Surface random slot semiconductor laser applied to refractive index sensing

Abstract

The application relates to a surface random slot semiconductor laser applied to refractive index sensing, belonging to the technical field of semiconductor lasers, and comprising a laser main body which is composed of an N-type waveguide layer, an active layer and a P-type waveguide layer from bottom to top, wherein a slot structure for realizing surface multi-diffraction-level light emission of the laser is arranged on the P-type waveguide layer, a single-layer graphene for isolating the surface of the laser and a measured substance is arranged on the upper surface of the P-type waveguide layer, and the measured substance is placed above the single-layer graphene. The structure parameters width, interval and number of the slot are taken as random values, and the width and interval of the slot are kept greater than 1 mu m, so that the light loss is different when the light passes through the measured substance film with different refractive indexes, and the size of the far-field intensity peak value is different. The peak value is extracted and fitted to obtain an intensity response curve, the curve can be used as a basis for judging the refractive index of the measured substance, and the cost of the laser is greatly reduced and the effect of improving the yield of the laser is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor laser, in particular to a surface random slot semiconductor laser applied to refractive index sensing. BACKGROUND

[0002] Semiconductor laser is the most popular laser till now with its unique advantages, and its annual production reaches billions of pieces. High-order surface grating semiconductor laser is widely applied to sensor, space laser communication, precision measurement, pumping solid laser and fiber laser, etc. due to its excellent spectral characteristics and coherence characteristics.

[0003] At present, the main grating structures etched on semiconductor laser are first-order DFB laser, second-order surface DFB laser and surface high-order grating laser, etc. DBR laser and DFB laser have low order and narrow slot, and need secondary epitaxy and high-resolution lithography and other complex, expensive and time-consuming processes. High-order grating can be made by contact lithography, but it has many diffraction orders and large loss.

[0004] Surface emitting laser can be made by vertical cavity surface emitting semiconductor laser (VCSEL) and horizontal cavity surface emitting semiconductor laser. There are two methods to realize surface emission by using horizontal cavity surface emitting laser, one is to make 45° mirror in the propagation direction of three-layer waveguide structure of the laser, and the other is to etch grating structure on the surface of the laser to realize surface emission of the laser by the action of grating diffraction.

[0005] The second-order surface grating DFB laser is currently used more, and this structure has only two orders, so only 0, ±1 diffraction orders exist, and only forward, backward, upward and downward light can be emitted, and light can be emitted along horizontal and vertical directions.

[0006] From the above, it is obvious that the prior art has inconvenience and defects in practical use, so it is necessary to improve. SUMMARY

[0007] In view of the defects in the prior art, the present application provides a surface random slot semiconductor laser applied to refractive index sensing, which realizes multi-peak light emission on the surface of the laser by using the characteristics of the surface slot semiconductor laser with many diffraction orders and large loss, and the light has different loss and far-field intensity when passing through different refractive index measured substances, and the refractive index of the measured substance is determined according to the change of the far-field peak value.

[0008] To achieve the above object, the present application provides the following technical scheme:

[0009] The application discloses a surface random slot semiconductor laser applied to refractive index sensing, which comprises a laser main body composed of an N-type waveguide layer, an active layer and a P-type waveguide layer from bottom to top, and a slot structure for realizing surface multi-diffraction order light emission of the laser is arranged on the P-type waveguide layer.

[0010] As an optimized scheme, the two end faces of the laser main body are provided with optical feedback structures for providing optical feedback.

[0011] As an optimized scheme, the optical feedback structures comprise high-reflection films or first-order grating structures.

[0012] As an optimized scheme, the upper surface of the P-type waveguide layer is provided with a single-layer graphene for isolating the surface of the laser and the measured substance.

[0013] As an optimized scheme, the single-layer graphene is placed above the measured substance.

[0014] As an optimized scheme, the P-type waveguide layer is formed into a ridge structure by etching, and the lateral light field is limited by the ridge structure.

[0015] As an optimized scheme, the N-type waveguide layer, the active layer and the P-type waveguide layer are combined into a three-layer flat waveguide structure, and the lateral light field is limited by the three-layer flat waveguide.

[0016] As an optimized scheme, the characteristic size of the slot structure is greater than 1 mu m.

[0017] As an optimized scheme, the characteristic size of the slot structure is random in width, spacing and number, and fixed in depth.

[0018] As an optimized scheme, the active layer is one of a multi-quantum well material, a quantum dot material or a bulk material.

[0019] As an optimized scheme, when the laser main body is applied to a refractive index sensor, the measured substance is one of a solid, a liquid and a gas.

[0020] Compared with the prior art, the application has the beneficial effects that:

[0021] This invention utilizes a high-order slotted structure to achieve surface emission of light. Due to its high order, it exhibits more diffraction orders and peak values ​​than low-order grating semiconductor lasers. This characteristic is used to fabricate a refractive index sensor. The peak intensities differ after light passes through materials with different refractive indices, and the peak intensities are fitted to an intensity response curve. The refractive index of the material is determined based on the peak intensities and the refractive index response curve. This invention leverages the high diffraction orders and high loss characteristics of surface slotted semiconductor lasers to achieve surface light emission, thus creating a structure for a surface slotted semiconductor laser applied to refractive index sensing.

[0022] Because its slot width is greater than 1μm, it can be operated using ordinary photolithography technology. This invention does not require complex, expensive and time-consuming process conditions such as secondary epitaxy and high-resolution photolithography, thus saving the manufacturing cost of the device.

[0023] This type of semiconductor laser has many diffraction orders, meaning that the light emitted from the laser surface has many far-field peaks. As the light passes through the test material with different refractive indices during emission, the light experiences varying losses, resulting in different far-field peak intensities. These different peaks can then be extracted and tracked to jointly determine the refractive index of the test material.

[0024] This type of laser can be used to detect the refractive index of gases, liquids, and solids;

[0025] It has fewer components, a compact structure, a small footprint, simple manufacturing process, and a low failure rate; it has a simple structure, a long service life, easy operation and control, and is easy to manufacture and install on a large scale, making it widely applicable. Attached Figure Description

[0026] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0027] Figure 1 This is a schematic diagram of the structure of the present invention;

[0028] Figure 2 This is the electric field model diagram for detecting NaCl concentration according to the present invention;

[0029] Figure 3 , Figure 4 This is a far-field intensity distribution diagram at 10 wavelengths from the surface of the substance to be tested for detecting the refractive index of NaCl solution according to the present invention.

[0030] Figure 5 This is a schematic diagram illustrating the extraction location of the peak refractive index of NaCl solution detected by this invention.

[0031] Figure 6 is the far-field peak extraction figure of the present application for detecting the refractive index of NaCl solution at -20 degrees;

[0032] Figure 7 is the far-field peak extraction figure of the present application for detecting the refractive index of NaCl solution at 4 degrees;

[0033] Figure 8 is the far-field peak extraction figure of the present application for detecting the refractive index of NaCl solution at 32 degrees;

[0034] Figure 9 is the optimal far-field intensity response distribution figure of the present application for application in different refractive index ranges;

[0035] Figure 10 is a structural schematic diagram of the slot structure of the present application.

[0036] In the figure: 1-N type waveguide layer; 2-active layer; 3-P type waveguide layer; 4-optical feedback structure; 5-slot structure; 6-single layer graphene; 7-substance to be measured. DETAILED DESCRIPTION

[0037] The embodiments of the technical solutions of the present application will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present application, and therefore only serve as examples, and cannot limit the protection scope of the present application.

[0038] As shown in Figures 1 to 10 , the surface random slot semiconductor laser applied to refractive index sensing includes a laser main body composed of N type waveguide layer, active layer and P type waveguide layer from bottom to top, and a slot structure 5 provided on the P type waveguide layer to realize multi-diffraction order light out of the laser surface.

[0039] The slot structure 5 includes a plurality of groove bodies opened on the P type waveguide layer in parallel along the transverse direction.

[0040] The structure parameters of the slot structure 5, such as width, pitch and quantity, are all highly random.

[0041] Some slot structures 5 with random values of structure parameters are arranged on the surface, and the purpose is to make the laser diffraction order more, the measurable range of the refractive index of the measured substance 7 increase, and the light will be lost when passing through the measured substance 7 when out of the exit. The loss is different when passing through the measured substance 7 with different refractive indexes, so the peak value of the far field is different, and then different peak values can be extracted and tracked to jointly judge the refractive index of the measured substance 7. The present application can realize the function of refractive index sensing without complex and time-consuming processes such as secondary epitaxy and high-resolution lithography.

[0042] The two end faces of the laser main body are provided with an optical feedback structure 4 to provide optical feedback.

[0043] The light feedback structure 4 comprises uniformly coating a high reflection film or etching a first-order grating structure.

[0044] The upper surface of the P-type waveguide layer is provided with a single-layer graphene 6 for isolating the laser surface and the measured substance 7.

[0045] The measured substance 7 is placed above the single-layer graphene 6.

[0046] The P-type waveguide layer is formed into a ridge structure by etching, and the lateral light field is limited by the ridge structure.

[0047] The N-type waveguide layer, the active layer and the P-type waveguide layer are combined into a three-layer slab waveguide structure, and the transverse light field is limited by the three-layer slab waveguide.

[0048] The feature size of the slot structure 5 is greater than 1 mu m.

[0049] The feature size of the slot structure is random in width, spacing and number, and fixed in depth.

[0050] The active layer is one of a multi-quantum well material, a quantum dot material or a bulk material.

[0051] When the laser body is applied to a refractive index sensor, the measured substance 7 is one of a solid, a liquid and a gas.

[0052] The transverse light field is limited by the three-layer slab waveguide, the lateral light field is limited by the ridge waveguide, the longitudinal light field is limited by the cleaved surface of the front and rear cavities and the light feedback, the high-order surface slot can provide light feedback and surface light emission, the active layer 2 provides gain, and the order from bottom to top is the N-type waveguide, the active layer and the P-type waveguide, the P-type waveguide has a ridge structure, the ridge structure is used to provide a lateral limiting effect, and the surface slot structure 5 is distributed on the ridge. A single-layer graphene 6 is placed on the surface of the semiconductor laser to isolate the laser surface and the measured substance 7, and the measured substance 7 film is placed above the graphene.

[0053] The active layer 2 of the high-order slot semiconductor laser applied to the refractive index sensor can be selected from a multi-quantum well, a quantum dot or a bulk material.

[0054] Lambda = m * lambda B / (2*n neff A grating with a grating period of n times of half wavelength is called an n-order grating, and the first-order grating has the characteristics or advantages that the light field components are only forward waves and backward waves, and there is no theoretical loss. The diffraction formula corresponding to the first-order grating is Theta is the incidence angle of the diffraction grating, which is theta = 90 degrees in the waveguide structure, and at this time That is, the light field components are only forward waves and backward waves, and there is no theoretical loss; the formula corresponding to the second-order surface grating is At this time, the light field components have forward wave, backward wave, upward wave and downward wave, and the characteristics are that only 0, ±1 diffraction orders exist, so the vertical light emission on the surface of the laser and the single-mode light emission in the horizontal direction can be realized by using a second-order grating; the formula corresponding to a high-order grating is The characteristics are that the order is much larger than that of a first-order grating and a second-order grating, the size is much larger than that of the first-order grating and the second-order grating, the light field diffraction order is more, the corresponding peak value is more, and the change of the far-field peak value intensity can be used to detect the refractive index of the measured substance.

[0055] The surface random slot semiconductor laser applied to refractive index sensing provided by the application is a slot structure with random width, spacing and number of structure parameters on the surface of the laser. Compared with the common high-order surface grating, the random slot has a larger measurable refractive index range, more far-field peaks and larger intensity change.

[0056] The low-order grating needs high-precision electron beam exposure, secondary epitaxy and other complex, high-difficulty and low-efficiency processes. Since the random slot structure is adopted in the application, the characteristic size of the slot on the surface of the semiconductor laser is greater than 1 micron, so the complex, expensive and time-consuming process conditions such as secondary epitaxy and high-resolution lithography are not needed.

[0057] The surface random slot semiconductor laser applied to refractive index sensing provided by the application has a single-layer graphene on the surface, which is used to isolate the surface of the laser and the measured substance.

[0058] The surface random slot semiconductor laser applied to refractive index sensing provided by the application has a measured substance with a uniform thickness above the graphene, and the thickness of the substance can be any thickness.

[0059] In order to better illustrate the application, the refractive index of a NaCl solution is taken as an example for simulating detection by using the sensor, and the refractive index is 1.342-1.402.

[0060] In the application example, an InP epitaxial structure is adopted, and the structure of the semiconductor laser is equivalent to a three-layer flat waveguide structure for more convenient simulation calculation, and the structure can realize lateral light field limitation. Taking an InP epitaxial structure with a wavelength of 1550 nm as an example, the thickness of the lower waveguide layer is 3.20 microns, the refractive index is 3.1681, the thickness of the active layer is 0.41 microns, the refractive index is 3.2827, and the thickness of the upper cladding layer is 1.85 microns, and the refractive index is 3.1529.

[0061] The semiconductor laser is a ridge structure and can realize lateral limitation, and a ridge structure is etched on the upper cladding layer, and the etching depth of the ridge is 1.65 microns, and the unetched depth, i.e., the thickness from the active layer, is 0.2 microns.

[0062] The cavity length of the semiconductor laser can be set according to specific conditions, and is set as 150 mu m long here.

[0063] The far field of the semiconductor laser is taken at 10 wavelengths of the measured substance film.

[0064] The structure parameters of the grating structure on the ridge are random values, the higher the randomness is, the more the detected peak values are, and the greater the intensity change is.

[0065] An equivalent two-dimensional model of the model is simulated by using a finite element method (COMSOL software), an electric field diagram simulated is shown as 2, far field distribution diagrams of different refractive index NaCl solutions are finally simulated, and a schematic diagram of extraction positions of refractive index peaks is shown as Figure 3 , Figure 4 , far field peak extraction diagrams of different positions are obtained, and an optimal intensity response curve of the detection refractive index is finally drawn as Figure 5 , Figures 6-8 , in the case that the peak value of the far field of a certain concentration of NaCl solution is known, the corresponding refractive index can be judged. Figure 9

[0066] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should be covered in the scope of the claims and the specification of the present application.​

Claims

1. A surface random slot semiconductor laser applied to refractive index sensing, characterized in that: The laser body is composed of an N-type waveguide layer (1), an active layer (2), and a P-type waveguide layer (3) from bottom to top, and satisfies the following structural and functional characteristics: A slot structure (5) for realizing multi-diffraction order light emission on the surface of the laser is arranged on the P-type waveguide layer (3), the slot structure (5) is a plurality of groove bodies arranged side by side in the transverse direction, and the characteristic dimensions width, pitch, and number are random values, the characteristic dimension is greater than 1 μm, and the general photolithography technology is adapted, without secondary epitaxy and high-resolution photolithography, and the depth is constant. The upper surface of the P-type waveguide layer (3) is completely covered by a single-layer graphene (6), and the single-layer graphene (6) is used to isolate the surface of the laser and the measured substance (7), so as to avoid device pollution or performance degradation caused by direct contact of the measured substance (7) with the laser, and does not affect the coupling of the optical field and the measured substance. The N-type waveguide layer (1), the active layer (2), and the P-type waveguide layer (3) are combined into a three-layer flat waveguide structure, and cooperate with the ridge structure formed by etching the P-type waveguide layer (3) to realize transverse and lateral light field restriction respectively, and ensure the stability of multi-diffraction order light emission. When the laser body is applied to refractive index sensing, the measured substance (7) is placed above the single-layer graphene (6), the multi-diffraction order light field of the slot structure (5) acts on the measured substance (7), different refractive indexes of the measured substance cause differential changes in the far-field intensity peak value, and the peak intensity response curve is used as a basis for judging the refractive index of the measured substance.

2. The surface random slot semiconductor laser for refractive index sensing according to claim 1, wherein: Both end surfaces of the laser body are provided with an optical feedback structure (4) for providing optical feedback.

3. The surface random slot semiconductor laser for refractive index sensing according to claim 2, wherein: The optical feedback structure (4) includes uniformly coating a high-reflection film or etching a first-order grating structure.

4. The surface random slot semiconductor laser for refractive index sensing according to claim 1, wherein: The single-layer graphene (6) is placed above the measured substance (7).

5. The surface random slot semiconductor laser for refractive index sensing according to claim 1, wherein: The P-type waveguide layer forms a ridge structure by etching, and realizes lateral light field restriction by using the ridge structure.

6. The surface random slot semiconductor laser for refractive index sensing according to claim 1, wherein: The N-type waveguide layer, the active layer (2), and the P-type waveguide layer are combined into a three-layer flat waveguide structure, and realize transverse light field restriction by using the three-layer flat waveguide.

7. The surface random slot semiconductor laser for refractive index sensing according to claim 1, wherein: The active layer (2) is one of a multi-quantum well material, a quantum dot material, or a bulk material.

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