JP4957234B2 - Optical signal transmission device - Google Patents

Description

  The present invention relates to an optical signal transmission device, and more particularly to an optical signal transmission device based on wavelength multiplexing technology.

  Currently, wavelength multiplexing technology is used to increase the transmission capacity of optical signals. In particular, when transmitting a long-distance optical signal, an optical fiber having a small transmission loss is used. The following technique is used as a technique for transmitting a large-capacity signal to a single optical fiber. That is, a plurality of light sources having different wavelengths are prepared, and a signal is added by an optical modulator to place a signal on each wavelength, or a direct light source is modulated and then a plurality of modulated lights are combined to form a single light source. The technology to couple to the optical fiber is used. On the other hand, on the light receiving side, the light is demultiplexed for each wavelength by the demultiplexer, and the optical signal is converted into an electric signal in the light receiving element provided at the tip of the demultiplexer.

  In optical signal transmission via a long-distance optical fiber, a plurality of distributed feedback semiconductor lasers with a small wavelength (frequency) spread are used for the light from the light source to prevent signal degradation based on the difference in transmission speed for each wavelength. The method is adopted. A wavelength multiplex transmission system using a plurality of light sources and multiplexers / demultiplexers has a basic configuration shown in Patent Document 1, for example. A similar method is shown in Figure 3.5-1 (a) on page 114 in the literature ("Photonic Network Revolution", Ultra-high-speed Photonic Network Development Promotion Council, issued in January 2002). Shown as a system.

  As a technique for making a single light source, for example, in Patent Document 2, the light of a single light source is wavelength-separated by a demultiplexer, and each wavelength-separated light is modulated and then combined by a multiplexer. An apparatus is disclosed in which, after passing through a single transmission line, the wavelength is again separated by a duplexer and converted into an electrical signal in a light receiving element.

Japanese Patent Application No. 11-103286 JP-A-7-79212

  In the conventional wavelength multiplexing communication, a plurality of light sources are required. Even if there is a single light source, a multiplexer that multiplexes optical signals and a demultiplexer that separates wavelengths of optical signals are required. Therefore, in order to avoid an increase in the cost of the entire device, it is an object to provide an optical signal transmission device having a simple device configuration that does not require these devices.

  In addition, since the signal deteriorates in the optical fiber during long-distance optical transmission, a distributed feedback laser with a small spectral spread during modulation is required, and an optical modulator with a small spectral spread during modulation is also required. However, the spread of the spectrum in the transmission path does not become a problem at a distance within the housing of an apparatus in an information processing apparatus or the like that has been increasingly required to perform large-capacity information communication in recent years. Therefore, it is an issue to provide a simple device based on a principle different from the conventional ones for the light modulator and the light receiving element by replacing the light source with an inexpensive device.

Optical signal transmission apparatus according to a first aspect of the present invention includes a light source for emitting light, a splitter for splitting the light into a plurality of paths are provided for each branch, by modulating the branched light An optical modulator for applying a signal to be transmitted to the light; a multiplexer for multiplexing the modulated light; and a single optical transmission line for transmitting the combined light;
An optical signal transmission device comprising: the same number or more of light receiving elements as the optical modulator, which receives the transmitted light and converts it into an electrical signal, wherein the optical modulator has a wavelength band of the light source. The wavelength bands that can be modulated are included, the wavelength bands that can be modulated by the optical modulators are different from each other, and the wavelength bands that can be modulated by the optical modulators It is configured to include at least one wavelength band capable of receiving light.

An optical signal transmission device according to a second aspect of the present invention includes a light source that emits light, a plurality of optical modulators that are provided in series in a propagation path of the light and modulate the light, and the modulated light. A single optical transmission line for transmission, and a number of light receiving elements equal to or more than the number of the optical modulators, which are provided in series with the light propagation path and receive the transmitted light and convert it into an electrical signal. The optical signal transmission device is configured such that a wavelength band that can be modulated by the optical modulator is included in a wavelength band of the light source , and each of the plurality of optical modulators has different wavelength bands that can be modulated. In addition, the light intensity in the wavelength band that can be modulated among the incident light from the light source is configured to be modulated according to an electric signal, and the wavelength band that can be received by the light receiving element is configured to be different. , For each of the optical modulators that can be modulated In, wherein the receivable wavelength band of the light receiving element is configured to include at least one.

  The optical signal transmission device according to the first development mode is characterized in that the principle for determining the wavelength band that can be modulated by the optical modulator and the wavelength band that can be received by the light receiving element are the same. .

  The optical signal transmission device of the second development form is characterized in that each of the optical modulator and the light receiving element includes an optical waveguide and an optical interference structure in the vicinity of the optical waveguide.

In an optical signal transmission device according to a third development mode, the optical modulator and the light receiving element each have a refractive index periodically in the optical waveguide, in the vicinity of the optical waveguide having an optical interaction, or both. It is characterized by having a changed structure.
In an optical signal transmission device according to a fourth development mode, the plurality of optical modulators each includes a first optical waveguide that guides incident light from the light source, and first interference light that guides interference light with respect to the incident light. Two optical waveguides, and the first optical waveguide and the second optical waveguide are arranged so that the incident light and the interference light interfere with each other.

  The optical signal transmission apparatus according to the present invention can realize optical signal transmission by wavelength multiplexing using only a single light source.

  Further, the optical signal transmission device according to the present invention does not require a duplexer for performing wavelength separation. Further, when the optical modulator and the light receiving element are arranged in series on a single transmission line, neither a branching unit nor a multiplexer is required.

  In the optical signal transmission device according to the present invention, a light source having a narrow spectrum spread and an optical modulator having a narrow spectrum spread at the time of modulation become unnecessary by selecting the wavelength by the optical resonance structure. Further, by performing transmission / reception with a pair of a modulator and a light receiving element having the same resonance structure, it is possible to reduce the influence due to the change in the optical characteristics due to the change in the environmental temperature, and to prevent the transmission performance from being lowered.

  An optical signal transmission device according to the present invention includes a light source, an optical modulator that provides a signal to be transmitted to the light emitted from the light source, and a light receiving device that receives the modulated light to which the signal is applied and converts the optical signal into an electrical signal. The wavelength band of the light modulator is included in the wavelength band that can be modulated by the light modulator, and the wavelength band that can be received by the light receiving element is included in the wavelength band that can be modulated by the light modulator. Features.

  An optical signal transmission device according to the present invention also receives a light source, a plurality of optical modulators that provide a signal to be transmitted to light emitted from the light source, and the modulated light to which the signal is applied, and converts the optical signal into an electrical signal. The number of light receiving elements equal to or more than the number of optical modulators to be converted is included. The wavelength band that can be received by at least one light receiving element may be included in the wavelength band that can be modulated by each optical modulator.

  Further, the optical signal transmission device includes means for branching the light emitted from the light source into a plurality of paths, and an optical modulator is provided for each branch, and the modulated light passing through the plurality of optical modulators is multiplexed. And a single optical transmission line that transmits the combined modulated light, and a light receiving element may be provided on the receiving side of the transmission line.

  In the above optical signal transmission device, the optical modulator is sequentially provided in the light propagation path, and has a large interaction with the light from the light source only in the wavelength band to which the signal is applied in each optical modulator. A plurality of light receiving elements having different wavelength bands in which light can be received may be sequentially provided in the path of propagation.

  Further, in the above optical signal transmission device, it is preferable that the principle for determining the wavelength band in the optical modulator and the light receiving element is the same.

  In the above optical signal transmission device, the optical modulator and the light receiving element preferably have an optical resonance structure provided in the vicinity of the optical waveguide.

  Further, in the above optical signal transmission device, the optical modulator and the light receiving element include a structure having periodically different refractive indexes provided in the optical waveguide and / or a nearby region having an optical interaction thereof, or both. May be.

  Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of an optical signal transmission apparatus according to a first embodiment of the present invention. In the present embodiment, the light source 1 is a super luminescence diode having a wide emission wavelength range, and the emission wavelength is in the range from 800 nm to 850 nm. The light from the light source 1 is branched into four by the branching device 2a. In the following, the case of multiplicity, that is, the case where the number of branches is four will be described as an example, but the number of multiplicity is not limited to four. After branching, light having the same spectrum and having an intensity of a quarter is guided to the optical modulators 3a to 3d connected in parallel. The optical modulators 3a to 3d convert electrical signals into optical signals in different wavelength bands. Here, for example, an optical modulator having center wavelengths λ ₁ to λ ₄ of 805 nm, 815 nm, 825 nm, and 835 nm and a modulation band of about 4 nm is used.

In FIG. 2 (a), it shows the wavelength lambda ₁ and lambda ₂ of the optical modulator an optical spectrum modulated by (3a and 3b in Fig. 1) schematically.

  In order to realize wavelength selectivity, for example, an interference type waveguide structure as shown in FIG. 3 is provided. In addition, in FIG. 3, the schematic diagram of the spectrum of incident light, an emitted light, and interference light is also shown. Light that gives a signal enters from the left side of the optical waveguide 7 and exits from the right side. On the other hand, interference light 12 is guided to the optical waveguide 8 in accordance with electric signals to the electrodes 9 and 10. Here, the optical waveguides 7 and 8 are close to each other and optically coupled. The signal modulation at the wavelength λ1 by the optical modulator 3a is set so that, for example, the light intensity at the wavelength λ1 is 0 when the electrical signal is ON, and the light intensity is 1 when the electrical signal is OFF. For example, when the wavelength of the interference light is set to λ1 and the electrical signal is ON, the interference light 12 having the wavelength λ1 guided to the optical waveguide 8 interferes with the incident light 11 to the optical waveguide 7 and is like the outgoing light 13 The spectral intensity at the wavelength λ1 may be set to 0.

  The light emitted from the single light source 1 is branched by the branching unit 2a, and signals are placed in different wavelength bands in the optical modulators 3a to 3d having different resonance wavelengths. Thereafter, the optical signal is multiplexed by the multiplexer 4 and transmitted by the single optical transmission line 5. Then, the transmitted optical signal is branched again by the branching unit 2b, and the optical signal is detected using the light receiving elements 6a to 6d having wavelength selectivity.

The center of the light receiving possible wavelength band of the light receiving elements 6a~6d are to ₁ lambda respectively and lambda _4, coincide with the center of modulatable wavelength band in the optical modulator 3 a to 3 d. Here, in order to make the wavelength bandwidth capable of receiving light narrower than 4 nm, which is the wavelength bandwidth that can be modulated by the corresponding optical modulator, for example, the wavelength bandwidth is set to 2 nm (see FIG. 2B). The wavelength dependency of the light reception may be based on the same principle as the wavelength selectivity in the optical modulator shown in FIG. The size of the selection range can be adjusted by adjusting the distance between the optical waveguide 8 and the optical waveguide 7 and the number of interference structures.

  In the case where an optical transmission path is provided for each different wavelength band, the outputs of the optical modulators 3a to 3d are directly sent to the light receiving elements 6a to 6d on a one-to-one basis without performing multiplexing and demultiplexing before and after transmission. To transmit.

  In this embodiment, how signals are transmitted is as follows. In FIG. 1, the outputs of a plurality of optical modulators 3 a to 3 d are multiplexed by a multiplexer 4, passed through a single optical transmission line 5, then branched by a splitter 2 b, and a plurality of wavelength selective systems are provided. An example of transmission to the light receiving elements 6a to 6d is shown. Here, in the plurality of optical modulators 3a to 3d, signals are carried by the intensity of the light at the corresponding wavelengths, but when they are combined, the degree of the intensity of the light at these wavelengths is Will be weakened. Therefore, in the light receiving elements 6a to 6d, the total light intensity is reduced to a fraction of the branch due to the intensity branching, and the change rate of the light intensity is also a change in the light intensity in the light modulators 3a to 3d. Decreases to a fraction of the rate. However, if only a specific wavelength is detected by the wavelength selection system of the light receiving elements 6a to 6d, an optical signal corresponding to the intensity of the wavelength can be detected.

According to this embodiment, the single light source 1 and the single optical transmission line 5 enable wavelength multiplexing communication in which signals are propagated on a plurality of wavelengths λ ₁ to λ ₄ .

  Next, a second embodiment will be described with reference to FIG. The light source 1, branching device 2a, multiplexer 4, optical transmission line 5, and light receiving elements 6a to 6d included in the optical signal transmission device are the same as those in the first embodiment (FIG. 1). There are two differences in the functions of the optical modulators 14a to 14d and the arrangement method of the light receiving elements.

  The outputs of the optical modulators 3a to 3d of the first embodiment (FIG. 1) were to change only the light intensity of a specific wavelength from the spectrum obtained by branching the spectrum of the light source 1 by the branching unit 2a. Assume that the outputs of the optical modulators 14a to 14d extract only light of a specific wavelength.

  At this time, in the spectrum of the light obtained by combining the outputs of the plurality of optical modulators 14a to 14d by the multiplexer 4, a signal is put on the intensity of the light intensity of the wavelength corresponding to each of the optical modulators 14a to 14d. It is in shape.

  The spectrum of the modulated light after being modulated by the optical modulators 14a to 14d and multiplexed by the multiplexer 4 is schematically shown in FIG. At each wavelength, the bias output from the optical modulator on which no signal is placed is 0, so that the difference between the 0 level and 1 level of signal detection in the light receiving elements 6a to 6d can be made large.

  Therefore, as shown in FIG. 4, it is possible to employ a configuration in which the light receiving elements 6a to 6d are arranged in series. The light intensity in the light receiving elements 6a to 6d in the apparatus of the second embodiment can be observed to be larger than that in the first embodiment.

  FIG. 5B is a diagram schematically illustrating wavelength bands that can be received by the light receiving elements 6a to 6d. Each peak of the modulated light spectrum illustrated in FIG. 5A includes a wavelength band in which each of the light receiving elements 6a to 6d can receive light.

  Next, a third embodiment will be described with reference to FIG. In the first and second embodiments, as shown in FIGS. 1 and 4, after the light from the light source having a wide spectrum is branched by the branching device 2a, the light using the light modulator in each branch is divided. Although the modulation is performed, in the third embodiment, the light intensity at each wavelength is modulated by the optical modulators 3a to 3d arranged in series without using the branching device. The functions of the optical modulators 3a to 3d here are as shown in FIG. 2, in which the electrical signals 0 to 1 are modulated to the light intensity 1 to 0 at the wavelengths that interact with each other, and the wavelengths that do not interact with each other. The light in the area is transmitted as it is.

  With this optical modulation, the optical modulators are connected in series without branching the light from the light source 1, and signals are sequentially placed in the wavelength bands that can be modulated by the respective optical modulators 3a to 3d. be able to.

  In this way, light in which different signals are placed in a plurality of wavelength regions by the light modulators 3 a to 3 d is transmitted to the light receiving elements 6 a to 6 d via the single optical transmission path 5. The light receiving elements 6a to 6d also have wavelength selectivity, and convert the intensity of light in a wavelength band that can be received respectively into electrical signals. In addition, when the light receiving element is provided with a wavelength selection mechanism that transmits light in a wavelength band that cannot be received as it is, the light receiving elements 6a to 6d can be connected in series like the light modulators 3a to 3d. As described above, the single light source 1 and the optical transmission line 5 enable wavelength-multiplexed signal transmission in which signals are respectively placed in a plurality of wavelength ranges.

  As described above, in any of the wavelength multiplexing systems of Examples 1 to 3, a light source having a wide emission spectrum is used, and a light modulator that interacts only with light of a specific wavelength in the spectrum and a light receiving element are combined. Has been. In order to improve the quality of the signal at the time of light reception, it is preferable that the light reception sensitivity for the unmodulated wavelength region is low. Therefore, it is preferable that the wavelength band that can be received by the light receiving element is included in the wavelength band that can be modulated by any one of the optical modulators.

  In general, in an optical element having wavelength selectivity, the selectivity depends on temperature. This is because the optical constant of the substance has temperature dependence. Consider a case where the transmission distance is short and the transmitting side and the receiving side are under the same temperature. Here, by making the principle of wavelength selectivity of the optical modulator and the light receiving element equal, when the ambient temperature changes, the wavelength bands of the respective devices show the same change. Therefore, it is possible to prevent a decrease in transmission quality even if the temperature changes.

  As the wavelength selectivity becomes sharper, that is, the both ends of the wavelength band rise sharper, the wavelength multiplexing property can be improved. Therefore, it is desirable that the optical modulator and the light receiving element interact only with light of a limited wavelength band. For example, sharp wavelength selectivity can be obtained by providing both the optical modulator and the light receiving element with an optical waveguide and a resonant structure optically coupled to the optical waveguide.

  In order to suppress the temperature dependence of the resonance structure, it is preferable to change the refractive index by changing the material or the structure. For example, as the resonance structure, a diffraction grating may be provided in the waveguide, and the refractive index may be periodically changed.

  Moreover, as long as the relationship of said wavelength band is satisfy | filled as light emission, an optical modulator, and a light receiving element, it is not limited to the implementation | achievement method of said wavelength selection. That is, any optical modulator that can perform light modulation in a wider range including the wavelength band in which the light receiving element can receive light may be used. Regarding the modulation mechanism of the optical modulator, the dependence of the absorption coefficient of the semiconductor thin film on the electric field strength may be used, or the coupling with the optical waveguide may be modulated by an external electric field.

  The light source needs to have an emission spectrum in a range including the wavelength band of the optical modulator, and if it satisfies this condition, it may be a super luminescence diode or use the nonlinearity of the optical fiber. A light source having a wide spectral width may be used. Further, since it is sufficient that the emission spectral band is wide, a semiconductor laser emitting light in a number of axial modes in the Fabry-Perot mode may be used as a light source, and the wavelength band of all the optical modulators may be included in the spectral band.

It is a block diagram of the optical signal transmission apparatus which concerns on 1st Example of this invention. (A) It is a figure which shows typically the optical spectrum after being modulated by the optical modulator which concerns on the 1st and 3rd Example of this invention. (B) It is a figure which shows typically the wavelength range which can receive light of a light receiving element. It is a figure which shows the Example of an optical modulator. FIG. 3 is a plan view of a waveguide through which light for giving a signal enters and exits, a waveguide that is arranged in the vicinity of the waveguide and that guides interference light with respect to incident light, and an electrode that guides the interference light. It is a block diagram of the optical signal transmission apparatus which concerns on 2nd Example of this invention. (A) It is a figure which shows typically the mode of the optical spectrum after being modulated by the optical modulator which concerns on the 2nd Example of this invention. (B) It is a figure which shows typically the wavelength range which can receive light of a light receiving element. It is a block diagram of the optical signal transmission apparatus which concerns on 3rd Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2a, 2b Branch device 3a-3d Optical modulator 4 Multiplexer 5 Optical transmission path 6a-6d Light-receiving element 7 Optical waveguide 8 with respect to signal light Optical waveguide 9, 10 with respect to interference light Electrode 11 for inducing interference light Schematic diagram of the spectrum of incident light 12 Schematic diagram of the spectrum of interference light 13 Schematic diagrams of the spectrum of outgoing light 14a to 14d Optical modulator

Claims (3)

A light source that emits light;
A branching device for branching the light into a plurality of paths;
An optical modulator that is provided for each branch and modulates the branched light to give a signal to be transmitted to the light;
A multiplexer for multiplexing the modulated light;
A single optical transmission line for transmitting the combined light;
An optical signal transmission device comprising: a light receiving element that receives the transmitted light and converts it into an electrical signal;
The wavelength band of the light source is configured to include a wavelength band that can be modulated by the optical modulator,
Each of the optical modulators is configured to have a different wavelength band that can be modulated,
An optical signal transmission device configured to include at least one wavelength band that can be received by the light receiving element in a wavelength band that can be modulated by each of the optical modulators. A light source that emits light;
A plurality of optical modulators that are provided in series in the light propagation path and modulate the light;
A single optical transmission line for transmitting the modulated light;
An optical signal transmission device provided in series with the light propagation path, and receiving the transmitted light and converting it into an electrical signal, the light modulator having the same number or more as the light modulator,
The wavelength band of the light source is configured to include a wavelength band that can be modulated by the optical modulator,
The plurality of optical modulators have different wavelength bands that can be modulated , and are configured to modulate the intensity of light in the wavelength band that can be modulated among incident light from the light source in accordance with an electrical signal. ,
The light receiving element is configured to receive different wavelength bands,
An optical signal transmission device configured to include at least one wavelength band that can be received by the light receiving element in a wavelength band that can be modulated by each of the optical modulators. Each of the plurality of optical modulators is
A first optical waveguide for guiding incident light from the light source;
A second optical waveguide for guiding interference light with respect to the incident light,
The optical signal transmission according to claim 1 or 2, wherein the first optical waveguide and the second optical waveguide are arranged so that the incident light and the interference light interfere with each other. apparatus.

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