CN108153000A - A kind of spectral line interval is equal to the frequency comb generator of optical fiber Brillouin frequency displacement - Google Patents

Abstract

The invention discloses a kind of frequency comb generating means based on stimulated Brillouin scattering and Electro-optical Modulation, it forms feedback control loop using continuous-wave laser, electro-optic phase modulator, optical fiber, photodetector and radio frequency amplifier, generate the radiofrequency signal that frequency of oscillation is equal to optical fiber Brillouin frequency displacement, utilize another electrooptic modulator of this radio frequency signals drive, generate the frequency comb that spectral line interval is equal to optical fiber Brillouin frequency displacement, by adjusting the operation wavelength of laser or the interval of frequency comb spectral line can be changed using the optical fiber with different Brillouin shifts.With it is existing the method for frequency comb is generated based on Electro-optical Modulation compared with, the present invention drives modulator without applied radio frequency signal, thus with higher stability and lower phase noise, and is easier realization photoelectricity and integrates.

Description

An Optical Frequency Comb Generator with Spectral Line Spacing Equal to Fiber Brillouin Frequency Shift

technical field

Electro-optic modulation of continuous laser light by radio frequency signal is a common method for generating optical frequency combs. The realization of this method requires an external radio frequency source. The invention relates to an optical frequency comb generating device based on stimulated Brillouin scattering and electro-optic modulation, which uses a continuous wave laser, an electro-optic phase modulator, an optical fiber, a photoelectric detection and a radio frequency amplifier to form an oscillation loop, and the frequency of generation is equal to that of the optical fiber distribution Oscillation mode of Liouin frequency shift, using this signal to drive another electro-optic modulator to generate an optical frequency comb. Therefore, the present invention does not require an external radio frequency signal, and can simultaneously generate a radio frequency signal whose frequency is the fiber Brillouin frequency shift and an optical frequency comb whose spectral line spacing is equal to this frequency, and the bandwidth of the generated optical frequency comb can also be modulated by cascaded electro-optic The device is expanded. The invention belongs to the technical field of photoelectric oscillators and optical frequency comb generators in the field of microwave photonics.

Background technique

In recent years, due to the wide application prospects of optical frequency combs in space navigation, optical precision measurement, arbitrary waveform generation and other fields, the generation of optical frequency combs has become one of the research hotspots in the field of microwave photonics. The existing optical frequency comb generation methods are mainly divided into three types. The first is a method based on a mode-locked laser, which requires the construction of a complex resonator, and the output spectrum is easily affected by the external temperature and the loss and dispersion of waveguide media such as optical fibers. The second is the method of using the nonlinear effect in the optical fiber. This method produces a large number of spectral lines, but the excitation of the nonlinear effect in the optical fiber requires high optical power, and the generated optical frequency comb is not highly tunable. The third method is based on the electro-optical modulator. This method has the outstanding advantages of good adjustability and high stability, and is currently the most commonly used method for generating optical frequency combs. For example, using a radio frequency signal to phase modulator the continuous light emitted by a laser can generate an optical frequency comb composed of multiple modulated sidebands. (Reference [1]: J. Zhang, J. Yu, N. Chi, Z. Dong, X. Li, Y. Shao, J. Yu, and L. Tao, "Flattened comb generation using only phase modulators driven by fundamental frequency sinusoidal sources with small frequency offset," Opt. Lett. 38(4), pp.552-554, 2013). By cascading two intensity modulators and a phase modulator, and driving the modulator with a 10GHz microwave signal, an optical frequency comb containing 38 spectral lines can be obtained within 1dB flatness (reference [2]: R.Wu , V.R.Supradeepa, C.M.Long, D.E.Leaird, and A.M.Weiner, "Generation of very flat optical frequency combs from continuous-wave lasers using cascaded intensity and phase modulators driven by tailored radio frequency waveforms," Opt. Lett.35(19) , pp.3234-3236, 2010). In addition, by setting the operating points of two cascaded intensity modulators, an optical frequency comb generator with adjustable spectral line spacing and number can also be designed. (Reference [3]: X.Zou, W.Pan, and J.Yao, "Tunable optical comb generation based on carrier-suppressed intensity modulation and phase modulation," Chin.Opt.Lett.8(5), pp.468 -470, 2010).

Although the above-mentioned methods based on electro-optic modulators can obtain flat optical frequency combs, they all require high-performance, low-noise microwave signal sources to provide driving signals. In this way, not only the cost is high, but also noise will be introduced, which will deteriorate the generated light Phase noise performance of frequency comb spectral lines. Compared with traditional RF signal sources, optoelectronic oscillators have the advantages of high Q value, stable frequency, low phase noise and small size (reference [4]: Huanfa Peng, Cheng Zhang, Xiaoopeng Xie, TaoSun, Peng Guo, Xiaoqi Zhu , Lixin Zhu, Weiwei Hu, and Zhangyuan Chen, "Tunable DC-60GHz RF Generation Utilizing a Dual-Loop Optoelectronic Oscillator Based on Stimulated Brillouin Scattering." J.Lightwave Technol., 33(13), pp.2707-2715, 2015) . In addition, using an optoelectronic oscillator instead of a traditional microwave signal source to drive an electro-optic modulator to generate an optical frequency comb makes it easier to realize a miniaturized optical frequency comb generator with optoelectronic integration. Aiming at the above situation, the invention utilizes the stimulated Brillouin scattering effect in the optical fiber and a phase modulator to generate photoelectric oscillation, and realizes an optical frequency comb generator whose spectral line interval is equal to the Brillouin frequency shift of the optical fiber.

Contents of the invention

The invention discloses an optical frequency comb generator which does not need an external microwave signal source and whose spectral line spacing is equal to the optical fiber Brillouin frequency shift. Specifically, the structure of the optical frequency comb generator involved in the present invention is shown in FIG. 1 . In the figure, the laser light output by the continuous wave laser (1) is divided into two branches by the optical coupler (2), and the light of the lower branch is amplified by the optical amplifier (3) and then reversely input into the optical fiber (5) through the circulator (4). ), stimulated Brillouin scattering in the fiber (5). The upper branch light passes through the electro-optic phase modulator (6) to generate ±1-order modulation sidebands. When the -1st order sideband of the signal light is within the gain bandwidth of the stimulated Brillouin scattering of the optical fiber (5), the sideband will be amplified. The +1-order sideband, the amplified -1-order sideband and the carrier are input to the optical coupler (7) through the circulator (4) and divided into two paths, one of which is sent to the photodetector (8) for photoelectric conversion. In this process, the +1-order sideband and the amplified -1-order sideband are respectively beat with the optical carrier to obtain a microwave signal with a frequency equal to the Brillouin frequency shift of the optical fiber (5), and this signal is amplified by the radio frequency amplifier (9) , the input to the radio frequency power splitter (10) is divided into two branches, one of which feeds back to drive the phase modulator (6) to form an oscillation loop. Another road radio frequency signal is divided into two roads by radio frequency power splitter (11) again, and one of them directly outputs, and can be used as radio frequency signal source or system detection signal; Another road passes radio frequency phase shifter (12), radio frequency amplifier (13) and The adjustable radio frequency attenuator (14) drives the electro-optical modulator (15) to modulate another laser beam output by the coupler (7), produces an optical frequency comb, and adjusts the radio frequency phase shifter (12) and the adjustable radio frequency attenuator ( 14) A flat optical frequency comb can be obtained.

The present invention has the following advantages:

1. The present invention uses a self-driven cascaded electro-optic modulator to generate an optical frequency comb. Compared with the traditional method, it does not need to input a radio frequency signal from the outside to drive the modulator, so it has higher stability and lower phase noise, and is more stable. Easy to realize optoelectronic integration.

2. The optical frequency comb spectral line interval realized by the present invention is equal to the Brillouin frequency shift of the optical fiber (5). Therefore, by adjusting the output wavelength of the continuous wave laser (1) or using optical fibers (5) with different Brillouin frequency shifts, the interval between the spectral lines of the optical frequency comb can be changed.

3. The output of one of the radio frequency power dividers (11) in the present invention can be used as a radio frequency signal source, and the output frequency interval is equal to the radio frequency oscillation of the optical fiber (5) Brillouin frequency shift, by adjusting the output wavelength of the continuous wave laser (1) Alternatively, optical fibers (5) with different Brillouin frequency shifts can be used to output radio frequency oscillation signals of different frequencies.

4, the scheme provided by the present invention also has good expansibility, after the phase modulator (15), a plurality of electro-optic intensity or phase modulators can also be cascaded, and the output signal of the radio frequency power splitter (11) can be used again After splitting, the cascaded electro-optic modulators are driven to output a flat optical frequency comb containing more spectral lines.

Description of drawings

Fig. 1: The device diagram of the optical frequency comb generator designed by the present invention.

Figure 2: The experimentally obtained spectrum diagram containing 9 flat optical frequency combs.

Figure 3: Spectrogram of the experimentally obtained oscillation signal.

Figure 4: Graph of the phase noise performance of the experimentally obtained oscillating signal.

specific implementation

The scheme of the optical frequency generator proposed by the present invention has been verified through experiments. The experimental device is shown in Figure 1. The experimental process and results are described below in conjunction with the accompanying drawings.

As shown in Figure 1, the working wavelength of the tunable continuous wave laser is set to 1550.2nm in the experiment, and the output power is 14dBm. The output light of this laser is divided into two paths by a 3dB coupler, and the light in the lower path is amplified by an erbium-doped fiber amplifier. , and enter the non-zero dispersion-shifted fiber with a length of 2km in reverse through the 2 ports of the circulator, and the output power of the amplifier is 12dBm to stimulate the stimulated Brillouin scattering effect in the non-zero dispersion-shifted fiber. When the -1st order sideband of the phase modulator output is within the gain bandwidth of stimulated Brillouin scattering, this sideband will be amplified. The light output by the optical fiber is input to the 10:90 coupler through the circulator and is divided into two paths. Among them, the path with a splitting ratio of 90% is photoelectrically converted by the photodetector. At this time, the +1 order sideband and the amplified -1 The first-order sidebands beat the carrier wave respectively to generate a beat frequency signal with a frequency equal to the Brillouin frequency shift of the optical fiber, and then amplified and fed back to the phase modulator to complete the loop oscillation. The stabilized oscillating signal drives the next-stage electro-optic phase modulator. By adjusting the RF phase shifter and variable RF attenuator, an optical frequency comb including 9 spectral lines within a 3dB bandwidth is finally obtained, as shown in Figure 2. The interval of spectral lines is equal to the frequency of the oscillating signal, and the oscillating frequency is equal to the Brillouin frequency shift of the non-zero dispersion-shifted fiber. The experimentally measured result is 10.67 GHz, as shown in Figure 3. Finally, the single-sideband phase noise of the oscillating signal was measured with a signal analyzer. As shown in Figure 4, the phase noise at a frequency offset of 10kHz is -85.0dBc/Hz.

Therefore, the feasibility of this invention has been verified by experiments.

In summary, the present invention has achieved the intended purpose.

Claims (4)

1. a kind of spectral line interval is equal to the frequency comb generator of optical fiber Brillouin frequency displacement, which is characterized in that frequency comb generator packet Include following device：The light of continuous-wave laser (1) output is divided into two branches through photo-coupler (2), and lower branch light is by image intensifer (3) optical fiber (5) is reversely input to through circulator (4) again after amplifying, electro-optic phase modulator (6) carries out phase tune to upper branch light System, modulated optical signal is divided into two-way after optical fiber (5) and optical circulator (4) are input to photo-coupler (7), wherein light all the way Light-to-current inversion is carried out through photodetector (8), after the electric signal of output is amplified by radio frequency amplifier (9), through RF Power Splitter (10) it is divided into two-way, wherein feeding back to electro-optic phase modulator (6) all the way, another way is divided into two by RF Power Splitter (11) again Road directly exports all the way, and another way is through radio-frequency phase shifter (12), radio frequency amplifier (13) and adjustable radio frequency attenuator (14) rear-guard Dynamic electrooptic modulator (15) is modulated the another way optical signal of photo-coupler (7) output, so as to generate frequency comb.

2. frequency comb generator described in claim 1, which is characterized in that do not need to external input radio frequency signals drive electric light phase Position modulator, and drive signal is provided by the optical-electronic oscillator that inner feedback loop is formed, the composition of this oscillator is included continuously Wave laser (1), photo-coupler (2), image intensifer (3), optical circulator (4), optical fiber (5), electro-optic phase modulator (6), light Coupler (7), photodetector (8), radio frequency amplifier (9) and RF Power Splitter (10).

3. frequency comb generator described in claim 1, which is characterized in that the frequency comb spectral line interval generated is equal to interior lights Electricity shakes the frequency of signal, this frequency is equal to the Brillouin shift of optical fiber (5), by the operating wave for adjusting continuous-wave laser (1) Length uses the optical fiber (5) with different Brillouin shifts, and the spectral line interval of output frequency comb can be changed.

4. frequency comb generator described in claim 1, which is characterized in that can be cascaded multiple after electrooptic modulator (15) Electro-optic intensity or phase-modulator, and it is new by being driven after the output of RF Power Splitter (11) again work(point, phase shift and power adjustment Cascade modulator, the thus exportable flat frequency comb for including more multiline.