Photonic Microwave Waveform Generator Using Monolithic Resonator Locking
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Solution Overview
Problem
Conventional electronic means are limited in generating high-frequency ultrabroad-bandwidth arbitrary microwave waveforms due to digital-to-analog converter technology limitations and high timing jitter, and existing microwave photonic devices are bulky and unsuitable for many applications.
Innovation Solution
A miniature, power-efficient agile photonic generator using self-injection locked lasers and monolithic optical microresonators, where two coherent light sources are locked to modes of a resonator apparatus, reducing the impact of ambient perturbations and enabling efficient decoupling of frequency and amplitude modulation, allowing for the generation of ultrabroad bandwidth microwave pulses with high spectral purity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional electronic means are used for arbitrary waveform generation, then the device structure is relatively simple, but the frequency range is limited to below 2 GHz and timing jitter is high
Solution Approach 1:
The patent replaces conventional electronic waveform generation mechanisms with a photonic system using mode-locked lasers. The laser generates ultrabroad bandwidth microwave pulses through optical frequency combs, achieving frequency ranges up to 100 GHz while maintaining low timing jitter through the inherent stability of optical resonators.
Solution Approach 2:
The patent changes the fundamental operating parameters by using optical frequencies instead of electronic frequencies. The mode-locked laser operates at optical frequencies (hundreds of THz) and generates microwave pulses through optical-to-electrical conversion, enabling frequency multiplication and extended bandwidth beyond conventional electronic limits.
2Speed
If microwave photonic devices are used to generate high-frequency waveforms, then the frequency range can extend to 100 GHz, but the device size becomes large and bulky
Solution Approach 1:
The patent implements nesting by integrating multiple functional components within the photonic integrated circuit: the microresonator generates optical frequency combs, which are then processed through modulators and detectors all on a single chip. This nested integration reduces the overall device volume from table-top scale to chip-scale dimensions.
Solution Approach 2:
The patent transitions from three-dimensional bulky optical components to two-dimensional planar photonic integrated circuits. The microresonator, waveguides, modulators, and detectors are all fabricated in a planar configuration on a semiconductor substrate, dramatically reducing the vertical dimension and overall device footprint.
3Volume of moving object
If lasers and spectrum shapers are placed close together in microwave photonic devices, then the device size is reduced, but the lasers become sensitive to ambient perturbations such as thermal variations and mechanical vibrations
Solution Approach 1:
The patent merges the laser and microresonator into a single integrated photonic structure where the laser is monolithically coupled to the resonator. This merging ensures that both components experience identical ambient perturbations, causing common-mode noise that can be rejected through differential detection or locking techniques.
Solution Approach 2:
The patent implements feedback control by locking the laser frequency to the microresonator modes. The microresonator serves as a stable reference, and feedback mechanisms (such as Pound-Drever-Hall locking) continuously adjust the laser frequency to track the resonator modes, compensating for thermal drift and mechanical vibrations.
4Speed
If conventional digital-to-analog converters are used, then the device complexity is low, but the bandwidth is limited and timing jitter is high
Solution Approach 1:
The patent replaces conventional digital-to-analog converters with a photonic frequency comb generator. The mode-locked laser naturally generates a comb of equidistant frequency lines through optical resonance, eliminating the need for complex electronic D/A conversion while achieving ultrabroad bandwidth and low jitter through optical physics.
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 enables the generation of microwave waveforms with spectral width exceeding 4 GHz and repetition rates exceeding 1 MHz, suitable for radar applications and wireless communications, with improved spectral purity and reduced size, overcoming the limitations of conventional technologies.
Implementation Method 1
a resonator apparatus coupled to the first and second coherent light sources to provide first and second optical output beams corresponding, respectively, to the first and second coherent light sources
Implementation Method 2
The first and second coherent light sources may be locked to modes of the resonator apparatus using, for example, optical, electronic, thermal or other types of a feedback configured to force frequencies of the coherent light sources to follow the modes of the resonator apparatus
Data Source
AI summary
The disclosure relates in some aspects to providing miniature power-efficient agile photonic generators of microwave waveforms. Illustrative examples use chip lasers integrated in close thermal proximity with one another to provide a miniature microwave arbitrary waveform generator (AWG). Due to the small size of the lasers and the close integration, common ambient fluctuations from the environment or other sources can be efficiently reduced, yielding improved spectral purity of generated radio-frequency (RF) signals. Tight physical integration also permits a small device footprint with minimal acceleration sensitivity. The lasers may be locked to cavities or other resonators to allow efficient decoupling of the frequency and amplitude modulation of the lasers to provide flexibility to the waveform generator. Exemplary devices described herein can produce frequency chirped signals for radar applications. The frequency chirp may be linear and/or nonlinear. Tuning methods are also described herein.