Tunable DBR Laser Grating Layout for Flat Optical Output
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Solution Overview
Problem
Wavelength-tunable optical transmitters with integrated DBR lasers, EA modulators, and SOAs face fluctuations in optical output due to optical loss in EA modulators and carrier-induced changes in DBR lasers, leading to decreased optical output as wavelength shortens.
Innovation Solution
A wavelength-tunable optical transmitter is designed with a DBR laser and EA modulator integrated along an optical axis, featuring a rear DBR region with a first diffraction grating and a front DBR region with a second diffraction grating, where the wavelength interval of reflection peaks in the front DBR region is greater than in the rear DBR region, and the average period of the first diffraction grating is larger than that of the second, optimizing the diffraction grating structure to minimize optical loss and maintain stable output across the wavelength range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the drive current of the DFB laser is increased to increase the intensity of light incident on the EA modulator, then the optical output can be increased, but the power consumption of the DFB laser increases and the extinction characteristics deteriorate
Solution Approach 1:
The patent combines a DFB laser and an EA modulator into a single integrated device structure. The DFB laser region and EA modulator region are formed in the same semiconductor substrate with shared waveguide structures, allowing the light generated by the DFB laser to directly modulate the EA modulator without external coupling, thereby improving extinction characteristics while maintaining optical output efficiency
Solution Approach 2:
The patent creates different functional regions within the integrated structure: the DFB laser region with specific quantum well composition for light generation, and the EA modulator region with different quantum well composition optimized for modulation. Each region has locally optimized properties that allow the DFB laser to operate at lower currents while maintaining sufficient optical output for effective modulation
2Illumination intensity
If the absolute value of the reverse voltage applied to the EA modulator is reduced to suppress light absorption, then the optical output can be increased, but the steepness of the extinction curve is reduced and the dynamic extinction ratio deteriorates
Solution Approach 1:
The EA modulator region uses quantum wells with specific composition ratios (InxGa1-xAsyP1-y) that are locally optimized for strong modulation effect at reduced reverse voltages. The different composition from the DFB laser region enables the modulator to achieve sufficient extinction ratio even when operated at lower voltage levels that would otherwise reduce optical output
3Illumination intensity
If an SOA is integrated at the light emitting end of the EADFB laser to increase optical output, then the output can be increased without excessively increasing the driving current, but the device complexity and manufacturing process complexity increase
Solution Approach 1:
The patent integrates multiple functional regions (DFB laser region, phase adjustment region, EA modulator region, and SOA region) into a single monolithic semiconductor device. All regions share common waveguide structures and are formed through integrated growth processes, reducing device complexity compared to separate component assemblies while achieving enhanced optical output through the SOA amplification function
4Illumination intensity
If the wavelength interval of reflection peaks and average period of diffraction grating are optimized in the DBR laser, then the optical output characteristic becomes flat across wavelength range, but the manufacturing precision requirements increase
Solution Approach 1:
The patent implements different diffraction grating structures in the front and rear DBR regions with specifically designed wavelength intervals and average periods. The front DBR region has a first diffraction grating with a specific wavelength interval and average period, while the rear DBR region has a second diffraction grating with different parameters. This local optimization of grating characteristics in different regions enables flat optical output across the wavelength range while managing manufacturing precision requirements through systematic design
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 results in improved wavelength dependency of optical output, providing a flat optical output characteristic with reduced fluctuations, especially on the short wavelength side, and maintaining high optical output across the entire wavelength-tunable range.
Implementation Method 1
a rear DBR region with a first diffraction grating and a reflection characteristic consisting of a plurality of reflection peaks, an active region producing an optical gain, and the front DBR region with a second diffraction grating and a reflection characteristic consisting of a plurality of reflection peaks
Implementation Method 2
The EA modulator includes a light absorption layer 2 composed of a MQW having a composition different from that of the DFB laser, and changes the light absorption amount of the light absorption layer 2 by voltage control performed by a modulation signal source 12
Data Source
AI summary
In a DBR laser of a wavelength-tunable transmitter, a rear DBR region, an active region, and a front DBR region are integrated along an optical axis direction. The diffraction grating structure is set so that an oscillation mode using a reflection peak on the shortest wavelength side among a plurality of reflection peaks corresponding to the wavelength-tunable band is easily oscillated the most in a state where a current to the two DBR regions of the SSG-BPFR is 0. The SSG-DBR laser is configured such that the average period value of the diffraction grating of the front DBR is larger than the average period value of the diffraction grating of the rear DBR. The diffraction grating is configured so that the wavelengths of the reflection peaks on the shortest wavelength side among the plurality of reflection peaks coincide with each other between the two DBR regions in a state where no current is supplied.