CN101504472A - Optical multiplexing/demultiplexing device - Google Patents
Optical multiplexing/demultiplexing device Download PDFInfo
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- CN101504472A CN101504472A CNA2009100043218A CN200910004321A CN101504472A CN 101504472 A CN101504472 A CN 101504472A CN A2009100043218 A CNA2009100043218 A CN A2009100043218A CN 200910004321 A CN200910004321 A CN 200910004321A CN 101504472 A CN101504472 A CN 101504472A
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Abstract
In an optical multiplexing/demultiplexing device are arranged in parallel and disposed on a substrate. The optical multiplexing/demultiplexing device is disposed with three or more Mach-Zehnder interferometers between the first and second optical input/output ports. The optical multiplexing/demultiplexing device divides, by wavelength, multiplexed light comprising first light and second light whose wavelengths are different and which are input to one of the first optical input/output ports and outputs the multiplexed light from each of the second optical input/output ports. The absolute value of an optical path difference DeltaL of each the Mach-Zehnder interferometers is constant. The optical multiplexing/demultiplexing device includes one or more each of a pair of two successive Mach-Zehnder interferometers where the sum of their optical path differences becomes +2 DeltaL or -2 DeltaL and a pair of two successive Mach-Zehnder interferometers where the sum of their optical path differences becomes 0.
Description
Technical field
The present invention relates to light signal is closed the photosynthetic ripple/partial wave element of ripple and partial wave.
Background technology
In the light custom system, need utilize an optical fiber to carry out being uplink and being downlink transfer to user's light transmission to the light transmission of base station from the base station from the user.Therefore, in uplink and downlink transfer, use the light of different wave length.Therefore, need close the photosynthetic ripple/partial wave element of ripple/partial wave to the light of these different wave lengths.
Photosynthetic ripple/partial wave the element that uses at user side is called as ONU (Optical NetworkUnit: optical network unit).The most of ONU that use are made of wavelength filter, photodiode and the laser diode of optical axis unanimity on space optics now.And, it is also known for the ONU (for example with reference to patent documentation 1) that does not need to make the optical axis unanimity by using optical waveguide.
And in recent years, the good use Si of production is attracted attention as the ONU of waveguide material.As this ONU, the known ONU that the ONU that uses the Mach-Zehnder interferometer, the ONU that uses directional coupler or use grating are arranged.
[patent documentation 1] Japanese kokai publication hei 8-163028 communique
But, the Si system ONU that uses directional coupler aspect the wavelength offset of light source a little less than.And element is the size of hundreds of μ m level, so be difficult to realize miniaturization.
And, use cycle that the Si system ONU of grating need make grating as below half of wavelength, so be difficult to carry out retrofit.
And then, use the wavelength dependency of the equivalent refractive index of the Si system ONU of Mach-Zehnder interferometer, the coupling coefficient of directional coupler etc. very big, so, in the employed wavelength coverage of ONU, can produce and crosstalk or the reduction of light intensity, thereby can't obtain desired characteristics.
Summary of the invention
The present invention finishes in view of above-mentioned this problem.Therefore, the objective of the invention is to, the photosynthetic ripple/partial wave element that uses the Mach-Zehnder interferometer is provided, it can reduce and crosstalk in the employed wavelength coverage of ONU, and, compared with the past can the inhibition strength loss, and can realize miniaturization.
The present inventor expects, by disposing the Mach-Zehnder interferometer as follows, can realize above-mentioned purpose: promptly, the optical path difference Δ L constant Mach-Zehnder interferometer of arranged in series more than 3 grades, and, the right optical path difference sum that continuous 2 grades Mach-Zehnder interferometer is formed be 0 to and the optical path difference sum for+2 Δ L or-2 Δ L to having respectively more than one.That is, the present invention has following technical characterictic.
Photosynthetic ripple of the present invention/partial wave element is set side by side with an end as the 1st light input/output port mouth and the other end the 1st and the 2nd optical waveguide as the 2nd light input/output port mouth on substrate, series connection is provided with the Mach-Zehnder interferometer that the 1st and the 2nd optical waveguide by between the 1st and the 2nd light input/output port mouth of the 1st and the 2nd optical waveguide more than 3 grades forms.
And, according to wavelength the glistening light of waves that closes of the 1st and the 2nd light of the different wave length that is input to any one the 1st light input/output port mouth is carried out partial wave, and respectively from the 2nd light input/output port mouth output of the 1st and the 2nd optical waveguide.
In this photosynthetic ripple/partial wave element, at the light of propagating in the described the 1st and the 2nd optical waveguide, the absolute value of the optical path difference Δ L of each Mach-Zehnder interferometer is constant.
And, have respectively more than one optical path difference sum for the Mach-Zehnder interferometer of+2 Δ L or-2 Δ L by continuous 2 grades form to and the optical path difference sum be 0 Mach-Zehnder interferometer by continuous 2 grades form right.
Use the 1st and the 2nd light wavelength, the optical path difference Δ L of each Mach-Zehnder interferometer is set at setting, thus, can carry out partial wave to input and output to the glistening light of waves that closes of the 1st and the 2nd light of any one the 1st light input/output port mouth according to wavelength, and respectively from the 2nd light input/output port mouth input and output.
Particularly, for example, be input under the situation of photosynthetic ripple/partial wave element from one the 1st light input/output port mouth, export the 1st light, export the 2nd light from another the 2nd light input/output port mouth from one the 2nd light input/output port mouth at the glistening light of waves that closes of the 1st and the 2nd light.
But in the 1st and the 2nd light, inverse process is set up too, so, for example, the 1st light that is input to photosynthetic ripple/partial wave element from one the 2nd light input/output port mouth via with above-mentioned opposite path, with the 2nd photosynthetic ripple, then from one the 1st light input/output port mouth output.
That is, with the 1st light as the upward signal of " user → base station " and under with the situation of the 2nd light as the downgoing signal of " base station → user ", this photosynthetic ripple/partial wave element can be brought into play function as ONU.
And, when in a Mach-Zehnder interferometer, optical path difference Δ L being defined as (optical path lengths of optical path length-Di 2 optical waveguides of the 1st optical waveguide), optical path difference be Δ L and-these two kinds of values of Δ L.
Therefore, under the right situation that the Mach-Zehnder interferometer of considering adjacent (continuously) 2 grades is formed, the optical path difference sum is 2 Δ L, 0 (zero), these three kinds of values of-2 Δ L.
In this photosynthetic ripple/partial wave element, have more than one optical path difference sum and be 2 Δ L or-2 Δ L by the Mach-Zehnder interferometer form right, and, have more than one optical path difference sum and be 0 (zero) by the Mach-Zehnder interferometer form right.
By such formation, can widen in the Mach-Zehnder interferometer with intersect the input and output of (cross) state light (the 2nd light) wave band and with the wave band of the light (the 1st light) of straight-through (bar) state input and output.
In this photosynthetic ripple/partial wave element, the wavelength that preferably ought establish respectively in the 1st and the 2nd optical waveguide of the 1st and the 2nd light is λ
1And λ
2(λ
2λ
1) time, Δ L is provided by following formula (1).
Δ L=(2m+1) * λ
1, and Δ L=2m * λ
2(wherein, m is a natural number) ... (1)
By such formation, wavelength X
1The 1st light propagate in photosynthetic ripple/partial wave element with pass-through state.And, wavelength X
2(λ
2λ
1) the 2nd light propagate in photosynthetic ripple/partial wave element with crossing condition.Its result, photosynthetic ripple/partial wave element can carry out wavelength separated to the 1st light and the 2nd light.
In this photosynthetic ripple/partial wave element, preferably export the 1st light from one the 2nd light input/output port mouth with pass-through state, and, export the 2nd light with crossing condition from another the 2nd light input/output port mouth.
In this photosynthetic ripple/partial wave element, preferably be that material forms the 1st and the 2nd optical waveguide with Si.
By such formation, can utilize the manufacturing process of Si semiconductor element easily to make photosynthetic ripple/partial wave element.
In this photosynthetic ripple/partial wave element, preferred the 1st and the 2nd optical waveguide and the cross sectional shape optical propagation direction quadrature that constitutes the curved waveguide part of Mach-Zehnder interferometer is a square shape, and, constitute the Mach-Zehnder interferometer the directional coupler part the 1st with the 2nd optical waveguide be following oblong-shaped with the cross sectional shape optical propagation direction quadrature: the length of the direction vertical with the substrate interarea is than long with the length of the direction of substrate main surface parallel.
By such formation, can make photosynthetic ripple/partial wave element not rely on polarized wave.
In this photosynthetic ripple/partial wave element, preferably utilize the waveguide of linearity and the equal a plurality of curvilinear waveguides of radius-of-curvature to form the curved waveguide part.
By such formation, can further reduce the 1st light in photosynthetic ripple/partial wave element and the loss of the 2nd light.
In above-mentioned photosynthetic ripple/partial wave element, the preferred wavelength dependency of the equivalent refractive index of the material that constitutes the 1st and the 2nd optical waveguide that utilizes is obtained optical path difference Δ L.
In above-mentioned photosynthetic ripple/partial wave element, the material that preferably constitutes the 1st and the 2nd optical waveguide is Si.
In above-mentioned photosynthetic ripple/partial wave element, be Δ λ preferably establishing the 1st and the 2nd light wavelength difference, establishing the 1st and the 2nd optical waveguide is Δ n at the equivalent refraction rate variance of the 1st and the 2nd light, and m is under the situation of positive integer, following formula (15) is set up, and optical path difference Δ L satisfies following formula (16).
Δn/n
2＝(1-Δλ/λ
2)/(2m)-Δλ/λ
2 …(15)
2n
2ΔL/λ
2＝(1-Δλ/λ
2)/(Δλ/λ
2+Δn/n
2) …(16)
Wherein, n
2Be the equivalent refractive index of optical waveguide at the 2nd light.
Another photosynthetic ripple/partial wave element of the present invention is set side by side with an end and is made as the 1st and the 2nd optical waveguide that the 1st light input/output port mouth and the other end are made as the 2nd light input/output port mouth on substrate, series connection is provided with the Mach-Zehnder interferometer that the 1st and the 2nd optical waveguide by between the 1st and the 2nd light input/output port mouth of the 1st and the 2nd optical waveguide more than 3 grades forms.
And, according to wavelength (wherein to the N wavelength of the different wave length that is input to any one the 1st light input/output port mouth, N is the integer of N 〉=3) the glistening light of waves that closes carry out partial wave, export (N-i) wavelength (wherein from the 2nd light input/output port mouth of the 1st optical waveguide, i is the integer of 1≤i≤N-1) light, and, from the light of the 2nd light input/output port mouth of the 2nd optical waveguide output i wavelength.
Here, when to establish m be integer more than 1, at the light of propagating in the described the 1st and the 2nd optical waveguide, the absolute value of the optical path difference Δ L of each Mach-Zehnder interferometer was constant.
And, have respectively more than one optical path difference sum for the Mach-Zehnder interferometer of+2 Δ L or-2 Δ L by continuous 2 grades form to and the optical path difference sum be 0 Mach-Zehnder interferometer by continuous 2 grades form right.
And then, following formula (15) ' and formula (16) ' set up simultaneously.
Δn/n
a＝Δm(1-Δλ/λ
a)/(2m)-Δλ/λ
a …(15)’
2n
aΔL/λ
a＝2m＝Δm(1-Δλ/λ
a)/(Δλ/λ
a+Δn/n
a) …(16)’
Wherein, Δ m is the integer that is provided by 2-N, λ
aBe reference wavelength, n
aBe the equivalent refractive index of optical waveguide at the light of reference wavelength.
The present invention has above-mentioned this technical characterictic.Thus, obtain the photosynthetic ripple/partial wave element of following use Mach-Zehnder interferometer: it can reduce and crosstalk in the employed wavelength coverage of ONU, and, compared with the past can the inhibition strength loss, and can realize miniaturization.
Description of drawings
Fig. 1 (A) is the planimetric map of the photosynthetic ripple/partial wave element of present embodiment, (B) is the side view of the photosynthetic ripple/partial wave element of present embodiment.
Fig. 2 (A) is the planimetric map of Mach-Zehnder interferometer, (B) is the cut-out end view drawing along the section of the A-A line of (A), (C) is the cut-out end view drawing along the section of the B-B line of (A).
Fig. 3 is the planimetric map that schematically shows the structure of Mach-Zehnder interferometer.
Fig. 4 is the major part amplification view of curved waveguide part.
Fig. 5 illustrates relation and the L between R/ Δ L and the θ
16Relation between/Δ L and the θ.
Fig. 6 (A) and (B) be that the simulation result of the relation between the width of coupling length and the 1st and the 2nd optical waveguide is shown in order to make directional coupler partly not rely on polarized wave.
Fig. 7 is the figure of acting characteristic of the photosynthetic ripple/partial wave element of explanation present embodiment.
Fig. 8 (A) and (B) be the figure that the variation of photosynthetic ripple/partial wave element is shown.
Fig. 9 is the figure of the variation of explanation photosynthetic ripple/partial wave element.
Figure 10 is used to obtain Δ n and n
aSimulation result.
Figure 11 is the performance plot that makes formula (15) pictorialization.
Embodiment
Below, with reference to the description of drawings embodiments of the present invention.In addition, each figure is only can understand shape, size and the configuration relation that degree of the present invention roughly illustrates each textural element.And, the following describes preferred structure example of the present invention, still, the material of each textural element and value conditions etc. only are preferences.Therefore, the present invention is not limited to following embodiment fully.And, in each figure, common textural element is marked same numeral and omits its explanation.
(structure)
The structure of the photosynthetic ripple/partial wave element of present embodiment is described with reference to Fig. 1～Fig. 9.Fig. 1 (A) is the planimetric map of photosynthetic ripple/partial wave element.Fig. 1 (B) is the side view of photosynthetic ripple/partial wave element.In addition,, consider to understand the easness of figure, in the zone of expression the 1st and the 2nd optical waveguide, mark oblique line at Fig. 1 (A) with (B).
With reference to Fig. 1 (A), photosynthetic ripple/partial wave element 10 is formed by substrate 12 and the 1st and the 2nd optical waveguide 14 and 16.Substrate 12 for example constitutes rectangular shape by being the 12a of lower floor of material with monocrystalline silicon and being that the upper strata 12b as covering of material constitutes with the silicon oxide layer.And in the 12b of upper strata, being set side by side with monocrystalline silicon is the 1st optical waveguide 14 and the 2nd optical waveguide 16 as fibre core of material.
The the 1st and the 2nd optical waveguide 14 and 16 is arranged on the position of the 1st smooth interarea 12e deep equality of the anomaly of measuring on the thickness direction.And, the 1st and the 2nd optical waveguide 14 and 16 and the 12a of lower floor between interval d be generally more than the 1 μ m, spill to the 12a of lower floor to prevent light.
The 1st optical waveguide 14 has the 1st light input/output port mouth 14a on a side 12c of substrate 12.And, on the 12d of another side of substrate 12, have the 2nd light input/output port mouth 14b.
Equally, the 2nd optical waveguide 16 has the 1st light input/output port mouth 16a on a side 12c of substrate 12.And, on the 12d of another side of substrate 12, have the 2nd light input/output port mouth 16b.
In the present embodiment, as an example, between the 1st light input/output port mouth 14a and 16a and the 2nd light input/output port mouth 14b and 16b, series connection is formed with 4 grades the Mach- Zehnder interferometer 18,20,22 and 24 that is formed by the 1st and the 2nd optical waveguide 14 and 16.
More particularly, Mach-Zehnder interferometer 18～24 is described in detail in the back with reference to Fig. 2 (A), still, from the 1st light input/output port mouth 14a and 16a side towards the 2nd light input/output port mouth 14b and 16b, series arrangement according to 18 → 20 → 22 → 24.
And, utilize between Mach-Zehnder interferometer 18 and the 1st light input/output port mouth 14a and the 16a to be connected usefulness optical waveguide 14c and to be connected with 16c.Equally, utilize between Mach-Zehnder interferometer 24 and the 2nd light input/output port mouth 14b and the 16b and is connected usefulness optical waveguide 14d and is connected with 16d.
Mach-Zehnder interferometer 18～24 is except the 1st optical waveguide 14 in curved waveguide part 18b～24b described later and the 2nd optical waveguide 16 which long these point, and structure is identical.
In the example shown in Fig. 1 (A), in Mach-Zehnder interferometer 18 and 20, the optical path length that forms the 1st optical waveguide 14 is longer than the 2nd optical waveguide 16, and, in Mach-Zehnder interferometer 22 and 24, the optical path length that forms the 2nd optical waveguide 16 is longer than the 1st optical waveguide 14.The the 1st and the 2nd optical waveguide 14 and 16 has respectively along the straight waveguide zone that forms directional coupler from the rectilinear direction of the 1st light input/output port mouth 14a and 16a to the 2 light input/output port mouth 14b and 16b.And then the 1st and the 2nd optical waveguide 14 and the 16 straight waveguide zones from front side are same positions to the final position on the rectilinear direction in curved waveguide zone.And the rectilinear direction start position in the straight waveguide zone of the 1st and the 2nd optical waveguide 14 and 16 from the curved waveguide zone to rear side is a same position.Therefore, about each Mach-Zehnder interferometer 18～24, establish the 1st and the 2nd optical waveguide 14 among curved waveguide part 18b～24b and 16 optical path difference, promptly " (optical path length of the 1st optical waveguide 14)-(optical path length of the 2nd optical waveguide 16) " be Δ L.At this moment, the absolute value of Δ L and Mach-Zehnder interferometer 18～24 are irrelevant, are constant.That is, for whole Mach-Zehnder interferometers 18～24, in curved waveguide part 18b～24b, the optical path difference of the 1st optical waveguide 14 and the 2nd optical waveguide 16 equates.In addition, the whole zone of curved waveguide part 18b～24b can be formed by bending area, perhaps, also can divide bending area in the part and the linearity region forms, and how to constitute is problem in the design.
And, this photosynthetic ripple/partial wave element 10 have respectively more than one optical path difference sum for the Mach-Zehnder interferometer of+2 Δ L or-2 Δ L by continuous 2 grades form to and the optical path difference sum be 0 Mach-Zehnder interferometer by continuous 2 grades form right.In the example shown in Fig. 1 (A), the former to being Mach- Zehnder interferometer 18 and 20 and 22 and 24, the latter to being Mach-Zehnder interferometer 20 and 22.
More particularly, obtain that continuous 2 grades Mach-Zehnder interferometer forms to the optical path difference sum in (18 and 20,20 and 22,22 and 24).So in " to 18 and 20 ", the optical path difference sum is 2 Δ L (=Δ L+ Δ L).In " to 20 and 22 ", the optical path difference sum is 0 (=Δ L+ (Δ L)).And in " to 22 and 24 ", the optical path difference sum is-2 Δ L (=(Δ L)+(Δ L)).Promptly, this photosynthetic ripple/partial wave element 10 have 2 (18 and 20 and 22 and 24) optical path difference sums for+2 Δ L or-2 Δ L by the Mach-Zehnder interferometer form right, and have 1 (20 and 22) optical path difference sum be 0 by the Mach-Zehnder interferometer form right.
Below, with reference to Fig. 7, illustrate the optical path difference sum for the Mach-Zehnder interferometer of+2 Δ L or-2 Δ L by continuous 2 grades form to (below be also referred to as " pass-through state to ") and optical path difference sum be 0 Mach-Zehnder interferometer by continuous 2 grades form (below be also referred to as " crossing condition to ") is made as more than one reason respectively.
The inventor makes pass-through state to constant with the right total logarithm of crossing condition, and the right quantity of increase and decrease pass-through state is carried out emulation.Its result increases the right quantity of pass-through state as can be known more, the wave band of pass-through state, is that the width W b of peak value par of curve 1 among Fig. 7 is wide more.
And as can be known, increasing the right quantity of crossing condition more, the wave band of crossing condition, is that the width W c of peak value par of curve 2 among Fig. 7 is wide more.
Thus, have more than one pass-through state at least respectively to right, thus, can make the wave band of pass-through state and crossing condition widen the admissible degree in practical aspect with crossing condition by photosynthetic ripple/partial wave element 10.
(structure of Mach-Zehnder interferometer)
Then, with reference to Fig. 2 (A)～(C), be that example describes its structure in detail with Mach-Zehnder interferometer 18.Fig. 2 (A) removes the upper strata 12b of substrate 12 and planimetric map that the waveguiding structure of Mach-Zehnder interferometer 18 is shown.Fig. 2 (B) is the cut-out end view drawing along the section of the A-A line of Fig. 2 (A).Fig. 2 (C) is the cut-out end view drawing along the section of the B-B line of Fig. 2 (A).
With reference to Fig. 2 (A), Mach-Zehnder interferometer 18 has directional coupler part 18a, 18a and curved waveguide part 18b.
The the 1st and the 2nd optical waveguide 14 and 16 directional coupler part 18a, 18a mutually combine to form the part of directional coupler, but these parts 18a, 18a are the parts that disposes the 1st and the 2nd optical waveguide 14 and 16 with the spaced and parallel of optically-coupled.
In addition, the 1st and the 2nd optical waveguide 14 among the curved waveguide part 18b and 16 optical path difference Δ L and realize that the design of the curved waveguide part 18b of Δ L narrates in the back.
And, with reference to Fig. 2 (B) and (C) as can be known, in directional coupler part 18a and curved waveguide part 18b, the 1st with the 2nd optical waveguide 14 and 16 height, i.e. vertical with optical propagation direction and vertical equal in length with the interarea 12e of substrate 12, but width, promptly vertical with optical propagation direction and parallel with the interarea 12e of substrate 12 length are different.
And in curved waveguide part 18b, the 1st cuts off and the shape of cross sections that obtain are square (with reference to Fig. 2 (B)) at the face vertical with optical propagation direction with 16 with the 2nd optical waveguide 14.That is, width W 1 and height H 1 equate.
Relative therewith, in directional coupler part 18a, the 1st and the 2nd optical waveguide 14 and 16 shape of cross section are that width is than the narrow oblong-shaped of curved waveguide part 18b, so height H 1 is bigger than width W 2.
Therefore, in the boundary portion of curved waveguide part 18b and directional coupler part 18a, the 1st and the 2nd optical waveguide 14 and 16 width change discontinuously.
In addition, narrate in the back about the width difference of the optical waveguide among directional coupler part 18a and the curved waveguide part 18b.
(about Δ L)
Then, the 1st and the 2nd optical waveguide 14 among the curved waveguide part 18b～24b of Mach-Zehnder interferometer 18～24 and 16 optical path difference Δ L are described.
Consider that the light wavelength that photosynthetic ripple/partial wave element 10 will close ripple/partial wave decides Δ L.Generally, in the Mach-Zehnder interferometer, suitably set curved waveguide optical path difference partly, thus, can make of the free position output of input light with pass-through state or crossing condition at the light wavelength of being imported.
With reference to Fig. 3, be described more specifically pass-through state and crossing condition.Fig. 3 is the planimetric map that schematically illustrates the structure of Mach-Zehnder interferometer.In Fig. 3, Mach-Zehnder interferometer M has 2 optical waveguide WG
1And WG
2At optical waveguide WG
1In be provided with input port IN
1With output port OUT
1Equally, at optical waveguide WG
2In be provided with input port IN
2With output port OUT
2
And, at input port IN
1And IN
2But the parallel optical waveguide WG that disposes in side optically-coupled ground
1And WG
2, form directional coupler HK
1Equally, at output port OUT
1And OUT
2But the parallel optical waveguide WG that disposes in side optically-coupled ground
1And WG
2, form directional coupler HK
2
At these directional couplers HK
1And HK
2Between, be formed with as making optical waveguide WG
1And WG
2The curved waveguide portion C of the crooked bending area and the combination zone of linearity region.
Here, the optical path difference of establishing the curved waveguide portion C of Mach-Zehnder interferometer M is Δ L.This Δ L is by (optical waveguide WG
1Optical path length)-(optical waveguide WG
2Optical path length) provide.And, establish from input port IN
1Wavelength in the input vacuum is the light L of λ.
At this moment, " with pass-through state output " expression is at directional coupler HK
1And HK
2In, do not produce light L to optical waveguide WG
2Power transfer, from optical waveguide WG
1Output port OUT
1Output light L.
And " with crossing condition output " expression is at directional coupler HK
1And HK
2In, the power of light L is to optical waveguide WG
2Shift, from optical waveguide WG
2Output port OUT
2Output light L.
Known according to the optical path difference Δ L of curved waveguide portion C and the relation between the light wavelength λ, deciding light L is that pass-through state still is crossing condition.That is, under the situation that following formula (2) is set up, light L is a crossing condition, and under the situation that following formula (3) is set up, light L is a pass-through state.
2πnΔL/λ＝2mπ …(2)
2πnΔL/λ＝(2m+1)π …(3)
Wherein, n is optical waveguide WG
1And WG
2Refractive index.And m is a natural number.
Return Fig. 1 once more, the optical path difference Δ L of photosynthetic ripple/partial wave element 10 is described.Photosynthetic ripple/partial wave element 10 utilizes the above-mentioned character of Mach-Zehnder interferometer, carries out the ripple/partial wave that closes of light.
That is, as shown in Figure 1, set the optical path difference Δ L of curved waveguide part 18b～24b, so that export the 1st smooth L with pass-through state
1, and export the 2nd smooth L with crossing condition
2Thus, photosynthetic ripple/partial wave element 10 can be to the 1st smooth L
1With the 2nd smooth L
2Close ripple/partial wave.
Then, enumerate actual numerical value, the method for the optical path difference Δ L of design curved waveguide part 18b～24b is described.
Here, establish the 1st smooth L
1With the 2nd smooth L
2Light for the general wavelength that uses in the light custom system.That is, establish the 1st smooth L
1Wavelength X in a vacuum
1VBe 1.3 μ m, and establish the 2nd smooth L
2Wavelength X in a vacuum
2VBe 1.49 μ m.
And, establish the 1st and the 2nd optical waveguide 14 and 16 couples the 1st smooth L
1Equivalent refractive index be n
1(=2.53), and establish the 1st and the 2nd optical waveguide 14 and 16 couples the 2nd smooth L
2Equivalent refractive index be n
2(=2.25).
Look out and export the 1st smooth L with pass-through state
1, and export the 2nd smooth L with crossing condition
2, and, during with these value substitution formulas (2) and formula (3), obtain following formula (4) and formula (5).
2πn
2ΔL/λ
2V＝2πΔL/λ
2＝2π×2.25ΔL/1.49＝2πm …(4)
2πn
1ΔL/λ
1V＝2πΔL/λ
1＝2π×2.53ΔL/1.3＝(2m+1)π …(5)
Wherein, λ
1Be illustrated in the 1st smooth L that propagates in the 1st and the 2nd optical waveguide 14 and 16
1Wavelength.Equally, λ
2Be illustrated in the 2nd smooth L that propagates in the 1st and the 2nd optical waveguide 14 and 16
2Wavelength.
Modus ponens (4) and formula (5) poor obtains Δ L=1.15 μ m.
With Δ L (=1.15) the substitution formula (4) obtained like this when obtaining m, m=1.729.But having m is the such condition of natural number, when not satisfying this condition, and the 2nd smooth L
2It or not crossing condition.By the design of waveguide, can make m=2 exactly, still, in general design, with near i.e. 2 the values (m=2) of 1.729 natural number as m.
Determined the value of m like this, so, when m=2 substitution formula once more (4) is asked Δ L, obtain Δ L=1.32 μ m.This is a net result.
That is, in Mach-Zehnder interferometer 18～24, the optical path difference Δ L that establishes curved waveguide part 18b～24b is 1.32 μ m, thus, can export the 1st smooth L with pass-through state
1, and export the 2nd smooth L with crossing condition
2Thus, can carry out the 1st smooth L
1With the 2nd smooth L
2Wavelength separated.
(about the waveguide of Si fine rule time Δ L)
In the project of (about Δ L),, the most general situation has been described about the computing method of Δ L.But, constituting optical waveguide WG
1And WG
2The big situation of the chromatic dispersion of refractive index of material under, by optimizing optical waveguide WG
1And WG
2Size, above-mentioned formula (2) and formula (3) are set up simultaneously.
Here, as constituting optical waveguide WG
1And WG
2The big material of chromatic dispersion of refractive index of material, for example can enumerate Si.
Below, describe this situation in detail.
As shown in Figure 1, set Δ L so that export the 1st smooth L with pass-through state
1(wavelength X
1V=1.3 μ m), and with crossing condition export the 2nd smooth L
2(wavelength X
2V=1.49 μ m), so above-mentioned formula (2) and formula (3) can be rewritten as following formula (2) ' and following formula (3) '.
2πn
1ΔL/λ
1V＝2mπ …(2)’
2πn
2ΔL/λ
2V＝(2m+1)π …(3)’
Wherein, n
1Be that optical waveguide is at wavelength X
1VThe equivalent refractive index of light, n
2Be that optical waveguide is at wavelength X
2VThe equivalent refractive index of light.
The Δ L of ' and formula (3) ' then can export the 1st smooth L with pass-through state if can obtain and satisfy formula (2) simultaneously
1, and export the 2nd smooth L with crossing condition
2
Therefore, establish Δ n=n
2-n
1With Δ λ=λ
2V-λ
1V, use these Δs n and Δ λ to obtain Δ L.When at first, get (2) difference of ' and formula (3) ' is out of shape, obtain following formula (14).
2ΔL＝λ
2V(λ
2V-Δλ)/(Δλn
2+λ
2VΔn) …(14)
In formula (14), establish wavelength X
2VFor designing the reference wavelength λ that payes attention to
a, establish optical waveguide at reference wavelength λ
aThe equivalent refractive index of light be n
a(=n
2).Then, with formula (14) substitution formula (2) ' when being out of shape, obtain following formula (15).
Δn/n
a＝(1-Δλ/λ
a)/(2m)-Δλ/λ
a …(15)
By formula (15) as can be known, by ratios delta n/n
aWith Δ λ/λ
aDecide the design conditions of Δ L.That is, only require that the integer m that the formula of sening as an envoy to (15) is set up gets final product.
But, in formula (15), at the 1st smooth L
1With the 2nd smooth L
2The known situation of wavelength under, Δ λ and λ
aIt is constant.Thus, in formula (15), unknown quantity only is Δ n/n
a
Can obtain Δ n and n by emulation
aFigure 10 illustrates this simulation result.In Figure 10, the left longitudinal axis illustrates optical waveguide at reference wavelength λ
aThe equivalent refractive index n of light
a(dimension is 1).The right longitudinal axis illustrates Δ n (dimension is 1).Transverse axis is illustrated in the size (μ m) of the optical waveguide of cutting off with the face of optical propagation direction quadrature.In addition, in this emulation, with the cross sectional shape of the optical waveguide of optical propagation direction quadrature be square shape.
In this emulation, change the size of optical waveguide, calculate Δ n at this moment and optical waveguide at reference wavelength λ
aThe equivalent refractive index n of the light of (=1.49 μ m)
aAccording to result shown in Figure 10, can obtain Δ n/n
a
Figure 11 is the performance plot that makes formula (15) pictorialization.In Figure 11, the longitudinal axis is Δ n/n
a(dimension is 1), transverse axis is the size of optical waveguide.In Figure 11, same with Figure 10, the cross sectional shape of optical waveguide also is a square shape.
Described 3 horizontal lines in Figure 11, this is substitution m=1,2,3 value and the Δ n/n that obtains respectively in formula (15)
aValue.And the curve among Figure 11 is the Δ n/n that is obtained by Figure 10
aValue.
With reference to Figure 11, the horizontal line of m=2 and the Δ n/n that obtains by Figure 10
aCurve be about 0.35 μ m and Δ n/n in the size of optical waveguide
aBe about 0.09 some intersection.That is, formula (15) is set up at this point as can be known.
Formula (14) is out of shape, obtains following formula (16).
2n
aΔL/λ
a＝2m＝(1-Δλ/λ
a)/(Δλ/λ
a+Δn/n
a) …(16)
Thus, if the Δ n/n that will obtain by Figure 11
aThe Δ L that (=0.09) then can be obtained and satisfy formula (2) simultaneously with other known quantity substitution formulas (16) ' and formula (3) '.Actual use formula (16) obtains Δ L=1.17 μ m when calculating.
Like this, constituting optical waveguide WG
1And WG
2The big situation of the chromatic dispersion of refractive index of material under, for example under the situation of Si fine rule optical waveguide, can obtain the Δ L that formula (2) and formula (3) are satisfied in strictness.
In addition, above-mentioned theory also can be applied to the light of N wavelength (N is the integer more than 3) is closed the photosynthetic ripple/partial wave element of ripple/partial wave.Here, " light to the N wavelength closes ripple/partial wave " expression is exported the light of (N-i) wavelength (wherein, i is the integer of 1≤i≤N-1) with crossing condition, and exports the light of i wavelength with pass-through state.
Under this situation, at the two ends of photosynthetic ripple/partial wave element, the difference of the interference number of times of wavelength is greater than 1.Thus, under this situation, formula (2) ' and formula (3) ' can be rewritten as following formula (17) with form more generally.
2πn
jΔL/λ
j＝2π(m+Δm) …(17)
Wherein, λ
jIndicate to close the light wavelength of ripple/partial wave, arrange (wherein, j be 1≤i≤N integer) in the short more mode of the big more wavelength of j.And, n
jBe that optical waveguide is λ at wavelength
jThe equivalent refractive index of light.Δ m is the value that is provided by 2-N.
Use formula (17) is when calculating, and under the situation of N wavelength, above-mentioned formula (15) and formula (16) can be deformed into following formula (15) respectively ' and formula (16) '.
Δn/n
a＝Δm(1-Δλ/λ
a)/(2m)-Δλ/λ
a …(15)’
2n
aΔL/λ
a＝2m＝Δm(1-Δλ/λ
a)/(Δλ/λ
a+Δn/n
a) …(16)’
Thus, by with above-mentioned same theory, constituting optical waveguide WG
1And WG
2The big situation of the chromatic dispersion of refractive index of material under, through type (15) ' and formula (16) ' can be obtained the value that can close the Δ L of ripple/partial wave to the light of N wavelength.
(realizing the design of the curved waveguide of Δ L)
With reference to Fig. 4, illustrate to be used for realizing the 1st and the 2nd optical waveguide 14 of above-mentioned optical path difference Δ L and 16 method for designing at curved waveguide part 18b～24b.Fig. 4 is the major part amplification view of curved waveguide part.In addition, the shape of curved waveguide part 18b～24b is identical, so, in the following description, be that example describes with curved waveguide part 22b.
It is that linearity region and the curvilinear waveguides with homogeneous radius-of-curvature are that bending area couples together that curved waveguide part 22b is designed to straight waveguide.
That is, as shown in Figure 4, the 1st optical waveguide 14 of curved waveguide part 22b is from the 1st light input/output port mouth 14a side, according to the order formation of curvilinear waveguides 50a → curvilinear waveguides 50b → straight waveguide 50c → curvilinear waveguides 50d → curvilinear waveguides 50e.
Here, in curvilinear waveguides 50a, 50b, 50d and 50e, radius of curvature R and arc chord angle θ equate respectively.And, about the length of straight waveguide 50c, use the 1st and the 2nd optical waveguide 14 among arc chord angle θ and the curved waveguide part 22b and 16 optical path difference Δ L, obtain from geometrical point and be Δ Lcos θ/(1-cos θ).
Equally, the 2nd optical waveguide 16 of curved waveguide part 22b is from the 1st light input/output port mouth 16a side, according to the order formation of curvilinear waveguides 51a → straight waveguide 51b → curvilinear waveguides 51c → straight waveguide 51d → curvilinear waveguides 51e.
Here, in curvilinear waveguides 51a and 51e, radius of curvature R and arc chord angle θ equate respectively.And the radius-of-curvature of curvilinear waveguides 51c is R, and arc chord angle is 2 θ.In addition, the R in above-mentioned the 1st optical waveguide 14 and θ are identical respectively values with R and θ in the 2nd optical waveguide 16.
And, about the length of straight waveguide 51b and 51d, use the 1st and the 2nd optical waveguide 14 in arc chord angle θ and the curved waveguide part and 16 optical path difference Δ L, obtain from geometrical point and be (Δ L/2)/(1-cos θ).
In the curved waveguide part 22b of this structure,, consider the minimum condition of in curved waveguide part 22b, propagating of light intensity loss in order to obtain R and θ.
Here, the light intensity loss of establishing the per unit length among curvilinear waveguides 50a, 50b, 50d, 50e, 51a, 51c and the 51e is α
RAnd the light intensity loss of establishing the per unit length among straight waveguide 50c, 51b and the 51d is α
S
And the light intensity losses of establishing in the junction surface of the junction surface of junction surface, curvilinear waveguides 51c and straight waveguide 51d of junction surface, straight waveguide 51b and curvilinear waveguides 51c of junction surface, curvilinear waveguides 51a and straight waveguide 51b of junction surface, straight waveguide 50c and curvilinear waveguides 50d of curvilinear waveguides 50b and straight waveguide 50c and straight waveguide 51d and curvilinear waveguides 51e is α
JRS
And the light intensity losses of establishing in the junction surface of curvilinear waveguides 50a and 50b and 50d and 50e is α
JRR
At this moment, the light intensity losses sum α of the 1st optical waveguide 14 among the curved waveguide part 22b
14L
14Provide by following formula (6).In addition, wherein, L
14The total length of the 1st optical waveguide 14 among the expression curved waveguide part 22b, α
14The loss of intensity of the per unit length of the 1st optical waveguide 14 among the curved waveguide part 22b is shown.
α
14L
14＝α
R4Rθ+(α
SΔLcosθ)/(1-cosθ)+2α
JRS+2α
JRR …(6)
And, the light intensity losses sum α of the 2nd optical waveguide 16 among the curved waveguide part 22b
16L
16Provide by following formula (7).In addition, wherein, L
16The total length of the 2nd optical waveguide 16 among the expression curved waveguide part 22b, α
16The loss of intensity of the per unit length of the 2nd optical waveguide 16 among the expression curved waveguide part 22b.
α
16L
16＝α
R4Rθ+(α
SΔL)/(1-cosθ)+4α
JRS …(7)
Generally known, radius of curvature R is more little, and the light intensity losses among curvilinear waveguides 50a, 50b, 50d, 50e, 51a, 51c and the 51e is big more.Therefore, hinted the θ that exists light intensity losses minimum by formula (6) and formula (7).
Therefore, in curved waveguide part 22b, obtain the minimum condition of light intensity losses of the 2nd optical waveguide 16 according to formula (7).In addition, the minimum condition of light intensity losses of obtaining minimum condition of the light intensity losses of the 2nd optical waveguide 16 rather than the 1st optical waveguide 14 be because, the optical path length of the 2nd optical waveguide 16 is grown than the 1st optical waveguide 14, therefore, light intensity losses is also big than the 1st optical waveguide.
That is, formula (7) is carried out differential, thus,, obtain following formula (8) as the minimum conditional of light intensity losses with θ.
d(α
16L
16)/d(θ)＝α
R4R-(α
SΔLsinθ)/(1-cosθ)
2＝0 …(8)
Formula (8) when being out of shape, is obtained following formula (9).
R/ΔL＝(α
S/α
R)×sinθ/{4(1-cosθ)
2} …(9)
According to formula (9) as can be known, the minimum condition of light intensity losses becomes the relation between θ and the standardized radius of curvature R/Δ L.
In Fig. 5, α is shown
S/ α
RThe total length L of standardized the 2nd optical waveguide 16 that the value substitution formula (7) of the R/ Δ L of=1 o'clock formula (9) and the relation between the θ (curve 1) and the R/ Δ L that will obtain according to this relation is obtained
16Relation between/Δ L and the θ (curve 2).
In Fig. 5, the left longitudinal axis illustrates R/ Δ L (dimension is 1), and the right longitudinal axis illustrates L
16/ Δ L (dimension is 1).Transverse axis illustrates θ (degrees, degree).
But, as known in the past, the light intensity losses α of the per unit length in the curvilinear waveguides
RLight intensity losses α with per unit length in the straight waveguide
SThe radius of curvature R of practicality about equally is more than the 5 μ m.
Therefore, getting R is 5 μ m, and uses the Δ L (=1.32 μ m) obtain in the project of (about Δ L), obtains R/ Δ L, during with the curve 1 of its substitution Fig. 5, obtains and can make light intensity losses α
16L
16Minimum θ is about 30 °.
And, during with the curve 2 of θ=30 ° and Δ L=1.32 μ m substitution Fig. 5, obtain and make light intensity losses α
16L
16The total length L of the 2nd minimum optical waveguide 16
16Be about 26 μ m.
That is,, also the total length of photosynthetic ripple/partial wave element 10 can be suppressed at about 200 μ m even consider the length of directional coupler part 18a～24a.
(about the width of directional coupler part and curved waveguide optical waveguide partly)
In the project of (structure of Mach-Zehnder interferometer), width W 2 situation slightly littler than the width W 1 of the optical waveguide of curved waveguide part 18b～24b of the optical waveguide of directional coupler part 18a～24a has been described.The reason of this situation is to make photosynthetic ripple/partial wave element 10 not rely on polarized wave.
In constituting the curved waveguide part 18b～24b of channel-type waveguide, in order not produce the polarized wave dependence, as long as knownly make the 1st to be square shape with 16 shape of cross section (shape of the section vertical) with optical propagation direction with the 2nd optical waveguide 14.
In view of the above, preferably make the 1st and the 2nd optical waveguide 14 of formation curved waveguide part 18b～24b and 16 shape of cross section be for example square shape of 0.3 μ m * 0.3 μ m.
The size of the shape of cross section by such design curved waveguide part 18b～24b, in curved waveguide part 18b～24b, the 1st and the 2nd optical waveguide 14 and 16 does not rely on polarized wave, and, for the 1st and the 2nd smooth L
1And L
2As single mode waveguide performance function.
In order to make directional coupler part 18a～24a not rely on polarized wave, need to regulate the shape of cross section of the 1st and the 2nd optical waveguide 14 and 16 and the coupling length (along the length of optical propagation direction) of directional coupler part 18a～24a.
More particularly, the inventor is at wavelength X
2VThe 2nd smooth L of (=1.49 μ m)
2, the width that changes coupling length and the 1st and the 2nd optical waveguide 14 and 16 carries out emulation, has determined directional coupler part 18a～24a not rely on the coupling length and the duct width of polarized wave.
At Fig. 6 (A) with this simulation result (B).Fig. 6 (A) and (B) among both commonly, the longitudinal axis is represented coupling length (μ m), transverse axis is represented the width (μ m) of the 1st and the 2nd optical waveguide 14 and 16.
And Fig. 6 (A) illustrates the situation that is spaced apart 0.3 μ m of establishing between the 1st and the 2nd optical waveguide 14 and 16, and Fig. 6 (B) illustrates the situation that is spaced apart 0.35 μ m of establishing between the 1st and the 2nd optical waveguide 14 and 16.
And at Fig. 6 (A) with (B), the curve 1 shown in the solid line illustrates about the coupling length of TE polarized wave and the relation between the duct width, and the curve 2 shown in the dotted line illustrates about the coupling length of TM polarized wave and the relation between the duct width.
In addition, at Fig. 6 (A) and (B) commonly, with curved waveguide part 18b～24b similarly, the height H that makes the 1st and the 2nd optical waveguide 14 and 16 is 0.3 μ m, carries out emulation.
With reference to Fig. 6 (A) as can be known, in directional coupler part 18a～24a, under the situation that is spaced apart 0.3 μ m of the 1st and the 2nd optical waveguide 14 and 16, curve 1 and 2 is about 13 μ m and duct width (transverse axis) at coupling length (longitudinal axis) and is about this point of 0.28 μ m and intersects.
And, with reference to Fig. 6 (B) as can be known, in directional coupler part 18a～24a, under the situation that is spaced apart 0.35 μ m of the 1st and the 2nd optical waveguide 14 and 16, curve 1 and 2 is about 21 μ m and duct width (transverse axis) at coupling length (longitudinal axis) and is about this point of 0.287 μ m and intersects.
This means that in the point of crossing of these curves 1 and curve 2, directional coupler part 18a～24a does not rely on polarized wave.But, comparison diagram 6 (A) and (B) time as can be known, both degree of tilt of curve 1 and curve 2 in Fig. 6 (A) all than in Fig. 6 (B), relaxing, so as can be known, the 1st and the 2nd optical waveguide 14 and 16 be spaced apart 0.3 μ m the time the polarized wave dependence of polarized wave dependence when being spaced apart 0.35 μ m little.
Thus, under the situation of the scale error when having considered the manufacturing of directional coupler part 18a～24a, even size is more or less inaccurate, the situation of Fig. 6 few with the deviation of top condition (A) (being spaced apart 0.3 μ m) is favourable at design aspect.
In addition, the following describes and utilize this emulation and be conceived to wavelength X
2VThe 2nd smooth L
2Design the reason of directional coupler part 18a～24a.
Utilizing monocrystalline silicon to form under the situation of the 1st and the 2nd optical waveguide 14 and 16, compare with the situation of utilizing quartzy formation optical waveguide, in the employed wavelength coverage of ONU (1.3～1.49 μ m), the wavelength dependency of directional coupler part 18a～24a is big, in the difference that produces about 4 times on the coupling length.That is wavelength X,
1VThe 1st smooth L of (1.3 μ m)
1With wavelength X
2VThe 2nd smooth L of (1.49 μ m)
2Compare, a little less than the coupling very.
Thus, with the 1st weak smooth L of pass-through state output coupling
1At design aspect is favourable.Under the situation of design like this, need export the 2nd smooth L with crossing condition
2But generally in the Mach-Zehnder interferometer, in order to export crossing condition with good extinction ratio, known needs are strictly set coupling length.On the other hand, even the known coupling length of strictly not setting, pass-through state also can be with good extinction ratio output.
Here it is only at the 2nd smooth L
2Design the reason of directional coupler part 18a～24a.
(action)
Referring again to Fig. 1, the action of the photosynthetic ripple/partial wave element 10 of present embodiment is described.
At first, consider from the 1st light input/output port mouth 14a photosynthetic ripple/partial wave element 10 inputs the 1st smooth L
1(wavelength X
1V=1.3 μ m) and the 2nd smooth L
2(wavelength X
2V=1.49 μ m) situation.
Under this situation, as mentioned above, with pass-through state, promptly export the 1st smooth L from the 2nd light input/output port mouth 14b
1On the other hand, as mentioned above, with crossing condition, promptly export the 2nd smooth L from the 2nd light input/output port mouth 16b
2
As under the situation of ONU, establish the 1st smooth L
1For from the upward signal of user to the base station, the 2nd smooth L2 is to user's downgoing signal from the base station.
Under this situation, the 1st smooth L1 (upward signal) from the 2nd light input/output port mouth 14b input exports from the 1st light input/output port mouth 14a with pass-through state.And, from the 2nd smooth L of the 1st light input/output port mouth 14a input
2(downgoing signal) exported from the 2nd light input/output port mouth 16b with crossing condition.
Then, with reference to Fig. 7, the acting characteristic of the photosynthetic ripple/partial wave element 10 of present embodiment is described.Fig. 7 is the simulation result of acting characteristic.The longitudinal axis illustrates the ratio (dimension be 1) of the output intensity of pass-through state and crossing condition with respect to input intensity, and transverse axis illustrates the light wavelength of input photosynthetic ripple/partial wave element 10.And in Fig. 7, the curve 1 shown in the solid line illustrates pass-through state, and the curve 2 shown in the dotted line illustrates crossing condition.
Photosynthetic ripple/partial wave the element 10 that is used for emulation utilizes the size that illustrates in the project of (structure)～(about the width of directional coupler part and curved waveguide optical waveguide partly) to design except following this point.
(1) fine setting of the coupling length of directional coupler part 18a～24a
Near the junction surface of directional coupler part 18a～24a and curved waveguide part 18b～24b, but the 1st and the 2nd optical waveguide 14 and 16 of formation curved waveguide part 18b～24b is close to the distance of optically-coupled.For this reason, the coupling length with directional coupler part 18a～24a is adjusted to 11.6 very short μ m.
(2) establishing the 1st and the 2nd optical waveguide 14 among curved waveguide part 18b～24b and 16 optical path difference Δ L is 1.344 μ m.
This is because the 1st and the 2nd optical waveguide 14 of consideration monocrystalline silicon system and 16 equivalent refractive index are regulated, so that the 1st smooth L
1(λ
1V=1.3 μ m) and the 2nd smooth L
2(λ
2V=1.49 μ m) be respectively the centre wavelength of pass-through state and crossing condition.
With reference to Fig. 7 as can be known, near these two states of crossing condition near pass-through state wavelength 1.3 μ m and the wavelength 1.49 μ m, carry out wavelength separated in wide wavelength coverage.The wave band that has carried out wavelength separated fully is about 50nm, can fully absorb the wavelength fluctuation of light source or the foozle of photosynthetic ripple/partial wave element 10.
And, can access intensity and input light intensity output light about equally.
(effect)
(1) as shown in Figure 7, the photosynthetic ripple/partial wave element 10 of present embodiment can produce the ground of crosstalking hardly, to the 1st smooth L
1With the 2nd smooth L
2Close ripple/partial wave.
(2) and, compared with the past as shown in Figure 7, the photosynthetic ripple/partial wave element 10 of present embodiment can reduce the loss of light intensity.
(3) and, the total length of the photosynthetic ripple/partial wave element 10 of present embodiment is about 200 μ m, compare with the ONU of in the past Si system Mach-Zehnder interferometer type, be small-sized.
(design conditions, variation etc.)
The situation of the 4 grades of Mach-Zehnder interferometers 18～24 that are connected in series has been described (1) in the present embodiment.But the number that constitutes the Mach-Zehnder interferometer of photosynthetic ripple/partial wave element 10 is not limited to 4 grades.
As long as have more than one pass-through state respectively, then be not limited to this progression to right with crossing condition.For example, also can be depicted as 3 grades as Fig. 8 (A).Under this situation, pass-through state to crossing condition to respectively being provided with one respectively.
And, also can be depicted as 6 grades as Fig. 8 (B).Under this situation, 3 pass-through states are set to right with 2 crossing condition.
The situation that the width of the 1st and the 2nd optical waveguide 14 and 16 is changed from W1 to W2 discontinuously (2) in the present embodiment, has been described in the boundary portion of curved waveguide part 18b～24b and directional coupler part 18a～24a.In this design, also light intensity losses can be suppressed at the enough levels in practical aspect.But,, preferably in boundary portion, make the width of the 1st and the 2nd optical waveguide 14 and 16 be the taper smooth change in order further to reduce light intensity losses.
(3) as illustrating in the project of (realizing the design of the curved waveguide of Δ L), in the present embodiment, utilize straight waveguide and curvilinear waveguides to form the curved waveguide part 18b～24b of Mach-Zehnder interferometer 18～24 with even radius-of-curvature.
But the curvilinear waveguides that also can make up different curvature radius designs curved waveguide part 18b～24b.
More particularly, also can design the curved waveguide part 60b of the Mach-Zehnder interferometer 60 that constitutes photosynthetic ripple/partial wave element 10 as shown in Figure 9.
That is, this Mach-Zehnder interferometer 60 is made of the 1st optical waveguide 62 and the 2nd optical waveguide 64.And, by these the 1st and the 2nd optical waveguides 62 and 64, form directional coupler part 60a and 60a and curved waveguide part 60b.
The 1st optical waveguide 62 of curved waveguide part 60b constitutes according to the order of curvilinear waveguides 66a → curvilinear waveguides 66b → curvilinear waveguides 66c → curvilinear waveguides 66d.
Here, in curvilinear waveguides 66a～66d, each radius of curvature R
2With arc chord angle θ
2Equate respectively.
The 2nd optical waveguide 64 of curved waveguide part 60b constitutes according to the order of curvilinear waveguides 68a → curvilinear waveguides 68b → curvilinear waveguides 68c → curvilinear waveguides 68d.
Here, in curvilinear waveguides 68a～68d, each radius of curvature R
1(≠ R
2) and arc chord angle θ
1(≠ θ
2) equate respectively.
In this curved waveguide part 60b, be used to realize the 1st and the 2nd optical waveguide 62 of optical path difference Δ L and 64 method for designing, with reference to the method for explanation in (realizing the design of the curved waveguide of Δ L).
That is,, consider the light intensity losses α among the curved waveguide part 60b at the 2nd long optical waveguide 64 of optical path length
64L
64Wherein, L
64The total length of the 2nd optical waveguide 64 among the expression curved waveguide part 60b, α
64The loss of intensity of the per unit length of the 2nd optical waveguide 64 among the expression curved waveguide part 60b.This loss of intensity α
64L
64Provide by following formula (10).
α
64L
64＝α
R14R
1θ
1＝α
R1{ΔL+4R
2sin
-1(R
1sinθ
1/R
2)}+4α
JRR …(10)
Wherein, α
R1It is the light intensity losses of the per unit length among curvilinear waveguides 68a～68d.And, α
JRRIt is the light intensity losses in the junction surface of the junction surface of junction surface, curvilinear waveguides 68b and 68c of curvilinear waveguides 68a and 68b and curvilinear waveguides 68c and 68d.
As shown in Figure 9, if R
2Infinity then can access more effective optical path difference Δ L.Thus, in formula (10), by establishing R
2→ ∞ obtains following formula (11).
α
64L
64＝α
R1(ΔL+4R
1sinθ
1)+4α
JRR …(11)
But in curved waveguide part 60b, the length that the 1st and the 2nd optical waveguide 62 and 64 is projected on the central shaft of Mach-Zehnder interferometer must equate, so, obtain following formula (12).
R
1＝ΔL/{4(θ
1-sinθ
1)} …(12)
With formula (12) substitution formula (11), net result obtains following formula (13).
α
64L
64＝α
R1ΔL{θ
1/(θ
1-sinθ
1)}+4α
JRR …(13)
By formula (13) as can be known, light intensity losses α
64L
64With respect to arc chord angle θ
1Change.And as can be known,
Preferred arc chord angle θ
1Bigger, at θ
1During=pi/2, light intensity losses α
64L
64Minimum.
Claims (10)
1. photosynthetic ripple/partial wave element, this photosynthetic ripple/partial wave element is set side by side with an end on substrate be that the 1st light input/output port mouth and the other end are the 1st and the 2nd optical waveguide of the 2nd light input/output port mouth,
Series connection be provided with more than 3 grades by the described the 1st and the 1st and the 2nd light input/output port mouth of the 2nd optical waveguide between the Mach-Zehnder interferometer that forms of the described the 1st and the 2nd optical waveguide,
According to wavelength the glistening light of waves that closes of the 1st and the 2nd different light of the wavelength that is input to any one described the 1st light input/output port mouth is carried out partial wave, and export from the 2nd light input/output port mouth of the described the 1st and the 2nd optical waveguide respectively, this photosynthetic ripple/partial wave element is characterised in that
At the light of propagating in the described the 1st and the 2nd optical waveguide, the absolute value of the optical path difference Δ L of each Mach-Zehnder interferometer is constant,
Have respectively more than one optical path difference sum for the Mach-Zehnder interferometer of+2 Δ L or-2 Δ L by continuous 2 grades form to and the optical path difference sum be 0 Mach-Zehnder interferometer by continuous 2 grades form right.
2. photosynthetic ripple according to claim 1/partial wave element is characterized in that,
When establishing the wavelength of the described the 1st and the 2nd light in the described the 1st and the 2nd optical waveguide respectively is λ
1And λ
2(λ
2λ
1) time, described optical path difference Δ L is provided by following formula (1):
Δ L=(2m+1) * λ
1, and Δ L=2m * λ
2(wherein, m is a natural number) ... (1).
3. photosynthetic ripple according to claim 2/partial wave element is characterized in that,
Export described the 1st light with pass-through state from described the 2nd a light input/output port mouth, and, described the 2nd light exported with crossing condition from another described the 2nd light input/output port mouth.
4. according to each the described photosynthetic ripple/partial wave element in the claim 1～3, it is characterized in that,
With Si is that material forms the described the 1st and the 2nd optical waveguide.
5. according to each the described photosynthetic ripple/partial wave element in the claim 1～3, it is characterized in that,
The the described the 1st and the 2nd optical waveguide and the cross sectional shape optical propagation direction quadrature that constitutes the curved waveguide part of described Mach-Zehnder interferometer is square shape, and,
Constitute described Mach-Zehnder interferometer directional coupler part the described the 1st with the 2nd optical waveguide be following oblong-shaped with the cross sectional shape optical propagation direction quadrature: the length of the direction vertical with described substrate interarea is than long with the length of the direction of described substrate main surface parallel.
6. photosynthetic ripple according to claim 5/partial wave element is characterized in that,
Utilize the waveguide and the equal a plurality of curvilinear waveguides of radius-of-curvature of linearity to form described curved waveguide part.
7. photosynthetic ripple according to claim 2/partial wave element is characterized in that,
The wavelength dependency of the equivalent refractive index of the material of utilization formation the described the 1st and the 2nd optical waveguide is obtained described optical path difference Δ L.
8. photosynthetic ripple according to claim 7/partial wave element is characterized in that,
Constitute the described the 1st and the material of the 2nd optical waveguide be Si.
9. according to claim 7 or 8 described photosynthetic ripple/partial wave elements, it is characterized in that,
Establishing the described the 1st and the 2nd light wavelength difference is Δ λ, and establishing the described the 1st and the 2nd optical waveguide is Δ n at the equivalent refraction rate variance of the described the 1st and the 2nd light, and m is under the situation of positive integer, following formula (15) is set up, and described optical path difference Δ L satisfies following formula (16)
Δn/n
2＝(1-Δλ/λ
2)/(2m)-Δλ/λ
2…(15)
2n
2ΔL/λ
2＝(1-Δλ/λ
2)/(Δλ/λ
2+Δn/n
2)…(16)
Wherein, n
2Be the equivalent refractive index of optical waveguide at the 2nd light.
10. photosynthetic ripple/partial wave element, this photosynthetic ripple/partial wave element is set side by side with an end on substrate be that the 1st light input/output port mouth and the other end are the 1st and the 2nd optical waveguide of the 2nd light input/output port mouth,
Series connection be provided with more than 3 grades by the described the 1st and the 1st and the 2nd light input/output port mouth of the 2nd optical waveguide between the Mach-Zehnder interferometer that forms of the described the 1st and the 2nd optical waveguide,
According to wavelength (wherein to the different N wavelength of the wavelength that is input to any one described the 1st light input/output port mouth, N is the integer of N 〉=3) the glistening light of waves that closes carry out partial wave, export (N-i) wavelength (wherein from the 2nd light input/output port mouth of described the 1st optical waveguide, i is the integer of 1≤i≤N-1) light, and, from the light of the 2nd light input/output port mouth of the 2nd optical waveguide output i wavelength, this photosynthetic ripple/partial wave element is characterised in that
When to establish m be integer more than 1,
At the light of propagating in the described the 1st and the 2nd optical waveguide, the absolute value of the optical path difference Δ L of each Mach-Zehnder interferometer is constant,
Have respectively more than one optical path difference sum for the Mach-Zehnder interferometer of+2 Δ L or-2 Δ L by continuous 2 grades form to and the optical path difference sum be 0 Mach-Zehnder interferometer by continuous 2 grades form right,
Following formula (15) ' and formula (16) ' set up simultaneously:
Δn/n
a＝Δm(1-Δλ/λ
a)/(2m)-Δλ/λ
a…(15)’
2n
aΔL/λ
a＝2m＝Δm(1-Δλ/λ
a)/(Δλ/λ
a+Δn/n
a)…(16)’
Wherein, Δ m is the integer that is provided by 2-N, λ
aBe reference wavelength, n
aBe the equivalent refractive index of optical waveguide at the light of reference wavelength.
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| JP2008029365 | 2008-02-08 | ||
| JP2008170095 | 2008-06-30 |
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| Publication Number | Publication Date |
|---|---|
| CN101504472A true CN101504472A (en) | 2009-08-12 |
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|---|---|---|---|
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108700706A (en) * | 2016-02-18 | 2018-10-23 | 日本电信电话株式会社 | Photosynthetic wave circuit |
-
2009
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108700706A (en) * | 2016-02-18 | 2018-10-23 | 日本电信电话株式会社 | Photosynthetic wave circuit |
| US10649144B2 (en) | 2016-02-18 | 2020-05-12 | Nippon Telegraph And Telephone Corporation | Optical multiplexing circuit |
| CN108700706B (en) * | 2016-02-18 | 2020-08-04 | 日本电信电话株式会社 | Optical multiplexer circuit |
| US11112563B2 (en) | 2016-02-18 | 2021-09-07 | Nippon Telegraph And Telephone Corporation | Optical multiplexing circuit |
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