CN101957534B - Ultra wide band photo-parametric amplifier based on silicone based surface plasma wave guide - Google Patents

Abstract

An ultra-broadband optical parametric amplifier based on a silicon-based surface plasmon waveguide in the field of semiconductor technology, including: a tunable laser, a pump laser, a surface plasmon waveguide, and an optical coupler, wherein: the output ends of the tunable laser and the pump laser are respectively It is connected with the optical coupler, and the optical coupler couples the pump light and the signal light and outputs them to the surface plasmon waveguide in sequence. In the present invention, the pumping light with a power of 0.5W and the signal light with a low power are incident into the waveguide structure with a length of 20 microns at the same time, and the signal light obtained at the output end has a gain of 14dB and a working bandwidth of 202 nanometers including S -band, C-band and L-band, the device size is 100nm×5nm×20μm, which enhances its nano-integration level, reduces the input pump light power, reduces energy consumption, and improves pump efficiency.

Description

Ultra-broadband Optical Parametric Amplifier Based on Silicon Surface Plasmon Waveguide

technical field

The invention relates to a device in the field of semiconductor technology, in particular to an ultra-broadband optical parametric amplifier based on a silicon-based surface plasmon waveguide.

Background technique

In recent years, nano-optics based on surface plasmon technology has received more and more attention. Surface plasmons break the diffraction limit of traditional dielectric waveguides, and can confine the light in the communication band to deep subwavelength waveguides, which can be like metal wires. Conduction electrons transport light at the nanometer scale, driving further reduction in device size and further increase in integration density. At the same time, as the chip gradually brings together multiple functions such as computing, storage, communication, and information processing, it promotes the realization of on-chip optical computing technology. In order to realize the logic and signal processing functions in optical computing, the nonlinear effect of optical devices needs to be used. Compared with electrical signal processing, the nonlinear signal processing of optical devices has ultra-fast response speed, and the processing bandwidth exceeds THz. However, large power and long distance are required to produce nonlinear effects, and its size and power consumption limit its application in integrated optical circuits. Due to the localization ability of surface plasmons to the deep sub-wavelength of light, its mode field area is greatly reduced, which makes it possible to enhance the nonlinear coefficient, reduce the threshold power and device length, so surface plasmons will be used in the future nano-optical integrated signal Applications are found in scientific areas such as processing devices and circuits. The paper "Plasmonics beyond the diffraction limit" in the journal Nature photonics systematically introduces passive and active nanodevices such as photodetectors based on surface plasmon waveguides , optical amplifier, etc.

At the same time, the doped fiber amplifier is based on the stimulated emission of dopant atoms, so its operating wavelength range mainly depends on the properties of the dopant atoms; Raman amplifiers also have similar properties, making the operating bandwidth of the two amplifiers only a few dozen Nano. But the optical parametric amplifier mainly depends on the third-order nonlinearity of the optical waveguide material rather than the properties of the doped atoms. In principle, as long as the phase matching of four-wave mixing is satisfied, the optical parametric amplifier can work in any wavelength range. Its operating bandwidth is mainly determined by the pump optical power, the nonlinearity of the waveguide and the dispersion. Therefore, it has great development prospects in increasing the working bandwidth of optical parametric amplifiers to make them far larger than doped fiber amplifiers and Raman amplifiers. Combining the ultra-high nonlinearity of surface plasmon waveguides, it is theoretically possible to design ultra-wide optical parametric amplifiers.

After searching the prior art, it was found that Mark A. Foster et al. of Cornell University in the United States published a paper (published in Nature, Vol.442, PP.960-963 (Natural Magazine), "Broad-band optical parametric gain on a silicon photonic chip (Broadband Optical Parametric Gain Based on Silicon Optical Waveguides)"). This literature reports the design of the C-band parametric amplifier. By optimizing the structural parameters of the silicon-based waveguide, an optical parametric amplifier with a device size of 300nm×600nm×6.4mm, a bandwidth of 70nm and a gain of 14dB is realized. The pump of this structure The power of Pu light is 1W. However, the bandwidth achieved by this prior art cannot support the increasing requirement for communication bandwidth (only limited to the C-band), and the input power is relatively high.

Contents of the invention

Aiming at the above-mentioned deficiencies in the prior art, the present invention provides an ultra-broadband optical parametric amplifier based on a silicon-based surface plasmon waveguide. In the waveguide structure with a diameter of 20 microns, the signal light obtained at the output end has a gain of 14dB and the working bandwidth is 202 nanometers, including S-band, C-band and L-band, and the device size is 100nm×5nm×20μm. The degree of its nano-integration is improved, and the input pump light power is reduced, the energy consumption is reduced, and the pump efficiency is improved.

The present invention is achieved through the following technical solutions. The present invention includes: a tunable laser, a pump laser, a surface plasmon waveguide and an optical coupler, wherein: the output ends of the tunable laser and the pump laser are connected to the optical coupler respectively, and the optical coupler The device couples the pump light and the signal light and outputs them to the surface plasmon waveguide.

The tunable laser is used to provide a signal light source, its output end can be connected with an optical attenuator to reduce its signal power, and its output wavelength range is 1300nm-1700nm.

The pumping laser is used to provide high-power pumping light required for the operation of the parametric amplifier. The wavelength of the pumping light output by it is 1550nm, and the output power ranges from 0.25W to 1W.

The optical coupler couples the pumping light and the signal light into one path of light, which is coupled into the waveguide.

The surface plasmon waveguide includes: a ridge-shaped silicon waveguide, a metal silver ladder structure layer and a polymer gap layer, wherein: the metal silver ladder structure layer is connected to the ridge-shaped silicon waveguide through the polymer gap layer in the vertical direction.

The outer width of the metal silver ladder structure layer is larger than the silicon base width of the ridge silicon waveguide, and the metal step width of the metal silver ladder structure layer is aligned with the silicon ridge of the ridge silicon waveguide.

When the present invention works, the low-power signal light with a wavelength of 1300nm-1700nm provided by the tunable laser and the pump light with a wavelength of 1550nm and a power of 0.5W provided by the pump laser are coupled into the device with a size of In the 100nm×5nm×20μm stepped structure hybrid surface plasmon waveguide, the signal light and pump light pass through the four-wave mixing effect in the waveguide, and the signal light and idle light with gain are generated at the output end of the waveguide. The optical spectrum analyzer displays the optical power, gain, and spectrum of the signal generated at the output of the waveguide.

Compared with the prior art, the present invention utilizes the surface plasmon waveguide to realize the ultra-broadband optical parametric amplifier for the first time, and introduces highly nonlinear polymer-regional regular poly 3-hexylthiophene (Region-RegularPoly(3-HexylThiophene) (RR-P3HT)) as a dielectric gap, enhances the nonlinear coefficient, increases the operating bandwidth of the optical parametric amplifier of the single pump light, covers the S-band, C-band and L-band bands, and reduces the The power of the pump light is input, thereby reducing energy loss and improving pumping efficiency.

Description of drawings

Fig. 1 is a system structure diagram of the present invention.

Fig. 2 is a schematic diagram of the surface plasmon waveguide structure.

Figure 3a is a schematic diagram of the electric field distribution of the surface plasmon structure obtained by COMSOL simulation software.

Fig. 3b is the magnitude distribution curve of the electric field in the x-axis direction of the surface plasmon structure.

Fig. 3c is a distribution curve of the electric field magnitude in the y-axis direction of the surface plasmon structure.

Figure 4a is a working principle diagram of degenerate four-wave mixing.

Figure 4b is a spectrogram of the four-wave mixing effect.

Fig. 5 is a graph showing the relationship between the group velocity dispersion D and the operating wavelength at different widths of the waveguide silicon substrate obtained through Comsol simulation.

Fig. 6 a is the signal power gain figure that the optical parametric amplifier of embodiment obtains by Matlab simulation;

Among them: the pump optical power is 0.5W, the working wavelength is 1550nm, and the waveguide length is 20μm.

Fig. 6 b is the optical parametric amplifier of the embodiment, the peak gain and 3-dB bandwidth diagram of the signal power obtained by Matlab simulation;

Among them: the pump optical power is 0.5W, the working wavelength is 1550nm, and the waveguide length is 20μm.

Detailed ways

The embodiments of the present invention are described in detail below. This embodiment is implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating procedures are provided, but the protection scope of the present invention is not limited to the following implementation example.

As shown in Figure 1, the device includes: a tunable laser 1, a pump laser 2, a surface plasmon waveguide 3 and an optical coupler 4, wherein the output ends of the tunable laser 1 and the pump laser 2 are respectively connected to the optical coupler 4 , the optical coupler 4 couples the pump light and the signal light and outputs them to the surface plasmon waveguide 3 .

The tunable laser 1 is used to provide a signal light source, its output end can be connected with an optical attenuator to reduce its signal power, and its output wavelength range is 1300nm-1700nm.

The pump laser 2 is used to provide the high-power pump light required for the operation of the parametric amplifier. The wavelength of the pump light output by it is 1550nm, and the output power ranges from 0.25W to 1W.

The optical coupler 4 mainly couples the pumping light and the signal light into one path of light, which is then coupled into the waveguide.

As shown in Figure 2, the surface plasmon waveguide 3 includes: a ridge-shaped silicon waveguide 5 with a size of W×H, a metal silver ladder structure layer 6 with a width of W1, and a polymer gap layer 7, wherein: the metal silver ladder structure Layer 6 is vertically connected to the ridged silicon waveguide 5 via a polymer spacer layer 7 . Where W is the width of the silicon ridge, H is the height of the silicon ridge, h is the thickness of the polymer gap above the silicon ridge, h1 is the height of the metal step layer, Hc is the thickness of the metal Ag layer (not considering the height of the metal step layer), Hs is The thickness of the silicon layer of the silicon ridge waveguide, W1 is the width of the metal Ag layer,

The width W of described metal silver ladder structure layer 6 _{is greater} than the silicon base width W of ridge silicon waveguide 5 (being SOI waveguide), and the metal step 8 width of metal silver ladder structure layer 6 is W and ridge silicon waveguide 5. The silicon ridges 9 are aligned, and the thickness of the metal steps 8 of the metal silver step structure layer 6 is h ₁ . It can be seen from the figure that the thickness of the polymer gap layer 7 on the lower surface of the metal step 8 is h, and the thickness of the polymer gap layer on the other lower surface of the metal is h+H+h ₁ .

When the device is working, the low-power signal light (20mW) with a wavelength of 1300nm-1700nm provided by the tunable laser and the pump light with a wavelength of 1550nm and a power of 0.5W provided by the pump laser are coupled into the The device size is 100nm×5nm×20μm (that is, the silicon ridge width W is 100nm, the thickness h of the polymer gap above the silicon ridge is 5nm, the waveguide length L is 20μm, and the other parameters are H=300nm, h ₁ =20nm, H _c = 100nm, H _s =200nm, W ₁ =300nm) in the stepped structure hybrid surface plasmon waveguide, the signal light and the pump light pass through the four-wave mixing effect in the waveguide, and the signal light with gain and the idle light. The optical spectrum analyzer displays the optical power, gain, and spectrum of the signal generated at the output of the waveguide. When the device is working, it can make full use of the high nonlinearity of the ladder-structure hybrid surface plasmon waveguide to achieve ultra-wide bandwidth signal gain.

As shown in Figure 3(a), the magnitude of the electric field under the conditions of W=50nm, H=300nm, h=5nm, h ₁ =20nm, H _c =100nm, H _s =200nm, and W ₁ =300nm is in the lateral direction (i.e. xy direction) distribution schematic diagram, Fig. 3 (b) is the distribution schematic diagram (x=0) of electric field magnitude in y direction, Fig. 3 (c) is the distribution schematic diagram (y=0) of electric field magnitude in x direction, wherein The coordinates of the origin are shown in Figure 3(a). From the figure, it can be seen that the electric field is strongly confined to the polymer gap layer with a thickness of h (that is, the black part in the figure is the main concentration of the electric field energy). The real part of its effective refractive index is 1.966057, and the imaginary part of its effective refractive index is 0.001437. Wherein h is selected as 5 nanometers, and its reason is, for the silver (Ag)-polymer gap-silicon (Silicon) waveguide structure, because the height of the polymer gap layer affects the silver/polymer interface surface plasmon in the bulk mode and the silicon waveguide mode When the gap layer is too large, the coupling of the two modes will be weakened, so that the light intensity cannot be stably confined in the polymer gap layer. When h is selected larger than 5 nm, the electric field will periodically switch between the surface plasmon mode on the silver/polymer surface and the waveguide mode in the ridge silicon waveguide, making the electric field not stably localized in the polymer gap layer. In this device, the thickness h of the polymer interstitial layer is selected to be 5 nanometers. By optimizing the height of the metal step layer, the best compromise between transmission loss and effective mode field area is obtained. The final optimal metal step layer height is 20nm, and by introducing a highly nonlinear polymer-Regional Poly 3-hexylthiophene (Region-RegularPoly(3-HexylThiophene)(RR-P3HT)) as a dielectric gap, the obtained The nonlinear coefficients γ of waveguides with widths of 10nm, 20nm, 50nm and 100nm on silicon base are 4.7×10 ⁶ W ^-1 m ^-1 , 2.35×10 ⁶ W ^-1 m ^-1 , 9.4×10 ⁵ W ^-1 m ^-1 and 4.7×10 ⁵ W ^-1 m ^-1 , the obtained nonlinear coefficient is three orders of magnitude (that is, thousands of times) that of the general silicon-based waveguide.

(公式4)，其中Es为信号电场，L为波导长度。在公式2中，γP0代表由于自相位调制以及交叉相位调制引起的相位偏差，对于一般的硅基波导，当群速度色散D小于0时，即不满足相位匹配条件时，其信号增益发生在很窄的波长范围之内一般为几个纳米。Figure 4a shows the working principle of degenerate four-wave mixing. A higher power pump light (with an angular frequency of ω _p ) and a lower power signal light (with an angular frequency of ω _s ) enter the device at the same time. In the surface plasmon waveguide of , through the four-wave mixing effect, at the output end of the waveguide, two pump photons with angular frequency ω _p will be converted into a signal photon (angular frequency ω _s ) and an idler photon (angular frequency is ω _i ), resulting in the amplification of the signal light. Figure 4b shows the spectrum characteristics of four-wave mixing. The three photons mentioned above satisfy the law of energy conservation, that is, 2ω _p =ω _s +ω _i (Formula 1). The parametric gain parameter g is given by the following formula: g ² =-Δβ(Δβ/4+γP ₀ ) (Formula 2), where P ₀ is the pump optical power, Δβ is the mismatch of the linear wave vector determined by the waveguide Attribute determination (dispersion) is: Δβ=β _s +β _i -2β _p (Formula 3), where βs, βi, βp are the propagation constants of signal light, idle light and pump light. Without considering the attenuation of the pump light, the power gain Gs of the signal is

(Equation 4), where Es is the signal electric field and L is the waveguide length. In Equation 2, γP0 represents the phase deviation caused by self-phase modulation and cross-phase modulation. For a general silicon-based waveguide, when the group velocity dispersion D is less than 0, that is, when the phase matching condition is not satisfied, the signal gain occurs in a very The narrow wavelength range is generally a few nanometers.

Figure 5 shows the group velocity dispersion of different waveguide silicon ridge widths. It can be seen from the figure that the group velocity dispersion, ie, D, of all waveguide sizes is less than 0, that is, the phase matching is not satisfied. The reason is as follows, because the effective refractive index of the surface plasmon waveguide is proportional to the cube of the refractive index of silicon, and silicon has a very large normal group velocity dispersion (D is less than 0) at a wavelength of 1550nm, thereby increasing the silicon The material dispersion of silicon makes the material dispersion of silicon play a dominant role in the total dispersion, and the obtained group velocity dispersion D is all less than 0. It can also be seen from the figure that the group velocity dispersion D of a large silicon ridge width is closer to 0, which satisfies more phase matching, because the waveguide dispersion with a wider silicon ridge compensates more material dispersion.

As shown in Fig. 6a, the signal gain of four-wave mixing obtained by Matlab simulation according to Formula 1-Formula 5 under the condition of a 20-micron long waveguide and 0.5W pump light power. In the normal dispersion region, that is, D is less than 0, the 3dB bandwidth of all waveguide structures obtained is hundreds of nanometers, which is much larger than that of ordinary SOI waveguides. The reason is as follows, because the gain bandwidth is denoted by Δβ based on Equation 3, and its magnitude is consistent with 4γP ₀ . This means that the larger the γ or P ₀ or even γP ₀ , the larger the tolerance range of Δβ, that is to say, the weaker the phase matching requirement, and the larger the frequency difference between the pump light and the signal light can be. Make the 3dB bandwidth larger. As shown in Figure 6b, the peak gain and 3-dB bandwidth diagram of the signal power obtained by Matlab simulation, when the silicon ridge width increases, the 3dB bandwidth becomes larger, because it can be seen from Figure 4 that its normal dispersion D is more is close to 0, but the peak signal gain decreases because its nonlinear coefficient γ becomes smaller. The resulting widest bandwidth is 202nm, including C-band, L-band, and S-band, with a peak signal gain of 14dB, a device size of 100nm×5nm×20μm, and an output optical power of 0.5W.

For the first time, this device proposes a SOI-integrated ultra-broadband optical parametric amplifier by introducing a super-nonlinear silicon-based ladder structure surface plasmon waveguide structure and a highly nonlinear polymer to achieve an ultra-broadband of more than 200 nanometers. Wide optical parametric amplifier (far greater than the 70nm operating bandwidth that can be obtained by the existing silicon-based waveguide under a single pump light), its signal gain is 14dB, and the input pump light power is 0.5W, compared with the prior art ( The pump optical power is 1W), which obviously reduces the energy loss and improves the pumping efficiency, and can work in the near-infrared and mid-infrared bands, which meets the increasing bandwidth demand in the field of optical communication. The waveguide size proposed by this device is 100nm× 5nm × 20μm, which is conducive to nanoscale integration.

Claims (1)

1. ultra-wideband-light parameter amplifier based on the silicon substrate surface plasma filled waveguide; Comprise: tunable laser, pump laser, surface plasma waveguide and photo-coupler; Wherein: the output terminal of tunable laser and pump laser links to each other with photo-coupler respectively; Photo-coupler exports the surface plasma waveguide to after with the coupling of pump light and flashlight successively; It is characterized in that: described surface plasma waveguide comprises the waveguide of ridged silicon, argent staircase structure layer and polymkeric substance clearance layer, and wherein: argent staircase structure layer links to each other with the waveguide of ridged silicon through the polymkeric substance clearance layer in vertical direction;

The outer silica-based width that is wider than the waveguide of ridged silicon of described argent staircase structure layer, the metal ladder width of argent staircase structure layer aligns with the silicon ridge of ridged silicon waveguide;

The width of described ridged silicon waveguide is W=50nm, highly is H=300nm,

The outer wide W of described argent staircase structure layer ₁=300nm,

The thickness h of described metal ladder ₁=20nm,

Be positioned at the thickness h=5nm of the polymkeric substance clearance layer of metal ladder lower surface;

The output terminal of described tunable laser reduces its signal power through connecting optical attenuator, and the output wavelength scope is 1300nm-1700nm;

The pumping light wavelength of the output of described pump laser is 1550nm, and the power bracket of output is 0.25W-1W.

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