Research on Solar Solid-State Lasers. Whispering gallery modes in Integrated Photonics design.
Photonics Precision Technologies - Precision with Light
In this edition of Photonics Precision Technologies - Precision with Light, a research news and new developments in the photonics industry and academic fields, I am honored to share a feature article (featured by myself, obviously) from Laser Focus World, where we all can read the details of work being done in Nova University of Lisbon by Prof. Dr. Dawei Liang. Dr. Dawei Liang is someone I know well personally, him having been a mentor of a previous work I have done with industrial lasers at Nova and a portuguese industrial innovative applications institute. He is a well regarded international (Chinese origin) expert in concentrated solar enegry harvesting with Solid-State Lasers, as well as in fiber optics, and Laser Physics in general.
In the work done with other researchers at Nova University of Lisbon’s CEFITEC, Departamento de Física, FCT, Universidade NOVA de Lisboa, 2829-516, Campus de Caparica, Portugal, awesomelly described in the Laser Focus World article we are presented with an ingenious engineering device based on Solid-State Laser Rods of Ce:Nd:YAG, a rare-earth material. Further, we learn more about the optical engineering components used in this research effort, such as a fused-silica aspheric lens of customised dimensions, a fascinating optical component device; as well as how this type of solar laser can find applications in many scientific and technological challenges. Further details below on this free to read edition.
In this edition we can also read about another fascinating recent research effort with photonic crystals micro-rings showing fractional optical angular momentum, These devices are used in modern photonics applications such as PICs (photonics intgrated cirtcuits) or can be tailor-made to suit particular cutting-edge applications. In the research we learn about a whispering gallery mode effect, a type of wave-like effect, that the designed device shows. The potential applications can be numerous, in fundamental Quantum Optics research, into control of quantum nodes in quantum networks, in bio-sensing and more. Of particular interest in this work is how enhanced ability to control non-linear photonics/optolelectronics effects could open the doors of further new innovative applications of photonics technologies.
Solar pumping converts broadband sunlight into efficient laser light
A novel three Ce:Nd:YAG rod solar-pumped laser achieves 4.64% solar-to-laser energy conversion efficiency.
A team of researchers led by Dawei Liang, an associate professor at NOVA University of Lisbon in Portugal, are eschewing semiconductor laser arrays and embracing the promise of direct solar pumping of solid-state lasers to overcome current performance limitations and enable reliable operation of spaceborne lasers for years.
How do you design a three-Ce:Nd:YAG rod solar laser system?
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Their heliostat mirror has 93.5% reflectivity and redirects incoming solar radiation toward the stationary parabolic mirror with a 1.5 m diameter, 60° rim angle, and 660 mm focal length. The parabolic mirror’s back surface is coated with silver, and its reflectivity is 80% for this primary mirror.
“Our solar laser head component is made of a large fused silica aspheric lens and three 2.5-mm-diameter, 25-mm-length Ce:Nd:YAG rods mounted within the single conical pump cavity (see Fig. 2, left),” says Liang. “And we aligned three small partial reflection 1064-nm output mirrors with corresponding laser rods (see Fig. 2, right).”
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“Our aspheric lens efficiently coupled the concentrated solar radiation from the focal zone into the three Ce:Nd:YAG rods within the single conical pump cavity,” Liang notes. “For end-pumping, we directly focus one part of the concentrated radiation onto the Ce:Nd:YAG rod through the high-reflection (1064-nm) end face of the rods by the aspheric lens. The coatings reflect the 1064 nm oscillating laser beam within the resonant cavity, while permitting the entrance of other useful solar rays for pumping.”
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The team’s solar laser may find wide-ranging applications such as earth, ocean, and atmospheric sensing, laser beaming, deep space communications, and space debris removal.
Liang and colleagues are now attempting to pump four and seven thin Ce:Nd:YAG rods within the conical pump cavity to enhance the solar-to-laser conversion efficiency to more than 5% and achieve total laser output power stability of less than 0.5% within the solar tracking error range of ±0.2°.
Whispering gallery modes with fractional optical angular momentum in photonic crystal micro-rings (Phys.org courtesy)
Whispering gallery modes, a type of wave that can travel around concave surfaces, have proved to be promising for the development of new technologies, particularly in photonics. Due to geometrical limitations, in circularly symmetric optical microresonators (i.e., micrometer-scale structures that can confine light) these modes exhibit integer quantized angular momentum values. While numerous effects take advantage of such modes, there are applications for which non-integer angular momentum may be desired.
"Our recent PRL paper builds on our previous work in Nature Photonics, where we introduced the structure of a 'microgear' photonic crystal ring," Xiyuan Lu, one of the researchers who carried out the study, told Phys.org. "In this new work, we demonstrate the half-integer orbital angular momentum of light, in comparison to the even numbers attained by the photonic crystal ring we previously studied, which gives integer orbital angular momentum of light similar to that inconventional micro-rings, referred to as 'whispering gallery modes'."
In their recent work, Lu and his colleagues set out to investigate new capabilities of the photonic crystal micro-rings introduced in their previous paper. The team also wished to explore how introducing multiple defects into their resonator would affect its localization capabilities and its spatial control of light.
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"The realization of the multiple defects in our device was also far from complicated, as we simply introduced multiple defect modulation across our ring," Lu said. "As a result of this unique design, we could achieve two functionalities, half-integer angular momentum or multiple defect localization, in silicon photonics, with a fabrication method that can be scalable."
Scalabe and simple design can yield impressive results. Sometimes simplicity pays off.
In initial tests, the ring-shaped micro-resonator developed by this team of researchers achieved highly promising results, exhibiting a high-Q and good coupling. In addition, the device can be integrated with nonlinear photonics, quantum photonics and bio-sensing applications, just as easily as whispering gallery modes in conventional micro-rings are integrated.
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Concluding:
In their next studies, the researchers plan to test the value of their design to achieve control over electromagnetic fields interacting with matter. More specifically, they plan to apply it to the development of nonlinear optical technologies and quantum optics made of atoms or quantum dots.
"We are interested to investigate the origin of the weak coupling, in order to control it better down the road," Lu said. "We are also looking into nonlinear optical interaction with the localized modes and quantum interaction with atoms and quantum dots in these devices."