Optical Modulator for Nonlinear Effect Suppression
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Solution Overview
Problem
Optical fiber communication systems face limitations in transmission distance due to nonlinear effects like self-phase modulation and cross-phase modulation, which restrict bit rate and increase costs, and existing solutions struggle to flexibly switch between modulation methods while managing device bandwidth effectively.
Innovation Solution
An optical transmission apparatus and method that employs a modulator capable of quadrature phase-shift keying (QPSK) and π/2 shift binary phase-shift keying (BPSK) modulation, controlled by a controller to reduce nonlinear effects, suppress bandwidth requirements, and facilitate flexible modulation method switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If DPSK modulation is used to increase bit rate, then transmission capacity is improved, but nonlinear effects (self-phase modulation and cross-phase modulation) increase and restrict transmission distance
Solution Approach 1:
The patent changes the modulation format from DPSK to DQPSK, which modifies the phase transition characteristics. DQPSK uses four phase states (0, π/2, π, 3π/2) instead of two, resulting in more gradual phase transitions that reduce the intensity variations causing nonlinear effects. This parameter change in modulation format allows higher bit rates while mitigating self-phase modulation and cross-phase modulation effects.
2Productivity
If symbol rate is increased to carry out large capacity communication, then transmission capacity is improved, but transmission distance is restricted in proportion to the square of symbol rate
Solution Approach 1:
The patent employs DQPSK modulation which encodes 2 bits per symbol instead of 1 bit per symbol in DPSK. This changes the relationship between bit rate and symbol rate, allowing higher transmission capacity at lower symbol rates, thereby extending transmission distance while maintaining large capacity communication.
3Length of stationary object
If polarization separation method is used to reduce symbol rate, then transmission distance is improved, but device complexity increases due to multiple light sources and polarization tracking
Solution Approach 1:
The patent uses a single light source that generates optical carrier waves, which are then modulated by a modulator capable of DQPSK modulation. This single light source performs multiple functions: generating the carrier, enabling high-order modulation for increased capacity, and avoiding the complexity of managing multiple light sources required by polarization separation methods.
4Productivity
If band restriction is applied to reduce occupied bandwidth, then overall transmission capacity is improved, but intercode interference increases due to carrier frequency offset
Solution Approach 1:
The patent changes the modulation scheme to DQPSK, which has different spectral characteristics compared to DPSK. The quadrature phase modulation provides better spectral efficiency and reduces intercode interference while maintaining acceptable bandwidth occupation, thereby improving both transmission capacity and signal reliability simultaneously.
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 solution reduces the influence of nonlinear effects, narrows bandwidth demands, and allows easy bias control and flexible switching between modulation methods, enhancing transmission distance and reducing costs.
Implementation Method 1
a modulator which can modulate light from a light source by quadrature phase-shift keying and can output the modulated light
Data Source
AI summary
An object of the invention is to provide an optical transmission apparatus capable of reducing the influence of nonlinear effect of an optical fiber, suppressing a band requested to a device from being widened, easily bias controlling a modulator, and flexibly switching plural modulation methods.An optical transmission apparatus 301 according to the invention includes a modulator 101 and a controller 102. The modulator 101 is a modulator capable of quadrapture phase-shift keying the light from a light source and outputting the light. The controller 102 controls the input signal to the modulator 101 and causes the modulator 101 to carry out a quadrapture phase-shift keying operation or a π/2 shift binary phase-shift keying operation.