Abstract
The centrosymmetric nature of silica fibre precludes the realisation of second-order nonlinear processes in optical fibre systems. Recently, the integration of 2D materials with optical fibres has opened up a great opportunity to develop all-fibre active devices. Here, we demonstrate high-efficiency second-order nonlinear frequency conversions in an optical microfibre assisted with few-layer gallium selenide (GaSe) nanoflakes. Attributed to the strong evanescent field of the microfibre and ultrahigh second-order nonlinearity of the GaSe nanoflakes, second harmonic generation (SHG) and sum-frequency generation (SFG) are effectively achieved with only sub-milliwatt continuous-wave (CW) lasers in the wavelength range of 1500–1620 nm, covering the C and L telecom bands. The SHG intensity from the microfibre is enhanced by more than four orders of magnitude with the assistance of the GaSe nanoflakes on fibre nonlinear processes. Moreover, in the SFG process, the intensity transfer between different frequencies can be effectively manipulated by changing the wavelengths and powers of two pump lasers. The realised strong second-order nonlinearity in the GaSe-integrated microfibre might expand the applications of all-fibre devices in all-optical signal processing and new light source generation at awkward wavelengths.
Highlights
Silica optical fibres exhibit intrinsic features such as ultralow loss, a high damage threshold, and a small mode field, enabling the possibility of long-haul communications and sensing
The centrosymmetric and amorphous properties of silica fibres preclude the possibility of second-order nonlinear processes, and the majority of studies and applications are based on its third-order nonlinearity[1], such as modulation instability[2], temporal solitons[3,4], ultrashort pulse mode locking[5], supercontinuum generation[6,7], third-harmonic generations (THGs)[8,9], frequency combs[10], etc
Pumped by two CW lasers, the second harmonic generation (SHG) and sum-frequency generation (SFG) can be excited from the gallium selenide (GaSe) nanoflakes
Summary
Silica optical fibres exhibit intrinsic features such as ultralow loss, a high damage threshold, and a small mode field, enabling the possibility of long-haul communications and sensing. The centrosymmetric and amorphous properties of silica fibres preclude the possibility of second-order nonlinear processes, and the majority of studies and applications are based on its third-order nonlinearity[1], such as modulation instability[2], temporal solitons[3,4], ultrashort pulse mode locking[5], supercontinuum generation[6,7], third-harmonic generations (THGs)[8,9], frequency combs[10], etc. Limited by the centrosymmetry of silica, there is no second-order nonlinear response in optical fibres. The material defects and fibre surface may induce weak second-order nonlinearity, the typical second-order nonlinear processes require enormously high peak power, on the order of 104 watts[11,12,13,14,15,16,17,18]
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