Optical wireless communication system and optical wireless communication device

Abstract

Provided is an optical wireless communication system comprising paired optical wireless communication devices (1), wherein: each optical wireless communication device (1) is provided with a plurality of optical transmission units (101) that transmit optical signals of a target wavelength, an optical multiplexing / demultiplexing unit (103) that multiplexes the optical signals transmitted by the optical transmission unit (101) to transmit the multiplexed optical signals to the counterpart optical wireless communication device (1) and demultiplexes optical signals from the counterpart optical wireless communication device (1) into optical signals of a plurality of wavelengths, and a plurality of optical reception units (102) that receive an optical signal of the target wavelength from among the optical signals demultiplexed by the optical multiplexing / demultiplexing unit (103); the respective target wavelengths of the optical transmission unit (101) and the optical reception unit (102) are alternately allocated in order of length; and between the paired optical wireless communication devices (1), the respective target wavelengths of the optical transmission unit (101) and the optical reception unit (102) are shifted one at a time.

Description

Optical wireless communication system and optical wireless communication device

[0001] The present disclosure relates to an optical wireless communication system including an optical wireless communication device that transmits and receives optical signals, and to the optical wireless communication device.

[0002] Free-space optical communications, primarily inter-satellite optical communications, are expected to become widespread. For example, Non-Patent Document 1, referring to ITU-T G.694.1, indicates that two wavelengths, 193.1 + n × 0.1 THz (n = -1, +20), are allocated for transmission and reception as inter-satellite communications standards.

[0003] Furthermore, these wavelengths are required to be software-switchable, i.e., the wavelengths for transmission and reception must be interchangeable. This is because in free-space optical communications, particularly inter-satellite optical communications, it is necessary to interchange the wavelengths for transmission and reception to avoid crosstalk between communicating devices. For example, in one of two devices, Tx is assigned to CH_A and Rx is assigned to CH_B, and in the other device, Rx is assigned to CH_A and Tx is assigned to CH_B. Each device is then able to interchange the wavelengths assigned to Tx and Rx.

[0004] The reason why the two wavelengths are so wide relative to the 100 GHz of the ITU-T grid is to facilitate wavelength separation.

[0005] Optical Communications Terminal (OCT) Standard Version 3.0

[0006] In spatial optical communication, there are two possible methods for improving the communication bandwidth: increasing the amount of information per wavelength, i.e., increasing the modulation speed, and increasing the number of wavelengths (WDM: Wavelength Division Multiplexing).

[0007] Increasing the modulation rate is a trade-off with receiver sensitivity. In inter-satellite optical communications, which require link lengths of several thousand kilometers, beam divergence in free space is unavoidable, and the power reaching the receiver is extremely low. Therefore, this method of increasing the modulation rate is not desirable because high receiver sensitivity is essential for the system.

[0008] In contrast, the method of increasing the number of wavelengths is a technology that improves the communication bandwidth without changing the modulation speed, and is widely used in optical fiber communications. On the other hand, in the communication shown in Non-Patent Document 1, as described above, it is necessary to programmatically switch between the transmission wavelength and the reception wavelength.

[0009] The most reliable method for achieving this wavelength switching is to prepare a device that corresponds to each wavelength, but this method poses the problem of increased size and cost of the device.

[0010] Another method for switching wavelengths is to use a tunable light source and switch the wavelength as needed. This method requires a tunable wavelength filter to separate the transmitting and receiving wavelengths. However, it is difficult to switch wavelengths using commonly used multilayer filters.

[0011] Furthermore, the wavelength grid (193.1+n×0.1 THz (n=−1, +20)) shown in Non-Patent Document 1 has only two wavelengths, one for transmission and one for reception. However, if multiple wavelengths are used in the future to realize larger capacities, the system will become very complicated regardless of which of the wavelength switching methods described above is used.

[0012] The present disclosure has been made to solve the above-mentioned problems, and aims to provide an optical wireless communication system that can implement a larger number of wavelengths and makes it easier to switch wavelengths than conventional systems.

[0013] The optical wireless communication system according to the present disclosure is an optical wireless communication system including a pair of optical wireless communication devices, each of which includes a plurality of optical transmitting units that transmit optical signals of a target wavelength, an optical multiplexing / demultiplexing unit that multiplexes the optical signals transmitted by the optical transmitting units and transmits the multiplexed optical signals to a counterpart optical wireless communication device, and demultiplexes the optical signals from the counterpart optical wireless communication device into optical signals of a plurality of wavelengths, and a plurality of optical receiving units that receive the optical signals of the target wavelengths from the optical signals demultiplexed by the optical multiplexing / demultiplexing units, wherein the wavelengths targeted by the optical transmitting units and the optical receiving units are wavelengths that are alternately assigned in length order, and the wavelengths targeted by the optical transmitting units and the optical receiving units between the pair of optical wireless communication devices are shifted by one.

[0014] According to the present disclosure, the above-described configuration allows a larger number of wavelengths to be implemented than in the past, and wavelength switching becomes easier.

[0015] FIG. 1 is a diagram illustrating an example of the configuration of an optical wireless communication system according to a first embodiment. FIG. 2 is a diagram illustrating an example of the allocation of wavelengths targeted by the optical wireless communication system according to the first embodiment. FIG. 3 is a diagram illustrating an example of the configuration of a first optical wireless communication device according to the first embodiment. FIG. 4 is a diagram illustrating an example of the configuration of a second optical wireless communication device according to the first embodiment. FIG. 5 is a diagram illustrating an example of the configuration of a first optical wireless communication device according to a second embodiment. FIG. 6 is a diagram illustrating an example of the configuration of a first optical wireless communication device according to a third embodiment. FIG. 7 is a diagram illustrating an example of the setting of a band targeted by a first wavelength filter in the third embodiment. FIG. 8 is a diagram illustrating an example of the configuration of a first optical wireless communication device according to a fourth embodiment. FIG. 9 is a diagram illustrating an example of the configuration of a second optical wireless communication device according to the fourth embodiment.

[0016] Hereinafter, embodiments will be described in detail with reference to the drawings. Embodiment 1. Fig. 1 is a diagram showing an example of the configuration of an optical wireless communication system according to embodiment 1. The optical wireless communication system is a system that includes a pair of optical wireless communication devices 1 and performs communication between the pair of optical wireless communication devices 1. As shown in Fig. 1, this optical wireless communication system includes a first optical wireless communication device 1-1 and a second optical wireless communication device 1-2.

[0017] In this case, when it is necessary to distinguish between the optical wireless communication device 1 and the components of the optical wireless communication device 1, suffixes (-1, -2) are added to the reference numerals.

[0018] In addition, the following description will be given taking as an example communication between satellites 10 equipped with the optical wireless communication device 1 as an example of communication performed by the optical wireless communication device 1. However, the communication performed by the optical wireless communication device 1 is not limited to this, and may be communication with land or aircraft, for example, and the same configuration of the optical wireless communication device 1 can be applied.

[0019] 2 shows an example of the arrangement of wavelengths targeted by the optical wireless communication system according to the first embodiment. As shown in FIG. 2, the wavelengths targeted by the optical wireless communication system are arranged in a 21-wavelength grid at 100 GHz intervals. In the example of FIG. 2, the wavelength grid is the wavelength grid (193.1 + n × 0.1 THz (n = 0, ..., 20)) specified in ITU-T G. 694.1. The 100 GHz interval corresponds to approximately 0.8 nm. In FIG. 2, λ ０ ~λ ２０ indicates the wavelengths targeted by the optical wireless communication system.

[0020] The first optical wireless communication device 1-1 is mounted on a first satellite 10-1 and communicates with a second optical wireless communication device 1-2 as a counterpart, as shown in Fig. 1. The first optical wireless communication device 1-1 includes a plurality of first optical transmitters (Tx) 101-1, a plurality of first optical receivers (Rx) 102-1, and a first optical multiplexer / demultiplexer (AWG) 103-1 as shown in Fig. 3.

[0021] The first optical transmitting section 101-1 transmits an optical signal of a target wavelength to the first optical multiplexing / demultiplexing section 103-1.

[0022] For example, a semiconductor laser is used as the first optical transmitter 101-1. Examples of the semiconductor laser include a DML (Directly Modulated Laser) and an EML (Electro-absorption Modulator Integrated Laser Diode) that integrates an optical modulator. The oscillation wavelength of the DML and the oscillation wavelength of the EML have temperature characteristics of, for example, about 0.08 nm / K, and the wavelength of the output optical signal can be changed by changing the temperature.

[0023] The first optical receiving section 102-1 receives an optical signal of a target wavelength from among the optical signals demultiplexed by the first optical multiplexing / demultiplexing section 103-1.

[0024] The first optical receiving unit 102-1 may be, for example, an APD (Avalanche Photo Diode), which can receive light in any wavelength band to which it has sensitivity, regardless of temperature.

[0025] The wavelengths targeted by each of the first optical transmitting units 101-1 and each of the first optical receiving units 102-1 are wavelengths that are targeted by the first optical wireless communication device 1-1 and are alternately assigned in order of length. In the example of FIG. 3, each of the first optical transmitting units 101-1 has a λ ０ , λ ２ , ..., λ １８ and assigns λ to each first optical receiving unit 102-1. １ , λ ３ , ..., λ １９ is assigned.

[0026] The first optical multiplexing / demultiplexing unit 103-1 is an optical waveguide having multiple ports for multiplexing / demultiplexing optical signals. This first optical multiplexing / demultiplexing unit 103-1 has the function of demultiplexing wavelength-multiplexed light into multiple ports and the function of multiplexing light of specific wavelengths input to the multiple ports. That is, the first optical multiplexing / demultiplexing unit 103-1 multiplexes optical signals transmitted by the first optical transmitting unit 101-1 and transmits the multiplexed optical signals to the second optical wireless communication device 1-2, and also demultiplexes optical signals transmitted by the second optical wireless communication device 1-2 into optical signals of multiple wavelengths.

[0027] 3, an AWG (Array Waveguide Grating) is used as the first optical multiplexing / demultiplexing section 103-1. The AWG is an optical waveguide made of quartz, silicon, silicon nitride, or the like.

[0028] The spectral characteristics of this AWG have a temperature dependency of, for example, about 0.08 nm / K, and exhibit a behavior in which the port of the corresponding wavelength shifts to the adjacent one as the temperature changes. When an AWG made of quartz is used as the first optical multiplexing / demultiplexing unit 103-1, as shown in Figures 3 and 5, the first optical transmitting unit 101-1 is connected to the first port (port 1) and the first optical receiving unit 102-1 is connected to the second port (port 2), and the first optical transmitting unit 101-1 and the first optical receiving unit 102-1 are alternately connected to each port. In Figure 5, reference numeral 51 denotes a wavelength that can be used for communication in the optical wireless communication system.

[0029] If the first optical multiplexing / demultiplexing unit 103-1 is an AWG, the first optical wireless communication device 1-1 may include a temperature control unit that controls the temperature of the first optical multiplexing / demultiplexing unit 103-1. If the first optical transmitting unit 101-1 is a DML or EML, the first optical wireless communication device 1-1 may include a temperature control unit that controls the temperature of the first optical transmitting unit 101-1.

[0030] The second optical wireless communication device 1-2 is mounted on a second satellite 10-2 and communicates with the first optical wireless communication device 1-1 as a counterpart, as shown in Fig. 1. The second optical wireless communication device 1-2 includes a plurality of second optical transmitters (Tx) 101-2, a plurality of second optical receivers (Rx) 102-2, and a second optical multiplexer / demultiplexer (AWG) 103-2 as shown in Fig. 4.

[0031] The second optical transmitter 101-2 transmits an optical signal of the target wavelength to the second optical multiplexer / demultiplexer 103-2.

[0032] For example, a semiconductor laser is used as the second optical transmitter 101-2. The semiconductor laser may be, for example, a DML or an EML with an integrated optical modulator. The oscillation wavelength of the DML and the oscillation wavelength of the EML have a temperature characteristic of, for example, about 0.08 nm / K, and the wavelength of the output optical signal can be changed by changing the temperature.

[0033] The second optical receiving section 102-2 receives an optical signal of a target wavelength from among the optical signals demultiplexed by the second optical multiplexing / demultiplexing section 103-2.

[0034] The second optical receiving unit 102-2 may be, for example, an APD, which can receive light in a wavelength band to which it has sensitivity, regardless of temperature.

[0035] The wavelengths targeted by each second optical transmitting unit 101-2 and each second optical receiving unit 102-2 are wavelengths that are targeted by the second optical wireless communication device 1-2 and are alternately assigned in order of length. In the example of FIG. 4, each second optical transmitting unit 101-2 is assigned a λ １ , λ ３ , ..., λ １９ and assigns λ to each second optical receiving unit 102-2. ２ , λ ４ , ..., λ ２０ is assigned.

[0036] The second optical multiplexing / demultiplexing unit 103-2 is an optical waveguide having multiple ports for multiplexing / demultiplexing optical signals. This second optical multiplexing / demultiplexing unit 103-2 has the function of demultiplexing wavelength-multiplexed light into multiple ports and the function of multiplexing light of specific wavelengths input to the multiple ports. In other words, the second optical multiplexing / demultiplexing unit 103-2 multiplexes optical signals transmitted by the second optical transmitting unit 101-2 and transmits the multiplexed optical signals to the first optical wireless communication device 1-1, and also demultiplexes the optical signals transmitted by the first optical wireless communication device 1-1 into optical signals of multiple wavelengths.

[0037] 3, an AWG is used as the second optical multiplexing / demultiplexing section 103-2. The AWG is an optical waveguide made of quartz, silicon, silicon nitride, or the like.

[0038] The spectral characteristics of this AWG have a temperature dependency of, for example, about 0.08 nm / K, and exhibit a behavior in which the port of the corresponding wavelength shifts to the adjacent one as the temperature changes. When an AWG made of quartz is used as the second optical multiplexing / demultiplexing unit 103-2, the second optical transmitting unit 101-2 and the second optical receiving unit 102-2 are alternately connected to each port, such that the second optical transmitting unit 101-2 is connected to the first port (port 1) and the second optical receiving unit 102-2 is connected to the second port (port 2), as shown in Figures 4 and 5.

[0039] If the second optical multiplexing / demultiplexing unit 103-2 is an AWG, the second optical wireless communication device 1-2 may include a temperature control unit that controls the temperature of the second optical multiplexing / demultiplexing unit 103-2. If the second optical transmitting unit 101-2 is a DML or EML, the second optical wireless communication device 1-2 may include a temperature control unit that controls the temperature of the second optical transmitting unit 101-2.

[0040] 3 to 5, the wavelengths targeted by the first optical transmitting unit 101-1 and the first optical receiving unit 102-1 in the first optical wireless communication device 1-1 are shifted by one from the wavelengths targeted by the second optical transmitting unit 101-2 and the second optical receiving unit 102-2 in the second optical wireless communication device 1-2. That is, in the examples of FIGS. 3 to 5, the wavelengths targeted by each of the first optical transmitting units 101-1 are λ ０ , λ ２ , ..., λ １８ On the other hand, the wavelengths targeted by each second optical transmitter 101-2 are λ １ , λ ３ , ..., λ １９ 3 to 5, the wavelengths targeted by each of the first optical receiving units 102-1 are λ １ , λ ３ , ..., λ １９ , whereas the wavelengths targeted by each second optical receiving unit 102-2 are λ ２ , λ ４ , ..., λ ２０The target wavelengths are shifted by one.

[0041] Note that when the first optical multiplexing / demultiplexing unit 103-1 and the second optical multiplexing / demultiplexing unit 103-2 are AWGs, the wavelengths are shifted as described above, resulting in ports in each of the first optical multiplexing / demultiplexing unit 103-1 and the second optical multiplexing / demultiplexing unit 103-2 that cannot be used for communication. In the examples of FIGS. 3 and 5, the first port (port 1) of the ports of the first optical multiplexing / demultiplexing unit 103-1 is a port that cannot be used for communication. In other words, the first optical wireless communication device 1-1 operates at 19 waves from the short wavelength side. Similarly, in the examples of FIGS. 4 and 5, the 20th port (port 20) of the ports of the second optical multiplexing / demultiplexing unit 103-2 is a port that cannot be used for communication. In other words, the second optical wireless communication device 1-2 operates at 19 waves from the long wavelength side.

[0042] Furthermore, the wavelength settings of the first optical wireless communication device 1-1 and the second optical wireless communication device 1-2 can be reversed programmatically. That is, for example, if the optical transmitting unit 101 is a DML or EML, it is possible to adjust the wavelength of the optical signal from the optical transmitting unit 101 by adjusting the temperature setting value for the optical transmitting unit 101. Also, for example, if the optical multiplexing / demultiplexing unit 103 is an AWG, it is possible to adjust the wavelength corresponding to the port of the optical multiplexing / demultiplexing unit 103 by adjusting the temperature setting value for the optical multiplexing / demultiplexing unit 103. Therefore, by making these adjustments, it is possible to reverse the wavelength settings of the first optical wireless communication device 1-1 and the second optical wireless communication device 1-2 programmatically.

[0043] 2 to 4 show only the parts relevant to the present disclosure among the components of the optical wireless communication device 1. However, in an actual device, at the input / output ports of the optical multiplexing / demultiplexing unit 103, there are provided mechanisms such as a circulator that separates the transmitted and received optical signals, a booster optical amplifier for the transmitted optical signal or a low-noise optical amplifier for the received optical signal, or an optical scanning mechanism that performs tracking between satellites 10.

[0044] Next, an example of the operation of the optical wireless communication system according to the first embodiment will be described. Communication is performed between the first optical wireless communication device 1-1 mounted on the first satellite 10-1 and the second optical wireless communication device 1-2 mounted on the second satellite 10-2 through the following operations. In the following, it is assumed that the optical transmitting unit 101 is a DML or EML, and the optical multiplexing / demultiplexing unit 103 is an AWG. In the following, a case is shown in which the settings for the second optical wireless communication device 1-2 are changed based on the settings for the first optical wireless communication device 1-1, but the reverse is also possible.

[0045] First, for example, the temperature setting value for the second optical multiplexing / demultiplexing unit 103-2 in the second optical wireless communication device 1-2 is increased by 10°C relative to the temperature setting value for the first optical multiplexing / demultiplexing unit 103-1 in the first optical wireless communication device 1-1. As a result, the positional relationship of the port with respect to the wavelength shifts to the next position by approximately 0.8 nm (0.08 nm / K × 10K) due to the temperature dependency of the second optical multiplexing / demultiplexing unit 103-2. Furthermore, for example, the temperature setting value for the second optical transmitting unit 101-2 in the second optical wireless communication device 1-2 is changed by 10°C relative to the temperature setting value for the first optical transmitting unit 101-1 in the first optical wireless communication device 1-1. As a result, the wavelength changes by 0.8 nm due to the temperature characteristics of the second optical transmitting unit 101-2.

[0046] These adjustments make it possible to reverse the wavelength allocation of the second optical transmitting unit 101-2 and the second optical receiving unit 102-2 in the second optical wireless communication device 1-2 from the initial state, thereby shifting the wavelengths targeted by the first optical transmitting unit 101-1 and the first optical receiving unit 102-1 in the first optical wireless communication device 1-1 and the wavelengths targeted by the second optical transmitting unit 101-2 and the second optical receiving unit 102-2 in the second optical wireless communication device 1-2 by one wavelength.

[0047] However, the shortest wavelength in the first optical wireless communication device 1-1 and the longest wavelength in the second optical wireless communication device 1-2 cannot be used for communication. Note that, because the wavelength dependency of the optical receiving unit 102 is small, changes in the wavelength of the optical signal that accompany changes in the temperature setting value for the optical multiplexing / demultiplexing unit 103 do not affect the receiving sensitivity. Therefore, there is no need to change the settings for the optical receiving unit 102.

[0048] After that, communication is performed between the first optical wireless communication device 1-1 and the second optical wireless communication device 1-2.

[0049] In the above description, the temperature dependence of the AWG is 0.08 nm / K. However, the temperature dependence of the AWG is not limited to this, and can vary significantly depending on the design and material selection of the AWG. In contrast, in the optical wireless communication device 1 according to the first embodiment, even if the temperature dependence of the AWG changes, it can be accommodated by simply adjusting the temperature setting value, and the basic operation described above remains applicable.

[0050] Furthermore, not only a DML or EML whose oscillation wavelength changes depending on temperature but also a wavelength-tunable laser may be used for the optical transmitter 101. In this case, a method normally used for controlling the wavelength of a wavelength-tunable laser, such as heating by a heater or applying an electric field, is used.

[0051] Next, a description will be given of the effects of the optical wireless communication device 1 according to the first embodiment. First, the optical wireless communication device 1 according to the first embodiment can allocate many wavelengths, thereby enabling an improvement in communication capacity.

[0052] Furthermore, the optical wireless communication device 1 according to the first embodiment can be changed between two types of settings with the same configuration. In the above example, the optical wireless communication device 1 with the same configuration can be used for the first satellite 10-1 and the second satellite 10-2. Therefore, the optical wireless communication device 1 according to the first embodiment not only enables the device to be made smaller, but also enables the number of varieties to be reduced, making it possible to manufacture the device more cheaply than conventional devices.

[0053] Furthermore, in the optical wireless communication device 1 according to the first embodiment, wavelengths are alternately allocated between the optical transmitting unit 101 and the optical receiving unit 102, which facilitates wavelength changes. As a result, the optical wireless communication device 1 according to the first embodiment requires a simple configuration and also enables reductions in power consumption and heat generation. For example, in a wavelength multiplexing system, if transmission signals with multiple wavelengths are allocated on the short-wave side of the ITU-T grid and reception signals with multiple wavelengths are allocated on the long-wave side, switching between transmission and reception settings requires a large change in wavelength, which requires a large amount of power and a complex mechanism.

[0054] As described above, according to the first embodiment, the optical wireless communication system includes a pair of optical wireless communication devices 1, each of which includes a plurality of optical transmitters 101 that transmit optical signals of a target wavelength, an optical multiplexing / demultiplexing unit 103 that multiplexes the optical signals transmitted by the optical transmitters 101 and transmits the multiplexed optical signals to the corresponding optical wireless communication device 1, and demultiplexes the optical signals from the corresponding optical wireless communication device 1 into optical signals of a plurality of wavelengths, and a plurality of optical receivers 102 that receive the optical signals of the target wavelengths from the optical signals demultiplexed by the optical multiplexing / demultiplexing unit 103. The wavelengths targeted by the optical transmitters 101 and the optical receivers 102 are alternately assigned in order of length, and the wavelengths targeted by the optical transmitters 101 and the optical receivers 102 are shifted by one between the pair of optical wireless communication devices 1. Furthermore, according to the first embodiment, the optical multiplexing / demultiplexing unit 103 is an AWG. Furthermore, according to the first embodiment, the optical wireless communication system includes a temperature controller that controls the temperature of the optical multiplexing / demultiplexing unit 103. As a result, the optical wireless communication system according to the first embodiment can implement a larger number of wavelengths than conventional systems, and wavelength switching becomes easier.

[0055] According to the first embodiment, the optical wireless communication device 1 includes a plurality of optical transmitting units 101 that transmit optical signals of target wavelengths, an optical multiplexing / demultiplexing unit 103 that multiplexes the optical signals transmitted by the optical transmitting units 101 and transmits the multiplexed optical signals to the corresponding optical wireless communication device 1, and demultiplexes the optical signals from the corresponding optical wireless communication device 1 into optical signals of multiple wavelengths, and a plurality of optical receiving units 102 that receive the optical signals of the target wavelengths from the optical signals demultiplexed by the optical multiplexing / demultiplexing unit 103, and the wavelengths that are the targets of the optical transmitting units 101 and the optical receiving units 102 are wavelengths that are assigned alternately in order of length. As a result, the optical wireless communication device 1 according to the first embodiment can implement a larger number of wavelengths than conventional devices and can easily switch between wavelengths.

[0056] Second Embodiment. Figure 6 is a diagram showing a configuration example of a first optical wireless communication device 1-1 according to a second embodiment. In the first optical wireless communication device 1-1 according to the second embodiment shown in Figure 6, a first optical amplifier (SOA) 104-1 is added to the first optical wireless communication device 1-1 according to the first embodiment shown in Figure 3. The other configuration example of the first optical wireless communication device 1-1 according to the second embodiment shown in Figure 6 is similar to the configuration example of the first optical wireless communication device 1-1 according to the first embodiment shown in Figure 3, and the same reference numerals are used, and only the different parts will be described. Furthermore, although not shown, a second optical wireless communication device 1-2 according to the second embodiment is also configured similarly to the first optical wireless communication device 1-1 according to the second embodiment.

[0057] The first optical transmitter 101-1 in the second embodiment is a DML or EML.

[0058] A first optical amplifying section 104-1 is provided for each first optical transmitting section 101-1 between the first optical transmitting section 101-1 and the first optical multiplexing / demultiplexing section 103-1. This first optical amplifying section 104-1 amplifies the optical signal transmitted by the corresponding first optical transmitting section 101-1. In FIG. 6, an SOA (Semiconductor Optical Amplifier) ​​is used as the first optical amplifying section 104-1.

[0059] The first optical transmitting unit 101-1 and the first optical amplifying unit 104-1 may be configured by being monolithically integrated on a single semiconductor chip, or may be configured by the first optical amplifying unit 104-1 in a separate package being connected to the first optical transmitting unit 101-1 spatially optically or by using optical fiber.

[0060] Moreover, the first optical multiplexing / demultiplexing section 103-1 in the second embodiment multiplexes the optical signals amplified by the first optical amplifying section 104-1 and transmits the multiplexed optical signals to the second optical wireless communication device 1-2.

[0061] Next, an example of the operation of the optical wireless communication device 1 according to the second embodiment will be described. When coupling to an AWG or single-mode fiber is essential in the optical wireless communication device 1, a DML or EML operating in a single mode is required as the optical transmitting unit 101. Under such constraints, the optical transmitting unit 101 does not have a very high output, for example, 100 mW or less, and is unable to obtain the output of several hundred mW to several watts required for long-distance free-space optical communication. In contrast, the optical wireless communication device 1 according to the second embodiment includes an optical amplifier 104 on the output side of the optical transmitting unit 101, which is a DML or EML, to amplify the light input to each port of the optical multiplexing / demultiplexing unit 103. As a result, the optical wireless communication device 1 according to the second embodiment can obtain the output of several hundred mW to several watts required for long-distance free-space optical communication.

[0062] Next, the effects of the optical wireless communication device 1 according to the second embodiment will be described. In the optical wireless communication device 1 according to the second embodiment, it is possible to strengthen the light input to each port of the optical multiplexing / demultiplexing unit 103. Therefore, in the optical wireless communication device 1 according to the second embodiment, an optical amplifier, for example, a fiber amplifier such as an EDFA, is not required in the stage subsequent to the optical multiplexing / demultiplexing unit 103, or a low-gain optical amplifier can be applied in the stage subsequent to the optical multiplexing / demultiplexing unit 103. As a result, the optical wireless communication device 1 according to the second embodiment enables the device to be simplified and made smaller in size.

[0063] As described above, according to the second embodiment, the optical transmitting unit 101 is a DML or EML, the optical wireless communication device 1 includes an optical amplifying unit 104 that amplifies the optical signal transmitted by the optical transmitting unit 101, and the optical multiplexing / demultiplexing unit 103 multiplexes the optical signals amplified by the optical amplifying unit 104 and transmits the multiplexed optical signals to the destination optical wireless communication device 1. As a result, the optical wireless communication system according to the second embodiment can strengthen the output light to the optical multiplexing / demultiplexing unit 103 in addition to the effects of the first embodiment.

[0064] Third Embodiment. Figure 7 is a diagram showing a configuration example of a first optical wireless communication device 1-1 according to a third embodiment. In the first optical wireless communication device 1-1 according to the third embodiment shown in Figure 7, a first wavelength filter 105-1 is added to the first optical wireless communication device 1-1 according to the first embodiment shown in Figure 3. The other configuration example of the first optical wireless communication device 1-1 according to the third embodiment shown in Figure 7 is similar to the configuration example of the first optical wireless communication device 1-1 according to the first embodiment shown in Figure 3, and the same reference numerals are used, and only the different parts will be described. Furthermore, although not shown, a second optical wireless communication device 1-2 according to the third embodiment is also configured similarly to the first optical wireless communication device 1-1 according to the third embodiment.

[0065] The first wavelength filter 105-1 is provided for each first optical receiving unit 102-1 between the first optical receiving unit 102-1 and the first optical multiplexing / demultiplexing unit 103-1. This first wavelength filter 105-1 transmits optical signals of two wavelengths that the corresponding optical receiving unit 102 can target, out of the optical signals demultiplexed by the first optical multiplexing / demultiplexing unit 103-1, and blocks optical signals of other wavelengths. For example, in FIG. 7, different wavelengths are incident on the first optical receiving unit 102-1 connected to the second port (port2) when it is made to function as the first optical wireless communication device 1-1 and when it is made to function as the second optical wireless communication device 1-2. Specifically, λ １ , λ ２ Therefore, in this case, the first wavelength filter 105-1 has a band that covers these two wavelengths, as shown by the dotted lines in FIG.

[0066] The first wavelength filter 105-1 may be configured by being monolithically integrated on the chip on which the first optical multiplexing / demultiplexing section 103-1 is fabricated, or may be configured by being externally connected via an optical fiber or the like.

[0067] Next, an example of the operation of the optical wireless communication device 1 according to the third embodiment will be described. It is known that AWGs generally generate about 40 dB of crosstalk between ports. When receiving signals with more than 10 wavelengths as in the first embodiment, the crosstalk of each wavelength is accumulated, and the total amount of crosstalk may worsen by 10 dB or more. In contrast, the optical wireless communication device 1 according to the third embodiment is provided with a bandpass filter that allows specific wavelengths to pass, thereby cutting out irrelevant wavelengths.

[0068] Next, the effects of the optical wireless communication device 1 according to the third embodiment will be described. In the optical wireless communication device 1 according to the third embodiment, it is possible to improve the reception performance by filtering the crosstalk generated in the AWG. Furthermore, by providing a filter that covers two wavelengths as shown in FIG. 8, it is possible to realize the switchable operation as shown in the first embodiment.

[0069] In the above description, the optical wireless communication device 1 according to the first embodiment is configured to further include the wavelength filter 105. However, the present invention is not limited to this configuration, and the optical wireless communication device 1 according to the second embodiment may be configured to further include the wavelength filter 105, and the same effects as those described above can be obtained.

[0070] As described above, according to the third embodiment, the optical wireless communication device 1 includes a wavelength filter 105 provided for each optical receiving unit 102, which transmits optical signals of two wavelengths that can be targeted by the corresponding optical receiving unit 102 out of the optical signals demultiplexed by the optical multiplexing / demultiplexing unit 103, and the optical receiving unit 102 receives the optical signals that have passed through the wavelength filter 105. As a result, the optical wireless communication device 1 according to the third embodiment can block unnecessary wavelengths in addition to the effects of the first and second embodiments.

[0071] Fourth Embodiment. FIG. 9 is a diagram showing a configuration example of a first optical wireless communication device 1-1 according to a fourth embodiment. In the first optical wireless communication device 1-1 according to the fourth embodiment shown in FIG. 9, a cyclic AWG is used as the first optical multiplexing / demultiplexing section 103-1, as compared to the first optical wireless communication device 1-1 according to the first embodiment shown in FIG. 3. The other configuration example of the first optical wireless communication device 1-1 according to the fourth embodiment shown in FIG. 9 is similar to the configuration example of the first optical wireless communication device 1-1 according to the first embodiment shown in FIG. 3, and the same reference numerals are used, and only the different parts will be described. Similarly, FIG. 10 is a diagram showing a configuration example of a second optical wireless communication device 1-2 according to the fourth embodiment. In the second optical wireless communication device 1-2 according to the fourth embodiment shown in FIG. 10, a cyclic AWG is used as the second optical multiplexing / demultiplexing section 103-2, as compared to the second optical wireless communication device 1-2 according to the first embodiment shown in FIG. 4. Other configuration examples of the second optical wireless communication device 1-2 according to embodiment 4 shown in Figure 10 are similar to the configuration example of the second optical wireless communication device 1-2 according to embodiment 1 shown in Figure 4, and the same symbols are used, and only the different parts will be described.

[0072] The first optical multiplexing / demultiplexing unit 103-1 is a cyclic AWG, which has periodic wavelength characteristics.

[0073] The second optical multiplexing / demultiplexing section 103-2 is a cyclic AWG, which has periodic wavelength characteristics.

[0074] That is, the cyclic AWG has a temperature dependency of, for example, about 0.08 nm / K, and exhibits a behavior in which the port of the corresponding wavelength shifts to the adjacent port when the temperature is changed, similar to the AWG shown in the first embodiment. On the other hand, in the cyclic AWG, as shown in FIGS. 9 and 10, the two wavelengths that can be targeted by the final port (port 20) are λ １９ , λ ０ That is, these are the final wavelength and the first wavelength among the wavelengths targeted by the optical wireless communication system according to the fourth embodiment.

[0075] In this case, among the wavelengths targeted by the optical wireless communication system shown in FIG.２０ The wavelengths targeted by the optical wireless communication system according to the fourth embodiment are λ ０ ~λ １９ This becomes:

[0076] Furthermore, when the first optical multiplexing / demultiplexing unit 103-1 and the second optical multiplexing / demultiplexing unit 103-2 are cyclic AWGs, the wavelengths are shifted as described above, so that no ports in the first optical multiplexing / demultiplexing unit 103-1 or the second optical multiplexing / demultiplexing unit 103-2 are left unusable for communication.

[0077] Next, an example of the operation of the optical wireless communication device 1 according to the fourth embodiment will be described. As shown in FIGS. 9 and 10, for example, in the first optical wireless communication device 1-1, λ ０ ~λ １９ In the second optical wireless communication device 1-2 in which the wavelength is shifted, λ ０ An optical signal of is input.

[0078] Next, the effects of the optical wireless communication device 1 according to the fourth embodiment will be described. In the first embodiment, each optical wireless communication device 1 has one port that cannot be used for communication. In contrast, in the optical wireless communication device 1 according to the fourth embodiment, by providing cyclicity to the optical multiplexing / demultiplexing unit 103, it is possible to eliminate ports that cannot be used for communication, thereby improving communication capacity.

[0079] In the above description, the optical wireless communication device 1 according to the first embodiment has a configuration in which a cyclic AWG is used as the optical multiplexing / demultiplexing unit 103. However, the present invention is not limited to this configuration, and the optical wireless communication device 1 according to the second embodiment or the optical wireless communication device 1 according to the third embodiment may have a configuration in which a cyclic AWG is used as the optical multiplexing / demultiplexing unit 103, and the same effects as those described above can be obtained.

[0080] As described above, according to the fourth embodiment, the optical multiplexing / demultiplexing unit 103 is a cyclic AWG. As a result, the optical wireless communication system according to the fourth embodiment can improve communication capacity in addition to the effects of the first to third embodiments.

[0081] It should be noted that the embodiments may be freely combined, or any of the components in each embodiment may be modified, or any of the components in each embodiment may be omitted.

[0082] The optical wireless communication system according to the present disclosure can implement a larger number of wavelengths than conventional systems, and makes it easier to switch wavelengths, making it suitable for use in optical wireless communication systems equipped with optical wireless communication devices that transmit and receive optical signals.

[0083] 1 Optical wireless communication device, 1-1 First optical wireless communication device, 1-2 Second optical wireless communication device, 10 Satellite, 10-1 First satellite, 10-2 Second satellite, 101 Optical transmitting unit, 101-1 First optical transmitting unit, 101-2 Second optical transmitting unit, 102 Optical receiving unit, 102-1 First optical receiving unit, 102-2 Second optical receiving unit, 103 Optical multiplexing / demultiplexing unit, 103-1 First optical multiplexing / demultiplexing unit, 103-2 Second optical multiplexing / demultiplexing unit, 104 Optical amplification unit, 104-1 First optical amplification unit, 105 Wavelength filter, 105-1 First wavelength filter.

Claims

1. An optical wireless communication system comprising a pair of optical wireless communication devices, wherein the optical wireless communication devices comprise: a plurality of optical transmitting units that transmit optical signals of target wavelengths; an optical multiplexing / demultiplexing unit that multiplexes the optical signals transmitted by the optical transmitting units and transmits the multiplexed optical signals to the counterpart optical wireless communication device, and demultiplexes the optical signals from the counterpart optical wireless communication device into optical signals of multiple wavelengths; and a plurality of optical receiving units that receive the optical signals of target wavelengths from the optical signals demultiplexed by the optical multiplexing / demultiplexing unit; wherein the wavelengths targeted by the optical transmitting units and the optical receiving units are wavelengths that are alternately assigned in order of length; and between the pair of optical wireless communication devices, the wavelengths targeted by the optical transmitting units and the optical receiving units are shifted by one.

2. The optical wireless communication system according to claim 1, wherein the optical multiplexing / demultiplexing unit is an AWG.

3. The optical wireless communication system according to claim 1, wherein the optical multiplexing / demultiplexing unit is a cyclic AWG.

4. An optical wireless communication system according to claim 2 or 3, characterized in that the optical wireless communication device is provided with a temperature control section that controls the temperature of the optical multiplexing / demultiplexing section.

5. An optical wireless communication system according to any one of claims 1 to 4, characterized in that the optical transmitting unit is a DML or EML, the optical wireless communication device comprises an optical amplifier unit that amplifies the optical signal transmitted by the optical transmitting unit, and the optical multiplexing / demultiplexing unit multiplexes the optical signal amplified by the optical amplifier unit and transmits it to the optical wireless communication device that is the other party.

6. The optical wireless communication system according to any one of claims 1 to 5, characterized in that the optical wireless communication device comprises a wavelength filter provided for each optical receiving unit, which transmits optical signals of two wavelengths that can be targeted by the corresponding optical receiving unit out of the optical signals demultiplexed by the optical multiplexing / demultiplexing unit, and the optical receiving unit receives the optical signals that have passed through the wavelength filter.

7. An optical wireless communication device comprising: a plurality of optical transmitting units that transmit optical signals of target wavelengths; an optical multiplexing / demultiplexing unit that multiplexes the optical signals transmitted by the optical transmitting units and transmits the multiplexed optical signals to the optical wireless communication device at the other end, and demultiplexes the optical signals from the optical wireless communication device at the other end into optical signals of multiple wavelengths; and a plurality of optical receiving units that receive the optical signals of target wavelengths from the optical signals demultiplexed by the optical multiplexing / demultiplexing units, wherein the wavelengths targeted by the optical transmitting units and the optical receiving units are wavelengths that are allocated alternately in order of length.

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