JPS63165816A - Optical attenuator - Google Patents

Abstract

PURPOSE:To obtain an optical attenuator capable of electrically controlling an attenuation factor by forming an area having a different refractive index on a part of a base showing double refraction when a voltage is impressed to form a waveguide and impressing a voltage in the prescribed direction of the base. CONSTITUTION:The waveguide 3 into which impurity is diffused is formed on the base 1. Independent electrode plates 2x, 2y, 2z are formed on six faces of the base 1. The electrode plates 2x, 2y, 2z can impress voltages respectively in the x, y and z directions of the base 1. When a voltage is impressed to the electrode plates, the refractive indexes of the waveguide 3 and the base 1 are changed. When the refractive index of the waveguide 3 is increased, the attenuation is dropped, and on the other hand the attenuation can be increased by reducing the refractive index of the waveguide 3. Thus, the attenuation of the optical attenuator can be controlled by controlling the voltages of respective electrode plates.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical attenuator, and particularly to an optical attenuator used in optical communications.

[Conventional technology]

With the recent development of optical communication technology, various optical devices have been developed. Among these, optical attenuators are devices that are playing an increasingly important role as devices for evaluating and adjusting optical communication systems, and are inserted in the middle of optical fiber transmission lines to transmit optical signals. It has a damping function.

Generally, such an optical attenuator attenuates an optical signal by reflecting or absorbing a portion of the optical signal, or by transmitting only light with a specific plane of polarization. Therefore, the attenuation rate of each device is determined by the reflectance, absorption rate, or angle of the plane of polarization. Some devices have a fixed attenuation rate, while others have a variable attenuation rate by changing reflectance or the like.

[Problem that the invention seeks to solve]

However, the conventional variable attenuation rate optical attenuator changes the attenuation rate by mechanically changing the structure of the optical system, and therefore has a problem in that the controllability of the attenuation rate is poor. For example, when the attenuation rate is controlled by an external control circuit, a transducer is required to convert an electrical control signal from the control circuit into a mechanical displacement.

Therefore, an object of the present invention is to provide an optical attenuator whose attenuation rate can be electrically controlled.

[Means for solving problems]

In the present invention, a substrate made of a crystal that exhibits birefringence by applying a voltage is prepared, a region with a different refractive index is provided in a part of the substrate, this region is used as a waveguide, and the substrate is guided in a predetermined direction. An optical attenuator is further provided with an electrode for applying a voltage, and the attenuation rate can be controlled by the voltage applied to this electrode.

〔Example〕

The present invention will be described below based on illustrated embodiments.

FIG. 1 is an external view of the basic structure of an optical attenuator according to an embodiment of the present invention. This optical attenuator has electrode plates 2x12y and 2Z formed on six surfaces of a rectangular parallelepiped-shaped substrate 1. For convenience of explanation, an external view of the two rectangular parallelepiped-shaped substrate 1 is shown in FIG.

The substrate 1 is made of a crystal that exhibits birefringence when a voltage is applied, and x, y, and z in the figure each indicate the direction of each crystal axis. A waveguide 3 is provided in a part of this substrate 17. This waveguide 3 is a region having a different refractive index from that of the substrate 1. For example, by diffusing impurities into the crystal constituting the base lfl, can be formed. In the case of this example, a lithium niobate crystal was used as the substrate 1, and the waveguide 3 was formed by diffusing titanium as an impurity into this crystal.

The optical attenuator is constructed by forming independent electrode plates 2x, 2y, and 2z on the six surfaces of the 20-substrate 1.

As shown in Figure 1, a pair of electrode plates 2x are provided facing each other so as to sandwich the substrate 1 from the X direction, and a pair of electrode plates 2y are provided so as to sandwich the substrate 1 from the X direction. 2Z are provided facing each other so as to be sandwiched therebetween from the Z direction.

In this way, the electrode 122 can be moved in the X direction of the substrate 1 using the electrode plate 2x, and in the X direction of the substrate 1 using the electrode plate 2y.
It is possible to apply voltages in two directions of the substrate 1 using the two directions.

When this optical attenuator is inserted into an optical fiber transmission system,
The optical signal is attenuated while traveling in the waveguide 3 in two directions as shown in the figure. The light traveling within this waveguide 3 has two modes. That is, the waveguide mode and the radiation mode. The waveguide mode is a mode in which light propagates while being confined within the waveguide 3, and when the refractive index of the waveguide 3 is higher than the refractive index of the substrate 1, the light travels in this mode. On the contrary, waveguide 3
When the refractive index of is lower than that of the group fFi,l,
The light will be emitted into the substrate l and will be in a radiation mode.

In reality, both modes are degenerate, and the attenuation rate by this optical attenuator is determined by the coupling rate between the two degenerate modes. As the proportion of waveguide modes increases, the attenuation rate decreases, and as the proportion of radiation modes increases, the attenuation rate increases.

The coupling rate between both modes can be changed by applying a voltage to the electrode plate 2.

Generally, the dielectric constant within the waveguide 3 is expressed in a tensor system. Before a voltage is applied to the electrode plate 2, this dielectric constant tensor has only a diagonal component, but when a voltage is applied, a non-diagonal component appears, and the coupling ratio between both modes changes in each direction. . For example, considering light polarized in the X direction, the coupling rate between the waveguide mode and the radiation mode in the X direction can be changed by applying a voltage to the pair of electrode plates 2y. Similarly, in the X direction, the coupling rate can be changed by changing the voltage applied to the pair of electrode plates 2x. After all, by controlling the voltage value applied to each electrode plate 2, it becomes possible to control the attenuation rate of the optical attenuator.

In the above embodiment, one pair of electrode plates were provided in each of the x, y, and z directions, but in the present invention, in short, it is possible to generate some kind of electric field in the waveguide 3 to change the refractive index. If possible, the electrode plate may be provided in any position.

〔Effect of the invention〕

As described above, according to the present invention, in an optical attenuator, by applying a voltage to a substrate including a waveguide, the refractive index of the substrate is changed, and coupling between the mode of light traveling through the waveguide and the radiation mode is achieved. Since the rate is changed, the attenuation rate can be electrically controlled.

[Brief explanation of the drawing]

FIG. 1 is an external view showing the basic structure of an optical attenuator according to an embodiment of the present invention, and FIG. 2 is an external view of a substrate that is one component of the optical attenuator shown in FIG. 1...Substrate, 2x, 2y, 2z...electrode plate, 3...
waveguide. Applicant: NEC Corporation Representative

Claims (1)

[Claims] A substrate made of a crystal that exhibits birefringence when a voltage is applied, a waveguide that is a region with a different refractive index provided in a part of this substrate, and an electrode for applying a voltage in a predetermined direction of the substrate. An optical attenuator comprising: