Optical Transmitter Chirp Reduction via Etalon Filtering
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Solution Overview
Problem
Direct modulation in optical communication systems limits transmission distance due to wavelength chirp, which degrades waveforms in optical fibers, and existing indirect modulation techniques require additional costly devices and precise temperature control for wavelength selective filters.
Innovation Solution
An optical transmitter with multiple optical modules, a multiplexer, an etalon filter, and a monitoring unit, where each module includes a semiconductor laser diode, a thermo-electric controller, and a TEC driver, modulates signal lights with specific wavelengths to maximize transmittance variation across the etalon filter, reducing chirp and eliminating the need for multiple temperature controllers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If direct modulation of semiconductor laser diode is used to increase transmission speed, then transmission speed is improved, but wavelength chirp occurs causing waveform degradation and limiting transmission distance
Solution Approach 1:
The patent extracts and removes the harmful wavelength chirp component from the directly modulated laser signal by using an optical filter to eliminate the OFF-level light component, thereby maintaining high transmission speed while reducing waveform degradation
Solution Approach 2:
The patent converts the harmful wavelength chirp effect into a beneficial filtering mechanism by utilizing the spectral characteristics of chirped light to selectively pass only the desired signal components through the optical filter, transforming the distortion into a useful wavelength-selective property
2Length of moving object
If indirect modulation techniques such as electro-absorption or Mach-Zender modulation are used to overcome transmission distance limitation, then transmission distance is improved, but device complexity and cost increase due to additional devices
Solution Approach 1:
The patent merges the direct modulation capability with optical filtering in a single integrated structure, combining the simplicity of direct modulation with the distance extension capability of indirect modulation techniques, thereby achieving long transmission distance without increasing device complexity
Solution Approach 2:
The patent introduces an optical filter as an intermediary element between the directly modulated laser and the optical fiber, which mediates the harmful chirp effect while preserving the benefits of direct modulation, enabling extended transmission distance with minimal additional complexity
3Length of moving object
If CML technique with etalon filter is used to reduce chirp and extend transmission distance, then transmission distance is improved, but device size increases due to requirement of multiple temperature controllers
Solution Approach 1:
The patent implements a universal temperature control mechanism that serves multiple optical modules simultaneously, allowing a single temperature controller to manage the etalon filter for multiple wavelength channels, thereby extending transmission distance without proportionally increasing device size
Solution Approach 2:
The patent segments the temperature control function into independent controllable units, where each optical module can be controlled individually or in groups, allowing flexible configuration that reduces the total number of temperature controllers needed while maintaining precise control for extended transmission distance
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 enhances transmission speed and distance by minimizing chirp-induced waveform degradation and reduces the size and complexity of the transmitter, enabling longer-distance high-speed data communication without the need for multiple thermo-electric controllers.
Implementation Method 1
a semiconductor laser diode (hereafter denoted as LD) to emit signal light by providing the driving current modulated with high frequencies
Implementation Method 2
the carrier density in the active layer of the LD varies in the ON level when the driving current is substantially provided and in the OFF level when the driving current is absent, which shifts the emission wavelength of the LD and has been called as the chirp or the wavelength chirp
Implementation Method 3
the optical fiber that transmits the signal light inherently has the dispersion, that is, the velocity of the light transmitted therein slightly depends on the wavelength of the light
Implementation Method 4
the etalon filter, which has a periodic transmittance with a period substantially coinciding with the preset wavelength span of signal light
Implementation Method 5
The thermo-electric controller, typically a Peltier device, controls a temperature of the LD
Data Source
AI summary
An optical transmitter that multiplexes a plurality of signal light each having less chirp characteristic by the CML technique is disclosed. The optical transmitter comprises a plurality of optical modules, a plurality of TEC controllers each driving the TEC in the optical module, a de-multiplexer that de-multiplexes the output of respective modules, an etalon filter, and a monitoring unit that monitors the component of the signal light output from respective modules. The TEC controller controls the temperature of the LD in the module such that two emission wavelengths of the LD each corresponding to the ON level and the OFF level is set in both side of one of the critical wavelengths of the etalon filter where the transmittance thereof becomes a maximum.