JPS6051682B2 - Optical mode discriminator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thin film type optical mode discriminator comprising a dielectric layer and a metal layer.

For this type of thin film optical mode discriminator, for example, a dielectric layer having a relatively high refractive index is laminated on a dielectric substrate having a relatively low refractive index, and the dielectric layer is stacked to form a desired optical mode discriminator. A structure in which a certain thickness is partially etched and removed is known.

However, in the optical mode discriminator created in this way, there is an irregularity in the boundary surface due to etching on the surface or side surface of the dielectric layer, which is about the wavelength of light, and this poor surface precision causes a large light scattering loss. This was a cause of a decrease in revitalization efficiency.

The present invention aims to alleviate these drawbacks, and has achieved this by using a structure in which a dielectric layer having a relatively large refractive index and a metal layer with a desired pattern are laminated, as shown in the drawings below. will be explained in detail. Fig. 1 is a plan view showing an embodiment of the present invention, and Fig. 2 is a plan view showing an embodiment of the present invention.
It is a sectional view along the Y direction.

In FIGS. 1 and 2, 1 is a dielectric substrate with a relatively small refractive index, 2 is a dielectric layer with a relatively high refractive index, and 3 is a material with the same (or different) refractive index as the dielectric substrate 1. A relatively small dielectric layer, 4 is air, 5 is a metal layer, and 6 is an incident beam of light. Coupling of the input and output light with the incident beam of light 6 in the dielectric layer 2 can take place via prism couplers 7a, 7b. In this embodiment, the dielectric substrate 1, the dielectric layer 2, the dielectric layer 3, and the metal layer 5 are made of SiO2 substrate and Al, respectively.

O. An Al2O3 layer 2 of several thousand amps is deposited on the SiO2 substrate 1 using a high frequency sputtering method (or C, V, D method or other method), and then a SiO2 layer and an Al layer are used.
The second layer 3 is deposited by a high-frequency sputtering method (or C.V.D method or other method) similar to that of the dielectric layer 2, and the A1 layer 5 is deposited by a mask evaporation method (or a photolithography method after vapor deposition) of several thousand amps. It is constructed by attaching it by etching method, etc.).
If the film thickness of the dielectric layer 3 is appropriately selected in such a configuration, the difference in attenuation constant between the TE mode light 6a and the TM mode light 6b propagating through the dielectric layer 2 becomes significantly large. Therefore, an optical discriminator that extracts the light 6a of mode 2 can be obtained.

Next, the reason why the difference in attenuation constant between the TE mode light 6a and the TM mode light 6b becomes significantly large due to such a configuration will be described.

The relationship between the propagation constant β of light in the dielectric 2, the attenuation constant α of light, the film thickness T2 of the dielectric 2, and the film thickness b of the dielectric 3 is well known with b=0 (for example, AppIiedOpti
cs Vol. No. 5 A. (Reisinger)) The relational expression can be expressed as an extension of the following expression. Here (for TM mode), λo is the wavelength of light in vacuum, El, ε2, ε3, E4,
ε5 is the wavelength λ.

, the dielectric constant of each substance of the dielectric substrate 1, dielectric layer 2, dielectric layer 3, air 4, or metal layer 5, T2 is the thickness of the thin film dielectric layer serving as the optical transmission path, and b is the intermediate insulating layer. 3
, N is the order of light, Nl, rl2, j, n4, j are the dielectric substrate 1, dielectric layer 2, dielectric layer 3,
This is the refractive index of the substance of the air 4 or the metal layer 5, respectively. The materials of the dielectric substrate 1, dielectric layer 2, dielectric layer 3, and metal layer 5 are SlO2, Al2O3, SiO2,
With Al, n1=1.48, r12=1.68, n3=
1.48, n5=1.2-J7. Wavelength 6328 as O
A(7) Numerical analysis of He-Ne laser light reveals that a 6000A Al2O3 layer is used as the dielectric layer 2.
When a 1000A (7) SiO2 layer is used as the dielectric layer 3, the discrimination ratio between TE mode and TM mode is 40 dB.
You can get something like that.

Incidentally, the coupling of input and output light with the incident beam light 5 in the dielectric layer 2 is performed by forming a diffraction grating on the surface of the dielectric layer 2 in addition to the prism coupler 7, and by interference with the incident beam light 6. You can also do it.

Furthermore, in the above embodiments, a metal layer is laminated on a dielectric layer with a relatively high refractive index via a dielectric layer with a relatively low refractive index, but the metal layer is directly stacked on the dielectric layer with a relatively high refractive index. may be laminated.

As explained above, according to the present invention, since the scattering of light at the boundary surface can be reduced, it has advantages such as high efficiency and easy manufacture.

[Brief explanation of the drawing]

FIG. 1 is a plan view of an optical mode discriminator showing an embodiment of the present invention, and FIG. 2 is a sectional view taken along the X-Y line in FIG. 1.

Claims (1)

[Claims] 1 A first dielectric layer having a relatively high refractive index laminated on a dielectric base having a low refractive index, and a second dielectric layer having a relatively low refractive index laminated on the first dielectric layer via a second dielectric layer having a relatively low refractive index. a metal layer, the thickness of the second dielectric layer is set to be relatively thin in accordance with the mode to be discriminated, and the metal layer is disposed in a discrimination region. Optical mode discriminator that discriminates single mode light from