Yosi Shani

Analysis of mode propagation in optical waveguide devices by Fourier expansion

A general method for calculating the solution of the scalar wave equation for the field propagating through integrated optical devices is presented. The method is capable of a three-dimensional description and of treating problems with reflected waves. It consists of dividing the device into a series of sections of axially uniform waveguides. The modes in each section are found by expansion of the field in a two-dimensional Fourier series and solving the associated matrix eigenvalue problem. Propagation is then described by relating the mode amplitudes of each section to the previous one. The amplitudes are related by a matrix that is the product of the eigenvector matrices of the two sections. The method is illustrated by the analysis of an adiabatic mode transformer, the coupling of light from a semiconductor laser through free space to a waveguide, and the propagation through an adiabatic 3 dB coupler and Y branch. >

Calculation of the refractive indexes of lead chalcogenide salts and its application for injection lasers

The refractive indexes N of some commonly used lead and lead-tin chalcogenide salts (PbSnSe, PbSSe, PbSnTe) have been calculated for frequencies near the fundamental absorption edge. The calculations take into account the nonparabolicity of the bands and population effects, both in thermal equilibrium and under lasing conditions. In contrast to previous predictions, the interband dispersion is shown to give a major contribution both to the change of N , due to lasing conditions, and to the derivative dN/dn (where n is the minority carrier concentration). Good agreement has been obtained between our calculations and experimental results for the dispersion of N , for \epsilon_{\infty} , for the effective N in corrugated laser structures, and for the laser linewidth enhancement factor α. These calculations may be quite useful for the design of injection lasers and infrared devices.

77 K cw operation of distributed Bragg reflector Pb1−xSnxSe/ Pb1−x−yEuySnxSe diode lasers

Distributed Bragg reflector Pb1−xSnxSe/ Pb1−x−yEuySnxSe double heterostructure stripe geometry diode lasers were fabricated using molecular beam epitaxy. We observed cw single mode operation between the heat‐sink temperatures 66 and 81 K at λ≊7.8 μm with an average tuning rate of 0.8 cm−1/K. Single mode continuous tuning over a relatively wide range of 6 cm−1, with an average tuning rate of 0.026 cm−1/mA, was obtained at 77 K.

Metal clad Pb/sub 1-x/Sn/sub x/ Se/Pb/sub 1-x-y/Eu/sub y/ Sn/sub x/Se distributed feedback lasers

Distributed-feedback Pb/sub 1-x/Sn/sub x/Se double heterostructure stripe geometry diode lasers fabricated using molecular-beam epitaxy are discussed. These lasers operate in the CW mode up to 90 K and in the pulse mode up to 100 K. They are unique in their low tuning rate with injection current 4 cm/sup -1//A, and in that they withstand high CW injection currents without damage. These features are probably the result of the metal cladding layer located on top of the gratings. >

Pb/sub 1-x/Sn/sub x/Se/Pb/sub 1-x-y/Eu/sub y/Sn/sub x/Se corrugated diode lasers

The design, fabrication, and testing of distributed Bragg reflector (DBR), distributed feedback (DFB), and grating coupled emission (GCE) Pb/sub 1-x/Sn/sub x/Se/Pb/sub 1-x-y/Eu/sub y/Sn/sub x/Se double heterostructure stripe geometry molecular-beam-epitaxy (MBE) grown diode lasers are discussed. The DBR and DFB lasers are the first Pb-salt corrugated lasers to operate in CW (continuous) mode at temperatures above that of liquid nitrogen. For the GCE lasers, a narrow far field distribution of approximately 5 degrees was obtained for the first time. >

Distributed Bragg reflector Pb1−xSnxSe/Pb1−x−yEuySnxSe diode lasers with a broad single‐mode tuning range

Distributed Bragg reflector Pb1−xSnxSe/Pb1−x−yEuySnxSe double heterostructure stripe geometry diode lasers were fabricated using molecular‐beam epitaxy. Single‐mode cw operation at about 7.8 μm was obtained for heat‐sink temperatures in the range 25–75 K. the single‐mode continuous tuning range was 10 cm−1. Tuning the diodes via the injection current, a range of 24 cm−1 was completely covered with single‐mode emission. The reason for this wide tuning range was mode hopping to lower frequencies rather than the usual hopping to higher frequencies.Distributed Bragg reflector Pb1−xSnxSe/Pb1−x−yEuySnxSe double heterostructure stripe geometry diode lasers were fabricated using molecular‐beam epitaxy. Single‐mode cw operation at about 7.8 μm was obtained for heat‐sink temperatures in the range 25–75 K. the single‐mode continuous tuning range was 10 cm−1. Tuning the diodes via the injection current, a range of 24 cm−1 was completely covered with single‐mode emission. The reason for this wide tuning range was mode hopping to lower frequencies rather than the usual hopping to higher frequencies.

Calculation of the refractive index of lead-tin-telluride for infrared devices

The refractive index N of lead-tin-telluride is calculated for frequencies near the fundamental absorption edge. The contribution to N from electron states near the band-edges is calculated more exactly than in previous works and a new expression for the contribution from the high frequency region is proposed. Good agreement is obtained between our calculations and experimental results. The change of N due to gain in injection laser is also calculated and it is shown that it cannot be neglected.

The far field of PbSnTe injection lasers

The far field of PbSnTe injection lasers, perpendicular to the junction plane, was measured. The results are shown to be in good agreement with theoretical predictions. Design considerations are given for constructing laser structures having an improved far-field pattern.

Metal-clad waveguides for Pb-salt diode lasers

Pb-salt waveguides with a metal-clad layer are discussed. It is shown that for TE modes one can assume that E(y) = 0 at the metal-semiconductor boundary, while for TM modes the complex formalism should be used. It is also shown that lasers with a metal-clad waveguide should have only a small increase in their threshold current while operating in a TE mode and that they should operate in a TE mode since their TM modes generally have high threshold current.

Highly collimated laser beams from grating coupled emission Pb1−xSnxSe/Pb1−x−yEuySnxSe diode lasers

Grating coupled emission Pb1−xSnxSe/Pb1−x−yEuySnxSe double‐heterostructure stripe‐geometry diode lasers were fabricated using molecular beam epitaxy. Low‐divergence far‐field patterns of ∼5° for multimode operation and ∼2° for single‐mode operation were obtained. These are the lowest values ever achieved with Pb salt lasers.