Injection Locked Laser Transceiver Crossing Point Control

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Solution Overview

Problem

In wavelength division multiplexed passive optical networks (WDM-PON), the use of injection locked (IL) lasers results in increased bit error rates due to noise and distortion, limiting the efficiency of information transmission on a single optical fiber.

Innovation Solution

An optical transceiver with an injection locked laser transmitter module, driver circuitry to adjust the crossing point of the modulating RF signal, a low-pass filter to reduce high-frequency noise, and a decision threshold circuit to lower the signal decision threshold, all controlled by a microcontroller to adaptively improve transmission and reception characteristics.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If injection locked lasers are used to reduce cost, then device cost decreases, but bit error rate increases due to noise and distortion

Engineering Contradiction:

Improvedevice costVSAvoidbit error rate

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent adjusts key signal parameters including the crossing point of the modulating RF signal, the decision threshold level, and filter bandwidth. By optimizing these parameters specifically for injection locked lasers, the system achieves acceptable bit error rates while maintaining the cost advantage of using IL lasers instead of more expensive alternative laser types.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The system implements adaptive feedback mechanisms where the microcontroller continuously monitors transmission quality and dynamically adjusts the crossing point and decision threshold parameters. This closed-loop feedback allows the system to compensate for the inherent noise and distortion of injection locked lasers, maintaining reliable communication despite the cheaper laser type.

Inventive Principle:

Principle #23Feedback

2Device complexity

If injection locked lasers are used, then device complexity decreases, but signal distortion increases leading to higher bit error rates

Engineering Contradiction:

Improvelaser system complexityVSAvoidsignal distortion

Core Design Contradiction:

Device complexityVSLoss of information

Solution Approach 1:

The system applies preliminary distortion compensation by pre-adjusting the crossing point of the modulating RF signal before transmission. The driver circuitry is configured to shape the signal in advance to counteract the known distortion characteristics of injection locked lasers, thereby reducing signal degradation before it occurs during transmission.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent introduces intermediary signal processing components including a low-pass filter to remove high-frequency noise and a decision threshold circuit to cleanly separate signal levels. These intermediary elements act as mediators that clean up the distorted signal from the simple injection locked laser, recovering the original information without requiring a more complex laser source.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Device complexity

If simple routing function is used at branching point, then network complexity decreases, but information transmission capacity is limited

Engineering Contradiction:

Improvenetwork complexityVSAvoidinformation transmission capacity

Core Design Contradiction:

Device complexityVSProductivity

Solution Approach 1:

The patent employs wavelength division multiplexing to give the single trunk fiber and simple branching point multiple functional channels. Each wavelength carries independent information streams to different subscribers, allowing the simple physical infrastructure to support high information transmission capacity through logical multi-functionality of the optical wavelengths.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 bit error rates and improves communication efficiency over optical networks by mitigating noise and distortion, enabling the use of less expensive IL lasers while maintaining high performance.

Implementation Method 1

a low-pass filter to reduce high frequency noise

Methodology Applied

Scientific EffectFiltering: Filter (electronic)

Implementation Method 2

The IL laser is effectively tuned to the wavelength associated with the pass band of the BLS filter

Methodology Applied

Scientific EffectInjection locking:

Implementation Method 3

seeded by a filtered broadband light source (BLS)

Methodology Applied

Scientific EffectFiltering: Filter (optical)

Data Source

PatentUS9236949B1Laser transceiver with improved bit error rate

Publication Date: 2016.01.12 APPLIED OPTOELECTRONICS INC(US)

AI summary

An optical transceiver generally includes an injection locked (IL) laser configured to generate a transmit (Tx) optical signal for transmission over an optical network and a laser driver circuit configured to modulate the IL laser based on a Tx data signal. The Tx data signal may be provided to the optical transceiver for transmission over the optical network. The Tx data signal may include a crossing point level associated with a transition between a first signal level and a second signal level. The optical transceiver may also include a crossing point control circuit configured to apply distortion to the Tx data signal, the distortion to increase the crossing point level.