Backlight module, viewing mode switching method thereof, and display device including the backlight module

A backlight module, comprising:

• an upper backlight unit, comprising an upper light source and an upper light guide plate configured to receive light from the upper light source, the upper light guide plate being substantially rectangular and having at least one first side edge and at least one second side edge, the first side edge being a longer side and substantially parallel to a first axis, and the second side edge being a shorter side and substantially parallel to a second axis, wherein the first axis is non-parallel to the second axis;
• and
• a lower backlight unit, located beneath the upper backlight unit;
• wherein the upper light source is positioned adjacent to the at least one second side edge of the upper light guide plate and extends along the second axis, such that light emitted from the upper light source propagates within the upper light guide plate along the first axis to generate an asymmetric light field;
• wherein the backlight module further comprises two prism sheets disposed between the upper backlight unit and the lower backlight unit, wherein each of the prism sheets has a plurality of stripe microstructures facing the upper backlight unit, and wherein extension directions of the stripe microstructures of the two prism sheets are perpendicular to each other.