Synchronous mode-locking of solid-state lasers by difference frequency generation
O. B. Jensen, A. K. Hansen, M. Chi, and P. Tidemand-Lichtenberg
Abstract
This Letter introduces a novel, to the best of our knowledge, method for achieving mode-locking and synchronization of mode-locked output pulses from two lasers. The proposed technique leverages parametric gain from difference frequency generation. Specifically, a Nd:YAG laser is mode-locked by single-pass mode-locked pulses from a mode-locked Ti:sapphire laser using an intracavity nonlinear crystal. When the continuous-wave laser is not actively pumped, the system functions as a synchronously pumped optical parametric oscillator. This novel approach has the potential to enable new devices, especially for pump-probe applications or for generation of mode-locked pulses in spectral regions where conventional mode-locked devices are typically not available.
Unidirectional ring laser operation and tunable single-frequency emission using differential parametric gain
O. B. Jensen, M. Helmark, A. G. Urskov, and P. Tidemand-Lichtenberg
Abstract
In this Letter, a novel approach for unidirectional operation of a 1064 nm solid-state ring laser is demonstrated based on difference frequency mixing. Unidirectional operation is achieved exploiting the directional parametric gain from a single-pass diode laser, facilitated through a periodically poled LiNbO3 crystal. In addition to achieving unidirectional operation, the nonlinear process further enables the generation of single-frequency mid-infrared light. Using a single-pass tapered diode laser, tunable in the range from 780 to 815 nm, the generated mid-infrared signal covers the 2.9 to 3.5 µm range while optimizing the phase-match condition of the difference frequency generation process.
Photon Pair Source based on PPLN-Waveguides for Entangled Two-Photon Absorption
Tobias Bernd Gäbler, Patrick Hendra, Nitish Jain, Markus Gräfe
Abstract
Fluorescence excitation by absorption of entangled photon pairs offers benefits compared to classical imaging techniques, such as the attainment of higher signal levels at low excitation power while simultaneously mitigating phototoxicity. However, current entangled photon pair sources are unreliable for fluorescence detection. In order to address this limitation, there is a need for ultra-bright entangled photon pair sources. Among the potential solutions, sources utilizing nonlinear waveguides emerge as promising candidates to facilitate fluorescence excitation through entangled photons. In this paper, a source consisting of a periodically poled lithium niobate waveguide is developed and its key characteristics are analyzed. To demonstrate its suitability as key component for imaging experiments, the entangled two-photon absorption behavior of Cadmium Selenide Zinc Sulfide quantum dot solutions is experimentally investigated.
Frequency-bin-encoded entanglement-based quantum key distribution in a reconfigurable frequency-multiplexed network
Anahita Khodadad Kashi and Michael Kues
Abstract
Large-scale quantum networks require dynamic and resource-efficient solutions to reduce system complexity with maintained security and performance to support growing number of users over large distances. Current encoding schemes including time-bin, polarization, and orbital angular momentum, suffer from the lack of reconfigurability and thus scalability issues. Here, we demonstrate the first-time implementation of frequency-bin-encoded entanglement based quantum key distribution and a reconfigurable distribution of entanglement using frequency-bin encoding. Specifically, we demonstrate a novel scalable frequency-bin basis analyzer module that allows for a passive random basis selection as a crucial step in quantum protocols, and importantly equips each user with a single detector rather than four detectors. This minimizes massively the resource overhead, reduces the dark count contribution, vulnerability to detector side-channel attacks, and the detector imbalance, hence providing an enhanced security. Our approach offers an adaptive frequency-multiplexing capability to increase the number of channels without hardware overhead, enabling increased secret key rate and reconfigurable multi-user operations. In perspective, our approach enables dynamic resource-minimized quantum key distribution among multiple users across diverse network topologies, and facilitates scalability to large-scale quantum networks.
Demonstration of an 8-Gbit/s quadrature-phase-shift-keying coherent underwater wireless optical communication link using coherent heterodyne detection under scattering conditions
Yuxiang Duan, Huibin Zhou, Zile Jiang, Muralekrishnan Ramakrishnan, Xinzhou Su, Wing Ko, Yue Zuo, Hongkun Lian, Ruoyu Zeng, Yingning Wang, Zixun Zhao, Moshe Tur, and Alan E. Willner
Abstract
In this paper, we experimentally demonstrate an 8-Gbit/s quadrature-phase-shift-keying (QPSK) coherent underwater wireless optical communication (UWOC) link under scattering conditions at 532 nm. At the transmitter, we generate the 532-nm QPSK signal using second-harmonic generation (SHG), where the 1064-nm signal modulated with four phase levels of an 8-phase-shift-keying (8-PSK) format is phase doubled to produce the 532-nm QPSK signal. To enhance the receiver sensitivity, we utilize a local oscillator (LO) at the receiver from an independent laser source. The received QPSK data beam is mixed with the independent LO for coherent heterodyne detection. Results show that the bit error rates (BERs) of the received QPSK signal can reach below the 7% forward error correction (FEC) limit under turbid water with attenuation lengths (γL) up to 7.4 and 6.1 for 2- and 8-Gbit/s QPSK, respectively. The corresponding receiver sensitivities are −34.0 and −28.4 dBm for 2- and 8-Gbit/s QPSK, respectively.
Photon Pair Source based on PPLN-Waveguides for Entangled Two-Photon Absorption
Tobias Bernd Gäbler, Patrick Hendra, Nitish Jain, Markus Gräfe
Abstract
Fluorescence excitation by absorption of entangled photon pairs offers benefits compared to classical imaging techniques, such as the attainment of higher signal levels at low excitation power while simultaneously mitigating phototoxicity. However, current entangled photon pair sources are unreliable for fluorescence detection. In order to address this limitation, there is a need for ultra-bright entangled photon pair sources. Among the potential solutions, sources utilizing nonlinear waveguides emerge as promising candidates to facilitate fluorescence excitation through entangled photons. In this paper, a source consisting of a periodically poled lithium niobate waveguide is developed and its key characteristics are analyzed. To demonstrate its suitability as key component for imaging experiments, the entangled two-photon absorption behavior of Cadmium Selenide Zinc Sulfide quantum dot solutions is experimentally investigated.
Yuk Shan Cheng, Kamalesh Dadi, Toby Mitchell, Samantha Thompson, Nikolai Piskunov, Lewis D. Wright, Corin B. E. Gawith,Richard A. McCracken & Derryck T. Reid
Abstract
Cosmological and exoplanetary science using transformative telescopes like the ELT will demand precise calibration of astrophysical spectrographs in the blue-green, where stellar absorption lines are most abundant. Astrocombs— lasers providing a broadband sequence of regularly-spaced optical frequencies on a multi-GHz grid—promise an atomically-traceable calibration scale, but their realization in the blue-green is challenging for current infrared laser-based technology. Here, we introduce a concept achieving a broad, continuous spectrum by combining second-harmonic generation and sum frequency-mixing in an MgO:PPLN waveguide to generate 390–520 nm light from a 1 GHz Ti:sapphire frequency comb. Using a Fabry-Pérot filter, we extract a 30 GHz sub-comb spanning 392–472 nm, visualizing its thousands of modes on a high-resolution spectrograph. Experimental data and simulations demonstrate how the approach can bridge the spectral gap present in second harmonic-only conversion. Requiring only ≈100 pJ pulses, our concept establishes a new route to broadband UV-visible generation at GHz repetition rates.
Emma Pearce, Nathan R. Gemmell, Jefferson Flórez, Jiaye Ding, Rupert F. Oulton, Alex S. Clark, and Chris C. Phillips
Abstract
Infrared (IR) imaging is invaluable across many scientific disciplines, from material analysis to diagnostic medicine. However, applications are often limited by detector cost, resolution and sensitivity, noise caused by the thermal IR background, and the cost, portability and tunability of infrared sources. Here, we describe a compact, portable, and low-cost system that is able to image objects at IR wavelengths without an IR source or IR detector. This imaging with undetected photons (IUP) approach uses quantum interference and correlations between entangled photon pairs to transfer image information from the IR to a wavelength which can be detected with a standard silicon camera. We also demonstrate a rapid analysis approach to acquire both phase and transmission image information. These developments provide an important step towards making IUP a commercially viable technique.
Bond-Selective Imaging of Cells by Mid-Infrared Photothermal Microscopy in High Wavenumber Region
Yeran Bai, Delong Zhang and Chen Li
Abstract
Using a visible beam to probe the thermal effect induced by infrared absorption, mid-infrared photothermal (MIP) microscopy allows bond-selective chemical imaging at submicron spatial resolution. Current MIP microscopes cannot reach the high wavenumber region due to the limited tunability of the existing quantum cascade laser source. We extend the spectral range of MIP microscopy by difference frequency generation (DFG) from two chirped femtosecond pulses. Flexible wavelength tuning in both C-D and C-H regions was achieved with mid-infrared power up to 22.1 mW and spectral width of 29.3 cm⁻¹. Distribution of fatty acids in live human lung cancer cells was revealed by MIP imaging of the C-D bond at 2192 cm⁻¹.
Compact and versatile OPG-OPA based on a periodically poled nonlinear crystal pumped by femtosecond Ytterbium fiber laser
Valerian Freysza , Gabriel Amiard-Hudebinea , Yoann Zaouterb , and Eric Freysza
Abstract
A 10 mm long PPLN crystal pumped by 125 nJ, 250 fs pulses centered at 1035 nm yielded by Yb3+ femtosecond fiber oscillator generates femtosecond signal and idler pulses tunable in the 1.35 µm – 1.65 µm and 2.6 µm – 4.2 µm spectral ranges. A numerical model accounting for both second- and third-order nonlinear processes well agree with the recorded signal conversion efficiency (up to 42%), the spectral and temporal profile of the generated pulses. Pulse to pulse stability is drastically improved injecting this compact and versatile device with a continuum generated in a photonic fiber. Further improvements are discussed.
