Siddharth Joshi

Quantum dash based single section mode locked lasers for photonic integrated circuits

We present the first demonstration of an InAs/InP Quantum Dash based single-section frequency comb generator designed for use in photonic integrated circuits (PICs). The laser cavity is closed using a specifically designed Bragg reflector without compromising the mode-locking performance of the self pulsating laser. This enables the integration of single-section mode-locked laser in photonic integrated circuits as on-chip frequency comb generators. We also investigate the relations between cavity modes in such a device and demonstrate how the dispersion of the complex mode frequencies induced by the Bragg grating implies a violation of the equi-distance between the adjacent mode frequencies and, therefore, forbids the locking of the modes in a classical Bragg Device. Finally we integrate such a Bragg Mirror based laser with Semiconductor Optical Amplifier (SOA) to demonstrate the monolithic integration of QDash based low phase noise sources in PICs.

Dynamic characteristics of undoped and p-doped Fabry-Perot InAs/InP quantum dash based ridge waveguide lasers for access/metro networks

In this paper, we report the characteristics of InAs/InP quantum dashes (QDash) based lasers emitting around 1.55 μm. An unprecedented high modal gain of ∼100 cm−1 is obtained for an optimized active structure by stacking 12 QDash layers. Directly modulated lasers allowed achieving a modulation bandwidth of ∼10 GHz and a Henry factor around 5. Thanks to p-type doping, the Henry factor value is reduced down to 2.7 while the modulation bandwidth still amounts to ∼10 GHz. This shows that doping of the active region is important to improve the dynamic characteristics of QDash lasers.

On the nature of the linewidth enhancement factor in p-doped quantum dash based lasers

P-doped quantum dash based lasers have shown superior dynamic performance as compared to their un-doped counterparts. This improvement in performance is strongly observed in line-width enhancement factor. These devices show a dramatic reduction in the αH parameter, resulting in very low chirp. This letter discusses the nature line-width enhancement factor of p-doped quantum dash lasers as opposed to un-doped counterparts. Owing to the p-doping a low and bias-stable alpha parameter is demonstrated.

Mode locked InAs/InP Quantum dash based DBR Laser monolithically integrated with a semiconductor optical amplifier

In this paper we present the first demonstration of a InAs/InP Quantum Dash based mode Locked Laser (MLL) compatible with uncooled operation. For integration purpose, we designed a Distributed Bragg Reflector (DBR) mirror in order to close the cavity without disturbing the mode-locking efficiency. As a demonstration of integration, we fabricated such DBR monolithically integrated with a semiconductor optical amplifier. This opens the way to the integration e.g. of frequency comb generators in photonic integrated circuits.

Coherent terabit communications using a quantum-dash mode-locked laser and self-homodyne detection

We transmit 18 GBd 16QAM signals on 25 spectral lines of a quantum-dash mode-locked laser diode, achieving a 1.562 Tbit/s aggregate data rate. Phase noise is cancelled by self-homodyne detection using LO tones transmitted with the signal.

Silicon photonics WDM transmitter with single section semiconductor mode-locked laser

Abstract We demonstrate a wavelength domain-multiplexed (WDM) optical link relying on a single section semiconductor mode-locked laser (SS-MLL) with quantum dash (Q-Dash) gain material to generate 25 optical carriers spaced by 60.8 GHz, as well as silicon photonics (SiP) resonant ring modulators (RRMs) to modulate individual optical channels. The link requires optical reamplification provided by an erbium-doped fiber amplifier (EDFA) in the system experiments reported here. Open eye diagrams with signal quality factors (Q-factors) above 7 are measured with a commercial receiver (Rx). For higher compactness and cost effectiveness, reamplification of the modulated channels with a semiconductor optical amplifier (SOA) operated in the linear regime is highly desirable. System and device characterization indicate compatibility with the latter. While we expect channel counts to be primarily limited by the saturation output power level of the SOA, we estimate a single SOA to support more than eight channels. Prior to describing the system experiments, component design and detailed characterization results are reported including design and characterization of RRMs, ring-based resonant optical add-drop multiplexers (RR-OADMs) and thermal tuners, S-parameters resulting from the interoperation of RRMs and RR-OADMs, and characterization of Q-Dash SS-MLLs reamplified with a commercial SOA. Particular emphasis is placed on peaking effects in the transfer functions of RRMs and RR-OADMs resulting from transient effects in the optical domain, as well as on the characterization of SS-MLLs in regard to relative intensity noise (RIN), stability of the modes of operation, and excess noise after reamplification.

Monolithic Integration on InP of a DML and a Ring Resonator for Future Access Networks

The future technology migration in access networks compels the development of key innovative transmitters operating at 10 Gb/s around 1550 nm and capable of transmitting data in extended reach passive optical networks (>60 km). A laser modulated directly appears to be a low cost and a simple solution to address these needs. However, the extinction ratio and the distance of transmission are limited by frequency chirping inherent to high bit rate modulation at 1550 nm. In this letter, we demonstrate the monolithic integration of a directly modulated lasers and a ring resonator (RR) and show the possibility to engineer the RR with specific frequency modulation efficiency. The ring is used as an optical eye reshaper, which enables the increase of the extinction ratio above 9 dB. Transmissions up to 65 km with 5.8 dBm of modulated optical power coupled into the fiber are demonstrated, proving the feasibility of our transmitter for the next generation passive optical network stage 2.

QDash-Based Directly Modulated Lasers for Next-Generation Access Network

In this letter, we report the strong effect of p-doping on dynamic performances of QDash lasers. Therefore, we demonstrate 10 Gb/s transmission in standard single mode fiber up to 65 km with a dynamic extinction ratio using directly modulated lasers based on this material and commercial Fabry-Pérot etalon filter.

Beyond 25 Gbit/s directly modulated, directly detected OFDM using channel flattening by a Fabry-Perot filter

We experimentally demonstrate the joint use of OFDM and channel flattening effect provided by a Fabry-Perot filter to allow higher than 25 Gbit/s direct intensity modulated, directly detected transmission over up to 75 km SSMF.

Phase-noise compensated carriers from an optical frequency comb allowing terabit transmission

By comparison to a stable reference laser, the phase noise of a frequency comb from a quantum-dash mode-locked laser can be compensated. The quality of the resulting carriers allows the transmission of data at a rate of 1 Tbit/s in a single polarization over a distance of 75 km using a standard forward error correction.