JP3934462B2 - Wireless system and transmitter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultra-high frequency radio system, and more particularly to a radio system as a high-speed data communication system using millimeter waves and THz waves.
[0002]
[Prior art]
NTT Communication Energy Laboratories has developed a wireless communication system with a maximum data transmission rate of 2.5 Gbit / s. It was revealed at the “NTT R & D Forum in Atsugi” held on October 15, 2001. The maximum data transmission rate of a wireless communication system has been about 1 Gbit / second so far.
A millimeter wave in the 120 GHz band was used as the radio frequency of the carrier wave. However, since it is difficult to directly modulate the same wavelength, the following method was adopted. That is, first, a 120 GHz optical pulse signal is generated and amplitude-modulated by an optical modulator. The modulated optical pulse signal was received by a photodiode capable of responding to a high-speed signal, and the output signal was directly input to the slot antenna and converted into a radio signal for transmission. The transmission data is 1.25 Gbit / sec data of 1000BASE-SX. The transmission / reception distance demonstrated is less than 1 m. The transmission output is 1 mW. NTT intends to direct this technology to large-capacity wireless links between buildings, high-speed wireless LANs in offices, wireless video transmission in homes, and so on.
[0003]
[Problems to be solved by the invention]
In general, a frequency range from 300 GHz to 10 THz, which is called a THz wave, is between light waves and radio waves, and gaps have been generated in the use of electromagnetic waves. Development of this frequency band has been strongly demanded by the spread of broadband in recent years and the rapid increase in wireless usage. Since the carrier frequency is high, the modulation frequency can be increased, and application to high-speed data communication is expected first.
However, in order to generate a THz wave, there is no choice but to use a complicated and large-sized method such as using two laser devices and using the beat of this, and portability is the attribute that has been most strongly demanded for radio. Will be greatly impaired. In addition, laser light has a lower C / N ratio than radio waves, so that it is difficult to realize optical heterodyne communication. Unlike radio waves, there are many restrictions when used for communication. Therefore, various modulation schemes cannot be used as in the case of using radio waves, and binary amplitude modulation is exclusively used in optical communication.
One of the problems in creating THz waves is that it is difficult to apply direct modulation. For this reason, the system described in the above-mentioned case of NTT is used. Data modulation is performed on an optical pulse signal having a pulse period corresponding to a carrier wave of THz wave using an optical modulator, a composite signal is generated, and then light detection (demodulation) is performed using a photodiode to remove the light component, Data-modulated THz waves are extracted.
However, the photodiode used in this method needs to have a small area because it needs to reduce its capacity in order to increase the response speed (operation frequency), and cannot handle a large amount of power.
For this reason, it is extremely difficult in principle to simultaneously realize the high-speed operation of the photodiode and increase the output thereof. In addition, since different manufacturing processes are required for the optical pulse signal generator, optical modulator, and optical demodulator (photodiode), assembly is performed using discrete components, resulting in mass productivity (economic efficiency), reliability, and miniaturization. The difficulty still remains.
An object of the present invention is to provide a wireless system having a configuration that can be mass-produced and that is small in size so as to be easily handled and that can further reduce costs.
[0004]
[Means for Solving the Problems]
In order to achieve the above object, an invention according to claim 1 includes an optical pulse generator that generates an optical pulse signal having the same repetition frequency as a desired carrier frequency, and a transmitter, and the transmitter includes: An optical pulse signal generated from the optical pulse generator is modulated using a data signal to generate a composite signal, and an optical component is removed from the composite signal generated by the optical modulator and directed to the antenna. Output optical demodulator, and the optical modulator and the optical demodulator are integrated on a substrate made of the same material .
According to a second aspect of the present invention, there is provided a first optical modulator for generating an optical pulse signal having the same repetition frequency as a desired carrier frequency by performing pulse modulation on coherent light, and the first optical modulation. A second optical modulator that modulates an optical pulse signal generated from the optical signal using a data signal and generates a composite signal; an optical component is removed from the composite signal generated by the second optical modulator; An optical demodulator for output to the transmitter, wherein the first optical modulator, the second optical modulator, and the optical demodulator are integrated on a substrate made of the same material. It is characterized by.
According to a third aspect of the present invention, there is provided the transmitter according to the second aspect, and a variable pulse signal generator that changes a repetition frequency of the optical pulse signal by inputting a signal to the first optical modulator. It is characterized by having.
According to a fourth aspect of the present invention, there is provided a variable pulse signal generator for changing a duty ratio of a repetition frequency of the optical pulse signal by inputting a signal to the transmitter according to the second aspect and the first optical modulator. And .
[0005]
DETAILED DESCRIPTION OF THE INVENTION
The wireless system of the present invention employs a configuration in which an optical pulse signal generator, an optical modulator, and an optical demodulator are formed on the same substrate using a nonlinear optical material. At the same time, it is easy to integrate the accompanying electronic circuit on the same substrate. In the following embodiments, the carrier frequency is set to 100 GHz because of the ease of realizing the peripheral circuit, but it goes without saying that it can be used in the THz wave region as well.
FIG. 1 is a configuration diagram of a radio system according to the first embodiment of the present invention. The wireless system includes an optical pulse signal generator 1 and a transmitter 2. The transmitter 2 includes an optical modulator 3 and an optical demodulator 4.
In this wireless system, a 100 GHz carrier wave is modulated with a data signal having a maximum frequency of 1 GHz. The operation will be described below. An optical pulse signal having a pulse frequency of 100 GHz shown in FIG. 2 generated by the optical pulse signal generator 1 is input to the optical modulator 3. The optical transformer 3 modulates the optical pulse signal using the data signal shown in FIG. 3 to obtain the composite signal shown in FIG.
By removing an optical component from this signal using the optical demodulator 4, a data-modulated 100 GHz THz wave shown in FIG. 5 can be obtained. By introducing this to the antenna, harmonic components other than the carrier wave of 100 GHz are removed, and high-speed wireless data communication using a target carrier frequency of 100 GHz can be performed.
[0006]
The feature of the wireless system according to the first embodiment is that the optical modulator 3 and the optical demodulator 4 are manufactured as the transmitter 2 on the same substrate. For example, a modulator that can be driven easily can be manufactured by forming an electrode in a waveguide using an optical element having strong nonlinearity such as DAST or a high-molecular nonlinear optical material.
As described above, in the conventional technology, the optical modulator and the optical demodulator are configured by discrete parts made of different materials, and thus are not suitable for mass production. In addition to the large size, there is still a problem in stability, such as requiring adjustment between parts.
The wireless system according to the first embodiment can make a large number of the same devices on the same substrate in the transmitter 2 shown in FIG. 1, and is freed from these problems. Further, since compatibility with the integrated circuit is good, integration with peripheral circuits such as an optical modulator driver is easy.
There is an example in which a photodiode is used in the optical demodulator, but it is difficult to achieve high speed and high output at the same time for the reasons described above, but the present invention has few such problems.
FIG. 6 is a configuration diagram of a radio system according to the second embodiment of the present invention. In the second embodiment, all units are manufactured on the same substrate, and further downsizing, cost reduction, and high stability are achieved compared to the first embodiment.
[0007]
Hereinafter, the operation will be described. The first optical modulator 3-1 (having the function of the optical pulse signal generator 1 in FIG. 1) receives, for example, a 1.3 μm coherent light (carrier wave) produced by a laser diode. The optical pulse signal shown in FIG. 2 is created by performing 100 GHz pulse modulation by the optical modulator 3-1. Using the second optical modulator 3-2, this optical pulse signal is modulated with the data signal shown in FIG. 3 to produce a composite signal shown in FIG. Since the subsequent operations are the same as those in the first embodiment, a description thereof will be omitted.
The coherent light of the light source used for generating the optical pulse signal is used as a medium for generating the THz wave, and is finally removed by the optical demodulator 4. Therefore, even if there is a defect that causes a problem when using direct light as a carrier wave, such as a difference in wavelength, slight wavelength fluctuation, and chirping, it does not cause a problem for the above-described reason. This means that an expensive light source such as a high-performance laser diode is not required, and an inexpensive wireless system can be realized.
FIG. 7 is a configuration diagram of a radio system according to the third embodiment of the present invention. The third embodiment is based on the configuration of the second embodiment, and further includes a variable pulse signal generator 5.
In the present embodiment, when the optical pulse signal shown in FIG. 2 is produced, the pulse repetition frequency can be continuously changed by the variable pulse signal generator 5, so that the frequency of the THz wave can be changed continuously. Yes. Compared to the THz wave generation method using a laser, it has a large degree of freedom, and therefore has high adaptability to various applications. For example, application to CDMA using frequency hopping can be mentioned.
Here, in the third embodiment shown in FIG. 7, instead of changing the pulse repetition frequency of the variable pulse signal generator 5, the duty ratio of the 100 GHz repetition pulse shown in FIG. 2 can be changed.
As can be seen from Fourier transform of this repetitive pulse, when the duty ratio is 50%, the intensity of 100 GHz, which is the fundamental wave component, becomes maximum. That is, the output of the THz wave can be made variable by changing the duty ratio. Therefore, when using a plurality of THz waves while moving in the same space, it is possible to cope with the problematic interference by dynamically changing the output, and the influence can be reduced.
[0008]
【The invention's effect】
As described above, according to the first aspect of the present invention, a large number of transmitters having the same configuration can be manufactured on the same substrate, and wireless that can be reduced in size, priced, and stabilized. A system can be provided. In addition, since compatibility with an integrated circuit is good, integration with peripheral circuits such as a modulator driver becomes easy.
According to invention of Claim 2, size reduction, price reduction, and high stability can be achieved further.
According to the invention described in claim 3, since the pulse repetition frequency can be continuously changed, the frequency of the THz wave can be continuously changed.
According to the fourth aspect of the present invention, it is possible to deal with interference that becomes a problem when using a plurality of THz waves while moving in the same space by dynamically changing the output, and the influence can be reduced. .
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a radio system according to a first embodiment of the present invention.
FIG. 2 is a diagram showing an optical pulse signal.
FIG. 3 is a diagram illustrating a data signal.
FIG. 4 is a diagram illustrating a composite signal.
FIG. 5 is a diagram showing a data-modulated 100 GHz THz wave.
FIG. 6 is a configuration diagram of a radio system according to a second embodiment of the present invention.
FIG. 7 is a configuration diagram of a radio system according to a third embodiment of the present invention.
[Explanation of symbols]
1 Optical pulse signal generator 2 Transmitter 3 Optical modulator 4 Optical demodulator

Claims (4)

An optical pulse generator for generating an optical pulse signal having the same repetition frequency as a desired carrier frequency, and a transmitter,
The transmitter modulates an optical pulse signal generated from the optical pulse generator using a data signal to generate a composite signal, and an optical component from the composite signal generated by the optical modulator. With an optical demodulator that removes and outputs to the antenna,
A radio system, wherein the optical modulator and the optical demodulator are integrated on a substrate made of the same material . By performing pulse modulation on the coherent light, a first optical modulator that generates an optical pulse signal having the same repetition frequency as a desired carrier frequency, and an optical pulse signal generated from the first optical modulator A second optical modulator that modulates using a data signal and generates a composite signal, and an optical demodulator that removes an optical component from the composite signal generated by the second optical modulator and outputs the resultant signal to an antenna A transmitter comprising:
The transmitter, wherein the first optical modulator, the second optical modulator, and the optical demodulator are integrated on a substrate made of the same material . 3. A radio comprising: the transmitter according to claim 2; and a variable pulse signal generator that changes a repetition frequency of the optical pulse signal by inputting a signal to the first optical modulator. system. A transmitter according to claim 2, and a variable pulse signal generator that changes a duty ratio of a repetition frequency of the optical pulse signal by inputting a signal to the first optical modulator. Wireless system.

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