Continuous Wavelength Tuning Range Research Articles

Output Characteristics of External-Cavity Mode-Hop-Free Tunable Laser Source in C+L Band

Tunable laser sources with a wide wavelength tuning range, mode-hop-free (MHF) operation, and high spectral purity are essential for applications such as high-resolution spectroscopy, coherent detection, and intelligent fiber sensing. In this paper, we present a wide-range tunable laser source that operates without mode hopping, based on external cavity feedback using a semiconductor gain chip as the laser gain medium. The wavelength, power, and spectral characteristics of the laser are experimentally measured. A wide MHF continuous wavelength tuning range from 1480 nm to 1620 nm with a side-mode suppression ratio of more than 61.65 dB is achieved. An output optical power of more than 11.14 dBm with good power stability can also be realized in the full C+L band. This proposed external-cavity tunable laser source features a narrow intrinsic linewidth and MHF tunable radiation with a maximum sweep speed of 200 nm/s, enabling practical applications such as high-resolution vector spectrum analysis.

Manipulating the Spectral-Temporal Characteristics of Multi-GHz Ultrashort Pulses by Leveraging the Nonlinear Phase Modulation and CW-Seeded Four-Wave Mixing

Ultrashort pulse fiber lasers with multi-GHz repetition rates have recently attracted significant attention in various fields. However, the parameter tunability of multi-GHz ultrashort pulse fiber lasers is inherently limited by their miniaturized design, particularly the central wavelength and transform-limited pulsewidth. To this end, here we propose a method for externally manipulating the spectral-temporal characteristics of multi-GHz ultrashort pulses by exploring continuous-wave (CW)-seeded four-wave mixing (FWM) and nonlinear phase modulation (NPM) driven by miniaturized mode-locked fiber laser with a multi-GHz fundamental repetition rate. We first conduct a theoretical investigation on the picosecond-pulse-driven CW-seeded FWM, and then study the NPM for manipulating the spectral-temporal performance of multi-GHz ultrashort pulses, i.e., associated with the CW-seeded FWM for pulsewidth tunability. Then, we perform experiments to validate the theoretical findings, and a pulsewidth tuning range of 598 fs – 5.3 ps is achieved. Furthermore, a continuous wavelength tuning range from 1520 nm to 1550 nm is obtained. The experimental results show good agreement with the numerical simulation results. These efforts can provide a promising route to realize high-quality multi-GHz ultrashort pulses with flexible tunability of wavelength and pulsewidth through manipulating the spectral-temporal characteristics.

High-SMSR wavelength-swept laser with a CL-band mode-hopping free tuning range

A high side-mode suppression ratio external-cavity wavelength-swept laser system with a wide mode-hopping free tuning range is developed. The proposed wavelength-swept laser is based on a single-angled facet gain chip in a classical Littman-Metcalf external-cavity configuration using a blazed diffraction grating as the feedback element. The output power, side-mode suppression ratio, and tunable range of the external-cavity wavelength-swept laser system are experimentally measured. Wide mode-hopping-free continuous wavelength tuning range about 100 nm in CL-band with a side-mode suppression ratio of more than 65.64 dB are realized. An output optical power of more than 14.12 dBm over the entire tunable region can also be achieved. The proposed external-cavity wavelength-swept laser system allows simultaneously high side-mode suppression ratio and no mode-hopping tunable radiation, thus opening a door for practical applications such as optical modulation schemes.

Study on external cavity diode laser with a wide mode-hopping free tuning range

A wide mode-hopping free and narrow linewidth tunable laser diode source with a Littman-Metcalf arrangement based on a diffraction grating is presented. Several experiments are carried out to demonstrate the tuning characteristics and spectral linewidth of the proposed external-cavity diode laser source. A wide no mode-hopping continuous wavelength tuning range about 59.13 nm in ultra-C-band with a narrow spectral linewidth of less than 100 kHz is obtained. An optical signal to noise ratio of more than 65 dB and an output power more than 14.8 dBm over the whole tuning range can also be realized in a long-term free running condition. The proposed tunable laser allows simultaneously mode-hopping free and narrow linewidth tunable radiation, thus opening a door for practical application such as coherent detection.

Tunable Laser via High-Density Integration of DFB Lasers With High Precision Wavelength Spacings

Fast optical switches have the potential of lowering the cost, power, and latency of today’s data-center networks. The on-off switching of DFB lasers in arrays is poised to provide extremely fast switching because the on-off time of a DFB laser is the level of sub-nanosecond. However, the key of the DFB laser array based tunable laser lies in the high precision control of the lasing wavelength. In this letter, we proposed and experimentally demonstrated a tunable laser by integrating 16 DFB lasers based on the reconstruction-equivalent-chirp (REC) technique. Without using the conventional e-beam lithography, an equivalent <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda $ </tex-math></inline-formula> /4 phase-shift is fabricated in each DFB laser to ensure the single-longitudinal-mode (SLM) yield. Moreover, high precise wavelength spacing is realized. Wavelength deviations of 89.3% DFB lasers are within ±0.2 nm. The output power of all the channels is above 7 mW, and the relative intensity noise is below −130 dB/Hz. By on-off switching the lasers, sixteen channels with 2.4-nm spacing can be fast switched. The switching time between any two channels is less than 50 ns. In addition, a wide-band continuous wavelength tuning range of 38.4 nm can be obtained with a small temperature variation of 18 °C. Owing to the REC technique, the tunable laser via high-density integration of DFB lasers is demonstrated with simple fabrication, high SLM yield, and high wavelength precision, which opens up a path for wide-band and especially fast tunable lasers.

Enhanced Tuning Performance of In-Series REC-DFB Laser Array

In this study, a tunable in-series multi-wavelength distributed feedback laser array (DFB-MLA) based on reconstruction-equivalent-chirp (REC) technique with simple wavelength tuning scheme is presented and experimentally demonstrated. Unlike traditional DFB laser tuned by thermal-electric cooler (TEC), the proposed laser tuned by injection current can realize faster wavelength-tuning and reduce TEC power consumption. By comparing the thermal influence of different structures of heatsink blocks, several optimized block structures are selected for appropriate thermal conductivity and controllable heat dissipation, resulting in a broad and continuous wavelength tuning range. The proposed in-series DFB-MLA on optimized heatsink achieves better tuning performance with a wavelength tuning range of ~2.4 nm per channel from 40 to 120 mA and stable output power of over 20 mW compared to the laser mounted on the standard heatsink block with the tuning range of 1.4 nm per channel. Furthermore, the tunable laser keeps good single-mode stability, with a side mode suppressing ratio (SMSR) of over 40 dB. Thus, this study provides a new perspective for designing a low-cost continuous tunable semiconductor laser with a simple tuning mechanism in the future.

All-fiber narrow-linewidth ring laser with continuous and large tuning range based on microsphere resonator and fiber Bragg grating.

We demonstrate an all-fiber single-longitudinal-mode (SLM) narrow-linewidth ring laser stabilized by a microsphere resonator and fiber Bragg gratings (FBGs) with a large continuous wavelength tuning range from 1540 nm to 1570 nm. In the experiment, stable lasing with a linewidth smaller than 5 kHz was obtained. The laser wavelength was linearly and continuously tuned in the range of 0.15 nm by increasing the pump power and discretely tuning with a step of 0.1 nm by stress-controlled FBGs. The tuning range of the proposed laser configuration was determined by the FBG, and the SLM state was ensured by the coupling between the few-mode tapered fiber and the microsphere, which was simpler in alignment than other ring lasers utilizing microresonators.

Over 5-W Passively Q-Switched Mid-Infrared Fiber Laser With a Wide Continuous Wavelength Tuning Range

We report efficient high-average-power, high-energy passively Q-switched operation of an Er3+-doped fluoride fiber laser at room temperature with wavelength-tunable resonator configuration utilizing a plane ruled grating for wavelength selection. The fiber laser produced stable Q-switched pulses with a maximum average output power of 5.16 W at 2811.7 nm and a maximum pulse energy of $27.7~\mu \text{J}$ at 2834.6 nm for 30.5-W launched pump power and could be tuned over a wavelength range of 90 nm from 2762.5 to 2852.5 nm, with > 4-W average power over the range of 76.1 nm. Our results present fivefold increase in output power over previously published values directly attained from ~3- $\mu \text{m}$ passively Q-switched fiber lasers and firmly establish a fiber laser as a compact, wavelength-tunable, multiwatt, tens of microjoules mid-infrared pulse source with large scope of both industrial and scientific applications.

III-V-on-silicon three-section DBR laser with over 12 nm continuous tuning range.

Device and tuning characteristics of a novel heterogeneously integrated III-V-on-silicon three-section distributed Bragg reflector (DBR) laser are presented. The laser exhibits a continuous wavelength tuning range of more than 12 nm. Thermal tuning is achieved through carrier injection in the passive tuning layer of a III-V tunable twin-guide membrane. Single-mode lasing with a side-mode suppression ratio larger than 30 dB over the entire tuning range is realized through implementation of a sidewall-corrugated silicon-on-insulator waveguide grating as one of the laser mirrors.

Mode coupling in hybrid square-rectangular lasers for single mode operation

Mode coupling between a square microcavity and a Fabry-Pérot (FP) cavity is proposed and demonstrated for realizing single mode lasers. The modulations of the mode Q factor as simulation results are observed and single mode operation is obtained with a side mode suppression ratio of 46 dB and a single mode fiber coupling loss of 3.2 dB for an AlGaInAs/InP hybrid laser as a 300-μm-length and 1.5-μm-wide FP cavity connected to a vertex of a 10-μm-side square microcavity. Furthermore, tunable single mode operation is demonstrated with a continuous wavelength tuning range over 10 nm. The simple hybrid structure may shed light on practical applications of whispering-gallery mode microcavities in large-scale photonic integrated circuits and optical communication and interconnection.

Spectroscopic properties of UV active medium Ce3+:LiSr0.8Ca0.2AlF6

The aim of this work is phase composition and near UV spectroscopic studies of UV active media in fluoride crystals with colquiriite structure, such as Ce3+:LiSr0.8Ca0.2AlF6. Colquiriite structure mixed crystals show higher segregation coefficient of Ce3+ activator ions than common LiCaAlF6 hosts. An important result is based on the fact that this enhancement was achieved for two types of Ce3+ centers in a multisite Ce:LiSr0.8Ca0.2AlF6 system. Thus, it provides a higher gain coefficient for the 5d–4f transitions of Ce3+ ions and it spans a wider continuous wavelength tuning range between 280 and 320nm for tunable Ce:LiSr0.8Ca0.2AlF6 laser systems.

Thin-disk Raman laser operation of Yb:YVO4/YVO4 around 1120 nm

We present diode-pumped Yb:YVO4/YVO4 thin-disk Raman laser operation around 1120 nm. The thin-disk crystals, Yb:YVO4, and the Raman crystal, YVO4, are cut with 250 μm and 20 mm, respectively. In multimode configurations, up to 0.91 W of Raman laser output power and a maximum slope efficiency of 10% are demonstrated corresponding to a pump power of 10 W. A continuous wavelength tuning range of 54 nm from 1096 to 1150 nm with a maximum output power of 320 mW at 1126 nm is confirmed.

A Matrix-Grating Equivalent Phase Shifted Laser Array With 25-nm Wavelength Tuning Range

A matrix-grating equivalent phase shifted (MG-EPS) eight-wavelength distributed-feedback (DFB) semiconductor laser array is experimentally demonstrated. This device contains eight index-coupled DFB semiconductor laser diodes with a V-junction combiner, which have wavelength channel spacing of ~3.37 nm, with quarter-wave EPS structures. 25-nm continuous wavelength tuning range is achieved by changing the temperature, with side mode suppression ratios >42 dB within the entire tuning range. Meanwhile, because of the quarter-wave equivalent phase shift structures, no mode-hopping problems have been observed and good single-longitudinal mode operation is achieved. This device is promising for cost-effective applications of wavelength division multiplexing systems.

Yb:YAl_3(BO_3)_4 as gain material in thin-disk oscillators: demonstration of 109 W of IR output power

The first demonstration of an Yb:YAl3(BO3)4 thin-disk laser is reported. An output power of 109 W with an optical efficiency of 50.2% was achieved in multimode CW-operation which is to the best of our knowledge a significant record performance compared to previous reports on CW-lasers with this material. At a lower power level of 19.3 W the material proved its suitability for efficient operation with an optical efficiency of 60.4%. In fundamental-mode operation the extracted output power was 10.4 W with an optical efficiency of 44.5% and a beam propagation factor M(2) = 1.39. The broad emission bandwidth of the material was confirmed by measuring a continuous wavelength tuning range from 1001 to 1053 nm with a maximum output power of 36 W at 1040 nm.

Electro-thermal tuning of MEMS VCSEL with giant wavelength-temperature dependence

We demonstrate the electro-thermal tuning of a MEMS VCSEL with a thermally actuated SiO2/semiconductor cantilever. The wavelength-temperature dependence of the MEMS VCSEL could be increased as large as 0.46nm/K, which is 6 times larger than that of conventional single-mode lasers. A micro-heater is integrated nearby the cantilever structure. A continuous wavelength tuning range of 4.7nm is obtained with heating power of 29mW.

Ultra-rapid dispersion measurement in optical fibers

We present a novel method to measure the chromatic dispersion of fibers with lengths of several kilometers. The technique is based on a rapidly swept Fourier domain mode locked laser driven at 50kHz repetition rate. Amplitude modulation with 400MHz and phase analysis yield the dispersion values over a 130nm continuous wavelength tuning range covering C and L band. The high acquisition speed of 10micros for individual wavelength-resolved traces Deltat(lambda) can reduce effects caused by thermal drift and acoustic vibrations. It enables real-time monitoring with update rates >100Hz even when averaging several hundred acquisitions for improved accuracy.

Studies on strain and temperature characteristics of a slanted multimode fiber Bragg grating and its application in multiwavelength fiber Raman ring laser

Detailed strain and temperature characteristics of a 2/spl deg/ slanted multimode fiber Bragg grating (MFBG) are developed theoretically and observed experimentally. Results show that the strain and temperature sensitivities are almost the same for different transmission dips of the 2/spl deg/ slanted MFBG. Utilizing two characteristics of the 2/spl deg/ slanted MFBG, namely 1) resonant wavelength intensities strongly affected by excited mode propagating before the grating and 2) uniform strain sensitivities of different resonant wavelengths, a switchable and tunable multiwavelength fiber Raman ring laser is realized. The configuration is simple and multipurpose. Results show that the laser can generate single-, dual-, three-, four-, and five-wavelength lasing by switching between each operation if a mode scrambler (MS) that is inserted in front of the slanted MFBG is adjusted; furthermore, a 4.2-nm continuous wavelength-tuning range is achieved by straining the slanted MFBG when the MS is fixed.

Cascaded strongly gain-coupled (SGC) DFB lasers with 15-nm continuous-wavelength tuning

More than 15 nm of continuous wavelength tuning range has been obtained by means of temperature tuning and current setting in three-section grating-cascaded strongly gain-coupled distributed-feedback lasers. Within the entire wavelength tuning range, a sidemode-suppression ratio beyond 50 dB, a linewidth of less than 10 MHz, and a fiber-coupled output power of more than 5 dBm were achieved.

Wavelength-tunable actively mode-locked erbium-doped fiber ring laser using a distributed feedback semiconductor laser as mode locker and tunable filter

A wavelength-tunable actively mode-locked erbium fiber ring laser was demonstrated using a distributed feedback semiconductor laser as an intensity mode locker and a tunable optical filter. Very stable optical pulse trains at gigabit repetition rates were generated using harmonica mode locking. The supermode noise was suppressed to 60 dB below the signal level and the root-mean-square timing jitter (0.45 kHz–1 MHz) was found to be about 1% of the pulse duration. A continuous wavelength tuning range of 1.8 nm was achieved by changing the semiconductor laser temperature from 11.4 to 30 °C.

Matrix-grating strongly gain-coupled (MC-SGC) DFB lasers with 34-nm continuous wavelength tuning range

A matrix-grating strongly gain-coupled (MG-SGC) distributed-feedback laser structure has been demonstrated to exhibit a continuous wavelength tuning range of about 34 nm. A simple tuning mechanism was employed, and a sidemode-suppression-ratio of beyond 50 dB within the entire tuning range was achieved. This device can be potentially used in dense wavelength-division-multiplexed systems for cost effective applications.