CN112952551B - Surface emitting laser element with mixed grating structure and its making process - Google Patents
Surface emitting laser element with mixed grating structure and its making process Download PDFInfo
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- H01S5/00—Semiconductor lasers
- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
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Abstract
The grating layer of the surface-emitting laser element is divided into a first grating region and a second grating region in at least a first horizontal direction. The second grating region is located in a middle region of the grating layer, and the first grating region is located in an outer region of the grating layer. Each of the first grating region and the second grating region comprises a plurality of micro-grating structures. The grating periods of the micro-grating structures in the first grating region conform to the following mathematical formula:
and, the grating period of the micro-grating structures in the second grating region is in accordance with the following mathematical formula:
wherein lambda is the grating period length, lambda is the lasing wavelength of the laser, n eff Is the equivalent refractive index of the semiconductor waveguide, m=1 and o=2. Therefore, the first grating region is a first-order grating structure region, and the second grating region is a second-order grating structure region, so as to form a hybrid grating structure on the grating layer. The surface emitting laser element is a light emitting surface defined by the second grating region for emitting laser vertically.
Description
Technical Field
The present invention relates to a surface emitting laser device with a hybrid grating structure and a method for fabricating the same, and more particularly, to a surface emitting laser device with a hybrid grating structure comprising a first-order grating structure region and a second-order grating structure region disposed in a grating layer and a method for fabricating the same.
Background
The semiconductor laser (semiconductor laser) or laser diode (laser diode) has the advantages of small volume, low power consumption, quick response, impact resistance, long service life, high efficiency, low price and the like, and is widely applied to photoelectric system products such as optical wave communication, information systems, household appliances, precision measurement, optical fiber communication and the like. The distributed feedback laser (Distributed Feedback Laser: DFB laser for short) has the characteristics of simple process, single-mode output, suitability for long-distance transmission, etc., and the laser signal generated by the distributed feedback laser can maintain a good signal-to-noise ratio after long-distance transmission, so that the distributed feedback laser has become a widely used light source in current optical wave communication and optical fiber communication systems.
Referring to fig. 1, a schematic cross-section of a typical surface-emitting distributed feedback laser (Surface Emitting Distributed Feedback Laser: SE-DFB laser for short) is shown, which sequentially comprises, from bottom to top: a semiconductor substrate 91, a lower cladding layer (SCH) layer, an active layer 92 (active region layer), a glazing confinement layer, a spacer layer, a grating layer 93, an upper cladding layer 94, and a contact layer. The SE-DFB laser is generally classified as either a first order grating structure design or a second order grating structure design, depending on the design differences in the period of the plurality of micro-grating structures included in the grating layer. The first-order or second-order grating structure design is determined according to the following formula:
Wherein lambda is the period (grading period) length of two adjacent micro grating structures, lambda is the wavelength (wavelength) of laser emitted by SE-DFB laser, n eff Is the equivalent refractive index (effective refractive index) of the semiconductor waveguide, and m is the so-called "order" value. It can be seen that when m=1, the period value Λ of the micro-grating structure substantially corresponds to half the laser wavelength λ (i.e. λ/2), and the micro-grating structures included in the grating layer may be referred to as first-order grating structures (First order grating). When m=2, the period value Λ of the micro-grating structure substantially corresponds to the laser wavelength λ (i.e. λ), and the micro-grating structures included in the grating layer are called second-order grating structures (Second order grating). At this time, there are first-order and second-order diffraction, respectively, corresponding to the coupling constants (coupling constant) K1 (related to the plane light extraction efficiency) and K2 (related to the in-plane cavity efficiency).
Assuming that the micro-grating structure is in the shape of teeth (see FIG. 1), the different order grating structure designs result in an in-plane resonant cavity coupling constant (K m )，K m Proportional to Sin [ pi ] m ratio]/(pi.m). Wherein m is an "order" value; the ratio refers to the duty cycle of the grating, i.e. as shown in FIG. 1 ratio = a/; where a is the gap value between two adjacent micro-grating structures. Referring to fig. 2, to compare the ratio value with the in-plane resonant cavity coupling constant (K) when m=1 and m=2 m ) Graph of the relationship of the values. As can be seen from fig. 2, comparing the curves of m=1 (first order grating structure) and m=2 (second order grating structure), it is known that the efficiency of forming an in-plane resonant cavity by the second order grating structure is generally lower than that of the first order grating structure.
The SE-DFB laser formed according to the second-order grating structure design has many advantages, such as small exit angle, and capability of testing and burn-in wafer state (on wafer test and burn-in). Moreover, unlike the conventional edge-emitting (DFB) laser, the principle of the SE-DFB laser formed by designing the second-order grating structure is to manufacture the micro-grating structure with a period value of lambda/n eff In this way, a second-order diffraction (diffraction) of a micro-grating structure is utilized on an in-plane (in-plane), a forward and a backward mode in a waveguide are coupled together to form a resonant cavity (cavity) to emit laser (laser), and the laser is coupled and emitted from the top surface of the SE-DFB laser.
Since the SE-DFB laser formed by the second-order grating structure design operates with both the first and second orders simultaneously occurring on the optical mode, besides the above-mentioned low-efficiency second-order diffraction as a cavity feedback (cavity feedback), there is an additional first-order diffraction light output coupling loss (light output coupling loss), so that such devices often need a larger area and a larger critical current value (threshold current; abbreviated as Ith) to operate.
Accordingly, the present invention provides a novel design of surface-emitting distributed feedback laser that integrates the first-order and second-order grating structures on the same grating layer. The first-order grating structure design with low loss is utilized to serve as a high-efficiency reflection feedback (feedback) area to be placed on the laser end face, and the second-order grating structure design is only used near the light emergent area of the middle laser face. In this way, a desired balance can be achieved between pursuing a high slope efficiency (meaning this larger second order grating structure region) and a low critical current value Ith (meaning this smaller second order grating structure region). And a lambda/4-Shift phase difference grating structure can be introduced into the center of the second-order grating structure region, so that the laser field can be modal stabilized and the light-emitting coupling light efficiency can be improved.
Disclosure of Invention
The main objective of the present invention is to provide a surface emitting laser device with a hybrid grating structure and a method for fabricating the same, wherein a hybrid grating structure comprising a first-order grating structure region and a second-order grating structure region is disposed in a grating layer, so as to achieve a desired balance between a desired high slope efficiency (slope efficiency) and a low threshold current value Ith. And a lambda/4-Shift phase difference grating structure can be introduced into the center of the second-order grating structure region, so that the laser field can be modal stabilized and the light-emitting coupling light efficiency can be improved.
It is another object of the present invention to provide a surface emitting laser device that converts the same concept as the main object described above from a one-dimensional grating structure to a two-dimensional photonic crystal surface emitting laser (photonic crystal surface emitting laser; PCSEL). A first-order photonic crystal (photonic crystal) is disposed around the laser element, and a second-order photonic crystal is disposed only at the intermediate light extraction, and a phase difference structure is appropriately introduced to operate the mode. It is also possible to deploy several light-emitting sites simultaneously (i.e. only second-order photonic crystals at the light-emitting sites) to achieve a multi-light source two-dimensional array phase lock (2D array phase lock) like effect.
In order to achieve the above-mentioned object, the present invention provides a surface-emitting laser device with a hybrid grating structure, which can generate a laser with a laser wavelength; the surface-emitting laser element includes:
a semiconductor stacked structure capable of generating the laser with the laser wavelength when receiving a current and emitting the laser from an emitting surface of the semiconductor stacked structure, wherein the emitting surface is positioned on a top surface of the semiconductor stacked structure;
the grating layer is positioned on the semiconductor stacking structure and is provided with a plurality of micro-grating structures distributed and arranged along at least one first horizontal direction;
Wherein the grating layer is divided at least in the first horizontal direction into the steps of: at least one first grating region and at least one second grating region, wherein each first grating region and each second grating region respectively comprise a plurality of micro-grating structures; wherein, the grating periods of the micro-grating structures in the first grating region conform to the following mathematical formula:
and, the grating period of the micro-grating structures in the second grating region is in accordance with the following mathematical formula: />
Wherein lambda is the grating period length, lambda is the lasing wavelength of the laser, n eff Is the equivalent refractive index of the semiconductor waveguide, m and o are positive integers, m and o are unequal, and o is an even multiple of m;
the light-emitting surface is defined by the second grating region.
In one embodiment, m=1 and o=2; thus, the first grating region is also referred to as a first order grating structure region and the second grating region is also referred to as a second order grating structure region, thereby forming a hybrid grating structure in the grating layer; wherein the laser light is emitted vertically from the light-emitting surface defined by the second grating region.
In one embodiment, the grating layer further includes a phase difference grating structure; the phase difference grating structure is positioned near the middle of the first horizontal direction in the second grating region, and the width of the phase difference grating structure can provide a phase difference distance, so that a phase difference exists between the micro grating structures positioned at the two sides of the phase difference grating structure in the first horizontal direction; the phase difference grating structure provides the phase difference distance being one quarter of the laser wavelength.
In one embodiment, the number of the second grating regions is one and is located in a middle region of the grating layer in the first horizontal direction, so that the first grating region is substantially divided into a left part and a right part in the first horizontal direction by the second grating region located in the middle; wherein the width of the second grating region in the first horizontal direction is between one sixth and one half of the total width of the grating layer; the widths of the left and right portions of the first grating region that are separated are substantially equal.
In an embodiment, the grating layer also has a plurality of micro-grating structures along a second horizontal direction, and the second horizontal direction is perpendicular to the first horizontal direction; the grating layer is also divided into at least one first grating region and at least one second grating region in the second horizontal direction, and each first grating region and each second grating region respectively comprise a plurality of micro-grating structures; therefore, when viewed from the direction perpendicular to the top surface of the semiconductor stacked structure, the micro-grating structures are arranged in a dot-like array on the grating layer, and at least one rectangular light-emitting surface is defined by the second grating region in the first horizontal direction and the second grating region in the second horizontal direction in a cooperative manner.
In one embodiment, the grating layer further includes a two-phase difference grating structure; one of the phase difference grating structures is positioned near the middle of the second grating area in the first horizontal direction, and the other phase difference grating structure is positioned near the middle of the second grating area in the second horizontal direction; the width of the phase difference grating structure can provide a phase difference distance, so that a phase difference exists between the micro grating structures positioned at two sides of the phase difference grating structure in the first horizontal direction and the second horizontal direction respectively; the phase difference grating structure provides the phase difference distance being one quarter of the laser wavelength.
In one embodiment, the second grating region is located in a middle region of the grating layer in the first horizontal direction and the second horizontal direction; the second grating region is located in a central region of the top surface of the semiconductor stack structure when viewed from a direction perpendicular to the top surface of the semiconductor stack structure, and the first grating region is substantially located around an outer peripheral region of the second grating region; the width of the second grating region in the first horizontal direction and the second horizontal direction is between one sixth and one half of the total width of the grating layer in the first horizontal direction and the second horizontal direction respectively.
In an embodiment, the top surface of the semiconductor stack structure includes a plurality of light emitting surfaces arranged in an array and independently existing, the grating layer is provided with the second grating region in each of the light emitting surfaces in the first horizontal direction or the second horizontal direction, and other regions of the grating layer except the light emitting surfaces are provided with the first grating region in the first horizontal direction or the second horizontal direction; therefore, a plurality of small light emitting surfaces which are independent and arranged in an array can be defined on the top surface of the semiconductor stacked structure.
To achieve the above object, the present invention provides a method for manufacturing a surface emitting laser device with a hybrid grating structure, comprising the following steps:
step (A): forming a semiconductor stacked structure on a semiconductor substrate by a semiconductor epitaxial process; the semiconductor stacking structure can generate a laser with a laser wavelength when receiving a current, and the laser is emitted from a light emitting surface of the semiconductor stacking structure, wherein the light emitting surface is positioned on the top surface of the semiconductor stacking structure;
step (B): forming a grating layer on the semiconductor stacked structure by using electron beam printing and nano-imprinting processes; the grating layer is provided with a plurality of micro-grating structures which are arranged along at least one first horizontal direction;
Step (C): forming an upper cladding layer and a contact layer on the grating layer by a semiconductor epitaxy process and a yellow light process, wherein the upper cladding layer and the contact layer are positioned above the grating layer;
wherein the grating layer is divided at least in the first horizontal direction into the steps of: at least one first grating region and at least one second grating region, wherein each first grating region and each second grating region respectively comprise a plurality of micro-grating structures; wherein, the grating periods of the micro-grating structures in the first grating region conform to the following mathematical formula:
and, the grating period of the micro-grating structures in the second grating region is in accordance with the following mathematical formula: />
Wherein lambda is the grating period length, lambda is the lasing wavelength of the laser, n eff Is the equivalent refractive index of the semiconductor waveguide, m and o are positive integers, m and o are unequal, and o is an even multiple of m;
the light-emitting surface is defined by the second grating region.
In order to achieve the above object, the present invention provides a surface-emitting laser device for generating laser light having a laser wavelength, the surface-emitting laser device comprising:
a semiconductor stacked structure capable of generating the laser with the laser wavelength when receiving a current and emitting the laser from an emitting surface of the semiconductor stacked structure, wherein the emitting surface is positioned on a top surface of the semiconductor stacked structure;
The photonic crystal layer is positioned on the semiconductor stacking structure and is provided with a plurality of micro-photonic crystal structures distributed and arranged along a first horizontal direction and a second horizontal direction, and the second horizontal direction is perpendicular to the first horizontal direction; wherein the photonic crystal layer is divided into the first horizontal direction and the second horizontal direction respectively, and includes: at least one first photonic crystal region and at least one second photonic crystal region, wherein each of the first photonic crystal region and the second photonic crystal region comprises a plurality of micro-photonic crystal structures; wherein the photonic crystal periods of the plurality of micro-photonic crystal structures in the first photonic crystal region conform to the following mathematical formula:
and, the photonic crystal period of the plurality of micro-photonic crystal structures in the second photonic crystal region is in accordance with the following mathematical formula: />
Wherein lambda is the period length of the photonic crystal, lambda is the lasing wavelength of the laser, n eff Is the equivalent refractive index of the semiconductor waveguide, m and o are positive integers, m and o are unequal, and o is an even multiple of m;
the light-emitting surface is defined by the second photonic crystal region.
In one embodiment, the photonic crystal layer further includes a two-phase difference photonic crystal structure; one of the phase difference photonic crystal structures is positioned near the middle of the second photonic crystal region in the first horizontal direction, and the other phase difference photonic crystal structure is positioned near the middle of the second photonic crystal region in the second horizontal direction; the width of the phase difference photonic crystal structure can provide a phase difference distance, so that a phase difference exists between the two micro-photonic crystal structures which are respectively positioned at the two sides of the phase difference photonic crystal structure in the first horizontal direction and the second horizontal direction; the phase difference distance provided by the phase difference photonic crystal structure is one quarter of the laser wavelength.
In an embodiment, the top surface of the semiconductor stack structure includes a plurality of light emitting surfaces arranged in an array and independently existing, the photonic crystal layer is provided with the second photonic crystal region at each light emitting surface in the first horizontal direction or the second horizontal direction, and other regions of the photonic crystal layer except the light emitting surfaces are provided with the first photonic crystal region in the first horizontal direction or the second horizontal direction; therefore, a plurality of small light emitting surfaces which are independent and arranged in an array can be defined on the top surface of the semiconductor stacked structure.
Drawings
FIG. 1 is a schematic cross-sectional view of a typical surface-emitting distributed feedback laser (Surface Emitting Distributed Feedback Laser: SE-DFB laser for short).
Fig. 2 is a graph comparing ratio values (ratio) of m=1 to m=2 to in-plane resonator coupling constants (K m ) Graph of the relationship of the values.
Fig. 3A, 3B and 3C are a schematic perspective view, a schematic cross-sectional view and a schematic top view of a first embodiment of a surface-emitting distributed feedback Laser (Surface Emitting Distributed Feedback Laser, SE-DFB Laser) with a hybrid grating structure according to the present invention.
Fig. 4 is a schematic diagram of a grating layer of a typical edge-emitting DFB laser device.
Fig. 5A to 5D are graphs showing intensity distribution along the ridge of a laser guiding pattern obtained by simulating the laser element of the first embodiment of the present invention with four structural variations of L2 length varying from 0 μm, 50 μm, 100 μm to 150 μm, respectively; wherein L2 is the length of the second grating region.
Fig. 6A to 6D are graphs showing normalized gain (g×l) and detuning relation (δl) obtained by simulating the laser element according to the first embodiment of the present invention with four structural variations of L2 length varying from 0 μm, 50 μm, 100 μm to 150 μm, respectively.
FIG. 7 is a graph showing the relationship between the Threshold gain (L2 length) obtained by simulating the laser device according to the first embodiment of the present invention with four structural variations of L2 length ranging from 0 μm, 50 μm, 100 μm to 150 μm.
Fig. 8 and 9 are a schematic perspective view and a schematic top view of a grating layer of a second embodiment of a surface-emitting laser device according to the present invention.
Fig. 10 is a schematic top view of a grating (or photonic crystal) layer of a surface-emitting laser device with a hybrid grating (or photonic crystal) structure according to a third embodiment of the present invention.
FIG. 11 is a schematic top view of a grating layer of a fourth embodiment of a surface-emitting laser device with a hybrid grating (or photonic crystal) structure according to the present invention.
Fig. 12A and 12B are schematic diagrams of a conventional distributed feedback laser device with a pure first-order grating structure and a micro-grating structure of a surface-emitting laser device with a first-order and second-order hybrid grating structure according to the present invention, respectively.
Fig. 13A to 13C are schematic views showing several steps of a method for manufacturing a surface emitting laser device with a hybrid grating structure according to the present invention.
Fig. 14 is a schematic perspective view of a fifth embodiment of a surface emitting laser device with a hybrid grating structure according to the present invention.
List of reference numerals:
10 to the substrate 11 to the lower coating layer
12 to a lower light limiting layer 13 to an active layer
14-glazing limiting layer
16 to grating layer 162 to first grating region
163-second grating zone 164-phase difference grating structure
17 to upper cladding layer 18 to contact layer
191. 192 to metal layer 21 to light-emitting surface
Detailed Description
In order to more clearly describe the surface emitting laser element with the mixed grating structure and the method thereof
The manufacturing method will be described in detail below with reference to the drawings.
Referring to fig. 3A, 3B and 3C, a schematic perspective view, a schematic cross-sectional view and a schematic top view of a grating layer of a first embodiment of a surface-emitting distributed feedback Laser (Surface Emitting Distributed Feedback Laser, SE-DFB Laser) with a hybrid grating structure according to the present invention are shown. As shown in fig. 3A, 3B and 3C, in the first embodiment, the surface-emitting distributed feedback (SE-DFB) laser device of the present invention can be roughly divided into a structure including: a semiconductor stack, a Grating layer (Grating) 16, and two metal layers 191, 192. The semiconductor stacked structure can generate laser with laser wavelength lambda when receiving a preset current, and enables the laser to vertically and upwardly emit from a light emitting surface 21 of the semiconductor stacked structure, and the light emitting surface 21 is positioned on a top surface of the semiconductor stacked structure, so that the semiconductor stacked structure conforms to the structure of a general surface emitting laser diode element. The grating layer 16 is disposed on the semiconductor stack structure, and the grating layer 16 has a plurality of micro-grating structures distributed along at least a first horizontal direction.
In this embodiment, the semiconductor stack structure includes: a semiconductor substrate 10, a lower cladding layer 11 (SCH) on the semiconductor substrate 10, a lower light confining layer 12 (Separated Confinement Hetero-Structure) on the lower cladding layer 11, an active layer 13 (active region layer) on the lower light confining layer 12, a upper light confining layer 14 on the active layer 13, and a Spacer layer (Spacer, not shown) on the upper light confining layer 14. Wherein the grating layer 16 is located on the spacer layer; the semiconductor stacked structure further includes: an upper cladding layer 17 is located on the grating layer 16, and a Contact layer 18 (Contact) is located on the upper cladding layer 17. The upper metal layer 192 is located above the contact layer 18, and the lower metal layer 191 is located below the substrate 10.
In general, the principle of operation of a distributed feedback laser diode device is that electrons and holes are injected into an active layer, and a carrier Barrier (Barrier) is limited to a Quantum Well (Quantum Well) to generate a material gain. The limiting principle is that the barrier layer has a higher material energy gap than the quantum well layer, so that a lower quantum energy level is formed in the quantum well, and once the carrier is trapped, the carrier is not easy to escape. The laser field is confined by upper and lower cladding layers in a rectangular elongated cavity formed by the upper and lower SCH layers and the active layer. The limiting principle is that the upper and lower cladding layers have lower optical refractive index n values (Low Refractive Index) than the upper and lower SCH layers and the active layer, and the optical field forms a mode in a material with a higher n value and propagates by the principle of total reflection. The degree of quantum well coupling of the Optical field to the active layer determines the Modal Gain (Modal Gain), which is the higher the easier it is to overcome the Optical Loss (Optical Loss) to reach Lasing (Lasing), and the easier it is to lower the threshold current value at which Lasing occurs (otherwise referred to as pumping threshold current; threshold Current).
In an embodiment of the present invention, the semiconductor substrate 10 may be an indium phosphide (InP) substrate, and the lower cladding layer 11, the lower light-confining layer 12, the active layer 13, the upper light-confining layer 14, and the upper cladding layer 17 are sequentially formed on the InP substrate 10 in a bottom-up epitaxial process. Wherein the InP substrate 10, the lower cladding layer 11, and the lower light-confining layer 12 all have n-type doping. The upper capeBoth the cladding layer 17 and the contact layer 18 have a p-type doping. The material of the lower cladding layer 11 and the upper cladding layer 17 is InP. The material of the active layer 13 may be In 1-x- y Al x Ga y As, where x and y are real numbers between 0 and 1. The material of the contact layer 18 may be InGaAs. The material of the lower light confining layer 12 and the upper light confining layer 14 may be In 1-z Al z As, where z is a real number between 0 and 1. The parameters such as the material composition, the structure thickness, the doping concentration of each layer in the semiconductor stacked structure of the present invention can be selected from the known parameters of the general conventional distributed feedback laser, and are not the technical features of the present invention, so details thereof are not repeated, and the parameters such as the material composition, the structure thickness, the doping concentration of each layer in the semiconductor stacked structure of the present invention are not limited to the embodiments described in this paragraph.
In this embodiment, the grating layer 16 is disposed in the upper cladding layer 17 of the semiconductor stack structure, and the grating layer 16 has a plurality of micro-grating structures arranged along at least a first horizontal direction. The grating layer 16 is distinguished at least in the first horizontal direction as comprising: at least one first grating region 162 and at least one second grating region 163, each of the first grating region 162 and the second grating region 163 comprises a plurality of micro-grating structures. Wherein, the grating periods of the micro-grating structures in the first grating region 162 conform to the following formula:
and, the grating periods of the micro-grating structures in the second grating region 163 conform to the following formula: />
Wherein lambda is the grating period length, lambda is the lasing wavelength of the laser, n eff Is the equivalent refractive index of the semiconductor waveguide, m and o are both positive integers, m and o are unequal, and o is an even multiple of m. The light-emitting surface 21 is defined by the second grating region 163. In the first embodiment, m=1 and o=2; thus, theThe first grating region 162 is also referred to as a first order grating structure region, and the second grating region 163 is also referred to as a second order grating structure region, thereby forming a hybrid grating structure in the grating layer 16; the laser light is emitted vertically upwards from the light emitting surface 21 defined by the second grating region 163.
In this embodiment, the grating layer 16 further includes a phase-difference grating structure 164. The phase-difference grating structure 164 is located near the middle of the second grating region 163 in the first horizontal direction, and the width of the phase-difference grating structure 164 can provide a phase-difference distance, so that a phase difference exists between the micro-grating structures located at two sides of the phase-difference grating structure 164 in the first horizontal direction; the phase difference grating structure 164 provides a phase difference distance of one quarter of the laser wavelength (i.e., lambda/4-Shift). By arranging the lambda/4-Shift phase difference grating structure in the center of the second-order grating structure area, the laser field of the laser element can be stable in mode and the light-emitting coupling light efficiency can be improved. And, the number of the second grating regions 163 is one and is located in a middle area of the grating layer 16 in the first horizontal direction, so that the first grating region 162 is substantially divided into left and right parts in the first horizontal direction by the second grating region 163 located in the middle. Wherein the width of the second grating region 163 in the first horizontal direction is between one sixth and one half of the total width of the grating layer 16; the width of the left and right portions of the first grating region 162 that are separated are substantially equal. Thus, the surface emitting laser device of the present invention integrates the first-order and second-order grating structures in the same grating layer 16. The first-order grating structure design with low loss is utilized to serve as a high-efficiency reflection feedback (feedback) area to be placed on the laser end face, and the second-order grating structure design is only used near the light emergent area of the middle laser face. In this way, a desired balance can be achieved between pursuing a high slope efficiency (meaning this larger second order grating structure region) and a low critical current value Ith (meaning this smaller second order grating structure region).
Take a typical edge-emitting DFB laser device as shown in fig. 4 as an exampleThe related mathematical operation of the method using Transfer Matrix (reference book: semiconductor laser technology, lu Tingchang Wang Xingzong, five south Press) includes:
sigma (sigma) 2 ＝K 2 -δ 2 . Wherein: lambda, n eff The lambda and i are respectively laser wavelength, modal equivalent refractive index, grating period and i; k is the coupling constant and the coupling correlation between the optical field and the grating in the structure; a (or R) and B (or S) are electric field intensities advancing rightward and leftward. If the simulation is performed by using the laser device according to the first embodiment of the present invention shown in fig. 3A to 3C, the following conditions and results are calculated:
total length l=l1+l2=250 μm of the laser element. Wherein L is the total length of the laser element in the first horizontal direction, L2 is the length of the middle second-order grating structure region, and L1 is the sum of the lengths of the two first-order grating structure regions located at the left and right sides of L2. The simulation was performed with four structural variations of L2 length variations from 0 μm, 50 μm, 100 μm to 150 μm, respectively. The coupling constant (coupling constant) K1 of the first-order grating structure region is 12cm -1 The coupling constant (coupling constant) K2 of the second-order grating structure region is 5cm -1 . The front and back end surfaces of the laser element are designed to be Antireflection (AR) and the reflectivity is 0.1%. The intensity distribution graph of the laser guided mode along the ridge obtained by the simulation is shown in fig. 5A to 5D (R 2 ->(right propagation)+S 2 <- (left production); in the graph, the X-axis is L (longitudinal normalized position Longitudinal Normalized Position), and the Y-axis is |E| 2 (Arb. Unit, arbitrary unit); l2 is the length of the second order grating structure region. The normalized gain (g×l) and detuning relationship (δl) graphs obtained by simulation are shown in fig. 6A to 6D. The relationship between the critical gain (Threshold gain) and the different L2 lengths obtained by the simulation is shown in FIG. 7. As can be seen from the foregoing fig. 5A to 5D, fig. 6A to 6D, and fig. 7, the larger the L2 region (second-order grating structure region) is, the higher the light extraction efficiency is, and as can be seen from fig. 7, the larger the L2 region (second-order grating structure region)The larger the structural region), the higher Ith (critical current) is. Thus, by the above design, a trade-off between low threshold and high output power can be made to achieve a desired value by adjusting the appropriate length ratio of the L2 region (second level grating structure region), such as but not limited to: an optimal balance between the high slope efficiency (slope efficiency) and the low threshold current value Ith is obtained when the width L2 of the L2 region (second level grating structure region) in the first horizontal direction is between 1/6 and 1/2 of the total width L of the grating layer, which is difficult to achieve in the conventional art (pure second level grating structure DFB laser device).
The same concept can be converted from a one-dimensional grating structure to a two-dimensional photonic crystal surface emitting laser (photonic crystal surface emitting laser; PCSEL for short). A first-order photonic crystal (photonic crystal) is disposed around the laser element, and a second-order photonic crystal is disposed only at the intermediate light extraction, and a phase difference structure is appropriately introduced to operate the mode. It is also possible to deploy several light-emitting sites simultaneously (i.e. only second-order photonic crystals at the light-emitting sites) to achieve a multi-light source two-dimensional array phase lock (2D array phase lock) like effect.
Since most of the components in the other embodiments of the present invention described below have the same or similar structures or functions as those in the previous embodiments, the same or similar components will be given the same names and numbers directly, and details thereof will not be repeated.
Referring to fig. 8 and 9, a schematic perspective view and a schematic top view of a grating layer of a second embodiment of a surface emitting laser device according to the present invention are shown. In the second embodiment, the surface emitting laser device may be a surface emitting DFB laser device or a photonic crystal surface emitting laser device (PCSEL), which generally includes a semiconductor stack structure and a grating layer 16 (or photonic crystal layer) on the semiconductor stack structure. The semiconductor stacked structure can generate laser with laser wavelength lambda when receiving a predetermined current, and the laser is emitted vertically upwards from a light emitting surface 21 on the top surface of the semiconductor stacked structure. The semiconductor stacking structure sequentially comprises the following components from bottom to top: a semiconductor substrate 10, a lower cladding layer 11, a lower light confining layer (SCH) 12, an active layer 13, a upper light confining layer 14, the grating layer 16 (or photonic crystal layer), an upper cladding layer 17, a contact layer (not shown), and a metal layer (not shown).
In this embodiment, the grating layer 16 (or photonic crystal layer) not only has a plurality of micro-grating (or photonic crystal) structures distributed and arranged along at least a first horizontal direction, but also has a plurality of micro-grating (or photonic crystal) structures along a second horizontal direction. The second horizontal direction is perpendicular to the first horizontal direction, and the second horizontal direction is perpendicular to the first horizontal direction and the emergent direction of the laser. The grating layer 16 (or photonic crystal layer) is distinguished in the first horizontal direction as comprising: at least one first grating (or photonic crystal) region 162 and at least one second grating (or photonic crystal) region 163, each of the first grating (or photonic crystal) region 162 and the second grating (or photonic crystal) region 163 comprises a plurality of micro-grating (or micro-photonic crystal) structures, respectively. The grating layer 16 (or photonic crystal layer) is also similarly divided into layers including: at least one first grating (or photonic crystal) region 162 and at least one second grating (or photonic crystal) region 163, wherein each of the first grating (or photonic crystal) region 162 and the second grating (or photonic crystal) region 163 also comprises a plurality of micro-grating (or micro-photonic crystal) structures. Wherein, in either the first horizontal direction or the second horizontal direction, the grating (or photonic crystal) periods of the micro-grating (or photonic crystal) structure in the first grating (or photonic crystal) region 162 conform to the following mathematical formula: 
And, the grating (or photonic crystal) period of the micro-grating (or micro-photonic crystal) structure in the second grating (or photonic crystal) region 163 is in accordance with the following mathematical formula: />
Where lambda is the grating (or photonic crystal) period length and lambda is the laserN of the laser wavelength of (1) eff Is the equivalent refractive index of the semiconductor waveguide, m=1 and o=2. Thus, the first grating (or photonic crystal) region 162 is also referred to as a first order grating (or photonic crystal) structure region, and the second grating (or photonic crystal) region 163 is also referred to as a second order grating (or photonic crystal) structure region, thereby forming a hybrid grating structure (or hybrid photonic crystal structure) in the grating layer 16 (or photonic crystal layer). The laser light is emitted vertically upwards from the light emitting surface 21 defined by the second grating (or photonic crystal) region 163. Thus, when viewed from a top view perpendicular to the top surface of the semiconductor stack structure (as shown in fig. 9), the micro-grating (or micro-photonic crystal) structures are arranged in a dot array on the grating (or photonic crystal) layer 16, and the second grating (or photonic crystal) region 163 in the first horizontal direction and the second grating (or photonic crystal) region 163 in the second horizontal direction cooperatively define at least one rectangular light-emitting surface 21.
In addition, in the present embodiment, the second grating (or photonic crystal) region 163 is located in a middle region of the grating (or photonic crystal) layer 16 in the first horizontal direction and the second horizontal direction. In other words, the second grating (or photonic crystal) region 163 is located at a central region of the top surface of the semiconductor stack structure when viewed from a direction perpendicular to the top surface of the semiconductor stack structure, and the first grating (or photonic crystal) region 162 substantially surrounds an outer peripheral region of the second grating (or photonic crystal) region 163. The width of the second grating (or photonic crystal) region 163 in the first horizontal direction and the second horizontal direction is between one sixth and one half of the total width of the grating (or photonic crystal) layer 16 in the first horizontal direction and the second horizontal direction, respectively.
Referring to fig. 10, a schematic top view of a grating (or photonic crystal) layer of a surface-emitting laser device with a hybrid grating (or photonic crystal) structure according to a third embodiment of the present invention is shown. The laser device structure of this third embodiment is largely identical to the second embodiment shown in fig. 8 and 9, with the only difference that in the third embodiment shown in fig. 10, a two-phase difference grating (or photonic crystal) structure 164 is included in the grating (or photonic crystal) layer. One of the phase difference grating (or photonic crystal) structures 164 is located near the middle in the first horizontal direction within the second grating (or photonic crystal) region 163, and the other of the phase difference grating (or photonic crystal) structures 164 is located near the middle in the second horizontal direction within the second grating (or photonic crystal) region 163. The width of the phase difference grating (or photonic crystal) structure 164 may provide a phase difference distance such that there is a phase difference between the micro-grating (or photonic crystal) structures located on both sides of the phase difference grating (or photonic crystal) structure 164 in the first horizontal direction and the second horizontal direction, respectively. In this embodiment, the phase difference distance provided by the phase difference grating (or photonic crystal) structure 164 is one quarter of the laser wavelength.
Referring to fig. 11, a schematic diagram of a grating layer of a surface-emitting laser device with a hybrid grating (or photonic crystal) structure according to a fourth embodiment of the present invention is shown in top view. The laser device structure of the fourth embodiment is the same as the second embodiment shown in fig. 8 and 9, except that in the fourth embodiment shown in fig. 11, the top surface of the semiconductor stacked structure includes a plurality of light emitting surfaces 21 arranged in an array and independently present, the grating (or photonic crystal) layer is provided with the second grating (or photonic crystal) region 163 at each of the light emitting surfaces 21 in the first horizontal direction or the second horizontal direction, and other regions of the grating (or photonic crystal) layer except for the light emitting surfaces 21 are provided with the first grating (or photonic crystal) region 162 in the first horizontal direction or the second horizontal direction; therefore, a plurality of independent small light emitting surfaces 21 which are arranged in an array can be defined on the top surface of the semiconductor stacked structure, and the light emitting effect similar to that of a plurality of laser small light source arrays can be achieved.
Referring to fig. 12A and 12B, a schematic diagram of a conventional distributed feedback laser device with a pure first-order grating structure and a micro-grating structure of a surface-emitting laser device with a first-order and second-order hybrid grating structure according to the present invention are shown. As shown in fig. 12B, the design feature of the surface emitting laser device with the first-order and second-order hybrid grating structure of the present invention is to seamlessly integrate the regions 162, 163 of the first-order and second-order grating structures together, and introduce the phase difference grating structure 164 into the middle light-emitting region (light-emitting surface 21). The integration approach may be to remove the odd or even number of gratings from a specific area starting from the first order grating structure to form an area of the second order grating structure with twice the period. The same concept can be developed on a two-dimensional photonic crystal surface emitting laser (photonic crystal surface emitting laser; abbreviated as PCSEL), and the photonic crystal (photonic crystal) with the outer edge of the first stage can freely arrange the light emitting position of the photonic crystal with the inner region and the second stage.
Fig. 13A to 13C are schematic views showing several steps of a method for manufacturing a surface emitting laser device with a hybrid grating structure according to the present invention. A preferred embodiment of the method for manufacturing a surface-emitting laser device with a hybrid grating structure according to the present invention comprises the following steps:
step (A): as shown in fig. 13A, a semiconductor stack structure, a grating layer 16, and a protection layer are sequentially formed on a semiconductor substrate by Metal Organic Chemical Vapor Deposition (MOCVD) or other conventional semiconductor epitaxial processes. The semiconductor stacked structure can generate a laser with a laser wavelength when receiving a current, and the laser is emitted from a light emitting surface of the semiconductor stacked structure, wherein the light emitting surface is positioned on a top surface of the semiconductor stacked structure. The semiconductor stacking structure sequentially comprises the following components from bottom to top: the semiconductor substrate 10, a lower cladding layer 11, a lower light confining layer 12, an active layer 13, a upper light confining layer 14, and a spacer layer.
Step (B): as shown in fig. 13B, the grating layer 16 on the semiconductor stacked structure is processed by an E-Beam printing (E-Beam Writer) and Nano-Imprint (Nano-Imprint) process to form a micro-grating structure having a plurality of micro-grating structures aligned along at least a first horizontal direction. Wherein the grating layer is divided at least in the first horizontal direction into the steps of: at least one first grating region 162 located at both sides and at least one second grating region 1 located in the middle region 63, each of the first grating region 162 and the second grating region 163 includes a plurality of micro-grating structures. And, a phase difference grating structure 164 is disposed near the center of the second grating region 163. Wherein, the grating periods of the micro-grating structures in the first grating region 162 conform to the following formula:
and, the grating periods of the micro-grating structures in the second grating region 163 conform to the following formula: />
Wherein lambda is the grating period length, lambda is the lasing wavelength of the laser, n eff Is the equivalent refractive index of the semiconductor waveguide, m and o are both positive integers, m and o are unequal, and o is an even multiple of m. The light-emitting surface is defined by the second grating region 163.
Step (C): as shown in fig. 13C, an upper cladding layer 17 and a contact layer 18 are formed on the grating layer 16 by conventional semiconductor epitaxy and photolithography processes, and are located above the grating layer 16.
Fig. 14 is a schematic perspective view of a fifth embodiment of a surface-emitting laser device according to the present invention. The laser device structure of this fifth embodiment is largely identical to that of the first embodiment shown in fig. 3A, with the only difference that in the fifth embodiment shown in fig. 14, a grating (or photonic crystal) layer 16 is located in the lower cladding layer 11 to constitute a P-side down (P-side down) surface emitting laser device.
The above-described embodiments should not be construed as limiting the applicable scope of the present invention, but rather as limiting the scope of the invention encompassed by the technical spirit and equivalent variations defined by the claims of the present invention. All such equivalent changes and modifications as made by the claims of this invention will not depart from the spirit and scope of the present invention, and should be construed as further embodiments of the present invention.
Claims (9)
1. A surface-emitting laser element having a hybrid grating structure for generating laser light having a laser wavelength, the surface-emitting laser element comprising:
a semiconductor stacked structure capable of generating the laser with the laser wavelength when receiving a current and emitting the laser from an emitting surface of the semiconductor stacked structure, wherein the emitting surface is positioned on a top surface of the semiconductor stacked structure;
the grating layer is positioned on the semiconductor stacking structure and is provided with a plurality of micro-grating structures distributed and arranged along at least one first horizontal direction;
wherein the grating layer is divided at least in the first horizontal direction into the steps of: at least one first grating region and at least one second grating region, wherein each first grating region and each second grating region respectively comprise a plurality of micro-grating structures; wherein, the grating periods of the micro-grating structures in the first grating region conform to the following mathematical formula: 
And, the grating period of the micro-grating structures in the second grating region is in accordance with the following mathematical formula: />
Wherein lambda is the grating period length, lambda is the lasing wavelength of the laser, n eff Is the equivalent refractive index of the semiconductor waveguide; wherein m=1 and o=2; the first grating region is also called a first-order grating structure region, and the second grating region is also called a second-order grating structure region, so as to form a hybrid grating structure on the grating layer; wherein the light-emitting surface is defined by the second grating region, and the laser light is emitted vertically from the light-emitting surface;
the grating layer is also provided with a plurality of micro-grating structures along a second horizontal direction, and the second horizontal direction is perpendicular to the first horizontal direction; the grating layer is also divided into at least one first grating region and at least one second grating region in the second horizontal direction, and each of the first grating region and the second grating region in the second horizontal direction respectively comprises a plurality of micro-grating structures; therefore, when viewed from the direction perpendicular to the top surface of the semiconductor stacked structure, the micro-grating structures are arranged in a dot array on the grating layer, and the rectangular light-emitting surface is cooperatively defined by the second grating region in the first horizontal direction and the second grating region in the second horizontal direction;
The grating layer further comprises a two-phase difference grating structure; one of the phase difference grating structures is positioned near the middle of the second grating area in the first horizontal direction, and the other phase difference grating structure is positioned near the middle of the second grating area in the second horizontal direction; the width of the phase difference grating structure can provide a phase difference distance, so that a phase difference exists between the micro grating structures positioned at two sides of the phase difference grating structure in the first horizontal direction and the second horizontal direction respectively; the phase difference grating structure provides the phase difference distance being one quarter of the laser wavelength.
2. The surface-emitting laser device with hybrid grating structure according to claim 1, wherein the second grating region is located at an intermediate region of the grating layer in the first horizontal direction and the second horizontal direction; the second grating region is located in a central region of the top surface of the semiconductor stack structure when viewed from a direction perpendicular to the top surface of the semiconductor stack structure, and the first grating region is substantially located around an outer peripheral region of the second grating region; the width of the second grating region in the first horizontal direction and the second horizontal direction is between one sixth and one half of the total width of the grating layer in the first horizontal direction and the second horizontal direction respectively.
3. The surface-emitting laser device with hybrid grating structure according to claim 1, wherein the top surface of the semiconductor stack structure comprises a plurality of light-emitting surfaces arranged in an array and independently existing, the grating layer is provided with the second grating region at each light-emitting surface in either the first horizontal direction or the second horizontal direction, and the other regions of the grating layer except the light-emitting surfaces are provided with the first grating region in either the first horizontal direction or the second horizontal direction; therefore, a plurality of small light emitting surfaces which are independent and arranged in an array can be defined on the top surface of the semiconductor stacked structure.
4. The surface emitting laser element with hybrid grating structure of claim 1, wherein the semiconductor stack structure comprises:
a semiconductor substrate;
a lower cladding layer (claddinglayer) on the semiconductor substrate;
a lower light confinement (SCH) layer on the lower cladding layer;
an active layer (active regionlayer) on the lower light confining layer;
a glazing limiting layer located on the active layer;
a spacer layer on the glazing confinement layer; wherein the grating layer is positioned on the spacer layer;
An upper cladding layer disposed on the grating layer; and
a contact layer is disposed on the upper cladding layer.
5. A method for manufacturing a surface emitting laser device having a hybrid grating structure, comprising the steps of:
step (A): forming a semiconductor stacked structure on a semiconductor substrate by a semiconductor epitaxial process; the semiconductor stacking structure can generate a laser with a laser wavelength when receiving a current, and the laser is emitted from a light emitting surface of the semiconductor stacking structure, wherein the light emitting surface is positioned on the top surface of the semiconductor stacking structure;
step (B): forming a grating layer on the semiconductor stacked structure by using electron beam printing and nanoimprint process; the grating layer is provided with a plurality of micro-grating structures which are arranged along at least one first horizontal direction;
step (C): forming an upper cladding layer and a contact layer on the grating layer by a semiconductor epitaxy process and a yellow light process, wherein the upper cladding layer and the contact layer are positioned above the grating layer;
wherein the grating layer is divided at least in the first horizontal direction into the steps of: at least one first grating region and at least one second grating region, wherein each first grating region and each second grating region respectively comprise a plurality of micro-grating structures; wherein, the grating periods of the micro-grating structures in the first grating region conform to the following mathematical formula: 
And, the grating period of the micro-grating structures in the second grating region is in accordance with the following mathematical formula: />
Wherein lambda is the grating period length, lambda is the lasing wavelength of the laser, n eff Is the equivalent refractive index of the semiconductor waveguide; wherein m=1 and o=2; the first grating region is also called a first-order grating structure region, and the second grating region is also called a second-order grating structure region, so as to form a hybrid grating structure on the grating layer;
wherein the light-emitting surface is defined by the second grating region, and the laser light is emitted vertically from the light-emitting surface;
the grating layer is also provided with a plurality of micro-grating structures along a second horizontal direction, and the second horizontal direction is perpendicular to the first horizontal direction; the grating layer is also divided into at least one first grating region and at least one second grating region in the second horizontal direction, and each of the first grating region and the second grating region in the second horizontal direction respectively comprises a plurality of micro-grating structures; therefore, when viewed from the direction perpendicular to the top surface of the semiconductor stacked structure, the micro-grating structures are arranged in a dot array on the grating layer, and the rectangular light-emitting surface is cooperatively defined by the second grating region in the first horizontal direction and the second grating region in the second horizontal direction;
The grating layer further comprises a two-phase difference grating structure; one of the phase difference grating structures is positioned near the middle of the second grating area in the first horizontal direction, and the other phase difference grating structure is positioned near the middle of the second grating area in the second horizontal direction; the width of the phase difference grating structure can provide a phase difference distance, so that a phase difference exists between the micro grating structures positioned at two sides of the phase difference grating structure in the first horizontal direction and the second horizontal direction respectively; the phase difference grating structure provides the phase difference distance being one quarter of the laser wavelength.
6. The method of claim 5, wherein the second grating region is located in a middle region of the grating layer in the first horizontal direction and the second horizontal direction; the second grating region is located in a central region of the top surface of the semiconductor stack structure when viewed from a direction perpendicular to the top surface of the semiconductor stack structure, and the first grating region is substantially located around an outer peripheral region of the second grating region; the width of the second grating region in the first horizontal direction and the second horizontal direction is between one sixth and one half of the total width of the grating layer in the first horizontal direction and the second horizontal direction respectively.
7. The method of claim 5, wherein the top surface of the semiconductor stack structure includes a plurality of light emitting surfaces arranged in an array and independently present, the grating layer is provided with the second grating region at each of the light emitting surfaces in either the first horizontal direction or the second horizontal direction, and the other regions of the grating layer except the light emitting surfaces are provided with the first grating region in either the first horizontal direction or the second horizontal direction; therefore, a plurality of small light emitting surfaces which are independent and arranged in an array can be defined on the top surface of the semiconductor stacked structure.
8. A surface-emitting laser element that generates laser light having a laser wavelength, the surface-emitting laser element comprising:
a semiconductor stacked structure capable of generating the laser with the laser wavelength when receiving a current and emitting the laser from an emitting surface of the semiconductor stacked structure, wherein the emitting surface is positioned on a top surface of the semiconductor stacked structure;
the photonic crystal layer is positioned on the semiconductor stacking structure and is provided with a plurality of micro-photonic crystal structures distributed and arranged along a first horizontal direction and a second horizontal direction, and the second horizontal direction is perpendicular to the first horizontal direction; wherein the photonic crystal layer is divided into the first horizontal direction and the second horizontal direction respectively, and includes: at least one first photonic crystal region and at least one second photonic crystal region, wherein each of the first photonic crystal region and the second photonic crystal region comprises a plurality of micro-photonic crystal structures; the photonic crystal periods of the photonic crystal structures in the first and second horizontal directions in the first photonic crystal region are all in accordance with the following mathematical formulas: 
And the photonic crystal periods of the plurality of micro-photonic crystal structures in the second photonic crystal region in the first horizontal direction and the second horizontal direction are both in accordance with the following mathematical formula: />
Wherein lambda is the period length of the photonic crystal, lambda is the lasing wavelength of the laser, n eff Is the equivalent refractive index of the semiconductor waveguide; wherein m=1 and o=2;
the light-emitting surface is defined by the second photonic crystal region, and the laser is emitted vertically from the light-emitting surface;
when viewed from the direction perpendicular to the top surface of the semiconductor stacked structure, the micro-photonic crystal structures are arranged in a dot array on the photonic crystal layer, and the rectangular light-emitting surface is cooperatively defined by the second photonic crystal region in the first horizontal direction and the second photonic crystal region in the second horizontal direction;
the photonic crystal layer further comprises a two-phase difference photonic crystal structure; one of the phase difference photonic crystal structures is positioned near the middle of the second photonic crystal region in the first horizontal direction, and the other phase difference photonic crystal structure is positioned near the middle of the second photonic crystal region in the second horizontal direction; the width of the phase difference photonic crystal structure can provide a phase difference distance, so that a phase difference exists between the two micro-photonic crystal structures which are respectively positioned at the two sides of the phase difference photonic crystal structure in the first horizontal direction and the second horizontal direction; the phase difference distance provided by the phase difference photonic crystal structure is one quarter of the laser wavelength.
9. The surface-emitting laser device of claim 8, wherein the top surface of the semiconductor stack structure includes a plurality of light-emitting surfaces arranged in an array and independently present, the photonic crystal layer is provided with the second photonic crystal region at each of the light-emitting surfaces in either the first horizontal direction or the second horizontal direction, and other regions of the photonic crystal layer except the light-emitting surfaces are provided with the first photonic crystal region in either the first horizontal direction or the second horizontal direction; therefore, a plurality of small light emitting surfaces which are independent and arranged in an array can be defined on the top surface of the semiconductor stacked structure.
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