Single-mode Polymer Optical Waveguides Research Articles

Synthesis and characterization of fluorinated polyimide doped with NaYF4 nanocrystals for optical waveguide applications

Fluorinated polyimide materials were selected for their exceptional flexibility, high thermal stability, and minimal absorption loss. These materials were subsequently employed in the production of single-mode polymer optical waveguide devices using photolithography. In this study, a fluorinated polyimide material doped with NaYF4 nanocrystals was prepared and confirmed to exhibit low absorption loss near 1550 nm, which is within the common communication window. The refractive index of the fluorinated polyimide films was precisely adjusted by the NaYF4 doping, the adjustable ranges for the refractive index were 1.95% and 1.72% for doped and undoped, respectively. Secondly, utilizing the NaYF4 nanocrystals doped-fluorinated polyimide materials, a three-layer single-mode polymer optical waveguide device for C-band (near 1550 nm) optical interconnection was fabricated by etching the underlying cladding and employing silicon nitride as a mask. The transmission performance of the device was excellent, with a total waveguide coupling and transmission loss of 1.502 dBm.

Low loss single-mode polymer optical waveguide with circular cores

We experimentally demonstrate that the Mosquito method is capable of fabricating single-mode polymer optical waveguides with multiple cores while maintaining an identical mode-field diameter among them. The Mosquito method we developed is a technique to form circular cores in polymer waveguides using a commercially available microdispenser and multi-axis syringe scanning robot. However, the core shape tends to deteriorate from a circle because of the monomer flow due to the needle scan. We also demonstrate both theoretically and experimentally for the first time in this paper that the needles with a tapered outer form or just titled straight needles enable to form cores with a high circularity even if those cores are dispensed on any heights from the substrate surface.

Polarization Dependence of Optical Properties of Single-Mode Polymer Optical Waveguides Fabricated Under Different Processes at 1310/1550 nm

We experimentally investigate the polarization dependence of the optical properties of single-mode polymer optical waveguides. We compare two types of waveguides composed of the same polymer materials: step-index square-core waveguides fabricated using the direct curing method and graded-index (GI) circular-core waveguides fabricated using the Mosquito method. We demonstrate that the GI circular-core single-mode waveguides exhibit remarkably small dependence of optical loss on the polarization angle, which is less than 0.1 dB polarization dependent loss (PDL) at both 1310 and 1550 nm wavelengths. This steady polarization property is attributed to the material stress free to the composing polymers during the fabrication process of the Mosquito method and to parabolic GI profile formed in symmetric circular core.

Circular core single-mode 3-dimensional crossover polymer waveguides fabricated with the Mosquito method.

We experimentally fabricate circular core 3-dimensional (3D) crossover single-mode polymer optical waveguides using a photomask free unique fabrication technique named the Mosquito method for realizing channel shuffling. The 3D crossover structure is accomplished by forming four cores (2 ch. × 2 ch.) with different heights: the last two channels cross over the first two channels with horizontal and vertical core bending. We compare the insertion losses between the fabricated 3D single-mode crossover waveguide and 3D S-bend core waveguides fabricated separately, which correspond to the lower and upper channels in the crossover waveguide. Then, we investigate the effect of the core crossover on the loss, and find that almost negligible additional loss is observed. The average insertion losses of this 6-cm long 3D crossover single-mode waveguide are 3.95 and 3.81 dB at 1310 nm, and 5.74 and 4.80 dB at 1550-nm wavelength, for the lower and upper channels, respectively. The interchannel crosstalk in this crossover waveguide is observed to be lower than -40 dB, while the 1 dB radial alignment tolerance is ± 1.7 and ± 2.1 µm at 1310 and 1550 nm, respectively. These results suggest that the fabricated circular core single-mode 3D crossover polymer waveguides could have a great impact for high-bandwidth-density on-board and inter-chip optical interconnect applications.

Circular core single-mode polymer optical waveguide fabricated using the Mosquito method with low loss at 1310/1550 nm.

We fabricate low-loss single-mode (SM) polymer optical waveguides using a photomask-free simple technique named the Mosquito method. The insertion losses of a 5-cm long SM polymer waveguide fabricated are 2.52 dB and 4.03 dB at 1310- and 1550-nm wavelengths, respectively. The coupling loss between a single-mode fiber and the waveguide is as low as 0.5 dB including the Fresnel reflection. The 0.5-dB misalignment tolerance in the radial direction is ± 2.0 μm at 1550 nm. The Mosquito method is promising for fabricating SM polymer optical waveguides compatible with silicon photonics chips.

Comparison of epoxy- and siloxane-based single-mode optical waveguides defined by direct-write lithography

This paper reports on the fabrication and characterization of single-mode polymer optical waveguides at telecom and SOI compatible wavelengths; by making a comparison between an epoxy and a siloxane polymer waveguide material system (both commercially-available). The proposed waveguides can be used in short-reach optical interconnects targeting chip-to-chip communication on the interposer level or providing a coupling interface between single-mode optical fibers and photonic integrated circuits (PICs). This technology enables the integration of optoelectronic chips for photonic packaging purposes. First, the single-mode dimensions (4×4μm2 and 5×5μm2) for both materials at selected wavelengths (1.31μm and 1.55μm) were determined based on the refractive index measurements. Then, the waveguides were patterned by a direct-write lithography method. The fabricated waveguides show a high-quality surface with smooth sidewalls. The optical propagation losses were measured using the cut-back method. For the siloxane-based waveguides, the propagation losses were found to be 0.34dB/cm and 1.36dB/cm at 1.31μm and 1.55μm respectively while for the epoxy-based waveguides the losses were 0.49dB/cm and 2.23dB/cm at 1.31μm and 1.55μm respectively.

Laser Direct Writing of Single-Mode Polysiloxane Optical Waveguides and Devices

Using a custom-built laser direct writing system, single-mode polymer optical waveguides, and devices for board-level optical interconnects were fabricated. A novel photopatternable polysiloxane material was developed that combines low-loss, simple, and large-area processability, and reliability during manufacturing and system operation. The polysiloxane waveguides were designed with quadratic cross sections of 5.5 $\times$ 5.5 µm2 and a refractive index contrast of 0.0086 between core and cladding polymer for single-mode operation at the wavelength of 1.3 µm. A straight waveguide propagation loss of 0.28 dB/cm was achieved. A wide range of passive optical devices, including Y-splitters, directional couplers, and Mach–Zehnder interferometers were successfully fabricated and characterized. The results prove that the presented combination of material and process technology is a viable implementation for short distance board-level optical links.

Demonstration of balanced coherent detection using polymer optical waveguide integrated distributed traveling-wave photodetectors

We have demonstrated balanced coherent detection using distributed balanced traveling-wave photodetectors integrated with single mode polymer optical waveguides. Balanced distributed traveling-wave photodetectors having 3 dB bandwidth of 20 GHz exhibited 20 dB signal to noise ratio improvement measured at 15 GHz modulation frequency in a balanced coherent detection demonstration.

Design and Fabrication of Monolithic Distributed Traveling-Wave Photodetectors Integrated With Polymer Optical Waveguides

We have designed and fabricated monolithic distributed balanced traveling-wave metal-semiconductor-metal photodetectors (MSM PDs) distributed along single-mode polymer optical waveguides. We demonstrate that monolithically integrated polymer optical waveguides on a semiconductor can provide efficient optical interconnects in an optoelectronic circuit. A responsivity of 0.44 A/W and a 3-dB bandwidth of 10 GHz were obtained in a PD array with five MSM PDs. A high photocurrent of 7.3 mA was measured in an array having eight MSM PDs. Impulse response measurements were performed and the results were compared with frequency domain results.

Heat-resistant singlemode optical waveguides using fluorinated polyimides

Singlemode polymer optical waveguides are fabricated using fluorinated polyimides. The optical waveguides exhibit a low loss of less than 0.3dB/cm parallel to the waveguide plane (TE polarisation) at 1.3μm, and have thermal and moisture stability.