M.S. Lin

Measurements and modeling of the harmonic distortion in InGaAsP distributed feedback lasers

Measurements of the second harmonic distortion in 1.3 mu m InGaAsP distributed feedback lasers are reported. At low modulation frequencies ( approximately 50 MHz), the second harmonic distortion exhibits a minimum at a certain bias current. The minimum, in general, is not observed at high modulation frequencies ( approximately 1 GHz). A model of the harmonic distortion, based on the equivalent electrical circuit of the laser, is presented to explain the observed behavior. The spatial hole burning effect in the active region introduces additional nonlinearity, its effects can be significant compared to that of the leakage path. >

Fabrication and performance characteristics of buried-facet optical amplifiers

The fabrication, performance characteristics, and design rules of buried-facet optical amplifiers are described. Chip gain of 25 dB, gain ripple of <1 dB, and gain difference of ≤1 dB for TE- and TM-polarized light are observed. The gain ripple and polarization dependence of gain correlate well with the ripple and polarization dependence of the amplified spontaneous emission spectrum. The performance of buried-facet amplifiers is comparable to that of cleaved-facet amplifiers with very good antireflection (R<10−4) coatings. The buried-facet design reduces the requirement on antireflection coatings and makes the fabrication process more reproducible.

Measurements of transient response on lossy microstrips with small dimensions

Measurements were made of the behavior of transient pulses on terminated microstrips with small dimensions (2.5 mu m thick and 10-40 mu m wide). The dependence of transient behavior on the width, length, and dielectric thickness of microstrips is reported, providing a guide for choosing design parameters of lossy microstrips. The experimental results indicate that these small microstrips can be used for high-speed digital signal transmission, with a rise time at least as short as 40 ps, provided that the line resistance is taken into account and that proper termination is used. Pulse attenuations are found to be consistent with purely resistive losses when the skin effect is included; no significant losses can be attributed to the polyimide dielectric. The reflection from the interface between the lossless and lossy lines is experimentally shown to be small for well-matched cases, but to be appreciable for poorly matched cases. The standard transmission theory for lossy lines under the conditions of these experiments is used successfully to describe the experimental results. >

Temperature dependence of polarization characteristics in buried facet semiconductor laser amplifiers

The temperature dependence of gain and amplified spontaneous power for both TE and TM modes in semiconductor laser amplifiers are measured. Experiments are performed on three selected amplifier types, with higher TE, higher TM, and equal TE-TM gains, respectively. The gain differences are significantly reduced at higher temperature for the TE-dominant and TM-dominant amplifiers. For amplifiers with equal TE-TM gains, the TE and TM gains remain equal at high temperature. The measurements of the amplified spontaneous power show similar similar characteristics. More importantly, less polarization-sensitive gain characteristics can be obtained with some decrease in maximum gain by raising the operating temperature. The experimental results are explained by using the gain equations of the semiconductor laser amplifier. >

Static and dynamic characteristics of DFB lasers with longitudinal nonuniformity

Static and dynamic characteristics of 1.55- mu m distributed-feedback (DFB) lasers with longitudinal nonuniformity in optical intensity and carrier density are discussed. The nonuniformity is manifested in soft light-current threshold and varying differential quantum efficiency, blue-shifted static tuning, and free-carrier induced FM response.<<ETX>>

Nearly dispersion-penalty-free transmission using blue-shifted 1.55- mu m distributed feedback lasers

Nearly dispersion-penalty-free transmission over 40 km of nondispersion-shifted single-mode fiber was demonstrated using blue-shifted 1.55- mu m distributed feedback lasers. This good system performance is attributed to the narrow and blue-shifted modulated optical spectrum which is in turn associated with the soft turn-on light-current characteristics. Transmission experiments using lasers with hard turn-on light-current characteristics give rise to broad modulated spectra and higher dispersion penalties.<<ETX>>

Monitoring the performance of a semiconductor optical amplifier

Measurements of optical gain and spontaneous emission of optical amplifiers show that the latter is a good measure of the former. A device structure is fabricated where a photodetector is integrated next to the amplifier. A fraction of the spontaneous emission from the amplifier impinges on the photodetector in this device producing a photocurrent. The photodetector current is found to be a monotonic function of the amplifier gain. Hence, the photodetector output can be used to monitor the performance of the amplifier.

Nonlinearity Of Buried Heterostructure Lasers Under Amplitude Modulation

Intermodulation and harmonic distortions of buried heterostructure distributed feedback lasers can be low enough for many applications, like cable television and microwave subcarrier transmissions. This paper discusses the theoretical analysis and measured values of these distortions. The results indicate that the nonlinearities of lasers are dependent on the modulation frequency, the operating temperature, and the physical structure of the lasers.

Performance characteristics of buried facet optical amplifiers

The fabrication and performance characteristics of buried-facet optical amplifiers are described. Chip gain of >25 dB, gain ripple of <1 dB, and gain difference of <1 dB for TE and TM polarized light are observed. The gain ripple and polarization dependence of gain correlate well with the ripple and polarization dependence of the amplified spontaneous emission spectrum. Although the performance of buried-facet amplifiers is found to be comparable to that of cleaved facet amplifiers with very good antireflection (R<10/sup -4/) coatings, the buried-facet design reduces the requirement on antireflection coatings and makes the fabrication process more reproducible.<<ETX>>

Temperature dependence of the harmonic distortion in InGaAsP distributed feedback lasers

Measurements are reported of the second‐harmonic distortion in 1.3‐μm InGaAsP distributed feedback lasers operating at different temperatures. A minimum of the second‐harmonic distortion exists at a particular bias current when the laser is operating at low temperature (10 °C). The minimum shifts to a higher bias current when the operating temperature is raised. At an even higher temperature, the minimum dissappears. A temperature‐dependent model of the second‐harmonic distortion, based on an equivalent circuit analysis, is presented to explain the experimental results.