KR101953861B1 - Optical receiving apparatus having improved receiving performance for multilevel optical signal and method thereof - Google Patents

Abstract

The present invention relates to an optical reception apparatus improved in multi-level optical signal reception performance, which can optimize the reception performance by grasping reception characteristics of an optical signal received at multi-levels in an installation environment without a separate measuring device, and to a method thereof. The optical reception apparatus automatically estimates a reference voltage set for optimal multi-level classification in accordance with a characteristic of a used avalanche photodiode in a state where the optical reception apparatus is installed without a separate precision measuring instrument or a connection configuration for measurement in an actual installment environment by setting a limit reference voltage of a limit amplifier configured in a reception unit to provide optimal reception performance considering the characteristic of the avalanche photodiode of a current optical reception apparatus by simply performing the optical reception apparatus as required after actual installation.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an optical receiving apparatus and a method for receiving multilevel optical signals,

The present invention relates to an optical receiving apparatus and method with improved multi-level optical signal reception performance, and more particularly, to a multi-level optical receiving apparatus and a method for receiving multi-level optical signals, Level optical signal reception performance is improved.

With the introduction of 5G mobile communication, the spread of high-quality services, and the spread of IoT (Internet of Things) equipment, the communication capacity required by the subscriber's network is increasing rapidly. Therefore, the bandwidth required for optical communication used in the subscriber network and the metro network is also increasing rapidly.

In this way, the optical communication system that requires a steep increase in the required bandwidth is used. However, the NRZ (NonReturn to Zero) modulation method is used, in which the intensity of the optical signal is divided into two levels of '1' or '0'. However, when NRZ communication is used for 25 Gigabit, 50 Gigabit and 100 Gigabit broadband communication, it is difficult to develop due to bit switching time of the femtosecond level. Due to this background, various studies to apply a modulation scheme (for example, PAM (Pulse Amplitude Modulation) 4 or PAM 8) using a multilevel optical signal capable of transmitting a plurality of data through one signal transmission It is progressing.

Passive optical network (PON) technology, which is widely used as a subscriber network technology in optical communication, is configured to configure a high-speed subscriber network and is configured to process simultaneous access of a plurality of subscribers through a time division scheme or a wavelength division scheme. Among these methods, a cost-effective time-sharing method is mainly used, and EPON (Ethernet PON) according to IEEE (Institute of Electrical and Electronics Engineers) 802.3av / ah, International Telecommunication Union-Telecommunication Standardization Sector (ITUT) G.984 / GPON (Gigabit PON) according to 7 is representative.

In the configuration of such a PON, a single optical line terminal (OLT) installed in the telephone company and an ONT (Optical Network Terminal) or an ONU (Optical Network Unit) of a plurality of subscribers are connected to a remote node, (Point-to-Multipoint) network structure through an optical splitter (using an optical splitter).

1, the OLT 10 and the ONT 20 are connected to each other through an optical line, and the direct communication through the optical line is performed by the optical transceivers 11 and 21.

Although there are various factors affecting the communication quality of the optical network, the characteristics of the optical transceiver laser diode and the characteristics of the photodiode of the optical transceiver are considered as the factors directly determining the communication quality.

As shown in the figure, the transceivers 11 and 21 include a transmitter 11a and a transmitter 21a for providing a light source of a wavelength set by a laser diode, a laser diode And receiving units 11b and 21b for receiving light of the set wavelength provided.

The laser diode of the transmitter of the optical transceiver has characteristic curves for the slope of the output and the saturation current (Isat) according to the threshold current (Ith) and the input current, which are different for each manufacturer and individual product, As a result, the characteristic curves change as the threshold current increases and the slope decreases.

Further, in the case of a photodiode in which the output of the laser diode having such a deviation is received through the optical line and classified according to the level, the photocurrent output characteristic according to the received optical power differs from one manufacturer to another. In particular, Avalanche Photo Diode (APD), which has high efficiency and high sensitivity and can operate at high speed, is used for high speed signal reception of Gbps or higher. Such avalanche photodiodes rapidly expand the response to photoelectrons due to their structural characteristics So that different reception characteristics are obtained even by a slight process variation.

Currently, the optical transceiver that is commonly used is a modulation scheme based on a non-return-to-zero (NRZ) code of 0 and 1, and the output can be divided into 0 or 1. Therefore, a linear section of the characteristic curve of the laser diode is selected and used as a usage section. Since the laser diode used for the purpose of responding to the NRZ code must have a certain linear range, a linear characteristic of the laser diode is not good depending on the manufacturer or the product, and the avalanche photodiode is also similar to the NRZ modulation The present invention is intended to provide a photocurrent differentiated by a high speed response, so that even if there is some variation in the photocurrent output characteristic according to the received optical power, it is used as a product of the same standard.

However, in order to achieve higher-speed communication, a PAM (Pulse Amplitude Modulation) -4 / 8, which can transmit 2-bit or 3-bit data as one optical signal by dividing a signal to be transmitted to the laser diode into 4 levels or 8 levels, Modulation scheme is also emerging. In this case, there arises a problem of using a high-priced product having a high uniformity and a wide linear region.

The use of a high quality laser diode or a high quality avalanche photodiode greatly increases the cost. Even if such a high quality laser diode or avalanche photodiode is used, if the performance degradation due to use or the characteristic change due to the environment occurs, In order to understand the exact characteristics of each, there is a need for dedicated measurement equipment, so that the manufacturing yield is lowered. In addition, transmission and reception are used in opposition to each other, and the characteristics of the optical cable for the transmission There is a problem that it is difficult to confirm the deterioration in the performance or the use in the actual installation environment with the dedicated measuring equipment every time.

As a result, in the case of a multi-level optical signal for high-speed communication, both the transmitting side and the receiving side that generate the multi-level optical signal must have characteristics that support high linearity. Among them, various factors including the transmission side deviation, Even in the reflected installation environment, the receiver linearity, which requires precise multi-level distinction, is more important.

There have been some researches to detect or compensate for the characteristics of laser diodes, but there has been little research to improve the reception resolution according to the characteristics of the avalanche photodiodes. , A technique for performing multi-level optimization according to the optical reception characteristics of the avalanche photodiode in an actual installation environment has not yet been provided.

Korean Patent No. 10-1541975 [Title of the invention: Optical communication receiver and chip used therein] Korean Patent No. 10-1513372 entitled " Optical Communication Receiver Controlling Gain or Transconductance "

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems and provide an apparatus and a method for automatically determining a multi-level classification according to characteristics of a used avalanche photodiode in a state where the apparatus is installed without a separate precision meter or connection for measurement in an actual installation environment And a limit reference voltage of a limit amplifier formed in the receiver is set by estimating a reference voltage set.

It is another object of the present invention to provide a method and apparatus for receiving a test pattern promised from a counterpart transmission unit in an actual installation environment, classifying a voltage according to a received optical signal according to a test pattern, estimating a reference voltage set for classifying each classification, It is possible to improve the resolution reflecting the characteristic of the individual avalanche photodiodes showing different characteristics according to the actual use environment and it is possible to perform such a process every time when it is necessary during the initial installation as well as during use, Level optical signal reception performance that can always provide an optimum reception performance even when a plurality of optical signals are generated.

It is still another object of the present invention to provide an optical receiver device with improved multilevel optical signal reception performance that can improve communication quality at low cost by optimizing the reception performance between the devices at the transmitter level through a relatively simple configuration And a method thereof.

The optical receiving apparatus with improved multi-level optical signal reception performance according to an embodiment of the present invention receives a multi-level optical signal according to a test pattern predetermined from a partner optical transmission apparatus connected through an optical line and outputs a corresponding photocurrent A transimpedance amplifier for converting and amplifying photodiode photocurrents of the light receiving unit into a receiving voltage and a receiving voltage of the transimpedance amplifier for each pattern of the test pattern, And a limiting amplifier that separately amplifies the received voltage of the transimpedance amplifier according to a reference voltage set estimated by the controller and provides the received voltage to a plurality of different output voltages.

As an example, the test pattern may be a set of data provided to provide various multilevel optical signals.

As an example, the control unit may divide the reception voltage of the transimpedance amplifier by dividing the reception voltage corresponding to the different data based on the data of the promised test pattern, and divide each data based on the distribution range of the reception voltages stored for each data The reference voltage can be estimated between the reception voltage range of each data.

As an example, the controller may change the photodiode reverse bias voltage of the light receiving unit to one of a plurality of preset voltages when there is a voltage belonging to a voltage distribution range of different data areas among reception voltages stored for each data.

For example, the test pattern storage unit may store a test pattern, which is a transmission pattern of a multilevel signal promised to the other optical transmission apparatus, and provide the test pattern storage unit to the control unit.

As an example, the photodiode may be an avalanche photodiode.

As an example, the multilevel optical signal may be an optical signal according to PAM-4 or PAM-8 modulation.

As an example, the controller operation may be performed in accordance with an initial drive or a predetermined period or a separate external request signal.

According to another aspect of the present invention, there is provided a method of receiving multilevel optical signals, the method comprising: receiving optical signals and outputting corresponding photocurrents; receiving optical signals transmitted through the optical receiver through a light receiving unit including an avalanche photodiode, Converting the avalanche photodiode photocurrent of the light receiving unit into a receiving voltage through a transimpedance amplifier and amplifying the amplified photocurrent of the avalanche photodiode photocurrent to a receiving voltage through the transimpedance amplifier; Estimating a reference voltage set capable of distinguishing each pattern by classifying the received voltage of the transimpedance amplifier according to each pattern of the promised test pattern; Differential amplification to provide multiple different output voltages It is characterized by including the steps:

As an example, the test pattern may be a set of data provided to provide various multilevel optical signals.

For example, the step of estimating the reference voltage set may include calculating the reception voltage of the transimpedance amplifier by dividing the reception voltage corresponding to the different data based on the data of the promised test pattern, And estimating a reference voltage capable of distinguishing each data between a range of the reception voltage distribution for each data.

For example, the step of estimating the reference voltage set may include a step of estimating a set of reference voltages, wherein when a voltage belonging to a voltage distribution range of a different data region among reception voltages stored for each data exists, the avalanche photodiode reverse bias voltage of the light- And a step of changing to one.

The optical receiving apparatus and method with improved multilevel optical signal receiving performance according to the embodiment of the present invention can be used in a practical installation environment without the need for a separate precision measuring instrument or connection for measurement, And the limit reference voltages of the limit amplifier formed in the receiver are set so that the avalanche photodiode characteristics of the current optical receiver can be determined by performing a simple operation as required after actual installation Thereby providing an optimal reception performance.

In addition, in the actual installation environment, a test pattern promised from the counterpart transmitter is received, the voltage according to the received photocurrent is classified according to the test pattern, and the reference voltage set for classifying each classification is estimated, Even if the launch photodiode is used, it is possible to improve the reception resolution reflecting the characteristics according to the actual use environment. Since this process can be performed at the time of initial installation as well as at the time of use, even if environmental change or deterioration occurs, The high-resolution usable interval above the level is effectively distinguished, thereby providing the best reception performance at all times.

Furthermore, it is possible to optimize the reception performance between the devices at the transmitter level only through a relatively simple configuration, thereby improving the communication quality at a low cost, and it is possible to improve the usability because the performance improvement cost is low and the compatibility can be maintained.

1 is a configuration example of a general passive optical network.
2 is a diagram illustrating an optical line connection of an optical transceiver applied to a general passive optical network.
FIG. 3 is a diagram for comparing laser diode output resolution according to the NRZ modulation method and the PAM 4 modulation method; FIG.
4 is a characteristic graph showing the optical reception characteristics of the avalanche photodiode in correspondence with the NRZ modulation method.
5 is a characteristic graph showing the light receiving characteristics of the avalanche photodiode in correspondence with the PAM 4 modulation method.
6 is a conceptual diagram showing a photocurrent range for distinguishing each received optical signal in the PAM 4 modulation scheme.
7 is a characteristic graph showing characteristic deviations between a plurality of avalanche photodiodes for the same received optical signal.
8 is a conceptual diagram showing the reason for the reduction in reception performance due to the difference in characteristics of different avalanche photodiodes in the PAM 4 modulation method.
9 is a configuration diagram showing an optical communication system showing a multi-level optical receiver and a corresponding counterpart optical transmitter according to an embodiment of the present invention.
10 is an exemplary conceptual diagram for explaining a test pattern, a corresponding multi-level signal, and a reference voltage set estimation method of a multi-level optical receiving apparatus that receives the multi-level signal.
11 is a flowchart for explaining an operation procedure of the present invention.

It is noted that the technical terms used in the present invention are used only to describe specific embodiments and are not intended to limit the present invention. In addition, the technical terms used in the present invention should be construed in a sense generally understood by a person having ordinary skill in the art to which the present invention belongs, unless otherwise defined in the present invention, and an overly comprehensive It should not be construed as meaning or overly reduced. In addition, when a technical term used in the present invention is an erroneous technical term that does not accurately express the concept of the present invention, it should be understood that technical terms that can be understood by a person skilled in the art can be properly understood. In addition, the general terms used in the present invention should be interpreted according to a predefined or context, and should not be construed as being excessively reduced.

Furthermore, the singular expressions used in the present invention include plural expressions unless the context clearly dictates otherwise. The term "comprising" or "comprising" or the like in the present invention should not be construed as necessarily including the various elements or steps described in the invention, Or may include additional components or steps.

In addition, terms including ordinals such as first, second, etc. used in the present invention can be used to describe elements, but the elements should not be limited by terms. Terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, wherein like reference numerals refer to like or similar elements throughout the several views, and redundant description thereof will be omitted.

In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. It is to be noted that the accompanying drawings are only for the purpose of facilitating understanding of the present invention, and should not be construed as limiting the scope of the present invention with reference to the accompanying drawings.

Particularly, although a transmitter applied to a passive optical network (PON) apparatus is described as an example of the present invention, the optical receiver according to an embodiment of the present invention can be used not only for a PON, And thus the technology category is not limited to the receiving device of the transmitter for the PON and covers various optical receiving devices for optical communication.

FIG. 3 is a diagram for comparing laser diode output resolution according to the NRZ modulation method and the PAM 4 modulation method.

Generally, a transmitter of an optical transceiver includes a digital analog converter (DAC) for converting data to be transmitted into an analog signal, a laser diode driver (LDD) and a laser diode (LD) for driving the laser diode, A monitoring photodiode (MPD) is configured to monitor the output of the laser diode.

Since the laser diode constituting the transmitter of the optical transceiver is for remote digital optical communication, even if there is environmental change or deterioration of its own, it is necessary to be able to distinguish the signal. For example, in the case of using NRZ modulation with input 0 and 1, The output of 0 and the output of 1 provided from the diode can be clearly distinguished from each other. The ratio of the light intensity of the first level to the light intensity of the zero level is referred to as an extinction ratio. For example, if the extinction ratio is 3 dB, it means that the difference between the light intensity at the 0 level and the light intensity at the 1 level is doubled.

The larger the extinction ratio is, the smaller the BER (Bit Error Rate) of the transmitted data becomes, and this is almost completely inversely proportional. Therefore, in order to maintain the extinction ratio when operating the laser diode, the control current is varied by feedback through the monitoring photodiode And maintains the extinction ratio for the use period.

However, such a monitoring photodiode is used for feedback, and since there is a characteristic and a deviation in such a photodiode, it is difficult to use it as a purpose for grasping the characteristics of the laser diode.

3A and 3B illustrate characteristic curves of the laser diode. As shown in the graph, the threshold current (the current at the time when the output starts changing) and the saturation current (the current at the time when the output does not increase) (I0 to I1) having high linearity are selected as the usable period.

The laser diode shown in FIG. 3A is an exemplary high-quality laser diode in which a substantial region of the control region has a linear characteristic, and the output difference (difference between P0 and P1) of the use region is significant. That is, since the extinction ratio is high, it is possible to provide high reliability in the NRZ modulation type communication.

3B, when the control region is divided into a plurality of levels, the output difference between the outputs P0 to P3 according to the control currents I0 to I3 is greatly reduced, Which means that the optical receiver must have a fairly high resolution to clearly distinguish them from each other. That is, in case of providing 2-level optical output, the extinction ratio will be determined by the output ratio of P0 and P3. However, when the level is divided into 4 levels, the extinction ratio is reduced to 1/3.

On the other hand, the illustrated case is an example of a high-quality laser diode in which a considerable region of the control region has a linear characteristic. Even in this case, since the transmitted light amount is transmitted through the light ray transmission differently, If the quality is inevitably lowered and the quality of the laser diode used is not good, this problem will become even more serious.

4 is a characteristic graph showing the optical reception characteristics of the avalanche photodiode in correspondence with the NRZ modulation method.

The avalanche photodiode is designed to increase the efficiency and sensitivity by forming a secondary carrier for incident photons by placing a region of diffuse light in contrast to a general photodiode. Due to high photoelectric conversion efficiency and high-speed operation, Most avalanche photodiodes will be used.

These avalanche photodiodes have characteristic curves as shown, and in order to generate electron-hole pairs by the incident photons, a reverse voltage must be applied in the same manner as a general photodiode.

The avalanche photodiode outputs an abrupt photocurrent by an incident photon when a reverse bias voltage of a predetermined magnitude or more is applied. Since the linear photodiode has a constant section linear region as shown in the figure, A receiving circuit is constituted.

As shown, in the case of an NRZ modulated signal in which two different optical powers (0.25 and 2 in the example shown) are received, the avalanche photodiode outputs photocurrents A0 and A1 that exhibit relatively large differences, It is possible to distinguish the level of the optical signal.

In the characteristic curve of the illustrated avalanche photodiode, it can be seen that the shape of the characteristic curve is different according to the received optical power even when the bias voltage is the same. That is, the reception characteristic of one avalanche photodiode differs depending on the amount of received light, which means that the change of the received photocurrent according to the different amount of light in the same reference (BV1) is nonlinear.

If the amount of received light is changed in the NRZ modulation scheme providing two different levels and in the PAM 4 modulation scheme becoming four different levels, the nonlinearity of the photocurrent according to the amount of received light causes a considerable problem.

5 is a characteristic graph showing the optical reception characteristics of the avalanche photodiode corresponding to the PAM 4 modulation method. As shown in FIG. 5, the output photocurrent A0 To A3), it can be seen that the degree of change is not linear.

As such, the avalanche photodiode outputs a nonlinearly varying photocurrent with respect to the received linear optical power variation, thus causing a problem in the classification of the resolution increase of four different levels.

As described above with reference to FIG. 3, when the avalanche photodiodes having the characteristics as shown in FIG. 5 are a plurality of levels in which the optical output according to the PAM 4 modulation of the laser diode is divided into the size difference of similar level, Level optical signal, it is possible to display the levels of the output photocurrent due to the reception of the multi-level optical signal, in which the distinction is ambiguous.

However, in the case of a general optical receiver, since the photocurrent of the avalanche photodiode is not used as it is but the photocurrent is converted into the voltage through the transimpedance amplifier and amplified, the difference between the levels of the optical signals can be distinguished If so, the level difference can be distinguished based on the converted amplified voltage.

FIG. 6 is a conceptual diagram showing a photocurrent range for distinguishing each received optical signal in the PAM 4 modulation scheme. In FIG. 6, after a partial region shown in FIG. 5 is enlarged, the intermediate value between the photocurrents is set as a reference for dividing the level.

As shown in the figure, in the case of the photocurrent A0 outputted when the received optical power, that is, the received optical power level is the smallest, the change in the environment due to reception (change in the transmission side, change in the optical path, reception noise, Even if there is a change in some photocurrents due to deterioration of the photocurrent due to deterioration of the photocurrent, etc.), if the photocurrent belonging to the range (a rectangular region with reference to A0) is output, In the case of the output photocurrent A3, if a photocurrent belonging to the range (a rectangular area based on A3) is output even if there is a change in some photocurrent due to an environmental change due to reception, the photocurrent can be classified into the highest level.

However, all kinds of general semiconductor devices have characteristic deviations in each kind of products, whether they are the same product, in each process line, in the same process line, in each wafer, and in each wafer.

In particular, in the case of the avalanche photodiode, as described above, even if only a small number of photons are incident, the photocoupler is configured to increase the output photocurrent by causing a couple of electron-hole pairs of several tens to several hundreds of times like an avalanche, (For example, impurity doping drift) of the diode manufacturing process (usually forming a drift region between p + and n + regions and an avalanche region of p) .

FIG. 7 is a characteristic graph showing characteristic deviations between a plurality of avalanche photodiodes for the same received optical signal. Even in the environment of the same received optical signal as the bias voltage BV1, the photocurrent output of each avalanche photodiode has a considerable difference dA).

Such a difference may occur between the avalanche photodiodes sold in the same product, and in the case of different products or manufacturers, such characteristic deviations may become larger. In the conventional NRZ environment classified as '1' or '0' It is difficult to fix the photocurrent sorting criterion of the avalanche photodiode for distinguishing the plural levels when a multi-level optical signal is received.

FIG. 8 is a conceptual diagram illustrating the reason for the reduction in the reception performance due to the difference in characteristics of different avalanche photodiodes in the PAM 4 modulation method. As shown in FIG. 8A, the first avalanche photodiode And the photocurrent according to the measured optical signals of different levels and the range of the reception level classification based on the photocurrent.

According to such a reception level classification range, multiple levels of the received light can be classified into the photocurrent range even if there is some noise in the received optical signal.

The range of the reception level classification is divided into two stages in the NRZ signaling method, and the deviation according to the production lot and the production method of the avalanche photodiode was allowed. However, in the case of multi-level (PAM 4 3-level, PAM 8 7-level), the range of the received level can not be relied on even slight photocurrent deviations such as production lot and production process 8b.

That is, as shown in the figure, the photocurrent output when the received light quantity is the smallest (for example, 0 to 3) is smaller than the received level classification range (the displayed hatched areas) provided by the first avalanche photodiode, (Horizontally shaded area: a range to which level 1 belongs) in the case where the received light amount is the second lowest optical signal level, and the received light amount becomes the second lowest optical signal level (for example, 3), the photocurrent outputted from the photodetector belongs to a range in which the amount of light received is classified into the range of the second largest optical signal level The level of the received optical signal can not be normally discriminated if an avalanche photodiode having the characteristics as shown in FIG. 8B is used.

Particularly, even if the optical receiving apparatus using the same avalanche photodiode is used, the optical power characteristic of the entire received light changes depending on the optical path when the actual installation environment is changed, so that a problem as shown in FIG.

Accordingly, in the present invention, even if an avalanche photodiode having various deviations is used, it is possible to identify the optimum multi-level optical signal automatically by grasping the characteristics thereof, and to provide a separate precision measuring device or a connection Level optical signal corresponding to the connected multilevel optical transmission device in the state in which the multilevel optical transmission apparatus is installed without any configuration.

9 is a configuration diagram showing an optical communication system showing a multi-level optical receiving apparatus 200 and a corresponding optical transmitting apparatus 100 according to an embodiment of the present invention. Basically, PAM 4 is described as an example, but a higher resolution PAM 8 modulation scheme may be used, or a higher resolution may be applied depending on the technology.

Since one optical transceiver and one optical receiver are substantially formed in one transceiver, a separate optical transmitter may be disposed adjacent to the multilevel optical receiver 200 to constitute one transceiver, The multilevel optical transmission apparatus 100 may also be disposed adjacent to a separate optical receiving apparatus to form one transceiver. That is, since the multilevel optical transmitting apparatus 100 and the multilevel optical receiving apparatus 200 shown in FIG. 1 can be combined together in the transceiver according to the embodiment of the present invention, Lt; / RTI >

In the illustrated embodiment, only the multilevel optical transmitter 100 of one transceiver and the multilevel optical receiver 200 of the other transceiver among the parallel configurations will be described as an example.

The illustrated embodiment of the present invention is a multi-level optical receiving apparatus that receives a multi-level optical signal provided by a counterpart multi-level optical transmitting apparatus 100 at a remote location through an optical line 10 in an environment installed according to an actual network configuration The multilevel optical receiving apparatus 200 according to the present invention is capable of automatically grasping the avalanche photodiode characteristics of the multi-level optical transmitting apparatus 100 connected to the multilevel optical transmitting apparatus 100 via the optical line 10, And receives the test pattern to grasp the reception characteristics of the avalanche photodiode.

As shown in the figure, the counterpart multilevel optical transmission apparatus 100 includes a driving unit 110 for driving the laser diode 120, a test pattern storage unit 140 for storing information on an appointed test pattern, And controls the driving unit 110 according to the test pattern stored in the pattern storage unit 140 so as to output the multilevel optical signal according to the promised test pattern through the laser diode 120. [

Here, the promised test pattern is a series of data sets provided to provide various multi-level optical signals, and one test pattern may be transmitted once or plural times, and various kinds of test patterns may be transmitted once or several times . This may be performed during initial driving or setting, or may be performed according to an external control signal to the control unit 130 (a control signal of the equipment in which the optical transmitter is configured or a control signal in response to a request of the counterpart transceiver).

For example, in a situation where the equipment A configured with the transceiver including the multilevel optical transmission device 100 and the equipment B configured with the transceiver including the multilevel optical reception device 200 are configured, It is possible that the equipment A can request the equipment B to perform the reception optimization process and vice versa and the transceiver configured in the equipment A and the transceiver configured in the equipment B can be mutually agreed upon Such as an initial drive or an appointed time of the transceiver, or at the request of one transceiver.

The multilevel optical receiving apparatus 200 according to an embodiment of the present invention receives a multilevel optical signal according to a predetermined test pattern from a counterpart multilevel optical transmission apparatus 100 connected through a light path 10, A transimpedance amplifier (TIA) 220 for converting and amplifying the avalanche photodiode photocurrent of the light receiving unit 210 into a receiving voltage, A test pattern storage unit 250 for storing information on a test pattern and a test pattern storage unit 250 for storing a received voltage of the transimpedance amplifier 220 in accordance with a predetermined test pattern stored in the test pattern storage unit 250, The control unit 240 estimates a reference voltage set 235 that can classify each pattern according to the input voltage of the transimpedance amplifier 220 and the received voltage of the transimpedance amplifier 220 to the control unit 240 Separately amplifying a reference voltage according to the estimated set 235 is configured to include a limiting amplifier 230 is provided with a plurality of different output voltages.

The test pattern stored in the test pattern storage unit 250 is the same as the test pattern information stored in the test pattern storage unit 140 of the optical transmitting apparatus 100 as a series of data sets provided to provide various multi- . Of course, since the control unit 240 may include such a test pattern itself, the test pattern storage unit 250 is not essential.

The light receiving unit 210 including the avalanche photodiode may include an avalanche photodiode and a circuit configuration (a reverse bias voltage providing unit, etc.) necessary for operating the avalanche photodiode.

The control unit 240 stores the received voltage of the transimpedance amplifier 220 by dividing the received voltage corresponding to the different data based on the data of the test pattern promised and storing each data on the basis of the distribution range of the received voltages stored for each data The reference voltage that can be discriminated can be estimated between the reception voltage range of each data, which will be described in more detail with reference to FIG.

10 is an exemplary conceptual diagram for explaining a test pattern, a corresponding multi-level signal, and a reference voltage set estimation method of a multi-level optical receiving apparatus that receives the multi-level signal.

As shown in FIG. 10A, FIG. 10A shows an example of a test pattern for PAM 4. For convenience of explanation, the test pattern is divided into two bits.

As shown in the figure, the actual test pattern after the predetermined preparation signals 1111 ... 11 is configured such that 2-bit data that can be displayed at one time at four different levels used in the PAM 4 are changed. That is, the 2-bit data patterns shown in FIG. 10A represent four different levels as shown in FIG. 10B, and a test pattern can be configured to clearly distinguish each pattern. For example, n patterns may be listed, the distribution of the patterns included may be similar, and such a set of test patterns may be repeated many times, and a plurality of different test patterns may be provided.

The multilevel optical transmission apparatus 100 controls the driving unit 110 according to the test pattern stored in the test pattern storage unit 140 to output a multilevel optical signal according to the promised test pattern through the laser diode 120, The light receiving unit 210 of the multilevel optical receiving apparatus 200 receives the multilevel optical signal transmitted through the optical line 10 and outputs a photocurrent for the multilevel optical signal. The light receiving unit 210 includes an avalanche photodiode provided with a predetermined bias voltage in a reverse direction, and the avalanche photodiode outputs a photocurrent corresponding to a characteristic inherent to the intensity of the multilevel optical signal. Since the photocurrent is different for each avalanche photodiode and difficult to predict for each intensity of the received optical signal, the characteristics of the currently configured avalanche photodiode corresponding to the actually received multilevel optical signal must be confirmed.

The transimpedance amplifier 220 amplifies the photocurrent output from the light receiving unit 210 into a voltage and outputs the amplified voltage as a reception voltage. The control unit 240 converts the received voltage into a test pattern stored in the test pattern storage unit 250 It is classified according to.

That is, if the multi-level optical signal received this time corresponds to the test pattern data '00', the received voltage is classified according to the data '00', and if the received optical signal corresponds to the test pattern data '01' 00 ',' 01 ',' 10 ', and' 11 ', which represent each pattern, by classifying the received voltage as corresponding to data' 01 '.

If the reception voltages according to the test patterns of several tens to several hundreds are classified according to the patterns, the received voltages according to the pattern data can be classified as shown in FIG. 10C.

This means the actual reception range of the reception voltage for each pattern of the multilevel optical signal based on the characteristics of the avalanche photodiode configured in the current multilevel optical receiving apparatus 200. In other words, .

10D, the reference voltages LV2 to LV4 that can distinguish each pattern data based on the distribution range of the reception voltages stored for each pattern data can be estimated between the reception voltage distribution ranges for the respective data. For example, It is possible to estimate a reference voltage in the middle of a corresponding area after detecting an area having no reception voltage between reception voltage distribution areas for each pattern data. Further, it is possible to estimate the additional reference voltages LV1 and LV5 by referring to the distribution range of the reception voltages.

The reference voltage sets LV1 to LV5 serve as a reference for determining which pattern data the received voltage obtained by converting the photocurrent of the avalanche photodiode to the transimpedance amplifier with respect to the received multilevel optical signal is divided into pattern data, The reception voltage can be classified into one of '00', '01', '10', and '11'. If necessary, it may be regarded as noise when LV1 or less or LV5 or more.

The control unit 240 may perform the reference voltage set estimation on the basis of the accumulated voltage of the received multi-level optical signal for all the test patterns, or the multi-level optical signal according to the test pattern Or may be performed in real time. Alternatively, when a plurality of test patterns are used, or when the same test pattern is repeated a plurality of times, each unit test pattern may be performed and then performed.

The limiting amplifier 230 operates by referring to the reference voltage set (LV1 to LV5 in the embodiment) estimated by the control unit 240. The limiting amplifier 230 outputs the voltage belonging to the specific range as the target voltage When the reception voltage of the transimpedance amplifier 220 is between LV1 and LV2, the reference voltage set is amplified. When the received voltage is between LV1 and LV2, And amplifies and outputs the amplified data to an output voltage indicating '10' if it is between LV3 and LV4 and amplifies and outputs the amplified data to an output voltage that indicates data '11' if it is between LV4 and LV5 .

If the reception voltage of the transimpedance amplifier 220 is equal to or lower than LV1 or equal to or higher than LV5, it may be regarded as noise and may not operate.

On the other hand, it is preferable that the reception voltage received with the specific pattern data does not overlap with the reception voltage region of the other pattern data as shown in 10d, so that the reference voltage estimation succeeds. However, It may occur that the reference voltage can not be estimated by overlapping with the voltage region. Therefore, if the reference voltage is estimated after the unit test pattern is performed, if the reference voltage is estimated, the succeeding unit test pattern or the succeeding reference voltage estimation based on the previous unit test pattern may be used. Of course, it may be a problem due to simple noise. Therefore, if the received voltage of the specific pattern data belongs to the received voltage region of the other pattern data after the unit test pattern is performed, the corresponding received voltage may be excluded.

In addition, when a voltage belonging to a voltage range of a different data region is present among the reception voltages stored for each data (substantially, the reception voltage received in the specific pattern data is a voltage region The back bias voltage of the avalanche photodiode of the light receiving unit 210 may be changed to one of a plurality of preset voltages. For example, referring to FIG. 5, the embodiment of the present invention grasps the photocurrent characteristic according to the light reception of the avalanche photodiode based on the present bias voltage BV1, However, it may be difficult to distinguish the optical signals of different levels among the received multi-level optical signals due to deterioration of performance or the like if the photocurrent characteristics are similar to the current bias voltage of the avalanche photodiode that converts the optical signals into the photocurrent. Therefore, if the reference voltage estimation by the unit test pattern fails after the provision of several candidate bias voltages BV1 to BVn, the control unit 240 changes the bias voltage of the light reception unit 210 to the next candidate, It is possible to reduce the possibility of the reference voltage estimation failure and reflect the characteristics of the avalanche photodiode adaptively.

Through this, a multi-level optical signal according to the test pattern promised by the relative optical transmission apparatus is received from the relative optical transmission apparatus, the voltage according to the received photocurrent is classified according to the test pattern, and a reference voltage set for distinguishing each classification (pattern data) It is possible to improve the resolution reflecting the characteristics of the individual avalanche photodiodes showing different characteristics according to the received optical power according to the actual use environment.

This process can be performed only once at the initial installation, but it can be performed when the actual transmitter is performed at the startup of the configured devices, periodically, or when the communication performance is lowered. Therefore, even if the environment changes or the performance deteriorates, Lt; RTI ID = 0.0 > and / or < / RTI > state reception performance.

11 is a flowchart for explaining an operation procedure of the present invention.

As shown in the figure, the counterpart multilevel optical transmission apparatus starts to provide the multi-level optical signal according to the test pattern previously promised through the laser diode according to the predetermined time or predetermined condition.

A multilevel optical receiving apparatus according to an embodiment of the present invention receives a multilevel optical signal through an optical line. The avalanche photodiode of the multilevel optical receiving apparatus generates a photocurrent corresponding to the received optical signal, The transimpedance amplifier of the device converts and converts the photocurrent into a voltage to generate the receive voltage.

The control unit of the multilevel optical receiving apparatus classifies the received voltage of the transimpedance amplifier according to the promised test pattern.

The control unit estimates a reference voltage set capable of distinguishing each pattern in consideration of the distribution area of the reception voltage classified according to the pattern.

The limiting amplifier of the multilevel optical receiving apparatus that receives the receiving voltage of the transimpedance amplifier amplifies the receiving voltage by using the estimated reference voltage set and provides it with a plurality of different output voltages so that the receiving voltage is multiplied by the multi- .

For example, in the case of the multi-level of the PAM 4 modulation scheme, the controller divides the received test pattern into 2-bit data '00', '01', '10', '11' And the limiting amplifier identifies the reception voltage belonging to the voltage range corresponding to '00', '01', '10', and '11' through the corresponding reference voltage set to distinguish them And outputs it to one of a plurality of voltages preset in advance.

Thus, it is possible to optimize the reception performance between the devices at the transmitter level only through a relatively simple configuration, thereby improving the communication quality at a low cost.

Meanwhile, the control unit of the above-mentioned optical transmitting apparatus or optical receiving apparatus may be composed of an electronic circuit including a combination of active and passive elements having a control function, and may be constituted by a chip including a microcontroller or equivalent control means And the concrete implementation method thereof may encompass various known methods.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or essential characteristics thereof. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

100: Multilevel optical transmitter 110:
120: laser diode 130:
140: Test pattern storage unit 200: Multilevel optical receiver
210: optical receiver 220: transimpedance amplifier
230: Limiting amplifier 235: Reference voltage set
240: control unit 250: test pattern storage unit

Claims (12)

A light receiving unit including a photodiode receiving a multilevel optical signal according to a predetermined test pattern from a partner optical transmission apparatus connected through an optical line and outputting a corresponding photocurrent;
A transimpedance amplifier for converting and amplifying photodiode photocurrent of the light receiving unit into a receiving voltage;
A control unit for classifying a received voltage of the transimpedance amplifier according to each pattern of the promised test pattern and estimating a reference voltage set capable of distinguishing each pattern;
And a limiting amplifier for amplifying the received voltage of the transimpedance amplifier according to a reference voltage set estimated by the controller to provide a plurality of different output voltages,
The test pattern is a set of data provided to provide various multi-level optical signals,
Wherein the controller divides the received voltage of the transimpedance amplifier by the received test pattern data and divides the received voltage corresponding to the different data, And the voltage is estimated between the reception voltage distribution range for each data, respectively.
delete delete The method of claim 1, wherein the control unit changes the photodiode reverse bias voltage of the light receiving unit to one of a plurality of preset voltages when there is a voltage belonging to a voltage distribution range of different data areas among the reception voltages stored for the data Wherein the light receiving device has improved performance of receiving multi-level optical signals.
The optical transmission apparatus according to claim 1, further comprising a test pattern storage unit for storing a test pattern, which is a transmission pattern of a multilevel signal promised to the partner optical transmission apparatus, and providing the test pattern to the control unit. Optical receiver.
The optical receiver according to claim 1, wherein the photodiode is an avalanche photodiode.
The optical receiver of claim 1, wherein the multi-level optical signal is an optical signal according to PAM-4 or PAM-8 modulation.
The optical receiver as claimed in claim 1, wherein the controller operation is performed according to an initial driving operation or a predetermined period or a separate external request signal.
Receiving a multilevel optical signal according to a predetermined test pattern from a counterpart optical transmission apparatus connected through an optical line through a light receiving unit including an avalanche photodiode receiving an optical signal and outputting a corresponding photocurrent;
Converting and converting the avalanche photodiode photocurrent of the light receiving portion into a receiving voltage through a transimpedance amplifier;
The control unit classifying the received voltage of the transimpedance amplifier for each pattern of the promised test pattern and estimating a reference voltage set capable of distinguishing each pattern;
Amplifying the received voltage of the transimpedance amplifier according to a reference voltage set estimated by the controller, and providing the amplified voltage to a plurality of different output voltages,
The test pattern is a set of data provided to provide various multi-level optical signals,
Wherein the step of estimating the reference voltage set comprises: dividing the received voltage of the transimpedance amplifier by the received test data corresponding to different data, And estimating a reference voltage capable of distinguishing data between a range of receiving voltage distributions for each data, respectively.
delete delete [12] The method of claim 9, wherein the step of estimating the reference voltage set comprises: if a voltage belonging to a voltage distribution range of a different data region among the reception voltages stored for each data exists, the avalanche photodiode reverse bias voltage of the light reception unit is preset And converting the received signal into one of a plurality of voltages.

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