Optical Phase Modulator Reducing Harmonic Content
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Solution Overview
Problem
Existing optical phase modulators face challenges in controlling the harmonic content of phase-modulated signals, particularly the second harmonic at twice the desired modulation frequency, which affects their performance in applications like optical communications and sensing.
Innovation Solution
The use of an optical phase modulator with a modulating waveguide section and a resistive heater, driven by an electric drive signal with a time-varying component oscillating at half the modulation frequency and no time-constant component, to control the refractive index and phase of the input light signal, thereby reducing harmonic content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional optical phase modulator is driven with a standard modulating signal, then phase modulation is achieved, but significant second harmonic content is generated at twice the modulation frequency
Solution Approach 1:
The patent applies periodic action by driving the optical phase modulator with a modulating signal at half the desired modulation frequency. This causes the phase modulator to be updated twice per modulation cycle, effectively achieving the target modulation frequency while suppressing the second harmonic through the specific timing and symmetry of the periodic updates.
Solution Approach 2:
The patent changes the operating parameters by using a drive signal with zero time-constant component (no DC offset) and oscillating at half the modulation frequency. This parameter change in the drive signal characteristics transforms the quadratic phase response into a waveform that eliminates the second harmonic while maintaining the fundamental modulation frequency.
2Productivity
If the modulating signal frequency is increased to achieve higher data rates, then communication speed improves, but harmonic distortion and spectral interference increase
Solution Approach 1:
By updating the phase modulator at half the target frequency with proper periodic timing, the system achieves higher effective modulation frequencies without proportionally increasing harmonic distortion. The periodic nature of the drive signal at half-frequency, combined with the quadratic phase response, naturally suppresses even harmonics including the problematic second harmonic.
Solution Approach 2:
The patent converts the harmful quadratic nonlinearity that normally generates second harmonics into a beneficial feature. By exploiting the quadratic phase response with a half-frequency drive signal having zero DC component, the second harmonic terms cancel out, transforming what was previously a source of distortion into a mechanism for harmonic suppression.
3Stability of the object's composition
If a time-constant component is added to the modulating signal to improve phase control, then phase stability improves, but second harmonic content increases
Solution Approach 1:
The patent achieves phase stability without a time-constant component by using periodic action at half the modulation frequency. The symmetric periodic updates provide the necessary phase control while the zero-DC nature of the drive signal prevents generation of second harmonic content that would otherwise result from adding a DC offset.
Solution Approach 2:
Instead of adding a time-constant component to stabilize phase (conventional approach), the patent inverts the approach by using a purely AC drive signal at half frequency. This inversion eliminates the DC component that causes second harmonics while the periodic nature provides the necessary phase stability through controlled temporal variations.
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 approach effectively reduces the second harmonic content in the phase-modulated light signal, enhancing spectral purity and improving the performance of optical phase modulators in various applications, including optical communications and sensing.
Implementation Method 1
a resistive heater in thermal contact with the modulating waveguide section; and a phase modulator driver configured to apply a drive voltage or electric current having a time-varying component oscillating at half the modulation frequency and no time-constant component to the resistive heater to generate heat that is transferred into the modulating waveguide section
Implementation Method 2
a modulating waveguide section for receiving and supporting propagation of the input light signal, the modulating waveguide section having an effective refractive index that depends linearly on temperature
Data Source
AI summary
An optical phase modulation device for modulating a phase of an input light signal at a modulation frequency is provided, which can be used in integrated photonics applications. The device can include an optical phase modulator, for example a thermo-optic phase shifter having an effective refractive index that depends linearly temperature, configured to impart a phase shift to the input light signal, the phase shift varying quadratically in response to an applied modulating electric drive signal. The device can also include a phase modulator driver configured to apply the electric drive signal to the optical phase modulator, the electric drive signal having a time-varying component oscillating at half the modulation frequency and no time-constant component, thereby imparting the phase shift, modulated at the modulation frequency, to the phase of the input light signal to produce a phase-modulated light signal. Optical phase modulation systems and methods are also disclosed.