Nonlinear frequency conversion in bismuth-doped tellurite suspended core fiber

We have developed a new kind of tellurite glass with composition 70.5TeO₂–12ZnO–10Na₂O–7.5Bi₂O₃ by conventional melting–quenching techniques. A suspended-core fiber (SCF) with a triangular-shaped core (~ 2.9 μm) has been drawn from an extruded perform. Several nonlinear frequency conversion processes are being demonstrated, which point to the potential of such a fiber.     

Laser diode pumped bismuth-doped optical fiber amplifier for 1430 nm band

A 24 dB gain bismuth-doped fiber amplifier at 1430 nm pumped by a 65 mW commercial laser diode at 1310 nm is reported for the first time (to our knowledge). A 3 dB bandwidth of about 40 nm, a noise figure of 6 dB, and a power conversion efficiency of about 60% are demonstrated. The temperature behavior of the gain spectrum is examined.     

Furnace chemical vapor deposition bismuth-doped silica-core holey fiber

A bismuth-doped-pure-silica holey fiber is fabricated using a fiber preform made by the furnace chemical vapor deposition method. The spectroscopic properties of the fiber are studied, and laser action at λ=1450 nm with an efficiency of 12% is demonstrated.     

Raman-assisted parametric frequency conversion in a normally dispersive single-mode fiber

We demonstrate efficient frequency conversion with large frequency shifts of an anti-Stokes signal into a parametrically seeded Stokes idler, which is generated by a highly mismatched three-wave mixing interaction and subsequent Raman amplification in a normally dispersive single-mode fiber. The use of non-phase-matched waves in Raman-assisted three-wave mixing interactions overcomes the strict spectral limitations imposed by phase-matching conditions in parametric frequency-conversion processes.     

Amplification of picosecond pulses and gigahertz signals in bismuth-doped fiber amplifiers

We demonstrate the capability for amplification of picosecond pulses in two bismuth-doped alumosilicate fibers. A spectrally filtered supercontinuum source is used to provide a train of picosecond pulses at discrete wavelengths within the gain bandwidth of bismuth fiber amplifiers. With a 30 m length of active fiber, a small signal gain at 1160 nm of over 20 dB is observed. In addition, we assess the viability of amplification of high repetition rate signals in such amplifiers, applying a 10 GHz modulation to a continuous wave Raman fiber laser operating at 1178 nm, finding that such signals are amplified without noticeable distortion.     

Picosecond pulse shaping in a semiconductor-coated D-shaped fiber

Amorphous films of alpha-SiC:H and alpha-Si:H were deposited upon the flat surfaces of D-shaped fibers. Interaction of light with the semiconductor films occurred through evanescent coupling. Pulse shaping on a picosecond time scale was observed in 3.5-cm-long fibers with optical powers of <10 W, enhancing the effective nonlinearity by a factor of 10(3) .     

Efficient Raman frequency conversion of high‐power fiber lasers in diamond

We report high‐power frequency conversion of a Yb‐doped fiber laser using a double‐pass pumped external‐cavity diamond Raman oscillator. Pumping with circular polarization is shown to be efficient while facilitating high‐power optical isolation between the pump and Raman laser. We achieved continuous‐wave average power of 154 W with a conversion efficiency of 50.5% limited by backward‐amplified light in the fiber laser. In order to prove further scalability, we achieved a maximum steady‐state Raman‐shifted output of 381 W with 61% conversion efficiency and excellent beam quality using 10 ms pump pulses, approximately a thousand times longer than the transient thermal time‐constant. No power saturation or degradation in beam quality is observed. The results challenge the present understanding of heat deposition in Raman crystals and foreshadow prospects for reduced thermal effects in diamond than originally anticipated. We also report the first experimental evidence for stimulated Brillouin scattering in diamond.

     

Picosecond pulse amplification in a core-pumped large-mode-area erbium fiber

Amplification in a single-clad, large-mode-area erbium fiber as an alternative to double-clad Er-Yb amplifiers is presented. Both signal and pump are coupled through a mode-matched splice into the fundamental mode, which ensures preferential gain in the fundamental mode while minimizing the amplified spontaneous emission (ASE). The 875 microm(2) effective area of the Er fiber enables amplification of 6 ps pulses at 1.55 microm wavelength by approximately 33 dB in a single stage to >25 kW peak power with low nonlinear pulse distortion and a diffraction-limited output beam with M(2)<1.1.     

Picosecond flat-top pulse generation using dual-mode fiber Mach-Zehnder interferometers

We report on an optical fiber Mach-Zehnder interferometer made by offset splicing a dual-mode fiber with two single-mode fibers. The extinction ratio can be tuned from less than 1 dB to greater than 28 dB by rotating the dual-mode fiber along its axial direction. The interferometer is utilized as a pulse shaper to convert a 2.5 ps Gaussian pulse to a 5.2 ps flat-top pulse.     

Photonic quasicrystals for nonlinear optical frequency conversion

We present a general method for the design of 2-dimensional nonlinear photonic quasicrystals that can be utilized for the simultaneous phase matching of arbitrary optical frequency-conversion processes. The proposed scheme--based on the generalized dual-grid method that is used for constructing tiling models of quasicrystals--gives complete design flexibility, removing any constraints imposed by previous approaches. As an example we demonstrate the design of a color fan--a nonlinear photonic quasicrystal whose input is a single wave at frequency omega and whose output consists of the second, third, and fourth harmonics of omega, each in a different spatial direction.     

Picosecond ultrasonics time resolved spectroscopy using a photonic crystal fiber

We present a broadband picosecond ultrasonics time resolved spectroscopy. Detection of picosecond coherent acoustic phonons using a wavelength continuum generation in a photonic crystal fiber (PCF) with femtosecond laser pulses is developed. Measurements are performed for selected wavelengths of a broad wavelength probe pulse within a bandwidth of 250 nm with an 825 nm center wavelength on two samples made of tungsten and of gallium arsenide.     

Intermodal interference induced significant frequency modulation to amplitude modulation conversion in a broadband large-mode-area fiber laser

The conversion of the FM-to-AM effect induced by intermodal interference in the broadband large-mode-area (LMA) fiber laser was first investigated theoretically and experimentally. The numerical simulation results show that the spectrum transfer functions are different at different positions of the LMA fiber end face owing to the intermodal interference, so the output broadband pulses are different. We attain the similar results in the experiment when measuring the output pulse with the single mode fiber sampling oscilloscope. Whereas there is no amplitude modulation for the output pulse when measured by the bulk detector owing to the orthogonal characteristic of the eigenmodes.     

Multiplex frequency conversion of femtosecond laser pulses in trefoil and quatrefoil channels of a holey fiber

We report that trefoil and quatrefoil silica channels with sizes ranging from 0.6 μm to as large as 4–5 μm in a holey fiber can strongly confine the light field and act as highly nonlinear waveguides. Supercontinuum emissions, efficient dispersive-wave generation and parametric four-wave-mixing processes were achieved in these channels with sub-nanojoule femtosecond Ti:sapphire laser pulses. Two dispersion curves corresponding to two orthogonal modes in each channel were simulated and used to explain the experimental results. PACS 42.81.Gs; 42.81.Qb     

Efficient microwave-induced optical frequency conversion

Frequency conversion process is studied in a medium of atoms with a configuration of levels, where transition between two lower states is driven by a microwave field. In this system, conversion efficiency can be very high by virtue of the effect of electromagnetically induced transparency (EIT). Depending on intensity of the microwave field, two regimes of EIT are realized: “dark-state” EIT for the weak field, and Autler-Townes-type EIT for the strong one. We study both cases via analytical and numerical solution and find optimum conditions for the conversion. Received 13 December 1999 and Received in final form 6 March 2000     

Adiabatic processes in frequency conversion

Adiabatic evolution, an important dynamical process in a variety of classical and quantum systems providing a robust way of steering a system into a desired state 1 - 5 , was introduced only recently to frequency conversion 6 - 9 . Adiabatic frequency conversion allowed the achievement of efficient scalable broadband frequency conversion 8 , 9 and was applied successfully to the conversion of ultrashort pulses, demonstrating near‐100% efficiency for ultrabroadband spectrum 10 - 16 . The underlying analogy between undepleted pump nonlinear processes and coherently excited quantum systems was extended in the past few years to multi‐level quantum systems, demonstrating new concepts in frequency conversion, such as complete frequency conversion through an absorption band 17 - 20 . Additionally, the undepleted pump restriction was removed, enabling the exploration of adiabatic processes in the fully nonlinear dynamics regime of nonlinear optics 21 - 26 . In this article, the basic concept of adiabatic frequency conversion is introduced, and recent advances in ultrashort physics, multi‐process systems, and the fully nonlinear dynamics regime are reviewed.     

Erbium doped fiber ring laser for optical wavelength conversion

We experimentally investigate the gain saturation effect of a piece of 8 m long Erbium doped fiber (EDF), we introduce a theoretical model for the EDF ring loop, and our simulation results show very good cross-gain modulation (XGM) and wavelength conversion. We also experimentally investigate the XGM in an EDF ring loop system. Based on the study of the XGM in the EDF ring loop system, a wavelength conversion is designed with the EDF ring loop system. The EDF ring loop systems as a wavelength conversion is experimentally demonstrated by converting a sinusoidal modulated optical signal at wavelength of 1551 nm to an optical signal at wavelength of 1553.3 nm.