| Summary: | 碩士 === 國立清華大學 === 光電工程研究所 === 95 === We numerically simulated the characteristics of linearly chirped signal generation utilizing optically injected semiconductor laser. The optically injected laser system consists of two lasers with similar intrinsic parameters and wavelength. The slave laser is injected by the master laser. By tuning the operating parameters, the optically injected semiconductor laser can be operated in different instable regions. There are stable-locking, chaotic oscillation (CO), period-one oscillation (P1), period-two oscillation (P2) and high order oscillation regions. Four schemes will be used to generate linearly chirped signal: (1) direct current modulation on slave and on (2) master laser, respectively, while the slave laser is operated in stable-locking region. (3) The third scheme is modulating the injection strength of the slave laser directly while which is operated in the P1 region. (4) The last one is modulating the injection strength by current modulation on the master laser while the optically injected slave laser is operated in the P1 region. The relation between modulation index, modulation period, bandwidth and chirp rate will be studied. We also show the dependence of linearity on chirp rate. We can generate a linearly chirped signal with bandwidth more than 30 GHz and with high linearity when the laser is operated in stable-locking region. On the other hand, a complicate electronics free method can used to generate signal in RF range by utilizing period-one oscillation region.
The signal used in the intensity modulation continuous wave (IMCW) laser ranging system is a linearly chirped signal. The signal will be transmitted toward the target and the reflected signal will be collected by a photo-diode. The frequency difference between the two signals caused by the delay time of reflected signal can be used to estimate the range of the target. We investigate the effect of linearity and bandwidth on the linewidth that determinates the resolution of the ranging system. We show the high linearity of the linearly chirped signal generated by laser operating in and a 1.5 m resolution is achieved.
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