- 标题
- 摘要
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- 实验方案
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Time-resolved frequency chirp control of semiconductor lasers using digital signal processing
摘要： The theoretical possibility of precisely controlling the time-resolved chirp in a directly modulated semiconductor laser using a single drive digital-to-analog converter (DAC) controlled via a novel digital signal processing (DSP) algorithm is investigated. A semi-analytical expression for the requisite drive current is obtained through algebraic back-calculation of the large signal laser rate equations, in tandem with a ?rst-order numerical approximation of the optical power and chirp functional relationship. A 25-GHz peak-to-peak frequency modulation (FM) at a bit-rate of 28-Gb/s is demonstrated at a 6 dB extinction ratio, while completely suppressing the transient chirp contribution. Furthermore, a bipolar frequency chirp signal resulting in a di?erential phase shift keying (DPSK) modulation format at a bit-rate of 28-Gb/s was achieved with an error vector magnitude (EVM) below 1%. A 5-bit look-up table (LUT) was found to be adequate for capturing the requisite DSP drive current needed to fully suppress the transient chirp as demonstrated by preliminary optical link simulations at 28-Gb/s.
关键词： Time-resolved frequency chirp,Adiabatic chirp,Digital signal processing,Transient chirp,Directly modulated semiconductor laser
更新于2025-09-23 15:19:57
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Nonlinear Fiber Optics || Self-phase modulation
摘要： The ?rst nonlinear effect that we focus on is the self-phase modulation (SPM), a phenomenon that leads to spectral broadening of optical pulses [1–9]. SPM is the temporal analog of self-focusing of CW beams occurring inside any nonlinear medium with n2 > 0. It was ?rst observed in 1967 in the context of transient self-focusing of optical pulses propagating through a CS2-?lled cell [1]. By 1970, SPM had been observed in solids and glasses by using picosecond pulses. The earliest observation of SPM in optical ?bers was made with a ?ber whose core was ?lled with CS2 liquid [7]. This work led by 1978 to a systematic study of SPM in a silica-core ?ber [9]. This chapter considers SPM as a simple example of the nonlinear effects that can occur inside optical ?bers. Section 4.1 is devoted to the case of pure SPM as it neglects the GVD effects and focuses on spectral changes induced by SPM. The combined effects of GVD and SPM are discussed in Section 4.2 with emphasis on the SPM-induced frequency chirp. Section 4.3 presents two analytic techniques and uses them to solve the NLS equation approximately. Section 4.4 extends the analysis to include the higher-order nonlinear effects such as self-steepening.
关键词： GVD,self-steepening,spectral broadening,optical pulses,frequency chirp,SPM,nonlinear effects,NLS equation,self-phase modulation
更新于2025-09-12 10:27:22
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Multi-Target Detection Method Based on Variable Carrier Frequency Chirp Sequence
摘要： Continuous waveform (CW) radar is widely used in intelligent transportation systems, vehicle assisted driving, and other fields because of its simple structure, low cost and high integration. There are several waveforms which have been developed in the last years. The chirp sequence waveform has the ability to extract the range and velocity parameters of multiple targets. However, conventional chirp sequence waveforms suffer from the Doppler ambiguity problem. This paper proposes a new waveform that follows the practical application requirements, high precision requirements, and low system complexity requirements. The new waveform consists of two chirp sequences, which are intertwined to each other. Each chirp signal has the same frequency modulation, the same bandwidth and the same chirp duration. The carrier frequencies are different and there is a frequency shift which is large enough to ensure that the Doppler frequencies for the same moving target are different. According to the sign and numerical relationship of the Doppler frequencies (possibly frequency aliasing), the Doppler frequency ambiguity problem is solved in eight cases. Theoretical analysis and simulation results verify that the new radar waveform is capable of measuring range and radial velocity simultaneously and unambiguously, with high accuracy and resolution even in multi-target situations.
关键词： continuous wave radar systems,Doppler ambiguity,variable carrier frequency chirp sequence,multi-target detection
更新于2025-09-10 09:29:36