High-repetitive frequency millimeter-wave signal generation using multi-cascaded external modulators based on carrier suppression technique

We have numerically and experimentally investigated how to generate high-repetitive frequency millimeter (mm)-wave using multi-cascaded intensity modulators based on optical carrier suppression (OCS) scheme. We have found the rule how to generate the high-repetitive frequency mm-wave by adjusting the repetitive frequency of the radio-frequency (RF) signals and the phase relation between the RF signals on the intensity modulators. Based on this rule, we have experimentally demonstrated to generate over 80 GHz optical mm-wave.     

Optical mm-wave generation by using external modulator based on optical carrier suppression

In this paper, we have theoretically investigated the transmission performance of the optical millimeter (mm)-wave generated by using an external modulator based on optical carrier suppression for the first time. According to our theory, the data signals carried by the optical mm-wave are transmitted in the dispersion fiber without fading but are degraded greatly because of the time shift of the code edges, which still limits the transmission distance. The experimental results agree well with our theory.     

Carrier generation and IF signal up-conversion using optical injection locking and stimulated Brillouin scattering

We theoretically investigate the intermediate frequency (IF) signal up-conversion with dual modes modulation (DMM) and single-mode modulation (SMM) of two single sideband (SSB) modulation modes for radio-over-fiber (RoF) systems. The simulation results indicate that the SMM can overcome the dispersion-induced power penalties of the generated carrier and up-converted IF signals. Then, we experimentally demonstrate an approach for RF carrier generation with SSB modulation and IF signal up-conversion with SMM using a combination of direct modulation in an injection-locked distributed feedback (DFB) laser and stimulated Brillouin scattering (SBS). The experimental results are compared with the predictions of the numerical simulation in SMM condition, and both are in good agreement with each other. The advantages and limits of the proposed method are discussed.     

Harmonic signal generation and frequency upconversion using selective sideband Brillouin amplification in single-mode fiber

Harmonic signal generation and frequency upconversion at millimeter-wave bands are experimentally demonstrated by using selective sideband Brillouin amplification induced by stimulated Brillouin scattering in a single-mode fiber. The harmonic signals and frequency upconverted signals are simultaneously generated by the beating of optical sidebands, one of which is Brillouin amplified. By using this method, we successfully demonstrate generation of third-harmonic millimeter waves at 32.55 GHz with f(LO) of 10.85 GHz and upconversion of 10 Mbps quadrature-shift keyed data at f(IF) of 1.55 GHz into a 30 GHz band with more than 17 dB RF power gain.     

晶体级联方式的宽带三倍频方案分析

 讨论了入射基频光频谱宽度、两块和频晶体失谐角对KDP晶体Ⅰ/Ⅱ/Ⅱ类角度失谐级联方式的三倍频光功率谱分布的影响,分析了影响三倍频效率的因素。研究结果表明,第二块和频晶体得到的三倍频光的功率谱分布与基频光功率谱分布及失谐角有关,三倍频光频谱宽度近似为基频光的3倍,采用该方案的三倍频可有效抑制由于基频光时间相位调制导致的三倍频光强随时间分布的不均匀,并能有效提高大带宽条件下的三倍频转换效率。同时,采用该方案的三倍频,对级联的两块和频晶体厚度及失谐角调整精度要求不高,在实验上有很大的可操作性。     

晶体级联方式宽带三倍频方案的参数优化

 针对时间位相调制的宽带激光,采用分步离散傅里叶变换及四阶龙格－库塔算法进行数值模拟计算。讨论了采用KDP晶体级联方式时,入射基频光的光强、带宽以及晶体厚度对三倍频转换效率的影响。对采用一块РⅠ类二倍频晶体、一块Ⅱ类和一块Ⅰ类双混频晶体的级联宽带三倍频方式进行了晶体参数的优化。研究结果表明,使用两块级联的KDP晶体作为混频晶体,不仅能有效地提高带宽较宽条件下三倍频光的转换效率,还可以显著增大宽带三倍频的动态范围。经优化后,带宽1.11 nm时入射基频光强在3～8 GW/cm²范围内的三倍频转换效率可保持在60％～70％,比采用单倍频单混频方案时增大了30％～40％。     

Intra-cavity second-harmonic and sum-frequency generation in a diode-pumped broadband Yb-doped fibre laser

Intra-cavity nonlinear frequency mixing in a diode-pumped, broadband Yb-doped fibre laser has been investigated. Second-harmonic generation of the fibre output, second-harmonic generation of the residual pump beam and sum frequency mixing between the two was achieved simultaneously, resulting in three colour operation in the blue-green region. Including the nonlinear crystal inside the cavity is also shown to be effective in reducing fluctuations in the output power.     

RF arbitrary waveform generation using tunable planar lightwave circuits

We demonstrate photonically-assisted generation of RF arbitrary waveforms using planar lightwave circuits (PLCs) fabricated on silica-on-silicon. We exploit thermo-optic effects in silica in order to tune the response of the PLC and hence reconfigure the generated waveform. We demonstrate the generation of pulse trains at 40 GHz and 80 GHz with flat-top, Gaussian, and apodized profiles. These results demonstrate the potential for RF arbitrary waveform generation using chip-scale photonic solutions.     

Numerical study on the efficient generation of 351 nm broadband pulses by frequency mixing of broadband and narrowband Nd: glass lasers

Efficient frequency-tripling of phase-modulated broadband Nd:glass laser pulses is of interest to inertial confinement fusion. We report and theoretically study an efficient frequency-tripling scheme for 351 nm broadband pulses generation by use of broadband and narrowband Nd:glass lasers. Based on the conventional two-crystal doubling and tripling baseline configuration, employing an additional narrowband laser can increase the bandwidth acceptance of Nd:glass up to 320 GHz, which is 3.5 times larger than that of using the conventional configuration. The proposed scheme may also dramatically reduce the conversion of amplitude modulation from the frequency modulation. The efficiency sensitivities on both the fundamental intensity and the doubler orientation are discussed for practical applications.     

Femtosecond pulse generation using stimulated Raman scattering in integrated silicon optical waveguide device

To generate ultrafast femtosecond optical pulses, we propose a model of an integrated device consisting of a Mach-Zehnder interferometer (MZI) with two symmetric 3 dB directional couplers and a straight waveguide based on the single-mode silicon-on-insulator (SOI) optical waveguide. The principle of pulse generation in the presented device is based on the strong stimulated Raman scattering (SRS) in silicon; the center wavelength of the pulse generated is tunable by changing the center wavelength of the co-propagating pump pulse. Numerical results show that, when a continuous wave (CW) with a weak power at 1670 nm wavelength and a pump pulse with a high peak power at 1550 nm wavelength are co-propagating, a narrow femtosecond pulse with a pulse width (full width at half maximum, FWHM) of ∼60 fs (FWHM of the pump pulse is 166.5 fs) can be achieved in the device proposed. In addition, when the waveguide length, pump peak power, and pump-pulse width are fixed, the properties of generated femtosecond pulse depend strongly on the incident chirp of the pump pulse and the CW power.     

Optical millimeter-wave generation and transmission system for 1.25 Gbit/s downstream link using a gain switched laser

In this paper, we propose a novel and cost effective system for optical millimeter-wave (mm-wave) generation and transmission of downstream data based on a gain switched laser (GSL). The GSL produces an optical comb spectrum that can be appropriately filtered to generate two optical sidebands spaced by more than 4 times the repetition rate of the GSL. These sidebands are modulated by baseband data and then transmitted via optical fiber to the remote antenna unit (RAU). At the RAU, the two sidebands are heterodyned using a photodetector to generate the electrical modulated mm-wave signal, before demodulation using self mixing. We demonstrate the distribution of 1.25 Gbit/s data OOK modulated onto a 60 GHz carrier, similar to that used in the IEEE 802.15.3c draft standard, over fiber lengths up to 62 km.     

On the carrier generation and HD signal transmission using the millimeter-wave radio over fiber system

The dual sideband optical carrier suppression (DSB-OCS) technique is employed in the optical carrier generation for 40 GHz radio over fiber (ROF) system. A dual electrode Mach-Zehnder modulator (DE-MZM) with the minimum transmission bias (MiTB) technique is employed to build the system. The results show that, a 40 GHz carrier is successfully generated with the amplitude up to −29 dBm and signal to noise ratio (SNR) of 35 dB and a high definition (HD) signal is successfully transmitted using the system. Finally, the bit error rate (BER) measurement is carried out for the system with 1.25 Gbps OOK signal showing an error free 40 GHz ROF system with almost no penalty between the back to back and 20 km fiber for a BER of 10⁻⁹.     

Low distortion, continuously tunable, positive and negative time delays by slow and fast light using stimulated Brillouin scattering

We demonstrate a single optical timing module that can provide both tunable delay and advancement with low distortion using a reconfigurable gain medium based on stimulated Brillouin scattering. Dual-stage intensity modulation method is used to achieve optimized gain profiles for both slow- and fast-light operation. Using 6.5 ns Gaussian pulses, we demonstrate a continuous temporal adjustment from a fractional advancement of 0.31 to a fractional delay of 0.82, giving more than a full pulse width of total tunability.     

Efficient multi-frequency generation of ultrashort light pulses using stimulated Raman scattering and optical parametric amplification

Optical parametric amplification of multi-frequency seed pulses generated in a mixture of compressed hydrogen and methane by stimulated Raman scattering of 1 ps, 1 kHz laser pulses at 395.8 nm has been studied. Efficient generation of spectrally narrow ultrashort pulses with a spatial distribution close to the Gaussian profile of the pump beam was obtained in the visible and near infrared ranges.     

High carrier suppression double sideband modulation using polarization state rotation filter and optical external modulator

We propose a high carrier suppression double sideband modulation technique using a Mach-Zehnder modulator (MZM) and an integrated polarization state rotation filter (PSRF), which is designed to improve the carrier suppression ratio. With the functions of MZM and PSRF, about 30 dB carrier suppression ratio relative to first-order sidebands is demonstrated. Moreover, we demonstrate the optical generation of microwave/millimeter-wave signals by beating the carrier suppressed double sideband (DSB-SC) lightwave signals. The experimental results show that the improvement of carrier suppression ratio with PSRF can effectively cancel the modulating RF frequency component. A tunable and high purity microwave signal, which is limited by the bandwidth of MZM and photodetector (PD), is obtained, and it does not suffer from obvious phase noise degradation with 25 km transmission.