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 ______.

31.  The process by which experience or practice results in a relatively permanent change in behavior or potential behavior is known as ______.

49.  Which of the following is true?

18.  When light from a small object is focused directly on the blind spot, the object will ______.