Tunable External Cavity Diode Laser Research Articles

Design and Simulation of Silicon‐Based Tunable External Cavity Diode Lasers in the 1967-2033 nm Wavelength Range

Design and Simulation of Silicon‐Based Tunable External Cavity Diode Lasers in the 1967-2033 nm Wavelength Range

Review of 1.55 μm Waveband Integrated External Cavity Tunable Diode Lasers

The 1.55 μm waveband integrated external cavity tunable diode lasers have excellent merits such as their small volume, low cost, low power consumption, wide tuning range, narrow linewidth, large side mode suppression ratio, and high output power. These merits have attracted many applications for the lasers, such as in wavelength division multiplexing, passive optical networks, mobile backhaul, and spectral sensing technology. In this paper, firstly, the basic structure and principle of integrated external cavity tunable diode lasers are introduced, and then two main integrated structures of 1.55 μm waveband external cavity tunable diode lasers are reviewed and compared in detail, namely the hybrid integrated structure and monolithic integrated structure of 1.55 μm waveband integrated external cavity tunable diode lasers. Finally, the research progress in 1.55 μm waveband integrated external cavity tunable diode lasers in the last decade are summarised, and the advantages and disadvantages of 1.55 μm waveband integrated external cavity tunable diode lasers are analysed. The results show that, with the transformation of optical communication into more complex modulation formats, it is necessary to integrate miniature 1.55 μm waveband external cavity tunable diode lasers. Low-cost integrated 1.55 μm waveband external cavity tunable diode lasers are expected to be used in the next generation of optical transceivers in small-factor modules.

Study on the Technique for Wavelength Modulation Spectroscopy with Narrow Band Interference Filter Based External Cavity Diode Laser

In this study, an improved tunable external cavity diode laser (ECDL) is proposed. It is on the basis of narrow band interference filter, and its theoretical research is carried out as the light source of tunable diode laser absorption spectrum-wavelength modulation spectrum (TDLAS-WMS) system. The proposed model can use piezoelectric ceramic actuator to change and modulate its output central wavelength so that the laser central wavelength could periodically scan the absorption spectral band of the desired gas. Compared with the tunable monolithic diode laser, the narrow band interference filter based tunable ECDL might be able to accurately sense the type and concentration of a large variety of gases. Therefore, it can be used in the TDLAS-WMS system for high precision gas sensing and is expected to replace the tunable monolithic diode laser.

External-cavity diode laser-based near-infrared broadband laser heterodyne radiometer for remote sensing of atmospheric CO2.

A near-infrared broadband (1500-1640 nm) laser heterodyne radiometer (LHR) with a tunable external-cavity diode laser as the local oscillator is developed and the relative transmittance, which represents the absolute relationship between the measured spectral signals and the atmospheric transmittance, is derived. High-resolution (0.0087 cm-1) LHR spectra in the spectral region of 6248.5-6256 cm-1 were recorded for the observation of atmospheric CO2. Combined with the relative transmittance, the preprocessed measured LHR spectra, the optimal estimation method, and the Python scripts for computational atmospheric spectroscopy, the column-averaged dry-air mixing ratio of CO2 of 409.09 ± 8 ppmv in Dunkirk, France on February 23, 2019, was retrieved, which is consistent with GOSAT and TCCON data. The near-infrared external-cavity LHR demonstrated in the present work has a high potential for use in developing a robust, broadband, unattended, and all-fiber LHR for spacecraft and ground-based atmospheric sensing that offers more channel selection for inversion.

1.7 THz tuning range pivot-point-independent mode-hop-free external cavity diode laser.

A novel mode-hop-free (MHF) tunable external cavity diode laser (ECDL) is demonstrated without mechanical pivot-point tuning. By corotating a periscope with an etalon and a narrow band pass (NBP) filter inside an external cavity, the cavity single longitudinal mode selection can be maintained, and continuous tuning can be achieved with optimal synchronization. A MHF continuous tuning range of 1.7 THz has been achieved with a semiconductor gain chip at the wavelength of 652 ± 2 nm experimentally, and the theoretical tuning range can reach over 4.8 THz. The laser linewidth is estimated to be less than 1 MHz (FWHM) by a scanning Fabry-Perot (F-P) and a Michelson interferometer. 1 mW output power with variation of less than 10% in the tuning region of roughly 1.7 THz has been demonstrated.

Development of a Near-Infrared Photoacoustic System for Selective, Fast, and Fully Automatized Detection of Isotopically Labeled Ammonia.

Different environmental and industrial technologies seek for fast and automatic ammonia detection systems, capable of the selective measurement of the concentration of its isotopes at sub-ppm levels, without any interference with the common contaminants. In this work, we report the quasi-simultaneous measurement of 14NH3 and 15NH3 concentrations based on a near-infrared diode laser-based photoacoustic system. Using a widely tunable external cavity diode laser, four nearby wavelengths within the range of 1531.3–1531.8 nm were optimal circumstances for sensitive detection, while avoiding interference with water vapor. Subsequently, a more robust distributed feedback diode laser was employed to tune the laser wavelength on the sub-second timescale by varying its driving current rather than using much slower temperature tuning. The detection limit of our system is 0.15 and 0.73 ppm for 14NH3 and 15NH3 (with an accuracy below 0.1%), respectively, and the response time is 3.5 s.

High bandwidth frequency modulation of an external cavity diode laser using an intracavity lithium niobate electro-optic modulator as output coupler

We present a novel approach to high bandwidth laser frequency modulation. A lithium niobate chip is used as an intracavity electro-optic modulator in a tunable cateye external cavity diode laser. The modulator is conveniently integrated with the cateye output coupler, providing a unique approach to high bandwidth frequency stabilization and linewidth narrowing. The intracavity modulator feedback was successfully operated below 1 V and achieved superior frequency noise suppression compared to conventional feedback through diode injection current modulation. A closed loop bandwidth of 1.8 MHz was demonstrated, and the laser linewidth reduced to around 1 Hz as measured by the heterodyne measurement.

Laser stabilization to neutral Yb in a discharge with polarization-enhanced frequency modulation spectroscopy

Isotope selective optical excitation of atoms is important for experiments with neutral atoms, metrology, and work with trapped ions, including quantum information processing. Polarization-enhanced absorption spectroscopy is used to frequency stabilize a tunable external cavity laser diode system at 398.9 nm for isotope selective photoionization of neutral Yb atoms. This spectroscopy technique is used to measure isotope resolved dispersive features from transitions within a see-through configuration ytterbium hollow-cathode discharge lamp. This Doppler-free dichroic polarization spectroscopy is realized by retro-reflecting a laser beam through the discharge and analyzing the polarization dependent absorption with balanced detection. The spectroscopy signal is recovered using lock-in detection of frequency modulation induced by current modulation of the external cavity laser diode. Here, we show an order of magnitude improvement in the long-term stability using polarization-enhanced absorption spectroscopy of Yb compared to polarization spectroscopy.

Development of an interference-filter-type external-cavity diode laser for resonance ionization spectroscopy of strontium.

A frequency tunable external-cavity diode laser (ECDL) using a narrow bandwidth (∼0.3 nm) interference filter has been developed for resonance ionization spectroscopy of strontium (Sr) with high isotopic selectivity. Improved wavelength and single mode stabilities of this interference-filter-type ECDL (IF-ECDL) over a commonly used (also home-made) Littrow-type ECDL were theoretically expected and experimentally confirmed by both a wavelength meter and a home-made Fabry-Perot interferometer. The measured spectral profile of the dominant isotope 88Sr using our IF-ECDL in the 689.4 nm intercombination transition shows that the Lorentzian component (∼1.3 MHz) of the spectrum width is consistent with the obtained fringe width of the interferometer. High 90Sr isotopic selectivity of ∼104 with respect to 88Sr is expected in this transition, which indicates that even if the manufacturing accuracy is not comparable to commercial Littrow-type ECDLs, our compact IF-ECDL having sufficient wavelength stability is a promising laser source for background-free analysis of radioactive 90Sr in marine samples.

Construction and Characterization of External Cavity Diode Lasers Based on a Microelectromechanical System Device

Widely tunable external cavity diode lasers (ECDLs) with a narrow linewidth have become a powerful tool for a variety of applications. The difficulty of the present generation of ECDLs is that they are designed as laboratory instruments and are limited due to their size, high costs, and sensitivity to external influences. In this paper, we present our new ECDL design based on a microelectromechanical system (MEMS) device. This design overcomes the previous drawbacks and offers an outstanding improvement of the most important properties. Moreover, it can be adapted to any wavelength of interest and by using MEMS technology, costs can be reduced.

An Ultra-High-SMSR External-Cavity Diode Laser with a Wide Tunable Range around 1550 nm

In this paper, a widely tunable external cavity diode laser (ECDL) with an ultra-high side mode suppression ratio (SMSR) was fabricated. Three configurations were constructed to investigate the relationship between the grating features and the SMSR. When a 1200 grooves/mm grating with a first order diffraction efficiency of 91% is utilized in the external-cavity laser system, a maximum SMSR of 65 dB can be achieved. In addition, the tunable range reaches 209.9 nm. The results show that the laser performance can be improved by proper high grating groove number and first-order diffraction efficiency.

1550 nm external cavity diode laser with enhanced SMSR based on polarization mismatch by grating rotation.

A tunable external cavity diode laser (ECDL) with high side-mode suppression ratio (SMSR) is demonstrated. The ECDL is operated at both strong and weak feedback steady states with single longitudinal mode. Compared with the strong feedback mode, the SMSR of the weak feedback mode is significantly enhanced by rotating the grating along the axis of the incident beam, which changes the polarization orientation versus the grating grooves. The highest SMSR of the weak feedback mode is 54dB at the injection current of 300mA. The tunable range of the ECDL with weak feedback mode reaches 130.9nm.

A tunable external cavity laser operating at excited states of bimodal-sized quantum-dot

In this paper, a tunable external cavity diode laser (ECDL) based on the first excited states of two independent quantum dot (QD) ensemble has been demonstrated. The device exhibits stabilized lasing with high-power of 120 mW. We attribute the excellent output characteristics of the QD ECDL to carrier radiation recombination in high energy states, which has higher degeneracy than low energy states and can accommodate more carriers. The linewidth of ECDL is less than 0.2 nm, which is also much narrower than most of QD ECDLs as reported. Preliminary discussion attributes the spectra feature to the lower QD density and independent carrier transitions. The tunable range is 28.9 nm (970.1–999 nm) and the wavelength shift with the injection current is 0.7 nm A−1.

Slope efficiency of integrated external cavity hybrid lasers: A general model and analysis

The integrated tunable external cavity diode laser (ECDL) plays an important role in many emerging applications, such as LiDAR, integrated free-space optical communication, integrated nonlinear optics, quantum information processing, and data center optical interconnects. Based on the III-V/silicon or III-V/silicon nitride hybrid integration, chipscale tunable ECDL could achieve a broad wavelength tuning range (>100nm) and very narrow linewidth (<10kHz) with the help of micro-ring resonators. However, most hybridly integrated ECDLs exhibit a low slope efficiency (<0.1W/A), which severely limits the laser performance. We have developed a general numerical model for the hybrid laser and investigated several methods to improve its slope efficiency. We show that the slope efficiency of the hybrid laser can be efficiently increased by controlling the external cavity phase, improving the coupling between the laser chip and passive chip, using optimized anti-reflection and high reflection coatings, and reducing the laser intrinsic loss. We have also experimentally built an arrayed waveguide grating (AWG) based hybrid laser and shown that the numerical simulation results match well with the experimental results.

Multicascade-linked synthetic wavelength digital holography using an optical-comb-referenced frequency synthesizer.

Digital holography (DH) is a promising method for non-contact surface topography because the reconstructed phase image can visualize the nanometer unevenness in a sample. However, the axial range of this method is limited to the range of the optical wavelength due to the phase wrapping ambiguity. Although the use of two different wavelengths of light and the resulting synthetic wavelength, i.e., synthetic wavelength DH, can expand the axial range up to several hundreds of millimeters, its axial precision does not reach sub-micrometer. In this article, we constructed a tunable external cavity laser diode phase-locked to an optical frequency comb, namely, an optical-comb-referenced frequency synthesizer, enabling us to generate multiple synthetic wavelengths within the range of 32 µm to 1.20 m. A multiple cascade link of the phase images among an optical wavelength ( = 1.520 µm) and 5 different synthetic wavelengths ( = 32.39 µm, 99.98 µm, 400.0 µm, 1003 µm, and 4021 µm) enables the shape measurement of a reflective millimeter-sized stepped surface with the axial resolution of 34 nm. The axial dynamic range, defined as the ratio of the axial range ( = 2.0 mm) to the axial resolution ( = 34 nm), achieves 5.9 × 105, which is larger than that of previous synthetic wavelength DH. Such a wide axial dynamic range capability will further expand the application field of DH for large objects with meter dimensions.

Dynamics of a green high-power tunable external-cavity broad-area GaN diode laser

Although external-cavity feedback with a grating is widely used to achieve a tunable high-power narrow-linewidth broad-area diode laser (BAL) system, the dynamics of such a system is seldom studied. In this paper, the temporal dynamics of a tunable high-power green external-cavity diode laser system based on a GaN BAL and Littrow external-cavity is investigated experimentally. The regular pulse package oscillation (PPO) is observed just above the threshold. The oscillating period of the pulse package decreases with the increasing injected current. As the current increases further, the pulse package oscillates irregularly, and finally changes to a chaotic state. The PPO is observed, for the first time to our knowledge, in a BAL with an external-cavity grating feedback.

Narrow-line external cavity diode laser micro-packaging in the NIR and MIR spectral range

Narrow-linewidth tunable diode lasers are an important tool for spectroscopic instrumentation. Conventional external cavity diode lasers offer high output power and narrow linewidth. However, most external cavity diode lasers are designed as laboratory instrument and do not allow portability. In comparison, other commonly used lasers, like distributed feedback lasers (DFB) that are capable of driving a handheld device, are limited in power and show linewidths which are not sufficiently narrow for certain applications. We present new miniaturized types of tunable external cavity diode laser which overcome the drawbacks of conventional external cavity diode lasers and which preserve the advantages of this laser concept. Three different configurations are discussed in this article. The three types of miniaturized external cavity diode laser systems achieve power values of more than 50 mW within the 1.4 $$\mu$$ m water vapor absorption band with excellent side-mode suppression and linewidth below 100 kHz. Typical features outstand with respect to other type of laser systems which are of extended use such as DFB laser diodes. The higher output power and the lower linewidth will enable a higher sensitivity and resolution for a wide range of applications.

Integral force feedback control with input shaping: Application to piezo-based scanning systems in ECDLs.

In this paper, a hybrid control system is developed by integrating the closed-loop force feedback and input shaping method to overcome the problem of the hysteresis and dynamic behavior in piezo-based scanning systems and increase the scanning speed of tunable external cavity diode lasers. The flexible hinge and piezoelectric actuators are analyzed, and a dynamic model of the scanning systems is established. A force sensor and an integral controller are utilized in integral force feedback (IFF) to directly augment the damping of the piezoelectric scanning systems. Hysteresis has been effectively eliminated, but the mechanical resonance is still evident. Noticeable residual vibration occurred after the inflection points and then gradually disappeared. For the further control of mechanical resonance, based on the theory of minimum-acceleration trajectory planning, the time-domain input shaping method was developed. The turning sections of a scanning trajectory are replaced by smooth curves, while the linear sections are retained. The IFF method is combined with the input shaping method to control the non-linearity and mechanical resonance in high-speed piezo-based scanning systems. Experiments are conducted, and the results demonstrate the effectiveness of the proposed control approach.

500 mW tunable external cavity diode laser with narrow line-width emission in blue-violet region

A tunable external cavity diode laser (ECDL) system with narrow line-width emission at 410nm is presented. Based on a commercially available laser diode and a Littrow arranged reflective holographic grating, a maximum output power over 500mW with line-width of about 50pm is achieved at the rated current. The power efficiency is over 85% and the threshold decreases over 20% compared to the free-running laser diode. Manual tuning range over 5nm is achieved around threshold condition and over 2nm at high injection currents up to 500mA with side mode suppression ratio larger than 20dB.

Frequency comb calibrated frequency-sweeping interferometry for absolute group refractive index measurement of air.

The absolute group refractive index of air at 194061.02GHz is measured in real time using frequency-sweeping interferometry calibrated by an optical frequency comb. The group refractive index of air is calculated from the calibration peaks of the laser frequency variation and the interference signal of the two beams passing through the inner and outer regions of a vacuum cell when the frequency of a tunable external cavity diode laser is scanned. We continuously measure the refractive index of air for 2h, which shows that the difference between measured results and Ciddor's equation is less than 9.6×10-8, and the standard deviation of that difference is 5.9×10-8. The relative uncertainty of the measured refractive index of air is estimated to be 8.6×10-8. The data update rate is 0.2Hz, making it applicable under conditions in which air refractive index fluctuates fast.