Novel tunable twin-guide lasers with a carrier-control tuning layer

The realization of a coherent frequency-modulated continuous-wave LIDAR aimed for the accurate measurement of short distances employing a distributed feedback tunable twin-guide laser diode is demonstrated. Theoretical calculations on the ultimate limits in accuracy of distance measurements as determined by the laser phase noise are carried out. A relative accuracy of 8x 10-5 (8 μm) for a single-shot measurement has been achieved at a distance of 10 cm, which is significantly better than expected from the laser linewidth. The results presented here prove the predictions calculated from theory.

Miniaturized tunable lasers are important as light sources in optical networks and sensing systems. However, challenges remain in realizing a low-cost on-chip tunable laser with high tuning accuracy and wide tuning range. Here, an external-cavity tunable laser integrated by using a pair of coupled-ring resonators as a reflector onto a single silicon chip is designed and demonstrated. The silicon coupled-ring reflector provides simultaneous tuning of the central reflective wavelength and the free spectral range of the entire cavity to guarantee phase matching. The effective optical length of the coupled-ring reflector is controlled by the complementary thermo-optic and free-carrier dispersion effects, thus enabling high-resolution wavelength fine-tuning while maintaining wide wavelength tuning range. Experimentally, the tunable laser has high external-cavity efficiency (22%) and high wavelength tuning accuracy (2 pm) throughout the 41.6 nm tuning range. Potential applications of the external-cavity tunable laser include optical networks, optical sensing, and on-chip optoelectronic systems.

The wavelength tuning and intensity modulation characteristics are presented for three types of twin-guide (TG) lasers entirely fabricated by metalorganic vapour phase epitaxy (MOVPE). A wide continuous tuning range of 5.3 nm is obtained for the tunable twin-guide (TTG) laser. The TTG lasers, however, have the drawbacks of output power reduction and spectral linewidth broadening during tuning. A new type of tunable laser, the complementary twin-active-guide (CTAG) laser, is proposed, and its tuning characteristics are presented for the first time. A wide continuous tuning range over 4 nm is obtained, although the thermal effect is more dominant than carrier effects. The CTAG structure enables suppression of the spectral linewidth broadening induced by the injected carrier recombination shot noise (IRSN) during tuning. The characteristics of the TG lasers modulated by reverse bias are presented, and the possibility of using these TG lasers for wavelength tuning is studied.

Multi-wavelength distributed feedback laser array (DFB-MLA) based tunable semiconductor lasers have been widely used owing to the high mode stability and simple wavelength tuning scheme. In this paper, we proposed and experimentally demonstrated a matrix-grating tunable DFB laser array. And the reconstruction-equivalent-chirp (REC) technique is utilized to simplify grating fabrication and realize precise control of the grating phase. Traditionally, the laser is tuned by thermal-electric cooler (TEC), with large power consumption, slow wavelength tuning capability, and added device. To improve the wavelength tuning speed of laser, we varied laser's injection current instead of adjusting TEC's temperature. In addition, we analyzed the thermal influence of submount on the laser and then chose the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> as the submount material for its low thermal conductivity and poor heat dissipation, resulting in wide wavelength tuning range via injection current. The DFB-MLA chip achieves a better tunable effect as the lasers can be tuned at 3.5-3.7 nm per channel from 50 to 120 mA with stable output power of over 3 mw as contrasted with the laser on the AlN submount being tuned at 1.4-1.5 nm per channel. And the chip has a side-mode suppressing ratio (SMSR) of over 35 dB and strong stability of wavelength in the repeated experiments. The proposed method may give a new way to realize the wide tuning range tunable DFB laser with a simple wavelength tuning mechanism in the future, especially for the applications of uncooled low-cost tunable lasers.

Tunable laser diodes are now widely used in dense wavelength division multiplexing (DWDM) optical fiber networks. A wide tunability range and good frequency stability are generally required, without mode hopping. Special applications require fast frequency measurement. Unfortunately, commercially available classical spectral measurement systems are much too slow for that purpose. In this paper, we present a new and low-cost system dedicated to fast spectral measurements based on a Michelson interferometer. The free spectral range (FSR) of the interferometer must be carefully optimized. We have designed optimized and tested an experimental system that can quickly analyze with good accuracy the tunability range of tunable distributed Bragg reflector (DBR) laser diodes, and their possible mode hopping. Our set-up can also be used for other spectral measurements (linewidth, chirp, Henry's alpha enhancement factor, spectral and power monitoring). After theoretical analysis of our experimental set-up, we finally present the fast spectral measurements results obtained with a typical 1550 nm two sections DBR QW (quantum well) laser diode. Our measurements have been obtained within less than 500 ps, which is much faster than limits induced by switching thermal effects in laser diodes, and that speed could still be increased.

Fiber-optic sensors have experienced great interest in research and development since their invention. Dedicated measurement systems are essential for utilization and development of these sensors. Instruments based on tunable lasers are established devices for the demodulation of such sensors. We introduce and demonstrate a tunable laser measurement system based on a widely tunable monolithic laser diode (TML). It is capable of demodulating different types of fiber-optic sensors, although we focus on the interrogation of fiber Bragg grating (FBG) sensors. The rapid tuning of the laser's wavelength is critical for achieving high measurement rates. However, the high tuning rate is demanding and requires careful characterization. We present a method for this and show, to our knowledge for the first time, data on the rapid tuning through the whole spectrum of this type of laser diode. We propose a modified centroid algorithm that can cope with nonequidistantly sampled spectra caused by the laser's functional principle. Finally, we demonstrate the dynamic performance of the new measurement system in an application: An FBG-based acceleration sensor is demodulated at a 5-kHz sample rate during a vibrational test showing the potential of the approach.

We show a fully integrated, coherently combined laser system in the InP-Si3N4 hybrid platform. Coherent combining of two InP-based gain chips is obtained with a combining efficiency of ~92%. Besides, we demonstrate narrow-linewidth, tunable diode lasers in InP/GaAs-Si3N4 platform. The Si3N4 photonic integrated circuit performs as a tunable external cavity for both InP and GaAs gain chips simultaneously. Single frequency lasing at 1.55 and 1 um is simultaneously obtained on a single chip with the spectral linewidths of 18-kHz and 70-kHz respectively. We also obtain wide-angle beam steering by using the wide wavelength tuning range provided by dual-band diode lasers.

A new asymmetric dual quantum well laser diode with a segmented contact is proposed. With inhomogeneous current injection, the lasing wavelength can be changed quasi-continuously over 22 nm, which is much wider than any tuning range previously reported. To achieve such wide-range tuning, it is found to be essential that the length of the cavity and each segment (and the mirror reflectivity) of the laser diode should be within an optimized range. In the asymmetric dual quantum well laser diode structure used in the present experiment, in particular, the cavity length should be such that light of a shorter wavelength lases under homogeneous excitation.

Vertical-cavity surface-emitting lasers (VCSELs) are used for oxygen monitoring via tunable diode laser spectroscopy at 760nm wavelength. For the desired application, novel polarization-stable laser diodes based on AlGaAs were developed. We present measurements of the pressure-broadening coefficients of the electric dipole forbidden oxygen A-Band b¹&#931;^g ₊ -> X³&#931;^g ₊ transition at 760nm. For the first time the pressure-broadening coefficients were determined with a temperature tuned vertical-cavity surface-emitting laser. Because of special techniques of polarization stabilization with a combination of a dielectric surface grating and a surface relief the VCSELs have a mode hop-free tuning range of more than 7nm and a sidemode suppression of more than 30dB. This provides a low cost laser diode system with a wide tuning range, which enables the possibility of simultaneous measurement of temperature, pressure and oxygen concentration in air, high pressure measurements and also a higher accuracy of oxygen concentration measurements due to averaging over 18 absorption lines.

A mid-infrared spectrometer with a tuning range of >400 cm(-1) in the C-H stretching region of the spectrum has been designed and constructed. The spectrometer is based on the difference-frequency generation of two tunable diode lasers in periodically poled lithium niobate waveguides. Tuning is achieved by varying a single parameter, the wavelength of one of the near-infrared input lasers. The instrument can be tuned over the entire tuning range in less than 1 s. By taking advantage of the wide tuning range, the instrument has been used to analyze a mixture of methane, ethylene, and propylene. Each of these major components was measured with an accuracy of better than 2% (where the error is defined as a percentage of the measured value) in a single 30 s long scan. When optimized, the spectrometer has the potential to meet both the performance requirements and the practical requirements for real-time process control in petrochemical manufacturing. The general principles for the design of mid-infrared spectrometers with wide tuning ranges are explained, including the use of variable waveguide fabrication recipes to create broad phase-matching resonances (which lead to broad tuning) in the desired location.

TOPTICA's continuously tunable laser, the CTL, enables mode‐hop‐free wavelength tuning up to 120 nm with narrow linewidth and highest accuracy. With applications in device characterization, quantum and materials analysis, it is ideal for any application requiring high precision mode-hop free laser operation over a wide tuning range. In this demo, Dr. Rudolf Neuhaus demonstrates how to operate the laser with the fully digital, low noise and drift DLC pro controller using intuitive touch screen controls. To illustrate the convenient features of the laser and DLC pro controller, the system is connected to a spectroscopy cell and the transmission spectra is measured by a photodiode and recorded by the DLC pro with the ability to review the data live and adjust operating parameters accordingly, including the ability to lock the laser to a specific laser line. For more information about the CTL, contact us at sales@toptica-usa.com.

The ClO fundamental absorption band near 850/cm is observed, with a tunable PbSnTe diode laser used as a source of monochromatic radiation. The chlorine monoxide concentration in the absorption tube was measured indirectly via a UV transmission technique. Frequencies and assignments for the ClO lines, and band centers and rotational constants for the ClO fundamental vibration, are tabulated. Diatomic vibration-rotation transitions within and between electronic substates are discussed. The tunable diode laser is valuable for studying the hyperfine structure. The IR spectroscopic technique is developed in order to monitor chlorine monoxide concentration in the stratosphere, since the short-lived ClO is a crucial intermediate participant in reactions involving destruction of stratospheric ozone.

A model based on the transfer matrix method (TMM), for the analysis of photon density distribution in Three Section Distributed Bragg Reflector (DBR) Tunable Laser Diode, is presented. This model provides longitudinal distribution of photon density in each section of laser for different values of grating and phase current. It is shown that both grating and phase current caused to a downward shift of photon density distribution profile. Simulation shows that, photon density distribution has a peak at the active-passive interface.

GaAs-AIGaAs GRIN-SCH-SQW tunable DBR laser diodes are fabricated by EB lithography, ion implanta- tion, and two-step MOVPE growth. Active and passive wave- guides are monolithically integrated by the compositional dis- ordering of quantum-well heterostructures using silicon ion implantation. First-order gratings and rib waveguides are adopted with EB lithography to improve lasing characteristics, and they have wide application to photonic integrated circuits. Waveguide losses of partially disordered GRIN-SCH-SQW passive waveguides are as low as 4.4 cm-' at the lasing wave- length. A narrow linewidth as low as 560 kHz and a frequency tuning of more than 2.9 THz are obtained. The results show that this fabrication process is useful for photonic integrated circuits.

Optical ring or disk resonators can trap traveling optical waves in a closed path, for example, in a waveguide loop or silicon disk cavity. Energy can be added to or extracted from the cavity with the help of waveguide directional couplers. Ring/disk resonators can be fabricated with high quality factor (Q) in diverse material platforms. The high Q of these devices makes them very sensitive to small variations in (i) optical path length (phase), (ii) optical path loss (attenuation), and (iii) coupling coefficient. Any change in the optical path length can cause a shift in the resonance frequency of the ring. Whereas, the change in path loss and coupling coefficient can lead to a change in the Q of the resonator. The micro or nano opto-electro-mechanical systems (MOEMS/NOEMS) provide unique flexibility with a wide change in the tuning parameters. The tuning is obtained by either (i) displacement of the detached parts or (ii) strain in the waveguide/disk. Displacement of a structure detached from the ring/disk closer to the evanescent field can increase the effective refractive index or attenuation. The displacement of a waveguide in the directional coupler altering the gap can change the coupling coefficient. Strain from various sources can lead to refractive index (phase) and absorption changes, in addition to changing the dimensions. Mechanical, electrothermal, piezoelectric, electrostatic, and magnetic actuators have been demonstrated with MOEMS. Mechanical latching has been used to achieve nonvolatile tuning. Multi-beam supported, freestanding, and diaphragm supported structures have shown applications in sensing, optical switching, and energy conversion. MOEMS/NOEMS has recently been shown to provide the desired properties of modern sensors and photonic integrated circuits (PICs) such as low optical power consumption, high resolution, wide tuning range, low complexity, small footprint, low actuator power consumption, and compatibility with standard fabrication technologies. This chapter will start by briefly covering the basics of MOEM tuned ring/disk resonators. Then, the current technology aspects such as tuning mechanism, actuator types, and the fabrication technology will be discussed along with recent innovations. Furthermore, the evolution into NOEMS with specialized applications and materials will be emphasized along with emerging trends.