Parallel signal transmission system

Abstract

The present disclosure is a parallel signal transmission system comprising: a transmission device that transmits a parallel signal by using a wavelength-multiplexed signal; a reception device that receives the wavelength-multiplexed signal from the transmission device and outputs the parallel signal; and a wavelength switching unit that is connected between the transmission device and the reception device and that changes at least one of the transmission wavelengths of the parallel signal so as to reduce the skew of the parallel signal in the reception device.

Description

Parallel signal transmission system 【0001】 This disclosure relates to a technology for long-distance transmission of parallel signals. 【0002】 Image sensing technology is becoming increasingly important for human and object recognition in autonomous driving and surveillance cameras. In this context, image analysis using artificial intelligence and machine learning is indispensable. Recently, products incorporating image analysis capabilities into camera image sensors have been announced (Non-Patent Literature 1). 【0003】 However, advanced image processing in image sensor processors, such as image signal processors and application processors, increases the camera's power consumption. Therefore, it is preferable to separate the image processing processor from the camera and locate it remotely, utilizing abundant power and computing resources. In this case, a configuration where the processor is located in a data center is envisioned. Thus, long-distance transmission is required to send the information of each pixel output from the image sensor to the remote processor. 【0004】 Some image sensors and processors use parallel signals for communication. Therefore, it is necessary to transmit parallel signals simultaneously from the image sensor to the processor. In this regard, using wavelength division multiplexing technology to transmit parallel signals over optical fiber allows for simultaneous and low-latency transmission of parallel signals to the processor. 【0005】Sony Semiconductor Solutions Corporation, "Commercialization of Two Types of Intelligent Vision Sensors Equipped with World's First AI Processing Function," News Release 2020 / 5 / 14; Tektronix, "MIPI D-PHY / C-PHY Planning Overview and Latest Evaluation Method Using an Oscilloscope," TIF2024 (2024); Fibermall, "XNUMX Types of Wavelength Division Multiplexing (WDM) Technologies," 2024 / 7 / 11; Smartoptics, "16-channel O-band DWDM mux / demux with Monitor Ports," 2024 / 10 / 17; M. E. Vieira Segatto et al., "Use of fiber gratings for bit skew compensation in all optical bit parallel WDM systems," Opt. Commun., 190 (2001), 165-171. 【0006】 However, as the transmission distance of the optical transmission line becomes longer, wavelength dispersion occurs, which causes a problem of skew between parallel signals. Therefore, the parallel signal transmission system of the present disclosure aims to improve the skew of parallel signals and enable long-distance transmission of the parallel signals that can be transmitted thereby. 【0007】 The parallel signal transmission system of the present disclosure is a parallel signal transmission system that transmits parallel signals using wavelength multiplexed signals, and includes means for changing wavelengths in an optical transmission line that carries the parallel signals. 【0008】 Specifically, the parallel signal transmission system of the present disclosure includes: a transmission device that transmits parallel signals using wavelength multiplexed signals; a reception device that receives the wavelength multiplexed signals from the transmission device and outputs the parallel signals; and a wavelength switching unit that is connected between the transmission device and the reception device and changes at least any one of the transmission wavelengths of the parallel signals so that the skew of the parallel signals in the reception device is reduced. 【0009】Specifically, the parallel signal transmission method of the present disclosure includes: a first step in which a transmission device transmits a parallel signal using a wavelength division multiplexed signal; and a second step in which a reception device receives the wavelength division multiplexed signal from the transmission device and outputs the parallel signal. Between the first step and the second step, a wavelength switching unit connected between the transmission device and the reception device includes a third step of changing at least one of the transmission wavelengths of the parallel signal so that the skew of the parallel signal in the reception device becomes small. 【0010】 The parallel signal transmission system of the present disclosure may further include an image sensor that outputs the parallel signal, and a processor that generates an image captured by the image sensor using the parallel signal. 【0011】 The parallel signal may include a clock signal used to generate the image from the parallel signal. In this form, the transmission device transmits the clock signal using a wavelength close to one end of the use band of the transmission wavelength of the parallel signal. The wavelength switching unit changes the transmission wavelength of the clock signal to a wavelength close to the other end of the use band of the transmission wavelength of the parallel signal. 【0012】 In addition, the above disclosures can be combined as much as possible. 【0013】 According to the present disclosure, the skew of the parallel signal is improved, thereby enabling long-distance transmission of the parallel signal that can be transmitted. 【0014】 An example of the system configuration of the present disclosure is shown. An example of the system configuration of the present disclosure is shown. A specific example of wavelength allocation is shown. An example of the system configuration of the present disclosure is shown. An example of the system configuration of the present disclosure is shown. The specific configuration of the communication station building is shown. An example of the configuration of the integration unit is shown. An example of the intensity waveform of the MIPI signal is shown. An example of the group delay characteristic in DWDM is shown. An example of the transmission distance in DWDM is shown. An example of the transmission distance with respect to the wavelength arrangement of the clock signal is shown. An example of the transmission distance is shown. An example of the transmission distance at the wavelength in the C band is shown. An example of the group delay characteristic in LWDM is shown. An example of the transmission distance in LWDM is shown. An example of the transmission distance with respect to the wavelength arrangement of the clock signal is shown. 【0015】 Embodiments of this disclosure will be described in detail below with reference to the drawings. However, this disclosure is not limited to the embodiments shown below. These examples are illustrative, and this disclosure can be implemented in various modified and improved forms based on the knowledge of those skilled in the art. In this specification and in the drawings, components with the same reference numerals refer to the same components. 【0016】 (First Embodiment) Figure 1 shows an example of the system configuration of this embodiment. The parallel signal transmission system of this embodiment transmits the signal output from the image sensor 96 to the processor 97 using the optical transmission path 90, and the processor 97 generates an image. 【0017】 Among the signal formats used for signal transmission from the image sensor 96 to the processor 97, some use parallel signals. For example, the MIPI (Mobile Industry Processor Interface Alliance) signal format used in smartphones and tablets can be cited. 【0018】 The parallel signal contains information about each pixel that makes up the image. Therefore, it is necessary to transmit the parallel signal simultaneously from the image sensor 96 to the processor 97. In this respect, if the parallel signal is transmitted over an optical fiber using wavelength division multiplexing technology, the parallel signal can be transmitted to the processor 97 simultaneously and with low latency. 【0019】 MIPI is a parallel signal that transmits signals while repeating two different voltage amplitudes. In the low-amplitude high-speed mode (HS mode), image information and header information are stored. In the high-power mode (LP mode) with a large amplitude, no information is generally stored. 【0020】In MIPI, the parallel signals include a clock signal used to generate the image. In particular, in D-Phy, the most widely used physical layer standard in MIPI, the clock signal and up to four main signals are transmitted in parallel. Since each signal is a differential signal using two signal lines, a total of 10 signals are transmitted in parallel in the D-Phy standard. In this disclosure, a pair of differential signals is represented by "+" and "-". 【0021】 In the main signal, when transitioning from LP mode to HS mode, the two differential signals transition with a time difference. The processor 97 recognizes this time difference in the MIPI signals and starts receiving the HS mode. In parallel transmission, the transmission distance is limited by the occurrence of signal delay differences (skew). For example, according to Non-Patent Literature 2, when transmitting 4K quality at 30 fps, the transmission speed is about 1.5 Gbps / lane, and the allowable signal skew is ±133 ps. 【0022】 Currently, long-distance transmission of parallel signals from an image sensor 96 uses a method in which a serializer (Ser) converts the parallel signal to a series signal for long-distance transmission, and then a deserializer (Des) converts it back to a parallel signal. Non-patent document 3 describes how long-distance transmission is achieved using SerDes technology. However, due to signal loss and other factors, the transmission distance is limited to about 15m. On the other hand, the distance from a terminal to a data center is generally several tens to 100km, and it is quite possible that the distance from the image sensor 96 to the processor 97 is of a similar magnitude. For this reason, it is necessary to enable MIPI signal transmission over distances of several tens of kilometers, and preferably up to 100km. 【0023】 If the optical transmission line 90 uses optical fiber, low-latency signal transmission is possible. In this embodiment, an E / O conversion function 98 converts the MIPI signal from the image sensor 96 into an optical signal, and an O / E conversion function 99 converts the MIPI signal transmitted in the optical transmission line 90 into an electrical signal. This enables long-distance transmission of MIPI signals using the optical transmission line 90, and allows image generation in the processor 97. 【0024】When transmitting MIPI D-Phy signals optically, a configuration in which each signal line is assigned to a different wavelength and then subjected to WDM (Wavelength Deposition Modeling) is conceivable. Various methods for WDM wavelength assignment are known, including LWDM (Non-Patent Literature 3), in which wavelengths are assigned at intervals of 200 GHz to 800 GHz from 1269 nm to 1318 nm in the O band, and DWDM (Non-Patent Literature 4), in which wavelengths are assigned at intervals of 200 GHz from 1296 nm to 1313 nm. MIPI D-Phy can be transmitted using wavelength division multiplexing signals with 10 wavelengths. Therefore, the following embodiments show examples using these wavelength bands. 【0025】 Non-patent document 5 discloses a method for suppressing signal skew using chirpted fiber gratings (CFGs) to achieve 100 km bit parallel transmission. However, since chirpted fiber gratings are individually optimized for transmission path characteristics, the system implementation cost increases. 【0026】 Therefore, the transmission system of this disclosure enables long-distance transmission of parallel signals from the image sensor 96 using an optical transmission path 90. The following will be a specific explanation using an example where the parallel signal is an MIPI signal. 【0027】 (Second Embodiment) Figure 2 shows an example of the system configuration of the present disclosure. In the parallel signal transmission system of this embodiment, a transmitting device 91, a wavelength swapping unit 93, and a receiving device 92 are connected in order between the image sensor 96 and the processor 97. The transmitting device 91 is equipped with an E / O conversion function 98, and the receiving device 92 is equipped with an O / E conversion function 99. The transmitting device 91 and the wavelength swapping unit 93 are connected by an optical transmission path 90-1, and the wavelength swapping unit 93 and the receiving device 92 are connected by an optical transmission path 90-2. 【0028】The parallel signal transmission system of this embodiment performs the parallel signal transmission method of the present disclosure. Specifically, the following procedure is performed in order: • Procedure S1: The image sensor 96 captures an image and outputs a MIPI signal. • Procedure S2: The transmitting device 91 transmits the MIPI signal output from the image sensor 96 using a wavelength division multiplexing signal. • Procedure S3: The wavelength swapping unit 93 changes at least one of the transmission wavelengths of the MIPI signal so that the skew of the MIPI signal in the receiving device 92 is reduced. • Procedure S4: The receiving device 92 receives the wavelength division multiplexing signal from the transmitting device 91 and outputs the MIPI signal. • Procedure S5: The processor 97 uses the MIPI signal to generate the image captured by the image sensor 96. 【0029】 In this configuration, procedure S2 corresponds to the first procedure, procedure S3 corresponds to the third procedure, and procedure S4 corresponds to the second procedure. In addition, the image sensor 96 may capture an image in procedure S1. In this configuration, the processor 97 generates the image. 【0030】 Figure 3 shows a specific example of wavelength allocation. As an example, it shows a system that transmits MIPI signals with one lane for the clock signal and four lanes for the main signals. Each signal is a differential signal. The transmitter 91 receives the main signals sigN+ and sigN-, where N is an integer of 4 or less. The transmitter 91 also receives the clock signals CLK+ and CLK-. 【0031】 In this embodiment, the transmitting device 91 comprises a transmitting unit 11 and a multiplexing unit 12, and the receiving device 92 comprises a demultiplexing unit 21 and a receiving unit 22. In the transmitting unit 11, each signal line is emitted as an optical signal by 2(N+1) optical transmitters, each having a different wavelength. Each wavelength is assigned according to, for example, DWDM or LWDM. For example, the differential signal of a clock signal is λ １ and λ ２ It is assigned to the optical fiber. In the multiplexing section 12, light of each wavelength is incident on a single optical fiber. As a result, the wavelength-multiplexed signal is transmitted through the optical transmission path 90-1. 【0032】The wavelength-division multiplexed signal transmitted through the optical transmission path 90-1 is demultiplexed into each wavelength in the demultiplexing section 31 provided in the wavelength switching section 93. The multiplexing section 32 switches and multiplexes the transmission wavelengths so as to suppress the skew generated in the optical transmission path 90-1. This switching of the transmission wavelength can be realized by converting an optical signal into an electrical signal and inputting the electrical signal to an optical transmitter having a light source of a desired wavelength to generate an optical signal. The multiplexing section 32 makes the wavelength-division multiplexed signal enter the optical transmission path 90-2. 【0033】 The wavelength switching section 93 changes at least any one of the transmission wavelengths of the MIPI signals so that the skew of the MIPI signals in the receiving device 92 becomes small. For example, the transmission wavelengths of the respective MIPI signals are switched so that the delay of each wavelength in the optical transmission path 90-1 can be compensated in the optical transmission path 90-2. For example, the wavelengths are switched so as to be centrosymmetric. 【0034】 In the present embodiment, differential signals are transmitted using adjacent wavelengths. In this case, by switching the wavelengths so as to be centrosymmetric, the order of the transmission wavelengths of the differential signals is switched. Therefore, the skew between the differential signals can be reduced. 【0035】 Note that, in the present embodiment, all of the transmission wavelengths of the MIPI signals in the optical transmission paths 90-1 and 90-2 are switched, but a part of the transmission wavelengths of the MIPI signals in the optical transmission paths 90-1 and 90-2 may be used. For example, of wavelengths λ １ ~λ １０ , only two wavelengths of λ １ and λ ２ may be switched with λ １ ~λ １０ of λ ９ and λ １０ . 【0036】 Further, in the present embodiment, an example in which the used bands of the transmission wavelengths of the MIPI signals in the optical transmission paths 90-1 and 90-2 are exactly the same is shown, but these may be different. For example, in the optical transmission path 90-1, a band of wavelengths λ １ ~λ １０ may be used, and for the transmission wavelengths of the MIPI signals in the optical transmission path 90-2, a band of wavelengths λ ３ ~λ １２ may be used. 【0037】 The parallel signal transmission system of this embodiment includes a wavelength swapping unit 93, which allows parallel signals to arrive at the demultiplexing unit 94 simultaneously. The demultiplexing unit 21 splits the signal light of each wavelength from the optical transmission path 90-2. In the receiving unit 22, optical receivers corresponding to each wavelength receive the signal light, and MIPI signals are output to the processor 97. Therefore, in this embodiment, the processor 97 can generate an image using the MIPI signals. 【0038】 (Third Embodiment) Figure 4 shows an example of the system configuration of the present disclosure. In the parallel signal transmission system of this embodiment, as shown in the system configuration of Figures 2 and 3, N pairs of wavelength swapping units 93-1 and 93-2 are connected between the transmitting device 91 and the receiving device 92. The parentheses surrounding the wavelength swapping units 93-1 and 93-2 indicate that the configuration within the parentheses is connected in multiple stages N times, where N is an integer. 【0039】 The transmitting device 91 and the receiving device 92 operate in the same manner as in Figure 1. The wavelength swapping unit 93-1 has the same function as in Figure 1. The wavelength swapping unit 93-2 swaps the transmission wavelengths to reproduce the wavelength allocation in the optical transmission path 90#1. 【0040】 In this embodiment, the optical transmission path 90-2 in Figures 2 and 3 can be made to be the total distance of optical transmission path 90#N and optical transmission path 90#N+1. Therefore, by adopting this embodiment, the transmission distance can be further extended. 【0041】 (Fourth Embodiment) Figure 5 shows an example of the system configuration of the present disclosure. In this embodiment, a relay network 900 is connected between the transmitting device 91 and the receiving device 92. Thus, the present disclosure can also be configured as a parallel signal relay transmission system combined with a relay transmission function. In this embodiment as an example, a system is shown that transmits MIPI signals with one lane for the clock signal and four lanes for the main signal. The transmitting device 91, wavelength swapping unit 93, and receiving device 92 function in the same manner as in Figure 1. 【0042】The wavelength-division multiplexed signal from the transmitting device 91 is converted into a digital signal at the communication station building 80-1 and transmitted to the relay network 900. The communication station building 80-2 receives the digital signal from the relay network 900 and transmits the wavelength-division multiplexed signal to the receiving device 92. Since digital transmission occurs in the relay network 900, no skew occurs. Therefore, further extension of the transmission range becomes possible. 【0043】 An integration unit 70 is located in the nearest communication station building 80-1 to the image sensor 96. The integration unit 70 receives the wavelength division multiplexed signals transmitted in parallel, converts them from analog to digital, and encodes them using a predetermined method. The encoded signals are transmitted to the relay network 900 and relayed to the nearest station building to the signal transmission destination (in this case, communication station building 80-2). 【0044】 In this embodiment, the wavelength swapping unit 93 is provided in the communication station building 80-2. Figure 6 shows the specific configuration of the communication station building 80-2. The communication station building 80-2 also includes a decomposition unit 81 and a multiplexing unit 82. 【0045】 In the decomposition unit 81, the signal encoded in the integration unit 70 is decoded, converted from digital to analog, and then output from the port corresponding to the wavelength assigned by the transmission unit. This results in the output of a parallel signal. The wavelength swapping unit 93 swaps the wavelengths of the parallel signal output from the decomposition unit 81 and outputs it to the multiplexing unit 82. The multiplexing unit 82 combines the optical signals with swapped wavelengths and inserts them into the optical transmission line 90-2. As a result, the wavelength-multiplexed signal with swapped wavelengths is transmitted to the receiving device 92 using the optical transmission line 90-2. 【0046】 Figure 7 is a diagram of the configuration of the integration unit 70. The integration unit 70 includes a demultiplexer 71, a photodetector 72, an AD converter 73, a buffer 74, a transmission unit 75, and an optical transmitter 76. Wavelength-division multiplexed signals that have propagated through the optical transmission line 90-1 are demultiplexed into individual wavelengths by the demultiplexer 71. The demultiplexed optical signals are received by photodetectors 72#1 to 72#2N and converted into electrical signals. Each of the resulting electrical signals is converted into digital signals by AD converters 73#1 to 73#2N. The digital data from AD converters 73#1 to 73#2N is stored in buffers 74#1 to 74#2N. 【0047】The buffer 74 recognizes when the MIPI signal waveform transitions from HS mode to LP mode, or from LP mode to HS mode, and outputs the stored digital data to the transmission unit 75. The transition between HS mode and LP mode can be achieved by identifying changes in signal strength. Alternatively, the transition from LP mode to HS mode can be achieved by identifying the transition time difference between the two signal lines. 【0048】 The transmission unit 75 serializes the digital data received from the buffer 74 and sends it to the optical transmitter 76. Here, in order to facilitate the selection of the transmission wavelength in the wavelength swapping unit 93, the digital data may also be assigned a transmission wavelength identifier before serialization. It is preferable to serialize the digital data transmitted by signal light of a wavelength with a small group delay time in the optical transmission path 90-1, as this suppresses the occurrence of transmission delay in the transmission unit 75. 【0049】 The optical transmitter 76 converts the digital data obtained from the transmission unit 75 into an optical signal and injects it into the relay network 900. At this time, the optical signal can be an intensity-modulated signal or an optical coherent signal. 【0050】 Referring to Figure 8, an example of how to distinguish between HS mode and LP mode in buffer 74 is described. Figure 8 shows the intensity waveforms of MIPI signals on signal lines sign+ and sign-, where n is an integer between 1 and N+1. At the time the MIPI signal is output from the image sensor 96, the mark voltage for LP mode is 1.2V and the space voltage is 0V, while the mark voltage for HS mode is 0.3mV and the space voltage is 0.1mV. Therefore, when the vertical resolution is 3 bits or more, different symbols can be assigned to the mark and space in HS mode. 【0051】 If we assume that the low-voltage side of the signal strength is 0 and assign a 23-bit symbol, then in LP mode the most significant bit of the symbol during marking will be 1, and in HS mode the most significant bit of the symbol during marking and spacing will be 0. 【0052】Therefore, by identifying the most significant bit of the assigned symbol, it is possible to distinguish between HS mode and LP mode and recognize the transition timing between modes. Also, since the most significant bit of the symbol during a space in LP mode is 0, it is possible to identify the time when one of sign+ and sign- is a mark and the other is a space, and recognize the transition timing from LP mode to HS mode. 【0053】 As described above, the wavelength-swapping parallel signal transmission system of this embodiment can be combined with a relay transmission function. In the relay network 900, the signal waveform is transmitted as digital information by analog-to-digital conversion, so it does not affect the skew of the parallel signal. Therefore, by using optimal wavelength allocation and optical transmission lines 90-1 and 90-2 of allowable distance, it becomes possible to transmit MIPI signals over long distances based on DWDM and LWDM. 【0054】 Although the configuration described here assumes that the integration unit 70 is located in the communications building 80-1, the same functionality can be achieved even if the integration unit 70 is located in the user's home. 【0055】 (Fifth Embodiment) An example of applying the configuration shown in Figure 3, described in the second embodiment, to DWDM will be described. Figure 9 shows the wavelength dependence of the group delay time in a single-mode fiber (SMF, core radius 4.2 μm, relative refractive index difference between core and cladding 0.35%) with solid lines. The circles indicate the group delay time at the wavelength of the DWDM. The number of wavelengths for DWDM is 16, and 10 of these wavelengths are selected to transmit the MIPI signal. In this case, the numbers are assigned from the long wavelength side, i.e., λ １ =1312.58nm, λ ２ = Starting from 1311.43 nm, λ １５ =1296.68nm, λ １６ Let's assume it equals 1295.56 nm. 【0056】 All of these wavelengths are assigned to the shorter wavelength side of the zero-dispersion wavelength of SMF. For example, λ ５ = When 1308 nm is taken as CLK+, λ １０The skew with the assigned signal was 4.8 ps / km. Therefore, if wavelength swapping is not performed, and the upper limit of the skew of the receiving device 92 is set to 133 ps, the limit of the transmission distance will be 133 / 4.8 = 27.7 km. 【0057】 For the distances of optical transmission paths 90-1 and 90-2 shown in Figure 3, the maximum and minimum skew observed by the receiving device 92 were calculated. Here, as an example of the skew observed in the configuration shown in Figure 3, the wavelength used for MIPI signal transmission is λ of DWDM. １ ~λ １０ Let's assume that one of the clock signals (here, CLK+) is λ ２ This shows the case when transmission is performed. The wavelength swapping is centrally symmetric, as shown in Figure 3. 【0058】 Figure 10 shows the applicable distances for optical transmission lines 90-1 and 90-2. The reference is a signal-to-signal skew of ±133 ps, required when transmitting 4K resolution at 30 fps. The solid line indicates the condition where the maximum skew is 133 ps, and the dashed line indicates the condition where the minimum skew is -133 ps. Within the distance conditions enclosed by the solid and dashed lines (gray area), the skew is within ±133 ps for all wavelengths. Therefore, in this configuration, optical transmission line 90-1 is applicable up to 110 km, and optical transmission line 90-2 is applicable up to 100 km. This shows a significant expansion in the transmittable distance compared to the 27.7 km shown in Figure 9 without wavelength swapping. 【0059】 (Sixth Embodiment) In MIPI, the clock signals CLK+ and CLK- are used as a reference when reading out the main signal, so the wavelength arrangement of the clock signals affects the transmission distance of the MIPI signal. Therefore, we investigated the wavelength arrangement of the clock signals when DWDM is applied to the configuration shown in Figure 3 described in the second embodiment. 【0060】 Figure 11 shows an example of transmission distance for the wavelength arrangement of a clock signal. The horizontal axis shows the wavelength number to which the clock signal is assigned, and the vertical axis shows the maximum total distance of the transmittable optical transmission paths 90-1 and 90-2 (sometimes referred to as the "maximum total distance"). The black and white circles represent the transmission wavelengths λ, respectively. １ ~λ １０ and λ７ ~λ １６ This shows the case where the transmission wavelength λ ７ ~λ １６ Regarding the transmission wavelength λ １ ~λ １０ For comparison, the values ​​obtained by subtracting 6 from the wavelength number are plotted on the horizontal axis. 【0061】 Regardless of which wavelength is assigned to the clock signal, the maximum total distance exceeds 100 km, surpassing the transmission distance limit of 27.7 km when wavelengths are not changed. １ ~λ １０ In this case, the clock signal is assigned to wavelength numbers 2 and 9, and the transmission wavelength is λ ７ ~λ １６ In this case, the total distance of optical transmission lines 90-1 and 90-2 was maximized when the clock signal was assigned to wavelength numbers 8 and 15. These wavelength numbers are all wavelengths that are one wavelength closer to the center from both ends of the transmission wavelength bandwidth. 【0062】 Therefore, by assigning the clock signal to a wavelength slightly closer to the center from both ends of the transmission wavelength bandwidth, the distance over which MIPI signals can be transmitted can be extended. For example, the transmitting device 91 uses the transmission wavelength λ １ ~λ １０ wavelength λ near one end of the operating bandwidth １ ~λ ３ The clock signal is transmitted using one of the following. The wavelength swapping unit 93 then sets the transmission wavelength λ １ ~λ １０ wavelength λ near the other end of the operating bandwidth ８ ~λ １０ The clock signal is transmitted using one of the following methods. The transmitting device 91 uses a wavelength λ ８ ~λ １０ Using one of the above, the wavelength exchange unit 93 has a wavelength λ １ ~λ ３ You may change it to one of the following. 【0063】 (Seventh Embodiment) In this embodiment, the λ in the fifth embodiment １ ~λ １０ The transmission wavelength is λ １ ~λ １６The applicable distance for each optical transmission path was examined when the wavelength was increased to 16 wavelengths. Here, as an example, the transmission wavelength of the clock (CLK+) is λ. ３ As shown in Figure 3, the wavelength swapping is centrally symmetric. 【0064】 Figure 12 shows the applicable distances for optical transmission lines 90-1 and 90-2. The solid and dashed lines indicate the conditions under which the maximum and minimum skew of the transmitted signals are 133 ps / km and -133 ps / km, respectively. The gray area represents the transmission distance conditions under which skew within the acceptable range is achieved for both transmitted signals. It can be seen that both optical transmission lines 90-1 and 90-2 are capable of transmission up to 40 km. This embodiment is preferable because it allows for increasing the number of MIPI signal lines to 16, thereby achieving broadband performance. 【0065】 (Eighth Embodiment) In the fifth and sixth embodiments, O-band DWDM wavelengths were used, but similar transmission distance conditions can be found with C-band DWDM wavelengths. Figure 13 shows the applicable distances of optical transmission paths 90-1 and 90-2 when C-band DWDM wavelengths are used. Here, as an example, 10 wavelengths of light with frequencies between 193.1 THz and 194.0 THz were selected at 100 GHz intervals to be used as transmission wavelengths, and the light with a frequency of 193.2 THz was used as the clock (CLK+). 【0066】 The solid and dashed lines represent the distance conditions where the maximum and minimum skew at the transmission wavelength are 133 ps and -133 ps, respectively, and the distances in the gray area are applicable. As shown in Figure 13, the required skew can be satisfied for all signal lines even in C-band DWDM. Here, both optical transmission lines 90-1 and 90-2 are shown up to 25 km, but applicable transmission distances for longer distances can be designed using a similar approach. Similarly, DWDM in L-band can also be designed. In this embodiment, the use of the C-band, which has lower optical fiber loss, is preferable because it improves the signal-to-noise ratio and enables high-capacity transmission. 【0067】(Ninth Embodiment) In this embodiment, an example of applying the configuration shown in Figure 3 in the second embodiment to LWDM will be described. Figure 14 shows the wavelength dependence of the group delay time in a single-mode fiber (SMF, core radius 4.2 μm, relative refractive index difference between core and cladding 0.35%) with solid lines. The circles indicate the group delay time at the wavelength of the LWDM. The number of wavelengths for the LWDM is 12, and 10 of these wavelengths are selected to transmit the MIPI signal. At this time, the numbers are assigned from the long wavelength side, i.e., λ １ =1318.35nm, λ ２ = Starting from 1313.73 nm, λ １１ =1273.54nm, λ １２ Let's assume it equals 1269.23 nm. For example, λ ５ = When 1300.05 nm is set as CLK+, λ １０ The skew with the assigned signal is 51.4 ps / km. Therefore, if wavelength swapping is not performed, and the upper limit of the receiver skew is set to 133 ps, the transmission distance limit will be 133 / 51.4 = 2.6 km. 【0068】 Figure 15 shows an example of transmission distance. The maximum and minimum skew observed by the receiving device 92 were calculated for the distances of optical transmission paths 90-1 and 90-2 shown in Figure 3. Here, as an example of the skew observed in the configuration shown in Figure 3, the wavelength used for MIPI signal transmission is the λ of LWDM. １ ~λ １０ Let's assume that one of the clock signals (here, CLK+) is λ ２ This shows the case when transmission is performed. The wavelength swapping is centrally symmetric, as in the case shown in Figure 3. 【0069】Figure 15 uses a signal-to-signal skew of ±133 ps as a reference when transmitting 4K image quality at 30 fps. The solid line shows the condition where the maximum skew is 133 ps, and the dashed line shows the condition where the minimum skew is -133 ps. In the distance conditions enclosed by the solid and dashed lines (gray area), the skew is within ±133 ps for all wavelengths. Therefore, in this configuration, optical transmission line 90-1 is applicable up to 7 km, and optical transmission line 90-2 is applicable up to 6 km. This is preferable because the transmission distance is extended compared to the limit of 2.6 km shown in Figure 14 when wavelength swapping is not performed. 【0070】 (Tenth Embodiment) In MIPI, the clock signals CLK+ and CLK- are used as a reference when reading out the main signal, so the wavelength arrangement of the clock signals affects the transmission distance of the MIPI signal. Therefore, we investigated the wavelength arrangement of the clock signals when LWDM is applied to the configuration shown in Figure 3 described in the second embodiment. 【0071】 Figure 16 shows an example of transmission distance for the wavelength arrangement of a clock signal. The horizontal axis shows the wavelength number to which the clock signal is assigned, and the vertical axis shows the maximum total distance of the optical transmission paths 90-1 and 90-2 that can transmit the signal. The black and white circles indicate the transmission wavelength λ １ ~λ １０ and λ ３ ~λ １２ This shows the case of λ. ３ ~λ １２ Regarding the transmission wavelength λ １ ~λ １０ For comparison, the values ​​obtained by subtracting 2 from the wavelength number are plotted on the horizontal axis. 【0072】 Regardless of which wavelength is assigned to the clock signal, the maximum total distance exceeds 6 km. Therefore, regardless of which wavelength is assigned to the clock signal, the transmission distance limit of 2.6 km, as shown in Figure 14 when wavelength swapping is not performed, is exceeded. The transmission wavelength is λ １ ~λ １０ When the clock signal was assigned to wavelengths 2 and 9, the total distance of optical transmission paths 90-1 and 90-2 was maximized. Also, when the transmission wavelength was λ ３ ~λ １２When the clock signal was assigned to wavelengths 4 and 11, the total transmission distance was maximized. These wavelengths are all one wavelength closer to the center from both ends of the transmission wavelength bandwidth. Therefore, by assigning the clock signal to wavelengths slightly closer to the center from both ends of the transmission wavelength bandwidth, the transmission distance of the MIPI signal can be extended. 【0073】 (Other Embodiments) The apparatus of the present invention can also be realized by a computer and a program, and the program can be recorded on a recording medium or provided via a network. The program of this disclosure is a program for causing a computer to realize each function of the apparatus of this disclosure, and a program for causing a computer to execute each procedure of the method performed by the apparatus of this disclosure. 【0074】 As described above, this disclosure provides a function to transmit MIPI signals in parallel from an image sensor to the nearest optical communication station using WDM, and to swap the transmission wavelength at any point in the optical transmission path. By optimizing the wavelength swap to cancel out signal skew that occurs in the optical transmission path, the transmission distance of MIPI signals can be extended. The parallel signal transmission system of this disclosure enables long-distance transmission of parallel signals such as MIPI signals, and by separating the power-hungry processor from the camera, it is possible to reduce the power consumption of the camera. 【0075】 Furthermore, this disclosure is not limited to MIPI signals; it can be applied to any parallel signal where skew is a problem, and the same effects and advantages can be obtained. For example, the parallel signal from image sensor 96 may be a parallel signal from multiple image sensors 96. Also, the parallel signal from image sensor 96 may include signals from other sensors. Moreover, it may be a parallel signal from any other device instead of image sensor 96. In other words, it is widely applicable to applications that transmit multiple differential signals simultaneously. 【0076】11: Transmitting section 12, 32, 82: Multiplexing section 21, 31: Demultiplexing section 22: Receiving section 70: Integration section 71: Demultiplexer 72: Photodetector 73: AD converter 74: Buffer 75: Transmission section 76: Optical transmitter 80-1, 80-2: Communication station 81: Demultiplexing section 90, 90-1, 90-2: Optical transmission line 91: Transmitting device 92: Receiving device 93, 93-1, 93-2: Wavelength swapping section 96: Image sensor 97: Processor 98: E / O conversion function 99: O / E conversion function 900: Relay network

Claims

1. A parallel signal transmission system comprising: a transmitting device that transmits a parallel signal using wavelength division multiplexing; a receiving device that receives the wavelength division multiplexing signal from the transmitting device and outputs the parallel signal; and a wavelength swapping unit connected between the transmitting device and the receiving device, which changes at least one of the transmission wavelengths of the parallel signal so as to reduce the skew of the parallel signal in the receiving device.

2. The parallel signal transmission system according to claim 1, further comprising: an image sensor that outputs the parallel signal; and a processor that generates an image captured by the image sensor using the parallel signal, wherein the parallel signal includes a clock signal used to generate the image.

3. The parallel signal transmission system according to claim 2, wherein the transmitting device transmits the clock signal using a wavelength close to one end of the bandwidth used for the transmission wavelength of the parallel signal, and the wavelength swapping unit changes the transmission wavelength of the clock signal to a wavelength close to the other end of the bandwidth used for the transmission wavelength of the parallel signal.

4. A parallel signal transmission method comprising: a first step in which a transmitting device transmits a parallel signal using wavelength division multiplexing signals; a second step in which a receiving device receives wavelength division multiplexing signals from the transmitting device and outputs the parallel signal; and a third step between the first and second steps in which a wavelength swapping unit connected between the transmitting device and the receiving device changes at least one of the transmission wavelengths of the parallel signal so as to reduce the skew of the parallel signal in the receiving device.

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