Display apparatus and method for controlling the same

A method for controlling a display apparatus, wherein the display apparatus comprises a liquid crystal lens with a plurality of adjustable focal lengths, and the liquid crystal lens comprises a first transparent electrode layer and a second transparent electrode layer which are arranged in a stacked manner and a liquid crystal layer between the first transparent electrode layer and the second transparent electrode layer, wherein the second transparent electrode layer comprises a first electrode sub-layer and a second electrode sub-layer which are arranged in a stacked manner, the first electrode sub-layer comprises N concentric first annular electrodes, and the second electrode sub-layer comprises N concentric second annular electrodes, wherein N is a positive integer, and the first annular electrodes and the second annular electrodes are alternately spaced in a direction parallel with the first transparent electrode layer;

• wherein the method comprises:
• power on the first transparent electrode layer;
• and
• dividing the 2N annular electrodes layer into x electrode groups, wherein each electrode group comprises m adjacent annular electrodes and x=int (2N/m);
• numbering the x electrode groups in sequence in a radial direction starting from a center of the annular electrode, and powering off the odd-numbered electrode groups and powering on the even-numbered electrodes groups, whereby an equivalent focal length of the liquid crystal lens with a plurality of adjustable focal lengths is:
• fm=m*f1,
• wherein f1 is a minimum focal length of the liquid crystal lens and m is a positive integer smaller than N,
• wherein a first non-electrode region is formed between each two adjacent first annular electrodes, a second non-electrode region is formed between each two adjacent second annular electrodes, and
• orthographic projections of the first annular electrodes on a first transparent substrate coincide with orthographic projections of the second non-electrode regions on the first transparent substrate,
• wherein the N concentric first annular electrodes, the N concentric second annular electrodes and the liquid crystal layer form N equivalent phase grating units, and each equivalent phase grating unit comprises two steps, wherein a first step of the two steps corresponds to the first annular electrode and a second step of the two steps corresponds to the second annular electrode;
• an outer diameter of a first step of a jth equivalent phase grating unit is:
• r
• j
• ,
• 1
• =
• (
• 2
• ⁢
• j
• -
• 1
• )
• ⁢
• f
• 1
• ′
• ⁢
• λ
• n
• 2
• ⁢
• (
• 1
• -
• (
• 2
• ⁢
• j
• -
• 1
• )
• 4
• ⁢
• n
• 2
• ⁢
• f
• 1
• ′
• )
• 1
• /
• 2
• ;
• an outer diameter of a second step of the jth equivalent phase grating unit is:
• r
• j
• ,
• 2
• =
• 2
• ⁢
• jf
• 1
• ′
• ⁢
• λ
• n
• 2
• ⁢
• (
• 1
• -
• j
• ⁢
• ⁢
• λ
• 2
• ⁢
• n
• 2
• ⁢
• f
• 1
• ′
• )
• 1
• /
• 2
• ;
• wherein f1′ is a focal length of the liquid crystal lens, λ is a wavelength of incident light, n2 is a refractive index of an external medium in contact with a surface of the liquid crystal lens, j is a serial number of an equivalent phase grating unit numbered in such a manner as to increase in a radial direction starting from a center of the equivalent phase grating units;
• a width of a jth first annular electrode is:
• dj,1=rj,1−rj-1,2;
• and
• a width of a jth second annular electrode is:
• dj,2=rj,2−rj,1.

A display apparatus, comprising:

• a light guide module comprising a light incident region and a light emergent region;
• a display module, arranged corresponding to the light incident region of the light guide module and configured to display images;
• and
• a liquid crystal lens with a plurality of adjustable focal lengths, arranged between the display module and the light guide module and corresponding to the light incident region of the light guide module, and configured to form virtual images with different depths of field for the images displayed on the display module,
• wherein the light guide module is configured to guide light exited from the liquid crystal lens to propagate in a direction from the light incident region to the light emergent region within the light guide module,
• wherein the light guide module comprises:
• a light guide plate;
• a light guide-in grating, arranged corresponding to the light incident region and at a side of the light guide plate facing away from the liquid crystal lens, and configured to guide light from the liquid crystal lens into the light guide plate;
• and
• a light guide-out grating, arranged corresponding to the light emergent region and at a same side with the light guide-in grating, and configured to guide the light in the light guide plate to an eye of a user,
• wherein a maximum half angle of view of the display apparatus is:
• ω
• ⁡
• (
• d
• )
• max
• =
• arcsin
• ⁡
• (
• n
• -
• 1
• 2
• )
• ,
• wherein ω(d)max is the maximum half angle of view, n is a refractive index of the light guide plate, and a grating constant corresponding to the maximum half angle of view is
• d
• =
• 2
• ⁢
• λ
• n
• +
• 1
• .