JP3249960B2 - Array grating type optical multiplexer / demultiplexer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to optical frequency multiplexing (F
The present invention relates to an array grating type optical multiplexer / demultiplexer used in a DM) communication system or an optical wavelength division multiplexing (WDM) communication system.

[0002]

2. Description of the Related Art FIG. 4 shows a basic structure of an array grating type optical multiplexer / demultiplexer. In the figure, the array grating type optical multiplexer / demultiplexer is
N input channel waveguides 1 formed on substrate 10
1, first sector slab waveguide 12, predetermined waveguide length difference Δ
This is a configuration in which a channel waveguide array 13 composed of M waveguides that are sequentially elongated by L, a second sector slab waveguide 14, and N output channel waveguides 15 are sequentially connected.

FIG. 5 is an enlarged view showing a structure near the second fan-shaped slab waveguide 14. As shown in FIG. The same applies to the first sector slab waveguide 12. In FIG, R represents the radius of curvature of the sector slab waveguide 14, 2a each waveguide core width of the channel waveguide array 13 and the output channel waveguide 15, D ₁ is in each waveguide of the channel waveguide array 13 core opening width, d is the channel waveguide waveguide spacing at the slab waveguide boundaries of the array 13 (d equally spaced), D ₂ are each waveguide of the output channel waveguide 15 core opening width, S is output channel Waveguide spacing at the slab waveguide boundary of waveguide 15 (hereinafter referred to as spacing of output channel waveguides 15).
The same applies to the case of the distance between the input channel waveguides 11. ), H ₁ and h ₂ indicate the length of each tapered waveguide portion.

Here, in the conventional array grating type optical multiplexer / demultiplexer, the intervals S of the output channel waveguides 15 are equal. Similarly, the intervals between the input channel waveguides 11 are also equal, and the interval between the input channel waveguides 11 and the interval between the output channel waveguides 15 are set to be the same.

In such a configuration, light incident from a predetermined input channel waveguide 11 spreads by diffraction in the first sector slab waveguide 12, and the channel waveguide array 13 arranged perpendicular to the diffraction plane. It is led to. In the channel waveguide array 13, since each waveguide is sequentially elongated by the waveguide length difference ΔL, the light propagating through each waveguide and reaching the second sector slab waveguide 14 has a waveguide length difference ΔL. Is generated. Since this phase difference varies depending on the optical frequency, when the light is focused on the input end of the output channel waveguide 15 by the lens effect of the second sector slab waveguide 14, it is focused on a different position for each optical frequency. That is,
The waveguide of the output channel waveguide 15 operates as an optical demultiplexer in which the waveguide of the output channel waveguide 15 is selected according to the frequency of the light incident from the input channel waveguide 11. In addition, it can be similarly operated as an optical multiplexer by passing through the reverse path.

FIG. 6 shows measurement results of filter characteristics of a conventional array grating type optical multiplexer / demultiplexer. Core width 2a = 7 μm, core thickness 2t = 7 μm, relative refractive index difference Δ of each channel waveguide
= 0.75%. H ₁ = 1 mm, D ₁ = 20 μm,
h ₂ = 0.5 mm, D ₂ = 12 μm, R = 14.4 mm, d = S
= 22 μm, ΔL = 79 μm, diffraction order m = 74, N = 16, M
= 100.

At this time, the filter characteristics of the conventional array grating type optical multiplexer / demultiplexer are such that the transmission center wavelengths of the output channel waveguides 15 are equally spaced (in FIG. 6, 0.64 nm spacing (wavelength 1.55 μm).
80 GHz interval in m band)). In the second fan-shaped slab waveguide 14, the change of the focused spot position x with respect to the wavelength λ (or the optical frequency f) is as follows, when + x is taken to the right in FIG. 6, Δx / Δλ = −RΔL / λ ₀ d, Δx / Δf = −RΔL / f ₀ d (1) Here, λ ₀ is the center wavelength of the wavelength multiplexed signal, and f ₀ (= c / λ ₀ ) is the center optical frequency. Equation (1)
Since R, ΔL, d, λ ₀ , and f ₀ are all constant values, it can be seen that the change of the focused spot position x with respect to the light wavelength λ (light frequency f) is constant. Therefore, the output channel waveguide 15 (input channel waveguide 14)
Are arranged at equal intervals, it can be seen that the intervals of the wavelength-division multiplexed signal light (frequency multiplexed signal light) to be demultiplexed are also constant as shown in FIG.

[0008]

In the conventional array grating type optical multiplexer / demultiplexer, when the optical frequencies (wavelengths) of the frequency multiplexed signal light (wavelength multiplexed signal light) are equally spaced, the frequency is increased by four-wave mixing. There is a problem that crosstalk occurs between multiplexed signal lights (wavelength multiplexed signal lights). Here, four-wave mixing means that three light waves of optical frequencies f _i , f _j , f _k (k ≠ i, j) interact via the third-order nonlinear susceptibility χ ⁽³⁾ of the optical fiber. , A non-linear process that generates a light wave of optical frequency f _F = f _i + f _j −f _k . In frequency multiplexed signal light (wavelength multiplexed signal light) in which optical frequencies (wavelengths) are arranged at equal intervals, a new light wave generated by four-wave mixing overlaps with another signal frequency and causes crosstalk.

Therefore, in order to suppress crosstalk due to four-wave mixing, it is necessary to make the frequency interval (wavelength interval) of the optical signal unequal, and accordingly, the optical frequency filter of the optical multiplexer / demultiplexer must correspond to this. Characteristics (optical wavelength filter characteristics)
Also needed to be unevenly spaced.

Further, in order to be able to change the center wavelength of the demultiplexing characteristic in response to the requirements of the system and fluctuations in parameters at the time of fabrication, the optical frequency filter characteristics of the optical multiplexer / demultiplexer (optical wavelength filter Characteristics) also needed to be unequally spaced.

It is an object of the present invention to provide an array grating type optical multiplexer / demultiplexer in which the center wavelength of the demultiplexing characteristic is changed by changing the position of the input waveguide.

[0012]

An array grating type optical multiplexer / demultiplexer according to the present invention is characterized in that the distance between the input channel waveguides and the distance between the output channel waveguides are different.

[0013]

The array grating type optical multiplexer / demultiplexer according to the present invention is formed such that the distance between the input channel waveguides and the distance between the output channel waveguides are different from each other, thereby changing the position of the input waveguide. The center wavelength of the wave characteristic can be changed.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The basic structure of an array grating type optical multiplexer / demultiplexer according to the present invention is almost the same as that of the conventional one. That is,
As shown in FIG. 4, the input channel waveguides 11 formed on the substrate 10, the first sector slab waveguides 12, and the M waveguides that are sequentially elongated by a predetermined waveguide length difference ΔL are formed. In this configuration, a channel waveguide array 13, a second fan-shaped slab waveguide 14, and N output channel waveguides 15 are sequentially connected.

A feature of the present invention is that an input channel waveguide 1 is provided.
Although the interval of 1 and the interval of the output channel waveguide 15 are both equal, they are different from each other. FIG.
3 is an enlarged view showing a structure near a first sector slab waveguide 12 and a second sector slab waveguide 14. FIG.

In this embodiment, in this embodiment, the interval between the input channel waveguides 11 is S + δs (equal interval), and the interval between the output channel waveguides 15 is S (equal interval). However, the center waveguide position of the input channel waveguide 11 is
Δs = S / 10 = 2.
It was 2 μm. Other parameters were the core width 2a of each channel waveguide = 7 μm, the core thickness 2t = 7 μm, and the relative refractive index difference Δ = 0.75%. H ₁ = 1 mm, D ₁ = 20
μm, h ₂ = 0.5 mm, D ₂ = 12 μm, R = 14.4 mm,
d = 22 μm, ΔL = 79 μm, diffraction order m = 74, N = 16,
M = 100. At this time, in the case of 16 channels (N = 16), the i-th (i = 1 to 16) waveguide position counted from the left side of the input channel waveguide 11 is shifted from the conventional position by φ.
_i is as follows: φ _i = (i−8) δs (2)

A mask was manufactured based on such parameters, and an array grating type optical multiplexer / demultiplexer of this embodiment was manufactured using a silica-based optical waveguide. First, an SiO ₂ lower cladding layer was deposited on the Si substrate (10) by a flame deposition method, and then a core layer of SiO ₂ glass doped with GeO ₂ as a dopant was deposited, followed by transparent vitrification in an electric furnace. next,
Using the patterns shown in FIGS. 1 and 4 based on the above design, the core layer was etched to produce an optical waveguide portion. Finally, a SiO ₂ upper cladding layer was deposited again.

When the demultiplexing characteristics of the array grating type optical multiplexer / demultiplexer thus manufactured were measured, the following results were obtained. Where δλ = channel interval / 10 = 0.064
nm (8 GHz).

When the wavelength multiplexed signal light enters the sixth input waveguide, (λ ₀ −2δλ) is applied to the seventh output waveguide.
Is emitted, and the other output waveguide has a wavelength of 0.64 nm.
(80 GHz) signal lights having different intervals were sequentially emitted.

When wavelength-multiplexed signal light is incident on the seventh input waveguide, light having a wavelength of (λ ₀ −δλ) is emitted on the eighth output waveguide, and the other output waveguides have a wavelength of 0.64 nm. Different signal lights were sequentially emitted.

When wavelength-division multiplexed signal light enters the eighth input waveguide, light having a wavelength of λ ₀ is emitted to the ninth output waveguide, and different signal lights at 0.64 nm intervals are output to the other output waveguides. Emitted sequentially.

When the wavelength-division multiplexed signal light enters the ninth input waveguide, light having a wavelength of (λ ₀ + δλ) is emitted to the tenth output waveguide, and the other output waveguides have different intervals of 0.64 nm. Signal light was sequentially emitted.

When the wavelength-division multiplexed signal light enters the tenth input waveguide, (λ ₀ + 2δλ) is applied to the eleventh output waveguide.
Is emitted, and the other output waveguide has a wavelength of 0.64 nm.
(80 GHz) signal lights having different intervals were sequentially emitted.

From the above results, in the array grating type optical multiplexer / demultiplexer of this embodiment, the wavelength multiplexed signal light is made different by making the interval between the input channel waveguides 11 and the interval between the output channel waveguides 15 different. The center wavelength of the demultiplexing characteristic when the light enters the input waveguide can be set as λ ₀ + jδλ (j is a positive or negative integer) (3). That is, the center wavelength of the demultiplexing characteristic can be changed according to the required conditions.

Further, even when the center wavelength deviates from the set value of the system due to a parameter change at the time of manufacturing the array grating type optical multiplexer / demultiplexer, adjustment is made by changing the input position of the input channel waveguide 11 to be used. Can be.

(Reference Example) FIG. 2 is an enlarged view showing the structure near the second sector slab waveguide 14 in the reference example.

[0027] In view, in the present embodiment, s _i is the distance between the output channel waveguide 15 counted from the left (i-1) -th and the i-th (i = 2 to N). Other parameters are the same as those of the conventional configuration shown in FIG. The broken lines in the figure indicate the positions of the output channel waveguides 15 at equal intervals (S = 22 μm) in the conventional array grating type optical multiplexer / demultiplexer shown in FIG. Further, whether the input channel waveguides 11 are equally spaced or unevenly spaced, the following unequally spaced optical frequency filter characteristics can be obtained.

Core width 2a of each channel waveguide = 7 μm,
The core thickness was 2t = 7 μm, and the relative refractive index difference Δ = 0.75%. H ₁ = 1 mm, D ₁ = 20 μm, h ₂ = 0.5 mm,
₂ = 12 μm, R = 14.4 mm, d = 22 μm, ΔL = 79 μ
m, diffraction orders m = 74, N = 16, M = 100, and s ₂ = S−δs, s ₃ = S−δs, s ₄ = S + δs, s ₅ = interval s _i of the output channel waveguide 15. _{S + δs, s 6 = S} -δs, s 7 = S-δs, s 8 = S + δs, s 9 = S + δs, s 10 = S-δs, s 11 = S-δs, s 12 = S + δs, s 13 = S + δs, s ₁₄ = S−δs, s ₁₅ = S−δs, s ₁₆ = S + δs (4) However, δs = S / 4 = 5.5 μm.

FIG. 3 shows the results of measuring the demultiplexing characteristics of the array grating type optical multiplexer / demultiplexer manufactured based on such parameters. As can be seen from this figure, it has been confirmed that the wavelength multiplexed signal light (frequency multiplexed signal light) split for each waveguide of the output channel waveguide 15 has unequal intervals. In addition, by using such unequally-spaced wavelength multiplexed signal light (frequency multiplexed signal light), unnecessary light components having a frequency f _F = f _i + f _j −f _k generated by four-wave mixing and other signal light are used. The frequency can be different.
Thus, it is possible to prevent the four-wave mixing light from overlapping with another signal frequency and causing crosstalk.

[0030]

As described above, in the array grating type optical multiplexer / demultiplexer according to the present invention, the center wavelength of the demultiplexing characteristic can be changed by changing the position of the input waveguide. It is possible to easily cope with parameter fluctuations during manufacturing.

Therefore, the array grating type optical multiplexer / demultiplexer of the present invention can be used as a very useful element for large-capacity and long-distance optical communication using optical wavelength division multiplexing or optical frequency division multiplexing.

[Brief description of the drawings]

FIG. 1 is an enlarged view showing a structure near a first sector slab waveguide 12 and a second sector slab waveguide 14. FIG.

FIG. 2 is an enlarged view showing a structure near a second fan-shaped slab waveguide 14.

FIG. 3 is a diagram showing measurement results of the demultiplexing characteristics of an array grating type optical multiplexer / demultiplexer.

FIG. 4 is a diagram showing a basic configuration of an array grating type optical multiplexer / demultiplexer.

FIG. 5 is an enlarged view showing a structure near a second fan-shaped slab waveguide 14.

FIG. 6 is a diagram showing measurement results of the demultiplexing characteristics of a conventional array grating type optical multiplexer / demultiplexer.

[Explanation of symbols]

 Reference Signs List 10 substrate 11 input channel waveguide 12 first sector slab waveguide 13 channel waveguide array 14 second sector slab waveguide 15 output channel waveguide

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-244105 (JP, A) JP-A-6-194539 (JP, A) JP-A-6-250030 (JP, A) JP-A-7- 225359 (JP, A) JP-A-8-69021 (JP, A) US Patent 5002350 (US, A) IEICE Technical Report, Vol. 94 No. 301 (1994); 25-31 (58) Field surveyed (Int.Cl. ⁷ , DB name) G02B 6/12-6/14 G02B 6/28 G02B 5/18

Claims (1)

(57) [Claims] 1. A channel waveguide array comprising: an input channel waveguide; an output channel waveguide; a plurality of waveguides that are sequentially elongated by a predetermined waveguide length difference; An array grating formed with a first fan-shaped slab waveguide connecting a waveguide and the channel waveguide array and a second fan-shaped slab waveguide connecting the channel waveguide array and the output channel waveguide In the optical multiplexer / demultiplexer, an interval between the input channel waveguides at a boundary between the input channel waveguide and the first sector slab waveguide, the second sector slab waveguide and the output channel waveguide are provided. An array grating type optical multiplexer / demultiplexer, wherein the spacing between output channel waveguides at the boundary between the two is different.