JPH08223121A - Optical reception equipment - Google Patents

Abstract

PURPOSE: To receive an errorless high-speed digital optical signal by outputting the voltage value based on the division ratio of plural slice levels as a slice level and taking the output or a comparator as a digital electric signal output. CONSTITUTION: A photo diode 11 converts light to electricity, and an amplifier 12 converts the current to a voltage. Since frequency bands of the diode 11 and the amplifier 12 are sufficiently high, an output waveform 44a of the amplifier 12 exhibit the pulsation approximately equal to that or the light waveform. The output of the amplifier 12 is inputted to three comparators 13, 14, and 15 different by slice levels to output digital waveformes 45a, 46a, and 47a. Then, the output of the comparator 13 has the AC component cut through a filter circuit 18, and a voltage corresponding to the duty ratio of the output waveform 45a is detected ana is inputted to the positive input terminal of a differential amplifier 16. The voltage set by a variable resistance 20 is inputted to the negative input terminal, and the output is used as the slice level of the comparator 13 as it is.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical receiver used for digital information transmission using an optical fiber.

[0002]

2. Description of the Related Art In information transmission through an optical fiber, a laser diode capable of high-speed digital modulation is generally used as a transmitting element, and a photodiode is used as a light receiving element to transmit light modulated by an electric signal. .

A conventional optical transmission and reception device will be described below. FIG. 6 is a block diagram showing the configuration of a conventional optical transmission and reception device. In FIG. 6, 1 is a laser drive circuit, 2 is a laser diode, and 3 is a lens, and these elements constitute an optical transmitter. 4 is an optical fiber, 5 is a photodiode, 6 is an amplifier, 7 is a filter circuit that outputs a slice level, 8 is a comparator that compares the slice level with the amplifier 6 and outputs a binarized signal, and 9 is an output buffer. , These elements constitute an optical receiver.

FIG. 7 is a waveform diagram showing operation waveforms of respective parts of the conventional optical device and receiving device. In FIG. 7, 34 is an input signal waveform input to the optical transmitter, 35 is a current waveform output from the laser drive circuit 1, and 36 is a laser diode 2.
Is the optical waveform output by the optical fiber 4 and 37a and 37b.
Is an optical waveform output to the optical receiving device through the optical path, 38a and 38b are output waveforms of the amplifier 6, 39a and 39b are slice levels, and 40a and 40b are output waveforms of the comparator 8.

Operation of the conventional device is shown in FIGS. 6 and 7.
Will be explained. The digital electric signal to be transmitted is serialized and input to the optical transmitter. The laser drive circuit 1 modulates the current flowing through the laser diode 2 in substantially the same shape as the input signal waveform 34, and the current has a waveform 35. The laser diode 2 emits little light when the input digital electric signal is "0" because the current flowing therethrough is near the threshold value when the input digital electric signal is "0". The digitally modulated optical waveform 36 is condensed by the lens 3 and input to the optical fiber 4.

Pulsations peculiar to the laser diode 2 occur in the digitally modulated optical waveform 36, and those in which the pulsations gradually converge are called relaxation oscillations, and those in which the pulsations last are called self-pulsation. The amplitude of these pulsations may be higher than the original amplitude of the data, but since the frequency of the pulsations is generally sufficiently higher than the data rate of the digital transmission signal, it is a practical problem due to the frequency band limitation effect of the transmission path. Often does not become. That is, the optical fiber 4 to be used has a high frequency limiting effect called dispersion, and the longer the distance, the lower the transmittable frequency band. Therefore, the pulsation of the optical waveform 37a after passing through the long-distance optical fiber 4 is reduced, and a waveform close to the original input signal waveform 34 is obtained. The light passing through the optical fiber 4 is guided to the light receiving section of the optical receiving device. The photodiode 5 generates a current proportional to the received light, which is current-voltage converted and amplified by the transimpedance type amplifier 6. The output waveform of the amplifier 6 has almost the same shape as the input light waveform as seen at 38a in FIG.

The comparator 8 outputs the output waveform 38 of the amplifier 6.
a and the slice level 39a are compared and binarized. Two
A slice level 39a used for quantification is obtained by averaging the output waveform 38a of the amplifier 6 by the filter circuit 7. Since the transmitted digital signal is preset so that the data “0” and the data “1” are generated at the same probability, the slice level using the average value is automatically set near the center of the output waveform 38a of the amplifier 6. Is set to. It can be seen that the output 40a of the comparator 8 is output to the outside of the optical receiving device through the buffer 9 and the waveform is almost equal to the input digital electric signal to the optical transmitting device, and information can be transmitted without error.

[0008]

However, in the configuration of the conventional optical receiving apparatus, the pulsation of the optical waveform 36 output from the laser diode 2 is attenuated by the frequency band limiting effect due to the dispersion of the long optical fiber 4, When transmission is performed using the short optical fiber 4, the optical waveform 37b having pulsation is directly input to the optical receiving device because the frequency band limiting effect of the optical fiber 4 is not present, and the output waveform of the amplifier 6 becomes as shown in 38b. Slice level 3 at this time
Since 9 is higher than the bottom of the pulsating portion of the output waveform 38b of the amplifier 6, the output waveform of the comparator 8 has a pulse in response to the pulsating portion as shown at 40b, which causes a serious data error.

In order to remove the error, it is necessary to remove the pulsating component of the input waveform before the input to the comparator 8, and the frequency characteristic of the amplifier 6 of the optical receiver is lowered or the output of the amplifier 6 is reduced. A method of inserting a low-pass filter between the input of the comparator 8 and the pulsation is adopted. However, in either case, there is a great possibility of degrading the original signal component as well, especially those that have been band-limited for short-distance transmission will further reduce the transmission band in long-distance transmission, so the data of the information to be transmitted will decrease. The performance was deteriorated, for example, the rate had to be reduced and used. Alternatively, when the length of the optical fiber 4 to be used is long, one having a high frequency characteristic is used, and when the length of the optical fiber 4 is short, one having a low frequency characteristic is used. It was necessary to prepare an optical receiver according to the waveform.

Therefore, the present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide an optical receiving apparatus capable of receiving a high-speed digital optical signal without error regardless of the length of the optical fiber or the received optical waveform. I am trying.

[0011]

In order to achieve the above object of the present invention, a photodiode for converting a transmission optical signal into a current, an amplifier for amplifying an output of the photodiode, an output of the amplifier and a first amplifier, The duty ratios of the outputs of the first, second, and third comparators and the first comparator, which output the binarized signal by comparing with the second and third slice levels, respectively, become the predetermined first value. As described above, the first slice level control circuit for controlling the first slice level and the second slice level for controlling the second slice level so that the duty ratio of the output of the second comparator becomes a predetermined second value. A slice level control circuit; and a third slice level control circuit for outputting an intermediate value between the first and second slice levels as a third slice level.
The output of the comparator is used as a digital electric signal output.

[0012]

With the above-described structure, the present invention can output a digital reception signal without error even when the pulsation peculiar to the laser diode appears in the reception waveform due to a factor such as a short optical fiber. In addition, error-free high-speed digital signal transmission can be performed without depending on the length of the optical fiber.

[0013]

Embodiments of the present invention will be described below. FIG. 1 is a block diagram showing the configuration of the optical receiving apparatus of the first embodiment of the present invention. In FIG. 1, 11 is a photodiode,
Reference numeral 12 is a transimpedance type amplifier. 1
Reference numerals 3, 14 and 15 are comparators, 16 and 17 are differential amplifiers, 18 and 19 are filter circuits, 20 and 21 are variable resistors, 22 is a voltage divider, and 23 is an output buffer. The filter circuit 18, the variable resistor 20 and the differential amplifier 16 are the first
Of the slice level control circuit of the filter circuit 1
9, the variable resistor 21, and the differential amplifier 17 constitute a second slice level control circuit, and the voltage divider 22 constitutes a third slice level control circuit.

FIG. 2 is a waveform diagram showing the operation of the optical receiving apparatus of the first embodiment of the present invention. In FIG. 2, 44a and 44b are output waveforms of the amplifier 12, 45a and 45b are output waveforms of the comparator 13, 46a and 46b are output waveforms of the comparator 14, 47a and 47b are output waveforms of the comparator 15, and 48a and 48b are differential. An output waveform of the amplifier 16 and a slice level input to the comparator 13, 49a and 49b are output waveforms of the differential amplifier 17 and a slice level input to the comparator 14, and 50a and 50b are output waveforms of the voltage divider 22. Which is the slice level input to the comparator 15. In the reference numerals of FIG. 2, 44a, 45a, 46
The waveforms denoted by a, 47a, 48a, 49a, and 50a are waveforms when the optical fiber is short, and 44b, 45b, and 46a.
The waveforms indicated by b, 47b, 48b, 49b, and 50b are waveforms when the optical fiber is long.

The operation will be described below. First, a case where the pulsation of received light is large when the optical fiber is relatively short will be described. The photodiode 11 converts light into a current, and the transimpedance type amplifier 12 performs current-voltage conversion. Photodiode 11 and amplifier 1
Since the frequency band of 2 is sufficiently high, the output waveform 44a of the amplifier 12 exhibits pulsation almost equal to the optical waveform. Amplifier 12
Output is input to three comparators 13, 14 and 15 having different slice levels, and 45a,
The digital waveforms shown at 46a and 47a are output. The AC component of the output of the comparator 13 is cut through the filter circuit 18, and the voltage corresponding to the duty ratio of the output waveform 45a of the comparator 13 is detected. The detected duty ratio is input to the positive input terminal of the differential amplifier 16,
On the other hand, the voltage set by the variable resistor 20 is input to the negative input terminal of the differential amplifier 16. The output of the differential amplifier 16 is used as it is as the slice level of the comparator 13. If the output voltage of the filter circuit 18 is lower than the set voltage of the variable resistor 20, the output of the differential amplifier 16 decreases and the slice level 48a of the comparator 13 decreases. Then, the duty ratio of the output waveform of the comparator 13 decreases and the output of the filter circuit 18 increases. In this way, the comparator 13 and the filter circuit 1
8. The feedback circuit is constituted by the differential amplifier 16, and the duty ratio of the output waveform 45a of the comparator 13 can be controlled to a predetermined value by adjusting the variable resistor 20. On the other hand, the comparator 14 and the filter circuit 1
Similarly, a feedback circuit is configured by 9, the differential amplifier 17, and the variable resistor 21, and the duty ratio of the output waveform 46a of the comparator 14 can be controlled to a predetermined value by adjusting the variable resistor 21.

The effect of controlling the duty ratio to a predetermined value will be described with reference to FIG. FIG. 3 is a graph showing the relationship between the slice level and the duty ratio of the optical receiver according to the first embodiment of the present invention. In FIG. 3, the horizontal axis represents the slice level and the vertical axis represents the duty ratio. The output waveform of the amplifier 12 is shown in the horizontal direction at the top of the graph corresponding to the fact that the upper and lower sides of the slice level are shown on the horizontal axis.

The operation of the optical receiver when the optical fiber is short and the pulsation appears in the received waveform will be described with reference to FIG. Reference numeral 44a is an output waveform of the amplifier 12, and a curve representing the slice level versus duty ratio at this time is 51a. When the slice level is lower than the output waveform of the amplifier 12, that is, when the operating point is on the left side of the curve 51a, the duty ratio is 100%. Conversely, when the slice level is sufficiently higher than the output waveform of the amplifier 12, that is, when the operating point is on the right side of the curve 51a, the duty ratio is 0%. When the slice level is applied to a portion of the output waveform of the amplifier 12 where there is no pulsation, the duty ratio is in the vicinity of 50% and the inclination is small. At this time, the output of the comparator can output binary data having no error.

Here, the output duty ratio of the comparator 13 is set to 30% by the variable resistor 20. In FIG. 3, 52a is an operating point of the comparator 13,
The slice level is applied to the pulsating portion of the output waveform 44a of the amplifier 12. The variable resistor 21 is set so that the duty ratio of the output of the comparator 14 is 70%. In FIG. 3, 53a is an operating point of the comparator 14, and the slice level is applied to the bottom portion of the output waveform 44a of the amplifier 12. Here, the slice level input to the comparator 15 is set by the voltage divider 22 to positions 54a at equal intervals from the slice level of the comparator 13 and the slice level of the comparator 14, and the amplifier 1
The output of the comparator can output binarized data without error because it is applied to a portion of the output waveform of No. 2 where there is no pulsation. Only the output of the error-free comparator 15 out of the three comparators is output to the outside through the output buffer 23.

Next, the operation when the optical fiber is long is shown in FIG.
Will be explained. Reference numeral 44b denotes an output waveform of the amplifier 12, in which the pulsating portion that appeared when the optical fiber is short disappears, the rising and falling edges become gentle, and the waveform amplitude becomes small. A curve representing the slice level versus duty ratio at this time is 51b. The setting of the variable resistors 20 and 21 is 30% and 70%, respectively, but the operating points of the comparators 13 and 14 are 5 and 5, respectively.
2b and 53b. The slice level input to the comparator 15 is set by the voltage divider 22 at positions 54b that are equidistant from the slice level of the comparator 13 and the slice level of the comparator 14, and is located at approximately the center of the output waveform of the amplifier 12. It is possible to output a binarized signal that is hardly affected and has no error.

As described above, even when the lengths of the optical fibers greatly differ, it is possible to receive a high-speed digital optical signal without changing the circuit settings.

FIG. 4 is a block diagram showing the configuration of the optical receiving apparatus of the second embodiment of the present invention, and FIG. 5 is a waveform diagram showing the same operation. In FIG. 4, 11 is a photodiode, 12 is a transimpedance type amplifier, 14 and 15 are comparators, 17 is a differential amplifier, 19 is a filter circuit, 2
Reference numeral 1 is a variable resistor, 22 is a voltage divider, and 23 is an output buffer.

In FIG. 5, 44a and 44b are output waveforms of the amplifier 12, 55a and 55b are comparators 1.
4 output waveforms, 56a and 56b are comparators 15
, 57a and 57b are output waveforms of the differential amplifier 17 and are slice levels input to the comparator 14, and 58a and 58b are outputs of the voltage divider 22 and are slice levels input to the comparator 15. In FIG. 5, 44a, 45a, 56a, 57a, 58a
Is a waveform when there is a large pulsation in the optical reception waveform due to the short optical fiber, and 44b, 45b, 56b, 57
b and 58b are waveforms when the optical reception waveform has almost no pulsation because the optical fiber is long.

The operation will be described below. The operations of the photodiode 11 and the amplifier 12 shown in FIG. 4 are exactly the same as those in the first embodiment, and the output waveform 44a of the amplifier 12 is the same as that in the first embodiment. Amplifier 12
The output of is input to two comparators 14 and 15 having different slice levels, and 55a and 5a, respectively.
The digital waveform shown in 6a is output. Comparator 14
The AC component of the output is cut through the filter circuit 19, and the voltage corresponding to the duty ratio of the output waveform 55a of the comparator 14 is detected. The detected duty ratio is input to the positive input terminal of the differential amplifier 17, while the voltage set by the variable resistor 21 is input to the negative input terminal of the differential amplifier 17. The output of the differential amplifier 17 is directly used as the slice level 57a of the comparator 14. A feedback circuit is configured by the comparator 14, the filter circuit 19, and the differential amplifier 17, and the duty ratio of the output waveform of the comparator 14 is variable resistor 21.
Controlling to the value set by is almost the same as that of the component of the same name described in the first embodiment.

The relationship between the slice level and the duty ratio of the output waveform is exactly the same as that shown in FIG. If the duty ratio of the output waveform of the comparator 14 set by the variable resistor 21 is set to 60% to 90%, the slice level 57a of the comparator 14 can follow almost the bottom portion of the output waveform 44a of the amplifier 12.
In this embodiment, the duty ratio of the comparator 14 is about 70.
It is set to%.

The first input terminal of the voltage divider 22 is connected to the output of the differential amplifier 17, the second input terminal is connected to the positive power supply voltage, and the output terminal of the voltage divider outputs the slice level of the comparator 15. Since the voltage difference between the first input terminal and the output terminal of the voltage divider 22 is sufficiently smaller than the voltage difference between the second input terminal and the output terminal, the operation of the voltage divider 22 is the first input voltage of the differential amplifier. It is approximately equal to the output of 17 plus a certain amount of offset. That is, the slice level 58a of the comparator 15 is offset slightly above the bottom of the output waveform 44a of the amplifier 12 and does not affect the pulsating portion, so the comparator 15 outputs the output waveform 56a without error. The output waveform 56a of the comparator 15 is provided with sufficient voltage level and current supply capability through the output buffer 23 and is output as digital data to the outside of the optical receiving device.

On the other hand, even when the optical fiber is long, the slice level 57b of the comparator 14 is the output waveform 4 of the amplifier 12.
4b, the slice level 58b of the comparator 15 is arranged above the bottom portion of the output waveform 44b of the amplifier 12 with an offset. 12 does not exceed the peak of the output waveform 44b.
b can be output.

As described above, in the present embodiment, the fluctuation of the power level of the input light needs to be limited in order to add a certain amount of offset to the bottom portion to make the slice level, and it is necessary to limit the output light power of the optical transmitter to be used. Although there are restrictions and the like, it is similar to the first embodiment that it is possible to sufficiently cope with the fluctuation of the waveform caused by the change of the length of the optical fiber.

[0028]

As described above, according to the present invention, high-speed digital data can be output without error even when pulsation appears in the optical reception waveform due to factors such as a short optical fiber. Further, it is possible to configure an optical receiving device that can cope with the length of the optical fiber without changing the main body.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an optical receiving device according to a first embodiment of the present invention.

FIG. 2 is a waveform diagram showing the operation of the optical receiving apparatus according to the first embodiment of the present invention.

FIG. 3 is a graph showing the relationship between the slice level and the duty ratio of the optical receiver according to the first embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration of an optical receiving device according to a second embodiment of the present invention.

FIG. 5 is a waveform diagram showing the operation of the optical receiving apparatus according to the second embodiment of the present invention.

FIG. 6 is a block diagram showing a configuration of a conventional optical transmission and reception device.

FIG. 7 is a waveform diagram showing operation waveforms of respective parts of a conventional optical transmission and reception device.

[Explanation of symbols]

 11 Photodiode 12 Amplifier 13, 14, 15 Comparator 16, 17 Differential Amplifier 18, 19 Filter Circuit 20, 21 Variable Resistor 22 Voltage Divider 23 Output Buffer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G02B 6/42 H01L 31/10

Claims (2)

[Claims] 1. An optical receiver for converting a digital transmission optical signal into a digital electric signal and outputting the digital electric signal, the photodiode converting the digital transmission optical signal into a current, and an amplifier for amplifying the output of the photodiode. , A first, a second and a third comparator which respectively compare the amplifier output with the first, second and third slice levels and output a binarized signal, and a duty of the output of the first comparator. A first slice level control circuit that controls the first slice level so that the ratio becomes a predetermined first value, and a duty ratio of the output of the second comparator becomes a predetermined second value. A second slice level control circuit for controlling the second slice level, and a voltage value according to a predetermined division ratio between the first slice level and the second slice level. And a third slice level control circuit for outputting a slice level, the light receiving device characterized by the output of the third comparator to the digital electrical signal output. 2. An optical receiving device for converting a digital transmission optical signal into a digital electric signal and outputting the digital electric signal, the photodiode converting the digital transmission optical signal into a current, and an amplifier for amplifying the output of the photodiode. , A bottom detection circuit that detects the bottom of the output waveform of this amplifier corresponding to a low light emission level, an offset circuit that adds a fixed amount of offset to the output of this bottom detection circuit, and the output of the amplifier and the output of the offset circuit. An optical receiving device comprising: a comparator for comparing and outputting a binarized signal, wherein an output of the comparator is a digital electric signal output.