Demultiplexer based on integrated concave grating

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Sun, Zhijian
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With the use of Wavelength Division Multiplexing (WDM) technology, the information capacity of a fiber optic communication system is greatly increased. The key components in WDM systems are wavelength multiplexers and demultiplexers. Integrated concave diffraction gratings may serve as WDM demultiplexers. The typical channel spacing of a demultiplexer based on integrated concave gratings reported by other groups is around 1 nm. In this thesis, we demonstrated an integrated concave grating demultiplexer with 60 output channels and 0.144 nm channel spacing. The fiber-to-fiber insertion loss for the demultiplexer is from 18.6 dB for the longest wavelength channel to 29.8 dB for the shortest wavelength channel. Another integrated concave grating demultiplexer reported in this thesis has 120 output channels and 0.29 nm channel spacing. The fiber-to-fiber loss for this demultiplexer is between 20 dB and 30 dB for most channels. Simulation results shows that the high insertion loss and the loss difference from channel to channel are predominantly due to waveguide absorption and increase dramatically for wavelengths below 1539 nm. Demultiplexers with 256 output channels and 0.2 nm channel spacing; 64 output channels and 0.3 nm channel spacing; 64 output channels and 0.6 nm channel spacing are also addressed in this thesis. The polarization dependent losses for all demultiplexers are around 0.45 dB. The birefringence is typically 1.2 nm for our demultiplexers. A layer structure used to control the birefringence is studied. In the future WDM networks, an integrated multiwavelength laser is required. Such a laser can be formed by integrating a concave diffraction grating with semiconductor amplifiers. Concave gratings with multiple passbands make it difficult to control the absolute lasing wavelength. A chirped concave gratings only has one dominant passband, therefore is a good candidate for multiwavelength laser. Concave gratings with several chirping schemes are investigated in this thesis. The extinction ratio between the dominant passband and other passbands can be as high as 20.9 dB. Demultiplexers based on chirped concave gratings are designed.