Disclosure of Invention
The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art, and provide a spectrum shaping device and method, which can select one or more wavelength points according to a target spectrum response to adjust the corresponding spectrum response, thereby achieving the effect of adjusting any spectrum response, and reducing power consumption while greatly improving adjustment efficiency.
The invention specifically adopts the following technical scheme to solve the technical problems:
a narrow bandwidth mach-zehnder interferometer comprised of two identical counter-couplers: the first reverse coupler and the second reverse coupler are connected, a reverse coupling port of the first reverse coupler is connected with an adding port of the second reverse coupler, a through port of the first reverse coupler is connected with an input port of the second reverse coupler, and an input port of the first reverse coupler and a through port of the second reverse coupler are respectively used as an input port and an output port of the narrow-bandwidth Mach-Zehnder interferometer.
Preferably, the narrow bandwidth mach-zehnder interferometer is prepared by a photonic integration method.
A spectrum shaping device comprises a group of serial narrow-bandwidth Mach-Zehnder interferometers according to any one of the above technical schemes, wherein interference wavelengths of the group of narrow-bandwidth Mach-Zehnder interferometers are different.
A spectral shaping method, which changes the spectral component of the input optical signal of the spectral shaping device at the wavelength corresponding to the interference wavelength of at least one narrow-bandwidth mach-zehnder interferometer by adjusting the transmission coefficient of the at least one narrow-bandwidth mach-zehnder interferometer in the spectral shaping device, thereby realizing the spectral shaping of the input optical signal.
Preferably, the adjustment of the transmission coefficient of the narrow bandwidth mach-zehnder interferometer is achieved based on thermo-optic effects and/or carrier dispersion effects.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
the invention realizes a narrow-bandwidth Mach-Zehnder interferometer with extremely narrow bandwidth for the first time based on a reverse coupler, can realize the adjustment of 0-100% of the transmission spectral response at the interference wavelength by adjusting the transmission coefficient, and further realizes the effect of adjusting any spectral response based on the serial form of a plurality of narrow-bandwidth Mach-Zehnder interferometers with different interference wavelengths. Compared with the prior art, the spectrum shaping device has the advantages of simpler structure, easier manufacture, greatly improved spectrum adjustment efficiency and greatly reduced required power consumption.
Detailed Description
In recent years, with the development of photonic integrated circuit technology and the proposal of programmable photonic integrated circuit concept, the development period and cost can be greatly reduced, and the method has very wide application and development prospects. However, existing programmable photonic integrated circuits require resetting of each phase shifter when adjusting the spectral response, which reduces the efficiency of the adjustment and adds additional energy consumption and waste of resources. In order to solve the problem, the solution idea of the invention is to perform interference of a narrow-bandwidth specific wavelength based on a narrow-bandwidth Mach-Zehnder interferometer constructed by a reverse coupler, realize effective adjustment and only adjust the transmission coefficient of the wavelength, and further select one or more wavelength points according to a target spectral response on the basis to adjust the spectral response corresponding to the wavelength point, thereby achieving the effect of adjusting any spectral response, greatly improving the adjustment efficiency and simultaneously reducing the power consumption.
Specifically, the technical scheme adopted by the invention is as follows:
a narrow bandwidth mach-zehnder interferometer comprised of two identical counter-couplers: the first reverse coupler and the second reverse coupler are connected, a reverse coupling port of the first reverse coupler is connected with an adding port of the second reverse coupler, a through port of the first reverse coupler is connected with an input port of the second reverse coupler, and an input port of the first reverse coupler and a through port of the second reverse coupler are respectively used as an input port and an output port of the narrow-bandwidth Mach-Zehnder interferometer.
A spectrum shaping device comprises a group of serial narrow-bandwidth Mach-Zehnder interferometers according to any one of the above technical schemes, wherein interference wavelengths of the group of narrow-bandwidth Mach-Zehnder interferometers are different.
A spectral shaping method, which changes the spectral component of the input optical signal of the spectral shaping device at the wavelength corresponding to the interference wavelength of at least one narrow-bandwidth mach-zehnder interferometer by adjusting the transmission coefficient of the at least one narrow-bandwidth mach-zehnder interferometer in the spectral shaping device, thereby realizing the spectral shaping of the input optical signal.
For the public to understand, the technical scheme of the invention is further explained in detail by a specific embodiment and the accompanying drawings:
the embodiment is realized based on a silicon-based photonics integration method, and all components are integrated on a chip, so that the miniaturization of a product is realized. Of course, the technical solution of the present invention is still feasible for discrete devices, but the reverse coupler is difficult to implement, and special processing needs to be performed on the optical fiber. Therefore, the technical scheme of the invention is preferably realized by a photon integration method.
With Chrostowski L (Chrostowski L, Hochberg M. silicon Photonics Design: From Devices to Systems [ M)]141-143), etc., the basic structure and operation principle of which are shown in fig. 1, the backward coupler is a four-port device based on a directional coupler and a bragg grating, and the four ports are input, backward coupling, through, and add, respectively. If the input to it at the input port contains the wavelength λ0Continuous light with a certain wavelength range inside, the backward coupling port outputs the wavelength of lambda0The other part is directly output along the original waveguide, and the coupled energy proportion can be changed by adjusting the length of the backward coupler, controlling the temperature and the like. In addition, the coupled wavelength lambda can be changed by designing different waveguide and Bragg grating geometric shapes and the like0。
The narrow bandwidth mach-zehnder interferometer provided by the present invention is shown in fig. 2, and is composed of two inverse couplers, and the connection mode of the two inverse couplers is as follows: the light to be adjusted is input through the input port of the reverse coupler 1, the reverse coupling port and the through port of the reverse coupler 1 are respectively connected with the input port and the adding port of the reverse coupler 2, and the through port of the reverse coupler 2 is used as the output of the narrow-bandwidth Mach-Zehnder interferometer. The waveform of each port is shown in FIG. 2, and the wavelength of the backward coupling is λ0Can only enter at wavelength with the remainder of the light output through0Interference occurs. Unlike the existing mach-zehnder interferometer, the mach-zehnder interferometer has an extremely narrow bandwidth, so that the spectral components at the interference wavelength corresponding to the narrow bandwidth mach-zehnder interferometer in the input optical signal can be changed by adjusting the transmission coefficient of the narrow bandwidth mach-zehnder interferometer.
The adjustment mode of the transmission coefficient of the narrow-bandwidth Mach-Zehnder interferometer can adopt a scheme similar to that of a conventional silicon-based Mach-Zehnder modulator; at present, two mature ideas are based on thermo-optic effect and carrier dispersion effect to adjust, and the two ways can be carried out independently or combined with each other. These two methods are briefly described below.
First, the thermo-optic effect is that the change of temperature can cause the change of the refractive index of the material, and the thermo-optic effect coefficient of the silicon material is large, and the thermo-optic effect can be calculated by the following formula:
Δnthermo-optic=1.87×10-4ΔT[K] (1)
wherein, Δ nthermo-opticΔ T is the change in temperature in Kelvin K for the change in refractive index of the material due to the thermo-optic effect.
The propagation constant β of light in the waveguide is determined by:
where λ is the wavelength of light, neffIs the effective index of refraction of the waveguide.
For this narrow bandwidth mach-zehnder interferometer, the phase difference between the two interfering beams determines the intensity of the output spectral response, which can be expressed as:
φ=(β2-β1)L (3)
wherein phi is the phase difference of the two beams, beta1、β2Respectively the propagation constants of the upper and lower waveguides of the interferometer.
According to the formulas (1), (2) and (3), when the temperature changes, the refractive index can be changed due to the thermo-optic effect, so that the propagation constant of light is changed, the phase difference of two beams of light is further changed, and the coherent phase is long when phi is even multiple of pi, and the output is maximum; when phi is an odd multiple of pi, coherent cancellation occurs, and the output is 0; between the two, the output magnitude varies continuously with phi, i.e. different phase differences correspond to different output light intensities, and the output waveform is shown in fig. 2.
The thermo-optic effect has no additional loss to the device, but the adjusting speed is relatively slow, while the free carrier dispersion effect in the silicon material makes up for the defect, the carrier dispersion effect is an indirect electro-optic effect, the change of the carrier is utilized to cause the change of the absorption coefficient and the refractive index, and the common three utilization mechanisms are as follows: a carrier accumulation mode, a carrier injection mode, and a carrier dissipation mode. The following explanation selects the common carrier injection method:
the change in refractive index Δ n and the change in absorption coefficient Δ α caused by injection of carriers can be expressed as follows:
wherein e is unit charge, c is light velocity in vacuum, epsilon0Is the vacuum dielectric constant, N is the refractive index of silicon, N is the injected carrier density, m*μ is the carrier mobility for the carrier effective mass.
By adopting the prior art, for example, a p-i-n type carrier injection structure provided by Lockwood D J (Lockwood D J, Pavesi L. silicon photonics: compositions and integration [ M ]. Springer,2011:16-19.) and the like, the injection of carriers into a silicon core can be realized, and the absorption coefficient and the refractive index are changed according to the formulas (4) and (5), and the propagation constant of light can be changed accordingly according to the formulas (2) and (3), so that the phase difference of two beams of light is changed, and the light with different intensities can be output in principle.
The interference intensity can be continuously adjusted through the two modes, and the transmission coefficient of the narrow-bandwidth Mach-Zehnder interferometer can be adjusted from 0 to 100 percent, so that effective adjustment is achieved, and only the wavelength lambda is adjusted0The spectral response of (c).
As shown in fig. 3, n points λ with different coupling wavelengths are designed1、λ2、λ3…λnThe narrow-bandwidth mach-zehnder interferometers of (a) can be connected in series to form a spectrum shaping device capable of adjusting any spectral response. For any input light, the transmission coefficient of the narrow bandwidth mach-zehnder interferometer corresponding to a wavelength point may be adjusted according to the target spectral response to adjust the spectral response of the wavelength point, thereby producing an arbitrary output spectral response.
In conclusion, the adjusting method is visual, simple and convenient, the adjusting process is efficient, the power consumption is low, and the used devices are simple in structure and easy to realize in an integrated mode, so that the high-efficiency arbitrary spectral response adjustment can be realized at low cost, the method can be widely applied to the occasions of hyperspectral imaging, microwave signal processing, arbitrary waveform formation and the like, and has extremely high application value.