CN102043255B - Polarization interference-based full-light OFDM signal multiplexing and demultiplexing device - Google Patents

Abstract

The present invention relates to a device for realizing multiplexing and demultiplexing functions for Orthogonal Frequency Division Multiplexing (OFDM) signals by using the principle of polarization interference. The demultiplexing device of the present invention consists of N-1 basic structural units

It is composed of stages in series (N is the number of subcarriers contained in the OFDM signal), and the optical signal undergoes polarization splitting, time delay and phase shift, and polarization interference in each basic unit; the inverted use of the demultiplexing device is multiplexing The optical signal can realize the operation functions of Fourier inverse transform and Fourier transform respectively for the data sequence information carried by the optical signal through the multiplexing and demultiplexing device. The invention adopts the all-optical method to complete the Fourier transform and inverse transform operation functions required for OFDM signal multiplexing and demultiplexing, effectively eliminating the limitation of electronic processing speed; compared with other all-optical OFDM methods, this realization device has strong expandability and is easy to implement For the multiplexing and demultiplexing of sub-channel signals when the number of optical carriers is large, it has adjustable functions and strong flexibility.

Description

All-optical OFDM signal multiplexing and demultiplexing device based on polarization interference

technical field

The invention belongs to a signal processing device in an optical communication system, and specifically relates to an optical device based on polarization interference, which completes fast Fourier transform (FFT) and inverse transform (IFFT) in an all-optical form, and realizes orthogonal frequency division multiplexing Multiplexing and demultiplexing of (OFDM) signals.

Background technique

With the popularization of high-speed Internet and the rapid development of various communication services, the global information transmission volume is growing explosively, which puts forward higher requirements for the transmission performance of optical communication networks. The research and application of advanced optical modulation technology is very important to realize the transmission of ultra-large capacity and ultra-long-distance optical signals.

OFDM is a multi-carrier multiplexing technology. By performing serial-to-parallel conversion processing on the data at the receiving end of the system, the high-speed signal transmitted in the single-channel link is converted into multiple low-speed sub-channel signals modulated or demodulated in parallel. Strong interference capability, high spectral efficiency, good dispersion tolerance, etc., have great application prospects in high-speed long-distance optical communication systems. OFDM has been widely used in wireless communication systems. It uses electronic devices to perform inverse fast Fourier transform and Fourier transform to realize signal multiplexing and demultiplexing. This method is costly to implement and is limited by electrical processing speed. Realizing OFDM in an all-optical form can effectively reduce the requirements on the operating speed of electronic devices at the transceiver end of the system, and has a good application prospect in ultra-high-speed optical signal processing.

At present, some achievements have been made in the research of all-optical OFDM system at home and abroad. For example, the Chinese invention patent "All-optical Fourier Transformer, Inverse Transformer and an Orthogonal Frequency Division Multiplexing System" proposes to use a planar waveguide coupler structure to realize all-optical discrete Fourier transform and its inverse transform operation; and For example, literature (see Arthur James Lowery, "Design of arrayed-waveguide grating routers for use as optical OFDM demultiplexers," Opt. Express 18, 14129-14143, 2010) proposes to achieve the same function based on the waveguide grating routing structure. Both of the above two device structures are relatively complex and have no expandability, and it is difficult and costly to implement multiplexing and demultiplexing of OFDM signals containing a large number of subcarriers. In addition, the thermo-optic effect of the silicon-based waveguide is used in the coupler structure to introduce the phase shift of each branch, which is more complicated to realize; the structure of the waveguide grating routing device is fixed, without adjustable function, and the flexibility is poor.

Contents of the invention

The present invention proposes an optical device that realizes Fourier transform and its inverse transform function based on the polarization interference effect, realizes multiplexing and demultiplexing of multiple subcarriers in an all-optical manner, and can effectively alleviate OFDM at the transceiver end of a high-speed optical communication system. The dependence on electronic devices in the signal processing process also has the advantages of strong scalability and good flexibility.

级串联形式组成，第k级共有

个并联基本单元，k为正整数且

，N为OFDM信号子载波的个数；每个基本单元包括输入光纤准直器、偏振分束器、半波片、相位延迟器、偏振分波、合波器件以及输出光纤准直器； A kind of OFDM signal demultiplexing device realizing all-optical fast Fourier transform of the present invention is characterized in that: it is mainly composed of N-1 basic units

It is composed of stages in series, and the kth stage has a total of

parallel basic units, k is a positive integer and

, N is the number of OFDM signal subcarriers; each basic unit includes an input fiber collimator, a polarization beam splitter, a half-wave plate, a phase retarder, a polarization splitter, multiplexer and an output fiber collimator;

The phase retarder is composed of a time-delay crystal and a phase-shift crystal, and the time-delay crystal refers to a birefringent crystal that causes a certain relative time delay between a pair of orthogonal linearly polarized lights after polarization splitting; the phase A shift crystal refers to a birefringent crystal that introduces a specific phase difference between a pair of orthogonal linearly polarized lights after a time-delay crystal;

The length of each basic unit delay crystal in the kth level is: ,

为晶体双折射率差； where c is the speed of light,

is the crystal birefringence difference;

个并联基本单元中第i个基本单元的相移晶体长度为：

，其中

，

为子信道中心波长，i为正整数且

。 at class k

The phase-shift crystal length of the i-th basic unit in parallel basic units is:

,in

,

is the center wavelength of the subchannel, i is a positive integer and

.

The present invention carries out following conversion to signal:

表示系统接收端输入OFDM信号在码元时间T内的n个等间隔采样值，即时域数据序列；为

经过OFFT之后的频域数据序列，即

在时间T内唯一对应的子信道信号频率分量，m为子信道标号。 In the formula,

Indicates that the receiving end of the system inputs the OFDM signal n equal-spaced sampling values within the symbol time T, the instant domain data sequence; for

The frequency domain data sequence after OFFT, namely

The unique corresponding sub-channel signal frequency component within time T, m is the sub-channel label.

级基本单元处理后转化为N束信号光由不同的光纤准直器输出，完成N个子载波的分离；光纤准直器保证信号光以平行光方式实现偏振干涉过程，并将分离后提取的子信道信号耦合进光纤。 The signal light is coupled into the first-level basic unit by the fiber collimator, and the arbitrary polarization state signal is converted into two orthogonal linearly polarized lights separated in space by the polarization beam splitter and the half-wave plate, and the two are phase-delayed After the delay and phase shift related to the wavelength are generated by the device, the polarized light interference phenomenon occurs in the components with a certain phase difference in the same polarization direction, and the interference results of different wavelengths are different. The orthogonal linearly polarized light is coupled into the next-level basic unit by the collimator; each basic unit performs polarization splitting, introduces relative phase difference and polarized light interference process on a beam of input light incident to the structure, and outputs The two beams of light are spatially separated; thus the whole device passes a beam of signal light to be demultiplexed through

The first-level basic unit is converted into N beams of signal light after being processed by different fiber collimators to complete the separation of N subcarriers; the fiber collimator ensures that the signal light realizes the polarization interference process in the form of parallel light, and separates the extracted The channel signal is coupled into the optical fiber.

The polarizing beam splitter can be a displacement crystal, which splits the signal light incident on the structural unit into a pair of orthogonal linearly polarized lights, that is, ordinary light and extraordinary light (o light and e light), and the half-wave plate can be used to Convert the two into the same polarization state to realize the processing of any polarization state signal; the polarization splitter and multiplexer device can be composed of two displacement crystals and a half-wave plate to realize the polarization interference result in a pair of orthogonal Linearly polarized light output.

：主要由

个基本单元级联组成，N为OFDM信号子载波的个数；每个基本单元包括输入光纤准直器、偏振分束器、半波片、相位延迟器、偏振分波、合波器件以及输出光纤准直器； Based on the same idea, the present invention also proposes an OFDM signal demultiplexing device that realizes all-optical fast Fourier transform and has an adjustable function, which can realize separate demultiplexing of any subcarrier contained in the OFDM signal with switching function, characterized in that

:Mainly by

It consists of cascaded basic units, and N is the number of OFDM signal subcarriers; each basic unit includes an input fiber collimator, a polarization beam splitter, a half-wave plate, a phase retarder, a polarization splitter, a multiplexer, and an output Fiber collimator;

The phase retarder is composed of a time-delay crystal and a phase-shift crystal with an adjustable structure. The time-delay crystal refers to a birefringence that causes a certain relative time delay between a pair of orthogonal linearly polarized lights after polarization splitting. crystal;

， The delay crystal length of the basic unit of the kth level is:

,

where c is the speed of light, is the crystal birefringence difference;

的

个结果中选择取值，调节光楔结构对应不同i值即可确定该有效厚度。其中

，

为子信道中心波长，

为晶体双折射率差。 The phase-shift crystal refers to a birefringent crystal that introduces a specific phase difference between a pair of orthogonal linearly polarized lights after passing through a time-delay crystal. The phase-shift crystal is an optical wedge structure, and its optical axis is parallel to the crystal surface. And perpendicular to the incident direction of the light beam, a mechanically adjustable device capable of longitudinally moving the light wedge controls the effective thickness of the light beam passing through the light wedge, and the effective thickness of the phase-shift crystal with the light wedge structure in the kth basic unit is the same as the Corresponding to the number of subcarriers, its thickness is in

of

The effective thickness can be determined by selecting a value from one result and adjusting the optical wedge structure corresponding to different i values. in

,

is the subchannel center wavelength,

is the crystal birefringence difference.

级串联形式组成，第k级共有

个并联的基本单元，k为正整数且

，N为OFDM信号子载波的个数。复用装置中各基本单元组成器件与权利要求1所述的解复用装置基本单元组成器件完全相同，但信号通过各器件的顺序刚好倒置。所述全光OFDM信号复用装置为N×1端口器件，可看作全光解复用装置对光信号处理的逆过程。完成N个子载波复用需要串联形式的N-1个基本单元组成，每级单元组成器件的参数设置与对应解复用装置一致，其具体对信号进行如下变换： Also based on this technical idea, the present invention proposes an OFDM signal multiplexing device for realizing all-optical inverse fast Fourier transform, which is characterized in that: it mainly consists of N-1 basic units

It is composed of stages in series, and the kth stage has a total of

basic units connected in parallel, k is a positive integer and

, N is the number of OFDM signal subcarriers. The components of each basic unit in the multiplexing device are exactly the same as those of the basic unit of the demultiplexing device described in claim 1, but the order in which the signals pass through the components is just reversed. The all-optical OFDM signal multiplexing device is an N×1 port device, which can be regarded as the reverse process of the optical signal processing by the all-optical demultiplexing device. To complete the multiplexing of N subcarriers, it needs to be composed of N-1 basic units in series. The parameter settings of each level of unit components are consistent with the corresponding demultiplexing device. Specifically, the signal is transformed as follows:

表示系统发送端输入至OIFFT运算模块的N路子信道数据信号，即频域数据序列；

为

经转换后得到的时域数据序列，n为OFDM信号在一个码元周期T内的采样时刻。 In the formula,

Represents the N sub-channel data signals input to the OIFFT operation module by the system sending end, that is, the frequency domain data sequence;

for

In the time-domain data sequence obtained after conversion, n is the sampling moment of the OFDM signal within one symbol period T.

The present invention has the following advantages: compared with using electronic devices to perform Fourier transform and inverse transform on data, this method completes the multiplexing and demultiplexing of OFDM signals in an all-optical manner, effectively alleviating the impact of electronic rate on signals in high-speed optical communication systems. processing limitations; compared with other all-optical OFDM methods, this implementation device has strong scalability, and it is easy to realize the multiplexing and demultiplexing processing of OFDM signals when the number of optical carriers is large, and it has adjustable functions, and its simplified structure does not change The separate extraction of any sub-channel signal can be realized under the condition of the device composition, and the flexibility is strong; in addition, the device is composed of cascaded passive devices, the structure is relatively compact, and the realization process is mature.

Description of the drawings

Fig. 1 is a functional schematic diagram of the basic unit of the device;

Figure 2 (1) is a schematic structural diagram of an OFDM all-optical demultiplexing device;

Figure 2 (2) is a schematic diagram of the structural composition of the basic unit in Figure 2 (1);

Fig. 3 is a structural schematic diagram of an adjustable device for separately extracting one subcarrier in an OFDM signal;

Fig. 4 is the structural representation of OFDM all-optical multiplexing device;

Fig. 5(1) and Fig. 5(2) are two application example diagrams of the present invention.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings.

Fig. 1 is a functional schematic diagram of the basic unit of the device of the present invention. The polarization beam splitter performs polarization splitting on the input signal, and after delay and phase shift processing, two beams of linearly polarized light with a phase difference are obtained. The polarization interference effect occurs between the two, and the output result after multi-level interference is equivalent to the OFFT operation function. When the device is used upside down, it is equivalent to the OIFFT operation function. The transfer function of the basic unit is:

in is produced by a time-delay crystal, and the length of the time-delay crystal in the k-th basic unit is:

（ k为正整数且

）  （1）

( k is a positive integer and

) (1)

为晶体双折射率差； c is the speed of light,

is the crystal birefringence difference;

个并联基本单元中第i个基本单元的相移晶体长度分别为： at class k

The phase-shift crystal length of the i-th basic unit in parallel basic units They are:

           （2）

(2)

，

为子信道中心波长，i为正整数且

。 in

,

is the center wavelength of the subchannel, i is a positive integer and

.

个并联基本单元中第i个基本单元的相移晶体产生的附加相移值

分别为： Then the k-th level

The additional phase shift value produced by the phase shift crystal of the i-th basic unit in parallel basic units

They are:

           （3）

(3)

级串联结构的N-1个基本单元组成，为1×N端口器件，每个基本结构单元标号为

，它表示该基本单元为串联结构中的第k级中并联的第i个基本单元（i为正整数且

）。如图2所示，该装置用光纤准直器11将接收端输入信号以平行光形式耦合进入第一级基本单元

，每个基本单元均由偏振分束器件、相位延迟器件和偏振分波、合波器件构成。偏振分束器包括位移晶体12和半波片13，入射光经位移晶体12发生双折射而分束为偏振态正交的两束线偏振光（o光和e光），其中一路光的偏振态经半波片13旋转90°后与另一路出射光偏振态一致。在空间上分离且具有相同偏振态的两束光一起通过由延时晶体14和相移晶片15构成的相位延迟器，两者之间产生特定相位差，在同一偏振方向上具有一定相位差的分量发生干涉，不同波长光的干涉结果不同，将以一对正交线偏振光形式输出。通过偏振分波、合波器件将此干涉结果分别输出：经相位延迟器后的出射光经位移晶体12后形成四束线偏振光，将具有相同光谱成分的线偏振光用半波片13转化为同一偏振态，再由位移晶体12将其合束，从而此四束光合为一对正交线偏振光分别由两个并联的光纤准直器11耦合入射进入下一级基本单元。信号光经过第二级基本单元的处理过程与第一级类似，只是其中延时晶体14和相移晶片15结构参数不同，具体参数按照式（1）和式（2）设置。每个基本单元均对入射的一束信号光进行偏振分光、引入延时和相移以及偏振光干涉后将其转化为一对正交线偏振光输出，构成各级基本单元的器件完全相同但结构参数均存在差异。经第k级基本单元处理后出射光为

束，如图2（1）所述，整个装置将接收的单信道OFDM信号经过级基本单元处理后解复用为N个子信道的输出光信号分别由光纤准直器11输出，从而实现N个子载波的分离；装置中的光纤准直器11保证信号光以平行光方式完成偏振干涉过程，并将分离后提取的子信道信号耦合进光纤。 Fig. 2 is a device structure diagram for realizing all-optical demultiplexing of an OFDM signal comprising N subcarriers, which consists of

It is composed of N-1 basic units in a cascaded structure, which is a 1×N port device, and each basic structural unit is labeled as

, which means that the basic unit is the i-th basic unit connected in parallel in the k-th stage in the series structure (i is a positive integer and

). As shown in Figure 2, the device uses a fiber collimator 11 to couple the input signal at the receiving end into the first-level basic unit in the form of parallel light

, each basic unit is composed of a polarization beam splitter, a phase delay device, and a polarization splitter and multiplexer. The polarizing beam splitter includes a displacement crystal 12 and a half-wave plate 13. The incident light undergoes birefringence through the displacement crystal 12 and is split into two beams of linearly polarized light (o light and e light) with orthogonal polarization states. The polarization of one path of light is After being rotated by 90° by the half-wave plate 13, the state is consistent with the polarization state of the other outgoing light. The two beams of light that are separated in space and have the same polarization state pass through the phase retarder composed of the delay crystal 14 and the phase shift chip 15 together, and a specific phase difference is generated between the two. The components interfere, and the interference results of different wavelengths of light are different, and will be output in the form of a pair of orthogonal linearly polarized light. The interference results are respectively output through the polarization splitting and multiplexing devices: the outgoing light after the phase retarder passes through the displacement crystal 12 to form four beams of linearly polarized light, and the linearly polarized light with the same spectral composition is converted with a half-wave plate 13 They are in the same polarization state, and then combined by the displacement crystal 12, so that the four beams are combined into a pair of orthogonal linearly polarized lights, which are respectively coupled and incident by two parallel fiber collimators 11 into the next basic unit. The processing process of the signal light through the second-level basic unit is similar to the first-level, except that the structural parameters of the delay crystal 14 and the phase-shift chip 15 are different, and the specific parameters are set according to formula (1) and formula (2). Each basic unit performs polarization splitting, introduces delay and phase shift, and polarized light interference on an incident beam of signal light, and then converts it into a pair of orthogonal linearly polarized light outputs. The devices that constitute the basic units at all levels are identical but There are differences in structural parameters. After being processed by the k-level basic unit, the outgoing light is

beam, as shown in Figure 2 (1), the entire device passes the received single-channel OFDM signal through The output optical signals that are demultiplexed into N sub-channels after being processed by the first-level basic unit are respectively output by the fiber collimator 11, thereby realizing the separation of N subcarriers; the fiber collimator 11 in the device ensures that the signal light is polarized in a parallel light manner The interference process, and the sub-channel signals extracted after separation are coupled into the optical fiber.

Figure 3 is a schematic structural diagram of a demultiplexer with adjustable functions, which can essentially be regarded as a branch in the complete demultiplexer shown in Figure 2 (1). The shift chip is an optical wedge structure. By adjusting the effective thickness of the optical wedge to cause the change of the optical path difference, it can produce different phase shifts for the signal light, and obtain different combinations of phase shift values at all levels to realize the extraction of any pair of output ports. For the switching of a sub-channel signal, the number of devices required by the demultiplexing device is greatly reduced, and the structure is relatively simplified. The simplified device shown in Figure 3 can more easily demultiplex OFDM signals containing a large number of subcarriers by increasing the number of cascaded basic units without changing the physical structure of the entire device, with flexible functions and strong scalability.

级串联的N-1个基本单元组成，为N×1端口器件。组成该装置的器件与相应的解复用装置完全相同，但信号处理过程反向，即实现装置顺序倒置，可看作是图2（1）所示反方向处理过程。如图4所示，经并行调制后的N个子载波由光纤准直器11同时输入该复用装置的N个输入端口，相邻两子载波经相同的第一级基本单元处理后，出射的N/2束信号光再由光纤准直器11耦合进入下一级基本结构单元，经

级处理后的出射光即为合成的OFDM信号，可直接耦合进入光纤传输。 Fig. 4 is the structural diagram of the OFDM signal all-optical multiplexing device that synthesizes and comprises N subcarriers, and it consists of

It consists of N-1 basic units connected in series and is an N×1 port device. The devices that make up the device are exactly the same as the corresponding demultiplexing device, but the signal processing process is reversed, that is, the device sequence is reversed, which can be regarded as the reverse processing process shown in Figure 2 (1). As shown in Figure 4, the N subcarriers modulated in parallel are simultaneously input to the N input ports of the multiplexing device by the fiber collimator 11, and after the adjacent two subcarriers are processed by the same first-level basic unit, the outgoing N/2 beams of signal light are then coupled into the next basic structural unit by the fiber collimator 11, and then

The outgoing light after stage processing is the synthesized OFDM signal, which can be directly coupled into the optical fiber for transmission.

Fig. 5 is a schematic diagram of two specific application embodiments of the present invention. As shown in Fig. 5(1), the sending end and the receiving end of the system respectively use the devices described in Fig. 4 and Fig. 2 or Fig. 3 to realize multiplexing and demultiplexing of OFDM signals. The mode-locked laser 2 generates ultra-short optical pulses with a repetition frequency equal to the frequency interval of adjacent OFDM sub-channels, which are divided into N paths by the power splitter 3, and then loaded with data information by the modulator 4, and then enter the N inputs of the all-optical multiplexing device 5 port, after passing through the all-optical multiplexing device, the OFDM signal including N sub-channels is obtained, and after being processed by the optical band-pass filter 6 and the optical amplifier 7, it enters the optical fiber link 8 for transmission. The received signal enters the OFDM all-optical demultiplexing device 9 that completes the OFFT operation function after being filtered out by the optical amplifier 7 and the band-pass filter 6, and separates each sub-channel signal. If the demultiplexing device 9 is a 1×1 port device with an adjustable function as shown in FIG. 3 , only one sub-channel signal can be extracted separately. The output signal can eliminate the interference of other channels under the control of the optical sampling gate 10, and its sampling rate is equal to the symbol rate. After demultiplexing, the extracted sub-channel signals are restored by the demodulator 11 to the data signal.

As shown in Figure 5(2), N continuous lasers 12 at the transmitting end of the system output N beams of continuous optical carriers, whose frequency interval is equal to the center frequency interval of OFDM adjacent subcarriers, and the optical carriers are respectively controlled by the modulator 4 under the symbol synchronization control condition After downloading the data information, the N channels of sub-channel signals are combined by the power combiner 13 to obtain an OFDM signal. The receiving end of the system adopts the above-mentioned demultiplexing device, and its signal processing process is the same as that of the system shown in Figure 5 (1).

The above-mentioned figures are all descriptive and non-restrictive to the description of the present invention. For example, in the polarized light interference process, time delay and phase shift can not only be produced by birefringent crystals, but also can be produced by polarization beam splitters and glass components; In the basic unit of phase shift introduced by crystal, the relative phase shift value can be introduced by making the two beams of linearly polarized light after polarization splitting and delay pass through the phase shift crystal, or only one of the beams of light can pass through the crystal. The other beam is directly incident on the polarization splitting and combining devices; as shown in Figure 2 (2), the polarization splitting and combining devices can also be composed of displacement crystals and roof prism components; The pulse sequence can be obtained by combining a single continuous laser with an external modulator, where the external modulator is controlled by a clock divider to keep it synchronized with the data clock; the N independent continuous optical carriers at the transmitting end in Figure 5 (2) can be obtained by a frequency-locked comb Spectra were obtained using precision spectrum cutting techniques.

Claims (5)

1. An all-optical OFDM signal demultiplexing device based on polarization interference, characterized in that: it is mainly composed of N-1 basic units in a log ₂ N-level series connection form, and the k-level has 2 ^{k- 1} parallel basic unit, k is a positive integer and ∈[1, log ₂ N], N is the number of OFDM signal subcarriers; each basic unit includes input fiber collimator, polarization beam splitter , half-wave plate, phase retarder, polarization splitting and combining device and output fiber collimator; The phase retarder is composed of a time-delay crystal and a phase-shift crystal, and the time-delay crystal refers to a birefringent crystal that causes a certain relative time delay between a pair of orthogonal linearly polarized lights after polarization splitting; the phase A shift crystal refers to a birefringent crystal that introduces a specific phase difference between a pair of orthogonal linearly polarized lights after a time-delay crystal; The length of each basic unit delay crystal in the kth level is:

Among them, c is the speed of light, Δn is the crystal birefringence difference; T is the symbol time; The phase-shift crystal length of the i-th basic unit in the 2 ^k-1 parallel basic units of the k-th level is:

Where q=2 ^k-1 , 2 ^k-1 +1,...2 ^k -1, λ is the center wavelength of the subchannel, i is a positive integer and ∈[1,2 ^k-1 ]. 2. The all-optical OFDM signal demultiplexing device based on polarization interference according to claim 1, characterized in that: the polarization beam splitter is a displacement crystal, and the signal light incident on the basic unit The beam is split into a pair of orthogonal linearly polarized light, that is, ordinary light and extraordinary light (o light and e light), using half The wave plate can convert the two into the same polarization state, and realize the processing of any polarization state signal. 3. The all-optical OFDM signal demultiplexing device based on polarization interference according to claim 1 or 2, characterized in that: the polarization splitting and combining device consists of two displacement crystals and a half-wave plate The configuration realizes outputting the result of polarization interference as a pair of orthogonal linearly polarized lights. 4. An all-optical OFDM signal demultiplexing device based on polarization interference, characterized in that: it is mainly composed of log ₂ N basic unit cascades, and N is the number of OFDM signal subcarriers Number; each basic unit includes an input fiber collimator, a polarization beam splitter, a half-wave plate, a phase retarder, a polarization splitting and multiplexing device, and an output fiber collimator; The phase retarder is composed of a time-delay crystal and a phase-shift crystal with an adjustable structure. The time-delay crystal refers to a birefringence that causes a certain relative time delay between a pair of orthogonal linearly polarized lights after polarization splitting. crystal; The delay crystal length of the basic unit of the kth level is:

Among them, c is the speed of light, Δn is the crystal birefringence difference; T is the symbol time; The phase-shift crystal refers to a birefringent crystal that introduces a specific phase difference between a pair of orthogonal linearly polarized lights after passing through a time-delay crystal. The phase-shift crystal is an optical wedge structure, and its optical axis is parallel to the crystal surface. And perpendicular to the incident direction of the light beam, a mechanically adjustable device capable of longitudinally moving the light wedge controls the effective thickness of the light beam passing through the light wedge, and the effective thickness of the phase-shift crystal with the light wedge structure in the kth basic unit is the same as the Corresponding to the number of subcarriers, its thickness is in Select the value from the 2 ^k-1 results, and adjust the wedge structure corresponding to different i values to determine the effective thickness, where q=2 ^k-1 , 2 ^k-1 +1,...2 ^k -1, λ is The center wavelength of the sub-channel, Δn is the crystal birefringence difference. 5. An all-optical OFDM signal multiplexing device based on polarization interference, characterized in that: it is mainly composed of N-1 basic units in a log ₂ N-level series connection form, and the kth level has a total of

A basic unit connected in parallel, k is a positive integer and ∈ [1, log ₂ N], N is the number of subcarriers of the OFDM signal; each basic unit in the multiplexing device constitutes the device described in claim 1 The basic unit components of the demultiplexing device are exactly the same, but the order in which the signals pass through each device is just reversed.

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