JP2007207803A - Optical transmitting module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical transmitting module using a method of connecting a lead pin and a flexible substrate wherein mechanical strength is hard to be reduced and mismatching of impedance is suppressed. <P>SOLUTION: A flexible substrate 30 is provided with a rear GND conductor pattern 304 having partly a hole-like part without a conductor. Thus, a higher area and a lower area of an impedance in a signal line 301 than 50 Ω are alternately, and the length of each of areas is appropriately set so as to prevent mismatching of impedance of the signal line. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical transmission module for 10 Gbit / s using a semiconductor laser element, and more particularly to an optical transmission module incorporating a Peltier element and using a flexible printed circuit board as an output unit.

  Along with miniaturization of optical communication transceivers, miniaturization of optical transmission modules is progressing. Currently, an optical transmission module having a transmission rate of 10 Gbit / s with a transmission distance of 10 km or less has a direct-modulation type laser diode element mounted on a TO-CAN casing, and the casing and the main board of the transceiver are connected using a flexible board. What is connected is the mainstream. Non-Patent Document 1 describes an external view and the like of the transmitter. Non-Patent Document 1 connects an external connection lead pin of a housing and a through hole provided in a flexible substrate. This shortens the length of the lead pin between the optical transmission subassembly housing and the line pattern on the flexible substrate, and reduces the parasitic inductance due to the lead pin, thereby suppressing mismatching from the impedance of the input signal line and optical output. The waveform was good.

  In recent years, there has been an increasing demand for miniaturization of optical transmission modules having a transmission distance of 40 km or more. Specifically, a small module having a housing width of 6 mm is proposed in XMD-MSA (10 Gbit / s Miniature Device Multi Source Agreement). Usually, in an optical transmission module having a transmission distance of 40 km or more, the required number of external terminals increases by 8 or more from the number of external terminals of the optical transmission module having a transmission distance of 10 km or less by mounting a Peltier element. In addition, since the lead pins are usually arranged in a row, the pitch between the lead pins needs to be 0.67 mm or less.

  When connecting the lead pin through the flexible substrate, it is necessary to provide a hole portion through which the lead pin passes and a land portion on which the bonding material rides on the flexible substrate. At this time, since the clearance between adjacent land portions cannot be made large, a short circuit between the lead pin and the flexible substrate is likely to occur, and it is difficult to increase the number of pins. For example, to penetrate a lead pin of φ0.2 mm. A hole of φ0.3 mm is required on the flexible substrate. Further, the land portion on which the bonding material is placed needs to have a diameter of about 0.5 mm concentrically with the hole portion. If the distance between adjacent lands is set to 0.3 mm in order to prevent a short circuit due to the bonding material, the pin pitch is required to be 0.8 mm or more. If the housing width is 6 mm, the number of pins is approximately six.

On the other hand, when the flexible substrate is connected in parallel to the lead pins, a hole on the flexible substrate is not necessary, so that a clearance between the land portions can be increased. As a result, it is possible to increase the number of lead pins. In order to join a lead with a width of 0.2 mm, the width of the pad on the flexible substrate may be 0.35 mm. When the spacing between adjacent pads is 0.3 mm, the pin pitch is 0.65 mm and the housing width is 6 mm. In this case, it is possible to arrange approximately eight pins.
Non-Patent Document 2 describes an optical transmission module (optical transmission subassembly) in which a flexible substrate is connected to lead pins.

"10Gbps 850nm VCSEL HFE619x-56x", [online], April 20, 2005, Advanced Optical Components, [Searched on December 9, 2005], Internet <URL: http://www.advancedopticalcomponents.com/product /documents/HFE6x9x-56x_000.pdf#search=> XMD MSA committee, "XMD04 Physical Interface of LC TOSA Type 2 Package", Rev. 1.2, January 17, 2006

  However, in the connection pattern between the lead pin and the flexible substrate, the pattern width needs to be set slightly larger than the width of the lead pin in order to maintain the connection strength. Furthermore, it is inevitable that the impedance of the signal line greatly deviates from 50Ω due to restrictions on the relative dielectric constant and thickness of a general flexible substrate. When the pad width is 0.35 mm, the relative permittivity of a general flexible substrate is 3.2, and the thickness is 50 μm, the impedance of the signal line is extremely small compared to about 20Ω and 50Ω. If the pattern length of the connecting portion is simply shortened to suppress impedance mismatch, there is a problem that the mechanical strength at the connecting portion becomes insufficient.

  The present invention provides an optical transmission module using a method of connecting a lead pin and a flexible board without impairing impedance mismatch without impairing mechanical strength at a connection portion.

  In the present invention, by using a flexible substrate in which a GND conductor pattern having a hole pattern without a conductor is formed on a part of a back conductor, a region where the impedance of the signal line is higher than 50Ω and a region where the impedance is lower than 50Ω are alternately arranged along the transmission direction. Arranging and appropriately setting the length of each region suppresses the mismatch of the impedance of the signal line.

  The above-described problem is that a light-emitting element, a modulation element that modulates light from the light-emitting element and converts it into an optical signal, and a temperature adjusting unit that adjusts the temperature of the light-emitting element are incorporated in the housing and connected to the modulation element. A printed circuit board that is surface-connected between a plurality of lead pins including a plurality of lead pins and a plurality of pads on the surface of the printed circuit board, wherein the printed circuit board includes a signal line and a signal line connected to one of the plurality of pads on the surface An optical transmission module including a ground line formed on both sides and a ground pattern connected to the ground line on the back surface thereof, and having a slit-like notch on the ground pattern on the pad back surface connected to the signal line, Can be achieved.

  Also, a lead pin that is built in the housing and includes a light emitting element, a modulation element that modulates light from the light emitting element and converts the light into an optical signal, and temperature adjusting means that adjusts the temperature of the light emitting element, and is connected to the modulation element The printed circuit board can be achieved by an optical transmission module having an impedance converter.

  It is possible to obtain a good optical output waveform by suppressing the mismatch of the impedance of the signal line.

Hereinafter, embodiments of the present invention will be described using examples with reference to the drawings. Note that the same reference numerals are assigned to the same parts, and description thereof is not repeated.
An embodiment will be described with reference to FIGS. Here, FIG. 1 is a block diagram of the optical transmission module subassembly. FIG. 2 is a perspective perspective view of a connection portion between the optical transmission module subassembly and the flexible printed circuit board. FIG. 3 is a perspective plan view of a connection portion between the optical transmission module subassembly and the flexible printed circuit board. FIG. 4 is a cross-sectional view of a connection portion between the optical transmission module subassembly and the flexible printed circuit board. FIG. 5 is a Smith chart for explaining the impedance of the connection portion between the optical transmission module subassembly and the flexible printed circuit board.

  In FIG. 1, a common cathode (signal ground) of the EA modulator 12 and the laser diode 11 of the EA modulator integrated laser diode is output from a lead pin 22. For the sake of simplicity, only one signal grant is shown, but in reality, two signal grants are provided so as to sandwich the anode lead pin 21 of the EA modulator 12. The thermistor 14 is connected to the signal ground, and the other end of the thermistor is a thermistor lead pin 27. The signal ground is connected to the cathode of the photodiode 13 for light output monitoring, and the anode of the photodiode 13 is output from the lead pin 25. At least the EA modulator integrated laser diode and the thermistor 14 are mounted on a TEC (Thermo-Electric Cooler) 15 and the temperature is controlled by the TEC 15. At this time, both ends of the TEC 15 are connected to the lead pins 23 and 24, and the temperature is controlled from the outside based on the temperature detected by the thermistor 14.

  The forward light of the laser diode 11 is modulated by the integrated EA modulator 12. The modulated optical signal is coupled to an optical fiber (not shown) by an optical coupling system (not shown) and transmitted. The back light of the laser diode 11 is received by the photodiode 13, and the drive current is controlled so that the output of the laser diode 11 is constant. This drive current is supplied from the lead pin 26. On the other hand, the modulated electrical signal of the EA modulator 12 is supplied from the lead pin 21 via the signal line 16 having an impedance of 50Ω.

  In FIG. 2, the housing 10 and the flexible substrate 30 are connected by lead pins 21 and 22 with an interval of 0.6 mm. Here, the lead pin 21 is connected to the signal line 16 and the lead pin 22 is connected to the signal ground. The conductor pattern 301 on the surface of the flexible substrate 30 is a signal line. Further, the GND pattern 302 on the surface of the flexible substrate 30 is provided via the via 303. The flexible substrate 30 is connected to the GND pattern 304 on the back surface. On the back surface near the tip of the lead pin 21 of the conductor pattern 301, a slit-shaped back surface GND pattern hole portion (notch portion) 305 having a width of 1.0 mm is formed in the GND pattern 304.

In FIG. 3, the connection portion between the optical transmission module subassembly and the flexible printed circuit board can be divided into four regions I, II, III, and IV depending on the cross-sectional structure. That is, the region I is a gap portion between the housing 10 and the flexible substrate 30. The separation region II is a portion where the pad width of the flexible substrate is 0.35 mm and the back surface GND pattern 305 is present. Region III is a portion where the pad width of the flexible substrate is 0.35 mm and there is no back side GND pattern 305. The region IV is a portion where the wiring width of the flexible substrate is 80 μm (micrometer, 0.08 mm) and the back surface GND pattern 305 is present.
The length of each region in the signal line direction is region I: 0.6 mm, region II: 1.15 mm, region III: 1.0 mm, and region IV is about 15 mm.

  4, (a) is a cross-sectional view of region I, (b) is a cross-sectional view of region II, (c) is a cross-sectional view of region III, and (d) is a cross-sectional view of region IV. In addition, the position of a cross section is a direction shown to the area | region IV of FIG. 3, and only a cross-sectional part is shown in each figure (a side part is not shown in figure).

  Region I in FIG. 4A is composed of lead pins 21 and 22, and the periphery thereof is air. The lead pin has a width of 0.2 mm, a height of 0.1 mm, and a pin pitch of about 0.67 mm. The impedance of the signal line at that time is about 140Ω, which is larger than 50Ω.

  In the region II of FIG. 4B, a sufficient mechanical strength of the connecting portion can be obtained by setting the width of the conductor pattern 301 on the surface to 0.35 mm which is slightly larger than the lead pin width. Furthermore, since the pitch of the lead pins is 0.67 mm, the width between the conductor patterns 301 and 302 on the surface is 0.32 mm, and it is possible to simultaneously secure a width in which a short circuit of the bonding material does not occur. Here, in region II, the impedance is set to be smaller than 20Ω and 50Ω by providing the conductor pattern 304 on the back surface. Here, the relative dielectric constant of the flexible substrate was 3.2, and the thickness was 50 μm.

In the region III of FIG. 4C, the impedance is set larger than 95Ω and 50Ω by providing the hole 305 in the conductor pattern on the back surface while keeping the same size as the region II on the front surface.
In the region IV of FIG. 4D, the impedance is adjusted to 50Ω by setting the width of the conductor pattern 301 on the surface to about 80 μm.

  In FIG. 5, since the impedance of the signal line 16 is 50Ω, when the frequency is 10 GHz, the impedance of the signal line starts from 50Ω in the region I and is clockwise depending on the length of the signal propagation direction centering on 140Ω. Moving. Since the length of the signal propagation direction in the region 41 is 0.6 mm, the impedance is about 50.7Ω + j15.4Ω.

  In the region II, by setting the impedance intentionally lower than 50Ω, the impedance moves clockwise from the end point of the region I depending on the length of the signal propagation direction around 20Ω.

In the region III, the impedance of the signal line moves clockwise from the end point of the use region II depending on the length of the signal propagation direction around 95Ω.
As a result, the total impedance of the region I to the region III can be reduced to 49.8Ω and almost 50Ω. As a result, it was possible to match the impedance of the region IV.

In this way, regions I and III with high impedance and regions II with low impedance are alternately arranged, and by adjusting the length of each region, the impedance of the line is prevented from deviating from 50Ω, and a good optical output waveform is obtained. . Here, the case of the three regions I, II, and III has been described, but the same effect can be obtained even if the number of regions is three or more by alternately arranging regions having a higher impedance than 50Ω and regions having a lower impedance. . Increasing the number of regions can be realized by arranging two or more backside conductor pattern holes 305. Such a configuration is effective in a configuration in which the housing of the subassembly and the flexible substrate are connected by lead pins with an interval exceeding 0.4 mm.
The region I having a high impedance and the region II having a low impedance are indispensable configurations for connecting the housing and the flexible substrate. However, the high-impedance region III is a region formed intentionally and can be called an impedance converter.

A frequency of 10 GHz corresponds to a modulated electrical signal bit rate of 10 Gbit / s, and a suitable optical transmitter having a bit rate of approximately 10 Gbit / s can be realized. Here, an optical transmitter having a bit rate of approximately 10 Gbit / s is a SONET specification having a bit rate of 9.95 Gbit / s, 10.7 Gbit / s, 11.1 Gbit / s, and a bit rate of 10.3 Gbit / s, Including, but not limited to, the 11.3 Gbit / s 10 Gbit Ether specification.
In this specification, the optical transmission module is a module including a structure in which a flexible printed circuit board is connected to the optical transmission module subassembly.

It is a block diagram of an optical transmission module subassembly. It is a perspective perspective view of the connection part of an optical transmission module subassembly and a flexible printed circuit board. It is a see-through | perspective plan view of the connection part of an optical transmission module subassembly and a flexible printed circuit board. It is sectional drawing of the connection part of an optical transmission module subassembly and a flexible printed circuit board. It is a Smith chart explaining the impedance of the connection part of an optical transmission module subassembly and a flexible printed circuit board.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Housing, 11 ... Laser diode, 12 ... EA modulator, 13 ... Photodiode, 14 ... Thermistor, 15 ... TEC (Thermo-Electric Cooler), 16 ... Signal line, 21-27 ... Lead pin, 30 ... Flexible substrate , 301 ... Conductor pattern, 302 ... Front surface GND pattern, 303 ... Via, 304 ... Back surface GND pattern, 305 ... Back surface GND pattern hole.

Claims (5)

In an optical transmission module that includes a light emitting element, a modulation element that modulates light from the light emitting element and converts the light into an optical signal, and a temperature adjusting unit that adjusts the temperature of the light emitting element.
A printed circuit board for surface connection between a plurality of lead pins including a lead pin connected to the modulation element and a plurality of pads on the surface thereof;
The printed circuit board includes a signal line connected to one of the plurality of pads on a surface thereof, a ground line formed on both sides of the signal line, and a ground pattern connected to the ground line on a back surface thereof,
An optical transmission module comprising a slit-like notch in the ground pattern on the back surface of the pad connected to the signal line. In an optical transmission module that includes a light emitting element, a modulation element that modulates light from the light emitting element and converts the light into an optical signal, and a temperature adjusting unit that adjusts the temperature of the light emitting element.
A printed circuit board for surface connection between a plurality of lead pins including a lead pin connected to the modulation element and a plurality of pads on the surface thereof;
The optical transmission module, wherein the printed circuit board includes an impedance converter. The optical transmission module according to claim 1 or 2, wherein
The optical transmission module, wherein the casing and the printed circuit board are arranged with a gap of 0.4 mm or more. The optical transmission module according to claim 1 or 2, wherein
An optical transmission module having a bit rate of approximately 10 Gbit / s. The optical transmission module according to claim 1,
The width of the notch in the signal transmission direction is approximately 1 mm.

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