JPH05164924A - Waveguide type device with wavelength flattening monitor - Google Patents

Abstract

PURPOSE:To provide a waveguide type device with a monitor which has no wavelength dependency upon a monitor output and provides the same monitor ratio or an optional monitor ratio with at least two wavelengths. CONSTITUTION:A coupled waveguide 15 is at a center axis interval of 15mum from a directional coupler part input waveguide and the both constitute a directional coupler part 40. Light propagated in the input waveguide 10 is distributed by a branch part 20 to a branch part 30 and a monitor waveguide 12. Light in the monitor waveguide 12 is partially distributed by the directional coupler part 40 to the coupled waveguide 15 and the remaining light is outputted to a monitor output waveguide 16.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide type device having a monitor in which the wavelength dependence of the monitor output is flattened, and more particularly to a flattened wavelength that can obtain a desired monitor ratio at least at two wavelengths. The present invention relates to a waveguide device with a monitor.

[0002]

2. Description of the Related Art Optical monitor devices are used for level monitoring (monitoring) of optical power propagating in a fiber or a waveguide device. The monitor function can be achieved by cascading directional couplers and unequal branching ratio splitters, which are individual components, to an optical fiber or a waveguide device. Alternatively, in the case of a waveguide type device formed on a substrate, a waveguide type device with a monitor can be obtained by incorporating a waveguide type directional coupler or an unequal branching ratio branching device into the optical waveguide section in the substrate. It seems possible.

[0003]

However, since the directional coupler and the unequal branching ratio brancher generally have wavelength dependence, the monitor output is wavelength dependent as it is, and the monitor ratio ( There was a problem that (monitor output ÷ input level) changed.

For example, in the case of a directional coupler formed by the present inventors by the two-stage thermionic exchange method and consisting of two single mode waveguides arranged with a center axis interval of 16 μm, the wavelength of 1.
The ratio of bond length between 31 μm and 1.55 μm was 1: 1.66. Therefore, when 2% of light is monitored at a wavelength of 1.31 μm, the monitor ratio at a wavelength of 1.55 μm is 5% or more.

Further, for example, in the case of the unequal branching ratio branching device produced by the present inventors by the above-mentioned manufacturing method, in which the main waveguide is a straight waveguide and the monitor waveguide is branched at a branching angle of 3 degrees, the wavelength is 1 The monitor ratio at 0.31 μm is 5% and the wavelength is 1.5
The monitor ratio at 5 μm was 7.5%.

In any case, it has been experimentally found that it is difficult to construct a wavelength flattening monitor with a single monitor optical circuit. Therefore, 1.31 μm or 1.55 μm
When using a waveguide type device with an optical monitor such as these connected to an optical fiber or a waveguide type device that propagates the optical signal of, it is necessary to convert according to the branching ratio of the used wavelength. was there.

[0007]

Means for Solving the Problems An unequal branching ratio branching device for extracting a part of light in the waveguide as monitor light is connected to a waveguide to be monitored formed on a substrate, and the extracted monitor light is A directional coupler section for extracting a part of the monitor light is connected to the propagating monitor waveguide.

First, the general principle will be described. The two wavelengths are represented by λ1 and λ2 (> λ1). The monitor amount of the unequal branching ratio brancher is m (λ), the effective coupling area length of the directional coupler connected to one branch (monitoring waveguide) of the unequal branching ratio brancher is a, and the coupling length is If L (λ), the output of the bar port output waveguide of this directional coupler is m (λ) × cos ² (π / 2 · a / L (λ)). The conditions under which are equal are

[Formula 1] m (λ1) × cos ² (π / 2 · a / L (λ1)) = m (λ2) × cos ² (π / 2 · a / L (λ2)) (1) is there.

If the values of m (λ) and L (λ) are determined in Equation 1, a solution can be numerically found for a.

To explain the operating principle in the case of the bar port in terms of words, with respect to the monitor light on the long wavelength side that is excessively branched by the unequal branching ratio brancher, the monitor light on the short wavelength side in the next directional coupler will be described. You are shaving more than you are. The above case is the case of the bar port output waveguide, but in the case of the cross port waveguide, the solution can be similarly obtained by replacing cos with sin.

In the case of the formula 1, the monitor ratio for the input light is set to the same value for the two wavelengths, but the monitor ratio for the output light can be flattened in wavelength. That is, if the monitor amount at a certain wavelength is m (λ), the amount of light output to the main waveguide of the unequal branching ratio splitter is 1-m (λ). Further, letting T (λ) be the transmittance of the waveguide device connected to the main waveguide (output level of a certain output waveguide / input level of the main waveguide), the following Expression 2 may be satisfied.

[0012]

[Formula 2] {1-m (λ1)} × T (λ1): m (λ1) × cos ² (π / 2 · a / L (λ1)) = {1-m (λ2)} × T (λ2 ): M (λ2) × cos ² (π / 2 · a / L (λ2)) (2)

[Formula 3] m (λ1) / [{1-m (λ1)} × T (λ1)] × cos ² (π / 2 · a / L (λ1)) = m (λ2) / [{1-m (Λ2)} × T (λ2)] × cos ² (π / 2 · a / L (λ2)) (3) Therefore, after all, m (λ1) and m (λ2) Instead, it is understood that m (λi) / [{1-m (λi)} × T (λi)] (i = 1, 2) may be used.

For example, in the ideal case of 16 branches, T (λ
i) = 1/16. Here, m (λ1) = 0.0
3, and m (λ2) = 0.045, m (λ in Equation 1
The following values 0.0309 / 16 0.0471 / 16 may be used in place of 1) and m (λ2).

Since the present invention is a method of designing a wavelength flattening monitor, applicable waveguide devices are ion-exchange waveguides on glass substrates, silica-based waveguides by flame deposition on Si substrates, and LiNbO ₃ substrates. It is a waveguide type device of all waveguides such as the Ti diffusion waveguide, the compound semiconductor waveguide, and the plastic waveguide by selective polymerization of monomers.

[0015]

According to the above construction, the same monitor ratio for two wavelengths,
Alternatively, an arbitrary monitor ratio can be realized.

[0016]

1 is a plan view showing an embodiment of a waveguide type device with a wavelength flattening monitor according to the present invention. Substrate 1 is an optical grade borosilicate glass substrate containing Na and K ions suitable for ion exchange, and substituting a part of oxygen with fluorine to lower the refractive index. A waveguide having a pattern as shown in FIG. 1 was formed on the substrate 1 by a two-step electric field application ion exchange method. A detailed description of the two-step electric field application ion exchange method is omitted here, but it is disclosed by Hashizume et al.

In FIG. 1, 1 is a glass substrate, 10 is an input waveguide, 20 is a branch portion, 11 is a main waveguide, 12 is a monitor waveguide, 30 is a 1 × 16 branch waveguide portion, and 13 is a curved waveguide. , 14 is an input waveguide of the directional coupler section, 40 is a directional coupler section, 15 is a coupling waveguide, and 16 is a monitor output waveguide.

The near-field image (mode profile) of each waveguide has a horizontal axis diameter of 10.1 μm and a vertical axis waveguide of 9.2 μm.
m, and the coupling loss with the single mode fiber is 0.1 d
It was B or less.

The main waveguide 11 is on the same straight line as the input waveguide 10, and the angle θ between the monitor waveguide 12 and the main waveguide 11 is 4 degrees. The monitor ratio m (λ) of the monitor waveguide is 4.2% at a wavelength of 1.31 μm and 5.0 at a wavelength of 1.55 μm.
%Met. Ratio of monitor ratios at two wavelengths m (λ2) /
m (λ1) was 1.19.

The radius of curvature of the bending waveguide 13 is 60 mm, and the loss due to bending is suppressed to 0.05 dB or less.

The coupling waveguide 15 is located at a center axis interval of 15 μm from the directional coupler section input waveguide 14, and the two constitute a directional coupler section 40. The coupling length L (λ) of the directional coupler 40 is 3.8 mm at a wavelength of 1.31 μm and 2.2 mm at a wavelength of 1.55 μm, and the ratio L (1.3) thereof.
1) / L (1.55) was 1.7.

The length (= effective coupling region length) of the coupling waveguide 15 of the directional coupler section 40 is 710 μm, and the coupling amount of the monitor output waveguide 16 which is a bar port is 1.31 wavelength.
91.6% at μm, 76.5 at wavelength 1.55 μm
%Met. The ratio of the amount of coupling at the two wavelengths is 1 / 1.1.
It was 97.

In the above-described embodiment, the light propagating through the input waveguide 10 is distributed to the 1 × 16 branch 30 and the monitor waveguide 12 at the branch 20. In the directional coupler section 40, a part of the light in the monitor waveguide 12 is coupled to the coupling waveguide 1
The remaining light is divided into five and is output to the monitor output waveguide 16.

The light in the 1 × 16 branch section 30 is branched into each of the 16 output waveguides. 1 × 1 caused by the branching unit 20
The apparent loss increase of the 6-branch 30 is 0.19 dB at a wavelength of 1.31 μm and 0.22 dB at a wavelength of 1.55 μm, and the difference between the two is about 0.04 dB (corresponding to 100: 99.2). There is.

In the above embodiments, the length of the coupling waveguide 15 in the directional coupler section 40 is set to be equal to or less than the coupling length. It is possible in principle if the equation of (1) in which cos is changed to sin is satisfied.

Various waveguide patterns other than those of the embodiment can be considered. Further, although the monitored light is taken out by the fiber, the light power level information may be taken out as an electric signal by disposing a photodiode on the end face of the monitor output waveguide or the like to receive the light.

[0027]

In the above embodiment, the monitor ratio extracted to the monitor output waveguide 16 is about 3.8% from 4.2% × 0.916 at the wavelength of 1.31 μm, and the wavelength of 1.
At 55 μm, it was about 3.8% from 5.0% × 0.765, and was almost equal to 4% ± 0.4% at both wavelengths.

Wavelengths in between and wavelengths in the vicinity thereof (λ =
1.25 to 1.60 μm), the fluctuation of the branching ratio is ±
It was within 0.4%. Therefore, the monitor ratios can be made substantially the same for the two wavelengths λ1 and λ2.

As described above, according to the present invention, the same monitor ratio or an arbitrary monitor ratio can be realized for two wavelengths.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of the present invention.

FIG. 2 shows an effective coupling area length a / L (λ2) standardized by a coupling length L (λ2) at a certain wavelength (λ2) and a monitor ratio ratio m (λ2) / m (λ1) at two wavelengths. Relationship 2
Graph showing the ratio of bond lengths L (λ1) / L (λ2) at two wavelengths as a parameter

[Explanation of symbols]

 1 ... glass substrate 11 ... main waveguide 12 ... monitor waveguide 15 ... coupling waveguide 20 ... branch part 30 ... 1 x 16 branch part 40 ... ... Directional coupler

Claims (1)

[Claims] 1. An input waveguide formed on a substrate, an unequal branching ratio splitter coupled to the input waveguide, and a directional coupling coupled to one output waveguide of the unequal branching ratio splitter. Flattening monitor comprising a waveguide, a monitor waveguide coupled to one output waveguide of the directional coupler, and a main waveguide device coupled to the other output waveguide of the unequal branching ratio splitter. Waveguide device.