Periodic Reporting for period 1 - UNISON (UNIVERSAL SENSOR BASED ON ELECTRICALLY-PUMPED MID-INFRARED SPECTROMETER ON SILICON CHIPS)
Período documentado: 2024-03-01 hasta 2025-02-28
In a world increasingly threatened by climate change and environmental pollution, the need for accurate detection and quantification of greenhouse and toxic gases has never been more pressing. The European Union's ambitious Action Plan, "Towards a Zero Pollution for Air, Water, and Soil," sets the stage for urgent action to safeguard our environment and public health. However, current technologies for detecting these gases face significant limitations in terms of size, cost, and complexity, hindering their widespread use in critical applications such as environmental monitoring networks and wearable electronics.
UNISON is an EU funded groundbreaking project poised to transform mid-infrared spectroscopy and address these pressing challenges head-on. The project's overarching objective is clear: to develop a highly scalable platform for infrared spectroscopy building on frequency comb and dual comb spectroscopy that combines cutting-edge performance with compact design, thus enabling widespread deployment in various applications.
UNISON's pathway to impact is guided by a three-pronged approach, each focusing on ambitious physical and technological challenges: generating wide bandwidth frequency combs on silicon-germanium photonic circuits through innovative techniques, integrating novel cascade laser sources with silicon-germanium photonic circuits, providing efficient and compact power sources for the frequency comb spectrometers and designing and optimizing a compact, broadband interaction region for trace gas detection.
UNISON project focus on environmental protection and public health and highlight the importance of interdisciplinary collaboration in addressing complex challenges. The expected impacts are significant and far-reaching. By enabling high-resolution spectroscopy in the mid-infrared range, the project promises to revolutionize environmental monitoring, industrial process control, and public health surveillance. With its compact and cost-effective design, UNISON has the potential to democratize access to advanced spectroscopic techniques, empowering communities and decision-makers to take proactive measures towards a cleaner and safer future.
UNISON is an EU funded groundbreaking project poised to transform mid-infrared spectroscopy and address these pressing challenges head-on. The project's overarching objective is clear: to develop a highly scalable platform for infrared spectroscopy building on frequency comb and dual comb spectroscopy that combines cutting-edge performance with compact design, thus enabling widespread deployment in various applications.
UNISON's pathway to impact is guided by a three-pronged approach, each focusing on ambitious physical and technological challenges: generating wide bandwidth frequency combs on silicon-germanium photonic circuits through innovative techniques, integrating novel cascade laser sources with silicon-germanium photonic circuits, providing efficient and compact power sources for the frequency comb spectrometers and designing and optimizing a compact, broadband interaction region for trace gas detection.
UNISON project focus on environmental protection and public health and highlight the importance of interdisciplinary collaboration in addressing complex challenges. The expected impacts are significant and far-reaching. By enabling high-resolution spectroscopy in the mid-infrared range, the project promises to revolutionize environmental monitoring, industrial process control, and public health surveillance. With its compact and cost-effective design, UNISON has the potential to democratize access to advanced spectroscopic techniques, empowering communities and decision-makers to take proactive measures towards a cleaner and safer future.
During RP1, progress has been made towards each of the project objectives.
1. The coupling of cascade lasers with SiGe photonics circuits is investigated through two different integration schemes: monolithic integration or butt coupling integration via flip chip bonding. Progress has been made in the two approaches : GaSb growth on SiGe templates with low number of antiphase boundaries has been successfully obtained; for the butt coupling approach, the fabrication process has been defined and initial challenges have been solved for both the SiGe platform fabrication and the flip chip bonding of QCL on Si carrier.
2. Mid-IR frequency comb sources are developed in different configurations, providing complementary advantages in terms of sensing devices.
- Electro optical frequency comb provides tunable frequency comb sources. They are generated through integrated mid-IR modulators. Within UNISON, high speed and high performance integrated mid-IR modulators are under development. During RP1, a strategy has been selected to overcome the efficiency and loss tradeoff and preliminary tests in terms of material crystalline properties have been reported. Furthermore, it has been shown that the bandwidth of Schottky diode-based modulator is larger than 7 GHz .
- Frequency comb cascade lasers are a solution of choice to achieve comb sources in the mid-IR and nonlinear supercontinuum generation (SCG) is a potential solution to extend their bandwidth. Within UNISON, SCG in SiGe waveguide has been optimized, showing that the required pump peak power to achieve 500cm-1 bandwidth is reduced to 300-400W.
- The fast gain dynamics of frequency comb QCL strongly restricts the formation of ultrashort pulses in QCLs, leading to FM-comb formation. In order to produce sub-picosecond pulses with several watts of peak power, pulse compression of initial high-power FM-combs is developed. A first generation of on chip pulse compressor in SiGe waveguides has been successfully demonstrated.
- ICL gain dynamics has been investigated in depth and the reason that no passive mode-locking in ICLs has been observed so far has been understood. New designs can now be studied to reduce the gain recovery times.
- A novel approach for frequency comb cascade laser has been proposed recently, namely the Quantum Walk Combs (QWCs) that present ideal characteristics for controllable broadband combs in the mid-IR. Within UNISON, ICL quantum walk combs have been demonstrated for the first time, while the output power of QCL quantum walk comb has been increased by one order of magnitude.
- The possibility to generate Kerr comb in SiGe waveguide has been studied in depth, and innovative SiGe graded layer design are under study to maximize the nonlinearity and minimize propagation losses.
3. Full on-chip integration requires the development of on chip sensing device based on optical waveguides proving a large evanescent field. During RP1, 2 schemes have been selected for the development of a broadband on chip sensor. Simulations have been performed, and fabrication will resume in RP2.
4. Finally, besides the separated development of individual building blocks, effort is pushed to prepare the final demonstration of integrated dual comb spectroscopy scheme. To do so, quantum walk frequency sources are already under test for dual comb measurement, and a discussion has been initiated and pursued to define the scenario for the final proof of concept demonstrators.
1. The coupling of cascade lasers with SiGe photonics circuits is investigated through two different integration schemes: monolithic integration or butt coupling integration via flip chip bonding. Progress has been made in the two approaches : GaSb growth on SiGe templates with low number of antiphase boundaries has been successfully obtained; for the butt coupling approach, the fabrication process has been defined and initial challenges have been solved for both the SiGe platform fabrication and the flip chip bonding of QCL on Si carrier.
2. Mid-IR frequency comb sources are developed in different configurations, providing complementary advantages in terms of sensing devices.
- Electro optical frequency comb provides tunable frequency comb sources. They are generated through integrated mid-IR modulators. Within UNISON, high speed and high performance integrated mid-IR modulators are under development. During RP1, a strategy has been selected to overcome the efficiency and loss tradeoff and preliminary tests in terms of material crystalline properties have been reported. Furthermore, it has been shown that the bandwidth of Schottky diode-based modulator is larger than 7 GHz .
- Frequency comb cascade lasers are a solution of choice to achieve comb sources in the mid-IR and nonlinear supercontinuum generation (SCG) is a potential solution to extend their bandwidth. Within UNISON, SCG in SiGe waveguide has been optimized, showing that the required pump peak power to achieve 500cm-1 bandwidth is reduced to 300-400W.
- The fast gain dynamics of frequency comb QCL strongly restricts the formation of ultrashort pulses in QCLs, leading to FM-comb formation. In order to produce sub-picosecond pulses with several watts of peak power, pulse compression of initial high-power FM-combs is developed. A first generation of on chip pulse compressor in SiGe waveguides has been successfully demonstrated.
- ICL gain dynamics has been investigated in depth and the reason that no passive mode-locking in ICLs has been observed so far has been understood. New designs can now be studied to reduce the gain recovery times.
- A novel approach for frequency comb cascade laser has been proposed recently, namely the Quantum Walk Combs (QWCs) that present ideal characteristics for controllable broadband combs in the mid-IR. Within UNISON, ICL quantum walk combs have been demonstrated for the first time, while the output power of QCL quantum walk comb has been increased by one order of magnitude.
- The possibility to generate Kerr comb in SiGe waveguide has been studied in depth, and innovative SiGe graded layer design are under study to maximize the nonlinearity and minimize propagation losses.
3. Full on-chip integration requires the development of on chip sensing device based on optical waveguides proving a large evanescent field. During RP1, 2 schemes have been selected for the development of a broadband on chip sensor. Simulations have been performed, and fabrication will resume in RP2.
4. Finally, besides the separated development of individual building blocks, effort is pushed to prepare the final demonstration of integrated dual comb spectroscopy scheme. To do so, quantum walk frequency sources are already under test for dual comb measurement, and a discussion has been initiated and pursued to define the scenario for the final proof of concept demonstrators.
While substantial progress has been made towards each of the intermediate objective planned in RP1, key results have already been obtained:
- During RP1 ICL gain dynamics has been investigated in depth with a dedicated pump-probe experiment. Interestingly, two time constants where obtained, showing the presence of a very fast response below 2 ps, followed by a slower recovery time longer than 60 ps. As the typical roundtrip time of such ICL devices lies in the order of ~50-200 ps, the gain recovery thus happens too fast for passive mode-locking with a saturable absorber. This explains why no passively mode-locked pulses have been observed in ICLs yet. The findings of this study have been published in [1] where the experiment is explained in more detail.
- Nonlinear supercontinuum generation (SCG) in SiGe waveguide is a solution to extend the bandwidth of QCL comb sources. However, in previously reported SCG generation, high power (up to 2 kW peak power) was required. Therefore, further efforts are made within UNISON to reduce the required peak power intensity to trigger soliton fission and SCG. Within RP1, SCG from SiGe waveguide has been optimized, showing that the required pump peak power to achieve 500cm-1 bandwidth is reduced to 300-400W. This result is currently under submission [2]
[1] Pilat F., et al. “Fast Gain Dynamics in Interband Cascade Lasers”, Laser Photonics Rev 2025, 19, 2400867. https://doi.org/10.1002/lpor.202400867(se abrirá en una nueva ventana)
[2] V. Turpaud, et al., “Low-power supercontinuum generation in Ge-rich SiGe waveguides from 4 to 13 µm wavelength”, under submission
- During RP1 ICL gain dynamics has been investigated in depth with a dedicated pump-probe experiment. Interestingly, two time constants where obtained, showing the presence of a very fast response below 2 ps, followed by a slower recovery time longer than 60 ps. As the typical roundtrip time of such ICL devices lies in the order of ~50-200 ps, the gain recovery thus happens too fast for passive mode-locking with a saturable absorber. This explains why no passively mode-locked pulses have been observed in ICLs yet. The findings of this study have been published in [1] where the experiment is explained in more detail.
- Nonlinear supercontinuum generation (SCG) in SiGe waveguide is a solution to extend the bandwidth of QCL comb sources. However, in previously reported SCG generation, high power (up to 2 kW peak power) was required. Therefore, further efforts are made within UNISON to reduce the required peak power intensity to trigger soliton fission and SCG. Within RP1, SCG from SiGe waveguide has been optimized, showing that the required pump peak power to achieve 500cm-1 bandwidth is reduced to 300-400W. This result is currently under submission [2]
[1] Pilat F., et al. “Fast Gain Dynamics in Interband Cascade Lasers”, Laser Photonics Rev 2025, 19, 2400867. https://doi.org/10.1002/lpor.202400867(se abrirá en una nueva ventana)
[2] V. Turpaud, et al., “Low-power supercontinuum generation in Ge-rich SiGe waveguides from 4 to 13 µm wavelength”, under submission