Integrated Photonics Devices For Light Manipulation

The invention of the Internet has brought human into the information age,which requires faster transmission and larger capacity.At this historic moment,integrated optics has emerged,replacing electrons with photons and replacing traditional discrete optical devices with integrated optical devices,which has many advantages such as compact size,low power consumption,large bandwidth,good stability and low cost.Now,it plays an increasingly important role in the fields of optical interconnection,optical sensing and optical computing.As a key element for separating and combining optical signals in integrated optics,the optical power splitter has been widely used in many photonic integrated circuits.And many works have been done on it,however,there are still some problems,such as wavelength sensitivity,polarization sensitivity,large size and only can work for the fundamental mode.In this thesis,for different application,we studied broadband power splitter and multimode power splitter,respectively.In addition,currently,a single wavelength division multiplexing technology can not satisfy people's need for larger bandwidth.To further expand the transmission capacity,multiple multiplexing technologies,such as mode multiplexing and polarization multiplexing,should be combined.For the mode multiplexing technology,mode conversion and coupling are the research hotspots.Therefore,in this thesis,we studied two kinds of mode(de)multiplexers,which can be used for mode division multiplexing transmission system based on few-mode fiber in 850 nm and 1550 nm wavelength band,respectively.Firstly,we analyzed the mode characteristic in the planar optical waveguide,which were derived by the waveguide theory.Next,we introduced some numerical algorithms commonly used in practical optical device design.Besides,the fabrication process and testing methods were also introduced.In one word,we described the planar optical waveguide technology from four aspects:theory,simulation,fabrication and testing.Secondly,in order to achieve a compact broadband optical power splitter,we proposed and demonstrated a 2×2 3 dB power splitter using a subwavelength-grating-assisted asymmetric directional coupler.The subwavelength-grating is used to engineer the refractive index and the dispersion of the coupler,so that an ultra-compact and large-bandwidth optical power splitter can be achieved.For the designed device,the length of the coupling region is only 5.25?m,while the operating bandwidth can reach 300 nm and the power splitting ratio is better than 3±0.4 dB.The experimental results are consistent with the simulation results.Then,in order to achieve a multimode power splitter,we proposed a multimode interference coupler with a shallowly-etched multimode region.By engineering the refractive index contrast of the coupler,the phase error of higher-order modes can be reduced,so that a perfect imaging can be achieved for multiple input modes.For the designed device,it can support two input modes,TE0 and TE1 modes.For the TE0 input mode,the excess losses and the imbalances are respectively less than 0.4 dB and 0.12 dB in the wavelength range of 1.5-1.6?m,while for the TE1 input mode,the excess losses and the imbalances are respectively less than 0.5 dB and 0.2 dB in the wavelength range of 1.53-1.58?m.Thirdly,in order to abtain a mode(de)multiplexer for two-mode transmission at 850 nm in the standard single mode fiber,we propsed a mode(de)multiplexer based on dual-core adiabatic taper using SU-8 ridge optical waveguides,so that LP01 and LP11a modes can be(de)multiplexed.For the designed device,the excess losses and the inter-mode crosstalk are respectively less than 0.66 dB and-31 dB in the wavelength range of 0.75-0.95?m.Then,in order to abtain a(de)multiplexer for mode division multiplexing transmission with dual-polarization at 1550 nm in the few mode fiber,we proposed a(de)multiplexer based on monolithic integration,so that six modes of LP01,LP11a and LP11b with dual polarizations can be(de)multiplexed,which greatly expands the transmission capacity.For the designed device,it can not only achieve a high coupling efficiency with the few-mode fiber,but also be easy to integrate with other optical devices.It provides a practical solution for future large-capacity optical communication networks.Finally,we made our conclusions to the main work and outlook for the future researches.