Optical Device Monitoring Waveguide Bias Shift
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Solution Overview
Problem
In optical modulators, a bias shift between output signal light and monitor light occurs due to phase variations from mixing of 0th-order and higher-order mode lights, leading to suboptimal transmission quality, especially at higher bit rates, as existing techniques fail to suppress this bias shift effectively.
Innovation Solution
The optical device incorporates a monitoring optical waveguide with a reduced width region to separate higher-order mode light from 0th-order mode light, using a reflection groove to reflect only the 0th-order mode light while cutting off higher-order mode light, thereby reducing bias shift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a monitoring optical waveguide is used to fetch monitor light for feedback control, then operation point control accuracy is improved, but bias shift occurs due to phase variations from mode light mixing
Solution Approach 1:
The monitoring optical waveguide incorporates a reduced width region with specific dimensional characteristics that create local optical properties different from the main waveguide. This local quality change enables selective mode filtering to suppress bias shift while maintaining monitoring functionality
Solution Approach 2:
The waveguide width parameter is changed in the reduced width region to a specific value that differs from the main waveguide width. This parameter change modifies the optical mode structure to filter out higher-order modes and reduce phase variations causing bias shift
2Productivity
If higher-order mode light is included in monitor light, then light coupling efficiency is improved, but phase variation increases causing bias shift
Solution Approach 1:
The reduced width region extracts or removes higher-order mode light from the monitor light while allowing 0th-order mode light to pass through. This extraction eliminates the harmful phase variations caused by higher-order modes while maintaining the essential monitoring function
Solution Approach 2:
By changing the waveguide width parameter in the reduced width region, the optical mode characteristics are modified to selectively transmit 0th-order modes and suppress higher-order modes, thereby reducing phase variation
3Reliability
If waveguide width is reduced to filter higher-order modes, then bias shift is suppressed, but insertion loss increases
Solution Approach 1:
The waveguide width reduction is applied locally only in the monitoring optical waveguide's reduced width region, not throughout the entire waveguide structure. This localized approach filters higher-order modes while minimizing overall insertion loss
Solution Approach 2:
Instead of reducing the waveguide width throughout the entire monitoring optical waveguide, the invention applies partial width reduction only in the specific reduced width region. This partial action achieves mode filtering while reducing the cumulative insertion loss that would result from full-width reduction
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 significantly reduces bias shift, improving transmission quality by minimizing phase deviations between output signal and monitor light, even at higher bit rates, and allows for accurate feedback control of bias voltage.
Implementation Method 1
a monitoring optical waveguide with a reduced width region for separating higher-order mode light from 0th-order mode light
Implementation Method 2
using a reflection groove to reflect only the 0th-order mode light while cutting off higher-order mode light
Data Source
AI summary
An optical device including (a) a substrate having an electro-optic effect; (b) a modulating optical waveguide formed on a surface layer portion of said substrate and forming an interference optical modulator for modulating input light; (c) an output optical waveguide formed on said surface layer portion of said substrate and connected to a downstream side portion of said modulating optical waveguide; and (d) a branching monitoring section for monitoring branched light of light propagated along said output optical waveguide and emitted from an outgoing end face of said substrate. The output waveguide has a reduced width region in which the waveguide width is reduced.