CN201237651Y - Mono-mode light path using multimode waveguide - Google Patents

Abstract

The utility model discloses a single mode optical path using multimode waveguide. The technical problem to be solved is as follows: small curve radius is allowed in the SOI integrated optical loop so as to increase the density of the integrated optical loop. The utility model adopts the following technical proposal: the single mode optical path using multimode waveguide forms an optical path unit by the serial connection of the multimode waveguide and a mode filter optical path. Compared with the prior art, the utility model uses multimode waveguide in the optical path; the whole optical path can work in a single mode state, thus relieving the limitation that the waveguide needs to be single mode; a waveguide structure with strong transverse refractivity comparison can be used, the curve radius is shortened, the density of the optical light is increased; simultaneously the overall performance of the optical light is not effected; and the problem that the requirements to manufacturing accuracy are too demanding is relieved.

Description

Use the single mode light path of multimode waveguide

Technical field

The utility model relates to a kind of integrated opto-electronic device, particularly a kind of single mode light path of using multimode waveguide or other multi-mode structure in light path.

Background technology

In the past, when design PIC photon integrated circuit PIC, requiring it to form optical waveguide is single mode waveguide, operates under single mode condition to guarantee whole loop, do not have higher order mode in the loop or the coupled interface place be excited.If the composition waveguide in loop is not a single mode waveguide; after higher order mode is excited; a plurality of guided modes can be along duct propagation; and each guided mode is carrying the part of optical signal power; modal dispersion that the result is serious and coupling loss at random (when discontinuous and coupled interface take place) can make the signal distortion, even can not be worked fully in whole loop.

But the condition of monomode optical waveguide is too harsh sometimes: what make the waveguide single mode operation is to reduce the constraint of waveguide to light wave at all, and this has just directly caused the increase of required bending radius, thereby reduces integrated light circuit density.A typical example is silicon (SOI) optical waveguide on insulator, as shown in Figure 1.Fig. 1 (a) is an initial SOI garden wafer, comprises silicon layer 8 and imbeds silicon dioxide layer 2, and the body silicon layer 7 below imbedding silicon dioxide layer 2; The cross-sectional view of the ridge waveguide 1 that is become by initial SOI garden wafer process is shown in Fig. 1 (b), imbed silicon dioxide layer 2 as its lower caldding layer, on silicon layer 8, form the wave guide ridge 4 of convex shape and the dull and stereotyped district of ridge waveguide (the slab region of the ridge waveguide) 5 of both sides thereof by etching or selective oxidation, wave guide ridge 4 belows are ridge waveguide core (ridge waveguide core) 3, it comprises the zone from the upper surface of wave guide ridge 4 to the lower surface of silicon layer 8, and upper caldding layer (top cladding) 6 can be air or silicon dioxide or other low-index materials.

Ridge waveguide 1 refractive index of Xing Chenging is configured at last: the refractive index n in wave guide ridge 4, ridge waveguide core 3, the dull and stereotyped district 5 of ridge waveguide _f, lower caldding layer 2 refractive index ns _s, upper caldding layer 6 refractive index ns _cBecause the contrast (n of strong material refractive index in SOI _f=3.48 and n _cOr n _s=1.44～1.8 contrasts), satisfy the single mode operation condition in order to make waveguide, must reduce it when ridge waveguide design contrasts at horizontal effective refractive index: the effective planar waveguide mode refractive index contrast between dull and stereotyped district 5 of waveguide and the ridge waveguide core 3 place flat boards, arrive to a certain degree when this contrast is little, higher order mode will lose horizontal restriction, thereby become radiation mode but not guided mode.

Compare with the silicon dioxide that generally adopts at present and the material system of polymkeric substance, material refractive index in the soi structure is to wanting high a lot, in order to reach single mode condition (keeping and the similar horizontal junction area of general single mode fiber simultaneously), the contrast of its horizontal effective mode refractive index is especially little.This point makes SOI ridge waveguide 1 can not allow little bending radius, and integrated light circuit density is low.And if improve loop density, must significantly reduce the horizontal junction area of waveguide, and this can make waveguide loss increase, and birefringent phenomenon is serious, and light path is too harsh to the requirement of manufacturing accuracy.

Summary of the invention

The purpose of this utility model provides a kind of single mode light path of using multimode waveguide, and the technical matters that solve is to allow little bending radius in the integrated light circuit of SOI, improves integrated light circuit density.

The utility model is by the following technical solutions: a kind of single mode light path of using multimode waveguide, the single-mode optics route multimode waveguide of described use multimode waveguide and the mode filter light path composition optical path unit that is connected in series.

Multimode waveguide of the present utility model forms reflective optical system or multimode coupling end face by deep etching or end face coating.

Multimode waveguide of the present utility model is the ridge waveguide of deep etching, the rectangular waveguide of complete etching or the waveguiding structure with high-index-contrast.

The single mode waveguide that mode filter of the present utility model is led a little less than being, multiple-mode interfence instrument, waveguide pinhole arrangement or the single mode waveguide that is bent.

Be provided with mode converter between multimode waveguide of the present utility model and the mode filter.

The connected mode that the single mode light path of use multimode waveguide of the present utility model adopts one group of above optical path unit to connect with optical path unit.

The single mode light path of use multimode waveguide of the present utility model connects one group of above parallel optical path unit after adopting the connected mode of connecting.

The optical path unit that multimode waveguide of the present utility model and mode filter are formed adopts a mode filter and a plurality of multimode waveguide section to be connected in series.

The utility model compared with prior art, use multimode waveguide in the light path, whole optical path can be operated in the single mode state, having removed waveguide itself must be the restriction of single mode, can use to have tyrannical waveguiding structure to refractive index contrast, dwindles bending radius, increase light path density, simultaneously, the overall performance of light path is unaffected, has alleviated manufacturing accuracy is required too harsh problem.

Description of drawings

Fig. 1 (a) is an initial SOI garden wafer silicon chip synoptic diagram.

Fig. 1 (b) is for having silicon now at SOI ridge waveguide synoptic diagram.

Fig. 2 (a) is traditional single mode waveguide integrated optical circuit principle schematic.

Fig. 2 (b) is the utility model integrated optical circuit principle schematic.

Fig. 3 is an embodiment synoptic diagram of the present utility model.

Fig. 4 is another embodiment synoptic diagram of the utility model.

Fig. 5 is unusual three dimensional pattern transducer.

The integrated optical circuit unit that Fig. 6 is connected with the multimode waveguide that is used for bending for a kind of mode converter.

Fig. 7 is the optical branching device complete configuration structural representation that utilizes the utility model to constitute.

Embodiment

The single mode light path of use multimode waveguide of the present utility model, be called for short SMC, structural principle is as follows: from essence, if a certain section or a few sections of light path is multimode waveguide, as long as guaranteeing higher order mode is not excited at its inlet, place filter membrane device structure at its rear portion, whole optical path just can be kept single mode operation.

Fig. 2 (a) is traditional single mode waveguide integrated optical circuit, and among the figure: whole process is the planar light integrated circuit 11 of single mode waveguide, input end single-mode fiber 13, output terminal single-mode fiber 14.Fig. 2 (b) utilizes the integrated optical circuit of the use multimode waveguide of SMC structure for the utility model, uses the planar light integrated circuit 12 of multimode waveguide, input end single-mode fiber 13, output terminal single-mode fiber 14.Traditional whole process is in the planar light integrated circuit 11 of single mode waveguide, the total losses of optical fiber-integrated optical circuit-optical fiber can be provided by formula (1a), and the utility model utilizes the total losses of optical fiber-integrated optical circuit-optical fiber of integrated optical circuit 12 of the use multimode waveguide of SMC structure to be provided by formula (1b):

${\mathrm{\α}}_{\mathrm{SMW}}={\⟨{\mathrm{\Φ}}_F\·{\stackrel{\‾}{\mathrm{\Ψ}}}_{\mathrm{SMW}}\⟩}^2+\⟨{\stackrel{\‾}{\mathrm{\Φ}}}_F\·\underset{K}{\mathrm{\Σ}}\⟨{\mathrm{\Φ}}_F\·{\stackrel{\‾}{\mathrm{\Ψ}}}_R^K\⟩{\mathrm{\Ψ}}_R^k\·{\mathrm{\η}}_R^k\⟩---\left(1a\right)$

${\mathrm{\α}}_{\mathrm{SMC}}={\⟨{\mathrm{\Φ}}_F\·{\stackrel{\‾}{\mathrm{\Ψ}}}_{\mathrm{MMW}}^0\⟩}^2+\⟨{\stackrel{\‾}{\mathrm{\Φ}}}_F\·\underset{K}{\mathrm{\Σ}}\⟨{\mathrm{\Φ}}_F\·{\stackrel{\‾}{\mathrm{\Ψ}}}_{\mathrm{MMW}}^K\⟩{\mathrm{\Ψ}}_{\mathrm{MMW}}^k\·{\mathrm{\η}}_{\mathrm{MMW}}^k\⟩---\left(1b\right)$

In the formula (1a), Φ F is the optical fiber guided mode, Ψ _SMWBe the basic mode of single mode waveguide, Ψ ^k _RBe the radiation mode of single mode waveguide, and η ^k _RBe these radiation modes from transmission coefficient end to end.On the principle, if the length long enough of integrated optical circuit chip, η ^k _R=0, thus second of formula (1a) do not play practical function, and in formula (1a), keep second, be for the principle of SMC is described.In formula (1b),

Be the main mould of multimode waveguide,

Be higher order mode, and η ^k _MMWIt is the transmission coefficient of these higher order modes.Comparison expression (1a) and formula (1b) can be seen, if formula of making (1b) and formula (1a) equate, the utility model based on the integrated optical circuit of SMC will be on effect the integrated optical circuit with traditional based on single mode waveguide the same.And formula (1b) method equal with formula (1a) also just come into plain view: must force to make η ^k _MMW=0, as long as accomplish this point, although there is multimode waveguide to exist in the integrated optical circuit, light path still can be operated in the single mode state, and this point can realize by add mode filter in light path.Core concept of the present utility model that Here it is.

Fig. 3 is the utility model by the embodiment of waveguide lens and the combination of pin hole mode filter, and to add pin hole similar with lens in the non-Wave Guiding Optics of tradition.On using, it will be the coupling entrance of a functional chip; Among the figure: optical chip profile 21, the waveguide lens 22 that optical chip 21 forms by etching in edge; Waveguide pin hole 23; The silicon area 24 that is not etched; The silica zone 25 of deposition of silica again after being etched; Give incident beam 26 signals among the figure.

From the light beam of single-mode fiber incident, converged by the waveguide lens 22 at chip edge, there is not the laterally slab guide zone (being actually multimode waveguide section) of restriction by one then with infinite multimode, arrive waveguide pin hole 23.This waveguide pin hole can with might filter at the higher order mode that chip edge excites, thereby the single mode of light path operation after guaranteeing.

Fig. 4 (a) be the utility model by incident multimode waveguide section, the multiple-mode interfence instrument and a little less than lead the embodiment of single mode waveguide combination, comprise incident coupling port waveguide 32, multiple-mode interfence instrument 33, spot-size converter 34, a little less than lead single mode waveguide 35.

Incident coupling port waveguide 32 is a multimode waveguide, mode filter by one section multiple-mode interfence instrument 33 and a little less than lead single mode waveguide 35 and form the lossless connection between spot-size converter 34 realizations 33 and 35; Multiple-mode interfence instrument 33 guarantees to remove all even order patterns, and a little less than lead single mode waveguide 35 and guarantee all odd order patterns of filtering.A little less than to lead single mode waveguide 35 are single mode ridge waveguides, the distance suitable on its both sides loads parallel silicon area, the distance of institute's silicon area that loads and wave guide ridge makes not to be had to influence to main mould, but influential to the even mould of high-order.

Fig. 4 (b); Fig. 4 (c); Fig. 4 (d) is the several modes that possible excite in the coupling port light field propagation condition by described mode filter.The main mould of Fig. 4 (b) is by the situation of mode filter; The situation that the strange mould of Fig. 4 (c) is filtered by multiple-mode interfence instrument 33; Lead the situation that single mode waveguide 35 filters a little less than the even mould quilt of Fig. 4 (d).

Fig. 5 is a unusual three dimensional pattern transducer, the optics that is used between multimode waveguide and the mode filter connects, unusual three dimensional pattern transducer is by the silicon chip 41 of silicon dioxide or the encirclement of other low-index materials, comprise low level flat board 44, high-order flat board 45, shoulder 46, wave guide ridge 49, its incident end face 42, outgoing end face 47, incident end face dominant waveguide mode formula 43, the exit end ground roll is led holotype 48

Incident end face 42 towards optical fiber is ridge waveguides of a deep etching, and its dominant waveguide mode formula 43 has the circle that is complementary with fiber mode to lining and size, and such ridge waveguide is a multimode waveguide; Thereafter wave guide ridge 49 lateral dimensions narrow down gradually, and the lateral dimension of shoulder 46 broadens gradually, this waveguiding structure that gradually changes not only makes incident end face dominant waveguide mode formula 43 gradually change into the exit end ground roll and leads holotype 48, its horizontal restriction to light wave simultaneously weakens, can become radiation mode and decay at the coupling end face higher order mode that may excite, thereby play the effect of certain mode filter.

As shown in Figure 6, the integrated optical circuit unit that is connected with the multimode waveguide that is used for bending for a kind of mode converter; Except reducing coupling loss, SMC allows to use the narrow ridge waveguide of deep etching to reduce required bending radius, improves light path density.Among the figure: initial silicon flat board 51 originates in the SOI circular wafer; Light engraving erosion ridge waveguide 52, deep etching ridge waveguide 53; Deep etching ridge waveguide 53 since to light in horizontal strong restrictions, can be formed with the bending 54 of very little bending radius.The structure of Fig. 6 can be placed on after the device of Fig. 4, can with a little less than lead the multimode waveguide 53 that strong restriction is returned in single mode waveguide 35 conversion.

The structure of the utility model SMC can repeatedly be used in integrated optical circuit, and by different configure interconnected, Fig. 7 has provided the complete configuration of utilizing the utility model to constitute optical branching device.The left side is an input end, and the right is an output terminal.Multimode waveguide section MWS 1 is in order to improve the coupling efficiency with optical fiber, and its heel mode filter 1 is eliminated issuable higher mode in coupling process (Fig. 3, or Fig. 4, or embodiment shown in Figure 5 just can use here).Can be provided with mode converter between multimode waveguide and the mode filter, connect to realize low-consumption optical between the two.When optical fiber and waveguide fully on time, main luminous power all can be coupled to the basic mode of waveguide, to higher mode seldom, and to the part of higher mode, tell as preceding institute, be equivalent to the radiation mode loss that when being coupled, causes, and mode filter 1 the effect here is exactly to guarantee that this part is attenuated to the power in the higher mode is the same with radiation mode by mode mismatch with single mode waveguide.After mode filter 1, multimode waveguide section 2 is for mode conversion that may need and bending.On the principle, in the architecture of SMC, after each multimode waveguide section, can follow a mode filter.But in practice, might not do like this.Strictly speaking, guaranteed in follow-up multimode waveguide section MWS, to have only main mould to be excited at the mode filter behind the coupled interface, and do not had higher order mode.If waveguide is desirable (not owing to makes cause discontinuous), this have only the state of main mould transmission to keep always, and the mode filter of back is just unnecessary.In actual light path design, because the discontinuous main mould that causes is always inevitable to the conversion of higher order mode, mode filter need add the multimode sensitive part in light path, is affected with the function that prevents light path.These mode filters can be not influential to the overall loss of light path, even because in light path based on single mode waveguide, and the discontinuous conversion that also can cause main mould to radiation mode, final result's meeting is the same with the SMC that has added mode filter.The connected mode that the single mode light path of use multimode waveguide adopts one group of above optical path unit to connect with optical path unit connects one group of above parallel optical path unit after the connected mode of series connection.The optical path unit that described multimode waveguide and mode filter are formed also can adopt a mode filter and a plurality of multimode waveguide section to be connected in series.

Claims (8)

1. single mode light path of using multimode waveguide is characterized in that: the single-mode optics route multimode waveguide of described use multimode waveguide and the mode filter light path composition optical path unit that is connected in series.

2. the single mode light path of use multimode waveguide according to claim 1 is characterized in that: described multimode waveguide forms reflective optical system or multimode coupling end face by deep etching or end face coating.

3. the single mode light path of use multimode waveguide according to claim 2 is characterized in that: described multimode waveguide is the ridge waveguide of deep etching, the rectangular waveguide of complete etching or the waveguiding structure with high-index-contrast.

4. use the single mode light path of multimode waveguide according to claim 3, it is characterized in that: the single mode waveguide that described mode filter is led a little less than being, multiple-mode interfence instrument, waveguide pinhole arrangement or the single mode waveguide that is bent.

5. according to the single mode light path of arbitrary described use multimode waveguide in the claim 1 to 4, it is characterized in that: be provided with mode converter between described multimode waveguide and the mode filter.

6. the single mode light path of use multimode waveguide according to claim 5 is characterized in that: the connected mode that the single mode light path of described use multimode waveguide adopts one group of above optical path unit to connect with optical path unit.

7. the single mode light path of use multimode waveguide according to claim 6 is characterized in that: the single mode light path of described use multimode waveguide connects one group of above parallel optical path unit after adopting the connected mode of connecting.

8. the single mode light path of use multimode waveguide according to claim 5 is characterized in that: the optical path unit that described multimode waveguide and mode filter are formed adopts a mode filter and a plurality of multimode waveguide section to be connected in series.

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