Semiconductor Laser Beam Expanding Structure for High-Speed Output
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Solution Overview
Problem
High-speed semiconductor lasers face limitations in modulation bandwidth and output light power due to decreased relaxation oscillation frequency and susceptibility to optical damage at the end surface, particularly when increasing injection current.
Innovation Solution
A semiconductor laser with an optical waveguide structure featuring a beam expanding structure at the light output end surface, comprising a lower waveguide layer, active layer of multiple quantum wells, and an upper waveguide layer, where the upper waveguide layer is formed as a ridge with a beam expanding structure that reduces light power density and improves beam quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If injection current is increased to improve output light power and modulation bandwidth, then relaxation oscillation frequency increases and output power improves, but the end surface of the semiconductor laser suffers optical damage or burns up
Solution Approach 1:
The patent introduces a beam expanding structure that changes the spatial distribution of light in the horizontal direction. By expanding the beam width at the output end surface, the light power is distributed over a larger area, effectively reducing the power density at any single point on the end surface. This dimensional change in light distribution allows higher total output power without increasing the peak power density that causes end surface damage.
Solution Approach 2:
The beam expanding structure creates non-uniform light distribution across the end surface, with lower power density at critical regions. The structure is designed with specific geometric parameters (expansion angle, length) that optimize the local power density distribution, protecting vulnerable areas while maintaining overall high output power capability.
2Productivity
If injection current is increased to improve modulation bandwidth, then relaxation oscillation frequency moves toward high frequency direction, but optical damage occurs at the end surface
Solution Approach 1:
The beam expanding structure modifies the spatial characteristics of the output beam by increasing its width in the horizontal direction. This dimensional change reduces the power density at the end surface, allowing the laser to operate at higher injection currents that enable broader modulation bandwidth without suffering from optical damage.
3Power
If light power density at end surface is increased to improve output power, then output light power increases, but the laser cavity end surface becomes susceptible to optical damage
Solution Approach 1:
The beam expanding structure increases the spatial extent of the light beam in the horizontal direction at the output end surface. This dimensional expansion distributes the total light power over a larger area, reducing the power density (power per unit area) at any given point on the end surface, thereby preventing optical damage while maintaining high total output power.
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 beam expanding structure enhances beam quality, increases output power, and improves high-frequency response characteristics by reducing light power density at the end surface, allowing for higher injection currents without causing optical damage, thus expanding modulation bandwidth.
Implementation Method 1
the beam expanding structure may have a beam expanding portion with a shape gradually contracted inwards from the light output end surface... the beam expanding portion may have a horizontal divergence angle of 5° to 20°
Implementation Method 2
the light incident end surface may be coated with a high-reflection film
Implementation Method 3
the light output end surface may be coated with an antireflection film
Implementation Method 4
an active layer of multiple quantum wells
Data Source
AI summary
The present invention discloses a semiconductor laser comprising an optical waveguide structure which may include a lower waveguide layer, an active layer of multiple quantum wells and an upper waveguide layer, which are successively stacked from bottom to top, a grating layer being formed on upper portion of the active layer, wherein the upper waveguide layer, a cladding layer and a contact layer are formed as a ridge which has a light incidence end surface and a light output end surface, wherein a beam expanding structure is formed on one end of the output end surface. The beam expanding structure has a beam expanding portion with a shape gradually contracted inwards from the light output end surface. Preferably, the beam expanding portion has a horizontal divergence angle of 5° to 20°.