Search

In this talk we show how slow and fast light effects arising from the nonlinear gain and refractive index dynamics within semiconductor optical amplifiers can be used to control the phase shift of microwave frequency signals. Theoretical predictions with experimental conformation will be shown as to how continuous phase shifting can be achieved and pay particular attention to the noise issue that arises in such phase shifters. Finally, applications of such phase shifters, including realizations of tunable microwave notch filters and tunable optoelectronic oscillators will be presented.

We report on a unique lasing mechanism observed in quantum dash Gain media. While the gain media is electrically pumped below lasing threshold, a strong optical pulse excites carriers by two photon absorption into high energy states of the quantum dashes and wetting layer. Fast inter band carrier relaxation and capture processes into the ground states of the quantum dashes result in increased gain followed by lasing at the gain peak irrespective of the stimulating pulse wavelength. The temporal response of the lasing line is examined on a 40 GHz scope and full characterization of the pulse by the XFROG scheme is performed. We show the lasing mechanism to be governed mainly by the wetting layer dynamics and extract a direct measurement of the carrier-carrier scattering time constant.

We report on measurements of phase shifting using cross gain modulation in a quantum dash semiconductor optical amplifier

Ultrafast cross saturation dynamics of inhomogeneously broadened InAs/InP quantum dash optical amplifiers were characterized by multi-wavelength pump probe spectroscopy. Carrier relaxation processes are identified and quantified for the first time.

The conventional distributed feedback and distributed Bragg reflector edge-emitting lasers employ buried gratings, which require two or more epitaxial growth steps. By using lateral corrugations of the ridge-waveguide as surface gratings the epitaxial overgrowth is avoided, reducing the fabrication complexity, increasing the yield and reducing the fabrication cost. The surface gratings are applicable to different materials, including Al-containing ones and can be easily integrated in complex device structures and photonic circuits. Single-contact and multiple contact edge-emitting lasers with laterally-corrugated ridge waveguide gratings have been developed both on GaAs and InP substrates with the aim to exploit the photon-photon resonance in order to extend their direct modulation bandwidth. The paper reports on the characteristics of such surface-grating-based lasers emitting both at 1.3 and 1.55 μm and presents the photon-photon resonance extended small-signal modulation bandwidth (> 20 GHz) achieved with a 1.6 mm long single-contact device under direct modulation. Similarly structured devices, with shorter lengths are expected to exceed 40 GHz small-signal modulation bandwidth under direct modulation.

We describe dynamical four wave mixing (FWM) functionalities of an GaInP photonic crystal waveguide. A W1 waveguide was used to wavelength convert 100 ps pulses and for sampling a 10.56 Gbit/s data stream so as to time demultiplex it into 16 or 32 channels. In all cases, the extracted pulses at the idler wavelength are undistorted and have a high signal to noise ratio proving the high efficiency and the versatility of the FWM process in the GaInP PhC waveguides we used.

Error-free wavelength conversion of a 40 Gb/s DPSK signal is presented in a wavelength range of 45 nm using a dual pump four-wave mixing scheme in a 1.3 μm quantum-dot semiconductor optical amplifier.

We present a scheme to extend the frequency operation of phase shifters based on slow light in semiconductor optical amplifiers. We show that phase-shifting can be performed on microwave signals at frequencies approaching 100 GHz.

InP-based two-section distributed Bragg reflector lasers employing surface defined lateral gratings, which are compatible with low-cost nanoimprint technology, were fabricated. A newly developed inductively coupled plasma reactive ion etching process was utilized for obtaining large aspect ratios and good device performance. The lasers operate in a single mode up to 50°C under continuous-wave conditions. A modulation bandwidth of about 10 GHz was obtained for 0.9-mm-long devices.

We describe a tunable fiber laser operating at 2μm and beyond based on narrow band parametric amplification and a Tm doped intracavity fiber filter. Nanosecond pulses at ∼1MHz with a 20W peak power are demonstrated

We investigate Four-Wave-Mixing in dispersion-engineered Photonic Crystal Waveguide. For 100ps pulses, the instantaneous conversion efficiency is −24 dB and for single ps pulses we demonstrate a 3dB parametric gain for Watt level pump powers.

Structural properties of an ultrathin, 4.5 nm, erbium-oxide film and electrical properties of metal–oxide–semiconductor structure based on it are described. The evolution of the dielectric constant, total charge density, breakdown electric field, and leakage current density with annealing temperature in an oxygen environment are reported. The dielectric constant in the as-deposited state is relatively low, ∼7, possibly because the initial deposition forms ErO (with low polarizibility) rather than Er2O3. Annealing causes a transformation of ErO to Er2O3 but at the same time it initiates the growth of an interfacial SiO2 layer so that the effective dielectric constant is reduced to 5.5. Using the 4.5 nm film following annealing at up to 750 °C, we demonstrate an effective oxide thickness in the range 2.4–3.2 nm, with a leakage current density as low as 1–2×10−8 A/cm2 at an electric field of 106 V/cm and a breakdown electric field of 0.8–1.7×107 V/cm. A shift of the flat band voltage to the positive side and...

We report an advanced millimeter-wave source comprising two bipolar heterojunction photo transistors: one serving as a self oscillator and the second as an optoelectronic modulator. Optical injection locking of the first as well as analog and digital modulation of the second have been demonstrated.

International audience; We present an experimental and numerical investigation of the influence of filtering the red-shifted modulation on the linearity of a microwave-photonics link with a CPO-based phase shifter. Different behavior versus SOA bias current are evidenced.

We present a detailed model for carrier dynamics in tunneling injection quantum dot lasers. The model includes the spatial dependence of the mobile carriers and the coupling between mobile carriers and confined carriers.

International audience; We show theoretically and validate experimentally the effect of filtering on the nonlinear behavior of slow and fast light links based on coherent population oscillations in semiconductor optical amplifiers. The existence of a dip in the power-versus-current characteristics for the fundamental frequency, as well as for the third-order intermodulation product, is clearly evidenced. These two dips occur at different bias currents. Their depths increase as the filtering strength of the red sideband is increased, and they completely vanish in the unfiltered case. Influence on the microwave photonics link is discussed.

We highlight the importance of the delay arising from optical filters in slow-light-based microwave phase shifting systems. We calculate the filter delay numerically from the measured amplitude response by using the well-known Kramers–Kronig relations. The complex filter transmission response is then incorporated within a numerical model with which we explain phase shifting results obtained from experiments employing semiconductor optical amplifiers as slow light elements.

Coupling efficiency between a laser diode and a single-mode fiber can be greatly increased by using a lensing scheme to match their respective modes. We propose a simple method to selectively etch a fiber end to produce a conical lens whose base coincides with the fiber core. If needed, this lens may be fire polished or arc melted into a hemispherical lens of the same diameter. We present a general theoretical design of both these lenses. We find that high coupling efficiency is expected in cases of practical interest. Initial experimental results are reported in which coupling losses as low as 3 dB were obtained.

We report a large nonlinear response in a 1.3mm long GaInP photonic crystal waveguide. The wide band gap of GaInP (1.9 eV) ensures that no two photon absorption takes place for photons at 1.55mm improving the nonlinear performance. The nonlinearity is enhanced by a resonance effect due to the waveguide end facet reflectivities as well as by the low group velocity exhibited by the waveguide. A low CW input pump power of approximately 2mW causes a very large change in the nonlinear refractive index coefficient which manifests itself in a large, approximately p /3 phase shift in the Fabry Perot fringes. The extracted effective nonlinear coefficient g varies from 3.4 x 105W-1m-1 at short wavelengths to 2.2 x 106W-1m-1 near the band edge. These values are several orders of magnitude larger than those obtained in reported nonlinear experiments which exploit the Kerr effect. We postulate therefore that the observed nonlinearity is due to a hybrid phenomenon which combines the Kerr effect and an index change which is induced by local heating that results from the residual linear absorption. The efficient nonlinear phase shift was also exploited in a fast dynamic experiment where we demonstrated wavelength conversion with 100ps wide pulses proving the potential for switching functionalities at multi GHz rates. The index change required for this switching experiment can not be obtained, at the power levels used here, with a g value of a few thousands W-1m-1 which is a typical Kerr coefficient in similar waveguides. Hence, we conclude that the hybrid nonlinearity is sufficiently fast to enable switching with a time scale of at least 100ps.

We present an analytical model to calculate the signal to noise ratio of a slow light based microwave phase shifter that uses semiconductor optical amplifiers. The model includes dynamic noise effects and is confirmed experimentally.

GaAs substrates were pre-patterned by electron beam (e-beam) lithography and wet-chemically etched holes. The hole structures, presented here, enable growth of site-controlled InAs quantum dots with low dot density in the range of 10^8cm^-^2 by molecular beam epitaxy (MBE). In order to reduce defect related non-radiative recombination processes at the etched surface, wet-chemical etching and a modified growth of stacked quantum dot layers are developed. The total buffer layer thickness could be increased to 55nm GaAs by only one overgrowth step of a quantum dot seed layer in comparison to strain-coupled multi-stacked structure with typically 10nm buffer layer thickness between each stack.

We report a large third order nonlinear response in an InGaP photonic crystal waveguide. The nonlinearity is enhanced by a resonance effect due to the waveguide end facet reflectivities and the large group index.

In this paper, we present detailed modeling and experiments of the noise properties of a single-stage microwave phase-shifting element based on slow light propagation in a semiconductor optical amplifier. A wideband large-signal model is used to calculate the performance dependencies on gain, input power, and modulation frequency for the case where the red-shifted sideband at the amplifier output is suppressed.

We report highly efficient four wave mixing in a GaInP photonic crystal waveguide. Owing to its large bandgap, the ultrafast Kerr nonlinearity of GaInP is not diminished by two photon absorption and related carrier effects for photons in the 1550 nm range. A four-wave-mixing efficiency of -49 dB was demonstrated for cw pump and probe signals in the milliwatt range, while for pulsed pumps with a peak power of 25 mW the conversion efficiency increased to -36 dB. Measured conversion efficiency dependencies on pump probe detuning and on pump power are in excellent agreement with a simple analytical model from which the nonlinear parameter gamma is extracted. Gamma scales approximately with the square of the slow down factor and varies from 800 W(-1) m(-1) at a pump wavelength lambda(p)=1532 nm to 2900 W(-1) m(-1) at lambda(p)=1550 nm. These values are consistent with those obtained from self phase modulation experiments in similar devices.

We report highly efficient four wave mixing in InGaP photonic crystal waveguides. Conversion efficiencies of −52.5dB for two ∼1mW CW signals, and −38.8dB for a 1.4mW CW probe and a 14.4mW pulsed pump were demonstrated.

The authors present a three-level rate equation model, describing structurally dependent modulation bandwidth limitations in quantum-well lasers. They demonstrate an enhanced damping as well as a capacitivelike rolloff in the modulation response due to the transport time and carrier injection bottleneck. They also show that, for relatively short transport times, the dominant effect is that of damping, and they calculate an approximated explicit expression for a structure-dependent nonlinear gain compression coefficient. >

We demonstrate the use of an InP-GaInAs photo heterojunction bipolar transistor as a millimeter wave transducer. A 45-GHz carrier signal is generated by mixing two optical signals impinging on the optical port at the base. Simultaneously, the base electrode is fed by an electrical signal which modulates the 45 GHz carrier. Analog modulation capabilities were characterized in terms of the modulation depth and linearity while digital modulation was evaluated by a measurement of bit error rates.

We demonstrate experimentally and describe analytically two important noise contributions in saturated semiconductor optical amplifiers. The first is spontaneous emission power enhancement that is due to the increased and spatially dependent inversion factor. The second is caused by a nonlinear interaction between the saturating signal and the amplifier noise that, in the optical domain, causes a distinct modification of the noise spectrum over a narrow bandwidth. This modification manifests itself as a noise power decrease in the detected electronic domain.

We present a novel method for the generation of synchronized short pulses at high repetition rates from Er-doped silica fiber lasers. The method employs coupling of an optical pulse train to a passively mode-locked fiber laser. The injected signal repetition rate is slightly detuned from the modal spacing of the fiber laser, such that a subset of the latter modes is injection locked, yielding a high-repetition-rate pulse train. By injecting a 2-GHz train of relatively broad optical pulses at an average power of 100 μW, we achieved a train of 6-ps pulses at rates of 40 GHz from the harmonically locked fiber laser.

Harmonic injection locking can generate pulse trains at high repetition rates from passively mode-locked lasers. We have examined experimentally the mutual interaction of noise with the locking process. For injected signals with large timing and amplitude noise, the mode-locked fiber laser generated a pulse train with reduced noise. Injected signals with low timing and amplitude noise were employed for the reduction of the internal noise of the passively mode-locked laser. The achieved output pulse-to-pulse timing jitter in the range of 20-2500 Hz was ~0.6 ps, comparable with that of actively stabilized fiber lasers.

Pure phase-modulation mode locking of an extended-cavity semiconductor laser, operating near 1.5 microm, is demonstrated. The mode-locked laser uses a two-section optical amplifier that provides both gain and phase modulation.

We report optical near field characterization of a GaAs photonic crystal waveguide which is side coupled to a nano cavity. We observe the effect of the metal coated probe on the resonance wavelength and the intensity distribution. The measurements fit well to finite difference time domain simulations.

We demonstrate multi wavelength processing in a broad band 1550 nm quantum dash optical amplifier. Two 10 Gbit/s signals, spectrally separated by 30 nm are individually wavelength converted via four wave mixing (FWM) with no cross talk. High power signal levels cause depletion of high energy and wetting layer states resulting in some homogenizing of the gain medium and generation of cross FWM components near each channel due to FWM in the other channel. These do not affect the cross-talkless multichannel processing except when the two channels use equal detuning between signal and pump.

We report an experimental characterization of additive noise from a single-stage phase shifter based on slow and fast light propagation in a bulk semiconductor optical amplifier. We examine the influence of redshifted sideband suppression and optical input power on the signal-to-noise ratio (SNR) of the detected signal. We conclude that in spite of the up to a 6 dB reduction in the detected noise, the SNR remains dominated by the decrease in the detected signal power.

We describe systematic measurements of the gain and delay spectra in a slow light system based on stimulated Brillouin scattering in optical fibers. The measurements yield the system complex transfer function with which delays and signal distortion can be calculated for any input signal. The theoretical predictions are confirmed experimentally for single pulses as well as 50 Mb/s data streams in a system which employs pump modulation to modify the gain and delay spectra of the SBS process.

P-doped and undoped quantum dot (QD) semiconductor optical amplifiers (SOA) are compared regarding their static and dynamic characteristics. The amplified spontaneous emission and gain curves are evaluated for p-doped and undoped devices exhibiting a gain per length of 10 dB/mm and 7 dB/mm, respectively. P-doped and undoped devices having 22 dB and 23.5 dB chip gain, respectively, were compared in small signal measurements. Cross-gain modulation (XGM) experiments show an enhancement of the small-signal bandwidth from 25 GHz for the p-doped SOAs to 40 GHz for undoped QD SOAs at the same current density. However, p-doped QD SOAs also achieve small-signal bandwidths beyond 40 GHz at larger bias.

This paper describes the influence of electron beam irradiation and constant voltage stress on the electrical characteristics of metal-insulator-semiconductor structures, with double layer high-k dielectric stacks containing HfTiSiO:N and HfTiO:N films. The changes in the electrical properties were caused by charge trapping phenomena which is similar for e-beam irradiation and voltage stress cases. It was shown the advantages of an alternative methodology based on α-V representation (α= d[ln(J)]d[ln(V)] ) to distinguish different current flow mechanisms in ultra thin insulators in different voltage regimes.

Mode-locked lasers (MLLs) and semiconductor optical amplifiers (SOAs) based on quantum dot (QD) gain material will impact the development of next generation networks like the 100Gb/s Ethernet. Hybrid mode-locked lasers consisting of a monolithic two section device presently already generate picosecond pulse trains at 40 GHz with an extremely low jitter in the range of 200 fs under optimum operating conditions. A detailed chirp analysis which is prerequisite for optical time division multiplexing applications is presented. QD SOAs are showing superior performance for linear amplification as well as nonlinear signal processing. Wavelength conversion via cross-gain modulation is shown to have a small signal bandwidth beyond 40 GHz under high bias current injection. This makes QD SOAs much superior to conventional SOAs.

We describe the use of a semiconductor optical amplifier as an intra cavity, continuous phase tuning element in an optoelectronic oscillator. A tuning range larger than 3 MHz is demonstrated in a 10 GHz oscillator.

Semiconductor optical amplifiers acting as slow light elements offer large phase shifts provided that their output spectra are filtered prior to detection. The filtering affects their noise properties which are described in this paper.

A full model for the phase of detected sinusoidal signals with large modulation indices after propagation through a semiconductor optical amplifier is presented with a comparison to a small signal model and an experimental confirmation.

The characteristics of active optical filters based on distributed Bragg reflector (DBR) laser diodes are described. The authors present a theoretical model for the small and large signal filter response which can be used to optimize the filter design and operating point. The large signal filter response is dominated by a variety of nonlinear effects, including a wavelength domain bistability. The authors describe a series of experiments in which the predicted filter characteristics are demonstrated. The authors present detailed measurements of the filter transfer function in both transmission and reflection modes under low and high power injection. For the small signal measurements a powerful technique which uses the swept frequency concept is presented. For the large signal regime, measurements of both frequency pulling and wavelength domain bistability are presented. >

We report electrical characteristics of Ta2O5 films deposited by a simple electron beam gun evaporator. We describe thickness-dependent characteristics for films with thicknesses of 7–130 nm. An equivalent SiO2 thickness of 3.5–4.5 nm for films whose leakage current density at an electric field of 106 V/cm is lower than 10−7 A/cm2 is demonstrated.

We describe long-distance analog microwave-fiber optic links with bandwidths larger than six and a half octaves at an upper frequency in the 1.5-2 GHz range. The links exhibit highly linear performance with harmonic and intermodulation distortions determining the overall spurious-free dynamic ranges. Two configurations are presented, each capable of overcoming limitations imposed by fiber nonlinearities and each employing a custom optical amplifier which maintains a low-noise figure under saturated conditions. For fiber lengths of tens of kilometers, representing losses of 10-16 dB, the basic links have a noise figure of 38 dB and second and third order spurious free dynamic ranges of 103 dB/Hz/sup 1/2/ and 105 dB/Hz/sup 2/3/, respectively, over their entire bandwidth.

We demonstrate multi wavelength processing in a broad band 1550 nm quantum dash optical amplifier. Two 10 Gbit/s signals, spectrally separated by 30 nm are individually wavelength converted via four wave mixing with no cross talk.

We Study a modification of classical FM spectroscopy in the cases where several electromagnetic fields are FM modulated, each in a different manner. This complex spectrum scans a multi-photon resonant atomic medium with the output detected by a phase-sensitive scheme. The demodulated output signal reveals the spectroscopic features of the probed medium. The case in which two different carriers are FM modulated at the same frequency and index but with an opposite phase with respect to each other is analyzed theoretically. This configuration is essential for probing Coherent Population Trapping (CPT) resonances induced by a directly modulated diode laser. Employing a macroscopic model to describe the physical properties of CPT leads to a superb fit between predicted and measured CPT characteristics.

Wavelength conversion using cross-gain modulation in quantum dot semiconductor optical amplifiers is investigated. Small signal measurements reveal that with increasing bias the cross-gain modulation converts from low efficiency, limited to 10 GHz bandwidth to a very efficient one with bandwidths well exceeding 40 GHz. Two different saturation mechanisms are responsible for this pronounced influence of the bias current: a) total carrier depletion which leads to a slow broadband cross gain saturation and b) spectral hole burning which causes spectrally narrowband high speed XGM. With increasing current the saturation by depleting the carrier reservoir, which feeds the quantum dots, is minimized and therefore spectral hole burning becomes more dominant. Large signal wavelength conversion experiments using 50 ps pulses indicate that efficient high speed cross gain modulation is feasible for pump and probe signal detuning up to 10 nm. With increasing detuning larger pulse broadening and a decreasing efficiency is observed, consistent with the small signal results.

We demonstrate a direct correspondence between FM parameters used in a frequency-locked loop that is based on multifield FM spectroscopy and the stability of a small-scale coherent population trapping atomic clock. Optimized FM parameters lead to an Allan deviation of 2.8 x 10(-11)/square root tau, while the clock stability deteriorates in a predictable manner for the other FM parameters.

We describe optimization of frequency locked loop in atomic clock which is based on coherent population trapping in 87Rb-D2 transition. The clock performance was optimized to have an Allan deviation of 2.8middot10-11 at 1 sec.