Planar Lightwave Circuit Research Articles

6-mode and 10-mode photonic lantern mode multi/demultiplexers based on silica planar lightwave circuit

We propose a 6-mode and 10-mode photonic lantern mode multiplexer based on two- and three-layer silica planar lightwave circuitry, respectively. The 6-mode multiplexer has transmission greater than −0.19 dB at a wavelength of 1550 nm for the E11, E21, E12, E22, E31, and E13 modes. The 10-mode multiplexer is designed to only excite selected modes (E11, E21, E12, E22, E31, E13, E32, E23, E41, and E14 modes), used for fiber transmission. Each mode has transmission greater than −1.15 dB, at a wavelength of 1550 nm.

Temperature characterizations of silica asymmetric Mach-Zehnder interferometer chip for quantum key distribution

Quantum key distribution (QKD) system based on passive silica planar lightwave circuit (PLC) asymmetric Mach–Zehnder interferometers (AMZI) is characterized with thermal stability, low loss and sufficient integration scalability. However, waveguide stresses, both intrinsic and temperature-induced stresses, have significant impacts on the stable operation of the system. We have designed silica AMZI chips of 400 ps delay, with bend waveguides length equalized for both long and short arms to balance the stresses thereof. The temperature characteristics of the silica PLC AMZI chip are studied. The interference visibility at the single photon level is kept higher than 95% over a wide temperature range of 12 °C. The delay time change is 0.321 ps within a temperature change of 40 °C. The spectral shift is 0.0011~nm/0.1 °C. Temperature-induced delay time and peak wavelength variations do not affect the interference visibility. The experiment results demonstrate the advantage of being tolerant to chip temperature fluctuations.

Polarization-insensitive quantum key distribution using planar lightwave circuit chips

Self-stabilizing the quantum key distribution (QKD) system is essential to evaluate eavesdroppers’ information accurately. We develop and verify a polarization-insensitive time-bin decoder chip for QKD with the hybrid asymmetric Faraday-Michelson interferometer (AFMI) based on the planar lightwave circuit (PLC). Compared with existing chip-based QKD works, the scheme can intrinsically compensate for the polarization perturbation to quantum signals and thus work at arbitrary temperatures. We experimentally verify the chips in a time-bin QKD system at the clocking rate of 1.25 GHz and obtain an average secure key rate (SKR) of 1.34 Mbps over a 50 km fiber channel with an optimized analysis model. The steady variations of the quantum bit error and SKR with random polarization disturbance demonstrate that PLC-based AFMIs are available for developing self-stable QKD systems.

PLC-Based Arrayed Waveguide Grating Design for Fiber Bragg Grating Interrogation System.

A fiber Bragg grating (FBG) interrogator is a scientific instrument that converts the wavelength change of FBG sensors into readable electrical signals. To achieve miniaturization and integration of FBG interrogator, we designed and fabricated a 36-channel array waveguide grating (AWG) on silica-based planar lightwave circuits (PLC) as a key device in a built FBG interrogation system. It is used to achieve continuous demodulation in C-band, while maintaining high resolution. This AWG has a 1.6 nm channel spacing, 3-dB bandwidth of 1.76 nm, non-adjacent channel crosstalk of −29.76 dB, and insertion loss of 3.46 dB. The dynamic range of the FBG interrogation system we built was tested to be 1522.4–1578.4 nm, with an interrogation resolution of 1 pm and accuracy of less than 1 pm in the dynamic range of 1523.16–1523.2 nm. The test results show that the FBG interrogation technology, based on AWG, can realize FBG wavelengths accurately demodulated, which has high application value in aerospace, deep sea exploration, and environmental monitoring, as well as other fields.

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.

PLC-Based Integrated Refractive Index Sensor Probe with Partially Exposed Waveguide

This paper proposes a simple, high-efficiency refractive index (RI) sensor, with a structure based on the planar lightwave circuit (PLC) probe type. The optical sensor has a 1 × 2 splitter structure with reference and sensing channels, each consisting of a U-shaped waveguide structure that is configured by connecting C bends. This design allows for the sensor device to have a probe structure wherein the surface interconnected with activity devices (i.e., an optical source and optical detector) is placed on one side. The reference channel is bent with a minimum optical loss, and the sensing channel has a bent structure, involving a C-bend waveguide with a maximum loss. The C-bend waveguide with a maximum loss is conformally aligned to have a trench structure with the same bending radius, designed to selectively expose the sidewall of the core layer. The local index contrast varies depending on the material in contact with the trench, resulting in a change in the optical output power of the waveguide. The sensitivity of the proposed sensor was 0 and 2070 μW/refractive index unit (RIU) for the reference and sensing channels, respectively, as the RI changed from 1.385 to 1.445 at a 1550 nm wavelength. These results suggest that the proposed structure enables efficient RI measurement through the use of a simple dip-type method.

Silica-based planar lightwave circuits with high resistance against blue light for visible-light application

We propose two novel types of waveguide, Zr-doped and non-doped silica, for high-power visible-light applications. We fabricated these waveguides and investigated their resistance against blue light. Both Zr-doped and non-doped silica waveguides showed one order of magnitude higher resistance against blue light compared with conventional Ge-doped silica waveguides. A comparison of their resistances indicated that Zr-doped silica waveguides are useful against blue light powers up to about 20 mW and non-doped silica waveguides have more potential for higher resistance against blue light powers over 20 mW.

Experimental Research on In Situ Uniaxial Tensile Response of Silica-Based PLC Optical Splitters

In this study, the mechanical and optical properties of silica-based planar lightwave circuit (PLC) optical splitters under uniaxial tensile loading are studied by building an in situ experimental test platform. The tensile test results revealed that the adhesively-bonded fiber array-PLC chip joints are weak areas of the PLC optical splitter. Combined with the real-time monitoring of the optical performance index insertion loss (IL) during the tensile test, it was found that the changing trend of ΔIL-time curves is related to the deformation, damage, and debonding process of the weak area. Based on the experimental results and phenomena, the correspondence between ΔIL at 1.55 μm wavelength and the damage degree of PLC optical splitters is established, that is, ΔIL in (−5 dB; 0 dB], (−15 dB; −5 dB], and (−∞, −15 dB] belong to light damage, moderate damage, and severe damage, respectively. This research can provide a useful reference for damage characteristics analysis and reliability design of PLC optical splitters.

Practical Quantum Key Distribution Module Based on Planar Lightwave Circuit

Many improvements are required to bring quantum key distribution (QKD) from the laboratory to the commercial market, such as simplifying structure and enhancing stability. In this letter, a QKD module based on planar lightwave circuit (PLC) has been proposed. The chip inside module is based on silica-silicon material and composed of various optical splitter, asymmetric Mach–Zehnder interferometer and directional coupler. The module can allow users adjust temperature stably. The interference visibility can be high to 96% merely by controlling and stabilizing temperature and voltage of the module through self-interfering method which showed its potential in practical application.

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.

Ultra-dense interferometric chain architecture for datacom and telecom applications

Further increase in the density of integrated planar lightwave circuits (PLCs) depends on the introduction of compact guided-wave layout solutions. We describe a novel architecture for coiling multistage interferometric devices with densities reaching the theoretical limit. Our approach is validated by the design, fabrication, and deployment of state-of-the-art PLCs based on the proposed architecture for use in datacom and telecom applications.

Universal ultra-sensitive refractive index sensor based on an integrated SiO2 asymmetric Mach-Zehnder interference filter (AMZIF)

This paper proposes an integrated universal ultra-sensitive refractive index sensor that is applicable for many kinds of liquid. The sensor is SiO2 asymmetric Mach-Zehnder interference filter (AMZIF) with a reference window and a sensing window on different arms. The formula derivation shows that the sensitivity of AMZIF is directly proportional to the arm length, and its measurement range can be expanded by reducing the diffraction order. The sensor is fabricated using standard planar lightwave circuit (PLC) technology, and the tested sensitivity reaches 21193.3 nm per refractive index unit (nm/RIU). With appropriate reference material, the universal AMZIF sensor can measure the refractive index of any liquid whose refractive index is between 1.33 ∼ 1.45 and the sensitivity remains above 20000 nm/RIU.

Quantum key distribution transmitter chip based on hybrid-integration of silica and lithium niobates

A quantum key distribution transmitter chip based on hybrid-integration of silica planar light-wave circuit (PLC) and lithium niobates (LN) modulator PLC is presented. The silica part consists of a tunable directional coupler and 400-ps delay line, and the LN part is made up of a Y-branch, with electro-optic modulators on both arms. The two parts are facet-coupled to form an asymmetric Mach–Zehnder interferometer. We successfully encode and decode four BB84 states at 156.25-MHz repetition rate. Fast phase-encoding of 0 or π is achieved, with interference fringe visibilities 78.53% and 82.68% for states |+〉 and |–〉, respectively. With the aid of an extra off-chip LN intensity modulator, two time-bin states are prepared and the extinction ratios are 18.65 dB and 15.46 dB for states |0〉 and |1〉, respectively.

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.

Low-loss 1 × 256 optical power splitter

A low-loss 1 × 256 optical power splitter is designed and fabricated using silica-based planar lightwave circuit technology on a 6-in. quartz substrate. The measured results show that the insertion loss, uniformity, and wavelength-dependence loss (WDL) of a 1 × 256 splitter are <26.2, 1.97, and 1.83 dB, respectively, in the wavelength range from 1.26 to 1.63 μm. The insertion loss, uniformity, and WDL of a 1 × 256 splitter are <25.62, 1.33, and 1.03 dB, respectively, in the normal communication wavelength range from 1.31 to 1.55μm. The polarization dependence loss is <0.16 dB in the wavelengths of 1.31 and 1.55 μm.

Zr-doped Silica-based Planar Lightwave Circuits with High Resistance Against Blue Light

Zr-doped Silica-based Planar Lightwave Circuits with High Resistance Against Blue Light

Polarization-insensitive interferometer based on a hybrid integrated planar light-wave circuit

Interferometers are essential elements in classical and quantum optical systems. The strictly required stability when extracting the phase of photons is vulnerable to polarization variation and phase shift induced by environment disturbance. Here, we implement polarization-insensitive interferometers by combining silica planar light-wave circuit chips and Faraday rotator mirrors. Two asymmetric interferometers with temperature controllers are connected in series to evaluate the single-photon interference. Average interference visibility over 12 h is above 99%, and the variations are less than 0.5%, even with active random polarization disturbance. The experiment results verify that the hybrid chip is available for high-demand applications like quantum key distribution and entanglement measurement.

Silica-silicon based planar lightwave circuit quantum key distribution decoding chip for multi-protocol

Silica-silicon planar lightwave circuit (PLC) has the advantages of miniaturization, low cost, and low loss, and it provides a stable, highly integrated, and practical platform for quantum key distribution (QKD). A quantum decoding chip based on this platform which have potential to be compatible for multi-protocols has been designed and measured. The chip consists of three variable optical splitters (VOSs), two Mach-Zehnder interferometers (AMZIs) and four variable directional couplers (VDCs). The results of experiment show that the chip can achieve up to 98.6% interference visibility with measured delay times of 405 ps and 402 ps for two AMZI respectively under temperature control. The extinction ratio for the phase states is kept between 23 and 25 dB for 6 h without active phase correction. The chip has advantageous to achieve high interference visibilities and low quantum bits error rate (QBER).

Integrated-optics pressure sensor with improved range and sensitivity based on a SiO2 arrayed waveguide grating (AWG) and a 3D printed stereolithography resin module

An integrated optical pressure sensor based on a SiO2 arrayed waveguide grating (AWG) and a phase amplifying pressure block (PAPB) 3D-printed with stereolithography resin is described in this paper. Theoretical analysis of the AWG shows that its sensitivity can be improved by applying pressure on the PAPB instead of the whole chip. This scheme is shown to be feasible by mechanical simulation of a 1 mm-thick SiO2 chip. We use the standard planar lightwave circuit (PLC) process to fabricate a SiO2 AWG and 3D print the PAPB using stereolithography resin SOMOS Imagine 8000. Adding the PAPB module to the AWG chip improves the sensitivity of the sensor by 9 times, and the measuring range reaches 80 MPa. The resolution of the device reaches 0.0007% FS (full scale).

The Method of Lines Analysis of TE Mode Propagation in Silica based Optical Directional Couplers

Optical directional couplers fabricated using planar light wave circuit (PLC) technology are versatile tools in integrated photonics devices. They have the advantages of small size, high consistency, ability for high volume production, and excellent possibility to be integrated with electronics circuits. Optical waveguide couplers are mainly utilized as power dividers, optical switches, and wavelength division multiplexers/de-multiplexers (WDM). A number of methods have been used to analyze directional couplers, such as coupled mode theory (CMT), the beam propagation method (BPM), the method of lines (MoL), finite-difference methods (FDM), and finite element methods (FEM). Among these numerical approaches, MoL is the simplest method to analyze mode propagation inside directional couplers because it has the advantages of very fast convergence and accurate solutions for one-dimensional structures. The objective of this study was to analyze the propagation of TE modes in optical directional couplers by using MoL. The parameters used, i.e. waveguide width, refractive index, and wavelength, were taken from the characteristics of silica-on-silicon directional couplers that were used in fabrication. MoL is considered a special finite-difference method, which discretizes a one- or two-dimensional wave equation in the transverse direction and uses an analytical solution for the propagation directions. Basically, MoL is a semi analytical numerical method with the advantages of numerical stability, computational efficiency, and calculation time reduction. Further, we explored the possibility of using directional couplers as optical switching devices.