Pump Light Source Research Articles

Self-controlled all-optical label and payload separator for variable length bursts in a time-serial IM/DPSK scheme

We demonstrate an all-optical label and payload separator based on nonlinear polarization rotation in a semiconductor optical amplifier. The proposed scheme uses a variable packet length composed of a label and payload information signal modulated intensity modulation and differential phase-shift keying (DPSK) format, respectively. The separation is obtained by using the payload signal itself, exploiting the DPSK feature of being power constant, as a pumping light source. Therefore, the proposed scheme is asynchronous and does not need an external control signal.

Light-shift suppression in laser optically pumped vapour-cell atomic frequency standards

We present a novel scheme for reducing the AC Stark effect in optical-microwave double-resonance spectroscopy and its application for efficient suppression of the light-shift-related instabilities in laser-pumped gas-cell atomic clocks. The method uses a multi-frequency pump light field that can be easily produced by frequency modulation of the single-frequency pump laser. We show theoretically that variations of the light shift with both laser frequency and light intensity can be strongly suppressed with properly chosen pump light spectra. Suitable modulation parameters can be found for both the case of pure frequency modulation as well as for pump light spectra showing amplitude-modulation contributions, as usually found for current modulation of diode lasers. We experimentally demonstrate the method for a Rb atomic clock using a frequency-modulated distributed Bragg-reflector laser diode as pump light source.

Agile and highly efficient wavelength conversion using highly nonlinear fiber for optical code-labeled packets

Wavelength conversion enhances transparency, interoperability, and efficient wavelength resource utilization in wavelength-division-multiplexing networks. Several devices are used for wavelength conversion, such as the electroabsorption modulator, semiconductor optical amplifier, periodically poled lithium niobate modulator, and highly nonlinear fiber (HNLF). HNLF is promising because it offers high conversion efficiency and phase-preservation between the input and output signals; it also provides immunity from pattern effects. Furthermore, a combination of HNLF and a distributed-feedback laser diode (DFB-LD) array used as a pump light source enables agile wavelength conversion for photonic packet switch networks. In this letter, we discuss our demonstration of agile and highly efficient wavelength conversion of optical code-labeled packets by using HNLF and an eight-DFB-LD array module. We obtained a switching time of less than 1 ns, and the wavelength stability of the LD pump was within 0.04 nm.

High-speed optical FSK modulator for optical packet labeling

We described a novel optical label swapping (OLS) technique for optical packet systems using frequency-shift-keying (FSK) optical labeling. High-speed optical FSK signal can be generated by using an external FSK modulator consisting of four optical phase modulators. The FSK modulator was based on optical single-sideband (SSB) modulation technique, and comprised of traveling-wave electrodes for high-speed frequency switching. We demonstrate 10 Gbps FSK transmission, and simultaneous modulation by FSK and intensity modulation (IM). OLS using double-sideband modulation was also demonstrated, where this technique can be used for a bundled wavelength-domain-multiplexing (WDM) channels without using an array of pumping light sources.

III-N based short-wavelength LEDs, LUCO-LEDs, and lasers

Results are presented on the effect of using GaN templates with homogeneously reduced defect density on the performance of violet- und UV-emitting (AlGaIn)N LEDs, as well as on the use of such LED chips as pump light sources in three-phosphor white luminescence conversion LEDs (LUCO-LEDs). For LED chips emitting at 385 nm, an improvement in electroluminescence efficiency by a factor of two was found for growth on 8 x 10 7 cm -2 defect density templates compared to direct growth on sapphire. Further we report on the fabrication and on-wafer testing of violet-emitting ridge waveguide (AlGaIn)N quantum well diode lasers with etched laser facets, grown on sapphire using conventional low-temperature GaN nucleation layer technology as well as on the above low defect density GaN templates. In on-wafer pulsed-mode operation a 35% reduction in threshold current density was achieved for the latter, resulting in a minimum injected power at threshold of 0.9 W for 500 μm x 2 μm ridge laser diodes with uncoated facets.

Trace gas monitor based on difference frequency generation at 4�?m using mass-production laser diodes as pump and signal light sources

New pump and signal laser sources for difference frequency generation (DFG) at 4 μm are described. A laser diode with a 980 nm fiber Bragg grating and a 785 nm Fabry-Perot (FP) laser diode were coupled into an optical fiber and mixed in a periodically poled Mg-doped lithium niobate (PPMgLN ) crystal, resulting in efficient mid-IR DFG. The DFG power was measured to be 0.23 μW for a pump power of 5 mW and a signal power of 50 mW with a slope efficiency of 0.92 mW/W2. A Doppler-broadened absorption spectrum of N2O at 2485.2 cm-1 (3.927 μm) was observed in a 0.1 m-long gas cell at a pressure of 133 Pa. The spectral linewidth of the DFG source was estimated to be 161 MHz (FWHM) for an averaging time of 700 ms. Real-time monitoring of N2O in a multipass cell with an optical path length of 36 m at a concentration level of 1 ppm was demonstrated.

The effect of injection seeding on terahertz parametric oscillation

AbstractWe report on the use of injection seeding to narrow the terahertz‐wave linewidths of terahertz parametric light sources [a terahertz parametric generator (TPG) and a terahertz parametric oscillator (TPO)] using a LiNbO3 crystal and a Nd:YAG laser (wavelength 1.06 µm) as a pump light source. In this technique, the light of a Yb:fiber laser (wavelength 1.07 µm) operating in CW mode is injected into the LiNbO3 crystal, which brings about the narrowing of the terahertz‐wave spectral line. Our experiments confirm that injection seeding into the TPG not only narrows the terahertz‐wave spectral line but also greatly improves the input‐output characteristics. When we injection‐seeded a TPO pumped by light from a Nd:YAG laser with a single‐longitudinal‐mode spectrum, we obtained a 200‐MHz spectral line width, which approaches the Fourier‐transform limit. That is, our spectral linewidth was limited by the resolution of the measurement system. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 86(1): 26–35, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.1115

Pulse broadening in a Ne–CuBr–Zn laser system by optical resonance pumping

A Zn atom is employed as the light source for optical resonance pumping to a high lying energy level of the Cu atom, thereby depopulating both the Cu lower laser level and enhancing the upper laser level via cascading decays that is carried out simultaneously. The width of the lasing pulse broadened by 220% and the peak value increased by 180%. The cascading decay route was clarified by observing the fluorescence lines, λ=675.1, 793.5, and 809.0 nm, thereby specifying five levels of excitation loop.

Collisional coalescence of photoexcited midgap states in anMXchain compound

The pumping-power dependence of the time decay of the long-lived photoinduced midgap absorption has been studied in an MX chain compound $[{\mathrm{Pt}(\mathrm{en})}_{2}]{[\mathrm{Pt}(\mathrm{en})}_{2}{\mathrm{Cl}}_{2}{](\mathrm{B}\mathrm{F}}_{4}{)}_{4},(\mathrm{en})$ being ethylenediamine. The 476.5 nm light of a cw Ar-ion laser is used as the pumping light source. In addition to an extremely nonexponential time decay, the life time of the midgap band is found to vary as ${K}_{0}^{\ensuremath{-}2}$ with the absorption intensity ${K}_{0}$ induced by the laser pumping. This decay behavior is explained well in terms of the Torney-McConnell survival-probability function, $S(\ensuremath{\zeta}{)=e}^{8\ensuremath{\zeta}}\mathrm{erfc}\sqrt{8\ensuremath{\zeta}}$ with $\ensuremath{\zeta}{=A}_{0}^{2}Dt,$ peculiar to the geminate coalescence of unequilibrated states in one dimension, where ${A}_{0},$ D, and t are the initial density of the unequilibrated states, diffusion coefficient, and time, respectively. The observed midgap states are confirmed from this finding to collapse through diffusion-limited mutual collisions in locally disordered PtCl chains. Our previous data on temperature and sample dependencies are reviewed within the framework of this collisional geminate coalescence model.

In-line optical phase-sensitive amplifier with pump light source controlled by optical phase-lock loop

This paper describes an in-line optical phase-sensitive amplifier (PSA) with a pump laser whose optical phase is locked to that of a randomly modulated signal by using an optical phase-lock loop (OPLL). The OPLL is designed with the capability of optical phase locking at an arbitrary relative phase. Experimental evaluation is presented of the OPLL employing a newly developed external cavity semiconductor ring laser with a spectrum linewidth of less than 20 kHz. Employing this pump laser with the OPLL in conjunction with a 4.4-km long nonlinear fiber Sagnac interferometer (NFSI) yields optical phase-sensitive gain of up to 11 dB. A randomly modulated signal is successfully amplified and confirmed offering a clear eye-opening.

1.65 µm band fibre Raman amplifier pumpedby wavelength-tunableamplified spontaneous emission light source

A high-gain (33 dB) and wideband (over 40 nm) 1.65 µm fibre Raman amplifier is realised using a novel pump light source. The light source emits intense amplified spontaneous emission light with a tunable wavelength (1540–1563 nm) and broad linewidth.

Broadband lossless DCF using Raman amplificationpumped by multichannel WDM laser diodes

Broadband Raman amplification is demonstrated in a dispersion compensating fibre (DCF). A polarisation combined four channel wavelength division multiplexing 14 xxnm laser diode unit is used for the pumping light source. Losses in the DCF are completely compensated for by means of the Raman gain over 50 nm bandwidth within /spl plusmn/0.5 dB variation.

A Tunable 1.6 μm Band Optical Time-domain Reflectometer

A tunable 1.6 μm band optical time-domain reflectometer (OTDR) is reported which uses a tunable Raman fiber laser (RFL). The RFL optical peak power of 7 W at 1652 nm was obtained by using a tunable Q-switched Er 3+ -doped fiber ring laser (QERL) as a pump light source, and a Raman fiber with a small mode field diameter. By using this RFL, an OTDR dynamic range over 22.5 dB was achieved in the wavelength region from 1650 nm to 1680 nm with a spatial resolution of 100 m.

Reliable 1.01-μm band laser diode pumped praseodymium-doped In/Ga-based fluoride fiber amplifiers at 1.3 μm

A practical 1.3 /spl mu/m optical fiber amplifier with reliable 1.01-/spl mu/m band laser diode pump light sources and an efficient praseodymium-doped In/Ga-based fluoride fiber is presented. A praseodymium-doped In/Ga-based fluoride fiber is characterized using measurable parameters, and amplified characteristics are theoretically analyzed. Signal output power of +16.2 dBm (42 mW) is achieved for an amplifier pumped by four 1.01-/spl mu/m band laser diodes. By using the amplifier as a power booster, data of 2.5 Gb/s is successfully transmitted more than 100 km.

In-line phase-sensitive amplifierwith optical-PLL-controlled internal pump light source

Randomly modulated signal pulses from an independent source are successfully amplified by a phase-sensitive amplifier with an internal pump light source whose optical phase is locked to that of the injected signal using an optical phase-locked loop.

Polarization Insensitive Wavelength Conversions by a LiNbO3 Waveguide Using a Multi-Ring Configuration

A novel configuration is proposed for polarization insensitive wavelength conversions using a LiNbO3 waveguide with a periodically domain inverted structure. The proposed configuration consists of multiple rings, which are connected by a polarization sensitive wavelength converter such as the LiNbO3 waveguide described. One ring containing a pump light source is used to pump the wavelength converter bidirectionally, while the other rings containing a polarization beam splitter and a 90° polarization rotator are used to couple in the input signal and extract the converted light. The proposed method is proven experimentally by the wavelength conversion based on sum frequency generation.

Optical phase-sensitive amplificationusing two phase-locked light sources

Optical phase-sensitive amplification using individual pump and signal light sources is presented for the first time. In the experiment, optical phase of pump and signal light is locked by an optical phase-locked loop (OPLL). Stable optical phase-locking is achieved and optical phase-sensitive amplification with a gain of 12 dB is successfully demonstrated using a nonlinear Sagnac interferometer.

Characterization of a confocal microscope for time-resolved photon counting fluorescence

A confocal microscope setup is developed for time-resolved fluorescence measurements. It is added to a traditional cuvette time-resolved setup, with a pumped Ti-Sa light source. The temporal resolution of 37 ps (FWHM) is not degraded, in comparison with the cuvette setup also described. These setups allow both decay lifetime and anisotropy relaxation time determination. Fluorescence correlation spectroscopy (FCS) is used to determine the observation point size. When associated with the calcium probe calcium green, calcium concentration in single cells can be determined in 10 ms by simultaneous acquisition of early and late fluorescence photons.

Pulsed alkali pump light sources for Nd:YAG lasers

Pulsed arc discharges in alkali metal vapours are investigated for use as pump light sources for Nd:YAG lasers. Alkali lamps have a very high radiation efficiency and emit strong lines near the laser pump bands. These absorption bands are fitted by the emission spectrum of sodium and potassium lamps by changing the vapour pressure and input power. The spectral radiation distributions of the lamps are measured by a spectrograph with a gated OMA system. Ray tracing calculations for a laser cavity are used to evaluate the efficiency of the alkali radiation emission for Nd:YAG pumping. The results show that the excitation efficiency of the alkali lamps is twice as high as that of usually used rare gas lamps. For sodium resonance lines the side-on spectral radiance is calculated by a radiation transport model to estimate the pressure and the temperature profile. The results indicate that the alkali vapour lamps could be used as pump light sources with high efficiencies and low heat loading of the laser cavity.

Coherence effects in a photorefractive ring oscillator

We discuss here the unidirectional photorefractive ring oscillator taking into account the finite coherence time of the pumping light source. We exactly solve wave mixing equations and demonstrate how the loss of coherence due to propagation in an external cavity affects the performance of the oscillator.