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KYOCERA Develops Temperature Characteristics-Free Etalon Filter

Crystal device applies atomic diffusion bonding technique for first time in the industry, contributing to downsizing and energy saving in tunable laser modules for optical communication WDM

December 12, 2012
Kyocera Corporation (President: Tetsuo Kuba) today announced that its wholly owned subsidiary Kyocera Crystal Device Corporation (President: Shigeaki Kinori), in charge of development and manufacturing of crystal devices, has succeeded in developing a temperature characteristics-free etalon filter -- a crystal device which has applied the atomic diffusion bonding technique for the first time in the industry*1.

Photo:Kyocera Crystal Device Corporation's new temperature characteristics-free etalon filter
Kyocera Crystal Device Corporation's new temperature characteristics-free etalon filter
(0.5mm increments shown)


Product name Temperature characteristics-free etalon filter (C type)
Applications Tunable laser module for optical communications and industrial use
External dimensions >1.2mm squared
Temperature characteristics ±0.15pm/°C typ. (pm/°C = 10-12m/°C)
Availability Starting in January 2013
Production facilities KYOCERA Crystal Device Hokkaido Corporation (Japan)


An etalon filter is a component which detects deviations in multiple light wavelengths in high-capacity optical communication transmissions systems. For this new product, Kyocera Crystal Device has realized a temperature characteristics-free etalon filter with high-accuracy, high-reliability and smaller size due to its success in developing a crystal device applying the atomic diffusion bonding technique. The product will be available on a sample basis starting January 2013.

Main Features

1. Industry-leading product specifications enable freedom from temperature characteristics
The new product has achieved an industry-leading level of temperature characteristics of ±0.15pm/°C. This was achieved by applying a design technique combining positive temperature characteristic crystals with negative temperature characteristic crystals and an advanced crystal processing technique, along with industry's first application of the atomic diffusion bonding technique. Furthermore, since the temperature characteristics-free etalon filter does not require a Peltier device for temperature adjustment, it can contribute to downsizing and energy conservation in tunable laser modules.

2. Industry's first crystal device to apply atomic diffusion bonding technique
The atomic diffusion bonding technique is a direct bonding technique developed by Tohoku University's Professor Takehito Shimatsu. It entails bonding the wafer and substrate together without applying heat, pressure or voltage, nor using organic adhesives. Through the joint-development with Professor Shimatsu's research group, Kyocera Crystal Device has succeeded in bonding a crystal wafer in an extremely thin metal film thickness of several atomic layers to several dozen nanometers*2 with high strength by applying the atomic diffusion bonding technique for crystal devices. This method has solved the problems of optical contact*3, a conventional bonding method with lower bonding strength, and that of bonding using organic adhesive, for which the management of bonding thickness is difficult. It has also improved accuracy and reliability while reducing the size of the etalon filter.

Development Background

An etalon filter is a component which monitors whether oscillation of light wavelength is steadily conducted in the tunable laser module -- an essential device used for high-capacity optical communication transmission systems -- which transforms electric signals to optical signals for oscillation.

In recent years, optical communication has become increasingly essential to achieve higher capacity and higher transmission speeds with the dramatic increase in information volume due to the rapid spread of the Internet and transmission of high-volume data. To respond to such requirements, the utilization of the WDM*4 transmission system, which can transmit more optical signals (information volume) with one piece of optical fiber, has become the mainstream method. Since a WDM transmission system requires many tunable laser modules for each station from mid- to long-distance to short-distance transmissions, further reduction in size and electric power consumption is required.

As the product does not require a Peltier device for temperature control due to the aforementioned features, it can contribute to reduction in the size and electric power consumption of tunable laser modules. Even with its small size, this product has realized freedom from temperature characteristics, high accuracy and high reliability, and has superior stability against changes in external temperature.

Kyocera Crystal Device has an integrated production system, in which all the processes from cultivation of crystal materials to design, processing, coating and characteristics evaluation are all conducted internally. The company will continue to enhance its support of optical transmission-related fields in order to contribute to the further progress and development of high-capacity, high-speed optical communications networks.

Reference Material

1. Industry-leading level temperature characteristics
The temperature characteristic of this newly developed product, ±0.15pm/°C, has been significantly improved from 5.4pm/°C in our conventional product (crystal etalon filter N type).

Transmission Characteristics

Conventional product (N type)
Photo:Conventional product (N type)
Newly developed product (C type)
Photo:Newly developed product (C type)


2. Advanced crystal processing technique
A stable and steady bonding condition has been realized with our proprietary flat surface processing technique and high-level washing technique, which Kyocera Crystal Device has developed over more than fifty years of experience in the industry.

Specifications
Product name Temperature characteristics-free etalon filter (C type)
Main specs ·External dimension: >1.2mm squared
·Adaptive wavelength: 1,520 to 1,620nm
·Temperature characteristics: ±0.15pm /°C typ.
·FSR: 50/100GHz
·Extinction ratio or reflectance: Custom

*1 As of November 15, 2012. Based on a survey by Kyocera Crystal Device.
*2 1 nanometer (nm) = 1.0x10-9m.
*3 Bonding method that does not use adhesive but bonds flat surfaces of the wafer together.
*4 WDM: Wavelength Division Multiplexing. A communication technology that utilizes optical fiber.