A new on-chip Fourier transform spectrometer has been developed for spectrum analysis application. This spectrometer, based on a thermally tuned Mach-Zehnder Interferometer(MZI) with silicon photonics technology, is small size, light weight and low power consumption. Experimental data have acquired in the O-band domain and the processing chain to convert raw data to spectral data is described. These experimental results show that the spectral resolution is close to the one expected, but also that the signal to noise ratio is limited by various factors. We discuss the origin of those limitations and suggest solutions to circumvent them.
The optical on-chip integration technology can be used to realize spectrum analysis. Compared with the traditional bulky high performance optical spectrum analyzer which is always used in laboratory, on-chip spectrometer has the advantages of chip-scaled, low-cost and suitable for detection in complicated environment. For example, it can be utilized for detection of toxic gases such as carbon monoxide and hydrogen fluoride. In the past decade, several kinds of on-chip spectrometer, dispersive spectrometer and Fourier transform spectrometers, have been demonstrated as promising candidates for wide range of spectral application. In this paper, a digital Fourier transform spectrometer based on an interferometer whose arms consist of several optical switches which are connected by Mach-Zechnder Interferomter (MZI) with different arm lengths is demonstrated. The optical switch based on thermo-optic effect is used to select the different arms of an MZI, so the combination of optical switches and MZIs can lead to a series of different optical path difference. The proposed on-chip spectrometer is designed for Original-band (O-band) and the prospective spectral resolution is 0.3 nm. The future effort will focus on the test of the proposed spectrometer and the followed data processing including dispersive compensation and spectral reconstruction.
In the silicon photonics field, coupling occupies an important position of propagating the light from the space to the waveguide. There are two normal coupling way. The one is end-face coupling and the other one is surface coupling. And the more popular way is to use the surface coupling, which can be put on anywhere of the chip and is much easier to measure. The specific surface coupling format is grating coupler. Grating coupler can be both input and output coupler and match the fiber to propagate the light from and to the space. However, the one-dimensional grating coupler, used in the most of silicon photonic chips, has polarization selectivity and can only transfer one single mode (TE mode) in the waveguide. That means the half of the light would be wasted during coupling. In order to improve the efficiency of the coupler, two-dimensional grating coupler is a better solution. It has two orthogonal waveguides and propagate the transverse-electric (TE) mode with opposite directions. And the transverse-magnetic (TM) mode is transferred to the TE mode when the light changes the propagating direction. In this paper, the two-dimensional grating coupler is designed to match the light whose wavelength is from 1260 nm to 1290 nm. The calculation and simulation method is finitedifference time domain (FDTD). After modeling and optimizing the structure, the coupling efficiency is 26.8%.
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