Optical-Wireless Hybrid Transmission Using Polarization-Coupled Signals

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Solution Overview

Problem

Conventional optical-wireless hybrid transmission systems are complex and expensive due to the need for high-frequency optical modulators and optical amplifiers, especially when handling broadband millimeter-wave signals, and require RF-band components and optical amplifiers, which increase costs and complexity.

Innovation Solution

The system employs a central office with an optical transmitter that sends a polarization-coupled optical signal to a base station, where the signal is modulated by an RF signal and then transmitted back, using a single-mode optical source and polarization-coupling to achieve high-sensitivity detection without the need for RF-band components or optical amplifiers, utilizing orthogonal-polarization-coupling and automatic frequency control to stabilize intermediate frequencies.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If high-frequency optical modulators and optical amplifiers are used to handle broadband millimeter-wave signals, then signal transmission capability is improved, but system complexity and cost increase

Engineering Contradiction:

Improvesignal transmission capabilityVSAvoidsystem complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent extracts and removes the RF-band components (optical modulators and optical amplifiers) from the optical receiver, replacing them with a direct photodetection approach that converts optical signals directly to electrical signals, thereby simplifying the system while maintaining broadband signal transmission capability

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent substitutes the mechanical/electrical RF-band modulation and amplification system with an optical heterodyne detection system that directly converts optical signals to electrical signals at intermediate frequencies, eliminating the need for complex RF components

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If RF-band components and optical amplifiers are installed in the optical receiver, then signal reception sensitivity is improved, but system cost increases

Engineering Contradiction:

Improvesignal reception sensitivityVSAvoidsystem cost

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

The patent replaces expensive, complex RF-band components and optical amplifiers with a simpler, more cost-effective photodetection system that achieves comparable or superior sensitivity through direct optical-to-electrical conversion at intermediate frequencies

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Solution Approach 2:

The patent changes the operating parameters by detecting signals at intermediate frequencies rather than at high RF frequencies, allowing the use of simpler, cheaper components while maintaining or improving reception sensitivity

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If a simple system configuration is used without RF-band components, then system complexity and cost are reduced, but signal detection sensitivity may deteriorate

Engineering Contradiction:

Improvesystem complexityVSAvoidsignal detection sensitivity

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent introduces an intermediary approach by using optical heterodyne detection that converts high-frequency optical signals to intermediate frequencies before electrical detection, allowing simple system configuration while maintaining high detection sensitivity through the intermediary frequency conversion process

Inventive Principle:

Principle #24Intermediary (Mediator)

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 allows for high-sensitivity detection of optical signals with a simple and cost-effective system, reducing the need for complex components and expanding wireless coverage while lowering system costs.

Implementation Method 1

a photodetector which photodetects a coupled optical signal output from the optical coupler and outputs an electrical signal

Methodology Applied

Scientific EffectPhotoelectric Effect: Photoelectric Effect

Implementation Method 2

a polarization-coupling part which orthogonal-polarization-couples the second single-mode optical signal with the third single-mode optical signal

Methodology Applied

Scientific EffectPolarization: Polarisation

Data Source

PatentUS7583896B2Optical-wireless hybrid transmission system and optical-wireless hybrid transmission method

Publication Date: 2009.09.01 NIPPON TELEGRAPH & TELEPHONE CORP

AI summary

An optical transmitter of an optical-wireless hybrid transmission system according to the invention outputs a first single-mode optical signal (center frequency: fC1) to an optical receiver, generates a polarization-coupled optical signal by orthogonal-polarization-coupling a second single-mode optical signal (center frequency: fC2) with a third single-mode optical signal (center frequency: fC3) so as to give the two waves orthogonal polarization directions and the same optical power, and transmits the generated polarization-coupled optical signal to a base station as an optical carrier signal. The optical receiver couples a modulated optical signal transmitted from the base station with the optical signal output from the optical transmitter, demodulates an electrical signal having intermediate frequencies fIF1 and fIF2 that is obtained by photodecting a resulting coupled optical signal, and generates transmit-data by filtering a resulting output signal.