JP2000275444A - Light emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an incoherent light source high in luminance by exciting a phosphor with semiconductor laser beam guided through a fiber-type light wave guide path and taking out luminescence by the phosphor to outside of the fiber-type light wave guide path. SOLUTION: Light emitted from a semiconductor laser 10 is collected onto an end surface of an optical fiber through a lens 11 and guided to a core portion 13. Reflection films 15, 16 are formed on the end surface of the optical fiber 12. Phosphor 17 is added to a clad 14 of the optical fiber 12. Because a part of semiconductor laser light (wavelength λ1) guided into the optical fiber 12 penetrates into the clad 14, the phosphor 17 emits light (luminescent center wavelength λ2) using the laser light as exciting light. This light is taken out of an outgoing end surface of the optical fiber 12. At this time, the oscillation wavelength λ1 of the semiconductor laser 10 as the exciting light and the luminescent wavelength λ2 of the phosphor must satisfy the relation λ1< λ2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a light emitting device used as a light source.

[0002]

2. Description of the Related Art Solid state light emitting devices such as light emitting diodes (LEDs) are used as light sources for display devices and traffic signals. In such an application, a high-efficiency and low-cost device is required together with high reliability of the device. Although LEDs have higher reliability than conventional light bulbs and fluorescent tubes, they have the following problems. That is,
When an LED molded in a resin package is viewed as a light source, the area of the light emitting portion is relatively large, and the parallelism of emitted light is poor. For this reason, when collimating LED light using an optical system or trying to narrow down to an extremely small spot, it is not possible to use all of the emitted light, and the available light output is greatly reduced. There is. On the other hand, for example, if a semiconductor laser is used, highly efficient collimated light or a very small spot can be obtained. However, in the case of a semiconductor laser, since it is coherent light,
There is a problem of safety and the like when used for a light source of a display device or the like.

Another problem with LEDs is that high-power light emission over a large area is difficult. The driving current of the LED is usually as small as about 20 mA, and a high output light source cannot be obtained with one LED. If the LED chip is made large, a certain high-output light emission can be obtained, but the temperature inside the chip rises remarkably, and there is a limit to the large area.

[0004]

As described above, when a solid-state light emitting device such as an LED is used as a light source, it is difficult to obtain a point light source having a high luminance, and it is difficult to obtain high output light emission in a large area. There was a problem.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an incoherent light source having high luminance.

[0006]

The gist of the present invention is to realize a light source with high efficiency and high brightness by exciting a phosphor added to a fiber with a laser beam.

That is, the present invention comprises a semiconductor laser and a fiber-type optical waveguide doped with a fluorescent substance. The fluorescent substance is excited by the semiconductor laser light guided through the fiber-type optical waveguide to emit light by the fluorescent substance. It is characterized by being taken out of the fiber type optical waveguide.

Further, the present invention is characterized in that a reflecting mirror is provided on the emission end face of the fiber-type optical waveguide, the reflecting mirror having high reflection with respect to the wavelength of the semiconductor laser light and low reflection with respect to the emission wavelength of the phosphor. And

Further, the present invention is characterized in that a reflecting mirror which is highly reflective with respect to the emission wavelength of the phosphor is provided on the semiconductor laser light incident end face of the fiber type optical waveguide.

The present invention is also characterized in that the semiconductor laser is made of a compound semiconductor containing nitrogen.

According to the present invention, high-output incoherent light having a small light-emitting area can be obtained. Further, according to the present invention, high-output incoherent light emitting in a large area can be obtained.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the illustrated embodiments.

FIG. 1 is a diagram showing a schematic configuration of a light emitting device according to a first embodiment of the present invention. In the figure, 10 is a semiconductor laser, 11 is a lens, and 12 is an optical fiber. Light emitted from the semiconductor laser 10 is condensed on the end face of the optical fiber by the lens 11 and guided to the core 13. The lens 11 may be in various forms. For example, a sapphire ball lens or the like can be used. Reflection films 14 and 15 are formed on the end face of the optical fiber 12. The phosphor 17 is added to the cladding 14 of the optical fiber. Since a part of the semiconductor laser light (wavelength λ ₁ ) guided in the optical fiber seeps into the cladding 14, the phosphor 17 emits light using this light as excitation light (emission center wavelength λ ₂ ). . This light is emitted from the output end face of the optical fiber 12 (right side in the figure).
Is taken out to the outside.

It is necessary that the oscillation wavelength λ ₁ of the semiconductor laser 10 and the emission wavelength λ _{2 of the} phosphor as excitation light satisfy the following relationship.

(Equation 1) As a semiconductor laser, for example, a blue laser using InGaN as an active layer (wavelength λ ₁ = 390 to 430 nm) or an ultraviolet laser using GaN as an active layer (wavelength λ ₁ = 360)
380 nm). Further, a GaAlBN laser having a shorter wavelength may be used.

As the phosphor to be added, any of phosphors having emission peak wavelengths of red, green and blue may be added, or three kinds may be added simultaneously. In the former case, monochromatic light emission with a narrow spectrum width, that is, excellent color purity, is obtained, and in the latter case, a white light source is obtained.

In this embodiment, the phosphor is added to the cladding of the optical fiber. However, the phosphor may be added to the core having a large excitation light confinement coefficient, or may be added to both the core and the cladding. Good.

Here, the excitation light wavelength λ ₁ of the reflection films 14 and 15 is
Let r ₁ , r _{2 be} the reflectivities of the phosphors, and let t ₁ , t ₂ be the transmissivities of the phosphors for the emission wavelength λ ₂ , respectively, between the incident excitation light output P ₁ and the emitted visible light output P ₂ There is the following relationship:

(Equation 2)

(Equation 3)

(Equation 4) Here, η is the coupling efficiency of the excitation light to the optical fiber, γ is the conversion efficiency of the excitation light to the visible wavelength by the phosphor, and a is the ratio of loss other than conversion to the visible wavelength.

It is desirable that the reflectivity of the reflection film 15 is high for the excitation light and low for the emission visible wavelength. The most desirable state is perfect reflection for λ _{1 and} perfect transmission for λ ₂ . That is,

(Equation 5) Further, it is desirable that the reflectivity of the reflection film 14 is high with respect to the emission visible wavelength. Most preferably

(Equation 6) It is. It is easy to set the reflectivity of each reflection film independently for the _two wavelengths λ ₁ and λ ₂ by using a multilayer film.

When r ₁ is close to 0, that is, when the film is a non-reflection film for excitation light, a resonator for laser light is formed by the laser and the optical fiber. When r ₁ is a value between 0 and 1, the optical fiber functions as an external resonator for semiconductor laser light. In this case, the impedance matching condition (the condition that the reflection becomes 0) as the external resonator is given by the following equation.

(Equation 7) If (5) and (7) hold, (2),
(3) _{P 2} from the equation is given by the following equation.

(Equation 8) For example, if η = 0.5, γ = 0.5, and a = 0.1,
P ₂ = 0.31P ₁ becomes, so that the conversion efficiency of about 30% as a whole is obtained.

A feature of this embodiment is that incoherent visible light can be extracted from a minimum region. This is because, in FIG. 1, light of λ ₂ is emitted from the end face of the fiber.

FIG. 2 is a diagram showing a schematic configuration of a light emitting device according to a second embodiment of the present invention. In the figure, 20 is a semiconductor laser, 21 is a lens, and 22 is an optical fiber. The basic part of this embodiment is the same as that of FIG. The difference from FIG. 1 is that the core of the optical fiber is 2
3 and 24 are doubled. The relationship between these refractive indices is shown on the right side of the figure. Phosphor 28 is added to the outer core. Thereby, the visible light by the phosphor is guided through the core 24 and emitted from the end face,
Incoherent visible light can be emitted from a region smaller than in the first embodiment.

The emitted light can be easily collimated into a parallel light or focused on a minimum spot by using a lens.

FIG. 3 shows an embodiment according to the third embodiment of the present invention.
FIG. 2 is a diagram illustrating a schematic configuration of an optical device. 30 is a semiconductor laser in the figure.
31 is a lens, 32 is an optical fiber to which a phosphor is added.
Reference numeral 33 denotes a collimation lens. In this embodiment
Use diffraction gratings 34 and 35 in place of the reflection film.
The excitation light (wavelength)
λ ₁) Are formed.

FIG. 4 is a sectional view showing a schematic configuration of a light emitting device according to a fourth embodiment of the present invention. This figure shows a cross section of an optical fiber doped with a phosphor. In the figure, 40 is an optical fiber, and 41 is a reflection film. A metal film, a dielectric multilayer film, or the like can be used as the reflection film.

In the present embodiment, the structure is such that visible light from the phosphor is emitted from the side of the fiber.
By providing the reflection film 41, light is emitted only to one side.

FIG. 5 is a diagram showing a schematic configuration of a light emitting device according to a fifth embodiment of the present invention. In the figure, reference numeral 50 denotes a semiconductor laser, 51 denotes a lens, 52 denotes an optical fiber coupler (star coupler), and 53 denotes a fiber array to which a phosphor is added.

In this embodiment, the light emitted from the semiconductor laser 51 is condensed by a lens 51 and branched by an optical fiber coupler 52 into a fiber array. The cross section of each fiber of the fiber array is, for example, as shown in the embodiment of FIG. 4, and visible light is emitted upward from the side surface of the fiber.

In the present embodiment, a surface light source of visible light can be obtained. For example, if three types of phosphors, red, green and blue, are used to emit white light, the phosphor can be used as a liquid crystal backlight. be able to.

[0029]

As described in detail above, according to the present invention,
High output incoherent light with a small light emitting area can be obtained. Further, according to the present invention, high-output incoherent light emitting in a large area can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a schematic structure of a light emitting device according to a first embodiment.

FIG. 2 is a sectional view showing a schematic structure of a light emitting device according to a second embodiment.

FIG. 3 is a perspective view showing a schematic structure of a light emitting device according to a third embodiment.

FIG. 4 is a sectional view showing a schematic structure of a light emitting device according to a fourth embodiment.

FIG. 5 is a perspective view showing a schematic structure of a light emitting device according to a fifth embodiment.

[Explanation of symbols]

 10, 20, 30, 50 --- Semiconductor laser 11, 21, 31, 33, 51 --- Lens 12, 22, 32, 40 --- Optical fiber 13, 23 --- -Core 14, 25----Clad 15, 16, 26, 27-Reflective film 17, 28, 42-Phosphor 53---Fiber array

Claims (4)

[Claims] 1. A semiconductor laser comprising: a semiconductor laser; and a fiber-type optical waveguide doped with a fluorescent material. The fluorescent material is excited by the semiconductor laser light guided through the fiber-type optical waveguide, and the light emitted by the fluorescent material is emitted by the fiber-type optical waveguide. A light emitting device, which is taken out of the wave path. 2. An emission end face of the fiber-type optical waveguide is provided with a reflecting mirror which reflects high the wavelength of the semiconductor laser light and low reflects the emission wavelength of the phosphor. Item 2. The light emitting device according to item 1. 3. The light-emitting device according to claim 1, wherein a reflecting mirror which is highly reflective to an emission wavelength of the fluorescent material is provided on a semiconductor laser light incident end face of the fiber type optical waveguide. apparatus. 4. The light emitting device according to claim 1, wherein the semiconductor laser is made of a compound semiconductor containing nitrogen.