Optical transmission module

Abstract

To provide an optical transmission module that prevents degradation of frequency characteristics of optical signals in a high frequency region.SOLUTION: An optical transmission module includes a metal stem having a signal terminal extending in a first direction, a dielectric block containing a dielectric and having a circuit mounting surface parallel to the first direction, an optical mounting surface parallel to the first direction, and a heat conducting surface intersecting the first direction, an optical semiconductor element mounted on the circuit mounting surface, a temperature control element which is arranged between the metal stem and the heat conducting surface in the first direction and connected to the heat conducting surface, a lens mounted on the optical mounting surface, and a substrate which extends along the first direction and is connected to the signal terminal. The optical semiconductor element is electrically connected to the signal terminal through the substrate, and the circuit mounting surface is arranged between the optical mounting surface and the heat conducting surface in the first direction.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to an optical transmission module.

Background Art

[0002] Patent Document 1 discloses a semiconductor optical modulation device in which a semiconductor optical modulation element is disposed on a temperature control module mounted on a metal stem. Patent Document 1 discloses that a capacitor is connected to a signal line, and the value of the capacitor is set to perform impedance matching in the semiconductor optical modulation element.

[0003] Patent Document 2 discloses a semiconductor optical modulation device in which a lead pin, a signal line, a signal conductor, and a semiconductor optical modulation element are connected to each other by bonding wires.

[0004] Patent Document 3 discloses an optical subassembly including a spacer that electrically connects the back surface of a relay substrate and a pedestal.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] In an optical transmission module, when converting a high-speed electrical signal into an optical signal for transmission, the loss of the electrical signal increases in a high-frequency region of 30 GHz or higher, and the frequency characteristics of the optical signal deteriorate.

[0007] The present disclosure provides an optical transmission module that suppresses degradation of the frequency characteristics of an optical signal in a high-frequency region.

Means for Solving the Problem

[0008] The present disclosure includes a metal stem having a signal terminal extending in a first direction, a dielectric block including a dielectric and having a circuit mounting surface parallel to the first direction, an optical mounting surface parallel to the first direction, and a heat conduction surface intersecting the first direction, an optical semiconductor element mounted on the circuit mounting surface, a temperature control element disposed between the metal stem and the heat conduction surface in the first direction and connected to the heat conduction surface, a lens mounted on the optical mounting surface, and a substrate extending along the first direction and connected to the signal terminal. The optical semiconductor element is electrically connected to the signal terminal via the substrate, and the circuit mounting surface is disposed between the optical mounting surface and the heat conduction surface in the first direction. The optical transmission module is as described above.

Advantages of the Invention

[0009] According to the optical transmission module of the present disclosure, degradation of the frequency characteristics of an optical signal in a high-frequency region can be suppressed.

Brief Description of the Drawings

[0010]

Figure 1

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Figure 10

Embodiments for Carrying Out the Invention

[0011] [Description of Embodiments of the Present Disclosure] First, the embodiments of the present disclosure will be listed and described.

[0012] (1) The optical transmission module of the present disclosure includes a metal stem having signal terminals extending in a first direction, a dielectric block including a dielectric and having a circuit mounting surface parallel to the first direction, an optical mounting surface parallel to the first direction, and a heat conduction surface intersecting the first direction, and an optical semiconductor element mounted on the circuit mounting surface. Further, the optical transmission module of the present disclosure includes a temperature control element disposed between the metal stem and the heat conduction surface in the first direction and connected to the heat conduction surface, a lens mounted on the optical mounting surface, and a substrate extending along the first direction and connected to the signal terminals. And the optical semiconductor element of the optical transmission module of the present disclosure is electrically connected to the signal terminals via the substrate, and the circuit mounting surface is disposed between the optical mounting surface and the heat conduction surface in the first direction. According to the optical transmission module of the present disclosure, deterioration of the frequency characteristics of the optical signal in the high-frequency region can be suppressed.

[0013] (2) The dielectric block of the optical transmission module of the present disclosure has empty spaces between the circuit mounting surface and the temperature control element, and between the circuit mounting surface and the heat conduction surface. According to the optical transmission module of the present disclosure, by having empty spaces, the frequency characteristics of the optical signal in the high-frequency region can be further improved.

[0014] (3) The distance in the direction intersecting the first direction between the circuit mounting surface and the heat conduction surface in the optical transmission module of the present disclosure is 450 micrometers or more. According to the optical transmission module of the present disclosure, by setting the distance in the direction intersecting the first direction to 450 micrometers or more, the frequency characteristics of the optical signal can be further improved in the high-frequency region.

[0015] (4) The distance in the first direction between the circuit mounting surface and the temperature control element in the optical transmission module of the present disclosure is 450 micrometers or more. According to the optical transmission module of the present disclosure, by setting the distance in the first direction between the circuit mounting surface and the temperature control element to 450 micrometers or more, the frequency characteristics of the optical signal can be further improved in the high-frequency region.

[0016] (5) The optical semiconductor element of the optical transmission module of the present disclosure emits signal light in the first direction, the lens is mounted on the optical mounting surface so that the signal light is incident thereon, and the circuit mounting surface and the optical mounting surface are parallel to the first direction. According to the optical transmission module of the present disclosure, by making the circuit mounting surface and the optical mounting surface parallel to the first direction, the mounting of the optical semiconductor element and the lens on the dielectric block can be facilitated. Further, according to the optical transmission module of the present disclosure, by making the heat conduction surface intersect the first direction, the dielectric block on which the optical semiconductor element and the lens are mounted can be mounted on the temperature control element.

[0017] (6) The optical transmission module of the present disclosure further includes a temperature measurement element mounted on the circuit mounting surface for measuring the temperature of the optical semiconductor element. According to the optical transmission module of the present disclosure, the temperature adjustment of the optical semiconductor element can be made more accurate by using the temperature measured by the temperature measurement element mounted on the circuit mounting surface.

[0018] (7) The dielectric block of the optical transmission module of the present disclosure is formed of ceramics. According to the optical transmission module of the present disclosure, by making the dielectric block ceramics, deterioration of the frequency characteristics can be suppressed.

[0019] (8) The optical transmission module of the present disclosure further has a transmission line on the circuit mounting surface. According to the optical transmission module of the present disclosure, by having a transmission line on the circuit mounting surface, the transmission characteristics of the electrical signal to the optical semiconductor element can be improved.

[0020] [Details of Embodiments of the Present Disclosure] A specific example of the optical transmission module of the present disclosure will be described below with reference to the drawings. It should be noted that the present invention is not limited to these examples, and is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0021] Regarding the descriptions in the specifications and drawings according to each embodiment, for components having substantially the same or corresponding functions, the same reference numerals may be used to omit redundant descriptions. Also, for ease of understanding, the scales of the respective parts in the drawings may be different from the actual ones.

[0022] In directions such as parallel, right angle, orthogonal, horizontal, vertical, up and down, left and right, etc., a deviation that does not impair the effects of the embodiment is allowed. The shape of the corner is not limited to a right angle, and may be rounded in an arc shape. Parallel, right angle, orthogonal, horizontal, and vertical may include substantially parallel, substantially right angle, substantially orthogonal, substantially horizontal, and substantially vertical. For example, substantially parallel means that even if two lines or two planes are not completely parallel to each other, they can be treated as parallel to each other within the range allowable in manufacturing. For other substantially right angle, substantially orthogonal, substantially horizontal, and substantially vertical, similarly to substantially parallel, it is intended that the mutual positional relationship between two lines or planes falls within the range allowable in manufacturing.

[0023] ≪First Embodiment≫ The optical transmission module 1 according to the first embodiment will be described. FIG. 1 is a perspective view of the optical transmission module 1 according to the first embodiment. FIG. 2 is a side view of the optical transmission module 1 according to the first embodiment. FIG. 3 is a top view of the optical transmission module 1 according to the first embodiment.

[0024] Note that, for convenience of explanation, an XYZ orthogonal coordinate system may be shown in the figures. For example, for a coordinate axis perpendicular to the plane of the drawing, when a cross mark is shown inside the circle of the coordinate axis, it represents that the direction deeper than the plane of the drawing is the positive region of the coordinate axis, and when a black dot is shown inside the circle of the coordinate axis, it represents that the front side with respect to the plane of the drawing is the positive region of the coordinate axis. However, the coordinate system is mainly for indicating directions for explanation and does not limit the coordinates of the optical transmission module and each component etc. of the present disclosure.

[0025] Note that, in the present disclosure, unless otherwise specified, the Z axis is the output direction of the optical signal of the optical transmission module 1. The X axis and the Y axis are respectively perpendicular to the Z axis. Also, unless otherwise specified, the coordinate axes with the same name shown in each figure represent the same ones as each other. For example, the X axis in FIG. 1 represents the same one as the X axis in FIG. 2. Note that the side view of FIG. 2 corresponds to the side view when the optical transmission module 1 is viewed from the positive region of the X axis toward the negative region of the X axis. The top view of FIG. 3 corresponds to the top view when the optical transmission module 1 is viewed from the positive region of the Y axis toward the negative region of the Y axis.

[0026] The optical transmission module 1 converts an electrical signal into an optical signal. And the optical transmission module 1 outputs the optical signal along one direction. The optical transmission module 1 includes a metal stem 10, a dielectric block 20, an optical semiconductor element 30, a temperature control element 40, a lens 50, and a substrate 60. The optical transmission module 1 may further include a cylindrical housing (not shown), and the optical semiconductor element 30 may be hermetically sealed by the housing and the metal stem 10. The optical transmission module is, for example, a coaxial type TOSA (Transmitter Optical Sub-Assembly).

[0027] [Metal stem 10] The metal stem 10 has a substantially disk-shaped base 11, signal terminals 12, and a fixing member 13. The base 11 has a through hole 11h. The signal terminals 12 are provided penetrating through the through hole 11h. The signal terminals 12 extend in the Z-axis direction (the first direction). The signal terminals 12 have, for example, a columnar outer shape with a central axis parallel to the Z-axis. The signal terminals 12 are fixed to the base 11 by a fixing member 13 filled in the through hole 11h. The signal terminals 12 are insulated from the base 11 by the fixing member 13. The fixing member 13 is, for example, a glass material for sealing.

[0028] The base 11 is formed of metal. By forming the base 11 of metal, the heat generated on the heat dissipation surface 40S2 of the temperature control element 40 is conducted to the outside.

[0029] The metal stem 10 has a planar inner surface 11S. For example, the inner surface 11S intersects the direction in which the signal terminals 12 extend. One end of the signal terminal 12 in the +Z direction protrudes in the +Z direction from the inner surface 11S. Also, one end of the signal terminal 12 in the -Z direction protrudes in the -Z direction from the surface (outer surface) opposite to the inner surface 11S. A support portion 14 is provided extending in the +Z direction from the inner surface 11S of the metal stem 10. Note that another member may be mounted on the metal stem 10 as the support portion 14. For example, the support portion 14 is a block having a quadrangular prism-shaped outer shape extending in the Z-axis direction, and the end surface of the block in the -Z direction may be adhered to the inner surface 11S. The block of the support portion 14 is formed of, for example, metal. In that case, the metal stem 10 and the support portion 14 can be electrically connected by adhering with a conductive adhesive. By making the support portion 14 a member different from the metal stem 10, the position of the support portion 14 adhered to the inner surface 11S can be freely changed. Note that the block of the support portion 14 may be formed of an insulating material. A substrate 60 is mounted in the +Y direction with respect to the support portion 14 and fixed to the support portion 14.

[0030] In FIG. 1, the optical transmission module 1 has one signal terminal 12. However, depending on the function of the optical transmission module 1, it may have a plurality of terminals similar to the signal terminal 12. For example, it may have terminals for supplying a power supply voltage to the optical semiconductor element 30 and the temperature control element 40, a terminal for providing a reference potential, a terminal for transmitting an electrical signal for control, and the like.

[0031] [Dielectric block 20] The dielectric block 20 holds the optical semiconductor element 30 and the lens 50. The dielectric block 20 is integrally formed of a dielectric such as ceramics, for example. The ceramics is aluminum nitride, for example. By forming the dielectric block 20 of ceramics, deterioration of the frequency characteristics of the electrical signal propagating through the signal pattern 21 on the circuit mounting surface 20S1 described later can be suppressed.

[0032] The shape of the dielectric block 20 will be described. FIG. 4 is a perspective view of the dielectric block 20 of the optical transmission module 1 according to the first embodiment. FIG. 5 is a side view of the dielectric block 20 of the optical transmission module 1 according to the first embodiment. FIG. 5 corresponds to a side view when the dielectric block 20 is viewed from the positive region of the X-axis toward the negative region of the X-axis.

[0033] The dielectric block 20 has a substantially rectangular parallelepiped shape with a part near the center of the upper surface facing the +Y direction protruding in the +Y direction. The dielectric block 20 has a circuit mounting surface 20S1, an optical mounting surface 20S2, and an upper surface 20S4 in the +Y direction. The circuit mounting surface 20S1, the optical mounting surface 20S2, and the upper surface 20S4 are planes extending along the X-axis direction and the Z-axis direction, respectively. The circuit mounting surface 20S1 is located in the +Y direction with respect to the optical mounting surface 20S2 and the upper surface 20S4. When viewed from the +Y direction, the circuit mounting surface 20S1 is disposed between the optical mounting surface 20S2 and the upper surface 20S4. The dielectric block 20 has a vertical surface 20S6 perpendicular to the Z-axis direction connecting the circuit mounting surface 20S1 and the optical mounting surface 20S2. Also, the dielectric block 20 has a vertical surface 20S7 perpendicular to the Z-axis direction connecting the circuit mounting surface 20S1 and the upper surface 20S4. The vertical surfaces 20S6 and 20S7 are planes extending along the X-axis direction and the Y-axis direction, respectively. Note that the connection portions between the vertical surface 20S6 and the optical mounting surface 20S2 and between the vertical surface 20S7 and the upper surface 20S4 may each form a fillet.

[0034] The dielectric block 20 has a heat conduction surface 20S3 in the -Z direction. The heat conduction surface 20S3 is a plane extending along the X-axis direction and the Y-axis direction. Also, the dielectric block 20 has a front surface 20S5 in the +Z direction, a side surface 20S8 in the +X direction, a side surface 20S9 in the -X direction, and a bottom surface 20S10 in the -Y direction. The front surface 20S5 is a plane extending along the X-axis direction and the Y-axis direction. The side surfaces 20S8 and 20S9 are planes extending along the Y-axis direction and the Z-axis direction. The bottom surface 20S10 is a plane extending along the X-axis direction and the Z-axis direction.

[0035] The distance between the -Z direction end of the circuit mounting surface 20S1 and the heat conduction surface 20S3 is set to have a width W in the Z-axis direction. In other words, when viewed from the +Y direction, the distance between the circuit mounting surface 20S1 and the temperature control surface 40S1 of the temperature control element 40 is the width W. The temperature control surface 40S1 will be described later. The width W is the distance in the Z-axis direction between the circuit mounting surface 20S1 and the heat conduction surface 20S3.

[0036] Also, in the Y-axis direction, the circuit mounting surface 20S1 and the +Y-direction end of the heat conduction surface 20S3 are separated from each other by a depth H. The depth H is the distance in the Y-axis direction (the direction intersecting the Z-axis direction) between the circuit mounting surface 20S1 and the heat conduction surface 20S3. When the circuit mounting surface 20S1 and the upper surface 20S4 are parallel to each other, the depth H corresponds to the distance between the circuit mounting surface 20S1 and the upper surface 20S4. When the dielectric block 20 is connected to the temperature control element 40, there is a free space SP between the circuit mounting surface 20S1 and the upper surface 20S4 in the Y-axis direction, and between the vertical surface 20S7 and the heat conduction surface 20S3 in the Z-axis direction. The free space SP is defined by the plane including the circuit mounting surface 20S1, the upper surface 20S4, the vertical surface 20S7, and the plane including the heat conduction surface 20S3 with respect to the Y direction and the Z direction. The free space SP is defined by the side surfaces 20S8 and 20S9 with respect to the X direction. The free space SP is an empty space and is a portion without the material constituting the dielectric block 20.

[0037] (circuit mounting surface 20S1) An optical semiconductor element 30 is mounted on the circuit mounting surface 20S1. Also, a capacitor, a resistor, etc. may be mounted on the circuit mounting surface 20S1. A conductive pattern is formed on the circuit mounting surface 20S1. For example, a signal pattern 21 and a ground pattern 25 are formed on the circuit mounting surface 20S1. The signal pattern 21 and the ground pattern 25 are examples of conductive patterns and are each formed of a conductive material. The signal pattern 21 surrounded by the ground pattern 25 is, for example, a transmission line that transmits a signal input from the signal terminal 12. By using the signal pattern 21 as a transmission line, the transmission characteristics of an electrical signal to the optical semiconductor element 30 can be improved. The optical semiconductor element 30 is installed on the ground pattern 25.

[0038] In addition to the optical semiconductor element 30, at least any one of, for example, a termination resistor, a termination capacitor, a bypass capacitor, and terminals may be mounted on the circuit mounting surface 20S1. Further, a plurality of conductive patterns other than the signal pattern 21 and the ground pattern 25 may be formed on the circuit mounting surface 20S1. These plurality of conductive patterns, the termination resistor, the termination capacitor, the bypass capacitor, etc. may constitute a peripheral circuit for causing the optical semiconductor element 30 to perform a predetermined operation.

[0039] (Optical mounting surface 20S2) A lens 50 is mounted on the optical mounting surface 20S2. The optical mounting surface 20S2 is provided in the -Y direction with respect to the circuit mounting surface 20S1 in consideration of the size of the lens 50 so that the optical axis of the lens 50 coincides with the optical axis LA of the optical signal output from the optical semiconductor element 30 when the lens 50 is mounted. For example, the distance between the circuit mounting surface 20S1 and the optical mounting surface 20S2 is set according to the outer shape of the lens 50 so that the optical signal output from the optical semiconductor element 30 mounted on the circuit mounting surface 20S1 is appropriately incident on the lens 50 when the lens 50 is mounted on the optical mounting surface 20S2. For example, the optical mounting surface 20S2 is formed so as to be parallel to the circuit mounting surface 20S1. Thereby, the optical signal (beam) output from the optical semiconductor element 30 in the +Z direction can be perpendicularly incident on the incident surface of the lens 50 provided perpendicular to the optical mounting surface 20S2. For example, in the Y-axis direction, the distance between the optical mounting surface 20S2 and the circuit mounting surface 20S1 is determined according to the distance from the circuit mounting surface 20S1 to the light signal emission point of the optical semiconductor element 30 and the distance from the optical mounting surface 20S2 to the central axis (optical axis) of the lens 50. The lens 50 is fixed to the optical mounting surface 20S2 using, for example, a curable resin.

[0040] The circuit mounting surface 20S1 on which the optical semiconductor element 30 is mounted and the optical mounting surface 20S2 on which the lens 50 is mounted both face in the +Y direction. That is, the circuit mounting surface 20S1 and the optical mounting surface 20S2 are planes perpendicular to the Y-axis direction, that is, parallel to the Z-axis direction. Since the circuit mounting surface 20S1 and the optical mounting surface 20S2 face in the same direction, components such as the optical semiconductor element 30 and the lens 50 can be mounted from the same direction. The optical semiconductor element 30 is mounted on the circuit mounting surface 20S1 so as to output an optical signal in the +Z direction. That is, the optical semiconductor element 30 is mounted on the circuit mounting surface 20S1 such that the optical axis LA of the output optical signal is along the Z-axis direction.

[0041] (Thermal conduction surface 20S3) The thermal conduction surface 20S3 is connected to the temperature control surface 40S1 of the temperature control element 40. The dielectric block 20 is cooled or heated by the temperature control element 40 when the thermal conduction surface 20S3 is connected to the temperature control surface 40S1 of the temperature control element 40.

[0042] [Optical semiconductor element 30] The optical semiconductor element 30 generates an optical signal modulated by an electrical signal input from the signal terminal 12. The optical semiconductor element 30 emits the optical signal in the direction of the optical axis LA. The optical semiconductor element 30 includes, for example, a laser diode or an electro-absorption type optical modulator. When the optical semiconductor element 30 is an electro-absorption type optical modulator, a laser diode for generating the optical signal to be modulated may be provided on the same semiconductor chip. For example, the optical semiconductor element 30 may be a modulator integrated type semiconductor laser in which an electro-absorption type optical modulator is integrated. The optical axis LA is provided at a predetermined distance from the circuit mounting surface 20S1 in the +Y direction according to the structure of the optical semiconductor element 30.

[0043] The optical semiconductor element 30 is connected to the signal pattern 21 by the bonding wire BW4. Also, the optical semiconductor element 30 is connected to a termination resistor (not shown) by, for example, the bonding wire BW5 and is connected to the ground pattern 25 via the termination resistor.

[0044] [Temperature control element 40] The temperature control element 40 cools or heats the dielectric block 20. The temperature control element 40 is, for example, a thermoelectric cooler (TEC (Thermoelectric Cooler)). The temperature control element 40 includes a plurality of Peltier elements 45 that are Peltier - joined. Then, when power is supplied from a terminal provided on the metal stem 10 (not shown), the temperature control element 40 cools or heats the component attached to the temperature control surface 40S1. For example, in order to maintain the peak wavelength of the optical signal at a predetermined value, it is necessary to keep the temperature of the optical semiconductor element 30 at a predetermined laser temperature. For example, when the temperature outside the optical transmission module 1 is higher than the predetermined laser temperature, the temperature control element 40 cools the temperature control surface 40S1 to keep the temperature of the optical semiconductor element 30 at the predetermined laser temperature. When the temperature outside the optical transmission module 1 is lower than the predetermined laser temperature, the temperature control element 40 heats the temperature control surface 40S1 to keep the temperature of the optical semiconductor element 30 at the predetermined laser temperature.

[0045] The temperature control element 40 is provided between the metal stem 10 and the heat conduction surface 20S3 of the dielectric block 20. Specifically, the temperature control element 40 is provided between the inner surface 11S of the base 11 of the metal stem 10 and the heat conduction surface 20S3 of the dielectric block 20. The temperature control surface 40S1 of the temperature control element 40 is connected to the heat conduction surface 20S3 of the dielectric block 20. For example, the heat conduction surface 20S3 is fixed to the temperature control surface 40S1 by an adhesive. Also, the heat dissipation surface 40S2 on the side opposite to the temperature control surface 40S1 of the temperature control element 40 is connected to the inner surface 11S of the metal stem 10. For example, the heat dissipation surface 40S2 is fixed to the inner surface 11S by an adhesive. The heat dissipation surface 40S2 dissipates heat when the temperature control surface 40S1 absorbs heat (cools), and absorbs heat when the temperature control surface 40S1 dissipates heat (heats). The temperature control surface 40S1 and the heat dissipation surface 40S2 are parallel to each other. Thereby, the optical axis LA can be provided perpendicular to the inner surface 11S of the metal stem 10.

[0046] The temperature control element 40 includes a substrate 41, a substrate 42, and a plurality of Peltier elements 45. The plurality of Peltier elements 45 are provided between the substrate 41 and the substrate 42. The substrate 41 has a temperature control surface 40S1 in the +Z direction. Also, the substrate 42 has a heat dissipation surface 40S2 in the -Z direction. By flowing a current in a predetermined direction through the plurality of Peltier elements 45, the heat absorbed by the substrate 41 is dissipated by the substrate 42, and the dielectric block 20 connected to the temperature control surface 40S1 is cooled. Further, by flowing a current in a direction opposite to the predetermined direction through the plurality of Peltier elements 45, the heat absorbed by the substrate 42 is dissipated by the substrate 41, and the dielectric block 20 connected to the temperature control surface 40S1 may be heated.

[0047] [Lens 50] The lens 50 is an optical lens that condenses the optical signal emitted from the optical semiconductor element 30. The lens 50 is formed of, for example, optical glass. The lens 50 has, for example, an incident surface in the -Z direction and an emission surface in the +Z direction. The lens 50 receives the optical signal emitted from the optical semiconductor element 30 at the incident surface and outputs the optical signal as parallel light from the emission surface.

[0048] The lens 50 is mounted on the optical mounting surface 20S2 of the dielectric block 20. The lens 50 is fixed to the optical mounting surface 20S2 by, for example, an adhesive. The adhesive is, for example, an ultraviolet curable resin. When fixing the lens 50 to the optical mounting surface 20S2, the position of the lens 50 (alignment) is adjusted so that the central axis (optical axis) of the lens 50 coincides with the optical axis LA of the optical signal output from the optical semiconductor element 30 in the X-axis direction and the Y-axis direction, and then it is fixed. The lens 50 has a bottom surface facing the optical mounting surface 20S2. For example, an uncured adhesive is applied between the bottom surface of the lens 50 and the optical mounting surface 20S2, heated after alignment, and irradiated with ultraviolet rays to cure the adhesive and fix the lens 50 to the optical mounting surface 20S2. For example, the incident surface and the exit surface of the lens 50 are perpendicular to the bottom surface of the lens 50. Note that since the optical signal output from the optical semiconductor element 30 spreads in the X-axis direction and the Y-axis direction as it travels in the +Z direction, the position of the lens 50 in the Z-axis direction with respect to the optical mounting surface 20S2 may be determined by adjusting (aligning) the position of the lens 50 in the Z-axis direction while monitoring the intensity of the parallel light output from the lens 50 with a light receiving element.

[0049] [Substrate 60] The substrate 60 transmits the electrical signal from the signal terminal 12 to the optical semiconductor element 30. The substrate 60 extends along the Z-axis direction. The substrate 60 has a signal pattern 61, a ground pattern 65, and a ground pattern 66 on the upper surface 60S in the +Y direction. The signal pattern 61, the ground pattern 65, and the ground pattern 66 are formed of, for example, metal. The signal pattern 61 is connected to the signal terminal 12. The ground patterns 65 and 66 are grounded. The signal pattern 61 transmits the electrical signal input from the signal terminal 12. The electrical signal converted by the optical semiconductor element 30 into an optical signal includes, for example, high-frequency components of 30 GHz or more. In order not to deteriorate the waveform quality of the electrical signal, the signal pattern 61 is formed so as to constitute a transmission line together with the ground pattern 65 and the ground pattern 66.

[0050] One end of the signal pattern 61 is connected to the signal pattern 21 on the circuit mounting surface 20S1 by a bonding wire BW1, for example. The ground pattern 65 is connected to the ground pattern 25 on the circuit mounting surface 20S1 by a bonding wire BW2. The ground pattern 66 is connected to the ground pattern 25 on the circuit mounting surface 20S1 by a bonding wire BW3. The bonding wires BW1, BW2, and BW3 are formed to extend along the X-axis direction when viewed from the +Y direction. For example, the positions of one ends of the bonding wires BW1, BW2, and BW3 in the X-axis direction on the upper surface 60S of each are the same as each other. Also, the positions of the other ends of the bonding wires BW1, BW2, and BW3 in the X-axis direction on the circuit mounting surface 20S1 of each are the same as each other. The lengths of the bonding wires BW1, BW2, and BW3 are preferably set short. The lengths of the bonding wires BW1, BW2, and BW3 may be set to the same length as each other. Incidentally, the position of the upper surface 60S of the substrate 60 in the Y-axis direction is preferably close to the position of the circuit mounting surface 20S1 of the dielectric block 20 in the Y-axis direction. By bringing the position of the upper surface 60S in the Y-axis direction closer to the position of the circuit mounting surface 20S1 in the Y-axis direction, the lengths of the bonding wires BW1, BW2, and BW3 can be shortened.

[0051] The other end of the signal pattern 61 is connected to the signal terminal 12. More specifically, the other end of the signal pattern 61 is connected to one end protruding from the inner surface 11S of the signal terminal 12. The connection between the other end of the signal pattern 61 and one end of the signal terminal 12 may be made by soldering or by wire bonding. The other end of the signal pattern 61 and one end of the signal terminal 12 are preferably close to each other from the viewpoint of signal transmission. For example, the position on the inner surface 11S of the support portion 14 may be determined so that the other end of the signal pattern 61 and one end of the signal terminal 12 are close to each other.

[0052] <Operation of the optical transmission module 1> [Electro-optical response] The frequency characteristics of the electro-optical response of the optical transmission module 1 are shown in FIG. 6. The vertical axis of the graph in FIG. 6 represents the electro-optical response (unit: decibel (dB)). Also, the horizontal axis of the graph in FIG. 6 represents the signal frequency (unit: gigahertz (GHz)). The electro-optical response represents the magnitude of the signal intensity of the optical signal output from the optical semiconductor element 30 with respect to the signal intensity of the electrical signal input to the signal terminal 12. The value on the vertical axis represents, for example, a value based on the signal intensity value of the optical signal at a frequency of 1 GHz or less. Since the value of the electro-optical response shown in FIG. 6 becomes more negative as the degradation of the optical signal increases, it is preferably close to 0. In FIG. 6, the frequency characteristics of the optical transmission module 1 (solid line L1) and the frequency characteristics of the optical transmission module provided with the dielectric block 20z shown in FIG. 10 in place of the dielectric block 20 as a comparative example (dashed line Lz) are shown. The frequency characteristics shown in FIG. 6 represent the results of analyzing the electro-optical response of the optical transmission module using electromagnetic field analysis.

[0053] The optical transmission module of the comparative example includes a dielectric block 20z in which a dielectric block 23z and a dielectric block 24z are joined, in place of the dielectric block 20 of the optical transmission module 1. The dielectric block 23z is a carrier on which the optical semiconductor element is mounted. The dielectric block 24z is a submount for mounting the dielectric block 23z. The bottom surface of the dielectric block 23z facing the -Y direction is connected to the upper surface of the dielectric block 24z facing the +Y direction. In order to join the dielectric block 23z to the dielectric block 24z, for example, a conductive thin film is provided on the joining portion of the dielectric block 23z and the dielectric block 24z (that is, the bottom surface of the dielectric block 23z and the upper surface of the dielectric block 24z). The conductive thin film is formed of, for example, a metal.

[0054] The solid line L1 is an example of the frequency characteristics of the electro - optical response of the optical transmission module 1. The dashed line Lz is an example of the frequency characteristics of the electro - optical response of the optical transmission module of the comparative example. By comparing the solid line L1 and the dashed line Lz, the optical transmission module 1 has less fluctuation in the electro - optical response and has a flatter characteristic up to a higher frequency than the optical transmission module of the comparative example. In particular, for the optical transmission module of the comparative example, the electro - optical response drops significantly around a frequency of 45 to 50 GHz. In the frequency characteristics, such a drop (deterioration) in the electro - optical response at a specific frequency is called a dip, and the frequency at which the dip occurs is sometimes called the dip frequency. The optical transmission module 1 has excellent flatness characteristics in the range from a frequency of 1 GHz or less to a frequency of 60 GHz without a significant drop in the electro - optical response. The inventors found that although no dip occurs in the optical transmission module using the dielectric block 20z of the comparative example when the signal frequency is 30 GHz or less, a dip occurs when the signal frequency becomes 30 GHz or more. For example, in the comparative example, a large dip occurs at the dip frequency fz = 47 GHz. The inventors further found that by using the dielectric block 20 instead of the dielectric block 20z, the dip is significantly improved. However, although the influence of the parasitic capacitance due to the above - mentioned conductive thin film is suppressed, it is also found that a dip still occurs. For example, in the solid line L1 of FIG. 6, although the magnitude is less than 3 dB at the dip frequency f1 = 43 GHz, a dip occurs.

[0055] Next, the dip found in the optical transmission module 1 of the present embodiment will be described. Regarding the optical transmission module 1, the characteristics when the width W and the depth H in FIG. 5 are changed will be described. The width W and the depth H correspond to parameters related to the shape of the empty space SP formed by the dielectric block 20 and the temperature - control element 40. Here, electromagnetic field analysis was performed on the dip frequency around a frequency of 40 GHz of the electro - optical response.

[0056] FIG. 7 is a diagram showing the dip frequency when the width W of the optical transmission module 1 according to the first embodiment is changed. The value of the depth H set in the electromagnetic field analysis of FIG. 7 is 450 micrometers. The vertical axis of the graph in FIG. 7 is the dip frequency (unit: gigahertz (GHz)). The horizontal axis of the graph in FIG. 7 is the depth W (unit: micrometer (μm)).

[0057] FIG. 8 is a diagram showing the dip frequency when the depth H of the optical transmission module 1 according to the first embodiment is changed. The value of the width W set in the electromagnetic field analysis of FIG. 8 is 450 micrometers. The vertical axis of the graph in FIG. 8 is the dip frequency (unit: gigahertz (GHz)). The horizontal axis of the graph in FIG. 8 is the depth H (unit: micrometer (μm)).

[0058] By increasing each of the width W and the depth H, the value of the dip frequency can be increased. The inventors have found that the cause of the relatively small dip as shown by the solid line L1 in FIG. 6 is the stray capacitance between the circuit mounting surface 20S1 and the temperature control surface 40S1 of the temperature control element 40. Therefore, it has also been found that increasing each of the width W and the depth H can reduce the stray capacitance between the circuit mounting surface 20S1 and the temperature control surface 40S1 of the temperature control element 40. For example, increasing each of the width W and the depth H increases the volume of the empty space. For example, since the empty space SP is filled with air, the relative permittivity is approximately 1. When, for example, the optical semiconductor element 30 is hermetically sealed, the empty space SP is filled with a sealing gas. On the other hand, when the empty space SP is filled with a dielectric forming the dielectric block 20, the relative permittivity becomes greater than 1. For example, the relative permittivity of aluminum nitride is 8 or more at a frequency of 1 MHz. Therefore, by providing the empty space SP, the above-described stray capacitance can be significantly reduced. Thus, the inventors have found that when the signal frequency becomes as high as 30 GHz or more, by reducing the stray capacitance between the circuit mounting surface 20S1 and the temperature control surface 40S1 of the temperature control element 40, the dip frequency can be made higher than the signal band, and deterioration of the frequency characteristics of the optical signal can be suppressed. For example, by suppressing deterioration due to the dip of the frequency characteristics of the optical signal, the waveform quality of the optical signal transmitted from the optical transmission module 1 can be improved. Note that the width W is preferably 300 micrometers or more. In particular, the width W is more preferably 450 micrometers or more. Also, the depth H is preferably 300 micrometers or more. In particular, the depth H is more preferably 450 micrometers or more.

[0059] <Function and Effect> By mounting the optical semiconductor element 30 on the circuit mounting surface 20S1 of the dielectric block 20, the optical transmission module 1 according to the first embodiment can suppress deterioration of the frequency characteristics of the electro-optical response.

[0060] In addition, by using the integrally formed dielectric block 20 in the optical transmission module 1 according to the first embodiment, the number of components can be reduced and the number of mounting steps can be reduced. Also, by using the integrally formed dielectric block 20 in the optical transmission module 1 according to the first embodiment, the cost of the dielectric block portion for mounting the optical semiconductor element 30 can be reduced.

[0061] Furthermore, by providing a vacant space between the circuit mounting surface 20S1 and the temperature control surface 40S1 of the temperature control element 40, the stray capacitance between the circuit mounting surface 20S1 and the temperature control surface 40S1 can be reduced, and deterioration of the frequency characteristics of the electro-optical response can be suppressed.

[0062] ≪Second Embodiment≫ In order to control the temperature control element 40, a temperature measurement element 80 for measuring the temperature on the circuit mounting surface 20S1 may be mounted on the circuit mounting surface 20S1.

[0063] FIG. 9 is a top view of the optical transmission module 2 according to the second embodiment.

[0064] The optical transmission module 2 further includes a temperature measurement element 80 in addition to the optical transmission module 1. The temperature measurement element 80 is mounted on the circuit mounting surface 20S1 of the dielectric block 20. The temperature measurement element 80 is, for example, a thermistor, a thermocouple, or a resistance temperature detector. Note that the type of the temperature measurement element 80 is not limited as long as it can measure temperature. The temperature control element 40 is controlled using the temperature measured by the temperature measurement element 80 so that the temperature of the optical semiconductor element 30 becomes a desired temperature.

[0065] <Operation and Effect> The optical transmission module 2 according to the second embodiment can control the temperature of the optical semiconductor element 30 with higher precision than the optical transmission module 1 according to the first embodiment. More specifically, the optical transmission module 2 according to the second embodiment includes a temperature measurement element 80 on the circuit mounting surface 20S1, so that the temperature measurement element 80 can be arranged close to the optical semiconductor element 30. By arranging the temperature measurement element 80 close to the optical semiconductor element 30, the temperature of the optical semiconductor element 30 can be measured more accurately. By accurately measuring the temperature of the optical semiconductor element 30, the optical transmission module 2 can more accurately control the temperature of the optical semiconductor element 30 by the temperature control element 40. Further, the temperature measurement element 80 has improved followability of temperature measurement with respect to changes in the temperature of the optical semiconductor element 30. Therefore, the optical transmission module 2 can control the temperature of the optical semiconductor element 30 more responsively to temperature changes.

Description of Reference Numerals

[0066] 1, 2 Optical transmission module 10 Metal stem 11 Base 11h Through-hole 11S Inner surface 12 Signal terminal 13 Fixing member 14 Support portion 20 Dielectric block 20S1 Circuit mounting surface 20S2 Optical mounting surface 20S3 Heat conduction surface 20S4 Upper surface 20S5 Front surface 20S6, 20S7 Vertical surfaces 20S8, 20S9 Side surfaces 20S10 Bottom surface 21 Signal pattern 25 Ground pattern 30 Optical semiconductor element 40 Temperature control element 40S1 Temperature control surface 40S2 Heat dissipation surface 41 Substrate 42 Substrate 45 Peltier element 50 Lenses 60 Substrate 61 Signal Pattern 65, 66 Ground Pattern 80 Temperature Measurement Element BW1, BW2, BW3, BW4, BW5 Bonding Wire SP Free Space 20z, 23z, 24z Dielectric Block

Claims

1. A metal stem having signal terminals extending in a first direction, a dielectric block including a dielectric, integrally formed by the dielectric, having a circuit mounting surface extending in the first direction and a second direction intersecting the first direction, an optical mounting surface parallel to the first direction, and a heat conduction surface intersecting the first direction, an optical semiconductor element mounted on the circuit mounting surface, a temperature control element disposed between the metal stem and the heat conduction surface in the first direction and connected to the heat conduction surface, a lens mounted on the optical mounting surface, a substrate extending along the first direction and connected to the signal terminals, comprising, the optical semiconductor element is electrically connected to the signal terminals via the substrate, the circuit mounting surface is disposed between the optical mounting surface and the heat conduction surface in the first direction, the dielectric block has empty spaces between the circuit mounting surface and the temperature control element and between the circuit mounting surface and the heat conduction surface, a distance in a third direction intersecting the first direction and the second direction between the circuit mounting surface and the heat conduction surface is 450 micrometers or more, an optical transmission module.

2. A metal stem having signal terminals extending in a first direction, a dielectric block including a dielectric, integrally formed by the dielectric, having a circuit mounting surface parallel to the first direction, an optical mounting surface parallel to the first direction, and a heat conduction surface intersecting the first direction, an optical semiconductor element mounted on the circuit mounting surface, a temperature control element disposed between the metal stem and the heat conduction surface in the first direction and connected to the heat conduction surface, a lens mounted on the optical mounting surface, a substrate extending along the first direction and connected to the signal terminals, comprising, the optical semiconductor element is electrically connected to the signal terminals via the substrate, the circuit mounting surface is disposed between the optical mounting surface and the heat conduction surface in the first direction, the dielectric block has empty spaces between the circuit mounting surface and the temperature control element and between the circuit mounting surface and the heat conduction surface, a distance in the first direction between the circuit mounting surface and the temperature control element is 450 micrometers or more, an optical transmission module.

3. the optical semiconductor element emits signal light in the first direction, the lens is mounted on the optical mounting surface such that the signal light is incident thereon, the circuit mounting surface and the optical mounting surface are parallel to the first direction, The optical transmission module according to claim 1 or claim 2.

4. Further comprising a temperature measurement element mounted on the circuit mounting surface for measuring the temperature of the optical semiconductor element. The optical transmission module according to any one of claims 1 to 3.

5. The dielectric block is formed of ceramics. The optical transmission module according to any one of claims 1 to 4.

6. The circuit mounting surface further has a transmission line. The optical transmission module according to any one of claims 1 to 5.

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