Improved temperature range for laser diode modules using high-CTE glasses

Abstract

A laser diode module includes a substrate made from a metal having a coefficient of thermal expansion within a range of 10 - 25 ×10-6 / °K, an optical component made from a fluorinated glass with a coefficient of thermal expansion within a range of 12- 18 ×10-6 / °K, and a first adhesive disposed between the substrate and the optical component to bond the optical component to the substrate.

Description

IMPROVED TEMPERATURE RANGE FOR LASER DIODE MODULES USING HIGH-CTE GLASSES Cross-Reference to Related Application(s)

[0001] This International PCT Patent Application relies on and claims priority to United States Provisional Patent Application Serial No.63 / 664,381, filed on June 26, 2024, the entire contents of which are incorporated herein by reference. Field of the Invention

[0002] The present invention concerns constructions for laser diode modules, specifically laser diode modules that involve high power lasers. More specifically, the present invention concerns the selection of materials for the optical components incorporated into laser diode modules where the coefficient of thermal expansion (“CTE”) of the optical material for the optical components is selected to be compatible with the CTE of the substrate on which the optical components are disposed. Description of the Related Art

[0003] Laser diode modules are known to those skilled in the prior art.

[0004] Laser diode modules typically include a plurality of laser diodes disposed on a substrate.

[0005] The laser diode modules also include a plurality of optical components disposed on the same substrate. The laser light emitted by the laser diodes passes through one or more of the optical components before the laser light is directed to an optic fiber.

[0006] Laser diodes, especially those used by high power laser systems, generate heat, which must be dissipated to avoid damage to the laser diode module.

[0007] To remove excess heat, the laser diodes typically are mounted atop a substrate made from a material that readily dissipates heat. Metals typically are used for the substrate.

[0008] To further enhance heat removal, the substrate may include cooling fins and / or cooling channels.

[0009] The optical components that are used in conjunction with laser diodes typically are made from optical glass.

[0010] As should be apparent to those skilled in the art, CTEs for metals typically are much larger than CTEs for optical glass.

[0011] Due to the discrepancy between the CTE for the substrate and the CTE for the optical components adhered thereto, when the laser diode module operates and generates heat, the metal substrate will expand to a greater extent than the optical components adhered thereto.

[0012] It is possible, therefore, that the optical components might warp, become misaligned, or become dislodged from the substrate during operation of a laser diode module. Any of these effects could result in the laser diode module becoming inoperable.

[0013] To address the discrepancy between the CTE for the substrate and the CTE for the optical components, the present invention offers one or more solutions, as discussed in greater detail hereinbelow. Summary of the Invention

[0014] The present invention offers one or more solutions to address the discrepancy between the CTE for the substrate and the CTE for the optical components.

[0015] In one embodiment, the present invention provides a laser diode module that includes, inter alia, a substrate made from a metal having a coefficient of thermal expansion within a range of 10 – 25 ×10-6 / °K, an optical component made from a fluorinated glass with a coefficient of thermal expansion within a range of 12 – 18 ×10-6 / °K, and a first adhesive disposed between the substrate and the optical component to bond the optical component to the substrate.

[0016] It is contemplated that the fluorinated glass may permit wavelengths of light between 350 nm and 2000 nm to pass therethrough.

[0017] In one contemplated embodiment, the adhesive may be at least one of an epoxy, a multi- part epoxy, a solder, a metal solder, a room temperature vulcanizing epoxy, a UV-cured epoxy, a thermal cured epoxy, and a glue.

[0018] It is also contemplated that the adhesive is solder.

[0019] In another contemplated embodiment, the laser diode module is constructed so that the optical component is at least one of a lens, a mirror, a beam-splitter, a beam-combiner, a partialreflector, a prism, a fast axis collimator, a slow axis collimator, a PMUX, or a wavelength selective optic.

[0020] Here, the wavelength selective optic may be a short-pass filter or long-pass filter.

[0021] According to another contemplated embodiment, the laser diode module also may include a buffer layer bonded to the adhesive and a second adhesive disposed between the buffer layer and the adhesive, bonding the buffer layer to the optical component, where the buffer layer is made from a material with a coefficient of thermal expansion within a range of 5 – 25 ×10-6 / °K.

[0022] In this contemplated embodiment, the buffer layer may be a ceramic, such as alumina.

[0023] In this embodiment, the adhesive and the second adhesive are contemplated to be a solder.

[0024] Alternatively, the adhesive may be a glue and the second adhesive may be a solder.

[0025] Still further, the adhesive and the second adhesive may be a glue.

[0026] It is contemplated that the laser diode module will be adapted to operate across a temperature range of -80 °C to 120 °C.

[0027] Still further advantages and features of the present invention will be made apparent by the discussion presented hereinbelow. Brief Description of the Drawings

[0028] The present invention will now be described in connection with the drawings appended hereto, in which:

[0029] Fig.1 is a perspective view of a laser diode module constructed in a manner consistent with the prior art;

[0030] Fig.2 is a graphical side view of the mounting configuration for one optical component known in the prior art;

[0031] Fig.3 is a graphical side view of the mounting configuration for one optical component according to a first embodiment of the present invention; and

[0032] Fig.4 is a graphical side view of the mounting configuration for one optical component according to a second embodiment of the present invention;Detailed Description of Embodiment(s) of the Invention

[0033] The present invention will now be described in connection with several examples and embodiments. The present invention should not be understood to be limited solely to the examples and embodiments discussed. To the contrary, the discussion of selected examples and embodiments is intended to underscore the breadth and scope of the present invention, without limitation. As should be apparent to those skilled in the art, variations and equivalents of the described examples and embodiments may be employed without departing from the scope of the present invention.

[0034] In addition, aspects of the present invention will be discussed in connection with specific materials and / or components. Those materials and / or components are not intended to limit the scope of the present invention. As should be apparent to those skilled in the art, alternative materials and / or components may be employed without departing from the scope of the present invention.

[0035] In the illustrations appended hereto, for convenience and brevity, the same reference numbers are used to refer to like features in the various examples and embodiments of the present invention. The use of the same reference numbers for the same or similar structures and features is not intended to convey that each element with the same reference number is identical to all other elements with the same reference number. To the contrary, the elements may vary from one embodiment to another without departing from the scope of the present invention.

[0036] Still further, in the discussion that follows, the terms “first,” “second,” “third,” etc., may be used to refer to like elements. These terms are employed to distinguish like elements from similar examples of the same elements. For example, one fastener may be designated as a “first” fastener to differentiate that fastener from another fastener, which may be designated as a “second fastener.” The terms “first,” “second,” “third,” are not intended to convey any particular hierarchy between the elements so designated.

[0037] It is noted that the use of “first,” “second,” and “third,” etc., is intended to follow common grammatical convention. As such, while a component may be designated as “first” in one instance, that same component may be referred to as “second, “third,” etc., in a separate instance. The use of “first,” “second,” and “third,” etc., therefore, is not intended to limit the present invention.

[0038] Before addressing various aspects and features of the present invention, a brief overview of a conventional laser diode module is first presented.

[0039] Fig. 1 provides a perspective view of a laser diode module 10 according to one configuration known in the prior art.

[0040] The laser diode module 10 includes a substrate 12 onto which a plurality of laser diodes 14, 16 are mounted. The laser diodes are separated into first laser diodes 14 and into second laser diodes 16. The first laser diodes 14 are disposed along a first side of the substate 12, and the second laser diodes 16 are disposed along a second side of the substrate 12.

[0041] The substrate 12 may be made from a metal, such as aluminum, copper, and alloys thereof, because these metals have a high heat conductivity, among other attractive features.

[0042] When the laser diode module 10 is in operation, first light 30 is emitted from the first laser diodes 14 and second light 32 is emitted from the second laser diodes 16.

[0043] The first light 30 emitted from the first laser diodes 14 passes through the first fast axis collimators 18. The first light 30 then passes through the first slow axis collimators 22. The first light 30 is then reflected by the first mirrors 26 to the polarization multiplexor (“PMUX”) 38.

[0044] Similarly, the second light 32 emitted from the second laser diodes 16 passes through the second fast axis collimators 20, the second slow axis collimators 24, and is reflected by the second mirrors 28 to the PMUX 38.

[0045] The first and second mirrors 26, 28 redirect the first and second light 30, 32, resulting in first and second redirected light 34, 36.

[0046] The first and second redirected light 34, 36 propagates to the PMUX 38. At the PMUX 38, the first and second redirected lights 34, 36 are combined into a single light stream.

[0047] Specifically, at the PMUX 38, the second redirected light 36 is redirected, as transverse light 40. The transverse light 40 is then redirected to be parallel with the first redirected light 34.

[0048] The light exiting from the PMUX 38 is labeled as the output light 42. The output light 42 from the PMUX 38 propagates to a third mirror 44 where the output light 42 is directed as reflected output light 46.

[0049] The reflected output light 46 is directed into an optical output terminal 48 and then to an optical fiber 50.

[0050] The construction and operation of the PMUX 38, the optical output terminal 48 and the optical fiber 50 are conventional and, therefore, are not discussed in further detail herein.

[0051] As also illustrated in Fig. 1, first and second electrical leads 52, 54 are disposed proximate to the first and second laser diodes 14, 16 to power the first and second laser diodes 14, 16.

[0052] With respect to the laser diode module 10, the term “optical components” encompasses the first and second fast axis collimators 18, 20, the first and second slow axis collimators 22, 24, the first and second mirrors 26, 28, the PMUX 38, and the third mirror 44. Each of these optical components typically is made from optical glass, at least in part.

[0053] While not intended to be limiting of the present invention, the term “optical glass” typically refers to glass that has a high purity and well-defined optical properties. The well-defined optical properties include, but are not limited to, chemical stability, hardness, and scratch resistance. In addition, optical glass typically is colorless and is devoid of defects and / or imperfections such as stones (pieces of unmelted glass), seeds (bubbles), or cords (unevenly mixed glass).

[0054] As discussed above, different materials have different coefficients of thermal expansion. As noted above, the term “coefficient of thermal expansion” is abbreviated as “CTE.”

[0055] “Thermal expansion” is a property of every material. Simply stated, thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature. When the temperature of a material increases, the material typically expands, because the atoms and / or molecules in the material have greater energy and, therefore, vibrate at increasingly greater rates. The CTE is a way to quantify the thermal expansion of a material across a change in temperature.

[0056] As a general rule, the coefficient of thermal expansion is measured as a change in a linear dimension of the material subjected to the temperature change. As such, the CTE of a material typically is expressed as a distance (also referred to as the “strain”) divided by the temperature change. For example, the CTE may be expressed in units of (microinches / inch) / °F, (micrometers / meters) / °C, or (micrometers / meters) / °K. In the instant discussion, following standard conventions, when CTE is discussed, the units are expressed in the metric system as “(numeric value) / °K,” unless otherwise indicated.

[0057] As should be apparent to those skilled in the art, materials expand in three dimensions. As such, the CTE may be expressed volumetrically.

[0058] In the discussion that follows, the CTEs identified for a particular material should be understood to be linear CTEs unless otherwise indicated.

[0059] As should be understood by those skilled in the art, the CTE for a metal typically is much greater than the CTE for glass. As such, across a wide temperature range, the length of a metal will expand or contract to a much greater extent than the same length of glass.

[0060] This difference in expansion and / or contraction between metals and glasses presents an engineering challenge when constructing a laser diode module, such as the laser diode module 10 illustrated in Fig.1.

[0061] In particular, as noted above, the substrate 12 typically is made from a metal, such as copper, aluminum, or alloys thereof. Metals are chosen for the substrate, because the laser diodes 14, 16 generate considerable heat when they are operational. The heat needs to be removed so that the laser diodes 14, 16 do not overheat. Metals are excellent heat conductors, which is why they are employed for the substrate 12, among other reasons. Moreover, aluminum and copper are typically employed, because these two metals have high thermal conductivities, among other advantages.

[0062] In addition, while not illustrated, it is common for the substrate 12 to include cooling features to assist with the dissipation of heat generated by the laser diodes 14, 16. For example, the substrate 12 may include cooling fins and / or cooling channels. The cooling fins and / or cooling channels may be exposed to and / or contain a cooling fluid to remove heat generated by the laser diodes 14, 16.

[0063] The optical components of the laser diode module 10 typically are adhered to the substrate 12 via an adhesive, epoxy, or solder. It is noted that other adherents may be employed other than adhesives, epoxies, or solder without departing from the scope of the present invention.

[0064] As used herein, the term “adhesive” is intended to refer to a substance that is capable of holding materials together, in a functional manner, by attaching the surfaces of the materials to one another. Once adhered, the surfaces resist separation. Adhesives encompass, but are not limited to, materials such as cement, mucilage, glue, paste, epoxies, multi-part epoxies, solder, metal solder, room temperature vulcanizing (“RTV”) epoxies, UV-cured epoxies, thermal cured epoxies, and the like.

[0065] The term “epoxy” typically refers to a subgroup of adhesives that are polymeric. In particular, epoxies encompass organic compounds made up of chains of carbon linked to otherelements such as hydrogen, oxygen, and / or nitrogen. Like adhesives, epoxies also hold the surfaces of materials together so that they resist separation.

[0066] The term “solder” typically refers to a low-melting alloy that can be used to join two or more materials together. Often, solders are alloys that are based on lead, tin, brass, or silver, and the like. It is noted that the use of the term “solder” herein is not intended to be limited to alloys of only these metals. Other solders may be employed without departing from the scope of the present invention.

[0067] With continued reference to Fig.1, and as should be apparent to those skilled in the art, when the laser diode module 10 heats up due to operation of the laser diodes 14, 16, the expansion rate of the optical components typically differs from the expansion rate of the substrate 12. Specifically, the optical components tend to expand to a much smaller degree than the substrate 12 because they are made from optical glass.

[0068] When the ΔT is controlled within a narrow range, the discrepancy between the expansion of the optical components and the expansion of the substrate 12 is sufficiently small that the difference may have a minimal effect on the alignment of the optical components with one another and / or with the laser diodes 14, 16. However, when the laser diode module 10 operates across a very large ΔT, the discrepancy may not be insignificant.

[0069] When the ΔT is large, it is possible that the optical components may become misaligned with one another or with the laser diodes. Significant misalignments can be catastrophic, because the laser light generated by the laser diodes 14, 16 may strike components of the laser diode module 10 other than the optical components, damaging those components. Alternatively, it is possible that the discrepancy may be so great that the optical components might fracture or become dislodged from the adhesive, epoxy, or solder securing the optical components to the substrate 12. Again, the result may be catastrophic.

[0070] To avoid these challenges, the present invention explores the use of high CTE glass for the optical components. The embodiments presented herein capitalize on the understanding that selecting glass for the optical components that has a CTE closer in magnitude to the CTE of the substrate 12 will result in a smaller (less severe) mismatch between the CTE of the optical components and the CTE of the substrate. Among other benefits, by selecting optical glass with a high CTE, it becomes possible to construct a laser diode module that is capable of operating across a much larger temperature range than laser diodes modules 10 that are known in the prior art.

[0071] As a general rule, high CTE glass is defined as a glass with a CTE of ≥ 12 × 10-6 / °K (the units are X (µm / m) / °K, which becomes X × 10-6 / °K). Standard CTE glass has a CTE of between 3 × 10-6 / °K and 12 × 10-6 / °K. Low CTE glass has a CTE of less than 3 × 10-6 / °K.

[0072] With respect to the laser diode module 10 illustrated in Fig.1, the optical components typically are made from standard CTE glass. In particular, as should be understood by those skilled in the art, it is common for the first and second fast axis collimators 18, 20, the first and second slow axis collimators 22, 24, and the first and second mirrors 26, 28, the PMUX 38, and the third mirror 44 to be made from standard CTE glass with an average CTE in a range of 4 × 10-6 / °K – 8 × 10-6 / °K. In fact, typically, most optical components are made from standard CTE glass with a CTE in a range of 4 × 10-6 / °K – 8 × 10-6 / °K.

[0073] Fig.2 is a graphical illustration of a portion of the laser diode module 10 illustrated in Fig. 1, showing an enlarged detail with respect to one of the optical components, which is designated as optical component 56. In Fig.2, the optical component 56 may be any one of the first and second fast axis collimators 18, 20, the first and second slow axis collimators 22, 24, and the first and second mirrors 26, 28, the PMUX 38, and the third mirror 44, for example. The optical component is made from standard CTE glass with a CTE defined by the relationship 4 × 10-6 / °K ≤ CTE ≤ 8 × 10-6 / °K. As noted, this range for the CTE of the optical component 56 is typical for the prior art.

[0074] In the illustrated example, the optical component 56 is disposed atop the substrate 12. The substrate 58 may be made from aluminum, for example. Aluminum has a reported CTE of 23.6 × 10-6 / °K.

[0075] Alternatively, the substrate 12 may be made from copper. The CTE for copper is reported as 17.6 × 10-6 / °K.

[0076] As should be immediately apparent, the CTE for the optical component 56 is considerably lower than the CTE for the substrate 12. In fact, the ratio of the CTE for the substrate 12 to the CTE for the optical component is 23.6:8 – 23.6:4 or 2.95 – 5.9. If copper is used as the substrate 12, the ratio is 17.6:8 – 17.6:4 or 2.2 – 4.4.

[0077] As illustrated in Fig.2, the optical component 56 is adhered to the substrate 12 via an adhesive 58. Here, the adhesive is an epoxy.

[0078] As should be apparent to those skilled in the art, when the optical component 56 is adhered to the substrate 12 via the epoxy adhesive 58, this method of construction is simple andinexpensive. Due to its simplicity, this method is also easy to implement in a production environment.

[0079] As noted, this prior art approach is suitable for cases where the optical component 56 has a CTE in the range of 4 – 8 × 10-6 / °K and the metal substrate has a CTE in a range of 15 – 25 × 10-6 / °K, under the condition that the temperature range for operation of the laser diode module 10 be maintained within a predefined operational range. Specifically, prior art laser diode modules 10 typically operate in the operational range of about -20 °C to about 70 °C (ΔT = 90 °C). For some prior art laser diode modules, this operational range is even smaller. Examples of other prior art operational temperature ranges include 0 °C to 55 °C (ΔT = 55 °C) and -20 °C to 60 °C (ΔT = 80 °C).

[0080] Significantly, the lower limit for the operational range for prior art laser diode modules is -20 °C. Also significantly, the upper limit for the operational range for prior art laser diode modules is 70 °C, defining a maximum temperature difference, ΔT, of only 90 °C.

[0081] To address the limitations that are associated with the narrow operational temperature range of laser diode modules 10 known in the prior art, those skilled in the art have employed a number of solutions.

[0082] In a first known example in the prior art, the adhesive 58 is selected to act as a “buffer” between the optical component 56 and the substrate 12. Here, the adhesive 58 is selected from a group of epoxies that exhibit a degree of elasticity. This allows the adhesive 58 to flex between the metal substrate 12 and the glass optical component 56 over the operational temperature range.

[0083] Being flexible, the adhesive 58 reduces the occurrence of misalignment of the optical component 56, because the adhesive 58 “absorbs” some of the strain between the optical component 56 and the substrate 12 as the optical component 56 and the substate 12 expand and contract.

[0084] However, it is noted that flexible adhesives present at least one challenge when constructing a laser diode module 10. Specifically, because flexible adhesives 58 are elastic, they do not always maintain a rigid orientation between the optical component 56 and the substrate 12. As such, the optical component 56 may move slightly out of alignment across the operational temperature range. Misalignments may become larger as the laser diode module 10 cycles between hot and cold temperatures.

[0085] In addition, flexible adhesives 58 may be prone to distortions if exposed to high humidity and / or strong vibrations, for example. Here again, the adhesive 58 may cause the optical component 56 to become misaligned.

[0086] In summary, the use of a flexible adhesive 58 may help to maintain the alignment of the optical component 56 across the full operational range of -20 °C – 70 °C. However, as noted, the use of a flexible adhesive 58 also introduces problems when the laser diode module 10 is operated.

[0087] In a second solution to avoid misalignment of the optical component 56, breakage of the optical component 56, and / or dislodgement of the optical component 56 from the substrate 12 during operation of the laser diode module 10, those skilled in the art also have elected to employ metals for the substrate 12 that have low CTEs. Specifically, it has been known for those skilled in the art to employ metals with low CTEs that are commensurate in magnitude with the CTE of the glass of the optical component 56. In fact, this solution is employed most often in laser diode modules 10 known in the prior art.

[0088] One disadvantage with selecting materials for the substrate 12 with a low CTE that that metals with CTEs that are less than 8 × 10-6 / °K usually have poor thermal conductivity. Since heat dissipation is advantageous for acceptable operation of a laser diode module 10, low CTE metals generally are poor choices for the substrates 12 of high-power laser modules.

[0089] In a third solution to the problem of mismatch between the CTE of the optical component 56 and the substrate 12, those skilled in the art have elected to introduce a buffer material between the optical component 56 and the substrate 12.

[0090] Under ideal circumstances, a buffer layer 60 has a CTE that lies halfway between the CTE of the optical component 56 and the CTE of the substrate 12. Theoretically, by selecting a material for the buffer layer 62 that lies midway between the CTE for the substrate 12 and the CTE for the optical component 56, the buffer layer 60 will expand about ½ of the amount of both the substrate 12 and the optical component 56. As such, the buffer layer 60 will experience ½ of the strain from the substrate 12 and ½ from the optical component 56. As a result, the buffer layer 60 should be able to maintain the operational position of the optical component 56 across the operational temperature range of the laser diode module 10.

[0091] In practice, however, it is extremely difficult to engineer a construction for a laser diode module 10 where the buffer layer 60 has a CTE that is between the CTE of the substrate 12 and the optical component 56.

[0092] Still further, the buffer layer 60 typically is made from a material with an extremely low CTE. Ceramics, such as alumina (Al2O3) (also referred to as aluminum oxide), may be used for the buffer layer 60. Alumina has a reported CTE of 10.3 × 10-6 / °K.

[0093] When the CTE of the buffer layer 60 is close to the CTE of the optical component 56, as in this example, the buffer layer 60 may not provide a thermally expansive / elastic buffer suitable to address misalignment of the optical component 56 over the entire operational temperature range of the laser diode module 10.

[0094] In one prior art example, the buffer layer 60 of alumina may be bonded to the substrate 12 with a very elastic adhesive, epoxy, or solder 58. In this example, both the adhesive 58 and the buffer layer 60 help to mitigate the thermal expansion of the substrate 12 versus the optical component 56.

[0095] As also illustrated in Fig.2, since the buffer layer 60 is alumina, which is a ceramic, another layer of adhesive 62, preferably a flexible adhesive, is needed to bond the optical component 56 to the buffer layer 60. The adhesive 62 is the same as the adhesive 58.

[0096] One negative associated with reliance on the incorporation of the buffer layer 60 and the adhesive layers 58, 62 into the construction of the laser diode module 10 is that the manufacturing process is made more complex due to the addition of steps and materials. This increases the cost and time for manufacturing the laser diode module 10. Moreover, by adding the adhesive layers 58, 62 and by adding the buffer layer 60, there are additional areas where a failure of the construction may occur. As a result, the addition of the buffer layer 62 and the adhesive layers 58, 62 may result in the construction of a less reliable laser diode module 10.

[0097] As noted above, a fourth solution is to limit the operational temperature range, ΔT, of the laser diode module 10. The smaller the operational temperature range, ΔT, the smaller the difference in expansion between the substrate 12 and the optical component 56.

[0098] As should be immediately apparent, limiting the operational temperature range, ΔT, of the laser diode module 10 limits the operability of the laser diode module 10 to specific environments. Therefore, this prior art solution is undesirable, as a general rule.

[0099] As should be apparent to those skilled in the art, any one or more of these solutions may be employed simultaneously to improve the operation of the laser diode module 10 by reducing the possibility of optical misalignment, optical dislodgement, and / or optical fracture, among others. However, these solutions are considered to be inadequate in many instances, because the solutions limit the laser diode module 10 to specific environments. More robust solutions are desired.

[0100] At present, there is a need for laser diode modules to operate across a larger operational range than the traditional -20 °C to 70 °C range. Primarily, the current desire is to extend the operational temperature range ΔT from -63 °C to 120 °C, or across a total change in temperature of 183 °C. This broad temperature range is useful particularly in harsh conditions, such as those that may be experienced in space, for example.

[0101] The prior art laser diode module 10 is incapable of operating with a ΔT from -63 °C to 120 °C. As noted above, the prior art laser diode module is limited to an operating temperature range, ΔT, of -20 °C to 70 °C range.

[0102] Fig.3 provides a graphical illustration of a portion of a laser diode module 64 according to the present invention. Specifically, Figs.3 is a graphical side view showing the disposition of one optical component 66 on a substrate 68. As illustrated, the optical component 66 is adhered to the substrate 68 via an adhesive 70. The adhesive may be a glue, epoxy, and / or solder as discussed above.

[0103] The laser diode module 64 employs a high CTE glass for the optical component 66. The optical component 66 may be a lens, a mirror, a beam-splitter, a beam-combiner, a partial reflector, a prism, or a wavelength selective optic, such as a short-pass filter, long-pass filter, fast axis collimator, slow axis collimator, or PMUX, for example.

[0104] The high CTE glass for the optical component 66 is contemplated to be fluorinated glass that has a CTE of 12 – 18 ×10-6 / °K. As should be immediately apparent, a high CTE of 12 – 18 ×10-6 / °K is much closer to the CTE for aluminum (23.6 × 10-6 / °K) or for copper (17.6 × 10-6 / °K) than the standard CTE glass used for the optical component 56, which has a CTE of 4 – 8 × 10-6 / °K.

[0105] With a CTE of 12 – 18 × 10-6 / °K, the ratio of the CTE for an aluminum substrate 68 to the CTE for the optical component 66 is 23.6:18 – 23.6:12 or 1.31 – 1.97. If copper is used as the substrate, the ratio is 17.6:8 – 17.6:4 or 0.98 – 1.47.

[0106] With renewed reference to the laser diode module 10, the CTE ratio between the CTE of the substrate 12 and the CTE of the optical component 56 is 2.95 – 5.9 for aluminum and 2.2 – 4.4 for copper. When fluorinated glass is used for the optical component 66, according to the present invention, the CTE ratio between the CTE of the substrate 68 and the CTE of the optical component 66 is 1.31 – 1.97 for aluminum and 0.98 – 1.47 for copper.

[0107] From this comparison, it becomes apparent that the CTE ratios for prior art devices are greater than 2.2. The CTE ratios for the present invention, by contrast, are less than 2.0. It is contemplated, therefore, that the present invention will combine substrates 68 and optical components 66 with CTEs where the CTE ratio, which is the CTE for the substrate 68 divided by the CTE for the optical component 66 is less than 2.0.

[0108] As should be apparent from the foregoing, the CTE for fluorinated glass is very closely matched to the CTE for copper. The ratio lies in a range of 0.98 – 1.47, which encompasses a 1:1 ratio. As such, when fluorinated glass is used to construct the optical component 66 and copper is used for the substrate 68, there is a near optimal match between the CTEs for the two components. As a result, when the optical component 66 and the substrate 68 expand across the operational temperature range ΔT of -63°C – 120°C.

[0109] For purposes of the present invention, it is contemplated that the CTE of the glass forming at least a part of the optical component 66 will fall in a range of 12 – 18 ×10-6 / °K. Still further, the range of the CTE for the optical component 66 may be in a range of 13 – 17 ×10-6 / °K, 14 – 16 ×10-6 / °K, or around 15 ×10-6 / °K. Moreover, the CTE for the glass for the optical component may be any one of 12 ×10-6 / °K ± 1 ×10-6 / °K, 13 ×10-6 / °K ± 1 ×10-6 / °K, 14 ×10-6 / °K ± 1 ×10-6 / °K, 15 ×10-6 / °K ± 1 ×10-6 / °K, 16 ×10-6 / °K ± 1 ×10-6 / °K, 17 ×10-6 / °K ± 1 ×10-6 / °K, or 18 ×10-6 / °K ± 1 ×10-6 / °K, without departing from the scope of the present invention.

[0110] As noted above, the CTE for the substrate 68 is contemplated to be 17.6 ×10-6 / °K for copper or 23.6 ×10-6 / °K for aluminum. Since the substrate may be made from alloys of copper and aluminum, it is contemplated that the CTE for the substrate 68 will fall within a range of 17 – 24 ×10-6 / °K.

[0111] Since other metals may be employed for the substrate 68, a wider range of CTEs may be applicable. Other contemplated ranges for the CTE of the substrate 68 may be 10 – 25 ×10-6 / °K, 11 – 24 ×10-6 / °K, 12 – 23 ×10-6 / °K, 13 – 22 ×10-6 / °K, 14 – 21 ×10-6 / °K, 15 – 20 ×10-6 / °K, 16 – 19 ×10-6 / °K, and 17 – 18 ×10-6 / °K. Moreover, the CTE for the substrate 68 may be any oneof 10 ×10-6 / °K ± 1 ×10-6 / °K, 11 ×10-6 / °K ± 1 ×10-6 / °K, 12 ×10-6 / °K ± 1 ×10-6 / °K, 13 ×10-6 / °K ± 1 ×10-6 / °K, 14 ×10-6 / °K ± 1 ×10-6 / °K, 15 ×10-6 / °K ± 1 ×10-6 / °K, 16 ×10-6 / °K ± 1 ×10-6 / °K, 17 ×10-6 / °K ± 1 ×10-6 / °K, 18 ×10-6 / °K ± 1 ×10-6 / °K, 19 ×10-6 / °K ± 1 ×10-6 / °K, 20 ×10-6 / °K ± 1 ×10-6 / °K, 21 ×10-6 / °K ± 1 ×10-6 / °K, 22 ×10-6 / °K ± 1 ×10-6 / °K, 23 ×10-6 / °K ± 1 ×10-6 / °K, 24 ×10-6 / °K ± 1 ×10-6 / °K, or 25 ×10-6 / °K ± 1 ×10-6 / °K, without departing from the scope of the present invention.

[0112] As should be apparent, the ratio of the CTE for the optical component 66 divided by the CTE for the substrate 68 is contemplated to fall within a range of 25 / 12 or 2.08:1 to 10 / 18 or 0.56:1. To this point, any other specific ratio within this range also is contemplated to fall within the scope of the present invention.

[0113] As illustrated in Fig.3, the optical component 66 is adhered to the substrate 68 via an adhesive 70. Since the CTE for the optical component 66 closely correlates with the CTE for the metal substrate 68, the adhesive 70 need not be a flexible adhesive, as required to construct the laser diode module 10.

[0114] As noted above, to accommodate the large discrepancy between the CTE for the substrate 12 and the CTE for the optical component 56, the adhesive(s) 58, 62 were contemplated to be flexible adhesives. The flexibility of the adhesives 58, 62 accommodated the different expansions of the materials over the operational temperature range ΔT. The flexible adhesives 58, 62 helped to maintain the optical component 56 in an acceptable optical alignment with other optical components.

[0115] The adhesive 70 for the laser diode module 64 according to the present invention is contemplated to be a more rigid adhesive. A more rigid adhesive may be used, because there is a smaller (or nonexistent) difference between the CTE of the substrate 68 and the CTE of the optical component 66. As a result, the adhesive 70 does not need to be flexible to accommodate large differences in the expansion rates of the optical component 66 and the substrate 68. A more rigid adhesive 70 necessarily results in better optical alignment of the optical component 66 over the operational temperature range ΔT.

[0116] With respect to the adhesive 70, it is contemplated that the adhesive 70 may be an epoxy (consisting of one or more parts), RTV (room temperature vulcanizing) adhesive, solder, or other conceivable material whereby the adhesive 70 initially is in a liquid or semi-liquid state to join the optical component 66 to the substrate 68. After curing, the adhesive 70 is contemplatedto become solid and / or rigid (or semi-rigid). In the context of the adhesive 70, the terms epoxy, glue, cement, fixative, or sealant are considered synonymous.

[0117] Still further, it is noted that the laser diode module 64 is contemplated to require only a single layer of adhesive 70. Again, because the CTE of the optical component 66 is closely matched to the CTE of the substrate 68, additional intermediate materials are not needed as in the case for the construction of the laser diode module 10.

[0118] As noted above, the operational temperature range ΔT is contemplated to encompass, at a minimum, a range of temperatures from -63°C to 120°C. Due to the close match between the CTE for the optical component 66 and the CTE of the substrate 68, it is contemplated that the operational temperature range ΔT may be expanded from -80°C to 120°C, thereby increasing the operational temperature range to a ΔT of 200°C.

[0119] With renewed reference to the optical component 66, it is noted that the fluorinated glass is contemplated to be suitable for use with wavelengths, generated by the laser diodes 14, 16, between 350nm and 2000nm.

[0120] Fig. 4 is a graphical illustration of another embodiment of a portion of a laser diode module 72 according to the present invention.

[0121] In this illustration, a buffer layer 74 is bonded to the substrate 68 via a first adhesive 76. The optical component 66 is bonded to the buffer layer 74 via a second adhesive 78. The first adhesive 76is contemplated to be the same material as the second adhesive 78. The buffer layer 74 is contemplated to be alumina, as discussed in connection with the laser diode module 10 illustrated in Fig.2.

[0122] The buffer layer 74 should not be understood to be limited solely to alumina. To the contrary, the buffer layer 74 may be made from any material with a CTE within a range of 5 – 25 ×10-6 / °K.

[0123] The first adhesive 76 and the second adhesive 78 may be a multi-part epoxy (i.e., a hardener and a resin), metal solder, a room temperature vulcanizing (“RTV”) epoxy, a UV-cured epoxy, a thermal cured epoxy, glue, solder, or some combination thereof, as appropriate.

[0124] As discussed hereinabove, the embodiments of the present invention are exemplary only and are not intended to limit the present invention. Features from one embodiment are interchangeable with other embodiments, as should be apparent to those skilled in the art. As such,variations and equivalents of the embodiments described herein are intended to fall within the scope of the claims appended hereto.

Claims

What is claimed is:

1. A laser diode module, comprising: a substrate made from a metal having a coefficient of thermal expansion within a range of 10 – 25 ×10-6 / °K; an optical component made from a fluorinated glass with a coefficient of thermal expansion within a range of 12 – 18 ×10-6 / °K; and a first adhesive disposed between the substrate and the optical component to bond the optical component to the substrate.

2. The laser diode module according to claim 1, wherein the fluorinated glass permits wavelengths of light between 350 nm and 2000 nm to pass therethrough.

3. The laser diode module according to claim 1, wherein the adhesive is at least one of an epoxy, a multi-part epoxy, a solder, a metal solder, a room temperature vulcanizing epoxy, a UV- cured epoxy, a thermal cured epoxy, and a glue.

4. The laser diode module according to claim 3, wherein the adhesive is the solder.

5. The laser diode module according to claim 1, wherein the optical component is at least one of a lens, a mirror, a beam-splitter, a beam-combiner, a partial reflector, a prism, a fast axis collimator, a slow axis collimator, a PMUX, or a wavelength selective optic.

6. The laser diode module according to claim 5, wherein the wavelength selective optic is a short-pass filter or long-pass filter.

7. The laser diode module according to claim 1, further comprising: a buffer layer bonded to the adhesive; and a second adhesive disposed between the buffer layer and the adhesive, bonding the buffer layer to the optical component,wherein the buffer layer is made from a material with a coefficient of thermal expansion within a range of 5 – 25 ×10-6 / °K.

8. The laser diode module according to claim 7, wherein the buffer layer is a ceramic.

9. The laser diode module according to claim 8, wherein the ceramic is alumina.

10. The laser diode module according to claim 7, wherein the adhesive and the second adhesive are a solder.

11. The laser diode module according to claim 7, wherein the adhesive is a glue and the second adhesive is a solder.

12. The laser diode module according to claim 7, wherein the adhesive and the second adhesive are a glue.

13. The laser diode module according to claim 1, wherein the laser diode module is adapted to operate across a temperature range of -80 °C to 120 °C.

Images