High-κ semiconductor lasers

Abstract

To provide novel semiconductor lasers.SOLUTION: A semiconductor laser may include an active region having a longitudinal axis, a rear facet end and a front facet end. The front facet end emits an output beam of the semiconductor laser. The semiconductor laser may include a plurality of diffraction gratings positioned along the longitudinal axis of the active region. The diffraction gratings include a first diffraction grating positioned proximate to the rear facet end of the active region, and at least one additional diffraction grating positioned longitudinally between the first diffraction grating and the front facet. The first diffraction grating has a first κ value, and the at least one additional diffraction grating has at least a second κ value, the first κ value being greater than the second κ value.SELECTED DRAWING: Figure 1

Description

Related Applications

[0001]

[0001] This application is related to U.S. patent application Ser. No. 17 / 176,968, filed on February 16, 2022, entitled "HIGH KAPPA SEMICONDUCTOR LASERS," the entire disclosure of which is expressly incorporated herein by reference. [Technical Field]

[0002] This disclosure relates to semiconductor lasers, and more particularly to distributed feedback (DFB) semiconductor lasers having a high-κ grating adjacent the rear of the laser. [Background technology]

[0003] 1 and 2, a conventional semiconductor wafer 10 is shown having a substrate 11 and multiple distributed feedback (DFB) lasers 12 formed thereon. The conventional DFB lasers 12 formed on the wafer 10 suffer from phase variations in the rear facet grating, resulting in unpredictable yields. Referring to FIG. 1, the distribution of good DFB lasers 12 (solid ovals) and bad DFB lasers 12 (hollow ovals) on a portion of the wafer 10 is shown. This distribution is a function of the relative alignment of the electron beam lithography that defines the grating and the conventional lithography that defines the facet locations.

[0004]

[0004] Increasing the quantity of good DFB lasers 12 (solid ovals) is desirable for several reasons. First, the yield of good lasers produced by the manufacturing process is increased. Second, for a laser array formed by continuous side-by-side lasers 12 arranged side-by-side on a substrate 11, the quality of the continuous lasers 12 must be good. Summary of the Invention

[0005] In one exemplary embodiment of the present disclosure, a semiconductor laser is provided, comprising: an active region having a longitudinal axis, a rear facet edge, and a front facet edge, the front facet edge emitting an output beam from the semiconductor laser; 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 the rear facet edge of the active region and at least one additional diffraction grating disposed longitudinally between the first diffraction grating and the front facet edge, the first diffraction grating having a first κ value and the at least one additional diffraction grating having at least a second κ value, the first κ value being greater than the second κ value.

[0006] In one example, the first κ value is at least 80 / cm. In one variation, the first κ value is at least 100 / cm.

[0007]

[0007] In another example, the first κ value is in the range of 80 / cm to 300 / cm, and the second κ value is in the range of 10 / cm to 50 / cm. In one variation, the second κ value is in the range of 20 / cm to 50 / cm. In another variation, the second κ value is in the range of 20 / cm to 40 / cm. In another variation, the second κ value is in the range of 10 / cm to 40 / cm. In yet another variation, the first κ value is in the range of 80 / cm to 300 / cm.

[0008]

[0008] In another example thereof, the first κ value is at least 80 / cm, and the second κ value is in the range of 10 / cm to 50 / cm.

[0009]

[0009] In yet another example thereof, the ratio of the first κ value to the second κ value is 1.5 to 20.

[0010]

[0010] In yet another example thereof, the ratio of the first κ value to the second κ value is 1.6 to 20.

[0011]

[0011] In yet another example thereof, the ratio of the first κ value to the second κ value is 2-20.

[0012] In yet another example thereof, the first diffraction grating is a uniform grating.

[0013] In yet another example thereof, the at least one additional diffraction grating includes a quarter-wave shift (QWS) grating.

[0014] In yet another example thereof, the at least one additional diffraction grating includes a chirped grating.

[0015] In yet another example thereof, the at least one additional diffraction grating includes an asymmetric corrugated pitch modulated (ACPM) grating system. In one variation thereof, the asymmetric corrugated pitch modulated (ACPM) grating system includes a rear uniform grating longitudinally disposed adjacent to the first grating, a front uniform grating longitudinally disposed adjacent to the front facet edge, and at least a third grating longitudinally disposed between the rear and front uniform gratings, the rear uniform grating, the third grating, and the front uniform grating being sequential. In one variation thereof, the first grating has a first pitch, the rear uniform grating has a second pitch, the third grating has a third pitch, and the front uniform grating has a fourth pitch, the third pitch being different from the first pitch, the second pitch, and the fourth pitch.

[0016] In yet another example thereof, the at least one additional grating comprises a discontinuous asymmetric wave-shaped pitch-modulated grating system. In one variation thereof, the discontinuous asymmetric wave-shaped pitch-modulated grating system comprises a rear uniform grating longitudinally disposed proximate the first grating, a front uniform grating longitudinally disposed proximate the front facet edge, and at least a third grating longitudinally disposed between the rear and front uniform gratings, wherein at least one of the rear and front uniform gratings is longitudinally separated from the third grating by a region. In another variation thereof, the discontinuous asymmetric wave-shaped pitch-modulated grating system includes a rear uniform grating longitudinally disposed proximate the first diffraction grating, a front uniform grating longitudinally disposed proximate the front facet edge, and at least a third grating longitudinally disposed between the rear uniform grating and the front uniform grating, the rear uniform grating and the third grating longitudinally separated by a first region, and the front uniform grating and the third grating longitudinally separated by a second region. In one variation thereof, the first grating has a first pitch, the rear uniform grating has a second pitch, the third grating has a third pitch, and the front uniform grating has a fourth pitch, the third pitch being different from the first pitch, the second pitch, and the fourth pitch.

[0017] In yet another example thereof, the at least one additional diffraction grating provides a continuously variable pitch between the first grating and the front facet.

[0018]

[0018] In another example, the semiconductor laser further comprises a first reflective coating provided on the front facet end of the active region and having a reflectivity of less than 5%, and a second reflective coating provided on the rear facet end of the active region and having a reflectivity of less than 5%.

[0019]

[0019] In another exemplary embodiment of the present disclosure, a semiconductor laser array is provided. The semiconductor laser array includes a semiconductor substrate and a plurality of semiconductor lasers formed on the semiconductor substrate. Each of the plurality of semiconductor lasers includes an active region having a longitudinal axis, a rear facet end, and a front facet end, the front facet end emitting an output beam of the semiconductor laser, 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 disposed proximate the rear facet end of the active region and at least one additional diffraction grating disposed longitudinally between the first diffraction grating and the front facet end, the first diffraction grating having a first κ value and the at least one additional diffraction grating having at least a second κ value, the first κ value being greater than the second κ value.

[0020] In one example, the first κ value is at least 80 / cm. In one variation, the first κ value is at least 100 / cm.

[0021]

[0021] In another example, the first κ value is in the range of 80 / cm to 300 / cm, and the second κ value is in the range of 10 / cm to 50 / cm. In one variation, the second κ value is in the range of 20 / cm to 50 / cm. In another variation, the second κ value is in the range of 20 / cm to 40 / cm. In another variation, the second κ value is in the range of 10 / cm to 40 / cm. In yet another variation, the first κ value is in the range of 80 / cm to 300 / cm.

[0022]

[0022] In another example thereof, the first κ value is at least 80 / cm, and the second κ value is in the range of 10 / cm to 50 / cm.

[0023]

[0023] In yet another example thereof, the ratio of the first κ value to the second κ value is 1.5 to 20.

[0024]

[0024] In yet another example thereof, the ratio of the first κ value to the second κ value is 1.6 to 20.

[0025]

[0025] In yet another example thereof, the ratio of the first κ value to the second κ value is 2-20.

[0026] In yet another example thereof, the first diffraction grating is a uniform grating.

[0027] In yet another example thereof, the at least one additional diffraction grating includes a quarter-wave shift (QWS) grating.

[0028] In yet another example thereof, the at least one additional diffraction grating includes a chirped grating.

[0029] In yet another example thereof, the at least one additional diffraction grating includes an asymmetric corrugated pitch modulated (ACPM) grating system. In one variation thereof, the asymmetric corrugated pitch modulated (ACPM) grating system includes a rear uniform grating longitudinally disposed adjacent to the first grating, a front uniform grating longitudinally disposed adjacent to the front facet edge, and at least a third grating longitudinally disposed between the rear and front uniform gratings, the rear uniform grating, the third grating, and the front uniform grating being sequential. In one variation thereof, the first grating has a first pitch, the rear uniform grating has a second pitch, the third grating has a third pitch, and the front uniform grating has a fourth pitch, the third pitch being different from the first pitch, the second pitch, and the fourth pitch.

[0030] In yet another example thereof, the at least one additional grating comprises a discontinuous asymmetric wave-shaped pitch-modulated grating system. In one variation thereof, the discontinuous asymmetric wave-shaped pitch-modulated grating system comprises a rear uniform grating longitudinally disposed proximate the first grating, a front uniform grating longitudinally disposed proximate the front facet edge, and at least a third grating longitudinally disposed between the rear and front uniform gratings, wherein at least one of the rear and front uniform gratings is longitudinally separated from the third grating by a region. In another variation thereof, the discontinuous asymmetric wave-shaped pitch-modulated grating system includes a rear uniform grating longitudinally disposed proximate the first diffraction grating, a front uniform grating longitudinally disposed proximate the front facet edge, and at least a third grating longitudinally disposed between the rear uniform grating and the front uniform grating, the rear uniform grating and the third grating longitudinally separated by a first region, and the front uniform grating and the third grating longitudinally separated by a second region. In one variation thereof, the first grating has a first pitch, the rear uniform grating has a second pitch, the third grating has a third pitch, and the front uniform grating has a fourth pitch, the third pitch being different from the first pitch, the second pitch, and the fourth pitch.

[0031] In yet another example thereof, the at least one additional diffraction grating provides a continuously variable pitch between the first grating and the front facet.

[0032]

[0032] In another example, each semiconductor laser further comprises a first reflective coating provided on the front facet end of the active region and having a reflectivity of less than 5%, and a second reflective coating provided on the rear facet end of the active region and having a reflectivity of less than 5%.

[0033]

[0033] The above and other features and advantages of the present disclosure, as well as the manner in which they are realized, will become more apparent and will be better understood by reference to the following description of exemplary embodiments taken in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0034] [Figure 1] 1 is a representative diagram of a conventional semiconductor wafer having multiple DFB lasers formed thereon. [Figure 2] 2 is a representative diagram of a vertical cross section of each of two DFB lasers formed on the semiconductor wafer of FIG. 1. [Figure 3] FIG. 1 is a representative diagram of a vertical cross section of an exemplary DFB laser having a high-κ grating positioned proximate to the rear facet of the laser and one or more low-κ gratings positioned between the high-κ grating and the front facet of the laser. [Figure 4] FIG. 1 is a representative diagram of a vertical cross section of an exemplary DFB laser having a high-κ grating positioned adjacent to the rear facet of the laser and a low-κ grating positioned between the high-κ grating and the front facet of the laser. [Figure 5] FIG. 1 is a representative diagram of a vertical cross section of an exemplary DFB laser having a high-κ grating positioned close to the rear facet of the laser and a low-κ quarter-wave-shifted grating positioned between the high-κ grating and the front facet of the laser. [Figure 6] FIG. 1 is a representative diagram of a vertical cross section of an exemplary DFB laser having a high-κ grating positioned adjacent to the rear facet of the laser and a low-κ chirped grating positioned between the high-κ grating and the front facet of the laser. [Figure 7] FIG. 1 is a representative diagram of a vertical cross section of an exemplary DFB laser having a high-κ grating positioned proximate to the rear facet of the laser and a low-κ asymmetric corrugated pitch-modulated grating system positioned between the high-κ grating and the front facet of the laser. [Figure 8] FIG. 1 is a representative diagram of a vertical cross section of an exemplary DFB laser having a high-κ grating positioned proximate to the rear facet of the laser and a low-κ discontinuous asymmetric corrugated pitch-modulated grating system positioned between the high-κ grating and the front facet of the laser. [Figure 9] FIG. 1 is a representative diagram of a vertical cross section of an exemplary DFB laser having a first structural configuration including a high-κ grating disposed proximate to the rear facet of the laser and a low-κ grating system disposed between the high-κ grating and the front facet of the laser. [Figure 10] FIG. 1B is a representative diagram of a vertical cross section of an example DFB laser having a second structural configuration including a high-κ grating disposed proximate to the rear facet of the laser and a low-κ grating system disposed between the high-κ grating and the front facet of the laser. [Figure 11] FIG. 10 is a representative diagram of a vertical cross section of an example DFB laser having a third structural configuration including a high-κ grating disposed proximate to the rear facet of the laser and a low-κ grating system disposed between the high-κ grating and the front facet of the laser. [Figure 12] FIG. 1C is a representative top view of an exemplary DFB laser having a fourth structural configuration including a high-κ grating disposed proximate to the rear facet of the laser and a low-κ grating system disposed between the high-κ grating and the front facet of the laser. DETAILED DESCRIPTION OF THE INVENTION

[0035]

[0046] Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set forth herein illustrate exemplary embodiments of the present invention, and such exemplifications are not to be construed as limiting the scope of the present invention in any way.

[0036]

[0047] For the purposes of promoting an understanding of the principles of the present disclosure, reference will now be made to the embodiments illustrated in the drawings described below. The embodiments disclosed herein are not intended to be exhaustive or to limit the disclosure to the precise form disclosed in the following detailed description. Rather, these embodiments are chosen and described so that others skilled in the art can utilize their teachings. Thus, no limitation on the scope of the disclosure is intended. Corresponding reference characters indicate corresponding parts throughout the several views.

[0037]

[0048] The terms "couples," "coupled," and "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.

[0038]

[0049] 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 indicated, the numerical parameters set forth in the specification and appended claims are approximations that may vary depending upon the desired properties sought to be obtained by those of ordinary skill in the art using the teachings disclosed herein.

[0039]

[0050] 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 component or feature and should not be narrowly construed as conferring a particular ordering of the components or features.

[0040]

[0051] Referring to FIG. 2, a pair of conventional semiconductor DFB lasers 12A and 12B are shown. Each laser 12 includes an active layer 14A, 14B, an n-type cladding layer 16A, 16B, and a p-type cladding layer 18A, 18B. The active layers 14A, 14B have longitudinal axes 20A, 20B. The active layers 14A, 14B are longitudinally bounded by rear facets 30A, 30B and front facets 32A, 32B. The rear facets 30A, 30B are provided with a high-reflectivity coating. An exemplary high-reflectivity coating reflects 70% or more of incident light. The front facets 32A, 32B are provided with a low-reflectivity coating. An exemplary low-reflectivity coating reflects a maximum of 5% of incident light.

[0041]

[0052] Lasers 12A, 12B include diffraction gratings 40A, 40B along longitudinal axes 20A, 20B. Looking at regions 42A, 42B adjacent to rear facets 30A, 30B, the diffraction gratings 40A, 40B have different spacings from the rear facets 30A, 30B. This spacing difference cannot be controlled with existing manufacturing methods. For example, for a 200 nanometer (nm) period grating 40A, 40B, the alignment of the grating teeth adjacent to the rear facets 30A, 30B must be aligned and controlled to better than 50 nm. If this is not possible, the yield of functional lasers on wafer 10 will be reduced. Furthermore, this spacing difference affects the relative phase of the light reflected by the facets and the light reflected by the grating, which affects the laser's performance.

[0042]

[0053] Referring to Figure 3, a semiconductor DFB laser 100 is shown. The laser 100 is formed on a semiconductor substrate 101, as is known in the art. More typically, multiple lasers 100 are formed side-by-side on the substrate 101. Typically, a portion of the substrate 101 and each laser is separated from the other portions to provide a single laser unit. However, a larger portion of the substrate 101 containing multiple side-by-side lasers may be separated as a unit. Multiple side-by-side lasers 100 form a laser array.

[0043]

[0054] Laser 100 comprises an active layer 102, an n-type cladding layer 104, and a p-type cladding layer 106. Active layer 102, n-type cladding layer 104, and p-type cladding layer 106 each extend along a longitudinal axis 110 from a front facet 112 of laser 100 to a rear facet 114 of laser 100. Laser 100 comprises a lattice system 120 in p-type cladding layer 106 that extends along the longitudinal axis 110 of laser 100. In an embodiment, lattice system 120 extends from the front facet 112 of laser 100 to the rear facet 114 of laser 100. In an embodiment, the lattice system 120 does not extend to the front facet 112 and / or the rear facet 114, but rather leaves a gap on a portion of the active layer 102 proximate the front facet 112 and / or the rear facet 114. In an embodiment, the n-type cladding layer 104 is disposed above the active layer 102, and the p-type cladding layer 106 is disposed below the active layer 102.

[0044]

[0055] Grating system 120 includes multiple gratings. In embodiments, grating system 120 is continuous from a first grating located adjacent to rear facet 114 of laser 100 to a second grating located adjacent to front facet 112 of laser 100. In embodiments, grating system 120 is discontinuous from a first grating located adjacent to rear facet 114 of laser 100 to a second grating located adjacent to front facet 112 of laser 100. In embodiments, grating system 120 may be located below active layer 102.

[0045]

[0056] As shown in FIG. 3 , the grating system 120 includes a high-κ grating 122 positioned adjacent to the rear facet 114 of the laser 100 and one or more low-κ gratings 124 positioned longitudinally between the high-κ grating 122 and the front facet 112 of the laser 100. As referred to in the art, the κ value of a grating is the coupling coefficient of the grating. The placement of the high-κ grating adjacent to the rear facet 114 of the laser 100 increases the coupling strength of the grating system 120 in this region of the laser 100. The high-κ grating 122 acts as a high-reflectivity mirror. In embodiments, the high-κ grating 122 is fabricated simultaneously with one or more low-κ gratings 124, so the phase of the reflection from the high-κ grating 122 is known, ensuring the performance of the laser 100. This increases the yield of lasers 100 formed on a semiconductor wafer 10 and the performance of adjacent lasers 100 on a semiconductor wafer 10 used in a laser array. In an embodiment, the front facet 112 and the rear facet 114 each include a low reflectivity coating that avoids phase variations in the reflection of light in the active layer 102 .

[0046]

[0057] The κ values ​​of the high-κ grating 122 and the low-κ grating(s) 124 of the grating system 120, as well as the ratio of the κ values ​​of the high-κ grating 122 to the low-κ grating 124 of the grating system 120, affect various characteristics of the laser 100, such as its threshold current, slope, wavelength, and side-mode suppression ratio (SMSR). As shown in FIG. 5 , the high-κ grating 122 of the grating system 120 is a uniform grating, and the low-κ grating 124 is a quarter-wave-shifted (QWS) grating. Simulations of the laser 100 were performed with various κ values ​​for the high-κ grating 122 and the low-κ grating 124. The quarter-wave-shifted grating 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 and second grating structures. The high-κ grating 122 and the low-κ grating 124 each had an exemplary pitch of 203 nanometers (nm). The high-κ grating 122 had an exemplary longitudinal length of 100 micrometers (μm), the low-κ grating 124 had an exemplary longitudinal length of 799 μm, and the phase jump was located near the back end of the low-κ grating 124, proximate to the high-κ grating 122 (e.g., 266 nm from the back end of the low-κ grating 124). Other dimensions may also be implemented for the laser 100.

[0047]

[0058] Based on simulations, it has been found that, among other benefits, a κ value of at least 100 / cm for high-κ grating 122 results in a threshold current of 25 milliamps (mA) for laser 100. It has also been found that, among other benefits, a κ value for high-κ grating 122 in the range of 80 / cm to 200 / cm and a κ value for low-κ grating 124 in the range of 10 / cm to 50 / cm results in a threshold current of laser 100 below 25 milliamps (mA) (resulting in a ratio of the κ value of high-κ grating 122 to the κ value of low-κ grating 124 in the range of 1.6 to 20). In particular, having the κ value of the high-κ grating 122 in the range of 80 / cm to 300 / cm and the κ value of the low-κ grating 124 in the range of 10 / cm to 40 / cm has the advantage that the slope of the laser 100 is at least 0.1 milliwatts per milliampere (mW / mA) (resulting in a ratio of the κ value of the high-κ grating 122 to the κ value of the low-κ grating 124 in the range of 2 to 20). In particular, having a κ value for high-κ grating 122 in the range of 80 / cm to approximately 200 / cm and a κ value for low-κ grating 124 in the range of 10 / cm to 50 / cm can have the advantage of resulting in an SMSR of laser 100 of at least 40 decibels (dB) (resulting in a ratio of the κ value of high-κ grating 122 to the κ value of low-κ grating 124 in the range of 1.6 to 20), and having a κ value for low-κ grating 124 in the range of 10 / cm to 55 / cm can have the advantage of resulting in an SMSR of laser 100 of at least 30 decibels (dB) (resulting in a ratio of the κ value of high-κ grating 122 to the κ value of low-κ grating 124 in the range of 1.5 to 20).

[0048]

[0059] In embodiments, the κ values ​​of the high κ gratings 122 of the grating system 120 are at least 80 / cm. In embodiments, the κ values ​​of the high κ gratings 122 of the grating system 120 are at least 100 / cm. In embodiments, the κ values ​​of the high κ gratings 122 of the grating system 120 are between 80 / cm and 200 / cm. In embodiments, the κ values ​​of the high κ gratings 122 of the grating system 120 are at least 80 / cm, and the κ values ​​of the low κ gratings 124 of the grating system 120 are in the range of 10 / cm to 50 / cm. In embodiments, the κ values ​​of the high κ gratings 122 of the grating system 120 are in the range of 80 / cm to 200 / cm, and the κ values ​​of the low κ gratings 124 of the grating system 120 are in the range of 10 / cm to 50 / cm. In an embodiment, the κ value of the high κ lattice 122 of the lattice system 120 is in the range of 80 / cm to 200 / cm, and the κ value of the low κ lattice 124 of the lattice system 120 is in the range of 20 / cm to 40 / cm. In an embodiment, the ratio of the κ values ​​of the high κ lattice 122 to the low κ lattice 124 of the lattice system 120 is in the range of 1.5 to 20. In an embodiment, the ratio of the κ value of the high κ lattice 122 to the low κ lattice 124 of the lattice system 120 is in the range of 2 to 20.

[0049]

[0060] As described herein, the above simulations were performed based on the configuration shown in Figure 5. Similar results may be obtained with the configuration of Figure 4, in which the low-κ grating 124 of the grating system 120 is a uniform grating, and the configuration of Figure 6, in which the low-κ grating 124 of the grating system 120 is a chirped grating. In embodiments, at least one additional grating 124 provides a continuously variable pitch between the high-κ grating 122 and the front facet 112.

[0050]

[0061] 7, the laser 100 includes an asymmetric corrugated pitch modulation (ACPM) grating system as the low-κ grating 124. The asymmetric corrugated pitch modulation (ACPM) grating system includes a rear uniform grating 130 having a longitudinal length 132 positioned adjacent to the high-κ grating 122, a front uniform grating 134 having a longitudinal length 136 positioned adjacent to the front facet 112, and a grating 138 having a longitudinal length 140 positioned longitudinally between the rear uniform grating 130 and the front uniform grating 134. The grating 138 has a different pitch than the grating 130 and the grating 134. The rear uniform grating 130, the grating 138, and the front uniform grating 134 are contiguous, and the phase is aligned between regions of the low-κ grating 124. In an embodiment, the high-κ grating 122 has a first pitch, the rear uniform grating 130 has a second pitch, the grating 138 has a third pitch, and the front uniform grating 134 has a fourth pitch, where the third pitch is different from the first pitch, the second pitch, and the fourth pitch.

[0051]

[0062] Referring to FIG. 8 , the laser 100 includes a discontinuous asymmetric wave-pitch-modulated grating system as the low-κ grating 124. The discontinuous asymmetric wave-pitch-modulated grating system includes a rear uniform grating 150 positioned proximate the high-κ grating 122 and having a longitudinal length 152, a front uniform grating 154 positioned proximate the front facet 112 and having a longitudinal length 156, and a grating 158 positioned longitudinally between the rear uniform grating 150 and the front uniform grating 154 and having a longitudinal length 160. The grating 158 has a different pitch than the gratings 150 and 154. The rear uniform grating 150 and the grating 158 are longitudinally separated by a region 162, and the front uniform grating 154 and the grating 158 are longitudinally separated by a region 164. In one example, the regions 162 and 164 each do not include any grating structure. For example, regions 162 and 164 may each be composed of p-type cladding material and may not have any lattice structure. In another example, regions 162 and 164 may each include a block of a material different from the p-type cladding material and may not have any lattice structure. Thus, rear uniform grating 150 and grating 158 are discontinuous, and front uniform grating 154 and grating 158 are also discontinuous. In an embodiment, grating 158 is continuous with one of rear uniform grating 150 and front uniform grating 154. In an embodiment, high-κ grating 122 has a first pitch, rear uniform grating 150 has a second pitch, grating 158 has a third pitch, and front uniform grating 154 has a fourth pitch, where the third pitch is different from the first pitch, the second pitch, and the fourth pitch.

[0052]

[0063] Due to several structural features of the laser 100, the configuration shown in Figure 3 may have a high-κ grating 122 adjacent to the rear facet 114, with a low-κ grating 124 longitudinally located between the high-κ grating 122 and the front facet 112. Examples are provided in Figures 9-12. Each of Figures 9-12 shows an exemplary structure, although in various embodiments, these exemplary structures may be combined.

[0053]

[0064] 9, the low-κ grating 124 is shown as a uniform grating.124 Height d is greater than 122 These gratings form the high-κ grating 122. As shown, the pitch of each of the high-κ grating 122 and the low-κ grating 124 is the same, although in embodiments they may be different.

[0054]

[0065] 10, low-κ grating 124 is shown as a uniform grating. Multiple gratings (illustratively, gratings 170 and 172) are vertically stacked to form high-κ grating 122. As shown, the pitches of high-κ grating 122 and low-κ grating 124 are the same, although in some embodiments they may be different.

[0055]

[0066] Referring to FIG. 11, pitch P 122 The high-κ grating 122 is shown as a uniform grating having a thickness of 122. The low-κ grating 124 is also formed by a grating of the same thickness as 122, but with many of the "teeth" removed from the grating to reduce its strength.

[0056]

[0067] Referring to the plan view of FIG. 12, the lateral width w 122 The high-κ grating 122 is shown as a uniform grating having a κ of 0.05 mm. The low-κ grating 124 is formed by reducing κ by gaps in the lateral width of the grating teeth. As shown in FIG. 12, the laser 100 may include a ridge 118 extending along the longitudinal length of the laser 100.

[0057]

[0068] Among other advantages of the configuration of laser 100 in the embodiments disclosed herein, the phase of the reflected light from the rear facet is determined by the high-κ grating, not by the position of facet 114 relative to grating 112. This allows the threshold current, slope, and other characteristics of laser 100 to be optimized by engineering the characteristics of various embodiments of low-κ grating 124, such as QWS, uniform, chirped, etc. Furthermore, a known phase can be selected to tolerate back reflections due to external reflections or increased front facet reflection due to, for example, refractive index mismatch from the epoxy (0% to 4% reflection from the epoxy on front facet 112). Additionally, the lengths and respective characteristics of high-κ and low-κ gratings 122 and 124 (such as the position of the π phase shift in a QWS grating) can be selected to optimize laser power and SMSR.

[0058]

[0069] As the solder making the electrical connections to the laser 100 cools, thermal expansion mismatch between the solder, the laser, and the submount(s) can cause chirp in the grating system 120 of the laser 100. Another advantage of being able to control the phase of the light reflected from the back of the laser back into the active layer 102, particularly by the high-κ grating 122, is that the phase can be controlled to account for expected chirp introduced during manufacturing by solder, etc.

[0059]

[0070] While this invention has been described as having exemplary designs, it is possible to further modify it within the spirit and scope of this 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 present disclosure as come within known custom or practice in the art to which this invention pertains. [Explanation of symbols]

[0060] 100...semiconductor DFB laser, 102...active layer, 110...longitudinal axis, 112...front facet, 114...rear facet, 120...grating system, 122...high-κ grating, 124...low-κ grating.

Claims

1. A semiconductor laser, an active region having a longitudinal axis, a rear facet end, and a front facet end, the front facet end emitting an output beam from the semiconductor laser; 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 the rear facet edge of the active region and at least one additional diffraction grating disposed longitudinally between the first diffraction grating and the front facet edge, the first diffraction grating having a first K value and the at least one additional diffraction grating having at least a second K value, the first K value being greater than the second K value; A semiconductor laser comprising:

2. 2. The semiconductor laser of claim 1, wherein the first κ value is at least 80 / cm.

3. 3. The semiconductor laser of claim 2, wherein the first κ value is at least 100 / cm.

4. 2. The semiconductor laser according to claim 1, wherein the first κ value is in the range of 80 / cm to 300 / cm, and the second κ value is in the range of 10 / cm to 50 / cm.

5. 5. The semiconductor laser according to claim 4, wherein the second κ value is in the range of 20 / cm to 50 / cm.

6. 5. The semiconductor laser according to claim 4, wherein the second κ value is in the range of 20 / cm to 40 / cm.

7. 5. The semiconductor laser according to claim 4, wherein the second κ value is in the range of 10 / cm to 40 / cm.

8. 2. The semiconductor laser of claim 1, wherein the first κ value is at least 80 / cm and the second κ value is in the range of 10 / cm to 50 / cm.

9. 2. The semiconductor laser according to claim 1, wherein a ratio of the first κ value to the second κ value is 1.5 to 20.

10. 2. The semiconductor laser according to claim 1, wherein a ratio of the first κ value to the second κ value is 1.6 to 20.

11. 2. The semiconductor laser according to claim 1, wherein a ratio of the first κ value to the second κ value is 2 to 20.

12. 2. The semiconductor laser of claim 1, wherein the first diffraction grating is a uniform grating.

13. 10. The semiconductor laser of claim 1, wherein the at least one additional grating comprises a quarter-wave shift (QWS) grating.

14. 10. The semiconductor laser of claim 1, wherein the at least one additional grating comprises a chirped grating.

15. 10. The semiconductor laser of claim 1, wherein the at least one additional grating comprises an asymmetric corrugated pitch modulation (ACPM) grating system.

16. 16. The semiconductor laser of claim 15, wherein the asymmetric corrugated pitch modulation (ACPM) grating system includes a rear uniform grating longitudinally disposed proximate to the first grating, a front uniform grating longitudinally disposed proximate to the front facet edge, and at least a third grating longitudinally disposed between the rear uniform grating and the front uniform grating, wherein the rear uniform grating, the third grating, and the front uniform grating are contiguous.

17. 17. The semiconductor laser of claim 16, wherein the first grating has a first pitch, the rear uniform grating has a second pitch, the third grating has a third pitch, and the front uniform grating has a fourth pitch, and the third pitch is different from the first pitch, the second pitch, and the fourth pitch.

18. 10. The semiconductor laser of claim 1, wherein said at least one additional grating comprises a discontinuous asymmetric corrugated pitch-modulated grating system.

19. 20. The semiconductor laser of claim 18, wherein the discontinuous asymmetric corrugated pitch-modulated grating system includes a rear uniform grating longitudinally disposed proximate to the first diffraction grating, a front uniform grating longitudinally disposed proximate to the front facet edge, and at least a third grating longitudinally disposed between the rear uniform grating and the front uniform grating, wherein at least one of the rear uniform grating and the front uniform grating is longitudinally separated from the third grating by a region.

20. 20. The semiconductor laser of claim 19, wherein the first grating has a first pitch, the rear uniform grating has a second pitch, the third grating has a third pitch, and the front uniform grating has a fourth pitch, and the third pitch is different from the first pitch, the second pitch, and the fourth pitch.

21. 19. The semiconductor laser of claim 18, wherein the discontinuous asymmetric corrugated pitch-modulated grating system comprises a rear uniform grating longitudinally disposed proximate to the first diffraction grating, a front uniform grating longitudinally disposed proximate to the front facet edge, and at least a third grating longitudinally disposed between the rear uniform grating and the front uniform grating, wherein the rear uniform grating and the third grating are longitudinally separated by a first region, and the front uniform grating and the third grating are longitudinally separated by a second region.

22. 10. The semiconductor laser of claim 1, wherein said at least one additional grating provides a continuously variable pitch between said first grating and said front facet.

23. 10. The semiconductor laser of claim 1, further comprising: a first reflective coating on the front facet end of the active region, the first reflective coating having a reflectivity of less than 5%, and a second reflective coating on the rear facet end of the active region, the second reflective coating having a reflectivity of less than 5%.

24. a semiconductor substrate; A plurality of semiconductor lasers formed on the semiconductor substrate, each of which is an active region having a longitudinal axis, a rear facet end, and a front facet end, the front facet end emitting an output beam of the semiconductor laser; a plurality of semiconductor lasers comprising: a plurality of gratings disposed along the longitudinal axis of the active region, the gratings including a first grating disposed proximate the rear facet edge of the active region and at least one additional grating disposed longitudinally between the first grating and the front facet edge, the first grating having a first K value and the at least one additional grating having at least a second K value, the first K value being greater than the second K value; A semiconductor laser array comprising:

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