Periodic Reporting for period 1 - versacomb (Versatile optical frequency comb)
Reporting period: 2023-09-01 to 2025-02-28
Optical frequency combs are a groundbreaking class of light sources that have transformed fields such as precision measurement and optical analysis. They enable the generation of a spectrum composed of equally spaced, phase-coherent lines, which can act as a ruler for light. This unique property opens the door to a wide range of high-impact applications—from ultra-precise timekeeping and fundamental physics experiments to next-generation telecommunication systems and advanced medical diagnostics.
Despite their potential and significant progress in recent years, the widespread adoption of optical frequency combs remains limited. Most current systems are still custom-built, optimized for specific experiments, and largely restricted to laboratory environments. One of the key barriers is the lack of versatile, stable, and user-friendly sources that combine high performance with commercial viability.
This project aims to tackle that gap by developing a high-quality optical frequency comb source with three essential characteristics:
• Versatile repetition rate to adapt to different use cases (10 MHz-10 GHz)
• Excellent stability for reliable long-term operation
• High output power to make the technology usable across a broader range of applications.
To achieve this, the project investigates and leverages the strengths of the three main approaches to frequency comb generation: mode-locked lasers, electro-optic modulators, and microresonator-based combs. Each of these technologies offers distinct benefits but also suffers from limitations—such as fixed repetition rates, poor stability, or low power output.
By integrating novel design strategies and innovative components, the project seeks to overcome these limitations and deliver a compact, robust, and scalable solution. The resulting system would not only enhance the capabilities of existing research infrastructures but also open up new application areas—from field-deployable instruments to industrial systems requiring precision optical sources.
Despite their potential and significant progress in recent years, the widespread adoption of optical frequency combs remains limited. Most current systems are still custom-built, optimized for specific experiments, and largely restricted to laboratory environments. One of the key barriers is the lack of versatile, stable, and user-friendly sources that combine high performance with commercial viability.
This project aims to tackle that gap by developing a high-quality optical frequency comb source with three essential characteristics:
• Versatile repetition rate to adapt to different use cases (10 MHz-10 GHz)
• Excellent stability for reliable long-term operation
• High output power to make the technology usable across a broader range of applications.
To achieve this, the project investigates and leverages the strengths of the three main approaches to frequency comb generation: mode-locked lasers, electro-optic modulators, and microresonator-based combs. Each of these technologies offers distinct benefits but also suffers from limitations—such as fixed repetition rates, poor stability, or low power output.
By integrating novel design strategies and innovative components, the project seeks to overcome these limitations and deliver a compact, robust, and scalable solution. The resulting system would not only enhance the capabilities of existing research infrastructures but also open up new application areas—from field-deployable instruments to industrial systems requiring precision optical sources.
The project followed a rigorous combination of numerical modeling, experimental implementation, and iterative optimization to develop a high-performance frequency comb system. The underlying is the combination of coherent driving, incoherent gain (erbium dioped fiber amplifiers) and phase modulation.
Key achievements include:
• Double-cavity design and implementation:
We designed and constructed a double-cavity system based on extensive numerical simulations. These confirmed the core hypothesis: broadband, high-power, tunable frequency combs can be generated with this configuration.
• Gain clamping and spontaneous soliton formation:
We demonstrated that gain clamping significantly enhances saturation power, allowing for the spontaneous formation of cavity solitons in an erbium-doped active cavity—something not previously achievable in our setups.
• Novel stabilization method:
Traditional stabilization using average power or an auxiliary signal is ineffective in the multi-soliton regime. We developed a new approach using spectral filters, providing a signal proportional to cavity detuning. This method achieved long-term stability of multi-soliton states.
• Towards soliton crystals:
Although many solitons can form, they tend to bunch randomly due to mutual interactions. To create equidistantly spaced solitons—a soliton crystal—we used external phase modulation (rather than intracavity modulation) for higher power compatibility. While this reduces the synchronization range, it is effective in trapping solitons.
• Controlled soliton generation:
Creating a single soliton per slot is challenging due to soliton merging and annihilation. Rather than scanning the detuning (which provides a narrow parameter window), we introduced a novel excitation method. This approach allowed us to progressively fill the cavity up to 99%. However, maintaining long-term stability remains difficult, mainly due to pump laser noise.
• Simulation and future improvements:
We successfully reproduced the destabilizing effects of noise in simulation and identified methods to counteract it. Ongoing work focuses on implementing these stabilization strategies experimentally.
• High-power, polarization-maintaining (PM) system:
A new fully PM setup was developed to maximize output power and polarization stability. This configuration would support the generation of a very high power soliton crystal at 10 GHz, offering a major advantage for industrial applications.
• Thermal stabilization:
We also explored thermal stabilization techniques to achieve indefinite stability once noise issues are addressed.
Key achievements include:
• Double-cavity design and implementation:
We designed and constructed a double-cavity system based on extensive numerical simulations. These confirmed the core hypothesis: broadband, high-power, tunable frequency combs can be generated with this configuration.
• Gain clamping and spontaneous soliton formation:
We demonstrated that gain clamping significantly enhances saturation power, allowing for the spontaneous formation of cavity solitons in an erbium-doped active cavity—something not previously achievable in our setups.
• Novel stabilization method:
Traditional stabilization using average power or an auxiliary signal is ineffective in the multi-soliton regime. We developed a new approach using spectral filters, providing a signal proportional to cavity detuning. This method achieved long-term stability of multi-soliton states.
• Towards soliton crystals:
Although many solitons can form, they tend to bunch randomly due to mutual interactions. To create equidistantly spaced solitons—a soliton crystal—we used external phase modulation (rather than intracavity modulation) for higher power compatibility. While this reduces the synchronization range, it is effective in trapping solitons.
• Controlled soliton generation:
Creating a single soliton per slot is challenging due to soliton merging and annihilation. Rather than scanning the detuning (which provides a narrow parameter window), we introduced a novel excitation method. This approach allowed us to progressively fill the cavity up to 99%. However, maintaining long-term stability remains difficult, mainly due to pump laser noise.
• Simulation and future improvements:
We successfully reproduced the destabilizing effects of noise in simulation and identified methods to counteract it. Ongoing work focuses on implementing these stabilization strategies experimentally.
• High-power, polarization-maintaining (PM) system:
A new fully PM setup was developed to maximize output power and polarization stability. This configuration would support the generation of a very high power soliton crystal at 10 GHz, offering a major advantage for industrial applications.
• Thermal stabilization:
We also explored thermal stabilization techniques to achieve indefinite stability once noise issues are addressed.
This project has delivered several advances beyond the current state of the art in frequency comb technology:
• Numerical models and simulations:
Comprehensive simulations of gain dynamics, noise effects, and feedback mechanisms enabled optimized system design and predictive insight into complex nonlinear behaviors.
• Advanced stabilization techniques:
The introduction of spectral filtering and thermal control for cavity stabilization provides a novel path to long-term soliton state maintenance, particularly in regimes where standard techniques fail.
• Gain clamping for soliton generation:
By coupling to a laser for gain clamping, we enabled spontaneous soliton formation in previously inaccessible regimes.
• Controlled soliton writing and merging:
We developed new techniques for controlled soliton trapping, critical for producing soliton crystals. The approach enables near-complete cavity filling—a key requirement for practical comb deployment.
• Design of high-output power PM system:
Our fully polarization-maintaining system is designed to offer both higher output power and environmental robustness, which are essential for commercial viability.
To move towards real-world applications and commercial viability, the following steps are necessary:
• Further research: Improve long-term stability by mitigating pump noise and expanding the operating parameter range.
• Demonstration systems: Build prototype systems for targeted application environments (e.g. telecom, LIDAR, metrology).
• Access to funding and markets: Support from innovation programs and industrial partnerships will be crucial to refine the product and access emerging markets.
• IPR and standardization: Protecting the novel stabilization and comb generation techniques will be important for commercialization.
• International collaboration: Engaging with academic and industrial partners worldwide will help validate performance and accelerate uptake.
• Numerical models and simulations:
Comprehensive simulations of gain dynamics, noise effects, and feedback mechanisms enabled optimized system design and predictive insight into complex nonlinear behaviors.
• Advanced stabilization techniques:
The introduction of spectral filtering and thermal control for cavity stabilization provides a novel path to long-term soliton state maintenance, particularly in regimes where standard techniques fail.
• Gain clamping for soliton generation:
By coupling to a laser for gain clamping, we enabled spontaneous soliton formation in previously inaccessible regimes.
• Controlled soliton writing and merging:
We developed new techniques for controlled soliton trapping, critical for producing soliton crystals. The approach enables near-complete cavity filling—a key requirement for practical comb deployment.
• Design of high-output power PM system:
Our fully polarization-maintaining system is designed to offer both higher output power and environmental robustness, which are essential for commercial viability.
To move towards real-world applications and commercial viability, the following steps are necessary:
• Further research: Improve long-term stability by mitigating pump noise and expanding the operating parameter range.
• Demonstration systems: Build prototype systems for targeted application environments (e.g. telecom, LIDAR, metrology).
• Access to funding and markets: Support from innovation programs and industrial partnerships will be crucial to refine the product and access emerging markets.
• IPR and standardization: Protecting the novel stabilization and comb generation techniques will be important for commercialization.
• International collaboration: Engaging with academic and industrial partners worldwide will help validate performance and accelerate uptake.