|Publication number||USRE43416 E1|
|Application number||US 13/008,506|
|Publication date||May 29, 2012|
|Priority date||Feb 2, 2005|
|Also published as||US7359113, US7929202, US20060268397, US20090046354, WO2006084063A2, WO2006084063A3|
|Publication number||008506, 13008506, US RE43416 E1, US RE43416E1, US-E1-RE43416, USRE43416 E1, USRE43416E1|
|Inventors||Simarjeet S. Saini, Jerry L. Bowser, Vincent K. Luciani, Peter J. S. Heim, Mario Dagenais, Ryan Enck|
|Original Assignee||Thorlabs Quantum Electronics, Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (22), Non-Patent Citations (2), Classifications (8), Legal Events (2)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application is related to, and claims priority from, U.S. Provisional Patent Application Ser. No. 60/649,307, filed on Feb. 2, 2005, of the same title, the disclosure of which is incorporated here by reference.
The present invention relates generally to semiconductor optical amplifiers and, more particularly, to semiconductor optical amplifiers having an injection current with a non-uniform density across the device.
Technologies associated with the communication of information have evolved rapidly over the last several decades. Optical information communication technologies have evolved as the technology of choice for backbone information communication systems due to, among other things, their ability to provide large bandwidth, fast transmission speeds and high channel quality. Semiconductor lasers and optical amplifiers are used in many aspects of optical communication systems, for example to generate optical carriers in optical transceivers and to generate optically amplified signals in optical transmission systems. Among other things, optical amplifiers are used to compensate for the attenuation of optical data signals transmitted over long distances.
There are several different types of optical amplifiers being used in today's optical communication systems. In erbium-doped fiber amplifiers (EDFAs) and Raman amplifiers, the optical fiber itself acts as a gain medium that transfers energy from pump lasers to the optical data signal traveling therethrough. In semiconductor optical amplifiers (SOAs), an electrical current is used to pump the active region of a semiconductor device. The optical signal is input to the SOA from the optical fiber where it experiences gain due to stimulated emission as it passes through the active region of the SOA.
The electrical pumping current is typically injected via an electrode. Consider, for example, the ridge-waveguide type SOA 28 structure illustrated in the cross-section of
The injection electrode can be fabricated along the length of the device as a metallization layer 40 contacting the top semiconductor ridge layer 39 by first removing dielectric material 41 prior to deposition of the metallization layer 40 as seen in
Accordingly, Applicants have developed SOA devices and methods which provide for control of the injection current and injection current density to, among other things, provide SOAs which have improved gain linearity, reduced crosstalk, and better efficiency through optimized current utilization.
Systems and methods according to the present invention address this need and others by providing efficient SOA devices and methods of operating such devices. According to exemplary embodiments of the present invention, semiconductor optical amplifiers have an injection current density which is controlled to provide, among other things, both a low noise figure at the input stage of the device and a high saturation power at the output stage of the device. According to one exemplary embodiment, this can be accomplished by varying the electrical resistance of the injection electrode along the length of the device to achieve a non-uniform injection current density. More specifically, the injection current density can be increased at the input stage of the device and increased at the output stage of the device as compared to the center region of the device. According to an exemplary embodiment, this can be accomplished by providing a patterned opening of the dielectric layer below the metallization layer which provides a varying resistance along the length of the device.
For example, according to one exemplary embodiment of the present invention, a semiconductor optical amplifier includes a substrate, a gain section, disposed on the substrate, for providing gain to an optical signal, a current injection electrode for receiving current and providing the current to the gain section, wherein a current density associated with the current varies across a length of the gain section.
According to another exemplary embodiment of the present invention, a method for amplifying an optical signal includes the steps of providing a gain section on a substrate, injecting a pumping current into the gain section and varying a current density associated with the current across a length of the gain section.
The accompanying drawings illustrate exemplary embodiments of the present invention, wherein:
The following detailed description of the invention refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. Also, the following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims.
Devices and methods according to exemplary embodiments of the present invention provide semiconductor optical amplifiers whose overall efficiency of operation is improved. One challenge posed by conventional SOAs is that the gain of the device varies as a function of the power of the optical signal. It will be appreciated that as the applications for SOAs vary, so do the optical power levels. Accordingly, for system design purposes, it would be preferable to provide SOAs wherein the gain is relatively constant as a function of optical power levels. As mentioned earlier, the gain of an SOA can be expressed as a function of the material gain coefficient g. However, this gain coefficient varies as:
where P is the optical power in the SOA. Those skilled in the art will appreciate that increasing the saturation power of semiconductor optical amplifiers therefore has the resulting benefit of reducing gain variations relative to optical power. Accordingly, one of the objects of the present invention is to provide SOAs and methods of making SOAs which have increased saturation power relative to conventional devices. According to exemplary embodiments of the present invention, this can be accomplished by varying the injection current density along the length of the device, i.e., along the gain region of the device.
Varying the injection current density along the length of the gain region can be accomplished in a number of different ways. According to one exemplary embodiment of the present invention, this is accomplished by varying the series resistance in the injection electrode. By, for example, creating a tailored pattern of openings in the dielectric layer 41, as compared to the uniform rectangular opening depicted by the hidden lines in
In this example, the series resistance in the contact electrode varies linearly as a function of the contact hole spacing as shown by the graph of
Plot 66 resulted from measurements taken from yet another similar device wherein the contact via spacing varied from 4 μm at the output side of the device to 50μ at the input side of the device. This device was measured to have a saturation power of 19.0 dBm. Thus, it can be seen that the larger range over which the contact via spacing is increased from the output side of the device to the input side of the device, the greater the resulting saturation power of the device for the same value of injection current. In this example the center-to-center spacing between contact vias varied linearly along the length of the device, however, those skilled in the art will appreciate that other distributions can be used such as an exponential or parabolic variation of the via spacings along the length of the device.
However, Applicants have also realized that increasing the saturation power of SOAs using this exemplary technique has some tradeoffs. More specifically, as seen in the graph of
However, for some applications, the device length may be constrained. Thus, another aspect of the present invention involves, for example, selecting a contact hole spacing that provides increased saturation power with an acceptable small-signal gain while also decreasing the noise figure. Accordingly, another exemplary embodiment will now be described with respect to
According to the purely illustrative example shown in
The noise figure for the exemplary SOA package was also measured by injecting a known input power and measuring the output optical signal to noise ratio close to the signal. The noise figure for a purely exemplary SOA device built in accordance with the contact electrode layer 100 was measured to be 5.5 dB at 1530 nm and 5.6 dB at 1550 nm. The dependence of noise figure on current was also evaluated. The noise figure dropped sharply with current around the transparency current and then remained nearly constant after approximately five times the transparency current.
According to another exemplary embodiment of the present invention, the current injection electrode can be fabricated as shown in
The above-described exemplary embodiments are intended to be illustrative in all respects, rather than restrictive, of the present invention. Thus the present invention is capable of many variations in detailed implementation that can be derived from the description contained herein by a person skilled in the art. For example, the present invention is not limited to patterning of only one contact electrode as a technique for varying the injection current density along the length of the device. More than one current injection electrode can be provided. Additionally, or alternatively, variable resistance can be introduced below the metallization layer by etching or otherwise varying the resistance of the top semiconductor contact layer. All such variations and modifications are considered to be within the scope and spirit of the present invention as defined by the following claims. No element, act, or instruction used in the description of the present application should be construed as critical or essential to the invention unless explicitly described as such. Also, as used herein, the article “a” is intended to include one or more items.
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|1||Saini, S. S., et al., A Semiconductor Optical Amplifier with High Saturation Power, Low Noise Figure and Low Polarization Depedent Gain Over the C-Band 17th Annual Meeting IEEE Lasers and Electro-Optics Society (LEOS 2004), vol. 1, No. 8-9, 2004, pp. 102-103.|
|2||Saini, S. S., et al., A Semiconductor Optical Amplifier with High Saturation Power, Low Noise Figure and Low Polarization Dependent Gain Over the C-Band, 17th Annual Meeting IEEE Lasers and Electro-Optics Society (LEOS 2004), vol. 1, Nov. 8-9, 2004, pp. 102-103.|
|Cooperative Classification||H01S5/0425, H01S2301/04, H01S5/22, H01S5/50|
|European Classification||H01S5/50, H01S5/042E|
|Apr 5, 2012||AS||Assignment|
Owner name: THORLABS QUANTUM ELECTRONICS, INC., NEW JERSEY
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:ENCK, RYAN;REEL/FRAME:027994/0484
Effective date: 20120326
|Oct 15, 2015||FPAY||Fee payment|
Year of fee payment: 8