FM Sideband Research Articles

Bandwidth measurements of ultrahigh-frequency optical detectors using the interferometric FM sideband technique

A frequency modulated semiconductor laser and an interferometer are used as a source of very high frequency amplitude modulation to measure the response of optical detectors. This new technique does not require a laser with a flat, or even known, frequency response, and measures the detector response at frequencies well above the modulation frequency applied to the laser. The response of several InGaAs p-i-n detectors has been measured to 22 GHz using 1.3- and 1.55-μm semiconductor lasers modulated at only 500 MHz. These measurements were not limited by the measurement method, which may be capable of measuring bandwidths substantially in excess of 20 GHz.

Optically induced modulation in FM sideband injection-locked laser diodes

The spectrum of a slave laser in which two different wave-lengths are injected is investigated. A simple rate equation analysis is in reasonable agreement with the experiment and accounts for the asymmetrical response of the induced FM.

Fine structure of frequency chirping and FM sideband generation in single-longitudinal-mode semiconductor lasers under 10-GHz direct intensity modulation

The fine structure of the dynamically broadened spectral line of a single-longitudinal-mode InGaAsP laser under large-signal direct intensity modulation at 10 GHz was studied. It is shown that the frequency-chirped spectral line has a characteristic FM modulation spectrum with many sidebands at 10-GHz intervals and with an asymmetry due to the superposition of the a.m. modulation.

35 GHz microwave signal generation with an injection-locked laser diode

A new technique for sinusoidal intensity modulation of light, based on injection-locking of two longitudinal modes of a single laser to FM sidebands of another laser, is described. A 35 GHz microwave signal with a linewidth of less than 10 Hz was generated.

Microwave signal generation with injection-locked laser diodes

Heterodyne detection of the light from two slave lasers injection locked to FM sidebands of a modulated master laser is used to generate a narrowband microwave signal at 10.5 GHz.

Optical injection locking of X-band FET oscillator using coherent mixing of GaAlAs lasers

A 9.6 GHz GaAs FET oscillator was optically injection locked at the fundamental frequency. The locking bandwidth was 1.6 MHz. The optical injecting signal was generated using coherent mixing of two semiconductor lasers injection locked by different FM sidebands of another laser.

Sitar spectrum properties

The main strings of a sitar are tuned to pitches corresponding closely to F3♯, C2♯, G2♯, G3♯, G3♯, C4♯, and C5♯ (i.e., in 4ths, 5ths, and octaves). Playing is predominantly on the F3♯ string, the tonic (sa) being at the 7th fret (C4♯). There are also 11 sympathetic strings tuned to the notes of the raga. The measured and calculated inharmonicity is far less than that of Western stringed instruments. Sitar strings are thin, giving small stiffness inharmonicity and low wave impedance that reduces random inharmonicities from bridge/belly resonances. String length variations from first mode rolling and/or sliding on the curved bridge profile produces FM and AM sidebands of ±f1 from the upper partials. These components join with both plucked and sympathetic string partials to give harmonically related narrow-band clumps. The resulting tone has complex time behavior but well-marked pitch. Tuning to just frequency ratios is required since the beats arising from excitation of a mistuned string are not smeared by roughness due to inharmonicity. Raman's observation that plucking at L/4 need not remove the 4th partial from the tone is confirmed. Bridge-generated FM/AM provides part of the explanation; shock excitation of sympathetic strings via the bridge provides the rest.

FM sideband injection locking of diode lasers

The injection locking of a laser diode to FM sidebands of a second, modulated laser has been investigated. Locking to sidebands as far as 9.5 GHz removed from the fundamental lasing frequency was observed.

Interferometric measurements with laser FM sidebands

Hysteresis in piezoelectric transducers down to 20 Å and gas pressure changes as small as 10 mTorr are measured by locking a laser FM sideband to an interferometer resonance. In addition, rapid monitoring of large excursion motions with 200-Å accuracy is achieved using an ’’optical frequency comb’’ consisting of multiple FM sidebands.

The effects of small contaminating signals in nonlinear elements used in frequency synthesis and conversion

Many electronic systems use nonlinear elements to add or subtract two frequencies or to multiply or divide a frequency by an integer. Some level of contamination by small undesired signals is always present and the ability to predict the effects produced by their passage through the nonlinear elements is important in analyzing system performance. These effects can often be predicted, for frequency mixing (addition and subtraction), multiplication and division, by decomposition of the contaminating signal into equivalent AM and FM sidebands whose effects are more easily estimated. One important effect that occurs in frequency division is a sampling process which translates the frequencies of the interfering signals. A method for predicting these effects is explained and experimental results, demonstrating the application and applicability of the method, are reported.

Detection of frequency modulation at large modulation frequencies

Several studies have been made of the minimum frequency excursions Δf required for detection of frequency modulation, with modulation frequency fm. [E. Zwicker, Acustica, 2, 125–133 (1952) R. H. Kay and D. R. Matthews, J. Physiol. 225, 657–677 (1972)]. The graph of minimum Δf vs fm has a pronounced peak at large values of fm. Further, the minimum Δf increases with decreasing signal intensity. The present paper shows that these results may be understood if fm detection at larger fm is regarded as the detection of the first lower sideband masked by the carrier. From available masking and modulation data it appears that fm sidebands beyond the first do not contribute to detection. To test this idea joint experiments on sine tone masking and fm detection were performed. In each case the masker frequency equaled the carrier frequency, fc of the modulated signal. The signal to be detected had frequency equal to the side band frequency, fc−fm. The results of the experiment support the masked-first-sideband model for fm detection at high modulation frequencies. [Work supported by NSF grant BNS 20225.]

Mössbauer study of FM sidebands produced by the RF magnetic field applied to an iron foil

AbstractThe formation of rf sidebands in the Mössbauer spectra of metallic iron as a result of the application of an external rf magnetic field is studied. The dependence of the sideband intensities on the rf field intensity and the thickness of the sample is discussed. Experiments show that the formation of sidebands is connected with atomic vibrations induced within the foil by the rf field applied. Basing on the experimental spectra obtained, modulation indices are calculated in accordance with the FM theory. The results obtained are interpreted in terms of the modified magnetostriction model. The dependence of sideband formation on the coating of the foil with a damping medium is studied. It is found that covering of the sample surface with a silicon grease, adhesive tape, or metallic zinc causes a considerable damping of the sidebands and in some cases causes their complete quenching. This effect has been attributed to the dissipation of energy generated within the sample by the rf field. If the acoustic resistivity of the medium covering the sample is higher than that of air the energy transferred from the foil to the environment increases and the sidebands are damped.

Experiments on the Interaction of Light and Sound for the Advanced Laboratory

We describe an advanced laboratory experiment in which both Raman-Nath and Bragg diffraction of light by acoustic waves in water are observed in the sound frequency range from 5 to 45 MHz. The apparatus consists of a laser, light detector, rf power source, quartz transducer, and homemade water cell. We discuss the theory of Raman-Nath diffraction, Bragg diffraction, and the criteria for the manifestation of each. The measured Raman-Nath diffracted orders give a visual display of FM sidebands. We discuss a quantitative relationship between the incident and diffracted light and the sound for Bragg diffraction in terms of a three-wave parametric process. Stanford students in the Advanced Applied Physics Laboratory have successfully performed this experiment during the past three years.

Discovery of electrostatic sound wave modes in a plasma in klystron oscillators

During tests of two-cavity klystron CW oscillators which are spacecharge focused, unusual FM sidebands were discovered. These modulation sidebands could only be detected with a sensitive discriminator and were found to result from video frequency oscillations. The video signals have been shown to be electrostatic sound wave modes of a beam-generated plasma and are similar to those investigated by Crawford (1961). Although they were discovered in the RF spectrum, they were also observable in the collector current.

Comparison of split channel FM and single sideband for land mobile services

Comparison of split channel FM and single sideband for land mobile services