CN107171172A - A kind of unfixed optical triangulation shape impulse generator of modulation index - Google Patents

Abstract

An optical triangular pulse generator with an unfixed modulation index, involving the fields of optoelectronic devices, microwave photonics, and all-optical data processing. The continuous wave laser (1) is first connected to a single-drive Mach-Zehnder modulator (3), and the sine wave local oscillator The device (2) is connected to the driving port of the single-drive Mach-Zehnder modulator (3), and the single-drive Mach-Zehnder modulator (3) is then connected to the optical power splitter (4), and the optical power splitter (4) is connected to the polarization control A device (5) and a polarization controller (6), so that the separated two optical signals are respectively placed in orthogonal polarization states, and the polarization controller (6) is followed by an adjustable delay line (7), which is used for the upper and lower A time delay is introduced between the branches, and then combined into one branch by a polarization beam concentrator (8), thereby outputting a triangular optical pulse train.

Description

An Optical Triangular Pulse Generator with Unfixed Modulation Index

technical field

The invention relates to the fields of optoelectronic devices, microwave photonics, and all-optical data processing, in particular to an optical triangular pulse generator with an unfixed modulation index.

Background technique

All-optical signal processing is the key to solving major problems in telecommunication fields such as large bandwidth and high-speed communication in terms of optical throughput. In all-optical signal processing, the triangular optical pulse has a wide range of applications in all-optical signal processing because of its special linear rising edge and linear falling edge, and mutually symmetrical time-domain characteristics. Therefore, the triangular optical pulse is generated in the optical system. has great research value. Using cross-phase modulation with triangular pulses, all-optical wavelength conversion from optical time division multiplexing to wavelength division multiplexing can be realized, and partial signal regeneration can also be realized. All-optical techniques that multiply optical pulses in the time or frequency domain also rely on triangular pump pulses introduced in cross-phase modulation. Frequency translation, pulse compression, and signal regeneration of all-optical signals can also be achieved using cross-phase modulation with triangular pump pulses. In addition, a two-fold improvement in the performance of self-phase-modulated wavelength converters based on fiber and offset filtering can be achieved using triangular pulses. In addition, triangular microwave signals are also widely used in modern radar and antenna systems, radio frequency communication systems, electronic equipment test and measurement, etc., so outputting stable triangular signals has great research value. Therefore, the photonic triangular pulse generator is considered to be a very important device for future all-optical networks.

In recent years, a series of research results of triangular optical pulse photon generators have been reported internationally. One solution is to use an optical comb generator or a mode-locked laser as a coherent light source, input it into the spectrum shaper, and adjust the input waveform to obtain the expected output waveform. For example, in 2011, J.Ye et al. from Southwest Jiaotong University mentioned a method using two cascaded filters as a spectrum shaping unit combined with FTTM to obtain triangular optical pulses (Ye J, Yan L, PanW, et al .Photonic generation of triangular-shaped pulses based on frequency-to-time conversion[J].Optics letters. 2011,36(8):1458-1460.). But this scheme needs an ultrashort pulse source, which makes the cost higher and the structure more complicated. In order to reduce costs, a continuous wave laser can be used as a light source to obtain triangular light pulses. For example, people such as J.Li have proposed the mode of harmonic fitting, utilize Mach-Zehnder modulator and optical fiber dispersion element to produce symmetrical triangular pulse (J.Li, X.Zhang, B.Hraimel, T.Ning, Performance Analysis of a Photonic-Assisted Periodic Triangular-Shaped Pulses Generator. Lightwave Technology, Journal of, 2012.30(11):p.1617-1624.). This scheme relies on the relationship between fiber dispersion and driving frequency, so the tuning performance is poor. Another solution is to etch and superimpose the light envelope in the time domain. For example, J. Yang et al. proposed to use the injection locking process of distributed feedback semiconductor lasers to complete the generation of desired harmonic signals, and then superimpose these signals with a suitable power ratio and time delay to obtain triangular optical pulses (Y. Jiang , C.Ma, G.Bai, Z.Jia, Photonic Generation of Triangular Waveform Utilizing Time-Domain Synthesis. Photonics Technology Letters, IEEE, 2015.27(16):p.1725-1728.). But the tuning is not flexible enough, and the system is more complicated. The above-mentioned triangular optical pulse generator is not flexible enough to tune, and the system structure is relatively complicated. Therefore, it is very necessary to design an optical triangular pulse generator with a simple structure, low price, and flexible tuning. The invention can realize the tuning of the repetition frequency only by adjusting the driving frequency and time delay of the radio frequency signal.

Contents of the invention

The invention provides a low-cost optical triangular pulse generator with an unfixed modulation index. Different from the traditional generation method, this device uses a continuous wave laser as the light source, and uses a single-drive Mach-Zehnder modulator to make it work at the quadrature bias point, and the output optical signal is similar to a sinusoidal signal. The sinusoidal signal is divided into upper and lower paths through an optical power splitter, the upper branch passes through a polarization controller, and the lower branch passes through a polarization controller and an adjustable delay line. A certain delay is introduced by adjusting the adjustable delay line. By adjusting the polarization controllers of the upper and lower branches, the two signals are superimposed in the state of orthogonal polarization without introducing coherent interference. Next, the upper and lower branch signals are combined by a polarization beam bundler to obtain a triangular optical pulse with a tunable repetition rate. This device only uses cheap continuous wave laser as light source, thus greatly reducing the cost. The modulation index of this scheme will no longer be fixed at a value, but can be adjusted within an appropriate range, and taking into account the drift of the bias point, this device has high commercial value.

The technical scheme of the present invention: an optical triangular pulse generator with an unfixed modulation index, characterized in that: the triangular pulse generator includes a continuous wave laser, a single-drive parallel Mach-Zehnder modulator, a sine wave local oscillator, a power Distributor, polarization controller, polarization bundler, adjustable delay line; the specific connection method is:

The optical output terminal of the continuous wave laser is connected to the optical input terminal of the single-drive Mach-Zehnder modulator, the electrical output terminal of the sine wave local oscillator is connected to the electric drive port of the single-drive Mach-Zehnder modulator, and the single-drive Mach-Zehnder modulator The optical output end is connected to the optical input end of the optical power splitter, the first output end and the second output end of the optical power splitter are respectively connected to the optical input ends of two polarization controllers, and the optical output end of one polarization controller is connected to the polarization bundle The optical input end of the polarization controller, the optical output end of a polarization controller is connected to the optical input end of the adjustable time delay line, the optical output end of the adjustable time delay line is connected to the optical input end of the polarization bundler, and the optical output end of the polarization bundler Outputs triangular light pulses.

adjusting the output voltage V _bias of the bias voltage source, and its range is 1.94≤ΔV _bias ≤2.06; setting the bias of the single-drive Mach-Zehnder modulator at the quadrature transmission point;

Modulation factor Where V _RF is the amplitude of the driving signal, V _π is the half-wave conversion voltage of the single-drive Mach-Zehnder modulator, and V _π =4V. The range of β is 0.92≤β≤1.57.

The adjustable delay line (7) introduces a delay τ, and its range is 6.1ps≤τ≤479ps.

The frequency of the sinusoidal signal output by the sinusoidal local oscillator (2) is f _RF , and its range is _{1GHz≤fRF≤40GHz} ;

After the above settings, the output of the polarization beam concentrator (8) is a triangular light pulse with a repetition frequency of f=f _RF .

Concrete working principle of the present invention is as follows:

The expression of the light field output by a continuous wave laser is:

E ₀ (t)＝E ₀ exp(jω ₀ t) (1)

where E ₀ and ω ₀ denote its amplitude and angular frequency, and then the optical signal is input to a single-drive Mach-Zehnder modulator. The RF signal used to drive the SD-MZM is V _RF cos(Ωt), where V _RF and Ω represent the amplitude and frequency of the RF signal. When the extinction ratio of SD-MZM is ε _r = ∞, the light field distribution at the output end of SD-MZM is:

where V _π represents the half-wave conversion voltage of SD-MZM. The light intensity expression of point A is:

Among them, the modulation index The value of β can be changed by adjusting the amplitude of the driving signal.

The cross-polarization unit consists of a 50:50 optical coupler, two polarization controllers, an adjustable delay line and a polarization bundler. The optical signal output from the single-drive Mach-Zehnder modulator is divided into two branches, and the signals of the upper and lower branches are adjusted to the direction of orthogonal polarization by the polarization controller. A certain delay is introduced by adding an adjustable delay line in the lower branch. The two signals are then combined by a polarization beam bundler. The light field distribution after the output of the polarization beam concentrator is:

Since the signals of the two branches are combined in the state of orthogonal polarization, there is no coherent interference between them. Therefore, the corresponding light intensity expression is:

In order to better study the relationship between the triangular light pulse and the above parameters (β, τ and Ω), the above expression is expanded as:

in:

o(Ω) represents high-order harmonics, which can be ignored when β is small.

Fourier expansion of an ideal triangular waveform:

Comparing formula (6) and formula (8), in order to obtain an approximate triangular microwave signal, it should satisfy:

A ₁ =9A ₃ (9)

Combined with formula (7), we can get the relationship between parameters (β and τ, Ω):

The beneficial effects of the present invention are specifically as follows:

The present invention does not involve complex structures, fully utilizes the principle of electro-optical modulation, and produces a triangular wave with a high repetition rate by photonics; the pulse repetition frequency in the present invention has the characteristics of continuous tunability, and only changing the frequency of the local oscillator can control the triangular wave The pulse repetition frequency is tuned; and the scheme uses an inexpensive continuous wave laser, which can greatly reduce the acquisition cost.

Description of drawings

Figure 1 is an optical triangular pulse generator with variable modulation index.

Fig. 2 is a schematic diagram of a time-domain waveform of a triangular wave generated by a triangular optical pulse generating device (frequency f = 1 GHz).

Fig. 3 is a schematic diagram of a time-domain waveform of a triangular wave generated by a triangular optical pulse generator (frequency f = 10 GHz).

Fig. 4 is a schematic diagram of a time-domain waveform of a triangular wave generated by a triangular optical pulse generating device (frequency f = 30 GHz).

Fig. 5 is a schematic diagram of a time-domain waveform of a triangular wave generated by a triangular optical pulse generating device (frequency f = 40 GHz).

detailed description

A kind of optical triangular pulse generator whose modulation index is not fixed will be further described below in conjunction with accompanying drawings 1 to 5.

Embodiment one

An optical triangular pulse generator whose modulation index is not fixed, as shown in Figure 1, is characterized in that: the triangular pulse generator comprises a continuous wave laser 1, a sine wave local oscillator 2, a single-drive Mach-Zehnder modulator 3 , power splitter 4, polarization controller 5, polarization controller 6, adjustable time delay line 7, polarization bundler 8; the specific connection method is:

The optical output terminal of the continuous wave laser 1 is connected to the optical input terminal of the single-drive Mach-Zehnder modulator 3, the electrical output terminal of the sine wave local oscillator 2 is connected to the electric drive port 31 of the single-drive Mach-Zehnder modulator 3, and the single-drive Mach-Zehnder modulator 3 The optical output end of the Zehnder modulator 3 is connected to the optical input end of the optical power splitter 4, and the first output end 41 and the second output end 42 of the optical power splitter 4 are connected to the light of the polarization controller 5 and the polarization controller 6 respectively. The input end, the optical output end of the polarization controller 5 is connected to the first input end 81 of the polarization bundler 8, the optical output end of the polarization controller 6 is connected to the optical input end of the adjustable time delay 7, and the light of the adjustable time delay line 7 The output end is connected to the light input end of the polarization beam bundler 8, and the light output end of the polarization beam bundler 8 outputs a triangular light pulse.

Adjusting the output voltage V _bias =2V of the bias voltage source; setting the bias of the single-drive Mach-Zehnder modulator at the quadrature transmission point;

Adjust modulation factor Where V _RF is the amplitude of the driving signal, V _π is the half-wave conversion voltage of the single-drive Mach-Zehnder modulator, and V _π =4V.

Adjust the adjustable delay line to make the delay τ=479ps.

The output sinusoidal signal frequency of the sine wave local oscillator is f _RF =1 GHz;

The value of the extinction ratio ε _r of the modulator in this embodiment is 20dB, the value of V _bias is 2V, f _RF =10GHz, β=0.92, V _π =4V, τ=479ps. After the above adjustments, the output of the polarization beam concentrator is a triangular light pulse with a repetition frequency of f=f _RF =1 GHz, corresponding to the time domain curve shown in FIG. 2 .

Embodiment two

An optical triangular pulse generator whose modulation index is not fixed, as shown in Figure 1, is characterized in that: the triangular pulse generator comprises a continuous wave laser 1, a sine wave local oscillator 2, a single-drive Mach-Zehnder modulator 3 , power splitter 4, polarization controller 5, polarization controller 6, adjustable time delay line 7, polarization bundler 8; the specific connection method is:

The optical output terminal of the continuous wave laser 1 is connected to the optical input terminal of the single-drive Mach-Zehnder modulator 3, the electrical output terminal of the sine wave local oscillator 2 is connected to the electric drive port 31 of the single-drive Mach-Zehnder modulator 3, and the single-drive Mach-Zehnder modulator 3 The optical output end of the Zehnder modulator 3 is connected to the optical input end of the optical power splitter 4, and the first output end 41 and the second output end 42 of the optical power splitter 4 are connected to the light of the polarization controller 5 and the polarization controller 6 respectively. The input end, the optical output end of the polarization controller 5 is connected to the first input end 81 of the polarization bundler 8, the optical output end of the polarization controller 6 is connected to the optical input end of the adjustable time delay 7, and the light of the adjustable time delay line 7 The output end is connected to the light input end of the polarization beam bundler 8, and the light output end of the polarization beam bundler 8 outputs a triangular light pulse.

adjusting the output voltage V _bias of the bias voltage source = 1.94V; setting the bias of the single-drive Mach-Zehnder modulator at the quadrature transmission point;

Adjust modulation factor Where V _RF is the amplitude of the driving signal, V _π is the half-wave conversion voltage of the single-drive Mach-Zehnder modulator, and V _π =4V.

Adjust the adjustable delay line to make the delay τ=33.7ps.

The output sine signal frequency of the sine wave local oscillator is f _RF =10GHz;

The extinction ratio ε _r of the modulator in this embodiment is 20dB, V _bias is 1.94V, f _RF =10GHz, β=1.1, V _π =4V, τ=33.7ps. After the above adjustments, the output of the polarization beam focuser is a triangular light pulse with a repetition frequency of f=f _RF =10 GHz, corresponding to the time domain curve shown in FIG. 3 .

Embodiment Three

An optical triangular pulse generator whose modulation index is not fixed, as shown in Figure 1, is characterized in that: the triangular pulse generator comprises a continuous wave laser 1, a sine wave local oscillator 2, a single-drive Mach-Zehnder modulator 3 , power splitter 4, polarization controller 5, polarization controller 6, adjustable time delay line 7, polarization bundler 8; the specific connection method is:

The optical output terminal of the continuous wave laser 1 is connected to the optical input terminal of the single-drive Mach-Zehnder modulator 3, the electrical output terminal of the sine wave local oscillator 2 is connected to the electric drive port 31 of the single-drive Mach-Zehnder modulator 3, and the single-drive Mach-Zehnder modulator 3 The optical output end of the Zehnder modulator 3 is connected to the optical input end of the optical power splitter 4, and the first output end 41 and the second output end 42 of the optical power splitter 4 are connected to the light of the polarization controller 5 and the polarization controller 6 respectively. The input end, the optical output end of the polarization controller 5 is connected to the first input end 81 of the polarization bundler 8, the optical output end of the polarization controller 6 is connected to the optical input end of the adjustable time delay 7, and the light of the adjustable time delay line 7 The output end is connected to the light input end of the polarization beam bundler 8, and the light output end of the polarization beam bundler 8 outputs a triangular light pulse.

adjusting the output voltage V _bias of the bias voltage source = 2.06V; setting the bias of the single-drive Mach-Zehnder modulator at the quadrature transmission point;

Adjust modulation factor Where V _RF is the amplitude of the driving signal, V _π is the half-wave conversion voltage of the single-drive Mach-Zehnder modulator, and V _π =4V.

Adjust the adjustable delay line to make the delay τ=25ps.

The output sine signal frequency of the sine wave local oscillator is f _RF =30GHz;

The value of the extinction ratio ε _r of the modulator in this embodiment is 20dB, the value of V _bias is 2.06V, f _RF =30GHz, β=1.5, V _π =4V, τ=25ps. After the above adjustments, the output of the polarization beam concentrator is a triangular light pulse with a repetition frequency of f=f _RF =30 GHz, corresponding to the time domain curve shown in FIG. 4 .

Embodiment four

An optical triangular pulse generator whose modulation index is not fixed, as shown in Figure 1, is characterized in that: the triangular pulse generator comprises a continuous wave laser 1, a sine wave local oscillator 2, a single-drive Mach-Zehnder modulator 3 , power splitter 4, polarization controller 5, polarization controller 6, adjustable time delay line 7, polarization bundler 8; the specific connection method is:

The optical output terminal of the continuous wave laser 1 is connected to the optical input terminal of the single-drive Mach-Zehnder modulator 3, the electrical output terminal of the sine wave local oscillator 2 is connected to the electric drive port 31 of the single-drive Mach-Zehnder modulator 3, and the single-drive Mach-Zehnder modulator 3 The optical output end of the Zehnder modulator 3 is connected to the optical input end of the optical power splitter 4, and the first output end 41 and the second output end 42 of the optical power splitter 4 are connected to the light of the polarization controller 5 and the polarization controller 6 respectively. The input end, the optical output end of the polarization controller 5 is connected to the first input end 81 of the polarization bundler 8, the optical output end of the polarization controller 6 is connected to the optical input end of the adjustable time delay 7, and the light of the adjustable time delay line 7 The output end is connected to the light input end of the polarization beam bundler 8, and the light output end of the polarization beam bundler 8 outputs a triangular light pulse.

Adjusting the output voltage V _bias =2V of the bias voltage source; setting the bias of the single-drive Mach-Zehnder modulator at the quadrature transmission point;

Adjust modulation factor Where V _RF is the amplitude of the driving signal, V _π is the half-wave conversion voltage of the single-drive Mach-Zehnder modulator, and V _π =4V.

Adjust the adjustable delay line to make the delay τ=6.1ps.

The output sinusoidal signal frequency of the sine wave local oscillator is f _RF =40GHz;

The value of the extinction ratio ε _r of the modulator in this embodiment is 20dB, the value of V _bias is 2V, f _RF =40GHz, β=1.57, V _π =4V, τ=6.1ps. After the above adjustments, the output of the polarization beam concentrator is a triangular light pulse with a repetition frequency of f=f _RF =40 GHz, corresponding to the time domain curve shown in FIG. 5 .

Claims (2)

1. A kind of optical triangular pulse generator that modulation index is not fixed, as shown in Figure 1, it is characterized in that: this triangular pulse generator comprises, continuous wave laser (1), sine wave local oscillator (2), single driver Mach-Zehnder modulator (3), power divider (4), polarization controller (5), polarization controller (6), adjustable time delay line (7), polarization bundler (8); the specific connection method is : The optical output terminal of the continuous wave laser (1) is connected to the optical input terminal of the single-drive Mach-Zehnder modulator (3), and the electrical output terminal of the sine wave local oscillator (2) is connected to the single-drive Mach-Zehnder modulator (3). The electric drive port (31), the optical output end of the single-drive Mach-Zehnder modulator 3 is connected to the optical input end of the optical power splitter (4), the first output end (41) and the second output end (41) of the optical power splitter (4) The output end (42) is respectively connected to the optical input end of the polarization controller (5) and the polarization controller (6), and the optical output end of the polarization controller (5) is connected to the first input end (81) of the polarization beam concentrator (8) , the optical output end of the polarization controller (6) is connected to the optical input end of the adjustable time delay (7), and the optical output end of the adjustable time delay line (7) is connected to the second input end (82) of the polarization bundler (8) ), the light output end of the polarization beam concentrator (8) outputs a triangular light pulse. 2. a kind of modulation index is not fixed optical triangular pulse generator according to claim 1, is characterized in that: adjusting the output voltage V _bias of the bias voltage source, and its range is 1.94≤ΔV _bias ≤2.06; setting the bias of the single-drive Mach-Zehnder modulator at the quadrature transmission point; Modulation factor Where V _RF is the amplitude of the driving signal, V _π is the half-wave conversion voltage of the single-drive Mach-Zehnder modulator, and V _π =4V. The range of β is 0.92≤β≤1.57. The adjustable delay line (7) introduces a delay τ, and its range is 6.1ps≤τ≤479ps. The frequency of the sinusoidal signal output by the sinusoidal local oscillator (2) is f _RF , and its range is _{1GHz≤fRF≤40GHz} ; After the above settings, the output of the polarization beam concentrator (8) is a triangular light pulse with a repetition frequency of f=f _RF .