JP2004080539A - Apparatus and method for passive optical transmission - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus for passive optical transmission for long-range transmission of a wide-band signal with an improved S/N ratio. <P>SOLUTION: The apparatus for passive optical transmission for modulating a light emitted from a light source by a modulation signal in an optical modulator, and transmitting the modulated light, is provided with an optoelectronic transducer to translate the light to an electric signal, and an amplifier to amplify the modulation signal and apply the amplified modulation signal into the optical modulator. The electric signal transferred by the optoelectronic transducer is used as a power source for the amplifier. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a passive optical transmission device and a passive optical transmission method, and more particularly, to a passive optical transmission device and a passive optical transmission method for optically transmitting a broadband signal.
[0002]
[Prior art]
In general, light that receives a television wave or the like with an antenna and changes the amount of light by directly applying a signal voltage of a modulation signal generated by the antenna to an optical modulator to transmit the signal to a television receiver or a video device. Since the transmission device can directly modulate the light from the light source with the radio wave (modulation signal) received by the antenna, the transmission device can transmit the signal without supplying power from the outside without power supply.
[0003]
Also, when an insulating optical fiber or the like is used as the transmission line, it is less susceptible to external electrical noise than a coaxial cable, etc., and the transmission line is less likely to be damaged by lightning strikes etc. Therefore, it is widely used as a transmission path.
[0004]
[Problems to be solved by the invention]
However, the conventional passive optical transmission device as described above modulates light with a modulation signal from an antenna. However, in the case of a weak radio wave, the signal voltage of the modulation signal becomes low. It must be used to enhance the signal at a particular frequency. In this case, since the resonance frequency is limited by the setting of the resonance circuit, the bandwidth is narrowed. For example, this method cannot be applied to a case where a wide band signal such as a television signal is transmitted through a plurality of channels. In addition, since the degree of modulation is weak, it is difficult to perform long-distance transmission of a signal.
[0005]
The present invention has been made in view of the above points, and in a parasitic optical transmission device and a parasitic optical transmission method, an S / N ratio can be improved to perform efficient optical transmission, and further a wideband signal can be transmitted. It is an object of the present invention to provide a parasitic optical transmission device and a parasitic optical transmission method capable of transmitting.
[0006]
[Means for Solving the Problems]
In order to solve the above problems, the present invention employs means for solving the problems having the following features.
[0007]
An invention according to claim 1 is a parasitic optical transmission device for transmitting a modulated signal by modulating light emitted from a light source by an optical modulator, wherein the photoelectric conversion element converts the light into an electric signal; And an amplifier for applying the amplified modulation signal to the optical modulator, and using the electric signal converted by the photoelectric conversion element as a power supply of the amplifier.
[0008]
According to the first aspect of the present invention, the modulation signal can be amplified by operating the amplifier without power supply using the photoelectric conversion element. In addition, since optical modulation is performed by the amplified modulation signal, the degree of modulation can be increased, and the S / N ratio can be improved to perform efficient optical transmission. Further, by using an amplifier, a signal in a wide band can be transmitted without restriction on the transmission band.
[0009]
The invention described in claim 2 is characterized in that the photoelectric conversion element receives external light and / or partial light branched from the light source and converts the light into an electric signal.
[0010]
According to the second aspect of the present invention, by using external light and / or partial light branched from the light source, the amplifier can be operated without power feeding to amplify the modulation signal.
[0011]
The invention described in claim 3 is characterized in that a polarization-independent polarizer is provided between the light source and the optical modulator on the optical modulator side.
[0012]
According to the third aspect of the present invention, it is possible to reduce the attenuation of the light amount generated by the polarizer and the disturbance of the polarization and the fluctuation of the light amount mainly generated by the optical fiber or the like. Further, the S / N ratio can be improved.
[0013]
According to a fourth aspect of the present invention, in the parasitic optical transmission method in which a modulated signal is transmitted by modulating light emitted from a light source by an optical modulator, the light is converted into an electric signal using a photoelectric conversion element. The electric signal converted by the photoelectric conversion element is used as a power supply of an amplifier for amplifying the modulation signal, and the modulation signal amplified by the amplifier is applied to the optical modulator.
[0014]
According to the fourth aspect of the present invention, it is possible to operate the amplifier without power supply using the photoelectric conversion element and amplify the modulation signal. In addition, since optical modulation is performed by the amplified modulation signal, the degree of modulation can be increased, and the S / N ratio can be improved to perform efficient optical transmission. Further, by using an amplifier, a signal in a wide band can be transmitted without restriction on the transmission band.
[0015]
The invention described in claim 5 is characterized in that the photoelectric conversion element receives external light and / or partial light branched from the light source and converts the light into an electric signal.
[0016]
According to the fifth aspect of the invention, by using light from the outside and / or a part of the light branched from the light source, the amplifier can be operated without power feeding to amplify the modulation signal.
[0017]
The invention described in claim 6 is characterized in that the light emitted from the light source is polarized by a polarization-independent polarizer before entering the light modulator.
[0018]
According to the sixth aspect of the present invention, it is possible to reduce the attenuation of the light amount generated by the polarizer and the disturbance of the polarization and the fluctuation of the light amount mainly generated by the optical fiber or the like. Further, the S / N ratio can be improved.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention is directed to an optical transmission device that transmits light by modulating light from a light source with a modulation signal.For example, even when the modulation signal is weak, there is no power supplied from the outside and light modulation with a high modulation degree is performed. The main purpose is to provide a photoelectric conversion element so as to generate an electric signal (voltage) from light and operate an amplifier with the generated voltage to amplify and modulate a modulation signal.
[0020]
If the above-mentioned contents are explained in detail, for example, after irradiating the light transmitted from the laser light source through the optical fiber to the photoelectric conversion element to generate electricity, and operating the amplifier by the generated electricity, the antenna A weak radio wave (modulation signal) received from the above-mentioned device is amplified by the amplifier and applied to the modulation electrode of the optical modulator. As a result, the degree of light modulation can be increased without supplying power from the outside, the S / N ratio can be improved, and long-distance transmission of video signals and the like with a wide band can be performed.
[0021]
Further, by using an insulating optical fiber for the transmission line, the transmission line is less susceptible to lightning strikes and the like.
[0022]
In general, in order to operate the optical modulator efficiently, light incident on the optical modulator is linearly polarized, and a polarizer is used to adjust the polarization direction to a fixed direction. However, since the polarization direction of light changes in a complicated manner with time due to bending of an optical fiber, a change in temperature, or the like, signal fluctuation occurs. Further, when unpolarized light is polarized using a normal polarizer, the light power is attenuated by about 3 dB.
[0023]
Therefore, by using a polarization-independent polarizer that does not depend on the polarization direction of the incident light as the polarizer, it is possible to reduce the attenuation of the light amount and to reduce the disturbance of the polarization and the fluctuation of the light amount mainly caused by an optical fiber or the like. Since polarized light can be obtained without loss, a parasitic optical transmission device with an improved S / N ratio can be provided.
[0024]
Here, the polarization-independent polarizer is a polarizer that converts polarized light having a predetermined polarization direction, and is disclosed in, for example, Japanese Patent Application Laid-Open No. 11-174225 filed by the present applicant. ing.
[0025]
Here, as an example of the polarization-independent polarizer, a polarization-independent polarizer disclosed in the above publication will be described with reference to the drawings.
[0026]
FIG. 1 is a diagram illustrating an example of a polarization independent polarizer.
[0027]
The polarization independent polarizer 1 of FIG. 1 is configured to include a rutile birefringent element 2, a half-wave plate 3, a birefringent element 4, and a composite birefringent element 5.
[0028]
The rutile birefringent element 2 has a thickness d and an optical axis in the OA direction, and birefringently separates the input light into ordinary light O having polarization planes orthogonal to each other and extraordinary light E. The 波長 wavelength plate 3 rotates the polarization direction of the ordinary light O emitted from the rutile birefringent element 2 by 90 degrees, and emits the ordinary light O ′ having the same polarization direction as the polarization direction of the extraordinary light E. The complex birefringent element 5 is formed by bonding two birefringent elements 4 a and 4 b having a thickness of ・ · d and having an optical axis in the OA direction, and extraordinary light emitted from the rutile birefringent element 2. By birefringing E and the ordinary light O ′ emitted from the half-wave plate 3 in a direction approaching each other, it is possible to obtain polarized light having one optical axis independent of the polarization direction of the incident light.
[0029]
By using the polarization independent polarizer 1 described above, it is possible to convert the light into a polarized light having a preset polarization direction with high conversion efficiency. When the ordinary polarizer is used, it is possible to improve the disorder of the polarization direction and the fluctuation of the light amount, which are caused by the above, and the unavoidable decrease of the light amount.
[0030]
Next, an embodiment of the present invention will be described with reference to the drawings. The embodiments described below show one embodiment of the present invention, and do not limit the present invention, and can be arbitrarily changed within the scope of the present invention.
[0031]
FIG. 2 is a schematic configuration diagram illustrating an embodiment of the passive optical transmission device according to the present invention.
[0032]
2 includes a laser light source 11, an optical fiber 12, an optical circulator 13, an input polarization-independent polarizer 14, an optical beam splitter 15, an optical modulator 16, and an optical reflector 17. , A photoelectric conversion element 18, an amplifier 19, an antenna 20, and a television receiver 21.
[0033]
First, light emitted from the laser light source 11 used as a carrier wave enters the optical fiber 12a, and the optical circulator 13 outputs the light incident from the optical fiber 12a to the optical fiber 12b as it is. Further, by entering the above-mentioned input polarization independent polarizer 14, the light is emitted as polarized light having one polarization direction.
[0034]
Here, the state of polarization of incident light in the input polarization independent polarizer 14 will be described with reference to the drawings.
[0035]
FIG. 3 is a diagram illustrating an example of polarization when an input polarization-independent polarizer is used.
[0036]
As shown in FIG. 3A, the polarization direction of the light before being incident on the input polarization independent polarizer 14 changes with time due to the influence of the distortion of the optical fiber 12b and a change in temperature from the traveling direction of the light. However, since the input polarization independent polarizer 14 performs polarization as described with reference to FIG. 1, the polarization direction preset for the input polarization independent polarizer 14 shown in FIG. Can be output. That is, by using the input-polarization-independent polarizer 14, it is possible to reduce a loss at the time of conversion into polarized light.
[0037]
By configuring the input polarization-independent polarizer 14 so as to be close to the light beam splitter 15 and the optical modulator 16, the change in the transmission path of the light polarized by the input polarization-independent polarizer 14 can be obtained. Therefore, light can be stably branched by the light beam splitter 15, and loss of light used in modulation by the light modulator 16 can be reduced.
[0038]
Next, the light output from the input polarization-independent polarizer 14 is split by the light beam splitter 15 to the optical modulator 16 side and the photoelectric conversion element 18a side and transmitted.
[0039]
The light transmitted to the photoelectric conversion element 18a is converted into an electric signal by the photoelectric conversion element 18a and output to the amplifier 19. The amplifier 19 can be operated by the power from the photoelectric conversion element 18a, amplifies the television wave (modulation signal) received by the antenna 20, and applies the amplified modulation signal (voltage) to the optical modulator 16.
[0040]
The optical modulator 16 forms, for example, an optical waveguide 16-2 on the optical crystal substrate 16-1 having an electro-optic effect for splitting incident light into two and then rejoining the split light, and forming the two split optical waveguides. The modulation electrodes 16-3 are arranged in the vicinity of the wave path 16-2. However, the configuration of the optical modulator in the present invention is not limited to this.
[0041]
The optical modulator 16 receives the light branched by the optical beam splitter 15 and inputs a voltage from the antenna 20 to the modulation electrode 16-3 while passing through the optical waveguide 16-2, thereby forming an optical waveguide. 16-2 causes a different refractive index change. Thereafter, when the two branched lights merge, phase modulation occurs due to the phase difference between the two lights, and the incident light can be modulated.
[0042]
In addition, since the light modulator 16 has the light reflecting plate 17, the light reflected by the light reflecting plate 17 can be modulated. Therefore, the degree of modulation of the light incident on the light modulator 16 can be increased. Can be.
[0043]
Next, the optical signal modulated by the optical modulator 16 passes through the optical beam splitter 15 and the input polarization independent polarizer 14 as it is, and enters the optical circulator 13. The optical circulator 13 outputs an optical signal input from the optical fiber 12b to the optical fiber 12c. The output optical signal is converted into an electric signal by the photoelectric conversion element 18b and input to the television receiver 21.
[0044]
As described above, according to the parasitic optical transmission device 10 shown in the present embodiment, the modulation degree in the optical modulator 16 can be increased by amplifying the modulation signal from the antenna 20 by the amplifier 19, The S / N ratio is improved, and long-distance transmission of video signals with a wide band becomes possible. In addition, by using the input polarization independent polarizer 14, efficient transmission with little loss can be performed. Here, FIG. 4 schematically shows the state of the incident light amount at the point A and an example of the optical signal transmitted to the photoelectric conversion element 18b.
[0045]
FIG. 4A is a diagram showing the relationship between the amount of light emitted from the input polarization-independent polarizer 14 and the time at point A in FIG. As shown in FIG. 4A, light having a constant light amount is emitted at point A. FIG. 4B is a diagram showing the relationship between the light amount and the time of an optical signal that has been optically modulated by the optical modulator 16 input to the photoelectric conversion element 18b. As shown in FIG. 4B, the use of the input-polarization-independent polarizer 14 can reduce fluctuations in the amount of light caused by disturbance of polarization or the like, so that the S / N ratio is improved and efficient transmission is performed. be able to.
[0046]
In the present invention, the device configuration of the above-described parasitic optical transmission device 10 is not limited to this. For example, a configuration may be adopted in which an electric signal obtained by the photoelectric conversion element 18b is retransmitted using another antenna. .
[0047]
Further, an electric signal may be generated by using light from the outside such as sunlight or an electric lamp instead of the light radiated from the laser light source 11 for the light irradiated to the photoelectric conversion element 18a. Further, a voltage may be applied to the amplifier 19 from a battery or the like. Here, FIG. 5 is a schematic configuration diagram illustrating a second embodiment of the passive optical transmission device according to the present invention.
[0048]
The passive optical transmission device 30 in FIG. 5 does not include the light beam splitter 15 and is installed so that the photoelectric conversion element 18a can directly irradiate sunlight, compared with the passive optical transmission device 10 in FIG. Reference numeral 18 a is configured to convert light from sunlight into an electric signal and supply the electric signal to the amplifier 19.
[0049]
With the configuration as shown in FIG. 5, the amplifier 19 can be operated by an electric signal converted from sunlight, and the amplifier 19 amplifies a modulation signal from the antenna 20, so that the optical modulator Since the degree of modulation at 16 can be increased, the S / N ratio is improved and long-distance transmission of video signals with a wide band becomes possible. In the above-described second embodiment, the external light that can be received by the photoelectric conversion element 18a is not limited to the above, and may have any light energy.
[0050]
The configuration of the parasitic optical transmission device described in the embodiment is not limited to the above. For example, by combining the configuration of the parasitic optical transmission device described above, the light from the laser light source 11 and the sunlight Alternatively, a configuration in which light from the outside such as can be incident may be adopted.
[0051]
As described above, by using the parasitic optical transmission device or the parasitic optical transmission method of the present invention, it is possible to operate the amplifier without the power using the photoelectric conversion element and amplify the modulation signal. Further, since optical modulation is performed by the amplified modulation signal, the degree of modulation can be increased, and optical transmission with an improved S / N ratio can be performed. Further, by using an amplifier, a transmission band can be widened as compared with a method of increasing the degree of modulation using a resonance circuit. For example, a signal having a wide band such as a television signal can be transmitted on a plurality of channels.
[0052]
Furthermore, by using a polarization-independent polarizer, transmission loss can be reduced and fluctuations in the amount of light generated due to polarization disorder or the like can be reduced, so that the S / N ratio can be improved.
[0053]
The passive optical transmission device according to the present invention can also be used as a transmission path on a high mountain, under the sea, underground, or the like where power supply is difficult.
[0054]
【The invention's effect】
As described above, according to the present invention, the degree of modulation can be increased by amplifying a weak electric signal by the amplifier and applying the amplified voltage to the light modulation element to modulate the light intensity. Thereby, optical transmission of a broadband signal can be performed without power supply.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an example of a polarization independent polarizer.
FIG. 2 is a schematic configuration diagram illustrating an embodiment of a parasitic optical transmission device according to the present invention.
FIG. 3 is a diagram illustrating an example of polarized light when an input polarization-independent polarizer is used.
FIG. 4 is a diagram schematically illustrating a state of light transmitted from a laser light source 11 at a point A and an example of an optical signal transmitted to a photoelectric conversion element 18b.
FIG. 5 is a schematic configuration diagram illustrating a second embodiment of the parasitic optical transmission device according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Polarization-independent polarizer 2 Rutile birefringent element 3 1/2 wavelength plate 4 Birefringent element 5 Complex birefringent element 10, 30 Parasitic optical transmission device 11 Laser light source 12 Optical fiber 13 Optical circulator 14 Input polarization-independent polarizer Reference Signs List 15 light beam splitter 16 light modulator 17 light reflection plate 18 photoelectric conversion element 19 amplifier 20 antenna 21 television receiver

Claims (6)

In a passive optical transmission device in which a modulation signal modulates light emitted from a light source by an optical modulator and transmits the light,
A photoelectric conversion element that converts light into an electric signal,
An amplifier that amplifies the modulation signal and applies the amplified modulation signal to the optical modulator,
A non-feeding optical transmission device, wherein the electric signal converted by the photoelectric conversion element is used as a power supply of the amplifier. The parasitic optical transmission device according to claim 1, wherein the photoelectric conversion element receives external light and / or partial light branched from the light source and converts the light into an electric signal. The passive optical transmission device according to claim 1, wherein a polarization-independent polarizer is provided between the light source and the optical modulator on the optical modulator side. In a passive optical transmission method in which a modulation signal is transmitted by modulating light emitted from a light source by an optical modulator,
Convert light into electrical signals using photoelectric conversion elements,
The electric signal converted by the photoelectric conversion element, as a power supply of an amplifier that amplifies the modulation signal,
A parasitic optical transmission method, wherein the modulation signal amplified by the amplifier is applied to the optical modulator. The non-feeding optical transmission method according to claim 4, wherein the photoelectric conversion element receives external light and / or partial light branched from the light source and converts the light into an electric signal. The non-feeding optical transmission method according to claim 4 or 5, wherein the light emitted from the light source is polarized by a polarization independent polarizer before being input to the optical modulator.

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