Optical Endless Phase Shifter Using Segmented Mach-Zehnder Stages
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Solution Overview
Problem
Existing optical endless phase shifting devices face challenges such as high intrinsic insertion loss and the need for fast switching and phase reset, which are not feasible in many applications, particularly in coherent detection and laser stabilization.
Innovation Solution
The proposed optical endless phase shifting device employs a Mach-Zehnder structure with a push-pull configuration using controllable optical phase shifters in both stages, allowing for continuous phase shifting without the need for high-speed switching or phase reset, by switching phase shifters between zero and π, thus achieving an endless phase shift range with reduced insertion loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a phase modulator is used to create a phase shift between 0 and 4π with switching, then endless phase shifting is achieved, but fast switches and fast modulator phase reset are required which increases device complexity and difficulty of operation
Solution Approach 1:
The phase shifting function is segmented into two independent stages: a first stage with a phase modulator providing continuous phase shift, and a second stage with a switchable phase shifter providing discrete 0 or π phase shift. This segmentation allows each stage to operate independently without requiring fast switching or phase reset, thereby reducing device complexity while maintaining endless phase shifting capability.
Solution Approach 2:
The first stage uses a dynamic phase modulator that can continuously adjust the phase shift, while the second stage uses a static switchable phase shifter. This dynamic-static combination allows the system to achieve endless phase shifting without requiring fast switching operations, simplifying the overall device operation.
2Ease of operation
If an IQ-modulator structure is used for continuous phase modulation, then endless phase shifting is achieved without fast switching, but the intrinsic insertion loss is 6 dB which increases energy loss
Solution Approach 1:
The invention merges the advantages of two different approaches: the continuous phase modulation capability of IQ-modulators and the low insertion loss of simple phase shifters. By combining a continuous phase modulator in the first stage with a switchable phase shifter in the second stage, the system achieves both continuous phase control and reduced energy loss.
Solution Approach 2:
The system changes the operating parameters of the phase modulator to provide a phase shift range of 0 to π instead of the conventional 0 to 2π or 0 to 4π. This parameter change, combined with the switchable π phase shift in the second stage, achieves endless phase shifting with lower insertion loss.
3Loss of energy
If the phase modulator phase shift range is limited to 0 to π, then insertion loss is reduced, but the phase shifting range is restricted
Solution Approach 1:
The second stage with switchable π phase shift is nested after the first stage with continuous phase shift. This nested configuration allows the limited 0 to π phase shift of the first stage to be extended to an unlimited phase shift range by adding integer multiples of π through the second stage, thereby maintaining both low insertion loss and full adaptability.
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 solution provides a lower intrinsic insertion loss and eliminates the requirement for synchronous fast switching, enabling efficient phase shifting for coherent detection and laser stabilization while maintaining signal integrity.
Implementation Method 1
A passive optical splitter device receives, at an input port, an optical input signal and to split the input signal into a first and a second partial signal
Implementation Method 2
each of the first and second branches of the first stage comprising a controllable optical phase shifter, wherein the phase shifter in the first branch is configured to shift the phase of the first partial signal by a positive predetermined phase shift
Implementation Method 3
the combiner device being configured to output a first combined signal at a first output port and a second combined signal at a second output port
Data Source
Figure 1~2b
Figure 3a~3d
Figure 4~5b
AI summary
The invention relates to an optical endless phase shifting device for shifting an optical input signal by a desired phase shift comprising a first (102) and a second stage (104), the first stage (102) comprising a Mach-Zehnder structure that is operated in push-pull configuration and that creates a differential phase shift (ϕ). The first stage outputs combined signals (Ssin, Scos) which are further phase shifted by an additional phase shift of zero or π in the second stage (104) by phase shifters (118, 120) provided in both arms of the second stage or in a first arm only. These additionally phase-shifted signals are again combined to at least one output signal (Sout,1, Sout,2). A control device (106) controls the phase shifters in the first stage and the second stage in such a way that an endless shifting capability is provided by switching one of the phase shifters or the single phase shifter of the second stage to the respective other value when the differential phase shift (ϕ) reaches (and would exceed) a given range of the differential phase shift (ϕ) of [0;π/2] in the configuration with two phase shifters (118, 120) in the second stage (104) or [0;π/2] in the configuration with only one phase shifters (118) in the second stage (104). Further, the invention relates to a method for endless shifting of an optical input signal by a desired phase shift.