Optical transmitter / receiver and its control device

Abstract

The present disclosure provides an optical transmitter / receiver that facilitates setting so as to use the minimum necessary power consumption. This optical transmitter / receiver for receiving / transmitting an optical signal in which information is encoded as intensity or phase of light, comprises an optical receiver having a light receiving element that receives the optical signal, and is configured such that setting parameter dependencies of power consumption, the optical sensitivity of the light receiving element, and a noise amount generated in the optical receiver in accordance with an operation condition of the optical receiver, are outputted to a control device which determines a setting parameter for the optical transmitter / receiver.

Description

[Technical field]

[0001] The present invention relates to an optical transceiver and a control device thereof. [Background technology]

[0002] With the constant development and spread of various applications such as social media and video distribution, and the construction of data centers and infrastructure for fifth-generation mobile communications systems (5G), the Internet continues to expand around the world, and the capacity of optical communications, which serves as its backbone, is also steadily increasing.

[0003] Accordingly, there is a demand for high-speed optical transceivers that are capable of large-capacity transmission and have a low cost relative to their capacity, not only for long-distance communications between distant cities but also for medium-distance communications and even short-distance communications within data centers.

[0004] In the past, optical transceivers using the direct intensity modulation method, which has a simple configuration, have been used in short-distance communications. However, against the background described above, digital coherent optical transmission technology that significantly increases transmission capacity has gradually been introduced (for example, see Non-Patent Document 1). Optical transceivers used in digital coherent optical transmission include a digital signal processor, an optical modulator, and a local light source, and can significantly increase transmission capacity by transmitting and receiving signal light by modulating and demodulating both the phase and intensity of light. Optical transceivers that transmit and receive digital coherent light can achieve a communication capacity of 400 Gbps or more per wavelength, and can achieve low costs relative to the transmission capacity.

[0005] In this conventional technology, an optical transmitter (TX) modulates the phase of light emitted from an integrated tunable laser assembly (ITLA) using an optical modulator, and further performs polarization multiplexing before transmitting. The optical transmitter (TX) may also modulate the phase and intensity of light emitted from the ITLA, and further performs polarization multiplexing before transmitting. An optical receiver (RX) includes a dual polarization optical hybrid (DPOH), a photodiode, a transimpedance amplifier, and an integrated tunable laser array. The DPOH receives the local light from the ITLA and the received signal light, and outputs the interference between these lights. The photodiode receives the light output from the DPOH, performs photoelectric conversion, and outputs an electrical signal. The transimpedance amplifier amplifies the electrical signal output from the photodiode. The electrical signal amplified by the transimpedance amplifier is digitally processed by a DSP (digital signal processor) located after the optical receiver (RX), and the transmitted signal is restored in DP-16QAM (dual polarization 16-level quadrature amplitude modulation) or DP-QPSK (dual polarization quadrature phase shift keying).

[0006] Optical receivers (RX) that transmit and receive digital coherent light have a built-in local light source and a complex device configuration due to the signal processing in the electrical stage DSP. However, because they use the optical phase in addition to the amplitude, they can increase the transmission capacity per wavelength, and digital processing makes it possible to process various imperfections such as dispersion, so they have been widely used, especially in long-distance optical communications.

[0007] In recent years, the transmission rate has been increasing, and it is now possible to transmit at 100 Gb / s or 400 Gb / s with a single unit. In addition, optical transceivers (TX / RX) that use silicon photonics and have an ultra-compact optical transmitter (TX) and optical receiver (RX) arranged adjacent to each other have also come into use.

[0008] Optical networks that can be configured using such optical transceivers are not limited to configurations in which one-to-one transceiver pairs are used, but also configurations in which the combination of optical transceivers (TX / RX) changes dynamically, such as by using a ROADM (reconfigurable optical add / drop multiplexer).In the conventional optical transceivers used here, it is assumed that the performance and power of each transceiver are constant. [Prior art documents] [Non-patent literature]

[0009] [Non-Patent Document 1] Yutaka Miyamoto et al., "Ultra-large capacity digital coherent optical transmission technology," NTT Technical Journal, 2011, vol. 23, No. 3, pp. 13-18 Summary of the Invention

[0010] In this context, conventional optical receivers and transmitters had the following problems: Their performance was constant, and basically, any combination of optical receivers and transmitters always maintained a constant transmission capacity. Even if the distance between two optical receivers and transmitters set as a communication pair at a certain point in time was close and there was a margin in their transmission capacity, they were used as they were because it was difficult to calculate the performance margin in advance.

[0011] Optical receivers and transmitters that transmit and receive coherent light have components that require power consumption, such as a driver IC, a transimpedance amplifier, a local light source, and a DSP (digital signal processor), and each element consumes power. There is room for reducing power consumption, such as by adjusting the output current of the driver IC and the algorithm settings of the DSP equalizer. With conventional optical receivers and transmitters, it is difficult to accurately predict how much performance margin there is until they are actually used, and as a result, it is difficult to calculate how much margin there is for reducing the power of each of the multiple elements of the optical receiver and transmitter. Therefore, conventional optical receivers and transmitters use power with settings that allow for a large margin, making it difficult to efficiently reduce power depending on the situation.

[0012] The present disclosure has been made to address such issues, and makes it easy to configure optical transceivers to consume the minimum amount of power required depending on the combination of communication pairs of optical transceivers, the individual performance of the optical transceivers, environmental conditions, etc.

[0013] In order to achieve such an object, one embodiment of the present invention is an optical transceiver for transmitting and receiving an optical signal in which information is encoded in the phase and intensity of light, comprising an optical receiver having a light receiving element for receiving an optical signal, and configured to output to a control device of the optical transceiver the amount of noise generated in the optical receiver, the optical sensitivity of the light receiving element, and the dependence of power consumption on setting parameters according to the operating conditions of the optical receiver. Another embodiment of the present invention is an optical transceiver for transmitting and receiving an optical signal in which information is encoded in the phase and intensity of light, comprising an optical transmitter having a modulator for generating an optical signal, and configured to output to a control device of the optical transceiver the optical intensity according to the current input to the modulator, the SNR of the optical transmitter, and the dependence of power consumption on setting parameters according to the operating conditions of the optical transmitter such as the power supply voltage, gain, and temperature. Yet another embodiment of the present invention is the above-mentioned control device for the optical transceiver, configured to calculate setting parameters of the optical transceiver based on information output from the optical transceiver, and transmit the calculated parameters to the optical transceiver.

[0014] According to an embodiment of the present invention, it becomes easy to set an optical receiver or an optical transmitter to consume the minimum necessary power consumption depending on the combination of communication pairs. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram for explaining a conventional optical transceiver and control device. [Diagram 2] 1 is a diagram for explaining an optical transceiver and a control device according to an embodiment of the present invention; [Diagram 3] 1 is a schematic diagram illustrating the configuration of an optical transceiver according to an embodiment of the present invention; [Figure 4] 3A to 3C are diagrams illustrating the operation of an optical transceiver and a control device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. The same or similar reference symbols indicate the same or similar elements, and duplicated explanations may be omitted. Prior to the description of the embodiment of the present invention, a conventional optical transceiver and control device will be described.

[0017] Fig. 1 is a diagram for explaining a conventional optical transceiver and control device. As shown in Fig. 1, the communication system has two optical transceivers (TX / RX) 10 that form a communication pair, a switching device 20 such as an optical add / drop multiplexer (OADM) connected in a ring shape by an optical fiber 40, and an amplifier 30 such as an erbium-doped optical fiber amplifier (EDFA). The two TX / RX 10 are each connected to the OADM 20. The OADM 20 and the EDFA 30 are connected to a control device 50. The OADM 20 sets a communication path between the two TX / RX 10 based on a control signal from the control device 50.

[0018] 2 shows an optical network including an optical transceiver (TX / RX) 100 and a control device 500 according to the first embodiment of the present invention. This network is composed of a plurality of TX / RX 100, a switching device such as an OADM 20, a control device 500 that controls the TX / RX 100 and the OADM 20, and optical fibers 40 that connect the OADMs 20. In this network, the combination of the communication path and the optical transceivers 100 at both ends of the path dynamically changes according to the communication needs. The path switching is determined by the control device 500, and the switching itself is performed by a switching device 20 such as an OADM included in the network.

[0019] The control device 500 determines a communication path required at that time based on information from an external communication device or a computer device operated by an operator, but the path is not necessarily unique. The control device 500 also determines some setting parameters for the optical transceiver 100.

[0020] 3 shows the configuration of an optical transceiver (TX / RX) 100 according to this embodiment. The TX / RX 100 includes an optical receiver (RX) 110, an optical transmitter (TX) 120, a digital signal processor (DSP) 130, and a control unit (CTRL) 131.

[0021] The RX 110 includes an optical circuit 111 such as a DPOH and a PD, a TIA (transimpedance amplifier) ​​112, and a local light source (ITLA) 113. The TX 120 includes a modulator driver (DRV) 121, an optical Maher-Zehnder (MZ) modulator 122, and a local light source (ITLA) 123. The TX 120 may include an optical amplifier such as an SOA 124 or an EDFA 125. A digital signal processor (DSP) of the TX / RX 100 is configured to transmit and receive signals to and from the optical receiver 110 and the optical transmitter 120. The CTRL 131 is connected to the DSP 130, the control device 500, and the optical receiver 110 and the optical transmitter 120. The CTRL 131 controls the components of the optical receiver 110 and the optical transmitter 120 based on a control signal from the control device 500. Instead of using two local light sources, ITLA113 and ITLA123, it is also possible to use a single light source ITLA in which light is split into two local light sources.

[0022] The TX / RX100 has adjustable parameters such as the output current of the modulator driver 121 supplied to the optical MZ modulator 122, the optical intensity of the local light sources 113 and 123, the amplification factor of the optical amplifiers 124 and 125, and the length of an electric filter (not shown) in the DSP 130. The power consumption of each element changes when these parameters are adjusted. Here, the output current of the modulator driver 121 refers to a drive current when the output section of the modulator driver 121 has no or small resistance inside the driver, such as an open collector configuration, and is configured to drive a built-in resistor of the optical MZ modulator 122, but it may be any current or voltage of the modulator driver 121 itself, including cases where the driver does not have an open collector configuration. The dependence of the SN on the adjustment parameters such as the output current is output to the control device 500. These data may be data acquired in advance during the inspection or design stage of a part or the whole of the TX / RX100 and stored in an internal memory of the TX / RX100.

[0023] The control unit 131 of the TX / RX100 also outputs environmental conditions at a certain point in time, that is, the power supply voltage, gain, temperature, and wavelength, as well as the current dependency of the thermal noise density of the TIA 112 and the shot noise density (frequency density) of the ITLA 113 converted based on these, as data to the control device 500. These data are data acquired in advance during the inspection or design stage of a part or the whole of the TX / RX100 and stored in the internal memory of the TX / RX100.

[0024] The operation of the optical transceiver 100 and the control device 500 of this embodiment will be described with reference to Fig. 4. In Fig. 4, two optical transceivers 100a and 100b form a communication pair. Fig. 4 shows an optical transmitter (TX) 120a and an optical receiver (RX) 110b forming the optical transceiver 100a, a TX 120b and a RX 100b forming the optical transceiver 100b, a TX / RX 100b, an EDFA 30a arranged on a path between the TX 120b and the RX 110a, and an EDFA 30b arranged on a path between the TX 120a and the RX 110b. The control device 500 is communicably connected to the optical transceivers 100a and 100b, and the EDFAs 30a and 30b.

[0025] In step S101, the control device 500 determines two optical transceivers (TX / RX) 100a and 100b that form a communication pair, and a route between the TX / RX 100a and the TX / RX 100b. The method of determining the TX / RX 100a and the TX / RX 100b and the route connecting them is arbitrary. Information on the TX / RX 100a and the TX / RX 100b and the route connecting them may be input to the control device 500 from a computer operated by an operator.

[0026] In step S102, information on the path including the TX / RX 100a and 100b is collected. At least one of the TX / RX 100a and 100b outputs data on the bit error rate (BER) required for establishing communication and the environmental conditions of the optical receiver (RX) 110 to the control device 500, and the control device 500 receives the data on the environmental conditions. The BER required for establishing communication is the error rate occurring in the DSP 130, and is, for example, 1×10 -3 This value is determined by the forward error correction (FEC) capability used by the DSP 130. If the BER is below this value, the DSP will use error correction to ensure communication is established with a BER of, for example, 1×10 -12 The BER in Fig. 4 can be corrected to min indicates the error rate occurring in the DSP 130. The data on the environmental conditions includes data on the power supply voltage, gain, temperature, and wavelength, as well as the current dependence of the thermal noise density of the TIA 112 and the shot noise density (frequency density) of the ITLA 113, which are converted based on these. R in FIG. pd is the average optical sensitivity of the PD included in the optical circuit 111 of the RX110, and I eq is the thermal noise density of the TIA 112, and is an example of data related to the RX 110 output from the TX / RX 100 to the control device 500. tx (I out ) is the S / N ratio (current ratio) of the TX 120 itself, and is an example of data related to the TX 120 output from the TX / RX 100 to the control device 500. Furthermore, the S / N ratio in FIG. ase is an example of data output from the EDFA 30 to the control device 500. The TX / RX 100 and the EDFA 30 supply information required for the calculation described below to the control device 500. When the environmental condition dependency of the TX / RX 100 and the EDFA 30 is taken into consideration in the calculation, the TX / RX 100 and the EDFA 30 supply the environmental condition dependency to the control device 500 as information required for the calculation.

[0027] In step S103, the control device 500 calculates the configuration parameters of the components of the RXs 110a and 110b and the TXs 120a and 120b of the TXs / RXs 100a and 100b based on data received from at least some of the TXs / RXs 100a and 100b and the EDFAs 30a and 30b. The determined configuration parameters include configuration parameters that satisfy the BER received from the TXs / RXs 100a and 100b and that result in lower power consumption of the TXs / RXs 100a and 100b and the EDFAs 30a and 30b. The configuration parameters may include the configuration parameters of the EDFA 125.

[0028] In step 104, the control device 500 supplies the calculated setting parameters to the TX / RX 100a and 100b, and the TX / RX 100a and 100b configure the RX 110 and the TX 120 based on the supplied setting parameters. The control device 500 also supplies the calculated setting parameters to the EDFAs 30a, 30b, and 125, and configures the EDFAs 30a, 30b, and 125. outtxitla is the intensity of the light output by the ITLA123 in the TX120 (local light intensity), and I out is an output current of the DRV 121 in the TX 120, and is an example of data related to the TX 120 transmitted from the control device 500 to the TX / RX 100. outrxitla is an example of data related to RX110 transmitted from the control device 500 to the TX / RX100. Furthermore, Gain in Fig. 4 is an example of data such as a current value associated with an amplification factor transmitted from the control device 500 to the EDFA 30. Steps S101 to S104 can be performed each time the path is changed or the conditions change.

[0029] More specifically, the method of using noise information is as follows: Since a certain level of SNR is required to decode a signal with a bit error rate sufficient to establish communication in the DSP, the parameters of the TX / RX100 should be set so that the amount of noise is limited so that the SNR is kept above a certain level.

[0030] Noise in a coherent system includes ASE noise generated by an optical amplifier (e.g., EDFA 30) on the transmission path, thermal noise inside the TIA 112 of the optical receiver 110, shot noise caused by photocurrent in the PD included in the optical circuit 111, which is prominent in a coherent system that uses strong local light, etc. Furthermore, the inherent performance of the optical transmitter 120 can also be expressed by the SNR.

[0031] signal amplitude S pp is obtained by multiplying the local light signal strength and signal light strength of the local light source 113 in the optical receiver 110 and the local light sensitivity and signal light sensitivity of a photodetector element such as a PD included in the optical circuit 111 inside the optical receiver 110.

[0032]

number

[0033] R is the average optical sensitivity of the optical receiver 110 (the ratio of the optical current to the optical intensity), and P LO is the local light intensity, P sig is the signal light intensity, and α is a constant that depends on the modulation format such as QPSK / QAM, the differential configuration of the optical receiver 110, and the like.

[0034] From here, since we are assuming that the noise is not extremely large, we can assume that the noise is additive, and the signal-to-noise ratio (SNR) is expressed as follows:

[0035]

number

[0036] If the optical sensitivity R is different between the local light (LO) side and the signal light (sig) side, both the numerator and denominator of Equation 2 should be R 2 R LO ×R sig It can also be done like this.

[0037] Thermal noise σ TIA is the reduced thermal noise density I at the input of the TIA112 eq (unit: A / rtHz) and the bandwidth f of the optical receiver 110 BWRX It is described as follows using:

[0038]

number

[0039] Shot noise σ shot is the input current of the TIA112 (the input current value I PD ) and is written as follows:

[0040]

number

[0041] e is the charge of the electron, I PDave is the average photocurrent of the PD, f BWRX is the bandwidth of the optical receiver 110. If the Common Mode Rejection Ratio (CMRR) has an effect on this bandwidth, it can also be added to calculate the SNR. When the measurement unit of the optical SNR (OSNR) is dB / 0.1 nm (for a wavelength of 1.55 μm, a wavelength shift of 0.1 nm corresponds to a frequency shift of 12.5 GHz), it is expressed by the following formula.

[0042]

number

[0043] In this embodiment, in order to eliminate the influence of the band of the amplifier (EDFA 30) and the like, the converted noise amount (thermal noise density) at the input section (TIA 112) of the RX 110 is used.

[0044] Furthermore, if the influence of imperfections in the optical transmitter 120 is treated in the same way as noise and is added on the assumption that the influences can be added independently, the following can be done.

[0045]

number

[0046] It is also known that the SN and BER can be converted using a formula corresponding to the format, such as QPSK, mQAM, etc. By using such a formula, the minimum necessary SN can be calculated from the minimum communicable BER determined by the DSP 130.

[0047] In addition, since the information obtained from the optical transceiver 100 is density with respect to the noise frequency (in the case of a 64 Gbps electrical signal, the frequency is approximately 30 GHz), RX The amount is multiplied by f BWRX is determined almost by the transmission rate and is set by a digital filter inside the DSP 130 of the optical transceiver 100 (for example, in the case of a transmission rate of 64 Gbps, it is about half that, 32 GHz, or more).

[0048] In the above formula, f BWRX uses the same value for all noise, but slightly different values ​​may be used for each type of noise depending on device measurements.

[0049] The data on the noise amount of the receiver and the SN ratio of the transmitter, etc., to be output may be calculated by separately measuring the noise density characteristics and band characteristics of the device, stored in the control unit 131, etc., and output to the control device 500. Alternatively, the data on the noise amount of the receiver and the transmitter, etc. to be output may be stored in the control unit 131, etc., and output to the control device 500, using the above-mentioned formula for converting BER to SN, and the SN calculated from the result of the BER characteristics obtained by inspecting a part or the whole of the TX / RX100. Also, by setting the SN to a value larger than the minimum necessary SN with a certain margin, it is possible to establish stable communication even if the characteristics fluctuate slightly.

[0050] SNR in the assumed signal path tot Setting parameters such as a current associated with the local light intensity of the local light source 113 of the RX 110, a current value associated with the gain of the optical amplifiers 124 and 125 such as an SOA and an EDFA, and an output current of the modulator driver 121 of the TX 120 can be determined so that the power consumption is equal to or less than a predetermined value for establishing transmission and the overall power consumption is reduced as much as possible.

[0051] Default SNR tot However, the communication threshold SNR th If the SNR is larger than the SNR by a certain amount, the SNR tot As long as I is greater than the limit, communication can basically be established. From this formula, we can calculate how much the SN ratio can be degraded and still establish communication, so I out By changing the SNR tx When the I out In this way, communication can be established. outIn addition, it is possible to adjust all characteristics, such as the gain of the amplifiers in the path and the optical intensity of the ITLAs 113 and 123 of the optical transceiver 100, to minimize power consumption. If lowering the power consumption of a particular component is a high priority, it is also possible to set the power consumption of that component to be lowered preferentially within the range in which communication can be established. In addition, if there is a factor that fluctuates, such as optical intensity, it is also possible to set the worst condition of the expected fluctuating factor in the currently set path so that communication can always be established within the expected range of fluctuation.

[0052] Also, the SN may be calculated by adding noise not described above. For example, in the case of the integrated optical transceiver 100 in which the optical transmitter (TX) and the optical receiver (RX) are arranged adjacent to each other as described above, the control unit 131 may output the output amplitude dependency of the input conversion transmission / reception crosstalk noise in the TIA 112 caused by the TX 120 in addition to the current dependency of the thermal noise density and the shot noise density as data output from the control unit 131 to the control device 500. The control device 500 may set each parameter of the TX / RX 100 in consideration of the input conversion transmission / reception crosstalk noise in the TIA 112 having the output amplitude dependency of the TX 120. Note that, in FIG. 4, the communication path from the optical transmitter 120b on one side to the optical receiver 110a is described for the communication between the optical transceiver 100a and the optical transceiver 100b, but the control device 500 can similarly process the communication path from the optical transmitter 120a on the other side to the optical receiver 110b. [Explanation of symbols]

[0053] 10 Optical Transmitter / Receiver (TX / RX) 20 Switching Equipment (OADM) 30 Amplifier (EDFA) 40 Optical Fiber 50 Control device 100 Optical Transmitter / Receiver (TX / RX) 110 Optical Receiver (RX) 111 Optical circuit (DPOH / PD) 112 Transimpedance Amplifier (TIA) 113 Local Light Source (ITLA) 120 Optical transmitter (TX) 121 Modulator Driver (DRV) 122 Optical Mahalanobismuth-Zehnder (MZ) Modulator 123 Local Light Source (ITLA) 124 Optical Amplifier (SOA) 125 Optical Amplifier (EDFA) 130 Digital Signal Processor (DSP) 131 Control section (CTRL) 500 Control device

Claims

1. An optical transceiver for transmitting and receiving an optical signal in which information is encoded in the phase and intensity of light, an optical receiver having a light receiving element for receiving the optical signal; an optical transceiver configured to output to a control device of the optical transceiver an amount of noise generated in the optical receiver, an optical sensitivity of the light receiving element, and a dependency of power consumption on setting parameters in accordance with operating conditions of the optical receiver.

2. the operating conditions of the optical receiver include at least one of a power supply voltage, a gain, and a temperature; 2. The optical transceiver according to claim 1, wherein the noise amount includes at least one of thermal noise and shot noise.

3. An optical transceiver for transmitting and receiving an optical signal in which information is encoded in the phase and intensity of light, an optical transmitter having a modulator for generating the optical signal; Dependence of optical intensity according to a current input to the modulator, an S / N ratio of the optical transmitter, and power consumption on setting parameters according to operating conditions of the optical transmitter including at least one of a power supply voltage, a gain, and a temperature. to a control device of the optical transceiver.

4. An optical transceiver according to claim 1, an optical transceiver according to claim 3, and an optical transceiver according to claim 1 and 5. The control device connected to an optical communication system to which the optical transceiver according to claim 3 is connected and which includes a switching device that dynamically switches a path between the optical transceiver according to claim 1 and the optical transceiver according to claim 3, receiving the amount of noise generated in the optical receiver included in the optical transceiver according to claim 1, transmission / reception crosstalk noise and power consumption caused by the optical transmitter of the optical transceiver according to claim 3, and the optical intensity according to the current input to the modulator in the optical transmitter of the optical transceiver according to claim 3, the S / N ratio of the optical transmitter, and the power consumption dependence on setting parameters, and calculating setting parameters for the optical transceiver according to claim 3; A control device configured to transmit the calculated setting parameters to the optical transceiver according to claim 3.

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