Zhilei Huang

Strong Optomechanical Coupling in Nanobeam Cavities based on Hetero Optomechanical Crystals

A hetero optomechanical crystal nanobeam cavity with high mechanical frequency of 5.88 GHz is proposed. By enhancing the overlap between optical and strain field, an optomechanical coupling rate as high as 1.31 MHz is achieved.

Broadband switching functionality based on defect mode coupling in W2 photonic crystal waveguide

Broadband switching functionality realized by an ultra-compact W2 photonic crystal waveguide (PCW) is demonstrated with an integrated titanium/aluminum microheater on its surface. Due to the enhanced coupling between the defect modes in W2 PCW, switching functionality with bandwidth up to 24 nm is achieved by the PCW with footprint of only 8 μm × 17.6 μm, while the extinction ratio is in excess of 15 dB over the entire bandwidth. Moreover, the switching speed is measured by alternating current modulation. Response time for this thermo-optic switch is 11.0 ± 3.0 μs for rise time and 40.3 ± 5.3 μs for fall time, respectively.

Optomechanical crystal nanobeam cavity with high optomechanical coupling rate

An optomechanical crystal nanobeam cavity, only by increasing the radius of air holes in the defect region, is proposed and optimized for a high optomechanical coupling rate. In our proposed cavity, the photonic and phononic defect modes are simultaneously confined by each corresponding bandgap, and the overlap of the optical and mechanical modes can be improved simply by adjusting the radius of the air holes. Accordingly, an optomechanical coupling rate (g) as high as 1.16 MHz is obtained, which is the highest coupling rate among the reported optomechanical crystal cavities. What’s more, the proposed cavity also exhibits a high mechanical frequency of 4.01 GHz and a small effective mass of 85 fg for the fundamental mechanical mode.

Compact Thermo-Optic Switch Based on Tapered W1 Photonic Crystal Waveguide

A compact thermo-optic switch based on the cutoff effect of slow-light mode of a tapered W1 photonic crystal waveguide (PCW) is demonstrated with an integrated microheater. Due to the low-group-index taper, the coupling loss of the slow-light PCW is reduced, and a high switching extinction ratio (ER) is attained. Moreover, three types of microheaters are evaluated for the power consumptions, heating transfer efficiency, and temperature uniformities, and an optimized slab microheater is utilized. As a result, low switching power of 8.9 mW and high ER of 23.5 dB are achieved experimentally, while the length of W1 PCW is only 16.8 μm.

Photonic Crystal Nanobeam Cavity With Stagger Holes for Ultrafast Directly Modulated Nano-Light-Emitting Diodes

A photonic crystal nanobeam cavity with stagger holes in InP/InGaAsP/InP heterostructure is proposed for ultrafast directly modulated nano-light-emitting diodes (nanoLEDs). With stagger holes, the quality factor <i>Q</i> can be engineered in the range of 10² ~ 10⁴ while keeping a small mode volume (<i>V</i>_eff). As a result, the modulation speed of nanoLEDs can be dramatically improved by a small <i>V</i>_eff to enhanced spontaneous emission (SpE) rate and a moderate <i>Q</i> to counterbalance SpE lifetime and photon lifetime of the cavity. In our simulation, the direct modulation bandwidth could be higher than 60 GHz with optimal <i>Q</i> value of 2150 and <i>V</i>_eff of 2.3( λ₀/2<i>n</i>)³.

High-mechanical-frequency characteristics of optomechanical crystal cavity with coupling waveguide.

Optomechanical crystals have attracted great attention recently for their ability to realize strong photon-phonon interaction in cavity optomechanical systems. By far, the operation of cavity optomechanical systems with high mechanical frequency has to employ tapered fibres or one-sided waveguides with circulators to couple the light into and out of the cavities, which hinders their on-chip applications. Here, we demonstrate larger-centre-hole nanobeam structures with on-chip transmission-coupling waveguide. The measured mechanical frequency is up to 4.47 GHz, with a high mechanical Q-factor of 1.4 × 103 in the ambient environment. The corresponding optomechanical coupling rate is calculated and measured to be 836 kHz and 1.2 MHz, respectively, while the effective mass is estimated to be 136 fg. With the transmission waveguide coupled structure and a small footprint of 3.4 μm2, this simple cavity can be directly used as functional components or integrated with other on-chip devices in future practical applications.

Broadband thermo-optic switch based on a W2 photonic crystal waveguide

Broadband thermo-optic switch based on an ultra-compact W2 photonic crystal waveguide (PCW) is demonstrated with an integrated titanium/aluminum microheater on its surface. The operating principle relies on shifting a transmission-dip caused by the enhanced coupling between the defect modes in W2 PCW. As a result, broadband switching functionality with larger extinction ratio can be attained. Moreover, microheaters with different width are evaluated by the power consumptions and heating transfer efficiency, and an optimized slab microheater is utilized. Finally, switching functionality with bandwidth up to 24 nm (1557~1581 nm) is measured by the PCW with footprint of only 8μm×17.6 μm, while the extinction ratio is in excess of 15 dB over the entire bandwidth. What’s more, the switching speed is obtained by the measurement of alternating current modulation. Response time for this thermo-optic switch is 11.0±3.0 μs for rise time and 40.3±5.3 μs for fall time, respectively.

Demonstration of hetero optomechanical crystal nanobeam cavities with high mechanical frequency

Optomechanical crystal is a combination of both photonic and phononic crystal. It simultaneously confines light and mechanical motion and results in strong photon-phonon interaction, which provides a new approach to deplete phonons and realize on-chip quantum ground state. It is promising for both fundamental science and technological applications, such as mesoscopic quantum mechanics, sensing, transducing, and so on. Here high optomechanical coupling rate and efficiency are crucial, which dependents on the optical-mechanical mode-overlap and the mechanical frequency (phonon frequency), respectively. However, in the conventional optomechanical-crystal based on the same periodical structure, it is very difficult to obtain large optical-mechanical mode-overlap and high phonon frequency simultaneously. We proposed and demonstrated nanobeam cavities based on hetero optomechanical crystals with two types of periodic structure. The optical and mechanical modes can be separately confined by two types of periodic structures. Due to the design flexibility in the hetero structure, the optical field and the strain field can be designed to be concentrated inside the optomechanical cavities and resemble each other with an enhanced overlap, as well as high phonon frequency. A high optomechanical coupling rate of 1.3 MHz and a high phonon frequency of 5.9 GHz are predicted theoretically. The proposed cavities are fabricated as cantilevers on silicon-on-insulator chips. The measurement results indicate that a mechanical frequency as high as 5.66 GHz is obtained in ambient environment, which is the highest frequency demonstrated in one-dimensional optomechanical crystal structure.

Integrated optomechanical crystal cavity

Optomechanical crystals are combinations of photonic and phononic crystals, which simultaneously control optical and acoustic waves with nanoscale periodic structure and form optomechanical systems with high mechanical frequency and lager photon-phonon interaction. We proposed a nanobeam cavity based on hetero optomechanical crystal with two types of periodic structures, where the optical and mechanical modes separately confined by two periodic structures. A mechanical frequency as high as 5.66 GHz was achieved while the working wavelength of the optical cavity was maintained at 1.55 μm. Besides, due to the flexibility introduced by the hetero structure, the optical field and the strain field were designed to be concentrated inside the optomechanical cavities and resemble each other with an enhanced overlap. As a result, the optomechanical coupling rate, which represents the interaction strength between photon and phonon, was as high as 1.31 MHz. Also we proposed and optimized an optomechanical crystal nanobeam cavity, only by increasing the radius of air holes in the defect region, for small effective mass. A very small effective mass of 85 fg was estimated. By far, the on-chip cavity optomechanical systems has to be with the help of tapered fibers or one-sided waveguide with circulator to couple the light into or out. Here we demonstrated larger center-hole nanobeam structures with on-chip transmission waveguide coupling. The mechanical frequency was measured up to 4.47 GHz, with a high mechanical Q-factor of 1.4 × 103 in ambient environment. The corresponding optomechanical coupling rate and the effective mass were estimated to be 836 kHz and 136 fg, respectively. With transmission waveguide coupled structure and small footprint of only 3.4 μm2, this simple cavity can be directly used as functional components and integrated with other on-chip devices in future practical applications.

Design and Fabrication of Optomechanical Crystal Nanobeam Cavity with High Optomechanical Coupling Rate

An optomechanical crystal nanobeam cavity with high optomechanical coupling rate is proposed and fabricated. Only by adjusting the radius of the air holes, the cavity realizes an optomechanical coupling rate as high as 1.24 MHz.