2017 was quite a year for Corning Incorporated (NYSE:GLW). Shares enjoyed an almost 32% gain -- and are already up an additional 8% since the beginning of the new year. The stock was propelled upward by a stream of good news including huge orders and new investments from existing customers, announcements of new and innovative product lines, and strong signs of growth from existing business segments.

But with the recent run-up in shares, is all the good news already factored into the stock price? Let's look under the hood at Corning's business and see if its shares should remain a buy for investors.

A business-model metamorphosis

Corning makes most of its money from its display technologies business segment, which makes special glass substrates used in LCD (liquid crystal display) screens. A variety of different devices, including televisions, computer monitors, and tablets, use LCD screens. In the company's most recently reported quarter, core earnings in this division declined to $227 million, a 16% decrease year over year. Increasing volume was more than offset by a decline in glass prices and higher costs as Corning invested in new manufacturing facilities abroad.

Corning scientists test flexibility of glass sheet.

Corning is quickly becoming a diversified business as other glass divisions are growing sales faster than its Optical Communications division. Image source: Corning Inc.

Returns in this division have historically been inconsistent, as they are often dependent on glass prices and the exchange value of the yen. If this division were all Corning had going for it, I would warn investors to stay away. After all, who wants to invest in a company whose success relies upon factors outside its control?

Fortunately, Corning has four more business divisions that, combined, generated 47% of Corning's core earnings in the third quarter. Two of these divisions, optical communications and specialty materials, are showing strong growth, which is buoying the company as its display technologies division attempts a recovery.

Here's a look at all five of Corning's divisions and the earnings growth each is showing:

Corning Inc Division 2017 Q3 Core Earnings 2016 Q3 Core Earnings Change
Display technologies $227 million $270 million (16%)
Optical communications $111 million $98 million  13%
Environmental technologies $34 million $35 million (3%)
Specialty materials $71 million $44 million 61%
Life sciences $21 million $21 million 0%

Data source: Corning Inc. 

Gorilla-sized growth ahead

In addition to manufacturing glass for LCDs, Corning makes Gorilla Glass, the tough and flexible glass that now covers 5 billion devices worldwide, and optical fiber, the backbone of the world's connectivity infrastructure. Corning's Gorilla Glass is such an integral part of smartphones today that the company was the first ever recipient of Apple's (NASDAQ:AAPL) Advanced Manufacturing Fund. Apple awarded Corning $200 million earlier this year that went to Corning's manufacturing facility in Kentucky, where Gorilla Glass is made.

In the third quarter, Corning saw the strongest growth from its specialty materials division, where Gorilla Glass is accounted for. In the conference call, CEO Wendell Weeks was confident in the product's prospects:

Today, Gorilla Glass is seeing broader adoption than ever before. Over the past few months, leading smartphone manufacturers adopted our glass on their new devices. Advanced glass offers several benefits over other materials like metal or plastic. Along with improved wireless charging, advanced glass on the back also enables improved reception. It allows for new levels of design and customization.

For the quarter, net sales in specialty materials grew a robust 26% to $373 million, while the division's earnings rose an even more incredible 61% to $71 million. Even better, Weeks said the company expects sales to double "over the next several years."

A moat 1 billion kilometers wide

Gorilla Glass is not the only Corning product showing strong growth. The company is also the world's largest -- and lowest-cost -- producer of optical fiber. Last year, Corning announced it had now manufactured 1 billion kilometers of optical fiber, or about a third of all fiber-optic cable ever produced in the history of the world. That's quite a feat! That it can now produce optical fiber cheaper than any competitor also gives the company an impressive economic moat. In December, Corning widened its moat even further when it acquired 3M's communications markets division for about $900 million.

As worldwide data use and connectivity needs grow, the demand for optical fiber should only increase. In the third quarter, Corning's optical communications division experienced sales growth of 13% and core earnings growth of 15%. Optical communications had about $3 billion in net sales in 2016; management expects that to grow to $5 billion in sales by 2020, or about twice the rate of the telecommunications industry.

A compelling buy at today's valuation

As the bull market continues, many companies' valuations are beginning to look a bit frothy. Not Corning's. Based on its trailing-12-months core EPS of $1.74, the company's stock is trading at a P/E ratio of 19, below the market's average. Another plus: Corning's management has remained shareholder-friendly. Since October 2015, the company has reduced outstanding shares by 29% through share buybacks. Corning's dividend yield is currently about 1.8%, but management raised the payout by 15% in 2017 and promises to boost it by double digit percentages again in 2018.

Corning is poised to benefit from macro trends, expects growth, has a rising dividend and shareholder-friendly management, and trades at an attractive valuation -- and so it remains a buy in my eyes.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.