OKI develops DFB laser with integrated EA modulator
Oki Electric plans to begin shipping the new device in sample quantities in October 2001.
There has been a strong need for the integration of EA modulators and lasers, since optical couplings between the discrete modulator and laser degrade the light output power. The new product consists of a 40 Gb/s EA modulator in a monolithic integration with a DFB semiconductor laser light source*1, resulting in more compact and less power-consuming optical sources for 40 Gb/s operations.
The rapid growth of the IT industry has stimulated the demand for high-capacity optical communications that can rapidly transfer large quantities of information. Currently, 10 Gb/s optical communications systems are being used as backbone optical networks, and 40 Gb/s optical systems are expected in one or two years.
Oki Electric's discrete EA modulator, which uses InP/InGaAsP and owned ridge waveguide structure*2, boast superior high-speed modulation. Oki Electric's discrete EA modulator, the first to support 40 GHz bandwidth, is under sample shipping prior to the other competitors. And this time, Oki has succeeded to integrate a DFB laser with the 40Gb/s EA modulator.
Product Overview
A 40 Gb/s modulation requires reduced capacitance of the EA modulator. Oki Electric, by utilizing its ridge waveguide structure and by reducing the length of the EA modulator to 100 microns, has achieved a reduction of a capacitance. In general, there is a tradeoff between the capacitance and the modulator extinction ratio (the ratio of transmittance between its "on" and "off" conditions), since a decrease in the modulator length to reduce the capacitance increases the difficulty of achieving a practical extinction ratio.
To solve this problem in its new product, Oki Electric optimized the detuning wavelength between the laser and EA modulator by adjusting the composition of the InGaAsP quantum absorption layer.@ As a result, the dynamic extinction ratio larger than 10 dB (=12 dB) has been achieved for the first time with the 40 Gb/s EA modulator-integrated DFB lasers.
- Modulation bandwidth: 41GHz
- Dynamic extinction ratio: 12dB (at 3V)
- Output wavelength: 1550nm
- Optical output: +8dBm (under CW operation)
Details of the development are scheduled to be announced in a presentation (paper no. MJ-3 by invitation) at Optical Fiber Communications 2001 (OFC 2001) from March 17 to 22 in Anaheim, California. OFC 2001 is the world's most authoritative international conference regarding optical communications.
Notes:
*1 DFB laser
A Distributed Feedback laser. A DFB laser has a relatively wide spectrum, and many resonant modes within that spectrum, making it tend toward multi-longitudinal mode oscillation. In the DFB laser, the fine pitch grating is fabricated in the laser cavity to select one of these resonant mode to result in lasing operation with one particular longitudinal mode.
*2 Ridge waveguide structure
A kind of waveguide structures which are used to confine the optical beams in restricted area. There are two types of waveguides used frequently: one is buried heterostructure waveguide and the other is ridge waveguide. Ridge waveguide is preferable to achieve the lower capacitance, although it requires more strict fabrication tolerances.
About Oki Electric Industry Co., Ltd.
Founded more than a century ago in 1881, Oki Electric Industry Co., Ltd. is Japan's first telecommunications manufacturer headquartered in Tokyo, Japan. With more than 21,000 employees worldwide, Oki Electric provides customers with top-notch products and technologies for telecommunication systems, information systems and electronic devices. Visit Oki's global web site at http://www.oki.com/.