Repetition Rate Optical Pulse Train Research Articles

Pulsed microwave photonic vector network analyzer based on direct sampling.

Pulsed VNAs enabling large dynamic measurement at a low pulse duty cycle are necessary for the characterization of active devices due to the overheating damage risk under continuous wave stimulation. In this paper, we proposed a pulsed microwave photonic vector network analyzer (p-MPVNA) based on direct sampling. With the broad system bandwidth of the p-MPVNA and undersampling technique, pulsed signals are received thru asynchronous wideband detection, and pulsed S-parameters are calculated thru vector superposition. In asynchronous wideband detection, the continuous spectrum of the pulsed signal is discretized into multiple frequency components. A low repetition rate optical pulse train undersamples the pulsed signal, and the discretized frequency components are aliased. The frequency components in the main lobe including most energy of the pulse signal are vector superimposed to calculate the pulsed S-parameter. The proposed p-MPVNA has a dynamic range decreases rate of 10log(duty cycle) when pulse duty cycle is below 10% , which is much slower than that of 20log(duty cycle) for classical narrowband detection. An experimental p-MPVNA is established for validation. A 6 to 18 GHz microwave amplifier is measured with continuous and pulsed power supply and the measured gain curves are consistent with the results from a commercial VNA. The system dynamic range decrease with pulse duty cycle is verified by the pulsed S-parameter measurement of a 10 GHz low pass filter under continuous and pulsed stimulation.

Phase Noise of Optical Pulse Trains Generated by Talbot Effect in Frequency Shifting Loops

High repetition rate optical pulse trains are essential for a wide range of applications, including photonic-assisted sampling. Among the different solutions proposed so far, Talbot lasers, based on the generation of an optical frequency comb in a frequency shifting loop, are a simple yet efficient source of short transform-limited pulses. By controlling the comb spectral phase, the repetition rate is reconfigurable. It can be set to a (possibly large) multiple of the comb spacing and reach the GHz range, while only requiring a low bandwidth synthesizer (typ. 100 MHz). The noise characteristics of this pulse trains is a key factor for its application. Therefore, we investigate the phase noise properties of Talbot lasers. In particular, we prove theoretically and demonstrate experimentally that the phase noise at high offset frequency from the carrier, does not depend on the multiplication factor $q$ . We also demonstrate that the phase noise at low offset frequencies, which increases as $20 \log q$ , can be strongly reduced by a simple locking technique. Finally, we show that in addition to their reconfigurability, Talbot lasers can provide timing jitters at 8.2 GHz as low as 350 fs (integrated from $10^{5}$ Hz to the Nyquist frequency), making them suitable candidates for time metrology applications.

Highly tunable repetition-rate multiplication of mode-locked lasers using all-fibre harmonic injection locking

Higher repetition-rate optical pulse trains have been desired for various applications such as high-bit-rate optical communication, photonic analogue-to-digital conversion, and multi-photon imaging. Generation of multi GHz and higher repetition-rate optical pulse trains directly from mode-locked oscillators is often challenging. As an alternative, harmonic injection locking can be applied for extra-cavity repetition-rate multiplication (RRM). Here we have investigated the operation conditions and achievable performances of all-fibre, highly tunable harmonic injection locking-based pulse RRM. We show that, with slight tuning of slave laser length, highly tunable RRM is possible from a multiplication factor of 2 to >100. The resulting maximum SMSR is 41 dB when multiplied by a factor of two. We further characterize the noise properties of the multiplied signal in terms of phase noise and relative intensity noise. The resulting absolute rms timing jitter of the multiplied signal is in the range of 20 fs to 60 fs (10 kHz–1MHz) for different multiplication factors. With its high tunability, simple and robust all-fibre implementation, and low excess noise, the demonstrated RRM system may find diverse applications in microwave photonics, optical communications, photonic analogue-to-digital conversion, and clock distribution networks.

Gigahertz repetition rate, sub-femtosecond timing jitter optical pulse train directly generated from a mode-locked Yb:KYW laser

We show that a 1.13 GHz repetition rate optical pulse train with 0.70 fs high-frequency timing jitter (integration bandwidth of 17.5 kHz-10 MHz, where the measurement instrument-limited noise floor contributes 0.41 fs in 10 MHz bandwidth) can be directly generated from a free-running, single-mode diode-pumped Yb:KYW laser mode-locked by single-wall carbon nanotube-coated mirrors. To our knowledge, this is the lowest-timing-jitter optical pulse train with gigahertz repetition rate ever measured. If this pulse train is used for direct sampling of 565 MHz signals (Nyquist frequency of the pulse train), the jitter level demonstrated would correspond to the projected effective-number-of-bit of 17.8, which is much higher than the thermal noise limit of 50 Ω load resistance (~14 bits).

Single- and dual-wavelength pulse train generation in frequency-modulated Er–Yb lasers up to [formula omitted

In this paper we present recent results obtained on the generation of ultra-high repetition rate optical pulse trains at 1.5 μm in asynchronously frequency-modulated Er–Yb : glass lasers. Nearly transform-limited pulse trains at either single or dual carrier wavelength with repetition rates up to ∼20 GHz are generated by means of an external fiber Bragg grating. These pulse trains are of great potential interest for soliton-based optical transmission systems.

High-repetition-rate optical pulse generation byusing chirped optical pulses

A very high repetition rate optical pulse train is generated by using a chirped optical pulse train obtained with a dispersive medium and an optical pulse laser source. Adjusting the group-velocity dispersion (GVD) of the dispersive medium, we can obtain an optical pulse train at a repetition rate which is a multiple of that of the optical pulse laser source initially used. We have successfully generated a 50 to 400 GHz optical pulse train synchronised with an external clock by using a 10 GHz pulse source and optical fibre as the dispersive medium. We have also numerically confirmed this result.

Nonlinear, dispersion-free 10 GHz optical pulse train transmission in distributed erbium-doped fibre

The transmission of a 10 GHz repetition rate optical pulse train over a 28.5 km long distributed erbium-doped fibre amplifier is reported. In the linear dispersion regime, the pulses broaden so that the tails of adjacent pulses overlap. However, given sufficiently high signal powers, the optical Kerr effect causes pulse narrowing back to the original 18 ps pulsewidth.