Patent Publication Number: US-2005117904-A1

Title: Integrated optical transmitter, receiver for free space optical communication and network system and application apparatus thereof

Description:
FIELD OF THE ART  
      The present invention relates to a transmitter, receiver and application apparatuses thereof enabling an optical wireless link (“OWLL”) using communication method in which optical signals are transmitted/received through the free space, i.e., the air, and a free space optical network (“FSON”) system using the OWLL.  
     BACKGROUND OF THE INVENTION  
      The 21th century information communication society requires a social environment in which the subscribers can exchange the large amount of information at high speed, and such high speed communication becomes possible due to the improvements of the wireless communication technique of high frequency band and high speed optical communication technique using optical fibers. The study of optical communication which started in 1970s has progressed recent ten and some years to minimize the transmission loss to extend the transmission distance and to transmit a large amount of information at high speed, and now the optical communication system is in the stage of practical use, that is, the band width of the core optical communication network is over 100 Gbps, and it may reach some Tbps by 2000s. However, the technique providing the information at over tens of Mbps speed for the final user or subscriber is not developed so much.  
      Roles of optical communication technique, which secure the high speed, parallelism, and large capacity, are very important to establish very high speed broadband integrated services communication network. The conventional wireless communication system, which transmits data at tens of kbps speed in PCS system of 2 GHz, is not enough to provide wireless multimedia service. In this regard, studies about IMT-2000 having maximum data transmission rate of 2 Mbps, which is called as the third generation wireless communication, are in progress, and now it is in the stage of practical user. However, the next generation multimedia system for very high rate data transmission such as HDTV requires tens to hundreds Mbps rate data transmission for the subscribers, therefore, the IMT-2000 cannot be a final solution.  
      The next generation multimedia is a system and service which make various information such as text, data, audio, graphic, photo, animation, image, etc. to produce, collect, transmit, and process integrally, and the multimedia industry means the industrial field related to those activities. Recently, the multimedia information industry goes in the direction of digitalization, bi-directionization, asynchronization, and integrallization of image, sound, etc. in the content, form, and exchange method due to the development of the technologies in computer and communication fields. The effect of the technology development to the industrial structure is evolutional. For the most important obstacle to the present multimedia service, the performance of the communication network having insufficient capacity is pointed out, and the role of locomotive to progressive reproduction of the next generation multimedia is given to providing the communication network of very high speed and large capacity for individual subscribers economically.  
      It is considered that the only network technology which able to provide the very high speed and large capacity information for individual subscribers is the fiber-to-the-home (“FTTH”), however, in case of the FTTH, the installation is difficult, and the cost of installation is large because additional cost is required to lay the optical fiber underground as well as the communication device. Moreover, it requires additional steps of aligning between the optical fiber and laser diode (“LD”) or photo detector (“PD”) for the optical transmitting/receiving module. The present invention pursues very economical and easily installable optical transmitting/receiving module which enabling FSON which can solve the problems of the FTTH instead of the wireless communication network using coaxial cables and microwave (“MW”) transmitting/receiving device such as high frequency oscillator, modulator, etc. to connect the base station (“BS”) and the central base station (“CBS”) such as mobile service switching center.  
      Until now, the FSON is used as the back-up system for the existing wire network utilizing the advantages that the service can be provided instantly because the installation is easy and fast and that the communication protection is guaranteed physically, or most efforts are concentrated on development of high power transceiver focusing point-to-point connection considering quick installation, therefore, it is not used so practically.  
      Therefore, the present invention suggests economical transmitting/receiving modules for FSON suitable to provide the very high speed and large capacity information for a plurality of users or subscribers stably using OWLL and FSON system using OWLL different from the existing simple point-to-point type.  
     SUMMARY OF THE INVENTION  
      The new OWLL and FSON system leaded to resolve the problems and limits of the above described convention technology has differences to the conventional wire/wireless communication network in that they can provide the complex multimedia communication service such as high-speed internet, point-to-point and point-to-multiple point data, audio, and image transmission with very high speed, large capacity, stability, and efficiency preparing the next generation multimedia era.  
      The OWLL and FSON system in which basic blocks are set according to the transmission distance and transmission rate and such blocks are combined in various way to provide very high speed and large capacity information without being affected by the position and distance of the subscriber is the communication system of completely new concept for very high speed and large capacity communication system. The OWLL and FSON system should be robust to the turbulence of the air, temperature gradient, snow, rain, fog, etc. and able to change the intensity and direction of the optical output, bit-rate, etc. adaptively according to the surrounding environments. In addition, it should be constituted as a system able to monitor, control, and operate the transmitting/receiving status integrally.  
      The necessities for OWLL and FSON system are the economical transmitter, receiver, and various application apparatuses thereof enabling the OWLL and FSON system. Therefore, the object of the present invention is to provide the transmitter, receiver, and various application apparatuses thereof for OWLL and FSON.  
      Another object of the present invention is to provide the transmitter, receiver, and various application apparatuses thereof for OWLL, which are small, light, cheap, stable, and reliable.  
      To achieve the above objects, the present invention provides transmitting/receiving apparatuses for providing OWLL and FSON information communication service in which light source(s) such as laser diode, photo-electric device(s) for optical transmission and reception such as photo detector, and related circuit(s) are formed on one printed circuit board, and the printed circuit board and the optics modules are manufactured as standardized modules to be easily assembled with each other.  
      To achieve the above objects, the present invention provides transmitting/receiving apparatuses for providing OWLL and FSON information communication service in which light source(s) such as laser diode, photo-electric device(s) for optical transmission and reception such as photo detector, and related circuit(s) are formed on one printed circuit board, and the printed circuit board and the optics modules are manufactured as standardized modules to be easily assembled with each other.  
      That is, a transmitter for free space optical communication according to the present invention comprises: a semiconductor substrate; a light source formed on the substrate; a photo detector formed on the substrate for detecting the light from the light source; a current driver and automatic output controller circuit integrally formed on the substrate for driving the light source using the input signals from the outside and controlling the output power of the light source using the signals from the photo detector; a frame, where the substrate is fixed, having a plurality of pins for electrical connection to the outside; and an optics module formed to be assembled with the frame for receiving the light from the light source and transmitting the received light to the external free space.  
      Here, the light source is preferably a laser diode or a light emitting diode. The optics module comprises: a lens; and a lens holder being able to adjust the focal length of the lens, and an aspheric lens or a Fresnel lens can be used for the lens.  
      In addition, the transmitter of the present invention further includes a first screw unit formed to be integrated or assembled with the frame; and a second screw unit formed to be integrated or assembled with the optics module to make the frame and the optics module be assembled using the first and second screw units. The light from the transmitter is eye-safe.  
      A receiver for free space optical communication according to the present invention comprises: a semiconductor substrate having a first and a second faces being opposite to each other; a photo detector formed on the first face of the substrate; an optical receiver circuit integrally formed on the first face of the substrate for transforming and outputting the signals received from the photo detector; a frame, where the substrate is fixed, having a plurality of pins for electrical connection to the outside; and an optics module formed to be assembled with the frame for receiving the light from the external free space and transmitting the received light to the photo detector.  
      Here, the optical receiver circuit comprises a terminal for monitoring the magnitude of input signal at the outside of the optical receiver circuit, and it is preferable that the receiver further includes a display unit connected to the terminal via at least one of the plurality of pins of the frame for displaying the magnitude of input signal to the outside of the receiver or the magnitude of input signal can be transferred to the base station at the outside of the receiver.  
      Also, the receiver of the present invention has a first screw unit formed to be integrated or assembled with the frame; and a second screw unit formed to be integrated or assembled with the optics module to make it possible for the frame and the optics module to be assembled using the first and second screw units.  
      On the other hand, the optics module is arranged in a row with the optical receiver circuit and the photo detector or parallel to the second face on or above the second face side. In case of the latter, the frame has an aperture exposing a part of the second face opposite to the part of the first face where the light source is formed, the optics module is a lens formed on the second face of the substrate, and the aperture exposes a part where the lens is formed. The lens can be formed by etching or coating.  
      A transceiver for free space optical communication according to the present invention comprises: a semiconductor substrate; a light source formed on the substrate; a first photo detector formed on the substrate for detecting the light from the light source; a current driver and automatic output controller circuit integrally formed on the substrate for driving the light source using the input signals from the outside and controlling the output power of the light source using the signals from the first photo detector; a second photo detector formed on the substrate; an optical receiver circuit integrally formed on the substrate for transforming and outputting the signals received from the second photo detector; a frame, where the substrate is fixed, having a plurality of pins for electrical connection to the outside; a transmitting optics module formed to be assembled with the frame for receiving the light from the light source and transmitting the received light to the external free space; and a receiving optics module formed to be assembled with the frame for receiving the light from the external free space and transmitting the received light to the second photo detector.  
      Here, the transceiver further includes a first screw unit formed to be integrated or assembled with the frame and adjacent with the part of the substrate where the light source is formed; a second screw unit formed to be integrated or assembled with the frame and adjacent with the part of the substrate where the second photo detector is formed; a third screw unit formed to be integrated or assembled with the transmitting optics module; and a fourth screw unit formed to be integrated or assembled with the receiving optics module, and it is preferable that the frame and the transmitting optics module are assembled using the first and third screw units and the frame and the receiving optics module are assembled using the second and fourth screw units.  
      The transmitting optics module and the receiving optics module can face to the same side, and the transmitting optics module and the receiving optics module have the same configuration or different configurations from each other.  
      Here, it is possible to fix a first and a second frames on one printed circuit board after fixing a first and a second substrates on the first and second frames after forming the light source, first photo detector, current driver and automatic output controller circuit on the first substrate and forming the second photo detector and optical receiver circuit for optical communication on the second substrate.  
      The transceiver of the present invention may provide a connection with an optical fiber link. That is, a transceiver according to another embodiment of the present invention comprises: a semiconductor substrate; a first light source formed on the substrate; a first photo detector formed on the substrate for detecting the light from the first light source; a first current driver and automatic output controller circuit integrally formed on the substrate for driving the first light source using the input signals from the outside and controlling the output power of the first light source using the signals from the first photo detector; a first optical receiver circuit integrally formed on the substrate and connected to the first current driver and automatic output controller circuit for providing the first current driver and automatic output controller circuit with input signals; a second photo detector connected to the first optical receiver circuit for providing the first optical receiver circuit with input signal; a first optical fiber adaptor connected to the second photo detector for connecting the second photo detector to an optical fiber; a third photo detector formed on the substrate; a second optical receiver circuit integrally formed on the substrate for transforming and outputting the signals received from the third photo detector; a second current driver and automatic output controller circuit integrally formed on the substrate for receiving signals from the second optical receiver circuit; a second light source connected to the second current driver and automatic output controller circuit and driven by the second current driver and automatic output controller circuit; a second optical fiber adaptor connected to the second light source for connecting the second light source to an optical fiber; a frame, where the substrate is fixed, having a plurality of pins for electrical connection to the outside; a transmitting optics module formed to be assembled with the frame for receiving the light from the first light source and transmitting the received light to the external free space; and a receiving optics module formed to be assembled with the frame for receiving the light from the external free space and transmitting the received light to the third photo detector.  
      Here, the second photo detector and the second light source may be packaged in TO-cans, respectively, or formed directly on the substrate.  
      Moreover, the transceiver of the present invention provides a connection to the Ethernet using a media converter, and a transceiver of another embodiment for this purpose comprises: a semiconductor substrate; a light source formed on the substrate; a first photo detector formed on the substrate for detecting the light from the light source; a current driver and automatic output controller circuit integrally, formed on the substrate for driving the light source using the input signals from the outside and controlling the output power of the light source using the signals from the first photo detector; a second photo detector formed on the substrate; an optical receiver circuit integrally formed on the substrate for transforming and outputting the signals received from the second photo detector; a frame, where the substrate is fixed, having a plurality of pins for electrical connection to the outside; a transmitting optics module formed to be assembled with the frame for receiving the light from the first light source and transmitting the received light to the external free space; a receiving optics module formed to be assembled with the frame for receiving the light from the external free space and transmitting the received light to the second photo detector; and a media converter circuit, integrally formed on the substrate and connected to the current driver and automatic output controller circuit and the optical receiver circuit, for transforming the signals transmitted from the optical receiver circuit to Ethernet signals and for transforming Ethernet signals received from the outside to the current driver and automatic output controller circuit and transmitting it, and having UTP (unshielded twisted-pair) port for transmitting and receiving Ethernet signals to and from the outside.  
      A transponder for free space optical communication according to the present invention comprises a semiconductor substrate; a light source formed on the substrate; a first photo detector formed on the substrate for detecting the light from the tight source; a current driver and automatic output controller circuit integrally formed on the substrate and connected to the light source for driving the light source using the input signals from the outside and controlling the output power of the light source using the signal from the first photo detector; a multiplexer circuit integrally formed on the substrate and connected to the current driver and automatic output controller circuit for multiplexing the input signals from the outside and outputting the multiplexed signals to the current driver and automatic output controller circuit; a second photo detector formed on the substrate; an optical receiver circuit integrally formed on the substrate for transforming and outputting the signals received from the second photo detector; a demultiplexer circuit integrally formed on the substrate and connected to the optical receiver circuit for receiving signals from the optical receiver circuit and outputting demultiplexed signals; a frame, where the substrate is fixed, having a plurality of pins for electrical connection to the outside; a transmitting optics module formed to be assembled with the frame for receiving the light from the first light source and transmitting the received light to the external free space; and a receiving optics module formed to be assembled with the frame for receiving the light from the external free space and transmitting the received light to the second photo detector.  
      A transponder for free space optical communication according to another embodiment of the present invention comprises: a first semiconductor substrate; a first photo detector formed on the first substrate; an optical receiver circuit integrally formed on the first substrate for transforming and outputting the signals received from the first photo detector; a demultiplexer circuit, integrally formed on the first substrate, having an input port connected to the optical receiver circuit for receiving signals from the optical receiver circuit, a drop port for distributing a part of demultiplexed signals, and an output port for outputting the rest of the demultiplexed signals; a first frame, where the first substrate is fixed, having a plurality of pins for electrical connection to the outside; a second semiconductor substrate; a light source formed on the second substrate; a second photo detector formed on the substrate for detecting the light from the light source; a current driver and automatic output controller circuit integrally formed on the second substrate and connected to the light source for driving the light source using the input signals from the outside and controlling the output power of the light source using the signals received from the second photo detector; a multiplexer circuit, integrally formed on the second substrate, having an input port for receiving signals from the output port of the demultiplexer, an add port for receiving additional signals from the outside, and an output port for outputting multiplexed signal to the current driver and automatic output controller circuit; a second frame, where the second substrate is fixed, having a plurality of pins for electrical connection for the outside; a printed circuit board where the first and second frames are fixed at a predetermined interval; a transmitting optics module formed to be assembled with the printed circuit board for receiving the light from the first light source and transmitting the received light to the external free space; and a receiving optics module formed to be assembled with the printed circuit board for receiving the light from the external free space and transmitting the received light to the second photo detector. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic diagram showing a transmitter for free space optical communication according to an embodiment of the present invention.  
       FIG. 2  is a block diagram showing an example of a current driver and automatic output controller circuit used in the transmitter shown in  FIG. 1 .  
       FIGS. 3 and 4  are schematic diagrams showing transmitters for free space optical communication according to another embodiments of the present invention.  
       FIG. 5  is a schematic diagram showing a receiver for free space optical communication according to an embodiment of the present invention.  
       FIG. 6  is a block diagram showing an example of an optical receiver circuit used in the receiver shown in  FIG. 5 .  
       FIGS. 7 and 8  are schematic diagrams showing transmitters for free space optical communication according to another embodiments of the present invention.  
       FIG. 9  shows a transceiver for free space optical communication according to an embodiment of the present invention.  
       FIG. 10  shows a transceiver for free space optical communication according to another embodiment of the present invention.  
       FIG. 11  shows a transceiver for free space optical communication accessible via optical fiber link according to an embodiment of the present invention:  
       FIG. 12  shows a transceiver for free space optical communication accessible via optical fiber link according to another embodiment of the present invention.  
       FIG. 13  is a schematic diagram showing a transceiver for free space optical communication able to connect to the Ethernet according to another embodiment of the present invention.  
       FIG. 14  shows an example of a transponder for free space optical communication according to the present invention.  
       FIGS. 15 and 16  are schematic diagrams showing the transmitting and receiving parts of a transponder for free space optical communication whose transmitting and receiving parts are separated according to an embodiment of the present invention, respectively.  
       FIG. 17  is a layout diagram showing a receiver for free space optical communication according to another embodiment of the present invention.  
       FIGS. 18 through 20  are sectional diagrams showing receivers for free space optical communication according to another embodiments of the present invention. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION  
      Now, preferred embodiments of the present invention will be described in detail with reference to accompanying drawings.  
      First, a structure of a transmitter for free space optical communication will be described.  FIG. 1  is a schematic diagram showing a transmitter  100  for free space optical communication according to an embodiment of the present invention, and  FIG. 2  is a block diagram showing an example of a current driver and automatic output controller circuit used in the transmitter shown in  FIG. 1 .  
      As shown in  FIG. 1 , a current driver and automatic output controller integrated circuit (“IC”)  130  is formed on a semiconductor substrate  101  made of silicon (“Si”), etc. in a transmitter  100 . The current driver and automatic output controller IC  130  can be formed in various ways, and an example thereof is shown in  FIG. 2 . That is, it includes an input amplifier  1302  receiving an input signal from the outside and amplifying the signal and a LD driver circuit  1304  driving the LID  110 , the light source, using the signal amplified through the input amplifier  1302 , and the signal detected through the PD  120  is amplified by the light detecting amplifier  1306 , transmitted to the automatic output control circuit  1308 , and used to control the LD driver circuit  1304 . In addition, the current driver and automatic output controller IC  130  is manufactured according to known IC manufacturing process.  
      On the substrate  101  on which the current driver and automatic output controller IC  130  is formed, a laser diode (“LD”)  110 , which is a light source to transmit a light carrying an free space optical communication signal to the free space outside of the transmitter  100  is formed. A light emitting diode (“LED”) can be used as the light source as well as LD. For LDs, various kinds of LDs such as Febry-Perot LD, distributed feedback LD (“DFB-LD”), vertical cavity surface emitting laser (“VCSEL”), etc. can be used. The light from the LD  110  is collimated through an optics module  140  and transmitted to the free space. It is related to the transmission distance of the transmitter which kind of light sources is used. Transmitters can be classified for very short distance (less than 100 m), short distance (50-300 m), middle distance (150-500 m), and long distance (500-2000 m), and, for example, a VCSEL having a nominal wavelength of 0.85*10-6 m is preferably used for the very short distance transmitter as the light source. In addition, the nominal wavelength of the light from the LD can be 1.3*10-6 m or 1.55*10-6 m if the transmitter according to the present invention is used for the middle distance of less than 500 m or short distance of less than 300 m free space optical communication. It is preferable that the light from the light source satisfies the safety standard for human body including the eyes.  
      Moreover, a photo detector (“PD”)  120  is formed on the PCB  101  adjacent to the LD  110  having a little bit of space between them to detect the light from the LD  110 . For PD  120 , various kinds of devices such as MSM (metal-semiconductor-metal) PD, PIN (inversely biased P—N junction) PD, APD (avalanche photodiode), etc. can be used. The PD  120  detects the light from the LD  110  and uses it as a signal to control the output of the LD  110 .  
      The current driver and automatic output controller IC  130  formed on the substrate  101  has a plurality of bonding pads  103  to provide the connection with the circuit, and the LD  110  and PD  120  are connected to the parts providing connections to corresponding connecting parts in the current driver and automatic output controller IC  130  among bonding pads  103 . That is, the LD  110  is connected to the LD driver circuit  1304  of  FIG. 2 , and the PD  120  is connected to the light detecting amplifier  1306  in  FIG. 2 . Since the LD  110  is placed on the part connected to an optics module, a separate connecting part  109  can be formed to connect to the current driver and automatic output controller IC  130 .  
      The process of forming the current driver and automatic output controller IC  130  on the substrate  101  follows a general semiconductor manufacturing process, and the PD  120  can be formed together in the circuit manufacturing process if needed. In case of LD  110 , an LD device formed separately is attached on the substrate  101 . Manufactured substrate  101  is fixed on an IC frame  107 , and bonding pads  103  provided for the IC  130  are wire bonded with bonding pads  104  of the ID frame  107  to be connected to the outside via pins  108  of the IC frame  107 .  
      On the other hand, the optics module  140  is constituted of a lens  141  and a lens holder  142 , and it is fixed on the IC frame  107  where the substrate  101  on which the light source  110 , PD  120 , and IC  130  are formed is fixed. The lens  141  may be an aspheric lens or a Fresnel lens. Since a Fresnel lens can be manufactured easily by using an injection method, etc., it has an advantage to reduce the manufacturing cost of the transmitter. At this tinge, it is preferable that the lenses are standardized for transmission distances to manufacture the transmitter. In addition, the lens holder  142  is formed to adjust the position of the lens  141  before and behind in the optics module  140  to adjust the focal distance according to the use of the transmitter.  
      The light from the light source  110  is collimated by the lens  141  to a proper extent to be received by a receiver, and the nominal beam divergence of the light from the transmitter is 1*10-3 radian.  
      On the other hand, the optics module  140  and IC freme  107  are formed as standardized blocks to be assembled with each other easily, and they are fixed together after assembling.  FIGS. 3 and 4  show examples of the transmitter which have screw units to assemble the optics module and IC frame. As shown in  FIG. 3  or  4 , screw units  350  in  FIG. 3  and  450  in  FIG. 4  are formed on both sides of the optics modules  340  in  FIG. 3  and  440  in  FIG. 4  and the IC frames  307  in  FIG. 3  and  407  in  FIG. 4  to assemble two parts by turning the screws. The screw units can be formed integrally with the IC frame or optics module, or they can be formed to be assembled with the IC frame or optics module. In  FIGS. 3 and 4 , the assembled forms by turning the screws are shown. In  FIGS. 3 and 4 , other components have similar structures as described with reference to  FIG. 1 , the similar components are indicated as similar symbols. To form screw units for the optics module and IC frame, it is possible to form frame surrounding the optics module or IC frame and form screw units therein.  
      When the screw units are formed, it is preferable that the screw units of the standardized gauge are formed in optics module having lenses of various sizes and IC frames including ICs which are also standardized for each of the transmission distances are formed, two parts of which can be assembled according to the needs. Then, it is possible to optionally mount lenses of small or large diameter according to the needs such as the transmission distance, reliability, etc. for the same IC frame. That is, according to the present invention, it is very easy to manufacture a transmitter of proper standard because the IC frame and optics module can be easily assembled by a method of forming screw units, etc.  
      In addition, it is preferable that an output window transparent to the wavelength of the light source is provided outside of the optics module to install the transmitter outdoors. A protective cover or heater to confront the change of humidity or temperature can also be provided.  
      Now, a structure of a receiver free space optical communication will be described.  FIG. 5  is a schematic diagram showing a receiver for free space optical communication according to an embodiment of the present invention, and  FIG. 6  is a block diagram showing an example of an optical receiver circuit used in the receiver shown in  FIG. 5 .  
      In the receiver  500 , a optical receiver IC  530  having an example structure shown in  FIG. 6  is formed on a substrate  510  made of Si, etc. The optical receiver IC  530  can be constituted of a pre-amplifier (“TIA” which is a trans-impedance amplifier)  5302  to amplify the signal from a PD  510 , a signal amplifier  5304  to amplify the signal transmitted from the pre-amplifier  5302 , an automatic gain controller  5306  to control the gain of the received signal, a data recovery circuit  5308  to recover the data from the received signal, a clock generation circuit  5310  to extract the clock from the received signal and transmit it to the data recovery circuit  5308 , etc. The optical receiver IC  530  is also manufactured according to known IC manufacturing process.  
      On the substrate  501 , the PD  510  to detect a light received from the free space outside of the receiver is formed. For PD  510 , various kinds of devices such as MSM PD, PIN PD, APD, etc. can be used as used in the transmitter  100 . A connecting part  509  to connect the PD  510  to the optical receiver IC  530  is also formed.  
      The process of forming the PD  510  and the optical receiver IC  530  on the substrate  501  follows a general semiconductor manufacturing process, and the PD  510  and the optical receiver IC  530  can be formed together in the same manufacturing process. Completed substrate  501  is fixed on an IC frame  507 , and bonding pads  503  provided for the IC  530  are wire bonded with bonding pads  504  of the ID frame  507  for the optical receiver IC  530  to be connected to the outside via pins  508  of the IC frame  507 .  
      The light received from the outside is collected via an optics module  540  and transmitted to the PD  510 . The optics module  540  is constituted of a lens  541  and a lens holder  542  similar to the transmitter  100 . For lens  521 , an aspheric lens or Fresnel lens can be used as in the transmitter  100 . The efficiency of the beam collection can be maximized if a Fresnel lens  5411  is used. In addition, since the Fresnel lens can be easily manufactured by using a very economical way such as an injection method, etc., it is more advantageous to secure economical efficiency of transmitter and/or receiver for FSON than any other lenses. Moreover, since the Fresnel lens has a large numerical aperture, which makes the acceptance angle large, it is possible to receive the light signal easily and effectively.  
      It is preferable to make the optics module and IC frame of the receiver as standardized blocks to be assembled with each other easily as in the transmitter.  FIGS. 7 and 8  show examples of the receiver which have screw units to assemble the optics module and IC frame. As shown in  FIG. 7  or  8 , screw units  750  in  FIG. 7  and  850  in  FIG. 8  are formed on both sides of the optics modules  740  in  FIG. 7  and  840  in  FIG. 8  and the IC frames  701  in  FIG. 7  and  801  in  FIG. 8  to assemble two parts by turning the screws. As in the transmitter, the screw units can be formed integrally with the IC frame or optics module, or they can be formed to be assembled with the IC frame or optics module. Screw units may be formed to have a standard gauge able to assemble the lens of a proper size according to needs. In  FIGS. 7 and 8 , the assembled form by turning the screws is shown. In  FIGS. 7 and 8 , other components have similar structures as described with reference to  FIG. 5 , the similar components are indicated as similar symbols. To form screw units for the optics module and IC frame, it is possible to form frames surrounding the optics module or IC frame and form screw units therein.  
      The fact that the transmitter and receiver should constantly have reliability is a very important function of the free space optical communication system. In case of OWLL, there is a possibility for the intensity of a signal to be degraded if the alignment between the transmitter and the receiver becomes wrong different from the optical fiber communication link. Therefore, the alignment between the transmitter and the receiver should be monitored constantly if it maintains good condition or not. For this purpose, a monitoring terminal  539  to monitor the intensity of the received signal constantly can be provided according to the embodiment of the present invention as shown in  FIG. 5 . In addition, it is possible to display the intensity of the signal received to the receiver by connecting the monitoring terminal  330  to a display device (not shown). As the display device, an LED of a visible ray can be used. Addition to the displaying the intensity externally, it is possible to report the extent of degradation of the signal obtained on the optical receiver circuit to the central base station which manages and administrates the whole FSON system.  
      The conventional transceiver for fiber optical communication using optical fiber needs a precise packaging which spends a long time to align and pig-tail between the LD and the fiber or between the PD and the fiber to an extent of minuteness of some μm. Therefore, the cost of manufacturing the conventional transceiver is very high. On the other hand, the transceiver for OWLL and FSON as suggested in the present invention has a advantage to be manufactured very economically. That is, since the transceiver for OWLL and FSON as suggested in the present invention is very economical, the FSON system can be more economical than FTTH (fiber-to-the-home) system.  
      In case of the receiver, it is preferable that it accepts only the light in which the transmitter outputs selectively. The output light of the transmitter is the light having nominal wavelength of 0.85*10-6 m, 1.3*10-6 m, 1.55*10-6 m, etc. as described above. For this purpose, it is preferable to provide an input window transparent only to the light in which the transmitter outputs and able to shield the normal light in front of the optics module of the receiver. To install the receiver outdoors, it may also need to provide a protective cover or heater.  
       FIG. 9  shows an all-in-one transceiver (“TRX”) for OWLL and FSON system in which a transmitter and a receiver are formed as one module. Since the OWLL and FSON system is basically a bi-directional communication system, the transmitter and the receiver tend to be used together other than used separately. The transmitter in  FIG. 9  is that the transmitter and the receiver shown in  FIGS. 1 and 5 , respectively, are formed integrally for this purpose.  
      As shown in  FIG. 9 , a transmitting/receiving IC  930  is formed integrally on a semiconductor substrate  901 , and an LD  910  and a PD  920  for light transmitting module and a PD  960  for light receiving module are formed together on the substrate  901 . An IC frame on which the semiconductor substrate  901  is fixed is assembled with a transmitting optics module  940  and a receiving optics module  990 . The other structures are similar to those of the transmitter  100  and the receiver  500 . If the transceiver is formed like this, the light transceiver becomes very small. Therefore, this structure is useful when the size of the optics module can be very small.  
      However, transceivers often face to each other when an OWLL is constituted. In this case, the light signal may input to the light source of the transmitting optics module of the transceiver as well as the receiving optics module, and sometimes, large optics modules of a few to several tens cm scale are needed. Therefore, a prescribed space should be maintained between the transmitting part and the receiving part of the transceiver, and it is advantageous to constitute the circuits of transmitting and receiving part separately.  
      In  FIG. 10 , an example of the transceiver in which the circuits of the transmitting and receiving parts are separated is shown. As shown in  FIG. 10 , a current driver and automatic output controller IC  1030  for transmitting part and an optical receiver IC  1080  for receiving part are formed on different semiconductor substrates  1001  and  1051 . An LD  1010  and a PD  1020  are formed together on the substrate  1001  for transmitting part and connected to the current driver and automatic output controller IC  1030 , and a PD  1060  is formed on the substrate  1051  for receiving part and connected to the optical receiver IC  1080 . Each substrate  1001  or  1051  is fixed on an IC frame  1007  or  1057 , and those IC frames are placed on another substrate  1050  having an appropriate interval between them. The interval between transmitting and receiving parts can be determined properly by the size of the optics module forming the transceiver, etc. A transmitting optics module  1040  and a receiving optics module  1090  are assembled to the light source 1010  of transmitting part and the PD  1060  of receiving part, respectively.  
      In the transceivers  900  and  1000  shown in  FIGS. 9 and 10 , the transmitting optics modules  940  and  1040  and receiving optics modules  990  and  1090  can be manufactured as standardized modules and assembled with IC frames or substrates as in the transmitter  100  and the receiver  500  described above, and assembling method can also be same as used in the transmitter  100  or receiver  500 . In addition, The transceivers  900  and  1000  shown in  FIGS. 9 and 10  can have all characteristics of the transmitter  100  and receiver  500  described above For the transmitting and receiving optics modules  940  and  1040 , it is possible to use the same standard or different standards. Moreover, in the transceivers shown in  FIGS. 9 and 10 , the transmitting optics module  940  and  1040  and receiving optics modules  990  and  1090  are installed in the same direction, however, they can be installed in different directions. For this purpose, the positions of the circuits and optical devices formed on the substrate can be properly adjusted.  
      On the other hand, OWLL and FSON system of the present invention can be effectively used by combining with the existing optical communication system using optical fibers. For this purpose, the transceiver of the present invention may include the constitution of the transceiver for optical fiber communication to provide the optical fiber link.  
       FIG. 11  shows a structure of a transceiver for free space optical communication accessible via an optical fiber link according to an embodiment of the present invention. As shown in  FIG. 11 , in addition to a first current driver and automatic output controller circuit and a first optical receiver circuit for free space optical communication, a second current driver and automatic output controller circuit and a second optical receiver circuit for optical fiber communication are formed integrally on one semiconductor substrate  1101 . An LD  1110  and a PD  1120  connected to the first current driver and automatic output controller circuit and a PD  1160  connected to the first optical receiver circuit are also formed on the substrate  1101 . The substrate  1101  is fixed on an IC frame  1107  and wire bonded  1105 . A transmitting optics module  1140  and a receiving optics module  1190  are assembled to the free space optical communication side of the IC frame  1107 , and a PD  1172  for the second optical receiver circuit and an LD  1176  for the second current driver and automatic output controller circuit are connected to optical fiber communication side to receive the signal transmitted from the optical fiber link and transfer to the first current driver and automatic output controller circuit and to transfer the signal transmitted from the first optical receiver circuit to the optical fiber link, respectively. For this purpose, the PD  1172  and the LD  1176  are connected to the optical fiber links via optical fiber adapters  1174  and  1178 , respectively. At this time, the PD  1172  and the LD  1176  for optical fiber communication can be packages mounted on TO-cans.  
      It is possible to form the photo devices such as PD and LD for optical fiber communication together on the semiconductor substrate instead of connecting from the outside of the substrate.  FIG. 12  shows a structure of a transceiver in which the photo devices for optical fiber communication are formed on the semiconductor substrate as described above.  
      As shown in  FIG. 12 , a light source  1276  and a photo detector  1277  of transmitting part and a photo detector  1272  of receiving part for optical fiber communication are formed on a semiconductor substrate  1201  on which a circuit part  1230  is formed. Next, the light source  1276  and the photo detector  1272  are connected to optical fiber links via optical fiber adapters  1278  and  1274 , respectively.  
      It is possible to form the transmitting and receiving parts of the optical transceivers  1100  and  1200  shown in  FIGS. 11 and 12  on separate semiconductor substrates and fix them on PCB substrates to have prescribed intervals as in the transceiver in  FIG. 10 . That is, after forming the first current driver and automatic output controller circuit and the second optical receiver circuit on one semiconductor substrate and he first optical receiver circuit and the second current driver and automatic output controller circuit on the other semiconductor substrate, each part is fixed on another substrate. As described above, this structure is advantageous when an appropriate interval should be maintained between the transmitting and receiving parts.  
      In addition, OWLL and FSON system of the present invention can be effectively used by combining with the existing Ethernet or LAN. For this purpose, Ethernet signals and signals of the optical transceiver of the present invention are transformed to each other using a media converter. The device for this purpose is shown in  FIG. 13 .  
      That is, a media converter circuit for data transformation is formed integrally on a semiconductor substrate  1301  together with the current driver and automatic output controller circuit and the optical receiver circuit. The media converter circuit is connected to an unshielded twisted-pair (“UTP”) port  1370  for connection to the Ethernet via a pin  1308  connected to the media converter circuit part of the IC  1330 .  
      However, sometimes the transceiver for OWLL and the media converter should be connected using an optical fiber link because the UTP cable for Ethernet is not able to use for long distance. For example, it is the case that the position of the transceiver for OWLL is far from the position of the subscriber such as a roof of the building. Then, the data signal of the transceiver should be conveyed to the media converter near the subscriber via light. In this case, the optical transceiver having communication function with the optical fiber link described with reference to  FIGS. 11 and 12  can be used to connect to the external media converter.  
      The subscriber network using FSON can be tried in various forms. Both ring type network and star type network using ATM (asynchronous transfer mode) are possible, and tree, bus, and mesh type networks are also possible. When the network is formed, sometimes there is a case that a node uses some data by itself and relays the other data to another node after transmitting/receiving data of large bandwidth from/to the central base station. In this case, a transmitting/receiving module needs a function of multiplexing/demultiplexing.  FIG. 14  shows an example of a transponder for OWLL according to the present invention having multiplexing/demultiplexing function.  
      As shown in  FIG. 14 , an IC  1430  including a MUX/DEMUX circuit as well as a current driver and automatic output controller circuit of the transmitting side and an optical receiver circuit of the receiving side is formed on a semiconductor substrate  1401  The MUX/DEMUX circuit multiplexes the data transmitted from the input pin, transmits them to the current driver and automatic output controller circuit of the transmitting part, demultiplexes the signals received from the optical receiver circuit, and transmits them to the output pin. An LD  1410  and PDs  1420  and  1460  are formed on the semiconductor substrate  1401 , and the other structures are similar to those in the transceiver  1000  shown in  FIG. 10 .  
      In case that the subscriber network is constituted as a ring network using ATM method, it is necessary to have add/drop function in which signals of some bandwidths among transmitted signals are distributed to the subscriber and signals received from the subscriber are added and transmitted with transmitted signals.  FIGS. 15 and 16  show examples of the transponder for FSON having the above-described function. However, in case of FSON system of ring network, directions of transmission and reception are generally different. Therefore, if the transceiver is manufactured as all-in-one type, it may be difficult to use for FSON system. In this regard, the transponder having separate transmitting part and receiving part is formed according to an embodiment of the present invention, and  FIGS. 15 and 16  show the structures of the transmitting and receiving parts of the transponder described above.  
      As shown in  FIG. 15 , the transmitting part includes an LD  1510 , a PD  1520 , and an IC  1530  including a current driver and automatic output controller circuit for transmission and a MUX circuit formed on a semiconductor substrate  1501 . The IC frame  1507  on which the IC  1530  is fixed is provided with a Data In pin provided with data from the receiving part and a Data ADD pin provided with data to be added on the place where the transceiver is installed. The IC frame  1507  is assembled with the transmitting optics module  1540 .  
      The receiving part is shown in  FIG. 16 . A PD  1610  and an IC  1630  including an optical receiver circuit for reception and a DEMUX circuit are formed on a semiconductor substrate  1601 . An IC frame  1606  on which the IC  1630  is fixed is provided with a Data Out pin providing data to the transmitting part and a Data DROP pin providing data to the place where the transceiver is installed. The IC frame  1607  is assembled with a receiving optics module  1640 .  
      As described above, if the transmitting part and the receiving part are formed as separate modules, it can be easily installed though the directions of transmission and reception are different.  
      On the other hand, receivers according to embodiments described above have a constitution in which a receiving optics module, photo detector, and optical receiver circuit are arranged serially, but it is possible to place the receiving optics module to be perpendicular with the substrate on which the photo detector and the optical receiver circuit are formed. If so, the substrate may have an additional function of filtering the visible rays, and it is possible to form the lens directly on the semiconductor substrate by etching or coating. Now, those embodiments are described in detail.  
       FIG. 17  is a layout diagram showing a structure of a receiver according to another embodiment of the present invention in the direction of the substrate on which a photo detector and an optical receiver circuit are formed, and  FIG. 18  is a sectional view of the receiver taken along the line XVIII-XVIII in  FIG. 17 .  
      As shown in  FIG. 17 , an optical receiver IC  1730  and a photo detector  1710  are formed on a semiconductor substrate  1701 , and the substrate  1701  is fixed on an IC frame  1707  and wire bonded  1705 . The structure of the substrate is similar to the receiver of  FIG. 5  described above. On the other hand, in case of the embodiment shown in  FIGS. 17 and 18 , a lens  1840  of an optics module  1840  is formed in perpendicular direction with the substrate  1701 , which can be known from the sectional structure thereof. In addition, the IC frame  1707  have an aperture  1850  to expose a semiconductor area on which the PD  1710  is formed. Then, the light concentrated via the lens  1840  is transferred to the PD  1710  through the substrate  1701  made of Si, etc. Therefore, it is possible to pass a desired light selectively by selecting the substrate material.  
      Moreover, a lens can be formed directly using a semiconductor substrate without installing a separate lens outside of the substrate. In this case, the manufacturing process of the optical receiver becomes simple, and the size of the receiver becomes smaller.  
       FIG. 19  shown a sectional view of a receiver in which a lens is formed by etching on the opposite side of the semiconductor substrate on which an optical receiver circuit and a PD are formed according to the present invention. The layout structure of the receiver shown in  FIG. 19  is similar to that shown in  FIG. 17 . A lens  1940  is formed by etching on the opposite surface (lower surface in the drawing) of the substrate  1901  to the surface (upper surface in the drawing) on which an optical receiver circuit  1930  and a PD  1910  are formed. The lens  1940  can be manufactured using etching process of the conventional semiconductor manufacturing process. An aperture to expose the lens  1940  is formed in an IC frame  1907  on which the substrate  1901  is fixed. Since the lens  1940  is formed using the substrate  1901  on which the IC is formed without using separate material, the size of the receiver becomes smaller and the manufacturing process becomes simple.  
      A lens can be formed using coating method. According to an embodiment shown in  FIG. 20 , a lens  2040  is formed by coating on the opposite surface (lower surface in the dragging) of the substrate  2001  to the surface (upper surface in the drawing) on which a PD  2010  and an IC  2030  are formed. The lens  2040  can be manufactured using coating process of the conventional semiconductor manufacturing process. The layout structure of the receiver is similar to that shown in  FIG. 17 , and an aperture to expose the lens  2040  is formed in an IC frame  2007  on which the substrate  2001  is fixed.  
      It is apparent that the characteristics of the receivers described with reference to  FIGS. 17 through 20  can be applicable to the receiver and the application apparatuses thereof.  
      While the present invention has been described in detail with reference to the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.  
      [Industrial Applicability] 
      The OWLL and FSON system having various advantages comparing to the conventional optical fiber communication system can be established using the transmitter, receiver, and application devices thereof according to the present invention. In addition, the transmitter, receiver, and application devices thereof according to the present invention are small, light, cheap, and standardized. At the same time, the transmitter, receiver, and application devices thereof according to the present invention can provide various functions required in the FSON system, and the provide those functions stably and reliably.