LOC Laser Diode Waveguide Structure for Fast-Axis Single-Mode Emission
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Solution Overview
Problem
High power laser diodes with large optical cavities face challenges in achieving single mode lasing operation at high efficiency due to the onset of higher order modes, which deteriorate beam quality and reduce power and efficiency, especially with conventional designs that attempt to reduce p-waveguide thickness to offset quantum wells.
Innovation Solution
The development of laser diode structures with thin p-waveguide thickness and specific refractive index profiles, such as double n-clad and double waveguide designs, that out-couple higher order modes by using outer and inner cladding layers with distinct refractive indices, ensuring single mode operation in the vertical direction while maintaining high efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If p-waveguide thickness is reduced to offset quantum wells, then quantum well offset is improved, but higher order modes are excited and beam quality deteriorates
Solution Approach 1:
The waveguide structure is segmented into multiple functional layers: a thin p-waveguide layer for quantum well offset, an n-waveguide layer for optical confinement, and intermediate layers for mode control. This segmentation allows each layer to be optimized independently - the thin p-waveguide achieves quantum well offset while the n-waveguide and intermediate layers prevent higher order mode excitation through controlled refractive index profiling.
2Power
If large optical cavity is used for high power, then power output is improved, but higher order modes are excited and efficiency is reduced
Solution Approach 1:
The optical cavity employs local quality variations through spatially differentiated refractive index profiling. The n-waveguide layer and intermediate layers create localized regions of high optical confinement exactly where needed - in the active region and near the quantum wells - while allowing the overall cavity to maintain large dimensions for high power output. This localized optimization ensures single mode operation throughout the extended cavity length.
3Use of energy by moving object
If thin p-waveguide is used, then voltage and series resistance are reduced, but optical confinement is weakened and higher order modes occur
Solution Approach 1:
The waveguide structure employs asymmetric design where the p-waveguide layer is intentionally made thin for low resistance, while the n-waveguide layer is designed with greater thickness and optimized refractive index to provide the primary optical confinement function. This asymmetric division of functional responsibilities allows the thin p-waveguide to minimize electrical losses while the asymmetrically designed n-waveguide compensates for the reduced optical confinement that would result from the thin p-waveguide structure.
4Device complexity
If conventional single clad structure is used, then device complexity is reduced, but higher order modes cannot be suppressed and single mode operation is lost
Solution Approach 1:
The patent transitions from a conventional single-clad structure to a multi-clad structure with distinct n-clad and p-clad layers having different refractive indices. This dimensional expansion in the vertical layering provides an additional degree of freedom for optical mode control. The intermediate layers between the n-waveguide and p-waveguide create a refined refractive index profile that enables precise suppression of higher order modes while maintaining manageable device complexity through systematic layer 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
These designs achieve single mode lasing with improved beam quality and reduced power consumption, extending device lifetime and reducing energy consumption by effectively suppressing higher order modes and enhancing optical confinement.
Implementation Method 1
the outer and inner cladding layers having, respectively, first and second indices of refraction, the first index of refraction of the outer cladding layer being greater than the second index of refraction of the inner cladding layer and greater than an effective index of refraction of the first order mode so as to out-couple it from the waveguide
Implementation Method 2
The laser diode has an optical cavity defined by a p-side of the laser diode, an n-side of the laser diode, and an active region located between the p- and n-sides; and adjacent cladding layers on one or both of the p- and n-sides
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
Laser diodes are configured to suppress lasing of a first and higher order modes along a fast axis of an optical beam emitted by the laser diode. An optical cavity is defined by a p-side of the laser diode, an n-side of the laser diode, and an active region located between the p- and n-sides. The n-side has an n-waveguide layer forming at least a portion of a waveguide having a quantum well offset towards the p-side. According to some embodiments, double cladding layers out-couple higher order modes. According to other embodiments, double waveguides (e.g., symmetric and asymmetric) reduce gain applied to higher order modes.