JP2008283003A - Visible light-emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light-emitting device which can emit light, having superior stability and high luminance and which can be made compact. <P>SOLUTION: A visible light-emitting device comprises a first semiconductor light-emitting element for emitting visible light and a first semiconductor optical amplifier for amplifying output light from the first semiconductor light-emitting element. The first semiconductor light-emitting element emits a green light, and the first semiconductor optical amplifier amplifies the green light. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a visible light emitting device that outputs visible light, for example, a visible light emitting device using a semiconductor laser (LD: Laser Diode) or a light emitting diode (LED: Light Emitting Diode).

  As a backlight light source of a liquid crystal display which is one of visible light emitting devices, there is one using LEDs. The reason why the LED is used instead of the conventional cold cathode discharge lamp (CCFL) is that the LED is composed of three primary colors (RGB: Red / Green / Red / R), Green (G), and Blue (B). This is because a narrow emission wavelength band that matches the wavelength of the blue color filter can be selected, and miniaturization and longevity are possible.

The emission wavelength band of the LED can be controlled by changing the material of the active layer (light emitting layer) of the LED chip and its crystal composition.
From yellow green to red, a quaternary mixed crystal of aluminum, gallium, indium, phosphorus ((Al _X Ga _1-X ) _0.5 In _0.5 P) is used, and this aluminum, gallium, indium, phosphorus ((Al _{X Ga 1-X) 0.5 in} 0.5 P) system (hereinafter, the LED of to as AlInGaP-based), it is possible to adjust the emission wavelength by changing the Al composition x.

The green blue, using a ternary mixed crystal of gallium indium nitride _{(ln X Ga 1-X N} ) , the gallium indium nitride _{(ln X Ga 1-X N} ) system (hereinafter, InGaN-based The light emission wavelength can be adjusted by changing the indium composition x.
In this way, the LCD backlight using LEDs can improve its color reproducibility.

By the way, in the spectrum of natural light such as sunlight, green near the center of the visible region is large, and blue and red at the end of the visible region are small. Human visibility is also high in green. For this reason, in order to reproduce the color, high luminance is required in the green wavelength band. In general, the brightness of green needs to be five times higher than that of red or blue.
However, in an LED, the emission efficiency of green (InGaN-based) is determined by its material characteristics, and the luminous efficiency is lower than that of red (AlInGaP-based) and blue (InGaN-based). In other words, since the characteristics are actually opposite to those required, two or more green LEDs are used (RGGB method) when all the three primary colors of RGB are covered by direct light emission of LEDs. For this reason, the size of the light emitting device increases depending on the arrangement of the plurality of green LEDs.

Apart from this, some projectors use an optical engine using RGB semiconductor lasers as a light source. The reason for using the semiconductor laser is that it requires high-power beam light with good directivity. Also in this case, as the blue and green semiconductor lasers, those using a ternary mixed crystal of gallium, indium, nitride (ln _X Ga _1-X N) can be considered as in the LED.

However, since this InGaN-based semiconductor laser is particularly green and has low luminous efficiency, it cannot be put into practical use by itself.
In general, an lnGaN-based material has no problem in its lifetime if the current density is relatively small as in an LED, but a semiconductor laser that concentrates current in a narrow stripe region has an oscillation threshold density of 3 [kA / cm. ² ] Since a high current density is required, there is a problem in reliability (life) when trying to perform a high output operation.

Therefore, for green, in particular, a technique such as a fiber laser or SHG (Second Haromonic Generation) is used without using an lnGaN semiconductor laser.
However, these techniques have poor luminous efficiency. In addition, a fiber laser requires a fiber wound with several tens of [cm] or more, and the SHG technology requires a several [cm] SHG crystal. Will grow in size.

Next, as an LED that outputs white light, there is one that excites a phosphor with a blue LED (see, for example, Patent Document 1). As an example, there is an LED package in which a yellow phosphor is mixed. Such white LEDs are not suitable for LCD backlight light sources that require color reproducibility, but have been put to practical use in inexpensive backlights and general lighting.
Also in this case, in order to realize a point light source, it is conceivable to use a blue semiconductor laser in place of the blue LED and excite phosphors concentrated in a narrow area. However, a high-power semiconductor laser has a problem in reliability.
Further, when the current is concentrated in the stripe region of one semiconductor laser, the heat generation in a narrow region is extremely large, and thus the reliability is further adversely affected.

  Also, when the light intensity in the waveguide (resonator) of the semiconductor laser increases, the waveguide mode tends to become unstable due to the spatial hole burning effect or the like.

In addition, the semiconductor laser emits output from both the front and rear end faces. Actually, it wants to increase the light output from one direction, that is, the front (front), and the output from the rear (rear) is monitored (detected). It is not necessary except for use as light). However, due to its structure, it is difficult to increase the output in only one direction.
Although there is a method of providing a highly reflective film on the rear surface, since the light distribution in the axial direction becomes non-uniform, the waveguide mode tends to become more unstable.

As described above, in the case of using a semiconductor laser which is a spatial light source and is a point light source, there is a problem that it is difficult to increase the output due to the invention due to the high current density and the instability of the waveguide mode. This problem is conspicuous in crystal-defective InGaN blue semiconductor lasers or green semiconductor lasers.
In addition, with only a semiconductor laser, there is a problem that it is difficult to improve the light emission efficiency by providing a difference in the output before and after the waveguide stripe and increasing the output only at the front.
Furthermore, when a fiber laser or SHG is used instead of the LED or the semiconductor laser, there is a problem that the size of the light emitting device increases.
JP 2004-363635 A

  The present invention provides a light emitting device capable of stably obtaining a high-brightness light output and reducing the size of the device. Furthermore, a light emitting device capable of obtaining a predetermined chromaticity is provided.

  According to one aspect of the present invention, a first semiconductor light emitting element that emits visible light and a first semiconductor optical amplifier that amplifies output light from the first semiconductor light emitting element are provided. A visible light emitting device is provided. In the present specification, “visible light” includes near-ultraviolet light that can excite a phosphor that emits visible light.

  According to the present invention, it is possible to provide a visible light emitting device that can obtain high-luminance light emission with excellent stability and a small device size.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the visible light emitting device according to the embodiment of the present invention, a semiconductor optical amplifier (SOA) is provided on the output side of the semiconductor laser, and the output from the semiconductor laser is amplified by the SOA.

  FIG. 1 is a diagram illustrating a configuration of a visible light emitting device according to a first embodiment of the present invention. The visible light emitting device according to the first embodiment includes a semiconductor laser 1 that emits green light, and a semiconductor optical amplifier (SOA) 5 that has a gain spectrum at a green wavelength that is the emission wavelength of the semiconductor laser 1. It is equipped with.

  The front surface of the semiconductor laser 1 (the surface on the output side of the emitted light) and the rear surface of the SOA 5 (the surface on which the output light from the semiconductor laser 1 is incident) of the SOA 5 are brought close to each other. The semiconductor laser 1 and the SOA 5 are arranged.

FIG. 2 is a perspective view showing a configuration example of the semiconductor laser 1.
The semiconductor laser shown in FIG. 2, by using the ternary mixed crystal of gallium indium nitride _{(ln X Ga 1-X N} ), it is obtained by adjusting the emission wavelength to green by changing the indium composition x .

This InGaN-based (InGaN / AlGaN-based) semiconductor laser has an n-type GaN layer 20, an n-type AlGaN cladding layer 21, an ln _X Ga _1-X N MQW (Multi-Quantum) on the surface of the n-type GaN substrate 12. An active layer (light emitting layer) 30 having a well structure, an n-type AlGaN cladding layer 22 and a p-type GaN layer 40 are sequentially grown to form a stacked structure shown in FIG. A GaN substrate is expensive, but has a low defect density and good cleavage. For this reason, recently, an n-type GaN substrate is used without using a sapphire substrate or a SiC substrate.

Further, in order to form a waveguide structure, a part of the n-type AlGaN cladding layer 22 on the p-type GaN layer 40 side is removed to leave the mesa stripe 200 (this structure is a “ridge waveguide”). Etc.). On both sides of the mesa stripe 200, an insulating oxide film such as SiO ₂ is deposited for flattening and current blocking, and BCB (Benzocyclobutene) resin or the like is further provided (the composite layer of both is designated as 210). . Finally, the p-electrode 100 is formed on the surface of the p-type GaN layer 40 and the n-electrode 110 is formed on the back surface of the n-type GaN substrate 12. A gold wire 120 is bonded to the p electrode 100.

FIG. 3 is a perspective view showing a configuration example of the SOA 5.
The SOA shown in FIG. 3 has basically the same layer structure as the InGaN-based green semiconductor laser shown in FIG. That is, an n-type GaN layer 20a, an n-type AlGaN cladding layer 21a, an active layer 30a, an n-type AlGaN cladding layer 22a, and a p-type GaN layer 40a are sequentially grown on the surface of the n-type GaN substrate 12a to obtain a mesa stripe 200a. Both sides of the (ridge waveguide) are filled with a composite layer 210a such as an oxide film and BCB resin to form a p-electrode 100a and an n-electrode 110, and a gold wire 120a is bonded to the p-electrode 100a.

The active layer 30a, similar to the light emitting layer 30 shown in FIG. 2, which forms a MQW structure of ln X _Ga 1-X _N, so as to have a spectral gain to wavelength of the green output from the green semiconductor laser of FIG. 2 (To amplify the green wavelength), the indium composition x is adjusted. Thereby, the gain spectrum of the SOA can be matched with the emission wavelength of the semiconductor laser.

  However, unlike the semiconductor laser 1, dielectric anti-reflection (AR) coatings 300 and 301 are applied to both cleaved end faces before and after the SOA 5. Since these AR coatings 300 and 301 can reduce the reflectance to 1 [%] or less, optical feedback from both reflection end faces becomes small, and laser oscillation is difficult even when current is applied.

  As shown in FIG. 1, the green-emitting semiconductor laser 1 and the SOA 5 having a green gain are arranged on the substrate 10 so that the waveguide stripes thereof face each other closely. Thereby, efficient optical coupling can be realized.

  The insertion graph in FIG. 1 is a graph showing the light intensity distribution in the SOA 5. As shown in this graph, the green light emitted from the semiconductor laser 1 and incident on the waveguide of the SOA 5 is amplified by gain while being guided, and has a relative light intensity stronger than that emitted from the semiconductor laser 1. Green light is output from the SOA 5.

  Generally, in order to obtain a large gain in the SOA, a large amount of current is passed or the waveguide length is increased. However, since the current density is likely to deteriorate due to crystal defects, a method of increasing the waveguide length is adopted.

  For example, when the resonator length of the semiconductor laser 1 is 300 [μm], the waveguide length of the SOA 5 is 600 [μm] or more. Since the waveguide length of the SOA 5 is about several [mm] even if it is sufficiently long, the size of the entire light emitting device can be made considerably smaller than that of a conventional fiber laser or SHG. Although a plurality of SOAs can be arranged in multiple stages, it is more effective to increase the waveguide length because an optical coupling loss occurs at the coupling part of each stage.

  Further, in the SOA 5 waveguide, the guided light is simply amplified as a traveling wave, so that oscillation mode stability can be obtained. In addition, since the output light (emitted light) from the SOA 5 is guided light, narrow directivity can be maintained.

  In addition, since the current flowing through the semiconductor laser 1 can be kept low and the current flowing through the SOA 5 can be increased, the front output of the semiconductor laser 1 can be preferentially amplified, which is efficient. That is, with the semiconductor laser alone, it is difficult to increase the efficiency only at the front because it is difficult to provide a difference between the outputs on the front and rear sides of the resonator (waveguide stripe), but by providing the SOA 5, the efficiency only at the front can be improved. .

  As described above, according to the first embodiment, by providing the SOA 5 on the front surface of the semiconductor laser 1, high-luminance green light with excellent stability can be obtained and a compact light emitting device is provided. it can.

FIG. 4 is a diagram illustrating a configuration of a visible light emitting device according to the second embodiment of the present invention.
The visible light emitting device of the second embodiment includes a blue-emitting semiconductor laser 2 and an SOA 6 having a gain spectrum at a blue wavelength that is an emission wavelength of the semiconductor laser 2.

  The light emitting device of the second embodiment shown in FIG. 4 is obtained by changing the light to be amplified from green to blue light emission in the light emitting device of the first embodiment shown in FIG. In other words, the semiconductor laser 1 emitting green light is changed to the semiconductor laser 2 emitting blue light, and the SOA 5 having a gain spectrum in green is changed to the SOA 6 having a gain spectrum in a blue wavelength. The arrangement positional relationship between the semiconductor laser 2 and the SOA 6 is the same as that of the semiconductor laser 1 and the SOA 5 in the first embodiment.

  One configuration example of the semiconductor laser 2 is a semiconductor laser having the structure shown in FIG. 2, in which the emission wavelength is adjusted to blue by changing the indium composition x. Further, in the SOA 6 having the structure shown in FIG. 3, the indium composition x is adjusted so that the blue wavelength has a spectral gain (amplifies the blue wavelength).

  As shown in the insertion graph of FIG. 4, the blue light emitted from the semiconductor laser 2 and incident on the waveguide of the SOA 6 is amplified with gain while being guided, and is more relative light than the emitted light from the semiconductor laser 2. Intense blue light is output from the SOA 6.

  As described above, according to the second embodiment, by providing the SOA 6 on the front surface of the semiconductor laser 2, high-luminance blue light having excellent stability can be obtained as in the first embodiment. And a compact light emitting device can be provided.

  The semiconductor laser 2 of the second embodiment may output any wavelength light from blue to near ultraviolet. In this case, the SOA 6 has a gain spectrum for blue light or near ultraviolet light output from the semiconductor laser 2.

  FIG. 5 is a plan view (top view) showing the configuration of the visible light emitting device according to the third embodiment of the present invention. 5 and the subsequent drawings, the same elements as those described with reference to the previous drawings are denoted by the same reference numerals, and detailed description thereof is omitted.

  The light emitting device of the third embodiment shown in FIG. 5 includes a light emitting unit 400, a semiconductor laser / SOA drive unit IC (drive unit) 600, and a wiring 500 that electrically connects these units. ing.

  The light emitting unit 400 includes a green emitting semiconductor laser 1, a blue or near ultraviolet (hereinafter referred to as blue) emitting semiconductor laser 2, a red emitting semiconductor laser 3, an SOA 5 having a gain spectrum at a green wavelength, SOA 6 having a gain spectrum at a blue wavelength or near ultraviolet wavelength, photodetectors (photodiodes) 401, 402, 403 for monitoring the optical output of each semiconductor laser, half mirrors 501, 502, and each half Photodetectors (photodiodes) 404 and 405 for monitoring the reflected light of the mirror are provided on the substrate 10. The stripes 1a, 2a, 3a, 5a, 6a at the center in the longitudinal direction of the respective semiconductor lasers and SOAs schematically show the waveguide portions.

  The light-emitting unit 400 includes a combination of a green light semiconductor laser 1 and an SOA 5, a blue light or near ultraviolet light semiconductor laser 2 and an SOA 6, and three primary color RGB emitters composed of a red light semiconductor laser 3. It is configured as one light emitting unit.

  The red semiconductor laser 3 uses, for example, an AlInGaP-based (AlInGaP / GaAs-based) material, has few defects, and has a high output product for DVD writing or the like, so there is no need to arrange an SOA in front of it. .

  The photodetectors 401, 402, and 403 are provided on the rear surfaces of the respective semiconductor lasers 1, 2, and 3, detect the rear light emission output of each semiconductor laser, and output the monitor output (detection signal) to the drive unit. 600 respectively.

  FIG. 6 is a block diagram for explaining automatic power control (APC: Automatic Power Control) by the drive unit 600 in the visible light emitting apparatus according to the third embodiment of the present invention.

  As illustrated in FIG. 6, the drive unit 600 includes a green light control unit 601, a blue light control unit 602, and a red light control unit 603. The driving unit 600 performs automatic power control on the final RGB output of the light emitting unit 400 independently for each color in accordance with the detection signal input from the light emitting unit 400. That is, the output of the semiconductor laser 3 is directly controlled for red (R), the output of the semiconductor laser is controlled to a constant value for each of green (G) and blue (B), and the final light output is controlled. Earn the shortfall by adjusting the SOA gain.

  The red light control unit 603 controls the drive current Ire of the red semiconductor laser 3 in accordance with the detection signal Sre from the photodetector 403, thereby controlling the red light output.

  For green (G), the green light control unit 601 adjusts the drive current Igr1 of the green semiconductor laser 1 according to the detection signal Sgr1 from the light detector 401, and sets the monitor output of the green semiconductor laser 1 to a constant value. At the same time, the applied current Igr2 of the SOA 5 is adjusted in accordance with the detection signal Sgr2 from the photodetector 404 to control the amplification gain of the SOA 5, thereby controlling the final green light output.

  Similarly, the blue light control unit 602 controls the monitor output of the blue semiconductor laser 2 to a constant value by adjusting the drive current Ibl1 of the blue semiconductor laser 2 in accordance with the detection signal Sbl1 from the photodetector 402. The applied current Ibl2 of the SOA 6 is adjusted according to the detection signal Sbl2 from the photodetector 402 to control the amplification gain of the SOA 5, thereby controlling the final green light output.

  The half mirrors 501 and 502 and the photodetectors 404 and 405 will be described. The gain spectra of the SOAs 5 and 6 themselves also have temperature characteristics, and there are variations in optical coupling with the semiconductor laser, so that it is difficult to precisely control the final light output. Therefore, half mirrors 501 and 502 whose transmittance is much larger than the reflectance and whose transmission / reflection ratio is determined are respectively installed on the front surfaces (output surface side) of the SOAs 5 and 6, and the reflection of these half mirrors. The light is monitored by photodetectors 404 and 405 installed beside the half mirror. The drive unit 600 controls the current applied to the SOAs 5 and 6 based on these monitor outputs (detection signals), whereby the final light output intensity from the SOAs 5 and 6 can be controlled with high precision.

  As described above, according to the third embodiment, high-luminance red light, green light, and blue light with excellent stability can be obtained, and a compact white or mixed-color light emitting device can be provided. Chromaticity can be adjusted with high accuracy by individually controlling the emission of light, green light, and blue light.

  FIG. 7 is a plan view (top view) showing the configuration of the visible light emitting device according to the fourth embodiment of the present invention. The light emitting device of the fourth embodiment shown in FIG. 7 is the light emitting device of the second embodiment (see FIG. 4), in which a wavelength conversion material 700 is provided on the front surface (light output side) of the SOA. It is.

  As the wavelength conversion material 700, for example, a yellow phosphor such as YAG (Yttrium Aluminum Garnet) is used. The blue light output with a narrow emission angle from the semiconductor laser 2 is efficiently input to the wavelength conversion material 700, and the yellow light emission from the wavelength conversion material 700 and the blue light emission from the semiconductor laser 2 are mixed together, resulting in a high brightness pseudo A white output can be obtained. Further, by changing the type of phosphor, for example, by using a green phosphor or a red phosphor, a green or red spectrum can be obtained, and a high luminance light output with a desired chromaticity can be obtained.

  Further, as the wavelength conversion material 700, a composite ceramic crystal (MGC) may be used in addition to the phosphor material. In MGC, a single crystal phase in which a single crystal is doped with a rare earth element having a wavelength conversion function and a transparent single crystal phase having a refractive index close to each other are intertwined without gaps, and each phase is connected as a crystal body. Bending, branching, reconnecting and having a continuous structure. Therefore, a simple phosphor is similar in structure and is not. In addition to the binary MGC (binary MGC) having two types of phases as described above, there are three-way MGC (ternary MGC) and four-way MGC (quaternary MGC) having three or more phases. Can also be used.

  As described above, according to the fourth embodiment, the wavelength conversion material 700 is provided at the subsequent stage (front light output side) of the semiconductor optical amplifier, so that the chromaticity of visible light can be adjusted efficiently. Therefore, it is possible to obtain a light emitting device that emits high-luminance white light or desired mixed color light.

  In the above-described embodiment of the present invention, the semiconductor light emitting element has been described by taking an InGaN semiconductor laser as an example for green or blue and an AlInGaP semiconductor laser as an example for red. This is because the semiconductor laser has a sharp directivity, and is easily coupled efficiently with the SOA waveguide. However, the semiconductor light emitting device according to the present invention may be an LED (end face light emitting type or top surface light emitting type). In this case, it is desirable to use an LED package in which an LED chip is embedded in a resin lens, or to provide an external lens to sharpen directivity. As the green or blue LED, for example, an InGaN-based LED (top emission type) shown in FIG. 8 or FIG. 9 may be used.

8 includes an n-type GaN layer 20, an active layer (light-emitting layer) 30 having an MQW (Multi-Quantum Well) structure of ln _X Ga _1-X N, and a p-type GaN layer on the surface of the sapphire substrate 13. 40 is grown sequentially.
9 includes an n-type GaN layer 20, an active layer (light emitting layer) 30 having an MQW structure of ln _X Ga _1-X N, and a p-type GaN layer 40 on the surface of the n-type SiC substrate 14. , Are grown sequentially. In the embodiment of the present invention, these LEDs can also be used.

It is a side view showing the structure of the visible light light-emitting device concerning the 1st Embodiment of this invention. It is a perspective view which shows the structural example of the semiconductor laser concerning embodiment of this invention. 1 is a perspective view showing a structural example of a semiconductor optical amplifier according to an embodiment of the present invention. It is a side view showing the structure of the visible light light-emitting device concerning the 2nd Embodiment of this invention. It is a top view showing the structure of the visible light light-emitting device concerning the 3rd Embodiment of this invention. It is a block diagram explaining the automatic power control (APC) in the visible light light-emitting device concerning the 3rd Embodiment of this invention. It is a top view showing the structure of the visible light light-emitting device concerning the 4th Embodiment of this invention. It is a perspective view which shows the structural example of the other semiconductor light-emitting device concerning embodiment of this invention. It is a perspective view which shows the structural example of the other semiconductor light-emitting device concerning embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Green semiconductor laser, 2 Blue semiconductor laser, 3 Red semiconductor laser, 5 Green semiconductor optical amplifier (green SOA), 6 Blue semiconductor optical amplifier (blue SOA), 10 Substrate,
12 n-type GaN substrate, 13 sapphire substrate, 14 SiC substrate, 20, 20a n-type GaN layer, 21, 21a, 22, 22a n-type AlGaN cladding layer, 30 active layer (light emitting layer), 30a active layer, 40, 40a p-type GaN layer, 100, 100a p electrode, 110, 110a n electrode, 120, 120a gold wire, 200, 200a mesa stripe, 300, 301 non-reflective coating, 400 light emitting unit, 401, 402, 403, 404, 405 light Detector, 500 wiring, 501,502 half mirror, 600 drive unit, 601 green light control unit, 602 blue light control unit, 603 red light control unit, 700 wavelength conversion material, Ibl1 blue semiconductor laser drive current, Ibl2 blue SOA application Current, Igr1 Green Semiconductor laser drive current, Igr2 Green SOA application current, Ire red semiconductor laser drive current, Sbl1 blue semiconductor laser detection signal, Sbl2 blue SOA detection signal, Sgr1 green semiconductor laser detection signal, Sgr2 green SOA detection signal, Sre red semiconductor laser detection signal

Claims (6)

A first semiconductor light emitting element that emits visible light;
A first semiconductor optical amplifier that amplifies output light from the first semiconductor light emitting element;
A visible light emitting device comprising: The first semiconductor light emitting element emits green light,
The visible light emitting device according to claim 1, wherein the first semiconductor optical amplifier amplifies the green light. The first semiconductor light emitting element emits blue light or near ultraviolet light,
The visible light emitting device according to claim 1, wherein the first semiconductor optical amplifier amplifies the blue light or near ultraviolet light. A second semiconductor light emitting element that emits visible light having a wavelength different from that of the visible light;
First control means for controlling at least one of a light emission output of the first semiconductor light emitting element and an amplification gain of the semiconductor optical amplifier;
Second control means for controlling the light emission output of the second semiconductor light emitting element;
The visible light emitting device according to claim 1, further comprising:   The visible light emitting device according to claim 1, further comprising wavelength conversion means for converting a wavelength of output light of the first semiconductor optical amplifier.   The visible light emitting device according to claim 1, wherein the semiconductor light emitting element is a semiconductor laser.

Images