Optical: systems and elements – Optical amplifier – Optical fiber
Patent
1997-03-20
1999-06-29
Moskowitz, Nelson
Optical: systems and elements
Optical amplifier
Optical fiber
359134, 359163, 385 1, 385134, G02B 640, H01S 306, G02F 109
Patent
active
059176482
DESCRIPTION:
BRIEF SUMMARY
This invention relates to packaged optical amplifier assemblies to which an optical signal can be applied at an input and an amplified optical signal is provided at an output. The invention relates particularly to optical amplifier assemblies in which amplification is provided by means of an optical amplifying fibre pumped by an optical pump.
The process of optical amplification by optical amplifying fibres is well known and will not be described in detail in this application. In broad terms, the core region of the optical fibre contains a dopant, for example erbium ions, which once optically excited can provide optical gain to an optical signal of suitable wavelength propagating along the fibre. The dopant is excited by passing an optical pump signal of a suitable wavelength along the fibre. For example, an erbium doped fibre can provide amplification to optical signals of wavelengths in the range 1520 nm to 1580 nm when pumped by an optical pump signal of wavelength of about 1480 nm or 980 nm. Suitable fibres and optical pumps for providing amplification at various wavelengths are readily available commercially.
A currently available packaged optical amplifier assembly is shown schematically at FIGS. 1 and 2. It includes a number of commercially available optical components whose pigtails are spliced together to form the required optical circuit for the amplifier. FIG. 1 shows, schematically, an assembled packaged optical amplifier 102. FIG. 2 shows the components of the package of FIG. 1 laid out as a key to show more clearly how the components are interconnected.
The optical amplifier assembly 102 is packaged in a housing comprising two interlocking metal compartments 104 and 106, the former holding passive optical components, the latter holding a printed circuit board (PCB) 108 on which are mounted optical components with electrical connections. The associated electronic components on the PCB are not shown. Fibre splices will be indicated by reference to the splice protectors which surround them.
Optical signals to be amplified by the optical amplifier assembly 102 are coupled to an input pigtail 110 by connecting to it a source optical fibre (not shown). The input pigtail 110 is coupled to the input pigtail of an input isolator 112 by splice 114, the output pigtail of which is coupled to a first pigtail of an input dichroic wavelength division multiplexer (WDM) 116 by splice 118. The output pigtail of a first laser diode optical pump 120 is coupled to a second pigtail of the dichroic WDM 116 by a splice 122. The WDM 116 outputs a combined input optical signal and optical pump signal at a third pigtail which is spliced to a first end 124 of a 30 m long erbium-doped, silica based fibre 126 by a splice 128.
The amplifying fibre 126 is wound on a pair of bobbins 130 and 132.
A second end 134 of the amplifying fibre 126 is coupled to a first pigtail of an output dichroic WDM 136 by a splice 138. The output pigtail of a second laser diode optical pump 138 is coupled to a second pigtail of the output WDM 136 by a splice 139. The output WDM 136 outputs the optical pump signal to the second end 134 of the amplifying fibre 126 whilst outputting an amplified optical signal received from the second end 134 of the amplifying fibre 126 to an output optical isolator 140, the pigtails of the output WDM 136 and output isolator 140 being coupled by a splice 142.
The output pigtail of the output isolator 140 is coupled to the input pigtail of an optical fibre coupler 144 by a splice 146. One output pigtail of the coupler 144 is coupled to the input pigtail of a monitor diode 148 by a splice 150, a second output pigtail of the coupler 144 being coupled to an output pigtail 152 of the packaged amplifier 102 by a splice 154.
The optical pump 120 co-pumps the amplifying fibre 126 whilst the optical pump 138 counter-pumps the amplifying fibre 126.
There are several disadvantages associated with such prior art assemblies. The packages are bulky because of the constraints set by the minimum radius of curvature of the pigtails
REFERENCES:
patent: 4804256 (1989-02-01), Wilson
patent: 5105307 (1992-04-01), Nishiyama et al.
patent: 5121451 (1992-06-01), Grard etal.
Delavaux et al, IEEE Photonics Technology Letters, 6, 1994-Mar, #3, pp. 376-379.
Nakagawa et al, Jour. of Lightwave Tech., vol. 9, #2, Feb. 1991, pp. 198-208.
Article entitled In-Line (Pigtailed) Polarization-Independent Optical Isolator by W.L. Emkey et al., Optical Fiber Communication Conference, 1989 Technical Digest Series, vol. 5, Conference Edition, Feb. 6-9, 1989, p.14g.
Hewlett--Packard Company
Moskowitz Nelson
LandOfFree
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