Search Results (28)

Heavy metal fluoride glasses (HMFGs), particularly fluorozirconate glass systems such as ZBLAN have attracted considerable attention due to their unique physical properties, including low phonon energies, wide transparency from the UV to the mid-IR, and high rare-earth ion doping solubility, making them promising materials for photonic applications. This review provides an overview of fluoride glass synthesis methods, structural characteristics, and physical properties of fluorozirconate glasses, with emphasis on glass processing conditions, thermal, mechanical, and optical properties. The structural characteristics are discussed in terms of zirconium–fluorine polyhedral networks and their compositional dependence, while physical properties are analyzed, including glass transition behavior, crystallization tendency, elastic moduli, and infrared transmission. Rare-earth doped Er³⁺, Ho³⁺, and Tm³⁺ ZBLAN glasses are also discussed, which exhibit efficient emissions in the near and mid-IR spectral regions. Although significant progress has been achieved, limitations related to thermal stability, mechanical strength, and incomplete understanding of structure–property relationships persist. Future research should therefore focus on compositional optimization and predictive structural modeling to enable the design of improved fluoride glasses for various applications. Full article

Ultrafast fiber lasers operating near 2 μm have emerged as a critical platform for advancing mid-infrared photonics due to their narrow pulse durations, high peak powers, and broad tunability. These sources exploit the rich energy-level structures of Tm³⁺ and Ho³⁺ doped fibers and reside within an atmospheric transmission window, enabling applications spanning nonlinear microscopy, precision micromachining, optical frequency metrology, biophotonics, and free-space optical communication. Recent progress in low-loss fiber fabrication, dispersion-engineered cavity design, and mode-locking technologies has significantly expanded the performance boundaries of 2 μm ultrafast fiber lasers. This review systematically examines the underlying pulse-formation mechanisms and categorizes state-of-the-art mode-locking approaches. Representative laser architectures are compared with respect to pulse duration, energy scalability, repetition-rate enhancement, spectral characteristics, and environmental stability. Key application pathways in high-resolution spectroscopy, biomedical diagnostics, and mid-IR supercontinuum generation are highlighted. Finally, the remaining challenges and prospective research directions are discussed to inform the development of next-generation ultrafast photonic sources in the 2 μm band. Full article

The year 2024 marks the 30-year anniversary of the quantum cascade laser (QCL), which is becoming the leading laser source in the mid-infrared (mid-IR) range. Since the first demonstration, QCL has undergone tremendous development in terms of the output power, wall plug efficiency, spectral coverage, wavelength tunability, and beam quality. Owing to its unique intersubband transition and fast gain features, QCL possesses strong nonlinearities that makes it an ideal platform for nonlinear photonics like terahertz (THz) difference frequency generation and direct frequency comb generation via four-wave mixing when group velocity dispersion is engineered. The feature of broadband, high-power, and low-phase noise of QCL combs is revolutionizing mid-IR spectroscopy and sensing by offering a new tool measuring multi-channel molecules simultaneously in the μs time scale. While THz QCL difference frequency generation is becoming the only semiconductor light source covering 1–5 THz at room temperature. In this paper, we will introduce the latest research from the Center for Quantum Devices at Northwestern University and briefly discuss the history of QCL, recent progress, and future perspective of QCL research, especially for QCL frequency combs, room temperature THz QCL difference frequency generation, and major challenges facing QCL in the future. Full article

This study reports the production of mid-infrared (MIR) porous anodic alumina (PAA)-based microcavities with tunable optical quality. The spectral position of the cavity resonance peak (λ_C), along with its intensity (I_R) and Q-factor, varies depending on the geometric positioning of the cavity layer within the multilayer stack of alternating low- and high-porosity layers, as well as the type of cavity produced—either by high voltage (Cv_H-type) or low voltage (Cv_L-type) pulses. In most cases, PAA microcavities with Cv_H-type cavity layers exhibited superior light confinement properties compared to those with Cv_L-type cavities. Additionally, shifting the cavity layer from the center toward the edges of the multilayer stack enhanced the intensity of the resonance peak. For PAA microcavities with Cv_H-type cavity layers, the highest intensity (I_R = 53%) and the largest Q-factor (Q = 31) were recorded at λ_C of around 5.1 µm. The anodization approach used in this study demonstrates significant potential for designing PAA-based microcavities with high optical performance in the MIR spectral region, especially with further refinement of electrochemical parameters. These findings pave the way for the development of new photonic materials specifically tailored for the MIR spectral range, broadening their applications in various optoelectronic and sensing technologies. Full article

This research investigates the visible upconversion luminescence which is induced by multiphoton absorption of soft glass fiber defects. The study of this phenomenon has thus far been restricted to standard silica fibers. We observed the emission of green and cyan light as a consequence of fiber material ionization. We investigate both the commercial ZBLAN step index and in-house-made tellurite nanostructured graded-index fibers. For the latter, the analysis of the luminescence signal permits us to determine the core and cladding refractive index difference. Upconversion luminescence is a powerful tool for characterizing soft glass fibers and a promising platform for innovative photonic technologies and mid-IR applications. Full article

The chirped pulse amplification (CPA) systems based on transition-metal-ion-doped chalcogenide crystals are promising powerful ultrafast laser sources providing access to sub-TW laser pulses in the mid-IR region, which are highly relevant for essential scientific and technological tasks, including high-field physics and attosecond science. The only way to obtain high-peak power few-cycle pulses is through efficient laser amplification, maintaining the gain bandwidth ultrabroad. In this paper, we report on the approaches for mid-IR broadband laser pulse energy scaling and the broadening of the gain bandwidth of iron-doped chalcogenide crystals. The multi-pass chirped pulse amplification in the Fe:ZnSe crystal with 100 mJ level nanosecond optical pumping provided more than 10 mJ of output energy at 4.6 μm. The broadband amplification in the Fe:ZnS crystal in the vicinity of 3.7 μm supports a gain band of more than 300 nm (FWHM). Spectral synthesis combining Fe:ZnSe and Fe:CdSe gain media allows the increase in the gain band (~500 nm (FWHM)) compared to using a single active element, thus opening the route to direct few-cycle laser pulse generation in the prospective mid-IR spectral range. The features of the nonlinear response of carbon nanotubes in the mid-IR range are investigated, including photoinduced absorption under 4.6 μm excitation. The study intends to expand the capabilities and improve the output characteristics of high-power mid-IR laser systems. Full article

The development and investigation of miniature narrow-line coherent light sources based on microresonators with low-power-consumption whispering gallery modes (WGMs) is an actual trend in modern photonics. Raman WGM microlasers can operate at wavelengths inaccessible to traditional laser media and provide a huge pump frequency tuning range. Here, we propose and theoretically study multicascade Raman microlasers based on soft tellurite TeO₂–WO₃–Bi₂O₃ glass WGM microresonators (microspheres) which can operate in the near-IR and mid-IR with the pump in the telecommunication range. Thanks to a large Raman gain (120 times exceeding the maximum Raman gain of silica glass) and a huge Raman frequency shift of 27.5 THz for this glass, the Raman waves at 1.83 µm, 2.21 µm, 2.77 µm, and 3.7 µm in the first, second, third, and fourth cascades, respectively, are theoretically demonstrated with a pump at 1.57 µm. We analyze in detail the influence of different factors on the characteristics of the generated Raman waves, such as microsphere diameters, Q-factors, pump powers, and detuning of the pump frequency from exact resonance. We also solve a thermo-optical problem to show that the temperature of a soft glass microresonator heated due to partial thermalization of pump power remains below the glass transition temperature. To the best of our knowledge, mid-IR tellurite glass Raman WGM microlasers have not been studied before. Full article

Broadband supercontinuum (SC) fiber sources covering the mid-IR range have many significant applications, largely due to their compactness, reliability, and ease of use. However, most of the existing SC fiber sources cannot boast of either high reliability or a wide bandwidth. Thus, supercontinuum sources based on silica fibers are robust, but are not capable of generating SC in the mid-IR range. Sources based on soft glasses (tellurite, chalcogenide, etc.) generate broadband SC in the mid-IR range but are not used commercially, due to the poor mechanical and chemical characteristics of such fibers. In this work, we propose a new approach consisting of cascade generation of a supercontinuum sequentially in a silica photonic crystal fiber (PCF) and a germanate fiber. Using a standard ytterbium chirped-pulse amplification (CPA) laser system for pumping, we have demonstrated a supercontinuum in the range of 450–2950 nm in PCF and germanate fiber firmly connected by a standard fusion splicing technique. Further optimization of the cascade pump will make it possible to create a compact and reliable all-fiber SC source from the visible to mid-IR range. Full article

Silicon-based photodetectors are attractive as low-cost and environmentally friendly optical sensors. Also, their compatibility with complementary metal-oxide-semiconductor (CMOS) technology is advantageous for the development of silicon photonics systems. However, extending optical responsivity of silicon-based photodetectors to the mid-infrared (mid-IR) wavelength range remains challenging. In developing mid-IR infrared Schottky detectors, nanoscale metals are critical. Nonetheless, one key factor is the Fermi-level pinning effect at the metal/silicon interface and the presence of metal-induced gap states (MIGS). Here, we demonstrate the utilization of the passivated surface layer on semiconductor materials as an insulating material in metal-insulator-semiconductor (MIS) contacts to mitigate the Fermi-level pinning effect. The removal of Fermi-level pinning effectively reduces the Schottky barrier height by 12.5% to 16%. The demonstrated devices exhibit a high responsivity of up to 234 μA/W at a wavelength of 2 μm, 48.2 μA/W at 3 μm, and 1.75 μA/W at 6 μm. The corresponding detectivities at 2 and 3 μm are 1.17 × 10⁸ cm Hz^1/2 W⁻¹ and 2.41 × 10⁷ cm Hz^1/2 W⁻¹, respectively. The expanded sensing wavelength range contributes to the application development of future silicon photonics integration platforms. Full article

This paper investigates the use of a miniaturized filter based on a triangular lattice of holes in a photonic crystal (PhC) slab. The plane wave expansion method (PWE) and finite-difference time-domain (FDTD) techniques were utilized to analyze the dispersion and transmission spectrum, as well as the quality factor and free spectral range (FSR) of the filter. A 3D simulation has demonstrated that for the designed filter, an FSR of more than 550 nm and a quality factor of 873 can be attained by adiabatically coupling light from a slab waveguide into a PhC waveguide. This work designs a filter structure that is implemented into the waveguide and is suitable for a fully integrated sensor. The small size of the device provides a strong potential for the realization of large arrays of independent filters on a single chip. The fully integrated character of this filter has further advantages such as reducing power loss in coupling light from sources to filters and also from filters to waveguides. The ease of fabrication is another benefit of completely integrating the filter. Full article

In recent years, 3D printing glass optics has gained massive attention in industry and academia since glass could be an ideal material to make optical elements, including the lens. However, the limitation of materials and printing methods has prevented 3D printing glass optics progress. Therefore, we have developed a novel printing strategy for germanate glass printing instead of pure silica. Moreover, compared with traditional multi-component quartz glass, germanate glass has unmatched advantages for its mid-infrared (MIR) transparency and outstanding visible light imaging performance. Furthermore, compared with non-oxide glass (fluoride glass and chalcogenide glass), germanate glass has much better mechanical, physical, and chemical properties and a high refractive index. Germanate glass has been widely applied in remote sensing, ranging, environmental detection, and biomedical detection. However, it is difficult to shape, cast, polish, and grind for optical and photonics applications such as imaging optics and laser-collimation optics. These drawbacks have made germanate glass inaccessible to complex optical elements and greatly increased their cost. In this report, we use germanate glass fibers with a diameter of 125 µm based on fiber-fed laser heating technology to fabricate an mm-size optical application. In this paper, we combine the fiber-fed laser heating technology with an optimized temperature control process to manufacture high-precision optical elements. Germanate glass optics can be printed with excellent visible light and IR transparency and a smooth surface with roughness under 4 nm. By optimizing the layer-by-layer 3D printing process and the thermal feedback in the printing process, we avoid cracks and minimize surface deformation. This work shows the possibility of the mm-size glass optical elements 3D printing and widens its application for IR optics. Full article

This paper reveals special design features of the proposed highly nonlinear circular-lattice-silicon-core and silica-doped-with-fluorine (1%) cladding-composite photonic crystal fiber (PCF) in the Mid-infrared region of the spectrum. A region of small negative group velocity dispersion (GVD), managed higher order dispersions (HODs), and unique nonlinearity of silicon have been used to demonstrate a supercontinuum broadening from 1500 nm to 4700 nm with consumption of low input power of 400 W over short fiber distances. It will be also shown that the fiber’s high-level engineered structure finally results in a simple manufacturing process compared with other designed nano-sized silicon PCFs. The designed fiber could have massive potential in gas sensing, soliton effect pulse compression, spectroscopy, material processing, etc. Full article

As the silicon photonics field matures and a data-hungry future looms ahead, new technologies are required to keep up pace with the increase in capacity demand. In this paper, we review current developments in the near-IR and mid-IR group IV photonic modulators that show promising performance. We analyse recent trends in optical and electrical co-integration of modulators and drivers enabling modulation data rates of 112 GBaud in the near infrared. We then describe new developments in short wave infrared spectrum modulators such as employing more spectrally efficient PAM-4 coding schemes for modulations up to 40 GBaud. Finally, we review recent results at the mid infrared spectrum and application of the thermo-optic effect for modulation as well as the emergence of new platforms based on germanium to tackle the challenges of modulating light in the long wave infrared spectrum up to 10.7 $\mathsf{\mu }$m with data rates of 225 MBaud. Full article

Exploration and implementation of silicon (Si) photonics has surged in recent years since both photonic component performance and photonic integration complexity have considerably improved. It supports a wide range of datacom and telecom applications, as well as sensors, including light detection and ranging, gyroscopes, biosensors, and spectrometers. The advantages of low-loss Si WGs with compact size and excellent uniformity, resulting from the high quality and maturity of the Si complementary metal oxide semiconductor (CMOS) environment, are major drivers for using Si in photonics. Moreover, it has a high refractive index and a reasonably large mid-infrared (MIR) transparency window, up to roughly 7 μm wavelength, making it beneficial as a passive mid-IR optical material. Several gases and compounds with high absorption properties in the MIR spectral region are of prodigious curiosity for industrial, medicinal, and environmental applications. In comparison to current bulky systems, the implementation of Si photonics devices in this wavelength range might allow inexpensive and small optical sensing devices with greater sensitivity (S), power usage, and mobility. In this review, recent advances in Si integrated photonic sensors working in both near-infrared (NIR) and MIR wavelength ranges are discussed. We believe that this paper will be valuable for the scientific community working on Si photonic sensing devices. Full article

Manipulating optical signals in the mid-infrared (mid-IR) range is a highly desired task for applications in chemical sensing, thermal imaging, and subwavelength optical waveguiding. To guide highly confined mid-IR light in photonic chips, graphene-based plasmonics capable of breaking the optical diffraction limit offer a promising solution. However, the propagation lengths of these materials are, to date, limited to approximately 10 µm at the working frequency f = 20 THz. In this study, we proposed a waveguide structure consisting of multilayer graphene metamaterials (MLGMTs). The MLGMTs support the fundamental volume plasmon polariton mode by coupling plasmon polaritons at individual graphene sheets over a silicon nano-rib structure. Benefiting from the high conductivity of the MLGMTs, the guided mode shows ultralow loss compared with that of conventional graphene-based plasmonic waveguides at comparable mode sizes. The proposed design demonstrated propagation lengths of approximately 20 µm (four times the current limitations) at an extremely tight mode area of 10⁻⁶A₀, where A₀ is the diffraction-limited mode area. The dependence of modal characteristics on geometry and material parameters are investigated in detail to identify optimal device performance. Moreover, fabrication imperfections are also addressed to evaluate the robustness of the proposed structure. Moreover, the crosstalk between two adjacent present waveguides is also investigated to demonstrate the high mode confinement to realize high-density on-chip devices. The present design offers a potential waveguiding approach for building tunable and large-area photonic integrated circuits. Full article