Patent ID: 12197051

DESCRIPTION OF EMBODIMENTS

Hereinafter, an optical inspection circuit according to an embodiment of the present invention will be described with reference toFIG.1. This optical inspection circuit includes an optical modulator102formed on a substrate101and a photodiode103formed on the substrate101in the vicinity of the optical modulator102.

The optical modulator102comprises an optical waveguide, and the optical waveguide has a core comprising a semiconductor. The optical modulator102can be configured of, for example, a Mach-Zehnder optical modulator in which a carrier abstraction type phase shifter including a pn junction formed in a rib type optical waveguide whose core is formed of silicon and a multi-mode interferometer are combined. This optical modulator can be manufactured by the heretofore known semiconductor device manufacturing technology such as the widely known lithography technology, ion implantation technology, thin film deposition technology, crystal growth technology, and etching technology.

The photodiode103is, for example, a germanium photodiode which is configured of a germanium layer selectively formed on the core comprising a semiconductor (for example, silicon) and a pn junction formed on both sides and upper and lower sides of this layer. The photodiode103can be manufactured by the heretofore known semiconductor device manufacturing technology such as the widely known lithography technology, ion implantation technology, thin film deposition technology, crystal growth technology, and etching technology.

In addition, optically connected to the optical modulator102is a first optical waveguide104as an input waveguide, which is constituted of an optical waveguide having a core comprising a semiconductor. In addition, optically connected to the optical modulator102is a second optical waveguide105as an output waveguide, which is constituted of an optical waveguide having a core comprising a semiconductor. In addition, optically connected to the photodiode103is a third optical waveguide106as an input waveguide, which is constituted of an optical waveguide having a core comprising a semiconductor.

In addition, the optical modulator102and the photodiode103are electrically connected by a wire107. An electrical signal which is photoelectrically converted by the photodiode103and is outputted is electrically transmitted by the wire107and is inputted to the optical modulator102. The optical modulator102modulates continuous light, inputted via the first optical waveguide104, by the electrical signal inputted via the wire107and outputs the modulated continuous light to the second optical waveguide105.

For example, the wire107is a high frequency line comprising a signal wire171and grounding wires172and173. The signal wire171connects an electrode pad121of the optical modulator102and an electrode pad131of the photodiode103. The grounding wire172connects an electrode pad122of the optical modulator102and an electrode pad132of the photodiode103. The grounding wire173connects an electrode pad123of the optical modulator102and an electrode pad133of the photodiode103.

In addition, optically connected to the third optical waveguide106via an optical fiber109is an optical modulator110. The optical modulator110modulates continuous light emitted from a light source111and outputs the modulated continuous light to the optical fiber109. The light source111comprises, for example, a semiconductor laser.

In addition, optically connected to the first optical waveguide104is an optical fiber112, and inputted to the optical fiber112is continuous light emitted from a light source113. The light source113comprises, for example, a semiconductor laser.

In this optical inspection circuit, first, the modulated light (signal light) emitted from the light source111and modulated by the optical modulator110is received via the optical fiber109and the third optical waveguide106by the photodiode103. The modulated light received by the photodiode103is photoelectrically converted to a modulated electrical signal and is outputted via the wire107to the optical modulator102.

In addition, the continuous light emitted from the light source113is inputted via the optical fiber112and the first optical waveguide104to the optical modulator102. The continuous light inputted to the optical modulator102is modulated by the optical modulator102, which is driven by the inputted modulated electrical signal, is outputted from the second optical waveguide105and is taken out by the optical fiber114.

Hereinafter, an optical inspection method according to an embodiment of the present invention will be described with reference toFIG.2. First, in a first step S101, continuous light emitted from a light source113is made incident via a first optical waveguide104to an optical modulator102. Next, in a second step S102, modulated light modulated by an optical modulator110is made incident to a photodiode103. As described above, a modulated electrical signal is outputted from the photodiode103, to which the modulated light is made incident, to the optical modulator102. The optical modulator102modulates the inputted continuous light by the modulated electrical signal received by the photodiode103and outputs the modulated continuous light.

Thereafter, in a third step S103, the modulated light outputted from the optical modulator102is evaluated. By conducting evaluation such as comparison between the modulated light outputted from the optical modulator102and taken out from the optical fiber114and the modulated light outputted from the optical modulator110(inputted to the photodiode103), inspection of the optical modulator102at a wafer level can be implemented.

As described above, according to the present embodiment, without requiring a probe card which is excellent in high frequency characteristics and a high frequency cable for connecting a probe card outside a wafer and a device on the wafer, the inspection of the optical modulator102at the wafer level can be implemented.

For example, when with respect to power of the light inputted to the photodiode103, a voltage of the electrical signal which the photodiode103outputs is measured, change of the voltage occurs as shown inFIG.3. As shown inFIG.3, when light of approximately one mW is inputted to the photodiode103, a voltage of approximately 0.15 V is generated.

On the other hand, a result of measuring relationship between a voltage of an electrical signal inputted (applied) to the optical modulator102and light outputted from the optical modulator102is shown inFIG.4. As shown inFIG.4, it is seen therefrom that when an electrical signal of a voltage of approximately 0.2 V is applied to the optical modulator102, change of approximately 0.5 dB occurs in the outputted light.

Next, a light pulse (modulated light) of one mW at peak power is inputted to the photodiode103connected to the optical modulator102by the wire107, and as a result of this, a light output waveform of the modulated light outputted from the optical modulator102is shown inFIG.5. As is predicted from the results shown inFIG.3andFIG.4, the light modulated signal of approximately 0.5 dB is outputted, and it is indicated that the optical inspection circuit according to the present embodiment enables characteristic inspection of the optical modulator102.

Next, another optical inspection circuit according to the embodiment of the present invention will be described with reference toFIG.6. This optical inspection circuit includes an optical modulator102formed on a substrate101and a photodiode103formed on the substrate101in the vicinity of the optical modulator102. In addition, optically connected to the optical modulator102are a first optical waveguide104and a second optical waveguide105. In addition, optically connected to the photodiode103is a third optical waveguide106. In addition, the optical modulator102and the photodiode103are electrically connected by a wire107. The configuration of these is similar to that of the optical inspection circuit described with reference toFIG.1.

This optical inspection circuit further includes an optical distributor115which distributes inputted signal light to the first optical waveguide104and the third optical waveguide106. In addition, the optical inspection circuit includes a wavelength filter116which takes out light having a predetermined wavelength from light outputted from the optical modulator102. The optical distributor115and the wavelength filter116are formed on the substrate101. In addition, each of the optical distributor115and the wavelength filter116comprises an optical waveguide having a core comprising a semiconductor.

The optical distributor115is to distribute inputted light power to a plurality of optical waveguides and can be configured of, for example, a Y-branch circuit. In addition, the optical distributor115can also be configured of a multi-mode interferometer. In addition, the optical distributor115can also be configured of a directional coupler. The wavelength filter116can be configured of a two-output optical circuit having wavelength dependence. The wavelength filter116can be configured of, for example, an array diffraction grating, an asymmetric Mach-Zehnder interferometer, a directional coupler, or the like.

In this optical inspection circuit, continuous light and modulated light are multiplexed and the multiplexed light is inputted to the optical distributor115. The optical distributor115distributes the multiplexed continuous light and the modulated light. Accordingly, the multiplexed continuous light and the modulated light are inputted to both of the optical modulator102and the photodiode103. In this configuration, a modulated electrical signal generated by the photodiode103by the modulated light in the multiplexed light is used, and the optical modulator102modulates inputted light. The multiplexed continuous light and the modulated light are inputted to the optical modulator102, and of this inputted light, the continuous light is targeted for the modulation and the modulated light becomes noise. The light corresponding to the noise is eliminated by the wavelength filter116. This optical inspection circuit has excellent effects which allow a number of the optical waveguides for inputting to be reduced to one.

Next, still another optical inspection circuit according to the embodiment of the present invention will be described with reference toFIG.7. This optical inspection circuit includes a plurality of optical modulators102a,102b, and102cformed on a substrate101and a photodiode103formed on the substrate101in the vicinity of the optical modulator102a,102b,102c.

Optically connected to the optical modulator102aare a first optical waveguide104aand a second optical waveguide105a. Optically connected to the optical modulator102bare a first optical waveguide104band a second optical waveguide105b. Optically connected to the optical modulator102care a first optical waveguide104cand a second optical waveguide105c. In addition, optically connected to the photodiode103is a third optical waveguide106.

In addition, each of the optical modulators102a,102b, and102cand the photodiode103are electrically connected by a wire107a. The wire107acan be formed by, for example, wire bonding. In addition, the wire107acan also be configured of the heretofore known multilayer wiring structure formed in a surface layer of the substrate101.

This optical inspection circuit has excellent effects which allow the plurality of optical modulators102a,102b, and102cto be inspected by the modulated electrical signal generated by one photodiode103.

Next, yet another optical inspection circuit according to the embodiment of the present invention will be described with reference toFIG.8. This optical inspection circuit includes an optical modulator102formed on a substrate101and a plurality of photodiodes103a,103b, and103cformed on the substrate101in the vicinity of the optical modulator102.

In addition, optically connected to the optical modulator102are a first optical waveguide104and a second optical waveguide105. In addition, optically connected to the photodiode103ais a third optical waveguide106a. In addition, optically connected to the photodiode103bis a third optical waveguide106b. In addition, optically connected to the photodiode103cis a third optical waveguide106c.

In addition, the optical modulator102and the photodiode103are electrically connected by a wire107b. The photodiodes103a,103b, and103cwhose number is plural are series-connected to the optical modulator102by the wire107b. The wire107bcan be formed by, for example, wire bonding. In addition, the wire107bcan also be configured of the heretofore known multilayer wiring structure formed in a surface layer of the substrate101. By employing this optical inspection circuit, the plurality of photodiodes103a,103b, and103cis used, and a modulated electrical signal having further large voltage can be thereby generated, and thus, the optical inspection circuit has excellent effects which enables inspection of a characteristic, which requires a large voltage, among modulation characteristics of the optical modulator102.

As described hereinbefore, according to embodiments of the present invention, since on the substrate on which the optical modulator is formed, the photodiode is formed, and the optical modulator and the photodiode are electrically connected by the wire, inspection of an optical circuit such as an optical modulator at a wafer level can be further easily and further inexpensively implemented.

Note that the present invention is not limited to the above-described embodiment and it is apparent that many modifications and combinations can be implemented by those having ordinary skill in the art without departing from the spirit and scope of technical idea of the present invention.

REFERENCE SIGNS LIST

101Substrate102Optical modulator103Photodiode104First optical waveguide105Second optical waveguide106Third optical waveguide107Wire109Optical fiber110Optical modulator111Light source112Optical fiber113Light source114Optical fiber121,122,123Electrode pad131,132,133Electrode pad171Signal wire172,173Grounding wire