Lattice Gain Equalizer With Polarization-Rotating Folded Waveguides
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Solution Overview
Problem
Conventional gain equalizers using lattice optical circuits suffer from significant polarization-dependent loss (PDL) due to birefringence, which affects the transmission spectrum and cannot be completely eliminated.
Innovation Solution
A gain equalizer design incorporating 2M optical waveguide circuits with a folding connection structure that rotates the polarization direction of light by 90 degrees, pairing lattice optical circuits with the same gain equalization spectrum to offset PDL, and optionally utilizing a reciprocating motion to further reduce polarization dependence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a lattice optical circuit is used for gain equalization, then gain spectrum flattening is achieved, but polarization-dependent loss (PDL) increases significantly
Solution Approach 1:
The patent divides the lattice optical circuit into multiple stages, with each stage containing directional couplers and waveguides. By segmenting the circuit into discrete stages, the invention can independently control and compensate for polarization effects at each stage, reducing overall PDL while maintaining gain equalization functionality.
Solution Approach 2:
The patent utilizes phase shifters to dynamically adjust the phase difference between waveguides in each stage. By changing the phase parameter, the system can compensate for polarization-dependent effects and maintain consistent gain equalization performance across different polarization states of input light.
2Reliability
If multiple stages of Mach-Zehnder interferometers are connected to achieve gain equalization, then gain spectrum control is improved, but optical loss increases
Solution Approach 1:
The patent merges the gain equalization function with the lattice optical circuit structure itself, rather than using separate Mach-Zehnder interferometer stages. This integration allows the lattice circuit to perform both waveguide switching and gain equalization simultaneously, reducing overall optical loss while maintaining spectrum control capability.
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 design achieves a gain equalizer with reduced PDL and lower power consumption by effectively canceling out polarization-dependent losses and allowing for flexible gain equalization spectra with reduced phase modulation requirements.
Implementation Method 1
a folding connection structure that connects input/output waveguides of a pair of optical waveguide circuits, the folding connection structure rotating a polarization direction of propagating light by 90 degrees
Implementation Method 2
a phase of light propagating through the waveguides is controlled by a phase shift that employs a change in refractive index due to the thermo-optic effect, caused by applying heat to either one of the arm waveguides
Implementation Method 3
By adjusting a phase difference between the optical signals propagating through the two waveguides configuring the arm waveguide of the directional coupler at the front stage, the interference in the directional coupler at the rear stage can also be adjusted, thereby controlling a transmission spectrum for a wavelength of the propagating light
Data Source
AI summary
A gain equalizer using a lattice optical circuit with a smaller polarization-dependent loss is provided. The gain equalizer includes: 2M optical waveguide circuits formed on a substrate, wherein M is an integer of 1 or more, including M pairs of optical waveguide circuits, each pair of optical waveguide circuits having the same gain equalization spectrum; and a folding connection structure that connects input/output waveguides of a pair of optical waveguide circuits, the folding connection structure rotating a polarization direction of propagating light by 90 degrees,