Monolithic MOPA Laser Wavelength Control Under Power Changes
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Solution Overview
Problem
High-power semiconductor lasers used as optical pump sources face challenges in maintaining a fixed lasing wavelength due to dependence on external fiber Bragg gratings, which add cost, have limited effectiveness, and introduce optical loss.
Innovation Solution
A monolithic master oscillator-power amplifier (MOPA) device with a single spatial mode DFB laser structure and separate electrical contacts for the master oscillator and power amplifier sections, allowing for simultaneous control of electrical currents to maintain constant wavelength and vary output power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an external fiber Bragg grating (FBG) is used for wavelength stabilization, then the lasing wavelength can be stabilized, but the device complexity increases and optical loss is introduced
Solution Approach 1:
The patent integrates the wavelength stabilization function directly into the semiconductor laser structure by forming a Bragg grating within the laser cavity itself, rather than using a separate external FBG. This merging of functions eliminates the need for additional external components while maintaining wavelength stabilization capability.
Solution Approach 2:
The patent extracts the wavelength stabilization function from the external FBG component and relocates it into the laser cavity structure. By taking out the stabilization function and embedding it within the laser itself, the system eliminates dependency on external components and reduces overall device complexity.
2Reliability
If an external fiber Bragg grating (FBG) is used for wavelength stabilization, then the lasing wavelength can be stabilized, but optical loss increases
Solution Approach 1:
The patent combines the wavelength stabilization function with the laser emission process by integrating the Bragg grating within the laser cavity. This eliminates the need for light to pass through an external FBG, thereby removing the associated optical losses while maintaining stabilization effectiveness.
3Power
If the power amplifier current is increased to increase output optical power, then the output power increases, but the wavelength drifts due to temperature changes
Solution Approach 1:
The patent implements a feedback control mechanism where the controller monitors the relationship between amplifier current and wavelength, and automatically adjusts the oscillator current to compensate for temperature-induced wavelength drift. This closed-loop feedback ensures wavelength stability is maintained even as output power varies.
Solution Approach 2:
The patent dynamically adjusts the oscillator current parameter in response to changes in amplifier current. By changing this electrical parameter, the system compensates for thermal effects and maintains constant wavelength despite variations in output optical power.
4Adaptability or versatility
If separate electrical contacts are used for master oscillator and power amplifier sections, then independent control of wavelength and power is enabled, but the manufacturing complexity increases
Solution Approach 1:
The patent divides the semiconductor laser structure into distinct master oscillator and power amplifier sections with separate electrical contacts. This segmentation allows independent control of each section, enabling separate optimization of wavelength (via oscillator current) and power (via amplifier current) while maintaining a manufacturable integrated structure.
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 solution eliminates the need for external fiber Bragg gratings, improving wavelength stability and reducing optical loss, while allowing for independent control of output power and wavelength, enhancing the performance of semiconductor laser-based pump sources.
Implementation Method 1
a Bragg grating (150) for providing a distributed optical feedback therein and for defining a laser wavelength
Implementation Method 2
a power amplifier (PA) section (130) comprising a semiconductor amplifier structure optically following the single spatial mode DFB laser structure and integrally coupled thereto for amplifying the laser light (117)
Implementation Method 3
a controller (230) configured to vary simultaneously the first and second electrical currents in opposite directions so that when the second electrical current through the PA section (120) is increased for increasing an optical power of the output light (161), the first electrical current through the MO section (120) is decreased so as to maintain a laser wavelength constant
Data Source
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AI summary
The invention provides a wavelength-controlled pump MOPA laser and a method of operation thereof. A monolithic semiconductor MOPA laser chip (100) has a DFB-laser based master oscillator (120) and a power amplifier section (130) formed in a same monolithic waveguide, and separate MO and PA electrodes (111,112) for individual control of current injection into the MO and PA sections. The laser wavelength is defined by the DFB grating (150) and is kept fixed by suitably controlling the MO current to compensate for a thermal crosstalk from the PA section, or tuned by suitably changing the MO current or direct heating of the DFB region. Stabilisation may be performed with a photodetector at the output and a look-up table in order to control the currents provided to the MO and the PA section.