RESUMEN
We have designed and fabricated a hybrid integrated laser source with full C-band wavelength tunability and high-power output. The external cavity laser is composed of a gain chip and a dual micro-ring narrowband filter integrated on the silicon nitride photonic chip to achieve a wavelength tuning range of 55 nm and a SMSR higher than 50 dB. Through the integration of the semiconductor optical amplifier in the miniaturized package, the laser exhibits an output power of 220 mW and linewidth narrower than 8 kHz over the full C-band. Such a high-power, narrow-linewidth laser diode with a compact and low-cost design could be applied whenever coherence and interferometric resolutions are needed, such as silicon optical coherent transceiver module for space laser communication, light detection and ranging (LiDAR).
RESUMEN
We demonstrate a new optical pulse amplitude modulation (PAM) scheme where joint ultrastable time-frequency and gigabit ethernet data transfer with the same laser wavelength is realized. Time transmission is compatible with the White Rabbit (WR) based on gigabit ethernet networks, and frequency transmission is achieved by using 100MHz radio frequency (RF) modulation and the round-trip compensation methods. The laser is on-off keying (OOK) modulated by the WR signal, the RF and WR signal are modulated by optical PAM in a Mach-Zehnder interferometer modulator (MZM), and the local and remote site are connected by 96km urban fiber in Shanghai. The experimental results demonstrate that the frequency instabilities are 5.7E-14/1 s and 5.9E-17/104s, and the time interval transfer of 1 pulse per second (PPS) signal with less than 300fs stability after 104 s are obtained. This novel scheme can transmit frequency signals at hydrogen-maser-level stability in the gigabit ethernet network.
RESUMEN
Fiber-optic time and frequency synchronization technology demonstrates ultra-high synchronization performance and has been gradually applied in various fields. Based on frequency synchronization, this study addressed the problems of period ambiguity and initial phase uncertainty of the phase signal to realize the coherent transmission of the phase. An absolute phase marking technology was developed based on high-speed digital logic with zero-crossing detection and an optimized control strategy. It can realize picosecond-level absolute phase marking and provide a picosecond-level ultra-low peak-to-peak jitter pulse marking signal to eliminate phase period ambiguity and determine initial phase and transmission delay. Thus, by combining the high-precision phase measurement capability of the synchronized frequency signal and long-distance ambiguity elimination capability of the pulse-per-second signal, a high-precision remote coherent phase transmission over an optical fiber is realized. After frequency synchronization, the peak-to-peak jitter between the local and remote phase-marking signals can be only 3.3 ps within 10,000 s measurement time. The uncertainty of the coherent phase transmission is 2.577 ps. This technology can significantly improve the phase coherence of fiber-optic time and frequency transmission and provide a new approach to achieve peak-to-peak picosecond-level reference phase marking and high-precision fiber-optic remote coherent phase transmission. This demonstrates broad application prospects in coherence fields such as radar networking.
RESUMEN
A linearly swept laser source over broadband with a fast sweep rate and narrow linewidth is realized using a novel optoelectronic scheme based on a multi-wavelengths (mutually coherent) injected distributed feedback (DFB) laser. Under the condition of multi-wavelengths injection, the injection-locking and four-wave mixing (FWM) process can occur simultaneously in the DFB laser, inducing a swept laser source with a sweep range of 100 GHz and sweep rate of 10 THz/s. Furthermore, with the phase noise character analyzation of the swept laser source, the phase noise deterioration due to the radio frequency (RF) signal is studied quantitatively. Besides the influence of the RF signal noise, the phase noise deterioration in the FWM process can be suppressed completely with the phase-locked pump beam and signal beam based on the injection-locking principle. This low phase noise swept laser source with sub-kilohertz linewidth could have wide applications in lidar.
RESUMEN
Single frequency laser sources with low frequency noise are now at the heart of precision high-end science, from the most precise optical atomic clocks to gravitational-wave detection, thanks to the rapid development of laser frequency stabilization techniques based on optical or electrical feedback from an external reference cavity. Despite the tremendous progress, these laser systems are relatively high in terms of complexity and cost, essentially suitable for the laboratory environment. Nevertheless, more and more commercial applications also demand laser sources with low noise to upgrade their performance, such as fiber optic sensing and LiDAR, which require reduced complexity and good robustness to environmental perturbations. Here, we describe an ultralow noise DFB fiber laser with self-feedback mechanics that utilizes the inherent photothermal effect through the regulation of the thermal expansion coefficient of laser cavity. Over 20 dB of frequency noise reduction below several tens of kilohertz Fourier frequency is achieved, limited by the fundamental thermal noise, which is, to date, one of the best results for a free-running DFB fiber laser. The outcome of this work offers promising prospects for versatile applications due to its ultralow frequency noise, simplicity, low cost, and environmental robustness.
RESUMEN
We demonstrate a high-stability and multithreading coherent receiver for simultaneous distribution of stabilized optical and radio frequencies (RFs). The technique is based on a monolithic electroabsorption modulator integrated with a distributed feedback laser, which can purify and amplify the optical carrier while recovering the RF signal as a high-speed photodetector. The large-dynamic-range and high-bandwidth phase-locking system preserves the stability of the receiver for optical and RF signals to 3.5×10-20 and 6.4×10-18 at 1000 s, respectively. Furthermore, a dual-stabilization system using this novel receiver is proposed for simultaneous transfer of ultrastable optical carriers and RF signals over a 263 km fiber link. The transferred frequency stabilities of the optical carrier and the 9.1 GHz signal are 6.5×10-20 and 1.6×10-17, respectively, for an averaging time of 10,000 s.
RESUMEN
A novel optical injection locking amplifier with acousto-optic modulator based phase modulation and a coherent detection scheme for optical frequency transfer applications is experimentally demonstrated in this study. A commercial distributed feedback diode laser is injection-locked to the resonant frequency of the optical signal with an optical fiber path length of hundreds of kilometers. This provides approximately 59 dB gain and ensures that the input carrier frequency fractional stability can be as good as 10-20 at 1000 s. The amplifier was tested for the transfer of a commercial narrow-linewidth laser in a 180 km fiber link to a remote site with only a single amplification step. The transferred frequency at the remote end reached 10-20 at 20000 s, which is suitable for optical frequency distribution and remote comparison between optical atomic clocks.
RESUMEN
Atomic clocks based on laser-cooled atoms are widely used as primary frequency standards. Deploying such cold atom clocks (CACs) in space is foreseen to have many applications. Here we present tests of a CAC operating in space. In orbital microgravity, the atoms are cooled, trapped, launched, and finally detected after being interrogated by a microwave field using the Ramsey method. Perturbing influences from the orbital environment on the atoms such as varying magnetic fields and the passage of the spacecraft through Earth's radiation belt are also controlled and mitigated. With appropriate parameters settings, closed-loop locking of the CAC is realized in orbit and an estimated short-term frequency stability close to 3.0 × 10-13τ-1/2 has been attained. The demonstration of the long-term operation of cold atom clock in orbit opens possibility on the applications of space-based cold atom sensors.
RESUMEN
A ground-based double-pulse integrated path differential absorption (IPDA) instrument for carbon dioxide (CO2) concentration measurements at 1572 nm has been developed. A ground experiment was implemented under different conditions with a known wall located about 1.17 km away acting as the scattering hard target. Off-/offline testing of a laser transmitter was conducted to estimate the instrument systematic and random errors. Results showed a differential absorption optical depth (DAOD) offset of 0.0046 existing in the instrument. On-/offline testing was done to achieve the actual DAOD resulting from the CO2 absorption. With 18 s pulses average, it demonstrated that a CO2 concentration measurement of 432.71±2.42 ppm with 0.56% uncertainty was achieved. The IPDA ranging led to a measurement uncertainty of 1.5 m.
RESUMEN
The design process and simulation method of a multipass absorption cell used for the frequency stabilization of the reference seeder laser in integrated path differential absorption (IPDA) lidar are presented. On the basis of the fundamental theory of the Herriott multipass cell comprising two spherical mirrors, the initial parameters of the multipass cell, which has an optical path greater than 10 m and consists of two biconic mirrors, were calculated. More than 30 light spots were distributed on each mirror, and the distance between adjacent spots was mostly optimized to greater than six times the beam waist. After optimization, the simulated transmittance spectrum and associated differential signal were obtained. The interference induced by surface scattering was also simulated, and its influence on the differential signal was analyzed. A correspondence between the simulated results and the testing data was observed.
RESUMEN
We describe a highly reliable optical system designed for a rubidium space cold atom clock (SCAC), presenting its design, key technologies, and optical components. All of the optical and electronic components are integrated onto an optimized two-sided 300 mm×290 mm×30 mm optical bench. The compact optical structure and special thermal design ensure that the optical system can pass all of the space environmental qualification tests including both thermal vacuum and mechanical tests. To verify its performance, the optical system is carefully checked before and after each test. The results indicate that this optical system is suitably robust for the space applications for which the rubidium SCAC was built.
RESUMEN
The frequency of a distributed feedback diode laser (DFB-LD) is stabilized on Cesium ((133)Cs) D(2) saturated absorption lines by the polarization rotated optical feedback method (PROF). Different from the conventional frequency stabilization methods by adjusting the LD pump current, no extra electrical feedback is needed with the PROF. The self-homodyne beat spectra FWHM linewidth of the DFB laser is measured to be 1.1 MHz, greatly reduced by a factor of about 40 from its free-running linewidth of 44 MHz; and the optical frequency drift is reduced from 96 MHz down to 6.6 MHz.
