CN101833138B - Method for manufacturing polarization-independent grating coupler - Google Patents
Method for manufacturing polarization-independent grating coupler Download PDFInfo
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- CN101833138B CN101833138B CN2010101612384A CN201010161238A CN101833138B CN 101833138 B CN101833138 B CN 101833138B CN 2010101612384 A CN2010101612384 A CN 2010101612384A CN 201010161238 A CN201010161238 A CN 201010161238A CN 101833138 B CN101833138 B CN 101833138B
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Abstract
The invention provides a method for designing a T-shaped groove grating structure. An output coupler is realized by adopting different coupling principles for two modes so as to realize efficient coupling output by adopting the same structure for a TE mode and a TM mode simultaneously. The coupling efficiencies of the TE mode and the TM mode within a wavelength range of 1,480 to 1,580nm are both above 50 percent; and the coupling efficiencies of the two modes reach 58 percent when the wavelength is 1,550nm. The polarization dependent loss (PDL) of the coupler within a wavelength range of 1,510 to 1,580nm is less than 0.05dB and the PDL of the coupler is only 3.6*10<-3>dB when the wavelength is 1,550nm. The designed grating coupler realizes a coupling output function with high coupling efficiency, low polarization dependent loss and high bandwidth, has the advantages of simple structure, convenient manufacturing and small volume, is compatible with a standard CMOS process, and can provide technical support for the design and manufacturing of a polarization-independent device.
Description
Technical field
The present invention relates to the optically-coupled field, particularly a kind of integrated grating coupling mechanism has the characteristic of polarization irrelevant.
Background technology
Integrated silicon-based optical system because its little device size, and with traditional integrated circuit CMOS technology favorable compatibility, become a focus of present research.Many micro-nano devices have been realized on silica-based integrated, like laser instrument, modulator, wave filter, coupling mechanism, buffer or the like.And grating is used to realize the coupling mechanism function, has that coupling area is little, the coupling efficiency advantages of higher, thereby is widely used in the planar optical system.
But grating is the same with other optical micro/nano devices, makes device exist than big-difference for the effective refractive index of TE, TM pattern owing to size is little, thereby has caused the relevant problem of device polarization.Can solve device polarization relevant problem (D.A.Peyrot, T.V.Galstian, and R.A.Lessard through the photoinduction birefringent phenomenon; " Polarization independentgrating coupling in planar wave-guide using photo-inducedbirefringence; " Proc.SPIE 4833,719 (2002) .), but it has adopted special polarization sensitive material; And relate to the polarization exposure technique, practicality and ubiquity are little.Method through the growth stress layer is adjusted to zero (D.-X.Xu with the effective refractive index difference of TE, TM pattern; P.Cheben; D.Dalacu, A.
S.Janz, B.Lamontagne; M.-J.Picard; And W. N.Ye, " Eliminating the birefringence insilicon-on-insulator ridge waveguides by use of cladding stress, " Opt.Lett.29; 2384 (2004) .); Also can solve the relevant problem of polarization, but increase aftertreatment technology step and extra material, and the additional thickness that its increase stressor layers is introduced has also limited device size to littler development.
Summary of the invention
The method for designing that the purpose of this invention is to provide a kind of T type groove optical grating construction; Take the different coupling principle to realize output coupler to two kinds of patterns; Thereby realized adopting the same structure to TE, TM pattern high-level efficiency coupling simultaneously output, near the 1550nm optical communicating waveband, realized the polarization-independent grating coupler of high-level efficiency, wide bandwidth, low Polarization Dependent Loss (PDL).The concrete technical scheme that adopts is following:
A kind of method for making of polarization-independent grating coupler comprises the steps:
(1) calculates the cycle T of TM pattern according to grating coupling Bragg condition
TM
(2) calculate the cycle T of TE pattern according to the grating condition of resonance
TE
(3) make T
TM=T
TE, try to achieve the upper layer of material thickness of said polarization-independent grating coupler, with the T of this moment
TMOr T
TEBe set to the cycle of this polarization-independent grating coupler;
(4) utilize above-mentioned upper layer of material thickness of trying to achieve and cycle to make vertical Slot grating;
(5) one group of light engraving erosion of etching grating on the groove top of above-mentioned vertical slot grating; Make above-mentioned vertical Slot grating become T type groove grating; Regulate the etching width and the etching depth of said light engraving erosion grating; Make TE Mode Coupling output efficiency maximum, TM Mode Coupling efficient is unaffected, and the T type groove grating that form this moment is the polarization-independent grating coupler of being asked.
Cycle T of the present invention
TMBe λ/n
Eff TM, wherein, λ is a coupled wavelength, n
Eff TMEffective refractive index for the TM pattern.
The present invention is in the cycle T of calculating the TE pattern
TEIn, at first light field is strapped among the Bragg grating resonator, at this moment, the work of TE pattern grating coupler is to follow the grating condition of resonance, thus the grating cycle T
TEIn (2a ± 1) λ/4
Neff TETo a λ/2n
Eff TEIn the scope, wherein, n
Eff TEBe the effective refractive index of TE pattern, λ is a coupled wavelength, and a is a positive integer.
The material of polarization-independent grating coupler of the present invention can be any material that TE and TM pattern is existed effective refringence.
The present invention has realized that the coupling efficiency that the coupling efficiency of TE, TM pattern in the 1480-1580nm wavelength coverage all is higher than 50%, two kind of pattern has all reached 58% in the 1550nm wavelength; And at the Polarization Dependent Loss (PDL) of 1510-1580nm wavelength coverage intercoupler less than 0.05dB, be merely 3.6 * 10 in the 1550nm wavelength
-3DB, the grating coupler that is designed have realized high coupling efficiency, the coupling output function of hanging down Polarization Dependent Loss, wide bandwidth.
The invention provides a kind of method for designing of novel polarization-independent grating coupler; Be compared to polarization irrelevant device in the past; Its device architecture is simple, easy to make, volume is little, and with the CMOS process compatible of standard, will technical support be provided for the design and the manufacturing of polarization irrelevant device.
Description of drawings
Fig. 1 schematic diagram of the present invention and structural drawing; Dark grey partly is a silicon about among the figure; Middle white partly is a silicon dioxide, and figure (a) is the vertical Slot grating to the TM pattern, and figure (b) is the Bragg grating resonator to the TE pattern; Figure (c) is the T type groove grating of TM pattern, and figure (d) is the T type groove grating of TE pattern.The figure (a) and (b) have been illustrated the variation in light path in coupling mechanism to the variation of (c), (d) arrow, scheme (c), (d) is the grating coupler structure of being invented.
Embodiment
The method for designing that the purpose of this invention is to provide a kind of simple in structure, novel polarization-independent grating coupler of be prone to making.Embodiment is divided following five steps:
1. try to achieve the cycle T of TM pattern according to grating coupling Bragg condition
TM
Usually based on the TE to same wavelength of grating Bragg condition, the grating coupler of TM pattern, because the two big effective refractive index is poor, its grating cycle has very big difference.And we consider that the TM pattern still follows the grating Bragg condition and be coupled here, then its grating cycle T
TMShould be λ/n
Eff TM(λ is a coupled wavelength, n
Eff TMEffective refractive index for the TM pattern) about, to the Slot effect of TM pattern, the cutting of TM grating is adopted vertical Slot groove structure to derive energy and is realized the high-level efficiency coupling.
2. try to achieve the cycle T of TE pattern according to the grating condition of resonance
TE
To the TE pattern, at first light field is strapped among the Bragg grating resonator.At this moment, the work of TE pattern grating coupler is to follow the grating condition of resonance, thus the grating cycle T
TEShould be in (2a ± 1) λ/4
Neff TETo a λ/2
Neff TEIn the scope, wherein, n
Eff TEBe the effective refractive index of TE pattern, λ is a coupled wavelength, and a is a positive integer.
3. make cycle T
TMWith cycle T
TEEquate that the upper silicon layer thickness of trying to achieve is as the upper silicon layer thickness of coupling mechanism, the cycle of this moment is the cycle of coupling mechanism;
Because the expression formula in grating cycle and inequality in the step 1,2; Even the effective refractive index of TE pattern and TM pattern (with relating to parameters such as upper silicon layer thickness) is inequality like this; Through suitable design grating parameter, just can let same optical grating construction satisfy the Bragg condition of TM pattern and the condition of resonance of TE pattern simultaneously.
We are through regulating the thickness of the silica-based grating upper silicon layer of SOI, make that the cycle of above resonance grating to the TE pattern is identical with the cycle of the conventional coupling grating of TM pattern.Concrete realization then can be when calculating the maximum coupling efficiency of the corresponding TM pattern of different upper silicon layer thickness cycle at cycle and the grating tuning-points place of TE pattern, be linked to be two curves, the intersections of complex curve place be the upper silicon layer thickness of asking and grating cycle.
4. utilize above-mentioned upper silicon layer thickness and grating cycle to make vertical Slot grating;
5. at one group of light engraving erosion of groove top etching grating of the vertical slot grating of above-mentioned making, form T type groove grating, make TE Mode Coupling output efficiency maximum, TM Mode Coupling efficient is unaffected, and the grating of this moment is the polarization irrelevant coupling mechanism that is designed.
To the TE pattern; Add one group of light engraving erosion at quarter grating seizes out with the luminous energy that is strapped in the resonator on the top of resonator optical grating construction (being the vertical Slot optical grating construction that obtains in the step 4); Thereby realize the high efficiency coupling of TE pattern, and add the almost not influence of light engraving erosion grating pair TM Mode Coupling at quarter.Through regulating the etching width and the etching depth of top light engraving erosion grating, further optimize the performance of T type grating, can realize polarization-independent grating coupler.
In order to obtain better effect, can also regulate the etching depth and the etching width of vertical Slot grating.
The making of this polarization irrelevant coupling mechanism can be adopted electron beam lithography to carry out alignment and make, and also can adopt the gray-level light lithography to make.When adopting beamwriter lithography to carry out alignment; Carry out twice beamwriter lithography and etching respectively; Produce Slot optical grating construction and light engraving erosion optical grating construction; Thereby realize T type optical grating construction; Even the alignment error of alignment makes the grating groove between Г type-T type-
type, change, coupling mechanism still can be realized high-level efficiency polarization irrelevant coupling performance.And when adopting the gray-level light lithography to make, then only need when program design, carry out corresponding exposure setting to groove, and obtain T type mask layer, carry out etching again, promptly can realize device architecture.
In addition, this structure is not only limited in the silica-base material and uses, and exists for TE, TM pattern in the material of effective refringence all can use.
During to this coupling mechanism check; At first near the light source the 1550nm wavelength is received the input end of Polarization Controller; Then with the light of Polarization Controller output shown in arrow in Fig. 1 (c), (d) left side waveguide, be passed in the coupling mechanism, the light-receiving of the grating face top output of coupling mechanism is in photo-detector; Regulate Polarization Controller then; Observe the luminous energy size that detector receives, constant as if the luminous energy size that detector in the adjustment process is received, then this grating coupler has been realized the polarization irrelevant coupling function.
Claims (2)
1. the method for making of a polarization-independent grating coupler comprises the steps:
(1) calculates the cycle T of TM pattern according to grating coupling Bragg condition
TM
(2) calculate the cycle T of TE pattern according to the grating condition of resonance
TE
(3) make T
TM=T
TE, try to achieve the upper layer of material thickness of said polarization-independent grating coupler, with the T of this moment
TMOr T
TEBe set to the cycle of this polarization-independent grating coupler;
(4) utilize the cycle of above-mentioned upper layer of material thickness of trying to achieve and setting to make vertical Slot grating;
(5) one group of light engraving erosion of etching grating on the groove top of above-mentioned vertical slot grating; Make above-mentioned vertical Slot grating become T type groove grating; Regulate the etching width and the etching depth of said light engraving erosion grating; Make maximum when it in TE Mode Coupling output efficiency, when TM Mode Coupling efficient is unaffected, this moment, the T type groove grating of etching formation was the polarization-independent grating coupler of being asked;
Described cycle T
TMBe λ/n
Eff TM, wherein, λ is a coupled wavelength, n
Eff TMEffective refractive index for the TM pattern;
Said in the cycle T of calculating the TE pattern
TEIn, at first light field is strapped among the Bragg grating resonator, at this moment, the work of TE pattern grating coupler is to follow the grating condition of resonance, thus the grating cycle T
TEAt (2a ± 1) λ/4n
Eff TETo a λ/2n
Eff TEIn the scope, wherein, n
Eff TEBe the effective refractive index of TE pattern, λ is a coupled wavelength, and a is a positive integer.
2. method for making according to claim 1 is characterized in that, the material of described polarization-independent grating coupler can be any material that TE and TM pattern is existed effective refringence.
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| CN102692682B (en) * | 2012-06-12 | 2013-07-17 | 中国科学院上海微系统与信息技术研究所 | Grating coupler and manufacturing method thereof |
| CN107076932B (en) * | 2015-06-11 | 2019-10-18 | 华为技术有限公司 | A kind of grating coupler and preparation method |
| EP3499278A1 (en) * | 2017-12-13 | 2019-06-19 | Thomson Licensing | A diffraction grating structure comprising several grating lines |
| CN112415652B (en) * | 2020-10-15 | 2023-09-01 | 北京工业大学 | Waveguide grating coupler array |
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| US5920588A (en) * | 1996-04-11 | 1999-07-06 | Fujitsu Limited | Method and device for generation of phase conjugate light and wavelength conversion, and system having the device |
| CN1293399C (en) * | 2004-03-19 | 2007-01-03 | 中国科学院半导体研究所 | Method for realizing silicon based silicon dioxde waveguide polarization irrelevancy by employing non-planar process |
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