WO2001084750A1

WO2001084750A1 - Optical dispersion compensating device and optical dispersion compensating method using the device

Info

Publication number: WO2001084750A1
Application number: PCT/JP2001/003769
Authority: WO
Inventors: Kazuro Kikuchi; Yuichi Takushima; Mark Kenneth Jablonski; Yuichi Tanaka; Haruki Kataoka; Kenji Furuki; Noboru Higashi; Kazunari Sato; Shiro Yamashita
Original assignee: Oyokoden Lab Co., Ltd.
Priority date: 2000-05-01
Filing date: 2001-05-01
Publication date: 2001-11-08
Also published as: AU2001252667A1

Abstract

An optical dispersion compensating device which eliminates a serious communication trouble caused by wavelength dispersion encountered in a signal transmitting over an optical fiber in an optical communication having a communication bit rate of at least 10 Gbps, especially at least 40 Gbps, which is large in bandwidth and in polar zone for a group velocity delay time, which is produced by serially connecting a plurality of multi-layer-film elements capable of dispersion compensating by using group velocity delay time-wavelength characteristics, and which is used, after various selections for connecting, to subject to cubic dispersion compensating an optical signal having a wide wavelength band containing a wavelength band of 1260-1700 nm.

Description

Light dispersion compensating element and light dispersion compensation method using the element

In the following description of the present invention, dispersion means chromatic dispersion, optical dispersion compensation is also simply referred to as dispersion compensation, and optical dispersion compensating element is simply referred to as dispersion compensating element. This is also simply referred to as a dispersion compensation method.

The present invention relates to an element capable of compensating for a second- or higher-order (hereinafter described) dispersion occurring in optical communication using an optical fiber as a transmission line (hereinafter, an element capable of changing the second-order dispersion, or a second-order dispersion). Similarly, an element capable of compensating for the third-order dispersion described later includes an element capable of changing the third-order dispersion or a third-order dispersion compensating element. The present invention relates to a dispersion compensating element and a dispersion compensating method using the element.

More specifically, the present invention particularly relates to a dispersion compensating element capable of compensating for a tertiary or higher order dispersion, or a dispersion compensating element capable of performing a secondary and tertiary or higher order dispersion compensation, and an element thereof. And a dispersion compensation method using the same. The dispersion compensating element used in the dispersion compensating method of the present invention may be only the tertiary dispersion compensating element described above, or may include a unit for changing the incident position of incident light in the incident plane described later. Yes, and in some cases, not only third-order or higher dispersion compensation, but also second-order dispersion compensation can be configured, sometimes implemented in the case, and not implemented in the case There may be a so-called chip shape or wafer shape. The dispersion compensating element of the present invention includes all of these forms, and can take various forms depending on purposes such as use and sale.

In the present invention, the second-order dispersion compensation means "compensating for the slope of the dispersion of the wavelength-time characteristic curve described later with reference to FIG. 7A". 7A to compensate for the bending of the wavelength-time characteristic curve described later. " Background art In optical communications that use optical fibers for communication transmission lines, there is a need for longer-distance communication transmission lines and higher communication bit rates with the development of technology and the expansion of the range of use. I have. In such an environment, dispersion generated when transmitting an optical fiber becomes a serious problem, and various attempts have been made to compensate for dispersion. At present, second-order variance is a major problem, and various compensations have been proposed, and some of them have been effective to some extent, albeit limited.

However, as the demand for optical communication becomes more sophisticated, compensation for second-order dispersion alone during transmission is not sufficient, and compensation for third-order dispersion is becoming an issue.

Hereinafter, a conventional second-order dispersion compensation method will be described with reference to FIGS. 7A to 7C and FIG.

Fig. 8 is a diagram illustrating the dispersion versus wavelength characteristics of a single-mode optical fiber (hereinafter, also referred to as SMF), a dispersion compensation fiber, and a dispersion shift fiber (hereinafter, also referred to as DSF). In FIG. 8, reference numeral 601 is a graph showing the dispersion-wavelength characteristic of the SMF, 602 is a graph showing the dispersion-wavelength characteristic of the dispersion compensating fiber, 603 is a graph showing the dispersion-wavelength characteristic of 0 SF, and the vertical axis represents the dispersion. This is a graph with the horizontal axis representing wavelength.

As can be seen in Fig. 8, the dispersion increases as the wavelength of the light input to the fiber increases from 1.3 m to 1.8 μm in the SMF, and the wavelength of the input light increases in the dispersion compensation fiber. The variance decreases as the length increases from 1. 3 111 to 1. 7 πι. In the DSF, the dispersion decreases as the wavelength of the input light increases from 1.2 μπι to around 1.55 μπι, and the wavelength of the input light changes from around 1.55 / ^ 111 to 1.8 / xm. As the length increases, the variance increases. In DSF, in conventional optical communication at a communication bit rate of about 2.5 Gbps (2.5 gigabits per second), dispersion does not cause a problem when the wavelength of the input light is around 1.55 μιη.

7A to 7C are diagrams mainly explaining a second-order dispersion compensation method.FIG. 7A shows a wavelength-time characteristic and a light intensity-time characteristic, and FIG. 7B shows a second-order characteristic using an SMF and a dispersion compensating fiber. FIG. 7C is a diagram for explaining an example of transmission on a transmission line configured with only SMFs.

7A to 7C, reference numerals 501 and 511 denote characteristics of signal light before input to the transmission path. 530 is a transmission line composed of SMF 531, and 502 and 512 are transmissions of signal light having the characteristics of the graphs shown by reference numerals 501 and 511. A graph showing the characteristics of the signal light when the signal light is transmitted through the transmission line 530 and output from the transmission line 530 is shown.A transmission line 520 is composed of the dispersion compensating fiber 52 1 and the SMF 522. And 5 13 are graphs showing the signal light characteristics when the signal light having the characteristics of the graphs denoted by reference numerals 501 and 51 1 is transmitted through the transmission line 520 and output from the transmission line 520. It is. Reference numerals 504 and 514 indicate that the signal light having the characteristics of the graphs denoted by reference numerals 501 and 511 is transmitted through the transmission line 520 and output from the transmission line 520, and is described later by the present invention. 6 is a graph showing the characteristics of signal light when the desired third-order dispersion compensation is performed, and almost coincides with the graphs indicated by reference numerals 501 and 511. Graphs 501, 502, 503, and 504 are graphs in which the vertical axis represents wavelength and the horizontal axis represents time (or time), respectively. Graphs 511, 512, 513, 514 Is a graph with the light intensity on the vertical axis and time (or time) on the horizontal axis. Reference numerals 524 and 534 denote transmitters, and 525 and 533 denote receivers.

As described above, the conventional SMF increases the dispersion as the wavelength of the signal light increases from 1. to 1.8, so the group velocity delay due to dispersion is reduced in high-speed communication and long-distance transmission. Occurs. In the transmission path 530 constituted by the SMF, the signal light is greatly delayed on the long wavelength side as compared with the short wavelength side during transmission, as shown in graphs 502 and 512. For example, in high-speed communication and long-distance transmission, the changed signal light may not be able to be received as an accurate signal because it overlaps with the preceding and following signal lights.

In order to solve such a problem, conventionally, for example, as shown in FIG. 7B, dispersion is compensated (hereinafter, also referred to as correction) using a dispersion compensating fiber. The conventional dispersion compensating fiber solves the problem of SMF that the dispersion increases as the wavelength increases from 1.3 μπι to 1.8 μ, and as described above, the wavelength is 1.3 μ χα. It is designed so that the variance decreases with increasing length from 1.8 _μm to _{1.8 μm} . The dispersion compensating fiber can be used, for example, by connecting a dispersion compensating fiber 521 to an SMF 522 as shown by a transmission line 520 in FIG. In the transmission line 520, the signal light is delayed more in the long wavelength side than in the short wavelength side in the SMF 522, and the dispersion compensation

In 2 1, the short wavelength side is delayed more than the long wavelength side, As shown in the graphs 503 and 513, the amount of change can be suppressed smaller than the changes shown in the graphs 502 and 512.

However, in the above-mentioned conventional method of compensating for the second-order chromatic dispersion using the dispersion compensating fiber, the chromatic dispersion of the signal light transmitted through the transmission line is represented by the state of the signal light before input to the transmission line, that is, as shown in FIG. Dispersion compensation cannot be performed up to the shape of 0 1, and the limit is to compensate up to the shape of graph 503. As shown in graph 503, in the conventional second-order chromatic dispersion compensation method using a dispersion compensation fiber, the light of the central wavelength of the signal light is compared with the light of the short wavelength side and the light of the long wavelength side. Without delay, only the light of the component on the shorter wavelength side and the longer wavelength side than the light of the central wavelength component of the signal light is delayed. Then, as shown in the graph 513, a ripple may be generated in a part of the graph.

These phenomena are becoming serious problems such as the inability to receive accurate signals as the need for longer transmission distances and higher communication speeds increases in optical communications. For example, in a high-speed communication that transmits 10,000 km at a communication bit rate of 40 Gbps (40 gigabits per second) and a high-speed communication that transmits a distance of the order of 1,000 km at 80 Gbps, these phenomena occur. It is of great concern and of great concern. In such high-speed communication, it is considered difficult to use a conventional optical fiber communication system. For example, it is necessary to change the material of the optical fiber itself. It is a serious problem from a viewpoint.

It is difficult to perform such dispersion compensation only with second-order dispersion compensation, and third- or higher-order dispersion compensation is required.

Conventionally, there is a DSF as an optical fiber that reduces the second-order dispersion for light near 1.55 m in wavelength (hereinafter, the optical fiber is simply referred to as fiber). As is clear from the characteristics of FIGS. 7A and 8, the third-order dispersion compensation, which is the subject of the present invention, cannot be performed.

In realizing high-speed and long-distance optical communications, third-order dispersion is increasingly recognized as a major problem, and compensation for it is becoming an important issue. Many attempts have been made to solve the third-order dispersion compensation problem, but a third-order dispersion compensator or compensation method that can sufficiently solve the conventional problems has not yet been put into practical use. An example using a fiber formed with a diffraction grating as a method of compensating for third-order dispersion has been reported, but it has fatal disadvantages such as the inability to perform necessary compensation, large loss, and large dimensions. In addition, the price is high and practical application is not expected. As an example of the optical dispersion compensating element used for the third-order dispersion compensation, the present inventors have proposed a dispersion compensating element using a multilayer film such as a dielectric, which has been proposed separately from the present invention, and succeeded in third-order dispersion compensation. However, we were able to make significant progress in conventional optical communication technology. As a demand for high-speed optical communication and long-distance communication, third-order dispersion compensation is ideally performed when the communication bit rate is increased to 4 OGb ps or 80 Gb ps, for example. In order to sufficiently compensate for the third-order dispersion in multi-channel optical communication, it is necessary to realize dispersion compensation elements and dispersion compensation methods that can sufficiently compensate for the second- and third-order dispersion in a wider wavelength range. Is desired. As one of the proposals, the present inventors have proposed a third-order dispersion compensator capable of adjusting the wavelength band of the group velocity delay and the delay time of the group velocity delay separately from the present invention. In particular, one method of inexpensively implementing a third-order or higher-order dispersion compensating element that performs dispersion compensation suitable for each channel wavelength is a wavelength-tunable dispersion compensation (that is, a dispersion compensation target wavelength can be selected). A compensation element has been proposed. However, it is very difficult to obtain a dispersion compensating element having a group velocity delay time-wavelength characteristic such that sufficient dispersion compensation can be performed in a wide wavelength range using only these dispersion compensating elements alone.

The present invention has been made in view of such a point, and an object of the present invention is to provide a wide dispersion which has not been practically used in the past and a sufficient dispersion compensation over a wavelength range, particularly a third-order dispersion. An optical dispersion compensator with excellent group velocity delay time-wavelength characteristics that can perform compensation is provided at a low cost in a state of high reliability and suitable for mass production. A dispersion compensation method and a dispersion compensation element that enable third- or higher-order dispersion compensation using a multilayer element having a band and delay time adjustment function, or a combination of second- and third-order dispersion compensation. It is an object of the present invention to provide a dispersion compensation method and a dispersion compensation element that can be performed.

More specifically, the object of the present invention is as follows: o band (1260-1360 nm), E-band (1360-1460 nm), S-band (1460-1530 nm), C-band (1 530—1565 nm), L—band (1 565— At least one extreme value in at least one of the wavelength bands of each band called the U-band (16625 nm) An object of the present invention is to configure a dispersion compensating element using a multilayer film having a group velocity delay time-wavelength characteristic curve and to realize accurate dispersion compensation in each communication wavelength range. That is, the optical dispersion compensating element is designed to have a group velocity delay time-wavelength characteristic capable of compensating for the above-mentioned dispersion occurring in communication over a wavelength band of several tens of nm that has not been practically used in the past. It is an object of the present invention to provide a light dispersion compensation method using a low-cost, highly reliable and small communication system capable of compensating the dispersion of the entire signal light using the light dispersion compensation element. Disclosure of the invention

The present invention relates to a dispersion compensating element, and also relates to a dispersion compensating method for compensating dispersion by constructing a dispersion compensating element substantially equivalent to the dispersion compensating element of the present invention. In the description, the content of the dispersion compensating element of the present invention will be described as the dispersion compensating element used in the dispersion compensation method of the present invention, and will also serve as the description of the dispersion compensating method.

The most significant feature of the dispersion compensating element used in the dispersion compensation method of the present invention is that at least two elements capable of performing dispersion compensation or at least two parts of the element capable of performing dispersion compensation (hereinafter, referred to as The element capable of performing dispersion compensation and the element capable of performing dispersion compensation are collectively referred to as an element capable of performing dispersion compensation), and are connected in series along the optical path of signal light. That is, it has a dispersion compensation element using a multilayer film (hereinafter, also simply referred to as a multilayer film element).

In order to achieve the object of the present invention, in the optical dispersion compensating element used in the optical dispersion compensating method of the present invention, the element capable of performing the dispersion compensation uses a group velocity delay time-wavelength characteristic of a multilayer film. An optical dispersion compensating element capable of performing dispersion compensation by performing the method, wherein the group velocity delay time-wavelength characteristic curve of the multilayer film has at least one pole in a wavelength band to be subjected to dispersion compensation or in a wavelength region in the vicinity thereof. And the group velocity delay time of the optical dispersion compensating element used in the optical dispersion compensating method of the present invention. The shape of the wavelength characteristic curve differs from the group velocity delay time-wavelength characteristic curve of the element capable of performing dispersion compensation, which constitutes the optical dispersion compensation element used in the optical dispersion compensation method of the present invention, in general. ing.

The optical dispersion compensating element of the present invention having the multilayer film can basically be applied to any wavelength range. The present invention provides a great effect by using an optical dispersion compensating element using a multilayer film having a group velocity delay time-wavelength characteristic curve having at least one extreme value in a wavelength range of 1260 to 1700 nm which is currently being watched. Can be raised.

More specifically, according to the present invention, the O-band (1260-1360 nm), the E-band (1360-1460 nm), the S-band (1460-1530 ηm), the C-band ( 1 530_1565 nm), L-band (1565-1625 nm), U-band (1625-1675 ηm) A dispersion compensating element using a multilayer film having a group velocity delay time-wavelength characteristic curve having an extreme value can be configured, and accurate dispersion compensation can be performed in each communication wavelength range. In order to achieve the object of the present invention, an optical dispersion compensating element of the present invention is an optical dispersion compensating element that can be used for optical communication using an optical fiber in a communication transmission path and can compensate for dispersion as chromatic dispersion. Thus, it is possible to perform dispersion compensation as a multilayer element using a multilayer film having at least three reflective layers having different light reflectivities and at least two light transmitting layers formed between the reflective layers. A structure in which a plurality of elements or at least a plurality of parts of the element capable of performing dispersion compensation as an element capable of performing dispersion compensation are connected in series along the optical path of the signal light. It is characterized by

An example of the optical dispersion compensating element of the present invention is characterized in that there are a plurality of connection methods or connection paths of the plurality of elements capable of performing dispersion compensation.

An example of the optical dispersion compensating element of the present invention is characterized in that a connection method or a connection path of the plurality of elements capable of performing dispersion compensation can be selected from outside the optical dispersion compensating element. '

Examples of the optical dispersion compensating element of the present invention include a device capable of performing the plurality of dispersion compensation. It is characterized in that the method of connecting the element includes a method by reflection on the incident surface of the multilayer film element arranged oppositely.

An example of the optical dispersion compensating element of the present invention is that the means for selecting the connection method or the connection path of the plurality of elements capable of performing dispersion compensation from outside the optical dispersion compensating element is an electric means. Features.

In order to achieve the object of the present invention, an optical dispersion compensation method according to the present invention is an optical dispersion compensation method for performing communication by compensating for dispersion in optical communication using an optical fiber in a communication transmission line, comprising: A plurality of devices capable of performing dispersion compensation as a multilayer device using a multilayer film having at least three reflective layers having different ratios and at least two light transmitting layers formed between the reflective layers are provided. Alternatively, at least a plurality of portions of the element capable of performing dispersion compensation as an element capable of performing dispersion compensation are connected in series along the optical path of the signal light to the optical dispersion compensating element. This is characterized in that dispersion compensation is performed by injecting light.

An example of the optical dispersion compensation method of the present invention is to pass signal light transmitted through an optical fiber through the optical dispersion compensation element before wavelength separation for each receiving channel to compensate for at least tertiary dispersion. It is characterized by:

An example of the optical dispersion compensating method of the present invention is as follows. An optical dispersion compensating element configured by connecting a plurality of elements capable of performing the dispersion compensation in series is 1260 to 1360 nm, 1336 0 to 1460 nm, 1460 to 1550 nm, 1530 to: 1565 nm, 1565 to 1625 nm, 1625 to 1670 It is characterized by having a group velocity delay time-wavelength characteristic curve having at least one extreme value in at least one wavelength range of a wavelength range of 5 nm.

An example of the optical dispersion compensation method according to the present invention is characterized in that a plurality of types of connection methods of elements capable of performing dispersion compensation in the optical path of signal light can be selected. An example of the optical dispersion compensation method of the present invention is that the multilayer film used in at least one element capable of performing dispersion compensation constituting the optical dispersion compensation element has a center wavelength of incident light; The thickness of each layer of the multilayer film when considered as an optical path length for the light of the above is a multilayer film having a thickness of a value almost an integral multiple of λ / 4, and the multilayer film has a thickness of λ. 1/4 times the layer with the higher refractive index Η and the film thickness 1/4 times the lower the refractive index Re, the layer H is composed of a plurality of layers in which the layer L is combined, and the layer H is any one of S i, G e, T i 0 ₂ , T a ₂ 〇 ₅ , and N b ₂ O _s It is characterized by being formed of a layer consisting of

An example of the optical dispersion compensation method of the present invention is such that at least one of the multilayer devices has a thickness of at least one stacked film constituting a multilayer film of the multilayer device, and the film thickness of the multilayer film is parallel to a light incident surface of the multilayer film. This is characterized by a multilayer film element using a multilayer film that changes in the in-plane direction in a simple cross section, that is, in the in-plane direction of incidence.

An example of the optical dispersion compensation method of the present invention is characterized in that the layer L is formed using a material having a lower refractive index than the material used for the layer H.

Examples of optical dispersion compensation method of the present invention, the layer L is characterized by being formed by a layer consisting of S I_〇 _2.

An example of the optical dispersion compensation method according to the present invention is characterized in that at least one multilayer film has at least two film thickness change directions in the in-plane direction of the multilayer film. I have.

An example of the optical dispersion compensation method of the present invention includes an adjusting unit that engages with an element capable of performing the dispersion compensation and adjusts a film thickness of at least one laminated film of the multilayer film. A special feature is that means for changing the light incident position on the incident surface of the film is provided.

In the example of the light dispersion compensating element used in the light dispersion compensation method of the present invention, at least one kind of a multilayer film (described later) can be used as the multilayer film. That is, a multilayer film having at least five types of laminated films having different optical properties (that is, at least five layers having different optical properties such as light reflectance and film thickness). Have at least three types of reflective layers including at least two types of reflective layers having different light reflectances from each other, and have at least two light transmitting layers in addition to the three types of reflective layers. The one of the three types of reflective layers and the one of the two light transmitting layers are alternately arranged, and the multilayer film is a first layer in order from one side in a thickness direction of the film. The first layer as a reflection layer, the second layer as a first light transmission layer, the third layer as a second reflection layer, the fourth layer as a second light transmission layer, and the third reflection layer Some fifth layer The center wavelength of the incident light is defined as λ, and in the first to fifth layers, it is considered as the center wavelength of the incident light; the optical path length for L light (hereinafter, also simply referred to as the optical path length). (Hereinafter, simply referred to as film thickness or film thickness) Force S, an integral multiple of / 4 ± 1% (hereafter, integral multiple of / 4, or λ / 4 The film thickness of the multilayer film is 1/4 times I (hereinafter, ± 1% of 1/4 times λ). A layer having a higher refractive index (hereinafter referred to as a layer having a thickness of 1/4 times L) (hereinafter also referred to as a layer）) and a layer having a lower refractive index having a thickness of 1/4 times (hereinafter referred to as a layer). L), also known as L).

The multilayer film Α is a layer in which the five-layer laminated film, that is, the first to fifth layers are combined one by one in the order of layer H and layer L in order from one side in the thickness direction of the multilayer film. (Hereinafter, also referred to as HL layer) 3 sets (a layer combining the layer HI layer and the layer L 1 layer is referred to as an HL layer 1 set; the same applies hereinafter). The second layer and the layer L, which are formed by laminating 10 sets of the layer H and the layer obtained by combining the layer H (that is, the layer formed by laminating two layers H, hereinafter also referred to as the HH layer), 3rd layer composed of 7 sets of layers and HL layers, 4th layer composed of 38 sets of HH layers, 1 layer and 13 layers of HL A multi-layered film composed of a set and a fifth layer formed by laminating

Instead of the second layer formed by laminating 10 sets of the HH layers of the multilayer film A, the multilayer film B is replaced by a film having the same direction as that of the multilayer film A. In order from one side in the thickness direction ”, three sets of HH layers and a combination of layers L and L (that is, a layer formed by stacking two layers of L. Hereinafter, the layer of LL is also referred to) 3 sets of HH layers, 3 sets of LL layers, 2 sets of LL layers, and 1 set of HH layers as a multilayer film formed by laminating in this order.

Instead of the fourth layer formed by stacking 38 sets of the HH layers of the multilayer film A or B in the multilayer film C, the fourth layer is the same as in the case of the multilayer film A. Direction (in order from one side in the thickness direction of the film), 3 sets of HH layers, 3 sets of LL layers, 3 sets of HH layers, 3 sets of LL layers, 3 sets of HH layers 3 sets, 3 sets of LL layers, 3 sets of HH layers, 3 sets of LL layers, 3 sets of HH layers, 3 sets of LL layers, 3 sets of HH layers Set, 3 sets of LL layers, 3 sets of HH layers, 3 sets of LL layers, 2 sets of HH layers A multilayer film,

A layer in which the multilayer film D is formed by laminating the five-layered film, that is, the first to fifth layers in this order from one side in the thickness direction of the multilayer film, and combining layers one by one in the order of layer H. The first layer consists of five sets of LH layers, the second layer consists of seven sets of LL layers, one layer H and one layer of LH. 3rd layer composed of 7 sets and 4 layers composed of 5 7 layers of LL, 1 layer H and 13 layers of LH laminated Each layer is formed by the fifth layer

With a multilayer film,

A first layer in which the multilayer film E is formed by laminating two sets of HL layers in order of the five-layer laminated film, that is, the first to fifth layers, from one side in the thickness direction of the multilayer film. , A second layer composed of 14 sets of HH layers, a third layer composed of one set of layer L and 6 sets of HL layers, and 24 layers of HH. A fourth layer composed of set laminations, a layer L is a multilayer film composed of one layer and an HL layer composed of a fifth layer composed of 13 layers laminated, and

Instead of the second layer formed by stacking 14 sets of HH layers of the multilayer film E, the multilayer film F is replaced by a “film” in the same direction as in the case of the multilayer film E. From one side in the thickness direction '', 3 sets of HH layers, 3 sets of LL layers, 3 sets of HH layers, 3 sets of LL layers, 2 sets of HH layers A set, one set of LL layers and one set of HH layers are laminated in this order to form a multilayer film formed of a laminated film,

Instead of the fourth layer formed by laminating 24 sets of HH layers of the multilayer film E or F, the fourth layer has the same direction as that of the multilayer film E. 3 sets of HH layers, 3 sets of shino layers, 3 sets of HH layers, 3 sets of LL layers, 3 sets of HH layers in order from one side in the thickness direction of the film 3 sets of LL layers, 3 sets of HH layers, 3 sets of LL layers, 2 sets of HH layers, 1 set of LL layers, 1 set of HH layers A multilayer film formed by laminating in this order, a multilayer film H, wherein the five-layer laminated film, that is, the first to fifth layers are one in the thickness direction of the multilayer film. The first layer consists of four sets of LH layers, the second layer consists of nine sets of LL layers, one layer H and six layers of LH. The third set consisting of stacking sets Layer, a fourth layer composed of 35 sets of LL layers, and a fifth layer composed of one layer H and 13 layers of LH layers. Multi-layer film. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram illustrating optical dispersion compensation according to the present invention.

FIG. 2 is a cross-sectional view of the multilayer film of the present invention.

FIG. 3 is a perspective view of the multilayer film of the present invention.

FIG. 4 is a group velocity delay time-wavelength characteristic curve of the multilayer film of the present invention.

FIG. 5A is a graph showing a group velocity delay time-wavelength characteristic of one element capable of performing dispersion compensation, which is a basic element of the dispersion compensation element of the present invention.

FIG. 5B is a diagram illustrating a method of improving the group velocity delay time-wavelength characteristic using a plurality of elements capable of performing dispersion compensation according to the present invention. The group velocity delay time of the optical dispersion compensating element of the present invention connected in series It is a graph showing sex.

FIG. 5C is a diagram for explaining a method of improving the group velocity, the delay time and the wavelength characteristic by using a plurality of elements capable of performing the dispersion compensation according to the present invention, and the element capable of performing the dispersion compensation. 6 is a graph showing the group velocity delay time versus wavelength characteristic of the optical dispersion compensating element of the present invention in which three are connected in series.

FIG. 5D is a diagram illustrating a method of improving the group velocity delay time one wavelength characteristic using a plurality of elements capable of performing dispersion compensation according to the present invention. 6 is a graph showing the group velocity delay time versus wavelength characteristic of the optical dispersion compensating element of the present invention in which three are connected in series. .

FIG. 6A is a diagram illustrating an example of the optical dispersion compensating element of the present invention, and illustrates an example in which two elements capable of performing dispersion compensation are connected in series to form an optical dispersion compensating element. FIG.

FIG. 6B is a diagram illustrating an example of the optical dispersion compensating element of the present invention, and illustrates an example in which three elements capable of performing dispersion compensation are connected in series to form an optical dispersion compensating element. FIG.

FIG. 6C is a diagram for explaining an example of the optical dispersion compensating element of the present invention. In the multilayer film whose film thickness changes in the incident plane direction, two signal light incident positions are shown. FIG. 4 is a diagram illustrating an example in which an optical dispersion compensating element is configured by being connected in series along a navigation route.

FIG. 6D is a diagram illustrating an example of the optical dispersion compensating element of the present invention, and is a diagram illustrating an example in which the optical dispersion compensating element of the present invention is mounted in one case.

FIG. 7A is a diagram for explaining a method of compensating for second and third order chromatic dispersion, and is a diagram for explaining a wavelength-time characteristic and a light intensity-time characteristic.

FIG. 7B is a diagram for explaining a method for compensating the second and third order chromatic dispersion, and is a diagram for explaining a transmission path.

FIG. 7C is a diagram illustrating a method of compensating for the second and third order chromatic dispersion, and is a diagram illustrating a transmission path.

FIG. 8 is a graph showing dispersion-wavelength characteristics of a conventional optical fiber.

FIG. 9A is a plan view showing another embodiment of the present invention.

FIG. 9B is a front view of the embodiment. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Each drawing used for the description schematically shows dimensions, shapes, arrangement relations, and the like of each component so that the present invention can be understood. For convenience of description of the present invention, the magnification may be partially changed in the drawings, and the drawings used in the description of the present invention may not necessarily be similar to the actual products and descriptions in the embodiments and the like. Also, in each of the drawings, the same components are denoted by the same reference numerals, and redundant description may be omitted.

Fig. 1 is a diagram illustrating a method of compensating dispersion generated in communication using an optical fiber as a transmission line with an optical dispersion compensator. Reference numeral 111 denotes signal light remaining after compensating for secondary dispersion. The group velocity delay time vs. wavelength characteristic curve showing the third order dispersion of the dispersion compensating element, 1102 is the group velocity delay time vs. wavelength characteristic curve of the dispersion compensating element, and 1103 is the signal having the dispersion characteristic of curve 1101. A group velocity delay time-wavelength characteristic curve between the wavelength bands λ to λ ₂ to be compensated after the light dispersion is compensated by the dispersion compensation element having the dispersion characteristic of the curve 1102, and the vertical axis is the group velocity The delay time and the horizontal axis are wavelength.

2 to 4 are diagrams for explaining the optical dispersion compensating element according to the present invention. FIG. 2 is a cross-sectional view of a multilayer film described later, FIG. 3 is a perspective view of a multilayer film having a changed film thickness, and FIG. 5 is a graph showing a group velocity delay time versus wavelength characteristic curve of a multilayer film.

FIG. 2 is a diagram schematically illustrating a cross section of a multilayer film used as an example of the tertiary dispersion compensation element of the present invention. 2, reference numeral 100 denotes a multilayer film as an example of the optical dispersion compensating element of the present invention, 101 denotes an arrow indicating the direction of incident light, 102 denotes an arrow indicating the direction of output light, 103, 104 is a reflective layer having a reflectivity of less than 100% (hereinafter also referred to as a reflective film), 105 is a reflective layer having a reflectivity of 98 to: L 00%, and 108 and 109 are light The transmission layer, 1 1 1 and 1 1 2 are cavities. Further, reference numeral 107 denotes a substrate, for example, which is made of 117 glass.

The reflectances R (103), R (104), and R (105) of each of the reflective layers 103, 104, and 105 in FIG. 2 are R (103) ≤R (1 04) ≤R (1 05). It is preferable in terms of mass production that the reflectance of each layer is set to be different from each other at least between the reflective layers adjacent to each other with the light transmitting layer interposed therebetween. That is, incident light is incident The reflective layer is formed so that the reflectance of each reflective layer with respect to the central wavelength L of the incident light gradually increases from the side toward the thickness direction of the multilayer film. Then, the reflectance of each reflective layer with respect to the wavelength; I light is defined as 60% ≤R (103) ≤77%, 96% ≤R (104) ≤99.8%, 98% ≤R (105). By setting the range to satisfy the relationship of R (103), R (104), and R (105), the group velocity delay time-wavelength characteristic curve as shown in FIGS. Obtainable. It is more preferable that R (10 3) <R (104) <R (105), and it is more preferable that R (105) be close to or equal to 100%. Performance can be further enhanced.

Then, in order to make the optical dispersion compensating element of the present invention easier to manufacture, it is preferable to select the conditions for forming each reflective layer so that the intervals when considered as the optical path length between adjacent reflective layers are different from each other, The design accuracy of the reflectance of each reflective layer can be relaxed, and the film thickness is the wavelength; a combination of unit films of 1/4 of I (films with an integral multiple of λ / 4) A multilayer film used for a dispersion compensator can be formed, and a third-order dispersion compensator having high reliability and excellent mass production I "can be provided at low cost.

Although the thickness of the unit film of the multilayer film is described to be a quarter of the wavelength, this is within the range of an error allowed in the formation of the film in mass production, as described above. 4 means that the present invention is at λ / 4 ± 1%; it means a film thickness of I / 4, and even in this range, the present invention has a particularly great effect. Emit. Therefore, in the present invention, the film thickness in this range is referred to as 1/4 thickness. In particular, by setting the thickness of the above unit film to /4±0.5% (in this case, I-no 4 has no error; meaning Ζ4), there is little variation without impairing mass productivity. Thus, a highly reliable multilayer film can be formed, and an optical dispersion compensating element as described later with reference to FIGS. 5A to 5D and FIGS. 6A to 6D can be provided at low cost.

Also, the multi-layer film according to the present invention is described as being formed by laminating unit films having a thickness of λ / 4. This is a method of forming one unit film and then forming the next unit film. Force that can form a multi-shear film by repeating this process. In general, a film with a thickness of an integral multiple of fly / 4 is continuously formed. Such a multilayer film is naturally included in the multilayer film of the present invention. Then, some examples of the multilayer film of the present invention could be formed by using a film forming step of continuously forming the reflection layer and the transmission layer.

FIG. 3 is a diagram illustrating an example in which the thickness of the multilayer film 100 is changed in an in-plane direction of a later-described incident surface 220 of the multilayer film 100 of FIG.

In FIG. 3, reference numeral 200 denotes a multilayer film as an example of the optical dispersion compensating element of the present invention, 201 denotes a first reflective layer, 202 denotes a second reflective layer, and 203 denotes a third reflective layer. A reflective layer, 205 is a substrate, 206 is a first light transmitting layer, 207 is a second light transmitting layer, 211 is a first cavity, 211 is a second cavity, 220 is the light incident surface, 230 is the arrow indicating the direction of the incident light, 240 is the arrow indicating the direction of the emitted light, 250 is the arrow indicating the direction of the first film thickness change, 26 0 is an arrow indicating a second film thickness change direction, and 270 and 271 are arrows indicating a direction in which an incident position of incident light is moved.

In FIG. 3, for example, on a substrate 205 made of, for example, BK-7 glass (trade name of Schott, Germany), a third reflection layer 203, a second light transmission layer 207, The second reflection layer 202, the first light transmission layer 206, and the first reflection layer 201 are sequentially formed.

As the thickness of the first light transmission layer 206 changes in the direction indicated by the arrow 250 in FIG. 3 (the thickness gradually increases from right to left in the figure), and the second light transmission The multilayer film is formed so that the thickness of the layer 207 changes in the direction indicated by the arrow 260 (the thickness gradually increases from the front of the figure to the other side). The thicknesses of the first to third reflective layers are the first, second, and third when the wavelength when the resonance wavelengths of the first and second cavities match the center wavelength of the incident light; L. The film thickness is formed such that the reflectance of each reflective layer of No. 3 satisfies the same conditions as the conditions of R (103), R (104) and R (105).

FIG. 4 shows a multilayer film (hereinafter also referred to as a light dispersion compensation element) 200 as an example of the light dispersion compensation element of the present invention. Light is incident, the emitted light is obtained in the direction of arrow 240, and the group velocity when the incident position of the incident light is moved in the direction of arrow 270 or 271 in Fig. 3 as described later When delayed This is for explaining the manner in which the inter-wavelength characteristic curve changes.

Fig. 4 shows the group velocity delay time vs. wavelength characteristic curve when the incident light having the center wavelength; L is incident on the incident position 280 to 282, the vertical axis represents the group velocity delay time, and the horizontal axis represents the wavelength. It is. By appropriately selecting the conditions for changing the film thickness in the directions indicated by the arrows 250 and 260 of the reflective layer 201 to 203 and the light transmitting layer 206 and 207, When the incident position of the incident light on the incident surface 220 is moved in the direction indicated by the arrow 270, the group velocity delay time is maintained while maintaining the shape of the group velocity delay time-wavelength characteristic curve substantially the same. (1) The center wavelength of the wavelength characteristic curve. (For example, the wavelength giving the extreme value in the group velocity delay time-wavelength characteristic curve 2801 of the substantially symmetrical shape in FIG. 4) changes, and from that position in the direction indicated by the arrow 271 When the incident position is moved, the wavelength; L. The shape of the group velocity delay time-wavelength characteristic curve can be changed as shown by the curves 2811 and 2812 in FIG. Each curve in FIG. 4 is obtained when the film thickness of each film is monotonically increased in the directions of arrows 250 and 260 in FIG.

Band center wavelength at curve 2801-1282. Is set at an appropriate wavelength in the graph of FIG. 4 for the purpose of dispersion compensation, but may be, for example, approximately the center of the wavelength range of the curve shown in FIG. It may be determined appropriately according to the purpose. In addition, it is not necessary to check the correspondence between the wavelengths of the characteristic points of the curve, such as the extreme wavelengths of the curves 2801-128, in advance. is there.

Thus, for example, first, the center wavelength of the incident light to be dispersion-compensated; the band center wavelength λ corresponding to I. The incident position of the incident light is moved in the direction of arrow 270 so as to match, and the content of the guarantee to be compensated for dispersion, that is, the dispersion situation of the incident light is adapted and used for dispersion compensation The shape of the group velocity delay time-wavelength characteristic curve is selected from, for example, the curves in Fig. 4, and the incident position is set in the direction indicated by the arrow 271 in Fig. 3 accordingly. By selecting each point as indicated by 282, the dispersion compensation required for the signal light can be effectively performed.

As is clear from the shape of the group velocity delay time-wavelength characteristic curve in FIG. 4, tertiary dispersion compensation is performed using the optical dispersion compensating element of the present invention, for example, using the curve 2801. The second-order minute dispersion compensation can be performed by using a portion of the curve 2811 or 2812 that is relatively close to a linear component.

As described above with reference to FIGS. 2 to 4, the “element capable of performing a dispersion compensating element” used in the present invention is described. It is clear from the explanation of each curve in FIG. 4 that the following dispersion can be compensated to some extent.

However, the wavelength bandwidth of dispersion compensation that can be compensated by itself as an “element capable of performing a dispersion compensating element” is around 1.5 nm for the signal light whose wavelength is around 1.55 im, and the group velocity delay time is 3 In many cases, this is in the order of ps (picoseconds), and if the wavelength bandwidth of dispersion compensation is widened to support multiple channels of optical communication, the group velocity delay time is short enough to allow sufficient dispersion compensation. It is difficult to obtain, and it is desirable that further improvements be made in order to use it widely and practically in actual communications. Therefore, the present invention will be described in more detail with reference to FIGS. 5A to 5D and FIGS. 6A to 6D.

FIGS. 5A to 5D are diagrams illustrating a method of improving the group velocity delay time-wavelength characteristic by using a plurality of elements capable of performing dispersion compensation as described above, for example, and FIG. 5A is used in the present invention. Group velocity delay time vs. wavelength characteristic curve with one element that can perform dispersion compensation. Figure 5B shows the shape of the group velocity delay time vs. wavelength characteristic curve, and the peak of the group velocity delay time vs. wavelength characteristic curve. Group velocity delay of the optical dispersion compensating element of the present invention in which two elements capable of performing dispersion compensation having different wavelengths (hereinafter, also referred to as extreme values) giving values (hereinafter, also referred to as extreme values) are connected in series. Figure 5C shows the group velocity delay-time-wavelength characteristic curve of the optical dispersion compensating element of the present invention in which three elements capable of performing dispersion compensation with almost the same characteristic and different extreme wavelengths are connected in series. Figure 5D shows the group velocity The group velocity delay time vs. wavelength characteristic of the optical dispersion compensating element used in the optical dispersion compensation method of the present invention in which three elements capable of performing dispersion compensation differing in the shape of the delay time versus wavelength characteristic curve and the extreme wavelength are connected in series. In each case, the vertical axis represents the group velocity delay time, and the horizontal axis represents the wavelength.

5A to 5D, reference numerals 301 to 309 denote the group velocity delay time-wavelength characteristic curves of one element capable of performing dispersion compensation used in the present invention, and 310 denotes the present invention. Of the group velocity delay time-wavelength characteristic curve used for Group delay time-wavelength characteristic curve when two elements that can compensate for each other are connected in series, and 311 is almost the same shape of the group velocity delay time-wavelength characteristic curve used in the present invention. Group velocity delay time-wavelength characteristic curve when three elements capable of performing dispersion compensation with different extreme wavelengths are connected in series, and 3 1 2 is also an extreme value for the group velocity delay time-wavelength characteristic curve. It is a group velocity delay time-wavelength characteristic curve when three elements capable of performing dispersion compensation with different wavelengths are connected in series. In Fig. 5A, the symbol a is the wavelength band for dispersion compensation, and b is the extreme value of the group velocity delay time. .

In FIG. 5B and FIG. 5C, the extremum of the group velocity delay time of the group velocity delay time vs. wavelength characteristic curve 310 is 1.6 times that of a single element capable of performing dispersion compensation, The wavelength band to be compensated is about 1.8 times, and the extremum of group velocity delay time vs. wavelength characteristic curve 3 1 1 is about 2.3 times that of a single group velocity delay time. The bandwidth is about 2.5 times that of a single device that can perform dispersion compensation. In Fig. 5D, the extreme value of the group velocity delay time in the curve of the group velocity delay time-wavelength characteristic 312 is about three times the wavelength band for dispersion compensation, which is about three times that of a single element that can perform dispersion compensation. The area is about 2.3 times that of a single element capable of performing dispersion compensation. The extreme value of the group velocity delay time of the group velocity delay time-wavelength characteristic curve of the element capable of performing dispersion compensation using a multilayer film as described in FIGS. It varies depending on the configuration conditions of each reflection layer and each light transmission layer of the multilayer film. For example, the wavelength band for dispersion compensation is relatively wide as shown by the curve 307 in FIG. Group velocity delay-wavelength characteristic curve where the value is not too large, or the group velocity delay time-wavelength characteristic curve where the wavelength band for dispersion compensation is narrow but the extreme value of the group velocity delay time is large as shown by curve 308 In addition, it is possible to realize an element capable of performing dispersion compensation having various characteristics. - ₍ Multilayer films used in an element capable of performing such dispersion compensation include, for example, the multilayer films A to H described in the section of “Disclosure of the Invention”. When an element capable of performing dispersion compensation was created using H, the extreme value of the group velocity delay time was 3 ps (picoseconds) for signal light with a wavelength of about 1.55 μm. A group velocity delay time-wavelength characteristic curve with a dispersion compensation wavelength band of 1.3 to 2.0 nm was realized. A plurality of devices capable of performing this dispersion compensation are connected in series, and the wavelength band for dispersion compensation having a group velocity delay-one wavelength characteristic capable of compensating for dispersion due to optical fiber transmission is 15 nm. Can be realized. This + optical dispersion compensating element is used as a third-order dispersion compensating element for a 30-channel communication system in which the wavelength is around 1.55 μηι and the bandwidth of each channel is 0.5 nm and the bandwidth is 0.5 nm.

When optical communication of 60 km transmission was performed at the equivalent of 0 Gbps, the communication could be performed without any harm to the third-order dispersion.

In addition, the group velocity delay time vs. wavelength characteristic curve in FIG. 4 and the group velocity delay time vs. wavelength characteristic curve in FIG. By properly selecting the wavelength characteristics, not only the third-order dispersion but also the second-order dispersion could be compensated.

The example of the optical dispersion compensating element in which at least two elements capable of performing dispersion compensation of the present invention are connected in series has a group velocity delay time-wavelength characteristic necessary for compensating third-order or higher dispersion. In order to realize an optical dispersion compensating element, it is desirable to use at least one element capable of performing dispersion compensation of group velocity delay time-wavelength characteristics having an extreme value in a wavelength region to be compensated for dispersion.

In order to more effectively perform dispersion compensation of a communication transmission line, it is desirable to improve the group velocity delay time-wavelength characteristic curve as an optical dispersion compensating element. As one method for this, there is a method having means for adjusting the group velocity delay time-wavelength characteristic of an element capable of performing dispersion compensation.

As a method, as described with reference to FIGS. 2 and 3, the signal light in an element capable of performing dispersion compensation by changing the thickness of the light transmitting layer and the reflecting layer of the multilayer film in the direction of the incident plane. By changing the relative incident position of the element, the group velocity delay time-wavelength characteristic of the element capable of performing dispersion compensation can be raised. The means for changing the incident position of the incident light is realized by moving at least one of the optical dispersion compensating element 200 or the incident position itself of the incident light with respect to the position of the incident light. As the light dispersion compensating element or means for moving the incident light, various choices can be made depending on the circumstances, such as the circumstances in which the light dispersion compensating element is used, the cost, and the characteristics. For example, Depending on the cost or the circumstances of the equipment, it is possible to use a method that uses manual means such as screws, and to make adjustments for accurate adjustment or even when manual adjustment is not possible. For example, it is effective to use an electromagnetic step motor or continuous drive motor, and it is also effective to use a piezoelectric motor using PZT (lead zirconate titanate). It is. In addition, the incidence position can be easily and accurately selected by using a prism and a two-core collimator that can be combined with these methods, or by selecting the incidence position by an optical means such as using an optical waveguide. be able to.

Wherein each layer of the multilayer film of the element capable of performing dispersion compensation used for optical dispersion compensation device of the present invention, the thickness created by the wave of S I_〇 ₂ of ion-assisted deposition of 4 minutes film (hereinafter, Ion'ashisu Layer L), and a layer H formed of a TiO ₂ ion-assisted film having a quarter wavelength thickness. Wherein S i 〇 ₂ ions (the layers) assist film called layer 1 set of LH in one layer and T i O ₂ of the ion assist film (layer H) 1-layer combination layer of, for example, a layer of "LH 5 "Laminating a set" means "layer L, layer H, layer L, layer H, layer L, layer H, layer L, layer H, layer H, layer H, layer H, layer one by one. It means that.

Similarly, the layer of the LL is called the thickness was formed overlapping two layers L which is composed of the ion-assisted film S I_〇 ₂ quarter wavelengths layer substantially set of LL. Therefore, for example, “three layers of LL are stacked” means “formed by stacking six layers L”.

As the composition of the film forming the layer H, although an example of a dielectric, the present invention is not limited thereto, as the same dielectric material as T i 0 ₂ Other T io ₂ , T a ₂ 〇 _5, N b ₂ 〇 ₅ or the like can be used, further, in addition to the dielectric material, it is also possible to form a layer H with S i and G e. When the layer H is formed using Si or Ge, there is an advantage that the layer H can be formed thinner than the optical properties. In addition, although the example of S i 0 ₂ was shown as the composition of the layer L, S i 〇 ₂ is a force S that has the advantage of being able to form the layer L at low cost and high reliability. The present invention is not limited to this. Not If the layer L is formed of a material whose refractive index is lower than the refractive index of the layer H, a light dispersion compensating element exhibiting the above effects of the present invention can be realized.

Further, in the present embodiment, the layer L and the layer H constituting the multilayer film are formed by ion-assisted vapor deposition, but the present invention is not limited to this, and ordinary vapor deposition, sputtering, ion plating, and the like are performed. The present invention exerts a great effect even when a multilayer film formed by the above method is used.

The light dispersion compensating element of the present invention can be used by appropriately holding a wafer-like element such as a multilayer film 200 as a light dispersion compensating element shown in FIG. In the thickness direction, that is, in the direction of thickness, that is, in the direction from the incident surface 220 to the substrate 205, for example, perpendicularly, the chip is cut into small pieces. The form has various possibilities, for example, it can be used as a compensating element. In any case, the main effects described in the present invention can be obtained.

6A to 6D are diagrams for explaining an example of the optical dispersion compensating element of the present invention, and FIG. 6A is a diagram illustrating a configuration of an optical dispersion compensating element by connecting two elements capable of performing the dispersion compensation in series. FIG. 6B shows an example in which three elements capable of performing the dispersion compensation are connected in series to form a light dispersion compensation element, and FIG. 6C shows a case where the film thickness changes in the direction of the incident plane. Figure 6D shows an example in which two points of incidence of signal light are connected in series along the signal light path on a multilayer film to form an optical dispersion compensator. FIG. 9 is a diagram showing an example in which a dispersion compensating element is mounted in one case.

6A to 6D, reference numerals 410, 420, 430, and 440 denote optical dispersion compensating elements of the present invention, 411, 412, 421 to 423, 442, and 443 denote elements capable of performing dispersion compensation, and 416 denotes a dispersion compensation element. Multilayer films used in devices that can be used, 415, 4151, 4152, 426, 436, '446, are optical fibers, 413, 4131, 414, 4141, 424, 425, 434, Reference numerals 435, 444, and 445 denote arrows indicating the traveling direction of the signal light, reference numeral 417 denotes a lens, reference numeral 418 denotes a two-core collimator comprising a lens 417 and optical fibers 4151 and 4152, reference numeral 441 denotes a case, and reference numeral 431 denotes an incident surface. Performing wafer-shaped dispersion compensation, which is configured so that dispersion compensation can be performed by forming a multilayer film whose thickness changes inward on the substrate 432 and 433 are “elements that can perform dispersion compensation”, respectively.

In FIG. 6A, the signal light that has entered in the direction of arrow 4 13 enters the element 4 11 that can perform dispersion compensation, and the element 4 1 that can receive dispersion compensation and perform dispersion compensation. Emitted from 1 and transmitted through fiber 4 15 to be able to perform dispersion compensation Entering element 4 12, and then subjected to dispersion compensation again to be able to perform dispersion compensation 4 2 The optical fiber 4 15 is transmitted in the direction of the arrow 4 14.

Reference numeral 4112 is a cross-sectional view for explaining the internal structure of a portion of the element 411 capable of performing dispersion compensation, which is surrounded by the curve 4111. The optical fibers 4 15 1 and 4 15 2 and the lens 4 17 constitute a two-core collimator 4 18, and the signal light that has traveled along the optical fiber 4 15 1 in the direction of the arrow 4 1 3 1 is a lens 4 17 Pass through and enter the multilayer film 4 16. The multilayer film 4 16 has the group velocity delay time-wavelength characteristic shown in FIG. 5A, and the signal light that has entered the multilayer film 4 16 through the optical fiber 4 15 1 and the lens 4 17. Is subjected to tertiary dispersion compensation, passes through the reproduction lens 4 17, enters the optical fiber 4 15 2, travels in the direction of the arrow 4 1 4 1, and is capable of performing dispersion compensation 4 1 It is incident on 2. The signal light that has been further subjected to dispersion compensation by the element 4 12 capable of performing dispersion compensation exits from the element 4 12 capable of performing dispersion compensation, and passes through the optical fiber 4 15 with an arrow 4 1 4 The light is emitted in the direction indicated by.

The optical dispersion compensating element 410 of the present invention shown in FIG. 6A has the group velocity delay time-wavelength characteristic shown in FIG. 5B, and the signal light incident on the optical dispersion compensating element 410 Is subjected to dispersion compensation according to the group velocity delay time-wavelength characteristic shown in FIG. 5B, and is emitted from the optical dispersion compensating element 410.

Similarly, in the optical dispersion compensating element 420 shown in FIG. 6B, the signal light that has entered the optical dispersion compensating element 420 from the direction of the arrow 424 is also capable of performing dispersion compensation. In the process of sequentially entering and exiting 4 23, for example, dispersion compensation is performed according to the group velocity delay time vs. wavelength characteristic curve as shown in FIG. The optical fiber 4 26 travels in the direction indicated by the arrow 4 25.

Fig. 6C shows the part of the element 431 that can perform dispersion compensation formed on the same wafer instead of the elements 411 and 4122 that can perform dispersion compensation in Fig. 6A. The optical dispersion compensator 430 is an example in which 4 3 2 and 4 3 3 are connected in series along the signal light path using an optical fiber 4 36. This is the same as described in the above. However, it is clear from the above description that the method of dispersion compensation is different depending on the group velocity delay time-wavelength characteristic of the element capable of performing dispersion compensation.

9A and 9B show a modification of FIG. 6C. In this example, for example, a semiconductor substrate 700 is used as a substrate of the element 431 capable of performing dispersion compensation, and the portions 432 and 433 of the element 431 capable of performing dispersion compensation. The movable parts 720 and 703 arranged in a matrix in the vertical and horizontal directions are formed on the surface on which the movable parts are arranged. An even number of elements (hereinafter, also referred to as a matrix element plate) in which elements capable of performing dispersion compensation, which are elements using a multilayer film as described above (also referred to as a multilayer element) are formed.

For example, an electrode is arranged on the movable portion on the matrix-like element plate. In each movable part, the inclination on the surface of the matrix-like element plate changes according to the state of the voltage applied to the electrode. Therefore, the perpendicular direction of the incident surface of the element on which the dispersion compensation can be performed is changed.

The even number of matrix element plates 7 1 1 and 7 1 2 are appropriately placed two by two with the incident surfaces of the elements capable of performing dispersion compensation formed thereon facing each other. They are arranged so as to be alternately incident on the opposing matritas-like element plates 71 1, 71 2. Then, the inclination of the incident surface of the element capable of performing each dispersion compensation on the opposing matrix-shaped element plate is controlled as necessary, and dispersion compensation is performed as an optical path through which the signal light passes. By selecting elements that can be connected in series by selecting elements that can perform dispersion compensation, the characteristics and number of elements that can perform dispersion compensation are selected, and the group velocity delay time vs. wavelength characteristic curve as illustrated in Figs. Can be realized. Here, the optical connection between the elements capable of performing each dispersion compensation, that is, the formation of an optical path, is performed by disposing the input / output terminals as the entire dispersion compensating element or by opposing each of the two elements. Use fiber collimators as shown in Figs. However, the optical path between the incident surfaces of the elements capable of performing the dispersion compensation on the matrix-like element plates arranged opposite to each other can be configured to be performed by reflection between the respective incident surfaces.

For example, 100 × 10, that is, 100 elements capable of performing dispersion compensation are formed on each of the matrix element plates, and two such matrix element plates are opposed to each other as described above. For example, three sets of elements can be formed, and dozens to hundreds of elements can be compensated, including optical path formation by reflection between elements that can perform dispersion compensation and optical path formation by a fiber collimator. Are connected in series in the optical path of the signal light to form an optical path, thereby forming a dispersion compensating element. Then, a plurality of optical paths can be formed in the same dispersion compensating element by appropriately selecting a combination of elements capable of performing the dispersion compensation according to the circumstances of the incident light using electric means or the like. .

The inventors of the present invention have shown that a matrix-like element plate on which elements capable of performing such dispersion compensation can be stably mass-produced by applying a semiconductor manufacturing technique and a multilayer film forming technique. Confirmed by experiment.

By doing so, the insertion loss of the dispersion compensating element as a whole can be extremely reduced, and multi-channel dispersion compensation can be performed by the same dispersion compensating element. A small-sized dispersion compensator having excellent dispersion compensation characteristics can be provided at low cost.

FIG.6D shows an optical dispersion compensating element 4440 in which elements 442 and 443 capable of performing the same dispersion compensation as in FIG.6A are incorporated in the same case 441. Although not shown, the element 4 43 that can perform dispersion compensation uses a multilayer film in which the film thickness changes in the direction of the plane of incidence of the multilayer film described with reference to FIG. It has means for adjusting the incident position. The incident position adjusting means can adjust the incident position by using a control circuit provided in a force case 441 (not shown).

Using the optical dispersion compensating element according to the present invention having such a configuration, dispersion is compensated in a communication system transmitting 60 km at a communication bit rate of 40 Gbps, and as a result, extremely excellent dispersion compensation can be performed. Signal light is transmitted through the optical dispersion compensator. The loss due to passing was as low as 1 dB or less. It can be said that this loss is much better than the loss due to a single second-order dispersion compensator using a conventional fiber grating, which is as large as 3 to 6 dB. As described above, the light dispersion compensating element of the present invention and the light dispersion compensating method using the element have been described centering on the light dispersion compensating element of the present invention.The most notable features of the light dispersion compensating method of the present invention are as follows. Multiple devices capable of dispersion compensation are connected in series to provide a wide wavelength band, for example, 1260 ~: L 360 nm, 1360 ~ 1460 ηm, 1460 ~ 1530 nm, 1530 ~ 1565 nm, 1565 ~ 1625 nm, 1625-: The dispersion compensator is configured to have a group velocity delay time-wavelength characteristic curve that has at least one extreme value in any one wavelength range of 1675 nm, and is optimal for communication conditions It is also possible to compensate for the extreme values at multiple wavelengths in the wavelength range of 1260 to 1700 nm, for example, by using a function that can be selected with a switching switch as a whole as a dispersion compensation element. Group speed with delay time Configuring the dispersion compensation element so as to have a length characteristic curve possible and that Do. The present invention makes use of such a large degree of freedom to make it possible to perform second- and third-order dispersion compensation required in actual communication, and makes use of many conventional optical communication systems. It enables high-speed and long-distance communication. Industrial applicability

As described above, the present invention has been described in detail. According to the present invention, good dispersion compensation of each channel is performed by preparing various group velocity delay time-wavelength characteristic curves described with reference to FIGS. 5B to 5D. In addition to this, good dispersion compensation of multiple channels can be performed. The dispersion compensation by the optical dispersion compensating element of the present invention has a particularly large effect in the third-order or higher dispersion compensation, and in addition to the second-order dispersion compensation by appropriately adjusting the group velocity delay time-wavelength characteristic. Can also be performed. INDUSTRIAL APPLICABILITY The present invention is indispensable for practical use of high-speed and long-distance optical communication such as transmitting 10,000 km at 4 OGb ps, has a wide use range, and greatly contributes to the development of the optical communication field. Things.

The light dispersion compensating element using the special multilayer film according to the present invention is compact and mass-produced. Since it is suitable and can be provided at a low price, it greatly contributes to the development of optical communication.

The use of the optical dispersion compensating element of the present invention makes it possible to use many of the existing optical communication systems, and has a great social and economic effect.

Claims

The scope of the claims

1. An optical dispersion compensating element that can be used for optical communication using an optical fiber as a communication transmission line and that can compensate for dispersion as chromatic dispersion, and has at least three reflective layers with different light reflectivities. And a plurality of devices capable of performing dispersion compensation as a multilayer film device using a multilayer film having at least two light transmission layers formed between the light emitting layer and the reflection layer, or performing dispersion compensation. An optical dispersion compensating element comprising at least a plurality of element parts capable of performing dispersion compensation as an element connected in series along an optical path of signal light.

2. The optical dispersion compensating element according to claim 1, wherein there are a plurality of connection methods or connection paths of the plurality of elements capable of performing dispersion compensation.

3. The optical dispersion compensating element according to claim 1, wherein a connection method or a connection path of the plurality of elements capable of performing dispersion compensation can be selected from outside the optical dispersion compensating element. Light dispersion compensating element.

4. The optical dispersion compensating element according to claim 2, wherein the method of connecting the plurality of elements capable of performing dispersion compensation includes a method by reflection on an incident surface of the multilayer film element disposed to face. An optical dispersion compensating element characterized by being included.

5. The optical dispersion compensating element according to claim 3, wherein the means for selecting a connection method or a connection path of the plurality of elements capable of performing dispersion compensation from outside the optical dispersion compensating element is an electrical means. An optical dispersion compensating element, comprising:

6. In an optical dispersion compensation method for performing communication by compensating for dispersion as chromatic dispersion in optical communication using an optical fiber as a communication transmission line, the method comprises: Multi-layer with at least two light transmitting layers formed At least a plurality of devices capable of performing dispersion compensation as a multilayer film device using a layer film, or at least a portion of a device capable of performing dispersion compensation as a device capable of performing dispersion compensation. An optical dispersion compensation method characterized in that signal light is made incident on an optical dispersion compensating element configured by connecting a plurality of locations directly along an optical path of signal light to perform dispersion compensation.

7. The optical dispersion compensation method according to claim 6, wherein the signal light transmitted through the optical fiber is passed through the optical dispersion compensating element before being wavelength-separated for each receiving channel, and at least a third-order dispersion is reduced. An optical dispersion compensation method characterized in that the compensation is performed.

8. The optical dispersion compensating method according to claim 6, wherein the optical dispersion compensating element configured by connecting a plurality of elements capable of performing the dispersion compensation in series is 1260 to 136 O nm, 1360 to 1360 nm. 1460 nm, 1460 to 1530 nm, 1530 to: 1565 nm, 1565 to 1625 ηm, group velocity delay time with at least one extreme value in at least one wavelength range of 1625 to 1675 nm An optical dispersion compensation method characterized by having a wavelength characteristic curve.

9. The optical dispersion compensation method according to claim 6, wherein a plurality of ways of connecting elements capable of performing dispersion compensation in the optical path of the signal light can be selected.

10. The optical dispersion compensation method according to claim 6, wherein the multilayer film used in at least one element capable of performing dispersion compensation constituting the optical dispersion compensation element has a center wavelength of incident light. The multilayer film when considered as an optical path length with respect to the light having a thickness of approximately an integral multiple of λ / 4; and the multilayer film has a thickness Composed of a layer た, which is 1/4 times the layer with the higher refractive index, and the layer with a thickness of 1/4 times λ, the layer with the lower refractive index, 1 times the thickness of λ. Wherein the layer で is formed of any one of Si, Ge, Ti02, Ta205, and Nb205.

11. The optical dispersion compensation method according to claim 6, wherein at least one of the multilayer devices has a thickness of at least one multilayer film constituting a multilayer film of the multilayer device. An optical dispersion compensation method characterized by being a multilayer element using a multilayer film that changes in an in-plane direction in a cross section parallel to a light incident surface, that is, in an in-plane direction.

12. The optical dispersion compensation method according to claim 10, wherein the layer L is formed using a material having a lower refractive index than the material used for the layer H. Dispersion compensation method.

13. The optical dispersion compensation method according to claim 12, wherein the layer L is formed of a layer made of Si02.

14. The method of compensating for optical dispersion according to claim 11, wherein at least one multilayer film has at least two film thickness changing directions in which the film thickness changes in the inward plane of the multilayer film. An optical dispersion compensation method, comprising:

15. The optical dispersion compensating method according to claim 11, wherein the adjusting means adjusts a film thickness of at least one of the multilayer films by engaging with an element capable of performing the dispersion compensation. Alternatively, there is provided means for changing a light incident position on the incident surface of the multilayer film.