Dispersion flattened photonic crystal fiber with high nonlinearity for supercontinuum generation at 1.55 μm

A robust design for a photonic crystal fiber (PCF) based on pure silica with small normal dispersion and high nonlinear coefficient for its dual concentric core structure is presented.This design is suitable for flat broadband supercontinuum (SC) generation in the 1.55-μm region.The numerical results show that the nonlinear coefficient of the proposed eight-ring PCF is 33.8 W -1 ·km -1 at 1550 nm.Ultraflat dispersion with a value between -1.65 and -0.335 ps/(nm·km) is obtained ranging from 1375 to 1625 nm.The 3-dB bandwidth of the SC is 125 nm (1496–1621 nm),with a fiber length of 80 m and a corresponding input peak power of 43.8 W.The amplitude noise is considered to be related to SC generation.For practical fabrication,the influence of the random imperfections of airhole diameters on dispersion and nonlinearity is discussed to verify the robustness of our design.     

Compensation-free, all-fiber-optic, two-photon endomicroscopy at 1.55 μm

We present an all-fiber-optic scanning multiphoton endomicroscope with 1.55 μm excitation without the need for prechirping femtosecond pulses before the endomicroscope. The system consists of a 1.55 μm femtosecond fiber laser, a customized double-clad fiber for light delivery and fluorescence collection, and a piezoelectric scan head. We demonstrate two-photon imaging of cultured cells and mouse tissue, both labeled with indocyanine green. Free-space multiphoton imaging with near-IR emission has previously shown benefits in reduced background fluorescence and lower attenuation for the fluorescence emission. For fiber-optic multiphoton imaging there is the additional advantage of using the soliton effect at the telecommunication wavelengths (1.3-1.6 μm) in fibers, permitting dispersion-compensation-free, small-footprint systems. We expect these advantages will help transition multiphoton endomicroscopy to the clinic.     

Geometrical dependence of optical negative index meta-materials at 1.55 μm

We have studied the geometry dependency of fishnet-like negative refractive index meta-materials (NIMs), and developed a process to fabricate such NIMs using nanoimprint lithography (NIL) in a controlled way for it to achieve negative refractive index in the desired frequency range. As an example, we fabricated a fishnet structure with a minimum negative refractive index of −1.7 at 1560 nm, which was only 10 nm off the targeted wavelength of 1550 nm.     

Long range surface plasmon polariton waveguides at 1.31 and 1.55 μm wavelengths

We investigate characteristics of gold metal strip waveguides based on long range surface plasmon polaritons (LRSPPs) along thin metal strips embedded in a polymer for practical applications at the telecommunication wavelengths of 1.31 and 1.55 μm. Guiding properties of the gold strip waveguides are theoretically and experimentally evaluated with the limited thickness and width up to ∼20 nm and ∼10 μm, respectively. The lowest propagation loss of ∼1.4 dB/cm is obtained with a 14.5-nm-thick and 2-μm-wide gold strip at 1.55 μm. With a single-mode fiber, the lowest coupling loss of ∼0.4 dB/facet is achieved with a 14.5-nm-thick and 5-μm-wide gold strip at 1.55 μm. The lowest insertion losses are obtained 8-9 dB with 1.5 cm-long gold strips of a limited thickness and width at both the wavelengths. We demonstrate a 10 Gbps optical signal transmission via the LRSPP waveguide with a 14 nm-thick, 2.5 μm-wide, and 4 cm-long gold strip. These LRSPP waveguides have potential applications for optical interconnects and communications.     

A 168-km ultra-long-range OTDR measurement at a wavelength of 1.55 μm

A Rayleigh backscattered signal and Fresnel reflection over a 167.6-km and a 251.2-km long pure silica-core fiber (PSF) with fiber loss 0.176 dB/km, and a 138.6-km and a 206.5-km long Ge-doped core dispersion shifted fiber (DSF) with fiber loss 0.218 dB/km have been observed with ultra-long-range optical time domain reflectometry (OTDR) using a 1.55-μm high-power semiconductor laser (LD) and InGaAs-APD with a low dark current at room temperature. The Rayleigh backscattered signal level and fiber loss are strongly dependent on the fiber dopant materials and fiber structural parameters. DSF gives a better SNR for short length fibers because the Rayleigh backscattered signal level is larger than PSF, but because the DSF loss is also larger, PSF gives a better SNR for fibers longer than the critical length. Accordingly, the dynamic range of OTDR in the different fiber types such as PSF and DSF becomes different. One-way backscattered dynamic ranges of 29.5 dB for the PSF and about 30.2 dB for the DSF at room temperature have been achieved.     

Highly birefringent photonic crystal fiber with low confinement loss at wavelength 1.55 μm

High birefringent and low confinement loss of photonic crystal fiber is reported at wavelength 1.55 μm via Full-Vectorial Finite Element Method (FV-FEM). By suitable designing of three ring hexagonal solid core fiber and also by introducing a pair of large holes along x-axis near the core region, high modal birefringence 3 × 10⁻³ and low confinement loss 0.019 dB/km are found at wavelength 1.55 μm.     

Generation of a squeezed state at 1.55 μm with periodically poled LiNbO3

We report on the generation of a squeezing vacuum at 1.55 μm using an optical parametric amplifier based on periodically poled LiNbO 3.Using three specifically designed narrow linewidth mode cleaners as the spatial mode and noise filter of the laser at 1.55 μm and 775 nm,the squeezed vacuum of up to 3.0 dB below the shot noise level at 1.55 μm is experimentally obtained.This system is compatible with standard telecommunication optical fibers,and will be useful for continuous variable long-distance quantum communication and distributed quantum computing.     

Single-mode transmitting modules for fiber-optics lines operating at wavelengths 1.3 and 1.55 μm

Optoelectronic sources for the 1.3- and 1.55-m bands have been developed on the basis of InGaAsP/InP heterostructures in the form of modules that include a Peltier microcooler, a temperature sensor, and a photodiode monitor. The properties of single-mode sources are presented and the technique of is discribed of coupling them to single-mode fibers using a taper and a microlens lightguide pigtail. Data on the influence of parasitic and some results on high-frequency modulation and information transmission are given.Optoelectronics Laboratory, Lebedev Physics Institute. Translated from Preprint No. 137 of the Lebedev Physics Institute, Academy of Sciences of the USSR, Moscow, 1989.     

Performance of In0.47Ga0.53As metal-semiconductor-metal hybrid receiver at 1.55 μm

We report on the performance at 1.55 m of a hybrid receiver combining an In_0.47Ga_0.53As metal-semiconductor-metal photodetector (with buried AllnAs buffer layer) with a GaAs MESFET preamplifier. A bit error rate of 10^-9 is measured at 1 Gbps with nonreturn to zero pseudorandom bit sequence (2¹⁵–1) at a received optical power of –19 dBm. Modification of the preamplifier design and a reduction of bond pad size could improve the sensitivity by 6–7 dB.     

Highly coherent terahertz wave generation with a dual-frequency Brillouin fiber laser and a 1.55 μm photomixer

Thanks to a portable dual-frequency Brillouin fiber laser and a 1.55 μm photomixer, we report the generation of a highly coherent kilohertz level submillimeter wave emission. Low-cost telecommunications components are used to achieve very simple source architecture. The photomixer is composed of a unitravelling carrier photodiode integrated with an antenna. An emission at 316 GHz is observed and analyzed thanks to heterodyne detection with a signal-to-noise ratio >65 dB and a ~1 kHz linewidth. The phase noise of the proposed source has the same performance at 1.7 and 316 GHz. We show that this source has comparable or better phase noise compared to electrical oscillators and the tunability is much wider.     

Efficient laser emissions at 1.06 μm of swift heavy ion irradiated Nd:YCOB waveguides

We report on the fabrication of Nd:YCOB (Nd:YCa(4)O(BO(3))(3)) optical waveguides by using 170 MeVAr(8+) ion irradiation at an ultralow fluence of 2×10(12) ions/cm(2). The confocal microphotoluminescence investigation on the produced waveguides has shown the well-preserved fluorescence features within the guiding layer with respect to the bulks. Under the optical pump at wavelength of 810 nm, continuous wave waveguide lasers at 1061.2 nm have been generated at room temperature with a high slope efficiency of ~67.9%.     

Efficient intracavity second-harmonic generation at 1.06 μm in a BiB3O6 (BIBO) crystal

We report, for the first time, efficient intracavity second-harmonic generation (SHG) at 1.06 μm in a non-linear optical crystal, BiB₃O₆ (BIBO), at a type-I phase-matching direction of (θ,ϕ)=(168.9°,90°), performed with a LD end-pumped cw Nd:YVO₄ laser. A cw SHG output power of 364 mW has been obtained using a 1.9-mm-thick BIBO crystal. The optical conversion efficiency was 12.2% and the corresponding effective intracavity SHG efficiency was determined to be 32.4%. It was found that the intracavity SHG efficiency is greater than that obtained with a type-II phase-matching KTiOPO₄ (KTP) crystal with a thickness of 3 mm. The effective non-linear optical coefficient (d_eff) ratio of BIBO to that of KTP, determined experimentally, is 1.23:1. Received: 7 May 2001 / Revised version: 6 July 2001 / Published online: 19 September 2001     

High power 4.65 μm single-wavelength laser by second-harmonic generation of pulsed TEA CO2 laser in AgGaSe2 and ZnGeP2

A high power 4.65 ??m single-wavelength laser by second-harmonic generation (SHG) of TEA CO₂ laser pulses in silver gallium selenide (AgGaSe₂) and zinc germanium phosphide (ZnGeP₂) crystals is reported. Experimental results show that the average output power of SHG laser is not only restricted by the damage threshold of the nonlinear crystals, but also limited by the irradiated power of fundamental-wave laser depending on the operating repetition-rate. It is found that ZnGeP₂ can withstand higher 9.3 ??m laser irradiation intensity than AgGaSe₂. As a result, using a parallel array stacked by seven ZnGeP₂ crystals, an average power of 20.3 W 4.65 ??m laser is obtained at 250 Hz. To the best of our knowledge, it is the highest output power for SHG of CO₂ laser by far.     

Supercontinuum generation at 1.55μm using highly nonlinear photonic crystal fiber for telecommunication and medical applications

In this paper, we present a theoretical calculation of a highly nonlinear germanium (Ge) doped photonic crystal fiber with all-normal group velocity dispersion to design a supercontinuum (SC) light source at 1.55 μm. By doping 3% higher refractive index Ge inside the host silica, the nonlinear coefficient is increased to a value as large as 60.5 W^?1 km^?1 at 1.55 μm. A 10 dB bandwidth of a 120 nm SC spectrum for a 2.5 ps input optical pulse and a 10 dB bandwidth of a 190 nm SC spectrum for a 1.0 ps input optical pulse have been found using the same fiber length of 200m and input optical power of 18 W. The coherent lengths of the generated SC light sources are found to be 8.8 μm for a 2.5 ps input optical pulse and 5.6 μm for a 1.0 ps input optical pulse. Therefore, the highest longitudinal resolution at 1.55 μm is found to be about 4.0 μm for biological tissues.     

Polarization entanglement generation at 1.5 μm based on walk-off effect due to fiber birefringence

In this Letter, a linear scheme to generate polarization entanglement at 1.5 μm based on commercial polarization maintained dispersion shifted fiber (PM-DSF) is proposed. The birefringent walk-off effect of the pulsed pump light in the PM-DSF provides an effective way to suppress the vector scattering processes of spontaneous four-wave mixing. A 90 deg offset of fiber polarization axes is introduced at the midpoint of the fiber to realize the quantum superposition of the two correlated photon states generated by the two scalar processes on different fiber polarization axes, leading to polarization entanglement generation. Experiments of the indistinguishable property on single-side and two-photon interference in two nonorthogonal polarization bases are demonstrated. A two-photon interference fringe visibility of 89±3% is achieved without subtracting the background counts, demonstrating its great potential in developing highly a efficient and stable fiber based polarization-entangled quantum light source at the optical communication band.     

Optical parametric generation in CdSiP2 at 6.125 μm pumped by 8 ns long pulses at 1064 nm

A 21.4 mm long noncritically cut CdSiP2 crystal, pumped by 8 ns pulses at 1064 nm in a double-pass configuration for pump, signal, and idler, generated 523 μJ, 5.8 ns idler pulses at 6.125 μm. The average power of 52.3 mW at the repetition rate of 100 Hz is the highest ever achieved at such wavelengths with direct down conversion from the 1 μm spectral range.     

A novel coupled quantum well structure with large field-induced refractive index change and low absorption loss at 1.55 μm

In future networks, very-high-speed and high-capacity di-rect optical switching systems will play a very importantrole, and an optical switching device is considered to be akey device for the construction of such high-speed opticalswitching systems or photonic integrated circuits[1]. Soit is imperative for optical switching device to search fora material with high-speed and large field-induced re-fractive index change in the case of low absorption loss.It is well known that a large electric fi…     

Intersubband transitions in InxAl（l-x）N/InyGa（l-y）N quantum well operating at 1.55 μm

In this paper, we theoretically study the effects of doping concentration ND and an external electric field on the intersubband transitions in InxAl（l-x）N/InyGa（l-y）N single quantum well by solving the Schrodinger and Poisson equations self-consistently. Obtained results including transition energies, the band structure, and the optical absorption have been discussed. The lowest three intersubband transitions （E2 -El）, （E3 -El）, and （E3 -E2） are calculated as functions of doping concentration ND. By increasing the doping concentration ND, the depletion effect can be reduced, and the ionized electrons will compensate the internal electric field which results from the spontaneous polarization. Our results show that an optimum concentration ND exists for which the transition 0.8 eV （1.55 μm） is carried out. Finally, the dependence of the optical absorption α13（ω） on the external electric field and doping concentration is studied. The maximum of the optical absorption can be red-shifted or blue-shifted through varying the doping concentration and the external electric field. The obtained results can be used for designing optical fiber telecommunications operating at 1.55 μm.