| Summary: | 博士 === 臺灣大學 === 光電工程學研究所 === 95 === Abstract
Multimode interference (MMI) structures were widely studied previously. The functions of interest were mainly for power splitting due to some disadvantages. However, the MMI structures have many advantages which are not replaceable. Therefore, it is important to improve the disadvantages for practical applications.
The first disadvantage of MMI device is wavelength sensitive, which leads to restricted applications. To reduce the wavelength insensitivity in optical network applications, the demand of light source with a specific wavelength is needed, especially for power splitters. For this reason, a wideband criterion for MMI splitter is proposed. The basic principle is based on reducing the interference length difference and making it shorter than the spot size for constructive mode interference. Simulation results show the spectra of proposed MMI splitter is wide enough (1.26-1.61um) to cover the fiber communication band and the size of the splitter is more compact than that of the conventional MMI or Y-branch splitter.
MMI devices were usually used for all-equal or all-unequal power splitting. When the device is used for different varieties of power splitting, interconnection of the devices make the fabrication cost to high to be realizable. These limitations are the second disadvantage of MMI device.
In this work, MMI couplers with a width of arbitrary-exponent binomial function are proposed. The proposed structure includes the conventional, butterfly, and parabolic structure such that the proposed MMI device can be used for equal and unequal power splitting. With a proper choice of the exponent of a binomial function, several equal and unequal optical powers splitting ratio can be obtained. For comparison, the optical power splitting ratios, total transmission, and coupler length of the proposed MMI couplers are discussed.
Finally, proposed MMI structures and arrayed waveguide grating (AWG) devices are combined to demonstrate the application in the improvement of cyclic arrayed waveguide grating devices. The basic idea is that each access waveguide of the proposed cyclic AWG consists of an MMI region and a taper waveguide. Simulation results show that the 1dB-bandwidth of the proposed device can be as wide as one half of the channel spacing and the corresponding nonuniformity is smaller than 1dB. Therefore, flat-top passband and uniform spectral response can be obtained.
The improvement of the performance of MMI structure makes it of great interest for both academic studies and practical applications.
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