Unbalanced Mach-Zehnder Interferometer Bidirectional Filter

The patent transforms the beam-splitter from a wavelength-independent 50:50 configuration to a wavelength-dependent configuration with asymmetric splitting ratios. The first beam-splitter has a first splitting ratio for first wavelengths and a second splitting ratio for second wavelengths, while the second beam-splitter has corresponding asymmetric ratios. This parameter change enables selective wavelength routing that reduces insertion loss and cross-talk while maintaining manageable device complexity through systematic design.

The optical interleaver is segmented into multiple functional components: a first beam-splitter, a second beam-splitter, a first delay line, and a second delay line. Each component performs a specific function in the wavelength separation process. This segmentation allows optimization of each component's performance characteristics, achieving low insertion loss and cross-talk through coordinated operation of individual segments rather than relying on a single complex beam-splitter.

The patent implements wavelength-dependent asymmetric splitting ratios in both beam-splitters to minimize cross-talk. The first beam-splitter routes different proportions of first and second wavelengths to different paths, and the second beam-splitter similarly discriminates between wavelengths. This parameter optimization achieves cross-talk reduction to approximately -17 dB while maintaining a structured but manageable device configuration through systematic wavelength-selective routing.

The delay lines serve as intermediary components between the beam-splitters, providing optical path length differences that enhance wavelength separation. The first delay line introduces a first optical path length difference for first wavelengths, while the second delay line introduces a second optical path length difference for second wavelengths. These intermediaries facilitate precise wavelength discrimination, reducing cross-talk without requiring overly complex beam-splitter designs.

The patent optimizes the optical path length differences in the unbalanced Mach-Zehnder interferometers to achieve cross-talk minimization. By carefully selecting the first and second optical path length differences, the system achieves cross-talk of approximately -17 dB. The design maintains practical device complexity by using a finite number of discrete components with well-defined parameters, avoiding the need for continuously variable or excessively complex structures.

The patent replaces complex mechanical wavelength selection mechanisms with optical interference-based wavelength separation. Instead of using mechanically adjustable components or complex moving parts, the system uses fixed unbalanced Mach-Zehnder interferometers where wavelength separation is achieved through optical path length differences and interference effects. This substitution reduces mechanical complexity while achieving superior cross-talk performance through optical field manipulation.