Optical Amplifier Wavelength Offset for Spontaneous Emission Noise Reduction
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Solution Overview
Problem
Incoherent light source devices, such as those combining a super luminescent diode (SLD) with a semiconductor optical amplifier, suffer from noise generation due to spontaneous emission, which is not adequately reduced despite efforts to suppress noise in the amplified light output.
Innovation Solution
The central wavelength of the input light is set to be longer than the central wavelength of the gain characteristics of the optical amplifier, allowing low-energy charges on the long wavelength side to contribute to amplification, thereby reducing noise. Additionally, a filter may be used to widen the wavelength width and adjust the intensity of the amplified light to suppress peak values and achieve desired intensity levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the central wavelength of input light is matched to the central wavelength of gain characteristics, then amplification efficiency is maximized, but noise from spontaneous emission increases
Solution Approach 1:
The patent changes the wavelength parameter of the input light to be longer than the central wavelength of the gain characteristics. This parameter shift reduces the amount of low-energy carriers that do not contribute to amplification, thereby reducing spontaneous emission noise while maintaining sufficient amplification efficiency
2Object-affected harmful factors
If incoherent light source is used, then interference fringes are suppressed, but signal-to-noise ratio deteriorates
Solution Approach 1:
The patent uses an incoherent light source to skip through the problem of interference fringes, and then applies optical amplification with wavelength optimization to rush through the noise problem by reducing spontaneous emission through parameter optimization
Solution Approach 2:
By changing the wavelength parameter of the input light relative to the gain characteristics, the patent reduces noise while maintaining the incoherent light source benefits
3Object-generated harmful factors
If semiconductor optical amplifier operates in gain saturation region, then noise in input light is suppressed, but amplification characteristics become nonlinear
Solution Approach 1:
The patent optimizes the wavelength parameter and input light intensity to achieve a balance where noise is suppressed through partial saturation while maintaining acceptable linearity for inspection applications
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 approach effectively reduces noise in the light source device, improving the signal-to-noise ratio and enhancing the accuracy of semiconductor inspections by minimizing temporal fluctuations in intensity.
Implementation Method 1
an optical amplifier that receives the incoherent light as input light, amplifies an intensity of the input light, and outputs amplified light
Implementation Method 2
Excitation charge that does not contribute to amplification of light in the optical amplifier emits energy as spontaneous emission light. The noise is estimated to be generated due to such spontaneous emission light.
Data Source
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AI summary
A light source device includes a light source that generates incoherent light, and an optical amplifier having gain characteristics indicating a gain at each wavelength, which receives the incoherent light output by the light source as input light, and outputs amplified light obtained by amplifying the input light, and a central wavelength of an intensity distribution indicating an intensity at each wavelength of the input light is a wavelength longer than a central wavelength of the gain characteristics indicating a gain at each wavelength of the optical amplifier.