KR20020031899A - System for immunizing optical noise in an optical wireless system - Google Patents

Abstract

PURPOSE: A system for an optical noise erasable differential detection in a wireless light connection device is provided to remove the influence of a noise light effectively without using an optical filter or an electric filter by amplifying a detection voltage from a photo diode differently and removing a noise component. CONSTITUTION: The first and second photo diodes(10,12) having the same property are connected thereto in serial. A differential amplifier(20) differently amplifies a detection voltage from each photo diodes(10,12), and removes a noise component. A multiplication of a combination ratio of a noise light by a differential amplifying ratio in each photo diodes(10,12) must be '1' for removing the noise component and increasing a signal to noise ratio.

Description

Optical noise cancellation type differential detection system in wireless optical connection device {SYSTEM FOR IMMUNIZING OPTICAL NOISE IN AN OPTICAL WIRELESS SYSTEM}

The present invention relates to an optical noise canceling technology of a wireless optical connection device, and more particularly, to an optical noise cancellation type differential detection system in a wireless optical connection device that differentially amplifies an optical signal to cancel the influence of noise light.

In general, the wireless optical connection device refers to a device capable of transmitting / receiving data wirelessly in a free space without using a signal transmission medium such as an optical fiber.

Such a wireless optical connection device is low in cost, low in power consumption, has a good radiation security because it is limited in a certain direction, and has a wide range of available frequency bands. It is a trend. In addition, since the connection cables between the devices are almost unnecessary, the initial installation cost and maintenance cost of the cable can be reduced, and unlike the outdoor, it is not sensitive to changes in the atmosphere of the air, and there is little mutual interference with the existing radio communication frequency. Recently, research on this has been actively conducted.

By the way, as described above, the wireless optical connection device is simple in structure and can be implemented as a relatively inexpensive device. However, since the free space is used as a transmission medium, it is affected by ambient noise such as sunlight, fluorescent lamps, and incandescent lamps. Bar technology to minimize the influence of such noise is essential.

The filtering technique is one of such noise canceling techniques. In order to prevent the influence of ambient noise generated in a wireless optical connection device, an optical filter is generally used to remove noise light components in front of the photodetector, or at the rear of the photodetector. This refers to a technique for canceling noisy light using an electrical filter. However, this filtering technology has a disadvantage in that noise light having a wavelength similar to that of signal light is introduced or electrical noise similar to signal components is included.

Accordingly, the present invention has been made to solve the above-mentioned problem, and by adopting a differential detection method that differentially amplifies the detection voltage from the photodiode to remove noise components, the effect of noise light is eliminated without the use of an optical filter or an electrical filter. It is an object of the present invention to provide an optical noise canceling differential detection system in a wireless optical connection device for efficient cancellation.

According to an embodiment of the present invention for achieving the above object, an optical noise cancellation type differential detection system in a wireless optical connection device, two photodiodes (PD) having the same characteristics are connected in series with each other; An optical noise canceling differential detection system in a wireless optical connection device, comprising a differential amplifier for differentially amplifying a detection voltage from each photodiode (PD) to remove noise components.

According to another embodiment of the present invention, an optical noise canceling differential detection system in a wireless optical connection device having an x-axis and a y-axis motor and automatically aligned with signal light has the same characteristic of being connected in series with each other. First and second photodiodes PD_0 and PD_5; A differential amplifier for differentially amplifying detection voltages from the first and second photodiodes PD_0 and PD_5 to remove noise components; Third and fourth photodiodes PD_1 and PD_3 positioned symmetrically at the same distance with respect to the first photodiode PD_0 and detecting the position of the signal light on the x-axis; Fifth and sixth photodiodes PD_2 and PD_4 positioned symmetrically at the same distance with respect to the first photodiode PD_0 and detecting the position of the signal light on the y-axis; A first driving circuit for driving the x-axis motor in response to the signal light position detection signals of the third and fourth photodiodes PD_1 and PD_3; And a second driving circuit for driving the y-axis motor in response to the signal light position detection signals of the fifth and sixth photodiodes PD_2 and PD_4. to provide.

According to still another embodiment of the present invention, there is provided an optical noise cancellation type differential detection system in a wireless optical connection device, comprising: a light source for signal generation; A first polarizing plate mounted in a direction coinciding with polarization of the signal light generated from the light source and transmitting the signal light; A second polarizing plate mounted in a direction perpendicular to the polarization of the signal light generated from the light source to block the signal light; A first photodiode positioned to correspond to the first polarizer; A second photodiode positioned corresponding to the second polarizing plate; An optical noise canceling differential detection system in a wireless optical connection device, comprising a differential amplifier for differentially amplifying detection voltages from first and second photodiodes to remove noise components.

1 is a block diagram of an optical noise cancellation type differential detection system in a wireless optical connection device according to an embodiment of the present invention;

2 is a signal to noise ratio (SNR) graph of the differential detection system of FIG.

3 is a graph illustrating optical noise comparison when signal light is received by a single photodiode and signal light is received by the differential detection system of FIG. 1;

4 is a graph of comparison of interference when signal light is received by a single photodiode and signal light is received by the differential detection system of FIG.

FIG. 5 is a graph of comparison of optical noise when signal light is received by the differential detection system of FIG. 1 using approximate average noise detection according to another embodiment of the present invention, and when signal light is received by a single photodiode; FIG.

6 is a block diagram illustrating a signal light automatic alignment differential detection system according to another embodiment of the present invention;

FIG. 7 is a graph illustrating a signal light automatic alignment process in the differential detection system of FIG. 6.

8 is a block diagram of a polarizing plate applied differential detection system according to another embodiment of the present invention;

FIG. 9 is a diagram exemplarily illustrating optical feedback noise cancellation in the differential detection system of FIG. 8; FIG.

10 is a graph comparing optical feedback cancellation results in a conventional system with optical feedback cancellation results in a polarization plate applied differential detection system of FIG. 8;

11 is a block diagram of a wireless optical relay apparatus using a differential detection system according to another embodiment of the present invention;

12A is a waveform diagram of a camera output and monitor input signal when using a single photodiode;

12B is a waveform diagram of a camera output signal and a monitor input signal when a differential detection system according to the present invention is used.

FIG. 13 is a block diagram illustrating an apparatus for separating a wireless optical channel using a differential detection system according to another embodiment of the present invention; FIG.

14A and 14B are experimental results waveform diagrams respectively separated from a mixed state of a digital signal and an analog signal using the wireless optical channel separation device of FIG.

<Explanation of symbols for the main parts of the drawings>

10, 12, 60, 61, 62, 63, 64, 65, 83, 84: photodiode

20, 66, 85: differential amplifier

80: light source

81, 82: polarizer

101: differential detection unit

102: signal amplification unit

103: light source driver

The optical noise canceling differential detection system in the wireless optical connection device according to the present invention eliminates the influence of ambient noise light including the wavelength similar to the signal light in the wireless optical connection, detects only the signal component, and detects the adjacent channel light of the wavelength similar to the signal light. It is characterized by eliminating interference and detecting only a corresponding channel signal, and separating each signal component from an overlapping region of mutually independent channel light.

As a preferred embodiment for highlighting the features of the present invention, an optical noise cancellation differential detection system using approximate average noise detection in a wireless optical connection, an optical noise cancellation differential detection system that automatically aligns with a signal light in a wireless optical connection, and An optical noise canceling differential detection system using a polarizer in a wireless optical connection is provided.

Hereinafter, preferred embodiments of the present invention will be described in detail with the accompanying drawings.

1 is a block diagram of an optical noise canceling differential detection system in a wireless optical connection device according to an embodiment of the present invention, and includes a first photodiode 10, a second photodiode 12, and a differential amplifier ( 20).

As shown, the first and second photodiodes 10, 12 having the same characteristics are connected in series with each other, and a differential amplifier () is provided from each of these photodiodes 10, 12. Differential amplification of the detected voltage eliminates noise components.

At this time, in order to remove such noise components and maximize the signal to noise ratio (SNR), that is, the signal-to-noise ratio, the product of the combined ratio of the noise light and the differential amplification ratio of each photodiode 10 and 12 is 1. Should be

2 is an SNR graph of the differential detection system of FIG. 1, it can be seen that when the differential detection system according to the present invention is used, the SNR is improved as compared to the conventional system using a single photodiode. That is, the amount (ΔSNR) at which the signal-to-noise ratio is improved depends on the coupling ratio of the signal light and the noise light, and the differential gain ratio (β / α). The product of and the differential gain ratio should be 1 to cancel out. As a result of the applicant's experiment, it was confirmed that the differential detection system according to the present invention improves the SNR by about 20 dB or more while the intensity of the noise light is similar to that of the signal light.

As described above, the differential detection system shown in FIG. 1 is a technique of canceling the influence of the noise light by making the product of the coupling ratio of the noise light and the differential gain ratio equal to one. In other words, in a linear optical connection of LOS (Line of sight) method, the signal light travels in a specific direction, and the distribution of noise light due to lighting facilities or sunlight does not change greatly depending on the position of the photodiode. Since the coupling ratio of the noise light in the two photodiodes 10 and 12 is close to 1, the differential gain ratio for the output voltages of the two photodiodes 10 and 12 is 1, thereby eliminating the influence of the noise light. Can be.

FIG. 3 is a graph of comparison of optical noise when signal light is received by a single photodiode and signal light is received by the differential detection system of FIG. 1.

The upper graph waveform of FIG. 3 represents a state in which a noise component of an incandescent lamp indoors and digital data, which are signal lights, are mixed and received when data is transmitted between two PCs using a wireless optical connection. By the differential detection system according to the present invention, a noise component disappears and only a signal component is received.

4 is a crosstalk comparison graph when signal light is received by a single photodiode and signal light is received by the differential detection system of FIG. 1, and an upper graph waveform shows a state in which different wireless light data are mixed and a lower graph The waveform shows a state where interference is canceled using the differential detection system according to the present invention. In other words, even when interference occurs from adjacent channel light, the effect of interference can be eliminated by making the product of the coupling ratio of the interference and the differential gain ratio equal to one.

FIG. 5 is a graph of comparison of optical noise when signal light is received by the differential detection system of FIG. 1 using approximate average noise detection according to another embodiment of the present invention, and when signal light is received by a single photodiode.

In the lower graph waveform of FIG. 5, when the wireless light is received using a single photodiode, it can be seen that the influence of the noise light due to the moving shadow of the object is generated in the presence of the noise light. In the upper graph waveform of FIG. 5 using the differential detection system, it can be seen that noise is canceled and only signal light is received. As can be seen in Figure 5, differential detection using the approximate average noise voltage, it is possible to reduce the output voltage fluctuations caused by the instantaneous change in the noise light coupling ratio that can be caused by the movement of objects or people. That is, when configuring the wireless optical connection in an environment where the spatial distribution of the noise light changes frequently, if the differential detection system according to the present invention is applied, the noise light cancellation efficiency may be maximized.

6 is a block diagram illustrating a signal light auto-alignment differential detection system according to still another embodiment of the present invention, wherein the photodiode 60 to 65, the differential amplifier 66, the driving circuit 67, the X axis, and the like are shown. Y-axis motors 68 and 69 are included.

The embodiment of FIG. 6 is an automatic alignment type differential detection system for canceling the influence of noise light in a wireless optical connection, and preventing a change in output voltage generated when the traveling direction of light is moved due to a slight alignment change of the signal light source. It uses the photodiode array perpendicular to to sense the center of light and drives the motors corresponding to the x and y axes, and automatically adjusts the photodiode array to be at the center of the signal light, while differentially detecting the effects of noise light. It is characterized by erasing.

As shown in Fig. 6, the automatic alignment differential detection circuit has six photodiodes PD (60 to 65) on an xy plane perpendicular to the signal light when the signal light travels perpendicular to the ground in the wireless light connection. ) Is fixedly arranged to form a PD array. The PD array is mounted on two motors 68 and 69 that are perpendicular to each other to move their position in the x-y axis direction according to the detection signal. Each of the motors 68 and 69 is connected by a linear rail and a cog wheel (not shown) so as to move in the tangential direction and the rotational direction, and these two rails are provided in the x-y axis direction.

Among the six PDs, PD_0 (60) and PD_5 (65) are differential detection photodiodes for canceling noise light and detecting signal components, and PD_1 (61), PD_2 (62), PD_3 (63), and PD_4 (64). ) Is a motor driving photodiode. In this case, the operation principle of the differential detection circuit including the PD_0 (60), the PD_5 (65), and the differential amplifier (66) is described in detail with reference to FIG.

The motor driving photodiodes, that is, the PD_1 61, the PD_2 62, the PD_3 63, and the PD_4 64 are located symmetrically with respect to the PD_0 60 at the same distance d. PD_1 (61) and PD_3 (63) detects the position of the signal light on the x-axis to drive the x-axis motor 69, PD_2 (62) and PD_4 (64) detects the position of the signal light on the y-axis The y-axis motor 68 is driven. The process of operating the motor by detecting the position of light is the same on the x and y axes.

At this time, the driving of the x-axis motor 69 and the y-axis motor 68 is performed by the control operation of the drive circuit 67. The operation principle of the drive circuit 67 will be described by taking the x-axis motor 69 as an example.

PD_1 61 and PD_3 63 generate photocurrent in proportion to the intensity of the signal light at each position, and detection voltages Vpd_1 and Vpd_3 are generated in the respective load resistors in proportion to the photocurrent. At this time, the PD_1 61 and the PD-3 63 have the same response and the load resistance is the same. The voltage difference Vpd_3-Vpd_1 is amplified by applying Vpd_1 and Vpd_3 to the negative (-) and (+) input terminals of the differential amplifier 66, and then driving the x-axis motor 69 with a current proportional to this voltage difference.

FIG. 7 is a graph illustrating the automatic alignment of signal light in the differential detection system of FIG. 6, in which the center of the light and the center of the light detector coincide with each other when the center of the signal light deviates from the photodetector. It is a drawing plotting the state which the output voltage of a component recovers to the state just before a movement of light generate | occur | produced through simulation.

On the other hand, Figure 8 is a block diagram of a polarizing plate applied differential detection system according to another embodiment of the present invention, the light source 80, polarizing plates 81, 82, photodiodes 83, 84 and differential An amplifier 85.

As shown in Fig. 8, the light source 80 may be composed of, for example, a laser diode, and has a signal generation light source in which a single direction polarization (arrow indicated by the signal light of the light source 80) is set. to be. Normally, incandescent and fluorescent lamps used for indoor lighting are noisy lights and usually no polarization is defined in a single direction.

In FIG. 8, the receiving unit is a differential detection circuit consisting of two photodiodes 83 and 84 and one differential amplifier 85, and the polarizing plates 81 and (in front of each photodiode 83 and 84). 82) is installed. The polarizing plate 81 provided at the front end of the photodiode 83 is mounted in a direction coinciding with the polarization of the signal light, and the polarizing plate 82 provided at the front end of the photodiode 84 is mounted so as to be perpendicular to the polarization of the signal light.

Therefore, signal light is detected in the photodiode 83 but signal light is not detected in the photodiode 84. Therefore, the noise light is detected with similar intensity in both photodiodes 83 and 84 because the polarization is not defined in a single direction, regardless of the direction of the polarizer. That is, in the photodiode 83, the signal light and the noise light are detected in a mixed state, and in the photodiode 84, the signal light is blocked and only the noise light is detected.

As described above, in the embodiment of FIG. 8, the polarization plate is used in the differential detection circuit for canceling the noise light to improve the noise canceling ability. In addition, when two optical signals having similar wavelengths overlap each other in a space and interference occurs, the polarizers may be vertically attached to each receiver to easily detect and separate the respective optical signals.

FIG. 9 is a diagram illustrating an example of optical feedback noise cancellation in the differential detection system of FIG. 8. FIG. 9 is a view illustrating a diffuser type non-line-of-sight type indoor wireless optical communication using a reflector. It may be possible to eliminate the effects of interference due to optical feedback that may occur.

FIG. 10 is a graph comparing the optical feedback cancellation result of the conventional system and the optical feedback cancellation result of the polarization plate applied differential detection system of FIG. 8. The upper waveform of FIG. 10 is a case where the influence of the optical feedback is severe. The lower waveform of FIG. 10 shows a state where the optical feedback is canceled by using the differential detection system.

11 is a block diagram of a wireless optical relay apparatus using a differential detection system according to another embodiment of the present invention, and includes a differential detector 101, a signal amplifier 102, and a light source driver 103.

The differential detector 101 of the wireless optical repeater of FIG. 11 cancels the noise light by using a differential detection method and detects only signal components. The signal components are again strong through the amplifier 102 and the light source driver 103. And outputs the signal light. That is, the embodiment of FIG. 11 is a case where the differential detection system is applied to the wireless optical repeater, and it is possible to solve the signal output reduction which is often generated in the wireless optical connection section.

Such a differential detection type wireless optical repeater may be used, for example, in a wireless optical connection section for transmitting an image signal between a CCD camera and a monitor installed indoors.

12A and 12B compare NTSC image signals input to the reception monitor for the case where a single photodiode is used for the wireless optical repeater and the differential detection system, respectively, when the wireless optical repeater is exposed to strong noise light. will be.

That is, FIG. 12A is a waveform diagram of a camera output signal and a monitor input signal when a single photodiode is used. The lower waveform shows a signal transmitted through a monitor when a single photodiode is used in a wireless optical repeater. As shown in FIG. 12A, it can be seen that strong noise light exists in the camera output signal and the monitor input signal.

On the other hand, Figure 12b is a waveform diagram of the camera output and monitor input signal when using the differential detection system according to the present invention, as shown in the lower waveform, it will be seen that the noise light is canceled and only the signal component is transmitted.

FIG. 13 is a block diagram illustrating an apparatus for separating a wireless optical channel using a differential detection system according to another embodiment of the present invention.

As shown, the wireless optical channel separator 130 has a function of separating two signal components separately at a point where two independent wireless optical signals overlap each other. According to the present invention, a digital signal and an analog signal are separated using a differential detection channel separator at a point where a digital optical signal transmitted between a PC and an analog optical signal transmitted between a microphone and a speaker are mixed so that each signal can be independently received. Wireless light connection is implemented.

Differential detection channel separators can consist of three identical photodiodes and two differential amplifiers, in which two differential detection systems are connected in parallel.

14A and 14B are waveform diagrams of experiment results separated from a mixture of digital and analog signals using the wireless optical channel separation apparatus of FIG. 13.

As described above, preferred embodiments of the present invention have been described in detail, but are not limited thereto, and other modified embodiments, for example, may be adjacent in a wireless optical connection for high-speed signal transmission between units or boards in various systems. Differential detection systems can also be utilized to cancel interference by light, which will be readily apparent to those skilled in the art.

Therefore, by applying the optical noise canceling technology according to the present invention, such as the configuration of the high-speed optical transmission path between buildings using the wireless optical connection, the indoor infrared LAN, and the board-to-board optical connection requiring wireless high-speed connection in various systems It is easy to implement, and nevertheless, the noise canceling efficiency is superior to the conventional wireless optical connection device.

Claims (6)

In the optical noise cancellation type differential detection system in a wireless optical connection device, Two photodiodes PD having the same characteristics connected in series with each other; And a differential amplifier for differentially amplifying the detected voltages from the respective photodiodes (PD) to remove noise components. The method of claim 1, The system, And an optical noise canceling differential detection system in a wireless optical connection device, characterized in that the product of the coupling ratio of the noise light and the differential amplification ratio of each photodiode (PD) is 1. An optical noise cancellation type differential detection system in a wireless optical connection device having an x-axis and a y-axis motor and automatically aligned with signal light, First and second photodiodes PD_0 and PD_5 having the same characteristics connected in series with each other; A differential amplifier for differentially amplifying detection voltages from the first and second photodiodes PD_0 and PD_5 to remove noise components; Third and fourth photodiodes PD_1 and PD_3 positioned symmetrically at the same distance with respect to the first photodiode PD_0 and detecting a position of signal light on an x-axis; Fifth and sixth photodiodes PD_2 and PD_4 positioned symmetrically at the same distance with respect to the first photodiode PD_0 and detecting a position of signal light on a y-axis; A first driving circuit for driving the x-axis motor in response to signal light position detection signals of the third and fourth photodiodes PD_1 and PD_3; Optical noise cancellation type differential detection in a wireless optical connection device, characterized in that the second drive circuit for driving the y-axis motor corresponding to the signal light position detection signal of the fifth and sixth photodiode (PD_2, PD_4) system. The method of claim 3, wherein The first driving circuit, A photocurrent is generated according to the signal light position detection signals of the third and fourth photodiodes PD_1 and PD_3, and a detection voltage proportional to the photocurrent is generated. And an optical noise canceling differential detection system in a wireless optical connection device, characterized in that a voltage difference is generated in addition to an input terminal to drive the x-axis motor by a current value proportional to the voltage difference. The method of claim 3, wherein The second drive circuit, A photocurrent is generated according to the signal light position detection signals of the fifth and sixth photodiodes PD_2 and PD_4, and a detection voltage proportional to the photocurrent is generated. And generating a voltage difference in response to an input terminal to drive the y-axis motor by a current value proportional to the voltage difference. In the optical noise cancellation type differential detection system in a wireless optical connection device, A signal light source; A first polarizing plate mounted in a direction coinciding with polarization of signal light generated from the light source and transmitting the signal light; A second polarizing plate mounted in a direction perpendicular to the polarization of the signal light generated from the light source to block the signal light; A first photodiode positioned corresponding to the first polarizer; A second photodiode positioned to correspond to the second polarizer; And a differential amplifier for differentially amplifying the detected voltages from the first and second photodiodes to remove noise components.