Tunable and broadband microwave frequency combs based on a semiconductor laser with incoherent optical feedback

Based on a semiconductor laser （SL） with incoherent optical feedback, a novel all-optical scheme for generating tunable and broadband microwave frequency combs （MFCs） is proposed and investigated numerically. The results show that, under suitable operation parameters, the SL with incoherent optical feedback can be driven to operate at a regular pulsing state, and the generated MFCs have bandwidths broader than 40 GHz within a 10 dB amplitude variation. For a fixed bias current, the line spacing （or repetition frequency） of the MFCs can be easily tuned by varying the feedback delay time and the feedback strength, and the tuning range of the line spacing increases with the increase in the bias current. The linewidth of the MFCs is sensitive to the variation of the feedback delay time and the feedback strength, and a linewidth of tens of KHz can be achieved through finely adjusting the feedback delay time and the feedback strength. In addition, mappings of amplitude variation, repetition frequency, and linewidth of MFCs in the parameter space of the feedback delay time and the feedback strength are presented.

Controllable microwave frequency comb generation in a tunable superconducting coplanar-waveguide resonator

Frequency combs are useful in a wide range of applications,such as optical metrology and high-precision spectroscopy.We experimentally study a controllable frequency comb generated in a tunable superconducting coplanarwaveguide resonator in the microwave regime.A two-tone drive is applied on one of the resonance modes of the resonator and comb generation is observed around the resonance frequency of the resonator.Both central frequency and teeth density of the comb are precisely controllable,and the teeth spacing can be adjusted from Hz to MHz.Moreover,we show that a few hundreds of sidebands can be generated using a sufficiently strong drive power and the weakest drive power needed to generate the comb can be reduced to approach the quantum limit.These experimental results can be qualitatively explained via theoretical analysis.

Tunable off-resonant Rydberg microwave frequency comb spectroscopy based on metawaveguide coupled Rydberg atoms

Studying Rydberg microwave frequency comb(MFC)spectroscopy helps increase the working bandwidth of the Rydberg receiver.This Letter demonstrates off-resonant Rydberg MFC spectroscopy in a meta-waveguide-coupled Rydberg atomic system.An off-resonant MFC field couples with the Rydberg atoms through a meta-waveguide.The system can receive the microwave field in the working band from 0.5 GHz to 13.5 GHz,and the MFC spectroscopy covers a span of 36 MHz at three different arbitrarily-chosen frequencies of 2 GHz,3 GHz,and 5.8 GHz.The MFC spectrum that covers a wide range of 125 MHz is also verified.This work is significant for tunable wide-band instant microwave signal detection in the Rydberg atomic system,which is useful in microwave frequency metrology,communication,and radar.

Ultra-flat broadband micro wave frequency comb generation based on optical frequency comb with a multiple-quantumwell electro-absorption modulator in critical state

In this paper,we proposed a novel ultra・flat broadband microwave frequency comb(MFC)generation based on optical frequency comb(OFC)with a multiplequantum-well electroabsorption modulator(MQW-EAM)in critical state.The scheme is simple and easy to adjust.The performance of the MFC generation scheme is investigated using software Optisystem.The results show that the comb spacing of MFC can be adjusted from 5 to 20 GHz by changing RF signafs frequency and the MFC is almost independent on the linewidth of the tunable laser diode.The performance of the MFC can be improved by reasonably increasing the voltage of the RF,the smallsignal gain of the Erbium-doped fiber amplifier(EDFA)and the responsivity of the photodetector.The MFC generated by this scheme has 300 GHz effective bandwidth with 15 comb lines,whose power variation is 0.02 dB,when the components9 parameters in the Optisystem are set as follows:the power of tunable laser diode(TLD)is 0 dBm,the wavelength is 1552.52 nm,and linewidth is 1 MHz;RF signaPs frequency is 20 GHz and the voltage is 10 V;the reverse bias voltage of MQW-EAM is 6.92 V;the small-signal gain of the EDFA is 40 dB;the responsivity of the photodetector(PD)is 1 A/W.