KR100583648B1 - Straight-waveguide type variable optical attenuator based on thermo-optic effect - Google Patents

Abstract

The present invention relates to a thermo-optical variable optical attenuator that can be efficiently applied to the configuration of an integrated device including an optical attenuator array since a linear attenuation characteristic and a wide attenuation area can be obtained even in a simple linear waveguide structure. A characteristic composition is adopted in which the metal heating wires at an angle with the waveguide are biased to one side. The spatial distribution of the thermo-optic refractive index change induced by this composition causes light deflection by combining the light propagating in the waveguide into the cladding region, so that the light remaining in the core region of the waveguide by controlling the temperature difference between the substrate and the metal hot wire. By controlling the output of the variable light attenuation effect can be obtained.

Variable optical attenuator, thermo-optic effect, optical deflection effect, linear waveguide, integrated optics.

Description

Straight waveguide type variable optical attenuator based on thermo-optic effect             

1 is a plan view of a thermo-optic variable optical attenuator according to an embodiment of the present invention.

2 is a cross-sectional view taken along the line AA ′ of FIG. 1.

3 and 4 are distribution charts of the effective refractive indices when the temperature increase at the position where the temperature rise is greatest at the center height of the waveguide core is 10 K and 30 K, respectively, for the structure shown in FIGS.

5 and 6 are graphs showing the results of calculating light propagation under the effective refractive index distribution conditions of FIGS. 3 and 4, respectively.

7 is a graph illustrating output characteristics of a variable optical attenuator according to a change in the structure illustrated in FIGS. 1 and 2.

8 to 10 show modifications of the variable light attenuator shown in FIG. 1.

Explanation of symbols for the main parts of the drawings

11: input waveguide

12: output waveguide

13: light attenuation

14: waveguide core of the optical attenuation portion

15: metal heating wire

16: cladding

17: substrate

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable optical attenuator, and more particularly, to a thermo-optical variable optical attenuator that can obtain linear attenuation characteristics and a wide attenuation area by employing a simple hot wire structure in a linear waveguide, and is easy for efficient integrated device construction.

A variable optical attenuator is an element that can control the attenuation of an input optical signal by using an electrical or mechanical method. It is widely used for output equalization between channels of a wavelength-division multiplexing (WDM) system. In order to easily adjust the light output of the wavelength channel in parallel, a linear waveguide structure, which is easy for parallel integration in general, and attenuation characteristic that varies linearly in dB is required.

Most of the variable optical attenuators in use today have a method of mechanically controlling the loss of a fiber or the coupling between two fibers, a method using a micro-electro-mechanical system (MEMS), or a waveguide. It uses the thermo-optic effect of the material, but the optical fiber method has a wide range of light attenuation and good linearity of the attenuation characteristics, but has the disadvantages of large volume of device, slow operation speed and high basic loss. In the case of the method, the operating speed is very fast and the operating power is low, but it is difficult to integrate with other waveguide devices. On the other hand, the method using the thermo-optic effect adopted in the present invention has an advantage of having an appropriate operating speed of about milliseconds, showing an operation characteristic irrespective of polarization, and very easy in integration.

Variable optical attenuator using thermo-optic effect can be classified into Mach-Zehnder interferometer type, multimode waveguide type, single mode linear waveguide type, etc. according to its structure. Although a variable optical attenuator having characteristics has been proposed, in general, the basic loss of the device is large, there is a problem in the stability of the output, and in other cases, it is still an important problem to obtain the linear attenuation characteristics.

Accordingly, an object of the present invention is to provide a thermo-optic variable optical attenuator having linear attenuation characteristics over a wide attenuation region in a linear waveguide structure.

As a technical means for achieving the above object, the first aspect of the present invention is a substrate, a cladding positioned on the substrate, a core located inside the cladding, positioned on the cladding, inclined at a predetermined angle with a longitudinal direction of the core The present invention provides a variable optical attenuator including a single or a plurality of hot wires oriented to the left or right side of the core.

The basic principle of the invention is as follows. When a current flows through a metallic hot wire of a characteristic composition, the waveguide condition of the light traveling in the waveguide structure is changed due to the temperature distribution in the waveguide structure induced by the temperature rise of the metal hot wire and thus the spatial distribution of the refractive index change. Refraction and deflection of light occur, resulting in a change in the output of light traveling through the core region of the waveguide. At this time, the refraction and deflection characteristics of the light and the attenuation characteristics thereof are different depending on the composition and position of the metal heating wire, so it is necessary to select an appropriate composition and position to drive an efficient optical attenuator.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, embodiments of the present invention may be modified in various forms, and the scope of the present invention should not be construed as being limited by the embodiments described below. Embodiments of the present invention are provided to more fully explain the present invention to those skilled in the art.

1 is a plan view of a thermo-optic variable optical attenuator according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along line AA ′ of FIG. 1. 1 and 2, the optical attenuator comprises an input waveguide 11, an output waveguide 12 and a waveguide 14 of the optical attenuator 13 all composed of a straight channel waveguide in a single mode, one or continuous on top of the waveguide. The plurality of metal heating wires 15, which are positioned at sq., Form an angle with the waveguide core 14 of the light attenuation portion, and are completely biased toward one region with respect to the waveguide core 14. In FIG. 2, the thermo-optic variable light attenuator includes a substrate 17, a cladding 16 located on the substrate 17, a waveguide core 14 located inside the cladding 16, and a metal heating wire 15 located on the cladding 16. It consists of.

3 and 4 illustrate the same height as the center of the core 14 when the thermo-optic coefficients of the core 14 and the cladding 16 are equal to −0.00012 K ⁻¹ in the light attenuator structure represented in FIGS. 1 and 2. The distribution of the effective indexes when the temperature increase (hereinafter referred to as ΔT) at the position where the temperature rise is greatest is 10 K and 30 K, respectively, and the calculation at this time is the refractive index of the cladding 16. The 1.500 and the refractive index of the core 14 are 1.503, the width and height of the waveguide core 14 and the width of the metal heating wire 15 are 5 μm, respectively, and the height of the metal heating wire 15 from the top of the core 14 is 6 μm, the height from the bottom of the core 14 to the substrate 17 is 12 μm, the length of the metal heating wire is 4 mm, and the angle α between the core 14 and the metal heating wire 15 is 0.3 °. The result is. 3 and 4, the direction of the z axis coincides with the longitudinal direction of the core, and the direction of the x axis is perpendicular to the longitudinal direction of the core, where x = 0 is the position corresponding to the center of the core. As shown in FIG. 3, when ΔT is 10 K, the peripheral refractive index is still low compared to the refractive index of the core 14, so that the attenuation effect of the light traveling to the core 14 does not appear much, but ΔT is 30 K. In the case of FIG. 4, since the refractive index of the surroundings is higher than that of the core 14, the light traveling to the core 14 is coupled to the cladding 15, so that the light is deflected in the direction of + x along the distribution of the refractive indexes. .

5 and 6 show the results of calculating light propagation under the effective refractive index conditions of FIGS. 3 and 4, respectively. It can be seen that FIG. 6 having ΔT of 30K exhibits a larger light attenuation effect than FIG. 5 having ΔT of 10K.

FIG. 7 summarizes the results of calculating the light attenuation characteristics when the length L, the angle α, and the number of the metal heating wires of the metal heating wire 15 have different values, and are linear in the respective calculation conditions. It can be seen that the attenuation characteristics are well represented. The values of α used in the calculation, 0.3 ° and 1.1 °, are the conditions under which the largest attenuation can be obtained when L has a value of 4 mm or 1 mm, respectively. In the structure of 4 mm in length and 4 in length and α = 0.3 ° L = 4 mm, the similar attenuation characteristics can be obtained. In this case, the optical attenuator operating area is about 37 dB and linear attenuation is obtained. It can be seen that the visible section is in the range of approximately 2 to 35 dB. However, the attenuation region obtained in FIG. 7 is not the maximum range that can be obtained through the present invention, and it is also possible to obtain a wider attenuation region of 50 dB or more by utilizing the light attenuation portion 13 longer.

The embodiments described above are for the purpose of explanation of the invention and are not intended to be limiting, and various substitutions, modifications, and changes are possible without departing from the spirit of the invention. In addition, if the ordinary expert in the technical field of the present invention, within the scope of the technical idea of the present invention, the metal hot wire of the above-described composition is deformed into a curved shape as shown in FIG. It will be appreciated that various embodiments are possible, such as changing the degree of bias of the metal heating wire, or employing a heating wire in parallel with the waveguide separately from the metal heating wire.

The thermo-optic variable optical attenuator having the characteristic metal hot wire composition as described above has a wide light attenuation area of more than 37 dB even in a straight waveguide composition, and shows a linear attenuation characteristic in the range of 2 to 35 dB, thereby using the variable light Efficient integrated optical devices including attenuators and arrays thereof can be implemented.

Claims (3)

Board; A cladding positioned over the substrate; A core located within the cladding; Located above the cladding, inclined at an angle to the longitudinal direction of the core, wherein the area of the portion larger than half includes a single or a plurality of hot wires outside of one side (ie, left or right) of the core. Variable optical attenuator. The method of claim 1, The hot wire is a variable light attenuator, characterized in that any one of a straight form, a curved form, a straight line form, and a combination thereof. The method of claim 1 or 2, Variable light attenuator, characterized in that it further comprises a hot wire parallel to the longitudinal direction of the core.

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