Investigation of Free Space Optical Detection Module Operating at the Wavelength Range of 8-12 μm
The paper presents the construction and test results of a long-term radiation detector module for free space optical communication operated at the wavelength range of 8–12 μm. In the module a Polish detector manufactured in the company Vigo System S.A. was applied. High sensitivity of the detection module was achieved through a multi-layered heterostructure HgCdTe with immersion lens, which is optimized for the radiation detection at the wavelength of 10 μm. Detector noises were reduced as a result of detector cooling by means of four-stage thermoelectric cooler. The developed detection module is dedicated to design a next-generation optical data link. The link will be characterized by a greater range in difficult weather conditions in relation to the currently offered links operating at the shorter wavelengths.
Transmitter for free-space optics with an integrated driver
The paper presents a model of a free space optical transmitter operating in the wavelength range of 8-12 μm. In the transmitter, a quantum cascade laser controlled by a special driver was applied. The driver provides the control of the energy, repetition rate and duration of radiation pulses. In the described transmitter, generation of pulses with high duty cycle is also provided, making it possible to use the data link with either RZ or NRZ coding. In the frame of the study, the impact of laser working conditions on the data link operation was determined.
Growth of Hg‐based alloys by the traveling heater method
Oriented (Hg,Cd)Te single crystals have been grown by the traveling heater method. The crystals were grown in the 〈111〉A and 〈111〉B directions. Growth along the 〈111〉B direction yields single crystals whereas those grown in the 〈111〉A direction show a high density of microtwins. The crystalline quality as determined by chemical etching and x‐ray rocking curves indicates that the crystals have a low‐line defect density. The dislocation density is found to be in the 3×104 cm−2 to 2×105 cm−2 range and the subgrain boundary density is lower for crystals grown in the 〈111〉B direction. Thermal analysis was carried out using a finite element model. The analysis shows that a convex interface can be achieved under the appropriate thermal conditions and the simulations are found to be in good agreement with the experimental data. The macrostructure of the crystals clearly indicate that when the interface is convex a single crystal is obtained but when the interface becomes concave, crystals are nucleated at the amp...