Planar Lightwave Circuit Platform Research Articles

Broadband design of silica-PLC mode-dependent-loss equalizer for 2LP-mode transmission systems.

A new configuration of mode-dependent-loss (MDL) equalizer for two linearly-polarized mode transmission systems using the silica planar lightwave circuit platform is proposed. This device acts as an LP01-mode attenuator (precisely, LP01/LP21 mode converter) to adjust the MDL keeping a high transmission of the LP11 modes. Almost all components constructing the device are based on the adiabatic mode conversion, which brings broadband operation. Especially, a newly proposed E12/E22 mode converter plays a key role in broadband MDL equalization. It is numerically revealed that the flattened spectra with designated transmission can be obtained for the wavelength from 1200 nm to 1650 nm.

Generation of balanced pulse pairs based on a dual-chip coupling structure.

An asymmetric Mach-Zehnder interferometer (AMZI) is an essential device to generate pulse pairs in quantum key distribution systems. An AMZI based on a dual-chip coupling structure in a silica-on-silicon planar light wave circuit platform is proposed, which includes a variable optical splitter (VOS), a delay line (DL), and a directional coupler (DC). The AMZI chip is divided into a VOS-DL part and a DC part, and the two parts are independently manufactured and then coupled. Since the DC part occupies the smallest area of the AMZI chip and is most sensitive to manufacturing errors, separate production can reduce the process difficulty and fabrication errors. In the experiment, balanced pulse pairs with a delay time of 402ps are obtained in the condition of single photon transmission, and the excess loss is 0.8dB. This dual-chip coupling structure can improve the yield and reduce the manufacturing cost when producing large chips.

Mode-selective switch on silica-based PLC platform

Optical mode switch is a crucial component for the mode-division multiplexing (MDM) system. In this paper, we demonstrate a thermo-optical (TO) mode-selective switch on silica-based planar lightwave circuit (PLC) platform. The 2 × 1 thermo-optical (TO) mode-selective switch based on Mach–Zehnder interferometer consists of an adiabatic coupler and a symmetric Y-branch. The input optical mode E00 (E10) is converted to E10 (E00) mode while the light is coupled from different input ports by changing the working state of heater. With 2% index-contrast, a compact mode switch on silica-based PLC platform is fabricated. According to experimental results, the fabricated mode-selective switch shows an insertion loss lower than 5 dB and a mode extinction ratio higher than 24 dB for two modes at 1550 nm. The crosstalk is lower than −10.54 dB from 1500 nm to 1600 nm. The power consumption for two modes are 433.24 mW and 440.15 mW, respectively. The rise time and fall time of the switch are 560.9μs and 794.8μs.

Advancements in waveguide architectures using high-performance silica-on-silicon platform - INVITED

Novel applications in optical coherence tomography (OCT) and LiDAR systems have become possible due to performance characteristics of a state-of-the-art silica-on-silicon planar lightwave circuit (PLC) platform. We have achieved ultra-low propagation losses of <0.009 dB/cm with unmatched phase control in a polarization-insensitive way, enabling a range of real-time advanced vision and imaging applications utilizing k-clocks and analog frequency sampling architectures.

Low Power Consumption Hybrid-Integrated Thermo-Optic Switch with Polymer Cladding and Silica Waveguide Core

Taking advantage of the large thermo-optical coefficient of polymer materials, a hybrid-integrated thermo-optic switch was designed and simulated. It is also compatible with the existing silica-based planar light-wave circuit (PLC) platform. To further reduce the power consumption, we introduced the air trench structure and optimized the structural parameters of the heating region. This scheme is beneficial to solving the problem of the large driving power of silica-based thermo-optic switches at this stage. Compared with the switching power of all-silica devices, the power consumption can be reduced from 116.11 mW (TE) and 114.86 mW (TM) to 5.49 mW (TE) and 5.96 mW (TM), which is close to the driving power of the reported switches adopting polymer material as the core. For the TE mode, the switch's rise and fall times were 121 µs and 329 µs. For the TM mode, the switch times were simulated to be 118 µs (rise) and 329 µs (fall). This device can be applied to hybrid integration fields such as array switches and reconfigurable add/drop multiplexing (ROADM) technology.

Four-stage cascaded variable optical attenuator with large attenuation range for quantum key distribution

A four-stage cascaded variable optical attenuator (VOA) with a large attenuation range is presented. The VOA is based on a Mach–Zehnder interferometer (MZI) and fabricated in a silica-based planar lightwave circuit (PLC) platform. The thermo-optic effect is used to achieve intensity modulation. The measured maximum attenuation of the four-stage cascaded VOA is 88.38 dB. The chip is also tested in a quantum key distribution (QKD) system to generate signal and decoy states. The mean photon number after attenuation of the four-stage cascaded VOA is less than 0.1, which can meet the requirement of QKD.

Wavelength (DE)MUX-and-Switch Based on 5.5%-Δ-Silica PLC/Silicon Photonics Hybrid Platform

Silicon-based optical media present several desirable properties for a wide range of applications. Herein, we propose a novel hybrid integration scheme that combines a silicon photonics platform and a 5.5%--silica planar-lightwave circuit (PLC) platform. By exploiting the performance advantages of each platform, we fabricated a polarization-insensitive low-crosstalk 8 8 silicon photonics switch butt-jointed with a compact 5.5%--silica PLC-based 100-GHz 8-channel arrayed waveguide grating (AWG). The device was driven by a smartphone-sized (9 cm 13.5 cm) control board. The fabricated device exhibits a fiber-to-fiber insertion loss of 12.6 dB, an average polarization-dependent loss of less than 0.57 dB, and less than -40 dB leakage to non-target output ports. We also demonstrate two uses of the proposed device. The first is the DEMUX and Switch operation, in which the spectrally divided light by the AWG is routed to an arbitrary output port by a subsequent switch. The second is the Switch and MUX operation, in which arbitrary wavelengths from arbitrary input ports are merged by the AWG. No spectral degradation was observed in either operation. These results demonstrate the potential of the 5.5%--PLC/silicon photonics hybrid platform for compact, low-power, and fast-switching applications.

Realization of high interference visibility based on silica-on-silicon planar lightwave circuit

Quantum key distribution can realize unconditional security of communication. Here, a quantum decoding chip based on silica-on-silicon planar lightwave circuit (PLC) platform, which is compatible for multiprotocol has been demonstrated. PLC technology provides stability, high integration, and practicality for the chip, whereas silica-on-silicon material makes it low loss and low cost. The chip is integrated with three variable optical splitters, two asymmetric Mach–Zehnder interferometers, and four variable directional couplers. The interference visibility is investigated by self-interfering method, and the results showed it is high to 98.2% under temperature control. The extinction ratio for the phase states is kept between 23 and 25 dB for 6 h without active phase correction.

Six-mode scrambler based on cascaded side-wall grating waveguides

A six-mode scrambler based on cascaded side-wall long-period-grating waveguides on a silica planar lightwave circuit (PLC) platform is proposed for mode-division-multiplexing (MDM) transmission. The device can be fabricated with only one-step etching since it does not use a surface grating. A mode-dependent loss (MDL) of the system is estimated and the MDL can be reduced with a multiple scrambling operation. Two gratings proposed here and a fiber-pigtailed module containing these gratings are fabricated and the expected proof-of-concept mode scrambling operation is confirmed. It is found that the connection between few-mode fiber (FMF) and PLC chip seems to be the dominant loss of the module. Considering these losses, the measured results are in good agreement with the calculated results.

2D Waveguided Bessel Beam Generated Using Integrated Metasurface-Based Plasmonic Axicon

Near-field imaging of the propagation of a diffraction-free Bessel-type beam in a guided wave configuration generated by means of a metasurface-based axicon lens integrated on a silicon waveguide is reported. The operation of the axicon lens with a footprint as small as 11µm2 is based on local engineering of the effective index of the silicon waveguide with plasmonic nanoresonators. This generic approach, which can be adapted to different types of planar lightwave circuit platforms, offers the possibility to design nano-engineered optical devices based on the use of plasmonic resonators to control light at the nanoscale.

Ultra-compact on-chip metaline-based 13/16 μm wavelength demultiplexer

In this paper, we report an experimental demonstration of enabling technology exploiting resonant properties of plasmonic nanoparticles, for the realization of wavelength-sensitive ultra-minituarized (4 μm×4 μm) optical metadevices. To this end, the example of a 1.3/1.6 μm wavelength demultiplexer is considered. Its technological implementation is based on the integration of gold cut-wire-based metalines on the top of a silicon-on-insulator waveguide. The plasmonic metalines modify locally the effective index of the Si waveguide and thus allow for the implementation of wavelength-dependent optical pathways. The 1.3/1.6 μm wavelength separation with extinction ratio between two demultiplexers’ channels reaching up to 20 dB is experimentally demonstrated. The considered approach, which can be readily adapted to different types of material planar lightwave circuit platforms and nanoresonators, is suited for the implementation of a generic family of wavelength-sensitive guided-wave optical metadevices.

Cascaded all-optical operations in a hybrid integrated 80-Gb/s logic circuit.

We demonstrate logic functionalities in a high-speed all-optical logic circuit based on differential Mach-Zehnder interferometers with semiconductor optical amplifiers as the nonlinear optical elements. The circuit, implemented by hybrid integration of the semiconductor optical amplifiers on a planar lightwave circuit platform fabricated in silica glass, can be flexibly configured to realize a variety of Boolean logic gates. We present both simulations and experimental demonstrations of cascaded all-optical operations for 80-Gb/s on-off keyed data.

A flattop PLC polymer waveguide interleaver based on folded two-stage-cascaded Y-junction Mach–Zehnder interferometers

We demonstrate realization of a flattop Y-Junction Planar Optical Waveguide Interleaver (YJPOWI) with a channel spacing of 100GHz through a novel scheme of folded cascaded two-stage unbalanced Mach–Zehnder interferometers (MZI) fabricated on a polymer Planar Lightwave Circuit (PLC) platform. The characteristic 0.5dB passbands of the interleaver centered at ITU wavelength grids at its two output ports were 50 and 45GHz, respectively. The operating bandwidth of the device spanned the entire C band of a fiber amplifier and it is compact in size (1.3×1.4cm2). In addition, the device is easy to fabricate and do not require any individual heater to trim its performance.

Optimization of time-domain header processing filters using genetic algorithms

We present genetic algorithms as optimization tools for the design of header recognition filters based on time-delay lines. The fitness parameter in the selection process is the discrimination of the target against all other bit patterns. For phase-shift-keyed headers, optimized filters exhibit improved discrimination compared with the matched filter. Time-domain filtering with no ambiguities is also achieved for specific amplitude-shift-keyed headers. Delay-line-based time-domain filters can be implemented in a planar lightwave circuit platform by simple phase and amplitude adjustments on the time delay taps.

A bidirectional module integrated on a planar lightwave circuit with a coated WDM filter

We have developed a cost-effective 2.5 Gb s−1 wavelength-division multiplexing (WDM) bidirectional module using two integrated optical subassemblies, which are composed of a planar lightwave circuit (PLC) platform for upstream operation and a silicon optical bench (SiOB) platform for downstream operation. The module is constructed by employing a flip-chip bonding method with passive alignment using a distributed feedback laser diode (DFB-LD) with a monitoring waveguide photodiode (PD) on a PLC platform and a receiver with a PIN-PD on an SiOB platform. We investigated the optical performance of the transmitter based on the PLC platform and the receiver subassembly module based on the SiOB platform, respectively.

Multichip Integration on a PLC Platform for 16$\,\times\,$16 Optical Switch Module Using Passive Alignment Technique

We have integrated eight sets of four-channel semiconductor optical amplifier (SOA) array chips on a silica-based planar lightwave circuit (PLC) platform for 16 times 16 optical switch module by flip-chip bonding technique. To accurately bond eight sets of the arrayed SOA chips on a PLC platform, two methods of two-step assembly and one-step assembly were tried. Among the results of two assembly methods, one-step assembly was estimated to be desirable in respect of the horizontal and vertical bonding accuracy. The bonding accuracy was measured to be within 0.5 mum. Also, we demonstrated 16 times 16 optical switch module.

Circularly Polarized External Cavity Laser Hybrid Integrated With a Polyimide Quarter-Wave Plate on Planar Lightwave Circuit

We propose and demonstrate a circularly polarized external cavity laser (ECL) hybrid integrated on a planar lightwave circuit (PLC). The ECL is composed of a spot-size converter integrated laser diode, a UV-written grating, and a polyimide quarter-wave plate on the PLC using hybrid-integration technology. The polyimide quarter-wave plate of an 8.8-mum thickness was inserted in a trench with a 20-mum width and a 300-mum depth on the PLC platform, and fixed with a UV-curable adhesive. The ECL hybrid integrated with the polyimide wave plate becomes highly circular-polarized with a degree of circular polarization of 0.992. This circularly polarized ECL operated with a sidemode suppression ratio of >50 dB at ~1550 nm.

Integrated-Holographic Coarse-Wavelength-Division Multiplexers Patterned by DUV Photolithography

We demonstrate monolithically integrated four and eight-channel coarse-wavelength-division multiplexers with low insertion loss (IL) and wide flat-top passbands based on integrated-holographic filters. Like thin-film filters (TFFs), integrated-holographic filters function via a multipath interference and thus offer flexible passband control without the IL penalty that passband shaping typically incurs in single-mode angularly dispersive devices. Unlike TFF-based multiplexers, the multiplexers described here are based on the silica-on-silicon planar lightwave circuit platform rather than discrete optics and thus uniquely provide powerful TFF-like filtering function in fully integrated format. The multiplexer performance demonstrated is superior to the integrated solutions demonstrated to date, and competitive with discrete TFF-based devices

Fabrication of a TFF-Attached WDM-Type Triplex Transceiver Module Using Silica PLC Hybrid Integration Technology

An optical triplex transceiver (TRx) module, which consists of thin-film filter (TFF)-attached wavelength-division multiplexer (WDM) and photodiode (PD) carriers, has been fabricated using a silica planar lightwave circuit (PLC) hybrid integration technology. Two types of TFFs were attached to a diced sidewall of a silica-terraced PLC platform to realize the TFF-attached WDM. The PD carriers with a 45deg mirror, on which receiving surface-illuminated PDs were bonded, were assembled with the PLC platform to form receiver (Rx) parts. As the main performances of the packaged TRx module, a very clear transmitter (Tx) eye pattern and minimum Rx sensitivity of -25.7 dBm were obtained under a 1.25-Gb/s Tx-Rx operation for digital applications. For an analog Rx application, a module responsivity of about 0.8 A/W was achieved, and a second-order intermodulation distortion value of less than -70 dBc at an optical modulation index of 40% was obtained under a two-tone test of 400 and 450 MHz

1.3-$mu$m Four-Channel$,times,$10-Gb/s Parallel Optical Transceiver With Polymer PLC Platforms for Very-Short-Reach Applications

A four-channel times10-Gb/s parallel optical transceiver for high-capacity very-short-reach applications was developed. The transceiver module was fabricated with low-cost components such as polymer planar lightwave circuit (PLC) platforms and 1.3-mum Fabry-Perot laser diodes (FPLDs). The polymer PLC platform enables the FPLDs or waveguide photodiodes (WGPDs) to be butt-coupled to the polymer waveguide by low-cost passive alignment. Using 1.3-mum FPLDs and single-mode fibers (SMFs) achieves reliable transmission over 600 m. Widening the spacing between the waveguides up to 1 mm suppressed the interchannel crosstalk to below -39 dB. The fabricated transceiver was operated at 10 Gb/s per channel and it successfully demonstrated 600-m error-free transmission. The sensitivity of each channel was better than -14 dBm with an interchannel-crosstalk penalty of less than 0.7 dB