Laser module
A laser module, includes: an optical fiber; n laser diodes LD i (i=1, 2, . . . , n) arranged in an order corresponding to a descending order of optical path lengths LO i of optical paths respectively extending from the laser diodes LD i to the optical fiber; and n collimating lenses SL i respectively disposed in the optical paths to be distant from the respective laser diodes LD i and from the optical fiber. When a distance from each of the laser diodes LD i to a corresponding one of the collimating lenses SL i is defined as a collimation length LC i , at least one of a collimation length LC 1 and a collimation length LC n differs from a certain distance SL that is set with respect to each of the collimating lenses SL i .
1. A laser module, comprising:
an optical fiber;
n laser diodes LD i (i=1, 2, . . . , n) arranged in an order corresponding to a descending order of optical path lengths LO i of optical paths respectively extending from the laser diodes LD i to the optical fiber, wherein the laser diodes LD i , respectively emit laser beams LB i ; and
n S-axis collimating lenses SL i respectively disposed in the optical paths to be distant from the respective laser diodes LD i and from the optical fiber, wherein
each of the laser diodes LD i and each of the S-axis collimating lenses SL i constitute a part of n unit optical systems which respectively couple the laser beams LB i and a laser beam propagated through the optical fiber,
a collimation length LC i is defined as a distance from each of the laser diodes LD i to a corresponding one of the S-axis collimating lenses SL i ,
the laser module is configured to have either an odd number or an even number of the unit optical systems, such that:
in a case where a total number of the unit optical systems is the odd number, a certain distance SL is defined as a collimation length LC i of a predetermined unit optical system whose optical path length LO i is an intermediate value of optical path lengths among the unit optical systems, and
in a case where the total number is the even number, a certain distance SL is defined as a collimation length LCi of a predetermined unit optical system whose optical path length LOi is closest to an intermediate value of optical path lengths among the unit optical systems,
at least one of a collimation length LC 1 and a collimation length LC n differs from the certain distance SL, such that the largest one of incident angles β i , at which rays of a laser beam LB 1 or laser beam LB n enter the optical fiber, is reduced,
the collimation length LC 1 corresponds to a laser diode LD 1 and the collimation length LC n corresponds to a laser diode LD n ,
the certain distance SL is set such that optical paths of rays of a laser beam emitted from each of the laser diodes LD i included in the predetermined unit optical system are parallel to one another or diverged after the rays have passed through the corresponding one of the S-axis collimating lenses SL i included in the predetermined unit optical system,
an S-axis collimating lens SL 1 is disposed to satisfy SL<LC 1 ,
a laser diode LD m is defined as a laser diode that is included in a unit optical system whose optical path length LO i is longer than an optical path length of the predetermined unit optical system and is shorter than the optical path length LO 1 , and
an S-axis collimating lens SL j corresponding to a laser diode LD j (2≤j≤m, 2≤m≤n−1) is disposed to satisfy SL<LC m <LC j <LC 1 .
2. The laser module as set forth in claim 1 , wherein an S-axis collimating lens SL n is disposed to satisfy LC n <SL.
3. The laser module as set forth in claim 2 , wherein
a laser diode LD 1 is defined as a laser diode that is included in a unit optical system whose optical path length LO i is shorter than an optical path length of the predetermined unit optical system and is longer than the optical path length LO n , and
an S-axis collimating lens SL k corresponding to a laser diode LD k (1≤k≤n−1) is disposed to satisfy LCn<LCk≤LC 1 <SL.
4. The laser module as set forth in claim 1 , further comprising:
n mirrors M i that are respectively disposed in the optical paths extending from the laser diodes LD i to the optical fiber, wherein
each of the mirrors M i is (i) distant from a corresponding one of the laser diodes LD i and from the optical fiber and (ii) disposed between a corresponding one of the S-axis collimating lenses SL i and the optical fiber, and
each of the mirrors M i is disposed to bend, at a predetermined angle, a corresponding one of the optical paths extending from the laser diodes LD i to the optical fiber.
5. The laser module as set forth in claim 4 , further comprising:
a substrate that has a mounting surface S on which the laser diodes LD i the S-axis collimating lenses SL i and the mirrors M i are mounted, wherein
the mounting surface S includes n sub-mounting surfaces SS i having a step-like configuration in which heights of the sub-mounting surfaces SS i descend toward the optical fiber,
on each of the sub-mounting surfaces SS i a corresponding one of the laser diodes LD i a corresponding one of the S-axis collimating lenses SL i and a corresponding one of the mirrors M i are mounted.
6. A laser module, comprising:
an optical fiber;
n laser diodes LD i (i=1, 2, . . . , n) arranged in an order corresponding to a descending order of optical path lengths LO i of optical paths respectively extending from the laser diodes LD i to the optical fiber, wherein the laser diodes LD i respectively emit laser beams LB i ; and
n S-axis collimating lenses SL i respectively disposed in the optical paths to be distant from the respective laser diodes LD i and from the optical fiber, wherein
each of the laser diodes LD i and each of the S-axis collimating lenses SL i constitute a part of n unit optical systems which respectively couple the laser beams LB i and a laser beam propagated through the optical fiber,
a collimation length LC i is defined as a distance from each of the laser diodes LD i to a corresponding one of the S-axis collimating lenses SL i ,
the laser module is configured to have either an odd number or an even number of the unit optical systems, such that:
in a case where a total number of the unit optical systems is the odd number, a certain distance SL is defined as a collimation length LC i of a predetermined unit optical system whose optical path length LO i is an intermediate value of optical path lengths among the unit optical systems, and
in a case where the total number is the even number, a certain distance SL is defined as a collimation length LCi of a predetermined unit optical system whose optical path length LOi is closest to an intermediate value of optical path lengths among the unit optical systems,
at least one of a collimation length LC 1 and a collimation length LC n differs from the certain distance SL, such that the largest one of incident angles β i , at which rays of a laser beam LB 1 or laser beam LB n enter the optical fiber, is reduced,
the collimation length LC 1 corresponds to a laser diode LD 1 and the collimation length LC n corresponds to a laser diode LD n ,
the certain distance SL is set such that optical paths of rays of a laser beam emitted from each of the laser diodes LD i included in the predetermined unit optical system are converged after the rays have passed through the corresponding one of the S-axis collimating lenses SL i included in the predetermined unit optical system,
an S-axis collimating lens SL n is disposed to satisfy SL<LC n ,
a laser diode LD m is defined as a laser diode that is included in a unit optical system whose optical path length LO i is longer than an optical path length of the predetermined unit optical system and is shorter than the optical path length LO n , and
an S-axis collimating lens SL j corresponding to a laser diode LD j (m≤j≤n−1, 2≤m≤n−1) is disposed to satisfy SL<LC m ≤LC j <LC n .
7. The laser module as set forth in claim 6 , wherein an S-axis collimating lens SL 1 is disposed to satisfy LC 1 <SL.
8. The laser module as set forth in claim 7 , wherein
a laser diode LD 1 is defined as a laser diode that is included in a unit optical system whose optical path length LO i is longer than an optical path length of the predetermined unit optical system and is shorter than the optical path length LO 1 , and
an S-axis collimating lens SL k corresponding to a laser diode LD k (2≤k≤1) is disposed to satisfy LC 1 <LCk≤LC 1 <SL.
9. The laser module as set forth in claim 6 , further comprising:
n mirrors M i that are respectively disposed in the optical paths extending from the laser diodes LD i to the optical fiber, wherein
each of the mirrors M i is (i) distant from a corresponding one of the laser diodes LD i and from the optical fiber and (ii) disposed between a corresponding one of the S-axis collimating lenses SL i and the optical fiber, and
each of the mirrors M i is disposed to bend, at a predetermined angle, a corresponding one of the optical paths extending from the laser diodes LD i to the optical fiber.
10. The laser module as set forth in claim 9 , further comprising:
a substrate that has a mounting surface S on which the laser diodes LD i , the S-axis collimating lenses SL i , and the mirrors M i are mounted, wherein
the mounting surface S includes n sub-mounting surfaces SS i having a step-like configuration in which heights of the sub-mounting surfaces SS i descend toward the optical fiber,
on each of the sub-mounting surfaces SS i a corresponding one of the laser diodes LD i , a corresponding one of the S-axis collimating lenses SL i and a corresponding one of the mirrors M i are mounted.