A laser beam may pass through an optical waveguide at any incident angles as long as the incident angle is smaller than the maximum acceptance angle.

A laser system has a single longitudinal mode operation when homogeneous broadening dominates in its gain medium.

The refractive index of the cladding of an optical fiber is higher than that of the core, so that light can be confined and propagate along the core.

When the wavelength of a laser is smaller than the single-mode cut-off wavelength of a fiber, the propagation of the laser in the fiber may become multimode.

To select a material as a laser gain medium, a two-level system is preferred, because it can be easily obtained.

A light going through an optical waveguide can be viewed as that field patterns are formed across the waveguide due to standing waves and the field patterns propagate alone the waveguide.

45.  It is extremely rare for people to recall events that occurred before the age of ______.

A laser may have different transvers modes.

38.  What we are thinking of at any given moment, or what we commonly know as “consciousness,” is ______.

23.  Our awareness of various mental processes such as making decisions, daydreaming, reflecting, and concentrating is called ______.