Tapered SOA Waveguide in Optical Transmitters for Pattern Effect Control
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Solution Overview
Problem
The integration of a semiconductor optical amplifier (SOA) with a distributed feedback (DFB) laser in optical transmitters leads to limited design freedom and deteriorates optical waveform quality due to the pattern effect, which is exacerbated by non-uniform carrier density and consumption within the SOA.
Innovation Solution
A tapered waveguide structure is introduced in the SOA, where the waveguide width gradually reduces along the optical waveguide direction to uniformly distribute carrier density and suppress the pattern effect, maintaining the same manufacturing process as the DFB laser.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If an SOA is monolithically integrated with a DFB laser using the same manufacturing process, then manufacturing complexity is reduced and production efficiency is improved, but the design freedom of the SOA structure is limited and optical waveform quality deteriorates
Solution Approach 1:
The patent applies local quality by introducing a tapered waveguide structure specifically in the SOA region while maintaining the standard structure in other parts. The waveguide width gradually changes from 2.0 μm at the input end to 1.0 μm at the output end, creating a localized structural variation that uniformly distributes carrier density and suppresses the pattern effect, thereby improving optical waveform quality without changing the overall monolithic integration approach
Solution Approach 2:
The patent changes the geometric parameter of the waveguide width along the optical propagation direction. By gradually reducing the waveguide width from 2.0 μm to 1.0 μm in the SOA region, the optical confinement factor changes continuously, which affects the carrier consumption distribution and suppresses the pattern effect, thus improving optical waveform quality while maintaining manufacturing simplicity
2Power
If the SOA length is increased to achieve higher output power, then amplification capability is improved, but the pattern effect is exacerbated and optical waveform quality deteriorates
Solution Approach 1:
The patent applies local quality by introducing a tapered waveguide structure specifically in the SOA region while maintaining the standard structure in other parts. The waveguide width gradually changes from 2.0 μm at the input end to 1.0 μm at the output end, creating a localized structural variation that uniformly distributes carrier density and suppresses the pattern effect, thereby improving optical waveform quality without changing the overall monolithic integration approach
Solution Approach 2:
The patent introduces dynamic characteristics by creating a gradual transition in the waveguide structure. The tapered waveguide provides a continuous change in optical confinement along the propagation direction, which dynamically adjusts the carrier consumption rate to maintain uniform carrier density even in longer SOA structures, allowing high output power without waveform deterioration
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 tapered structure effectively mitigates optical waveform deterioration, ensuring high output and improved transmission quality by uniformly distributing carrier consumption, even in longer SOA lengths.
Implementation Method 1
an active layer 4 composed of a multi quantum well (MQW) and oscillates at a single wavelength determined by a driving current source 8 and a diffraction grating 5 formed in a resonator
Implementation Method 2
an electro-absorption (EA) modulator configured to modulate oscillation light of the DFB laser
Implementation Method 3
a semiconductor optical amplifier (SOA) having an active region with an identical composition as the active region of the DFB laser and configured to amplify signal light from the EA modulator
Data Source
AI summary
In the present disclosure, in an EADFB laser in which an SOA has been integrated, a new configuration in which deterioration of optical waveform quality is solved or mitigated while keeping characteristics that a manufacturing process can be simplified by using the same layer structure is indicated. In the optical transmitter of the present disclosure, a waveguide structure having a tapered structure in at least a part of the SOA waveguide is adopted. A width of the waveguide is changed to be reduced in an SOA region, and an amount of carrier consumption is made uniform in an optical waveguide direction. A waveguide width is continuously reduced in an optical waveguide direction in the SOA so that the optical confinement coefficient is reduced, and light power distributed in an active layer region is made constant.