熔锥型光纤声光可变衰减器

利用耦合模理论对光纤熔锥声光器件进行了数值模拟,得到了全光纤声光衰减器传输谱和可调谐性。分析了带宽与声波长、耦合长度的关系。数值分析结果表明,声波在光纤熔锥中引起的轴向电介质微扰、耦合长度和工作波长都会对器件的传输谱产生影响,选择合适的设计参数可以制作较为理想的声光衰减器。实验上获得了损耗小于0．2dB,带宽大于200nm,动态范围为20dB的单模光纤熔锥可变衰减器,所得结果与理论分析相符合。这种器件可用于光纤通信及光纤传感。     

Fiber optical based parametric amplifier in a highly nonlinear fiber (HNLF) by using a ring configuration

A four-wave mixing (FWM) effect in a fiber-based optical parametric amplifier (FOPA) is reported. The novelty in the setup used is a ring cavity as opposed to the commonly used method of linear cavity. This reduces the required pump power, P _p, for the amplification of the signals and also the generation of the idlers. The achieved gain for signal amplification is about 30?dB with a P _p of 25?dBm. It has a flat gain response within range of 22?nm from 1570?nm to 1592?nm, with an average value of 28?dB within the 3?dB region. The average conversion efficiency is approximately ?5?dB, with a peak value of ?4?dB within the 2?dB region, with a range of 24?nm from 1576?nm to 1600?nm.     

All-optical NRZ-to-RZ format conversion at 10 Gbit/s with 1-to-4 wavelength multicasting exploiting cross-phase modulation & four-wave-mixing in single dispersion-flattened highly nonlinear photonic crystal fiber

All-optical NRZ-to-RZ format conversion with a function of wavelength multicasting is proposed in this paper, which is realized by exploiting cross-phase modulation (XPM) and four-wave-mixing (FWM) in a dispersion-flattened highly nonlinear photonic crystal fiber (DF-HNL-PCF). The designed format converter is experimentally demonstrated, for which the 1-to-4 wavelength multicasting is achieved simultaneously by filtering out two FWM idler waves and both blue-chirped and red-chirped components of the broadened NRZ spectrum induced by XPM. Moreover, the wavelength tunability and dynamic characteristics of the proposed NRZ-to-RZ format converter are also exploited using the different central wavelengths of an optical clock signal and varying the input optical power at a DF-HNL-PCF in our experiment. It is shown that the designed format converter can possess a wide range of operational wavelength over 17 nm, an optimal extinction ratio of 11.6 dB, and a Q-factor of 7.1, respectively. Since the proposed scheme uses an optical fiber-based configuration and is easy for implementation, it can be very useful for future applications in advanced fiber-optic communication networks.     

SOA-based multi-wavelength source

A simple fiber laser configuration based on a semiconductor optical amplifier (SOA) is proposed for obtaining multi-wavelength oscillation at room temperature, in which a Sagnac loop mirror is used as the wavelength selective component. The SOA has a flat gain of approximately 23dB within a bandwidth of 12 nm at a small input signal power. The loop mirror was constructed using a 3dB coupler and polarization maintaining fiber (PMF). The output spectrum of the proposed laser can be adjusted by controlling the bias current of the SOA and is quite stable at room temperature. At a bias current of 150 mA, six lines are obtained with at least ?40 dBm output power and 25dB signal-to-noise ratio (SNR). The channel spacing and number of lines is determined by the length of polarization maintaining fiber (PMF) used in the loop mirror. The channel spacing of the proposed laser is 1.49 nm with a PMF 3 m. The multi-wavelength comb output can also be tuned by adjusting the operating temperature of the SOA. The multi-wavelength laser has the advantage of a simple configuration, stability at room temperature, a broad wavelength band, and no need for optical pump lasers.     

外腔激光器实现波长变换的理论及实验

理论上从半导体激光器的速率方程出发,利用其增益饱和效应,提出了光纤光栅外腔半导体激光器实现波长变换的理论模型。利用此模型对入射波为高斯波时的波长变换进行了数值模拟。实验实测了光纤光栅外腔半导体激光器的波长变换前后的谱线,得到带宽 0.1nm,边模抑制比为37.9dB 的激光谱线,并且利用此波长的外腔激光器得到了波长转换间隔为 8nm 的激光谱线。理论分析和实验结果证明,光纤光栅外腔半导体激光器在实现波长变换方面具有很好的线性响应特性。     

Design of cascaded volume holographic gratings to increase the number of channels for an optical demultiplexer

The design and demonstration of a holographic optical demultiplexer based on cascaded volume holographic gratings are presented. By serially adding a second holographic grating, which has a different grating period, slant angle, and center wavelength compared with those of the first grating, the operating wavelength range of the optical demultiplexer could be expanded, and, therefore, the number of channels of the holographic demultiplexer is doubled. As a result of the experiment, a 0.4 nm spaced 130- channel demultiplexer with a channel uniformity of 3.5 dB, a 3 dB bandwidth of 0.12 nm, and channel cross talk of -20 dB is experimentally achieved.     

High efficiency terahertz-wave photonic crystal fiber optical parametric oscillator

We theoretically propose phase matched terahertz (THz)-wave generation via degenerate four-wave mixing (FWM) in a fiber optical parametric oscillator (FOPO) with our newly designed photonic crystal fiber (PCF). Perfect phase matching is realized when we locate the pump wavelength in the normal group-velocity dispersion (GVD) regime. The generated THz-wave can be tuned from 4.7578 to 5.9015?THz by varying the pump wavelength. Moreover, peak power of 27.38?W at 5.9015?THz with conversion efficiency of 1.37% is realized when the pump peak power of 2000?W is at 4.675?μm in our FOPO.     

Concatenation performance of optical packet switches that incorporate wavelength converters based on four-wave mixing in semiconductor optical amplifiers

Four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs) has been acknowledged as a useful wavelength conversion technique especially due to its ability to convert sequences of ultra fast pulses but also simultaneously a number of wavelengths. An analysis is used to investigate the concatenation performance of optical packet switch that incorporate wavelength or waveband converters based on FWM in SOAs.     

Broadband and efficient wavelength conversion in a slot-width switching silicon–organic hybrid waveguide

We propose a slot-width switching (SWS) silicon–organic hybrid waveguide for broadband and efficient wavelength conversion. By switching the slot width of different lengths, the quasi-phase-matching can be obtained. Compared with width-modulated silicon-on-insulator (SOI) waveguide, the non-linear absorption can be ignored in slot waveguide which is filled with p-toluene sulphonate. Consequently, the conversion efficiency at a particular signal wavelength is improved, and the 3-dB conversion bandwidth is also extended. The numerical simulation results indicate that, for a continuous-wave pump at 1550 nm, a conversion bandwidth of 570 nm and a peak conversion efficiency of 11.32 dB can be realized in a 7.5-mm-long SWS waveguide, which is better than that of width-modulated SOI waveguide.     

Optical Characteristics and the Linewidth Enhancement Factor Measured from InAs/GaAs Quantum Dot Laser Diodes

We report the optical characteristics and the linewidth enhancement factor (alpha-factor) of InAs/GaAs quantum dot (QD) laser diodes (LDs) with a 5-mum-wide stripe and 1-mm-long cavity. Continuous wave (CW) operation of the laser yielded a kink-free output power of 160 mW with an external efficiency of 0.35 W/A. The threshold current was 28 mA and the lasing occurred at 1286 nm, solely at the ground state (GS) up to a current of 345 mA, without switching to the excited state (ES). Then, to estimate the alpha-factor of the LDs, we investigated the differential gain and wavelength shift versus the current. The differential gain was 2.37 cm^-1/mA at 1286 nm, and the wavelength shift was 0.00046 nm/mA, which resulted in an alpha-factor of 0.057 at 1286 nm. The alpha-factor decreased with increasing wavelength. To the best of our knowledge, this is the lowest value of the alpha-factor that has been reported so far, indicating that our QD-LD has excellent beam quality under high-power operation due to the elimination of the filamentation.     

Broadband wavelength conversion in hydrogenated amorphous silicon waveguide with silicon nitride layer

Broadband wavelength conversion based on degenerate four-wave mixing is theoretically investigated in a hydrogenated amorphous silicon (a-Si:H) waveguide with silicon nitride inter-cladding layer (a-Si:HN). We have found that enhancement of the non-linear effect of a-Si:H waveguide nitride intermediate layer facilitates broadband wavelength conversion. Conversion bandwidth of 490 nm and conversion efficiency of 11.4 dB were achieved in a numerical simulation of a 4 mm-long a-Si:HN waveguide under 1.55 μm continuous wave pumping. This broadband continuous-wave wavelength converter has potential applications in photonic networks, a type of readily manufactured low-cost highly integrated optical circuits.     

Wavelength-dependent characteristics of modulo Nlambda0 optical wavefront control

A Fourier analysis treatment of the wavelength dependences associated with modulo lambdar optical path control, treating the general case of a modulo lambdar optical path difference function OPD (x, y) mod lambdar in which the reset wavelength lambdar, is allowed to be an integer multiple of a nominal wavelength lambda0, lambdar=Nlambda0, is presented. Equations are derived describing the wavelength-dependent characteristics of the diffraction efficiency and the wavefront errors associated with all diffracted orders. The results are applied to the cases of diffraction of a planar wavefront and compensation of large aberrations and show that over an extended spectral bandwidth the output field consists of multiple diffracted orders with a range of fractional wavefront errors that diminishes with increasing reset multiple N, but does not reach the diffraction limit associated with conventional optics.     

Multisection optical parametric–Raman hybrid amplifier for terabit+ WDM systems

We demonstrate flat-gain wide bandwidth Raman-Fiber optical parametric hybrid amplifier for wavelength division multiplexed systems (WDM). Raman-parametric amplifiers exploit system non-linearities which are otherwise inevitable in evolving WDM systems. Investigations show that the pumps of parametric amplifier and Raman amplifier can be carefully selected at wavelengths, to give gain over complementary bandwidth regions, resulting in wide bandwidth with low gain ripple. Results show a flat gain of 24.3 dB for 12 × 100 Gbps WDM system with lowest ripple of less than 2.78 dB reported over 220 nm bandwidth for Raman-FOPA hybrid.     

Fabrication and characterization of dye mixture doped polymer optical fiber as a broad wavelength optical amplifier

Rhodamine 6G and Rhodamine B dye mixture doped polymer optical fiber amplifier (POFA), which can operate in a broad wavelength region (60 nm), has been successfully fabricated and tested. Tunable operation of the amplifier over a broad wavelength region is achieved by mixing different ratios of the dyes. The dye doped POFA is pumped axially using 532 nm, 10 ns laser pulses from a frequency doubled Q-switched Nd: YAG laser and the signals are taken from an optical parametric oscillator. A maximum gain of 22.3 dB at 617 nm wavelength has been obtained for a 7 cm long dye mixture doped POFA. The effects of pump energy and length of the fiber on the performance of the fiber amplifier are also studied. There exists an optimum length for which the amplifier gain is at a maximum value.     

Wavelength conversion based on FWM in a HNLF by using a tunable dual-wavelength erbium doped fibre laser source

In this paper, we propose and demonstrate a cost-effective wavelength converter utilising a highly nonlinear fibre (HNLF) and a tunable dual-wavelength fibre laser as the pump source. The proposed system uses only the pump source and a signal probe to generate a partially degenerate four-wave mixing (FWM) effect. An FWM conversion efficiency of ?12?dB is obtained at pump and signal powers at +13.3?dBm and +5 dBm, respectively, and it is predicted that a higher conversion efficiency is possible if a high power dual-wavelength fibre laser source is used.     

Generation and optical parametric amplification of picosecond supercontinuum

We have demonstrated the output characteristics of optical parametric amplification (OPA) seeded by a supercontinuum (SC) generated in deionized water excited by 1064 nm. The SC spectrum (from 426 to 943 nm) overlaps well with the tuning range of a 355 nm pumped OPA for both the signal and idler. The tunable range covers from 430 to 2035 nm, with a maximum overall energy conversion efficiency of 32% in the OPA stage. A FWHM bandwidth of 54 nm near the degeneracy point from 658 to 760 nm can be generated by using a collinear OPA. Chirping of the SC pulses is also investigated with the OPA technique. The time delay between the 430 nm component and the 567 nm component of the generated SC due to chirp is measured to be -10.72 ps, increasing almost linearly with the wavelength.     

Dispersion engineering of a silicon-nanocrystal-based slot waveguide for broadband wavelength conversion

A proposal for broadband wavelength conversion using four-wave mixing is presented based on a slot waveguide with silicon nanocrystals (Si-nc's) as the optical nonlinear material. The dispersion of the waveguide is engineered to realize a flat dispersion as well as a small effective mode area for better nonlinear interaction by optimizing the waveguide dimensions. The conversion performance is synthetically analyzed and numerical results show that a bandwidth of over 400?nm and an efficiency of -2.38?dB can be achieved using a pump power of 150?mW in a 4?mm long Si-nc slot waveguide with slot width of 50?nm, slab width of 310?nm, and height of 305?nm.     

宽带铋基掺铒光纤放大器增益及噪声特性研究

利用Er3 离子四能级结构速率方程组和光功率传输方程组,数值模拟了铋基掺铒光纤放大器(EDFA)的增益及噪声特性,模拟结果与实验报道结果取得了很好的一致。同时,详尽地分析了增益及噪声特性与光纤长度、泵浦功率和输入信号功率的关系,优化了放大器的性能,从理论上得出一个20dB增益带宽达76nm、噪声系数接近4dB的铋基EDFA。研究表明了铋基掺铒光纤放大器适合用作于现代DWDM系统中C L波段的光纤放大器。     

Influence of spectral broadening on femtosecond wavelength conversion based on four-wave mixing in silicon waveguides

Femtosecond wavelength conversion in the telecommunication bands via four-wave mixing in a 1.5 mm long silicon rib waveguide is theoretically investigated. Compared with picosecond pulses, the spectra are greatly broadened for the femtosecond pulses due to self-phase modulation and cross-phase modulation in the four-wave mixing process, and it is difficult to achieve a wavelength converter when the pump and signal pulse widths are close to or less than 100 fs in the telecommunication bands because of the spectral overlap. The influence of the spectral broadening on the conversion efficiency is also investigated. The conversion bandwidth of 220 nm and peak conversion efficiency of -8 dB are demonstrated by using 500 fs pulses with higher efficiency than the picosecond pulse-pumped efficiency when the repetition rate is 100 GHz.     

10 Gbit/s tunable dual-wavelength nonreturn-to-zero-to-return-to-zero data-format transformer based on a non-direct-current-biased fabry-perot laser diode

We demonstrate the conversion of a nonreturn-to-zero (NRZ)-formatted electrical data stream into a wavelength-tunable return-to-zero (RZ)-formatted optical pulse code by externally seeding a synchronously sinusoidal-modulated Fabry-Perot laser diode (FPLD) with optical pseudorandom binary-sequence data at 10 Gbits/s (Gbps). The FPLD without a dc-biased current was modulated by use of a power-amplified sinusoidal wave signal (approximately 25.6 dBm) as an NRZ-to-RZ data-format transformer, which is regeneratively amplified by a closed-loop erbium-doped fiber amplifier. The gain switching and on-off keying operation of the FPLD is initiated under the seeding of self-feedback and external-injection signals. A maximum wavelength tuning range of 30 nm with a side-mode suppression ratio of greater than 36 dB is obtained. The power penalty of the NRZ-to-RZ data-format conversion at 10 Gbps is 1.5 dB.