Mohammed Alaloul

On-chip integration of mid-wave infrared (MWIR) absorption spectroscopy gas sensors is a powerful approach to mass-producing compact and inexpensive devices and systems. Moreover, this approach opens new horizons for sophisticated applications in environmental monitoring, quality control, and internet-of-things networks. Nonetheless, further development of integrated photonic devices that can operate at the MWIR band is essential. Towards that end, we propose an MWIR graphene photodetector that is integrated into silicon-on-sapphire (SOS) slot waveguides for on-chip absorption spectroscopy applications. This configuration boosts the electric field distribution of the guided mode, which enhances the effective absorption of graphene. In addition, the presence of the guided mode in the slotted air region permits significant interaction with the analyte gas, which is a significant advantage for absorption spectroscopy. The sensing performance of the device is quantified by investigating its minimum detectable concentration of the three most prevalent greenhouse gases in the United States: carbon dioxide (CO ₂ ), methane (CH ₄ ), and nitrous oxide (N ₂ O). Numerical results reveal that sub-ppb detection of these gases is achievable at the chip scale. These promising findings pave the way for the emergence of novel designs of portable, inexpensive, and highly sensitive sensors that are integrated into miniaturized electronic-photonic chipsets.

The ultrafast response and broadband absorption of all-optical graphene switches are highly desirable features for on-chip photonic switching. However, because graphene is an atomically thin material, its absorption of guided optical modes is relatively low, resulting in high saturation thresholds and switching energies for these devices. To boost the absorption of graphene, we present a practical design of an electrically-biased all-optical graphene switch that is integrated into silicon slot waveguides, which strongly confine the optical mode in the slotted region and enhance its interaction with graphene. Moreover, the design incorporates a silicon slab layer and a hafnia dielectric layer to electrically tune the saturation threshold and the switching energy of the device by applying direct-current voltages of < 0.5 V. Using this device, a high extinction ratio of 10.3 dB, a low insertion loss of < 0.7 dB, and an ultra-efficient switching energy of 79 fJ/bit at 0.23 V bias are attainable for a 40 µ m long switch. The reported performance metrics for this device are highly promising and are expected to serve the needs of next-generation photonic computing systems.

Monolayer transition metal dichalcogenides (TMDCs), like MoS₂, MoSe₂, WS₂, and WSe₂, feature direct bandgaps, strong spin–orbit coupling, and exciton–polariton interactions at the atomic scale, which could be harnessed for efficient light emission, valleytronics, and polaritonic lasing, respectively. Nevertheless, to build next-generation photonic devices that make use of these features, it is first essential to model the all-optical control mechanisms in TMDCs. Herein, a simple model is proposed to quantify the performance of a 35- μ m-long Si₃N₄ waveguide-integrated all-optical MoSe₂ modulator. Using this model, a switching energy of 14.6 pJ is obtained for a transverse-magnetic (TM) and transverse-electric (TE) polarized pump signals at λ = 480 nm. Moreover, maximal extinction ratios of 20.6 dB and 20.1 dB are achieved for a TM and TE polarized probe signal, respectively, at λ = 500 nm with an ultra-low insertion loss of <0.3 dB. Moreover, the device operates with an ultrafast recovery time of 50 ps, while maintaining a high extinction ratio for practical applications. These findings facilitate modeling and designing novel TMDC-based photonic devices.

Graphene has emerged as an ultrafast photonic material for on-chip all-optical modulation. However, its atomic thickness limits its interaction with guided optical modes, which results in a high switching energy per bit or low modulation efficiencies. Nonetheless, it is possible to enhance the interaction of guided light with graphene by nanophotonic means. Herein, we present a practical design of an all-optical modulator that is based on graphene and hexagonal boron nitride (hBN) heterostructures that are hybrid integrated into silicon slot waveguides. Using this device, a high extinction ratio (ER) of 7.3 $\,$ dB, an ultra-low insertion loss (IL) of $< 0.6\,$ dB, and energy-efficient switching ( $< 0.33\,$ pJ/bit) are attainable for a 20 $\mu$ m long modulator with double layer graphene. In addition, the device performs ultrafast switching with a recovery time of $< 600\,$ fs, and could potentially be employed as a high-performance all-optical modulator with an ultra-high bandwidth in the hundreds of GHz. Moreover, the modulation efficiency of the device is further enhanced by stacking additional layers of graphene-hBN heterostructures, while theoretically maintaining an ultrafast response. The proposed device exhibits highly promising performance metrics, which are expected to serve the needs of next-generation photonic computing systems.

Graphene has emerged as an ultrafast photonic material for on-chip all-optical switching applications. However, its atomic thickness limits its interaction with guided optical modes, resulting in a high switching energy per bit. Herein, we propose a novel technique to electrically control the switching energy of an all-optical graphene switch on a silicon nitride waveguide. Using this technique, we theoretically demonstrate a 120 µm long all-optical graphene switch with an 8.9 dB extinction ratio, 2.4 dB insertion loss, a switching time of ∼ 16 × . This technique paves the way for the emergence of ultra-efficient all-optical graphene switches that will meet the energy demands of next-generation photonic computing systems, and it is a promising alternative to lossy plasmon-enhanced devices.

Graphene has emerged as an ultrafast photonic material for on-chip photodetection. However, its atomic thickness limits its interaction with guided optical modes, which in turn weakens the photoresponse of waveguide-integrated graphene photodetectors. Nonetheless, it is possible to enhance the interaction of guided light with graphene by nanophotonic means. Herein, we propose a practical design of a plasmon-enhanced photovoltaic double-graphene detector that is integrated into 5 $\mu$ m long titanium nitride slot waveguides. The use of double-graphene in this configuration yields a high responsivity of 2.18 A/W and more for a 0.5 V bias, across the telecom C-band and beyond. Moreover, the device operates at an ultra-high-speed beyond 100 GHz with an ultra-low noise equivalent power of $<\!35\,$ pW/ $\sqrt{\text{Hz}}$ . The reported features are highly promising and are expected to serve the needs of next-generation optical interconnects.

Graphene has emerged as an ultrafast optoelectronic material for on-chip photodetector applications. The 2D nature of graphene enables its facile integration with complementary metal–oxide semiconductor (CMOS) microelectronics and silicon photonics, yet graphene absorbs only ∼ 2.3 % of light. Plasmonic metals can enhance the responsivity of graphene photodetectors, but may result in CMOS-incompatible devices, depending on the choice of metal. Here we propose a plasmon-enhanced photothermoelectric graphene detector using CMOS-compatible titanium nitride on the silicon-on-insulator platform. The device performance is quantified by its responsivity, operation speed, and noise equivalent power. Its bandwidth exceeds 100 GHz, and it exhibits a nearly flat photoresponse across the telecom C-band. The photodetector responsivity is as high as 1.4 A/W (1.1 A/W external) at an ultra-compact length of 3.5 µm, which is the most compact footprint reported for a graphene-based waveguide photodetector. Furthermore, it operates at zero-bias, consumes zero energy, and has an ultra-low intrinsic noise equivalent power ( N E P < 20 p W / H z ).