WO2002054630A1

WO2002054630A1 - Wireless optical communication system

Info

Publication number: WO2002054630A1
Application number: PCT/KR2001/002307
Authority: WO
Inventors: Su-Chan Kim; Myung-Soo Ahn; Se-Ho Park; Jung-Hyuck Cho; Seung-Yong Shin
Original assignee: Standard Laser System Co., Ltd
Priority date: 2000-12-29
Filing date: 2001-12-29
Publication date: 2002-07-11
Also published as: KR20020056827A

Abstract

The disclosure is relevant to a wireless optical communication system including: a network interface connected to a network; a transmitter, being connected to the network interface, for converting a transmission data signal of the network into a laser beam th at radiates into a free space; and a receiver for converting the laser beam into a reception data signal. With the present invention, it is easy to install or remove the system even at downtown areas or mountain fields because of reduced working steps for laying transmission lines. The laser beam containing data information greatly enhances qualities of data transmission. As the laser beam, not visible light, is indistinguishable and transmitted through free space, it does not expose an installation place and maintains security of communication.

Description

WIRELESS OPTICAL COMMUNICATION SYSTEM

Technical Field

The present invention relates to wireless optical communication systems in general, and more specifically to wireless optical communication systems capable of safely transmitting data with high quality by being connected to a communication network through a free space.

Background Art There are various kinds of data transmission means, associated with the recent promotions of LAN (Local Area Network), WAN (Wide Area Network), or Internet communications.

It is usual, in implementing the data transmission, to construct a network system with wires, e.g., coaxial cables or RF, in a local area, while with optical fibers by an optical communication technique in a wide area.

The data transmission through wires (e.g., coaxial cables or RF) or optical fibers needs a specific line for transmitting data. The specific transmission line is scaled in accordance with several parameters such as transmittal sections, distances, speeds (or a data rate), and data capacities. And, an installation cost rises according to the scale of the transmission line.

Network providers are demanded to provide high-quality data transmission services with lower costs for installation and maintenance. For instance, the need for cost reduction becomes more pronounced in the case of data transmission over a wide area or in a high-density downtown area, for a special purpose. Moreover, it may be preferable for data transmission equipments, which provide high-speed data services at specific places (e.g., mountain areas) during a short term, to be easily installable and removable. Also, there is a need for stationing a data transmission service with low-cost and high-security when it is necessary to manage a network in various manners for the purpose of rendering security for data transmitted therethrough.

Disclosure Of Invention

It is an object of the invention, in order to obviate or mitigate one or more of the above identified shortcomings of the prior art, to provide a wireless optical communication system capable of transmitting data at a higher speed with high capacity and quality by employing a laser beam containing the data to be transferred.

Brief Description of the Drawings

Figure 1 is a block diagram schematically illustrating a connection feature between a network and a wireless optical commumcation system according to the present invention.

Figure 2 is a block diagram illustrating a functional construction of a transmission block employed in the wireless optical communication system shown in Figure 1.

Figure 3 is a block diagram illustrating another functional construction of the transmission block employed in the wireless optical communication system shown in Figure 1. Figure 4 is a block diagram illustrating a construction of a line driver shown in Figures 2 and 3.

Figure 5 is a block diagram illustrating a construction of an output amplifier unit shown in Figures 2 and 3. Figure 6 is a block diagram illustrating a construction of a signal transmitter unit shown in Figures 2 and 3.

Figure 7 schematically illustrates an optical signal transmitter, which is shown in Figure 6, constructed in a cylindrical optics.

Figure 8 schematically illustrates an optical signal transmitter, which is shown in Figure 6, constructed in a prismatic optics.

Figure 9 schematically illustrates an optical signal transmitter, which is shown in Figure 6, constructed in a spherical/non-spherical optics.

Figure 10 schematically illustrates an optical signal transmitter, which is shown in Figure 6, constructed in a fiber optics. Figure 11 is a block diagram illustrating a functional construction of a reception block employed in the wireless optical communication system shown in Figure 1.

Figure 12 illustrates the demultiplexer unit interposed between an optical unit and a signal receiver shown in Figure 11.

Best mode for Carrying Out the Invention

According to an aspect of the invention, there is provided a wireless optical communication system for transmitting and receiving data through a free space between networks, between a device and a network, or between devices, the system comprising: a network interface connected to a network; a transmission block, being connected to the network interface, for converting a transmission data signal into a laser beam that radiates into the free space; and a reception block for converting the laser beam from the free space into a reception data signal.

The transmission block comprises: a data input buffer for storing the transmission data signal from the network; a signal modulator for frequency- modulating an output of the data input buffer; a laser driver for generating a laser drive signal; a laser generator for creating the laser beam from an output of the signal modulator in response to the laser drive signal; an output amplifier unit for amplifying the laser beam; and a signal transmitter unit for condensing the amplified laser beam on a predetermined pattern.

The laser driver is associated with a line driver for dividing the output of the signal modulator into a plurality of signals. The laser driver is also associated with a feedback controller for detecting the laser beam from the laser generator and for generating a laser output control signal to regulate an output level of the laser beam.

The output amplifier unit is associated with a multiplexer for multiplexing laser beams from a plurality of laser generators. The signal transmitter unit comprises: convex lenses arranged at both input and output ends to condense the laser beam; and a plurality of cylindrical lenses arranged on a path between the convex lenses to accord vertical and horizontal divergence angles of the laser beam.

Meanwhile, the reception block comprises: an optical unit for condensing the laser beam received from the free space; a demultiplexer unit for demultiplexing a laser beam supplied from the optical unit; a signal receiver for converting the demultiplexed laser beam into an electrical signal; a signal demodulator for demodulating the electrical signal into a data signal; and a data output buffer for applying the demodulated data signal into the network as the reception data signal.

According to another aspect of the invention, the transmission block comprises: a data input buffer for receiving the transmittal data signal from the network; a line driver for dividing an output of the data input buffer into a plurality of signals; a laser driver for generating a laser drive signal; a laser generator for creating the laser beam in response to the laser drive signal; an external signal modulator for frequency-modulating the laser beam output from the laser generator; an output amplifier unit for amplifying the frequency- demodulated laser beam output from the external signal modulator; and a signal transmitter unit for condensing the amplified laser beam on a predetermined pattern.

The laser driver is associated with a feedback controller for detecting the laser beam from the laser generator and for generating a laser output control signal to regulate an output level of the laser beam. The output amplifier unit is associated with a multiplexer for multiplexing laser beams from a plurality of laser generators. The signal transmitter unit comprises convex lenses arranged at both input and output ends to condense the laser beam, and a plurality of cylindrical lenses arranged on a path between the convex lenses to accord vertical and horizontal divergence angles of the laser beam. Now, a preferred embodiment of the invention will be explained in conjunction with the drawings of Figures 1 through 11.

Figure 1 illustrates an interconnecting feature between plural networks with a wireless optical communication system according to an embodiment of the invention, including first and second networks 100 and 1000, network interfaces 200 and 900, transmitters 300 and 800, receivers 500 and 700, and a free space 600. The reference numeral 150 denotes a wireless optical communication system that includes the network interface 200, the transmitter 300, and the receiver 500. As shown in Figure 1, the first and second wired networks, 100 and 1000, communicate with each other through the free space 600, being associated with the wireless optical communication system 150.

When the wireless optical communication system 150 comprising with a network interface 200 conducts data transmission between the networks and the wireless optical communication system, a transmitter 300 emits optical signals into the free space from the network system, and a receiver 500 accepts optical signals from the free space.

The wireless optical communication system 150 is applicable to transmit and receive digital data signals of audio/video sets, or text signals of various communication modes such as SDH (synchronous digital hierarchy) /SONET (synchronous optical network), ATM (asynchronous transfer mode), and gigabit Ethernet, and fast Ethernet. The system 150 can also transmit and receive analog signals.

Figure 2 shows an internal construction of the transmitter 300 employed in the wireless optical communication system 150, including a data input buffer 310, a signal modulator 320, a line driver 330, a laser driver 340, a laser generator 350, an output amplifier unit 360, a signal transmitter unit 370, an optical filter 380, a RF generator 400, a heat sink 410, and a feedback controller 420.

The data input buffer 310, the signal modulator 320, the RF generator

400, the line driver 330, the laser driver 340, the laser generator 350, and the feedback controller 420 are constructed in an electrical system, while the output amplifier 360, the signal transmitter unit 370, and the optical filter 380 in an optical system.

First, the data input buffer 310 temporarily stores data to be transmitted. The data held in the data input buffer 310 is modulated into a signal having a frequency to be transmittable. The frequency source for the modulation in the signal modulator 320 is supplied from the RF generator 400. A signal from the signal modulator 320 is applied to the line driver 330.

The line driver 330 is disposed to correspond one-to-one with the lager generator 350, or a plurality of laser driver 330 may be arranged in accordance with the number of lager generator 350.

The laser driver 340 is provided to activate the lager generator 350, and has a number equal to the number of lager generator 350.

The laser driver 340 applies a current of 10~40mA to the laser generator 350 which generates a frequency in the range of lMHz~10GHz. The laser driver 340 is further connected to the heat sink 340 that discharges heat from the laser driver 340 to regulate a temperature thereof. As the laser beams emitted from the generator 350 are in the range of wavelengths near infrared rays, close to visible light, there are provided a plurality of the laser generators, e.g., four, in order to conduct a stable transmission operation. Therefore, the laser drivers are arranged in one-to-one correspondence with the laser generators.

Between the laser driver 340 and the laser generator 350 is connected the feedback controller 420 to detect the strength of a laser beam emitted from the laser generator 350 by means of a photo diode, and to control the laser driver 340 in accordance with the detected value of the strength. As a result, the strength of the laser beam emitted from the laser generator 350 is regulated by the laser driver 340 that adjusts the laser strength in accordance with a feedback operation by the feedback controller 420.

The output amplifier unit 360 is positioned at an output terminal of the laser generator 350, being constructed of EDFA (erbium-doped fiber amplifier), NDFA (neodymium-doped fiber amplifier), YDFA (ytterbium-doped fiber amplifier), or PDFFA (praseodymium-doped fluoride fiber amplifier).

The signal transmitter unit 370 contributes to an efficient transfer of an amplified output from the output amplifier unit 360 to a reception side. Two kinds of transmission methods may be performed using the signal transmitter unit 370. The first one is to maintain a width of a laser beam in a constant range by means of an optical device or an optical material, or to transform a laser beam, which oscillates with a long wavelength vertically or horizontally, into a Gaussian pattern. The second one is to set a dimension of a laser beam in a constant range or a predetermined level by means of a reflective microscopic optics such as the Newtonian or the Cassegrain, or a refractive microscopic optics.

Figure 3 illustrates another available construction of the transmitter employed in the wireless optical communication system shown in Figure 1, including the data input buffer 310, the line driver 330, the laser driver 340, the laser generator 350, the output amplifier unit 360, the signal transmitter unit 370, the optical filter 380, an external signal modulator 430, the RF generator 400, the heat sink 410, the feedback controller 420, and the multiplexer 440.

In Figure 3, components for modulating signals, i.e., the external signal modulator 430 and the RF generator 400, are disposed at the output terminal of the laser generator 350, while Figure 2 lays them, i.e., the signal modulator 320 and the RF generator 400, between the data input buffer 310 and the laser driver 340. The RF generator 400 supplies a source frequency to the external signal modulator 430. Thus, a data signal from the data input buffer 310 is applied to the laser driver 340 just through the line driver 330.

The multiplexer 440, which is connected to an output terminal of the external signal modulator 430, is composed with the construction of WDM (wavelength division multiplexing) or diffraction grating. Such architecture for transmission may be helpful in increasing data capacities and the number of data channels. And, it is possible to transmit data signals different from each other to individual reception devices, the data signals being each applied to plural laser generators. Such a manner is useful to accomplish a point-to-point or a point-to- multipoint communication mode.

Figure 4 details a construction of the line driver 330 shown in Figures 2 and 3, including a data input circuit 332, a signal amplifier 334, and a signal distributor 336.

The data input circuit 332 outputs a data signal modulated by the signal modulator, or an output signal of the data input buffer 310, in response to a call from the signal amplifier 334. The signal amplifier 334 amplifies a data signal provided from the data input circuit 332. Since the voltage level with ECL (emitter coupled logic) or PECL (psuedo ECL), of the data signal from the signal modulator 320, is low under IV, it is hard to obtain a normal communication characteristic due to data losses and noises when a low-level data signal is inputted to laser drivers, and thus a plurality of laser drivers, e.g., four laser drivers, is required. Therefore, the data signal from the data input circuit 332 is amplified at the signal amplifier 334, enough to be immune the losses and noises, before being distributed through the signal distributor 336 and then applied to the laser driver 340. Figure 5 illustrates a construction of the output amplifier unit 360 shown in Figures 2 and 3, including an EDFA (erbium-doped fiber amplifier) 362, an NDFA (neodymium-doped fiber amplifier) 364, an YDFA (ytterbium-doped fiber amplifier) 366, and a PDFFA (praseodymium-doped fluoride fiber amplifier) 368. It is available to fabricate the output amplifier with any one of the EDFA 362, the NDFA 364, the YDFA 364, and the PDFFA 368.

Figure 6 shows a construction of the signal transmitter unit 370 shown in Figures 2 and 3, including an optical transmitter 372, a Newtonian transmitter 374, a Cassegrain transmitter 376, and a refractive transmitter 378. It is also available to fabricate the output amplifier with any one of the optical transmitter 372, the Newtonian transmitter 374, the Cassegrain transmitter 376, and the refractive transmitter 378.

Figure 7 illustrates a cylindrical optics comprising the optical transmitter shown in Figure 6, including plano-convex lenses 431, 437, and 439, cylinder lenses 433 and 435, and a pinhole 438.

The convex lens 431 is arranged to narrow a divergence angle of a transmission light source emitted from the laser generator 350. The cylinder lens 433 is formed to have curvature along a vertical axis (or meridional plane), making a vertical divergence angle be identical to a horizontal divergence angle thereof. And, the cylinder lens 435 is formed to have curvature along a horizontal axis (or a sagittal plane), making a horizontal divergence angle identical to a vertical divergence angle thereof. As a result, a beam (or light) passing through the cylinder lenses, 433 and 435, has a divergence angle that is the same along vertical and horizontal axes. Meanwhile, the convex lens 437 condenses a beam transmitted through the cylinder lenses in order to prepare a spatial-frequency filtering against the beam. Then, the beam condensed at the convex lens 437 is filtered into a spatial frequency through the pinhole 438. As a final step, the filtered beam from the pinhole 438 is emitted from the convex lens 439 with a predetermined divergence angle adjusted thereat.

Figure 8 illustrates a prism optics comprising the optical transmitter shown in Figure 6, including plano-convex lenses 441, 447, and 449, prisms 443 and 445, and a pinhole 448.

The convex lens 441 is formed to condense a beam from a transmission light source, and the prisms 443 and 445 accord a vertical divergence angle to a horizontal divergence angle. The convex lens 447 condenses a beam transmitted through the prisms, 443 and 445, in order to prepare a spatial- frequency filtering against the beam. Then, the beam condensed at the convex lens 447 is filtered into a spatial frequency through the pinhole 448. The filtered beam from the pinhole 448 is finally emitted from the convex lens 449 with a predetermined divergence angle adjusted thereat.

Figure 9 exemplary illustrates a spherical/non-spherical mirror system constructing the optical transmitter shown in Figure 6, including plano-convex lenses 451, 457, and 459, spherical/non-spherical mirrors 453 and 455, and a pinhole 458.

The convex lens 451 is formed to narrow a divergence angle of a transmission light source. The beam passing through the convex lens 451 has the same divergence angles along vertical and horizontal axes by the spherical non-spherical mirrors 453 and 455. The convex lens 457 condenses a beam transmitted passing through the mirrors, 453 and 455, in order to prepare a spatial-frequency filtering against the beam. Then, the beam condensed at the convex lens 457 is filtered into a spatial frequency through the pinhole 458. The filtered beam from the pinhole 458 is finally emitted from the convex lens 459 with a predetermined divergence angle adjusted thereat.

Figure 10 illustrates a fiber optics comprising the optical transmitter shown in Figure 6, being composed of plano-convex lenses 461 and 467, a double concave lens 463, an optical fiber 465, and a pinhole 448.

The convex lens 441 is formed to narrow a divergence angle of a transmittal light source, and the concave lens 463 reduces a convergence angle of the beam passing through the convex lens 461. The optical fiber 465 corrects a pattern of the beam from the transmittal light source, and filters its frequency.

The filtered beam through the optical fiber 465 is finally emitted from the convex lens 467 with a predetermined divergence angle adjusted thereat.

Figure 11 illustrates an embodied construction of the receiver 500 employed in the wireless optical communication system 150 shown in Figure 1, which includes a data output buffer 510, a signal demodulator 520, a RF generator 530, a signal receiver 540, a demultiplexer unit 550, an optic unit 560, and an optical filter 570.

First, an invisible laser beam is received at the optical unit 560 through the optical filter 570. A beam output from the optical unit 560, which is formed, for example, a microscopic optics, is converted into an optical signal discriminated into frequency bands at the demultiplexer unit 550. The signal receiver 540 converts the optical signal, which is provided from the optical unit 560, into an electrical signal.

The signal receiver 540 is constructed with a photo diode so as to obtain better sensitivities to light in the range of visible light and infrared rays. It is more efficient to receive a beam if the photo diode is associated with useful optical devices such as ball lenses or corn mirrors at the front stage thereof.

The signal demodulator 520 demodulates an output signal of the signal receiver 540, and a data signal from the demodulator 520 is applied to the data output buffer 510.

Figure 12 shows a construction of the demodulator 550 disposed between the signal receiver 540 and the optical unit 560, including an optical demultiplexer (Demux) 561, a wavelength division (WD) demultiplexer 563, and a diffraction grating (DG) demultiplexer 565.

The demultiplexer unit 550 may be composed of any one of the optical demultiplexer 561, the wavelength division demultiplexer 563, and the diffraction grating demultiplexer 565.

According to the aforementioned descriptions, the present invention is advantageous in preparing high-quality data transmission infrastructure with lower costs for installation and maintenance in the case of data transmission through a wide area or in a dense downtown, or for a special purpose. Moreover, the invention provides high-speed data services at specific places (e.g., mountain areas) during a short term, being easily installable and removable. Further, the present invention helps to set a data transmission service with low-cost and high-security when it is necessary to manage a network in various manners for the purpose of rendering security to data transmitted therethrough.

The laser beam employed in the present communication system is efficient to enhance qualities of high speed data in a high speed rate, and also advantageous to obtain better security data because of its invisible characteristics, contrary to visible light, non-disclosure of the installation place, and transmission through a free space.

Claims

What Is Claimed Is:

1. A wireless optical communication system for transmitting and receiving data through a free space between networks, between a device and a network, or between devices, the system comprising: a network interface connected to a network; a transmission block, being connected to the network interface, for converting a transmittal data signal into a laser beam that radiates into the free space; and a reception block for converting the laser beam into a reception data signal.

2. The system of claim 1, wherein the transmission block comprises: a data input buffer for receiving the transmission data signal; a signal modulator for frequency-modulating an output of the data input buffer; a laser driver for generating a laser drive signal; a laser generator for creating the laser beam from an output of the signal modulator in response to the laser drive signal; an output amplifier unit for amplifying the laser beam; and a signal transmitter unit for condensing the amplified laser beam on a predetermined pattern.

3. The system of claim 2, wherein the laser driver is associated with a line driver for dividing the output of the signal modulator into a plurality of signals.

4. The system of claim 2, wherein the laser driver is associated with a feedback controller for detecting the laser beam from the laser generator and for generating a laser output control signal to regulate an output level of the laser beam.

5. The system of claim 2, wherein the output amplifier unit is associated with a multiplexer for multiplexing laser beams from a plurality of laser generators.

6. The system of claim 2, wherein the signal transmitter unit comprises: convex lenses arranged at both input and output ends to condense the laser beam; and a plurality of cylindrical lenses arranged on a path between the convex lenses to accord vertical and horizontal divergence angles of the laser beam.

7. The system of claim 1, wherein the reception block comprises: an optical unit for condensing the laser beam transmitted through the free space; a demultiplexer unit for demultiplexing a laser beam supplied from the optical unit; a signal receiver for converting the demultiplexed laser beam into an electrical signal; a signal demodulator for demodulating the electrical signal into a data signal; and a data output buffer for applying the demodulated data signal into the network as the reception data signal.

8. The system of claim 1, wherein the transmission block comprises: a data input buffer for receiving the transmission data signal; a line driver for dividing an output of the data input buffer into a plurality of signals; a laser driver for generating a laser drive signal; a laser generator for creating the laser beam in response to the laser drive signal; an external signal modulator for frequency-modulating the laser beam output from the laser generator; an output amplifier unit for amplifying the frequency-demodulated laser beam output from the external signal modulator; and a signal transmitter unit for condensing the amplified laser beam on a predetermined pattern.

9. The system of claim 8, wherein the laser driver is associated with a feedback controller for detecting the laser beam from the laser generator and for generating a laser output control signal to regulate an output level of the laser beam.

10. The system of claim 8, wherein the output amplifier unit is associated with a multiplexer for multiplexing laser beams from a plurality of laser generators.

11. The system of claim 8, wherein the signal transmitter unit comprises: convex lenses arranged at both input and output ends to condense the laser beam; and a plurality of cylindrical lenses arranged on a path between the convex lenses to accord vertical and horizontal divergence angles of the laser beam.