Quantum-dash Mode-locked Laser Research Articles

An instantaneous frequency measurement system based on quantum dash mode-locked laser

An instantaneous frequency measurement system based on quantum dash mode-locked laser

Investigation of Phase Noise in a Radio-Over-Fiber Link Based on an InAs/InP Quantum-Dash Mode-Locked Laser

Investigation of Phase Noise in a Radio-Over-Fiber Link Based on an InAs/InP Quantum-Dash Mode-Locked Laser

Performance of quantum-dash mode-locked lasers (QD-MLLDs) for high-capacity coherent optical communications.

We investigate the capabilities and limitations of quantum-dash mode-locked lasers (QD-MLLDs) as optical frequency comb sources in coherent optical communication systems. We demonstrate that QD-MLLDs are on par with conventional single-wavelength narrow linewidth laser sources and can support high symbol rates and modulation formats. We manage to transmit 64 quadrature amplitude modulation (QAM) signals up to 80 GBd over 80 km of standard single-mode fiber (SSMF), which highlights the distinctive phase noise performance of the QD-MLLD. Using a 38.5 GHz (6 dB bandwidth) silicon photonic (SiP) modulator, we achieve a maximum symbol rate of 104 GBd with 16QAM signaling and a maximum net rate of 416 Gb/s per carrier in a single polarization setup and after 80 km-SSMF transmission. We also compare QD-MLLD performance with commercial narrow-linewidth integrable tunable laser assemblies (ITLAs) and explore their potential for use as local oscillators (LOs) and signal carriers. The QD-MLLD has 45 comb lines usable for transmission at a frequency spacing of 25 GHz, and an RF linewidth of 35 kHz.

Colorless Coherent TDM-PON Based on a Frequency-Comb Laser

Coherent reception becomes an interesting option when data rates in time-division-multiplexed (TDM) passive optical networks (PONs) grow beyond 50 Gbit/s. Controlling the wavelength, i.e., the optical frequency, and the phase of the laser acting as local oscillator (LO) is one of the main technical challenges in the design of coherent TDM PONs. In the optical network units (ONUs), low-cost lasers are required, which come at the expense of wavelength variations and drifts over multiple nanometers due to fabrication imperfections, and temperature variations. This contradicts the requirement of wavelength-stable LOs in coherent receivers. The use of a wavelength locker circuit and a temperature controller is considered as too complex for applications in access networks. In this work, we propose a novel colorless coherent architecture with high resilience to ONU laser wavelength drifts of up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 4 nm ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 0.5 THz) for future 100 Gbit/s PON. It allows the use of distributed feedback lasers at the ONU side. This is rendered possible by generating a frequency comb with carefully chosen free spectral range in a quantum-dash mode-locked laser diode at the optical line terminal. In upstream operation, the frequency comb serves as an LO, whereas the same information is modulated onto all comb lines for the case of downstream. As a result, the ONU laser can drift over the entire comb bandwidth without substantial performance penalty. We experimentally demonstrate downstream and upstream operation with an aggregated raw data rate of 96 Gbit/s, respectively. We further introduce advanced digital signal processing (DSP) methods including a coarse frequency offset compensation (CFOC) and a multiple-input multiple-output (MIMO) equalizer to improve the performance of our concept. We show that the receiver sensitivity can be increased by 3 dB for a high-bandwidth receiver when using a 6 × 2 MIMO equalizer scheme. A 4 × 2 MIMO equalizer scheme enables colorless reception even with a limited-bandwidth receiver.

Reconfigurable microwave photonic filter based on a quantum dash mode-locked laser.

We demonstrate a reconfigurable microwave photonic (MWP) filter using a quantum dash (QDash) mode-locked laser (MLL) that can generate an optical frequency comb (OFC) with ∼50 comb lines and a free spectral range of 25 GHz. Thanks to the large number of comb lines, the MWP filter responses can be easily programmed by tailoring the OFC spectrum. We implement MWP filter responses with Gaussian, sinc, flat-top, and multiple peaks, as well as demonstrate that tuning of the central frequency. We achieve a minimum 3 dB bandwidth of ∼100 MHz for a sinc-shaped MWP filter, while the maximum out-of-band rejection can be up to ∼30 dB with Gaussian apodization. Our results show that the QDash-MLL is a promising OFC source for developing integrated and reconfigurable MWP filters.

Ultra-fast optical ranging using quantum-dash mode-locked laser diodes

Laser-based light detection and ranging (LiDAR) is key to many applications in science and industry. For many use cases, compactness and power efficiency are key, especially in high-volume applications such as industrial sensing, navigation of autonomous objects, or digitization of 3D scenes using hand-held devices. In this context, comb-based ranging systems are of particular interest, combining high accuracy with high measurement speed. However, the technical complexity of miniaturized comb sources is still prohibitive for many applications, in particular when high optical output powers and high efficiency are required. Here we show that quantum-dash mode-locked laser diodes (QD-MLLD) offer a particularly attractive route towards high-performance chip-scale ranging systems. QD-MLLDs are compact, can be easily operated by a simple DC drive current, and provide spectrally flat frequency combs with bandwidths in excess of 2 THz, thus lending themselves to coherent dual-comb ranging. In our experiments, we show measurement rates of up to 500 MHz—the highest rate demonstrated with any ranging system so far. We attain reliable measurement results with optical return powers of only – 40 dBm, corresponding to a total loss of 49 dB in the ranging path, which corresponds to the highest loss tolerance demonstrated so far for dual-comb ranging with chip-scale comb sources. Combing QD-MLLDs with advanced silicon photonic receivers offers an attractive route towards robust and technically simple chip-scale LiDAR systems.

32QAM WDM transmission at 12 Tbit/s using a quantum-dash mode-locked laser diode (QD-MLLD) with external-cavity feedback.

Chip-scale frequency comb generators lend themselves as multi-wavelength light sources in highly scalable wavelength-division multiplexing (WDM) transmitters and coherent receivers. Among different options, quantum-dash (QD) mode-locked laser diodes (MLLD) stand out due to their compactness and simple operation along with the ability to provide a flat and broadband comb spectrum with dozens of equally spaced optical tones. However, the devices suffer from strong phase noise, which impairs transmission performance of coherent links, in particular when higher-order modulation formats are to be used. Here we exploit coherent feedback from an external cavity to drastically reduce the phase noise of QD-MLLD tones, thereby greatly improving the transmission performance. In our experiments, we demonstrate 32QAM WDM transmission on 60 carriers derived from a single QD-MLLD, leading to an aggregate line rate (net data rate) of 12 Tbit/s (11.215 Tbit/s) at a net spectral efficiency (SE) of 7.5 bit/s/Hz. To the best of our knowledge, this is the first time that a QD-MLLD optical frequency comb has been used to transmit an optical 32QAM signal. Based on our experimental findings, we perform simulations that show that feedback-stabilized QD-MLLD should also support 64QAM transmission with a performance close to the theoretical optimum across a wide range of technically relevant symbol rates.

56 Gb/s/λ over 1.3 THz frequency range and 400G DWDM PAM-4 transmission with a single quantum dash mode-locked laser source.

The continued evolution of high capacity data center interconnects (DCI) requires scalable transceiver design. The Gigabit Ethernet (GbE) family of standards targets cost-effective and increased capacity transmission through the use of coarse wavelength division multiplexing (CWDM) and direct detection. Moving beyond near-term GbE deployments, multi-wavelength optical sources will be required to enable spectrally efficient WDM transmission, as well as small form-factor transceiver design. This work highlights the capability of a single section 32.5 GHz quantum-dash mode locked laser to provide >Tb/s capacity by demonstrating successful 50 Gb/s/λ pulse amplitude modulation transmission on modes spanning a >1 THz frequency range. Additionally, true 400G DWDM (8×56 Gb/s) C-band transmission is successfully demonstrated with the Q-Dash MLL, resulting in a spectral efficiency of 1.54 b/s/Hz.

Mode Locked Laser Phase Noise Reduction Under Optical Feedback for Coherent DWDM Communication

Single section quantum dash (QDash) mode locked lasers (MLL) can provide a flat and broadband optical frequency comb with low energy consumption, operational simplicity and large-scale low-cost production possibilities. MLL longitudinal modes can be employed as single carriers with a regular spectral spacing in a dense wavelength division multiplexing (DWDM) link, making them promising components for next generation DWDM transceivers. However, individual modes of a MLL suffer from relatively high phase noise while high capacity coherent transmission requires carriers with low phase noise. Optical feedback, which is a well-known method to reduce the linewidth of a single mode laser, can be used to stabilize comb lasers. This article reports on the investigation of phase noise properties of comb lines delivered from a single section QDash MLL under optical feedback and shows that each MLL longitudinal mode optical linewidth can be drastically narrowed. It enables coherent transmission with extended link budget over 50 km at Tbit/s line rates.

Comb-based WDM transmission at 10 Tbit/s using a DC-driven quantum-dash mode-locked laser diode.

Chip-scale frequency comb generators have the potential to become key building blocks of compact wavelength-division multiplexing (WDM) transceivers in future metropolitan or campus-area networks. Among the various comb generator concepts, quantum-dash (QD) mode-locked laser diodes (MLLD) stand out as a particularly promising option, combining small footprint with simple operation by a DC current and offering flat broadband comb spectra. However, the data transmission performance achieved with QD-MLLD was so far limited by strong phase noise of the individual comb tones, restricting experiments to rather simple modulation formats such as quadrature phase shift keying (QPSK) or requiring hardware-based compensation schemes. Here we demonstrate that these limitations can be overcome by digital symbol-wise blind phase search (BPS) techniques, avoiding any hardware-based phase-noise compensation. We demonstrate 16QAM dual-polarization WDM transmission on 38 channels at an aggregate net data rate of 10.68 Tbit/s over 75 km of standard single-mode fiber. To the best of our knowledge, this corresponds to the highest data rate achieved through a DC-driven chip-scale comb generator without any hardware-based phase-noise reduction schemes.

Coherent WDM transmission using quantum-dash mode-locked laser diodes as multi-wavelength source and local oscillator.

Quantum-dash (QD) mode-locked laser diodes (MLLD) lend themselves as chip-scale frequency comb generators for highly scalable wavelength-division multiplexing (WDM) links in future data-center, campus-area, or metropolitan networks. Driven by a simple DC current, the devices generate flat broadband frequency combs, containing tens of equidistant optical tones with line spacings of tens of GHz. Here we show that QD-MLLDs can not only be used as multi-wavelength light sources at a WDM transmitter, but also as multi-wavelength local oscillators (LO) for parallel coherent reception. In our experiments, we demonstrate transmission of an aggregate net data rate of 3.9 Tbit/s (23 × 45 GBd PDM-QPSK, 7% FEC overhead) over 75 km standard single-mode fiber (SSMF). To the best of our knowledge, this represents the first demonstration of a coherent WDM link that relies on QD-MLLD both at the transmitter and the receiver.

Optoelectronic mixer with a photoconductive switch for 1550 nm wavelengths

We demonstrate an optoelectronic mixer based on an ultrafast InGaAs photoconductive switch and its use in an innovative heterodyne detection system for Radio over Fibre transmission. The advantage of the proposed switch is its relatively flat response curve in a wide frequency range up to 67 GHz. Two mixing schemes are presented through I-Q modulated data-stream down-conversion. The data can modulate either the electrical signal or the optical signal. In case the electrical signal is modulated, a mode-locked semiconductor laser diode is used as an optical local oscillator at the self-oscillating frequency of 24.5 GHz. The InP based quantum-dash mode-locked laser emitting in the 1570 nm wavelength range is stabilized by a feedback loop and shows a low phase noise in order to increase the mixing performances of the detection apparatus. In a second experiment, the photoconductive switch is combined with a continuous wave laser to demonstrate the feasibility of down converting an optically provided data-stream with an electrical local oscillator.

WDM Orthogonal Subcarrier Multiplexing Based on Mode-Locked Lasers

The (de)modulation of broadband orthogonal subchannels relying on all-analogue signal processing potentially achieves high-capacity orthogonal subcarrier multiplexing (OSCM) electro-optical transceivers with low power consumption and latency. Overall transmission rates can be multiplied by employing wavelength division multiplexing (WDM) technology. Mode-locked lasers (MLL) are relevant optical frequency combs, as they produce a high number of comb tones while presenting a small footprint and low power consumption. Unlike baseband transmission, the use of high-frequency subchannels in OSCM systems overcomes the high relative intensity noise that MLL comb tones present at low frequencies. This paper reports a direct-detection real-time all-analogue WDM/OSCM experiment that emulates a 432 Gbit/s (20 × 21.6 Gbit/s) electro-optical transceiver. The 20 optical carriers were generated by a state-of-the-art quantum-dash MLL. The net data rate after considering forward error correction overheads is still higher than 400 Gbit/s. This is the highest capacity achieved in real-time broadband all-analogue WDM/OSCM links to date.

Mitigation of mode partition noise in quantum-dash Fabry-Perot mode-locked lasers using Manchester encoding and balanced detection.

We propose the use of Manchester encoding in conjunction with balanced detection to overcome the mode partition noise (MPN) limit of quantum-dash Fabry-Perot mode-locked lasers (QD-MLLs) used as multi-wavelength sources in short-reach applications. The proposed approach is demonstrated for a 10-mode laser, each carrying a 10-Gb/s signal. We show that bit-error-rate floors as high as 10-4 when traditional non-return-to-zero (NRZ) modulation is employed with a single-ended detection scheme can be pushed below 10-9 thanks to the introduction of Manchester encoding together with balanced detection. The benefit of the scheme could be attributed to the spectral shift of the Manchester spectrum, resulting in a smaller overlap with the high-relative intensity noise (RIN) region present at low frequencies, and the use of balanced detection. We clarify the origin of the performance improvement through comparisons of single-ended and balanced detection and the use of a RIN emulation technique. We unambiguously show that the use of balanced detection plays the leading role in MPN mitigation enabled by Manchester modulation.

Mitigation of relative intensity noise of quantum dash mode-locked lasers for PAM4 based optical interconnects using encoding techniques.

Quantum dash (Q-Dash) passively mode-locked lasers (PMLLs) exhibit significant low frequency relative intensity noise (RIN), due to the high mode partition noise (MPN), which prevents the implementation of multilevel amplitude modulation formats such as PAM4. The authors demonstrate low frequency RIN mitigation by employing 8B/10B and Manchester encoding with PAM4 modulation format. These encoding techniques reduce the overlap between the modulation spectral content and the low-frequency RIN of the Q-dash devices, at the expense of increased overhead. The RIN of the 33.6 GHz free spectral range Q-dash PMLL was characterized, and the results obtained show very high levels of RIN from DC to 4 GHz, but low levels for higher frequencies. The performance improvement for 28 GBaud 8B/10B and Manchester encoded PAM4 signal has been demonstrated compared to the case when no encoding is used. Finally, the effect of RIN on the system performance was demonstrated by comparing the bit error rate (BER) performance of the PAM4 signaling obtained with an external cavity laser (ECL) to those obtained with Q-dash PMLL.

Amplitude and Phase Noise of Frequency Combs Generated by Single-Section InAs/InP Quantum-Dash-Based Passively and Actively Mode-Locked Lasers

We investigate the amplitude and phase noise of an optical frequency comb based on InAs/InP quantum-dash mode-locked laser. The laser demonstrates low relative intensity noise (< −125 dB/Hz) and phase noise in the passive mode-locking regime. By actively mode-locking the laser, we observe a reduction in the flicker FM noise and timing jitter, as a result of which the optical linewidth decreases, and hence the effective bandwidth compatible with optical coherent systems increases by more than 50% to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 1.1$ </tex-math></inline-formula> THz.

Asymmetric corner frequency in the 1/f FM-noise PSD of optical frequency combs generated by quantum-dash mode-locked lasers

We experimentally investigate the corner frequency in the 1/f frequency noise of the longitudinal modes of an InAs/InP quantum-dash based single-section passive mode-locked laser. The corner frequency features a strong asymmetry across the optical frequency comb with the values ranging from 10 MHz in the low-frequency side to 180 MHz in the high-frequency side. Actively mode-locking the laser induces a reduction in the corner frequency as it changes from 3 MHz in the low-frequency side to 70 MHz in the high-frequency side and the asymmetry persists.

Correlation coefficient measurement of the mode-locked laser tones using four-wave mixing.

We use four-wave mixing to measure the correlation coefficient of comb tones in a quantum-dash mode-locked laser under passive and active locked regimes. We study the uncertainty in the measurement of the correlation coefficient of the proposed method.

Multi-Format Wavelength Conversion Using Quantum Dash Mode-Locked Laser Pumps

We investigate and compare the performance of wavelength conversion for two different non-return-to-zero (NRZ) modulation formats at 40 Gb/s: on off keying (OOK) and differential phase-shift keying (DPSK). To achieve wide wavelength coverage and integrability, we use a dual pump scheme exploiting four-wave mixing in semiconductor optical amplifiers. For phase stability, we use a quantum-dash mode-locked laser (QD-MLL) as a multi-wavelength source for the dual pumps, with tunability provided by the output filter. The significant sidelobes of the DPSK spectrum (relative to OOK) require the balancing of the pump proximity to the original signal (facilitating high conversion efficiency) with the signal degradation from the pump spectrum overlapping the converted DPSK signal. We achieve a conversion efficiency near –3.6 dB for OOK and –5.4 dB for DPSK across a 12 nm tuning range with low input powers (1 dBm). We measure bit error rate (BER) and obtain error free transmission (BER &lt; 10−9) with a power penalty less than 2 dB for OOK and 3 dB for DPSK.

Laser sources for microwave to millimeter-wave applications [Invited

We present several laser sources dedicated to advanced microwave photonic applications. A quantum-dash mode-locked laser delivering a high-power, ultra-stable pulse train is first described. We measure a linewidth below 300 kHz at a 4.3 GHz repetition rate for an output power above 300 mW and a pulse duration of 1.1 ps after compression, making this source ideal for microwave signal sampling applications. A widely tunable (5–110 GHz), monolithic millimeter-wave transceiver based on the integration of two semiconductor distributed feedback lasers, four amplifiers, and two high-speed uni-traveling carrier photodiodes is then presented, together with its application to the wireless transmission of data at 200 Mb/s. A frequency-agile laser source dedicated to microwave signal processing is then described. It delivers arbitrary frequency sweeps over 20 GHz with high precision and high speed (above 400 GHz/ms). Finally, we report on a low-noise (below 1 kHz linewidth), solid-state, dual-frequency laser source. It allows independent tuning of the two frequencies in the perspective of the implementation of a tunable optoelectronic oscillator based on a high-Q optical resonator.