JPH0287123A - Optical function device - Google Patents

Abstract

PURPOSE:To optimize the wavelength selectivity of a grating for demultiplexing by using an induction refractive index type grating which is formed with a standing wave generated by the interference of an exciting light wave. CONSTITUTION:Light waves 6a and 6b for excitation are entered into a channel waveguides from both ends and propagated in both directions and then standing waves are generated in the channel waveguide with both light waves 6a and 6b. The grating 5 which is periodic refractive index variation corresponding to the intensity distribution of the standing waves is formed in the channel waveguide 4 through optical induction refractive index effect and the period and refractive index modulation factor of the induction grating are determined by the wavelength and power density of the exciting light waves 6a and 6b respectively. Consequently, the characteristics of the grating can be optimized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical functional device, and particularly to a wavelength demultiplexing device for waveform multiplexed optical transmission.

(Prior art) Conventionally, devices using multilayer interference!IQ filters or gratings have been proposed as wavelength demultiplexing devices for wavelength multiplexed optical transmission.In particular, waveguide type grating demultiplexing devices have been proposed using Si Integration with the photodetector has been attempted using substrates such as
5uhara et al.

” Monolithic integrated
icro-gratings and photodio
des for wave length dem
ultiplexing.

App l, Phys, Lett, 40.2. p,
+20 (Jan, 1982)).

[Problem to be solved by the invention]

However, such built-in demultiplexing gratings have the problem that manufacturing errors, that is, deviations in grating period and refractive index change, result in deterioration in demultiplexing performance such as deviations in selected wavelengths and reductions in efficiency. Was.

(Means for Solving the Problems) According to a typical aspect of the present invention, a light-induced refractive index change effect (photorefractive effect) is used as a demultiplexing grating.
In this method, two excitation light waves are propagated through a waveguide that generates a waveform, and wavelength demultiplexing is achieved using a refractive index grating induced by a standing wave caused by interference between these waves.

(Function) By controlling the wavelength and optical power of the excitation light wave, it is possible to control the period and refractive index modulation of the induced refractive index grating, thereby optimizing (fine adjustment) the characteristics of the grating. can be done. Furthermore, since the light pattern can be formed instantaneously, high-speed response is possible.

(Example〕 FIG. 1 is an explanatory diagram showing the basic concept of the present invention.

1 is a Si substrate, 2 is a 5in2 buffer layer, and 3 is a chalcogenide thin film (for example, As, S3), which exhibits a photo-induced refractive index effect and forms a slab waveguide. 4 is a channel waveguide formed by forming a ridge type structure within the same slab waveguide. Light waves 6a for excitation are emitted from both ends of the channel waveguide.
, 6b are input and propagated in both directions, a standing wave is generated by the two intersecting waves 6a and 6b in the channel waveguide. A grating 5 whose refractive index changes periodically according to the intensity distribution of a standing wave is formed in the channel waveguide 4 through a photo-induced refractive index effect. The period and refractive index modulation degree of the induced grating are respectively the excitation light wave 6a.

6b wavelength and power density. When the wavelength of the excitation light wave is λ^ and the equipolarized refractive index of the channel waveguide is nA, the period of the formed grating is given by the following equation.

80=λA/(2nA) Further, the refractive index modulation amount ΔnA depends on the power of the excitation light wave.

Of the guided light 7 that enters the grating 5 from the slab waveguide 3, only the light waves that satisfy the Bragg condition are output as diffracted waves 9, and other light waves pass through as transmitted light 8 without being diffracted. The Bragg condition for wavelength selection is given by the following equation.

λ,=2n, ΔASinθ.

Here, λ1 and nl are the wavelength and equipolarized refractive index of the selected light wave, respectively. Further, θ1 indicates the angle of incidence.

The diffraction efficiency η1 can be written using the grating width D (corresponding to the channel waveguide width). On the other hand, the wavelength selection width Δλ can be evaluated as Δλ/λ ~ A/D.

By controlling the optical wavelength and optical power of the excitation light waves 6a and 6b, the center selection wavelength can be adjusted and the diffraction efficiency can be maximized, making it possible to configure a grating demultiplexing device that can compensate for manufacturing errors.

Note that in this explanatory drawing, the input/output means for the excitation light wave and the detected light wave are omitted and not specified, but means such as end face coupling using a lens can generally be used.

Figure 2 is a schematic diagram showing a first embodiment of the present invention. Here, a plurality of channel waveguides 12 and 13 are formed, and gratings with different periods are connected to the optical fibers IO at both ends.
It is induced by standing waves output from a, IOb and lla, llb. The light to be detected is transmitted through the optical fiber 16.
to form a guided light beam that is end face coupled and collimated by a waveguide lens 17.

A plurality of wavelength components contained in the light to be detected are separated by a grating to generate diffracted light, which is individually detected by pn type photodiodes 14 and 15 formed on the Si substrate 1-1, and wavelength separation is performed. .

Each demultiplexed wavelength λ1. The wavelength of the excitation light is controlled according to λ2 so that the grating period induced in the channel waveguide satisfies the Bragg condition. At the same time, the direction of the channel waveguide is changed to the Bragg incidence angle θ3. Each must be tilted so as to match θ2. As a grating excitation light source, it is effective to use a high power laser such as a YAG laser, a CO2 laser, or a dye laser.

As an example, when using a CO□ laser with a wavelength IO of 26 μm, the equipolarized refractive index is n A = 2.3 (As2S3), and the period of the formed grating is ΔE = 2.3 μm.
m. When θ1=4° n,=2.4, the demultiplexed wavelength λ1 becomes λ,=0.77 μm.

Since the excited grating disappears as the standing wave caused by the pumping light disappears, wavelength demultiplexing is possible only during the time when the pumping light is being output, and time sampling of the signal light using pulsed light can be performed. By finely adjusting the wavelength of the excitation light source so that the desired demultiplexed wavelength is efficiently selected,
Manufacturing errors can be compensated for.

In the above example, a chalcogenide thin film was used as a material that induces a change in refractive index, but LiNbO3
It goes without saying that similar effects can be obtained by using materials such as , BSO, etc.

Husband A Billionth FIG. 3 shows a second embodiment according to the invention.

In this embodiment, slab waveguide light is used as excitation light for inducing the grating. In FIG. 3, the excitation light is guided through optical fibers lOa and lOb and coupled to the slab waveguide at the waveguide end face, forming slab waveguide light that is collimated by waveguide lenses 20a and 20b. Grading is induced by the interference pattern of standing waves generated by these two excitation light waves. A plurality of such gratings are formed within the slab waveguide to perform wavelength demultiplexing. If the crossing angle of the excitation slab waveguide light is 206, then the grating period AA can be calculated as follows. λ^ and nA are the wavelength and equipolarized refractive index of the pumping slab guided light, respectively.

Laughing Arashi 1j FIG. 4 shows a third embodiment of the present invention, in which a grating is induced in the channel waveguide 12, as in the schematically described embodiment. The light to be detected passes through the waveguide lens 1 after end face coupling.
7 and undergoes diffraction by the induced grating. The width of the grating is made smaller than that in the first embodiment to expand wavelength selectivity so that substantially the same diffraction efficiency can be obtained over the entire wavelength range of wavelength-multiplexed light waves. The diffracted waves are Fourier-transformed by the waveguide lens 30 in the latter stage, and the spot position differs depending on the wavelength, and can be independently detected by a sensor array such as a CCD. Thereby, the wavelength of the optical signal propagated via the optical fiber 16 can be detected.

The configuration of this example is RF using surface acoustic waves (S to W).
It is similar to an optical spectrum analyzer for signals, and if the detected light is a single wavelength and multiple spectra are superimposed on the excitation light, it becomes possible to perform spectrum analysis on the optical wavelength of the excitation light, which is useful in applications.

〔Effect of the invention〕

As explained above, by using an induced refractive index type grating, which is formed by a standing wave caused by interference of an excitation light wave, as a demultiplexing grating, it becomes possible to control the period and refractive index modulation of the grating.
This has the effect of optimizing the wavelength selectivity of the demultiplexing grating.

Furthermore, since the induced crating is generated only during the excitation light pulse, ultra-high-speed signal sampling is also possible.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram explaining the present invention in detail, FIG. 2 is a schematic diagram of a wavelength demultiplexing device showing a first embodiment of the present invention, and FIGS. FIG. 3 is a schematic diagram of a wavelength demultiplexing device showing second and third practical examples. l... Substrate, 2... 5in2 buffer layer, 3... Glass waveguide, 412.13... Channel waveguide, 5... Photo-induced grating, 6a, 6b... Exciton 7. ...Incidence light, 8...Transmitted light, 9...Diffracted light, 10a, lOb, lla, Ilb, 16-
・Optical fiber, 17.20a, 20b, 21a,
21b, 30---Waveguide lens, 14, 15...pn photodiode 31...CO
D sensor array patent applicant Canon Corporation

Claims (1)

[Scope of Claims] 1) A waveguide configured using at least a part of a material that produces a photo-induced refractive index change effect that causes a refractive index change depending on light intensity, and two or more waveguides in the waveguide. 1. An optical functional device comprising means for inputting excitation light waves such that the excitation light waves intersect with each other, and generating an induced grating by a standing wave of the excitation light waves. 2) The optical functional device according to claim 1, wherein the waveguide is a channel waveguide. 3) The optical functional device according to claim 1, wherein the waveguide is a slab waveguide.