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Intensity modulation and direct detection (IM/DD) with pulse amplitude modulation (PAM) is a cost-effective option for intra- and inter-data center (DC) applications. Due to current demand on DC data traffic, transmission rates beyond 200 Gbit/s/ $\lambda $ are desirable. However, employing commercially available lower bandwidth components introduces severe inter-symbol interference (ISI). In addition, to achieving high-speed data rates, digital signal processing (DSP) schemes like Tomlinson-Harashima precoding (THP) and decision feedback equalizer (DFE) can increase tolerance against ISI. In this letter, we show an experimental comparison of PAM-4, PAM-6 and PAM-8 modulation formats with and without THP on the transmitter-side and Volterra nonlinear equalizer (VNLE) on the receiver-side. We provide also results with and without duobinary (DB) encoding on the transmitter side and DFE on the receiver side. The experiment is conducted using an O-band electro-absorption modulated laser over transmission distances up to 20 km.

Vertical-cavity surface-emitting lasers (VCSELs) for 200+ Gbit/s single fiber data transmission across OM5 multimode fiber with a heat to bit rate ratio (HBR) of only 240 fJ/bit based on coarse wavelength division multiplexing (CWDM) are presented. Tuning the cavity photon lifetime is demonstrated to lead to an increase of the data rate in concert with a reduction of the HBR. The VCSELs are emitting at 850 nm, 880 nm, 910 nm, and 940 nm, the present IEEE 802.3 coarse wavelength multiplexing standard.

Directly current-modulated 980-nm vertical-cavity surface-emitting lasers (VCSELs) with oxide-aperture-diameters of $1.5~\mu \text{m}$ exhibit a small-signal −3 dB modulation bandwidth of 31 GHz and a single-mode light-output-power of 3 mW with a side-mode-suppression-ratio (SMSR) of 49 dB at 25 °C at a forward bias current of 3 mA. At 85 °C, the maximum bandwidth is about 25 GHz, the peak power is about 2 mW, and the SMSR remains 49 dB. The bandwidth for a 5.5- $\mu \text{m}$ oxide-aperture-diameter VCSEL reaches 26 and 21 GHz at 25 °C and 85 °C, respectively, with corresponding maximum multi-mode optical output power of about 10 and 6 mW.

Photonic band crystal semiconductor lasers generating gain-switched picosecond pulses in the 1060-nm spectral range are demonstrated. The unique ultra-broad laser waveguide allows the simultaneous delivery of high output power and high beam quality, enabling the generation of optical pulses with peak brightness up to 130 MWcm -2 sr -1 . The spectral dynamics are investigated by external filtering of the laser emission. The effects of the filter bandwidth and central wavelength on the resulting optical pulse characteristics are identified. By properly chosen filter parameters, it is found that the higher order relaxation oscillation part of the optical pulse is completely suppressed even at the highest injected pulse currents, also resulting in a pulse width reduction down to less than 21.5 ps.

In this paper, we present a systematic investigation of passive mode-locked InAs/InP quantum-dash lasers in terms of frequency and timing stability. Mode-locking features are analyzed using the frequency domain approach based on the concept of supermodes. It is shown that the phase of adjacent longitudinal modes is correlated over 1.3-THz frequency span. The observed strong coherence between modes enables low timing jitter and a long-term stability of the repetition rate frequency within 5×10-8 over 100 s.

In this paper, we describe generation and application of wide narrow linewidth optical frequency combs using dual-mode injection-locking of InP quantum-dash mode-locked lasers. First, the dependence of the RF locking-range on the device's absorber voltage is experimentally investigated. Under optimized absorber voltage, a continuous wide RF locking-range of ${\approx}{\rm 400}~{\rm MHz}$ is achievable for lasers with 21 GHz repetition rate. The total RF locking-range of ${\approx}{\rm 440}~{\rm MHz}$ is possible considering locking-range for positive and negative absorber voltages. This wide tuning ${>}2{\%}$ of the repetition rate, a record for a monolithic mode-locked laser, is reported from a two-section device without any additional passive section or extended-cavity for repetition rate tuning. It is shown that the effective RF locking-range in dual-mode injection corresponds to the optical locking-range and repetition rate tuning under CW injection, which is wider when the free-running mode-locking operation is “less stable.” The widest comb consists of 35 narrow lines within 10 dB of the peak, spanning ${\approx}{\rm 0.7}~{\rm THz}$ and generating 3.7 ps pulses. Second, we show the first demonstration of multi pump phase-synchronization of two 10 Gb/s DPSK channels in a phase-sensitive amplifier using dual-mode injection-locking technique. The phase-sensitive amplifier based on the “black box” scheme shows more than 7 dB phase-sensitive gain and error free performance for both input channels with 1 dB penalty.

This paper reports on recent results on passively mode-locked InAs/InP quantum-dot-based lasers. These low-dimensional structures have proved very attractive in improving most of the properties of these devices. Subpicosecond pulse generation at repetition rates up to beyond 300 GHz has readily been demonstrated. Ultranarrow RF linewidths reach record values of less than 1 kHz. Controlled optical feedback allows a further reduction of this linewidth yielding extremely low timing jitter. A comparison of single-section and standard two-section lasers is given for the first time. These performances open the way to various applications at 1.55 μm, including very high bit rate all-optical signal processing, frequency comb generation, radio over fiber, and low-noise all-optical oscillators.

We report optical injection-locking in 21-GHz single-section and two-section InAs/InP 1.5-μm quantum-dash mode-locked lasers. Two distinct mode-locked regimes were observed and successfully locked to the optically injected light. The single-section laser only operates as a self-mode-locked laser while the two-section laser could operate as both a self-mode-locked laser and saturable-absorber dominated mode-locked laser. The continuous-wave (CW) injection-locked self-mode-locked laser shows wide tuning of the mode-locked frequency (≈270 MHz) within the locking range. The CW injection-locked saturable-absorber dominated mode-locked laser demonstrates wide optical spectrum, and 5.5 t reduction in the time-bandwidth product of the pulses. Using dual-mode injection, strong reduction of timing jitter ( ≈235 fs) is possible leading to the generation of a wide coherent frequency comb. Coherence between all the modes and the master laser is confirmed by measuring the RF beat note of each mode with a narrow linewidth laser.

We introduce a novel scheme for the simultaneous reduction of time-bandwidth product (TBP) and RF linewidth of quantum-dash two-section mode-locked lasers using optical injection-locking and filtered optical feedback. The optical injection-locked laser, double-locked with optical feedback showed 2× TBP reduction and RF linewidth reduction by two orders of magnitude. This stabilization technique is implemented in an all-optical arrangement without optical/electrical conversion which is ideal for high-repetition-rate devices and photonic integration.