Frequency stabilization of a traveling-wave semiconductor ringlaser using a fiber resonator as a frequency reference

A fiber resonator with a temperature drift rate of better than 5×10^-4° C/hour is used for controlling the frequency stability of a 1.3 μm wavelength external cavity semiconductor ring laser. A frequency stability of about 600 KHz/hour is achieved     

Fourier-limited 1.6-ps pulses with variable repetition rate from 1to 26 GHz by passive mode-locking of a semiconductor laser in anexternal cavity

By passive mode-locking of a semiconductor laser (λ=1.3 μm) in an external cavity, 1.6 ps sech²-shaped pulses are generated with variable repetition rates from 1 to 26 GHz, presently limited only by the geometry of the set-up. The time-bandwidth product is between 0% and 40% over the theoretical limit. Wavelength tuning up to 50 nm is possible     

External-cavity semiconductor laser with focusing grating mirror

A novel external-cavity semiconductor laser with a focusing grating mirror (FGM), which enables a single-mode oscillation at a specified wavelength, is proposed. The optical properties of the FGM, which is a computer-generated holographic grating with chirp and bend structure, are numerically analyzed. An optimally designed FGM for realizing laser oscillation at a specific wavelength of 1.30 μm is fabricated by using a computer-controlled electron-beam writing system. The fabricated FGM with grating area of 1×1 mm² is combined as an external feedback mirror with an InGaAsP-InP semiconductor laser of 1.3 μm wavelength range, and the lasing characteristics are experimentally measured. Stable and single-mode oscillations with spectral line width less than 10 MHz are observed     

Wide-span optical frequency comb generator for accurate opticalfrequency difference measurement

An optical frequency comb (OFC) generator was realized for accurate optical frequency difference measurement of 1.5 μm wavelength semiconductor lasers by using a high frequency LiNbO₃ electrooptic phase modulator which was installed in a Fabry-Perot cavity. It was confirmed that the span of the OFC was wider than 4 THz. By using semiconductor lasers whose spectrum linewidths were narrowed to 1 kHz and a sensitive optical balanced-mixer-receiver for measuring beat signal between the sideband of the comb and the laser, we demonstrated a frequency difference measurement up to 0.5 THz with a signal-to-noise ratio higher than 61 dB, and a heterodyne optical phase locking with a heterodyne frequency of 0.5 THz in which the residual phase error variance was less than 0.01 rad². The maximum measurable frequency difference, which was defined as the sideband frequency with the signal-to-noise ratio of 0 dB, was estimated to be 4 THz     

Simultaneous absolute frequency control of laser transmitters inboth 1.3 and 1.55 μm bands for multiwavelength communication systems

Absolute frequency control will be an essential part of future dense WDM systems. In this paper, we demonstrate two promising techniques that allow the absolute frequency control of an ensemble of laser transmitters operating in both the 1.3 and 1.55 μm bands. First, a Michelson interferometer is absolutely calibrated by means of a frequency-stabilized master DFB laser. This interferometer provides an ensemble of evenly-spaced absolute frequency references that covers both the 1.3 and 1.55 μm regions. Lasers are frequency-locked to transmission nulls of this interferometer with a precision of a few hundred MHz. The second technique allows full flexibility in channel frequency assignment and relies on frequency offset control of an ensemble of laser sources relative to a master reference laser. The frequency comparator is based on a surface-emitting nonlinear semiconductor multilayer waveguide. This technique provides simultaneous frequency measurement and control of lasers in both bands with a precision of a few GHz     

Tunable laser-diode-pumped Nd:YAG microcrystal lasers at 1.4 μm

TEM₀₀ laser operation of a monolithic Nd:YAG crystal laser has been achieved on three transitions at 1.414 μm, 1.444 μm and at 1.431 μm with laser diode pumping at 808 nm. The laser threshold was 1.5 W and the maximum output power 50 mW. The gain linewidths at 1.414 μm and 1.444 μm were determined by means of temperature tuning the microcrystal lasers. Calculations for designing tunable single frequency microcrystal lasers have been performed     

Proposal of a GaInAs/GaInAsP/InP antiguided filter laser arrayoperating in single longitudinal mode

The authors propose a type of in-phase lateral- and single-longitudinal-mode laser array, the so-called antiguided filter laser array (AFLA), in which an antiguided filter region is inserted between a positive-index-guided multiple-strip array region with a shallow corrugation grating and a high-reflectivity region with deep corrugation. Threshold current as low as 100 mA was obtained for a five-element laser array with active region length of 300 μm and total emitter width of 18 μm, using five-pairs of Ga_0.3In _0.7As (3 nm)/GaInAsP (10 nm) compressively strained quantum wells     

Frequency stabilization of 1.55 μm DFB laser diode usingvibrational-rotational absorption of 13C2H2 molecules

The vibrational-rotational absorption of ¹³C₂H₂ molecules (VRAMs) in the 1.52-1.55 μm region was investigated in detail. On the basis of this investigation, frequency stabilization of 1.55-μm distributed-feedback (DFB) laser diodes was demonstrated. Frequency stability to within 2 MHz peak/peak fluctuation was achieved at the 1.54949-μm wavelength. In addition, frequency stabilizations in the wavelength regions of 1.53 μm and 1.54 μm were also carried out by using the strong absorption lines of ¹³C₂H₂ VRAM in these wavelength regions. The spectral width of the frequency-stabilized DFB laser diode was found to be 25 MHz. The absolute frequency was found to be stabilized at least to within 25 MHz by the measurement of beat spectrum     

Novel FSK heterodyne single-filter detection system using no IFfrequency lock

A frequency-shift keyed (FSK) modulation/single-filter detection system which does not require an intermediate-frequency (IF) locking loop is reported. This system utilizes a laser frequency-locked to an atomic line (krypton 2p₈-3d₁" transition at 1.5224 μm) as both transmitter and local oscillator. As a result, communication can be initiated without any manual adjustment to match the wavelengths of transmitter and local oscillator lasers. No significant degradation in the receiver sensitivity was observed due to the slight frequency dither used to lock the laser frequency to an atomic transition line     

Mode locking of a Nd:YAlO3 laser at 1.08 and 1.34 μmwavelengths using a single LiIO3 crystal

Passive mode locking of a Nd:YAlO₃ laser at 1.08 and 1.34 μm using a nonlinear mirror based on second harmonic generation is described. A single 30° cut frequency-doubling LiIO₃ crystal was used to mode lock both transitions, demonstrating the superiority of this mode-locking technique over that using saturable absorbers. Pulses as short as 50 ps at 1.08 μm and 15 ps at 1.34 μm were obtained. A comparative analysis of the mode-locking performance at the two fundamental wavelengths is presented, indicating that the longer pulse duration at 1.08 μm is due to the higher gain and an insufficient number of round-trips in the pulse train development     

Film-level hybrid integration of AlGaAs laser diode with glasswaveguide on Si substrate

A ridge-waveguide AlGaAs laser diode (LD) was integrated with a SiO₂-Ta₂O₅ embedded waveguide on a Si substrate by using a film-level hybrid integration technique of semiconductor epitaxial film. CW operation of the LD was achieved at room temperature. The LD-waveguide butt-coupling loss was 9 dB, and the loss due to misalignment was estimated at 3 dB, which corresponds to a displacement of about 1 μm in both the vertical and lateral directions     

高功率266 nm全固态单频连续波激光器研究进展

高功率单频连续波266 nm激光在大容量信息存储、高分辨光谱监测及高精度紫外光刻等领域具有重要应用价值,近年来已成为国内外紫外激光领域的研究热点之一。文中首先综合比较了用于产生高功率266 nm紫外激光的非线性光学晶体基本性能,并根据主要的激光器频率锁定方法,重点分析了H?nsch-Couillaud (H-C)频率锁定和Pound-Drever-Hall (PDH)频率锁定方法的优缺点以及连续波单频266 nm激光器发展现状,介绍了本课题组最新研究成果,即基于H-C频率锁定方法实现了功率1.1 W的单频连续波266 nm紫外激光稳定输出。最后,针对进一步提升全固态单频连续波266 nm激光器性能亟需解决的问题和可能解决路径进行了简要分析和展望。     

Tunable infrared generation using a femtosecond 250 kHz Ti:sapphireregenerative amplifier

A mode-locked Ti:sapphire regenerative amplifier system pumped with a single argon ion laser produces μJ energy 100 femtosecond pulses of 800 nm wavelength at 250 kHz repetition rate. Pumping a Type II BaB₂O₄ (BBO) optical parametric amplifiers (OPA) with this output generates 500 nJ infrared pulses and continuous tuning from 1.1 μm to beyond 2.5 μm. Difference frequency generation of the signal idler output from this OPA source in AgGaS₂ produces 60 nJ mid infrared pulses and continuous tuning from 2.4 μm to beyond 12 μm     

Use of laser diodes locked to atomic transitions in multiwavelengthcoherent communications

The possibility of building multiwavelength coherent communication systems based on low-cost semiconductor lasers in the 0.8 μm range locked to rubidium linear absorption is investigated. The values of frequency offset between the resonances of both the D₂ (780 nm) and D₁ (794.7 nm) lines are considered. A simple two-carrier FDM set-up using three resonances of the D₂ line is presented and the optical frequency offsets are measured     

Semiconductor microlenses fabricated by one-step focused ion beamdirect writing

We fabricated a refractive semiconductor micro-lenses using a focused ion beam (FIB) direct writing technique. The simple one-step FIB process produced high-quality micro-lenses of silicon, the most popular and low cost semiconductor material used in optoelectronics. A spherical Si microlens with a nominal lens diameter of 48 μm exhibited a radius curvature and focal length of 100 and 40 μm, respectively. The maximum derivation between the measured and designed profiles is less than λ/100. The surface roughness, RMS, measured by use of atomic force microscope in 1× 1 μm² square area, is 1.1 nm. This microlens fabrication method could be readily applicable due to the simplicity in processing and the high-quality results     

Coherent frequency-domain reflectometry for characterization ofsingle-mode integrated-optical waveguides

Based on the principles of optical frequency domain reflectometry (OFDR), a highly resolving and sensitive technique suitable for detecting, localizing, and quantifying weakly reflecting irregularities in single-mode optical waveguides is developed. A distributed feedback (DFB)-laser diode at λ₀≅1.3 μm tuned within a range of Δλ≅6 nm and Δv≅1 THz, respectively, is used as a source in the experimental arrangement. An auxiliary interferometer is employed so that the tuning need not be linear in time, in contrast to early implementations. At present, with waveguide structures on InP under test, a spatial resolution of 50 μm and a dynamic range of about 60 dB are obtained. These data surpass OFDR results published so far. Prospects of closing the gap to coherence-domain reflectometric results and specific advantages make OFDR a promising technique     

Frequency-locking of 1.5-μm InGaAsP lasers to an atomic kryptonline without dithering the laser frequency

The frequency-locking of a 1.5-μm distributed-feedback (DFB) laser to an atomic Kr 2p₈-3d"₁ transition at 1.5244 μm that does not dither the laser frequency is discussed. Instead, the frequency-discriminant signal was obtained by dithering the Kr line with a small AC magnetic field using the Zeeman effect. The frequency shift of this Kr line was measured to be 1.25 MHz/G, and is linearly proportional to the applied magnetic field. Since the technique avoids dithering of the laser frequency without adding complexity in the servo-loop, it is well suited for developing master oscillators to be used in optical wavelength-division-multiplexed (WDM) networks     

Mid-infrared fluoride fiber lasers in multiple cascade operation

CW fiber laser cascades in an Er³⁺-doped fluorozirconate fiber operating simultaneously at 2.7 μm/1.55 μm or at 3.45 μm/2.7 μm/1.55 μm pumped around 650 nm are reported. Output powers of nearly 20 mW at 1.55 μm and 1.2 mW around 2.7 μm were obtained with a nonoptimized experimental setup for the 2.7 μm/1.55 μm cascade. At 1.55 μm a laser efficiency of 5% was achieved. By varying the parameters of the experimental setup, additional effective simultaneous laser action at 3.45 μm was demonstrated     

Characterization of a distributed feedback laser withair/semiconductor gratings embedded by the wafer fusion technique

Wafer fusion between patterned or structured wafers is very useful in the construction of new optical materials and/or devices that have submicrometer-order structures inside semiconductors. In order to investigate the feasibility of wafer fusion for this purpose, a distributed feedback (DFB) laser wafer developed which has air/semiconductor gratings that are embedded using the wafer fusion technique. In this paper, the characteristics of the newly developed DFB laser and the coupling coefficient are investigated. Single-longitudinal-mode oscillation at 1.28 μm is achieved under pulsed conditions at room temperature with a low threshold current density of 1.3 kA/cm², and the coupling coefficient is estimated to he approximately 100 cm^-1. In addition, high-power surface emission (over 6 mW) is demonstrated due to the large difference between the refractive index of air and that of InP. These results indicate the feasibility of applying wafer fusion techniques to form submicrometer structures in semiconductors, and several other applications are expected