Low Chromatic Dispersion Research Articles

Silicon-on-Nitride Waveguide With Ultralow Dispersion Over an Octave-Spanning Mid-Infrared Wavelength Range

The proposed silicon-on-nitride (SON) waveguide exhibits an ultrabroadband (4200 nm), low chromatic dispersion in the mid-infrared (MIR) wavelength region from 2430 to 6630 nm. It has two zero-dispersion wavelengths within the span. Even at 6 , the nonlinear coefficients of the SON waveguides are still comparable with the ones of integrated waveguides around 1550 nm, which are widely used for octave-spanning nonlinear process. This enables a potential nonlinear optical platform for broadband signal processing across the over-one-octave MIR bandwidth.

Efficient Carrier-Envelope Offset Locking with a Simplified Configuration of an f-to-2f Interferometer

We demonstrate a carrier-envelope-offset (CEO) locking of a frequency comb in the 1.5-µm band with 500-pJ laser pulse energy. To achieve the CEO locking in the 1.5-µm band with low laser pulse energy, we improve the efficiency of the laser coupling into our tellurite photonic crystal fiber using angled V-groove splicing. In addition, we use a minimum number of optics in a collinear f-to-2f interferometer to avoid connection and propagation losses. Our method does not need any devices for group delay adjustment. Since we use a short, highly nonlinear fiber with low chromatic dispersion for octave-spanning supercontinuum (SC) generation, the group delay between the short- and long-wavelength on an octave-wide SC spectrum is about 3 ps, which does not cause serious degradation of the CEO beat signal.

Accuracy of Waveform Spectrum Analysis for Ultrashort Optical Pulses

We investigate the waveform power spectrum (WPS) measurement of ultrashort pulses using the nonlinear Kerr effect in an optical waveguide. Our study focuses on a recent experiment reporting the WPS measurement of 260-fs pulses using a 6-cm-long, highly nonlinear chalcogenide (ChG) planar waveguide. By numerical simulation of the underpinning nonlinear propagation, we show the importance of low chromatic dispersion in the waveguide for avoiding measurement inaccuracy due to bandwidth narrowing and asymmetric distortion of the WPS. We also show the distortion effect of excessive input power on broadening the WPS bandwidth. In comparison to using conventional nonlinear fibers, highly nonlinear ChG waveguides are shown to generally enable a more accurate and broadband measurement of shorter pulses over a multiterahertz frequency range, and for a wider ranging signal wavelength. Furthermore, higher order dispersion effects are also avoided. Experiments with nonlinear fiber show its capability to measure the WPS of high-speed 640-Gb/s data signals, albeit for broader pulses and with less wavelength flexibility. Furthermore, the WPS is used to effectively retrieve the signal autocorrelation waveform. The factors impacting the measurement accuracy is compared to other recent experiments using ChG and silicon waveguides. Analysis shows that extending the technique to pulses shorter than 260 fs requires further optimizing the ChG waveguide dispersion, which would benefit broadband signal processing in general.

Design of highly birefringent chalcogenide glass PCF: A simplest design

In this article, a new simplified structure of a highly birefringent chalcogenide As2Se3 glass photonic crystal fiber (PCF) is designed and analyzed by using fully vectorial finite element method. The effective indices, confinement loss, birefringence, and chromatic dispersion of fundamental polarized mode are calculated in the proposed PCF for a wide wavelength range. To maintain the polarization in chalcogenide As2Se3 glass PCF, we enlarged two of the central air holes and reduced two transverse air holes for achieving high birefringence. This helps in creating an effective index difference between the two orthogonal polarization modes. It is also shown that As2Se3 glass PCF provides lower chromatic dispersion and less confinement loss compared to silica PCF of the same structure in wavelength range 1.3 to 1.8μm and hence such chalcogenide As2Se3 glass PCF have high potential to be used in dispersion compensating and birefringence application in optical communication systems. In addition to this, the polarization mode dispersion (PMD) result of the proposed PCF is also reported.

Interleaver Using an Arrayed-Waveguide Grating-Lens-Grating Configuration for Spectrally Efficient Systems

We propose an optical interleaver using an arrayed waveguide grating-lens-grating cascade and a 3-dB coupler. It has a narrow channel spacing, high-order Gaussian passbands, and low chromatic dispersion. We demonstrate a 16.7-GHz version for spectrally efficient wavelength-division-multiplexed systems.

PDM-QPSK: on the system benefits arising from temporally interleaving polarization tributaries at 100Gb/s

We experimentally study, over a dispersion-managed link relying on low chromatic dispersion fibre, the origins of the system benefits provided by temporally interleaving the polarization tributaries of 100Gb/s coherent RZ-PDM-QPSK by half a symbol period. Hence, we demonstrate that the amount of benefits provided by this technique is dependent on the configuration of the WDM transmission system.

An Endlessly Single-Mode Photonic Crystal Fiber With Low Chromatic Dispersion, and Bend and Rotational Insensitivity

A single-mode photonic crystal fiber (PCF) with low chromatic dispersion, low bend, and rotational sensitivity is presented. The transverse electric field vector distributions of the fundamental, higher order and fundamental space filling modes, their effective indices, chromatic dispersion, confinement, bending and rotational losses are reported using full-vector finite-element method (FEM). In addition, the endlessly single mode behavior is demonstrated by employing the V parameter of the proposed PCF. It has also been shown that the proposed PCF design is insensitive to bends and rotations.

Bending Effects on Highly Birefringent Photonic Crystal Fibers With Low Chromatic Dispersion and Low Confinement Losses

Photonic crystal fibers (PCFs) with elliptical air-holes located in the core area that exhibit high birefringence, low losses, enhanced effective mode area, and low chromatic dispersion across a wide wavelength range have been presented. The effects of bending on birefringence, confinement losses and chromatic dispersion of the fundamental mode of the proposed PCFs have been thoroughly investigated by employing the full vectorial finite element method (FEM). Additionally, localization of higher order modes is presented. Also, effects of angular orientation on bending loss have been reported. Significant improvement on key propagation characteristics of the proposed PCFs are demonstrated by carefully altering the desired air hole diameters and their geometries and the hole-to-hole spacing.

Novel design of photonic crystal fibres with low confinement losses, nearly zero ultra-flatted chromatic dispersion, negative chromatic dispersion and improved effective mode area

A novel photonic crystal fibre (PCF) with a low confinement loss and nearly zero ultra-flatted chromatic dispersion and negative chromatic dispersion at a wide telecommunication window is presented. Important PCF design parameters, such as the effects of air holes and geometrical parameters on the effective index, confinement losses, chromatic dispersion and effective mode area, have been thoroughly investigated by employing the full vectorial finite element method. Significant reduction of the confinement loss and low chromatic dispersion of the PCF, with three rings of air holes, has been obtained by carefully incorporating additional air holes.

Direct UV-Written Integrated Optical Beam Combiner for Stellar Interferometry

In this paper, we report the fabrication of an optical-beam combiner for stellar interferometry by means of direct ultraviolet (UV) writing. The component is shown to have good performance (fringe contrast > 95%, total loss ~0.7, -40-dB crosstalk, broadband operation covering at least the range 1.49-1.65 mum, and low differential chromatic dispersion). The overall performance exceeds that of similar components currently used for astronomical research. This result, combined with the fast-prototyping ability of UV writing, opens up new possibilities for the realization of highly optimized integrated-optical components for astronomical research

Dispersion and Confinement Loss Control in Modified Hexagonal Photonic Crystal Fibers

This paper presents a novel technique for the control of chromatic dispersion and confinement loss in hexagonal photonic crystal fibers (H-PCFs). It is demonstrated that it is possible to obtain very low chromatic dispersion of 0 ± 0:38 ps/(nm·km) in the wavelength range of 1.41 to 1.66 μm and confinement loss of less than 0.0001 dB/km from a six ring modified H-PCF (MH-PCF). The higher order dispersion at 1.55 μm is about −0.001 ps/(nm2-km).

Large-pitch kagome-structured hollow-core photonic crystal fiber

We report the fabrication and characterization of a new type of hollow-core photonic crystal fiber based on large-pitch (approximately 12 microm) kagome lattice cladding. The optical characteristics of the 19-cell, 7-cell, and single-cell core defect fibers include broad optical transmission bands covering the visible and near-IR parts of the spectrum with relatively low loss and low chromatic dispersion, no detectable surface modes and high confinement of light in the core. Various applications of such a novel fiber are also discussed, including gas sensing, quantum optics, and high harmonic generation.

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.

Characterization of fluoride fibers for the Optical Hawaiian Array for Nanoradian Astronomy project

We report on the interferometric characterization of a pair of 300 m long single-mode non-polarization-maintaining fibers designed for the Optical Hawaiian Array for Nanoradian Astronomy ('OHANA) project whose goal is to realize a kilometric near-infrared astronomical array by connecting the large telescopes of the Mauna Kea observatory with single-mode fibers. The fluoride glass fibers are operated in the astronomical K band (2.0-2.4 microm) in which their attenuation is low. We have measured very low differential chromatic dispersion, and the wideband fringe visibility is 0.9 if the two fiber arms have the same temperature. The thermal sensitivity of fibers with respect to their interferometric properties has been studied. The differential chromatic dispersion of the fibers is highly sensitive to the temperature difference. On the contrary, the coherent loss due to mismatch of polarization states is not significantly dependent on the temperature difference. Compensation of thermally induced differential dispersion by use of CaF2 glass plates is demonstrated.

Flat-top interleavers with chromatic dispersion compensator based on phase dispersive free space Mach–Zehnder interferometer

In this paper, novel interleavers using circular cavities (CC) in a Mach–Zehnder interferometer (MZI) has been presented and demonstrated for the first time, in which CCs act as phase dispersive mirrors which exhibit a periodic dependence on the frequency of light. Three implementation schemes have been proposed and investigated. Theoretical analysis shows the spectral characteristics of each scheme in a 50-GHz channel spacing application. Furthermore, the chromatic dispersion (CD) of each output comb can be flattened within passband by appending an additional CC. The result shows that the proposed designs with novel interferometer technique can simultaneously provide flat top passbands, high isolation stopband and low CD value as well.

12.5-GHz Spacing Compact and Low-Loss Interleave Filter Using 1.5%<tex>$Delta$</tex>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.

Evaluation by Monte Carlo simulations of the power limits and bit-error rate degradation in wavelength-division multiplexing networks caused by four-wave mixing.

Fiber nonlinearities can degrade the performance of a wavelength-division multiplexing optical network. For high input power, a low chromatic dispersion coefficient, or low channel spacing, the most severe penalties are due to four-wave mixing (FWM). To compute the bit-error rate that is due to FWM noise, one must evaluate accurately the probability-density functions (pdf) of both the space and the mark states. An accurate evaluation of the pdf of the FWM noise in the space state is given, for the first time to the authors' knowledge, by use of Monte Carlo simulations. Additionally, it is shown that the pdf in the mark state is not symmetric as had been assumed in previous studies. Diagrams are presented that permit estimation of the pdf, given the number of channels in the system. The accuracy of the previous models is also investigated, and finally the results of this study are used to estimate the power limits of a wavelength-division multiplexing system.

All-fiber format compression of frequency chirped pulses in air-guiding photonic crystal fibers.

Air-cored, photonic band-gap crystal fibers exhibiting low nonlinearity and anomalous chromatic dispersion in spectral ranges inaccessible to conventional fibers can be used in the realization of all-fiber-format pulse compressors with unprecedented peak powers and wavelength diversity. Linear compression of inherently chirped and prestretched pulses by factors ranging from 20 to 80 around 1.0 and 1.5 microm have allowed generation of pulses as short as 163 fs. The results show that totally integrated femtosecond fiber laser sources can be realized throughout the visible and near-infrared and point to the possibility of megawatt peak and tens of watt average in-fiber power levels.

Compact and Low-Loss Interleave Filter Employing Lattice-Form Structure and Silica-Based Waveguide

This paper describes a compact and practical interleave filter with uniform multi/demultiplexing properties and a wide operational wavelength range realized by using a lattice-form structure and a silica-based waveguide. In the design, we optimized the bandwidth by controlling the lattice stage number and the loss ripple in the spectrum. Moreover, we propose a novel coupler with a large fabrication tolerance, a new tandem configuration that provides uniform characteristics and low dispersion, a polarization dependence compensation method, and a folded configuration, which are effective in realizing a high-performance interleave filter. Based on the above techniques, we fabricated a 50-GHz channel spacing interleave filter by using planar-lightwave-circuit technologies and demonstrated that it performed well throughout the C-band, exhibiting a low insertion loss of about 2 dB, a low chromatic dispersion of within +/-20 ps/nm, a 1-dB passband width of over 34 GHz, and a 30-dB stopband width of over 25 GHz, which are sufficient for a 10-Gbps transmission system.

Impact of Chromatic and Polarization-Mode Dispersions on DPSK Systems Using Interferometric Demodulation and Direct Detection

We study the impact of chromatic dispersion (CD) and first-order polarization-mode dispersion (PMD) on systems using binary differential phase-shift keying (2-DPSK) or quaternary DPSK (4-DPSK) with nonreturn-to-zero (NRZ) or return-to-zero (RZ) formats. These signals are received using optical preamplification, interferometric demodulation, and direct detection. We consider the linear propagation regime and compute optical power penalties at fixed bit-error ratio (BER). In order to evaluate the BER precisely taking account amplifier noise, arbitrary pulse shapes, arbitrary optical and electrical filtering, CD, and PMD, we introduce a novel model for DPSK systems and compute the BER using a method recently proposed by Forestieri for on-off keying (OOK) systems. We show that when properly applied, the method yields highly accurate results for DPSK systems. We have found that when either the NRZ or RZ format is used, 2-DPSK exhibits lower power penalties than OOK in the presence of CD and first-order PMD. RZ-2-DPSK, as compared with NRZ-2-DPSK, incurs smaller penalties due to PMD, but offers no advantage in terms of CD. 4-DPSK, as it has twice the symbol duration of OOK or 2-DPSK for a given bit rate, incurs much lower CD and PMD power penalties than either of these techniques. RZ-4-DPSK is especially promising, as it offers CD and PMD penalties significantly smaller than all other techniques, including NRZ-4-DPSK.