Planar Lightwave Circuit Research Articles

Low-Loss Y-Branch Waveguides Designed by Wavefront Matching Method

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In this paper, we describe the procedure for designing low-loss Y-branch waveguides by the wavefront matching (WFM) method, and report experimental results as proof of concept. The designed Y-branches were fabricated using silica-based planar lightwave circuit (PLC) technology. A Y-branch fabricated with a 0.45%-<formula formulatype="inline"><tex Notation="TeX">$\Delta$</tex> </formula> waveguide exhibited a low excess loss of less than 0.2 dB over a wide wavelength range of 1250 to 1650 nm. In addition, we demonstrate that the WFM-designed Y-branches enable us to provide compact 1 <formula formulatype="inline"> <tex Notation="TeX">$\times$</tex></formula> 32 splitters with an average insertion loss of 16.0 dB at a wavelength of 1550 nm. In addition, we present some experimental results obtained using samples with different <formula formulatype="inline"> <tex Notation="TeX">$\Delta$</tex></formula> values, and show that our design method is more efficient for a higher <formula formulatype="inline"><tex Notation="TeX">$\Delta$</tex> </formula> waveguide suitable for functional PLC devices. </para>

FABRICATION OF MACH-ZEHNDER INTERFEROMETOR BASED ON PLANAR WAVEGUIDE FOR THE APPLICATION OF BIOSENSORS

In this paper, designed and simulated Power Splitter (PS) integrated Mach-Zehnder interferometer (MZI) based planar waveguide devices (which is called here a PS-MZI). Moreover, we fabricated optical waveguide based on the PS-MZI for application to the biosensor. The integrated optical structure is sensitive to refractive index change induced due to the interaction of the evanescent field with an immobilized biological sample placed on one of the two arms of the interferometer. The PS-MZI sensor was preceded by a Y -junction, which splits the input power between the sensor and a reference branch to minimize the effect of optical power variations. The waveguide were optimized at a wavelength of 1550 nm and fabricated according to the design rule of 0.45 delta%, which is the difference of refractive index between the core and clad. The fabrication of PS-MZI optical waveguides was performed by a conventional planar lightwave circuit (PLC) fabrication process. The PS-MZI optical waveguides were measured of the optical characteristics for the application of biosensors.

An optical power combiner/wavelength demultiplexing module for hybrid WDM FTTX

An optical device scheme that serves simultaneously as a power combiner for upstream and wavelength demultiplexer for downstream signals is presented. The design concept is validated experimentally by an optical module based on off-the-shelf discrete optical components. An integrated device based on planar lightwave circuit (PLC) is proposed and analyzed in which a multi-mode interference (MMI) device is utilized to separate the upstream 1310 nm signal from the downstream 155x nm signals. The dense WDM function is realized through an arrayed-waveguide-grating (AWG). Design guidelines and optimization procedure for the device are discussed by way of examples.

Low-loss, compact waveguiding with TE mode in metal/dielectric waveguides for planar lightwave circuit

We propose a low-loss metal/dielectric waveguide for compact planar lightwave circuit. The basic waveguide structure is a metal-defined high-index-contrast strip waveguide based on silicon/silica. As the guide is designed for TE single mode waveguiding, extremely low propagation loss (e.g. <0.04dB/cm), very low bend loss (e.g. 0.0043dB/90°-turn) and small waveguide pitch of zero-crosstalk are theoretically achievable, and can be further improved by compromising with component size and density. Examples of multi-bends and device integration are demonstrated with numerical simulations. The proposal is compatible with silicon technology and appealing for development of silicon-based planar lightwave circuit.

Small Bend Structures Using Trenches Filled With Low-Refractive Index Material for Miniaturizing Silica Planar Lightwave Circuits

We have proposed the fabrication of small bend structures using trenches along both sides of the core, filled with low-refractive index material, in order to miniaturise silica planar lightwave circuits. The minimum bending radius of a silica waveguide was reduced from 2 mm to 200 mum by filling the trenches with low-refractive index material. The local lateral relative refractive index difference (Delta) was increased to 8.64%. We fabricated cascade S-shaped waveguides to estimate a bend loss of the proposed structure. Moreover, we applied those structures to arrayed-waveguide gratings (AWG)s. Both 8-channel, 100-GHz channel-spacing and 8-channel, 12.5-GHz channel-spacing AWGs were successfully fabricated. Compared with conventional AWGs, sizes of these devices were reduced by factors of about 2 and 4, respectively.

Crosstalk comparison of lattice-form optical interleaver with different coupler structures

Lattice circuit made from a cascade of couplers and delay-lines is a popular approach for optical interleaver based on planar lightwave circuit (PLC) technology. Different coupler structures can be employed in the lattice circuit, including 1-stage directional couplers (DCs), 4-stage DCs, and 2-stage multimode interference (MMI) couplers. We fabricated optical interleavers with above three coupler structures, respectively. The experimental results prove that the latter two coupler structures can help to reduce crosstalk, which meets the simulation results well.

An athermal delay interference circuit using trenches filled with low-refractive index material

Recently, various types of silica-based planar lightwave circuits (PLCs) have been used for optical networks. However, silica exhibits large temperature dependence, so the temperature of silica-based PLCs needs to be controlled. We can reduce the cost and the energy budget of optical equipment by using athermal waveguides. We propose an athermal optical waveguide comprised of trenches filled with low-refractive index material. The propagation constant of the waveguide is determined by the refractive indices of the core and the low-refractive index material; their thermo-optic coefficients have opposite signs, and therefore the temperature dependence of the waveguide can be suppressed. A 1-bit delay circuit was designed for a 12.5Gbit/s differential phase shift keying receiver using the athermal waveguide, and it displayed a wide operating temperature range.

Arrayed Waveguide Gratings and Their Application Using Super-High-.DELTA. Silica-Based Planar Lightwave Circuit Technology

This paper reviews our recent progress on arrayed wave-guide gratings (AWGs) using super-high-Δ silica-based planar lightwave circuit (PLC) technology and their application to integrated optical devices. Factors affecting the chip size of AWGs and the impact of increasing relative index difference Δ on the chip size are investigated, and the fabrication result of a compact athermal AWG using 2.5%-Δ silica-based waveguides is presented. As an application of super-high-Δ AWGs to integrated devices, a flat-passband multi/demultiplexer consisting of an AWG and cascaded MZIs is presented.

Analysis and Development of Fixed and Variable Waveband MUX/DEMUX Utilizing AWG Routing Functions

We develop and analyze a new waveband multi/demultiplexer that exploits the routing functions of arrayed-waveguide gratings (AWG). The device can accommodate multiple input/output fibers simultaneously and be implemented monolithically using silica planar lightwave circuit (PLC) technology. We analyze AWG port usage for variants of the proposed multi/demultiplexers. The important characteristic of the device, its coherent and incoherent crosstalk performance is investigated. A technique to reduce the crosstalk is presented. We extend the capability of the device so that the waveband bandwidth can be changed by adding small switches. Experiments confirm the excellent performance of the proposed waveband multi/demultiplexer.

Integrated-optic digital-to-analogue converter for recognising multiwavelength pulse patterns

A planar lightwave circuit based device is proposed that can recognise optical multiwavelength pulse patterns based on digital-to-analogue conversion. The device consists of a splitter with variable splitting ratios, delay lines and an arrayed-waveguide grating based wavelength multiplexer, and requires no optical gates. 80 Gbit/s and four-bit label recognition experiments were successfully carried out with the device.

Low loss, small crosstalk offset crossing structure for large-scale planar lightwave circuits

A low loss, small crosstalk offset crossing structure for a Si wire waveguide is proposed. We analyzed the properties of the structure for both the TE and TM modes by 2-D FDTD (two-dimensional finite difference time domain) simulation. By optimizing the offset crossing structure, a transmission loss of 0.021dB, and crosstalk of -55.0dB was achieved with a crossing angle of 20 degrees for the TE mode. A transmission loss of 0.070dB, and crosstalk of -48.6dB was also achieved with the same crossing angle for the TM mode. The low losses achieved with a small crossing angle makes this structure very useful for highly integrated optical matrix switches, etc.

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.

Long-distance entanglement-based quantum key distribution over optical fiber

We report the first entanglement-based quantum key distribution (QKD) experiment over a 100-km optical fiber. We used superconducting single photon detectors based on NbN nanowires that provide high-speed single photon detection for the 1.5-mum telecom band, an efficient entangled photon pair source that consists of a fiber coupled periodically poled lithium niobate waveguide and ultra low loss filters, and planar lightwave circuit Mach-Zehnder interferometers (MZIs) with ultra stable operation. These characteristics enabled us to perform an entanglement-based QKD experiment over a 100-km optical fiber. In the experiment, which lasted approximately 8 hours, we successfully generated a 16 kbit sifted key with a quantum bit error rate of 6.9 % at a rate of 0.59 bits per second, from which we were able to distill a 3.9 kbit secure key.

Centralized Frequency Stabilization With Wide Capture Range Using MZI-AWG in DWDM-PON

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This letter proposes a centralized frequency stabilization technique for uplink signals in dense wavelength- division-<?Pub _nolinebreak=""?> multiplexed passive optical networks; it is based on dithering the transmission spectra of the demultiplexer. To ensure that the proposed technique achieves a wide capture range, a planar lightwave circuit is developed that incorporates a Mach–Zehnder interferometer and two arrayed waveguide gratings. Experimental results show that the wide capture range of <emphasis emphasistype="italic"><formula formulatype="inline"> <tex Notation="TeX">$\pm$</tex></formula></emphasis>25 GHz is established without any significant power penalty. </para>

Demonstration of Compact and Low-Loss Athermal Arrayed-Waveguide Grating Module Based on 2.5%-Δ Silica-Based Waveguides

We demonstrated a compact and low-loss athermal arrayed-waveguide grating (AWG) module utilizing silica-based planar lightwave circuit (PLC) technology. Spot-size converters based on a vertical ridge-waveguide taper were integrated with a 2.5%-Δ athermal AWG to reduce the loss at chip-to-fiber interface. Spot-size converters based on a segmented core were formed around resin-filled trenches for athermalization formed in the slab to reduce the diffraction loss at the trenches. A 16-channel athermal AWG module with 100-GHz channel spacing was fabricated. The use of a 2.5%-Δ athermal chip with a single-side fiber array enabled a compact package of the size of 41.6×16.6×4.5 mm3. Athermal characteristics and a small insertion loss of 3.5–3.8 dB were obtained by virtue of low fiber-to-chip coupling loss and athermalization with low excess loss.

Design of PLC Triplexer Using Three Waveguide Interferometer

A novel planar lightwave circuit(PLC) triplexer using a three-waveguide interferometer(TWI) is proposed and examined using the transfer matrix and the beam propagation methods. The proposed triplexer consists of two three-waveguide couplers and three waveguides connecting the couplers. Simulation for the TWI triplexer shows the excess losses of 0.03 dB and 0.94 dB with the crosstalks of -22.3 dB and -14.5 dB in reception, respectively, for the wavelength of 1490- and 1550-nm, while showing the excess loss of 1.75 dB in transmission for the wavelength of 1310 nm. The proposed design shows compact feature as short as 11.5 mm for the refractive-index contrast of 0.45%.

A planar lightwave circuit based micro interrogator and its applications to the interrogation of multiplexed optical fiber Bragg grating sensors

Optical fiber Bragg grating sensors have found potential applications in many fields, but the lack of a simple, field deployable and low cost interrogation system is hindering their deployment. To tackle this, we have developed a micro optical sensor interrogator using a monolithically integrated planar lightwave circuit based echelle diffractive grating demultiplexer and a detector array. The design and development of this device are presented in this paper. It has been found that the measurement range of this micro interrogator is more than 25 nm with better than 1 pm resolution. This paper also reports the applications of the micro interrogator developed to the monitoring of commercial optical fiber Bragg grating (FBG) temperature sensors and mechanical sensors. The results obtained are very satisfactory and in some cases, they are better than those obtained using commercial bench top lab equipment.

Compact and low-loss bent hollow waveguides with distributed Bragg reflector

In this study, a hollow bent waveguide with distributed Bragg reflectors (DBR) in silicon substrate was presented theoretically and experimentally. We used the two-dimensional finite-difference time-domain method to simulate bending transmission efficiencies for arc- and cut-type 90 degrees -bent waveguides. The air core was embedded by Si(3)N(4)/SiO(2) multilayer. The multilayer stacks were deposited by using plasma-enhanced chemical vapor deposition on the top and bottom of air core. The lowest 90 degree bending loss is around 3.9dB for the arc-type bending waveguides and 0.8dB for cut-type bending waveguides, respectively. This waveguide demonstrates a possibility for higher density of integration in planar light wave circuits.

Quantum Hadamard Gate Implementation Using Planar Lightwave Circuit and Photonic Crystal Structures

An all optical method has been proposed for quantum Hadamard gate implementation. This quantum gate was realized by using Y-junction beam splitter. Normal modes in waveguides have been used as quantum bit. This all optical gate can be used in quantum computation and communication. The proposed Hadamard gate has potential of being more compact and easily realized compared to other optical implementations. By using planar lightwave circuit in implementation, the width of Yjunction input waveguide, width of each branch, angle of bend and length of bend were obtained 1 micron, 0.75 micron, 45Âo and 0.75 micron, respectively. By using planar lightwave circuit in implementation, the radius of large air holes and the radius of small holes were obtained 0.2 ands 0.1 micron, respectively. The index of substrate was 1.325. Implementation based on photonic crystal structures and planar lightwave circuit technology was used in integrated optics.

360$^{\circ}$ Star Coupler for Detecting Subwavelength Features

We propose a novel 360deg star coupler. We show theoretically how this coupler can detect perfectly conducting cylinders with radii significantly smaller than a wavelength, in the far field. We experimentally demonstrate detection of a metal probe using the 360deg star coupler in a silica planar lightwave circuit. With improvements, this coupler may be able to perform subwavelength 2D imaging.