50-GHz Repetition Gain Switching Using a Cavity-Enhanced DFB Laser Assisted by Optical Injection Locking
50-GHz Repetition Gain Switching Using a Cavity-Enhanced DFB Laser Assisted by Optical Injection Locking
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DOI：
10.1109/jlt.2020.2973198
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发表时间：
2020-04-01
影响因子：
4.7
通讯作者：
Sudo, Tsurugi
中科院分区：
文献类型：
--
作者：
Liu, Zhixin;Matsui, Yasuhiro;Sudo, Tsurugi
我们演示了通过增益开关注入锁定分布反馈（DFB）激光器以50 GHz的重复速率产生脉冲。由于光子-光子共振（PPR）和失谐加载的共同作用，DFB激光器的小信号BW从30 GHz提高到52 GHz。失谐加载效应是通过利用频率相关的腔损耗来实现的，这导致有效差分增益的增加，从而相应地增加了弛豫振荡频率。除了小信号测量外，我们还表明，尽管由于大信号啁啾而导致失谐负载条件的动态变化，但PPR和失谐负载效应也可以用于改善大信号增益切换。通过用50 ghz的射频信号调制激光器，我们从增益开关激光器获得了50 ghz的重复频率脉冲，证实了增益增强效应在大信号调制中仍然有效。随后，我们用强外部种子光注入锁定增益开关激光器，抑制啁啾并产生间隔为50 GHz的相干频率。光注入锁定（OIL）进一步增强了大信号BW，导致时域脉冲宽度更窄，为9.5 ps（反卷积后为6.2 ps），三个边带峰值距离频域峰值的70%以上（全宽一半最大值为130 GHz）。假设线性啁啾，脉冲可以进一步压缩到2.4 ps。
We demonstrate pulse generation at a repetition rate of 50 GHz by gain switching an injection-locked distributed feedback (DFB) laser. The small-signal BW of the DFB laser was enhanced from an intrinsic BW of 30 GHz to 52 GHz due to the joint effects of photon-photon resonance (PPR) and detuned loading. The detuned loading effect is achieved by exploiting the frequency-dependent cavity loss, which results in an increase of the effective differential gain, and correspondingly, the relaxation oscillation frequency. In addition to small-signal measurements, we show that the PPR and the detuned loading effects can also be utilized to improve large signal gain-switching, despite the dynamic changes of the detuned loading condition due to the large signal chirp. By modulating the laser with 50-GHz RF signals, we obtained 50-GHz repetition rate pulses from the gain-switched laser, confirming that the BW enhancement effects are still valid for large-signal modulation. Subsequently, we optically injection lock the gain-switched laser with strong external seeding light, which suppresses the chirp and creates coherent frequency tones with 50 GHz spacing. The optical injection locking (OIL) further enhances the large-signal BW, resulting in narrower pulse width of 9.5 ps (6.2 ps after deconvolution) in the time domain and three sideband peaks above 70% from the peak in the frequency domain (full width half maximum of 130 GHz). Assuming linear chirp, the pulse could be further compressed to 2.4 ps.