Monolithic laser array with non-uniform laser spacing

Abstract

To provide a monolithic laser array that includes a non-uniform laser.SOLUTION: An example monolithic laser array provides a substantially uniform temperature distribution and includes a substrate, a first set of lasers disposed on the substrate and separated by a first distance, and a second set of lasers disposed on the substrate and separated by a second distance greater than the first distance. The disclosed monolithic laser array yields an output with a very narrow optical spectral width.SELECTED DRAWING: Figure 1A

Description

[Technical field]

[0001] For laser arrays using multiple lasers, operating temperature differences can have adverse effects on performance. [Background technology]

[0002] In particular, in some lasers, high temperatures can affect the laser emission wavelength, resulting in a broad optical spectrum. Summary of the Invention [Problem to be solved by the invention]

[0003] The subject matter of this disclosure is directed to solving one or more of the problems set forth above, or at least reducing the effects of one or more of the problems set forth above. [Means for solving the problem]

[0004]

[0003] According to the present disclosure, a monolithic laser array uses a plurality of individual lasers arranged with non-uniform spacing, a geometric design to produce an output with a narrow optical spectral width, and a substantially uniform junction temperature distribution across the array.

[0005]

[0004] These and other features of the present disclosure will become more fully apparent from the following description and appended claims set forth below.

[0005] To further clarify the above and other features of the present disclosure, a more particular description of the subject matter will be provided by reference to specific examples thereof which are illustrated in the accompanying drawings, it being understood that these drawings illustrate only some examples of the subject matter and therefore should not be considered limiting of its scope. [Brief description of the drawings]

[0006] [Figure 1A] FIG. 1A shows a monolithic array of lasers. [Figure 1B]

[0007] FIG. 1B is a graphical representation of the temperature change of the monolithic array of lasers of FIG. 1A. [Figure 1C] FIG. 1C is a graphical illustration of the temperature change of the monolithic array of lasers of FIG. 1A. [Figure 2A]

[0008] FIG. 2A shows another monolithic array of lasers. [Figure 2B]

[0009] FIG. 2B is a graphical representation of the temperature change of the monolithic array of lasers of FIG. 2A. [Figure 2C] FIG. 2C is a graphical illustration of the temperature change of the monolithic array of lasers of FIG. 2A. [Figure 3A]

[0010] FIG. 13 illustrates yet another monolithic array of lasers. [Figure 3B]

[0011] FIG. 3B is a graphical representation of the temperature change of the monolithic array of lasers of FIG. 3A. [Figure 3C] FIG. 3B is a graphical representation of the temperature change of the monolithic array of lasers of FIG. 3A. [Figure 3D] FIG. 3B is a graphical representation of the temperature change of the monolithic array of lasers of FIG. 3A. [Figure 4A]

[0012] FIG. 13 illustrates yet another monolithic array of lasers. [Figure 4B]

[0013] FIG. 4B is a graphical representation of the temperature change of the monolithic array of lasers of FIG. 4A. [Figure 4C] FIG. 4B is a graphical representation of the temperature change of the monolithic array of lasers of FIG. 4A. [Figure 4D] FIG. 4B is a graphical representation of the temperature change of the monolithic array of lasers of FIG. 4A. [Figure 5A]

[0014] FIG. 5A is a graphical illustration of an exemplary temperature distribution of a monolithic array of non-uniform 1D lasers. [Figure 5B]FIG. 5B is a graphical illustration of an exemplary temperature distribution of a monolithic array of non-uniform 1D lasers. [Figure 5C] FIG. 5C is a graphical illustration of an exemplary temperature distribution of a monolithic array of non-uniform 1D lasers. [Figure 5D] FIG. 5D is a graphical illustration of an exemplary temperature distribution of a monolithic array of non-uniform 1D lasers. [Figure 5E] FIG. 5E is a graphical illustration of an exemplary temperature distribution of a monolithic array of non-uniform 1D lasers. [Figure 5F] FIG. 5F is a graphical illustration of an exemplary temperature distribution of a monolithic array of non-uniform 1D lasers. [Figure 6A]

[0015] FIG. 6A is a graphical illustration of the temperature change of a monolithic array of 1D lasers separated by a linear constant C according to the example of FIG. 2A. [Figure 6B] FIG. 6B is a graphical illustration of the temperature change of a monolithic array of 1D lasers spaced apart by a linear constant C according to the example of FIG. 2A. [Figure 7A]

[0016] FIG. 7A is a graphical illustration of the temperature change of a monolithic array of 2D lasers separated by a linear constant C according to the example of FIG. 4A. [Figure 7B] FIG. 7B is a graphical illustration of the temperature change of a monolithic array of 2D lasers spaced apart by a linear constant C according to the example of FIG. 4A. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007]

[0017] A monolithic laser array using non-uniform spacing is disclosed. In particular, the exemplary monolithic laser array is arranged in a geometric design to provide an output with a narrow optical spectral width and a substantially uniform junction temperature distribution across the array.

[0008]

[0018] As disclosed herein, the spacing of the lasers in a monolithic laser array stabilizes the temperature between the lasers, providing an output with a narrow optical spectrum and substantially uniform thermal performance across the lasers comprising the array.

[0009]

[0019] For many monolithic arrays using multiple lasers (e.g., semiconductor lasers), the junction temperature in each semiconductor laser may be different. For example, lasers in the center of a uniformly spaced laser array system may exhibit relatively high operating temperatures, as opposed to lasers at the edges of the array with relatively low operating temperatures. As a result, the temperature difference across the array, from the laser with the highest operating temperature to the laser with the lowest operating temperature, may be quite large.

[0010]

[0020] Such temperature differences can have adverse effects on laser performance. For example, the laser emission output, e.g., wavelength, can be affected by the junction temperature. Thus, significant temperature differences can result in different laser emission wavelengths for different lasers in the array. As a result, the optical spectral width of the laser emission from the array is much wider than that of a single emitter.

[0011]

[0021] To address these issues, a geometric design is disclosed that includes multiple lasers with non-uniform spacing in an array, thereby achieving a more uniform temperature distribution. By using non-uniformly spaced lasers in an array, the temperature difference between the hottest and coldest lasers can be reduced, beneficially resulting in a reduction in the laser emission spectral width.

[0012]

[0022] Exemplary one-dimensional (1D) and two-dimensional (2D) monolithic laser arrays are disclosed that use multiple semiconductor lasers arranged in a non-uniform pattern. Both the 1D and 2D arrays are defined by a laser-to-laser distance that is relatively sparse at the center of the array and relatively dense at the ends of the array. Using the disclosed geometric designs, the junction temperature is uniform from laser to laser. The temperature difference between the hottest and coldest lasers is smaller.

[0013]

[0023] Thermal simulation data validates the performance of the non-uniformly distributed laser arrays, with both 1D and 2D laser arrays exhibiting more uniformly distributed heat and more stable laser junction temperatures across the lasers compared to uniform laser distribution. In some examples, the temperature difference between the hottest laser in the array and the coldest laser in the array is significantly reduced. In examples, the temperature difference in the non-uniform 1D array is reduced by about half (e.g., from about 20K to about 10K for 1D laser arrays) or more (e.g., from about 26K to 11.5K for 2D laser arrays) in pulsed mode. For example, assuming a spectral shift of 0.5 nanometers per Kelvin, the spectral width can be reduced by more than 5 nanometers using this novel geometric design.

[0014]

[0024] In some examples, the lasers used may include one or more of ridge-type single quantum well (SQW) or multiple quantum well (MQW) semiconductor lasers, buried heterostructure (BH) SQW or MQW lasers, distributed feedback (DFB) or distributed Bragg reflector (DBR) lasers, vertical cavity surface emitting lasers (VCSELs), photonic crystal surface emitting lasers, InP-based lasers, GaAs-based lasers, GaSb-based lasers, GaN-based lasers, or other suitable lasers. However, while some disclosed examples relate to 1D and 2D laser arrays, in some examples, three-dimensional (3D) laser arrays may use the principles disclosed herein. Furthermore, although one or more laser types and / or wavelengths are described in some examples, the application of the concepts disclosed herein is not limited to a particular laser or wavelength. In some examples, lasers operating using wavelengths of 940 nanometers, 980 nanometers, 1350 nanometers, 1480 nanometers, and / or 1550 nanometers are disclosed as a non-limiting list of examples.

[0015]

[0025] The disclosed monolithic laser arrays may provide advantages for a variety of applications, such as three-dimensional sensing, including light detection and ranging (LIDAR), and telecommunications transmission, to name a non-limiting list of examples.

[0016]

[0026] FIG 1A shows a monolithic array of lasers 100. As shown, the array 100 is arranged as a one-dimensional (1D) array including uniformly spaced lasers 102 on a substrate 104. In the example of FIG 1A, the distance X between the lasers 102 in the array 100 may be fixed (e.g., about 22 micrometers). In other words, the distance or spacing between each laser 102 and each adjacent laser 102 is uniform. In some examples, the 1D lasers may be ridge lasers or other similarly configured laser devices.

[0017]

[0027] 1B and 1C provide graphical illustrations of temperature variation of the monolithic array of lasers of FIG. 1A. The figures provide data from a laser array 100 using a heat sink of about 300 K with an operating current of about 6 A and a pulsed mode with a duty cycle of about 5%. The graphs show a maximum ridge temperature T(K) of about 352 K and a minimum ridge temperature T(K) of about 332 K, with a difference of about 20 K. As shown in the example of FIG. 1C, the peak temperatures represent the corresponding laser junction temperatures.

[0018]

[0028] In an effort to reduce the difference between the maximum and minimum ridge temperatures, a non-uniform laser array is disclosed. The example of Figure 2A shows another monolithic array 200 of lasers. As shown, the array 200 is arranged as a one-dimensional (1D) array including non-uniformly spaced lasers 202 on a substrate 204.

[0019]

[0029] In the disclosed example, lasers 202 located in the central section of the array (e.g., closer to the centerline 206) have wider spacing between the lasers 202, as opposed to lasers located in the end sections, which have narrower spacing between the lasers.

[0020]

[0030] The change in distance Y1 between the lasers 202 of the first set 208A and the change in distance Y2 between the lasers 202 of the second set 208B may be calculated to form a constant difference across the array. In one example, the distance between adjacent lasers may be calculated by a linear change (e.g., according to Equations 1-4 disclosed herein). In another example, the distance between adjacent lasers may be calculated by an exponential change. In yet another example, the distance between adjacent lasers may be calculated by a polynomial. In some examples, the distance between the lasers of the first set in the array may be calculated by one of a linear change, an exponential change, or a polynomial change, while the distance between the lasers of the second set in the array may be calculated by another of a linear change, an exponential change, or a polynomial change.

[0021]

[0031] For example, the distance between lasers in an array can vary based on the distance from the centerline 206 of the array. In the example of Figure 2A, lasers 202 located near the centerline 206 are separated by a greater distance than lasers 202 located at the edges of the substrate 204.

[0022]

[0032] The distance between the lasers 202 in the array 200 may be calculated or determined based on one or more equations. For example, the distance value Y may be calculated according to Exemplary Equation 1 or Exemplary Equation 2, depending on whether the distance between the lasers is to be decreased or increased, respectively. Equation 1: Y=X-NC Equation 2: Y=X+NC

[0033] where X is a typical distance between the lasers, N is an integer (e.g., 1, 2, 3, 4, 5, etc.), and C is a constant determined based on the desired dimensions of the monolithic laser array, the particular application for the monolithic laser array, or other appropriate measure.

[0023]

[0034] In the example of FIG. 2A , a first distance Y1 between the lasers of the first set 208A may be calculated according to exemplary Equation 3, while a second distance Y2 between the lasers of the second set 208B may be calculated according to exemplary Equation 4. Formula 3: Y1=X-4C Formula 4: Y2=X+5C

[0035] In the example of Equation 1 through Equation 4, X may represent a uniform distance between the lasers (eg, about 22 micrometers), and C is a constant based on the desired dimensions of the monolithic laser array (eg, about 2 micrometers).

[0024]

[0036] Although Equations 1 through 4 express X as the distance between uniformly distributed lasers (e.g., the distance X shown in FIG. 1A), X may be any value and is not necessarily associated with a uniformly distributed laser array.

[0025]

[0037] In some examples, a given laser may be included in both the first and second set of lasers, and thus which set of lasers and adjacent lasers includes the first set or the second set is defined by the distance between the adjacent lasers.

[0026]

[0038] Although shown as two sets of lasers, there may be three, four, five, six, seven, eight, nine, ten or more sets of lasers distributed around the monolithic laser array. Each set may have different distances between the lasers within the set of lasers and / or between adjacent sets of lasers, or two or more sets may have the same distances between the lasers and / or adjacent sets.

[0027]

[0039] Figures 2B and 2C provide a graphical illustration of the temperature change of the monolithic array of lasers of Figure 2A, for example, a heat sink of about 300 K at an operating current of about 6 A in a pulsed mode with a duty cycle of about 5%. In the example of Figures 2B and 2C, the thermal simulation validates the concept that a non-uniform laser array distribution results in a more uniform heat distribution.

[0028]

[0040] For example, the example of Figure 1C shows a maximum ridge temperature T(K) of 352, and a minimum ridge temperature T(K) of 332, with a difference of about 20 K. The example of Figure 2C shows a maximum ridge temperature T(K) of 349, and a minimum ridge temperature T(K) of 339, resulting in a difference of about 10 K. Thus, a non-uniform distribution of lasers over an array shows a smaller difference between the maximum and minimum ridge temperatures when compared to an array with a uniform laser distribution.

[0029]

[0041] 3A illustrates yet another monolithic array of lasers 300. As shown, the array 300 is arranged as a two-dimensional (2D) array including uniformly spaced lasers 302 on a substrate 304. In the example of FIG. 3, the distance X between the lasers 302 in the array 300 can be fixed (e.g., about 22 micrometers). In other words, the distance or spacing between each laser 302 and each neighboring laser 302 is uniform.

[0030]

[0042] 3B, 3C, and 3D provide graphical illustrations of the temperature change of the monolithic array of lasers of FIG. 3A.

[0043] Similar to array 100 of Figure 1A, a non-uniform 2D array of lasers has been disclosed with the goal of reducing the difference between maximum and minimum ridge temperatures. Figure 4A shows yet another monolithic array of lasers 400. As shown, array 400 is arranged as a two-dimensional (2D) array including non-uniformly spaced lasers 402 on a substrate 404.

[0031]

[0044] In the disclosed example, lasers 402 positioned in a central section 406 of the array (e.g., at, around, or near the geometric center 407 of the array 400) have wider spacing between the lasers 402, as opposed to lasers 410 positioned in the end sections, where the lasers have closer spacing between the lasers.

[0032]

[0045] The change in distance Y1 between the lasers 402 of the first set 408A in the end section 410 and the change in distance Y2 between the lasers 402 of the second set 408B in the center section 406 can be calculated to produce a constant difference across the array. In one example, the distance between adjacent lasers can be calculated with a linear change (e.g., according to Equations 1-4 disclosed herein). In the example of Equation 3 and Equation 4, X can be assigned a value of approximately 25 micrometers, N can be assigned a value of 1, and C can be assigned a value of approximately 8 micrometers. In some examples, the value of X can correspond to Y3, or the distance separating the first set 408A and the second set 408B.

[0033]

[0046] In another example, the distance between adjacent lasers may be calculated by an exponential change. In yet another example, the distance between adjacent lasers may be calculated by a polynomial. In some examples, the distance between a first set of lasers in the array may be calculated by one of a linear change, an exponential change, or a polynomial change, while the distance between a second set of lasers in the array may be calculated by another of a linear change, an exponential change, or a polynomial change.

[0034]

[0047] 4B, 4C, and 4D provide graphical illustrations of the temperature change of the monolithic array of lasers of FIG. 4A.

[0048] 5A through 7B provide further graphical illustrations of temperature data for the non-uniform laser arrays disclosed herein, including a comparison with a uniform laser array.

[0035]

[0049] 5A through 5F provide graphical illustrations of example temperature distributions of a monolithic array of non-uniform 1D lasers where the constant C varies when applied to Equations 3 and 4. For example, FIG. 5A shows an example temperature distribution associated with a C value of 0 micrometers, FIG. 5B shows an example temperature distribution associated with a C value of 0.55 micrometers, FIG. 5C shows an example temperature distribution associated with a C value of 0.7 micrometers, FIG. 5D shows an example temperature distribution associated with a C value of 1 micrometer, FIG. 5E shows an example temperature distribution associated with a C value of 2 micrometers, and FIG. 5F shows an example temperature distribution associated with a C value of 3 micrometers.

[0036]

[0050] As shown, the maximum and minimum temperatures may vary depending on the selected value of C and the difference between the maximum and minimum temperature values.

[0051] Furthermore, the simulation data indicates that the 2D uniform laser array 300 (with a uniform laser distance of about 25 micrometers) produces a maximum ridge temperature T(K) of about 392 K and a minimum ridge temperature T(K) of about 366 K, with a difference of about 26 K. In contrast, the experimental data indicates that the 2D non-uniform laser array 400 (with a non-uniform laser distance with a linear variation of about 25 micrometers + / - NC according to Equations 1-4) produces a maximum ridge temperature T(K) of about 385 K and a minimum ridge temperature T(K) of about 372 K, with a difference of about 13 K. Thus, the thermal simulation data validates the concept that a non-uniformly distributed 2D array produces a more uniform thermal distribution that narrows the optical spectral width.

[0037]

[0052] 6A and 6B provide a graphical illustration of the temperature change of a monolithic array of 1D lasers separated by a linear constant C, according to the example of FIG. 2A. For example, over a range of values ​​for the constant C (applied to Equations 1-4), the temperature difference between the hot and cold lasers is reduced from about 20 K to about 9.5 K.

[0038]

[0053] For example, for a constant value C=0, the maximum ridge temperature T(K) is about 352K and the minimum ridge temperature T(K) is about 332K, with a difference of about 20K.

[0054] In contrast, for a constant value of C=2, there is a maximum ridge temperature T(K) of about 349.5K and a minimum ridge temperature T(K) of about 340K, with a difference of about 9.5K.

[0039]

[0055] 7A and 7B provide a graphical illustration of the temperature change of a monolithic array of 2D lasers separated by a linear constant K, according to the example of FIG. 4A. For example, over a range of values ​​for the constant C (applied to Equations 1-4), the temperature difference between the hot and cold lasers is reduced from about 25 K to about 11.5 K.

[0040]

[0056] For example, for a 2D non-uniform laser array 400, when the distance between adjacent lasers is calculated using a linear constant C=0, the maximum ridge temperature T(K) is equal to about 392 K and the minimum ridge temperature T(K) is equal to about 367 K. As a result, the difference between the maximum and minimum ridge values ​​is about 25 K. At a linear constant value of C=10, the difference decreases to 11.5 K. Thus, the thermal simulation data validates the concept that a non-uniformly distributed 2D array results in a more uniform thermal distribution that narrows the spectral width.

[0041]

[0057] The above description of preferred and other embodiments is not intended to limit or restrict the scope or applicability of the inventive concepts conceived by applicants. With the benefit of this disclosure, it will be understood that the features described above with any embodiment or aspect of the disclosed subject matter may be used alone or in combination with any other described features in any other embodiment or aspect of the disclosed subject matter. [Explanation of symbols]

[0042] 100 Laser, Array 102 Laser 104 Base material 200 Monolithic Array, Array 202 Laser 204 Base material 206 Center line 208A First Set 208B Second Set 300 Laser, Array 302 Laser 304 Base material 400 Laser, Array 402 Laser 404 Base material 406 Central Section 407 Geometric Center 410 Laser 410 End Section 408A First Set 408B Second Set

Claims

1. a first set of lasers spaced a first distance apart; a second set of lasers spaced apart a second distance greater than the first distance; and A monolithic laser array comprising:

2. 10. The monolithic laser array of claim 1, wherein one or more lasers of the first set or the second set of lasers are one-dimensional (1D) lasers.

3. 3. The monolithic laser array of claim 2, wherein the second set of 1D lasers is positioned proximate to a centerline of the array.

4. 4. The monolithic laser array of claim 3, wherein the first set of 1D lasers is positioned on an opposite side of the centerline relative to a position of the second set of 1D lasers in the array.

5. 3. The monolithic laser array of claim 2, wherein the first set or the second set of 1D lasers includes two lasers.

6. 10. The monolithic laser array of claim 1, wherein one or more lasers of the first set or the second set of lasers are two-dimensional (2D) lasers.

7. 7. The monolithic laser array of claim 6, wherein the second set of 2D lasers are arranged around a center of the array.

8. 8. The monolithic laser array of claim 7, wherein the first set of 2D lasers is positioned on the opposite side of the center relative to a position of the second set of 2D lasers in the array.

9. 7. The monolithic laser array of claim 6, wherein the first set or the second set of 2D lasers includes four lasers.

10. 10. The monolithic laser array of claim 1, wherein the first distance is calculated by one of a linear equation, an exponential equation, or a polynomial equation.

11. 2. The monolithic laser array of claim 1, wherein the first distance Y １ Is Y １ =X-NC, where X is the typical distance between the lasers, N is an integer, and C is a constant for a monolithic laser array.

12. 2. The monolithic laser array of claim 1, wherein the second distance Y ２ Is Y ２ =X+NC, where X is the typical distance between the lasers, N is an integer, and C is a constant.

13. 10. The monolithic laser array of claim 1, wherein the first distance or the second distance is in a range between 5 micrometers and 30 micrometers.

14. 10. The monolithic laser array of claim 1 , wherein one or more lasers of the first or second set of lasers are one or more of a ridge-type single quantum well (SQW) or multiple quantum well (MQW) semiconductor laser, a buried heterostructure (BH) SQW or MQW laser, a distributed feedback (DFB) or distributed Bragg reflector (DBR) laser, a vertical cavity surface emitting laser (VCSEL), a photonic crystal surface emitting laser, an InP-based laser, a GaAs-based laser, a GaSb-based laser, a GaN-based laser, or other suitable laser.

15. 10. The monolithic laser array of claim 1 further comprising a substrate supporting the first and second sets of lasers.

16. 1. A monolithic laser array for providing a substantially uniform temperature distribution, comprising: A substrate; a first set of lasers disposed on the substrate and spaced a first distance apart; a second set of lasers disposed on the substrate and spaced apart a second distance greater than the first distance; A monolithic laser array comprising:

17. 17. The monolithic laser array of claim 16, further comprising a third set of lasers disposed on the substrate and spaced apart a third distance.

18. 17. The monolithic laser array of claim 16, wherein one or more lasers of the first set or the second set of lasers are one-dimensional (1D) lasers; a first pair of the first and second sets of 1D lasers are disposed on a first portion of the substrate, and a second pair of the first and second sets of 1D lasers are disposed on a second portion of the substrate, the first and second portions being separated by a centerline of the array; Monolithic laser array.

19. 17. The monolithic laser array of claim 16, wherein one or more lasers of the first set or the second set of lasers are two-dimensional (2D) lasers.

20. 20. The monolithic laser array of claim 19, wherein the second set of 2D lasers are arranged around a center of the substrate, and one or more of the first set of 2D lasers are arranged on the substrate around the second set.

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