High reliability optical splitters composed of silica-based planar lightwave circuits

Optical splitters are essential for the construction of optical networks such as fiber-to-the home systems. These devices should exhibit not only good optical characteristics such as low loss and polarization insensitivity but also long-term reliability. Silica-based planar lightwave circuits (PLCs) on Si can form one of the most suitable Y-branching splitters because they have the advantages of low loss, low coupling loss to optical fibers and high reproducibility[l]. When PLC splitters are used in practice, the input and output fibers must be connected to waveguides. Therefore, it is necessary to establish a precise connection technique and confirm its long-term stability. However, neither the connection performance of splitters with up to 32 ports nor the long-term reliability of fiber-connected splitters have yet been evaluated in detail. Here, we describe the connection performance and reliability of 1×8 and 1×32 splitter modules. We have chosen strict Bellcore requirements [2] as the first step in evaluation of the PLC splitter reliability. The requirements are recognized as a standard for reliability tests on optical devices, and define the optical criteria as well as the test conditions.

Silica-based planar lightwave circuit (PLC) devices are starting to be introduced into commercial optical communication systems. PLC devices such as optical splitters, wavelength-insensitive coupler (WINC) arrays, and hybrid- integrated wavelength-division-multiplexing (WDM) transceivers are used to construct cost effective optical access systems. In trunk lines, on the other hand, arrayed-waveguide gratings (AWG) are employed for dense WDM systems to increase the transmission capacity. This paper reviews the current status and recent progress on these practical PLC devices.

The large refractive index contrast between silicon nitride and silicon dioxide allows silicon nitride/dioxide planar waveguides to have a small mode size and low radiation bending loss compared with doped silicon dioxide waveguides. Small waveguide bend with low radiation loss can help make small integrated planar lightwave circuits (PLCs), and also high-Q waveguide ring resonators. This presentation will talk about the design, fabrication and characterization of low loss silicon nitride/dioxide planar waveguide devices including waveguide bend, waveguide cross, and leaky mode waveguide polarizer. The key contribution of this work is the use of the lateral mode interference (LMI) 3dB splitter to accurately measure the loss of the planar lightwave circuit devices. We will also talk about the waveguide ring resonators with silicon nitride/dioxide materials. The application for photonic biochemical sensors will also be discussed.

Silica-based planar lightwave circuits (PLC) provide various important devices for both optical wavelength division multiplexing (WDM) networks and optical access networks. This paper is an overview of recent progress in PLC technology including optical power splitters, arrayed-waveguide gratings, thermo-optic switches, and hybrid integrated PLCs.

Design optimization of a novel integrated triplexer based on planar lightwave circuit (PLC) for fiber-to-the-home applications is described. The two-mode interference coupler and Mach-Zehnder interference are used to construct the filter chip. Simulation results of high isolation and low insertion loss are gotten for proposed design. Technique tolerance is improved for fabricating device.

The 3-dimensional interconnection of waveguides in planar lightwave circuits (PLCs) is demonstrated for the first time. By writing 3-dimensional waveguides that cross other waveguides, the femtosecond laser successfully interconnects PLC waveguides with low loss.

A waveguide lens, composed of multistage polymer-filled thin grooves in a silica planar lightwave circuit (PLC) is proposed and a low-loss structure has been designed. A waveguide lens in a silica slab waveguide has been fabricated using reactive ion etching (RIE) and formed by filling with polymer. Both an imagding optical system and a Fourier-transform optical system can be configured in a PLC using a waveguide lens. It renders the PLC functional and its design flexible. To obtain a shorter focal length with a low insertion loss, it is more effective to use a multistage lens structure. An imaging optical system and a Fourier-transform optical system with a focal length of less than 1000 µm were fabricated in silica waveguides using a multistage lens structure. The lens imaging waveguides incorporate a 16–24-stage lens, with insertion losses of 4–7 dB. A 4 ×4 optical coupler, using a Fourier-transform optical system, utilizes a 6-stage lens with losses of 2–4 dB.

Along with the wide deployment of cloud computing services, the introduction of optical interconnect technology has supported the rapid growth of data throughput in datacenter over the last couple of years. So far, multimode fiber (MMF) links have been widely installed in datacenter networks, hence the limitation of bandwidth distance product of MMF links is a current issue. In the future, wavelength division multiplexing (WDM) transmission technology could be applied even to the MMF links, by which the transmission capacity could increase because multiple optical signals with different wavelengths are multiplexed in one fiber.In, this paper, Y-branched polymer optical waveguide couplers with SI and GI square cores are fabricated using the imprint method in order to apply to a multiplexing (MUX) device in the MMF WDM links. To fabricate low loss MUX devices, three different Y-branch structures are designed and actually fabricated. Then, their optical characteristics are compared. It is confirmed that the loss of GI waveguide is lower than that of SI waveguide, independent of the multiplexing structure, because the light leakage at the multiplexing region (two-cores junction) could be reduced due to the strong light confinement effect.

To develop polarization-insensitive semiconductor optical amplifier (SOA) gates into more efficient and functional optical components by using hybrid integration with a planer lightwave circuit (PLC) platform, vertical tapered spot-size converters were integrated into a SOA gate with a narrow mesa-stripe structure of submicrometer width leading to low coupling loss (2.6 dB). Very-low polarization dependence of gain ( 30 dB) were achieved in a wide wavelength range (40 nm). High-speed (<1 us) gate operation was also demonstrated. These results indicate that the spot-size converted SOA integrated on a PLC platform will perform well in wavelength-division-multiplexing (WDM) applications.

Chapter 3 - Optical Technologies in Passive Optical Access Networks

Micro-ring resonator based all-optical Arithmetic and Logical Unit

A normally dark 1×1 switch is demonstrated in a planar lightwave circuit. The design is based on a highly asymmetric Y-branched polymeric waveguide. This device exhibits an attenuation level of 50 dB when no electrical power is applied, and it has an excess loss of 0.2 dB when the switch is activated. The design and experimental work are described. In addition, the serial integration of this device with other integrated optical devices and circuits is studied.

The diffraction gratings are widely used in Space-flight satellites for spectrograph instruments or in ground-based telescopes in astronomy. The diffraction gratings are one of the key optical components of such systems and have to exhibit very high optical performances. HORIBA Jobin Yvon S.A.S. (part of HORIBA Group) is in the forefront of such gratings development for more than 40 years. During the past decades, HORIBA Jobin Yvon (HJY) has developed a unique expertise in diffraction grating design and manufacturing processes for holographic, ruled or etched gratings. We will present in this paper an overview of diffraction grating technologies especially designed for space and astronomy applications. We will firstly review the heritage of the company in this field with the space qualification of different grating types. Then, we will describe several key grating technologies developed for specific space or astronomy projects: ruled blazed low groove density plane reflection grating, high-groove density holographic toroidal and spherical grating, and finally transmission Fused Silica Etched (FSE) grism-assembled grating. We will not present the Volume Phase Holographic (VPHG) grating type which is used in Astronomy.

This paper proposes a polarization beam splitter operating at terahertz frequencies. The beam splitter utilizes cyclo-olefin copolymer as the material and introduces two hollow elliptical structures to divide the fiber core into two parts. The characteristics of this fiber are analyzed using the finite element method, and the influence of various structural parameters on the polarization splitting properties is studied in detail. By optimizing the structural parameters of the fiber, a terahertz polarization beam splitter with a bandwidth of 0.08 THz and a low transmission loss of 0.071 dB/cm is achieved at the center frequency of 1 THz with a length of 2.81 cm. This fiber achieves significant breakthroughs in operating bandwidth and transmission loss, making it of great value for the design and research of polarization beam splitters and having important applications in optical communication systems and optical networks.

A low cost optical transmitter/receiver module is essential for optical subscriber systems. Hybrid integration of optical components and alignment free assembly are effective techniques for such low cost module. We newly developed a bi-directional optical transmitter/receiver module using passive alignment techniques for a laser diode (LD) mounting on a Planar Lightwave Circuit (PLC). Compact module size of 26mm X 10mm X 3mm is achieved. A spot-size converted laser diode is passively mounted on a PLC chip by detecting each alignment marks on the LD and the PLC chip. Low optical coupling loss of less than 4.5 dB is attained. The PLC chip has the function of Y branch. Alignment marks for LD mounting and a V-groove for fiber alignment are also fabricated on the PLC chip. A fiber is self-aligned on the V-groove. The PLC chip and the other components such as a sub assembled dual photo diode and a receiver-amplifier are also built in a ceramic package. The output power of the transmitter/receiver module is +2dBm at the LD drive current at 45mA. Responsivity of over 0.35A/W is realized. Minimum optical received power of -38dBm at the 50Mb/s burst signal was obtained.