CN105656544B - A kind of Clock extraction chip based on micro-ring resonator - Google Patents

Abstract

The invention discloses a kind of Clock extraction chip based on micro-ring resonator, belongs to all-optical signal processing technical field.Including two parts of micro-loop optical parametric oscillator and micro-loop filter.Wherein micro-loop optical parametric oscillator is made of the big ring of spiral, the first subring and the second subring, and the big ring of spiral overcomes ring to be lost as nonlinear dielectric for parametric amplifier effect to occur；Respectively added with electrode in two subrings, optical parametric oscillator transmission spectrum is controlled by applying alive mode so that the clock signal only extracted circle transmission in the oscillator.Micro-loop filter is used to inhibit the interference of high-order four-wave mixing component, improves clock signal quality.Compared with existing clock Recovery, the advantages of Clock Extraction chip proposed by the present invention combines two kinds of technologies of passive filtering and active oscillating, the clock signal of high quality can be directly obtained in silicon based photon chip, greatly improves the integrated level of such device.

Description

An all-optical clock extraction chip based on microring resonator

technical field

The invention relates to the technical field of all-optical signal processing, in particular to an all-optical clock extraction chip realized by using a microring resonator.

Background technique

With the continuous improvement of network bandwidth, all-optical signal processing technology will play an important role in future large-capacity, strong real-time optical fiber communication networks. As one of its core functions, the all-optical clock extraction technology directly obtains the constant-rate optical clock from the input signal, and participates in the retiming process of the signal 3R regeneration, and at the same time serves as a control signal to regulate the optical switch matrix. Therefore, in the all-optical switch node, the Play an important role.

At present, there are two ways to realize all-optical clock extraction: passive filtering and active oscillation. The passive filtering method mainly relies on the comb filter characteristics of the device to obtain the optical clock signal. This method is simple in principle, but due to the limitation of the device processing technology, the fineness and adjustability of the comb filter cannot meet the actual needs. The extracted clock The quality is not high; the active oscillation method is similar to the principle of the laser, and the signal clock needs to be extracted by mode locking in the active feedback structure. At present, it is mainly used in self-pulsation distributed feedback laser (SP-DFB) and in high nonlinear fiber (HNLF) Or implemented in a fiber ring cavity formed by a semiconductor optical amplifier (SOA). The quality of the clock signal extracted by the active oscillation method is high, and it has become a hot research direction. However, the control of SP-DFB is complex, the rate is limited, and the fiber ring cavity is bulky and susceptible to environmental temperature disturbances. This makes the all-optical clock extraction technology based on the active oscillation method need to seek a breakthrough at the device level to improve the performance of this type of device. Integration and reduce system energy consumption.

With the rapid development of silicon photonics technology, various optical devices composed of silicon-on-insulator (SOI) are expected to become the core devices for building large-scale photonic integrated chips in the future due to their advantages of high integration and mature manufacturing process. Researchers have used the comb filter characteristics of microring resonators to realize the clock extraction function, but limited by the fineness of the device, the quality of the extracted clock is not high, and further shaping processing is required by the post-shaping system [W. Yang, Y. Yu, M. Ye, et al., IEEE Photonics Technology Letters, 2014, 26(3): 293-296.]. This solution increases the complexity of the system, which is not conducive to forming an integrated clock extraction chip. Therefore, it is necessary to provide a chip-level clock extraction solution that can directly obtain high-quality clock signals.

Contents of the invention

The technical problem to be solved by the present invention is to provide an all-optical clock extraction chip based on a micro-ring resonator, that is, to overcome the problem of clock quality degradation caused by low fineness in the existing micro-ring resonator clock extraction scheme, and to obtain a micron Mode locking is achieved in a photonic chip of the order of magnitude, reducing the sensitivity of the device to ambient temperature.

In order to solve the problems of the technologies described above, the present invention adopts the following technical solutions:

An all-optical clock extraction chip based on a microring resonator, characterized in that: it includes a microring optical parametric oscillator and a microring filter; the RZ (return-to-zero code) optical signal of the clock to be extracted and the continuous pumping light enter together In the microring optical parametric oscillator, use parametric amplification to form mode locking, and output the extracted clock signal and high-order four-wave mixing components at the download end of the oscillator; the above signals are then input into the microring filter to filter out High-order four-wave mixing components to improve clock signal quality.

The microring optical parametric oscillator includes a helical macroring, a first subring and a second subring. The RZ optical signal with an optical carrier frequency of f _RZ and the continuous pump light with a frequency of f _CW enter the helical ring of the optical parametric oscillator, and use the parametric amplification effect to generate a clock signal. By oscillating and transmitting in the ring, continuous parametric gain is obtained, and finally the mode locking condition is reached, and the extracted clock signal and high-order four-wave mixing products, as well as the injected RZ optical signal and continuous pump light are output at the download end of the helical ring; The above signal enters the first sub-ring and the second sub-ring, electrodes are added to both sub-rings, and the carrier concentration in the sub-rings is controlled by applying voltage to adjust the center wavelength of the two sub-rings respectively, so that the optical parametric oscillator The center frequency of the transmission spectrum envelope is consistent with the extracted optical carrier frequency f _CL of the clock signal, while the carrier frequencies f _RZ and f _CW of the RZ optical signal and continuous pump light are filtered out to suppress the input optical oscillation. Finally, the extracted clock signal and high-order four-wave mixing components are output at the download end of the second sub-ring.

The spiral macrocycle of the optical parametric oscillator requires that the RZ optical signal and the continuous pumping light carrier frequency are consistent with the resonance wavelength of the spiral macrocycle, and the rate R _b of the input signal is an integer multiple of the free spectrum range (FSR) of the spiral macrocycle . The parametric gain comes from two parts: one part is the gain provided by the continuous pump light, which is used to make up most of the ring loss; the other part is provided by the input RZ optical signal, which makes the total gain of the extracted clock signal greater than the ring loss, A sustained oscillation effect is produced in a microring optical parametric oscillator, that is, mode locking is achieved.

The micro-ring filter is an optical band-pass filter formed by micro-ring resonators. In the microring filter, the voltage is used to control the carrier concentration to adjust the filter center frequency to align with the extracted clock signal optical carrier frequency, and the filter bandwidth matches the clock rate. By designing the ring length of the microring resonator, the high-order four-wave mixing component falls on the stop band of the filter, suppressing the interference of the high-order component to the clock signal, and improving the quality of the clock signal.

The existing microring resonator clock extraction schemes only use the comb filter characteristics of the device, but due to the limitation of device manufacturing accuracy, the clock signal extracted by this type of scheme has a large amplitude jitter, so a post-shaping system is required. Increased complexity of clock extraction. However, the present invention utilizes the parametric amplification effect in the helical macroring to achieve mode locking, and improves the fineness of the microring resonator through active oscillation, so that high-quality clock signals can be obtained directly, and the signal processing cost is reduced. At the same time, the large helical ring and two sub-rings together form a filtering system, and the cascading method of three rings effectively improves the bandwidth of the filtering system to support clock extraction of high-speed signals.

The traditional all-optical clock extraction unit based on a fiber parametric oscillator, whose nonlinear medium is a highly nonlinear optical fiber with a length of hundreds of meters, is easily affected by the refractive index change caused by ambient temperature disturbance, making it unable to work stably for a long time. However, the present invention uses parameter amplification to obtain mode locking in micron-scale integrated photonic devices, which not only improves the integration degree of the device, but also reduces the influence of temperature drift on the clock extraction performance.

Description of drawings

Fig. 1 is a schematic diagram of an all-optical clock extraction chip based on a microring resonator of the present invention.

Fig. 2 is a schematic diagram of spectral characteristics extracted by the all-optical clock of the present invention.

Fig. 3 is an eye diagram of the RZ optical signal and the extracted clock signal of the present invention.

Detailed ways

FIG. 1 is a schematic diagram of an all-optical clock extraction chip based on a microring resonator proposed by the present invention. The chip includes a microring optical parametric oscillator and a microring filter.

The microring optical parametric oscillator includes a helical macroring, a first subring and a second subring. The helical macroring is a single microring with a long ring length. As a nonlinear medium, the microring will undergo a parametric amplification process to provide the parametric amplification effect required for clock extraction. In order to obtain a better parametric gain, the cross-sectional size of the microring needs to consider the waveguide dispersion, so that the zero dispersion wavelength of the helical macroring is close to the working wavelength, so as to meet the phase matching condition of the parametric amplification. The input optical signal includes two: RZ optical signal and continuous pumping light, and their optical carrier frequencies are f _RZ and f _CW respectively. In order to realize all-optical clock extraction, the input optical signal meets the following conditions: (1) the optical carrier frequency is consistent with the resonant wavelength of the helical macrocycle; (2) the rate R _b of the RZ optical signal is an integer multiple of the free spectral range of the helical macrocycle. According to the requirement of item (2), to realize the clock extraction of 40Gb/s optical signal in the helical macroring made of Si ₃ N ₄ material, the length of the ring needs to be 3.79 mm. In order to reduce the chip area occupied by the ring, the large ring is designed in a spiral shape as shown in Figure 1 to minimize the chip size. At the same time, the bending radius of the helical large ring needs to be larger than 100 microns, so as to reduce the bending loss of the waveguide and the influence on the dispersion. When the input optical signal meets the above two conditions, the extracted clock signal will obtain two parts of parametric gain: one part comes from the continuous pump light to make up most of the ring loss; the other part is provided by the input RZ optical signal, which part The gain makes the total gain of the extracted clock signal greater than the ring loss, and produces a continuous oscillation effect in the optical parametric oscillator, that is, realizes mode locking. Through the parametric process in the helical macrocycle, the extracted clock signal and the four-wave mixing product will be generated, and the above-mentioned signal, the input RZ optical signal and the continuous pumping light are input to the first and second sub-phases through the download end of the helical macrocycle in the ring. The schematic diagram of the spectral characteristics extracted by the all-optical clock is shown in Figure 2.

The helical macroring, the first sub-ring and the second sub-ring simultaneously constitute a filtering system, and the purpose of the filtering system is to ensure that only the extracted clock signal is oscillated and amplified in the microring optical parametric oscillator. The three-ring cascading helps to increase the bandwidth of the filtering system so that it can support the clock extraction requirements of high-speed signals. Electrodes are added to the first and second sub-rings, and the resonance wavelengths of the two sub-rings can be regulated by applying electric fields U ₁ and U _2. On the one hand, it makes it coincide with the resonance wavelength of the helical macroring, and on the other hand, the optical parametric oscillator The center frequency of the transmission spectrum envelope is consistent with the extracted optical carrier frequency f _CL of the clock signal, while the carrier frequencies f _RZ and f _CW of the RZ optical signal and continuous pump light fall on the stop band of the filter system to suppress Enter the effect of light oscillations. Through the combined effect of the spiral macroloop and the filtering system, the extracted clock signal and high-order four-wave mixing components will be output at the download end of the second sub-loop.

The micro-ring filter is composed of an optical band-pass filter formed by a micro-ring resonator. This filter will be used to filter out the interference signal in the download end of the second sub-ring and improve the quality of the clock signal. Electrodes are added to the microring resonator, and the carrier concentration is controlled by applying a voltage _U3 to adjust the center frequency of the filter to align with the optical carrier frequency of the extracted clock signal, and the filter bandwidth matches the clock rate. On the other hand, by designing the ring length of the microring resonator, the high-order four-wave mixing component falls on the stop band of the filter, which can suppress the interference signal and further improve the quality of the clock signal. The eye diagram of the input optical RZ signal and the extracted clock signal is shown in Figure 3.

Claims (4)

1. a kind of Clock extraction chip based on micro-ring resonator, it is characterised in that：Including micro-loop optical parametric oscillator With micro-loop filter；The RZ optical signals and continuous pump light of clock to be extracted enter micro-loop optical parametric oscillator jointly In, it is locked using parameter amplification formation mode, in the clock signal of the downloading end output extraction of the micro-loop optical parametric oscillator With high-order four-wave mixing component；The clock signal of the extraction of the micro-loop optical parametric oscillator output and high-order four-wave mixing point Amount is input to again in micro-loop filter, filters out high-order four-wave mixing component to promote clock signal quality.

2. a kind of Clock extraction chip based on micro-ring resonator as described in claim 1, it is characterised in that：It is described micro- Ring optical parametric oscillator includes the big ring of the cascade spiral of tricyclic, the first subring and the second subring；Optical carrier frequency is the RZ of fRZ Optical signal and the continuous pump light that frequency is fCW, are entered in the big ring of spiral of micro-loop optical parametric oscillator, are put using parameter Big effect generates clock signal；By the oscillation transmission in the ring, obtains and continue parametric gain, be finally reached mode locking item Part, in the RZ optical signals and company of the clock signal and high-order four-wave mixing product and injection of the big ring downloading end output extraction of spiral Continuous pump light；The clock signal and high-order four-wave mixing product and the RZ optical signals of injection of the extraction of the big ring output of spiral Enter the first subring and the second subring with continuous pump light, all added with electrode in two subrings, by applying alive mode control Carrier concentration to adjust the centre wavelength of two subrings respectively in system ring so that micro-loop optical parametric oscillator transmission spectrum packet The centre frequency of network and the clock signal optical carrier frequency f of extraction_CLUnanimously, the carrier frequency of RZ optical signals and continuous pump light f_RZ、f_CWIt is filtered out；Finally in the clock signal and high-order four-wave mixing component of the output extraction of the second subring downloading end.

3. a kind of Clock extraction chip based on micro-ring resonator as claimed in claim 2, it is characterised in that：It is described micro- The big ring of the spiral of ring optical parametric oscillator requires the humorous of the optical carrier frequency of RZ optical signals and continuous pump light and the big ring of spiral It shakes consistent wavelength, the rate R of the RZ optical signals of input_bIt is the integral multiple of the free spectral range of the big ring of spiral.

4. a kind of Clock extraction chip based on micro-ring resonator as described in claim 1, it is characterised in that：It is described micro- Ring wave filter is the optical band pass filter formed by micro-ring resonator, and carrier concentration is controlled using voltage in micro-loop filter To adjust filter centre frequency, it is set to be aligned with the clock signal optical carrier frequency of extraction, and optical band pass filter bandwidth It is matched with clock rate；It is long that micro-ring resonator ring is adjusted simultaneously, and high-order four-wave mixing component is made to fall in filter stop bend.