Compensation of dispersion in optical fibers for the 1.3-1.6 μmregion with a grating and telescope

The transmission of ultrashort optical pulses over long distances in optical fibers is limited by pulse broadening due to group velocity dispersion. A grating and telescope dispersion compensator with group velocity dispersion of equal magnitude and opposite sign can compensate for the fiber dispersion. The possible benefits of such dispersion compensation in the 1.3-1.6-μm wavelength region are investigated. The results show that compensation of first-order dispersion at 1.55 μm in a fiber with zero dispersion near 1.3 μm is primarily limited by the second-order dispersion of the grating and the telescope compensator. For a wavelength slightly greater than the zero dispersion wavelength, both the first- and second-order group velocity dispersion can be canceled by the grating and telescope dispersion compensator, allowing transmission exceeding 100 Gb/s over 100 km     

Dispersion compensation over 270 km at 10 Gbit/s using anoffset-core chirped fibre Bragg grating

A 120 mm long fibre Bragg grating, adjustably chirped by an offset-core technique, compensates for dispersion in a 10 Gbit/s optical communication system operating at 1054 μm over 270 km of non-dispersion-shifted fibre. Simultaneous compensation of fibre dispersion and source chirp in a directly modulated system is also described     

Fabrication of wavelength-insensitive 8×8 star coupler

The fabrication and performance of a wavelength-insensitive 8×8 star coupler is described. The integrated-optic star coupler consists of two fan-shaped channel waveguide arrays facing each other and a slab waveguide region located in between. The wavelength-insensitive light splitting was realized by properly tailoring the mode coupling in the input array region. The coupler exhibits low-average excess losses of α=1.4 dB (standard deviation σ=0.40 dB) at λ=1.3 μm and α=1.7 dB (σ=0.44 dB) at λ= 1.55 μm, respectively     

High resolution OCDR using 1.55 μm supercontinuum source andquadrature spectral detection

A supercontinuum source is used with a static Michelson interferometer to perform high-resolution optical coherence-domain reflectometry (OCDR) at 1.55 μm. Quadrature spectral detection enables compensation for both the undesirable spectral shape of the source and for the dispersion in the system. A resolution of less than 5 μm in fibre (full width at half maximum) at 1.55 μm is obtained     

Negative-chirp electroabsorption modulator using low-wavelengthdetuning

The negative chirp of an electroabsorption modulator having an α-parameter value of 0 to -0.5, at an input light wavelength of 1.55-1.56 μm, has been developed by optimizing the bandgap energy of an InGaAsP bulk absorption layer. We have demonstrated successful transmission with 10 Gb/s NRZ modulation over a 100-km span of standard fiber without resort to dispersion compensation     

Suppression of fringe diffraction in localized holographic exposurefor DFB laser arrays

A six-wavelength MQW DFB laser array emitting around 1.55 μm realized in a single holographic lithography is described. Fringe-free localized grating isolation is attained using a mask with a novel aperture-edge design. The first-order grating periods as well as the ridge locations can be varied in a large span. The high throughput of holographic lithography is extended to multiwavelength DFB arrays     

Analysis of 40 Gb/s TDM-transmission over embedded standard fiberemploying chirped fiber grating dispersion compensators

Nonreturn-to-zero (NRZ)- and return-to-zero (RZ)-transmission formats are investigated for 1.55 μm 40 Gb/s fiber grating dispersion compensated standard fiber transmission. The RZ-format is shown to give a twofold increase in transmission distance compared with the conventional NRZ-format. In addition, a larger power margin is obtained at the expense of a reduced dispersion tolerance. System guidelines are proposed relating the pulse width, equalizer spacing, input power and maximum transmission distance. The results are compared with prior theoretical works at 40 Gb/s using equalizer fiber and optical phase conjugation     

Compensation of fibre chromatic dispersion in optical heterodynedetection

Compensation of fibre chromatic dispersion in coherent optical fibre transmission is demonstrated. The chromatic dispersion of a 70 km single-mode fibre with 1.3 μm zero dispersion wavelength is compensated for using a microstrip line equaliser in the intermediate frequency band. Amplitude distortion due to fibre chromatic dispersion at 1.55 μm wave-length is reduced to below 2.5 % with the equaliser     

GaInAsP dual wavelength laser

The fabrication and performance characteristics of a dual wavelength laser emitting near 1.3 μm and 1.55 μm are described. The lasers are of the etched mesa buried heterostructure type, and utilise semi-insulating InP layers both the lateral optical confinement and current confinement. The 1.55 μm emission is at a single wavelength by virtue of the frequency selective feedback provided by a grating etched on the substrate. The lasers have threshold currents in the 20 to 40 mA range, and have quantum efficiencies comparable to single emitter lasers     

Multiplexed identical broad-band-chirped grating interrogationsystem for large-strain sensing applications

We report here a simple and low-cost technique for extreme strain measurement. The overlapping of a chirped sensor grating with an identical reference device provides a novel mechanism for measuring strain. This system permits a linear relationship between strain and resultant optical power. The maximum sensing range of the system is determined by the bandwidths of the gratings employed. A 20-nm chirped grating facilitates a sensing range up to 20 000 μϵ. This paper also demonstrates an arrangement for multiplexing up to four gratings, which can be rapidly and truly simultaneously interrogated     

Low dispersion penalty and wide temperature range operation over120 K with 1.55 μm strained MQW-DFB laser module

STM 16 (2.488 Gbit/s) system operation over a wide DFB chip temperature range of more than 120 K (from -25°C to +95°C) is presented with dispersion penalty below 1 dB after transmission across 100 km standard fibre. DFB operation at 1.55 μm with a high sidemode suppression ratio of 40 dB is achieved within -40°C to +95°C. The lasers were realised using a BRS lateral structure and a quaternary InGaAsP MQW stack with six compressively strained quantum wells and a highly detuned DFB grating     

Planar lightwave circuit dispersion equalizer

The authors report an integrated-optic dispersion equalizer fabricated on a planar lightwave circuit (PLC). This PLC dispersion equalizer is composed of several asymmetrical Mach-Zehnder interferometers cascaded in series. The dispersion equalizer has a high degree of design flexibility and can compensate for both normal and anomalous fiber dispersions at any center wavelength. Moreover, the equalizer can be applied to WDM transmission systems. This equalizer employing five asymmetrical interferometers is fabricated and its measured dispersion values are +834 and -1006 ps/nm. The effectiveness of the equalizer is demonstrated in a 2.5 Gb/s transmission experiment with a 1.3 μm zero-dispersion fiber at 1.55 μm. Also, its performance is evaluated theoretically     

Chirp compensation in mode-locked DFB laser diodes with extendedcavity

The spectro-temporal behavior of actively mode-locked fiber-external-cavity DFB lasers at 1.55 μm is analyzed in detail. Experiments are performed with multiquantum-well InGaAsP lasers of different lengths and different phase-amplitude coupling factors. Transform-limited picosecond pulses are generated with pulsewidth adjustable over half a decade by changing the RF conditions and the device length. As in the case of conventional laser diodes with external grating, the smallest time-bandwidth products are obtained for modulation frequencies to the high-frequency side of the mode-locking band. This result is presently described in terms of chirp compensation by the DFB cavity dispersion. An analytical expression of the pulse compressibility is established from a steady-state mode-locking equation including refractive index variations and cavity dispersion effects. Gain parameters entering the expression are separately evaluated from standard rate equations. A good agreement is found between experimental and theoretical results     

Tunable, picosecond pulse generation using a compressed, modelockedlaser diode source

The generation of pulses shorter than 6 ps, tunable from 1.26 to 1.32 μm, is discussed. The source of these pulses consists of a mode-locked external-cavity 12.3-μm InGaAsP diode laser with grating feedback combined with a compressor which is a grating pair containing an internal telescope. The dispersion in the compressor can be tuned in both magnitude and sign to optimally compensate the chirp in the mode-locked external cavity laser at each wavelength     

Gain-coupled DFB lasers with a titanium surface Bragg grating

The improved performance of gain-coupled DFB lasers incorporating a titanium surface Bragg grating and a strained layer multiquantum well active region for operation at 1.55 μm is presented. Besides the essentially simplified fabrication process, the incorporation of the metallic, absorptive grating yields stable singlemode operation with a high sidemode suppression     

啁啾布喇格光栅法布里-珀罗滤波器

为了获得窄的自由光谱范围和可控的精细度,采用了将平行双通道波导用啁啾布喇格光栅完全反向耦合,在耦合区入口处制作解理面反射镜的方法,将光栅色散引入法布里-珀罗腔内,同时保持了解理面反射镜对精细度的控制.得到法布里-珀罗滤波器的自由光谱范围不仅决定于腔长,还决定于色散,通过调整光栅参数获得在大范围内可控的自由光谱范围.数值模拟和分析结果表明,这种啁啾布喇格光栅法布里-珀罗滤波器可以在传统双镜法布里-珀罗滤波器尺寸下获得千倍量级压缩的自由光谱范围,而精细度的调整不影响自由光谱范围.     

Gain monitoring of erbium-doped fiber amplifiers by detectingspontaneous emission

Gain monitoring by detecting the spontaneous emission (SE) emitted by 0.98-μm laser diode (LD) pumped erbium-doped fiber amplifiers was investigated using three erbium-doped fibers (EDF's) with different absorption coefficients at 1.55 μm (α). Unfavorable 0.98-μm scattered light was observed and removed by an optical filter. The minimum gain accuracy was less than ±0.21 dB for EDF-b (α=1.5 dB/m) with launched pump powers (P_p) from 10 to 30 mW. The minimum gain reproducibility over a 9-h period was ± 0.015 dB for EDF-a (α=3.3 dB/m) at P_p=20 mW     

A study of wet oxidized AlxGa1-xAs forintegrated optics

An investigation of wet oxidized Al_xGa_1-xAs layers in integrated optical applications is reported. Refractive index and thickness shrinkage of wet oxidized Al_xGa_1-xAs layers are measured using spectroscopic ellipsometry. A Cauchy fit to the refractive index is found in the wavelength range between 0.3 and 1.6 μm. The refractive index at 1.55 μm is found to be 1.66±0.01 with little dispersion around 1.55 μm. Very low loss single-mode waveguides with metal electrodes showing very low polarization dependence of loss coefficient are fabricated using wet oxidized Al_xGa_1-xAs layers as upper cladding. Optical polarization splitters are also designed and fabricated from the same type of waveguides taking advantage of increased birefringence. Designs utilizing wet oxidized Al_xGa_1-xAs are compared with conventional designs using only compound semiconductor heterostructures     

Repeated wavelength conversion of 10 Gbit/s signal usingwavelength-tunable semiconductor lasers

Repeated wavelength conversion of 10 Gbit/s pseudorandom non-return-to-zero signals is demonstrated using superstructure grating distributed Bragg reflector lasers operating in the 1.55-μm wavelength region. Error-free and very low-power-penalty wavelength conversion can be achieved in both first and second wavelength conversion for a fixed converted wavelength over a broad wavelength range from 1.486 to 1.573 μm (about 90-nm wide). The power penalty of the transmitted signal light through the first wavelength conversion device increases when the converted wavelength is switched from 1.544 to 1.573 μm periodically at a repetition frequency of 40 MHz. The increase in power penalty, however, is less than 6 dB even when the bit error rate is 10^-12     

Optimum linear pulse compression of a gain-switched 1.5 μm DFBlaser

We report on pulse compression measurements of a 1.5 μm gain-switched strained multi-quantum well distributed feedback semiconductor laser. Experiments with eight normal dispersion fiber lengths show that the optimum compression may be achieved at a dispersion value about half of the one usually calculated using a gaussian pulseshape model. Pulse compression measurements are well reproduced by a simple model involving rate equations. Effective linewidth enhancement factors, α_eff, deduced from this model reveal increasing values with pumping conditions. We show that this nonlinear behaviour is in agreement with an intensity dependence of α_eff