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We present observation of ultra-narrow spectral modes in the generation of the random fiber laser by using a technique of optical heterodyning in real-time. We found that such modes have a spectral width below 3 MHz. The modes are spatially extended over the whole cavity and remain for tens of roundtrip times.

We directly observe ultra-narrow spectral modes in the generation of the random fiber laser by using a technique of optical heterodyning in real-time. These solitary spectral features appear slightly above the threshold of generation. We found that such modes could have a spectral width well below 3 MHz. These modes are spatially extended over the fiber laser length, and remain for tens of roundtrip times.

This paper presents low phase noise optical heterodyne millimeter-wave signals generation and data transmission using an ultra-low noise InAs/InP quantum-dash dual-wavelength DFB laser for potential applications in high capacity 5G mm-wave-over fiber mobile fronthaul links., Laser Applications Conference 2020, October 13–16, 2020, Washington, D.C. US

In this paper, we describe a portable system for measuring the indenter velocity in hardness meters implemented according to the Leeb method. The developed system is a fiber interferometer, in which a radiation source is a semiconductor laser with a wavelength of 1550 nm. The presented experimental results confirm the ability of the system to measure indenter velocities with an uncertainty of 0.001 m/s, which satisfies the requirements of the standards for this method of measuring hardness.

Background Carrier generation based on optical heterodyning techniques where a beat signal is generated from the mixing of two light sources can be interesting solution due to ease on tunability. The free running heterodyning scheme benefits with a very wide tuning capability and the generated carrier can be freely adjusted. However, the drawbacks come in the form of frequency stability. Heterodyning of two optical frequencies coming from a single laser cavity has shown its potential on improvement of frequency stability. Methods The impact of the laser parameters (i.e., optical power and linewidth) on the quality of the generated carrier (i.e., phase/frequency stability and carrier-to-noise ratio) is analyzed for a 25×64 elements PAA system. An optically generated carrier signal using a dual-frequency distributed feedback waveguide laser in ytterbium doped aluminum oxide (Al2O3:Yb3+) is analyzed and experimentally demonstrated in this paper. The carrier signal is used for downconversion of the signal received from a phased array antenna (PAA) of a DVB-S (Digital Video Broadcasting-Satellite) system. Results An optical frequency locked loop (OFLL) to stabilize the generated carrier is implemented which results in a microwave frequency at ∼14 GHz with a phase noise of -75 dBc/Hz at 1 MHz offset from the center frequency and gives a loop settling time of 12 μs. By using the proposed OFLL, the long term and the short term frequency stability of the generated carrier has an Allan deviation of more than 1×10−10 for an averaging time of 1000 s and a standard deviation of 39.4 kHz, respectively. The lasers linewidth should be in the order of tens of Hz, with a maximum relative intensity noise (RIN) of -107 dB/Hz and a minimum optical power of 0.94 mW. Conclusions The optical carrier generation by OFLL using a DFL to comply with the requirements of the standard carrier used in commercial LNBs has been investigated. The detailed analysis of the OFLL scheme is presented. Specifications requirement on carrier power, linewidth and relative intensity noise of the optically generated carrier have been addressed. The optical carrier generation is experimentally demonstrated and the requirements on CNR have been determined by measuring the noise floor and the optical carrier power. The measured values are compared with the calculated values and found to be very close.

Performance of optical heterodyning and external modulation by using an electro-optical modulator technique is evaluated. The first approach is carried out by beating two optical signals with a wavelength spacing corresponding to the desired microwave or millimeter-wave frequency continually tuned. The second technique requires only a single laser source along with a Mach-Zehnder Intensity Modulator (MZ-IM). Due to the available electrical bandwidth of the photodetector used, the experimental results are limited to the frequency range of 13 GHz. All experimental results are validated by a series of simulations using the VPI software. Signal-to-Noise ratio (SNR) and Phase-Noise parameters are measured.

Microwave photonic techniques, such as optical heterodyning of two correlated laser sources upon photo-detection, have been proposed to generate high purity millimeter wave (mmWave) signals. This approach is particularly suitable for RF frequencies where mmWave electronic are costly and difficult to implement. Additionally, radio-over-fiber allows an efficient remote delivery of the mmWave signal by transmitting the reference optical signal though low-loss high bandwidth optical fiber links. Laser characteristics, such as relative intensity noise and phase noise together with optical fiber characteristics are of maximum importance in such applications. In this paper, laser models with different degrees of complexity are discussed and compared to assess their suitability in the design of radio-over-fiber links and radar systems based on the optical heterodyning method.

Generation of microwave signals by optical heterodyning has been an active area of research in the field of Microwave Photonics. Though this approach offers great flexibility in choosing the microwave frequency, issues related to frequency stability and phase noise performance are inherent to it. The effect of laser phase noise on heterodyned output is mathematically analyzed, simulated and practically demonstrated. Design of hardware-efficient Optical Phase Locked Loop (OPLL) that overcomes the issues of phase noise and frequency instability is proposed. Frequency stability and phase noise tracking achieved by the proposed OPLL is demonstrated experimentally. Highly stable microwave signals, exhibiting phase noise as low as −105 dBc/Hz at 10 KHz offset (limited by the phase noise of the reference source used in the experiment), are successfully generated by the proposed approach. The generated microwave signals have been shown to be devoid of spurious components and harmonics.

A spectral optoelectronic system combining a collinear acousto-optic cell fabricated of calcium molybdate single crystal and a positive electronic feedback is proposed first and examined theoretically and experimentally. The feedback signal is formed at the cell output due to the optical heterodyning effect with the use of an unconventional regime of cell operation. It is shown that the feedback enables controlling spectral characteristics of the acousto-optic cell, resulting in enhancing the spectral resolution and the accuracy of optical wavelength determination. In the experiment, maximal filter passband narrowing was as great as 37 times.

We have established the millimeter-wave ellipsometry based on the photonics technology, and applied it for measuring the complex dielectric constant of human skin in vivo in 90-140GHz band. The millimeter wave is generated by a uni-traveling-carrier photodiode using optical heterodyning of two 1.55-µm light signals. The measured dielectric constant is fitted well with the Debye relaxation model.

An all-optical premodulation-free microwave frequency up/down-conversion method is presented based on stimulated Brillouin scattering in optical fibers for bidirection radio-over-fiber systems. Through optical heterodyning between the modulated optical carrier and the Stokes light, the microwave signal of 1.5 GHz is up-converted to 9 and 12 GHz, and the microwave signal of 9 GHz is down-converted to 1.5 GHz. The unexpected microwaves are more than 7 dB suppressed by loading the signal to convert with the optical-carrier-suppressed modulation.

A procedure for changing the spectral characteristics of injection lasers by Doppler-signal optical heterodyning by changing the injection current is discussed. Results of current tuning of the radiation frequency, coherence, and other characteristics of AlGaAs-heterolasers by using the above procedure under conditions of c.w. lasing are reported.

We report high-resolution real-time measurements of spectrum evolution in a fibre. The proposed method combines optical heterodyning with a technique of spatio-temporal intensity measurements revealing fast spectral dynamics of cavity-based systems.

We propose the use of optical nanoantennas for new-generation photonic nanodevices. We report the design and realization of enhanced optoelectronic photomixers taking advantage of the strong field localization and enhancement at the nanoantenna gap. We achieve high-power THz photomixers based on field-emission nanodiodes integrated with nanomanipulated conical antennas or clusters of nanobowtie antennas. We also demonstrate high quantum-efficiency phototriodes based on cross-slot nanoantennas forming the gate-electrode aperture.

Principles of light propagation in PLZT recently developed for intensity modulation are extended to optical heterodyning. The use of frequency shifter in a Michelson's type He—Ne laser interferometer is demonstrated, a 20 kHz difference frequency and Λ/20 resolution being achieved.

The Photorefractive Receiver Study was a 12 month study into concepts related to the application of photorefractive materials as adaptive beam combining elements for an optical heterodyne receiver. This study concentrates on the behavior of and requirements for the photorefractive element. A set of parameters and approaches for the photorefractive element was selected and a theoretical model constructed to predict performance. An experiment was designed and fabricated to illustrate the dependencies predicted by the theoretical model. All model and experimental results are described and summarized. Photorefractive Effect, Adaptive Beam Combining, Optical Heterodyne Receiver

Heterodyning surface electromagnetic wave (SEW) interferometer for measuring SEW phase velocity and the corresponding metal plasma frequency is described. Plasma frequency measurements for gold and copper are reported.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Attenuation coefficient and phase velocity of transversal and longitudinal acoustic waves in TaCl ‐ TaBr mixed crystals have been investigated by Bragg light diffraction on the acoustic waves. The measurements were carried out at the frequencies from 200 to 1200 MHz at home temperature. Moreover, the phase velocity was determined by using Raman‐Nath diffraction and optical heterodyning at 10 MHz. The investigations shown, that the change of acoustic properties in the investigated mixed crystals is nonadditive. Nonlinear interaction constants have been calculated taking into consideration various factors, which can influence on the propagation of acoustic waves in mixed crystals. The results were compared with similar investigations in NaCl ‐ NaBr mixed crystals.

Heterodyne frequency measurements are reported for twenty optically pumped laser lines from various molecules including COF2, CD3F,13CD3F, and C2H5I.

The role of the illuminating spot diameter on signal detection in laser Doppler vibrometry is emphasized. Practical methods for beam expansion in reducing the spot size are described. These include beam expansion before as well as after the original focusing lens. Some experimental results describing spot size-related signal improvement are also presented.

An investigation was made of the operation of a ring laser (λ = 3.39 μ ) with a methane cell in the case when the frequencies of the opposite waves were split in the presence of a power peak. A method was developed for obtaining a smooth profile of the peak, locking of the half-sum of the wave frequencies to the average frequency of the absorption line of methane was confirmed, and automatic frequency stabilization was achieved.

Continuously variable time compression, expansion, and inversion, with the corresponding changes in frequency, of rf signals in the range of 10 to 100 MHz, are described. By using a simple optical heterodyning technique and high‐speed scanning of a laser beam, an rf signal, ``stored'' as an acoustic signal in a quartz bar, can be processed or ``read out'' in a variety of ways. Although present equipment has limited the amount of processing and frequency range of the signals that can be handled, it is felt that input signal frequencies are restricted only by the acoustic properties of the delay medium and the output frequencies will be limited by the response of the photodetector.

Sixteen FIR laser lines have been observed by optical pumping of CD 3 OH with a tunable single-mode TEA CO 2 laser. Particularly large outputs are observed at 70.6 μm (10 P20 pump), 69.9 μm (10 R22), 42.3 μm (10 R6), and 105.3 μm and 41.7 μm (10 R8).

A light beat method for generating frequency markers on the diffraction efficiency versus frequency curve of acousto-optic (AO) cells is described. The output signal of a photodetector detecting all of the Bragg-diffracted laser beams produced by an AO cell driven by the sum of a chirp signal and a multifrequency signal has been calculated and experimentally confirmed. This method can be applied in the testing and aligning procedure of AO cells and in the field of AO spectrum analysis of signals.

A first approach to frequency shifting of far-infrared radiation by optically induced “moving” refractive index gratings in semiconductors is reported. The factors determining the performance of this frequency shifting technique are inferred using a one-dimensional analytical model. In a proof-of-principle experiment frequency shifting of 119 μm radiation was observed up to 80 MHz using a 300 mW, 488 nm Ar+ laser for optical excitation.

The observation and quantative measurement of optical heterodyne detection at 337 μm using a HCN laser and an epitaxial n-type GaAs photoconductor are reported. The measured NEP amounted 1.4 × 10−14 W Hz−1.

Acoustic‐phase conservation in ultrasonic imaging by Bragg diffraction is experimentally verified by optical heterodyning. The results suggest the possibility of a phase‐contrast Bragg imaging system with simultaneous display of phase and amplitude information.

New frequency calibration tables are required to keep abreast of the resolution attainable by currently available tunable lasers. One key to the generation of tables with requisite accuracy involves accurate heterodyne frequency measurements; another key consists of reliable fitting and analysis. Coordinated activity in NBS involves selection of suitable molecular calibration candidates, their frequency measurement and analysis, and dissemination of the results in the form of frequency calibration tables. Current status of these efforts is described.

A survey of heterodyne mixers is presented for the wavelengths of 40 μm to 1000 μm as reported in the literature to date.© (1977) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

This work describes an instrument for the noninvasive measurement of cutaneous blood flow velocity. The system utilizes the Doppler shift of laser light backscattered from moving red blood cells in the cutaneous microcirculation, the shift being obtained by an optical heterodyning technique. Comparison is made between this technique and the 133xenon clearance technique in measuring cutaneous flow in the forearms of normal volunteers. Variations in flow were obtained by inducing different degrees of solar erythema with an ultraviolet sunlamp. A Y on X linear regression yielded a regression coefficient = 0.89 (p less than 0.001, n = 16) between the two methods. The laser Doppler method appear to represent a practical technique for clinical evaluation of cutaneous blood flow in any skin surface.

An experimental investigation was made of the frequency spectrum of the stimulated emission from an argon laser at ?=514.5 nm in the region of of anomalous competition with a line at ?=488 nm. The relationship between the frequency spectrum and the nature of the optical competition was determined. A mechanism explaining the anomalous interaction between these lines was put forward.

A simple, efficient optical arrangement for the laser Doppler velocimeter is described which requires no optical heterodyning alignment, and is extremely quick and easy to set up in experimental work. It has the additional advantages of measuring two-dimensional flows, and ease in traversing the flow systems. The system is stable and insensitive to stress and vibrations.

The application of a high accuracy, wide bandwidth optical heterodyne interferometer to the inspection of surfaces is described and sample data are given. The data format should make the system particularly suitable for automatic inspection systems.

Procede d'assemblage de faisceaux de fibres sous forme de reseau bidimensionnel pour alimenter un reseau de detecteurs