JPH01259306A - Waveguide type optical wavelength filter and optical multiplexer and demultiplexer - Google Patents

Abstract

PURPOSE:To remarkably improve an isolation between wavelengths, and also, to reduce an insertion loss by providing a tapered part which has widened a waveguide interval on input/output end parts of two pieces of optical waveguides. CONSTITUTION:A tapered part C is provided on end parts of a main waveguide 1 and a sub-waveguide 2 of an optical multiplexer and demultiplexer so that a waveguide interval is widened to S2 S1, and also, the waveguide width is also varied gradually. According to this constitution, a light beam of wavelength lambda1 to be eliminates shifts to the sub-waveguide 2 from a coupling part of B, passes through the tapered part of C and becomes a radiation light beam 7. On the other hand, a light beam of passing wavelength lambda2 repeats a light wave shift in the coupling part of B and returns to the main waveguide 1, and the light beams of wavelength lambda1 and lambda2 are separated. I such a way, by providing the tapered part C, the coupling of mismatching between optical modes can be reduced, the isolation is improved remarkably, and also, the insertion loss can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a waveguide-type optical multiplexer/demultiplexer with a high degree of wavelength separation, particularly in relation to transmission using an optical fiber.

[Conventional technology]

The directional coupler in the conventional optical wavelength filter is Takato,
It consisted of a configuration in which waveguides were arranged in parallel, as shown in Jinguji et al., "Waveguide Type Optical Wavelength Filter," 1986, Institute of IEICE, 903, pp. 4-74.

[Problem to be solved by the invention]

The structure of the directional coupler according to the above conventional technology is shown in Fig. 2. (a) shows the conventional structure, (b) shows the mode mismatch at the b end, and (c) shows the mode mismatch at the c end. In addition, 1 is a main waveguide and 2 is a sub waveguide. Light of wavelength to be removed 6
changes from the main waveguide to the sub-waveguide, and the end of the sub-waveguide (
It is radiated from C) as shown in '7.

In this prior art directional coupler, the ends of the sub-waveguides such as b and C are arranged close to the main waveguide. Therefore, the light propagating through the main waveguide is b and C
mode inconsistency occurs.

This is shown in FIGS. 2(b) and 2(C).

This mismatch (the portion where the mode patterns do not overlap in (b) and (Q)) causes a loss in b and a reduction in isolation due to leakage of unnecessary light in c.

FIG. 3 shows changes in the multiplexing/demultiplexing characteristics due to this. The solid line represents the ideal characteristics, and the broken line represents the actual characteristics of the conventional example. It can be seen that the passband loss increases and the stopband attenuation decreases.

FIG. 4 shows the results of quantitatively determining these inferiorities through numerical calculations. The auxiliary lines in the figure correspond to the structure of the conventional example. From now on, in the conventional structure, 20
In particular, it is impossible to obtain inter-wavelength isolation of more than ciB, and a loss of 0.04 dB (0.02 x 2 locations) cannot be avoided.

Deterioration of inter-wavelength isolation is a serious problem in practical use. An object of the present invention is to solve these problems.

[ll! Means to solve the problem]

The above purpose is to provide a taper (a structure in which the waveguide spacing, waveguide width, etc. gradually change) at the end of the coupler to reduce the influence of discontinuities corresponding to s and c in Figure 2. This is achieved by

[Effect]

The cause of the deterioration of isolation and increase in loss is the mismatch between optical modes in the unbalanced part. Therefore, in order to suppress these occurrences, it is sufficient to reduce the inter-mode mismatch.The taper provided at both ends of the coupler has the function of weakening the coupling at both ends, thereby reducing the inter-mode mismatch. This has the effect of reducing matching. This makes it possible to sufficiently reduce the deterioration in fishing characteristics.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. The figure (a) is a top view, and (b) is a cross-sectional view taken along line A-A'. In the figure, the range indicated by the arrow B is the part that mainly contributes to bonding, and the range indicated by C is the part that mainly contributes to bonding. It is a tapered part. The light with the wavelength (λl) to be removed is transferred to the sub-waveguide 2 side at the coupling part B, passes through the taper part C, and becomes the emitted light 7.
On the other hand, the light with the passing wavelength (λ2) is the result of B.
＼ Since the light wave transition is repeated an even number of times at the junction and then returns to the main waveguide, the lights of wavelengths λl and λ2 are separated.

The tapered portion (c), which is a feature of the present invention, is formed by widening the waveguide spacing (St→Sz).

As a result, the discontinuous portion (sub-waveguide end) that causes isolation deterioration and insertion loss increase is placed at a position away from the main waveguide, and the effects thereof are greatly alleviated. From the calculation results in Figure 4, it is sufficient to set the value of 82 > 10 μm to 8 degrees, and the length of the 0 part will be approximately < l wm, so the increase in element length due to the addition of the 0 part will hardly be a problem. Learn.

Furthermore, the fact that the emission direction of the unnecessary radiation light 7 is shifted from the direction of the main waveguide 1 due to the failure of the 0 part is also effective in reducing the leakage of unnecessary light.

FIG. 5 is a diagram showing another embodiment of the present invention.

A feature of the present invention is that a multistage filter is constructed using two sub waveguides. The center wavelengths of the multi-stage filters can be selected to be the same or different values. Also, if you want to shorten the element length, use the tapered part C of the sub-waveguide in the first stage.
-1 and the tapered part C-2 of the subsequent sub-waveguide may be arranged so as to overlap each other.The configuration shown in Fig. 5 is a two-stage filter, but in the same way, It is also possible to configure filters.

FIG. 6 is a diagram showing another embodiment of the present invention.

In this embodiment, an optical multiplexer/demultiplexer with high inter-wavelength isolation is constructed by combining the wavelength separation function of the directional coupler in the first stage and the wavelength filter function in the subsequent stages. In the same figure (a), one stage of the coupler serving as an optical filter is added after the first stage coupler, and in the same figure (b), the same 2-stage coupler is added.
This is a combination of optical wavelength filters in stages. The waveguide of each coupler has a tapered structure at both ends to improve its characteristics. In the figure, the structure of the couplers in all stages is shown to be the same, but it is also possible to select them independently to vary the wavelength characteristics.

〔Effect of the invention〕

According to the present invention, it is possible to achieve a significant improvement in inter-wavelength isolation of an optical wavelength filter (20 dB→40 dB) and a reduction in insertion loss.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the first embodiment of the present invention, Figure 2 (,) is a conventional structure diagram, and Figures (b) and (c) are light mode pattern diagrams at each part of Figure (a). , FIG. 3 is a wavelength characteristic diagram of a conventional structure, FIG. 4 is a diagram showing theoretical calculation results showing the effects of the present invention, and FIGS. 5 and 6 are diagrams showing another embodiment of the present invention. . DESCRIPTION OF SYMBOLS 1... Main waveguide, 2... Sub 1 waveguide, 3... Clat layer, 4... Buffer layer, 5... Substrate, 6... Light with wavelength λ1, 7... Synchrotron radiation, 8... Light with wavelength λ2, 9
... Wavelength λ1 1st E (α) Field 2 Mouth (α): 1 no/11 (b) Yang 3 Country χ1 Shinsha Table 4 Kuwai 5 Σ

Claims (1)

[Scope of Claims] A directional coupler configured by arranging one or two optical waveguides in parallel is provided with a tapered structure in which the spacing between the waveguides is widened at at least one of its input and output ends. Features of waveguide type optical wavelength filter. 2. The optical wavelength filter according to claim 1, wherein the optical wavelength filters are connected in series in multiple stages. 3. An optical multiplexer/demultiplexer characterized in that the optical wavelength filter according to claim 1 or claim 2 is connected to both output waveguides of a directional coupler configured by arranging two optical waveguides in parallel. .