Rudolf F. Kazarinov

Longitudinal mode self‐stabilization in semiconductor lasers

A general mechanism of self‐stabilization of longitudinal modes in semiconductor lasers is presented. The stabilization is due to the modulation of the inverted population by the beating of the fields of lasing and nonlasing modes, thereby modulating the rate of stimulated emission. This leads to two optical nonlinearities: one causing gain suppression of nonlasing modes and the other causing coupling of pairs of nonlasing modes that are equally separated from the laser line. The two nonlinearities nearly cancel, but their net effect is a weak suppression of the nonlasing modes and stabilization of the lasing mode. Buried optical guide lasers were stabilized in a single longitudinal mode for currents greater than 6mA above threshold. The mode intensity spectra of the lasers were measured over 5 decades and converted to gain spectra, which could be compared with the theory. The gain spectrum is parabolic at threshold. At 20 mA above threshold it remains continuous at the laser line but narrows and becomes ...

Analysis of gain in determining T/sub 0/ in 1.3 /spl mu/m semiconductor lasers

Rapid decrease of differential gain has been determined to dominate the temperature dependence of threshold current in 1.3-/spl mu/m multiquantum well and bulk active lasers giving rise to low values of T/sub 0/. Extensive experimental characterization of each type of device is described. Results are presented for the dependence of gain on chemical potential and carrier density as a function of temperature. The data indicate the important role of the temperature-insensitive, carrier density dependent chemical potential in determining differential gain. Modeling of the temperature dependence of threshold carrier density in MQW and bulk active lasers based on a detailed band theory calculation is described. The calculated value of T/sub 0/ depends on the structure of the active layer, e.g., multiquantum well versus bulk. However, the calculated values are substantially higher than measured. >

Polarization-independent silica-on-silicon Mach-Zehnder interferometers

The birefringence induced by compressive strain in silica waveguides on silicon substrates is compensated with a silicon nitride patch placed below the core. We demonstrate Mach-Zehnder interferometers with polarization-independent spectral response, including a compensated Mach-Zehnder interferometer suitable for stabilization of multiple laser sources in a dense wavelength division multiplexed fiber optic communication network. Furthermore, we show how silicon nitride can also be used to compensate polarization dependent losses. Polarization independence achieved with a silicon nitride patch is applicable to a wide variety of other devices such as arrayed waveguide grating multiplexers and Bragg reflectors. >

Direct measurement of the carrier leakage out of the active region in InGaAsP/InP laser heterostructures

Leakage of electrons out of the active region of InGaAsP/InP laser heterostructures at different temperatures was measured by a purely electrical method. Comparison of the obtained results with the results of modeling indicates that special attention should be paid to the acceptor doping levels in the p cladding layer immediately adjacent the active region. Lower acceptor concentration may lead to unacceptably high thermionic leakage. >

Wavelength chirp and dependence of carrier temperature on current in MQW InGaAsP-InP lasers

In this paper, we derive a relation between the wavelength chirp and carrier temperature in semiconductor lasers. The coefficient relating the change in carrier temperature and chirp is expressed in terms of the temperature derivative of the optical gain, and two parameters describing the variation of refractive index produced by the variation of optical gain due to change of carrier quasi-Fermi level separation or carrier temperature. We have measured these parameters for MQW InGaAsP lasers, Using this data, we estimated the rate of the temperature increase with current above threshold in these devices, which is 0.13 K/mA.

Role of p-doping profile in InGaAsP multiquantum well lasers: comparison of simulation and experiment

We study the role of p-doping on the characteristics of InGaAsP/InP multi-quantum well lasers through detailed simulations and experiments. The static and dynamic characteristics of a series of 1.3 μm lasers with varying p-i junction placement were measured. The device characteristics were simulated including carrier transport, capture of carriers into the quantum wells, quantum mechanical calculation of the levels and optical gain in the wells and solution for the optical mode. The simulations were self consistent and carried out as a function of device bias. The simulations account for the trends observed with p-doping profile. In particular, the simulated optical gain and small signal resonance frequencies agree well with the measurements. The trend of larger resonance frequency with increased p-doping in the active layer of the laser depends on both the gain and the carrier transport through the multi-quantum well region.

Modeling of gain for InGaAsP-based lasers

Experimental and theoretical results for gain in bulk and multiquantum well active layer 1.3 micrometers InGaAsP based lasers are reported. Gain, loss, transparency energy, and carrier density have been measured in the subthreshold regime at room temperature and elevated temperatures. Gain has been calculated using an eight band k(DOT)p model for the electronic structure and a conventional density matrix formulation. The calculated and experimental results for the gain spectra, the gain versus density, the chemical potential (quasifermi level separation) versus density, and the gain versus chemical potential are compared at room temperature and 85 C. There is aagreement at several points, but the model substantially underestimates the temperature sensitivity of the gain which has been found in the experiments to be an important factor in the overall temperature sensitivity of threshold current.

Experimental study of physical parameters of semiconductor lasers

We discuss various experimental methods for measurements of the optical gain, transparency wavelength and optical loss. We discuss existing methods as well as newly developed. It is also shown how this set of measurements allows for characterization of other laser parameters, such as linewidth enhancement factor, differential gain, and wavelength chirp. We illustrate how these techniques are used for improving the laser performance for different applications.

Effect of carrier heating on static linearity of MQW InGaAsP/InP lasers

Carrier heating can degrade the linearity of the light-current (L-I) characteristics of a laser diode, which is a critical parameter for devices used in cable television (CATV) systems. On the basis of experimental estimation of the carrier heating rate above threshold, we consider the contributions of different mechanisms through which carrier heating can cause static nonlinearity. Comparison with measured L-I characteristics shows that the contribution of carrier heating to L-I nonlinearity is considerably less than previously estimated. We conclude that the carrier heating effect is not a dominant mechanism in producing the intermodulation distortions.

Simultaneous laser wavelength locking and spectral filtering using fiber Bragg grating

We demonstrate an optical scheme allowing for simultaneous wavelength locking and spectral filtering using a single fiber Bragg grating. We observe substantial increase of extinction ratio and reduction of the wavelength chirp. The scheme also provides stable wavelength necessary for dense WDM system applications.