Surface Emitting Laser Stepped Mirror for Wide Far Field
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Solution Overview
Problem
Surface emitting lasers used in electrophotographic apparatuses face challenges due to a large beam radius at the near field point leading to a small spread angle in the far field, resulting in reduced image resolution and sensitivity to positional shifts, which affects the intensity distribution within the optical system.
Innovation Solution
A surface emitting laser with a stepped structure on its front mirror, where the optical path length difference between central and outer areas satisfies specific conditions, producing a phase difference that modifies the near field complex amplitude to achieve a wider, flatter far field intensity profile.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a surface emitting laser with a large emission area is used to provide sufficient optical output, then the beam radius at the near field point increases, but the spread angle in the far field becomes small, resulting in reduced image resolution
Solution Approach 1:
The invention applies local quality by creating a stepped structure on the front mirror surface where the central portion has a different height than the peripheral portion. This local structural variation modifies the optical path length locally, causing a phase difference that transforms the Gaussian beam profile into a flatter far-field intensity distribution, thereby improving image resolution while maintaining sufficient optical output.
Solution Approach 2:
The invention changes the optical path length parameter by introducing a stepped structure with specific height differences. The optical path length difference between the central and peripheral portions is controlled to satisfy a specific relationship (λ/4 < L ≤ 3λ/4), which transforms the beam's far-field characteristics and achieves a wider, flatter intensity distribution.
2Power
If a surface emitting laser with a large beam radius at the near field point is used, then the optical output is sufficient, but the far field intensity distribution becomes narrow and peaked, making it sensitive to positional shifts
Solution Approach 1:
The stepped structure creates local quality differences in the optical path, with the central portion having a longer optical path than the peripheral portion. This local variation introduces a phase difference that flattens the far-field intensity distribution, reducing sensitivity to positional shifts and improving system reliability.
Solution Approach 2:
The invention applies preliminary anti-action by pre-compensating for the sensitivity to positional shifts through the stepped structure design. By intentionally creating a phase difference before the beam enters the optical system, the system becomes more robust against misalignment, effectively counteracting potential positional errors in advance.
3Stability of the object's composition
If a Gaussian beam profile is used from the surface emitting laser, then the fundamental mode oscillation is achieved, but the far field intensity distribution is narrow and peaked, reducing image quality
Solution Approach 1:
The stepped structure on the front mirror introduces local quality variations in the optical path length. The central portion with different height creates a phase difference that modifies the Gaussian profile, transforming it into a flatter far-field intensity distribution while preserving the fundamental mode oscillation characteristics.
Solution Approach 2:
The invention changes the phase parameter of the beam by introducing an optical path length difference through the stepped structure. This parameter change transforms the beam's far-field characteristics from a narrow peaked distribution to a wider flatter distribution, improving image quality while maintaining fundamental mode operation.
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 enhances the spread angle and stability of the far field intensity distribution, improving image resolution and reducing the impact of positional shifts, making the surface emitting laser more suitable for electrophotographic applications.
Implementation Method 1
a difference L between an optical path length in a first area defined in a central part of an emission area and an optical path length in a second area defined on an outer side of the first area within the emission area satisfies the following expression: (1/4+N)λ<L≤(3/4+N)λ
Implementation Method 2
producing a phase difference that modifies the near field complex amplitude
Implementation Method 3
a surface emitting laser that oscillates at a wavelength λ
Implementation Method 4
the profile of the electric field amplitude of the fundamental mode 130 can be approximated to a Gaussian function
Implementation Method 5
a plurality of semiconductor layers including a rear mirror 112, an active layer 114, and a front mirror 116 are provided on a semiconductor substrate 110, whereby a vertical cavity is formed
Implementation Method 6
A current confinement structure 118 is provided in the front mirror 116. The current confinement structure 118 regulates the electric current flowing through the active layer 114
Implementation Method 7
The current confinement structure 118 has a higher refractive index in a central portion thereof than in a peripheral portion thereof. Such a structure is referred to as a waveguide structure
Data Source
AI summary
The present invention provides a surface emitting laser that provides a sufficient optical output and is suitable as a light source intended for electrophotographic apparatuses, and a surface-emitting-laser array and an image forming apparatus each including the surface emitting laser.The surface emitting laser includes a first stepped structure on a front surface of a front mirror. In the first stepped structure, a difference L between an optical path length in a first area and an optical path length in a second area satisfies the following expression:(¼+N)λ<|L|<(¾+N)λwhere N is an integer.