CN1450383A - Clad modulation wave guide type electro-optical modulator - Google Patents

Abstract

A cladding modulation waveguide electro-optical modulator belongs to the technical field of optical communication devices. Address waveguide propagation loss and large birefringence in the core. The invention consists of a core layer and a cladding layer. The cladding layer adopts nonlinear electro-optic materials, and the core layer adopts electro-optical active materials. By only using electro-optic materials for the cladding layer of the waveguide, the effective refractive index of the waveguide changes with the modulation voltage, thereby achieving purpose of modulation. By adopting the invention, the transmission loss of the modulator can be reduced, and the coupling length between the traveling wave electrode and the waveguide can be increased, thereby increasing the modulation frequency.

Description

Cladding modulated waveguide electro-optic modulator

technical field

The invention belongs to the technical field of optical communication devices, in particular to optoelectronic devices such as waveguide electro-optical modulators.

Background technique

Waveguide electro-optic modulators are mainly realized by using electro-optic materials, such as LiNbO ₃ ferroelectric crystals, semiconductor materials, and polarized polymers, to generate electro-optic effects under the action of an electric field. When the modulation electric field acts, due to the electro-optic effect, the refractive index of the core layer or the equivalent refractive index of the waveguide changes with the modulation field, which causes the light propagation phase to also change with the modulation field, realizing light modulation.

At present, waveguide core layer modulation is adopted in the design of waveguide optical modulators, that is, the core layer is made of electro-optical materials. For related patents, refer to US2003/0002766Al (PUB No.). For the polymer waveguide optical modulators that have been rising in recent years, in order to increase the nonlinear coefficient or electro-optic coefficient, polymers with high chromophore content are usually used as the core material, which makes the optical loss of the polymer modulator relatively High, which seriously hinders the practical progress of polymer waveguide modulators. In the US patent with the authorized patent number 20030002766Al, the cladding layer and the core layer of the waveguide are both LiNbO ₃ electro-optical materials, and its essence still belongs to the traditional core layer modulation method. Most waveguide electro-optic modulators modulated by the core layer are in the form of Mach-Zehnder interferometer (MZI). There are many ways to implement the MZI electro-optic modulator, and Figure 1 is a schematic diagram of one of the push-pull types. Where (a) is a cross-sectional view of the waveguide, and (b) is a top view. 1 is Si or SiO ₂ substrate, 2 is the lower cladding layer of the waveguide, 3 is the core layer of the waveguide, which is made of electro-optic material, and its electro-optic coefficient is usually relatively large, 4 is the upper cladding layer of the waveguide, 5 is the buffer layer, 6 , 7 and 8 are metal electrodes. For high-speed modulation, traveling wave electrodes are generally used. In figure (b), the light wave enters from the input waveguide 9, passes through the first Y branch 11, and then the energy of the light wave is divided into two parts, which are respectively transmitted along the interference arms 13 and 14, and are respectively modulated in the two interference arms. Respective additional phase lag ΔΦ=(π/λ)Γn _eff ³ γ ₃₃ VL (Γ is the reduction factor, n _eff is the effective refractive index of the waveguide transmission mode, γ ₃₃ is the electro-optic coefficient, V is the modulation voltage, L is the electrode length ) with a sign difference (that is, Push-Pull), the two beams of light are combined by the second Y branch 12 to generate an interference effect, and finally the modulated light is output in the output waveguide 10 .

As for the core layer modulated waveguide electro-optic modulator, the device loss reported in the general literature is mostly as high as ten or even twenty dB. It is generally believed that the insertion loss should be at the level of several dB to meet the practical requirements, and the propagation loss of the waveguide should be below 1dB/cm. Due to the relatively large loss, the length of the modulation region is bound to be limited, that is, the interaction distance between the light wave and the microwave is limited, which is unfavorable for further increasing the modulation frequency. In addition, since the core of the waveguide is a material with a large electro-optic coefficient, the electro-optic effect generated under the action of the modulated electric field leads to a large birefringence in the core, which will introduce considerable polarization in the bending part of the waveguide and when coupling with the optical fiber. related losses.

Contents of the invention

The invention proposes a cladding modulation waveguide type electro-optic modulator, aiming to solve the problems of waveguide propagation loss and large birefringence in the core layer.

A cladding modulation waveguide electro-optic modulator of the present invention is composed of a core layer and a cladding layer, and is characterized in that the cladding layer is made of a nonlinear electro-optic material, and the core layer is made of an electroless photoactive material.

The cladding modulation waveguide electro-optic modulator is further characterized in that the cladding layer is made of polymer material containing chromophore, and the core layer is made of polymer or inorganic material without chromophore.

In the cladding modulation waveguide electro-optic modulator involved in the present invention, the cladding (ie 2 and 4 in FIG. 1 ) of the waveguide structure adopts nonlinear electro-optic materials; the core layer uses non-electro-optic active materials. When the external modulation field acts on the cladding layer, the refractive index of the electro-optical material changes, and the modulation of light is realized. Compared with the traditional core layer modulation method, this method does not have any strict requirements on specific implementation, so it is also easy to implement.

The cladding modulation waveguide type electro-optic modulator of the present invention has the advantages of low optical transmission loss, weak birefringence phenomenon of the core layer, increased freedom of selection of core layer materials, and the like. In addition, with the reduction of loss, the length of the modulator's modulation region or the interaction distance between the light wave and the microwave signal can also be larger, which can reduce the half-wave voltage and further increase the modulation frequency. Therefore, the present invention can improve the performance of waveguide optical modulators.

Description of drawings

Fig. 1 Schematic diagram of the waveguide electro-optic modulator modulated by the push-pull MZI core layer, in which (a) is a cross-sectional view of the waveguide, and (b) is a top view.

Fig. 2 Schematic diagram of the MZI cladding-modulated polymer waveguide electro-optic modulator, in which (a) is a cross-sectional view of the waveguide, and (b) is a top view.

Figure 3. The working principle diagram of the push-pull MZI-type cladding-modulated waveguide optical modulator. The core layer is made of inorganic materials. In the figure (a) is the cross-sectional view of the waveguide, and (b) is the top view.

Detailed ways

FIG. 2 shows Embodiment 1 of the present invention, and FIG. 3 shows Embodiment 2 of the present invention.

The embodiment shown in FIG. 2 is a Mach-Zehnder interferometer-type cladding modulation polymer waveguide waveguide modulator. The cladding material is PMMA polymer doped with chromophore, which has electro-optic activity, and the core layer is polyimide. Where (a) is a cross-sectional view of the waveguide, and (b) is a top view. When making, first vapor-deposit Cr/Au electrode 7 on clean Si or SiO ₂ substrate 1, called substrate electrode or lower electrode; then spin-coat lower cladding 2 and solidify, corona polarization; 2, spin-coat the waveguide core layer 3 and cure it, and etch the pattern of the waveguide core layer; spin-coat the upper cladding layer 4 while curing and corona polarization; evaporate the Cr/Au top layer electrode 6 and etch the electrode pattern; finally cut and Polished end faces.

Its working principle is: the light wave enters from the input waveguide 9, and after passing through the first Y branch 11, the energy of the light wave is divided into two parts, which are respectively transmitted along the interference arms 13 and 14, wherein the light wave is modulated in the interference arm 14, and a phase is added Delay ΔΦ, the two beams of light are combined by the second Y branch 12 to produce interference effect, and finally the modulated light is output in the output waveguide 10 . In the area of the interference arm 14, the modulated signal (microwave) is coupled through the input port 16 of the traveling wave electrode 15, and then output from the output port 17. Here, as long as the traveling wave electrode is optimally designed, the best speed matching can be achieved to obtain a large modulation bandwidth.

Figure 3 shows the structure and working principle of the push-pull Mach-Zehnder interferometer-type cladding-modulated waveguide optical modulator, where (a) is a cross-sectional view of the waveguide, and (b) is a top view. The material of the waveguide lower cladding layer 2 and the waveguide upper cladding layer 4 is nonlinear ADK77 polymer, and the core layer 3 is an inorganic material SiON. The buffer layer 5, the metal electrodes 6, 7, and 8 are all the same as those shown in Fig. 1, and the marks on the input waveguide 9, the first Y branch 11, the interference arms 13, 14, the second Y branch 12, and the output waveguide 10 are also the same as those shown in Fig. 1, its working principle is basically the same as that of Embodiment 1, the only difference is that the light waves are modulated simultaneously in the two interference arms 13 and 14.

Claims (2)

1. A cladding modulation waveguide type electro-optic modulator, consisting of a core layer and a cladding layer, is characterized in that the cladding layer adopts a nonlinear electro-optic material, and the core layer adopts an electroless photoactive material. 2. The cladding-modulated waveguide electro-optic modulator according to claim 1, characterized in that the cladding layer is made of a polymer material containing a chromophore, and the core layer is made of a polymer or an inorganic material without a chromophore.

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