The Space Interferometry Mission, scheduled for launch in 2008, is an optical stellar interferometer with a 10 meter baseline capable of micro-arcsecond accuracy astrometry. A mission-enabling technology development program is underway at JPL, including the design and test of heterodyne interferometer metrology gauges to monitor the separation of optical components of the stellar interferometer. The gauges are required to have a resolution of 15 picometers and to track the motion of mirrors over several meters. We report laboratory progress in meeting these goals.
MEMS technology uses photolithography and etching of silicon wafers to enable mechanical structures with less than 1
&mgr;m tolerance, important for the miniaturization of imaging systems. In this paper, we present the first silicon MEMS
digital auto-focus camera for use in cell phones with a focus range of 10 cm to infinity. At the heart of the new silicon
MEMS digital camera, a simple and low-cost electromagnetic actuator impels a silicon MEMS motion control stage on
which a lens is mounted. The silicon stage ensures precise alignment of the lens with respect to the imager, and enables
precision motion of the lens over a range of 300 &mgr;m with < 5 &mgr;m hysteresis and < 2 &mgr;m repeatability. Settling time is <
15 ms for 200 &mgr;m step, and < 5ms for 20 &mgr;m step enabling AF within 0.36 sec at 30 fps. The precise motion allows
COTS optics to maintain MTF > 0.8 at 20 cy/mm up to 80% field over the full range of motion. Accelerated lifetime
testing has shown that the alignment and precision of motion is maintained after 8,000 g shocks, thermal cycling from - 40 C to 85 C, and operation over 20 million cycles.
Narrow linewidth (< 100 KHz) semiconductor lasers are expected to be a key technology in NASA's stellar interferometry missions to search for planets around nearby stars. Long coherence length lasers are needed for precise (20 pm to 5 nm) measurements of the optical path difference. This work discusses results using the self-heterodyne delay technique to measure 1.3 um InP based DFB lasers. We will also address practical issues concerning detection and elimination of back reflections, choice of fiber length and resolution, and measurement of laser l/f and current supply noise.
Heterodyne interferometer laser gauges are used in space- based astronomical interferometers to very accurately measure and compensate for variations in starlight pathlength. Bragg cells have been traditionally used to generate the heterodyne signal by shifting the frequency of the laser light. This paper presents the development and qualification of an integrated optic frequency shifter (IOFS) which offers improved performance and reliability compared with Bragg cell technology. The most critical advantage of the IOFS for space applications is that it enables fiber optic metrology source integration, which facilitates the integration process and result in more reliable and compact heterodyne interferometer laser gauges.
We describe the development, functional performance, and space-qualification status of a Metrology Source suitable for implementation of space-based metrology systems with picometer-level relative displacement measurement and micron-level absolute displacement measurement resolution. The Metrology Source consists of the following components: lasers, frequency stabilization system, frequency shifters, and frequency modulators. All components are interconnected by polarization maintaining fibers to facilitate integration into a lightweight space-qualifiable module.
This paper reports on the design, modeling, fabrication, and characterization of a novel silicon bulk micromachined vibratory rate gyroscope and a 3-axes rotation sensing system using this new type of microgyroscopes designed for microspacecraft applications. The new microgyroscope consists of a silicon four leaf clover structure with a post attached to the center. The whole structure is suspended by four thin silicon cantilevers. This device is electrostatically actuated and detects Coriolis induced motions of the leaves capacitively. A prototype of this microgyroscope has a rotation responsivity (scale factor) of 10.4 mV/deg/sec with scale factor nonlinearity of less than 1%, and a minimum detectable noise equivalent rotation rate of 90 deg/hr, at an integration time of 1 second. The bias stability of this microgyroscope is better than 29 deg/hr. The performance of this microgyroscope is limited by the electronic circuit noise and drift. Planned improvements in the fabrication and assembly of the microgyroscope will allow the use of Q-factor amplification to increase the sensitivity of the device by at least two to three orders of magnitude. This new vibratory microgyroscope offers potential advantages of almost unlimited operational life, high performance, extremely compact size, low power operation, and low cost for inertial navigation and altitude control.
The effects of radiation on fused biconical taper wavelength division multiplexers are presented. The polarization sensitivity of these devices before and after irradiation is discussed. Preliminary results on the effects of irradiating different regions of the device, and comparisons between the effects of proton and Co60 radiation sources are also given. A theoretical model that takes into account the index change in the Ge-doped cores of the optical fibers used to make these devices agrees well with experimental observations. This indicates that index changes in the fiber may be primarily responsible for the effects of radiation on these devices.
A new method of polarization alignment into PM fiber based on electronic coherent detection is presented. The electric field resulting from interference between the polarization eigenmodes of a PM fiber at a linear polarizer when the light coupled into the fiber is amplitude modulated is solved for. The results of polarization alignment experiments using a current modulated laser diode are compared with the theory. Even though current modulation of a laser diode produces a complicated electric field, it is shown that the measurements made in the experiments agree well with the simple model. The new method is used to align the input to a PM fiber coupler with a polarization extinction ratio (PER) of 25 dB (limited by coupler crosstalk) and to align into a 1 km long PM fiber with a PER of 20 dB (limited by fiber crosstalk).