Filter module

1. A filter module including a first optical fiber collimator, a second optical fiber collimator, and a filter located between the first and second optical fiber collimators:

wherein the first optical fiber collimator includes a first optical fiber, a first optical fiber chip for holding the first optical fiber, and a first lens;

wherein the second optical fiber collimator includes a second optical fiber, a second optical fiber chip for holding the second optical fiber, and a second lens;

wherein the filter is located between and coaxial with the first and second lenses, and the filter, the first lens, and the second lens form a center piece of the filter module, in which the center piece holds the optical axes of facing lenses and the filter such that the optical axes are aligned, the facing lenses being the first and the second lenses, and the center piece being integrally formed of the filter and the facing lenses;

wherein each of the first and second optical fiber chips includes a capillary for holding the corresponding optical fiber and a cylindrical capillary holder for holding the capillary, and wherein each capillary holder is adhered to the corresponding lens with adhesive; and

wherein each capillary holder is provide with a recess, the recess being located between the capillary holder and the corresponding capillary, and the recess facing the corresponding lens.

2. The filter module according to claim 1 , wherein the first and second lenses are gradient index rod lenses.

3. The filter module according to claim 2 , wherein the filter is formed on the end face of one of the first and second lenses.

4. The filter module according to claim 2 , wherein the first and second lenses each have an optical axis and a slant end, the slant end being inclined relative to the optical axis by a predetermined angle, and wherein each of the first and second lenses is provided with a mark used for matching the phases of the slant ends.

5. The filter module according to claim 4 , wherein each of the first and second optical fiber chips is provided with a mark used for aligning the position relative to the corresponding lens.

6. The filter module according to claim 1 , wherein the first and second optical fiber chips are fixed to the center piece in a state where the positions of the first and second optical fiber chips are adjusted relative to the center piece.

7. The filter module according to claim 1 , wherein the first optical fiber comprises a single optical fiber, and wherein the second optical fiber comprises two optical fibers.

8. The filter module according to claim 7 , wherein the ends of the first and second optical fibers are ground to have the same inclined angles as those of the slant ends of the first and second lenses.

9. The filter module according to claim 1 , wherein the center piece includes a lens holder that is a cylindrical tube for holding the filter and the facing lenses.

10. The filter module according to claim 1 , further comprising an outer tube for accommodating the first and second optical fiber collimators in a sealed state.

11. The filter module according to claim 10 , wherein the lens holder is fitted to and fixed to the outer tube.

12. The filter module according to claim 1 , wherein the first and second lenses are gradient index rod lenses each having a metal-plated outer circumference, wherein the center piece includes a cylindrical lens holder having a plated inner circumference, and wherein the first and second lenses are inserted into and soldered to the lens holder.

13. The filter module according to claim 12 , wherein the center piece includes an outer tube, the outer tube being fitted to and fixed to the outer circumference of the lens holder.

14. A filter module including a first optical fiber collimator, a second optical fiber collimator, and a filter located between the first and second optical fiber collimators:

wherein the first optical fiber collimator includes a first optical fiber, a first optical fiber chip for holding the first optical fiber, and a first rod lens;

wherein the second optical fiber collimator includes a second optical fiber, a second optical fiber chip for holding the second optical fiber, and a second rod lens;

wherein the filter is located between and coaxial with the first and second rod lenses and is fixed to the second rod lens, and the filter, the first rod lens, and the second rod lens form a center piece of the filter module, in which the center piece holds the optical axes of facing lenses and the filter such that the optical axes are aligned, the facing lenses being the first and the second lenses, and the center piece being integrally formed of the filter and the facing lenses; and the first and second rod lenses each have an optical axis and a slant end, the slant end being inclined relative to the optical axis by a predetermined angle, and each of the first and second rod lenses being provided with a mark used for matching the phases of the slant ends; and the first optical fiber comprises a single optical fiber, and the second optical fiber comprises two optical fibers;

wherein each of the first and second optical fiber chips includes a capillary for holding the corresponding optical fiber and a cylindrical capillary holder for holding the capillary, and wherein each capillary holder is adhered to the corresponding lens with adhesive; and

wherein each capillary holder is provide with a recess, the recess being located between the capillary holder and the corresponding capillary, and the recess facing the slant end of the corresponding lens.