WO2018018477A1

WO2018018477A1 - Optical transmission method, apparatus and system

Info

Publication number: WO2018018477A1
Application number: PCT/CN2016/091963
Authority: WO
Inventors: 周恩波; 张强; 张亮; 左天健
Original assignee: 华为技术有限公司
Priority date: 2016-07-27
Filing date: 2016-07-27
Publication date: 2018-02-01
Also published as: CN109565337A; CN109565337B

Abstract

Provided are an optical transmission method, apparatus and system, relating to the technical field of communications. The method comprises: encoding an N-level pulse amplitude modulation (PAM-N) signal to be transmitted to obtain a first encoded signal, wherein the first encoded signal comprises N-1 first positive integer levels, 1 zero level, and N-1 negative integer levels, with N≥3 and N being an integer; respectively deviating the N-1 first positive integer levels or the N-1 negative integer levels by a first deviation amount, so that the first encoded signal is switched to a second encoded signal, wherein the first deviation amount is a decimal; modulating the second encoded signal into an optical signal; and sending the optical signal to an optical receiver. By means of the method, an optical receiver can demodulate a PAM-N optical signal by using a direct detection method when an encoded signal of the PAM-N signal comprises a negative level, so as to reduce the complexity of an optical sender and an optical receiver.

Description

Optical transmission method, device and system

Technical field

The present invention relates to the field of communications technologies, and in particular, to an optical transmission method, apparatus, and system.

Background technique

In an optical transmission system, a multi-level (three or more) pulse amplitude modulation (PAM-N) is a commonly used modulation signal modulated by data to be transmitted. After the optical transmitter acquires the PAM-N signal to be transmitted, the PAM-N signal is encoded, and the encoded coded signal is modulated into an optical signal, and the optical signal is transmitted to the optical receiver through the optical fiber. After receiving the optical signal, the optical receiver demodulates the optical signal into an electrical signal and decodes the electrical signal to obtain a PAM-N signal.

At present, the optical receiver can demodulate the optical signal by means of direct detection or coherent detection. Direct detection refers to square detection of the level information carried in the optical signal by the photodetector to obtain an electrical signal (the level value in the electrical signal is the square value of the level information). Coherent detection is a series of processes such as mixing a local oscillator signal with the optical signal to obtain an electrical signal.

Generally, the optical transmitter adopts different encoding methods, and the above encoded signals may include different level information, for example, including only 0 level and positive level, or include 0 level, positive level, and negative level. When the encoded signal includes only the 0 level and the positive level, since the absolute values of 0 and the positive integer are still 0 and a positive integer, the optical receiver can demodulate the received optical signal by direct detection. When the coded signal further includes a negative level, since the direct detection cannot obtain a negative level, the optical receiver needs to demodulate the optical signal by means of coherent detection.

However, when the coded signal includes a negative level, if the optical receiver is required to demodulate the optical signal by means of coherent detection, both the optical transmitter and the optical receiver need to add digital signal processing (DSP) modules and integration. Coherent Receiver (English: Intradyne Coherent Receiver, ICR) and local oscillator laser (English: LocalOscillator, LO) and other modules, thus making the design of optical receivers and optical transmitters more complex, resulting in power consumption of optical transmitters and optical receivers Increase, cost increases.

Summary of the invention

Embodiments of the present invention provide an optical transmission method, apparatus, and system, such that an optical receiver can perform a direct detection on a PAM-N optical signal when a coded signal of a PAM-N signal includes a negative level. Demodulation to reduce the complexity of optical transmitters and optical receivers.

In order to achieve the above object, embodiments of the present invention adopt the following technical solutions:

In a first aspect, an embodiment of the present invention provides an optical transmission method, including:

The N-level pulse amplitude modulation (PAM-N) signal to be transmitted is encoded to obtain a first encoded signal, the first encoded signal comprising N-1 first positive integer levels, 1 zero level and N-1 negative integer levels, N≥3, N is an integer; the N-1 first positive integer levels or the N-1 negative integer levels are respectively offset by a first bias Transmitting to convert the first encoded signal into a second encoded signal, the first offset being a fraction; modulating the second encoded signal into an optical signal; and transmitting the optical signal to an optical receiver.

Embodiments of the present invention provide an optical transmission method capable of biasing a first positive integer level or a negative integer level in a first encoded signal of a PAM-N signal by a first offset of a decimal value Moving, obtaining a second encoded signal, and modulating the second encoded signal into an optical signal for transmission to a receiver, so that the optical receiver directly detects and determines the optical signal, and the acquired 2N-1 levels are included. N-1 positive fractional levels, so that the optical receiver can convert the N-1 positive fractional levels to the restored N-1 negative integer levels when recovering the 2N-1 levels And determining that the zero point in the 2N-1 levels is the restored zero level, and determining N-1 positive integer levels in the 2N-1 levels as the restored N-1 first a positive integer level to obtain the restored first encoded signal, or to convert the N-1 positive fractional levels to the recovered N-1 first positive integer levels, and determine the 2N-1 The zero point in the level is the zero level after recovery. And converting the N-1 second positive integer levels of the 2N-1 levels into the restored N-1 negative integer levels to obtain the restored first encoded signal, and the optical receiver can The restored first encoded signal is decoded to obtain a restored PAM-N signal. That is, by the optical transmission method, when the optical receiving connection can include a negative level in the encoded signal of the PAM-N signal, the optical signal of the PAM-N can also be demodulated by direct detection, thereby reducing the optical transmitter and the light. The complexity of the receiver reduces the power consumption of the optical transmitter and optical receiver.

Optionally, the first offset is a decimal between -1 and 1.

In a second aspect, an embodiment of the present invention provides an optical transmission method, including:

Receiving an optical signal transmitted by the optical transmitter; directly detecting and determining the optical signal, acquiring 2N-1 levels, the 2N-1 levels including N-1 second positive integer levels, 1 zero power And N-1 positive fractional levels, N≥3, N is an integer; recovering the 2N-1 levels to obtain the restored first encoded signal, the restored first encoded signal including after recovery N-1 first positive integer levels, 1 zero level after recovery and N-1 negative integer levels after recovery; the recovered N-1 first positive integer levels are the N- a second positive integer level, the recovered zero level is the one zero level, and the restored N-1 negative integer levels are converted by the N-1 positive fractional levels Or, the restored N-1 first positive integer levels are converted by the N-1 positive fractional levels, and the restored one zero level is the one zero level, after the recovery The N-1 negative integer levels are converted by the N-1 second positive integer levels; the recovered first encoded information encoded signal is decoded to obtain the restored PAM-N signal.

Embodiments of the present invention provide an optical transmission method capable of directly detecting an optical signal of a PAM-N signal and acquiring 2N-1 levels, since the optical transmitter modulates the encoded signal of the PAM-N signal into Before the optical signal, the first integer offset of the decimal value is used to offset the negative integer level or the positive integer level of the first encoded signal of the PAM-N signal, and therefore, 2N-1 acquired by the optical receiver The level includes N-1 positive fractional levels, so that the optical receiver can convert the N-1 positive fractional levels to the restored N-1 when recovering the 2N-1 levels. Negative integer level, and determining that the zero point of the 2N-1 levels is the recovered zero level, and determining the 2N-1 levels N-1 positive integer levels are recovered N-1 first positive integer levels to obtain the restored first encoded signal, or convert the N-1 positive fractional levels to recovered N a first positive integer level, and determining that the zero point of the 2N-1 levels is the recovered zero level, and the N-1 second positive integers of the 2N-1 levels are Converting to the restored N-1 negative integer levels to obtain the restored first encoded signal, and the optical receiver can decode the recovered first encoded signal to obtain the restored PAM-N signal. . That is, by the optical transmission method, when the optical receiving connection can include a negative level in the encoded signal of the PAM-N signal, the optical signal of the PAM-N can also be demodulated by direct detection, thereby reducing the optical transmitter and the light. The complexity of the receiver reduces the power consumption of the optical transmitter and optical receiver.

Optionally, the optical signal is a signal obtained by the optical transmitter modulating the second encoded signal, where the second encoded signal is an N-1 first positive integer level or N-1 in the first encoded signal of the optical transmitter. The negative integer levels are respectively offset by a signal obtained by the first offset, the first offset being a fraction.

Optionally, recovering 2N-1 levels, including: determining N-1 second positive integer levels as restored N-1 first positive integer levels; determining 1 zero level for recovery The following one zero level; shifting N-1 positive fractional offsets by a first offset, respectively, obtaining N-1 third positive integer levels, and N-1 third positive integers The levels are respectively inverted to obtain the restored N-1 negative integer levels, and the first offset is a decimal.

Optionally, recover 2N-1 levels, including:

N-1 second positive integer levels are respectively inverted to obtain N-1 negative integer levels after recovery; 1 zero level is determined as one zero level after recovery; N-1 positive The fractional level is offset by the first offset, respectively, and the restored N-1 first positive integer levels are obtained, and the first offset is a decimal.

Optionally, the first offset is a decimal between -1 and 1.

In a third aspect, an embodiment of the present invention provides an optical transmitter, including: a processing unit, a modulating unit, and a communication unit, where the processing unit is configured to encode and acquire an N-level pulse amplitude modulation PAM-N signal to be transmitted. a first encoded signal, the first encoded signal comprising N-1 first positive integer levels, 1 zero level and N-1 negative integers a level, N ≥ 3, N is an integer; the processing unit is further configured to offset the N-1 first positive integer levels or the N-1 negative integer levels by a first offset, respectively Converting the first encoded signal into a second encoded signal, the first offset is a fraction; the modulating unit is configured to modulate the second encoded signal converted by the processing unit into an optical signal; the communication unit is configured to: The optical signal modulated by the modulation unit is transmitted to the optical receiver.

Embodiments of the present invention provide an optical transmitter capable of performing a first positive integer level or a negative integer level in a first encoded signal of a PAM-N signal by a first offset of a decimal value Offset, obtaining a second encoded signal, and modulating the second encoded signal into an optical signal for transmission to a receiver, so that the optical receiver directly detects and determines the optical signal, and obtains 2N-1 levels. Including N-1 positive fractional levels, so that the optical receiver can convert the N-1 positive fractional levels to the recovered N-1 negative integers when recovering the 2N-1 levels Leveling, and determining that the zero point in the 2N-1 levels is the recovered zero level, and determining N-1 positive integer levels in the 2N-1 levels as the restored N-1 a first positive integer level to obtain the restored first encoded signal, or to convert the N-1 positive fractional levels to the restored N-1 first positive integer levels, and determine the 2N-1 The zero point of the levels is the recovered zero level, and the N-1 second positive integer levels of the 2N-1 levels are converted to the restored N-1 Integer level, to obtain a first encoded signal restoration, and thus the optical receiver may decode the first encoded signal recovery, PAM-N signal is obtained after the recovery. That is, by the optical transmission method, when the optical receiving connection can include a negative level in the encoded signal of the PAM-N signal, the optical signal of the PAM-N can also be demodulated by direct detection, thereby reducing the optical transmitter and the light. The complexity of the receiver reduces the power consumption of the optical transmitter and optical receiver.

Optionally, the first offset is a decimal between -1 and 1.

In a fourth aspect, an embodiment of the present invention provides an optical receiver, including a communication unit, a photodetecting unit, and a processing unit, configured to receive an optical signal sent by an optical transmitter, where the photodetecting unit is configured to The optical signal received by the communication unit is directly detected and determined to acquire 2N-1 levels, the 2N-1 levels including N-1 second positive integer levels, 1 zero level and N-1 positive Decimal level, N≥3, N is integer The processing unit is configured to recover the 2N-1 levels acquired by the photodetecting unit to obtain a restored first encoded signal, where the restored first encoded signal includes the restored N-1 a first positive integer level, a restored zero level and a recovered N-1 negative integer level; the recovered N-1 first positive integer levels are the N-1 second a positive integer level, the restored zero level is the one zero level, and the restored N-1 negative integer levels are converted by the N-1 positive fractional levels; or The restored N-1 first positive integer levels are converted by the N-1 positive fractional levels, and the recovered one zero level is the one zero level, and the restored N-1 The negative integer level is converted by the N-1 second positive integer levels; the processing unit is further configured to decode the restored first encoded signal to obtain the restored PAM-N signal.

The optical receiver provided by the embodiment of the invention can directly detect the optical signal of the PAM-N signal and acquire 2N-1 levels, because the optical transmitter modulates the encoded signal of the PAM-N signal. Before the optical signal, the first integer offset of the decimal value is used to offset the negative integer level or positive integer level of the first encoded signal of the PAM-N signal, and therefore, the 2N-1 obtained by the optical receiver The level includes N-1 positive fractional levels, so that the optical receiver can convert the N-1 positive fractional levels to the restored N-1 when recovering the 2N-1 levels. a negative integer level, and determining that the zero point of the 2N-1 levels is the recovered zero level, and determining N-1 positive integer levels in the 2N-1 levels as recovered N-1 first positive integer levels to obtain the restored first encoded signal, or to convert the N-1 positive fractional levels to the restored N-1 first positive integer levels, and determine The zero point of the 2N-1 levels is the recovered zero level, and the N-1 second positive integer levels of the 2N-1 levels are converted into the restored N-1 negative integers. The number level is obtained to obtain the restored first encoded signal, and the optical receiver can decode the restored first encoded signal to obtain the restored PAM-N signal. That is, by the optical transmission method, when the optical receiving connection can include a negative level in the encoded signal of the PAM-N signal, the optical signal of the PAM-N can also be demodulated by direct detection, thereby reducing the optical transmitter and the light. The complexity of the receiver reduces the power consumption of the optical transmitter and optical receiver.

Optionally, the optical signal is a signal obtained by the optical transmitter modulating the second encoded signal, The second coded signal is a signal obtained by the optical transmitter shifting N-1 first positive integer levels or N-1 negative integer levels in the first coded signal by a first offset, respectively. The offset is a decimal.

Optionally, the processing unit is specifically configured to determine that the N-1 second positive integer levels are N-1 first positive integer levels, and offset the N-1 positive fractional offsets respectively. An offset, obtaining N-1 third positive integer levels, and respectively inverting N-1 third positive integer levels to obtain N-1 negative integer levels, the first offset being Decimal.

Optionally, the processing unit is specifically configured to invert the N-1 second positive integer levels respectively, obtain N-1 negative integer levels, and offset N-1 positive decimal levels respectively. Offset, obtaining N-1 first positive integer levels, the first offset being a fraction.

In a fifth aspect, an embodiment of the present invention provides an optical transmission system, comprising the optical transmitter according to the above third aspect, and the optical receiver according to any one of the fourth aspect or the fourth aspect.

According to the optical transmission system provided by the embodiment of the present invention, the optical transmitter can offset the positive integer level or the negative integer level in the first encoded signal of the PAM-N signal by using the first offset of the decimal value. Obtaining a second encoded signal, and modulating the second encoded signal into an optical signal and transmitting the optical signal to the optical receiver, so that the optical receiver directly detects and determines the optical signal, and the acquired 2N-1 levels include N - a positive fractional level such that the optical receiver can convert the N-1 positive fractional levels to the recovered N-1 negative integer levels upon restoration of the 2N-1 levels, And determining that the zero level of the 2N-1 levels is the restored zero level, and determining N-1 positive integer levels in the 2N-1 levels as the restored N-1 first a positive integer level to obtain the restored first encoded signal, or to convert the N-1 positive fractional levels to the recovered N-1 first positive integer levels, and determine the 2N-1 The zero point in the level is the zero level after recovery, and the N-1 second positive integer levels in the 2N-1 levels are converted into the restored N-1 Integer level, to obtain a first encoded signal restoration, and thus the optical receiver may decode the first encoded signal recovery, PAM-N signal is obtained after the recovery. That is, by the optical transmission method, when the optical receiving connection can include a negative level in the encoded signal of the PAM-N signal, the optical signal of the PAM-N can also be directly detected. Line demodulation reduces the complexity of the optical transmitter and optical receiver and reduces the power consumption of the optical transmitter and optical receiver.

DRAWINGS

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the embodiments or the description of the prior art will be briefly described below. Obviously, the drawings in the following description are only It is some embodiments of the invention.

1 is a schematic structural diagram of an optical transmission system in the prior art;

2 is an interaction diagram of an optical transmission method according to an embodiment of the present invention;

3 is a schematic structural diagram of an optical transmitter according to an embodiment of the present invention;

4 is a schematic structural diagram of an optical receiver according to an embodiment of the present invention;

FIG. 5 is a schematic diagram of an optical transmission system according to an embodiment of the present invention.

detailed description

The technical solutions in the embodiments of the present invention are clearly and completely described in the following with reference to the accompanying drawings in the embodiments of the present invention. It is obvious that the described embodiments are only a part of the embodiments of the present invention, but not all embodiments.

As shown in FIG. 1 , it is a conventional optical transmission network architecture, including an optical transmitter and an optical receiver, and an optical transmitter and an optical receiver are connected by optical fibers. The optical transmitter is configured to modulate an electrical signal to be transmitted into an optical signal, and send the optical signal to an optical fiber for transmission. After receiving the optical signal, the optical receiver restores the optical signal to an electrical signal.

At present, when the PAM-N signal is used for data transmission, if the encoded signal of the PAM-N signal includes a negative level, when the optical receiver receives the optical signal modulated by the encoded signal, the optical receiver needs to use coherent detection. The way the optical signal is demodulated. However, if the optical receiver demodulates the optical signal by means of coherent detection, both the optical transmitter and the optical receiver need to add devices such as modules, ICRs, and LOs, so that the design of the optical receiver and the optical transmitter is more complicated. The power consumption of the optical transmitter and the optical receiver is increased, and the cost is high.

To this end, an embodiment of the present invention provides an optical transmission method, so that an optical receiver can demodulate an optical signal of the PAM-N by using a direct detection method when the encoded signal of the PAM-N signal includes a negative level. And recovering the negative level in the encoded signal, from It reduces the power consumption of optical transmitters and optical receivers.

As shown in FIG. 2, an embodiment of the present invention provides an optical transmission method, where the method may include:

S101. The optical transmitter encodes the PAM-N signal to be transmitted, and obtains a first encoded signal, where the first encoded signal includes N-1 first positive integer levels, one zero level, and N-1 negative integer powers. Flat, N≥3, N is an integer.

In the embodiment of the present invention, the PAM-N signal may be a PAM-3 signal, a PAM-4 signal, a PAM-5 signal, or the like. The optical transmitter can encode the PAM-N signal by using a multi-binary modulation coding technique to obtain 2N-1 levels, that is, the first encoded signal. Specifically, the 2N-1 levels are -N+1 volts (V), -N+2V, ..., 0V, ..., N-2V, N-1V, that is, the 2N-1 levels. It includes N-1 first positive integer levels, 1 zero level and N-1 negative integer levels.

Illustratively, taking the PAM-4 signal as an example, the PAM-4 signal includes four levels, 0V, 1V, 2V, and 3V, respectively. After the optical transmitter encodes the PAM-4 signal by using a multi-binary modulation coding method, seven levels can be obtained, including three negative integer levels of -3V, -2V, and -1V, and one 0V. Level, 3 first positive integer levels 1V, 2V and 3V.

Specifically, the process of encoding the PAM-N signal by the optical transmitter can be referred to the detailed description in the Ethernet standard (IEEE 802.3bj), and details are not described herein again.

S102. The optical transmitter shifts the N-1 first positive integer levels or the N-1 negative integer levels by a first offset to convert the first encoded signal into a second encoded signal. The first offset is a decimal.

In the embodiment of the present invention, the first offset may be a positive fraction or a negative fraction, and the optical transmitter may mark N-1 positive integer levels in the first encoded signal by a decimal or mark the decimal number. N-1 negative integer levels in a coded signal.

Specifically, if the optical transmitter marks the N-1 first positive integer levels with a decimal, the optical transmitter may offset the first positive integer level of the first encoded signal by a first offset. Transmitting, such that the N-1 first positive integer levels are converted to N-1 fractional levels, such that the first encoded signal is converted to a second encoded signal, ie, the second encoded signal is encoded Includes N-1 fractional levels, 1 zero level, and N-1 negative integer levels.

Illustratively, the first encoded signal obtained after encoding the PAM-4 signal includes 7 levels of -3V, -2V, -1V, 0V, 1V, 2V, and 3V, respectively, assuming a first offset of -0.5 The optical transmitter converts the three first positive integers in the first encoded signal by an average of -0.5, and converts the three fractional levels to 0.5V, 1.5V, and 2.5V, respectively, so that the PAM-4 signal corresponds to The seven levels included in the second coded signal are -3V, -2V, -1V, 0V, 0.5V, 1.5V, and 2.5V, respectively.

Optionally, if the optical transmitter marks the N-1 negative positive integer levels with a decimal, the optical transmitter may offset the N-1 negative integer levels in the first encoded signal by a first offset. So that the N-1 negative integer levels are converted to N-1 fractional levels, such that the first encoded signal is converted to a second encoded signal, ie, the second encoded signal includes N-1 fractional levels, 1 zero level and N-1 first positive integer levels.

Exemplarily, assuming that the first offset is +0.3, the optical transmitter can electrically average the three negative integers of the first encoded signal of the PAM-4 signal by +0.3, and convert the three decimal levels to three decimal levels. -2.7V, -1.7V, and -0.7V, so that the second encoded signal corresponding to the PAM-4 signal includes seven levels of -2.7V, -1.7V, -0.7V, 0V, 1V, 2V, and 3V, respectively. Level.

It should be noted that the above-mentioned N-1 fractional levels obtained by shifting N-1 first positive integers or negative integer levels may be positive fractional levels or average negative fractional levels. It can also include positive fractional and negative fractional levels. The specific result is related to the first offset. For example, the first offset is 1.5, and after N-1 negative integer levels are cheap, the N-1 negative integer levels include -1.5V, -0.5V, and 0.5V.

Preferably, in the embodiment of the present invention, the first offset may be taken as a decimal between -1 and 1, such that whether the offset is N-1 integer levels or N-1 negative The integer level is offset, and after the offset, the sign of the level is kept constant, thereby reducing the probability that the negative level and the positive level are disordered.

S103. The optical transmitter modulates the second encoded signal into an optical signal.

Specifically, in the embodiment of the present invention, the optical transmitter may input the second encoded signal into a push-pull modulator for modulation, such as a Mach-Zehnder modulator. Mach–Zehnder modulator, MZM). Further, in the implementation of the present invention, after the optical transmitter inputs the second encoded signal into the MZM, the second encoded signal may be modulated by using a zero-crossing modulation method. Since the amplitude of the second encoded signal is modulated by the zero-crossing modulation method, the modulated optical signal is more resistant to the relative intensity noise of the light source (English: Relative Intensity Noise, RIN). It can be understood that the zero-crossing modulation method can suppress the carrier, thereby reducing the transmission power when the optical transmitter transmits the optical signal, and improving the performance of the optical transmission system.

It should be noted that, after the optical receiver directly detects the received optical signal, the square value of the value corresponding to the level information carried in the optical signal is obtained. Therefore, in the embodiment of the present invention, the optical transmitter will When the second coded signal is modulated into an optical signal, the optical transmitter needs to perform a square root processing on the second coded signal, that is, the values of 2N-1 levels in the second coded signal are separately opened, and then the signal is turned on. The second encoded signal processed by the square is converted into an optical signal, so that the optical receiver receives the optical signal, and after directly detecting the optical signal, can obtain an effective electrical signal.

For example, if the seven levels in the second encoded signal of the PAM-4 signal are -2.7V, -1.7V, -0.7V, 0V, 1V, 2V, and 3V, respectively, the second code after the square root processing 7 levels in the signal

V,

V, 0V, 1V,

V and

V. If the seven levels in the second coded signal are -3V, -2V, -1V, 0V, 0.5V, 1.5V, and 2.5V, respectively, after the square root processing, 7 of the second coded signals The levels are

V,

V, 0V,

V,

V and

V.

Wherein, the specific method of modulating the second coded signal into the optical signal by using the zero-crossing modulation method of the push-pull modulator can be referred to the process of modulating the coded signal by the push-pull modulator in the prior art. Let me repeat.

S104. The optical transmitter sends the optical signal to the optical receiver.

It can be understood that after the optical transmitter acquires the optical signal, the optical signal can be sent to the corresponding optical fiber and sent to the optical receiver.

S105. The optical receiver receives the optical signal sent by the optical transmitter.

S106. The optical receiver directly detects and determines the optical signal, and acquires 2N-1. Levels, the 2N-1 levels include N-1 second positive integer levels, 1 zero level and N-1 positive fraction levels.

In the example of the present invention, after receiving the optical signal, the optical receiver directly detects the optical signal, and directly inputs it into the photodetector, and the photodetector detects the level information carried in the optical signal, and detects The detected level information is judged to acquire the 2N-1 levels.

It can be understood that the level information obtained by the light receiving and detecting the optical signal may be inaccurate with the level information sent by the optical transmitter due to the influence of the system performance or due to the difference in the received power of the optical receiver. Therefore, the optical receiver needs to make a decision on the detected level information.

For example, if the level information originally required to be transmitted by the optical transmitter is 0V and 1V, the decision criterion may be 0.5, and the level information detected by the optical receiver is 0.2V, 1.2V, that is, the detected level information is compared with When the level information transmitted by the optical transmitter is offset by 0.2V, when the optical receiver determines the detected level information, the electrical average of less than 0.5 is determined to be 0V, and the electrical average greater than 0.5 is determined to be 1V. Among them, the judgment criteria can be set according to actual needs.

Further, in order to avoid distortion of level information acquired by the optical receiver after directly detecting the optical signal, the optical receiver may perform clock algorithm processing and equalization algorithm processing on the detected level information.

For a specific implementation manner of the clock algorithm processing, the equalization algorithm processing, and the determination of the level information, refer to the related description in the prior art, and details are not described herein again.

Exemplarily, it is assumed that the optical signal received by the optical receiver is modulated by the second encoded signal of the PAM-4 signal after the square root processing, if the seven levels in the second encoded signal are respectively

V,

V, 0V, 1V,

V and

V, the optical receiver directly detects the optical signal and determines that the seven levels are 2.7V, 1.7V, 0.7V, 0V, 1V, 2V, and 3V. If the seven levels in the second coded signal are respectively

V,

V, 0V,

V,

V and

V, the optical receiver directly detects the optical signal and determines that the seven levels are 3V, 2V, 1V, 0V, 0.5V, 1.5V, and 2.5V. That is, the seven levels obtained by the optical receiver by directly detecting the optical signal include three positive decimal levels, one zero level, and three second positive integer levels.

S107. The optical receiver recovers the 2N-1 levels to obtain the restored first encoded signal, where the restored first encoded signal includes the restored N-1 first positive integer levels, and after recovery. 1 zero level and N-1 negative integer levels after recovery; N-1 first positive integer levels after recovery are the N-1 second positive integer levels, 1 zero after recovery The level is the one zero level, and the restored N-1 negative integer levels are converted by the N-1 positive fractional levels; or, the restored N-1 first positive integer levels are determined by The N-1 positive fractional level is converted, and the restored zero level is the one zero level, and the restored N-1 negative integer levels are determined by the N-1 second positive integers. Flat conversion income.

It should be noted that, in the embodiment of the present invention, since the optical receiver of the receiving end (ie, the optical receiver) may not completely recover the first encoded signal of the transmitting end (ie, the optical transmitter), in order to distinguish the first end of the transmitting end, The coded signal and the first coded signal recovered by the receiving end are still referred to as the first coded signal at the transmitting end, and the first coded signal recovered by the receiving end is referred to as the restored first coded signal. Similarly, the first positive integer level recovered by the receiving end is called the first positive integer level after recovery, and the negative integer level recovered by the receiving end is called the restored negative integer level, and the zero level recovered by the receiving end. It is called the zero level after recovery.

Further, if the optical transmitter marks the negative integer level with a decimal, the optical receiver needs to recover N-1 positive decimals among 2N-1 levels when recovering the detected 2N-1 levels. The level is converted to the restored N-1 negative integer levels.

Specifically, the optical receiver recovers the 2N-1 levels, and the optical receiver determines that the N-1 second positive integer levels are the restored N-1 first positive integer levels. Determining that the one zero level is the restored zero level; shifting the N-1 positive fractional level offsets by a first offset, respectively, to obtain N-1 third positive integer levels, and The N-1 third positive integer levels are respectively inverted to obtain the restored N-1 negative integer levels.

Exemplarily, after the optical receiver directly detects and determines the received optical signal, the obtained seven levels are sequentially 2.7V, 1.7V, 0.7V, 0V, 1V, 2V. And 3V, the optical receiver can maintain the three second positive integer levels of the seven levels unchanged, that is, determine that the three second positive integer levels are respectively the restored first positive integer level. The optical receiver shifts the three positive decimal levels of the seven levels according to a first offset used by the optical transmitter, ie, +0.3, to be converted into three third positive integer levels. The three third positive integer levels are sequentially 3V, 2V, and 1V, and then the three third positive integer levels are sequentially inverted to obtain the restored three negative integer levels, which are -3V, -2V, and -1V. Then, the optical receiver recovers the acquired 7 levels, and can obtain 7 levels in the restored first encoded signal, respectively -3V, -2V, -1V, 0V, 1V, 2V, and 3V. That is, in the embodiment of the present invention, the optical receiver can acquire the restored first encoded signal of the PAM-4 signal.

Optionally, if the optical transmitter marks the positive integer level with a decimal, the optical receiver needs to recover N-1 of the 2N-1 levels when recovering the detected 2N-1 levels. The fractional level is converted to the restored N-1 second integer levels.

Specifically, the optical receiver recovers the 2N-1 levels, and the optical receiver respectively inverts the N-1 second positive integer levels to obtain the restored N-1 negative integers. Level, and shifting N-1 positive fraction levels by a first offset, respectively, to obtain the restored N-1 first positive integer levels.

Exemplarily, after the optical receiver directly detects and determines the received optical signal, the obtained seven levels are sequentially 3V, 2V, 1V, 0V, 0.5V, 1.5V, and 2.5V, and the optical receiver is The three positive integer levels of the seven levels can be inverted respectively to obtain three negative integer levels, which are -3V, -2V, and -1V, respectively, and the three negative integer levels are recovered. The last 3 negative integer levels. The optical receiver sequentially performs reverse direction offset according to a first offset used by the optical transmitter, that is, -0.5, and three positive decimal levels of the seven levels, to convert the three positive fractional levels into The three positive integer levels are sequentially 1V, 2V, and 3V, and the three positive integer levels are the three first positive integer levels after recovery. Then, after the optical receiver recovers the acquired 7 levels, the 7 levels in the restored first encoded signal of the PAM-4 signal can be obtained, that is, in the embodiment of the present invention, the optical receiver can Obtaining the restored first encoded signal. Wherein, the reverse direction offset refers to when the optical transmitter marks a positive integer level with a decimal, if the light transmission is the first The N-1 positive integer levels in the code signal are offset by +M, and the optical reception shifts the N-1 positive fractions detected by it to -M, M is the first offset.

S108. The optical receiver decodes the restored first encoded signal to obtain the restored PAM-N signal.

Correspondingly, the optical receiving interface may decode the restored first encoded signal by using a multiple binary code modulation technique to obtain the restored PAM-N signal.

It can be understood that since the restored first encoded signal and the first encoded signal may have slight errors, the PAM-N signal obtained by decoding the restored first encoded signal may also have slight errors. In the embodiment of the present invention, the PAM-N signal recovered by the light reception is referred to as the restored PAM-N signal.

Specifically, the process of decoding the restored first encoded signal by the optical receiver can be referred to the prior art, and is not described in detail herein.

In summary, the optical transmission method provided by the embodiment of the present invention enables the optical receiving interface to be capable of directly detecting the optical signal of the PAM-N when the encoded signal of the PAM-N signal includes a negative level. Demodulation is performed to reduce the complexity of the optical transmitter and the optical receiver, and to reduce the power consumption of the optical transmitter and the optical receiver.

Further, in the embodiment of the present invention, the coding mode used by the optical transmitter to encode the PAM-N signal (for example, the coding method in IEEE802.3bj) can reduce the bandwidth requirement of the optical transmitter and the optical receiver, According to the optical transmission method provided by the embodiment of the present invention, it is possible to realize modulation of 40 to 50 Gbps using a 10 GHz optical transmitter and an optical receiver, or to realize modulation of 100 Gbps using a 25 GHz optical transmitter and an optical receiver, and compared with a conventional modulation solution. The modulation scheme also reduces the carrier-signal power ratio of the optical signal corresponding to the encoded signal, thereby improving system performance.

The optical transmission method provided by the embodiment of the invention makes the design of the optical transmitter and the optical receiver simple, and can implement a low-power optical module package, for example, a small package pluggable transceiver with a power consumption requirement of less than 1.5W. :Small Form-factor Pluggables (SFP) package, or Quad-SFP interface (QSFP) package with less than 3.5W power consumption.

As shown in FIG. 3, an embodiment of the present invention provides an optical transmitter, including: a processing unit 10, a modulating unit 11, and a communication unit 12. The processing unit 10, the modulating unit 11, and the communication unit 12 can be connected through a communication bus 13. The system bus 13 may include a data bus, a power bus, a control bus, and a signal status bus. For convenience of representation, only one thick line is shown in FIG. 3, but it does not mean that there is only one bus or one type of bus.

The processing unit 10 can be an encoder, a central processing unit (English: central processing unit, abbreviation: CPU), and can also be other dedicated processors, general-purpose processors, digital signal processors (English: digital signal processing, referred to as DSP) ), application specific integrated circuit (ASIC), field-programmable gate array (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware Components, etc. The general purpose processor may be a microprocessor or the processor or any conventional processor or the like.

The modulation unit 11 can be a push-pull modulator.

The communication unit 12 can be a transceiver, a transceiver circuit, or a communication interface, etc., for supporting information exchange between the optical transmitter and the optical receiver.

The optical transmitter may further include a storage unit 14 for storing code programs and data in the optical transmitter, and the storage unit 14 may include a volatile memory, such as a random access memory ( English: random-access memory, abbreviation: RAM); the memory 14 may also include non-volatile memory (English: non-volatile memory), such as read-only memory (English: read-only memory, abbreviation: ROM), Flash memory (English: flash memory), hard disk (English: hard disk drive, abbreviated: HDD) or solid state drive (English: solid-state drive, abbreviation: SSD); the memory 14 may also include the above types of memory combination. It is possible to implement or carry out the various illustrative logical blocks, modules and circuits described in connection with the present disclosure. The processing unit may also be a combination of computing functions, such as a group comprising one or more microprocessor combinations, a DSP and a microprocessor. And so on.

Specifically, in the embodiment of the present invention, the processing unit 10 is configured to encode an N-level pulse amplitude modulation PAM-N signal to be transmitted, and acquire a first encoded signal, where the first encoded signal includes N-1. The first positive integer level, 1 zero level and N-1 negative integer levels, N ≥ 3, N is an integer.

The processing unit 10 is further configured to offset the N-1 first positive integer levels or the N-1 negative integer levels by a first offset, respectively, to convert the first encoded signal Converted to a second encoded signal, the first offset being a fractional number.

The modulating unit 11 is configured to modulate the second encoded signal converted by the processing unit 10 into an optical signal.

The communication unit 12 is configured to send the optical signal modulated by the modulation unit 11 to an optical receiver.

Optionally, the first offset is a decimal between -1 and 1.

An optical transmitter according to an embodiment of the present invention is capable of biasing a first positive integer level or a negative integer level in a first encoded signal of a PAM-N signal by a first offset of a decimal value Moving, obtaining a second encoded signal, and modulating the second encoded signal into an optical signal for transmission to a receiver, so that the optical receiver directly detects and determines the optical signal, and the acquired 2N-1 levels are included. N-1 positive fractional levels, so that the optical receiver can convert the N-1 positive fractional levels to the restored N-1 negative integer levels when recovering the 2N-1 levels And determining that the zero point in the 2N-1 levels is the restored zero level, and determining N-1 positive integer levels in the 2N-1 levels as the restored N-1 first a positive integer level to obtain the restored first encoded signal, or to convert the N-1 positive fractional levels to the recovered N-1 first positive integer levels, and determine the 2N-1 The zero point in the level is the zero level after recovery, and the N-1 second positive integer levels in the 2N-1 levels are converted to the restored N-1 negative The number of levels to obtain a first encoded signal restoration, and thus the optical receiver may decode the first encoded signal recovery, PAM-N signal is obtained after the recovery. That is, by the optical transmission method, when the optical receiving connection can include a negative level in the encoded signal of the PAM-N signal, the optical signal of the PAM-N can also be directly detected. Line demodulation reduces the complexity of the optical transmitter and optical receiver and reduces the power consumption of the optical transmitter and optical receiver.

As shown in FIG. 4, an embodiment of the present invention provides an optical receiver, including: a communication unit 20, a photodetection unit 21, and a processing unit 22, the communication unit 20, the photodetection unit 21, and the processing unit. 22 can be connected by a communication bus 23, which can include a data bus, a power bus, a control bus, and a signal status bus. For convenience of representation, only one thick line is shown in FIG. 4, but it does not mean that there is only one. Root bus or a type of bus.

The communication unit 20 can be a transceiver, a transceiver circuit, or a communication interface, etc., for supporting information exchange between the optical receiver and the optical transmitter.

The photodetecting unit 21 may include a photodetector, a decision module, and the like.

The processing unit 22 may be a decoder, a CPU, or other dedicated processors, general purpose processors, DSPs, ASICs, FPGAs, or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, and the like. The general purpose processor may be a microprocessor or the processor or any conventional processor or the like.

The optical receiver may further include a storage unit 24 for storing code programs and data in the optical transmitter, and the storage unit 24 may include a volatile memory such as a RAM; the memory 24 may also include non-easy Loss memory, such as ROM, flash memory, HDD or SSD; the memory 24 may also include a combination of the above types of memory. It is possible to implement or carry out the various illustrative logical blocks, modules and circuits described in connection with the present disclosure. The processing unit may also be a combination of computing functions, such as one or more microprocessor combinations, a combination of a DSP and a microprocessor, and the like.

Specifically, in the example of the present invention, the communication unit 20 is configured to receive an optical signal sent by the optical transmitter.

The photodetecting unit 21 is configured to directly detect and determine the optical signal received by the communication unit 20, and acquire 2N-1 levels, and the 2N-1 levels include N-1 seconds. Positive integer level, 1 zero level and N-1 positive fractional levels, N≥3, N is an integer.

The processing unit 22 is configured to recover the 2N-1 levels acquired by the photo detecting unit 21 to obtain a restored first encoded signal, where the restored first encoded signal includes after recovery N-1 first positive integer levels, 1 zero level after recovery and N-1 negative integer levels after recovery; said restored N-1 first positive integer levels are said N-1 second positive integer levels, the recovered one zero level is the one zero level, and the restored N-1 negative integer levels are from the N-1 The result of the positive fractional level conversion; or, the restored N-1 first positive integer levels are converted by the N-1 positive fractional levels, and the recovered one zero level is One zero level is described, and the recovered N-1 negative integer levels are converted by the N-1 second positive integer levels.

The processing unit 22 is further configured to decode the restored first encoded signal to obtain the restored N-level pulse amplitude modulated PAM-N signal.

Optionally, the optical signal is a signal obtained by the optical transmitter to modulate a second encoded signal, and the second encoded signal is an optical transmitter that uses N-1 first positive integers in the first encoded signal. A signal obtained by shifting the first offset by a flat or N-1 negative integer level, the first offset being a fraction.

Optionally, the processing unit 22 is specifically configured to determine that the N-1 second positive integer levels are the restored N-1 first positive integer levels; determining the one zero power Leveling is one zero level after the recovery; shifting the N-1 positive fractional level offsets by a first offset, respectively, acquiring N-1 third positive integer levels, and The N-1 third positive integer levels are respectively inverted to obtain the restored N-1 negative integer levels, and the first offset is a decimal.

Optionally, the processing unit 22 is specifically configured to invert the N-1 second positive integer levels to obtain the restored N-1 negative integer levels; and determine the 1 a zero level is the one zero level after the recovery; and the N-1 positive fractional levels are respectively offset by a first offset, and the restored N-1 first positive integers are obtained. Flat, the first offset is a decimal.

Optionally, the first offset is a decimal between -1 and 1.

As shown in FIG. 5, an embodiment of the present invention provides an optical transmission system, including: an optical transmitter as described in FIG. 3, and an optical receiver as shown in FIG.

The optical transmitter and the optical receiver in the optical transmission system provided by the embodiment of the present invention are capable of performing the optical transmission method as described in FIG. 2 . For a specific payment method, refer to the related description in the foregoing embodiment shown in FIG. 2, and details are not described herein again.

According to the optical transmission system provided by the embodiment of the present invention, the optical transmitter can offset the positive integer level or the negative integer level in the first encoded signal of the PAM-N signal by using the first offset of the decimal value. Obtaining a second encoded signal, and modulating the second encoded signal into an optical signal and transmitting the optical signal to the optical receiver, so that the optical receiver directly detects and determines the optical signal, and the acquired 2N-1 levels include N -1 positive fractional level, Therefore, the optical receiver can convert the N-1 positive decimal levels to the restored N-1 negative integer levels when recovering the 2N-1 levels, and determine the 2N-1 electrical The zero level in the plane is the zero level after recovery, and the N-1 positive integer levels in the 2N-1 levels are determined to be the restored N-1 first positive integer levels for recovery. After the first encoded signal, or converting the N-1 positive fractional levels to the restored N-1 first positive integer levels, and determining that the zero point in the 2N-1 levels is recovered Zero level, and converting N-1 second positive integer levels of the 2N-1 levels into recovered N-1 negative integer levels to obtain the restored first encoded signal, thereby The optical receiver can decode the restored first encoded signal to obtain a restored PAM-N signal. That is, by the optical transmission method, when the optical receiving connection can include a negative level in the encoded signal of the PAM-N signal, the optical signal of the PAM-N can also be demodulated by direct detection, thereby reducing the optical transmitter and the light. The complexity of the receiver reduces the power consumption of the optical transmitter and optical receiver.

It will be clearly understood by those skilled in the art that for the convenience and brevity of the description, only the division of each functional module described above is exemplified. In practical applications, the above function assignment can be completed by different functional modules as needed. The internal structure of the device is divided into different functional modules to perform all or part of the functions described above. For the specific working process of the system, the device and the unit described above, reference may be made to the corresponding process in the foregoing method embodiments, and details are not described herein again.

In the several embodiments provided by the present application, it should be understood that the disclosed system, apparatus, and method may be implemented in other manners. For example, the device embodiments described above are merely illustrative. For example, the division of the modules or units is only a logical function division. In actual implementation, there may be another division manner, for example, multiple units or components may be used. Combinations can be integrated into another system, or some features can be ignored or not executed. In addition, the mutual coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection through some interface, device or unit.

The unit described as a separate component may or may not be physically separated, and the component displayed as a unit may or may not be a physical unit. To be located in one place, or distributed to multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of the embodiment.

In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above integrated unit can be implemented in the form of a software functional unit.

The integrated unit, if implemented in the form of a software functional unit and sold or used as a standalone product, may be stored in a computer readable storage medium. Based on such understanding, all or part of the technical solution may be embodied in the form of a software product stored in a storage medium, including a plurality of instructions for causing a computer device (which may be a personal computer, a server, Either a network device or the like) or a processor performs all or part of the steps of the method described in various embodiments of the invention. The storage medium is a non-transitory medium, including: a flash memory, a mobile hard disk, a read only memory, a random access memory, a magnetic disk, or an optical disk, and the like, which can store program code.

The above is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily think of changes or substitutions within the technical scope of the present invention. It should be covered by the scope of the present invention. Therefore, the scope of the invention should be determined by the scope of the claims.

Claims

An optical transmission method, comprising:

The N-level pulse amplitude modulated PAM-N signal to be transmitted is encoded to obtain a first encoded signal, the first encoded signal comprising N-1 first positive integer levels, 1 zero level and N-1 negative Integer level, N≥3, N is an integer;

And shifting the N-1 first positive integer levels or the N-1 negative integer levels by a first offset to convert the first encoded signal into a second encoded signal, The first offset is a decimal;

Modulating the second encoded signal into an optical signal;

The optical signal is transmitted to an optical receiver.
The method of claim 1 wherein

The first offset is a fraction between -1 and 1.
An optical transmission method, comprising:

Receiving an optical signal transmitted by the optical transmitter;

Directly detecting and determining the optical signal to obtain 2N-1 levels, the 2N-1 levels including N-1 second positive integer levels, 1 zero level, and N-1 positive fractions Level, N≥3, N is an integer;

Restoring the 2N-1 levels to obtain a restored first encoded signal, the restored first encoded signal including the restored N-1 first positive integer levels, and the restored 1 Zero level and N-1 negative integer levels after recovery; the recovered N-1 first positive integer levels are the N-1 second positive integer levels, the recovered One zero level is the one zero level, and the restored N-1 negative integer levels are converted by the N-1 positive fractional levels; or, the recovered N- One first positive integer level is converted by the N-1 positive fractional levels, the recovered one zero level is the one zero level, and the restored N-1 a negative integer level is converted from the N-1 second positive integer levels;

Decoding the restored first encoded signal to obtain a recovered N-level pulse amplitude modulated PAM-N signal.
The method of claim 3 wherein:

The optical signal is a signal obtained by the optical transmitter modulating a second encoded signal, and the second encoded signal is an N-1 first positive integer level in the first encoded signal of the optical transmitter or N-1 negative integer levels are respectively offset by a signal obtained by a first offset, the first offset being a fraction.
The method according to claim 4, wherein said recovering said 2N-1 levels comprises:

Determining, the N-1 second positive integer levels are the restored N-1 first positive integer levels;

Determining that the one zero level is one zero level after the recovery;

And shifting the N-1 positive fractional level offsets by a first offset, respectively acquiring N-1 third positive integer levels, and taking the N-1 third positive integer levels respectively In contrast, the recovered N-1 negative integer levels are obtained, and the first offset is a decimal.
The method according to claim 4, wherein said recovering said 2N-1 levels comprises:

And inverting the N-1 second positive integer levels respectively to obtain the restored N-1 negative integer levels;

Determining that the one zero level is one zero level after the recovery;

The N-1 positive fractional levels are respectively offset by a first offset, and the restored N-1 first positive integer levels are obtained, and the first offset is a decimal.
Method according to claim 5 or 6, characterized in that

The first offset is a fraction between -1 and 1.
An optical transmitter, comprising: a processing unit, a modulating unit, and a communication unit,

The processing unit is configured to encode an N-level pulse amplitude modulated PAM-N signal to be transmitted, to obtain a first encoded signal, where the first encoded signal includes N-1 first positive integer levels, 1 zero Level and N-1 negative integer levels, N≥3, N is an integer;

The processing unit is further configured to respectively shift the N-1 first positive integer levels or the N-1 negative integer levels by a first offset to convert the first encoded signal The second encoded signal, the first offset is a decimal;

The modulating unit is configured to modulate the second encoded signal converted by the processing unit into an optical signal;

The communication unit is configured to send the optical signal modulated by the modulation unit to an optical receiver.
The optical transmitter of claim 8 wherein:

The first offset is a fraction between -1 and 1.
An optical receiver, comprising: a communication unit, a photodetection unit, and a processing unit,

The communication unit is configured to receive an optical signal sent by the optical transmitter;

The photodetecting unit is configured to directly detect and determine the optical signal received by the communication unit, and acquire 2N-1 levels, where the 2N-1 levels include N-1 second positive integers Level, 1 zero level and N-1 positive fractional levels, N≥3, N is an integer;

The processing unit is configured to recover the 2N-1 levels acquired by the photo detecting unit to obtain a restored first encoded signal, where the restored first encoded signal includes a restored N - 1 first positive integer level, 1 zero level after recovery and N-1 negative integer levels after recovery; said restored N-1 first positive integer levels being said N- a second positive integer level, the recovered zero level is the one zero level, and the restored N-1 negative integer levels are from the N-1 positive decimals Level conversion is obtained; or, the restored N-1 first positive integer levels are converted by the N-1 positive fractional levels, and the restored one zero level is the 1 Zero level, the recovered N-1 negative integer levels are converted by the N-1 second positive integer levels;

The processing unit is further configured to decode the restored first encoded signal to obtain the restored N-level pulse amplitude modulated PAM-N signal.
The optical receiver according to claim 10, characterized in that

The optical signal is a signal obtained by the transmitter to modulate a second encoded signal, and the second encoded signal is an N-1 first positive integer level or N- in the first encoded signal of the transmitter. A negative integer level is respectively offset by a signal obtained by a first offset, the first offset being a fraction.
The optical receiver according to claim 11, wherein

The processing unit is specifically configured to determine that the N-1 second positive integer levels are the restored N-1 first positive integer levels; determining the one zero level is the recovery a subsequent zero level; shifting the N-1 positive fractional level offsets by a first offset, respectively, acquiring N-1 third positive integer levels, and acquiring the N-1 The third positive integer level is respectively inverted to obtain the restored N-1 negative integer levels, and the first offset is a decimal.
The optical receiver according to claim 11, wherein

The processing unit is specifically configured to invert the N-1 second positive integer levels to obtain the restored N-1 negative integer levels; and determine the one zero level as the Determining a zero level after recovery; shifting the N-1 positive fractional levels by a first offset, respectively, and acquiring the restored N-1 first positive integer levels, An offset is a decimal.
The optical receiver according to claim 12 or 13, wherein

The first offset is a fraction between -1 and 1.
An optical transmission system, comprising:

An optical transmitter according to claim 8 or 9, and an optical receiver according to any of claims 10-14.