为了突破高速电模数转换器采样速率和时延控制精度对测频带宽的限制,文中提出了一种采用光脉冲欠采样的超宽带、高分辨率数字测频方法。利用被动锁模激光器的超短光脉冲,产生间隔可控的多波长光脉冲串,通过电光调制器,对待测信号进行采样,最后通过光探测器阵列转化为电信号进行测频计算。此方法利用光脉冲的采样带宽高、时延控制精确、波分复用技术等特点,结合欠采样的Multiple Signal Classification算法进行宽带频率测量。通过对实际应用条件进行的数值模拟和理论计算表明,该方法可以实现20GHz带宽范围内的高精度多信号频率分辨。
An actively mode-locked laser with tunable repetition rate is proposed and experimentally demonstrated based on a programmable electrical pattern generator.By changing the repetition rate of the electrical patterns applied on the in-cavity modulator,the repetition rate of the output optical pulse sequences changes accordingly while the pulse width of the optical pulse train remains almost constant.In other words,the output ultra-short pulse train has a tunable duty cycle.In a proof-of-principle experiment,optical pulses with repetition rates of 10,5,2.5 and 1.25 GHz are obtained by adjusting the electrical pattern applied on the in-cavity modulator while their pulse widths remain almost unchanged.
