News Column

Patent Issued for Surface Emitting Laser, Light Source, and Optical Module

July 2, 2014



By a News Reporter-Staff News Editor at Journal of Engineering -- Furukawa Electric Co., Ltd. (Tokyo, JP) has been issued patent number 8755422, according to news reporting originating out of Alexandria, Virginia, by VerticalNews editors.

The patent's inventors are Shimizu, Hitoshi (Tokyo, JP); Kawakita, Yasumasa (Tokyo, JP).

This patent was filed on July 21, 2011 and was published online on June 17, 2014.

From the background information supplied by the inventors, news correspondents obtained the following quote: "The present invention relates to a surface emitting laser, a light source, and an optical module.

"Surface emitting lasers that emit laser light at a wavelength in 850-nm band have been mainly used as light sources for optical interconnection. An integrated circuit (IC) driver normally drives the surface emitting laser of 850-nm band at 3.3 volts, with respect to the energy bandgap of a GaAs-based quantum well of an active layer of the surface emitting laser of this type.

"However, not only the surface emitting lasers for optical interconnection, but all the surface emitting lasers are desired to reduce power consumption in the market. To reduce power consumption in such surface emitting lasers, a method of using a surface emitting laser having an oscillation wavelength longer than 850 nm, in which the energy bandgap of the active layer is lowered, and that can further reduce the bias voltage has been studied. By using a strained InGaAs quantum well for the active layer in order to increase the oscillation wavelength, a differential gain is increased and the power consumption can be further reduced.

"Conventional surface emitting lasers having a wavelength longer than 850 nm have a structure disclosed in, for example, N. Suzuki, et al., '25-Gbps operation of 1.1-.mu.m-range InGaAs VCSELs for high-speed optical interconnections', OFA4, OFC2006. The surface emitting laser includes a selectively-oxidized current confinement layer. In the surface emitting laser, distributed Bragg reflector (DBR) mirrors that are multilayer reflection mirrors formed of a periodic structure of a high refractive index layer and a low refractive index layer are used as an optical resonator, and a p-side electrode is formed above the upper DBR mirror.

"However, there is a problem that, when a bias current equal to or larger than a threshold current is applied to a surface emitting laser having a conventional structure, power consumption of the surface emitting laser increases."

Supplementing the background information on this patent, VerticalNews reporters also obtained the inventors' summary information for this patent: "It is an object of the present invention to at least partially solve the problems in the conventional technology.

"According to one aspect of the present invention, there is provided a surface emitting laser including a substrate, a lower multilayer mirror and an upper multilayer mirror of a periodic structure of a high refractive index layer and a low refractive index layer formed on the substrate, a first-conductivity-type contact layer and a second-conductivity-type contact layer formed between the lower multilayer mirror and the upper multilayer mirror, an active layer formed between the first-conductivity-type contact layer and the second-conductivity-type contact layer, a current confinement layer formed between the second-conductivity-type contact layer and the active layer and including a current injection portion and a current confinement portion surrounding the current injection portion, a first composition gradient layer and a second composition gradient layer formed facing each other across the current confinement layer, the first composition gradient layer being arranged on the second-conductivity-type contact layer side and the second composition gradient layer being arranged on the active layer side, a first-conductivity-type side electrode formed on the first-conductivity-type contact layer, and a second-conductivity-type side electrode formed on the second-conductivity-type contact layer. The first composition gradient layer and the second composition gradient layer are formed such that bandgap energy of each of the layers is monotonically decreased from the current confinement layer to an adjacent layer and approach bandgap energy of the adjacent layer in a growth direction. The second-conductivity-type cladding layer includes material for reducing mobility of carrier. Carrier concentration of the second composition gradient layer is equal to or more than carrier concentration of the current injection portion of the current confinement layer.

"According to another aspect of the present invention, there is provided a light source including a surface emitting laser and a controller that applies a modulation voltage with approximately same positive and negative amplitudes from a bias voltage to the surface emitting laser. The surface emitting laser includes a substrate, a lower multilayer mirror and an upper multilayer mirror of a periodic structure of a high refractive index layer and a low refractive index layer formed on the substrate, a first-conductivity-type contact layer and a second-conductivity-type contact layer formed between the lower multilayer mirror and the upper multilayer mirror, an active layer formed between the first-conductivity-type contact layer and the second-conductivity-type contact layer, a current confinement layer formed between the second-conductivity-type contact layer and the active layer and including a current injection portion and a current confinement portion surrounding the current injection portion, a first composition gradient layer and a second composition gradient layer formed facing each other across the current confinement layer, the first composition gradient layer being arranged on the second-conductivity-type contact layer side and the second composition gradient layer being arranged on the active layer side, a first-conductivity-type side electrode formed on the first-conductivity-type contact layer, and a second-conductivity-type side electrode formed on the second-conductivity-type contact layer. The first composition gradient layer and the second composition gradient layer are formed such that bandgap energy of each of the layers is monotonically decreased from the current confinement layer to an adjacent layer and approach bandgap energy of the adjacent layer in a growth direction. The second-conductivity-type cladding layer includes material for reducing mobility of carrier. Carrier concentration of the second composition gradient layer is equal to or more than carrier concentration of the current injection portion of the current confinement layer.

"According to still another aspect of the present invention, there is provided an optical module including a surface emitting laser that includes a substrate, a lower multilayer mirror and an upper multilayer mirror of a periodic structure of a high refractive index layer and a low refractive index layer formed on the substrate, a first-conductivity-type contact layer and a second-conductivity-type contact layer formed between the lower multilayer mirror and the upper multilayer mirror, an active layer formed between the first-conductivity-type contact layer and the second-conductivity-type contact layer, a current confinement layer formed between the second-conductivity-type contact layer and the active layer and including a current injection portion and a current confinement portion surrounding the current injection portion, a first composition gradient layer and a second composition gradient layer formed facing each other across the current confinement layer, the first composition gradient layer being arranged on the second-conductivity-type contact layer side and the second composition gradient layer being arranged on the active layer side, a first-conductivity-type side electrode formed on the first-conductivity-type contact layer, and a second-conductivity-type side electrode formed on the second-conductivity-type contact layer. The first composition gradient layer and the second composition gradient layer are formed such that bandgap energy of each of the layers is monotonically decreased from the current confinement layer to an adjacent layer and approach bandgap energy of the adjacent layer in a growth direction. The second-conductivity-type cladding layer includes material for reducing mobility of carrier. Carrier concentration of the second composition gradient layer is equal to or more than carrier concentration of the current injection portion of the current confinement layer.

"The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiment of the invention, when considered in connection with the accompanying drawings."

For the URL and additional information on this patent, see: Shimizu, Hitoshi; Kawakita, Yasumasa. Surface Emitting Laser, Light Source, and Optical Module. U.S. Patent Number 8755422, filed July 21, 2011, and published online on June 17, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8755422.PN.&OS=PN/8755422RS=PN/8755422

Keywords for this news article include: Furukawa Electric Co. Ltd.

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Source: Journal of Engineering


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