Self-Heterodyne Spectrometer Using Uni-Traveling-Carrier Photodiodes for Terahertz-Wave Generators and Optoelectronic Mixers
Self-Heterodyne Spectrometer Using Uni-Traveling-Carrier Photodiodes for Terahertz-Wave Generators and Optoelectronic Mixers
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DOI：
10.1109/jlt.2014.2321004
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发表时间：
2014-10
影响因子：
4.7
通讯作者：
S. Hisatake;Jae-Young Kim;K. Ajito;T. Nagatsuma
中科院分区：
文献类型：
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作者：
S. Hisatake;Jae-Young Kim;K. Ajito;T. Nagatsuma
介绍了一种使用商用单行载流子光电二极管(UTC-PD)作为光电转换器(O/E)和光电混频器(OEM)的自外差太赫兹(THz)频域光谱仪。由两个频率失谐的自由运转的1.55μm激光二极管(LD)混合产生的光强拍频被用作光电转换器的光电混合的光源，并被用作OEM的光本地振荡器(LO)信号。利用电光移频器对光LO信号的频率进行相干移位，从而利用自由振荡LD作为差拍源来实现外差检测。我们研究了光谱仪的灵敏度特性与二极管偏置电压和光学LO能级的关系。当射频功率为-16dBm时，在300 GHz下，最大信噪比达到47dBm，锁定时间常数为23.4ms。相位测量的标准偏差为0.73°，其中幅度噪声极限标准偏差为0.25°。测量了系统在200~1450 GHz范围内的响应，与利用UTC-PD输出功率的频率特性计算出的响应很好地吻合。结果表明，UTC-PD不仅是高功率太赫兹波产生器的候选材料，也是宽带太赫兹OEM的候选材料。将UTC-PD与自由运行的LDS集成在同一衬底上，采用相同的工艺步骤，将显著降低当前光谱仪的成本和尺寸。
We demonstrate a self-heterodyne terahertz (THz) frequency-domain spectrometer in which commercially available uni-traveling-carrier photodiodes (UTC-PDs) are used as opticalto-electrical (O/E) converter and optoelectronic mixer (OEM). The optical intensity beat generated by mixing two frequency-detuned free-running 1.55 μm laser diodes (LDs) is used as a source for the photomixing at the O/E converter, and as an optical local oscillator (LO) signal for the OEM. The frequency of the optical LO signal is coherently shifted with an electrooptic frequency shifter so that the heterodyne detection is realized using free-running LDs for the beat source. We investigate the sensitivity characteristics of the spectrometer as functions of diode bias voltage and optical LO level. The maximum signal-to-noise ratio of 47 dB for the RF power of -16 dBm is achieved at 300 GHz with the lock-in time constant of 23.4 ms. The standard deviation of the phase measurement is 0.73°, where the amplitude noise limited standard deviation is 0.25°. We measure the system response ranging from 200 to 1450 GHz and find that it fits well the response which is calculated using the frequency characteristics of the output power of the UTC-PDs. Our results show that UTC-PDs are promising candidates not only for the high-power terahertz wave generator, but also for the wideband THz-OEM. Integration of UTC-PDs with free-running LDs on the same substrate with the same process steps would significantly reduce the cost and size of the present spectrometer.