Amplitude and frequency modulation characteristics of widelytunable GCSR lasers

The amplitude (AM) and frequency (FM) modulation responses of a grating assisted codirectional coupler with rear sampled grating reflector laser were measured over a 40-nm tuning range. The extracted modulation bandwidth varied between 3 and 4 GHz and parameters as parasitic cutoff, maximum relaxation frequency and K-factor were extracted from curve fittings to the AM response. The frequency modulation measurements revealed low chirp despite the large tunability of the device. The linewidth enhancement factor was calculated from the AM and FM measurements. The values ranges from three to nine for ten different operating wavelengths     

Measurement of a VPE-transported DFB laser with blue-shiftedfrequency modulation response from DC to 2 GHz

The frequency modulation characteristics of a VPE-transported 1.53 μm wavelength GaInAsP-InP DFB semiconductor diode laser was measured. Below approximately 0.7 mW optical output power per facet, it exhibited a smooth, blue-shifted, frequency modulation response from DC to 2 GHz. In the modulation frequency range of 10 MHz to 100 MHz it exhibited a |Δf/ΔI| of 0.5-1.8 GHz/mA, depending on the biasing level     

Characterization of the modulation and noise properties of athree-electrode DFB laser

The modulation and noise properties of a three-electrode DFB laser have been measured. At proper biasing, the frequency modulation response could be chosen to be in phase or 180° out of phase with respect to the intensity modulation by selecting the modulated electrode. Applying a first order equalization/filter, a flat frequency modulation response was measured up to 5 GHz. A 20-dB broadband suppression of the intensity modulation was accomplished when modulating two sections in push-pull. The spectral densities of the FM and intermodulation noise were measured showing remarkably flat intermodulation and FM noise spectra     

Pure frequency modulation or intensity modulation with suppressed frequency chirp using active Bragg reflector integrated laser

The modulation properties of a laser structure which consists of an active Bragg reflector (300 mu m) integrated with an uncorrugated gain region (600 mu m) have been measured. The laser exhibited a flat FM response and very low spurious intensity modulation when modulating the current in the Bragg reflector. Furthermore, broadband intensity modulation with suppressed frequency chirp could also be achieved. An inhomogeneous linewidth enhancement factor alpha caused by the uneven carrier density distribution between the two sections gives a qualitative explanation to our results.<>     

Relative intensity noise and linewidth measurements of a widelytunable GCSR laser

The intensity and frequency noise of a grating assisted codirectional coupler with rear sampled grating reflector laser with 40-nm tuning range and 35-dB sidemode suppression ratio (SMSR) have been measured. The linewidth varies from 430 kHz to 4 MHz as a function of tuning. The resonance frequency, intrinsic bandwidth and damping factor for this device were extracted from the relative intensity noise (RIN) measurements. At high bias, the RIN is -150 dB/Hz and the maximum resonance frequency is 4.5 GHz     

Semiconductor laser amplifier optimization: an analytical andexperimental study

Long-wavelength semiconductor laser amplifiers are investigated with respect to spectral gain properties such as peak gain wavelength shift and width of gain curve, employing different structural parameters such as thickness of the active layer and amplifier length. The model takes into account Auger recombination, thermal effects, and spontaneous emission. It is shown that there exists an optimum thickness of the active layer with respect to current density for a given gain and that increased length of the amplifier allows higher gains and reduced variation of peak gain wavelength with respect to variation of peak gain at the expense of increased saturation by amplified spontaneous emission and increased excess noise. An experimental verification of the theoretical model is reported     

Measurements and theory of correlation between terminal electricnoise and optical noise in a two-section semiconductor laser

The correlation between the terminal voltage noise and the intensity and frequency noise is characterized experimentally and theoretically for a two-section distributed Bragg reflector (DBR) laser. An all-electric feedback scheme for noise reduction is proposed and analyzed theoretically     

Optical properties of deep ice at the South Pole: absorption

We discuss recent measurements of the wavelength-dependent absorption coefficients in deep South Pole ice. The method uses transit-time distributions of pulses from a variable-frequency laser sent between emitters and receivers embedded in the ice. At depths of 800-1000 m scattering is dominated by residual air bubbles, whereas absorption occurs both in ice itself and in insoluble impurities. The absorption coefficient increases approximately exponentially with wavelength in the measured interval 410-610 nm. At the shortest wavelength our value is approximately a factor 20 below previous values obtained for laboratory ice and lake ice; with increasing wavelength the discrepancy with previous measurements decreases. At ~415 to ~500 nm the experimental uncertainties are small enough for us to resolve an extrinsic contribution to absorption in ice: submicrometer dust particles contribute by an amount that increases with depth and corresponds well with the expected increase seen near the Last Glacial Maximum in Vostok and Dome C ice cores. The laser pulse method allows remote mapping of gross structure in dust concentration as a function of depth in glacial ice.     

A Michelson interferometer with balanced detection for thecharacterization of modulation and noise properties of semiconductorlasers

A Michelson interferometer with balanced detection, built to study semiconductor lasers, is analyzed. The quantum noise due to vacuum fluctuations, coupling losses, detector quantum efficiency, and spatial mode mismatches are included in the analysis. The limits for frequency noise detection and the sensitivity of the interferometer are examined. It is observed that under ordinary measurement conditions the frequency noise can only be measured up to slightly above the cavity bandwidth of the laser. Comprehensive measurement procedures are proposed, and experimental results showing the frequency modulation response, measured from 10 kHz to 8 GHz, of a three-section distributed feedback (DFB) laser and the frequency noise spectra, measured from 30 MHz to 8 GHz, of a two-section distributed Bragg reflector (DBR) laser are presented. These results reveal new cavity detuning effects in the noise characteristics of tunable DBR lasers     

Spontaneous emission factor in post microcavity lasers

The first measurements of the spontaneous emission coupling efficiency (/spl beta/) for electrically pumped microcavity lasers with transverse photon confinement are reported. The influence of scattering losses and carrier diffusion on microcavity lasers is investigated, A /spl beta/ of 0.01 is measured at 126 K in a 3-/spl mu/m diameter device with optimal gain-cavity detuning.