Optical receiver evaluation method and optical receiver evaluation apparatus
There are provided an evaluation method and an evaluation device for an optical receiver capable of evaluating only a phase error between optical 90-degree hybrids with high accuracy even when there is a skew between channels in the optical receiver. In the evaluation method and the evaluation device for the optical receiver including optical 90-degree hybrids, a phase error between the optical 90-degree hybrids is calculated by calculation of decomposing a transfer function of the optical receiver into a product of matrixes to evaluate the optical receiver.
1. A method of evaluating an optical receiver including optical 90-degree hybrids, the method comprising:
decomposing a transfer function of the optical receiver into a product of matrixes; and
evaluating the optical receiver by calculating a phase error between the optical 90 -degree hybrids by the product of the matrixes.
2. The method of evaluating the optical receiver according to claim 1 , wherein decomposing the transfer function into the product of the matrixes comprises decomposing a matrix indicating the transfer function of the optical receiver into a product of a shear matrix, a scaling matrix, and a rotation matrix, and wherein evaluating the optical receiver comprises obtaining the phase error between the optical 90-degree hybrids of the optical receiver from a coefficient of the shear matrix.
3. The method of evaluating the optical receiver according to claim 2 , wherein the shear matrix is obtained by decomposing the matrix indicating the transfer function of the optical receiver into a product of a rotation matrix and an upper triangular matrix by QR decomposition and decomposing the upper triangular matrix into a product of the shear matrix and the scaling matrix.
4. An evaluation device that evaluates an optical receiver including optical 90-degree hybrids, the evaluation device comprising:
a processor,
non-transitory computer readable medium having stored thereon executable code that is executable by the processor,
a transmission unit and a reception unit connected via a transmission path,
wherein the transmission unit includes a known signal generator that generates a series of known signals, an optical transmitter, and, when executed by the processor, the executable code causes the processor to function as a transmitter compensation unit that acquires an estimation result of a transfer function of the optical transmitter from a transmitter transfer function estimation unit of the reception unit and compensates for the transfer function of the optical transmitter,
wherein the reception unit includes an optical receiver, and, when executed by the processor, the executable code causes the processor to function as a receiver compensation unit, first receiver transfer function estimation unit, second receiver transfer function estimation unit, and the transmitter transfer function estimation unit,
wherein an estimated transfer function of the optical receiver is decomposed by the evaluation device into terms of a phase error between the 90-degree hybrids, a gain imbalance between channels, and remaining rotation, and
wherein the optical receiver is evaluated.
5. The evaluation device that evaluates the optical receiver according to claim 4 , wherein the transmitter transfer function estimation unit estimates the transfer function of the optical transmitter from a provisional transfer function of the optical receiver and first digital data acquired by the reception unit when a first known signal is transmitted from the transmission unit to the reception unit,
wherein the first receiver transfer function estimation unit estimates the provisional transfer function of the optical receiver from digital data acquired by the reception unit when an Amplified Spontaneous Emission (ASE) signal is input to an input end of the optical receiver, and
wherein the second receiver transfer function estimation unit estimates the transfer function of the optical receiver from the estimated transfer function of the optical transmitter and second digital data acquired by the reception unit when a second known signal is transmitted from the transmission unit to the reception unit.