Wide Wavelength Tuning Research Articles

A Widely and Continuously Tunable Single-Mode Transmitter Based on a Hybrid Microcavity Laser

A method for achieving the single-mode and efficient unidirectional emission of a whispering gallery mode (WGM) semiconductor laser is presented herein. Hybrid square-rectangular lasers (HSRLs) and hybrid square/rhombus-rectangular lasers (HSRRLs) consisting of a Fabry–Pérot (FP) cavity and a square or rhombus cavity microcavity are described. In addition, a transmitter optical subassembly (TOSA) based on an HSRRL chip was fabricated, which has a wide and continuous wavelength tuning range. Wavelength channels from 1555.75 nm to 1568.15 nm with a spacing of 50 GHz were demonstrated with a good side mode suppression ratio (SMSR) and good output power. These devices have the potential to meet the typical requirements of optical communication networks.

Widely tunable reflection by a hybrid ion-doped positive-negative chiral nematic liquid crystal under an electric field.

In this study, a new methodology, in which the cation and chiral agent are doped in positive and negative nematic liquid crystal mixture to form cation-doped positive-negative chiral nematic liquid crystals (PN-CNLCs), is proposed. These PN-CNLCs are capable of achieving a wide wavelength tuning range close to 90 nm under the action of a high-frequency electric field. The dielectric interaction between these two liquid crystals with different dielectric anisotropies in the electric field allows for the effective change of the pitch of the CLCs. We discovered the tilting of the pitch in the PN-CNLCs by a series of well-designed validation experiments. The experimental results prove the symmetrical helix is formed along the alignment direction in PN-CNLCs. Furthermore, the experiments demonstrated that an increase in voltage does not directly affect the pitch, but it increases the tilt angle of the helix axis with respect to the normal of the LC cell. This study offers, to our knowledge, a novel perspective on the tuning performance of CLCs under electric field conditions, by integrating the properties of positive and negative liquid crystals. This finding not only contributes to the understanding of the electric field response mechanism of CLCs but also provides new avenues for the application of CLCs in fields such as wavelength tuning.

Inverse design of ultranarrow and high-efficiency color filters based on tandem convolutional neural networks

In this paper, an ultranarrow, high-efficiency color filter based on a two-dimensional grating nanostructure array is realized by a tandem inverse design network. The tandem inverse designed network is generated by connecting an inverse network with a pre-trained forward network. The tandem convolutional neural network successfully overcame the non-uniqueness problem of the training data. The performance of the networks is verified by a test set of 2592 data points, and the average MSE of the prediction results of the tandem network is 1.01 × 10−3. Extremely low error indicates that the tandem network can learn and capture the distribution characteristics of the transmission spectrum and give a reasonable design of the structural parameters. Finally, we obtained multiple inverse-designed transmissive color filters with ultranarrow linewidths and high efficiency, with central wavelengths between 480 nm and 630 nm. The linewidth and efficiency of each kind of color filter are less than 10.6 nm and higher than 60%. Narrow linewidths and wide wavelength tunability result in high color accuracy and a broad color gamut of the filters. The filters with two-dimensional metallic nanostructure array also show polarization-independent characteristics. Compared with the traditional method, this method can quickly and accurately design the structural parameters corresponding to the spectral response, which provides a new method for the nanostructure design.

Output Characteristics of External-Cavity Mode-Hop-Free Tunable Laser Source in C+L Band

Tunable laser sources with a wide wavelength tuning range, mode-hop-free (MHF) operation, and high spectral purity are essential for applications such as high-resolution spectroscopy, coherent detection, and intelligent fiber sensing. In this paper, we present a wide-range tunable laser source that operates without mode hopping, based on external cavity feedback using a semiconductor gain chip as the laser gain medium. The wavelength, power, and spectral characteristics of the laser are experimentally measured. A wide MHF continuous wavelength tuning range from 1480 nm to 1620 nm with a side-mode suppression ratio of more than 61.65 dB is achieved. An output optical power of more than 11.14 dBm with good power stability can also be realized in the full C+L band. This proposed external-cavity tunable laser source features a narrow intrinsic linewidth and MHF tunable radiation with a maximum sweep speed of 200 nm/s, enabling practical applications such as high-resolution vector spectrum analysis.

790–1000 nm continuously-tunable fiber-based femtosecond laser source

We report a 790–1000 nm tunable femtosecond laser source by second harmonic generation (SHG) of a 1580–2000 nm soliton self-frequency shift (SSFS) fiber laser. The SSFS fiber laser with an all polarization-maintaining fiber configuration consists of passively mode-locked figure-9 Er-doped fiber oscillator, two-stage fiber amplifiers and a nonlinear fiber, delivering femtosecond Raman solitons in a tunable range of 1580 to 2016 nm. The tunable Raman solitons are further injected into a specifically-designed chirped periodically-poled lithium niobite (CPPLN) crystal for efficient SHG, and therefore femtosecond pulses with wide wavelength tuning from 790 to 1000 nm are obtained. The shortest pulse duration is < 100 fs at 890 nm, and the average power is 7.55 mW with a repetition rate of 44.9 MHz. This is, to the best of our knowledge, the first demonstration of a < 1000 nm broadband tunable fiber-based femtosecond source almost covering the whole short-wavelength near-infrared spectrum, which may have important applications in the nonlinear microscopy, biomedical imaging, and material processing.

Stable and wavelength-tunable multiwavelength laser for high-rate measurement device independent quantum key distribution

Measurement device independent quantum key distribution (MDI QKD) has attracted growing attention for its immunity to attacks at the measurement unit, but its unique structure limits the secret key rate. Utilizing the wavelength division multiplexing (WDM) technique and reducing error rates are effective strategies for enhancing the secret key rate. Reducing error rates often requires active feedback control of wavelengths using precise external references. However, for a multiwavelength laser, employing multiple references to stabilize each wavelength output places stringent demands on these references and significantly increases system complexity. Here, we demonstrate a stable, wavelength-tunable multiwavelength laser with an output wavelength ranging from 1270 to 1610 nm. Through precise temperature control and stable drive current, we passively lock the laser wavelength, achieving remarkable wavelength stability. This significantly reduce the error rate, leading to an almost doubling of the secret key rate compared to previous experiments. Furthermore, the exceptional wavelength stability offered by our multiwavelength laser, combined with the WDM technique, has further boosted the secret key rate of MDI QKD. With a wide wavelength tuning range of 5.1 nm, our multiwavelength laser facilitates flexible operation across multiple dense wavelength division multiplexing channels. Coupled with high wavelength stability and multiple wavelength outputs simultaneously, this laser offers a promising solution for a high-rate MDI QKD system.

Ultra-highly sensitive dual gases detection based on photoacoustic spectroscopy by exploiting a long-wave, high-power, wide-tunable, single-longitudinal-mode solid-state laser.

Photoacoustic spectroscopy (PAS) as a highly sensitive and selective trace gas detection technique has extremely broad application in many fields. However, the laser sources currently used in PAS limit the sensing performance. Compared to diode laser and quantum cascade laser, the solid-state laser has the merits of high optical power, excellent beam quality, and wide tuning range. Here we present a long-wave, high-power, wide-tunable, single-longitudinal-mode solid-state laser used as light source in a PAS sensor for trace gas detection. The self-built solid-state laser had an emission wavelength of ~2 μm with Tm:YAP crystal as the gain material, with an excellent wavelength and optical power stability as well as a high beam quality. The wide wavelength tuning range of 9.44 nm covers the absorption spectra of water and ammonia, with a maximum optical power of ~130 mW, allowing dual gas detection with a single laser source. The solid-state laser was used as light source in three different photoacoustic detection techniques: standard PAS with microphone, and external- and intra-cavity quartz-enhanced photoacoustic spectroscopy (QEPAS), proving that solid-state laser is an attractive excitation source in photoacoustic spectroscopy.

Integrated Electro‐Optically Tunable Narrow‐Linewidth III–V Laser

Herein, an integrated electro‐optically tunable narrow‐linewidth III–V laser with an output power of 738.8 μW and an intrinsic linewidth of 45.55 kHz at the C band is demonstrated. The laser cavity is constructed using a fiber Bragg grating (FBG) and a tunable Sagnac loop reflector (TSLR) fabricated on thin‐film lithium niobate. The combination of the FBG and the electro‐optically tunable TSLR offers the advantages of single spatial mode, single frequency, narrow linewidth, and wide wavelength tunability for the electrically pumped hybrid integrated laser, which features a frequency tuning range of 20 GHz and a tuning efficiency of 0.8 GHz V−1.

Highly efficient and widely tunable Si3N4 waveguide-based optical parametric oscillator.

We demonstrate an efficient and widely tunable synchronously pumped optical parametric oscillator (OPO) exploiting four-wave mixing (FWM) in a silicon nitride (Si3N4) waveguide with inverted tapers. At a pump pulse duration of 2 ps, the waveguide-based OPO (WOPO) exhibited a high external pump-to-idler conversion efficiency of up to -7.64 dB at 74% pump depletion and a generation of up to 387 pJ output idler pulse energy around 1.13 μm wavelength. Additionally, the parametric oscillation resulted in a 64 dB amplification of idler power spectral density in comparison to spontaneous FWM, allowing for a wide idler wavelength tunability of 191 nm around 1.15 μm. Our WOPO represents a significant improvement of conversion efficiency as well as output energy among χ3 WOPOs, rendering an important step towards a highly efficient and widely tunable chip-based light source for, e.g., coherent anti-Stokes Raman scattering.

5-Watt level widely wavelength-tunable UV output from a frequency-doubled Alexandrite laser

We demonstrate a record 5-Watt level, wavelength tunable, continuous-wave UV output based on a diode-pumped Alexandrite laser employing intra-cavity second harmonic generation. A wide wavelength tuning range from 364nm to 402nm was achieved.

(Invited) Transistor-Injected Quantum-Cascade Devices: Novel Sources for Mid-Wave Infrared Emission

Quantum Cascade Lasers (QCLs) [1] are important sources for coherent mid-wave infrared (MWIR) light that find widespread use in applications such as molecular spectroscopy, free-space optical communications, and defense countermeasures. These applications demand tunability of emission wavelength and high output powers. The conventional QCL is a two-terminal n-i-n device in which an externally applied bias establishes the necessary electric field in the cascade region for proper alignment of the quantum states, defines the emission wavelength, and also determines the current through the cascade structure. Because QCLs are 2-terminal devices, changing bias directly changes both wavefunction overlap and energy separation. The spectral location and magnitude of the gain peak thus has a strong dependence on applied voltage, impacting the capability to modulate. To overcome these limitations, the transistor-injected quantum-cascade laser (TI-QCL) has been proposed [2]. The TI-QCL is a three-terminal device in which the cascade region is placed within a heterojunction bipolar transistor. In forward-active mode the current injection is controlled by a forward-biased emitter-base junction, and the reverse bias on the base-collector junction is used to control the electric field for alignment of the quantum states. This novel structure enables the decoupling of emission wavelength and output power. This extra control positions the TI-QCL to impact a wide range of applications such as spectroscopy with its wide tunability, and free-space communication with its capability to separately modulate power and frequency.Previously, transistor characteristics and near-infrared (NIR) band-to-band base emission was demonstrated in a GaAs design [3, 4] before moving to an InP-based design [5]. We will review the progress made to push the TI-QCL concept towards full functionality, focusing on InP-based epitaxial designs. A self-consistent Schrodinger-Poisson solver and non-equilibrium Green’s function method is used to aid in the active-region design of the structure, which is optimized for a peak emission wavelength of 8.27 μm as shown in Figure 1 [6]. A wide wavelength tunability from approximately 7.8 μm to 8.8 μm is projected based on computational analysis. The InP-based structure is grown using molecular beam epitaxy by IntelliEpi; a cross-section of the material is depicted in Figure 2. It contains an active-region composed of 30 repeated periods of In0.41Ga0.59As/In0.36Al0.64As strain-balanced superlattice. The devices are fabricated using standard III-V processing. An image of a fabricated TI-QCL bar consisting of a sloped, 20 μm wide emitter mesa and evaporated SiO2 as the passivation layer is depicted in Figure 3. The fabricated devices are diced and cleaved into 2 to 4 mm x 500 μm die and mounted onto In-plated copper mounts followed by wire bonding. The devices are electrically characterized at room temperature, 77 K, and 18 K. Under cryogenic temperatures, the common-base characteristics exhibit negative differential resistance (NDR) in collector current at all emitter injection currents as shown in Figure 4, which signifies tunneling transport through the quantum cascade superlattice region. The base current also exhibits corresponding NDR behavior and switching in the band-to-band NIR light (1.57 m) output from the In0.53Ga0.47As base is experimentally observed when biased in a region where transport through the cascade region is rejected due to quantum state misalignment.

Dynamically tunable broadband output coupling of optical oscillators based on non-cyclic geometric phase mirror

We present a uniquely versatile and efficient mirror system capable of real-time fine-tuning in reflection and transmission properties across a broad wavelength range and at a high optical power. Leveraging the principles of the non-cyclic geometric phase (GP) acquired by the clockwise and counterclockwise beams of the Sagnac interferometer satisfying the anti-resonant condition on propagation through the quarter-wave plate, half-wave plate, and quarter-wave plate combination having fast axes oriented at 45° (fixed), θ (variable), and −45° (fixed) with respect to the vertical, respectively, our mirror system offers dynamic transmission control across 0–100% without the need for realignment. Notably, the GP-based mirror (GP-mirror) preserves the polarization state of the reflected beam, making it ideal for polarization-sensitive applications. The wavelength insensitivity of the GP enables seamless operation of the mirror across a wide wavelength range. As a proof-of-principle, we use the GP-mirror as the output coupler of a continuous-wave, green-pumped, doubly resonant optical parametric oscillator (DRO) based on a 30-mm-long MgO:sPPLT crystal and obtain stable operation at high powers over a wide wavelength tuning range. For a pump power of 5 W, the DRO provides an output power of 2.45 W at an extraction efficiency as high as 49% when operated at optimum output coupling. The DRO shows a maximum pump depletion of 89% and delivers an optimum output power across a tuning range ≥90 nm. The demonstrated concept offers a promising approach for advancing the capabilities and control of coherent optical sources tunable across different spectral regions and in all time scales from continuous-wave to ultrafast femtosecond domain.

Tuning stability enhancement of all-fiber acousto-optic tunable filter based on multi-piezoelectric transducer

All-fiber acousto-optic tunable filters (AOTFs) have advantages of wide wavelength tuning range, fast tuning speed and low insertion loss. The resonance wavelength of the all-fiber AOTF can be tuned by adjusting the driving frequency of the piezoelectric transducer (PZT). In general, the driving voltage needs to be tuned in wide range in the wavelength tuning process, due to the existence of resonance frequency of the PZT. In this work, we propose and demonstrate a stability-enhanced all-fiber AOTF based on multi-PZT, which can reduce the dependence on the resonant frequency of a single PZT. In the experiment, the acousto-optic coupling efficiency can maintain larger than 80%, when the resonance wavelength of the AOTF is tuned from 1400 nm to 1600 nm, under the condition of a fixed driving voltage. The high tuning stability of the proposed multi-piezoelectric driving configuration can facilitate the practical applications of the all-fiber AOTF, such as the laser wavelength tuning, wavelength-division-multiplexing optical communication, fast optical spectroscopy, and so on.

Wide-wavelength-tunable distributed Bragg reflector laser diode with high thermal efficiency.

We proposed a thermally-tuned distributed Bragg reflector (DBR) laser diode that has a high tuning efficiency over a wide wavelength tuning range. The laser diode is composed of a gain, a phase control (PC), and a DBR region, and its wavelength is tuned coarsely and finely by the micro-heaters on the DBR and PC regions, respectively. To improve the tuning efficiency, we developed a technique for fabricating a thermal isolation structure through a reverse mesa etching process, replacing the complex process that uses an InGaAs sacrificial layer. The DBR laser diodes (DBR-LD) fabricated using this method effectively confines heat generated by the heater, resulting in an approximate tuning range of 40 nm. This technology, which has achieved nearly four times larger wavelength tuning range than the thermally-tuned DBR-LDs without a thermal isolation structure, is considered suitable for the cost-effective development of wide-wavelength-tuning DBR-LD light sources.

Mechano-Chemical Synthesis and Characterization of Undoped and Mn2+ Doped Cspb(Br1-xClx)3 Halide Perovskite for Light Source Application

All-inorganic halide perovskites (HPs) continue to be of current interest for light source applications (e.g. lasers, LED’s) because of their high emission quantum yields and wide wavelength tunability due to compositional engineering [1]. The development of red and near-IR emitting lead halide perovskites, however, has been hampered by low emission efficiency and instability of iodine based compositions at room temperature. Recent studies employing transition metal or lanthanide doping have demonstrated an alternative approach to achieve red and near-IR emitting HPs structures [2-4]. In this study we report results of the mechano-chemical synthesis of undoped and manganese (Mn) doped CsPb(Br1-xClx)3 halide perovskites as emitting materials for light source development. Mechano-chemical synthesis is considered a green chemistry method avoiding the use of complex and time-consuming reactions, energetic-enabled conditions, expensive precursor sources, and hazardous reagents, catalysts, additives, and surfactants. Mechano-chemical synthesis experiments were performed employing a high energy ball-mill and 5N purity lead halide and cesium halide powders. The prepared HPs were evaluated by optical microscopy, SEM, TEM, XRD, and fluorometric measurements. Under UV optical excitation a Mn doped CsPbCl3 sample exhibited a broad red emission band centers at ~615nm, which was slightly red-shifted compared to the emission from a melt-grown Mn: CsPbCl3 crystals (see Figure 1). Post synthesis optimization strategies for HPs were also explored including thermal treatment, high-pressure studies, and solvent dependency. Comparative studies of the emission properties of undoped and Mn doped CsPb(Br1-xClx)3 prepared by mechano-chemical synthesis, microwave-assisted synthesis, and melt-synthesis will also be presented.AcknowledgmentThis work was supported by the Army Research Office (grant W911NF1810447) and National Science Foundation (grant NSF-DMR 1827820-PREM).

E-band widely tunable, narrow linewidth heterogeneous laser on silicon

We demonstrate a heterogeneously integrated laser on silicon exhibiting a sub-20 kHz Lorentzian linewidth over a wavelength tuning range of 58 nm from 1350 to 1408 nm, which are record values to date for E-band integrated lasers in the literature. Wide wavelength tuning is achieved with an integrated Si ring-resonator-based Vernier mirror, which also significantly reduces the Lorentzian linewidth. Such a record performance leverages a mature heterogeneous III–V/Si platform and marks an important milestone in E-band optical fiber communications and in reaching visible wavelengths via second harmonic generation for optical atomic clock applications.

Suppressing phase disproportionation in quasi-2D perovskite light-emitting diodes

Electroluminescence efficiencies and stabilities of quasi-two-dimensional halide perovskites are restricted by the formation of multiple-quantum-well structures with broad and uncontrollable phase distributions. Here, we report a ligand design strategy to substantially suppress diffusion-limited phase disproportionation, thereby enabling better phase control. We demonstrate that extending the π-conjugation length and increasing the cross-sectional area of the ligand enables perovskite thin films with dramatically suppressed ion transport, narrowed phase distributions, reduced defect densities, and enhanced radiative recombination efficiencies. Consequently, we achieved efficient and stable deep-red light-emitting diodes with a peak external quantum efficiency of 26.3% (average 22.9% among 70 devices and cross-checked) and a half-life of ~220 and 2.8 h under a constant current density of 0.1 and 12 mA/cm2, respectively. Our devices also exhibit wide wavelength tunability and improved spectral and phase stability compared with existing perovskite light-emitting diodes. These discoveries provide critical insights into the molecular design and crystallization kinetics of low-dimensional perovskite semiconductors for light-emitting devices.

Widely tunable 2 µm optical vortex from a Tm:YAP laser

In this paper, we report on a wide wavelength tuning optical vortex carrying orbital angular momentum (OAM) of ±ħ, from a thulium-doped yttrium aluminum perovskite (YAP) laser employing a birefringent filter. The OAM is experimentally found to be well maintained during the whole wavelength tuning process. The Laguerre–Gaussian (LG0,+1) mode with a tuning range of 58 nm from 1934.8 to 1993.0 nm and LG0,-1 mode with a range of 76 nm from 1920.4 to 1996.6 nm, are, respectively, obtained. This is, to the best of our knowledge, the first experimental implementation of wavelength tuning for a scalar vortex laser in the 2 µm spectral range, as well as the broadest tuning range ever reported from the vortex laser cavity. Such a vortex laser with robust structure and straightforward wavelength tuning capability will be an ideal light source for potential applications in the field of optical communication with one additional degree of freedom.

Design and Development of Hybrid Halide Perovskites in Laser Devices

Organic-inorganic hybrid halide perovskite is a significant semiconductor material in photonics. Their outstanding optoelectronic characteristics have been reported, increasing energy conversion efficiency of perovskite solar battery by up to 25.5%, which is expected to be major competitors in silicon industry. According to the fundamentals of physics, a viable candidate for a light emitter must really be a superior direct band gap material. Even though there are a lot of papers on perovskite-based light emitting devices in this area, the corresponding laser devices are still lack of research. Here, since the first publication of lasing in hybrid perovskites in the 1990s, great effort has been made especially in 2014. Halide perovskites have the potential to revolutionize the nanophotonics field due to their solution-processed gain medium, almost defect-free semiconductor formation, high luminous efficiency, flexibility of nanostructure, excellent stability, and wide wavelength tunability. This article highlights the important researches on the optical gain from diverse hybrid halide perovskite material and the future challenges of lasing.

Directly Modulated Tunable Single-Mode Lasers Based on a Coupled Microcavity

In this work, we investigate an alternative directly modulated laser solution with applications to multiwavelength 25 Gb/s systems. The presented solution is based on a hybrid square/rhombus-rectangular laser (HSRRL), which consists of a Fabry–Pérot (FP) cavity and a square/rhombus microcavity (SRM). This structure is implemented and demonstrates single-mode lasing over a wide wavelength tuning range (30.8 nm). Single-mode operation is achieved with a side-mode suppression ratio (SMSR) greater than 30 dB and a linewidth of 10 MHz. Furthermore, with an electrical 3 dB bandwidth of 10 GHz. It is possible to directly modulate at 25 Gb/s with promising performance. These devices are simple and they are expected to meet the cost and power requirements of current networks.