Scanning Spectral Filter for Optical Ghost Suppression in OSAs
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Solution Overview
Problem
Grating-based optical spectrum analyzers suffer from optical ghosts, which are spurious spectral features generated at different spectral locations from the main signals, complicating measurements and challenging in compact designs.
Innovation Solution
Implementing a tunable spectral filter, such as a band-pass, low-pass, or high-pass filter, that moves synchronously with the scanning spectral window of the OSA to eliminate or reduce optical ghosts, allowing the main signal to be analyzed effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a grating-based optical spectrum analyzer is used, then spectral analysis capability is provided, but optical ghosts appear as spurious spectral features
Solution Approach 1:
The patent extracts and removes the harmful optical ghosts from the optical path by introducing a spectral filter that selectively blocks ghost wavelengths while allowing main signal wavelengths to pass through. This separates the harmful spectral components from the useful signal.
Solution Approach 2:
The patent introduces a spectral filter as an intermediary element between the diffraction grating and the detector. This mediator selectively transmits or blocks specific wavelengths, thereby eliminating optical ghosts without affecting the main spectral measurement function.
2Volume of moving object
If the OSA is made compact, then device size is reduced, but eliminating spectral ghosts becomes more challenging
Solution Approach 1:
The patent addresses the compact design challenge by implementing the spectral filter in the spectral domain rather than requiring spatial separation. The filter operates in wavelength space, allowing ghost elimination without increasing the physical footprint of the device.
Solution Approach 2:
The patent changes the optical parameters by introducing a spectral filter with specific transmission characteristics. This allows the system to maintain compact dimensions while achieving ghost elimination through parameter-based spectral control rather than spatial separation.
3Measurement precision
If a spectral filter is added to eliminate ghosts, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent designs the spectral filter to serve multiple functions: eliminating optical ghosts, reducing stray light, and maintaining spectral measurement accuracy. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in device complexity.
Solution Approach 2:
The patent combines the ghost elimination function with the existing spectral analysis function by integrating the spectral filter into the existing optical path. This merging of functions avoids adding separate independent subsystems and minimizes overall device complexity.
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 solution effectively eliminates optical ghosts without compromising optical performance, reduces stray light, and enables a smaller overall size for the OSA by shortening propagation paths and allowing components to be closer together.
Implementation Method 1
a diffraction grating monochromator may receive an optical input signal to be measured
Implementation Method 2
a scanning element and one or more filters. The optical pre-processing block may process the optical input signal
Data Source
AI summary
A monochromator apparatus in a grating-based optical spectrum analyzer (OSA) includes a diffraction grating, a reflector element, and a tunable spectral filter. The tunable spectral filter may include a band-pass filter, a low-pass filter, a high-pass filter, or a linear variable filter, for example. A spectral window of the filter may move synchronously with the scanning spectral window of the OSA. A high-pass filter implementation may be introduced during a subsequent portion of the OSA window before the optical ghost signal starts appearing. The filter may either be linearly scanned across the optical beam, angularly tuned, or introduced in a subsequent portion of the OSA scanning window.