CN112596166B - Optical signal sampling pulse generator based on time-mode interleaved multiplexing - Google Patents
Optical signal sampling pulse generator based on time-mode interleaved multiplexing Download PDFInfo
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- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
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- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/2804—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers
- G02B6/2861—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers using fibre optic delay lines and optical elements associated with them, e.g. for use in signal processing, e.g. filtering
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Abstract
The invention provides an optical signal sampling pulse generator based on time-mode interleaving multiplexing, which comprises: the waveguide delay line (701) is composed of N sections of waveguides with different widths; the optical splitter (2) is used for generating N optical pulse signals to correspond to N sections of waveguides, wherein the first optical pulse signal is directly input into the first section of waveguide, the Kth optical pulse signal is coupled into the Kth section of waveguide after mode conversion, and K is more than or equal to 2 and less than or equal to N; n optical pulse signals in different modes enter the waveguide delay line from different width positions respectively, so that the waveguide delay line (701) outputs the optical pulse signals in different modes and delayed time. The optical signal sampling pulse generator improves the integration level of an optical structure, reduces the length of a waveguide delay line, and achieves the effects of reducing the size and reducing the optical loss.
Description
Technical Field
The invention relates to the technical field of silicon-based optoelectronic devices, in particular to an optical signal sampling pulse generator based on time-mode interleaved multiplexing.
Background
A high-speed optical communication system is an important application direction of high-speed digital signal processing, data transmission and processing by using optical signals gradually become a research hotspot, and a device for performing analog-to-digital conversion by using optical signals is an optical ADC. High-speed optical ADC systems can be divided into optical-assisted ADCs, optical-sampling optical-quantization ADCs, and optical-sampling electrical-quantization ADCs. The optical auxiliary type optical ADC needs to trigger an electrical sampling structure by using an external optical signal, and essentially still belongs to electrical sampling; the optical sampling optical quantization type ADC needs to perform signal quantization by using a nonlinear material, but the nonlinear coefficient of the existing material is limited, and it is difficult to realize high-precision sampling quantization.
In an optical sampling electric quantization ADC system, in order to realize high-speed sampling, a pulse generation module in an optical ADC is responsible for converting an original pulse signal emitted by a laser into a high-frequency sampling signal. The current pulse generation schemes can be classified into a pulse generation scheme based on optical time division multiplexing and a pulse generation scheme based on time-wavelength interleaving multiplexing according to the conversion principle of the pulse signal. The pulse generation scheme based on optical time division multiplexing needs to realize time domain interleaved multiplexing of optical pulses by means of discrete devices in a three-dimensional space, for example, a free-space optical delay line is constructed by using an optical fiber delay line or a mirror structure in the three-dimensional space, and the scheme is not easy to integrate, large in size and sensitive to mechanical vibration. In the pulse generation scheme based on time-wavelength interleaving multiplexing, the pulse generator can be constructed by using elements in integrated optics, and the implementation of the pulse time-domain interleaving multiplexing requires the following three processes: (1) And wavelength demultiplexing is carried out on the multi-wavelength pulse signal emitted by the laser by using a wavelength division demultiplexer. (2) Each wavelength signal after wavelength demultiplexing enters different spatially independent delay line waveguides, and then relative time delay is generated when optical signals with different wavelengths are transmitted in the delay line waveguides. (3) The optical pulse signals with different wavelengths, which generate relative time delay, are combined by a wavelength division multiplexing structure to form a high-frequency sampling pulse. Although this scheme can be implemented with on-chip device integration, it requires a wavelength division multiplexing structure and a wavelength division demultiplexing structure to process the optical signals before and after interleaving multiplexing, for example, a micro ring structure or an arrayed waveguide grating structure is used, but the micro ring structure needs to introduce a thermo-optical modulation or electro-optical modulation active structure to perform wavelength calibration due to wavelength shift caused by process deviation, so that the complexity of the system is increased, and the arrayed waveguide grating structure increases the system area due to its large size. In addition, optical pulse signals of different wavelengths are respectively transmitted in the spatially independent delay line waveguides, so that the size of the device is large.
Disclosure of Invention
Technical problem to be solved
In view of the above problems, the present invention provides an optical signal sampling pulse generator based on time-mode interleaved multiplexing, which is used to at least partially solve the technical problems of complex system and large device size of the conventional device.
(II) technical scheme
The invention provides an optical signal sampling pulse generator based on time-mode interleaving multiplexing, which comprises: a waveguide delay line 701 composed of N segments of waveguides having different widths; the optical splitter 2 is used for generating N optical pulse signals to correspond to N sections of waveguides, wherein the first optical pulse signal is directly input into the first section of waveguide, the Kth optical pulse signal is coupled into the Kth section of waveguide after mode conversion, and K is more than or equal to 2 and less than or equal to N; the N optical pulse signals in different modes enter the waveguide delay line from different width positions, so that the waveguide delay line 701 outputs the optical pulse signals in different modes and with different delays.
Further, the waveguide delay line 701 has a winding structure formed by N sections of U-shaped waveguides, where each section of U-shaped waveguide includes one curved waveguide and two straight waveguides.
Further, waveguides of different widths in the waveguide delay line 701 are connected by tapered waveguides.
And further, the optical mode coupler comprises at least one optical mode coupler, wherein the optical mode coupler comprises a curved waveguide 401 and a straight waveguide 402, and the straight waveguide 402 is close to the straight waveguide of the waveguide delay line 701 and is used for coupling the Kth optical pulse signal into the Kth U-shaped waveguide after mode conversion, and K is more than or equal to 2 and less than or equal to N.
Further, one output port 300 of the optical splitter 2 has the same cross-sectional size as the input port 700 of the waveguide delay line 701, and the remaining output ports of the optical splitter 2 have the same cross-sectional size as the input port 400 of the optical mode coupler.
Further, the optical mode couplers are respectively disposed at different path length positions of the waveguide delay line 701.
Further, the structures of the waveguide delay line 701, the optical mode coupler, and the optical splitter 2 include a stripe structure and a ridge structure.
Further, the optical splitter 2 includes an optical power splitter and an optical wavelength demultiplexing type splitter, wherein the optical wavelength demultiplexing type splitter includes a micro-ring and micro-disk structure, an arrayed waveguide grating structure, a diffraction step grating structure, a cascade mach-zehnder interferometer structure, a bragg grating waveguide structure, and an F-P interference cavity structure.
Further, the optical splitter 2 includes a TE mode single polarization optical splitter, a TM mode single polarization optical splitter, and a TE and TM mixed mode polarization optical splitter; the optical mode couplers include TE mode single polarized optical mode couplers, TM mode single polarized optical mode couplers, and TE and TM mixed mode polarized optical mode couplers.
Further, the structure of the optical mode coupler includes a structure of a single coupler, a structure of a cascade coupler.
(III) advantageous effects
According to the optical signal sampling pulse generator based on time-mode interleaving multiplexing provided by the embodiment of the invention, after an input optical pulse sequence passes through an optical beam splitter, the input optical pulse sequence enters a delay line waveguide at different positions of the delay line waveguide, undergoes different transmission times, reaches an outlet of a waveguide delay line at different moments, and is converted into an integral multiple high repetition frequency optical pulse sequence, so that the time-mode interleaving multiplexing of a pulse signal is realized, the wavelength calibration problem in a wavelength division multiplexing and demultiplexing structure is avoided, the size of a system is reduced, and the integration level of a pulse generation module is improved.
Drawings
FIG. 1 schematically shows a schematic diagram of an optical signal sampling pulse generator based on time-mode interleaved multiplexing according to an embodiment of the present invention;
FIG. 2 is a schematic diagram illustrating the time delay of an optical pulse signal in a 4-mode optical signal sampling pulse generator based on time-mode interleaved multiplexing according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a 4-mode optical signal sampling pulse generator based on time-mode interleaved multiplexing according to an embodiment of the present invention;
figure 4 schematically illustrates a schematic diagram of an optical mode coupler according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments and the accompanying drawings.
An embodiment of the present disclosure provides an optical signal sampling pulse generator based on time-mode interleaved multiplexing, referring to fig. 1, including: a waveguide delay line 701 composed of N segments of waveguides having different widths; the optical splitter 2 is used for generating N optical pulse signals to correspond to N sections of waveguides, wherein the first optical pulse signal is directly input into the first section of waveguide, the Kth optical pulse signal is coupled into the Kth section of waveguide after mode conversion, and K is more than or equal to 2 and less than or equal to N; the N optical pulse signals in different modes enter the waveguide delay line from different width positions, so that the waveguide delay line 701 outputs the optical pulse signals in different modes and with different delays.
The width of the waveguide delay line increases step by step along with the optical transmission path, for example, the section 701 of the waveguide delay line is a straight waveguide with a fixed width, the section 703 of the waveguide delay line is another straight waveguide with a fixed width, the width of the section 703 of the waveguide delay line is wider than that of the section 701 of the waveguide delay line, and the waveguides with different widths are used for coupling to obtain optical pulse signals with different modes. The waveguide delay line allows multiple optical modes to be transmitted within the waveguide, the multiple optical modes being transmitted within the same waveguide of varying width, the transmission lengths of the different optical modes being different. The optical beam splitter 2 is a 1 XN optical coupler based on the multi-mode interference principle, and an input port 1 of the optical beam splitter receives an emergent signal of a laser light source; which has the function of splitting an input optical signal into a plurality of output ports. The optical splitter 2 has N output ports with the same structure, wherein one output port is directly connected to the input port of the waveguide delay line 701, and the remaining N-1 output ports are respectively connected to the input ports of the N-1 optical mode couplers for mode conversion. The optical signal sampling pulse generator can be of a strip structure or a ridge structure.
According to the invention, by utilizing the difference of the transmission path lengths and the group refractive indexes of different optical modes in the multimode waveguide, the multimode optical pulse signals generate relative time delay (see fig. 2) in the transmission process, and the optical pulse signals of different modes are transmitted in the same waveguide delay line, so that the total length of the waveguide delay line is reduced, the size of a device is reduced, the use of an active structure for wavelength tuning alignment in a time-wavelength staggered multiplexing structure is avoided, and the power consumption of the device is reduced.
On the basis of the above embodiment, the waveguide delay line 701 has a roundabout structure formed by N sections of U-shaped waveguides, where each section of U-shaped waveguide includes one curved waveguide and two straight waveguides.
The path shape of the waveguide delay line 701 is a roundabout structure on the whole, the roundabout structure is composed of a plurality of sections of U-shaped waveguides, the U-shaped waveguides can be composed of two bent waveguides and one straight waveguide, and the straight waveguides of the two U-shaped waveguides are connected. The U-shaped waveguide may also be a U-shaped structure composed of several arc-shaped waveguides, and in short, the purpose of the detour structure is to reduce the waveguide length of the optical mode couplers 401, 501 and 601, thereby reducing the time required for coupling the optical signal at the output port of the optical splitter into the delay line waveguide, and improving the compactness of the pulse generator. According to the invention, the optical pulse signals in different modes are collected in the same waveguide delay line through the roundabout structure for transmission, and compared with the time-wavelength interleaving multiplexing scheme in which the optical pulses with different wavelengths are transmitted in different delay line waveguides, the total length of the waveguide delay line can be effectively reduced, so that the area size of the device can be reduced.
On the basis of the above embodiment, waveguides with different widths in the waveguide delay line 701 are connected by tapered waveguides.
The waveguide delay line 701 is a waveguide with gradually increasing width, and the width of the delay line waveguide is widened once through a tapered waveguide 702 every time a certain transmission length is passed.
On the basis of the above embodiment, the optical mode coupler further comprises at least one optical mode coupler, where the optical mode coupler comprises a curved waveguide 401 and a straight waveguide 402, and the straight waveguide 402 is close to the straight waveguide of the waveguide delay line 701, and is used to couple the kth optical pulse signal into the kth section of U-shaped waveguide after mode conversion, where K is greater than or equal to 2 and less than or equal to N.
The optical mode couplers are formed of a curved waveguide 401 and a straight waveguide 402, the input port 400 of the optical mode coupler being the same size as the output port 301 of the optical splitter, each optical mode coupler comprising an input waveguide of fixed width abutting the delay line straight waveguide and coupling the optical pulse signal from the optical splitter within the input waveguide into the delay waveguide. The optical coupler may be a symmetrical structure or an asymmetrical structure, where symmetrical means that the cross-sectional dimension of the waveguide 401 is the same as the cross-sectional dimension of the waveguide 703. The optical mode coupler is based on the waveguide mode index matching principle, for example, when the effective refractive index of the TE0 optical mode in the waveguide 401 is the same as the effective refractive index of the TE1 optical mode in the waveguide 703, the TE0 optical mode in the waveguide 401 can be efficiently coupled into the waveguide 703 and transmitted in the form of the TE1 optical mode in the waveguide 703. The optical mode coupler may be a straight waveguide based coupling structure or a curved waveguide based coupling structure.
Based on the above embodiment, one output port 300 of the optical splitter 2 has the same cross-sectional size as the input port 700 of the waveguide delay line 701, and the other output ports of the optical splitter 2 have the same cross-sectional size as the input port 400 of the optical mode coupler.
The same cross-sectional size of the output port 300 and the input port 700 is to simplify the structure of the delay line waveguide, so that the optical signal of the output port 300 can directly enter the waveguide 701 and be stably transmitted.
On the basis of the above embodiment, the optical mode couplers are respectively disposed at different path length positions of the waveguide delay line 701.
Different optical mode couplers are arranged at nodes with different lengths of the waveguide delay line 701, so that input optical pulse trains enter from different positions of the waveguide delay line 701, experience different transmission times and reach an outlet of the waveguide delay line at different moments, and relative delay is formed when the optical pulse trains reach the position of the output port 703'.
On the basis of the above embodiments, the structures of the waveguide delay line 701, the optical mode coupler, and the optical splitter 2 include a stripe structure and a ridge structure.
The time-mode staggered multiplexing type pulse generator with the strip structure has the characteristics of simple etching process but sensitive optical transmission loss on the side wall of the waveguide; the time-mode interleaving multiplexing type pulse generator with the ridge structure has the characteristics of small waveguide loss and high requirement on the precision of etching depth.
On the basis of the above embodiment, the optical splitter 2 includes an optical power splitter and an optical wavelength demultiplexing type splitter, where the optical wavelength demultiplexing type splitter includes a micro-ring and micro-disk structure, an arrayed waveguide grating structure, a diffraction step grating structure, a cascaded mach-zehnder interferometer structure, a bragg grating waveguide structure, and an F-P interferometric cavity structure.
The optical power beam splitter is used for equally splitting the power of each incident light pulse signal to each output port, and has the advantages of simple structure and excellent power beam splitting uniformity; the optical wavelength demultiplexing beam splitter is used for splitting incident optical pulses with different wavelengths to different output ports, and has the advantage of splitting multi-wavelength optical pulse signals. The optical wavelength demultiplexing type beam splitter of the micro-ring, the micro-disk, the Bragg grating waveguide structure and the F-P interference cavity structure is suitable for the condition with higher requirement on the compactness of a device, the optical wavelength demultiplexing type beam splitter of the array waveguide grating and the diffraction step grating structure is suitable for the condition with larger wavelength quantity for demultiplexing, and the optical wavelength demultiplexing type beam splitter of the cascade Mach-Zehnder interferometer structure is suitable for the condition with less wavelength channel quantity and lower requirement on the compactness of the device.
On the basis of the above embodiment, the optical splitter 2 includes a TE mode single polarization optical splitter, a TM mode single polarization optical splitter, and a TE and TM mixed mode polarization optical splitter; the optical mode couplers include a TE mode single polarized optical mode coupler, a TM mode single polarized optical mode coupler, and a TE, TM mixed mode polarized optical mode coupler.
Assuming that the optical signal propagates in the z direction within the waveguide, the x direction can be understood as the lateral direction and the y direction as the longitudinal direction. The TE mode is an optical mode in which the transverse component of the optical field is larger than the longitudinal component, and is suitable for pulse delay based on the TE polarization mode, and the TM mode is an optical mode in which the transverse component of the optical field is smaller than the longitudinal component, and is suitable for pulse delay based on the TM polarization mode. In addition, the mode of the optical splitter 2 is matched to the mode of the optical mode coupler, which would otherwise cause optical loss of the signal.
On the basis of the above embodiments, the structure of the optical mode coupler includes a structure of a single coupler, a structure of a cascade coupler.
The structure of the single coupler has the characteristic of simple structure, and the structure of the cascade coupler has the characteristic of complex structure but more flexible power beam splitting.
The working process of the optical signal sampling pulse generator is as follows: the original pulse optical signal emitted by the laser enters the multimode interference coupling area 2 through the input port 1 of the optical beam splitter, and the optical beam splitter equally splits the power of each incident optical pulse signal to each output port based on the multimode interference coupling principle. Subsequently, the optical pulse signal in the output port 300 enters the input port 700 of the delay line waveguide and is transmitted in the 0-order mode form in the delay line waveguide 701, the width of the delay line waveguide is widened from the width of the waveguide 701 to the width of the waveguide 703 at the position of the tapered waveguide 702, the optical pulse signal in the delay line waveguide 701 is transmitted in the 0-order mode form in the tapered waveguide 702 and enters the waveguide 703, and the optical pulse signal entering the waveguide 703 is still transmitted in the fundamental mode form.
Further, the optical pulse signals in the remaining output ports of the optical splitter enter the optical mode couplers at different positions respectively and are coupled into different positions of the delay line waveguide to be transmitted in the delay line waveguide. As shown in fig. 1, the output optical pulse signal of the output port 301 of the optical splitter enters the optical mode coupler 401 through the input port 400, and is coupled into the delay line waveguide 703 through the coupling region 402 and transmitted in the first-order mode in the waveguide 703, due to the difference of transmission paths, a difference occurs between the time when the optical signal from the output port 300 of the 1 × N optical splitter in the waveguide 703 and the time when the optical signal from the output port 301 of the optical splitter reach the output port 703 of the delay line waveguide, and the relative time difference between the optical pulse signals reaching the output port 703' can be adjusted by reasonably designing the lengths of the delay line waveguides 701, 702, and 703, so that time-domain interleaved multiplexing of optical pulse signals in different modes is realized.
The invention carries out time domain interleaving multiplexing on the optical pulse signals in different modes, thereby avoiding the use of a wavelength division multiplexing and demultiplexing device which needs to process multi-wavelength signals, and avoiding the problem of wavelength calibration among the optical signals with different wavelengths caused by process deviation. On the other hand, an active structure is not used inside, all structures for time-mode interleaving multiplexing are passive structures, and an electrical modulation structure or a thermal modulation structure is not needed, so that the power consumption requirement is reduced. On the other hand, the waveguide adopts a structure mainly made of silicon materials, and a silicon-based optoelectronic device applied to a communication waveband has the advantages of low optical loss, miniaturization and compatibility with a CMOS (complementary metal oxide semiconductor) process, so that the on-chip function integration with other devices and the reduction of manufacturing cost are facilitated.
The following describes a specific embodiment of the present invention, which is based on a 4-mode optical signal sampling pulse generator with time-mode interleaved multiplexing, comprising: a 1 × 4 optical splitter; 3 optical mode couplers, which couple the output optical signals of 3 output ports of the 1 × 4 optical splitter into the subsequent multimode waveguide delay line and transmit the output optical signals in different modes; the output port of the 1 delay line waveguide supports 4 TE optical modes for transmission, and the optical modes generate relative time delay in the transmission process due to the difference of the transmission length and the group refractive index.
Fig. 3 is a schematic top view of a 4-mode optical signal sampling pulse generator based on time-mode interleaved multiplexing, in this embodiment, an SOI substrate (fig. 4) is used, the top silicon layer has a thickness of 220nm, and an optical pulse signal is transmitted in the top silicon layer optical waveguide. As shown in fig. 3, the 4-mode time-mode interleaving multiplexing structure includes: 1 x 4 optical splitter input port 1, splitter body 2 and output ports 300, 301, 302 and 303, optical mode couplers 401, 501 and 601 based on the asymmetric DC coupler principle, waveguide delay line structures 701, 702, 703, 704, 705, 706, 707 and 708.
Specifically, an optical pulse signal incident from an external laser enters through the input port 1The optical pulse signals enter a main body area 2 of a 1 × 4 optical beam splitter, then the optical pulse signals in the output port 300 of the optical beam splitter directly enter an input port 700 of a delay line waveguide, the delay line waveguide 701 is a single-mode waveguide with a width of 450nm, the optical pulse signals are transmitted in a TE0 order mode in the delay line waveguide 701, at the position of a tapered waveguide 702, the width of the delay line waveguide is widened from the 450nm width of the waveguide 701 to a 930nm width of the waveguide 703, optical signal transmission supporting the TE0 order mode and the TE1 order mode in the delay line waveguide 703, the optical pulse signals in the delay line waveguide 701 are transmitted in the tapered waveguide 702 in the TE0 order mode and enter the waveguide 703, and the optical pulse signals are transmitted in the TE0 order mode after entering the waveguide 703. Further, the group refractive index n of the optical pulse is used g And the transmission path L can calculate the transmission time t of the optical pulse in the delay line waveguide 701,
where c is the speed of light in vacuum, L is the length of the delay line waveguide 701 and L =2065 μm, the group index of refraction n for the TE0 mode propagating in the waveguide 701 g =4.30, whereby the transit time of the TE0 optical mode transported in the waveguide 701 is calculated to be
As shown in fig. 3, the output optical pulse signal of the second output port 301 of the 1 × 4 optical splitter enters the optical mode coupler 401 through the input port 400, and is coupled into the delay line waveguide 703 through the coupling region 402 and transmitted in the TE1 order mode in the waveguide 703, in order to implement the coupling process, the width of the coupling waveguide 401 is 450nm, the effective refractive index of the TE0 order mode allowed to be transmitted inside the coupling waveguide is 2.352, the width of the delay line waveguide 703 is 930nm, and the effective refractive index of the TE1 order mode allowed to be transmitted inside the delay line waveguide is 2.352, based on the mode coupling principle of the optical waveguide, the TE0 order mode transmitted in the waveguide 401 can be coupled into the waveguide through the coupling region 402 and converted into the TE1 order mode in the waveguide 703 for optical transmission, and the structure of the optical mode coupler is shown as an exampleIntended as shown in fig. 4. Further, the group refractive index n of the optical pulse is used g And the transmission path L can calculate the transmission time t of the light pulse in the delay line waveguide,
where c is the speed of light in vacuum, L is the length of the delay line waveguide 703 and L =1868 μm, the group index of refraction n for the TE0 mode propagating in the waveguide 703 g =3.87, group refractive index n for TE1 optical mode transported in waveguide 703 g =4.40, thereby calculating the propagation time of the TE0 optical mode and the TE1 optical mode propagating in the waveguide 703 as
Thus, the optical signal from the 1 × 4 optical splitter output port 300 and the optical signal from the 1 × 4 optical splitter output port 301 in the waveguide 703 pass through the waveguide 703 at different times and reach the tapered waveguide 704 at different times. At the position of the tapered waveguide 704, the width of the delay line waveguide is widened from 930nm width of the waveguide 703 to 1400nm width of the waveguide 705, optical signal transmission of the TE0 order mode, the TE1 order mode and the TE2 order mode is supported in the delay line waveguide 705, the TE0 order mode optical pulse signal in the delay line waveguide 703 enters the delay line waveguide 705 through the tapered waveguide 704 and is still transmitted in the form of the TE0 order mode in the waveguide 705, and the TE1 order mode optical pulse signal in the delay line waveguide 703 enters the delay line waveguide 705 through the tapered waveguide 704 and is still transmitted in the form of the TE1 order mode in the waveguide 705.
Further, as shown in fig. 3, the output optical pulse signal at the third output port 302 of the 1 × 4 optical splitter enters the optical mode coupler 501 through the input port 500 and is coupled into the delay line waveguide 705 through the coupling region 502 and transmitted in the second order mode in the waveguide 705, in order to realize this coupling processThe width of the coupling waveguide 501 is 450nm, the effective refractive index of the TE0 mode allowed to be transmitted inside the coupling waveguide is 2.352, the width of the delay line waveguide 705 is 1415nm, and the effective refractive index of the TE2 mode allowed to be transmitted inside the delay line waveguide is 2.352, as can be known from the mode coupling principle of optical waveguides, the TE0 mode transmitted inside the waveguide 501 can be coupled into the waveguide 705 through the coupling region 502 and converted into the TE2 mode inside the waveguide 705 for optical transmission. Further, the group refractive index n of the optical pulse is used g And the transmission path L can calculate the transmission time t of the light pulse in the delay line waveguide,
where c is the speed of light in vacuum, L is the length of the delay line waveguide 705 and L =1693 μm, the group index of refraction n for the TE0 mode propagating in the waveguide 705 g =3.78, group refractive index n for TE1 optical mode transported in waveguide 705 g =4.00, group refractive index n for TE2 optical mode transported in waveguide 705 g =4.43, and the propagation time of the TE0 optical mode, the TE1 optical mode, and the TE2 optical mode propagating in the waveguide 705 is calculated as
Thus, optical signals from the 1 × 4 optical splitter output port 300, optical signals from the 1 × 4 optical splitter output port 301, and optical signals from the 1 × 4 optical splitter output port 302 within the waveguide 705 will pass through the waveguide 705 at different times and thus reach the tapered waveguide 706 at different times. At the position of the tapered waveguide 706, the width of the delay line waveguide is widened from 1400nm width of the waveguide 705 to 1900nm width of the waveguide 707, optical signal transmission of a TE 0-order mode, a TE 1-order mode, a TE 2-order mode and a TE 3-order mode is supported in the delay line waveguide 707, a TE 0-order mode optical pulse signal in the delay line waveguide 705 enters the delay line waveguide 707 through the tapered waveguide 706 and is still transmitted in the waveguide 707 in the form of the TE 0-order mode, a TE 1-order mode optical pulse signal in the delay line waveguide 705 enters the delay line waveguide 707 through the tapered waveguide 706 and is still transmitted in the waveguide 707 in the form of the TE 1-order mode, and a TE 2-order mode optical pulse signal in the delay line waveguide 705 enters the delay line waveguide 707 through the tapered waveguide 706 and is still transmitted in the form of the TE 2-order mode in the waveguide 707.
Further, as shown in fig. 3, the output optical pulse signal of the fourth output port 303 of the 1 × 4 optical splitter enters the optical mode coupler 601 through the input port 600, and is coupled into the delay line waveguide 707 through the coupling region 602 and is transmitted in the TE3 mode in the waveguide 707, in order to implement this coupling process, the width of the coupling waveguide 601 is 450nm, the effective refractive index of the TE0 mode allowed to be transmitted inside the coupling waveguide is 2.352, the width of the delay line waveguide 707 is 1900nm, and the effective refractive index of the TE3 mode allowed to be transmitted inside the delay line waveguide is 2.352, based on the mode coupling principle of optical waveguides, the TE0 mode transmitted in the waveguide 601 can be coupled into the waveguide 707 through the coupling region 602 and converted into the TE3 mode in the waveguide 707 for optical transmission. Further, the group refractive index n of the optical pulse is used g And the transmission path L can calculate the transmission time t of the optical pulse in the delay line waveguide, where c is the speed of light in vacuum, and since this embodiment only relates to the relative delay design of 4 optical modes, the length of the waveguide 707 can be approximated to 0 when the optical signal reaches the output port 708 of the delay line waveguide immediately after being coupled into the delay line waveguide 707 through the coupling region 602, so that the total transmission time of the optical signal from the 1 × 4 optical splitter output port 303 in the delay line waveguide is 0, and thus the optical signal from the 1 × 4 optical splitter output port 300, the optical signal from the 1 × 4 optical splitter output port 301, the optical signal from the 1 × 4 optical splitter output port 302, and the optical signal from the 1 × 4 optical splitter output port 303 in the waveguide 707 pass through the waveguide 707 at different times, and finally, at the delay line 707At the position of the output port 708 of the waveguide, there are optical pulse signals of 4 modes, namely, TE 0-order mode, TE 1-order mode, TE 2-order mode and TE 3-order mode, which are respectively from different output ports of the 1 × 4 optical splitter, and the total time of transmission of each optical mode in the delay line waveguide can be obtained by respectively adding the calculation results of the transmission time of each optical mode in different delay line waveguides.
t TE3 ＝t TE3_707 ＝0
t TE2 ＝t TE2_707 +t TE2_705 ＝25.0ps
t TE1 ＝t TE1_707 +t TE1_705 +t TE1_703 ＝22.6+27.4＝50.0ps
t TE0 ＝t TE0_707 +t TE0_705 +t TE0_703 +t TE0_701 ＝21.3+24.1+29.6＝75ps
Therefore, the total transmission time of the TE3 order mode, the TE2 order mode, the TE1 order mode and the TE0 order mode in the delay line waveguide is respectively 0, 25ps,50ps and 75ps, and the transmission time of the TE3 order mode, the TE2 order mode, the TE1 order mode and the TE0 order mode in the delay line waveguide sequentially forms an arithmetic progression so as to form relative delay. The relative time difference when the optical pulse signals of the 4 modes reach the output port 708 can be adjusted by reasonably designing the lengths of the delay line waveguides with different widths, that is, the time domain interleaving multiplexing of the optical pulse signals of the 4 modes is realized. The transmission of the optical pulse signal within the pulse generator is shown in fig. 2. In fig. 2, a single optical pulse from a laser first enters the input port of an optical splitter, is then split into 4 optical signals by a 1 × 4 optical splitter and arrives at the output port of the optical splitter at the same time, and then arrives at the output port of a delay line waveguide at different times with a relative delay of 25ps between adjacent pulses.
In summary, the present invention provides an optical signal sampling pulse generator based on time-mode interleaving multiplexing, which utilizes the refractive index difference and the transmission path length difference of different optical mode groups in a waveguide to implement pulse delay, and transmits optical pulse signals of different modes in the same delay line waveguide to implement time-domain interleaving multiplexing of laser outgoing pulses with a pure passive structure, so that the optical signal sampling pulse generator can be widely applied to various fields such as high-speed signal processing.
It should be further noted that the same elements in the embodiments are denoted by the same or similar reference numerals, and the shapes and sizes of the respective structures in the drawings do not reflect actual sizes and proportions, but merely illustrate the contents of the embodiments of the present invention.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (8)
1. An optical signal sampling pulse generator based on time-mode interleaved multiplexing, comprising:
a waveguide delay line (701) composed of N sections of waveguides with different widths; the waveguide delay line (701) is of a roundabout structure formed by N sections of U-shaped waveguides, and each section of U-shaped waveguide comprises a bent waveguide and two straight waveguides; the waveguides with different widths in the waveguide delay line (701) are connected through a tapered waveguide;
the optical splitter (2) is used for generating N optical pulse signals to correspond to the N sections of waveguides with different widths, wherein the first optical pulse signal is directly input into the first section of waveguide, the Kth optical pulse signal is coupled into the Kth section of waveguide after mode conversion, and K is more than or equal to 2 and less than or equal to N;
n optical pulse signals in different modes enter the waveguide delay line (701) from different width positions respectively, so that the waveguide delay line (701) outputs the optical pulse signals in different modes and with different delays.
2. The time-mode interleaved multiplexing based optical signal sampling pulse generator of claim 1 further comprising at least one optical mode coupler, the optical mode coupler comprising a curved waveguide (401) and a straight waveguide (402), the straight waveguide (402) being in close proximity to the straight waveguide of the waveguide delay line (701) for mode-converting the kth optical pulse signal into a kth section of U-shaped waveguide, wherein 2 ≦ K ≦ N.
3. The time-mode interleaved multiplexed based optical signal sampling pulse generator of claim 2 wherein one output port (300) of said optical splitter (2) is the same cross-sectional size as the input port (700) of said waveguide delay line (701) and the remaining output ports of said optical splitter (2) are the same cross-sectional size as the input port (400) of said optical mode coupler.
4. The time-mode interleaved multiplexing based optical signal sampling pulser of claim 2 wherein said optical mode couplers are respectively disposed at different path length positions of said waveguide delay line (701).
5. The time-mode interleaved multiplexing based optical signal sampling pulser according to claim 2, wherein the structure of the waveguide delay line (701), the optical mode coupler and the optical beam splitter (2) comprises a stripe structure or a ridge structure.
6. The time-mode interleaved multiplexing based optical signal sampling pulser according to claim 1, wherein the optical splitter (2) comprises an optical power splitter or an optical wavelength demultiplexing splitter, wherein the structure of the optical wavelength demultiplexing splitter comprises a micro-ring and micro-disk resonant structure, an arrayed waveguide grating structure, a diffractive echelle grating structure, a cascaded mach-zehnder interferometer structure, a bragg grating waveguide structure, or an F-P interferometric cavity structure.
7. The time-mode interleaved multiplexing based optical signal sampling pulse generator according to claim 2 wherein said optical beam splitter (2) comprises a TE mode single polarization beam splitter, a TM mode single polarization beam splitter or a TE and TM mixed mode polarization beam splitter; the optical mode coupler comprises a TE mode single polarized optical mode coupler, a TM mode single polarized optical mode coupler, or a TE and TM mixed mode polarized optical mode coupler.
8. The time-mode interleaved multiplexing based optical signal sampling pulser of claim 2 wherein the structure of the optical mode coupler comprises a single coupler structure or a cascaded coupler structure.
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