Development and design of a phase-locked loop in the subterahertz and terahertz ranges for a harmonic of the signal of a centimeter-wave synthesizer

Abstract

We describe a phase-locked loop of a backward-wave oscillator in the range 667-857 GHz for the 34th-45th harmonic of the reference signal of a centimeter-wave synthesizer. Multiplication of the reference-synthesizer frequency in the phase-locked loop is performed by using a subharmonic mixer based on semiconductor superlattices. The mixer, operated at room temperature, has a nonlinear electron conductance.Great interest in the terahertz range, shown by many researchers, is stipulated by new possibilities of studies, primarily in the field of microwave spectroscopy of high and superhigh resolution. Development of new terahertz devices also stimulates radio-astronomical studies to a considerable extent [1,2].At present, studies in the field of microwave and radio spectroscopy are restricted by the limited access to terahertz devices. First of all, this is related to the fact that until recently, effective sources and detectors of terahertz radiation have been absent. The majority of terahertz sources had either low intensity, as thermal sources, or were bulky and not tunable with respect to frequency, as molecular lasers. The only source of wideband coherent radiation, a backward-wave oscillator (BWO), operates at frequencies of up to 1250 GHz. Recently, a spectrometer based on a femtosecond laser [3] and capable of solving various problems such as spectroscopy of biological molecules [4], liquids [5,6], and solids [7,8] has been developed. The spectral resolution of such spectrometers does not exceed 1 GHz, which is insufficient for high-resolution spectroscopy.The necessary condition for achieving high and superhigh resolution in spectroscopy is the presence of a source of radiation with a narrow spectrum and exact setting of the radiation frequency. The spectroscopic requirements to the parameters of the frequency and spectrum of a high-quality radiation source are usually determined by the necessity to resolve the Doppler line broadening (of the order of 10 −6 ) and to measure the frequencies of spectral lines and the shifts of their centers with accuracy up to 10 −8 -10 −10 . Development of terahertz sources with a narrow spectrum and exact setting of the frequency with the subsequent transfer of the radiation frequency to the high-frequency region of the terahertz range by multiplication is now a topical problem.The main part of such a terahertz source is a frequency synthesizer which is a system of successive multiplication (based on phase locking of oscillators of various ranges) of the frequency of a reference synthesizer operated, as a rule, in the centimeter-wave range. The submillimeter-wave synthesizer described for the first time in [9] and operated at frequencies of up to 840 GHz has 6 loops of frequency multiplication. Usually, planar semiconductor Schottky diodes are used as a nonlinear element in harmonic mixers of

Investigation of terahertz radiation influence on rat glial cells

“…In order to irradiate cell culture with broadband THz radiation, a backward wave oscillator (BWO) source operating in 0.12 -0.18 THz frequency range was used [31]. The experimental setup is shown in the Fig.…”

Methods and instruments of high-resolution transient THz spectroscopy for diagnostics of socially important diseases

“…The use of mixers and multipliers based on quantum semiconductor superlattices (QSSLs) [17] led to development of a number of precise methods and instruments for various applications. As a result, a unique set of frequency synthesizers based on backward-wave oscillators (BWOs), covering the range from 667 to 1100 GHz, was designed [18] with application of QSSL harmonic mixers, which provide efficient frequency conversion (with numbers of harmonics from 37 to 55) to the THz range.…”

THz analyzers for breath research

“…In the THz range the effective multipliers and mixers are based on superlattice structures (SL). The SL are more effective for frequency transformation and detection than Schottky diodes, since Schottky diodes have lower values of inertness and parasitic capacitances and presence of negative differential conductivity (up to 1 THz) on the volt-ampere characteristic [16]. Application of a SL multiplier and spectral pure Gunn generator has enabled a harmonic generation up to 8 THz [17].…”