# Frequency-Octupling Millimeter-Wave Optical Vector Signal Generation via an I/Q Modulator-Based Sagnac Loop

^{1}

^{2}

^{3}

^{*}

## Abstract

**:**

## 1. Introduction

^{−3}. Comparing these results with the existing schemes, the scheme we proposed has key advantages in that it can meet the requirements for high frequency applications for frequency-octupling without precoding, and the signal is also immune to fiber chromatic dispersion since the baseband vector signal only modulates one sideband.

## 2. Principle

## 3. Simulation Results

^{1/2}, the dispersion slope was 0.075 ps/nm

^{2}.km, the attenuation coefficient was 0.2 dB/km and the chromatic dispersion was 16.75 ps/nm.km. The orthogonally polarized sidebands were sent to the polarizer and then received by the PD. Figure 5b shows the RF spectra of the generated vector mm-wave signal. A 16QAM mm-signal at 80 GHz was generated when the modulated sideband and the unmodulated sideband beat each other.

^{−3}when the power of the received optical signal was larger than −5.8 dBm or −4 dBm. The 4 Gbaud 16QAM signal caused a 1.8 dB power penalty versus the 2 Gbaud case. Figure 7b shows the measured BER curves of the 16QAM signal with 4 Gbaud at 80 GHz in the condition of BTB and a 20 km SMF transmission. When the received optical power was greater than −5.5 dBm and −4 dBm, the BER was under 1 × 10

^{−3}. Therefore, a 1.5 dB power penalty was caused. In the system, the main imperfection that could introduce noise is the insertion loss of the MZM, it is 5–7 dB. However, only one of the ±4st-order sidebands is modulated, meaning that power fading due to the fiber dispersion in generated signal is well suppressed. Thanks to this modulation form, the influence of beat noise on the system can be better reduced. The scheme we proposed is free from fiber chromatic dispersion. It can be seen the results agree with our theoretical analysis well.

## 4. Conclusions

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

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**Figure 1.**Schematic diagrams for the frequency-octupling 16QAM mm-wave signal generation and the spectra after different points.

**Figure 3.**The output optical spectra of the (

**a**) DP-QPSK modulator and (

**b**) fiber Bragg grating (FBG).

**Figure 5.**(

**a**) The output optical spectra of the polarization beam splitter (PBS). (

**b**) The output electrical spectra of the photodetector (PD).

**Figure 6.**Eye diagrams of the (

**a**) I branch and the (

**b**) Q branch of the 16QAM signal at 80 GHz after a 20 km single-mode fiber (SMF) transmission. (

**c**) The generated 16QAM signal constellation at 80 GHz after a 20 km SMF transmission.

**Figure 7.**BER versus received optical power in the case of a (

**a**) 2 and 4 Gbaud 16QAM signal after a 20 km SMF transmission. (

**b**) BTB and a 20 km SMF transmission.

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**MDPI and ACS Style**

Yang, Z.; Qu, K.; Liu, X.
Frequency-Octupling Millimeter-Wave Optical Vector Signal Generation via an I/Q Modulator-Based Sagnac Loop. *Symmetry* **2019**, *11*, 84.
https://doi.org/10.3390/sym11010084

**AMA Style**

Yang Z, Qu K, Liu X.
Frequency-Octupling Millimeter-Wave Optical Vector Signal Generation via an I/Q Modulator-Based Sagnac Loop. *Symmetry*. 2019; 11(1):84.
https://doi.org/10.3390/sym11010084

**Chicago/Turabian Style**

Yang, Zhixian, Kun Qu, and Xiang Liu.
2019. "Frequency-Octupling Millimeter-Wave Optical Vector Signal Generation via an I/Q Modulator-Based Sagnac Loop" *Symmetry* 11, no. 1: 84.
https://doi.org/10.3390/sym11010084