CN107643561B - A kind of low-loss terahertz polarization beam splitter - Google Patents
A kind of low-loss terahertz polarization beam splitter Download PDFInfo
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- CN107643561B CN107643561B CN201711081180.0A CN201711081180A CN107643561B CN 107643561 B CN107643561 B CN 107643561B CN 201711081180 A CN201711081180 A CN 201711081180A CN 107643561 B CN107643561 B CN 107643561B
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Abstract
The invention discloses a kind of low-loss terahertz polarization beam splitters, its first medium layer and the arrangement of second dielectric layer longitudinal gap, third dielectric layer is respectively with first medium layer and second dielectric layer square crossing, and wherein third dielectric layer and first medium layer intersection constitute the first fibre core；Third dielectric layer and second dielectric layer intersection are hung with dielectric cylinder；Third dielectric layer passes through the center of circle of medium round tube and both ends are fixedly connected with the inner wall of medium round tube, and the both ends of first medium layer and second dielectric layer are fixedly connected with the inner wall of medium round tube, and whole is in total internal reflection structure.The present invention effectively reduces material absorption loss, effective to shorten polarization beam apparatus length, reduces the device loss of polarization beam apparatus.
Description
Technical field
The present invention relates to Terahertz coupled apparatuses, belong to technical field of optical fiber communication, in particular to a kind of low-loss terahertz
Hereby polarization beam apparatus.
Background technique
Terahertz (Terahertz, THz) typically refers to electromagnetic wave of the frequency within the scope of 0. 1 ~ 10 THz,
Wave band be located at the microwave in electromagnetic spectrum and it is infrared between.THz radiation is in many fields, such as communication, sensing, imaging, spectroscopy
There are the potentiality of application with medicine.Whole THz system is generally made of three major parts: THz radiation source, optical waveguide and detection
Device.Currently, THz radiation source and detector become closer to practical, but THz optical fiber and device are also in theoretical and laboratory research
Stage, the reason is that the low-loss transparent material to optical fiber and optical fibre device needed for forming this wave band is deficienter.Therefore big portion
THz system is divided mainly to use free-space propagation method to realize the transmission of THz wave, however this needs accurate calibration and dimension
Shield, while the loss (variation of such as ambient humidity) that external environment also can cause THz wave big, and THz system is huge.Existing rank
Section, the high efficiency of transmission of THz wave have become the bottleneck for influencing Terahertz Technology development.Therefore the THz with high-quality is developed
Optical fiber and its device have important scientific meaning and practical value.
Fibre optic polarizing beam splitter is one kind of directional couple device, has important application in terms of fiber optic communication and sensing
Value.Nearest THz wave fibre optic polarizing beam splitter causes the attention of domestic and international scientific worker, and Terahertz coupled apparatus is set
The key of meter mainly has at 3 points, and first is to be distributed mainly on fibre core guided modes energy in air, reduces material absorption loss；The
Second is that shortening coupled apparatus length, reduce transmission loss；Third is to reduce external environment to change the influence for transmitting THz wave.
Shanshan Li et al. [Shanshan Li, et al., " Terahertz polarization splitter based on
Orthogonal microstructure dual-core photonics crystal fiber, " Apply Optics,
2013,52,3305] the twin-core THz wave beam splitter based on coupling principle is proposed, because its fibre core is porous, core mode energy
It is aerial that amount can effectively be distributed in air, reduces material absorption loss, and core mode transmission be based on total internal reflection principle,
Core mode transmission is free from the influence of the external environment, but that structure is complicated is not easy to manufacture for this coupled apparatus.Symmetrical crux twin-core
Terahertz polarization beam splitter [Zhu Yuanfeng, a kind of terahertz polarization beam splitter, China, ZL201310666221.8,2016-01-
20], the foundational model field characteristic distributions of crux doped core optical fiber are: the mode distributions of x-polarisation mould are wider in the direction x, and y is inclined
The mode distributions of vibration mould are relatively narrow in the direction x.Two fibre core spacing are adjusted in the case that thickness of dielectric layers is certain can make the x of two fibre cores inclined
The mould field of vibration mould has more overlapping region, and the mould field of y-polarisation mould is hardly overlapped, therefore x-polarisation mould can be between two fibre cores
Free coupling, and y-polarisation mould is effectively limited in the fibre core of input.Fiber lengths are equal to a coupling of x-polarisation mould
When length, two polarization modes are efficiently separated, and polarization beam apparatus length is only a coupling length of x-polarisation mould, to make y-polarisation
The mould field of mould is not overlapped, and two fibre core spacing are required sufficiently large, and a coupling length of x-polarisation mould cannot be effectively reduced, polarization point
The transmission loss of beam device or relatively high.[Hongzhi Chen the et al., " Terahertz such as Hongzhi Chen
polarization splitters based on total and partial coupling in dual slotted
Core polymer fiber:comparison and analysis, " IEEE Photonics Journal, 2017,9,
7103315] the asymmetric twin-core polarization beam apparatus of skeleton fibre core is proposed, the basic mode of each fibre core has high birefringence special
Property, by adjusting structural parameters, at same frequency, the effective refractive index of the x-polarisation mould of two fibre cores is equal, and y-polarisation mould
Effective refractive index has biggish difference, and x-polarisation mould can completely couple between two fibre cores, and y-polarisation mode coupling is weaker, polarization beam apparatus
Length be x-polarisation mould a coupling length, the length of polarization beam apparatus can be reduced to 1cm, effectively reduce rate polarization beam splitting
The transmission loss of device, but beam splitter structure is more complex, and manufacture difficulty is larger.
Summary of the invention
In view of the above shortcomings, the present invention, which provides, a kind of is able to achieve low-loss, shorter and from external disturbance the THz of length
Polarization beam apparatus, to be effectively reduced the transmission loss of rate polarization beam apparatus.
Above-mentioned purpose is implemented with the following technical solutions in the present invention.A kind of low-loss terahertz polarization beam splitter, first is situated between
Matter layer and second dielectric layer longitudinal gap arrangement, third dielectric layer respectively with first medium layer and second dielectric layer square crossing,
Wherein third dielectric layer and first medium layer intersection constitute the first fibre core；Third dielectric layer and second dielectric layer intersection are hung
There is dielectric cylinder, the dielectric cylinder is the second fibre core；Third dielectric layer passes through the center of circle of medium round tube and both ends and medium are round
The inner wall of pipe is fixedly connected, and the both ends of first medium layer and second dielectric layer are fixedly connected with the inner wall of medium round tube, and first
Dielectric layer, third dielectric layer and medium round tube inner wall surround first kind airport；First medium layer, third dielectric layer, second are situated between
Matter layer, dielectric cylinder and medium round tube inner wall surround the second class airport；Second dielectric layer, third dielectric layer, dielectric cylinder with
Medium round tube inner wall surrounds third class airport；First kind airport, the second class airport and third class airport are respectively
The two sides of three dielectric layers；First medium layer, second dielectric layer, third dielectric layer, first other than first fibre core and the second fibre core
As fibre cladding, whole is in total internal reflection for class airport, the second class airport, third class airport and the medium round tube of periphery
Structure.
Preferably, the space D 1 of first fibre core and the second fibre core are as follows: D1 >=400 μm.
Preferably, the thickness d of the second dielectric layer1Or the thickness d of third dielectric layer1Are as follows: d1≥10μm。
Preferably, the thickness d of the first medium layer2With the thickness d of second dielectric layer or third dielectric layer1Than are as follows: d2/
d1≥4/3。
The solution have the advantages that: two fibre core sizes can be more distributed in much smaller than operating wavelength, core mode energy
It closes in the airport of fibre core, effectively reduces material absorption loss.First fibre core has high birefringence characteristic, y-polarisation mould
Effective refractive index be greater than x-polarisation mould effective refractive index, the y-polarisation of the second fibre core and the effective refractive index of x-polarisation mould are equal,
Adjusting optical fiber structure parameter appropriate can make the effective refractive index of the x-polarisation mould of the first fibre core and the second fibre core equal, and y-polarisation
The effective refractive index of mould differs, and has high birefringence characteristic in conjunction with the first fibre core, x-polarisation mould can be in the first fibre core and the second fibre core
Between freely couple, and y-polarisation mould is effectively limited in the fibre core of input.Fiber lengths are equal to a coupling of x-polarisation mould
When closing length, two polarization modes are efficiently separated, and polarization beam apparatus length is only a coupling length of x-polarisation mould, this side
Method effectively shortens polarization beam apparatus length, reduces the device loss of polarization beam apparatus.With the first fibre core and the second fibre core
Space D1Reduction, polarization beam apparatus length can reduce, and polarization beam apparatus device loss reduces, but with D1Reduction, y is inclined
Vibration mould can generate part coupling, and polarization beam apparatus extinction ratio reduces, therefore requires D here1≥400μm.The thickness of second dielectric layer
The thickness of degree and third dielectric layer is d1, first medium layer 3 with a thickness of d2, thickness of dielectric layers is too small to will increase manufacture difficulty,
So that device performance is unstable, therefore it is required that the thickness d of second dielectric layer1Or the thickness d of third dielectric layer1Meet: d1≥
10μm.To make the first fibre core that there is high birefringence characteristic, the coupling of y-polarisation mould is reduced, requires the thickness of first medium layer here
d2With the thickness d of second dielectric layer or third dielectric layer1Than meeting: d2/d1≥4/3。
Detailed description of the invention
Fig. 1 is the structural schematic diagram of terahertz polarization beam splitter of the present invention；
Fig. 2 is x-polarisation coupling super model electric field strength distribution map of the invention；
Fig. 3 is x-polarisation surprise super model electric field strength distribution map of the invention；
Fig. 4 is y-polarisation coupling super model electric field strength distribution map of the invention；
Fig. 5 is x-polarisation surprise super model electric field strength distribution map of the invention；
Fig. 6 is polarization beam apparatus length of the invention with D1Change curve；
Fig. 7 is polarization beam apparatus device loss of the invention with D1Change curve；
Fig. 8 is normalized power in the first fibre core A of the invention in D1With the change curve of transmission range at=450 μm；
Fig. 9 is normalized power in the second fibre core B of the invention in D1With the change curve of transmission range at=450 μm；
Figure 10 is the change curve of extinction ratio of the invention with frequency.
In figure: 1. first medium layers, 2. second dielectric layer, 3. third dielectric layers, 4. dielectric cylinders, 5. medium round tubes, 6.
First kind airport, 7. second class airports, 8. third class airports, the first fibre core of A., the second fibre core of B..
Specific embodiment
Below in conjunction with drawings and examples, the invention will be further described.As Fig. 1 gives THz polarization point of the invention
The cross-sectional view of beam device, third dielectric layer 3 is arranged in transverse direction, the different first medium layer 1 of two thickness in medium round tube 5
It is arranged in longitudinal direction at certain intervals with second dielectric layer 2, forms rock-steady structure with the medium round tube 5 in outside.First medium layer 1 with
The quadrature component of third dielectric layer 3 is the first fibre core, is denoted as fibre core A；The quadrature component of second dielectric layer 2 and third dielectric layer 3
Place's one dielectric cylinder 4 of suspension is the second fibre core, is denoted as fibre core B, and the first fibre core A has high birefringence characteristic, and y-polarisation mould is effectively rolled over
Rate is penetrated higher than x-polarisation Effective index, the second fibre core B does not have high birefringence characteristic, and two polarization modal refractive index are equal.It adjusts
Optical fiber structure parameter can make the effective refractive index of the x-polarisation mould of two fibre cores equal, meet phase-matching condition, and y-polarisation mould is then not
Meet.Input light is inputted in the first fibre core A, and after the coupling length distance for transmitting x-polarisation mould, x-polarisation mould will be coupled to
Second fibre core B, and y-polarisation mould is bound in the first fibre core A, thus realize the separation of two polarization modes, polarization beam apparatus length
For a coupling length of x-polarisation mould.
Embodiment 1:
Low-loss terahertz polarization beam splitter structure (as shown in Figure 1) of the present invention, air refraction nair=1.0, optical fiber
Host material is selected as cyclic olefine copolymer Topas, refractive index n=1.5258, the thickness of first medium layer 2 and third dielectric layer 3
d1=30 μm, the thickness d of second dielectric layer 12=50 μm, the interior diameter of medium round tube 5 is D=5000 μm, medium round tube 5 with a thickness of
500 μm, the spacing of the first fibre core A and the second fibre core B are D1.In D1At=600 μm, Fig. 2, Fig. 3, figure 4 and figure 5 respectively show x
The electric field strength distribution map of odd super model, x-polarisation coupling super model, y-polarisation surprise super model and y-polarisation coupling super model is polarized, as can be seen from Figure x
Polarizing odd super model and coupling super model can intercouple, and two y-polarisation super models hardly happen coupling, therefore when transmission range is
Two polarization modes can be separated effectively when the coupling length of x-polarisation mould.
The second dielectric layer or third thickness of dielectric layers d provided in this example1=30 μm, first medium layer thickness d2=50 μm,
d2/d1=5/3, certain d1Value can be smaller, to reduce material absorption loss, but thickness of dielectric layers is too small that will increase production difficult
Degree, so that device performance is unstable, therefore it is required that the thickness d of second dielectric layer 21Or the thickness d of third dielectric layer 31It is full
Foot: d1≥10μm.To make the first fibre core A that there is high birefringence characteristic, the coupling of y-polarisation mould is reduced, requires first medium here
The thickness d of layer 12With the thickness d of second dielectric layer 2 or third dielectric layer 31Than meeting: d2/d1≥4/3。
Fig. 6 is the length of polarization beam apparatus with D1Change curve, polarization beam apparatus length is with D as can be seen from Figure1's
Reduce and reduce, this advantageously reduces device transmission loss, even if the y-polarisation mould in the first fibre core A and the second fibre core B is effective
In the case that refractive index is not equal, the core space D of the first fibre core A and the second fibre core B1Y-polarisation mould remains to that part occurs when sufficiently small
Coupling, this is unfavorable for reducing extinction ratio, therefore it is required that the space D of the first fibre core A and the second fibre core B1Meet: D1≥400μm。
Fig. 7 is the loss of polarization beam apparatus with D1Change curve, it can be seen that the loss of x-polarisation mould and y-polarisation mould is equal
With D1Reduction and reduce, this is mainly polarization beam apparatus length with D1Reduction and the reason of shorten.
Work as D1=450 μm, at 1THz, Fig. 8 gives the normalization light function of x-polarisation mould and y-polarisation mould in the first fibre core A
Rate is respectively with the change curve of transmission range；Fig. 9 gives the optical power of x-polarisation mould and y-polarisation mould in the second fibre core B and distinguishes
With the change curve of transmission range.It is seen that the normalized power of x-polarisation mould is in transmission range in the first fibre core A
Zero is reduced to when 1.27cm, the energy of energy transmission y-polarisation mould into the second fibre core B, the first fibre core A is with transmission distance at this time
From increase and reduce, but reduced energy is not transferred in the second fibre core B, but absorption loss and limitation loss
Effect caused by collective effect, in the second fibre core B, the energy of y-polarisation mould is almost nil.When transmission range is 1.27cm,
X- polarization mode and y- polarization mode are exported from the first fibre core A and the second fibre core B respectively, realize efficiently separating for two polarization modes,
Corresponding device total losses are respectively 0.53dB and 0.67 dB.
Figure 10 gives the extinction ratio of x-polarisation mould and y-polarisation mould, when frequency is 1THz, D1=450 μm of polarization beam splitting
The x-polarisation mould of device and the extinction ratio of y-polarisation mould are respectively-48.3dB and-83.7dB, in 0.96-1.044THz range, D1=
The x-polarisation mould of 450 μm of beam splitter and the extinction ratio of y-polarisation mould can be lower than -15dB, bandwidth 0.084THz.
Claims (4)
1. a kind of low-loss terahertz polarization beam splitter, which is characterized in that first medium layer and second dielectric layer longitudinal gap row
Cloth, third dielectric layer respectively with first medium layer and second dielectric layer square crossing, wherein third dielectric layer and first medium layer
Intersection constitutes the first fibre core；Third dielectric layer and second dielectric layer intersection are hung with dielectric cylinder, and the dielectric cylinder is
Second fibre core；Third dielectric layer passes through the center of circle of medium round tube and both ends are fixedly connected with the inner wall of medium round tube, first medium
The both ends of layer and second dielectric layer are fixedly connected with the inner wall of medium round tube, first medium layer, third dielectric layer and medium circle
Inside pipe wall surrounds first kind airport；In first medium layer, third dielectric layer, second dielectric layer, dielectric cylinder and medium round tube
Wall surrounds the second class airport；Second dielectric layer, third dielectric layer, dielectric cylinder and medium round tube inner wall surround third class air
Hole；First kind airport, the second class airport and third class airport are respectively in the two sides of third dielectric layer；First fibre core and
First medium layer, second dielectric layer, third dielectric layer, first kind airport, the second class airport, third class other than two fibre cores
As fibre cladding, whole is in total internal reflection structure for airport and the medium round tube of periphery.
2. low-loss terahertz polarization beam splitter according to claim 1, which is characterized in that first fibre core and second
The space D of fibre core1Are as follows: D1≥400μm。
3. low-loss terahertz polarization beam splitter according to claim 1, which is characterized in that the thickness of the second dielectric layer
Spend d1Or the thickness d of third dielectric layer1Are as follows: d1≥10μm。
4. low-loss terahertz polarization beam splitter according to claim 1, which is characterized in that the thickness of the first medium layer
Spend d2With the thickness d of second dielectric layer or third dielectric layer1Than are as follows: d2/ d1≥4/3。
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| CN110361813A (en) * | 2019-08-16 | 2019-10-22 | 江西师范大学 | A kind of twin-core Hz optical fiber coupler |
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| CN102156328B (en) * | 2011-04-11 | 2012-05-30 | 中国计量学院 | Y-shaped porous hollowed slab terahertz wave polarizing beam splitter |
| CN103091770B (en) * | 2012-12-28 | 2015-10-28 | 江苏大学 | A kind of photonic crystal fiber polarization beam splitting device |
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