Optical Path Routing With Fixed Phase Difference for QKD Encoding

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Solution Overview

Problem

Existing quantum communication systems face challenges in encoding quantum states with minimal phase instability and drift, leading to high Quantum Bit Error Rate (QBER) and lower secret key rate (SKR) in Quantum Key Distribution (QKD) protocols.

Innovation Solution

An optical device with a light routing element and a phase controlling element is used to direct light pulses into different optical paths, providing a fixed phase difference between them, eliminating the need for high-speed, switchable phase modulators and minimizing phase instabilities, thereby encoding multiple quantum states with reduced complexity and power consumption.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If high-speed switchable phase modulators are used to encode quantum states, then encoding speed and versatility are improved, but phase instability and drift increase

Engineering Contradiction:

Improveencoding speedVSAvoidphase stability

Core Design Contradiction:

SpeedVSStability of the object's composition

Solution Approach 1:

The device segments the optical path into multiple fixed paths (first optical path, second optical path, etc.), each with a predetermined fixed phase difference. Instead of using a single switchable phase modulator, the system divides the encoding function across multiple static paths, eliminating the need for high-speed switching and reducing phase instability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Instead of actively switching phase modulators to change phase differences dynamically, the invention inverts the approach by using fixed optical paths with predetermined phase differences. The phase encoding is achieved by selecting which fixed path the light takes, rather than actively modulating the phase, thereby eliminating phase drift associated with switching.

Inventive Principle:

Principle #13The other way round (Inversion)

2Adaptability or versatility

If switchable phase modulators are used to provide variable phase differences, then adaptability is improved, but device complexity increases

Engineering Contradiction:

Improvephase encoding flexibilityVSAvoidmodulator switching complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The optical system is segmented into multiple discrete optical paths, each with a fixed phase difference. This segmentation provides adaptability by allowing selection of different paths for different encoding requirements, while simplifying the device by replacing complex switchable modulators with static optical components.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The fixed optical paths with predetermined phase differences serve multiple encoding functions. By selecting different paths or combinations of paths, the system can encode multiple quantum states without requiring separate modulators for each state, thereby reducing device complexity while maintaining versatility.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Productivity

If high-speed phase modulators are used for quantum state encoding, then encoding capability is improved, but power consumption increases

Engineering Contradiction:

Improveencoding capabilityVSAvoidpower consumption

Core Design Contradiction:

ProductivityVSUse of energy by moving object

Solution Approach 1:

The invention inverts the conventional approach by replacing active high-speed phase modulators with passive fixed optical paths. The encoding capability is maintained through path selection rather than active modulation, dramatically reducing power consumption while preserving the ability to encode multiple quantum states.

Inventive Principle:

Principle #13The other way round (Inversion)

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 solution reduces phase instabilities and drift, resulting in lower QBER and higher SKR, enhancing the reliability and efficiency of quantum communication systems.

Implementation Method 1

a light routing element coupled to a first optical path and a second optical path such that light received by the light routing element is directed into one of the first optical path or the second optical path

Methodology Applied

Scientific EffectLight routing:

Implementation Method 2

a phase controlling element provided in the first optical path such that there is provided a pre-determined fixed phase difference between a light pulse routed through the first optical path and a light pulse routed through the second optical path

Methodology Applied

Scientific EffectPhase control:

Implementation Method 3

a combiner coupling the first optical path and second optical path into a single output path

Methodology Applied

Scientific EffectOptical combining:

Data Source

PatentUS12519548B2Optical device

Publication Date: 2026.01.06 KK TOSHIBA

AI summary

An optical device comprising: a light routing element coupled to a first optical path and a second optical path such that light received by the light routing element is directed into one of the first optical path or the second optical path; a combiner coupling the first optical path and second optical path into a single output path; a controller applying a control signal to said light routing element, the control signal indicating whether a portion of the light received by the light routing element is directed into the first optical path or into the second optical path; a phase controlling element provided in the first optical path such that there is provided a pre-determined fixed phase difference between a light pulse routed through the first optical path and a light pulse routed through the second optical path.