CN214845872U - QPSK modulator based on mode separation - Google Patents
QPSK modulator based on mode separation Download PDFInfo
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- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 claims abstract description 54
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Abstract
The utility model relates to a QPSK modulator based on mode separation. The utility model comprises a silicon nitride device layer and a silicon device layer; the silicon nitride device layer comprises a TM grating coupler, TM polarized light in the TM grating coupler is coupled into a spot size converter, the spot size converter is connected with the silicon nitride waveguide, the TM polarized light spot after compression coupling is transmitted in the silicon nitride waveguide, and light is coupled into the lower silicon device layer through a coupling wedge structure between the silicon nitride layers; the silicon device layer comprises a TE grating coupler, TE polarized light in the TE grating coupler is coupled into a spot size converter, the spot size converter is connected with the silicon waveguide, the TE polarized light spots after compression coupling are transmitted in the silicon waveguide, and meanwhile TM polarized light spots of the upper silicon nitride device layer enter the lower silicon waveguide through the coupling wedge-shaped structure between the silicon layers. The utility model discloses a polarization diversity's coupling, light source and the encapsulation of device are more simple, have reduced the encapsulation cost.
Description
Technical Field
The utility model relates to a QPSK modulator based on mode separation belongs to semiconductor photoelectron signal transmission technical field.
Background
Global information communication requires an optical transmission system having high spectral efficiency, a high data transmission rate per channel, and low cost. Advanced optical modulation formats, as well as wavelength division and polarization division multiplexing techniques, are key drivers to improve spectral efficiency and aggregate data rates within the limited spectral bandwidth of available optical amplifiers. High capacity coherent optical transmitters and receivers require many advanced optical components such as modulators, detectors, power splitters/combiners, polarization splitters, wavelength multiplexing filters, etc. These components are ideally implemented on Photonic Integrated Circuits (PICs), which have the advantages of precise optical path control, compact size, low power consumption, and potentially low packaging cost.
Digital coherent communication systems with advanced modulation formats have attracted a great deal of attention for high transmission rates in optical fiber networks. 100Gb/s digital coherent systems based on QPSK format have been introduced into long haul optical fiber networks. In order to extend the digital coherent system to the metropolitan area network, it is necessary to reduce the size of the transmission apparatus and to reduce the cost thereof, and therefore, a small-sized, low-cost optical apparatus is indispensable. An IQ modulator based on Mach-Zehnder interferometer (MZI) and a waveguide for Polarization Division Multiplexing (PDM) are integrated together, are key optical equipment, have small occupied area and are suitable for pluggable small-size digital coherent digital transceivers in metropolitan area networks. Monolithic silicon modulators are an attractive candidate for small-size, low-cost modulators in such applications.
However, extensive research on silicon waveguide modulators has focused on increasing the modulation rate and reducing the drive voltage of silicon-based modulators. Nevertheless, silicon modulators typically still perform better than LiNbO3The modulator difference is due in part to the weak electro-optic effect in silicon modulators that use free carrier induced refractive index changes. As a result, most of the reported silicon modulators focus on-off keying (OOK) modulation formats, which are suitable for short distances where the requirements on extinction ratio and linearity are not highApplication is carried out. However, the QPSK modulation scheme has been studied only in the early stage. Meanwhile, for the current modulator structure, due to the single-mode structure design, the device needs to be subjected to polarization control debugging before being tested and used, and the loss and the test difficulty of the device are increased. Therefore, the present invention implements QPSK modulation by using a mode separation method.
Disclosure of Invention
The to-be-solved technical problem of the utility model is: the utility model provides a QPSK modulator based on mode separation, the encapsulation that has realized polarization diversity's coupling, light source and device is more simple, has reduced the encapsulation cost.
The utility model adopts the technical scheme that: a QPSK modulator based on mode separation comprises an upper silicon nitride device layer and a lower silicon device layer; wherein the upper silicon nitride device layer comprises: the TM grating coupler 1 is characterized in that TM polarized light in the TM grating coupler 1 is coupled into a first spot size converter 3, the first spot size converter 3 is connected with a silicon nitride waveguide 4, the TM polarized light spot after compression coupling is transmitted in the silicon nitride waveguide 4, and light is coupled into a lower silicon device layer through a silicon nitride interlayer coupling wedge-shaped structure 22 in an interlayer coupler 6;
the lower silicon device layer includes: a TE grating coupler 2, TE polarized light in the TE grating coupler 2 is coupled into a second spot size converter 3, the second spot size converter 3 is connected with a silicon waveguide 5, the TE polarized light spot after compression coupling is transmitted in the silicon waveguide 5, and a TM polarized light spot of an upper silicon nitride device layer enters a lower silicon waveguide 5 through an inter-silicon layer coupling wedge-shaped structure 21 in an interlayer coupler 6; the silicon waveguide 5 is connected with the MMI7 and used for dividing the polarized light spots into four paths to enter the modulation arm 8, wherein the upper in-phase optical path adopts a similar MZI structure to perform I signal modulation, and the lower orthogonal optical path also adopts a similar MZI structure to perform Q signal modulation; the modulated signals all enter the MMI7 to be subjected to light interference beam combination; the optical phase shifter 9 is positioned at the rear end of the MMI of the upper in-phase optical path and is used for performing optical phase conversion to enable the optical phase to be different from the phase difference of pi/2 between the lower path Q signal; the two modulated BPSK optical signals pass through the polarization beam combiner 23 and then output QPSK signals through the output waveguide 10.
As a further proposal of the utility model, the distance between the upper silicon nitride device layer and the lower silicon nitride device layer is 100-250nm, and silicon dioxide material is filled between the two layers.
As a further aspect of the present invention, the TM grating coupler 1 is located on the upper silicon nitride device layer, which has a uniform period and duty ratio, for coupling of TM polarized light.
As a further aspect of the present invention, the TE grating coupler 2 is located on the lower silicon device layer, and has a uniform period and duty ratio for coupling of the TE polarized light.
As a further aspect of the present invention, the first spot size converter 3 and the second spot size converter 3 are tapered structures for compressing the light field into the light waveguide.
As a further aspect of the present invention, there are four modulation arms 8, which are respectively located inside the MZI-like structure; by applying IQ signals to the MZI structure, the phase modulation can be carried out on an internal optical field, the modulation method is thermo-optical modulation, electro-optical modulation or free carrier effect, and through the modulation, the optical phases of the upper arm and the lower arm of the MZI structure can be changed, so that the BPSK modulation is completed.
As a further aspect of the present invention, the split ratio of the MMI7 is 50: 50.
as a further aspect of the present invention, the light phase shifter 9 adjusts the phase difference between the light wave of the in-phase path and the light wave of the orthogonal path through the DC voltage to satisfy pi/2.
As a further aspect of the present invention, the upper silicon nitride device layer and the lower silicon nitride device layer are optically exchanged through the interlayer coupler 6, the interlayer coupler 6 is two stacked wedge structures, and light is transferred from the upper optical path to the lower optical path through the wedge structures.
The utility model has the advantages that:
the utility model discloses a TE and TM grating can regard as the beam splitter function of I passageway and Q passageway again as the coupling interface of single mode light source promptly. The device realizes the coupling of polarization diversity, namely two polarization modes which are vertical to each other can be coupled into a chip, so that the two polarization states can be simultaneously operated in an optical chip, and the requirement of TE and TM polarization conversion when the device works is avoided. Meanwhile, the grating coupler is used as a coupling interface, so that the packaging of the light source and the device is simpler, and the packaging cost is reduced. In conclusion, the utility model has potential application value and prospect, and is expected to be applied to future optical communication networks.
Drawings
FIG. 1 is a schematic diagram of the basic structure of the modulator of the present invention;
FIG. 2 is a schematic cross-sectional view of a modulating arm of the modulator of the present invention;
FIG. 3 is a diagram of an interlayer coupling structure;
fig. 4 is a schematic diagram of the grating structure suitable for TM mode of the present invention;
fig. 5 is a schematic diagram of a grating structure suitable for the TE mode of the present invention;
FIG. 6 is a simulation result of an interlayer coupling structure;
fig. 7 is a result of a modulation simulation of the device.
The various reference numbers in FIGS. 1-7: the optical waveguide coupler comprises a 1-TM grating coupler, a 2-TE grating coupler, a 3-spot-size converter, a 4-silicon nitride waveguide, a 5-silicon waveguide, a 6-interlayer coupler, a 7-MMI, an 8-modulation arm, a 9-optical phase shifter, a 10-output waveguide, an 11-P type doped region, a 12-N type doped region, a 13-P + type doped region, a 14-N + type doped region, a 15-P + + type doped region, a 16-N + + type doped region, a 17-silicon dioxide cladding layer, an 18-silicon dioxide buried oxide layer, a 19-metal electrode, a 20-contact hole, a 21-silicon interlayer coupling wedge structure, a 22-silicon nitride interlayer coupling wedge structure and a 23-polarization beam combiner.
Detailed Description
The present invention will be further described with reference to the accompanying drawings and specific embodiments.
Example 1: as shown in fig. 1-7, a QPSK modulator based on mode separation includes an upper silicon nitride device layer and a lower silicon device layer; wherein the upper silicon nitride device layer comprises: the TM grating coupler 1 is characterized in that TM polarized light in the TM grating coupler 1 is coupled into a first spot size converter 3, the first spot size converter 3 is connected with a silicon nitride waveguide 4, the TM polarized light spot after compression coupling is transmitted in the silicon nitride waveguide 4, and light is coupled into a lower silicon device layer through a silicon nitride interlayer coupling wedge-shaped structure 22 in an interlayer coupler 6;
the lower silicon device layer includes: a TE grating coupler 2, TE polarized light in the TE grating coupler 2 is coupled into a second spot size converter 3, the second spot size converter 3 is connected with a silicon waveguide 5, the TE polarized light spot after compression coupling is transmitted in the silicon waveguide 5, and a TM polarized light spot of an upper silicon nitride device layer enters a lower silicon waveguide 5 through an inter-silicon layer coupling wedge-shaped structure 21 in an interlayer coupler 6; the silicon waveguide 5 is connected with the MMI7 and used for dividing the polarized light spots into four paths to enter the modulation arm 8, wherein the upper in-phase optical path adopts a similar MZI structure to perform I signal modulation, and the lower orthogonal optical path also adopts a similar MZI structure to perform Q signal modulation; the modulated signals all enter the MMI7 to be subjected to light interference beam combination; the optical phase shifter 9 is positioned at the rear end of the MMI of the upper in-phase optical path and is used for performing optical phase conversion to enable the optical phase to be different from the phase difference of pi/2 between the lower path Q signal; the two modulated BPSK optical signals pass through the polarization beam combiner 23 and then output QPSK signals through the output waveguide 10.
As a further proposal of the utility model, the distance between the upper silicon nitride device layer and the lower silicon nitride device layer is 100-250nm, and silicon dioxide material is filled between the two layers.
As a further aspect of the present invention, the TM grating coupler 1 is located on the upper silicon nitride device layer, which has a uniform period and duty ratio, for coupling of TM polarized light.
As a further aspect of the present invention, the TE grating coupler 2 is located on the lower silicon device layer, and has a uniform period and duty ratio for coupling of the TE polarized light.
As a further aspect of the present invention, the first spot size converter 3 and the second spot size converter 3 are tapered structures for compressing the light field into the light waveguide.
As a further aspect of the present invention, there are four modulation arms 8, which are respectively located inside the MZI-like structure; by applying IQ signals to the MZI structure, the phase modulation can be carried out on an internal optical field, the modulation method is thermo-optical modulation, electro-optical modulation or free carrier effect, and through the modulation, the optical phases of the upper arm and the lower arm of the MZI structure can be changed, so that the BPSK modulation is completed.
As a further aspect of the present invention, the split ratio of the MMI7 is 50: 50.
as a further aspect of the present invention, the light phase shifter 9 adjusts the phase difference between the light wave of the in-phase path and the light wave of the orthogonal path through the DC voltage to satisfy pi/2.
As a further aspect of the present invention, the upper silicon nitride device layer and the lower silicon nitride device layer are optically exchanged through the interlayer coupler 6, the interlayer coupler 6 is two stacked wedge structures, and light is transferred from the upper optical path to the lower optical path through the wedge structures.
The silicon nitride waveguide 4 is a strip waveguide with a width of 600nm and a height of 450 nm. The silicon waveguide 5 is a strip waveguide having a width of 500nm and a height of 220 nm. The modulation arm 8 is a ridge row optical waveguide of the reverse compensation PN type. The ridge central region is a reverse PN junction formed by a P-type doped region 11 and an N-type doped region 12 and is connected with a lower flat plate layer, and the flat plate layer consists of a P + type doped region 13 and an N + type doped region 14 and is connected with an external P + + type doped region 15 and an N + + type doped region 16. And metal electrodes 19 are deposited on the P + + type doped regions 15 and the N + + type doped regions 16 to form ohmic contacts. An electrode contact hole 20 is formed above the metal electrode 19 and connected to an external modulation signal. Wherein the implanted ions of the P-type doped region 11, the P + type doped region 13 and the P + + type doped region 15 are boron particles with concentrations of 4e17cm-3，6e17cm-3，1e20cm-3. The implanted ions of the N-type doped region 12, the N + type doped region 14 and the N + + type doped region 16 are phosphorus particles with concentrations of 4e17cm-3，6e17cm-3，1e20cm-3. The metal electrode 19 is made of Al material, and the diameter of the contact hole is 5 micrometers. The period of the upper TM grating coupler 1 is 985nm, and the duty ratio is 0.5. The period of the TE grating coupler 2 is 625nm and the duty cycle is 0.5. Wherein the silicon nitride device layer and the silicon device layer have a layer spacing of 250 nm. The interlayer coupler 6 adopts a wedge shapeThe dislocation distance L between the inter-silicon layer coupling wedge-shaped structure 21 and the inter-silicon nitride layer coupling wedge-shaped structure 22 in the structure, the interlayer coupler 6offsetIs 1 micron. The width of the wedge-shaped structure is shifted along the direction of light propagation.
The silicon nitride device layer and the silicon device layer process of the embodiment mainly comprise the following steps:
(1) a silicon dioxide buried oxide layer 18 is formed on a silicon substrate, then a layer of thin film silicon is deposited, and HF and No. 1 liquid are used for cleaning the silicon surface for later use.
(2) And coating a layer of photoresist on the film, carrying out exposure and development on the photoresist, removing the photoresist, cleaning, and etching silicon to form a silicon device layer.
(3) Depositing a layer of SiO with a thickness of 250nm on top of the silicon device layer by LPCVD2And (3) a layer.
(4) By LPCVD on SiO2A silicon nitride layer film with a thickness of 400nm is deposited on the layer. And high temperature annealing treatment at 1100 deg.C is carried out
(5) And coating a layer of photoresist on the silicon nitride layer film, exposing and developing the photoresist, removing the photoresist, cleaning, and etching the silicon nitride material to form a silicon nitride device layer.
(6) Depositing a layer of SiO on top of a silicon nitride device layer by PECVD2The layer serves as the silica cladding 17 of the device.
Fig. 6 and 7 are optical field patterns and modulation patterns of device simulation of the structure at 1550 wave band. Therefore, the light of the silicon nitride device layer can be smoothly coupled into the silicon waveguide layer through the interlayer coupling device. And by the mode separation method, the device realizes QPSK modulation under the condition of polarization independence.
The principle of the utility model is that:
the silicon nitride layer comprises a TM grating coupler which is used as a coupling interface of the single-mode optical fiber and the modulator, and a spot size converter connected with the coupler and used for converting and transmitting TM light in the grating into a silicon nitride waveguide; an inter-silicon nitride wedge coupling structure for coupling light into the underlying silicon waveguide layer. The silicon layer comprises a TE grating coupler which is used as a coupling interface of input light; the coupler is connected with the spot size converter and used for transmitting TE light in the grating into the silicon waveguide in a compression mode, and the silicon interlayer wedge-shaped coupling structure is used for coupling light of the upper silicon nitride wedge-shaped coupling structure into the lower silicon waveguide; and the four silicon-based modulation arms are used for modulating the I signal and the Q signal. Four MMI structures, wherein two of the MMI structures are used for splitting the branches, and the other two MMI structures are used for combining the branches; and the optical phase shifter is used for connecting the phase difference of the medium light waves of the I modulator and the Q modulator to satisfy pi/2, so that the I signal and the Q signal are synthesized into a QPSK modulation signal.
After a single-mode light beam enters, the TM grating coupler of the silicon nitride can couple TM polarized light in the single-mode light into TM light which enters the silicon nitride waveguide, the TE grating coupler of the lower layer silicon can couple the light into the silicon waveguide, and meanwhile, the light of the silicon nitride layer is also coupled into the silicon waveguide through the interlayer coupling structure. At this time, the light entering the silicon waveguide is modulated by an optical signal through the modulation arm, and finally, a QPSK optical signal is output.
The above-described embodiments can be implemented individually or in various combinations, and such variations are within the scope of the present invention.
It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the term "comprises" or any other variation thereof is intended to cover a non-exclusive inclusion, such that an article or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such article or apparatus. Without further limitation, an element defined by the phrase "comprising … …" does not exclude the presence of additional like elements in the article or device comprising the element.
The above embodiments are merely for illustrating the technical solutions of the present invention and are not to be construed as limiting, and the present invention is described in detail with reference to the preferred embodiments. It should be understood by those skilled in the art that various modifications and equivalent substitutions may be made to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention, and all the modifications and equivalents should be covered by the scope of the claims of the present invention.
Claims (9)
1. A QPSK modulator based on mode separation, comprising: comprises an upper silicon nitride device layer and a lower silicon device layer; wherein the upper silicon nitride device layer comprises: the TM grating coupler (1), TM polarized light in the TM grating coupler (1) is coupled into a first spot size converter (3), the first spot size converter (3) is connected with a silicon nitride waveguide (4), the TM polarized light spot after compression coupling is transmitted in the silicon nitride waveguide (4), and light is coupled into a lower silicon device layer through a silicon nitride interlayer coupling wedge-shaped structure (22) in an interlayer coupler (6);
the lower silicon device layer includes: a TE grating coupler (2), TE polarized light in the TE grating coupler (2) is coupled into a second spot size converter (3), the second spot size converter (3) is connected with a silicon waveguide (5), the compressed and coupled TE polarized light spot is transmitted in the silicon waveguide (5), and meanwhile, a TM polarized light spot of an upper silicon nitride device layer enters a lower silicon waveguide (5) through an inter-silicon layer coupling wedge-shaped structure (21) in an interlayer coupler (6); the silicon waveguide (5) is connected with the MMI (7) and used for dividing the polarized light spots into four paths to enter a modulation arm (8), wherein an upper in-phase optical path adopts a similar MZI structure to perform I signal modulation, and a lower orthogonal optical path also adopts a similar MZI structure to perform Q signal modulation; the modulated signals all enter an MMI (7) to carry out light interference beam combination; the optical phase shifter (9) is positioned at the rear end of the MMI of the upper in-phase optical path and is used for carrying out optical phase conversion so that the phase difference between the optical phase shifter and the lower path Q signal is pi/2; the two modulated BPSK optical signals pass through a polarization beam combiner (23) and then are output as QPSK signals through an output waveguide (10).
2. The QPSK modulator according to claim 1, wherein: the distance between the upper silicon nitride device layer and the lower silicon nitride device layer is 100-250nm, and a silicon dioxide material is filled between the two layers.
3. The QPSK modulator according to claim 1, wherein: the TM grating coupler (1) is located on an upper silicon nitride device layer, has uniform period and duty ratio and is used for coupling TM polarized light.
4. The QPSK modulator according to claim 1, wherein: the TE grating coupler (2) is positioned on the lower silicon device layer, has uniform period and duty ratio and is used for coupling TE polarized light.
5. The QPSK modulator according to claim 1, wherein: the first spot size converter (3) and the second spot size converter (3) are of conical structures and are used for compressing an optical field into a light spot with a waveguide-like size and coupling the light spot into the optical waveguide.
6. The QPSK modulator according to claim 1, wherein: four modulation arms (8) are arranged and are respectively positioned inside the MZI-like structure; by applying IQ signals to the MZI structure, the phase modulation can be carried out on an internal optical field, the modulation method is thermo-optical modulation, electro-optical modulation or free carrier effect, and through the modulation, the optical phases of the upper arm and the lower arm of the MZI structure can be changed, so that the BPSK modulation is completed.
7. The QPSK modulator according to claim 1, wherein: the split ratio of the MMI (7) is 50: 50.
8. the QPSK modulator according to claim 1, wherein: the optical phase shifter (9) adjusts the phase difference of the light waves of the in-phase circuit and the orthogonal circuit to meet pi/2 through direct-current voltage.
9. The QPSK modulator according to claim 1, wherein: the upper silicon nitride device layer and the lower silicon nitride device layer are subjected to optical exchange through an interlayer coupler (6), the interlayer coupler (6) is of two stacked wedge-shaped structures, and light is transferred from an upper optical path to a lower optical path through the wedge-shaped structures.
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