Offset Cascaded Optical Filters for Flat Passbands
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Solution Overview
Problem
Current manufacturing limitations make it difficult to produce optical filters with very shallow pass-band slopes, leading to excessive nonlinear distortions in DWDM systems, especially in the 1550 nm and 1310 nm ranges, which hinder the use of DWDM networks for analog modulated signals.
Innovation Solution
The solution involves cascading pairs of broadband optical filters with offset center wavelengths to create a flat, narrowband filter profile, minimizing distortions by ensuring equal transmission of wavelengths within the passband.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional single broadband optical filters are used, then manufacturing is easier and device complexity is lower, but the pass-band slopes are excessively large causing excessive nonlinear distortions
Solution Approach 1:
The patent divides a single broadband filter into multiple narrower-band filters with offset center wavelengths. Each filter has a flatter pass-band, and when cascaded, they collectively form a narrowband filter with a flat composite pass-band, eliminating the excessive slopes of conventional single filters.
Solution Approach 2:
The patent combines multiple broadband optical filters in a cascaded configuration to achieve the desired narrowband filtering with flat pass-band. The merging of multiple filters with offset center wavelengths produces the composite filter response that satisfies both narrowband and flatness requirements.
2Productivity
If narrowband filters with small channel spacings are used, then DWDM transmission capability is improved, but pass-band slopes become steeper causing excessive CSO and CTB distortions
Solution Approach 1:
The patent segments the narrowband filtering function into multiple filters with offset center wavelengths. Each segment (individual filter) has a gentler slope, and their combination achieves the narrow channel spacing requirement while maintaining acceptable distortion levels.
Solution Approach 2:
The patent applies different center wavelength offsets to different filters in the cascade, creating local variations in the filtering characteristics. This allows each filter to contribute to the overall narrowband response while individual pass-bands remain relatively flat, reducing localized slope effects.
3Loss of information
If analog modulated signals are transmitted through conventional narrowband filters, then data transmission capability is improved, but signal degradation increases due to excessive nonlinear distortions
Solution Approach 1:
The patent segments the filtering function to reduce the slope magnitude that causes nonlinear distortions. By using multiple filters with offset center wavelengths, the composite filter achieves narrowband selection with reduced pass-band slopes, thereby minimizing CSO and CTB distortions in analog modulated signals.
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 CSO and CTB distortions, enabling the use of DWDM networks for analog modulated signals by producing filters with flat, narrowband profiles that minimize signal degradation.
Implementation Method 1
Optical filters use the principle of interference. Alternating layers of an optical coating are built up upon a substrate, selectively reinforcing certain wavelengths of light and interfering with other wavelengths.
Data Source
AI summary
A cascaded pair of broad bandwidth optical filters provides an overlap in pass-bands that forms a flat, narrow band optical filter. A first band-pass filter is operable to receive the optical signal and to transmit a first portion of the optical signal. The second band-pass filter receives the first portion of the optical signal transmits a second portion of the optical signal. The first band-pass filter has a first corner-pass wavelength of λa, a first corner-stop wavelength of λb, and a first pass-band center wavelength λpb1 such that λa≦λpb1≦λb. The second band-pass filter has a second corner-pass wavelength of λc, a second corner-stop wavelength of λd, and a second pass-band center wavelength λpb2 such that λc≦λpb2≦λd, wherein λa<λc<λb<λd. As such, the combined pass-band is λc≦λpb3≦λb.