JPH05256702A - Analyzer of light spectrum - Google Patents

Abstract

PURPOSE:To measure the spectrum of high output power from an optical fiber with good accuracy by inserting an optical attenuator plate between a concave mirror and a diffraction grating. CONSTITUTION:When the light enters via an optical fiber 1 from an optical connector provided at an optical input part, the light is changed to a parallel light beam by a collimator mirror 2. Thereafter, the light is attenuated to the suitable level by a continuously variable attenuator plate 8 and a stepped variable attenuator plate 9. The light is then diffracted corresponding to the wavelength by a diffraction grating 3, reflected by a plane mirror 4 and a condenser mirror 5 to enter a photodetecting sensor 7 through a slit 6. The plates 8, 9 are inclined to the optical axis and formed in a chevron-like configuration. Accordingly, the shift of the luminous fluxes due to the refraction at the plates 8, 9 is offset, and the optical systems in front of and in the rear of the plates 8, 9 can be aligned separately. The photodetector circuit is prevented from being saturated, so that the spectrum of the measuring light of the decreased input level is obtained while the shape of the original spectrum of the transmitted light is maintained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical spectrum analyzer, and more particularly to an optical spectrum analyzer for measuring wavelength of high output semiconductor laser output light or the like via an optical fiber.

[0002]

2. Description of the Related Art FIG. 2 is a schematic diagram showing the structure of a spectroscopic section of a conventional optical spectrum analyzer based on dispersion spectroscopy. Incident light from the optical fiber 1 is converted into parallel rays by the collimator mirror 2 and then enters the diffraction grating 3. Light is diffracted by the diffraction grating 3 at different angles depending on the wavelength, and only the light of the wavelength that has passed through the slit 6 through the plane mirror 4 and the condenser mirror 5 is input to the light receiving sensor 7 and converted into photocurrent there. To be done.

Therefore, by rotating the diffraction grating 3, it is possible to measure the spectrum of the light propagating through the optical fiber 1 at the resolution determined by the slit 6. In an actual analyzer, an optical chopper is placed immediately after the optical fiber 1 to perform synchronous detection in order to enable detection of low level light. The output current of the light receiving sensor 7 is amplified by a preamplifier or the like so that a high measurement dynamic range (for example, 60 dB or more) can be obtained.

[0004]

In the conventional optical spectrum analyzer described above, the optical input is 0 dBm (= 1 m).
If it exceeds W), there is a problem in that the light receiving circuit is saturated and an accurate optical spectrum measurement cannot be performed. For example, in the case of measuring a 1550 nm high-power semiconductor laser using a pulse, the optical power propagating through the optical fiber has a peak of 50 mW, and its spectrum is as shown in FIG. 3 (a). When is put into a conventional spectrum analyzer as it is, the spectrum is crushed at the top as shown in FIG. 3C due to saturation in the light receiving circuit.

In order to suppress the optical input to 0 dBm or less and to avoid saturation of the light receiving circuit, a method of attenuating 20 dB by an external optical attenuator can be considered, but this method uses an optical fiber on the light emitting element side and a spectrum analyzer. The optical attenuator is inserted between the optical fiber on the side of the optical fiber and the optical attenuator. The optical mode propagated to the measuring instrument side does not necessarily reproduce the intensity of the propagation mode of the input side optical fiber. For example, the measurement light spectrum when the light of the spectrum shown in FIG. 3A is incident is as shown in FIG. 3D, and although the saturation can be avoided, the half-value width of the wavelength is different.

Further, when an external optical attenuator is used, an optical connector is required on the input side and the output side of the optical attenuator, which causes variations in coupling reproducibility when the connection and disconnection are repeated. That is, the spectrum of the light propagating through the optical fiber behind the optical connector on the output side of the optical attenuator is as shown in FIG. It will change.

As described above, the conventional optical spectrum analyzer has a problem that the optical spectrum cannot be accurately measured for the optical fiber propagating light of high power level.

[0008]

In the optical spectrum analyzer of the present invention, an input light from an optical fiber is converted into parallel rays by a concave mirror, and then is incident on a diffraction grating to be dispersed. An optical attenuating plate is inserted between the diffraction grating and the diffraction grating.

[0009]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of a spectroscopic unit according to an embodiment of the present invention. Light is incident from the optical connector provided in the optical input section through the optical fiber 1, the incident light is converted into parallel rays by the collimator mirror 2, and then the continuous variable attenuation plate 8 and the step variable attenuation plate 9 are used. It is attenuated to an appropriate level. After that, it is diffracted by the diffraction grating 3 according to the wavelength, is reflected by the plane mirror 4 and the condenser mirror 5, and is reflected by the slit 6
It passes through and enters the light receiving sensor.

Each of the attenuating plates has no difference in the amount of attenuation depending on the wavelength, and the attenuating plates are arranged so as to be inclined with respect to the optical axis. Each attenuating plate is arranged to be inclined with respect to the optical axis, because the reflected light from the attenuating plate is
This is to prevent an external resonator from being formed between the end face of the optical fiber 1 and the surface of the light receiving sensor 7 to confuse the mode, and the V-shape is used for each inclined attenuation plate. This is because the deviations of the light beams due to refraction are canceled each other so that the optical systems before and after the attenuation plate can be aligned independently.

By properly attenuating the intensity of the input light using this attenuator, it is possible to avoid the saturation of the light receiving circuit, and as shown in FIG. It is possible to obtain a measurement light spectrum with a lowered level while maintaining the shape of (a)].

The attenuation amount of the two optical attenuating plates can be manually specified and set from the front panel of the optical spectrum analyzer. Alternatively, control CP until the intensity level reaches a set level that is appropriately lower than the saturation level.
It may be adjusted by U. The range of the attenuation amount that can be set by the two optical attenuating plates is, for example, up to 20d.
When it is B, the measurement level range (for example, 0 to −60 dBm) of the conventional optical spectrum analyzer is moved upward (ie,
20 to -60 dBm).

[0013]

As described above, since the optical spectrum analyzer according to the present invention is provided with the attenuator inside the spectroscopic unit, the present invention allows the optical fiber which cannot be accurately measured conventionally. It becomes possible to measure the optical spectrum of the high light output with high accuracy.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a spectroscopic unit according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a conventional spectroscopic unit.

FIG. 3 shows an example of a high-level input optical spectrum to be measured and a corresponding measurement optical spectrum according to an embodiment and a conventional example.

[Explanation of symbols]

1 ... Optical fiber, 2 ... Collimating mirror, 3 ...
Diffraction grating, 4 ... Plane mirror, 5 ... Focusing mirror,
6 ... Slit, 7 ... Light receiving sensor, 8 ... Continuous variable attenuation plate, 9 ... Step variable attenuation plate.

Claims (1)

[Claims] 1. An optical spectrum analyzer in which light input through an optical fiber is converted into parallel rays by a collimator and then is incident on a diffractive element, where the light is split between the collimator and the diffractive element. An optical spectrum analyzer characterized in that an optical attenuating plate is arranged.