JPS63501327A - light distribution system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] “Light distribution system” TECHNICAL FIELD This invention relates to light distribution systems.

In particular, the present invention provides for the service and provide two-way communication between the exchange and the user. This invention relates to a light distribution system. Of course, it also provides optical fiber communication lines to users. such as video signals, high-fidelity signals or high-speed data communications. High-capacity communication links are established between exchanges and users so that they can handle can be established between.

Several proposals have been made to provide fiber optic links from exchanges to users. However, these proposals have drawbacks. In one proposal, the exchange would connected to each user by means of installed optical fibers. This is received from the exchange. It is relatively expensive because it requires providing and installing a separate fiber to the laser. Sara First, the exchange requires an independent transmitter/receiver for each fiber. a certain age In the switching arrangement, from the switching center each user is connected to the loop by a coupling element. One loop is proposed that extends to all users connected to the exchange and back to the exchange. It has been. However, this arrangement does not provide a satisfactory level of reliability. at and near the user's building to establish that A fairly high quality of equipment is required in terms of the actual equipment at the site.

It is therefore an object of the present invention to provide a relatively inexpensive system for two-way communication from the switching center to the user. The purpose of this invention is to provide a light distribution system.

According to the invention, optical distribution for two-way communication from a switching center to up to N user stations A system is provided, and the above system includes an exchange transmitter, an exchange receiver, and the above transmitter. and a switching center coupler for coupling the receiver to the optical fiber communication line; 8 to each user station required in the above system. Has one fiber lead connected to the fiber tails of the book A passive N-port directional coupler is provided, and each user station has a user station transmitter, a user station receiver, to connect the fiber tail to the user station transmitter and user station receiver. Includes station coupler.

The invention will now be further described with reference to the accompanying drawings. In this drawing , FIG. 1 is a block diagram of one configuration of the optical distribution system of the present invention, FIG. 2A, FIG. 2B, and FIG. and Figure 2C are graphs showing the characteristics of this system. FIG. 3 is a schematic diagram of one frame for the signal transmitted in this system, Figures 4A and 4B are schematics of alternative frames for transmitted signals in the signal. Schematic diagram, Figure 5 is a block diagram of an alternative light distribution system; Figures 68-6D are possible Transmitter spectrum and optical filter characteristics, Figure 7 schematically shows the line code for clock regeneration, Figure 8 shows the replacement schematically depicts a circuit for phase recovery of a clock at a station; FIG. 9 is a waveform diagram useful for understanding the operation of the circuit of FIG. 8.

The system shown in FIG. The optical fiber line is preferably a single module, comprising a transmitter 2 and an exchange receiver 4. It is a coded optical fiber. Lines 6 and 8 are two of the three-boat directional coupler lO. form the input/output ports of the Coupler 10 forms optical fiber line 12 The fiber optic line 12 has other input/output ports, and the fiber optic line 12 is connected via a connector 16. and is connected to one end of a relatively long optical fiber communication line 14. Coupler lO is passive device, the passive device is a part of the device that twists two optical fibers together and is fused. These two optical fibers are melted so that there are four fiber sections extending from formed by a technique known in the art for removing one optical fiber section. be done.

Line 14 is connected from the exchange to one group of, say, 16 users of the system. It extends to a convenient point. This system consists of a fused splice 22 connection. A 16 point fiber with one input/output fiber 20 connected to the other end of the line 14. It includes a one-way directional coupler 18. Coupler 18 typically means a fused connection 28. Thus, 16 inputs/in the form of optical fibers connected to the optical fiber tail 26 It has an output port 24. Combiner! 8, 16 optical fibers are twisted together. The result is that the 15 radiating optical fibers are removed after being applied and melted. It is formed in the same manner as the combiner 10. The optical fiber tail 26 is connected to the coupler 18 from the coupler 18. For example, it can be used up to one user's location, such as an office or home.゛ Each user station 3b includes a user transmitter 32, a user receiver 34, and a receiver 32, respectively. a three-bottom coupler 36 having fiber boats 38 and 40 connected to and 34; including. The transmitter "82" is a laser, which can be cheaper than the transmitter "LED" It may also include a transmitter. The other boat 42 of the coupler 36 is a means of connecting the lid 4. is connected to the end of the optical fiber tail 26 by. ``Dissolved connections 22 and 28 It is probably important to use the fused connections 22 and 28 because the It has a relatively small return loss, which is 26 dB, and as much as 7 dB. This is because the temperature is high.

The exchange center and user station are equipped with the same transmitter, and communication to and from the exchange center is possible. Let us consider the operation of this system that performs continuous simultaneous transmission.

All reflections at connector 44 of user station 30 reflect back to the exchange. Return: The minimum attenuation of the exchange's transmission is given by the following equation.

A, = RLP 10 Ao + AF 10 AE Here, RLP is the return loss of the connector 44 of 1. .

Ao is the end-to-end attenuation of the system including all couplers, and A is the end-to-end attenuation of the system including all couplers. The fiber from which the coupler is removed, the end-to-end attenuation of line 14, AE is the excess attenuation of the multi-boat coupler 18.

Typical values are RL P==17dBSAo=(29-35)dB, AF=(5 -20) dBSAE=4 dB. Therefore, A, = (46-76) dB pi It is. The exchange's transmission is reflected back to the exchange by the connector 16 at the exchange. The amount of attenuation of the signal is A -RL +2A3 px px Here, RL is the return loss of the connector 16, px A3 is the attenuation amount of the 3-bot coupler lO. Typical values are RL = 17dB, A3=4dB. Therefore, px A = 25dB px It is. The NEXT of the 3-point coupler 10 exceeds 40 dB. be made explicit. Therefore, (A, , A and the electric potential of the coupler next pt px The combined crosstalk (calculated as the sum of forces) is approximately 25 dB, with the dominant The item is a reflection from connector 16 at the exchange.

The desired signal at receiver 4 is to provide a reasonable margin for detection (assuming that must be at least 6 dB higher than losstalk. Therefore, if If all transmitters are identical (same power and same spectral characteristics), the optical The total attenuation of the path is reduced to 1 on each occasion of satisfactory signal reception at the exchange receiver 4. It cannot exceed 9dB. If 8dB is allowed for two 3-voice combiners, If accepted, this means that the main distribution fiber 14, multi-board coupler 18 and leaves an overall loss of 1 IdB for the fiber tail 26. Typically, eight The multi-board coupler to which the receiving station 30 is connected has a loss number of about 12 dB, resulting in As such, such a system is not particularly satisfactory. Four stations 3o are set up. The system operates with approximately 4 dB loss in fiber 14 when It is possible to create However, when the loss in fiber 14 is so small, other It is necessary to consider the reflection of

coupled by reflection at connector 4 of station 30, whose typical value is 25 dB. When crosstalk becomes dominant, the analysis from the user terminal produces very similar results. give fruit.

Therefore, when having typical values for the losses mentioned above, as shown in FIG. Simple systems such as .

This system operates in burst mode operation for the most part to eliminate crosstalk issues. This can be avoided by making it work.

Now, let's consider the operation of this system using burst transmission.

Type I exchange sending W12 waits for a response after sending to the first station 30.

The exchange then waits for its response after transmitting to the second station. The same applies below. .

Type 2 Exchange transmitter 2 transmits to all user stations 30 in TDM mode. After that, the user station responds after an appropriate guard time.

Type 3 Exchange transmitter 2 transmits all the time, and the user Take your time and respond.

For type 1 systems, when exchange transmitter 2 is transmitting, connector 16 The effect of these reflections typically causes the exchange signal to be about 25 dB lower than the transmitted signal. This is to return the information to the station receiver 4. At this time, since there is no signal from the desired receiver, this signal The number is of little importance. Because that signal is removed in receiver 4 This is because it is possible.

The exchange's transmitted signal is reflected back to the exchange by all reflections on connector 44. The minimum attenuation of A,=RLP+Ao+AF+AE It is. here, RLP is the return loss of one connector 44, and Ao is the optical system including all couplers. AP is the end-to-end attenuation of the fiber, excluding all couplers. The amount of attenuation between AE and AE is the excess loss of the multi-boat coupler 18.

This combined reflected signal eventually becomes almost the user's transmission from the user transmitter Ia32. will most likely match. If the transmitter with the same power is If it is assumed that the signal coupling at the exchange receiver 4 is used in both The combined reflection ratio is px Typical values are RLP=17dB, AF=(5-29)dB, and AE=4dB. be. Therefore, to R -=(26-41)dB Aεpi This value is suitable for reliable detection.

When a user is transmitting, the effect of the user's connector 44 is a fraction (1/ signal) is returned to the user receiver 34. This signal is sent to the user's receiver 32. This may cause problems in changing the phase of the clock. for this reason For this purpose, receiver 34 preferably takes into account the time required for reflection back to receiver 34. The transmitter is turned off during transmission for a short period of time after the transmission is completed. However, In most practical systems, the attenuation between stations is due to the interstation signal being lost in the noise. The more expensive it is.

FIG. 3 shows one user with one user for a type I burst mode system. A typical frame structure for individual communications is shown. Of course this frame It is recognized that the configuration is repeated for each station 30 connected to the system. Will.

If there are eight stations 30 and the period time is T seconds, then each station has T/ Communication between each station (burst from the exchange and burst to the exchange) must be completed in N seconds. Must be. The number of bits of information in one burst is (one channel (typically 144,000 bits/sec in each direction in the It is 4000.

With the header shown in FIG. 4+T144000) bits, and the burst from the station to the exchange is (16+T1 44000) bits.

Therefore, the time allotted to each station is the time for transmitting information and the system It is the total time required for the information to be transmitted via the network. Transmission time T a is 64+TX144000 16+TX144000Ta=+□ 8.448xlO” 8.448xlO’ The transmission time Tt is Here, L is the length of the fiber 14 plus the length of the fiber tail 26. be.

(2) is the propagation speed in the fiber (2 x 10'km/sec).

now, Tt+Ta=T/N Lxlo-’+(80+Tx288x103)/8.448xlO”=T/N shall be. Here, if N=16 and T=4 milliseconds, Lxl　0-'+( 80+4x288)/8.448x106=4X10"/16 L = 10.42km becomes.

The distance between the exchange and the farthest station is the period time - the time between consecutive communications with one station. Strongly dependent on time. If this time is very short, the arrival at those destinations A high proportion of the overall time required to wait for a signal for arrival. Also, the above time When is longer than the period time, the burst length becomes longer in active transmission operations. This will result in a higher proportion of the total time. The period time is also introduced into the local loop is the delay added directly to the delay for speaker echo calculation. the result As such, it is necessary to keep this cycle time short, from 1 ms to 4 ms. are typically available.

FIGS. 2A to 2C illustrate a type l having a signal structure as shown in FIG. Typical computational results plotted in graphs for the operating characteristics of a burst mode system. It is a fruit. In these graphs, the line system is 8.448 Mbit/s , there is a 1 ms loop delay in Figure 2A, and there is a loop delay of 1 ms in Figure 2B. There is a 2 ms delay in Figure 2C, and a 4 ms delay in Figure 2C. Ru. Circles and crosses are values for 8-passage system and 166-passage system, respectively. That is, the number of user stations 30 connected to the coupler 18 is , the exchange sends out a TDM burst containing information for all stations 30. So When, after receiving a burst from the exchange, the station The analysis of the reflex response is the same as the analysis of the type I system described above.

A suitable burst from the exchange to the exchange is shown in Figure 4A, and from the exchange to the exchange. The burst is as shown in FIG. 4B.

Station I responds immediately and records the end of the exchange's burst. At that time, station 2 until the burst from 1 clears the multiport combiner 18 and the information must wait until the information arrives at the multiport combiner. Therefore, This latency depends on the burst length from station 1 and the length of the burst between stations 1 and 2. Depends on the delay in tail 26. If the burst length is fixed at 160 bits Assume that the period time is 1 millisecond. Now, in Fiber Tail 26 The maximum length difference is lkm (5 microseconds or approximately 40 bits at 8.448 Mbit/s). station 2 must count 200 bit intervals before transmitting. stomach. Station 3 must count 400, and station 4 must count 600. No. The same applies below. As a result, there are 16 stations in the local loop. A Type 2 system with a delay of 1 millisecond can run up to 32 km of fiber. It is possible to have a length. This is true for most applications. and as a result, special capacity for trade-off for some relay distances), thereby reducing the There may be value in providing additional services.

A Type 3 system is preferably the system shown in block diagram form in FIG. It is used in conjunction with the system layout. The system in Figure 5 uses a filter at the exchange. essentially the same as in FIG. 1, except that 46 is provided between the transmitter and the coupler lO. Same as shown.

Furthermore, the transmitter 2 uses a coupler IO, for example, a laser laser outputting optical power of OdBm. Equipped with an iode. In one typical system, a receiver at station 30 The power will be approximately -35 dBm. Between user station receiver 32 and transmitter 34 Assuming that there is a minimum separation of 25 dB at Since the signal is from transmitter 32, the output power from user transmitter 34 is −20 dBm. must be smaller than If the signal level from transmitter 32 is -20 dB m, then the level at the exchange receiver 4 will be -55 dBm. There will be. Therefore, the next at the exchange end is a suitable merge for detection. must be greater than 65 dB to avoid establishing a signal. Therefore, exchange The filter 46 at the station provides at least a 40 dB reduction in the exchange's transmission wavelength. FIG. 6A shows the output 4 at the wavelength transmitted from the exchange oscillator 2. 8 is represented by a graph. FIG. 6B shows the wavelength response of filter 46; The answer has a notch 50 at the transmit wavelength. Figure 6C shows the transmission at the user station. A typical output 52 from an LED transmitter with transmitter 32 is shown.

FIG. 6D shows a typical received output from filter 46 passing through exchange receiver 4. 54 is schematically shown. The effect of filtering is small at output 54, which is The signal from the station transmitter 2 is filtered and selectively extracted.

This system transmits 34M bits in the downstream direction, ie from the switching center to the user station 30. /second, and in the upstream direction, 8.5 Mbit/second. Downstream information speed degree, it provides stereo hi-fi broadcast transmission and or other services This is the speed at which it can be done.

The frame configuration for the system of FIG. 5 can vary widely. Why This is because the transmitter 2 of the exchange transmits continuously.

The difference between type l and type 2 systems is shorter in type 2 systems There is a waiting cycle. Therefore, the relay distance for a given system that is when it is possible in a type l system. receiver 32 for a number of minutes (1/hour) greater than the number of minutes (1/hour) between can be configured to provide clock information at the same time.

The user only receives one burst of clock information each period. When the clock information received at station 30 is a Type 1 or Type 3 system, Type 2 systems are more bursty than either of the two systems. subordinate So, a line code with very high clock content is Used to help maintain stability. Figure 7 shows one possible line. It shows the code. CMI may be used as an alternative.

When the clock at the exchange is used to send data to the user, the exchange does not need to extract the clock from the user's transmission.

However, determining the phase of the received signal in order to receive data from the user station is difficult. There is a need to establish This means that the phase detection circuit 57 shown in FIG. Therefore, it is possible to execute. This system (exchange clock frequency has an incoming signal input 56 that is oversampled (at a frequency eight times higher than exchange office The appropriate phase of the clock is as illustrated in the frame configurations of Figures 3 and 4B. is determined by analyzing the sampled received signal during the transmission period. Ru. The sampling is input from clock generator 58 to analog-to-digital converter 60. It is executed using the clock provided by The output of the analog-to-digital converter 60 is 8 A clock is input to the shift register 62 of the stage, and the clock is input to the shift register 62 of the first stage of the shift register 62. and outputs A and B of the second stage are connected to a logic circuit 64. The output from circuit 64 is 3 It is connected to the frequency divider of the counter 66 and the frequency divider' of the 8 counter 68. counter 6 The output from 8 is connected to the fourth stage of register 62. In this circuit, the most The output from the recently sampled analog-to-digital converter 60 is always previously sampled. is compared with the output output. If three consecutive comparisons yield "less than" , then the fourth sample will be the largest sampled value and therefore the received approaching the peak of the waveform. If the largest sampled value is Once identified, successive data bits are processed by taking a value every 8th sample. can be established. This technique is based on the input to the transducer 60 and the This instant is graphically illustrated in FIG. 9 which shows this moment. When the signal-to-noise ratio is high , the circuit shown in Fig. 8 appropriately detects the phase from the eight phases of the conversion clock. will supply.

Many modifications will be apparent to those skilled in the art without departing from the spirit and scope of the invention. There will be.

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Claims (1)

[Claims] 1. Optical distribution system for two-way communication from switching center to up to N user stations (30) The system includes an exchange transmitter (2), an exchange receiver (4), and the above system. For coupling the transmitter (2) and receiver (4) to the fiber optic communication line (14). the switching center coupler (10), the fiber communication line (14) and the system N fiber tails (t ails) (26) with one fiber lead (20) connected to Equipped with an N-port directional coupler (18), each user station has a user station transmitter (32), The user station receiver (34) and fiber tail (26) are connected to the user station transmitter (32) and an optical distribution system including a station coupler (36) for connection to a user station receiver (34); Tem. 2. The exchange coupler and the exchange coupler (10, 36) are equipped with a 3-port coupler, and the exchange One input/output port (12) of the coupler is connected to the line ( 14) The system according to claim 1, which is connected to. 3. The single fiber lead wire (20) is connected to the line 14 by a fused connection 22. and the N-port coupler 18 is connected to the tail (26) by a fused connection (28). The device according to claim 1 or 2 has a connected and selected output port (24). system. 4. Tail (26) is connected to user station (30) by connector (44) A system as claimed in any above claim. 5. The exchange transmitter (2) includes a laser or LED, and the exchange transmitter (32) includes a laser or LED. or any of the above-claimed systems comprising LEDs. 6. The exchange transmitter (2) transmits to each user station 30, and before transmitting to the next station. Any above-claimed system waits for a response formed by the transmitter 32 of that station. stem. 7. The transmission to and from each station 30 is a signal having first and second parts. The first part is for transmission to the station and contains multiple bits. a column segment, a station address segment, and a data transmission segment; The second part is for transmission from the station and is a multi-bit frame segment, Claim 6 includes a station address segment and a data transmission segment. system. 8. The exchange transmitter (2) transmits to the station in TDM mode, and the exchange transmitter (32) transmits to the station in TDM mode. ) transmits to the exchange in a predetermined sequence. 5. The system according to any one of clauses 5 to 5. 9. A signal whose transmission to each station 30 includes a first column segment and N subframes. frame, with each subframe containing a station address segment and a data transmission segment. transmission from the station is carried out in bursts, each burst being a column segment. Claims beginning with The system according to paragraph 8. 10. The exchange transmitter (2) transmits simultaneously to all stations, and the exchange transmitter (3) transmits to all stations simultaneously. 2) transmits data to the switching center in a predetermined sequence. The system according to any one of clauses 5 to 5. 11. The exchange transmitter (2) includes a laser diode producing an output of wavelength λ, A filter (46) with a long λ and a notch serves as an exchange receiver (4) and an exchange combiner. 11. The system according to claim 10, wherein the system is connected between (10) and (10). 12. The phase of the transmission received at the exchange in relation to the synchronization signal sent by the exchange In the above request, a phase detector (57) for detecting the shift is provided at the exchange. A system according to any one of the claims.