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We report on an index-coupled distributed feedback (DFB) quantum cascade lasers (QCLs) of high single-mode stability by using of a grating reflector (GR) to reflect effectively light of a specific wavelength. Fabrications of the QCLs were performed with λ∕4 equivalent phase shift (EPS) or sampled Moiré grating (SMG) structure, which regulates the light intensity distribution in the cavity and coupling strength. Both EPS-GR and SMG-GR QCLs demonstrate a high emission wavelength precision and a side-mode-suppression-ratio (SMSR) of 24.5 dB at the injection current of 5 A and the pulse width of 5 μs, offering considerable output power even at the edge of the gain spectrum. Furthermore, we investigated the arrays of EPS-GR and SMG-GR QCLs with lower threshold current and higher output power by introducing semi-insulated InP (Fe) ranging from 8.25 to 8.67 μm and 8.16–8.63 μm, respectively. The present QCLs via a GR are prospective for applications requiring single-mode stability and wide tunability.

High-power, low-threshold stable single-mode operation buried distributed feedback quantum cascade laser by incorporating sampled grating emitting at λ ~ 4.87 μm is demonstrated. The high continuous wave (CW) output power of 948 mW and 649 mW for a 6-mm and 4-mm cavity length is obtained at 20 °C, respectively, which benefits from the optimized optical field distribution of sampled grating. The single-mode yields of the devices are obviously enhanced by controlling cleaved positions of the two end facets precisely. As a result, stable single-mode emission and mode tuning linearly without any mode hopping of devices are obtained under the different heat sink temperatures or high injection currents.

A 20-channel distributed feedback (DFB) quantum cascade laser (QCL) arrays based on uniform buried grating have been demonstrated. In pulsed mode, peak power reaches 80 mW and slope efficiency reaches 167 mW/A for 2.5-mm-long laser in the arrays at room temperature. The loss difference of two band-edge mode increases when reflectivity of the front facet becomes small, which prevents the mode hopping. The device shows linear tuning after the anti-reflectivity coating is deposited in the front facet, maintaining peak power of 64 mW. The whole chip covers a tuning range of 64 cm-1, centering at 8.3 μm, with side-mode-suppression-ratio over 20 dB at room temperature.

Co-packaged optics for next-generation data center switches require novel photonic packaging and optical interconnect solutions to increase bandwidth and decrease manufacturing costs. An optoelectronic glass substrate with integrated ion-exchanged (IOX) single-mode waveguides for photonic integrated circuit (PIC) packaging and fiber cable connectivity is demonstrated in an effort to reduce the overall packaging complexity. The single-mode glass waveguides were fabricated and evaluated to be thermally stable at 110oC for more than 5 years. Laser singulated optical end-facets and laser-formed passive alignment features yield an average connector loss of 0.68 dB when end-coupled to standard MTP- 16™ connectors.

In this work, quantum cascade lasers (QCLs) based on strain compensation combined with two-phonon resonance design are presented. Distributed feedback (DFB) laser emitting at ~ 4.76 μm was fabricated through a standard buried first-order grating and buried heterostructure (BH) processing. Stable single-mode emission is achieved under all injection currents and temperature conditions without any mode hop by the optimized antireflection (AR) coating on the front facet. The AR coating consists of a double layer dielectric of Al2O3 and Ge. For a 2-mm laser cavity, the maximum output power of the AR-coated DFB-QCL was more than 170 mW at 20 °C with a high wall-plug efficiency (WPE) of 4.7% in a continuous-wave (CW) mode.

The instability of mode-locked pulses underneath Q-switched envelop limits the applications of Q-switched and mode-locked (QML) lasers. In this paper we present a developed theoretical model for QML laser at 1.3 µm. By adjusting the characteristics of the electro-optic modulator, V3+:YAG crystal, and laser resonator, stable single mode-locked pulse at 1.3 µm can be obtained at the pump power of 9 W. So far as we know, it is the first time to obtain single mode-locked pulses in QML laser at 1.3 µm by numerical simulation. Keywords: Single mode-locked pulse, Electro-optic modulator, Rate equations, Q-switched and mode-locked

Short-wavelength (4.25 μm) distributed-feedback quantum cascade laser operating in continuous wave (cw) mode at room temperature with low power consumption was presented. Stable single-mode operation with a side-mode-suppression-ratio above 25 dB was maintained for the whole measured current and temperature range by enlarging gain difference and strong grating coupling. Because of the strong coupling, very low threshold current and power consumption were achieved. For a device of 9-μm-wide and 2-mm-long, the cw threshold current and power consumption at 293 K were as low as 126 mA and 1.45 W, respectively. All results above were from the device without using buried heterostructure geometry.

Ever more precise radial velocity instruments are needed to observe potential earth-like exoplanet targets that are beyond the range of current generation high resolution echelle spectrographs. Meanwhile, extreme adaptive optics systems at 8 meter class facilities have made ground based observations possible at the diffraction limit. In the field of Doppler spectroscopy, one way to take advantage of these AO capabilities is by the development of ultra-stable single mode fiber fed spectrographs.1 Coupling the light efficiently into SMFs with an extreme adaptive optics system offers significant advantage in removing modal noise, reducing instrument size, enabling superior environmental control and curbing cost. We report the design and challenges in building an ultra-stable spectrograph for the near infrared range. The design wavelength range is 650 to 1500 nm.

Stable single mode operation of distributed feedback quantum cascade lasers operating in room-temperature continuous-wave mode is reported. Feedback is provided by the second-order grating in a both index- and loss-dominated coupling scheme. Reliable single mode emission at λ ∼ 4.7 μm with a side-mode suppression ratio ∼30 dB is observed. A linear tuning of wavelength with heat-sink temperature or injection current indicates the stable single mode operation without mode hopping.

The influence of external optical feedback (EOFB) on the lasing characteristics of 1.55-mum antiresonant reflecting optical waveguide (ARROW) vertical-cavity surface-emitting lasers (VCSELs) with various core radii are analyzed theoretically. It is found that ARROW VCSELs with large core radii (i.e., > 4 mum) respond more sensitively to EOFB than that with small core radii (i.e., les 4 mum). Furthermore, strong EOFB-driven ARROW VCSELs with large radii show more difficult to sustain single-mode chaotic oscillation than those with small radii. This is because radiation loss margin of ARROW reduces with the increase of core radii so that the presence of carrier spatial-hole burning deteriorates the stable single-mode operation of VCSELs. However, if the dimensions of ARROW as well as the radius of injection current aperture can be selected appropriately, stable single-mode chaotic light sources can be obtained from EOFB-driven ARROW VCSELs with large core radius.

We have developed single-mode vertical-cavity surface-emitting laser (VCSELs) with a mode selective aperture (MSA) in the DBR mirror that exhibits a high-order transverse-mode filtering effect. The VCSELs with an MSA were fabricated using standard intracavity-contacted VCSEL processes without any additional steps resulting from the simultaneous formation of the MSA and current aperture via a single-step oxidation. The VCSELs fabricated with a current aperture and MSA diameter of 5 and 7 μm, respectively, exhibited a stable single-mode operation with a side mode suppression ratio of over 35 dB and a divergence angle below 10° for the entire drive current range.

A stable single-mode operation mechanism in distributed feedback (DFB) lasers with wirelike active regions was theoretically investigated by taking into account "gain matching" between standing wave profiles of each resonant mode and periodic active regions. As a result, it was clarified that the resonant modes at the longer wavelength side of the stopband have higher modal gain than those at the shorter wavelength side and that the oscillation takes place at the longer wavelength side resonant mode nearest to the stopband. The influence of the cleaved facet with respect to the grating phase was also analyzed. The measured spectral properties of buried heterostructure GaInAsP/InP DFB lasers consisting of wirelike active regions, such as a subthreshold gain spectrum and the lasing wavelength with respect to the stop band, agreed well with theoretical results. Finally, it was confirmed that a stable single-mode operation was preserved even after a room temperature continuous wave aging of 7300 h at bias current of around 10/spl times/ the threshold.

This paper describes the design and operation of a stable narrow-linewidth linearly polarized fiber ring laser using a polarization-maintaining (PM) erbium-doped fiber as a saturable absorber. The effect of the PM fiber on suppressing mode hopping is experimentally demonstrated and optimum conditions for single-mode operation are identified. Laser output power is /spl sim/ 4.7 mW at 1535 nm for a pump power of 94 mW, the polarization extinction ratio is 24.8 dB, the SNR is larger than 45 dB, the relative intensity noise is below -104 dB/Hz at frequencies above 150 kHz, and the linewidth is less than 1.5 kHz. Potential applications of the fiber laser for interferometric or spectroscopic fiber sensors are briefly discussed.

In semiconductor lasers, nonlinear phenomena inside the active medium change the side-mode gain with respect to the static threshold-gain. For a given side mode, the sign and the magnitude of the change depend on the lasing-mode optical power and on the wavelength detuning from the lasing mode. If the side-mode gain is enhanced, mode-hopping can occur toward a side mode whose loss is higher than the lasing-mode one. Conversely, in the case of side-mode-gain suppression, the side-mode loss can be smaller with no mode-hop. In this paper, effects of carrier-density pulsation, carrier heating, and spectral-hole burning on the conditions of stable single-mode operation in grating-tuned single-mode extended-cavity semiconductor lasers are investigated. Taking into account the external cavity spectral selectivity and mode coupling, we present a theoretical analysis of experimental results. We perform calculations that compare well with the experimental data obtained with a 1.55-/spl mu/m extended-cavity laser.

We report an index-coupled distributed feedback quantum cascade laser by employing an equivalent phase shift (EPS) of quarter-wave integrated with a distributed Bragg reflector (DBR) at λ∼5.03 μm. The EPS is fabricated through extending one sampling period by 50% in the center of a sampled Bragg grating. The key EPS and DBR pattern are fabricated by conventional holographic exposure combined with the optical photolithography technology, which leads to improved flexibility, repeatability, and cost-effectiveness. Stable single-mode emission can be obtained by changing the injection current or heat sink temperature even under the condition of large driving pulse width.

In this paper, stable single-mode operation at high temperatures is produced by the surface-relief-integrated vertical cavity surface emitting laser (VCSEL). The gain-cavity mode detuning technique is employed to realize high operating temperatures for the VCSEL. The surface relief is etched in the centre of the top side as a mode discriminator for the fundamental mode output, and the threshold current minimum is 1.94 mA at high temperatures by the gain-cavity mode detuning technique. Maximum single-fundamental-mode output power of 0.45 mW at 80 °C is obtained, and the side mode suppression ratios (SMSRs) are more than 30 dB with increasing temperature and current, respectively.

International audience; High power single-mode pump laser diodes operating around 980nm are key components for Erbium-doped devices. Much effort is still currently devoted to improve both their wavelength stability and their achievable output power, while maintaining a stable single-mode operation.Usually, the emission wavelength is stabilized by an external Fiber Bragg Grating (FBG). This configuration requires free-space optics between the laser diode output facet and the fiber or a lensed fiber to ensure an efficient coupling efficiency. This constraint increases fabrication costs, dimensions and mechanical instabilities. Moreover, the maximum achievable output power is limited because a high optical power density can damage the laser facets. To increase the achievable output power, a solution consists in using Broad-Area Laser Diodes (BALD), which are multimode emitters that are composed of large active ribbons with width of some hundreds of micrometers. The objective is then to improve the beam quality by locking the BALD emission on its transverse fundamental mode. We propose in this article to insert an integrated adiabatic transition between the multimode laser and a single-mode FBG. This taper, made by ion-exchange in glass, provides a coupling efficiency of -22.0dB from the multimode laser emission to the single-mode fiber. An optical feedback of -34dB demonstrates the stabilization of the BALD spectrum at the Bragg wavelength. The spectrum of the device is characterized by a maximum side-mode suppression ratio of 35dB, a RMS spectral width of (0.16 ± 0.04) nm and a frequency shift with current of -12GHz/100mA.

In this paper we report the fabrication of a robust, tunable single-longitudinal-mode compound-ring Er/sup 3+/-doped fiber laser. The laser is fundamentally structured on an all-fiber compound-ring resonator in which a dual-coupler fiber ring is inserted into the main cavity. When combined in tandem with a mode-restricting intracavity tunable bandpass filter, the compound-ring resonator ensures single-longitudinal-mode laser oscillation. The laser can provide up to 20 mW output power over much of its 1525 to 1570 nm wavelength tuning range. The short-term linewidth of the laser output measured is less than 5 kHz. The laser frequency is actively stabilized for a long time by exploiting the inherent filter nature of the compound-ring resonator. The reduction of an associated frequency modulation is also discussed in detail.

By an improved optimization of the grating profile, an asymmetric three phase-shift (3PS) distributed feedback (DFB) laser structure is shown to achieve stable single mode oscillation up to high current injection levels. The analysis of those structures enhances the possibility of attaining high mode selectivity whilst ensuring almost flat profiles for the intracavity field distribution. The transfer matrix-method has been applied to evaluate the above-threshold performance of the asymmetric 3PS-DFB laser, namely the mode selectivity and the flatness versus biasing current. Outstanding improvements have been shown in comparison with the quarterly-wavelength-shifted DBF structure or with other similar but symmetric DFB structures referred in literature.

Terahertz (THz) range is an area of the electromagnetic spectra which has lots of applications but it suffers from the lack of simple working devices which can emit THz radiation, such as the high performance mid-infrared (mid-IR) quantum cascade lasers (QCLs) [1] based on InP technology [2]. The applications for the THz can be found in astronomy and space research, biology imaging, security, industrial inspection, etc. Unlike THz QCLs based on the fundamental oscillators, which are limited to cryogenic operations, semiconductor THz sources based on nonlinear effects of mid-IR QCLs do not suffer from operating temperature limitations, because mid-IR QCLs can operate well above room temperature. THz sources based on difference frequency generation (DFG) utilize nonlinear properties of asymmetric quantum structures, such as QCL structures.

There is much recent interest in atomic clocks with low power consumption, ultra-small volume, and long-term instabilities below, e.g., 10−11 over one day. Mobile satellite navigation and the synchronization of communication networks are most prominent applications. For example, miniaturized atomic clocks would be important elements for the precision time protocol (PTP), which is an approach to distribute synchronization over next-generation IP-based packet networks.

The regions in parameter space of stable single mode operation of a quasioptical gyrotron are determined theoretically for a number of configurations. A pencil beam is found to give rise to large operating regimes where single mode operation is stable. These regions shrink dramatically when an annular beam is considered. However, stable operation can be restored by slightly tilting the axis of the cavity.

In this paper we report the fabrication of a short, robust, single-mode Er/sup 3+/ fiber-grating laser. This laser is proven by the successful outcome of a long-term bit-error-rate test at the 10/sup -15/ level in a 5- G/s fiber transmission experiment. In the process we present a new pumping geometry, the elucidation of one origin of relaxation oscillations that have plagued previous lasers and the demonstration of a simple electronic feedback scheme for suppressing them. This prototype source shows real promise for use in a high-speed communications system. >

We report that an 850-nm vertical-cavity surface-emitting laser with a planar higher order mode absorber, formed by shallow Zn diffusion (

Vertical-cavity surface-emitting lasers (VCSELs) emitting at 894.6 nm wavelength have been fabricated for Cs-based atomic clock applications. For polarization control, a previously developed technique relying on the integration of a semiconducting surface grating in the top Bragg mirror of the VCSEL structure is employed. More specifically, we use a so-called inverted grating. The VCSELs are polarized orthogonal to the grating lines with no far-field diffraction side-lobes for sub-wavelength grating periods. Orthogonal polarization suppression ratios exceed 20 dB. The polarization stability has been investigated at different elevated substrate temperatures up to 80 °C, where the VCSEL remains polarization-stable even well above thermal roll-over. For the purpose of integration with the atomic clock microsystem, flip-chip-bondable VCSEL chips have been realized. Sub-mA threshold currents and sufficient output powers in the milliwatt range are achieved. The required modulation bandwidth of more than 5 GHz is reached at only 0.5mA bias. Maximum bandwidths above 10 GHz have been measured even at elevated temperatures up to 80 °C. Modulation current efficiency factors larger than 12 GHz/√mA are achieved at room temperature. Moreover, the intrinsic modulation characteristics of the VCSELs are investigated by precise curve fitting of measured small-signal modulation response curves and relative intensity noise spectra. A K-factor of less than 0.4 ns and a maximum 3 dB bandwidth exceeding 22 GHz are obtained.

Based on the modified ramp and fire technique, a novel injection seeding approach with real-time resonance tracking is successfully demonstrated in a single-frequency Nd:YAG pulsed laser. Appling a high-frequency sinusoidal modulation voltage to one piezo actuator and an adjustable DC voltage to another piezo actuator for active feedback, single-mode laser output with high-frequency stability is obtained, and the effect of the piezo hysteresis on the frequency stability can be eliminated for a laser diode pumped Q-switched Nd:YAG laser at a repetition rate of 400 Hz.

We propose a microgear cavity having a grating with the same period as that of a whispering galley mode standing wave. The FDTD simulation indicates that nonlasing modes having different order or phase are strongly suppressed and the stable single mode lasing is obtained.

A stable, 1.13 MW single-mode oscillation was obtained at 170 GHz in a short-pulse gyrotron with a high-order volume mode TE 31,8 . The maximum efficiency was 30%, and no power degradation due to mode competition was observed. This result indicates the potential for the development of a 170 GHz, 1 MW, CW gyrotron which is required for electron cyclotron heating and current drive of large fusion devices.

We describe hybrid lasers combining a semiconductor gain section and fiber cavity with integrated chirped Bragg reflector. These devices have produced output powers of 27.5 mW in a narrow linewidth (400 KHz) stable single longitudinal mode. The use of a chirped reflector to stabilize the single mode output, and correct grating orientation are described. The laser output has a side‐mode suppression ratio of over 55 dB at 27.5 mW output, and relative intensity noise (RIN) below 160 dB/Hz.

We report that an 850 nm VCSEL with a planar higher-order mode absorber formed by shallow Zn diffusion (

Direct frequency‐modulated operation of ridge‐guided linear grating‐surface‐emitting laser arrays is reported. Simultaneous far‐field and spectral measurements of these devices at 1 GHz modulation rates show that both single longitudinal mode and single spatial mode operation are maintained.

A design of single-mode distributed feedback quantum cascade lasers (DFB-QCLs) with surface metal grating is described. A rigorous modal expansion theory is adopted to analyse the interaction between the waveguide mode and the surface plasmon wave for different grating parameters. A stable single-mode operation can be obtained in a wide range of grating depths and duty cycles. The single-mode operation of surface metal grating DFB-QCLs at room temperature for λ = 8.5 µm is demonstrated. The device shows a side-mode suppression ratio of above 20 dB. A linear tuning of wavelength with temperature indicates the stable single-mode operation without mode hopping.

Graded photonic heterostructures (GPH) can be regarded as energy wells for photons. We show that judicious engineering of such photonic wells, obtained by tailoring the grading and the slit width of the GPH resonator, allows one to ensure spectrally single-mode emission on the fundamental symmetric mode in the whole lasing dynamical range of terahertz quantum cascade lasers. Furthermore, the radiative character of the symmetric mode leads to single-mode emission with mW output power in continuous-wave operation, as well as to single-lobed far-field beam patterns. A careful combination of theoretical analysis and experimental observations reveals that the results stem from interplay between mode competition and spatial hole burning effects.

An array of highly disordered i-ZnO:Al(3%) random cavities, which have 1 μm width, 150 nm thickness, and 2 mm length, is sandwiched between n-ZnO:Al(5%) and p-GaN/sapphire substrate to form an array of heterojunctions. The random cavities, which are electrically isolated and optically coupled with the adjacent random cavities, are laterally separated by a 1 μm wide Al2O3 dielectric insulator. Stable single-mode operation is observed from the laser diode array under high electrical pumping (i.e., >6×threshold current) at room temperature.

High-power, narrow-linewidth single-mode lasers have many applications in lightwave systems, particularly as sources in externally modulated communications systems. The ability to produce these devices with a t ightly controlled operating wavelength is very important.

The green noise in intracavity-doubled Nd:YVO4 lasers can be eliminated by single-mode operation of the device, although good long-term stability remains a problem. We have studied the threshold when multimode operation sets in, with both respect to polarization modes and longitudinal modes, as a function of various cavity parameters. It is demonstrated that the device is sensitive to perturbations in the birefringence and the optical path length of the elements in the cavity. The influence of energy migration and intensity-dependent losses that are due to frequency conversion is also discussed. Good control of the cavity temperature and dimensions is a key point for long-term stability.

Stable, single‐mode, linearly polarized emission has been achieved with a free‐electron laser (FEL) oscillator for pulses of up to 30 μs when gain differences are used to select between a limited number of cavity modes. The frequency‐ and phase‐modulation noise spectra are monitored by heterodyning and homodyning techniques, and the measured linewidth is near 70 kHz at 31 GHz. The FEL oscillator mechanism is inherently frequency stable and step tunable over a practical range of control parameters determined primarily by the stability of the electron beam voltage.

A distributed-feedback (DFB) laser emitting at 1.3-μm wavelength has been optimally designed to achieve stable single-mode operation well above threshold current. We fabricated DFB lasers with first-order corrugation in a newly developed buried heterostructure. One end of the laser cavity is as cleaved and the other end is low reflectivity coated. Optimum designing has been done on the structure taking account of phases of corrugation at facets and also the effect of spatial hole burning in the longitudinal direction caused by the nonuniform field distribution. The important result is that the spatial hole burning in the longitudinal direction drastically deteriorates the stable single-mode operation at the high optical output power level when the product of the coupling coefficient and the laser length is large. The configuration has been designed to minimize the nonuniformity of the optical field in the longitudinal direction. The optimally designed lasers exhibited a very low threshold total scattering. We discuss the effects of this on the autocorrelation function, as both the cluster size and scattering vectors are varied, the shape of the predicted values of the autocorrelation function is compared with experimental results.

Optimum design for stable single mode operation has been done for an asymmetric facet reflectivity type InGaAsP/InP DFB laser emitting at 1.3 μm. The design takes into account phase corrugation at both facets and the effect of spatial hole burning in the longitudinal direction realized in single mode operation with high efficiency.

We have reported that in aysmmetric mirror reflectivity GaInAsP/InP DFB laser, a high single longitudinal mode (SLM) operation yield was achieved by adjusting a KL to to be 0.5 to 1 and a power reflectivity of a low reflecting end to be 0.05 when the other end is as cleaved [1]. This is because that an axial hole burning effect which breaks SLM operation at high output power is not serious as to reduce the gain difference. In such a weakly coupled case, there is a possibility of unnecessary Fabry-Perot (FP) mode lasing due to a mismatch between a gain peak wavelength and a lasing wavelength of DFB mode when a temperature is changed. Here we have examined an effect of the mismatch for 1.3µm DFB lasers, and made clear an optimum region of the wavelength mismatch. With this optimization, low threshold high efficiency DFB lasers with high SLM operation yield over a wide temperature range have been realized.

A simple extension to the technique of "pre-lase" Q-switching ensures that a TEMoo mode, Q-switched Nd:YAG laser produces single longitudinal mode oscillation on every shot.

The injection of optical radiation from a master oscillator into a diode-laser array provides a means for achieving a single-lobed single-frequency output beam at power levels exceeding 100-mW cw. In our study of injection locking in diode-laser arrays, we used a single-frequency tunable cw dye laser as a master oscillator. This approach provides us with considerable control over the injection wavelength, bandwidth, intensity, and spatial profile. With a commercial ten-element diode-laser array operating at 100-mW output, we observe a single-lobed off-axis far-field beam pattern when a single element at either end of the array is injected at milliwatt power levels. In injection-locking conditions, a diode-laser linewidth of ≤2 MHz and a detuning range of several tens of gigahertz were measured. We also observe an angular scanning (1.2°) of the emission angle of the single-lobed output beam of the diode-laser array as the injection wavelength is varied over 50 GHz. This angular steering capability is of potential importance for the rapid direct pointing and scanning of diode-laser arrays.

A small helium-neon gas laser was assembled and tested. The unit features temperature-compensated cavity design, electromagnetically tunable cavity length, wide axial mode separation to assure single TEM oon mode operation, control circuitry for frequency sweep and AFC, and rugged coaxial construction. The re-entrant mirror mounts and the invar main-body assure negligible changes of the cavity length during warm-up and with changes of temperature, through proper choice of the respective expansion lengths. The high-gain double-walled plasma tube renders single-ended power output in excess of 200 microwatts at the 6328 A wavelength.

Hybrid DBR lasers composed of a semiconductor Fabry-Perot laser diode and a fiber Bragg grating have been demonstrated. In our approach, we use a single-angled facet laser diode and a conically lensed grating to obtain stable single-longitudinal mode operation over more than 85 mA current range with high side mode suppression ratio and narrow linewidth.