JPH0231515B2 - HAKUMAKUHIKARIDOHAKINOSOSHI - Google Patents

Description

[Detailed Description of the Invention] 3.1 Industrial Application Field The present invention relates to a novel evanescent laser device.

3.2 Prior Art Although optical communication has already entered the practical stage, the only place where light is actually used is in its transmission system.
All other parts use general electric circuits. However, due to its high frequency, the amount of information that light can transmit is much larger than that of electrical systems, there is no noise caused by induced radio waves, and there is less loss due to heat generated in the transmission medium. If optical functional devices, especially optically controlled optical functional devices, are put into practical use, not only will there be many elements that can be expected of them, but their integration is also considered to be extremely advantageous, and various studies are being conducted in various fields. .

Among optical functional elements, optical amplifiers or optical oscillators are considered to be particularly important, and semiconductor junction lasers are currently used as light sources for optical communications. Apart from this, bidirectional amplification systems and evanescent lasers are being considered that are directly connected to or integrated with optical waveguide systems constituting transmission systems or optical integrated circuits.

Evanescent lasers were first observed in 1971 by Shank et al. of Bell Laboratories, who placed an optical fiber in alcohol containing a dye capable of laser oscillation and excited the dye with an N ₂ laser. Since the output light is directly coupled into the waveguide, it is distinctive in that it does not require any elements for coupling the light into the waveguide. Using this system,
A team from the University of California and the Max Planck Institute has shown that input light at a certain frequency can be effectively amplified. The inventors also demonstrated the relationship between the imaginary part of the complex propagation constant of an optical waveguide and the inherent gain of the amplification medium, and clarified that the gain can be measured using this system. . It was also confirmed that amplified vibrations were generated by combining this with a directional coupler.

By adding a resonator to this amplification system, laser oscillation occurs here. Shank as this resonator
have devised a distributed cavity waveguide using a grading waveguide. Furthermore, a Fabry-Perot resonator can be formed by making the end face of the waveguide a half mirror, or by using a cup mirror to take out the optical path to the outside of the waveguide and then sandwiching it between mirrors.

3.3 Problems to be Solved by the Invention However, various problems arise with the resonator installation method described above. First, in the case of a distributed resonator waveguide, fine processing of the grating is required, but for example, when integrating, it is desirable that the unit element be as simple as possible, and such complex shapes is not appropriate. Therefore,
It is preferable to use a Fabry-Perot type resonator. However, in the Fabry-Perot type resonator that has been known so far, it is installed substantially outside the waveguide as described above, and integration is still difficult in such a form.

3.4 Means for solving the problem A thin film optical waveguide having a higher refractive index than this is provided on the substrate, and a thin film optical waveguide made of or including a laser medium and having a refractive index higher than that of the optical waveguide is provided in contact with this optical waveguide. In an evanescent laser device in which a low active layer is provided on the side opposite to the substrate, the film thickness of the part of the optical waveguide in contact with the active layer is relatively thicker than that of other parts, and The thickness change has a step shape, and the side surfaces of the steps are parallel to each other and perpendicular to the interface between the active layer and the optical waveguide.

The relationship between the substrate and the optical waveguide in the present invention is the same as the relationship normally required between them, and if the refractive index of the substrate is N _S and the refractive index of the optical waveguide is N _G , then N _S
＜ _NG Must be. Any material may be used as long as it is transparent in the wavelength range used. For example, quartz, glass, metal oxides,
These include salt crystals, plastics, and thermosetting resins. An active layer made of a laser medium or a substance containing a laser medium is provided on this thin film optical waveguide having a refractive index N _G . If the refractive index of this active layer is N _A , then N _A <N _G must be satisfied. The material of the active layer can usually be a laser medium or a substance containing a laser medium, such as ruby, YAG or glass containing Nd ³⁺ ions, NaF crystal with a color center, or a polymer material containing a dye. can.

In the present invention, the part of the optical waveguide in contact with the active layer is raised in a step shape relative to other parts, and the part where the film thickness changes stands perpendicular to the interface with the active layer. Keep it facing up. Further, this plane must also be perpendicular to the traveling direction of the light guided within the optical waveguide.

3.5 Action The active layer is excited by irradiating it from above with a beam from a pumping light source, such as an N ₂ laser or a He-Ne laser, which is focused into a long thin beam using a cylindrical lens. The longitudinal direction of the beam is made to coincide with the direction in which light is extracted within the waveguide. The light excited in the active layer is coupled and guided to the waveguide below, where it is resonantly amplified between both end faces of the step-shaped part, and at the same time, a part of it is extracted to a relatively thin part of the film. , propagates in the waveguide. The thickness of the waveguide and the thickness of the step portion are determined based on the wavelength and mode of the propagating light.

3.6 Effects of the Invention Since the present invention is an element in which a part of the waveguide is a resonator, miniaturization and integration are easy. Therefore, if a part of an optical integrated circuit is to be used as an oscillation element or an amplification element, the waveguide of that part can be processed as in the present invention, and the present invention will greatly contribute to the integration of optical circuits. can be done.

3.7 Examples Next, the present invention will be explained in more detail using examples.

An example of the present invention is shown in FIGS. 1 to 4.

FIG. 1 is a diagram viewed obliquely from above, and FIGS. 2 to 4 are a plan view and side views of FIG. 1 viewed from the X direction and Y direction, respectively.

In Figs. 1 to 4, 1 is the active medium, 2 is the step-like raised part of the waveguide, and the active medium 1 is shown in the X direction.
3 is a waveguide, and 4 is a substrate. The pumping light is linearly focused using a cylindrical lens on the part indicated by the dashed line in FIGS. 1 and 2, and the active medium is excited to oscillate a laser beam. The oscillated light is coupled and guided to the waveguide convex portion 2, and is resonantly amplified between both end surfaces 2A and 2B of this portion. Then, it is taken out to the waveguide 3.

Other embodiments of the present invention are shown in FIGS. 5 to 10. Figure 5 is a view seen diagonally from above, and Figures 6 to 10 are plan views and X ₁ , X ₂ , Y ₁ , Y ₂ respectively.
FIG. In this example, a wavelength selective medium is incorporated into the resonator in order to achieve single wavelength oscillation. 1 in Figures 5 to 10
is the active medium, 2 is the step-shaped raised part of the waveguide,
3 is a waveguide, 4 is a substrate, and 5 is a wavelength selection medium. For the wavelength selection medium 5, for example, when rhodamine-6G is used as the active medium, Cds or the like may be used.

3.8 Test example Corning 7059 glass on fused silica substrate 4
RF sputtering was performed to form a waveguide 3 with a thickness of approximately 0.5 μm. Next, a mask 10 as shown in FIG. 11 was applied and sputtering was continued to form step-like raised portions 2. Then 1x for polyurethane
A methyl ethyl ketone solution of polyurethane monomer containing 10 ^-2 mol/Kg of rhodamine 6G is applied onto the waveguide and heated at 60°C for 30 minutes to evaporate the solvent and cure. The polyurethane film containing Rhodamine 6G formed in this way was cut with a cutter, the part other than the step-shaped part was peeled off, and the first
A thin film device similar to the one shown in the figure was fabricated.
In addition, as a comparative example, Corning 7059 glass was RF sputtered onto a fused silica substrate.
A thin film device was fabricated in which a waveguide with a film thickness of 0.5 μm was formed and a top layer of a thin polyurethane film containing rhodamine 6G was attached without providing a step-like protrusion.

A laser light source 1 is attached to these two types of optical waveguide elements.
1 passes through a quadrilateral aperture and is condensed into a line by a cylindrical lens 12 to irradiate pumping light 13. FIG. 12 shows the case where pumping light is irradiated onto an object without step-like protuberances. The width of the N ₂ laser beam focused on the active medium 2 is about 0.1 mm to 0.3 mm, and the minimum output beam diameter is also about the same. In this example, the output light is decoupled and extracted using a prism 14.

As a result of observation using a far-field pattern, the spread of the beam 15 in the y-axis direction is very large in the case without the step-like protuberance, and although some transverse modes are observed in the y-axis direction, the rest is not large. On the other hand, in the case of the step-shaped raised portion of the present invention, the beam does not spread out and shows a spot shape, and the beam has a fine periodic structure in both the X-axis direction and the Y-axis direction. ing. The existence of this periodic structure indicates that there is a certain degree of coherency.

The characteristics observed in such step-shaped waveguides can be cited as characteristics of lasers. Furthermore, as shown in Fig. 13, two pinholes 1
The output lights from 6 and 17 were taken out and interfered with to obtain an interference far-field pattern between the two beams. 1st
Figure 4 shows the microphotometry results. From these results, it is estimated that the spatial coherency of the output light from the step waveguide is 80% within 0.6 mm, and the temporal coherency is 10 μm or more.
At first glance, these numbers seem to be poor in terms of the coherency of the laser beam, but it should be taken into consideration that this laser is multi-mode and has many vibrations, and was obtained using light waves in a nearly continuous spectral range of about 100 A. For example, the actual coherency in each mode is much higher than this.

[Brief explanation of drawings]

Fig. 1 is a perspective view showing one embodiment of the present invention;
The figure is a plan view of FIG. 1, FIG. 3 is a side view seen from the X direction of FIG. 1, FIG. 4 is a side view seen from the Y direction of FIG. 1, and FIG. A perspective view showing the embodiment, FIG. 6 is a plan view of FIG. 5, and FIG. 7 is a plan view of FIG. 5.
Fig. 8 is a side view seen from the X ₁ direction of Fig. ₅ , Fig. 9 is a side view seen from the Y 1 direction of Fig. 1, and Fig. 10 is a side view seen from the Y ₁ direction of Fig. 5. FIG _{. 11} is a side view showing an example of the method of forming the waveguide raised portion of the present invention, and FIG. 12 is a perspective view showing a state in which the evanescent laser element is excited. 13 is a perspective view showing a state in which interference between two beams is generated with the output light of the device of the present invention, and FIG. 14 shows the microphotometry results of a far-field pattern obtained by the method shown in FIG. 13. It is a graph. 1... Active medium, 2... Waveguide raised portion, 3...
...Waveguide, 4...Substrate.

Claims (1)

[Claims] 1. A thin-film optical waveguide with a higher refractive index than this is provided on a substrate, and in contact with this optical waveguide, an active layer consisting of or containing a laser medium and having a lower refractive index than the optical waveguide is called a substrate. In the evanescent laser device provided on the opposite side, the film thickness of the part in contact with the active layer of the optical waveguide is relatively thicker than the film thickness of other parts, and the film thickness changes in a step-like manner. A thin film optical waveguide functional element characterized in that the side surfaces of the steps are parallel to each other and perpendicular to the interface between the active layer and the optical waveguide.