Semiconductor laser

Abstract

Disclosed are semiconductor lasers having active regions with a longitudinal axis, a first facet end, and a second facet end. The second facet end emits a primary output beam from each semiconductor laser. The first facet end may have a low reflectivity coating. The first facet end may be non-perpendicular to the longitudinal axis of the active region. The semiconductor lasers may be distributed feedback (DFB) lasers having multiple gratings along the longitudinal axis of the active region. The multiple gratings may include three different gratings. The first grating may be spaced a first distance from the third grating along the longitudinal axis of the active region. The second grating may be spaced a second distance from the third grating along the longitudinal axis of the active region.

Description

Related Applications

[0001]

[0001] This application is related to U.S. patent application Ser. No. 17 / 204,550, "SEMICONDUCTOR LASERS," filed on March 17, 2021, the entire disclosure of which is expressly incorporated by reference into this specification. [Technical field]

[0002] This disclosure relates to semiconductor lasers, and more particularly to distributed feedback (DFB) semiconductor lasers having multiple gratings. [Background technology]

[0003]

[0003] Referring to Figure 1, a conventional semiconductor laser 10 is shown having multiple distributed feedback (DFB) gratings 12. The conventional semiconductor laser 10 includes an active layer 14, an n-type cladding layer 16, and a p-type cladding layer 18. The active layer 14 has a longitudinal axis 20. The active layer 14 is bounded longitudinally by a rear facet 30 and a front facet 32. The rear facet 30 is provided with a high reflectivity coating. An exemplary high reflectivity coating reflects 50% or more of the incident light. The front facet 32 ​​is provided with a low reflectivity coating. An exemplary low reflectivity coating reflects less than 5% of the incident light.

[0004]

[0004] The plurality of DFB gratings 12 includes a rear standard grating 40 located adjacent to the rear facet 30 and having a longitudinal length 42, a front standard grating 44 located adjacent to the front facet 32 ​​and having a longitudinal length 46, and a third grating 48 located between the rear standard grating 40 and the front standard grating 44 and having a longitudinal length 50. The rear standard grating 40 and the third grating 48 are separated by a region 52, and the front standard grating 44 and the third grating 48 are separated by a region 54. Each of the regions 52 and 54 does not include any grating structure. For example, each of the regions 52 and 54 is composed of a p-type cladding material, and there may be no grating structure. In another example, each of the regions 52 and 54 includes a block of a material different from the p-type cladding material, and there may be no grating structure. Thus, the rear standard grating 44 and the third grating 48 are discontinuous, and the third grating 48 and the front standard grating 44 are also discontinuous. The third grating 48 has a different pitch than the rear standard grating 40 and the front standard grating 44.

[0005] 2, the longitudinal length of the active layer 14 is approximately 150 microns (μm), the longitudinal length 42 of the rear standard grating 40 is approximately 25 μm, the longitudinal length 46 of the front standard grating 44 is approximately 75 μm, and the longitudinal length 50 of the third grating 48 is approximately 50 μm. It is understood that the longitudinal lengths of the regions 52 and 54 are approximately 100 nanometers (nm) or 300 nm and are not shown in FIG.

[0006] The semiconductor laser 10 has an active layer made of III-V material, an n-type cladding layer 16 made of III-V material, and a p-type cladding layer 18 made of III-V material. The pitch of the rear standard grating 40 is around 200 nm. Summary of the Invention

[0007] In one exemplary embodiment of the present disclosure, a semiconductor laser is provided that includes an active region having a longitudinal axis, a first facet end, and a second facet end, the second facet end emitting an output beam from the semiconductor laser, a first low-reflectivity coating on the first facet end of the active region, a second low-reflectivity coating on the second facet end of the active region, and a plurality of diffraction gratings disposed along the longitudinal axis of the active region. The plurality of diffraction gratings includes a first diffraction grating positioned proximate a first facet end of the active region, a second diffraction grating positioned proximate a second facet end of the active region, and a third diffraction grating positioned between the first and second diffraction gratings, the first diffraction grating being spaced a first distance from the third diffraction grating along a longitudinal axis of the active region and the second diffraction grating being spaced a second distance from the third diffraction grating along the longitudinal axis of the active region, the first distance and the second distance each being greater than zero.

[0008] In one example, the midpoint of the third grating along the longitudinal axis of the active region is located closer to the second facet edge of the active region than to the first facet edge of the active region. In one variation, the midpoint of the third grating is located along the longitudinal axis of the active region approximately 60% of the length of the active region from the first facet edge. In another variation, the third grating includes a first end and a second end spaced apart along the longitudinal axis of the active region, the second end of the third grating being located more than twice as far from the second facet edge of the active region than the first end of the third grating is along the longitudinal axis of the active region. In another variation, the midpoint of the third grating is located at least 40% spaced from the first facet edge relative to the total length from the first facet edge to the second facet edge.

[0009]

[0009] In another example, the midpoint of the third diffraction grating is positioned along the longitudinal axis of the active region at a spacing from the first facet end within a range of approximately 30% to approximately 70% of the total length from the first facet end to the second facet end.

[0010]

[0010] In another example, the third diffraction grating includes a first end and a second end spaced apart along a longitudinal axis of the active region, and the second end of the third diffraction grating is positioned along the longitudinal axis of the active region more than twice as far from the second facet edge of the active region as the first end of the third diffraction grating.

[0011]

[0011] In yet another example thereof, the midpoint of the third diffraction grating is positioned along the longitudinal axis of the active region at a distance from the first facet end that is at least 40% of the total length from the first facet end to the second facet end.

[0012] In yet another example thereof, each of the first diffraction gratings has a first constant pitch and the second diffraction grating has a second constant pitch. In one variation thereof, the first constant pitch is equal to the second constant pitch.

[0013]

[0013] In yet another example thereof, the midpoint of the third diffraction grating is positioned along the longitudinal axis of the active region at a distance from the first facet edge of at least 47% of the total length from the first facet edge to the second facet edge.

[0014]

[0014] In yet another example thereof, the midpoint of the third diffraction grating is positioned along the longitudinal axis of the active region at a distance from the first facet end that is at least 53% of the total length from the first facet end to the second facet end.

[0015]

[0015] In yet another example thereof, the midpoint of the third diffraction grating is positioned along the longitudinal axis of the active region at a distance from the first facet end that is at least 60% of the total length from the first facet end to the second facet end.

[0016] In yet another embodiment thereof, the third grating is a corrugated pitch modulated grating.

[0017] In yet another embodiment thereof, the third grating is a quarter-wave shift grating structure.

[0018] In another exemplary embodiment thereof, a semiconductor laser is provided comprising: an active region having a longitudinal axis, a first facet end and a second facet end, the first facet end being non-perpendicular to the longitudinal axis and the second facet end emitting an output beam from the semiconductor laser, a first low reflectivity coating on the second facet end of the active region, and a plurality of diffraction gratings disposed along the longitudinal axis of the active region. The plurality of diffraction gratings includes a first diffraction grating positioned proximate a first facet end of the active region, a second diffraction grating positioned proximate a second facet end of the active region, and a third diffraction grating positioned between the first and second diffraction gratings, the first diffraction grating being spaced a first distance from the third diffraction grating along a longitudinal axis of the active region and the second diffraction grating being spaced a second distance from the third diffraction grating along the longitudinal axis of the active region, the first distance and the second distance each being greater than zero.

[0019] In one example, a midpoint of the third grating along the longitudinal axis of the active region is located closer to the second facet edge of the active region than to the first facet edge of the active region.

[0020] In another example thereof, the midpoint of the third grating is disposed along the longitudinal axis of the active region at a spacing from the first facet edge that is in the range of about 30% to about 70% of the total length from the first facet edge to the second facet edge. In one variation thereof, the midpoint of the third grating is disposed along the longitudinal axis of the active region at about 60% of the length of the active region from the first facet edge. In another variation thereof, the third grating includes a first end and a second end spaced apart along the longitudinal axis of the active region, the second end of the third grating being disposed more than twice as far from the second facet edge of the active region as the first end of the third grating is disposed along the longitudinal axis of the active region. In yet another variation thereof, the midpoint of the third diffraction grating is disposed along the longitudinal axis of the active region at a spacing from the first facet edge of at least 40% of the total length from the first facet edge to the second facet edge.

[0021]

[0021] In another example, the third diffraction grating includes a first end and a second end spaced apart along the longitudinal axis of the active region, and the second end of the third diffraction grating is positioned along the longitudinal axis of the active region more than twice as far from the second facet edge of the active region as the first end of the third diffraction grating.

[0022]

[0022] In yet another example thereof, the midpoint of the third diffraction grating is positioned along the longitudinal axis of the active region at a distance from the first facet end that is at least 40% of the total length from the first facet end to the second facet end.

[0023] In yet another example thereof, each of the first diffraction gratings has a first constant pitch and the second diffraction grating has a second constant pitch. In one variation thereof, the first constant pitch is equal to the second constant pitch.

[0024]

[0024] In yet another example thereof, the midpoint of the third diffraction grating is positioned along the longitudinal axis of the active region at a distance from the first facet edge of at least 47% of the total length from the first facet edge to the second facet edge.

[0025]

[0025] In yet another example thereof, the midpoint of the third diffraction grating is positioned along the longitudinal axis of the active region at a distance from the first facet end that is at least 53% of the total length from the first facet end to the second facet end.

[0026]

[0026] In yet another example thereof, the midpoint of the third diffraction grating is positioned along the longitudinal axis of the active region at a distance from the first facet end that is at least 60% of the total length from the first facet end to the second facet end.

[0027] In yet another embodiment thereof, the semiconductor laser further comprises a second low reflectivity coating disposed on the first facet end of the active region.

[0028] In another example thereof, the third grating is a corrugated pitch modulated grating.

[0029] In another example thereof, the third diffraction grating is a quarter-wave shift grating structure. [Brief description of the drawings]

[0030] The foregoing and other features and advantages of the present disclosure, as well as the manner in which the same are achieved, will become more apparent and will be better understood by reference to the following description of illustrative embodiments taken in conjunction with the accompanying drawings. [Figure 1] FIG. 1 is a representative diagram of a conventional distributed feedback semiconductor laser including multiple gratings spaced apart along the longitudinal axis of the active region. [Diagram 2] 2 is a representative diagram of the lengths of a plurality of diffraction gratings in the conventional distributed feedback semiconductor laser of FIG. 1. [Diagram 3] FIG. 2 is a representative side view of an exemplary distributed feedback semiconductor laser of the present disclosure including multiple gratings spaced along the longitudinal axis of the active region and a low-reflectivity coating on the front facet and a low-reflectivity coating on the rear facet. [Figure 4] 4 is a representative top view of the exemplary distributed feedback semiconductor laser of FIG. 3. [Diagram 5] FIG. 1 is a representative side view of an exemplary distributed feedback semiconductor laser of the present disclosure including multiple gratings spaced apart along the longitudinal axis of the active region, a low reflectivity coating on the front facet, and an angled, uncoated rear facet angled in the yz plane. [Figure 6] 6 is a representative top view of the example distributed feedback semiconductor laser of FIG. 5 with an angled uncoated rear facet in the xy plane instead of the yz plane shown in FIG. 5. [Figure 7] FIG. 1 is a representative side view of an exemplary distributed feedback semiconductor laser of the present disclosure including multiple gratings spaced along the longitudinal axis of the active region and a low-reflectivity coating on the front facet and a low-reflectivity coating on the rear facet angled in the yz-plane. [Figure 8] FIG. 2 is a representative diagram of another exemplary distributed feedback semiconductor laser of the present disclosure including multiple gratings spaced along the longitudinal axis of the active region and a grating with reduced κ by a drop grating technique. [Figure 9] 4 is a representation of a first example of grating lengths for each of a plurality of gratings of the example distributed feedback semiconductor laser of FIG. 3. [Figure 10] 4 is a representation of a second example of lengths of each of the multiple diffraction gratings of the example distributed feedback semiconductor laser of FIG. 3. [Figure 11] 4 is a representation of a third example of grating lengths for each of the multiple gratings of the example distributed feedback semiconductor laser of FIG. 3. [Figure 12] 4 is a representation of a fourth example of grating lengths for each of the multiple gratings of the example distributed feedback semiconductor laser of FIG. 3. [Figure 13] 5 is a representation of a fifth example of grating lengths for each of the multiple gratings of the example distributed feedback semiconductor laser of FIG. 3. [Figure 14] FIG. 9 shows a comparison of the overall yield of example devices described in FIGS. 4-8 that meet side mode suppression ratio thresholds versus the conventional distributed feedback semiconductor laser of FIG. 2 at multiple temperatures. Corresponding reference characters indicate corresponding parts throughout the multiple views. The illustrations described herein are illustrative of an exemplary embodiment of the invention, and such illustrations should not be construed as limiting the scope of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031]

[0046] For the purpose of promoting an understanding of the principles of the present disclosure, reference will now be made to the embodiments illustrated in the following drawings. The embodiments disclosed herein are not intended to be exhaustive or to limit the disclosure to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so as to enable those skilled in the art to utilize their teachings. Thus, no limitation of the scope of the present disclosure is intended. Corresponding reference characters indicate corresponding parts throughout the various drawings.

[0032]

[0047] The terms "couples," "coupled," "coupler," and variations thereof are used to include both configurations where two or more components are in direct physical contact, and configurations where two or more components are not in direct contact with each other (e.g., the components are "coupled" through at least a third component), but still cooperate or interact with each other.

[0033]

[0048] Unless otherwise specified, all numbers expressing size, quantities, and physical properties of features used in the specification and claims are understood to be modified in all instances by the term "about." Accordingly, unless otherwise specified, the numerical parameters set forth in the specification and appended claims are approximations that may vary depending upon the desired properties one of ordinary skill in the art would seek to obtain using the teachings disclosed herein.

[0034]

[0049] At times throughout this disclosure and in the claims, numerical terms such as first, second, third, and fourth are used in connection with various components or features. Such use is not intended to indicate an ordering of the components or features. Rather, the numerical terms are used to aid the reader in identifying the referenced components or features and should not be narrowly construed as conferring a particular ordering of the components or features.

[0035]

[0050] Referring to Figure 3, a side view of an exemplary semiconductor laser 100 having multiple distributed feedback (DFB) gratings 112 is shown. Figure 4 is a top view of the semiconductor laser 100. The semiconductor laser 100 comprises an active layer 114, an n-type cladding layer 116, and a p-type cladding layer 118. The active layer 114 has a longitudinal axis 120. The active layer 114 is bounded longitudinally by a rear facet 130 and a front facet 132. In an embodiment, the n-type cladding layer 116 is disposed below the active layer 114 and the p-type cladding layer 118 is disposed above the active layer 114.

[0036]

[0051] The front facet 132 is provided with a low reflectivity coating. An exemplary low reflectivity coating reflects up to approximately 5% of the incident light. In the embodiment shown in Figures 3 and 4, the rear facet 130 is provided with a low reflectivity coating and is perpendicular to the longitudinal axis 120 of the semiconductor laser 100. An exemplary low reflectivity coating reflects up to approximately 5% of the incident light. With reference to Figures 5 and 6, another embodiment of the semiconductor laser 100' is shown in which the rear facet 130 is uncoated and angled with respect to the longitudinal axis 120 of the semiconductor laser 100. In the example shown in Figure 5, the rear facet 130 is angled in the YZ plane. In the example shown in Figure 6, the rear facet 130 is angled in the XY plane. Referring to FIG. 7, another embodiment of a semiconductor laser 100″ is shown in which the rear facet 130 is provided with a low reflectivity coating and angled in the YZ plane with respect to the longitudinal axis 120 of the semiconductor laser 100. An exemplary low reflectivity coating reflects up to approximately 5% of the incident light. The use of a low reflectivity coating or angled facets can eliminate the effect of facet phase on the SMSR yield of the device and reduce gradient variations across the operating temperature of the semiconductor laser 100, 100′, 100″, as compared to the high reflectivity coating of the conventional semiconductor laser 10 of FIG.

[0037]

[0052] 3 and 4, the plurality of DFB gratings 112 includes a rear standard diffraction grating 140 positioned adjacent to the rear facet 130 and having a longitudinal length 142, a front standard diffraction grating 144 positioned adjacent to the front facet 132 and having a longitudinal length 146, and a third grating 148 positioned between the rear standard diffraction grating 140 and the front standard diffraction grating 144 and having a longitudinal length 150.

[0038]

[0053] The rear standard grating 140 and the grating 148 are separated by a region 152, and the front standard grating 144 and the grating 148 are separated by a region 154. The regions 152 and 154 each do not include any grating structure. For example, the regions 152 and 154 each consist of p-type cladding material and there may be no grating structure. In another example, the regions 152 and 154 each include a block of a material different from the p-type cladding material and there may be no grating structure. Thus, the rear standard grating 144 and the grating 148 are discontinuous, and the grating 148 and the front standard grating 144 are also discontinuous. In the illustrated embodiment, the grating 148 is a corrugated pitch modulated (CPM) grating.

[0039]

[0054] In an embodiment, the grating 148 is a quarter-wave shift (QWS) grating structure. The quarter-wave shift grating structure includes a first grating region and a second grating region, each having a constant grating pitch and depth. The first grating region and the second grating region are joined with a phase jump π at the interface between the first grating structure and the second grating structure. In an embodiment, instead of the CPM structure of the grating 148, the quarter-wave shift grating structure may exclude the regions 152 and 154. In an embodiment, instead of the CPM structure of the grating 148, the quarter-wave shift grating structure maintains the regions 152 and 154.

[0040]

[0055] The semiconductor laser 100 may have a ridge waveguide structure or a buried heterostructure as shown in Figures 4 and 6. Exemplary materials for the n-type cladding layer 116 include III-V materials. Exemplary materials for the p-type cladding layer 118 include III-V materials. Exemplary materials for the active layer 114 include III-V materials.

[0041]

[0056] Referring to FIG. 3, the rear standard grating 140 has a constant pitch. In an embodiment, the constant pitch is approximately 200 nanometers (nm), although longer or shorter pitches may be implemented. In an embodiment, the rear grating 140 may be a chirped grating with a non-constant pitch. In an embodiment, the front standard grating 144 has a constant pitch. In an embodiment, the constant pitch is approximately 200 nanometers (nm), although longer or shorter pitches may be implemented. In an embodiment, the front grating 144 may be a chirped grating with a non-constant pitch. In an embodiment, the pitch of the rear standard grating 140 is equal to the pitch of the front standard grating 144. In an embodiment, the pitch of the rear standard grating 140 is not equal to the pitch of the front standard grating 144. In an embodiment, the pitch of the grating 148 is less than the pitch of the rear standard grating 140 and the pitch of the front standard grating 144. In an embodiment, the pitch of the grating 148 is longer than the pitch of the rear standard grating 140 and the pitch of the front standard grating 144 .

[0042]

[0057] 8, another embodiment of the laser 100 is shown in which the front grating 144' has a reduced grating strength by a drop grating pitch method in which the front grating 144' lacks a portion of the periodic grating structure. In an embodiment, the grating strength of one or more portions of the DFB gratings 112 can be reduced to adjust the power distribution along the longitudinal axis 120 of the laser 100. In an embodiment, one or more portions of the DFB gratings 112 can be a uniform grating or a chirped grating.

[0043]

[0058] 9-13 show various exemplary embodiments of laser 100. All of the illustrated embodiments have an overall length of approximately 150 microns (μm), although shorter or longer lasers may be produced. Additionally, all of the illustrated embodiments have a length of grating 148 of approximately 50 μm, while shorter or longer gratings 148 may be produced. Additionally or alternatively, the midpoint of grating 148 may be shifted toward rear facet 130 or front facet 132, such as within a range of approximately 30% to approximately 70%. For example, in a laser 100 with a length of 150 μm, the midpoint of grating 148 may be approximately 45 μm (approximately 30%) from rear facet 130 to approximately 105 μm (approximately 70%) from rear facet.

[0044]

[0059] Referring to Figure 9, an example of the laser 100 of Figure 3 is provided. The longitudinal length of the active layer 114 is approximately 150 microns (μm), the longitudinal length 142 of the rear standard grating 140 is approximately 65 μm, the longitudinal length 146 of the front standard grating 144 is approximately 35 μm, and the longitudinal length 150 of the grating 148 is approximately 50 μm. The rear facet 130 and the front facet 132 are each provided with a low reflectance coating. In an embodiment, the rear facet 130 is perpendicular to the longitudinal axis of the active layer 114 and is provided with a low reflectance coating. In an embodiment, the rear facet 130 is angled relative to the longitudinal axis of the active layer 114 and is provided with a low reflectance coating. In an embodiment, the rear facet 130 is angled relative to the longitudinal axis of the active layer 114 and is uncoated.

[0045]

[0060] Referring to Figure 10, an example of the laser 100 of Figure 3 is provided. The longitudinal length of the active layer 114 is approximately 150 microns (μm), the longitudinal length 142 of the rear standard grating 140 is approximately 55 μm, the longitudinal length 146 of the front standard grating 144 is approximately 45 μm, and the longitudinal length 150 of the grating 148 is approximately 50 μm. The rear facet 130 and the front facet 132 are each provided with a low reflectance coating. In an embodiment, the rear facet 130 is perpendicular to the longitudinal axis of the active layer 114 and is provided with a low reflectance coating. In an embodiment, the rear facet 130 is angled relative to the longitudinal axis of the active layer 114 and is provided with a low reflectance coating. In an embodiment, the rear facet 130 is angled relative to the longitudinal axis of the active layer 114 and is uncoated.

[0046]

[0061] Referring to Figure 11, an example of the laser 100 of Figure 3 is provided. The longitudinal length of the active layer 114 is approximately 150 microns (μm), the longitudinal length 142 of the rear standard grating 140 is approximately 45 μm, the longitudinal length 146 of the front standard grating 144 is approximately 55 μm, and the longitudinal length 150 of the grating 148 is approximately 50 μm. The rear facet 130 and the front facet 132 are each provided with a low reflectance coating. In an embodiment, the rear facet 130 is perpendicular to the longitudinal axis of the active layer 114 and is provided with a low reflectance coating. In an embodiment, the rear facet 130 is angled relative to the longitudinal axis of the active layer 114 and is provided with a low reflectance coating. In an embodiment, the rear facet 130 is angled relative to the longitudinal axis of the active layer 114 and is uncoated.

[0047]

[0062] Referring to Figure 12, an example of the laser 100 of Figure 3 is provided. The longitudinal length of the active layer 114 is approximately 150 microns (μm), the longitudinal length 142 of the rear standard grating 140 is approximately 35 μm, the longitudinal length 146 of the front standard grating 144 is approximately 65 μm, and the longitudinal length 150 of the grating 148 is approximately 50 μm. The rear facet 130 and the front facet 132 are each provided with a low reflectance coating. In an embodiment, the rear facet 130 is perpendicular to the longitudinal axis of the active layer 114 and is provided with a low reflectance coating. In an embodiment, the rear facet 130 is angled relative to the longitudinal axis of the active layer 114 and is provided with a low reflectance coating. In an embodiment, the rear facet 130 is angled relative to the longitudinal axis of the active layer 114 and is uncoated.

[0048]

[0063] Referring to Figure 13, an example of the laser 100 of Figure 3 is provided. The longitudinal length of the active layer 114 is approximately 150 microns (μm), the longitudinal length 142 of the rear standard grating 140 is approximately 25 μm, the longitudinal length 146 of the front standard grating 144 is approximately 65 μm, and the longitudinal length 150 of the grating 148 is approximately 50 μm. The rear facet 130 and the front facet 132 are each provided with a low reflectance coating. In an embodiment, the rear facet 130 is perpendicular to the longitudinal axis of the active layer 114 and is provided with a low reflectance coating. In an embodiment, the rear facet 130 is angled relative to the longitudinal axis of the active layer 114 and is provided with a low reflectance coating. In an embodiment, the rear facet 130 is angled relative to the longitudinal axis of the active layer 114 and is uncoated.

[0049]

[0064] 9-13 are given in Table 1. The ratios of the longitudinal length 142, the longitudinal length 146, and the longitudinal length 150 to the length of the active layer 114 are given in Table 2. The ratios of the trailing edge, leading edge, and midpoint of the grating 148 to the distance to the rear facet 130 are given in Table 3.

[0050] [Table 1] [Table 2] [Table 3]

[0065] In an embodiment, the midpoint of the grating 148 along the longitudinal axis 120 of the active region 114 is located closer to the facet edge 132 of the active region 114 than to the facet edge 130 of the active region 114. In an embodiment, the midpoint of the grating 148 may be located along the longitudinal axis 120 of the active region 114 within about 30% to about 70% from the rear facet 130. In an embodiment, the midpoint of the grating 148 may be located along the longitudinal axis 120 of the active region 114 within about 33% to about 60% from the rear facet 130.

[0051]

[0066] In embodiments, the rear end 160 of the grating 148 may be disposed along the longitudinal axis 120 of the active region 114 more than twice as far from the facet edge 132 of the active region 114 as the front end 162 of the grating 148. In embodiments, the front end 162 of the grating 148 may be disposed along the longitudinal axis 120 of the active region 114 up to approximately 37% of the total longitudinal length of the active region 114 from the facet edge 132.

[0052]

[0067] 14, a chart 170 illustrates a simulation of the percentage of devices meeting the side mode suppression ratio (SMSR) yield threshold (e.g., SMSR>37 kB) for each of the devices of FIGS. 9-13 and 2 at multiple operating temperatures. The leftmost bar for each device is at an operating temperature of −40° C. The center bar for each device is at an operating temperature of 25° C. The rightmost bar for each device is at an operating temperature of 95° C. As shown, compared to the device of FIG. 2, the devices of FIGS. 9-11 each have a higher percentage at each operating temperature. Additionally, moving the grating system 148 forward compared to the device of FIG. 2 results in a higher percentage of devices meeting the SMSR yield threshold for multiple operating temperatures. Thus, using a low reflectivity coating on the facet edge 130 and moving the grating system 148 toward the facet edge 132 results in a higher percentage of SMSR yield compared to the device of FIG. 2 at the operating temperatures shown. Among other benefits, the use of a low reflectivity coating on facet 130 eliminates any phase shift at facet 130 and thus the effect of the phase shift on the device SMSR yield and laser slope, as shown in FIGS.

[0053]

[0068] The laser slope of the device of FIG. 9 is higher than that of the device of FIG. 2 at an operating temperature of 25° C. Furthermore, the laser slope over the entire range of −40° C. to 95° C. is tighter for the device of FIG. 9 compared to the device of FIG. 2. Notably, the advantage of having a tighter slope over the entire temperature range is that the tracking error is smaller for the device of FIG. 9 compared to the device of FIG. 2. The high frequency 3 dB bandwidth (GHz) of each of the devices of FIGS. 9-13 generally has a wider 3 dB bandwidth than the design of FIG. 2 due to the smaller attenuation coefficient.

[0054]

[0069] By replacing the high reflectivity coating of laser 10 with a low reflectivity coating of laser 100 and / or an angled rear facet of laser 100, near 100% SMSR yield, increased front facet power, and / or improved high speed modulation performance can be achieved based on the grating characteristics.

[0055]

[0070] While the invention has been described as having an exemplary design, it is possible to further modify it within the spirit and scope of the disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the disclosure as come within known custom or practice in the art to which this invention pertains.

Claims

1. 1. A semiconductor laser, comprising: an active region having a longitudinal axis, a first facet end, and a second facet end, the second facet end emitting an output beam from the semiconductor laser; a first low reflectivity coating disposed on the first facet edge of the active region; a second low reflectivity coating disposed on the second facet edge of the active region; and a plurality of diffraction gratings disposed along the longitudinal axis of the active region, the plurality of diffraction gratings including a first diffraction grating disposed proximate to a first facet edge of the active region, a second diffraction grating disposed proximate to a second facet edge of the active region, and a third diffraction grating disposed between the first diffraction grating and the second diffraction grating, the first diffraction grating being spaced a first distance along the longitudinal axis of the active region from the third diffraction grating and the second diffraction grating being spaced a second distance along the longitudinal axis of the active region from the third diffraction grating, the first distance and the second distance each being greater than zero; A semiconductor laser comprising:

2. 2. The semiconductor laser of claim 1 , wherein a midpoint of the third grating along the longitudinal axis of the active region is located closer to the second facet edge of the active region than to the first facet edge of the active region.

3. 2. The semiconductor laser of claim 1 , wherein a midpoint of the third diffraction grating is disposed along the longitudinal axis of the active region at a spacing from the first facet edge within a range of about 30% to about 70% of the total length from the first facet edge to the second facet edge.

4. 3. The semiconductor laser of claim 2, wherein the midpoint of the third diffraction grating is disposed along the longitudinal axis of the active region approximately 60% of the length of the active region from the first facet edge.

5. 3. The semiconductor laser of claim 2, wherein the third grating includes a first end and a second end spaced apart along the longitudinal axis of the active region, the second end of the third grating being disposed more than two times farther along the longitudinal axis of the active region from the second facet edge of the active region than the first end of the third grating.

6. 3. The semiconductor laser of claim 2, wherein the midpoint of the third diffraction grating is disposed along the longitudinal axis of the active region at a spacing from the first facet edge that is at least 40% of the total length from the first facet edge to the second facet edge.

7. 2. The semiconductor laser of claim 1, wherein the third grating includes a first end and a second end spaced apart along the longitudinal axis of the active region, the second end of the third grating being disposed along the longitudinal axis of the active region more than two times farther from the second facet edge of the active region than the first end of the third grating.

8. 2. The semiconductor laser of claim 1 , wherein a midpoint of the third diffraction grating is disposed along the longitudinal axis of the active region at a spacing from the first facet edge that is at least 40% of the total length from the first facet edge to the second facet edge.

9. 2. The semiconductor laser of claim 1, wherein each of the first gratings has a first constant pitch and each of the second gratings has a second constant pitch.

10. 10. The semiconductor laser of claim 9, wherein the first constant pitch is equal to the second constant pitch.

11. 2. The semiconductor laser of claim 1 , wherein a midpoint of the third diffraction grating is disposed along the longitudinal axis of the active region at a spacing from the first facet edge that is at least 47% of the total length from the first facet edge to the second facet edge.

12. 2. The semiconductor laser of claim 1 , wherein a midpoint of the third grating is disposed along the longitudinal axis of the active region at a spacing from the first facet edge that is at least 53% of the total length from the first facet edge to the second facet edge.

13. 2. The semiconductor laser of claim 1 , wherein a midpoint of the third grating is disposed along the longitudinal axis of the active region at a spacing from the first facet edge that is at least 60% of the total length from the first facet edge to the second facet edge.

14. 2. The semiconductor laser of claim 1, wherein the third grating is a corrugated pitch-modulated grating.

15. 2. The semiconductor laser of claim 1, wherein the third grating is a quarter-wave shift grating structure.

16. 1. A semiconductor laser, comprising: an active region having a longitudinal axis, a first facet end, and a second facet end, the first facet end being non-perpendicular to the longitudinal axis, the second facet end emitting an output beam from the semiconductor laser; a first low reflectivity coating disposed on the second facet edge of the active region; a plurality of diffraction gratings disposed along the longitudinal axis of the active region, the plurality of diffraction gratings including a first diffraction grating disposed proximate to a first facet edge of the active region, a second diffraction grating disposed proximate to a second facet edge of the active region, and a third diffraction grating disposed between the first diffraction grating and the second diffraction grating, the first diffraction grating being spaced a first distance along the longitudinal axis of the active region from the third diffraction grating and the second diffraction grating being spaced a second distance along the longitudinal axis of the active region from the third diffraction grating, the first distance and the second distance each being greater than zero; A semiconductor laser comprising:

17. 17. The semiconductor laser of claim 16, wherein a midpoint of the third grating along the longitudinal axis of the active region is located closer to the second facet edge of the active region than to the first facet edge of the active region.

18. 17. The semiconductor laser of claim 16, wherein a midpoint of the third diffraction grating is disposed along the longitudinal axis of the active region at a spacing from the first facet edge within a range of about 30% to about 70% of the total length from the first facet edge to the second facet edge.

19. 20. The semiconductor laser of claim 17, wherein the midpoint of the third diffraction grating is disposed along the longitudinal axis of the active region approximately 60% of the length of the active region from the first facet edge.

20. 18. The semiconductor laser of claim 17, wherein the third grating includes a first end and a second end spaced apart along the longitudinal axis of the active region, the second end of the third grating being disposed along the longitudinal axis of the active region more than two times farther from the second facet edge of the active region than the first end of the third grating.

21. 18. The semiconductor laser of claim 17, wherein the midpoint of the third diffraction grating is disposed along the longitudinal axis of the active region at a spacing from the first facet edge that is at least 40% of the total length from the first facet edge to the second facet edge.

22. 17. The semiconductor laser of claim 16, wherein the third grating includes a first end and a second end spaced apart along the longitudinal axis of the active region, the second end of the third grating being disposed along the longitudinal axis of the active region more than two times farther from the second facet edge of the active region than the first end of the third grating.

23. 17. The semiconductor laser of claim 16, wherein a midpoint of the third diffraction grating is disposed along the longitudinal axis of the active region at a spacing from the first facet edge that is at least 40% of the total length from the first facet edge to the second facet edge.

24. 17. The semiconductor laser of claim 16, wherein each of the first gratings has a first constant pitch and each of the second gratings has a second constant pitch.

25. 25. The semiconductor laser of claim 24, wherein the first constant pitch is equal to the second constant pitch.

26. 17. The semiconductor laser of claim 16, wherein a midpoint of the third grating is disposed along the longitudinal axis of the active region at a spacing from the first facet edge that is at least 47% of the total length from the first facet edge to the second facet edge.

27. 17. The semiconductor laser of claim 16, wherein a midpoint of the third grating is disposed along the longitudinal axis of the active region at a spacing from the first facet edge of at least 53% of the total length from the first facet edge to the second facet edge.

28. 17. The semiconductor laser of claim 16, wherein a midpoint of the third grating is disposed along the longitudinal axis of the active region at a spacing from the first facet edge of at least 60% of the total length from the first facet edge to the second facet edge.

29. 17. The semiconductor laser of claim 16, further comprising a second low reflectivity coating on the first facet end of the active region.

30. 17. The semiconductor laser of claim 16, wherein the third grating is a corrugated pitch modulated grating.

31. 17. The semiconductor laser of claim 16, wherein the third grating is a quarter-wave shifted grating structure.

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