Surface-Coupled Reflective Electro-Absorption Modulators for Polarization Diversity

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Solution Overview

Problem

Existing optical transmitters using waveguide-based electro-absorption modulators are polarization-dependent, making it difficult to construct devices capable of handling polarization-division-multiplexed signals effectively without expensive polarization-control equipment.

Innovation Solution

The use of surface-coupled reflective electro-absorption modulators in interferometer arms, which are insensitive to polarization fluctuations, allowing for polarization-diverse operation without the need for polarization controllers or polarization-maintaining fibers, by receiving input light and outputting modulated light orthogonally to the device plane.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If waveguide-based electro-absorption modulators are used, then the device structure is compact and manufacturable, but the device becomes polarization-dependent requiring expensive polarization-control equipment

Engineering Contradiction:

ImprovemanufacturabilityVSAvoidpolarization independence

Core Design Contradiction:

Ease of manufactureVSAdaptability or versatility

Solution Approach 1:

The device is divided into two independent interferometers (first and second interferometers) with separate modulator arrays, each handling different polarization components. This segmentation allows each interferometer to be optimized for its specific function while collectively achieving polarization-division multiplexing capability without requiring polarization control in individual components

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The surface-coupled modulators are designed to handle multiple polarization states simultaneously through their reflective geometry and surface coupling mechanism. The modulators serve dual purposes: maintaining polarization independence while enabling PDM signal generation, eliminating the need for separate polarization control equipment

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Reliability

If polarization controllers and polarization-maintaining fibers are used, then polarization stability is improved, but device complexity and cost increase

Engineering Contradiction:

Improvepolarization stabilityVSAvoidequipment complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent extracts and removes the polarization control function from the traditional component list. By using surface-coupled modulators with reflective geometry, the polarization management is inherently handled by the modulator structure itself rather than requiring separate polarization controllers and polarization-maintaining fibers, thus reducing overall device complexity

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The surface-coupled modulators are self-sufficient in handling polarization diversity. Their reflective surface coupling mechanism automatically adapts to different polarization states without external control, making the system self-managing regarding polarization stability and eliminating the need for additional polarization control equipment

Inventive Principle:

Principle #25Self-service

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 enables the generation of polarization-division-multiplexed optical output signals with reduced costs, as it eliminates the requirement for expensive polarization-control equipment, while maintaining polarization diversity and stability across varying input light conditions.

Implementation Method 1

surface-coupled reflective electro-absorption modulators... each of the reflective electro-absorption modulators being configured to receive input light and output modulated light substantially orthogonally to the planar surface

Methodology Applied

Scientific EffectElectro-absorption: Absorption (EM radiation)

Implementation Method 2

an optical circuit optically coupled to the plurality of reflective electro-absorption modulators to form a first optical interferometer... configured to generate a first modulated optical signal by optically combining the modulated light outputted by the respective reflective electro-absorption modulators

Methodology Applied

Scientific EffectOptical interference: Interference

Data Source

PatentUS10411807B1Optical transmitter having an array of surface-coupled electro-absorption modulators

Publication Date: 2019.09.10 NOKIA SOLUTIONS & NETWORKS OY

AI summary

An optical data transmitter in which surface-coupled reflective electro-absorption modulators are placed into different interferometer arms and operated in a manner that enables the optical data transmitter to transmit an optical output signal modulated using PAM, QPSK, or QAM modulation. In some embodiments, the optical data transmitter is configured to generate a PDM optical output signal by using two such interferometers and a quarter-wavelength plate configured to cause the output polarizations of the two interferometers to be mutually orthogonal. The electro-absorption modulators are surface-coupled in the sense that, in operation, each of these devices receives input light and outputs modulated light along a direction that is substantially orthogonal to the main plane of the device. In an example embodiment, an electro-absorption modulator includes a PIN diode comprising an MQW structure and implemented using a stack of relatively thin semiconductors layers that are parallel to the main plane of the device.