S.D. Perrin

Discrete electroabsorption modulators with enhanced modulation depth

In this paper, we present an investigation into factors that limited the median modulation depth of a batch of packaged discrete waveguide EA modulators to 23 dB at a wavelength of 1.55 /spl mu/m. Results from detailed measurements of the DC absorption and photocurrent spectra are used to show how stray parasitic light can perturb the absorption characteristic and reduce the modulation depth of these high-speed multiple-quantum-well modulators. A novel ridged deeply etched buried heterostructure EA modulator design is presented in which stray light is removed from the immediate vicinity of the guided mode. The key structural difference between these and the previous devices is that they employ a much thicker Fe-doped InP current blocking layer that was grown by atmospheric pressure MOVPE using PCl/sub 3/ for planarization. Detailed measurements of the DC absorption spectra of a packaged ridged deeply etched buried heterostructure device confirm that stray light causes only a minor perturbation on its absorption characteristics. Consequently the new batch of EA modulator modules have a higher median modulation depth of 40 dB, as well as lower fiber-to-fiber insertion losses and picosecond pulse generation capabilities that are very similar to the previous devices which were used in 40 Gb/s optically time division multiplexed experiments.

Pulsed electrical operation of 1.5-μm vertical-cavity surface-emitting lasers

Vertical cavity surface emitting lasers operating in the 1.3- and 1.5-/spl mu/m wavelength ranges are highly attractive for telecommunications applications. However, they are far less well-developed than devices operating at shorter wavelengths. Pulsed electrically-injected lasing at 1.5 /spl mu/m, at temperatures up to 240 K, is demonstrated in a vertical-cavity surface-emitting laser with one epitaxial and one dielectric reflector. This is an encouraging result in the development of practical sources for optical fiber communications systems.<<ETX>>

Reflective SOAs for spectrally sliced WDM-PONs

We have given the first quantitative description of the amplitude squeezing effect in semiconductor optical amplifiers/modulators and shown how this effect can be exploited in a spectrally-sliced WDM-PON. A system demonstration of 8 Gigabit Ethernet channels over 25 km of standard access fibre was presented.

40 Gbit/s modulator with low drive voltage and high optical output power

A 40 Gbit/s electroabsorption modulator module with low drive voltage (2.1 V/sub pk-pk/), low dynamic insertion loss (11 dB) and high optical output power (1 dBm) is described.

A novel twin-ridge-waveguide optical amplifier switch

A novel twin ridge-waveguide optical amplifier switch is reported. The technique of hydrogen passivation of acceptors has been applied to decrease the current spreading in the region between the ridges. The incorporation of a passive waveguide below the active waveguide leads to the result that using 1.53 mu m TE polarized light, through and cross states, each with only 1 dB insertion loss, fiber-to-fiber, can be selected in a device of 360 mu m length by varying the currents to each ridge with a total current of 140 mA. A minimum crosstalk of less than -33 dB was achieved when the cross state was selected. This is the first report of a twin ridge-waveguide amplifier switch with such a low-loss, low-polarization sensitivity, and low crosstalk.<<ETX>>

Applications of electroabsorption modulators in high bit-rate extended reach transmission systems

We report the demonstration of 1310 nm and 1550 nm electroabsorption modulators as high output power, low dispersion penalty transmitters in unrepeatered, uncompensated 80-104 km 10 Gbit/s and 2.4-40 km 40 Gbit/s SMF-28 fibre links.

Temperature dependent operation of 1.5 μm GaInAsP/InP VCSELs

VCSELs are an important technology with many characteristics such as high modulation bandwidth, low-threshold currents and single-mode behaviour that make them suitable for telecommunications applications. InGaAsP/InP is one material system that has been used to manufacture devices that operate in the 1.55 μm region. However, the room temperature performance of VCSELs using this material system fall below those devices using AlGaAs/GaAs operating at shorter wavelengths. Therefore, it is of interest to investigate the temperature dependence of these long wavelength devices. In this paper we describe the experimental results on an array of 64 InGaAsP/InP VCSELs and ultra-bright LEDs designed to emit at 1.5 μm. We also take a simple theoretical model and compare the results with theory.

GaInAsP/InP vertical-cavity surface-emitting laser for 1.5-μm operation

Long-wavelength vertical cavity surface emitting lasers (VCSELs) operating in the 1.3μm to 1.5μm wavelength range are ideal light sources for optical fibre communication applications. However, a number of problems have hindered progress in the development of cost-effective long wavelength VCSELs. These are (a) intrinsically high non-radiative losses, (b) difficulty in fabricating highly reflecting mirrors, lattice-matched to InP, and (c) the disparity between the predicted and observed temperature dependence of the operation of the devices. In this report we present the results of our studies concerning the pulsed operation of a bulk GaInAsP/InP VCSEL fabricated at BT laboratories. The device is tailored to emit at around 1.5 μm at room temperature. The structure has a 45 period n-doped GaInAsP/InP bottom Distributed Bragg Reflector (DBR), and a 4 period Si/Al 2 O 3 dielectric top reflector. Spectral electroluminescence (EL) from a 16 μm diameter window is measured in the pulsed injection mode. Device parameters are recorded in the temperature range between 90 K and 240K. Threshold current exhibits an approximate parabolic temperature dependence with a broad minimum of J th = 13.2 kA cm -2 , at temperatures between 170K and 195K. Temperature dependence of the threshold current is compared with the theoretical calculations which consider radiative transitions with and without k-selection. Best agreement with the experimental results is obtained when a partial k- selection model, with an energy broadening of about 4.4 meV, is used in the calculations.

Wavelength-tunable in-line Fabry-Perot laser with lateral-grating-assisted vertical codirectional coupled filter

We propose a new wavelength-tunable laser structure, in-line Fabry-Perot (IFP) laser with lateral-grating-assisted vertical codirectional coupled filter (LGAVCF). Wavelength tuning is obtained by applying a single tuning current to LGAVCF section of the device. The IFP laser is basically a distributed feedback laser with a novel grating structure that provides ten equally spaced longitudinal modes. The integrated LGAVCF selects one of these modes allowing stable single-mode operation to be achieved. A grating-assisted vertical codirectional coupled filter with periodic changes in width instead of thickness was used to simplify the fabrication process.

Integrated lossless InGaAsP/InP 1-to-4 optical switch

The fabrication and performance of a 1-to-4 channel optical splitter/combiner are described. The design is based on the integration of a number of twin-guide amplifiers interconnected by active ridge waveguides. Lossless operation is seen fiber-to-fiber for all four ports for TE input light, with a 3-dB bandwidth of 20 nm. >