Bi-directional Optical Module WDM Filter Edge Geometry

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Solution Overview

Problem

The existing bi-directional optical modules with a one-package configuration suffer from degraded optical crosstalk performance due to the adjacent mounting of semiconductor laser diodes and photodiodes, where transmitting light is diffusely reflected by the WDM filter, causing stray light to be received by the photodiode.

Innovation Solution

A bi-directional optical module design featuring a WDM filter with an edge surface that makes an obtuse angle to the primary surface, preventing light reflection from coupling with the photodiode, thereby enhancing optical crosstalk performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If the LD and PD are adjacently mounted in a one-package configuration, then the module size is miniaturized, but the optical crosstalk performance is degraded due to stray light from diffuse reflection by the WDM filter

Engineering Contradiction:

Improvemodule sizeVSAvoidoptical crosstalk

Core Design Contradiction:

Volume of moving objectVSObject-affected harmful factors

Solution Approach 1:

The WDM filter edge surface is designed with an asymmetric obtuse angle configuration rather than a conventional right angle. This asymmetric geometry causes transmitted light to reflect at angles that direct it away from the PD active area, effectively reducing optical crosstalk while maintaining the compact one-package structure

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The obtuse angle is specifically applied to the edge surface of the WDM filter where light transmission occurs, creating a localized geometric feature that controls light reflection patterns. This local modification targets the specific problem area (stray light generation at the filter edge) without changing the overall module structure

Inventive Principle:

Principle #3Local quality

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

The obtuse angle configuration significantly reduces optical crosstalk, as evident from improved bit error ratio (BER) performance, with a degradation of 0.8 dBm compared to 2.8 dBm in conventional modules, and minimizes stray light interference, reflecting the module's improved signal quality.

Implementation Method 1

a wavelength division multiplexing (WDM) filter to reflect the first light toward the single fiber and to transmit the second light toward the PD

Methodology Applied

Scientific EffectWavelength division multiplexing:

Implementation Method 2

a WDM filter selectively passes the receiving light from the fiber and reflects the transmitting from the LD

Methodology Applied

Scientific EffectOptical reflection: Reflection

Implementation Method 3

an optical film showing the WDM function is formed

Methodology Applied

Scientific EffectWavelength selective filtering: Filter (optical)

Data Source

PatentUS8005367B2Bi-directional optical module with improved optical crosstalk

Publication Date: 2011.08.23 SUMITOMO ELECTRIC INDUSTRIES LTD

AI summary

The bi-directional optical module, which installs the receiver and the transmitter within one package, is disclosed with an improved optical crosstalk. The optical module provides a lens, a WDM filter and a photodiode (PD) on an axis of the single mode fiber coupled with the module, while, a laser diode (LD) in a position perpendicular to the optical axis. The WDM filter provides a multi-layered optical film on a primary surface and an edge in a side far from the LD and the (PD) makes an obtuse angle to the primary surface so as to prevent light from the LD and reflected at this edge from entering the PD.