KR100880122B1 - Optical device having optical power loss reducing region near waveguide and method thereof - Google Patents

Abstract

An optical device having optical power loss reducing region near optical waveguide and a manufacturing method thereof are provided to secure enough optical output in a device of identical length by reducing optical power loss generated by a bending of an optical waveguide. An optical device having optical power loss reducing region near optical waveguide comprises an optical waveguide(103) and one or more optical power loss reducing region(106). The optical waveguide has a curve region(II). The optical power loss reducing region is positioned near the optical wave guide, and is operated in order to prevent an optical power loss inside the optical waveguide.

Description

Optical device having an optical loss reduction area around the optical waveguide, and a manufacturing method therefor {OPTICAL DEVICE HAVING OPTICAL POWER LOSS REDUCING REGION NEAR WAVEGUIDE AND METHOD THEREOF}

The present invention relates to an optical device, and more particularly, to an optical device capable of increasing optical power while maintaining a single mode without increasing the length of the device by providing an optical loss reduction area around the optical waveguide, and a method of manufacturing the same. .

A semiconductor light emitting device is a device that emits energy in the form of light when electrons and holes are recombined when a current is applied to a p-n junction. Representative examples of such semiconductor light emitting devices include a light emitting diode (LED), a laser diode, and the like.

LED is a device that uses spontaneous emission light of active layer with low energy band gap and is located between semiconductor layers with large energy band gap, and has a wide wavelength bandwidth and low power output of several orders of magnitude. Has In general, the light output of the LED increases with the intensity of the current applied to the active layer. However, only a fraction of the electrical energy is converted to light energy, and a significant amount is not converted to light energy and accumulates as thermal energy inside the LED. Accordingly, only a part of the current applied to the active layer is converted into light energy, and at a certain degree or more of current, it is difficult to generate a high light output due to the thermal energy accumulated therein.

Laser diodes are devices that utilize stimulated emission light in an active layer. Once oscillation occurs which increases the coherence of light, all light emitted from the active layer is amplified with the same direction and phase, resulting in very high light output compared to LEDs. On the other hand, there are several resonant modes for each wavelength in the resonator constituting the laser diode. Among these, only a few wavelengths having a large gain are selectively oscillated, so that the wavelength bandwidth is between several kHz and several hundred MHz. Otherwise the wavelength bandwidth is narrow.

Superluminescent diodes (SLDs) are semiconductor light emitting devices having both wide wavelength bandwidth characteristics of LEDs and high light output characteristics of laser diodes. Therefore, a high brightness light emitting device can be realized by increasing the light output of the LED or increasing the wavelength bandwidth of the laser diode. That is, the high brightness light emitting device may be referred to as a "laser diode in which resonance mode does not occur" or "oscillating LED".

In the conventional laser diode, two opposing mirror surfaces constituting the resonator are composed of cleaving planes obtained by parallel cleaving cladding layers of the active layer and upper and lower portions of the active layer. The resonance mode of a conventional laser diode is formed by electrodes and cleavage surfaces that determine an area for applying current to the active layer. In order to form the electrode of the laser diode, an insulating thin film is formed on the substrate on which the active layer is provided, and only the portion requiring the current injection is selectively removed. The shape of the electrode is determined by the shape of the portion from which the insulating thin film is removed. The electrode of the laser diode has a straight line shape and is perpendicular to the cleaved surface to form a resonance mode.

The high brightness light emitting device can be formed by modifying a laser diode. However, when the electrode of the high brightness light emitting device is formed in a straight line shape perpendicular to the cleavage plane (parallel to the normal of the cleavage plane) as in the laser diode, a Fabry-Perot mode through reflection is formed in the resonator, resulting in high luminance. In order to prevent it from functioning as a laser diode rather than a light emitting device, there is a difficulty in coating an antireflection film having a reflectance of about 10 ⁻⁵ or less on the cleaved surface.

Hereinafter, with reference to the accompanying Figures 1a and 1b, the problem of manufacturing a high brightness light emitting device according to the prior art will be described in more detail.

1A is a perspective view showing a schematic structure of a conventional high brightness light emitting device formed by modifying a ridge type laser diode.

Cleavage surfaces CP1 and CP2 serving as mirror surfaces in the laser diode are cleaved at both ends of the first cladding layer 11, the active layer 12, and the second cladding layer 13 stacked on a substrate (not shown). These are the faces obtained by. An electrode SE which injects current into the active layer 12 to induce light emission is formed on the second cladding layer 13 covering the active layer 12. An area of the second cladding layer 13, the active layer 12, and the first cladding layer 11 that overlaps with the electrode SE and has the same shape as the electrode serves as the waveguide 14. In Fig. 1A, reference numerals 15 and 16 denote an insulating film and a metal film, respectively.

In order to prevent the formation of the resonance mode, that is, to prevent the light having sufficiently obtained light gain through the active layer from being reflected from the cleaved surfaces CP1 and CP2 across the waveguide 14, at least one cleaved surface CP1 or CP2) should be coated with anti-refelection (AR) coating with a material with a reflectance of about 10 ^-5 . However, the AR coating process having a reflectance of about 10 ^-5 is a very precise and rigorous process, which has disadvantages in terms of technology reproducibility, mass productivity, and price competition.

As an alternative to prevent resonance mode formation without antireflection coating, a high brightness light emitting device including a J-shaped electrode JE is proposed as shown in FIG. 1B. The J-shaped electrode JE consists of a straight region I, a curved region II and an oblique region III. The diagonal region III of the electrode has a constant inclination angle θ with respect to the normal of the cleaved surface CP1. The magnitude of the inclination angle θ depends on the output light wavelength of the high brightness light emitting device to be obtained. By providing the curved region II between the linear region I and the diagonal region III, the reflection of light between the two cleaved surfaces CP1 and CP2 is suppressed to form a resonance mode in the J-shaped waveguide formed under the electrode. Can be prevented.

In optical devices with waveguides, the most common method of increasing light output is to widen the waveguide width (Ww). However, increasing the width of the waveguide (Ww) increases the single-mode requirement (k ₀ Ww (n _a ^2- n _c ² ) ^1/2 <p, where "k ₀ " is a constant, "na" is the refractive index of the waveguide region, "nc" is the refractive index of the second cladding region, the difference in refractive index between the waveguide and the second cladding region should be small. In this case, when light enters the curved region II from the linear region I of the waveguide, optical loss due to the bending of the curved region II occurs. The optical loss due to the use of the electrode having the curved region is shown not only in the above-described high brightness light emitting device but also in the reflective semiconductor optical amplifier (ROSA).

In order to reduce the light loss, the degree of bending of the curved region II should be gentle. Therefore, in order to secure the inclination angle [theta] of a desired size while bending the curved area II smoothly, the curved area II must be sufficiently long. That is, the length of the device should be long, which has the disadvantage of causing a cost increase.

The present invention provides an optical device capable of reducing the optical loss caused by the bending of the optical waveguide and maintaining the single mode at the same time, and a method of manufacturing the same.

An optical device according to an embodiment of the present invention, the optical waveguide having at least a portion of the curved region; And at least one optical loss reduction region located adjacent to the optical waveguide and operative to prevent optical loss in the optical waveguide.

An optical device manufacturing method according to an embodiment of the present invention comprises the steps of forming an optical waveguide having at least a portion curved region; And forming at least one optical loss reduction region adjacent to the optical waveguide and operative to prevent optical loss in the optical waveguide.

The light emitting device according to the embodiments of the present invention includes an optical loss reduction region having a lower refractive index than the cladding layer in the cladding layer around the optical waveguide curve region, thereby increasing the light output while maintaining a single mode without increasing the length of the device. Can be. That is, by reducing the optical loss caused by the bending of the optical waveguide, it is possible to secure a relatively sufficient light output in the device of the same length, and can reduce the manufacturing cost of the device.

Hereinafter, with reference to the accompanying Figures 2 to 7 will be described in detail a preferred embodiment of the present invention.

2 is a perspective view showing the structure of a high brightness light emitting device 100 according to an embodiment of the present invention. The active layer 101 outputs light of at least one wavelength, and the first and second cladding layers 102a and 102b surrounding the active layer 101 confine the light output from the active layer 101. Both ends of the first cladding layer 102a, the active layer 101, and the second cladding layer 102b stacked on the substrate (not shown) form two cleaved surfaces CP1 and CP2. In this embodiment, the distance between the two cleaved surfaces CP1 and CP2, that is, the length of the high brightness light emitting element is 2.5 mm.

The insulating film 104 and the metal film 105 are sequentially positioned on the second cladding layer 102b. The metal film portion in which the insulating film 104 is not formed between the second cladding layer 102b is an electrode (E). It functions as a function, and electrons can be supplied to the active layer 101.

The electrode E is in contact with a part of the second cladding layer 102b covering the active layer 101, and at least part thereof has a curved area. One end of the electrode E starts at the cleaved surface CP1 and the other end reaches the cleaved surface CP2. In an embodiment of the present invention, the electrode E may have a J shape. One end and the other end of the J-shaped electrode E are in contact with the straight region I and the diagonal region III, respectively, and the straight region I and the diagonal region III are connected to the curved region II. In the embodiment in which the high luminance light emitting device 100 has a length of 2.5 mm, the length of the straight region I of the electrode E having a J shape is 1 mm, and the straight lengths of the curved region II and the diagonal region III are The sum is 1.5 mm. The radius of curvature of the curved region (II) is 10 mm, and the length of the arc with the radius of curvature 10 mm is about 1.2 mm.

The optical waveguide 103 is formed of the second cladding layer 102b, the active layer 101, and the first cladding layer 102a of the portion overlapping with the electrode E to have the same shape as the electrode E. FIG. Therefore, when the electrode E has a J shape as in the above-described embodiment, the waveguide 103 also has a J shape including a straight region I, a curved region II, and an oblique region (III).

As shown in FIG. 2, when the metal film 105 forming the electrode E covers all of the second cladding layer 102b, the second cladding layer 102b and the metal not forming the optical waveguide 103 may be formed. An insulating film 104 is provided to insulate the film 105. That is, the insulating film 104 is formed on the second cladding layer 102b and the light loss reduction region 106 which are not in contact with the electrode E. FIG.

The light loss reduction region 106 positioned in the second cladding layer 102b around the optical waveguide 103 has a lower refractive index than the second cladding layer 102b. Preferably, the light loss reduction region 106 is located in the curved region II of the optical waveguide 103 or in the second cladding layer 102b around the curved region II and the diagonal region III. As such, since the optical loss reduction region 106 having a relatively low refractive index is provided around the curved region II of the waveguide, more light exists in the curved region II having a relatively large difference in refractive index from the outside. . Therefore, the light loss that may occur while passing through the curved region II is reduced, and thus the light output through the diagonal region III can be increased.

2 shows an example in which the light loss reduction region 106 is implemented in one trench form according to an embodiment of the present invention, and FIG. 3 shows the light loss reduction regions 106a to 106d implemented in multiple trenches according to another embodiment. ) The linear distance "s" between the optical loss reduction regions 106 and 106a to 106d shown in FIGS. 2 and 3 and the electrode E (the waveguide 103 under the electrode is 2 µm to 8 µm and the width "W" is 2 More than 1 m, the depth "d" is not less than 1 m, and the sum of the lengths ("Lb" + "Ls") of the curved region II and the diagonal region III of the waveguide 106 ranges from 1 mm to 2 mm. The sizes of, s, W, d, Lb, and Ls are not limited thereto, and various modifications are possible, and in the above-described embodiments, the light loss reduction regions 106 and 106a to 106d are implemented with empty trenches. However, the trench may be filled with a material such as polyimde, etc. In addition, the shape of the light loss reduction regions 106 and 106a to 106d is limited to the rectangular trench shown in FIGS. 2 and 3. The light loss reduction region is formed only on one side of the optical waveguide in the embodiment shown in FIG. It is not limited to this.

In the high luminance light emitting device having a wide wavelength bandwidth, light of a wavelength corresponding to energy levels in a ground state and an excited state is mainly generated. Typically, when designing a waveguide of a high luminance light emitting device, the width of the device, the depth of etching when forming the ridge, and the inclination angle of the curved area are set so that the output light has a wavelength corresponding to the energy level of the excited state. By this design condition, more light having a wavelength different from that of the output light may be lost while passing through the curved area. By providing a light loss reduction region having a relatively low refractive index around the curved region of the waveguide as in the present invention, not only the output light but also the light having a wavelength different from that of the output light have a relatively small refractive index with respect to the outside. Lost.

4 is a schematic view showing an epi structure and an energy level of the high luminance light emitting device 100 shown in FIGS. 2 and 3. According to an embodiment, an n ⁺ -GaAS based compound semiconductor substrate may be used as the substrate sub of the high luminance light emitting device 100.

The active layer 101 includes InGas quantum dots formed by alternately stacked InAs layers and GaAs layers. An active layer according to the present embodiment 101 has the quantum dots of the size of 5 nm In _{0 .15 0 .85} As GaAs obtained by alternately depositing the GaAs and InAs of 38 nm thickness of 0.8 nm in thickness. In this embodiment, the active layer 101 is formed of a multilayer quantum dot layer, and light of about 1.3 mu m wavelength is emitted from each quantum dot layer. According to another exemplary embodiment, the active layer 101 may be implemented as a multilayer quantum dot layer emitting light having different wavelengths. For example, the active layer 101 has a CQD (chirped quantum dot) structure including a quantum dot layer having a wavelength corresponding to recombination energy of electrons and holes having a thickness of 1.2 μm, a quantum dot layer corresponding to 1.25 μm, and a quantum dot layer corresponding to 1.3 μm. ) Can be implemented. The active layer 101 of the quantum dot structure is usually formed using a well-known Stranski-Krastinov (SK) mode or ALE (Atomic Layer Epitaxy) mode.

First geulrae dingcheung (102a) and a second cladding layer (102b) is formed of a thickness of 1.5 ㎛-Al _0.3 Ga _0.7 As layer n and _{p-Al 0 .3 Ga 0 .7} As layers, respectively. When the n ⁺ -GaAs-based compound semiconductor is used as the substrate sub as in the above-described embodiment, the first cladding layer 102a formed on the substrate may include the AlGaAs-based compound semiconductor doped with Si. It can be obtained by growing in a phase.

First candles having the same lattice constant as the cladding layers 102a and 102b between the first cladding layer 102a and the active layer 101, and between the active layer 101 and the second cladding layer 102b, respectively. The grid layer SLa and the second superlattice layer SLb may be further included. In this embodiment the first superlattice layer (SLa) and second superlattice layers (SLb) is formed by alternately stacked 18 times the Al _{0 .3} Ga _{0 .7} As layer and the GaAs layer having a thickness of 2nm, respectively.

According to another embodiment, a first ohmic contact layer (OCLa) between the substrate Sub and the first cladding layer 102a and on the second cladding layer 102b in contact with a metal film (not shown), respectively. ) May further include a second ohmic layer OCLb. In this embodiment, the first ohmic layer OCLa is formed of n-GaAs having a thickness of 500 nm, and the second ohmic layer OCLb is formed of p ⁺ -GaAs having a thickness of 400 nm. The second ohmic layer (OCLb) may be formed by growing a GaAs-based compound semiconductor doped with Zn on the p-type second cladding layer 102b.

The material and thickness of each layer mentioned in the above embodiments are only examples, and the technical scope of the present invention is not limited thereto.

Hereinafter, the light loss reduction effect of the high brightness light emitting device according to the embodiment of the present invention will be described with reference to FIGS. 5 to 7. 5 and 6 are graphs showing characteristics of a high brightness light emitting device having a J-shaped electrode E and a trench-type light loss reducing region shown in FIG. 2. The width | variety of the linear region I of a J-shaped electrode is 6 micrometers. The length of the electrode is 2.5 mm, the length of the linear region is 1 mm, and the sum of the linear lengths (Lb + Ls) of the curved region II and the diagonal region III is 1.5 mm. The radius of curvature of the curved area is 10 mm and the length of the arc with a radius of curvature of 10 mm is about 1.2 mm. The light loss reduction region 106 is a trench having a width W of 20 μm and a depth d of about 1.1 μm, and the trench is located at a distance S from the curve and the oblique region of the electrode E. Located.

5 is a graph showing the current-light characteristics according to the presence or absence of the light loss reduction region and the distance between the electrode and the light loss reduction region of the high luminance light emitting device, and the distance S between the electrode E and the light loss reduction region 106. Are 2, 4, 6, and 8 μm, respectively. When there is a trench (with an optical loss reduction area), at an injection current of 0.8 A, when the distance S between the electrode E and the optical loss reduction area 106 is 8, 6, 4, 2 μm, The light output is 6 mW, 13 mW, 23.5 mW, 27 mW, and it can be seen that the light output rapidly increases as the distance S becomes shorter. At an injection current of 0.8 A, it can be seen that the light output of the high luminance light emitting device without the light loss reduction region (trench) is increased up to 48 times as compared with the case of about 0.56 mW. In addition, the increase in the light output as the distance S decreases means that the light loss reduction effect increases as the trench and waveguide get closer.

6 is a graph showing EL (electroluminescence) spectral characteristics of a high luminance light emitting device. When the current is 100 mA, an EL peak appears around the 1300 nm wavelength. It can be seen that as the current increases, a new EL peak appears around the 1180 nm wavelength. Such characteristics are typical EL characteristics of high-brightness light emitting devices using quantum dots. EL peaks around 1300 nm are based on the energy level in the ground state, and EL peaks around 1180 nm are due to the energy level in the excited state. The full width half maximum (FWHM) of the EL spectrum at the ground state and the excited state was measured at 31 nm and 18 nm, respectively.

FIG. 7 is a graph showing current-light characteristics according to the presence or absence of a light loss reduction region and a distance between an electrode and a light loss reduction region of a high brightness light emitting device having a length of 1.6 mm according to another embodiment of the present invention. The high luminance light emitting device has a J-shaped electrode having a straight region of 1 mm and a curved region and an oblique region of 0.6 mm in length. The radius of curvature of the curved area is 3.5 mm and the length of the arc with a radius of curvature of 3.5 mm is about 0.3 mm. The width of the electrode is 6 mu m. The light loss reduction region is implemented with a trench having a width W of 20 μm and a depth d of about 1.1 μm. FIG. 7 compares the current-optical characteristics of four high-brightness light emitting devices having a distance S between the electrode E and the light loss reduction region 106 of 2, 4, 6, and 8 μm.

In the absence of the trench, the maximum light output is only 0.26 mW, whereas the light output increases when the trench is provided. In addition, the maximum light output was measured from 0.5 mW to 1.2 mW, 3.4 mW and 5 mW while the distance S between the electrode E and the light loss reduction region 106 was reduced to 8, 6, 4, and 2 μm. . In the case of a high brightness light emitting device having a length of 1.6 mm, the intensity of output light is remarkably improved by providing a light loss reducing area as in the case of a high brightness light emitting device having a length of 2.5 mm, and the distance between the light loss reducing area and the waveguide is It can be seen that the shorter the greater the intensity of the output light.

The embodiments and effects of the present invention described above have been described with reference to a high brightness light emitting device, but the present invention can be applied to various types of optical devices having electrodes having curved regions. For example, light that can be realized by forming a high reflection layer on the cleaved surface CP1 adjacent to the linear region I of the electrode among the cleaved surfaces CP1 and CP2 of the high luminance light emitting device shown in FIG. 2 or 3. An amplifier (Reflective Semiconductor Optical Amplifier, ROSA) may also be an embodiment of the present invention. The J-type electrode of the ROSA extends from the high reflection film and has one end portion having a linear region, the other end portion having an oblique region, and a curved region connecting one end portion and the other end portion.

It is to be understood that the above described embodiments are merely illustrative of some of the various embodiments employing the principles of the present invention. It will be apparent to those skilled in the art that various modifications may be made without departing from the spirit of the invention.

Figure 1a is a perspective view showing a schematic structure of a conventional high brightness light emitting device formed by modifying a ridge type laser diode.

Figure 1b is a perspective view showing a schematic structure of a high brightness light emitting device including a conventional J-shaped electrode.

Figure 2 is a perspective view showing a schematic structure of a high brightness light emitting device according to an embodiment of the present invention.

3 is a perspective view showing a schematic structure of a high luminance light emitting device according to an embodiment of the present invention.

4 is a schematic view showing an epi structure and an energy level of the high luminance light emitting device 100 shown in FIGS. 2 and 3.

5 is a graph showing current-light characteristics of a high luminance light emitting device according to the presence or absence of an optical loss reduction region and a distance between an electrode and an optical loss reduction region.

6 is a graph showing EL (electroluminescence) spectral characteristics of the high luminance light emitting device according to the embodiment of the present invention.

7 is a graph showing the current-light characteristics of the high luminance light emitting device according to the presence or absence of the light loss reduction region and the distance between the electrode and the light loss reduction region.

Claims (15)

As an optical element, An optical waveguide at least partially having a curved region; And At least one optical loss reduction region located adjacent to the optical waveguide and operative to prevent optical loss in the optical waveguide Optical device comprising a. The method of claim 1, The optical waveguide has an J shape having a straight region, a curved region and an oblique region. The method of claim 1, The optical waveguide, An active layer for outputting light having at least one wavelength; And A cladding layer adjacent to the active layer, the cladding layer having a first refractive index that constrains light emitted from the active layer. Optical device comprising a. The method of claim 3, The optical loss reduction region has a second refractive index smaller than the first refractive index. The method of claim 4, wherein The optical loss reduction region is an optical device implemented as a trench. The method of claim 3, An optical device further comprises an electrode for supplying a current to the active layer. The method of claim 3, The active layer has a quantum well structure or a quantum dot structure. The optical device of claim 1, wherein the optical device of claim 1 is superluminescent diodes (SLD). The method according to any one of claims 3 to 7, And a reflective film formed on one surface of the cladding layer and the active layer. The method of claim 9, The electrode, An end portion extending from the reflective film and having a linear region; The other end having an oblique area; And An optical element which is a J-shaped electrode having a curved area connecting the one end and the other end. The method of claim 10, The optical device is a reflective semiconductor optical amplifier (ROSA). Forming an optical waveguide at least partially having a curved region; And Forming at least one optical loss reduction region located adjacent to the optical waveguide and operative to prevent optical loss within the optical waveguide Optical device manufacturing method comprising a. The method of claim 12, The optical waveguide, An active layer for outputting light having at least one wavelength; And A cladding layer adjacent to the active layer, the cladding layer having a first refractive index that constrains light emitted from the active layer. Optical device manufacturing method comprising a. The method of claim 13, The optical loss reduction region has a second refractive index smaller than the first refractive index. The method according to any one of claims 12 to 14, Forming the light loss reduction region, Etching the cladding layer to form a trench.

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