JP2002134765A - Spectrum photodetector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-resolution spectrum photodetector at low cost, using a polychromater system of simple structure. SOLUTION: An array type detector 5 comprises a plurality of photodiode elements, arranged vertically in two lateral rows, while alternating the light- receiving faces of the photodiode elements in the upper and lower rows. Since a separated light from a concave diffraction grating 2 impinges on the array- type detector 5 perpendicular to the longitudinal direction thereof, an InGaAs photodiode element 6 in the upper or lower stage is irradiated with the peak of each multiplex wavelength without fail. Consequently, the peak intensities and peak positions can be detected accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spectral photodetector used for optical communication, and more particularly to a high-density optical wavelength division multiplexing (hereinafter, DWDM).
The present invention relates to a technique for receiving an optical signal with high accuracy.

[0002]

2. Description of the Related Art In recent years, a WDM transmission system for transmitting a plurality of optical signals in a single-core optical fiber has been developed, so that the transmission capacity can be dramatically increased without adding an optical fiber. became. Furthermore, a transmission system suitable for long-distance transmission is put into practical use by a high-density optical wavelength division multiplexing (DWDM) transmission system that multiplexes a large number of optical signals at very narrow wavelength intervals in a low-loss band in optical fiber characteristics. Has been

In such an optical wavelength division multiplexing transmission, it is necessary to perform monitoring for monitoring an optical signal multiplexed at each device such as a relay point or a termination point. When performing this monitoring, the multiplexed optical signal is spectrally separated and monitored for each multiplexed wave. A device having the spectral function is called a spectral unit. The spectroscopic means includes a diffraction grating, a prism, an optical filter, and the like, and a diffraction grating is frequently used for the above-described monitoring. Further, as a photodetector for detecting an optical signal spectrally separated for each optical spectrum by the spectral means, various photodiodes having optical sensitivity characteristics corresponding to the wavelength of the optical signal are used.

In the case of optical communication, 700 to 20
Of the near-infrared wavelength band of 00 nm, in particular,
A wavelength range of 1600 nm is used. This wavelength range is
Silicon (Si) photodiodes, which can be covered by germanium (Ge) avalanche photodiodes but have high noise but have excellent characteristics such as small size, light weight, and low cost, are not suitable for this wavelength range. It cannot be applied because it has no light receiving sensitivity. Therefore, high sensitivity in this wavelength range
Indium gallium arsenide (In
GaAs) photodiodes are used.

[0005] The spectral photodetector provided with the above-mentioned spectral means and photodetector can be roughly classified into a monochromator system and a polychromator system. The monochromator method is a method of scanning a wavelength by rotating a diffraction grating, and the polychromator method is to dispose an array-type detector on an image forming plane of spectrum to detect the entire wavelength range at once. It is a method to do. The polychromator system has a simple structure because the relationship between the input position of the optical signal, the diffraction grating, and the array-type detector is fixed, and the real-time measurement is possible because all wavelength range data can be acquired at once. is there.

FIG. 5 is a diagram showing a configuration example of a conventional spectral photodetector. The spectral light receiving device 101 shown in this example includes an optical fiber 1, a concave diffraction grating 2, and an array type detector 3. The optical fiber 1 may be a general dispersion-unshifted single-mode fiber.
Dispersion shift suitable for long-distance transmission by WDM
Single mode fiber. The concave diffraction grating 2 serving as a spectral unit has a blazed grating (grating groove) formed by, for example, a holographic exposure method or an etching method. Also,
The array type detector 3 has a plurality of InGaAs photodiode elements arranged in a row.

The spectral light receiving device 101 shown in FIG. 1 functions as follows. That is, the optical signal input from the optical fiber 1 is diffracted by the concave diffraction grating 2 in accordance with the wavelength, and the light is split and incident on the array type detector 3. In addition, it is common to arrange a collimator so that light incident on the array type detector 3 becomes parallel light, but illustration is omitted here. Here, assuming that the concave diffraction grating 2 is fixed (does not rotate), the state of the diffracted light received by the array type detector 3 is shown in FIG.

FIG. 6 is an image diagram showing a state in which an optical signal (diffracted light) split by the splitting means (concave diffraction grating 2) is incident on the array type detector 3. The array-type detector 3 is, for example, one in which 128 InGaAs photodiode elements 4 are arranged in a line. The width of the light receiving surface of the InGaAs photodiode elements 4 is 15 μm, and the pitch interval is 25 μm. Shall be In the DWDM here, 1530 to 1560
It is assumed that 32 wavelengths are multiplexed in the wavelength range of μm, and each multiplexed wave on the optical spectrum that is incident on the array-type detector 3 after being separated has a width of about 100 μm (hereinafter referred to as a wavelength width). ). That is, four I per wave
The nGaAs photodiode elements 4 correspond to detect the light intensity of each peak, the peak position, and the like. However, a dead zone is inevitably formed between the arrangement of the InGaAs photodiode elements 4 for manufacturing reasons. Since a gap (hereinafter, referred to as a dead space) exists with a width of 10 μm, if the irradiation position of the wavelength peak comes to this dead space, it is no longer possible to detect an accurate peak intensity and position. That is, for example, the peak position is determined by observing which photodiode element 4 out of approximately four adjacent photodiode elements 4 has a higher intensity signal, and the wavelength peak position is determined. Based on this, it is monitored whether or not the wavelength accuracy is within a predetermined standard. However, if an accurate peak position cannot be detected, it is naturally impossible to monitor the accurate wavelength accuracy.

Conventionally, therefore, the concave diffraction grating 2 shown in FIG. 5 is rotated by a rotation driving unit (not shown) to shift the spectral arrival path to the array type detector 3,
The dead band is compensated by synthesizing the wavelength detection information obtained at a plurality of points to improve the resolution (detection accuracy).

[0010]

However, the above-mentioned conventional spectral photodetector has the following problems. That is, when the spectroscopic means is not rotated (polychromator method), the resolution is significantly reduced due to the influence of the dead space of the array type detector. On the other hand, if the spectroscopic means is rotated (compensation with the monochromator method), the resolution is improved, but a rotation drive mechanism and a wavelength tuning circuit are required, and the structure becomes very complicated, resulting in high cost. Not only inviting them, but also increasing the failure rate.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and has as its object to provide a low-cost and high-resolution spectral photodetector using a polychromator system having a simple structure. I do.

[0012]

According to a first aspect of the present invention, there is provided a spectral photodetector according to the present invention, wherein a plurality of wavelength-division multiplexed optical signals arriving via an optical fiber are separated by a plurality of spectroscopic means. In a spectral photodetector that separates light for each light wavelength and detects a plurality of light wavelengths with an array-type detector, the array-type detector is arranged by displacing two rows of parallel photodiode arrays so as to interpolate a dead zone with each other. It is characterized by having done.

A second aspect of the present invention is a spectral photodetector according to the present invention, wherein a wavelength-division multiplexed optical signal arriving via an optical fiber is divided into a plurality of optical wavelengths by a spectral means, and an array type detector is provided. In the spectral photodetector for detecting a plurality of light wavelengths, the array type detector is characterized in that a light receiving surface of a photodiode alone forming an array is formed as a parallelogram.

A third aspect of the present invention is a spectral photodetector according to the present invention, wherein a wavelength-division multiplexed optical signal arriving via an optical fiber is divided into a plurality of light wavelengths by a spectral means, and an array type detector is provided. In a spectral light receiver for detecting a plurality of light wavelengths, a half mirror that separates the spectrum from the spectral means into transmitted light and reflected light, and a first array-type detector that receives the transmitted light of the half mirror. A second array-type detector for receiving the reflected light of the half mirror, wherein the first array-type detector and the second array-type detector are arranged so as to be shifted from each other so as to interpolate a dead zone. It is characterized by.

In a fourth aspect of the present invention, a wavelength division multiplexed optical signal arriving via an optical fiber is divided into a plurality of light wavelengths by a spectroscopic means. A spectroscopic light receiver for detecting a plurality of light wavelengths at a micro lens sheet for condensing the spectrum from the spectroscopic means, and the light condensed by the micro lens sheet is applied to an effective light receiving surface of the array type detector. It is characterized by being arranged correspondingly.

According to a fifth aspect of the present invention, there is provided the spectral photodetector according to any one of the first to fourth aspects, wherein the array type detector is formed of an InGaAs photodiode. Features.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on illustrated embodiments. FIG. 1 is a diagram showing an array-type detector in a first embodiment of a spectral photodetector according to the present invention, and is a plan view seen from an optical axis of incident light incident on the array-type detector. . The configuration of the spectral photodetector is the same as that of the conventional arrangement shown in FIG. 5, and the concave diffraction grating 2 is assumed to be fixed. That is, the configuration is such that the array type detector 3 of FIG. 5 is replaced with the array type detector 5 shown in FIG.

In the array type detector 5 shown in FIG. 1, PD rows 6a and 6b each composed of a plurality of photodiode elements are arranged so as to be shifted in a direction substantially orthogonal to the optical axis of light incident on the array type detector. In addition, the light receiving surface of the photodiode element forming the PD row 6a is configured to be alternate with the light receiving surface of the photodiode element forming the PD row 6b. Specifically, InGaAs photodiode elements 6a1 to 6an are arranged in the PD row 6a, and InGaAs photodiode elements 6b1 to 6bn are arranged in the PD row 6b. Each of the InGaAs photodiode elements 6 has the same size as the above-described conventional one, and the same applies to the dead space width between elements adjacent to each other in the lateral direction.

Here, the positional relationship between the InGaAs photodiode elements 6 in each PD row will be described. The light receiving surface positions of the InGaAs photodiode elements 6a1 to 6an in the PD row 6a are arranged so as to compensate for the dead space in the PD row 6b. Conversely, the light receiving surface positions of the InGaAs photodiode elements 6b1 to 6bn in the PD row 6b are arranged so as to compensate for the dead space in the PD row 6a. That is, since the spectrum from the concave diffraction grating 2 is incident perpendicularly to the longitudinal direction of the array type detector 5, the peak of each multiplexed wavelength must be PD
Since the light is applied to the InGaAs photodiode elements 6 in the row 6a or the PD row 6b, the peak intensity and the peak position can be accurately detected.

If a spectral photodetector is constructed using the array-type detector 5 as described above, the array-type detector 5 is arranged such that photodiode arrays arranged in two rows are shifted from each other so as to interpolate the dead zone. Therefore, the dead zone is eliminated, and the detection accuracy (resolution) can be improved.

Next, FIG. 2 is a view showing an array type detector in a second embodiment of the spectral photodetector according to the present invention. The configuration of the spectral photodetector is the same as that of FIG. 1, and only the array type detector is replaced. The array type detector 7 shown in FIG.
s photodiode elements 8 are arranged, and the InG
It is characterized in that the shape of the light receiving surface of the aAs photodiode element 8 is a parallelogram. What should be noted here is
When the spectrum from the concave diffraction grating 2 is immediately incident on the array type detector 7 perpendicularly to the longitudinal direction, any one of I
In order to irradiate the nGaAs photodiode element 8,
It is necessary to arrange the adjacent InGaAs photodiode elements 8 so as to overlap in a direction substantially orthogonal to the optical axis of the incident light.

InGaAs having the light receiving surface formed as described above
By arranging the photodiode elements 8, the peak of each multiplexed wavelength is always irradiated to any of the InGaAs photodiode elements 8, so that the peak intensity and the peak position can be detected accurately.

When a spectral photodetector is constructed using the array type detector 7 as described above, the adjacent type InGaAs photodiode element 8 having a light receiving surface formed in a parallelogram has an incident light beam. Since they are arranged so as to overlap each other in a direction substantially perpendicular to the axis, there is no dead zone, and the detection accuracy (resolution) can be improved with an extremely simple structure. The InGa used for the array type detector 7
It is needless to say that the same effect can be obtained even if the light receiving surface of the As photodiode element 8 is made triangular or trapezoidal and the direction is alternately inverted by 180 degrees.

Next, FIG. 3 is a view showing a third embodiment of the spectral photodetector according to the present invention. The spectroscopic light receiver 20 shown in FIG. 1 includes a half mirror 10 for dividing the spectrum from the fixedly arranged concave diffraction grating 9 into transmitted light and reflected light, and an array-type detector 3a for receiving the spectrum transmitted through the half mirror 10 ( A first array type detector) and a half mirror 10
And an array-type detector 3b (second array-type detector) that receives the spectrum reflected by the light source. The half mirror 10 and the two array-type detectors 3a and 3b are both fixedly arranged, and the array-type detectors 3a and 3b
Is similar to the array type detector 3 shown in FIG. What should be noted here is the arrangement relationship of the array type detectors 3a and 3b, and the arrangement is such that the mutual dead spaces are interpolated.

That is, the multiplexed optical signal incident from the optical fiber 1 is split by the concave diffraction grating 9 and is incident on the half mirror 10. The half mirror 10 splits the light into transmitted light and reflected light. At this time, it is preferable that the transmitted light and the reflected light have the same light intensity level. And
The spectrum transmitted through the half mirror 10 is transmitted to the array type detector 3a.
However, since there is a dead space,
In order to interpolate this dead space, half mirror 1
The resolution is improved by detecting the spectrum reflected at 0 by the array-type detector 3b and synthesizing the detection results obtained by the array-type detector 3a and the array-type detector 3b.

That is, the spectroscopic light receiver 20 shown in this example is
It realizes the same detection sensitivity as the spectral photodetector shown in FIG. 1, and the number of components is increased as compared with the spectral photodetector shown in FIG. 1. However, even if an inexpensive off-the-shelf array type detector is used, A high-resolution spectral photodetector can be realized.

Next, FIG. 4 is a view showing an array type detector in a fourth embodiment of the spectral photodetector according to the present invention. Note that the configuration of the spectral photodetector is the same as that of FIG. 1, and only the array type detector is replaced. The spectral photodetector shown in this figure is characterized in that a microlens sheet 11 is arranged in front of the light receiving surface of the array type detector 3. Micro lens sheet 11
Has a light-condensing function, and is arranged such that a microlens corresponds to each of the photodiode elements of the array-type detector 3.

That is, as described with reference to FIG. 6, there is a dead space in the array type detector 3, but the light from the concave diffraction grating 2 is condensed by the microlens sheet 11 to avoid this dead space. Like InGaAs
Irradiation is performed only on the light receiving surface of the photodiode element 4. For this reason, the spectrum located between the InGaAs photodiode elements 4 is always irradiated to any of the light receiving surfaces by the microlens sheet 11, so that the dead zone is eliminated and the peak intensity can be accurately detected. In this example, in order to detect the peak position, the adjacent In
What is necessary is just to perform a process of relatively comparing the light intensity detection outputs of the GaAs photodiode elements 4 and determining the peak position based on the comparison result. For example, when two adjacent InGaAs photodiode elements 4 detecting light intensity at a high level have the same detection level, it is determined that a peak exists at an intermediate position between the two elements.

As described above, the InGa of the array type detector 3
If the spectral photodetector is provided with the microlens sheet 11 for condensing the spectrum for each light receiving surface of the As photodiode element 4, even if an inexpensive off-the-shelf array type detector is used, there is no dead zone and the detection accuracy (resolution) ) Can be improved.

As described above, the spectral photodetector according to the present invention includes the incident position of the wavelength-multiplexed optical signal from the optical fiber 1 and the like, the spectral means such as the concave diffraction grating 2 and the first to fourth spectral receivers.
The dead zone (dead space between elements) of the array-type detector is interpolated while real-time monitoring is enabled by using a simple structure polychromator system in which the array-type detector shown in the embodiment is fixedly arranged. With such a configuration, a high-resolution spectral photodetector can be realized.

[0031]

As described above, the spectral photodetector according to the present invention is constructed by fixedly arranging the incident position of the wavelength-division multiplexed optical signal, the spectroscopic means and the array type detector, and performing spectroscopy by the spectroscopic means. Since the light signal is irradiated onto the light-receiving surface of the array-type detector without any leakage, a low-cost and high-resolution spectral light-receiving device can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of a spectral photodetector according to the present invention.

FIG. 2 is a diagram showing a second embodiment of the spectral light receiving device according to the present invention.

FIG. 3 is a diagram showing a third embodiment of the spectral photodetector according to the present invention.

FIG. 4 is a diagram showing a fourth embodiment of the spectral photodetector according to the present invention.

FIG. 5 is a diagram showing an example of the configuration of a conventional spectral light receiving device.

FIG. 6 is a diagram showing a configuration example of a conventional array type detector.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Optical fiber 2 ... Diffraction grating 3, 3a, 3b ... Array type detector 4 ... PD (photodiode) 5 ... Array type detector 6a1-6an ... PD (Photo Diode) 6b1 to 6bn PD (photodiode) 7 Array detector 8 PD (photodiode) 9 Diffraction grating 10 Half mirror 11 Microlens sheet 20 ... Spectral light receiver 101 ... Spectral light receiver

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) H04B 10/10 10/22 F term (Reference) 5F049 MA01 MB07 NA09 NA10 NB01 NB10 RA02 TA12 TA14 TA20 5F088 AA01 AB07 BA16 BB01 BB10 EA03 JA14 JA20 5K002 AA07 BA05 BA15 BA21 CA12 DA31 FA01

Claims (5)

[Claims] 1. A spectral photodetector, wherein a wavelength-division multiplexed optical signal arriving via an optical fiber is divided into a plurality of light wavelengths by a spectral means, and a plurality of light wavelengths are detected by an array type detector. The array-type detector is a spectral photodetector characterized by disposing two rows of parallel photodiode arrays so as to interpolate a dead zone with each other. 2. A spectral photodetector, wherein a wavelength multiplexed optical signal arriving via an optical fiber is divided into a plurality of light wavelengths by a spectral means, and a plurality of light wavelengths are detected by an array type detector. An array type detector, wherein the light receiving surface of the photodiode alone forming the array is formed as a parallelogram. 3. A spectral photodetector, wherein wavelength-division multiplexed optical signals arriving via an optical fiber are divided into a plurality of light wavelengths by a spectral means, and a plurality of light wavelengths are detected by an array type detector. A half mirror that divides the spectrum from the spectral means into transmitted light and reflected light, a first array-type detector that receives the transmitted light of the half mirror, and a second array-type that receives the reflected light of the half mirror A spectral receiver comprising a detector, wherein the first array-type detector and the second array-type detector are arranged so as to be shifted from each other so as to interpolate a dead zone. 4. A spectral photodetector, wherein a wavelength multiplexed optical signal arriving via an optical fiber is divided into a plurality of light wavelengths by a spectral means, and a plurality of light wavelengths are detected by an array type detector. A spectral photodetector, comprising: a microlens sheet for condensing the spectrum from the spectroscopic means, wherein the light condensed by the microlens sheet is arranged so as to correspond to an effective light receiving surface of the array type detector. 5. The spectral photodetector according to claim 1, wherein said array type detector is formed of an InGaAs photodiode.