Communication system, transmission device, and communication method

Abstract

A communication system is provided with: a direct modulation laser that outputs an optical signal carrying information to be delivered; an injection circuit that injects a current into the direct modulation laser; a control unit that controls an operation of the direct modulation laser by controlling an operation of the injection circuit; and a reception device that receives the optical signal. The direct modulation laser is provided with: a laser active region of a distributed feedback type; and an optical feedback region that is optically connected to one end, in a waveguide direction, of the laser active region and that has an optical waveguide structure in which a reflection point is formed in the waveguide direction. The control unit causes the direct modulation laser to operate under a plurality of predetermined mutually-different conditions, and causes the direct modulation laser to output the optical signal for conveying the information under each of the conditions.

Description

Communication system, transmitting device, and communication method

[0001] The present invention relates to a communication system, a transmitting device, and a communication method.

[0002] To increase the speed of optical communications, it has been proposed to use a directly modulated laser (see Non-Patent Documents 1 and 2) that uses photon-photon resonance (PPR) in optical communications (see Non-Patent Document 1). Specifically, the structure of such a directly modulated laser is a structure that includes a distributed feedback laser active region and an optical feedback region that is optically connected to one end of the laser active region in the waveguiding direction and has an optical waveguide structure in which a reflection point is formed in the waveguiding direction.

[0003] Suguru Yamaoka et al., “Directly modulated membrane lasers with 108 GHz bandwidth on a high-thermal-conductivity silicon carbide substrate”, Nature Photonics 15, 28-35 (2021)Suguru Yamaoka et al., “Uncooled 100-GBaud Directly Modulated Membrane Lasers on SiC Substrate”, Journal of Lightwave Technology, Vol.41, No.11, June 1 (2023)

[0004] As described in Non-Patent Documents 1 and 2, the occurrence of photon-photon resonance occurs when the frequency detuning or phase difference between two modes, the main mode of laser oscillation and a mode in the optical feedback region such as a Fabry-Perot (FP) mode, is within a predetermined range. Therefore, controlling the frequency and phase is important for the occurrence of photon-photon resonance.

[0005] However, the characteristics of the laser active region change depending on aging and the surrounding environment, and the frequency of the optical feedback region changes depending on the phase of the reflection. Furthermore, lasers are driven by an electric current, which generates heat, so the laser oscillation mode changes depending on the electric current. Moreover, this change is difficult to predict because it is not simply proportional to the amount of current.

[0006] As a result, photon-photon resonance may not be achieved, resulting in unstable communication.

[0007] In view of the above circumstances, an object of the present invention is to provide a technique for improving the stability of optical communications using photon-photon resonance.

[0008] One aspect of the present invention is a communication system comprising: a directly modulated laser that outputs an optical signal carrying information to be transmitted; an injection circuit that injects current into the directly modulated laser; a control unit that controls the operation of the directly modulated laser by controlling the operation of the injection circuit; and a receiving device that receives the optical signal, wherein the directly modulated laser comprises a distributed feedback laser active region and an optical feedback region that is optically connected to one end of the laser active region in a waveguiding direction and has an optical waveguide structure in which a reflection point is formed in the waveguiding direction; and the control unit operates the directly modulated laser under a plurality of mutually different predetermined conditions, and causes the directly modulated laser to output an optical signal carrying the information under each of the conditions.

[0009] One aspect of the present invention is a transmitting device comprising: a directly modulated laser that outputs an optical signal carrying information to be transmitted; an injection circuit that injects current into the directly modulated laser; and a control unit that controls the operation of the directly modulated laser by controlling the operation of the injection circuit, wherein the directly modulated laser comprises a distributed feedback laser active region and an optical feedback region that is optically connected to one end of the laser active region in a waveguiding direction and has an optical waveguide structure in which a reflection point is formed in the waveguiding direction, and the control unit operates the directly modulated laser under a plurality of mutually different predetermined conditions, and causes the directly modulated laser to output an optical signal carrying the information under each of the conditions.

[0010] One aspect of the present invention is a communication method executed by a communication system comprising: a directly modulated laser that outputs an optical signal carrying information to be transmitted; an injection circuit that injects current into the directly modulated laser; a control unit that controls the operation of the directly modulated laser by controlling the operation of the injection circuit; and a receiving device that receives the optical signal, wherein the directly modulated laser comprises a distributed feedback laser active region and an optical feedback region that is optically connected to one end of the laser active region in a waveguiding direction and has an optical waveguide structure in which a reflection point is formed in the waveguiding direction; the control unit operates the directly modulated laser under a plurality of mutually different predetermined conditions and causes the directly modulated laser to output an optical signal carrying the information under each of the conditions, and the communication method includes an output step in which the control unit causes the directly modulated laser to output an optical signal carrying the information under each of the conditions.

[0011] According to the present invention, it is possible to improve the stability of optical communications that use photon-photon resonance.

[0012] 1 is an explanatory diagram for explaining a communication system according to an embodiment. FIG. 2 is an explanatory diagram for explaining a first example of the structure of a directly modulated laser according to an embodiment. FIG. 3 is an explanatory diagram for explaining a second example of the structure of a directly modulated laser according to an embodiment. An example of a graph showing the relationship between the light intensity output by a directly modulated laser according to an embodiment and the current value of a bias current. A diagram showing examples of current values ​​that satisfy the nth condition according to an embodiment. A diagram showing an example of the hardware configuration of a transmitting device according to an embodiment. A diagram showing an example of the hardware configuration of a receiving device according to an embodiment. A flowchart showing an example of the flow of processing executed by a communication system according to an embodiment. An explanatory diagram for explaining a communication system according to a modified example. A first explanatory diagram for explaining the pigeonhole principle according to a modified example. A second explanatory diagram for explaining the pigeonhole principle according to a modified example. A third explanatory diagram for explaining the pigeonhole principle according to a modified example.

[0013] 1 is an explanatory diagram illustrating a communication system 100 according to an embodiment. The communication system 100 includes a transmitting device 1 that transmits an optical signal, and a receiving device 2. The receiving device 2 receives the optical signal output by the transmitting device 1.

[0014] The transmitter 1 includes a directly modulated laser 11, an injection circuit 12, and a control unit 13 including a processor 91 such as a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), or an NPU (Neural Network Processing Unit), and a memory 92, all connected by a bus.

[0015] The directly modulated laser 11 is a directly modulated laser that outputs an optical signal carrying information to be transmitted (hereinafter referred to as "information to be transmitted"). The laser (optical signal) output from the directly modulated laser is the optical signal output from the transmitting device 1.

[0016] The directly modulated laser 11 has a known structure capable of exhibiting photon-photon resonance (see, for example, Non-Patent Documents 1 and 2). Specifically, the directly modulated laser 11 has a structure including a distributed feedback laser active region and an optical feedback region that is optically connected to one end of the laser active region in the waveguiding direction and has an optical waveguide structure in which reflection points are formed in the waveguiding direction. The optical feedback region may be, for example, a Fabry-Perot optical feedback region with an optical waveguide structure in which reflection points are formed at both ends in the waveguiding direction. The optical feedback region may also be formed, for example, by a DBR (Distributed Bragg Reflector).

[0017] The laser active region has a structure in which an active layer made of a quantum structure, such as a III-V semiconductor like InGaAs, is sandwiched between cladding layers. A grating is formed in the cladding layers. Therefore, the laser active region is a distributed feedback type. The quantum structure may be, for example, a multiple quantum well or quantum dot. Therefore, the laser active region alone (i.e., without the optical feedback region) is, for example, a distributed feedback (DFB) laser.

[0018] The Fabry-Perot type optical feedback region has a waveguide with an end face in the waveguiding direction that has high reflectivity, so the Fabry-Perot type optical feedback region can be said to be a resonator with reflection points formed at both ends in the waveguiding direction.

[0019] The laser active region and the optical feedback region are formed on, for example, a substrate, which may be the same substrate on which the laser active region and the optical feedback region are formed.

[0020] In such a directly modulated laser 11, photon-photon resonance occurs when the frequency detuning (hereinafter referred to as "inter-mode detuning") between two modes, the laser oscillation mode in the absence of an optical feedback region (hereinafter referred to as "laser active region mode") and the mode of the optical feedback region, is within a predetermined range. The mode of the optical feedback region is a Fabry-Perot (FP) mode if the optical feedback region is of the Fabry-Perot type. If the optical feedback region is a DBR, it is a DBR mode. For the mechanism of occurrence of photon-photon resonance, see, for example, Non-Patent Documents 1 and 2.

[0021] FIG. 2 is an explanatory diagram illustrating a first example of the structure of a directly modulated laser 11 according to an embodiment. The directly modulated laser 11 in the example of FIG. 2 shows region 110 as an example of a distributed feedback laser active region, and region 120 as an example of an optical feedback region. FIG. 2 shows that region 120 is optically connected to one end of region 110 in the waveguiding direction. In the example of FIG. 2, the optical feedback region is formed by a waveguide 121, which is a Fabry-Perot type waveguide. Therefore, the optical feedback region in the example of FIG. 2 is of the Fabry-Perot type.

[0022] Surface 113 in Fig. 2 is a surface connecting region 110 and region 120. Points on surfaces 113 and 114 in Fig. 2 are examples of reflection points formed in the Fabry-Perot type optical feedback region. Arrow K in Fig. 2 indicates the waveguiding direction.

[0023] In the example of Fig. 2, the region 110 includes a DBR 111 and a DFB 112, and the DBR 111 is connected to one end of the DFB 112 in the waveguiding direction. The DFB 112 is a DFB laser. The DBR 111 is a DBR (Distributed Bragg Reflector) that reflects only laser light of a predetermined frequency from among laser light that can be generated by the DFB 112. Therefore, in the example of Fig. 2, the region 110 itself functions as a single-mode laser due to the coupling between the DBR 111 and the DFB 112.

[0024] 2, the region 110 includes a DBR, but the region 110 does not necessarily need to include a DBR. For example, the region 110 may include a DFB having a length of ¼λ in the waveguide direction, and may not include a DBR. λ is the frequency of the laser generated by the DFB 112 alone.

[0025] 3 is an explanatory diagram illustrating a second example of the structure of the directly modulated laser 11 according to the embodiment. To simplify the following explanation, components having the same functions as those in FIG. 2 are assigned the same reference numerals as those in FIG. 2, and the explanation thereof will be omitted.

[0026] The directly modulated laser 11 in the example of Figure 3 shows region 110 as an example of a distributed feedback laser active region, and region 120a as an example of an optical feedback region. Figure 3 shows that region 120a is optically connected to one end of region 110 in the waveguiding direction. In the example of Figure 3, the optical feedback region is composed of a DBR. In the example of Figure 3, DBR 121a is an example of a DBR that constitutes the optical feedback region. Because it is a DBR, multiple reflection points exist in the waveguiding direction. In Figure 3, arrow K indicates the waveguiding direction.

[0027] 3, the region 110 includes a DBR, but the region 110 does not necessarily need to include a DBR. For example, the region 110 may include a DFB having a length of ¼λ in the waveguide direction, and may not include a DBR. λ is the frequency of the laser generated by the DFB 112 alone.

[0028] 4 is an example of a graph showing the relationship between the optical intensity output from the directly modulated laser 11 and the current value of the bias current in this embodiment. The horizontal axis of FIG. 4 represents the current value of the bias current. The vertical axis of FIG. 4 represents the optical intensity output from the directly modulated laser 11.

[0029] As shown in Figure 4, a kink exists in the graph showing the relationship between light intensity and the bias current value. As described in Non-Patent Documents 1 and 2, it is known that in a kink, the inter-mode detuning is not zero, but is close to zero. Therefore, photon-photon resonance occurs at a current value that is close to but lower than the current value that generates a kink.

[0030] 4 indicate current value ranges that cause photon-photon resonance. That is, when a bias current having a current value belonging to region A1, region A2, region A3, or region A4 is injected into the directly modulated laser 11, photon-photon resonance occurs.

[0031] As shown in Figure 4, regions A1 to A4 are all simply connected regions in a one-dimensional topological space (hereinafter referred to as "current value topological space") in which each point indicates a different current value. As shown in Figure 4, regions A1 to A4 have different nearest kinks. Furthermore, regions A1 to A4 are regions in which photon-photon resonance occurs.

[0032] Therefore, different regions among regions A1 to A4 are unconnected in the current value phase space. In this way, regions A1 to A4 are all examples of simply connected regions in the current value phase space, where each point indicates a current value that causes photon-photon resonance (hereinafter referred to as a "PPR region").

[0033] Note that all current values ​​in the regions A1 to A4 are the current value I ＴＯ The current value is lower than that.

[0034] Returning to the explanation of Fig. 1, the injection circuit 12 is a circuit that injects a current into the directly modulated laser 11.

[0035] The control unit 13 controls the operation of each functional unit included in the transmitting device 1. Therefore, the control unit 13 controls, for example, the operation of the injection circuit. By controlling the operation of the injection circuit, the current injected into the directly modulated laser is controlled. Therefore, the control unit 13 controls the operation of the injection circuit, thereby controlling the operation of the directly modulated laser.

[0036] The control unit 13 executes, for example, a laser control process. The laser control process is a process of operating the directly modulated laser 11 under a plurality of mutually different predetermined conditions and causing the directly modulated laser 11 to output an optical signal carrying information to be transmitted under each of the conditions. For example, if the condition is that the bias current injected into the directly modulated laser 11 has a current value of Q1, the control unit 13 controls the operation of the injection circuit 12 to cause the injection circuit 12 to output a current having a bias current value of Q1 that carries the information to be transmitted. As a result, the directly modulated laser 11 operates under a bias current with a current value of Q1 and generates an optical signal carrying the information to be transmitted.

[0037] <Effects of Laser Control Processing> When the directly modulated laser 11 is operated under a plurality of mutually different predetermined conditions, the possibility that photon-photon resonance occurs under any of the conditions increases compared to when the laser is operated under only one condition. Therefore, when information to be transmitted is output under each of the conditions, the possibility that the receiving device 2 receives an optical signal generated using photon-photon resonance increases compared to when information to be transmitted is output under a single condition. Therefore, the transmitting device 1 that executes the laser control processing can improve the stability of optical communication that uses photon-photon resonance.

[0038] <First Example of Laser Control Processing> A first processing will be described as a first example of the laser control processing. The control unit 13 performs, for example, the first processing. The first processing is processing in which the directly modulated laser 11 is operated under N different conditions (N is an integer of 2 or more) from a first condition to an Nth condition that are predetermined, and an optical signal carrying information to be transmitted is output from the directly modulated laser 11 under each of the N different conditions. The N different predetermined conditions from the first condition to the Nth condition are one example of a plurality of different predetermined conditions in the laser control processing.

[0039] Therefore, in the first process, the optical signal carrying the information to be transmitted is output by the directly modulated laser 11 a total of N times. For example, a case will be described in which the information to be transmitted is text data showing the character string "Hello World." In this case, in the first process, the directly modulated laser 11 operating under the first condition outputs an optical signal carrying the text data showing the character string "Hello World."

[0040] Directly modulated laser 11 operating under the second condition also outputs an optical signal carrying text data indicating the character string "Hello World". Directly modulated laser 11 operating under the third condition also outputs an optical signal carrying text data indicating the character string "Hello World". This is repeated for directly modulated laser 11 operating under the fourth condition, and so on up to directly modulated laser 11 operating under the Nth condition.

[0041] It should be noted that the operations from the operation of the directly modulated laser 11 under the first condition to the operation of the directly modulated laser 11 under each of the Nth conditions do not necessarily have to be performed in order from the first condition to the Nth condition, and may be performed, for example, randomly, as long as each condition is performed once.

[0042] The n-th condition (n is an integer between 1 and N) includes a first n-th condition and a second n-th condition. The first n-th condition is a condition that the bias current value, which is the current value of the bias current injected into the directly modulated laser 11, is equal to or greater than a reference current value, which is a predetermined current value. The second n-th condition is a condition that the difference between the bias current value and the reference current value is expressed as (n-1)W using a reference value W, which is a predetermined value.

[0043] It has been stated that the reference value W is a predetermined value, but more specifically, the reference value W is a predetermined value that satisfies the conditions that it is smaller than the size of a PPR region of a predetermined size, and that the value of (n-1) times the reference value W is greater than the size of a PPR region of the above-mentioned predetermined size.

[0044] <Effects of the First Process> The effects of the first process will be described using a specific example for ease of understanding. As a specific example, the case where N=5 will be taken as an example.

[0045] 5 is a diagram showing examples of current values ​​that satisfy the n-th condition in the embodiment. More specifically, Fig. 5 shows examples of current values ​​that satisfy the n-th condition when the relationship between the optical intensity output from the directly modulated laser 11 and the current value of the bias current is represented by the graph in Fig. 4.

[0046] 5 indicates the current value I1 that satisfies the first condition and the optical intensity when a bias current of the current value I1 is injected into the directly modulated laser 11. Therefore, the current value I1 indicated by the point P1 in FIG. 5 is an example of a current value that satisfies the first condition.

[0047] 5 indicates the current value I2 that satisfies the second condition and the optical intensity when a bias current of the current value I2 is injected into the directly modulated laser 11. Therefore, the current value I2 indicated by the point P2 in FIG. 5 is an example of a current value that satisfies the second condition.

[0048] 5 indicates the current value I3 that satisfies the third condition and the optical intensity when a bias current of the current value I3 is injected into the directly modulated laser 11. Therefore, the current value I3 indicated by the point P3 in FIG. 5 is an example of a current value that satisfies the third condition.

[0049] 5 indicates the current value I4 that satisfies the fourth condition and the optical intensity when a bias current of the current value I4 is injected into the directly modulated laser 11. Therefore, the current value I4 indicated by the point P4 in FIG. 5 is an example of a current value that satisfies the fourth condition.

[0050] 5 indicates the current value I5 that satisfies the fifth condition and the optical intensity when a bias current of the current value I5 is injected into the directly modulated laser 11. Therefore, the current value I5 indicated by the point P5 in FIG. 5 is an example of a current value that satisfies the fifth condition.

[0051] In the example of Fig. 5, the reference current value is a current value I1 indicated by point P1. ＴＯ 5, the reference value W has a relationship with the current values ​​I1, I2, I3, I4, and I5 as follows: W=I2-I1=I3-I2=I4-I3=I5-I4.

[0052] In the example of FIG. 5, the current value I5 is the current value I ＴＯ is lower than the current value I5 and the current value I ＴＯ The reference current value I ＴＯ The difference between this and ≡ / 2 is greater than one PPR region. Therefore, in the example of FIG. 5, the reference value W satisfies the condition that it is smaller than the size of a PPR region of a predetermined size, and the condition that the value (n-1) times the reference value W is greater than the size of a PPR region of the predetermined size. Also, in the example of FIG. 5, the current value obtained by adding (N-1) times the reference value W to the reference current value is the current value I at which thermal rollover occurs. ＴＯ Smaller than.

[0053] In the example of FIG. 5, the current value obtained by adding (N-1) times the reference value W to the reference current value is the current value I ＴＯ The current value obtained by adding (N-1) times the reference value W to the reference current value is the current value I at which thermal rollover occurs. ＴＯ It may be larger.

[0054] According to the pigeonhole principle, at least one of the five current values ​​from current value I1 that satisfies the first condition to current value I5 that satisfies the fifth condition in the example of Fig. 5 should belong to the PPR region. Fig. 5 shows that current value I4 that satisfies the fourth condition is a current value that belongs to the PPR region.

[0055] Therefore, in the example of Figure 5, at least one of the first optical signal, the second optical signal, the third optical signal, the fourth optical signal, and the fifth optical signal is an optical signal in a state in which photon-photon resonance is occurring.

[0056] The first optical signal is an optical signal generated by the directly modulated laser 11 into which a bias current of a current value I1 is injected. The second optical signal is an optical signal generated by the directly modulated laser 11 into which a bias current of a current value I2 is injected. The third optical signal is an optical signal generated by the directly modulated laser 11 into which a bias current of a current value I3 is injected. The fourth optical signal is an optical signal generated by the directly modulated laser 11 into which a bias current of a current value I4 is injected. The fifth optical signal is an optical signal generated by the directly modulated laser 11 into which a bias current of a current value I5 is injected.

[0057] At least one of the first optical signal, the second optical signal, the third optical signal, the fourth optical signal, and the fifth optical signal is an optical signal in a state in which photon-photon resonance is occurring, and therefore, receiving device 2 that receives these five optical signals can receive an optical signal generated using photon-photon resonance. This reduces the chance that receiving device 2 will not receive an optical signal generated using photon-photon resonance, improving the stability of optical communication using photon-photon resonance.

[0058] For the sake of simplicity, the explanation has been given up to now using the case where N=5 as an example, but the same applies to any N of 2 or more.

[0059] In this way, the first process improves the stability of optical communication using photon-photon resonance. Therefore, the transmitting device 1 that executes the first process can improve the stability of optical communication using photon-photon resonance.

[0060] The pigeonhole principle is described in the modified example, so please refer to it if necessary.

[0061] 6 is a diagram showing an example of the hardware configuration of the transmitting device 1 in an embodiment. The transmitting device 1 includes a control unit 13 that is a control unit including a processor 91 such as a CPU, GPU, or NPU, and a memory 92, which are connected by a bus, and executes a program. By executing the program, the transmitting device 1 functions as a device including a directly modulated laser 11, an injection circuit 12, the control unit 13, an interface unit 14, and a storage unit 15.

[0062] More specifically, the processor 91 reads out a program stored in the storage unit 15 and stores the read program in the memory 92. When the processor 91 executes the program stored in the memory 92, the transmitting device 1 functions as a device including the directly modulated laser 11, the injection circuit 12, the control unit 13, the interface unit 14, and the storage unit 15.

[0063] The control unit 13 acquires, for example, information stored in the storage unit 15. Specifically, the process of acquiring information stored in the storage unit 15 is a read process.

[0064] The interface unit 14 includes a communication interface for connecting the transmission device 1 to an external device. The interface unit 14 communicates with the external device via a wired or wireless connection.

[0065] The external device is, for example, a device that is a sender of the information to be transmitted. The interface unit 14 acquires the information to be transmitted by communicating with the device that is the sender of the information to be transmitted. The control unit 13 controls the operation of the directly modulated laser 11 to generate an optical signal that carries the information to be transmitted obtained by the interface unit 14.

[0066] The interface unit 14 may be configured to include input devices such as a mouse, keyboard, or touch panel. The interface unit 14 may be configured as an interface that connects these input devices to the transmitting device 1. In this way, the input devices of the interface unit 14 accept input of various information to the transmitting device 1 via wired or wireless connections. Note that signals or information do not necessarily need to be input to the communication interface of the interface unit 14, but may also be input to the input devices of the interface unit 14. Therefore, information to be transmitted may be input to the input devices of the interface unit 14, for example.

[0067] The storage unit 15 is configured using a computer-readable storage medium device (non-transitory computer-readable recording medium) such as a magnetic hard disk device or a semiconductor storage device. The storage unit 15 stores various information related to the transmission device 1. The storage unit 15 stores various information generated by the operation of the control unit 15, for example. The storage unit 15 may exist on a cloud, for example.

[0068] 7 is a diagram showing an example of the hardware configuration of the receiving device 2 in an embodiment. The receiving device 2 is equipped with a control unit 21 that is a control unit including a processor 93 such as a CPU, GPU, or NPU, and a memory 94, which are connected via a bus, and executes a program. By executing the program, the receiving device 2 functions as a device including a receiver 20, the control unit 21, an interface unit 22, and a storage unit 23.

[0069] More specifically, the processor 93 reads the program stored in the storage unit 23 and stores the read program in the memory 94. The processor 93 executes the program stored in the memory 94, causing the receiving device 2 to function as a device including the receiver 20, the control unit 21, the interface unit 22, and the storage unit 23.

[0070] The receiver 20 receives the optical signal output from the transmitter 1 and converts it into an electrical signal. The receiver 20 is, for example, a photoelectric conversion element. The electrical signal obtained by the conversion by the receiver 20 is output to, for example, the control unit 21.

[0071] The control unit 21 controls the operation of each functional unit included in the receiving device 2. The control unit 21 controls the operation of, for example, the receiver 20. The control unit 21 acquires the electrical signal obtained by the receiver 20. The control unit 21 executes processing based on the acquired electrical signal, for example. The processing based on the acquired electrical signal is, for example, processing to acquire information to be transmitted and output the information to be transmitted to a predetermined output destination. The predetermined output destination is, for example, a display device included in the interface unit 22. The control unit 21 acquires information stored in, for example, the memory unit 23. The processing to acquire information stored in the memory unit 23 is, specifically, reading.

[0072] The interface unit 22 is configured to include a communication interface for connecting the receiving device 2 to an external device. The interface unit 22 communicates with the external device via a wired or wireless connection. The external device is, for example, a display device that displays the information to be transmitted under the control of the control unit 21. The external device is, for example, a speaker that outputs the information to be transmitted as sound under the control of the control unit 21. In this way, the external device may be, for example, an output device that outputs the information to be transmitted as an image or sound under the control of the control unit 21.

[0073] The external device may be, for example, the transmitting device 1. The control unit 21 may transmit the result of analysis based on the optical signal received by the receiver 20 to the transmitting device 1 via the interface unit 22, for example.

[0074] The interface unit 22 may be configured to include input devices such as a mouse, keyboard, or touch panel. The interface unit 22 may be configured as an interface that connects these input devices to the receiving device 2. In this way, the input devices of the interface unit 22 accept input of various information to the receiving device 2 via wired or wireless connections. Note that signals or information do not necessarily have to be input to the communication interface of the interface unit 22, but may also be input to the input devices of the interface unit 22.

[0075] The interface unit 22 outputs, for example, various types of information. The interface unit 22 includes, for example, a display device such as a CRT (Cathode Ray Tube) display, a liquid crystal display, or an organic EL (Electro-Luminescence) display, and a speaker. The interface unit 22 may be configured as an interface that connects these display devices or speakers to the receiving device 2. Therefore, the interface unit 22 may output, for example, information input to an input device of the interface unit 22 as an image or sound.

[0076] The storage unit 23 is configured using a computer-readable storage medium device (non-transitory computer-readable recording medium) such as a magnetic hard disk device or a semiconductor storage device. The storage unit 23 stores various information related to the receiving device 2. The storage unit 23 stores various information generated by the operation of the control unit 21, for example. The storage unit 23 may exist on a cloud, for example.

[0077] <Example of Processing Flow Executed by Communication System 100> Figure 8 is a flowchart showing an example of processing flow executed by the communication system 100 in the embodiment. The control unit 13 acquires transmission target information (step S101). The control unit 13 executes laser control processing (step S102). By executing the laser control processing, multiple lasers carrying the transmission target information (i.e., optical signals carrying the transmission target information) are output from the transmitting device 1. Next, the receiving device 2 receives each optical signal output from the transmitting device 1 (step S103).

[0078] The transmitting device 1 configured in this manner executes laser control processing, which allows the transmitting device 1 to improve the stability of optical communication using photon-photon resonance, as described in <Effects of Laser Control Processing>.

[0079] The communication system 100 configured in this manner also includes the transmitting device 1. Therefore, the communication system 100 can improve the stability of optical communication that uses photon-photon resonance.

[0080] (Modification) <Second Example of Laser Control Processing> Fig. 9 is an explanatory diagram illustrating a communication system 100a according to a modification. For simplicity of explanation, components having the same functions as those in Fig. 1 or 6 are denoted by the same reference numerals and will not be described below.

[0081] The communication system 100a differs from the communication system 100 in that a transmission device 1a is provided instead of the transmission device 1. The transmission device 1a differs from the transmission device 1 in that a heater 16 is further provided.

[0082] The heater 16 generates heat to provide heat to the optical feedback region of the directly modulated laser 11. The heater 16 is, for example, a heater. The heater 16 may be integrated in the optical feedback region, for example.

[0083] The control unit 13 may control the operation of the directly modulated laser 11 by controlling not only the operation of the injection circuit 12 but also the operation of the heater 16. In this case, the control unit 13 may execute, for example, a second process. The second process is an example of a laser control process. The second process is a process of operating the directly modulated laser 11 under each of a plurality of mutually different predetermined laser control conditions and causing the directly modulated laser 11 to output an optical signal carrying information to be transmitted under each of the plurality of laser control conditions.

[0084] The plurality of different predetermined laser control conditions are a plurality of predetermined conditions in which at least one of the heat generation amount and the bias current value of the heater 16 is different, and some of the predetermined conditions are a plurality of different predetermined conditions in which the heat generation amount is different from the others. Therefore, the laser control conditions belonging to the laser control condition set, which is a set of laser control conditions, do not match each other, and at least one of the heat generation amount and the bias current value of the heater 16 is different from the others.

[0085] Some laser control conditions in the set of laser control conditions have different heat generation amounts from the other laser control conditions, so the set of laser control conditions does not indicate a single type of heat generation amount.

[0086] In the second process, the control unit 13 operates the directly modulated laser 11 under each laser control condition belonging to the set of laser control conditions, and outputs an optical signal carrying the information to be transmitted. Therefore, if there are N laser control conditions belonging to the set of laser control conditions, the second process is executed, and N optical signals carrying the information to be transmitted are output from the transmitting device 1.

[0087] Note that all of the laser control conditions in the set of laser control conditions may have the same bias current value. In this case, the control unit 13 changes the heat generation amount of the heater 16 to the value indicated by each laser control condition without changing the bias current value, and operates the directly modulated laser 11 under each laser control condition to output an optical signal.

[0088] The relationship between the laser control conditions and the processing executed by the control unit 13 in the second process will be described in more detail. For example, the laser control conditions will be described where the heat generation amount is Q2 and the bias current injected into the directly modulated laser 11 has a current value of Q3. In this case, the control unit 13 controls the operation of the heater 16 to generate heat of the amount Q2, and controls the operation of the injection circuit 12 to output a bias current with a current value Q3 that carries the information to be transmitted to the injection circuit 12. As a result, the directly modulated laser 11 operates under the bias current with a current value Q3 and the heat generation amount Q2, and generates an optical signal that carries the information to be transmitted.

[0089] <Effects of the Second Process> Heat generated by the heater 16 is applied to the optical feedback region of the directly modulated laser 11, causing the temperature of the optical feedback region to rise and the refractive index to change. As a result, the mode of the optical feedback region changes. More specifically, the frequency of the mode of the optical feedback region changes.

[0090] As a result, even if the bias current value is fixed, the inter-mode detuning changes depending on the amount of heat generated. Therefore, if the directly modulated laser 11 is operated under a plurality of laser control conditions with different amounts of heat generated, the possibility of operating the directly modulated laser 11 under a laser control condition that exhibits photon-photon resonance increases compared to when the directly modulated laser 11 is operated under a single laser control condition. This reduces the chance that the receiving device 2 will not be able to receive an optical signal generated using photon-photon resonance, improving the stability of optical communication using photon-photon resonance.

[0091] In this way, the second process improves the stability of optical communication using photon-photon resonance. Therefore, the transmission device 1a of this modified example configured as above can improve the stability of optical communication using photon-photon resonance.

[0092] The communication system 100a configured in this manner also includes the transmitting device 1a, and therefore the communication system 100a can improve the stability of optical communication that uses photon-photon resonance.

[0093] In the communication system 100 or 100a, the control unit 21 of the receiving device 2 may determine whether the optical signal was generated in a state where optical-optical resonance occurred by, for example, including a predetermined bit sequence in a preamble based on the N optical signals received by the receiving device 2, measuring the bit error rate (BER) of the signals, and then selecting the optical signal with the smallest BER.

[0094] Furthermore, the receiving device 2 may transmit the result of the determination to the transmitting device 1 or 1a. In this case, the transmitting device 1 or 1a may change the conditions for operating the directly modulated laser 11 in accordance with a predetermined rule based on the obtained result of the determination. The changed conditions may be, for example, a condition in FIG. 5 that adjusts the initial bias value so that the overlap of N bias points with respect to the PPR region is maximized.

[0095] <Pigeonhole principle> The pigeonhole principle will now be explained.

[0096] Fig. 10 is a first explanatory diagram illustrating the pigeonhole principle in the modified example, Fig. 11 is a second explanatory diagram illustrating the pigeonhole principle in the modified example, and Fig. 12 is a third explanatory diagram illustrating the pigeonhole principle in the modified example.

[0097] Fig. 10 shows a closed interval of length a in one-dimensional real number space. In the example of Fig. 10, the length a is four times the length b. The bounded open interval R901 shown in Fig. 10 is the interval with the largest average value among the four intervals obtained by dividing the closed interval of length a into four equal parts.

[0098] FIG. 11 is a second explanatory diagram illustrating the pigeonhole principle in a modified example. FIG. 11 shows a scene in which five values ​​are specified at equal intervals from the position indicating the minimum value within the closed interval of length a shown in FIG. 10. Arrows Y101, Y102, Y103, Y104, and Y105 indicate the specified values. In the example of FIG. 11, all of the specified values ​​are outside the bounded open interval R901. In the example of FIG. 11, the interval between the specified values ​​is not narrower than the width of the bounded open interval R901. Furthermore, the difference between the maximum and minimum values ​​of the specified values ​​is wider than the width of the bounded open interval R901.

[0099] Fig. 12 is a third explanatory diagram illustrating the pigeonhole principle in a modified example. Fig. 12 shows a scene in which six values ​​are specified at equal intervals from the position indicating the minimum value within a closed interval of length a. Each of the arrows Y201, Y202, Y203, Y204, Y205, and Y206 points to the specified values.

[0100] In the example of Fig. 12, the value indicated by the arrow Y205 is a value within the bounded open interval R901. Therefore, in the example of Fig. 12, one of the specified values ​​is a value within the bounded open interval R901. In the example of Fig. 12, unlike the example of Fig. 11, the interval between the specified values ​​is narrower than the width of the bounded open interval R901. Furthermore, the difference between the maximum and minimum values ​​of the specified values ​​is wider than the width of the bounded open interval R901.

[0101] When specifying a value that belongs to a desired interval, if you specify multiple values ​​such that the interval between the specified values ​​is narrower than the size of the specified interval and the difference between the maximum and minimum values ​​of the specified values ​​is wider than the width of the specified interval, you can specify at least one value that belongs to the specified interval. The bounded open interval R901 is an example of a desired interval. This is the pigeonhole principle.

[0102] As can be seen from the explanations of FIGS. 10 to 12, based on the pigeonhole principle, even if the number of values ​​to be specified is finite, it is possible to specify values ​​that belong to a desired interval.

[0103] The transmitting device 1 may be implemented using a plurality of information processing devices connected to each other via a network so as to be able to communicate with each other. In this case, the processes executed by the control unit 13 may be distributed among the plurality of information processing devices.

[0104] The receiving device 2 may be implemented using a plurality of information processing devices connected to each other via a network so that they can communicate with each other. In this case, the processes executed by the control unit 21 may be distributed among the plurality of information processing devices.

[0105] Note that all or part of the functions of the communication system 100, the transmitting device 1, and the receiving device 2 may be realized using hardware such as an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array). The program may be recorded on a computer-readable recording medium. Examples of computer-readable recording media include portable media such as flexible disks, magneto-optical disks, ROMs, and CD-ROMs, and storage devices such as hard disks built into computer systems. The program may be transmitted via a telecommunications line.

[0106] Although an embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention.

[0107] REFERENCE SIGNS LIST 100...communication system, 1...transmitter, 2...receiver, 11...directly modulated laser, 12...injection circuit, 13...controller, 14...interface, 15...storage, 16...heater, 20...receiver, 21...controller, 22...interface, 23...storage, 111...DBR, 112...DFB, 120, 120a...optical feedback region, 121...waveguide, 121a...DBR, 91...processor, 92...memory, 93...processor, 94...memory

Claims

1. A communications system comprising: a directly modulated laser that outputs an optical signal carrying information to be transmitted; an injection circuit that injects current into said directly modulated laser; a control unit that controls the operation of said injection circuit to thereby control the operation of said directly modulated laser; and a receiving device that receives said optical signal, wherein said directly modulated laser comprises a distributed feedback laser active region and an optical feedback region that is optically connected to one end of said laser active region in a waveguiding direction and has an optical waveguide structure in which a reflection point is formed in the waveguiding direction, and said control unit operates said directly modulated laser under a plurality of mutually different predetermined conditions, and causes said directly modulated laser to output an optical signal carrying said information under each of said conditions.

2. The communication system according to claim 1, wherein the plurality of mutually different predetermined conditions comprise N (N is an integer of 2 or greater) mutually different conditions from a first predetermined condition to an Nth predetermined condition, wherein the nth condition (n is an integer of 1 or greater and N or less) includes a first nth condition that a bias current value, which is the current value of a bias current injected into the directly modulated laser, is equal to or greater than a reference current value, which is a predetermined current value, and a second nth condition that a difference between the bias current value and the reference current value is expressed as (n-1)W using a reference value W, which is a predetermined value, and wherein the reference value W satisfies the following conditions: that the reference value W is smaller than the size of a PPR region of a predetermined size, which is a simply connected region in a current value phase space, which is a one-dimensional phase space, where each point indicates a different current value, and where each point indicates a current value that causes photon-photon resonance; and that a value (n-1) times the reference value W is greater than the size of the PPR region.

3. The reference current value is the current value I at which thermal rollover occurs. ＴＯ The communication system according to claim 2 , wherein the ratio is ½ of the ratio.

4. The current value obtained by adding (N-1) times the reference value W to the reference current value is the current value I at which thermal rollover occurs. ＴＯ The communication system of claim 2 .

5. The communication system of claim 1, further comprising a heater that generates heat to provide heat to the optical feedback region, wherein the control unit also controls the operation of the heater, thereby controlling the operation of the directly modulated laser, and wherein the plurality of different predetermined conditions are a plurality of predetermined conditions in which at least one of the amount of heat generated by the heater and the bias current value, which is the current value of the bias current injected into the directly modulated laser, is different, and some of the predetermined conditions have a different amount of heat generated from the others.

6. A transmitting device comprising: a directly modulated laser that outputs an optical signal carrying information to be transmitted; an injection circuit that injects current into the directly modulated laser; and a control unit that controls the operation of the directly modulated laser by controlling the operation of the injection circuit, wherein the directly modulated laser comprises a distributed feedback laser active region and an optical feedback region that is optically connected to one end of the laser active region in the waveguiding direction and has an optical waveguide structure in which a reflection point is formed in the waveguiding direction, and the control unit operates the directly modulated laser under a plurality of mutually different predetermined conditions, and causes the directly modulated laser to output an optical signal carrying the information under each of the conditions.

7. A communication method implemented by a communication system comprising: a directly modulated laser that outputs an optical signal carrying information to be transmitted; an injection circuit that injects current into said directly modulated laser; a control unit that controls the operation of said injection circuit to thereby control the operation of said directly modulated laser; and a receiving device that receives said optical signal, wherein said directly modulated laser comprises a distributed feedback laser active region and an optical feedback region that is optically connected to one end of said laser active region in the waveguiding direction and has an optical waveguide structure in which a reflection point is formed in the waveguiding direction; and said control unit operates said directly modulated laser under a plurality of mutually different predetermined conditions and causes said directly modulated laser to output an optical signal carrying said information under each of said conditions, said communication method comprising: an output step in which said control unit causes said directly modulated laser to output an optical signal carrying said information under each of said conditions.

Images