超低压选择区域生长法制备产生10GHz重复率超短光脉冲的级联电吸收调制器与分布反馈激光器单片集成光源

采用超低压(22×１０^２Pa)选择区域生长(selective area growth, SAG)金属有机化学气相沉积(metal-organic chemical vapor deposition, MOCVD)技术成功制备了InGaAsP/InGaAsP 级联电吸收调制器(electroabsorption modulator, EAM)与分布反馈激光器(distributed feedback laser, DFB)单片集成光源的新型光电器件.实验结果表明，采用该技术制备的器件 关键词： 超低压 选择区域生长 集成光电子器件 超短光脉冲     

64 GHz optical millimeter-wave generation by octupling 8 GHz local oscillator via a nested LiNbO3 modulator

A novel scheme to generate a 64 GHz optical millimeter (mm)-wave via a nested LiNbO₃ Mach-Zehnder modulator with an 8 GHz local oscillator is proposed and simulated. Since the frequency response of the modulator and the local oscillator frequency are greatly reduced, the bandwidth requirements of the optical and electrical components in the transmitter are significantly decreased. The simulation results show that the generated optical mm-wave signal maintains good performance even after being transmitted over 20 km standard single-mode fiber.     

New directions in sub-10-fs optical pulse generation

Sub-10-fs pulse generation has reached a maturity and robustness that gave rise to a rapid increase of new ultrafast applications. Some of these novel applications rely on the octave-spanning spectral width, the coherence properties, or the extremely high peak intensity of femtosecond lasers, which sets them apart from the traditional use of femtosecond lasers in ultrafast spectroscopy. In this review, we concentrate on the sub-10-fs regime and first discuss the state of the art in ultrashort pulse generation. We then report on ultrabroadband wavelength conversion schemes and dispersion control by chirped mirrors. We also review advances in pulse characterization methods, with which we can measure pulse properties with much higher accuracy than simple autocorrelation methods and which support even a bandwidth in the single-cycle regime. With the recent demonstrations of pulses with a duration of merely two optical cycles, a regime is entered where the relative phase between the carrier and the envelope of the pulse starts to play a role. We discuss methods to measure and control the carrier–envelope phase and point out applications in frequency metrology. A wealth of further novel directions and developments in femtosecond research is reviewed in this article.     

Terahertz pulse generation via optical rectification in photonic crystal microcavities

Using a three-dimensional fully vectorial nonlinear time-domain analysis, we numerically investigate generation of terahertz radiation by pumping a photonic crystal microcavity out of resonance. High quality factors and a quadratic susceptibility lead to few-cycle terahertz pulses via optical rectification. Material dispersion as well as linear and nonlinear anisotropy is fully accounted for.     

Sub-10-fs pulse generation from a blue laser-diode-pumped Ti:sapphire oscillator

Pulses as short as 8.1 fs were generated from a blue laser-diode-pumped Kerr-lens mode-locked Ti:sapphire oscillator, with an average power of 27 m W and a repetition rate of 120.6 MHz. The full width at half-maximum exceeds 146 nm, benefitting from the dispersion management by a combination of a low-dispersion fused silica prism pair and a series of double-chirped mirrors. To the best of our knowledge, this is the first time to generate sub-10-fs pulses from a laser diode directly pumped Ti:sapphire oscillator.     

10 GHz, 2.4 ps pulse generation using a single-stage dual-drive Mach-Zehnder modulator

This Letter reports on picosecond pulse generation at a repetition of 10 GHz by using a single-stage electro-optic LiNbO(3) Mach-Zehnder modulator, stressing the simplicity of its setup. It is analytically and experimentally proved that dual-arm modulation with in-phase sinusoidal signals having slightly different amplitudes generated a highly coherent optical comb with a great spectral flatness and a parabolic phase relationship in its spectrum. The generated comb was Fourier synthesized and shaped into an ultrashort pulse train with an optical bandpass filter and a dispersive fiber. The pulse source was highly stable, exhibiting an ultralow timing jitter of less than 130 fs.     

Compact 10 GHz loopback arrayed-waveguide grating for high-fidelity optical arbitrary waveform generation

We demonstrate a high-performance optical arbitrary waveform shaper based on a single 10 GHz arrayed-waveguide grating with 64 loopback waveguides and integrated amplitude and phase modulators on each waveguide. The design is compact and self-aligning and allows for bidirectional operation. The device's complex transfer function is manipulated and measured over the full 640 GHz passband. To demonstrate optical arbitrary waveform shaping, high-fidelity 15-line shaped waveforms are measured with cross-correlation frequency-resolved optical gating.     

Raman amplification and optical short pulse generation in a waveguide with periodic gain

In this paper a new configuration of amplification is proposed for Raman amplification. In this new configuration a spatial periodic Raman gain is used to amplify a CW Raman seed that generates a short optical pulse taking into account the SPM, XPM, walk-off and pulse depletion. The amplification process is accomplished by using an intense pump pulse where its energy is transferred through SRS effect. A CW weak seed is used to represent the signal to be amplified and for pump is used a Gaussian pulse. We discuss the advantages to this configuration. First, this scheme means that the Raman-gain coefficient assumes a periodic characteristic and like a modulation process, it gives possibility to control the energy transfer from the pump to Raman seed. Second, the efficient use of the parameters of the periodic Raman coefficient function, like amplitude and frequency of the modulation, can result in a more efficient control of the signal amplification. This new configuration provides some very interesting features in the Raman amplification process when compared to the standard procedure. A complete discussion of this configuration is presented.     

Fiber optical parametric oscillator for sub-50 fs pulse generation: optimization of fiber length

We demonstrate generation of 48fs pulses with linear chirp using a short (27mm) fiber optical parametric oscillator (FOPO), which is synchronously pumped by a mode-locked ytterbium-doped fiber laser. We also study the pulse quality for both the short- and long-wavelength operation where the fiber length inside of the oscillator varies from 17 to 61mm. The optimal pulse duration is observed only in the short-wavelength operation. Furthermore, we model the FOPO system as a single-pass parametric amplifier including dispersive pulse broadening and walk-off between the pump and output. The optimal condition arises from the minimization of the walk-off and dispersion. When walk-off is large, the parametric amplification process is most efficient over some reduced effective fiber length, leading to an upper limit in the amount of the observed pulse broadening.     

Bright and dark 40 GHz parabolic pulse generation using a picosecond optical pulse train and an arrayed waveguide grating

We demonstrate parabolic optical pulse generation by manipulating the intensity and phase of individual longitudinal modes of a 40 GHz picosecond optical pulse train in the spectral domain. Bright and dark parabolic pulses were generated from a 40 GHz mode-locked fiber laser using a 64-channel arrayed waveguide grating pulse shaper. The obtained parabolic pulse, which can easily generate a linear chirping, is useful for a number of applications to optical signal processing applications, including pulse compression and time-domain optical Fourier transformation.     

Novel 60 GHz RoF system with optical single sideband mm-wave signal generation and wavelength reuse for uplink connection

In order to improve RF frequency to achieve higher bandwidth and larger capacity, we propose a novel scheme to generate optical single sideband (SSB) millimeter-wave, in which frequency doubling of local radio frequency (RF) is obtained by using one integrated Mach–Zehnder modulator (MZM), and we theoretically investigate the generating principle of SSB. The optical SSB modulation scheme is employed to generate 60 GHz optical mm-wave and the 2.5 Gb/s baseband signal is simultaneously up-converted at the central station (CS) for downlink transmission, and the optical carrier is reused for uplink connection at the base station (BS). The full-duplex 2.5 Gb/s data are successfully transmitted over 40 km standard single-mode fiber (SMF-28) for both uplink connection and downlink connection with less than 2-dB power penalty. Results show the novel 60 GHz RoF system with optical SSB mm-wave signal generation using optical frequency doubling is feasible and we can obtain simple cost-efficient configuration and good performance over long-distance transmission.     

THz generation via optical rectification with ultrashort laser pulse focused to a line

We report on efficient THz pulse generation via optical rectification with femtosecond laser pulses focused to a line by a cylindrical lens. This configuration provides phase-matched conditions in the superluminal regime. 35 pJ THz pulses have been generated with this technique in a stoichiometric LiNbO₃ crystal pumped by 2 μJ femtosecond laser pulses at room temperature. An unusual superquadratic rise of the THz pulse energy with the laser pulse energy has been observed at high laser energies. This extraordinary energy dependence of the THz generation efficiency is explained by self-focusing of the laser beam in the crystal. Z-scan measurements and comparison of the THz pulse spectra created with laser pulses having different energies confirm this interpretation.     

Performance enhanced down-stream signalling for next generation long-reach 10 Gbit/s passive optical networks

In this paper, we have analyzed the signal processing methods both in digital and optical domain to enhance the transmission performance of downstream signalling in long reach passive optical networks (LR-PONs). The impact of non-linear (NL) equalization through signal processing, i.e. Volterra Equalization (VE), Digital Backpropagation (BP) and Optical Phase Conjugation with Non-linearity Module (OPC-NM) is investigated, in 10 Gbit/s (XG) DP-QPSK long-reach wavelength division multiplexed (WDM) PONs without midspan repeaters over 120 km standard single mode fibre (SMF) link for down-stream signals. Due to the compensation of optical Kerr effects, the sensitivity penalty is reduced to 2 dB by BP algorithm, 1.5 dB by VE algorithm and 2.69 dB by OPC-NM. Moreover, with the implementation of NL equalization technique we are able to get the transmission distance of 126.6 km SMF for the 1:1024 split-ratio at 5 GHz channel spacing in the non-linear region. Furthermore, the concept of super passive optical network (S-PON) is also evaluated, which involves a repeater stage consisting of optical amplifiers, to study the feasibility for receiver side signal processing and simplification.     

Five-optical-cycle pulse generation in the mid infrared from an optical parametric oscillator based on aperiodically poled lithium niobate

We describe an optical parametric oscillator based on aperiodically poled lithium niobate that generates nearly transform-limited 53-fs duration pulses at a center wavelength of 3mum, corresponding to only 5 optical cycles. Results are presented illustrating the effect of pump- and grating-period chirp on the idler pulses, and a configuration capable of producing idler bandwidths in excess of 700 nm is discussed.     

Output properties of 1.57 μm intracavity pumped optical parametric oscillator

A 1.57 μm eye-safe laser is realized by placing a KTP crystal into a diode-end-pumped, acousto-optically (AO) Q-switched Nd:YVO4 laser. For the first time, the 1.06 μm pumping laser with a concave–concave cavity is used to lower the threshold of the intracavity-pumped optical parametric oscillator (IPOPO). The pumping threshold and output characteristics of the OPO are analyzed by changing repetition rate of the AO Q-switch and output mirrors with different transmissivity at 1.57 μm. The results show that the pumping threshold will decrease with the lower output transmissivity and the lower repetition rate, but the narrower output pulse width can be obtained with the higher output transmissivity.     

Cryogenic 35 GHz pulse ENDOR probehead accommodating large sample sizes: Performance and applications

The construction and performance of a cryogenic 35 GHz pulse electron nuclear double resonance (ENDOR) probehead for large samples is presented. The resonator is based on a rectangular TE₁₀₂ cavity in which the radio frequency (rf) B₂-field is generated by a two turn saddle ENDOR coil crossing the resonator along the sample axis with minimal distance to the sample tube. An rf power efficiency factor is used to define the B₂-field strength per square-root of the transmitted rf power over the frequency range 2–180 MHz. The distributions of the microwave B₁- and E₁-field, and the rf B₂-field are investigated by electromagnetic field calculations. All dielectrics, the sample tube, and coupling elements are included in the calculations. The application range of the probehead and the advantages of using large sample sizes are demonstrated and discussed on a number of paramagnetic samples containing transition metal ions.     

Nanostructured fibers for sub‐10 fs optical pulse delivery

A novel fiber technology is presented that enables the transmission of 200 nm wide spectra over meter‐long distances with minimal temporal reshaping and acceptable losses down to about 3 dB/m. Delivery of a 10 fs pulse over nearly meter distance is experimentally demonstrated, which sets a new standard for the fiber‐based delivery of few‐cycle pulses. Numerical simulations provide insight into the unique guiding mechanism in the novel hollow‐core fiber technology, enabling dispersion parameters that are within an order of magnitude of those available in free space propagation.     

Wavelength-agile mid-infrared (5-10 microm) generation using a galvano-controlled KTiOPO4 optical parametric oscillator

A wavelength-agile mid-infrared (IR) ZnGeP2 (ZGP) optical parametric oscillator (OPO) using a galvano-controlled double-crystal KTiOPO4 (KTP) OPO was demonstrated. The mid-IR wavelength was tuned by varying the KTP OPO pump wavelength while the ZGP crystal angle remained fixed. Rapid tuning of the KTP OPO was achieved by changing the crystal angle by using the galvano scanner. Our mid-IR source can jump to a different wavelength without scanning through the intermediate wavelengths while also permitting continuous-wavelength scanning. The mid-IR source can be tuned from approximately 5to10 microm at a phase-matching angle of 51 degrees , while the pump wavelength is controlled in the 1.95-2.2 microm range.     

Adjusting the properties of the photon generated via an optical parametric oscillator by using a pulse pumped laser

The cavity-enhanced spontaneous parametric down-conversion far below threshold can be used to generate a narrow-band photon pair efficiently. Previous experiments on the cavity-enhanced spontaneous parametric down-conversion almost always utilize continuous wave pump light, but the pulse pumped case is rarely reported. One disadvantage of the continuous wave case is that the photon pair is produced randomly within the coherence time of the pump, which limits its application in the quantum information realm. However, a pulse pump can help to solve this problem. In this paper, we theoretically analyze pulse pumped cavity-enhanced spontaneous parametric down-conversion in detail and show how the pump pulse affects the multi-photon interference visibility, two-photon waveform, joint spectrum and spectral brightness.     

Direct generation of a 10 GHz 816 fs pulse train from an erbium-fiber soliton laser with asynchronous phase modulation

By employing the technique of asynchronous mode locking, we have successfully demonstrated direct generation of stable 10 GHz 816 fs pulse trains with a supermode-suppression ratio >70 dB from a hybrid mode-locked Er-fiber laser. When the modulation frequency deviates from the cavity harmonic frequency by 15-40 kHz, stable femtosecond soliton pulses are formed. Our results demonstrate that asynchronous mode locking can act as an effective mechanism for achieving a shorter pulse width and for stabilizing high-repetition-rate pulse trains in soliton fiber lasers.