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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Experimental Evidences of Non-Hermitian Mode-Locking in Fibre Laser
摘要： Mode-locking (ML) is an established technique used to generate high-power, ultrashort (from ps to fs) light pulses in lasers. Mode-locking techniques could be classified into two broad categories: active mode-locking (AML), for example achieved by an external periodic (in time) modulation of the loss coefficient, or passive mode-locking (PML), for example via a saturable absorber. Active mode-locking could be achieved by a periodic (in time) modulation of the loss coefficient, or phase mode-locking (PML), via a periodic modulation of the length of the cavity. In an amplitude mode-locking (AML) the periodic modulation of the loss coefficient synchronizes the phases of the cavity modes, resulting in a train of pulses. In a phase mode-locking (PML), the periodic modulation of the cavity length results in a phase modulation of the cavity modes, leading to a frequency comb. In this sense, the phase mode-locking is a particular case of the more general frequency comb generation in lasers. In the case of the non-Hermitian mode-locking the periodic modulation of the loss coefficient is replaced by a periodic modulation of the non-Hermitian potential, which can be achieved by a periodic (in time) modulation of the loss coefficient, or by a periodic modulation of the gain coefficient. The non-Hermitian mode-locking could be achieved by a periodic modulation of the non-Hermitian potential, which can be achieved by a periodic (in time) modulation of the loss coefficient, or by a periodic modulation of the gain coefficient. The non-Hermitian mode-locking is a particular case of the more general frequency comb generation in lasers with non-Hermitian potentials. In this paper we propose a new type of mode-locking – non-Hermitian mode-locking (NML) – realized in frequency domain. Non-Hermitian unidirectional coupling between the modes in frequency domain can be achieved by a simultaneous amplitude and phase mode-locking with the phases of both modulations properly shifted one with respect to another. The NML regime is fixed at λ=1.55 μm.
关键词： laser,mode-locking,non-Hermitian,frequency comb
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Direct Frequency Comb Spectroscopy with an Immersion Grating
摘要： Direct frequency comb spectroscopy (DFCS) in the mid-infrared region, especially in the long mid-infrared region (>5 μm), is a powerful technique for atmospheric remote sensing and fundamental spectroscopy such as studies of C60. DFCS has been demonstrated in Fourier transform spectroscopy, dual-comb spectroscopy, and techniques involving a dispersive spectrometer. Although a dispersive spectrometer with a virtually-imaged phase array (VIPA) can probe transient molecules by recording spectra within 10 μs, it has the disadvantages of low throughput and limited-bandwidth, which present challenges for sensitive, broadband detection at high time resolution. In this work, we overcame the challenges of a VIPA spectrometer by developing a direct frequency comb spectrometer in the 8.5 μm region using an immersion grating. A preliminary demonstration was reported at 4 μm in this conference two years ago. The spectrometer provides the capability to perform precise spectroscopy of transient and large molecules in the long mid-infrared region.
关键词： fundamental spectroscopy,atmospheric remote sensing,immersion grating,Direct frequency comb spectroscopy,mid-infrared
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Soliton Combs Generation Due to Parametric up and Down Conversion in a Microring Resonator with Quadratic Nonlinearity
摘要： Frequency comb generation in microring resonators has been intensively studied in the last decade. Frequency combs have applications in precision measurements and optical signal processing. The discrete nature of whispering gallery modes allows microresonators to be natural candidates for frequency comb generation. However, dispersive effects avoid homogeneous spacing between frequency comb lines and for that reason they need to be balanced. Thus, it is essential to generate optical solitons which are, by definition, a result of a balance between the dispersive and nonlinear properties of a resonator.
关键词： microring resonator,quadratic nonlinearity,soliton combs,frequency comb generation
更新于2025-09-11 14:15:04
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A Multiband Transparent Transponder Based on Reconfigurable Optical Frequency Combs for Cross Connection of Intersatellite and Satellite Ground
摘要： In this paper, a parallel multiband frequency-conversion scheme for satellite applications based on a single optical frequency comb is proposed, and a recon?gurable satellite transponder is designed for future multiband broadband satellites. In addition, we establish a test system of onboard multiband frequency-conversion on the strength of microwave photonics and, a proof-of-concept experiment is demonstrated in which a Ka-band signal is converted to other satellite frequency bands. The experimental results reveal our system feasibility, and the bit error rate of recovered baseband data is less than 10–9. Moreover, the optical frequency combs can be recon?gured by adjusting the parameters of the local oscillator and optical modulator.
关键词： multi-band frequency conversion,Microwave photonics,recon?gurable satellite transponder.,optical frequency comb
更新于2025-09-10 09:29:36
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Microring resonator-based photonic system for terahertz signal generation
摘要： We propose a photonic system based on add–drop microring resonator and mode-locked laser for terahertz (THz) signal generation. A mode-locked laser acts as an input source to the microring resonator. The transfer characteristics of the microring resonator generate Lorentzian shaped pulses at the output ports of the microring resonator. These series of pulses obtained are then investigated in two approaches; in the ?rst approach, the output of the microring resonator is given to a photodetector which generates 33 THz pulses separated by a spacing of 1 THz with a full width at half maximum (FWHM) of 0.15 THz. In the second approach, the output of the microring resonator is given to an optical ?lter to extract a particular frequency component. In this case, a single THz carrier with a FWHM of 0.2618 THz is obtained. The THz frequency components generated by the proposed photonic system can act as carriers for communication between the indoor user and the base station of a pico/femto cell in a 5G environment.
关键词： THz signal generation,Microwave photonics,Microring resonator,Frequency comb generation,Mode-locked laser
更新于2025-09-10 09:29:36
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[IEEE 2018 IEEE Photonics Conference (IPC) - Reston, VA, USA (2018.9.30-2018.10.4)] 2018 IEEE Photonics Conference (IPC) - On-Chip Optical Frequency Comb Generation for RF Photonic Applications
摘要： We review several key problems in microresonator frequency comb generation for RF photonic applications, including comb intensity noise and power conversion efficiency, and show some preliminary demonstrations based on mode-locked and low-noise Kerr combs including programmable complex-tap signal processing and true-time-delay beamforming.
关键词： RF photonic applications,low-noise,mode-locked,optical frequency comb,Kerr comb,microresonator
更新于2025-09-09 09:28:46
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Photon echoes from an atomic frequency comb affected by population relaxation
摘要： The atomic frequency comb (AFC) is a promising approach for quantum memory, yet creating an ideal AFC only in the ground-state population remains a challenge. We studied an imperfect AFC initially created in the population inversion between the excited and ground states and redistributed due to population relaxation in a three-level system where a long-lived metastable state plays a crucial role. A theoretical model has been developed to treat the storage of a weak input pulse and retrieval in the form of a photon echo. By comparing theory with experimental results we have studied the echo efficiency and overall attenuation of an input pulse in the AFC affected by both its initial spectral structure and the population relaxation.
关键词： atomic frequency comb,population relaxation,quantum memory,three-level system,photon echo
更新于2025-09-09 09:28:46
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Scanning frequency comb microscopy—A new method in scanning probe microscopy
摘要： A method for superimposing a microwave frequency comb (MFC) on the DC tunneling current in a scanning tunneling microscope (STM) is described in which a mode-locked laser is focused on the tunneling junction. The MFC is caused by optical rectification of the regular sequence of laser pulses due to the nonlinear current-voltage characteristics of the tunneling junction. Hundreds of harmonics, at integer multiples of the laser pulse-repetition frequency, are generated with a metal tip and sample. However, the harmonics have less power with a resistive sample due to the loss in its spreading resistance. The microwave power is greatest at a tip-sample distance that is unique for each sample resistivity. This distance may be set by using different pairs of the applied DC bias and the set-point for the DC tunneling current. However, the laser, and not the applied DC bias or the DC tunneling current, is the source of energy for the MFC so they are not required. Feedback control of the tip-sample distance may be based on maximizing the attowatt-level microwave power of the harmonics, which have a signal-to-noise ratio of 20 dB. This method shows promise for nondestructive carrier profiling of semiconductors with true sub-nanometer resolution which is essential in the continued progress below the 40-nm technology node. It may enable carrier profiling with 2-D materials such as graphene, and it also shows promise for finer resolution in images of biological materials or other resistive samples.
关键词： optical rectification,microwave frequency comb,resistive sample,feedback control,scanning tunneling microscope
更新于2025-09-04 15:30:14
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Searching for exoplanets using a microresonator astrocomb
摘要： Orbiting planets induce a weak radial velocity (RV) shift in the host star that provides a powerful method of planet detection. Importantly, the RV technique provides information about the exoplanet mass, which is unavailable with the complementary technique of transit photometry. However, RV detection of an Earth-like planet in the ‘habitable zone’ requires extreme spectroscopic precision that is only possible using a laser frequency comb (LFC). Conventional LFCs require complex filtering steps to be compatible with astronomical spectrographs, but a new chip-based microresonator device, the Kerr soliton microcomb, is an ideal match for astronomical spectrograph resolution and can eliminate these filtering steps. Here, we demonstrate an atomic/molecular line-referenced soliton microcomb for calibration of astronomical spectrographs. These devices can ultimately provide LFC systems that would occupy only a few cubic centimetres, thereby greatly expanding implementation of these technologies into remote and mobile environments beyond the research lab.
关键词： radial velocity,microresonator,astrocomb,Kerr soliton microcomb,laser frequency comb,exoplanets
更新于2025-09-04 15:30:14