Broadband Optical Modulator Research Articles

Al nanowire-embedded silicon for broadband optical modulation: Forming mechanism and optical performance

In recent decades, silicon has been widely used in light regulation devices, owing to its wideband high refractive index and low dispersion. To meet the increasing demands for various applications, optical modulation techniques appear of great potential to enhance the optical performance of Si-based devices. However, challenges still remain in achieving precise control over the band structure and resonance modes without introducing complex artificial structures. In this study, a composite film composed of silicon embedded with high fraction aluminum nanowires was developed by magnetron sputtering. It was revealed that the formation of aluminum nanowires was attributed to the spontaneous phase separation between silicon and aluminum, which was strongly dependent on the filling fraction and surface diffusion length of the aluminum during the co-sputtering process. The composite microstructure was precisely regulated by manipulating adatom diffusion and reevaporation through ion bombardment, thereby modifying its broadband optical properties. Moreover, exceptional electromagnetic properties were achieved by incorporating aluminum nanowires into silicon, as evidenced by the metallic behaviors in the short-wavelength regime and dielectric properties in the infrared spectrum range.

Highly stable pulsed fiber laser generation modulated by chromium iodide film

Abstract Highly stable pulsed fiber lasers are key optical components in optical communication, optical sensing, and precision micromachining systems due to the high beam quality, high peak power, and compact configurations. However, the available optical modulators in the fiber laser suffer from the operation bandwidth limitations and poor long-term physicochemical stability. Here, we have investigated the broadband nonlinear optical absorption behavior of the chromium iodide (CrI3) film, which exhibits broadband saturable absorption towards the mid-infrared regime and excellent long-term stability. The conventional soliton fiber laser operating at telecom wavelength has been obtained from an Er3+-doped fiber laser (EDFL) utilizing CrI3 film with a signal-to-noise ratio (SNR) of 92.4 dB and a pulse width of 492 fs. In addition, a passively Q-switched operation around 2.8 μm has also been obtained from an Er3+-doped ZBLAN fiber laser (EDZFL) modulated by the CrI3 film with a SNR of 46.8 dB and a pulse width of 766 ns. The demonstration shows that the CrI3 film exhibits robust broadband optical modulation, and may make inroads for developing highly stable ultrafast optoelectronic devices.

Symmetrical dual-sideband oppositely chirped differential FMCW LiDAR.

A differential FMCW LiDAR for high-precision distance measurements of remote non-stationary targets is proposed and demonstrated experimentally. The required positive and negative symmetrically oppositely chirped laser beams are generated synchronously through a fixed-frequency laser by employing externally unified broadband optical phase modulation and symmetrical dual-sideband optical filtering. After coaxial transmission and reception, orthogonally polarized optical beat signals containing target distance and vector velocity data are de-chirped separately by optical in-phase and quadrature demodulations and then synchronously received by four-channel photoelectric balance detectors. After differential processing of the received beat signals and a fast Fourier transform, it is possible to implement real-time simultaneous range and vector velocity measurements. The inherent symmetrically oppositely chirped optical frequency make it possible to measure the target distance immune to the internal random phase noise introduced by the spectral linewidth of the frequency-swept laser and the external random phase noise introduced by atmospheric turbulence, speckle, and vibration. Meanwhile, the measurement of the target velocity is immune to the nonlinearity of the frequency-swept laser. These results encourage an approach to overcome the barriers of coherence length, nonlinearity, and external noise, and implement simultaneous real-time ranging and velocimetry of long-range, rapid-moving targets.

GHz Compact Laser Enabled by GaSb Nanowires as Saturable Absorbers

Owing to the narrow bandgap and excellent optoelectronic properties, III‐Sb nanowires (NWs) enable efficient optical response from near‐infrared to mid‐infrared, making them ideal candidates for broadband optical modulation. Herein, high‐purity GaSb NWs with controlled density are prepared on the transparent substrates of glasses. The phase purity and crystallinity of as‐prepared GaSb NWs are verified by X‐ray diffraction. Z‐scan and I‐scan techniques are adopted to investigate the nonlinear optical modulation properties, displaying a high modulation depth of 40% (at 1 μm wavelength) for the GaSb NWs with growth time of 30 min. Furthermore, the as‐prepared GaSb NWs are used as the saturable absorber elements in a waveguide laser cavity, demonstrating efficient Q‐switched mode‐locked lasers with a repetition rate of 8.2 GHz and a pulse duration of 31 ps (operating at 1 μm wavelength). All results show the great potential of GaSb NWs for the ultrafast laser and nonlinear optical applications.

Monolithic Saturable Absorber with Gallium Arsenide Nanowires Integrated on the Flexible Substrate for Optical Pulse Generation.

In this work, we demonstrated a kind of flexibly monolithic saturable absorber (SA) with GaAs nanowires (NWs) on polyimide (PI) plastic substrate for broadband optical modulation at 1.0 and 1.5 µm, separately. The monolithic SA sample was prepared by the metalorganic vapor phase epitaxy (MOVPE) method. The crystal structure and element analysis were examined carefully by high-resolution scanning transmission electron microscopy (HRSTEM) and energy-dispersive X-ray spectroscopy (EDX). We observed a high-density distribution of NWs on the flexible substrate by scanning electron microscopy (SEM). In addition, linear and nonlinear optical properties of the sample were examined by testing the photoluminescence and absorption properties, which showed its potential application as an optical switch due to the pure semiconducting properties. After the characterizations, we experimentally demonstrated this monolithic SA for laser modulation at 1.0 and 1.5 µm, which yielded the minimum optical pulse widths of 1.531 and 6.232 µs, respectively. Our work demonstrated such a kind of monolithic flexible NW substrate-integrated device used for broadband optical modulation, which not only eased the integration process of NWs onto the fiber endface, but also proved the potential of easily integrating with more semiconducting nanomaterials (e.g., graphene, MoS2, …) to realize monolithic active flexible photonic systems, such as a microscale phase modulator, delay-line, and so on, paving an easy avenue for the development of both active and flexible photonic devices.

2D Nb<sub>2</sub>CT<sub><i>x</i></sub> MXene/MoS<sub>2</sub> heterostructure construction for nonlinear optical absorption modulation

Two-dimensional (2D) nonlinear optical mediums with high and tunable light modulation capability can significantly stimulate the development of ultrathin, compact, and integrated optoelectronics devices and photonic elements. 2D carbides and nitrides of transition metals (MXenes) are a new class of 2D materials with excellent intrinsic and strong light-matter interaction characteristics. However, the current understanding of their photo-physical properties and strategies for improving optical performance is insufficient. To address this issue, we rationally designed and <italic>in situ</italic> synthesized a 2D Nb₂C/MoS₂ heterostructure that outperforms pristine Nb₂C in both linear and nonlinear optical performance. Excellent agreement between experimental and theoretical results demonstrated that the Nb₂C/MoS₂ inherited the preponderance of Nb₂C and MoS₂ in absorption at different wavelengths, resulting in the broadband enhanced optical absorption characteristics. In addition to linear optical modulation, we also achieved stronger near infrared nonlinear optical modulation, with a nonlinear absorption coefficient of Nb₂C/MoS₂ being more than two times that of the pristine Nb₂C. These results were supported by the band alinement model which was determined by the X-ray photoelectron spectroscopy (XPS) experiment and first-principal theory calculation. The presented facile synthesis approach and robust light modulation strategy pave the way for broadband optoelectronic devices and optical modulators.

MIL-68(Al) and MIL-68(Fe) as broadband optical modulators for Q-switching fiber lasers operating at 2 and 2.9 μm

We investigated 2 and 2.9 μm mid-infrared fiber lasers passively Q-switched by MIL-68(Al) and MIL-68(Fe), which were fabricated via the hydrothermal method. The modulation depth of MIL-68(Al) was found to be 9.12% at 1.99 μm. And the modulation depths of MIL-68(Fe) were found to be 18.89% and 15.79% at 1.99 μm and 2.87 μm, respectively. We report Q-switching pulse generation in both Tm3+-doped and Ho3+/Pr3+ co-doped fiber lasers by using the as-prepared MIL-68 (M, M = Al3+, Fe3+) as SAs. The center wavelengths were at 1.99 μm and 2.87 μm, respectively. These results indicate that MIL-68(M) has wideband nonlinear optical properties and promising application prospects in the field of optical modulators at 2- and 2.9-μm mid-infrared waveband. Work clearly accessible to a broad readership.

Sea‐Urchin‐MnO2 for Broadband Optical Modulator

AbstractManganese dioxide (MnO2) is considered to be one of the nanomaterials with enormous value in research and application because of its high theoretical specific capacitance, large specific surface area and porosity, excellent electron transfer ability, and excellent light absorption ability. However, exploring superior nonlinear absorption of MnO2 in the broadband spectrum is still the key challenge to harvesting their greatest potential. In this paper, the optical modulator based on MnO2 is fabricated, and its nonlinear optical performance is measured. The results indicate that the modulation depth is 4.4% and the saturable intensity is 32.8 MW cm−2 at 1.5 µm region. What's more fascinating is that the modulator based on MnO2 is integrated into Er‐doped and Tm‐doped fiber resonators to successfully demonstrate its broadband mode‐locking operations. The coexistence of harmonic bound state pulse and conventional soliton pulse, as well as dual‐wavelength solitons, have been obtained in a communication window and conventional soliton in a 2 µm‐band can be also achieved. This demonstrates that MnO2 serves as a broadband optical modulator, which makes MnO2 more competitive in the future ultrafast photonics and helps to expand the frontier of photonic technology.

Broadband 1T-polytype tantalum disulfide saturable absorber for solid-state bulk lasers

1T-polytype tantalum disulfide ( 1 T-TaS 2 ), an emerging strongly correlated material, features a narrow bandgap of 0.2 eV, bridging the gap between zero-bandgap graphene and large-bandgap 2D nonlinear optical (NLO) materials. Combined with its intense light absorption, high carrier concentration, and high mobility, 1 T-TaS 2 shows considerable potential for applications in broadband optoelectronic devices. However, its NLO characteristics and related applications have rarely been explored. Here, 1 T-TaS 2 nanosheets are prepared by chemical vapor deposition. The ultrafast carrier dynamics in the 400–1100 nm range and broadband NLO performance in the 515–2500 nm range are systematically studied using femtosecond lasers. An obvious saturable absorption phenomenon is observed in the visible to IR range. The nonlinear absorption coefficient is measured to be − 22.60 ± 0.52 cm MW − 1 under 1030 nm, which is larger than that of other typical 2D saturable absorber (SA) materials (graphene, black phosphorus, and MoS 2 ) under similar experimental conditions. Based on these findings, using 1 T-TaS 2 as a new SA, passively Q-switched laser operations are successfully performed at 1.06, 1.34, and 1.94 μm. The results highlight the promise of 1 T-TaS 2 for broadband optical modulators and provide a potential candidate material system for mid-IR nonlinear optical applications.

Demonstration of Tunable Fano Resonances in a Meta-material Absorber Composed of Asymmetric Double Bars with Bent Arms

In this paper, a metal–insulator-metal (MIM) plasmonic absorber consisting of asymmetric double bars with bent arms located on top of a silica layer coated on a metal film is proposed, and its resonant features are analyzed. The suggested structure supports both Fano and dipole perfect absorption resonances at the near-infrared region (NIR). The asymmetry introduced into the structure can be induced by changing the bending angle or rotation angle of one of the antennas, while the other one remains fixed. Simulation results demonstrate that by applying both asymmetry factors to the structure, one can have two individual Fano peaks at the same time. It is shown that the magnitude, central wavelength, and line width of the Fano peaks are adjustable by controlling the geometrical parameters of the structure. It is also indicated that the quality factor (Q-factor) of the Fano resonance is inversely related to the degree of asymmetry introduced into the structure. According to the simulations, an ultra-narrow resonance peak with a bandwidth of 1.87 nm at the wavelength of 710 nm (corresponding to a Q-factor of 387) can be obtained by controlling the geometrical parameters. It is also discussed that the absorptivity of Fano and the dipole peaks can be adjusted inversely, by manipulating the grapheme chemical potential. The ratio of the absorptivity to the chemical potential of graphene about 275%/eV and 226%/eV is calculated for the Fano peak and dipole peak, respectively. Accordingly, the presented structure is an adjustable NIR absorber with a fully tunable absorption spectrum which can be utilized in various applications from tunable reflectors and photo-detectors to ultra-narrowband and broadband optical modulators.

A broadband optical modulator based on rib-type silicon waveguide including graphene and h-BN layers

The rapid growth of THz communication systems needed a high data transfer rate in the broadband communication range. Increasing the amount of modulation depth increases the amount of transmission and, as a result, increases the transmitted data. In this paper, a broadband optical modulator based on rib-type silicon waveguides, including graphene and h-BN layers, is designed. In this proposed structure, Hexagonal Boron Nitride (h-BN) layers are embedded between graphene layers. This structure contains a rib-type Si waveguide and operates for the broadband wavelength from 1300 nm to 1800 nm. The maximum modulation depth is 2.23 dB/µm with 2.23 dB/µm loss at 1800 nm. We achieved a high figure of merit as high as 1.3. The modulation depth at 1550 nm is 1.13 dB/µm with 1.1 dB/µm loss. The proposed modulator has a 669 GHz modulation bandwidth.

Surface functionalization of Ta4C3 MXene for broadband ultrafast photonics in the near-infrared region

Recently, MXene has set off a great research boom in the optoelectronic field benefiting from its strong conductivity, eminent broadband absorption, and tailorable electronic/optical properties. In this paper, two-dimensional tantalum carbide (Ta4C3) MXene nanosheets were successfully synthesized based on a two-step liquid exfoliation strategy. Firstly, the role of surface termination with different adsorption structures on the electronic and diverse optical properties of Ta4C3Tx MXene were firstly investigated theoretically via first-principles with density functional theory. Interestingly, the simulation revealed that the oxidized and hydroxylated Ta4C3 MXene featured significantly enhanced optical absorption properties in the near-infrared (NIR) band compared with the pristine bare Ta4C3 nanosheets. Besides, the third-order nonlinear optical (NLO) characteristics of the surfaced terminated Ta4C3 nanosheets were measured by the typical Z-scan techniques at 1 μm. The maximum effective nonlinear absorption coefficient was determined to be -0.78 cm/GW, indicating the great potential as a nonlinear material in NIR band. The nonlinear refractive index, real and imaginary parts of the third-order NLO susceptibility were also obtained. Furthermore, the endowment as an excellent broadband optical modulator was strongly acknowledged utilizing Ta4C3 MXene as saturable absorbers for NIR mode-locking operation at 1044 nm and 1557 nm, respectively. Both highly stable dissipative soliton and traditional soliton pulses were generated. Our results demonstrated the excellent broadband nonlinear absorption in NIR regime of terminal functionalized Ta4C3 MXene and might open a new avenue to the Ta4C3-based advanced ultrafast photonic devices.

Broadband Optical Phase Modulation by Colloidal CdSe Quantum Wells.

Two-dimensional (2D) semiconductors are primed to realize a variety of photonic devices that rely on the transient properties of photogenerated charges, yet little is known on the change of the refractive index. The associated optical phase changes can be beneficial or undesired depending on the application, but require proper quantification. Measuring optical phase modulation of dilute 2D materials is, however, not trivial with common methods. Here, we demonstrate that 2D colloidal CdSe quantum wells, a useful model system, can modulate the phase of light across a broad spectrum using a femtosecond interferometry method. Next, we develop a toolbox to calculate the time-dependent refractive index of colloidal 2D materials from widely available transient absorption experiments using a modified effective medium algorithm. Our results show that the excitonic features of 2D materials result in broadband, ultrafast, and sizable phase modulation, even extending to the near infrared because of intraband transitions.

Materials for emergent silicon-integrated optical computing.

Progress in computing architectures is approaching a paradigm shift: traditional computing based on digital complementary metal-oxide semiconductor technology is nearing physical limits in terms of miniaturization, speed, and, especially, power consumption. Consequently, alternative approaches are under investigation. One of the most promising is based on a "brain-like" or neuromorphic computation scheme. Another approach is quantum computing using photons. Both of these approaches can be realized using silicon photonics, and at the heart of both technologies is an efficient, ultra-low power broad band optical modulator. As silicon modulators suffer from relatively high power consumption, materials other than silicon itself have to be considered for the modulator. In this Perspective, we present our view on such materials. We focus on oxides showing a strong linear electro-optic effect that can also be integrated with Si, thus capitalizing on new materials to enable the devices and circuit architectures that exploit shifting computational machine learning paradigms, while leveraging current manufacturing infrastructure. This is expected to result in a new generation of computers that consume less power and possess a larger bandwidth.

Numerical Analyze of a Broadband Optical Modulator Based on Bilayer Graphene and h-BN in the Wavelength range of 1300 to 1800 nm with High Extinction Ratio

Numerical Analyze of a Broadband Optical Modulator Based on Bilayer Graphene and h-BN in the Wavelength range of 1300 to 1800 nm with High Extinction Ratio

Broadband few-layer niobium carbide MXene as saturable absorber for solid-state lasers

Recently, niobium-carbide (Nb2C) nanosheets, a member of MXene family, have gained significant attention because of their unique physical and chemical properties. Here, the few-layer Nb2C nanosheets were synthesized by a combination of selective etching and liquid cascade centrifugation. The broadband absorption properties of the few-layer Nb2C nanosheets were systematically investigated by the open-aperture Z-scan technique. The results indicate the excellent saturable absorption responses of Nb2C nanosheets, revealing the promising optical modulate application of Nb2C in solid-state lasers. Using the Nb2C saturable absorber (SA), passively Q-switched solid-state lasers from visible to near-infrared range were realized, which presented a promising alternative for a broadband optical modulator. Furthermore, a passively mode-locked laser at 1.06 μm was successfully achieved based on the Nb2C SA. A pulse duration of 13.5 ps was produced with the maximum average output power of 426 mW and a repetition rate of 99.1 MHz. To the best of our knowledge, this is the first time to use Nb2C nanosheets as a broadband SA for the solid-state lasers. The results may promote further applications of 2D optoelectronic materials from visible to near-infrared range.

Small footprint symmetrical graphene hybrid plasmonic waveguides for high-speed broadband optical modulation

In this work, nanowire-based symmetrical graphene hybrid plasmonic waveguides for possible broadband optical modulation have been proposed. The full-vectorial finite element method has been employed to analyze the modal properties and modulation characteristics of the proposed structures. The fundamental supermode supported by these geometries is evolved from a near-field coupling between metallic and dielectric nanowires. Here, the strong optical capacitance effect in the low-index dielectric gap region has been exploited to enhance light–graphene interaction in the subwavelength device size. Thus, the optical absorption of graphene significantly increases. Therefore, the structures even with their small footprints offer a very high extinction ratio and small energy consumption per bit (as low as 0.9 fJ/bit), simultaneously with appreciably high modulation bandwidth at the telecommunication wavelength. A substantially small variation of modulation performance for a broad range of operation wavelength and gap widths suggest their broadband operability. Furthermore, the modulation performance has been studied incorporating the optical anisotropy of graphene. Thus, the proposed waveguides show a good promise in high-speed broadband optical modulation.

Hybrid broadband optical modulator based on multi-layer graphene structure and silver nano-ribbons

In this paper, a broadband optical modulator based on plasmonic hybrid structures has been investigated that shows good performance in the wavelength range of 1300 to 1800 nm. The proposed modulator consists of Multi-layer graphene with two silver nano-ribbons and an h-BN dielectric layer embedded between the graphene layers. The presence of silver nano-ribbons has created a waveguide in the mid-structure. Our results show that strong coupling of surface plasmon polaritons to this waveguide increases the light interaction with graphene, improves the subwavelength confinement, and ultimately enhances the modulation effects of this proposed modulator. The proposed modulator shows a modulation depth of 17.55 dB/μm with a loss of 1.47 dB/μm at wavelength of 1.55 μm.

All-optical modulation with 2D layered materials: status and prospects

Abstract Optical modulation technique plays a crucial role in photonics technologies, and there is an ever-increasing demand for broadband and ultrafast optical modulation in the era of artificial intelligence. All-optical modulation is known to be able to operate in an ultrafast way and has a broadband response, showing great potential in applications for ultrafast information processing and photonic computing. Two-dimensional (2D) materials with exotic optoelectronic properties bring tremendous new opportunities for all-optical modulators with excellent performance, which have attracted lots of attention recently. In this review, we cover the state-of-art all-optical modulation based on 2D materials, including graphene, transitional metal dichalcogenides, phosphorus, and other novel 2D materials. We present the operations mechanism of different types of all-optical modulators with various configurations, such as fiber-integrated and free-space ones. We also discuss the challenges and opportunities faced by all-optical modulation, as well as offer some future perspectives for the development of all-optical modulation based on 2D materials.

Broadband optical modulation in a zinc-oxide-based heterojunction via optical lifting

Broadband electro-absorptive optical modulation in a zinc-oxide (ZnO)-based heterojunction is demonstrated. The presence of high-density two-dimensional electron gas (2DEG) at the bottom of conduction band offset in a MgZnO-CdZnO heterojunction is shown to exhibit electrically tunable optical absorption in the regions well below the material bandgap. Electrons confined near the heterojunction are lifted across the potential barrier on optical excitation. Optical modulation with an extinction ratio of 8 dB is reported at an operating wavelength of 527 nm. The extinction ratio remains around 7–8 dB over a wide bandwidth of 115 nm, providing an excellent opportunity to explore ZnO-based heterojunctions to realize a broadband optical modulator for applications in optical communication and interconnects.