Photodiode Isolation via Current Blocking Layer in Photonic Circuits

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

In wavelength division multiplexed (WDM) optical communication systems, the integration of receiver node components, particularly balanced photodetectors, faces challenges due to unintended electrical paths formed by undoped waveguides, which can lead to current flow between photodiodes, preventing accurate light sensing.

Innovation Solution

A current blocking layer comprising alternating p and n-type doped semiconductor layers is introduced between the output waveguides and photodiodes, forming reverse-biased pn-junctions that limit current flow and improve light sensing accuracy by isolating photodiodes within depletion regions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If undoped waveguides are used to connect MMI coupler to photodiodes, then optical signal transmission is achieved, but electrical current can flow between photodiodes through the waveguide, preventing accurate light sensing

Engineering Contradiction:

Improvelight sensing accuracyVSAvoidunintended current flow

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

Doped semiconductor layers are introduced as intermediary elements between the waveguide and photodiodes. These layers form pn-junctions that create depletion regions, acting as electrical barriers that block unwanted current flow while allowing optical signals to pass through via evanescent coupling.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The electrical conductivity parameter of the waveguide region is changed by introducing doped semiconductor layers. These layers have different doping concentrations than the undoped waveguide, creating regions of high electrical resistance that block current flow between photodiodes while maintaining optical transmission properties.

Inventive Principle:

Principle #35Parameter changes

2Use of energy by moving object

If photodiodes are placed in direct contact with waveguide output portions, then evanescent coupling of light is achieved, but electrical isolation between photodiodes is lost

Engineering Contradiction:

Improveoptical coupling efficiencyVSAvoidelectrical isolation

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The region between the waveguide and photodiode is segmented into multiple doped semiconductor layers with alternating doping types. This segmentation creates multiple pn-junctions in series, each contributing to the electrical isolation while collectively maintaining optical coupling efficiency through evanescent field interaction.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A composite structure is formed by combining undoped waveguide materials with doped semiconductor layers. This composite arrangement provides both optical transmission properties from the waveguide and electrical isolation properties from the doped layers, achieving dual functionality.

Inventive Principle:

Principle #40Composite materials

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This configuration effectively blocks current flow between photodiodes, allowing them to accurately sense incoming light, thereby enhancing the performance of balanced photodetectors in WDM systems by isolating electrical paths and improving signal detection.

Implementation Method 1

an interface between the first and second doped semiconductor layers constitutes a first pn-junction. The first and second doped semiconductor layers are provided between the first photodiode and the first output portion of the waveguide

Methodology Applied

Scientific Effectpn-junction: Diode

Implementation Method 2

the first pn-junction is configured to be biased such that the first pn-junction is included in a first depletion region, and the second pn-junction is configured to be biased such that the second pn-junction is included in a second depletion region

Methodology Applied

Scientific Effectdepletion region:

Implementation Method 3

one of which may be provided in contact with the output waveguides of the MMI coupler so that light output from the MMI coupler evanescently couples into the photodiodes

Methodology Applied

Scientific Effectevanescent coupling:

Data Source

PatentUS8269297B2Photodiode isolation in a photonic integrated circuit

Publication Date: 2012.09.18 INFINERA CORP

AI summary

Consistent with the present disclosure, a current blocking layer is provided between output waveguides carrying light to be sensed by the photodiodes in a balanced photodetector, and the photodiodes themselves. Preferably, the photodiodes are provided above the waveguides and sense light through evanescently coupling with the waveguides. In addition, the current blocking layer may include alternating p and n-type conductivity layers, such that, between adjacent ones of such layers, a reverse biased pn-junction is formed. The pn-junctions, therefore, limit the amount of current flowing from one photodiode of the balanced detector to the other, thereby improving performance.