Showing papers on "Injection locking published in 1998"

Low-phase-noise millimeter-wave generation at 64 GHz and data transmission using optical sideband injection locking

Abstract: The 60-GHz band is proposed for the radio link frequency in broad-band cellular systems. 140-155-Mb/s transmission experiments are reported with optically generated millimeter-waves at frequencies in the 60-GHz band. By applying the sideband injection locking technique, the remotely generated millimeter-wave signals depict quartz accuracy and low phase noise <-100 dBc/Hz at offset frequencies 21 MHz.

Dynamic behavior and locking of a semiconductor laser subjected to external injection

Abstract: In this paper, we analyze the phenomena arising when a monomode semiconductor laser is subjected to external injection from another laser. The system stability is investigated as a function of detuning and of the relative injected power. Different regimes, spanning from phase locking to chaos and coherence collapse, are described by analytical and numerical methods for weak and moderate injection. Previous theoretical studies are extended by describing the inverse transition from chaos to stability and by deriving the final locking condition. Also, further investigation on the coherence collapse regime has been performed. Besides contributing to the exploration of an interesting fundamental phenomenon, the results of this analysis are useful for different applications, including coherent detection and chaotic cryptography.

Experimental demonstration of modulation bandwidth enhancement in distributed feedback lasers with external light injection

Abstract: The frequency response of a semiconductor distributed feedback (DFB) laser under optical injection locking has been studied experimentally. It is shown that strong injection locking is very effective at increasing the relaxation oscillation frequency of DFB lasers. Bandwidth enhancement as high as 3.7 times has been achieved for the first time.

Oscillator with clock output inhibition control

Abstract: An oscillator with temperature compensation produces a stable clock frequency over wide variations of ambient temperature, and it includes an oscillation generator, two independent current generators, a transition detector and a clock inhibitor. The outputs of the two programmable, independent current generators are combined to provide a capacitor charging current that is independent of temperature. The oscillator is capable of three modes of operation: fast mode, slow/low power mode and sleep mode, which are controlled by the transition detector in response to external control signals. When the transition detector transitions from one mode to another, it controls the clock inhibitor to block a clock output of the oscillator generator for a predetermined number of clock cycles to allow the clock output to stabilize. The oscillator is implemented on a single, monolithic integrated circuit.

Superharmonic injection locked oscillators as low power frequency dividers

Abstract: Superharmonic injection locking is investigated in a new theoretical approach. Low power frequency dividers are designed using injection locked oscillators with cascode transistors. The Rockwell 0.5 /spl mu/m CMOS process is used to design a 3 mW injection locked frequency divider in the 1800 MHz frequency range. A 200 MHz maximum locking range is achieved in simulations. 2SC3302 Toshiba NPN transistors are also used to build a 1.75 mW injection locked frequency divider in the 800 MHz frequency range to verify the theory.

Single-mode operation of a laser-diode array with frequency-selective phase-conjugate feedback.

Abstract: A new technique for single-mode operation of laser-diode arrays is presented A gain-guided GaAlAs laser diode array is coupled to an external frequency-selective phase-conjugate feedback system that contains a photorefractive barium titanate crystal, a Fabry–Perot etalon, and a spatial filter The etalon is the key component, and it forces the array, which has low spatial and spectral coherence when it runs freely, to oscillate in a single spatial and a single longitudinal mode At a drive current of two times the threshold current, the far-field pattern is reduced to only 14 times the diffraction limit, the spectral bandwidth is less than 002??nm, and the coherence length is increased by a factor of 70 The technique has general validity and can be applied to various other multimode laser systems

Observation of two distinct phase states in a self-phase-locked type II phase-matched optical parametric oscillator

Abstract: We demonstrate self-phase locking in a type II phase-matched optical parametric oscillator by mutual injection locking. An intracavity quarter-wave plate provides polarization mixing between the orthogonally polarized signal and idler that induces signal–idler self-phase locking when their frequency difference is within the capture range. We observed two distinct phase states that differ in their oscillator thresholds and their signal–idler phase differences, in good agreement with theory.

Experimental investigation of injection locking of fundamental and subharmonic frequency-modulated active mode-locked laser diodes

Abstract: Narrow linewidth and stabilized light injection is employed to reduce the phase noise and stabilize the frequencies of individual teeth of an active mode-locked laser diode (ML-LD) which is modulated by both fundamental and subharmonic frequencies of the cavity free-spectral range (FSR). We demonstrate accurate frequency control of the ML-LD using an injection seed light with linewidth of less than 100 kHz and frequency of exactly 193.1 THz; the light is generated by offset-locking to an absorption line of H/sup 13/C/sup 15/N. The teeth of the injection-locked ML-LD are anchored at 193.1 THz and are generated with 25- or 12.5-GHz sparing at the fundamental or subharmonic modulations, respectively, The teeth also have the linewidth of less than 100 kHz and the absolute frequency accuracy of better than 10 MHz. These values are the same as those of the injection seed light. The residual phase noise of the injection-locked ML-LD, estimated from the self-heterodyne spectrum, is less than 1 kHz at 20 dB down.

Performance of active antenna oscillator arrays under modulation for communication systems

Abstract: Active antenna oscillator arrays have been considered in millimetre-wave communication systems to increase power levels for low cost radio modules, and in radar systems for high power generation. In this paper, the authors have investigated the performance of active antenna oscillator arrays, particularly the data-rate limitations, the modulation effects on the radiation pattern, and the bit error rate performance of these arrays, in practical applications. Also, a closed-form solution for the phase dynamics of a single injection-locked oscillator has been derived.

Suppression of second harmonic distortion in directly modulated distributed feedback lasers by external light injection

Abstract: The suppression of second harmonic distortion in directly modulated semiconductor distributed feedback lasers by optical injection locking has been experimentally demonstrated. Reduction of second harmonic distortion by more than 10 dB has been observed over a wide range of bias currents and modulation frequencies.

Apparatus for and method of synchronising oscillators within a data communication system

Abstract: A method and apparatus is provided for locking a local oscillator to a reference oscillator. The reference oscillator is arranged to transmit a signal containing two reference pilot tones in a signal sideband. The apparatus samples the received signal and makes a frequency shifted copy where the shift is equal to the expected separation between the reference tones. The non-shifted and shifted signals are then combined in the frequency domain to constructively reinforce one of the reference pilot tones which is then searched for. Once the tone has been identified, a correction to the local oscillator frequency is calculated. The apparatus may be of particular use in a radio telemetry system in which it is important that the frequency of the local oscillators in the transmitters and receivers are very accurately matched to each other and where, in order to reduce interference, all the clocks used in the system are locked to a master clock.

Phase noise of a resonant-tunneling relaxation oscillator

Abstract: Experimental results are presented for the phase noise of a relaxation oscillator consisting of a resonant-tunneling diode in series connection with a transmission line, one end of which is shorted. Unlike constant-wave negative-resistance oscillators, the resonant-tunneling relaxation oscillator (RTRO) emits a sequence of sharp current pulses that are mode locked to the fundamental mode of the cavity formed by the short-circuited transmission line. The phase noise in the RTRO was investigated with and without injection locking by a weak sinusoidal source. Injection-locking gain of 51 dB was measured for fundamental injection locking. Subharmonic injection locking was demonstrated out to the 12th subharmonic. Also, timing jitter as low as 200 fs was measured for an RTRO that emitted ∼ 30 ps pulses at a repetition rate of 1.1 GHz.

A method for generation of optical FM signal through injection locking

Abstract: This paper proposes a scheme for the generation of optical frequency modulation (FM) signals through direct modulation and injection locking of semiconductor lasers. The method is simple and effective. The amplitude modulation of the AM-FM optical carrier generated through direct modulation can be drastically reduced by an injection-locked semiconductor laser. For this purpose, the AM limiting property of the injection-locked semiconductor laser has been investigated theoretically in detail. The FM index and the second harmonic distortion of the resulting FM signal at the output of the AM limiter has also been calculated.

Subharmonically injection locked 94 GHz MMIC HEMT oscillator using coplanar technology

Abstract: A coplanar subharmonically injection locked VCO for 94 GHz with a tuning range of 4.5 GHz was developed, using 0.15 /spl mu/m AlGaAs-InGaAs-GaAs PM-HEMTs. A phase noise of -71 dBc/Hz at 1 MHz offset from the carrier was measured for the unlocked VCO. Using 3/sup rd/ subharmonic injection locking, a phase noise of -106 dBc/Hz at 1 MHz offset (-91 dBc/Hz at 100 KHz offset) for the locked VCO with a locking range of 1 GHz was achieved.

Noise control of a master harmonic oscillator coupled to a set of satellite harmonic oscillators

Abstract: The overall gain is defined as the ratio of the stored energy in the isolated master harmonic oscillator to that in the coupled one. This gain is composed of two distinct factors: The first factor, the external input power gain, relates to the ratio of the external input power into the isolated master harmonic oscillator to that into the coupled one. The second factor, the loss factor gain, relates to the ratio of the loss factor of the coupled master harmonic oscillator to that of the isolated master harmonic oscillator. Both loss factors are in reference to the stored energy in the master harmonic oscillator only. It has been customary to assume the first factor to be unity and, thus the overall gain and the loss factor gain have been assumed to be identical. It is argued here that often this assumption is not valid. Therefore, noise control measures that are based on this assumption may have been wrongly evaluated. A few examples that illustrate the disparity between the overall gain and the loss factor gain are cited in this paper.

A compact injection-locked Nd:YAG laser for gravitational wave detection

Abstract: We have designed and characterized a diode-pumped injection-locked Nd:YAG laser suitable for precision metrology. The laser uses a simple side-pumped laser architecture and is compact, efficient, stable, and scalable. The frequency stability of the injection-locked slave laser is shown to be limited by the monolithic master oscillator and its intensity noise is 4/spl times/10/sup -6/ Hz/sup -1/2/ at 1 kHz.

Demonstration of an analog fiber-optic link employing a directly modulated semiconductor laser with external light injection

Abstract: We demonstrate an analog fiber-optic link employing a directly modulated semiconductor distributed-feedback (DFB) laser under optical injection locking. The results show that injection locking can significantly improve performances of analog fiber-optic systems at frequencies considerably beyond the bandwidth of free-running semiconductor lasers.

Synchronous carrier recovery circuit and injection locked oscillator

Abstract: A simple carrier recovery circuit capable of accurately detecting and synchronizing an incoming carrier frequency without the use of a phase locked loop (PLL) is provided. Instead of a PLL, the carrier recovery circuit includes an injection locked oscillator. The injection locked oscillator includes an input for connection to the received modulated signal. The gain of an inverter stage of a amplifier in the injection locked oscillator is modulated by the received modulated signal using an injection transistor connected between the power source and the output of the inverter stage. The gate of the injection transistor receives a signal corresponding to the received modulated signal.

Observation of optical bistability in a GaAlAs semiconductor laser under intermodal injection locking.

Abstract: Experimental observation of optical bistability in a semiconductor laser under intermodal injection locking is reported for what is believed to be the first time. It is seen that a change in injection power of several microwatts or master laser frequency detuning of a few hundred megahertz can induce a change of as much as several hundred gigahertz in the lasing frequency of the slave laser. The results are in qualitative agreement with theoretical predictions.

Mutual injection locking between two DFB LDs which lase at frequencies separated by one Fabry-Perot mode spacing

Abstract: A new type of mutual injection locking between two distributed feedback laser diodes (DFB LDs) of the same structure is proposed and experimentally confirmed. The lasing frequencies and the spectra are locked and stabilised when the lasing frequency difference of the two LDs was equal to one Fabry-Perot mode spacing.

Optical amplifier and laser light generating apparatus

Abstract: In order to prevent two pumping lasers (54,56) from overlapping in oscillation wavelength due to injection locking by return light in a apparatus using double pumping lasers, the apparatus is configured to enter optical outputs from the pumping lasers into a fiber grating (60) using a PANDA fiber through a half mirror and to reflect them back to the pumping lasers. The fiber grating has two main axes whose reflective wavelengths lambda 1, lambda 2 are different only by approximately 0.4 nm, and locks the laser oscillation wavelength of one of the pumping lasers to the wavelength lambda 1 and the laser oscillation wavelength of the other pumping laser to the wavelength lambda 2. Light passing through the fiber grating is entered into erbium-doped optical fibers (48U,48D) through a 3 dB coupler and WDM couplers (50U,50D) to excite the erbium-doped optical fibers.

Chaos in coupled semiconductor lasers with an electronic delayed feedback caused by injection locking

Abstract: We proposed and demonstrated a novel hybrid chaotic system using injection locking in coupled laser diodes. This system consists of double laser diodes, a Fabry-Perot etalon, and an electronic delay feedback. The bifurcation diagram route to chaos and variation of the temporal waveform of the output light intensity were observed relative to the feedback gain. Some peculiar bifurcation properties, which were caused by a strong nonlinear effect due to injection locking, were observed. We also analyzed the experimental results using Van der Pole equations coupled with rate equations. The results of theoretical analysis showed good agreement with the experimental results.

Laser phase-locking techniques for LISA: Experimental status

Abstract: Phase-locking of a slave laser to weak incoming light is an essential ingredient of the laser transponders to be used in LISA. Here we report on an experiment to evaluate such a weak-light phase-locking scheme, in which two independent diode-pumped Nd:YAG non-planar ring oscillators are locked together with a 15 MHz frequency offset. With a weak-light intensity of 17 nW we observe close to shot-noise limited performance of the phase locking system over a frequency range from 800 Hz down to 10 Hz. Excess noise is observed at lower frequencies—reaching two orders of magnitude above the shot-noise limit at 10−4 Hz—most probably due to seismic and temperature effects on the optical layout. The level of the unlocked relative phase fluctuations is observed to be anomalously low, compared with that deduced from separate experiments in which one of the lasers was frequency stabilized to a reference cavity [1,2]. The possibility of partial injection locking of the lasers due to leakage light cannot be excluded. Caution in interpretation of the results is therefore warranted.

Nonlinear travelling pulses in laser injection locking

Abstract: A complex order parameter description of laser injection locking in homogeneously broadened class-A ring lasers is presented starting from the multimode Maxwell-Bloch laser equations in the case of a long cavity. Far above the lasing threshold and in the case of a weak injected signal tuned to a mode-pulled laser resonance, a phase equation is derived in the form of an overdamped sine-Gordon equation, which reveals the existence of stable travelling soliton-like pulse solutions to the laser equations. When going close to the lasing threshold, the existence of a Lyapunov functional for the laser dynamics is proposed on the basis of an amplitude equation, which is derived from the laser equations by use of asymptotic techniques. Such an analysis indicates metastability of the locked solution and a spontaneous transition to travelling soliton-like pulses. This transition bears a close analogy with commensurate-incommensurate transitions found in many solid-state and hydrodynamic systems.