Longitudinal Mode Hopping Research Articles

Single frequency erbium fiber external cavity semiconductor laser

A novel external cavity configuration for stable single frequency operation of the semiconductor laser is demonstrated. By using an erbium doped fiber as the external cavity, longitudinal mode-hopping is suppressed, ensuring single frequency operation. Employing a 3 m long fiber cavity, resolution-limited optical linewidths of a kHz are obtained.

Bistable Optical Devices Using Laser Diodes Coupled to Interference Filters

A bistable optical device was demonstrated by using the longitudinal mode hopping of the laser diode and the narrow transmission spectrum of an interference filter. The device is capable of converting changes in the wavelength of the laser diode into changes in intensity by transmitting it through the filter. Exclusive OR operation was observed with the use of triple signal outputs. In addition, an optical switch-off phenomenon was confirmed by directly injecting a pulse 500 ps wide into an external dye laser.

Bistable Optical Devices using Laser Diodes coupled to Interference Filters.

A bistable optical device was demonstrated by using the longitudinal mode hopping of the laser diode and the narrow transmission spectrum of an interference filter. The device is capable of converting changes in the wavelength of the laser diode into changes in intensity by transmitting it through the filter. Exclusive OR operation was observed with the use of triple signal outputs. In addition, an optical switch-off phenomenon was confirmed by directly injecting a pulse 500 ps wide into an external dye laser.

Interference fringes in the far field of short-external-cavity InGaAsP diode lasers: a method for longitudinal mode control

Interference fringes in the far field of short-external-cavity InGaAsP diode lasers are discussed and explained. The interference occurs between light emitted from the front laser facet and light emitted from the rear laser facet that is reflected forward by the external mirror. The change in the relative phase of light emitted from each facet caused by a change in the longitudinal mode results in a shift of position of a portion of the fringes in the far field. This shift can be detected and processed to produce a discrimination signal that is used in a feedback control system to detect or prevent longitudinal mode hops. The control system has a response time as short as 15 ms and can prevent mode hops caused by drift, mechanical shock, or laser tuning; the technique permitted complete frequency tuning over the range of operation of the laser. The behavior of the control system was analyzed with the help of a model that can be used to optimize the control system.

Low frequency noise of a 980 nm InGaAs/GaAs strained quantum well laser

The longitudinal mode hopping and the related terminal electrical noise in InGaAs/GaAs ridge single quantum well (SQW) lasers are investigated. It is found that electrical mode hopping has a Lorentzian dependence. The correlation with the optical noise is experimentally shown in the low-medium frequency range. Measurements of this electrical-optical correlation give a high value of this parameter (0.8≤γ 2 ≤0.9) when the longitudinal mode hopping is present

Electrical noise measurements on laser diodes for monitoring of optical feedback and mode hopping

By measuring the wideband electrical noise voltage at the diode terminal, several laser characteristics can be monitored entirely without optical equipment. The letter describes the application of electrical noise measurements to the study of longitudinal mode hopping and optical feedback-induced noise from, for example, optical fibres.

GaInAsP/InP surface-emitting lasers with current confining structure

In order to reduce the threshold current of GaInAsP/InP surface-emitting (SE) lasers, we search for an effective current confining structure and examined several types; round-low-mesa, round-high-mesa/polyimide-buried, buried-heterostructure (BH), and planar-buried-heterostructure (PBH). The minimum threshold current was reduced down to 18 mA at 77 K and the threshold current density was estimated to be reduced to 3 kA/cm2. The operating temperature has been raised to -10°C (263 K). The longitudinal-mode hopping was first observed for GaInAsP/InP SE lasers. The effective refractive index for GaInAsP/InP SE lasers was 4-5, that was almost the same as conventional edge-emitting lasers.

Correlation of low-frequency intensity and frequency fluctuations in GaAlAs lasers

The intensity and frequency noise in single-mode GaAlAs lasers have been measured and the correlation between these instabilities investigated. The measurements were made over the range from 10 Hz to 25 kHz in CSP, TJS, and BH laser structures. It is found that the coherence function for frequency noise and intensity noise from one facet is near unity at the lasing threshold, decreases rapidly with decreasing current below threshold, and also decreases, but more slowly, as the current is increased above threshold. Qualitatively similar behavior is found for the correlation between intensity noise from the two laser facets. Junction voltage fluctuations are not correlated with the other types of noise, except when longitudinal mode hopping is occurring. A model in which both intensity and frequency noise are related to local current variations and optical backscattering in the diode active region is developed to explain the results.

Correlation of Low-Frequency Intensity and Frequency Fluctuations in GaAlAs Lasers

The intensity and frequency noise in single-mode GaAlAs lasers have been measured and the correlation between these instabilities investigated. The measurements were made over the range from 10 Hz to 25 kHz in CSP, TJS, and BH laser structures. It is found that the coherence function for frequency noise and intensity noise from one facet is near unity at the lasing threshold, decreases rapidly with decreasing current below threshold, and also decreases, but more slowly, as the current is increased above threshold. Qualitatively similar behavior is found for the correlation between intensity noise from the two laser facets. Junction voltage fluctuations are not correlated with the other types of noise, except when longitudinal mode hopping is occurring A model in which both intensity and frequency noise are related to local current variations and optical backscattering in the diode active region is developed to explain the results.

SEQUENTIAL EXCITATION OF LONGITUDINAL MODES IN GaAs LASERS

Experimental evidence is presented which demonstrates that, in the vicinity of threshold, GaAs lasers exhibit longitudinal mode hopping, in agreement with the theory of Popov et al.