Planar Lightwave Circuit Technology Research Articles

Interleave filter based on coherent optical transversal filter

The principle of the transversal interleave filter previously proposed as a novel class of interleave filter is described. The principle of a conventional 1 /spl times/ 1 coherent optical transversal filter is reviewed. Then, the fundamental operating principle and the three design conditions required for the novel interleave filter are explained. As examples, three types of filter design, namely 1) a general/transposed design; 2) an asymmetric design; and 3) a symmetric design, are presented, and their interleave filter characteristics are discussed. The designed interleave filters with a free spectral range of 100 GHz was fabricated using silica-based planar lightwave circuit (PLC) technology. The asymmetric design achieved a wide 3-dB passband width of 55 GHz, whereas an ordinary lattice-form interleave filter could not realize a 3-dB passband width larger than 50 GHz because of the halfband property. A small polarization-dependent wavelength shift of 0.01 nm is demonstrated by inserting a single half waveplate in the middle of the circuit. The general/transposed and symmetric designs realized a practical interleave filter with a boxlike transmission spectrum and low chromatic dispersion. The two-stage interleave filter formed by cascading the general and transposed designs has the advantages of a low crosstalk of less than -46 dB and a wide 20-dB stopband width of 40 GHz, whereas the single-stage symmetric design has an extremely small chromatic dispersion of within /spl plusmn/5 ps/nm. In addition, the design concept to realize a 1/spl times/N transversal interleave filter is extended.

Y-branch waveguides with stabilized splitting ratio designed by wavefront matching method

We designed optical Y-branch waveguides with a stabilized splitting ratio by using a new design approach based on the wavefront matching method. The designed Y-branches were fabricated using silica-based planar lightwave circuit technology. We suppressed any variation in the splitting ratio of the Y-branch experimentally and obtained excess losses of <0.35 dB over a wide wavelength range of 1.3-1.7 μm.

Mach-Zehnder interferometer exactly aligned with ITU grid frequencies

We propose a new Mach-Zehnder interferometer (MZI) that can align passband/rejection-band centers exactly with an arbitrary frequency grid. The proposed MZI incorporates phase-generating couplers, which generate a nonlinear frequency-dependent phase to control the absolute frequency and the dispersion of the waveguide refractive index simultaneously. As an example, we present an MZI that is exactly aligned with the 50-GHz spaced International Telecommunication Union grid. We fabricated the proposed MZI using silica-based planar lightwave circuit technology and demonstrated an MZI with a frequency error of less than /spl plusmn/0.3 GHz over a wide frequency range of 10 THz.

Integrated-optic variable delay line and its application to a low-coherence reflectometer

We propose a large-scale variable delay line based on planar light-wave circuit technology and its application as a reference arm in an optical low-coherence reflectometer. This variable delay line is composed of 16 asymmetrical delay arm pairs sandwiched between 2 optical switches, which select the path for a needed delay. This configuration enables us to eliminate the need for a moving part in the reflectometer. We can scan the reference arm over a length of 262.1 mm with a step of less than 1.0 microm in air and achieve reflectometer sensitivity of about -47 dB.

Optical Wavelet Signals Processing and Multiplexing

We present compact integrable architectures to perform the discrete wavelet transform (DWT) and the wavelet packet (WP) decomposition of an optical digital signal, and we show that the combined use of planar lightwave circuits (PLC) technology and multiresolution analysis (MRA) can add flexibility to current multiple access optical networks. We furnish the design guidelines to synthesize wavelet filters as two-port lattice-form planar devices, and we give some examples of optical signal denoising and compression/decompression techniques in the wavelet domain. Finally, we present a fully optical wavelet packet division multiplexing (WPDM) scheme where data signals are waveform-coded onto wavelet atom functions for transmission, and numerically evaluate its performances.

Integrated-optic encoder/decoder for time-spreading/wavelength-hopping optical CDMA

We demonstrate an integrated-optic encoder/decoder for time-spreading/wavelength-hopping optical code division multiple access. It is composed of a wavelength multi/demultiplexer and variable delay lines fabricated by using silica-based planar lightwave circuit technology. We evaluated the device characteristics, including those of the key components and the encoding/decoding operation, and confirmed its flexible code assignment ability and good auto/cross correlations. We then tested the performance of the encoder/decoder by undertaking bit error rate measurements with 10-Gb/s pseudorandom binary sequence signals and confirmed its applicability to optical layer multicast routing and its ability to compensate for bit skew caused by fiber chromatic dispersion.

Flexible waveband optical networking without guard bands using novel 8-skip-0 banding filters

Novel five-band 8-skip-0 band filters realized in silica waveguide planar lightwave circuit technology were successfully used to demonstrate versatile wavelength-division-multiplexed (WDM) optical networking. Forty C-band channels spaced 100 GHz apart grouped in five bands of eight channels each allowed WDM networking without loss of any channel within the available optical bandwidth. We demonstrate simultaneous transport of 10 and 40 Gb/s with rate-appropriate optical add-drop nodes.

Applications of fiber Bragg grating sensors and high-speed interrogation techniques

We are developing several kinds of fiber Bragg grating (FBG) sensors for application in river surveillance monitoring, civil structural monitoring, aerospace health monitoring, and so on. In this paper we describe highly precise FBG sensing systems, specifically water-level sensors, as a practical example. We have achieved sensor accuracy of ± 0.1% F.S., i.e. ± 1 cm for a full measurement range of 10 m in water level. For other applications, FBG interrogation techniques are described for high-frequency vibration monitoring or acoustic emission detection. In this FBG interrogation system, optical filters based on planar lightwave circuit (PLC) technology are used to measure the wavelength of the reflected light from each FBG sensor. We discuss two types of the optical filter, a Mach–Zehnder interferometer (MZI) and an arrayed waveguide grating (AWG). The wavelength shift of the FBG sensor due to strain or temperature change is determined through direct detection of the light intensity ratio from the output ports of the optical filter. We have made a FBG interrogation unit which allows four-channel FBGs to be connected in series to measure strain in the x, y, and z directions as well as temperature. Copyright © 2005 John Wiley & Sons, Ltd.

Optical Switch and Optical Attenuator based on Planar Lightwave Circuits and MEMS Technologies

Optical Switch and Optical Attenuator based on Planar Lightwave Circuits and MEMS Technologies

Differential-phase-shift quantum key distribution experiment with a planar light-wave circuit Mach–Zehnder interferometer

A differential-phase-shift quantum key distribution experiment was carried out with a planar light-wave circuit (PLC) Mach-Zehnder interferometer. This scheme has two advantages: it requires no polarization control and has a high repetition frequency, provided that a stable interferometer is available. Stable polarization-insensitive operation was achieved with an interferometer fabricated by PLC technology. Raw key creation at a rate of 3076 bits/s with a 5.0% quantum bit-error rate was achieved over 20 km of fiber. The stability of the PLC interferometer was examined.

12.5-GHz Spacing Compact and Low-Loss Interleave Filter Using 1.5%&amp;lt;tex&amp;gt;$Delta$&amp;lt;/tex&amp;gt;Silica-Based Waveguide

We describe the fabrication of a compact lattice-form waveguide interleave filter with a narrow channel spacing of 12.5 GHz. The circuit size was reduced to 1/4 the size of the original circuit by employing a novel folding layout and a waveguide with a high refractive index difference (/spl Delta/) of 1.5% that can reduce the minimum bending radius to 2 mm. The 12.5-GHz spacing interleave filter was fabricated on a single chip by using silica-based planar lightwave circuit technology. We achieved a low insertion loss of <2.3 dB, a wide 1-dB passband width of >8.1 GHz, a 20-dB stopband width of >7.3 GHz, a low crosstalk of <-25 dB, and a low chromatic dispersion of within /spl plusmn/300 ps/nm.

A Novel Method to Measure Refractive Index of Liquid and Curable Liquid Substances

A novel method to measure refractive index (RI) of liquid and curable liquid substances is presented. Planar microlenses with two refracting interfaces facing each other are fabricated with a planar lightwave circuit technology. A liquid, whose RI is to be determined, is filled between the two refracting surfaces and the width of the beam passing through the lens is measured. By comparing the measured beam width with the analytical results, the RI of the liquid can be determined accurately. This method is applicable for measurements of RI absolute values of almost any liquid or curable liquid substances, and can routinely achieve a precision of 1/spl times/10/sup -4/ by using a simple setup with a standard beam profiler. The method easily enables measurements of RI dependences on temperature, wavelength, polarization, etc.

Planar Hybrid Polymer–Silica Microlenses With Tunable Beamwidth and Focal Length

Thermally tunable planar microlenses have been fabricated with a hybrid process utilizing silica-on-silicon and polymer planar lightwave circuit technologies. The silica microlens has a double concave gap filled with an optical polymer. The lens collimates the light beam with a beamwidth of less than 450 /spl mu/m at distances up to 100 mm. The experiments presented demonstrate that by varying the lens temperature in a range of 60/spl deg/C the beamwidth can be tuned by /spl plusmn/40% at different distances from the lens. The beam-propagation-method simulations show that adjusting the lens curvature can control the beamwidth tunability range and thermal sensitivity. That allows optimization of the lens designs for different applications.

A new theoretical basis of higher-derivative optical differentiators

This paper presents a new theoretical basis of higher-derivative finite-impulse response (FIR) optical differentiators for high-speed optical signal processing. A numerical differentiation algorithm, namely, the backward Taylor series expansion and the digital signal processing technique are employed, for the first time, to develop a generalized theory of a pth-derivative FIR optical differentiator. The proposed differentiators are synthesized using a simple integrated-optic transversal filter structure based on the silica-based planar lightwave circuit (PLC) technology, which is compact and compatible with fiber optics. The proposed pth-derivative differentiator only requires p+1 waveguide arms of the transversal filter. By means of computer simulations, the differentiators are shown to be capable of processing Gaussian pulses with high accuracy. We also show the application of a first-derivative differentiator for optical dark-soliton detection and for the generation of an ultrashort optical pulse train. Although the analysis is directed at integrated optical differentiators, the methodology and the results are applicable to other physical systems such as free-space and guided-wave optical signal processors.

Two-dimensional microlens arrays in silica-on-silicon planar lightwave circuit technology

Two-dimensional (2-D) microlens arrays have been fabricated with silica-on-silicon planar lightwave circuit (PLC) technology. Several experimental techniques and computer simulation methods are applied to characterize properties of single and double microlens arrays, with one and two refracting surfaces, respectively. Systematic comparison of the measured and simulated beam propagation profiles enables optimi- zation of the lens and module design resulting in higher input-output coupling efficiency. The insertion losses of the lens-slab-lens optical modules with 90-mm-long slab waveguides are measured to be 2.1 and 3.5 dB for the double and single lens modules, respectively. Comprehen- sive analysis reveals the major loss contributions. Excess losses of the modules caused by variations of the lens curvatures, material refractive indexes, light wavelength, etc., can be controlled within the acceptable limits. Further possibilities for the module loss reduction are discussed. Fairly weak wavelength dependence as well as overall stability of the module properties indicate that the microlens arrays are suitable for dense wavelength division multiplexing (DWDM) photonic networks. © 2003 Society of Photo-Optical Instrumentation Engineers.

Adaptive minimum mse controlled plc optical equalizer for chromatic dispersion compensation

With the advent of very high-bit-rate optical communication systems (40 Gb/s and beyond) and the progressive transformation of the optical layer in a real networking layer, a channel-by-channel adaptive optical equalization will be needed. An adaptive optical equalizer for chromatic dispersion compensation, based on planar lightwave circuit (PLC) technology and controlled by a minimum mean square error (MSE) strategy, is proposed here. It is shown in a rigorous manner how the PLC parameters are to be adjusted and that the control algorithm is effective even with a few stages PLC equalizer, performing better than other nonadaptive control techniques. An analysis of the dynamic behavior of the equalizer shows that, in a realistic time-varying scenario, it can easily adapt to slow channel variations and is able to quickly restore a minimum MSE condition after an abrupt chromatic dispersion variation.

Design and analysis of a control system for an optical delay-line circuit used as reconfigurable gain equalizer

The design and analysis of a control system for a coherent two-port lattice-form optical delay-line circuit used as reconfigurable gain equalizer is presented. The design of the control system, which is based on a real device model and a least-square optimization method, is described in detail. Analysis on a five-stage device for the 32 possible solutions of phase parameters showed that, for some filter characteristics, the variations in power dissipation can vary up to a factor of 2. Furthermore, the solution selection has influence on the optimization result and number of iterations needed. A sensitivity analysis of the phase parameters showed that the allowable error in the phase parameters should not exceed a standard deviation of π/500 in order to achieve a total maximal absolute accuracy error not greater than approximately 0.6 dB. A five-stage device has been fabricated using planar lightwave circuit technology that uses the thermooptic effect. Excellent agreement between simulations and measurements has been achieved.

Quantum Computations with Transverse Modes of an Optical FieldPropagating in Waveguides

A fully optical method to perform quantum computation with transverse modesof the optical field propagating in waveguide is proposed by supplying theprescriptions for a universal set of quantum gates. The proposal for quantumcomputation is based on implementing a quantum bit with two normal modes ofmulti-mode waveguides. The proposed C-NOT gate has the potential of beingmore compact and easily realized than some optical implementations, since itis based on planar lightwave circuit technology and can be constructed byusing Mach-Zehnder interferometer having semiconductoroptical amplifiers with very large refractive nonlinearity in its arms.

Parameter extraction during thermal cycling and optical backreflection measurements of bidirectional optoelectronic modules

In this paper, we discuss the conditions under which we can correctly extract a variety of module parameters of single mode bidirectional optoelectronic duplexer and diplexer modules during relatively slow thermal cycling between -40/spl deg/C and +85/spl deg/C. The obtained values of parameters such as tracking error, optical crosstalk, and the laser diode characteristic temperature have been compared for bidirectional modules from different manufacturers and the impact on these parameters of different interconnect techniques, like microoptic (Mo), silicon optical bench, and planar lightwave circuit technologies is discussed. It is shown that there is a conflict between small threshold currents and good temperature stability for InGaAsP-based Fabry-Perot laser diodes emitting at 1300 and 1550 nm. Then the results of spatially low coherence reflectometry for the different bidirectional module types are presented.

Proposal of a Bragg grating assisted MMIMI-coupler for tunable add-drop multiplexing

The author proposes a novel optical device for tunable add-drop multiplexing. The device is based on a Bragg grating assisted MMIMI-coupler. The analysis is based on the mode propagation theory. Polymer planar lightwave circuit technology is presently the most promising technology for realizing this kind of device.