JP5631774B2 - Optical transmission module - Google Patents

Description

  The present invention relates to an optical transmission module using a TO-CAN package and an FPC board.

As the amount of information communication over the Internet increases in recent years, it is required to increase the capacity of the photonic network system that supports it. In the data center, it is considered that demand for processing 40Gb / s signals transmitted from the backbone system at the same speed will increase in the future. In order to meet this demand, a directly modulated laser (DML) is expected as a 40 Gb / s optical semiconductor light source. Because DML is smaller than Electroabsorption Modulator Integrated DFB Laser (EA-DFB Laser) and LiNbO ₃ (LN) modulator and is easy to manufacture, it is small and low cost. It is because it is thought that it is suitable for conversion. Conventionally, a 40 Gb / s optical semiconductor light source has been put to practical use in a form of being mounted on XLMD-MSA (Non-patent Document 1) for a transmission distance of 2 km (VSR) for interconnecting routers. In fact, 40Gb / s operation using DML has also been reported (Non-Patent Documents 2 and 3). In these forms, the electrical signal sent from the optical transceiver is transmitted to the optical transmission module using an expensive high-frequency connector or cable, and there is a problem in miniaturization and cost reduction. Considering the rapidly increasing demand in data centers, there is a demand for the realization of a smaller and lower cost 40Gb / s DML module.

  Therefore, we aimed to realize DML 40Gb / s operation using a Transistor-Outline (TO) -CAN package and a flexible printed circuit (FPC) board.

Based on the drawings, the optical transmission module capable of 40 Gb / s operation will be further described. As shown in FIG. 32A, conventionally, a 40 Gb / s electric signal, which is a high-frequency electric signal, is supplied from an optical circuit 1 (PCB: Printed circuit board) 1 of an optical transceiver, etc. The configuration is such that the optical transmission module 6 manufactured using the multilayer ceramic package 5 is transmitted through the cable 2 and the high-frequency connector 3. The optical transmission module 6 having such a configuration has the following two problems.
(1) Since the high-frequency connector 3 and the high-frequency cable 2 are used to transmit a high-frequency electrical signal, it is difficult to reduce the size and cost of the optical transmission module 6 (the size of the high-frequency connector 3 limits the size reduction). .
(2) The monolithic ceramic package 5 is expensive, and this also makes it difficult to reduce the cost of the optical transmission module 6.

  The problem with the prior art was that it was not possible to propose a small, low-cost optical transmission module other than this to achieve low transmission loss and low reflection loss for high-speed electrical signals of 40 Gb / s. there were.

  Accordingly, an object of the present invention is to realize a significant reduction in size and cost from the conventional 40 Gb / s optical transmission module 6. The basic configuration is shown in FIG.

  As shown in FIG. 32 (b), the optical transmission module 11 of the present invention uses the FPC board 12 for the problem (1) of the prior art, and from the PCB 1 or the like through the FPC board 12. The electrical signal is transmitted to the optical transmission module 11. In general, when the high frequency connector 3 is used, a commercially available GPPO (registered trademark) or K connector (registered trademark) is used. These are fixed in size and costly. On the other hand, when the FPC board 12 is used, the optical transmission module 11 can be greatly downsized because it can be designed freely. Since the cost of the FPC board 12 is determined only by the material cost and processing cost of the FPC board 12, the cost of the optical transmission module 11 can be greatly reduced as compared with the case where the high frequency connector 3 is used.

  Further, the optical transmission module 11 of the present invention uses the TO-CAN package 13 for the problem (2) of the prior art. The reason why the cost of the TO-CAN package 13 can be greatly reduced as compared with the multilayer ceramic package 5 is that the TO-CAN package 13 can be manufactured only by pressing, so that the manufacturing cost can be significantly reduced. .

XLMD MSA, web site, http://www.xlmdmsa.org/ K. Nakahara, T. Tsuchiya, T. Kitatani, K. Shinoda, T. Taniguchi, T. Kihara and M. Aoki, "High extinction ratio operation at 40-Gb / s direct modulation in 1.3-mm InGaAlAs-MQW RWG DFB lasers, "in Proc. OFC, Anaheim, USA, 2006, Paper OWC5. K. Otsubo, M. Matsuda, S. Okumura, A. Uetake, M. Ekawa and T. Yamamoto, "Low-driving-current high-speed direct modulation up to 40 Gb / s using 1.3-mm semi-insulating buried- heterostructure AlGaInAs-MQW distributed reflector laser, "in Proc. OFC, San diego, USA, 2009, Paper OThT6.

  Next, a description will be given focusing on the configuration using the TO-CAN package 13 and the FPC board 12. To date, there is no conventional technology that can achieve 40 Gb / s operation with this configuration. FIG. 33 shows the configuration of the optical transmission module in a report realizing 10 Gb / s or 25 Gb / s operation. FIG. 33A shows a report up to the conventional 10 Gb / s operation, and FIG. 33B shows a report up to the conventional 25 Gb / s operation.

As shown in FIG. 33A, in the optical transmission module operating at 10 Gb / s, the FPC board 12 is bent 90 degrees and connected to the coaxial pin 22 of the TO-CAN package 13. In this configuration, a high-frequency electric signal (RF signal) is rotated by 90 degrees at the connection portion between the coaxial pin 22 and the FPC board 12 and transmitted to the coaxial pin 22. Therefore, the bending loss of the RF signal at this connection portion becomes a problem.
Furthermore, due to the portion of the coaxial pin 22 exposed to the air (air gap portion), the characteristic impedance of the coaxial pin 22 deviates from the design value, and transmission loss and reflection loss are induced. As shown in FIG. 34, the periphery of the coaxial pin 22 is filled with an insulator such as glass 24 or air. The characteristic impedance of the portion of the coaxial pin 22 filled with the glass 24 is determined by the relative dielectric constant ε _r of the glass 24 filling the periphery of the coaxial pin 22, its diameter, and the diameter of the central conductor (coaxial pin 22). Is done. If the portion of the coaxial pin 22 filled with the glass 24 is set to have a characteristic impedance of 50Ω, the characteristic impedance of the portion of the coaxial pin 22 exposed to the air (portion of the air gap) starts from 50Ω. Shift. This is because the characteristic impedance of the portion of the central conductor (coaxial pin 22) exposed to the air is determined by the diameter of the central conductor (coaxial pin 22) and the relative dielectric constant ε _r of the air, and the central conductor (coaxial pin 22). The diameter of the exposed portion of the air is the same as the diameter of the portion of the central conductor (coaxial pin 22) that is filled with the glass 24, but the relative permittivity ε _r of air is the relative permittivity ε of the glass 24. _This is because it is different from _r .

  On the other hand, as shown in FIG. 33B, in the optical transmission module operating at 25 Gb / s, the RF signal is transmitted straight without being bent by 90 degrees at the connection portion between the FPC board 12 and the coaxial pin 22. Therefore, compared to the case of 10 Gb / s, the configuration can suppress the bending loss of the RF signal. However, the deterioration of the electrical characteristics at the air gap is induced in the same manner as in the case of 10 Gb / s. Therefore, in order to realize an optical transmission module capable of operating at 40 Gb / s, it is required to design a stricter characteristic impedance than an optical transmission module operating at 10 Gb / s or 25 Gb / s.

  Accordingly, the present invention has been made in view of the above-mentioned problems in an optical transmission module using a TO-CAN package and an FPC board. An RF signal of 40 Gb / s can be obtained with low transmission loss and low reflection loss. It is an object of the present invention to provide an optical transmission module having a configuration capable of transmitting from a substrate to the inside of a TO-CAN package.

The optical transmission module of the first invention for solving the above-mentioned problems is
It has a TO-CAN package and an F PC board,
The back surface of the TO-CAN package and the front end surface of the FPC board are arranged via an air gap, and the coaxial pins arranged in the TO-CAN package and the FPC board are arranged in parallel. Has been
Spacing of the FPC substrate before and Symbol coaxial pins, so that the 0 or 0.1mm or less, the coaxial pins is connected to the high-frequency signal transmission line disposed on a surface of said FPC board,
A plurality of DC pins arranged in the TO-CAN package are bent and connected to a DC signal line arranged on the back side of the FPC board,
The coaxial pin inside the TO-CAN package is connected to a high-frequency signal line disposed on a high-frequency circuit board disposed inside the TO-CAN package,
The high-frequency signal line disposed on the high-frequency circuit board, the resistor disposed inside the TO-CAN package, and the optical semiconductor element disposed inside the TO-CAN package are electrically connected,
From the high-frequency signal line disposed on the surface of the FPC board, through the high-frequency signal line and the resistor disposed on the coaxial pin and the high-frequency circuit board, conducting a high-frequency electrical signal to the optical semiconductor element,
The resistance value of the resistor is 40Ω or more and 45Ω or less,
A direct current is conducted to the optical semiconductor element through a DC pin located farthest from the coaxial pin among the plurality of DC pins and a connecting portion between the DC pin serving as a heat generating portion and the DC signal line. It is characterized by having a configuration.

The optical transmission module of the second invention is the optical transmission module of the first invention.
The FPC substrate is made using an LCP material.

Further, the optical transmission module of the third invention is the optical transmission module of the first or second invention, wherein the high-frequency signal line disposed on the high-frequency circuit board is connected to the resistor via the first wire,
The resistor is connected to the optical semiconductor element through a second wire.

The optical transmission module of the fourth invention is the optical transmission module of the third invention,
A characteristic impedance of the resistor, the second wire, and the optical semiconductor element is 50Ω.

The optical transmission module of the fifth invention is the optical transmission module of the first or second invention, wherein the resistor is arranged together with a high-frequency signal line arranged on the high-frequency circuit board,
The high-frequency signal line disposed on the high-frequency circuit board is connected to a DFB laser through a wire.

The optical transmission module of the sixth invention is the optical transmission module of the fifth invention,
A characteristic impedance of the resistor, the wire, and the optical semiconductor element is 50Ω.

Further, the optical transmission module of the seventh invention is the optical transmission module of any one of the first to sixth inventions,
The optical semiconductor element is a direct modulation laser.

  According to the present invention, the high frequency signal in which the coaxial pins are arranged on the surface of the FPC board so that the distance (air gap) between the coaxial pin FPC boards arranged in the TO-CAN package is 0 or more and 0.1 mm or less. A plurality of DC pins connected to the line and bent on the TO-CAN package are bent and connected to a DC signal line placed on the back side of the FPC board, and the coaxial pin is connected to the TO-CAN package. Connected to the high-frequency signal line arranged on the high-frequency circuit board arranged inside the package, the high-frequency signal line arranged on the high-frequency circuit board, the resistor arranged inside the TO-CAN package, and the inside of the TO-CAN package The optical semiconductor element is electrically connected to the optical semiconductor element from the high-frequency signal line disposed on the surface of the FPC board via the coaxial pin, the high-frequency signal line disposed on the high-frequency circuit board, and the resistor. Conduct high-frequency electrical signals through Optical transmission module that can transmit 40Gb / s RF signal from the FPC board to the inside of the TO-CAN package with low transmission loss and low reflection loss because the value is 40Ω or more and 45Ω or less Can be realized.

(A) is sectional drawing of the optical transmission module (when there is an air gap) which concerns on the embodiment of this invention, (b) is the optical transmission module (when there is no air gap) which concerns on the embodiment of this invention. FIG. (A) is a schematic diagram of a cross section of an FPC substrate using a ceramic material, and (b) is a schematic diagram of a cross section of an FPC substrate using an LCP material. (A) is a photograph of the prototype FPC board, (b) is a diagram showing the electrical characteristics (calculation and measurement results) of the prototype FPC board. (A) is a perspective view of an FPC board using a ceramic material as a substrate material, (b) is a perspective view of an FPC board using an LCP material as a substrate material, and (c) is an FPC board using a ceramic material as a substrate material. It is a figure which shows the electrical property (calculation result) of the FPC board | substrate which used LCP material as a board | substrate material. (A) is sectional drawing of the optical transmission module (HFSS calculation model) which concerns on the embodiment of this invention, (b) is a perspective view (C direction arrow of (a) of the said optical transmission module (HFSS calculation model) Figure). It is a schematic diagram of the connection part of the coaxial pin of a TO-CAN package and the high frequency signal track | line of an FPC board. Electrical characteristics of the FPC board: a diagram showing the calculation results of (dependence on distance ΔW of the ground electrode and the high-frequency signal transmission line S ₂₁ / S ₁₁ characteristics), the electrical characteristics when ΔW is 0.4mm in (a) (B) shows the electrical characteristics when ΔW is 0.3 mm, and (c) shows the electrical characteristics when ΔW is 0.2 mm. Is a diagram showing relationship between ΔW and S ₁₁ characteristics (calculation result). (A) is a perspective view of an optical transmission module according to an embodiment of the present invention, and (b) is a cross-sectional view of the optical transmission module. (A) is explanatory drawing of the air gap Z in the connection part of a coaxial pin and an FPC board | substrate, (b) is a figure which shows the influence on the electrical property of the air gap Z. FIG. (A) is explanatory drawing of height direction deviation (DELTA) h in the connection part of a coaxial pin and an FPC board, (b) is a figure which shows the influence on the electrical property of height direction deviation (DELTA) h. (A) is explanatory drawing of space | interval (DELTA) W of a high frequency signal track | line and a ground electrode, (b) is a figure which shows the dependence with respect to the space | interval (DELTA) W of a high frequency signal track | line and a ground electrode. (A) is a perspective view of an FPC board without a ground electrode, (b) is a perspective view of an FPC board with a ground electrode, and (c) is an FPC board without a ground electrode and an FPC board with a ground electrode. It is a figure which shows an electrical property. It is explanatory drawing of the fixing method (connection) of the TO-CAN package and FPC board which comprise the optical transmission module which concerns on the embodiment of this invention, (a) is a perspective view of the back side of the said optical transmission module (B) shows a cross-sectional view of the optical transmission module, (c) shows a rear view of the TO-CAN package, and (d) shows an FPC board in the rear view of the TO-CAN package. ing. (A) is a rear view of the TO-CAN package with three DC pins, and (b) is a rear view of the TO-CAN package with four DC pins. It is a perspective view which shows arrangement | positioning inside a TO-CAN package. (A) is a rear view of the optical transmission module (TO-CAN package) according to the embodiment of the present invention, (b) is a view of the FPC board as seen from the coaxial pin side (a view in the direction of arrow A in (a)). , (C) is a rear view of the optical transmission module (TO-CAN package) (with (a) rotated 180 degrees), and (d) is a view of the FPC board viewed from the DC pin side (B in (c)). Direction arrow view). It is sectional drawing of the optical transmission module which concerns on Example 1 of this invention. It is a figure which shows the dimension of the optical transmission module which concerns on Example 1 of this invention. It is a figure which shows the structure of the optical transmission module which concerns on Example 1 of this invention. It is sectional drawing which shows the example of mounting inside a TO-CAN package. It is a figure which shows the figure which shows the structure (flow of RF signal) of the optical transmission module which concerns on Example 1 of this invention. It is a figure which shows the influence which a resistance value and an air gap have on an electrical property. It is a figure which shows the small signal characteristic of the optical transmission module which concerns on Example 1 of this invention. It is a figure which shows the 40 Gb / s modulation characteristic (eye waveform at the time of 40 Gb / s operation | movement) of the optical transmission module which concerns on Example 1 of this invention. It is a figure which shows the structure (flow of RF signal) of the optical transmission module which concerns on Example 2 of this invention. It is a figure which shows the state which connected the optical fiber to the optical transmission module which concerns on Example 3 of this invention. It is sectional drawing of the optical transmission module which concerns on Example 3 of this invention. It is a dimensional drawing of the produced FPC board, (a) shows the surface of an FPC board and (b) shows the back of an FPC board. It is sectional drawing which shows the mounting example inside the TO-CAN package in the optical transmission module which concerns on Example 4 of this invention. It is a schematic diagram of an electric signal fed to a direct modulation laser. (A) is a block diagram of a conventional optical transmission module using a multilayer ceramic package, a high frequency connector and a high frequency cable, and (b) is a basic configuration diagram of an optical transmission module using the TO-CAN package and FPC board of the present invention. is there. (A) is a sectional view of a conventional optical transmission module using a TO-CAN package and an FPC board, and (b) is a sectional view of another conventional optical transmission module using a TO-CAN package and an FPC board. It is explanatory drawing of the influence of an air gap.

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

  In the present invention, the optical transmission module having the configuration as shown in FIG. 1B is used so that the air gap at the connection between the FPC board 12 and the TO-CAN package 13 is zero. FIG. 1A shows the definition of the air gap. As shown in FIG. 1A, the air gap is a distance between the back surface of the TO-CAN package 12 and the tip of the FPC board 12. FIG. 1B shows a schematic diagram of an actual connection method. The purpose of this connection method was to transmit a 40 Gb / s RF signal from the FPC board 12 to the inside of the TO-CAN package 13 with low transmission loss and low reflection loss.

The optical transmission module of the present invention is mainly composed of three elements. These three elements are described in detail below.
(1) FPC board structure (material selection / signal line design) to achieve low transmission loss and low reflection loss.
(2) Connection method between FPC board and TO-CAN package.
(3) An FPC board fixing method for realizing the connection method of (2).

  The FPC board 12 is a signal line for transmitting an electrical signal for driving the optical transmission module from the PCB (see FIG. 32B) to the optical transmission module. When driving an optical transmission module with a direct modulation laser (DML) mounted inside as an optical semiconductor element, the 40 Gb / s high-frequency electrical signal (RF signal) for driving the LD part of the DML is reduced to DML. It is necessary to supply power with transmission loss and low reflection loss. The problem is to realize a high-frequency signal line (RF signal line) with low transmission loss and low reflection loss on the FPC board 12. Therefore, selection of a material when manufacturing the FPC board 12 will be described first.

2A shows a schematic cross-sectional view of an RF signal line 52 of an FPC board 51 manufactured using a conventional ceramic material, and FIG. 2B shows an FPC manufactured using an LCP (liquid crystal polymer) material. The cross-sectional schematic diagram of the RF signal track | line 26 of the board | substrate 12 is represented. The LCP material (relative permittivity ε _r : 4) has a relative permittivity ε _r smaller than that of the ceramic material. Therefore, if the FPC board 12 and the FPC board 51 have the same board thickness, and the widths W _LCP and W _ceramic of the RF signal lines 26 and 52 are designed so that the characteristic impedance is 50Ω, the RF signal when a ceramic material is used. than the width W _Ceramic line 52, can be more of LCP material is wider design width W _LCP of the RF signal line 26. The merit of designing the wide width W _LCP of the RF signal line 26 is that the electric field is strongly coupled to GND, and the bending loss and transmission loss of the RF signal line 26 can be reduced.

First, the validity of the calculation method used in this study will be explained. All calculations were performed using Ansoft HFSS (high frequency circuit simulator).
FIG. 3A shows a photograph of the FPC board 12 used for calculation / measurement. The substrate material of the FPC board 12 is LCP. An RF signal line 26 examined by HFSS and a conventional DC signal line (DC line) 27 are formed. FIG. 3B shows a measurement result and a calculation result regarding the result of the characteristic evaluation of the manufactured FPC board 12. As the frequency increases, S ₂₁ representing transmission loss gradually decreases. S ₂₁ in the vicinity of 30GHz was obtained a value of both the calculation results and measurement results -0.5 dB. On the other hand, as the frequency increases, S ₁₁ representing reflection loss gradually increases. S ₁₁ in the vicinity of 30GHz was obtained a value of both the calculation results and measurement results -16 dB. It can be seen that the result agrees well with the calculation. The difference between calculation and measurement above 35 GHz reflects the result of insufficient measurement jig bandwidth. Thus, it was found that the calculation was good and the experimental results could be reproduced, and the calculation method was valid. In the following, the effect of various parameters on electrical characteristics will be examined using calculations.

Next, ceramic and LCP were used as substrate materials for the FPC substrate, and RF signal lines in each case were studied. FIG. 4A is a diagram of a connection portion between the FPC 51 in the case of a ceramic material and the coaxial pin 22 of the TO-CAN package 13, and FIG. 4B is a diagram of the FPC board 12 and the TO-CAN package 13 in the case of an LCP material. It is a figure of the connection part of the coaxial pin 22. FIG. 4C shows the result of calculating the electrical characteristics for each case of FIG. 4A and FIG.
As a commonly used value, the thickness of the FPC boards 12 and 51 was 0.21 mm. The widths W _LCP and W _ceramic of the RF signal lines 26 and 52 for setting the characteristic impedance to 50Ω are uniquely determined when the thickness of the FPC substrates 12 and 51 and the material (relative dielectric constant) of the FPC substrates 12 and 51 are determined. Is done. The design values of the widths W _LCP and W _ceramic of the RF signal lines 26 and 52 are 0.4 mm and 0.18 mm when ceramic and LCP are used as the substrate materials of the FPC substrates 12 and 51, respectively. A comparison of the electrical characteristics when both are connected so that the air gap is 0 mm will be described.
As shown in FIG. 4C, as the frequency increases, S ₂₁ representing transmission loss gradually decreases. The ceramic material showed a sharp decrease, whereas the LCP material was less than -0.3 dB even at 40 GHz. On the other hand, as the frequency increases, S ₁₁ representing reflection loss gradually increases. The S ₁₁ at 40 GHz deteriorates to −13 dB at 40 GHz for ceramic materials, while a good value of −17 dB can be secured for LCP materials. Generally, in order to obtain good characteristics, it is necessary to suppress electric reflection to -15 dB or less. This result shows that the characteristics necessary for 40 GHz operation can be secured by using LCP as the substrate material of the FPC board 12.

  The structure of the RF signal line using LCP as the substrate material of the FPC board was studied. The purpose is to realize an RF signal line with low transmission loss and low reflection loss. FIG. 5A and FIG. 5B respectively show a cross-sectional view and a top view of a connection portion between the FPC board 12 and the coaxial pin 22 of the TO-CAN package 13. The thickness of the FPC board 12 is 0.05 mm, which is a common value used in the 10 Gb / s technology. The length of the FPC board 12 is also 10 mm which is a general value. The diameter of the conductor of the coaxial pin 22 of the TO-CAN package 13 is set to 0.3 mm, which is a general value used in the technology of 10 Gb / s. Considering the connection with the coaxial pin 13, the width of the connection portion 26a in the RF signal line 26 of the FPC board 12 is set to 0.3 mm. As shown in FIG. 5B, it was considered to arrange a ground electrode (GND) 28 on the upper surface of the FPC board 12 with an interval ΔW [mm] from the RF signal line 26.

FIGS. 6A and 6B are schematic diagrams of the connection portion 26 a in the coaxial pin 22 of the TO-CAN package 13 and the RF signal line 26 of the FPC board 12. When only the coaxial pin 22 is considered as shown in FIG. 6A, when the characteristic impedance of the portion of the coaxial pin 22 embedded in the glass 24 (the portion in the range of L _{1 in} the figure) is matched to 50Ω, The characteristic impedance of the portion of the coaxial pin 22 exposed to the air (the portion in the range of L1 in the figure) becomes larger than 50Ω. On the other hand, when focusing on the FPC board 12, when the characteristic impedance of the RF signal line 26 (the portion in the range of L3 in the figure) is matched to 50Ω, the ground electrode 28 disposed on the upper surface (front surface) of the FPC 12 and the RF signal line When the interval ΔW of 26 is reduced, the characteristic impedance of the RF signal line 26 in the portion where the ground electrode 28 is disposed (the portion in the range of L _{4 in} the figure) becomes smaller than 50Ω. By connecting the two, the value of ΔW is examined so that the characteristic impedance of the connection matches 50Ω. Actually, the calculation was performed by increasing ΔW to 0.1 to 0.5 mm.

FIGS. 7A, 7B and 7C show the calculation results of the S ₂₁ / S ₁₁ characteristics when ΔW = 0.4 mm, ΔW = 0.3 mm and ΔW = 0.2 mm. The smaller the ΔW, the lower the impedance of the RF signal line 26 of the FPC board 12 because the ground electrode 28 approaches the RF signal line 26. If only the coaxial pin 22 is considered, the portion of the coaxial pin 22 exposed to the air has a high impedance. By connecting the high-impedance coaxial pin 22 to the RF signal line 26 (connection portion 26a) of the low-impedance FPC board 12, the impedance at this connection point as a whole is considered to approach 50Ω. Therefore, the calculation shows that the smaller the ΔW is, the better the result is obtained with less degradation of the S ₁₁ characteristic.

FIG. 8 is a graph in which ΔW is plotted on the horizontal axis and the calculation result of the value of S ₁₁ at 40 GHz is plotted on the vertical axis. As ΔW becomes smaller, the S ₁₁ characteristic at the connection point shows a better value. It is desirable to S ₁₁ characteristics are below -15dB is ΔW is 0.3mm or less. On the other hand, there is a limit in manufacturing to reduce ΔW. This is because when soldering is used, solder oozes out, so it is desirable that ΔW be 0.2 mm or more. According to the calculation results, it can be seen that good characteristics are exhibited when ΔW = 0.1 to 0.3 mm.
This calculation is the result when the thickness of the FPC board 12 is 0.05 mm, the diameter of the coaxial pin 22 is 0.3 mm, and the width 26 mm of the connection portion 26 a of the RF signal line 26 on the FPC board 12. Even when the thickness of the substrate 12 is 0.05 mm, the diameter of the coaxial pin 22 is 0.4 mm, and the width of the connecting portion 26 a of the RF signal line 26 on the FPC substrate 12 is 0.4 mm, ΔW is good between 0.1 and 0.3 mm. It was confirmed that the calculation result was obtained.

  When the TO-CAN package 13 is used, an RF signal is transmitted using the coaxial pin 22. When connecting the coaxial pin 22 and the FPC board 12, it is necessary to arrange the ground electrode 28 around the connection part 26 a of the RF signal line 26 in the FPC board 12 and match the impedance of the connection part 26 a to 50Ω. It becomes. In particular, in order to realize 40 Gb / s operation, it is necessary to suppress impedance mismatching. For this reason, it is necessary to examine and determine the value of ΔW.

FIG. 9 shows a conceptual diagram of a connecting portion (no air gap) between the TO-CAN package 13 and the FPC board 12 constituting the optical transmission module. FIG. 9A is a view of the optical transmission module as viewed from the back, and FIG. 9B is a cross-sectional view of the optical transmission module. By connecting as shown in FIG. 9, the deviation of the characteristic impedance due to the air gap is suppressed. For this purpose, a connection method (connection work procedure) will be described below.
(1) First, the FPC board 12 and the coaxial pin 22 are made parallel.
(2) Next, the front end surface of the FPC board 12 is pressed against the back surface (wall) 13 of the TO-CAN package 13 (that is, the back surface of the bottom portion 13b and the back surface of the glass 24) to eliminate the air gap.
(3) Next, the positions of the coaxial pin 22 and the RF signal line 26 are confirmed from above, and the positions of both are aligned.
(4) Next, the front end surface of the FPC board 12 and the portion of the back surface 13 of the TO-CAN package 13 against which the front end surface is pressed are fixed by soldering.
(5) Further, the RF signal line 26 and the coaxial pin 22 are also fixed by soldering.

Temporarily, the influence which it has on the electrical property when the air gap Z exists as shown in FIG. As shown in FIG. 10B, when the air gap Z increases from 0 mm to 0.5 mm, S ₁₁ increases from −18 dB to −9 dB at 40 GHz. In order to obtain -15 dB in order to obtain good characteristics using high-frequency device characteristics, the air gap Z needs to be 0.1 mm or less. In the conventional connection method, for example, the connection method introduced at 10 Gb / s and 25 Gb / s, it is impossible to make the air gap of the connection part 0.1 mm or less in this way because of the structure. According to the configuration of the present invention, the air gap can be practically zero, and thus it is possible to ensure good S ₁₁ .

Next, FIG. 11 shows the influence on the electrical characteristics of the deviation (height deviation) Δh in the height direction at the connection portion between the coaxial pin 22 and the FPC board 12. As shown in FIG. 11A, the height shift and Δh are distances between the lower side of the coaxial pin 22 and the surface (upper surface) of the FPC board 12. As shown in FIG. 11B, the air gap Z was fixed to 0 mm, and the height deviation Δh was changed from 0.1 mm to 0.3 mm. According to the calculation, when Δh is 0.1 mm, S ₁₁ is −20 dB at 40 GHz, whereas when Δh is 0.3 mm, the deterioration is −14 dB and −15 dB. Therefore, it is desirable that the height deviation Δh is 0.2 mm or less. With the conventional method that reported 25 Gb / s operation, it is impossible to make the height deviation 0.2 mm or less. With the configuration of the present invention, the height deviation can be made virtually zero, so that a favorable S ₁₁ can be ensured.

  Next, the FPC thickness was set to 0.21 mm, and other effects were also calculated. For example, the dependency on the distance ΔW between the RF signal line 26 and the ground electrode 28 shown in FIG. 12A is shown in FIG. Note that the air gap Z = 0 mm, the height deviation Δh = 0.2 mm, and the width W of the RF signal line 2 = 0.32 mm. It has been found that when the thickness of the FPC board 12 is 0.051 mm, the characteristic is not greatly deteriorated when the thickness is 0.21 mm. Further, as shown in FIGS. 13 (a) and 13 (b), it was calculated whether or not the ground electrode 28 was inserted into the connecting portion of the FPC board 12 (both the air gap Z was 0 mm). As shown in (c), no significant characteristic difference was observed.

  These calculation results show that when the FPC board 12 is 0.21 mm thick, it is the air gap Z and the height deviation Δh that have a great influence on the electrical characteristics. The connection method was shown to be very useful.

  Next, in order to realize the connection method proposed in (2) above, a method for fixing (connecting) the FPC board, which is a component of the optical transmission module of the present embodiment, and the TO-CAN package will be described.

FIG. 14 shows an explanatory diagram of the connection method. FIG. 14A shows a perspective view of the back side of the connecting portion between the FPC board 12 and the TO-CAN package 13 of the optical transmission module, and FIG. 14B shows a cross-sectional view thereof. In these drawings, reference numeral 21 denotes a place where the FPC board 12 and the TO-CAN package 13 are soldered.
FIGS. 14C and 14D are rear photographs of the TO-CAN package 13 and show the arrangement of the high-frequency coaxial pins 22 and a plurality of direct current (DC) pins 23. Hereinafter, the plurality of DC pins 23 are also referred to as a first DC pin 23, a second DC pin 23, and a third DC pin 23 in order from left to right in FIGS. 14 (c) and 14 (d). The coaxial pin 21 is a cylindrical conductor, is an insulator provided on the bottom portion 13a of the TO-CAN package 13, passes through the central portion of the cylindrical glass 24, and is coaxial with the glass 24 (that is, around the periphery). Both sides of the TO-CAN package 13 protrude outside (to the right in FIG. 14B) and inside (to the left in FIG. 14B). Each DC pin 23 also penetrates the bottom portion 13 a and both side portions protrude to the outside and inside of the TO-CAN package 13.

  As shown in FIGS. 14A to 14D, the TO-CAN package 13 includes a coaxial pin for conducting a high-frequency electrical signal to an optical semiconductor element mounted inside the TO-CAN package 13. 22 and a plurality of DC pins 23 are arranged in parallel. A method of fixing the FPC board 12 using these pins 22 and 23 will be described.

First, as shown in FIGS. 14A and 14B, the FPC board 12 is aligned with the coaxial pin 22 and the other three DC pins 23 so that the height deviation is 0 and the air gap is 0. Deploy. Then, the FPC board 12 and the TO-CAN package 13 are fixed using solder at the soldering location 21. That is, the entire front end surface of the FPC board 12 (that is, the entire width direction of the FPC board 12 indicated by an arrow D in FIG. 14A) is connected to the back surface 13b of the TO-CAN package 13 by soldering. Yes. Further, the coaxial pin 22 (portion protruding outside the TO-CAN package 13) and the high-frequency signal line (RF signal line) 26 arranged on the surface of the FPC board 12 are also connected by soldering.
Thereafter, the DC pins 23 and the FPC board 12 are fixed using solder as shown in FIG. That is, each DC pin 23 (the part protruding outside the TO-CAN package 13) under the FPC board 12 extends straight in parallel with the FPC board 12 as shown by a one-dot chain line in FIG. In this state, it is bent upward (in the direction of the FPC board 12) as shown by an arrow E to obtain a state indicated by a solid line in FIG. 14B, and three positions on the back surface of the FPC board 12 (DC signal lines arranged on the back surface). ) By soldering (soldering location 25).

  Next, a method for wiring the DC pins 23 will be described. FIGS. 15A and 15B show photographs of the TO-CAN package 13 viewed from the back side. In FIG. 15A, three DC pins 23 are provided, but the number of DC pins 23 can be increased according to the size of the TO-CAN package 13. FIG. 15B shows a case where four DC pins 23 are provided. Hereinafter, the four DC pins 23 are also referred to as a first DC pin 23, a second DC pin 23, a third DC pin 23, and a fourth DC pin 23 in order from left to right in FIG. .

  FIG. 16 shows the internal arrangement of the TO-CAN package 13. In the illustrated example, a DML 31, a high-frequency circuit board 32, a monitor PD 33, a chip resistor 35 of 40Ω to 45Ω, a thermistor 36, and the like are arranged inside the TO-CAN package 13. The DC pin 23 is used for LD injection current, monitor PD 33 and thermistor 36 when the DML 31 is mounted inside the TO-CAN package 13. Each element (DML laser 31, monitor PD 33, thermistor 36) inside the TO-CAN package 13 is connected to each DC pin 23 using a gold wire. Only the high-frequency coaxial pin 22 is connected to the high-frequency circuit board 32 inside the TO-CAN package 13 using solder.

  The arrangement of the pins 22 and 23 will be described. FIG. 17 shows the arrangement of the pins 22 and 23 when the FPC board 12 is connected to the TO-CAN package 13. 17A and 17B show the case where the first to fourth DC pins 23 are located below the FPC board 12, and the first to fourth DC pins 23 are located above the FPC board 12. FIG. FIG. 17C and FIG. The second DC pin 23 is closest to the position of the coaxial pin 22. The fourth DC pin 23 is located farthest from the coaxial pin 22. As described above, the DC pin 23 is used for LD injection current, for the monitor PD 23, and for the thermistor 36 when DML is mounted. However, the DC pin 23 is also used for driving the temperature adjusting element as necessary. In the example of FIGS. 17B and 17D, the outermost DC signal line 27a of the two short DC signal lines 27a provided on the back surface of the FPC board 12 is the furthest away from the coaxial pin 22. The fourth DC pin 23 is connected by soldering, and the third DC pin 23 is connected by soldering to the inner DC signal line 27a. Two DC signal lines 27 are provided on the surface of the FPC board 12, and the outer DC signal line 27 a of the two DC signal lines 27 is connected to the outer DC signal line 27 of the FPC board 12. The inner DC signal line 27 is electrically connected to the inner DC signal line 27 through the through hole (not shown) of the FPC board 12. .

  A case where the DC pin 23 is used only for the LD injection current, the monitor PD 23, and the thermistor 36 will be described. In this case, the largest current flowing through the DC pin 23 is the DC pin 23 for LD injection current. When the DC pin 23 is connected to the back surface of the FPC board 12, heat is generated by a current flowing through the connecting portion between the DC pin 23 and the FPC board 12 (see the heat generating part 41 in FIG. 17D). Then, the temperature of the RF signal line 26 is increased by conducting heat from the connection portion to the RF signal line 26. When a thermal gradient occurs in a part of the RF signal line 26 due to this temperature rise, the characteristic impedance of the RF signal line 26 changes, and as a result, the electrical characteristics of the RF signal line 26 are deteriorated. In particular, since the FPC board 12 is as thin as 0.05 mm, this effect appears remarkably. Therefore, it is desirable that the DC line for the LD and the connection portion be separated from the RF signal line 26 as much as possible. Therefore, the fourth DC pin 23 located farthest from the coaxial pin 22 (RF signal line 26) is allocated for the LD injection current.

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

[Example 1]
(Construction)
FIG. 18 shows a configuration diagram of the optical transmission module according to the first embodiment of the present invention. In the optical transmission module of the first embodiment, the FPC board 12 and the DC wiring board 62 are soldered to the front surface (upper surface) and back surface (lower surface) of the hard metal base 61, respectively, and the integrated base 61 and FPC board are integrated. 12 and the DC wiring board 62 are sandwiched between the coaxial pin 22 and the DC pin 23 of the TO-CAN package 13 so that there is no air gap and no height shift. The RF signal for driving the DML mounted in the TO-CAN package 13 is transmitted through the RF signal line of the FPC board 12 placed on the hard metal base 61.

(Size)
The FPC substrate 12 was made of LCP material. The thickness of the FPC board 12 was 0.2 mm and the length was 10 mm. The dimensions of the connecting portion between the TO-CAN package 13 and the FPC board 21 are as shown in FIG. That is, the diameter of the coaxial pin 22 is 0.3 mm, the width of the connection portion 26a of the RF signal line 26 is 0.3 mm, and the width of the RF signal line 26 away from the connection portion 26a is 0.32 mm. As described in the embodiment, since the air gap and the height shift greatly affect the characteristics, the FPC board 22 and the TO-CAN package 13 are connected so that the air gap becomes zero as shown in FIG.

(Implementation procedure)
FIG. 20 shows the configuration of the optical transmission module of the first embodiment. The diameter of the TO-CAN package 13 is 7.4 mm. As a mounting flow, necessary elements are mounted in the TO-CAN package 13, and the lens cap 63, ferrule holder 65, ferrule 66, optical fiber 64, and the like are connected, and then the FPC board 12 is connected. First, the procedure for mounting the internal elements of the TO-CAN package 13 will be described. A simple connection diagram inside the TO-CAN package 13 is shown in FIG. 21A, and a photograph is shown in FIG. As shown in FIG. 21, a DML 31 is used as an optical semiconductor element mounted inside the TO-CAN package 13. The DML 31 has an LD unit 31a.

  The mounting of elements in the TO-CAN package 13 and the connection between the TO-CAN package 13 and the FPC board 12 were performed in the following procedure.

(1) The DML 31 is soldered to the heat sink 37 (mainly AlN is used) using die bonding.
(2) Next, the heat sink 37 is soldered to the center of the TO-CAN package 13 using die bonding.
(3) The high-frequency circuit board 32, the chip resistor 35 of 40Ω to 45Ω, the monitor PD 33, and the thermistor 36 are mounted in the TO-CAN package 13 as shown in FIGS. 20 and 21 using silver paste or solder.
(4) The high frequency circuit board 32 and the coaxial pin 22 are soldered.
(5) The high frequency circuit board 32, the DML 31 (LD unit 31a), the 40Ω to 45Ω chip resistor 35, the monitor PD 33, and the like are wired using the wire 67.
(6) Attach the lens cap 63 to the TO-CAN package 13 by seam welding.
(7) The optical fiber 64 is YAG welded to the TO-CAN package 13 after the lens cap 63 is welded.
(8) The FPC board 12 is connected as described above to the TO-CAN package 13 on which the elements are mounted after completing the steps up to (7).

  The arrangement of elements inside the TO-CAN package 13 in the first embodiment will be described. FIG. 22 is a schematic diagram of the flow of the RF signal. The RF signal transmitted from the FPC board 12 is then transmitted in the order of coaxial pin 22 → high frequency circuit board 32 (inside the TO-CAN package 13) → chip resistance 35 of 40Ω to 45Ω → DML 67. The RF signal lines (high-frequency signal lines) 32a of the FPC board 12, the coaxial pin 22, and the high-frequency circuit board 32 are all designed to match 50Ω. Since the resistance of the semiconductor element (DML 31) is generally about 5 to 10Ω, when the wire 67 is directly connected to the semiconductor element (DML 31) from the high-frequency circuit board 32 matched to 50Ω, the impedance suddenly increases from 50Ω to 5Ω. It becomes 10Ω and induces a large electric reflection. In order to suppress this, a resistor 35 of about 40Ω to 45Ω is placed in front of the semiconductor element (DML 31). The value of the resistor 35 is determined so that the total resistance of the semiconductor element (DML 31), the resistor 35, and the wire 67 used for connection is 50Ω.

  In the present invention, the deterioration of the connecting portion between the FPC board 12 and the coaxial pin 22 that has deteriorated the characteristics most in the prior art is suppressed by setting the air gap to 0 mm to 0.1 mm. Therefore, a 40 Gb / s RF signal can be transmitted to the high frequency circuit board 32 with little deterioration. In addition to this, good characteristics can be obtained by using the connection method of the resistor 35 of 40Ω to 45Ω and the DML 31 described above.

FIG. 23 shows the influence of the value of the resistor 35 placed in front of the DML 31 and the air gap (Z [mm]) on the S ₁₁ characteristics (at 40 GHz). All results are calculation results. If the FPC board 12 and the TO-CAN package 13 are connected so that the air gap is 0 to 0.1 mm or less, and the resistance 35 in front of the DML 31 is 35 Ω to 48 Ω, the S ₁₁ characteristic at 40 GHz can be reduced to -15 dB or less. It is shown that.

  From the above, it can be seen that, in addition to the connection method that takes a sufficiently small air gap, the overall impedance can be matched to 50Ω and good characteristics can be obtained by matching the resistance of the element to 50Ω.

(Experimental result)
FIG. 24 shows the small signal response characteristics of the manufactured TO-CAN module (optical transmission module) of the first embodiment. As described above, the DML 31 is mounted inside the TO-CAN package 13, and a 40Ω resistor 35 is disposed in front of the DML 31. FIG. 23 also shows the results of only elements having the same characteristics. The E-O 3dB bandwidth of the TO-CAN module (optical transmission module) is 29GHz, which is inferior to that of the 35GHz device alone. Thus, it was possible to secure good characteristics capable of 40 Gb / s operation with the configuration of the TO-CAN package 13 and the FPC board 12 without using an expensive connector and an expensive multilayer ceramic package.

FIG. 25 shows the 40 Gb / s modulation characteristics of the manufactured TO-CAN module. As a high-frequency electric signal, 40 Gb / s, NRZ, PRBS2 ³¹ -1 was used. A clear 40 Gb / s modulation waveform was confirmed for the TO-CAN module 13 equipped with a 1.3 mm direct modulation laser (DFB laser). The light output and extinction ratio were confirmed to be sufficient values.

[Example 2]
FIG. 26 shows the configuration of the optical transmission module according to the second embodiment of the present invention. In the second embodiment, the following one point is changed from the first embodiment. That is, the configuration of the chip resistor 35 and the high-frequency circuit board 32 placed immediately before the DML 31 is changed.
In the second embodiment, a resistance portion 81 of 40Ω to 45Ω is embedded in the high frequency circuit board 32. The characteristic impedance of the resistance unit 81, the wire 67, and the DML 31 is set to 50Ω. The high-frequency signal line 32a of the high-frequency circuit board 32 is generally formed by patterning an Au material using photolithography. Resistor 81 is similarly formed of Ta ₂ N metal on high-frequency circuit board 32. The resistance value of the resistance portion 81 is largely changed by the film thickness of Ta ₂ N, and then finely adjusted by the pattern dimension. For example, consider a case where a 40Ω resistor 81 is embedded. First, the film thickness of Ta ₂ N is formed so that the resistance value becomes 100Ω / □ (meaning the resistance value per area). Thereafter, L _{2 is set} to 0.3 mm, for example. L ₁ automatically becomes 0.12 mm in consideration of the resistance value around the area. Therefore, the resistance value can be changed by changing the values of L ₁ and L ₂ .

In the second embodiment, compared to the configuration in which the chip resistor 35 of the first embodiment is placed in front of the DML 31, there is an advantage that the work for arranging the elements is simplified and the number of wires 67 can be reduced. Therefore, impedance mismatch at the wire 67 can be suppressed, and an improvement in electrical characteristics is expected.
Furthermore, since the resistance portion 81 can be arranged away from the DML 31, the influence of heat generation can be suppressed compared to the first embodiment. If the influence of heat generation can be suppressed, the DML 31 can be operated at a low temperature, and high output characteristics can be obtained.

[Example 3]
(Construction)
FIG. 27 shows a configuration diagram of an optical transmission module according to Embodiment 3 of the present invention. In the first embodiment (FIG. 20), the FPC board 12 is placed on the hard metal base 61. However, in the third embodiment, only the FPC board 12 is used as shown in FIG. FIG. 28 shows a structural diagram in which the FPC board 12 is connected to the TO-CAN package 13 as described in the embodiment. The electrical wiring for driving the DML 31 is configured to conduct the RF signal to the RF signal line formed on the FPC board 12. The DC component was supplied from the DC wiring board on the lower side of the FPC board 12. The arrangement of the DC pin 23 is as described in the embodiment. The internal configuration of the TO-CAN package 13 is the same as that of the first embodiment.

(Size)
The FPC substrate 12 was made of LCP material. The thickness of the FPC board 12 was 0.05 mm and the length was 10 mm. The dimensions of the connecting portion of the FPC board 12 are shown in FIG. That is, the width of the connection part 26a with the coaxial pin 22 in the RF signal line 26 is 0.3 mm, and the width of the RF signal line 26 away from the connection part 26a is 0.1 mm. As described in the embodiment, since the air gap greatly affects the characteristics, the FPC board 12 and the TO-CAN package 13 are connected so that the air gap becomes zero as shown in the structural diagram of FIG.

The superiority of the LCP material over the ceramic material is as described in the embodiment.
The advantage of the third embodiment over the first embodiment is that the number of parts is reduced and the cost is reduced, and compatibility with the 10 Gb / s technology is produced. Compared to the first embodiment, the electrical GND strength (in the first embodiment, the entire thick metal base 61 falls to the GND, but in the second embodiment, only the metallized portion on the back surface serves as the GND) The electrical characteristics are lowered due to weakness. However, since the air gap, which is the biggest cause of characteristic deterioration, is suppressed, a clear optical eye waveform can be obtained even at 40 Gb / s operation.

[Example 4]
(Construction)
FIG. 30 shows a structural diagram of an optical transmission module according to the fourth embodiment of the present invention. Unlike the third embodiment, in the fourth embodiment, an electric signal for driving the DML 31 is divided into an RF signal component (Vpp) and a DC signal component (I _LD ). As shown in FIG. 30, the RF signal component (Vpp) passes through the coaxial pin 22 from the FPC board 12 and the optical semiconductor element (DML 31) inside the TO-CAN package 13 in the same manner as the RF signal components of the first to third embodiments. Is supplied with power. The DC signal component (I _LD ) is conducted through the DC pin 23 of the TO-CAN package 13 in the same manner as the current injected into the DFB laser unit 31b of the first and second embodiments, and then the optical semiconductor element using the wire 67 Power is supplied to (DML31). The DC pin 32 is arranged in the same manner as described in the embodiment. FIG. 32 shows the current I _LD that varies with the RF signal Vpp.

Compared with the third embodiment, the fourth embodiment can input the RF signal component (Vpp) and the DC signal component (I _LD ) separately, so that the amount of current passing through the resistor 35 of 40Ω to 45Ω can be reduced. Can greatly reduce the amount of heat generated in By suppressing the heat generated by the resistance 35 of 40 to 45Ω, the temperature of the optical semiconductor element (DML 31) is prevented from increasing due to heat conduction, and as a result, the temperature of the optical semiconductor element (DML 31) during operation is decreased. Can do. When the temperature of the optical semiconductor element (DML 31) during operation is lowered, the threshold current of the optical semiconductor element (DML 31) can be lowered and the output is improved, so that superior characteristics can be obtained.

It should be noted that the dimensions of the components in the optical transmission module (TO-CAN module) may be dimensions other than those shown in the embodiment as long as the components fit in the TO-CAN package 13.
Moreover, although LCP is used as the substrate material of the FPC board 12 in the above embodiment and each example, other materials may be used as the substrate material of the FPC board 12.
Moreover, although the above embodiment and each example are aimed at 40 Gb / s operation, the present invention can be applied in a high frequency band of 25 Gb / s to 100 Gb / s.

  The present invention relates to an optical transmission module using a TO-CAN package and an FPC board, and an RF signal of 25 Gb / s to 100 Gb / s (for example, 40 Gb / s) can be transmitted from the FPC board with low transmission loss and low reflection loss. -It is useful when applied to the realization of an optical transmission module that can transmit to the inside of the CAN package.

1. Electrical circuit of optical transceiver (PCB)
2 High-frequency cable 3 High-frequency connector 5 Multilayer ceramic package 6 Optical transmission module 11 Optical transmission module 12 FPC board 13 TO-CAN package 13a Bottom of TO-CAN package 13b Rear surface of TO-CAN package 21 Solder location 22 Coaxial pin 23 DC Pin 24 Glass 25 Location to be soldered 26 High-frequency signal line (RF signal line)
26a Connection part of RF signal line 27 DC signal line 28 Ground electrode 31 Direct modulation laser (DML)
31a LD section 32 high frequency circuit board 32a high frequency signal line 33 monitor PD
35 40Ω to 45Ω chip resistance 36 Thermistor 37 Heat sink 41 Heat generating part 51 FPC board 52 RF signal line 61 Metal base 62 DC wiring board 63 Lens cap 64 Optical fiber 65 Ferrule holder 66 Ferrule 67 Wire 81 Resistance part of 40Ω to 45Ω

Claims (7)

It has a TO-CAN package and an F PC board,
The back surface of the TO-CAN package and the front end surface of the FPC board are arranged via an air gap, and the coaxial pins arranged in the TO-CAN package and the FPC board are arranged in parallel. Has been
Spacing of the FPC substrate before and Symbol coaxial pins, so that the 0 or 0.1mm or less, the coaxial pins is connected to the high-frequency signal transmission line disposed on a surface of said FPC board,
A plurality of DC pins arranged in the TO-CAN package are bent and connected to a DC signal line arranged on the back side of the FPC board,
The coaxial pin inside the TO-CAN package is connected to a high-frequency signal line disposed on a high-frequency circuit board disposed inside the TO-CAN package,
The high-frequency signal line disposed on the high-frequency circuit board, the resistor disposed inside the TO-CAN package, and the optical semiconductor element disposed inside the TO-CAN package are electrically connected,
From the high-frequency signal line disposed on the surface of the FPC board, through the high-frequency signal line and the resistor disposed on the coaxial pin and the high-frequency circuit board, conducting a high-frequency electrical signal to the optical semiconductor element,
The resistance value of the resistor is 40Ω or more and 45Ω or less,
A direct current is conducted to the optical semiconductor element through a DC pin located farthest from the coaxial pin among the plurality of DC pins and a connecting portion between the DC pin serving as a heat generating portion and the DC signal line. An optical transmission module characterized by having a configuration. The optical transmission module according to claim 1,
The optical transmission module, wherein the FPC board is made using an LCP material. The optical transmission module according to claim 1 or 2,
A high-frequency signal line disposed on the high-frequency circuit board is connected to the resistor via a first wire;
The optical transmission module, wherein the resistor is connected to the optical semiconductor element through a second wire. The optical transmission module according to claim 3,
An optical transmitter module, wherein the resistor, the second wire, and the optical semiconductor element have a characteristic impedance of 50Ω. The optical transmission module according to claim 1 or 2,
The resistor is disposed together with a high-frequency signal line disposed on the high-frequency circuit board,
The optical transmission module, wherein the high-frequency signal line disposed on the high-frequency circuit board is connected to an optical semiconductor element through a wire. The optical transmission module according to claim 5, wherein
An optical transmission module, wherein the resistor, the wire, and the optical semiconductor element have a characteristic impedance of 50Ω. In the optical transmission module according to any one of claims 1 to 6,
An optical transmission module, wherein the optical semiconductor element is a direct modulation laser.