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Abstract: We theoretically analyzed the gain characteristics of an integrated semiconductor quantum dot (QD) fiber amplifier (SQDFA) by using a 2×2 tapered fiber coupler with a PbS QD-coated layer. The asymmetric structure of the fiber coupler is designed to have a maximum working bandwidth around 1550-nm band and provide a desired optical power ratio of the output signals. By using 600mW of 980-nm pump, 10dB gain of a 1550-nm signal is estimated with the gain efficiency of 4.5dB/cm. [Copyright &y& Elsevier]

Abstract: A PbS quantum dot coated (QD-coated) tapered fiber amplifier with a broad bandwidth is theoretically demonstrated. The QD layer is coated on the surface of a tapered fiber and is excited by the evanescent wave of a pump. An optical gain of 10.5dB, with a 160-nm broad bandwidth of at 1530-nm center wavelength, is achieved. The gain efficiency is over 4dB/cm. This QD-tapered fiber amplifier has a concentration control of the QDs, a lower insertion loss, and shows good suppression of amplified spontaneous emission (ASE), while its structure is also quite simple. Therefore, the proposed fiber amplifier has great potential in fiber-optic communication systems. [Copyright &y& Elsevier]

Sensitive mid‐infrared (MIR) spectroscopy is highly demanded in various fields ranging from industrial inspection, biomedical diagnosis to astronomical observation. However, the detection sensitivity of conventional MIR spectrometers is severely limited by excessive noises for existing infrared sensors, which hinders widespread use in photon‐scarce scenarios. Here, a broadband MIR single‐photon time‐stretch spectrometer is devised and implemented based on high‐fidelity spectral upconversion and time‐correlated coincidence counting. Specifically, a nanophotonic supercontinuum illumination covering 2.4–4.2 µm is nonlinearly converted to the near‐infrared band, where low‐loss single‐mode fiber and high‐performance silicon detector can be leveraged to facilitate dispersive operation and sensitive detection, respectively. The arrival time for the dispersed upconversion photons is precisely registered with a low‐timing‐jitter photon counter, which enables us to obtain a high spectral resolution about 0.5 cm−1 under a low‐light‐level illumination down to 0.14 photons/nm/pulse. In comparison to previous MIR upconversion spectrometers, the presented time‐stretch architecture favors single‐pixel simplicity and high‐throughput acquisition for the single‐photon spectral measurement. The achieved MIR spectroscopic features of broadband spectral coverage, sub‐wavenumber resolution, single‐photon sensitivity, and room‐temperature operation would stimulate immediate applications in material and life sciences. [ABSTRACT FROM AUTHOR]

Sensitive and fast mid‐infrared (MIR) spectroscopy is highly attractive in a variety of applications including astronomical observation, pharmaceutical synthesis, and environmental monitoring. However, the performance of conventional MIR spectrometers has long been hindered by the limited sensitivity of narrow‐bandgap detectors and/or the deficient brightness of broadband light sources. Here, an ultra‐sensitive and broadband MIR upconversion spectrometer, which integrates a supercontinuum source covering 1.5–4.2 μ$\umu$m based on a silicon nitride nanophotonic waveguide, is devised and integrated. High‐efficiency and low‐noise nonlinear frequency upconversion is realized based on coincidence pulsed pumping with spectro‐temporal optimization, which enables leverage of silicon detectors for facilitating MIR single‐photon spectroscopy at 0.2 photons/nm/pulse. Furthermore, the upconversion‐based array spectrometer is manifested with high‐speed spectral acquisition rates beyond 200 kHz, which is about tenfold faster than the state‐of‐the‐art scan rates for FTIR‐based spectrometers at a comparable spectral resolution. The achieved features of broadband spectral coverage, single‐photon sensitivity, and sub‐MHz refreshing rate might open up new possibilities for infrared transient spectral measurements in combustion analysis, high‐throughput sorting, and reaction tracking, among others. [ABSTRACT FROM AUTHOR]

Integrated nonlinear photonics, combined nonlinear optics with state‐of‐the‐art photonic integration, play a crucial role in chip‐integrated technologies including optical frequency combs, molecular spectroscopy, and quantum optics. Optical materials with favorable properties are the foundation to promote integrated photonic devices with bandwidth, efficiency, and flexibility in high‐volume chip‐scale fabrication. In this work, a newly developed chalcogenide glass‐Ge25Sb10S65 (GeSbS) is presented for nonlinear photonic integration and for dissipative soliton microcomb generation. The GeSbS features wide transparency (0.5–10 µm), strong nonlinearity (1.3 × 10−18 m2 W−1), and low thermo‐refractive coefficient (3.1 × 10−5 K−1), and is complementary metal oxide semiconductor (CMOS)‐compatible in fabrication. In this platform, chip‐integrated optical microresonators with an average intrinsic quality (Q) factor of ≈1.97 × 106 are implemented, and lithographically controlled dispersion engineering is carried out. In particular, both a bright soliton‐based microcomb with bandwidth of 240 nm (≈1440–1680 nm) and a dark‐pulse comb with bandwidth of 80 nm (≈1510–1590 nm) are generated in a single microresonator in its separated fundamental polarized mode families.The ten‐milliwatt level of soliton microcomb operation power facilitates the monolithically integrated photonic circuits. The results provide a potential material platform for integrated nonlinear photonics for highly compact and high‐intensity nonlinear interactions in visible and infrared regions. [ABSTRACT FROM AUTHOR]

Photonic integrated Raman lasers have extended the wavelength range of chip‐scale laser sources and have enabled applications including molecular spectroscopy, environmental analysis, and biological detection. Yet, the performance is strongly determined by the pumping condition and Raman shift value of nonlinear medias, leaving challenges to have a widely and continuously tunable Raman laser (e.g., over 100 nm). Here, photonic engineered Raman lasers based on chip‐integrated chalcogenide microresonators are demonstrated. The home‐developed chalcogenide photonic platform is of high nonlinearity, wide transparency, and low loss. The strong and broadband material Raman response has promised rich dynamics of Raman lasing. Indeed, both single‐mode Raman lasing and a broadband Raman‐Kerr comb, which are found engineered by tuning the dispersion of the chalcogenide microresonator, are demonstrated. The single‐mode Raman laser, together with its cascaded modes, supports a gap‐free tuning range over 140 nm, while the threshold power is as low as 3.25 mW. The results may contribute to the understanding of Raman and Kerr nonlinear interactions in dissipative and nonlinear microresonators, and on application aspect, may pave a way to integrated and efficient laser sources that is desired in spectroscopic applications in the infrared. [ABSTRACT FROM AUTHOR]

B Bright Soliton Microcombs b In article number 2200219, Bin Zhang, Zhaohui Li, and co-workers have generated a soliton microcomb based on a home-developed integrated chalcogenide glass-GeSbS chip, with the overall pumping power of the ten-milliwatt level. In particular, both a bright soliton-based microcomb with a bandwidth of 280 nm ( 1440-1680 nm) and a dark-pulse comb with a bandwidth of 80 nm ( 1510-1590 nm) are generated pumped in a single GeSbS microresonator. [Extracted from the article]

Optical frequency combs enable precision measurements in fundamental physics and have been applied to a growing number of applications, such as molecular spectroscopy, LIDAR and atmospheric trace-gas sensing. In recent years, the generation of frequency combs has been demonstrated in integrated microresonators. Extending their spectral range to the visible is generally hindered by strong normal material dispersion and scattering losses. In this paper, we report the first realization of a green-light frequency comb in integrated high- Q silicon nitride (SiN) ring microresonators. Third-order optical non-linearities are utilized to convert a near-infrared Kerr frequency comb to a broadband green light comb. The 1-THz frequency spacing infrared comb covers up to 2/3 of an octave, from 144 to 226 THz (or 1327-2082 nm), and the simultaneously generated green-light comb is centered around 570-580 THz (or 517-526 nm), with comb lines emitted down to 517 THz (or 580 nm) and up to 597 THz (or 502 nm). The green comb power is estimated to be as high as −9.1 dBm in the bus waveguide, with an on-chip conversion efficiency of −34 dB. The proposed approach substantiates the feasibility of on-chip optical frequency comb generation expanding to the green spectral region or even shorter wavelengths. [ABSTRACT FROM AUTHOR]