Optical isolators are essential components for highly demanding applications, enabling the use of single frequency lasers. With their capability to design micro-integrated laser systems, the availability of single frequency laser diodes in the visible wavelength region, led to a demand for suitable micro-integrated optical isolators for visible wavelength, e.g. for micro-integrated ECDL laser and MOPA modules. Unlike for the near infrared, micro-integrated optical isolators for the wavelength region between 680 and 1000 nm are not available so far, limiting or even hindering use of micro-integrated laser sources for space mission with photonic, spectroscopic and quantum-technological mission payloads. To overcome this issue, a micro-optical isolator for space application for visible wavelengths has been developed. The design specifically features a low stress crystal mount with a symmetric heat removal essential for good isolation, the avoidance of beam deflection, and a large allowable temperature range. Moreover, the high homogeneity of the magnetic field enables at least 40dB single stage isolation, limited by polarizers and crystal properties. Structural and thermo-elastic analyses have been performed to ensure a space qualifiable design. The properties of the CdMnTe crystals, such as Verdet constant, transmission, optical loss, and polarization, around the generic wavelength of 780 nm have been measured. At 1064 and 780 nm an optical and thermal characterization of the CdMnTe crystals at high power (up to 1.4 W) has been carried out. The isolator design as well as the measurement results will be presented.
We report on processing, characterization and lifetime qualification of lateral single-mode laser diodes emitting at a wavelength of λ = 1064 nm. The lasers were designed to meet the specifications for the Bose-Einstein Condensate and Cold Atom Laboratory (BECCAL). Ridge waveguide lasers (RWL) were investigated in aging experiments in order to assess the material quality of the ridge waveguide amplifiers (RWA) used in the BECCAL modules. Both RWA and RWL
have a cavity length of L = 6 mm and a ridge width of w = 5 μm, eventually tapered to 15 μm towards the front facet, yielding an optical power of Pop = 830 mW ex facet for ≥500 mW into a single mode fiber. A four-lot lifetest with temperatures from T = 20°C to 30°C and optical powers from Pop = 1.5 W to 1.7 W was performed aimed at estimating the parameters of accelerated aging. The thermal activation energy of Ea = 0.80 eV and the power stress exponent of n = 5.45 were obtained. Due to catastrophic optical damage (COD) at the laser facets, the batch with standard facet passivation failed to meet the specified reliability R > 99% at the operational time of top = 10,000 h. Using improved passivation technique by cleaving the laser bars in ultra-high vacuum (UHV) followed by ZnSe epitaxy yields a successful suppression of facet degradation. The reliability of 1064 nm RWLs with improved passivation was estimated to be close to R = 100% demonstrating the qualification of the RWA for BECCAL.
Within the DLR project COMPASSO, optical clock and link technologies will be evaluated in space on the Bartolomeo platform attached to the Columbus module of the ISS. The system utilizes two iodine-based frequency references, a frequency comb, an optical laser communication and ranging terminal and a GNSS disciplined microwave reference. While COMPASSO is specifically dedicated to test optical technologies relevant for future satellite navigation (i.e. Galileo), the technologies are also crucial for future missions related to Earth observation and science. The optical frequency reference is based on modulation transfer spectroscopy (MTS) of molecular iodine near a wavelength of 532 nm. An extended cavity diode laser (ECDL) at a wavelength of 1064 nm is used as light source, together with fiber-optical components for beam preparation and manipulation. The laser light is frequency-doubled and sent to a mechanically and thermally highly stable free-beam spectroscopy board which includes a 20 cm long iodine cell in four-pass configuration. The iodine reference development is lead by the DLR-Institute of Quantum Technologies and includes further DLR institutes, space industry and research institutions. Phase B of the project will be finalized soon and an Engineering Model of the iodine reference, which represents the flight models in form, fit and function, will be realized by mid 2023. The launch of the COMPASSO payload is planned for 2025. Additional presentation content can be accessed on the supplemental content page.
The Ferdinand-Braun-Institute has been developing high-power, narrow-linewidth semiconductor lasers for precision spectroscopy applications in harsh environments for more than ten years. Starting with hybrid-integrated diode laser chips and micro-optics on a ceramic platform for Bose-Einstein condensation experiments in a drop tower, the institute is now developing, qualifying and, in many cases, already delivering fully-packaged, multi-functional modules for application on platforms including sounding rockets, the International Space Station (ISS) and nano-satellites. We present the latest generation of electro-optical modules, which is designed to accommodate any two semiconductor chips. This includes, amongst others, the ECDL-MOPA, where the laser architecture consists of an ECDL and a semiconductor optical amplifier, both hybrid-integrated into a sealed package within a footprint of a conventional smartphone (but with a height of approx. 23 mm). The single-mode, polarization-maintaining optical fiber output delivers, for instance, 570 mW of power and a free-running FWHM linewidth of approximately 30 kHz (within a timescale of 1 ms) at the operating wavelength of 1064.49 nm. One such module has already been successfully launched on a sounding rocket mission in May 2018.
Employing compact quantum sensors in field or in space (e.g., small satellites) implies demanding requirements on components and integration technologies. Within our work on integrated sensors, we develop miniaturized, ultra-stable optical setups for optical cooling and trapping of cold atomic gases. Besides challenging demands on alignment precision, and thermo-mechanical durability, we specifically address ultra-high vacuum (UHV) compatibility of our integration technologies and optical components. A prototype design of an UHV-compatible, crossed beam optical dipole trap setup and its application within a cold atomic quantum sensor is described.
First qualification efforts on adhesive micro-integration technologies are presented. These tests are conducted in application-relevant geometries and material combinations common for micro-integrated optical setups. Adhesive aging will be investigated by thermal cycling or gamma radiation exposure. For vacuum compatibility testing, a versatile UHV testing system is currently being set up, enabling residual gas analysis and measurement of total gas rates down to 5•10-10mbar l/s at a base pressure of 10-11 mbar, exceeding the common ASTM E595 test.
We present the status of our efforts to develop very compact and robust diode laser modules specifically suited for quantum optics experiments in the field and in space. The paper describes why hybrid micro-integration and GaAs-diode laser technology is best suited to meet the needs of such applications. The electro-optical performance achieved with hybrid micro-integrated, medium linewidth, high power distributed-feedback master-oscillator-power-amplifier modules and with medium power, narrow linewidth extended cavity diode lasers emitting at 767 nm and 780 nm are briefly described and the status of space relevant stress tests and space heritage is summarized. We also describe the performance of an ECDL operating at 1070 nm. Further, a novel and versatile technology platform is introduced that allows for integration of any type of laser system or electro-optical module that can be constructed from two GaAs chips. This facilitates, for the first time, hybrid micro-integration, e.g. of extended cavity diode laser master-oscillator-poweramplifier modules, of dual-stage optical amplifiers, or of lasers with integrated, chip-based phase modulator. As an example we describe the implementation of an ECDL-MOPA designed for experiments on ultra-cold rubidium and potassium atoms on board a sounding rocket and give basic performance parameters.
Red emitting diode lasers with a narrow spectral line-width and continuous tuning are requested as light sources for
interferometric measurements with nm-accuracy. Tuning ranges of about 25 GHz together with a spectral line-width
smaller than 10 MHz are necessary.
A current-tunable miniaturized 633 nm external cavity diode laser (ECDL) will be presented. The resonator is
formed without moving parts between the front facet of a semiconductor gain medium and a reflection Bragg grating
(RBG). The RBG has a high reflectivity larger than 95% in a small spectral bandwidth, which is approximately
equal to the targeted tuning range. Within this bandwidth, the ECDL is tunable by changing the injection current of
the gain medium. The length of the resonator is selected so short, that the distance between the laser modes is larger
than the tuning range. Herewith, single mode operation should be guaranteed. The device is mounted on an aluminum
nitride bench with a footprint of 5 mm x 10 mm. ECDLs using gain media with different front facet
reflectivities of 30% and 70% will be compared. Moreover, results for a device encapsulated in a silicon based gel
will be presented.
For a device with 30% front facet reflectivity in air, a maximal output power of 10 mW was achieved. The tuning
range without any mode-hops was 34 pm, i.e. 25 GHz. The line-width was smaller than 10 MHz. The emitted beam
was approximately diffraction limited with a M2 ≈ 1.1 in both directions.
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