Abstract
This paper presents a frequency-modulated optical signal generator in the THz band. The proposed method is based on a fast optical frequency sweep of a single narrowband laser diode used together with an optical fiber interferometer. The optical frequency sweep using a single laser diode is achieved by generating short current pulses with a high amplitude, which are driving the laser diode. Theoretical analysis showed that the modulation frequency could be changed by the optical path difference of the interferometer or optical frequency sweep rate of a laser diode. The efficiency of the optical signal generator with Michelson and Fabry–Perot interferometers is theoretically analyzed and experimentally evaluated for three different scenarios. Interferometers with different optical path differences and a fixed optical frequency sweep rate were used in the first scenario. Different optical frequency sweep rates and fixed optical path differences of the interferometers were used in the second scenario. This paper presents a method for optical chirp generation using a programmable current pulse waveform, which drives a laser diode to achieve nonlinear optical sweep with a fixed optical path difference of the interferometer. The experimental results showed that the proposed signals could be generated within a microwave (1–30 GHz) and THz band (0.1–0.3 THz).
Highlights
In recent years, demand for high bandwidth, high frequency, and high-speed signal transmission has been increasing rapidly
It consists of an unbalanced fiber interferometer (Michelson or Fabry–Perot interferometer), which allows a compact and robust device realization, a single Distributed Feedback (DFB) laser diode, and a current pulse generator utilized for a fast Optical Frequency Sweep (OFS) of the DFB laser diode
Our method is based on the assumption that the same amount of a charge is applied to the DFB laser diode at different the current pulse (Ts) to ensure a constant Optical Frequency Sweep Range (OFSR)
Summary
Demand for high bandwidth, high frequency, and high-speed signal transmission has been increasing rapidly. This paper proposes a new method for generating a frequency-modulated optical signal within the THz band that utilizes a fast Optical Frequency Sweep (OFS) of narrowband laser diode source and an unbalanced optical fiber interferometer. In [7,8,9], the authors proposed a linear wavelength sweep method based on the waveform modeling of a DFB laser diode’s driving current pulse, which can enable a modulation frequency tuning rate equal to the current pulse repetition rate. The main advantage of the proposed signal generator is the generation of complex waveforms, such as optical linear-frequency chirp signal using a special design of pulse current waveform, which drives a laser diode and produces a nonlinear OFS. Experimental results showed that signals up to 1.25 THz could be generated using the proposed design of a signal generator
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