CN113759460A - Polarization-independent variable optical attenuator - Google Patents
Polarization-independent variable optical attenuator Download PDFInfo
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- CN113759460A CN113759460A CN202111075019.9A CN202111075019A CN113759460A CN 113759460 A CN113759460 A CN 113759460A CN 202111075019 A CN202111075019 A CN 202111075019A CN 113759460 A CN113759460 A CN 113759460A
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B2006/12083—Constructional arrangements
- G02B2006/12085—Integrated
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B2006/12083—Constructional arrangements
- G02B2006/12107—Grating
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B2006/12133—Functions
Abstract
The invention discloses a polarization-independent variable optical attenuator, which comprises: the grating coupler comprises a first two-dimensional grating coupler, a second two-dimensional grating coupler, a plurality of first spot size converters, a plurality of second spot size converters, a plurality of first silicon-based single-mode optical waveguides, a plurality of second silicon-based single-mode optical waveguides and a PIN electrical structure. The variable optical attenuator of the invention uses the planar optical waveguide, and has the advantages of high speed, small volume, low cost, easy integration and the like; the two-dimensional grating coupler has polarization independence, and can transmit light with any polarization regardless of input light.
Description
Technical Field
The invention belongs to the technical field of optical communication, and particularly relates to a polarization-independent variable optical attenuator.
Background
With the invention of wavelength division multiplexing and erbium-doped fiber amplifiers at the end of the last century, large-capacity, long-distance fiber-optic communications have been widely developed over the past two decades. At present, optical fiber communication is developing towards short-distance communication, the application of the optical fiber communication in the directions of metropolitan area networks and local area networks is increasingly diversified, and optical passive networks are rapidly developing. The short-distance high-speed optical fiber communication requires that the optical module is as small as possible, the short-distance high-speed optical fiber communication puts forward higher requirements on the integration level of the optical module, high-density high-speed packaging and the like are already proposed at present, but the requirements of future small packaging cannot be met, and the silicon-based optoelectronic technology can enable the size of the optical module to be remarkably reduced, so that the silicon-based optoelectronic technology has great potential in the future. Meanwhile, with the adoption of the 5G construction, data with low delay, high speed and wide bandwidth are uploaded and downloaded between 5G base stations and between the base stations and a communication center, and the number of required optical modules is more than several times of 4G. The optical module is a core component of optical communication and mainly completes photoelectric conversion. The optical module is widely applied to communication equipment as a core device, and is a key for realizing high bandwidth, low time delay and wide connection of 5G. With the accelerated development of 5G, the optical module industry in China is rapidly developed.
Since the last century, information transmission technology has undergone the transition from electrical to optical and from time division multiplexing to wavelength division multiplexing, optical attenuators have come into force, and adjustable optical attenuators capable of realizing dynamic light intensity changes are one of the components of dense wavelength division multiplexing systems. The variable optical attenuator quantitatively attenuates an optical signal, and an optical attenuation value can be adjusted according to requirements, so that the variable optical attenuator is one of the most basic passive devices in optical fiber communication and is an important optical device in a modern optical communication system. The variable optical attenuator is widely used in dense wavelength division multiplexing optical fiber network, mainly to realize the dynamic monitoring of the optical power between each channel in the system and the transmission system, and at the same time to control the gain of the optical amplifier. In an optical module, optical power needs to be reduced to achieve an optimum bit error rate, and an optical fiber attenuator needs to be used. The intensity of the optical signal received by the light receiving device needs to be within a certain range, and the optical power cannot be too strong or too weak. Otherwise, the service life of the device is shortened or the device cannot work normally. The optical fiber attenuator can reduce the energy of optical signals, and avoids the distortion of an optical receiver caused by the ultra-strong input optical power to the optical passive device with the attenuated input optical power.
In recent years, variable optical attenuators of different materials and structures have been reported, such as variable optical attenuators of the micro-electromechanical system type, variable optical attenuators of the liquid crystal type, variable optical attenuators of the displacement type, and variable optical attenuators of the planar optical waveguide type. Although the attenuator in the existing optical network is mainly the adjustable optical attenuator of the traditional micro-electromechanical system structure, the adjustable optical attenuator of the structure has the disadvantages of large volume, high power consumption and difficulty in integrating with other devices. The planar optical waveguide type adjustable optical attenuator is the fastest developed branch recently, and has the advantages of high speed, small volume, better temperature stability and easiness in integration. The variable optical attenuator based on the planar optical waveguide technology can be realized in various ways, such as Mach-Zehnder interferometer, electro-absorption modulation, curved optical waveguide, and the like.
Compared with a micro-electro-mechanical system type variable optical attenuator: the micro-electro-mechanical system type adjustable optical attenuator is large in size, high in power consumption and slow in reaction time, so that the micro-electro-mechanical system type adjustable optical attenuator is not easy to integrate. The rotation angle of the reflector is controlled by the MEMS reflector applied with voltage, and the change of the rotation angle enables the light spot of the reflector to be totally or partially reflected to one of the two output optical fibers or move in the two output optical fibers after passing through the collimating lens. However, when no voltage or a small voltage is applied, part of the reflected light from the mirror will be fed back into the input fiber, thereby affecting the overall performance. Therefore, an additional isolator with higher isolation is required, which increases the cost of the device.
In addition, chinese patent application publication No. CN113050302A in the prior art discloses a silicon-based variable optical attenuator, which can significantly improve the antistatic level of the silicon-based variable optical attenuator by providing the silicon-based variable optical attenuator and the manufacturing method thereof.
The silicon-based adjustable optical attenuator designed in CN113050302A has a complex structure and high manufacturing difficulty. The input and output ends of the waveguide are all single-mode waveguides, and the influence on the polarization state is not mentioned.
Therefore, in order to solve the above technical problems, it is necessary to provide a polarization-independent variable optical attenuator.
Disclosure of Invention
In view of the above, the present invention provides a polarization-independent variable optical attenuator, which has the advantages of a planar optical waveguide, such as small volume, low cost, and easy integration, and has polarization independence, and can transmit whatever polarization is input.
In order to achieve the above object, an embodiment of the present invention provides the following technical solutions:
a polarization-independent variable optical attenuator, the variable optical attenuator comprising:
the optical fiber coupler comprises a first two-dimensional grating coupler and a second two-dimensional grating coupler, wherein the first two-dimensional grating coupler is used for splitting a first optical signal, the second two-dimensional grating coupler is used for outputting a second optical signal after the optical signals are combined, and the polarization states of the first optical signal and the second optical signal are the same;
the first spot size converters are in optical communication connection with the first two-dimensional grating coupler, and the second spot size converters are in optical communication connection with the second two-dimensional grating coupler;
the first silicon-based single-mode optical waveguides are in optical communication connection with the first spot size converter, and the second silicon-based single-mode optical waveguides are in optical communication connection with the second spot size converter;
and the PIN electrical structures are used for absorbing optical signals to realize the attenuation of the optical signals, and are in optical communication connection with the first silicon-based single-mode optical waveguide and the second silicon-based single-mode optical waveguide.
In an embodiment, the first two-dimensional grating coupler is in optical communication with a first optical fiber, the second two-dimensional grating coupler is in optical communication with a second optical fiber, and the first optical fiber and the second optical fiber are single-mode optical fibers.
In one embodiment, the interface of the first optical fiber is perpendicular to the surface of the first two-dimensional grating coupler, and the first optical signal is perpendicular to the surface of the first two-dimensional grating coupler and located at the center of the first two-dimensional grating coupler; the interface of the second optical fiber is vertical to the surface of the second two-dimensional grating coupler, and the second optical signal is vertical to the surface of the second two-dimensional grating coupler and is positioned at the central position of the second two-dimensional grating coupler.
In one embodiment, the first two-dimensional grating coupler is a four-channel input coupler, and is configured to implement four-channel uniform beam splitting of the first optical signal; the second two-dimensional grating coupler is a four-channel output coupler and is used for combining four-channel optical signals and outputting a second optical signal.
In an embodiment, the tunable optical attenuator includes four first silicon-based single-mode optical waveguides and four second silicon-based single-mode optical waveguides, and optical paths of optical signals in the first silicon-based single-mode optical waveguides are equal to optical paths of optical signals in the second silicon-based single-mode optical waveguides.
In an embodiment, the first silicon-based single mode optical waveguide and the second silicon-based single mode optical waveguide include a plurality of curved waveguides and/or a plurality of straight waveguides.
In an embodiment, the first silicon-based single mode optical waveguide and the second silicon-based single mode optical waveguide are ridge waveguides made of silicon materials.
In one embodiment, the PIN electrical structure comprises:
a substrate;
a lower cladding layer on the substrate;
the device layer is positioned on the lower cladding layer and comprises a P-type doped region, an N-type doped region and an intrinsic region, and the intrinsic region is positioned between the P-type doped region and the N-type doped region;
an upper cladding layer on the device layer;
the electrode comprises a first electrode electrically connected with the P-type doped region and a second electrode electrically connected with the N-type doped region;
the P-type doped region and the N-type doped region are connected through the intrinsic region, and carriers in the intrinsic region absorb the energy of photons in an optical signal to realize the attenuation of the optical signal.
In one embodiment, the P-type doped region includes a plurality of P-type doped regions with different doping types and/or doping ranges and/or doping concentrations, and the N-type doped region includes a plurality of N-type doped regions with different doping types and/or doping ranges and/or doping concentrations; and/or the presence of a gas in the gas,
a forward voltage is applied between the first and second electrodes to facilitate movement of carriers.
In one embodiment, the substrate is a silicon substrate; and/or the presence of a gas in the gas,
the lower cladding and/or the upper cladding are/is a silica layer; and/or the presence of a gas in the gas,
a plurality of through holes are formed in the upper cladding layer above the P-type doped region and the N-type doped region in an etching mode, conductive columns are formed in the through holes, and the first electrode and the second electrode are electrically connected with the P-type doped region and the N-type doped region through the conductive columns in the through holes respectively; and/or the presence of a gas in the gas,
the height of the intrinsic region is larger than that of the P-type doped region and the N-type doped region.
The invention has the following beneficial effects:
the variable optical attenuator of the invention uses the planar optical waveguide, and has the advantages of high speed, small volume, low cost, easy integration and the like;
the two-dimensional grating coupler is adopted, has polarization independence, and can transmit light regardless of the input polarized light;
the two-dimensional grating coupler is a complete vertical coupler and has the advantages of strong alignment tolerance capability, easiness in on-chip test, low cost and the like.
Drawings
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments described in the present application, and other drawings can be obtained by those skilled in the art without creative efforts.
FIG. 1 is a schematic diagram of a variable optical attenuator according to an embodiment of the present invention;
FIG. 2 is a cross-sectional view of a PIN electrical structure in an embodiment of the invention;
FIG. 3a is a graph of the effective refractive index of a PIN electrical structure as a function of voltage in accordance with one embodiment of the present invention;
FIG. 3b is a graph of optical waveguide transmission loss versus voltage for a PIN electrical structure in an embodiment of the present invention;
FIG. 4a is a graph of normalized optical transmission spectrum of the variable optical attenuator with P1 polarization state as a function of voltage according to an embodiment of the present invention;
FIG. 4b is a graph of normalized optical transmission spectrum of the variable optical attenuator with P2 polarization state as a function of voltage according to an embodiment of the present invention;
FIG. 5 is a graph showing the peak wavelength optical power of the variable optical attenuator at different voltages as a function of voltage according to an embodiment of the present invention.
Detailed Description
In order to make those skilled in the art better understand the technical solution of the present invention, the technical solution in the embodiment of the present invention will be clearly and completely described below with reference to the drawings in the embodiment of the present invention, and it is obvious that the described embodiment is only a part of the embodiment of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention discloses an adjustable optical attenuator, which comprises:
the first two-dimensional grating coupler is used for splitting a first optical signal, the second two-dimensional grating coupler is used for outputting a second optical signal after the optical signals are combined, and the polarization states of the first optical signal and the second optical signal are the same;
the first spot size converters are in optical communication connection with the first two-dimensional grating coupler, and the second spot size converters are in optical communication connection with the second two-dimensional grating coupler;
the first silicon-based single-mode optical waveguides are in optical communication connection with the first spot size converter, and the second silicon-based single-mode optical waveguides are in optical communication connection with the second spot size converter;
and the PIN electrical structure is used for absorbing the optical signal to realize the attenuation of the optical signal, and is in optical communication connection with the first silicon-based single-mode optical waveguide and the second silicon-based single-mode optical waveguide.
The variable optical attenuator of the present invention is further described with reference to the following embodiments.
Referring to fig. 1, a polarization-independent variable optical attenuator in an embodiment of the present invention includes two bidirectional two-dimensional grating couplers, eight spot size converters, eight silicon-based single-mode optical waveguides, and four PIN electrical structures.
The two-dimensional grating coupler comprises a first two-dimensional grating coupler 11 and a second two-dimensional grating coupler 12, the first two-dimensional grating coupler 11 is used for splitting a first optical signal, the second two-dimensional grating coupler 12 is used for outputting a second optical signal after the optical signals are combined, and the polarization states of the first optical signal and the second optical signal are the same.
Specifically, the first two-dimensional grating coupler 11 is connected to a first optical fiber (not shown) in optical communication, the second two-dimensional grating coupler 12 is connected to a second optical fiber (not shown) in optical communication, and the first optical fiber and the second optical fiber are single-mode optical fibers. The interface of the first optical fiber is vertical to the surface of the first two-dimensional grating coupler, and a first optical signal in the first optical fiber is vertical to the surface of the first two-dimensional grating coupler and is positioned in the center of the first two-dimensional grating coupler; the interface of the second optical fiber is vertical to the surface of the second two-dimensional grating coupler, and a second optical signal output by the second two-dimensional grating coupler is vertical to the surface of the second two-dimensional grating coupler and is positioned at the center of the second two-dimensional grating coupler.
In this embodiment, the first two-dimensional grating coupler 11 and the second two-dimensional grating coupler 12 are both four-channel input couplers, the first two-dimensional grating coupler 11 is configured to implement four-channel uniform beam splitting of a first optical signal (i.e., an input optical signal), and the second two-dimensional grating coupler 12 is configured to implement beam combining of four-channel optical signals and output a second optical signal (i.e., an output optical signal).
The spot size converter comprises four first spot size converters 21 and four second spot size converters 22, the first spot size converter 21 is connected with the first two-dimensional grating coupler 11 in an optical communication mode, and the second spot size converter 22 is connected with the second two-dimensional grating coupler 12 in an optical communication mode. The mode spot converter can realize mode conversion and adiabatic light transmission between the two-dimensional grating coupler and the silicon-based single-mode optical waveguide.
The spot size converters in this embodiment are tapered structures, four first spot size converters 21 complete transmission of an optical signal from the first two-dimensional grating coupler 11 to the first silicon-based single-mode optical waveguide 31, and four second spot size converters 22 complete transmission of an optical signal from the four-way second silicon-based single-mode optical waveguide 32 to the second two-dimensional grating coupler 12.
The optical waveguide structure comprises four first silicon-based single-mode optical waveguides 31 and four second silicon-based single-mode optical waveguides 32, wherein the first silicon-based single-mode optical waveguides and the second silicon-based single-mode optical waveguides are ridge waveguides made of silicon materials, an optical field is well limited in a waveguide core layer, and low loss and single-mode transmission of optical signals inside the device can be achieved. The first silica-based single mode optical waveguide 31 is in optical communication with the first spot size converter 21 and the second silica-based single mode optical waveguide 32 is in optical communication with the second spot size converter 22. The silicon-based single-mode optical waveguide is used as a main medium for optical signal transmission and is used for realizing low loss and single-mode transmission of optical signals in the device.
The PIN electrical structure 40 is configured to absorb an optical signal to implement attenuation of the optical signal, in this embodiment, four PIN electrical structures are provided, and each PIN electrical structure 40 is in optical communication connection with one group of the first silicon-based single mode optical waveguides 31 and the second silicon-based single mode optical waveguides 32.
The optical path of the optical signal in each first silicon-based single mode optical waveguide 31 and the optical path of the optical signal in each second silicon-based single mode optical waveguide 32 are equal and have the same phase change, and the first silicon-based single mode optical waveguide and the second silicon-based single mode optical waveguide include a plurality of curved waveguides and/or a plurality of straight waveguides.
The first silica-based single mode optical waveguide 31 and the second silica-based single mode optical waveguide 32 in this embodiment are arranged in central symmetry in fig. 1. Taking the second silica-based single mode optical waveguide 32 outlined by the dashed line as an example, the second silica-based single mode optical waveguide 32 includes a first curved waveguide 321, a second curved waveguide 322, a third curved waveguide 323, a fourth curved waveguide 324, and a straight waveguide 325.
Wherein the first curved waveguide 321 is a curved waveguide with an angle of 135 °; the second curved waveguide 322 is a curved waveguide with an angle of 180 °; the third curved waveguide 323 is a curved waveguide with an angle of 45 °; fourth curved waveguide 324 is a curved waveguide having an angle of 90. Angularly, the first curved waveguide 321 is equal to the sum of the angles of the third curved waveguide 323 and the fourth curved waveguide 324, and the optical path difference is complemented by the straight waveguide 325. Thus, the optical path length of each optical signal output by the spot size converter can be ensured to be the same.
It should be understood that the silica-based single-mode optical waveguide in this embodiment is described by taking 4 segments of curved waveguides and one segment of straight waveguides as examples, and in other embodiments, other numbers of curved waveguides and/or straight waveguides may be used, and any optical waveguide that can ensure equal optical paths falls within the scope of the present invention.
As shown in connection with fig. 2, PIN electrical structure 40 in the present embodiment includes:
a substrate 41, which is a silicon substrate in this embodiment;
a lower cladding layer 42 on the substrate, the lower cladding layer being a silica layer in this embodiment;
a device layer disposed on the lower cladding layer, the device layer including a P-type doped region (P + +, P)431, an N-type doped region (N + +, N)432, and an intrinsic region 433, the intrinsic region (I)433 being disposed between the P-type doped region 431 and the N-type doped region 432, preferably, the intrinsic region has a height greater than the P-type doped region and the N-type doped region;
an upper cladding layer 44 on the device layer, the upper cladding layer being a silica layer in this embodiment;
the electrodes include a first electrode 451 electrically connected to the P-type doped region 431 and a second electrode 452 electrically connected to the N-type doped region 432, and the material of the electrodes is aluminum in this embodiment.
In this embodiment, a plurality of through holes are etched in the upper cladding layer above the P-type doped region and the N-type doped region, conductive pillars are formed in the through holes, and the first electrode and the second electrode are electrically connected with the P-type doped region and the N-type doped region through the conductive pillars in the through holes, respectively.
In order to ensure that the device can realize the attenuation function, the P-type doped region in the present application is connected to the first electrode (i.e. the electrode marked with "+" in fig. 1), and the N-type doped region is connected to the second electrode (i.e. the electrode marked with "-" in fig. 1), and the attenuation is realized to different degrees by controlling the voltage, and the second electrode is usually grounded.
The electrodes are electrically connected with the P-type doped region and the N-type doped region through the through holes and the metal conductive columns, and the distance between the two electrodes needs to be a certain distance away from the ridge waveguide, so that the function of the variable optical attenuator can be realized.
In the silicon-based optical waveguide adjustable optical attenuator designed based on the SOI substrate material in this embodiment, for different thicknesses of the silicon dioxide buried oxide layer and the top layer silicon, corresponding optimal designs for achieving the functional requirements are also different, so for convenience of description, the substrate material in this embodiment is defaulted to be specific implementation parameters, the thickness of the buried oxide layer is 2 μm, and the thickness of the top layer silicon is 220 nm.
In the variable optical attenuator, a P-type doped region 431 and an N-type doped region 432 are connected through an intrinsic region 433, and a carrier in the intrinsic region 433 absorbs the energy of a photon in an optical signal to realize the attenuation of the optical signal.
The PIN electrical structure 40 in this embodiment is formed by doping a ridge waveguide structure formed of a silicon material. The P-type doped region and the N-type doped region are respectively positioned in the flat plate layers on two sides of the ridge waveguide to form a PIN structure. The positive voltage is applied to the silicon material, the concentration of the current carrier in the intrinsic region (I) is rapidly increased, and the movement of the current carrier doped into the silicon-based single-mode optical waveguide can influence the refractive index of the PIN electrical structure of the silicon-based optical waveguide adjustable optical attenuator to change the refractive index, so that the absorption function of light can be realized, and the light can be attenuated.
The optical signal light enters the first two-dimensional grating coupler 11 through the first optical fiber, is divided into four light beams by the first two-dimensional grating coupler, is coupled and enters the silicon-based single-mode optical waveguide plane, and is transmitted in the four-path silicon-based single-mode optical waveguide 31 through the four first spot-size converters 21. Each first silica-based single mode optical waveguide 31 is embedded in a length of PIN electrical structure 40 and connected to PIN electrical structure 40 by second electrode 452. By adjusting the voltages applied to the first electrode 451 and the second electrode 452, the carrier concentration in the intrinsic region can be adjusted. The carrier can absorb the energy of the photon in the optical signal and makes transition in the energy level in the same energy band, when the photon in the optical signal is partially absorbed, the optical signal can be attenuated, and the absorption of the intrinsic region on the optical signal can be adjusted by adjusting the concentration of the carrier in the intrinsic region, so that the attenuation of the optical signal can be adjusted. The optical paths of the four paths of light of the first silicon-based single-mode optical waveguide are the same, so that the loss of the four paths of light is the same. The attenuated optical signal is transmitted to the second spot size converter 22 through the four paths of second silicon-based single-mode optical waveguides 32, and finally transmitted to the second two-dimensional grating coupler 22 to couple the four paths of optical signals and vertically output the four paths of optical signals to the second optical fiber, so that the attenuated optical signal can be obtained. The polarization state of the optical signal after being attenuated is the same as that of the optical signal before being attenuated, namely the polarization state before and after passing through the attenuator is unchanged, so the silicon-based optical waveguide variable optical attenuator is a polarization-independent type.
The device layer in this embodiment is a silicon device layer, silicon is used as a material, and the PIN electrical structure 40 of the silica-based optical waveguide variable optical attenuator is made into a ridge waveguide structure, wherein N, P represents different ion doping properties, and "+" represents ion doping concentration. The performance of the silicon-based optical waveguide variable optical attenuator can be optimized by changing the doping type, the doping area range and the doping concentration of the ions.
In addition, the width, height, slab region height, etc. of the PIN electrical structure 40 have a great influence on the performance of the silicon-based optical waveguide variable optical attenuator, and can be optimally designed.
A forward voltage is applied between the first electrode 451 and the second electrode 452 in this embodiment to promote movement of carriers.
FIG. 3a is a graph of the effective index of refraction of a PIN electrical structure as a function of voltage, with the index of refraction changing more rapidly as the voltage increases. Fig. 3b is a graph of optical waveguide transmission loss versus voltage for a PIN electrical structure, where as voltage increases, the loss increases, indicating that light is attenuated.
Fig. 4a is a graph of normalized optical transmission spectrum of the variable optical attenuator with P1 polarization state as a function of voltage, and fig. 4b is a graph of normalized optical transmission spectrum of the variable optical attenuator with P2 polarization state as a function of voltage. As can be seen from fig. 4a and 4b, the attenuation capability of the variable optical attenuator is enhanced with the increase of the voltage, and the attenuation is fast with the smaller voltage, so the smaller voltage can meet the requirement of the attenuation performance. Comparing fig. 4a and 4b, it can be seen that the normalized light transmission spectrum graphs of the light in different polarization states passing through the variable optical attenuator are the same, so the device of the present invention is a polarization-independent variable optical attenuator. In order to more clearly see the effect of voltage on the attenuation performance, the length of the adjustable optical attenuator in the present invention is set to 300 μm, and as can be seen from fig. 4a and 4b, the attenuation of the silica-based optical waveguide adjustable optical attenuator is about 25dB under the driving of 4V voltage.
FIG. 5 is a graph of the peak wavelength optical power of the adjustable optical attenuator under different voltages as a function of voltage, and it can be seen from FIG. 5 that the attenuation performance of the adjustable optical attenuator is higher as the voltage is increased.
According to the technical scheme, the invention has the following advantages:
the variable optical attenuator of the invention uses the planar optical waveguide, and has the advantages of high speed, small volume, low cost, easy integration and the like;
the two-dimensional grating coupler is adopted, has polarization independence, and can transmit light regardless of the input polarized light;
the two-dimensional grating coupler is a complete vertical coupler and has the advantages of strong alignment tolerance capability, easiness in on-chip test, low cost and the like.
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.
Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.
Claims (10)
1. A polarization-independent variable optical attenuator, comprising:
the optical fiber coupler comprises a first two-dimensional grating coupler and a second two-dimensional grating coupler, wherein the first two-dimensional grating coupler is used for splitting a first optical signal, the second two-dimensional grating coupler is used for outputting a second optical signal after the optical signals are combined, and the polarization states of the first optical signal and the second optical signal are the same;
the first spot size converters are in optical communication connection with the first two-dimensional grating coupler, and the second spot size converters are in optical communication connection with the second two-dimensional grating coupler;
the first silicon-based single-mode optical waveguides are in optical communication connection with the first spot size converter, and the second silicon-based single-mode optical waveguides are in optical communication connection with the second spot size converter;
and the PIN electrical structures are used for absorbing optical signals to realize the attenuation of the optical signals, and are in optical communication connection with the first silicon-based single-mode optical waveguide and the second silicon-based single-mode optical waveguide.
2. The variable optical attenuator of claim 1, wherein the first two-dimensional grating coupler is in optical communication with a first optical fiber, the second two-dimensional grating coupler is in optical communication with a second optical fiber, and the first and second optical fibers are single mode optical fibers.
3. The variable optical attenuator of claim 2, wherein the interface of the first optical fiber is perpendicular to the surface of the first two-dimensional grating coupler, and the first optical signal is perpendicular to the surface of the first two-dimensional grating coupler and located at the center of the first two-dimensional grating coupler; the interface of the second optical fiber is vertical to the surface of the second two-dimensional grating coupler, and the second optical signal is vertical to the surface of the second two-dimensional grating coupler and is positioned at the central position of the second two-dimensional grating coupler.
4. The variable optical attenuator of claim 1, wherein the first two-dimensional grating coupler is a four-channel input coupler for achieving four-channel uniform splitting of the first optical signal; the second two-dimensional grating coupler is a four-channel output coupler and is used for combining four-channel optical signals and outputting a second optical signal.
5. The variable optical attenuator of claim 4, wherein the variable optical attenuator comprises four first silica-based single mode optical waveguides and four second silica-based single mode optical waveguides, and the optical path lengths of the optical signals in the first silica-based single mode optical waveguides are equal to the optical path lengths in the second silica-based single mode optical waveguides.
6. The polarization-independent variable optical attenuator of claim 5, wherein the first and second silicon-based single mode optical waveguides comprise curved waveguides and/or straight waveguides.
7. The polarization-independent variable optical attenuator of claim 1, wherein the first and second silica-based single mode optical waveguides are rib waveguides made of a silicon material.
8. The polarization-independent variable optical attenuator of claim 1, wherein the PIN electrical structure comprises:
a substrate;
a lower cladding layer on the substrate;
the device layer is positioned on the lower cladding layer and comprises a P-type doped region, an N-type doped region and an intrinsic region, and the intrinsic region is positioned between the P-type doped region and the N-type doped region;
an upper cladding layer on the device layer;
the electrode comprises a first electrode electrically connected with the P-type doped region and a second electrode electrically connected with the N-type doped region;
the P-type doped region and the N-type doped region are connected through the intrinsic region, and carriers in the intrinsic region absorb the energy of photons in an optical signal to realize the attenuation of the optical signal.
9. The polarization-independent variable optical attenuator of claim 8,
the P-type doped region comprises a plurality of P-type doped regions with different doping types and/or doping ranges and/or doping concentrations, and the N-type doped region comprises a plurality of N-type doped regions with different doping types and/or doping ranges and/or doping concentrations; and/or the presence of a gas in the gas,
a forward voltage is applied between the first and second electrodes to facilitate movement of carriers.
10. The polarization-independent variable optical attenuator of claim 8,
the substrate is a silicon substrate; and/or the presence of a gas in the gas,
the lower cladding and/or the upper cladding are/is a silica layer; and/or the presence of a gas in the gas,
a plurality of through holes are formed in the upper cladding layer above the P-type doped region and the N-type doped region in an etching mode, conductive columns are formed in the through holes, and the first electrode and the second electrode are electrically connected with the P-type doped region and the N-type doped region through the conductive columns in the through holes respectively; and/or the presence of a gas in the gas,
the height of the intrinsic region is larger than that of the P-type doped region and the N-type doped region.
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