WO2020199187A1

WO2020199187A1 - Optical receiver structure

Info

Publication number: WO2020199187A1
Application number: PCT/CN2019/081456
Authority: WO
Inventors: Yujian Bao; Zhaoming Li
Original assignee: Lumentum Operations Llc
Priority date: 2019-04-04
Filing date: 2019-04-04
Publication date: 2020-10-08
Also published as: CN111786731A; WO2020199352A1

Abstract

A method, device, optical receiver, planar lightwave chip (PLC), photodiode (PD), transimpedance amplifier (TIA), clock and data recover (CDR), computer program product, and non-transitory computer-readable medium are provided. For example, a method may include manufacturing an optical transceiver by passive die bonding processes without the need of active alignment. Other implementations may be provided.

Description

OPTICAL RECEIVER STRUCTURE

Some implementations described herein provide a method to make an optical transceiver by passive die bonding processes without the need of active alignment. This improves the production efficiency and reduces the cost.

In some optical systems, there may be a gap between a photodiode (PD) and a planar lightwave chip (PLC) . Such a gap may be approximately 15 microns. This gap allows an active aligner to move the PLC on top of the PD until a best coupling is found. However, a larger gap decreases a coupling efficiency. As a result, some implementations described herein provide a die bond process to reduce the gap to 1-5 microns. In this way, some implementations improve a coupling efficiency between a PD and a PLC.

In some implementations, an optical receiver may include an optical demultiplexer (e.g., using free space filters or a PLC) , a photodiode array (PD) (e.g., a 4 channel PD) , and a transimpedance amplifier (TIA) (e.g., with clock data recovery (CDR) ) , which may be termed a TIA+CDR chip.

In some implementations, an assembly process for the optical receiver may include die bonding the PD and the TIA+CDR chip on a substrate. In some techniques, the assembly process may include actively aligning PLC optical waveguide outputs to an optically sensitive area of the PD. In some implementations, actively aligning may take a threshold amount of time (e.g., using a hill climbing algorithm that is used to find the highest photocurrent of PD) and may be a bottleneck of production efficiency. Thus, a compact structure may be provided that can be assembled using a die bond process only and without active alignment, as shown in Fig. 1.

In some implementations, the PD may be back-illuminated, and the optically sensitive area and the electrodes may be on opposite sides of a die. In some implementations, the PD is attached on top of a PLC output using a high accuracy die bond (e.g., with within 5 micrometers accuracy or a higher level of accuracy) . In some implementations, the TIA+CDR chip is attached on top of the PLC using a die bond process. In some implementations, the PD and the TIA+CDR are connected by a wire bond.

Further, a position of a receive optical subassembly (ROSA) and a transmit optical subassembly (TOSA) may be important for reducing cross-talk. In other words, the ROSA and the TOSA may be separated to minimize this cross-talk. In this case, connections from the ROSA to a module output may be relatively short to minimize noise.

In some implementations, the die bond technique may reduce process time. In some implementations, active alignment for the PD to the PLC positioning may also be used, but the process time for active alignment may be greater than a threshold. In some implementations, a die bond passively aligns the PD with the PLC, thereby minimizing the time required for alignment.

In some implementations, the TIA+CDR may be disposed on the right of PD, as shown in Fig. 2. In this case, it may be easier to connect electrical outputs (e.g., direct current (DC) and radio frequency (RF) ) to a flexible circuit or a rigid PCB. In this case, a matching block may be added under the TIA+CDR chip. The block may be made of silicon, thereby providing good coefficient of thermal expansion (CTE) matching with the PLC chip. In some implementations, a reflection surface of the PLC may be metal coated.

In some implementations, an RF trace length may be reduced as shown in Fig. 3. In this case, the PD is front-illuminated, and the optically sensitive area and the electrodes are on the same sides of the die. In some implementations, the PD is flip chip bonded onto a joint surface of the PLC and the TIA+CDR chip. In some implementations, PD photocurrent outputs are directly connected to the TIA+CDR chip by solder ball grids. In some implementations, to match a height of the PLC and the TIA+CDR chip, a substrate may be disposed under the TIA+CDR chip. In some implementations, a flip chip is attached directly to the TIA+CDR chip. In this case, the flip chip may minimize an RF trace length from the PD to the TIA+CDR chip, which may yield an improved RF performance relative to a wire connection. In some implementations, the TIA+CDR chip, the PD, and the PLC may form an integrated, rigid structure.

In some implementations, an optical device may include a PD attached on a PLC directly. In some implementations, an optical device may include a TIA (e.g., a TIA+CDR) attached on a PLC. In some implementations, an optical device may include a PD flip chip mounted on the TIA. Some implementations described herein provide a compact structure of an optical receiver, including a PLC, a PD, and a TIA (e.g., with or without CDR) .

In this way, the optical device achieves a PD attachment accuracy of less than 1 micron (e.g., a distance between the PD and PLC) . By achieving this attachment accuracy, an increased coupling efficiency between the PD and the PLC may be achieved with a die bond machine. Further, some implementations described herein achieve a shorter trace from the PD to the TIA by using a flip chip connection rather than a wire connection, thereby resulting in better RF performance.

The foregoing disclosure provides illustration and description but is not intended to be exhaustive or to limit the implementations to the precise form disclosed. Modifications and variations may be made in light of the above disclosure or may be acquired from practice of the implementations.

Even though particular combinations of features are recited in the claims and/or disclosed in the specification, these combinations are not intended to limit the disclosure of various implementations. In fact, many of these features may be combined in ways not specifically recited in the claims and/or disclosed in the specification. Although each dependent claim listed below may directly depend on only one claim, the disclosure of various implementations includes each dependent claim in combination with every other claim in the claim set.

No element, act, or instruction used herein should be construed as critical or essential unless explicitly described as such. Also, as used herein, the articles “a” and “an” are intended to include one or more items and may be used interchangeably with “one or more. ” Furthermore, as used herein, the term “set” is intended to include one or more items (e.g., related items, unrelated items, a combination of related items, and unrelated items, etc. ) , and may be used interchangeably with “one or more. ” Where only one item is intended, the phrase “only one” or similar language is used. Also, as used herein, the terms “has, ” “have, ” “having, ” or the like are intended to be open-ended terms. Further, the phrase “based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise.

Claims

A method, device, optical receiver, planar lightwave chip (PLC) , photodiode (PD) , transimpedance amplifier (TIA) , clock and data recover (CDR) , computer program product, and non-transitory computer-readable medium as substantially described herein with reference to and as illustrated by the accompanying drawings.