Hans Bissessur

Optical differential phase shift keying (DPSK) direct detection considered as a duobinary signal

Optical differential phase shift keying (DPSK) may be considered as a duobinary signal. Considering duobinary coding properties, we show theoretically and experimentally that the complicated Mach-Zehnder modulator used at the receiver side can be replaced by a standard narrow optical filter.

Accurate refractive index measurements of doped and undoped InP by a grating coupling technique

Accurate measurements of InP refractive indices in the 1300–1600 nm wavelength range are reported. They are obtained using the grating coupling technique within an asymmetrical slab waveguide where an intrinsic InP guiding layer was grown on a doped InP substrate (N=2×1018 cm−3). Modal indices are obtained with an absolute precision of a few 10−4 from either guided or reflected waves. Bulk refractive indices of intrinsic and N‐doped InP are then deduced from the allowed modes propagating in the layered structure. With sample temperature maintained to within 0.01 K, InP bulk indices are obtained with a typical accuracy of 5×10−4. Furthermore, a (2.02±0.02) 10−4 K−1 refractive index temperature coefficient has been measured for bulk InP at room temperature.Accurate measurements of InP refractive indices in the 1300–1600 nm wavelength range are reported. They are obtained using the grating coupling technique within an asymmetrical slab waveguide where an intrinsic InP guiding layer was grown on a doped InP substrate (N=2×1018 cm−3). Modal indices are obtained with an absolute precision of a few 10−4 from either guided or reflected waves. Bulk refractive indices of intrinsic and N‐doped InP are then deduced from the allowed modes propagating in the layered structure. With sample temperature maintained to within 0.01 K, InP bulk indices are obtained with a typical accuracy of 5×10−4. Furthermore, a (2.02±0.02) 10−4 K−1 refractive index temperature coefficient has been measured for bulk InP at room temperature.

Extremely small polarization independent phased-array demultiplexers on InP

Compact, polarization insensitive phased-array wavelength demultiplexers are demonstrated with a deep ridge waveguide. Good agreement with the modeling is found for the birefringence and the refractive index. Zero birefringence is effectively obtained around 1.53 /spl mu/m. The guiding structure allows curvatures of 100 /spl mu/m; thus, the grating size of the 4- and 16-channel demultiplexers is reduced to 0.33/spl times/0.30 and 1.1/spl times/1.1 mm/sup 2/, with crosstalk below -16 and -14 dB respectively. These are the smallest demultiplexers reported to date.

How to launch 1 W into single-mode fiber from a single 1.48-/spl mu/m flared resonator

The operation of 1.48-/spl mu/m flared resonators is thoroughly studied, both experimentally and theoretically: the accurate determination of threshold condition as a function of geometrical and material parameters, the study of emission spectra and astigmatism variations as a function of optical power level allow us to better understand the may these devices operate. The origin of modal distortion is then analyzed, and an original solution is proposed to increase the single-transverse-mode power at high injection level: it is shown that implanting the multiple-quantum-well active layer with protons efficiently enhances the filtering capability of the overall structure, and particularly that of the ridge waveguide, by bringing additional lateral absorption losses. The explanation of the filtering mechanism is successfully confirmed by simulations using the beam-propagation method. This technique finally allowed more than 1.3 W of continuous wave (CW) diffraction-limited power at 6 A. Low-modal-gain structures were then realized to reduce modal optical absorption in the implanted structures with a view to maintaining a high external efficiency and a reduced vertical divergence. Finally, a three-lens coupling system was designed and the effects of optical feedback minimized so as to obtain a very high coupling efficiency: with an improved laser design, 1.12 W of CW power were then coupled into single-mode fiber at 6.6 A, which represents 65% of the power emitted by the laser chip.

1.31-1.55-μm phased-array demultiplexer on InP

The first demultiplexers on InP at 1.31-1.55 /spl mu/m based on low-order waveguide arrays have been fabricated and characterized. We show the calculated and measured spectral responses of two devices with 6 and 10 waveguides in the grating. The on-chip loss of the devices is 4.5 dB and the crosstalks are down to -25 dB. Thanks to their large bandwidth, the devices are polarization insensitive and no strong influence of the temperature is seen.

Wavelength-versatile external fiber grating lasers for 2.5-Gb/s WDM networks

Using a semiconductor Fabry-Perot laser in a simple fiber grating laser configuration, we demonstrate single-mode operation with sidemode suppression ratio above 35 dB from 1485 to 1575 mn. In the wavelength-division-multiplexed window, we obtain 14-mA threshold current and 1.6-mW output power at a current of 40 mA, and show 2.5-Gb/s transmission with small penalty from 1540 to 1560 nm.

Effects of hole burning, carrier-induced losses and the carrier-dependent differential gain on the static characteristics of DFB lasers

A model solving the steady-state laser equations above threshold is presented. It calculates important laser parameters such as the threshold losses, emitted optical power, gain margin between the main and secondary modes and, spectral linewidth of any index-grating DFB laser structure. A more exact theoretical linewidth calculation considering nonuniform carrier densities and gain saturation is reported. Good agreement with experiments is found on phase-shifted lasers. The model is used to investigate the factors that determine the importance of spatial hole burning, and general design rules are proposed to reduce this effect. Gain compression combined with carrier-dependent losses is shown to limit the differential external efficiency and cause the emission wavelength to decrease and the spectral linewidth to rebroaden at high output power. >

Performance characterization of components with phase ripple for different 40 Gb/s formats

We investigate the relation between component phase ripple and system penalty by measuring the OSNR penalties with 40 Gb/s NRZ, RZ and CSRZ formats, and discuss the best estimator for the penalty.

Ridge laser with spot-size converter in a single epitaxial step for high coupling efficiency to single-mode fibers

We report on a 1.55-/spl mu/m InGaAsP MQW laser diode with an integrated spot-size converter fabricated in a single epitaxial step using conventional photolithography. The laser structure uses a conventional ridge guide for the active layers and a second larger ridge for the passive waveguide. Low-beam divergence of typically 9/spl deg//spl times/9/spl deg/ results in about 3-dB coupling losses, with a cleaved optical fiber.

3.2 Tb/s (80 /spl times/ 40 Gb/s) C-band transmission over 3 /spl times/ 100 km with 0.8 bit/s/Hz efficiency

We demonstrate 50 GHz-spaced 80 /spl times/ 40 Gbit/s WDM transmission over 300 km of TeraLight/spl trade/ fibre without polarisation demultiplexing, using the PSBT format. A record capacity of 3.2 Tbit/s is thus achieved over the C-band only, with a spectral efficiency of 0.8 bit/s/Hz.