Laser projecting device and light-combining lens

A laser projecting device, comprising:

• a light-combining lens formed as a one-piece structure and having a difference of refractive indexes therein that is less than 0.2, wherein the light-combining lens includes:
• a front portion including:
• a front collimation surface defining a front collimation path inside of the front portion;
• and a front reflection surface located at the front collimation path, wherein the front collimation path and the front reflection surface have an acute angle therebetween and jointly define a front reflection path;
• a rear portion including:
• a rear collimation surface defining a rear collimation path inside of the rear portion;
• a rear reflection surface located at the rear collimation path, wherein the rear collimation path and the rear reflection surface have an acute angle therebetween and jointly define a rear reflection path, and wherein the rear reflection surface allows light to pass therethrough from one side of the rear reflection surface that is opposite to the rear reflection path;
• and a light emergent surface arranged on a surface of the rear portion away from the front reflection surface;
• and an expanding portion disposed between the front portion and the rear portion along an arrangement direction, wherein the expanding portion includes:
• an expanding collimation surface defining an expanding collimation path inside of the expanding portion;
• and an expanding reflection surface located at the expanding collimation path, wherein the expanding collimation path and the expanding reflection surface have an acute angle therebetween and jointly define an expanding reflection path, and wherein the expanding reflection surface allows light to pass therethrough from one side of the expanding reflection surface that is opposite to the expanding reflection path;
• wherein the front reflection path, the expanding reflection path, and the rear reflection path are overlapped with each other in the light-combining lens so as to jointly define a light-combining path that extends outside of the light-combining lens from the light emergent surface;
• and a laser module corresponding in position to the light-combining lens and including:
• a substrate;
• and three laser emitters mounted on the substrate and respectively facing toward the front collimation surface, the rear collimation surface, and the expanding collimation surface, wherein the three laser emitters are configured to respectively emit lights traveling along the front collimation path, the expanding collimation path, the rear collimation path, and the light-combining path;
• wherein the light-combining lens and each of the three laser emitters have a separation distance therebetween, the separation distances corresponding to the three laser emitters are different from each other, and any one of the separation distances is smaller than a focal length of any one of the front collimation surface, the rear collimation surface, and the expanding collimation surface;
• wherein the front reflection surface, the expanding reflection surface, and the rear reflection surface are arranged in one row along the arrangement direction and are parallel to each other;
• wherein the front and the expanding portions are connected at the expanding reflection surface with an optical adhesive layer therebetween, and the rear and the expanding portions are connected at the rear reflection surface with another optical adhesive layer therebetween;
• and wherein the front portion, the rear portion, and the expanding portion have a same refractive index that is defined as a first refractive index, and each of the two optical adhesive layers has a second refractive index, and wherein a difference between the first refractive index and the second refractive index is less than 0.2 and greater than zero.