Ultrashort Optical Pulse Sources Research Articles

Multi-Band Radar Based on a Cavity-Less Ultra-Short Optical Pulse Source for Simultaneous Measurement of Distance and Velocity

Multi-Band Radar Based on a Cavity-Less Ultra-Short Optical Pulse Source for Simultaneous Measurement of Distance and Velocity

Photonic sampling analog-to-digital conversion based on time and wavelength interleaved ultra-short optical pulse train generated by using monolithic integrated LNOI intensity and phase modulator.

High-speed analog-to-digital conversion (ADC) is experimentally demonstrated by employing a time and wavelength interleaved ultra-short optical pulse train to achieve photonic sampling and using wavelength division demultiplexing to realize speed matching between the fast optical front-end and the slow electronic back-end. The sampling optical pulse train is generated from a cavity-less ultra-short optical pulse source involving a packaged device that monolithically integrates an intensity modulator and a phase modulator into a chip based on lithium niobate on insulator (LNOI). In the experiment, the fiber-to-fiber insertion loss of the packaged modulation device is measured to be 6.9 dB. In addition, the half-wave voltages of the Mach-Zehnder modulator and the phase modulator in the LNOI-based modulation device are measured to be 3.6 V and 3.4 V at 5 GHz, respectively. These parameters and the device size are superior to those based on cascaded commercial devices. Through using the packaged modulation device, two ultra-short optical pulse trains centered at 1541.40 nm and 1555.64 nm are generated with time jitters of 19.2 fs and 18.9 fs in the integral offset frequency range of 1 kHz to 10 MHz, respectively, and are perfectly time interleaved into a single pulse train with a repetition rate of 10 GHz and a time jitter of 19.8 fs. Based on the time and wavelength interleaved ultra-short optical pulse train, direct digitization of microwave signals within the frequency range of 1 GHz to 40 GHz is demonstrated by using a two-channel wavelength demultiplexing photonic ADC architecture, where the effective number of bits are 5.85 bits and 3.75 bits for the input signal at 1.1 GHz and 36.3 GHz, respectively.

Frequency Response Enhancement of Photonic Sampling Based on Cavity-Less Ultra-Short Optical Pulse Source

The influence of the residual pulse chirp and the spectrum shape from a cavity-less optical pulse source on the sampling performance is theoretically analyzed. According to the theoretical analysis, an optimization method for enlarging the operation bandwidth of a photonic sampling system based on a cavity-less ultra-short pulse source is proposed and experimentally demonstrated. Through biasing the Mach-Zehnder modulator in the cavity-less optical pulse source below its quadrature point, the output spectrum flatness can be greatly improved, which is beneficial for optimizing the photonic sampling frequency response introduced by the ultrashort optical pulse train. In the experiment, the 3-dB bandwidth of the photonic sampling frequency response is increased from less than 10 GHz to more than 35 GHz by using the proposed method without sacrificing the output signal-to-noise ratio.

Broadband multi-frequency microwave photonic up-conversion with tunable phase shift

A broadband multi-frequency microwave photonic up-conversion scheme with a tunable phase shift is proposed and demonstrated based on a cavity-less ultrashort optical pulse source and a dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM). In this scheme, the intermediate-frequency (IF) signal is loaded onto the optical frequency comb from a cavity-less ultrashort pulse source via carrier-suppressed double-sideband (CS-DSB) modulation by using a DP-DPMZM and a 90° electric hybrid coupler (HC). Through mutual beating between multi-groups of optical modulation sidebands and multi-tone optical carrier at the photodetector (PD), multi-frequency up-converted microwave signals are obtained after coherent superposition. Meanwhile, the phase of the generated signals can be continuously tuned through varying the bias voltages of the DP-DPMZM. Simulation results show that the multi-frequency up-conversion is with a 3-dB operation bandwidth of 36 GHz and a phase shift tuning range over 360°. Hence, this scheme is a potential candidate to simultaneously realize broadband multi-frequency operation and generate the large-scale tunable phase shift in modern radar systems.

Pulse Cluster Dynamics in Passively Mode-Locked Semiconductor Vertical-External-Cavity Surface-Emitting Lasers

Passively mode-locked lasers have become a topic of substantial research, as they are efficient sources of ultrashort optical pulses and essential to applications such as multiphoton microscopy and dual-comb spectroscopy. Here external cavity geometry has a great influence on performance, though, and also can lead to detrimental multipulse emission. The authors use a delay differential equation model, derived for these types of lasers and accounting for the external cavity geometry, to better understand the emergence of detrimental dynamics. The results are expected to further improve the performance of these systems.

Experimental Measurement of Fiber-Wireless Transmission via Multimode-Locked Solitons From a Ring Laser EDF Cavity

This paper describes a demonstration of soliton transmission over fiber-wireless (Fi-Wi) networks using mode-locked stable solitons over a 50-km-long fiber and a short-distance wireless link. Ultrashort optical pulse sources in the 1.5- $\mu\hbox{m} $ region are seen as increasingly important for achieving ultrahigh-speed optical transmission and signal processing at optical nodes. Mode-locked solitons were generated by a simple ring laser cavity incorporating a very thin layer of carbon nanotube (CNT), together with an erbium-doped fiber (EDF) laser used as an active bulk gain medium. Experimental measurements involved the transmission of the generated mode-locked soliton over a 50-km-long single-mode fiber (SMF), and a radio-frequency (RF) spectrum subsequently generated was a result of beating frequency of wavelengths launched into the photodetector at the other end of the SMF. This RF spectrum array was in the range of WiFi frequencies. System performance was evaluated by first selecting one of the RF carriers centered at 2.5 GHz via an RF bandpass filter and subsequently using this carrier to transmit quadrature phase-shift keying (QPSK) and 16-quadrature amplitude modulation (16-QAM) data signals. The described optical circuit, containing an EDF laser, a CNT, an SMF, and a wireless link, was shown to achieve ultrastable transmission of mode-locked soliton over a long-distance Fi-Wi network.

Semiconductor lasers enable advances in nonlinear biophotonics

The successful demonstration of two-photon excitation fluorescence imaging of biotissues,1 such as mouse kidney and brain cells, has spurred development of a variety of novel multiphoton imaging (MPI) technologies. For example, using near-IR optical pulses, MPI can peer deep into tissues for noninvasive profiling. Moreover, because the fluorescence occurs only at the focal point of IR optical pulses, very long-time imaging is possible. This minimizes the consumption of fluorescent material. Many MPI technologies depend on high peak-power (over a kilowatt) ultrashort optical pulse sources to efficiently induce various multiphoton, nonlinear optical effects inside biospecimens. But most current sources are mode-locked solid-state lasers, which are bulky, expensive, and require maintenance. Increasing the practical appeal of MPI will require ‘real-world’ alternatives. Semiconductor laser diodes (LDs) have enjoyed substantial success as dependable, low-cost, high-performance light sources in information and communication technologies. In addition to their usefulness as mass-produced IT devices, LDs also have potential applications in scientific and technological measurement systems. Here we report evidence of their relevance to nonlinear bioimaging. In our research, LDs serve as key, easy-tooperate devices for generating stable picosecond optical pulses. A subsequent increase in optical power using low-noise and low-nonlinear-effect amplifiers raises the optical pulse peak power to more than a kilowatt, making it suitable for MPI. Because of the high peak power, efficient wavelength conversions using second-order nonlinear materials (e.g., ferroelectric optical crystals) and third-order materials (e.g., optical fibers, liquids) are also possible. Figure 1 presents the basic concept of our optical pulse source in schematic form. Figure 1. Schematic for generating kilowatt peak power picosecond optical pulses using a semiconductor laser oscillator. LD: laser diode.

System-Performance Analysis of Optimized Gain-Switched Pulse Source Employed in 40- and 80-Gb/s OTDM Systems

The development of ultrashort optical pulse sources, exhibiting excellent temporal and spectral profiles, will play a crucial role in the performance of future optical time division multiplexed (OTDM) systems. In this paper, we demonstrate the difference in performance in 40- and 80-Gb/s OTDM systems between optical pulse sources based on a gain-switched laser whose pulses are compressed by a nonlinearly and linearly chirped fiber Bragg grating. The results achieved show that nonlinear chirp in the wings of the pulse leads to temporal pedestals formed on either side of the pulse when using the linearly chirped grating, whereas with the nonlinearly chirped grating, pedestals are essentially eliminated. In an OTDM system, these pedestals cause coherent interaction between neighboring channels, resulting in intensity fluctuations that lead to a power penalty of 1.5 dB (40 Gb/s) and 3.5 dB (80 Gb/s) in comparison to the case where the nonlinearly chirped grating is used. Simulations carried out with the aid of Virtual Photonics Inc. verify the results achieved.

Tunable ultra-short optical pulse source based on reflective semiconductor fiber ring laser

Ultra-short optical pulse source is one of key components in optical time-division multiplexing(OTDM) system. In this paper, a wavelength and repetition rato tunable actively mode-locked fiber ring laser based on cross-gain modulation in a reflective Semiconductor Optical Amplifier(SOA) is demonstrated. Theoretical model for this scheme is also established and output characteristics are calculated. Stable picosecond pulse trains with high extinction ratio at 10—40 GHz repetition rato are obtained. 30nm wavelength tuning range is also achieved in our proposed actively mode-locked laser.

Electrical equivalent model for an optical VCO in a PLL synchronization scheme for ultrashort optical pulse sources

The electrical modeling of complex electrooptical devices is a useful task for the correct design of its schemes and for the estimation of its performance. In this paper, we consider an electrooptical phase-locked loop (PLL) used to synchronize an RF system clock to the repetition rate of an optical pulsed source, realized by an active fiber mode-locking (ML) technique in the regenerative configuration. The synchronization scheme is suggested by a description of the pulsed source, for the first time, as an optical voltage-control oscillator (VCO). In particular, we present a simple new all-electrical model for the proposed optical VCO, and we verify its accuracy by the implementation of the whole PLL scheme at 2.5 and 10 GHz.

All-fiber integrated ∼10kW peak power ultrashort optical pulse source based on compression in aircore photonic band gap fiber

We demonstrate an all-fiber integrated, ∼10kW peak power, ∼1ps optical pulse source at a wavelength of 1.55μm based on compression in aircore photonic band gap fiber. A 10GHz pulse train was modulated at 10MHz in a Mach–Zehnder amplitude modulator with a ∼1ns transmission window before stretching in 100m of dispersion compensating fiber, amplifying, and recompressing in 10m of aircore photonic band gap fiber. Numerical simulations show that if the aircore fiber dispersion slope could be made negligible, the achievable peak power would be increased by a factor of approximately 2.

Measurement of ultrashort-radiation parameters by the method of chirped-pulsed spectral interferometry

A simple and reliable method for the measurement of the contrast of ultrashort pulses was implemented. It is based on the application of the principles of chirped-pulse spectral interferometry. The method is linear in terms of the field of the investigated radiation and is based on the measurement with interferometric precision of the spectrum of an amplified chirped pulse before it passes through a temporal compressor. It is shown that, when a recording system with a dynamic range of 102 is used, measurements of the contrast up to 105 are possible. The possibility of applying the method for the on-line monitoring of the parameters of the radiation of solid-state laser sources of ultrashort optical pulses is demonstrated. This is done by taking as an example the optimisation of the front end of a neodymium glass picosecond laser system generating ~1 ps pulses at its output.

Mode-locked ring laser with output pulse width of 0.4 ps

The output pulse width of a mode-locked ring laser composed of an erbium-doped fiber amplifier, Mach-Zehnder optical modulator, and optical band-pass filter depends largely on the repetition frequency and the wavelength characteristics of these optical circuit elements. In previous experiments, the output pulse width was in the order of 5 ps at a repetition frequency of 5 GHz. The principal reason was that the narrow passage band of the optical circuit elements made it extremely difficult to generate an ultra-short optical pulse. Consequently, we examined how to narrow the optical pulse width by flattening the wavelength characteristics of these optical circuit elements. Furthermore, we drove the optical modulator in the cavity using a frequency multiplier to operate at an effectively higher frequency By widening the wavelength passage band of all the devices in the optical circuit, we achieved an output pulse width of 0.4 ps at a repetition frequency of 5 GHz; the pulse peak power was more than +23 dBm, and the time-bandwidth product was 0.34. We successfully tested an ultra-short optical pulse source with an output pulse width of 0.4 ps with no external pulse compression using a mode-locked ring laser.

A duration-tunable, multiwavelength pulse source for OTDM and WDM communications systems

We describe a highly flexible ultrashort optical pulse source capable of generating duration-tunable pulses at single or multiple wavelengths. The technique we report is based on the filtering of the broad spectrum of femtosecond solitons which are generated using an electroabsorption modulator combined with nonlinear compression. The simplicity and robust nature of this source make it highly stable and we demonstrate the generation of pulses at a repetition rate of 10 GHz with durations in the femtosecond and picosecond regimes and the simultaneous generation of eight 10-GHz channels of picosecond pulses with a channel spacing of 3.5 nm.