JP2009238965A - Optical module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical module capable of reducing loss in DC bias in a terminal resistor and also preventing the effect on temperature control of a temperature controller. <P>SOLUTION: The optical module (10) includes a modulation signal terminal (6), an light modulator (2) connected with the modulation signal terminal, the terminal resistor (R1) connected with the light modulator, a bias resistor (R2) connected with the modulation signal terminal in parallel with the terminal resistor and having a resistance value smaller than that of the terminal resistor, and a DC bias terminal (7) for supplying DC bias to the light modulator via the bias resistor. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical module.

  In order to drive a modulator known as an electroabsorption modulator (EAM), a DC bias is required (see, for example, Patent Document 1).

JP 2006-128545 A

  FIG. 1 is a circuit diagram showing a configuration of a conventional optical module 200. As shown in FIG. 1, the optical module 200 includes a semiconductor laser 201, an optical modulator 202, a termination circuit 203, a bias unit 204, a modulation signal terminal 206, a DC bias terminal 207, and a drive input terminal 208.

  The drive input terminal 208 is connected to the semiconductor laser 201. The modulation signal terminal 206 is connected to the optical modulator 202 via the transmission line 205. The transmission line 205 and the optical modulator 202 are connected by a bonding wire L11. The optical modulator 202 is connected in parallel to the modulation signal terminal 206 and the termination circuit 203.

  The DC bias terminal 207 is connected to the optical modulator 202 via the bias unit 204 and the termination circuit 203. The termination circuit 203 includes a termination resistor R11 on the modulation signal terminal 206 side, and a capacitor C11 on the ground potential side. Termination resistor R11 and capacitor C11 are connected in series. The termination circuit 203 is connected to the transmission line 205 via the bonding wire L11 and the bonding wire L12.

  The bias unit 204 includes a choke coil L13 that cuts the modulation signal input from the modulation signal terminal 206. The bias unit 204 is connected between the termination resistor R11 of the termination circuit 203 and the capacitor C11.

  According to this configuration, the modulation signal leaking from the modulation signal terminal 206 to the DC bias terminal 207 side can be attenuated by the termination resistor R11. Thereby, the isolation of the modulation signal with respect to the DC bias terminal 207 can be increased.

  However, in the conventional optical module 200, since a DC bias is input to the optical modulator 202 via the termination resistor R11, loss of the DC bias due to the termination resistor R11 cannot be avoided. The value of the termination resistor R11 is determined according to the value of the termination impedance (for example, 50Ω). As a result, the value of the termination resistor R11 cannot be reduced unnecessarily.

  Further, the DC bias is converted into heat in the termination resistor R11. There is a problem that this heat has an influence such as canceling out temperature control of a temperature control device (not shown) of the semiconductor laser.

  An object of the present invention is to provide an optical module that can reduce a loss of a DC bias in a termination resistor and suppress an influence on temperature control of a temperature control device.

  An optical module according to the present invention includes a modulation signal terminal, an optical modulator connected to the modulation signal terminal, a termination resistor connected to the optical modulator, and a termination connected to the modulation signal terminal in parallel with the termination resistor. A bias resistor having a resistance value smaller than the resistor, and a DC bias terminal for supplying a DC bias to the optical modulator via the bias resistor are provided.

  In the optical module according to the present invention, a direct current bias is supplied to the optical modulator via the bias resistor instead of the termination resistor. In this case, the loss of DC bias can be reduced. Furthermore, the amount of heat generation is suppressed as compared with the case where a DC bias is passed through the termination resistor. Thereby, the influence with respect to temperature control of the temperature control apparatus by which the optical module which concerns on this invention is mounted can be suppressed.

  A first capacitor may be connected in series to the termination resistor. The first capacitor may be connected between the termination resistor and the optical modulator. In this case, the input of the DC bias to the termination resistor can be cut off.

  The first capacitor is configured by a laminated structure of a lower electrode, a dielectric, and an upper electrode provided on the carrier, the termination resistor is configured by a resistance film provided on the carrier, and one end of the first capacitor The other end may be connected to the ground potential on the back surface by a via hole connected to the lower electrode and provided through the carrier. In this case, it is not necessary to connect the termination resistor, the first capacitor, and the ground potential by a bonding wire. Thereby, a bonding wire can be reduced. As a result, termination characteristics can be improved.

  A choke coil may be connected in series to the bias resistor. In this case, the flow of the modulation signal is suppressed. Thereby, leakage of the modulation signal to the DC bias terminal is reduced.

  A damping resistor may be connected in parallel to the choke coil. In this case, resonance around the choke coil is suppressed. As a result, the leakage of the modulation signal to the DC bias terminal is reduced.

  The optical module according to the present invention may further include a second capacitor that connects the DC bias terminal and the ground potential. In this case, it is possible to further prevent the modulation signal from leaking to the DC bias terminal.

  ADVANTAGE OF THE INVENTION According to this invention, the loss of the direct current bias in a termination resistance can be reduced, and the influence on the temperature control of a temperature control apparatus can be suppressed.

  Hereinafter, the best mode for carrying out the present invention will be described.

  FIG. 2 is a circuit diagram showing the configuration of the optical module 10 according to the first embodiment of the present invention. As shown in FIG. 2, the optical module 10 includes a semiconductor laser 1, an optical modulator 2, a termination circuit 3, a bias unit 4, a modulation signal terminal 6, a DC bias terminal 7, and a drive input terminal 8.

  The drive input terminal 8 is connected to the semiconductor laser 1. A drive current is input from the drive input terminal 8 to the semiconductor laser 1. Thereby, the semiconductor laser 1 oscillates.

  The modulation signal terminal 6 is connected to the optical modulator 2 via the transmission line 5. The transmission line 5 and the optical modulator 2 are connected by a bonding wire L1. The optical modulator 2 is connected in parallel to the modulation signal terminal 6 and the termination circuit 3. A modulation signal is input to the optical modulator 2 from the modulation signal terminal 6 via the transmission line 5. Thereby, the optical modulator 2 modulates the laser light from the semiconductor laser 1 into an optical modulation signal.

  The termination circuit 3 is connected in parallel with the optical modulator 2 with respect to the modulation signal terminal 6. The termination circuit 3 includes a capacitor C1 on the modulation signal terminal 6 side and a termination resistor R1 on the ground potential side. Termination resistor R1 and capacitor C1 are connected in series. The termination circuit 3 is connected to the transmission line 5 via the bonding wire L1 and the bonding wire L2. By providing the termination circuit 3, the modulation signal from the modulation signal terminal 6 can be impedance-matched by the termination resistor R1.

  The DC bias terminal 7 is connected to the optical modulator 2 via the bias unit 4. The bias unit 4 is connected between the transmission line 5 and the bonding wire L1. The bias unit 4 has a structure in which a choke coil L3 and a bias resistor R2 are connected in series in this order from the DC bias terminal 7 side. Therefore, the bias resistor R2 is connected in parallel to the modulation signal terminal 6 and the termination resistor R1. The bias resistor R2 has a smaller resistance value than the termination resistor R1. For example, as a preferable example, when the resistance value of the termination resistor R1 is 50Ω, the bias resistor R2 has a resistance value of about 5Ω. The choke coil L3 can suppress the flow of high-frequency signals. Thereby, the choke coil L3 has a function of cutting the modulation signal input from the modulation signal terminal 6.

  In the present embodiment, since the optical modulator 2 and the termination resistor R1 are connected in parallel to the DC bias terminal 7, it is possible to suppress the DC bias from being input to the termination resistor R1. Further, in this embodiment, since the capacitor C1 is provided between the DC bias terminal 7 and the termination resistor R1, the input of the DC bias to the termination resistor R1 can be cut off.

  The bias resistor R2 has a function of attenuating a modulation signal leaking to the DC bias terminal 7 side. The resistance value (for example, 50Ω) of the termination resistor R1 is an appropriate value as the resistance value of the termination circuit. However, this resistance value is excessive as a value for attenuating the modulation signal leaking to the DC bias terminal 7 side. Accordingly, if the terminating resistor R1 is disposed between the DC bias terminal 7 and the optical modulator 2, the loss of the DC bias is increased. In comparison with this, in the present embodiment, a bias resistor R2 having a resistance value smaller than the termination resistor R1 is disposed between the DC bias terminal 7 and the optical modulator 2, so that the loss of the DC bias is reduced. Can be reduced. Further, the amount of generated heat is suppressed as compared with the case where a DC bias is passed through the termination resistor R1. Thereby, the influence with respect to temperature control of the temperature control apparatus with which the optical module 10 is mounted can be suppressed.

  The choke coil L3 and the damping resistor may be connected in parallel. In this case, resonance around the choke coil L3 is suppressed. As a result, the leakage of the modulation signal to the DC bias terminal 7 is further reduced.

  FIG. 3 is a plan view of the main part of the optical module 10. As shown in FIG. 3, the optical module 10 has a structure in which a mounting part 130 for mounting each element is disposed on the temperature control device 22. A semiconductor laser 1, an optical modulator 2, a termination circuit 3, a bias unit 4, and a transmission line 5 are mounted on the mounting unit 130. The semiconductor laser 1 and the optical modulator 2 are formed as one chip on the semiconductor substrate so that the optical modulator 2 is disposed on the optical axis of the laser light output from the semiconductor laser 1, and this is mounted on the mounting unit 130. Mounted on top.

  Furthermore, the lens 20 and the optical fiber connector 30 are disposed on the optical axis of the laser light output from the semiconductor laser 1. The lens 20 is disposed on the temperature control device 22. The temperature control device 22 is a device for controlling the temperatures of the semiconductor laser 1 and the optical modulator 2. In FIG. 3, an RF connector 21 is disposed as the modulation signal terminal 6.

  The transmission line 5 and the bias resistor R2 are connected by a bonding wire L4. The bias resistor R2 and the choke coil L3 are connected by a bonding wire L5. The semiconductor laser 1 and the drive input terminal 8 are connected by a bonding wire L6. The choke coil L3 and the DC bias terminal 7 are connected by a bonding wire L7.

  FIG. 4 is a cross-sectional view taken along the line AA in FIG. As shown in FIG. 4, the capacitor C1 has a structure in which a dielectric layer 102 and an upper electrode 101 are laminated on a lower electrode 103, and is mounted on a metallization 111 on the surface of a carrier 110 made of ceramics.

  The termination resistor R <b> 1 is configured by a resistance film formed on the carrier 110. One end of the termination resistor R1 is connected to the lower electrode 103 of the capacitor C1 by a metallization 111 on the surface of the carrier 110. The other end of the termination resistor R1 is connected to a via hole metal 120 provided through the back surface of the carrier 110 via a metallization 112 on the surface of the carrier 110. The via hole metal 120 is connected to the surface of the mounting part 130 on which the carrier 110 is mounted. The surface of the mounting part 130 is connected to the ground potential.

  In the present embodiment, among the termination resistor R1 and the capacitor C1 constituting the termination circuit 3, the capacitor C1 is disposed on the optical modulator 2 side, and the termination resistor R1 is disposed on the ground potential side. According to the configuration of FIG. 4, the electrodes at both ends of the termination resistor R1 are all disposed on the surface of the carrier 110, so the lower electrode 103 of the capacitor C1, the termination resistor R1 and the via hole disposed on the surface of the carrier 110. The metal 120 can be connected via metallization on the surface of the carrier 110.

  In this case, it is not necessary to connect the termination resistor R1, the capacitor C1, and the ground potential with a bonding wire. Thereby, bonding wires can be reduced in the termination circuit 3. As a result, high frequency characteristics can be improved.

  In comparison, when the termination resistor R1 is disposed on the optical modulator side and the capacitor C1 is disposed on the ground potential side, the bonding wire is between the termination resistor R1 and the capacitor C1 or between the capacitor C1 and the ground potential. Need to be connected. In this case, it is difficult to improve the high frequency characteristics.

  In the conventional example shown in FIG. 1, since the termination resistor R1 is used for attenuation of the modulation signal leaking to the DC bias terminal 207 side, it is necessary to connect the termination resistor R1 to the optical modulator 2 side. On the other hand, since the optical module 10 according to the present embodiment does not use the termination resistor R1 to attenuate the modulation signal leaking to the DC bias terminal 7, either the termination resistor R1 or the capacitor C1 is connected to the optical modulator 2. It can be determined arbitrarily.

  That is, the structure shown in FIG. 4 can be adopted because of the effect resulting from connecting the bias resistor R2 in parallel to the modulation signal terminal 6 and the termination resistor R1.

  FIG. 5 is a circuit diagram showing a configuration of an optical module 10a according to the second embodiment of the present invention. In FIG. 5, the same parts as those of the optical module 10 according to the first embodiment are denoted by the same reference numerals. The optical module 10a differs from the optical module 10 of FIG. 2 in that a capacitor C2 having one end connected to the ground potential is connected between the DC bias terminal 7 and the choke coil L3.

  The capacitor C2 is a capacitor for passing alternating current, and connects the modulation signal leaked through the bias resistor R2 and the choke coil L3 to the ground potential. In this case, leakage of the modulation signal to the DC bias terminal 7 and inflow of noise from the outside can be further prevented.

  FIG. 6 is a circuit diagram showing a configuration of an optical module 10b according to the third embodiment of the present invention. In FIG. 6, the same parts as those of the optical module 10 according to the first embodiment are denoted by the same reference numerals. The optical module 10b is different from the optical module 10 in FIG. 2 in that the bias unit 4 is connected to the termination circuit 3 side with respect to the optical modulator 2. That is, in this embodiment, the termination circuit 3 and the bias unit 4 are connected to the optical modulator 2 via the bonding wire L2.

  Also in this embodiment, since the bias resistor R2 is connected in parallel to the modulation signal terminal 6 and the termination resistor R1 as in the first embodiment, the loss of the DC bias is suppressed.

It is a circuit diagram which shows the structure of the conventional optical module. It is a circuit diagram which shows the structure of the optical module which concerns on 1st Example of this invention. It is a top view which concerns on the principal part of an optical module. FIG. 4 is a cross-sectional view taken along line AA in FIG. 3 and shows a cross-sectional structure of a termination resistor and a capacitor. It is a circuit diagram which shows the structure of the optical module which concerns on 2nd Example of this invention. It is a circuit diagram which shows the structure of the optical module which concerns on 3rd Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Optical modulator 3 Termination circuit 4 Bias part 6 Modulation signal terminal 7 DC bias terminal 8 Drive input terminal 10 Optical module C1 Capacitor L1, L2 Bonding wire L3 Choke coil R1 Termination resistance R2 Bias resistance

Claims (7)

A modulation signal terminal;
An optical modulator connected to the modulation signal terminal;
A termination resistor connected to the optical modulator;
A bias resistor connected in parallel with a termination resistor with respect to the modulation signal terminal and having a resistance value smaller than the termination resistor;
An optical module comprising: a DC bias terminal for supplying a DC bias to the optical modulator via the bias resistor.   The optical module according to claim 1, wherein a first capacitor is connected in series to the termination resistor.   The optical module according to claim 2, wherein the first capacitor is connected between the termination resistor and the optical modulator. The first capacitor is configured by a laminated structure of a lower electrode, a dielectric and an upper electrode provided on a carrier,
The termination resistor is composed of a resistance film provided on the carrier, and is connected to the lower electrode of the first capacitor at one end and a ground potential on the back surface by a via hole provided through the carrier at the other end. The optical module according to claim 3, wherein the optical module is connected to the optical module.   The optical module according to claim 1, wherein a choke coil is connected in series to the bias resistor.   6. The optical module according to claim 5, wherein a damping resistor is connected in parallel to the choke coil.   The optical module according to claim 1, further comprising a second capacitor that connects the DC bias terminal and the ground potential.

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