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Graphene Based Ultrafast Lasers

Final Report Summary - GRABFAST (Graphene Based Ultrafast Lasers)

The Marie Curie Career Integration Grant has successfully supported the permanent integration of the researcher (Prof. Zhipei Sun) into Aalto University. Now, he is a full professor at Aalto University.

Major scientific result summary of the project:

1. Development of two-dimensional layered materials based free-space photonics devices:

Various novel fabrication/integration methods have been developed for different applications (Details in our recent papers, Advanced Materials, 1705963 (2018); Advanced Materials, DOI:10.1002/adma.201704896 (2018)). For example, different free-space devices integrated with 2D materials, such as mirrors (2D Materials 4, 025095 (2017)), output couplers (Applied Physics Letters, 105, 221103 (2014)), prisms (Optica, 3, 151-158 (2016)), have been fabricated with various methods: Chemical vapour deposition equipment (Black Magic, Aixtron), available in the department, provides large-area (e.g. up to 6 inches) and high-quality graphene (Nano letters 17, 7539 (2017); Optica, 3, 151-158 (2016); IEEE Journal of Selected Topics in Quantum Electronics, 20, 1100705 (2014)) for photonic device integration; The researcher and his collaborators in Cambridge also printed 2D materials based large-area flexible devices (Advanced Functional Materials, 1800480(2018) for energy applications.

2. Development of two-dimensional layered materials based fiber photonics devices:

Various two-dimensional materials, such as graphene, were integrated in fiber/waveguide devices: Direct sandwiching of free-standing graphene or other nano-materials based polymer composites were employed to form integrated fiber devices with index-matching gel to reduce coupling loss (e.g. Optics Express 25, 30020 (2017); Nanoscale, 8, 1066-1072 (2016); Optics Express 23, 9947 (2015); Scientific Reports, 5, 9101 (2015); ACS Nano, 8, 4836 (2014)). Various silicon waveguide devices and their ring cavities (for light-matter interaction enhancement) also have been tested.

3. Development of ultrafast wide-band fiber lasers:

The researcher and his group built mid-infrared ultrafast fiber lasers at the optical “molecular fingerprint” region (2-10µm), crucial for gas sensors (Scientific Reports, 5, 16624 (2015); CLEO, CW1G.4 (2016)). They used commercially available Thulium fibers as gain materials for this spectral range. Short-pulse duration (down to ~136 fs) was achieved by stretched-pulse fiber laser design (CLEO, CW1G.4 (2016)). >450 mW output power was also obtained with a fiber amplifier approach (Scientific Reports, 5, 16624 (2015)); 2D materials based pulsed visible fiber lasers have been fabricated. Praseodymium doped ZBLAN fiber was tested to generate ultrafast pulses in the visible spectral range with various transition metal dichalcogenide (such as MoS2, WS2) (Nanoscale, 8, 1066-1072 (2016)); we recently demonstrated wavelength and pulse duration tunable ultrafast fiber laser (Scientific Reports, 8, 2738 (2018)); We also demonstrated the first graphene actively modulated fiber lasers (2D Mater. 4, 025095 (2017)). Our results present a simple and viable design towards broadband, high-repetition-rate, electrically modulated ultrafast lasers for various applications, such as telecommunications and spectroscopy.

4. Development of ultrafast high-power solid-state lasers mode-locked with graphene:

The researcher and his group demonstrated a passively mode-locked solid-state laser at the optical telecommunication wavelength of 1.3 μm with an absorption enhanced graphene saturable absorber mirror (GSAM). A λ/8 thick SiO2 layer between the single-layer graphene and the high-reflection mirror was used to enhance the nonlinear absorption of the GSAM by ~400%. With the SiO2 layer, we can control the unsaturated loss and saturation fluence of the GSAM with the adjustment of electric field intensity enhancement at the graphene layer. Ultrafast pulses as short as 8.8 ps were achieved in the GSAM mode-locked solid-state laser with an average output power of 0.44 W, corresponding to the pulse energy of 4 nJ and the pulse peak power of 0.45 kW, respectively. The results indicate that it is a reliable method to control the saturable absorption parameters of two-dimensional layered materials for ultrafast solid-state lasers.