Optical communication equipment, signal processing method and medium

Abstract

The invention discloses optical communication equipment such as an optical line terminal and an optical network unit, a signal processing method and a medium. An exemplary optical line terminal may include an optical carrier generator configured to generate at least a first optical carrier and a second optical carrier; the transmitter is connected with the optical carrier generator and is configured to modulate a downlink signal to the first optical carrier to form a downlink sending signal; and the optical coupler is used for coupling the downlink transmission signal and the second optical carrier for downlink transmission. The embodiment of the invention also provides a corresponding method implemented at the optical line terminal, an optical network unit and a corresponding implementation method, and a computer readable medium and a computer program product.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical communication technology, and more particularly, to an optical communication device in a passive optical network, a signal processing method and a computer readable storage medium. BACKGROUND

[0002] The dominant system architecture of current broadband optical access networks is based on the Passive Optical Network (PON) access technology. A series of PON standards with data rates up to 50 Giga bits per second (Gb / s) have been approved by multiple optical communication standard organizations, such as the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) and the Institute of Electrical and Electronics Engineers (IEEE).

[0003] In order to meet the bandwidth demand of end users growing in a geometric progression, the next generation of optical access networks is expected to achieve a data rate of 200 Gb / s to distinguish from the current PON optical network designed with a capacity of 50 G. At this data rate, due to the dispersion in optical signal transmission and the limited device bandwidth, the traditional intensity modulation (IM) and direct detection (DD) technology will be difficult to meet the power budget limit of the deployed Optical Distributed Network (ODN).

[0004] The coherent optical detection technology has become a research hotspot in academia and industry due to its high receiving sensitivity and spectral efficiency. However, the optical access network is very sensitive to cost, and the device structure of coherent reception is complex, which will greatly increase the equipment cost compared with the IM / DD scheme. Therefore, how to reduce the equipment cost of the optical communication system under the premise of ensuring the performance of coherent detection is a problem to be solved. SUMMARY

[0005] Various exemplary embodiments of the present application are intended to solve at least part of the above problems or issues.

[0006] According to a first aspect of the present application, an optical line terminal (OLT) is provided, comprising: an optical carrier generator configured to generate at least a first optical carrier and a second optical carrier; a transmitter connected with the optical carrier generator, configured to modulate a downlink signal onto the first optical carrier to form a downlink transmission signal; and an optical coupler for coupling the downlink transmission signal and the second optical carrier for downlink transmission.

[0007] In a second aspect, there is provided an optical network unit (ONU), comprising: a receiver configured to receive a downstream signal modulated on a first optical carrier; and a carrier regenerator configured to receive a second optical carrier and generate a local oscillator signal based on the second optical carrier, wherein the receiver is connected to the carrier regenerator and configured to perform coherent detection on the downstream signal using the local oscillator signal.

[0008] In a third aspect, there is provided a signal processing method at an optical line terminal, comprising: generating a first optical carrier and a second optical carrier; modulating a downstream signal on the first optical carrier to form a downstream transmission signal; and coupling the downstream transmission signal and the second optical carrier for downstream transmission. In some embodiments, the method further comprises: generating a third optical carrier, and performing coherent detection on a received upstream signal (e.g. optical single sideband signal) using the third optical carrier.

[0009] In a fourth aspect, there is provided a signal processing method at an optical network unit (ONU), comprising: receiving a downstream signal modulated on a first optical carrier; receiving a second optical carrier and generating a local oscillator signal based on the second optical carrier; and performing coherent detection on the downstream signal using the local oscillator signal. In some embodiments, the method further comprises: loading an upstream signal (e.g. optical single sideband signal) using the local oscillator signal.

[0010] In a fifth aspect, there is provided an apparatus, comprising: at least one processor; and at least one memory storing instructions which, when executed by the at least one processor, cause the apparatus to perform at least the method according to the third or fourth aspect.

[0011] In a sixth aspect, there is provided a computer program product comprising (computer executable) program instructions which, when executed (or run) by a processor, cause the processor to perform the method according to the third or fourth aspect.

[0012] The computer program product can comprise or can be embodied as a computer readable (storage) medium, etc., on which the computer executable computer program instructions are stored and / or directly loadable into an internal memory of a computer or its processor. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 A schematic diagram showing the configuration of a full-coherent receiver applied to a PON network;

[0014] Figure 2 A schematic diagram showing an optical communication system according to an example embodiment of the present application;

[0015] Figure 3A A schematic diagram showing a passive optical network communication system according to an example embodiment of the present application;

[0016] Figure 3B A structural composition diagram of a simplified coherent receiver is shown according to an example embodiment of the present application;

[0017] Figure 3C A structural composition diagram of a simplified OSSB transmitter is shown according to an example embodiment of the present application;

[0018] Figure 4 An analog model diagram of a passive optical network is shown according to an example embodiment of the present application;

[0019] Figure 5A 、 5B Schematic optical spectrum diagrams of a downstream signal and an upstream signal are shown respectively according to an example embodiment of the present application;

[0020] Figure 6A 、 6B Coherent detection analog diagrams of the downstream signal and the upstream signal are shown respectively;

[0021] Figure 7 A flow chart of a method implemented at an optical line terminal is shown according to an embodiment of the present application;

[0022] Figure 8 A flow chart of a method implemented at an optical network unit is shown according to an embodiment of the present application;

[0023] Figure 9 A schematic block diagram of an optical network device is shown according to an example embodiment of the present application.

[0024] The same or substantially the same elements, operations, steps, etc. shown in the various figures can be denoted by the same reference numerals. Not all elements, operations, steps, etc. can be shown in each figure for clarity. DETAILED DESCRIPTION

[0025] Example embodiments of the present application will be described in greater detail below, with reference to the accompanying drawings. It should be understood that the example embodiments described herein are not intended to limit the present application, and the present application can also be implemented in various other forms. The example embodiments are provided only to more completely and concretely understand the present application, and it should be understood that the present application is not limited by the precise forms described herein.

[0026] As mentioned above, coherent optical detection technology is proposed to achieve further improvement of data rate of PON network. Although the coherent scheme has higher receiving sensitivity, better spectral performance, easy upgrade, etc. than the IM / DD scheme, the corresponding PON network also has problems in cost, power consumption, etc. Figure 1The figure shows a schematic diagram of the structure of a fully coherent receiver applied to PON networks. As shown in frame (a), the fully coherent receiver consists of a local oscillator (LO), a polarization beam splitter (PBS), two 90° optical mixers, four balanced photodetectors (BPDs), four transimpedance amplifiers, and other components. The receiver of the IM / DD solution only requires a single preamplifier, an optical bandpass filter, an optical detector, and other components. It can be seen that the deployment of PON networks using a coherent solution will greatly increase equipment costs.

[0027] The number of components used in the receiver can be reduced to a certain extent by using heterodyne coherent detection and other technologies, such as Figure 1 As shown in the middle frame (b), it can reduce the number of components by about half compared to a fully coherent solution. However, it still requires a high-quality local oscillator (e.g., a laser) to output wavelength-stable local oscillator light for coherent beat frequency, which will impose a burden on cost and power consumption, making this technology difficult to implement. In addition to requiring more sophisticated components, the digital signal processing (DSP) in the coherent receiver will also be more complex than that of traditional PON networks. For 50G PON networks using the IM / DD solution, only linear feedforward equalization (FFE) and other algorithms are required for dispersion compensation, while coherent receivers require many complex algorithms such as frequency offset compensation, carrier recovery, in-phase / quadrature phase (I / Q) imbalance compensation, and MIMO algorithms for polarization demultiplexing. This will also greatly increase the cost and power consumption of applying coherent detection technology to PON networks.

[0028] In view of this, some aspects of the embodiments of the present application provide a composition architecture of optical communication equipment in a PON network and a corresponding signal processing method, by transmitting an optical carrier for coherent detection of a downlink signal while sending a downlink signal, and then processing the optical carrier on the receiving side of the downlink signal (for example, an optical network unit ONU) to obtain a local oscillator optical signal for coherent detection, thereby eliminating the need to use other expensive lasers in the ONU to generate local oscillator light, eliminating the local oscillator in the ONU, thereby saving the cost of the PON network system and effectively improving the optical signal processing performance.

[0029] Figure 2A schematic diagram of a communication system according to an exemplary embodiment of the present application is shown. As shown in the figure, the communication system can be part of a passive optical network, which includes an optical line terminal (OLT) 110 and an optical network unit (ONU) 120. Bidirectional communication can be performed between OLT 110 and ONU 120. For example, OLT 110 can send data / signals to ONU 120 via a downlink, and ONU 120 can send data / signals to OLT 110 via an uplink. Although only one optical network unit 120 is shown in the figure, it is understood that OLT 110 can perform optical communication with multiple optical network units via an optical distribution network (ODN).

[0030] like Figure 2 As shown, the optical line terminal OLT 110 may include an optical carrier generator 112, an OLT transmitter 114, a coupler 116, and an OLT receiver 118. The optical carrier generator 112 is configured to generate an optical carrier (or simply a carrier) after power-on and provide the corresponding optical carrier to the OLT transmitter 114, the coupler 116, and the OLT receiver 118. Preferably, the optical carrier generator 112 is an optical frequency comb generator that can provide multiple tones or optical carriers. For example, in the embodiment of the present application, the optical carrier generator 112 can generate a first optical carrier, a second optical carrier, and a third optical carrier having different frequencies or main wavelengths and provide them to the OLT transmitter 114, the coupler 116, and the OLT receiver 118, respectively.

[0031] The OLT transmitter 114 is connected to the carrier generator 112 and can receive a first optical carrier from the carrier generator 112, and simultaneously receive a downlink data signal to be transmitted, and modulate the downlink signal onto the first optical carrier to form a downlink transmission signal. In one embodiment, the OLT transmitter 114 may include a coding module 117, which can be used to perform space-time coding on the downlink transmission signal to form a space-time coded signal. Through space-time coding, single polarization heterodyne detection can be performed on the optical network unit 120 side, which is insensitive to polarization, thereby helping to reduce the complexity of the optoelectronic components on the optical network unit 120 side, which will be described in detail below.

[0032] Coupler 116 is connected to both optical carrier generator 112 and OLT transmitter 114 and can be used to couple the second optical carrier from optical carrier generator 112 with the downlink transmit signal from OLT transmitter 114 for downlink transmission. For example, the downlink transmit signal can be transmitted via an optical circulator and downlink optical fiber to a corresponding optical network unit 120 or end user.

[0033] The OLT receiver 118 is connected with the optical carrier generator 112, which can be configured to utilize the third optical carrier to perform coherent detection on the received upstream signal. For example, the OLT receiver 118 can receive the upstream optical signal from the optical network unit 120 through an optical circulator, and utilize the third optical carrier to perform coherent detection on the upstream optical signal. In an embodiment, the receiver can have Figure 1 The full-coherent receiver structure shown can also employ a single-polarization heterodyne receiver structure. Although Figure 2 The OLT receiver 118 is shown separately from the OLT transmitter 114, but it can be appreciated that the OLT receiver 118 and the OLT transmitter 114 can be integrated together to form an OLT transceiver to perform both transmission and reception operations.

[0034] As for the optical network unit ONU 120, it can include an ONU receiver 122, a carrier regenerator 124, and an ONU transmitter 126. The ONU receiver 122 is configured to perform signal detection and processing on the downstream optical signal. For example, it can receive the downstream signal modulated on the first optical carrier, and utilize the local signal generated by the carrier regenerator 124 to perform coherent detection on the downstream signal, thereby obtaining the electrical signal carrying the data information. As shown, the carrier regenerator 124 is electrically connected with the ONU receiver 122, which can receive the second optical carrier, generate the local signal based on the second optical carrier, and provide the local signal to the detection module in the ONU receiver 122 to facilitate coherent detection. According to an embodiment of the present application, the carrier regenerator 124 receives the optical carrier from the OLT 110 and uses it as the local signal, so that there is no need to configure a local oscillator in the ONU 120, which can save hardware cost. Figure 2

[0035] The ONU transmitter 126 is also connected with the carrier regenerator 124, which can be configured to load the upstream signal with the local signal generated by the carrier regenerator 124 for upstream transmission. In combination with the foregoing description, according to an embodiment of the present application, the local signal generated by the carrier regenerator 124 is used to assist both the reception of the downstream signal and the transmission of the upstream signal in the optical network unit ONU, which advantageously reduces the hardware space and significantly reduces the cost.

[0036] The technical solution of the embodiments of the present application can be applied to various Ethernet passive optical networks and gigabit passive optical networks. For example, by performing heterodyne coherent detection on the ONU side, a high-speed (e.g., 200 Gb / s) GPON can be implemented. In addition, only an optical carrier generator needs to be provided on the OLT side, without the need to configure an expensive laser source on the ONU, which can significantly reduce the hardware deployment cost for an optical network system with 1:n (n is for example 64) configuration.

[0037] Figure 3A ​A schematic diagram of a passive optical network communication system according to an exemplary embodiment of the present application is shown, which more specifically shows Figure 2 The structure and working principle of the communication system are described below. For the convenience of description, the same or similar components will be used as Figure 2 The same reference numerals are used, and some of the same reference numerals are used to more clearly describe the innovation of the present invention. Figure 2 The arrangement and functions of the same elements will be described briefly. Figure 3A Only one OLT 110 and one ONU 120 are shown in the figure, but it can be understood that the OLT 110 can communicate with multiple ONUs through the optical distribution network (the figure shows the optical splitter 130).

[0038] like Figure 3A As shown, optical carrier generator 112 can employ an optical frequency comb generator capable of generating multiple optical frequency combs in different wavelength bands. For example, it can generate a first optical carrier (frequency f0), a second optical carrier (frequency f1), and a third optical carrier (frequency f2) with different frequencies and provide them to OLT transmitter 114, coupler 116, and OLT receiver 118, respectively. The first optical carrier is used to carry downlink signals, the second optical carrier can serve as the main light source to remotely regenerate the local oscillator (LO) signal at the ONU, and the third optical carrier is used for coherent detection of uplink signals. In one embodiment, the frequency f1 of the second optical carrier can be between the frequency f0 of the first optical carrier and the frequency f2 of the third optical carrier. This helps to achieve frequency spacing between uplink and downlink signals, thereby reducing crosstalk between the signals. This will be described in detail later.

[0039] OLT transmitter 114 receives a first optical carrier and may also receive a data signal from an external data source (e.g., the Internet). It modulates the first optical carrier with the data signal to generate a downlink optical signal. Transmitter 114 may modulate the downlink data using orthogonal frequency division multiplexing (OFDM), quadrature phase shift keying (QPSK), quadrature amplitude modulation (QAM), or other suitable modulation formats to carry the information included in the downlink data on a high-frequency (f0) carrier.

[0040] In one embodiment, the OLT transmitter 114 may also perform space-time coding (Alamouti coding) on ​​the modulated signal in both polarization and time dimensions, forming a space-time coded signal that is then output to the coupler 116. Specifically, the downlink data is redundantly encoded onto multiple different polarization states, with the signal in each polarization state carrying the information included in the downlink data. This allows the coherent receiver on the ONU to receive the optical signal in any polarization state and decode it to obtain the information carried by the signal. In other words, the coherent receiver is insensitive to the polarization state of the received signal, enabling heterodyne detection. This helps simplify the optoelectronic components of the ONU receiver.

[0041] Coupler 116 has two input ports and one output port, one of which is used to receive the downstream signal output by OLT transmitter 114, and the other is used to receive the second optical carrier output by optical frequency comb generator 112, and the output port is used to output the coupled optical signal. Optical coupler 116 is further connected to the trunk fiber through circulator 119 and transmits the downstream signal.

[0042] OLT receiver 118 is also connected to circulator 119 to receive the upstream signal, i.e., circulator 119 enables bidirectional communication between OLT 110 and ONU 120, which is configured to connect OLT transmitter 114 to the fiber when transmitting the downstream signal, and to connect OLT receiver 118 to the fiber when receiving the upstream signal. After receiving the upstream signal, OLT receiver 118 can use the third optical carrier received from optical frequency comb generator 112 to coherently detect the upstream signal to obtain the data information carried in the upstream signal. In an embodiment, the frequency of the upstream signal is close to or equal to the frequency f2 of the third optical carrier, thereby facilitating coherent detection.

[0043] The downstream signal is transmitted to circulator 129 on the ONU 120 side through the fiber, which has the same function as the circulator on the OLT side and will not be described here. Tunable optical filter 128 is connected to circulator 129, which is configured to filter out optical signals of a specified wavelength or frequency from the received downstream signal. In an embodiment, tunable optical filter 128 can be implemented using a tunable silicon-based filter, a tunable liquid crystal filter, etc. As shown, it can filter out the downstream signal modulated on the first optical carrier with frequency f0 and send it to ONU receiver 122, and filter out the second optical carrier with frequency f1 and send it to carrier regenerator 124.

[0044] Carrier regenerator 124 is connected to ONU receiver 122 and ONU transmitter 126, which can filter, amplify, etc. the received second optical carrier as the local oscillator optical signal on the ONU side and provide it to ONU receiver 122 and ONU transmitter 126. In an embodiment, carrier regenerator 124 can use a Fabry-Perot laser diode (FP-LD), or use an optical amplifier (the specific arrangement will be described later), i.e., there is no need to configure an expensive laser such as an external cavity laser (ECL) as a local light source device in ONU 120, thereby significantly saving the hardware cost on the ONU side.

[0045] ONU receiver 122 is connected to carrier regenerator 124 to receive the local oscillator signal provided by carrier regenerator 124 for coherent detection. Figure 3B A schematic diagram of a simplified coherent receiver is shown. As Figure 3BAs shown, the coherent receiver mainly consists of an optical coupler 1222, a photo detector 1224 and a trans-impedance amplifier 1226. The optical coupler 1222 (e.g. a 3dB coupler) has two input ends to receive the downstream optical signal and the local oscillator light from the carrier regenerator 124 respectively. The coupled two-way signals are input into a balanced photo detector (BPD) composed of two photo detectors (PDs) with the same photoelectric performance. After beat frequency detection, two-way electrical signals are obtained. The trans-impedance amplifier 1226 can amplify the electrical signals for subsequent signal processing. Alternatively, a single photo detector can be used to replace the balanced photo detector, which can further reduce the structural composition of the receiver and lower the hardware cost.

[0046] The obtained electrical signals can be converted into digital signals through analog-digital conversion and digital signal processing to obtain the data information carried in the downstream signal. For example, signal down-conversion, space-time block decoding, data demodulation, etc. are performed to recover the information included in the downstream data. It should be noted that, for the embodiments of the present application, since the optical frequency comb generator 112 and the carrier regenerator 124 are used on the OLT 110 and ONU 120 sides, the frequency difference between the space-time encoded signal and the local oscillator light signal for the coherent receiver of the ONU 120 is fixed, so that no frequency offset compensation operation is needed in the digital signal processing, reducing the amount of calculation and improving the processing efficiency. Moreover, the application can be advantageously applied to the uplink burst signal detection.

[0047] The ONU transmitter 126 is electrically connected to the carrier regenerator 124, which can receive the local oscillator light signal generated by the carrier regenerator 124 to load the uplink signal for uplink transmission. That is, the carrier regenerator 124 regenerates the local oscillator light signal based on the second optical carrier received from the OLT 110, which is used not only for the coherent receiver 122 but also for the generation of the uplink signal of the ONU transmitter 126.

[0048] In an embodiment, the uplink signal is an optical single sideband (OSSB) signal, as shown in FIG. 4. Figure 3A As shown, the frequency of the uplink signal and the frequency range of the downstream signal are located on the two sides of the second optical carrier frequency f1 respectively, so that the uplink signal wavelength and the downstream signal wavelength in the optical network are separated without overlap, which can avoid the mutual interference of the downstream and uplink signal transmission due to reflection noise when transmitted in the same optical fiber.

[0049] Figure 3C A schematic diagram of a simplified OSSB transmitter is shown. As shown in FIG. 5, the OSSB transmitter mainly consists of a laser 502, a Mach-Zehnder modulator (MZM) 504 and a polarization controller 506. Figure 3CAs shown, the ONU transmitter 126 includes a dual-drive Mach-Zehnder modulator (DD-MZM) configured to generate the upstream signal by modulating the local oscillator signal with electrical signals. In an embodiment, the Mach-Zehnder modulator has two phase modulators (PMs) driven by two different electrical signals, one of which is and the other of which is where s represents the original data electrical signal, H (s) represents the Hilbert transform of the original data electrical signal, V π represents the half-wave voltage of the DD-MZM, specifically the voltage difference required to adjust the phase of the optical carrier from 0 to 180°, and x represents a normalization coefficient. Using the two driving signals, the DD-MZM adjusts the optical carrier signal (LO) from the carrier regenerator 124 to generate an optical single sideband signal. The optical single sideband signal can be output from the output end of the DD-MZM and transmitted upstream to the OLT 110 side via the circulator 129.

[0050] According to the technical solution of the embodiment of the application, the structure of the coherent receiving and transmitting device is simplified, the costly local oscillator device is omitted, and the algorithm of the digital signal processing is optimized, so that the high-speed PON system can be deployed in a more economical manner.

[0051] Figure 4 A simulation model schematic diagram of a passive optical network according to an exemplary embodiment of the application is shown, which can be used to verify the feasibility and performance of the embodiments of the application. In the simulation model, the VPI software is used for simulation, and the Matlab software is used for the digital signal processing algorithm. Figure 4 The structure of the optical network is shown in more detail in Figure 2 -3, and for the sake of brevity in the description, identical or similar components will be designated by identical reference numerals in Figure 2 -3, and for the sake of more clearly describing the innovations of the application, the arrangement and functions of some elements identical to Figure 2 -3 will be briefly described.

[0052] As Figure 4As shown, the optical line terminal (OLT) 110 mainly includes an optical frequency comb generator 112, an OLT transmitter 114, a coupler 116, and an OLT receiver 118. In an embodiment, the optical frequency comb generator 112 can include a signal source, a modulator, an optical filter, etc., the source signal (e.g., a 40 GHz sinusoidal signal) emitted by the signal source can be amplified by an electrical amplifier (e.g., a 40 GHz electrical amplifier) and used to drive the modulator, and the optical filter can be used to obtain an optical frequency comb with a predetermined frequency. For example, a laser emitted by an external laser is modulated by the modulator to generate an optical frequency comb, and the number of optical frequency combs can be changed by adjusting the parameters of the modulator. The optical frequency comb can pass through the optical filter to obtain an optical frequency comb with a desired frequency, and optionally, an optical amplifier can be used to amplify the generated optical frequency comb. For example, the optical frequency comb generator 112 can be used to generate a frequency comb with 3 optical carriers, and typically, the frequencies of the 3 optical carriers are 193.1 THz (f0), 193.14 THz (f1), and 193.18 THz (f2), respectively, where the frequency f1 is between the frequencies f0 and f2.

[0053] The wavelength division demultiplexer 113 is connected to the optical frequency comb generator 112 and can direct the 3 optical carriers to different branches, where the first optical carrier (frequency f0) is transmitted to the OLT transmitter 114. In an embodiment, the OLT transmitter 114 can be a dual-polarization coherent optical transmitter, which can modulate the first optical carrier using a digital subcarrier multiplexing (DSCM) signal with Alamouti encoding to modulate the optical signal onto the first optical carrier to form a downstream transmission signal. Figure 5A An exemplary optical spectrum diagram of the downstream Alamouti encoded signal is shown, where the encoded DSCM signal is modulated on the first optical carrier with a center frequency of 193.1 THz (f0), and the signal has 8 subcarriers (SCs) carrying 16 quadrature amplitude modulation (QAM) downstream data with a bandwidth of 8 GHz per subcarrier to achieve a data rate of 256 Gb / s. The frequency gap between the subcarriers is 2 GHz, so the total occupied bandwidth is 80 GHz, and the spectral range of all subcarriers carrying downstream data is on one side of the frequency of the second optical carrier (f1).

[0054] In an embodiment, the optical line terminal (OLT) 110 further includes an optical attenuator 115 connected to the optical frequency comb generator 112 and arranged in parallel with the OLT transmitter 114 between the optical frequency comb generator 112 and the optical coupler 116, and the wavelength division demultiplexer 113 directs the second optical carrier (frequency f1) to the optical attenuator 115 to attenuate the second optical carrier. For example, the attenuation rate can be controlled to make the power ratio of the second optical carrier to the downstream signal equal to or lower than a threshold value, so as to avoid or reduce interference with the transmission of the downstream signal.

[0055] The coupler 116 receives the downlink signal output by the OLT transmitter 114 and the attenuated second optical carrier output by the attenuator, and outputs a coupled optical signal (eg Figure 5A The combined signal shown in FIG. 1 is transmitted to the circulator 119, which transmits the downstream signal to the corresponding ONU 120 via an optical fiber (eg, a 20 km standard single mode optical fiber SSMF).

[0056] In one embodiment, the wavelength division multiplexer 113 further directs the third optical carrier (frequency f2) to the OLT receiver 118 for coherent detection of the uplink signal. The OLT receiver 118 is connected to the circulator 119, which can receive the uplink signal and demodulate the signal. The OLT receiver 118 may have Figure 1 The fully coherent receiver or single polarization intradyne receiver structure shown can also be used Figure 3B The demodulated signal is converted to digital by analog (ADC) and then processed by the OLT receiver DSP to recover the data information carried in the uplink signal.

[0057] Continue to refer to Figure 4 The optical network unit ONU 120 mainly includes an ONU receiver 122, a carrier regenerator 124, and an ONU transmitter 126. The downlink signal can be transmitted to the ONU receiver 122 and the carrier regenerator 124 via the circulator 129 and the beam splitter 123.

[0058] In carrier regenerator 124, the received optical wave signal is first filtered by optical filter 1242 to select a second optical carrier signal. Because the second optical carrier is attenuated at OLT 110, carrier regenerator 124 may include an optical amplifier 1244 (e.g., a semiconductor optical amplifier (SOA)) to amplify the second optical carrier to obtain sufficient optical power to serve as a local oscillator (LO) signal. The amplified second optical carrier is then filtered again by optical filter 1246 to obtain a high-amplitude, narrow-bandwidth LO signal. This signal is then provided to the ONU's receiver 122 and transmitter 126 via beam splitter 1248. This eliminates expensive light source equipment such as the external cavity laser (ECL) used in conventional coherent receivers in ONU 120, achieving significant cost savings.

[0059] In the ONU receiver 122, the downstream signal is first filtered by the optical filter 1221 to select the Alamouti encoded signal carried on the first optical carrier, and then can be output to the optical coupler 1222. The optical coupler 1222 can also receive the local oscillator signal from the carrier regenerator 124, and couple the downstream signal and the local oscillator signal, and the coupled optical signal is coherently detected by the optical detector 1224 to obtain an electrical signal. In an embodiment, the ONU receiver 122 can further include an amplifier (for example, a transimpedance amplifier), a filter 1223 to amplify and filter the electrical signal, and then convert the amplified electrical signal into a digital signal through an analog-to-digital converter 1225, and finally process the digital signal through a digital signal processor DSP 1227 to obtain the information carried in the downstream signal. For example, the DSP 1227 can perform signal down-conversion, space-time block decoding, data demodulation, etc. to recover the information included in the downstream data. For the coherent receiver of the ONU 120, the frequency difference between the Alamouti encoded signal and the local oscillator optical signal is fixed, so the frequency offset compensation operation can be omitted in the digital signal processing, reducing the amount of calculation and improving the processing efficiency.

[0060] For the ONU transmitter 126, in order to avoid mutual interference of bidirectional signal transmission in the optical fiber due to reflection noise, the uplink signal can be modulated by optical single sideband (OSSB) modulation technology, for example, the uplink signal is modulated to one side of the frequency spectrum range greater than the frequency f1, Figure 5B The schematic optical spectrum diagram of the uplink OSSB signal is shown, in which the encoded DSCM signal is modulated on a specific optical carrier with a center frequency of 193.15 THz, and the signal has 4 subcarriers (SCs), each subcarrier carries 16QAM format uplink data with a bandwidth of 4GHz, and an uplink data rate of about 64Gb / s can be obtained. As Figure 5B It is shown that the spectral range of all subcarriers carrying uplink data is located on one side of the frequency (f1) of the second optical carrier, in combination with Figure 5A It can be seen that the spectral range of the uplink signal and the downstream signal does not overlap, thereby avoiding the problem of mutual interference of uplink and downstream signals.

[0061] In one embodiment, the ONU transmitter 126 includes a dual-drive Mach-Zehnder modulator (DD-MZM) 1262, which can receive the local oscillator signal from the carrier regenerator 124 and use the local oscillator signal to load the uplink data signal. After the processed data is converted by DAC digital-to-analog conversion and then subjected to Hilbert transform and other processing, two different electrical signals are formed to drive the DD-MZM 1262. The DD-MZM 1262 adjusts the local oscillator signal (LO) from the carrier regenerator 124, thereby generating an optical single-sideband signal carrying the uplink data information. This signal can be sent uplink to the OLT 110 side via the circulator 129. For specific signal processing, please refer to Figure 3C The relevant description will not be repeated here.

[0062] Figure 6A 、 6B The following diagrams illustrate coherent detection simulations for downlink Alamouti-coded signals and uplink OSSB signals. Heterodyne coherent detection using a single photodetector (PD) and a balanced photodetector (BPD) is used for the downlink signal, while fully coherent detection is used for the uplink signal. The horizontal axis represents the received optical power (dBm), while the vertical axis represents the bit error rate (BER) of the received data at the ONU and OLT sides, respectively. This graph shows the BER curves as the bit error rate varies with received optical power.

[0063] See also Figure 6A Assuming a 2E-2 error level threshold after forward error correction (FEC), for downlink transmission, both BPD-based and single-PD coherent receivers have high receiver sensitivities of -31dBm and -25.5dBm, respectively. The 5.5dB performance difference between the two detection methods is due to the coupler (3dB) and the relative intensity noise (RIN) of the local oscillator signal. Therefore, the appropriate receiver structure can be selected based on the network power budget. For example, if the power budget allows, a simplified structure based on a single PD can be used; see [1]. Figure 6B For uplink transmission, although the frequency of the effective subcarrier is set in the range of f1 and f1+20GHz, a receiving sensitivity of about -26dBm can still be achieved.

[0064] The technical solution according to the embodiment of the present invention integrates heterodyne coherent detection, remote optical carrier regeneration, and optical single-sideband signal modulation technology, simplifies the structure of the coherent receiving and transmitting devices used in the passive optical network system, eliminates the costly local oscillator equipment, and optimizes the digital signal processing algorithms of the receivers at both the OLT and ONU ends. Therefore, high-speed (200Gb / s) optical access networks can be deployed in a more economical manner.

[0065] Figure 7 A flowchart of a method 200 implemented at an optical line terminal is shown according to embodiments of the present application. It is appreciated that the method 200 can be implemented, for example, at an optical line terminal (OLT) 110 as shown in FIG. 1. Figure 2 to Figure 4 A flowchart of a method 300 implemented at an optical network unit is shown according to embodiments of the present application. It is appreciated that the method 300 can be implemented, for example, at an optical network unit (ONU) 120 as shown in FIG. 1. Figure 2 to Figure 4 The method 200 is described below in conjunction with the OLT 110 as shown in FIG. 1.

[0066] In step 210, an optical carrier generator can generate a first optical carrier and a second optical carrier. In an embodiment, the optical carrier generator can further generate a third optical carrier. In an embodiment, the first optical carrier, the second optical carrier and the third optical carrier can be generated by an optical frequency comb generator.

[0067] In step 220, an OLT transmitter can modulate a downstream signal onto the first optical carrier to form a downstream transmission signal. In an embodiment, the downstream transmission signal can be space-time encoded after signal modulation to form a space-time encoded signal.

[0068] In step 220, an optical coupler can couple the downstream transmission signal and the second optical carrier for downstream transmission. In an embodiment, the second optical carrier can be input into the coupler after being attenuated by an attenuator.

[0069] In some embodiments, the method 200 can further include coherently detecting a received upstream signal using the third optical carrier.

[0070] Figure 8 A flowchart of a method 300 implemented at an optical network unit is shown according to embodiments of the present application. It is appreciated that the method 300 can be implemented, for example, at an optical network unit (ONU) 120 as shown in FIG. 1. Figure 2 to Figure 4 A flowchart of a method 300 implemented at an optical network unit is shown according to embodiments of the present application. It is appreciated that the method 300 can be implemented, for example, at an optical network unit (ONU) 120 as shown in FIG. 1. Figure 2 to Figure 4 The method 300 is described below in conjunction with the ONU 120 as shown in FIG. 1.

[0071] In step 310, an ONU receiver can receive a downstream signal modulated on a first optical carrier.

[0072] In step 320, a carrier regenerator can receive a second optical carrier and generate a local oscillator signal based on the second optical carrier.

[0073] In an embodiment, step 320 can include filtering a received optical wave signal to select the second optical carrier and amplifying the second optical carrier to generate the local oscillator signal.

[0074] In step 330, the downstream signal can be coherently detected using the local oscillator signal.

[0075] In an embodiment, step 330 can include receiving the downstream signal and the local signal, coupling the downstream signal and the local signal, and detecting the coupled optical signal to obtain an electrical signal.

[0076] In an embodiment, method 300 can further include amplifying the electrical signal, converting the amplified electrical signal into a digital signal, and processing the digital signal to obtain information carried in the downstream signal.

[0077] In some embodiments, method 300 can further include loading an upstream signal with the local signal. In an embodiment, this step can include generating an upstream signal by modulating the local signal with an electrical signal. In an embodiment, the upstream signal is an optical single sideband (OSSB) signal.

[0078] Figure 9 A block diagram illustrating a structure of an optical network device 400 according to an example embodiment of the present application is shown. The optical network device 400 can be implemented as the optical line terminal OLT 110 or the optical network unit ONU 120 described above. As shown, the network device 400 can include one or more processors 410, one or more memories 420, and one or more network interfaces 430, which can be communicatively connected to each other through a bus system 440. Figure 9

[0079] The processor 410 can be, for example, a central processing unit (CPU), a general-purpose processor, a controller, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or other programmable logic device, transistor logic, a hardware component, or any combination thereof. The processor 410 can run instructions and / or exchange data in the memory 420, thereby controlling other components coupled through the bus 440 to operate in cooperation, to perform the methods, steps, or functions described above.

[0080] The memory 420 can include various forms of storage media or be implemented using any suitable data storage technology, such as volatile and / or non-volatile memory. Volatile memory can include, but is not limited to, for example, random access memory (RAM), cache memory, and the like. Non-volatile memory can include, but is not limited to, read-only memory (ROM), hard disk, flash memory, and the like. The term "non-volatile" herein is a limitation on the medium itself (i.e., tangible and not a signal), not a limitation on the persistence of data storage (e.g., RAM or ROM). In addition, the at least one memory 420 can include, but is not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or any combination of the foregoing.

[0081] ​The memory 420 can include computer instructions 422 that can be executed by the processor 410 so that the processor 410 can control other components coupled through the bus 440 to operate in coordination to perform the methods, steps, or functions described above in relation to the optical line terminal OLT 110 or the optical network unit ONU 120.

[0082] The network interface 430 can be a device having a network data receiving and transmitting function such as a receiving circuit, a receiver, an I / O interface, etc.

[0083] According to exemplary embodiments of the present application, any one of the processor(s), the memory(s), and the interface(s) and any one of the units / devices shown can be implemented as a separate module, chip, chipset, circuit, etc., or one or more of them can be respectively implemented as a common module, chip, chipset, circuit, etc.

[0084] Some example embodiments also provide computer program code or instructions, which, when executed by one or more processors, can cause a device or apparatus to perform the processes described above. The computer program code for carrying out the processes of example embodiments can be written in any known or future developed programming language such as Java, C++, C, and Assembler. The computer program code can be provided to one or more processors or controllers of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the computer program code, when executed by the processor or controller, causes the machine to perform the functions / operations specified in the flow diagrams and / or block diagrams. The computer program code can be executed completely on a local computing device, partially on a local computing device and partially on a remote computing device, as one independent software package, partially on a local computing device and partially on a remote computing device, or completely on a remote computing device or server.

[0085] Some example embodiments also provide a computer program product or a computer readable medium having computer program code or instructions stored therein, which when executed by a processor, causes an optical channel protection device to perform the processing methods, steps, or functions described above. The computer readable medium can be any tangible medium which can contain or store a program for use by or in connection with an instruction execution system, apparatus, or device. The machine-readable medium can be a machine-readable signal medium or a machine-readable storage medium. The machine-readable medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of the machine-readable storage medium will include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0086] The above describes the basic principles of the present application in conjunction with the embodiments, but it should be noted that the advantages, benefits, effects and the like mentioned in the present application are only examples and are not limiting, and these advantages, benefits, effects and the like cannot be considered as necessary for each embodiment of the present application. In addition, the above specific details are only for the purpose of example and understanding, and are not limiting, and the above details do not limit the present application to the above specific details.

[0087] The terms "component", "module", "system" and the like used in the present application are used to represent computer-related hardware, software, firmware, special-purpose circuitry or logic, general-purpose hardware or controller or other computing devices, or some combination thereof. In addition, the modifiers "first", "second" and the like, as used throughout the specification and claims, are generally intended to distinguish different elements, operations, etc., rather than to indicate importance or any order.

[0088] Although some embodiments have been described, these embodiments have been given by way of example only and are not intended to limit the scope of the present application. Various modifications, substitutions, and alterations to the methods and systems described herein can be made without departing from the spirit of the present application. Accordingly, it is to be understood that the appended claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of various embodiments of the present application.

Claims

1. An optical line terminal (OLT) comprising: an optical carrier generator configured to generate at least a first optical carrier and a second optical carrier; a transmitter connected with the optical carrier generator, configured to modulate a downstream signal onto the first optical carrier to form a downstream transmission signal; and an optical coupler configured to couple the downstream transmission signal and the second optical carrier for downstream transmission. The optical carrier generator is further configured to generate a third optical carrier, and the optical line terminal further comprises:

2. An optical line termination as claimed in claim 1, wherein, a receiver connected with the optical carrier generator, configured to coherently detect a received upstream signal by using the third optical carrier. The transmitter comprises:

3. An optical line termination according to claim 1 or 2, wherein, an encoding module configured to space-time encode the downstream transmission signal to form a space-time encoded signal. 4.An optical network unit (ONU) comprising: a receiver configured to receive a downstream signal modulated on a first optical carrier; a carrier regenerator configured to receive a second optical carrier and generate a local oscillator signal based on the second optical carrier, wherein the receiver is connected with the carrier regenerator and configured to coherently detect the downstream signal by using the local oscillator signal. 5.The optical network unit of claim 4, further comprising: a transmitter connected with the carrier regenerator, configured to load an upstream signal by using the local oscillator signal. The upstream signal is an optical single sideband (OSSB) signal. The receiver comprises:

6. The optical network unit of claim 5, wherein, an optical coupler configured to receive and couple the downstream signal and the local oscillator signal; 7. The optical network unit of any of claims 4-6, wherein, an optical detector connected with the optical coupler, configured to detect the coupled optical signal and obtain an electrical signal; an amplifier configured to amplify the electrical signal; an analog-to-digital converter configured to convert the amplified electrical signal into a digital signal; and a digital signal processor (DSP) configured to process the digital signal to obtain information carried in the downstream signal. The carrier regenerator comprises: a filter configured to filter a received optical wave signal to select the second optical carrier; and 8. The optical network unit of any of claims 4-7, wherein, an optical amplifier connected with the filter, configured to amplify the second optical carrier. The transmitter comprises a Mach-Zehnder modulator (MZM) configured to generate an upstream signal by modulating the local oscillator signal by an electrical signal. 10.A signal processing method at an optical line terminal (OLT), comprising:

9. An optical network unit according to claim 5 or 6, wherein, generating a first optical carrier and a second optical carrier; modulating a downstream signal onto the first optical carrier to form a downstream transmission signal; and coupling the downstream transmission signal and the second optical carrier for downstream transmission. 11.The method of claim 10, further comprising: generating a third optical carrier and coherently detecting a received upstream signal by using the third optical carrier. 12.The method of claim 10, further comprising: space-time encoding the downstream transmission signal to form a space-time encoded signal. 13.A signal processing method at an optical network unit (ONU), comprising: receiving a downstream signal modulated on a first optical carrier; ​ ​ ​ receiving a second optical carrier, and generating a local oscillator signal based on the second optical carrier; and coherently detecting the downstream signal using the local oscillator signal.

14. The method of claim 13, further comprising: loading an upstream signal using the local oscillator signal.

15. The method of claim 13 or 14, wherein, coherently detecting the downstream signal using the local oscillator signal comprises: receiving the downstream signal and the local oscillator signal, and coupling the downstream signal and the local oscillator signal; and detecting the coupled optical signal and obtaining an electrical signal.

16. The method of claim 15, further comprising: amplifying the electrical signal; converting the amplified electrical signal into a digital signal; and processing the digital signal to obtain information carried in the downstream signal. generating a local oscillator signal based on the second optical carrier comprises:

17. The method of any one of claims 13-16, wherein, filtering the received optical wave signal to select the second optical carrier; and amplifying the second optical carrier to obtain the local oscillator signal. loading an upstream signal using the local oscillator signal comprises:

18. The method of claim 14, wherein, modulating the local oscillator signal by an electrical signal to generate the upstream signal.

19. A communication system comprising an optical line terminal according to any one of claims 1 to 3 and an optical network unit according to any one of claims 4 to 9.

20. An apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to perform at least the method of any one of claims 10-18.

21. A computer readable medium having stored thereon instructions that, when executed by a processor, cause the processor to perform the method of any one of claims 10 to 18.

22. A computer program product comprising instructions that, when executed by a processor, cause the processor to perform the method of any one of claims 10 to 18. ​

Images