Front-end double-window double-beam small-angle output superluminescent diode

Abstract

The front-end double-window double-beam small-angle output superluminescent diode belongs to the technical field of semiconductor light-emitting devices. The existing technology has light energy loss, high process difficulty, and it is difficult to improve the light output power. In the present invention, the cubic body of the superluminescent diode is composed of a lower electrode, a substrate, a lower limiting layer, a lower waveguide, and an active layer. The length and width of each layer of the body are the same, but the thickness is different; it is characterized in that the front-end double-window oblique waveguide of the superluminescent diode is composed of an upper waveguide, an upper limiting layer, a covering layer, and an upper electrode. The front-end double-window oblique waveguide is composed of two sections of oblique waveguide and one section of curved waveguide, and is etched on the body at one time. The front end face of the active layer and the corresponding parts of the front end faces of the two sections of oblique waveguides are both light exit windows, and the two light exit windows are made with the same anti-reflection coating.

Description

Technical Field

[0001] The invention relates to a front-end double-window double-beam small-angle output super radiant light emitting diode, belonging to the technical field of semiconductor light emitting devices. Background Art

[0002] SLD (Super Luminescent Diode) is a semiconductor light-emitting device with luminescence characteristics between LD (laser diode) and LED (light-emitting diode). It has the characteristics of high power, Gaussian wide spectrum, weak temporal coherence, high efficiency, etc. It is used as the light source in low-coherence interference detection systems such as fiber optic gyroscopes, optical time domain reflectometers, and optical coherence tomography.

[0003] In the process of forward current injection, when the electrons in the active layer with reverse distribution jump from the conduction band to the valence band or impurity energy level, they recombine with holes and release photons. These spontaneously radiated photons are amplified by the gain effect when propagating in a given cavity. SLD is a light emitting device characterized by internal one-way gain. The light emitting principle of SLD is similar to that of edge-emitting LD, both of which are stimulated amplification of spontaneous radiation; the difference between the two lies in whether there is oscillation and mode selection during the light emitting process. Edge-emitting LD uses the light reflection between the cleavage planes (cavity surfaces) at both ends of the cavity (full reflection at one end and partial reflection at the other end) to oscillate and select the mode to increase the light output power; while SLD uses the oblique waveguide structure and anti-reflection coating process to effectively reduce the reflectivity of the cavity surface, reduce light feedback, suppress the resonance of the FP cavity, and achieve wide-spectrum light emission.

[0004] The structural features of the existing SLD with an oblique waveguide structure and an anti-reflection coating are as follows. The device is composed of an upper electrode 1, a cover layer 2, an upper confinement layer 3, an upper waveguide 4, an active layer 5, a lower waveguide 6, a lower confinement layer 7, a substrate 8, and a lower electrode 9 from top to bottom. Figure 1 As shown, the lower electrode 9, substrate 8, lower limiting layer 7, lower waveguide 6, and active layer 5 constitute the cubic body of the device, and the length and width of each layer of the body are the same, but the thickness is different; the upper waveguide 4, upper limiting layer 3, cover layer 2, and upper electrode 1 constitute the parallelogram-shaped cylindrical oblique waveguide of the device, as shown in FIG. Figure 1 , Figure 2As shown, the top view shape is a parallelogram, the front face and rear face of the oblique waveguide are flush with the front face and rear face of the main body respectively, the front and rear direction of the oblique waveguide forms a certain angle θ with the front and rear direction of the main body, the front and rear direction of the oblique waveguide refers to the direction of the line connecting the midpoints of the front and rear opposite sides of the parallelogram, and the front and rear direction of the main body refers to the direction of the line connecting the midpoints of the front and rear opposite sides of the regular quadrilateral on the top surface of the cube. Different anti-reflection coatings are made on the front and rear faces of the main body active layer 5, respectively. On the premise of realizing the wide spectrum light emission of the device, on the one hand, the part corresponding to the front face of the active layer 5 and the front face of the oblique waveguide is the light emission window 10, thereby emitting high-power light, and the part corresponding to the rear face of the active layer 5 and the rear face of the oblique waveguide inevitably also has light output, such as Figure 2 As shown, on the other hand, it is also beneficial to extend the life of the device.

[0005] However, the prior art has its shortcomings, including: there is light energy loss caused by light emitting from the rear end face of the active layer 5, and this part of the power output cannot be effectively utilized, thereby reducing the effective light output of the device; the process is difficult, because the coatings made on the front end face and the rear end face of the active layer 5 are different, and different cavity mask processes are required to be used respectively, which not only increases the process steps, but also increases the process difficulty. For example, the materials of the front end face coating and the rear end face coating are different, and measures must be taken to prevent contamination of each other; the light output power is difficult to increase, and due to the limitation of the chip size, the length of the light-emitting cavity is limited, the effective gain area is small, and the saturation gain level is low, which directly limits the increase of the light output power of the device. Summary of the invention

[0006] In order to overcome the shortcomings of the existing SLD itself and its manufacturing process with an oblique waveguide structure and an anti-reflection coating, we invented a front-end double-window double-beam small-angle output superluminescent diode.

[0007] The front-end double-window double-beam small-angle output superluminescent diode of the present invention is composed of an upper electrode 1, a cover layer 2, an upper limiting layer 3, an upper waveguide 4, an active layer 5, a lower waveguide 6, a lower limiting layer 7, a substrate 8, and a lower electrode 9 from top to bottom. Figure 3 As shown, the lower electrode 9, substrate 8, lower limiting layer 7, lower waveguide 6, and active layer 5 constitute a cubic body of the superluminescent diode, and the length and width of each layer of the body are the same, but the thickness is different; it is characterized in that the front end double-window inclined waveguide of the superluminescent diode is constituted by the upper waveguide 4, upper limiting layer 3, cover layer 2, and upper electrode 1, as shown Figure 3 , Figure 4 As shown, the front-end double-window oblique waveguide is composed of two sections of oblique waveguide and one section of curved waveguide, and is etched once on the main body. The front end face of the active layer 5 and the parts corresponding to the front end faces of the two sections of oblique waveguide are both light exit windows 10, and the two light exit windows 10 are made with the same anti-reflection coating.

[0008] The technical effects of the present invention are as follows.

[0009] In the present invention, both end faces of the front double-window slanted waveguide are located at the front end of the superluminescent diode, and the two light exit windows 10 are located on the same side. In addition, the front double-window slanted waveguide also has the function of the existing slanted waveguide. The exit direction of the exit photons in the active layer 5 forms a certain angle θ with the normal line of the front end face of the active layer 5, such as Figure 4 As shown, the outgoing photons are easy to escape, and with the help of anti-reflection coating, the reflectivity of the outgoing photons in the light exit window 10 is greatly reduced; the photons moving in the opposite direction to the outgoing photons enter the waveguide range of another inclined waveguide due to the waveguide effect of the curved waveguide, and finally become outgoing photons and exit from another light exit window 10, avoiding the waste of light energy. At the same time, the resonance in the cavity is effectively suppressed, and low coherence, wide spectrum, and high-power light output are achieved; a related side effect is that, under the premise that the chip size remains unchanged, two light exit windows 10 at a certain distance emit light at the same time, so the lateral radius of the output light beam of the superluminescent diode of the present invention is widened, and the far-field spot becomes larger. When used in a low-coherence detection system, the detection area is expanded, for example, it can cover certain detection objects; when the mutual direction relationship of the two sections of inclined waveguides as one of the specific embodiments of the present invention is an open direction relationship, that is, the light emission directions of the two sections of inclined waveguides are open at a small angle 2θ, such as Figure 4 As shown, the far-field spot will be larger.

[0010] Since the two light exit windows 10 are not only located on the same side, but also made with the same anti-reflection coating, the coating can be made at one time, and there is no problem of contamination between the anti-reflection coatings of the two light exit windows 10, and there is no problem of increased process difficulty. At the same time, although the front-end double-window slanted waveguide is composed of two sections of slanted waveguides and one section of curved waveguide, it seems that the structure of the present invention is more complicated compared to the prior art using one slanted waveguide, but in the process of making the front-end double-window slanted waveguide, as in the prior art, the mask pattern is designed and etched once using a photolithography process, and there is no problem of increased process difficulty.

[0011] Compared with the existing single slant waveguide, under the premise of the same chip size, the front-end double-window slant waveguide in the present invention is significantly increased in length and area, thereby effectively increasing the cavity length, increasing the injection current pumping area, effectively reducing the differential resistance, and improving the saturated gain level and output power. The heat dissipation effect is also improved, the thermal resistance is effectively reduced, and the optical output power is further improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a three-dimensional schematic diagram of the overall structure of an existing SLD with an oblique waveguide structure and an anti-reflection coating. Figure 2It is a schematic top view of the local structure of an existing SLD with an oblique waveguide structure and an anti-reflection coating. Figure 3 It is a three-dimensional schematic diagram of the overall structure of the front-end double-window double-beam small-angle output superluminescent diode of the present invention, which is also used as a summary illustration. Figures 4 to 6 All of them are schematic diagrams of the present invention, including two aspects: one is the top-down shape of the front-end double-window slanted waveguide, including the top-down shape of the curved waveguide; the other is the direction relationship between the two sections of the slanted waveguide, including the double-window and double-beam light emitting conditions. DETAILED DESCRIPTION

[0013] The curved waveguide has two shapes when viewed from above. The first shape is a curved strip with equal width. The width of the curved waveguide in this shape is the same as the width a of the inclined waveguide. Figure 4 , Figure 6 The second type is a curved strip with a gradient width. The curved waveguide in this shape is wide at both ends and narrow in the middle. The width at both ends is the same as the width a of the inclined waveguide, as shown in FIG. Figure 5 The curved waveguide with the second top-view shape can further suppress the resonance.

[0014] There are two types of mutual orientation relationships between the two sections of the oblique waveguides. The first type is an open orientation relationship, in which the light emission directions of the two sections of the oblique waveguides are open at a small angle 2θ, such as Figure 4 , Figure 5 As shown; the second is a parallel direction relationship, in which the light emission directions of the two oblique waveguides are parallel, as shown Figure 6 The far-field spot of the output beam of the two oblique waveguides with the first mutual orientation relationship is larger. In this case, the superluminescent diode is used in the low-coherence detection system to expand the detection area. The superluminescent diode with the two oblique waveguides with the second mutual orientation relationship can provide another alternative for the application of SLD.

[0015] The width a of the oblique waveguide is 10 to 40 μm, such as 10 μm; the length b is 0.5 to 3 mm, such as 0.5 mm, such as Figure 5 shown.

[0016] When the top view shape of the curved waveguide is a curved strip with a gradually varying width, the middle ring width c of the curved waveguide is 5 to 10 μm, such as 5 μm. Figure 5 shown.

[0017] The light emitting directions of the two sections of the oblique waveguides form a small included angle 2θ, wherein the angle θ is 5 to 20°, such as 10°.

[0018] The manufacturing process of the front-end double-window double-beam small-angle output superluminescent diode of the present invention is as follows.

[0019] like Figure 3As shown, a semiconductor epitaxial growth process is adopted to sequentially grow a lower confinement layer 7 made of N-type GaAs and a lower confinement layer 8 made of N-type Al on a substrate 8 made of a high-doping concentration N-type GaAs. 0.5 GaAs lower waveguide 6, material is Al 0.2 GaAs / GaAs multi-quantum well structure active layer 5, material is P-type Al 0.5 An upper waveguide 4 is made of GaAs, an upper limiting layer 3 is made of P-type GaAs, and a covering layer 2 is made of high-doped P-type GaAs; an upper electrode 1 is made of Au / Ge / Ni on the covering layer 2 with a thickness of about 300nm, and a lower electrode 9 is made of Ti / Pt / Au on the lower side of the substrate 8 with a thickness of about 300nm. The upper electrode 1 and the lower electrode 9 are both made by first layering and then alloying; a semiconductor photolithography process is used to make a front-end double-window oblique waveguide, a mask is made according to the top view of the front-end double-window oblique waveguide, and the interface between the upper waveguide 4 and the active layer 5 is photolithographically etched; the front end face of the active layer 5 and the corresponding parts of the front end faces of the two sections of the oblique waveguides are both light exit windows 10, and the same anti-reflection coating is made on the two light exit windows 10.

Claims

1. A front-end double-window double-beam small-angle output superluminescent diode, which comprises, from top to bottom, an upper electrode (1), a cover layer (2), an upper confinement layer (3), an upper waveguide (4), an active layer (5), a lower waveguide (6), a lower confinement layer (7), a substrate (8), and a lower electrode (9), wherein: A cubic body of a superluminescent diode is formed by a lower electrode (9), a substrate (8), a lower limiting layer (7), a lower waveguide (6), and an active layer (5), wherein the layers of the body have the same length and width but different thicknesses; the invention is characterized in that a front end double-window slanted waveguide of the superluminescent diode is formed by an upper waveguide (4), an upper limiting layer (3), a cover layer (2), and an upper electrode (1), wherein the front end double-window slanted waveguide is composed of two sections of slanted waveguides and one section of curved waveguide and is formed by etching the body at one time, and the front end face of the active layer (5) and the portions corresponding to the front end faces of the two sections of slanted waveguides are both light exit windows (10), and the two light exit windows (10) are provided with the same anti-reflection coating; The curved waveguide has a top view shape of a curved strip with a gradually varying width. The curved waveguide in this shape is wide at both ends and narrow in the middle, and the widths at both ends are the same as the width a of the oblique waveguide; The two sections of the oblique waveguides have an open orientation relationship with each other, and the light emitting directions of the two sections of the oblique waveguides in this relationship are open at a small angle 2θ.

2. The front-end double-window double-beam small-angle output superluminescent diode according to claim 1, characterized in that: The width a of the oblique waveguide is 10~40μm; the length b is 0.5~3mm.

3. The front-end double-window double-beam small-angle output superluminescent diode according to claim 1, characterized in that: When the top-view shape of the curved waveguide is a curved strip with a gradient width, the middle ring width c of the curved waveguide is 5 to 10 μm.

4. The front-end double-window double-beam small-angle output superluminescent diode according to claim 1, characterized in that: The light output directions of the two oblique waveguides form a small included angle 2θ, where the angle θ is 5~20°.

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