Ultra-broad bandwidth array waveguide grating for high-speed backbone network transmission.

With the rapid development of the backbone network rates, there has been a gradual increase in channel spacing and bandwidth. The C&L band ultra-broad bandwidth array waveguide gratings (AWG) of 60-channel 100 GHz channel spacing are designed and fabricated based on silica waveguide. A new parabolic design is used to achieve ultra-broad bandwidth and good spectrum. For the C band ultra-broad bandwidth AWG, the peak insertion loss, uniformity, 0.5 dB bandwidth, 1 dB bandwidth and 3 dB bandwidth are 2.98 dB, 0.36 dB, 0.614 nm, 0.721 nm and 0.937 nm, respectively. For the L band ultra-broad bandwidth AWG, the peak insertion loss, uniformity, 0.5 dB bandwidth, 1 dB bandwidth and 3 dB bandwidth are 2.91 dB, 0.27 dB, 0.560 nm, 0.665 nm and 0.879 nm, respectively. To ensure ultra-broad bandwidth AWG operation at different temperatures, a temperature control circuit is integrated into the packaging design. It has been observed that the performances remain virtually unchanged within the temperature range of -15 to 65 degree. The ultra-broadband AWGs have been successfully tested to transmit 96 Gbaud signals and can be applied to 600 G/800 G backbone network transmission. By using the C&L ultra-broad bandwidth AWGs of 60-channel 100 GHz channel spacing, the total transmission speed over a single-mode fiber can reach 72Tbps/96Tbps.

Femtosecond laser inscribed chirped fiber Bragg gratings.

In this work, a method is proposed and demonstrated for fabrication of chirped fiber Bragg gratings (CFBGs) in single-mode fiber by femtosecond laser point-by-point inscription. CFBGs with bandwidths from 2 to 12 nm and dispersion ranges from 14.2 to 85 ps/nm are designed and achieved. The sensitivities of temperature and strain are 14.91 pm/°C and 1.21pm/µÎµ, respectively. Compared to the present phase mask method, femtosecond laser point-by-point inscription technology has the advantage of manufacturing CFBGs with different parameter flexibilities, and is expected to be widely applied in the future.

Variable optical attenuators based on SOI with 3 µm top silicon layer.

In this paper, electro-absorption variable optical attenuators (VOAs) have been designed and fabricated on silicon-on-insulator material with a 3 µm thick top silicon layer. We have simulated the impact of doping distance, doping width, doping depth, doping concentration, and doping length on VOA's power consumption at 20 dB attenuation. We have found that the power consumption of VOA at 20 dB attenuation will decrease as the doping distance and doping width get smaller, while the doping depth and doping concentration get larger. We have further demonstrated that the power consumption can also be reduced by increasing the doping length and by taking a series structure theoretically. In this paper, VOAs with different doping structures, doping distances, doping widths, and doping lengths have been fabricated, and the tested results have verified our theoretical analysis. With doping distance of 8 µm, doping width of 15 µm, doping length of 1 cm, doping concentration of 1×1019 cm-3, and doping depth of 0.9 µm, the power consumption of the series VOA at 20 dB attenuation is 470 mW, and the rising/falling time is 54 ns/49.5 ns.

Optimization of the classical interference visibility of an asymmetric Mach-Zehnder interferometer based on planar lightwave circuit technology.

Silicon-based devices offer great potential for quantum key distribution (QKD) with the benefits of miniaturization, scalability, complexity, and improved performance. Based on the planar lightwave circuit technology, a 200 ps delay-time asymmetric Mach-Zehnder interferometer (AMZI) decoding chip was designed and fabricated that can adjust the power ratio of the two arms by introducing a variable beam splitter. The measured delay time is approximately 200 ps, and the two output pulses' peaks can be balanced by loading an appropriate voltage on the variable beam splitter. The classical interference visibility of the AMZI versus temperature was studied, and it is highly temperature dependent. The interference visibility can reach as high as 99.72% under appropriate temperature control. This AMZI can act as a passive decoder in fiber-based QKD systems.

Polymer/silica hybrid integration add-drop filter based on grating-assisted contradirectional coupler.

A polymer/silica hybrid integration add-drop filter based on a grating-assisted contradirectional coupler fabricated through simple and low-cost contact lithography is proposed. First, the structure pattern of the add-drop filter was formed in the lower silica cladding by contact lithography and inductively coupled plasma (ICP) etching. Then an SU-8 film was fabricated on top of it by a spin-coating method, and an inverted-rib waveguide structure was formed. Next, the slab layer of the inverted-rib waveguide was removed by ICP etching. We observe a rejection band with an extinction ratio of 13 dB and a 3 dB bandwidth of 0.6 nm at a wavelength of 1509.4 nm from the through port, and a passband with a side-mode suppression ratio of 12 dB and a 3 dB bandwidth of 0.5 nm at a wavelength of 1509.4 nm from the drop port. The shift of the passband with a temperature over the range of 25-55°C is approximately 4.8 nm. This temperature dependence exhibits an average slope of -0.16 nm/°C.

Polymer/silica hybrid integration waveguide Bragg grating based on surface plasmon polaritons.

We proposed a device composed of a Bragg grating and a long-range surface plasmon polariton waveguide. The waveguide is formed by embedding a thin Au stripe in negative UV photoresist (SU-8 2005). The corrugated grating structure is created on a silica substrate using contact lithography and inductively coupled plasma etching, which is transferred onto the SU-8 2005 film by a spin coating process, producing a periodic modulation of refractive index along the waveguide. We achieve a transmission peak with an extinction ratio of 17 dB and a 3-dB bandwidth of 0.9 nm at a wavelength of 1575.2 nm. We achieve a reflection peak with a side-mode suppression ratio of 9.7 dB, a 3-dB bandwidth of 0.9 nm at a wavelength of 1575.2 nm when the heating electrode isn't working. The shift of the reflection peak with heating power over the range 0-6 mW is approximately 2.9 nm. This thermal dependence exhibits an average slope of -0.48 nm/mW.

Polymer thermal optical switch for a flexible photonic circuit.

Flexible and wearable optoelectronic devices are the new trend for an active lifestyle. These devices are polymer-based for flexibility. We demonstrated flexible polymer waveguide optical switches for a flexible photonic integrated circuit. The optical switches are composed of a single-mode inverted waveguide with dimensions of 5 µm waveguide width, 3 µm ridge height, and 3 µm slab height. A Mach-Zehnder structure was used in the device, with the Y-branch horizontal length of 0.1 cm, the distance between two heating branches of 30 µm, and the heating branch length of 1 cm. The optical field of the device was simulated by beam propagation to optimize the electrode position. The switching properties of the flexible optical switch with different working conditions, such as contact to the polymer, silicon, and skin, were simulated. The device was prepared based on the photo curved polymer and lithography method. The end faces of the flexible film device were processed using an excimer laser with optimized parameters of 28 mJ/cm2 and 15 Hz. The response rise time and fall time on the PMMA substrate were measured as 1.98 ms and 2.71 ms, respectively. The power consumption was 16 mW and the extinction ratio was 11 dB. The response rise and fall times on the Si substrate were measured as 1.08 ms and 1.62 ms, respectively. The power consumption was 17 mW and the extinction ratio was 11 dB. The demonstrated properties indicate that this flexible optical waveguide structure can be used in the light control area of a wearable device.

Optimized design and fabrication of polymer/silica thermo-optic switch with low power consumption.

In this paper, the power-consumption characteristics of a polymeric thermo-optic (TO) switch consisting of a silica under-cladding on silicon substrate, a polymer core surrounded with polymer upper-cladding, and aluminum heating electrodes with different widths were investigated. Norland optical adhesive 73 with a larger TO coefficient was selected as the core layer, which could reduce the power consumption effectively. The silica under-cladding, with large thermal conductivity, could shorten the response time. The influences of the heating electrode width and the air trench structure on the power consumption of the device were systemically studied. A device with different widths of electrodes was fabricated by using conventional semiconductor fabrication techniques and measured with the planar optical waveguide testing system. Under 1550-nm wavelength, the power consumption of the device would be reduced from 23.27 to 4.35 mW, while the heating electrode width was decreased from 25 to 7 µm. Furthermore, it would be reduced to 1.7 mW after the air trench structure was employed. The switching time of the device was also measured, which was about 200 µs.

Polymer/Silica Hybrid Waveguide Thermo-Optic VOA Covering O-Band.

In this paper, a polymer/silica hybrid waveguide thermo-optic variable optical attenuator (VOA), covering the O-band, is demonstrated. The switch is fabricated by simple and low-cost direct ultraviolet (UV) lithography. The multimode interferences (MMIs) used in the Mach-Zehnder interferometer (MZI)-VOA are well optimized to realize low loss and large bandwidth. The VOA shows an extinction ratio (ER) of 18.64 dB at 1310 nm, with a power consumption of 8.72 mW. The attenuation is larger than 6.99 dB over the O-band. The rise and fall time of the VOA are 184 µs and 180 µs, respectively.

Three-Dimensional Polymer Variable Optical Attenuator Based on Vertical Multimode Interference with Graphene Heater.

Low-power-consumption optical devices are crucial for large-scale photonic integrated circuits (PICs). In this paper, a three-dimensional (3D) polymer variable optical attenuator (VOA) is proposed. For monolithic integration of silica and polymer-based planar lightwave circuits (PLCs), the vertical VOA is inserted between silica-based waveguides. Optical and thermal analyses are performed through the beam propagation method (BPM) and finite-element method (FEM), respectively. A compact size of 3092 µm × 4 µm × 7 µm is achieved with a vertical multimode interference (MMI) structure. The proposed VOA shows an insertion loss (IL) of 0.58 dB and an extinction ratio (ER) of 21.18 dB. Replacing the graphene heater with an aluminum (Al) electrode, the power consumption is decreased from 29.90 mW to 21.25 mW. The rise and fall time are improved to 353.85 µs and 192.87 µs, respectively. The compact and high-performance VOA shows great potential for a variety of applications, including optical communications, integrated optics, and optical interconnections.

Plasmon coupling nanorice trimer for ultrahigh enhancement of hyper-Raman scattering.

A new tactic that using Ag nanorice trimer as surface-enhanced hyper Raman scattering substrate is proposed for realizing maximum signal enhancement. In this paper, we numerically simulate and theoretically analyze the optical properties of the nanorice trimer consisting of two short nanorices and a long nanorice. The Ag nanorice trimer can excite Fano resonance at optical frequencies based on the strong interaction between the bright and the dark mode. The bright mode is attributed to the first longitudinal resonance of the short nanorice pair, while the dark mode originates from the third longitudinal mode resonance of the long nanorice. The electric field distributions demonstrate that the two resonances with the largest field strength correspond to the first-order resonance of the long nanorice and the Fano resonance of the trimer, respectively. Two plasmon resonances with maximum electromagnetic field enhancements and same spatial hot spot regions can match spectrally with the pump and second-order Stokes beams of hyper Raman scattering, respectively, through reasonable design of the trimer structure parameters. The estimated enhancement factor of surface-enhanced hyper Raman scattering can achieve as high as 5.32 × 1013.

Theoretical investigation of a plasmonic substrate with multi-resonance for surface enhanced hyper-Raman scattering.

Because of the unique selection rule, hyper-Raman scattering (HRS) can provide spectral information that linear Raman and infrared spectroscopy cannot obtain. However, the weak signal is the key bottleneck that restricts the application of HRS technique in study of the molecular structure, surface or interface behavior. Here, we theoretically design and investigate a kind of plasmonic substrate consisting of Ag nanorices for enhancing the HRS signal based on the electromagnetic enhancement mechanism. The Ag nanorice can excite multiple resonances at optical and near-infrared frequencies. By properly designing the structure parameters of Ag nanorice, multi- plasmon resonances with large electromagnetic field enhancements can be excited, when the "hot spots" locate on the same spatial positions and the resonance wavelengths match with the pump and the second-order Stokes beams, respectively. Assisted by the field enhancements resulting from the first- and second-longitudinal plasmon resonance of Ag nanorice, the enhancement factor of surface enhanced hyper-Raman scattering can reach as high as 5.08 × 109, meaning 9 orders of magnitude enhancement over the conventional HRS without the plasmonic substrate.