Preparation method and structure of photonic integrated device

Abstract

The invention discloses a preparation method and a structure of a photonic integrated device, and the method comprises the steps: sequentially dividing a substrate into a front modulator region, a rear modulator region, a front grating region, a gain region and a rear grating region, and growing a first active layer after manufacturing a selected region epitaxial mask pattern in the gain region, the method comprises the following steps of: growing a first active layer in a front modulator region after mask etching operation, growing a second active layer in a front modulator region after mask etching operation, growing a third active layer in a grating region after mask etching operation, finally performing grating manufacturing, and completing manufacturing of a cladding layer, an electric contact layer, an inverted table shallow ridge waveguide structure, an electric isolation trench and an electrode. According to the method, integration of multiple materials is achieved through one-time selective area epitaxial growth and one-time butt joint growth, the material growth frequency is reduced, and the manufacturing cost is saved; the gain region and the rear modulator region realize forbidden band width offset through selective region epitaxial material growth, and multi-wavelength tuning and efficient modulation are realized through fluorescence wavelength difference design of each region, so that a solution can be provided for integration of a wide-wavelength tunable laser and a double-electro-absorption modulator.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor optoelectronic integrated devices, and in particular to a preparation method and structure of a photonic integrated device. Background Art

[0002] With the explosion of the internet and the rapid development of artificial intelligence, the demand for high-performance photonic integrated devices in the optical communications field is growing. In particular, the integration of wide-wavelength tunable lasers and electro-absorption modulators is crucial. These integrated devices can improve the flexibility and efficiency of signal transmission in high-speed optical communication systems and meet the growing demand for high-capacity data transmission. At the same time, the development trend of photonic integration technology is to pursue smaller, higher-performance, and lower-power devices, which has driven the exploration of innovative fabrication methods to achieve a high degree of integration of complex photonic functions.

[0003] Traditionally, photonic integrated devices have been fabricated using multiple docking growth techniques. While this technique can achieve a certain degree of device integration, it has significant drawbacks. On the one hand, the multiple growth processes are complex, docking accuracy is difficult to guarantee, and defects in the docking interface are easily introduced, thus affecting the optoelectronic performance and reliability of the device. On the other hand, the frequent material growth and etching steps lead to high manufacturing costs and low production efficiency, making it difficult to meet the needs of large-scale industrialization. Furthermore, existing technologies have shortcomings in achieving precise material design and performance optimization for different functional regions, such as the gain region, modulator region, and grating region, which limits the improvement of the overall device performance.

[0004] Therefore, it is necessary to provide a photonic integrated device and its preparation method, which can reduce the number of active layer growth times, reduce material growth costs and process complexity, thereby improving production efficiency, and provide an efficient and economical solution for the integration of wide-wavelength tunable lasers and single-ended dual electro-absorption modulators, so as to promote the development of photonic integrated devices towards high performance and low cost. Summary of the Invention

[0005] In view of this, the present invention provides a method and structure for preparing a photonic integrated device, which can solve the technical problems existing in the prior art, such as the difficulty in integrating a wide wavelength tunable range with an electro-absorption modulator, low device reliability, and high manufacturing cost.

[0006] In order to achieve the above technical objectives, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a method for preparing a photonic integrated device, comprising: Performing surface layout on the substrate, dividing the substrate surface into a front modulator region, a rear modulator region, a front grating region, a gain region and a rear grating region in sequence along the length direction; A selective epitaxial growth mask pattern is formed on the surface of the gain region of the substrate, wherein the selective epitaxial growth mask pattern is two parallel strips having the same length as the gain region and a preset spacing and width; Growing a first active layer on a portion of the substrate surface excluding a selective epitaxial growth mask pattern, then etching away the selective epitaxial growth mask pattern, forming a first butt-joint mask pattern in an area excluding a front modulator area, and etching away the first active layer excluding the first butt-joint mask pattern; Growing a second active layer on the surface of the front modulator region, and then etching away the first butting mask pattern; A second butting mask pattern is formed in the area outside the front grating area and the rear grating area, and the first active layer in the front grating area and the rear grating area is removed by etching; A third active layer is grown in the front grating region and the rear grating region using a butt-joint growth technique, and then the second butt-joint mask pattern is removed to form sampled gratings in the front grating region and the rear grating region; A cladding layer and an electrical contact layer are sequentially grown on the surface of the entire device, and an inverted shallow ridge waveguide structure is fabricated on the cladding layer and the electrical contact layer; Etching electrical isolation trenches on the electrical contact layer to achieve electrical isolation between the regions; P-side electrodes are fabricated on the electrical contact layer of each region, and N-side electrodes are fabricated on the entire surface of the substrate bottom after the substrate is thinned to complete the fabrication of the integrated device.

[0007] Furthermore, the fluorescence wavelength of the third active layer in the front grating region and the back grating region is 150-200 nm shorter than the fluorescence wavelength of the first active layer in the gain region.

[0008] Furthermore, the fluorescence wavelength of the second active layer in the front modulator region is 30-60 nm shorter than the fluorescence wavelength of the first active layer in the rear modulator region.

[0009] Furthermore, the lengths of the front modulator region and the rear modulator region are both 150 microns, the length of the front grating region is 50 microns, the length of the gain region is 300 microns, and the length of the rear grating region is 250 microns. Electrical isolation regions with a spacing of 50 microns are set between adjacent regions.

[0010] Furthermore, the first active layer includes, from bottom to top, a first lower waveguide layer, a first multi-quantum well layer, and a first upper waveguide layer; the thickness of the first lower waveguide layer and the first upper waveguide layer are both 100 nm.

[0011] Furthermore, the first multi-quantum well layer is formed by cross-growth of multiple quantum well layers and multiple barrier layers.

[0012] Furthermore, the second active layer includes, from bottom to top, a second lower waveguide layer, a second multi-quantum well layer, and a second upper waveguide layer; the thickness of the second lower waveguide layer and the second upper waveguide layer are both 80 nm, and the thickness of the second multi-quantum well layer is greater than that of the first multi-quantum well layer.

[0013] Furthermore, the method for removing the first active layer in the front grating region and the back grating region adopts an ICP etching method.

[0014] Furthermore, the width of the electrical isolation groove is 50 microns.

[0015] On the other hand, the present invention also provides a structure of a photonic integrated device, which is manufactured using the manufacturing method described in the above technical solution. The device comprises, from bottom to top, an N-side electrode, a substrate, an active layer, a cladding layer, an electrical contact layer, and a P-side electrode; The device is divided into a front modulator region, a rear modulator region, a front grating region, a gain region and a rear grating region in sequence along the length direction starting from one side; Among them, the gain region and the rear modulator region achieve bandgap width offset through selective epitaxial material growth; the optical fluorescence wavelength of the gain region is 150~200nm longer than that of the grating region material, and the optical fluorescence wavelength of the front modulator region material is 30-60nm shorter than that of the rear modulator region material.

[0016] Compared with the existing technology, the advantages of this method are: (1) Improved reliability: This method realizes the integration of the gain region material and the two modulator materials through one selective epitaxial growth and one docking growth, integrating the wide wavelength tunable laser with the two electro-absorption modulators. Compared with the existing technology that requires two docking preparation technologies, this method saves one active layer growth, can reduce the problem of docking interface defects caused by multiple docking epitaxial growth, and improves the reliability of the device.

[0017] (2) Reduced interface defects: In conventional technologies, multiple epitaxial growths are prone to interface defects, which can affect device performance. This method, however, reduces the number of growths by optimizing the process flow, thereby effectively reducing the occurrence of interface defects.

[0018] (3) Saving manufacturing costs: This method realizes the integration of multiple materials through one selective epitaxial growth and one docking growth, avoiding the traditional multiple growth and complex process steps, reducing production costs, and improving production efficiency. It provides an economical and efficient solution for the integration of wide-wavelength tunable lasers and single-ended dual electro-absorption modulators. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1A schematic flow chart of a method for preparing a photonic integrated device provided by the present invention; Figure 2 A schematic diagram of the structure of the substrate and area division provided by the present invention; Figure 3 A top view of the structure of the selective epitaxial mask pattern produced on the substrate surface provided by the present invention; Figure 4 A schematic diagram of the structure of fabricating a first butt-jointing mask and etching away the active material of the front modulator region provided by the present invention; Figure 5 A schematic structural diagram of the second active material of the modulator region before growth provided by the present invention; Figure 6 A top view of a second butting mask pattern outside the grating area provided by the present invention; Figure 7 A schematic diagram of the structure of the third active layer of the rear grating region and the front grating region obtained by using the butt-jointed growth technology provided by the present invention; Figure 8 A schematic diagram of the structure after the growth of the cladding layer and the electrical contact layer provided by the present invention; Figure 9 A cross-sectional view of an inverted shallow ridge waveguide structure fabricated on a cladding layer and an electrical contact layer provided by the present invention; Figure 10 A side view of the completed device provided by the present invention; In the figure, 1-front modulator region, 2-back modulator region, 3-front grating region, 4-gain region, 5-back grating region, 10-substrate, 11-selective epitaxial mask pattern, 12-first lower waveguide layer, 13 first multi-quantum well layer, 14-first upper waveguide layer, 15-second lower waveguide layer, 16-second multi-quantum well layer, 17-second upper waveguide layer, 18-second docking mask pattern, 19-third active layer, 20-grating, 21-cladding, 22-electric contact layer, 23-P-side electrode, 24-N-side electrode. DETAILED DESCRIPTION

[0020] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, and are not used to limit the scope of the present invention.

[0021] Example 1 See Figure 1 , Figure 1 A schematic flow chart of a method for preparing a photonic integrated device provided in this embodiment is shown, the method comprising: Step S101: performing surface layout on the substrate, dividing the substrate surface into a front modulator region, a rear modulator region, a front grating region, a gain region, and a rear grating region in sequence along the length direction; Step S102: fabricating a selective epitaxial growth mask pattern on the surface of the gain region of the substrate, wherein the selective epitaxial growth mask pattern is two parallel strips having the same length as the gain region and a preset spacing and width; Step S103: growing a first active layer on the substrate surface except for the selective epitaxial growth mask pattern, then etching away the selective epitaxial growth mask pattern, forming a first butt-joint mask pattern in the area except for the front modulator area, and etching away the first active layer outside the first butt-joint mask pattern; Step S104: growing a second active layer on the surface of the front modulator region, and then etching away the first butting mask pattern; Step S105: forming a second butting mask pattern in the area outside the front grating area and the rear grating area, and etching and removing the first active layer material in the front grating area and the rear grating area; Step S106: growing a third active layer in the front grating region and the rear grating region using a butt-joint growth technique, then removing the second butt-joint mask pattern, and fabricating sampled gratings in the front grating region and the rear grating region; Step S107: sequentially growing a cladding layer and an electrical contact layer on the surface of the entire device, and forming an inverted shallow ridge waveguide structure on the cladding layer and the electrical contact layer; Step S108: etching electrical isolation trenches on the electrical contact layer to achieve electrical isolation between the regions; Step S109: fabricating a P-side electrode on the electrical contact layer in each region, and fabricating an N-side electrode on the entire surface of the bottom of the substrate after thinning the substrate, thereby completing the fabrication of the integrated device.

[0022] The method for preparing a photonic integrated device provided in this embodiment integrates the gain region material and the two modulator materials through a single selective epitaxial growth and a single butt-joint growth, thereby integrating a wide-wavelength tunable laser with two electro-absorption modulators. Compared with the current two-butt-joint preparation technology, this method saves one active layer growth, can reduce the problem of butt-joint interface defects caused by multiple butt-joint epitaxial growths, and improves the reliability of the device; it also saves manufacturing costs and provides a solution for the integration of a wide-wavelength tunable laser and a single-ended dual electro-absorption modulator.

[0023] The following combination Figure 2-Figure 10 The above steps are demonstrated and explained in detail.

[0024] As a specific embodiment, the steps of the production method include: (1) An N-type indium phosphide substrate 10 is selected. According to the function of the integrated device, the surface of the substrate 10 is divided into a front modulator region 1, a rear modulator region 2, a front grating region 3, a gain region 4 and a rear grating region 5 along the length direction, as shown in FIG. Figure 2As shown in the figure, the front modulator region 1 and the rear modulator region 2 are both 150 microns long, the front grating region 3 is 50 microns long, the gain region 4 is 300 microns long, and the rear grating region 5 is 250 microns long. It should be noted that there are electrical isolation regions with a spacing of 50 microns between the functional regions to facilitate subsequent etching of electrical isolation trenches to achieve electrical isolation between the regions.

[0025] (2) A 150 nm thick silicon dioxide film is grown on the surface of the substrate 10, and a selective epitaxial mask pattern 11 is formed in the gain region 4. The selective epitaxial mask pattern 11 is two parallel strips with the same length as the gain region 4 and a preset spacing and width; Figure 3 As shown, Figure 3 1 is a top view of the substrate surface. The length of the parallel strips in the selective epitaxial mask pattern 11 is 300 microns, the width of the strips is 12 microns, and the spacing is 20 microns.

[0026] (3) Using MOCVD equipment, a first active layer is grown on the substrate surface except for the selective epitaxial mask pattern 11. The principle of this step is that when the reaction gas reaches the mask surface, it will diffuse around the mask pattern, thereby increasing the thickness of the area between the mask patterns.

[0027] The first active layer is an InGaAsP active layer, which includes, from bottom to top, a first lower waveguide layer 12, a first multi-quantum well layer 13, and a first upper waveguide layer 14. The first lower waveguide layer 12 is 100 nm thick. The first multi-quantum well layer 13 comprises six quantum well layers and seven barrier layers that grow in a cross-growth pattern. Each quantum well layer is 5 nm thick, and the barrier layers are 9 nm thick. The first upper waveguide layer 14 is 100 nm thick.

[0028] (4) Remove the selective epitaxial mask pattern 11 by hydrofluoric acid wet etching, and make a first butt-joint mask pattern in the area other than the front modulator area 1. The first butt-joint mask pattern is a silicon dioxide butt-joint mask pattern with a mask thickness of 250nm. Remove the first active layer on the surface of the front modulator area 1 other than the first butt-joint mask pattern by ICP etching. The overall structure at this time is as follows: Figure 4 shown.

[0029] (5) A second active layer is grown on the surface of the front modulator region 1 by MOCVD equipment. The second active layer is an InGaAsP active layer. The light fluorescence wavelength of the second active layer of the front modulator region 1 is 30-60nm shorter than the light fluorescence wavelength of the first active layer of the rear modulator region. From bottom to top, it includes a second lower waveguide layer 15, a second multi-quantum well layer 16 and a second upper waveguide layer 17. Among them, the thickness of the second lower waveguide layer 15 is 80nm; the second multi-quantum well layer 16 includes 9 quantum well layers and 10 barrier layers that grow crosswise with each other, the thickness of each quantum well layer is 10nm, and the thickness of each barrier layer is 5nm; the thickness of the second upper waveguide layer 17 is 80nm. The overall structure at this time is as follows Figure 5 shown.

[0030] It should be noted here that because the active layer of the front modulator area 1 needs to have a shorter light fluorescence wavelength than the active layer of the gain area 4, one epitaxial growth cannot simultaneously meet the needs of the active layers of the gain area and the modulation area. Therefore, a silicon oxide mask is used for protection, and the active layer previously grown in the front modulator area 1 is removed, and the active layer required by the front modulator area 1 is regrown.

[0031] (6) Remove the first docking mask pattern by hydrofluoric acid wet etching, and make a second docking mask pattern 18 in the area outside the front grating area 3 and the back grating area 5. The second docking mask pattern 18 is a silicon dioxide docking mask pattern with a thickness of 250nm, as shown in FIG. Figure 6 As shown, Figure 6 This is a top view of the device at this time.

[0032] (7) The active material (InGaAsP material) of the rear grating region 5 and the front grating region 3 is etched away by the ICP method, that is, the first active layer grown in step (4).

[0033] (8) The third active layer 19 is grown on the rear grating region 5 and the front grating region 3 using a butt-joint growth technique. The third active layer 19 is made of InGaAsP material, and its light fluorescence wavelength is 150nm shorter than that of the light fluorescence wavelength of the first active layer material of the gain region 4. Figure 7 The advantage of the fluorescence wavelength of the light in the grating region being smaller than that in the gain region is that the laser light emitted by the laser will not be absorbed by the grating material in the grating region, thus avoiding loss caused by material absorption.

[0034] (9) The second mating mask pattern 18 is removed by etching, and gratings 20 are formed in the front grating area 3 and the rear grating area 5.

[0035] (10) A 1.5 μm thick InP cladding layer 21 and a 300 nm thick InGaAs electrical contact layer 22 are grown on the surface of the entire device in sequence, as shown in FIG. Figure 8 As shown, an inverted shallow ridge waveguide structure is fabricated on the cladding layer 21 and the electrical contact layer 22, see Figure 9 , Figure 9 A cross-sectional view of the device.

[0036] (11) An electrical isolation groove with a width of 50 μm is etched on the electrical contact layer 22 of the ridge waveguide between each region to achieve electrical isolation between the front modulator region 1, the rear modulator region 2, the front grating region 3, the gain region 4 and the rear grating region 5.

[0037] (12) A P-side electrode 23 is fabricated on the electrical contact layer 22 of the front modulator region 1, the rear modulator region 2, the front grating region 3, the gain region 4, and the rear grating region 5. After the substrate 10 is thinned, an N-side electrode 24 is fabricated at the bottom of the entire device to complete the fabrication of the photonic integrated device. Figure 10 shown.

[0038] The method of this embodiment achieves the integration of the gain region material and the two modulator materials through a single selective epitaxial growth and a single docking growth, integrating a wide-wavelength tunable laser with two electro-absorption modulators. Compared with the previous two-dock preparation technology, this method saves one active layer growth, can reduce the problem of docking interface defects caused by multiple docking epitaxial growths, and improves the reliability of the device; it also saves manufacturing costs and provides a solution for the integration of a wide-wavelength tunable laser and a single-ended dual electro-absorption modulator.

[0039] Example 2 The embodiment of the present invention further provides a structure of a photonic integrated device, which is manufactured using the method for manufacturing a photonic integrated device described in Example 1. Figure 10 As shown, the device includes, from bottom to top, an N-side electrode 24, a substrate 10, an active layer, a cladding layer 21, an electrical contact layer 22, and a P-side electrode 23; The laser is divided into a front modulator region 1, a rear modulator region 2, a front grating region 3, a gain region 4 and a rear grating region 5 in sequence along the length direction starting from one side; Among them, the gain region 4 and the rear modulator region 2 achieve bandgap width offset through selective epitaxial material growth; the optical fluorescence wavelength of the gain region 4 is 150~200nm longer than the optical fluorescence wavelength of the materials of the front grating region 3 and the rear grating region 5, and the optical fluorescence wavelength of the front modulator region 1 material is 30-60nm shorter than the optical fluorescence wavelength of the rear modulator region 2.

[0040] In the integrated device structure provided in this embodiment, the gain region and the rear modulator region achieve bandgap shifts through selective epitaxial material growth. Reasonable adjustment of the bandgap can control the absorption and emission characteristics of photons in different regions. Therefore, the bandgap shift in the gain region helps improve optical gain efficiency and enhance optical signal intensity. The bandgap shift in the rear modulator region facilitates effective electro-absorption modulation, precisely controlling the modulation depth and speed of the optical signal, thereby improving the overall photon transmission and modulation performance of the device. The optical fluorescence wavelength of the gain region is 150-200nm longer than that of the front and rear grating regions, creating a significant spectral difference from the grating region and providing a basis for achieving wide-wavelength tunability. The optical fluorescence wavelength of the front modulator region material is 30-60nm shorter than that of the rear modulator region. This wavelength difference design facilitates modulation of optical signals in different bands, improving the device's tuning flexibility and signal processing efficiency in optical communication systems.

[0041] The device also integrates a wide-wavelength tunable laser with two electro-absorption modulators to form a compact photonic integrated device structure. This integrated design reduces connection losses and optical mode mismatch between devices, improving the compatibility and stability of the photonic integrated system. The longer optical fluorescence wavelength in the gain region facilitates more efficient optical amplification and broadens the laser's tuning range; the shorter optical fluorescence wavelength in the pre-modulator region facilitates fast-response electro-absorption modulation, increasing the signal modulation rate. This structure, which optimizes material properties, enables the device to better meet the requirements of optical communication systems for high speed, large capacity, and flexible wavelength tuning.

[0042] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing a photonic integrated device, characterized in that: include: Performing surface layout on the substrate, dividing the substrate surface into a front modulator region, a rear modulator region, a front grating region, a gain region and a rear grating region in sequence along the length direction; A selective epitaxial growth mask pattern is formed on the surface of the gain region of the substrate, wherein the selective epitaxial growth mask pattern is two parallel strips having the same length as the gain region and a preset spacing and width; Growing a first active layer on a portion of the substrate surface excluding a selective epitaxial growth mask pattern, then etching away the selective epitaxial growth mask pattern, forming a first butt-joint mask pattern in an area excluding a front modulator area, and etching away the first active layer excluding the first butt-joint mask pattern; Growing a second active layer on the surface of the front modulator region, and then etching away the first butting mask pattern; A second butting mask pattern is formed in the area outside the front grating area and the rear grating area, and the first active layer in the front grating area and the rear grating area is removed by etching; A third active layer is grown in the front grating region and the rear grating region using a butt-joint growth technique, and then the second butt-joint mask pattern is removed to form sampled gratings in the front grating region and the rear grating region; A cladding layer and an electrical contact layer are sequentially grown on the surface of the entire device, and an inverted shallow ridge waveguide structure is fabricated on the cladding layer and the electrical contact layer; Etching electrical isolation trenches on the electrical contact layer to achieve electrical isolation between the regions; P-side electrodes are fabricated on the electrical contact layer of each region, and N-side electrodes are fabricated on the entire surface of the substrate bottom after the substrate is thinned to complete the fabrication of the integrated device.

2. The method for preparing a photonic integrated device according to claim 1, wherein: The fluorescence wavelength of the light of the third active layer in the front grating region and the back grating region is 150-200 nm shorter than the fluorescence wavelength of the light of the first active layer in the gain region.

3. The method for preparing a photonic integrated device according to claim 1, wherein: The fluorescence wavelength of the light of the second active layer in the front modulator region is 30-60 nm shorter than the fluorescence wavelength of the light of the first active layer in the rear modulator region.

4. The method for preparing a photonic integrated device according to claim 1, wherein: The lengths of the front modulator region and the rear modulator region are both 150 microns, the length of the front grating region is 50 microns, the length of the gain region is 300 microns, and the length of the rear grating region is 250 microns. Electrical isolation regions with a spacing of 50 microns are set between adjacent regions.

5. The method for preparing a photonic integrated device according to claim 1, wherein: The first active layer includes, from bottom to top, a first lower waveguide layer, a first multi-quantum well layer and a first upper waveguide layer; the thickness of the first lower waveguide layer and the first upper waveguide layer are both 100 nm.

6. The method for preparing a photonic integrated device according to claim 5, wherein: The first multi-quantum well layer is formed by cross-growth of multiple quantum well layers and multiple barrier layers.

7. The method for preparing a photonic integrated device according to claim 5, wherein: The second active layer includes, from bottom to top, a second lower waveguide layer, a second multi-quantum well layer, and a second upper waveguide layer; the thickness of the second lower waveguide layer and the second upper waveguide layer are both 80 nm, and the thickness of the second multi-quantum well layer is greater than that of the first multi-quantum well layer.

8. The method for preparing a photonic integrated device according to claim 1, wherein: The method for removing the first active layer in the front grating region and the back grating region adopts an ICP etching method.

9. The method for preparing a photonic integrated device according to claim 1, wherein: The width of the electrical isolation trench is 50 microns.

10. A structure of a photonic integrated device, characterized in that: The device is manufactured by the manufacturing method according to any one of claims 1 to 9, and the device comprises, from bottom to top, an N-side electrode, a substrate, an active layer, a cladding layer, an electrical contact layer, and a P-side electrode; The device is divided into a front modulator region, a rear modulator region, a front grating region, a gain region and a rear grating region in sequence along the length direction starting from one side; Among them, the gain region and the rear modulator region achieve bandgap width offset through selective epitaxial material growth; the optical fluorescence wavelength of the gain region is 150~200nm longer than that of the grating region material, and the optical fluorescence wavelength of the front modulator region material is 30-60nm shorter than that of the rear modulator region material.

Images