Optical receiving device

Abstract

To provide an optical receiving apparatus that ensures bandwidth characteristics according to the baud rate of an optical signal.SOLUTION: In an optical transmission system in which a plurality of optical transmitting apparatuses are all optically connected to an optical coupler, a plurality of optical receiving apparatuses are all optically connected to an optical splitter, and the optical coupler and the optical splitter are connected via an optical transmission line, an optical receiving device 80 includes a PD (Photodiode) 132 that converts a main signal Sf2, which is an optical signal, into an electrical data signal, a control unit 150 that changes an adjustment value of peaking based on the baud rate of the main signal Sf2, and a TIA (Transimpedance Amplifier) 131 which is an amplifier that changes band characteristics of the PD 132 based on the adjustment value changed by the control unit 150.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This matter concerns an optical receiving device. [Background technology]

[0002] It is known that optical receivers used in digital coherent optical transceivers incorporate transimpedance amplifiers. Furthermore, in IMDD transmission systems that are not digital coherent transmission systems, a technique is known to address the loss of high-frequency signals propagating through internal high-frequency lines consisting of printed circuit boards and electrical connectors within the optical transceiver by applying peaking to the frequency characteristics using analog circuit technology (see, for example, Patent Document 1).

[0003] In addition, transimpedance amplifiers with core circuits equipped with frequency peaking control functions are known (see, for example, Patent Document 2). Various peaking techniques are also known (see, for example, Patent Documents 3 and 4). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2015-146515 [Patent Document 2] Japanese Patent Publication No. 2013-090128 [Patent Document 3] Japanese Patent Publication No. 2011-217321 [Patent Document 4] Japanese Patent Publication No. 2013-150154 [Overview of the project] [Problems that the invention aims to solve]

[0005] Incidentally, research is being conducted on optical receiving devices that utilize peaking to receive optical signals at higher baud rates. For example, research is being conducted on receiving optical signals at high baud rates, such as around 130 Gbaud, which are beyond the range of low baud rates like 64 Gbaud to medium baud rates like 96 Gbaud.

[0006] However, increasing the baud rate may reduce frequency utilization efficiency. Additionally, increasing the baud rate may increase the amount of bandwidth constriction experienced within the ROADM (Reconfigurable Optical Add / Drop Multiplexer) installed in the optical transmission path.

[0007] From this perspective, it is preferable to realize an optical receiving device that can not only receive high-baud rate optical signals but also optical signals in the low-baud rate to medium-baud rate range, thus supporting a wide range of baud rates.

[0008] Here, if the bandwidth characteristics of the optical receiver are fixed to, for example, a bandwidth characteristic that can receive low-baud rate optical signals, the bandwidth characteristics of high-baud rate optical signals may be distorted by the set bandwidth characteristics, potentially degrading transmission performance. For this reason, it is assumed that the bandwidth characteristics of the optical receiver will be fixed to a bandwidth characteristic that can receive high-baud rate optical signals. This makes it possible to receive optical signals in the range from low to high baud rates without distortion.

[0009] However, when receiving a low-bitrate optical signal with the bandwidth characteristics of the optical receiver fixedly set to the bandwidth characteristics capable of receiving a high-bitrate optical signal, the following problems occur. That is, in wavelength division multiplexing, signal components of another optical signal adjacent to the optical signal exist in the region between the set bandwidth characteristics and the low-bitrate optical signal. This signal component may reduce the amplification factor of an amplifier such as a TIA (Transimpedance Amplifier) provided in the optical receiver, and thus may deteriorate the signal quality of the optical signal. Thus, when the bandwidth characteristics of the optical receiver are fixedly set to the bandwidth characteristics capable of receiving a high-bitrate optical signal, although the optical signal is not distorted in wavelength division multiplexing using a low-bitrate optical signal, there is a risk that the transmission performance will deteriorate due to the signal components of the adjacent optical signals.

[0010] Therefore, in one aspect, an object is to provide an optical receiver that ensures bandwidth characteristics corresponding to the bitrate of an optical signal.

Means for Solving the Problem

[0011] In one embodiment, An optical receiver capable of receiving optical signals of multiple baud rates, a conversion device that converts an optical signal into an electrical data signal, Before receiving a control unit that changes an adjustment value for peaking based on the bitrate of the optical signal, and an amplifier that changes the bandwidth characteristics of the conversion device based on the adjustment value changed by the control unit.

Effect of the Invention

[0012] Bandwidth characteristics corresponding to the bitrate of the optical signal can be ensured.

Brief Description of the Drawings

[0013] [Figure 1] Fig. 1(a) is an example of an optical transmission system. Fig. 1(b) is a diagram for explaining an example of the bandwidth characteristics of a WDM (Wavelength Division Multiplexing) signal and the bandwidth characteristics of an optical receiver. [Figure 2] Fig. 2 is a block diagram showing an example of an optical receiver. [Figure 3] Figure 3 illustrates an example of the bandwidth characteristics of an optical receiver. [Figure 4] Figure 4(a) is an example of a TIA circuit diagram. Figure 4(b) is an example of a VGA (Variable Gain Amplifier) ​​circuit diagram. [Figure 5] Figure 5 illustrates an example of the change in bandwidth characteristics of ICR (Intradyne Coherent Receivers). [Figure 6] Figure 6 illustrates an example of noise components superimposed on an adjacent main signal. [Figure 7] Figure 7 is a flowchart showing an example of the operation of the control unit according to the first embodiment. [Figure 8] Figure 8(a) illustrates an example of a control table. Figure 8(b) illustrates an example of a change in the bandwidth characteristics of an optical transmitter. [Figure 9] Figure 9 is a flowchart showing an example of the operation of the control unit according to the second embodiment. [Figure 10] Figure 10 illustrates an example of mathematical formula information. [Modes for carrying out the invention]

[0014] The following will explain the implementation of this project with reference to the drawings.

[0015] (First Embodiment) As shown in Figure 1(a), the optical transmission system ST includes a plurality of optical transmitters 10, 20, and 30 and a plurality of optical receivers 70, 80, and 90. The optical transmitters 10, 20, and 30 are all optically connected to an optical multiplexer 40. The optical receivers 70, 80, and 90 are all optically connected to an optical demultiplexer 60. The optical multiplexer 40 and the optical demultiplexer 60 are connected via an optical transmission path 50. The optical transmission path 50 includes, for example, an optical fiber.

[0016] Optical transmitters 10, 20, and 30 transmit main signals with different center frequencies. In this embodiment, the main signal is described as an example of an optical signal, but control signals that control the optical transmitters 10, 20, and 30 and the optical receivers 70, 80, and 90 may be used instead of the main signal. For example, optical transmitter 20 transmits a main signal Sf2 with a center frequency f2. Optical transmitters 10 and 30 are basically the same as optical transmitter 20, so a detailed explanation is omitted.

[0017] The optical multiplexer 40 combines the main signals Sf1, Sf2, and Sf3 transmitted from the optical transmitters 10, 20, and 30, respectively, to generate a WDM signal Sfz. The optical multiplexer 40 then transmits the WDM signal Sfz to the optical transmission path 50. When combining the main signals Sf1, Sf2, and Sf3, the optical multiplexer 40 narrows the spacing between adjacent main signals Sf1 and Sf2, and between adjacent main signals Sf2 and Sf3, as shown in Figure 1(b), to generate the WDM signal Sfz. This improves the frequency utilization efficiency.

[0018] The optical demultiplexer 60 receives the WDM signal Sfz that has passed through the optical transmission path 50. The optical demultiplexer 60 demultiplexes the WDM signal Sfz into main signals Sf1, Sf2, and Sf3. The optical demultiplexer 60 transmits, for example, the main signal Sf2 to the optical receiver 80. As a result, the optical receiver 80 receives the main signal Sf2. The optical receivers 70 and 90 are basically the same as the optical receiver 80, so a detailed explanation is omitted.

[0019] Here, as shown in Figure 1(b), the bandwidth characteristic L4 of the optical receiver 80 is sufficiently maintained relative to the bandwidth characteristic L1 of the main signal Sf2 transmitted from the optical transmitter 20. As a result, the shape of the bandwidth characteristic L1 of the main signal Sf2 is not distorted due to the bandwidth characteristic L4 of the optical receiver 80. Consequently, a degradation in the signal quality of the main signal Sf2 can be suppressed.

[0020] However, because the bandwidth characteristic L4 is excessively wide compared to the bandwidth characteristic L1, when receiving the main signal Sf2, the optical receiver 80 also receives signal components AL and AH, which are part of other main signals Sf1 and Sf3 adjacent to the main signal Sf2, in addition to receiving the main signal Sf2.

[0021] As will be explained in more detail later, the optical receiver 80 is equipped with a TIA as an amplifier, and when the optical receiver 80 receives signal components AL and AH, the amplification factor of the TIA may decrease due to the signal components AL and AH. This can degrade the signal quality of the main signal Sf2, and consequently, the transmission performance of the optical transmission system ST may decrease.

[0022] To suppress such a decrease in transmission performance, it is desirable to make the shape of the bandwidth characteristic L4 of the optical receiver 80 closer to the shape of the bandwidth characteristic L1 of the main signal Sf2, thereby suppressing the reception of signal components AL and AH. As will be described in detail later, in this embodiment, the shape of the bandwidth characteristic L4 is adaptively adjusted using peaking to bring it closer to the shape of the bandwidth characteristic L1. As a result, even if the shape of the bandwidth characteristic L1 changes according to the baud rate of the main signal Sf2, it is possible to secure a bandwidth characteristic L4 that is close in shape to the shape of the bandwidth characteristic L1.

[0023] Referring to Figure 2, the details of the optical receiver 80 will be explained. Note that the optical receivers 70 and 90 have basically the same configuration as the optical receiver 80, so a detailed explanation will be omitted.

[0024] As shown in Figure 2, the optical receiver 80 includes a receiving-side DSP (Digital Signal Processor, hereinafter referred to as RxDSP) 110 and an ADC (Analogue Digital Converter) 120. The optical receiver 80 also includes an ICR 130, an ITLA (Integrable Tunable Laser Assembly) 140, and a control unit 150. The ICR 130 is an example of a conversion device. The ICR 130 is an integrated circuit that houses a TIA 131 and a PD (Photodiode) 132 in a single package.

[0025] The PD132 receives the main signal Sf2 transmitted from the optical transmitter 20 and transmitted via the optical transmission line 50. The PD132 receives the main signal Sf2 via the local light emission (i.e., laser light) output from the ITLA140, converts the main signal Sf2 into a current signal, and outputs it to the TIA131. The TIA131 converts the current signal output from the PD132 into a voltage signal, amplifies the voltage signal to an amplitude suitable for the ADC120, and outputs the amplified voltage signal to the ADC120 as an electrical data signal. In this way, the ICR130 uses the PD132 and TIA131 to receive the input main signal Sf2 and convert it into a data signal. The ADC120 converts the data signal from analog format to digital format and outputs it to the RxDSP110.

[0026] The RxDSP110 receives the data signal output from the ADC120. The RxDSP110 performs various digital signal processing operations. For example, the RxDSP110 fixedly compensates for losses in the optical transmitter 20, optical receiver 80, and optical transmission line 50 of the data signal. Specifically, the RxDSP110 performs chromatic dispersion compensation, skew compensation, and bandwidth characteristic compensation. In addition, the RxDSP110 adaptively compensates for waveform distortion of the main signal Sf2 caused by polarization mode dispersion and polarization-dependent losses occurring on the optical transmission line 50 of the data signal.

[0027] Furthermore, the RxDSP110 performs digital demodulation (or demapping) on ​​the data signal according to the baud rate and modulation scheme (specifically, multi-level modulation) set by the control unit 150. This detects symbols from the data signal and converts them into bit data, demodulating the OTU (Optical Channel Transport Unit) frame from the data signal. In addition, the RxDSP110 extracts FEC (Forward Error Correction) from the OTU frame and performs data error correction. The RxDSP110 also converts the OTU frame into a client signal and transmits it to the client network. The client signal is, for example, an Ethernet® signal.

[0028] The control unit 150 includes a processor and memory, and controls the operation of RxDSP110, ICR130 (specifically TIA131), and ITLA140, as shown in Figure 2. The processor includes, for example, a CPU (Central Processing Unit). The memory includes volatile memory such as RAM (Random Access Memory) and non-volatile memory such as ROM (Read Only Memory). The control unit 150 may also be an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit).

[0029] The control unit 150 performs various settings on the RxDSP 110 and TIA 131 according to the control from the operating terminal 25. The operating terminal 25 may be a PC (Personal Computer) or a smart terminal (e.g., a tablet terminal). As will be described in detail later, for example, when a signal type including baud rate, multi-level modulation scheme, frame format, etc. is input from the operating terminal 25 to the control unit 150, the control unit 150 determines or calculates a peaking adjustment value according to the baud rate and sets the peaking adjustment value in the TIA 131.

[0030] The bandwidth characteristics of the optical receiver 80 will be explained with reference to Figures 3 and 4. The following references may be consulted as needed. (1) Laura Aschei, et al, “A 42-GHz TIA in 28-nm CMOS With Less Than 1.8% THD for Optical Coherent Receivers”, IEEE SOLID-STATE CIRCUITS LETTERS, VOL. 3, p.238-241, JULY 2020 (2) Japanese Patent Publication No. 2013-090128 (Patent Document 2)

[0031] The bandwidth characteristics (specifically, frequency characteristics or gain characteristics) of the optical receiver 80 are expressed as a composite bandwidth characteristic of the devices through which data signals pass, among the various devices provided by the optical receiver 80. In this embodiment, as described above, data signals pass through the devices ADC120 and ICR130. On the other hand, data signals do not pass through the device ITLA140. Therefore, as shown in Figure 3, the bandwidth characteristic L4 of the optical receiver 80 is expressed as a composite bandwidth characteristic of the bandwidth characteristics L2 of ADC120 and L3 of ICR130.

[0032] Here, in order to avoid distorting the shape of the bandwidth characteristic L1 of the main signal Sf2, it is desirable that the shape of the bandwidth characteristic L4 of the optical receiver 80 be slightly larger than the shape of the bandwidth characteristic L1 of the main signal Sf2, and that the two shapes be similar. As a result, as described above, the signal component AH present in the region between the bandwidth characteristic L4 of the optical receiver 80 and the bandwidth characteristic L1 of the main signal Sf2 is reduced, and the degradation of the signal quality of the main signal Sf2 is suppressed.

[0033] The TIA131 in the ICR130 has a characteristic or function called peaking, which amplifies the amplitude component in the bandwidth characteristic L3 of the ICR130, thereby extending the bandwidth characteristic L3. In this embodiment, such a characteristic or function is referred to as the peaking characteristic. Therefore, as shown in Figure 3, even if the bandwidth characteristic L2 of the ADC120 is insufficient (or lacking) compared to the bandwidth characteristic L1 of the main signal Sf2, the bandwidth characteristic L4 of the optical receiver 80 can be extended by utilizing the peaking characteristic to extend the bandwidth characteristic L3 of the ICR130.

[0034] As shown in Figure 4(a), the TIA131 includes an input terminal 171, a reactance 172, an LNTA (Low-Noise Transimpedance Amplifier) ​​173, multiple VGAs 174, 175, 176, an output buffer 177, and an output terminal 178. Both the input terminal 171 and the output terminal 178 include pads (specifically high-frequency pads) and ESD (Electrostatic Discharge) protection circuits.

[0035] VGA174, 175, and 176 all adjust their gain based on the control voltage. Additionally, TIA131 may include a DC offset removal circuit 179 that senses the DC (Direct Current) output voltage of the output buffer 177 and supplies a correction current to VGA175 corresponding to the output voltage.

[0036] The current signal output from PD132, passing sequentially through input terminal 171 and reactance 172, is input to LNTA173. LNTA173 converts the current signal into a voltage signal while reducing the noise contribution to VGA174, 175, and 176 due to the increase in gain, and outputs it to VGA174. VGA174 adjusts the gain based on the control voltage to amplify the amplitude of the low-frequency band (hereinafter referred to as the low-frequency component) of the voltage signal to an amplitude suitable for ADC120, and outputs the amplified voltage signal to VGA175.

[0037] VGA175 further amplifies the low-frequency components of the amplified voltage signal output from VGA174 by adjusting the gain based on the control voltage, and outputs it to VGA176. VGA176 further amplifies the low-frequency components of the amplified voltage signal output from VGA176 by adjusting the gain based on the control voltage, and outputs it to output buffer 177. Output buffer 177 outputs the voltage signal as a data signal to output terminal 178. Output terminal 178 outputs the data signal.

[0038] Here, as shown in Figure 4(b), the VGA175 consists of an amplifier circuit 181 and a variable feedback resistor R Fincludes the amplifier circuit 181 and the variable feedback resistor R F are connected in parallel. The input terminals of the amplifier circuit 181 and the variable feedback resistor R F are connected to VGA174. The output terminals of the amplifier circuit 181 and the variable feedback resistor R F are connected to VGA176.

[0039] The control unit 150 adjusts the value of the control voltage V F applied to the variable feedback resistor R CONT (automatic gain control), so that the resistance value of the variable feedback resistor R F changes. When the resistance value of the variable feedback resistor R F changes, the gain of the amplifier circuit 181 changes. That is, by adjusting the value of the control voltage V F applied to the variable feedback resistor R CONT (automatic gain control), the gain of the amplifier circuit 181 can be increased or decreased. Thus, the control unit 150 amplifies the amplitude of the low-frequency component of the voltage signal.

[0040] Also, VGA175 exhibits peaking characteristics. More specifically, as shown in FIG. 4(b), VGA175 includes a peaking circuit 182 for adjusting peaking. The peaking circuit 182 includes an emitter series feedback resistor R E and a peaking capacitor C E . The emitter series feedback resistor R E and the peaking capacitor C E are connected in parallel. One end of the emitter series feedback resistor R E is connected to the amplifier circuit 181. Although not shown, one end of the emitter series feedback resistor R E is connected to the emitter of the transistor included in the amplifier circuit 181. The other end of the emitter series feedback resistor R E is grounded. The peaking capacitor C E [[ID= forty-two]] can be realized by using a variable capacitor such as a MIM (Metal-Insulator-Metal) capacitor, a MOS (Metal-Oxide-Semiconductor) capacitor, or a varactor capacitor. For example, the peaking capacitor C EBy using a variable capacitance such as a varactor, the peaking amount can be adjusted, and the bandwidth of the amplification circuit 181 can be improved.

[0041] The control unit 150 controls the peaking capacitance C E The control voltage V applied to it CONT By adjusting the value of (peaking adjustment value), the emitter series feedback resistor R E and peaking capacity C E The combined resistance value changes. When the combined resistance value changes, the gain of the amplification circuit 181 changes. That is, the control unit 150 changes the peaking capacitance C. E The control voltage V applied to it CONT By adjusting the value of the (peaking adjustment value), the gain of the amplification circuit 181 can be increased or decreased. In this way, the control unit 150 amplifies the amplitude of the high-frequency component of the voltage signal using the peaking characteristics.

[0042] Therefore, if the control unit 150 controls the amplification of the high-frequency components of the voltage signal, the bandwidth characteristic L3 of the ICR130 can be expanded. Conversely, if the control unit 150 controls the amplitude of the high-frequency components of the voltage signal, the bandwidth characteristic L3 of the ICR130 can be reduced.

[0043] Therefore, by pre-associating the baud rate of the main signal Sf2 with a constant corresponding to the above voltage value (hereinafter referred to as the peaking adjustment value) using a control table or formula, the peaking adjustment value corresponding to the baud rate can be determined or calculated. This identifies the voltage value corresponding to the peaking adjustment value, and the bandwidth characteristic L3 of the ICR130 is expanded or narrowed.

[0044] For example, as shown in Figure 5, the TIA131 can extend the bandwidth characteristic L3-M of the ICR130 corresponding to a medium baud rate to the bandwidth characteristic L3-H of the ICR130 corresponding to a high baud rate. Similarly, the TIA131 can reduce the bandwidth characteristic L3-M of the ICR130 corresponding to a medium baud rate to the bandwidth characteristic L3-L of the ICR130 corresponding to a low baud rate. Therefore, by combining the bandwidth characteristic L2 of the ADC120 and the bandwidth characteristic L3-H of the ICR130, the bandwidth characteristic L4 of the optical receiver 80 is expanded. Conversely, by combining the bandwidth characteristic L2 of the ADC120 and the bandwidth characteristic L3-L of the ICR130, the bandwidth characteristic L4 of the optical receiver 80 is reduced.

[0045] Therefore, if the bandwidth characteristic L1 of the main signal Sf2 is a bandwidth characteristic L1-H corresponding to a high baud rate, as shown in Figure 6, then by utilizing the peaking characteristic, the bandwidth characteristic L4 of the optical receiver 80 will approximate the shape of the bandwidth characteristic L1-H. In other words, the TIA131 should determine the bandwidth characteristic L3-H (see Figure 5) of the ICR130 so that the bandwidth characteristic L4 of the optical receiver 80 approximates the shape of the bandwidth characteristic L1-H.

[0046] On the other hand, even if the bandwidth characteristic L1 of the main signal Sf2 is the bandwidth characteristic L1-L corresponding to a low baud rate, by utilizing the peaking characteristic, the bandwidth characteristic L4 of the optical receiver 80 approximates the shape of the bandwidth characteristic L1-L. In other words, the TIA131 only needs to determine the bandwidth characteristics L3-L (see Figure 5) of the ICR130 so that the bandwidth characteristic L4 of the optical receiver 80 approximates the shape of the bandwidth characteristics L1-L.

[0047] As shown in Figure 6, if the bandwidth characteristic L1 of the main signal Sf2 is the bandwidth characteristic L1-L corresponding to a low baud rate, the frequency bandwidth becomes narrower compared to the bandwidth characteristic L1-H. If a bandwidth characteristic L4 that approximates the shape of the bandwidth characteristic L1-H is fixedly set, this bandwidth characteristic L4 becomes excessively wide compared to the bandwidth characteristic L1-L. As a result, a region appears between this bandwidth characteristic L4 and the bandwidth characteristics L1-L where the signal component of another main signal Sf3 adjacent to the main signal Sf2 exists. In such a case, this signal component reduces the amplification factor of the TIA131, which may degrade the signal quality of the main signal Sf2.

[0048] However, as described above, in this embodiment, even if the bandwidth characteristic L1 of the main signal Sf2 is the bandwidth characteristic L1-L corresponding to a low baud rate, by utilizing the peaking characteristic, the bandwidth characteristic L4 of the optical receiver 80 approximates the shape of the bandwidth characteristic L1-L. As a result, the region where the signal component of the main signal Sf3 exists does not appear, or this region becomes very small. Consequently, in the transmission of WDM signals, the degradation of the signal quality of the main signal Sf2 caused by the signal component of the main signal Sf3 can be suppressed, and a decrease in the transmission performance of the optical transmission system ST can be avoided.

[0049] In this embodiment, the low baud rate can be, for example, 60 Gbaud or 64 Gbaud. The medium baud rate can be, for example, 90 Gbaud or 96 Gbaud. The high baud rate can be, for example, 120 Gbaud or 130 Gbaud.

[0050] Next, the operation of the control unit 150 according to the first embodiment will be described with reference to Figures 7 and 8.

[0051] First, as shown in Figure 7, the control unit 150 receives the signal type input from the operation terminal 25 (step S1). As described above, the signal type includes the baud rate, modulation scheme, frame format, etc., of the main signal Sf2. The control unit 150 accepts the signal type as the setting for the main signal Sf2.

[0052] Upon receiving a signal type, the control unit 150 determines a peaking adjustment value (step S2). As shown in Figure 8(a), the control unit 150 is equipped with a memory 151, which stores a control table 152. The control table 152 defines the correspondence between baud rate and peaking adjustment value. Therefore, when the control unit 150 receives a signal type, it can determine a peaking adjustment value corresponding to the baud rate included in the signal type. In the control table 152, the lower the baud rate, the lower the peaking adjustment value. That is, in the control table 152, smaller baud rates are associated with smaller peaking adjustment values. In addition, although the peaking adjustment value in the first embodiment is shown in hexadecimal, it may be in a format other than hexadecimal.

[0053] Once the peaking adjustment value is determined, the control unit 150 sets the peaking adjustment value to TIA131 (step S3) and terminates the process. This sets the control voltage V corresponding to the peaking adjustment value. CONT The value of (Peaking adjustment value) is the peaking capacity C E When applied (see Figure 4(b)), the bandwidth characteristic L3 of the ICR130 changes.

[0054] Therefore, for example, if the signal types include high baud rates, the shape of the bandwidth characteristic L4 of the optical receiver 80 approximates the shape of the bandwidth characteristic L1-H of the main signal Sf2 with a high baud rate, as shown in Figure 8(b). If the signal types include low baud rates, the shape of the bandwidth characteristic L4 of the optical receiver 80 approximates the shape of the bandwidth characteristic L1-L of the main signal Sf2 with a low baud rate, as shown in Figure 8(b). In this way, the optical receiver 80 according to the first embodiment can ensure a bandwidth characteristic L4 corresponding to the baud rate of the main signal Sf2.

[0055] (Second Embodiment) Next, the operation of the control unit 150 according to the second embodiment will be described with reference to Figures 9 and 10.

[0056] First, as shown in Figure 9, the control unit 150 receives the signal type output from the operation terminal 25 (step S11). The process in step S11 is basically the same as the process in step S1, so a detailed explanation is omitted.

[0057] Upon receiving the signal type, the control unit 150 calculates the peaking adjustment value (step S12). Here, as shown in Figure 10, the control unit 150 holds the setting formula information 153. In other words, the control unit 150 has formula information set in advance. The formula information includes the peaking adjustment value (hexadecimal) = 1B (hexadecimal) × baud rate + D5 (hexadecimal). Constants such as 1B (hexadecimal) and D5 (hexadecimal) can be appropriately determined according to the design, experiment, etc.

[0058] Thus, the control unit 150 defines the correspondence between the baud rate and the peaking adjustment value. Therefore, when the control unit 150 receives a signal type, it can calculate the peaking adjustment value corresponding to the baud rate included in the signal type. In this formula information, the lower the baud rate, the lower the peaking adjustment value. That is, in this formula information, a smaller baud rate results in a smaller peaking adjustment value. Also, although the peaking adjustment value in the second embodiment is shown in hexadecimal, it may be in a format other than hexadecimal.

[0059] Once the peaking adjustment value is calculated, the control unit 150 sets the peaking adjustment value to TIA131 (step S13) and terminates the process. This sets the control voltage V corresponding to the peaking adjustment value. CONT The value of (Peaking adjustment value) is the peaking capacity C E When applied (see Figure 4(b)), the bandwidth characteristic L3 of the ICR130 changes.

[0060] Therefore, for example, if the signal types include high baud rates, the shape of the bandwidth characteristic L4 of the optical receiver 80 approximates the shape of the bandwidth characteristic L1-H of the main signal Sf2 with a high baud rate. If the signal types include low baud rates, the shape of the bandwidth characteristic L4 of the optical receiver 80 approximates the shape of the bandwidth characteristic L1-L of the main signal Sf2 with a low baud rate. In this way, even with the optical receiver 80 according to the second embodiment, it is possible to secure a bandwidth characteristic L4 corresponding to the baud rate of the main signal Sf2.

[0061] Although preferred embodiments of the present invention have been described in detail above, the present invention is not limited to any specific embodiment, and various modifications and changes are possible within the scope of the gist of the invention as described in the claims.

[0062] Furthermore, the following additional information is disclosed regarding the above explanation. (Note 1) An optical receiving device comprising: a conversion device that converts an optical signal into an electrical data signal; a control unit that changes a peaking adjustment value based on the baud rate of the optical signal; and an amplifier that changes the bandwidth characteristics of the conversion device based on the adjustment value changed by the control unit. (Note 2) The optical receiving device according to Note 1, characterized in that the peaking is a characteristic that amplifies the amplitude component in the bandwidth characteristics of the conversion device. (Note 3) The optical receiving device according to Note 1 or 2, characterized in that the amplifier changes the bandwidth characteristics of the conversion device by adjusting the peaking based on the adjustment value. (Note 4) The optical receiving device according to Note 1 or 2, characterized in that the control unit includes a memory for storing a table that defines the correspondence between the baud rate and the adjustment value, and determines the adjustment value according to the baud rate based on the table. (Note 5) The optical receiving device according to Note 4, characterized in that the correspondence is such that the adjustment value decreases in accordance with the decrease in the baud rate. (Note 6) The optical receiving device according to Note 1 or 2, characterized in that the control unit holds mathematical formula information that defines the correspondence between the baud rate and the adjustment value, and calculates the adjustment value according to the baud rate based on the mathematical formula information. (Note 7) The optical receiving device according to Note 6, characterized in that the correspondence is such that the adjustment value decreases in accordance with the decrease in the baud rate. [Explanation of Symbols]

[0063] ST Optical Transmission Systems 70, 80, 90 Optical receiving device 110 RxDSP 120 ADC 130 ICR 131 TIA 132 PD 140 ITLA 150 Control Unit 151 memory 152 Control Table 153 Setting Formula Information 175 VGA 182 Peaking Circuit

Claims

1. An optical receiving device capable of receiving optical signals of multiple baud rates, A conversion device that converts optical signals into electrical data signals, A control unit that modifies the peaking adjustment value based on the baud rate of the optical signal before reception, An amplifier that changes the bandwidth characteristics of the conversion device based on the adjustment value changed by the control unit, An optical receiving device equipped with the following features.

2. The aforementioned peaking is a characteristic that amplifies the amplitude component in the bandwidth characteristics of the conversion device. The optical receiving device according to feature 1.

3. The amplifier changes the bandwidth characteristics of the conversion device by adjusting the peaking based on the adjustment value. The optical receiving device according to claim 1 or 2.

4. The control unit includes a memory that stores a table defining the correspondence between the baud rate and the adjustment value, and determines the adjustment value according to the baud rate based on the table. The optical receiving device according to claim 1 or 2.

5. The control unit holds mathematical formula information that defines the correspondence between the baud rate and the adjustment value, and calculates the adjustment value according to the baud rate based on the mathematical formula information. The optical receiving device according to claim 1 or 2.

6. The control unit acquires information regarding the baud rate of the first optical signal before receiving the first optical signal included in the plurality of baud rate optical signals, Based on the information regarding the baud rate, the adjustment value is changed. The optical receiving device according to feature 1.

7. The control unit acquires information regarding the baud rate from an external device. The optical receiving device according to feature 6.

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