CN102164017B - Waveguide chip structure for four-way parallel digital modulation and orthogonal multiplexing - Google Patents

Abstract

The invention discloses an optical DFT (discrete Fourier transform) waveguide chip structure for four-way parallel digital modulation and orthogonal multiplexing, which comprises a Y-shaped waveguide cascade structure, four dual-driven Mach-Zehnder modulator arrays and four all ODFT (optical discrete Fourier transform) waveguide units; and by using the optical DFT waveguide chip structure, under a lower electrical modulation rate, the information transmission with a higher speed is realized, the requirement for electronic processing speed is lowered, the limitation on electronic bottleneck isbroken through effectively, and the utilization rate of a communication bandwidth is greatly enhanced. According to the invention, a 100Gbps transmission code rate can be achieved just by using a 12.5Gbps electrical modulation rate, thereby reducing the system complexity, and effectively improving the bandwidth utilization rate of a single channel in a DWDM (dense wavelength division multiplexing) system, so the optical DFT waveguide chip structure is expected to be used for the signal modulation and orthogonal multiplexing of an optical communication backbone network. In the invention, basedon the advanced photonic integration technology, a waveguide structure for realizing all optical Fourier transform is designed, and the dual-driven Mach-Zehnder modulator arrays are integrated; and meanwhile, the structure is compact, and the power consumption is greatly reduced.

Description

Waveguide chip structure with four channels of parallel digital modulation and quadrature multiplexing

technical field

The present invention relates to the technical field of optical communication and photon integration, and in particular to a waveguide chip structure based on optical discrete Fourier transform for four-way parallel digital modulation and orthogonal multiplexing, which is used in a backbone network dense wavelength division multiplexing system Single-channel signal modulation, using a lower modulation rate to achieve high-speed code rate signal transmission.

Background technique

In the field of optical communication, the channel spacing of dense wavelength division multiplexing system (DWDM) has been reduced to 100GHz. However, due to the four-wave mixing effect and the existence of wavelength drift, it is difficult to further reduce the wavelength spacing. How to make full use of the bandwidth resources of a single channel has become a major technical hotspot in the optical communication backbone transmission network.

According to the traditional method, people use the time division multiplexing technology (TDM) in the electrical domain or the optical domain in order to fully utilize the channel capacity of a single channel. However, with the increase of the code rate, especially when it is higher than 10Gbps, the use of time division multiplexing technology to transmit optical signals will impose stricter restrictions on fiber dispersion and intersymbol crosstalk, and the higher the operating rate of optoelectronic devices, the higher the cost. Expensive and therefore limited to a large extent.

In order to further improve bandwidth utilization, all-optical quadrature phase modulation technology (OQPSK) has been developed in recent years. This technology uses four phase information of light, so that one optical signal can represent two symbol information; When the modulation rate is increased, the transmission rate is doubled. However, if the transmission code rate is to reach more than 100Gbps, it is not enough to simply use QPSK technology; then there is a quadrature amplitude modulation technology (QAM), which uses the optical phase information and performs amplitude modulation at the same time, so that a single Optical signals represent more symbol information, which improves bandwidth utilization to a greater extent.

However, quadrature amplitude modulation (QAM) will impose stringent requirements on the rate of the digital-to-analog converter. As we all know, compared with optical signal processing, the speed of electronic information processing is greatly limited (currently in the order of hundreds of megahertz), which is the so-called electronic bottleneck effect.

Therefore, in order to achieve a transmission code rate on the order of hundreds of gigahertz, it is necessary to rely on optical information processing technology and reduce the requirement for electrical modulation rate. In order to solve this problem, we have done sufficient investigation and research in order to find a method of photonic information processing to achieve a greater increase in bandwidth utilization and anti-dispersion and intersymbol interference at a lower electrical modulation rate. transmission performance.

There is a very important concept in photon information processing, which is the Fourier transform, which is a transformation algorithm between the frequency domain and the time domain: it can represent a time domain signal as the sum of orthogonal frequency domain components, In this way, the frequency domain information can be solved; it can also be reversed, and the information on the frequency domain can be transformed into a time domain signal. From this, it is related to the field of digital optical communication. In theory, the optical discrete Fourier transform algorithm can be used to realize the multiplexing of signals; A time-domain signal is transmitted, and then the inverse algorithm is used to demultiplex the information in the frequency domain, thereby improving bandwidth utilization. We got inspiration from it and thought of designing a specific optical waveguide structure to realize this process through photonic integration technology.

Contents of the invention

(1) Technical problems to be solved

In view of this, the main purpose of the present invention is to utilize photon integration technology to provide a waveguide chip structure of multi-channel parallel quadrature phase modulation (OQPSK) and all-optical discrete Fourier transform (ODFT), so as to realize The function of achieving high bit rate transmission under the modulation rate. In our specific embodiment, 4 groups (8 routes) of parallel 12.5Gbps electrical modulation signal sources and 12.5GHz optical pulse generators are used, and through the chip structure of the present invention, one optical pulse is divided into four routes of signals, respectively Perform quadrature phase modulation, and then undergo all-optical discrete Fourier transform to achieve 100Gbps signal transmission.

(2) Technical solution

In order to achieve the above object, the technical scheme adopted in the present invention is as follows:

A four-way parallel digital modulation and orthogonal multiplexing waveguide chip structure based on optical discrete Fourier transform, the waveguide chip structure includes a Y-shaped waveguide cascade structure, four dual-drive Mach-Zehnder modulator arrays and The all-optical discrete Fourier transform waveguide unit realizes quadrature phase modulation (QPSK) and quadrature multiplexing of four parallel optical pulses.

In the above solution, the Y-shaped waveguide cascaded structure consists of the first Y-shaped waveguide Y1, the second Y-shaped waveguide Y2, the third Y-shaped waveguide Y3, the fourth Y-shaped waveguide Y4, the fifth Y-shaped waveguide Y5 and the sixth Y-shaped waveguide. The Y-shaped waveguide Y6 is cascaded to ensure that the optical distance of each corresponding channel is equal. Among them, the splitting ratio of the two waveguide branches of the first Y-shaped waveguide Y1 is 3:1, and the former is connected to the second Y-shaped waveguide Y2, the latter is connected to the fourth dual-drive Mach-Zehnder modulator array M4; the splitting ratio of the two waveguide branches of the second Y-shaped waveguide Y2 is 2:1, the former is connected to the third Y-shaped waveguide Y3, and the latter is connected to The third dual-drive Mach-Zehnder modulator array M3; the splitting ratio of the two waveguide branches of the third Y-shaped waveguide Y3 is 1:1, respectively connected to the first dual-drive Mach-Zehnder modulator array M1 and the second dual-drive Mach Zender modulator array M2.

In the above solution, the four dual-drive Mach-Zehnder modulator arrays include a first dual-drive Mach-Zehnder modulator array M1, a second dual-drive Mach-Zehnder modulator array M2, and a third dual-drive Mach-Zehnder modulator array M1. The array M3 and the fourth dual-drive Mach-Zehnder modulator array M4 are respectively used for digital modulation of all-optical signals, wherein the first dual-drive Mach-Zehnder modulator array M1 and the second dual-drive Mach-Zehnder modulator array M1 The array M2, the third dual-drive Mach-Zehnder modulator array M3 and the fourth dual-drive Mach-Zehnder modulator array M4 are arranged in parallel; the signal electrodes I1, Q1, I2, Q2, I3, Q3, I4, and Q4 pass through the bottom leads of the chip , an external digital modulation signal source; the electrode GND is the ground electrode.

In the above scheme, the four all-optical discrete Fourier transform waveguide units include a first all-optical discrete Fourier transform waveguide unit F1, a second all-optical discrete Fourier transform waveguide unit F2, and a third all-optical discrete Fourier transform waveguide unit. Fourier transform waveguide unit F3 and the fourth all-optical discrete Fourier transform waveguide unit F4, wherein, the first all-optical discrete Fourier transform waveguide unit F1, the second all-optical discrete Fourier transform waveguide unit F2, the third all-optical discrete Fourier transform waveguide unit F2, The all-optical discrete Fourier transform waveguide unit F3 and the fourth all-optical discrete Fourier transform waveguide unit F4 are respectively connected with four parallel first dual-drive Mach-Zehnder modulator arrays M1 and second dual-drive Mach-Zehnder modulators The array M2, the third double-driven Mach-Zehnder modulator array M3 and the fourth double-driven Mach-Zehnder modulator array M4 are connected through waveguides.

In the above-mentioned scheme, it is characterized in that the four all-optical discrete Fourier transform waveguide units are composed of four sections of waveguides respectively, and each section of waveguides is selected to have a subsection of length L doped with lithium niobate to obtain additional phase shift. The phase shift value of the additional phase shift is set according to the discrete Fourier transform formula.

(3) Beneficial effects

As can be seen from the foregoing technical solutions, the present invention has the following beneficial effects:

1. The four-way parallel digital modulation and orthogonal multiplexing waveguide chip structure provided by the present invention adopts photon integration technology and integrates a dual-drive Mach-Zehnder modulator MZM array to realize parallel digital modulation and four-way optical signal modulation. Orthogonal multiplexing.

2. The four-way parallel digital modulation and orthogonal multiplexing waveguide chip structure provided by the present invention is based on optical discrete Fourier transform, and realizes multiplexing of multiple optical signals through orthogonal encoding of optical phases; The waveguide chip structure can transmit high-speed signals using lower-rate devices. Compared with traditional time-division multiplexing technology, it greatly improves the tolerance of dispersion and intersymbol crosstalk, and improves the transmission performance of communication systems.

Description of drawings

Fig. 1 is the schematic diagram of the waveguide chip structure of four-way parallel digital modulation and orthogonal multiplexing provided by the present invention;

Fig. 2 is a schematic structural view of the right discrete Fourier transform waveguide unit F1 in the four-way parallel digital modulation and orthogonal multiplexing waveguide chip structure provided by the present invention;

Fig. 3 is a specific implementation diagram of the present invention in an actual communication system.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be described in further detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

The four-way parallel digital modulation and orthogonal multiplexing waveguide chip structure provided by the present invention adopts photon integration technology and integrates a dual-drive Mach-Zehnder phase modulator array to realize parallel digital modulation and quadrature of four-way optical signals. reuse.

As shown in Figure 1, Figure 1 is a schematic diagram of a four-way parallel digital modulation and orthogonal multiplexing waveguide chip structure provided by the present invention. The quadrature phase modulation (QPSK) and quadrature multiplexing of four parallel optical pulses are realized by using a device array and four all-optical discrete Fourier transform waveguide units.

Wherein, the Y-shaped waveguide cascade structure consists of a first Y-shaped waveguide Y1, a second Y-shaped waveguide Y2, a third Y-shaped waveguide Y3, a fourth Y-shaped waveguide Y4, a fifth Y-shaped waveguide Y5 and a sixth Y-shaped waveguide. The waveguide Y6 is cascaded to ensure that the optical distances of each corresponding channel are equal. Among them: the splitting ratio of the two waveguide branches of the first Y-shaped waveguide Y1 is 3:1, the former is connected to Y2, and the latter is connected to M4 ; The splitting ratio of the two waveguide branches of the second Y-shaped waveguide Y2 is 2:1, the former is connected to Y3, and the latter is connected to M3; the splitting ratio of the two waveguide branches of the third Y-shaped waveguide is 1:1, respectively connected to The cascade relationship of M2 and M1; Y1, Y2, Y3, Y4, Y5, and Y6 is shown in Figure 1.

The four dual-drive Mach-Zehnder modulator arrays include a first dual-drive Mach-Zehnder modulator array M1, a second dual-drive Mach-Zehnder modulator array M2, a third dual-drive Mach-Zehnder modulator array M3, and a second dual-drive Mach-Zehnder modulator array M1. Four double-drive Mach-Zehnder modulator arrays M4, which are respectively used for digital modulation of all-optical signals, in which: M1, M2, M3, and M4 are arranged in parallel, respectively composed of upper and lower waveguides doped with lithium niobate, two The signal electrode (I, Q) and the ground electrode (GND) are composed.

具体方法通过控制铌酸锂的掺杂浓度来实现。请参见表1。The four all-optical discrete Fourier transform waveguide units include a first all-optical discrete Fourier transform waveguide unit F1, a second all-optical discrete Fourier transform waveguide unit F2, and a third all-optical discrete Fourier transform waveguide unit. Unit F3 and the fourth all-optical discrete Fourier transform waveguide unit F4, wherein: four waveguide units (F1, F2, F3, F4) are respectively connected with four parallel Mach-Zehnder modulators (M1, M2, M3, M4 ) are connected by waveguides. The four all-optical discrete Fourier transform waveguide units are each composed of four sections of waveguides to realize pulse delay and phase shift, that is, optical discrete Fourier transform. Among them, the length difference between two of the four-section waveguide branches is the space width of the optical pulse used, and each section of the waveguide selects a sub-section with a length of z doped with lithium niobate at an appropriate concentration to obtain an additional phase shift, the additional phase shift The phase shift value of is set according to the discrete Fourier transform formula, that is, for the nth waveguide channel in the kth all-optical Fourier transform waveguide unit, the phase shift value is

The specific method is realized by controlling the doping concentration of lithium niobate. See Table 1.

Δn为掺杂引入的波导折射率变化，通过控制铌酸锂掺杂浓度来调节；λ₀为所采用的通信光波长。FIG. 2 is a schematic structural diagram of the right discrete Fourier transform waveguide unit F1 in the four-way parallel digital modulation and orthogonal multiplexing waveguide chip structure provided by the present invention. Take this as an example to describe in detail below. As shown in the figure, the third waveguide channel (W3) is longer than the first waveguide channel (W1), and the fourth waveguide channel (W4) is two pulse widths longer than the second waveguide channel (W2). The second waveguide channel (W2) is longer than the first waveguide channel (W1) by an optical path of one pulse width. The optical path difference is used to realize the timing arrangement of optical pulses, and the shaded part is doped with lithium niobate to realize optical phase shifting. The specific method is to select the waveguide segments (P1, P2, P3, P4) with a length of z to inject lithium niobate to change the refractive index of the waveguide, so as to realize additional phase shift. The relationship between the additional phase shift and the change of refractive index is expressed as

Δn is the waveguide refractive index change introduced by doping, which can be adjusted by controlling the doping concentration of lithium niobate; λ ₀ is the wavelength of the communication light used.

数值参看下表。Branch length L and additional phase shift of the discrete Fourier transform waveguide unit in the present invention

Refer to the table below for values.

Table 1:

Note: T _p is the pulse width, c is the speed of light, that is, c=3·10 ⁸ m/s, L ₀ in the table is the reference length of the waveguide branch,

Choose reasonably according to the chip size.

Referring to Fig. 3 again, the optical pulse sequence of a specific frequency is firstly generated by the optical pulse generator, and sent from the A port to the four-way parallel digital modulation and orthogonal multiplexing waveguide chip structure provided by the present invention. Four dual-drive Mach-Zehnder modulators (MZM) are used for quadrature phase modulation (QPSK) of four optical pulses. The driving signals are provided by external signal sources, and there are 8 synchronous parallel modulation signals in total. Taking the modulation code rate of each signal as 12.5Gbps as an example, the required optical pulse frequency is 12.5GHz, and the pulse width Tp is controlled to be 20ps or less, which is triggered by the clock of the modulation signal source.

经过第k个双驱动马赫曾德调制器(M_k)的正交相位调制(QPSK)，加载的调制信号为I_k和Q_k，通过本发明的第k个全光离散傅里叶波导单元，可以得到由4个脉冲组成的脉冲序列，即完成该脉冲的全光离散傅里叶变换，在数学上可以表示为：In terms of design, in the absence of a modulation signal, by controlling the doping concentration of lithium niobate or adjusting the bias voltage, it is ensured that the phase difference between the two arms of each dual-drive Mach-Zehnder modulator is π/2; the modulation signal adopts Non-return-to-zero code NRZ, the code rate is 12.5Gbps, the logic "1" drive level causes the waveguide arm of each dual-drive Mach-Zehnder modulator to generate an additional π phase shift; after the four optical pulse sequences are modulated, respectively Enter four discrete Fourier transform units (F1, F2, F3, F4). In such a discrete Fourier transform unit, each modulated optical pulse is divided into four branches, which respectively pass through different waveguide channels, resulting in different delays and phase shifts, where the length of the waveguide channel and See Table 1 for additional phase shifts; then superimposed together, a full-optical discrete Fourier transform is performed. Assume a rectangular light pulse

Through the quadrature phase modulation (QPSK) of the kth dual-drive Mach-Zehnder modulator ( _Mk ), the loaded modulation signals are Ik _{and Qk} , and pass through the kth all-optical discrete Fourier waveguide unit of the present invention , a pulse sequence consisting of 4 pulses can be obtained, that is, the all-optical discrete Fourier transform of the pulse can be obtained, which can be expressed mathematically as:

$P_{k,m}=\frac{1}{4}(I_k+i\·Q_k)\&Center\; Dot;\exp \left[j\frac{\mathrm{\π}(k-1)(m-1)}{2}\right]{\stackrel{\&Right\; Arrow;}{\mathrm{E.}}}_{\left(t\right)}$ m is the pulse number, m=1, 2, 3, 4 (1)

Four such pulse sequences are superimposed together and output from the B port to complete a complete 4×4 optical discrete Fourier transform. The result is that four channels of optical signals are multiplexed into one channel for transmission. The mathematical expression is as follows:

$S_m=\frac{1}{4}\underset{k=1}{\overset{4}{\mathrm{\Σ}}}(I_k+i\·Q_k)\&Center\; Dot;\exp \left[j\frac{\mathrm{\π}(k-1)(m-1)}{2}\right]{\stackrel{\&Right\; Arrow;}{\mathrm{E.}}}_{\left(t\right)}$ m=1, 2, 3, 4 (2)

At the receiving end of the system, the signal can be demultiplexed by using the inverse discrete Fourier transform.

The invention also utilizes the optical communication system simulation software OptiSystem to carry out system simulation, and verifies the feasibility of this structure. If each multiplexed signal adopts the QPSK modulation system, eight parallel dual-drive Mach-Zehnder modulators with a rate of only 12.5Gbps can be used to achieve 100Gbps data transmission without the need for 100Gbps modulators or optical switches, which greatly reduces system complexity and cost. Simulation results show that the structure can transmit signals accurately, and the demodulated data is consistent with the original data.

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (3)

1. waveguide chip structure based on the modulation of four tunnel Parallel Digital of light discrete Fourier transform and orthogonal multiplex, it is characterized in that, this waveguide chip structure comprises Y type waveguide cascade structure, four two Mach zehnder modulators array and four full light discrete Fourier transform Wave guide units of driving, realized quadrature phase modulation and the orthogonal multiplex of four road parallel light pulses, wherein:

Described Y type waveguide cascade structure is formed by a Y type waveguide Y 1, the 2nd Y type waveguide Y 2, the 3rd Y type waveguide Y 3, the 4th Y type waveguide Y 4, the 5th Y type waveguide Y 5 and 6 cascades of the 6th Y type waveguide Y, be used for guaranteeing that passage light path corresponding to each road all equates, wherein, two Waveguide branching splitting ratios of the one Y type waveguide Y 1 are 3: 1, the former accesses the 2nd Y type waveguide Y 2, and the latter accesses the 4th pair and drives Mach zehnder modulators array M4; Two Waveguide branching splitting ratios of the 2nd Y type waveguide Y 2 are 2: 1, and the former accesses the 3rd Y type waveguide Y 3, and the latter accesses the 3rd pair and drives Mach zehnder modulators array M3; Two Waveguide branching splitting ratios of the 3rd Y type waveguide Y 3 are 1: 1, access respectively first pair and drive Mach zehnder modulators array M1 and second couple of driving Mach zehnder modulators array M2;

Described four pairs of drivings Mach zehnder modulators arrays comprise that first pair drives a Mach zehnder modulators array M1, second couple of a driving Mach zehnder modulators array M2, the 3rd couple of driving Mach zehnder modulators array M3 and the 4th a couple of driving Mach zehnder modulators array M4, it is respectively applied to carry out the Digital Modulation of full light signal, wherein, first pair drives a Mach zehnder modulators array M1, second couple of a driving Mach zehnder modulators array M2, the 3rd couple of driving Mach zehnder modulators array M3 and the 4th a pair of driving Mach zehnder modulators array M4 parallel arranged; Signal electrode I1, Q1, I2, Q2, I3, Q3, I4, Q4 go between by chip bottom, external digital modulation signals source; Electrode GND is grounding electrode;

Described four full light discrete Fourier transform Wave guide units comprise the first full light discrete Fourier transform Wave guide unit F1, the second full light discrete Fourier transform Wave guide unit F2, the 3rd full light discrete Fourier transform Wave guide unit F3 and the 4th full light discrete Fourier transform Wave guide unit F4, wherein, the first full light discrete Fourier transform Wave guide unit F1, the second full light discrete Fourier transform Wave guide unit F2, the 3rd full light discrete Fourier transform Wave guide unit F3 and the 4th full light discrete Fourier transform Wave guide unit F4 drive a Mach zehnder modulators array M1 with four parallel first pair respectively, second pair drives Mach zehnder modulators array M2, the 3rd pair drives Mach zehnder modulators array M3 and is connected by waveguide with the 4th a couple of driving Mach zehnder modulators array M4;

The 3rd full light discrete Fourier transform Wave guide unit F3 and the 4th full light discrete Fourier transform Wave guide unit F4 access respectively a Waveguide branching of the 4th Y type waveguide Y 4, carried out one tunnel light pulse of additional phase shift by the 3rd full light discrete Fourier transform Wave guide unit F3 and superpose in the 4th Y type waveguide Y 4 with the road light pulse of being carried out additional phase shift by the 4th full light discrete Fourier transform Wave guide unit F4, the light pulse after the stack enters a Waveguide branching of the 5th Y type waveguide Y 5; Another Waveguide branching of the 5th Y type waveguide Y 5 is connected in the second full light discrete Fourier transform Wave guide unit F2, carried out one tunnel light pulse and the again stack in the 5th Y type waveguide Y 5 of the light pulse after the described stack of additional phase shift by the second full light discrete Fourier transform Wave guide unit F2, the light pulse after the stack enters a Waveguide branching of the 6th Y type waveguide Y 6 again; Another Waveguide branching of the 6th Y type waveguide Y 6 is connected in the first full light discrete Fourier transform Wave guide unit F1, carried out one tunnel light pulse of additional phase shift and the light pulse further stack in the 6th Y type waveguide Y 6 after the described again stack by the first full light discrete Fourier transform Wave guide unit F1, the light pulse after this further superposes is by the output of B port.

2. according to claim 1 based on four tunnel Parallel Digital modulation of light discrete Fourier transform and the waveguide chip structure of orthogonal multiplex, it is characterized in that, described four full light discrete Fourier transform Wave guide units all are made of four sections waveguides respectively, each section waveguide is all chosen long for the subsegment doped lithium columbate of L, obtains additional phase shift.

According to claim 2 based on the light discrete Fourier transform the modulation of four tunnel Parallel Digital and the waveguide chip structure of orthogonal multiplex, it is characterized in that, the phase-shift value of described additional phase shift arranges according to the discrete Fourier transform formula.

Images