An optical waveguide unit comprising: a plurality of reflecting units being the same in structure, each reflecting unit being any one or a combination of any two of: a metal layer, a total reflecting layer, and a dielectric reflecting layer; and a plurality of sub waveguides stacked on each other, each of two opposite sides of each sub waveguide in a stacking direction of the plurality of sub waveguides being provided with one reflecting unit, at least two of the plurality of sub waveguides having different heights in the stacking direction, and lossless region angles of the at least two sub waveguides having the different heights being different, the lossless region angle of each sub waveguide being an incidence angle of light incident on a surface of the sub waveguide, said surface being parallel to the stacking direction, the lossless region angle allowing the light to participate in imaging, wherein the plurality of sub waveguides are categorized into a plurality of categories based on their heights, heights of sub waveguides in each category are the same, and a height of a i th category satisfies: H i = W ⋅ tan arcsin sin θ i / n / 2, where θ i is a predetermined angle selected within an observation angle range, that is, the incident angle of the beam when the light just satisfies the lossless region, θ i being the lossless region angle of each sub waveguide in the i th category, n is a refractive index of the sub waveguide; W is a width of each sub waveguide in the i th category that is in a direction perpendicular to the surface of the subwaveguide, and characterized in that, heights of sub waveguides in each category of the plurality of categories are inversely proportional to the quantity of the sub waveguides in the category of the plurality of categories. a plurality of reflecting units being the same in structure, each reflecting unit being any one or a combination of any two of: a metal layer, a total reflecting layer, and a dielectric reflecting layer; and a plurality of sub waveguides stacked on each other, each of two opposite sides of each sub waveguide in a stacking direction of the plurality of sub waveguides being provided with one reflecting unit, at least two of the plurality of sub waveguides having different heights in the stacking direction, and lossless region angles of the at least two sub waveguides having the different heights being different, the lossless region angle of each sub waveguide being an incidence angle of light incident on a surface of the sub waveguide, said surface being parallel to the stacking direction, the lossless region angle allowing the light to participate in imaging, wherein the plurality of sub waveguides are categorized into a plurality of categories based on their heights, heights of sub waveguides in each category are the same, and a height of a i th category satisfies: H i = W ⋅ tan arcsin sin θ i / n / 2, where θ i is a predetermined angle selected within an observation angle range, that is, the incident angle of the beam when the light just satisfies the lossless region, θ i being the lossless region angle of each sub waveguide in the i th category, n is a refractive index of the sub waveguide; W is a width of each sub waveguide in the i th category that is in a direction perpendicular to the surface of the subwaveguide, and characterized in that, heights of sub waveguides in each category of the plurality of categories are inversely proportional to the quantity of the sub waveguides in the category of the plurality of categories.