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Electrical tuning and mode locking of an external-cavity semiconductor laser with an ultrashort (0.4 mm) fiber-Bragg-grating (FBG) reflector are studied theoretically and experimentally. Evolution of electrical tuning of longitudinal modes in a laser with broad-bandwidth FBG is analyzed theoretically. Tuning over an 11.4-nm range was experimentally possible by mechanically changing the connectorized FBG reflector in the external cavity of a diode laser package. With a 40%-reflection FBG, the external cavity laser was mode locked and generated at < 50-ps optical pulses at (6.3 plusmn 0.3) GHz within a broad frequency range of 600 MHz. The authors have simulated the intensity-modulation response of this laser and have shown that the broad frequency range mode locking of these lasers is determined by a chirp-related resonance rather than an external cavity resonance. The theoretical analysis agrees with the experimental results

The effect of intraband carrier relaxation on the threshold characteristics of InGaAsP quantum well (QW) lasers is studied. The dependence of the intraband hole-hole relaxation time τ int on temperature and carrier density is analyzed. It is shown that taking into account the finiteness of τ int and its dependence on temperature and carrier density strongly affects the gain and the threshold current density of QW lasers.

Broad-band absorption bleaching in erbium-doped fiber by in-band narrow-linewidth pumping is reported. For the first time, spectra of absorption bleaching of erbium-doped fiber is measured and the refractive index changes inferred through the Kramers–Kronig relations in this true two-level system in order to understand its operation in the external cavity of a laser.

A new method is proposed for transverse mode selection in high-power, broad-waveguide, separate-confinement, heterostructure quantum-well lasers by orienting the front mirror at an angle other than normal to the direction of radiation propagation. The dependence of the mode reflection coefficients on the laser mirror parameters is investigated. Optimal values are found for the mirror inclination angles and the thicknesses and refractive indices of the dielectric coating at which the fundamental guide mode dominates. The possibility of a 1.2-fold increase in the output power of a broad-waveguide, separate-confinement, heterostructure quantum-well diode laser is demonstrated.

We use the direct temporal domain approach to design spectrally periodic optical filters for pulse repetition rate multiplication (PRRM) with envelope shaping. In particular, we demonstrate a tunable lattice-form Mach-Zehnder interferometer using Silica-based planar lightwave circuit (PLC) for arbitrary 4-bit binary amplitude code generation at 40 GHz and to increase the repetition rate of a 10 GHz input pulse train to 20 GHz or 40 GHz. In addition to PRRM and envelope shaping, the device also has the capability of arbitrary phase coding.

We study the feasibility of a radio-over-fiber (ROF) link with external modulation and an unamplified photodetector; we show high-quality (EVM -38 dB, RF power -1 dBm) 64-QAM- OFDM transmission when optimizing the photodiode impedance matching and the modulator bias point.

Modeling of a hybrid semiconductor external-cavity laser with an intra-cavity saturable absorber is presented. In this paper the simulations are based on a modified transmission line laser model for an external fiber grating laser. The designed model of a DFECL takes into account time-domain evolution of the dynamic grating due to the standing wave in the external cavity and high-power bleaching of the doped-fiber absorption. In contrast to the previous models of such a hybrid laser, here the properties of the dynamic grating strongly depend on the internal power inside the cavity, which causes the absorption bleaching. Modeling results of lasers at 980 nm and 1490 nm are presented.

We report on the first experiments of optical microwave generation by heterodyne beating of two doped-fiber semiconductor external-cavity lasers (DFECL). Our measurements show that minor side-mode beating in DFECL affect the optical heterodyne beat signal. Using the RF methods we study the side-mode suppression in the DFECL.

A numerical transmission line model for semiconductor lasers with long external fibre cavities and fibre grating reflectors is reported. The model is applied to high-power 980 nm lasers and shows good agreement with experiments in the coherence collapse regime (CCR). The numerical approach has been used to model the saturable absorber in the external cavity of the semiconductor laser with the external fibre grating in the "coherence enhanced regime" (CER). Our simulations show for the first time how line-narrowing evolves in CER lasers.

The effect of carrier-carrier relaxation and carrier-phonon relaxation on threshold characteristics of quantum well (QW) lasers is studied. Carrier relaxation time considerably depends on temperature, carrier density, and quantum well width. It is shown that in this case the gain coefficient becomes a more pronounced function of temperature and carrier density.

The effect of carrier-carrier relaxation on threshold and power-current characteristics of InAs and GaAs quantum well (QW) lasers is studied. Dependence of carrier relaxation time on temperature and carrier density is considered. It is shown that in this case the gain coefficient becomes a more pronounced function of temperature and carrier density, and threshold current density increases drastically.

We demonstrate a tunable pulse repetition rate multiplier using a silica-based planar lightwave circuit (PLC). The PLC is a six-stage lattice-form Mach-Zehnder interferometer which can be tuned thermally to generate 20- and 40-GHz output pulse trains from a 10-GHz input. We use a nonlinear optical loop mirror as a wavelength converter to perform intensity-to-field conversion to eliminate pulse-to-pulse phase fluctuations in the higher-rate output pulse trains. Moreover, we use wavelength multicasting (simultaneous wavelength conversion) to generate multiple pulse trains (4 × 20 GHz and 4 × 40 GHz in the example shown here) from a single 10-GHz input.

A new method of additional transverse mode selection in high- power broad-waveguide separate confinement heterostructure quantum-well lasers by means of facet inclination is proposed. Theoretical investigation of mode selection and numerical calculations for GaAs-AlGaAs BW-SCH-QW laser with inclined facet with wavelength 860 nm and wide range of waveguide width has been carried out. The possibility of reducing power density on the mirror keeping single-mode generation and thus increasing fundamental mode output power 1.2 times is shown.

We present an experimental study of tuning characteristics and wavelength stability of a 1490 nm doped fiber external cavity laser. The standing wave in the erbium-doped fiber in an external-cavity laser causes spatial hole burning and absorption modulation and forms a dynamic grating. The dynamic grating can effectively suppress side modes and eliminate wavelength fluctuations in the laser. The operating wavelength of this hybrid laser is shown for the first time to our knowledge to be smoothly tunable by changing the semiconductor laser drive current or temperature.

The ultimate spectrum-narrowing and side-mode suppression due to the presence of a saturable absorber in an external cavity of a fiber Bragg grating semiconductor laser is numerically simulated. The proposed algorithm describes an effect of absorption bleaching in a saturable absorber using earlier measurements and shows the evolution of a dynamic grating in the laser cavity. The simulations confirm for the first time an empirical theory of spectral line narrowing in a laser with an intra-cavity saturable absorber.

We report on the spectral analysis of the first 1490 nm external cavity laser with an intra-cavity erbium-doped fiber. Self-mode beating and heterodyne beating methods are employed to measure the side mode suppression ratios and to study the effect of the rare-earth doped fiber on the spectrum of the external-cavity laser. Experimental and simulated results show a substantial decrease in the number of the external-cavity modes and a side-mode suppression ratio of >15 dB.

The authors report on the performance of a 1.55 /spl mu/m single frequency semiconductor external fibre grating laser with high temperature stability. The laser shows low static and dynamic chirp when directly modulated at rates up to 10 Gbit/s.

We demonstrate the generation of 20 GHz and 40 GHz pulse trains using a tunable planar lightwave circuit (PLC) and nonlinear wavelength conversion. The PLC is a 6-stage lattice-form Mach-Zehnder interferometer fabricated in silica-on-silicon technology.