Silica-based Planar Lightwave Circuit Research Articles

Experimental Demonstration of Stability of Silica-based Planar Lightwave Circuit for Medium Power RGB Laser Sources

Experimental Demonstration of Stability of Silica-based Planar Lightwave Circuit for Medium Power RGB Laser Sources

Variable Mode-Dependent-Loss equalizer based on Silica-PLC for Three-Mode transmission

We present a low-loss and compact silica-based planar lightwave circuit (PLC) mode-dependent loss (MDL) equalizer for three-mode transmission with a variable range of 2.5 dB. The proposed device utilizes a Mach-Zehnder interferometer (MZI) structure to selectively attenuate the LP01 mode while maintaining low insertion loss for the LP11a,b modes. We demonstrate that the device effectively reduces differential modal gain (DMG) in a three-mode transmission system. Additionally, we successfully equalize the pump-power dependence of the DMG in a two-LP mode erbium-doped fiber amplifier (EDFA) to less than 0.5 dB over the entire C-band. We also show that the variable range has a tradeoff relationship with the wavelength bandwidth, where too large a variable range results in non-negligible wavelength dependencies. Consequently, fixed equalizers are advantageous when large MDL compensation is required, while variable equalizers are effective for fine-tuning MDL of less than 1.2 dB.

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.

A Transponder Aggregator With Efficient Use of Filtering Function for Transponder Noise Suppression

Colorless, directionless, and contentionless reconfigurable optical add/drop multiplexing (CDC-ROADM) provides highly flexible physical layer network configuration. Such CDC-ROADM must operate in multiple wavelength bands which are being increasingly implemented in optical transmission systems. The operation in C+L bands requires switch devices used in CDC-ROADM to also be capable of multiband operation. Recent studies on wavelength division multiplexing (WDM) systems have pointed out the impact of amplified spontaneous emission (ASE) noise generated by signals of different wavelengths, which causes OSNR degradation. Therefore, it is desirable to filter out the ASE noise from different transponders when multiplexing multiple wavelengths at the transmitter side, especially in a system with non-wavelength selective combiners such as directional couplers and multicast switches. The use of transponder aggregators with filtering functions, such as the M × N wavelength selective switch (WSS), is preferable for this filtering. However, the downside of these devices is that it is difficult to provide economical multiband support. Therefore, we propose an economical transponder aggregator configuration by allowing a certain amount of ASE superposition and reducing the number of filtering functions. In this paper, we fabricated a prototype of the proposed transponder aggregator by combining silica-based planar lightwave circuit technology and C+L band WSS, both commercially available, and verified its feasibility through transmission experiments. The novel transponder aggregator is a practical solution for a multiband CDC-ROADM system with improved OSNR performance.

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.

Efficient and scalable edge coupler based on silica planar lightwave circuits and lithium niobate thin films

Recently, lithium niobate on insulator (LNOI) has emerged as a promising photonic integration platform for optical communication due to its outstanding material properties. However, an optical coupler that features high-efficiency is essential to improve the practicability of LN devices. In this work, we proposed a high coupling efficiency and scalable edge coupler, which consists of silica-based planar lightwave circuit (PLC) and LN bilayer taper. The silica-based PLC is positioned on the bottom of LN bilayer taper, which serves as the optical interface connecting the LNOI waveguide to the fiber. The silica-based PLC is interfaced to optical fibers through butt-coupling. Then, LN bilayer taper transfers the light form silica PLC to LN ridge waveguide through adiabatic coupling and converts it gradually into the fundamental mode. When coupled to an ultra-high numerical aperture fiber (UHNA), the simulation results show a low coupling loss of 0.11 dB and 0.128 dB per facet for TE and TM mode, respectively. The scalability of the coupler for large numbers of channels has been proven, which meets the performance requirements of LN devices employed in high-bandwidth, multi-channel systems. These results open a path for lithium niobate photonic integration circuit (PIC) and low-cost optical packaging.

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.

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.

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

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.

Realization of simultaneous balanced multi-outputs for multi-protocols QKD decoding based on silica-based planar lightwave circuit* *Project supported by the National Key Research and Development Program of China (Grant No. 2018YFA0306403) and the National Nature Science Foundation of China (Grant No. 61805232).

Silica-based planar lightwave circuit (PLC) devices can reduce transmission loss and cost in a quantum key distribution (QKD) system, and have potential applications in integration and production. A PLC-based quantum decoding integrated chip for multi-protocols is designed and fabricated, which is composed of variable optical splitters (VOSs), asymmetric Mach–Zehnder interferometers (AMZIs), and variable directional couplers (VDCs). Balanced pulse-pairs of four outputs are obtained simultaneously with measured delay times of 405 ps and 402 ps, respectively. The chip has advantages in achieving high interference visibility and low quantum bit error rate (QBER).

Surface Mount Technology for Silica-Based Planar Lightwave Circuit and Its Application to Compact 16×16 Multicast Switch

We demonstrated a compact 16×16 multicast switch (MCS) made from a silica-based planar lightwave circuit (PLC). The switch utilizes a new electrical connection method based on surface mount technology (SMT). Five electrical connectors are soldered directly to the PLC by using the standard reflow process used for electrical devices. We reduced the chip size to half of one made with conventional wire bonding technology. We obtained satisfactory solder contacts and excellent switching properties. These results indicate that the proposed method is suitable for large-scale optical switches including MCSs, variable optical attenuators, dispersion compensators, and so on.

Fabrication and demonstration of ultra-compact 3D measurement module using silica-based planar lightwave circuit

We fabricated an ultra-compact optical module using a silica-based planar lightwave circuit (PLC) for performing three-dimensional (3D) measurements. The module with a fiber, camera, lens, and flexible printed circuits is small enough to be attached to a tube with an inner diameter of 2.5 mm. The PLC is used as a fringe projector with a phase-modulation function and substrate for mounting the camera. A 3D measurement system based on a phase-shifting method was constructed using the module, and 3D profile measurements were performed on objects with thicknesses of 1.0, 2.0, and 3.0 mm. The experimental results indicated that the reconstructed shapes of the objects were clear enough for them to be recognized and the measurement variation was about 0.1 mm.

4 × 4 MIMO fiber-wireless transmission based on an integrated four-channel directly modulated optical transceiver

In this paper, an integrated compact four-channel directly modulated analog optical transceiver is proposed and fabricated. The 3 dB bandwidth of this optical transceiver exceeds 20 GHz, and the measured spurious-free dynamic range is up to 91.2 dB·Hz2/3. The optical coupling efficiency (CE) is improved by using a precise submicron alignment technique for lens coupling in a transmitter optical subassembly, and the highest CE is achieved when the oblique angle of the arrayed waveguide grating using a silica-based planar lightwave circuit (AWG-PLC) in receiver optical sub assembly is set to 42°. Based on the proposed optical transceiver, we have experimentally demonstrated a 6.624 Gbit/s 4×4 multi-input multioutput (MIMO) 16-quadrature amplitude modulation orthogonal frequency division multiplexing (16QAM-OFDM) radio signal over 15.5 km standard single mode fiber, together with 1.2 m wireless transmission in both an uplink and a downlink. To cope with the channel interference and noise of the fiber-wireless transmission system, a low-complexity MIMO demodulation algorithm based on lattice reduction zero-forcing (LR-ZF) is designed. In our experiment, 1.6 dB power penalty is achieved by using the proposed LR-ZF algorithm, compared to the commonly used zero-forcing algorithm. Moreover, this LR-ZF algorithm has much less complexity than the optimal maximum-likelihood sequence estimation (MLSE) at a given transmission performance. These results not only demonstrate the feasibility of the integrated optical transceiver for MIMO fiber-wireless application but also validate that the proposed LR-ZF algorithm is effective to eliminate the interference for hybrid fiber-wireless transmission.

Single-photon interference using silica-based AMZI with phase modulation

An asymmetric Mach-Zehnder interferometer (AMZI) which comprised a variable optical attenuator (VOA), a thermo-optic phase modulator (TOPM) and a delay line of 740 ps was designed and fabricated using silica-based planar lightwave circuit technology. Two identical AMZI chips were connected in series to demonstrate the single photon interference in the middle pulse. The experimental results showed the TOPM can modulate the phase difference between the double pulses. The single photon interference visibility was dependent on the temperature and the polarization of the input light. The observed maximum visibility was 98.38% when the temperature of temperature controller (TEC) was 10 °C. And the interference visibility was dependent on the polarization of the input light. The AMZI could form the basis of the passive decoder in the future quantum cryptography systems.

Design of Transmission-Type Refractive Index Sensor, Based on Silica Planar Lightwave Circuit Using Combination of Refractive Angle and Phase Measurements.

A transmission-type refractive index sensor, based on planar lightwave circuit (PLC) technology is proposed. In the proposed structure, we introduce a combination of coarse measurements, using the dependence of the angle of refraction and fine measurement, and the dependence of the phase on the refractive index to measure the absolute refractive index precisely, without expensive optical measurement equipment. The theoretical model of the proposed refractive index sensor is derived based on Fourier optics and transfer function to simulate its performance. The simulation results for the use of the 2.5%-Δ silica-based PLC technology indicate that the proposed structure has the potential to achieve a refractive index error of approximately 1 × 10−6 RIU or less when a monitored power deviation of ±0.05 dB is accepted.

High Assembly Tolerance and Cost-Effective 100-Gb/s TOSA With Silica-PLC AWG Multiplexer

A low-cost hybrid-integrated transmitter optical sub-assembly (TOSA) for a 100-Gb/s coarse wavelength division multiplexing (CWDM) transceiver with high assembly tolerance has been demonstrated. We have proposed a novel two-lens configuration for the coupling between distributed feedback laser diodes and a silica-based planar lightwave circuit arrayed waveguide grating to relax the lenses assembly requirement. For this TOSA, the 1-dB assembly tolerances of all lenses are over ±15 μ m. Furthermore, we use a flexible printed circuit to connect the interior and exterior of the TOSA for radiofrequency signal transmission instead of the conventional ceramic feed-through box. Finally, a TOSA was packaged with a size of 22 mm × 10.7 mm × 4.5 mm. Error-free transmission over a 10-km single-mode fiber was successfully achieved when all four lanes were driven simultaneously with a total bit rate of 4 × 25.78125 Gb/s at an operating temperature of 25 °C.

Low-cost hybrid integrated 4 × 2578 Gb/s CWDM TOSA for 10 km transmission using DFB-LDs and an arrayed waveguide grating multiplexer

We have developed a cost-effective and highly compact 100-Gb/s coarse wavelength division multiplexing (CWDM) transmitter optical subassembly (TOSA) using lens-free hybrid integration. To achieve large alignment tolerances, distributed feedback laser diodes (DFB-LDs) are butt-coupled to a four-channel silica-based planar lightwave circuit (PLC) arrayed waveguide grating, with the silicon sub-mounts and PLC adhesively bonded. Then, a flexible printed circuit is employed to connect the internal DFB-LDs and the exterior of the TOSA package for radiofrequency signal transmission, eliminating the expensive ceramic feed-through. The packaged CWDM TOSA, which is 15.8 mm×7.0 mm×6.0 mm in size, shows a side-mode suppression ratio of >40 dB, a 3 dB bandwidth of >18 GHz, and error-free transmission with an average optical output power of >0 dBm and dynamic extinction ratio of >4.0 dB at 25.78125 Gb/s over a 10 km single-mode fiber for all four lanes.