JP2016018969A - Optical module, optical transceiver module, and flexible substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical module capable of achieving enhancement of high frequency characteristics at a low cost, and to provide an optical transmitter receiver module, and a flexible substrate.SOLUTION: An optical module includes an optical semiconductor element, a housing for housing the optical semiconductor element, a lead terminal penetrating the housing while being insulated electrically therefrom, and connected electrically with the optical semiconductor element, and a wiring board on which a signal line connected electrically with the lead terminal is formed. The signal line includes a first signal line extending with a first width, a second signal line extending with a second width narrower than the first width, an open stub, and a through hole end through which the lead terminal penetrates. The second signal line and open stub are arranged in series connection, between the first signal line and through hole end.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an optical module, an optical transceiver module, and a flexible substrate.

  For example, an optical module including an optical semiconductor element is used for optical communication. Such an optical module further includes a housing, and the optical semiconductor element is accommodated in the housing. Such an optical module further includes a lead terminal for transmitting an electrical signal. The lead terminal penetrates the casing and is not electrically connected to the casing body (that is, insulated). An end portion inside the housing of the lead terminal that penetrates the housing is connected to an optical semiconductor element accommodated in the housing by a wire or the like. Such an optical module includes a wiring substrate connected to an end portion of the lead terminal outside the housing. The end of the lead terminal is connected to a signal line formed on the wiring board.

  In general, reflection of an electric signal is likely to occur at a mismatched portion of the characteristic impedance in the transmission line, and the electric signal that propagates is distorted, affecting the high-frequency characteristics of the optical module. In the optical module described above, mismatching of characteristic impedance is, for example, between the portion of the lead terminal that penetrates the housing and the wiring board, or the portion of the lead terminal that penetrates the housing and the housing. It can occur between the part projecting into the body and the like.

  For example, Patent Literature 1 and Patent Literature 2 disclose techniques for compensating for mismatches in characteristic impedance and suppressing such mismatches. The can-package type optical semiconductor device disclosed in Patent Document 1 includes a stem provided with a digging in the welded portion of the lead pin in order to improve the adhesion between the bottom surface of the stem and the surface of the flexible circuit board to be bonded. (See FIG. 2). Due to the improved adhesion, an increase in inductance in the lead pin is suppressed. Further, in the flexible printed circuit board disclosed in Patent Document 2, the wiring pattern formed on the flexible printed circuit board is processed so that the change in impedance at the joint between the flexible printed circuit board and the lead pin is alleviated. The characteristics of the optical waveform are ensured.

JP 2006-080418 A JP 2009-295717 A

  In recent years, optical modules have been desired to further reduce costs as well as improve high-frequency characteristics. Therefore, an inexpensive configuration is desired not only for the optical semiconductor element but also for the housing and the peripheral member that accommodates the optical semiconductor element. However, if the package is specially processed to relieve the impedance mismatch, as in the stem disclosed in Patent Document 1, the cost is increased due to the addition of the processing steps and the reduction in the amount. Moreover, the wiring pattern of the flexible printed circuit board disclosed in Patent Document 2 has a limit in improving high-frequency characteristics.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide an optical module, an optical transceiver module, and a flexible substrate that can realize improvement of high-frequency characteristics at low cost.

  (1) In order to solve the above-described problems, an optical module according to the present invention includes an optical semiconductor element, a casing that houses the optical semiconductor element, and the casing is electrically connected to the casing. An optical module comprising: a lead terminal electrically insulated from the optical semiconductor element; and a wiring board on which a signal line electrically connected to the lead terminal is formed. The signal line includes a first signal line portion extending with a first width, a second signal line portion extending with a second width narrower than the first width, an open stub portion, and the lead terminal. And the second signal line portion and the open stub portion are connected in series between the first signal line portion and the through hole end portion. Be placed.

  (2) In the optical module according to (1), the second signal line portion and the open stub portion are arranged in this order from the first signal line portion to the end of the through hole. May be.

  (3) In the optical module according to (1) or (2), the second signal line portion and the open stub portion are formed in a region of the wiring board connected to the housing. May be.

  (4) In the optical module according to any one of (1) to (3), the housing has a through hole for penetrating the lead terminal, and the diameter of the through hole is 1 mm or less. There may be.

  (5) In the optical module according to any one of (1) to (4), the lead terminal may protrude 1 mm or more inside the casing.

  (6) In the optical module according to any one of (1) to (5), a portion where the casing is connected to the wiring board is a stem, and an outer diameter of the stem is 5.6 mm or less. It may be.

  (7) An optical transceiver module according to the present invention is an optical transceiver module comprising the optical module according to any one of (1) to (6) above and another optical module, and the optical module and the optical module One of the other optical modules may be an optical transmitter, and the other may be an optical receiver.

  (8) A flexible substrate according to the present invention includes a first signal line portion extending at a first width, and a lead that penetrates the housing of the optical module and is electrically insulated from the housing. A signal line including a through-hole end for penetrating and connecting the terminal, a second signal line portion extending at a second width narrower than the first width, and an open stub portion is formed. The second signal line portion and the open stub portion may be connected in series between the first signal line portion and the end portion of the through hole. Good.

  According to the present invention, there are provided an optical module, an optical transceiver module, and a flexible substrate that can realize improvement in high-frequency characteristics at low cost.

It is sectional drawing which shows the structure of the optical module which concerns on the 1st Embodiment of this invention. It is a front view of a stem concerning a 1st embodiment of the present invention. It is sectional drawing of the stem which concerns on the 1st Embodiment of this invention. It is a top view of the flexible substrate concerning a 1st embodiment of the present invention. It is a top view of the flexible substrate which concerns on the 2nd Embodiment of this invention. It is a figure which shows the reflective characteristic of an optical module. It is a Smith chart which shows the impedance change of an optical module.

  Hereinafter, embodiments of the present invention will be described specifically and in detail based on the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiments, and the repetitive description thereof will be omitted. In addition, the figure shown below demonstrates the Example of embodiment to the last, Comprising: The magnitude | size of a figure and the reduced scale as described in a present Example do not necessarily correspond.

[First Embodiment]
FIG. 1 is a sectional view showing the structure of an optical module 20 according to the first embodiment of the present invention. The optical module 20 according to the embodiment is a CAN optical transmission module (for example, TOSA). The optical module 20 includes a semiconductor laser element 4 and a housing 10. The housing 10 is composed of a stem 1 and a cap 9 and is electrically grounded. The semiconductor laser element 4 is accommodated in the housing 10.

  The optical module 20 includes four lead terminals 2, and the four lead terminals 2 are a pair (two) of lead terminals 2a, one lead terminal 2b, and one lead terminal 2c. It is. The lead terminal 2 is also called a lead or a lead pin. The lead terminals 2a and 2b penetrate the stem 1 and are not electrically connected to the stem 1 (that is, insulated). In order to penetrate the lead terminals 2a and 2b, the stem 1 has a through-hole penetrating in the thickness direction (direction extending perpendicularly to the bottom surface of the stem 1). Lead terminals 2a and 2b are arranged inside the through hole, and the lead terminals 2a and 2b are held inside the through hole by an insulator 3 filled in a space between the side surface of the through hole and the lead terminals 2a and 2b. And is electrically insulated from the stem 1. The lead terminal 2 c is welded to the stem 1 and is electrically connected to the stem 1. Here, the insulator 3 is a glass material, for example. The pair of lead terminals 2 a are terminals that are electrically connected to the semiconductor laser element 4 and transmit a modulated electric signal to the semiconductor laser element 4. The optical module 20 is driven by a differential method. The lead terminal 2 b is a terminal for supplying power to members other than the semiconductor laser element 4. The lead terminal 2b is connected to, for example, a photodiode (not shown) that monitors the output of the semiconductor laser element 4. The optical module 20 may not necessarily include the lead terminal 2b when a photodiode is not necessary.

  The optical module 20 includes a wiring board on which signal lines are formed. Here, the wiring board is a flexible board 7 (flexible printed board: FPC), and the flexible board 7 is disposed in contact with the stem 1 (housing 10). Each of the four lead terminals 2 has a portion protruding outward from the stem 1 (housing 10). The flexible substrate 7 has four through holes (through holes) corresponding to the arrangement of the lead terminals 2. The four lead terminals 2 are respectively passed through the four through holes of the flexible substrate 7, and the lead terminals 2 and the flexible substrate 7 are joined by the solder 8. The main feature of the optical module according to this embodiment is the configuration of the flexible substrate 7, and particularly the shape of a signal line that is electrically connected to the lead terminal 2 a. Details of this will be described later.

  A pedestal 1 a is fixed to the surface of the stem 1 (the surface inside the housing 10), and the pedestal 1 a is electrically connected to the stem 1. A heat dissipation substrate 5 is attached to the base 1a using a solder material, a conductive adhesive, or the like, and the semiconductor laser element 4 is fixed to the upper side of the heat dissipation substrate 5. The heat dissipation substrate 5 is formed of an insulating material (for example, aluminum nitride) having a high thermal conductivity and a thermal expansion coefficient close to that of the semiconductor laser element 4. Metallized wiring is formed on the surface of the heat dissipation substrate 5.

  As shown in FIG. 1, the lead terminal 2 a protrudes from the stem 1 to the inside of the housing 10. The end of the lead terminal 2 a inside the housing 10 is electrically connected to the metallized wiring formed on the surface of the heat dissipation substrate 5 via the wire 6. The semiconductor laser element 4 and the metallized wiring are also electrically connected via another wire 6.

  An opening is formed in the cap 9, and a lens 11 is disposed in the opening, and the casing 10 is airtight. The lens 11 collects the light emitted from the semiconductor laser element 4 and emits the light to the outside of the housing 10, and the emitted light propagates through the optical fiber.

  FIG. 2A is a front view of the stem 1 according to the embodiment, and FIG. 2B is a cross-sectional view of the stem 1 according to the embodiment. The appearance of the stem 1 has a disk shape, and the bottom surface of the stem 1 is a circle having an outer diameter of 5.6 mm. 2A and 2B show a state in which the lead terminal 2a passes through the stem 1 and is fixed. The cross section shown in FIG. 2B is a cross section taken along the line IIB-IIB in FIG. 2A. Of the lead terminal 2a, a portion that penetrates the inside of the stem 1 is a coaxial portion, and the coaxial portion, the stem 1, and the insulator 3 constitute a coaxial line.

  FIG. 3 is a top view of the flexible substrate 7 according to this embodiment. The signal line pattern shown in FIG. 3 is formed on the front surface of the flexible substrate 7, and a conductor layer is formed on the back surface. The signal line pattern and the conductor layer constitute a microstrip line. Here, FIG. 3 shows a pair of microstrip lines connected to a pair of lead terminals 2a. A differential transmission line is formed on the flexible substrate 7 by a pair of microstrip lines. Yes. Each of the pair of signal lines formed on the flexible substrate 7 includes a first signal line portion 12 extending from a terminal disposed on the lower side of FIG. 3 to the upper side of FIG. 3 with a first width, and a lead terminal 2a. A second signal line portion 14a and an open stub portion, which are arranged in series between the land pattern 13 (through hole end portion) through which the first signal line passes, and the first signal line portion 12 and the land pattern 13. 15a. The lower end of each first signal line portion 12 is a terminal, and a pair of terminals are connected to a driving device (not shown), and a differential electrical signal output from the driving device is applied to the flexible substrate 7. The signal is transmitted to the semiconductor laser element 4 through the formed differential transmission line and the pair of lead terminals 2a. The land pattern 13 is connected to the lead terminal 2 a through the lead terminal 2 a and is an end portion (through hole end portion) of the signal line formed on the flexible substrate 7. The second signal line portion 14a extends in the longitudinal direction of FIG. 3 with a second width, and the second width is narrower than the first width. In the present embodiment, the pair of first signal line portions 12 extend from the lower side to the upper side at a predetermined interval in order to avoid the land pattern connected to the lead terminal 2c and to extend beyond the predetermined width. And stretch further upward. The second signal line portion 14a is connected so that the upper end of the first signal line portion 12 in the figure overlaps the center line. The open stub portion 15 a has a fan shape and is disposed in contact with the land pattern 13.

  The pair of first signal line portions 12 are designed to match the output impedance of the connected drive device, and the width of the first signal line portion 12 is the first width. Here, each of the first signal line portions 12 is impedance-matched to 25Ω. Each of the second signal line portions 14a has a second width (narrower than the first width) and has a higher impedance than the first signal line portion 12, so that the inductive ( Acts on the dielectric). Since the open stub portion 15a has a lower impedance than the first signal line portion 12, it acts on capacity (capacitance). Therefore, the second signal line portion 14a and the open stub portion 15a form an impedance matching circuit. In other words, an impedance matching circuit is disposed between the first signal line portion 12 and the land pattern 13, and the impedance matching circuit includes a second signal line portion 14a and an open stub portion 15a connected in series. Yes. In the impedance matching circuit according to this embodiment, the second signal line portion 14a and the open stub portion 15a are arranged in this order from the first signal line portion 12 to the land pattern 13.

  As described above, impedance mismatch can occur in the lead terminal 2a. Impedance mismatch also occurs at the junction between the lead terminal 2a and the land pattern 13, but the dominant impedance mismatch is caused by the portion of the lead terminal 2a that penetrates the inside of the stem 1 (coaxial portion) and the housing 10. It is thought that it has arisen between the part (inner protrusion part) which protrudes inside. This is because the inner protruding portion has a large inductance component with respect to the coaxial portion. Such an inductance component is canceled out by the impedance matching circuit formed on the flexible substrate 7, so that impedance mismatch is suppressed and reflection characteristics are improved. Therefore, the high frequency characteristics of the optical module 20 are improved. In particular, in an inexpensive package for low-speed communication with a transmission speed of 2.5 Gbit / s or less, the inner projecting portion of the lead terminal 2a may project from the housing 10 by 1 mm or more for ease of processing, and the reflection characteristics. To affect. Therefore, the effect of the present invention is particularly remarkable when the inner protrusion is 1 mm or more.

  Unlike the patent document 1, the optical module according to this embodiment does not require special processing for the housing 10 (stem 1). The main feature of the present invention is the shape of the signal line pattern formed on the flexible substrate 7. The formation of the signal line pattern does not increase the number of manufacturing steps. That is, the optical module according to the embodiment can realize, for example, an optical module for 10 Gbit / s class high-speed optical communication using an inexpensive package for low-speed optical communication capable of mass production. According to this embodiment, an optical transmission module capable of outputting a 10 Gbit / s class high-speed optical signal is realized by using the stem 1 for low-speed communication.

  The open stub portion 15a shown in FIG. 3 has a fan shape, and the open stub portion 15a is arranged so that the center of the fan shape coincides with the center of the through hole inside the land pattern 13. . The electric signal propagating from the first signal line portion 12 through the land pattern 13 to the lead terminal 2a is subjected to an inductive action from the second signal line portion 14a and a capacitive action from the open stub portion 15a. Therefore, it can be said that the impedance matching circuit disposed between the first signal line portion 12 and the land pattern 13 has the second signal line portion 14a and the open stub portion 15a connected in series.

  Of the signal line formed on the flexible substrate 7, a portion that becomes an impedance matching circuit is a portion where impedance mismatching may occur (a joint portion between the land pattern 13 and the lead terminal 2 a, a coaxial portion of the lead terminal 2 a, and an inward protrusion). It is desirable to be placed as close as possible to the boundary of the part. Therefore, in the flexible substrate 7 shown in FIG. 3, the circular region indicated by the alternate long and short dash line is a region where the flexible substrate 7 and the housing 10 are in contact (connected), and the impedance matching circuit It is desirable to be formed in the region. In particular, when the wiring substrate is a flexible substrate, such a region is in contact with the housing 10 and is stably maintained on a flat surface, so that stable impedance matching can be realized.

  The housing 10 of the optical module according to this embodiment is a CAN type, and the portion where the housing 10 is connected to the flexible substrate 7 is the stem 1. The effect of the present invention becomes more prominent when connected to a lead terminal that penetrates the stem 1. Furthermore, when the outer diameter of the stem 1 is 5.6 mm or less, the effect is further enhanced. Further, the dominant impedance mismatching location is considered to be the boundary between the coaxial portion of the lead terminal 2a and the inner protruding portion, but the impedance mismatching has a diameter (inner diameter) of the through hole of the coaxial portion of 1 mm or less. It becomes more prominent when. Therefore, the present invention is optimal when the diameter of the through hole is 1 mm or less.

[Second Embodiment]
FIG. 4 is a top view of the flexible substrate 7 according to the second embodiment of the present invention. The flexible substrate 7 according to this embodiment is different from the flexible substrate 7 according to the first embodiment shown in FIG. 3 in the signal line pattern formed on the surface, but the other configurations are the first embodiment. Is the same. The configuration other than the flexible substrate 7 is also the same as that in the first embodiment.

  Each of the pair of signal lines according to the embodiment includes a first signal line part 12, a second signal line part 14b, an open stub part 15b, and a land pattern 13. As in the first embodiment, the pair of first signal line portions 12 expands and extends upward so as to avoid a land pattern connected to the lead terminal 2c. The second signal line portion 14b is connected so that the upper end of the first signal line portion 12 in the figure overlaps the inner edge. The open stub portion 15b has a rectangular shape, and the open stub portion 15b is connected so as to overlap the inner edge with the second signal line portion 14b, and between the land pattern 13 of the second signal line portion 14b. It is a horizontally long rectangular shape spreading outward in the lateral direction. Similar to the first embodiment, the second signal line portion 14b and the open stub portion 15b form an impedance matching circuit. Here, the dimension of the signal line in the optical transmission module having a transmission rate of 10 Gbit / s is described as an example. The open stub portion 15b has a width W1 (length in the horizontal direction in the figure) of 0.716 mm and a length L1 (length in the vertical direction in the figure) of 0.356 mm. The second width (length in the horizontal direction in the figure) of the second signal line portion 14b is 0.1 mm, and the length L2 (length in the vertical direction in the figure) is 0.435 mm. And the 1st width | variety (length of the horizontal direction of a figure) of the 1st signal track | line part 12 is 0.255 mm.

  The optical modules according to the first and second embodiments have the same effect, but the details will be described below. FIG. 5 is a diagram showing the reflection characteristics of the optical module. The broken line shown in FIG. 5 shows the reflection characteristic S (1,1) of the optical module having the signal line pattern according to the prior art, and the solid line shows the light according to the first (or second) embodiment. The reflection characteristic S (1, 1) of the module 20 is shown. In the figure, the vertical axis represents the reflection characteristic S (1,1) in the unit dB, the horizontal axis represents the frequency freq, and the unit is GHz. Here, unlike the present invention, the signal line pattern according to the prior art is a signal line pattern not provided with an impedance matching circuit. From the signal line pattern of the flexible substrate 7 according to the present embodiment, the second signal line portion. 14a (14b) and the open stub portion 15a (15b) are removed, and the first signal line portion 12 is extended and connected to the land pattern 13.

  The bandwidth in which the reflection characteristic of the optical module (broken line) according to the related art is −10 dB or less is 10.2 GHz or less, and such an optical module cannot be used as an optical transmission module in the 10 GHz band. Alternatively, when used, the optical waveform is distorted, and for example, a yield is generated with respect to the mask specification, resulting in an increase in cost. However, the band in which the reflection characteristic of the optical module (solid line) according to the embodiment is −10 dB or less extends to 13.4 GHz or less and 3.2 GHz to the high frequency side. Therefore, the high frequency characteristics of the optical module are improved, and the optical module according to this embodiment has a special effect.

  FIG. 6 is a Smith chart showing a change in impedance of the optical module. Similarly to FIG. 5, the broken line shown in FIG. 6 indicates the change in impedance of the optical module according to the related art, and the solid line indicates the change in impedance of the optical module according to the embodiment. It is standardized by. The curves (solid line and broken line) shown in FIG. 6 are impedance changes when the frequency is changed from 0 GHz to 20 GHz. A point m1 indicates the impedance at a frequency of 10 GHz. As shown in FIG. 6, a point m1 on the broken line is a point on the solid line by changing T1 (inductive) by the second signal line part and further changing T2 (capacitive) by the open stub part. m1 can be closer to the center (25Ω) of the Smith chart than the prior art (broken line), and impedance matching is improved, and in particular, reflection characteristics in a band of 10 GHz to 13 GHz are improved.

  The optical module according to the embodiment of the present invention has been described above. The optical module according to the above-described embodiment is a CAN-type optical transmission module (for example, TOSA), and the optical semiconductor element is a semiconductor laser element. However, the present invention is not limited to this. It may be a CAN type optical receiver module (for example, ROSA). In this case, the optical semiconductor element is a semiconductor light receiving element. An optical transceiver module (optical transceiver) according to the present invention includes the optical module according to the present invention and another optical module. When the optical module according to the present invention is an optical transmission module (or optical reception module), the other optical module is an optical reception module (or optical transmission module), and the other optical module is an optical module according to the present invention. It may be a module or a known optical module.

  Further, in the above-described embodiment, the dominant impedance matching point is the boundary between the coaxial portion and the inner protruding portion of the lead terminal 2a, and the inner protruding portion has a large inductance component with respect to the coaxial portion. In the impedance matching circuit, the second signal line and the open stub part are arranged in this order from the first signal line part to the land pattern. However, when the impedance matching is caused by the capacitance component, the impedance matching circuit arranges the open stub part and the second signal line in this order from the first signal line part to the land pattern in the opposite order. May be. Furthermore, although the case where the optical module according to the above-described embodiment includes a wiring board that forms a differential transmission line has been described, the present invention is not limited to this. For example, when there is one signal line, The transmission line may be a so-called single end. The present invention can be widely applied without being limited to the above-described embodiments.

  1 stem, 1a pedestal, 2, 2a, 2b, 2c lead terminal, 3 insulator, 4 semiconductor laser element, 5 heat dissipation substrate, 6 wire, 7 flexible substrate, 8 solder, 9 cap, 10 housing, 11 lens, 12 1st signal track | line part, 13 Land pattern, 14a, 14b 2nd signal track | line part, 15a, 15b Open stub part, 20 Optical module.

Claims (8)

An optical semiconductor element;
A housing for housing the optical semiconductor element;
A lead terminal that penetrates the housing and is electrically insulated from the housing and electrically connected to the optical semiconductor element;
A wiring board on which a signal line electrically connected to the lead terminal is formed; and
An optical module comprising:
The signal line includes a first signal line portion extending with a first width, a second signal line portion extending with a second width narrower than the first width, an open stub portion, and the lead terminal. Through-hole end through which
The second signal line portion and the open stub portion are arranged in series between the first signal line portion and the through hole end,
An optical module characterized by that. The optical module according to claim 1,
The second signal line part and the open stub part are arranged in this order from the first signal line part to the end of the through hole.
An optical module characterized by that. The optical module according to claim 1 or 2,
The second signal line portion and the open stub portion are formed in a region of the wiring board connected to the housing.
An optical module characterized by that. The optical module according to any one of claims 1 to 3,
The housing has a through hole for penetrating the lead terminal, and the diameter of the through hole is 1 mm or less.
An optical module characterized by that. The optical module according to any one of claims 1 to 4,
The lead terminal protrudes 1 mm or more inside the housing;
An optical module characterized by that. An optical module according to any one of claims 1 to 5,
The portion where the casing is connected to the wiring board is a stem, and the outer diameter of the stem is 5.6 mm or less.
An optical module characterized by that. An optical transceiver module comprising the optical module according to any one of claims 1 to 6 and another optical module,
Either one of the optical module and the other optical module is an optical transmitter, and the other is an optical receiver.
An optical transceiver module characterized by the above. A first signal line portion extending at a first width;
A through-hole end for penetrating and connecting to a lead terminal that penetrates the housing of the optical module and is electrically insulated from the housing;
A second signal line portion extending with a second width narrower than the first width;
A flexible substrate on which a signal line including an open stub portion is formed,
The second signal line portion and the open stub portion are connected in series between the first signal line portion and the through hole end,
A flexible substrate characterized by the above.

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