JP2723988B2 - Waveguide-type photodetector, optical integrated pickup, and optical integrated RF spectrum analyzer - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide type photodetector, an optical integrated pickup, and an optical integrated RF spectrum analyzer which can be applied to an optical disk pickup, a detector array for an optical spectrum analyzer, and the like. About.

[Conventional technology]

A waveguide optical system is known in which light is confined in a waveguide and guided, and the guided light is refracted or diffracted by a waveguide optical system and collected. Such a waveguide optical system can reduce the size and weight of the optical system by its use.
It is expected to be applied to optical disk pickups and the like.

Conventionally, as an application of a waveguide optical system to an optical disk pickup or the like, for example, ““ Optical integrated circuit of optical disk pickup ”” IEICE Technical Committee on Optical Quantum Electronics, IEICE Technical Report, OQE85-72, P39-46 (1985) ) ", Etc., a waveguide-type photodetection operation in which a photodetector is integrated in a waveguide of a waveguide optical system to form an optical integrated circuit has been proposed.

Here, a conventional waveguide-type photodetector will be briefly described with reference to FIG.

FIG. 5 shows a perspective view of a waveguide-type photodetector as an optical disk pickup. In this waveguide-type photodetector, a waveguide layer 33 on a Si substrate 31 and a buffer layer 32 is laminated. The semiconductor laser 34 as a light source is
Laser light emitted from the semiconductor laser 34 and coupled to the end face of the Si substrate 31 is guided through the waveguide layer 33. The light guided through the waveguide layer 33 passes through the grating 35, is diffracted by the condensing grating coupler 36, propagates in the air, and reaches the optical information recording medium 37. Then, the light reflected by the optical information recording medium 37 is again incident on the condensing grating coupler 36 and becomes guided light, diffracted by the grating 35, split into two light beams, and photodetectors 38a, 38b, 38c, Received at 38d.

The signals from the photodetector group 38 are extracted as a reproduction signal S, a focus error signal F ₀ , and a track error signal Tr by an arithmetic circuit as shown.

Here, each detection signal is output from each photodetector 38as, 38b, 38c, 38d.
Output signals respectively S _38a from, S _38b, S _38c, as _{S 38d, F 0 = (S} 38a + S 38d) - (S 38b + S 38c) Tr = (S 38c + S 38d) - (S 38a + S 38b) S = _S38a + _S38b + _S38c + _S38d .

In the focus error signal F ₀ , when the optical information recording medium 37 moves away from the pickup, F ₀ <0, and
When approaching, F ₀ > 0.

[Problems to be solved by the invention]

By the way, in the waveguide type photodetecting device having the configuration shown in FIG. 5, between the photodetectors 38a and 38b and between the photodetectors 38c and 38d are dead portions having no function as a photodetector. I have.
Usually, this interval is about 5 to 10 μm and cannot be set to 0 (zero).

In detecting a focus error signal, light beams are condensed between the photodetectors 38a and 38b and between the photodetectors 38c and 38d, respectively, during focusing. Therefore. When the condensed beam diameter is less than the distance of the photodetector, when the focus is shifted before and after the focal point, the value of the focus error signal F ₀ is zero, it is not the focus error signal is obtained. Usually, this phenomenon is referred to as “the focus error signal has no sensitivity”.
Further, if the diameter of the condensed beam increases and is substantially equal to the interval between the photodetectors, the state of "no sensitivity" disappears. However, the amount of change in the focus error signal when deviating from the time of focusing is small, and the detection sensitivity is reduced. Therefore, in order to obtain sufficient focus error signal sensitivity with the conventional apparatus shown in FIG.
Or increase the distance between the photodetectors 38a and 38b,
In addition, it is necessary to narrow the interval between the photodetectors 38c and 38d.

However, in the former method, the size of the optical pickup is increased, and the advantage of downsizing by optical integration is lost. In the latter method, as described above, since the interval between the photodetectors cannot be reduced to zero, the dead portion cannot be eliminated.

The present invention has been made in view of the above circumstances, and has a means for substantially eliminating a dead portion between photodetectors, and can provide a waveguide type photodetector capable of obtaining sufficient sensitivity of a focus error signal. It is another object of the present invention to provide an integrated optical pickup having the above-mentioned waveguide type photodetector and an integrated optical RF spectrum analyzer having the above-mentioned waveguide type photodetector.

[Means for solving the problem]

In order to achieve the above object, according to the present invention, in a waveguide-type photodetector in which at least two or more photodetector groups are integrated in a waveguide, there is provided a photodetector between adjacent photodetectors. A minute reflecting portion is provided in the waveguide corresponding to the light undetectable portion to reflect the guided light reaching the light undetectable portion toward the photodetector.

[Operation] Hereinafter, the basic configuration of the present invention and its operation will be described in the first.
This will be described with reference to the drawings.

In FIG. 1, two photodetectors are provided on a planar waveguide 1.
Although 2a and 2b are integrated, an undetectable portion 3 exists between the two photodetectors 2a and 2b. Therefore, in the present invention, as shown in FIG. 1, a configuration is provided in which a reflecting portion 4 that reflects guided light toward the photodetectors is provided corresponding to the interval between the two photodetectors 2a and 2b. .

Therefore, in the waveguide type photodetector having the configuration shown in FIG. 1, the waveguides 10a, 10a,
10b directly enters the photodetector 2a and is detected. Further, the guided lights 10f and 10g directly enter the photodetector 2b and are detected.
On the other hand, the guided lights 10c and 10d are reflected by the upper slope of the reflection unit 4 with respect to the figure and enter the photodetector 2a. In addition, guided light 10h,
The light 10e is reflected by the lower slope of the reflection unit 4 and enters the photodetector 2b.

As described above, in the waveguide-type photodetector having the configuration shown in FIG. 1, by providing the minute reflection portion in the undetectable portion between the photodetectors, the guided light reaching the undetectable portion is transmitted to the detector. A waveguide-type photodetector that can be guided toward and substantially eliminates a dead area between photodetectors, and an optical integrated pickup that has good sensitivity to a focus error signal by including the waveguide-type photodetector And by including the waveguide-type photodetector, an optical integrated RF with high spectral analysis accuracy
A spectrum analyzer can be obtained.

〔Example〕

Hereinafter, the present invention will be described in detail based on illustrated embodiments.

FIG. 2 (a) shows an example of a cross-sectional configuration of a detector portion of the waveguide type photodetector according to the present invention shown in FIG. 1, and the waveguide type photodetector in this embodiment is composed of Si (silicon). A) a buffer layer 6 is formed on the substrate 5 and the waveguide layer 1 having a higher refractive index than the buffer layer is formed on the buffer layer 6;

Further, as the light detection unit 2, for example, an n-type Si substrate
By diffusing a p-type dopant, a pn junction can be formed to provide a photodetector. This light detector 2
In the figure, the buffer layer is extremely thin, and the light guided through the waveguide layer 1 oozes out to the Si substrate 5 side in the thin region of the buffer layer 6 and is received by the photodetector 2. The signal photoelectrically converted by the light detection unit 2 is extracted between the electrode 9 and the substrate-side electrode 8.

Next, FIG. 2 (b) is a cross-sectional view showing one configuration of the reflection unit 4 shown in FIG. 1, and the reflection unit 4 has a layer configuration of the substrate 5, the buffer layer 6, and the waveguide layer 1. In the structure, a part of the waveguide layer 1 is removed. Also, in the cross section of the reflection part 4,
At least the thickness of the waveguide layer 1 or more is removed.
At this time, in order to efficiently reflect the guided light, there are the following two embodiments based on the present invention.

One of them uses total reflection, that is, when the equivalent refractive index of the waveguide in the waveguide mode of light guided through the waveguide layer 1 in FIG. The angle θi incident on the part 4 is set so that θi ≧ sin ⁻¹ N.

Another method is to form a metal film or a dielectric multilayer reflection increasing film on the cross section of the waveguide layer of the reflecting portion 4 when the angle at which the guided light enters the reflecting portion 4 is smaller than θi. is there.

In the above embodiment, an example in which a pn junction detector is formed as a photodetector has been described, but a pin structure may be adopted. Further, in this embodiment, the example in which the Si substrate is used as the substrate has been described. However, when the refractive index of the dielectric substrate having no absorption is lower than that of the waveguide layer 1, the buffer layer 6
May not be required. In this case, the photodetector can be manufactured by film formation of Amosfas Si. Although the cross section of the reflecting portion 4 is obtained by etching, it may be manufactured so that a part of the waveguide layer cannot be formed by masking at the time of forming the waveguide.

Next, an embodiment of the optical integrated pickup of the present invention will be described with reference to FIG.

FIG. 3 shows a plan view of an optical integrated pickup according to the present invention. In this optical integrated pickup, a waveguide layer 21 is formed on a Si substrate and a buffer layer (not shown).

In FIG. 3, reference numeral 15 indicates a grating, reference numeral 16 indicates a grating coupler, reference numerals 22a, 22b, 22c, and 22d indicate photodetectors, reference numeral 27 indicates a semiconductor laser, and reference numerals 29a, 29b, 29c, and 29d indicate electrodes. A reflecting portion 24a is provided between the photodetectors 22a and 22b, and a reflecting portion 24b is provided between the photodetectors 22c and 22d.
Are formed.

A semiconductor laser 27 serving as a light source is coupled to an end face of the waveguide layer 21, and laser light emitted from the semiconductor laser 27 is guided through the waveguide layer 21. Then, the guided light is transmitted through the grating 15, diffracted by the condensing grating coupler 16, emitted to the air, and condensed on an optical information recording medium (not shown). Then, the light reflected by the optical information recording medium again enters the condensing grating coupler 16, becomes guided light, is diffracted by the grating 15, and is split into two light beams. One of the split light beams is reflected by the above-described reflecting portion 24a and received by the photodetectors 22a and 22b. Also, the other light beam is reflected by the other side of the reflection portion 24b,
The light is received by the photodetectors 22c and 22d. Then, each photodetector 22
Output signals from a, 22b, 22c, 22d are output from the respective photodetectors 22a, 22b, 2
It is taken out from the attached electrodes 29a, 29b, 29c, 29d of 2c, 22d.

Now, in the optical integrated pickup having the configuration shown in FIG. 3, the optical detectors 22a and 22b and the optical detectors 22c and 22d
Although the light flux is condensed between the light detectors, since the reflection portions 24a and 24b are provided between the photodetectors as described above, all the light fluxes are emitted from any of the light detectors 22a, 22b and 22c. , 22d. At this time, the two reflection portions 24a, 24b
The arrangement is such that the light flux is exactly divided into two at the apex of each of the two slopes, so that when the optical information recording medium and the condensing grating coupler 16 are out of focus, even if there is a slight change, Since the amount of light divided by the units 24a and 24b changes and the amount of light received by the photodetector changes, a focus error signal can be obtained with high sensitivity.

Next, an embodiment of the optical integrated RF spectrum analyzer of the present invention will be described with reference to FIG.

FIG. 4 shows a plan view of the optical integrated RF spectrum analyzer, in which a Ti-diffused Lithium niobate waveguide manufactured by diffusing Ti (titanium) on a lithium niobate substrate (not shown) is shown. A well-known geodesic lens 45, 46 is formed in 41, and a transducer 48 for generating a surface acoustic wave is disposed between the two geodesic lenses 45, 46.

A semiconductor laser 47 serving as a light source is coupled to the end face of the waveguide 41, and also includes light receiving sections 42a, 42b, 42c, 42d, 42e, 42f, 42g,
The photodetector array 40 in which 42h and dead portions 43a, 43b, 43c, 43d, 43e, 43f, 43g are alternately provided, is coupled to the end face of the waveguide 41 opposite to the side to which the semiconductor laser 47 is coupled. ing. In addition, each dead part 43a, 43b, 43c, 43d, 43e, of the photodetector array 40,
43f, 43g, corresponding to the small reflecting portion 44a, 4 with two slopes
4b, 44c, 44d, 44e, 44f, and 44g are formed on the waveguide 41.

Now, in the optical integrated RF spectrum analyzer having the above configuration, the light from the semiconductor laser 47 is collimated by the geodesic lens 45 on the light source side, and then received by the photodetector array 40 by the next geodesic lens 46. The light is focused on the portion 42g. At this time, when an RF signal to be subjected to spectrum analysis is input to the transducer 48, a surface acoustic wave is generated and propagates between the two geodesic lenses 45 and 46 from below to above in FIG. At this time, since the guided light is diffracted by the surface acoustic wave, the light condensed by the geodesic lens 46 is shifted above the photodetector array 40. That is, light is received by a light receiving unit different from the light receiving unit 42g when the RF signal is not input to the transducer 48. Therefore, in the optical integrated RF spectrum analyzer shown in FIG. 4, according to the frequency of the RF signal, the guided light is transmitted to the light receiving section on the side of reference numeral 42a at a high frequency and to the light receiving section on the side of reference numeral 42f at a low frequency. Will be incident. That is, the frequency of the RF signal can be measured by the photodetector array 40.

By the way, in the conventional optical integrated RF spectrum analyzer, since the minute reflecting portions 44a, 44b, 44c, 44d, 44e, 44f, 44g are not provided, depending on the frequency, the guided light is insensitive to the light detecting portion 43a of the photodetector array 40. 43b, 43c, 43d, 43e, 43f, 43g may be incident, at this time, there is a problem that the signal can not be detected by the photodetector array or the signal level is low, according to the present invention , Minute reflecting portions 44a, 44b,
Since 44c, 44d, 44e, 44f and 44g are provided, no matter what RF signal is input, any one of the light receiving units can receive the guided light without fail, enabling accurate spectrum analysis. Become.

In the above embodiment, the shape of each minute reflecting portion is an isosceles triangle, but any shape may be used as long as the light beam can be divided and reflected evenly on both adjacent photodetectors. For example, two slopes each having an unequal triangular diameter may be used, and the slopes may have a convergence or divergence function as a curved surface as well as a straight line.

〔The invention's effect〕

As described above, according to the present invention, a micro-reflecting portion is provided in a non-light-receiving portion existing between a plurality of photodetectors integrated on a waveguide of a waveguide type photodetector, and a With the configuration in which the incoming guided light is reflected toward the photodetector, light that could not be received by the conventional device can be effectively guided to the photodetector of the photodetector and received. Therefore, the waveguide type photodetector according to the present invention,
As applied to the optical integrated pickup in the present invention,
When applied to a pickup such as an optical disk drive, detection sensitivity of a focus error signal or the like can be improved, and when applied to an optical integrated RF spectrum analyzer, accurate spectrum analysis can be performed.

[Brief description of the drawings]

1 and 2 are diagrams for explaining a basic configuration of a waveguide type photodetector according to the present invention, FIG. 3 is a plan view showing an optical integrated pickup according to the present invention, and FIG. Plan configuration diagram showing an optical integrated RF spectrum analyzer,
FIG. 5 is a plan view of an optical integrated pickup showing an example of a waveguide type photodetector according to the prior art. 1,21,41… waveguide layer, 2a, 2b, 22a, 22b, 22c, 22d, 42a, 42
b, 42c, 42d, 42e, 42f, 42g, 42h ... Photodetector, 4, 24a, 24b, 4
4a, 44b, 44c, 44d, 44e, 44f, 44g ..... small reflecting portions.

Claims (5)

(57) [Claims] 1. A waveguide-type photodetector comprising at least two or more photodetector groups integrated in a waveguide, wherein a light-detectable portion existing between adjacent photodetectors of the photodetector group is provided. Correspondingly, a waveguide-type photodetector characterized in that a microreflector for reflecting the guided light reaching the undetectable portion toward the photodetector is provided in the waveguide. 2. The waveguide-type photodetecting device according to claim 1, wherein said micro-reflecting portion is reflected by a waveguide-type photodetecting device in which the incident angle θi of the guided light is θi ≧ sin ⁻¹ N. apparatus. 3. The waveguide-type photodetecting device according to claim 1, wherein a metal film or a dielectric multilayer reflection increasing film is formed on a section of the waveguide layer of the minute reflecting portion. 4. A waveguide-type photodetector according to claim 1, 2 or 3, a semiconductor laser serving as a light source, coupled to an end face of a waveguide layer on which the waveguide-type photodetector is integrated; A grating through which the laser light emitted by the semiconductor laser is transmitted; and a laser beam transmitted through the grating, emitted into the air and focused on an optical information recording medium, and the laser light reflected by the optical information recording medium is reflected by the grating. An optical integrated pickup, comprising: a condensing grating coupler that is incident on the grating; and a mechanism for detecting the laser beam that is incident on the grating by the condensing grating coupler and transmitted through the grating with the waveguide-type photodetector. 5. A waveguide-type photodetector according to claim 1, 2, or 3, a semiconductor laser serving as a light source, coupled to an end face of a waveguide layer on which the waveguide-type photodetector is integrated; Two geodetic lenses disposed on the waveguide layer and through which the laser light emitted by the semiconductor laser sequentially transmits; and a surface acoustic wave generated between the two geodetic lenses disposed on the waveguide layer. An integrated optical RF spectrum analyzer, comprising: a transducer for detecting the laser beam transmitted through the two geodetic lenses by the waveguide-type photodetector.