JPS5943838B2 - blue light emitting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a compact blue light emitting device, particularly
The present invention relates to a device that combines a semiconductor laser typified by al-xAlxAs and a thin film optical waveguide to generate optical nonlinear interaction within the optical waveguide to obtain blue light emission.

Optoelectronics has made remarkable progress, and lasers in particular have undergone much research and development since their appearance, and have been applied in a wide variety of fields.

Furthermore, in recent years, applications in optical communications and optical information processing are expected. When considering these future applications, it is important to solidify elements and devices in the field of optoelectronics.
Miniaturization and integration must be promoted.

These efforts are currently progressing steadily, although they cannot be said to be sufficient.

Optical fibers as transmission lines are at the practical stage, and research is being actively conducted on solid-state, miniaturization, and integration of light receiving elements and optical circuit elements.

In particular, the fact that semiconductor lasers as light emitting sources are at the stage of practical use makes the future of optical applications bright.

However, at present, the wavelength range that can be obtained as a pn junction type semiconductor laser operating at room temperature that can be used practically is about 700 nm.
Regarding blue light emission with a short wavelength of 0λ to 9000λ, it is not easy to make a light emitting diode, and it is extremely difficult to realize a blue oscillation semiconductor laser diode, and no successful example has been reported yet.

Like argon gas lasers, conventional blue oscillation lasers that have been put into practical use are large and expensive, require water cooling, and consume large amounts of power.

It is an object of the present invention to overcome the conventional drawbacks and difficulties using a completely novel method, and to provide an inexpensive, compact, and low-power blue light emitting device.

FIG. 1 is a schematic diagram of an all-solid-state compact blue light emitting device according to the present invention, which is composed of a semiconductor laser 1 and an optical thin film waveguide 2 formed on a substrate 3.

The bonding is as described below, and as can be seen from the approximate dimensions in the figure, an element with a compact structure can be obtained. The principle of the present invention is essentially that an electromagnetic wave with high density optical energy interacts with an optically nonlinear medium, and a second harmonic of twice the frequency (H in wavelength) of the fundamental wave (primary light) is generated. It utilizes the generation of (secondary light).

Semiconductor lasers currently in practical use range from 7000A to 90A.
00λ range, and by multiplication the wavelength can be increased from 3500λ to 4
Blue light of approximately 500λ can be obtained.

In addition, in order to efficiently generate the second harmonic, it is necessary to propagate it at high optical energy density through a medium that has a nonlinear effect, but by using a nonlinear material as an optical waveguide structure, the output Even when a 0.1 to 1 watt semiconductor laser is used as the primary light, it is possible to achieve an energy density of 10 Vd or more.

Of course, for this purpose, it is necessary to efficiently introduce semiconductor laser light into the film, but this can be done by the method shown in FIG. 2, and there is no problem with miniaturization. Second
In the figure, a taper 4 is formed on the film at the end of the thin film 2 by vapor deposition or sputtering, and light 5 is incident on the tapered part. Next light is introduced into the film using the cut-off due to the film thickness of the light at the taper 4. do. Further, a grating 6 may be provided at the interface between the taper 4 and the thin film 2. As is well known, even in an optical waveguide type optical harmonic generation element, a second harmonic is not generated unless phase matching is achieved between the propagation modes of the primary light and the secondary light.

LiNbO3 and LiTa are excellent nonlinear optical materials.
There are O3 and solid solutions thereof. The LiNbO3 optical waveguide is fabricated by external diffusion of Ll ions and internal diffusion of metal ions. In addition, using LiTaO3 as a substrate,
LlNbO3 thin films are formed by the sputtering method, liquid phase growth method, or melt solidification method, but these methods have a small refractive index difference between the substrate part and the thin film part, and it takes 7000 ~
When a 9000λ semiconductor laser beam is used as the primary light, phase matching is impossible and harmonic generation is not realized. Ll
Thin film growth using a substrate that has a sufficiently large refractive index difference with NbO3 or the like and has a well-matched lattice constant has not been performed in the past. The present invention uses saphire α-Al2O, which has a much smaller refractive index than LiNbO6, LiTaO3, etc.
3 Using a single crystal as a substrate, Li is deposited by sputtering method etc.
{101 of Nbl-XTa)CO3 (O≦X≦1)
0} plane (commonly called Y plane) is formed to form a low-loss optical waveguide, which is used as a second harmonic generation element.

In this case, since the refractive index difference between the substrate and the waveguide is sufficiently large, the phase matching condition can be easily satisfied even in the target wavelength range. Figure 3 shows Saphire α-AI? LiN whose substrate is the {1012} plane (commonly known as the R plane) of the 203 single crystal.
Primary light (0.82μ) in the waveguide of the bO3 thin film (Y plane)
, the change in the propagation constant of secondary light (0.41μ) is shown with the film thickness as the horizontal axis.

In FIG. 3, as an example, both the primary light and the secondary light are set to the TE mode. As can be seen from this, phase matching between low-order modes is also possible, and efficient generation of second harmonics is expected. Next, an example of the device of the present invention will be shown.
EXAMPLE A R-plane of a saphire α-Al2O3 single crystal was optically polished and used as a substrate, and a LiNbO3 single crystal film was epitaxially grown on this soil by a high frequency bipolar sputtering method.

Since LiNbO3 undergoes compositional deviation during sputtering, a sintered body containing slightly more Li2O than the stoichiometric composition was used as a sputtering target. As for the spatuta conditions,
Aγ gas containing 40% 02 was used, and the gas pressure was 2 x 10-
It was set to 2t0rr. Substrate temperature 700℃, anode current 110℃
A LiNbO3 film with a thickness of 7350λ was grown at a sputtering rate of about 500λ/Hr. Next, after electrically polarizing the film in the easy axis direction, AS2S3 was deposited as a tapered film with a taper ratio of 100:1 as shown in FIG. It was installed as shown in the figure.

The semiconductor laser was driven with one pulse, and the laser output was approximately 100 mW.

The energy density of the laser light in the film is approximately 5 x 106 W x
It is considered to be d. As shown in Fig. 3, when the LiNbO3 film thickness is 7350λ, it is calculated that the TEI) mode of the primary light and the TEτ mode of the secondary light are phase matched. Blue light with good quality was detected and the efficiency was about 1%. LiNbO of this example
LlTaO3 or LiNbl instead of 3? XTaxO3(
Since it is possible to grow a single crystal film of 0≦X≦1 on an R-plane substrate of sapphire, it is of course possible to generate a similar second harmonic with these thin films.

As explained above, according to the present invention, by combining with a semiconductor laser, an all-solid-state and small-sized laser beam with a wavelength of 3500λ to 45% is achieved.
A coherent blue light emitting device of 00A can be obtained. Not only does such a device provide an all-solid-state blue laser light source that has not been available before, but also because light at this wavelength easily causes photochemical reactions and has good light focusing properties, it can be used as an optical printer (N
On-1mpactPrinter), holography,
Possible applications include.

Furthermore, by using a phosphor (such as ZnS), it is possible to easily obtain light of all visible wavelengths with high efficiency.

Since the small-sized blue light emitting device of the present invention can be expected to have a wide range of applications as described above, its industrial value is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of the device structure according to the present invention, and FIG.
The figure shows the coupling between the semiconductor laser and the thin film optical waveguide in the present invention, and Figure 3 shows the relationship between the film thickness and the propagation constant, and the intersection of the primary light and the secondary light on the graph is the phase matching film thickness. This is shown using the TE wave as an example. 1... Semiconductor laser, 2... LiNb
l-XTaxO3 thin film optical waveguide, 3...Sapphire single crystal substrate, 4...Taper, 5...
・Primary light, 6... Lattice, 7... Heat sink.

Claims (1)

[Claims] 1 Semiconductor laser and LiNb_1-x formed on the {1012} plane of sapphire α-Al_2O_3 single crystal
TaxO_3 (0 < A blue light emitting device.