Research On On-chip Integrated Optomechanical Devices

With the coming of the information age,the global data traffic has grown explosively.At the same time,optical communication and interconnect technologies have also made great progress.However,traditional discrete optical devices have been unable to meet the development demands of small size,low power consumption,high speed and low cost.Photonic integrated circuits have emerged as the times require.For the conventional integrated photonic devices,their structures are difficult to change once they are fabricated,which is not conducive to practical applications.Recently,the optical gradient force(OGF)in integrated photonic devices,which originates from the interaction between optically excited dipoles in a waveguide and the evanescent field of its adjacent waveguide,gets interesting attention.The OGF can cause the mechanical deformation of submicrometerscale waveguides and changes the effective refractive index of guided modes,which is called mechanical Kerr effect,and it could be up to several orders of magnitude larger than the conventional Kerr effect.Therefore,the OGF provides an extremely efficient tuning method for integrated photonic devices.In addition,integrated photonic devices have the advantages of small size,small mass and high energy density,so they provide an excellent platform for optomechanics.In this thesis,the on-chip integrated optomechanical devices were investigated.The research contents include: all-optical controllable microring resonator and non-reciprocal light transmission based on mechanical Kerr effect,electromagnetically induced transparency with a single optomechanical microring resonator,discrete optics in optomechanical waveguide arrays.The thesis is divided into following several sections:(1)A silicon optomechanical microring resonator was fabricated.Due to the strong mechanical Kerr effect induced by the optical gradient force,a tuning efficiency of 80GHz/m W and a wavelength tuning range of 2.56 nm were realized which was 61% of the free spectral range.By controlling the pump power,the device indicated three working regions,which were the cutoff region,amplified region and saturate region,respectively,and the all-optical control of the signal was realized.By analyzing the dynamic responses of the optomechanical microring resonator,it was proved that the device was driven by the optical gradient force,rather than other nonlinear effects.(2)On-chip,all-passive,low-power-consumption,and low-insertion-loss nonreciprocal light transmission was achieved by using the mechanical Kerr effect based on an optomechanical microring combined with a lossy component.A maximum non-reciprocal transmission ratio of 23 d B with an operating power of 251 μW and an insertion loss of 2.3d B was realized based on the strong mechanical Kerr effect.A scheme for realizing reconfigurable non-reciprocal devices was proposed,which can significantly broaden the non-reciprocal transmission bandwidth and the non-reciprocal power range of the device.Besides,detailed theoretical analysis and contrast experiments were presented,which demonstrated that the non-reciprocal transmission was caused by the mechanical Kerr effect and the thermal effect was negligible.(3)An all-optical realization scheme of electromagnetically induced transparency in a single optomechanical microring resonator was proposed and demonstrated.In order to reduce the size of the device,multimode waveguide bends based on modified Euler curves were designed.Due to the strong mechanical Kerr effect and well-designed microring resonator,two different order modes with a resonant frequency separation of 292 GHz(2.35nm)could be tuned into resonance when the control power was about 4.3 μW,and the electromagnetically induced transparency spectrum was achieved.(4)A subwavelength optomechanical waveguide array was designed and the propagation properties of light in this array were studied.Due to the strong mechanical Kerr effect,the optical self-focusing and self-defocusing phenomena could be realized in the array with the milliwatt-level incident powers and micrometer-level lengths.Compared with the conventional nonlinear waveguide arrays,the required incident powers and lengths of the waveguides were decreased by five orders of magnitude and one order of magnitude,respectively.Furthermore,it was proved that the optomechanical waveguide array could be used as a splitting-ratio-tunable beam splitter or an all-optical AND logic gate.