چكيده به لاتين
Haar Transform (HT) is one of the wavelet transforms that has high efficiency and speed and can easily be realized in all-optical form by photonic integrated circuits. Furthermore, the optical implementation of HT has attracted great attention in the field of processing and compression of high-volume optical data, especially in real-time communications, due to the elimination of Optical-to-Electrical-to-Optical (OEO) conversions and thus increasing the computational speed.
In this thesis, a new building block, based on the multimode interference coupler, has been designed to implement the basic optical HT. The advantage of the proposed HT converter over previous models is that its design, for different material platforms in various wavelengths, is based on the analytical equations rather than a trial and error method using the repetitive simulations and has a high manufacturing tolerance. Three building blocks, based on the proposed design, have been introduced and simulated in the wavelength of green light (532 nm) on three different material platforms that are transparent in the visible spectrum: Di-Ureasil (Di-U), Ge:SiO2 and TriPleX, whose dimensions are 3440×30, 1509×24 and 1200×18 µm2, respectively. Using the simulation results, the coupling ratios (CR) of 99:1% for the Di-U and Ge:SiO2 platforms and 100:0% for the TriPleX platform and the excess losses (EL) of 0.26, 0.22 and 0.18 dB are obtained for three platforms, respectively. The results, while proving good performance, show that by increasing the refractive index contrast, the efficiency also improves.
A photonic chip, based on our proposed building block, has been designed and simulated on the Di-U platform with a low refractive index contrast (about 0.2%) at the wavelength of 532 nm, in which the designed circuits implement 1st and 2nd order optical HT. The CRs of ~99:1% and ~1:2:46:1:1:46:2:1% are attained for 2-point 1st order and 8-point 2nd order HT, respectively, and for a 1×8 pixels array of a grayscale sample image, an optical compression rate of 75% is achieved.
Using TriPleX technology, which has a relatively high refractive index contrast (~27%) and offers a smaller footprint, another photonic chip has been designed, fabricated and characterized at the wavelength of 532 nm. The simulation and measurement results are well matched and verify the high performance and efficiency of the designed chip. For instance, the simulated and measured CRs for 1st order HT are 100:0% and 98:2%, respectively, and for 2nd order HT are 0:0:50:0:0:50:0:0 and 2:3:40:5:4:42:3:1, respectively. In order to control the phase of the input signals when testing the chip in the laboratory, active phase modulators (PM) have been designed at the input of the circuits, which has improved the measurement results. For example, by activating PM in one of the chip circuits, a 7% improvement in the measured CR is obtained.
