Optical module

The present invention relates to an optical module.

Patent Document 1 describes a flexible printed substrate and an electric device provided with the flexible printed substrate. This flexible printed circuit board has a surface layer on which four signal lines and ground lines are arranged, and a back surface on which a pair of betaland surfaces are arranged. Between the two betta land planes, there is a punching pattern in which the betta land plane does not exist.

Patent Document 2 describes a flexible wiring body. This flexible wiring body has a line pattern surface having a line pattern and a shield pattern surface which is a surface opposite to the line pattern surface and has a pair of shield patterns. Between the pair of shield patterns on the shield pattern surface, there is a bending line extending in the lateral direction.

Patent Document 3 describes a signal line which is a flexible printed substrate. The signal line includes an external terminal, a via hole, a signal line portion, and a connector portion. The signal line portion has a signal line and a ground conductor. The ground conductor includes a plurality of via hole conductors extending in the width direction of the circuit board, and an opening is formed between two adjacent via hole conductors.

<p><patcit num="1"><text>Japanese Unexamined Patent Publication No. 2004-88020</text></patcit><patcit num="2"><text>Japanese Unexamined Patent Publication No. 2007-281145</text></patcit><patcit num="3"><text>Japanese Unexamined Patent Publication No. 2012-134551</text></patcit></p>

<p>By the way, the coaxial optical transmitter that transmits and receives signals has a reinforcing plate between the stem of the optical transmitter and the FPC in order to prevent disconnection when the flexible printed circuit board (FPC) is bent. This reinforcing plate is attached to the optical transmitter so as to cover the stem. In addition, the impedance of the signal line on the FPC is designed to be 20Ω to 30Ω for an optical transmitter that directly modulates a laser diode (LD). This is because the impedance of the input of the LD is small and matches this impedance.</p><p>In recent years, as the amount of information transmitted in an optical communication system has increased, the amount of transmission required for an optical module has been steadily increasing. Therefore, when the optical transmitter that transmits / receives a signal of 25 Gbps or more has the above-mentioned reinforcing plate, there is a growing concern that the impedance will be disturbed from the design value and the waveform characteristics will be affected because the reinforcing plate is provided. On the other hand, if the FPC is not provided, high stress is applied to the base of the lead pin extending from the stem when the FPC is bent, and the lead pin may be disconnected at this point. Therefore, it is required that high stress is not applied to the lead pin when the reinforcing plate is removed and bent.</p><p>An object of the present invention is to provide an optical module capable of removing a reinforcing plate and avoiding high stress on a lead pin.</p>

<p>An optical module according to an embodiment of the present invention includes a coaxial housing, an optical subassembly having a plurality of lead pins extending from the housing in a direction along an optical axis, and a circuit for transmitting and receiving an electric signal to and from the optical subassembly. The circuit board mounted on the main surface and the main surface is arranged parallel to the optical axis, the optical subassembly and the circuit board are connected, the grounding pattern is provided on the back surface, the signal wiring is provided on the front surface, and the end of the optical subassembly is provided. A flexible printed circuit board (FPC) that bends at a portion is provided, and the FPC has a punching pattern in which a grounding pattern is not provided on the bending portion on the back surface, and has a grounding pattern at a portion adjacent to the bending portion on the front surface.</p>

<p>According to the present invention, it is possible to remove the reinforcing plate and avoid applying high stress to the lead pin.</p>

<figref num="1">FIG. 1 is a cross-sectional view showing an optical module according to an embodiment.</figref><figref num="2">FIG. 2 is a perspective view showing the optical subassembly, lead pins and FPC of the optical module of FIG.</figref><figref num="3">FIG. 3 is a diagram showing the surface of the FPC of FIG.</figref><figref num="4">FIG. 4 is a diagram showing the back surface of the FPC of FIG.</figref><figref num="5">5 (a) and 5 (b) are diagrams showing the results of simulating the received waveforms of the FPC of the example and the FPC of the comparative example.</figref>

Hereinafter, embodiments of the optical module according to the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same or corresponding elements are designated by the same reference numerals, and duplicate description is omitted.

FIG. 1 is a cross-sectional view showing an optical module 1 according to an embodiment. FIG. 2 is a perspective view showing an optical subassembly 3, a flexible printed circuit board (FPC) 10, and a lead pin 5 of the optical module 1. The optical module 1 complies with the SFP28 MSA (Small Form-factor Pluggable 28 Multi-Source Agreement), for example, and realizes 25 Gbps optical communication. As shown in FIG. 1, the optical module 1 includes a housing 2, an optical subassembly 3, an FPC 10, and a circuit board 4.

Housing 2 houses the optical subassembly 3, FPC10 and circuit board 4. The FPC 10 bends at the end of the optical subassembly 3 to electrically connect the optical subassembly 3 to the circuit board 4. The circuit board 4 has a main surface 4a, and a circuit for transmitting and receiving electric signals is mounted on the main surface 4a. The circuit board 4 is arranged with the main surface 4a parallel to the optical axis.

Optical subassembly 3 is a coaxial TOSA. The optical subassembly 3 receives an electric signal from the circuit board 4 via the FPC 10, converts the received electric signal into an optical signal, and transmits the received electric signal to the outside of the optical module 1. The optical subassembly 3 has a semiconductor laser and a coaxial housing 3a that houses the semiconductor laser. Housing 3a has a metal stem 3b. Housing 3a has a plurality of lead pins 5 extending from stem 3b. The lead pin 5 extends in the direction along the optical axis.

FIG. 3 is a diagram showing the surface 10A of the FPC 10. FIG. 4 is a diagram showing the back surface 10B of the FPC 10. The FPC 10 is connected to each of the stem 3b and the circuit board 4 in a U-shaped bend so that the front surface 10A faces the inside and the back surface 10B faces the outside. The FPC 10 has a flat plate shape extending in one direction, one end 10a side is fixed to the circuit board 4, and the other end 10b side is fixed to the stem 3b.

The surface 10A of the FPC 10 has a plurality of terminals 11a to 11g located at one end 10a in the longitudinal direction thereof, and signal wiring 12a and electrical wiring 12b, 12c connected to the terminals 11b, 11d, 11e, respectively. A high-frequency signal such as 25 Gbps is transmitted to the signal wiring 12a, and a DC signal for bias is transmitted to the electrical wirings 12b and 12c. Impedance matching is performed in the signal wiring 12a. Due to this impedance matching, the signal wiring 12a is thinner than the electrical wirings 12b and 12c.

The surface 10A of the FPC 10 has a plurality of connection holes 14 and a grounding pattern 15 on the other end 10b side in the longitudinal direction thereof, and a lead pin 5 is connected to each of the plurality of connection holes 14. The back surface 10B of the FPC 10 has terminals 11a to 11g and a grounding pattern 17 connected to each of the terminals 11a, 11c, 11f, 11g. Each of the terminals 11a to 11g is soldered to the terminals on the circuit board 4.

The FPC 10 has a pair of recesses 18 recessed in the width direction between the ground pattern 15 on the surface 10A and the terminals 11a to 11g. Further, the FPC 10 has a punching pattern 19 on which the grounding pattern 17 is not provided on the virtual line P connecting the pair of recesses 18 on the back surface 10B. The portion including the virtual line P connecting the pair of recesses 18 and the punching pattern 19 corresponds to a portion that is easier to bend than other portions of the FPC 10, that is, a portion A that bends. The punching pattern 19 exhibits an oval shape extending in the width direction of the FPC 10. The punching pattern 19 has a hole 19a penetrating the FPC 10 on the front and back. The holes 19a are provided in pairs in the width direction of the FPC 10. The holes 19a make it easier to bend the bent portion A.

The grounding pattern 15 on the surface 10A is provided at a position adjacent to the bent portion A, specifically, on the optical subassembly 3 side (lead pin 5 side) with respect to the portion A. By providing the grounding pattern 15 on the optical subassembly 3 side with respect to the portion A, even if the bent portion of the FPC 10 is offset from the portion A, it can be prevented from being offset to the lead pin 5 side. That is, the bent portion of the FPC 10 is likely to be offset from the portion A to the terminals 11a to 11g. Further, the grounding pattern 15 has a plurality of through holes 15a between the grounding pattern 17 and the grounding pattern 17 on the back surface 10B. The through hole 15a is a hole for connecting the ground pattern 15 on the front surface 10A and the ground pattern 17 on the back surface 10B, and each through hole 15a is filled with metal.

By the way, in the conventional case, in the optical module, the stem of the optical subassembly may be covered with a reinforcing plate in order to prevent excessive force from being applied to the base of the lead pin when the FPC is bent. However, if the stem is covered with a reinforcing plate, the impedance of the signal line may be disturbed from the design value, which may adversely affect the waveform characteristics. Further, if the configuration is such that the reinforcing plate is not simply covered, stress is concentrated on the base portion of the lead pin when the FPC is bent, so that a disconnection may occur at that portion.

Therefore, in the present embodiment, without using the above-mentioned reinforcing plate, a punching pattern 19 having no grounding pattern 17 is provided on a part of the back surface 10B of the FPC 10, and a grounding pattern is further provided at a position adjacent to the bending portion A of the front surface 10A. 15 is provided. In this way, by providing the bending portion A and providing the ground contact pattern 15 at the position adjacent to the portion A, the portion A can be easily bent positively when the FPC 10 is bent. Therefore, the stress concentrated on the base portion of the lead pin 5 can be relaxed, and the disconnection can be suppressed. Further, since the above-mentioned reinforcing plate can be eliminated, the disturbance of the impedance of the signal line can be suppressed.

5 (a) and 5 (b) show the results of comparing the received waveform of the optical module having the stem covered with the reinforcing plate and the received waveform of the optical module 1 of the present embodiment without the reinforcing plate. As shown in FIG. 5 (a), in the conventional optical module, the stability of the H level and the L level is low, and the rising and falling jitter is remarkable. On the other hand, as shown in FIG. 5B, the optical module 1 has less jitter and noise because it does not have a reinforcing plate, and it can be seen that the received waveform can be stabilized.

Although the embodiment of the optical module according to the present invention has been described above, the present invention is not limited to each of the above-described embodiments. That is, it is easily recognized by those skilled in the art that various modifications and changes are possible within the scope of the gist of the present invention described in the claims.

1 ... Optical Module, 2 ... Housing, 3 ... Optical Subassembly, 3a ... Housing, 3b ... Stem, 4 ... Circuit Board, 5 ... Lead Pins, 10 ... FPC, 10A ... front side, 10B ... back side, 10a ... one end, 10b ... other end, 11a ~ 11g ... terminal, 12a ... signal wiring, 12b, 12c ... electrical wiring , 14 ... connection hole, 15,17 ... ground pattern, 15a ... through hole, 18 ... recess, 19 ... punching pattern, 19a ... hole, A ... part, P ... Virtual line.