Coherent light generators – Particular component circuitry – Having noise suppression circuitry
Reexamination Certificate
2002-12-23
2004-12-07
Wong, Don (Department: 2828)
Coherent light generators
Particular component circuitry
Having noise suppression circuitry
C372S029010, C372S029011, C372S029020, C372S038010, C372S038020, C372S038070, C372S029015
Reexamination Certificate
active
06829268
ABSTRACT:
BACKGROUND
1. Field
Embodiments of the present invention relate to laser systems and, in particular, to tunable external cavity diode lasers systems.
2. Discussion of Related Art
Tunable lasers are deployed in such applications as telecommunication network test systems, spectroscopy research , and sensing for process control. They are also becoming recognized as essential components in the rapidly growing field of wavelength division multiplexing (“WDM”) for optical communication systems. There are various well-known or proprietary designs for tunable lasers and each is usually tailored for a particular use. The specific design depends on many factors, including the light beam (e.g., power, wavelength, tunability), operating environment (e.g., temperature), and practical considerations (e.g., size, cost).
FIG. 1
shows a typical tunable external cavity laser
100
. The laser
100
includes a gain medium
102
, which has one facet
104
anti-reflective (AR) coated and another facet
106
coated with a highly reflective material. The gain medium
102
is typically a diode laser. The light output from the facet
104
is collimated by a lens
108
onto a diffraction grating
110
, which diffracts the light towards a mirror
112
. The mirror
112
reflects a particular wavelength back to the grating
110
and the gain medium
102
. The facet
106
and the grating
110
form a cavity. The output of the laser
100
is the light beam
114
. To tune the laser to another wavelength, the mirror
112
is adjusted accordingly. There are other well-known tunable external cavity laser designs, such as a well-known Littrow external cavity laser, which has one or more frequency-selective components positioned in the cavity for tuning.
To ensure proper operation of any tunable laser including the tunable laser
100
, many of the parameters (e.g., power, wavelength, temperature) are controlled and monitored by servo control loops. It is common for each parameter to have its own separate control loop for setting, updating, and sampling laser parameters such as power, channel, and temperature. Separate loops can be problematic because each control loop operates asynchronously and the noise generated by sampling and/or updating from each loop could interfere with sampling of one or more of the other loops (cross talk). The noise may present itself as intermittent noise sources, which adds to the overall system noise and potentially degrades system performance. Typically, there are many control loops in a tunable laser system, thus many potential opportunities for cross talk. Noise also can come from a non-ideal ground plane, a power supply load change, unwanted coupling from digital I/O lines, or other sources.
Noise is commonly minimized by a combination of amplifying the signal of interest and filtering out the noise. However, as tunable lasers are moving towards smaller form factors noise compensation using amplifier circuits, filtering circuits, and other signal-to-noise ratio (SNR) increasing circuitry may not be appropriate.
REFERENCES:
patent: 6353623 (2002-03-01), Munks et al.
patent: 6400737 (2002-06-01), Broutin et al.
Batra Rajesh K.
Carney Robert A.
Koller Ken P.
Pontis George D.
Sprock Douglas A.
Intel Corporation
Wong Don
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