Wide continuous tuning LDs using hybrid resonant optical reflector

The wavelength tuning and intensity modulation characteristics are presented for three types of twin-guide (TG) lasers entirely fabricated by metalorganic vapour phase epitaxy (MOVPE). A wide continuous tuning range of 5.3 nm is obtained for the tunable twin-guide (TTG) laser. The TTG lasers, however, have the drawbacks of output power reduction and spectral linewidth broadening during tuning. A new type of tunable laser, the complementary twin-active-guide (CTAG) laser, is proposed, and its tuning characteristics are presented for the first time. A wide continuous tuning range over 4 nm is obtained, although the thermal effect is more dominant than carrier effects. The CTAG structure enables suppression of the spectral linewidth broadening induced by the injected carrier recombination shot noise (IRSN) during tuning. The characteristics of the TG lasers modulated by reverse bias are presented, and the possibility of using these TG lasers for wavelength tuning is studied.

We present the first photoacoustic spectrometer for gas sensing employing both the fundamental and the frequency-doubled radiation of a continuously tunable high-pressure CO2 laser with room temperature operation. A quasi-phase-matched diffusion-bonded GaAs crystal is used in the system for second-harmonic generation. A pulsed photoacoustic detection scheme with a non-resonant cell, equipped with an 80-microphone array, is employed. The wide continuous tuning range in the fundamental (9.2–10.7 μm) and the frequency-doubled (4.6–5.35 μm) regimes, together with the narrow linewidth of 540 MHz (0.018 cm-1) for the 10-μm region and of 1050 MHz (0.0315 cm-1) for the 5-μm region, allow the measurement of gas mixtures, individual species and isotope discrimination. This is illustrated with measurements on NO and CO2. The measured isotope ratio 15NO/14NO=(3.58±0.55)×10-3 agrees well with the literature (3.700×10-3) and demonstrates the good selectivity of the system.

A new topology for a tunable microwave photonic notch filter, which achieves a wide and continuous tuning range of FSR/2, is presented. The novel principle of tuning is based on changing optical variable attenuators only; consequently, a fixed wavelength laser can be used as the optical source. Experimental filter tuning results demonstrate a wide fractional tuning range of 50%, continuous tuning capability, and a notch filter shape that does not change as it is tuned, in very good agreement with predictions.

A study was made of an anomalously wide continuous tuning range of the emission frequency of an injection laser with an external resonator operating under conditions of self-stabilized single-frequency lasing. The self-stabilization was observed for a large number of lasers with different structures, both at room and liquid nitrogen temperatures. A study was made of the influence of the power, degree of coupling with the external part of the laser, resonator length, and pass band of a selective component on the continuous tuning range. In the self-stabilization regime this range was 10-30 times greater than the corresponding range for a laser operating under conventional conditions. A nontrivial feature of hopping between longitudinal laser modes at the limit of the tuning range was observed. This feature was explained on the basis of a theory proposed by Bogatov, Eliseev, Okhotnikov, Rakhval'skii, and Khairetdinov [Sov. J. Quantum Electron. 13, 1221 (1983)].

This paper presents a novel circuit topology of a tunable high-pass filter with a quasi-elliptic function response. A detailed theoretical analysis for the performance operating mechanism is demonstrated. With the assistance of mutually inductive coupling introduced, a pair of tunable transmission zeros (TZs) is synthesized at the lower passband edges and significantly improves the filter selectivity. Experiments are carried out by using the liquid crystal polymer bonded multilayer printed circuit board technology to validate the design. It is found that the implemented filter achieves a wide continuous tuning range covering from 1030 to 2150 MHz with low insertion loss, and which indeed are limited by the Schottky diodes used. It is also illustrated that two measured TZs are properly controlled at each tuning stage, which not only offers a sharp cutoff frequency response with a rejection level greater than 22 dB, but also provides an approximately unchanged response shape. Good agreement between the measured and simulated results can finally be observed.

All-solid-state single-frequency continuous-wave (CW) lasers have been applied in many fields of scientific research owing to their intrinsic advantages of high beam quality, low noise, narrow linewidth, and high coherence. In atom-based applications, single-frequency lasers should also be continuously tuned to precisely match their wavelengths with the transition lines of the corresponding atoms. Continuous frequency tuning of the laser is mainly achieved by continuously scanning the laser cavity length after the intracavity tuning element etalon is locked to an oscillating laser mode. However, the modulation signals necessary in current etalon locking systems increase the noise of the continuously tunable lasers and in some respects limit their applications in Frontier scientific research. Moreover, the obtained continuous frequency tuning range with the etalon locking technique is restricted by the free spectrum range of the adopted etalon. In this paper, we systematically summarize recent progress of the continuously tunable single-frequency CW lasers based on intracavity locked etalon, including the advanced etalon locking techniques and the tuning range expansion approach. As a result, the low noise and high stable all-solid-state single-frequency CW tunable lasers are successfully developed.

We have realized a laser platform based on GaAs diode lasers that allows for an operation in mobile exper-imental setups in harsh environments, such as on sounding rockets. The platform comes in two versions: a master-oscillator-power-amplifier and an extended cavity diode laser. Our very robust micro-optical bench has a footprint of 80 x 25 mm2. It strictly omits any movable parts. Master-oscillator-power-amplifier systems based on distributed feedback master oscillators for 767 nm and 780 nm narrow linewidth emission have been implemented by now. A continuous wave optical output power of > 1 W with a power conversion efficiency of > 25% could be achieved. The continuous tuning range of these lasers is on the order of 100 GHz, the linewidth at 10 μs is about 1 MHz. For applications demanding a narrower linewidth we have developed an extended cavity diode laser that achieves a linewidth of 100 kHz at 10 μs. These lasers achieve a continuous spectral tuning range of about 50 GHz and an continuous wave optical power up to 30 mW. The modules have been successfully vibration tested up to 29 gRMS along all three axes and passed 1500 g shocks, again along all 3 axes. Both, master-oscillator-power-amplifiers and extended cavity diode lasers, have been employed in sounding rocket experiments.

Using a transfer matrix method, the results of analysis of the spontaneous emission spectrum of a three-section phase-controlled distributed feedback (DFB) laser for implementing a continuously tunable optical filter are presented. The influence of various parameters-net field gain, coupling coefficient, phase shift and reflection coefficients-on the spectrum behavior are studied theoretically. The main-to subtransmission peak magnitude ratio can be chosen while varying the frequency, which demonstrates the tunability of the three-section phase-controlled DFB laser filter. Analysis shows that a three-section DFB laser (a passive phase shift control region between two DFB structures) presents a single-mode spontaneous emission spectrum operating over a wide continuous tuning range of less than 1 nm.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A wide continuous tuning range of 6.7 nm was achieved with a tunable distributed amplification distributed feedback (TDA-DFB) laser by employing an asymmetric periodic structure. A 36-channel operation with a 100 GHz grid was realised for an array of six TDA-DFB lasers integrated monolithically with a coupler and an amplifier.

Narrow linewidth fiber lasers are intensively studied during these years, for their wide use in coherent optical communication, optical fiber sensing, high-precision spectroscopy and many other industrial and military applications. A usual technique to suppress linewidth is narrow band filtering in the resonating structure of the laser. However, it is hard in fabrication for a tradition optical filter to achieve an ultra narrow pass band such as kilo-Hertz. In this paper, the parallel feedback structure is proposed and experimentally studied. A fiber laser with ultra narrow linewidth (15Hz detected) is achieved in laboratory, basing on the parallel feedback mechanism in a fiber ring cavity. In multimode fiber, each transverse mode has a different propagation constant. Equivalently, when a light beam propagates form single mode fiber to multimode fiber, it will split into a few parallel light paths with different propagation constants. The parallel feedback structure of a fiber ring laser is carried out by introducing one or more pieces of multi-mode fiber into its resonant cavity. Lasing light in the cavity must fit the restrictions of all light paths, thus linewidth of the laser output is suppressed. Ultra narrow linewidth can be achieved by carefully adjusting the amount and length of multi-mode fiber pieces. The narrowest linewidth achieved in laboratory is 15Hz detected by a delayed self-heterodyne interferometer with a 100km fiber delay line. In this work, we focus on pressuring linewidth, and mechanism of selecting and stabilizing mode isn't employed. Therefore, the narrow linewidth fiber laser isn't single-longitudinal-mode (SLM). A similar ring laser structure with bidirectional output is also experimental implemented, achieving a bandwidth of the same order. The bidirectional ring laser is the basic component of a laser gyroscope, and its linewidth is one key limiting factor of the gyroscope accuracy. This narrow linewidth bidirectional ring laser is a good candidate for accurate fiber laser gyroscope. Theory analysis and experiment shows the fiber ring laser based on parallel feedback structure is robust against environmental disturbance, achieving high stability and ultra narrow linewidth. The parallel feedback mechanism in optical circuits can also used in other applications demanding narrow linewidth.

ABSTRACTThe voltage‐controlled oscillator (VCO) with a wide tuning range and low phase noise is extensively employed in domains such as 5G, 6G, and satellite communication. This article commences with the phase noise model to conduct an analysis of the multicore VCO. Subsequently, the mode‐switching technology is elucidated. On this foundation, an X‐shaped compact equalizing on‐chip transformer design based on the inductor sharing technique is proposed. The transformer with three modes is devised to enhance the output frequency range of the VCO. Distinct from the traditional capacitive coupling, the alteration of the effective inductance value is accomplished through the coupling between the inductors to complete the regulation of the oscillation frequency range. The proposed VCO architecture, fabricated using a 40‐nm process, demonstrates a 52.3% continuous frequency tuning range, spanning from 24.7 to 42.2 GHz, as verified through post‐simulation. When the bias is at a 10 MHz, the phase noise varies within the range of −123 to −132 dBc/Hz while FoM and FoMT respectively fluctuate from 177 to 193 dBc/Hz and 191 to 208 dBc/Hz. Both phase noise and FoM are improved, with a minimal chip area of only 0.057 mm2.

This letter develops a method that is able to optimize the grating pivot position to obtain maximum continuous tuning range for a Littrow laser, and also verifies the method by implementation of a single-chip integrated laser using the microelectromechanical systems (MEMS) technology. The laser consists of a semiconductor gain chip, a microlens, and a MEMS blazed grating arranged in the Littrow configuration. The laser is integrated onto a single silicon chip while maintaining the ability of continuous tuning in a large range. It has a compact size of 2.0mm×1.5mm×0.6mm, and has obtained a tuning range of 30.3nm with a resolution of 0.03nm∕V2, a maximum power of 0.4dBm and a side mode suppression ratio of 26dB. Other merits include fast tuning speed, improved mechanical/wavelength stability, batch fabrication, and low cost.

We propose a solution for reconfigurable wired-wireless converged networks with high data rates, based on directly modulated tunable vertical cavity surface emitting lasers (VCSEL). Wired-wireless converged networks require simple and low-cost solutions for the generation of the UWB signal in the optical domain. Direct modulation of VCSEL in combination with optical filtering enable a low-cost generation of ultra-wideband (UWB) pulses. VCSEL typically show large direct modulation bandwidths 10 GBit/s due to their short cavity related short photon lifetime. Another advantage of the short cavity is its inherent large free spectral range (FSR) which enables ultra wide continuous wavelength tuning.

The frequency tuning of a surface micromachined film bulk acoustic resonator (FBAR), which integrates the tunable series capacitor and the piezoelectric resonating layer, had been demonstrated in previous publications. In the proposed structure, a movable piezoelectric cantilever is suspended above a bottom electrode. The air gap between the cantilever and the bottom electrode functions both as a tunable capacitor and an acoustic isolation. However, in case of electrostatic actuation, continuous tuning is limited in the range before the pull-in of the cantilever and is very small in prior art. In this paper, an improved design is suggested. By changing the the effective area ratio between the tunable capacitor and the piezoelectric resonating film, a larger continuous tuning range of 24.5MHz (0.39%) at a resonating frequncy of about 6.3GHz is realized. I. INTRODUCTION Film bulk acoustic resonators (FBARs) are microma- chined versions of the conventional piezoelectric resonators such as quartz crystals, with the advantages of small size, high frequency capability, high quality factor and CMOS- compatibility. In order to compensate for drifts from different origins such as aging, temperature change and fabricational inhomogeneities, a small range of frequency tuning is desired. Frequency tuning of a surface micromachined FBAR by electrostatic actuation has been designed and demonstrated in earlier works (1), (2), in which a vertically movable piezoelectric layer with a top electrode is suspended above a bottom electrode, as shown in Fig. 1. The air gap between the piezoelectric layer and the bottom electrode serves both as a tunable capacitor and as an acoustic isolation. Frequency tuning is realized by applying a DC voltage between the top and bottom electrode to electrostatically displace the suspended piezoelectric layer and thus change the air gap capacitance and the frequency response of the device. This design however only displays a very small continuous tuning range because of the pull-in of the cantilever by electrostatic actuation. In earlier works (2), only 1.9MHz (∼0.03% )o f continuous tuning was achieved before pull-in takes place. It is thus necessary to revise the design to meet the demand of a larger (> 0.2%) continuous tuning range. II. THE PRINCIPLE OF TUNING The electrical characteristics of an FBAR near its funda- mental mode of resonance can be approximated by a lumped- element circuit as shown in Fig. 2(a), in which the series RF signal+DC voltage

A mirror device for an external cavity diode laser is fabricated. To achieve a wide and continuous tuning range, mechanical linkage of two parallel rotation axes can rotate and translate the mirror, generating a virtual pivot point of the mirror motion. This mirror device is realized using a wafer-folding technique