Semiconductor Saturable Absorber Modulator for SBS Suppression
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Solution Overview
Problem
Current optical transmission systems face challenges with Stimulated Brillouin Scattering (SBS) effects and distortion due to chirp and dispersion, particularly in long-haul dispersive optical fiber media, limiting the power transmission capacity and introducing noise in 1550 nm systems.
Innovation Solution
An externally modulated optical transmission system using a semiconductor saturable absorber modulator with a specific biasing method and material composition to operate below the gain peak wavelength, reducing SBS and improving linearity, and incorporating a 2.4 GHz signal for SBS suppression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If directly modulated laser is used for analog signal transmission, then bandwidth requirements are reduced, but noise and distortion characteristics deteriorate due to chirp and fiber dispersion
Solution Approach 1:
The system separates the laser source from the modulation function by using an externally modulated laser. The laser generates continuous wave light while a separate modulator applies the RF signal, dividing the functions to avoid chirp-induced distortion while maintaining bandwidth efficiency.
Solution Approach 2:
An external modulator is introduced as an intermediary between the laser and the optical fiber. This modulator applies the RF signal to the laser output without causing chirp, thereby maintaining signal quality while achieving analog transmission with reduced bandwidth requirements.
2Power
If optical launch power is increased to improve transmission capacity, then SBS effects worsen and degrade system performance
Solution Approach 1:
A 2.4 GHz periodic signal is applied to the modulator to dither the optical output. This periodic modulation broadens the spectral width of the laser output, reducing the power spectral density and thereby suppressing SBS effects that occur at high optical launch powers.
Solution Approach 2:
The system changes the spectral parameters of the optical signal by applying RF dithering. This transforms the narrow spectral line into a broader spectrum, reducing the intensity at any single frequency and suppressing SBS while allowing higher total optical power to be launched.
3Reliability
If quantum well width is increased to improve optical absorption, then operating wavelength shifts away from the desired 1550 nm region
Solution Approach 1:
The patent adjusts the quantum well width parameter to optimize absorption while compensating for wavelength shifts. By carefully controlling the quantum well dimensions and composition, the system achieves strong optical absorption while maintaining operation in the 1550 nm region through precise parameter optimization.
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 enhances power transmission capacity, reduces noise, and improves linearity in long-haul optical fiber systems by effectively suppressing SBS and managing distortion, enabling higher performance in analog and digital RF signal transmission.
Implementation Method 1
a modulator portion (104) having an optical input optically coupled to the laser for receiving the coherent light output, and an optical output for transferring the modulated optical signal, wherein the modulator portion is transparent at a gain peak wavelength that is at least 10 nm greater than the wavelength of the coherent light output of the laser
Implementation Method 2
Stimulated Brillouin scattering (SBS) effects that depend on the optical launch power and the total fiber length may also degrade DWDM system performance
Data Source
AI summary
A semiconductor device comprising a substrate; a monolithic gain region disposed on the substrate and operable to produce optical gain in response to current injection, including a first electrode over a first portion of the gain region having a first length L1, with a first current I1 being applied; and a second electrode over a second portion of the gain region having a second length L2, with a second current I2 being applied; wherein I1/L1 is greater than I2/L2.