Phase Control Circuit for DQPSK Optical Receivers
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Solution Overview
Problem
High-speed optical data transmission systems face challenges with inter symbol interference (ISI) due to polarization mode dispersion (PMD) and chromatic dispersion (CD), which affect the recovery of signal energy across multiple time slots, and advanced modulation formats like DQPSK have reduced tolerance to frequency drifts and noise.
Innovation Solution
A phase control circuit using a dither signal, mixer, adder, integrator, and low-pass filter, along with a power detector tailored to remove clock signal components, is employed to minimize errors and maintain phase control in DQPSK and advanced modulation formats, utilizing two parallel delay interferometers for balanced detection and feedback control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multi-level signaling (e.g., DQPSK) is used to increase spectral efficiency, then the symbol rate is reduced and ISI is decreased, but the system tolerance to frequency drifts and noise is reduced
Solution Approach 1:
The patent implements a phase control circuit that continuously monitors the received signal and generates feedback to adjust the delay interferometer settings. This feedback mechanism compensates for frequency drifts and phase errors, maintaining reliable detection despite the reduced tolerance inherent in multi-level signaling schemes like DQPSK.
Solution Approach 2:
The system dynamically adjusts operational parameters including delay line settings and phase offsets based on received signal characteristics. By changing these parameters in response to detected errors or drift conditions, the system maintains optimal performance for multi-level modulation formats while compensating for their reduced noise and drift tolerance.
2Productivity
If higher data transmission rates are implemented, then productivity increases, but inter symbol interference (ISI) increases due to dispersion effects
Solution Approach 1:
The patent employs parallel delay interferometers that process different time slots or signal components separately. This segmentation allows independent equalization and interference mitigation for each channel, enabling high-speed transmission by processing multiple data streams in parallel while reducing the impact of ISI on each individual stream.
Solution Approach 2:
The phase control circuit acts as an intermediary between the received signal and the detection process. It pre-processes the signal by compensating for dispersion-induced phase errors and ISI before the final detection stage, thereby enabling higher data rates to be transmitted through the fiber optic channel with acceptable error rates.
3Productivity
If advanced modulation formats like DQPSK are used, then spectral efficiency is improved, but measurement precision for phase control becomes more difficult
Solution Approach 1:
The patent implements feedback control loops that continuously measure the received signal phase and amplitude, then adjust the delay interferometer settings accordingly. This closed-loop feedback system maintains precise phase control for DQPSK detection by compensating for drifts and errors in real-time, making the measurement process robust despite the complexity of the modulation format.
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 effectively reduces ISI and maintains phase control stability, enabling longer transmission distances or higher data rates with improved tolerance to noise and frequency drifts, even in the presence of chromatic dispersion and differential group delay.
Implementation Method 1
one delay interferometer (DI) in the case of DPSK or two parallel DIs in the case of DQPSK are inserted in the optical path at the receiver side to convert the differential phase modulation in to intensity modulation
Implementation Method 2
A power detector 24, which is tailored to remove clock signal components, provides a phase control signal
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
This invention relates to a phase control circuit for an optical receiver (1). The phase control circuit (9, 19) comprises a non-linear element (22) and a power detector (24). The non-linear element (22) has a rectifying characteristic, inputs the received electrical signal (7, 17) and provides a rectified signal at its output. The power detector (24) provides an error signal which is used to obtain a phase control signal (5) which is output by the phase control circuit. The invention further relates to a corresponding method for phase control of an optical receiver (1).