A novel optical device with wide-bandwidth wavelength conversionand an optical sampling experiment at 200 Gbit/s

This paper reports the characteristics of our proposed prototype optical parametric diffuser (OPD). An OPD is based on the theory of four-wave mixing (FWM) in a semiconductor optical amplifier (SOA). However, to improve the conversion bandwidth and FWM efficiency, the gain bandwidth is spread and the gain peak wavelengths are set to a wavelength near the FWM light on the short-wavelength side by combining different MQW active layers. We measured the optical gain characteristics; the fiber-to fiber gain was 16.1 dB and the gain bandwidth over 8 dB was 117 nm when driven at 200 mA dc, and 190 nm when driven by an 800 mA pulse current. In a wavelength-conversion experiment, a high conversion efficiency of ⩾-20 dB was obtained across a detuning wavelength bandwidth of 43 nm. A clear waveform was obtained in an optical sampling experiment to measure 200 Gbit/s optical data sequences     

Minimization of the impact of a broad bandwidth high-gain nonlinear preamplifier to the amplified spontaneous emission pedestal of the Vulcan petawatt laser facility

To generate petawatt pulses using the Vulcan Nd:glass laser requires a broad bandwidth high-gain preamplifier. The preamplifier used is an optical parametric amplifier that provides a total gain of 10(8) in three amplification stages. We report on a detailed investigation of the effect of the Vulcan optical parametric chirped pulse amplification (OPCPA) preamplifier on contrast caused by the amplified spontaneous emission (ASE) pedestal that extends up to 2 ns before the arrival of the main pulse. The contrast after compression is improved to 4x10(8) of the intensity of the main pulse using near-field apertures between the stages of the OPCPA preamplifier. Further reduction of the level of the ASE pedestal can be achieved at the cost of a reduction in amplified bandwidth by solely phosphate glass amplification after initial preamplification rather than a mixed glass amplification scheme.     

Optical add-drop multiplexers based on the antisymmetric waveguide Bragg grating

A novel optical add-drop multiplexer (OADM) based on a null coupler with an antisymmetric grating was designed and experimentally demonstrated. The antisymmetric grating exclusively produces a reflection with mode conversion in a two-mode waveguide. This improves the performance compared with previous demonstrations that used tilted Bragg gratings. Our design minimizes noise and cross talk produced by reflection without mode conversion. In addition, operational bandwidth and, versatility are improved while the compactness and simplicity of the null coupler OADM are maintained.     

Wavelength tuning in optically mode-locked semiconductor fiber ring lasers with linearly chirped fiber Bragg gratings

We demonstrate wavelength tuning in single-wavelength and multiwavelength semiconductor fiber ring lasers that are mode locked with an optically injected control signal. A semiconductor optical amplifier is used to provide gain as well as to function as an optically controlled mode-locking element. Linearly chirped fiber Bragg gratings--single or superimposed--are used to define the lasing wavelengths as well as to provide wavelength tunability and allow for multiwavelength operation. We obtain pulses of tens of picoseconds in duration when we inject a sinusoidal optical control signal into the laser cavity, and we can tune the lasing wavelength(s) over the reflection bandwidth(s) of the grating(s) by simply changing the frequency of the injected control signal.     

Broad-spectrum neodymium-doped laser glasses for high-energy chirped-pulse amplification

We have investigated two novel laser glasses in an effort to generate high-energy, broad-spectrum pulses from a chirped-pulse amplification Nd:glass laser. Both glasses have significantly broader spectra (>38 nm FWHM) than currently available Nd:phosphate and Nd:silicate glasses. We present calculations for small signal pulse amplification to simulate spectral gain narrowing. The technique of spectral shaping using mixed-glass architecture with an optical parametric chirped-pulse amplification front end is evaluated. Our modeling shows that amplified pulses with energies exceeding 10 kJ with sufficient bandwidth to achieve 120 fs pulsewidths are achievable with the use of the new laser glasses. With further development of current technologies, a laser system could be scaled to generate one exawatt in peak power.     

Theoretical performance of Bragg gratings based on long-range surface plasmon-polariton waveguides

A plasmon-polariton Bragg grating (PPBG) concept, based on the propagation of the long-range ss0b mode in structures comprising a thin metal film of finite width embedded in a homogeneous background dielectric, is discussed theoretically. The PPBGs are operated in an end-fire arrangement with access plasmon-polariton waveguides or optical fibers being directly butt-coupled to their input and output ports. A model for the PPBGs, which was recently proposed and validated experimentally for third order structures, is used to generate theoretical results describing their expected performance for various architectures. First order uniform periodic, interleaved, and apodized grating structures are considered and compared. Third order uniform periodic designs are also considered. The gratings investigated are based on a 20 nm thick Au film embedded in SiO2 and have a Bragg wavelength near 1550 nm. First order uniform periodic gratings provide the strongest reflection, with a maximum reflectance of about 97% being achievable over a length of a few millimeters and over a full width at half-maximum bandwidth of about 0.8 nm. The off-resonance insertion loss of the gratings can be as low as a few decibels. Specific Bragg wavelengths can easily be attained using interleaving without requiring extraordinary resolution from the fabrication process. Apodized designs providing low sidelobe levels are also investigated.     

Thermal-structural modeling of polymer Bragg grating waveguides illuminated by a light emitting diode

This study reports both analytical and numerical thermal-structural models of polymer Bragg grating (PBG) waveguides illuminated by a light emitting diode (LED). A polymethyl methacrylate (PMMA) Bragg grating (BG) waveguide is chosen as an analysis vehicle to explore parametric effects of incident optical powers and substrate materials on the thermal-structural behavior of the BG. Analytical models are verified by comparing analytically predicted average excess temperatures, and thermally induced axial strains and stresses with numerical predictions. A parametric study demonstrates that the PMMA substrate induces more adverse effects, such as higher excess temperatures, complex axial temperature profiles, and greater and more complicated thermally induced strains in the BG compared with the Si substrate.     

An ultra-compact tunable Bragg reflector based on edge propagating plasmons in graphene nanoribbon

A mid-infrared planar Bragg reflector, which is based on the fundamental edge plasmonic mode in the nanoribbons is proposed and numerically demonstrated in this paper. The simulation results calculated with the three-dimensional (3D) finite element method reveal that it shows superb wide-band filtering characteristics in the mid-infrared frequencies, and the bandwidth of stopband in the reflector can be dynamically modulated by varying the chemical potentials of corresponding nanoribbon waveguides. In addition, its band properties on the ribbon width are also analyzed. This kind of Bragg reflector exhibits extreme compactness of lateral scales and wonderful light confinement in both the longitudinal and the lateral directions, which is expected to have significant applications in constructing 3D highly integrated optical networks for signal processing.     

Optical gain and stimulated emission in periodic nanopatterned crystalline silicon

Persistent efforts have been made to achieve efficient light emission from silicon in the hope of extending the reach of silicon technology into fully integrated optoelectronic circuits, meeting the needs for high-bandwidth intrachip and interchip connects. Enhanced light emission from silicon is known to be theoretically possible, enabled mostly through quantum-confinement effects. Furthermore, Raman-laser conversion was demonstrated in silicon waveguides. Here we report on optical gain and stimulated emission in uniaxially nanopatterned silicon-on-insulator using a nanopore array as an etching mask. In edge-emission measurements, we observed threshold behaviour, optical gain, longitudinal cavity modes and linewidth narrowing, along with a collimated far-field pattern, all indicative of amplification and stimulated emission. The sub-bandgap 1,278 nm emission peak is attributed to A-centre mediated phononless direct recombination between trapped electrons and free holes. The controlled nanoscale silicon engineering, combined with the low material loss in this sub-bandgap spectral range and the long electron lifetime in such A-type trapping centres, gives rise to the measured optical gain and stimulated emission and provides a new pathway to enhance light emission from silicon.     

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.     

光纤光栅半导体激光器激射波长与Bragg波长的偏离

利用包含光纤布拉格光栅(FBG)反射率分布的光纤光栅外腔半导体激光器(FGSL)的理 论模型,对FGSL 的激射波长进行了研究。结果表明激射波长并不一定在FBG布拉格反射波长处;布拉格反射波长相对于激射波长的偏移量与FBG的反射率分布、半导体增益介质的增益谱分布及增益峰值波长有关;激射波长可大于或小于布拉格反射波长。     

Light Propagation in Singly and Doubly Periodic Planar Waveguides

Abstract

Light propagation in singly and doubly periodic planar waveguides is investigated with respect to future applications in integrated optics. The waveguides used in our experiments reveal, in the vicinity of Bragg reflection, a strong difference between the directions of phase and group velocities, the beam steering. A clear graphical representation of the observable propagation effects is given in wave-vector diagrams, showing the directional dispersion of the elementary waves in periodic structures, the Floquet-Bloch waves. The dispersion phenomena were measured with high accuracy, using selective wave excitation. In conjunction with straight tapered transitions to smooth planar waveguides, the periodic structures show a great variety of strong frequency and direction-dependent effects such as lateral beam shifting and focusing with a frequency-variant focal length. Ray optics of Floquet-Bloch waves is used to describe these phenomena. Complex interference patterns observable in the vicinity of Bragg reflection in doubly periodic structures are explained by the superposition of Floquet-Bloch waves. Examples of applications of planar periodic structures as highly selective frequency filters, optical multiplexers as well as frequency-tunable beam narrowing, focusing and expanding devices are given together with measured data.     

Optical parametric properties of ultraviolet-pumped cesium lithium borate crystals

We report the optical parametric properties of cesium lithium borate (CLBO) crystals pumped by UV radiation of the fourth-harmonic generation at 266 nm and the third-harmonic generation at 355 nm of a picosecond Nd:YAG laser. A special optical design was used to avoid damage to the optical elements by the UV-pumped beam at 266 nm. The optical parametric generator (OPG)/optical parametric amplifier (OPA) of the 266-nm-pumped CLBO covers the tuning range from 347 nm in the UV to 1137 nm in the near IR. The 355-nm-pumped CLBO OPG/OPA, on the other hand, is tunable from 447 to 1725 nm. The experimental tuning curves for each CLBO OPG/OPA were measured and compared with the theoretical tuning curves. With a double-pass OPG configuration and a pumping intensity of approximately 6 GW/cm2, the maximum conversion efficiency, including both the signal and the idler, was approximately 11% for the 266-nm-pumped CLBO and is greater than 16% for the 355-nm-pumped CLBO without taking into account the surface losses from the uncoated elements. The bandwidth of this double-pass CLBO OPG at various wavelengths was measured and compared with other optical parametric systems. Because of the small angular dispersion of CLBO, the bandwidth of the OPG and OPA systems is exceptionally narrow, especially for the 266-nm-pumped system. Without the use of any dispersion element, the bandwidth of the 266-nm-pumped system can be as narrow as 0.22 nm at wavelengths far from the degenerate point. Comparison between the experimental bandwidth and the theoretical calculation shows that the bandwidth of the UV-pumped CLBO OPG/OPA is limited mainly by the divergence of the pump beam.     

Seeded optical parametric generator with efficiency-enhanced mid-wave infrared beam output

A novel device with a simple architecture for high-power mid-wave infrared beam generation is proposed and analyzed using a realistic model that takes the diffraction of the beams into account. The device is a seeded efficiency-enhanced optical parametric generator based on an aperiodically poled MgO-doped LiNbO₃ grating in which two optical parametric amplification (OPA) processes are simultaneously phase matched. When pumped by a high-repetition-rate nanosecond-pulsed laser operating at 1064 nm, power conversion efficiency enhancement of the mid-wave infrared output at a wavelength of 3.8 μm (compared to what is achievable with a single OPA process) occurs. Also, a difference-frequency beam is generated. Multiple aperiodic gratings with varying relative strengths of the two optical parametric amplification processes are designed. The developed model is used for determining the optimum relative strengths of the two processes and input pump power levels for achieving the maximum mid-wave infrared conversion efficiency and output power for various crystal lengths.     

Seeded femtosecond optical parametric amplification in the mid-infrared spectral region above 3 mum

Femtosecond optical parametric amplification that results in microjoule mid-infrared pulses at wavelengths exceeding 3 mum is demonstrated. Narrow-band quasi-cw seeding at the signal wavelength is applied to ensure the generation of nearly transform-limited femtosecond pulses at the idler wavelength. The broad bandwidth of the parametric amplification provided by pumping with femtosecond pulses from a Ti:sapphire regenerative amplifier at high intensity results in idler pulse durations shorter than the pump pulse length. The potentials of three nonlinear optical crystals that belong to the potassium titanyl phosphate family are comparatively studied. At 1-kHz repetition rate our all-solid-state system produces highly synchronized ~100-fs pulses in the spectral range between 3 and 4 mum.     

Optical parametric chirped-pulse amplifier as an alternative to Ti:sapphire regenerative amplifiers

We demonstrated a high-pulse energy, femtosecond-pulse source based on optical parametric chirped-pulse amplification. We successfully amplified 1-microm broadband oscillator pulses to 31 mJ and recompressed them to 310-fs pulse duration, at a 10-Hz repetition rate. The gain in our system is 6 x 10(7), achieved by the single passing of only 40 mm of gain material pumped by a commercial Q-switched Nd:YAG laser. This relatively simple system replaces a more complex Ti:sapphire regenerative-amplifier-based chirped-pulse amplification system. Numerous features in design and performance of optical parametric chirped-pulse amplifiers make them a preferred alternative to regenerative amplifiers based on Ti:sapphire in the front end of high-peak-power lasers.     

Studies of magnetooptic effects for thin-film optical-waveguide applications

A computer study of mode conversion in thin-film optical waveguides using magnetooptic GdIG as a substrate is reported. The efficiency of the mode-converting structure is analyzed and compared to other structures in order to gain design insight. It is shown that 100-percent mode conversion (TErightleftarrowTM) is possible if both modes satisfy the phase condition required of mode propagation.     

Wavelength-tunable semiconductor pump diode for reconfigurable Raman amplification

We demonstrate a wavelength-tunable semiconductor pump diode for Raman amplification. Thediode is stabilized by a fiber Bragg grating (FBG) that can be continuously tuned over more than 20 nm. Tuning of the diode output wavelength is achieved by varying the center wavelength of the FBG, since the diode preferentially lases within the FBG bandwidth. We investigate the effects of wavelength tuning on the diode spectrum on its corresponding Raman gain, and on pump-pump four-wave mixing in fiber having zero-dispersion wavelength coincident with the Raman pumps.     

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。     

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.