Light-emitting module and methods for optically aligning and assembling the same

1. An optical alignment method for a light-emitting module that includes a housing unit, a light-emitting unit disposed in the housing unit, and a lens unit, said optical alignment method comprising:

(a) through image-capturing techniques, finding a light-emitting point of the light-emitting unit and a predetermined reference point, and determining a total optical path length between the light-emitting point and an imaging plane having a predetermined distance relation with the predetermined reference point;

(b) finding an imaginary first center line located at a position that divides the total optical path length into equal half distances;

(c) through image-capturing techniques, finding first and second edges of the lens unit that are opposite to each other in a direction of an optical path of light emitted by the light-emitting unit from the light-emitting point to the imaging plane, and determining a lens length between the first and second edges;

(d) finding an imaginary second center line located at a position that divides the lens length into equal half distances; and

(e) assembling the lens unit to the housing unit in such a manner that the imaginary second center line coincides with the imaginary first center line.

2. The optical alignment method of claim 1 , wherein, in step (a) and step (c), a charge-coupled device is used to perform image capturing.

3. The optical alignment method of claim 1 , wherein, in step (a), the predetermined reference point is provided on the housing unit and has a predetermined spacing from the imaging plane along the direction of the optical path, the total optical path length between the light-emitting point and the imaging plane being determined by adding the predetermined spacing to a distance between the light-emitting point and the predetermined reference point.

4. The optical alignment method of claim 3 , wherein two of the predetermined reference points are located respectively on opposite ends of the housing unit, the imaginary first center line intersecting the opposite ends of the housing unit.

5. The optical alignment method of claim 1 , wherein the imaginary second center line passes through opposite ends of the lens unit between the first and second edges.

6. An assembly method for a light-emitting module that includes

a light-emitting unit having a light-emitting point that emits light along an optical path,

a housing unit formed with a slot, and

a lens unit having opposite first and second edges,

said assembly method comprising:

(a) mounting the light-emitting unit in the housing unit such that the slot is on a plane parallel to the optical path;

(b) through image-capturing techniques and via the slot in the housing unit, finding the light-emitting point and a predetermined reference point, and determining a total optical path length between the light-emitting point and an imaging plane having a predetermined distance relation with the predetermined reference point;

(c) finding an imaginary first center line located at a position that divides the total optical path length into equal half distances;

(d) through image-capturing techniques, finding the first edge and the second edge of the lens unit, and determining a lens length between the first and second edges;

(e) finding an imaginary second center line located at a position that divides the lens length into equal half distances; and

(f) assembling the lens unit to the housing unit via the slot in such a manner that the optical path passes through the lens unit and that the imaginary second center line coincides with the imaginary first center line.

7. The assembly method of claim 6 , further comprising fixing the lens unit to the housing unit after step (f) using an adhesive.

8. The assembly method of claim 6 , wherein, in step (f), a pick-and-place machine is used to control placement of the lens unit in the housing unit.