CN101465692A - Modulation method and transmission device for single sideband optical signal of optical OFDM system - Google Patents

Abstract

The invention discloses a modulation method and an optical single sideband transmitting device for realizing single sideband optical signal through optical I and Q modulation in an optical orthogonal frequency division multiplexing system. This SSB modulation method and transmitting device only need to meet the following conditions—the electrical modulation signal input to the optical I, Q modulator Q road

In the case where (t) is the Hilbert transform of the I-channel input electrical modulation signal g(t) (g(t) is an arbitrary real signal), the optical Single sideband modulation; simultaneously the modulation method and the transmitting device of this single sideband optical signal can be applied in the orthogonal frequency division multiplexing (OFDM) system of light, it is characterized in that, not only applicable to the OFDM system of baseband, also applicable to For OFDM systems with radio frequency modulation. The invention has the advantages of simple structure, low cost, low signal processing requirement and compatibility with existing systems.

Description

Modulation method and transmitting device of single sideband optical signal in optical OFDM system

technical field

The invention relates to a novel modulation method and an optical SSB transmitting device for realizing SSB optical signals through optical I and Q modulation in an optical OFDM system, belonging to the category of optical fiber communication systems.

Background technique

Since the mid-1990s, the great success of the commercialization of the Internet has prompted the data communication business volume to maintain a double-digit or even triple-digit growth rate, and with the continuous development and maturity of some new data services in the network (for example: IPTV business, video on demand VOD business, etc.), it can be expected that this growth rate will continue. The continuous development of data communication services brings about an increasing demand for transmission capacity and transmission bandwidth. At present, the rate requirement for a single-channel optical transmission system has been increased from 10Gbit/s to 40Gbit/s or even 100Gbit/s. As we all know, increasing the traditional 10Gbit/s transmission system to 40Gbit/s or 100Gbit/s will face many challenges: 1) In the traditional 10Gbit/s transmission system, the intensity modulation-direct detection scheme (IM- DD), when using this scheme to transmit 40/100Gbit/s data, its spectral width becomes larger, the chromatic dispersion tolerance becomes 1/16 (1/100) of the original, and the PMD tolerance becomes the original 1 /4 (1/10), the nonlinear tolerance of the system also deteriorates sharply; 2) As the speed increases, the design and development of electronic devices becomes more difficult, and the requirements for optical devices will also increase, which will increase the cost of the system ; 3) Because the frequency spectrum becomes wider, the original DWDM system cannot be compatible with this single channel. In order to solve these problems, in recent years, researchers have gradually begun to study whether the technology existing in wireless can be introduced into the field of optical communication to solve these problems. Optical Orthogonal Frequency Division Multiplexing (O-OFDM) technology is based on this proposed for the purpose.

OFDM technology is a multi-carrier modulation (MCM) technology. It is a high-speed transmission technology widely adopted by communication standards such as IEEE 802.11G in wireless communication. It is a modulation technology with the highest spectrum utilization rate known so far. Its basic principle is: decompose the high-speed serial data stream into several parallel low-speed sub-data streams for simultaneous transmission; and in the frequency domain, it can be described as: divide a given channel into many orthogonal and overlapping sub-streams in the frequency domain Sub-channels, one sub-carrier is used for modulation on each sub-channel, and the carriers of each sub-channel are orthogonal to each other and transmitted in parallel.

If OFDM technology is introduced into the 40/100Gbit/s system, due to its basic principles and essential characteristics, it will bring many advantages to the high-speed transmission system: 1) Strong ability to resist chromatic dispersion and polarization mode dispersion ; 2) Higher spectrum utilization. These two points just overcome the above-mentioned main constraints generated when transmitting 100Gbit/s high-speed data in the traditional 10Gbit/s system, so optical OFDM technology is expected to occupy an important position in the next generation of optical communication systems.

At present, OFDM-based high-speed optical transmission systems mainly include two implementation schemes: coherent optical OFDM technology (CO-OFDM) and incoherent optical OFDM technology (IO-OFDM). CO-OFDM means that the receiving end of the system uses coherent demodulation, and IO-OFDM means that the receiving end of the system uses traditional direct detection. As far as the effect of suppressing dispersion is concerned, the use of CO-OFDM and IO-OFDM is similar, but if IO-OFDM is used, while effectively suppressing dispersion and polarization mode dispersion, the cost performance of the system is relatively high, so it is currently a major research hotspots. The main analysis here is the IO-OFDM system.

As mentioned earlier, dispersion is a major limiting factor in high-speed optical transmission systems, which is caused by the nature of dispersion, and when the spectrum of the transmitted signal is wider and the transmission distance is longer, the impact of dispersion on it is greater. bigger. Therefore, for the IO-OFDM system, when transmitting 40bit/s or 100Gbit/s, in order to further improve the system's ability to resist dispersion, the double-sideband signal should generally be converted into a single-sideband optical OFDM signal. There are currently two methods for generating SSB in the IO-OFDM system:

1) Modulate the baseband OFDM signal into the radio frequency domain first, and then filter out a sideband by using an optical filter.

2) Perform a series of signal processing on the baseband OFDM signal, and then use the processed signal to modulate a Mach-Zehnder modulator to achieve.

During the research and practice of the prior art, the inventors of the present invention have found that these two implementation methods have the following disadvantages:

Method 1): This technology mainly includes two disadvantages: first, it is difficult to realize the optical filter, and the cost is high; second, if the baseband signal is first transferred to the radio frequency domain and then transferred to the optical domain, it will increase the system In this case, the purpose of achieving strong anti-dispersion by using SSB to reduce the bandwidth of the system will be relatively weakened.

Method 2): Although this technology avoids the use of optical filters to generate SSBs, and can transmit baseband OFDM signals to reduce bandwidth requirements, the system needs to perform more complex signal processing on the original signals in order to obtain SSBs suitable for generating SSBs. The input electrical modulation signal of the optical signal, especially in the case of simulating optical transmission (especially subcarrier optical transmission), the original signal processing is more complicated. In this way, the complexity of the system is increased, and the difficulty of signal processing is increased.

In order to overcome the above disadvantages, the present invention proposes a modulation method for realizing single-sideband optical signals through optical I and Q modulation in an optical OFDM system.

Contents of the invention

In view of the above-mentioned shortcomings of the prior art, the present invention provides a modulation method and an optical SSB transmitting device for realizing SSB optical signals through optical I and Q modulation in an optical OFDM system, which can not only The cost is reduced, the complexity of system signal processing is reduced, and it can be compatible with current commercial optical I and Q modulation systems.

First, a brief introduction to the I and Q modulation of light: the I and Q modulation of light is a coherent modulation method of light, which is to drive two parallel optical external modulators (such as Mach-Zehnder modulators) The electrical signal on the Q circuit is modulated to the optical carrier, which is generally applicable to QPSK (Quadrature Phase-ShiftKeying, four-phase phase-shift keying), DQPSK (Difference Quadrature Phase-Shift Keying, differential quadrature phase-shift keying), M- ary QAM (M-ary Quadrature Amplitude Modulation, M-ary Quadrature Amplitude Modulation, M-ary Quadrature Amplitude Modulation) and other modulation types of coherent demodulation systems, and there are currently commercially available integrated modules, which are relatively simple to use. The optical external modulator in the present invention mainly adopts a double-arm driven Mach-Zehnder modulator (MZ modulator).

)MZ调制器上下臂的偏置电压设为：-V_π/2；4)光的I、Q调制器的输出结果满足与 $\mathrm{A\; exp}\left({2\mathrm{\πf}}_{\mathrm{carrier}}t\right)\×[1+g\left(t\right)+j\×\hat{g}\left(t\right)]$ (f_carrier为光载波)的单边带光信号的形式。According to one aspect of the present invention, a novel modulation method and transmitting device for realizing single-sideband optical signals through optical I and Q modulation are provided, and it is characterized in that, 1) the modulation method and transmitting device only need one Optical I, Q modulators; 2) For the electrical modulation signals input to the I and Q circuits of the optical I and Q modulators, the electrical modulation signals must meet: the signal on the Q circuit is the Hilbert transform of the I signal g(t), g(t) is an arbitrary real signal, and vice versa; 3) For the I and Q input electrical modulation signals, the I and Q MZ modulators correspond to The bias voltage needs to meet: the bias voltage of the upper and lower arms of the I channel (transmission g(t)) of the MZ modulator is set to: -V _π /4, and the Q channel (transmission g(t)

) The bias voltage of the upper and lower arms of the MZ modulator is set to: -V _π /2; 4) The output results of the optical I and Q modulators meet the requirements of $\mathrm{A\; exp}\left({2\mathrm{\πf}}_{\mathrm{carrier}}t\right)\×[1+g\left(t\right)+j\×\hat{g}\left(t\right)]$ (f _carrier is an optical carrier) in the form of a single sideband optical signal.

According to another aspect of the present invention, a novel modulation method and transmitting device for realizing single-sideband optical signals through optical I and Q modulation are provided, which can be applied to optical Orthogonal Frequency Division Multiplexing (OFDM) systems Among them, it is characterized in that it is not only applicable to baseband OFDM systems, but also applicable to radio frequency modulated OFDM systems.

The present invention realizes the single sideband optical signal through the optical I, Q modulator and has the following significant advantages:

1) The present invention can avoid the use of optical filters and reduce costs;

2) The present invention can be used as an electrical modulation signal of an optical external modulator to generate a single sideband optical signal without performing too much processing on the original signal, thereby reducing the difficulty of signal processing;

3) The optical I and Q modulators used in the present invention can be compatible with many modulation systems at present;

4) The present invention can adopt simple direct detection or self-difference detection at the receiving end.

Description of drawings

In order to illustrate the technology proposed by the present invention more clearly, the accompanying drawings that need to be used in the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. Ordinary technicians can also obtain other drawings based on these drawings without paying creative labor.

Fig. 1 is a structural diagram of a transmitting device for generating single sideband optical signals in the present invention;

FIG. 2 is a schematic diagram of a system flow at the transmitter end according to Embodiment 1 of the present invention;

Fig. 3 is the basic schematic diagram that electric domain OFDM signal produces among the present invention;

FIG. 4 is a schematic diagram of generating a single sideband optical signal modulation according to Embodiment 1 of the present invention;

Figures 5 to 7 are schematic diagrams of the frequency spectrum of the electrical domain baseband signal, the schematic diagram of the double sideband spectrum of the optical domain signal, and the schematic diagram of the single sideband in Embodiment 1 of the present invention;

FIG. 8 is a schematic diagram of a system flow diagram at the transmitter end according to Embodiment 2 of the present invention;

FIG. 9 is a schematic diagram of generating a single sideband optical signal modulation according to Embodiment 2 of the present invention;

Figures 10 to 13 are respectively schematic diagrams of electric domain baseband signal and radio frequency signal spectrum, optical domain signal double sideband spectrum and single sideband spectrum in Embodiment 2 of the present invention;

Detailed ways

The following will clearly and completely describe the technical solutions of the two embodiments of the optical SSB transmitting device and the OFDM-based system of the present invention with reference to the drawings in the present invention. Apparently, the described embodiments are only some of the embodiments of the present invention, but not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

Fig. 1 shows a structural diagram of a transmitting device for generating a single sideband optical signal according to the present invention.

This device mainly uses the optical I, Q modulator 102, which mainly includes two parallel optical external modulators 107, 108, a laser 109 and a coupler 119. The optical external modulators 107 and 108 are dual-arm driven Mach-Zehnder modulators (MZ modulators); the laser 109 is used to generate an optical carrier; the coupler 119 is used to couple the optical signals output by the two MZ modulators together. The following specifically introduces how to generate a single sideband optical OFDM signal through 102 .

信号)，就可得到其对应的单边带信号：

根据这一基本理论Leonard R.Kahn 1961年在Proceedings of the IRE上提出了“Compatible SingleSideband”理论，其中指出 $\hat{g}\left(t\right)=H\left(g\left(t\right)\right)=H(1+g\left(t\right)),$ 即

仍然是一个单边带的信号。所以本发明就是通过光的I、Q调制使输入的信号g(t)和

转换成上述单边带的形式 $\mathrm{A\; exp}\left({2\mathrm{\πf}}_{\mathrm{carrier}}t\right)\×[1+g\left(t\right)+j\×\hat{g}\left(t\right)]$ (f_carrier为光载波)，从而产生单边带的光信号。具体原理如下：According to the basic theory of single sideband signals in "Digital Communications" edited by John G. Proakis, we know that for any real signal g(t), by finding its Hilbert transform (

signal), the corresponding SSB signal can be obtained:

According to this basic theory, Leonard R. Kahn proposed the "Compatible SingleSideband" theory in Proceedings of the IRE in 1961, which pointed out $\hat{g}\left(t\right)=h\left(g\left(t\right)\right)=h(1+g\left(t\right)),$ Right now

Still a SSB signal. Therefore, the present invention is to make the input signal g(t) and

Converted to the above SSB form $\mathrm{A\; exp}\left({2\mathrm{\πf}}_{\mathrm{carrier}}t\right)\×[1+g\left(t\right)+j\×\hat{g}\left(t\right)]$ (f _carrier is an optical carrier), thereby generating a single sideband optical signal. The specific principles are as follows:

The basic modulation formula for driving the MZ modulator with dual arms on the I and Q roads is:

${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; j\&pi;</span>}<span\; class="notranslate">\; \&times;</span><span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; up</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; DC</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; up</span>}}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span><span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; j\&pi;</span>}<span\; class="notranslate">\; \&times;</span><span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; low</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; DC</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; low</span>}}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Here E _in and E _out are the field strength of the input light and output light of the MZ modulator, respectively; V _π is the half-wave voltage of the MZ modulator; V _{up_in} and V _{low_in} are the input electrical modulation on the upper and lower arms of the MZ modulator, respectively Signals; V _{DC_up} and V _{DC_low} are the bias voltages on the upper and lower arms of the MZ modulator, respectively. make:

${\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; up</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; DC</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; up</span>}}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; low</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; DC</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; low</span>}}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Substitute (2)(3) into (1) to get:

${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; j\&pi;</span>}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; [</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; j\&pi;</span>}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ]</span>$

$<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; j\&pi;</span>}<span\; class="notranslate">\; \&times;</span>\frac{{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&times;</span>\frac{{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>$

$<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; j\&pi;</span>}<span\; class="notranslate">\; \&times;</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; up</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; low</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; DC</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; up</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; DC</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; low</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

$<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&times;</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; up</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; low</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; DC</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; up</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; DC</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; low</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}<span\; class="notranslate">\; )</span>$

The laser 109 is used to generate the optical carrier E _m =Aexp(j2πf _carrier t), where A is the amplitude of the optical carrier, and f _carrier is the carrier frequency. 110 is a splitter, which divides the optical carrier generated by 109 into two paths 111 and 112, both of which are equal to E _in .

Bias voltage generators 113 and 116 respectively generate bias voltages required for modulating the I-way and Q-way MZ modulators. Here 113 generates a voltage of -V _π /4, and divides it into two circuits 114 and 115 as the driving voltage of the upper and lower arms of the I-way MZ modulator; similarly, 116 generates a voltage of -V _π /2, and divides it into The two circuits 117 and 118 are used as the upper and lower arm driving voltages of the Q-channel MZ modulator.

According to the above narration, the different values of each component of the I-way MZ modulator can be obtained as:

V _{up_in_I} = V _{low_in_I} = xV _π g(t) (5)

V _{DC_up_I} = V _{DC_low_I} = -V _π /4 (6)

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; up</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; in</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; Q</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; low</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; in</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; Q</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; x</span>}\frac{\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

V _{DC_up_Q} = V _{DC_low_Q} = -V _π /2 (8)

x is a real number less than 1, multiplied by x here is to make the two input electrical modulation signals sufficiently small, thereby reducing distortion of the modulation signal.

Substituting (5) and (6), (7) and (8) into (4) respectively, we can get:

${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; I</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&times;</span>\frac{\mathrm{<span\; class="notranslate">\; x</span>}{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 4</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}<span\; class="notranslate">\; )</span>$

$<span\; class="notranslate">\; =</span>\frac{\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; \&times;</span><span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; x\; g</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; x\; g</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 9</span>}<span\; class="notranslate">\; )</span>$

$<span\; class="notranslate">\; \&ap;</span>\frac{\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; \&times;</span><span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; x\; g</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>$

${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; Q</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&times;</span>\frac{\mathrm{<span\; class="notranslate">\; x</span>}\frac{\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}<span\; class="notranslate">\; )</span>$

$<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; x</span>}\frac{\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 10</span>}<span\; class="notranslate">\; )</span>$

$<span\; class="notranslate">\; \&ap;</span>\frac{\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; x</span>}\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>$

Here because π×xg(t)<<1, so cos(π×xg(t))≈1, sin(π×xg(t))≈π×xg(t), $\sin (\mathrm{\&pi;}\&times;x\frac{\sqrt{2}}{2}\hat{g}\left(t\right))\&ap;\mathrm{\&pi;}\&times;x\frac{\sqrt{2}}{2}\hat{g}\left(t\right).$ After E _{out_I} and E _{out_Q} are obtained, they are input to the coupler 119 .

The function of the coupler 119 is to couple the optical signals output by the I and Q channels together to complete optical I and Q modulation. The basic modulation formula is as follows, we take the output terminal 1 of the coupler, namely E _{l_out} 120:

$\left(\begin{array}{c}{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; out</span>}}\\ {\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; out</span>}}\end{array}\right)<span\; class="notranslate">\; =</span>\left(\begin{array}{cc}\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}}& \mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="j"\; filenames="A200910076418E00151.png"\; state="\{\{state\}\}">j</figure-callout></span>}\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}}\\ \mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="j"\; filenames="A200910076418E00151.png"\; state="\{\{state\}\}">j</figure-callout></span>}\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}}& \frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}}\end{array}\right)\left(\begin{array}{c}{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; I</span>}}\\ {\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; Q</span>}}\end{array}\right)<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 11</span>}<span\; class="notranslate">\; )</span>$

Substitute (9) and (10) into (11) to get:

${\mathrm{E.}}_{1\_\mathrm{out}}=\frac{1}{\sqrt{2}}\&times;{\mathrm{E.}}_{\mathrm{out}1}+j\&times;\frac{1}{\sqrt{2}}\&times;{\mathrm{E.}}_{\mathrm{out}2}$ (12)

$<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; \&times;</span><span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; x\; g</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; x</span>}\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>$

E _l-out 120 conforms to the SSB form described above: $\mathrm{A\; exp}\left(2\mathrm{\&pi;}{f}_{\mathrm{carrier}}t\right)\&times;[1+g\left(t\right)+j\&times;\hat{g}\left(t\right)].$ Therefore, a single sideband optical signal E _l-out 120 is generated by the optical I, Q modulation method of the present invention.

The first embodiment of the present invention is applicable to the optical single sideband modulation mode of the baseband digital OFDM signal; the second embodiment of the present invention is applicable to the optical single sideband modulation mode of the radio frequency modulated OFDM signal.

Embodiment 1, please refer to FIG. 2 for details. FIG. 2 is a schematic flowchart of a system at the transmitter end of this embodiment.

Step 201: The system starts, first input the number sequence {a _n } that needs to be transmitted in the optical transmission system.

Step 202: According to the basic principle of OFDM, process the input {a _n } to obtain the baseband OFDM signal m(t) and its Hilbert transform signal

信号。Referring to FIG. 3, FIG. 3 is a basic schematic diagram of OFDM signal generation. How to generate m(t) and

Signal.

For the {a _n } generated in step 201, the serial/parallel converter 301 first performs a serial-to-parallel conversion to convert the original serial bit data stream into a parallel bit data stream, and then enters the signal mapping module 302 .

The purpose of the signal mapping module 302 is to complete the corresponding modulation mapping for the parallel data stream according to the modulation method adopted by each subcarrier in the actual system, and form a modulation information sequence to input to the inverse Fourier transformer 303 .

The inverse Fourier transformer 303 obtains the time-domain sampling sequence of the OFDM modulated signal in the digital domain, and then passes through the parallel/serial converter 304 .

The parallel/serial converter 304 converts the parallel input OFDM modulated signal into a serial output signal {m _n }.

Then {m _n } is divided into two paths, one path is input to the digital/analog converter (D/A) 305, and the other path is entered into the Hilbert transformer 307.

The digital/analog converter 305 is to convert the digital signal {m _n } into an analog signal 306m(t), and 306m(t) is used as an input signal of the following step 203 to drive the I-way MZ modulator of the optical I and Q modulators .

也作为后面步骤203的一个输入信号用来驱动光I、Q调制器的Q路MZ调制器。The Hilbert transformer 307 includes a digital Hilbert transformer 307 and a digital/analog converter 308 . Compared with analog signals, it is much simpler and easier to perform Hilbert transform on digital signals, and it can be completed with existing digital signal processing chips. Therefore, when OFDM signals are still digital signals, Hilbert transform is performed on them. Transform, and then perform D/A on it to convert it into an analog signal ( $h\left[m\left(t\right)\right]=\hat{m}\left(t\right)$ ).

It is also used as an input signal in step 203 to drive the Q-way MZ modulator of the optical I and Q modulators.

信号分别驱动光的I、Q调制器的I路和Q路，从而产生一个单边带光的基带OFDM信号。参见图4，图4为产生单边带光的基带OFDM信号调制示意图。Step 203: m(t) and

The signals drive the I and Q channels of the optical I and Q modulators respectively, thereby generating a single-sideband optical baseband OFDM signal. Referring to FIG. 4, FIG. 4 is a schematic diagram of baseband OFDM signal modulation for generating single sideband light.

都是实信号，所以它们可以分别相当于图1单边带光信号发射装置中的两个输入信号100g(t)和

所以通过调制光的I、Q调制器即可实现图4中的单边带调制方法。Since m(t) and

are real signals, so they can be respectively equivalent to the two input signals 100g(t) and

Therefore, the SSB modulation method in Fig. 4 can be realized by modulating the light I and Q modulators.

The laser 404 in the optical I and Q modulator 401, the MZ modulators 402 and 403 on the I road and the Q road, the bias voltage modules 405 and 406 of the MZ modulator on the I road and the Q road, and the optical coupler 407 are respectively equivalent to The laser 109 in Fig. 1, the MZ modulator 107 and 108 on the I road and the Q road, the bias voltage module 113 and 116 of the MZ modulator and the optical coupler 119 on the I road and the Q road, and the initial value of these corresponding modules The settings are the same. The only difference is the input electric modulation signal on the I and Q circuits, but the meanings of 306, 309 and 100, 101 are the same. Therefore, the specific principle will not be repeated here. The output terminal 408 of the coupler is the same as 120 in FIG. 1 , which is a single sideband optical baseband OFDM signal.

FIG. 5 , FIG. 6 and FIG. 7 respectively describe a schematic diagram of a frequency spectrum of an electrical domain baseband signal, a schematic diagram of a double sideband spectrum of an optical domain signal, and a schematic diagram of a single sideband signal in this embodiment. From these three figures, it can be seen intuitively that when the electrical signal is baseband, the spectrum distribution of the optical single-side signal relative to the double-sideband signal comes.

Step 204: Input the generated SSB optical OFDM signal E _{l_out} into the optical fiber.

The embodiment of the present invention generates a single-sideband optical baseband OFDM signal through an optical I and Q modulation method. The single-sideband optical signal modulation method is simple, the system has strong anti-dispersion ability, and increases the transmission distance of the system.

In practical applications, there is also a method of modulating an OFDM signal in the radio frequency domain onto an optical carrier for single sideband transmission. The following embodiment 2 will describe the actual application process in detail.

Embodiment 2, refer to FIG. 8 for details. FIG. 8 is a schematic flowchart of a system at the transmitter end of this embodiment.

Step 801: The system starts, first input the number sequence {a _n } that needs to be transmitted in the optical transmission system.

Step 802: According to the basic principle of Orthogonal Frequency Division Multiplexing (OFDM), process the input {a _n } to obtain the baseband OFDM signal m(t) and its Hilbert transform signal

信号309。Referring to FIG. 2, FIG. 2 is a basic schematic diagram of OFDM signal generation. The specific generation steps and method are the same as step 202 in the first embodiment, and will not be repeated here. After step 802 still produces m(t) signal 306 and

Signal 309.

Step 803: Modulate the baseband OFDM signal into the radio frequency domain.

信号309并行输入到图9的模块901中进行射频调制，具体方法参考图9。To modulate the baseband signal into a radio frequency signal, the traditional method is to multiply the original signal by a radio frequency carrier Acos(2πf _RF t) (A is the amplitude of the carrier, and f _RF is the radio frequency frequency). Here, in order to generate SSB optical signals more easily in the future, the m(t) signal 306 and

The signal 309 is input in parallel to the module 901 in FIG. 9 for radio frequency modulation. Refer to FIG. 9 for the specific method.

Figure 9 mainly includes two parts, the first part 901 is to complete the modulation of the baseband OFDM signal to the radio frequency domain, and the second part 902 is to perform optical I and Q modulation to generate a single sideband optical signal.

信号309通过乘法器906与射频载波产生器904相乘得到：m(t)×sin(2πf_RFt)成为射频信号810。且将908和910分别输入到第二部分902完成步骤804的任务。The first part 901 is introduced here, and the m(t) signal 306 is multiplied by the multiplier 905 and the radio frequency carrier generator 903 to obtain: m(t)×cos(2πf _RF t) becomes the radio frequency signal 908;

The signal 309 is multiplied by the multiplier 906 and the radio frequency carrier generator 904 to obtain: m(t)×sin(2πf _RF t) becomes the radio frequency signal 810 . And input 908 and 910 respectively into the second part 902 to complete the task of step 804 .

Step 804: Input the modulated radio frequency OFDM signal into an optical I, Q modulator to generate a single sideband optical signal. The specific method mainly refers to module 902 in FIG. 9 .

First input to 902 are m(t)×cos(2πf _RF t) signal 908 and m(t)×sin(2πf _RF t) signal 910 generated in step 803 . According to "Communication Principles", we know:

H[m(t)×cos(2πf _RF t)]=m(t)×sin(2f _RF t) (13)

That is, the Hilbert transform of 908 is 910. In this way, 908 and 910 are equivalent to the signals 100 and 101 in the SSB optical signal transmitting device in FIG. 1 , so the SSB modulation method in the module 902 can be realized by modulating the light I and Q modulators.

The laser 904 in the module 902, the MZ modulators 912 and 913 on the I and Q routes, the bias voltage modules 914 and 915 of the MZ modulators on the I and Q routes, and the optical coupler 918 are respectively equivalent to the laser 109 in FIG. 1 , the MZ modulators 107 and 108 on the I and Q routes, the bias voltage modules 113 and 116 of the MZ modulators on the I and Q routes, and the optocoupler 119, and the initial values of these corresponding modules are set to be the same of. The only difference is the input electrical modulation signal on the I and Q circuits, but the meanings of 908, 910 and 100, 101 are the same. Therefore, the specific principle and process will not be repeated here. The output terminal 920 of the coupler is the same as 120 in FIG. 1 , which is a single sideband optical RF domain OFDM signal.

FIG. 10 , FIG. 11 , FIG. 12 and FIG. 13 respectively describe a schematic diagram of a spectrum of an electrical domain baseband signal, a schematic diagram of a spectrum of a radio frequency signal, a schematic diagram of a double sideband spectrum of an optical domain signal, and a schematic diagram of a single sideband in this embodiment. From these three figures, it can be seen intuitively that when the electrical signal is a frequency band, the spectrum distribution of the optical unilateral signal is relative to that of the double-sided band signal.

Step 805: Input the generated SSB optical OFDM signal into the optical fiber.

The method and transmitting device for generating single sideband optical signals through optical I and Q modulation of the present invention have been described in detail above, and the descriptions of the above embodiments are only used to help understand the method of the present invention and its core idea; At the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation and application scope. In summary, the content of this specification should not be construed as limiting the present invention. Various obvious changes made to the method without departing from the spirit of the method described in the present invention and the scope of the claims are within the protection scope of the present invention.

Claims (8)

1. A novel modulating method and transmitting device for realizing a single sideband optical signal through optical I and Q modulation, characterized in that: Only one optical I, Q modulator is needed. The optical I, Q modulator is to modulate the electrical signals on the I and Q circuits to the optical carrier by driving two parallel optical external modulators (the dual-arm driven MZ modulator is used here). . 2. According to claim 1, a novel modulating method and transmitting device for realizing single sideband optical signal through optical I, Q modulation, is characterized in that: For any input real signal g(t) and its Hilbert transform They are respectively used as the input electrical modulation signals of the I and Q circuits of the optical I and Q modulators, and can be converted into similar signals by modulating the optical carrier $\mathrm{Aexp}\left(2\mathrm{\&pi;}{f}_{\mathrm{carrier}}t\right)\&times;[1+g\left(t\right)+j\&times;\hat{g}\left(t\right)]$ The SSB optical signal form (f _carrier is the optical carrier), thus generating optical SSB modulation. 3. According to claim 1 and claim 2, a novel modulation method and transmitting device for realizing single sideband optical signals through optical I and Q modulation, for the input electrical modulation signals of I and Q circuits, I and Q The bias voltage corresponding to the MZ modulator of the road is characterized in that: The bias voltage of the upper and lower arms of the I-way MZ modulator is set to: -V _π /4 The bias voltage of the upper and lower arms of the Q-way MZ modulator is set to: -V _π /2. 4. According to claims 1-3, a novel modulation method and transmitting device for realizing single-sideband optical signals through optical I and Q modulation, applicable to optical orthogonal frequency division multiplexing (OFDM) The system is characterized by: Not only applicable to baseband OFDM system, but also applicable to OFDM system of radio frequency modulation; After the digital OFDM signal is generated, it is subjected to Hilbert transformation. 5. The modulation method for realizing the OFDM signal of single sideband light through the I and Q modulation of light according to claim 4, characterized in that, after the digital OFDM signal is generated, the Hilbert method is performed on it. The specific steps of transformation are: Step 1: Divide the generated digital baseband OFDM signal {m _n } into two paths; Step 2: perform digital/analog conversion (D/A) all the way to obtain the baseband OFDM signal m(t); Step 3: The other way first performs the Hilbert transform in the digital domain, and then performs the digital/analog conversion to obtain

$(h\left[m\left(t\right)\right]=\hat{m}\left(t\right)).$ 6. According to claim 2, 4, and 5, the modulation method for realizing single-sideband optical OFDM signal through optical I, Q modulation, the electrical modulation of the baseband OFDM system input to the optical I, Q modulator signal, characterized by: The I-way and Q-way input electrical modulation signals input to the optical I and Q modulators are respectively: xm(t),

(x is a real number less than 1). The purpose of multiplying by x here is to make the two input electrical modulation signals small enough to reduce the distortion of the modulation signal. 7. According to claim 2-5, the method for modulating the OFDM signal of single-sideband light through optical I and Q modulation, the electrical modulation of the RF-modulated OFDM system input to the optical I and Q modulator signal, characterized by: First, the obtained baseband OFDM signal m(t) and its Hilbert transform

Multiplied by the RF carrier, modulated into the RF domain, and then used as the input electrical modulation signals of the optical I and Q modulators respectively, that is, the I path: xm(t)×cos(2πf _RF t); the Q path:

(x is a real number less than 1). The purpose of multiplying by x here is to make the two input electrical modulation signals small enough to reduce the distortion of the modulation signal. 8. According to claim 1-7, the modulation method for realizing the OFDM signal of single sideband light through optical I, Q modulation, for the input OFDM electrical modulation signal of I, Q path, I, Q path MZ modulator The corresponding bias voltage is characterized by: The bias voltage of the upper and lower arms of the I-way MZ modulator is set to: -V _π /4 The bias voltage of the upper and lower arms of the Q-way MZ modulator is set to: -V _π /2.

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