JP2011249953A - Optical receiving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an optical receiving circuit capable of reducing a skew between optical fibers by flexibly adjusting optical length of each optical fiber, having a skew adjusting section located on the each optical fiber path through an optical signal demodulating section to an intensity modulation photoelectric conversion section.SOLUTION: An optical receiving circuit includes: an optical signal demodulating section that inputs and branches a phase modulated optical signal and outputs a differential optical intensity modulated signal composed of an in-phase component and a reverse phase component; optical fibers that individually input and propagate the in-phase component and the reverse phase component of the differential optical intensity modulated signal output by the optical signal demodulating section; an skew adjusting section that is located on any location along the length of the optical fibers and individually adjusts the skew of each of the optical fibers; and an intensity modulation photoelectric converting section that outputs an electrical signal based on the in-phase component and the reverse phase component of the differential optical intensity modulated signal output from the fibers.

Description

  The present invention relates to an optical receiver circuit of a phase modulation type optical communication module, and more particularly to skew adjustment of an optical fiber used in the optical receiver circuit.

  In the current digital information communication environment, communication means capable of handling a large capacity such as FTTH (Fiber To The Home) has been set up in each home, and a large capacity LAN (Loacal) such as Gigabit Ethernet (registered trademark) can be easily used in the office. (Area Network) can be constructed.

  The demand for large-capacity digital transmission has further extended to the demand for long-distance transmission. From the “light intensity modulation method”, which has been the mainstream of conventional optical communication methods, the “optical light” that is resistant to chromatic dispersion and polarization dispersion. It is shifting to “phase modulation system”. Among the optical phase modulation methods, DPSK (Differential Phase Shift Keying) and DQPSK (Differential Quadrature Phase Shift Keying) are expected as next-generation optical communication methods. Already, some of the submarine and backbone communication networks have already been replaced by these communication methods.

  On the receiving side of the DPSK and DQPSK optical communication systems, an optical signal demodulator (delay interferometer or the like) converts phase modulation into intensity modulation, and an intensity modulation photoelectric conversion unit (photodiode module or the like) converts it into an electrical signal. The optical signal demodulator outputs a pair of in-phase component and anti-phase component differential optical intensity modulation signals (2 ports in total) in the DPSK method, and two sets of in-phase component and anti-phase component differential light in the DQPSK method. The intensity modulation signal (4 ports in total) is output.

Such a conventional apparatus example will be described in detail with reference to the drawings. FIG. 7 is a diagram showing a configuration example of a conventional optical receiving circuit.
An optical signal from an optical transmission circuit (not shown) is input to the optical fiber 1.
The optical signal propagates through the optical fiber 1 and is input to the optical signal demodulator 2. The optical signal demodulator 2 is a DPSK delay interferometer, for example. The optical signal demodulator 2 converts the input optical signal into a differential optical intensity modulation signal, and outputs the differential optical intensity modulation signal to the optical fiber 3 (2 ports in the DPSK delay interferometer).
The differential light intensity modulation signal is propagated through the optical fiber 3, input to the intensity modulation photoelectric conversion unit 4, and converted into an electric signal.

An operation example of such an apparatus will be described in detail with reference to the drawings.
The optical signal phase-modulated by an optical transmission circuit (not shown) is input to the optical signal demodulator 2 through the optical fiber 1. The optical signal demodulator 2 divides the input optical signal into a set of differential optical intensity modulation signals composed of in-phase components and anti-phase components in, for example, a DPSK type delay interferometer, and the like. Respectively.
The differential optical intensity modulation signal of the in-phase component and the anti-phase component propagated by the two-port optical fiber 3 is converted into an electric signal by the intensity modulation photoelectric conversion unit 4.

  Patent Document 1 describes a configuration of an optical transmission system using a delay interferometer for demodulation of phase modulation.

JP 2006-352678 A

  In the conventional optical receiver circuit, the differential optical intensity modulation signal generated by the optical signal demodulator 2 is converted into an electric signal by the intensity modulation photoelectric converter 4. A differential optical signal delay difference (hereinafter referred to as skew) may occur due to the optical length difference of the optical fiber 3 of each port up to the photoelectric conversion unit 4. It is known that when this skew reaches several percent with respect to one bit time obtained from the signal bit rate, the transmission quality such as deterioration of OSNR (optical signal-to-noise ratio) tolerance is affected. For this reason, it is necessary to suppress this skew below a certain level. At present, the optical path length of the optical fiber 3 between the optical signal demodulator 2 and the intensity modulation photoelectric converter 4 is reduced when the optical receiver circuit is built. This can be done by making fine adjustments so that no skew occurs.

  However, in addition to the technical difficulty that the adjustment of the optical path length of the optical fiber 3 is on the order of submillimeters, there is a problem that the skew cannot be adjusted again after it has been made.

  Accordingly, an object of the present invention is to provide a skew adjustment unit on each optical fiber path from the optical signal demodulation unit to the intensity modulation photoelectric conversion unit, and freely adjust the optical length of each optical fiber, An object of the present invention is to realize an optical receiving circuit capable of reducing skew.

In order to solve such a problem, the invention according to claim 1 of the present invention,
An optical signal demodulator that inputs a phase-modulated optical signal and branches and outputs a differential optical intensity modulation signal composed of an in-phase component and an anti-phase component;
An optical fiber that inputs and propagates each of the in-phase component and the anti-phase component of the differential optical intensity modulation signal output by the optical signal demodulator;
A skew adjustment unit that is provided at any position of this optical fiber and individually adjusts the skew of each optical fiber;
An intensity modulation photoelectric conversion unit that outputs an electrical signal based on the in-phase component and the anti-phase component of the differential light intensity modulation signal output from the optical fiber;
It is characterized by providing.

Invention of Claim 2 is invention of Claim 1, Comprising:
The optical signal demodulator is a DPSK delay interferometer, and outputs a differential optical intensity modulation signal composed of a pair of in-phase components and anti-phase components.

Invention of Claim 3 is invention of Claim 1, Comprising:
The optical signal demodulator is a DQPSK delay interferometer, and outputs a differential optical intensity modulation signal composed of two sets of in-phase components and anti-phase components.

Invention of Claim 4 is invention in any one of Claims 1-3, Comprising:
The skew adjusting unit adjusts the skew by rotating the optical fiber in a circular shape.

Invention of Claim 5 is invention in any one of Claims 1-3, Comprising:
The skew adjusting unit adjusts the skew by bending the optical fiber with a guide having an adjustable curvature.

Invention of Claim 6 is invention of Claim 5, Comprising:
The guide is formed of bimetal.

Invention of Claim 7 is invention of Claim 5, Comprising:
The guide is formed of a shape memory alloy.

Invention of Claim 8 is invention in any one of Claims 1-3, Comprising:
The skew adjusting unit adjusts the skew by applying a stress in a direction perpendicular to the axis to the optical fiber.

Invention of Claim 9 is invention in any one of Claims 1-3, Comprising:
The skew adjusting unit adjusts the skew by applying an axial tensile or compressive stress to the optical fiber.

  According to the present invention, the optical signal demodulator inputs the phase-modulated optical signal, branches and outputs the differential optical intensity modulation signal composed of the in-phase component and the anti-phase component, and the optical fiber has the differential optical intensity. Each of the in-phase component and the opposite-phase component of the modulation signal is input and propagated, the skew adjustment unit individually adjusts the skew of each optical fiber, and the intensity modulation photoelectric conversion unit outputs the differential output from the optical fiber. Since an electric signal is output based on the in-phase component and the anti-phase component of the light intensity modulation signal, an optical receiver circuit capable of freely adjusting the optical length of each optical fiber and reducing the skew between the optical fibers. Can be realized.

It is the figure which showed the structure of one Example of this invention. It is the figure which showed the structure of the other Example of this invention. It is the figure which showed the structural example of the skew adjustment part. It is the figure which showed the structural example of the skew adjustment part. It is the figure which showed the structural example of the skew adjustment part. It is the figure which showed the structural example of the skew adjustment part. It is the figure which showed the structural example of the conventional optical receiver circuit.

Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing the configuration of an embodiment of the present invention. Here, the same components as those in FIG.
In FIG. 1, a skew adjustment unit 5 is attached to any position of a two-port optical fiber 3 and independently adjusts the skew of the optical fiber of each port.
For the skew adjusting unit 5, for example, a guide 51 having a groove in which the curvature can be adjusted and the optical fiber 3 is fitted is used.
The differential light intensity modulation signal propagated by the optical fiber 3 via the skew adjustment unit 5 is converted into an electric signal by the intensity modulation photoelectric conversion unit 4.

An example of the operation of such an apparatus will be described in detail with reference to FIG.
The optical signal demodulator 2 which is a DPSK delay interferometer splits the input optical signal into a pair of differential optical intensity modulation signals composed of in-phase components and anti-phase components, and supplies them to a 2-port optical fiber 3 respectively. Output.
The optical fiber 3 of each port is distorted by bending caused by the guide 51 of the skew adjusting unit 5, changes in physical length, refractive index, etc., and can also change the optical length of the optical fiber 3. The skew of the optical signal to be adjusted can be adjusted.
The differential light intensity modulation signal propagated by the two-port optical fiber 3 is converted into an electric signal by the intensity modulation photoelectric conversion unit 4.

  In this way, the optical signal demodulator 2 inputs the phase-modulated optical signal, branches and outputs the differential optical intensity modulation signal composed of the in-phase component and the anti-phase component, and the optical fiber 3 outputs the differential light. Each of the in-phase component and the opposite-phase component of the intensity modulation signal is input and propagated, and the guide 51 of the skew adjustment unit 5 bends the optical fiber 3 with an adjustable curvature to individually adjust the skew of each optical fiber 3. Since the intensity modulation photoelectric conversion unit 4 outputs an electric signal based on the in-phase component and the anti-phase component of the differential light intensity modulation signal output from the optical fiber 3, the optical length of each optical fiber 3 is adjusted. It is possible to realize an optical receiving circuit that can freely adjust the above and reduce the skew between the optical fibers 3.

  Although an example in which a DPSK delay interferometer is used for the optical signal demodulator 2 is shown, a DQPSK delay interferometer may be used. In this case, the optical signal demodulator 2 branches the input optical signal subjected to differential quaternary phase modulation into a differential optical intensity modulation signal composed of two sets of in-phase components and anti-phase components, for a total of 4 ports of optical fiber Therefore, the skew adjustment unit is attached to each of the four-port optical fibers.

  The optical signal demodulator 2 may be a DP-QPSK (digital coherent) phase signal demodulator. The DP-QPSK method is a method in which a local oscillation light is generated as a reference light in an optical receiving circuit, and a demodulation unit outputs a differential light intensity modulation signal based on a phase difference between the optical signal and the reference light. is there.

  Further, as shown in FIG. 2, a skew adjusting unit 6 may be provided for adjusting the skew by rotating each optical fiber in a circular shape (diameters Φ1 and Φ2 in FIG. 2) whose diameter can be adjusted.

  The skew adjustment unit may be configured to apply stress in a direction perpendicular to the axis of the optical fiber 3. In this case, for example, as shown in FIG. 3, the optical fiber 3 is sandwiched between a base portion 71 having a screw hole and a screw 72, and a stress applying portion that applies stress in a direction perpendicular to the axis of the optical fiber 3 by fastening the screw 72. 7 may be configured, or as shown in FIG. 4, a stress applying portion 8 that applies stress in a direction perpendicular to the axis of the optical fiber 3 may be configured by using a bimetal 81 whose bending changes depending on temperature. .

  As shown in FIG. 5, the skew adjusting unit may be configured to apply tensile or compressive stress in the axial direction of the optical fiber 3 by the stress applying unit 9.

  Further, a bimetal 511 may be used for the guide 51 as shown in FIG. In this case, it is possible to adjust the curvature of the guide 51 according to the temperature and adjust the skew generated according to the temperature change of the optical fiber 3 by utilizing the property that the bending method changes according to the temperature change.

  For the guide 51 and the stress applying portion 8, a shape memory alloy whose shape can be controlled by temperature, or a piezoelectric material such as lead zirconate titanate (PZT) that expands and contracts when an electric field is applied, is used instead of the bimetal. May be.

2 Optical signal demodulation unit 3 Optical fiber 4 Intensity modulation photoelectric conversion unit 5, 6 Skew adjustment unit 51 Guide 511 Bimetal 7, 8, 9 Stress application unit

Claims (9)

An optical signal demodulator that inputs a phase-modulated optical signal and branches and outputs a differential optical intensity modulation signal composed of an in-phase component and an anti-phase component;
An optical fiber that inputs and propagates each of the in-phase component and the anti-phase component of the differential optical intensity modulation signal output by the optical signal demodulator;
A skew adjustment unit that is provided at any position of this optical fiber and individually adjusts the skew of each optical fiber;
An intensity modulation photoelectric conversion unit that outputs an electrical signal based on the in-phase component and the anti-phase component of the differential light intensity modulation signal output from the optical fiber;
An optical receiver circuit comprising:   2. The optical receiver circuit according to claim 1, wherein the optical signal demodulator outputs a differential optical intensity modulation signal composed of a pair of in-phase components and anti-phase components by a DPSK delay interferometer.   2. The optical receiver circuit according to claim 1, wherein the optical signal demodulator is a DQPSK delay interferometer and outputs a differential optical intensity modulation signal comprising two sets of in-phase components and anti-phase components.   The optical receiver circuit according to claim 1, wherein the skew adjustment unit adjusts the skew by rotating the optical fiber in a circular shape.   The optical receiver circuit according to claim 1, wherein the skew adjusting unit adjusts the skew by bending the optical fiber with a guide having an adjustable curvature.   6. The optical receiver circuit according to claim 5, wherein the guide is formed of bimetal.   6. The optical receiver circuit according to claim 5, wherein the guide is made of a shape memory alloy.     The optical receiver circuit according to claim 1, wherein the skew adjusting unit adjusts the skew by applying a stress in a direction perpendicular to the axis to the optical fiber.     The optical receiver circuit according to claim 1, wherein the skew adjusting unit adjusts the skew by applying an axial tensile or compressive stress to the optical fiber.

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