circuit diagram of an optical component according to the first embodiment. FIG. 2A is a plan view of the microstrip line, and FIG. 2B is a cross-sectional view taken along the line AA of FIG. 3A is a perspective view of a microstrip line used in the comparative example, FIG. 3B is a cross-sectional view, and FIG. 3C is a plan view. FIG. 4 is a schematic diagram showing the intensity of the spectrum with respect to the frequency. FIG. 5 is a diagram illustrating a result of calculating λg / 2 with respect to the frequency. FIG. 6 is a diagram illustrating a measurement result of transmission loss with respect to w1 / W. FIG. 7A is a plan view of a microstrip line used in the second embodiment, and FIG. 7B is a cross-sectional view taken along line BB in FIG. 7A. FIG. 8A is a plan view of a microstrip line used in the third embodiment, and FIG. 8B is a cross-sectional view taken along line BB in FIG. 8A. FIG. 9A is a top view of the optical module according to the third embodiment with the cap removed, and FIG. 9B is a cross-sectional view taken along line AA of FIG. 9A.

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

  FIG. 1 is a circuit diagram of an optical component according to the first embodiment. As shown in FIG. 1, the input terminal 14 is electrically connected to the node N1 via the microstrip line 20 and the inductor L1. The anode of the light modulator 10 is electrically connected to the node N1, and the cathode of the light modulator 10 is grounded. Node N1 is grounded through inductor L2, capacitor C, and resistor R in series. The inductor L2, the capacitor C, and the resistor R form an impedance matching circuit 16. The impedance matching circuit 16 matches the termination impedance of the optical modulator 10 to, for example, 50Ω. In this case, for example, the resistance value of the resistor R is set to 50Ω, which is the same as the termination impedance.

  Inductors L1 and L2 are, for example, bonding wires. The capacitor C is, for example, a chip capacitor, and the resistor R is, for example, a chip resistor. The optical modulator 10 is, for example, an EA optical modulator. For example, a high-frequency signal output from a modulation drive IC (Integrated Circuit) is input to the input terminal 14.

  FIG. 2A is a plan view of the microstrip line, and FIG. 2B is a cross-sectional view taken along the line AA of FIG. The microstrip line 20 transmits a high-frequency signal input to the optical modulator 10. The microstrip line 20 includes a dielectric substrate 28, a signal line 22, a first conductor layer 24, and a second conductor layer 26. The dielectric substrate 28 is made of a dielectric material such as aluminum oxide. The signal line 22 is formed on the upper surface of the dielectric substrate 28. For example, the signal line 22 extends from the end of the dielectric substrate 28 to the end in the extending direction of the dielectric substrate 28. The first conductor layer 24 is formed on the entire lower surface of the dielectric substrate 28. The second conductor layer 26 is formed on the entire side surface of the dielectric substrate 28. Thus, the first conductor layer 24 and the second conductor layer 26 cover the lower surface and side surfaces of the dielectric substrate 28.

  The first conductor layer 24 and the second conductor layer 26 have the same constant potential. That is, the first conductor layer 24 and the second conductor layer 26 are electrically connected, and the first conductor layer 24 has a reference potential. In the first embodiment, it is grounded. The signal line 22, the first conductor layer 24, and the second conductor layer 26 are made of a metal such as Au or Cu, for example. The width of the dielectric substrate 28 is W, the height of the dielectric substrate 28 is H, the width of the signal line 22 is w1, and the distance between the signal line 22 and the second conductor layer 26 is w2. The characteristic impedance of the microstrip line 20 is mainly defined by the signal line 22 and the first conductor layer 24.

  Next, the comparative example compared with Example 1 is demonstrated. 3A is a perspective view of a microstrip line used in the comparative example, FIG. 3B is a cross-sectional view, and FIG. 3C is a plan view. Other configurations are the same as those of the first embodiment, and the description thereof is omitted. As shown in FIGS. 3A to 3C, the second conductor layer is not provided on the side surface of the microstrip line 20a of the comparative example. The microstrip line 20 a includes a dielectric substrate 28, a signal line 22 formed on the upper surface of the dielectric substrate 28, and a first conductor layer 24 formed on the lower surface of the dielectric substrate 28.

  As shown in FIG. 3A, a modulation signal 34, for example, a rectangular wave 38 is input from one end of the microstrip line 20a as indicated by an arrow. As shown in FIG. 3B, when the modulation signal 34 propagates through the signal line 22, an electric field 30 and a magnetic field 32 are generated in the dielectric substrate 28. As shown in FIG. 3C, the modulation signal 34 is transmitted mainly in the extending direction of the microstrip line 20a. However, there is an unnecessary mode 36 in which transmission is performed in a direction crossing the extending direction of the microstrip line 20a. Due to the unnecessary mode 36, unnecessary spurious is generated. Thereby, the optical waveform of the optical signal whose intensity is modulated by the optical modulator 10 deteriorates.

  FIG. 4 is a schematic diagram showing the intensity of the spectrum with respect to the frequency of the transmission signal. As shown in FIG. 4, a transmission signal transmitted through a transmission line generally appears at a frequency that is an odd multiple of the fundamental wave f0.

  In the microstrip line according to the first embodiment shown in FIGS. 2A to 2C, the second conductor layer 26 is formed on the side surface of the dielectric substrate 28. For this reason, an unnecessary mode of a signal in which the wavelength λg in the dielectric substrate 28 is longer than twice the width W of the dielectric substrate 28 (that is, 2 × W) is blocked.

  Referring to FIG. 4, for example, if the frequency for cutting off the unnecessary mode is fc, the unnecessary mode having a frequency lower than the frequency fc is cut off and the microstrip line 20 is not transmitted. In the example of FIG. 4, unnecessary modes that occur within the seventh-order frequency are blocked.

  FIG. 5 is a diagram illustrating a result of calculating λg / 2 with respect to the frequency. FIG. 5 shows the calculation result of the wavelength λg / 2 of the high frequency signal in the dielectric substrate 28 with respect to the frequency of the high frequency signal when the dielectric substrate 28 is made of aluminum oxide. For example, when the bit rate of the signal input to the microstrip line 20 is 25 Gb / s, the frequency of the fundamental wave is 12.5 GHz. In this case, the frequency of the seventh mode is 87.5 GHz. Therefore, if the width W is set to about 0.55 mm, the frequency fc becomes 90 GHz, and an unnecessary mode generated in the seventh-order frequency can be cut off.

  The height H of the microstrip line 20 of Example 1 is 0.15 mm, the length L is 2.60 mm, the width w1 of the signal line 22 is 0.14 mm, the dielectric substrate 28 is aluminum oxide, and the first conductor layer 24. The microstrip line 20 was fabricated using the second conductor layer 26 as gold. A microstrip line 20a of a comparative example was also produced with the same configuration as in Example 1 except that the second conductor layer 26 was not provided. The characteristic impedance at 40 GHz of the microstrip lines 20 and 20a of Example 1 and the comparative example was set to 50Ω.

  For example, in order to block unnecessary modes up to the third mode of the high-frequency signal transmitted by the microstrip line 20, the width W of the dielectric substrate 28 is set to the transmission signal wavelength λg in the dielectric substrate 28, and λg / (2 × 3) = λg / 6 or less is sufficient. In order to block the unnecessary mode up to the fifth order mode, the width W may be λg / (2 × 5) = λg / 10 or less. Further, in order to block the unnecessary mode up to the seventh order mode, the width W may be λg / (2 × 7) = λg / 14 or less. Note that when the high-frequency signal transmitted by the microstrip line 20 is a digital signal having a bit rate of FGb / s, the frequency of the high-frequency signal may be F / 2 GHz.

  FIG. 6 is a diagram illustrating a measurement result of the transmission loss S21 with respect to w1 / W. In FIG. 6, black circles indicate the microstrip line 20 of Example 1, and white circles indicate the microstrip line 20a of the comparative example. A straight line is a line connecting black and white circles. The transmission loss is defined by S21 with the input end of the microstrip line 20 or 20a at 40 GHz as port 1 and the output end as port 2. For w1 / W, the characteristic impedance is 50Ω. For example, w1 is fixed to 0.14 mm, H is fixed to 0.15 mm, and W is changed. As shown in FIG. 6, in the first embodiment, the transmission loss is −0.4 dB or less, which is favorable. On the other hand, the transmission loss is large in the comparative example. Furthermore, when w1 / W increases, the transmission loss of the comparative example increases. This is presumably because the electric field in the dielectric substrate 28 leaks out of the dielectric substrate 28 when the width W is reduced without the second conductor layer 26 being provided. From FIG. 6, w1 / W is preferably 0.31 or more, and more preferably 0.24 or more.

  According to the first embodiment, the microstrip line 20 has the second conductor layer 26 on the side surface of the dielectric substrate 28. As a result, unnecessary mode transmission can be blocked. Therefore, it is possible to suppress deterioration of the optical waveform of the optical signal whose intensity is modulated by the optical modulator 10.

  Further, the signal line 22 and the second conductor layer 26 are arranged in parallel on the upper surface of the dielectric substrate 28, and the signal line 22 and the second conductor layer 26 are disposed on the upper surface of the dielectric substrate 28. Is greater than the width w1 of the signal line 22. As a result, w1 / W can be increased, and transmission loss can be suppressed as shown in FIG.

  Example 2 is an example in which a microstrip line has a pad. FIG. 7A is a plan view of a microstrip line used in the second embodiment, and FIG. 7B is a cross-sectional view taken along line BB in FIG. 7A. In FIG. 7A, the via wiring 42 is indicated by a broken line. A sectional view taken along the line AA in FIG. 7A is the same as FIG. The circuit diagram of the optical component according to the second embodiment is the same as FIG.

  As shown in FIGS. 7A and 7B, a pad 40 is formed on the upper surface of the dielectric substrate 28 at the end of the microstrip line 20b. The pads 40 are formed on both sides of the signal line 22. The pad 40 and the first conductor layer 24 are electrically connected by a via wiring 42 that vertically penetrates the dielectric substrate 28. The pad 40 and the via wiring 42 are formed of a metal such as Au or Cu, for example.

  As shown in FIG. 7A, a substrate 50 is provided beside the end of the microstrip line 20b. The substrate 50 includes a dielectric substrate 56, a signal line 52, and a conductor layer 54. The signal line 52 is formed on the upper surface of the dielectric substrate 56. The conductor layer 54 is formed on the upper surface of the dielectric substrate 56 and is formed on both sides of the signal line 52. The dielectric substrate 56 is, for example, aluminum oxide, and the signal line 52 and the conductor layer 54 are, for example, a metal layer such as Au or Cu. The signal line 52, the conductor layer 54, and the dielectric substrate 56 form a coplanar line. The characteristic impedance of the coplanar line is mainly defined by the signal line 52 and the conductor layer 54. The coplanar line formed on the substrate 50 is, for example, at least a part of the inductor L1 between the microstrip line 20 and the node N1 in FIG.

  The upper surface of the pad 40 and the conductor layer 54 are electrically connected by a bonding wire 58. As a result, the conductor layer 54 has the same potential as the first conductor layer 24. The signal lines 22 and 52 are electrically connected by a bonding wire 58. As a result, the high-frequency signal transmitted through the microstrip line 20b is input to the coplanar line. The transmission line formed on the substrate 50 may be a microstrip line.

  Example 3 is another example in which the microstrip line has a pad. FIG. 8A is a plan view of a microstrip line used in the third embodiment, and FIG. 8B is a cross-sectional view taken along line BB in FIG. 8A. The AA sectional view of FIG. 8A is the same as FIG. The circuit diagram of the optical component according to Example 3 is the same as FIG.

  As shown in FIGS. 8A and 8B, a pad 40 is formed on the upper surface of the dielectric substrate 28 at the end of the microstrip line 20c. The pads 40 are formed on both sides of the signal line 22. One side of the pad 40 is in contact with the second conductor layer 26 to be electrically connected to the first conductor layer 24.

  As in FIG. 7A of the second embodiment, the upper surface of the pad 40 and the conductor layer 54 are electrically connected by a bonding wire 58. The signal lines 22 and 52 are electrically connected by a bonding wire 58.

  As shown in FIG. 7A of the second embodiment and FIG. 8A of the third embodiment, the first conductor layer 24 is electrically connected to the upper surface of the dielectric substrate 28 at the end of the microstrip line 20b or 20c. A pad 40 to be connected is provided. Thereby, for example, the adjacent conductor layer 54 and the first conductor layer 24 can be electrically connected.

  By providing the pad 40 between the signal line 22 and the second conductor layer 26, the microstrip line can be miniaturized.

  In the first to third embodiments, an EA optical modulator has been described as an example of the optical modulator 10. However, as the optical modulator 10, for example, a Mach-Zehnder optical modulator or an LN (lithium niobate) optical modulator is used. It may be used.

  The fourth embodiment is an example of an optical module including the optical component according to the first to third embodiments. FIG. 9A is a top view of the optical module according to Example 4 with the cap removed, and FIG. 9B is a cross-sectional view taken along line AA of FIG. 9A. It should be noted that the side of the sector pull 98 is shown not on the cross section but on the side. As shown in FIGS. 9A and 9B, in the optical module 106, the optical modulator 10, the semiconductor laser 12, the modulation drive IC 74 (drive driver), and the like are housed in the housing 84. Here, the optical modulator 10 and the semiconductor laser 12 are integrated on one chip. Further, wirings and wires connected to the semiconductor laser 12 are omitted.

  The housing 84 is made of, for example, metal. A TEC (Thermoelectric Cooler) 68 is disposed on the bottom surface of the casing 84. On the TEC 68, a carrier 70 made of an insulating material such as aluminum oxide or ceramic and having high thermal conductivity is disposed. A subcarrier 71 and a lens holder 78 are disposed on the carrier 70.

  On the subcarrier 71, a chip in which the dielectric substrate 50, the optical modulator 10, and the semiconductor laser 12 are integrated, and a photodetector 79 are arranged. A lens 80 is held in the lens holder 78. A signal line 52 is formed on the upper surface of the dielectric substrate 50. The dielectric substrate 50 corresponds to, for example, the substrate 50 in FIGS. 7A and 8A.

  Further, a heat sink 66 made of a metal such as copper tungsten (CuW) or copper molybdenum (CuMo) is disposed on the bottom surface of the housing 84. A substrate 72 having a modulation driving IC 74 and a transmission line 73 is disposed on the heat sink 66. The upper surface of the heat sink 66 and the upper surface of the subcarrier 71 are substantially the same height. A bridge 76 bridged between the upper surface of the heat sink 66 and the upper surface of the subcarrier 71 corresponds to the microstrip line 20, 20 b or 20 c used in the first to third embodiments.

  A lens 82 is held on the front side wall of the housing 84. Further, a receptacle 98 is fixed to the front surface of the housing 84. A feedthrough 60 mainly made of an insulator is embedded in the rear side wall of the housing 84. In the feedthrough 60, a wiring for electrically connecting the terminal 64 in the housing 84 and the terminal 62 outside the housing 84 is provided.

  The terminal 64 and the transmission line 73 of the substrate 72 are electrically connected by a bonding wire 90. The transmission line 73 and the modulation drive IC 74 are electrically connected by a bonding wire 92. The modulation drive IC 74 and the signal line 22 in the bridge 76 are electrically connected by a bonding wire 94. The signal line 22 in the bridge 76 and the signal line 52 on the substrate 50 are electrically connected by a bonding wire 96.

  An input signal, which is a high-frequency signal, is input to the modulation drive IC 74 from the terminal 62 via the wiring in the feedthrough 60, the terminal 64, the bonding wire 90, the transmission line 73, and the bonding wire 92. The modulation driver IC 74 amplifies the input signal and outputs it as a modulated electric signal. The output modulation signal is input to the signal line 52 via the bonding wire 94, the signal line 22 in the bridge 76, and the bonding wire 96 via the output terminal of the modulation driver IC 74. The signal line 52 is electrically connected to the electrode of the optical modulator 10 via a bonding wire. As a result, the modulation signal is input to the electrode of the optical modulator 10. The optical modulator 10 modulates the intensity of the output light of the semiconductor laser 12 and emits it. As described above, the output terminal of the modulation drive IC 74 and the electrode of the optical modulator are electrically connected by the bridge 76, and the modulation drive IC 74 modulates the optical modulator. The optical modulator 10 and a fiber (not shown) inserted into the receptacle 98 are optically coupled by lenses 80 and 82. Thereby, the light emitted from the optical modulator 10 is introduced into the fiber. The photodetector 79 detects the intensity of light emitted from the back surface of the semiconductor laser 12. A control circuit (not shown) feedback-controls the current applied to the semiconductor laser 12 according to the output of the photodetector 79. The TEC 68 keeps the temperatures of the semiconductor laser 12 and the optical modulator 10 constant. Thereby, the wavelength of the light emitted from the optical modulator 10 can be locked. The semiconductor laser 12 can be operated stably.

  As in the fourth embodiment, the subcarrier 71 mounts the optical modulator 10 as the first mounting member. The heat sink 66 mounts the modulation driving IC 74 as the second mounting member. The modulation driver IC 74 functions as an amplifier that outputs a high-frequency signal to the microstrip line 20, 20b, or 20c. The microstrip line 20, 20 b, or 20 c is mechanically connected by a connection portion (first connection portion) on the upper surface of the subcarrier 71 and a connection portion (second connection portion) on the upper surface of the heat sink 66. It is provided so as to bridge the subcarrier 71 and the heat sink 66. For this reason, a space exists on the lower surface of the microstrip line 20, 20b or 20c. As described above, the first mounting member (subcarrier 71) and the second mounting member (heat sink 66) are arranged apart from each other with the space therebetween, and the dielectric base of the bridge 76 is the first mounting member (subcarrier 71). ) And the second mounting member (heat sink 66). When the optical modulator 10 and the modulation drive IC 74 are mounted on separate mounting members (subcarrier 71 and heat sink 66), the distance between the modulation drive IC 74 and the optical modulator 10 becomes long. For this reason, an unnecessary mode is likely to occur via a transmission line that bridges the mounting member. Therefore, unnecessary spurious can be suppressed by using the microstrip line 20, 20b or 20c for the transmission line. Therefore, it is possible to suppress deterioration of the optical waveform of the optical signal whose intensity is modulated by the optical modulator.

  In the fourth embodiment, the example in which the signal transmission path including the first mounting member, the second mounting member, and the bridge 76 including the transmission line of the first to third embodiments is used for the optical module 106 has been described. . The signal transmission path according to the fourth embodiment may be used for devices other than the light modulation device.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

DESCRIPTION OF SYMBOLS 10 Optical modulator 20 Microstrip line 22 Signal line 24 1st conductor layer 26 2nd conductor layer 28 Dielectric base | substrate 40 Pad 42 Via wiring 66 Heat sink 71 Subcarrier

Claims (7)

A first mounting member;
A second mounting member disposed away from the first mounting member across a space;
A dielectric substrate disposed between the first mounting member and the second mounting member so as to bridge the space;
A signal line formed on the upper surface of the dielectric substrate;
A first conductive layer formed on a lower surface of the dielectric substrate and having a reference potential;
A second conductive layer electrically connected to the first conductive layer and formed on a side surface of the dielectric substrate;
A signal transmission path comprising:   The signal line and the second conductor layer are arranged in parallel on the upper surface of the dielectric substrate, and the distance between the signal line and the second conductor layer on the upper surface of the dielectric substrate is 2. The signal transmission line according to claim 1, wherein the signal transmission line is larger than a width of the signal line.   3. The signal transmission path according to claim 1, wherein the width of the dielectric substrate is 1/6 or less of a transmission signal wavelength in the dielectric substrate.   4. The signal transmission path according to claim 1, further comprising a pad electrically connected to the first conductor layer. 5.   5. The signal transmission path according to claim 4, further comprising a via wiring penetrating up and down the dielectric substrate and electrically connecting the pad and the first conductor layer.   The signal transmission path according to claim 4, wherein one side of the pad is in contact with the second conductor layer. A dielectric substrate, a signal line formed on the upper surface of the dielectric substrate, a first conductive layer formed on the lower surface of the dielectric substrate and having a reference potential, and electrically connected to the first conductive layer A signal transmission line comprising: a second conductor layer formed on a side surface of the dielectric substrate;
A first mounting member on which the optical modulator is mounted;
A second mounting member mounted with a modulation driver for modulating the optical modulator, and spaced apart from the first mounting member by a space;
Comprising
The signal transmission path is arranged by bridging the space between the first mounting member and the second mounting member on the space, and between the output terminal of the modulation driver and the electrode of the optical modulator. An optical modulation device characterized by being connected to each other.

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