Time domain mode multiplexing transmission method and time domain mode multiplexing transmission device

Abstract

To provide a time domain mode multiplexing transmission method and a time domain mode multiplexing transmission device, capable of mode multiplexing in the time domain.SOLUTION: In a time-domain mode multiplexing transmission device, a pulse light source 1 generates N coherent Hermite-Gaussian pulses of 0 to N-1 orders whose amplitudes are given by a Hermite-Gaussian function, and multiplexes them using them as signal light to realize mode multiplexing in the time domain and transmit them. In addition, a 90-degree optical hybrid circuit 6, a balanced photodetector 7, and a digital signal processing circuit 8 use the coherent Hermite-Gaussian pulse as a local light for detection, separation, and demodulation of the multiplexed signal light.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a time domain mode multiplexing transmission method and a time domain mode multiplexing transmission device using a Hermite-Gaussian pulse whose amplitude is given by a Hermite-Gaussian function. [Background technology]

[0002] Optical communication infrastructure has achieved a dramatic increase in capacity of more than 10,000 times over the past 40 years through many technological innovations. This increase in capacity has been achieved mainly by time division multiplexing (TDM) and wavelength division multiplexing (WDM). On the other hand, Internet traffic continues to grow exponentially at an annual rate of more than 40%, and further capacity expansion is required for the backbone optical transmission network. Therefore, in recent years, research and development of three new capacity-enhancing technologies (Multi technologies) called 3M, namely, multi-level transmission, space division multiplexing (SDM) transmission using multi-core fiber, and mode division multiplexing (MDM) transmission using multi-mode fiber, has been actively promoted (see, for example, Non-Patent Document 1).

[0003] Mode multiplexing transmission uses LP, the fundamental propagation mode of optical fiber. 01 In addition to the mode, LP 11 , L.P. 21 , L.P. 02This is a method of simultaneously transmitting information in higher modes such as those mentioned above. Mode multiplexing is useful as a high-density spatial multiplexing technology because it can increase the transmission capacity by N times through N-mode transmission while maintaining the standard outer diameter of the fiber at 125 μm. However, since crosstalk due to coupling between modes is unavoidable, it is necessary to perform mode separation after transmission using signal processing called MIMO (Multi-Input Multi-Output), and realizing this has been a challenge (for example, see Non-Patent Document 2).

[0004] Thus, what is called a normal mode in optical communications is a spatial mode that propagates through an optical fiber, and until now, there has been no transmission technology that introduces the concept of a mode to optical pulses that operate in the time domain and realizes mode multiplexing in the time domain.

[0005] Conventional optical pulses used in optical communications generally have waveforms using RZ (Return-to-Zero) pulses, i.e., Gaussian or Sech pulses. These pulses can be interleaved on the time axis to increase the speed by TDM. Recently, the inventor has devised a coherent optical Nyquist pulse as a new optical pulse for TDM to replace the RZ pulse (see, for example, Patent Document 1). The Nyquist pulse has a Sinc function shape and is characterized by periodically becoming zero in intensity. If the pulses are interleaved according to the period, the intensity of the adjacent pulses is always zero at the signal decision point, so that even if the adjacent pulses overlap, the signal can be decided without interference. As a result, the Nyquist pulse enables higher density and higher efficiency TDM than the conventional RZ pulse, and ultra-high speed transmission of 15 Tbit / s has been realized with a single wavelength, which was difficult with the conventional RZ pulse (see, for example, Non-Patent Document 3). [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] M. Nakazawa, M. Suzuki, Y. Awaji, and T. Morioka, “Space-Division Multiplexing in Optical Communication Systems: Extremely Advanced Optical Transmission with 3M Technologies”, Springer, 2022 [Non-Patent Document 2] R. Ryf, S. Randel, AH Gnauck, C. Bolle, A. Sierra, S. Mumtaz, M. Esmaeelpour, EC Burrows, R.-J. Essiambre, PJ Winzer, DW Peckham, AH McCurdy, and R. Lingle Jr, “Mode-Division Multiplexing Over 96 km of Few-Mode Fiber Using Coherent 6x6 MIMO Processing”, J. Lightwave Technol., February 2012, vol. 30, no. 4, p. 521-531 [Non-Patent Document 3] M. Yoshida, K. Kimura, T. Iwaya, K. Kasai, T. Hirooka, and M. Nakazawa, “Single-channel 15.3 Tbit / s, 64 QAM coherent Nyquist pulse transmission over 150 km with a spectral efficiency of 8.3 bit / s / Hz”, Opt. Express, September 2019, vol. 27, no. 20, p. 28952-28967 [Patent documents]

[0007] [Patent Document 1] Patent No. 5634296 Summary of the Invention [Problem to be solved by the invention]

[0008] Since the optical pulses used in TDM can only transmit one pulse at a time in one symbol time slot, ultra-high speed transmission using TDM requires an increase in the symbol rate, i.e., a narrower time slot width, and therefore an ultra-short pulse. However, since ultra-short pulses generally have a wide spectral width, the number of wavelengths that can be multiplexed by WDM within a limited frequency bandwidth is reduced. In other words, there is a trade-off between the increase in speed using TDM and the multi-channelization using WDM, and there has been an issue that there is a limit to the expansion of transmission capacity using TDM and WDM alone.

[0009] In recent digital coherent transmission, the capacity that can be transmitted per unit frequency (spectral efficiency) has been expanded by using a multilevel transmission technology called QAM (Quadrature Amplitude Modulation). However, there is a theoretical limit to the spectral efficiency called the Shannon limit, and it is difficult to overcome this limit by simply increasing the QAM level. As mentioned above, SDM transmission technology using multicore fibers and spatial modes has been actively researched, but there was a problem that it is difficult to expand the capacity that can be transmitted with a single core and single spatial mode by any method other than TDM, WDM, and multilevel modulation.

[0010] The present invention has been made to solve the above problems, and has as its object to provide a time-domain mode multiplexing transmission method and a time-domain mode multiplexing transmission device capable of mode multiplexing in the time domain. [Means for solving the problem]

[0011] In order to achieve the above object, a time domain mode multiplexing transmission method according to the present invention is characterized in that a coherent Hermite-Gaussian pulse whose amplitude is given by a Hermite-Gaussian function is used as signal light and local light.

[0012] A time domain mode multiplexing transmission device according to the present invention is characterized by comprising: coherent Hermite Gaussian pulse generating means for generating a coherent Hermite Gaussian pulse whose amplitude is given by a Hermite Gaussian function; signal light generating means for converting the coherent Hermite Gaussian pulse into signal light; local light generating means for converting the coherent Hermite Gaussian pulse into local light; and detection / separation / demodulation means for detecting, separating, and demodulating the signal light and the local light.

[0013] The time domain mode multiplexing transmission method according to the present invention can be suitably implemented by the time domain mode multiplexing transmission device according to the present invention. The time domain mode multiplexing transmission method and the time domain mode multiplexing transmission device according to the present invention can simultaneously transmit N pulses in a one-symbol time slot, so that it is possible to transmit N times the amount of information as compared to the conventional method. Furthermore, since it is not necessary to increase the symbol rate by TDM, it is possible to provide a high-speed optical transmission system using low-speed optical / electronic devices. Furthermore, it is possible to provide a high-efficiency, large-capacity optical transmission system using a conventional single-core, single spatial mode optical fiber.

[0014] In the time domain mode multiplexing transmission device according to the present invention, unlike the conventional TDM method, the coherent Hermite Gaussian pulse generating means is preferably configured to generate N coherent Hermite Gaussian pulses of orders 0 to N-1 in a time slot for one symbol and transmit them simultaneously. In the time domain mode multiplexing transmission method according to the present invention, it is preferable to generate N coherent Hermite Gaussian pulses of orders 0 to N-1 in a time slot for one symbol as the coherent Hermite Gaussian pulse and transmit them simultaneously. In this case, it is possible to realize N times the transmission capacity. Also, the N coherent Hermite Gaussian pulses may be synchronized with each other in the time domain.

[0015] Furthermore, the time domain mode multiplexing transmission method and the time domain mode multiplexing transmission device according to the present invention may realize demultiplexing by using the orthogonality of coherent Hermite Gaussian pulses. That is, in order to demultiplex an m-th order (0≦m≦N-1) coherent Hermite Gaussian pulse from N coherent Hermite Gaussian pulses, the m-th order coherent Hermite Gaussian pulse may be used as a local pulse to perform homodyne coherent detection. More specifically, in the time domain mode multiplexing transmission device according to the present invention, the signal light generating means may generate a signal in which N coherent Hermite Gaussian pulses are multiplexed as signal light, the local light generating means may generate an m-th order coherent Hermite Gaussian pulse as local light, and the detection separation demodulation means may perform homodyne coherent detection of the signal light and the local light, and integrate the detection signal after detection over a time slot for one symbol to demultiplex the m-th order Hermite Gaussian pulse from the N Hermite Gaussian pulses. Furthermore, in the time-domain mode multiplexing transmission method according to the present invention, an m-th order coherent Hermitian Gaussian pulse may be used as a local light, and signal light in which N coherent Hermitian Gaussian pulses are multiplexed may be subjected to homodyne coherent detection, and the detected signal after detection may be integrated over a time slot for one symbol, thereby demultiplexing an m-th order coherent Hermitian Gaussian pulse from the N coherent Hermitian Gaussian pulses. Effect of the Invention

[0016] According to the present invention, it is possible to provide a time-domain mode multiplexing transmission method and a time-domain mode multiplexing transmission device capable of mode multiplexing in the time domain. [Brief description of the drawings]

[0017] [Figure 1] 1 shows the time waveform aHGm(t) and frequency spectrum AHGm(ω) of a Hermite-Gaussian pulse of orders m=0 to 2, relating to a time domain mode multiplexing transmission device according to an embodiment of the present invention. [Diagram 2]1 shows the time waveform aHGm(t) and frequency spectrum AHGm(ω) of an m=3-5 order Hermite-Gaussian pulse in a time domain mode multiplexing transmission device according to an embodiment of the present invention. [Diagram 3] 1 is a block diagram showing a configuration of a time domain mode multiplexing transmission device according to an embodiment of the present invention; [Figure 4] 1 is a block diagram showing a configuration of a time domain mode multiplexing optical transmission system used in an experiment of a time domain mode multiplexing transmission device according to an embodiment of the present invention. [Diagram 5] These are (a-1) the waveform and (a-2) optical spectrum of a zero-order coherent Hermitian Gaussian pulse, (b-1) the waveform and (b-2) optical spectrum of a first-order coherent Hermitian Gaussian pulse, (c-1) the waveform and (c-2) optical spectrum of a second-order coherent Hermitian Gaussian pulse, and (d-1) the waveform and (d-2) optical spectrum of a third-order coherent Hermitian Gaussian pulse generated by the experimental system shown in Figure 4. [Figure 6] 1 shows (a-1) a back-to-back experiment (a result when a transmitter and a receiver are directly connected without a transmission line) showing the experimental result using a zeroth-order Hermite Gaussian pulse, and (a-2) a constellation of a 16 QAM signal after 450 km transmission, (b-1) a back-to-back experiment using a first-order Hermite Gaussian pulse and (b-2) a constellation of a 16 QAM signal after 450 km transmission, (c-1) a back-to-back experiment using a second-order Hermite Gaussian pulse and (c-2) a constellation of a 16 QAM signal after 450 km transmission, and (d-1) a back-to-back experiment using a third-order Hermite Gaussian pulse and (d-2) a constellation of a 16 QAM signal after 450 km transmission, of a time-domain mode multiplexing transmission device according to a first embodiment of the present invention. [Figure 7]14 shows (a-1) a constellation of a 16 QAM signal after back-to-back and (a-2) 450 km transmission showing an experimental result using a 0th order Hermite Gaussian pulse, (b-1) a constellation of a 16 QAM signal after back-to-back and (b-2) 450 km transmission showing an experimental result using a 1st order Hermite Gaussian pulse, (c-1) a constellation of a 16 QAM signal after back-to-back and (c-2) 450 km transmission showing an experimental result using a 2nd order Hermite Gaussian pulse, and (d-1) a constellation of a 16 QAM signal after back-to-back and (d-2) 450 km transmission showing an experimental result using a 3rd order Hermite Gaussian pulse, for a time-domain mode multiplexing transmission device of a second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. As mentioned above, the most common RZ pulse used in optical communications is the Gaussian pulse. The Gaussian function is given by the following equation (1).

[0019]

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[0020] The Gaussian function is known as the lowest-order function among functions called Hermite Gaussian functions. In general, the m-th order Hermite Gaussian function is given by the following formula (2).

[0021]

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[0022]

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[0023] Specifically, when m=0 to 6, it is defined by the following formulas (5-1) to (5-7).

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[0024] Moreover, the Fourier transform of the Hermite-Gaussian function is given by the following equation (6).

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[0025] Specifically, when m=0 to 6, the following formulas (7-1) to (7-7) apply.

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[0026] Figure 1 shows the case of m = 0 to 2, and Figure 2 shows the case of m = 3 to 5. HGm (t) and A HGm The shapes of (ω) are shown in these figures. As shown in these figures, the time waveform is an odd function when m is odd, and an even function when m is even. The spectrum has the same shape as the time waveform, and as the order increases, the sign is inverted and the real and imaginary parts are swapped. Specifically, when m is odd, it is an odd function with only an imaginary part, and when m is even, it is an even function with only a real part.

[0027] The Hermite Gaussian function is a function widely known in the fields of science and engineering, such as the higher-order eigensolution of the Schrödinger equation for a harmonic oscillator in quantum mechanics, the eigensolution of a higher-order beam in a laser resonator (Hermite Gaussian beam), etc. In addition, as shown in equation (6), it has properties such as its shape not changing even if it is Fourier transformed, and there is an orthogonal relationship between Hermite Gaussian functions of different orders, i.e., it satisfies the following equation (8).

[0028]

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[0029] A method for generating an optical pulse having such a Hermite Gaussian function as a pulse shape (hereinafter referred to as a Hermite Gaussian pulse) is disclosed by the inventor in Japanese Patent Application No. 2023-037273. That is, by inserting an optical filter with variable amplitude and phase characteristics into the resonator of an FM mode-locked laser and setting the amplitude and phase characteristics of the optical filter according to the order of the Hermite Gaussian function to be output, a Hermite Gaussian pulse of any order can be generated. The specific shape of the amplitude and phase characteristics of the optical filter is disclosed in Japanese Patent Application No. 2023-037273.

[0030] The configuration of a time domain mode multiplexing transmission device according to an embodiment of the present invention is shown in Fig. 3. The time domain mode multiplexing transmission device according to an embodiment of the present invention can suitably implement the time domain mode multiplexing transmission method according to an embodiment of the present invention. The time domain mode multiplexing transmission device according to an embodiment of the present invention includes N pulse light sources 1, N optical modulators 2 connected to the pulse light sources 1, N polarization multiplexing circuits 3 connected to the optical modulators 2, an optical fiber transmission line 4 to which outputs from the N polarization multiplexing circuits 3 are multiplexed and transmitted, a local pulse light source 5, a 90-degree optical hybrid circuit 6 to which the output from the optical fiber transmission line 4 and the output from the local pulse light source 5 are input, a balanced photodetector 7 connected to the 90-degree optical hybrid circuit 6, and a digital signal processing circuit 8 connected to the balanced photodetector 7.

[0031] In FIG. 3, the pulse light source 1 corresponds to a coherent Hermite Gaussian pulse generating means that generates a coherent Hermite Gaussian pulse, but the coherent Hermite Gaussian pulse generating means is not limited to being a pulse light source, and may be anything that can shape light that is not a pulse light source and generate a coherent Hermite Gaussian pulse, for example.

[0032] The optical modulator 2 corresponds to a signal light generating means for generating signal light using a coherent Hermite-Gaussian pulse. The local pulse light source 5 corresponds to a local light generating means for generating local light using a coherent Hermite-Gaussian pulse. The 90-degree optical hybrid circuit 6, the balanced photodetector 7, and the digital signal processing circuit 8 correspond to a detection / separation / demodulation means for detecting, separating, and demodulating the signal light and the local light.

[0033] On the transmitting side, N pulse light sources 1 are used to generate time-synchronized coherent Hermitian Gaussian pulses of orders 0 to N-1 at a repetition frequency R. The Hermitian Gaussian pulses of each order are independently data-modulated at a symbol rate R (the repetition frequency and value of the coherent Hermitian Gaussian pulse are always equal) using N optical modulators 2, and then polarization-multiplexed using a polarization multiplexing circuit 3 as necessary. The generated Hermitian Gaussian pulse trains of orders 0 to N-1 are multiplexed and then transmitted over an optical fiber transmission line 4. In the optical fiber transmission line 4, an Erbium-Doped Fiber Amplifier (EDFA) or a Raman amplifier is used to compensate for losses as necessary.

[0034] At the receiving side, the data signal light after transmission through the optical fiber transmission line 4 is multiplexed with a Hermite-Gaussian pulse of repetition frequency R and order m (0≦m≦N-1) output from a local pulse light source 5, and homodyne coherent detection is performed using a 90-degree optical hybrid circuit 6 and a balanced photodetector 7. Here, the local pulse output from the light source 5 is synchronized in phase and clock with the data signal light after transmission. An OPLL (Optical Phase-Locked Loop) circuit or an optical injection locking circuit is used for phase synchronization. The homodyne coherently detected data signal is subjected to the following mode multiplexing separation and demodulation processing using a digital signal processing circuit 8.

[0035] The N-mode multiplexed Hermite-Gaussian pulses of orders 0 to N-1 are expressed by the following equation (9).

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[0036] This is called the local emission a given by the m-th order Hermite-Gaussian pulse. HGm When homodyne detection is performed at (t), the detected signal is a(t) and a HGm (t), that is, given by the following equation (10).

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[0037] After this signal is A / D converted, the digital signal processing circuit 8 calculates the integral of the following equation (11).

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[0038] At this time, due to the orthogonal relationship (equation (8)) of the Hermite-Gaussian pulse, only the term in the following equation (12) remains in the integral of equation (11), and the rest are zero. As a result, it is possible to demultiplex the m-th order Hermite-Gaussian pulse from the N modes.

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[0039] The integration range of equation (11) is the time slot of one symbol, and strictly speaking, it is not -∞< t < ∞ as shown in equation (8). However, if the base of each order of the Hermite-Gaussian pulse is sufficiently attenuated within the time slot of one symbol, the integration range of equation (11) can be regarded as -∞< t < ∞.

[0040] In the following, the details of the time domain mode multiplexing transmission method and the time domain mode multiplexing transmission device according to the embodiment of the present invention will be described with reference to specific experimental examples. The configuration of the experimental system is shown in FIG. 4. In this experiment, four-mode multiplexing transmission is performed using N=4, i.e., 0th to 3rd order Hermite Gaussian pulses. Instead of preparing four Hermite Gaussian pulse light sources as a coherent Hermite Gaussian pulse generating means, for simplicity, a CW (Continuous Wave) light source (ECLD: External Cavity Laser Diode) that oscillates at a narrow linewidth and single frequency at a wavelength of 1.55 μm and an optical comb generator are used to generate the coherent Hermite Gaussian pulse. This light source is often used in coherent transmission.

[0041] Next, an optical pulse with a repetition rate of 10 GHz is generated from the optical comb generator, which is then split into five at the splitter. Four of these are used to generate 0th to 3rd order Hermite-Gaussian pulses using a waveform shaping filter called a Waveshaper (WS), and the remaining one is used as a pilot tone (Tone) for phase synchronization by extracting a frequency downshifted by 90 GHz from the center using an optical filter. The generated 0th to 3rd order Hermite-Gaussian pulses are modulated by a QAM signal with a symbol rate of 10 Gbaud generated by an arbitrary waveform generator (AWG). Specifically, each pulse is QAM-modulated by an IQ modulator (IQM) driven by the QAM signal. After adjusting the timing of each pulse using an optical delay line (Δτ), the four modes are combined and input to a polarization multiplexing circuit (Pol-MUX) for collective polarization multiplexing. A 10 GHz sinusoidal optical signal for distributing a 10 GHz clock signal is generated by a semiconductor laser and an optical intensity modulator, and is multiplexed with a signal optical pulse and a pilot tone, and then input into the optical fiber transmission line.

[0042] The transmission path is a 75 km span dispersion-managed fiber (50 km SLAF + 25 km IDF). At the receiving side, a pilot tone is extracted from the received signal light by an optical filter, and the frequency is upshifted by an optical frequency shifter (OFS), and then injected into a distributed feed-back laser diode (DFB-LD) used as a local light source. As a result, a local light phase-locked to the signal light via the pilot tone is obtained from the DFB-LD by injection locking. In parallel with this, a 10 GHz clock signal is extracted by another optical filter, and this clock signal drives an optical comb generator. Using this optical comb generator, an m-th (m=0-3) Hermite-Gaussian local pulse whose repetition frequency is synchronized with the signal light is generated, and homodyne coherent detection of the signal light is performed using a 90-degree optical hybrid circuit and a balanced photodiode (B-PD). The signal then passes through a low-pass filter (LPF) and undergoes A / D conversion before being subjected to mode demultiplexing and demodulation by a digital signal processor (DSP).

[0043] The waveforms of the generated 0th to 3rd order Hermite-Gaussian pulses are shown in Fig. 5(a-1) to (d-1) with the horizontal axis representing time and the vertical axis representing intensity, while Fig. 5(a-2) to (d-2) show the optical spectra corresponding to these waveforms with the horizontal axis representing time and the vertical axis representing power. The solid lines show the measured values, and the dashed lines show the theoretical values. It can be seen from Fig. 5 that the two are in good agreement.

[0044] [First embodiment] In the first embodiment of the present invention, the coherent Hermite-Gaussian pulses of each order are mode-multiplexed and transmitted with the same average power. Fig. 6 shows the result of 4-mode multiplexing of 10 Gbaud, 16 QAM signals and transmitting them over 450 km according to the first embodiment. The average power of each order is set to -4.0 dBm. Figs. 6(a-1) to (d-1) show back-to-back results (results when the transmitter and receiver are directly connected without a transmission line), and Figs. 6(a-2) to (d-2) show the constellations of the 16 QAM signals after 450 km transmission. In each figure, BER (Bit Error Rate) is an index representing the bit error rate, and EVM (Error Vector Magnitude) is an index representing the signal point dispersion (degree of deviation from the ideal value) on the constellation.

[0045] As shown in Figure 6, the error rate after transmission is 0th order: 1.3 × 10 -3 , 1st order: 2.7×10 -3 , 2nd order: 1.5×10 -3 , 3rd order: 1.6×10 -3 It is known that these error rate values ​​can be achieved by using forward error correction (FEC) technology. From the above, it has been demonstrated that time-domain multiplexing technology using coherent Hermite-Gaussian pulses can be realized.

[0046] [Second embodiment] In the second embodiment of the present invention, the coherent Hermite-Gaussian pulses of each order are transmitted by mode multiplexing with the peak power set to the same value. FIG. 7 shows the result of 450 km transmission of 10 Gbaud, 16 QAM signals multiplexed in four modes according to the second embodiment. The peak power of each order is set to the same value of 3.4 dBm. The average power of each order is 0th order: -5.1 dBm, 1st order: -3.8 dBm, 2nd order: -3.3 dBm, and 3rd order: -3.0 dBm. When comparing the waveforms of Hermite-Gaussian pulses with the same average power, the lower the order, the higher the peak power. Therefore, when comparing with the same peak power, the lower the order, the smaller the average power. FIG. 7(a-1) to (d-1) show the back-to-back constellations, and FIG. 7(a-2) to (d-2) show the constellations of the 16 QAM signal after 450 km transmission.

[0047] As shown in Fig. 7, the error rate after transmission is 0th order: 1.7 × 10 -3 , 1st order: 1.6×10 -3 , 2nd order: 1.4×10 -3 , 3rd order: 1.5×10 -3 It can be seen that better transmission characteristics are obtained compared to Figure 6. Therefore, just like Figure 6 (constant average power), it has been demonstrated that error-free transmission is possible with the method in Figure 7 by employing FEC. Note that in Figure 6, the performance slightly deteriorates when transmitted at the same average power because the lower the order pulse, the higher the peak power, making it more susceptible to the effects of nonlinear optical effects in the fiber. [Industrial Applicability]

[0048] As described above in detail, the present invention can realize mode multiplexed transmission in the time domain by utilizing the orthogonality of coherent Hermite-Gaussian pulses. As a result, it is possible to expand the capacity that can be transmitted per single wavelength without using TDM. In addition, by combining the present invention with TDM, WDM, and SDM technology using multicore fiber and multimode fiber, it is possible to provide a larger capacity transmission system. [Explanation of symbols]

[0049] 1 Pulsed light source 2 Optical Modulator 3 Polarization multiplexing circuit 4. Optical fiber transmission line 5. Local pulse light source 6 90 degree optical hybrid circuit 7. Balanced Photodetector 8 Digital signal processing circuit

Claims

1. A time-domain mode multiplexing transmission method using coherent Hermite-Gaussian pulses whose amplitudes are given by Hermite-Gaussian functions as signal light and local light.

2. 2. The time domain mode multiplexing transmission method according to claim 1, wherein N coherent Hermite-Gaussian pulses of orders 0 to N-1 are generated in a time slot for one symbol as the coherent Hermite-Gaussian pulses and transmitted simultaneously.

3. 3. The time domain mode multiplexing transmission method according to claim 2, wherein the N coherent Hermite-Gaussian pulses are synchronized with each other in the time domain.

4. 3. The time domain mode multiplexing transmission method according to claim 2, wherein an m-th order coherent Hermitian Gaussian pulse among the N coherent Hermitian Gaussian pulses is used as the local light, signal light in which the N coherent Hermitian Gaussian pulses are multiplexed is subjected to homodyne coherent detection, and the detected signal after detection is integrated over a time slot for one symbol, thereby demultiplexing the m-th order coherent Hermitian Gaussian pulse from the N coherent Hermitian Gaussian pulses.

5. 3. The time domain mode multiplexing transmission method according to claim 2, wherein the N coherent Hermite-Gaussian pulses are multiplexed and transmitted with the same average power.

6. 3. The time domain mode multiplexing transmission method according to claim 2, wherein the N coherent Hermite-Gaussian pulses are multiplexed and transmitted with the same peak power.

7. a coherent Hermite Gaussian pulse generating means for generating a coherent Hermite Gaussian pulse having an amplitude given by a Hermite Gaussian function; a signal light generating means for generating the coherent Hermite-Gaussian pulse as a signal light; a local light generating means for generating the coherent Hermite-Gaussian pulse as local light; a detection / separation / demodulation means for detecting, separating, and demodulating the signal light and the local light; A time domain mode multiplexing transmission device comprising:

8. The time domain mode multiplexing transmission device according to claim 7, characterized in that the coherent Hermite Gaussian pulse generating means is configured to generate N coherent Hermite Gaussian pulses of orders 0 to N-1 in a time slot for one symbol and transmit them simultaneously.

9. 9. The time domain mode multiplexing transmission apparatus according to claim 8, wherein said coherent Hermite-Gaussian pulse generating means is configured to synchronize said N coherent Hermite-Gaussian pulses with each other in the time domain.

10. the signal light generating means generates the signal light by multiplexing the N coherent Hermite-Gaussian pulses; the local light generating means sets an m-th order coherent Hermite-Gaussian pulse among the N coherent Hermite-Gaussian pulses as the local light; the detection / separation / demodulation means is configured to perform homodyne coherent detection of the signal light and the local light, and to integrate the detected signal over a time slot for one symbol, thereby demultiplexing the m-th order coherent Hermite-Gaussian pulse from the N coherent Hermite-Gaussian pulses.

9. A time domain mode multiplex transmission device according to claim 8.

11. 9. The time domain mode multiplexing transmission apparatus according to claim 8, wherein said coherent Hermite-Gaussian pulse generating means is configured to multiplex and transmit said N coherent Hermite-Gaussian pulses with the same average power.

12. 9. The time domain mode multiplexing transmission apparatus according to claim 8, wherein said coherent Hermite-Gaussian pulse generating means is configured to multiplex and transmit said N coherent Hermite-Gaussian pulses with the same peak power.

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