Two-lens optical system, beam combining module, projector, and method for assembling two-lens optical system

1. A two-lens optical system, comprising:

a first lens for use in collimation adjustment, the first lens being configured to move along only an optical axis of light emitted from a light source; and

a second lens for use in beam steering, the second lens being configured to move along only two axes perpendicular to the optical axis.

2. The two-lens optical system according to claim 1 , wherein

the light source, the first lens, and the second lens are arranged in this order along the optical axis.

3. The two-lens optical system according to claim 2 , wherein

(2/√3) f≤f 2 ≤3 f,

where f=(f 1 f 2 )/(f 1 +f 2 −s), where f is an effective focal length of the two-lens optical system;

f 1 is a focal length of the first lens;

f 2 is a focal length of the second lens; and

s is a separation between a back principal plane of the first lens and a front principal plane of the second lens.

4. The two-lens optical system according to claim 1 , wherein

the light source, the second lens, and the first lens are arranged in this order along the optical axis.

5. The two-lens optical system according to claim 4 , wherein

(3/2) f≤f 1 ≤2 f,

where f=(f 1 f 2 )/(f 1 +f 2 −s), where f is an effective focal length of the two-lens optical system;

f 1 is a focal length of the first lens;

f 2 is a focal length of the second lens; and

s is a separation between a back principal plane of the first lens and a front principal plane of the second lens.

6. The two-lens optical system according to claim 1 , further comprising:

a first support base on which the first lens is placed, the first support base being configured to constrain movement of the first lens; and

a second support base on which the second lens is placed, the second support base being configured to constrain movement of the second lens.

7. The two-lens optical system according to claim 1 , further comprising:

a first support base on which the first lens is placed, the first support base being configured to move the first lens; and

a second support base on which the second lens is placed, the second support base being configured to move the second lens.

8. A beam combining module, comprising:

m optical devices each including (i) a light source, (ii) a two-lens optical system according to claim 1 , and (iii) a mirror configured to reflect light emitted from the two-lens optical system, where m is an integer of 2 or more,

a first one of the optical devices including a reflective mirror as the mirror,

second through m-th ones of the optical devices each including a dichroic mirror as the mirror,

the beam combining module being configured such that light reflected on the mirror included in an n-th one of the optical devices passes through the mirror included in each of (n+1)th through m-th ones of the optical devices, where n is an integer of 1 or more, and 1≤n≤m−1.

9. The beam combining module according to claim 8 , wherein

the m optical devices further include m respective second lenses; and

the beam combining module further comprises a single second support base.

10. The beam combining module according to claim 8 , wherein

the respective light sources included in the m optical devices are placed on an identical plane.

11. A projector, comprising:

a beam combining module according to claim 8 .

12. A method for assembling a two-lens optical system,

the two-lens optical system including:

a first lens;

a first support base configured to constrain movement of the first lens in such a manner that the first lens is movable along only an optical axis of light emitted from a light source;

a second lens; and

a second support base configured to constrain movement of the second lens in such a manner that the second lens is movable along only two axes perpendicular to the optical axis,

the method comprising the steps of:

(a) moving the first lens along the optical axis for collimation adjustment of the two-lens optical system;

(b) after the step (a), moving the second lens along at least one of the two axes for beam steering of the two-lens optical system;

(c) after the step (a) or (b), fixing the first lens to the first support base; and

(d) after the step (b), fixing the second lens to the second support base.

13. A method for assembling a two-lens optical system,

the two-lens optical system including:

a first support base configured to move along only an optical axis of light emitted from a light source,

a first lens configured to move together with the first support base;

a second support base configured to move along only two axes perpendicular to the optical axis; and

a second lens configured to move together with the second support base,

the method comprising the steps of:

(a) moving the first support base for collimation adjustment of the two-lens optical system;

(b) after the step (a), moving the second support base for beam steering of the two-lens optical system;

(c) after the step (a) or (b), fixing the first lens to the first support base; and

(d) after the step (b), fixing the second lens to the second support base.