阅读说明：本技术 光纤耦合二极管激光模块及其组装方法 (Fiber-coupled diode laser module and assembling method thereof ) 是由 瓦迪姆·丘亚诺夫 德米特里·米弗塔库提诺夫 于 2020-03-26 设计创作，主要内容包括：尾纤型二极管激光器模块被配置为具有容纳多个多模芯片的壳体,该多模芯片被布置成至少一行并且在一个方向上输出各自的光束。每个输出光束在上游快轴准直器和下游慢轴准直器中准直,这些准直器在一个方向上彼此间隔开。准直的输出光束入射在各自的反射镜上,该反射镜使入射的输出光束在横向于所述一个方向的另一方向上重新定向。通过进一步迭代传播,输出光束构成在慢轴上发散的合成光束,同时向至少一个透镜传播,该透镜将合成光束沿慢轴聚焦在其焦平面中。输出光纤安装到壳体上,使得其芯端与聚焦合成光束的最小横截面共面,该最小横截面距焦平面下游间隔开预定距离。(The pigtailed diode laser module is configured to have a housing accommodating a plurality of multimode chips arranged in at least one row and outputting respective light beams in one direction. Each output beam is collimated in an upstream fast axis collimator and a downstream slow axis collimator, which are spaced apart from each other in one direction. The collimated output beams are incident on respective mirrors which redirect the incident output beams in another direction transverse to the one direction. By further iterative propagation, the output beam constitutes a composite beam diverging in the slow axis, while propagating towards at least one lens which focuses the composite beam in its focal plane along the slow axis. The output fiber is mounted to the housing such that its core end is coplanar with a minimum cross-section of the focused composite beam that is spaced downstream from the focal plane by a predetermined distance.)

1. A pigtailed diode laser module comprising:

a housing, the housing containing:

spaced multimode MM chips outputting respective parallel beams along paths;

an optical system configured to collimate the parallel output beams in respective slow axes, wherein the collimated beams define a composite beam that diverges along the path;

at least one focusing lens focusing the composite beam on its focal plane; and

an output optical fiber coupled to the housing and having a core end downstream of the focal plane, wherein a cross-section of the composite beam coupled into the core end is smaller than a cross-section of the composite beam in the focal plane.

2. The pigtailed diode laser module of claim 1 wherein the optical system comprises a plurality of slow-axis collimators (SACs), each slow-axis collimator located between and optically coupled to the MM chip and one focusing lens and configured to collimate the output beam in the slow axis.

3. The pigtailed diode laser module of claim 2, further comprising: a plurality of fast axis collimators coupled between respective chips and the SACs, the MM chips being arranged in at least one row and emitting respective output beams in a first direction.

4. The pigtailed diode laser module of claim 3 wherein the optical system further comprises a plurality of angularly adjustable mirrors, each mirror positioned between the SAC and a focusing lens and deflecting the collimated output beam in a second direction transverse to the first direction, the focusing lenses configured to focus the composite beam in both a fast axis and a slow axis.

5. The pigtailed diode laser module of claim 3, further comprising: at least one second focusing lens spaced upstream from the one focusing lens and configured to focus the composite beam on the fast axis.

6. The pigtailed diode laser module of claim 1, wherein the core end is spaced downstream of the focal plane of the one lens by a distance corresponding to a difference between the distances of the respective minimum and maximum cross-sections of the output beams emitted by the respective first and last MM chips from the one focusing lens, the first MM chip being closest to the lens and the last MM chip being furthest from the lens.

7. The pigtailed diode laser module of claim 1 wherein the core end is spaced downstream of the focal plane of the one lens by a distance corresponding to an average of distances between the one focusing lens and respective minimum cross-sections of the output beam downstream of the one focusing lens, wherein the MM chip is spaced apart from the one focusing lens by respective distances different from each other.

8. A method of manufacturing a pigtailed diode laser module comprising:

supplying power to the plurality of MM chips, thereby outputting corresponding parallel light beams;

collimating each parallel beam in a slow axis in a SAC optically coupled to and downstream of the MM chip, wherein the collimated beams propagate along a path and define a composite beam diverging along the path;

focusing the diverging composite beam at a focal plane of a focusing lens; and

separating the one focusing lens and a beam receiving core end of the output optical fiber from each other by a predetermined distance such that the composite beam is coupled to the receiving core end, wherein a cross-section of the focused composite beam at an entrance of the receiving core end is smaller than a cross-section of the beam in the focal plane.

9. The method of claim 8, wherein the one focusing lens focuses the diverging composite beam on a slow axis.

10. The method of claim 9, further comprising: each output beam is collimated in the fast axis by a fast axis collimator FAC located upstream of the SAC, and the diverging composite beam is focused in the fast axis by the one focusing lens.

11. The method of claim 10, further comprising: selectively adjusting an angular position of a selective mirror located between the second focusing lens and the corresponding SAC to adjust a focal plane of the one focusing lens located at a preferred position to be coplanar with an upstream core end of the output optical fiber on a fast axis of the combined beam.

12. The method of claim 8, further comprising: the output beams are collimated in respective fast axes by a plurality of FACs, each located upstream of the SAC, and the diverging composite beam is focused in the fast axis by a second focusing lens located between the MM chip and the one focusing lens.

13. The method of claim 8, further comprising:

positioning a minimum spaced cross-section of respective two output beams downstream of the one focusing lens, the two output beams being emitted by respective MM chips, wherein one of the MM chips is closest to the one focusing lens and the other MM chip is furthest from the one focusing lens;

determining a distance between the located minimum cross-sections; and

moving the one focusing lens upstream by the determined distance.

14. The method of claim 8, further comprising:

positioning a minimum cross-section of the respective output beam downstream of the one focusing lens;

determining a distance that is an average of the distances between the one focusing lens and the respective positioned cross-section; and

moving the one focusing lens upstream by the determined distance.

Technical Field

The present disclosure relates to fiber-coupled (pigtailed) multi-emitter multi-mode (MEMM) diode laser modules. Specifically, an improved optical coupling arrangement is disclosed that includes a pigtailed MEMM diode laser module configured with at least one lens spaced from the fiber core by a distance exceeding the lens focal length. The present disclosure further relates to a method of assembling the disclosed module.

Background

High efficiency, high power levels, and high spectral directional brightness are attractive characteristics of pigtailed diode laser modules used in many fields (e.g. material processing, offset printing, medical, solid-state laser pumping). Improving all of these characteristics is important for virtually all applications. This is especially important for laser diode pumped fiber lasers. Despite the ever increasing fiber laser power, the performance of high power fiber lasers still performs poorly due, at least in part, to the coupling loss of the pump light. The disclosed coupling device reduces losses to about 2% to 3%. Such a reduction is significant considering that even a one percent reduction in loss is considered to be a significant success.

A typical prior art high power multi-emitter multimode fiber coupled diode laser module 10 is shown in fig. 1 and 2 and is disclosed, for example, in U.S. patent No.7,764,723 to Ovtchinnikov et al ("the' 723 patent"), which is incorporated herein by reference in its entirety. At the most basic level, the diode laser emitters or chips 12 are supported by respective mounts 33 and output astigmatic beams 14 along optical paths. In fig. 1, each individual chip 12 in the array is stacked on top of each other. The various optics 16, 18, 20, and 22 collimate and shape the beams 14 of each emitter such that all of the beams 14 are combined into a single astigmatic composite beam 24. The composite beam 24 is directed to an optical fiber 30 and focused at a receive core end of the optical fiber 30, the receive core end of the optical fiber 30 being located in the focal plane F-F of the objective lens 22.

Each large area MM chip 12 emits a non-circular light beam 14 in a first direction. Due to the thin-plate geometry of diode lasers, their radiation propagates along the Z-axis and has a highly asymmetric lateral distribution of optical power density and diverges along the X-axis and the Y-axis. Each beam 14 is wider in its slow axis and narrower in its fast axis. Thus, the schematic shown generally has a Fast Axis Collimator (FAC)16 and a Slow Axis Collimator (SAC)18, with the beam 14 parallel in both the fast and slow axes. The plurality of light beams 14 are further combined by a set of mirrors 20 into a composite light beam 24, wherein the plurality of light beams 14 propagate in a second direction parallel to each other in the vertical plane.

Thus, the composite beam 24, collimated in two axes, impinges on and fills the area of the objective lens 22 such that the beam spot 36 is coupled to the core end 31 of the optical fiber 30, which core end 31 lies in the focal plane F-F of the Objective Lens (OL) 22. The' 723 patent teaches the use of a beam spot 36 that is as large as possible. Therefore, divergence of the light beam in the near field is least possible, and the brightness of the light beam irradiating the output optical fiber 30 is relatively good.

However, the above only applies to point-like light sources. The chip 12 has a plurality of spots that emit respective light rays. Thus, the chip is rather elongated compared to point-like light sources and is further referred to as extended light source or chip. The light beam 24 from the extended light source is not perfectly collimated, at least in the slow axis. Thus, when such a non-parallel beam is focused by the objective lens 22 along the slow axis onto the focal plane F-F, its beam spot may be too large to couple, or nearly couple, non-destructively to the core end of the fiber, as described below.

Fig. 3 shows a light ray diagram of a single extended light source 12. The chip 12 is located in the focal plane FP18 of the SAC 18, and the focal length of the SAC 18 is relatively short, e.g., less than 6 mm. If the light is emitted from a point source, it will be collimated in the Slow Axis (SA) by the SAC 18 and travel some distance to the OL22 as an ideal parallel beam 14, as shown by the dashed line. Thus, the point source will have a sharp image in the focal plane F-F of OL22 with a minimal beam spot or waist 25 formed in the focal plane F-F. The focal plane is determined asWhere f2 and f1 are the focal lengths of lens 22 and lens 18, respectively, and Δ is the size of the extended light source. However, the diode laser 12 has an array of multiple light emitting points, resulting in a single light beam 14 at an angle Divergence, where Θ Δ/2₁Starting approximately at the back focal point of OL 22. As the distance between the lens 18 and the lens 22 increases, the beam gradually expands in the slow axis and eventually impinges on the objective lens 22, as shown by the solid lines. Thus, the beam waist 25' of the beam in the focal plane FP 22 is much larger than the smallest spot 25 of an ideally collimated beam. The same logic should be applied to a composite beam 24 comprising a plurality of beams 14 diverging in the slow axis and emitted by the chips 12 of the module 10 of fig. 1 and 2. Of course, in order for the beam 24 to diverge significantly, the distance between the SAC 18 and the OL22 should be significant.

Fig. 4 and 5, discussed in conjunction with fig. 3, show the Slow Axis (SA) OL22 offset from the SAC 18 by respective first and second distances, the first distance (fig. 4) being shorter than the second distance (fig. 5). In fig. 4, similar to fig. 3, light rays R1-R3 (or spatial modes) from the respective three light emitting points of the extended diode laser 12 are substantially parallel to each other when impinging on the SAOL22 due to the small distance between the SAOL22 and the SAC. OL22 focuses the incident beam in its focal plane F-F where the respective waist (cross-section) is smallest. Thus, the beam waist of the composite focused beam causes the focused beam to be coupled into the core end without significant loss (if any). Thus, the image of the extended source is sharpest in the focal plane F-F, where the beam waist of the composite beam is smallest.

In contrast, fig. 5 shows a configuration where the distance between SAC and SAOL22 is long enough for the three light rays (red, blue and green) or spatial modes to diverge significantly and impinge on a larger area of SAOL 22. Although the image of the extended source is still the sharpest in the focal plane F-F, the spatial pattern continues to converge beyond the focal plane F-F. Thus, the smallest cross-section of the composite beam is formed at a distance D beyond the focal plane F-F. Installation of an output fiber with a core end located in the focal plane F-F results in optical losses due to the core diameter being smaller than the cross-section of the focused beam of fig. 5 in the focal plane. Optical power losses can result in poor throughput, overheating of module components, and damage to the output fibers.

Therefore, there is a need for a pigtailed MEMM diode laser module with an improved configuration.

There is also a need for a method of manufacturing the disclosed MEMM diode laser module.

Disclosure of Invention

The disclosed MEMM pigtailed diode laser module and the method of manufacturing the same differ from the known prior art in that: the Slow Axis Objective Lens (SAOL) is mounted such that the receiving end of the output optical fiber is spaced from the lens by a distance exceeding the focal length of the SAOL, i.e., exceeding the focal plane of the lens. Given that the present disclosure does not relate to image quality (image quality is highest in the focal plane), but rather to the collection of light (i.e., brightness), this seemingly counterintuitive configuration would be entirely logical. In the disclosed configuration, a plurality of extended light sources, such as diode lasers, are located in the focal plane of respective SACs spaced from the SAOL by a distance sufficient to significantly diverge the composite beam. To prevent the focused beam from being intercepted by the core of the optical fiber (the core being smaller than the cross-section of the focused beam in the focal plane of the SAOL), the optical fiber is located outside the focal plane. The distance between the SAOL and the fiber core of the optical fiber is increased such that the cross-section of the focused beam is sufficiently small to provide substantially lossless optical coupling to the core.

According to one aspect of the present disclosure, a diode laser module is configured with a housing that houses at least one row of MM diode lasers that emit respective parallel beams of light in a first direction. Each beam is collimated in the fast and slow axes by a pair of respective FACs and SAC, wherein SAC is spaced downstream from the respective FAC in the first direction. The disclosed module further includes a plurality of beam reflectors or mirrors that direct the individual collimated beams that make up the composite beam in a second direction, where the first and second directions are transverse to each other. At least one SAOL is located downstream of the last downstream reflector and is operative for focusing the composite beam on its focal plane at least along the slow axis. The module further has an optical fiber with an upstream end of the optical fiber aligned with the SAOL in the second direction. The upstream end of the optical fiber is mounted in the plane in which the combined beam has the smallest cross-section. The plane lies outside the focal plane.

The minimum cross-section of each beam component in the composite beam is located at different distances out of the focal plane due to the different distances of each light source from the SAOL. The diode laser closest to the SAOL outputs a beam component having the smallest cross-section at the shortest distance beyond the focal plane. The diode laser furthest from the SAOL emits a beam component whose smallest cross-section is spaced downstream from the focal plane by a larger distance than the diode laser closest to the SAOL in the upstream direction.

Accordingly, the disclosed method further comprises the steps of: the minimum cross-sections of the respective beams of the diode laser closest and the diode laser furthest downstream from the SAOL are determined and then the distance between them is determined. Finally, the disclosed method comprises the steps of: the SAOL is shifted upstream from its original position by the determined distance to provide a substantially lossless coupling of the composite beam to the core end.

Drawings

The above and other aspects, features will become more apparent from the following drawings, in which:

fig. 1 and 2 show a known prior art pigtailed MEMM diode laser module.

FIG. 3 is a light ray diagram associated with a single extended light source;

fig. 4 and 5 are respective ray diagrams illustrating operation of a single extended diode laser at a first distance and a second distance between the SAC and the SAOL, wherein the second distance is greater than the first distance;

fig. 6 and 7 respectively show optical schematic diagrams of the disclosed pigtailed MEMM diode laser module; and

fig. 8 shows the desired location of the minimum cross-section of the respective beams in fig. 6 and 7, depending on the distance the chip is spaced from the SAOL.

Fig. 9 and 10 show respective perspective views of the optical schematic of fig. 6 and 7, respectively.

Detailed Description

In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing.

Referring to fig. 6 and 7, the laser module 50 includes a plurality of spaced apart diode lasers or chips 12 (12)₁…12_n) Thereby outputting a corresponding parallel beam 14 in a first direction. Each die 12 is associated with beam shaping optics including FAC 16, SAK 18 and mirror 20. Each chip 12 is aligned in a first direction with a given FAC 16, SAC 18 and mirror 20, and these components together constitute a group 32 (fig. 7). Each beam 14 is first collimated in the fast axis by the FAC 16 and then collimated in the slow axis by the SAC 18. On the fast axis, the beam 14 is SM, while on the slow axis, the beam comprises a plurality of spatial modes (MM).

The light beams 14 are also redirected in a second direction transverse to the first direction by respective mirrors 20 and form a composite light beam 24. The group 32 is enclosed in a casing 34 having a bottom 15 made of heat-dissipating material and has respective chips 12, each coupled to a mount 33 also made of heat-dissipating material. The groups 32 (fig. 7) may be mounted on a common mounting 33 or on individual mounting 33 (fig. 2) contacted by the base 15. The architecture of the module 50 shown in fig. 6 and 7, respectively, is well known from us patents 7,764,723 and 8,711,894, which are incorporated herein by reference in their entirety.

In particular, FIG. 6 shows chips 12 mounted in rows₁To 12_n. In general, the modules 50 are configured as the two rows of chips 12 of FIG. 7 that are mounted on respective opposite sides of the composite beam 24 such that the groups 32 of one row are not aligned with the respective groups 32 of the other row in the first direction. The output fiber 30 is mounted in a ferrule (not shown) and aligned with the fast axis objective lens in a second direction26(FAOL) and SAOL 22.

It should be noted that the composite beam 24 is astigmatic with the smallest cross-sections or beam waists in the respective slow and fast axes spaced from each other. As shown in fig. 6, astigmatism can be corrected by mounting the FAOL26 upstream of the SAOL22 such that the respective focal planes of the lenses lie in the same plane. Alternatively, as shown in FIG. 7, wherein a single spherical, aspherical, cylindrical lens 36 may be used. Each of the schematic diagrams of fig. 6 and 7 may be configured with multiple objectives or a single objective, as explained in more detail below. However, since the beam waist along the fast axis is very deep (rayleigh parameters about 1 mm), the beam 24 can remain astigmatic. Thus, as long as the mirror 20 focuses the composite beam 24 on the fiber core, astigmatism may not be critical.

The distance between either of the SAC 18 and SAOL22 in both FIGS. 6 and 7 increases as the number of chips to meet higher output power requirements increases. Experiments have shown that in general, when the SAC 18 is configured to have a focal length exceeding, for example, about 6mm, the beam may diverge significantly in the slow axis.

In accordance with one aspect of the present disclosure, the SAOL22 is moved upstream from its original position (in which the SAOL, the focal distance f2 and the original focal plane Fo-Fo are all shown in dashed lines) to its new preferred position (in which the SAOL22 and the focal distance f2 and the new focal plane Fn-Fn are shown in solid lines). The distance D between the original position and the preferred position is in the range between about 50 and 500 μm and may be determined according to the disclosed method discussed below with reference to fig. 8. The output fiber 30 remains intact with its receiving end in the original focal plane Fo-Fo. The focal plane of FAOL26 coincides with the original focal plane Fo-Fo of SAOL22 before SAOL22 is shifted upstream. The desired distance to move the SAOL22 upstream from its original position is determined such that the smallest cross section of the composite beam in the slow axis is also located within the original focal plane Fo-Fo. In other words, the SAOL22 and the receiving core end are spaced apart by a distance equal to the focal length of the SAOL and the newly determined distance D, as described below. The schematic of fig. 6 can also be seen in fig. 9.

Referring specifically to fig. 7, the diode module 50 has an additional row of chips 12. As mentioned above, only one lens 36 is used in the illustrated configuration that serves as both FAOL and SAOL. In accordance with a salient feature of the present disclosure discussed above, the lens 36 is moved upstream from its original position, shown in phantom and including the receiving end of the optical fiber 30, to an optimal position by a determined distance D for the reasons discussed above. The optical schematic of fig. 7 is also shown in fig. 10.

Referring to fig. 5-7, beam 14₁…14_nFrom the corresponding chip 12₁…12_nThe output and propagates through different optical paths before impinging on the SAOL 22. The regions of the SAOL22 struck by the plurality of light beams 14 are different due to different optical paths. The region of smallest area is formed by the beam 14₁Of impact, due to the chip 12₁Closest to SAOL22 or 36, Beam 14₁Propagating on the shortest light path; while the largest area is driven from the chip 12_nEmitted light beam 14_nCovering, chip 12_nFurthest from the SAOL 22. Thus, beam 14₁To 14_nAre "focused" along the slow axis at various distances downstream from a focal plane F-F, which corresponds to the original position of the SAOL22 and includes the receiving end of the optical fiber 30. Respective light beams 14 emitted by the first and last chips of module 10₁And 14_nDetermines the distance D that the SAOL22 moves upstream from its original position. Alternatively, distance D may be determined as beam 14₁…14_nIs calculated as the average of all distances of the corresponding smallest cross-section.

Fig. 8, taken in conjunction with fig. 5-7, helps to illustrate the adjustment of the position of the SAOL in the context of the present disclosure. As will be readily understood by those of ordinary skill in the semiconductor arts, in mass production, once a sample such as a MEMM diode laser module is up-tuned, each subsequent module can be easily adjusted based on data obtained during sample tuning. Thus, once the SAOL is determined to move upstream by the determined distance D from its original position, this distance D will then be used in all other modules.

Thus, each chip 12 or only two chips in the test module (the chip closest to the SAOL and the chip furthest from the SAOL) are selectively rotatedChip) the minimum cross-section of each beam incident on the fiber 30 can be determined. As can be seen from fig. 8, curves 1 to 6 correspond to the respective light beams 14 of fig. 5 to 7₁…14_n. The minimum cross-section of each beam corresponds to the bottom area of the associated curve. Thus, corresponds to the signal from the chip 12₁Light beam 14 of₁Curve 1 of (a) has a minimum cross-section at a shortest distance downstream from the focal plane F-F, wherein the chip 12₁At the shortest distance upstream from the SAOL. The light beam 14n emitted from the distant chip 12n corresponds to the curve 6 and has a minimum cross-section at a second distance greater than the light beam 14₁Is located at the distance of the smallest cross section. Corresponding light beam 14₁And 14_nIs the desired uniform distance of all subsequent tunable modules, upstream from their original position, the SAOL is moved by this distance. Curve 7 shows the behavior of all beams after the composite beam is focused in FAOL 36. It can be seen that the SM light beam 14₁…14_nWith the respective beam spots on the fast axis lying in the same plane as the receive core end of the output optical fiber 30. In other words, each of the beams 14 is focused in the focal plane F-F of the SAOL22 on the fast axis before moving the SAOL22 by the distance D to its preferred position.

Referring to the structure of the single lens 36 of fig. 7, attention is paid not only to the lens adjustment of the slow axis but also to the lens adjustment of the fast axis. The displacement of the lens 36 from its original position on the slow axis by the distance D to the preferred position adversely affects the beam spot of the composite beam on the fast axis because the smallest beam spot on the fast axis lies within the original focal plane F-F when the lens 36 is in its original position. However, the angular adjustment of the mirror 20 can effectively compensate for the movement of the lens 36. Mirror 20 may be angularly adjusted so that beam 14 is incident on lens 36₁…14_nOpen at a greater angle and can be focused in the focal plane F-F of lens 36 when lens 36 is in the home position. The angular position of the mirror (e.g., distance D) may be used to adjust subsequent diode laser modules in mass production.

As one of ordinary skill in the art will readily recognize the above and further disclosed features of the modules and methods of the present invention may be used wherever possible and all together. Certain obvious modifications to the disclosed module can be readily ascertained by one of ordinary skill in the laser arts without departing from the scope of the present invention. For example, the disclosed chip may be mounted such that the respective output beams propagate in the same direction along the entire path until the combined beam is collimated on the slow axis and coupled into an optical fiber. This can be achieved by arranging the collimation and beam directing optics in a configuration that will be apparent to the skilled person. The modules of the present invention can work without FACS. Thus, while there has been shown and disclosed what is considered to be the most practical and preferred embodiments, it is apparent that departures from the disclosed configurations and methods will be apparent to those skilled in the art and may be made without departing from the spirit and scope of the invention.