WO1998013959A1

WO1998013959A1 - Optical transmission module and optical transmission system

Info

Publication number: WO1998013959A1
Application number: PCT/JP1996/002818
Authority: WO
Inventors: Hiroaki Hanawa; Makoto Haneda
Original assignee: Hitachi, Ltd.; Hitachi Microcomputer System, Ltd.
Priority date: 1996-09-27
Filing date: 1996-09-27
Publication date: 1998-04-02

Abstract

Let the received level of reference light of an optical transmission module (1, 1A) included in an optical transmission system be m, the transmitted level thereof be n, and the attenuation factor of the light signal fed from a subscriber line station unit (SLT) and received by a subscriber line network unit (ONU) (#1) be α (= received level/n). Then the optical output level of the subscriber line network unit (ONU) (#1) is mx1/α. Thus the ONU (#1) outputs the light signal of an output level which is the product of the input and the inverse number of the attenuation factor to the SLT, and hence the SLT receives the signal at the reference light received level m from any of the ONUs. Therefore, the gain control of the circuit which amplifies the received levels of a plurality of kinds of light signals having suffered different line losses and the resetting of the threshold voltage for detecting the logical value of the received signal are simplified or the circuits for controlling the gain and resetting the threshold voltage are eliminated.

Description

Description Optical transmission module and optical transmission system

The present invention relates to an optical transmission module and an optical transmission system, and more particularly to a technology that is effective when applied to introduce an optical cable such as an optical fiber into a subscriber system such as a telephone or an integrated service digital network (ISDN). . Background art

In information transmission using optical fibers, the flexibility of the information transmission system is high due to high bandwidth performance and electrical insulation, and all data including video is processed collectively as represented by multimedia. The dominance of optical transmission is outstanding. Today, optical cables such as optical fibers are being introduced to subscriber systems such as telephones and ISDN. In an optical transmission system, the circuit connected to the optical network and the network termination device will have an optical transmission module. The optical transmission module is a module that bidirectionally converts an optical signal and an electric signal. The optical transmitting side includes, for example, a laser diode and its driving circuit, and the optical receiving side includes a photo diode and a signal extracting circuit. Etc. are provided. Examples of documents describing the optical transmission system include “LSI Handbook”, pages 1004 and 1005, published by OM Corporation (December 25, 1960).

Fig. 11 shows an example of a system in which optical fibers are introduced into telephones and ISDN. ONU is for subscriber line network equipment, SLT is for subscriber line equipment ^. The subscriber line network device ONU and the subscriber line station device SLT include an optical transmission module that converts electric signals and optical signals in both directions. The optical transmission module is connected via an optical fiber cable.

In a network system represented by the above system, the distance of the subscriber line network device ONU to the subscriber line station device SLT varies, and the # 1 subscriber line network device ON U The optical signal level from the optical network is larger than the optical signal level from the # 2 subscriber line network device ONU. As such, when the optical signal levels from the various subscriber line network units 0NU are different, the subscriber line unit; in order for the SLT to determine these signals without error, depending on the input signal level, It is necessary to change the gain of the amplifier that widens it and change the threshold level of the circuit that identifies the logical value of the input signal so that the logical value of the input signal can be determined without error.

For this reason, the optical transmission module of the subscriber line network device SLT renews the gain control and threshold level of the amplifier for the data of each subscriber line network device X-ray equipment SLT can recognize all data.

However, in the above system, the transmission / reception characteristics of the light at the input / output points of the device are limited by the medium loss such as the branch loss due to the star force bra, the loss of the optical fiber, and the connection loss even though the transmission is 7 km as standard. output level - 7～- 2. is a 5 dBm, the light receiving power of the average value - circuit for the corresponding possible Geinkon trawl or threshold level changes with respect to _c such losses width that is 34 dBm Increases the cost of the optical receiver or optical transmission module.

The present invention has been made in view of the above circumstances, and has different line losses. The gain control of the circuit that amplifies the received optical reception level of multiple types and the process of resetting the threshold level for logical value judgment can be greatly simplified or the circuit for that can be eliminated. An object of the present invention is to provide an optical transmission system and an optical transmission module most suitable for such an optical transmission system.

The above and other objects and novel features of the present invention will become apparent from the following description of the present specification. Disclosure of the invention

An optical transmission system according to a first aspect of the present invention includes a communication host device and a plurality of communication terminal devices connected to the communication host device by an optical cable. The communication host device and the communication terminal device each include an optical transmission module connected to the optical cable. Each optical transmission module converts bidirectionally an electric signal and an optical signal into and out of input and output, and the optical transmission module of the communication terminal device has a transmission loss (also referred to as a line loss) between the communication terminal device and the communication host device. The output level of the optical signal is controlled according to the difference in (1), and the optical transmission module of the communication host device inputs an optical signal having substantially the same reception level from communication terminal devices having different transmission losses. According to this, in the communication host device, the gain control and the resetting of the threshold level of a circuit for amplifying a plurality of types of received signals suffering different line losses are greatly simplified or performed. Circuit is unnecessary. In addition, it is not necessary that the sensitivity of the photodiode receiving the optical signal in the communication host device be particularly high. Thus, the cost of the optical transmission system can be reduced. In particular, in a burst transfer mode for performing data transmission without supplying a synchronization signal separately from the data transmission signal, for example, in a system of a burst transmission system represented by a PDS system, a high transmission rate is conventionally used. Spirit It is considered that the gain control is indispensable, and in the above-mentioned system, the gain control and the resetting of the threshold level can be greatly simplified or the circuit for that can be eliminated even in the PDS system.

In the optical transmission system according to the second aspect of the present invention, the communication terminal devices in which the transmission loss of the optical signal ¹ is different from each other are substantially equal to an attenuation factor which is a ratio of the reduced optical input to the optical output of the communication host device. It has an optical transmission module that forms optical output with a reciprocal multiple. Also according to this, the optical transmission module of the communication i-host device can input optical signals having substantially the same reception level from communication terminal devices having different transmission losses.

In the optical transmission system according to the third aspect of the present invention, the optical transmission module included in the communication terminal device is configured based on an attenuation rate that is a ratio of the reduced input level to the light output level of the communication host device. The light output is controlled to be approximately the reciprocal of the attenuation rate with respect to the reference output level. Also according to this, the optical transmission module of the communication host device can input optical signals having substantially the same reception level from the communication terminal devices having different transmission losses.

In the optical transmission system according to the third aspect, the optical transmission module included in the communication terminal device includes a driver circuit that drives a laser diode based on an input electric signal, and a driver circuit that controls an operation of the driver circuit. Includes Ikuguchi Convenience Store. The microcomputer includes: a CPU; a storage unit in which a drive control data for determining a drive current for the laser diode according to a target light output is provided by the CPU; And D / Α conversion means for converting the obtained drive control data into an analog signal and providing the analog signal to the driver circuit, and determining the drive current of the laser diode.

In view of the current drive for the laser diode, the The outlet has a drive control data table for determining the drive current for the laser diode according to the target light output and the temperature, and the CPU controls the drive control according to the target light output and the temperature. Data can be selected from the table, and the selected drive control data can be given to the storage means as a reciprocal multiple of the marshal rate.

Further, at this time, the optical transmission module included in the communication terminal device may further include an optical receiver that converts the input optical signal into an electric signal by photodiode, amplifies the converted electric signal, and outputs the amplified electric signal. The CPU can input the electric signal converted by the optical receiving unit, and calculate the attenuation rate based on the electric signal.

In the optical transmission system according to the fourth parent point of the present invention, the optical transmission module included in the communication terminal device includes a first photoelectric conversion coefficient for converting an optical output signal received from the communication host device into a voltage signal Y. And a second photoelectric conversion coefficient (5) for converting an optical output signal in the communication host device into a voltage signal X (5 and a correction coefficient 7? = (ΧΖτ / (Υ / 5)). The light output is controlled by multiplying the drive control data corresponding to the light output signal in the host device by 7 times.

At this time, the optical transmission module included in the communication terminal device includes: a driver circuit that drives a laser diode based on an input electric signal; and a microphone opening unit that controls an operation of the driver circuit. It can be composed of The micro-computer includes: a CPU; a storage unit provided with a drive control data for setting a drive current of the laser diode by the CPU; and a drive control stored in the storage unit. D / A conversion means for converting the data into an analog signal and supplying the analog signal to the driver circuit, and determining the drive current of the laser diode. At this time, the drive control data corresponding to the optical output signal of the communication host device is 7? Multiplied. Further, the microcombiner has A / D conversion means for converting a received optical signal (analog signal) into a digital signal in order to obtain the electric signal Y.

The optical transmission module most suitable for the optical transmission system includes an optical transmission unit that converts an input electric signal into an optical signal and outputs the same, and an optical reception unit that converts the input optical signal into an electric signal and outputs the same. And a micro-computer for controlling the operation of the optical transmitter and the optical receiver, wherein the microphone-port convenience is based on an attenuation rate which is a ratio of an input level to a reference level of an optical signal. Is controlled to be approximately the reciprocal multiple of the attenuation rate with respect to the reference output level.

In this optical transmission module, the optical transmission unit includes a driver circuit that drives a laser diode based on a manually input electric signal, and the microcomputer includes a CPU, and a driving current for the laser diode. A drive means for determining drive control data according to the target light output, and a drive means for converting the drive control data stored in the memory means into an analog signal and providing the analog signal to the driver circuit; D / A conversion means for determining the drive current of the laser diode can be included. Further, when the microcomputer has a table of drive control data for determining a drive current for the laser diode according to the target light output, the CPU executes the drive according to the target light output. The control data is selected from the table and given to the storage means. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a block diagram of a PDS system which is an example of the optical transmission system according to the present invention.

Fig. 2 is a diagram for time division multiple access control in a PDS system. FIG. 7 is an explanatory diagram of designation of an uplink signal transmission timing.

FIG. 3 is a block diagram of an example of the optical transmission module.

FIG. 4 is a flowchart showing an example of the process of obtaining the attenuation factor and controlling the light output level taking this into account.

FIG. 5 is a diagram for explaining the principle of another method for controlling the optical output level in the subscriber network device.

FIG. 6 is an explanatory diagram of the temperature characteristics of the LD and the associated extinction failure and emission delay.

FIG. 7 is an explanatory diagram showing that the forward current Id required to obtain a certain light output is nonlinearly changed with temperature.

FIG. 8 is a circuit diagram showing a detailed example of an optical transmitter.

FIG. 9 is a circuit diagram of an example of a switching control circuit for controlling the on / off of the current path of the laser diode.

FIG. 10 is a flowchart showing an example of light output control using the correction coefficient 7? Explained in FIG. .

FIG. 11 is a block diagram exemplifying a PDS system. BEST MODE FOR CARRYING OUT THE INVENTION

《Optical transmission system》

FIG. 1 shows a block diagram of an optical transmission system according to one embodiment of the present invention. The figure shows an example of a system in which optical fibers are installed in telephones and ISDN. ONU is a subscriber line network device as a communication terminal device, SLT is a subscriber line station device as a communication host device, and EX is an exchange. The subscriber line network device 0NU and the subscriber line station device SLT include optical transmission modules 1 and 1A for bidirectionally converting an electric signal and an optical signal. Optical transmission module 1, 1 A is made from optical fiber OPF or passive element Connected via SCP. # 1 and # 2 attached to the subscriber line network device ONU are number information unique to the subscriber line network device ONU.

A network system represented by the above system is, for example, the PDS. This PDS system separates the time for transmitting signals in the upstream direction and the time for transmitting signals in the downstream direction in order to realize bidirectional communication at a single wavelength using one optical fiber ( Along with TCM: time axis reduction bidirectional multiplexing), signal transmission timing is controlled so that upward signals from each subscriber line network unit ONU do not collide (TDMA: time division multiple access control). Is done.

In the TCM, a downlink signal is transmitted from the subscriber line station device SLT to the subscriber line network device ONU in about half of the frame time, and a reverse uplink signal can be transmitted in the other half.

At the start of communication, TDMA measures the transmission delay time between the subscriber line equipment USLT and each of the subscriber line network devices ONU, and transmits the data from each subscriber line network device ONU. As shown in Fig. 2, the overhead (OH) signal is used to identify the address (identification number unique to each subscriber line network device) so that the burst signal does not overlap. Along with the designation, the transmission timing is instructed to each subscriber line network unit ONU. Since the upstream signal from each subscriber line network unit ONU has a random phase, the preamble required for the reproduction is added to the head of the upstream signal from each subscriber line network unit ONU by one byte. are doing. In this way, each subscriber line network device ONU transmits a burst signal at the specified transmission timing. The transmitted burst signal is passively multiplexed by a star power blur, and at the receiving point of the subscriber line station device SLT, the burst signal from each subscriber line network device 0NU is transmitted. Lined up in order. In this way, it is possible to accommodate a plurality of subscriber line network devices ONU using one optical fiber.

A difference of about 0 to 7 Km is allowed for each of the multiple lines split by the star power bra, and the corresponding line transmission loss occurs in optical transmission. The following considerations are made so that the optical reception level does not become random at the reception point of the subscriber line equipment SLT due to such transmission loss.

That is, the optical transmission modules 1 and 1A included in each of the subscriber line network device ONU and the subscriber line station device SL convert and input / output electrical and optical signals in both directions. The optical transmission module 1 of the subscriber line network device ONU controls the output level of the optical signal in accordance with the difference in transmission loss between the subscriber line device SLT and the optical network module of the subscriber line device SLT. The transmission module 1A inputs optical signals having substantially equal reception levels from the subscriber line network units ONU having different transmission losses. Specifically, the subscriber line network device ON U having different transmission loss of the optical signal is substantially opposite to the attenuation rate which is the ratio of the attenuated optical input to the optical output of the subscriber line station device SLT. It has an optical transmission module 1 that forms an optical output with a relationship several times higher. In other words, the optical transmission module 1 included in the subscriber line network device NUNU is based on an attenuation rate that is a ratio of the attenuated input level to the optical output level of the subscriber line station device SLT. The output is controlled to be approximately the reciprocal times the attenuation rate with respect to the reference output level. For example, assuming that the standard optical reception level of the optical transmission modules 1 and 1A in the entire system is m and the standard optical transmission level is n, the subscriber line network equipment 0NU (# 1) given from the subscriber line station equipment SLT. When the attenuation rate of the optical signal received by the subscriber line network is high (= reception level / n), the optical output level of the subscriber line network device ONU (# 1) is set to mxl / high. Also, When the attenuation rate at the ONU (# 2) of the subscriber line network is /? (Starting-level / n), the optical output level of the network device 0NU (# 2) is ni x. In this manner, the subscriber line network device 0 NU outputs an optical signal to the subscriber line station device SLT at an output level that is the reciprocal multiple of the input attenuation factor, and the subscriber line device SLT becomes Signals from any of the subscriber line network units 0NU can be received at the standard optical reception level m.

Therefore, as in the prior art, the transmission module 1 局 of the subscriber line station apparatus SL 、 is used to determine the logical value of the random reception level of each of the subscriber line network apparatus 0 NUs. Performs control (control of threshold voltage for logical value judgment) so that the subscriber line station equipment SLT can recognize all subscriber line network equipment 0 NU data. Can be completely eliminated. Further, it is possible to eliminate the need for a circuit configuration for performing such gain control and threshold voltage control on received data for each subscriber line network device ONU. Also, it is not necessary to make the sensitivity of the photodiode receiving the optical signal particularly high in the subscriber line equipment SLT. As a result, in a burst transfer mode in which data transmission is performed without supplying a synchronization signal different from the data signal, for example, in a burst transmission system typified by a PDS system, a high-precision gain is conventionally used. Although it was considered that control and the like were indispensable, the cost of the PDS optical transmission system can be reduced by adopting the system of this embodiment.

Needless to say, in the optical transmission module 1A of the subscriber line station device SLT, it is not necessary to control the optical transmission level using the decay rate described above. The control of the optical transmission level using the above-described attenuation rate is performed by software Therefore, the hardware configuration of the optical transmission modules 1 and 1A is made substantially the same, and there is no problem.

《Configuration of optical transmission module》

FIG. 3 shows a block diagram of the optical transmission module 1. The optical transmission module 1 shown in FIG. 1 includes an LD module 10, a driver circuit 11, and an input circuit 12, each of which constitutes an optical transmission unit (optical transmitter) and which is individually integrated into a semiconductor circuit. It comprises a pin photodiode 13, a preamplifier 14, a main amplifier 15, and an output circuit 16, each of which constitutes an optical receiving unit (optical receiver) and individually formed as a semiconductor integrated circuit. The LD module 10 includes a laser diode (also referred to as LD) 100 and a photo diode (also referred to as PD) 101 for monitoring. The optical output of the laser diode 100 is output to an optical output terminal 0 P OUT. The bin photodiode 13 receives an optical signal from an optical input terminal OP IN. The input circuit 12 is connected to the data input terminal DTIN, and the output circuit 16 is connected to the data output terminal DTOUT.

The input circuit 12 forms an input buffer circuit.

The driver circuit 11 includes an LD driver 110 and an auto power control circuit (APC) 111. The LD driver 110 controls a data signal supplied through the input circuit 12 and the LD 100 controls a target signal. The drive signal current is converted to the drive signal current required to obtain the specified optical output, and a DC bias current for guaranteeing the threshold current of the LD 100 is generated and supplied to the LD 100. The DC bias current is automatically controlled based on the detection result of the current (LD light output monitor current) detected by the PD 101 so that the light output is always constant at the APC 111. The optical output of the LD 100 is provided from an optical output terminal OPOUT to a transmission line such as an optical fiber.

The bin photodiode 13 is connected to the optical input terminal 0 PIN from the transmission line. The supplied optical signal is detected and converted into a received signal current. This signal current is converted into a low voltage signal by the preamplifier 14. The converted voltage signal is output to the main amplifier 15. The main amplifier 15 amplifies the input voltage signal to the ECL level. The output M path 16 that receives the output of the main amplifier 15 widens the input signal from the main amplifier 15 sufficiently, shapes the upper and lower parts of the waveform into a sliced signal, and uses this as a de-emphasis signal. Apply to data output terminal D TOUT

The optical transmission module 1 shown in FIG. 3 includes a microcomputer 17. The microcomputer 17 is not particularly limited, but includes a CPU (Central Processing Unit) 170, a RAM (Random Access Memory) 171, a ROM (Read Only Memory) 172, and an erasable and writable memory. It has a flash memory 173, which is an example of a nonvolatile storage device, and an input / output circuit (I / O) 174, which are coupled to an internal bus 175. Although not particularly limited, the ROM 172 is a mask ROM holding operation programs and constant data of the CPU 170, the RAM 171 is a work area of the CPU 170, and the flash memory 173 is a CPU 170 operation programs and control data are stored in a rewritable manner. The input / output circuit 174 comprises a D / A conversion circuit 176 comprising a plurality of D / A conversion channels and an input register, and an A / D converter comprising a plurality of A / D conversion channels and an output register. Including circuit 1 77 etc. The input register of the A / D conversion circuit 176 is accessed by the CPU 170, and the digital signal set in this register is converted to an analog signal.

The analog signal converted by the 0/8 conversion circuit 1Ί6 is supplied to the LD dryer 110, which causes the LD dryer 110 to drive the LD 100 with the drive signal current (modulation current) and the DC bias current ( Bias current). The A / D converter circuit 1Ί7 is connected to the PD 101 and preamplifier 14 The analog signal is converted into a digital signal, and the converted digital signal is made accessible by the CPU 170 via the output register.

The signal line indicated by 179 is a signal line for interfacing the microcomputer 17 with the outside of the optical transmission module 1 and is not particularly limited, but is a reset signal, data or command, or CPU operation programs to be stored in the flash memory 173 can also be exchanged.

The microcomputer 17 is a circuit that controls the entire optical transmission module 1. First, the control content is to control the light output level at the reciprocal multiple of the attenuation rate. The second is control to obtain the attenuation rate. Third, the drive control of the LD 100 considering the difference in temperature characteristics between the LD dryno 110 and the LD 100.

《Acquisition of attenuation rate and control of light output level considering it》

Fig. 4 shows the flow of control of the light output level taking into account the acquisition of the attenuation rate and that. Although not particularly limited, the acquisition of the attenuation rate is performed as part of the power-on reset processing by the CPU 170. This process is performed, for example, as a power-on process when the subscriber network device ONU is first installed. In this process, an arbitrary signal is transmitted from the subscriber line device SLT to the subscriber network device ONU at a standard optical transmission level. Using this transmission signal, an operation for obtaining the attenuation rate is performed. For example, the attenuation rate α is obtained by dividing the reception level by the standard optical transmission level (S 1). The standard light transmission level is stored in a predetermined storage area of the flash memory 173. To detect the reception level, the PD 13 detects the arbitrary signal transmitted from the subscriber line station device SLT to the subscriber network device 0NU, and amplifies the signal by the preamplifier 14 to obtain a signal. I / O circuit 1Ί4 A / D conversion circuit 1 7 7 The conversion is performed by referring to the CPU 170 via the output register. The arbitrary signal is output at a standard transmission level. The gain of preamplifier 14 is set to a specific value. The output of preamplifier 14 is converted to a digital signal by A / D conversion circuit 1Ί7 included in input / output circuit 174, and the converted digital signal is used as reception level by CPU 170 Referred to. The CPU 170 reads out the data of the standard light transmission level n from the flash memory 173, and calculates the attenuation factor based on the data of the standard light transmission level n and the data of the sampled reception level. The data of the standard optical transmission level n may be externally received through the signal line 179.

Next, the target light output instruction data D1 is calculated using the calculated attenuation factor and the standard light reception level m (S2). The data of the standard light reception level m is read out from a predetermined storage area of the flash memory 173 or externally supplied via a signal line 179. In accordance with the calculated target light output instruction data D1, the LD drive data D2 is read from the flash memory 173. Although not particularly limited, the LD drive data is tabulated according to the temperature and the target light output, as will be described in detail later. Reads the LD drive data D2 from the table in the flash memory 173.

The read LD drive data D 2 is the D / A conversion circuit of the input / output circuit 1 7

It is loaded into the input register 6 and converted to an analog signal and supplied to the LD driver 110. As a result, the LD dry line "110" generates a drive signal current for the LD 100. Thereafter, when an input signal is supplied from the input circuit 12, the LD 100 is driven accordingly. The current path is turned on and off, and the LD 100 is driven to emit and extinguish light (S 3) o In the above description, the LD drive data may be directly set to the inverse multiple of the attenuation rate. That is, the LD drive control data corresponding to the target light output and the temperature (atmospheric temperature of the optical transmission module) is selected from the table, and the selected LD drive control data is set to the reciprocal of the attenuation rate to obtain the DZA. Input of conversion circuit 1 76 6 Load at evening.

Here, the attenuation power and the target light output instruction data D 1 calculated as part of the power-on reset need not be stored inside the microcomputer 17, but the operation power of the microcomputer 17 As long as is not interrupted, the above settings are maintained. D2 is held in the input register of the D / A conversion circuit 1Ί6.

Fig. 5 shows a principle diagram of another control method of the optical output level in the subscriber network unit ONU.

In Fig. 5, PB is the optical output value of the optical transmission module 1A of the subscriber line device SLT, and PR is the optical input value received by the optical transmission module 1 of a certain subscriber line network device ONU. . Α (= X / P B) is a second photoelectric conversion coefficient for converting the optical output signal in the above-mentioned subscriber line device SLT into a voltage signal. 5 (= Y / PR) indicates that the optical transmission module 1 included in a certain subscriber line network device ONU converts the optical output signal received from the optical transmission module 1A of the subscriber line device SLT into a voltage signal. This is the first photoelectric conversion coefficient to perform. X and Y are the voltage signals at each. Therefore, the transmission loss between the subscriber line station apparatus SLT and a certain subscriber line network apparatus ONU can be represented by (X / a) (Y / δ).

Here, a is a unique value depending on the circuit characteristics of the optical transmission module, and is a known value. Also, the voltage signal X and the optical output value ΡΒ are known. Therefore, if (ΧΖ) / (Υ / δ) is the correction coefficient 77, If the received optical input value PR can be detected, the correction coefficient? Can be calculated. Based on this correction factor 7 ?, each of the subscriber line network units 0NU converts the optical signal into a subscriber line station device SLT with a specific correction factor of 7; Thus, the subscriber line station apparatus SLT can receive a signal from any of the subscriber line network apparatuses 0NU at a level corresponding to a standard optical output. Therefore, as described above, the transmission module 1A of the subscriber line station apparatus SLT is used to control the gain of the amplifier in order to determine the logical value of the random reception level for each of the subscriber line network apparatuses 0NU. And the threshold voltage control, and even if there is no circuit for performing such gain control and threshold voltage control, the subscriber line station equipment SLT is used for all subscriber lines. You will be able to recognize the network device ONU.

As described above, when an optical signal is output to the subscriber line equipment SLT at a correction factor of 77 with respect to the standard optical output, for example, PB, of the optical transmission module 1, the CPU 1 70 supplies drive control data for determining the drive current for the laser diode 100 based on the correction coefficient 77 to the input register of the D / A conversion circuit 176. The drive control data loaded in the input register is converted into an analog signal and supplied to the LD driver 110. Thus, the LD driver 110 generates a drive signal current of LD 100. Thereafter, when input data is supplied from the input circuit 12, the current path of the LD 100 is turned on / off accordingly, and the LD 100 is driven to emit light and extinguish.

《L D drive control》

In order to describe the drive control of the LD described in FIG. 5 in more detail, Now, the current drive control of the LD 100 will be described.

The LD 100 has a double heterojunction. When a forward current is applied to the double heterojunction, when the current exceeds a certain current value, the laser 100 starts laser oscillation and emits laser light. This current at the start of laser oscillation is called the threshold current (bias current) Ith. The magnitude of the forward current Id to be passed through the laser diode is determined according to the required light output. This forward current Id can be roughly expressed as Ith + Imod. I mod is referred to as the modulation current, and the optical output of the LD 10 is obtained by passing the modulation current out of the required forward current to the LD or cutting it off (called modulation current on / off control). Can be turned on / off. In optical communication using the LD 100, information is transmitted by turning on / off the optical output. In order to realize a high-speed response of turning on / off the optical output, it is most preferable to turn on / off the modulation current Imod of the forward current Id in a pulse shape.

The LD 100 has a temperature dependency on an optical output with respect to a forward current. Therefore, in order to correct the base voltage of the current source transistor arranged in the drive current path of the LD 100 in accordance with the temperature, the bias circuit of the current source transistor needs to have the temperature dependence of the band gear of the transistor and the diode. The utilized base spice circuit can be adopted.

However, the temperature characteristics of the LD 100 greatly differ depending on the temperature as illustrated in FIG. In addition, the characteristics of the threshold current and the modulation current differ depending on the temperature. That is, the forward current of the LD 100 required to obtain a predetermined light output differs depending on the temperature, and at this time, the threshold current included in the forward current also differs uniquely depending on the temperature. Therefore, the modulation current, which is the difference between the forward current and the threshold current, also changes in accordance with the temperature. In FIG. 6, the threshold currents I th (i), I th (j), I th (k) and the modulation currents I mod (i), I mod (j), and I mod (k) are large at each of the illustrated temperatures T (i), Τ (j), and T (k). Are very different. Therefore, the forward current I d required to obtain a certain light output is changed non-linearly with respect to temperature, as illustrated in FIG. Similarly, the threshold current and the modulation current are also nonlinearly changed. On the other hand, the current characteristic with respect to the temperature of the base bias circuit utilizing the temperature dependence of the band gap of a transistor or a diode is only changed linearly. Due to this hesitation, a base bias circuit that utilizes the temperature dependence of the bandgap of a transistor or a diode cannot accurately compensate for the LD drive current with respect to a temperature change.

At this time, at least the required light output must be obtained from the LD 100 in optical communication and the like. Therefore, in order to make the forward current flowing through the LD follow the temperature characteristics of the LD, the actual light emission output of the LD 100 is monitored by a photodiode (PD) 101, and the current corresponding to the monitored light emission output is required. The comparator determines whether the reference potential is lower or higher than the reference potential Vref corresponding to the output, and if the reference potential is lower than Vref, control can be performed to increase the bias current flowing to the LD. However, even if the feedback control increases the bias current and performs the auto power control to match the total forward current flowing through the LD 100 to the temperature characteristic of the LD 100, the light output of the LD 100 is reduced. The current that is turned on / off by a transistor that causes current to flow through the LD 100 for on / off control does not match the current temperature characteristics of the LD. For example, in FIG. 7, the forward current required to obtain the required light emission output for the LD at the temperature T (j) is I d (j). At this time, the drive that can be supplied by the drive circuit of the LD Assuming that the current is IC (j), the difference current is The power control adds to the bias current of the LD. This difference current is not subject to on / off control as a modulation current. As a result, the current value when the modulation current is turned off is larger than the threshold current, causing extinction failure, or the current value when the modulation current is turned off is smaller than the threshold current. The disadvantage is that light emission is delayed when the size is reduced.

For example, in Fig. 6, in an atmosphere of temperature (k), the modulation current that can flow in the current source transistor is I1 (Il <Imod (k)) due to the temperature characteristics of this transistor and the like. If so, a bias current I 2 (I 2> I th (k)) is passed through the bias transistor to obtain the light emission output P m. Then, when the modulation current I 1 is made zero to turn off the LD, the bias current flowing through the LD exceeds the threshold current I th (k) of the LD at the temperature T (k) at that time. This does not completely extinguish the LD. Further, in FIG. 6, in an atmosphere of temperature T (i), the modulated current that can be passed through the current source transistor depends on the temperature characteristic of the transistor, etc., so that I 3 (I 3> I th (i) ), A bias current I 4 (I 4 <I th (i)) flows in the bias transistor in order to obtain the light emission output Pm. In this state, if the modulation current I 3 is made zero to turn off the LD, the bias current flowing through the LD becomes the threshold current I th (i) of the LD at the temperature T (i) at that time. Therefore, the next time the LD is turned on, the LD must wait for a delay time until the modulation current flowing through the LD exceeds its threshold voltage I th (i). Is emitted. The optical transmission module 1 of the present embodiment takes into consideration the difference between the temperature characteristic of the laser diode 100 and the temperature characteristic of the LD Can control I am trying to. First, the contents will be described.

Fig. 8 shows a detailed example of the light transmission. The LD driver 110 includes a transistor Tr1 for determining a bias current flowing to the LD 100 and a transistor Tr2 for determining a modulation current for controlling on / off of the LD 100, for a current source. Provided as a transistor. Transistors Tr 3 and Tr 4 are switching transistors for controlling the on / off of the modulation current. The transistors Tr1 to Tr4 are npn-type bipolar transistors.

The transistors Tr 3 and Tr 4 are connected in parallel, the common emitter is connected to the collector of the transistor Tr 2, and the emitter of the transistor Tr 2 is connected to the negative power supply voltage V ee (eg, one 5.2 V). A power source of LD 100 is coupled to the collector of the transistor Tr3, and the anode of the LD 100 and the collector of the transistor Tr4 are connected to the other power supply voltage Vcc (for example, 0 V) such as the ground potential. V).

As shown in FIG. 9, a switching control circuit 114 for the transistors Tr 3 and Tr 4 includes a series circuit of the transistors Tr 5 and Tr 6 and a switching circuit for the transistors Tr 7 and Tr 8. A series circuit is placed between the pair of power supply voltages Vcc and Vee. The transistors Tr5 to Tr8 are npn-type bipolar transistors. The bases of the transistors Tr6 and Tr8 are biased at a predetermined voltage, and function as load resistors for the transistors Tr5 and Tr7. In other words, the series circuit of the transistors Tr 5 and Tr 6 and the series circuit of the transistors Tr 7 and Tr 8 each constitute an emitter follower circuit, and the emitter of the transistor Tr 5 At the pace of the transistor Tr3, the emitter of the transistor Tr7 is coupled to the base of the transistor Tr4. The bases of the transistors Tr5 and Tr7 are supplied with the differential output of the differential output amplifier AMP. When the inputs are inverted, the states of the base potentials of the transistors Tr3 and Tr4 are inverted. It has become. The output of the selector 122 is supplied to the amplifier AMP.

When the base potential of the transistor Tr 3 is set to a high level, the transistor Tr 3 shifts to a saturation state, and when the base of the transistor Tr 4 is set to a high level, the transistor Tr 4 shifts to a saturation state. Is done. The transition of the transistors Tr 3 and Τr 4 to the saturated state is performed in a complementary manner, whereby the transistors Tr 3 and される r are operated in a complementary manner to switch the current source. A modulation current is supplied to LD 100 in a pulse form via the transistor Tr 2.

As shown in FIG. 8, the transistor Tr1 has its collector coupled to the collector of the transistor Tr3, and its emitter coupled to the power supply voltage Vee via a resistor R1. This transistor Trl carries a bias current through Ld100 according to the base voltage applied to it.

The PD 101 is connected in series to the resistor R3, and is arranged in a reverse connection state between a pair of power supply voltages Vcc and Vee. The PD 101 flows a current according to the light emission output output from the LD 100.

In FIG. 8, an input / output circuit 17 4 of the microcomputer 17 is a digital-to-analog conversion circuit (D / A) 176 for converting a digital signal into an analog signal, and an analog signal. The analog signal is converted into a digital signal. The digital signal conversion circuit (A / D) 177 and other input / output circuits 178 are shown separately. The D / A 176 has two D / A conversion channels DAC 1 and DAC 2 and input registers I REG 1 and I REG 2 corresponding respectively thereto. A / D 177 is 5 A / D conversion channels A It has output registers 0 REG 1 to 0 REG 5 corresponding respectively to DC 1 to ADC 5.

The input registers I REG 1 and I REG2 corresponding to the D / A conversion channels D AC1 and D AC 2 are registers into which the D / A conversion target data is loaded by the CPU 170. The data loaded to the input registers I REGl and I REG 2 are D / A converted, and the analog signal obtained by this conversion is based on the base bias voltages of the transistors Tr 1 and Tr 2. Is done. As a result, the modulation current to be passed to the transistor Tr3 is determined by the control data set in the manual register I RG2 of the D / A conversion channel DAC2 by the CPU 170. That is, the modulation current to be passed to the transistor Tr3 is determined by the conductance control of the transistor Tr2. The conductance control of the transistor Tr 2 is called modulation current control. The bias current to be supplied to the LD 10 ° is determined by the control data set in the input register REG 1 of the D / A conversion channel DAC 1 by the CPU 170. That is, the bias current flowing through the LD 100 is determined by the conductance control of the transistor Tr1. The conductance control of the transistor Tr1 is called the bias current control of the LD.

In this way, the CPU 170 individually and arbitrarily controls the modulation current and the bias current that can be supplied to the LD 100 in accordance with the digit setting set for the D / A conversion channels DAC1 and DAC2. Can be. Therefore, the CPU 170 sets the D / A conversion channels D AC 1 and D AC 2 to the data conditions based on the temperature characteristics of the LD 100 etc. with respect to the usage conditions (operating atmosphere conditions) of the optical transmission module 1. In other words, in other words, the data corresponding to the threshold current of LD 100 at the operating ambient temperature at that time is set in D / A conversion channel D AC 1 and the required optical output is set to that value. By setting the data corresponding to the modulation current to be added to the threshold current to obtain the temperature under the temperature in the D / A conversion channel D AC 2, the LD 100 emits light without extinction error or emission delay. It becomes possible to drive. It goes without saying that the light emission output level (light emission intensity) of the LD 100 can also be controlled by controlling the magnitude of the bias current.

Also, the A / D conversion channels ADC1 to ADC5 are sequentially connected to a transistor Trl emitter voltage, a transistor Tr2 emitter voltage, a PD 101 anode voltage, and a temperature sensor. 1 Assigned to the input of the detection output voltage of 12, the output voltage of the preamplifier 14 (voltage level corresponding to the received optical output), and. The results of A / D conversion by the A / D conversion channels ADC1 to ADC5 with respect to the assigned input voltage are latched by the corresponding output registers OREG1 to OREG5. The CPU 170 accesses, via the path 175, the data latched in the output registers 0 REG 1 to 0 REG 5.

As a result, the CPU 170 adjusts the bias current flowing through the transistor Trl, the current flowing through the transistor Tr2, the current flowing through the PD 201, the output of the temperature sensor 10, and the output voltage of the preamplifier 14 as necessary. It can be monitored via the / D conversion circuit 177.

The output of the monitor PD101 is also made available for automatic power control. That is, the actual light emission output of the LD 100 is monitored by the PD 101, and whether or not the current corresponding to the monitored light emission output is smaller or larger than the reference potential V ref corresponding to the required light emission output is determined by a comparator 1 13. Judgment is made, and the bias current flowing to LD100 via the transistor Tr1 is increased or decreased according to the judgment result. Reference numeral 15 denotes an APC control circuit for forming a reference potential Vref, and the actual light emission output of the LD 100 is monitored by the PD 101, and the average value of the current corresponding to the monitored light emission output and the current value at that time are calculated. The reference potential V ref is initialized based on the average value (mark rate) of the amplifier AMP input signal. Although not particularly limited, the auto power control is made to assist the bias current control based on the output of the D / A 176. For example, when bias current control is performed based on the output of D / A 176, feedback control by the auto power control is repeated, assuming that the required emission output cannot be obtained. Do. However, in such a case, it is desirable that the control amount (the amount of increase or decrease of the bias current) of the feedback system by the auto power control should be relatively small.

The CPU 170 monitors the output current of the PD 101 via the A / D 177, compares the actual light output of the LD 100 with the light output of the LD 100, and It is possible to detect, for example, a state where the light output is lower than a predetermined value with respect to the target light output. The CPU 170 monitors the bias current actually flowing through the transistor Tr 1 via the A / D 177, and the monitored current value and the bias current flowing through the transistor Tr 1 via the D / A 176. The bias current can be detected based on the difference between the bias current and the bias current. Similarly, the CPU 170 monitors the modulation current actually flowing to the transistor Tr 2 via the A / D 177, and outputs the modulated current to the transistor Tr 2 via the D / A 176. By comparing the modulation current with the modulation current to be supplied, the abnormality of the modulation current can be detected based on the difference.

The LD drive control data for the modulation current control and the bias current control for driving the LD 100 are the data to be set in the DAC 1 and DAC 2 to obtain the target optical output. The table structure is provided for each ambient temperature, and is written in a predetermined area of the flash memory 173 of the microcomputer 170.

When the micro-computer overnight 1 駆動 0 drives the LD 100, The ambient temperature where the optical transmission module 1 is placed is obtained from the temperature sensor 112 via the A / D conversion channel ADC4. The light output to be output by the optical transmission module 1 is of a nature that is physically determined according to the communication environment in which it is placed. For example, an operation program of the CPU 170 or an external The CPU 170 is notified by an instruction from the CPU or a signal from a circuit such as a dip switch. Further, light emission output control based on the attenuation rate or light emission output control based on the correction coefficient? Is performed. Accordingly, the CPU 170 selects the required light emission output and the LD drive control data corresponding to the detected use environment temperature from the table of the flash memory 173. As a result, the threshold current and the modulation current according to the actual temperature characteristics of the LD 100 are given to the LD 100, and the LD 100 can be driven to emit light without a quenching error or a light emission delay.

FIG. 10 shows a flow chart of light output control using the correction coefficient described in FIG.

Correction factor? Control of the optical output level using 7 is performed as part of the power-on reset (or other resets). This processing is performed, for example, by power-on processing when the subscriber network device ONU is first installed. In this process, an arbitrary signal is transmitted from the subscriber line station apparatus SLT to the subscriber network apparatus 0NU at a standard optical transmission level. Using this transmission signal, a correction coefficient r? Is obtained. First, when a power-on reset is instructed, the CPU 170 measures the temperature of the optical transmission module 1 by the temperature sensor 112 (ST 1), and obtains a standard optical output under the temperature. The required LD drive control data (modulation current setting data for obtaining modulation current Im, and bias current setting data for obtaining bias current Ib) are stored in the flash memory 1 13 through D / A conversion channel Input register of DAC 1 and DAC 2 I REG 1 and I REG 2 Initialize (ST2). Next, the received light signal is monitored by the bin photodiode 13 (SΤ3). That is, the output of the preamplifier 14 is converted into a digital signal by the A / D conversion channel ADC 5, and the received result is monitored by the CPU 170 via the output register OREG 5 to monitor the received light. .

At this time, if the predetermined optical signal is supplied from the subscriber line unit SL # (the monitor voltage is not 0), a correction coefficient 7? Is calculated (S S5) _c , that is, the monitor voltage Is the voltage Y described in FIG. The conversion coefficient α, (5 is a known value from the circuit characteristics of each optical transmission module described in FIG. 5. The voltage X described in FIG. 5 is also a known voltage. The known values X, a, and ( _c are supplied externally via a signal line 179, or they are stored in the flash memory 173 in advance. Thereby, the CPU 170 can perform the operations described in FIG. Correction factor 77 = (X / a)

/ (γ / is calculated.

At this time, the optical output PB described in FIG. 5 corresponds to the modulation current setting data Im set in the step ST2. Therefore, in step ST6, Im is multiplied by 77 to obtain a new modulation current setting data Im. By providing the corrected modulation current setting data Im to the D / A conversion circuit 176, the modulation current is doubled as the modulation current set in step ST2 (ST7). Thereafter, when the input data is supplied from the input circuit 12, the current path of the LD 100 is turned on / off accordingly, and the LD 100 is driven to emit light and extinguish. In this way, the subscriber line unit SLT can receive a signal from any of the subscriber line network devices ONU at a level corresponding to the standard optical output.

The invention made by the present inventors will be specifically described based on the embodiments. However, it is needless to say that the present invention is not limited to this, and various changes can be made without departing from the gist of the present invention.

For example, the transmission mode is not limited to the PDS. The optical fiber is laid radially from the single-sided equipment, which makes each network terminator correspond to the one-sided circuit on a one-to-one basis, and a remote multiplexing device is installed ahead of it. However, the transmission medium may be further radially wired. It may also be a SONET-SDH system. Further, the optical transmission system of the present invention is not limited to a telephone or an ISDN, but is naturally applicable to a LAN (Local Area Network) and the like. Industrial applicability

As described above, the present invention can be widely applied to an optical transmission module that converts an optical signal and an electric signal in optical transmission, and an optical transmission module such as a PDS in which an optical fiber is introduced into a telephone or an ISDN subscriber system. Can be applied to the system.

Claims

The scope of the claims

1. A communication host device and a plurality of communication terminal devices connected to the communication host device by an optical cable, wherein the communication host device 11 and the communication terminal device are optical transmission modules respectively connected to the optical cable. Each of the optical transmission modules converts an electric signal and an optical signal bidirectionally to input and output, and the optical transmission module of the communication terminal device has a transmission loss between the communication terminal device and the communication host device. The output level of the optical signal is controlled according to the difference, and the optical transmission modules of the communication host device receive optical signals having substantially the same reception level from communication terminal devices having different transmission losses. Characteristic optical transmission system.

2. A communication host device, and a plurality of communication terminal devices connected to the communication host device by an optical cable, wherein the communication host device and the communication terminal device each include an optical transmission module connected to the optical cable. Each of the optical transmission modules converts an electrical signal and an optical signal bidirectionally to input and output, and the communication terminal device having different transmission loss of the optical signal includes an optical output of a communication host device. An optical transmission system comprising an optical transmission module that forms an optical output with a relationship that is approximately a reciprocal multiple of an attenuation rate that is a ratio of attenuated optical input to the optical transmission system.

3. Includes a communication host device and a plurality of communication terminal devices connected to the communication host device by optical cables, wherein the communication host device and the communication terminal device each include an optical transmission module connected to the optical cable. Each of the optical transmission modules converts an electrical signal and an optical signal bidirectionally to input and output, and the optical transmission module included in the communication terminal device has an optical output level corresponding to an optical output level of a communication host device. Based on the attenuation rate, which is the ratio of the attenuated input level, the optical output is compared with the reference output level by the above-mentioned attenuation rate. An optical transmission system characterized in that it is controlled to be approximately the reciprocal multiple of the above.

4. The optical transmission module included in the communication terminal device includes a driver circuit that drives a laser diode based on an input electric signal, and a microcomputer that controls an operation of the driver circuit. The micro computer includes a CPU and drive control data for determining a drive current for the laser diode according to a target light output.

Storage means obtained by the CPU; and D / A conversion means for converting the drive control data stored in the storage means into an analog signal and supplying the analog signal to the driver circuit to determine the drive current of the laser diode. 4. The optical transmission system according to claim 2, wherein the optical transmission system comprises:

5. The micro-computer has a drive control data table for determining a drive current for the laser diode according to the target light output and the temperature, and the CPU controls the drive current according to the target light output and the temperature. 5. The light according to claim 4, wherein the selected drive control data is selected from the table, and the selected drive control data is provided to the storage means by converting the selected drive control data into a reciprocal multiple of the attenuation rate. Transmission system.

6. The optical transmission module included in the communication terminal device further includes an optical receiving unit that converts the input optical signal into an electric signal by a photodiode, amplifies the converted electric signal, and outputs the amplified electric signal. The optical transmission system according to claim 5, wherein the CPU inputs the electric signal converted by the optical receiving unit, and calculates the attenuation rate based on the electric signal. .

7. Including a communication host device and a plurality of communication terminal devices connected to the communication host device by an optical cable, the communication host device and the communication terminal device Includes optical transmission modules respectively connected to the optical cable, each optical transmission module bidirectionally converts an electric signal and an optical signal to input and output, and the optical transmission module included in the communication terminal device. Is a first photoelectric conversion coefficient a for converting an optical output signal received from the communication host device into a voltage signal Y, and a second photoelectric conversion coefficient a for converting the optical output signal in the communication host device into a voltage signal X. The correction coefficient? 7 = (X / a) / (Y / c5) is obtained from the photoelectric conversion coefficient 5 and the data corresponding to the optical output signal in the host device is multiplied by 7 times. An optical transmission system characterized in that the optical output is controlled according to the time required.

8. The optical transmission module included in the communication terminal device includes: a driver circuit that drives a laser diode based on a human-operated electric signal; and a microcontroller that controls an operation of the driver circuit. The microcomputer includes: a CPU; a storage unit provided with drive control data for determining a drive current for the laser diode by the CPU; and a drive control data stored in the storage unit. DZA conversion means for converting the signal into an analog signal and supplying the analog signal to the driver circuit to determine the driving current of the laser diode. The CPU includes a drive control data corresponding to an optical output signal in the communication host device. 8. The optical transmission system according to claim 7, wherein the value is multiplied by seven to give the result to the storage means.

9. The micro-computer includes an A / D converter for converting an optical output signal received from the communication host device into a digitized signal, and a digital signal converted by the A / D converter. 9. The optical transmission system according to claim 8, further comprising: storage means for latching and being made accessible by said CPU.

1 0. An optical transmitter that converts the input electrical signal to an optical signal and outputs it. An optical receiver that converts the input optical signal into an electrical signal and outputs the electrical signal; and a microcontroller that controls operations of the optical transmitter and the optical receiver. The optical transmission mosh characterized in that the optical output is controlled to be approximately the reciprocal multiple of the attenuation rate with respect to the reference output level, based on the attenuation rate which is the ratio of the input level to the reference level. One note.

11. The optical transmission unit includes a driver circuit that drives a laser diode based on an input electric signal, and the microcomputer controls a CPU and a drive current for the laser diode according to a target optical output. Storage means for providing the drive control data for determination by the CPU, and converting the drive control data stored in the storage means into analog signals and providing the analog signals to the driver circuit; 10. The optical transmission module according to claim 10, further comprising D / A conversion means for determining a drive current of the optical transmission module.

12. The micro-computer has a drive control table for determining a drive current for a laser diode according to a target light output and a temperature, and the CPU has a target light output. And drive control data according to temperature

11. The optical transmission module according to claim 11, wherein evening is selected from the table, and the selected drive control data is provided to the storage unit by making it a reciprocal multiple of the attenuation rate. .

1 3. The optical receiving unit further includes a light receiving unit that converts an input optical signal into an electric signal by a photodiode, amplifies the converted electric signal, and outputs the amplified electric signal. The optical transmission module according to claim 12, wherein a signal is input, and the attenuation factor is calculated based on the electric signal.