# Daan LenstraEindhoven University of Technology | TUE · Department of Electrical Engineering

Daan Lenstra

Prof.dr.

## About

415

Publications

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Introduction

After my retirement from Delft University of Technology in 2010, I joined the Photonic Integration group of Prof. Meint Smit at Eindhoven University of Technology. My present position is Fellow of the Department of Electrical Engineering.

## Publications

Publications (415)

Using a rate-equation model we numerically evaluate the carrier concentration and photon number in an integrated two-section semiconductor laser, and analyse its dynamics in three-dimensional phase space. The simulation comprises compact model descriptions extracted from a commercially-available generic InP technology platform, allowing us to model...

A theoretical analysis is presented for a recently proposed high-speed µ-OLED optically pumped organic laser. We confirm that for this configuration, the laser threshold is reached at a lower current density than in the case of a direct-electrically pumped organic laser diode while generating pulses of order 15 ns duration. With a validated model f...

In the context of the quest for the organic laser diode, we address a key challenge to design and fabricate high-quality factor cavities compatible with electrical excitation of organic semiconductors. More precisely, we present the design of DFB micro-cavities for integration in organic laser diodes and their validation under optical pumping. To d...

The spectrum of the light emitted by a microcavity OLED is strongly time dependent on the nanosecond timescale after switch-on of the pump mechanism. This is one reason why
convincing confirmation of laser operation in such device is difficult. The simple theory here presented is helpful in interpreting observed light-emission behavior. One importa...

Using the Yamada model, the influence of saturable absorber length and mirror reflectivities on the excitability window of an integrated laser is investigated. A short absorber and low reflectivity mirrors are beneficial for a large excitability window.

A two-section semiconductor laser can exhibit excitability for certain parameter settings. When used as a photonic spiking neuron, it is relevant to investigate its sensitivity to noise due to, e.g., spontaneous emission. Under excitable conditions, the system emits irregularly timed noise-triggered pulses. Their statistics is analyzed in terms of...

We report experimental and theoretical investigations with an in-house fabricated Tris(8‐hydroxyquinoline)‐aluminum (Alq3)-based high-speed μ-OLEDs and demonstrate very promising optical pulse responses as short as 400 ps. With a model for an electrically pumped OLED, we simulate the emission of sub-nanosecond optical pulses. The model includes fie...

The self-spiking behavior of an integrated saturable absorber and gain section laser fabricated in an InP technology platform is analyzed. The gain, absorber and intensity dynamics are first inspected using the normalized Yamada model. This model shows excitable behavior as well as the relative refractory period, both of which are also present in b...

We present and analyze a simple model based on six rate equations for an electrically pumped organic diode laser. The model applies to organic host-guest systems and includes Stoke-shifted reabsorption in a self-consistent manner. With the validated model for the Alq3:DCM host-guest system, we predict the threshold for short-pulse laser operation....

We propose a new model for the organic laser diode based on rate equations for polarons, singlet and triplet excitons for both host and guest molecules, and photon densities. The proposed model is validated experimentally by comparing calculated and measured optical responses in the context of pulsed nanosecond electrical excitation of high-speed μ...

With the advent of integrated photonics, a crucial role is played by semiconductor diode lasers (SDLs) as coherent light sources. Old paradigms of semiconductor laser dynamics, like optical injection, external feedback and the coupling of lasers, regained relevance when SDLs were integrated on photonic chips. This Special Issue presents a collectio...

The rate equations for two delay-coupled quantum cascade lasers are investigated analytically in the limit of weak coupling and small frequency detuning. We mathematically derive two coupled Adler delay differential equations for the phases of the two electrical fields and show that these equations are no longer valid if the ratio of the two pump p...

Recently, Adachi and co-workers have reported convincing proof of stimulated emission in an organic heterostructure under electrical excitation [i]. This new organic laser diode opens a new era in the field of lasing with solid-state organic materials that covers the whole visible spectrum and can be patterned more easily than conventional III-V ma...

We have theoretically analyzed multi-stability of a symmetric ring laser operating in one single longitudinal mode in the presence of coherent back scattering and inversion-grating-induced mutual coupling of the clockwise and counter-clockwise modes. Our model takes into account the inversion grating created by the standing-wave pattern of the inte...

We present a route towards design and fabrication of a conceptually new type of optical feedback-insensitive integrated semiconductor ring laser with a weak optical isolator included in the ring. Although the approach has not resulted in the clear advantages that were aimed at, this detailed account of the process we believe is valuable to readers...

A unidirectional phase modulator consisting of tandem phase modulators is studied in detail for use as an integral part of an integrated optical isolator. The effects of non-linearity and residual amplitude modulation in the modulators, as well as the effect of the RF driving signals are captured in a phenomenological model for the first time. The...

An InP-based, monolithically-integrated multi-wavelength laser with optical feedback is presented. We demonstrate performance of dual-wavelength operation. Single-mode lasing is obtained for each of the two channels over ranges of 14 °C and 40 mA without mode-hopping. This is due to the combined filtering functions of an arrayed waveguide grating a...

We present a simple to process tunable laser, fabricated in a low-cost generic fabrication process and based on two coupled Fabry-Perot cavities. The complex coupling coefficients of the coupling element are analytically derived from a 3×3 MMI using coupled mode theory and chosen to maximize the SMSR during lasing operation. Additionally, one of th...

For our recently designed continuous-wave and single-frequency ring laser with intra-cavity isolator, we have formulated a rate-equation theory which accounts for two sources of mutual back-scattering between the clockwise and counterclockwise modes, i.e. induced by side-wall irregularities and due to inversion-grating-induced spatial hole burning....

External optical feedback can severely deteriorate the performance of semiconductor lasers. This work proposes an integrated laser design that can withstand tens of percent of off-chip feedback, without requiring the integration of magneto-optic materials. The proposed laser consists of a ring cavity with a weak intracavity optical isolator. Suffic...

Rate equations are derived for the coupled-cavity laser with a multimode-interference coupler. A strategy and scheme is indicated for iterative self-consistent numerical solution of the steady-state equations. The presence of the linewidth-enhancement parameter is explicitly taken into account. Locking in stable single-mode anti-phase operation is...

Rate equations are derived for the coupled-cavity laser with a multimode-interference coupler. A strategy and scheme is indicated for iterative self-consistent numerical solution of the steady-state equations. The presence of the linewidth-enhancement parameter is explicitly taken into account. Locking in stable single-mode anti-phase operation is...

We experimentally demonstrate a monolithically integrated laser with built-in weak optical feedback, which shows broad regions of operation without relaxation-oscillation-induced instabilities. The side mode suppression is >40 dB for all values of the feedback phase. The measured linewidth varied from 740 KHz to 14 MHz, depending on the feedback ph...

We experimentally demonstrate a laser which operates under weak optical feedback, showing two broad regions of operation without relaxation-oscillation induced instabilities and where high side-mode suppression above 40 dB is maintained, irrespective of the feedback phase.

A review is given of a number of lasers in a form of photonic integrated circuits realized on InP substrate using a generic integration approach. The potential of these photonic circuits lies in their compactness, low power consumption, and significant reduction of fabrication cost by realization in generic foundry runs. Generic integration platfor...

We experimentally demonstrate a laser with weak optical feedback, which shows broad regions of operation without relaxation-oscillation induced instabilities. Here, the side mode suppression is above 40 dB, independent of the feedback phase.

We present a 26 nm tunable Coupled Cavity Laser based on a novel interferometer and fabricated in a low-cost generic foundry process, with SMSR above 40 dB and fibre coupled power > 5mW.

We report the experimental demonstration of two coupled laser cavities via self-imaging interference in a multimode waveguide. The coupling is optimized by considering images formed by two coherent phase-delayed signals at the input of a 3 × 3 splitter. As a result, the complex transfer coefficients of the coupling element can be chosen to increase...

A tunable laser for single line gas spectroscopy is realized as a monolithic photonic integrated circuit in an InP based generic foundry platform. The laser operates at wavelengths around 2.0 μm and has a tuning range of 22 nm.

A tunable laser for single line gas spectroscopy is realized as a monolithic photonic integrated circuit in an InP based generic foundry platform. The laser operates at wavelengths around 2.0 μm and has a tuning range of 22 nm.

A tunable laser for single line gas spectroscopy is realized as a monolithic photonic integrated circuit in an InP based generic foundry platform. The laser operates at wavelengths around 2.0 μm and has a tuning range of 22 nm.

The S-shaped ring laser has been demonstrated to operate unidirectionally [1]. As back reflections in the out coupled light from such laser feeds the counter propagating mode, this laser could well be a promising source of coherent light with reduced sensitivity for optical feedback. However, the performance in terms of degree of unidirectionality...

We present a set of rate equations for the modal amplitudes and carrier-inversion moments that describe the deterministic multi-mode dynamics of a semiconductor laser due to spatial hole burning. Mutual interactions among the lasing modes, induced by high- frequency modulations of the carrier distribution, are included by carrier-inversion moments...

Semiconductor lasers often make use of external optical feedback, for various reasons, like single-mode selection, stabilization or linewidth narrowing. A draw-back of such method is that delayed feedback can easily lead to sustained relaxation oscillations (RO). The occurrence of the RO is sensitive to, among other things, the applied settings of...

A set of rate equations is derived describing the deterministic multi-mode dynamics of a semiconductor laser. Mutual interactions among the lasing modes, induced by high-frequency modulations of the carrier distribution, are described by carrier-inversion moments and lead to special spectral content of each spatial mode. The diffusion of carriers i...

Coupling of two Fabry-Perot cavities via a 3x3 Multimode Interference Reflector is presented. We measure SMSR close to 40 dB and a tuning range of 7 nm for 1.2 mm cavities with 5% length difference.

We theoretically investigate the stability of a single-mode semiconductor laser with weak optical feedback in the short external-delay regime. Although the laser is, in general, very sensitive to feedback-induced excitation of relaxation oscillations, we predict complete insensitivity for these oscillations when the product of oscillation frequency...

We theoretically investigate the stability of a single-mode semiconductor laser with weak optical feedback in the short external-delay regime. Although the laser is, in general, very sensitive to feedback-induced excitation of relaxation oscillations, we predict complete insensitivity for these oscillations when the product of oscillation frequency...

The stability of a novel monolithically integrated filtered-feedback laser is experimentally investigated as a function of the electrically controlled feedback phase. By backing them up with the results from a stability analysis model, we interpret the measurements in terms of feedback-induced dynamics. We show that this laser has excellent potenti...

We experimentally and theoretically investigate the stability of a single-mode integrated filtered-feedback laser as a function of the electrically controlled feedback phase. We interpret the measurements in terms of feedback-induced dynamics, compare them with the results from a stability analysis model for conventional feedback, and find good qua...

The stability of a novel monolithically integrated filtered-feedback laser is experimentally investigated as a function of the electrically controlled feedback phase. By backing them up with the results from a stability analysis model, we interpret the measurements in terms of feedback-induced dynamics. We show that this laser has excellent potenti...

Vertical cavity surface-emitting lasers (VCSELs) are a new type of semiconductor laser characterized by the spatial extent of their disk-shaped output apertures. As a result, a VCSEL supports several optical modes (patterns of light) transverse to the direction of light propagation. When any laser is coupled to other optical elements, there is unav...

In this paper, some of the activities towards the fabrication of photonic integrated circuits at the COBRA Research Institute are summarized. Firstly, rate equations are used for the understanding of instability and dynamics in multilongitudinal mode semiconductor lasers. Secondly, we report the results of our investigation on broad-bandwidth frequ...

In this paper, a monolithic waveguide device, named IRIS, is presented. The device consists of an array of concatenated semiconductor optical amplifiers and saturable absorbers. We have fabricated the devices in InP-InGaAsP bulk gain material and we have experimentally investigated picosecond pulse transmission through these devices. Operated as an...

We explain the polarization dependence of four wave mixing (FWM) quantum beats for semiconductors as essentially due to the spin phase correlations of photo-excited electrons, rather than to Coulomb interaction between the electrons. A theoretical analysis is given within the framework of optical Bloch equations for the light–semiconductor interact...

We analyze the photon-induced birefringence in semiconductors based on pump-probe setups, within the semiconductor Bloch equations formalism and the Luttinger–Kohn model for the band structure. When the pump and probe pulses are well separated in time, the anisotropic momentum space filling of the photo-excited electrons is the only mechanism causi...

We consider a multi-transverse-mode vertical-cavity surface-emitting laser (VCSEL) subject to optical feedback. The system is modeled by a partial differential equation for the spatial carrier population, which is coupled to delay differential equations for the electric fields of the participating transverse modes that are subject to external optic...

We investigate experimentally and theoretically the dynamics of a semiconductor laser subject to filtered optical feedback. Depending on the feedback strength we find dynamical regimes with different dependence on the feedback phase. In particular, the influence of the feedback phase on cw emission and on frequency oscillations is characterized exp...

Summary form only given. This paper studies theoretically two semiconductor lasers that are mutually delay-coupled via their optical fields, where the delay arises due to the finite propagation time of the light from one laser to the other. This paper concentrates on the dynamics within the locking region, that is the region where compound laser mo...

The use of a concatenated array of semiconductor optical amplifiers (SOA) and saturable absorbers (SA) as an integrated optical waveguide isolator for picosecond pulse operation is proposed in this paper. Numerical simulations are performed using SOA and SA rate equation models wherein the parameters used are valid for the InP/InGaAsP material.

Photonic Integrated Circuit (PIC) technology has revolutionized the application and fabrication of optoelectronic devices. Most affected by this development is the field of telecommunications, where both active and passive photonic devices are key components in the optical networks. PIC based optical components are cheaper to fabricate than their s...

We examine the description of quantum beats in four-wave mixing with bulk semiconductors within the framework of the Luttinger-Kohn model. An analytic expression for their dependence on the relative linear polarization of pump and probe is derived, taking only the band structure and coherent interaction of the light waves with the semiconductor med...

In this paper, we show how the "Bogatov effect" can be included in a robust way into a multimode rate equations model that takes account of multi-wave mixing effects through dynamical gratings burned in the carrier distribution. We reveal how this dynamics might induce changes in the shape of the gain curve which ultimately manifests itself as oper...

We numerically optimize an optical filter through a Genetic Algorithms (GA) in the context of high speed non-inverted wavelength conversion based on a single semiconductor optical amplifier (SOA). An optical filter is critical in the SOA-based wavelength converter because it enables high-speed operation through converting the ultra-fast chirp dynam...

This paper investigates a vertical-cavity surface-emitting laser (VCSEL) model in which the first two, rotationally symmetric, linearly polarised optical modes (LP01 and LP02) are excited. A general form of optical feedback is studied, in which the electric fields of the two modes can couple via the external-cavity round-trip. This is in contrast t...

Summary form only given. In this work, we numerically investigate the possibility of all-optical wavelength conversion at 1 Tb/s based on a single SOA and a Gaussian optical bandpass filter. A comprehensive model is employed to carry out the simulations for the carrier dynamics in an SOA. The ultrashort pulse propagation in an SOA is modeled throug...

Amplification of picosecond pulses with greatly reduced amplified spontaneous emission compared to a standard semiconductor amplifier (up to 30dB) and a large increase in coherent spectral bandwidth is demonstrated in devices we have fabricated.

We present for the first time a systematic analysis of the Q-factor and eye opening for wavelength conversion based on a single semiconductor optical amplifier and a detuned filter at 160 Gb/s.

We present for the first time a systematic analysis of the Q-factor and eye opening for wavelength conversion based on a single semiconductor optical amplifier and a detuned filter at 160 Gb/s.

We compare a variety of approximation schemes, all predicting the excitation structure of a semiconductor. All schemes are placed within one common framework, in which the electron self energy is the central quantity. In arriving at this self energy it turns out to be essential to screen the Coulomb interaction between electrons both statically and...

We investigate a system consisting of multiple ring lasers coupled by a single gain medium. All the ring lasers share a common feedback arm. The output power of an individual laser shows periodic oscillations as a function of time. The periodicity of the oscillation is determined by the ratio of the roundtrip times of the feedback arm and the ring...

We propose using genetic algorithms to numerically optimize optical band-pass filters (OBFs) for inverted and noninverted wavelength conversion based on semiconductor optical amplifiers. A fourth order Hermite-Gaussian sum series is used to describe the filter transfer function. Signal eye openings greater than 30 dB are obtained for both inverted...

Using an integrated colliding-pulse mode-locked semiconductor laser, we demonstrate the existence of nonlinear dynamics and chaos in photonic integrated circuits (PICs) by demonstrating a period-doubling transition into chaos. Unlike their stand-alone counterparts, the dynamics of PICs are more stable over the lifetime of the system, reproducible f...

We present a model of the double barrier resonant-tunneling diode (DBRTD), in which the tunneling is described in a 1D transfer matrix approach, based on full wave coherence, and in which the electronic potential is determined selfconsistently from the 3D charge distribution in the structure. Within this simple model, we are able to describe the di...

We study the dynamics and bifurcations of a semiconductor laser with delayed filtered optical feedback, where a part of the output of the laser reenters after spectral filtering. This type of coherent optical feedback is more challenging than the case of conventional optical feedback from a simple mirror, but it provides additional control over the...

Carrier heating in the valence band of a semicond- cutor optical amplifier is found to be significant compared to that from the conduction band, although the temperature change is smaller. Therefore it cannot be neglected. where vg is the group velocity, τhx is the time constant for carrier cooling process, Ux is the total energy density, Tx is the...

For a one-dimensional closed loop with only elastic scattering we discuss the development of electrical current under the influence of an induced electromotive force Emf. Our calculations show that, in contrast to what might be expected, the current development for not too small Emf's is similar to that of a dissipative system. This surprising beha...