CN214411760U

CN214411760U - Distributed feedback laser

Info

Publication number: CN214411760U
Application number: CN202120572260.1U
Authority: CN
Inventors: 吴猛; 刘朝明; 王涛
Original assignee: Yinlin Photoelectric Technology Suzhou Co ltd
Current assignee: Yinlin Photoelectric Technology Suzhou Co ltd
Priority date: 2021-03-19
Filing date: 2021-03-19
Publication date: 2021-10-15
Anticipated expiration: 2031-03-19

Abstract

The utility model discloses a distributed feedback laser, include: the laser epitaxial structure comprises a substrate and a plurality of epitaxial layers positioned on one side of the substrate; the first electrode layer is positioned on one side, far away from the substrate, of the upper contact layer; the first electrode layer, the upper contact layer and part of the upper optical field limiting layer form a ridge structure and a grating structure group, and the grating structure group is positioned on two sides of the ridge structure; the grating structure group comprises at least two sub-grating structures which are arranged along a first direction, and the grating periods L of the two sub-grating structures are different; the at least two sub-grating structures comprise at least one common lasing mode; the first direction is parallel to the plane of the substrate; and the second electrode layer is positioned on one side of the substrate far away from the epitaxial layer. The utility model discloses effectively reduce the device preparation degree of difficulty and preparation cost, reduce the light loss of device, increase grating preparation precision, show the performance that promotes the device.

Description

Distributed feedback laser

Technical Field

The embodiment of the utility model provides a relate to laser instrument technical field, especially relate to a distributed feedback laser instrument.

Background

Semiconductor lasers, also known as laser diodes, are lasers using semiconductor materials, such as gallium arsenide (GaAs), indium phosphide (InP), gallium nitride (GaN), aluminum nitride (AlN), cadmium sulfide (CdS), zinc sulfide (ZnS), etc., as working substances, and have the advantages of small volume, high efficiency, long life, etc. The Distributed Feedback (DFB) semiconductor laser has the characteristics of good single-mode characteristic, narrow full width at half maximum of a spectrum, high modulation rate and the like, has important application in the fields of laser communication, laser ranging, laser radar and the like, and is widely concerned by the industrial and academic fields.

Distributed Feedback Laser (DFB), a Distributed Feedback semiconductor Laser needs to be prepared with a grating mode to select. In general, to achieve high selectivity, a low-order grating, such as a first-order grating, is often used, i.e. the grating period L satisfies the grating equation: λ ═ 2nL, since the operating wavelength of the laser is short, so that the grating period L is small, which puts high demands on the lithography technology, only the high-cost and expensive electron beam exposure machine or holographic lithography technology can be adopted, resulting in high device manufacturing cost. More importantly, the grating period is very small, and the grating etching depth ratio is very large, so that a steep and smooth grating is difficult to form in the later dry etching process, the performance of the grating is seriously influenced, and the stability of the output wavelength of the DFB laser is finally influenced.

In order to solve the above problems, some researchers propose to select a mode by using a high-order grating, and since a plurality of modes exist in the high-order grating, the mode is unstable and mode hopping is easy to occur when the DFB laser operates, that is, the output wavelength of the DFB laser is easy to change along with the changes of injection current and operating environment, which seriously affects the practical application of the DFB laser.

SUMMERY OF THE UTILITY MODEL

In view of this, the embodiment of the utility model provides a distributed feedback laser to solve among the prior art that the sculpture that adopts the low order grating structure to lead to is with high costs, sculpture grating aspect ratio is difficult in order to form abrupt and smooth grating structure and adopt the high order grating structure to have a plurality of wavelength modes in later stage dry etching process, leads to the during operation mode unstable, easily takes place to jump the mode, easily changes along with the change of injection current and operational environment, seriously influences the performance of laser and practical application's technical problem.

In a first aspect, an embodiment of the present invention provides a distributed feedback laser, including:

the laser epitaxial structure comprises a substrate and a plurality of epitaxial layers positioned on one side of the substrate, wherein the plurality of epitaxial layers comprise a middle epitaxial layer and an upper optical field limiting layer and an upper contact layer which are sequentially positioned on one side, far away from the substrate, of the middle epitaxial layer;

the first electrode layer is positioned on one side, far away from the substrate, of the upper contact layer; the first electrode layer, the upper contact layer and part of the upper optical field limiting layer form a ridge structure and a grating structure group, and the grating structure group is positioned on two sides of the ridge structure; the grating structure group comprises at least two sub-grating structures which are arranged along a first direction, and the grating periods L of the two sub-grating structures are different; at least two of the sub-grating structures comprise at least one common lasing mode; the first direction is parallel to the plane of the substrate;

and the second electrode layer is positioned on one side of the substrate far away from the epitaxial layer.

Optionally, the grating structure group includes a first sub-grating structure, an ith sub-grating structure and an nth sub-grating structure which are sequentially connected along the first direction; n is more than or equal to 2 and is an integer, 1< i is less than or equal to N and i is an integer;

the first sub-gratingThe grating equation of the structure satisfies: m lambda 2n L₁，L₁The grating period of the first sub-grating structure is shown, n is the effective refractive index, lambda is the laser wavelength, m is more than or equal to 2, and m is a positive integer;

the grating equation of the ith sub-grating structure satisfies: g λ 2n L_i，L_iThe grating period of the ith sub-grating structure is shown, g is more than or equal to 2 and is a positive integer;

the grating equation of the Nth sub-grating structure satisfies: k λ 2n L_N，L_NThe grating period of the Nth sub-grating structure is defined, k is more than or equal to 2 and is a positive integer;

wherein m, g and k are all different and the minimum common factor is 1.

Optionally, the grating structure group includes a plurality of common lasing modes, where the plurality of common lasing modes include a reference lasing mode and a non-reference lasing mode;

the wavelength difference between any non-reference lasing mode and the reference lasing mode is δ λ, satisfying δ λ > 10 nm.

Optionally, the distributed feedback laser further includes a connection electrode;

the connection electrode covers the ridge structure and the grating structure group, the vertical projection of the connection electrode on the plane of the substrate covers the vertical projection of the ridge structure and the grating structure group on the plane of the substrate, and the thickness of the connection electrode is larger than that of the first electrode layer.

Optionally, the laser epitaxial structure further includes a dielectric layer;

the dielectric layer covers the side wall of the ridge structure, the side wall of the grating structure group and part of the upper surface of the upper optical field limiting layer.

Optionally, the middle epitaxial layer includes a buffer layer, a lower optical field limiting layer, a lower waveguide layer, an active region, and an upper waveguide layer, which are sequentially disposed on one side of the substrate.

The embodiment of the utility model provides a distributed feedback laser, a ridge structure and a grating structure group are formed by the first electrode layer, the upper contact layer and part of the upper optical field limiting layer, the grating structure group is arranged at two sides of the ridge structure, the grating structure group comprises at least two sub-grating structures arranged along the first direction, the grating period L of the two sub-grating structures is further different, according to the relation between the laser wavelength and the grating period L in the grating optical path, by adopting a plurality of sections of high-order gratings with different grating periods L, in the case of determining the lasing mode, i.e. the laser wavelength lambda, of a DFB laser, the at least two sub-grating structures are made to comprise at least one common lasing mode and, due to the different grating periods L, under the condition of adopting the high-order grating, the high-selectivity effect of the first-order grating can be realized, and the locking of one lasing mode of the DFB laser is realized. By adopting a multi-section high-order grating structure, on one hand, the grating period is increased, and the grating can be prepared by adopting a conventional low-cost exposure technology, so that the preparation difficulty and the preparation cost of the device are effectively reduced; furthermore, a high-order grating structure is adopted, so that the etching selection ratio in the grating preparation process is obviously reduced, the grating preparation precision is greatly improved, and the accurate control on the output wavelength of the DFB laser is realized; furthermore, a multi-section high-order grating structure is adopted to replace the traditional low-order grating, so that the scattering and absorption loss of light at the grating interface is effectively reduced, the optical loss of the DFB laser is obviously reduced, and the performance of the device can be effectively improved; on the other hand, even if a plurality of lasing modes exist when a high-order grating structure is adopted, only one common lasing mode is selected and emitted, the mode hopping of the working mode of the device is effectively prevented, the stability of the working mode of the laser is ensured, and the performance of the device in practical application is improved.

Drawings

Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments made with reference to the following drawings:

fig. 1 is a schematic cross-sectional view of an epitaxial structure of a distributed feedback laser according to an embodiment of the present invention;

FIG. 2 is a schematic surface view of an epitaxial structure after etching a ridge structure and a grating structure group;

FIG. 3 is a schematic cross-sectional view of the ridge structure along direction AA' of FIG. 2;

FIG. 4 is a schematic cross-sectional view of the set of grating structures of FIG. 2 taken along direction BB';

fig. 5 is a schematic cross-sectional view of a semiconductor laser structure after a dielectric layer is deposited by a distributed feedback laser according to an embodiment of the present invention;

fig. 6 is a schematic cross-sectional view of a semiconductor laser structure after a dielectric layer is stripped from a distributed feedback laser according to an embodiment of the present invention;

fig. 7 is a schematic cross-sectional view of a semiconductor laser structure after a second electrode is manufactured by a distributed feedback laser according to an embodiment of the present invention;

fig. 8 is a schematic flow chart of a method for manufacturing a distributed feedback laser according to an embodiment of the present invention;

fig. 9 is a schematic flow chart of another method for manufacturing a distributed feedback laser according to an embodiment of the present invention.

The following are the reference signs:

in the figure: 101 is a substrate, 102 is a buffer layer, 103 is a lower optical field confining layer, 104 is a lower waveguide layer, 105 is an active region, 106 is an upper waveguide layer, 107 is an upper optical field confining layer, 108 is an upper contact layer, 109 is a first electrode layer, 110 is a dielectric layer, 111 is a connection electrode, and 112 is a second electrode layer.

In fig. 2: the reference numeral 201 denotes a first sub-grating structure, 202 denotes a second sub-grating structure, and 203 denotes a third sub-grating structure.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be described in detail through the following embodiments with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some embodiments of the present invention, not all embodiments, and all other embodiments obtained by those skilled in the art without creative efforts based on the embodiments of the present invention all fall into the protection scope of the present invention.

Examples

The embodiment of the utility model provides a distributed feedback laser instrument. Fig. 1 is a schematic cross-sectional view of an epitaxial structure of a distributed feedback laser according to an embodiment of the present invention; fig. 2 is a schematic surface view of an epitaxial structure after a ridge structure and a grating structure group are etched by a distributed feedback laser provided in an embodiment of the present invention; FIG. 3 is a schematic cross-sectional view of the ridge structure along direction AA' of FIG. 2; fig. 4 is a schematic cross-sectional view of the grating structure set along direction BB' in fig. 2. As shown in fig. 1-4, a distributed feedback laser includes: the laser epitaxial structure comprises a substrate 101 and a plurality of epitaxial layers positioned on one side of the substrate 101, wherein the plurality of epitaxial layers comprise a middle epitaxial layer, and an upper optical field limiting layer 107 and an upper contact layer 108 which are sequentially positioned on one side of the middle epitaxial layer, which is far away from the substrate;

a first electrode layer 109 on the side of the upper contact layer 108 remote from the substrate 101; the first electrode layer 109, the upper contact layer 108 and part of the upper optical field limiting layer 107 form a ridge structure 10 and a grating structure group 20, and the grating structure group 20 is located on two sides of the ridge structure 10; the grating structure group 20 includes at least two sub-grating structures arranged along a first direction (as shown in the X direction in the figure), and there are two sub-grating structures with different grating periods L; the at least two sub-grating structures comprise at least one common lasing mode; the first direction is parallel to the plane of the substrate 101;

and a second electrode layer 112 located on a side of the substrate 101 remote from the epitaxial layer.

Illustratively, as shown in fig. 1 to 4, the distributed feedback laser provided by the embodiments of the present invention includes a laser epitaxial structure, the epitaxial structure is used as a main light emitting structure of the laser, the laser epitaxial structure includes a substrate 101 and a multi-layer epitaxial layer grown on one side of the substrate 101, wherein the substrate material may be a group III nitride material, such as: the group III nitride semiconductor DFB laser can be prepared by using a group III nitride as a substrate and any one or a combination of more than two of GaAs, InP, GaN, AlGaN, InGaN, AlN, sapphire, SiC, Si and SOI.

The multi-layer epitaxial layer comprises a middle epitaxial layer, as shown in FIG. 1, and optionally, a middle epitaxial layerThe epitaxial layer includes a buffer layer 102, a lower optical field confining layer 103, a lower waveguide layer 104, an active region 105, and an upper waveguide layer 106 sequentially disposed on one side of a substrate 101. Further, an upper optical field limiting layer 107 and an upper contact layer 108 are sequentially disposed on the side of the middle epitaxial layer away from the substrate 101. Wherein the materials of upper contact layer 108, upper optical field confining layer 107, lower optical field confining layer 103, upper waveguide layer 106 and active region 105 include Al_x1In_y1Ga_1-x1-y1As_x2P_y2N_1-x2-y2X1 is more than or equal to 0 and less than or equal to 1, y1 is more than or equal to 0 and less than or equal to 1, x2 is more than or equal to 0 and less than or equal to 1, y2 is more than or equal to 0 and less than or equal to 1, (x1+ y1) is more than or equal to 0 and less than or equal to 1, and x2+ y2 is more than or equal to 0 and less than or equal to 1. For example, the material GaN is selected to have different epitaxial layer materials according to the characteristics of the distributed feedback laser, so that the epitaxial layer has multiple selectable materials, which is not limited herein.

With continued reference to fig. 1, the first electrode layer 109 is located on the side of the upper contact layer 108 away from the substrate 101, and the first electrode layer 109 includes any one or a combination of two or more of materials Ni, Ti, Pd, Pt, Au, Al, TiN, ITO, AuGe, AuGeNi, ITO, ZnO, IGZO, and graphene, and has a function of better ohmic contact metal conduction.

An optical device consisting of a large number of parallel slits of equal width and equal spacing is called a Grating (Grating). The common grating is made by etching a large number of parallel notches on a glass sheet, the notches are opaque parts, and the smooth part between the two notches can transmit light, which is equivalent to a slit. The refined grating has thousands or even tens of thousands of nicks engraved within 1cm of width. Such a grating utilizing diffraction of transmitted light is called a transmission grating, and also a grating utilizing diffraction of reflected light between two scores, such as a grating in which a plurality of parallel scores are engraved on a surface coated with a metal layer and a smooth metal surface between two scores can reflect light, is called a reflection grating. Preferably, the embodiment of the present invention selects the reflective grating structure group.

The first electrode layer 109, the upper contact layer 108 and a part of the upper optical field limiting layer 107 are prepared to form a ridge structure 10 and a grating structure group 20, as shown in fig. 2, the grating structure group 20 is located on two sides of the structure 10, and it should be noted that the ridge structure 10 and the grating structure group 20 are prepared integrally and have the same material structure, as shown in fig. 3 and 4. According to the relationship between the laser wavelength and the grating period L in the grating optical path, when the grating period L of the grating structure is confirmed by only adopting the first-order grating, the writing precision of the grating period L is higher, but in the present application, by setting the grating structure group 20 to include at least two sub-grating structures arranged along the first direction (as shown in the X direction in the figure), the grating periods L of the at least two sub-grating structures are different, and by adopting the high-order grating with multiple sections of different grating periods L, under the condition of confirming the laser emission mode of the DFB laser, namely the laser wavelength λ, the grating periods L of the at least two sub-grating structures are reasonably set, so that the at least two sub-grating structures include at least one common lasing mode, wherein the common lasing mode includes the laser wavelength λ, because the different grating periods L meet at least one common lasing mode, under the condition of adopting the high-order grating, the high selectivity effect of the first-order grating on the laser emission mode, namely the laser wavelength lambda, can be realized, and the locking on the laser emission mode, namely the laser wavelength lambda, of the DFB laser can be realized.

When a multi-section high-order grating structure is adopted, on one hand, the grating period is increased, and the grating can be prepared by adopting a conventional low-cost exposure technology, so that the preparation difficulty and the preparation cost of a device are effectively reduced; furthermore, a high-order grating structure is adopted, so that the etching selection ratio in the grating preparation process is obviously reduced, the grating preparation precision is greatly improved, and the accurate control on the output wavelength of the DFB laser is realized; furthermore, a multi-section high-order grating structure is adopted to replace the traditional low-order grating, so that the scattering and absorption loss of light at the grating interface is effectively reduced, the optical loss of the DFB laser is obviously reduced, and the performance of the device can be effectively improved; on the other hand, even if a plurality of lasing modes exist when a high-order grating structure is adopted, only one common lasing mode is selected and emitted, the mode hopping of the working mode of the device is effectively prevented, the stability of the working mode of the laser is ensured, and the performance of the device in practical application is improved.

The second electrode layer 112 is located on the side of the substrate 101 away from the epitaxial layer, wherein the material of the second electrode layer 112 includes any one or a combination of two or more of Ni, Ti, Pd, Pt, Au, Al, TiN, ITO, AuGe, AuGeNi, ITO, ZnO, IGZO, and graphene. The second electrode layer 112 and the first electrode layer 109 form an ohmic contact electrode opposite to each other, so as to prepare for the subsequent preparation of external electrical connection of the laser.

To sum up, the embodiment of the utility model provides a pair of distributed feedback laser instrument, through at first electrode layer, go up the light field limiting layer and form ridge structure and grating structure group on contact layer and the part, grating structure group is located ridge structure both sides, it includes two at least sub-grating structures of arranging along the first direction to set up grating structure group, it is different to further set up the grating period L that has two sub-grating structures, according to relation of laser wavelength and grating period L in the grating optical path, under the condition that does not confine to first-order grating, adopt the form of high order grating combination, make two at least sub-grating structures include at least one public lasing mode. When a multi-section high-order grating structure is adopted, on one hand, the grating period is increased, and the grating can be prepared by adopting a conventional low-cost exposure technology, so that the preparation difficulty and the preparation cost of a device are effectively reduced; furthermore, a high-order grating structure is adopted, so that the etching selection ratio in the grating preparation process is obviously reduced, the grating preparation precision is greatly improved, and the accurate control on the output wavelength of the DFB laser is realized; furthermore, a multi-section high-order grating structure is adopted to replace the traditional low-order grating, so that the scattering and absorption loss of light at the grating interface is effectively reduced, the optical loss of the DFB laser is obviously reduced, and the performance of the device can be effectively improved; on the other hand, even if a plurality of lasing modes exist when a high-order grating structure is adopted, only one common lasing mode is selected and emitted, the mode hopping of the working mode of the device is effectively prevented, the stability of the working mode of the laser is ensured, and the performance of the device in practical application is improved.

Optionally, with reference to fig. 2, the grating structure group 20 includes a first sub-grating structure, an ith sub-grating structure and an nth sub-grating structure, which are connected in sequence along the first direction; n is more than or equal to 2 and is an integer, 1< i is less than or equal to N and i is an integer;

the grating equation of the first sub-grating structure satisfies: m lambda 2n L₁，L₁Is a first sub-grating structureN is the effective refractive index, lambda is the laser wavelength, m is greater than or equal to 2 and m is a positive integer;

wherein m, g and k are all different and the minimum common factor is 1.

Exemplarily, with continuing reference to fig. 2, the example that the grating structure group 20 includes a first sub-grating structure 201, a second sub-grating structure 202, and a third sub-grating structure 203 sequentially connected along a first direction (as shown in the X direction in fig. 2) is illustrated. Wherein, as shown along the X-direction in the figure, the grating period L of the first sub-grating structure 201₁Including the width a1 of the etched region and the width b1 of the un-etched region, the grating period L of the second sub-grating structure 202₂Including the width a2 of the etched region and the width b2 of the un-etched region, and the grating period L of the third sub-grating structure 203₃Including etched region width a3 and unetched region width b3, the change per grating period can be achieved by adjusting the size of etched region widths a1, a2, and a 3.

Wherein, the grating equation of the first sub-grating structure 201 satisfies: m lambda 2n L₁I.e. the grating period in the first sub-grating structure is L₁When the grating is used, m-order high-order grating with the laser wavelength of lambda is met, wherein n is the effective refractive index, m is more than or equal to 2, and m is a positive integer; the grating equation of the second sub-grating structure satisfies: g λ 2n L₂I.e. the grating period in the second sub-grating structure is L₂The grating meets the requirement of g-order high-order grating with the laser wavelength of lambda, wherein g is more than or equal to 2 and is a positive integer; the grating equation of the third sub-grating structure satisfies: k λ 2n L₃I.e. the grating period in the third sub-grating structure is L₃When the grating is used, the k-order high-order grating with the laser wavelength of lambda is satisfied, wherein k is more than or equal to 2 and is a positive integer; by setting the orders m, g and k of the grating to be different and the minimum common factor to be 1, the requirement that the multi-segment sub-grating structure has only one common grating is metCommon laser lasing mode.

Illustratively, according to the laser wavelength λ of the grating application and the requirement of the writing precision, it is preferable to select m, g and k to be greater than or equal to 20, that is, to select 20-order higher-order grating of the laser wavelength λ and higher-order grating above. The laser emission mode of the DFB laser, i.e. the laser wavelength λ, in which the grating structure group is applied is 450nm, is exemplified, wherein the effective refractive index n is 2.5, as shown in table 1. For example, if m is 20, the grating period of the first sub-grating structure 201 satisfies 20 λ ═ 2nL₁Period L of grating₁For 1800nm, g is chosen to be 24, and the grating period of the second sub-grating structure 202 satisfies 24 λ ═ 2nL₁Period L of grating₂For 2160nm, k is chosen to be 27, and the grating period of the third sub-grating structure 203 satisfies 27 λ ═ 2nL₃Period L of grating₃2430nm, and under the condition of definite laser wavelength λ, the first-order grating λ relative to the laser wavelength λ is 2nL, the grating period L is 90nm, and the grating period is L₁Grating period of L₂And a grating period of L₃The grating patterns are different and are enlarged by more than 20 times, namely the grating pattern is enlarged by more than 20 times, and the grating patterns can be prepared by adopting a conventional low-cost exposure technology, so that the preparation difficulty and the preparation cost of the device are effectively reduced. In addition, according to the selection characteristic of the grating to the laser wavelength λ, the first sub-grating structure 201 and the third sub-grating structure 203 have a common lasing mode with only the first-order grating λ being 2nL, so that the high selectivity of the first-order grating to the laser wavelength λ can be realized under the condition of adopting a combination of three stages of high-order gratings, and the laser lasing mode of the DFB laser can be locked. It should be noted that a high-order grating with a larger laser wavelength λ, such as a 51-order grating, may also be selected, where the grating period is 4590nm, as shown in table 1, the grating period is significantly increased, the writing accuracy is reduced, and the requirements can be met by common lithographic equipment, thereby reducing the production cost. More high order grating combinations are not listed here.

TABLE 1 Grating equation

It should be noted that the laser emission mode of the DFB laser, i.e. the laser wavelength λ, provided by the embodiment of the present invention satisfies the application of laser wavelength emitted by the laser in the market, and preferably, the laser wavelength λ range satisfies 200nm ≦ λ ≦ 2 μm. The present embodiment is only illustrated by taking the laser wavelength of 450nm as an example, and further wavelength applications are not detailed here.

In conclusion, according to a high-order grating equation satisfied by the laser wavelength lambda and the grating period L, the design of a multi-section high-order grating structure is adopted, the grating period L is greatly increased, and the etching selection ratio in the grating preparation process is obviously reduced, so that the grating preparation precision is greatly improved, and the accurate control of the output wavelength of the DFB laser is realized; the multi-section high-order grating structure is adopted to replace the traditional low-order grating, so that the scattering and absorption loss of light at the grating interface are effectively reduced, the optical loss of the DFB laser is obviously reduced, and the performance of the device can be effectively improved.

As a possible implementation, the grating structure group includes a plurality of common lasing modes, the plurality of common lasing modes including a reference lasing mode and a non-reference lasing mode; the wavelength difference between any non-reference lasing mode and the reference lasing mode is δ λ, satisfying δ λ > 10 nm.

Illustratively, according to the characteristics of the grating structure, in the case that the same grating period L is fixed, the grating equation of multiple laser wavelengths λ can be satisfied simultaneously, that is, the grating structure group includes multiple common lasing modes, the multiple common lasing modes include a reference lasing mode and a non-reference lasing mode, the wavelength difference between any one of the non-reference lasing modes and the reference lasing mode is δ λ, and δ λ > 10nm is satisfied, because of the difference of the manufacturing process, the Full Width at Half Maximum FWHM (Full Width Half Maximum, FWHM) of the laser spectrum emitted by the laser usually satisfies FWHM ≦ 15nm, and only one common lasing mode is selected by the grating structure group, so as to satisfy the DFB laserLaser light of single mode output is specific, preferably, only emitting a reference lasing mode, i.e., lasing mode of the laser wavelength λ. Illustratively, with continuing reference to table 1 and fig. 2, taking an example that the grating structure set includes two sub-grating structures, taking an example that the wavelength of the lasing mode is 450nm, when the first sub-grating structure 201 satisfies the 40-order grating equation with the wavelength of 450nm, and the grating period L is selected₁3600 nm; the second sub-grating structure 202 satisfies the 80-order grating equation with the wavelength of 450nm and the grating period L₂7200 nm. It is noted that the grating period L₁Simultaneously satisfies 41-order grating equation with the laser wavelength of 439nm and the grating period L₂And simultaneously, an 82-order grating equation with the laser wavelength of 439nm is satisfied, and at least two common lasing modes exist in the grating structure group to be locked. The wavelength of the non-reference lasing mode is 439nm, the wavelength difference delta lambda between the wavelength of the non-reference lasing mode and the wavelength of the reference lasing mode is 11nm, delta lambda is larger than 10nm, the reference lasing mode is usually located at the center of a spectrum curve of the grating structure group, the energy is highest, the wavelength difference delta lambda between the wavelength of the non-reference lasing mode 439nm and the wavelength of the non-reference lasing mode 450nm is 11nm, the condition of the grating selection laser mode for emitting is not met, and therefore, only one common lasing mode, namely the laser wavelength 450nm, is selected by the grating structure group for emitting. Through the parameter setting, the working mode of the device is effectively prevented from jumping, the stability of the working mode of the laser is ensured, and the performance of the practical application of the device is improved.

Fig. 5 is a schematic cross-sectional view of a semiconductor laser structure after a dielectric layer is deposited by a distributed feedback laser according to an embodiment of the present invention; fig. 6 is a schematic cross-sectional view of a semiconductor laser structure after a dielectric layer is stripped from a distributed feedback laser according to an embodiment of the present invention; fig. 7 is a schematic cross-sectional view of a semiconductor laser structure after a second electrode is prepared by a distributed feedback laser provided in an embodiment of the present invention.

As shown in fig. 5-7, optionally, the distributed feedback laser further comprises a connecting electrode 112; the connection electrode 112 covers the ridge structure 10 and the grating structure group 20, a vertical projection of the connection electrode 112 on the plane of the substrate 101 covers a vertical projection of the ridge structure 10 and the grating structure group 20 on the plane of the substrate 101, and the thickness of the connection electrode 112 is greater than that of the first electrode layer 110.

Exemplarily, as shown in fig. 7, since the widths of the ridge structure 10 and the grating structure group 20 are in the order of μm and the ohmic contact metal of the first electrode layer 109 is relatively thin, which is not beneficial to the actual production of electrical connection, by adding the ohmic contact metal with good conductivity, the vertical projection of the connection electrode 112 on the plane of the substrate 101 covers the vertical projection of the ridge structure 10 and the grating structure group 20 on the plane of the substrate 101, so as to ensure that the connection electrode 112 and the second electrode 113 form a stable electric field, and the thickness of the connection electrode 112 is set to be greater than the thickness of the first electrode layer 110, so as to form a thickened electrode, on one hand, the connection stability is increased, and on the other hand, the difficulty of preparing an external power supply by a laser is reduced.

On the basis of the above embodiment, the laser epitaxial structure further includes a dielectric layer 111; the dielectric layer 111 covers the sidewalls of the ridge structures 10 and the sidewalls of the grating structure groups 20 and a portion of the upper surface of the optical field confining layer 107.

Specifically, with continued reference to fig. 6 and 7, in order to ensure that the connection electrode 114 is only electrically connected to the first electrode layer 109, and to avoid introducing electrodes into the sidewalls of the ridge structure 10 and the sidewalls of the grating structure group 20 and part of the upper surface of the optical field limiting layer 107, which may affect the electric field distribution of the epitaxial structure of the laser, the sidewalls of the ridge structure 10 and the sidewalls of the grating structure group 20 and part of the upper surface of the optical field limiting layer 107 are covered with the dielectric layer 111, which forms an electrical insulation. Wherein the material of the second dielectric layer 111 comprises HfO₂、Si、SiO₂、SiN_x、SiON、Al₂O₃、AlON、SiAlON、TiO₂、Ta₂O₅、ZrO₂And MgO, polysilicon, and the like.

To sum up, the utility model provides a distributed feedback semiconductor laser structure and preparation method thereof has effectively reduced the device preparation degree of difficulty, has increased grating preparation precision by a wide margin, has reduced the optical loss of device, is finally showing and has promoted the device performance and reduced the device cost.

The embodiment of the utility model provides a preparation method of distributed feedback laser instrument for prepare the shown distributed feedback laser instrument of above-mentioned embodiment. Fig. 8 is a schematic flow chart of a method for manufacturing a distributed feedback laser device according to an embodiment of the present invention, as shown in fig. 8, the method for manufacturing a distributed feedback laser device includes:

s101, preparing a laser epitaxial structure, wherein the laser epitaxial structure comprises a substrate and a plurality of epitaxial layers located on one side of the substrate, and the plurality of epitaxial layers comprise a middle epitaxial layer and an upper optical field limiting layer and an upper contact layer which are sequentially located on one side, far away from the substrate, of the middle epitaxial layer.

Specifically, as shown in fig. 1, a plurality of epitaxial layers are sequentially grown on one side of a substrate 101, and each epitaxial layer includes a buffer layer 102, a lower optical field confining layer 103, a lower waveguide layer 104, an active region 105, an upper waveguide layer 106, an upper optical field confining layer 107, and an upper contact layer 108. Wherein the materials of upper contact layer 108, upper optical field confining layer 107, lower optical field confining layer 103, upper waveguide layer 106 and active region 105 include

Al_x1In_y1Ga_1-x1-y1As_x2P_y2N_1-x2-y2X1 is more than or equal to 0 and less than or equal to 1, y1 is more than or equal to 0 and less than or equal to 1, x2 is more than or equal to 0 and less than or equal to 1, y2 is more than or equal to 0 and less than or equal to 1, (x1+ y1) is more than or equal to 0 and less than or equal to 1, and x2+ y2 is more than or equal to 0 and less than or equal to 1. For example, the material GaN is selected to have different epitaxial layer materials according to the characteristics of the distributed feedback laser, so that the epitaxial layer has multiple selectable materials, which is not limited herein.

And S102, preparing a first electrode layer on one side of the upper contact layer, which is far away from the substrate.

Specifically, the epitaxial structure is cleaned, and as shown in fig. 3, a first electrode layer 109 is deposited on the upper contact layer 107 of the epitaxial wafer structure on the side away from the substrate 101, where the first electrode layer 109 includes any one or a combination of two or more of the materials Ni, Ti, Pd, Pt, Au, Al, Cr, TiN, ITO, AuGe, AuGeNi, and IGZO. Illustratively, Pt/Au can be selected and subjected to rapid thermal annealing in an air atmosphere, so that Pt/Au forms a better ohmic contact with the upper contact layer 108, and finally the first electrode layer 109 is prepared on the side of the upper contact layer 108 away from the substrate 101, so as to form an ohmic contact electrode of an epitaxial structure.

S103, etching the first electrode layer, the upper contact layer and part of the upper optical field limiting layer to form a ridge structure and a grating structure group; the grating structure groups are positioned on two sides of the ridge structure; the grating structure group comprises at least two sub-grating structures which are arranged along a first direction, and the grating periods L of the two sub-grating structures are different; the at least two sub-grating structures comprise at least one common lasing mode; the first direction is parallel to the plane of the substrate.

Specifically, the number of sub-grating structures of a high-order grating structure group to be prepared and the grating period L of each sub-grating structure are determined according to the lasing mode of the DFB laser. Taking a three-segment sub-grating structure with different etching periods L as an example, wherein as shown in the direction X in the figure, the grating period L1 of the first sub-grating structure 201 includes an etched region width a1 and an unetched region width b1, the grating period L2 of the second sub-grating structure 202 includes an etched region width a2 and an unetched region width b2, the grating period L3 of the third sub-grating structure 203 includes an etched region width a3 and an unetched region width b3, and the grating periods L of the sub-grating structures are different by controlling the sizes of the etched region widths a1, a2 and a 3. Specifically, the method of coating the laser epitaxial structure with glue, etc. is to use the conventional photolithography technique to photoetch the patterns of the ridge structure and the grating structure group, and then etch the first electrode layer 109, the upper contact layer 108 and part of the upper optical field limiting layer 107 to form the ridge structure 10 and the grating structure group 20, as shown in fig. 2 and 3, the grating structure group 20 is located at both sides of the ridge structure 10, and the grating period L obtained by etching satisfies the high-order grating equation of the laser wavelength λ.

And S104, preparing a second electrode layer on one side of the substrate far away from the epitaxial layer.

Illustratively, as shown in fig. 7, the prepared epitaxial structure is further thinned, ground and polished, and a second electrode layer 113 is prepared by depositing an ohmic contact metal on the side of the substrate 101 away from the epitaxial layer, so as to be opposite to the first electrode layer 109, and prepare an ohmic contact electrode pair.

And S105, carrying out scribing, cleavage, coating and splitting processes on the epitaxial structure to form the distributed feedback laser.

Specifically, according to the production requirement of the laser, reasonable scribing, cleavage, coating and splitting processes are further carried out on the epitaxial structure, and the required distributed feedback laser is prepared.

To sum up, the embodiment of the present invention provides a preparation method of distributed feedback laser, which obtains the form of multi-segment high-order grating combination by using conventional photolithography technique, so that at least two sub-grating structures include at least one common lasing mode. The multi-section high-order grating structure is adopted, so that the grating period is increased, and the preparation difficulty and the preparation cost of the device are effectively reduced; the etching selection ratio in the grating preparation process is obviously reduced, so that the grating preparation precision is greatly improved, and the accurate control of the output wavelength of the DFB laser is realized; furthermore, a multi-section high-order grating structure is adopted to replace a traditional low-order grating, so that the scattering and absorption loss of light at the grating interface are effectively reduced, the optical loss of the DFB laser is obviously reduced, and the performance of the device can be effectively improved.

On the basis of the foregoing embodiment, optionally, etching the first electrode layer, the upper contact layer, and a portion of the upper optical field confining layer to form a ridge structure and a grating structure group includes:

and etching the first electrode layer, the upper contact layer and part of the upper optical field limiting layer by adopting a dry etching process or a wet etching process to form a ridge structure and a grating structure group.

Specifically, referring to fig. 2, the first electrode layer 109, the upper contact layer 108, and a part of the upper optical field limiting layer 107 are etched by a dry etching process to form the ridge structure 10 and the grating structure group 20, and further, the etching smoothness of the sidewall surfaces of the ridge structure 10 and the grating structure group 20 can be effectively improved by a wet etching method, so that the problems of non-radiative recombination, electric leakage and the like caused by dry etching damage can be solved, the non-radiative recombination, the electric leakage and the like in the laser can be reduced, the threshold current of the device can be effectively reduced, and the performance and the reliability of the device can be improved.

Optionally, fig. 9 is a schematic flow chart of a method for manufacturing another distributed feedback laser according to an embodiment of the present invention, and as shown in fig. 9, the method for manufacturing a distributed feedback laser includes:

s201, preparing a laser epitaxial structure, wherein the laser epitaxial structure comprises a substrate and a plurality of epitaxial layers located on one side of the substrate, and the plurality of epitaxial layers comprise a middle epitaxial layer and an upper optical field limiting layer and an upper contact layer which are sequentially located on one side, far away from the substrate, of the middle epitaxial layer.

S202, preparing a first electrode layer on one side, far away from the substrate, of the upper contact layer.

S203, etching the first electrode layer, the upper contact layer and part of the upper optical field limiting layer to form a ridge structure and a grating structure group; the grating structure groups are positioned on two sides of the ridge structure; the grating structure group comprises at least two sub-grating structures which are arranged along a first direction, and the grating periods L of the two sub-grating structures are different; the at least two sub-grating structures comprise at least one common lasing mode; the first direction is parallel to the plane of the substrate.

And S204, depositing a dielectric layer on one side of the first electrode layer, which is far away from the substrate, wherein the dielectric layer covers the upper surfaces of the ridge structure and the grating structure group, the side wall of the ridge structure, the side wall of the grating structure group and part of the upper surface of the optical field limiting layer.

Specifically, as shown in fig. 5, a dielectric layer is deposited on a side of the first electrode layer away from the substrate, and the dielectric layer is made of an insulating dielectric film material, including SiO₂、SiN_x、SiON、Al₂O₃、AlON、SiAlON、TiO₂、Ta₂O₅、ZrO₂、HfO₂And the dielectric layer covers the upper surfaces of the ridge structure and the grating structure group, the side wall of the ridge structure, the side wall of the grating structure group and part of the upper surface of the optical field limiting layer.

And S205, removing the dielectric layers on the upper surfaces of the ridge structure and the grating structure group by adopting photoetching and etching technologies, and exposing the first electrode layer.

S206, preparing a connecting electrode on one side of the dielectric layer far away from the substrate, wherein the connecting electrode at least covers the exposed first electrode layer.

Specifically, the dielectric layer on the upper surface of the ridge structure and the grating structure group is removed by photolithography and etching techniques, and the first electrode layer is exposed, as shown in fig. 6, further, a connection electrode 112 is deposited on one side of the dielectric layer 111 away from the substrate, and the connection electrode 112 at least covers the exposed first electrode layer 109, as shown in fig. 7. Because the width of ridge structure 10 and grating structure group 20 is in the mu m magnitude and the ohmic contact metal of first electrode layer 109 is relatively thin, be unfavorable for actual production electric connection, through increasing the better ohmic contact metal of electric conductivity, make the perpendicular projection of connecting electrode 112 on the plane of substrate 101 place cover the perpendicular projection of ridge structure 10 and grating structure group 20 on the plane of substrate 101 place, guarantee that connecting electrode 112 and second electrode 113 form stable electric field, and the thickness that sets up connecting electrode 112 is greater than the thickness of first electrode layer 110, form the thickening electrode, increase connection stability on the one hand, on the other hand reduces the degree of difficulty that the external power supply was prepared to the laser.

And S207, preparing a second electrode layer on one side of the substrate far away from the epitaxial layer.

And S208, carrying out scribing, cleavage, film coating and splitting processes on the epitaxial structure to form the distributed feedback laser.

Alternatively, referring to fig. 1, the preparing the laser epitaxial structure includes:

a liner 101 is provided.

A buffer layer 102 is prepared on the substrate side.

A lower optical field confining layer 103 is provided on the side of the buffer layer 102 remote from the substrate 101.

The lower waveguiding layer 104 is prepared on the side of the lower optical field confining layer 103 remote from the substrate 101.

An active region 105 is prepared at a side of the lower waveguide layer 104 remote from the substrate 101.

An upper waveguide layer 106 is prepared on the side of the active region 105 remote from the substrate 101.

An upper optical field confining layer 107 is provided on the side of the upper waveguide layer 106 remote from the substrate 101.

An upper contact layer 108 is prepared on the side of the upper optical field confining layer 107 remote from the substrate 101.

Illustratively, a substrate material is provided, including any one or a combination of two or more of GaAs, InP, GaN, AlGaN, InGaN, AlN, sapphire, SiC, Si, and SOI, and the epitaxial structure is prepared in a direction away from the substrate 101 side. Specifically, a lower optical field confining layer 103 is formed on a side of the buffer layer 102 away from the substrate 101, a lower waveguide layer 104 is formed on a side of the lower optical field confining layer 103 away from the substrate 101, an active region 105 is formed on a side of the lower waveguide layer 104 away from the substrate 101, an upper waveguide layer 106 is formed on a side of the active region 105 away from the substrate 101, an upper optical field confining layer 107 is formed on a side of the upper waveguide layer 106 away from the substrate 101, and an upper contact layer 109 is formed on a side of the upper optical field confining layer 107 away from the substrate 101.

As a possible embodiment, a specific example is given, and an indium phosphide (InP) based semiconductor laser is produced based on the production method provided in the above example, as shown in fig. 1 to 7, and the specific production method is as follows:

providing an n-InP substrate 101 material, epitaxially growing a1 μm n-InP buffer layer, a1 μm n-InP lower optical field limiting layer, a 100nm AlGaAs lower waveguide layer, 8 pairs of AlGaInAs strained multiple quantum wells with a period thickness of 15nm, a 100nm InAlGaAs upper waveguide layer, a 1.5 μm p-InP upper optical field limiting layer and a 50nm p-InGaAs contact layer on the n-InP substrate 1 by adopting Metal Organic Chemical Vapor Deposition (MOCVD) equipment, and obtaining the structure shown in FIG. 1.

And cleaning the epitaxial wafer, performing rapid thermal annealing on the first electrode Ti/Au on the surface of the epitaxial wafer in an air atmosphere, and forming a first electrode layer 109 by ohmic contact with the upper contact layer p-InGaAs.

Performing glue coating, spin-coating a photoresist on the surface of the epitaxial wafer, photoetching patterns of a ridge structure and a grating structure group by adopting a conventional photoetching technology, and then performing Inductively Coupled Plasma (ICP) etching or wet etching by using a mixed solution of hydrogen peroxide sulfate and water to form the ridge structure and the grating structure group, as shown in fig. 2, 3 and 4.

Depositing a dielectric layer, and depositing a dielectric film of 200nm SiO on the surface of the epitaxial wafer at low temperature₂Passivating the device sidewall to form a dielectric layer, as shown in fig. 5; the photoresist over the set of ridge and grating structures is then stripped to expose the first electrode layer 109, as shown in fig. 6.

And adding a connecting electrode, spin-coating photoresist on the surface of the epitaxial wafer for photoetching, and then preparing a thickened electrode Cr/Au of the first electrode on the upper surface of the laser epitaxial wafer by combining a coating technology, a stripping technology and the like to form a connecting electrode with better ohmic contact, as shown in fig. 7.

The epitaxial wafer is thinned, ground and polished, and then a second electrode 112 is formed on the back side of the n-InP substrate 101, and the ohmic metal material may be Cr/Pt/Au, as shown in fig. 7.

And scribing, cleaving, coating and splitting to form the laser tube core.

The embodiment of the utility model provides a preparation method of distributed feedback semiconductor laser structure, the preparation obtains through adopting the form that conventional photoetching technique photoetching preparation obtained the combination of multistage high order grating, can realize the characteristic of first-order grating high selectivity, the realization is to indium (InP) base semiconductor laser's laser emission mode promptly laser wavelength lambda's locking, the device preparation degree of difficulty has effectively been reduced, grating preparation precision has been increased by a wide margin, the light loss of device has been reduced, finally showing and promoting the device performance and having reduced the device cost, satisfy high-demand practical application demand.

It should be noted that the foregoing is only a preferred embodiment of the present invention and the technical principles applied. Those skilled in the art will appreciate that the present invention is not limited to the specific embodiments described herein, but that the features of the various embodiments of the invention may be partially or fully coupled to each other or combined and may cooperate with each other and be technically driven in various ways. Numerous obvious variations, rearrangements, combinations, and substitutions will now occur to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail with reference to the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the scope of the present invention.

Claims

1. A distributed feedback laser, comprising:

2. The distributed feedback laser of claim 1, wherein the grating structure group comprises a first sub-grating structure, an ith sub-grating structure and an Nth sub-grating structure which are connected in sequence along the first direction; n is more than or equal to 2 and is an integer, 1< i is less than or equal to N and i is an integer;

the grating equation of the first sub-grating structure satisfies: m lambda 2n L₁，L₁The grating period of the first sub-grating structure is shown, n is the effective refractive index, lambda is the laser wavelength, m is more than or equal to 2, and m is a positive integer;

wherein m, g and k are all different and the minimum common factor is 1.

3. The distributed feedback laser of claim 1 wherein the set of grating structures comprises a plurality of common lasing modes, the plurality of common lasing modes comprising a reference lasing mode and a non-reference lasing mode;

4. The distributed feedback laser of claim 1 further comprising a connecting electrode;

5. The distributed feedback laser of claim 4 wherein said laser epitaxial structure further comprises a dielectric layer;

6. A distributed feedback laser as defined in claim 1 wherein said intermediate epitaxial layer comprises a buffer layer, a lower optical field confining layer, a lower waveguide layer, an active region and an upper waveguide layer disposed in that order on one side of said substrate.