JPH05173033A - Waveguide type optical branching filter - Google Patents

Abstract

PURPOSE:To improve crosstalk by providing a radiation mode means for radiating light with wavelength longer than that separated from a directional coupler to the outside of a waveguide between the directional coupler on the final stage and an output terminal. CONSTITUTION:In structure constituted of connecting plural directional couplers 12-1, 12-2 so as to form a multi-stage, the radiation mode means 31 for radiating wavelength longer than the wavelength lambda2 separated from the coupler 12-2 on the final stage is connected between the coupler 12-2 and the output terminal 14. After passing the coupler 12-2, an optical signal is turned to a state shown by a code 5a. The means 31 radiates an optical signal component 5a-1 belonging to the long wavelength side longer than the wavelength lambda2 to the outside of the optical wave 5a to improve crosstalk to be generated on the long wavelength side longer than the wavelength lambda2. Consequently an optical signal 5b whose crosstalk is improved even on the long wavelength side longer than the wavelength lambda2 is outputted from the output terminal 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide type optical demultiplexer.

A waveguide type optical demultiplexer is required to be able to demultiplex light of any wavelength and to have good crosstalk.

[0003]

2. Description of the Related Art As a waveguide type optical demultiplexer, a Mach-Zehnder (MZ) type structure and a structure using a directional coupler can be considered.

In the MZ type configuration, the wavelengths separated for each channel are determined by the difference in arm length,
There is a drawback that the arbitrary wavelength cannot be selected, and it cannot be applied when separating light of an arbitrary wavelength.

On the other hand, since the directional coupler can arbitrarily select the separation wavelength, it is applied to the case of separating the light of any wavelength.

FIG. 8 shows a conventional 1 using a directional coupler.
An example of the waveguide type optical demultiplexer 1 is built on a LiNbO ₃ chip (not shown).

Reference numeral 2 is a waveguide, and 3 is an input terminal.

An optical signal 7, which is a mixture of the optical signals 4, 5 and 6 having wavelengths λ ₁ , λ ₂ and λ ₃ , is input to the terminal 3. λ
₁ <λ ₂ <λ ₃ .

8-1 and 8-2 are first directional couplers,
It is connected in multiple stages. Reference numerals 9-1 and 9-2 are branched waveguides.

The directional couplers 8-1 (8-2) have the characteristics shown by the line I in FIG.

Reference numeral 10 is an output terminal, and 11 is a dummy terminal.

Reference numerals 12-1 and 12-2 denote second directional couplers, which are connected in multiple stages. Reference numerals 13-1 and 13-2 are branched waveguides.

The directional couplers 11-1 (11-2) have the characteristics shown by the line II in FIG.

Reference numeral 14 is an output terminal, and 15 is a dummy terminal.

Since the directional couplers 8-1 and 8-2 are connected in series, the characteristic on the output side of the directional coupler 8-2 in the subsequent stage is as follows.
The characteristic shown by the line I in FIG. 9 becomes the characteristic shown by a line I-1 in which they overlap.

As a result, the optical signals 4 and 5 having wavelengths λ ₁ and λ ₂ are filtered, and the optical signal 6a having a wavelength λ ₃ is output from the terminal 10.

Further, since the directional couplers 12-1 and 12-2 are connected in series, the characteristic on the output side of the directional coupler 12-2 in the subsequent stage is the characteristic shown by the line II in FIG. Overlapping lines
It has the characteristics shown in II-1.

As a result, the optical signal 4 having the wavelength λ _{1 and} the optical signal 6 having the wavelength λ ₃ are filtered, and the terminal 14 outputs the optical wave 5a having the wave signal λ ₂ .

From the terminal 16, a light wave 4a having a wavelength of λ ₁ is output.

Directional couplers 8-1, 8-2, 12-1, 12-2
Looking at the characteristics of, as shown in FIG. 9 and FIG.
The characteristics on the shorter wavelength side than the wavelength to be separated are stable.

Therefore, the directional couplers 8-1, 8-2, 12
By connecting -1 and 12-2 in multiple stages, crosstalk on the shorter wavelength side than the separation wavelength is improved as shown by reference numerals 17 and 18.

[0022]

However, the characteristics on the longer wavelength side of the wavelength λ ₁ to be separated by the directional couplers 12-1 and 12-2 are unstable as indicated by reference numeral 19 in FIG. ..

Therefore, as indicated by reference numeral 20 in FIG.
The curve becomes gentle, the optical signal component of the wavelength λ ₃ is also mixed, and the crosstalk deteriorates in the band on the longer wavelength side than the separation wavelength.

Therefore, an object of the present invention is to provide a waveguide type optical demultiplexer that solves the above problems.

[0025]

FIG. 1 shows the principle configuration of the present invention.

In the figure, parts corresponding to those shown in FIG. 8 are designated by the same reference numerals.

The waveguide type optical demultiplexer 30 has a structure in which the second directional couplers 12-1 and 12-2 are connected in multiple stages, and the directional coupler 12-2 at the final stage and the output. A radiation mode means 31 for radiating light having a wavelength longer than the separation wavelength λ ₂ of the directional coupler 12-2 to the outside of the waveguide is provided between the terminal 14 and the terminal 14.

[0028]

In the stage after passing through the final stage directional coupler 12-2, the optical signal is in the state indicated by reference numeral 5a.

The radiation mode means 31 converts the optical signal component 5a-1 on the longer wavelength side of the wavelength λ _{2 of the} light wave 5a into the waveguide 1.
The loss-wavelength characteristics are shown in Fig. 2, middle line II.
As shown by -2, crosstalk on the longer wavelength side than the wavelength λ ₂ is improved.

As a result, from the output terminal 14, the reference numeral 5b is given.
As indicated by, the optical signal with improved crosstalk is output on the longer wavelength side than the wavelength λ ₂ .

[0031]

FIG. 3 shows a waveguide type optical demultiplexer 40 according to an embodiment of the present invention.

In the figure, parts corresponding to those shown in FIGS. 1 and 8 are designated by the same reference numerals.

Reference numeral 41 is a bending waveguide, which constitutes the radiation mode means 31.

The bending waveguide 41 is constructed by bending the waveguide 9-2 a plurality of times in a zigzag shape with a radius R ₁ .

Here, the bending waveguide has the loss-wavelength characteristic shown in FIG.

In the figure, R ₁ and R ₂ are radii in which the waveguide is bent, and R ₁ > R ₂ .

Line III is the loss of the bending waveguide of radius R _1.
A wavelength characteristic is shown.

The line IV shows the loss-wavelength characteristic of the bending waveguide having the radius R ₂ .

As shown in the figure, the long-wavelength optical signal is radiated outside the waveguide in the bent waveguide portion, the loss of the long-wavelength optical signal is large, and the wavelength at which the loss increases can be controlled by the radius. It can be seen that the smaller the radius and the shorter the wavelength at which the loss increases. The bending waveguide 41 is
The radius R ₁ is set to a value such that the wavelength at which the loss increases becomes λ ₃ .

Two-stage second directional couplers 12-1, 12-2
FIG. 2 shows the loss-wavelength characteristic of the combination of the bending waveguide 41 and the bending waveguide 41.
It becomes as shown by the line II-2.

Therefore, the two-stage second directional coupler 12 is provided.
-1, 12-2, an optical signal having a spectrum shown by reference numeral 5a (see FIG. 1) is generated by the bending waveguide 4
In the process of passing through 1, the optical signal component 5a-1 on the longer wavelength side than the wavelength λ ₂ is radiated to the outside of the waveguide and removed.

As a result, from the output terminal 14, the reference numeral 5 is given.
As indicated by b, an optical signal with improved crosstalk is output on the longer wavelength side than the wavelength λ ₂ .

The waveguide 2 includes a bending waveguide 4 having a radius R _2.
5 is formed.

As a result, from the output terminal 16, the code 4
As indicated by b, an optical signal with improved crosstalk on the longer wavelength side than the wavelength λ ₁ is output.

FIG. 5 shows a waveguide type optical demultiplexer 50 according to another embodiment of the present invention.

In the figure, parts corresponding to those shown in FIGS. 1 and 8 are designated by the same reference numerals.

Reference numeral 51 denotes a divided sub-waveguide, which is formed adjacent to the waveguide 13-2 and divided on both sides of the waveguide 13-2 and along the waveguide 9-2 as shown in FIG. I am doing it.

Each of the split waveguides 51 functions to guide the light exuding from the waveguide 13-2 and to radiate the above light from the end portion 51a.

As a result, the split sub-waveguide 51 constitutes the radiation mode means 31 in FIG.

The waveguide 13-2 with the divided sub-waveguide 51 is
It has the loss-wavelength characteristic shown in FIG.

In the figure, l ₁ and l ₂ are the intervals between the waveguide 9-2 and the split sub-waveguide 51, and l ₁ > l ₂ .

Line V shows the loss-wavelength characteristic of the sub-waveguide with the interval l ₁ .

Line IV shows the characteristics of the sub-waveguide with the interval l ₂ .

As shown in the figure, the long wavelength optical signal is radiated from the waveguide into the sub-waveguide, the loss of the long wavelength optical signal is large, the wavelength at which the loss increases can be controlled by the interval, and the interval is It can be seen that the narrower the wavelength, the shorter the wavelength at which the loss increases.

The sub-waveguide 51 has a structure in which the interval l ₁ has a value such that the wavelength at which the loss increases becomes λ ₃ .

Two-stage second directional couplers 12-1, 12-2
FIG. 2 shows the loss-wavelength characteristics of the combination of
It becomes as shown by the line II-2.

Therefore, the two-stage second directional coupler 12 is provided.
-1, 12-2, the optical signal having the spectrum shown by reference numeral 5a is guided by the optical component 5a-1 on the longer wavelength side than the wavelength λ _{2 in the} process of passing through the waveguide 13-2. Waveguide 1
It exudes to the outside of 3-2, enters the sub-waveguide 51 and is guided, and is radiated to the end portion 51a and removed.

As a result, from the output terminal 14, the reference numeral 5 is given.
As indicated by b, an optical signal with improved crosstalk is output on the longer wavelength side than the wavelength λ ₂ .

In the waveguide 2, a split sub-waveguide 52 is formed with a space of l ₂ .

As a result, from the output terminal 16, the code 4
As indicated by b, an optical signal with improved crosstalk on the longer wavelength side than the wavelength λ ₁ is output.

[0061]

As described above, according to the invention of claim 1, the directional couplers are connected in multiple stages.
It can demultiplex an optical signal of any wavelength, and
Crosstalk on the shorter wavelength side than the demultiplexed wavelength can be improved, and the crosstalk of light on the longer wavelength side than the wavelength separated by the directional coupler can be improved by the configuration with the radiation mode means. Can be improved.

According to the second aspect of the present invention, it is possible to effectively radiate the optical signal on the wavelength side longer than the wavelength separated by the directional coupler.

According to the third aspect of the invention, it is possible to effectively radiate the optical signal on the longer wavelength side than the wavelength separated by the directional coupler.

[Brief description of drawings]

FIG. 1 is a principle configuration diagram of the present invention.

FIG. 2 is a diagram showing a loss-wavelength characteristic according to the configuration of FIG.

FIG. 3 is a diagram showing an embodiment of a waveguide type optical demultiplexer of the present invention.

FIG. 4 is a diagram showing a loss-wavelength characteristic of a bending waveguide.

FIG. 5 is a diagram showing another embodiment of the waveguide type optical demultiplexer of the present invention.

6 is an enlarged cross-sectional view taken along the line VI-VI in FIG.

FIG. 7 is a diagram showing a loss-wavelength characteristic of a configuration provided with a sub-waveguide.

FIG. 8 is a diagram showing an example of a conventional waveguide type optical demultiplexer.

FIG. 9 is a diagram showing a loss-wavelength characteristic of the first directional coupler in FIG.

FIG. 10 is a diagram showing a loss-wavelength characteristic of the second directional coupler in FIG.

[Explanation of symbols]

 2 Waveguide 3 Input terminal 4, 5, 6, 7 Input optical signal 5b Output optical signal 12-1, 12-2 Second directional coupler 13-1, 13-2 Waveguide 14 Output terminal 15 Dummy terminal 30 , 40, 50 Waveguide type optical demultiplexer 31 Radiation mode means 41 Bending waveguide 51 Divided sub-waveguide 51a End part

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H04B 10/02

Claims (3)

[Claims] 1. A waveguide type optical demultiplexer in which directional couplers (12-1, 12-2) are connected in multiple stages, wherein a directional coupler (12-2) at the final stage and an output terminal ( 14), a radiation mode means (31) for radiating light having a wavelength longer than the separation wavelength of the directional coupler to the outside of the waveguide (13-2).
A waveguide type optical demultiplexer characterized by being provided with. 2. The waveguide type optical demultiplexer according to claim 1, wherein the radiation mode means is a bent waveguide (41) formed by bending a waveguide. 3. The waveguide type optical demultiplexer according to claim 2, wherein the radiating mode means comprises a plurality of divided sub-waveguides (51) adjacent to the waveguide.