JP2001160787A - Optical radio access point - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical radio access point which is used for a small and inexpensive optical sub-carrier transmission-type radio access system with simple structure and small power consumption. SOLUTION: The optical radio access point is used for the radio access system based on an optical sub-carrier transmission system, which optically connects sub-carrier multiplex light to a photodiode, converts sub-carrier multiplex light into a high frequency signal by the photodiode and radiates the high frequency signal from an antenna through a bias circuit applying DC bias to the photodiode. The photodiode is set to be the high output photodiode (single travel-type high output photodiode, for example) whose high frequency power outputted from the photodiode single body is large and from which desired high frequency signal output is obtained. The optical radio access point has at least a means supplying the high frequency signal to the antenna without an amplification circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical wireless access point of a wireless access system based on an optical subcarrier transmission system which is suitably used in mobile communication using microwaves or millimeter waves, a wireless LAN system, a broadcast network, and the like. About.

[0002]

2. Description of the Related Art In the optical subcarrier transmission system, an optical wireless host station modulates a laser beam with a high-frequency wireless signal, transmits the modulated light to an optical wireless access point through an optical fiber, and converts the laser light into a wireless signal at the optical wireless access point. , A signal is transmitted to a wireless terminal by radio waves.

[0003] This outline will be described with reference to FIG. The system includes an optical wireless host station 21, an optical fiber 20, an optical wireless access point 22, and a wireless terminal 23. First,
The optical wireless host station 21 once superimposes the wireless signal to be transmitted on the laser light. This laser light is called subcarrier multiplexed light. The optical wireless host station 21 includes a transmitter 24 and a light source 25. That is, a high-frequency signal to be transmitted to the wireless terminal 23 is generated by the transmitter 24.
If the output level is appropriately amplified or attenuated so that the light source 25 can be driven, the conventional wireless transmitter can be used as it is. The light source 25 superimposes a high-frequency signal on light to generate subcarrier multiplexed light (SCM light). The generation method is
Two main types are known, laser diode (LD)
A direct modulation method and an external modulation method. In the LD direct modulation method,
A current exceeding a threshold value and a high-frequency signal are simultaneously applied to the LD to obtain intensity-modulated light proportional to the high-frequency signal. On the other hand, in the external modulation method, intensity-modulated light is obtained by using an external light modulator for laser light emitted at a constant intensity.

[0004] The SCM light is transmitted to the optical wireless access point 22 via the optical fiber 20. Where SC
The M light is returned to a high frequency signal by a photoelectric converter 26 including a photodiode and an amplifier. High frequency signal is antenna 2
Radiated from 7 into space. Light source 25, optical fiber 20,
Wireless signals are transmitted by the complex system of the photoelectric converter 26 because at a frequency shorter than a microwave, a wireless transmission path such as a coaxial cable has a larger loss than an optical fiber. Optical fibers are also superior to coaxial cables in terms of price.

[0005] Finally, the radiated radio signal is received by a radio terminal 23 comprising an antenna 27 and a receiver 28. If this method is applied to mobile communication and wireless LAN,
The access point is small and low-priced, which can contribute to miniaturization and low cost of the entire system.

FIG. 5 shows the configuration of an optical wireless access point based on the prior art. In the figure, 2 is an inductor, 3 is a power supply, 4 is a capacitor, 5 is an antenna, 6 is a lens, 8 is a pin photodiode (pin-PD), and 9 is an amplifier.

[0007] The laser light modulated by the high frequency signal is SC
The light is incident on the pin-PD 8 via the lens 6 as M light. The pin-PD is widely used in optical fiber communication because it can operate at high speed. In this configuration, the DC voltage of the power supply 3 is directly connected to the amplifier 9 and the pin-
The PD 8 is connected via the inductor 2. pi
The signal of the n-PD 8 is further connected to the amplifier 9 via the capacitor 4. The output of the amplifier 9 is transmitted to the antenna 5.

The details of the operation between the pin-PD 8 and the antenna 5 are as follows. Since a photodiode as a photodetector is generally used with a reverse bias, a power supply 3
Applies a reverse bias. Voltage is about -2 ~
It is about -5V. At this time, the capacitor 4 is inserted so that only the high-frequency component contained in the output of the pin-PD 8 is efficiently transmitted to the amplifier 9 in the next stage, and the high-frequency component for AC interruption is prevented so that the high-frequency component does not flow to the power supply side. The inductor 2 is inserted. The configuration of the inductor 2 and the capacitor 4 is generally called a bias tee. pin-PD
In this case, when a strong SCM light is irradiated, the band structure is modulated by the accumulation of carriers, and the output is likely to be saturated. If the incident SCM light is further strengthened, the device is likely to be destroyed.
Therefore, the pin-PD cannot output a large power or a large current. Therefore, the amplifier 9 is used to obtain sufficient high-frequency power. Naturally, power supply is required for the amplifier 9, and power is supplied from the power supply 3.
The high-frequency signal amplified by the amplifier 9 is radiated into the air by the antenna 5. The frequency can be realized by a conventional configuration from a microwave band of about 2 GHz to a millimeter wave band.

[0009] A problem with the conventional optical wireless access point is the output power of the pin-PD as described above. That is, since the power output from the pin-PD alone is small, if an optical wireless access point is constituted by the pin-PD alone, a sufficient service area cannot be covered. Then, by the amplifier and the power supply corresponding to it, it will be amplified to the desired high frequency power,
Amplifiers from the microwave band to the millimeter wave band are generally expensive,
Consumes a lot of power. As a result, the optical wireless access point has problems such as large size, high cost, and large power consumption.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems in the prior art, and to provide an optical wireless access point having a small size, a simple structure, low cost, and low power consumption. Is to do.

[0011]

Means for Solving the Problems In order to achieve the above object of the present invention, the present invention is configured as described in the claims. That is, a bias circuit that optically couples subcarrier multiplexed light to a photodiode, converts the subcarrier multiplexed light into a high-frequency signal with the photodiode, and applies a DC bias to the photodiode as described in claim 1. In an optical wireless access point used in a wireless access system based on an optical subcarrier transmission system that radiates the high-frequency signal from an antenna, a high-frequency power output from the photodiode alone is large and a desired high-frequency An optical wireless access point having at least means for supplying the high-frequency signal to the antenna without a high-output photodiode capable of obtaining a signal output, without a high-output photodiode, and without an amplifier circuit.

[0012] The high-output photodiode referred to here is a single-transport carrier photodiode that can hardly cause saturation and element destruction under strong light irradiation and can realize high-speed operation and high linearity. It can be applied to SCM transmission in the microwave to millimeter wave band, and can emit radio waves of sufficient intensity from the antenna without power amplification after photoelectric conversion. This operation can be realized not only at the time of the reverse bias but also at the time of the zero bias or the low bias, so that the bias circuit and the power supply can be omitted.

[0013] Also, as described in claim 2, claim 1
In the above, the high output photodiode is an optical wireless access point using a single traveling carrier photodiode.

[0014] Also, as described in claim 3, claim 1
3. The optical wireless access point according to claim 2, wherein the bias circuit is an optical wireless access point including at least an inductor for short-circuiting a high-output photodiode in a DC manner and a capacitor for supplying a high-frequency signal to an antenna. It is.

In addition, as described in claim 4, claim 1
3. The optical wireless access point according to claim 2, wherein the bias circuit supplies a power supply for applying a DC voltage to the high-output photodiode, an inductor for preventing a high-frequency current from flowing into the power supply, and a high-frequency signal to the antenna. An optical wireless access point including at least a capacitor.

In addition, as described in claim 5, claim 1
5. The optical wireless access point according to claim 4, wherein components other than an optical system for optically coupling said subcarrier multiplexed light to a high-output photodiode are hybridized on a single substrate. It is an integrated optical wireless access point.

Further, as described in claim 6, claim 1 is
5. The optical wireless access point according to claim 4, wherein components other than an optical system for optically coupling the subcarrier multiplexed light to a high-output photodiode are provided on a single semiconductor substrate. This is an optical wireless access point that is monolithically integrated.

An optical wireless access point according to the present invention comprises: a high-power photodiode for converting subcarrier multiplexed light into a high-frequency signal; an optical system for optically coupling the subcarrier multiplexed light to the high-power photodiode; An optical wireless access point having at least a bias circuit for applying a DC bias to a photodiode and an antenna for emitting a converted high-frequency signal.

Further, the high-output photodiode uses a single traveling carrier photodiode.
It is possible to arbitrarily select one or more of single traveling carrier photodiodes such as an end-incidence refraction type, a waveguide type, and a total reflection type, and apply them to the optical wireless access point.

In addition, the bias circuit includes at least an inductor for short-circuiting the high-output photodiode in a DC manner, and a capacitor for supplying a high-frequency signal to an antenna.

Further, the bias circuit includes at least a power supply for applying a DC voltage to the high-output carrier photodiode, an inductor for preventing a high frequency from flowing into the power supply, and a capacitor for supplying a high-frequency signal to an antenna. Things.

Further, the present invention has a structure in which the components of the optical wireless access point are hybrid-integrated on a single substrate.

Further, the present invention has a structure in which the components of the optical wireless access point are hybrid-integrated on a single semiconductor substrate.

With such a structure, an optical wireless access point in a wireless access system based on an optical subcarrier transmission system can be reduced in size, simplicity, cost, and
This has the effect of reducing power consumption. Further, since the number of optical wireless access points to be installed is enormous, the merits of lowering costs and lowering power consumption among the effects of the present invention are immense. In the present invention, the non-powered optical wireless access point that does not even require a power supply circuit is extremely small and can be easily arranged in any place such as in an office, a building, or on a power pole.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS <Embodiment 1> This embodiment is characterized in that a surface-incidence type single traveling carrier photodiode (UTC-PD) is used as a photodetector and that SCM light is supplied without power supply. The conversion to microwave or millimeter waves. In addition, as a reference about a surface incidence type single traveling carrier photodiode (UTC-PD),
(1) UTC-PD [Tadao Ishibashi, Satoshi Kodam
a, Naofumi Shimizu, and Tomofumi Furuta, “High-speed
response of uni-traveling-carrier photodiodes, ”J
pn.J.Appl.Phys.36,6263-6268 (1997)] and (2)
Uni-traveling carrier photodiode [Tadao Ishibashi, Naofumi Shimizu, Toshifumi Furuta, "On the output saturation of InP / InGaAs mono-traveling carrier photodiode"; IEICE, No.
2nd Workshop on Microwave Photonics (MWP), Paper MWP97-
13, p.21 (February 4, 1998)].

FIG. 1 is a schematic diagram showing a configuration of an optical wireless access point according to the present embodiment. In the figure,
1 is UTC-PD, 2 is an inductor, 4 is a capacitor,
5 is an antenna, and 6 is a lens. The SCM light transmitted by the optical fiber is transmitted to the UTC-PD by the lens 6.
The light is focused to 1. The peripheral circuit of the UTC-PD1 can be divided into DC and high frequency as follows. As a DC circuit, the right side of the capacitor 4 is cut off.
A short circuit is formed only by the TC-PD1 and the inductor 2. Therefore, the bias state of UTC-PD1 can be regarded as zero bias. As an AC circuit,
The portion below the inductor 2 is shut off and the UTC-PD1
Is introduced into the antenna 5 via the capacitor 4 and radiated from the antenna 5 into the air.

The details of UTC-PD are described in Japanese Patent Application No. 8-837.
04 (JP-A-9-275224), and a description thereof will be omitted. A feature of the UTC-PD is that saturation and element destruction hardly occur even under strong light irradiation, and high-speed operation and high linearity can be realized. Therefore,
If applied to SCM transmission in the microwave to millimeter wave band, radio waves having sufficient intensity can be emitted from the antenna without power amplification after photoelectric conversion. This operation can be realized not only at the time of reverse bias but also at the time of zero bias or low bias. Therefore, the bias circuit and the power supply can be omitted.

UTC-PD manufactured as described above
Is a 1.55 μm wavelength band and a subcarrier frequency of 5.8 GH
A conversion efficiency of 0.5 A / W (at zero bias) was shown for z-band SCM light. As the prototype antenna 5 of the first embodiment, a batch antenna having an impedance of 50Ω was used. Further, chip components were used for the inductor 2 and the capacitor 4 and all except for the lens 6 were hybrid-integrated on a ceramic substrate. UTC-PD1 has a wavelength of 1.55 μm, a subcarrier frequency of 5.8 GHz,
SCM with an average light intensity of 12.6 mW and a light modulation index of 100%
Light is incident, and 1 mW of 5.8 is applied at the input end of the antenna 5.
The microwave power in the GHz band could be confirmed. The receiver also confirmed that millimeter-wave power was radiated into the air.

<Embodiment 2> In this embodiment, an end-face incident refraction type single traveling carrier photodiode (UTC-RFPD) is used as a photodiode, and a power supply is not included in a bias circuit. In the UTC-PD described in the first embodiment, light is incident on the semiconductor substrate of the PD at right angles. In the case of UTC-PD, part of the incident light is not photoelectrically converted, and the conversion efficiency is not sufficient. For UTC-RFPD, a high-efficiency edge-incidence refraction type uni-traveling carrier photodiode [H. Fukano, Y. Mur
amoto, K. Takahata and Y. Matsuoka, “High efficiency
edge-illuminated uni-travelling-carrier-structure
refracting-facet photodiode, ”ELECTRONICS LETTERS,
35 (19), 1664-1665 (1999)], and only the features will be described here. The UTC-RFPD is characterized in that light is incident from the chip end face, and light that has not been absorbed in the structure is reflected again on the chip upper face, so that photoelectric conversion is efficiently performed. Therefore, UTC-RFPD is more efficient than UTC-PD. In fact, with UTC-RFPD, an efficiency of 0.8 A / W was obtained. In the second embodiment, a reverse bias of about -2 V is applied in consideration of the millimeter wave band application.

Embodiment 2 will be described with reference to FIG. In the figure, 2 is an inductor, 3 is a power supply, 4 is a capacitor, 5 is an antenna, 6 is a lens, and 7 is UTC-RF.
PD. The basic configuration is almost the same as in the first embodiment. The used photodiode is UTC-RFPD
Is as described above.

Here, the power supply included in the bias circuit will be described. UTC-PD and UTC-RFPD
Exhibits good frequency characteristics even at zero bias, but in a millimeter wave band such as the 60 GHz band, the efficiency is somewhat reduced at zero bias. To compensate for this,
In the second embodiment, the power supply 3 of -2 V is inserted. UTC
-If the surroundings of the RFPD 7 are described by DC operation, UTC-
It becomes a series circuit of the RFPD 7, the inductor 2, and the power supply 3.
This is equivalent to the power supply 3 having a voltage of −2 V being directly connected to the UTC-RFPD 7. The operation of the alternating current is the same as that of the first embodiment, and therefore the description is omitted.

The UTC-RFPD 7 of the optical wireless access point manufactured as described above has a wavelength of 1.55 μm.
Band, subcarrier frequency 60 GHz band, average light intensity 4.
SCM light having a light modulation index of 9% and a light modulation index of 100% was incident thereon, and 1 mW of microwave power in the 60 GHz band could be confirmed at the input end of the antenna 5.

<Embodiment 3> In this embodiment, all the components except the lens 6 are monolithically integrated. FIG.
FIG. 9 is a top view showing the configuration of the optical wireless access point exemplified in the third embodiment. In the figure, 4 is a capacitor, 6 is a lens, 10 is a guided single traveling carrier photodiode (UTC-WGPD), 11 is a meander line, 12 is a loop antenna, and 13 is an InP substrate.

The procedure for manufacturing the optical wireless access point according to the present embodiment is as follows. First, the InP substrate 1
On U.3, UTC-WGPD is manufactured. Thereafter, a wiring and insulating film process is performed. In the first wiring process, the meander line 11 and the loop antenna 12 are formed by vapor deposition and patterning. Next, an SiO ₂ film is formed by vapor deposition and patterning to form the capacitor 4. Finally,
The upper electrode of the capacitor 4 is formed on the capacitor 5 in the second wiring process. Here, the meander line 11 functions as an inductor to set the DC bias of the UTC-WGPD 10 to 0 V, that is, to function as a short circuit.
The high frequency component converted from the SCM light is supplied to the loop antenna 12 via the capacitor 4, and is radiated to space. A loop antenna whose circumference corresponds to one wavelength was used as the antenna. The directivity of the antenna was upward from the plane including the loop antenna (parallel to the paper). Finally, the lens 6 was optically coupled to the UTC-WGPD 10.

In the third embodiment, a 60 GHz band is assumed as a subcarrier frequency, and a capacitor 4, a meander line 11, a loop antenna 12, a UTC-WGPD 10
Was monolithically integrated on the InP substrate 13. Monolithic integration has simplified assembly and minimized high frequency losses between components.

In the first to third embodiments, the surface traveling type, the end surface refraction type, and the waveguide type have been described as examples of the single traveling carrier photodiodes. A single traveling carrier photodiode may be used as long as it has the same function and performance as a single traveling carrier photodiode.

Further, in the first to third embodiments, specific combinations are disclosed with respect to the form of the single traveling carrier photodiode, the presence or absence of a power supply, and the integration method. However, these combinations can be arbitrarily selected. It is.

[0038]

According to the present invention, it is possible to realize an optical wireless access point having an extremely small size, a simple structure, low cost, and low power consumption. If this is applied to a wireless access system based on the optical subcarrier transmission method,
Since access points, which account for a large portion of the total system cost, are inexpensive, the total system cost can be significantly reduced. Furthermore, since it is small, there is an advantage that an optical wireless access point can be installed at any place.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of a configuration of an optical wireless access point exemplified in Embodiment 1 of the present invention.

FIG. 2 is a schematic diagram illustrating an example of a configuration of an optical wireless access point exemplified in Embodiment 2 of the present invention.

FIG. 3 is a schematic diagram illustrating an example of a configuration of an optical wireless access point exemplified in Embodiment 3 of the present invention.

FIG. 4 is a schematic diagram showing a conventional optical subcarrier transmission system.

FIG. 5 is a schematic diagram showing a configuration of a conventional optical wireless access point.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... UTC-PD 2 ... Inductor 3 ... Power supply 4 ... Capacitor 5 ... Antenna 6 ... Lens 7 ... UTC-RFPD 8 ... Pin-PD 9 ... Amplifier 10 ... UTC-WGPD 11 ... Meander line 12 ... Loop antenna 13 ... InP board Reference Signs List 20 optical fiber 21 optical wireless host station 22 optical wireless access point 23 wireless terminal 24 transmitter 25 light source 26 photoelectric converter 27 antenna 28 receiver

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kaoru Yoshino 2-3-1 Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation F-term (reference) 5K002 AA03 AA06 BA07 DA09 DA21

Claims (6)

[Claims] 1. A sub-carrier multiplexed light is optically coupled to a photodiode, the sub-carrier multiplexed light is converted into a high-frequency signal by the photodiode, and the high-frequency signal is transmitted through a bias circuit for applying a DC bias to the photodiode. An optical wireless access point used in a wireless access system based on an optical subcarrier transmission system, which has a function of radiating an optical signal from an antenna. An optical wireless access point, comprising: at least a means for supplying the high-frequency signal to the antenna without a high-output photodiode capable of obtaining the above-mentioned, and without an amplifier circuit. 2. The optical wireless access point according to claim 1, wherein said high-power photodiode is a uni-traveling carrier photodiode. 3. The optical wireless access point according to claim 1, wherein the bias circuit includes at least an inductor for short-circuiting a high-output photodiode in a DC manner, and a capacitor for supplying a high-frequency signal to an antenna. An optical wireless access point, comprising: 4. The optical wireless access point according to claim 1, wherein said bias circuit comprises: a power supply for applying a DC voltage to a high-output photodiode; and an inductor for preventing a high frequency from flowing into said power supply. And a capacitor for supplying a high-frequency signal to the antenna. 5. An optical wireless access point according to claim 1, further comprising an optical system for optically coupling said subcarrier multiplexed light to a high-output photodiode. An optical wireless access point characterized by being hybrid-integrated on one substrate. 6. The optical wireless access point according to claim 1, further comprising an optical system for optically coupling said subcarrier multiplexed light to a high-output photodiode. An optical wireless access point which is monolithically integrated on a single semiconductor substrate.