Optical communication module

Abstract

The present invention curbs an increase in cost associated with an increase in the number of components and attains a more compact size for an optical communication module.　Provided is an optical communication module (20) having N pairs (where N is an even number) of transmitter / receiver units including an optical transmitter (TX) and an optical receiver (RX). The module comprises K (where K ≤ N / 2) optical circuit chips (25) and K fiber arrays (26) with respect to N digital signal processing circuit chips (22). A transmit signal input terminal group (25IN) of the optical transmitter (TX) and a receive signal output terminal group (25OUT) of the optical receiver (RX) are disposed along one side of the optical circuit chip (25), and the fiber array (26) is connected to the side opposite said one side.

Description

Optical Communication Module

[0001] The present invention relates to an optical communication module, and more particularly to an optical communication module including a plurality of transceiver units each including an optical transmitter and an optical receiver.

[0002] In recent years, the application range of optical communication modules and optical devices has expanded beyond long-distance communications to include links between data centers, mobile phone base stations, and edge routers, resulting in increasing demand for improved performance. To achieve this, it is necessary to closely arrange electronic devices (ICs such as DSPs, drivers, and TIAs) that process electrical signals and optical circuit chips, which are optical devices, in order to improve high-frequency characteristics. Development of co-packaged optics (CPOs), in which electronic devices and optical devices are mounted on the same substrate, has been progressing (see, for example, Non-Patent Documents 1 and 2). As the application range of optical communication modules and devices expands, there is an increasing demand for lower-cost CPOs.

[0003] Figure 1 shows the configuration of a conventional optical communications module with optical transmission and reception functions. Figure 1(a) shows the layout of each chip as seen from the top of an optical communications module 10. Two sets of transmission and reception units, each consisting of a digital signal processing circuit chip (DSP) 12, a driver circuit chip (DRV) 13, a transimpedance amplifier circuit chip (TIA) 14, an optical circuit chip 15, and a fiber array (FA) 16, are mounted on a package substrate 11. Optical signals are input and output via optical fiber 17 via the FA 16.

[0004] The DRV 13 amplifies the transmission electrical signal output from the DSP 12 and outputs it from a DRV output terminal group 13OUT. The TIA 14 receives the reception electrical signal output from the optical circuit chip 15 via a TIA input terminal group 14IN, amplifies it, and outputs it to the DSP 12.

[0005] The optical circuit chip 15 includes an optical transmitter configured with an optical modulator, an optical waveguide, a splitter, an optical attenuator, etc., and an optical receiver configured with a photodiode (PD), an optical waveguide, an optical attenuator, etc. It also includes a group of transmission signal input terminals 15IN for inputting transmission electrical signals from the DRV 13, and a group of reception signal output terminals 15OUT for outputting reception electrical signals to the TIA 14.

[0006] FIG. 2 shows the configuration of an optical circuit chip in a conventional optical communication module. The optical circuit chip 15 is an optical device integrating multiple optical circuit elements and optical waveguides connecting them. Many optical transmitters TX use a Mach-Zehnder interferometer (MZI) optical modulator MOD that utilizes the electro-optic effect. The MZI modulator MOD has a traveling-wave electrode 15E disposed on an optical waveguide in the optical axis direction from an input end that receives continuous wave light from a light source to an output end that outputs a transmitted optical signal. To achieve the desired electro-optic effect, the traveling-wave electrode 15E must have a predetermined length, which defines the length of the MZI modulator MOD in the optical axis direction. For example, while the size of an optical receiver RX is at most approximately 100 μm square, the length of the MZI modulator MOD in the optical axis direction is long, approximately 1 mm to 5 mm. In conventional optical communication modules, the optical transmitter TX and optical receiver RX are arranged in parallel, so the length of the optical circuit chip 15 in the optical axis direction depends on the length of the optical transmitter TX, i.e., the length of the modulator. This results in a problem that the chip size of the optical circuit chip 15 becomes large and there is space on the optical receiver RX side where no optical circuit elements are mounted, resulting in poor mounting efficiency of optical devices.

[0007] 1(b), the optical communication module 10 is configured by face-down mounting using a flip chip. In this case, when viewed from above, the transmission signal input terminal group 15IN, the reception signal output terminal group 15OUT, and the traveling wave electrode 15E of the optical circuit chip 15 are formed on the bottom surface of the chip. In FIGS. 1(a) and 2, the configuration seen through from the top surface is schematically shown.

[0008] FA 16 indicates the form of end face connection connected to the end face of the optical circuit chip 15. For example, as shown in Non-Patent Documents 1 and 2, a configuration can be applied in which an optical circuit chip is mounted face up and optical signals are input and output from the top surface of the optical circuit using a grating coupler or the like.

[0009] The DSP 12 has a plurality of transmission signal output terminals and reception signal input terminals on the side that outputs transmission electrical signals to the optical transmitter TX and the side that inputs reception electrical signals from the optical receiver (generally referred to as the line side). For example, a digital signal processing circuit chip based on the 400GBASE-DR4 standard has a total of eight transmission signal output terminals (positive and negative phase) and a total of eight reception signal input terminals for each of the four lanes.

[0010] In addition, in an optical communication module based on this standard, the number of fibers connected to the fiber array is nine: four each for transmitting and receiving optical signals, and one for inputting CW light from a light source to the optical transmitter TX.

[0011] In the above-described optical communications module 10, an example was shown in which two sets of transceiver units, each accommodating four lanes, are implemented, but to increase the transmission capacity of the optical communications network, an optical communications module with double the sets of transceiver units can be manufactured. However, in the conventional optical communications module 10 using CPO, it was necessary to connect the optical circuit chip 15 and fiber array 16 for each transceiver unit, which resulted in issues such as increased costs due to the increased number of components and an increase in the size of the optical communications module.

[0012] Ravi Mahajan, et al, "Co-Packaged Photonics For High Performance Computing Status Challenges And Opportunities," J. of Lightwave Technology, Vol. 40, No. 2, 2022.1.15.Rob Stone, et al, "Co-packaged Optics for Data Center Switching," 2020 ECOOC, 978-1-7281-7361-0 / 20 / $31.00 2020 IEEE.

[0013] One embodiment of the present invention is an optical communications module having N (N is an even number) sets of transmission / reception units, each including an optical transmitter and an optical receiver, characterized in that for N digital signal processing circuit chips, K (K≦N / 2) optical circuit chips and K fiber arrays are provided, and a group of transmission signal input terminals of the optical transmitter and a group of reception signal output terminals of the optical receiver are arranged along one side of the optical circuit chip, and the fiber array is connected to the side opposite to the one side.

[0014] This configuration makes it possible to suppress increases in costs due to an increase in the number of components, and to achieve a reduction in the size of the optical communications module.

[0015] FIG. 1 is a diagram showing the configuration of a conventional optical communications module having optical transmission and reception functions, FIG. 2 is a diagram showing the configuration of an optical circuit chip of a conventional optical communications module, FIG. 3 is a diagram showing the configuration of an optical communications module according to Example 1 of the present invention, FIG. 4 is a diagram showing the configuration of an optical communications module according to Example 2 of the present invention, FIG. 5 is a diagram showing the configuration of an optical circuit chip of an optical communications module according to Example 2, FIG. 6 is a diagram showing the configuration of an optical communications module according to Example 3 of the present invention, FIG. 7 is a diagram showing a first example of an optical circuit chip of an optical communications module according to Example 3, FIG. 8 is a diagram showing a second example of an optical circuit chip of an optical communications module according to Example 3, FIG. 9 is a diagram showing a third example of an optical circuit chip of an optical communications module according to Example 3, FIG. 10 is a diagram showing the configuration of an optical communications module according to Example 4 of the present invention, FIG. 11 is a diagram showing the configuration of an optical communications module according to Example 5 of the present invention, FIG. 12 is a diagram showing the configuration of an optical communications module according to Example 6 of the present invention, and FIG. 13 is a diagram showing the configuration of an optical communications module according to Example 7 of the present invention.

[0016] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0017] 3 shows the configuration of an optical communications module according to a first embodiment of the present invention. The arrangement of each chip is shown as viewed from above in an optical communications module 20 in which two sets of transceiver units each accommodating four lanes are mounted. Two sets of transceiver units, each consisting of a digital signal processing circuit chip (DSP) 22, a driver circuit chip (DRV) 23, and a transimpedance amplifier circuit chip (TIA) 24, are mounted on a package substrate 21. Materials such as silicon and InP can be used as the material for the substrate 21.

[0018] The difference from conventional optical communication modules is that the optical circuit chip 25 and fiber array (FA) 26 are integrated into one. A transmission signal input terminal group 25IN and a reception signal output terminal group 25OUT are arranged along one side of the optical circuit chip 25, and the FA 26 is connected to the side opposite to that side. The FA 26 houses 18 optical fibers 27, twice the number of optical fibers (9).

[0019] Assuming an optical communications module includes N (N is an even number) sets of transmitting and receiving units, it will have N digital signal processing chips (DSPs), K (K≦N / 2) optical circuit chips, and K fiber arrays (FAs). A group of transmission signal input terminals and a group of reception signal output terminals electrically connected to the DSPs are arranged along one side of the optical circuit chip, and the FAs are connected to the side opposite that side.

[0020] In conventional optical communication modules, doubling the number of sets of transmitting and receiving units increases the number of FAs, which leads to problems such as increased costs for the optical fiber connection process, costs associated with increased components, and an increase in the size of the optical communication module due to an increase in the area required for optical fiber connection. According to the configuration of Example 1, the optical fiber connection process can be halved, making it possible to suppress increases in costs and an increase in the size of the optical communication module.

[0021] 4 shows the configuration of an optical communications module according to a second embodiment of the present invention. The chip layout is shown as seen from above in an optical communications module 30 in which two sets of transceiver units accommodating four lanes are mounted. Two sets of transceiver units, each consisting of a digital signal processing circuit chip (DSP) 32, a driver circuit chip (DRV) 33, and a transimpedance amplifier circuit chip (TIA) 34, are mounted on a package substrate 31. The difference from conventional optical communications modules is that the optical circuit chip 35 has a different configuration and the fiber array (FA) 36 is integrated into one. The FA 36 accommodates 18 optical fibers 37, twice the number of nine.

[0022] 5 shows the configuration of the optical circuit chip of the optical communications module of Example 2. In the optical circuit chip 35, which is an optical device, a transmission signal input terminal group 35IN2 and a reception signal output terminal group 35OUT2 for one of the transmission / reception units are arranged along one side of the optical circuit chip 35, and the FA 36 is connected to the side opposite to the side. The transmission signal input terminal group 35IN1 and the reception signal output terminal group 35OUT1 for the other transmission / reception unit are arranged along the side perpendicular to the side. Furthermore, the reception signal output terminal group 35OUT1 is arranged closer to the side opposite to the side to which the FA 36 is connected than the transmission signal input terminal group 35IN1.

[0023] This configuration eliminates the space on the side of the optical receiver RX where no optical circuit elements are mounted, which has been conventionally formed, and allows the area of ​​the optical circuit chip 35 to be reduced, thereby achieving cost reduction.

[0024] FIG. 6 shows the configuration of an optical communications module according to a third embodiment of the present invention. FIG. 6( a) shows the layout of each chip as viewed from the top of an optical communications module 40. This shows the layout of each chip as viewed from the top of an optical communications module 40 in which two sets of transceiver units accommodating four lanes are mounted. Two sets of transceiver units, each consisting of a digital signal processing circuit chip (DSP) 42, a driver circuit chip (DRV) 43, and a transimpedance amplifier circuit chip (TIA) 44, are mounted on a package substrate 41. The difference from conventional optical communications modules is that the optical circuit chip 45 has a different configuration and the fiber array (FA) 46 is integrated into one. The FA 46 accommodates 18 optical fibers 47, twice the number of optical fibers (nine).

[0025] Furthermore, the difference from the first and second embodiments is that, in the optical circuit chip 45, the optical receiver RX and the optical transmitter TX are arranged in series in the optical axis direction of the optical modulator MOD. Accordingly, the DSP 42, the DRV 43, and the TIA 44 are arranged in series in the same optical axis direction, in this order, on the substrate 41. That is, the TIA 44 is arranged opposite one side of the optical circuit chip 45, and the DRV 43 is arranged between the DSP 42 and the TIA 44.

[0026] 6B, the optical communications module 40 is configured by face-down flip-chip mounting. The DRV 43 and the optical circuit chip 45 are connected by wiring 43W formed in the package substrate 41, and the optical circuit chip 45 and the TIA 44 are connected by wiring 43W.

[0027] FIG. 7 shows a first example of an optical circuit chip for an optical communications module according to a third embodiment. In an optical circuit chip 45, which is an optical device, a reception signal output terminal group 45OUT and an optical receiver RX are arranged along one side of the optical circuit chip 45, and an FA 46 is connected to the side opposite the side. Furthermore, a transmission signal input terminal group 45IN and an optical modulator MOD of the optical transmitter TX are arranged between the optical receiver RX and the side opposite the side. That is, while in conventional optical communications modules, the optical transmitter TX and the optical receiver RX are arranged in parallel along the optical axis of the optical circuit chip 15, in the third embodiment, they are arranged in series. The dashed lines indicate optical waveguides formed on the chip substrate, and also show a splitter 48 for distributing CW light from the light source to each optical modulator MOD of the optical transmitter TX.

[0028] In the substrate 41 using a silicon substrate, the CW light from the light source generally needs to be input in TE mode. Therefore, the optical fiber 47 connected via the FA 46 needs to be a polarization-maintaining fiber (PMF). On the other hand, the transmitted light output from the optical modulator MOD of the optical transmitter TX and the received light input received by the optical receiver RX are not regulated in polarization, and single-mode optical fiber (SMF) can be used.

[0029] The optical waveguide layout is such that the PMF can be connected outside the SMF connection position at the connection end face between the optical circuit chip 45 and the FA 46. That is, the received light input is located at the center of one side connecting to the FA 46, with the transmitted light output on both sides of that, and the CW light input on both sides of that. This is because PMFs generally have a larger fiber diameter than SMFs, making it easier to ensure tolerances when fabricating a fiber array. Furthermore, fiber arrays are generally constructed by arranging fiber cores on a glass substrate with a V-groove and sandwiching them between flat glass lid plates. Therefore, locating the PMF on the outside provides structural stability. In this way, an optical communications module with high precision and high optical coupling stability can be fabricated.

[0030] 8 shows a second example of the optical circuit chip of the optical communications module of Example 3. The optical circuit chip 55 is an example in which the layout of the optical waveguides of the optical circuit chip 45 is modified. As shown in Fig. 8, the optical circuit chip 55 and the FA 46 may be arranged so that the PMFs can be connected together at the center of the connection end faces.

[0031] 9 shows a third example of the optical circuit chip of the optical communications module of Example 3. The optical circuit chip 65 is an example in which the layout of the optical waveguide of the optical circuit chip 45 is modified. As shown in Fig. 9, the optical circuit chip 65 may be arranged in the center of the connection end face between the optical circuit chip 65 and the FA 46 so as to be able to receive the received optical signal received by the optical receiver RX.

[0032] According to the configuration of the third embodiment, similarly to the first and second embodiments, the area of ​​the optical circuit chips 45, 55, and 65 can be reduced, and costs can be reduced.

[0033] Furthermore, the photodiode (PD) of the optical receiver RX has a large capacitance, making it difficult to achieve impedance matching with the TIA. According to the configuration of Example 3, the reception signal output terminals 45OUT, 55OUT, and 65OUT of the optical receiver RX are close to the reception signal input terminals 44IN of the TIA 44, making it difficult for the high-frequency characteristics to deteriorate and improving the reception signal quality. Meanwhile, the distance between the transmission signal output terminals 43OUT of the DRV 43 and the transmission signal input terminals 45IN, 55IN, and 65IN of the optical transmitter TX is long. However, since the input impedance of the optical modulator MOD is set to approximately 20-50 Ω and the traveling-wave electrodes 45E, 55E, and 65E can also be set to any impedance, impedance matching is easy and signal quality degradation can be suppressed.

[0034] FIG. 10 shows the configuration of an optical communications module according to a fourth embodiment of the present invention. The top view of an optical communications module 70 is shown, showing the arrangement of each chip. Two sets of transceiver units, each containing four lanes, are mounted on a package substrate 71. Two sets of transceiver units, each consisting of a digital signal processing circuit chip (DSP) 72, are mounted on the package substrate 71. The difference from conventional optical communications modules is that the DSP 72 functions as a driver circuit (DRV) and a transimpedance amplifier circuit (TIA) in addition to its function as a digital signal processing circuit. The optical circuit chip 75 and fiber array (FA) 76 are integrated into one unit, as in the third embodiment. The FA 76 houses 18 optical fibers 77, twice the number of optical fibers (nine).

[0035] The DSP 72 has a group of transmission signal output terminals 72OUT connected to the group of transmission signal input terminals 45IN of the optical transmitter TX, and a group of reception signal input terminals 72IN connected to the group of reception signal output terminals 75OUT of the optical receiver RX.

[0036] According to the configuration of the fourth embodiment, similarly to the first to third embodiments, the area of ​​the optical circuit chip 75 can be reduced, and the overall size of the optical communications module 70 can be reduced, thereby achieving cost reduction.

[0037] 11 shows the configuration of an optical communications module according to a fifth embodiment of the present invention. The optical communications module 80 is an example in which two sets of the optical communications modules 70 according to the fourth embodiment are mounted on a package substrate 81. To increase the transmission capacity of the optical communications network, a plurality of optical communications modules 70 may be mounted.

[0038] 12 shows the configuration of an optical communications module according to Example 6 of the present invention. The optical communications module 90 is an example in which two sets of the optical communications module 70 according to Example 4 are mounted on an interposer substrate 98 on a package substrate 91.

[0039] Compared to Examples 1-5, the optical circuit chip 75 and the fiber array (FA) 76 are housed on the package substrate 91, so that the package substrate 91 can be covered with a lid (not shown). This lid makes it possible to realize an optical communications module 90 that is physically durable and can prevent the intrusion of dust and the like.

[0040] FIG. 13 shows the configuration of an optical communications module according to Example 7 of the present invention. The optical communications module 100 is an example in which optical communications modules 100A and 100B, each having two sets of transceiver units, are mounted on an interposer substrate 108 on a package substrate 101, as in Example 6. The optical communications module 100 differs from the optical communications modules 70 of Examples 4-6 in that it includes an optical circuit chip 105A and an optical circuit chip 105B. The optical circuit chips 105A and 105B have different optical waveguide layouts and are designed so that the connection positions of the FAs 106A and 106B are symmetrical with respect to the center of one side perpendicular to the longitudinal direction of the optical communications module 100 (the side where the optical communications modules 100A and 100B are in contact with each other). This allows the two adjacent FAs 106A and 106B to be positioned close to each other.

[0041] By consolidating the two FAs 106A and 106B near the center of one side of the optical communication module 100, the optical fiber 107 connected to the optical communication module 100 can also be consolidated, thereby minimizing the overall mounting area of ​​the optical communication module 100.

[0042] Furthermore, similarly to Example 6, the package substrate 101 can be covered with a lid (not shown). Pillars for supporting the lid must be placed at the four corners of the package substrate 101, and it is preferable to place these pillars away from the FA 106. Even if the number of optical communications modules mounted on the package substrate 101 increases, it is sufficient to place the fiber arrays (FA) of the optical communications modules that are close to the four corners of the package substrate 101 away from the four corners.

[0043] According to the configuration of Example 7, the FA 106 can be consolidated, so that it can be covered with a lid without increasing the substrate area, thereby realizing an optical communication module 100 with high physical durability.

[0044] 10, 20, 30, 40, 70, 80, 90, 100 Optical communication module 11, 21, 31, 41, 71, 81, 91, 101 Package substrate 12, 22, 32, 42, 72, 102 Digital signal processing circuit chip (DSP) 13, 23, 33, 43 Driver circuit chip (DRV) 14, 24, 34, 44 Transimpedance amplifier circuit chip (TIA) 15, 25, 35, 45, 55, 65, 75, 105 Optical circuit chip 16, 26, 36, 46, 76, 106 Fiber array (FA) 17, 27, 37, 47, 77, 107 Optical fiber 48, 58, 68 Splitter 98, 108 Interposer substrate

Claims

1. An optical communications module having N (N is an even number) sets of transmitting and receiving units, each including an optical transmitter and an optical receiver, characterized in that for N digital signal processing circuit chips, there are K (K≦N / 2) optical circuit chips and K fiber arrays, wherein a group of transmitting signal input terminals of the optical transmitter and a group of receiving signal output terminals of the optical receiver are arranged along one side of the optical circuit chip, and the fiber array is connected to the side opposite to the one side.

2. An optical communications module having N (N is an even number) sets of transmitting and receiving units, each including an optical transmitter and an optical receiver, characterized in that for N digital signal processing circuit chips, K (K≦N / 2) optical circuit chips and K fiber arrays are provided, the optical receiver and a received signal output terminal group of the optical receiver are arranged along one side of the optical circuit chip, the fiber array is connected to the side opposite to said side, and the optical transmitter and a transmitted signal input terminal group of the optical transmitter are arranged between the optical receiver and the opposite side.

3. The optical communications module according to claim 2, further comprising: a transimpedance amplifier circuit chip arranged opposite one side of said optical circuit chip; and a driver circuit chip arranged between said digital signal processing circuit chip and said transimpedance amplifier circuit chip.

4. An optical communications module as described in claim 2 or 3, characterized in that a received optical input to said optical receiver is arranged in the center of the side opposite to the one side, a transmitted optical output from said optical transmitter is arranged on both sides of said received optical input, and a CW optical input to said optical transmitter is arranged on both sides of said transmitted optical output.

5. An optical communications module as described in claim 2 or 3, characterized in that the connection positions between the optical circuit chip and the fiber array are arranged so that two adjacent fiber arrays among the K fiber arrays are adjacent to each other.

6. An optical communications module having two sets of transmitting / receiving units each including an optical transmitter and an optical receiver, comprising one optical circuit chip and one fiber array for two digital signal processing circuit chips, wherein the transmitting signal input terminal group of the optical transmitter and the receiving signal output terminal group of the optical receiver in one of the transmitting / receiving units are arranged along one side of the optical circuit chip, the fiber array is connected to the side opposite to the one side, and the transmitting signal input terminal group of the optical transmitter and the receiving signal output terminal group of the optical receiver in the other transmitting / receiving unit are arranged along the side perpendicular to the one side.

7. The optical communications module according to claim 1, 2 or 6, wherein the digital signal processing circuit chip and the optical circuit chip are flip-chip mounted on an interposer substrate on a package substrate.

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