pics4all | application note |

Optical gyroscopes

Modern airplanes, drones, guided missiles and spa-cecrafts require highly accurate and reliable inertialnavigation systems. One of the essential componentsof such systems is the gyroscope, a device thatmeasures the angular velocity of a flying object.Gyroscopes can be realized utilizing various techni-ques of rotation rate detection – mechanical,microelectromechanical or optical. Nowadays, theoptical gyros are widely deployed due to their com-pact dimensions combined with an excellent perfor-mance in terms of excellent stability and low powerconsumption, which are essential parameters inaviation and space applications.

An optical sensor of the angular velocity can be de-veloped using two basic configurations, both em-ploying the Sagnac effect. The first one is the

interferometric fiber-optic gyroscope (IFOG), inwhich the rotation rate is detected by measurementof the interference signal of two waves counter-pro-pagating through an optical fiber loop.

On the other hand, ring laser gyroscopes (RLG) em-ploy a laser operating in a ring resonator configura-tion. In such a laser, the oscillation frequencies forthe clock-wise (CW) and counter-clockwise (CCW)directions are split under rotation. The differencebetween the two frequencies can be extracted fromthe recorded beating signal.

Contemporary devices are typically constructedfrom discrete optoelectronic and fiber-optic compo-nents – lasers, light modulators, fiber couplers andphotodiodes. In spite of many attempts to miniaturi-zation and realizing an integrated device, so farthere is no such a product available on the market.

Photonic Integrated Circuitsfor Optical Gyroscope Systems

Photonic integrated circuits

Photonic integrated circuits (PICs) are considered asone of the most attractive and promising solutionsfor modern optoelectronics, with the potential im-pact similar to integrated electronic revolution Whilemicroelectronic devices consist of transistors, capa-citors and resistors, a PIC comprises lasers, modula-tors, photodetectors and passive waveguides, allmonolithically integrated on a single substrate.The PICs are nowadays extensively developed forcommercial use, with a specific focus on telecom,datacom and sensing applications.

PIC technology has now become accessible to userswithout cleanroom facilities, through so-called multi--project wafer runs and open foundries. Indiumphosphide based technology is commercially avai-lable through SMART Photonics and Heinrich HertzInstitute. Access is coordinated by the JePPIX platform:http://www.jeppix.eu/.

It seems that exploring the potential of photonic in-tegration technologies may enable further reductionof weight and energy consumption, while simulta-neously maintaining high performance. In particular,the generic platform of indium phosphide enablesfabrication of miniaturized and simultaneouslyhighly complex optoelectronic systems, comprisingboth active and passive elements – light amplifiers,modulators, detectors, connected through a ne-twork of passive optical waveguides.

Since 2013 the Institute of Microelectronics andOptoelectronics (IMiO) of Warsaw University of Tech-nology has been developing application specific pho-tonic integrated circuits (ASPICs) for implementationin new generation of optical gyroscope systems. Themonolithic optical chips have been realized in indiumphosphide based generic integration technologies.

The first investigated approach is the interferomet-ric fiber-optic gyroscope (IFOG) configuration, inwhich the rotation rate is measured by monitoringan interference signal using a dedicated ASPIC-based interrogator. Figure 1 presents a microscopepicture of the fabricated optical chip, which compri-ses a laser light source, 3 dB couplers, a phase mo-dulator and PIN photodiodes.

First characterization results are promising with res-pect to implementation of ASPIC-based interroga-tors in optical gyroscope systems. Figure 2 presentsa characteristic of the interference signal occurringunder rotation of an optical fiber coil, measuredusing the developed ASPIC.

Figure 1. Microscope photograph of the ASPIC interrogator forthe interferometric fiber-optic gyroscope system

Figure 2. A characteristic of the interference signal in a rotatingoptical fiber coil, measured using an ASPIC-based interrogator

Eastern Europe Design Hub

Institute of Microelectronics and Optoelectronics Warsaw University of Technology

Koszykowa 75, 00-662 Warsaw, Poland

Phone: +48 22 234 14 66

The second investigated approach is a fully integratedoptical gyro, which can be realized by implementa-tion of a single-frequency ring laser, together witha read-out circuit for beating signal detection. Figure 3presents a photograph of such an integrated device.

Measurement results obtained so far have provensingle frequency operation of the developed ringlaser (see Figure 4).

Expert support by PICs4All

If you are interested to know more about the use ofPIC technology for implementation in optical gyros-cope systems, as well as for use in any other appli-cation, please contact Eastern Europe Design Hub(EEDH) at Warsaw University of Technology, Poland.We are set up to help you in technical evaluation ofapplicability of photonic integrated circuits in yourproducts.

For our partners we offer full design and characteri-zation support, from the discussion of the very con-cept of the ASPIC, through technological consultingto the measurements in our photonics laboratories.In the framework of the EU H2020 PICs4All projectEEDH offers free-of-charge guidance to companies,research institutes and academia interested in deve-lopment and implementation of cutting-edge photo-nic devices in their commercial products.

The PICs4All consortium is funded under the EUHorizon 2020 programme and brings togetherexpertise of nine European application support cen-ters (ASCs) to support end-users in exploiting cut-ting-edge photonic integration technologies. TheASCs can guide you through the existing eco-sys-tem of designers, foundries, packaging and testservices.

EEDH Contact information:

Ryszard Piramidowicz (EEDH CEO): R.Piramidowicz@imio.pw.edu.pl

Stanislaw Stopinski (senior designer and technical manager): S.Stopinski@imio.pw.edu.pl

Figure 4. Recorded spectrum of the single frequency integratedring laser

Figure 3. Microscope photograph of the fully integrated opticalgyroscope based on a single-frequency ring laser