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A frequency-stabilized narrow-linewidth external cavity diode laser (ECDL) at the wavelength of the R18 carbon dioxide (CO2) absorption line for space-borne CO2 detection LIDAR is reported. The ECDL module based on the fiber Bragg grating (FBG) is integrated in a compact butterfly package, emitting at the wavelength of 1572.02 nm and provides continuous tunability of 22 GHz. A polarization-maintaining all-fiber ring resonator is used as a transfer cavity to transfer the long-term stability of a metrological frequency reference at 1550.12 nm to the target wavelength. The combination of narrowing linewidth technique and frequency stability transfer technique enables lasing with an intrinsic Lorentzian linewidth of 15 kHz as well as a relative frequency stability on the order of $10^{-12}$ for averaging time from 1 to 1000 s (minimum of $2.1\times 10^{-12}$ at 2 s). [ABSTRACT FROM AUTHOR]

We present a continuously tunable single-frequency continuous wave (CW) Ti:Sapphire (Ti:S) laser with modulation-free-locked intracavity lithium niobate (LiNbO3) birefringent etalon (BE), which is implemented by detecting the polarization state variation of the reflected laser beam from the BE. After the BE is stably locked, the continuous frequency-scanning range up to 40 GHz is obtained within the tuning range of 300 nm while the resonator length of the Ti:S laser is continuously scanned. Because the modulation signal is unnecessary in the presented Ti:S laser system, the influences of the extra modulation signal on the intensity noise as well as the frequency noise of the laser are thoroughly eliminated and the modulation-noise-free continuously tunable single-frequency CW Ti:S laser is successfully attained. [ABSTRACT FROM AUTHOR]

Integrating photonics with CMOS electronics in silicon is essential to enable chip-scale, electronic-photonic systems that will revolutionize classical and quantum communication and computing systems. However, the lack of an on-silicon isolator, capable of blocking unwanted back reflections and ensuring the stable operation of the laser, precluded many previous demonstrations from providing single-chip solutions. For most optical systems employing a laser, magneto-optic isolators have been indispensable, but such isolators are incompatible with silicon. To stabilize on-chip lasers, reflections-cancellation circuits were proposed as a way to reduce the reflections going back to the laser. Yet, a stable laser against time-varying back reflections was never demonstrated. Here we demonstrate a stable quantum well-distributed feedback (QWDFB) laser against slowly time-varying reflections using a reflections-cancellation circuit (RCC) on a foundry-produced, silicon-photonic (SiP) chip. The optical spectrum and the relative intensity noise (RIN) of the laser when the RCC was running is comparable to when an isolator was used. By accurately locking the laser in a stable optical feedback regime, the RCC further enhances the QWDFB laser performance by reducing its linewidth by a factor of 100, down to 3 kHz. Both results are enabled using novel techniques in the design, calibration, tuning, and control of the proposed SiP RCC. The optical insertion loss of the RCC is less than 1.5 dB for reflections smaller than −20 dB and can yield isolation ranges of up to 64 dB. Our device paves the way towards the mass production of fully integrated, low-cost electronic-photonic silicon chips without attaching magneto-optic isolators between the laser and the SiP chip. [ABSTRACT FROM AUTHOR]

A broadband continuously tunable SESAM all-fiber laser based on optical parametric generation (OPG) for coherent anti-stokes Raman scattering (CARS) imaging applications is presented in this article. This laser structure is built on all-polarization maintaining fibers yielding high environmental stability. The OPG is based on PM photonic crystal fiber as parametric gain pumped by a wavelength-tunable (1025 to 1055 nm) and repetition rate-tunable (3 MHz to 500 KHz) Yb-doped pulsed fiber laser. The all-fiber structure features free polarization adjustment in slow-axis tunable operation with a wavelength range from 770 to 940 nm for signal radiation and 1225 to 1510 nm for idler radiation. The pump and signal pulses (CARS-Stokes and CARS-pump respectively) are intrinsically overlapped, both spatially and temporarily, due to the four-wave mixing (FWM) generation and emitted from a single fiber end. The CARS-Stokes and CARS-pump pulse duration vary between 25 to 32 ps and 21 to 24 ps, respectively in the whole band, ensuring a good overlap of the generated signals, and both exhibit a Gaussian profile with high spatial beam quality. The frequency conversion allows to obtain a frequency difference between the generated signals from 1100 to 3300 cm−1. The reported low-cost laser source is ideal for bio-imaging applications, especially in CARS imaging, due to its compactness, simplicity, robustness and ease of handling. A patent has been filed based on this technology. [ABSTRACT FROM AUTHOR]

Multi-wavelength distributed feedback laser array based tunable semiconductor lasers have been widely used owing to their high mode stability and simple tuning scheme. Comparing with the in-parallel laser array, the in-series one can avoid a large power loss caused by the optical combiner. However, the single-mode stability of an in-series laser array is vulnerable to the reflections of other lasers. Here we experimentally demonstrated a tunable in-series laser array with high single-mode stability and high uniformity of wavelength spacing. To reduce the impact of such reflections, the Bragg gratings in different lasers were designed in phase, and the grating phase error was reduced by utilizing the reconstruction-equivalent-chirp technique. Besides, a three-section laser structure was applied in each laser to increase the priority of the dominant lasing mode. Four lasers with small wavelength-spacings of 2.5 nm were integrated in the in-series laser array. According to the measurement results of 40 in-series laser arrays (160 lasers), wavelength deviations of 90.6% lasers were within ±0.2 nm, average wavelength spacings of 97.5% of the measured laser arrays were deviated from the design within ±0.2 nm, and SMSRs of 96.3% lasers were above 45 dB. The output power was above 25 mW and the relative intensity noise was below −130 dB/Hz. Like the in-parallel laser array, the proposed laser array can be applied in either continuous wavelength tuning or fast channel switching. For the continuous wavelength tuning applications, the 10-nm tuning range was obtained with a temperature tuning range of less than 20 °C. For the fast channel switching applications, four channels with 2.5-nm spacing are available, and the switching time between two channels was less than 300 ns. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate a passively mode-locked all-fiber Tm laser with an all-fiber saturable absorber (SA) which operates based on the nonlinear multimode interference (NL-MMI) effect in a tapered graded-index multimode fiber (GIMF). The tapered GIMF SA demonstrates the nonlinear characteristics of modulation depth of 21.15%, and saturation fluence of $89.04~\mu \text{J}$ /cm2. We obtain stable fundamentally mode-locking operation at a pump threshold of 120 mW. The output soliton pulses have a center wavelength, spectral width, pulse duration and repetition rate of 1935 nm, 2.1 nm, 1.9 ps and 18.79 MHz, respectively. This is a simple, low-cost, stable, and convenient laser oscillator with many potential applications in eye-safe ultrafast photonics. [ABSTRACT FROM AUTHOR]

We report on the free-running and frequency stabilized operation of a ring resonator-tuned full-band tuneable laser. The laser is a monolithically integrated semiconductor ring laser tuneable over 34 nm, from 1522–1556 nm, fabricated using a commercially-available, InP-based, active-passive foundry technology. The mode selection is implemented using the Vernier effect by reverse-biasing voltage-controlled electro-optically tuned ring resonators. The laser exhibits a typical intrinsic linewidth of 110 kHz over the C-band and a side-mode suppression ratio (SMSR) exceeding 50 dB. The linewidth over the tuning range does not significantly vary, showing that the tuning mechanism does not cause linewidth broadening. The power dissipated in the tuning elements is 1.4 mW per ring. Using the same reverse bias voltage-controlled electro-optic tuning, we also demonstrate the locking of the laser to a high-finesse etalon using Poun–Drever–Hall frequency locking. Our implementation requires a single control loop because of the reverse bias tuning. All deployed tuning effects in the phase modulators have the same sign therefore resulting in a flatter frequency dependent phase response compared to current injection feedback. The control loop has a bandwidth of 500 kHz and a control range of 2.9 GHz. We report 1 kHz level linewidth for millisecond observation times for the stabilized laser. [ABSTRACT FROM AUTHOR]

In this paper we explain how to use rate equations to describe a laser that includes integrated optical feedback. We find a relation between the threshold current, the voltage drop at the gain section, output power, linewidth, and side mode suppression ratio, and show experimental results. [ABSTRACT FROM AUTHOR]

European Space Agency (ESA) considers picosecond mode-locked semi-conductor laser technology as a promising candidate for space applications in precision optical metrology systems. However, very challenging performance requirements should be met by such laser without additional amplification stages. In order to address this challenge, we realized two types of mode-locked edge emitting lasers operating at 990 nm wavelength. In particular, we demonstrate a very-long (13.5 mm) monolithic multi-section tapered laser reaching 201 pJ mode-locked pulses at low repetition frequency of 2.89 GHz with the pulse width that can be compressed down to 2.4 ps. We also report on a multi-section inverse bow-tie external cavity laser producing mode-locked pulses of 70 pJ energy and 6 ps width (0.73 fs after compressor) at 1.65 GHz pulse repetition frequency (PRF). The laser operates in an 80-mm-long external cavity. The PRFs of the two lasers can be continuously tuned over 9.8 and 9.1 MHz ranges, respectively. Active stabilization with a phase locking loop actuating on the driving current has allowed us to reach PRF relative stabilities of 1.15·10−10 and 2.9·10−10 on 1 s intervals for the two lasers. These performances fulfill the requirements of ESA for inter-satellite long distance measurements. [ABSTRACT FROM AUTHOR]

Semiconductor lasers that use high-order surface gratings formed with etched slots have simple fabrication. Such gratings however increase loss and have a small free-spectral range that can increase threshold, lower slope efficiency, and limit SMSR. In this paper, we look at the design of a grating and use 2, 3, and 4 period structures within a 37 ${\text{th}}$ order grating. At fixed temperature, a single period device should work best while temperature tuning requires a multiperiod device. We found that the two period grating structure works best among the multiperiod devices. A follow-on study with the scattering matrix model shows that the slope efficiency which is quite low in this study (about 0.1 mW/mA at best) can be improved to a value of upto 0.17 mW/mA by reducing the number of slots used to form the grating from the present design that has 24 slots to 18. [ABSTRACT FROM AUTHOR]

We demonstrate a technique to precisely control and stabilize the beat frequency of a photonic microwave signal generator based on beating the optical signals of two lasers on a high-speed photodetector. The approach does not require high-speed electronic circuitry, but allows the control of the generated signal frequency up to hundreds of GHz. The demonstrated technique can readily be integrated on a chip-scale device using heterogeneous silicon platform, opening possibilities for widespread use in signal generation, sensing, instrumentation, and communications. [ABSTRACT FROM PUBLISHER]

A tunable dual-wavelength thulium doped fiber laser is demonstrated experimentally. For the first time for the 2- \mu \textm wavelength band we propose the independent tuning of the generated laser lines based on fiber Bragg gratings and the use of a Hi-Bi fiber optic loop mirror for the fine adjustment of the cavity losses to obtain stable dual-wavelength operation. Dual-wavelength laser generation with the laser lines separation in the range from 0.3 to 6.5 nm is obtained. The laser emission exhibits an optical signal-to-noise ratio better than 56 dB. Improved stability with output power fluctuations less than 1 dB is observed in dual-wavelength generation with equal power of lines. [ABSTRACT FROM PUBLISHER]

In this paper, we present a method of self-detection of mode hops in a distributed Bragg reflector tunable laser using the voltage drop in the active section as a monitoring signal. Based on this method, a wavelength setting and stabilization algorithm that is tolerant to temperature variations is proposed. Wavelength locking for a period of more than seven days with an accuracy better than ±1.25 GHz has been achieved, meeting the ITU-T standard for 25 GHz channel spacing. Under forced changes in the operation temperature from 15° to 60°, with variations of 0.1°/s, the maximum allowed deviation of ±2.5 GHz for the ITU-T standard with 50 GHz channel spacing was kept. [ABSTRACT FROM PUBLISHER]

A high-stability wavelength-tunable single-frequency (SF) ytterbium-doped all-fiber compound ring laser has been demonstrated experimentally. The compound ring cavity is composed of a fiber optical tunable filter, a high-finesse ring filter, and a loop mirror filter. Three segments of ytterbium-doped fibers are employed as the gain medium or saturable absorber, respectively. The SF operation is observed to be stable during 1 h without mode hopping. The SF fiber laser achieves a wide-band tunability from 1030 to 1090 nm with maximum output slope efficiency of 7.95%. The power instability over 2 h gives standard deviation value of 1.34%. The average linewidth is 8.8 kHz and the relaxation oscillation frequency is at 62 kHz. [ABSTRACT FROM PUBLISHER]

The pulse repetition rate (RR) tuning and locking range (LR) as well as the pulse train timing stability of passively mode‐locked quantum‐well (QW) semiconductor lasers (SCLs) subject to single‐cavity optical self‐feedback (OFB) are investigated experimentally and by simulations. A simple and universal stochastic time‐domain model confirms the experimentally observed RR control and LR as well as timing jitter (TJ) improvement in QW SCLs subject to very long OFB cavities with lengths up to 73.1 m. In particular, the model allows predicting control potential and limits of the RR tuning, locking and TJ improvement depending on the choice of OFB delay length for time‐delay mode‐locked semiconductor laser stabilisation experiments. [ABSTRACT FROM AUTHOR]

We demonstrate a passively Q-switched erbium-doped fiber laser (EDFL) based on few-layer MoS2 as a saturable absorber (SA). Few-layer MoS2 is prepared by the chemical vapor deposition method. The prepared MoS2 is transferred onto the end face of a fiber connector to form a fiber-compatible MoS2-based SA. The saturation intensity and modulation depth of the MoS2 SA are measured to be 0.43 MW/cm2 and 33.2%, respectively. The Q-switched EDFL has an all-fiber linear cavity with two fiber Bragg gratings as the end mirrors. By inserting the MoS2 SA into the laser cavity, stable Q-switched operation is achieved at 1.55 μm. The laser has a pump threshold of 20.4 mW, a pulse repetition rate tunable from 10.6 to 173.1 kHz, and a minimum pulse duration of 1.66 μs. Our results show that few-layer MoS2 is a promising SA for Q-switching laser operation. [ABSTRACT FROM PUBLISHER]

A single-longitudinal-mode (SLM) fiber ring laser based on topological insulator (TI) Bi2Te3 saturable absorber (SA) had been experimentally demonstrated. The TI: Bi2Te3 nanosheets, which were fabricated through the bottom-up approach, were coated onto the microfiber as an efficient saturable absorber device to ensure the SLM operation. Combined with fiber Bragg grating, the output wavelength can be continuously tuned about 1 nm. Without any accurate cavity control, stable SLM operation without mode hopping had been conveniently achieved. Based on the Lorentzian fitting, the line-width was measured to be less than 10 kHz. The output power of SLM fiber laser can reach up to 23 mW, indicating that the proposed TI-based SA may be suitable for high-optical power SLM operation in the future. [ABSTRACT FROM PUBLISHER]

An innovative external cavity dual-mode laser has been developed for continuous-wave terahertz generation via photomixing. Photomixing is a method of generating terahertz radiation at the beat frequency developed by two input optical light modes. Dual-mode lasers are an intriguing option for photomixing sources because the differential frequency produced is stabilized by the common mode rejection ratio effect. The laser presented here utilizes an acousto-optic tunable filter for frequency selection, which creates an ultra-wideband tunable range and provides the potential for tuning speed on the order of microseconds. The unique design of this laser enables 100% solid state operation resulting in a robust and compact system for applications in terahertz imaging or spectroscopy. Operating at around 1550 nm, this laser is capable of producing differential frequencies between 300 GHz and 18 THz with a side-mode-suppression-ratio of 50 dB and peak amplitudes of over 0 dBm. The device presented here represents a significant achievement in the advancement of dual mode lasing technology for tunable terahertz generation with high phase and amplitude stability. [ABSTRACT FROM PUBLISHER]

An erbium fiber oscillator with dominating gain fiber length and an intracavity pulse shaper is experimentally demonstrated. The Kerr nonlinear phase shift induced in the fibers is suppressed by the pulse shaper, enabling high-energy (8.9 nJ) high-compression efficiency (93%) pulses of less than 270 fs duration (after linear dechirping) at modest (320 mW) pump power. A stably mode-locked spectrum corresponding to 19 nJ, 83 fs transform-limited pulse is achieved at 720 mW pump power. Wave-breaking-free pulse energy can be further enhanced by introducing stronger spectral phase modulation via the pulse shaper if more pump budget is available. We also demonstrate manipulation of the central wavelength and bandwidth of the output pulse by intracavity spectral amplitude modulation via the pulse shaper. [ABSTRACT FROM PUBLISHER]

A novel tunable dual-wavelength thulium-doped fiber laser is demonstrated experimentally. The wavelength-tuning by employing a high birefringence fiber Bragg grating is proposed in 2-μm band lasing for the first time. By adjusting the polarization controller, stable dual-wavelength operation at the wavelengths of 1941.40 and 1942.21 nm is obtained. The optical signal-to-noise ratio is better than 48 dB. A 15.5% slope efficiency is achieved using a 90% output coupling ratio for laser extracting. The wavelength-tuning range in dual-wavelength operation is as wide as 6.93 nm. [ABSTRACT FROM PUBLISHER]

We proposed and demonstrated a stable multiwavelength erbium-doped fiber laser by using a microfiber knot resonator (MKR)-based comb filter. By properly rotating the polarization controller, up to 11 lasing lines in a 3-dB bandwidth with 0.184-nm channel spacing were obtained. In addition, the lasing locations can be flexibly tuned by virtue of spectral filtering effect induced by the polarization-dependent isolator and the intracavity birefringence. The results demonstrated that the MKR could be employed as a high performance comb filter to realize a compact multiwavelength fiber laser. [ABSTRACT FROM PUBLISHER]

We have developed a tunable semiconductor double-chirped mirror with high negative dispersion grown by molecular beam epitaxy. The simplified numerical plane-wave reflection transfer method was applied to design the dispersive mirror structure. The multilayer stack was grown of AlAs/GaAs materials and capped by an SiNx antireflective layer. The group delay dispersion as well as reflectivity characteristic were continuously tunable across the mirror surface from 1080 to 1000 nm. Within this range, the negative value of the dispersion changed from -3850±100 fs2 over the 6 nm band around 1080 nm to -2200±100 fs2 over 13 nm around 1000 nm with the reflectivity from the range of 99.0÷99.2%. The mirror performance was tested in a diode-pumped femtosecond Yb:KYW oscillator. [ABSTRACT FROM PUBLISHER]

We demonstrate a stable gain-switched thulium fiber laser pumped with an acousto-optically modulated Er, Yb co-doped fiber laser at 1.56 \mum. The laser produced 1850 nm pulses with 2.5 \muJ pulse energy and 75 ns pulsewidth at a repetition rate of 500 kHz, resulting in a maximum average output power of 1.32 W and slope efficiency of 54.7% with respect to absorbed pump power. The dependence of laser output characteristics on the pump power and repetition rate was presented and discussed. Repetition rate of gain-switched pulses was tuned continuously from 68 kHz to over 1 MHz at the maximum pump power-level of 8 W. The broad tuning range of pulse repetition rate makes this laser suitable for various applications. [ABSTRACT FROM PUBLISHER]

A novel double-pumped ring cavity multiwavelength fiber optical parametric oscillator (MW-FOPO) with tunable wavelength spacing is proposed. In the MW-FOPO, we utilize a highly nonlinear dispersion-shifted fiber as the gain medium and a Mach-Zehnder interferometer as the comb-like filter. Twenty-four-wavelength lasing of the double-pumped MW-FOPO with a ripple less than ±4.3 dB and a wavelength spacing of about 0.8 nm in a wavelength range from 1541 to 1558 nm is experimentally demonstrated. The wavelength spacing can be continuously tuned and multiwavelength lasings with wavelength spacings of 0.08, 0.2, 0.4, and 0.8 nm are demonstrated, respectively. We discussed the power stability of the multiwavelength lasing of the double-pumped MW-FOPO. A comparison of the output spectra among the double-pumped MW-FOPO, the single-pumped MW-FOPO, and the multiwavelength erbium-doped fiber laser is also presented. [ABSTRACT FROM PUBLISHER]

Hyperfine structures of ^127I2 absorption transitions near 561 nm are observed via modulation transfer spectroscopy by a homemade Nd:YAG monolithic nonplanar ring laser with its second harmonic generation (SHG) using a single-pass PPMgO:LN crystal. The observed I2 transitions are assigned according to theoretical calculation results of the I2 B-X transition. Two Nd:YAG lasers are locked to the 15th component of the ^127I2 P(58)22-1 transition, and the measured frequency stability of these lasers is 1 \times 10^-13 for a 1-s averaging time. Frequency shifts with changing iodine cell vapor pressure and pump power are measured by observing the heterodyne beat between two I2-stabilized lasers. [ABSTRACT FROM AUTHOR]

A monolithic widely tunable semiconductor laser based. on a double-ring resonator is developed for use in a wavelength-routing switch. By using the double-ring resonator as a wavelength-selective filter, operation over a wide wave- length tuning range is achieved with a low tuning current. This low-tuning-current operation makes the laser very promising as a high-speed tunable light source for a wavelength-routing-based switch by effectively suppressing the thermal wavelength drift induced by current injection. In addition, the laser fabrication process is simpler compared to conventional distributed Bragg reflector tunable lasers. A tuning range of 50.0 nm, covering the entire C-band, is successfully demonstrated with an injection current of less than 5.2 mA. The wavelength drift caused by the thermal transients is less than 5 GHz. [ABSTRACT FROM AUTHOR]

This paper presents rapid, precise, and stable control of optical frequency for sampled-grating distributed Bragg reflector (SG-DBR) laser diode (LD) using a Z-cut quartz etalon supported at the middle point. The optical frequency of SG-DBR LD was controlled by the mode-hop-free three-electrode control method. As a result, stable mode operation and wide continuous tuning range without mode hopping have been realized. A 0.2-ms optical frequency tuning speed with a 4.35-THz tuning range and a 130-MHz control error of the optical frequency was demonstrated. A 1.1-MHz Allan deviation was reached at an integration time of 12 times 103 s. [ABSTRACT FROM PUBLISHER]

A stabilized and tunable single-longitudinal-mode erbium-doped fiber ring laser has been proposed and experimentally demonstrated. The laser is structured by combining the compound cavity with a fiber Fabry-Peacuterot tunable filter. An injection-locking technique has been used to stabilize the wavelength and output power of the laser. One of the longitudinal modes is stimulated by the injected continuous wave so that this mode is able to win the competition to stabilize the system. A minimum output power of 0.6 dBm and a signal-to-noise ratio of over 43 dB within the tuning range of 1527-1562 nm can be achieved with the proposed technique. A wavelength variation of less than 0.01 nm, a power fluctuation of less than 0.02 dB, and a short-term linewidth of about 1.4 kHz have also been obtained [ABSTRACT FROM PUBLISHER]

With the aim of developing a fast wavelength-tunable laser for advanced dynamic network reconfigurations or optical burst switching, a short-cavity (SC) distributed-Bragg-reflector (DBR) laser array with an active-DBR (ADBR) structure (SC-ADBR laser) was fabricated. First, it was experimentally confirmed that the ADBR structure compensates for optical loss and achieves stable single-mode operation during wavelength tuning. An artificial-laser-phase-adjustment technique in the SC-ADBR laser by precise adjustment of a DBR mirror was then proposed. By applying this technique to a six-channel SC-ADBR laser array, perfect wavelength accessibility across a 21-nm range was attained [ABSTRACT FROM PUBLISHER]

We propose to include a Bragg-wavelength-detuned (BWD) layer in a portion of the cavity of an index-coupled distributed feedback (DFB) laser to overcome the mode degeneracy problem. The new two-section DFB (TSDFB) lasers are experimentally demonstrated to have comparable device dimension and output characteristics as conventional DFB lasers but have much better spectral stability. High side-mode suppression ratio can be obtained over a wide range of current injection and temperature conditions when the laser is coated with anti-reflection coatings on both output facets. Wavelength tuning over 5.4 nm can be obtained by adjusting the heatsink temperature and levering the bias currents. With excellent mode stability, the TSDFB lasers are demonstrated to perform wavelength conversion with large extinction ratio, high conversion efficiency, and waveform reshaping capability. The wavelength conversion can cover 30-THz of input frequency that matches the frequency grid of the dense wavelength division multiplexing systems. Penalty-free conversion is also demonstrated. [ABSTRACT FROM PUBLISHER]

We propose a digitally tunable ring laser incorporating a ladder filter and a ring resonator. The widely tunable ladder filter consists of two input-output waveguides and a waveguide array, and it selects one channel from the periodic outputs of the ring resonator. With this device, the passband of the ladder filter is important in terms of obtaining stable lasing operation and it becomes narrower with increasing diffraction order. However, the free-spectral range of the filter is reduced with increasing diffraction order and this induces lasing mode instability. We therefore optimize the diffraction order of the ladder filter. The device is monolithically integrated by using the InP-InGaAsP material system. We achieved 37 channel 1000-GHz spacing digitally tunable laser operation. A promising way of improving the device performance is to use a chirped ladder filter because this filter has one dominant passband. [ABSTRACT FROM PUBLISHER]

We report on the development of the first 30 nm tunable laser diode utilizing a front sampled grating-distributed Bragg reflector (SG-DBR) and a rear superstructure grating DBR (SSG-DBR). A high output power greater than 18 mW was achieved with superior longitudinal mode stability, as well as an overall power variation of less than 3 dB for the well-defined laser. Furthermore, lasers integrated with a semiconductor optical amplifier (SOA) enabled the output power to be controlled independently both by the active current and the SOA current, as well as achieving a maximum output power of 45 mW. The side-mode suppression ratio was in excess of 40 dB for all the 50 GHz spaced wavelength channels. [ABSTRACT FROM PUBLISHER]

Ultrabroadband infrared transition metal ion-doped solid-state lasers have come of age and are increasingly being used in trace gas monitoring, remote sensing, telecommunications, ophthalmology, and neurosurgery. Operating at room temperature, they are stable, versatile, and easy to handle successors to the color center lasers. They are becoming the critical components in optical frequency standards, space-based remote sensing systems, and may soon find application in femtochemistry and attosecond science. The article reviews the principles and basic physics of these types of lasers, which are distinguished by their ability to support the shortest pulses down to single optical cycle durations and the ultimately broad tuning ranges. The paper further reviews the state of the art in the existing diode-pumped sources of broadly tunable continuous wave, and ultrashort pulsed radiation in the infrared, and provides examples of their successful application to supercontinuum generation, trace gas measurements, and ultrasensitive intracavity spectroscopy. Developments in such lasers as Cr:YAG, Cr:ZnSe, Cr:ZnS, as well as the recently proposed mixed Cr:ZnSxSe1-x laser, are discussed in more detail. These lasers nearly continuously cover the infrared spectral region between 1.3 and 3.1 μm. The gain spectra of these lasers perfectly match and extend toward the infrared spectra of such established ultrabroadband lasers, operating at shorter wavelengths between ∼0.7-1.3 μm, as Ti:sapphire, Cr:LiSAF/Cr:LiSGaF and Cr:forsterite. This opens up new opportunities for synthesis of single-cycle optical pulses and frequency combs in the infrared. [ABSTRACT FROM PUBLISHER]

A continuous-wave optical parametric oscillator (OPO) was phase locked to an optical frequency comb in the 830-nm region. The optical frequency of the OPO was controlled by changing the cavity length of the pump laser. The residual phase noise under phase locking was 220 mradrms. and the energy concentration to the carrier was 95 %. Furthermore, the optical frequency fluctuations of a free-running OPO were measured by using an optical frequency comb that was phase locked to an atomic clock. The measured fluctuations were around 10 MHz in an hour. [ABSTRACT FROM AUTHOR]

State-of-the-art distributed feedback (DFB) laser modules integrated with a wavelength monitor are presented that provide excellent wavelength stability. By adopting unique and compact configuration, wavelength deviations of as small as a few picometers have been achieved. The laser modules are improved also in the scope of high power, high reliability, and wavelength tunability. Reliability test results of the DFB laser diodes and modules confirm a sufficiently long lifetime of more than 25 years and a small wavelength drift of less than ±3 pm. The developed laser modules are fully applicable to ultradense wavelength-division multiplexing applications with the current narrowest channel spacing of 25 GHz. [ABSTRACT FROM PUBLISHER]

A simple design of a stable, smoothly wavelength-tunable picosecond pulse generator has been demonstrated using a dispersion-tuned, harmonically mode-locked fiber ring laser with a directly modulated semiconductor optical amplifier (SOA). The SOA functions as both a polarization-insensitive mode locker and a supermode noise suppressor. Near-linearly chirped pulses are generated and compressed to less than 4 ps when the intracavity dispersion is anomalous while 11-ps, near-transform-limited pulses are generated without compression when the dispersion is normal. Smooth wavelength tuning is achieved over more than 11 nm by only tuning the modulation frequency and pulse characteristics are stable over the entire tuning span. A simple numerical model successively simulates the operation principle of the system. The tuning range is determined by both the gain profile and the total intracavity dispersion. The dispersion and the SOA ensure the long-term stability of the system. [ABSTRACT FROM PUBLISHER]

We report on a widely tunable transmitter based on a sampled-grating distributed Bragg reflector (SG-DBR) laser monolithically integrated with a semiconductor optical amplifier (SOA) and an electroabsorption (EA) modulator. Modulated time-averaged powers in excess of 5 dBm, RF extinction ratios >10 dB, and error-free transmission at 2.5 Gb/s for 350 km of standard single-mode fiber have been demonstrated across a 40-nm tuning range. In CW mode of operation, the module meets all long-haul system requirements for externally modulated laser sources: stability, power (>10 mW), RIN (<-140 dB/Hz), and linewidth (<2 MHz) over 90 50-GHz spaced ITU channels. Implementation of wavelength, power, and mode control in module firmware ensures long-term stability for system deployment. Systematic investigations of accelerated aging performed on laser tuning and gain sections showed excellent wavelength stability and reliability with median times to failure of >100 yr for output wavelength stability and power across all channels. [ABSTRACT FROM PUBLISHER]

We report on a fully functional 2.5-Gb/s electroabsorption (EA)-modulated wavelength-selectable laser module meeting all long-haul transmission requirements for stability, chirp, power and linewidth over 20 channels on a 50-GHz grid. Based on a highly integrated InP chip comprising a distributed Bragg reflector (DBR) laser, semiconductor optical amplifier, power monitor, and EA-modulator, the compact transmitter module also contains optics and control circuits necessary to ensure simultaneous long-term wavelength and mode stability. We have achieved 2.5-Gb/s transmission on all 20 channels over 680 km of standard fiber [ABSTRACT FROM PUBLISHER]

Broad-band tunability of erbium-doped silica fiber ring lasers in the 1.48-1.62 μm wavelength band is demonstrated through modeling and experiment. Tunability over the erbium-doped fiber amplifier (EDFA) C- and L-bands is achieved with a simple laser design using a single gain medium working in deep saturation. A comprehensive numerical model based on an iterative solution of propagation rate equations and spectrally resolved Giles parameters was used to analyze the impact of various laser variables. The dependence of laser output power on total cavity loss, erbium-doped fiber length, pump power, and lasing wavelength has been investigated. The calculated laser characteristics have been found in good quantitative agreement with the experimentally obtained data. Experimental results concerning wavelength tunability, output power, and lasing wavelength repeatability/stability and spectral purity are also presented [ABSTRACT FROM PUBLISHER]

In this letter, we present the first 1.5-μm single frequency Fabry-Pérot laser device that is free of spatial hole burning. The laser was realized using erbium-doped LiNbO3 waveguide. The optical gain of this laser is spatially distributed in such a manner to coincide with the standing wave pattern of the oscillating laser field. Thereby, the spatial hole burning was eliminated. Clean 1531-nm single-frequency operation was demonstrated. [ABSTRACT FROM PUBLISHER]

A stably and widely tunable single-longitudinal-mode dual-wavelength erbium-doped fiber (EDF) laser is investigated for the generation of a tunable optical beat frequency. The lasing wavelength spacing is widely controlled in a range from 3.46 to 13.2 nm, which means that the tunable optical beat frequency in a range from 0.43 to 1.66 THz can be achieved. Nonlinear polarization rotation effect is implemented to stabilize and equalize outputs of the tunable dual-wavelength EDF laser. Since the dual-wavelength fiber laser has a single-longitudinal mode, the proposed dual-wavelength fiber laser is stable. [ABSTRACT FROM PUBLISHER]

We demonstrate 40-GHz phase stable short optical pulses generation using an electroabsorption modulator and cascaded phase modulators. The pulses are characterized with a small pedestal, ~2.1-ps pulsewidth, an extinction ratio larger than 23 dB, timing jitter less than 60 fs, and an optical signal-to-noise ratio over 40 dB over 30-nm tuning range. The high quality and phase stability of the pulses are further experimentally verified in a 4 × 40 GBaud differential quadrature phase-shift-keying (DQPSK) optical-time-division-multiplexing (OTDM) system. [ABSTRACT FROM PUBLISHER]

We propose and demonstrate an all-fiber scheme to generate a precisely tunable microwave signal by heterodyning the two cascaded single-frequency Brillouin fiber lasers (BFLs). The generated microwave frequency is equivalent to the offset between the first- and the second-order Stokes frequencies. The ~10 GHz generated signal exhibits high stability with a linewidth of 2.8 KHz. By controlling elastic strain to the fiber in the BFL, the microwave frequency can be tuned up to 270 MHz. Owing to frequency pulling effect (FPE) in BFL, the signal frequency can be continuously tuned in a range of 9.6 MHz within one free-spectral range (FSR) of 19.8 MHz, and the tuning accuracy is 100 KHz. [ABSTRACT FROM PUBLISHER]

We report on single-frequency operation and wide mode-hop-free tuning range of a diode laser-pumped vertical-external-cavity surface-emitting semiconductor laser producing up to 3 mW around 2.3 mum. An optically stable external cavity of only 1.4 mm is formed using a concave dielectric mirror of 2-mm radius. The maximum continuous tuning is about 500 GHz wide, obtained by a synchronized ramp of external cavity length and of the gain medium temperature. We used this tunable source to record a direct absorption spectrum of methane, which is found to match well a simulated spectrum from the HITRAN (high-resolution transmission molecular absorption database http://www.cfa.harvard.edu/hitran) database. [ABSTRACT FROM PUBLISHER]

A laterally coupled InGaAsP-InP distributed-feedback (DFB) laser operating around 1.55 mum was fabricated through a novel technique for the formation of metal surface gratings by holographic lithography. The self-aligned Cr DFB gratings were formed on the sidewalls as well as on both sides of the laser ridge by means of angled e-beam evaporation of Ti mask and metal-SiO2 lift-off on the top of ridges. For an uncoated 3-mum-wide and 300-mum-long cavity, the device emitted an output power of ~9.7 mW/facet at an injection current of 100 mA with a threshold current of 29 mA and a slope efficiency of 0.14 mW/mA per facet at 20 degC under continuous-wave mode. A stable single-mode emission near 1.54 mum with a sidemode suppression ratio of nearly 28 dB was observed and a tuning coefficient of 0.21 nm/K was obtained in the temperature range of 15 degC -55 degC. [ABSTRACT FROM PUBLISHER]

The authors demonstrate the drift in frequency of a static sampled-grating distributed Bragg reflector (SG DBR) laser module when it is subjected to direct modulation. The magnitude of drift and its settling time is characterized as a function of the index of modulation. Results show that when the directly modulated SG DBR is optically filtered, as in a dense wavelength-division-multiplexed system, a power penalty of 6.7 dB is incurred in comparison to the unfiltered case. [ABSTRACT FROM PUBLISHER]

The authors present an investigation of the wavelength stability of a tunable laser (TL) transmitter and its impact on the performance of a 2.5-Gb/s dense wavelength-division-multiplexed (DWDM) system. Performance of a DWDM system, employing such a TL, is characterized by examining the cross-channel interference caused by this drift when the channel spacing is set to 12.5 and 25 GHz. Results obtained show that the wavelength drift affects the system performance by introducing an error floor in the case of 12.5-GHz spacing. This error floor can be mitigated by increasing the blanking time of the TL during the channel transition, in order to reduce the wavelength drift [ABSTRACT FROM PUBLISHER]