Optical frequency comb shape data acquisition device and optical frequency comb shape adjustment method

Abstract

The present invention discloses an optical frequency comb shape data acquisition device and an optical frequency comb shape adjustment method. The device includes: a tunable laser source for generating light waves and dividing the light waves into a plurality of split light waves, a plurality of modulators for receiving the split light waves and connected to the tunable laser source, and an adjustment component for adjusting the number of subcarriers of each modulator and connected to each modulator. The present invention can use the collected electric spectrum as input data and the spectrum as output data to send to the neural network for training, so that the electric spectrum can be used to predict the spectrum, that is, the spectrum shape can be obtained with a light detector, avoiding the use of a spectrometer to observe the spectrum, greatly reducing the cost of the equipment. At the same time, the spectrum can also be used as input, and the DC bias and voltage gain can be used as output. In this way, when we need to adjust an optical frequency comb of any shape, the DC bias and voltage gain can be directly predicted, avoiding the use of the traversal method for manual adjustment.

Description

Technical Field

[0001] The present technology relates to the field of semiconductor manufacturing, and in particular to an optical frequency comb shape data acquisition device and an optical frequency comb shape adjustment method. Background Art

[0002] Optical frequency combs have many applications, such as radio frequency photonics [1] (1. V. Company, DE Leaird, and A. M. Weiner, Opt. Lett. 37, 3993 (2012).), all-optical signal processing [2] (2. PJ Delfyett, I. Ozdur, N. Hoghooghi, M. Akbulut, J. Davila-Rodriguez, and S. Bhooplapur, IEEE J. Sel. Top. Quantum Electron. 18, 258 (2012).) and wavelength division multiplexing (WDM) sources for optical communications [3-5] (3. F. Tian, ​​X. Zhang, J. Li, and L. Xi, J. Lightwave Technol. 29, 1085 (2011). 4. C. Chen, C. Zhang, D. Liu, K. Qiu, and S. Liu, Opt. Lett. 37, 3954(2012). 5. M. Fujiwara, M. Teshima, J. Kani, H. Suzuki, N. Takachio, and K.Iwatsuki, J.Lightwave Technol. 21, 2705 (2003).) Using an intensity modulator IM or a phase modulator PM to generate an optical frequency comb is a very simple and easy-to-use method. Using an IM (usually more than 10 dB) will cause a large insertion loss. In addition, each IM has a DC bias. By adjusting different DC biases, we can obtain optical frequency combs of different shapes. However, this structure has stability problems because the DC bias of the IM will change with changes in the external environment such as temperature, causing the shape and pitch amplitude of the generated optical frequency comb to change. Therefore, it is necessary to monitor and adjust the DC bias in real time to keep the shape of the optical frequency comb unchanged. PM is also an attractive way to generate optical frequency combs, because optical frequency combs based on phase modulators usually have much lower insertion loss and do not require a DC bias controller, so PM has a more stable spectrum than IM. The shape of the optical frequency comb generated by PM is very fixed and will not change with changes in the external environment. But at the same time, using PM alone cannot generate an optical frequency comb of any shape. In the application of optical frequency combs, the number of tones of the generated optical frequency comb, the amplitude of the tone, and the flatness between the tones are all very important indicators. In dense wavelength division multiplexing DWDM, the optical frequency comb is required to have many tones and high flatness.

[0003] Reference [6] (K. Ho and JM Kahn, IEEE PhotonicsTechnol. Lett. 5, 721 (1993)) proposed an optical frequency comb generator with a large number of tones using phase modulation based on an amplifier loop. However, strict loop length control is required, which makes the loop structure complicated. Cascaded phase modulators and intensity modulators can generate frequency-locked coherent optical multicarriers with high sound-to-noise ratio and flat amplitude [4, 5]. However, the subcarriers generated by the phase modulator driven only by the same frequency sinusoidal source usually have a large tone power difference (TPD). Therefore, multiple harmonic sinusoidal RF drive signals are required to produce a flat comb, and the phase relationship must be carefully controlled to obtain good performance [7, 8] (7. S. Ozharar, F. Quinlan, I. Ozdur, S. Gee, and PJ Delfyett, IEEE Photonics Technol. Lett. 20, 36 (2008). 8. Y. Lu, Y. Xing, and Y. Dong, Chin. Opt. Lett. 8, 316 (2010).). In the prior art, some scholars only use two sinusoidal frequency sources and several phase modulators in cascade to generate a flat optical subcarrier with low insertion loss. 21 stable comb tones with a frequency interval of 25 GHz were obtained, and the tone power difference was less than 3dB.

[0004] Figure 1 The working principle of the optical comb generation and power transmission of a two-stage phase modulator driven by a single fundamental frequency RF source with a small frequency offset is shown. Compared with [7, 8], the advantage of using cascaded phase modulators is that a higher modulation index can be obtained, thereby obtaining more subcarriers under the same electrical amplifier (EA) limitation and limited phase modulator driving voltage. The continuous wavelength light wave generated by the external cavity laser (ECL) is modulated by the cascaded two-stage phase modulators PM1 and PM2. PM1 is driven by a sinusoidal RF clock source with a frequency of f_S=25GHz and a driving voltage several times the half-wave voltage (Vπ) to obtain high-order subcarriers. In practical applications, due to the limitation of EA and the limitation of phase modulator driving voltage, a cascaded phase modulator (PM1; 1∼n) driven by multiple synchronized sinusoidal signals is used as the first-stage phase modulation. Phase shifters (PS) are used for the first-stage phase modulation to keep the driving signal synchronized. Each phase modulator is identical, and when the light wave generated by PM1 is input to PM2 for modulation, there is a small frequency difference between the frequency source of PM2 and the frequency source of PM1, and this frequency difference makes a flat output possible.

[0005] This scheme only uses a cascaded phase modulator and two sinusoidal frequency sources to achieve 21 stable comb tones with a frequency interval of 25 GHz, and the tone power difference is less than 3dB. However, since this scheme does not use an intensity modulator, the shape of the optical frequency comb that can be achieved by this scheme is limited, and it cannot adjust an optical frequency comb of any shape.

[0006] Since an intensity modulator needs to be added to generate multiple carriers of different shapes, and the DC bias will change with the external environment during the use of the intensity modulator, it is necessary to monitor the shape of the generated optical frequency comb in real time. However, adjusting the DC bias by observing the spectral shape of the spectrometer is an inefficient method. How to convert the spectrum into an electrical spectrum and use feedback to adjust the DC bias by monitoring the data of the electrical spectrum is a problem that needs to be solved urgently. Summary of the invention

[0007] The object of the present invention is to provide an optical frequency comb shape data acquisition device, which can convert a light spectrum into an electrical spectrum and feedback-adjust a DC bias by monitoring the data of the electrical spectrum.

[0008] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: an optical frequency comb shape data acquisition device, which includes: a tunable laser source for generating a light wave and dividing the light wave into a plurality of split light waves, a plurality of modulating parts for receiving the split light waves and connected to the tunable laser source, an adjusting component for adjusting the number of subcarriers of each modulating part and connected to each modulating part, a coupler for coupling the split light waves generated by each modulating part and connected to the modulating part respectively, a photodetector connected to the coupler and used for collecting the electric spectrum data of the coupled light waves, and a spectrometer connected to the coupler and used for collecting the spectrum data of the coupled light waves, a sub-acquisition part for collecting the voltage gain and DC bias data of the modulating part, the modulating part includes a basic modulating part and a shape modulating part, the shape modulating part includes a phase modulator for receiving the split light waves and an intensity modulator connected to the phase modulator, and the basic modulating part includes a plurality of cascaded phase modulators.

[0009] In another preferred embodiment, the regulating component includes a frequency source for generating frequency pulses, an electric amplifier and an electric attenuator, and the electric amplifier and the electric attenuator are connected in series between the frequency source and the phase modulator, or in series between the frequency source and the intensity modulator.

[0010] In another preferred embodiment, the light wave generated by the tunable laser source is divided into two paths, and there are two modulation parts, namely a shape modulation part and a basic modulation part, and the basic modulation part includes two cascaded phase modulators.

[0011] In another preferred embodiment, the adjustment component corresponding to each modulation part includes a frequency source, and several groups of the electric amplifiers and the electric attenuators respectively connected to the frequency source, the electric amplifier in each group is connected between the frequency source and the electric attenuator, and the electric attenuator is connected to the phase modulator or the intensity modulator.

[0012] The present invention also provides a method for adjusting the shape of an optical frequency comb based on the above device, which comprises the following steps:

[0013] a. Using an optical splitter on a tunable laser source to divide the light wave into two upper and lower split waves, the upper split wave generates a tunable optical frequency comb, and the lower split wave generates a fixed shape optical frequency comb. After the upper and lower optical frequency combs are beat, the electrical spectrum data, spectral data, voltage gain data and DC bias data are collected;

[0014] b. Establishing an ANN neural network model of the corresponding relationship between the input voltage gain data and DC bias data and the output electrical spectrum data and optical spectrum data;

[0015] c. Use part of the collected electric spectrum data, optical spectrum data, voltage gain data and DC bias data to train the neural network model, use the remaining data for network verification, and continuously adjust the neural network parameters until its output accuracy reaches 90%;

[0016] d. Use the trained neural network model and the electrical spectrum data to predict the spectral data, or use the trained neural network model, input the trace data of the spectrum we want, and predict the DC bias and voltage gain as output.

[0017] Another preferred method is that in step a, the frequencies of the split light waves of the upper path and the split light waves of the lower path are staggered by Δf, and the voltage gain of the split light waves of the lower path is adjusted to generate optical frequency combs of fixed shape and sufficient number; the voltage gain of the split light waves of the upper path is adjusted to change from 0dbm to Mdbm with a step size of Ndbm, and the DC bias of the intensity modulator is adjusted from 0.1V to LV with a step size of 0.1NV, and at the receiving end, the trace of the spectrum after the beat frequency and the electrical spectrum data of the oscilloscope are read from the spectrometer by program control using the commercial mathematical software MATLAB, and they are matched one by one with the voltage gain and DC bias data set in the upper branch.

[0018] In another preferred embodiment, M is divisible by N, and L is divisible by 0.1N.

[0019] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art: the present invention can use the collected electric spectrum as input data and the optical spectrum as output data to send to the neural network for training, so that the electric spectrum can be used to predict the optical spectrum, that is, the optical spectrum shape can be obtained with a photodetector PD, avoiding the use of a spectrometer to observe the optical spectrum, greatly reducing the cost of the equipment. At the same time, the optical spectrum can also be used as input, and the DC bias and voltage gain can be used as output. In this way, when we need to adjust an optical frequency comb of any shape, the DC bias and voltage gain can be directly predicted, avoiding the use of the traversal method for manual adjustment. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Attached Figure 1 The working principle of optical comb generation and power transmission for a two-stage phase modulator driven by a single fundamental frequency RF source with a small frequency offset;

[0021] Attached Figure 2 It is a structural schematic diagram of the present invention. DETAILED DESCRIPTION

[0022] The present invention will be further described below in conjunction with the embodiments shown in the accompanying drawings.

[0023] like Figure 2 As shown, first, a tunable laser source generates a continuous light wave and transmits it to the upper and lower branches respectively. The upper branch has a frequency source f s1 , two electrical amplifiers EA, two electrical attenuators Att, an intensity modulator, and a phase modulator. The lower branch is composed of a frequency source f s2 ,It is composed of two electrical amplifiers EA, two electrical attenuators Att and two phase modulators. After the modulation, the upper and lower lights pass through a 2×2 coupler again. At the output end of the coupler, one way goes to the spectrometer to collect spectrum data, and the other way goes to the photodetector PD to collect electrical spectrum data.

[0024] There is a small difference Δf between the frequencies of the sine waves output by the upper and lower frequency sources. Since the lower branch is composed of two phase modulators PM in cascade, the shape of the generated optical frequency comb is stable and will not change with changes in the environment; the upper branch has an intensity modulator that can adjust the electrical amplifier EA and the electrical attenuator Att to control the voltage gain, that is, the voltage gain, to control the number of subcarriers generated, and to obtain spectra of different shapes by adjusting the DC bias. After the upper and lower lights are mixed in the coupler, the optical signal can be converted into an electrical signal without a large bandwidth optical detector PD. The collected electrical spectrum, spectral data, and the gain, DC bias and other data of the upper branch are sent to the neural network for training.

[0025] Specifically, the optical frequency comb shape adjustment method includes the following steps:

[0026] a. Use the optical splitter on the tunable laser source to split the light wave into two upper and lower split waves, and adjust the frequency source f s1 To 7.5GHz, adjust the frequency source f s2 The frequency of the split light wave of the upper branch is 7.4 GHz, and the frequency of the split light wave of the lower branch is staggered by Δf=0.1 GHz. The voltage gain of the split light wave of the lower branch is adjusted to generate a fixed shape and a sufficient number of optical frequency combs; the voltage gain of the split light wave of the upper branch is adjusted from 0 dBm to M dBm with a step size of N dBm, and the DC bias of the intensity modulator is changed from 0.1 V to LV with a step size of 0.1 NV. At the receiving end, the trace of the spectrum after the beat frequency and the electrical spectrum data of the oscilloscope are read from the spectrometer by program control using the commercial mathematical software MATLAB, and the voltage gain and DC bias data set in the upper branch are matched one by one. M is divisible by N, L is divisible by 0.1N, M is optimally 30, and N is optimally 1;

[0027] b. Establishing an ANN neural network model of the corresponding relationship between the input voltage gain data and DC bias data and the output electrical spectrum data and optical spectrum data;

[0028] c. Use part of the collected electric spectrum data, optical spectrum data, voltage gain data and DC bias data to train the neural network model, use the remaining data for network verification, and continuously adjust the neural network parameters until its output accuracy reaches 90%;

[0029] d. Use the trained neural network model and the electrical spectrum data to predict the spectral data, or use the trained neural network model, input the trace data of the spectrum we want, and predict the DC bias and voltage gain as output.

[0030] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. An optical frequency comb shape data acquisition device, characterized in that: It comprises: a tunable laser source for generating a light wave and dividing the light wave into a plurality of split light waves, a plurality of modulating parts for receiving the split light waves and connected to the tunable laser source, an adjusting component for adjusting the number of subcarriers of each modulating part and connected to each modulating part, a coupler for coupling the split light waves generated by each modulating part and respectively connected to the modulating parts, a light detector connected to the coupler and used for collecting the electric spectrum data of the coupled light waves, and a spectrometer connected to the coupler and used for collecting the spectrum data of the coupled light waves, a sub-collecting part for collecting the voltage gain and DC bias data of the modulating part, the modulating part comprises a basic modulating part and a shape modulating part, the shape modulating part comprises a phase modulator for receiving the split light waves and an intensity modulator connected to the phase modulator, and the basic modulating part comprises a plurality of cascaded phase modulators.

2. The optical frequency comb shape data acquisition device according to claim 1, characterized in that: The regulating component includes a frequency source for generating frequency pulses, an electric amplifier and an electric attenuator, wherein the electric amplifier and the electric attenuator are connected in series between the frequency source and the phase modulator, or between the frequency source and the intensity modulator.

3. The optical frequency comb shape data acquisition device according to claim 1, characterized in that: The light waves generated by the tunable laser source are divided into two paths. The modulation parts have two parts, namely a shape modulation part and a basic modulation part. The basic modulation part includes two cascaded phase modulators.

4. The optical frequency comb shape data acquisition device according to claim 2, characterized in that: The adjustment component corresponding to each modulation part includes a frequency source, and several groups of electric amplifiers and electric attenuators respectively connected to the frequency source, the electric amplifier in each group is connected between the frequency source and the electric attenuator, and the electric attenuator is connected to the phase modulator or the intensity modulator.

5. A method for adjusting the shape of an optical frequency comb based on the device according to any one of claims 1 to 4, characterized in that: It includes the following steps: a. Using the optical splitter on the tunable laser source to split the light wave into two upper and lower split waves, the upper split wave generates a tunable optical frequency comb, and the lower split wave generates a fixed shape optical frequency comb. After the upper and lower optical frequency combs are beat, the electrical spectrum data, spectral data, voltage gain data and DC bias data are collected; b. Establishing an ANN neural network model of the corresponding relationship between the input voltage gain data and DC bias data and the output electrical spectrum data and optical spectrum data; c. Use part of the collected electric spectrum data, optical spectrum data, voltage gain data and DC bias data to train the neural network model, use the remaining data for network verification, and continuously adjust the neural network parameters until its output accuracy reaches 90%; d. Use the trained neural network model and the electrical spectrum data to predict the spectral data, or use the trained neural network model, input the trace data of the spectrum we want, and predict the DC bias and voltage gain as output.

6. The method for adjusting the shape of an optical frequency comb according to claim 5, characterized in that: In step a, the frequencies of the split light waves of the upper path and the split light waves of the lower path are staggered by Δf, and the voltage gain of the split light waves of the lower path is adjusted to generate optical frequency combs of fixed shape and sufficient number; the voltage gain of the split light waves of the upper path is adjusted to change from 0dbm to Mdbm with a step size of Ndbm, and the DC bias of the intensity modulator is adjusted from 0.1V to LV with a step size of 0.1NV. At the receiving end, the trace of the spectrum after the beat frequency and the electrical spectrum data of the oscilloscope are read from the spectrometer by program control using the commercial mathematical software MATLAB, and they are matched one by one with the voltage gain and DC bias data set in the upper branch.

7. The method for adjusting the shape of an optical frequency comb according to claim 6, characterized in that: M is divisible by N, and L is divisible by 0.1N.

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