JPS61248007A - Optical demultiplexer - Google Patents

Abstract

PURPOSE:To improve the resolution for demultiplexing by forming a grating to at least a part of a plane optical waveguide constituting a prism. CONSTITUTION:The waveguide type optical prism 4 formed with a diffraction grating is provided on the surface of the plane waveguide 1. The light signal transmitted from an optical fiber 11 is received by optical fibers 12, 13. The dispersion effect of the grating is added to the dispersion effect of the refractive angle when the light is made incident to the prism 4 and the diffraction angle when the light is emitted therefrom and therefore the separating angle between the different wavelengths increases. More specifically, the two wavelength dispersibility of the prism and grating is utilized and therefore the optical demultiplexer which is small in size and has the high resolution is constituted.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an optical demultiplexer that separates optical signals of different wavelengths in a wavelength division multiplexing optical communication system, and particularly relates to a waveguide that can be integrated with other optical components. Regarding type optical demultiplexers.

[Background of the invention]

In a wavelength division multiplexing optical communication system in which light of different wavelengths coexist, an optical demultiplexer is required that has the function of separating and extracting light of a desired wavelength. In the future, it is desired that this optical demultiplexer be able to be monolithically integrated with other optical components such as a photoreceiver.

Many types of bulk optical demultiplexers using prisms have been proposed. In addition, optical waveguide type prisms have already been reported by Tien et al. in the United States (
B. K. Tien et al.: "Two-layer structure of optical integrated circuits and formation of thin film prism lenses and reflective mirrors" Applied Physics Letters, Vol. 25, p. 547, 1974 (P., Ti.
en et al “Two-LayerConstr.
uction of Integrated 0pti
cal C1rcuitsand Formatio
n of Th1n Film Pr15m5
e Lensasand Reflectors"A
ppl, Phys, Lett, 24, 547.

(1974)), Figure 1 shows an example of the configuration of a conventional waveguide type optical demultiplexer using a prism, where 1 is a planar optical waveguide, and 2 is a thin film provided in a part of the planar optical waveguide. 11 is a transmission optical fiber, and 12 and 13 are optical fibers that receive the demultiplexed light.

To explain an example of the operation of the conventional optical demultiplexer configured as described above, first, light guided from the optical fiber 11 to the optical waveguide 1 is incident on the prism 2 at an incident angle θ1. The light incident on this prism 2 is refracted at a refraction angle θ2, but the value differs depending on the wavelength of the light. Further, the light from the prism 2 is emitted at a refraction angle θ, which also differs depending on the wavelength. Therefore, of the light guided from the optical fiber 11 to the optical demultiplexer, the light with the wavelength λ is coupled to the optical fiber 12, and the light with the wavelength λ2 is coupled to the optical fiber 13. The same applies when there are two or more optical signals with different wavelengths.

FIG. 2 shows a configuration example of a waveguide type optical demultiplexer using a grating, and 5 is a grating. The relationship between the incident angle α and the exit angle β to the grating 5 is sin a +ginβ=mλ/A. Here, m is the diffraction order, and λ is the wavelength and the grating constant. In this optical demultiplexer, the output angle β differs depending on the wavelength, as is clear from the above equation. Optical signals with different propagation directions are spatially separated while propagating through the planar optical waveguide, and λ1. The optical signals λ8 are each coupled into optical fibers 12.13.

The optical demultiplexer configured as described above has the disadvantage that the element length becomes longer if one resolution is to be increased because the difference in propagation direction between different wavelengths is small.

[Purpose of the invention]

An object of the present invention is to provide an optical demultiplexer with a short element length that eliminates the above-mentioned drawbacks.

[Summary of the invention]

The present invention is to improve the demultiplexing resolution by forming a grating in at least a portion of a planar optical waveguide constituting a prism.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 3 and 4.

FIG. 3 is a plan view of the element, and FIG. 4 is a sectional view of the prism portion. 1 is a planar optical waveguide, 4 is a waveguide type optical prism having a diffraction grating formed on its surface, and 11, 12, and 13 are transmission optical fibers and optical fibers for receiving separated optical signals.

In the optical demultiplexer configured as above, the dispersion effect of the grating expressed by the above formula is added to the dispersion effect of the refraction angle when entering the prism and the refraction angle when exiting the prism. The separation angle between them becomes large.

Such a grating may be formed not only on the top of the prism as shown in FIG. 4, but also on the interface between the optical waveguide layer 1 and the substrate 31 as shown in FIGS. 5 and 6, or on the surface of the optical waveguide layer. It is also possible to form it between the cladding layer 32 provided below and the substrate 31. At this time, it is not necessary that the region where the grating is formed and the region where the prism is formed completely coincide with each other, and it is clear that the same effect can be obtained even if the prism is formed in a portion of the region where the grating is formed.

Furthermore, in this example, a case has been described in which the waveguide-type optical prism formed in a part of the planar optical waveguide is made of the same material as the planar optical waveguide, but the prism has a higher refractive index dispersion than the material of the screen waveguide. It is clear that the separation angle of different wavelength optical signals becomes even larger when the optical fiber is made of a larger material.

〔Effect of the invention〕

As described above, according to the present invention, since the wavelength dispersion properties of the prism and the grating are utilized, it is possible to construct an optical demultiplexer that is small and has high resolution. ification.

It has the effect of contributing to sophistication.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a conventional prism-type optical demultiplexer, and FIG. 2 is a configuration diagram of a conventional grating-type optical demultiplexer. Figure 3 is a configuration diagram of an embodiment of the present invention, 4th to 6th rM
1 is a cross-sectional view of an embodiment of the present invention. 1... Planar optical waveguide, 2... Waveguide type optical prism,
4... Waveguide type optical prism having a grating on the upper surface, 5... Grating, 11... Optical fiber for transmission, 12.13... Optical fiber for light reception, 31...
- Substrate, 32... cladding layer. 3rd day 4th mouth

Claims (1)

[Claims] 1. In an optical demultiplexer that separates light of different wavelengths using a prism provided in a thin film optical waveguide, diffraction is applied to a part of the optical waveguide so as to overlap part or all of the prism. An optical demultiplexer characterized by a grating. 2. The optical demultiplexer according to claim 1, wherein the material constituting the prism is surrounded by a material having a smaller refractive index dispersion in the wavelength region of the signal light. .