Optical spectrum slicer

Details Optical spectrum slicer Optical spectrum slicer

2001-07-16

2003-09-30

Spector, David N. (Department: 2873)

Optical: systems and elements

Optical modulator

Light wave temporal modulation

C398S093000, C398S095000, C385S011000

Reexamination Certificate

active

06628448

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns an optical spectrum slicer for outputting discontinuous spectrum lights containing multiple spectral components each at predetermined wavelength spacing from a broad band continuous spectrum light having a wavelength region of a predetermined range, which is suitable as a light source for inspection and evaluation of optical parts, devices and systems in the dense wavelength division multiplexing optical communication or a light source for use in optical communication.
2. Statement of the Related Art
In optical communication using optical fibers as signal transmission lines, TDM (time division multiplexing) transmission has been conducted so far with an aim of higher bit-rate transmission of a great amount of information and, recently, WDM (wavelength division multiplexing) transmission has been noted for transmitting a further great amount of information along with popularization of internets.
The WDM transmission is a mode for multiplexing transmission of a plurality of optical signals of different wavelengths by way of a single optical fiber. As shown in
FIG. 12
, optical signals from light sources
41
, . . . of different wavelength are modulated by a modulator
42
, and guided by an optical multiplexer
43
into a single optical fiber
44
on the transmission side
40
, while an optical signal from the optical fiber
44
is separated on every wavelength by an optical demultiplexer
46
, converted into electric signals by photoreceiving devices
45
and then demodulated and taken out on the receiving side
45
.
At present, transmission of signals in several tens to one hundred channels independent of each other has been put to practical use by using a single optical fiber, which can provide advantages capable of bilateral transmission, transmission of different kinds of signals such as analog signals and digital signals simultaneously, and transmission of signals at high bit-rate and of large capacity while dividing them into channels each at low bit-rate and of small capacity, by the use of light of different wavelengths.
By the way, since lights of various wavelengths transmit through optical parts, devices and systems in the WDM optical communication, it is necessary to previously detect their optical characteristic on every wavelengths as to whether each of them has intended function to all of wavelengths used.
For example, in the system as shown in
FIG. 12
, if the wave separation characteristic of the demultiplexer
46
depends on the wavelength, there exist wavelengths that can be separated and those that can not be separated. Further, if the photoreceiving sensitivity of each of the photoreceiving devices
47
depends on the wavelength, there exist wavelengths that can be received at high sensitivity and can not be received at high sensitivity even for the lights of an identical intensity, so that it is not preferred in view of the WDM optical communication.
Then, lights at desired wavelengths are selectively take out, by controlling the wave length of a variable wavelength laser light source or transmitting a light outputted from an light emission diode through an interference filter, and discontinuous spectrum lights having a desired wavelength spacing are entered to the optical parts, devices and systems to previously detect the characteristics of the emission light.
However, since any one of the light sources described above can output only the light of a single wavelength, when a plurality of lights of different wavelengths are intended to be multiplexed, light sources are required by the number of channel, to increase the cost.
In a case of using a wavelength variable laser and converting the light into those of different wavelength while successively adjusting the wavelength different wavelength, it may suffice to use only one light source device. However, upon entering light while varying the wavelength, it takes much time for exactly matching to an optional wavelength and a long time is necessary for evaluation of characteristics regarding all the lights, for example, in 100 channels.
Further, in the WDM transmission, it is desirable to increase the density by setting the wavelength spacing between each of transmission lights to 1 nm or less (typically about 60 to 125 GHz by frequency spacing). However, even when the laser light sources are used by the number corresponding to the number of channels, it requires high level of technique and high cost to output discontinuous spectrum lights while controlling the spacing for the wavelength of adjacent laser lights at a high accuracy of 1 nm or less.
Further, since the interference filter for use in DWDM (dense wavelength division multiplexing) transmission has a multi-layered structure of 50 to 100 layers, it is not easy to design and manufacture the filter such that discontinuous spectrum lights can be outputted at the wavelength spacing of 1 nm or less between each of adjacent lights by controlling the thickness for each of the layers even to skilled manufacturers.
Then, if discontinuous spectrum lights at a predetermined wavelength spacing for use in WDM transmission can be obtained easily, optical characteristics (wavelength dependence) of optical parts, devices and systems used for the transmission system can be examined simply.
For example, as shown in
FIG. 13
, when a multiplexer
43
is connected to the output of a demultiplexer
46
and discontinuous spectrum lights of known spectral characteristics are entered to the demultiplexer
46
, optical characteristics of the multiplexer
43
and demultiplexer
46
can be checked easily.
In this case, when a demultiplexer
46
of known wavelength selectivity is used, the optical characteristics of the multiplexer
43
can be analyzed extremely simply. Further, when a multiplexer
43
of known wavelength selectivity is used, the optical characteristics of the demultiplexer
46
can be analyzed extremely easily.
OBJECT OF THE INVENTION
In view of the above, it is a technical subject of the present invention to provide an optical spectrum slicer capable of outputting discontinuous spectrum lights each at a desired wavelength spacing from a broad band continuous spectrum light in an extremely simple structure and at a reduced cost, without using special light sources or filters, and further capable of matching the wavelengths of the discontinuous lights to a desired wavelength spacing.
SUMMARY OF THE INVENTION
For solving the subject, the present invention provides an optical spectrum slicer for converting a broad band continuous spectrum light having an optional wavelength region into multiple discontinuous spectrum lights each at a predetermined wavelength spacing and outputting them comprising:
a birefringent device having two polarization axes each orthogonal to an optical axis and linear polarizers disposed at the light incident end and the light emission end of the birefringent device, with the direction of polarization being inclined by about 45° relative to each of the polarization axes, and a heat generator for variably controlling each of wavelengths while maintaining the wavelength spacing of the discontinuous spectrum lights by controlling the temperature of the birefringent device.
The term “direction of polarization” in the present specification means direction of vibration of a vibration vectors of an optical wave for light and means a direction along which the transmissibility of the linearly polarized light is maximum for the linear polarizer.
Further, the “frequency” is a function of “wavelength”. Accordingly, if the term “wavelength” used for describing the constitution of the present invention is replaced with the term “frequency”, this means an invention having quite technically equivalent constitution except for the expression of the term and, accordingly, such a reworded invention is also within the technical scope of the present invention.
According to the invention, when a broad band continuous spectrum light having an optional wavelength region, for

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