V Valentina Moskalenko

An introduction to InP-based generic integration technology

Photonic integrated circuits (PICs) are considered as the way to make photonic systems or subsystems cheap and ubiquitous. PICs still are several orders of magnitude more expensive than their microelectronic counterparts, which has restricted their application to a few niche markets. Recently, a novel approach in photonic integration is emerging which will reduce the R&D and prototyping costs and the throughput time of PICs by more than an order of magnitude. It will bring the application of PICs that integrate complex and advanced photonic functionality on a single chip within reach for a large number of small and larger companies and initiate a breakthrough in the application of Photonic ICs. The paper explains the concept of generic photonic integration technology using the technology developed by the COBRA research institute of TU Eindhoven as an example, and it describes the current status and prospects of generic InP-based integration technology.

Record bandwidth and sub-picosecond pulses from a monolithically integrated mode-locked quantum well ring laser

In this paper, we present the detailed characterization of a semiconductor ring passively mode-locked laser with a 20 GHz repetition rate that was realized as an indium phosphide based photonic integrated circuit (PIC). Various dynamical regimes as a function of operating conditions were explored in the spectral and time domain. A record bandwidth of the optical coherent comb from a quantum well based device of 11.5 nm at 3 dB and sub-picosecond pulse generation is demonstrated.

Integrated Extended-Cavity 1.5-μm Semiconductor Laser Switchable Between Self- and Anti-Colliding Pulse Passive Mode-Locking Configuration

We present the first integrated linear extended-cavity passively mode-locked (PML) semiconductor laser in which the operating mode can be switched electrically between two configurations. The first configuration is where the saturable absorber (SA) is located next to the output coupler, the so-called anti-colliding pulse mode-locking (ACPML) scheme. The second is where the SA is next to the high reflectance mirror, the self-colliding pulse mode-locking (SCPML) scheme. The 7.5-GHz PML was used to demonstrate experimentally the theoretical prediction that placing the SA next to the output coupler leads to a significant improvement in the laser stability and quality of the optical pulses. The experimental results show that the ACPML scheme allows for more deeply saturated SA due to the increase of optical power in the SA. The measurements of the RF spectra and autocorrelation traces confirm the superiority of the ACPML design in terms of pulse stability and width over the SCPML design for a wide range of operating conditions. The linewidth of the beat tone at the repetition rate was reduced by more than 60 times, the measured minimal autocorrelation width improved from 22 to 7.5 ps and a 3 dB increase in average output power was achieved.

Surface wave-induced enhancement of the Goos-Hänchen effect in one-dimensional photonic crystals

The excitation conditions of surface electromagnetic waves in one-dimensional photonic crystals (Bragg reflectors) are studied. Surface electromagnetic waves are visualized by the far-field optical microscopy of the surface of the photonic crystal. The enhancement of the Goos-Hänchen effect by surface electromagnetic waves excited in one-dimensional photonic crystals has been experimentally observed. The Goos-Hänchen shift reaches 30λ for a wavelength of λ = 532 nm.

A III-V-on-Si ultra-dense comb laser

Optical frequency combs emerge as a promising technology that enables highly sensitive, near-real-time spectroscopy with a high resolution. The currently available comb generators are mostly based on bulky and high-cost femtosecond lasers for dense comb generation (line spacing in the range of 100 MHz to 1 GHz). However, their integrated and low-cost counterparts, which are integrated semiconductor mode-locked lasers, are limited by their large comb spacing, small number of lines and broad optical linewidth. In this study, we report a demonstration of a III-V-on-Si comb laser that can function as a compact, low-cost frequency comb generator after frequency stabilization. The use of low-loss passive silicon waveguides enables the integration of a long laser cavity, which enables the laser to be locked in the passive mode at a record-low 1 GHz repetition rate. The 12-nm 10-dB output optical spectrum and the notably small optical mode spacing results in a dense optical comb that consists of over 1400 equally spaced optical lines. The sub-kHz 10-dB radio frequency linewidth and the narrow longitudinal mode linewidth (<400 kHz) indicate notably stable mode-locking. Such integrated dense comb lasers are very promising, for example, for high-resolution and real-time spectroscopy applications.

Theoretical Study of Colliding Pulse Passively Mode-Locked Semiconductor Ring Lasers With an Intracavity Mach–Zehnder Modulator

In this paper, we theoretically study the impact of an intracavity filter based on a Mach-Zehnder interferometer (MZI) on the pulses emitted by InGaAsP/InP passively mode-locked quantum well ring lasers. The filter allows to control the net gain curvature in the device, hereby providing for control over the modes that participate in the dynamics. Simulations of a traveling-wave model indicate that the pulsewidth can be controlled and reduced down to 500 fs. We present and verify a simple algorithm, which can be used for calculating the optimum values of the MZI parameters. The optimum parameters are then used in the study of an MZI passive-mode-locked laser under various operating conditions.

Integrated remotely tunable optical delay line for millimeter-wave beam steering fabricated in an InP generic foundry

A compact and fabrication-tolerant integrated remotely tunable optical delay line is proposed for millimeter-wave beam steering and is fabricated in an InP generic foundry. The proposed delay line is based on a spectrally cyclic-arrayed waveguide grating feedback loop. Its major features include the tolerant architecture with reduced chip size, and bi-directional operation with simplified remote tuning. Moreover, its cyclic feature guarantees further cascaded operations either for 2D radio beam steering or for high-resolution delay generation. The experimental results show less than 6.5-dB insertion loss of the integrated delay line. Five different delays from 0 to 71.6 ps are generated with less than 0.67-ps delay errors.

Pulse Narrowing and RF Linewidth Reduction of Integrated Passively Mode-Locked Laser in Anticolliding Design by Means of Spectral Tuning

In this paper, we present the first tunable extended cavity integrated passively mode-locked laser realized in an anticolliding design. The laser is realized as an InP-based photonic integrated circuit. A detailed study of the laser performance under various operating conditions is presented. The evolution of the radio-frequency (RF) spectrum and optical spectrum with the injection current to the optical amplifier is investigated. Tuning over 9 nm is achieved by injecting current in a distributed Bragg reflector section. We demonstrate that tuning of the optical spectrum toward shorter wavelengths, which increases absorption in the saturable absorber section, leads to an improvement of the mode-locked laser performance in terms of reduction of fundamental RF linewidth and reduction of the pulsewidths.

Laser research on an InP-based generic integration platform

In Europe a number of technology platforms for generic integration are being created for photonic integrated circuits (PICs); in Silicon, in passive dielectrics, and in Indium Phosphide. Such platforms are on the brink of commercialization, they offer a range of calibrated building blocks from which application specific PICs can be built and allow simplified, reduced cost access to a standardised technology, but presently only InP based platforms allow the integration of optical gain blocks; the essential feature of a semiconductor laser. The wavelength is constrained by the platform, usually C-band, but in the near future we expect other wavelengths in the 1.3μm-2.0μm range will be addressed. A frozen platform technology may not seem an ideal starting point for novel laser research but for what may be appear to be lost in epitaxial and process flexibility, much more is gained through a new-found ability to build up complex circuits quickly to deliver new and interesting laser based functionality. Building blocks such as reflectors (a distributed Bragg reflector (DBR) or a multimode interference reflector (MIR)), an amplifier section, and passive waveguides, can be built up by designers into integrated semiconductor lasers of a wide variety of types. This ready integration of novel sources with other circuit functionality can address a wide range of applications in telecoms, datacoms, and fibre based sensing systems. In this paper we describe a number of recent developments on generic InP-based platforms ranging from the fabrication of simple Fabry-Perot lasers, through tuneable DBR lasers, multi-wavelength comb lasers, picosecond pulse lasers and ring lasers.

Dynamics of colliding pulse passively semiconductor mode-locked ring lasers with an intra-cavity Mach-Zehnder modulator

The large number of applications in areas as optical communications, metrology and high-resolution imaging requires short stable and tunable optical pulses which can be generated by passively mode-locked lasers (PMLL). The pulse characteristics of PMLLs depend on the ratio of the saturation energies of the gain and of the saturable absorber (SA), of the available gain bandwidth and on the total cavity losses [1]. In addition, the pulse width can usually only be tuned by changing the bias current which does not leave the pulse energy invariant. In order to improve the performance of PMLLs several techniques were investigated which aim at engineering one of the crucial parameters controlling the pulse width. For instance, it was shown that the pulse width can be reduced by the increasing of field intensity profile in the SA [2] thereby modifying the effective saturation energies. On the other hand, the pulse duration could also in principle be reduced by extending the gain bandwidth as it would allow more modes to lase simultaneously. In [3] it was demonstrated that the gain bandwidth of a ring mode-locked laser can be significantly flattened by putting intra-cavity integrated frequency dependent filter. This filter was based on an asymmetrical Mach-Zehnder interferometer (MZI).