JP3403643B2 - Polarization-dependent precision measurement equipment - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization-dependent precision measuring instrument for measuring the polarization dependency of an optical device, which is applicable to an optical communication device using an optical fiber, an optical switch, an optical information processing device and the like. Regarding

[0002]

2. Description of the Related Art Considering the construction of an optical transmission processing system using light such as optical communication, optical switching, and optical information processing, the polarization dependence of each device becomes a serious problem. Therefore, in order to compensate for the optical loss in the optical fiber or the optical switch, a semiconductor laser type optical amplification element is used. This is a semiconductor laser as shown in FIG. 3 which has anti-reflection coating on both end faces. However, if the gain characteristic changes depending on the polarization state of the input signal light, the light receiving level on the light receiving side changes with time. It fluctuates, and the reception sensitivity is greatly reduced. Therefore, for each device, for example, polarization dependence of 0.5 dB
The following performance is required, and it is necessary to measure the polarization dependence.

At this time, it is necessary to carry out the measurement before mounting the fiber on a device such as a semiconductor laser type optical amplifying device to form a module, that is, in a chip state. Usually, in order to measure the polarization dependence, the polarization of the input light having a specific wavelength is rotated, and the gain at that time is measured.

Therefore, conventionally, the polarization dependence is measured by using a polarization controller in which a half-wave plate and a quarter-wave plate are combined. FIG. 4 shows the configuration of an apparatus for measuring polarization dependence using a conventional polarization controller. In FIG. 4, 1100 is a light source, 1101 is a polarization rotator, and 1102 is a quarter wavelength plate. 1103 is 1/2
Wave plates 1104, 1105 are spherical fibers, 1106
Is a semiconductor laser type optical amplification element to be measured, and 1107 is a light receiving element.

Here, the wave plate 110 is used to rotate the plane of polarization.
It is realized by mechanically rotating 2, 1103. At this time, it is the element TE (or T
It is the M) direction, and conversely, the TM (or TE) direction shows the minimum value. Therefore, the polarization dependence can be obtained (measured) by calculating the difference between the two.

By the way, TE mode is Transvers
e Electric mode, TM mode is Tran
sverse magnetic mode.

However, when the above-mentioned antireflection coating is not perfect and, for example, 0.5% reflection remains, the gain of the optical amplifying element has peaks and valleys (so-called ripples) depending on the wavelength. The state of this ripple differs between the TE direction and the TM direction. Gain states with and without ripple are shown in FIGS. 2 (A) and 2 (B). When there is a ripple as shown in FIG. 2 (A), depending on the wavelength, TE and T
The gain of M may change. Therefore, if the measurement is performed only at a specific wavelength, the overall polarization dependence (T
The tendency of (gain of E-gain of TM) cannot be obtained.

[0008]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention As mentioned above,
Conventionally, the input light of a certain specific wavelength is ¼ wavelength with a ½ wavelength plate.
The polarization dependence was measured by rotating the plane of polarization using a polarization controller combined with a wave plate. However, if there is residual reflection in the optical amplification element, T
The gains of E and TM change, and when measured at a specific wavelength, the overall polarization dependence (TE gain-TM
There was a problem that the gain of was not obtained.

Therefore, in view of the above points, an object of the present invention is to provide a polarization dependent precision measuring instrument capable of measuring the polarization dependence even in the presence of ripples.

[0010]

In order to achieve such an object, the invention of claim 1 provides means for emitting spontaneous emission light in a wide wavelength band, and among the emitted spontaneous emission light, Polarization switching means for switching between light having one linear polarization plane and light having a second linear polarization plane perpendicular to the first linear polarization plane, and the first linear polarization plane or the second linear polarization plane. Means for injecting an optical signal having a wavefront into the device under test, means for receiving the output light from the device under measurement through an optical fiber, and a fixed or variable optical bandpass for a part of the received output light So that the filter eliminates ripple
Averaged together cut out, and means for observing the intensity of the clipped output light, the first linear polarization and a second linear polarization of TE direction of the device under test, so as to match each TM direction And means for adjusting to. The invention of claim 2 has a broad wavelength band.
Means for emitting spontaneous emission light and the spontaneous emission emitted
Of the light, the light having the first linear polarization plane and the first linear polarization
Switch between wavefront and light with a second plane of linear polarization perpendicular to the wavefront
Polarization switching means, the first linear polarization plane or the
Inject an optical signal with the second linear polarization plane into the device under test
Means and output light from the device under test through an optical fiber
And receive the intensity of the received output light.
Means for averaging and observing so that
1 linear polarization plane and 2nd linear polarization plane
Adjust to match the TE and TM directions of the child respectively.
And a means for adjusting.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of a measurement system using the polarization-dependent precision measuring device of the present invention. In FIG. 1, reference numeral 101 is an optical fiber amplifier that outputs broadband spontaneous emission light having a wavelength band of 1530 to 1560 nm. Reference numeral 102 denotes a deflector that transmits only a specific linear polarization plane B (TE direction of the device under test). Reference numerals 103 and 104 denote polarization plane maintaining fibers that preserve the linear polarization plane.

Reference numeral 105 denotes a half-wave plate, which can be switched to switch between light having a linear polarization plane B and a linear polarization plane C (TM direction) perpendicular to the linear polarization plane B. The light that has passed through the half-wave plate 105 is input by the spherical fiber 119 to the device under test 120, that is, the device under test for which the polarization dependence is to be measured.
The output light from the device under test 120 is extracted through the front spherical fiber 121, and then the optical spectrum analyzer 122
Is incident on. The optical spectrum analyzer 122 monitors (observes) the wavelength spectrum of the incident light.

In such a structure, the optical spectrum analyzer 122 rotates the fiber 104 manually / automatically while monitoring the incident light.
The linear polarization plane B of the device under test is aligned with the TE direction,
The linear polarization plane C of the device under test is adjusted so as to match the TM direction. More specifically, when the device under test 120 has a ripple, the waveform as shown in FIG.
04 is rotated by trial and error, and TE light and T in FIG.
When the difference between the M lights becomes maximum, the linear polarization planes B and C become T
E. This corresponds to the TM direction. The spectrum obtained at this time is the measurement result. At this time, FIG. 2 (A)
As can be seen from Fig. 2, when the peaks and valleys are large and the numerical value of the polarization dependence cannot be determined, the resolution (resolution) of the optical spectrum analyzer is reduced, and averaging is performed.
The result as seen in (B) can be obtained.

When the adjustment of the above embodiment is performed, FIG.
When the dependence measurement is performed, the waveform has a linear broadband characteristic as shown in (B). The dependence measurement result appears as a difference between the optical gains of TE and TM. Therefore, it is possible to obtain the entire polarization dependence even in the case of an element having a ripple.

Instead of combining the above-mentioned optical fiber amplifier and a polarizer, a polarization-maintaining fiber amplifier,
Similar effects can be obtained by using LEDs and semiconductor lasers as means for emitting natural light in a wide wavelength band. Also, instead of the optical spectrum analyzer, a fixed or variable optical bandpass filter, PD, AP
The same effect can be obtained by using a means for measuring the intensity of light such as D or an optical power meter. At this time, when the band of the bandpass filter is small (for example, 1 nm), the influence of the ripple appears to be large. The ripple effect can be eliminated with.

[0017]

As described above, according to the present invention, spontaneous emission light having a wide wavelength band is input to the device under test. Since the spontaneous emission light is adjusted so as to have the polarization planes in the TE direction and the TM direction that have the maximum or minimum values in the linear waveform with respect to the wavelength of the wide band, the polarization dependence of the wide band is obtained. It becomes possible to measure.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a waveform diagram showing a measurement result of dependency.

FIG. 3 is a perspective view showing a structure of an optical amplification element.

FIG. 4 is a configuration diagram showing a configuration of a conventional example.

[Explanation of symbols]

101 (optical) fiber amplifier 102 Polarizer 103, 104 (polarization maintaining) fiber 105 1/2 is a wave plate 119,121 Tip spherical fiber 120 device under test 122 Optical Spectrum Analyzer

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields investigated (Int.Cl. ⁷ , DB name) G01M 11/00-11/08 G02F 1/29-7/00

Claims (2)

(57) [Claims] 1. A means for emitting spontaneous emission light having a wide wavelength band, a light having a first linear polarization plane and a second vertical plane perpendicular to the first linear polarization plane of the emitted spontaneous emission light. Polarization switching means for switching between light having a linear polarization plane of, and means for injecting an optical signal having the first linear polarization plane or the second linear polarization plane into the device under test, A means for receiving the output light through an optical fiber and a fixed or variable optical band for a part of the received output light.
The pass filter averages and cuts out so as to eliminate ripples, and a means for observing the intensity of the cut-out output light, and the first linear polarization plane and the second linear polarization plane are covered by the cover. A polarization-dependent precision measuring instrument, characterized in that it has means for adjusting so as to match the TE direction and the TM direction of the measuring element. 2. A hand for emitting spontaneous emission light in a wide wavelength band.
And stage, among the emitted spontaneous emission light, a first linear polarization
The light and the second linear polarization plane perpendicular to the first linear polarization plane
And a polarization switching means for switching between the first linear polarization plane and the second linear polarization plane.
Means for injecting an optical signal into the device under test and receiving the output light from the device under test through an optical fiber
And the intensity of the received output light without ripple
And a means for observing after averaging so that the first linear polarization plane and the second linear polarization plane are
Match the TE direction and TM direction of the measuring element.
Polarization dependence characterized by having means for adjusting
Precision measurement equipment.