CN111211486A

CN111211486A - Semiconductor laser

Info

Publication number: CN111211486A
Application number: CN202010148937.9A
Authority: CN
Inventors: 杨国文; 唐松
Original assignee: Dugen Laser Technology Suzhou Co Ltd
Current assignee: Dugen Laser Technology Suzhou Co Ltd
Priority date: 2020-03-05
Filing date: 2020-03-05
Publication date: 2020-05-29
Anticipated expiration: 2040-03-05
Also published as: CN111211486B

Abstract

The embodiment of the present application provides a semiconductor laser, semiconductor laser includes: a waveguide array comprised of a plurality of sub-waveguides; an optical coupler disposed at one end of the waveguide array; an anti-reflection film disposed at a light output end of the optical coupler; and the high-reflection film is arranged at the other end of the waveguide array. The application realizes the improvement of the optical output power of the semiconductor laser.

Description

Semiconductor laser

Technical Field

The application relates to the field of semiconductors, in particular to a semiconductor laser.

Background

Semiconductor lasers, which use semiconductor materials as working substances, have the advantages of being small and exquisite, efficient, long in service life, easy to integrate and the like, and are widely applied to the fields of imaging, communication, machining and the like. Due to the limitation of a physical structure, a traditional semiconductor laser cannot obtain high optical output power basically through a single tube, and can only realize high power output through a space beam combination method of laser bars such as direct optical fiber coupling, wavelength multiplexing, polarization multiplexing and the like.

However, direct fiber coupling is generally lossy for single-mode semiconductor lasers. In addition, due to the wavelength singleness, the spatial light combination cannot be realized by the wavelength multiplexing method, and the polarization states of the output light of the lasers on the same bar are generally the same, so the improvement of the output light power by adopting the polarization combination is very limited, and extra light loss is also brought.

Disclosure of Invention

An object of the embodiments of the present application is to provide a semiconductor laser, so as to improve the optical output power of the semiconductor laser.

A first aspect of an embodiment of the present application provides a semiconductor laser, including: a waveguide array comprised of a plurality of sub-waveguides; an optical coupler disposed at one end of the waveguide array; an anti-reflection film disposed at a light output end of the optical coupler; and the high-reflection film is arranged at the other end of the waveguide array.

In one embodiment, the waveguide array comprises: the first waveguide array is a ridge waveguide array, and one end of the first waveguide array is connected with the optical input end of the optical coupler; and the second waveguide array is a ridge waveguide array, and is arranged at the other end of the first waveguide array.

In one embodiment, the waveguide array and the optical coupler are both formed on a semiconductor epitaxial layer; the semiconductor epitaxial layer sequentially comprises from bottom to top: the quantum well structure comprises a substrate, a lower limiting layer, a quantum well, an upper limiting layer and an ohmic contact layer.

In an embodiment, the thickness of the ohmic contact layer is zero in a region where the first waveguide array and the optical coupler are formed on the semiconductor epitaxial layer.

In one embodiment, the ridge height of the ridge waveguide array is less than or equal to the total thickness of the ohmic contact layer and the upper limiting layer.

In an embodiment, a groove is disposed at a connection of the first waveguide array and the second waveguide array.

In one embodiment, the trench penetrates through the ohmic contact layer in the semiconductor epitaxial layer and extends to the upper limiting layer.

In one embodiment, the first waveguide array is comprised of straight waveguides; the second waveguide array is composed of one or more of straight waveguides, bent waveguides and tapered waveguides.

In one embodiment, the width of the optical coupler is greater than the total width of the waveguide array.

In one embodiment, the second waveguide array has an equal waveguide spacing and/or an equal single waveguide width with respect to the first waveguide array at an end thereof connected to the first waveguide array.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are required to be used in the embodiments of the present application will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and that those skilled in the art can also obtain other related drawings based on the drawings without inventive efforts.

Fig. 1 is a schematic structural diagram of a semiconductor laser according to an embodiment of the present application;

fig. 2 is a schematic structural diagram of a semiconductor laser according to an embodiment of the present application;

FIG. 3a is a schematic structural diagram of a tapered waveguide according to an embodiment of the present application;

FIG. 3b is a schematic structural diagram of a tapered waveguide according to an embodiment of the present application;

FIG. 3c is a schematic structural diagram of a tapered waveguide according to an embodiment of the present application;

fig. 4 is a schematic structural diagram of a semiconductor laser according to an embodiment of the present application;

fig. 5 is a schematic structural diagram of a semiconductor epitaxial layer according to an embodiment of the present application.

Reference numerals:

100-semiconductor laser, 110-waveguide array, 111-first waveguide array, 112-second waveguide array, 1121-first sub-waveguide, 1122-second sub-waveguide, 1123-third sub-waveguide, 113-groove, 120-optical coupler, 130-anti-reflection film, 140-high-reflection film, 150-semiconductor epitaxial layer, 151-substrate, 152-lower limiting layer, 153-quantum well, 154-upper limiting layer, 155-ohmic contact layer and 2-optical field convergence point.

Detailed Description

The technical solutions in the embodiments of the present application will be described below with reference to the drawings in the embodiments of the present application.

In the description of the present application, the terms "first," "second," and the like are used for distinguishing between descriptions and do not denote an order of magnitude, nor are they to be construed as indicating or implying relative importance.

In the description of the present application, the terms "horizontal", "vertical", "overhang" and the like do not imply that the components are absolutely required to be horizontal or overhang, but may be slightly inclined. For example, "horizontal" merely means that the direction is more horizontal than "vertical" and does not mean that the structure must be perfectly horizontal, but may be slightly inclined.

In the description of the present application, the terms "upper", "lower", "left", "right", "front", "back", "inner", "outer", and the like refer to orientations or positional relationships that are based on orientations or positional relationships shown in the drawings, or orientations or positional relationships that are conventionally found in the products of the application, and are used for convenience in describing the present application, and do not indicate or imply that the referenced devices or elements must have a particular orientation, be constructed in a particular orientation, and be operated, and thus, should not be construed as limiting the present application.

In the description of the present application, unless expressly stated or limited otherwise, the terms "disposed," "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; the two components can be directly connected or indirectly connected through an intermediate medium, and the two components can be communicated with each other. The specific meaning of the above terms in the present application can be understood in a specific case by those of ordinary skill in the art.

Please refer to fig. 1, which is a schematic structural diagram of a semiconductor laser 100 according to an embodiment of the present application. The semiconductor laser 100 includes: a waveguide array 110, an optical coupler 120, an anti-reflection film 130 and a high-reflection film 140, wherein the waveguide array 110 is composed of a plurality of sub-waveguides, the optical coupler 120 is disposed at one end of the waveguide array 110, the width of the optical coupler 120 is greater than the total width of the waveguide array 110, and in one embodiment, the width W of the optical coupler 120 is greater than the total width of the waveguide array 110₁Can range from 6 μm to 200 μm, and in one embodiment, the width W of the optical coupler 120₁May range from 6 μm to 50 μm.

The anti-reflection film 130 is disposed at the light output end of the optical coupler 120, and in one embodiment, the reflectivity of the anti-reflection film 130 is less than 5%, and in one embodiment, the reflectivity of the anti-reflection film 130 is less than 2.5%. The high reflective film 140 is disposed at the other end of the waveguide array 110, and in one embodiment, the reflectivity of the high reflective film 140 is not lower than 80%, and in one embodiment, the reflectivity of the high reflective film 140 is higher than 90%.

In one embodiment, the waveguide array 110 includes: the first waveguide array 111 and the second waveguide array 112, wherein the first waveguide array 111 and the second waveguide array 112 are both ridge waveguide arrays, and in an embodiment, ridge waveguides may be implemented by dry etching a P-type doped material, or by wet etching a P-type doped material.

One end of the first waveguide array 111 is connected to the optical input terminal of the optical coupler 120, and the second waveguide array 112 is disposed at the other end of the first waveguide array 111. In one embodiment, the length L of the first waveguide array 111₂Less than 500 μm, and in one embodiment, the length L of the first waveguide array 111₂Less than 50 μm.

In one embodiment, the length of the first waveguide array 111 can be zero, and the second waveguide array 112 is disposed at the light input end of the optical coupler 120.

In one embodiment, the first waveguide array 111 and the second waveguide array 112 are both composed of straight ridge waveguides, the waveguides of the first waveguide array 111 and the second waveguide array 112 have the same interval, the width of the single waveguide is the same, and the ridge is formedStrip width W ₂2 μm to 10 μm, and in one embodiment, the ridge width W₂Is 3 μm to 6 μm.

In one embodiment, the second waveguide array 112 has current injection to provide gain for the semiconductor laser 100, and the first waveguide array 111 and the optical coupler 120 have no current injection to provide absorption regions.

In one embodiment, the optical coupler 120 may be an MMI (multi-mode Interference) coupler, which uses the Self-Imaging Effect (SIE) principle to realize the functions of splitting and combining optical power. For the MMI coupler, after an optical field input into a ridge waveguide array of the MMI coupler propagates a certain transmission distance S through the MMI coupler, multi-mode interference causes energy to be concentrated, so that beam combination of multi-waveguide beams can be completed, and the energy is concentrated and coupled out together.

According to the above principle, if the length L of the multimode waveguide of the MMI coupler is set₁And the transmission distance S is equal, the light fields transmitted by the MMI coupler are combined into a fundamental transverse mode output, and the fundamental transverse mode output can be coupled by using a single optical fiber. If let L₁Slightly less than S, but L₁And the optical field of the emergent end face can realize the convergence of the optical field energy at a distance from the emergent end face due to the continuous multi-mode superposition interference without reducing the optical fiber coupling efficiency.

Therefore, the MMI coupler is selected to have a suitable length L₁The optical fiber coupling device can combine the optical fields, reduce the optical field energy density of the light-emitting end face and simultaneously not reduce the optical fiber coupling efficiency, thereby greatly improving the light-emitting power of the device. According to the optical transmission characteristics in the multimode waveguide, the optical transmission characteristics can be obtained by a guided mode transmission analysis method:

whereinL is the distance period of the self-image, λ is the wavelength, W_eIs the equivalent width of the fundamental mode in a multimode waveguide, n_rFor equivalent refractive index, the multimode waveguide has a width W, W for high index contrast waveguides_eW is approximately distributed; for low index differential waveguides, W_eSlightly larger than W.

For a single waveguide structure with a symmetrical design, i.e. the central axis of the waveguide array 110 coincides with the central axis of the optical coupler 120, the distance from the optical input port of the optical coupler 120 to the first optical field convergence point 2 is L/4; at this time, if the ridge wave derivative of the symmetrically designed waveguide array 110 is N, the distance from the optical input port of the optical coupler 120 to the first optical field convergence point 2 is L/4N. Therefore, if the distance from the optical input port of the optical coupler 120 to the first optical field convergence point 2 is defined as L', the length L of the optical coupler 120 is defined₁Between 0.6 xl 'and L', in one embodiment, the length L of the optical coupler 120₁Between 0.7 × L 'and 0.95 × L', the effect of the multimode interference of the optical coupler 120 is already nearly completed, the optical output port of the optical coupler 120 has optical field distribution wider than the fundamental transverse mode, so that the optical field energy density of the optical output end face is reduced, the emitted optical field can converge the optical field energy at a distance from the optical output end face due to continuous multimode superposition interference, the optical fiber coupling efficiency is not reduced, and the optical output power of the semiconductor laser 100 is greatly improved.

Fig. 2 is a schematic structural diagram of a semiconductor laser 100 according to an embodiment of the present disclosure. The semiconductor laser 100 includes: waveguide array 110, optical coupler 120, anti-reflective film 130, and high-reflective film 140. The waveguide array 110 includes: a first waveguide array 111 and a second waveguide array 112, wherein the first waveguide array 111 is composed of straight waveguides and the second waveguide array 112 is composed of straight waveguides and curved waveguides.

The high-reflection film 140 is disposed at one end of the second waveguide array 112, the other end of the second waveguide array 112 is connected to one end of the first waveguide array 111, and the one end of the second waveguide array 112 connected to the first waveguide array 111 and the first waveguide array 111 have equal waveguide intervals and/or equal single waveguide widths. The other end of the first waveguide array 111 is connected to the optical input terminal of the optical coupler 120, and the anti-reflection film 130 is disposed at the optical output terminal of the optical coupler 120.

In one embodiment, the second waveguide array 112 includes: the first sub-waveguide 1121 and the third sub-waveguide 1123 are both S-shaped curved waveguides, the second sub-waveguide 1122 is a straight waveguide, the waveguide width of the second sub-waveguide 1122 is equal to the waveguide width of the straight waveguide constituting the first waveguide array 111, and the first sub-waveguide 1121 and the third sub-waveguide 1123 are symmetrically arranged with respect to the second sub-waveguide 1122, so that the waveguide interval at the end of the second waveguide array 112 coated with the high-reflection film 140 is larger than the waveguide interval at the end connected with the first waveguide array 111, and the waveguides are distributed, thereby facilitating the preparation and heat dissipation of the waveguides. Meanwhile, in order to reduce loss by bending the waveguide as much as possible, the bending angle of the first sub-waveguide 1121 and the third sub-waveguide 1123 is less than or equal to 15 ° at any place of the S-shaped segment. In one embodiment, the S-shaped curved waveguide includes, but is not limited to, a double circular arc type, a rising inverse sine type, and a cosine function type.

In an embodiment, the sub-waveguides forming the second waveguide array 112 may be waveguide structures that are expanded outward, that is, the sub-waveguides of the second waveguide array 112 are plated with a high reflective film 140, and the waveguide width at one end is greater than the waveguide width at the other end, so that the area of the second waveguide array 112 is increased, and a larger injection current can be obtained, thereby increasing the output power.

In one embodiment, the sub-waveguides of the second waveguide array 112 include, but are not limited to, tapered waveguides and their composite structures, and the boundary line of a single tapered waveguide may be a straight line (as shown in fig. 3 a), a curved line (as shown in fig. 3 b), or a combination of straight lines with different tilt angles (as shown in fig. 3 c). In one embodiment, the individual waveguides forming the second waveguide array 112 may be partially tapered waveguides or may be all tapered waveguides. In one embodiment, the end width of the single tapered waveguide near the end of the high-reflection film 140 may range from 3 μm to 100 μm, and in one embodiment, the end width of the single tapered waveguide near the end of the high-reflection film 140 may range from 6 μm to 15 μm.

In one embodiment, the first waveguide array 111 is composed of straight waveguides, and the second waveguide array 112 is composed of one or more of straight waveguides, curved waveguides, and tapered waveguides.

Fig. 4 is a schematic structural diagram of a semiconductor laser 100 according to an embodiment of the present disclosure. The connecting position of the first waveguide array 111 and the second waveguide array 112 is provided with a groove 113, and the groove 113 is used for increasing the electrical isolation effect and further reducing the current diffusion. In one embodiment, the width of the trench 113 ranges from 0.5 μm to 50 μm, and in one embodiment, the width of the trench 113 ranges from 2 μm to 20 μm.

In one embodiment, the length of the first waveguide array 111 is zero, i.e., the first waveguide array 111 is not present in the waveguide array 110, and the trench 113 is disposed between the second waveguide array 112 and the light input end of the optical coupler 120.

In one embodiment, the material system of the semiconductor laser 100 includes, but is not limited to, InP, GaAs, GaN, GaSb, etc.

Fig. 5 is a schematic structural diagram of a semiconductor epitaxial layer 150 according to an embodiment of the present disclosure. The waveguide array 110 and the optical coupler 120 are both formed on a semiconductor epitaxial layer 150, and the semiconductor epitaxial layer 150 sequentially includes, from bottom to top: a substrate 151, a lower confinement layer 152, a quantum well 153, an upper confinement layer 154, and an ohmic contact layer 155. The waveguide array 110 is a ridge waveguide array having a ridge height less than or equal to the total thickness of the ohmic contact layer 155 and the upper confinement layer 154.

In one embodiment, the second waveguide array 112 has current injection to provide gain for the semiconductor laser 100, the first waveguide array 111 and the optical coupler 120 have no current injection, and the semiconductor epitaxial layer 150 includes, in order from bottom to top, only: substrate 151, lower confinement layer 152, quantum well 153, and upper confinement layer 154. In one embodiment, the removal of the highly P-doped ohmic contact layer 155 in the region can be achieved by dry etching or wet etching the uppermost layer material of the semiconductor epitaxial layer 150 to an etching depth of 50nm to 2 μm, in one embodiment, to an etching depth of 100nm to 600 nm.

In an embodiment, the second waveguide array 112, the first waveguide array 111, and the optical coupler 120 are all injected with current, and in an area where the first waveguide array 111 and the optical coupler 120 are formed on the semiconductor epitaxial layer 150, the semiconductor epitaxial layer 150 sequentially includes, from bottom to top: the substrate 151, the lower limiting layer 152, the quantum well 153, the upper limiting layer 154 and the ohmic contact layer 155, and the groove 113 is provided at the junction of the first waveguide array 111 and the second waveguide array 112, and the ohmic contact layer 155 with high conductivity at the groove 113 is etched, so that the injection current in the region of the second waveguide array 112 does not enter the regions of the first waveguide array 111 and the optical coupler 120, so as to increase the electrical isolation effect between the first waveguide array 111 and the second waveguide array 112. The injected current at the first waveguide array 111 and the optical coupler 120 is near the transparent current so that the region has lower optical loss or gain.

In one embodiment, when current is injected in the region of the optical coupler 120, the etching depth of the optical coupler 120 does not exceed the total thickness of the ohmic contact layer 155 and the upper confinement layer 154, i.e., the optical coupler 120 does not etch into the quantum well 153.

In one embodiment, when there is no current injection in the region of the optocoupler 120, the optocoupler 120 may etch into the upper confinement layer 154, the quantum well 153, or the lower confinement layer 152.

In one embodiment, the trench 113 extends through the ohmic contact layer 155 in the semiconductor epitaxial layer 150 and to the upper confinement layer 154. In one embodiment, the trench 113 is etched from the ohmic contact layer 155 down to a depth greater than 200nm to a depth above the quantum well 153, the width of the trench 113 along the waveguide array 110 is 0.5 μm to 50 μm, and in one embodiment, the width of the trench 113 along the waveguide array 110 is 2 μm to 20 μm.

The above are merely preferred embodiments of the present application and are not intended to limit the present application. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A semiconductor laser, comprising:

a waveguide array comprised of a plurality of sub-waveguides;

an optical coupler disposed at one end of the waveguide array;

an anti-reflection film disposed at a light output end of the optical coupler;

and the high-reflection film is arranged at the other end of the waveguide array.

2. A semiconductor laser as claimed in claim 1 wherein the waveguide array comprises:

the first waveguide array is a ridge waveguide array, and one end of the first waveguide array is connected with the optical input end of the optical coupler;

and the second waveguide array is a ridge waveguide array, and is arranged at the other end of the first waveguide array.

3. The semiconductor laser of claim 2, wherein the waveguide array and the optical coupler are each formed on a semiconductor epitaxial layer; the semiconductor epitaxial layer sequentially comprises from bottom to top: the quantum well structure comprises a substrate, a lower limiting layer, a quantum well, an upper limiting layer and an ohmic contact layer.

4. A semiconductor laser as claimed in claim 3 wherein the thickness of the ohmic contact layer is zero in the region where the first waveguide array and the optical coupler are formed on the semiconductor epitaxial layer.

5. A semiconductor laser as claimed in claim 3 wherein the ridge stripe height of the array of ridge waveguides is less than or equal to the total thickness of the ohmic contact layer and the upper confinement layer.

6. A semiconductor laser as claimed in claim 3 wherein the junction of the first waveguide array and the second waveguide array is provided with a trench.

7. A semiconductor laser as claimed in claim 6 wherein the trench passes through the ohmic contact layer in the semiconductor epitaxial layer and extends to the upper confinement layer.

8. A semiconductor laser as claimed in claim 2 wherein the first waveguide array is comprised of straight waveguides; the second waveguide array is composed of one or more of straight waveguides, bent waveguides and tapered waveguides.

9. A semiconductor laser as claimed in claim 1 wherein the width of the optical coupler is greater than the overall width of the waveguide array.

10. A semiconductor laser as claimed in claim 2 wherein the end of the second waveguide array connecting the first waveguide array has equal waveguide spacing and/or equal single waveguide width to the first waveguide array.