Frequency stabilization of a semiconductor diode laser with the Pound-Drever-Hall technique (see, e.g., Drever et al. 1983). In Stage I, the linewidth of the laser is passively stabilized to ~10 MHz level by keeping the temperature and diode current stable. The grating feedback in Stage II reduces the linewidth to a few MHz. In Stage III, an active feedback mechanism reduces the linewidth further to about 100 kHz range by locking the laser frequency to the FPI cavity or the Rb-cell. Some other components, e.g., Faraday isolator and polarization optics, are not shown in the layout. LD: laser diode; EOM: electro-optic modulator; RF: radio frequency; PD: photodetector; LO: local oscillator.