Research On Generation And Application Of High-Quality Optical Frequency Comb

Frequency locked multicarrier source, also known as optical frequency comb, is a kind of light source with fixed sub-carrier spacing. With the explosive growth of the global Internet data, research on high-speed, high-capacity, long-distance optical fiber communication system is imminent. The combination of higher order signal modulation format and multiplex scheme technique has become a very effective solution. The traditional multi-channel source is laser array, but the carriers used have some shortcomings such as not easy to coordinate synchronous, high cost and so on. So the optical frequency comb technique is rapidly introduced into the ultra high-speed optical fiber communication system, and has made a series of experiment reports with remarkable achievements which successfully increase the optical fiber communication transmission rate from Gb/s to Tb/s or even Pb/s. In addition, the optical frequency comb has a very broad application prospects such as microwave photonics, precision measurement, optical signal processing, etc.There are some schemes to generate optical frequency comb:1. Scheme based on a single or cascaded modulators;2. Scheme based on mode-locked laser;3. Scheme based on recycling frequency shifter;4. Scheme based on nonlinear effects of optical fiber. The optical frequency comb generation scheme based on cascaded optical modulator has some advantages such as relatively simple devices, carrier phase correlation and so on. The optical frequency comb generated by this program has many applications such as achieving ultrashort optical pulse, arbitrary waveform generator, channel receiver and so on. So this is an optical frequency comb generation scheme discussed in this article. Meanwhile optical frequency comb based on the recycling frequency shifter (RFS) has some advantages such as relatively large carrier number, adjustable carrier spacing, flatness, and low radio frequency (RF) voltage. It is often used as seed source in the high-speed optical fiber communication systems, and therefore the production scheme is also studied in this article. The main work of this paper includes the following sections:1. Describe the history and development trend of optical fiber communication, describe the common optical frequency comb generation methods and their advantages and disadvantages.2. Theoretical analysis of the principle of optical frequency comb generation based on the intensity modulator (IM) and the phase modulator (PM). Then introduce the key devices involved. Theoretical analysis of optical frequency comb generation scheme based on RFS and the key devices involved are introduced.3. Theoretical analysis of the factors that impact the flatness of optical frequency comb based on cascade modulators and propose new structure to upgrade the unflatness of the optical frequency comb from5.5dB to0.5dB. Besides theoretical analysis of the influence of amplified spontaneous emission noise (ASE) on the carrier to noise ratio(CNR) of optical frequency comb, and proposed using optical delay line filter to suppress the noise of optical frequency comb then improve the CNR of optical frequency comb. Building Nyquist-16QAM transmission system based on optical frequency comb certifies the validity of these methods for enhancing CNR of optical frequency comb.4. Theoretical analysis of the laser linewidth and optical bandpass filter influence on the flatness of optical frequency comb, the experimental and simulation results verify the above theoretical analysis accuracy. Given the indicators to select suitable laser and optical bandpass filter. Besides theoretical analysis of the laser linewidth and erbium doped fiber amplifier (EDFA) influence on the tone-to-noise ratio (TNR) of optical frequency comb. Experimental and simulation results verify the above theoretical analysis accuracy. In addition, given the indicators to select suitable laser and EDFA. 5. Given a simple introduction for the application of the optical frequency comb in terms of arbitrary waveform generator (AWG). Firstly introduce how to generate specific waveform by adjusting the parameters of the RF source loading on electro-optic modulator. Then describe the principle and feasibility of using the Fourier transform shaping, space modulator shaping and other technical means to achieve AWG.In summary, this paper starts from introducing the performance indicators of the optical frequency comb-he flatness and the TNR or CNR, and introduces the factors affect the optical frequency comb CNR and flatness based on the cascade modulators, given the appropriate improvement scheme to improve the indicators of the comb. In addition, this paper introduces the principle that how the related device influence carrier performance based on RFS, then validate it through simulation and experiment, given the criteria to select suitable devices. Finally, the application of optical frequency comb on AWG is briefly introduced. This study has some significance for the high quality optical frequency comb generation and application.