Echelle Diffraction Grating And MZI Array Based On-chip Imaging Spectrometers

Spectrometer is a key tool for people to understand and change the world.It plays an important role in production and scientific research.As the spectrometers become smaller and smaller with the technical development,the integrated Planar Lightwave Circuit(PLC)device can achieve high-resolution,miniaturized and multi-channel spectrometers.The advantages of portability,high-efficiency,and CMOS compatible make it a highly potential technical routing.However,the developed PLC spectrometers mostly target at bio-chemical sensing applications with a single light source.To our knowledge,the on-chip spectrometers have not been reported on the remote sensing applications.In this paper,we address the large wavelength range,polarization insensitivity,and multi-channel input requirements of push-broom imaging spectrometers used in satellites and planes and propose the on chip spectrometers for imaging spectrometer application.Both the echelle diffraction grating(EDG)spectrometer and the on-chip Fourier transform(FT)spectrometer are studied.The spectrometer chips are designed,fabricated and tested in our laboratory.The dissertation starts with the most basic component of PLC-waveguides.First,the electromagnetic theory for two dimensional planar waveguides is introduced.Then some numerical simulation methods are implemented to simulate the effective index,single mode characteristics,polarization dependent shifts,coupling efficiency related to waveguide spacing and dispersion of the waveguides.Comparisons between silicon nanowire waveguides and large scale waveguides have been made.It's concluded that the large scale waveguides were suitable for the imaging spectrometer application.Next,the one-stigmatic method and two-stigmatic method are introduced for the design of the EDG.The relationships between the design parameters of the grating structure and the performance of the EDG are discussed.Then we investigated the polarization compensation method of EDG to design a large wavelength range EDG with polarization insensitivity for the silicon nanowire waveguide platform.It was found that there was no polarization compensation for all wavelengths at the same time,and further negated the possibility of using nanowire waveguide.For the end of this chapter,we designed a SiON EDG spectrometer ranging from 650nm to 1000nm with the large cross-section waveguides.The simulation of the EDG was carried out by the scalar diffraction theory and the mode coupling efficiency was also calculated.The technology roadmap for the EDG spectrometer in the push-broom imaging spectrometer is proposed.By comparing the same-order diffraction and cross-order diffraction methods for multi-input waveguides,it is clear that same-order diffraction method has more advantages of the better channel uniformity and the lower loss.The cross-order method cannot apply to the low diffraction order condition.Using the SOI platform with 3?m top silicon,we designed the 129 input and 129 output multi channels EDG with wavelength ranging from 1250nm to 1750nm.The influence of the key fabrication process tolerance is simulated.The development and improvement of the photolithography,deep etching of silicon and grating teeth metal deposition is discussed.After analysis and improvement of the process problems for small devices,the EDG with 65 input waveguides and 65 output channels(129 output waveguides)were fabricated and tested.Based on a brief introduction of FTs and two static push-broom modes of FT imaging spectrometers,we proposed the roadmap to use the on-chip MZI array in the static window-broom imaging spectrometer without optical switches,which has Jacquinot advantages and Fellgett advantages.At the same time,it takes advantage of the small size and high integration of optical devices.Then the principle of FTs,especially the FTs based on the waveguide MZI array is discussed.The resolution and FSR of the FTs is calculated.The spectrometer chips based on the Si and SiON platforms are designed.The spectrometer chip manufactured by the Si platform was completely tested and analyzed.For the SiON platform,however,only performs simple tests and the improvement analysis is done due to the limitation of the wafer.Further research on the integration of FTs and sensors was studied.For the temporarily modulated interferometer,the cascaded double-ring sensor and a thermo-tuned MZI based FTs sensing method was proposed in this dissertation.The low-resolution FTs can detect the envelope of the double-ring sensor without requiring the filter,stable sensitivity and large detecting range compared to the intensity-detection method for the cascaded double-ring sensor.A spatially modulated interferometer for the dual camera cell phone is proposed and preliminary feasibility study was carried out.Finally,the dissertation is summarized and further research is planned.