JP2008113386A - Optical transmitter, optical receiver, and optical transmission system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical transmitter, optical receiver, and optical transmission system capable of obtaining a multi-level amplitude modulated optical signal of which an S/N is equal at multi-value levels by setting a multi-value level by detecting an extinction ratio of a multi-level optical signal output from the optical transmitter. <P>SOLUTION: An optical transmitter according to the present invention comprises: a data transmitting unit which outputs transmission data; a multi-value level setting unit for setting a multi-value level of an optical signal; a driving unit which converts an output of the data transmitting unit into a multi-level amplitude signal based on an output of the multi-value level setting unit; and a light emitting unit which converts an output signal of the driving unit into an optical signal. An optical receiver according to the present invention comprises: a light receiving unit which receives the optical signal from the light emitting unit; a first extinction ratio detecting unit for detecting an extinction unit of the optical signal from the output signal of the light receiving unit; an identification level setting unit which sets an identification level for determining the multi-value level of the output signal from the light receiving unit from an output of the extinction ratio detecting unit; and a multi-value level determining unit which determines the multi-value level of the output signal from the light receiving unit based on an output of the identification level setting unit. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical transmitter, an optical receiver, and an optical transmission system using the optical transmitter that transmit a multi-value amplitude modulated optical signal.

In conventional optical transceivers, digital transmission using binary signals is the mainstream. Recently, broadband transmission has been actively performed, and high-definition video signals have been transmitted, and higher transmission speeds are required. In optical communication, an electrical signal is converted into an optical signal that has been modulated at high speed using a laser, etc., transmitted through an optical fiber or space, and converted into an electrical signal using a light receiving element. Data transmission is performed. At present, digital transmission with binary signals is common, but in optical communication, lower speed light emitting and receiving elements are used to increase transmission speed and transmission efficiency, and to reduce costs. In order to achieve this, transmission schemes using multilevel transmission have been studied. When multilevel transmission is performed in optical communication, it is generally considered to apply multilevel amplitude modulation. In that case, as shown in FIG. 13, the intervals of the multilevel levels of the multilevel amplitude signal are set to be equal. This is because an electrical circuit can be realized with a simple configuration when considering a circuit configuration for modulating and demodulating a multi-value amplitude signal with an electrical signal. Patent Document 1 discloses a configuration for obtaining an optical signal subjected to multilevel amplitude modulation in which each multilevel level is equally spaced as shown in FIG.
Japanese Patent Application No. 2002-361046

  However, when an APD (avalanche photodiode) is used in order to increase the light receiving sensitivity of the optical receiver, there is a problem with a multi-level amplitude-modulated signal in which the multi-levels are equally spaced as described above. . In an optical receiver using a PD (photodiode) that does not have a multiplication effect, the thermal power of the preamplifier is dominant in the noise power. S / N is also equal. However, in an optical receiver using an APD with a large multiplication factor, the noise power increases as the received light power increases. Therefore, the interval between adjacent multilevel levels must be set larger as the multilevel level of optical power increases. , S / N is not equal, and as a result, the performance of the optical receiver deteriorates.

  The present invention solves the above-described conventional problems, and detects the extinction ratio of the multilevel optical signal output from the optical transmitter and sets the multilevel level, so that the S / N is reduced at each multilevel level. It is an object of the present invention to provide an optical transmitter, an optical receiver, and an optical transmission system that can obtain equal multi-value amplitude modulated optical signals.

  In order to solve the above-described conventional problems, an optical transmitter according to the present invention is an optical transmitter that outputs an optical signal that has been subjected to multilevel amplitude modulation, and includes a data transmission unit that outputs transmission data, Based on an extinction ratio setting unit that sets an extinction ratio, a multilevel level setting unit that sets a multilevel level of the optical signal based on an input from the extinction ratio setting unit, and an output of the multilevel level setting unit And a driving unit that converts the output of the data transmission unit into a multi-value amplitude signal, and a light emitting unit that converts the output signal of the driving unit into an optical signal.

  Furthermore, the optical receiver of the present invention is an optical receiver that receives an optical signal that has been subjected to multi-level amplitude modulation, and a light receiving unit that receives the optical signal, and an output signal of the light receiving unit, from which the optical signal is extinguished. A first extinction ratio detection unit that detects a ratio; an identification level setting unit that sets an identification level for determining a multilevel level of an output signal from the light receiving unit from an output of the extinction ratio detection unit; And a multi-value level determining unit that determines the multi-value level of the output signal from the light receiving unit based on the output of the identification level setting unit.

  Furthermore, in the optical transmitter and the optical receiver according to the present invention, the optical signal is subjected to multi-level amplitude modulation at a predetermined interval, and the predetermined interval is adjacent to the multi-level when the output power of the light emitting unit is larger. It is characterized by a large distance from the level.

  Furthermore, in the optical transmitter of the present invention, the extinction ratio setting unit detects an extinction ratio of the output of the light emitting unit from an output light detecting unit that detects an output of the light emitting unit and an output of the output light detecting unit. And a second extinction ratio detection unit, wherein the multilevel level setting unit sets a multilevel level based on an output from the second extinction ratio detection unit.

  Furthermore, in the optical transmitter of the present invention, the multi-level setting unit is configured to output the multi-level level based on an output of the second extinction ratio detection unit and an output of a light emission power setting unit that sets an output power of the light emission unit. It is characterized by setting a value level.

  Furthermore, the optical transmitter of the present invention is characterized in that the light emission power setting unit sets the output power of the light emitting unit based on the light reception power of the optical receiver.

  Furthermore, in the optical transmitter of the present invention, the light emission power setting unit has a light emission power detection unit that detects the light emission power of the optical signal from the output of the output light detection unit, and the output of the light emission power setting unit is The adjustment is based on the output of the light emission power detector.

  Furthermore, the optical receiver of the present invention is characterized in that the light receiving section is an avalanche photodiode.

  Furthermore, the optical transmission system of the present invention is an optical transmission system that transmits an optical signal that has been subjected to multi-level amplitude modulation, and a first speed adjusting unit that sets a transmission speed of the optical transmitter, and the first speed adjusting unit. Based on inputs from the data transmission unit that outputs transmission data, an extinction ratio setting unit that sets an extinction ratio of the optical signal, and an extinction ratio setting unit. A multi-level setting unit for setting a multi-level, a drive unit for converting the output of the data transmission unit into a multi-level signal based on the output of the multi-level level setting unit, and an output signal of the drive unit as an optical signal An optical transmitter having a light emitting unit that converts the signal into a signal; a second speed adjusting unit that sets a transmission speed of the optical receiver; a light receiving unit that receives an optical signal from the light emitting unit; Extinction that detects the extinction ratio of the optical signal from the output signal A discrimination level setting unit for setting a discrimination level for determining a multilevel level of an output signal from the light receiving unit from an output of the detection unit, the output of the extinction ratio detection unit, and the output of the second speed arbitration unit; An optical receiver having a multi-value level determination unit that determines a multi-value level of an output signal from the light receiving unit based on an output of the identification level setting unit, and a first speed arbitration unit and a first speed adjustment unit The second speed arbitration unit determines a transmission speed between the optical transmitter and the optical receiver.

  Furthermore, in the optical transmission system of the present invention, the optical signal is subjected to multi-value amplitude modulation at a predetermined interval, and the predetermined interval is a distance between adjacent multi-value levels as the output power of the light emitting unit is larger. Is characterized by large.

  Furthermore, in the optical transmission system of the present invention, the extinction ratio setting unit detects an extinction ratio of the output of the light emitting unit from an output light detecting unit that detects the output of the light emitting unit and the output of the output light detecting unit. A second extinction ratio detection unit, and the multilevel setting unit determines a multilevel level based on an output from the second extinction ratio detection unit and an output from the first speed arbitration unit. It is characterized by setting.

  Furthermore, in the optical transmission system of the present invention, the multi-level setting unit includes an output of the second extinction ratio detection unit, an output of a light emission power setting unit that sets an output power of the light emission unit, and the first The multi-value level is set based on the output of the speed arbitration unit.

  Furthermore, the optical transmission system of the present invention is characterized in that the light emission power setting unit sets the output power of the light emission unit based on the light reception power of the optical receiver.

  Furthermore, in the optical transmission system of the present invention, the light emission power setting unit has a light emission power detection unit that detects the light emission power of the optical signal from the output of the output light detection unit, and the output of the light emission power setting unit is The adjustment is based on the output of the light emission power detector.

  Furthermore, the optical transmission system of the present invention is characterized in that the light receiving unit is an avalanche photodiode.

  Furthermore, in the optical transmitter and the optical transmission system of the present invention, the light emitting unit has a plurality of light emitting elements, the driving unit has a plurality of outputs, and each output is 1 for one multilevel. Only one output is turned on, the other outputs are turned off, and each output is connected to each one or more light emitting elements of the light emitting section.

  Furthermore, in the optical transmitter and the optical transmission system according to the present invention, the driving unit includes a plurality of current sources, the plurality of current sources output currents to the light emitting units, respectively, and the multi-level setting unit The current amounts of the plurality of current sources are adjusted, and the ON / OFF combinations of the plurality of current sources differ for each of the multi-value levels according to the output of the data transmission unit.

  According to the present invention, by detecting the extinction ratio of the multi-level optical signal output from the optical transmitter and setting the multi-level, multi-level amplitude modulation is performed in which the S / N is equal at each multi-level. An optical transmitter, an optical receiver, and an optical transmission system that can obtain an optical signal can be provided.

  Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1)
FIG. 1 is a block diagram of an optical transmitter and an optical receiver according to Embodiment 1 of the present invention. The first embodiment includes an optical transmitter 1, an optical receiver 2, a light emitting unit 10, a drive unit 11, an extinction ratio setting unit 12, a data transmission unit 13, a multilevel level setting unit 15, a light receiving unit 20, an amplification unit 21, It comprises an extinction ratio detection unit 22, a data reception unit 23, a multilevel level determination unit 25, and an identification level setting unit 28. The optical transmitter 1 and the optical receiver 2 are devices that transmit data signals using optical signals. The extinction ratio setting unit 12 sets the extinction ratio value of the optical signal 9 and inputs the extinction ratio value to the multi-level setting unit 15. As described above, when the extinction ratio is different, the multilevel level interval of the signal subjected to multilevel amplitude modulation is set differently. Therefore, the multilevel level setting unit 15 receives each input from the extinction ratio setting unit 12. The value level is set so that the S / N is equal in each multilevel level. In the optical receiver using APD, the multi-level setting unit 15 has characteristics that when the optical power is increased N times, the signal power is squared N and the noise is increased N times. Each multi-value level is set according to the multi-value number. As an example, FIG. 12 shows the setting of the multi-value level when the extinction ratio is infinite and about 7 dB (in FIG. 12, when calculating the S / N between each multi-value level, light emission is easy for the sake of simplicity. It is calculated using the noise power generated at the higher power.) When the extinction ratio is infinite, the S / N between the multilevel levels becomes equal when the emission power is set to 1: 1.6: 2 in order from the bottom. When the extinction ratio is about 7 dB, the S / N ratio becomes equal by setting different ratios of 1: 1.3: 1.6 in order from the bottom. The drive unit 11 converts the data signal from the data transmission unit 13 into a multi-value amplitude signal based on the input from the multi-value level setting unit 15 and outputs the multi-value amplitude signal to the light-emitting unit 10. The light emitting unit 10 performs electrical / optical conversion on the input signal from the driving unit 11 and outputs light to the optical receiver 2. On the other hand, the optical receiver 2 performs optical / electrical conversion by the light receiving unit 20 and converts it into an electrical signal. The extinction ratio detection unit 22 detects the extinction ratio of the optical signal 9 received by the input from the light receiving unit 20 and outputs it to the discrimination level setting unit 28. Based on the detected extinction ratio, the identification level setting unit 28 determines an identification level for data identification of the multi-level amplitude modulated signal according to the multi-level number, and outputs it to the multi-level determination unit 25. The signal converted into the electrical signal by the light receiving unit 20 is amplified by the amplification unit 21 and then input to the multilevel level determination unit 25. The signal input to the multilevel level determination unit 25 is data-identified by the identification level set by the identification level setting unit 28, converted into a data signal, and output to the data reception unit 23. With the above configuration, the optical transmitter and the optical receiver can set and determine each multi-level according to the extinction ratio, and optimally set the S / N in the optical receiver using the APD. It becomes possible to do.

  As described above, when an optical signal that has undergone multilevel amplitude modulation is transmitted by an optical transmitter / receiver that uses APD, an optimal multilevel amplitude modulated signal corresponding to the noise characteristics of APD can be obtained.

  Although the multi-level setting unit is set so that the S / N is equal, it may be set so that the error rate at each multi-level is equal.

(Embodiment 2)
FIG. 2 is a block diagram of an optical transmitter and an optical receiver according to the second embodiment of the present invention. In FIG. 2, the same components as those in FIG.

  In the first embodiment, the optical transmitter 1 is configured to set the extinction ratio. However, when there are fluctuations in the current-optical power characteristics of the light emitting unit 10 due to temperature, power supply voltage fluctuations, etc., the expected extinction There is a possibility that the optical signal is output at a value different from the ratio, and the optimum S / N (or error rate) cannot be obtained. Therefore, a part of the output of the light emitting unit 10 is detected by the light receiving unit 16, and the extinction ratio detecting unit 14 detects the extinction ratio value from the detection result. The extinction ratio detected here is the ratio between the lowest optical power level and the highest optical power level among the multilevel levels. Based on the detection result, the multi-level setting unit 15 sets each multi-level between the lowest optical power level and the highest optical power level.

  As described above, by monitoring the output of the light emitting unit 10, even when the extinction ratio of the optical output signal fluctuates, the optical receiver 2 can be set to have an optimum S / N (or error rate). .

(Embodiment 3)
3, 4 and 5 are block diagrams showing the optical transmitter and the optical receiver according to the third embodiment of the present invention. 3, 4, and 5, the same components as those in FIGS.

  In FIG. 3, since the light emission power setting unit 17 changes the light emission power of the optical transmitter 1 as necessary, the lowest light power level of the multi-value level and the highest light power level are: It is specified in the multi-value level setting unit 15. At this time, consider increasing the light emission power from a certain point in time. When increasing the light emission power, increasing the same ratio between the lowest optical power level of the multi-level and the highest optical power level is inefficient, so the lowest optical power level of the multi-level It is conceivable to increase the level of the largest optical power without changing the value. Therefore, when the light emission power is changed by the light emission power setting unit 17, the extinction ratio of the optical signal 9 changes, and as described above, the S / N (or error rate) at each multilevel level changes. End up. For this reason, in the third embodiment, the multi-value level setting unit 15 determines the multi-value level from the output of the light emission power setting unit 17 and the output of the extinction ratio detection unit 14 that detects the extinction ratio of the optical signal 9. The configuration is set.

  In FIG. 4, the light reception power of the optical receiver 2 is detected by the light reception power detection unit 24 and the result is fed back to the light emission power setting unit 17. The light emission power setting unit 17 can set the light emission power as much as necessary so that the light reception power is increased by increasing the power.

  Further, in FIG. 5, a part of the output of the light emitting unit 10 is monitored by the light receiving unit 16, the light emission power is detected from the output, and the light emission power setting unit 17 adjusts the output. Even when the output power of 10 fluctuates, the light emission power can be set to a desired value.

  As described above, the optimum S / N (or error rate) is maintained in the optical receiver 2 by controlling the setting of the multi-level setting unit 15 based on the outputs of the light emission power setting unit 17 and the extinction ratio detection unit 14. In the above, it becomes possible to change the light emission power, and optimal optical transmission can be realized.

(Embodiment 4)
6 and 7 are block diagrams showing an optical transmitter and an optical receiver according to the fourth embodiment of the present invention. 6 and 7, the same components as those in FIGS.

  In FIG. 6, the optical transmitter 1 and the optical receiver 2 correspond to a plurality of transmission rates. For example, although a quaternary signal is used at a transmission rate of 100 Mbps, at a transmission rate of 200 Mbps, the multi-value number is changed according to the transmission rate by doubling the multi-value number to obtain an 8-value signal. In FIG. 6, when the optical transmitter 1 and the optical receiver 2 transmit, before the transmission, information about the transmission speeds corresponding to each of the speed arbitration units 18 and 26 is transmitted as optical signals or electrical signals. The transmission speed is determined by transmission using a signal control signal 99. When the transmission speed is determined, the multi-value number to be used is determined according to the transmission speed. In the optical transmitter 1, the speed arbitration unit 18 inputs the multi-value number to the multi-value level setting unit 15, and also receives the optical signal. In the device 2, the speed arbitration unit 26 inputs a multi-value number to the identification level setting unit 28. The multi-value level setting unit 15 sets a multi-value level from the output of the extinction ratio detection unit 14 and the output of the speed arbitration unit 18. Similarly, the identification level setting unit 28 sets the identification level from the output of the extinction ratio detection unit 22 and the output of the speed arbitration unit 26. Further, in FIG. 7, the multi-value level setting unit 15 sets the multi-value level in consideration of the output of the light emission power setting unit 17 as in the third embodiment.

  As described above, when the optical transmitter 1 and the optical receiver 2 support a plurality of transmission speeds, the multilevel level can be set in consideration of the necessary multilevel number, extinction ratio, and light emission power. Therefore, the optical receiver 2 can be set to have an optimum S / N or an error rate.

(Embodiment 5)
8 and 9 are block diagrams showing an optical transmitter and an optical receiver according to the fifth embodiment of the present invention. 8 and 9, the same components as those in FIGS. 1 to 7 are denoted by the same reference numerals, and the description thereof is omitted.

  FIG. 8 shows a configuration when the multi-value number is four. When “00”, “01”, “10”, “11” is input as binary data, the data transmission unit 13 outputs a signal to only one of the four outputs. The multi-level setting unit 15 sets a current amount of a current source provided in the driving unit 11. Here, the current amounts of the respective current sources are set to A, X, Y, and Z as shown in FIG. The light emitting unit 10 includes a plurality of light emitting elements, and one light emitting element is connected to each output of the driving unit 11. At this time, let us consider a case where “00” is input to the data transmission unit 13. When “00” is input, the data transmission unit 13 outputs a voltage signal equal to or lower than Vref to the upper left input terminal B1 of the driving unit 11, and the voltage equal to or lower than Vref to the remaining input terminals of B2, B3, and B4. Output a signal. Since the input terminal B1 is equal to or lower than Vref, the differential circuit having the input terminal B1 causes a current amount of A to flow through one light emitting element of the light emitting unit 10, and the other differential circuit supplies current to the light emitting element. Do not flush. Similarly, when “01” is input to the data transmission unit 13, only the differential circuit having the input terminal B2 allows a current to flow through the light emitting element. With the above configuration, each current of the light emitting unit 10 has a current amount of A in the light emitting unit when “01”, X when “01”, Y when “10”, and Z current when “11”. It will flow to the light emitting element. Here, the multi-value level setting unit 15 sets the current amounts A, X, Y, and Z of each current source as described in the first to fourth embodiments, so that the extinction ratio, the light emission power, and the multi-value are set. It is possible to set a multilevel level in consideration of the number.

  As described above, it is possible to obtain an optical transmitter that outputs an optical signal that has been subjected to multi-level amplitude modulation and that has an optimum S / N (or error rate) in the optical receiver 2.

  In FIG. 8, the multi-value number 4 is illustrated. However, if the multi-value number 8 is provided, the same effect can be obtained by providing eight differential circuits. By configuring the numbers together, multi-value amplitude modulation with different multi-value numbers becomes possible.

  Note that one light emitting element is connected to each differential circuit, but the same number of light emitting elements may be connected, such as two by three.

  In addition, although it was set as the structure by which one light emitting element was connected to each differential circuit, even if the number of light emitting elements connected to each operation circuit is not the same number by adjusting the electric current amount of each differential circuit, Any configuration may be used as long as the total optical output is subjected to multi-value amplitude modulation.

(Embodiment 6)
10 and 11 are block diagrams showing an optical transmitter and an optical receiver according to the sixth embodiment of the present invention. 10 and 11, the same components as those in FIGS. 1 to 9 are denoted by the same reference numerals, and the description thereof is omitted.

  FIG. 10 illustrates a configuration when the multi-value number is four. The data transmitter 13 outputs 2-bit parallel signals (D1, D2) of binary data (in FIG. 10, the output of the data transmitter 13 and the output of the AND operation are the potentials at which logic “1” is lower than Vref. Note that logic “0” is a potential higher than Vref). The multi-level setting unit 15 sets a current amount of a current source provided in the driving unit 11. Here, the current amount of each current source is set to A, X, Y, and Z as shown in FIGS. When the data transmission unit 13 outputs “0, 0” as “D1, D2,” signals higher than Vref are input to the input terminals B1, B2, B3 of the drive unit 11, so Only the current amount A by the current source installed in the light source becomes the drive current of the light emitting unit 10. Here, the current source at the lower right of the driving unit 11 causes the light emitting unit 10 to emit light to some extent even at the lowest light emitting level, whereas the frequency response characteristic becomes slow when the driving current is small. The frequency response characteristics can be improved. FIG. 11 shows the change of the drive current I with respect to the combination of (D1, D2). By adjusting the values of the current amounts A, X, Y, and Z of each current source, as shown in the right of FIG. 11, driving is performed such that the interval between adjacent multilevel levels increases as the emission power increases. Is possible.

  In the sixth embodiment, the driving current is changed depending on the combination of the current sources, and the configuration is different from the configuration in which only one current source of the fifth embodiment operates. It is also possible to configure so that only one current source operates as shown in FIG.

  The optical transmitter and the optical receiver according to the present invention can reduce the S / N at each multilevel even when an optical receiver using an APD is used in data transmission using an optical signal subjected to multilevel amplitude modulation. It has characteristics that can be set equally, and is useful as an input / output interface for devices and apparatuses that perform data transmission using optical transmission.

The block diagram which shows the structure of the optical transmitter and optical receiver of this invention The block diagram which shows the structure of the optical transmitter and optical receiver of this invention The block diagram which shows the structure of the optical transmitter and optical receiver of this invention The block diagram which shows the structure of the optical transmitter and optical receiver of this invention The block diagram which shows the structure of the optical transmitter and optical receiver of this invention The block diagram which shows the structure of the optical transmitter and optical receiver of this invention The block diagram which shows the structure of the optical transmitter and optical receiver of this invention The block diagram which shows the structure of the optical transmitter of this invention Drive current-light emission power characteristics and output waveform diagram of the optical transmitter of the present invention The block diagram which shows the structure of the optical transmitter of this invention Relationship diagram and output waveform diagram of transmission data-driving current of the optical transmitter of the present invention Output waveform diagram of optical transmitter of the present invention Output waveform diagram of conventional optical transmitter

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical transmitter 2 Optical receiver 10 Light emission part 11 Drive part 12 Extinction ratio setting part 13 Data transmission part 14 Extinction ratio detection part 15 Multi-value level setting part 16 Light receiving part 17 Light emission power setting part 18 Speed adjusting part 20 Light receiving part 21 Amplification unit 22 Extinction ratio detection unit 23 Data reception unit 24 Light reception power detection unit 25 Multilevel level determination unit 26 Speed arbitration unit 28 Discrimination level setting unit 9 Optical signal 99 Optical (electrical) signal

Claims (20)

An optical transmitter for outputting a multi-value amplitude modulated optical signal,
A data transmission unit for outputting transmission data;
An extinction ratio setting unit for setting an extinction ratio of the optical signal;
Based on an input from the extinction ratio setting unit, a multi-value level setting unit that sets a multi-value level of the optical signal;
A drive unit that converts the output of the data transmission unit into a multi-value amplitude signal based on the output of the multi-level setting unit;
An optical transmitter comprising: a light emitting unit that converts an output signal of the driving unit into an optical signal. An optical receiver for receiving a multi-value amplitude modulated optical signal,
A light receiving unit for receiving the optical signal;
A first extinction ratio detection unit that detects an extinction ratio of the optical signal from an output signal of the light receiving unit;
An identification level setting unit for setting an identification level for determining a multilevel level of an output signal from the light receiving unit from the output of the extinction ratio detection unit;
An optical receiver comprising: a multi-value level determination unit that determines a multi-value level of an output signal from the light receiving unit based on an output of the identification level setting unit.   The optical signal is subjected to multi-level amplitude modulation at a predetermined interval, and the predetermined interval has a larger interval between adjacent multi-level levels as a multi-level level having a larger output power of the light emitting unit. Item 5. The optical transmitter according to Item 1.   The optical signal is subjected to multi-level amplitude modulation at a predetermined interval, and the predetermined interval has a larger interval between adjacent multi-level levels as a multi-level level having a larger output power of the light emitting unit. Item 3. The optical receiver according to Item 2. The extinction ratio setting unit includes: an output light detection unit that detects an output of the light emitting unit; and a second extinction ratio detection unit that detects an extinction ratio of the output of the light emitting unit from the output of the output light detection unit. Have
4. The optical transmitter according to claim 1, wherein the multi-level setting unit sets a multi-level based on an output from the second extinction ratio detector. 5.   The multi-value level setting unit sets the multi-value level based on an output of the second extinction ratio detection unit and an output of a light emission power setting unit that sets an output power of the light emitting unit. The optical transmitter according to claim 5.   The optical transmitter according to claim 6, wherein the light emission power setting unit sets an output power of the light emission unit based on a light reception power of the optical receiver. The light emission power setting unit has a light emission power detection unit that detects the light emission power of the optical signal from the output of the output light detection unit,
The optical transmitter according to claim 6, wherein the output of the light emission power setting unit is adjusted based on the output of the light emission power detection unit.   The optical receiver according to claim 2, wherein the light receiving unit is an avalanche photodiode. In an optical transmission system for transmitting a multi-value amplitude modulated optical signal,
A first speed arbitration unit for setting a transmission speed of the optical transmitter;
A data transmission unit that outputs transmission data at a transmission rate based on the output of the first speed arbitration unit;
An extinction ratio setting unit for setting an extinction ratio of the optical signal;
Based on an input from the extinction ratio setting unit, a multi-value level setting unit that sets a multi-value level of the optical signal;
Based on the output of the multilevel level setting unit, a drive unit that converts the output of the data transmission unit into a multilevel signal;
An optical transmitter having a light emitting unit that converts an output signal of the driving unit into an optical signal;
A second speed arbitration unit for setting a transmission speed of the optical receiver;
A light receiving unit for receiving an optical signal from the light emitting unit;
An extinction ratio detection unit that detects an extinction ratio of the optical signal from an output signal of the light receiving unit;
An identification level setting unit for setting an identification level for determining a multilevel level of an output signal from the light receiving unit from the output of the extinction ratio detection unit and the output of the second speed arbitration unit;
An optical receiver having a multi-value level determination unit that determines a multi-value level of an output signal from the light receiving unit based on the output of the identification level setting unit;
An optical transmission system, wherein a transmission rate between an optical transmitter and an optical receiver is determined by a first speed arbitration unit and a second speed arbitration unit.   The optical signal is subjected to multi-level amplitude modulation at a predetermined interval, and the predetermined interval has a larger interval between adjacent multi-level levels as a multi-level level having a larger output power of the light emitting unit. Item 11. The optical transmission system according to Item 10. The extinction ratio setting unit includes: an output light detection unit that detects an output of the light emitting unit; and a second extinction ratio detection unit that detects an extinction ratio of the output of the light emitting unit from the output of the output light detection unit. Have
The multi-level setting unit sets a multi-level based on an output from the second extinction ratio detection unit and an output from the first speed arbitration unit. 11. The optical transmission system according to 11.   The multi-level setting unit is based on the output of the second extinction ratio detection unit, the output of the light emission power setting unit for setting the output power of the light emitting unit, and the output of the first speed arbitration unit, The optical transmission system according to claim 12, wherein the multi-value level is set.   The optical transmission system according to claim 13, wherein the light emission power setting unit sets an output power of the light emission unit based on a light reception power of the optical receiver. The light emission power setting unit has a light emission power detection unit that detects the light emission power of the optical signal from the output of the output light detection unit,
14. The optical transmission system according to claim 13, wherein the output of the light emission power setting unit is adjusted based on the output of the light emission power detection unit.   The optical transmission system according to claim 10, wherein the light receiving unit is an avalanche photodiode. The light emitting unit has a plurality of light emitting elements,
The drive unit has a plurality of outputs, and each output is turned on only for one multi-value level, the other outputs are turned off, and each output is 1 each of the light emitting unit. The optical transmitter according to claim 1, wherein the optical transmitter is connected to at least two light emitting elements. The light emitting unit has a plurality of light emitting elements,
The drive unit has a plurality of outputs, and each output is turned on only for one multi-value level, the other outputs are turned off, and each output is 1 each of the light emitting unit. The optical transmission system according to claim 10, wherein the optical transmission system is connected to at least two light emitting elements. The drive unit has a plurality of current sources,
The plurality of current sources each output a current to the light emitting unit,
The multi-value level setting unit adjusts the amount of current of the plurality of current sources,
9. The combination of ON / OFF of the plurality of current sources is different for each of the multi-value levels according to the output of the data transmission unit. 9. Optical transmitter. The drive unit has a plurality of current sources,
The plurality of current sources each output a current to the light emitting unit,
The multi-value level setting unit adjusts the amount of current of the plurality of current sources,
The optical transmission system according to any one of claims 10 to 16, wherein a combination of ON / OFF of the plurality of current sources is different for each of the multilevel levels according to an output of the data transmission unit.

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