JP3597912B2 - Optical filter - Google Patents

Description

[Industrial applications]
The present invention relates to an optical filter, and more particularly, to an optical filter capable of selecting an optical signal having a plurality of arbitrary wavelengths from an optical signal having a plurality of wavelengths.
[0001]
Optical filters have attracted attention as being usable in fields such as optical communication, optical switching, optical cross-connect, signal processing using light, and optical measurement. In particular, wavelength multiplexing has recently been used in the fields of optical switching and optical cross-connect. Research and development of devices aiming at high throughput due to the development of technology are active.
[0002]
[Prior art]
As an optical filter as described above, a filter using an acousto-optic effect (AO effect) as shown in FIG. 5 is conventionally known. FIG. 1A is a block diagram showing the optical filter, and FIG. 2B is a diagram showing a device layout corresponding to the block diagram.
[0003]
In the figure, reference numeral 21 denotes a polarization beam splitter (PBS), which receives wavelength-multiplexed random polarized lights λ ₁ , λ ₂ ,..., Λ _n from its input terminal B, and mutually outputs from its output terminals C and D, respectively. The optical signals (TM mode signal and TE mode signal) whose polarization planes are orthogonal to each other are separated and sent to the mode converters 22 and 23, respectively.
[0004]
In the mode converter 22, as shown in FIG. 3B, a high frequency signal of a predetermined frequency is applied to a surface acoustic wave (SAW) excitation electrode (IDT) to change only a specific wavelength λ _i from the TM mode to the TE mode. After conversion, the other wavelengths are output as they are and sent to the input terminal A of the polarizing beam splitter 24.
[0005]
Also, in the mode converter 23, only the wavelength λ _i is converted from the TE mode to the TM mode by supplying a high-frequency signal of a predetermined frequency to the excitation electrode, and the other wavelengths are passed as they are and the input terminal of the polarization beam splitter 24 is passed. Sent to B.
[0006]
Then, so as TE mode and filters light of a wavelength lambda _i of the TM mode in the polarizing beam splitter 24 is taken out from the output terminal C is polarization-non-filtered light of other wavelengths is extracted from the output terminal D ing.
[0007]
Thus, a polarization-independent optical filter is configured.
[0008]
[Problems to be solved by the invention]
An optical filter using such an acousto-optic effect requires a high-frequency oscillator to drive an excitation electrode (IDT), and has an oscillation frequency equal to the number of wavelengths to be selected when a plurality of wavelengths are selected simultaneously. However, there is a problem that the configuration is complicated and power consumption is increased.
[0009]
Therefore, an object of the present invention is to provide an optical filter having a simple configuration and low power consumption.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the optical filter according to the present invention has an optical signal input unit, a polarization splitting unit, an irreversible polarization plane rotator, an optical diffractor, an optical modulator, and a light reflecting unit. The light signal advances, and the light signal reflected by the light reflection unit returns to the light modulator, the light diffraction body, the polarization plane rotator, and the polarization separation unit in this order, and the light signal is reflected by the polarization separation unit. any one or more wavelength components of the separated into spatial orientation different from the input unit causes output from the optical signal output part diffracts the light modulator in optical diffraction element optical signal wavelength separation only Is an optical filter that is driven to transmit light, wherein the polarization separation unit is divided into first, second, and third polarization separation units, and one output side of the first polarization separation unit is Polarization plane for converting an optical signal having the same polarization plane as the other input optical signal to the second polarization splitting unit A first optical element for rotating by 90 ° is inserted, and the reflected light signal returned from the polarization plane rotator is separated into a spatial orientation different from that of the input light signal by the second polarization separation unit, and the separation is performed. One of the reflected light signals is converted into an optical signal having a polarization plane different from that of the other reflected light signal by a second optical element for rotating the plane of polarization by 90 °, and is given to the third polarization separation unit to be polarized and synthesized. It is characterized by doing.
[0011]
In the above optical filter, the polarization separation unit is divided into first, second, and third polarization separation units, and one input side of the first polarization separation unit is connected to the other input optical signal. An optical element for rotating the polarization plane by 90 ° to be converted into an optical signal having the same polarization plane and given to the second polarization separation unit is inserted, and the reflection from the polarization plane rotator is performed by the second polarization separation unit. Separating the optical signal into a spatial orientation different from that of the input optical signal and converting the one of the separated reflected optical signals into an optical signal having the same polarization plane as the other reflected optical signal by the optical element; Polarization synthesis can be performed by giving the signal to the separation unit.
[0012]
Further, in the above optical filter, the light reflecting portion may be a mirror having a curved surface that vertically reflects an optical signal transmitted through the optical modulator, or a mirror having a polygonal surface or a phase conjugate mirror instead of this mirror. May be used.
[0013]
Further, in the above optical filter, the amount of transmission through the optical modulator can be adjusted.
Further, a transmission type light diffracting body may be used.
[0014]
[Action]
In the optical filter according to the present invention, an optical signal is input from the optical signal input unit, and the optical signal is sent to the irreversible polarization plane rotator through the polarization separation unit, where the polarization plane is rotated. .
[0015]
The optical signal that has passed through the polarization plane rotator is further incident on the optical diffracting body, and is diffracted in a form that is separated into wavelength-multiplexed optical signal components for each wavelength.
[0016]
The optical signal diffracted by the optical diffractor is sent to the optical modulator. At this time, the optical modulator is driven so as to transmit only a desired arbitrary optical signal component. Only the optical signal component having the wavelength of? Is transmitted through the optical modulator and sent to the light reflecting section.
[0017]
The light reflecting portion may use a mirror having a surface that reflects incident light vertically, or a mirror having a polygonal surface or a phase conjugate mirror, and the optical signal reflected by such a light reflecting portion is The light passes through the optical modulator again and is sent to the optical diffraction body.
[0018]
Then, it returns to the wavelength multiplexed form again by this optical diffracting body, passes through the same optical axis, and returns to the above-mentioned polarization plane rotator, where the polarization plane is irreversible, that is, does not return to the original polarization plane Is rotated to a plane of polarization substantially orthogonal to the original plane of polarization, and returns to the polarization separation section. In this polarization separation section, since the polarization plane differs from the input optical signal by 90 °, the input light The signal is separated into a spatial direction different from the signal and is extracted from the optical signal output unit.
[0019]
Further, in such an optical filter, by adjusting the transmission amount of the optical modulator, it is possible to change the optical loss of an arbitrary wavelength.
[0020]
Furthermore, in the present invention, if the above-mentioned polarization splitting unit is single, it becomes a polarization-dependent optical filter. Instead, the optical signal is divided into first to third polarization separation units, and the first polarization separation unit separates an input optical signal into two optical signals having different polarization planes, and converts one of the optical signals to a polarization plane of 90. By changing the plane of polarization by the first optical element that is rotated by an angle, the two optical signals output from the first polarization separation unit are given to the second polarization separation unit so that the polarization planes of the two optical signals are the same. .
[0021]
In the second polarization splitting unit, the two input optical signals pass through as they are, are passed through the irreversible polarization plane rotator, are diffracted by the light diffracting body, and are transmitted through the optical modulator as described above. Is reflected again by the optical diffracting body, propagates on the same optical axis as the incident light beam, and returns to the second polarization separation section through the polarization plane rotator.
[0022]
The second polarization separation unit separates the two returned optical signals into spatial orientations different from the input optical signal and outputs the separated optical signals.
[0023]
The third as the one separated optical signal polarization plane of the second polarization separating part of the optical signal is different by changing the polarization plane by the second optical element is rotated 90 ° from the polarization To the polarization separation section.
[0024]
In the third polarization separation unit, the two input optical signals are polarization-synthesized and extracted as one optical signal from the optical signal output unit.
[0025]
By doing so, it is possible to configure an optical filter that does not depend on polarization.
[0026]
【Example】
FIG. 1 shows an embodiment (1) of an optical filter according to the present invention. In this embodiment, an optical signal input portion is formed by an input optical fiber 1 and a lens 2, and light input from the optical fiber 1 is formed. The signal is converted into a parallel beam by the lens 2.
[0027]
The parallel rays from the lens 2 pass through a polarization splitting film (or a polarizing beam splitter or a birefringent substance) 3 forming a polarization splitting section, and are sent to a Faraday rotator 4 forming an irreversible polarization plane rotator. .
[0028]
The Faraday rotator 4 rotates the plane of polarization of the optical signal transmitted through the polarization beam splitter 3 by 45 degrees, and the optical signal output from the Faraday rotator 4 further includes a diffraction grating 5 that forms an optical diffractor. And is separated and diffracted into optical signal components of individual wavelengths (λ _{1 to} λ ₄ ) that are wavelength-multiplexed.
[0029]
The optical signal components of each wavelength diffracted by the diffraction grating 5 are sent to an optical shutter array 6 forming an optical modulator (or a spatial light modulator or an optical modulator array). is driven by the optical shutter array drive system 10, a desired wavelength, for example, if desired only the wavelength lambda ₂ is that this is a transparent corresponding parts of the optical shutter array 6 at the wavelength lambda _2, is opaque to other parts To allow transmission.
[0030]
The optical shutter array drive system 10 can not only make the optical shutter array 6 transparent or opaque, but also make the optical shutter array 6 in a semi-transparent state between the optical shutter array 6 and take out an optical signal component of a desired wavelength in an attenuated form.
[0031]
The optical signal component of, for example, the wavelength λ ₂ transmitted through the optical shutter array 6 is reflected by a curved mirror 7 forming a light reflecting portion in a direction perpendicular to the incident direction.
[0032]
In addition, a mirror having a polygonal surface or a phase conjugate mirror may be used as the curved mirror 7.
[0033]
Optical signal component of the curved mirror 7 wavelength lambda ₂ came back after being reflected in the diffracted by the diffraction grating 5 is transmitted through the optical shutter array 6 is sent to the Faraday rotator 4 passes through the same optical axis as the incident beam .
[0034]
The Faraday rotator 4 is also rotated by 45 degrees and sent to the polarization splitting film 3, but the rotation in the Faraday rotator 4 is not reversible to return to the original polarization plane, but irreversible. Since the optical signal reflected by the curved mirror 7 has its polarization plane rotated by 45.degree. + 45.degree. = 90.degree. By the Faraday rotator 4, it has a polarization plane of the input optical signal. Differ by 90 °.
[0035]
In the example of FIG. 2, the light incident on the polarization splitting film 3 from the lens 2 is a polarization plane parallel to the paper surface, and the light incident on the polarization separation film 3 from the Faraday rotator 4 is shown as a polarization plane perpendicular to the paper surface. ing.
[0036]
Accordingly, in the polarization splitting film 3, the light is split and reflected by the light beam splitter 3, and is condensed by the lens 8 forming the optical signal output portion, and is output from the output optical fiber 9 which also forms the optical signal output. .
[0037]
In the optical filter shown in FIG. 1, depending on the plane of polarization of the input optical signal, the polarization may be reflected and separated by the polarization separation film 3 and may not be sent to the Faraday rotator 4. It is dependent.
[0038]
Therefore, in the embodiment (2) of the optical filter according to the present invention shown in FIG. 2 for making the polarization independent, the polarization separation film 3 shown in FIG. 1 is replaced with a polarization separation film forming a first polarization separation part. 31, a polarization separation film 32 forming a second polarization separation portion, and a polarization separation film 33 forming a third polarization separation portion.
[0039]
Then, the optical signal input from the optical fiber 1 and the lens 2 is separated into an optical signal component which goes straight as it is in the polarization separation film 31 and an optical signal component which is separated.
[0040]
Then, the separated optical signal is reflected by the reflecting mirror 11, and further the Faraday rotator as an optical element for rotating the polarization plane by 90 ° or the half-wave (λ / 2) plate 12 rotates the polarization plane by 90 °. Thereby, for example, in the illustrated example, the plane of polarization is changed from a plane of polarization perpendicular to the plane of the paper to a plane of polarization parallel (up and down) to the plane of the paper, and is sent to the polarization separation film 32 with the same polarization plane as the optical signal passed through the polarization separation film 31 as it is. .
[0041]
In the polarization splitting film 32, the two input optical signal components are passed as they are, and each of them passes through the Faraday rotator 4, the diffraction grating 5, and the optical shutter array 6 similarly to the embodiment (1) of FIG. The light is then sent to a curved mirror 7, reflected by the curved mirror 7, and returned to the polarization splitting film 32 via the optical shutter array 6, the diffraction grating 5, and the Faraday rotator 4.
[0042]
The optical signal reflected by the polarization separation film 32 is reflected and separated in a direction having an angle of 90 ° with respect to the optical signal input from the polarization separation film 31.
[0043]
Then, one of the two reflected light signals separated by the polarization separation film 32 in this way is orthogonal to the other separated reflected light signal because the polarization plane is rotated by 90 ° in the half-wave plate 13. It becomes the plane of polarization.
[0044]
Then, the optical signal output from the half-wave plate 13 and the optical signal separated from the polarization splitting film 32 and reflected by the reflecting mirror 14 are given to the polarization splitting film 33, where they are polarized and combined to form one An optical signal is output through the lens 8 and the output optical fiber 9 which constitute the optical signal output unit.
[0045]
The optical shutter array 6 can be composed of a polarization control element such as a twisted nematic liquid crystal or a Faraday rotator and a polarizer, can be driven by a voltage of several volts, and consumes a small amount of current, so that power consumption can be reduced.
[0046]
Further, the loss of the optical shutter array 6 can be adjusted in an analog manner by the optical shutter array drive system 10, so that an optical filter having an arbitrary optical loss characteristic with respect to the wavelength can be configured.
[0047]
FIGS. 3 and 4 show embodiments (3) and (4) using the transmission type optical diffraction grating 5 in FIGS. 1 and 2, respectively.
[0048]
【The invention's effect】
According to the optical filter according to the present invention described above, see already with less power consumption and easy construction without requiring a high-frequency oscillator or the like, and can provide an optical filter that is independent of the polarization Become.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment (1) of an optical filter according to the present invention.
FIG. 2 is a block diagram showing an embodiment (2) of the optical filter according to the present invention.
FIG. 3 is a block diagram showing an embodiment (3) of an optical filter according to the present invention.
FIG. 4 is a block diagram showing an embodiment (4) of an optical filter according to the present invention.
FIG. 5 is a diagram showing a conventional optical filter.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Input optical fiber 2 Lens 3, 31-33 Polarization separation film 4 Faraday rotator 5 Diffraction grating 6 Optical shutter array 7 Curved mirror 8 Lens 9 Output optical fiber 10 Optical shutter array drive system 12, 13 Same in the half-wave plate diagram Symbols indicate the same or corresponding parts.

Claims (6)

An optical signal input in the order of an optical signal input unit, a polarization separation unit, an irreversible polarization plane rotator, an optical diffractor, an optical modulator, and a light reflection unit advances, and the optical signal reflected by the light reflection unit Returns in the order of the optical modulator, the optical diffractor, the polarization rotator, and the polarization separation unit, and separates the light into a spatial orientation different from that of the optical signal input unit by the polarization separation unit and outputs the light from the optical signal output unit. the optical modulator causes to, an optical filter is driven so that only any one or more wavelength components of the optical signal diffracted by the wavelength demultiplexing by the optical diffraction element is transmitted,
An optical signal having the same polarization plane as one of the input optical signals at one output side of the first polarization splitter, wherein the polarization splitter is divided into first, second, and third polarization splitters; And a first optical element for rotating the polarization plane by 90 ° for application to the second polarization separation unit is inserted, and the reflected light signal returned from the polarization plane rotator is subjected to the second polarization separation. A second optical element that separates the reflected optical signal into a spatial orientation different from that of the input optical signal and rotates the plane of polarization of the one reflected optical signal by 90 °, and has a polarization plane different from the other reflected optical signal. An optical filter characterized in that the optical filter is converted into an optical signal and applied to the third polarization separation unit to combine the polarizations. 2. The optical filter according to claim 1 , wherein said light reflecting portion is a mirror having a curved surface for vertically reflecting an optical signal transmitted through said optical modulator. 3. The optical filter according to claim 2 , wherein a mirror having a polygonal surface is used instead of the mirror having the curved surface. 3. The optical filter according to claim 2 , wherein a phase conjugate mirror is used instead of the mirror having the curved surface. In the optical filter according to any one of claims 1 to 4, an optical filter, characterized in that to be able to adjust the amount of transmission of at optical modulator. The optical filter according to any one of claims 1 to 5, wherein the optical diffraction element is a transmission type.

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