WO2024009388A1

WO2024009388A1 - Light receiver

Info

Publication number: WO2024009388A1
Application number: PCT/JP2022/026702
Authority: WO
Inventors: 祥平小菅; 慈金澤
Original assignee: 日本電信電話株式会社
Priority date: 2022-07-05
Filing date: 2022-07-05
Publication date: 2024-01-11

Abstract

Provided is a light receiver in which degradation of the operating band is less likely to occur even when the distance between elements constituting the light receiver has changed. A light receiver of one embodiment comprises: a light receiving element (PD); a bias circuit that applies a bias voltage; a transimpedance amplifier (TIA); at least one subcarrier on which the PD, the bias circuit, and the TIA are mounted; and at least one high frequency wiring board that connects an upper surface of the PD and an upper surface of the bias circuit, and/or the upper surface of the PD and an upper surface of the TIA.

Description

optical receiver

The present disclosure relates to an optical receiver, and more particularly to a mounting technique for an optical semiconductor module for an optical receiver.

Conventionally, an optical receiver is known that includes a photodiode (PD) as a light receiving element, a bias circuit for driving the PD, and a transimpedance amplifier (TIA) (see, for example, Non-Patent Document 1). In particular, when the light receiving element is an avalanche photodiode (APD), it is difficult to drive it with the voltage supplied from the TIA, so a separate bias circuit is required.

FIG. 1 is a diagram showing a schematic configuration of a conventional optical receiver. FIG. 1(a) is a top view, and FIG. 1(b) is a sectional view. The optical receiver 100 shown in FIG. 1 includes a PD 101, a bias circuit 102 for driving the PD 101, and a TIA 104 that is an electric amplifier.

The PD 101 and the bias circuit 102 are arranged on a PD subcarrier 103, and the TIA 104 is arranged on a TIA subcarrier 105 different from the PD subcarrier 103. PD subcarrier 103 and TIA subcarrier 105 are dielectric carriers.

The bias circuit 102 is a capacitor that constitutes a bias circuit, and applies a reverse bias to the connected PD 101. The TIA 104 converts the current from the connected PD 101 into voltage. The bias circuit 102 (capacitor) located closest to the PD 101 affects the high frequency characteristics of the optical receiver 100.

A certain distance is provided between the bias circuit 102 and the PD 101, and between the PD 101 and the TIA 104, respectively. The PD 101 and the bias circuit 102 are electrically connected by a metal wire 106a. Similarly, the PD 101 and the TIA 104 are electrically connected by a metal wire 106b.

Note that the PD subcarrier 103 has a through hole, and an opening 103a is formed by the through hole. The PD 101 is arranged on the PD subcarrier 103 so that the signal light enters the light receiving surface on the back side of the PD 101 through the opening 103a.

As mentioned above, in order to transmit the photoelectrically converted signal in the optical receiver, the elements that make up the optical receiver need to be electrically connected. Metal wires are generally used for electrical connections between each element. This metal wire affects the frequency response characteristics of the optical receiver, so in order to operate the optical receiver over a wide band, it is necessary to mount the wire with an appropriate length in consideration of the frequency characteristics of each element. For example, in an optical receiver of over 100 Gbaud, it is said that by mounting wires of around 100 μm, it is possible to create a slight peaking in the frequency characteristics and widen the band. In order to implement wires of optimum length, it is necessary to provide a corresponding distance between elements. In addition, the band may change due to variations in wire length due to mounting tolerances. Therefore, in the case of wire mounting, there was a problem in that it limited the degree of freedom in the structural design of the optical receiver.

The present disclosure has been made in view of such problems, and its purpose is to provide an optical receiver in which the operating band is less likely to deteriorate even when the distance between elements constituting the optical receiver changes. It's about doing.

In order to achieve such an object, an optical receiver according to an embodiment of the present invention includes a photodetector (PD), a bias circuit that applies a bias voltage, a transimpedance amplifier (TIA), a PD, and a bias circuit. , and at least one high-frequency wiring board connecting at least one subcarrier carrying the TIA and at least one of the top surface of the PD and the top surface of the bias circuit, or the top surface of the PD and the top surface of the TIA. It is equipped with

According to this configuration, it is possible to provide an optical receiver in which the operating band is less likely to deteriorate even if the distance between the elements constituting the optical receiver changes.

It is a figure showing a schematic structure of a conventional type optical receiver, (a) is a top view, and (b) is a sectional view. 1 is a diagram showing a schematic configuration of an optical receiver according to an embodiment of the present disclosure, in which (a) is a top view, (b) is a cross-sectional view, (c) is a top view of a high frequency waveguide substrate, and (d) is a top view. FIG. 3 is a cross-sectional view of a high-frequency waveguide substrate. 1 is a diagram showing a schematic configuration of an optical receiver according to an embodiment of the present disclosure, in which (a) is a top view, (b) is a cross-sectional view, (c) is a top view of a high frequency waveguide substrate, and (d) is a top view. FIG. 3 is a cross-sectional view of a high-frequency waveguide substrate. 1 is a diagram showing a schematic configuration of an optical receiver according to an embodiment of the present disclosure, in which (a) is a top view, (b) is a cross-sectional view, (c) is a top view of a high frequency waveguide substrate, and (d) is a top view. FIG. 3 is a cross-sectional view of a high-frequency waveguide substrate. 1 is a diagram showing a schematic configuration of an optical receiver according to an embodiment of the present disclosure, in which (a) is a top view, (b) is a cross-sectional view, (c) is a top view of a high frequency waveguide substrate, and (d) is a top view. FIG. 3 is a cross-sectional view of a high-frequency waveguide substrate. 1 is a diagram showing a schematic configuration of an optical receiver according to an embodiment of the present disclosure, in which (a) is a top view, (b) is a cross-sectional view, (c) is a top view of a high frequency waveguide substrate, and (d) is a top view. FIG. 3 is a cross-sectional view of a high frequency waveguide substrate. 1 is a diagram showing a schematic configuration of an optical receiver according to an embodiment of the present disclosure, in which (a) is a top view, (b) is a cross-sectional view, (c) is a top view of a high frequency waveguide substrate, and (d) is a top view. FIG. 3 is a cross-sectional view of a high-frequency waveguide substrate. 1 is a diagram showing a schematic configuration of an optical receiver according to an embodiment of the present disclosure, in which (a) is a top view, (b) is a cross-sectional view, (c) is a top view of a high frequency waveguide substrate, and (d) is a top view. FIG. 3 is a cross-sectional view of a high-frequency waveguide substrate. FIG. 7 is a diagram showing the frequency response characteristic of the output section of the TIA of the optical receiver when receiving a 50 Gbaud signal light. FIG. 3 is a diagram showing the frequency response characteristic of the output section of the TIA of the optical receiver when receiving a 100 Gbaud signal light.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Identical or similar reference symbols indicate identical or similar elements, and repeated description will be omitted. The numerical values illustrated in the following description are not limited, and other numerical values can be used without departing from the gist of the present disclosure. In this specification, the Z direction of the XY plane is referred to as upward.

In an optical receiver according to an embodiment of the present disclosure, as shown in FIGS. 2 to 8, a high-frequency wiring board is used instead of metal wires for some or all of the connections between elements constituting the optical receiver. There is. Conventional optical receivers such as those mentioned above have a problem in that when the distance between the elements that make up the optical receiver deviates from the optimal value, the length of the metal wire changes and the band of the optical receiver deteriorates. . In contrast, in the configuration of the optical receiver according to the embodiment of the present disclosure, a high-frequency wiring board, which is a combination of an impedance line and a high-impedance line, is used for electrical connection between elements, thereby reducing the band deterioration of the optical receiver. It can be reduced.

(Embodiment 1)
With reference to FIG. 2, an optical receiver according to Embodiment 1 of the present disclosure will be described. 2(a) is a top view of the optical receiver 200 of this embodiment, and FIG. 2(b) is a sectional view of the optical receiver 200. The optical receiver 200 shown in FIG. 2 includes a PD 101, a bias circuit 102, a TIA 104, a PD subcarrier 203, and a TIA subcarrier 105.

The PD 101 and the bias circuit 102 are arranged on the upper surfaces of two opposing main surfaces (XY planes) of the PD subcarrier 203, which is a dielectric carrier. The PD subcarrier 203 differs from the PD subcarrier 103 shown in FIG. 1, which has a step on the top surface, in that the two opposing main surfaces of the PD subcarrier 203 are substantially parallel.

The TIA 104 is arranged on the upper surfaces of two opposing main surfaces (XY planes) of the TIA subcarrier 105, which is a dielectric carrier.

Similar to the optical receiver 100 described with reference to FIG. 1, in the optical receiver 100, a certain distance is provided between the bias circuit 102 and the PD 101, and between the PD 101 and the TIA 104. The PD 101 and the TIA 104 are electrically connected by a metal wire 106b.

The optical receiver 200 shown in FIG. 2 uses a high frequency wiring board 222 instead of the metal wire 106a for electrical connection between the PD 101 and the bias circuit 102 (capacitor). This is different from the receiver 100. The high frequency wiring board 222 is a combination of an impedance line and a high impedance line by appropriately designing the structure and dielectric material. Further, the optical receiver 200 is configured such that the connection surface, which is the top surface of the PD 101 bridged by the high-frequency wiring board 222, and the connection surface, which is the top surface of the bias circuit 102, are the same in height. By polishing the PD 101, the connection surface of the PD 101 and the connection surface of the bias circuit 102 can be aligned in height.

The impedance of the line on the high-frequency wiring board 222 can be adjusted by changing the width (X-axis direction) of the line 223a on the high-frequency wiring board 222. Specifically, if a narrow portion of the line 223a is provided, the impedance of that portion increases. By reducing the width of a portion of the designed line 223a that has a width corresponding to a particular impedance (eg, 50Ω), the portion of the line 223a becomes a line with a large impedance, ie, a high impedance line. In the present disclosure, a portion of the line 223a having a width corresponding to a specific impedance is expressed as an impedance line. The high frequency wiring board 222, which is a composite of the impedance line and the high impedance line as described above, can be realized by reducing the width of a portion of the line 223a in this manner. By partially changing the dielectric material constituting the high-frequency wiring board 222, a high-frequency wiring board 222 in which an impedance line and a high-impedance line are combined may be realized, and a combination of the structure of the high-frequency wiring board 222 and the dielectric material may be realized. By designing the high-frequency wiring board 222, which is a combination of an impedance line and a high-impedance line.

2(c) is a bottom view of the high frequency wiring board 222, and FIG. 2(d) is a sectional view of the high frequency wiring board 222. As shown in FIG. 2, the high frequency wiring board 222 has metal thin films formed on four surfaces of the dielectric 224 excluding the two main surfaces (ZX planes). A metal thin film formed on the lower surface of the dielectric 224, that is, the surface facing the upper surfaces of the PD 101 and the bias circuit 102, is separated by a slit. A thin film located at the center of the lower surface of the dielectric 224 constitutes a line 223a. A thin film located on the side of the lower surface of the dielectric 224 and separated from the line 223a by a slit is continuous with the thin film formed on the side (YZ plane) and upper surface of the dielectric 224, and constitutes a line 223b. The line 223a is a given bias potential shared from the bias circuit 102, and the line 223b is a reference potential such as ground.

Lines

223a and 223b of high-frequency wiring board 222 are placed in contact with bumps 221 formed on the upper surfaces of PD 101 and bias circuit 102.

FIG. 9 is a diagram showing the frequency response characteristic of the output section of the TIA 104 at 50 Gbaud. FIG. 10 is a diagram showing the frequency response characteristic of the output section of the TIA 104 at 100 Gbaud. 9 and 10, the characteristics of the conventional optical receiver as shown in FIG. 1 are shown by broken lines, and the characteristics of the optical transmitter according to the embodiment of the present disclosure are shown by solid lines. The characteristics shown in FIGS. 9 and 10 show frequency characteristics calculated while changing the distance (inter-element distance) between the PD and the bias circuit and between the PD and the TIA in the optical receiver.

First, referring to the frequency response characteristics of the conventional optical receiver in Fig. 9, the 3 dB band when the distance between elements is 300 μm is 51.0 GHz, and a band above 50 GHz, which is the Nyquist frequency of a 100 Gbaud signal, can be secured. It can be confirmed that as the distance between elements changes, the frequency in the 3 dB band decreases to below 50 GHz. On the other hand, in the proposed optical receiver in the present disclosure, that is, in the optical receiver using a high-frequency wiring board in which the impedance components of the

lines

223a and 223b are changed according to the distance between the elements, the distance between the elements is smaller than that in wire mounting. The decrease in the frequency in the 3 dB band due to the change in is small, and the frequency in the 3 dB band is 50 GHz or more at any inter-element distance. Thus, it can be seen that the proposed optical receiver in the present disclosure can operate in a band of 50 GHz or more, which is the Nyquist frequency of a 100 Gbaud signal.

Next, referring to the frequency characteristics at 100 Gbaud in Fig. 10, in a conventional optical receiver, the frequency required to secure a given response such as a 3 dB band decreases as the distance between elements changes; Such frequency reduction is not observed in the optical receiver proposed in the disclosure.

From the above, compared to conventional optical receivers, the proposed optical receiver of the present disclosure is able to secure a given frequency response due to the increased distance between elements and variations in the distance between elements that may occur during mounting. It was shown that it is possible to suppress the decrease in frequency caused by Further, in this embodiment, the verification is performed using baud rates of 100 Gbaud and 50 Gbaud, but similar effects can be obtained by redesigning the high frequency wiring board according to the applied baud rate.

(Embodiment 2)
With reference to FIG. 3, an optical receiver according to Embodiment 2 of the present disclosure will be described. 3(a) is a top view of the optical receiver 300 of this embodiment, and FIG. 3(b) is a sectional view of the optical receiver 300. 3(c) is a bottom view of the high frequency wiring board 222, and FIG. 3(d) is a sectional view of the high frequency wiring board 222.

The optical receiver 300 shown in FIG. 3 has a structure in which the height of the upper surface of the PD 101 bridged by the high-frequency wiring board and the upper surface of the bias circuit 102 are matched by a step provided on the upper surface of the PD subcarrier 303. This differs from the optical receiver 200 described with reference to FIG. 2, that is, the optical receiver 200 in which the height is adjusted by polishing the PD 101 disposed on the top surface of the PD subcarrier 203 without a step. In the configuration of this embodiment, there is no need to polish the PD, so the operational reliability of the PD is not impaired. The PD subcarrier 303 on which the back-illuminated PD 101 is mounted has an opening 303a formed by a through hole.

The other configuration of the optical receiver 300 is similar to the configuration of the optical receiver 200. The optical receiver 300 of this embodiment also has the same effects as the optical receiver 200 of the first embodiment.

(Embodiment 3)
With reference to FIG. 4, an optical receiver according to Embodiment 3 of the present disclosure will be described. 4(a) is a top view of the optical receiver 400 of this embodiment, and FIG. 4(b) is a sectional view of the optical receiver 400. 4(c) is a bottom view of the high frequency wiring board 222, and FIG. 4(d) is a sectional view of the high frequency wiring board 222.

The optical receiver 400 shown in FIG. 4 is different from the optical receiver 300 described with reference to FIG. different from. With the configuration of this embodiment, the number of members used can be reduced compared to the configurations of Embodiments 1 and 2. Subcarrier 403 is a dielectric carrier. The height difference provided on the upper surface of the subcarrier 403 matches the height of the upper surface of the PD 101 bridged by the high frequency wiring board and the upper surface of the bias circuit 102. The PD subcarrier 403 on which the back-illuminated PD 101 is mounted has an opening 403a formed by a through hole.

The other configuration of optical receiver 400 is similar to the configuration of optical receiver 200. The optical receiver 400 of this embodiment also has the same effects as the optical receiver 200 of the first embodiment.

(Embodiment 4)
With reference to FIG. 5, an optical receiver according to Embodiment 4 of the present disclosure will be described. 5(a) is a top view of the optical receiver 500 of this embodiment, and FIG. 5(b) is a sectional view of the optical receiver 500. 5(c) is a bottom view of the high frequency wiring board 222, and FIG. 5(d) is a sectional view of the high frequency wiring board 222.

The optical receiver 500 shown in FIG. 5 has a configuration in which a front-illuminated PD 501 is used instead of the back-illuminated PD 201 in the optical receiver 300 described with reference to FIG. As shown in FIG. 5, in the PD subcarrier 503 of the optical receiver 500, there is no need to provide an opening through which the signal light passes due to a through hole, and the number of mounting steps can be reduced. Subcarrier 503 is a dielectric carrier. The height difference provided on the top surface of the subcarrier 503 matches the height of the top surface of the PD 501 bridged by the high frequency wiring board and the top surface of the bias circuit 102.

The other configuration of optical receiver 500 is similar to the configuration of optical receiver 300. The optical receiver 500 of this embodiment also has the same effect as the optical receiver 300 of the second embodiment, that is, the same effect as the optical receiver 200 of the first embodiment.

(Embodiment 5)
With reference to FIG. 6, an optical receiver according to Embodiment 5 of the present disclosure will be described. 6(a) is a top view of the optical receiver 600 of this embodiment, and FIG. 6(b) is a sectional view of the optical receiver 600. 6(c) is a bottom view of the high frequency wiring board 222, and FIG. 6(d) is a sectional view of the high frequency wiring board 222.

The optical receiver 600 shown in FIG. 6 uses a metal wire 106a for connection between the bias circuit 102 (capacitor) and the PD 101 in the optical receiver 300 described with reference to FIG. This configuration uses a high frequency wiring board 222 for connection between the two. The height of the TIA 105 is adjusted to align the top surface of the PD 101 and the top surface of the TIA 104.

The configuration of the optical receiver 600 facilitates connection even if the spacing between the bumps 221 on the top surface of the PD 101 and the bumps 221 on the top surface of the TIA 104 are different. For example, the PD 101 and the TIA 104 can be easily connected by tapering the pattern of the

lines

223a and 223b formed on the back surface of the high-frequency wiring board 222 according to the spacing between the bumps 221.

The other configuration of the optical receiver 600 is similar to the configuration of the optical receiver 300. The optical receiver 600 of this embodiment also has the same effect as the optical receiver 300 of the second embodiment, that is, the same effect as the optical receiver 200 of the first embodiment.

(Embodiment 6)
With reference to FIG. 7, an optical receiver according to Embodiment 6 of the present disclosure will be described. 7(a) is a top view of the optical receiver 700 of this embodiment, and FIG. 7(b) is a sectional view of the optical receiver 700. 7(c) is a bottom view of a portion of the high frequency wiring board 222, and FIG. 7(d) is a sectional view of the high frequency wiring board 222.

In the optical receiver 700 shown in FIG. 7, the connection between the PD 101 and the TIA 104 in the optical receiver 300 described with reference to FIG. 3 is performed using a high frequency wiring board 222 instead of the metal wire 106b. It is the composition. The height of the TIA 105 is adjusted to align the top surface of the PD 101 and the top surface of the TIA 104. This is a configuration in which the length in the Y direction of the high frequency wiring board 222 used for connection between the PD 101 and the bias circuit 102 (capacitor) in the optical receiver 300 is increased. A single high-frequency wiring board 222 is placed on the top surface of the bias circuit 102, PD 101, and TIA 104, and the bumps 221 provided on the top surface of the bias circuit 102 and the bumps 221 provided on the top surface of the PD 101 connect to the line 223a and the bump 221 provided on the top surface of the PD 101. The bump 221 provided on the top surface of the PD 101 and the bump 221 provided on the top surface of the TIA 104 are connected by

lines

223a and 223b. The back surface of the single high-frequency wiring board 222 is not provided with

lines

223a and 223b that connect the bump 221 on the bias circuit 102 side and the bump 221 on the TIA 104 side provided on the top surface of the PD 101.

The optical receiver 700 shown in FIG. 7 can reduce the number of members for electrical connection between elements and the number of steps for mounting. Furthermore, in the case of using a front-illuminated PD501 (FIG. 5) instead of the back-illuminated PD201 in this embodiment, an opening can be provided in the center of the high-frequency wiring board 222 by a through hole penetrating the upper and lower surfaces. The signal light may be made incident on the light receiving surface of the APD 501. Since the current distribution in the

lines

223a and 223b of the high-frequency wiring board 222 is concentrated at the electrode edges (around the bumps 221), the high-frequency electrical signal is hardly degraded by making a through hole in the center of the high-frequency wiring board 222.

The other configuration of optical receiver 700 is similar to the configuration of optical receiver 300. The optical receiver 700 of this embodiment also has the same effect as the optical receiver 300 of the second embodiment, that is, the same effect as the optical receiver 200 of the first embodiment.

(Embodiment 7)
With reference to FIG. 8, an optical receiver according to Embodiment 7 of the present disclosure will be described. 8(a) is a top view of the optical receiver 800 of this embodiment, and FIG. 8(b) is a sectional view of the optical receiver 800. FIG. 8(c) is a bottom view of high-

frequency wiring boards

222a and 222b, and FIG. 8(d) is a cross-sectional view of high-

frequency wiring boards

222a and 222b.

In the optical receiver 800 shown in FIG. 8, the connection between the PD 101 and the TIA 104 in the optical receiver 300 described with reference to FIG. 3 is made using a high frequency wiring board 222b instead of the metal wire 106b. It is the composition. The high frequency wiring board 222a corresponds to the high frequency wiring board 222 in the optical receiver 300 described with reference to FIG. In the optical receiver 800, the height of the TIA 105 is adjusted in order to align the top surface of the PD 101 of the optical receiver 300 with the top surface of the TIA 104.

In the optical receiver 800, the high frequency wiring board 222b connecting the PD 101 and the TIA 104 can be constructed using a material different from the material composing the high frequency wiring board 222 connecting the bias circuit 102 and the PD 101. Further, when a front-illuminated PD 501 is used instead of the back-illuminated PD 101, there is no need to make a through hole in the PD subcarrier 303, and the number of mounting steps can be reduced.

The other configuration of optical receiver 800 is similar to the configuration of optical receiver 300. The optical receiver 800 of this embodiment also has the same effect as the optical receiver 300 of the second embodiment, that is, the same effect as the optical receiver 200 of the first embodiment.

An optical receiver is provided in which the operating band is less likely to deteriorate even when the distance between elements constituting the optical receiver changes.

100, 200, 300, 400, 500, 600, 700, 800

Optical receiver

101, 501 Photodiode (PD)
102 Bias circuit (capacitor)
103, 203, 303

PD subcarrier

103a, 303a, 403a Opening (through hole)
104 Transimpedance amplifier (TIA)
105

TIA subcarrier

106a, 106b wire 221

bump

222, 222a, 222b high

frequency wiring board

223a, 223b line 224 dielectric 403 subcarrier 503 PD subcarrier

Claims

A photodetector (PD),
a bias circuit that applies a bias voltage;
Transimpedance amplifier (TIA) and
at least one subcarrier carrying the PD, the bias circuit, and the TIA;
An optical receiver comprising: at least one high frequency wiring board connecting at least one between the top surface of the PD and the top surface of the bias circuit or between the top surface of the PD and the top surface of the TIA.
A lower surface of the bias circuit, the PD, and the TIA faces an upper surface of the at least one subcarrier;
The optical receiver according to claim 1, wherein the upper surface of the bias circuit, the upper surface of the PD, and the upper surface of the TIA are connected by a single high-frequency wiring board.
a lower surface of the bias circuit, the PD, and the TIA faces an upper surface of the at least one subcarrier;
The upper surface of the bias circuit and the upper surface of the PD are connected by a first high frequency wiring board,
The optical receiver according to claim 1, wherein the upper surface of the PD and the upper surface of the TIA are connected by a second high frequency wiring board that is separate from the first high frequency wiring board.
The optical receiver according to any one of claims 1 to 3, wherein the PD is a back-illuminated PD.
The optical receiver according to any one of claims 1 to 3, wherein the PD is a front-illuminated PD.
the bias circuit and the PD are installed on the top surface of the first subcarrier,
the TIA is installed on the top surface of the second subcarrier,
The optical receiver according to any one of claims 1 to 3, wherein the first subcarrier and the second subcarrier are separated.
The optical receiver according to any one of claims 1 to 3, wherein the bias circuit, the PD, and the TIA are installed on a single subcarrier.
The height of the top surface of the PD connected by the high frequency wiring board and the height of the top surface of the bias circuit, or the height of the top surface of the PD connected by the high frequency wiring board and the height of the top surface of the TIA. The light according to any one of claims 1 to 3, wherein at least one of the steps is adjusted by at least one of a step provided on the upper surface of the subcarrier or polishing the PD. receiver.