摘要:
An apparatus and method for measuring the thickness of a film having top and bottom surfaces. The apparatus includes a first coupler for generating a first probe light signal and a second probe light signal from a low coherence light source. The first probe light signal is directed toward the top surface of the film and the light leaving the top surface of the film is collected. Similarly, the second probe light signal is directed toward the bottom surface of the film and the light leaving the bottom surface of the film is also collected. Top and bottom partially reflecting reference surfaces are provided for generating reflections. The top reference surface reflects part of the light leaving the top surface back toward the top surface, and the bottom reference surface reflects light leaving the bottom surface of the film back toward the bottom surface of the film. The collected light is combined to form a collected light signal which is input to a receiver that determines the time delay between light reflected from the top surface of the film and the top reference surface and between the bottom surface of the film and the bottom reference surface. In the preferred embodiment of the present invention, the receiver is constructed from an optical autocorrelator or an optical spectrum analyzer that includes circuitry for providing the Fourier transform of the frequency domain spectrum measured from the collected light signal.
摘要:
A low-coherence reflectometer for use in measuring optical backscattering. The invention utilizes an optical attenuation in the reference arm of a Michelson interferometer to reduce the relative intensity noise. The invention obtains essentially the same performance as obtained with balanced detector schemes while maintaining the simplicity of the Michelson interferometer design and increased scan distance.
摘要:
A broadband tunable in-fiber filter includes a grating with divergent ridges which can be translated transversely of a side-polished optical fiber to vary the periodicity at an exposed evanescent field. The divergence is gradual so that at any given transverse position of the grating, the ridge interacting with the evanescent field are effectively parallel. The divergence is great enough so that a tuning-to-reflected bandwidth ratio of about 33:1 is demonstrated. The grating is fabricated in an amorphous silicon film on a fused quartz substrate. The film is coated with photoresist which is exposed to a holographic interference front. The substrate is tilted with respect to an interference front created by two spherically diverging beams to achieve the desired divergence. Subsequent processing, including etching are standard.
摘要:
An actual optical field spectrum is mixed down to baseband and can be observed directly to measure the optical field spectrum of an optical signal based on a local oscillator approach. This local oscillator approach is achieved without adding an additional local oscillator. A single optical source, such as a laser, is controlled by a modulation source for selectively modulating the optical signal produced by the optical source. Accordingly, the optical signal produced by the optical source alternates between two states, namely, an unmodulated state and a modulated state which carries the optical field spectrum of interest. Preferably, the optical signal produced by the optical source is routed to an optical conduit in parallel with an optical delay line. Although the two states of the optical signal produced by the optical source occur sequentially in time, they are mixed together concurrently after being channeled through the parallel optical circuit comprising the optical conduit and the optical delay line. The unmodulated state of the optical signal produced by the optical source serves as a local oscillator signal. The parallel combination of the optical conduit and the optical delay line together with a photodetector functions as a self-homodyne receiver when fed the unmodulated and modulated states of the optical signal produced by the optical source. The self-homodyned mixing of the unmodulated and modulated states of the optical signal produced by the optical source serves to frequency-translate the optical power spectrum to within the bandwidth of an analyzer, such as a microwave spectrum analyzer.
摘要:
An all fiber mode selector comprises a single-mode optical fiber and a double-mode optical fiber, each having a facing surface formed on one side of the cladding. The facing surfaces are juxtaposed in close facing relationship. The fibers are selected so that an optical signal propagating in the LP.sub.11 propagation mode of the double-mode optical fiber propagates at substantially the same phase velocity as an optical signal propagating in the LP.sub.01 propagation mode of the single-mode optical fiber. The evanescent fields of the two fibers interact to couple optical energy from the LP.sub.11 mode of the double-mode optical fiber to the LP.sub.01 mode of the single-mode optical fiber and vice versa.
摘要:
A fiber optic amplifier as disclosed, comprised of a fiber optic, monomode waveguide which has a core and cladding. Part of the cladding over a predetermined region is removed and replaced by an active medium capable of absorbing light energy at a first wavelength and emitting light energy at a second wavelength. The active medium is a lasing dye which has an index of refraction adjusted to be slightly less than the index of refraction of the fiber core. The amount of cladding which is removed is adjusted such that a predetermined amount of penetration of the evanescent field from a pump light signal coupled into an end of the fiber penetrates the active medium. A probe signal to be amplified causes stimulated emission from the excited dye molecules by penetration of its evanescent field into the dye in the region where the cladding is removed.In the preferred embodiment a recirculating pump is used to circulate dye through a cavity which is placed over the portion of the fiber where the cladding is removed. The dye molecules in contact with the surface caused by removal of the cladding are continually changed. A temperature control unit maintains the temperature of the dye such that its index of refraction remains tuned to an amount just less than the index of refraction of the core.
摘要:
Various methods and apparatuses are described in which an array of optical gain mediums capable of lasing are contained in a single integral unit. The array may contain four or more optical gain mediums capable of lasing. Each optical gain medium capable of lasing supplies a separate optical signal containing a band of wavelengths different than the other optical gain mediums capable of lasing in the array to a first multiplexer/demultiplexer. A connection for an output fiber exists to route an optical signal to and from a passive optical network.
摘要:
Various methods and apparatuses are described in which an array of optical gain mediums capable of lasing are contained in a single integral unit. The array may contain four or more optical gain mediums capable of lasing. Each optical gain medium capable of lasing supplies a separate optical signal containing a band of wavelengths different than the other optical gain mediums capable of lasing in the array to a first multiplexer/demultiplexer. A connection for an output fiber exists to route an optical signal to and from a passive optical network.
摘要:
Various methods and apparatuses are described in which an array of optical gain mediums capable of lasing are contained in a single integral unit. The array may contain four or more optical gain mediums capable of lasing. Each optical gain medium capable of lasing supplies a separate optical signal containing a band of wavelengths different than the other optical gain mediums capable of lasing in the array to a first multiplexer/demultiplexer. A connection for an output fiber exists to route an optical signal to and from a passive optical network.
摘要:
Various methods, systems, and apparatuses are described in which a light source (101) capable of lasing is wavelength locked by an injected light signal. The light source (101) capable of lasing, such as a Fabry-Perot laser diode, may have antireflective coating on one or more facets of the light source (101) capable of lasing. The light source (101) capable of lasing receives a spectral slice of a light signal from a broadband light source (113) to wavelength lock the output wavelength of the light source (101) capable of lasing within the bandwidth of the injected light signal. A current pump (141) may bias the light source (101) capable of lasing to operate as a reflective regenerate semiconductor optical amplifier so that the injected light is reflected back out a front facet after being amplified and wavelength locked. The current pump (141) may also bias the light source (101) capable of lasing such that the externally injected narrow-band light signal into the light source (101) capable of lasing suppresses the lasing modes outside of the bandwidth of injected incoherent light.