Hefei Research Institute uses ultrafast technology to build a GHz high-frequency photoelastic modulator

Recently, the research team of Sheng Zhigao of the High Magnetic Field Science Center of the Hefei Institute of Physical Sciences, Chinese Academy of Sciences, used ultrafast time-resolved pump detection technology to achieve birefringence modulation of GHz frequency induced by ultrafast coherent phonons in SrTiO3 crystals, and its operating frequency far exceeds the cutoff frequency of today’s commercial photoelastic modulators. The relevant research results were published in Advanced Science and patented the invention.

Specific materials with birefringence effects shape light. Photoelastic modulators operating on birefringence modulation technology are one of the core components of modern optical technology. At present, photoelastic modulators mostly use the mechanical stress provided by piezoelectric materials to drive photoelastic crystals to achieve birefringence modulation, and their operating frequency is limited by the resonant frequency of photoelastic/piezoelectric crystals, generally on the order of kHz. With the emerging needs of high-frequency signal processing and high-frequency optical communication, it is urgent to develop birefringence materials and modulation technologies with GHz operating frequencies.

In view of this situation, after a large number of material screening and technical exploration, Sheng Zhigao’s research group and collaborators found the GHz optical birefringence effect induced by ultrafast coherent phonons in perovskite SrTiO3 crystals with the help of ultrafast pump-detection system in the strong magnetic field magneto-optical laboratory, and realized optical manipulation. The research team used ultrafast laser pulses to generate coherent acoustic phonons with low damping in the transducer/SrTiO3 heterostructure. After a series of material screening, it is found that LaRhO3 semiconductor thin film can obtain relatively high photon-phonon energy conversion efficiency as a transducer layer. Further, in the optimized heterostructure, it is found that ultrafast coherent acoustic phonons can induce optical birefringence with GHz frequency in stress-sensitive SrTiO3 crystals. At the same time, the research team realized the optical manipulation of coherent phonons and their induced GHz birefringence through dual-pump technology. This reveals a mechanism of ultrafast optical birefringence modulation and lays a technical foundation for the application of GHz high-frequency acousto-optic devices.

Left: Schematic diagram of the principle of laser-induced acoustic phonon excitation SrTiO3 crystal GHz birefringence; Right: GHz birefringence modulation of SrTiO3 crystals with different crystal orientations.

The research work is supported by the National Key Research and Development Program, the National Natural Science Foundation of China, the Anhui Provincial Laboratory Direction Fund for Strong Magnetic Field and the High-end User Cultivation Fund of Hefei Science Center. (Source: Hefei Institute of Physical Sciences, Chinese Academy of Sciences)

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