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Design and Development of a Package for a Diluted Waveguide Electro-Absorption Modulator

The modulators improve the transmission of RF signals on optical fibers.

Externally coupled electroabsorption modulators (EAMs) are commonly used in order to transmit RF signals on optical fibers. Recently, an alternative device design with diluted waveguide structures was developed. Bench tests show benefits of lower propagation loss, higher power handling (100 mW), and higher normalized slope efficiency. Bench tests were performed in order to characterize the optical coupling of the EAM. The photo current maximum was offset from the optical power output maximum. The transmissions vs. bias voltage curves were measured, and an XY scanner was used to record the mode field of the light exiting from the EAM waveguide in each position. The Beam Propagation Method was used to simulate the mode field and the coupling efficiency. Based on the bench tests and simulation results, a design including mechanical, optical, and RF elements was developed.

The device studied is a dilute core waveguide (DCW) electroabsorption modulator (EAM). It has a similar structure as that of a high-saturation-power waveguide photodetector. The DCW EAM was designed to enhance the optical power handling and provide a greater spur-free dynamic range relative to a more conventional EAM design. The approach used to achieve this goal was to reduce the optical confinement factor at the electroabsorption (EA) layer in order to enhance the dynamic range and the maximum power of the EAM. This approach has some effects on the assembly methods that must be utilized to form a low-loss packaged device.

A dilute waveguide EAM device was designed in an effort to increase the maximum power and the dynamic range of the device. This design of the DCW EAM was intended to spatially separate the region of maximum photocurrent and photointensity. Using an optical test setup with a lensed fiber test method, it was shown that the axes of maximum photocurrent and photointensity are separated by a distance of ~0.4 um. Using these observations, an assembly process was developed for the DCW EAM.

The EAM Module Components. A butterfly package was used with seven electrical connection pins, one RF connector, and two fiber inlets. Two metal ferrules surround each fiber. One of the ferrules is used to fix the fiber to the submount. This is done via laser welding wherein a metal clip is placed over the ferrule. The base of the ferrule is welded to the submount,and the shoulder of the clip is welded to the ferrule. The second ferrule was located so it resides within the fiber port of the butterfly package.The module size, excluding the RF connector and electrical pins, is about 26 x 18 x 10 mm3
Measurements were reported for six DCW EAM modules. The average insertion loss of the module is about 7.6 db. Improvements on this insertion loss are possible with the use of a lensed fiber with an optimized mode field. Based on data, it was projected that an improvement of 0.7 db is expected if it were possible to substitute a lensed fiber with a mode field of 4 um instead of the lensed fiber used with a mode field of 3.3 um. It is also expected that with the maturation of the assembly process, a final insertion of 6 db would be achievable for the PCW EAM in its packaged state.

This work was done by Reinhard Erdmann, Richard J. Michalak, and Rebecca Bussjager of the Air Force Research Laboratory; Songsheng Tan, Nancy Stoffel, Charles Shick, Terrance McDonald, and Al Whitbeck of Infotonics Technology Center; and Ivan Shubin and Paul K. L. Yu of the University of California at San Diego. For more information, download the Technical Support Package (free white paper) at www.defensetechbriefs.com/tsp  under the Photonics category. AFRL-0133

Topics:
Assembling Fiber optics Fibers Lasers Manufacturing processes Metals Optics Optimization Photonics Powertrains Test procedures Transmissions Welding
This Brief includes a Technical Support Package (TSP).
Document cover
Design and Development of a Package for a Diluted Waveguide Electro-Absorption Modulator

(reference AFRL-0133) is currently available for download from the TSP library.

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    Defense Tech Briefs Magazine

    This article first appeared in the December, 2009 issue of Defense Tech Briefs Magazine (Vol. 3 No. 6).

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    Overview

    The document presents a conference paper detailing the design and development of a package for a diluted waveguide electro-absorption modulator (EAM). Authored by a team including Songsheng Tan, Nancy Stoffel, and others, the research focuses on enhancing the performance of EAMs, which are critical components in optical communication systems.

    The paper outlines the motivation behind the project, emphasizing the need for improved modulation techniques in fiber-optic links. The authors discuss the challenges associated with traditional modulators, such as high insertion loss and limited bandwidth, which can hinder the efficiency of data transmission. The proposed diluted waveguide EAM aims to address these issues by leveraging advanced materials and design strategies.

    Key findings include a summary of insertion loss measurements before and after assembly, with specific data provided for various modules tested at wavelengths of 1550 nm and 1570 nm. The results indicate a significant reduction in insertion loss, showcasing the effectiveness of the new packaging design. For instance, the final test results at 1550 nm show insertion losses ranging from 5.4 dB to 8.7 dB, which is a notable improvement over previous designs.

    The document also includes references to related works, highlighting the collaborative nature of the research and its grounding in existing literature. The authors cite several studies that have contributed to the understanding of high-speed, high-saturation photodetectors and modulators, reinforcing the relevance of their work within the broader context of optical technology advancements.

    Figures and tables within the paper provide visual representations of the data collected during testing, including photo current and intensity curves, which illustrate the performance characteristics of the EAM. The paper concludes with a discussion of the implications of these findings for future research and development in optical communication systems, suggesting that the advancements made could lead to more efficient and reliable data transmission methods.

    Overall, this document serves as a comprehensive overview of the innovative approaches taken in the design and development of a diluted waveguide EAM, contributing valuable insights to the field of photonics and optical communications.

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