An edge-type backlight module and a direct-type backlight module with a optical device are provided. The optical device comprises an array layer and a second refractive layer. The array layer has a first refractive index (n1) and contains pluralities of lenticular lens disposed on a base surface side by side. The lenticular lens contains a curving structure with a peak, a trough, a curvature radius (R), a width (P) and an altitude (H) between the peak and the trough. The trough is disposed on the base1 surface. The array layer has a first critical angle (θ1c) relative to the normal of the base surface and satisfies θ 1 ⁢ c = sin - 1 ⁡ ( 1 n 1 ) and H = R 1 + K ⁡ [ 1 - 1 - ( 1 + K ) ⁢ ( P 2 ⁢ R ) 2 ] . The conical constant (K) of the lenticular lens ranges from −2.1 to −1.5. The second refractive layer is adjacent to the array layer and has a second refractive index (n2) and a second critical angle (θ2c) relative to the normal line of the second refractive layer. The first refractive index (n1) is greater than the second refractive index (n2) and θ 2 ⁢ c = sin - 1 ⁡ ( n 2 n 1 ) is satisfied. Wherein the lenticular lens, the first critical angle (θ1c) and the second critical angle (θ2c) satisfy the equation of sin - 1 ⁡ ( 1 n 1 ) ≤ cot - 1 ⁡ ( H P / 2 )