Terahertz communication system

Abstract

The objective of the present disclosure is increase the degree of freedom in assigning terahertz optical signals with respective frequencies to respective terahertz wireless signal transmission units when accommodating a plurality of frequency bands by multiplexing a terahertz communication system.　In the present disclosure, when assigning terahertz optical signals with respective frequencies to respective terahertz wireless signal transmission units 2, a combination of terahertz optical signal assignments is switched among a plurality of combinations by a terahertz optical signal switching unit 3.

Description

Terahertz communication system

[0001] The present disclosure relates to terahertz communication systems on the order of 0.1 to 10 THz.

[0002] Terahertz communication systems of around 0.1 to 10 THz generate terahertz optical signals and transmit terahertz wireless signals (see Patent Document 1, Non-Patent Document 1, etc.). First, optical signals having different frequencies are optically coupled to generate a terahertz optical signal. Next, the terahertz optical signal is photoelectrically converted and the terahertz wireless signal is transmitted. Here, the envelope of the beat of the terahertz optical signal is in the terahertz band, but the area inside the envelope is in the optical communication band. Therefore, optical couplers and photoelectric converters that are applicable to optical communications can also be applied to terahertz communications.

[0003] JP 2010-062619 A

[0004] Tadao Nagatsuma, "Special Feature Commentary: Terahertz Technology Opens New Doors to Precision Engineering," "Ultra-High-Speed ​​Wireless Communications Opened Up by Terahertz Waves: Aiming to Realize Wireless Communications at the Same Speed ​​as Optical Fiber Communications," Journal of the Japan Society for Precision Engineering, Vol. 82, No. 3, pp. 221-224, 2016.

[0005] The configuration of a first terahertz communication system according to the prior art is shown in Fig. 1 (see Patent Document 1, etc.). The terahertz communication system S basically comprises one terahertz optical signal generator 1 and one terahertz wireless signal transmitter 2. The terahertz optical signal generator 1 comprises a signal light source 11, a local light source 12, an optical modulator 13, and an optical coupler 14. The terahertz wireless signal transmitter 2 comprises an opto-electrical converter 21, an amplifier 22, and an antenna 23.

[0006] The signal light source 11 and the local light source 12 output optical signals having different frequencies. The optical modulator 13 optically modulates the optical signal output by the signal light source 11 with a data signal. The optical coupler 14 optically couples the optical signal output by the optical modulator 13 with the optical signal output by the local light source 12. The photoelectric converter 21 photoelectrically converts the terahertz optical signal output by the optical coupler 14. The amplifier 22 amplifies the terahertz electrical signal output by the photoelectric converter 21. The antenna 23 transmits the terahertz electrical signal output by the amplifier 22 as a terahertz wireless signal.

[0007] The configuration of a second terahertz communication system according to the prior art is shown in Fig. 2 (see Non-Patent Document 1, etc.). The terahertz communication system S basically comprises one terahertz optical signal generation unit 1 and one terahertz wireless signal transmission unit 2. The terahertz optical signal generation unit 1 comprises a first light source 15, a second light source 16, an optical coupler 17, and an optical modulator 18. The terahertz wireless signal transmission unit 2 comprises an opto-electrical converter 21, an amplifier 22, and an antenna 23.

[0008] The first light source 15 and the second light source 16 output optical signals having different frequencies. The optical coupler 17 optically couples the optical signal output by the first light source 15 and the optical signal output by the second light source 16. The optical modulator 18 optically modulates the terahertz optical signal output by the optical coupler 17 with a data signal. The photoelectric converter 21 photoelectrically converts the terahertz optical signal output by the optical modulator 18. The amplifier 22 amplifies the terahertz electrical signal output by the photoelectric converter 21. The antenna 23 transmits the terahertz electrical signal output by the amplifier 22 as a terahertz wireless signal.

[0009] Here, there is a need to store a plurality of frequency bands by multiplexing the first and second terahertz communication systems S of the prior art. To this end, it is conceivable to simply parallelize N terahertz communication systems S. That is, it is conceivable to simply parallelize N terahertz optical signal generation units 1 and N terahertz radio signal transmission units 2. However, the degree of freedom in assigning terahertz optical signals having N frequencies to N terahertz radio signal transmission units 2 is reduced by simply parallelizing N terahertz communication systems S.

[0010] Therefore, in order to solve the above-mentioned problems, the present disclosure aims to increase the degree of freedom in assigning terahertz optical signals having respective frequencies to respective terahertz wireless signal transmitters when storing multiple frequency bands by multiplexing a terahertz communication system.

[0011] In order to solve the above problem, when allocating terahertz optical signals having respective frequencies to respective terahertz wireless signal transmitters, a multicast switch (MCS) or the like is used to switch the allocation combination of terahertz optical signals among a plurality of combinations.

[0012] Specifically, the present disclosure provides a terahertz communication system comprising: a terahertz optical signal generation unit that, when optically coupling optical signals having different frequencies to generate terahertz optical signals, sets a plurality of combinations of different frequencies of the optical signals and generates the terahertz optical signals having a plurality of frequencies; a plurality of terahertz radio signal transmission units that photoelectrically convert the terahertz optical signals having each frequency and transmit terahertz radio signals having each frequency; and a terahertz optical signal switching unit that, when allocating the terahertz optical signals having each frequency to each of the terahertz radio signal transmission units, is capable of switching the combination of allocation of the terahertz optical signals among a plurality of combinations.

[0013] According to this configuration, by multiplexing the terahertz communication system, when storing multiple frequency bands, the terahertz optical signal switching unit can increase the degree of freedom in assigning terahertz optical signals having each frequency to each terahertz wireless signal transmitting unit.

[0014] The present disclosure also provides a terahertz communication system, wherein M (M is an integer equal to or greater than 2) terahertz optical signal generation units generate terahertz optical signals having each of M frequencies, and the terahertz optical signal switching unit has inputs from the M terahertz optical signal generation units and outputs to N (N is an integer equal to or greater than M) terahertz wireless signal transmission units.

[0015] This configuration increases the degree of freedom in allocating terahertz optical signals having M frequencies to N terahertz radio signal transmitters. When N>M, the same terahertz optical signal can be allocated to multiple terahertz radio signal transmitters.

[0016] The present disclosure also provides a terahertz communication system, wherein the terahertz optical signal generation unit includes M first light sources that output optical signals having each of M frequencies (M is an integer equal to or greater than 2), and one second light source that outputs the optical signal having a frequency different from the M frequencies, and the terahertz optical signal switching unit includes inputs from the M first light sources and outputs N (N is an integer equal to or greater than M) optical signals to an optical coupler.

[0017] This configuration increases the degree of freedom in allocating terahertz optical signals having M frequencies to N terahertz wireless signal transmission units. Furthermore, one second light source is shared by M first light sources, and although the M frequencies of the terahertz optical signals are limited, the number of second light sources can be reduced. Furthermore, when N>M, the same terahertz optical signal can be allocated to multiple terahertz wireless signal transmission units.

[0018] The present disclosure also provides a terahertz communication system, wherein the terahertz optical signal generation unit includes M first light sources that output the optical signals having each of M frequencies (M is an integer greater than 2), and one second light source that outputs the optical signal having a frequency different from the M frequencies; and the terahertz optical signal switching unit is (1) disposed inside the terahertz optical signal generation unit, and includes inputs from the M first light sources and outputs of the M optical signals to an optical coupler, and (2) disposed between the terahertz optical signal generation unit and N terahertz wireless signal transmission units (N is an integer greater than M), and includes inputs of the M optical signals from the optical coupler and outputs of the N terahertz wireless signal transmission units.

[0019] This configuration increases the degree of freedom in allocating terahertz optical signals having M frequencies to N terahertz wireless signal transmission units. Furthermore, one second light source is shared by M first light sources, limiting the M frequencies of the terahertz optical signals, but reducing the number of second light sources. Furthermore, the same terahertz optical signal can be allocated to multiple terahertz wireless signal transmission units, reducing the number of optical couplers.

[0020] The present disclosure also provides a terahertz communication system, wherein the terahertz optical signal generation unit includes M first light sources that output the optical signals having each of M frequencies (M is an integer equal to or greater than 2), and M second light sources that output the optical signals having each of M frequencies different from the M frequencies, and the terahertz optical signal switching unit includes M inputs from the first light sources and the second light sources, and N (N is an integer equal to or greater than M) outputs of the optical signals to two inputs of an optical coupler.

[0021] This configuration increases the degree of freedom in allocating terahertz optical signals having M frequencies to N terahertz wireless signal transmission units. Furthermore, by combining M first light sources and M second light sources (provided that the optical signals generated by the terahertz optical signal generation unit are in the terahertz band and are optically modulated), the M frequencies of the terahertz optical signals can be diversified without any restrictions. Furthermore, when N>M, the same terahertz optical signal can be allocated to multiple terahertz wireless signal transmission units.

[0022] The present disclosure also provides a terahertz communication system, wherein the terahertz optical signal generation unit includes M first light sources that output the optical signals having respective frequencies among M frequencies (M is an integer greater than or equal to 2), and M second light sources that output the optical signals having respective frequencies among M frequencies that are different from the M frequencies; and the terahertz optical signal switching unit is (1) disposed inside the terahertz optical signal generation unit, and includes M inputs from the first light sources and the second light sources, and M outputs of the optical signals to two inputs of an optical coupler, and (2) disposed between the terahertz optical signal generation unit and N terahertz wireless signal transmission units (N is an integer greater than M), and includes M inputs of the optical signals from the optical coupler and N outputs to the terahertz wireless signal transmission units.

[0023] This configuration increases the degree of freedom in allocating terahertz optical signals having M frequencies to N terahertz wireless signal transmission units. Furthermore, by combining M first light sources and M second light sources (provided that the optical signal generated by the terahertz optical signal generation unit is in the terahertz band and is optically modulated), the M frequencies of the terahertz optical signal can be diversified without any restrictions. Furthermore, the same terahertz optical signal can be allocated to multiple terahertz wireless signal transmission units, thereby reducing the number of optical couplers.

[0024] The present disclosure also provides a terahertz communication system, further comprising a wavelength multiplexing unit arranged between the terahertz optical signal switching unit and the plurality of terahertz radio signal transmitting units, which wavelength-multiplexes the terahertz optical signals having a plurality of frequencies.

[0025] According to this configuration, terahertz optical signals wavelength-multiplexed in a plurality of frequency bands can be assigned to each terahertz wireless signal transmitter by an arrayed waveguide (AWG) or the like.

[0026] The present disclosure also provides a terahertz communication system, characterized in that the terahertz optical signal switching unit is capable of switching a combination of allocations of the terahertz optical signals among a plurality of combinations and performing time division multiplexing.

[0027] According to this configuration, terahertz optical signals that are switched over time between a plurality of frequencies by time division multiplexing can be assigned to each terahertz wireless signal transmitter.

[0028] The present disclosure also provides a terahertz communication system, wherein the terahertz optical signal generation unit (1) optically modulates the optical signal having one frequency with a data signal, and optically couples the optically modulated optical signal having one frequency with an optical signal having another frequency that is not optically modulated, or (2) optically couples the optical signal having one frequency with an optical signal having another frequency, and optically modulates the optically coupled optical signal with a data signal.

[0029] According to this configuration, the first or second conventional technique can be expanded, and terahertz optical signals having respective frequencies can be assigned to the respective terahertz wireless signal transmitting units.

[0030] The above-disclosed inventions can be combined as much as possible.

[0031] In this way, by multiplexing a terahertz communication system, the present disclosure can increase the degree of freedom in assigning terahertz optical signals having each frequency to each terahertz wireless signal transmitter when storing multiple frequency bands.

[0032] FIG. 1 is a diagram showing a configuration of a first terahertz communication system of the prior art. FIG. 2 is a diagram showing a configuration of a second terahertz communication system of the prior art. FIG. 3 is a diagram showing a configuration of a No. 1-1 terahertz communication system of the present disclosure. FIG. 4 is a diagram showing a configuration of a No. 1-2 terahertz communication system of the present disclosure. FIG. 5 is a diagram showing a configuration of a No. 1-3 terahertz communication system of the present disclosure. FIG. 6 is a diagram showing a configuration of a No. 1-4 terahertz communication system of the present disclosure. FIG. 7 is a diagram showing a configuration of a No. 1-5 terahertz communication system of the present disclosure. FIG. 8 is a diagram showing a configuration of a No. 1-6 terahertz communication system of the present disclosure. FIG. 9 is a diagram showing a configuration of a No. 1-7 terahertz communication system of the present disclosure. FIG. 10 is a diagram showing a configuration of a No. 1-8 terahertz communication system of the present disclosure. FIG. 11 is a diagram showing a configuration of a No. 2-1 terahertz communication system of the present disclosure. FIG. 12 is a diagram showing a configuration of a No. 2-2 terahertz communication system of the present disclosure. FIG. 13 is a diagram showing a configuration of a No. 2-3 terahertz communication system of the present disclosure. FIG. 14 is a diagram showing a configuration of a No. 2-4 terahertz communication system of the present disclosure. FIG. 15 is a diagram showing a configuration of a No. 2-5 terahertz communication system of the present disclosure. FIG. 16 is a diagram showing a configuration of a No. 2-6 terahertz communication system of the present disclosure. FIG. 1 is a diagram showing a configuration of a terahertz communication system according to No. 2-7 of the present disclosure. FIG. 2 is a diagram showing a configuration of a terahertz communication system according to No. 2-8 of the present disclosure. FIG. 3 is a diagram showing an example of a terahertz communication system according to No. 1-1 of the present disclosure. FIG. 4 is a diagram showing an example of a terahertz communication system according to No. 1-2 of the present disclosure. FIG. 5 is a diagram showing an example of a terahertz communication system according to No. 1-2 of the present disclosure. FIG. 6 is a diagram showing an example of a terahertz communication system according to No. 1-3 of the present disclosure. FIG. 7 is a diagram showing an example of a terahertz communication system according to No. 1-5 of the present disclosure. FIG. 8 is a diagram showing an example of a terahertz communication system according to No. 1-6 of the present disclosure. FIG. 9 is a diagram showing an example of a terahertz communication system according to No. 1-8 of the present disclosure. FIG. 10 is a diagram showing an example of a terahertz communication system according to No. 2-1 of the present disclosure.

[0033]

[0023] The following embodiments of the present disclosure will be described with reference to the accompanying drawings. The embodiments described below are examples of implementation of the present disclosure, and the present disclosure is not limited to the following embodiments.

[0034] (Configuration of the first terahertz communication system of the present disclosure) The first terahertz communication system of the present disclosure is an extension of the first terahertz communication system of the prior art. In the first terahertz communication system of the present disclosure, the frequency characteristics of the terahertz optical signal and the terahertz radio signal are different from those of the second terahertz communication system of the present disclosure, which will be described later, but the degree of freedom in allocation of the terahertz optical signal is the same.

[0035] The configuration of a terahertz communication system No. 1-1 of the present disclosure is shown in Fig. 3. The terahertz communication system S includes N terahertz optical signal generation units 1 and N terahertz wireless signal transmission units 2. Each terahertz optical signal generation unit 1 includes one signal light source 11, one local light source 12, one optical modulator 13, and one optical coupler 14. Each terahertz wireless signal transmission unit 2 includes one photoelectric converter 21, one amplifier 22, and one antenna 23.

[0036] In each terahertz optical signal generator 1, the signal light source 11 and the local light source 12 output optical signals having different frequencies. Here, the wavelength and frequency of the optical signal output by the signal light source 11 are expressed as (λ Ｓ１ , ..., λ ＳＮ ), (f Ｓ１ , ..., f ＳＮ ), and the wavelength and frequency of the optical signal output by the local light source 12 are (λ О１ , ..., λ ОＮ ), (f О１ , ..., f ОＮ ). The optical modulator 13 optically modulates the optical signal output by the signal light source 11 with the data signal. The optical coupler 14 optically couples the optical signal output by the optical modulator 13 with the optical signal output by the local light source 12. Then, the frequency of the terahertz optical signal output by the optical coupler 14 is expressed as (f １ , ..., f Ｎ ) = (|f Ｓ１ -f О１ |, ..., |f ＳＮ -f ОＮ |).

[0037] In each terahertz radio signal transmitter 2, the photoelectric converter 21 photoelectrically converts the terahertz optical signal output by the optical coupler 14 of one terahertz optical signal generator 1 (selected by the terahertz optical signal switching unit 3 described later). The amplifier 22 amplifies the terahertz electrical signal output by the photoelectric converter 21. The antenna 23 transmits the terahertz electrical signal output by the amplifier 22 as a terahertz radio signal. Then, the frequency of the terahertz radio signal output by the antenna 23 is expressed as (f １ , ..., f Ｎ ) = (|f Ｓ１ -f О１ |, ..., |f ＳＮ -f ОＮ |).

[0038] The terahertz communication system S includes a terahertz optical signal switching unit 3. Here, the terahertz optical signal switching unit 3 is a multicast switch (MCS) or the like, and includes inputs from N terahertz optical signal generation units 1 and outputs to N terahertz radio signal transmission units 2. In other words, when allocating terahertz optical signals having respective frequencies to the respective terahertz radio signal transmission units 2, the terahertz optical signal switching unit 3 is capable of switching the combination of allocation of terahertz optical signals among a plurality of combinations.

[0039] Therefore, by multiplexing the terahertz communication system S, when storing multiple frequency bands, the terahertz optical signal switching unit 3 can increase the degree of freedom in assigning terahertz optical signals having N types of frequencies to N terahertz radio signal transmission units 2.

[0040] The terahertz communication system S includes a wavelength multiplexing unit 4. The wavelength multiplexing unit 4 is disposed between the terahertz optical signal switching unit 3 and the N terahertz radio signal transmission units 2, and wavelength-multiplexes terahertz optical signals having multiple frequencies. Here, the wavelength multiplexing unit 4 includes inputs from the terahertz optical signal switching unit 3 with N outputs, and outputs to the N terahertz radio signal transmission units 2.

[0041] Therefore, by using an arrayed waveguide (AWG) or the like, terahertz optical signals wavelength-multiplexed in multiple frequency bands can be assigned to N terahertz radio signal transmitters 2. There is no need to route multiple outputs from the terahertz optical signal switching unit 3 to each of the terahertz radio signal transmitters 2; it is sufficient to simply connect one output from the wavelength multiplexing unit 4.

[0042] The configuration of a terahertz communication system No. 1-2 of the present disclosure is shown in Fig. 4. The following mainly describes the differences from the terahertz communication system No. 1-1 of the present disclosure.

[0043] The terahertz communication system S includes M terahertz optical signal generation units 1. The terahertz optical signal switching unit 3 includes inputs from the M terahertz optical signal generation units 1 and outputs to N terahertz radio signal transmission units 2 (N is an integer greater than M).

[0044] This increases the degree of freedom in allocating terahertz optical signals having M frequencies to N terahertz radio signal transmission units 2. Since N>M, the same terahertz optical signal can be allocated to multiple terahertz radio signal transmission units 2.

[0045] The configuration of a terahertz communication system No. 1-3 of the present disclosure is shown in Fig. 5. The following mainly describes the differences from the terahertz communication system No. 1-1 of the present disclosure.

[0046] The terahertz communication system S includes one terahertz optical signal generation unit 1, but does not include a terahertz optical signal switching unit 3. The terahertz optical signal generation unit 1 includes N signal light sources 11, one local light source 12, N optical modulators 13, and N optical couplers 14, and includes a terahertz optical signal switching unit 19 instead of the terahertz optical signal switching unit 3.

[0047] N signal light sources 11 output optical signals having respective frequencies among the N frequencies. One local light source 12 outputs an optical signal having a frequency different from the N frequencies, and divides the output into N signals for N optical couplers 14. The terahertz optical signal switching unit 19 has inputs from N optical modulators 13 and outputs to N optical couplers 14.

[0048] Therefore, it is possible to increase the degree of freedom in allocating terahertz optical signals having N kinds of frequencies to N terahertz wireless signal transmitters 2. One local light source 12 is shared by N signal light sources 11, and the N kinds of frequencies (|f Ｓｉ -f О |, i=1 to N), the number of local light sources 12 can be reduced.

[0049] The configuration of a terahertz communication system No. 1-4 of the present disclosure is shown in Fig. 6. The following mainly describes the differences from the terahertz communication system No. 1-3 of the present disclosure.

[0050] The terahertz optical signal generating unit 1 includes M signal light sources 11 and M optical modulators 13. The terahertz optical signal switching unit 19 includes inputs from the M optical modulators 13 and outputs to N optical couplers 14 (N is an integer greater than M).

[0051] Therefore, it is possible to increase the degree of freedom in allocating terahertz optical signals having M frequencies to N terahertz wireless signal transmitters 2. One local light source 12 is shared by M signal light sources 11, and the M frequencies (|f Ｓｉ -f О |, i=1 to M), it is possible to reduce the number of local light sources 12. Furthermore, since N>M, the same terahertz optical signal can be assigned to multiple terahertz wireless signal transmitters 2.

[0052] The configuration of a terahertz communication system No. 1-5 of the present disclosure is shown in Fig. 7. The following mainly describes the differences from the terahertz communication system No. 1-4 of the present disclosure.

[0053] The terahertz communication system S includes a terahertz optical signal switching unit 3. The terahertz optical signal generation unit 1 includes M optical couplers 14 (the local light source 12 outputs in M ​​divisions). The terahertz optical signal switching unit 19 includes inputs from M optical modulators 13 and outputs to M optical couplers 14. The terahertz optical signal switching unit 3 includes inputs from M optical couplers 14 and outputs to N terahertz radio signal transmission units 2 (N is an integer greater than M).

[0054] Therefore, it is possible to increase the degree of freedom in allocating terahertz optical signals having M frequencies to N terahertz wireless signal transmitters 2. One local light source 12 is shared by M signal light sources 11, and the M frequencies (|f Ｓｉ -f О |, i = 1 to M), it is possible to reduce the number of local light sources 12. Furthermore, since N>M, the same terahertz optical signal can be assigned to multiple terahertz wireless signal transmitters 2, and the number of optical couplers 14 can be reduced.

[0055] The configuration of a terahertz communication system No. 1-6 of the present disclosure is shown in Fig. 8. The following mainly describes the differences from the terahertz communication system No. 1-1 of the present disclosure.

[0056] The terahertz communication system S includes one terahertz optical signal generation unit 1, but does not include a terahertz optical signal switching unit 3. The terahertz optical signal generation unit 1 includes N signal light sources 11, N local light sources 12, N optical modulators 13, and N optical couplers 14, and includes a terahertz optical signal switching unit 19 instead of the terahertz optical signal switching unit 3.

[0057] The N signal light sources 11 output optical signals having respective frequencies among the N frequencies. The N local light sources 12 output optical signals having respective frequencies among the N frequencies different from the N frequencies. The terahertz optical signal switching unit 19 has inputs from the N optical modulators 13 and the local light sources 12, and outputs to two inputs of the N optical couplers 14.

[0058] This increases the degree of freedom in allocating terahertz optical signals having N frequencies to N terahertz wireless signal transmitters 2. By combining N signal light sources 11 and N local light sources 12 (provided that the optical signal generated by the terahertz optical signal generator 1 is in the terahertz band and is optically modulated), the N frequencies (|f Ｓｉ -f Оｊ |, i, j=1 to N) can be diversified without any restrictions.

[0059] The configuration of a No. 1-7 terahertz communication system of the present disclosure is shown in Fig. 9. The following mainly describes the differences from the No. 1-6 terahertz communication system of the present disclosure.

[0060] The terahertz optical signal generation unit 1 includes M signal light sources 11, M local light sources 12, and M optical modulators 13. The terahertz optical signal switching unit 19 includes inputs from the M optical modulators 13 and the local light sources 12, and outputs to two inputs of N optical couplers 14 (N is an integer greater than M).

[0061] This increases the degree of freedom in allocating terahertz optical signals having M frequencies to N terahertz wireless signal transmitters 2. By combining M signal light sources 11 and M local light sources 12 (provided that the optical signal generated by the terahertz optical signal generator 1 is in the terahertz band and is optically modulated), M frequencies (|f Ｓｉ -f Оｊ |, i, j=1 to M) can be diversified without any restrictions. Furthermore, since N>M, the same terahertz optical signal can be assigned to multiple terahertz wireless signal transmitters 2.

[0062] The configuration of a terahertz communication system No. 1-8 of the present disclosure is shown in Fig. 10. The following mainly describes the differences from a terahertz communication system No. 1-7 of the present disclosure.

[0063] The terahertz communication system S includes a terahertz optical signal switching unit 3. The terahertz optical signal generation unit 1 includes M optical couplers 14. The terahertz optical signal switching unit 19 includes inputs from M optical modulators 13 and local light sources 12, and outputs to two inputs of the M optical couplers 14. The terahertz optical signal switching unit 3 includes inputs from the M optical couplers 14 and outputs to N terahertz wireless signal transmission units 2 (N is an integer greater than M).

[0064] This increases the degree of freedom in allocating terahertz optical signals having M frequencies to N terahertz wireless signal transmitters 2. By combining M signal light sources 11 and M local light sources 12 (provided that the optical signal generated by the terahertz optical signal generator 1 is in the terahertz band and is optically modulated), M frequencies (|f Ｓｉ -f Оｊ |, i, j = 1 to M) can be diversified without any restrictions. Furthermore, since N>M, the same terahertz optical signal can be assigned to multiple terahertz wireless signal transmitters 2, and the number of optical couplers 14 can be reduced.

[0065] (Configuration of the second terahertz communication system of the present disclosure) The second terahertz communication system of the present disclosure is an extension of the second terahertz communication system of the prior art. In the second terahertz communication system of the present disclosure, the frequency characteristics of the terahertz optical signal and the terahertz radio signal are different from those of the first terahertz communication system of the present disclosure, but the degree of freedom in allocation of the terahertz optical signal is the same.

[0066] 11 shows the configuration of a terahertz communication system No. 2-1 of the present disclosure. The terahertz communication system S includes N terahertz optical signal generation units 1 and N terahertz wireless signal transmission units 2. Each terahertz optical signal generation unit 1 includes one first light source 15, one second light source 16, one optical coupler 17, and one optical modulator 18. Each terahertz wireless signal transmission unit 2 includes one photoelectric converter 21, one amplifier 22, and one antenna 23.

[0067] In each terahertz optical signal generation unit 1, the first light source 15 and the second light source 16 output optical signals having different frequencies. Here, the wavelength and frequency of the optical signal output by the first light source 15 are expressed as (λ １１ , ..., λ １Ｎ ), (f １１ , ..., f １Ｎ ), and the wavelength and frequency of the optical signal output by the second light source 16 are (λ ２１ , ..., λ ２Ｎ ), (f ２１ , ..., f ２Ｎ ). The optical coupler 17 optically couples the optical signal output by the first light source 15 and the optical signal output by the second light source 16. The optical modulator 18 optically modulates the terahertz optical signal output by the optical coupler 17 with a data signal. Then, the frequency of the terahertz optical signal output by the optical modulator 18 is expressed as (f １ , ..., f Ｎ ) = (|f １１ -f ２１ |, ..., |f １Ｎ -f ２Ｎ |).

[0068] In each terahertz radio signal transmitter 2, the photoelectric converter 21 photoelectrically converts the terahertz optical signal output by the optical modulator 18 of one terahertz optical signal generator 1 (selected by the terahertz optical signal switching unit 3 described later). The amplifier 22 amplifies the terahertz electrical signal output by the photoelectric converter 21. The antenna 23 transmits the terahertz electrical signal output by the amplifier 22 as a terahertz radio signal. Then, the frequency of the terahertz radio signal output by the antenna 23 is expressed as (f １ , ..., f Ｎ ) = (|f １１ -f ２１ |, ..., |f １Ｎ -f ２Ｎ |).

[0069] The terahertz communication system S includes a terahertz optical signal switching unit 3. Here, the terahertz optical signal switching unit 3 is a multicast switch (MCS) or the like, and includes inputs from N terahertz optical signal generation units 1 and outputs to N terahertz radio signal transmission units 2. In other words, when allocating terahertz optical signals having respective frequencies to the respective terahertz radio signal transmission units 2, the terahertz optical signal switching unit 3 is capable of switching the combination of allocation of terahertz optical signals among a plurality of combinations.

[0070] Therefore, by multiplexing the terahertz communication system S, when storing multiple frequency bands, the terahertz optical signal switching unit 3 can increase the degree of freedom in assigning terahertz optical signals having N types of frequencies to N terahertz radio signal transmission units 2.

[0071] The terahertz communication system S includes a wavelength multiplexing unit 4. The wavelength multiplexing unit 4 is disposed between the terahertz optical signal switching unit 3 and the N terahertz radio signal transmission units 2, and wavelength-multiplexes terahertz optical signals having multiple frequencies. Here, the wavelength multiplexing unit 4 includes inputs from the terahertz optical signal switching unit 3 with N outputs, and outputs to the N terahertz radio signal transmission units 2.

[0072] Therefore, by using an arrayed waveguide (AWG) or the like, terahertz optical signals wavelength-multiplexed in multiple frequency bands can be assigned to N terahertz radio signal transmitters 2. There is no need to route multiple outputs from the terahertz optical signal switching unit 3 to each of the terahertz radio signal transmitters 2; it is sufficient to simply connect one output from the wavelength multiplexing unit 4.

[0073] The configuration of a terahertz communication system No. 2-2 of the present disclosure is shown in Fig. 12. The following mainly describes the differences from the terahertz communication system No. 2-1 of the present disclosure.

[0074] The terahertz communication system S includes M terahertz optical signal generation units 1. The terahertz optical signal switching unit 3 includes inputs from the M terahertz optical signal generation units 1 and outputs to N terahertz radio signal transmission units 2 (N is an integer greater than M).

[0075] This increases the degree of freedom in allocating terahertz optical signals having M frequencies to N terahertz radio signal transmission units 2. Since N>M, the same terahertz optical signal can be allocated to multiple terahertz radio signal transmission units 2.

[0076] The configuration of a terahertz communication system No. 2-3 of the present disclosure is shown in Fig. 13. The following mainly describes the differences from the terahertz communication system No. 2-1 of the present disclosure.

[0077] The terahertz communication system S includes one terahertz optical signal generation unit 1, but does not include a terahertz optical signal switching unit 3. The terahertz optical signal generation unit 1 includes N first light sources 15, one second light source 16, N optical couplers 17, and N optical modulators 18, and includes a terahertz optical signal switching unit 20 instead of the terahertz optical signal switching unit 3.

[0078] The N first light sources 15 output optical signals having each of the N frequencies. One second light source 16 outputs an optical signal having a frequency different from the N frequencies, and splits the output into N signals for the N optical couplers 17. The terahertz optical signal switching unit 20 has inputs from the N first light sources 15 and outputs to the N optical couplers 17.

[0079] Therefore, it is possible to increase the degree of freedom in allocating terahertz optical signals having N kinds of frequencies to N terahertz wireless signal transmitters 2. Then, one second light source 16 is shared by N first light sources 15, and the N kinds of frequencies (|f １ｉ -f ２ |, i=1 to N), the number of second light sources 16 can be reduced.

[0080] The configuration of a terahertz communication system No. 2-4 of the present disclosure is shown in Fig. 14. The following mainly describes the differences from the terahertz communication system No. 2-3 of the present disclosure.

[0081] The terahertz optical signal generation unit 1 includes M first light sources 15. The terahertz optical signal switching unit 20 includes inputs from the M first light sources 15 and outputs to N optical couplers 17 (N is an integer greater than M).

[0082] Therefore, it is possible to increase the degree of freedom in allocating terahertz optical signals having M frequencies to N terahertz wireless signal transmitters 2. One second light source 16 is shared by M first light sources 15, and the M frequencies (|f １ｉ -f ２ |, i=1 to M), it is possible to reduce the number of second light sources 16. Furthermore, since N>M, the same terahertz optical signal can be assigned to multiple terahertz wireless signal transmitters 2.

[0083] The configuration of a terahertz communication system No. 2-5 of the present disclosure is shown in Fig. 15. The following mainly describes the differences from the terahertz communication system No. 2-4 of the present disclosure.

[0084] The terahertz communication system S includes a terahertz optical signal switching unit 3. The terahertz optical signal generation unit 1 includes M optical couplers 17 and M optical modulators 18 (the second light source 16 outputs in M ​​divisions). The terahertz optical signal switching unit 20 includes inputs from M first light sources 15 and outputs to M optical couplers 17. The terahertz optical signal switching unit 3 includes inputs from M optical modulators 18 and outputs to N terahertz radio signal transmission units 2 (N is an integer greater than M).

[0085] Therefore, it is possible to increase the degree of freedom in allocating terahertz optical signals having M frequencies to N terahertz wireless signal transmitters 2. One second light source 16 is shared by M first light sources 15, and the M frequencies (|f １ｉ -f О |, i = 1 to M), it is possible to reduce the number of second light sources 16. Furthermore, since N>M, the same terahertz optical signal can be assigned to multiple terahertz wireless signal transmitters 2, and the number of optical couplers 17 and optical modulators 18 can be reduced.

[0086] The configuration of a terahertz communication system No. 2-6 of the present disclosure is shown in Fig. 16. The following mainly describes the differences from the terahertz communication system No. 2-1 of the present disclosure.

[0087] The terahertz communication system S includes one terahertz optical signal generation unit 1, but does not include a terahertz optical signal switching unit 3. The terahertz optical signal generation unit 1 includes N first light sources 15, N second light sources 16, N optical couplers 17, and N optical modulators 18, and includes a terahertz optical signal switching unit 20 instead of the terahertz optical signal switching unit 3.

[0088] The N first light sources 15 output optical signals having respective frequencies among the N frequencies. The N second light sources 16 output optical signals having respective frequencies among the N frequencies different from the N frequencies. The terahertz optical signal switching unit 20 has inputs from the N first light sources 15 and second light sources 16 and outputs to two inputs of the N optical couplers 17.

[0089] Therefore, it is possible to increase the degree of freedom in allocating terahertz optical signals having N kinds of frequencies to N terahertz wireless signal transmitters 2. Then, by combining N first light sources 15 and N second light sources 16 (provided that the optical signal generated by the terahertz optical signal generator 1 is not only optically modulated but also in the terahertz band), the N kinds of frequencies (|f １ｉ -f ２ｊ |, i, j=1 to N) can be diversified without any restrictions.

[0090] The configuration of a terahertz communication system No. 2-7 of the present disclosure is shown in Fig. 17. The following mainly describes the differences from the terahertz communication system No. 2-6 of the present disclosure.

[0091] The terahertz optical signal generation unit 1 includes M first light sources 15 and M second light sources 16. The terahertz optical signal switching unit 20 includes inputs from the M first light sources 15 and second light sources 16 and outputs to two inputs of N optical couplers 17 (N is an integer greater than M).

[0092] Therefore, it is possible to increase the degree of freedom in allocating terahertz optical signals having M frequencies to N terahertz wireless signal transmitters 2. Then, by combining M first light sources 15 and M second light sources 16 (provided that the optical signal generated by the terahertz optical signal generator 1 is not only optically modulated but also in the terahertz band), M frequencies (|f １ｉ -f ２ｊ |, i, j=1 to M) can be diversified without any restrictions. Furthermore, since N>M, the same terahertz optical signal can be assigned to multiple terahertz wireless signal transmitters 2.

[0093] The configuration of a terahertz communication system No. 2-8 of the present disclosure is shown in Fig. 18. The following mainly describes the differences from the terahertz communication system No. 2-7 of the present disclosure.

[0094] The terahertz communication system S includes a terahertz optical signal switching unit 3. The terahertz optical signal generation unit 1 includes M optical couplers 17 and M optical modulators 18. The terahertz optical signal switching unit 20 includes inputs from M first light sources 15 and M second light sources 16, and outputs to two inputs of the M optical couplers 17. The terahertz optical signal switching unit 3 includes inputs from M optical modulators 18 and outputs to N terahertz radio signal transmission units 2 (N is an integer greater than M).

[0095] Therefore, it is possible to increase the degree of freedom in allocating terahertz optical signals having M frequencies to N terahertz wireless signal transmitters 2. Then, by combining M first light sources 15 and M second light sources 16 (provided that the optical signal generated by the terahertz optical signal generator 1 is not only optically modulated but also in the terahertz band), M frequencies (|f １ｉ -f ２ｊ |, i, j = 1 to M) can be diversified without any restrictions. Furthermore, since N>M, the same terahertz optical signal can be assigned to multiple terahertz wireless signal transmitters 2, and the number of optical couplers 17 and optical modulators 18 can be reduced.

[0096] (First and Second Terahertz Communication System Examples of the Present Disclosure) An example of the first-1st terahertz communication system of the present disclosure (see FIG. 3) is shown in FIG. 19. The optical couplers 14-1 to 14-4 each have a frequency (f Ｓ１ , f О１ ), (f Ｓ２ , f О２ ), (f Ｓ３ , f О３ ), (f Ｓ４ , f О４ The terahertz optical signal switching unit 3 has inputs from the optical couplers 14-1 to 14-4 and outputs to the photoelectric converters 21-1 to 21-4. The photoelectric converters 21-1 to 21-4 respectively couple optical signals having a frequency f １ , f ２ , f ３ , f ４ The terahertz optical signal having the following structure is photoelectrically converted. Time division multiplexing, which will be described later, is also possible in FIG.

[0097] The coverage areas C1, C2, C3, and C4 are each in the frequency band f １ , f ２ , f ３ , f ４ The mobile terminal T1 stores the frequency band f １ The mobile terminal T2 corresponds to the frequency band f ４ and can be received in the coverage area C4.

[0098] An example of the first-second terahertz communication system (see FIG. 4) of the present disclosure is shown in FIG. 20. Optical couplers 14-1 and 14-2 each couple a frequency (f Ｓ１ , f О１ ), (f Ｓ２ , f О２ The terahertz optical signal switching unit 3 has inputs from the optical couplers 14-1 and 14-2 and outputs to the photoelectric converters 21-1 to 21-4. The photoelectric converters 21-1 to 21-4 respectively couple optical signals having a frequency f １ , f １ , f ２ , f ２The coverage ranges C1, C2, C3, and C4 are respectively in the frequency band f １ , f １ , f ２ , f ２ The mobile terminal T1 stores the frequency band f １ In this case, the mobile terminal can move freely from the coverage area C1 to the coverage area C2. However, when multiple mobile terminals receive signals in the same frequency band, it is difficult for all the mobile terminals to move freely.

[0099] An example of a terahertz communication system No. 1-2 (see FIG. 4 ) according to the present disclosure is also shown in FIG. 21 . Furthermore, the terahertz optical signal switching unit 3 can switch among a plurality of combinations of terahertz optical signal allocations and perform time-division multiplexing. Here, the terahertz optical signal switching unit 3 may perform switching after acquiring location information of the mobile terminal, or may perform switching randomly regardless of the location information of the mobile terminal. Therefore, terahertz optical signals that are switched over time between a plurality of frequencies by time-division multiplexing can be assigned to each terahertz wireless signal transmission unit 2.

[0100] In a certain period of time division multiplexing shown in the left column of FIG. 21, the coverage areas C1, C2, C3, and C4 are respectively in the frequency band f １ , f １ , f ２ , f ２ The mobile terminal T1 stores the frequency band f １ , and can move freely from the coverage area C1 to the coverage area C2, but the mobile terminal T2 is in the frequency band f ２ and reception is not possible in the coverage areas C1 and C2.

[0101] In the next period of time division multiplexing shown in the right column of FIG. 21, the coverage areas C1, C2, C3, and C4 are respectively in the frequency band f ２ , f ２ , f １ , f １ The mobile terminal T1 stores the frequency band f １ , and can move freely from the coverage area C2 to the coverage area C3, and the mobile terminal T2 is in the frequency band f２ and can be received in the coverage areas C1 and C2.

[0102] Furthermore, even when multiple mobile terminals receive signals in the same frequency band, all of the mobile terminals can move freely. In Fig. 21, the mobile terminals do not have a frequency switching function, but as a modified example, the mobile terminals may have a frequency switching function. Here, it is assumed that the frequency switching time of the mobile terminals is longer than the switching time of the terahertz optical signal switching unit 3. Therefore, when the mobile terminals are moving while receiving signals, the terahertz optical signal switching unit 3 only needs to switch, and when the mobile terminals are not receiving signals, the mobile terminals only need to switch frequencies.

[0103] An example of the first-third terahertz communication system (see FIG. 5) of the present disclosure is shown in FIG. 22. The terahertz optical signal switching unit 19 is a terahertz optical signal switching unit for switching the frequency f Ｓ１ , f Ｓ２ , f Ｓ３ , f Ｓ４ and outputs to optical couplers 14-1 to 14-4. The optical couplers 14-1 to 14-4 receive, in any order, an optical signal having a frequency (f Ｓ１ , f О ), (f Ｓ２ , f О ), (f Ｓ３ , f О ), (f Ｓ４ , f О The photoelectric converters 21-1 to 21-4 optically couple optical signals having a frequency f １ , f ２ , f ３ , f ４ The coverage ranges C1, C2, C3, and C4 are respectively in the frequency band f １ , f ２ , f ３ , f ４ The mobile terminal T1 stores the frequency band f １ The mobile terminal T2 corresponds to the frequency band f ４ and can be received in the coverage area C4. Time division multiplexing is also possible in FIG.

[0104] An example of the terahertz communication system No. 1-5 (see FIG. 7) of the present disclosure is shown in FIG. 23. The terahertz optical signal switching unit 19 is a terahertz optical signal switching unit for switching the frequency f Ｓ１ , f Ｓ２ and outputs to optical couplers 14-1 and 14-2. The optical couplers 14-1 and 14-2 receive, in any order, an optical signal having a frequency (f Ｓ１ , f О ), (f Ｓ２ , f О The terahertz optical signal switching unit 3 has inputs from the optical couplers 14-1 and 14-2 and outputs to the photoelectric converters 21-1 to 21-4. The photoelectric converters 21-1 to 21-4 respectively couple optical signals having a frequency f １ , f １ , f ２ , f ２ The coverage ranges C1, C2, C3, and C4 are respectively in the frequency band f １ , f １ , f ２ , f ２ The mobile terminal T1 stores the frequency band f １ The mobile terminal T2 corresponds to the frequency band f ２ and can be received in the coverage area C4. Time division multiplexing is also possible in FIG.

[0105] An example of the terahertz communication system No. 1-6 (see FIG. 8) of the present disclosure is shown in FIG. 24. The terahertz optical signal switching unit 19 is a terahertz optical signal switching unit for switching the frequency f Ｓ１ , f Ｓ２ , f Ｓ３ , f Ｓ４ , f О１ , f О２ , f О３ , f О４ and outputs to two inputs of optical couplers 14-1 to 14-4. Ｓｉ , f Оｊ ) (i, j=1 to 4). The photoelectric converters 21-1 to 21-4 optically couple optical signals having frequencies f １ , f ２ , f ３ , f ４The coverage ranges C1, C2, C3, and C4 are respectively in the frequency band f １ , f ２ , f ３ , f ４ The mobile terminal T1 stores the frequency band f １ The mobile terminal T2 corresponds to the frequency band f ４ and can be received in the coverage area C4. Time division multiplexing is also possible in FIG.

[0106] An example of the terahertz communication system No. 1-8 (see FIG. 10) of the present disclosure is shown in FIG. 25. The terahertz optical signal switching unit 19 is a terahertz optical signal switching unit for switching the frequency f Ｓ１ , f Ｓ２ , f О１ , f О２ and outputs to two inputs of optical couplers 14-1 and 14-2. Ｓｉ , f Оｊ ) (i, j=1, 2). The terahertz optical signal switching unit 3 has inputs from the optical couplers 14-1 and 14-2 and outputs to the photoelectric converters 21-1 to 21-4. The photoelectric converters 21-1 to 21-4 respectively couple optical signals having a frequency f １ , f １ , f ２ , f ２ The coverage ranges C1, C2, C3, and C4 are respectively in the frequency band f １ , f １ , f ２ , f ２ The mobile terminal T1 stores the frequency band f １ The mobile terminal T2 corresponds to the frequency band f ２ and can be received in the coverage area C4. Time division multiplexing is also possible in FIG.

[0107] An example of the terahertz communication system No. 2-1 (see FIG. 11) of the present disclosure is shown in FIG. 26. Optical couplers 17-1 to 17-4 each couple a frequency (f １１ , f ２１ ), (f １２ , f ２２), (f １３ , f ２３ ), (f １４ , f ２４ The terahertz optical signal switching unit 3 has inputs from the optical couplers 17-1 to 17-4 and outputs to the photoelectric converters 21-1 to 21-4. The photoelectric converters 21-1 to 21-4 respectively couple optical signals having a frequency f １ , f ２ , f ３ , f ４ The terahertz optical signal having the following structure is photoelectrically converted. Time division multiplexing is also possible in FIG.

[0108] The coverage areas C1, C2, C3, and C4 are each in the frequency band f １ , f ２ , f ３ , f ４ The mobile terminal T1 stores the frequency band f １ The mobile terminal T2 corresponds to the frequency band f ４ and can be received in the coverage area C4.

[0109] The terahertz communication system of the present disclosure multiplexes the terahertz communication system, thereby increasing the degree of freedom in assigning terahertz optical signals having each frequency to each terahertz wireless signal transmitter when storing multiple frequency bands.

[0110] S: Terahertz communication system 1: Terahertz optical signal generation unit 2: Terahertz wireless signal transmission unit 3: Terahertz optical signal switching unit 4: Wavelength multiplexing unit 11: Signal light source 12: Local light source 13: Optical modulator 14, 14-1 to 14-4, 14-1, 14-2: Optical coupler 15: First light source 16: Second light source 17, 17-1 to 17-4: Optical coupler 18: Optical modulator 19: Terahertz optical signal switching unit 20: Terahertz optical signal switching unit 21, 21-1 to 21-4: Photoelectric converter 22: Amplifier 23: Antenna C1, C2, C3, C4: Coverage range T1, T2: Portable terminal

Claims

1. A terahertz communication system comprising: a terahertz optical signal generation unit that, when optically coupling optical signals having different frequencies to generate terahertz optical signals, sets a plurality of combinations of different frequencies of the optical signals and generates the terahertz optical signals having a plurality of frequencies; a plurality of terahertz radio signal transmission units that photoelectrically convert the terahertz optical signals having each frequency and transmit terahertz radio signals having each frequency; and a terahertz optical signal switching unit that, when allocating the terahertz optical signals having each frequency to each of the terahertz radio signal transmission units, is able to switch the combination of allocation of the terahertz optical signals among a plurality of combinations.

2. The terahertz communication system according to claim 1, wherein M (M is an integer equal to or greater than 2) terahertz optical signal generating units generate terahertz optical signals having respective frequencies from M frequencies, and the terahertz optical signal switching unit has inputs from the M terahertz optical signal generating units and outputs to N (N is an integer equal to or greater than M) terahertz wireless signal transmitting units.

3. The terahertz communication system according to claim 1, wherein the terahertz optical signal generation unit comprises M first light sources that output the optical signals having each of M frequencies (M is an integer of 2 or more), and one second light source that outputs the optical signal having a frequency different from the M frequencies, and the terahertz optical signal switching unit comprises inputs from the M first light sources and outputs N (N is an integer of M or more) of the optical signals to an optical coupler.

4. The terahertz communication system according to claim 1, wherein the terahertz optical signal generation unit comprises M first light sources that output the optical signals having each of M frequencies (M is an integer greater than 2), and one second light source that outputs the optical signal having a frequency different from the M frequencies; and the terahertz optical signal switching unit is (1) arranged inside the terahertz optical signal generation unit and comprises inputs from the M first light sources and outputs of the M optical signals to an optical coupler, and (2) arranged between the terahertz optical signal generation unit and N terahertz wireless signal transmission units (N is an integer greater than M) and comprises inputs of the M optical signals from an optical coupler and outputs of the N terahertz wireless signal transmission units.

5. The terahertz communication system according to claim 1, wherein the terahertz optical signal generation unit comprises M first light sources that output the optical signals having each of M frequencies (M is an integer of 2 or more), and M second light sources that output the optical signals having each of M frequencies different from the M frequencies, and the terahertz optical signal switching unit comprises M inputs from the first light sources and the second light sources, and N (N is an integer of 2 or more) outputs of the optical signals to two inputs of an optical coupler.

6. The terahertz communication system according to claim 1, wherein the terahertz optical signal generation unit comprises M first light sources that output the optical signals having each of M frequencies (M is an integer greater than or equal to 2), and M second light sources that output the optical signals having each of M frequencies different from the M frequencies; and the terahertz optical signal switching unit (1) is disposed inside the terahertz optical signal generation unit and comprises M inputs from the first light sources and the second light sources and M outputs of the optical signals to two inputs of an optical coupler, and (2) is disposed between the terahertz optical signal generation unit and N terahertz wireless signal transmission units (N is an integer greater than M) and comprises M inputs of the optical signals from the optical coupler and N outputs to the terahertz wireless signal transmission units.

7. A terahertz communication system according to any one of claims 1 to 6, further comprising a wavelength multiplexing unit arranged between the terahertz optical signal switching unit and the plurality of terahertz radio signal transmitting units, for wavelength multiplexing the terahertz optical signals having a plurality of frequencies.

8. A terahertz communication system according to any one of claims 1 to 6, characterized in that the terahertz optical signal switching unit is capable of switching the combination of allocations of the terahertz optical signals among a plurality of combinations and performing time division multiplexing.

9. A terahertz communication system according to any one of claims 1 to 6, wherein the terahertz optical signal generation unit (1) optically modulates the optical signal having one frequency with a data signal and optically couples the optically modulated optical signal having one frequency with an optical signal having another frequency that is not optically modulated, or (2) optically couples the optical signal having one frequency with an optical signal having another frequency and optically modulates the optically coupled optical signal with a data signal.

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