| Summary: | 碩士 === 國立臺灣科技大學 === 電子工程系 === 106 === We proposed a scheme to improve the transmission performance by using a diffraction grating filter for an optical transmission system with directly modulated lasers (DML) of insufficient bandwidth. The diffraction grating filter is used as a reshaping filter to convert the inherently frequency modulation (FM) associated with the amplitude modulation (AM) signals and then increase the high-frequency responses. The use of optical reshaping filter can provide three merits: extinction ratio (ER) improvement, extension of transmission distance of DML, and improvement of the frequency response of transmission system.
This work investigates the feasibility of combining a directly modulated laser of insufficient frequency response with optical reshaping filter to transmit high-speed signals. The investigation is conducted for the wavelength of 1.3 μm and 1.5 μm. An commercial software is used to simulate the DML-based high-speed optical transmission system, and then observe the performance enhancement after adding an optical filter, which acts as an optical equalizer from the FM-to-AM conversion. The performance enhancement is also verified by experimental measurements. We verify that the effect of placing the optical filter at the transmit end or the receive end leads to the same performance enhancement.
We realized the use of a directly modulated laser with 14-GHz bandwidth and a diffraction grating optical equalization filter to transmit 32 Gb/s NRZ and 28 Gbaud/s PAM-4 signals. The eye diagram and bit error rate are improved by using the optical equalizer. The increase in 3dB bandwidth by about 3GHz is demonstrated.
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